Kazushi Kimoto

Reflection and scattering analysis of sh-wave using a combined method of BEM and ray theory

A Boundary Element Method (BEM) is one of the most frequently used techniques for numerical simulation of ultrasonic nondestructive testing. In simulating a pulse-echo flaw detection test by a BEM, it is desirable that both transmission and reception points of ultrasound are included in the analysis model. However, numerical simulation with that model takes enormous computational time because the scale of the problem is characterized by the distance between these two points compared to the wave length and it is very large in this case. The objective of this study is to develop an efficient numerical method to carry out the simulation which covers the whole process of pulse-echo method concerning mechanical wave propagation. The approach adopted here is to use elastodynamic ray theory in addition to the conventional BEM. In this method, the reflection and propagation of waves in a defect-free region are evaluated by the ray theory and the scattered wave induced by defects by BEM. In this study, the combine...

A numerical modeling of contact SH-wave transducers

This paper discusses a numerical modeling of contact SH-wave transducers in conjunction with a BEM-based simulation technique for an ultrasonic testing. In the modeling, transmitters are modeled as distributed traction on the area of contact and receivers as a weight function to emulate averaging effect due to finite dimensions of receivers. The whole testing system is firstly formulated as an integral equation that involves the traction and the weight function. Using the integral equation, those unknown functions are then estimated from experimental data. In the last part of this paper, to examine validity of our modeling approach a numerical simulation of a pulse echo test is carried out and results are compared with experiments.

A LARGE SCALE ANALYSIS FOR ULTRASONIC WAVE PROPAGATION USING PARALLELIZED FDTD METHOD

A finite difference time domain method (FDTD) is based on a grid‐based time domain differential technique, in which wave equations are solved in a leapfrog manner. It is required to discretize a whole target domain into computational grids with an adequate size. Therefore computational burden increases if the computational domain is much larger than the wave length. To solve such a large‐scale problem in high speed, we apply a parallel computing technique to the FDTD. OpenMP is an interface to execute program codes in parallel using a shared memory system of computers. As an example of large‐scale analysis, SH wave propagations in concrete material are demonstrated in this study.

Inversion of Vibration Mode of an Immersion Ultrasonic Transducer

ABSTRACT An inversion method is proposed to obtain vibration characteristic of an immersion ultrasonic transmitter from radiated waveforms in water. A basic equation is the Rayleigh surface integral, which gives the relationship between wave pressures in water and the surface velocity of the transmitter. The inverse problem is to obtain the velocity distribution on the vibration surface to minimize the difference between Fourier amplitudes in theory and experiment in conjunction with the Tikhovon’s regularization scheme. The inversion method is applied to simulated water pressures and measured waveforms. It is shown that the Tikhonov’s regularization method is very effective to suppress excessive oscillations in the inverse analysis and the velocity distribution on the transducer’s surface is well reconstructed. It is, however, suggested that in practical application, more detailed mathematical modeling is necessary to obtain local variations of the velocity distribution.