Iwamoto Hiroyuki

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.

Arguably, noise suppression via active noise control is effective only within a fraction of the noise wavelength from an error sensor location. To expand the controllable region, it is a common practice to introduce the multi-channelization of a control system or sound power control of a noise source per se. It is also true, however, that they entail the following disadvantages: the multi-channelization causes complication, destabilization and increment of the computational burden control sound sources need placing close enough to the noise source to achieve sound power control, hence impracticable. To overcome the disadvantages mentioned above, this paper presents a global active noise control method using a parametric array loudspeaker (PAL). Driving the ultrasonic transducers comprising PAL with a proper time delay enables one to produce the wavefront of control sound similar to that of noise, thereby suppressing a noise propagation in the vicinity of the noise source, resulting in the generation of a global zone of quite. The validity of the method presented is then clarified numerically as well as experimentally. © 2013 The Japan Society of Mechanical Engineers.