Ryoji Kawai

Vibration of Asymmetric Rotor through Critical Speed with Limited Power Supply

The non-stationary vibration of an asymmetric rotor with limited power supply is studied using the asymptotic method. The many factors which affect the transient vibrating behaviour of the asymmetric rotor in passing through critical speed are studied in relation to the amplitude of motion, phase angle, energy, etc. by numerical calculation; that is, stiffness ratio of the asymmetric rotor, damping coefficients, driving torque (during both acceleration and deceleration) and so on. The experimental study using a simple model is added.

Startup Torsional Vibration of Rotating Machine Driven by Synchronous Motor

In this paper, electric-mechanical transient process by starting synchronous motors in the gear trained rotor system is investigated. The mathematical model is represented and it is numerically simulated to investigate the torsional vibration due to interaction between electrical and mechanical system. Then the characteristics of torsional vibration due to the interaction of electric and mechanical system, effect of backlash in the gear trained rotors and so on are studied. As the results, it is found that the interaction between electric and mechanical system is very big in the transient vibration of startup, nonlinearity of the system is strong in both the electric circuit and gear teeth meshing, the amplitude of transient vibration depends on the interaction of the electro-mechanical system and high frequency vibration is incurred due to backlash of the gears.

Modified theory of Bayesian estimation method to parameter identification of structures.

In the Bayesian parameter estimation method, the uncertainties of both experimental responses and theoretical model parameters are taken account of to identify the finite element model from experimental modal test results such as the natural frequencies and mode shapes of a structure. This paper presents a modified theory of the Bayesian parameter estimation method. In this theory, the Bayesian parameter estimation method is extended by normalizing the error function, and a constant that weights the parameter valuesto the test data can be reasonably determined; that is, a parameter identification that weights the experiment, or that weights the theory can be carried out quantitatively and easily. And constants that denote the various uncertainties of each parameter and response reflect the identified values. The effects of relative parameter and measurement uncertaities on the identified values are illustrated by two five-degrees-of-freedom models.

Wave propagation in a conical bar subjected to impulsive loadings and impact fracture.

The study of wave propagation in the machine-structures with varying cross-sectional parts has become very important from the view point of the impact strength of structures.In the present paper, first, the stress wave propagation and the impact fracture of a conical bar were treated experimentally. The changes of the crack location and the number of fracture points were investigated at several different impact velocities. Next the wave propagation in a conical bar was calculated by the finite element method, and its change with time was considered in detail. Furthermore the estimation of a crack location was tried.The results obtianed are as follows:(1) The wave speed, obtained from the experiment of the wave propagation in the conical bar, agreed with that of the one-dimensional theory.(2) When the impact velocity increased, the number of fracture points increased and the crack location approached to the top end of the conical bar.(3) The wave front of compressive strain was reflected at the top end as the tensile strain. These reflected tensile waves were superposed to the following tensile wave, and high tensile stress appeared often as observed in the experiment.(4) The crack location simulated in a conical bar of gypsum agreed fairly well with the experimental result.

Reliability Analysis of Structures under Seismic Excitation : Part I : Response ratio of structure having bi-linear spring behavior

This paper is the first report in a series of papers which concern the reliability analysis of mechanical component mounted on structures. In this paper, nonstationary random responses are obtained for one and two degrees of freedom systems with bi-linear hysteresis restoration force by using Fokker-Plank equation. The effects of the non-linear spring constant, eigenfrequency of the system and predominant frequency of the seismic excitation on the response and magnification factor are investigated.