Time-domain analysis of substructure of a floating offshore wind turbine in waves

This paper aims to analyze the dynamic response of a floating offshore wind turbine (FOWT) in waves. Instead of modeling the incident random wave by the traditional wave spectrum and superposition theory, an impulse response function method was used to simulate the incident wave. The incident wave kinematics were evaluated by a convolution of the wave elevation at the original point and the impulse response function in the domain. To check the validity of current wave simulation method, the calculated incident wave velocities were compared with analytical solutions; they showed good agreement. The developed method was then used for the hydrodynamic analysis of the substructure of the FOWT. A direct time-domain method was used to calculate the wave-rigid body interaction problem. The proposed numerical scheme offers an effective way of modeling the incident wave by an arbitrary time series

A 3D parallel Particle-In-Cell solver for extreme wave interaction with floating bodies

Floating structures are widely used for vessels, offshore platforms, and recently considered for deep water floating offshore wind system and wave energy devices. However, modelling complex wave interactions with floating structures, particularly under extreme conditions, remains an important challenge. Following the three-dimensional (3D) parallel particle-in-cell (PIC) model developed for simulating wave interaction with fixed bodies, this paper further extends the methodology and develops a new 3D parallel PIC model for applications to floating bodies. The PIC model uses both Lagrangian particles and Eulerian grid to solve the incompressible Navier-Stokes equations, attempting to combine both the Lagrangian flexibility for handling large free-surface deformations and Eulerian efficiency in terms of CPU cost. The wave-structure interaction is resolved via inclusion of a Cartesian cut cell method based two-way strong fluid-solid coupling algorithm that is both stable and efficient. The numerical model is validated against 3D experiments of focused wave interaction with a floating moored buoy. Good agreement between the numerical and experimental results has been achieved for the motion of the buoy and the mooring force. Additionally, the PIC model achieves a CPU efficiency of the same magnitude as that of the state-of-the-art OpenFOAM ® model for an extreme wave-structure interaction scenario

Numerical investigation of nonlinear wave interaction with a submerged object

Submerged objects are widely occurred in ocean and coastal engineering. Their presence influences the neighbouring flow field and even generates higher harmonic waves. A two-dimensional fully nonlinear numerical wave flume, based on a time-domain higher-order boundary element method is developed to investigate nonlinear interactions between regular waves and a submerged object. The incident wave is generated by the inner-source wavemaker. Fully nonlinear kinematics and dynamics boundary conditions are satisfied on the transient free surface. A mixed Eulerian-Lagrangian technique combined with the fourth- order Runge-Kutta scheme is used as the time marching process. A four-point method is used to separate bound and free harmonic waves. The proposed model is verified against the experimental and other numerical data for nonlinear waves scattering by a submerged trapezoid and a submerged horizontal cylinder, respectively. Numerical tests are performed to investigate the effects of submergence and characterised length of a submerged object, static water depth on the high free harmonics

Numerical and experimental modelling of wave interaction with fixed and floating porous cylinders

This is the final version. Available on open access from Elsevier via the DOI in this recordWe consider wave forces on fixed porous cylinders with and without a solid inner cylinder and wave-induced motions of floating cylinder with and without a porous outer cylinder. Comparisons between experimental measurements and numerical predictions from an iterative boundary element method (BEM) model are presented. The BEM model assumes that pressure drop across porous surface is proportional to the square of the velocity through the surface. It is shown that the BEM model is able to accurately predict the nonlinear variation of the forces with wave amplitude or motion amplitude. It is demonstrated that adding a porous outer cylinder to a solid vertical cylinder leads to increased excitation force on the combined structure. For floating cylinders adding a porous outer cylinder also leads to a corresponding increase in excitation force. However, the porous outer cylinder provides a larger increase in the damping, resulting in reduced motion response. Further numerical simulations indicate that placing the porous cylinder lower in the water column can lead to increased damping without the corresponding increase in excitation forces. It is shown that for low Keulegan Carpenter numbers, the damping coefficient for a porous cylinder is significantly higher than the viscous damping on a solid cylinder. The results suggest that porous materials could be beneficial for motion damping of floating structures.Engineering and Physical Sciences Research Council (EPSRC)National Natural Science Foundation of Chin

A study on wave energy array with CFD combined with multibody dynamic method

Sometimes, a wave energy array consists of more than one WEC via mechanical connected linking arms, in order to improve the system stability and increase the total output power. See the example of Squid WEC shown in Figure 1 Figure 1 layout of a WEC array Numerical study on this type of system is challenging because the dynamic response of one node is affected byother nodes and connecting mechanical elements. For example, the displacement in translational and rotational modes of one node can be restrained by the mechanical linking arms. In this study, a tool that combines Computational Fluid Dynamics (CFD) [2] and Multibody dynamic method [3] is developed to study the dynamic and hydrodynamic force responses of a WEC array under regular wave conditions. An array with 4-nodes is numerically simulated and the results are compared with the available wave tank experiment data. It is found that the predicted motion responses are in good agreement with the experimental approach. To figure out the viscous and nonlinear impact on WEC performance, a potential-flow based software, ProteusDS [4] is utilized to simulate this problem. The comparison between two sets of results indicates that the nonlinearity affects the WEC dynamic motion significantly, which is subtle with a potential-flow tool