low-frequency second-order drift-forces experimental ... · set 1: pink noise (0º & 20º...

Low-frequency second-order drift-forces

experimental validation for a Twin Hull

Shape Offshore Wind Platform - SATH

The Company

Introduction to SATH concept

Model testing motivation

Experiments

Numerical validation

Main conclusions

2

Layout

EERA DeepWind’2019| Araceli Martínez · Saitec Offshore Technologies | January 2019, Trondheim, Norway

3 EERA DeepWind’2019| Araceli Martínez · Saitec Offshore Technologies | January 2019, Trondheim, Norway

SATHTM INNOVATIVE FLOATING WIND SOLUTION

MAKING OFFSHORE WIND GLOBAL

Spin-off from International Infrastructure engineering company

Designing the future

Patented technology

CO

MP

AN

Y P

UR

PO

SE

The Company

4

Introduction to SATH concept


Floaters - Buoyancy

Heave plates - Motion dampers SPM – External turret Self-alignment with the Wind Direction - Stresses reduction

Transition piece -Interface tower-floater

CONCRETE LOW DRAFT SELF-STABLE

Swinging Around Twin Hull

Reduced construction and maintenance costs

2 MW – 6.5m 10 MW – 9.5m

Easily transportation

Internal bulkheads - Load transmission

5

Model testing motivation


OBJECTIVE

LIMITATIONS

METHODOLOGY

Collaboration Project

NUMERICAL CALIBRATION

Mooring System optimization

Potential theory assumptions

EXPERIMENTS at IFREMER (July 2018) - Mean Drift Coefficients extraction - Full-QTF Coefficients extraction

FAST

Sima

6

Experiments


Scale model

Wind turbine Computer-controlled

Qualysis Track motion

Load cells mooring system

Scale model 1/36 Full

prototype-2MW

Length (m) 1.72 61.92

Width (m) 0.85 30.6

Total height (m) 2.05 73.8

Draft (m) 0.2 7.35

Total Mass (kg) 82.8 3863116.8

7

Experiments


Soft Mooring Simple an linear setup for identification

of hydrodynamic coefficients.

Experiments set-up

VCG to decouple the pitch motion from

the mooring system forces.

8

Experiments


Calibration of waves

Test campaign planning

Tests in waves: periodic; irregular; pink noise Characterization tests: decay; tilt; pull out

Identification of mass properties

9

Experiments


Characterization tests – Global verification of the structure behaviour

Natural oscillation periods

Metacentric heights

Mooring stiffness

Linear & Quadratic damping

Saitec X (m) Trans GM(m) Long GM(m)

Stiffness (K)

10

Experiments


Tests in waves– Periodic waves

Extraction of the Mean Drift force Coefficients for different

incidence angles and wave steepness

OBJECTIVE

K = mooring stiffness measured (N/m) X = mean displacement measured (m) F = mean drift force (N) A = wave amplitude (m)

Wave elevation (m)

Stiffness curve (K/mm)

Surge (mm)

11

Experiments


Tests in waves– Periodic waves Test Matrix:

Set 1: head waves; no wind; different steepness Set 2: head waves; wind influence; Set 3: 20º waves; no wind;

Real model

Period Height Steepness

6.000 1.116 0.020

6.000 4.680 0.083 7.980 1.692 0.017

7.980 4.320 0.043

7.980 8.640 0.086

9.000 2.088 0.016 9.000 5.256 0.042

9.000 10.512 0.083

10.000 2.900 0.019

10.980 7.992 0.043

10.980 15.984 0.086

13.020 4.392 0.017

13.020 11.016 0.043

13.020 19.800 0.078

16.500 7.488 0.020

16.500 15.480 0.042 Potential theory over-estimates the coefficients Favourable steepness dependency

12

Experiments


Tests in waves– Irregular waves

Extraction of the full Quadratic Transfer Function coefficients

OBJECTIVE Second order signal analysis technique based on cross bi-spectral analysis

13

Experiments


Tests in waves– Irregular waves Test Matrix:

Set 1: pink noise (0º & 20º incidence) Set 2: sea-states along the 50 years environmental contour (0º & 20º incidence) Set 3: sea-states representative of operational conditions (0º & 20º incidence)

Favourable steepness dependency

0

10

20

30

40

50

60

70

0,04 0,06 0,08 0,10 0,12 0,14 0,16

F (

kN

/m2)

f (Hz)

Surge wave drift force coefficients (0 deg.)

Potential flow

Test 1117 (df = 0.007 Hz)

Test 1080 (df = 0.007 Hz)

Test 1119 (df = 0.007 Hz)

Test 1107 (df = 0.007 Hz)

Test 1109 (df = 0.007 Hz)

Test 1113 (df = 0.007 Hz)

Test 1105 (df = 0.007 Hz)

Test 1115 (df = 0.007 Hz)

0.02

3 0.01

9

0.01

2 0.01

9

0.03

6 0.03

7

0

20

40

60

80

100

120

0,00 0,10 0,20 0,30

F (

kN

/m2)

f (Hz)

Surge wave drift force coefficients (0 deg.)

Potential flow

Test 1117 (df = 0.007 Hz)

Test 1070 (df = 0.007 Hz)

Test 1080 (df = 0.007 Hz)

Test 1119 (df = 0.007 Hz)

Test 1107 (df = 0.007 Hz)

Test 1109 (df = 0.007 Hz)

Test 1113 (df = 0.007 Hz)

Test 1105 (df = 0.007 Hz)

Test 1115 (df = 0.007 Hz)

Test 1111 (df = 0.007 Hz)

14



Extraction of the Mean Drift Force Coefficients from tests

Correction of potential flow Mean Drift Coefficients f(steepness)

Time Domain Simulations using Newman’s Approximation

Frequency Domain Simulations (Based on potential theory)

Optimization of the mooring system design

15



Hs = 5m Tp = 8.8s

16



Hs = 7m Tp = 11s

17



Hs = 9.4m Tp = 13s

18



Hs = 9.7m Tp = 18s

19



Hs = 9.7m Tp = 16s

20



Hs = 5m Tp = 13s

21



22



23

Main conclusions


• Soft mooring set-up – Simplifications of results

• Only wave tests – No extra phenomena (wind or current)

• Duration of the tests – 3 hour sea-states

• Wave tank basin characteristics – No reflection

• Potential theory – Over-estimation of the results

• SATH Technology – Non-linear response for different wave steepness

• Newman’s Approximation – Verified for SATH concept

• Optimization of the mooring system – Adjustment of numerical models

Thank you for your attention

Araceli Martínez Rubio

[email protected]

low-frequency second-order drift-forces experimental ... · set 1: pink noise (0º & 20º...

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