Tomohisa Hashimoto

Numerical Simulation for Impact of Elastic Deformable Body against Rigid Wall under Fluid Dynamic Force

Numerical simulations of fluid-elastic body interaction problem are presented. In the verification of elastic body model for damped free vibration in stationary fluid, the present solutions agree reasonably well the analytical ones. We can successfully simulate flows around a largely moving and deforming elastic body and collisions of the elastic body with rigid surface under the fluid dynamic force by using the elastic body model. In future work, the elastic body model should be validated through comparison between the numerical result and experiment.

Comparison of Local Computational Approaches for Unsteady Viscous Incompressible Flows

Numerical simulations of 2D decaying homogeneous isotropic turbulence are presented using three local computational approaches, ACM, KRLNS equations and LBM, in order to investigate accuracy, efficiency and the capability to capture the correct transient behavior of the incompressible flows and the results are compared with the solutions obtained by the Pseudo-Spectral Method (PSM), which is the standard method for this problem. Parallel computations are carried out on a GPU by using the CUDA library provided by the NVIDIA and the speedup is investigated. It is found that all three methods can capture the transient flow fields and LBM is the most accurate and efficient approach for this kind of unsteady incompressible flow.

Parallel Computation of Vortex-Induced Vibration of a Circular Cylinder using Overset Grid

A parallel computational algorithm for overset grid using the data strucure of onedimensional listed type arrangement [1] has been developed for analyzing the flow field of complicated geometries. The parallel code is extended to dynamic problems of fluid-structure interaction. The procedure of parallel computation for moving overset grid according to the motions of structure is proposed and its performance is investigated for simulations of vortex-induced vibration of a circular cylinder. The present numerical results are compared with experimental data and other numerical results.

Computation of Two-phase Flow in Flip-chip Packaging Using Level Set Method

In flip-chip packaging technology, the underfill encapsulation is one of the important processes to obtain a significant improvement in fatigue lifetime for the solder joints between IC chip and substrate. The advanced design of electronic devices aiming at the enhancement of the performance involves the increase of the number of solder bumps, smaller size of the IC chip and smaller gap height between IC chip and substrate. That leads to various problems caused by the flow behavior, such as voids in underfill and mis-placed IC chip. The numerical analysis is more and more strongly required for simulating the underfill flow behavior, including the condition of dispensing the underfill material on the substrate. In fact, it is desirable to predict the filling time, the final fillet shape formed around IC chip and the occurrence of air trap especially around the solder bump in the underfill process, considering the effect of contact angle, viscosity and surface tension of the underfill material for increasing the reliability of flip-chip packaging.

Aerodynamic Performance of a Deforming Elastic Body in Supersonic Flow

Numerical simulations of fluid-structure interaction problem are one of the hot topics in today’s Computational Fluid Dynamics (CFD). It is an interesting problem that if an elastic body can greatly deform in response to the fluid dynamic force, what shape does it change into? What is the relation between the shape and its drag force like? For example, a parachute functions as equipment for the control of rate of descent. It is expanded by the fluid dynamic force and becomes the designated shape to increase the air resistance. Such a system of utilizing the fluid dynamic force is desirable from the point of view of saving energy. However we need to understand the every-changing flow field around a moving and deforming body.

Numerical Simulation of Underfill Flow in Flip-Chip Packaging

In flip-chip packaging technology, the underfill encapsulation is one of the important processes to obtain a significant improvement in fatigue lifetime for the solder joints between IC chip and substrate. The advanced design of electronic devices aiming at the enhancement of the performance involves the increase of the number of solder bumps, smaller size of the IC chip and smaller gap height between IC chip and substrate. That leads to making various problems caused by the flow behavior, such as voids in underfill and mis-placed IC chip. The numerical analysis is more and more strongly required for simulating the underfill flow behavior, including the condition of dispensing the underfill material on the substrate. In fact, it is desirable to predict the filling time, the final fillet shape formed around IC chip and the occurrence of air trap especially around the solder bump in the underfill process, considering the effect of contact angle, viscosity and surface tension of the underfill material for increasing the reliability of flip-chip packaging.

Numerical Simulation about Shape and Drag of Two-dimensional Elastic Body Deformed under Fluid Dynamic Force

This paper describes numerical simulation about the shape and its drag of an elastic body deformed under fluid dynamic force. The simulation is carried out with coupling the incompressible Navier-Stokes equations and the equations of motion of the elastic body. The equations of motion is formulated for elastic shell model which is composed of material particles connected with elastic springs and dampers. Relation between the shape and its drag force in response to the fluid dynamic force is investigated under the constraint for fixing the volume and the gravity center of the elastic body. While the viscous drag decreases with the deforming of elastic body under fluid dynamic force, the pressure drag further increases so that the total drag also increases.

Numerical Simulation for Motions of Two-dimensional Elastic Deformable Body in Fluid

This paper describes a numerical method for simulating fluid-structure interaction, especially two-dimensional fluid-elastic body interaction problems. A model is formulated for the elastic shell made of thin film. Numerical simulations of the incompressible unsteady flow around the moving and deforming elastic body in response to the fluid dynamic force are carried out by using the model. It is found that the proposed elastic body model could be useful for investigating the mechanism of the deformation of moving elastic shell.