Directivity-Based Passive Barrier for Local Control of Low-Frequency Noise
19 Dec 2018-Vol. 26, Iss: 04, pp 1850012
TL;DR: In this article, the authors proposed a novel concept of local mitigation of the transmitted transmission loss offered by a noise barrier separating two acoustic spaces in the low-frequency range, which can improve the transmission loss.
Abstract: This work concerns with improving the transmission loss offered by a noise barrier separating two acoustic spaces in the low-frequency range. A novel concept of local mitigation of the transmitted ...
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TL;DR: This work numerically investigates the diffraction management of longitudinal elastic waves propagating in a two-dimensional metallic phononic crystal and demonstrates that this structure acts as an “ultrasonic lens”, providing self-collimation or focusing effect at a certain distance from the crystal output.
Abstract: In this work, we numerically investigate the diffraction management of longitudinal elastic waves propagating in a two-dimensional metallic phononic crystal. We demonstrate that this structure acts as an “ultrasonic lens”, providing self-collimation or focusing effect at a certain distance from the crystal output. We implement this directional propagation in the design of a coupling device capable to control the directivity or focusing of ultrasonic waves propagation inside a target object. These effects are robust over a broad frequency band and are preserved in the propagation through a coupling gel between the “ultrasonic lens” and the solid target. These results may find interesting industrial and medical applications, where the localization of the ultrasonic waves may be required at certain positions embedded in the object under study. An application example for non-destructive testing with improved results, after using the ultrasonic lens, is discussed as a proof of concept for the novelty and applicability of our numerical simulation study.
1 citations
TL;DR: In this article, a method for determining the effects of fluids on the dynamic characteristics of an aerospace structure and the response of the structure when it is excited by the acoustical loads produced during a rocket launch, has been developed.
Abstract: In this study, a method for determining the effects of fluids on the dynamic characteristics of an aerospace structure and the response of the structure when it is excited by the acoustical loads produced during a rocket launch, has been developed. Elevated acoustical loads are critical in the design of large lightweight structures, such as solar arrays and communication reflectors, because of the high acceleration levels. The acoustic field generated during rocket launch can be considered as a diffuse field composed of many uncorrelated incident plane waves traveling in different directions, which impinge on the structure. A boundary element method was used to calculate the pressure jump produced by an incoming plane wave on an unbaffled plate and the fluid–structure coupled loads generated through plate vibration. This method is based on Kirchhoff’s integral formulation of the Helmholtz equation for pressure fields. The generalized force matrix attributed to the fluid loads was then formulated, taking the modes of the plate in vacuum as base functions of the structural displacement. These modes are obtained using a finite-element model. An iteration procedure was developed to calculate the natural frequencies of the fully coupled fluid–plate system. Comparison of the results obtained using the proposed method with those of other theories and experimental data demonstrated its efficiency and accuracy. The proposed method is suitable for analyzing plates of arbitrary shape subjected to any boundary conditions in a diffuse field for low to medium values of the frequency excitation range.
01 Dec 1997
TL;DR: A control law for tuning a variable stiffness vibration absorber to attenuate single frequency excitation in a non-collocated situation is developed and an experimental verification of this control law is shown.
Abstract: Presented in this paper is the development of a control law for tuning a variable stiffness vibration absorber to attenuate single frequency excitation in a non-collocated situation. The control law is comprised of two distinct parts. First, a feedback controller is used to obtain a ±90° phase condition between the motion of the vibration absorber mass and the location of interest. Next, a feedback based tuning strategy is used to precisely tune the vibration absorber for performance maximization. The feedback based tuning is based on the classical feedback structure of a regulating system and is used to tune the absorber such that the accelerometer voltage resulting from the measurement of vibration of the point of interest is minimized. An experimental verification of this control law is shown.
References
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TL;DR: In this paper, the authors show that thin membrane-type acoustic metamaterials can serve as a total reflection nodal surface at certain frequencies, which implies that several membrane panels can be stacked to achieve broad-frequency effectiveness.
Abstract: We show experimentally that thin membrane-type acoustic metamaterials can serve as a total reflection nodal surface at certain frequencies. The small decay length of the evanescent waves at these frequencies implies that several membrane panels can be stacked to achieve broad-frequency effectiveness. We report the realization of acoustic metamaterial panels with thickness ≤15 mm and weight ≤3 kg/m2 demonstrating 19.5 dB of internal sound transmission loss (STL) at around 200 Hz, and stacked panels with thickness ≤60 mm and weight ≤15 kg/m2 demonstrating an average STL of >40 dB over a broad range from 50 to 1000 Hz.
432 citations
TL;DR: In this article, the authors derived the radiation resistance of a finite rectangular panel from the total energy radiated to the far field, assuming that the panel is assumed to be supported in an infinite baffle.
Abstract: The radiation resistance corresponding to the natural modes of a finite rectangular panel is theoretically determined from the total energy radiated to the farfield. The panel is assumed to be simply supported in an infinite baffle. Asymptotic solutions for the low‐frequency region are derived, and curves covering the entire frequency range for various mode shapes and aspect ratios are obtained through numerical integration. When the ratio of the acoustic wavenumber to the panel wavenumber is a constant much less than unity, the radiation resistance for all modes is a minimum if the intranodal area (the area between adjacent node lines) is square, and increases with the aspect ratio of the intranodal area.
383 citations
TL;DR: In this article, the authors overview the active sound and vibration control field, first by putting it into a historical context, then by outlining the relevant control theory and implementations, and finally by describing some current practical applications.
Abstract: In many industrial and defense applications noise and vibration are important problems. The conventional method of treatment is to use passive damping techniques or to redesign the system. However, passive damping techniques are primarily effective at higher frequencies, and redesign is often costly and ineffective. In the last decade, active control of sound and vibration (at audio frequencies) has emerged as a viable technology to bridge this low-frequency technology gap. Recent developments have been propelled by the rapid technology growth in affordable and practical digital signal processing chips and, to a smaller degree, improvements in control transducers. In this article the authors overview the active sound and vibration control field, first by putting it into a historical context, then by outlining the relevant control theory and implementations, and finally by describing some current practical applications.
290 citations
TL;DR: In this article, active control of sound radiation from vibrating plates by oscillating forces applied directly to the structure is analytically studied, and it is shown that global attenuation of broadband radiated sound levels for low to mid-range frequencies can be achieved with one or two control forces, irrespective of whether the system is on or off resonance.
197 citations
TL;DR: In this paper, a theory on the generation mechanism of directional acoustic radiation from a supersonic jet is proposed based on the concept of instability of the shear layer at the boundary of the jet close to the nozzle.
Abstract: A theory on the generation mechanism of directional acoustic radiation from a supersonic jet is proposed. The theory is based on the concept of instability of the shear layer at the boundary of the jet close to the nozzle. Theoretical prediction of the directional wave pattern is found to agree with shadowgraphic observation.
139 citations