Marcio Michiharu Tsukamoto

Numerical Analysis for Hydrodynamic Motions of Floating Structure Using MPS Method

The authors started this research on estimation method of responses for floating structures using Computational Fluid Dynamics (CFD). This paper is first step, which has potential to be very valuable to the engineering community. The numerical method used in this study is the Moving Particle Semi-implicit (MPS) method

Numerical Study of the Motions in Shallow Water Waves of Floating Bodies Elastically Linked to Bottom

The motion of floating bodies linked elastically to the bottom of seas and waterways is of great interest in the analysis of the wave suppressing devices, such as wave breakers, and the behaviors of the floating structures, such as buoys and tension leg platforms (TLP). For the modeling of the dynamics, the coupling between the hydrodynamic loads due to waves and the restoring forces due to the elastic link must be considered. In some simpler cases, the analytical approaches are available. However, in case of large amplitude waves and floating bodies with complex geometries, the analytical solutions do not give accurate results. In the present study, a numerical model based on MPS (moving particle semi-implicit method) for the hydrodynamic loads coupled with the Hook’s Law for the restoring force is adopted to analyze the motion of floating bodies with one or several elastic links to the bottom of shallow water under large amplitude waves. Initially, the results of 2D numerical simulation of simple oscillating buoys are compared with the analytical and experimental ones to validate the numerical approach. After that, the approach is applied to the study of the shallow water wave supressing devices. Heave, surge and pitching motions of the floaters are assessed as well as the hydrodynamic coefficients to show the effect of the elastic links in the nonlinear wave hydrodynamics.Copyright

Validation Study of MPS (Moving Particle Semi-Implicit Method) for Sloshing and Damage Stability Analysis

The aim of this paper is to present validation studies of a CFD code based on MPS (Moving Particle Semi-implicit Method). In MPS method the fluid is represented by particles, and the particle interactions are governed by continuity and Navier-Stokes equations. It is a meshless method to simulate incompressible flow and it is able to simulate large surface distortion, fluid fragmentation and non-linear dynamics. For the validation studies, two cases with complex hydrodynamic phenomena were selected for experimental measurements in towing tank. The first one is the dynamics of a floating body in waves with an internal tank partial filled with water. In this way sloshing effects on the motion of the model can be evaluated. Usually, dynamics of the floating body and sloshing are calculated separately, by neglecting their coupling effects; the body’s motion is determined without sloshing and that motion is used to excite the liquid tank. Since the sloshing generates forces and moments, which may change the movement of the hull, sloshing forces and moments may act as a roll absorption device or can enlarger it. In MPS this coupled phenomena can be easily simulated, just by using particles representing water of the internal tank, water of the towing tank and structural particles representing the hull, the walls and the wave maker. The second phenomenon is the motions of a damaged hull from the moment soon after suffering damage until reaches the equilibrium position. This is an initial step of a validation study of the motion of a damage hull in waves, which will be compared with physical experiments. The comparisons between the numerical results obtained by the MPS with the experimental and theoretical ones show very good agreement, reinforcing the potential of MPS.Copyright

Numerical Study of the Effectiveness of a Moving Sloshing Suppression Device

In the present paper, a moving device to suppress sloshing is proposed and analyzed. The effectiveness of the suppressing device is evaluated by numerical simulations based on MPS (Moving particle semi-implicit) method. As the parameter of study, lateral forces on the tank walls are used. The results shows that the device reduces remarkably the lateral sloshing forces when filling ratio is low and it eliminates the occurrence of hydrodynamic impact on the tank ceiling when the filling ratio is high.Copyright

Experimental Study of Sloshing Effects in Roll Motion of Floating Units

Usually, the hydrodynamic loads due to sloshing are considered in the design of liquid cargo ship or floating units concerning the structural. Owing to the increasing size of these structures, resonant sloshing motions may occur and result in the amplification or attenuation of motion of the vessel. In order to assess the effect of sloshing, traditionally the motion of the vessel is calculated at first without considering the dynamic of the liquid inside the tank. After that, this motion of the vessel is inputted as excitation motion acting on the tank and, finally, the sloshing effect is evaluated. In the other words, the coupling effects of sloshing and sea wave in the vessel’s motion are ignored. A bibliographical survey shows that there are few studies that consider the effect of sloshing on the ship motion, acting as a passive device of absorption of the movements. The main goal of this research is to investigate experimentally the roll motion amplification and reduction due to sloshing. The coupling effects of sloshing and sea wave in the vessel’s motion are taking into account by recording the motions, in regular waves, of a free floating model with a partially filled liquid tank. For this purpose, a two-dimensional model is designed to carry out measurements with fixed cargo and partially filled liquid cargo. The experimental results are evaluated by comparing the measured motion of the free-floating model with fixed cargo against the results obtained by traditional approach. Then, the effects of sloshing on floating units are shown by comparison of the measurements from free-floating model with fixed cargo and liquid cargo. The results shown herein provide data for the validation of new numerical approaches for the study of the coupled motions of the floating units and sloshing.Copyright