Table of contents

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Table of contents

• Background and problem statement
• Implemented approach
• Example calculation
• Conclusions

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Background The OWEA project

• OWEA Verification of Offshore Wind Turbines
  part of RAVE
• research project at the German offshore test site
  alpha-ventus
• evaluation of extensive measurement campaign
• main objective reduction of uncertainties in
  load assumptions for the 5MW class and new
  support structure types

Universität Stuttgart
6x Multibrid M5000 6x REpower 5M
(Source BMU, Multibrid, REpower)
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Problem statement

• Shortcomings
• analysis frequently separated in
  rotor-nacelle-assembly (RNA) foundation?
  integrated analysis required? difficult in real
  life
• integrated design tools only with basic offshore
  features? lack of full complexity
• non-linear foundation/hydrodynamics
• braced/lattice structures
• lack of code validation withoffshore measurements

• Solution attempts
• rigorous modeling approach for integrated
  analysis under wind wave loading
• coupling commercial tools, providing
  state-of-the-art analysis
• combination of industry tools maintaining
  modularity and strength
• offshore code comparison collaboration (OC3) IEA
  Wind Annex 23 Subtask 2
• RAVE measurements OWEA project

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Tools used for the coupling

• aeroelastic wind turbine code Flex5
• widely-used tool in industry
• based on modal approach using 28 degrees of
  freedom (DOF)
• only capable of monopiles
• finite element code
• Poseidon by Institute for Steel Construction
  (Leibniz University Hannover)
• arbitrary offshore support structures possible
• unlimited number of DOF
• ASAS(NL) of ANSYS Inc. (forthcoming)

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Implementation component mode synthesis (i)
Sub-system Flex5
Sub-system FE code
Flex5
interface
Component mode synthesis (Treatment as
sub-systems with fixed interface)
FE code
Pictures W. de Vries, TU Delft
FE code

• ? systems equation of motion solved in FE code
• maintains the advantages of each code
• allows a combination of modal DOF and
  physical DOF

modeling
solution
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Implementation component mode synthesis (ii)

• mathematical formulation 2nd order equ. of
  motion
• system matrices composed by Flex5 and the
  FE-code

No couplingof internal sub-system DOF
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Implementation communication scheme

• Flex5 wind turbine code as executable
• contains rotor-nacelle-assembly (RNA) tower
  model
• aeroelastic force calculation

Flex5
tn1
tn-1
tn
MFlex, DFlex, SFlex, FAero
shared memory orDLL interface
FE-Code
Newmark Solver
Newmark Solver
tn1
tn-1
tn

• finite element code e.g. Poseidon as executable
• determination of hydrodynamic loads
• synthesis of the sub-systems in every time step
• time integration of systems equation of motion

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Reference models

• Models
• models of OC3 project within IEA Wind Annex 23
• 5MW offshore wind turbine (OWT) by NREL
• OC3 monopile OC3 tripod

Case 1 Monopile ? comparison of Flex5 alone with
Flex5-Poseidon ? aim check plausibility of the
implemented method ? corresponding results

• Case 2 Tripod
• comparison of the developed coupling with OC3
  results
• aim demonstrating the potential of the coupling

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Tripod excitation by aerodynamic loads
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Blade excitation by waves tripod monopile

• one regular wave train (f 0.25 Hz) on idling
  OWT
• spectrum of blade root bending moment ? first
  support structure eigenfrequencies are equivalent
  ( 0,28 Hz)

1st longitudinal bending eigenfrequency
wave frequency
1st blade flap mode
normalized powerspectradensity (scaled)
normalized powerspectradensity
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Conclusions

• Summary
• accurate modeling approach for integrated
  analysis
• coupling commercial tools, providing
  state-of-the-art features
• validated with original Flex5 OC3 load cases
• already applied in industry by REpower
• Outlook
• extension to the FE code ASAS(NL) ANSYS Inc.
• further verification with other simulation tools
  like Bladed
• validation with measurement data of the alpha
  ventus offshore test site

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• Thank you for your attention!

• Acknowledgement
• The OWEA project (No. 0327696A) is funded by the
  German Federal Ministry for the Environment,
  Nature Conservation and Nuclear Safety (BMU).
• Special thanks to P. Passon and his work for
  UpWind WP4 support structures