Hiroshi Matsuhisa

Modal response of a disk to a moving concentrated harmonic force

The steady state response of a stationary disk to a concentrated harmonic force moving in a concentric circular path at a constant velocity is analyzed. Formulation of the response with structural damping is derived as an eigenfunction series. The modal response is discussed in detail, with emphasis on the vibratory modes. The effect of imperfection in the axial symmetry is also discussed. It is found that the imperfection produces a much greater effect on the response near the resonance, but little effect on it off the resonance, and that standing waves both moving with the force and fixed on the disk can be formed. Certain aspects of the analysis are verified experimentally.

Experiment of Shock Vibration Control Using Active Momentum Exchange Impact Damper

In the authors’ previous study, we proposed a novel shock vibration control method using the active momentum exchange impact damper (AMEID). By using this method, the shock vibration of the vibratory system is greatly reduced by transferring part of its momentum to the damper mass. This feature is effective for suppressing the first large peak value of the acceleration response due to a shock load. However, the validity of AMEID for actual implementations has not yet been investigated. In this paper, the active control of shock vibration using AMEID under real conditions is evaluated by simulation and experiment. A one-degree-of-freedom vibratory system is used as the controlled object. The controller is designed using the linear quadratic regulator optimal control theory. Reductions in the acceleration response and transmitted force to the base are investigated using simulations. Experiments are carried out to verify the simulation results.

Analytical model of a magnetorheological damper and its application to the vibration control

Magnetorheological (MR) fluid and its damper have received a great deal of attention in the recent years. It is very useful for this MR controllable damper in the vibration control system, especially as a semi-active control device. To develop the control algorithms that take maximum advantage of the unique features of the MR damper a model must be developed that can adequately characterize the damper intrinsic behavior In this paper following a review of three mechanical models for MR damper the effect of these models on the vibration control is analyzed in a one-degree-of-freedom system. Numerical simulations are performed when the MR damper is used as the passive type damper on-off type damper and quasi-skyhook type damper. The results show that the models are less affecting the vibration control performance, and the MR damper appears the best control performance in the quasi-skyhook type.

Momentum-Exchange-Impact-Damper-Based Shock Response Control for Planetary Exploration Spacecraft

Upon landing of a spacecraft, a large shock load can lead to such undesirable responses as rebound, swing vibration, sideslip, and tripover of the spacecraft. This paper discusses the problem of controlling these shock responses by means of momentum exchange impact dampers, especially the active momentum exchange impact damper. The momentum exchange impact dampers are classified into two types: the passive momentum exchange impact damper composed of passive elements and the active momentum exchange impact damper that includes active actuators. The active momentum exchange impact damper can greatly reduce the effects of shock responses. First, landing systems consisting of momentum exchange impact dampers are designed to conduct simulations and modelatwo-leggedsystem.Thepassivemomentumexchangeimpactdampermechanismisaone-degree-of-freedom vibrationsystem.Theactivemomentumexchangeimpactdampermechanismemployselectricalmotorsasactuators inadditiontothepassivemomentumexchangeimpactdampercomponents.Toassesstheeffectivenessofthecontrol system, three cases are simulated: without momentum exchange impact damper, with passive momentum exchange impact damper, and with active momentum exchange impact damper. The results of the simulations show that the active momentum exchange impact damper is most effective in controlling spacecraft landing responses.

Radiation efficiency of a baffled circular plate in flexural vibration

Abstract The radiation efficiency of an edge-clamped circular plate, which is vibrating flexurally in one of its natural modes and is mounted in an infinite baffle, is theoretically determined from the total power radiated to the far field. The vibrations of the plate are investigated both by the classical plate theory and by the improved plate theory (Mindlin plate theory). Approximation formulae for the low frequency region are derived, and curves covering the entire frequency range for the first fifteen modes are obtained through numerical calculation. Except for frequencies much higher than the critical frequency, there exist some differences in the radiation efficiencies between the results obtainedby the two theories. The difference increases with the thickness of the plate and with the mode numbers, especially for modes having many nodal diameters.

Vibration control of a pendulum structure by a dynamic vibration absorber moving in both normal and tangential directions

There are two types of dynamic vibration absorbers (DVAs) for vibration reduction of a pendulum structure. The first one moving in the tangential direction of the pendulums orbit can reduce all kinds of vibrations but the effectiveness is quite poor when the DVA locates near the centre of oscillation. Conversely, the second one moving in the normal direction of the pendulums orbit can only reduce large vibration but has a good effect when the DVAs location is near the centre of oscillation. In this article, the authors propose the DVA, which can move in the normal and tangential directions at the same time. The proposed DVA can overcome the shortcoming of two DVAs moving in only one direction. Because the systems non-linearity is quite complex, a numerical method is used for obtaining the optimal parameters. Then, the authors introduce the convenient empirical formulas of optimal parameters based on the numerical results. The effect of the proposed DVA is demonstrated by the numerical calculations of free vibration of a ropeway gondola.

Proposal of active momentum exchange impact damper and its application to floor shock vibration control

The momentum exchange impact damper (MEID) has already proposed for reducing the shock vibration of the floor. In the MEID, the shock energy of the floor is suppressed by transferring a part of its kinetic energy to the damper mass during collision time. In this study, an active shock control using the momentum exchange impact damper (AMEID) and its application to reducing shock vibration of the floor is proposed. The floor is modeled as a one-degree-of-freedom system. The actuator is installed between the contact spring and the damper mass. A linear motor is assumed as the actuator. The LQR optimal control is applied to design the controller of AMEID. It is verified that the performance of AMEID is not affected by the mass ratio between the impact damper mass and the floor mass. In addition, the performance of AMEID is compared with the conventional passive momentum exchange impact damper (PMEID) and the conventional active control method in reducing the floor shock vibration. It is shown that the shock reduction performance obtained by AMEID is larger than that obtained by PMEID. Furthermore, the transmitted force obtained by AMEID is smaller than that of the conventional active control.

Dynamic absorber for ropeway gondola using Coriolis force

Wind-induced swinging of ropeway gondola can be reduced using dynamic absorbers. To maximize the performance of conventional dynamic absorbers, their location should be as high as possible. However, absorbers can not be installed at high positions due to interference issues with structures such as towers and stations. To address this problem, a new type of dynamic absorber that moves vertically is proposed. This absorber is composed of a mass supported by a spring. The mass moves in the radius direction (up and down) and it induces Coriolis force in the circumference direction to prevent the swing of gondola. If the natural frequency of the absorber is tuned to twice that of the gondola, the absorber moves spontaneously with a large amplitude due the resonance. This absorber is more effective when it is located at lower positions. The experiment with a small model and an actual gondola for 10 passengers were carried out and the results agreed well with the theoretical predictions.

Low-Frequency Noise Reduction Using a Piezoelectric Sound Absorbing Panel Using LR Circuit and Applied Voltage

This paper proposes a method of low-frequency noise reduction using piezoelectric elements. The piezoelectric element on the panel shunted with an inductance and a resistance works like a mechanical dynamic vibration absorber. Using this panel, low-frequency noise can be reduced. Further, by applying voltage that is related to displacement of the host structure to a piezo-electricelement, sound absorbing effect can be improved. Normal incidence sound absorption coefficient was theoretically formulated. Then, optimum values of the inductance and resistance were theoretically derived for two cases: one is the case to absorb noise of specific frequency, the other is the case to maximize amount of absorbed energy when noise that has uniform power spectrum such as white noise is incident. Effectiveness of the proposed method was investigated through simulations and experiments.© 2012 ASME

Theoretical and Experimental Investigation of a Method to Detect an Aortic Aneurysm from Pulse Waves

Early identification of aortic aneurysms is important for effective treatment. Although imaging systems have the ability to identify aortic aneurysms, high cost prevents their use for screening. On the other hand, pulse waves can be measured easily, and because pulse wave velocity is affected by the aortic aneurysm, there is a possibility to find an aortic aneurysm by pulse wave measurement. The aim of this study is to propose a method to find an aortic aneurysm from the pulse wave and to develop a measurement device. The aortic aneurysm causes the expansion of artery. The basic theory is based on the wave of a mechanical reactance silencer. The transfer functions of a pulse wave between brachial artery and anterior tibial artery were investigated. The transmission loss is increased by increase of the inner radius of an aortic aneurysm. The interval frequency of local minimum points of the transfer function correlates with the length of an aortic aneurysm. When the stiffness decreases, the characteristic impedance decreases, the pulse wave velocity decreases and the frequencies of the local peaks become low. It is therefore possible to estimate the size of an aortic aneurysm from the transfer function. The method to find an aortic aneurysm from the pulse wave was investigated theoretically and experimentally with silicone tubes. The relation between the transfer function and the pathological arterial change was clarified. This method can be used for diagnosis of aortic aneurysms.