Takeshi Fujikawa

A time integration method for analysis of dynamic systems using domain decomposition technique

This paper presents a precise and stable time integration method for dynamic analysis of vibration or multibody systems A total system is divided into several subsystems and then responses are calculated separately, while the coupling effect is treated equivalently as constant force during time steps By using iterative procedure to improve equivalent coupling forces, a precise and stable solution is obtained Some examples such as a seismic response and multibody analyses were carried out to demonstrate its usefulness

Bending vibration analysis of rotating machineries using multibody dynamics technology -- development of computer program RotB

This paper examines a computer program developed to analyze the vibration of rotating machineries based on theories of vibration and multibody dynamics (MBD). Bending vibration problems of rotating machineries have generally been categorized as either linear or nonlinear. Linear problems can be formulated by standard methods and nonlinear problems can be formulated by MBD methods. In our study, nonlinear problems are treated by the use of a general-purpose computer program, RecurDyn (RD). In the program we developed, rotor bending vibration analysis (RotB) structural properties such as shafts, rotating rotary disks, unbalanced masses and foundation structures are modeled as multibody elements. Also, nonlinearities such as contact, non-symmetrical shaft effects, bearing characteristics, nonlinear restoring and damping characteristics in the bearings are taken into account. The computational results demonstrate the validity of RotB.

Dynamic Characteristics of Secondary System Located on a Primary Structure for Aseismic Design of Piping or Vessels.

In order to estimate the seismic responses of a secondary system such as piping or vessels, its dynamic characteristics including the effect of the primary system should be calculated. In many cases dynamic characteristics of a primary structure as well as a secondary one are given by modal parameters. In this paper we present a method of calculating natural frequencies, damping ratios, participation factors, and mode shapes of the total system by synthesizing their modal parameters. Results calculated for some models by this method are compared with those obtained by the method of solving the total system directly. An example of application to aseismic design is demonstrated.

Aseismatic properties of copper tube, for pipe line services in building.

A Low Cycle vibration test was carried out for investigating the aseismatic properties of copper tubes. The low cycle fatigue strength shown in e-N curve and deformation characteristic expressed in terms of equivalent Youngs modulus and loss facter are obtained for hard drawn (H), annealed (O), partially annealed (OH), and brazed (socket) tubes. The responses of two simple models from sinusoidal excitation are predicted and evaluated by using the above test results and an approximate analysis method. The comparison with the experimental results show a good agreement when the damping values at supports are appropriately estimated.