Takuzo Iwatsubo

Investigation of a colloidal damper

A novel application of nanotechnology in the field of mechanical engineering, called colloidal damper (CD), is investigated. This device is complementary to the hydraulic damper (HD), having a cylinder-piston construction. Particularly for CD, the hydraulic oil is replaced by a colloidal suspension, which consists of a mesoporous matrix and a lyophobic fluid. In this work, the porous matrix is from silica gel modified by linear chains of n-alkylchlorosilanes and water is considered as an associated working fluid. A design solution from a practical point of view of the CD test rig and the measuring technique of the hysteresis are described. A brief review of the water physical properties relative to the CD concept is presented. Influence of the bonding density, length of the grafted molecule, pore diameter, and particle diameter on the CD hysteresis is investigated for distinctive types and mixtures of silica gels. Temperature variation during functioning is recorded and the CD cycle is interpreted from a thermodynamic standpoint. Variation of the CD dissipated energy and efficiency with pressure, water quantity, and relaxation time is illustrated. Experimental results are justified by the analysis of the water flow into the porous matrix, CD thermodynamics, and the mechanism of the energy dissipation. Our findings agree with the previously published data.

Simple and combination resonances of columns under periodic axial loads

The existence of combination resonances of columns under periodic axial loads has been surveyed for four typical cases of boundary conditions. A system of n coupled Mathieu equations is obtained by applying Galerkins method to the governing equation of motion for a continuous column. A first-order estimate of the regions of instability for the reduced system is calculated by using the resonance conditions. Relation between the structure of the parametric term and the possible existence of combination resonance is demonstrated for the four cases of boundary conditions. The stability charts are illustrated. Finally the effects of external and internal damping on combination resonances are discussed.

Parametric instability of clamped-clamped and clamped-simply supported columns under periodic axial load

The existence of combination resonance for clamped-clamped and clamped-simply supported columns under periodic axial loads is known from previous work. By applying the finite difference method to the equation of motion, the continuous system can be approximated by a discrete system having multiple degrees of freedom. Theoretical resonance conditions are obtained as a special case of those previously given by Hsu. The results of experimental observations are also presented, for both cases of end conditions. As the result of the theoretical and experimental investigations, the existence of the combination resonance of sum type is clarified for both cases. Especially for a clamped-clamped column the principal region of combination resonance is shown to be rather more important than the secondary regions of ordinary resonance.

Experimental Study of Dynamic Fluid Forces and Moments for a Long Annular Seal

The dynamic fluid reaction forces and moments of a long annular seal were experimentally studied. A new testing apparatus was constructed in order to measure restoring forces and moments caused by the cylindrical whirling motion of a rotor. Experiments were conducted at various rotor speeds, whirling speeds, and with different pressure drops across the long seal. The rotor and outer cylinder were set in concentric alignment. The tangential force component was derived from the measured fluid force in order to determine the unstable threshold

Transverse vibration of a rotor system driven by two cardan joints

The torque-induced transverse vibration of a rotor system driven by two Cardan joints is analyzed and the effects of the stiffness asymmetry of the rotor shaft supports, the damping force in the joints and the gyroscopic moment of the rotor on the dynamic stability of the system are evaluated. The analysis proves that both parametric and self-excited vibrations can occur due to the transmitted torque when the driving shaft and the driven shaft (rotor shaft) are inclined; the stiffness asymmetry of rotor supports does not always have the stabilizing effect which has been observed in a rotor system driven by a single Cardan joint [1]

Stability and non-stationary vibration of columns under periodic loads

The procedure of digital simulation to investigate the dynamic problems of continuous systems with a periodically time-varying parameter is first stated. Then the procedure is applied to the instability problem of a cantilevered column subjected to an axial periodic load (Euler-type problem) and to the problem of the same column subjected to a tangential periodic load (Beck-type problem). The principal regions of dynamic instability for the two problems are determined, and the non-stationary vibrations near the stability-instability critical regions are investigated. The relations between Euler-type and Beck-type problems are also investigated by using an analogue simulation method.

Hybrid Piezoelectric Damping for Structural Vibration Suppression

This paper aims at developing a new design method of the active-shunted hybrid type of piezoelectric damping system for structural vibration suppression. Piezoelements are actively driven with series tuned RL shunting circuits. Considering shunting circuits as compensators (or filters), both shunt resistors and active control gains are designed by using filtered LQ control theory. Experimental test and numerical simulation of a simple cantilevered beam demonstrate the structural damping capability of the hybrid piezoelectric damping system. Control effort by the active control could be reduced by the hybrid piezoelectric damping system.

Redesign of closed loop system for integrated design of structure and its vibration control system

This paper proposes a new integrated design method of structure-control combined system: such as several types of mechanical systems equipped with vibration control system in order to suppress the structural vibration. When the proposed method is applied to the design of a structure-control combined system, the closed loop pole placement of the reduced order model of the combined system is specified in advance as a design requirement. The proposed method is constructed from two steps: 1) output feedback control system is designed for the initial closed loop system in order to realize the specified closed loop pole placement; and 2) structural and vibration control system design parameters are simultaneously optimized to minimize the objective function subject to constraints on the pole placement. Scalar objective function is defined as a linear combination of several measures of the optimality of the structure design and the vibration control system design. The effectiveness of the proposed method is shown by the numerical example.

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.

Forces and Moments Due to Combined Motion of Conical and Cylindrical Whirls for a Long Seal

The mutual interaction effects of cylindrical and conical whirl on the dynamic fluid forces and moments, which act on a long annular seal, were studied experimentally. A whirling motion composed of cylindrical and conical whirls is actuated by intentionally giving the phase difference between the seal exit and inlet whirling movements. This whirling motion is believed to generate during actual pump running. The experiment was conducted by changing the phase difference, at various rotor speeds and with a pressure difference between the seal inlet and exit. The result of this study revealed that fluid forces and moments are greatly dependent on the phase difference of the whirl, namely the long seal has a significant coupling between displacements and rotations. Furthermore, dynamic fluid forces and moments were derived theoretically, assuming that total fluid force acting on the rotor could be determined by superposing fluid forces due to conical and cylindrical whirling movements. It was confirmed that the experimental results moderately agree with the theoretical values, if the rotor and seal are set in concentric alignment, the principle of superposition becomes applicable.