岩本 宏之

Suppression of noise and vibration in machine products is an important problem, and many methods have been studied. In particular, structural–acoustic coupled effects due to the weight reduction of machines cannot be ignored. In structural–acoustic coupled analysis, the finite-element method in which the acoustic space is described by sound pressure and the structure is described by displacement is often used. However, the eigenvalue analysis in that method takes a great deal of computational time because the mass and stiffness matrices are asymmetric. Instead, in this paper, we propose an efficient coupled analysis method for a three-dimensional acoustic space and a two-dimensional thin plate using a lumped-mass model. The proposed modeling method is derived systematically using Raviart–Thomas elements. In addition, we propose a coordinate transformation method that accelerates the calculations by reducing the number of degrees of freedom (DOF). In this way, a symmetric eigenvalue problem with no extra DOF is derived. The effectiveness of the proposed method is confirmed by numerical calculations. This analysis method is particularly effective for systems in which the acoustic space contributes to the majority of the DOF, since the acoustic space is sparse owing to the adoption of edge elements.

This study is concerned with an eigenvalue problem of a vibro-acoustic coupled system. In the conventional modal coupling method, the particle velocity normal to the surface of a panel is always calculated as zero, and the wave motion in the cavity cannot be directly treated. To overcome the problem, this study presents a novel formulation for a coupled system that expresses the correct boundary condition at the coupling plane and the wave motion in the cavity. First, a transfer matrix is introduced which can describe the characteristics of the sound field based on the wave dynamics. It is then clarified that if the panel vibration is regarded as the input to the cavity, the boundary condition of the sound field at the coupling plane should be a rigid wall. This is followed by the formulation of the eigenvalue problem of a vibro-acoustic coupled system. Finally, some numerical simulations are conducted, thereby clarifying the principles of the shift of natural frequencies and mode shapes, the accuracy of boundary condition at a coupling plane, and the orthogonality of coupled modes.

This paper is concerned with the generation of a quiet space in a rectangular cavity using active wave control methodology. It is the purpose of this paper to present the wave filtering method for a rectangular cavity using multiple microphones and its application to an adaptive feedforward control system. Firstly, the transfer matrix method is introduced for describing the wave dynamics of the sound field, and then feedforward control laws for eliminating transmitted waves is derived. Furthermore, some numerical simulations are conducted that show the best possible result of active wave control. This is followed by the derivation of the wave filtering equations that indicates the structure of the wave filter. It is clarified that the wave filter consists of three portions; modal group filter, rearrangement filter and wave decomposition filter. Next, from a numerical point of view, the accuracy of the wave decomposition filter which is expressed as a function of frequency is investigated using condition numbers. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that a quiet space is generated in the target space by the proposed method. (C) 2017 Elsevier Ltd. All rights reserved.

<p>The present paper deals with the vibration control of a suspended simple pendulum system, namely, a model of a crane rope and a load mass, by the lateral motion of the support. Wave control of the acceleration of the support was derived based on the connecting condition of a real pendulum (rope and mass) to multiple wave-controlled homogeneous simple pendulums that exist virtually above the support. Velocity and position feedback control of the support was added in order to position the support at other than the original position. During winding up or down of the load mass, the system becomes a non-homogeneous simple pendulum system and the wave propagation exhibits a kind of mode localization that reduces the vibration control performance. The feedback control canceled the mode localization and provided better control performance than the pure wave control. The effective feedback coefficients of systems during winding up and down of the load mass were investigated. Based on simulation and experimental results, the proposed control was demonstrated to be useful and practical for real crane systems.</p>

This paper deals with the active control of transmitted sound power from an acoustic enclosure in which noise sources are installed. With the aim of revealing an effective active control method of the enclosure, a simple model which is cuboid and composed of one elastic panel (upper surface) and five rigid walls is considered by theoretical simulations and experiments. The authors have previously proposed the active control method of transmitted sound power through a panel based on feedforward control which four point force actuators are located on the nodal lines at the frequency which the modal coupling cancellation phenomenon occurs. In this study, this method is applied to the target elastic panel of the enclosure. The simulation results show that the transmitted sound power and the control effect greatly depend on the location of the noise source in the enclosure. In the case that the noise source is located at the asymmetric point with respect to the center of the panel, the control effect may decrease because of the influence of the even-ordered structural modes, which can be excited by the odd-ordered acoustic modes. In order to improve the control effect, the method using both the feedforward control and the direct velocity feedback control is proposed. Finally, experiments were carried out to demonstrate the validity and feasibility of the proposed method.

This study presents the feedback control of flexural waves propagating in a rectangular panel. The objective of this paper (part 1) is to theoretically investigate the fundamental properties of the feedback wave control system. First, a transfer matrix method in the Laplace domain is introduced which is based on a wave solution of a rectangular panel. This is followed by the derivation of the characteristic equation and the feedback control laws for absorbing the reflected waves. Then, from a viewpoint of numerical simulations, the control performance of the proposed method is clarified. It is found that the reflected wave absorbing control enables inactivation of vibration modes since standing waves which cause resonant phenomena disappear from the structural vibration. Finally, the stability verification of the proposed control system is conducted using Nyquist diagram. It is shown that although the controller has unstable poles in some cases, the nominal control system is stable irrespective of whether the collocation holds or not. Furthermore, it is clarified that a wave-absorbing control system becomes robust for the parameter fluctuation if the uncontrolled region does not exist. (C) 2012 Elsevier Ltd. All rights reserved.

This study presents the feedback control of flexural waves propagating in a rectangular panel. The objective of this paper (part 2) is to experimentally implement the feedback wave control method which was proposed in part 1 of the two series papers. Firstly, based on the collocation of sensors and actuators, clustered velocity and displacement feedback (C-VDFB) is newly proposed. Next, linking C-VDFB with the active wave control proposed in part 1, it is clarified that the active wave control system can be realized to a limited extent. Then, from a viewpoint of numerical simulations, the characteristics of the feedback gains of C-VDFB and its control performance are clarified. It is shown that C-VDFB enables the inactivation of vibration modes at the target frequencies. Furthermore, it is clarified that even at the non-target frequencies, the proposed method sufficiently reduces the structural vibration. Finally, experiments on the reflected wave absorbing control using clustered direct velocity and displacement feedback are carried out. The experimental results show good agreement with those obtained in the simulation. (C) 2012 Elsevier Ltd. All rights reserved.

The experimental validation of a generalised approach to the sensing of orthogonal contributors to the global error (acoustic potential energy) within a coupled structural-acoustic cavity is presented. The goal is the measurement and control of the global error without any knowledge of the structural dynamics of the noise source, based on an acoustic centric decomposition approach that is applicable to any noise source. Two sensing approaches are attempted, structural and acoustic sensing, to measure the global error within the coupled enclosure. Once estimates of the global error are obtained, minimisation with an adaptive feedforward controller is implemented. The level of achieved attenuation in the global error is compared. The achieved level of attenuation is also compared to the maximum level of attenuation of the global error that can be achieved based on the disturbance/secondary source arrangement. The maximum level of attenuation is evaluated from experimental data, rather than pure theoretical methods. (C) 2012 Elsevier Ltd. All rights reserved.

This paper deals with the eigenvalue problem of a coupled rectangular cavity comprising five rigid walls and one flexible panel frequently employed in much literature. It is the purpose of this paper to derive explicitly the eigenpairs of the coupled cavity, which are yet to be found. First, the coupling orthogonality conditions the eigenpairs need to satisfy are derived, thereby enabling the verification of the eigenpairs newly sought or already existent. Using the coupling orthogonality conditions, the modal equation of the coupled cavity system is then obtained, permitting one to deal with a forced response of the coupled cavity. It is shown that the eigenfunctions governing the dynamics of the sound field are expressed as the infinite sum of degenerate eigenfunctions. The characteristic matrix equation is then derived, specifying the eigenpairs of the coupled cavity. In order to investigate the fundamental properties of the eigenpairs derived, a numerical analysis is conducted, revealing the presence of evanescent modes in addition to the conventional standing wave modes. Finally, an experiment is carried out, verifying the validity of the eigenpairs derived in the article. (C) 2012 Acoustical Society of America. [DOI: 10.1121/1.3682046]

This study presents active control of progressive waves in a rectangular cavity using wave filters, demonstrating the validity of the proposed method fi-om an experimental point of view. Firstly, a wave solution of a rectangular cavity is derived. This is followed by the derivation of wave filtering equation. It is found from the equation that the wave filter consists of modal fihers rearrangement filters and wave decomposition filters. Then, implementation of the wave filter using FIR filters is presented. Finally, experiment on the generation of a quiet space using the proposed wave filters is carried out, demonstrating that a quiet space is realized by the proposed method.

This study presents active boundary control of a rectangular cavity which enables to generate a quiet space in a certain region of the target system. Firstly, a transfer matrix method for the target system is introduced to describe the dynamics in the enclosure. This is followed by the derivation of an active boundary control laws. Then, from a viewpoint of numerical analyses, basic properties of the proposed method are verified. It is found that the proposed method enables the generation of a silent zone. © European Acoustics Association.

This paper presents global noise reduction in an enclosed sound field using feedback control based on the affinity between cluster control and suppression of acoustical energy density. First, an enclosed sound field is expressed in terms of a state space method. This is followed by the discussion on the validity of the acoustical energy density as a performance index of a control system. It is clarified here that the introduction of acoustical energy density results in the avoidance of uncontrollability. Next, the novel cluster control which is based on the suppression of acoustical energy density is proposed, its stability being analytically verified. Furthermore, from the viewpoint of numerical analyses, the validity of the proposed method is clarified. Finally, the relation between the proposed method and orthogonal contributors in an enclosed sound field is discussed, revealing that the conventional cluster control is the special case of the proposed method.

This paper presents the wave filtering method for a rectangular panel, which is necessary for a feedforward wave control system, and clarifies its validity in the control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the derivation of the wave filtering equations that indicates the structure of the filter. It is found that the proposed wave filter consists of a modal filter, a rearrangement filter and a wave decomposition filter. Then, from the viewpoint of numerical simulations, the characteristics of the wave propagation in a rectangular panel as well as the accuracy of the wave fitter are verified. For the evaluation of the filter accuracy, the condition number is used as a performance index. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that the reflected wave absorbing control enables the inactivation of vibration modes. (c) 2010 Elsevier Ltd. All rights reserved.

This paper is concerned with an active wave control method of a rectangular panel. It is the purpose of this paper to present a wave filtering method for the panel using smart modal sensors and its application to an adaptive feedforward control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the proposition of the design procedure of the wave filter using smart mode sensors. Then, from a viewpoint of numerical analyses, accuracy of the proposed method is verified using condition numbers of a filtering matrix. Furthermore, a multi-rate technique is introduced for approximation of the sub-filters in the wave filter, which reduces the computational burden. Finally, experiment on an adaptive feedforward control system using the proposed method is carried out. It is found that the reflected wave absorbing control enables the inactivation of vibration modes.

This paper is concerned with an active noise control for an enclosed sound field. It is the purpose of this paper to present an active wave control method of a three dimensional rectangular cavity and to clarify fundamental properties of the control system. Firstly, a transfer matrix method for the target system is newly introduced to describe the wave dynamics in the enclosure. This is followed by the derivation of feedforward control laws for absorbing reflected waves or eliminating transmitted waves. In the proposed method, the control laws are including the modal actuation scheme for uncontrolled direction. Then, from a viewpoint of numerical analyses, basic properties of the proposed method are verified. It is found that the transmitted wave eliminating control enables the generation of silent zone, and the reflected wave absorbing control enables the inactivation of acoustical modes in the controlled direction.

This study is concerned with cluster control for suppressing the acoustic power of the plate with asymmetric boundary conditions by controlling the element of vibration which contributes to the noise radiation. The conventional cluster control is based on the assumption that a target rectangular plate has symmetric boundary conditions. In this method, simple signal processing can be achieved by using symmetric property of mode shapes, and hence it is difficult to apply this method to the case in which the panel has asymmetric mode shapes. To cope with this problem, this paper proposes the application of the cluster control to the panel with asymmetric boundary conditions.

This paper is concerned with active wave control in three-dimensional enclosed sound field. It is the purpose of this paper to present a wave filtering method which extracts the target wave amplitude in real time and to clarify the validity of active wave control method for generating a quiet space using the proposed method. Firstly, a wave solution of a rectangular cavity is derived. This is followed by the derivation of wave filtering equation. It is found from the equation that the wave filter consists of modal filters rearrangement filters and wave decomposition filters. Then, from a viewpoint of numerical analyses, control effects of the transmitted wave eliminating control based on the proposed wave filter is clarified.

This paper is concerned with active vibration isolation and localization control for a sound insulation of a multiple-wall structure comprising multiple uniformed panels separated by enclosed air gaps. The model is supposed that the multiple-wall structure is subjected to and got through by the acoustic sound or the structure is vibrated by point forces put in an arbitrary component, radiating acoustic sound. It is the purpose of this paper to enhance the sound insulation of multiple walls via active control in an effort to isolate vibration in a designated point. To this end, the coupling terms between vibrating plates that is defined in this paper are suppressed by feedback control force given from reciprocal vibrations. In consequence, the vibration or sound energy is localized in a target component. And more, if the noise source is in a structure, the control can confine sound in a structure. In this paper, first, the vibration mechanisms of the multiple-wall structure are revealed by modal coupling theory, and the coupling terms are check out from the revealed mechanism. Next, the vibration insulation control with suppressing the coupling terms is offered to. Finally, with a view to verifying the validity of the control strategy, a numerical analysis is conducted.

The active control of radiation from large structures is a difficult, though important practical problem. The major reason for the difficulty is the 'system' size, as a large number of sensors and actuators are required for successful implementation, thus making it hard to design a robust, efficient system that integrates all sensors and actuators. This work examines the active attenuation of the global error, sound power, from the point of view of two sensing/control strategies that seek to be generalised; thus are applicable to a wide range of applications and are independent of knowledge of structural dynamics. In each approach the idea is that the required hardware can simply be attached, turned on, and immediately being to attenuate global noise. The two strategies are compared based on the level of attenuation of the global error sound power, the attenuation per total control force, and attenuation per actuator (in a structural-acoustic situation). The first strategy is the collocated-decentralised approach, which is built on measuring and controlling local vibration in an attempt to influence the global acoustic error. An alternative approach, termed the hybrid approach is firstly developed. The approach is termed 'hybrid' because it is a mix between a fully 'centralised' and 'decentralised' approach; but still measuring and controlling the global acoustic error directly. The attenuation of sound power is compared for both strategies on two structural sources; using 16 identically placed velocity sensors and 16 secondary point sources, in simulation in an attempt to suggest efficient sensing and control approaches for the global control of sound radiation from large structural sources. (C) 2010 Elsevier Ltd. All rights reserved.

This paper concerns the active vibration control of a rectangular panel using smart sensors from the viewpoint of an active wave control theory. The objective of this paper is to present a new type of filter which enables the measurement of the wave amplitude of a rectangular panel in real time for the application of an adaptive feedforward control system which inactivates vibration modes. Firstly, a novel wave filtering method using smart PVDF sensors is proposed. It is found that the shaping function of smart sensors is a complex function. To realize the smart sensor in a practical situation, a Hilbert transformer is utilized to implement a phase shifter of 90 degrees for broadband frequencies. Then, from the viewpoint of a numerical analysis, the characteristics of the proposed wave filter and the performance of the adaptive feedforward control system using the wave filter are discussed. Finally, experiments implementing the active wave control theory which uses the proposed wave filter are conducted, demonstrating the validity of the proposed method in suppressing the vibration of a rectangular panel.

Active wave control strategy enables the inactivation of vibration mode, which is valid for suppressing the vibration of a distributed parameter structure. However, when active wave control is applied, new vibration modes are produced in the uncontrolled region. To overcome this problem, this paper proposes a novel control strategy based on a hybrid combination of direct velocity feedback (DVFB) and active wave control. The two control methods have complementary qualities; DVFB is for improving the stability, and active wave control is for its unique control effects. First, a transfer matrix method in the Laplace domain is introduced to describe wave propagation phenomena of an Euler-Bernoulli beam. Then the wave filtering method which uses point sensors is presented. Based on the filtering method, the characteristic equation and control laws of the reflected wave absorbing control are derived. Next, the independence of the two control methods in the proposed hybrid control system is investigated by a numerical simulation. This is followed by the discussion of the stability problem of the hybrid control system via a Nyquist diagram method and three types of root loci. Finally, the control effects of the proposed control system are presented, demonstrating the validity of the proposed method.

This paper deals with active mode localization control of a periodic structure comprising a series of coupled identical components. Once mode localization occurs, vibration energy normally distributed throughout a whole system is intensively concentrated in a particular component of a periodic system, and hence needs to be eschewed because of localized stress. This paper begins by elucidating the causes of the mode localization phenomenon which is likely to happen in a periodic structure under some conditions. Numerical analysis is then performed, investigating the mode localization phenomenon from a viewpoint of dynamical compliances as well as mode behavior of a total system comprising coupled flexible beams with springs. It is shown that energy confinement in terms of disturbance forces takes place when mode localization takes place. In consideration of the energy confinement, active mode localization control is presented, enabling the vibration isolation from the disturbance energy. Finally, an experiment is carried out, demonstrating the validity of the proposed method for the purpose of actively isolating power flow form one subsystem to another.

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed. (C) 2009 Elsevier Ltd. All rights reserved.

This paper is concerned with active wave control of a distributed parameter structure. It is the purpose of this paper to present the active wave control method of it rectangular panel and to clarify fundamental properties of the control system. Firstly, a transfer matrix method for a rectangular panel is introduced to describe the wave dynamics of the structure. This is followed by the derivation of feedforward control laws for absorbing reflected waves or eliminating transmitted waves. In the proposed method, the control laws are including the modal actuation scheme for uncontrolled direction. Then, from a viewpoint of numerical analyses, basic properties of the proposed method are verified. It is found that the reflected wave absorbing control enables the inactivation of all vibration modes in the controlled direction and the transmitted wave eliminating control enables the generation of an almost vibration-free state. It is also found that some phenomena different from the case of a beam-like structure appear under certain boundary conditions. (C) 2009 Elsevier Ltd. All rights reserved.

This paper presents cluster vector-based control for generating a vibration-free state in the designated area of a target beam. Cluster control consisting of both cluster filtering and cluster actuation is shown, and the stability of a cluster control system is investigated. Cluster filtering aims at extracting the information necessary for control, while cluster actuation excites or suppresses the cluster filtering output without causing spillover. For generating a vibration-free state ill the designated area of a beam, where neither progressive waves nor reflected waves exist, state variables governing the vibration of a beam must be extracted and suppressed. A cluster vector-the common link between cluster filtering and cluster actuation-is introduced for this purpose. It is found that the suppression of a performance index, expressed in terms of the cluster vector, generates a vibration-free state of a beam, whereas the suppression of conventional orthogonal contributors, such as radiation modes, does not. Numerical simulation is performed, followed by an experiment, to verify the validity of the results. (C) 2008 Elsevier Ltd. All rights reserved.

This paper presents active boundary control-ABC-of an Euler-Bernoulli beam, which enables one to generate a desired boundary condition at any designated position of a target beam structure, thereby permitting the structure to possess desired properties characterized by the boundary condition. Furthermore, ABC has potential to create a completely vibration-free state in the designated area of a beam. This paper begins by presenting the principle of ABC using a transfer matrix method, the optimal control law of the ABC system being derived. It is found that, in addition to conventional four classical boundary conditions: free, pinned, clamped and sliding support, ABC can generate two more boundary conditions that may not be observed in real systems but realized by ABC. It is also found that as a result of applying ABC to a specific location, including a current conventional boundary of a beam, a completely vibration-free state in the target region of a beam can be realized. Finally, an experiment using an adaptive feedforward control was conducted, demonstrating that ABC enables the generation of a desired boundary condition at the designated location of a target beam, and of a completely vibration-free state of a beam. (c) 2007 Elsevier Ltd. All rights reserved.

This paper deals with the feedback wave control of a flexible beam using the wave filter constructed with four point sensors. The objective of this paper is to theoretically lay out the active wave control at free end of the beam which is independent of the disturbance positions. Firstly, the transfer matrix method and wave filtering method are extended to the Laplace domain. Next, based on the relation between the incident and reflected wave vectors at a free end, the control laws and characteristic equation of the control system are derived. Moreover, the control effects are presented from a viewpoint of a numerical analysis. It is found that the proposed method can eliminate the designated wave even if a disturbance acts around the control point. Finally, the stability of the control system is clarified by using root loci, showing that all poles are close to the critical damping.

This paper concerns the active vibration control of a flexible beam using smart sensors from the viewpoint of an active wave control theory. The objective of this paper is to present a new type of sensor which enables one to measure the wave amplitude of a flexible beam in real time for the application of use in an adaptive feed-forward control system. Firstly, a novel wave filtering, method using distributed parameter PVDF sensors is proposed. It integrates an infinite number of point sensors and has an integral calculation ability based on a proposed shaping function. Furthermore, the characteristics of the wave filter and the performance of the adaptive feed-forward control system using the wave filter are discussed. Finally, experiments adopting the active wave control theory which use the wave filter are conducted, demonstrating the validity of the proposed method in suppressing the vibration of a flexible beam.