Papers by Author: Yoshitaka Wada

Abstract: With the growth of computing technologies including both hardware and simulation algorithms, simulation models have become extremely large in scale. Nowadays the visualization of the huge result data obtained by the large scale simulation is one of the main bottlenecks through all the simulation procedures because such large scale simulation is generally conducted on computing servers such as supercomputers, while the visualization is done on local client environments. To avoid time consuming transfer of the result data from the computing server to the local client, we propose techniques for the server-side screening and network visualization of them in advance to their transfer. We demonstrate that our approach contributes to find out the region of interests in whole the result data by a numerical example.

Abstract: From a view point of engineering application, solid-liquid flow is one of the most practical phenomena, however MPS and other particle methods usually premises a constant size of all particles in the model.　In a realistic phenomenon, the size of those particles is different.　 Koshizuka et al. has proposed new algorithm for solid-liquid flow simulation which is multi-scale DEM-MPS method. The method can calculate solid -liquid flow with a large difference of the particle scale. However, its program code requires a DEM part and a MPS part, and actual phenomenon includes various scales of particles. In order to analyze solid-liquid flow with different particles, modified Laplacian model and variable cut-off radius MPS method is proposed. This modification can directly deals with small particles and large particles. Calculation cost is kept and visualization of the results has more reality by these modifications.

Abstract: Recent development of crack propagation analysis is rapidly advanced and its applications are being extended. Usually finite element method is utilized for the analysis. One of the most important tasks is mesh generation which requires fully automated system and no failures. It is very difficult to meet all geometrical and mechanical requirements for a surface mesh generation. Recent studies show a factory roof is easily generated under mixed mode loading. How to generate surface crack tetrahedral mesh without failures and surface crack analysis with factory roof are presented.

Abstract: Fracture in heat affected zone (HAZ) in welding has been a serious problem for the integrity of machines. Prediction of fracture behavior due to the residual stress field in HAZ is important. In this paper, S-Version FEM(S-FEM) is applied to simulate the crack growth under thermal and residual stress fields. For evaluation of stress intensity factor, virtual crack closure integral method (VCCM) is employed. In order to confirm the validity of this analysis, numerical results are compared with previously-reported analytical and experimental results. Then, crack growth analysis in piping structure with welding joint was conducted. The residual stress data was provided by JAEA, Japan Atomic Energy Agency, based on their numerical simulation. Using S-FEM, two- and three-dimensional analyses are conducted, and crack growth behavior under thermal stress field is studied and discussed.

Abstract: Fracture in heat affected zone (HAZ) in welding has been a serious problem for the integrity of machines. Prediction of fracture behavior due to the residual stress field in HAZ is important. In this paper, S-Version FEM(S-FEM) is applied to simulate the crack growth under thermal and residual stress fields. For evaluation of stress intensity factor, virtual crack closure integral method (VCCM) is employed. The residual stress data was provided by JAEA, Japan Atomic Energy Agency, based on their numerical simulation. SCC crack growth of a surface crack at inner suface of a pipe under thermal residual stress is simulated in three-dimensional filed. Distributions of residual stress is not axi-symmetric along pipe wall, and it affects the crack growth behavior. Ttwo cases, for axi-symmetric and non-symmetric thermal stress distributions, are assumed and crack growth behaviors are obtaiend and discussed.

Abstract: Fatigue crack growth under mixed mode loading conditions is simulated using S-version FEM. By using S-FEM technique, only local mesh should be re-meshed for new crack configuration, and it becomes easy to simulate crack growth. By combining with auto-meshing technique, local mesh easily re-meshed and curved crack path is modeled easily. Fully automatic crack growth simulation system in 3-dimensional problem is developed. Using this system, several kinds of plural surface cracks problems are simulated. It is shown that intereaction effect between two surface cracks appear in complicated manner depending on intial distances between two cracks.

Abstract: Fatigue crack growth under mixed mode loading conditions is simulated using S-version FEM (Superposition FEM, S-FEM). By using S-FEM technique, only local mesh should be re-meshed and it becomes easy to simulate crack growth. By combining with re-meshing technique, local mesh is re-meshed automatically, and curved crack path is modeled easily.

Abstract: There are several studies for developing web-based CAE applications to substitute existing CAE applications. CASOW is the web-based CAE system developed by the author. The approach for implementation of the system is to use fundamental technologies, for instance, HTML, HTTP, CSS and so on, because we cannot know whether new technologies will be alive or not. Certain technologies bring specific advantages to the applications, but a life time of the application would be short. Recently a great advantage of web interface is developed. Such a representative application is Google Maps which doesn’t require any special software components; however the application realizes interactiveness of the application. The technology is called Ajax which drastically overcomes the bad interactiveness on the web browser. On the other hand, high efficiency of analysis work with high performance computers produces many kinds of knowledge and a large amount of information. We are confronted with inefficient knowledge and information management in the network system. This paper presents the new web-based CAE system using Ajax and knowledge sharing framework with compatibility to web interface. The system is presented, and advantages of the interface, effectiveness of the API in the system and knowledge sharing framework are discussed.

Abstract: A non-triangulation inserting particle method is presented to prevent numerical fractures of SPH computations. The particles in those regions in which numerical fractures may occur are chosen at the beginning of SPH computations. And, the chosen particles are arrayed by the two different rules respectively according to the particle position relations. When the distance between each two chosen connected particles exceeds a certain value and neither of the corresponding two particles has fractured in SPH computations, a new particle is generated between those two ones and the position relation of particles is updated. The physical quantities that the new particle carries are obtained according to some given rules. The method and the same type of method in the reference are compared. The application of the method is analyzed. Conservation of mass and Conservation of momentum of the whole system are kept in this method. Several examples are given to validate the efficiency of the method to prevent numerical fractures.

Abstract: Due to more complex and severe design restrictions, more effective and faster finite element analyses are demanded. There are several ways to compute FE analysis efficiently: parallel computing, fast iterative or direct solvers, adaptive analysis and so on. One of the most effective analysis ways is the combination of adaptive analysis and multigrid iterative solver, because an adaptive analysis requires several meshes with difference resolutions and multigrid solver utilizes such meshes to accelerate its computation. However, convergence of multigrid solver is largely affected by initial shape of each element. An effective mesh improvement method is proposed here. It is the combination of mesh coarsening and refinement. A good mesh can be obtained by the method to be applied to an initial mesh, and better convergence is achieved by the improved initial mesh.