Transfer of Boussinesq Waves to a Navier-Stokes Solver: Application to Wave Loads on an Offshore Wind Turbine Foundation

2009 ◽  
Author(s):  
Erik Damgaard Christensen ◽  
Henrik Bredmose ◽  
Erik Asp Hansen
Keyword(s):  
Wind Turbine ◽  
Shallow Water ◽  
Offshore Wind ◽  
Navier Stokes ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Cfd Model ◽  
Wave Load ◽  
Boussinesq Model ◽  
Run Up

Wave load and wave run-up is a very important issue to offshore wind turbine foundations. These are often installed in relatively shallow water on for instance sand banks. Therefore the non-linear shoaling and subsequently the force and run-up are important to address. The paper presents a method to combine a Boussinesq model with a CFD model. This gives an accurate tool to estimate wave loads on the foundations at acceptable computational times.

Numerical Reproduction of Extreme Wave Loads on a Gravity Wind Turbine Foundation

2006 ◽  
Author(s):  
H. Bredmose ◽  
J. Skourup ◽  
E. A. Hansen ◽  
E. D. Christensen ◽  
L. M. Pedersen ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wave Climate ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Wave Loads ◽  
Load History ◽  
Wave Load ◽  
Extreme Wave ◽  
Run Up ◽  
A Current

A fully nonlinear 3D Navier Stokes solver with VOF (Volume of Fluid) treatment of the free surface is used to reproduce two extreme laboratory wave impacts on a gravity wind turbine foundation. The wave climate is irregular waves with a current. Numerical results for inline force, overturning moment and run-up are compared to measurements. The extreme wave loads for the two events are associated with slamming onto the under side of a horizontal platform placed 9.1m above the still water level. For such impacts, the computed wave loads are strongly sensitive to the shape of the incoming waves. A comparison with a Morison-type estimation of the wave loads shows that this much simpler approach can reproduce the overall trend of the wave load history, but not the extreme moment.

Impact of New Slamming Wave Design Method on the Structural Dynamics of a Classic, Modern and Future Offshore Wind Turbine

2017 ◽  
Author(s):  
Johan M. Peeringa ◽  
Koen W. Hermans
Keyword(s):  
Wind Turbine ◽  
Wave Train ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Wave Loads ◽  
Wave Load ◽  
Wave Impact ◽  
The Impact

In the WiFi-JIP project, the impact of steep (and breaking) waves on a monopile support structure was studied. Observations during model tests showed that large tower top accelerations occur due to a slamming wave. Using experiments and simulations results, a new formulation of the design load for a slamming wave was developed. Instead of the embedded stream function, as applied in industry, the wave train is generated with the nonlinear potential flow code Oceanwave3D. On the wave train a set of conditions is applied to find the individual waves, that are closest to the prescribed breaking wave and most likely cause a slamming impact. To study the effect of the new slamming load formulation on different sized offshore wind turbines, aero-hydroelastic simulations were performed on a classic 3MW wind turbine, a modern 4MW wind turbine and a future 10MW wind turbine. The simulations are performed with and without a slamming wave load. The slamming has a clear effect on the tower top acceleration. Accelerations due to the wave impact are highest for the 3MW model at the tower top and at 50m height. A serious tower top acceleration of almost 7m/s2 due to wave slamming is found for the 3MW turbine. This is an increase of 474% compared with the case of Morison wave loads only.

Study on the Dynamic Response for Floating Foundation of Offshore Wind Turbine

2011 ◽  
Author(s):  
Yougang Tang ◽  
Jun Hu ◽  
Liqin Liu
Keyword(s):  
Wind Turbine ◽  
Wind Farm ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Load ◽  
Mooring Lines ◽  
Floating Foundation ◽  
Wind Turbine System ◽  
Sea Area

The wind resources for ocean power generation are mostly distributed in sea areas with the distance of 5–50km from coastline, whose water depth are generally over 20m. To improve ocean power output and economic benefit of offshore wind farm, it is necessary to choose floating foundation for offshore wind turbine. According to the basic data of a 600kW wind turbine with a horizontal shaft, the tower, semi-submersible foundation and mooring system are designed in the 60-meter-deep sea area. Precise finite element models of the floating wind turbine system are established, including mooring lines, floating foundation, tower and wind turbine. Dynamic responses for the floating foundation of offshore wind turbine are investigated under wave load in frequency domain.

Fully Coupled Three-Dimensional Dynamic Response of a TLP Floating Wind Turbine in Waves and Wind

2012 ◽  
Author(s):  
G. K. V. Ramachandran ◽  
H. Bredmose ◽  
J. N. Sørensen ◽  
J. J. Jensen
Keyword(s):  
Wind Turbine ◽  
Dynamic Model ◽  
Three Dimensional ◽  
Geographic Location ◽  
Climatic Conditions ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Total System ◽  
Wave Loads ◽  
Aerodynamic Loads

A dynamic model for a tension-leg platform (TLP) floating offshore wind turbine is proposed. The model includes three-dimensional wind and wave loads and the associated structural response. The total system is formulated using 17 degrees of freedom (DOF), 6 for the platform motions and 11 for the wind turbine. Three-dimensional hydrodynamic loads have been formulated using a frequency- and direction-dependent spectrum. While wave loads are computed from the wave kinematics using Morison’s equation, aerodynamic loads are modelled by means of unsteady Blade-Element-Momentum (BEM) theory, including Glauert correction for high values of axial induction factor, dynamic stall, dynamic wake and dynamic yaw. The aerodynamic model takes into account the wind shear and turbulence effects. For a representative geographic location, platform responses are obtained for a set of wind and wave climatic conditions. The platform responses show an influence from the aerodynamic loads, most clearly through a quasi-steady mean surge and pitch response associated with the mean wind. Further, the aerodynamic loads show an influence from the platform motion through more fluctuating rotor loads, which is a consequence of the wave-induced rotor dynamics. In the absence of a controller scheme for the wind turbine, the rotor torque fluctuates considerably, which induces a growing roll response especially when the wind turbine is operated nearly at the rated wind speed. This can be eliminated either by appropriately adjusting the controller so as to regulate the torque or by optimizing the floater or tendon dimensions, thereby limiting the roll motion. Loads and coupled responses are predicted for a set of load cases with different wave headings. Based on the results, critical load cases are identified and discussed. As a next step (which is not presented here), the dynamic model for the substructure is therefore being coupled to an advanced aero-elastic code Flex5, Øye (1996), which has a higher number of DOFs and a controller module.

scholarly journals The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 8 (11) ◽  
pp. 859
Author(s):  
Thanh-Dam Pham ◽  
Hyunkyoung Shin
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Second Order ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Hydrodynamic Loads ◽  
Drift Motion ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

Key Contributors to Lifetime Accumulated Fatigue Damage in an Offshore Wind Turbine Support Structure

2017 ◽  
Author(s):  
Emil Smilden ◽  
Erin E. Bachynski ◽  
Asgeir J. Sørensen
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Control Strategies ◽  
Time Domain Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Support Structure ◽  
Wear And Tear ◽  
Collateral Effects

A simulation study is performed to identify the key contributors to lifetime accumulated fatigue damage in the support-structure of a 10 MW offshore wind turbine placed on a monopile foundation in 30 m water depth. The relative contributions to fatigue damage from wind loads, wave loads, and wind/wave misalignment are investigated through time-domain analysis combined with long-term variations in environmental conditions. Results show that wave loads are the dominating cause of fatigue damage in the support structure, and that environmental condtions associated with misalignment angle > 45° are insignificant with regard to the lifetime accumulated fatigue damage. Further, the results are used to investigate the potential of event-based use of control strategies developed to reduce fatigue loads through active load mitigation. Investigations show that a large reduction in lifetime accumulated fatigue damage is possible, enabling load mitigation only in certain situations, thus limiting collateral effects such as increased power fluctuations, and wear and tear of pitch actuators and drive-train components.

Experimental Study on the Wave Loads on Monopile and Jacket Type Support of Offshore Wind Turbines

2018 ◽  
Author(s):  
Jing Zhang ◽  
Qin Liu ◽  
Xing Hua Shi ◽  
C. Guedes Soares
Keyword(s):  
Experimental Study ◽  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wave Force ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Wave Loads ◽  
Morison Equation ◽  
Offshore Wind Turbines

As the offshore fixed wind turbine developed, more ones will be installed in the sea field with the depth 15–50 meters. Wave force will be one of the main forces that dominate the design of the wind turbine base, which is calculated using the Morison equation traditionally. This method can predict the wave forces for the small cylinders if the drag and inertia coefficients are obtained accurately. This paper will give a series scaled tests of monopile and jacket type base of the offshore wind turbine in tank to study the nonlinear wave loads.

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