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 coupled Particle-In-Cell (PIC)-Discrete Element Method (DEM) solver for fluid-solid mixture flow simulations

In this paper, a coupled Particle-In-Cell (PIC)-Discrete Element Method (DEM) model is developed for numerical simulations of complex fluid–solid mixture flows. The fluid–solid interaction part is solved using the hybrid Eulerian–Lagrangian PIC model, and the solid–solid interaction part is simulated using the Lagrangian DEM model. The PIC model gives the coupled PIC-DEM model both Eulerian efficiency and Lagrangian flexibility, compared to purely Lagrangian methods such as Smoothed Particle Hydrodynamics (SPH). The time step difference between the PIC model and the DEM model is handled using the idea of subcycles. In addition, a straightforward method is proposed for mitigating the issue of unphysical gaps between solids during collision due to the use of the Cartesian cut cell method for fluid–solid interaction. The PIC-DEM model is validated by physical experiments of the collapse of solid cylinder layers with and without water. Following that, the capability of the numerical model is further demonstrated through a more complex problem of solid dumping through fall pipes. The results show great potential of the PIC-DEM model being a useful tool for simulating complex fluid–solid mixture flows

A coupled Particle-In-Cell (PIC)-Discrete Element Method (DEM) solver for fluid-solid mixture flow simulations

In this paper, a coupled Particle-In-Cell (PIC)-Discrete Element Method (DEM) model is developed for numerical simulations of complex fluid–solid mixture flows. The fluid–solid interaction part is solved using the hybrid Eulerian–Lagrangian PIC model, and the solid–solid interaction part is simulated using the Lagrangian DEM model. The PIC model gives the coupled PIC-DEM model both Eulerian efficiency and Lagrangian flexibility, compared to purely Lagrangian methods such as Smoothed Particle Hydrodynamics (SPH). The time step difference between the PIC model and the DEM model is handled using the idea of subcycles. In addition, a straightforward method is proposed for mitigating the issue of unphysical gaps between solids during collision due to the use of the Cartesian cut cell method for fluid–solid interaction. The PIC-DEM model is validated by physical experiments of the collapse of solid cylinder layers with and without water. Following that, the capability of the numerical model is further demonstrated through a more complex problem of solid dumping through fall pipes. The results show great potential of the PIC-DEM model being a useful tool for simulating complex fluid–solid mixture flows

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 study of the hydrodynamic performance of a pile-restrained WEC-type floating breakwater

The hydrodynamic performance of a vertical pile-restrained Wave Energy Converter (WEC) type floating breakwater under regular wave action is simulated using a Particle-In-Cell (PIC) method based numerical model. The numerical results such as the heave motion of the breakwater and the capture width ratio of the integrated system are discussed and compared with experimental measurements.<br/