Yuzuru Sakai

A stabilized incompressible SPH method by relaxing the density invariance condition

A stabilized Incompressible Smoothed Particle Hydrodynamics (ISPH) is proposed to simulate free surface flow problems. In the ISPH, pressure is evaluated by solving pressure Poisson equation using a semi-implicit algorithm based on the projection method. Even if the pressure is evaluated implicitly, the unrealistic pressure fluctuations cannot be eliminated. In order to overcome this problem, there are several improvements. One is small compressibility approach, and the other is introduction of two kinds of pressure Poisson equation related to velocity divergence-free and density invariance conditions, respectively. In this paper, a stabilized formulation, which was originally proposed in the framework of Moving Particle Semi-implicit (MPS) method, is applied to ISPH in order to relax the density invariance condition. This formulation leads to a new pressure Poisson equation with a relaxation coefficient, which can be estimated by a preanalysis calculation. The efficiency of the proposed formulation is tested by a couple of numerical examples of dam-breaking problem, and its effects are discussed by using several resolution models with different particle initial distances. Also, the effect of eddy viscosity is briefly discussed in this paper.

Dynamic fracture toughness of LWR pressure vessel steel A508 Cl.3: A Japanese round-robin study

Abstract Three kinds of A508 Cl.3 forging for light water nuclear reactor pressure vessels are used to study dynamic strength and dynamic fracture toughness. The dynamic yield and tensile strengths are described as functions of temperature and strain rate. The plane strain dynamic fracture toughness is most appropriately measured by CT test using a high speed, hydraulic servo-controlled tensile testing machine. The 10 mm thick specimens which do not satisfy the plane strain conditions presented by ASTM E399 can give dynamic fracture toughness values which are as small as plane strain dynamic fracture toughness obtained with 100 mm thick specimens only if the condition of P max P Q ≤ 1·1 is satisfied. The plane strain dynamic fracture toughness is not affected by the rate of increase in stress intensity factor over its wide range. Its minimum value is well related to 2mm V-notched Charpy impact energy.

Effect of home reliner on occlusal relationships and oral mucosa

BACKGROUND For decades, many reports have expressed negative opinions about home reliner (HR), because it may result in residual ridge resorption. Recently, some clinical studies evaluated HR. However, the effect of HR on occlusal relationships and the oral mucosa remains unclear. Here, we dynamically analyzed the situation in which a patient applies HR to an upper complete denture. METHODS We numerically simulated the effect of HR on occlusal relationships and the oral mucosa. In the simulation, the thickness of HR was set to 2mm as a proper amount and 4mm as an excessive amount. The loading points were set at the center of the right and left occlusal surfaces of the denture. RESULTS Compared with the case without using HR, at proper amounts (2mm on the right and left sides), HR suppressed the depression of the ill-fitting denture, and stress on the oral mucosa was decreased. In the excessive HR model (4mm on the right and left sides), the vertical occlusal dimension was increased, and stress on the oral mucosa originally fitted with the denture base was increased. When the denture was modeled in an inclined position (2mm on the left side and 4mm on the right side), stress on the oral mucosa on the left buccal side was markedly increased. CONCLUSION It was found that when an improper amount of HR was applied, the occlusal vertical dimension increased and the oral mucosa was pressured more than that under non-HR conditions.

Modeling and SPH Analysis of Composite Materials

A number of SPH modeling and analysis examples using medical imaging devices such as computed tomography (CT) scan and MRI have seen an increase in the industrial field. In this study, we propose an image processing technique which can quantize the material properties by brightness value and generate three-dimensional (3D) SPH particle models from the sliced CT/MRI image data of composite materials. In the past, to reconstruct a 3D model by CT/MRI medical images, an unstructured grid approach (polygon) was often used to reproduce the complex geometry. However, this could not represent a solid model. We use CT/MRI medical image brightness to arrange for the initial particle coordinates by voxel method instead of polygon approach in this study. The 3D particle data are generated by using threshold selection by the brightness value. Using the proposed method here, we introduce the two-dimensional (2D) elastic analysis and the 3D elastic-plastic analysis for the carbon fiber-reinforced plastic material using the SPH method. It is concluded that SPH composite material analysis using image processing such as CT/MRI and microscope photographs is convenient for evaluating the composite materials.

Solder crack simulation using SPH particle method with submodeling technique

In order to improve the mechanical reliability of IC packages crack generation and its propagation which are caused by such as Chip Package Interaction (CPI) are being investigated by various simulation methods. In this study, Smoothed-particle hydrodynamics (SPH) were first applied to analyze the crack propagation in a solder ball in a Flip Chip Ball Grid Array (FCBGA). SPH simulation is a meshless Lagrangian technique which is appealing as a possible alternative to techniques currently used to analyze complicated structures, fracture of materials and high deformation events. In this study, the SPH algorithm has been developed to elasto-plastic analysis and fracture analysis in the field of semiconductor structural dynamics. Then, heat conduction analysis and structural analysis using SPH theory were performed to analyze thermal stresses in FCBGA. Also sub-modeling approach was used to simulate crack propagation in solder balls which links the deformation from the package level to the solder ball level. The results show the crack initiation and crack propagation in solder balls clearly. SPH method is suite for computing fracture of solid materials because of the meshless algorithm and successfully applicable to crack propagation problems of semiconductors.

Large Deformation Analysis by Smoothed Particle Hydrodynamics

Smoothed particle hydrodynamics (SPH)[1] is extended to the elastic-plastic large deformation analysis of metals and the hyper-elastic analysis of rubbers. The elastic-plastic analysis theory and the large deformation theory used in this study are fundamentally similar to those of FEM however the theories are applied at the particle points within a smoothing radius in SPH models. In this study the volume constant condition is imposed on the plastic deformation process using a pressure equation given by the particle density condition in a unit volume. Test problems show that the large deformation analysis by SPH leads to good stability and accuracy comparing with FEM results.© 2006 ASME

Elastic-Plastic and Frature Analysis of Mobile Phones Using SPH

Smoothed Particle Hydrodynamics (SPH) was invented by Lucy[1], Monaghan and Gingold [2] for gas dynamics problems in astrophysics and extended to treat solid continua in this decade[3]]. The SPH technique uses no underlying grid — it is a pure Lagrangian particle method. The absence of a mesh and the calculation of interactions among particles based on their separation alone that large deformations can be computed without difficulty. It is for this reason that SPH has the potential to be a valuable computational tool. In this paper we have been using the SPH algorithm to compute the structural analysis of the mobile phones without mesh data. Using the visualization software MPAVE the particle distributions for the mobile phone could be easily produced in 3 dimensions and the elastic-plastic analysis and the fracture analysis have been performed effectively. The results show the possibility for practical use of a particle method to 3 dimensional structural analysis of the usual industrial products.Copyright

Free Surface Flow Analysis by Smoothed Particle Hydrodynamics

In this study a new computational algorithm to enforce incompressibility in free surface flow analysis using Smoothed Particle Hydrodynamics (SPH) is presented. The method uses two steps. The first step is a fractional step for solving velocity field forward in time without incompressibility. Then the second step is computed to compensate the pressure Poisson equation using the mass constant equation in a particle field. This method is composed of the above two steps and is similar to SMAC (Simplified Marker and Cell) method commonly used in CFD. However in SPH simulation, the introduction of incompressibility of fluid is easily realized using the particle density concept and the boundary of free surface of fluid is also controlled conveniently by the concept. In this study the algorithm is applied to sloshing problems of vessels with fluid. The numerical results using this algorithm show good results in the behaviors of free surface flow and the pressure evaluations at the wall of the vessels.Copyright

Free Mesh Method by Using Object-Oriented Approach.

Free Mesh Method, which is a kind of meshless method, is simple, accurate and suitable for parallel computing. In this method, the total stiffness matrix is obtained by adding the temporary element matrices, so this method does not require connectivity between nodes and elements as an input infomation. This paper describes anapplication of Free Mesh Method in 2 dimension at the stage of creating a set of temporary triangular elements around each nodes. For implementation, this system is desgined by an Object-Oriented approach in order to provide a efficient program for every algorithm and data structure, from geometical point of view.

A Cooperative Study for the Evaluation of Crack Arrest Toughness of RPV Materials in Japan

Results are presented from an investigation of crack arrest toughness K a , on ASTM A533B Class 1 and A508 Class 3 steels using ASTM-proposed specimens and ESSO specimens. The results show that the values of K a , measured in accordance with the ASTM test method, increased with an increase in test temperature, and that the size requirements in the method were appropriate to obtain valid values of plane-strain crack arrest toughness K I a . It was also found that the ASTM and ESSO tests lead to about the same crack arrest toughness values when applied to large specimens of the same size. The lower bound of K I a data was significantly under that of K I c data on the test materials, though both bounds were well over the American Society of Mechanical Engineers (ASME) K I R curve.