Hideo Utsuno

Prediction of sound fields in cavities with sound absorbing materials

A three dimensional cavity was studied using the boundary element method. The sound absorbing material was considered as bulk reacting. Two cavity models were utilized to assess the accuracy of calculation: one was a cavity with a bulk of sound absorbing material within the interior, and the other was a larger cavity divided into two smaller cavities by a panel of the sound absorbing material.

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.

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

Time history theoretical analysis for stick-slip vibration of violin strings

The stick-slip vibration of violin string was completely formulated by using CA (Cellular Automaton) method in time history analysis. The local neighborhood rule of the CA method was derived for the travelling wave along the string, both ends of string, and the bow point. The key in success is that the bow point is to be fixed point and also to be velocity excited point at the same time. This means that reflected wave velocity is equal to the incidental wave velocity plus bow velocity. Displacement of arbitrary point of string is calculated and is compared with measured one. Excellent agreement of displacement suggests that CA method can simulate the stick-slip vibration of violin string. Acceleration time of the bow until it reaches a certain speed is also studied to form a complete Helmholtz waves. Step input and acceleration time within fundamental period is not valid to form Helmholtz wave. Acceleration time of more than four times of the fundamental period can substantially form Helmholtz waves.

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.

Interpolation Method of the Room Transfer Function of Sound Using Closely Located Four Point Microphone Method

The room transfer function (RTF) between the sound source and the evaluation point changes significantly according to their positions because of reflection. Therefore, the easy method to interpolate RTF at an arbitrary point with high precision must be developed. In this paper, a new method to interpolate RTF at an arbitrary point from the measured values at several points is proposed. The impulse response of RTF can be divided into the direct sound, early-reflected sounds and reverb sound. By closely located four point microphone method, the imaginary sound sources (ISS) of the early-reflected sounds at the measurement points are identified. The transfer function of early-reflected sounds at an arbitrary point can be interpolated from the identified ISSs. The transfer function of reverb sound at an arbitrary point can be interpolated linearly. The experiment in an office room showed that the interpolated value of RTF at an arbitrary point agreed with the measured value to some degree.

Prediction of the Noise Radiated from Moving Source on Road by Reciprocity Theorem and Interpolation of Transfer Function

In this paper, noise from a moving source on the road with sound insulation wall is studied. The noise diffracts on the upper edge of the wall and arrives at the evaluation point Q. Firstly, the noise source is placed at point Q, and the sound pressures are measured at point A and B on a line L which is regarded as the moving track on road. From the measured sound pressures, the transfer functions between the noise source at point Q and the point A and B are determined. The method to interpolate the transfer function at an arbitrary point on the line L between A and B is proposed in this study. Using the reciprocity theorem and the interpolated transfer function, it is able to predict the noise arrived at the evaluation point S from the moving source on the line L.

Hybrid Vibration Suppression of Flexible Structures Using Piezoelectric Elements

This paper describes a new hybrid vibration suppression technique for flexible structures using piezoelectric elements. There are two main methods to suppress vibration of flexible structures. One is active vibration control and the other is passive vibration suppression. The former is effective but has stability problems. While the latter avoids such instability, its controlling force is small. Hence, this paper proposes a new hybrid control composed of inductance, resistance and amplifier that is stable and effective. The optimum values of inductance and resistance used in the circuit can be determined by a simple formulation derived by the two fixed points method. This method is verified by experiments. The results demonstrate that the hybrid control is more effective than passive vibration suppression.

Variable Damping and Stiffness Vibration Control With Two Magnetorheological Fluid Dampers in Series

Vibration isolation methods that vary damping and stiffness have demonstrated excellent authority over system vibration, thus, potentially making them attractive for many applications. However, conventional devices for controlling variable stiffness are typically complicated and difficult to implement in most applications. To address this issue, a new method is proposed that requires two magnetorheological (MR) fluid dampers placed in series. With this configuration, variable damping and stiffness vibration control is simultaneously achieved by varying a small current to the MR dampers. This paper presents a theoretical and experimental analysis of a two degree-of-freedom system that is controlled by the MR dampers. Five different control schemes involving the variable damping and stiffness are explored. The time and frequency responses of the two degree-of-freedom system to a random input show that combined variable damping and stiffness control provides the best vibration isolation over a frequency range spanning the system’s two structural vibration modes. The experimental results agree well with the theoretical analysis.Copyright