iso phase 2 benchmarking iso 19905-1 (dis) validity ... - dnv

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File: l25316-r0 - iso validity check of kfels b class.doc

Noble Denton Consultants Ltd trading as GL Noble Denton Registered in England No. 5513434 Registered Office: Noble House, 39 Tabernacle Street, London, EC2A 4AA, UK

Distribution: ISO Committee Company: ABS Attn: Mr John Stiff Attn: W/S No: 05-130553 CTR 0

REPORT

ISO PHASE 2 BENCHMARKING

ISO 19905-1 (DIS)

VALIDITY CHECK

KFELS B CLASS

Report No: L25316 , Rev O , Dated 20-11-2010

The assessment has used adjusted leg-to-hull connection stiffness and other generic parameters of KFELS B-Class jack-up units. The results presented herein are for the purposes of benchmarking alone and are not representative of KFELS

B-Class jack-up units.

PHASE 2 BENCHMARKING

VALIDITY CHECK FOR KFELS B CLASS ISO 19905-1 (DIS)

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Report No: L25316 , Revision 0: O , Dated: 20th November 2010

File: L25316-R0 - ISO validity check of KFELS B Class.doc

REVISION DETAILS

Revision Date Description Author Checker Approver

0 20th Nov 10 Initial Issue YH MLH/ARM MJRH

DESCRIPTION OF CHANGES

Revision Section Change

INSERTED DOCUMENT/FILE REGISTER

Path and Filename Details of File



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CONTENTS

SECTION PAGE

1 EXECUTIVE SUMMARY 8

2 SCOPE OF WORK 9

2.1 INTRODUCTION 9 2.2 SCOPE OF WORK 9 3 SITE SPECIFIC ASSESSMENT OF THE KFELS B CLASS 11

3.1 GENERAL 11 3.3 ASSESSMENT SITUATIONS 13 3.4 RIG DATA 13 3.5 SITE DATA 14 3.6 METOCEAN DATA 14 3.7 MINIMUM HULL ELEVATION CHECK 15 3.8 GEOTECHNICAL AND GEOPHYSICAL DATA 15 3.9 LEG LENGTH RESERVE CHECK 16 3.10 LEG AND SPUDCAN BUOYANCY 16 3.11 HYDRODYNAMIC COEFFICIENTS 17 4 ALIGNMENT POINTS AND COMMENTS 22

4.1 GENERAL 22 4.2 ALIGNMENT POINT 1 - GEOTECHNICAL CALCULATIONS 22 4.3 ALIGNMENT POINT 2 - OVERALL SYSTEM CHECKS 27 4.4 ALIGNMENT POINT 3 - ENVIRONMENTAL LOADINGS 34 4.5 ALIGNMENT POINT 4 - STICK MODEL RESPONSES 38 4.6 ALIGNMENT POINT 5 - FINAL ASSESSMENT RESULTS 44 5 ISO / SNAME COMPARISON 48

5.1 INTRODUCTION 48 5.2 FOUNDATION INPUT PARAMETERS 48 5.3 NATURAL PERIODS 49 5.4 SWAY STIFFNESS 49 5.5 WIND LOADS 50 5.6 WAVE LOADS 51 5.7 DYNAMIC AMPLIFICATION FACTORS (DAF’S) 52 5.8 INERTIA LOADSETS 53 5.9 TOTAL QUASI-STATIC LOADING 54 5.10 UTILISATION CHECKS 57 5.11 CONCLUSION 58

REFERENCES 62



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APPENDIX A COMMENTS SUBMITTED TO ISO 75

APPENDIX B FINAL QUASI-STATIC RESULTS COMPARISON OF ISO & SNAME RESULTS TO ISO USING SNAME WIND 89



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FIGURES

Figure 3-1 Flow chart for the overall assessment 12

Figure 3-2 Chord section axes system 20

Figure 4-1: 3 Stick Leg Model (showing hull beam grillage) 30

Figure 4-2: Example portion of F.E. Model of Leg 31

Figure 5-1 - ISO predicted leg penetration resistance curves for the B-Class - SAND assessment 63

Figure 5-2 - SNAME predicted leg penetration resistance curves for the B-Class - SAND assessment 64

Figure 5-3 - ISO predicted V-H envelope for the B-Class - SAND assessment 65

Figure 5-4 - SNAME predicted V-H envelope for the B-Class - SAND assessment 66

Figure 5-5 - ISO predicted ultimate capacities and stiffnesses for the B-Class - SAND assessment 67

Figure 5-6 - SNAME predicted ultimate capacities and stiffnesses for the B-Class - SAND assessment 68

Figure 5-7 - ISO predicted leg penetration resistance curves for the B-Class - CLAY assessment 69

Figure 5-8 - SNAME predicted leg penetration resistance curves for the B-Class - CLAY assessment 70

Figure 5-9 - ISO predicted V-H envelope for the B-Class - CLAY assessment 71

Figure 5-10 - SNAME predicted V-H envelope for the B-Class - CLAY assessment 72

Figure 5-11 - ISO predicted ultimate capacities and stiffnesses for the B-Class - CLAY assessment 73

Figure 5-12 - SNAME predicted ultimate capacities and stiffnesses for the B-Class - CLAY assessment 74



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TABLES

Table 3-1 Assessment Situations of the Unit 13

Table 3-2 Assembled Rig Data 13

Table 3-3 Assembled Site Data 14

Table 3-4 Assembled Metocean Data 14 [1]

Table 3-5 Hull Elevation Check 15

Table 3-6 Assembled Foundation Data 15 [1]

Table 3-7 Leg Length Reserve Check 16

Table 3-8 Leg & Spudcan Buoyancy 16

Table 3-9 Hydrodynamic Surface Condition Levels 17

Table 3-10 Hydrodynamic Leg Sections for Site 1 (sand) 17

Table 3-11 Hydrodynamic Leg Sections for Site 2 (clay) 18

Table 3-12 Member Details for Hydrodynamics calculations 18

Table 3-13 Base Hydrodynamic Coefficients for Tubulars 19

Table 3-14 Chord hydrodynamic coefficients 20

Table 3-15 Equivalent Hydrodynamic Coefficients for Stick Leg Model 21

Table 4-1 Summary of Site 1 (sand) assessment key inputs and outputs from analyses 22

Table 4-2 Summary of Site 2 (clay) foundation key inputs and outputs from analyses 24

Table 4-3 Leg Length Reserve Check 27

Table 4-4 Wind Area Calculations (m ) 27 2

Table 4-5 Equivalent Hydrodynamic Coefficients for Stick Leg Model for Site 1 28

Table 4-6 Equivalent Hydrodynamic Coefficients for Stick Leg Model for Site 2 29

Table 4-7 Linear Natural Periods for hull sway condition (max hull weight = 10 070 tonnes) 31

Table 4-8 Natural Periods Alignment 32

Table 4-9 Hull Displacements and Sway Stiffness 32

Table 4-10 Footing reactions from gravity loadcase 33

Table 4-11 Wind Loads 34

Table 4-12 GLND vs BASS Wind Loads 35

Table 4-13 Wave / Current Loads (LF=1,15) 35

Table 4-14 Summary of actions considered 36

Table 4-15 DAF from the Dynamic MPME (Hull Weight = 10069,8t) 37 R

Table 4-16 DAF from the Dynamic MPME (Hull Weight = 8770,3t) 37 R

Table 4-17 DAF Alignment (Hull Weight = 10069,8t) 37 R

Table 4-18 Inertia Loads (LF=1.15) 38

Table 4-19 Inertia Loads Alignment (Hull Weight = 10069,8t) 38

Table 4-20 Total Loading Alignment (Hull Weight = 10069,8t) 39

Table 4-21 Hull Sways (m) 39

Table 4-22 Hull Sways Alignment (m) (Hull Weight = 10069,8t) 39



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Table 4-23 Footing Reactions for Site 1: Sand 40

Table 4-24 Footing Reactions for Site 1: Sand, Alignment (Hull Weight = 10069,8t) 40

Table 4-25 Footing Reactions at Site 2: Clay 41

Table 4-26 Footing Reactions at Site 2: Clay, Alignment (Hull Weight = 10069,8t) 41

Table 4-27 Lower Guide Reactions at Site 1: Sand 42

Table 4-28 Lower Guide Reactions at Site 2: Clay 43

Table 4-29 Footing Reactions from the Global Responses (Site: SAND; Units: MN) 44

Table 4-30 Footing Reactions from the Global Responses (Site: CLAY; Units: MN) 44

Table 4-31 Member Checks (Hull Weight = 10069,8t) 45

Table 4-32 Maximum Utilisations of the Chocks 46

Table 4-33 Final assessment results 46

Table 4-34 Final assessment results 47

Table 5-1 Foundation parameters 48

Table 5-2 Natural periods 49 [1]

Table 5-3 Wind loads 50

Table 5-4 Wave - Current Loads 51

Table 5-5 Averaged Dynamic amplification factors (DAFs) 52

Table 5-6 Inertia loadset 53

Table 5-7 Total quasi-static loading 54

Table 5-8 Hull sway 54

Table 5-9 Reactions in leg at base of rack chock - Maximum Hull Weight 55

Table 5-10 Reactions in leg at base of rack chock - Minimum Hull Weight 55

Table 5-11 Reactions at base of leg - Maximum Hull Weight 56

Table 5-12 Reactions at base of leg - Minimum Hull Weight 56

Table 5-13 Summary of critical structural utilisations - Site 1 (sand) 57

Table 5-14 Summary of critical structural utilisations - Site 2 (clay) 57

Table 5-15 Differences between ISO and SNAME 60



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1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1 EXECUTIVE SUMMARY The purpose of this work is to undertake a complete run through of the entire Draft International Standard (DIS) ISO 19905-1 and to make numerical comparisons to ensure that the results obtained are on reasonable compliance with the results from a similar analysis to the SNAME bulletin 5-5A (Ref [1]), as “Phase 2” benchmarking of the proposed ISO 19905-1 DIS (Ref [2]) document used for Site Specific Assessment of Mobile Offshore Units.

This analysis has been designed to check the validity of the ISO 19905-1 DIS results through the study of a typical jack-up design, KFELS B Class unit using adjusted leg-to-hull connection stiffness values. Assessment has been completed at the two typical locations, comparing to SNAME bulletin 5-5A (Ref [1]) following the completeness check undertaken in “Phase 1” benchmarking (Ref [3]). It is noted that because the assessment has used adjusted leg-to-hull connection stiffness values, the results presented are for the purposes of benchmarking alone, and are not representative of the B Class

This analysis using the entire ISO 19905-1 DIS document included the initial steps of; overall considerations, assembling the data, determining the analysis methods at different stages, finite element (FE) modelling, response analyses and the final assessment of structural strength of leg members and foundation capacities, etc. Excel spreadsheets, generally recognised commercial FE software PAFEC and two in-house programs, the analytical tool JUSTAS and the PAFEC-based FE programme FORCE-3, have been used to assist the analysis.

For each step, both input and output data are explicitly presented and the methods applied are extensively explained so that the entire process of the analysis can be followed and repeated. The intermediate results from each step were cross-checked with the Bennett & Associates (BASS), the consultant running parallel analyses for this unit before continuing to the next step. Any discrepancy is reported and the reasons are explained.

The ISO assessment results are compared to assessment results based on SNAME bulletin 5-5A (Ref[1]), presented in Section 5.

Comments relating to the ISO document regarding errors, omissions and ambiguities are included in Appendix A

The results from this assessment show that assessment using the ISO 19905-1 approach has been found to be valid, with total loading condition similar to that of SNAME; slightly less onerous than SNAME for site 1 (sand), and near-identical or slightly more onerous than SNAME for site 2 (clay).

For site 1 (sand) this is generally reflected in the utilisations, where ISO generally shows similar results to those of SNAME for the basic assessment checks (overturning / preload). However, the different methodology to assessing leg strength checks and foundation bearing capacity checks in ISO results in improved utilisations.

For site 2 (deep penetration in clay) the results show ISO to be more onerous for overturning capacity (based on a slightly increased loading condition and larger hull sway), but otherwise shows lower utilisations than when compared to SNAME. ISO leg and holding system strength checks are based on checks that allow for greater capacity, and likewise the horizontal foundation capacity (used as basis for sliding capacity checks) is significantly larger when calculated to ISO than to SNAME



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2.1

2.2

2 SCOPE OF WORK

INTRODUCTION

2.1.1 GL Noble Denton has been instructed by ABS, on behalf of the ISO benchmarking committee, to carry out the phase 2 benchmarking of the ISO 19905-1 “Petroleum and natural gas industries - Site-specific assessment of mobile offshore units - Part 1: Jack-Ups” (Draft Industry Standard) (ISO) (Ref [2]) which has been developed from SNAME bulletin 5-5A (Ref [1]).

2.1.2 The phase 2 benchmarking process involves the completion of a full site assessment analysis, running through the entire standard to check that the document is not only complete but that the specified methodology will yield reasonable and useful results. A comparison is also made with SNAME bulletin 5-5A Rev 3 (Ref [1]), with the inclusion of "SAGE fixity", from which the ISO document is derived. The intermediate results from each stage of the analysis have been checked against those calculated by Global Maritime, who have performed an identical analysis. Any differences have been resolved prior to recommencement of the analysis.

2.1.3 All questions which arose during the work and any clauses which caused doubt as to the exact methodology to follow are identified in the report with appropriate comments and the decisions which were made such that the analysis could be continued.

2.1.4 For the purpose of the benchmarking work, the use of in-house specialist programs normally used in routine assessment work has been avoided where possible with the results presented in open-format calculations, tables and graphs.

SCOPE OF WORK

2.2.1 The purpose of this work is to provide a validity check of the proposed ISO 19905-1 (DIS) (Ref [2]) document used for Site Specific Assessment of Mobile Offshore Units.

2.2.2 To perform this analysis a typical jack-up, location and metocean conditions were selected as shown below:

Jack-Up KFELS B Class unit

Location A typical sand foundation condition (Site 1)

A typical clay foundation condition (Site 2)

Metocean A 50-year extreme storm conditions based on operations manual design storm condition.



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2.2.3 The analysis following the ISO document has been divided into 5 alignment points for step by step comparisons:

Alignment Point 1: Calculate the leg penetration and foundation spring stiffnesses for the two interpreted soils conditions, one sand and one clay.

Alignment Point 2: Undertake the overall system geometry checks, calculate the wind areas and leg hydrodynamic coefficients, prepare a model that complies with the requirements of the standard, calculate both a pinned natural period and one incorporating spudcan fixity and also determine sway stiffness to a ‘unit’ loading applied to the hull.

Alignment Point 3: Determine loading directions, develop quasi-static wind, wave and current loads and calculate the dynamic amplification factors.

Alignment Point 4: Calculate the structural response and summarise the breakdown of loadings (wind, wave-current, inertia) and responses (hull sway, footing reactions and forces in legs at base of rack chock).

Alignment Point 5 - Final results: Assess the strengths, addressing the effects of any additional penetration, develop the chord and bracing loads and utilisation checks for the leg members, holding system and any remaining limit states set out in the standard.

2.2.4 The deliverables include a report that details the findings of the study. Some specific items that need to be brought out in the report include:

Executive Summary.

Completed Tables with inputs and outputs.

Inputs and outputs of the complicated calculations

Intermediate results and comments.

Full comments and results at Alignment Points. The report shall include quantification of any differences in results between the two consultants and the significance of those differences.

Detailed analysis of differences between SNAME and ISO.

Commentary on clauses which caused confusion or that required making assumptions.



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3.1

3.2

3 SITE SPECIFIC ASSESSMENT OF THE KFELS B CLASS

GENERAL

3.1.1 This site specific analysis is intended to follow the methods recommended in the ISO document while checking that the document is complete and generates reasonable results.

3.1.2 Figure 3-1 shows the flowchart from Figure 5.2-1 in the ISO document. It gives the guidance for a general analysis route and provides the basic structure of this analysis.

The site assessment analysis is based on an exemplary Keppel FELS B-Class jack-up unit adjusted leg-to-hull connection stiffness values, with the results at each alignment point cross checked with those of Bennet and Associates. The results at each alignment point along with those of Bennet and Associates and the equivalent SNAME analysis have been presented in the following sections. It is noted that because the assessment has used adjusted leg-to-hull connection stiffness values, the results presented are for the purposes of benchmarking alone, and are not representative of the B Class



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Figure 3-1 Flow chart for the overall assessment



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3.3 ASSESSMENT SITUATIONS

3.3.1 In this case, a KFELS B Class jack-up unit will be assessed for the two specific foundation/metocean combinations listed in Table 3-1.

Table 3-1 Assessment Situations of the Unit

Location Site 1 Site 2

Limit State ULS (Ultimate Limit States)

Exposure Level L1 = SI Manned Non- evacuated / C1 High Consequence

Associated criteria[1] 50-year individual extremes with action factor = 1,15

Local regulation Assume not applicable

Foundation type Sand Clay

Spudcan Reaction Point According to spudcan penetration as specified in Clause A.8.6.2

Centre of gravity CoGs assumed to be at the 3-leg centroid for maximum usage

Specific Hull Elevation wrt LAT Airgap = 15,20 m

[1] Determined by the limit state and the exposure level. [2] Specified by the client - the co-worker in this benchmarking.

3.4 RIG DATA

3.4.1 The rig data for this analysis is listed Table 3-2.

Table 3-2 Assembled Rig Data

Rig Type KFELS B Class

Drawings & specifications Key rig drawings held in house

Operation manual Held in house

Rack-chock [1] Kv = 1,479x106, Kh = 6,223x106

Upper-guide K = 1,133x105 (Gap = 4,8mm)

Lower-guide K = 2,446x107 (Gap = 19m)

Leg-hull connection stiffness[3] (tonnes/m)

Pinion [2] K = 1,429x105 (Backlash = 16mm)

Principle Dimensions:

Hull Length x Width x Height 68,58m x 63,40m x 7,78m

Leg Length including spudcan 157,58m

Weight & Centre of gravity

Hull lightship: 7 470,7 tonnes

LCG=40,94m, TCG=0,14m, VCG=10,28m [2]

Assessed Maximum Variable Load Assessed Minimum Variable Load

2 599,1 tonnes 1 299,6 tonnes

3 Legs including spudcans [4] 3 347,8 tonnes LCG=39,32m, TCG=0,0m

Preload (jacking reaction) 6 141,6 tonnes



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Spudcan dimensions

Height of spudcan 5,79m (from manual)

Maximum bearing area 152,40 m2 (from manual)

Height of max bearing area above tip 2,23m

Density of steel 7,85 tonnes/m3

Relevant modifications N/A

[1] Chock stiffness per chord [2] Stiffness per pinion pair [3] Stiffnesses, guide gaps and backlashes are artificial numbers provided by the rig designer for the

purposes of this analysis. [4] Centres of gravity measured from the leg centroid at the keel level, +ve fwd and to port.

3.5 SITE DATA

3.5.1 Two sites were assessed for the same rig as listed in Table 3-3 Assembled Site Data.

Table 3-3 Assembled Site Data

Site 1 Site 2

Site coordinates N/A N/A

Seabed type Sand Clay

Water depth (LAT) 106,7m 70m

3.6 METOCEAN DATA

3.6.1 The metocean conditions being assessed for the two sites are based on the ‘storm’ conditions agreed with Bennett & Associates (BASS) and are summarised in Table 3-4 Assembled Metocean Data[1].

Table 3-4 Assembled Metocean Data[1]

Site 1 Site 2

Water depth (LAT) (m) 106,7m 70m

Data type 50-year return individual extreme

Mean high water spring tide (m) Assume 0.0

Storm surge (m) Assume 0.0

Maximum wave height (m) 13,1 16,8

Associated period (s) 11,7 13,3

Significant wave height (m) 7,0 9,0

Peak period (s) 13,0 14,7

Specified airgap (m) 15,2

Current velocity profile (m/s) No current (0m/s)

1 minute wind speed (m/s) 51,4

Other Data Marine Growth = 12,5mm



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3.7 MINIMUM HULL ELEVATION CHECK

3.7.1 A hull elevation resulting in at least 1.5m clearance between the extreme wave crest and the underside of the hull shall be used. This must be checked before continuing the assessment.

3.7.2 The check which is based on the metocean data obtained previously is shown in Table 3-5

Table 3-5 Hull Elevation Check


Mean high water spring tide (m) Assume 0,0

Storm surge (m) Assume 0,0

Maximum wave crest height (m) 7,20 9,55

Extreme still water level (SWL) (m) = 7,20 9,55

Required margin (m) 1,50

Other allowances (m) N/A

Minimum required hull elevation (m) = 8,70 11,05

Specified hull elevation (m) = 15,20

If Airgap > = Minimum, ok; otherwise, re-define Airgap

OK OK

3.8 GEOTECHNICAL AND GEOPHYSICAL DATA

3.8.1 The foundation parameters obtained for the two locations following the ISO document are listed in Table 3-6.

Table 3-6 Assembled Foundation Data[1]


Soil type Sand Clay

Spudcan penetration (m) 1,95 34,07

Foundation Capacity

Vertical VLo (kN) 69 700 88 500

Horizontal HLo (kN) 8 400 19 900

Moment MLo (kN-m) 56 00 139 000

Foundation Stiffness

Vertical K1 (kN/m) 1 370 300 3 791 000

Horizontal K2 (kN/m) 1 299 300 2 603 000

Moment K3 (kN-m/rad) 26 485 900 147 935 000

Distance of effective penetration point above spudcan tip (m)

0,97 2,9



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3.9 LEG LENGTH RESERVE CHECK

3.9.1 The leg length reserve above the upper guides should reflect the uncertainty in the prediction of leg penetration and account for any settlement. The leg length reserve shall be at least 1,5 m.

3.9.2 The check based on the rig data and the metocean data obtained previously is listed in Table 3-8.

Table 3-7 Leg Length Reserve Check


Keel to top of Upper Guide (m) 15,26

Keel above sea level LAT (m) 15,20

Water depth LAT (m) 106,7 70,0

Spudan penetration (m) 1,95 34,07

Total length used (m) = 139,11 134,53

Leg length (m) 157.58

Leg length reserve (m) = 18,47 23,05

3.10 LEG AND SPUDCAN BUOYANCY

3.10.1 The leg and spudcan buoyancy at the two locations is reported in Table 3-8.

Table 3-8 Leg & Spudcan Buoyancy


Water Depth (m) 106,7 70,0

Spudcan height (m) 5,79

Single leg buoyancy (without spudcan) (tonnes) 134,8 129,1

Spudcan submerged buoyancy (tonnes) 25,7



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3.11 HYDRODYNAMIC COEFFICIENTS

3.11.1 The hydrodynamic modelling of the jack-up leg may be carried out by utilising “detailed” or “equivalent” techniques, corresponding to the levels of structural modelling.

3.11.2 In the equivalent leg model, the hydrodynamic coefficients are calculated corresponding to the equivalent diameter of each bay of the leg stick. In this analysis, the equivalent stick leg model was used to calculate the global reactions of the unit and thus the “equivalent” hydrodynamic model was used to compute the hydrodynamic coefficients.

3.11.3 The hydrodynamic properties defined for each section of the 3 legs are shown in Table 3-10 to Table 3-11. This data was calculated following the ISO methodology with the leg dimensions based on leg drawings held in house for the Keppel FELS B-Class.

Table 3-9 Hydrodynamic Surface Condition Levels

Site 1 Site 2

Water depth (m) 106,7 70,0

Mean high water spring tide (MHWS) (m) 0,0 0,0

Mean water level (MWL) (m) = 106,7 70,0

MWL + 2m = 108,7 72,0

Spudcan penetration beneath seafloor (m) 1,95 34,07

MWL above spudcan tip (m) = 108,65 104,07

Table 3-10 Hydrodynamic Leg Sections for Site 1 (sand)

Hydrodynamic Sections[1] Leg Section

Top of Section above can tip (m) Bow Leg (1) Port Leg (2) Stbd Leg (3)

1 4,74 1-spudcan [2]

2 8,23 2-rough[2]

3 15,27 3-rough

4 75,01 4-rough

5 100,61 4-rough [1] 4-rough(3) [1]

6 108,65 4-rough(1&2) [1] 4-rough(3) [1]

7 123,85 4-smooth(1&2) [1] 4-smooth(3) [1]

8 143,28 4-smooth(1&2) [1]

9 151,82 4-smooth

10 156,09 5-smooth

11 157,58 6-smooth

[1] Raw water structure varies between bow / port legs and starboard leg. [2] Spudcan hydrodynamic model was not considered. - No direct guidance provided in the ISO

document (Ref [2]).



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Table 3-11 Hydrodynamic Leg Sections for Site 2 (clay)

Hydrodynamic Sections[1] Leg Section

Top of Section above can tip (m) Bow Leg (1) Port Leg (2) Stbd Leg (3)

1 66,47 4-rough

2 92,08 4-rough 4-rough(3)

3 104,07 4-rough(1&2) 4-rough(3)

4 119,27 4-smooth(1&2) 4-smooth(3)

5 143,28 4-smooth(1&2)

6 151,82 4-smooth

7 156,09 5-smooth

8 157,58 6-smooth

[1] Same methods used for Site 1 table were applied here so the notes were omitted.

Table 3-12 Member Details for Hydrodynamics calculations

Input - Hydrodynamic Section 1 - Spudcan (ignored)

Input - Hydrodynamic Section 2-rough

Chord Horizontal Diagonal Internal RWS [1]

Length (m) 3,486 11,623 6,777 4,847 None

Diameter (m) 0,5468 [2] 0,2198 0,2198 0,1683 None

Angle to horizontal 90 0 30,96 0 None

Input - Hydrodynamic Section 3-rough


Length (m) 3,520 None 6,072 4,847 None

Diameter (m) 0,5468 [2] None 0,2198 0,1683 None

Angle to horizontal 90 None 16,85 0 None

Input - Hydrodynamic Section 4-rough & 4-smooth


Length (m) 8,534 11,623 7,210 4,847 8,534

Diameter (m) 0,5468 [2] 0,2198 0,2198 0,1683 0,337

Angle to horizontal 90 0 36,29 0 90

Input - Hydrodynamic Section 4-rough(1&2) & 4-smooth(1&2)


Length (m) 8,534 11,623 7,210 4,847 8,534 (leg

1&2)

Diameter (m) 0,5468 [2] 0,2198 0,2198 0,1683 0,610 (leg

1&2)

Angle to horizontal 90 0 36,29 0 90 (leg 1&2)



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Input - Hydrodynamic Section 4-rough(3) & 4-smooth(3)


Length (m) 8,534 11,623 7,210 4,847 8,534 (leg 3)

Diameter (m) 0,5468 [2] 0,2198 0,2198 0,1683 1,016 (leg 3)

Angle to horizontal 90 0 36,29 0 90 (leg 3)

Input - Hydrodynamic Section 5-smooth


Length (m) 4,267 11,623 7,210 4,847 None

Diameter (m) 0,5468 [2] 0,2198 0,2198 0,1683 None

Angle to horizontal 90 0 36,29 0 None

Input - Hydrodynamic Section 6-smooth


Length (m) 1,495 11,623 None 4,847 None

Diameter (m) 0,5468 [2] 0,2198 None 0,1683 None

Angle to horizontal 90 0 None 0 None

[1] Raw water structures considered were different in Leg 3 from Leg 1&2 at this level. Legs 1, 2 and 3 refer to the Bow, Port and Starboard by default in this report.

[2] The chord is formed with a split tube of diameter = 0.5468m and a rectangular tooth of length = 0.5879.

Table 3-13 Base Hydrodynamic Coefficients for Tubulars

Surface condition CDi CMi

Smooth (Above MWL + 2m) 0,65 2,0

Rough (Below MWL + 2m) 1,00 1,8

3.11.4 There is no site specific information on marine growth thickness and so a thickness of 12,5mm was applied to all leg members below MWL + 2m.



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3.11.5 The chord hydrodynamics are covered in the following section, Figure 3-2 shows the chord section axes system.

Figure 3-2 Chord section axes system

3.11.6 Based on A.7.3-7 and A.7.3-8 the chord member drag and inertia coefficients are calculated as follows:

Table 3-14 Chord hydrodynamic coefficients

Angle Smooth

(above MWL+2m) Rough

(below MSL+2m)

() CD CM De CD CM De

0 2,730 2,0 3,358 1,8

15 2,694 2,0 3,335 1,8

30 2,639 2,0 3,298 1,8

45 2,694 2,0 3,335 1,8

60 2,730 2,0 3,358 1,8

75 2,694 2,0 3,335 1,8

90 2,639 2,0 3,298 1,8

105 2,694 2,0 3,335 1,8

120 2,730 2,0 3,358 1,8

135 2,694 2,0 3,335 1,8

150 2,639 2,0 3,298 1,8

165 2,694 2,0 3,335 1,8

180 2,730 2,0

0,947

3,358 1,8

0,990

3.11.7 Rough values include the effect of marine growth, smooth values do not. Note CM does not change for marine growth.

3.11.8 The equivalent hydrodynamic coefficients for all leg sections and all flow directions were calculated using the methods defined in Clause A.7.3.2 of the ISO document (Ref [2]). A summary of the hydrodynamic coefficients at 0 , 30o, 45o and 90º flow directions (anti-clockwise, with 0 being flow onto the bow) is listed in Table 3-15.



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Table 3-15 Equivalent Hydrodynamic Coefficients for Stick Leg Model

Hydrodynamic Section

Flow direction CD.De (m) CM.D2 (m2) Added mass per unit length (t/m)

60 5,491

90 5,614 2 - Rough

135 5,556

4,307 1,402

60 5,328

90 5,453 3 - Rough

135 5,395

4,200 1,359

60 4,600

90 4,687 4 - Rough

135 4,649

3,565 1,237

60 4,873

90 4,960 4 - Rough(1&2)

135 4,922

4,054 1,413

60 4,305

90 4,391 4 - Rough(3)

135 4,353

4,389 1,532

60 3,216

90 3,318 4 - Smooth

135 3,275

3,209 1,178

60 3,393

90 3,495 4 - Smooth(1&2)

135 3,453

3,726 1,386

60 3,657

90 3,760 4 - Smooth(3)

135 3,717

4,056 1,519

60 3,318

90 3,433 5 - Smooth

135 3,383

3,351 1,186

60 3,670

90 3,829 6 - Smooth

135 3,755

3,897 1,286



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4.1

4.2

4 ALIGNMENT POINTS AND COMMENTS

GENERAL

4.1.1 The analysis using the ISO recommended approaches has been divided into 5 steps and at each step, the results were cross-checked with the BASS. This is called Alignment Points and is presented in this section.

4.1.2 All data presented as submission for alignment is duplicated in the following sections with comments on any differences at each alignment point.

ALIGNMENT POINT 1 - GEOTECHNICAL CALCULATIONS

4.2.1 A comparison of the initial geotechnical inputs and outputs between GLND and BASS for the Sand and Clay assessment cases are presented in Table 4-1 and Table 4-2.

4.2.2 Comments to the differences between Noble Denton and the BASS, and ambiguities arising from ISO are bulleted after each table for the Sand and Clay cases respectively.

Table 4-1 Summary of Site 1 (sand) assessment key inputs and outputs from analyses

Analysis GLND BASS units

7 100 7 143 tonnes

69,7 70,1 MN Preload footing reaction, VL

15 652 15 748 kips

4 314 - tonnes

42,3 - MN Stillwater footing reaction, VSW

9 511 - kips

Spudcan area, A 152,6 152,4 m2

Spudcan volume, V 353,3 353,3 m3

Rig Physical attributes

Tip to max. area length 2,23 2,23 m

Friction angle used 29 29 (34-5) degrees Penetration calculation

Tip penetration depth 195 1 95 m

Laterally projected area, As 6,3 - m2

Interface friction angle, 29 29 degrees V-H Envelope Calculation

Utilisation origin 0,5QV/R,VH 3 227 tonnes

7 100 7 143 tonnes Qv

69,7 70,1 MN

852 857 tonne QH

8,4 8,4 MN

5 734 5 779 tonne-m QM

56,3 56,7 MNm

Foundation yield surface definition

Fixity 'n' parameter 0,0 - -



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G 58 899

23 765 * √[Vswl / (101,3 *

A)] kPa

Relative Density 60 60 %

Poisson ratio, v 0,2 0,2 -

Kd1 1,0 - -

Kd2 1,0 - -

Kd3 1,0 - -

139 686 140 473 tonnes/m K1

1 370 1 378 MN/m

132 443 133 190 tonnes/m K2

1 299 1 307 MN/m

2 699 882 2 724 577 t-m/rad

Spudcan fixities

K3 26 485 26 728 MNm/rad

Initial comments arising from comparison with the BASS’s values - Site 1 (sand) assessment

Aside from initial differences in footing reactions arising due to leg and spudcan buoyancy the foundation parameters derived by GLND were in close agreement with those calculated by Bennett & Associates.

4.2.3 There was close agreement with the foundation parameters and it was agreed to use GLND’s values going forward



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Table 4-2 Summary of Site 2 (clay) foundation key inputs and outputs from analyses

Analysis GLND BASS units 7 143 7 143 tonnes

70,1 70,1 MN Preload footing reaction, VL

15 748 15 748 kips

4 357 - tonnes

42,7 - MN Stillwater footing reaction, VSW

9 606 - kips

Spudcan area, A 152,6 152,4 m2

Spudcan volume, V 353,3 353,3 m3

Rig Physical attributes

Tip to max. area length 2,23 2,23 m

Backflow density same as in-situ profile

same as in-situ profile

kN/m3

Angle of shearing resistance used - - degrees

Hcav 4,3 - m

Penetration calculation

Tip penetration depth 34,07 34,1 m

Laterally projected area, As 43,7 - m2

Su at max area, Suo 44 - kPa

Su at spudcan tip (Su,l) 47 - kPa

Interface friction angle, - - degrees

Utilisation origin 0,5QV/R,VH 3 923 - tonnes

Qvnet 6 674 - tonnes

a 0,91 - -

b 0,289 - -

V-H Envelope Calculation

CHdeep 0,30 - -

9 023 7 143 tonnes QV

88,5 70,1 MN

2 027 2 195 tonnes QH

19,9 21,5 MN

14 169 12 863 tonne-m QM

139,0 126,2 MNm

Fixity 'n' parameter -0,5 - -

Foundation yield surface definition

Yield Surface 'alpha'parameter 1,0 - -

Su used to determine G 47 - kPa

Relative Density - - %

G 33 991 35 700 kPa

OCR 1,0 1 -

Poisson ratio, v 0,5 0,5 -

Kd1 2,00 2,00 -

Kd2 2,06 2,06 -

Spudcan fixities

Kd3 2,41 2,41 -

386 404 405 952 tonnes/m K1 3 791 3 982 MN/m

265 331 279 138 tonnes/m K2 2 603 2 738 MN/m

15 080 064 15 837 345 t-m/rad

Spudcan fixities (continued)

K3 147 935 155 364 MNm/rad



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4.2.4 Following receipt of foundation values provided by BASS the following comments were submitted by ourselves clarifying the input parameters are assessment techniques used to derive the foundation values presented in Table 4-2.

Initial comments arising from comparison with values provided by BASS - Site 2 (clay) assessment:

Input parameters

The undrained shear strength and shear modulus values were interpolated as per the supplied soil profile information.

The overconsolidation ratio and bulk unit weight, however, were assumed to be constant within each soil unit

Penetration Calculation

We have used the average backflow unit weight for the backflow soil to calculate the backflow weight on top of the spudcan.

The Houlsby & Martin approach is not applicable in this instance as the value for Sum leads to a B/Sum ratio of 9.62 which is outside the range of applicability.

It is not clear how you would use Houlsby & Martin’s parameters in layered soils - should Sum be the Su at the top of each layer or at the seabed surface?

It is noted in Edwards et al. (Géotechnique 2005 No. 55, No. 10) showed that Houlsby & Martin’s values are notably lower (i.e. less accurate) than the upper and lower bound solutions derived by Martin and FE data.

No guidance is provided on how to average undrained shear strength with depth if a sand layer is encountered.

No guidance is provided in ISO on how to assess infill - in this case no sand is present at the seabed surface so we have assumed no infill occurs.

GLND has used Skempton’s bearing capacity and depth factors with an averaged Su.

We recognise that our load-penetration curve does not incorporate a detailed analysis of the initiation of backflow, and the corresponding spudcan buoyancy within the transition to full backflow, however the penetration resistance profile for penetrations greater than those required for full immersion of the spudcan in the soil is correct.

We note that the predicted spudcan penetration depths will limit the water depth that can be used in the subsequent engineering assessment stage of the benchmarking exercise.

V-H Capacities

The choice of whether to use an averaged Su or modified bearing capacity factor in the spudcan penetration calculations will lead to different ‘b’ values for horizontal capacity. With reference to the case of a flat circular footing at the surface we propose that the Su in the ‘b’ equation should be Su at the depth of the maximum plan area (i.e. Suo) is used.

The stillwater footing reaction presented in the FV-FH plot includes all water buoyancy, backflow weight and spudcan ‘soil buoyancy’.



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Fixities

It is unclear what G value should be used for the present benchmarking assessment; we have used an interpolated G value based on the values provided in the table - it is noted that this is significantly greater than 400Su (using Su at D+0.15B as per guidelines)

The guidance in the ISO document is unclear on what IrNC should actually be used - when should the data in Fig A.9.3-12 actually be used?

The symbol for overconsolidation ratio in Equation A.9.3-36 is still ‘O’ instead of ROC

We have assumed ‘n’=0 for the fixity degradation relationship. We have used the depth factors given in Table A.9.3-4 but note that these are

the same as those given in SNAME (2008) for a Poisson’s ratio of 0.0 (not appropriate for soil!) - not 0.5, as it should be for clay.

The unit weight for backflow, for use with any additional penetrations, has been taken as that at the depth of max. plan area.

We have recommended an adhesion factor, , of 1.0 due to the penetration depth and strength of the soil at that depth.

We have not used P-Y curves to supplement the spudcan fixities. For the predicted penetration depth, 2D/B>4, consequently we have used the

fixity depth factors for 2D/B=4.

4.2.5 From the above it is evident that the majority of differences between foundation assessment values arose from interpretation of the design soil profile rather than interpretation of ISO or differences in assessment technique.

4.2.6 After discussions of the above comments and revision by BASS of their foundation values, there was close agreement with the foundation parameters and it was agreed to use Noble Denton’s values going forward.



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4.3 ALIGNMENT POINT 2 - OVERALL SYSTEM CHECKS

4.3.1 At this point, the following calculations were submitted for alignment:

Overall system geometry checks (leg length reserve);

Wind area and leg hydrodynamic coefficients;

Natural periods (pinned, with 80% fixity and 100% fixity, with or without P-Delta effect);

Hull sagging.

In addition to these a model was prepared which complied with the requirements of the standard, where possible based on an existing model of the unit.

4.3.2 The leg length reserve check submitted is listed in Table 4-3.

Table 4-3 Leg Length Reserve Check

Location Site 1 (sand) Site 2 (clay)

Keel to top of Upper Guide (m) 15,3

Keel above sea level LAT (m) 15,2

Water depth LAT (m) 106,7 70,0

Spudan penetration (m) 2,0 34,,

Total length used (m) = 139,1 134,5

Leg length (m) 157,6

Leg length reserve (m) = 18,5 23,1

4.3.3 The wind area calculations are listed in Table 4-4. The 60 , 90º and 120º flow directions (anti-clockwise, with 0 being flow onto the bow) have been identified as the controlling cases in this analysis and thus only the calculation results for these directions are listed for comparison.

Table 4-4 Wind Area Calculations (m2)

Storm heading [1] Exc Shape Coefficient Inc. Shape Coefficient

60˚ 1 914 2 043

90˚ 1 860 1 993

120˚ 1 914 2 043 [1] Anti-clockwise, with 0,0˚ being flow onto the bow

4.3.4 Comparison of wind areas highlighted some differences between BASS and GLND. This is not down to the ISO code but differences arising from scaled dimensions used to derive the ‘block area approach’ used by both parties. No response was received from BASS to our email clarification of how our wind areas had been derived, and the values presented above were therefore taken as being aligned.



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4.3.5 The equivalent hydrodynamic coefficients for the stick-leg models at the two sites, following the ISO specifications, are listed in Table 4-5 and Table 4-6, respectively.

Table 4-5 Equivalent Hydrodynamic Coefficients for Stick Leg Model for Site 1

Top of Section above can tip (m)

Flow direction

CD.De (m) CM.D2 (m2) Added mass per unit length (t/m)

0 5,491

90 5,614 8,23

135 5,556

4,307 1,402

60 5,328

90 5,453 15,27

135 5,395

4,200 1,359

60 4,600

90 4,687 75,01 (Leg 3)

100,61 (Leg 1 & 2) 135 4,649

3,565 1,237

60 4,873

90 4,960 108,65 (Leg 1 & 2)

135 4,922

4,054 1,413

60 4,305

90 4,391 108,65 (Leg 3)

135 4,353

4,389 1,532

60 3,657

90 3,760 123,85 (Leg 3)

135 3,717

4,056 1,519

60 3,393

90 3,495

135 3,453 143,28

135 3,717

3,726 1,386

60 3,216

90 3,318 151,82

135 3,275

3,209 1,178

60 3,318

90 3,433 156,09

135 3,383

3,351 1,186

60 3,670

90 3.829 157,58

135 3.755

3,897 1,286



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Table 4-6 Equivalent Hydrodynamic Coefficients for Stick Leg Model for Site 2

Top of Section above can tip (m)

Flow direction

CD.De (m) CM.D2 (m2) Added mass per unit length (t/m)

60 4.600

90 4.687 66.47 (Leg 3)

92.08 (Leg 1 & 2) 135 4.649

3.565 1.237

60 4.873

90 4.960 104.07 (Leg 1 & 2)

135 4.922

4.054 1.413

60 4.305

90 4.391 104.07 (Leg 3)

135 4.353

4.389 1.532

60 3.657

90 3.760 119.27 (Leg 3)

135 3.717

4.056 1.519

60 3.393

90 3.495

135 3.453 143.28

135 3.717

3.726 1.386

60 3.216

90 3.318 151.82

135 3.275

3.209 1.178

60 3.318

90 3.433 156.09

135 3.383

3.351 1.186

60 3.670

90 3.829 157.58

135 3.755

3.897 1.286

4.3.6 GLND’s drag coefficients calculated based on chord member geometry according to ISO formulae were similar (2-6% difference) to those provided by BASS when excluding raw water structure. It was agreed that raw water structure should be included for assessment purposes (included in tabulated values above).



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4.3.7 The unit was modelled using the equivalent 3-leg stick model (see Figure 4-1) for global loading, in conjunction with the single detailed leg model (see Figure 4-2) for leg and holding system strength checks. The modelling methodology is described below:

The leg properties of the 3-leg model were calibrated against the characteristics of the detailed single leg model for a consistent approach;

The hull represented in the equivalent leg model is constructed of stiff beams representing the approximate stiffness of the actual hull;

The leg to hull connection is modelled in the equivalent leg model using an equivalent spring with calculated vertical and rotational stiffness’s. The detailed leg model leg to hull connection is represented by a series of springs and gaps arranged such that they represent the upper and lower guides, pinions and chocks.

(leg below hull cropped for reporting purposes)

Figure 4-1 - 3 Stick Leg Model (showing hull beam grillage)



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Figure 4-2 - Example portion of F.E. Model of Leg

4.3.8 The mass of the equivalent 3 leg model has been represented by adjusting the density of each element in the leg and the hull to produce the correct mass distribution over the whole unit. Different masses were used for different parts of the analysis, for example leg added mass was incorporated into the dynamic analysis model but was removed for the quasi-static analysis. It should be noted that most of the analyses were performed with gravity turned off in which case vertical forces are added to the model to represent the vertical effect of the mass distribution.

4.3.9 The mass of the detailed leg model was modelled by applying small vertical forces to each node in the model along the whole length of the leg instead of using either discrete or distributed masses as in this case gravity is turned off.

4.3.10 Leg inclination was incorporated into the detailed leg model by applying a series of vertical couples up the leg which summed to give the total leg inclination moment. The leg inclination moment was calculated assuming an offset of 0.5% of the leg length below the hull as stipulated in A.10.5.4.

4.3.11 The natural periods calculated using the in-house software FORCE-3 are listed in Table 4-7.

Table 4-7 Linear Natural Periods for hull sway condition (max hull weight = 10 070 tonnes)

Location Site 1 (Sand) Site 2 (Clay)

Pinned with No P-delta effect (s) 9,54 8,90

Pinned with P-delta effect (s) 10,58 9,50

80% fixity with P-delta effect (s) 7,83 5,74

100% fixity with P-delta effect (s) 7,60 5,65



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4.3.12 There were some initial discrepancies between the GLND and BASS results; this was resolved after investigation and attributed to differences in the leg section stiffness calculations. (The BASS natural periods were originally calculated based on the full chord section, i.e. including all the tooth area, while our calculation for chord section stiffness has included only 10% tooth area as suggested in the ISO document (Ref [2]). BASS then recalculated their chord section stiffness using 10% tooth area and re-submitted their natural periods for pinned conditions which are in closer agreement with GLND natural periods (see Table 4-8) below.

Table 4-8 Natural Periods Alignment

Location Site 1 (Sand) Site 2 (Clay)

Assessor GLND BASS GLND BASS

Pinned with No P-delta effect (s) 9,54 9,64 8,90 8,91

Pinned with P-delta effect (s) 10,58 10,32 9,50 9,64

4.3.13 The sway stiffness has been analysed with a unit loading of 1MN (102 tonnes) applied at the hull centre of gravity (CoG) for cases without p-delta loading. Results are summarised in Table 4-9.

Table 4-9 Hull Displacements and Sway Stiffness

Foundation conditions

Displacements (m) Sway stiffness (MN/m)

Site 1 (sand)

Pinned 0,196 5,09

Linear Fixity: 80% K3 (rot) 100% K3 (rot)

0,121 0,114

8,26 8,77

Site 2 (clay)

Pinned 0,171 5,86

Linear Fixity: 80% K3 (rot) 100% K3 (rot)

0,072 0,070

1,39 1,43

4.3.14 No comparable data was received from BASS



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4.3.15 Reactions are reported for a gravity loadcase with ‘pinned’ foundation restraint condition accounting for 25% hull sag. Footing reactions are reported in Table 4-10

Table 4-10 Footing reactions from gravity loadcase

Leg F-X (kN) F-Y (kN) F-Z (kN)

Bow -73 0 42 086

Port 36 -86 42 031

Stbd 36 86 42 031 Site 1 (sand)

Total 0 0 126 150

Bow -86 0 42 163

Port 43 -103 42 077

Stbd 43 103 42 077 Site 2 (clay)

Total 0 0 126 320

4.3.16 The difference in vertical reaction of approximately 170kN is due to additional leg buoyancy in the sand case attributed to a the combination of slightly greater penetration and increased waterdepth.

4.3.17 No comparable data was received from BASS.



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4.4 ALIGNMENT POINT 3 - ENVIRONMENTAL LOADINGS

4.4.1 At this point, the following calculations were submitted for alignment:

Loading direction for analysis

Quasi-static wave and current loads

Dynamic amplification factors (DAFs)

4.4.2 The worst case loading directions for, preload and foundation bearing capacity, leg and holding system strength and overturning capacity have been defined as 60, 90 and 120 degrees anticlockwise from the bow respectively for this assessment:

o 0

Storm Direction

+ve

4.4.3 Wind loads calculated by spreadsheet methods for a windspeed of 51,4m/s, inclusive of a load factor of 1.15 are presented in Table 4-11. Moment arms for different parts of the unit are presented with reference to the effective penetration.

Table 4-11 Wind Loads

Force / Arm

Storm Direction Leg Below Hull Hull Leg Above Hull

060˚ 158,7kN / 119,9m 4 785kN / 144,1m 444,0kN / 147,8m

090˚ 163,4kN / 119,1m 4 660kN / 143,8m 458,9kN / 147,8m Site 1 (sand)

120˚ 158,7kN / 119,1m 4 787kN / 144,1m 444,0kN / 147,8m

060˚ 114,4kN / 116,5m 4 786kN / 140,3m 558,3kN / 146,3m

090˚ 117,7kN / 116,5m 4 659kN / 140,0m 576,8kN / 146,3m Site 2 (clay)

120˚ 114,4kN / 116,5m 4 786kN / 140,3m 558,3kN / 146,3m

4.4.4 Note, the length of leg below the hull considered in the wind force calculations is calculated from the water surface to the keel level. The water surface elevation is different for each leg as it is calculated from the wave profile at the phase which corresponds to the maximum wave loading on the unit.

4.4.5 No comparative breakdown of wind loads was received from BASS but overall wind loads were provided, and comparison presented in Table 4-12



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Table 4-12 GLND vs BASS Wind Loads

GLND BASS

Storm

Direction Total Force (kN)

Total Moment(kN-m)

Total Force (kN)

Total Moment (kN-m)

060˚ 5 388 773 944 5 318 757 273

090˚ 5 282 757 414 5 211 743 563 Site 1 (sand)

120˚ 5 388 773 944 5 318 757 273

060˚ 5 458 766 340 5 479 745 047

090˚ 5 354 750 634 5 372 732 030 Site 2 (clay)

120˚ 5 458 766 340 5 479 745 047

4.4.6 Results show relatively close agreement - the differences are attributed to the models rather than the interpretation of ISO.

4.4.7 Quasi-static wave and current loads, calculated using the in-house software FORCE-3, are listed in Table 4-13. Wave and current Loads are presented in Table 4-13 are based on the leg sections and raw water structure previously detailed based on the following wave and current input parameters:

Significant wave height Hsrp = 7,0m Sand = 9,0m Clay

Peak wave period Tp = 13,0s Sand = 14,7s Clay

Current: (Surface and seabed) = 0,0 m/s

4.4.8 A wave kinematics reduction factor of 0.86 has been used with the ‘intrinsic’ wave period to determine the wave particle kinematics. A load factor of 1.15 has been applied.

4.4.9 Nit should be noted that a current velocity of zero applies to all cases so that no current loads were actually calculated in this analysis.

Table 4-13 Wave / Current Loads (LF=1,15)

GLND BASS

Storm

Direction Wave/Current Force (kN)

Wave/Current Moment [1]

(MN.m)

Wave/Current Force (kN)

Wave/Current Moment [1]

(MN.m)

060˚ 1 529 144 432 1 293 124 228

090˚ 1 484 140 893 1 377 132 097 Site 1 (sand)

120˚ 1 415 135 008 1 414 134 770

060˚ 3 071 265 923 2 521 217 875

090˚ 3 094 266 790 2 606 224 983 Site 2 (clay)

120˚ 3 013 260 680 2 607 225 696

[1] Moments taken from the point of effective penetration



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4.4.10 The wave loads calculated by BASS are about 8% less than those by GLND for the sand case while for the clay case the difference is up to 19% less. This may be due to the different way of using kinematics factors in the calculations.

4.4.11 The following table describes how each of the actions applied to the unit are modelled in the quasi-static analysis.

Table 4-14 Summary of actions considered

Action Modelling Details

a) Functional actions due to fixed and variable loads

Hull

Modelled as three lump masses located at each leg to hull connection along with a distributed mass across the hull structure. As gravity is turned off for most of the analyses three vertical forces are also applied to the three leg to hull connections to model the vertical effect of the masses.

Legs

Mass is distributed up the legs appropriately however when gravity is turned off the vertical effect is modelled by vertical forces distributed up the legs.

b) Hull sagging Moments applied at the leg to hull connections

c) Wind actions Horizontal forces applied directly to nodes in the model representing the leg below the hull, hull and leg above the hull (quasi-static analysis only).

d) Wave and current actions Applied as horizontal forces to nodes up the leg

e) Inertia actions Applied as a combination of horizontal forces and moments to the hull centre of gravity node (quasi-static analysis only)

f) Large displacement effects Accounted for the software

g) Conductor actions None

h) Other applicable actions None

4.4.12 The DAF’s presented in Table 4-15 and Table 4-16 below have been calculated for both the Sand and Clay cases. Relative velocity effects were not included in the ‘mass’ analysis and hence an explicit damping ratio of 7% was used in accordance with ISO.

4.4.13 Inertia actions can be determined from a dynamic amplification factor using either a single degree of freedom analysis (DAFS) or stochastic analyses (DAFR). In this benchmarking, a stochastic analysis was selected, in which a statistical method is used to determine the MPME of the dynamic response.

4.4.14 A short investigation has been performed to establish the required simulation length using the Winterstein/Jensen approach to acquire a stable DAF for all storm headings being considered. For each case this was performed using the same storm qualified at 3, 6 and 9hrs.

4.4.15 Storms were qualified as stipulated in Table A.7.3-4, whereby the statistics of the storm were shown to be within the limits specified for standard deviation, skewness, kurtosis and maximum crest elevation.



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4.4.16 Following the investigation appropriate 9 hr storms were generated and qualified using our in-house software JUSTAS. The wave-train simulation parameters were then input into our FORCE-3 software which was used to calculate the response and hence the 3hr MPME as described in Annex C.10.5.3.2-3 of ISO.

4.4.17 80% linearised spudcan fixity as shown in Table 3-6 has been included in the dynamic analyses for calculation of the DAFR’s as recommended in ISO Clause A.9.3.4.1 and Clause A.10.4.4.

4.4.18 The DAFR’s determined through the above processes using the FORCE-3 software were then smoothed using a weighted average approach, in order to minimise wave cancellation and reinforcement effects. GLND’s usual procedure for calculating weighted average DAF’s is to use 50% of the DAF for that heading and then add 25% from each of the DAF’s of the two adjacent headings (typically for 15-degree increments). The resulting DAF’s are listed in Table 4-15 and Table 4-16 below.

Table 4-15 DAFR from the Dynamic MPME (Hull Weight = 10069,8t)

Site 1 (sand) Site 2 (clay)

Storm Direction 60º 90º 120º 60º 90º 120º

BS DAFR 1,66 1,69 1,73 1,22 1,23 1,24

OTM DAFR 1,99 2,04 2,08 1,35 1,37 1,38

Table 4-16 DAFR from the Dynamic MPME (Hull Weight = 8770,3t)

Site 1 (sand) Site 2 (clay)


BS DAFR 1,54 1,56 1,59 1,20 1,21 1,22

OTM DAFR 1,80 1,83 1,87 1,34 1,36 1,38

4.4.19 GLND’s results are compared with BASS’s results in Table 4-17 below.

Table 4-17 DAFR Alignment (Hull Weight = 10069,8t)

Maximum hull weight GLND BASS


BS DAFR 1,66 1,69 1,73 1,58 1,55 1,58 Site 1 (Sand) OTM DAFR 1,99 2,04 2,08 1,86 1,81 1,91

BS DAFR 1,22 1,23 1,24 1,11 1,10 1,14 Site 2 (Clay) OTM DAFR 1,35 1,37 1,38 1,18 1,18 1,22

4.4.20 It was not expected that the DAFs from the two assessors would be identical, given the inherent variability in the calculation process and the differences between the models. The results show reasonable alignment with differences justified by differences in the models and approach used to determine the DAF’s. It was agreed to align to GLND’s DAF’s to move forward.



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4.5 ALIGNMENT POINT 4 - STICK MODEL RESPONSES

4.5.1 The following calculations have been submitted for alignment:

Summarised breakdown of loadings (wind, wave-current, inertia) and responses (hull sway, footing reactions and forces in legs at base of rack chock);

Reactions at the leg-to-hull and foundation interface levels based on the structural response incorporating fixity.

4.5.2 Loadings and response are based on the finite element “stick leg” model using the FORCE-3 bolt-on to the PAFEC finite element software. The final quasi-static analysis has been incorporated with 100% foundation fixity.

4.5.3 Wind loads are previously presented in Table 4-12

4.5.4 Wave and current loads are previously presented in Table 4-13

4.5.5 Inertial (dynamic) loads are summarised in Table 4-18 and Table 4-19. The inertia loads were calculated as (DAFR -1,0) x Wave-Current Load (Static). The load factor of 1.15 has been included in all the loads listed below. Inertia loads have been applied at the hull centre of gravity as a force and moment combination to accurately represent the BS and OTM contributions and also as forces applied to the legs above the upper guides.

Table 4-18 Inertia Loads (LF=1.15)

Hull Weight = 10069,8t Hull Weight = 8770,3t Location

Storm Heading Force (kN) Moment (MN-m) Force (kN) Moment (MN-m)

60º 1 009 142 988 826 115 546

90º 1 024 146 528 831 116 941 Site 1: Sand

120º 1 033 145 809 835 117 457

60º 676 93 073 614 90 414

90º 712 99 082 650 96 404 Site 2: Clay

120º 723 99 059 663 99 058

Table 4-19 Inertia Loads Alignment (Hull Weight = 10069,8t)

GLND BASS Location

Storm Heading Force (kN) Moment (MN-m) Force (kN) Moment (MN-m)

60º 1 009 142 988 933 133 422

90º 1 024 146 528 950 137 381 Site 1: Sand

120º 1 033 145 809 944 134 167

60º 676 93 073 574 78 994

90º 712 99 082 599 83 244 Site 2: Clay

120º 723 99 059 605 82 792



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4.5.6 The inertia loads from GLND and BASS show reasonable alignment with differences attributed to the different wave/current loads from which they are calculated.

4.5.7 The total loading condition is summarised in Table 4-20 (including P-Delta loads)

Table 4-20 Total Loading Alignment (Hull Weight = 10069,8t)

GLND BASS Case

Storm Direction Force (MN) Moment (MN-m) Force (MN) Moment (MN-m)

60º 7 927 1 061 7 554 1 158

90º 7 789 1 046 7 537 1 155 Site 1 (Sand)

120º 7 836 1 054 7 664 1 168

60º 9 204 1 106 8 605 1 132

90º 9 159 1 100 8 578 1 129 Site 2 (Clay)

120º 9 194 1 107 8 660 1 142

4.5.8 The total loading shows that our loading condition is greater than BASS on force but that similar overturning moments have been calculated.

4.5.9 The breakdowns of the model responses (hull sway, footing reactions and forces in legs just below lower guide) are listed in Table 4-21 ~Table 4-28. Note the coordinate system in our stick-leg model is defined with 0 degree heading from bow to stern while BASS used 0 degree heading from stern to bow when both storm heading directions are counter clockwise. The rig heading used in the following comparisons has followed our definition.

Table 4-21 Hull Sways (m)

Hull Weight = 10069,8t Hull Weight = 8770,3t Storm Heading

Site 1 (Sand) Site 2 (Clay) Site 1 (Sand) Site 2 (Clay)

60º 1.75 1.12 1.68 1.02

90º 1.73 1.07 1.59 1.00

120º 1.66 1.06 1.54 0.99

Table 4-22 Hull Sways Alignment (m) (Hull Weight = 10069,8t)

GLND BASS Storm Heading

Site 1 (Sand) Site 2 (Clay) Site 1 (Sand) Site 2 (Clay)

60º 1.75 1.12 1.66 1.00

90º 1.73 1.07 1.64 0.98

120º 1.66 1.06 1.69 0.98

4.5.10 The hull sways show reasonable alignment, although GLND’s hull sways are larger due to our greater wave/current loads.



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Table 4-23 Footing Reactions for Site 1: Sand


Leg Fh (kN) Fv (kN) M (kN-m) Fh (kN) Fv (kN) M (kN-m)

Bow 2904 27458 50669 2825 23789 47529

Port 2943 26409 49776 2855 22867 46411 60º

Starboard 2090 72319 206 2060 66826 206

Bow 2806 42095 60920 2659 37788 57330

Port 2904 15843 35551 2668 13626 31529 90º

Starboard 2090 68258 1678 2266 62068 29538

Bow 2531 56143 50394 2521 50894 59527

Port 2766 12949 29636 2560 10722 24780 120º

Starboard 2551 57114 47628 2560 51875 58262

Table 4-24 Footing Reactions for Site 1: Sand, Alignment (Hull Weight = 10069,8t)



Bow 2904 27458 50669 2776 28675 51395

Port 2943 26409 49776 2668 27733 51120 60º

Starboard 2090 72319 206 2217 70348 0

Bow 2806 42095 60920 2708 42271 50953

Port 2904 15843 35551 2600 17746 39652 90º

Starboard 2090 68258 1678 2237 66737 0

Bow 2531 56143 50394 2580 55789 32383

Port 2766 12949 29636 2492 14254 32618 120º

Starboard 2551 57114 47628 2472 56712 30676

4.5.11 The footing reactions show reasonable alignment given the differences in overall loading shown in Table 4-20.



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Table 4-25 Footing Reactions at Site 2: Clay



Bow 3394 30401 136614 3237 27036 137183

Port 3434 29616 137026 3267 26242 137311 60º

Starboard 2384 66306 35316 2649 60273 76449

Bow 3208 42085 125303 3149 37867 130208

Port 3365 21621 137899 3227 18502 137311 90º

Starboard 2590 62647 64648 2727 57182 89193

Bow 2904 53308 101740 2923 48579 113315

Port 3345 18874 137791 3237 15657 137330 120º

Starboard 2943 54151 99228 2972 49315 111726

Table 4-26 Footing Reactions at Site 2: Clay, Alignment (Hull Weight = 10069,8t)



Bow 3394 30401 136614 3129 32216 136222

Port 3434 29616 137026 3051 31490 135888 60º

Starboard 2384 66306 35316 2492 63157 80383

Bow 3208 42085 125303 3061 42291 133916

Port 3365 21621 137899 2943 24447 130728 90º

Starboard 2590 62647 64648 2580 60125 94353

Bow 2904 53308 101740 2904 52101 118956

Port 3345 18874 137791 2884 21965 126686 120º

Starboard 2943 54151 99228 2815 52788 117867

4.5.12 The footing reactions show reasonable alignment given the differences in overall loading shown in Table 4-20.



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Table 4-27 Lower Guide Reactions at Site 1: Sand

Site: SAND Storm

Heading Leg Fh (kN) Fv (kN) M (kN-m) [1]

Inclination Moment [1]

(kN-m)

Bow 2246 20326 342683 16871

Port 2276 19277 339603 9732 60º

Starboard 1717 65187 396726 44432

Bow 2109 34963 348137 25859

Port 2423 8819 338200 10795 90º

Starboard 1609 61028 383159 41937

Bow 1913 49011 354730 34491

Port 2472 5817 326487 7956

Hull Weight = 10069,8t

120º

Starboard 1874 49982 361597 35087

Bow 2158 16706 325457 14616

Port 2188 15794 328782 14051 60º

Starboard 1717 59596 376988 41059

Bow 1972 30656 322474 23217

Port 2207 6494 308279 8374 90º

Starboard 1776 54936 355701 38134

Bow 1913 43762 329126 31266

Port 2266 3590 300824 6586


120º

Starboard 1884 44753 335492 31874 [1] The additional leg moment due to leg inclination resulting from leg-hull clearances and hull

inclination is not included in the values in this column.



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Table 4-28 Lower Guide Reactions at Site 2: Clay

Site: CLAY Storm

Heading Leg Fh (kN) Fv (kN) M (kN-m)[1]

Inclination Moment [1]

(kN-m)

Bow 2188 23652 258415 17689

Port 2217 22887 261230 17235 60º

Starboard 1619 59056 300137 38584

Bow 1913 35159 261397 24485

Port 2403 14852 250596 12580 90º

Starboard 1628 55603 285805 36454

Bow 1746 46342 267391 31020

Port 2659 12076 252352 10986


120º

Starboard 1668 47186 273473 31509

Bow 2040 20189 235842 15734

Port 2060 19394 238334 15268 60º

Starboard 1854 53219 278888 35070

Bow 1854 30960 199074 22036

Port 2276 11684 209375 10765 90º

Starboard 1766 50168 199781 33272

Bow 1766 41634 210199 28267

Port 2551 8829 222098 9112


120º

Starboard 1697 42340 213495 28692

[1] The additional leg moment due to leg inclination resulting from leg-hull clearances and hull inclination is not included in the values in this column.

4.5.13 No comparable information on lower guide reactions has been received from BASS. The final assessment checks have been calculated using the GLND footing reactions and lower guide loads.



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4.6 ALIGNMENT POINT 5 - FINAL ASSESSMENT RESULTS

4.6.1 A summary of the final assessment result is presented in Table 4-29.

Table 4-29 Footing Reactions from the Global Responses (Site: SAND; Units: MN)

SAND Storm

Direction Leg Axial Shear

Preload UC

Bearing UC

Sliding UC

Bow 28.45 2.98 0.45 0,42 -

Port 27.47 3.00 0.43 0,44 - 60˚

Stbd 70.27 2.01 1.11 1,34 -

Bow 42.11 2.72 0.67 0,56 -

Port 17.57 3.14 0.28 0,70 0,67 90˚

Stbd 66.51 2.03 1.05 1,25 -

Bow 55.13 2.46 0.87 0,92 -

Port 15.02 3.03 0.24 0,76 0,73


120˚

Stbd 56.04 2.48 0.89 0,94 -

Bow 25.04 2.84 0.40 0,47 0,41

Port 24.21 2.86 0.38 0,49 0,43 60˚

Stbd 64.23 2.11 1.01 1,17 -

Bow 37.79 2.23 0.60 0,39 -

Port 17.82 2.34 0.28 0,62 0,60 90˚

Stbd 57.88 1.96 0.91 0,97 -

Bow 50.46 2.58 0.80 0,79 -

Port 11.61 3.01 0.18 0,87 0,84


120˚

Stbd 51.42 2.61 0.81 0,81 -

Table 4-30 Footing Reactions from the Global Responses (Site: CLAY; Units: MN)

CLAY Storm

Direction Leg Axial Shear

Preload UC

Bearing UC

Sliding UC

Bow 30.40 3.40 0.48 0,38 0,27

Port 29.62 3.43 0.46 0,36 0,27 60˚

Stbd 66.31 2.38 1.04 1,24 0,19

Bow 42.08 3.20 0.66 0,66 0,25

Port 21.62 3.37 0.34 0,22 0,26 90˚

Stbd 62.65 2.59 0.98 1,16 0,20

Bow 53.31 2.91 0.84 0,94 0,23

Port 18.88 3.34 0.30 0,20 0,26


120˚

Stbd 54.15 2.95 0.85 0,96 0,23



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Bow 27.04 3.24 0.42 0,30 0,25

Port 26.24 3.27 0.41 0,29 0,26 60˚

Stbd 60.27 2.64 0.95 1,10 0,21

Bow 37.87 3.15 0.59 0,55 0,25

Port 18.50 3.23 0.29 0,19 0,25 90˚

Stbd 57.18 2.72 0.90 1,04 0,21

Bow 48.58 2.93 0.76 0,80 0,23

Port 15.66 3.23 0.25 0,18 0,25


120˚

Stbd 49.31 2.97 0.77 0,82 0,23

4.6.2 The utilisation checks for the most critically loaded (port and stbd) legs for the 90 degree heading (worst from structural utilisations) are presented in Table 4-31.

Table 4-31 Member Checks (Hull Weight = 10069,8t)

Site Leg

Member Axial (kN)

Y-Bending (kN-m)

Z-Bending (kN-m)

Y-Shear (kN)

Z-Shear (kN)

Max Section Torque (kN-m)

Combined

Utilisation

Chord -30 320 -363,80 -27,81 41,99 113,9 -2,23 0,44

H Brace -1 018 5,073 -5,721 -1,973 1,091 2,262 0,24

Po r t

D Brace -1 027 -7,424 3,677 -1,134 1,967 0,096 0,31

Chord -51 680 -669,40 -24,03 3,18 240,0 -1,12 0,74

H Brace -669,8 0,793 -4,951 -1,656 0,069 1,964 0,16

SAND

S t bd

D Brace -783,2 -22,611 -4,811 1,013 -6,095 -1,739 0,28

Chord -22 400 -276,80 17,65 31,20 89,28 -4,48 0,32

H Brace -878,98 --0,654 5,343 -1,699 0,827 2,181 0,20

Po r t

D Brace -943,62 -5,820 3,366 -0,971 1,692 0,076 0,28

Chord -40 710 -532,40 18,70 26,63 191,5 -2,67 0,58

H Brace -666,43 0,600 4,598 -1,519 0,052 2,090 0,15

CLAY

S t bd

D Brace -832,80 -13,537 5,177 -1,511 3,592 -0,027 0,27

4.6.3 A summary of the member lengths and effective length factors used in determining the structural utilisations is provided below:

Chords: Member Length = 4,27m KY = 1,00 KZ = 1,00



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Horizontal Braces: Member Length = 5,68m KY = 0,90 KZ = 0,90 Diagonal Braces: Member Length = 6,76m KY = 0,90 KZ = 0,90

Note: The above effective lengths are different in some sections of the leg, those provided here apply to the critical elements reported in Table 4-31.

4.6.4 The critical holding system utilisation checks are summarised in Table 4-32 for the port and starboard legs for the 120 degree heading.

Table 4-32 Maximum Utilisations of the Chocks

Site Leg Load (MN) Allowable Load

(MN)[1] Utilisation

Port 28,50 85,47 0,33 Sand

Stbd 50,70 85,47 0,59

Port 20,9 85,47 0,25 Clay

Stbd 39,6 85,47 0,46

[1] The jacking system ultimate capacity = 98.30MN, Load factor = 1,15

4.6.5 The leg to spudcan connection strength has not been assessed for these assessments.

4.6.6 A summary of the final assessment result is presented in Table 4-33.

Table 4-33 Final assessment results

Criteria Site 1 (sand) Site 2 (clay)

Hull Elevation (m) Airgap = 15,2 >

Minimum clearance = 8,70

Airgap = 15,2 >

Minimum clearance = 11,05

Leg length reserve (m) 18,47 11,05

Spudcan penetration (m) 1,95 34,07

Utilisations Heading UC Heading UC

Overturning 120 0,78 120 0,70

Preload Capacity 60 1,11 60 1,04

Foundation bearing capacity

60 1,34 60 1,24

Additional settlements (m) 60 0,10 60 3,23

Windward leg sliding 120 0,84 60 0,27

Maximum Hull sway (m) 60 1,75 60 1,12

Leg chord strength[1] 90 0,74 90 0,58

Leg brace strength 90 0,31 90 0,28

Chock holding strength 120 0,59 120 0,46

[1] GLND have used the high strength equations given in A.12.6.2.4. This could be expected to cause a large difference in the utilisations if BASS have used the low strength equations.



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4.6.7 The alignment data provided by BASS are listed in Table 4-34, together with the utilisation checks from our analysis for comparison.

Table 4-34 Final assessment results

Criteria Site 1 (sand) Site 2 (clay)

Utilisations GLND BASS GLND BASS

Max Overturning 0,78 0,79 0,70 0,65

Preload Capacity 1,11 1,10 1,04 0,99

Leg chord strength 0,74 0,86 0,58 0,69

Leg brace strength 0,31 0,42 0,28 0,41

Chock holding strength

0,59 0,65 0,46 0,50

4.6.8 The overturning utilisations calculated by each consultant are very similar for the sand case but some 5% different to BASS’s for the clay case - it is possible BASS's numbers were for max hull weight for the clay case - there has been no response to our enquiries.

4.6.9 The GLND preload utilisations for both cases are marginally greater than those calculated by BASS. This is consistent with the maximum footing reaction force comparisons listed in Table 4-24 and Table 4-26.

4.6.10 The GLND leg chord and brace strength utilisation checks are all lower than those calculated by BASS. This is likely to be due to the difference in the lower guide reactions calculated by the two analysts and possibly that BASS are not using the high strength yield equations for leg chord strength checks. No response received from BASS to our discussion of final results.

4.6.11 During discussion of final results (alignment point 5) it was discovered that BASS are using an allowable rack-chock holding system capacity of 75,85MN. Had we used this allowable value (assuming inclusive of resistance factor) the rack chock UC’s would have been in closer agreement.

4.6.12 The foundation utilisation checks have not been provided by BASS and thus have not been included in this report.



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5.1

5.2

5 ISO / SNAME COMPARISON

INTRODUCTION

5.1.1 A comparison of the input parameters, intermediate and final assessment results determined from assessment following the ISO 19905-1 (DIS) and SNAME T&RB 5-5A Rev 3 approaches is summarised in the following sections:

FOUNDATION INPUT PARAMETERS

5.2.1 Geotechnical parameters calculated for the SNAME and ISO analyses are shown in Table 5-1. Please note the difference in penetration for both the sand and clay cases is not modelled in the analysis to provide for a more transparent comparison of the methods in later stages of the analysis.

5.2.2 For comparison purposes the ISO penetration was used as basis for the SNAME assessments (sand and clay respectively), but using the SNAME capacities and stiffnesses derived from SNAME penetration),

Table 5-1 Foundation parameters

Site Assessment Parameter ISO SNAME ISO / SNAME

Penetration (m) 1,95 2,00 98%

Vertical foundation stiffness (te/m) 139 686 139 645 100%

Horizontal foundation stiffness (te/m) 132 443 132 405 100%

Rotational foundation stiffness (te,m/rad) 2 699 882 2 889 159 93%

Vertical foundation capacity (te) 7 100 7 097 100%

Horizontal foundation capacity (te) 852 852 100%

Site 1 (Sand)

Moment foundation capacity (te,m) 5 734 5 930 97%

Penetration (m) 34,07 37,49 91%

Vertical foundation stiffness (te/m) 386 404 354 115 109%

Horizontal foundation stiffness (te/m) 265 331 266 808 99%

Rotational foundation stiffness (te,m/rad) 15 080 064 14 658 363 103%

Vertical foundation capacity (te) 9 023 7 095 127%

Weight of backfill (te) 1 880 - -

Net vertical foundation capacity 7 143 7 095 101%

Horizontal foundation capacity (te) 2 027 1 204 168%

Site 2 (Clay)

Moment foundation capacity (te,m) 14 169 15 750 90%

5.2.3 Comparison between the ISO and SNAME results above show that for site 1 (sand) the foundation fixity parameters are near-identical, and that for site 2 (clay) the ISO foundation vertical and rotational stiffnesses are marginally greater than the SNAME (SAGE) foundation stiffnesses whilst the horizontal foundation stiffness is approximately equal.



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5.3

5.2.4 The greater predicted penetration depth calculated using SNAME results in a shear modulus that is 8% greater than that calculated for the ISO case. The stiffness depth factors in the ISO document, however, are greater than those in SNAME for the case of a clay foundation (with Poisson ratio = 0.5). Consequently the overall stiffnesses calculated using the ISO document are very similar to those using SNAME (SAGE) (Table 5-1). As different depth factors are used for the vertical, horizontal and rotational stiffnesses, the ratio between the SNAME and ISO stiffnesses are different for each component stiffness.

NATURAL PERIODS

5.3.1 The natural periods with both the pinned and fixity conditions for the KFELS B Class following the two approaches are reported below:

Table 5-2 Natural periods[1]

Site Fixity ISO Nonlinear Period (s) SNAME Nonlinear Period (s)

Pinned 10,50 10,52

80% Rotational Fixity 7,83 7,83 Site 1 (Sand)

100% Rotational Fixity 7,60 7,62

Pinned 9,50 9,86

80% Rotational Fixity 5,74 5,93 Site 2 (Clay)

100% Rotational Fixity 5,65 5,83 [1]The periods reported are all sway periods with the maximum hull weight applied,

5.3.2 For Site 1 (sand), the natural periods from the ISO and the SNAME are almost identical. This is due to the similar foundation fixity predictions,

5.3.3 For Site 2 (clay), the natural periods from the SNAME cases are all longer than those calculated using the ISO. This is due to the lower rotational foundation stiffnesses used in the SNAME analysis as shown in Table 5-1,

5.3.4 It should be noted that the only difference between ISO and SNAME at this stage of the analysis is the foundation fixities.

5.4 SWAY STIFFNESS

5.4.1 For the same model with only differences in the foundation fixity conditions there is expected to be similar sway-stiffness increase for the SNAME case compared to the ISO assessment case due to the increased foundation rotational stiffness. No values are reported.



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5.5 WIND LOADS

5.5.1 Wind forces and moment arms are presented in Table 5-3 for 51,4 m/s wind speed and inclusive of the environmental load factor of 1,15. The moment arm is measured from the effective penetration.

Table 5-3 Wind loads

Force / Arm Site

Storm Direction

Leg Below Hull Hull Leg Above Hull

ISO 159kN / 116,7m 444kN / 147,7 m 60˚

SNAME 206kN / 116,7m 4 786kN / 143,8m

577kN / 147,7m

ISO 163kN / 116,7m 459kN / 147,7m 90˚

SNAME 212kN / 116,7m 4 660kN / 143,8m

597kN / 147,7m

ISO 159kN / 116,7m 444kN / 147,7m

Site 1 (Sand)

120˚ SNAME 206kN / 116,7 m

4 786kN / 143,8m 577kN / 147,7m

ISO 114kN / 106,3m 558kN / 140,4m 60˚

SNAME 149kN / 106,3m

4 786kN / 137,27m 726kN / 140,4m

ISO 118kN / 106,3m 577kN / 140,4m 90˚

SNAME 153kN / 106,3m

4 660kN / 137,27m 750kN / 140,4m

ISO 114kN / 106,3m 558kN / 140,4m

Site 2 (Clay)

120˚ SNAME 149kN / 106,3m

4 786kN / 137,27m 726kN / 140,4m

5.5.2 Note the length of leg below the hull considered in the wind force calculations is from the water surface to the keel level.

5.5.3 The wind loads presented above show identical hull wind loading between ISO and SNAME (single value presented), but that the wind load on the legs above and below the hull are lower for ISO than SNAME. This is due entirely to ISO recommending the use of a CD of 0,5 for leg drag above the waterline whereas SNAME recommends a CD of 0,65.



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5.6 WAVE LOADS

5.6.1 Wave-current forces and moments are presented in Table 5-4 for a 7,0m significant wave height with a 13,0s intrinsic period at Site 1 and 9,0m significant wave height with a 14,7s intrinsic period at Site 2. It should be noted that a zero current has been considered for assessment purposes. The forces and moments are inclusive of the environmental load factor of 1,15 with the moments calculated about the level of effective penetration,

Table 5-4 Wave - Current Loads

ISO SNAME

Storm

Direction Wave/Current Force (kN)

Wave/Current Moment (kN,m)

Wave/Current Force (kN)

Wave/Current Moment (kN,m)

60˚ 1 529 144 432 1 456 135 049

90˚ 1 484 140 893 1 420 132 100 Site 1 (Sand)

120˚ 1 415 135 008 1 351 126 485

60˚ 3 071 265 923 2 956 253 138

90˚ 3 094 266 790 2 976 255 005 Site 2 (Clay)

120˚ 3 013 260 680 2 898 247 895

5.6.2 The wave forces for the ISO case are slightly greater than those calculated to SNAME. This is due to the different calculation methods adopted with ISO using a kinematics reduction factor approach and SNAME using the traditional deterministic wave height approach.

5.6.3 It should be noted that the effects of apparent (as opposed to intrinsic) wave theory have not been incorporated into the ISO analysis for the KFELS B Class cases since a zero surface current velocity has been assumed,



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5.7 DYNAMIC AMPLIFICATION FACTORS (DAF’S)

5.7.1 The DAF’s shown below have been calculated for both the Sand and Clay cases, The Overturning and Base Shear DAF’s calculated for each heading has used a simulation length of 9hrs and a MPM exposure of 3hrs for the maximum hull weight case, Only the maximum hull weight cases are compared,

Table 5-5 Averaged Dynamic amplification factors (DAFs)

Overturning DAF Base Shear DAF Site Storm Heading

ISO SNAME ISO SNAME

60˚ 1,99 1,87 1,66 1,58

90˚ 2,04 2,06 1,69 1,71 Site 1 (sand)

120˚ 2,08 2,03 1,73 1,69

60˚ 1,35 1,37 1,22 1,25

90˚ 1,37 1,34 1,23 1,24 Site 2 (clay)

120˚ 1,38 1,33 1,24 1,22

5.7.2 GLND’s usual procedure for calculating weighted average DAF’s is to use 50% of the DAF for that heading and then add 25% from each of the DAF’s of the two adjacent headings (typically for 15-degree increments),

5.7.3 It can be seen from Table 5-5 that the SNAME DAF’s are very close to the ISO DAF’s given similar foundation stiffnesses. Differences are likely to arise from the following:

The use of different foundation stiffnesses for the ISO and SNAME analyses;

The inherent differences which occur when generating different storm data using different seeds.



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5.8 INERTIA LOADSETS

5.8.1 The following inertia loads were calculated and applied to the quasi-static models, Moments are calculated about the effective penetration,

Table 5-6 Inertia loadset

Inertia (Max hull weight) Inertia (Min hull weight) Site

Storm Heading ISO SNAME ISO SNAME

Force kN 1 009 887 826 734 60˚

Moment kN,m 142 988 125 656 115 546 101 103

Force kN 1 024 1 053 831 838 90˚

Moment kN,m 146 528 149 346 116 941 119 477

Force kN 1 033 976 835 791

Site 1 (Sand)

120˚ Moment kN,m 145 809 139 059 117 457 110 428

Force kN 676 750 614 686 60˚

Moment kN,m 93 073 93 801 90 414 85 695

Force kN 712 701 650 671 90˚

Moment kN,m 99 082 87 677 96 404 83 877

Force kN 723 648 663 671

Site 2 (Clay)

120˚ Moment kN,m 99 059 81 044 99 058 83 888

5.8.2 The inertia loadset is calculated directly from the wave/current loads and the DAF’s and therefore the differences in both of these are reflected in the inertia loads.



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5.9 TOTAL QUASI-STATIC LOADING

5.9.1 The following tables show the overall loading of the subject jack-up for the quasi-static analysis. The total load includes wind, wave/current and inertia loads. Moments are calculated about the effective penetration.

Table 5-7 Total quasi-static loading

Total Loading (Max hull weight)

Total Loading (Min hull weight) Site

Storm Heading

ISO SNAME ISO SNAME

Force kN 7 927 7 986 7 744 7 833 060˚

Moment kN.m 1 060 937 1 069 256 1 033 495 1 044 702

Force kN 7 789 8 005 7 596 7 790 090˚

Moment kN.m 1 045 594 1 074 899 1 016 006 1 045 030

Force kN 7 836 7 960 7 637 7 775

Site 1 (sand)

120˚ Moment kN.m 1 054 334 1 073 234 1 025 982 1 044 603

Force kN 9 204 9 141 9 143 9 076 060˚

Moment kN.m 1 106 426 1 092 765 1 103 766 1 084 659

Force kN 9 159 8 929 9 097 8 899 090˚

Moment kN.m 1 099 946 1 064 784 1 097 268 1 060 985

Force kN 9 194 8 972 9 134 8 995

Site 2 (clay)

120˚ Moment kN.m 1 107 169 1 074 716 1 104 473 1 077 559

5.9.2 The following tables show the overall response of the subject Jack-Up including the overall base shear and overturning moments. Note the overturning moments are calculated about the point of effective penetration.

Table 5-8 Hull sway

Total Loading (Max hull weight)

Total Loading (Min hull weight) Site

Storm Heading

ISO SNAME ISO SNAME

60˚ 1,75 1,76 1,68 1,69

90˚ 1,73 1,79 1,59 1,65 Site 1 (sand)

120˚ 1,66 1,70 1,54 1,58

60˚ 1,12 0,99 1,02 0,90

90˚ 1,07 0,93 1,00 0,85 Site 2 (clay)

120˚ 1,06 0,93 0,99 0,86



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Table 5-9 Reactions in leg at base of rack chock - Maximum Hull Weight

ISO SNAME Site

Storm Heading Moment

kNm Shear

kN Axial kN

Moment kN,m

Shear kN

Axial kN

342 683 2 246 20 326 346 430 2 305 20 366

339 603 2 276 19 277 349 982 2 335 19 316 60

396 726 1 717 65 187 400 297 1 756 65 109

348 137 2 109 34 963 360 831 2 237 34 963

338 200 2 423 8 819 349 893 2 551 8 260 90

383 159 1 609 61 028 397 305 1 697 61 577

354 730 1 913 49 011 364 029 1 991 49 178

326 487 2 472 5 817 335 306 2 551 5 454

Site 1 (sand)

120

361 597 1 874 49 982 370 985 1 942 50 159

258 415 2 188 23 652 321 670 2 433 22 485

261 230 2 217 22 887 321 376 2 423 21 621 60

300 137 1 619 59 056 343 350 1 158 60 224

261 397 1 913 35 159 308 426 2 080 34 767

250 596 2 403 14 852 298 126 2 394 13 852 90

285 805 1 628 55 603 320 395 1 295 55 711

267 391 1 746 46 342 316 176 1 736 46 362

252 352 2 659 12 076 299 892 2 560 10 781

Site 2 (clay)

120

273 473 1 668 47 186 314 509 1 619 47 186

Table 5-10 Reactions in leg at base of rack chock - Minimum Hull Weight

ISO SNAME Site


kNm Shear

kN Axial kN

Moment kN,m

Shear kN

Axial kN

325 457 2 158 16 706 328 939 2 207 16 697

328 782 2 188 15 794 332 353 2 227 15 784 60

376 988 1 717 59 596 380 500 1 736 59 615

322 474 1 972 30 656 335 080 2 090 30 656

308 279 2 207 6 494 321 640 2 325 5 798 90

355 701 1 776 54 936 369 808 1 815 55 642

329 126 1 913 43 762 337 258 1 982 43 939

300 824 2 266 3 590 308 309 2 325 3 227

Site 1 (sand)

120

335 492 1 884 44 753 343 801 1 942 44 940

235 842 2 040 20 189 289 689 2 207 19 326

238 334 2 060 19 394 289 395 2 197 18 531 60

278 888 1 854 53 219 313 233 1 550 53 720

199 074 1 854 30 960 282 234 2 001 30 519

209 375 2 276 11 684 272 326 2 197 11 193 90

199 781 1 766 50 168 295 379 1 560 49 864

210 199 1 766 41 634 292 240 1 844 41 300

222 098 2 551 8 829 275 955 2 374 8 211

Site 2 (clay)

120

213 495 1 697 42 340 290 670 1 727 42 065



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Table 5-11 Reactions at base of leg - Maximum Hull Weight

ISO SNAME Site


kNm Shear

kN Axial kN

Moment kN,m

Shear kN

Axial kN

50 669 2 904 27 458 51 326 2 894 27 497

49 776 2 943 26 409 50 423 2 943 26 448 60

206 2 090 72 319 284 2 080 72 241

60 920 2 806 42 095 61 509 2 855 42 095

35 551 2 904 15 843 34 688 2 963 15 284 90

1 678 2 090 68 258 2 060 2 129 68 817

50 394 2 531 56 143 50 100 2 551 56 309

29 636 2 766 12 949 28 959 2 806 12 586

Site 1 (sand)

120

47 628 2 551 57 114 47 137 2 570 57 290

136 614 3 394 30 401 144 011 3 600 30 068

137 026 3 434 29 616 142 834 3 600 29 204 60

35 316 2 384 66 306 0 1 933 67 807

125 303 3 208 42 085 140 283 3 335 42 350

137 899 3 365 21 621 125 470 3 335 21 435 90

64 648 2 590 62 647 41 899 2 256 63 284

101 740 2 904 53 308 100 356 2 874 53 945

137 791 3 345 18 874 117 230 3 257 18 364

Site 2 (clay)

120

99 228 2 943 54 151 96 658 2 845 54 759

Table 5-12 Reactions at base of leg - Minimum Hull Weight

ISO SNAME Site


kNm Shear

kN Axial kN

Moment kN,m

Shear kN

Axial kN

47 529 2 825 23 789 48 079 2 835 23 770

46 411 2 855 22 867 46 951 2 874 22 847 60

206 2 060 66 826 272 2 070 66 875

57 330 2 659 37 788 57 948 2 717 37 788

31 529 2 668 13 626 30 048 2 747 12 920 90

29 538 2 266 62 068 24 859 2 276 62 774

59 527 2 521 50 894 59 704 2 551 51 071

24 780 2 560 10 722 23 878 2 600 10 359

Site 1 (sand)

120

58 262 2 560 51 875 58 330 2 590 52 071

137 183 3 237 27 036 138 419 3 375 26 909

137 311 3 267 26 242 136 948 3 375 26 114 60

76 449 2 649 60 273 58 183 2 325 61 293

130 208 3 149 37 867 144 011 3 247 38 102

137 311 3 227 18 502 119 192 3 139 18 776 90

89 193 2 727 57 182 82 384 2 511 57 447

113 315 2 923 48 579 122 821 2 972 48 883

137 330 3 237 15 657 111 344 3 071 15 794

Site 2 (clay)

120

111 726 2 972 49 315 120 173 2 953 49 648



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5.10

5.9.3 The analysis results are combination effects of wind, wave and inertial loads, P-Delta effects and foundation fixities on the rig. Although the differences of the overall horizontal wind and wave loads between the ISO and the SNAME are no more than 5%, the difference for the hull sway is up to 18%, and for the lower guide reaction loads the difference is up to 12% on axial load, 16% on moment (for the maximum hull weight case) for the non critical legs, but there is close agreement on the critical (most highly loaded) legs.

UTILISATION CHECKS

5.10.1 The following table shows the structural utilisations calculated using both the ISO and SNAME methods

Table 5-13 Summary of critical structural utilisations - Site 1 (sand)

Utilisations Heading ISO SNAME ISO/SNAME

Overturning 120 0,78 0,78 100%

Preload Capacity 60 1,11 1,15 97%


60 1,34 1,54 87%

Additional settlements (m) 60 0,10 0,17 59%

Windward leg sliding 120 0,84 0,85 99%

Maximum Hull sway (m) 60 1,75 1,79 98%

Leg chord strength[1] 90 0,74 0,84 88%

Leg brace strength 90 0,31 0,31 100%

Chock holding strength 120 0,64 0,61 105%

Table 5-14 Summary of critical structural utilisations - Site 2 (clay)

Utilisations Heading ISO SNAME Difference

Overturning 120 0,70 0,63 111%

Preload Capacity 60 1,04 1,08 96%


60 1,24 1,50 83%

Additional settlements (m) 60 3,23 3,92 82%

Windward leg sliding 120 0,27 0,48 56%

Maximum Hull sway (m) 60 1,12 0,99 113%

Leg chord strength[1] 90 0,58 0,81 72%

Leg brace strength 90 0,28 0,37 76%

Chock holding strength 120 0,50 0,55 91%



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5.11 CONCLUSION

5.11.1 Comparison between the ISO and SNAME results above show that for site 1 (sand) the foundation fixity parameters are near-identical, and that for site 2 (clay) the ISO foundation vertical and rotational stiffnesses are marginally greater than the SNAME (SAGE) foundation stiffnesses whilst the horizontal foundation stiffness is approximately equal.

5.11.2 The greater predicted penetration depth calculated using SNAME results in a shear modulus that is 8% greater than that calculated for the ISO case. The stiffness depth factors in the ISO document, however, are greater than those in SNAME for the case of a clay foundation (with Poisson ratio = 0.5). Consequently the overall stiffnesses calculated using the ISO document are very similar to those using SNAME (SAGE) (Table 5-1). As different depth factors are used for the vertical, horizontal and rotational stiffnesses, the ratio between the SNAME and ISO stiffnesses are different for each component stiffness. The loading condition is similar; ISO results are slightly less onerous for site 1 (sand), and near-identical, or slightly more onerous for site 2 (clay) when compared to SNAME (Table 5-7); lower guide reaction loads the difference is up to 12% on axial load, 16% on moment (for the maximum hull weight case) for the non critical legs, but shows close agreement on the critical (most highly loaded) legs.

5.11.3 Overturning checks are similar for site 1 (sand), but more onerous when calculated to ISO compared to SNAME for site 2 (clay) - due to increased hull sway resulting from different foundation stiffnesses.

5.11.4 Whilst preload capacity checks are similar (ISO 3-4% better than SNAME), the foundation bearing capacity utilisations and additional settlement required are more pronounced (ISO 13-17% better than SNAME) due to the change in nature of the checks - particularly for deep foundation cases with backfill.

5.11.5 Leg sliding checks are near-identical for the shallow penetration case in sand (site 1), but significantly different (ISO almost half that of SNAME) for the deep penetration case into clay; mostly from the significantly increased horizontal capacity afforded by ISO (ISO horizontal capacity is 68% greater than SNAME)

5.11.6 Leg strength utilisations are less onerous when calculated to ISO based on use of the high strength yield equations and reduced buckling ‘B’-factor compared to SNAME. (More favourable strength checks would be expected with ISO for the same member loading conditions).

5.11.7 Chock strength checks are similar in magnitude between ISO and SNAME for both assessment cases, but reflect the change in overall loading and resistance factor (ISO’s 1/1,15 (0.87) to SNAME’s 0.85).

5.11.8 The ISO and SNAME assessment approaches differ in only a few key areas, the aim of this assessment has been to compare the overall analysis methodology from beginning to end to asses the effect of the combination of these differences,

5.11.9 Table 5-15 shows the main aspects of the analysis with the associated cause of the differences between ISO and SNAME,



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5.11.10 It has been mentioned that one particular difference between the ISO and the SNAME is the drag coefficient CD used in the wind load on the legs above and below the hull, The ISO recommends the use of a CD of 0,5 whereas SNAME recommends a CD of 0,65, Thus, another final quasi-static analysis of the ISO has been undertaken using the same wind loads on the legs above and below the hull to the SNAME, i,e,, CD = 0,65 and the results are compared with the above analyses as Appendix B



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Table 5-15 Differences between ISO and SNAME

Analysis step ISO/SNAME Cause of difference

Natural periods Up to 4% Different spudcan fixities Dynamic Amplification Factors (DAF’s)

Up to 5% Different spudcan fixities

Wind loads 3-4% Use of a different leg Cd values for leg above MWL+2m between ISO and SNAME

Wave/current loads Approx 5% ISO utilises a kinematics approach whereas

SNAME adopts the deterministic wave height approach

Inertia loads Up to 14% Different DAF’s

Different wave/current loads

Hull sways 3% (Sand case) / 15% (Clay case)

Different wind loads


Different inertia loads

Different foundation fixities and capacities

Different approach used to calculate Fr in the foundation iterations

Lower guide reactions Up to 12% on axial(BUT better match

on critical leg)

Different wind loads



Different foundation fixities and capacities

Different approach used to calculate Fr in the foundation iterations

Total base shear and overturning moments

BS up to 3% OTM up to 3%

Different environmental loads


Different foundation fixities and capacities which effect the hull sway and hence the overturning moment,

Structural utilisations e.g. 28% on chord

strength (clay)

Different quasi-static reactions

Different approach used to assess the structural utilisations (high yield equations and ‘B’ factor)

Different resistance factor on holding system strength,

Foundation utilisations

Preload 4% Bearing Capacity

17% (clay) Sliding 64% (clay)

Different quasi-static footing reactions

Different yield envelopes



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This report is intended for the sole use of the person or

company to whom it is addressed and no liability of any

nature whatsoever shall be assumed to any other party

in respect of its contents.

GL NOBLE DENTON

Signed: _________________________________________

Yongxia Hua, BEng., MSC., PhD.

Senior Structural Engineer, Jack-up and Geotechnical Engineering

Signed: ____________________________________

Mark Hayward, MEng..

Senior Principal Engineer, Jack-up and Geotechnical Engineering

Countersigned: ______________________________________

pp. Richard Stonor, B.Sc., Ph.D., C.Eng., MRINA

Manager, Jack-up and Geotechnical Engineering

Dated : London, 20th November 2010



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REFERENCES

[1] SNAME Technical and Research Bulletin 5-5A. ‘Recommended Practice for Site Specific Assessment of Mobile Jack-Up Units”, 1st Ed., Rev 2., Jan 2002.

[2] ISO 19905-1, “Petroleum and natural gas industries - Site-specific assessment of mobile offshore units - Part 1: Jack-Ups”, Draft DIS, 12, 2009.

[3] Noble Denton Report No. L22909, “PHASE 1 BENCHMARKING OF ISO 19905-1.9 -COMPLETENESS CHECK”, Rev 1, Apr, 2009.



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Location DetailsName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/ADepth of water : 106.7 m (350 ft) 106.7 350

Jack-up Unit DetailsName : Generic KFELS B ClassDesign : KFELS Mod V B Class

Calculated Spudcan Reactions at Seabed LevelPreload reaction : 7,100 tonnes (15,653 kips) 7,100 15,653Stillwater reaction : 4,314 tonnes (9,511 kips) 4,314 9,511

Expected Spudcan Tip Penetration 1.95 m (6 ft) 1.95 6

Average Soil Properties Used in Spudcan Penetration Analysis

' (kN/m3) cu top (kPa) cu bot (kPa) ' (o)1 0.0 SAND 11.0 - - 29.02 30.0 SAND 11.0 - - 29.03 - - - - - -4 - - - - - -5 - - - - - -6 - - - - - -7 - - - - - -8 - - - - - -

Spudcan Penetration Curve

spud_pen ISOv0 W.S. 05-130553 Calc: DHE Appvd: MJRH Date: 19-Nov-10

SPUDCAN PENETRATION ANALYSIS Generic KFELS B Class at Generic medium dense sand location for ISO Phase 2 Benchmarking

Layer Soil type

Spudcan Geometry

Average Soil PropertiesStarting Depth (m)

0

1

2

3

4

5

6

0 2000 4000 6000 8000 10000 12000 14000 16000

Vertical foundation load during preloading (tonnes)

Sp

ud

ca

n t

ip p

en

etr

ati

on

(m

)

0

2

4

6

8

10

12

14

16

18

0 5000 10000 15000 20000 25000 30000 35000

Vertical foundation load during preloading (kips)

Sp

ud

can

tip

pen

etra

tio

n (

ft)

Spu

dcan

pre

load

rea

ctio

n

Expected spudcan tip penetration = 1.95 m (6 ft).

Spu

dcan

stil

lwat

er r

eact

ion

Figure 5-1 - ISO predicted leg penetration resistance curves for the B-Class - SAND assessment



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Location DetailsName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/ADepth of water : 106.7 m (350 ft) 106.7 350

Jack-up Unit DetailsName : Generic KFELS B ClassDesign : KFELS Mod V B ClassMax. spudcan area : 152.6 m² (1643 ft²)Spudcan volume : 353.3 m³ (12477 ft³)Length from tip to max. area : 2.2 m (7 ft 4 in)

Calculated Spudcan Reactions at Predicted PenetrationPreload reaction : 7,097 tonnes (15,646 kips) 7,097 15,646Stillwater reaction 4,312 tonnes (9,506 kips) 4,312 9,506


Soil Parameters Used in Spudcan Penetration Analysis

Top of unit Base of unit ' (kN/m3) LB su (kPa) UB su (kPa) LB' (o) UB' (o)1 0.0 30.0 SAND 11.0 - - 29.0 29.0- - - - - - - - -- - - - - - - - -- - - - - - - - -- - - - - - - - -- - - - - - - - -- - - - - - - - -- - - - - - - - -


spud_pen v2.1 Soils Database Ref. W.S. 05-130553 Calc: DHE Checked: Appvd: RWPS Date: 19-Nov-10

SPUDCAN PENETRATION ANALYSIS Generic KFELS B Class at Generic medium dense sand location for ISO Phase 2 Benchmarking

Soil type

Spudcan Geometry

LayerDepth (m) Soil Properties

0

1

2

3

4

5

6

0 2000 4000 6000 8000 10000 12000 14000 16000


Sp

ud

ca

n t

ip p

en

etr

ati

on

(m

)

0

2

4

6

8

10

12

14

16

18

0 5000 10000 15000 20000 25000 30000 35000


Sp

ud

can

tip

pen

etra

tio

n (

ft)

Lower Bound

Average

Upper Bound

Spu

dcan

pre

load

rea

ctio

n

Expected spudcan tip penetration= 2.0 m (7 ft).

Spu

dcan

stil

lwat

er r

eact

ion

Soil Profile

Figure 5-2 - SNAME predicted leg penetration resistance curves for the B-Class - SAND assessment



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Location DetailsName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/A N, N/A EDepth of water : 106.7 m (350 ft) 106.7 350



Parameters Used in V-H Calculations

Expected spudcan tip penetration : 1.95 m (6 ft) 6Maximum spudcan contact area : 91.1 m2 (981 sq.ft) 981Laterally projected spudcan area : 6.3 m2 (68 sq.ft) 68Steel/sand interaction factor, : 29.0 o 29.0cu at maximum bearing area, cuo : 0 kPa 0

cu at spudcan tip, cut : 0 kPa 0

Preload resistance factor, R,PRE : 1.10

Partial resistance factor horizontal capacity, R,Hfc : 1.25

Partial resistance factor foundation capacity, R,VH : 1.10

V-H Bearing Capacity Envelope


Spudcan Geometry

Generic KFELS B Class at Generic medium dense sand location for ISO Phase 2 Benchmarking

V-H BEARING CAPACITY ENVELOPE

ISO DIS 19905-1

0

1000

2000

3000

4000

5000

6000

7000

8000

0 100 200 300 400 500 600 700 800 900 1000

Fh (tonnes)

Fv

(to

nn

es

)

0

2000

4000

6000

8000

10000

12000

14000

16000

0 500 1000 1500 2000

Fh (kips)

Fv

(kip

s)

Maximum Hull Weight

Minimum Hull Weight

Factored sliding capacity

Unfactored V-H capacity

Factored V-H capacity

Unfactored sliding capacity

Stillwater spudcan reaction (triangle)

Origin used for utilisation checks

}

Figure 5-3 - ISO predicted V-H envelope for the B-Class - SAND assessment



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Location DetailsName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/ADepth of water : 106.7 m (350 ft) 106. 350


Calculated Spudcan Reactions at Predicted PenetrationPreload reaction : 7,097 tonnes (15,646 kips) 7,097 15,646Stillwater reaction : 4,312 tonnes (9,506 kips) 4,312 9,506


Expected spudcan tip penetration : 2.0 m (7 ft) 7Maximum spudcan contact area : 97.5 m2 (1,049 sq.ft) 1,049Laterally projected spudcan area : 6.7 m2 (72 sq.ft) 72Steel/sand interaction factor, : 29.0 o 29.0cu at maximum bearing area, cuo : N.A. #######

cu at spudcan tip, cut : N.A. #######

Preload resistance factor, P : 0.90

Sliding resistance factor, Hfc or Hfs : 0.80

Resistance factor for combined V-H loads, VH : 0.90


spud_pen v2.1 Soils Database Ref. W.S. 05-130553 Calc: DHE Appvd: RWPS Date: 20-Nov-10

Spudcan Geometry

Generic KFELS B Class at Generic medium dense sand location for ISO Phase 2 BenchmarkingV-H BEARING CAPACITY ENVELOPE

SNAME (Rev. 3 January 2008)

0

1000

2000

3000

4000

5000

6000

7000

8000

0 100 200 300 400 500 600 700 800 900 1000

Horizontal load capacity (tonnes)

Ve

rtic

al

loa

d c

ap

ac

ity

(to

nn

es

)

0

2000

4000

6000

8000

10000

12000

14000

16000

0 500 1000 1500 2000

Horizontal load capacity (kips)

Ve

rtic

al

loa

d c

ap

ac

ity

(k

ips

)

Maximum Hull Weight

Minimum Hull Weight

Factored sliding capacity



Unfactored sliding capacity

Stillwater spudcan reaction

}

Figure 5-4 - SNAME predicted V-H envelope for the B-Class - SAND assessment



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Location Details Spudcan GeometryName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/A N, N/A EDepth of water : 106.7 m (350 ft) 106.7 350



Parameters Used in Fixity Calculations

Expected spudcan tip penetration : 1.95 m (6 ft) 6Maximum spudcan contact area : 91.1 m2 (981 sq.ft) 981Soil type : SandSoil backflow : YesBackflow unit weight: 11

Undrained shear strength, cu : N.A. kPa ######Overconsolidation ratio, OCR : N.A.Relative density, DR : 60 %Poisson's ratio, : 0.2

Calculated Vertical, Horizontal and Rotational Foundation Capacities

The following foundation capacities have been calculated in accordance with the 'ISO DIS 19905-1

These foundation capacities are for use with the ultimate vertical/horizontal/rotational capacityinteraction function for spudcan footings (Section A.9.3.3.2).

Vertical foundation capacity, VLO : 7100 tonnes (15,652 kips) 15,652

Horizontal foundation capacity, HLO : 852 tonnes (1,878 kips) 1,878

Moment foundation capacity, MLO : 5734 tonne.m (41,474 kips.ft) 41,474

Calculated Initial Vertical, Horizontal and Rotational Foundation Stiffnesses

In accordance with ISO DIS 19905-1

Vertical foundation stiffness, K1 : 139,686 tonnes/m (93,865 kips/ft)

Horizontal foundation stiffness, K2 : 132,443 tonnes/m (88,998 kips/ft)

Rotational foundation stiffness, K3 : 2,699,882 tonne.m/rad (19,528,287 kips.ft/rad)

80% of Rotational foundation stiffness, K3 : 2,159,906 tonne.m/rad (15,622,630 kips.ft/rad)

Stiffness degradation factor, n 0.0

NOTE: In accordance with Clause A.10.4.4.1.2 the initial linearised rotational stiffness used in

detailed dynamic calculations may typically be taken as 80-100% of the values determined above.79,344 7,523 6,602,882 5,282,30593,865 88,998 19,528,287 622,630


SPUDCAN FIXITY PARAMETERS

Figure 5-5 - ISO predicted ultimate capacities and stiffnesses for the B-Class - SAND assessment



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Location Details Spudcan GeometryName : Generic medium dense sand location for ISO Phase 2 BenchmarkingCoordinates : N/A N, N/A EDepth of water : 106.7 m (350 ft) 106.7 350




Expected spudcan tip penetration : 1.95 m (6 ft) 6Maximum spudcan contact area : 91.1 m2 (981 sq.ft) 981Soil type : SandSoil backflow : YesBackflow unit weight: 11

Undrained shear strength, cu : N.A. kPa ######Overconsolidation ratio, OCR : N.A.Relative density, DR : 60 %Poisson's ratio, : 0.2













Stiffness degradation factor, n 0.0


detailed dynamic calculations may typically be taken as 80-100% of the values determined above.79,344 7,523 6,602,882 5,282,30593,865 88,998 19,528,287 622,630



Figure 5-6 - SNAME predicted ultimate capacities and stiffnesses for the B-Class - SAND assessment



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Location DetailsName : Generic clay location for ISO Phase 2 BenchmarkingCoordinates : N/ADepth of water : 70.0 m (230 ft) 70.0 230


Calculated Spudcan Reactions at Seabed LevelPreload reaction VLo : 7,143 tonnes (15,748 kips) 7,143 15,748

Stillwater reaction : 4,357 tonnes (9,606 kips) 4,357 9,606Including spudcan and leg buoyancy.


Average Soil Properties Used in Spudcan Penetration Analysis

' (kN/m3) cu top (kPa) cu bot (kPa) ' (o)1 0.0 CLAY 4.0 2.4 27.3 -2 19.0 CLAY 5.8 27.3 40.5 -3 29.0 CLAY 5.8 40.5 50.3 -4 36.5 CLAY 5.8 50.3 67.0 -5 45.0 CLAY 8.0 67.0 96.4 -6 60.0 CLAY 8.0 96.4 96.4 -7 - - - - - -8 - - - - - -



SPUDCAN PENETRATION ANALYSIS Generic KFELS B Class at Generic clay location for ISO Phase 2 Benchmarking

Layer Soil type

Spudcan Geometry

Average Soil PropertiesStarting Depth (m)

0

5

10

15

20

25

30

35

40

45

50

0 2000 4000 6000 8000 10000 12000 14000

VL = QV-WBF,0+BS (tonnes)

Sp

ud

ca

n t

ip p

en

etr

ati

on

(m

)

0

20

40

60

80

100

120

140

160

0 5000 10000 15000 20000 25000 30000

VL = QV-WBF,0+BS (kips)

Sp

ud

can

tip

pe

ne

trat

ion

(ft

)

Spu

dcan

pre

load

rea

ctio

n

Expected spudcan tip penetration = 34.07 m (112 ft).

Sp

udca

n s

tillw

ate

r re

actio

n

Figure 5-7 - ISO predicted leg penetration resistance curves for the B-Class - CLAY assessment



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Jack-up Unit DetailsName : Generic KFELS B ClassDesign : KFELS Mod V B ClassMax. spudcan area : 152.6 m² (1643 ft²)Spudcan volume : 353.3 m³ (12477 ft³)Length from tip to max. area : 2.2 m (7 ft 4 in)

Calculated Spudcan Reactions at Predicted PenetrationPreload reaction : 7,095 tonnes (15,641 kips) 7,095 15,641Stillwater reaction 4,309 tonnes (9,500 kips) 4,309 9,500Including spudcan and leg buoyancy.


Soil Parameters Used in Spudcan Penetration Analysis

Top of unit Base of unit ' (kN/m3) LB su (kPa) UB su (kPa) LB' (o) UB' (o)1 0.0 19.0 CLAY 4.0 2.4 - 27.33 2.4 - 27.33 - -2 19.0 29.0 CLAY 5.8 27.33 - 40.46 27.33 - 40.46 - -3 29.0 36.5 CLAY 5.8 40.46 - 50.3 40.46 - 50.3 - -4 36.5 45.0 CLAY 5.8 50.3 - 67 50.3 - 67 - -5 45.0 60.0 CLAY 8.0 67 - 96.4 67 - 96.4 - -- - - - - - - - -- - - - - - - - -- - - - - - - - -


spud_pen v2.1 Soils Database Ref. W.S. 05-130553 Calc: DHE Checked: Appvd: RWPS Date: 20-Nov-10

SPUDCAN PENETRATION ANALYSIS Generic KFELS B Class at Generic clay location for ISO Phase 2 Benchmarking

Soil type

Spudcan Geometry

LayerDepth (m) Soil Properties

0

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50

0 2000 4000 6000 8000 10000 12000 14000


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ud

ca

n t

ip p

en

etr

ati

on

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)

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0 5000 10000 15000 20000 25000 30000


Sp

ud

can

tip

pe

ne

tra

tio

n (

ft)

Lower Bound

Average

Upper Bound

Spu

dcan

pre

load

rea

ctio

n

Expected spudcan tip penetration= 37.5 m (123 ft).

Spu

dcan

stil

lwat

er r

eact

ion

Soil Profile

Figure 5-8 - SNAME predicted leg penetration resistance curves for the B-Class - CLAY assessment



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Location DetailsName : Generic clay location for ISO Phase 2 BenchmarkingCoordinates : N/A N, N/A EDepth of water : 70.0 m (230 ft) 70.0 230





Expected spudcan tip penetration : 34.07 m (112 ft) 112Maximum spudcan contact area, A : 152.6 m2 (1,643 sq.ft) 1,643Laterally projected spudcan area, As : 43.7 m2 (470 sq.ft) 470Steel/sand interaction factor, : N.A. o 0.0cu at maximum bearing area, cuo : 44 kPa (919 lb/sq.ft) 919

cu at spudcan tip, cut : 47 kPa (982 lb/sq.ft) 982

Preload resistance factor, R,PRE : 1.10

Partial resistance factor horizontal capacity, R,Hfc : 1.56

Partial resistance factor foundation capacity, R,VH : 1.15



Spudcan Geometry

Generic KFELS B Class at Generic clay location for ISO Phase 2 Benchmarking

V-H BEARING CAPACITY ENVELOPE

ISO DIS 19905-1

0

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Fv

(to

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es

)

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ips

)

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Minimum Hull Weight

Fac

tore

d sl

idin

g ca

paci

ty



Unf

acto

red

slid

ing

capa

city

Stillwater spudcan reaction (triangle)

Origin used for utilisation checks (diamond)0,5QV/R,VH

}

Figure 5-9 - ISO predicted V-H envelope for the B-Class - CLAY assessment



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Calculated Spudcan Reactions at Predicted PenetrationPreload reaction : 7,095 tonnes (15,641 kips) 7,095 15,641Stillwater reaction : 4,309 tonnes (9,500 kips) 4,309 9,500Including spudcan and leg buoyancy.


Expected spudcan tip penetration : 37.5 m (123 ft) 123Maximum spudcan contact area : 152.6 m2 (1,643 sq.ft) 1,643Laterally projected spudcan area : 43.7 m2 (470 sq.ft) 470Steel/sand interaction factor, : N.A. 0.0cu at maximum bearing area, cuo : 49 kPa (1,023 lb/sq.ft) 1,023

cu at spudcan tip, cut : 52 kPa (1,086 lb/sq.ft) 1,086

Preload resistance factor, P : 0.90

Sliding resistance factor, Hfc or Hfs : 0.64

Resistance factor for combined V-H loads, VH : 0.85


spud_pen v2.1 Soils Database Ref. W.S. 05-130553 Calc: DHE Appvd: RWPS Date: 19-Nov-10

Spudcan Geometry

Generic KFELS B Class at Generic clay location for ISO Phase 2 BenchmarkingV-H BEARING CAPACITY ENVELOPE

SNAME (Rev. 3 January 2008)

0

1000

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7000

8000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Horizontal load capacity (tonnes)

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tic

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loa

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ap

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ity

(to

nn

es)

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Horizontal load capacity (kips)

Ve

rtic

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loa

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ty (

kip

s)

Maximum Hull Weight

Minimum Hull Weight

Fac

tore

d sl

idin

g ca

paci

ty



Unf

acto

red

slid

ing

capa

city

Stillwater spudcan reaction

}

Figure 5-10 - SNAME predicted V-H envelope for the B-Class - CLAY assessment



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Location Details Spudcan GeometryName : Generic clay location for ISO Phase 2 BenchmarkingCoordinates : N/A N, N/A EDepth of water : 70.0 m (230 ft) 70.0 230





Expected spudcan tip penetration : 34.07 m (112 ft) 112Maximum spudcan contact area : 152.6 m2 (1,643 sq.ft) 1,643Soil type : ClaySoil backflow : YesBackflow unit weight: 5.80

Undrained shear strength, cu : 47 kPa (979 lb/sq.ft) 979Overconsolidation ratio, OCR : 1.0Relative density, DR : N.A. %Poisson's ratio, : 0.5Adhesion factor, : 1.0




Vertical foundation capacity, Qv : 9023 tonnes (19,893 kips) 19,893Horizontal foundation capacity, QH : 2027 tonnes (4,469 kips) 4,469

Moment foundation capacity, QM : 14169 tonne.m (102,487 kips.ft) 102,487







Stiffness degradation factor, n -0.5


Generic KFELS B Class at Generic clay location for ISO Phase 2 Benchmarking


Figure 5-11 - ISO predicted ultimate capacities and stiffnesses for the B-Class - CLAY assessment



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Location Details Spudcan GeometryName : Generic clay location for ISO Phase 2 BenchmarkingCoordinates : N/ADepth of water : 70.0 m (230 ft) 70.0 230


Calculated Spudcan Reactions at Predicted PenetrationPreload reaction : 7,095 tonnes (15,641 kips) 7,095 15,641Stillwater reaction : 4,309 tonnes (9,500 kips) 4,309 9,500Including spudcan and leg buoyancy.


Expected spudcan tip penetration : 37.5 m (123 ft) 123Maximum spudcan contact area : 152.6 m2 (1,643 sq.ft) 1,643

Soil type : ClaySoil backflow : Yes

Undrained shear strength, cu : 52 kPa (1,083 lb/sq.ft) 1,083Overconsolidation ratio, OCR : 1.0Relative density, DR : N.A.Poisson's ratio, : 0.5

Calculated Vertical, Horizontal and Rotational Foundation Capacities SAGE

The following foundation capacities have been calculated in accordance with the 'SNAME TR&B 5-5AGuideline for the Site Specific Assessment of Mobile Jack-Up Units (Rev. 3 (Jan 2008)). Thesefoundation capacities are for use with the ultimate vertical/horizontal/rotational capacityinteraction function for spudcan footings (Section 6.3.4.2).




Calculated Initial Vertical, Horizontal and Rotational Foundation Stiffnesses SAGE

In accordance with SNAME T&RB 5-5A Section 6.3.4.3 (Rev. 3 (Jan 2008)):





NOTE: In accordance with SNAME T&RB (Rev. 3) recommendations (Section 6.3.4.6), the initial linearised rotational

stiffness used in detailed dynamic calculations may typically be taken as 80% of the values determined above.63,003 42,530 21,687,426 17,349,94237,954 179,287 106,024,140 819,312spud_pen v2.1 Soils Database Ref. W.S. 05-130553 Calc: DHE Appvd: RWPS Date: 19-Nov-10

Generic KFELS B Class at Generic clay location for ISO Phase 2 BenchmarkingSPUDCAN FIXITY PARAMETERS

Figure 5-12 - SNAME predicted ultimate capacities and stiffnesses for the B-Class - CLAY assessment



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APPENDIX A COMMENTS SUBMITTED TO ISO

HASE ENCHMARKINGP 2 B


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Report No: L25316, Revision: O , Dated 20th November 2010


1 2 (3) 4 5 (6) (7)

MB1

Clause No./ Subclause No./ Annex (e.g. 3.1)

Paragraph/ Figure/Table/Note (e.g. Table 1)

Type of com-ment2

Comment (justification for change) by the MB Proposed change by the MB Secretariat observations on each comment submitted

UK List of symbols for A9

ed as and bs are both defined as “bearing capacity squeezing factor” - presumably can’t have two identical descriptions for different parameters

Rename bs to “layer thickness squeezing factor”


ed Definition of CHdeep seems to have been corrupted Replace with definition given in A.9.3-16


ed Definition of D - add cross-reference to Figure 9.3-3 Add cross-reference


ed Equation for dc is only given in list of symbols and not in Appendix A.9

Include equation given for dc in A.9.3.2.2


ed Definition of FM as an “applied moment force” is incorrect - should be “applied moment”

Re-define FM as “applied moment”


ed Definition of fr Redefine more specifically as “Spudcan rotational stiffness reduction factor”


ed Definition of G Redefine more specifically as “soil shear modulus”


ed Definition of Hcav - use of “limiting” is not particularly clear or helpful

Remove “limiting”

Key:

1 MB = Member body (enter the ISO 3166 two-letter country code, e.g. CN for China; comments from the ISO/CS editing unit are identified by **) 2 Type of comment: ge = general te = technical ed = editorial NOTE Columns 1, 2, 4, 5 are

compulsory.



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Ed I note that the definition of ‘a’ used in Annex E1 is not the same as that definite in Appendix 9 - do they need to be differentiated, or should there also be a list of symbols for each Annex? Presently some symbols used in Annex E are not defined in the list of symbols.


Ed - Add definition for ns “load spread factor for projected area method”


Ed Definition of pa Provide value of 101,3 kPa in definition


Ed Definition of QMp erroneously refers to QMsv Replace QMsv with QMpv


Ed Definition of QMps refers to “fully seated spud conditions” Replace with “full contact of the entire underside of the spudcan with the sea floor”


Ed Definition of qo as “surface bearing resistance” needs rephrasing

Redefine qo as “vertical bearing capacity of spudcan for full contact of the underside of the spudcan with the sea floor” - in any case it should be Qo as in Annex E3 and not qo

UK List of symbols for A9 / A.9.3.2.6.4

Ed Definition of qmax and qo are potentially ambiguous Replace with “maximum vertical bearing capacity at d=dcrit, refer to Annex E3” - replace with Qpeak as in Annex E3


Ed Definition of rf is potentially ambiguous/unhelpful Suggest replacing definition with “normalised ratio of factored foundation action to the unfactored foundation bearing capacity envelope”


Ed Definition of sc - just give a value of 1.18 (=6.05/(2+)) as the values of Nq given in the document inherently include shape factor (see A.9.3.2.4) - i.e. there is the potential for confusion

Replace with sc=1.18

UK List of symbols for

Ed Definition of VLo erroneously refers to 3.69 Replace 3.69 with presumably 3.51



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A9


Ed Definition of Vsw - I do not understand the need to refer to ‘a solid rock foundation’ - what is the significance of this?

Replace part in brackets with: (the footing reaction to the self-weight of the jack-up unit, plus the reaction due to the submerged weight of any backfill on the spudcan, less the reaction due to the submerged weight of the soil displaced by the spudcan)


Ge/Ed Generally replace “effective submerged weight” with simply “submerged weight”


Ed Definition of alpha - alpha can be any value between 0 and 1.0, therefore providing these two values is potentially misleading

Replace values with a reference to A.9.3.3.3 for further details


Ed Definition for Replace with “rate of increase in undrained shear strength with depth”


Ed Definition for - presentation of units (degrees) is inconsistent with that for delta

Either put degrees in brackets or after a hyphen depending on ISO protocol (should units even be in list of symbols?)

UK A9 Ge There are various symbols and definitions of bearing capacity and footing loads - the use of Fv,in seems unnecessary and presumably can be replaced with VLo

Replace all instances of Fv,in with VLo ?

UK A.9.3.2.1.1 Ge No mention as to whether upper and lower bound soil strength profiles should be considered in spudcan penetrations analyses, or only ‘best estimate’

Upper and lower bound profiles should be considered.

UK A.9.3.2.1.1 Equation A.9.3-1.a

Te The equation does not include spudcan buoyancy contribution due to the volume of the spudcan within the soil below the max. plan area level

UK A.9.3.2.1.1 Equation A.9.3-1.b

Te The weight of backflow soil, defined in Equation A.9.3-2, includes all volume between lowest point of max. area and the base of the crater (and would hence include the spudcan volume above lowest point of max. area, whereas this volume is also included in Bs term) - clarification is needed as this could leave the potential for a significant “double-dip” if not treated carefully.

Panel 4 generally need to review figures, equations and descriptions involving backflow and spudcan buoyancy within Appendix 9. Even at the surface, there is spudcan buoyancy due to the volume of spudcan within the soil, furthermore the weight of backflowed soil must not include the volume of the spudcan above the lowest level of max. plan area.



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UK A.9.3.2.1.3 Ed “The soil beneath the spudcan fails as the foundation is loaded during preloading until equilibrium is achieved at the end of the preloading operation”

Replace with “The spudcan will penetrate into the seabed during preloading until the spudcan’s bearing capacity achieves equilibrium with the applied preload”

UK A.9.3.2.1.4 Ed “Backflow is the soil that flows from beneath the spudcan, around the sides, and onto the top and is more likely to occur in clays than in sands. Backflow can occur at shallow penetrations, but is more likely to occur at deeper penetrations. In very soft clays complete backflow is likely to occur. In firm to stiff clays and granular materials, where spudcan penetration is expected to be small, the possibility of backflow diminishes. In general, backflow due to additional penetration during elevated operations is not expected to occur. If it is predicted, the effects should be taken into account.” - backflow occurs straightaway in sand and depends on penetration depth in clays - can be rephrased to be more clear/efficient.

Replace with “Backflow is the soil that flows from beneath the spudcan, around the circumference and on to the top of the spudcan during penetration into the seabed. This occurs immediately in sands, should sufficient penetrations occur, and after a certain penetration depth in clays, which can be determined using the method described below. ”

UK A.9.3.2.1.4 Figure A.9.3-6

Ed Key below Figure A.9.3-6 refers to ‘e’ for the cavity however I cannot see where this is used in either figure.

Remove?

UK A.9.3.2.1.4 for example

Te Although reference is made to infill, no guidance is provided for quantifying infill. For example if there is a layer of sand at the seabed surface should it be assumed that this will subsequently completely infill the crater if the seabed is shown to be mobile? (this could result in a very significant additional vertical footing load)

Guidance needed from Panel 4

UK A.9.3.2.1.4 Eqn A.9.3-2 & Fig A.9.3-5

te The definitions of Hcav in Equation A.9.3-2 and Fig A.9.3-5 suggest that a portion of the spudcan volume would be included in calculating the weight of backfill.

See earlier comment regarding spudcan volume and backfill

UK A.9.3.2.1.4 Ed “the penetration resistance offered by a localised backflow mechanism becomes independent of depth of penetrations exceeding B”

Clarify that this penetration refers to D and not tip penetration depth. This statement of fact needs a reference.

UK A.9.3.2.1.4

Te “the penetration resistance offered by a localised backflow mechanism

becomes independent of depth of penetrations exceeding B” - this appears to be inconsistent with both Skempton’s depth factor equation and Houlsby & Martin’s BC factors which are recommended in the ISO.

Panel 4 should agree the point at which the backflow mechanism becomes independent of penetration depth



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UK A.9.3.2.1.4 Ed Reference to Table A.9.3-1 should read Table A.9.3-2 Correct Table reference

UK A.9.3.2.1.4 Figure A.9.3-6

Ed More details are required in order for the user to calculate Hcav - the plot in Figure A.9.3-6 is not helpful in itself, rather the equation should be written in the text along with some explanation of how to obtain Hcav

Propose using the text from the original OTC paper:

UK A.9.3.2.1.4 Figure A.9.3-6

Symbol ‘X’ in the key that refers to undrained shear strength

Should be replaced with Su

UK A.9.3.2.2 Table A.9.3-2

Ed The caption should emphasise that these assume homogeneous strength.

Replace caption with “Bearing capacity factors for rough circular plate on homogeneous clay”

UK A.9.3.2.2 Ed Cross reference to A.9.3.2.8 before Table A.9.3-2 should be replaced with A.9.3.2.6

Replace cross-reference

UK A.9.3.2.2 Table A.9.3-2

Te Presumably these values (and those in Annex E1) can be interpolated; is the error involved in linearly interpolating Houlsby & Martin’s tabulated values in Annex E1 acceptable for other depth and values? (i.e. you would need to interpolate using four tabulated values in order to

Guidance required from Houlsby



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find the Ncscdc for a combination of D/B and values that are not explicitly given in the tables).

UK A9.3.2.2 Te It is not clear whether Houlsby & Martin’s values can be used for a clay layer that is not at the surface

Guidance needed from Houlsby - Can it be used? if so, would Sum refer to the undrained shear strength at the top of the layer or still at the sea floor surface?

UK A9.3.2.2 / Annex E1

Te Edwards et al. (Géotechnique 2005 No. 55, No. 10) showed that Houlsby & Martin’s bearing capacity factors values are notably lower (i.e. less accurate) than the upper and lower bound solutions derived by Martin and FE data.

The likely errors involved in using Houlsby & Martin’s values compared to the latest research should be quantified and noted in the text, else refer to values in Edwards and Martin’s papers

UK A.9.3.2.2 Te No guidance is provided on how to average undrained shear strength with depth if a sand layer is encountered.

Suggest adding guidance from Panel 4 (Dave Menzies?)

UK A9.3.2.4 Eq. A.9.3-5 Te Depth factors are not included in this equation - can occasionally be relevant for very loose sand locations

Add depth factors

UK A.9.3.2.6.4 Te Equation given in SNAME for use with projected area method is floating at the bottom of the diagram

Add equation properly and add explanation and notes to diagram as in SNAME:

UK A.9.3.3.1 Ed “the maximum moment and horizontal capacities which, with the vertical capacity, are the principal coordinates of the yield interaction surface.”

Suggest replacing with “the maximum moment and horizontal capacities which, with the vertical capacity, are the principal dimensions of the yield interaction surface.”

UK A.9.3.3.1 Ed “The shape of the yield surface for shallow foundations is Change relevant instances of “parabolic” to



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parabolic” “paraboloidal”, also “elliptic” to “ellipsoidal” as the yield surface is 3-dimensional

UK A.9.3.3.1 Ed - Change cross-reference to A.9.3.2.2.5 to A.9.3.2.1.5

UK A.9.3.3.1 Ed “load-penetration equations given in A.9.3.2.3 through A.9.3.2.8” - incorrect sections

Replace with “load-penetration equations given in A.9.3.2.2 through A.9.3.2.6”

UK A.9.3.3.1 Figure A.9.3-12

Ed Is it appropriate to refer to V, H and M? Replace with QV, QH and QM?

UK A.9.3.3.2 Equation A.9.3-16

Te The choice of whether to use an averaged Su or modified bearing capacity factor in the spudcan penetration calculations will lead to different ‘b’ values for horizontal capacity.

Su in the ‘b’ equation should be replaced with Suo - the undrained strength at the depth of the max. plan area.

UK A.9.3.3.2 Te “with backfill” formulae for Fv need clarification as to how to calculate backfill appropriately (see earlier comments)


Te Qvnet formula (after second equals sign) - this Qv-Ap’o definition ignores cavity depth and spudcan buoyancy and is potentially confusing and could lead to misunderstandings. (note Figure A.9.3-7 defines p’o as the overburden pressure without consideration of spudcan buoyancy and cavity depth).

Remove Qvnet = Qv-Ap’o definition and corresponding “Note 2”.


Ed definition of Su,a has a spelling mistake: “sstrength” Replace “sstrength” with “strength”

UK A.9.3.3.2 Te As definition - should this be the whole laterally projected area of the spudcan or just the lower portion in contact with the non-backflow soil?

Clarification required from Templeton

UK A.9.3.4.1 Ed Description of elastic solutions can be more specific to emphasise that these are derived for rough-based circular footings with a flat base (as opposed to a typical spudcan)

Replace “elastic solutions for a rigid disk” with “elastic solutions for a rough, flat-based rigid disk”

UK A.9.3.4.1 Te With reference to soil shear modulus, G: “An upper or lower bound value should be selected” - when should you use which?

Add clarification from Panel 4

UK A.9.3.4.1 Te There is no mention of the cross-coupling stiffness, K4 which links horizontal footing displacements and footing rotations to moment and horizontal loads respectively.

This should at least be discussed if K4 is not to be specified.



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Consideration of K4 is required for all conical footings, and for flat-based footings for v<0.5

Furthermore the choice of seabed reaction point in A.8.6.2 will have an influence on the K4 values.

The guidance provided in A.8.6.2 for the determination of the seabed reaction point should be reviewed (suggest by Houlsby and/or Martin) and included in discussion.

UK A.9.3.4.2.1 Table A.9.3-4

Te The data presented for the depth factors are not from Bell’s thesis (as referenced) and are for Poisson’s ratio = 0.0 - these are not appropriate for soils

Replace values in table with the tables for various Poisson Ratios provided in SNAME (2008)

UK A.9.3.4.2.2 Te “cyclic degradation reduces the horizontal bearing capacity by 30%” - surely this should be in the section on bearing capacities, not foundation stiffnesses.

Move or copy the part referring to bearing capacities to A.9.3.3.2

UK A.9.3.4.2.3 Eqn A.9.3-34

Ed The two terms in the denominator should be added, not subtracted.

UK A.9.3.4.3 Ed It would seem to make more sense for A.9.3.4.3 to appear before A.9.3.4.2, as G is required for the expressions in A.9.3.4.1. K1, 2 and 3 should be determined before stiffness depth factors, etc. are applied

Move A.9.3.4.3 to before A.9.3.4.2

UK A.9.3.4.3 Te The guidance provided for IrNC is unclear - when, for example, should the data in Fig A.9.3-12 actually be used?

Clarification required from Panel 4 (Andersen?)


Ed The symbol for overconsolidation ratio in is still ‘O’ instead of ROC

Replace ‘O’ with ROC

UK A.9.3.4.3 Te “except in areas with carbonate clays or clayey silts…” Panel 4 should provide comments/guidance for such situations

UK A.9.3.4.3 Eq. 9.3-36 Te Is the Su value referred to different from Su in Figure A.9.3-12? (which is from a Direct Simple Shear test)

Clarification required and/or consistency between figure and text (Andersen?)

UK A.9.3.4.3 and A.9.3.4.4

Ed Is it intended for the paragraph “The recommendations given above… …upper-bound values of G” to be duplicated in both A.9.3.4.3 and A.9.3.4.4?

Suggest rationalising

UK A.9.3.5.3 Te Should the factored sliding line should continue above Fv/Qv=0.5 until it meets the factored V-H envelope? Otherwise the factored sliding line will not touch the factored V-H envelope and the two factored envelopes (sliding and V-H) will be disjointed.

Propose that the factored sliding line should continue until it touches factored V-H envelope

UK A.9.3.5.3 Ed - Suggest adding "and in A.9.3.3.3 for Fv < 0.5 Qv"



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to the end of the first sentence

UK A.9.3.6.1 A.9.3-14 te Flow chart does not mention the Nonlinear continuum foundation model described in A.9.3.4.2.5

Suggest adding reference to A.9.3.4.2.5 in rectangular box with A.9.3.4.2.4

UK A.9.3.6.2 Table A.9.3-5

te Appears to be an error in equation for Clay with embedment less than 1.0 times spudcan diameter as the two expressions for clay appear not to be equal for D/B=1.0

Suggest checking with Templeton

UK A.9.3.6.2 ed The description “is small” needs to be specifically linked to Table A.9.3-5 (at least 2 occurrences)

Replace “is small” with “less than the corresponding limiting horizontal reaction given by Table A.9.3-5”

UK A.9.3.6.2 te It is not clear the technical basis for the following statement: “Additional penetration can increase the soil resistance, but to increase the horizontal capacity to 0,1VLo the additional penetration is about 10% of the spudcan diameter and outside tolerable limits.” Surely this depends on , , etc.

Replace with “Although additional penetration can increase the soil resistance, it is possible for such additional penetrations to exceed those tolerable by the unit.”

UK A.9.3.6.4 Eq. A.9.3-43 Ed The definition and position of the resistance factor is confusing - if it is a resistance factor surely it should be multiplied by the resistance?

According to the text the resistance factor is used to divide the capacities, however in the equation it is used to multiply the actions - although strictly correct according to the definition it is rather confusing!

Suggest using rewriting equation such that the capacities and origins are each individually divided by the resistance factor and not the environmental response point.

UK A.9.3.6.4 Eq. A.9.3-43 Ed The symbol QVH,f appears in the equation but is not defined until after Figure A.9.3-15

Move definition from below Figure A.9.3-15 to below Eq. A.9.3-43

UK A.9.3.6.4 Te The definition of QVH is not clear, this is apparently the point at which the vector intersects the unfactored envelope, so how can it be calculated by dividing the capacities from A.9.3.5 by the resistance factor?!

Section A.9.3.6.4 needs a re-write - it is presently extremely confusing !

UK A.9.3.6.4 Figure A.9.3-15

Te Example V-H envelope is only presented for sand Provide example ‘clay’ envelope

UK A.9.3.6.4 Figure A.9.3-15

Te - Include in the example V-H envelope some laterally projected area component for sliding line

UK A.9.3.6.4 Figure A.9.3- Te I am not completely clear how the V-H envelope would look like for a spudcan that penetrates through very soft

Panel 4 should review this situation to check that a sensible V-H envelope is produced by the present



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15 clay into underlying sand - what would it look like for V/Qv<0.5? There would be significant backflow weight, hence would the ellipse shift upward along the vertical load axis?

guidelines

UK A.9.3..6.4 Figure A.9.3-15

Ed Spelling errors Change both instances of “multipiled” to “multiplied”

UK A.9.3..6.4 Figure A.9.3-15

Ed Layout is unclear for definition of QVH,f

UK A.9.3.6.4 Figure A.9.3-15

Te - Add points indicating typical range of Vsw values or a figure to explain the “Note” below Figure A.9.3-15

UK A.9.3.6.6 Te “The displacement associated with this "virtual" preload is then obtained from the load-penetration curve”

If upper and lower bound load-penetration curves are produced, should additional settlements be determined using LB curve, steepest of all 3 or only with the best-estimate curve

Propose using the steepest of all three curves and include this recommendation in the text.

UK A.9.3.6.7 Ed Typographical error: “The settlements due to bearing capacity failure during to preloading”

Replace with “The settlements due to bearing capacity failure during preloading”

UK A.9.4.2 Te No explicit mention of ‘rack phase differences’ here Add reference to RPDs or suggest references

UK A.9.4.5 Te Add a further recommendation regarding mitigation of leg extraction difficulties.

“It is prudent, and a matter of good practice, to ensure that a unit’s jetting system is fully functional prior to installation at a location where penetration into cohesive soils is predicted”

UK A.9.4.6 Ed “References:” appears at end of section Remove

UK A.10 A.10.4.4.1.2 te Currently this part of the document specifies an initial linearised rotational stiffness of 80-100% of the calculated value. Additional guidance is requested to clarify when it would be appropriate to use 100% initial linearised stiffness.

Add additional guidance (although from which Panel, I’m unsure)

UK A.12 A.12.5.2.2 ed The reference to A.12.5.2.3 should be to A.12.5.2.4 Correct the reference

UK A.12 A.12.6.3.2 ed In the descriptions of Mby and Mbx there are references to equations A.12.6-29 and A12.6-28 respectively. These references do not exist.

Correct these references to A.12.6-25 and A12.6-24 respectively.



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UK Annex E1 Te Comments required stating that backflow has not been modelled by Houlsby & Martin due to the boundary conditions used in their analysis - hence the bearing capacity factors may not be suitable for penetrations approaching and beyond Hcav

Propose Houlsby adds comments to that effect

UK Annex E1 Figure E.1-1 Ed Bearing capacity defined as Q in the Key to Figure E.1-1 but referred to as Fv in the tables.

UK Annex E1 Figure E.1-1 Ed Key below Figure E.1-1 states “NOTE Note: based on”… Remove one of the ‘Note’s’

UK Annex E2 Ed Use of symbol and arrow for FV,in is inconsistent with rest of document

Replace FV,in with Qvo

UK Annex E3 Te/Ed Generally this section seems out-of-place in the ISO, for example many such sections could also be introduced for various aspects of geotechnical analysis such as clay overlying clay, scour, etc. etc.

If it is intended to be kept then it needs significant revision which includes references to Lee et al. 2009 OTC paper and a detailed description of Teh’s proposed method of analysis

Propose removing this section and simply adding in Appendix A.9.3.2.6.4 references to the relevant technical papers

UK F.3 Para 1 ed “Sections that are not been” Replace with “Sections that have note been”

UK F.3 - te P should be changed to Pu to be consistent with the rest of the document in this whole section

Implement the proposed change

UK F.3 - te Prismatic member checks. P/Py should be capped at 1.00 for the surface interaction equations to prevent the equations from going out their intended range

Add additional limits to the existing equations

UK F.3 - te The surface interaction equations should include a P/Py term. Otherwise the utilisation is only related to bending and not axial loads.

Discussion is required to decide how the P/Py term should be incorporated into the equations.

UK F.3 Fig F.3-3 ed “When Mx 0:” Replace with “When Mz 0:”

UK F.3 Fig F.3-4 te It would be useful to explain the meaning of K as it is described in Alan Dyer’s thesis

Add explanation for K

UK A.7.3.2.3 Eq A.7.3-2 note

Ed A typo in De = slD /( i

2I It should be slD /i

2I or slD /)( i

2I



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UK A.12.3.4.3 Table 12.3-1 Te Effective width calculations for Slender Components, a) Compression flange internal components and c) Web internal components under bending and/or compression, are plausible.

“a) Compression flange internal components” is considered to be redundant.

UK A.6.4.2 General Ed No reference to qualifying / sense-checking supplied metocean data

Include one-liner to check data-sets provided satisfy waveheight & period relationships

UK A.6.4.2.7 Para 1 Te Reference to gamma of 1.0 Make clear that this if for DAF calculation only, and that a default gamma of 3.3 is used for wave period relationship calculations (as per after gamma vs Tp/Tz table.

UK A.6.4.2.7 Para 4 Te Advice for Gamma’s when using JONSWAP presented - no other guidance given for other spectrums

Include guidance

UK A.6.4.6.2 Vz definition Te Vz defined w.r.t ‘mean’ water level - surely this should be storm water level (LAT+t+s) assessed ?

Amend MWL to SWL

UK A.7.3.2.4 Para 3 Ed Reference to MWL inconsistent with MSL in same paragraph

Amend to MSL

UK A.7.3.4.1 Te No guidance given on wind on legs below the hull - assume to be determined based on peak wave-phase loading condition (reduced exposed leg length) rather than still-water leg length

Include guidance

UK A.7.3.4.2 Table A.7.3-5

Te Shape coefficients for leg sections recommend using tubular CDi of 0.5. GLND surprised by this change from SNAME’s use of CDe based on ‘smooth’ coefficient of 0.65.

Review decision for change - possible impact is 10% reduction of wind loads on legs when using ISO compared to SNAME.

UK A.8.5.7 Para 1 Ed The reference to A.8.5.7 refers to its own paragraph. Either delete or change reference to A.8.2.3

UK A.8.2.3 Ed No reference to mass modelling in any of the modelling options from fully detailed FE model to equivalent stick model

Suggest add reference to 8.7 (mass modelling) and A.8.7.

UK 8.7 (& A.8.7|) Ed Breakdown of masses to be included in analysis may be better suited in A.8.7 rather than 8.7

Relocate list of masses to be included currently listed after para 1 in 8.7 to A.8.7

UK C.2 C.2-12a Ed The h in equation C.2-12a should be squared and not multiplied by 2.

Square the h term and remove the multiplier.

UK Flowchart fig Determine Responses

Ed Reference to 10.3-10.5 instead of 10.5, and to fig 10.3.1



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5.1 box

UK A.7.3.3.3 Fig A.7.3-1 Te The variables shown on each axis of the chart are not defined in the document. For example on the Y axis does H refer to the significant or maximum wave height?.

Include these variables in the charts nomenclature

UK A.10.5.2.2.1 Fig A.10.5-1 (b)

Te No equation is presented for the calculation of Fin. This should be included as it is fundamentally different to the equation used for the SDOF method.

Include the relevant equation for Fin such that the user does not use the equation presented for the SDOF method by accident.

UK A.10.5.2.2.2 Para ‘2)’ Te This statement is inaccurate and misleading to the reader.

The word ‘peak’ should be changed to ‘trough’ and the reference to natural period should be changed to wave period. Alternatively the paragraph should be reworded to specify under which exact conditions the SDOF method may be un-conservative. This problem is also not exclusive to the SDOF method and therefore the text should be moved to a higher level in the document.

UK A.12.4.3 Table A.12.4-1

Te ‘lateral loading’ of members not qualified - wave/current loading (which may be lower than self weight loads per member) or structural point loads e.g. guide loads

Qualify ‘lateral loading’ e.g. does wave/current loading qualify (which may be lower than self weight loads per member) or is this intended to be structural point loads e.g. guide loads



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APPENDIX B FINAL QUASI-STATIC RESULTS COMPARISON OF ISO & SNAME RESULTS TO ISO USING SNAME WIND

Summary of critical structural utilisations - Site 1 (sand)

Utilisations Heading ISO SNAME ISO with

SNAME WIND

Overturning 120 0,78 0,78 0,80

Preload Capacity 60 1,11 1,15 1,12


60 1,34 1,54 1,36

Additional settlements (m)

60 0,10 0,17 0,11

Windward leg sliding 120 0,84 0,85 0,88

Maximum Hull sway (m)

60 1,75 1,79 1,80

Leg chord strength[1] 90 0,74 0,84 0,76

Leg brace strength 90 0,31 0,31 0,32

Chock holding strength 120 0,64 0,61 0,64

Summary of critical structural utilisations - Site 2 (clay)

Utilisations Heading ISO SNAME ISO with

SNAME WIND

Overturning 120 0,70 0,63 0,72

Preload Capacity 60 1,04 1,08 1,07


60 1,24 1,50 1,28

Additional settlements (m) 60 3,23 3,92 3,40

Windward leg sliding 120 0,27 0,48 0,29

Maximum Hull sway (m) 60 1,12 0,99 1,22

Leg chord strength[1] 90 0,58 0,81 0,59

Leg brace strength 90 0,28 0,37 0,28

Chock holding strength 120 0,50 0,55 0,50

iso phase 2 benchmarking iso 19905-1 (dis) validity ... - dnv

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