黒田 雅治

In order to suppress the structure-borne sound radiated by a vibrating plate, the vibration must be controlled. Unlike the conventional vibration control method which aims merely to eliminate the vibration, this paper rather uses the vibration itself to urge the cancellation mechanism of sound. First, with a view to elucidating the generation mechanism of the structure-borne sound, an acoustic intensity distribution pattern is measured experimentally at each vibration mode of a plate. Then, from a viewpoint of negative acoustic intensity observed in the acoustic distribution patterns, the cancellation mechanism of the sound is discussed, and the reduction of the acoustic power due to the negative intensity being investigated. In addition, it is pointed out that the radiation patterns proposed by Maidanik do not hold good for some vibration modes. Finally, the relationship between the radiation efficiency, the radiation power and the vibration level is clarified.

This study is concerned with several aspects of the nonlinear vibration of a body levitated by an electromagnetic force. Firstly, from the viewpoint of analyzing the qualitative properties of the vibrations. The fundamental characteristics of the electromagnetic levitation system are investigated using phase plane portraits and Poincare maps. Secondly, a periodic motions are identified as chaotic vibrations by their quantitative properties, such as Lyapunov exponents, fractal dimension and power spectra. Finally, on the basis of the above-mentioned study, the control of chaotic vibration using neural networks containing recurrent paths is investigated. Two architectures of the neural networks, Jordan-type and Elman-type networks, are shown to work as adaptive nonlinear feedback controllers. It is further shown that the neural networks controller can suppress the chaotic vibration more effectively than a PD feedback controller can.

This paper considers the active control of a vibrating thin plate from the viewpoint of a power flow control methodology. It is the purpose of this paper to elucidate the generation mechanism of power flow patterns induced in an actively controlled thin plate. Particular emphasis is placed upon the vortex-type response pattern, which has the potential for realizing energy confinement into a specific area of the plate. Firstly, it is shown that two vibration modes dominate the plate response in the case of vortex-type power flow near the optimum condition for suppressing the plate vibration. Vibration intensity is derived for these two vibration modes. An energy stream function for the vibration intensity field is then introduced, to whose contour the vibration intensity vector proves to be tangential. From the characteristics of the stream function, the number and direction of the vortices are predicted. Finally, it is shown that the period of the vortex is not always the same as the exciting period, but rather equal to some integer times the exciting period.

In order to suppress structure-borne sound radiated from a vibrating plate, vibration control of the plate is of primary importance. Instead of conventional vibration control methods which aim to merely eliminate the vibration, in this paper, utilization of the vibration to accelerate the cancellation mechanism of structure-borne sound is considered. First, with a view to clarifying the generation mechanism of structure-borne sound, acoustic intensity is considered at each vibration modal resonance frequency. From these distribution patterns of acoustic intensity the cancellation mechanism of the sound due to the existence of negative acoustic intensity is discussed, and an attempt to interpret the meaning of the negative acoustic intensity is made. In addition, it is shown that radiation patterns often taken for granted do not necessarily hold true for some vibration modes. Furthermore, the relationship between the radiation efficiency, radiated power and active control effect for suppressing the vibration is discussed. Finally, it is shown that the inherent cancellation mechanism is achieved not only spatially but also temporally in the acoustic field. © 1993, The Japan Society of Mechanical Engineers. All rights reserved.

Feedforward control of sound and vibration using a neural network-based control system is considered. By using a back propagation method, an adaptive algorithm is derived which enables stable adaption of the neural controller for this purpose, while providing the capacity to maintain causality within the control scheme. The neural network controller is shown to be able to compensate for the introduction of harmonics by the control actuator by producing a control signal, derived from a pure tone reference signal, which contains some level of harmonics. Also, the neural network controller is seen to be able to compensate for a distorted reference signal in a manner superior to that of a linear controller. Furthermore, experiments are undertaken which demonstrate the utility of the proposed arrangement, showing it to be the equal of a linear control system in performance for a linear control problem, and superior for a nonlinear control problem.

This study is concerned with several aspects of the nonlinear vibration of a body levitated by an electromagnetic force. Firstly, from the viewpoint of analyzing the qualitative properties of the vibrations, the fundamental characteristics of the electromagnetic levitation system are investigated using phase plane portraits and Poincare maps. Secondly, aperiodic motions are identified as chaotic vibrations by their quantitative properties, such as Lyapunov exponents, fractal dimension and power spectra. Finally, on the basis of the above-mentioned study, the control of chaotic vibration using neural networks containing recurrent paths is investigated. Two architectures of the neural networks, Jordan-type and Elman-type networks, are shown to work as adaptive nonlinear feedback controllers. It is further shown that the neural networks controller can suppress the chaotic vibration more effectively than a PD feedback controller can.

This paper considers the active control of a vibrating thin plate from the viewpoint of a power flow control methodology. It is the purpose of this paper to elucidate the generation mechanism of power flow patterns induced in an actively controlled thin plate. Particular emphasis is placed upon the vortex-type response pattern, which has the potential for realizing energy confinement into a specific area of the plate. Firstly, it is shown that two vibration modes dominate the plate response in the case of vortex-type power flow near the optimum condition for suppressing the plate vibration. Vibration intensity is derived for these two vibration modes. An energy stream function for the vibration intensity field is then introduced, to whose contour the vibration intensity vector proves to be tangential. From the characterintics of the stream function, the number and direction of the vortices are predicted. Finally, it is shown that the period of the vortex is not always the same as the exciting period, but rather equal to some integer times the exciting period.

Over the last twenty years a great deal of work has been devoted to obtaining expressions describing the radiation efficiencies of structural mode shape functions, in an effort to qualify the radiation characteristics of the structure. These modal radiation efficiencies cannot, however, be used directly in the calculation of total radiated acoustic power, as this latter quantity is not equal to the sum of the acoustic power radiated by each mode vibrating on its own. This paper addressed the problem of using modal radiation efficiencies to calculate the total acoustic power output of a simply supported rectangular panel. It is shown that there is an extremely simple way to use modal radiation efficiencies to calculate the total acoustic power output of the panel, the accuracy of which is limited only by the same low frequency constraints placed upon the accuracy of the modal radiation efficiencies themselves.

This paper considers the active control of a vibrating thin plate from the viewpoint of a power flow control methodology. It is the purpose of this paper to elucidate the generation mechanism of power flow patterns induced in an actively controlled thin plate. Firstly, this paper shows that power flow patterns such as the straight type, diverting type and vortex type are dependent upon both specific dominant vibration modes and locations of control and disturbance forces. Using modal energy, the dominant vibration modes are made clear. Then, by using the vibration modes, a methodology showing how the power flow patterns are constructed is presented. In addition to the power flow patterns mentioned above, a saddle-point type is found under a special set of circumstances. Finally, the generation mechanism of the saddle-point type is discussed by utilizing a vorticity function derived from an energy stream function in a vibration intensity field.

This paper considers the problem of sensing structural vibration to provide an error signal to adaptive feedforward control systems implemented to globally attenuate both structural and acoustic disturbances. It is shown that designing a control system which simply aims to minimize structural vibration is not necessarily the best approach, particularly in structural/acoustic problems. Rather, by considering the governing equation of the global error criterion of interest, it is possible to derive orthogonal groups of structural modes which contribute to the error criterion as a set. It is these orthogonal groupings which should be sensed as an error signal by an adaptive feedforward control system (and minimized in amplitude), a task which is easily accomplished using shaped piezoelectric polymer film sensors. Specific examples relating to the minimization of radiated acoustic power of a simply supported plate are given, showing that the use of a vibration-based error signal is a practical alternative to the use of an acoustic signal.

This parer deals with the active vibration control of a flexible beam using the active sink method proposed in the previous papers. It is the purpose of this paper to present control laws of the active sink method with feedback control. First, by using a transfer matrix method, this paper describes the active sink system with displacement feedback. Then, two kinds of control laws are derived, one is to eliminate the reflection waves at the active sink point and the other to make the transmitted waves null. From a viewpoint of numerical analysis, the fundamental caracteristics of the active sink system are clarified. If the final goal of the vibration control is to make all the vibration modes inactive, the corresponding optimal control law is obtained by the active sink method. Therefore, by comparing the conventional control method such as velocity feedback with the active sink method, the causes of the incapability of the velocity feedback are clarified. Finally, the stability problem of the active sink system is discussed.

This paper deals with the active control of power flow of a vibrating plate. It is the purpose of this paper to present a wave control method of a distributed parameter system such as a beam or a plate. This paper also aims to show the results of visualizing wave propagation. Unlike a conventional modal based control method, this method has the potential of suppressing all the vibration modes of a structure. First, from an analytical point of view, this paper presents three kinds of flow patterns in controlled vibration intensity; that is, (1) straight flow patterns from exciting point to control point, (2) S-shaped flow patterns, and (3) rotational flow patterns around the exciting point and control point. Then, the existence of these patterns is verified experimentally. Next, relationships between vibrational and acoustical intensity are discussed, and also the acoustic power and acoustic pressure in terms of these patterns are clarified. Furthermore, the characteristics of the rotational patterns are clarified, and a mean to generate the vortex of vibration intensity at an arbitrary position of a plate is presented.

This parer deals with the active vibration control of a flexible beam using the active sink method proposed in the previous papers. It is the purpose of this paper to present control laws of the active sink method with feedback control. First, by using a transfer matrix method, this paper describes the active sink system with displacement feedback. Then, two kinds of control laws are derived, one is to eliminate the reflection waves at the active sink point and the other to make the transmitted waves null. From a viewpoint of numerical analysis, the fundamental caracteristics of the active sink system are clarified. If the final goal of the vibration control is to make all the vibration modes inactive, the corresponding optimal control law is obtained by the active sink method. Therefore, by comparing the conventional control method such as velocity feedback with the active sink method, the causes of the incapability of the velocity feedback are clarified. Finally, the stability problem of the active sink system is discussed.

This paper deals with the active control of power flow of a vibrating plate. It is the purpose of this paper to present a wave control method of a distributed parameter system such as a beam or a plate. This paper also aims to show the results of visualizing wave propagation. Unlike a conventional modal based control method, this method has the potential of suppressing all the vibration modes of a structure. First, from an analytical point of view, this paper presents three kinds of flow patterns in controlled vibration intensity; that is, (1) straight flow patterns from exciting point to control point, (2) S-shaped flow patterns, and (3) rotational flow patterns around the exciting point and control point. Then, the existence of these patterns is verified experimentally. Next, relationships between vibrational and acoustical intensity are discussed, and also the acoustic power and acoustic pressure in terms of these patterns are clarified. Furthermore, the characteristics of the rotational patterns are clarified, and a mean to generate the vortex of vibration intensity at an arbitrary position of a plate is presented.

This paper deals with the active vibration control of a flexible beam with various kinds of boundary conditions. It is the purpose of this paper to investigate the relationship between the power flow and the vibrational energy accumulated in the beam. First, from the viewpoint of the conventional feedforward control method, the role of the power flow to suppress the vibrational energy is discussed. Next, by using a transfer matrix method, this paper derives the control law of the active sink method whose principle has been presented in the previous paper. Then, it is shown that all the vibration modes of a beam with arbitrary boundary conditions are suppressed by the active sink method. It is also shown that the power flow due to the active sink method is different from that of an infinite beam. Furthermore, this paper points out that there exist notches in the frequency characteristics of the power flow, and these are independent of vibration modes. Finally, an experiment is carried out to verify the existence of the active sink.

This paper deals with the active vibration control of a flexible beam with various kinds of boundary conditions. It is the purpose of this paper to investigate the relationship between the power flow and the vibrational energy accumulated in the beam. First, from the viewpoint of the conventional feedforward control method, the role of the power flow to suppress the vibrational energy is discussed. Next, by using a transfer matrix method, this paper derives the control law of the active sink method whose principle has been presented in the previous paper. Then, it is shown that all the vibration modes of a beam with arbitrary boundary conditions are suppressed by the active sink method. It is also shown that the power flow due to the active sink method is different from that of an infinite beam. Furthermore, this paper points out that there exist notches in the frequency characteristics of the power flow, and these are independent of vibration modes. Finally, an experiment is carried out to verify the existence of the active sink.

With a view to applying the active wave control method for suppression of all vibration modes of a large scale-structure, a new type of moment-driven actuator using a piezo-electric ceramic is presented. Actuators for this purpose are required to be small and light, and still have enough power to control low-frequency vibration. From the viewpoint of applying moment control, two control laws for the active sink method are derived; one is to eliminate incident waves and the other to suppress transmitted waves. A standing wave suppression type state control method, which makes possible the dormancy of vibration modes, is also presented. Next, the ABC method is presented, by means of which a vibration-free state in a beam is achieved. The control effects due to thess methods are discussed. Experimental results using the moment-driven actuators are also presented, demonstrating the effectiveness of these methods. Finally, the effect of structural damping of a beam on the control effect of the wave control method is discussed, and the relationship between power flow and structural damping clarified.

This paper deals with the active control of structure-borne sound radiating from a vibrating plate. It is the purpose of this paper to clarify the characteristics of the system response when the sound radiation is suppressed by controlling structural power flow. As a result of applying power flow control, the authors have already shown that there are basically three resultant response patterns in vibration intensity flow: straight, S-shaped and vortex. Relationships between the acoustic intensity and vibration intensity of these patterns are investigated in this paper. Particular emphasis is placed upon the vortex-type response pattern, which has the potential for realizing mode localization. A novel method for producing a power flow vortex at an arbitrary position on the plate is introduced. Furthermore, it is shown that there exists a situation where the direction of the acoustic intensity and vibration intensity vortices are completely opposite. It also turns out that there is a sound pressure null above the vortex center.

This paper deals with the active control of structure-borne sound emitted from a vibrating plate. From the viewpoint of a feedforward control method, the suppression of the plate vibration is achieved. First, in order to control the vibration of a distributed parameter system such as a plate, a beam, etc, this paper proposes two kinds of vibration control methods: one is the progressive-wave type and the other the standing-wave type. Then, the characteristics of the sound radiated from the controlled plate are clarified. As a result, it is shown that there exist two types in radiation efficiency: one is a peak type and the other a notch type. Furthermore, a wave visualization system is constructed, making it possible to observe progressive waves propagating on the plate. By using this system, the validity of the control methods proposed in this paper is verified. Finally, the cancellation mechanism of the sound due to the existence of the negative acoustic intensity is discussed, and the reduction of the acoustic power because of that is investigated.

This paper deals with the vibration control method of a flexible beam. It is the purpose of this paper to present a new control method, the ABC method (Active Boundary Control method), which makes it possible not only to suppress all the vibration modes of the flexible beam, but also to realize the completely vibration-free state in the flexible beam. First, this paper presents the principle of the ABC method, and then the necessary conditions for the optimal ABC system are derived. According to this method, two more boundary conditions are introduced in addition to the conventional four boundary conditions. If the ABC method is applied to the driving point where the disturbance acts, it becomes possible to suppress all the vibration modes of the flexible beam. By applying the ABC method to the conventional boundary condition, it is also possible to realize the completely vibration-free state in the flexible beam.

This paper deals with the vibration control method of a flexible beam. It is the purpose of this paper to present a new control method, the ABC method (Active Boundary Control method), which makes it possible not only to suppress all the vibration modes of the flexible beam, but also to realize the completely vibration-free state in the flexible beam. First, this paper presents the principle of the ABC method, and then the necessary conditions for the optimal ABC system are derived. According to this method, two more boundary conditions are introduced in addition to the conventional four boundary conditions. If the ABC method is applied to the driving point where the disturbance acts, it becomes possible to suppress all the vibration modes of the flexible beam. By applying the ABC method to the conventional boundary condition, it is also possible to realize the completely vibration-free state in the flexible beam.

This paper deals with the active control of structure-borne sound emitted from a vibrating plate. From the viewpoint of a feedforward control method, the suppression of the plate vibration is achieved. First, in order to control the vibration of a distributed parameter system such as a plate, a beam, etc, this paper proposes two kinds of vibration control methods: one is the progressive-wave type and the other the standing-wave type. Then, the characteristics of the sound radiated from the controlled plate are clarified. As a result, it is shown that there exist two types in radiation efficiency: one is a peak type and the other a notch type. Furthermore, a wave visualization system is constructed, making it possible to observe progressive waves propagating on the plate. By using this system, the validity of the control methods proposed in this paper is verified. Finally, the cancellation mechanism of the sound due to the existence of the negative acoustic intensity is discussed, and the reduction of the acoustic power because of that is investigated.

In order to suppress the structure-borne sound emitted from a vibrating plate, the vibration must be controlled. Unlike the convenional vibration control method which aims merely to eliminate the vibration, this paper rather uses the vibration to urge the cancellation mechanism of the sound. First, with a view to clarifying the generation mechanism of the structure-borne sound, the acoustic intensity is measured at each vibration mode. Then, from the distribution patterns of the acousic intensity, the cancellation mechanism of the sound due to the existence of the negative acoustic intensity is discussed, and the reduction of the acoustic power because of that is investigated. In addition, it is shown that the radiation patterns taken for granted so far do not hold good for some vibration modes. Moreover, from a viewpoint of a numerical simulation, the relationship between the radiation efficiency, the radiation power and the vibration level is discussed.