Liang-Yee Cheng

A Numerical Study on Oil Leakage and Damaged Stability of Oil Carrier

The objective of the present paper is to carry out a study on coupled transient process of the oil leakage and the damaged stability of a crude oil carrier. For this purpose, numerical simulations based on MPS (Moving particle Semi-Implicit) method are carried out considering a two dimensional small scaled model and the oil-water multiphase flow with free surface. The results are compared with that obtained by the stability analysis software SSTAB, which provides the final list angle in case of the damage, and show good agreement.© 2010 ASME

A domain decomposition strategy for hybrid parallelization of moving particle semi-implicit (MPS) method for computer cluster

The MPS is a particle method developed to simulate incompressible flows with free surfaces that has several applications in nonlinear hydrodynamics. Much effort has been done to handle the large amount of particles required for simulating practical problems with desired refinement. However, the efficient use of the currently available computational resources, such as computer cluster, remains as a challenge. The present paper proposes a new strategy to parallelize the MPS method for fully distributed computing in cluster, which enables to simulate models with hundreds of millions of particles and keeps the required runtime within reasonable limits, as shown by the analysis of scalability and performance. The proposed strategy uses a non-geometric dynamic domain decomposition method that provides homogeneous load balancing and for very large models the scalability is supra-linear. Also, the domain decomposition (DD) is carried out only in the initial setup. As a result, the DD method is based on renumbering of particles using an original fully distributed sorting algorithm. Moreover, unlike the usual strategies, none of the processors require access to global data of the particles on any time step. Therefore, the limit for the maximum size of the model depends more on the total memory of the allocated nodes than the quantity of the local memory of each node. Thus, by extending the application of MPS method to very large models, this study contributes to consolidating the method as a practical tool to investigate complex engineering problems.

Modelling of water demand in building supply systems using fuzzy logic

This paper presents a method to establish the design flow rate adopting probabilistic and possibilistic approaches to model the subjective behaviour of the users that affects strongly the duration of usage of sanitary appliances. At first, the Monte Carlo method is used to determine the instance of usage of the sanitary appliances. After that, fuzzy logic is applied to determine the duration of the shower. As a result, historical records of the use of the sanitary appliances and the flow rate during the peak period can be generated. The design flow rate obtained by the simulation is about 23% lower than that assessed by the Brazilian standard, based on deterministic approach, and closer to the values calculated by the probabilistic model. Practical application: As the processing cost is extremely low, the simulation based on the proposed method is also an efficient means to obtain a quite accurate estimate of the flow rate for the sizing of water supply systems and water meters in water sub-metering systems.

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

Particle Based Numerical Analysis of Green Water on FPSO Deck

The green water phenomenon is boarding of sea water onto the deck due to high amplitude waves, which can cause several damages to the equipment on deck. In the present paper the green water phenomenon on three-dimensional models is analyzed using the Moving Particles Semi-Implicit Method (MPS), a fully lagrangian method for incompressible flow. This work is focused on the validation of the method comparing the numerical results with experimental results for green water on reduced scale models. The pressure on sensors over the deck of the models shows good agreement with experimental data.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