Abstract

Main objective of this study are as follows;
① To carry out the coupled analysis between ISPH and MBD.
② To define the computational method of interaction between particle based fluid and floating body.
③ To develop the coupled analysis program of ISPH and MBD.
④ To introduce the developed program by applying the behavior analysis of floating-type WEC in wave conditions.

In this study, ISPH method was emplyed to calculate the motion of the fluid. GPGPU based parallel ISPH solver was developed to decrease the computational time. When the number of particles is about 100,000, the parallel process is faster fifty times than sequence process. To verify the ISPH analysis solver, the SPH tool of ABAQUS and ANSYS Fluent were used. The dam-breaking and lid-driven cavity flow simulation are carried out to verify the developed code. In the dam-breaking simulation, the shape of free surface, the velocity and the pressure of fluid are compared with ABAQUS. The shape of free surface and the velocity of fluid show good agreements. Regarding the pressure fields, the pressure noise is verified with ABAQUS result, on the other hand, ISPH significantly reduces the pressure noise in comparison with ABAQUS.
Multi-body dynamics program is developed to analyze the dynamic behavior of the multi-body system. Cartesian coordinates and Euler parameters are used to define the translational motion and the rotational motion. RecurDyn which is a commercial multi-body dynamics program developed by FunctionBay is used to verify the MBD solver. Result of MBD solver show a good agreement with RecurDyn. The computational algorithm for the coupled analysis is defined, and FAMCAP(Fluid and Multi-body dynamics Coupled Analysis Program) that is in-house program was developed. The fluid-body interaction technique is developed at the acceleration level to solve the coupled problem. The fluid force is calculated from the acceleration of rigid particles and it is applied to the rigid body as the external force. The coupled analysis between ISPH and MBD is carried out by using this technique.
For an application of the developed program, the dynamic behavior of floating-body type wave power generation system is considered. A numerical wave maker based on the linear wavemaker theory and the wave absorber using an exponential function to remove the reflected wave from the opposite boundary are used. The experiment is carried out to verify the wave motion reproduced by ISPH and the pendulum model is used to verify the simulation of fluid-body interaction. The wave height, wave period and the pendulum motion of a body were compared with experiments. The wave motion for nine wave conditions is compared, and the pendulum motion for five wave conditions of rigid was compared. In the case of wave motion, simulation results show a good agreement with experiments. In the case of pendulum motion of body, R.M.S. error of the amplitude for each period is calculated and showed an error of maximum 12.2%.
The dynamic behavior of floating type wave energy converter(WEC) is analyzed. The WEC system used in this study consists of the hydrodynamic subsystem and the power take-off(PTO) subsystem. A rectangular shaped floating body is considered. The regular and irregular wave conditions are considered for the motion of floating type WEC system. The irregular wave is reproduced by the superposition of two or more wave conditions based on the linear wave maker theory. The motion of a floating body shows the tendency similar to the wave motion. When the floating body pulls and releases the rope, the rotational motion of generator shows a distinct difference.
As a mentioned, the rotational velocity of the generator is decreased when the rope pulls the floating body. Since the power of the generator is determined by the rotational velocity of the generator, the same tendency is verified. The FAMCAP can be utilized not only in the modeling of the particle-based fluid and the multi-body system but also the coupled analysis between ISPH and MBD. The efficient computing is possible by using the NVIDIA''s CUDA. As a result, It is considered that the FAMCAP can be applied to the problem of the coupled analysis of fluid and multi-body system.