Loads and response from steep and breaking waves on monopiles

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1 Downloaded from orbit.dtu.dk on: Jan 12, 2016 Loads and response from steep and breaking waves on monopiles Bredmose, Henrik; Schløer, Signe; Sahlberg-Nielsen, Lasse; Slabiak, Peter ; Larsen, Torben J.; Kim, Taessong ; Paulsen, Bo Terp; Bingham, Harry B.; Jacobsen, Niels Gjøl; Tornfeldt Sørensen, Jacob; Schlütter, Flemming ; Nielsen, Anders Wedel Publication date: 2013 Link to publication Citation (APA): Bredmose, H., Schløer, S., Sahlberg-Nielsen, L., Slabiak, P., Larsen, T. J., Kim, T.,... Nielsen, A. W. (2013). Loads and response from steep and breaking waves on monopiles [Sound/Visual production (digital)]. Danish Wind Power Research 2013, Fredericia, Denmark, 27/05/2013 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal? If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

2 Loads and response from steep and breaking waves on monopiles With contributions from Henrik Bredmose Signe Schløer Lasse Sahlberg-Nielsen Peter Slabiak Torben J. Larsen Taessong Kim Bo Terp Paulsen J Harry Bingham Niels Gjøl Jacobsen Jacob Tornfeldt Sørensen Henrik Bredmose Associate prof, DTU Wind Energy Flemming Schlütter Anders Wedel Nielsen Statkraft

3 Hydrodynamic loads Simplest: Linear wave kinematics and Morison equation Better: Fully nonlinear wave kinematics and Morison equation Advanced: CFD and coupled CFD Zang and Taylor (2010)

4 Wave loads on offshore wind turbines ForskEL. DTU Wind, DHI, DTU MEK Task D: Task A: Physical validation test Boundary conditions for phase resolving wave models Task C: Task B: Aero-elastic response to fully nonlinear waves CFD computation of monopile loads

5 Forces from a fully nonlinear potential flow solver OceanWave3D, Engsig-Karup et al (2009) Allan Engsig-Karup, Harry Bingham and Ole Lindberg

6 Response in bottom of tower Fully nonlinear waves versus linear waves Schløer et al (OMAE 2012)

7 The OC4 jacket Jacket and reference turbine modelled in Hawc2. Fully nonlinear wave loads. Storm sea state. Turbine standstil. Severe ringing/impulsive excitation. Torben Juul Larsen Taesong Kim Larsen et al Europ. Offsh. Wind 2011

8 Wave loads on offshore wind turbines ForskEL. DTU Wind, DHI, DTU MEK Task D: Task A: Physical validation test Boundary conditions for phase resolving wave models Task C: Task B: Aero-elastic response to fully nonlinear waves CFD computation of monopile loads

9 The OpenFOAM CFD solver Open source CFD toolbox Vast attention during last 3 years This study: interfoam solver 3D incompressible Navier-Stokes two phases (water and air) VOF treatment of free surface Waves2foam wave generation toolbox has been developed and validated (Niels Gjøl Jacobsen PhD thesis 2011; Paper in Int. J. Num. Meth. Fluids) OMAE2010

10 Platform height of 8.96m t=58.8s Bredmose & Jacobsen OMAE 2011

11 Platform height of 8.96m t=58.9s

12 Platform height of 8.96m t=59.0s

13 Platform height of 8.96m t=59.1s

14 Platform height of 8.96m t=59.2s

15 Platform height of 8.96m t=59.3s

16 Platform height of 8.96m t=59.4s

17 Platform height of 8.96m t=59.5s

18 Platform height of 8.96m t=59.6s

19 Platform height of 8.96m t=59.7s

20 Platform height of 8.96m t=59.8s

21 Platform height of 8.96m t=59.9s

22 Platform height of 8.96m t=60.0s

23 Platform height of 8.96m t=60.1s

24 Platform height of 8.96m t=60.2s

25 Platform height of 8.96m t=60.3s

26 Platform height of 8.96m t=60.4s

27 Platform height of 8.96m t=60.5s

28 What is ringing? Excitation of natural frequency by higher-harmonic forcing from nonlinear waves ^ F fnatural f fw 2fw 3fw

29 Detailed calculation of forces from steep regular waves secondary load cycle Bo Terp Paulsen

30 Third-harmonic force compared to FNV theory Terp Paulsen et al IWWWFB 2012

31 Coupling of OpenFOAM and OceanWave3D Compute outer flow field with potential flow wave model Compute inner field with wave-structure interaction with CFD-VOF model Terp Paulsen et al (2012)

32 Coupling of OpenFOAM and OceanWave3D Terp Paulsen et al (2012)

33 Coupling of OpenFOAM and OceanWave3D Terp Paulsen et al (2012)

34 Coupling of OpenFOAM and OceanWave3D Terp Paulsen et al (2012)

35 Wave loads on offshore wind turbines ForskEL. DTU Wind, DHI, DTU MEK Task D: Task A: Physical validation test Boundary conditions for phase resolving wave models Task C: Task B: Aero-elastic response to fully nonlinear waves CFD computation of monopile loads

36 Wave loads Task D Physical validation test New tests at DHI with a rigid and a flexible structure DHI: Flemming Schlütter Anders Wedel Nielsen Jacob Tornfeldt Sørensen DTU: Henrik Bredmose Torben Larsen Signe Schløer Bo Terp Paulsen Harry Bingham

37 Wave loads Task D Physical validation test PVC pipe Scale 1:80 Two masses right natural frequencies (1,2)

38 Experimental setup side-view top-view of wave gauges

39 Results and brief analysis for flexible pile Irregular JONSWAP waves, unidirectional h=20m Tp=14s Hs=11m Free surface elevation 0.15m from pile Measured inline force on pile Acceleration of top point Displacement of top point

40 Results and brief analysis

41 continuous forcing of 1st natural mode Impulsive load from breaking from wave-nonlinearity /near breaking wave

42 Which waves give the largest accelerations? acceleration Fx in top accelerometer [m/s2] Bredmose et al (OMAE 2013)

43 Which waves give the largest accelerations? Bredmose et al (OMAE 2013)

44 Numerical reproduction of experiments FEM model Linear wave detection Nonlinear wave transformation Force model

45 Wave transformation

46 Response, h=40.8 m

47 Response, h=20.8 m

48 Wave loads on offshore wind turbines ForskEL. DTU Wind, DHI, DTU MEK Task D: Task A: Physical validation test Boundary conditions for phase resolving wave models Experiments with flexible monopile Impulsive response Numerical reproduction Higher-harmonic loads (ringing loads) Coupling of pot flow model and CFD Structural excitation from nonlinear waves Task C: Task B: Aero-elastic response to fully nonlinear waves CFD computation of monopile loads

49 Loads and response from steep and breaking waves on monopiles Henrik Bredmose, Associate prof, DTU Wind Energy