Hideomi Ohtsubo’s research while affiliated with The University of Tokyo and other places

For the simulation of rock fall, the robust rigid body dynamic simulation algorithm based on the technique used in the computer graphics field was developed. The rotation of rigid body was represented using quaternion was used and voxel based collision detection algorithm was developed. The strategy for determining time step was described. Several examples are shown to demonstrate theefficiency, robustness and applicability to the non-convex objects of the method, and comparedwith polygon based method. It was shown that by changing the level of voxel representation, it was possible to control the accuracy and computational efficiency.

In this paper, a new approach to crack propagation analysis for large scale or complicated geometry structures is presented. That is the connection of mesh superposition technique and the extended finite element method. The former is a technique that increases the accuracy of analysis locally by superimposing additional mesh of higher resolution onto the mesh that represents the rough deformation of the structure. In this technique, the boundaries and nodes of both meshes do not have to coincide with each other. In the latter technique, the discontinuity across the crack segment and singularity around the crack tips are represented in the approximation by enriching the nodal degrees using partition of unity condition. This technique does not require meshes to conform to the crack geometry and this enables crack propagation procedure with no re-meshing process by connecting both techniques, it becomes possible to analyse crack growth models of large scale and complicated shape with highly flexible modelling and no remeshing process. By using this approach, some numerical examples are analysed and appropriate results are obtained. Copyright © 2007 John Wiley & Sons, Ltd.

For the rigid body simulation, robust and efficient rigid body dynamic simulation algorithm is developed. The rotation of rigid body is represented using quaternion and volume based collision detection algorithm is developed. The rigid body is subdivided into voxel, and collision detection is carried out with spheres that include voxels. The strategy for determining time step was described. Several examples are shown to demonstrate the efficiency, robustness and applicability to the non-convex objects of the method, and compared with polygon based method. It was shown that by changing the level of sphere subdivision, it was possible to control the accuracy and computational efficiency.

There are non-negligible errors exist in FEM solutions especially in the vicinity where several structural parts are connected. Traction forces on the boundary of these structural parts create discontinuous stress distribution. A post-processing technique with consideration of the traction force and mechanical behaviour is successively applied resulting in modifying FEM stress solutions accurately. It is also noted that the deformation a structure is classified into global and local deformations, and the local deformation can be modified if structural information are available. The proposed method is applied into the real ship structure and its validity is examined.

A novel multi-scale method has been proposed for estimating the in-plane displacements of LSI lithography mask. In order to verify the applicability of proposal method, the mask of simple pattern has been simulated. The simulated results agree with experimental mask feature qualitatively. Moreover, simulation for real device pattern shows full-chip simulation can be performed in practical short time by using this method.

For the rigid body simulation, robust and efficient rigid body dynamic simulation algorithm is developed. The rotation of rigid body is represented using quaternion and volume based collision detection algorithm is developed. The rigid body is subdivided into voxels, and collision detection is carried out with spheres that include voxels. The strategy for determining time step is described. Several examples are shown to demonstrate the efficiency, robustness and applicability to the non-convex objects of the method, and compared with polygon-based method. It is shown that by changing the level of sphere subdivision, it is possible to control the accuracy and computational efficiency.

In shape optimization, an optimal shape is generated by moving some nodes of an initial mesh. But there are many cases that meshes can not follow the movement of nodes. In this paper, the shape optimization technique using mesh superposition method is proposed. In the present technique, the shape of design domain is represented by local mesh to allow flexible shape control. The shape of the local mesh is controlled by basis vector method. Several examples which can not optimize in the conventional optimization technique are shown to demonstrate the effectivity of the present method.

In this paper, the multi-level finite cover method is extended to adaptive analysis and applied to the fracture analysis. Finite cover method (FCM) employs the concept of mathematical cover from Manifold method, and applied to the voxel analysis. FCM-CLSA enables the multi-level distribution of voxel. For the indicator of sub-division of voxel, a posteriori error estimation and accuracy of geometric representation is considered. For the representation of crack propagation the removal of te voxel at the area where fracture occurred is proposed and by this approach it was shown that the representation of crack propagation can be carried out much easier than the traditional approach in which geometrical reprenentation of crack is needed, while keeping the necessary accuracy by keeping the size of voxel small enough where fracture occurs. 2 dimensional example of avalanche is shown to demonstrate the capability of the approach.

In shape optimization, an optimal shape is generated by moving some nodes of an initial mesh. But there are many cases that meshes can not follow the movement of nodes. In this paper, the shape optimization technique using mesh superposition method is proposed. In the present technique, the shape of design domain is represented by local mesh to allow flexible shape control. The shape of the local mesh is controlled by basis vector method. Several examples which can not optimize in the conventional optimization technique are shown to demonstrate the effectivity of the present method.