A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/1
MAESTRO-Waveby DRS-DS, USA
NDAR, France
A METHOD OF APPLYINGLINEAR SEAKEEPING PANEL PRESSURE
TOFULL SHIP STRUCTURAL MODELS
Ming Ma - DRS Defence Solutions, USAChengbi Zhao - SCUT, ChinaNick Danese - NDAR, France
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/2
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Introduction
State of the art review
The MAESTRO / MAESTRO-Wave integrated approach
MAESTRO-WAVE Comparison
Extreme Load Analysis / Design Wave
Spectral Fatigue Analysis
Conclusion
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/3
MAESTRO-Waveby DRS-DS, USA
NDAR, France
M.A.E.STR.O. (Dr. Hughes, DRS-DS) FE everywhere FE as a design tool 1980 : adequacy parameters, limit state analysis 1996 : graphical interactive topological modelling 2000 : added mass, DNV HSLC equivalency factors 2004 : sparse solver 2008 : COM-MAESTRO 2011 : MAESTRO - NAPA Steel one click 2012 : MAESTRO - Seakeeping one click Extreme Load Analysis / Design Wave Spectral Fatigue Analysis 16 April 2012 : MAESTRO 10 with MAESTRO-Wave released
Introduction.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/4
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Balanced ModelUnbalanced Model
FE analysis of floating structures requires hydro-s/d balancing.
Significance of equilibrium for finite element analysis.
Unbalanced
Balanced
Draft
3.96m 4.07m
Trim -0.382 Deg
0.437 Deg
Weight Distribution Buoyancy Distribution
VBM VBM
3-node deflection shape 2-node deflection shape
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/5
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Panel based hydrodynamic analysis is computational intensive, coarser meshes Customarily, two different mesh models are maintained: Hydrodynamic (coarser)
and Structural (finer)
In some cases, the hydrodynamic analysis may not use a surface model at all, still need to get panel pressures for FE (MAESTRO-Wave does).
Hydrodynamic mesh Structural mesh
Hull form
Hydrostatics
HydrodynamicsStructures
…
Design Spiral
Transfer hydrodynamic loads to a FE model.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/6
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Load mapping methods.
Direct pressure mapping PROS: Intuitive, easy for third party development CONS: unbalanced structural model, “inertia relief” corrective approach
(ABS, 2010) modifies accelerations, potentially unrealistic.
Source strength mapping (BV, 2008) PROS: structural model is balanced by definition CONS: may be difficult for third party users (no access to source strengths
and mapping facilities)
HYDRODYNAMIC MESH STRUCTURAL MESH
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/7
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Hydrostatic restoring forces
Equations of motion:
Hydrostatic restoring matrix:Using pressure integration
Inconsistency
Hydrostatic restoring force matrix.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/8
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Panel pressure correction methods.
For each panel, the elemental Forces and Moments are:
By the original hydrostatic restoring matrix:
By the pressure integration:
BV’s proposed approach: adding a gravity term to all FE elements in the complete ship model
MAESTRO’s approach: adding correction nodal forces using Quadratic Programming to wet nodes only
Quadratic Programming
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/9
MAESTRO-Waveby DRS-DS, USA
NDAR, France
MAESTRO integrated approach.
One mesh used for both FE and hydrodynamics
One Graphical User Interface FE model supplies weights, CGs, etc. Embedded linear frequency domain 3D panel
hydrodynamic analysis• The hydrodynamic model is generated from the
FE wet panels and nodes• Source strengths mapped to FE mesh =
hydrodynamic equilibrium by default• Nodal force adjustment uses Quadratic
Programming (heave, pitch), not inertia Fully integrated structural analysis
• Extreme Load Analysis / Design Wave• Spectral Fatigue Analysis
Failure mode evaluation (structural adequacy, limit states), the heart of first principles FE
9
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/10
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Hydrodynamic comparisons.
S175
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/11
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Hydrodynamic comparisons, cont'd.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/12
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Hydrodynamic comparisons, cont'd.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/13
MAESTRO-Waveby DRS-DS, USA
NDAR, France
An integrated solution:NAPASteelFE exportMAESTRO-WaveELA/SFA Failure mode evaluation
Structural Model FEA Model
Hydrodynamic Model VBM RAOs of all sections
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/14
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Design Waves.
• If the static load case is balanced andif the hydrodynamic loads are balanced, thenthe combined load case is balanced, by definition.
• Then, the FE response analysis can be run directly.
• Wet elements automatically receive hydrostatic loads, while Dry elements do not
• MAESTRO will balance the static load case.
• MAESTRO-Wave will balance the corresponding hydrodynamic load cases using panel pressures on the FE mesh and quadratic programming for heave and pitch correction.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/15
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Extreme DesignCase #4 with 180deg Shift
Extreme Design WaveCase #4 with 180deg Shift
Extreme DesignCase #4
Extreme Design WaveCase #4
Design Waves: dynamic, s/p static, combined.
Extreme DesignCase #1
Extreme DesignCase #1 with 180deg Shift
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/16
MAESTRO-Waveby DRS-DS, USA
NDAR, France
ELA - Extreme Load Analysis calculation procedure.
Full Ship Structural Model
Short/Long Term Extreme Loads
Hull GirderUltimateStrength
Local Structural Failures
ELAStrength Assessment
Cached Unit Wave Load Database
(Accelerations, Panel Pressure)
Hull Girder Global Loads RAO Wave Spectrum
Hull Girder Global LoadsResponse Spectrum
Extreme Load for Each Sea State
Operational Conditions
)()(, 0 VPPTHPTTn s
zi
Equivalent Extreme Regular Wave
StaticLoadUnitWaveScaleDLyyScale
dlp
)(
max
Long/Short TermEnvironment
12 Headings30 Frequencies
5 Speeds
MAESTRO FE model
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/17
MAESTRO-Waveby DRS-DS, USA
NDAR, France
SFA – Spectral Fatigue Analysis calculation procedure.
Cached Unit Wave Stress Response
Database
S-N Curves Miner’s Rule
12 Headings30 Frequencies
5 Speeds
esAllSeaStat
i
miii
n
nn
m
p
fppmKTD
k
10
1
2/ 12
2
1
10
100
1000
1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Number of Cycles
Stre
ss R
ange
(N/m
m2)
BCD
FF2
E
G
W
Stress Range PDF
Full Ship Structural Model
Cached Frequency Domain Stress RAO Database
Coarse Mesh Full Ship Fatigue
Damage Screening
Fine Mesh Selected Area Fatigue
Damage Assessment
Element Stress RAO Wave SpectrumMAESTRO FE model
Element Stress Response Spectrum
Operational Conditions (speed, heading)
Long TermEnvironment
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/18
MAESTRO-Waveby DRS-DS, USA
NDAR, France
SFA – Coarse mesh full model fatigue screening.
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/19
MAESTRO-Waveby DRS-DS, USA
NDAR, France
Obtain wet FE mesh from MAESTROExport it to hydrodynamic code using MAESTRO-WaveFrom the discretized boundary integral equations obtain the panel source strength
of each potentialMap the source strengths of each panel to the FE meshCompute hydrodynamic added mass, damping and restoring coefficients by
integrating the wet panels (FE panels ≡ hydro panels)Construct the equations of motion, obtain the motion RAOsCompute the panel pressures on the FE mesh and the corrective restoring
nodal forcesLoad the FE model by applying panel pressures (unbalanced model) MAESTRO-Wave balances the FE model by applying corrective forces
using quadratic programming
What was that all about ?
A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/20
MAESTRO-Waveby DRS-DS, USA
NDAR, France
MAESTRO-Wave : integrates FE and seakeeping
Full model, supports any shape
Purpose-dense mesh (very coarse to very fine)
Runs ELA and SFA at once
Fast, use in every day design work (mesh density speed)
Neutral format interface file (.wet)
Interfaces / integrates with any seakeeping code
One-stop ship-shop
Conclusion.