A Validation Study of Applying the CIP Method and the MPS Method to 2-D Tank Sloshing

Changhong Hu*, Makoto Sueyoshi *, Ryuji Miyake +, Tingyao Zhu + , Hirotsugu Dobashi +

*Research Institute for Applied Mechanics, Kyushu University Kasuga, Fukuoka, Japan

+ Nippon Kaiji Kyokai (ClassNK) Midori-ku, Chiba, Japan

ABSTRACT Two numerical models, a CIP (Constrained Interpolation Profile) based method and a MPS (Moving Particle Semi-implicit) method, which have been developed and improved in RIAM, Kyushu University for years, have been used to simulate the sloshing flow of liquid in a two-dimensional tank. The purpose of this research is to validate the CIP based method and the MPS method against experimental data with a rectangular tank. The tank is subjected to rolling motions. The transient behavior obtained from the simulation is compared to the experimental observation. Discussion is made on the features of these two numerical models for such tank sloshing problem. KEY WORDS: Violent sloshing; CFD simulation; validation; CIP; MPS. INTRODUCTION Liquid cargo carriers usually operate in partially filled conditions. When those ships are oscillating in waves, the liquid inside the tank responds and sloshing occurs. In some cases, sloshing forces acting on tank structure can be large enough to cause local structural deformation or damage. Moreover, in recent years the size of membrane-type LNG tanks is increasing due to the demand for larger payload of this kind of ships. As a result, the difference between ship motion excitation frequencies and tank sloshing natural frequencies is decreasing; and the rate of occurrence of structural failures due to sloshing is therefore expected to rise in future. Violent sloshing is a strongly nonlinear problem, which may involve complicated hydrodynamics phenomena such as high-speed liquid impacts on tank walls, breaking waves, jets, liquid droplets formation and air bubbles entrainment. Theoretical analyses on the liquid sloshing are generally limited to linear problems. Experiments have been the most important source of practical information about violent sloshing. However, high cost and small scale are the obstacles for obtaining necessary information by experiments. CFD simulations are becoming more and more important in violent sloshing studies. Numerical approach may be the only practical research tool capable of full-scale predictions. However, still too many uncertainties exist in current CFD

methods. Extensive researches, especially validation against to experiments, are required. In Research Institute for Applied Mechanics, Kyushu University, two different numerical methods, the CIP-based Cartesian grid method and the MPS based particle method, have developed for violent sloshing computation. As shown in Fig.1, the CIP-based method is a finite difference method (FDM) while the MPS method is a meshless particle method. These two methods are relatively new CFD approaches used in marine hydrodynamics.

CIP-Based Method

FDM method Tank-fixed coordinate system Two-phase flow

y

x

MPS Method

x

y

Particle method Earth-fixed coordinate system Single-phase flow

Fig.1 Two CFD methods for sloshing computation

In the CIP-based Cartesian grid method, the tank sloshing problem is treated as a multi-phase problem that includes water and air flows. The fluid is viscous and can be assumed as compressible or incompressible. The CCUP method (Yabe et al, 2000) is adopted as the flow solver. A fixed Cartesian grid that covers the air and the water is used. The free surface is considered as an inner interface that is calculated by an interface capturing method. Hu and Kashiwagi (2004) and Kishev et al (2006) have applied the CIP-based Cartesian grid method to violent sloshing simulation, in which different CIP-type interface capturing

Proceedings of the Nineteenth (2009) International Offshore and Polar Engineering ConferenceOsaka, Japan, June 21-26, 2009Copyright © 2009 by The International Society of Offshore and Polar Engineers (ISOPE)ISBN 978-1-880653-53-1 (Set); ISSN 1098-618

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