20170207 Yang V4 - UTMISutmis.org/media/2017/03/2-Analysis-of-fatigue-chatacteristics-in... ·...

Shun-Han Yang (Hedy)p. 1

2017-02-07

SHIPPING AND MARINE TECHNOLOGYDIVISION OF MARINE TECHNOLOGY

UTMIS Nätverksmöte

Analysis of fatigue characteristics in mooring lines and power cables for wave energy converters

PhD student: Shun-Han Yang (Hedy)Supervisor: Professor Jonas W. RingsbergCo-supervisor: Adjunct professor Erland Johnson

Chalmers University of TechnologyDepartment of Shipping and Marine TechnologyDivision of Marine Technology


2017-02-07


Wave energy converter system (WEC)


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Power cable

HubWEC

Wave and current

Mooring line

Wave energy converter system (WEC)

• Challenge: design for long-term conditions with regard to mechanical service life of mooring lines and power cables

• Need: an established design and evaluation methodology


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Fatigue life• Mooring system and

configuration• Low voltage power

cable

WEC energy performance

Environmental loads and factors

• Wave load• Ocean current• Marine biofouling


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Objective

• Develop a complete numerical analysis procedure for the mooring lines and power cables used in WEC systems – Compare and recommend

simulation procedures– Assess and compare

parameters that will enhance fatigue lives


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Methodology

1. Hydrodynamic and structural response analyses

2. Stress and fatigue analyses3. Energy performance analysis4. Parametric analysis


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1. Hydrodynamic and structural response analyses of the WEC system

• Hydrodynamic response of the WEC buoy– Radiation-diffraction panel

method and drag effect from Morison equation

– 6 DOFs rigid body motion– DNV Sesam package,

including HydroD and SIMO in DeepC

• Hydrodynamic and structural response of the mooring lines and power cable– Nonlinear time-domain– Nonlinear finite element

method– Axial force and bending

moment– DNV DeepC (Riflex)

De‐coupled analysis—separate and sequential steps

Coupled analysis—the complete system is solved simultaneously (DNV DeepC)


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• First-principle design

• Stress analysis– Mooring: axial stress– Power cable: axial and

bending stresses

2. Stress and fatigue damage analyses of the mooring lines and power cable

• Material property: S-N curve– Mooring: DNV (2010)– Power cable: Nasution et al.

(2013)

• Fatigue damage evaluation– Stress-based approach– Basquin’s equation– Palmgren-Miner rule– Rainflow cycle counting method


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3. Energy performance analysis of the WEC

• Instantaneous absorbed power = PTO linear damping coeff.×(velocity in heave direction)2


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4. Parametric analysis

• Structural design parameters Properties of the cable Mc [kg/m] EI [Nm2] Lc [m] 2 2.75 6 50 200 400 70 82 Case 1 × × × Case 2 × × × Case 3 × × × Case 4 × × × Case 5 × × × Case 6 × × × Case 7 × × × Case 8 × × × Case 9 × × × Case 10 × × × Case 11 × × × Case 12 × × × Case 13 × × × Case 14 × × × Case 15 × × × Case 16 × × × Case 17 × × × Case 18 × × ×

4-mooring

3-mooring


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4. Parametric analysis

• Structural design parameters• Environmental loads

– Sea states– Wave and current direction

Hs [m] Tz [s] 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 Sum

12.5 0 0 0 0 0 0 0 1 2 3 0 0 0 0 6 11.5 0 0 0 0 0 0 0 2 7 0 0 0 0 0 9 10.5 0 0 0 0 0 0 0 11 10 0 0 0 0 0 21

9.5 0 0 0 0 0 0 6 42 10 0 0 0 0 0 58 8.5 0 0 0 0 0 2 29 87 2 0 0 0 0 0 120 7.5 0 0 0 0 0 14 107 103 2 0 0 0 0 0 226 6.5 0 0 0 0 0 44 267 33 5 1 0 0 0 0 350 5.5 0 0 0 0 7 166 337 37 7 2 0 1 0 0 557 4.5 0 0 0 0 43 558 136 32 14 5 1 1 0 0 790 3.5 0 0 0 1 371 563 123 48 19 6 2 1 0 0 1134 2.5 0 0 4 179 877 303 130 71 33 16 7 2 0 0 1622 1.5 0 0 221 1014 501 220 146 110 66 36 16 3 1 0 2334 0.5 644 367 684 248 107 142 162 192 117 64 19 22 3 4 2775

Sum 644 367 909 1442 1906 2012 1443 769 294 133 45 30 4 4 10002


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Example of Results


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Simulation procedures –mooring analysis


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Power cable: hydrodynamic and structural response analyses


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Fatigue–wave height–wave period matrix


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Parametric analysis: effect of environmental loads


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Summary and conclusions

• Simulation procedure– A coupled analysis should be used in order to make an appropriate

structural fatigue analysis of mooring systems and power cables.

• Parametric analysis– Parametric studies should be carried out in order to be able to

compare the influence from design parameters and environmental factors.

– Challenges arisen due to ocean environment.

• Power cable– Global model is not sufficient to obtain fatigue life of the cable, a

local model is needed.


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Future work

• Validation of numerical models (experiment completed in October 2016)

• Development of a local model for the power cable• Investigation of different mooring materials

We look forward to fruitful cooperationwith both national and international partners.

For detailed project information, please contact:

PhD student Shun-Han Yang ([email protected])Professor Jonas W. Ringsberg ([email protected])Adjunct Professor Erland Johnson ([email protected])

20170207 Yang V4 - UTMISutmis.org/media/2017/03/2-Analysis-of-fatigue-chatacteristics-in... ·...

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