Nobuo Tanaka

Bio: Nobuo Tanaka is an academic researcher from Tokyo Metropolitan University. The author has contributed to research in topics: Sound power & Vibration. The author has an hindex of 17, co-authored 139 publications receiving 953 citations.

On feedforward active control of sound and vibration using vibration error signals

Abstract: The problem of sensing structural vibration to provide an error signal for vibration source‐based adaptive feedforward control systems implemented to attenuate globally both structural and acoustic disturbances is considered. It is shown that designing a control system that 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 that contribute to the error criterion as a set. It is these orthogonal groupings that should be sensed as an error signal by an adaptive feedforward control system (and minimized in amplitude), a task that could be accomplished using shaped piezoelectric polymer film sensors or discrete measurement/modal filtering techniques. Specific examples relating to the minimization of radiated acoustic power and acoustic potential energy in a coupled enclosure are given...

Calculating total acoustic power output using modal radiation efficiencies

Abstract: Over the last 20 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.

Active noise control using a steerable parametric array loudspeaker

Abstract: Arguably active noise control enables the sound suppression at the designated control points, while the sound pressure except the targeted locations is likely to augment. The reason is clear; a control source normally radiates the sound omnidirectionally. To cope with this problem, this paper introduces a parametric array loudspeaker (PAL) which produces a spatially focused sound beam due to the attribute of ultrasound used for carrier waves, thereby allowing one to suppress the sound pressure at the designated point without causing spillover in the whole sound field. First the fundamental characteristics of PAL are overviewed. The scattered pressure in the near field contributed by source strength of PAL is then described, which is needed for the design of an active noise control system. Furthermore, the optimal control law for minimizing the sound pressure at control points is derived, the control effect being investigated analytically and experimentally. With a view to tracking a moving target point, a steerable PAL based upon a phased array scheme is presented, with the result that the generation of a moving zone of quiet becomes possible without mechanically rotating the PAL. An experiment is finally conducted, demonstrating the validity of the proposed method.

Active Wave Control of a Flexible Beam. Proposition of the Active Sink Method.

Abstract: This paper deals with the flexural wave control of a flexible beam with an infinite number of vibration modes. It is the purpose of this paper to present a new vibration control method, the active sink method, which makes it possible to suppress all vibration modes of the flexible beam. Unlike a conventional vibration control method which attempts to suppress several vibration modes already excited, the active sink method seeks to keep all the vibration modes inactive. First, this paper presents the principle of the active sink method and shows a means of realizing its system. Next, in order to describe the principle of the active sink method mathematically, transfer matrices of a beam using a progressive wave solution to the wave equation are obtained. Then, the optimal conditions for the active sink system are derived, and the fundamental characteristics of the system are discussed. Finally, from the vdewpoint of vibration intensity analysis, the validity of the active sink method is clarified.

Modal control of a rectangular plate using smart sensors and smart actuators

Abstract: This paper is concerned with modal control of a rectangular plate using both smart sensors and smart actuators. Since filtering and actuation are related, discussion of a smart sensor comes first followed by that of the counterpoint?a smart actuator. This paper begins by discussing an ideal case of modal control comprising extraction and activation of a target structural mode of a plate. Then, for the purpose of implementing a modal control system, three-dimensional smart sensors and actuators are introduced, the design procedure being investigated. Taking into consideration the practicability, two-dimensional smart sensors and actuators for modal filtering and modal actuation, respectively, are presented, and then the number, location and shaping function of the two-dimensional modal sensors and actuators are clarified. Furthermore, the extraction and actuation of the (1, 3) mode of a simply supported rectangular panel using the smart sensors and actuators is shown. Finally, a modal feedback control system is constructed utilizing both the smart sensors and the smart actuators, demonstrating the effectiveness at suppressing the particular structural mode of interest without causing spillover.

Inducing Passive Nonlinear Energy Sinks in Vibrating Systems

Abstract: We study the inducement of passive nonlinear sinks in linear vibrating systems. These are substructures that absorb vibrational energy in a one-way, irreversible fashion. The systems considered are composed of strongly coupled, grounded damped linear oscillators with a strongly nonlinear attachment at the end. Applying a complex averaging technique we derive a set of modulation equations that is directly amenable to physical interpretation, and provides insight into the energy pumping phenomenon. For the case of a two DOF system we show that nonlinear energy pumping occurs when a certain frequency of envelope modulation crosses through zero; then the dynamics of the envelope modulation of the motion resemble the dynamics of a forced rigid body. For the case of an impulsively loaded multi-DOF chain with a nonlinear attachment at the end, we show that after some initial transients the response of the nonlinear attachment sets to a motion dominated by a fast frequency identical to the lower bound of the propagation zone of the linear chain. This feature reduces the study of energy pumping in the chain to a two DOF equivalent problem. The applications of the energy pumping phenomenon to practical engineering problems are discussed.

Ultrathin low-frequency sound absorbing panels based on coplanar spiral tubes or coplanar Helmholtz resonators

Abstract: Performance of classic sound absorbing materials strictly depends on their thickness, with a minimum of one-quarter wavelength to reach full sound absorption. In this paper, we report ultrathin sound absorbing panels that completely absorb sound energy with a thickness around one percent of wavelength. The strategy is to bend and coil up quarter-wavelength sound damping tubes into 2D coplanar ones, and embed them into a matrix to form sound absorbing panel. Samples have been designed and fabricated by 3D printing. Efficacies of sound absorption by these panels were validated through good agreement between theoretical analysis and experimental measurements.

Recent Advances on Active Noise Control: Open Issues and Innovative Applications

Abstract: The problem of acoustic noise is becoming increasingly serious with the growing use of industrial and medical equipment, appliances, and consumer electronics. Active noise control (ANC), based on the principle of superposition, was developed in the early 20th century to help reduce noise. However, ANC is still not widely used owing to the effectiveness of control algorithms, and to the physical and economical constraints of practical applications. In this paper, we briefly introduce some fundamental ANC algorithms and theoretical analyses, and focus on recent advances on signal processing algorithms, implementation techniques, challenges for innovative applications, and open issues for further research and development of ANC systems.

Understanding Active Noise Cancellation

Abstract: 1.What do we mean by secondary English teaching? 2. Language study and standard English in secondary English teaching 3.Drama in English 4.Teaching literature in secondary English 5.Teaching Media in secondary English 6.What do you need to know about the law? 7.What do we mean by the Reflective Practitioner? 8.What do we mean by your continuing professional development?