mooring line dynamics of a semi- submersible wind energy ... · orcaflex • ‘lump mass and...
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Mooring Line Dynamics of a Semi-submersible Wind Energy Platform: Cross Validation of Two Commercial Numerical Codes with Experimental DataPresenter : Rachel Chester Role : Researcher Institution : University College Cork
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INTRODUCTION
Mooring Line Dynamics of a Semi-submersible Wind Energy Platform: Cross Validation of Two Commercial Numerical Codes with Experimental
Data
Content
• Methodology• Numerical Software• Experimental Data & Tank Testing• Validation Results • Conclusions and Future Work
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METHODOLOGY
• Dataset taken from Atlantic Marine Energy Test Site (AMETS) in Belmullet, Ireland
• Testing regular and irregular wave loads
• With and without a constant wind load
Environment
X
Location of the Atlantic Marine Energy Test Site in Belmullet, Ireland
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METHODOLOGY
• INNWIND Semi-submersible floating platform
• 5 MW Reference Turbine
• 3 Leg Catenary Mooring System
Technology
Example semi-submersible platform [Source: DNV-GL]
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METHODOLOGY
• Response Amplitude Operators (RAOs)
• Fairlead Loads
• Acceleration at Hub Height
Focus Points
Example semi-submersible platform [Source: DNV-GL]
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NUMERICAL SOFTWARE
ORCAFLEX & FLEXCOM
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NUMERICAL SOFTWAREOrcaFlex
• ‘Lump mass and spring method’
• Line is dicretised into series of elements connected by nodes
• Nodes calculate effective tension, bending moments and shear forces
• Elements deal with axial and torsional properties
Illustration of lump mass and spring method [Source: OrcaFlex]
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NUMERICAL SOFTWAREFlexcom
• Finite element formulation
• Utilises up to 10 integration points to distribute forces evenly across each element
• 14 degree of freedom hybrid beam-column allows fully coupled axial bending and torque
Illustration of 14 degrees hybrid finite element [Source: Flexcom]
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EXPERIMENTAL DATATank Testing
• Tank testing conducted at Lir National Ocean Testing Facility, Cork
• 1:36 Froude scale
• Equivalent of 100m water depth
• Instrumentation:• Load cells at fairlead interface• Wave elevation probes• Qualisys motion capture system
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EXPERIMENTAL DATATaut Line & Spring Method
• Spring attached at interface between taut line and anchor
• Springs used to replicate load-displacement curve
• Method unrestricted by basin size.
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EXPERIMENTAL DATATaut Line & Spring Method
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RESULTSRAOs
• Reasonable agreement between all 6 degrees of freedom
• Resonance responses all in agreement
• Numerical models produce lower resonance displacement
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0,900,940,981,021,061,101,141,181,22
Hs 1.5mTp 9.2s
Hs 2.5mTp 9.0s
Hs 2.5mTp 11.0s
Hs 2.5mTp 12.0s
Hs 2.5mTp 15.0s
Hs 3.4mTp 12.0s
Hs 4.0mTp 12.0s
Hs 2.5mTp 15.0sU 8.6m/s
Hs 5.5mTp 15.0s
U 11.4m/s
P90/
P50
Ratio
Simulation
Fairlead Loads
Tank Test Flexcom OrcaFlex
RESULTSFairlead Loads
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RESULTSFairlead Loads
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0,900,940,981,021,061,101,141,181,22
Hs 1.5mTp 9.2s
Hs 2.5mTp 9.0s
Hs 2.5mTp 11.0s
Hs 2.5mTp 12.0s
Hs 2.5mTp 15.0s
Hs 3.4mTp 12.0s
Hs 4.0mTp 12.0s
Hs 2.5mTp 15.0sU 8.6m/s
Hs 5.5mTp 15.0s
U 11.4m/s
P90/
P50
Ratio
Simulation
Fairlead Loads
Tank Test Flexcom OrcaFlex
RESULTSFairlead Loads
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RESULTSFairlead Loads
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RESULTSAcceleration at Hub Height
0,000,050,100,150,200,250,300,350,40
Hs 1.5mTp 9.2s
Hs 2.5mTp 9.0s
Hs 2.5mTp 11.0s
Hs 2.5mTp 12.0s
Hs 2.5mTp 15.0s
Hs 3.4mTp 12.0s
Hs 4.0mTp 12.0s
Hs 2.5mTp 15.0sU 8.6m/s
Hs 5.5mTp 15.0s
U 11.4m/s
RMS
of A
ccel
erat
ion
(m/s
2)
Simulation
Acceleration at Hub Height
Tank Test Flexcom OrcaFlex
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CONCLUSIONS
• Two scaled mooring systems displayed very similar results;
• OrcaFlex and Flexcom showed broadly similar behavior throughout;
• Some discrepancies between numerical and physical models for wave loading scenarios:
Discrepancies are minimized when dominant wind loading is considered;
Discrepancies can be attributed to the absence of mid-frequency responses in irregular wave loading.
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FUTURE WORK
Incorporation of variable wind loading:
• SIL fan in tank testing• Incorporation of FAST• Using wind turbine updates in numerical software
Tank testing with SIL fan [Source: INNWind]
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