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: In this paper, the buckling response of variable stiffness composite (VSC) plates subjected to spatially varying fiber volume content as well as fibre misalignments, yielding a multiscale sensitivity analysis.
Abstract: It is well known that fabrication processes inevitably lead to defects in the manufactured components. However, thanks to the new capabilities of the manufacturing procedures that have emerged during the last decades, the number of imperfections has diminished while numerical models can describe the ground truth designs. Even so, a variety of defects has not been studied yet, let alone the coupling among them. This paper aims to characterise the buckling response of Variable Stiffness Composite (VSC) plates subjected to spatially varying fibre volume content as well as fibre misalignments, yielding a multiscale sensitivity analysis. On the one hand, VSCs have been modelled by means of the Carrera Unified Formulation (CUF) and a layer-wise (LW) approach, with which independent stochastic fields can be assigned to each composite layer. On the other hand, microscale analysis has been performed by employing CUF-based Mechanics of Structure Genome (MSG), which was used to build surrogate models that relate the fibre volume fraction and the material elastic properties. Then, stochastic buckling analyses were carried out following a multiscale Monte Carlo analysis to characterise the buckling load distributions statistically. Eventually, it was demonstrated that this multiscale sensitivity approach can be accelerated by an adequate usage of sampling techniques and surrogate models such as Polynomial Chaos Expansion (PCE). Finally, it has been shown that sensitivity is greatly affected by nominal fibre orientation and the multiscale uncertainty features.
17 citations
TL;DR: In this article, an analytical description of active structural acoustical control of vibration isolation with a plate-shell coupled foundation is presented, which is composed of a two-stage isolation and a flexible supporting plate coupled with an elastic cylindrical shell, which are connected via passive active mounts.
16 citations
TL;DR: In this article, a free vibration porous composite plate is constructed with a multi-layer model in a metal matrix containing uniform or non-uniformly distributed open-cell internal pores.
Abstract: Plates are commonly used in many engineering disciplines, including aerospace. With the continuous improvement in the capacity of high value-added airplanes, large transport aircrafts, and fighter planes that have high strength, high toughness, and corrosion resistance have gradually become the development direction of airplane plate structure production and research. The strength and stability of metal plate structures can be improved by adding reinforced materials. This paper studies graphene platelets (GPLs) reinforced with a free vibration porous composite plate. The porous plate is constructed with a multi-layer model in a metal matrix containing uniform or non-uniformly distributed open-cell internal pores. Considering the random and directional arrangement of graphene platelets in the matrix, the elastic modulus of graphene composites was estimated using the Halpin–Tsai micromechanical model, and the vibration frequencies of graphene composite were calculated using the differential quadrature method. The effects of the total number of layers, GPL distribution pattern, porosity coefficient, GPL weight fraction, and boundary conditions on the free vibration frequency of GPLs reinforced porous composite plates are studied, and the accuracy of the conclusions are verified by the finite element software.
8 citations
TL;DR: In this article, the influence of non-periodic rainbow resonators on the vibration attenuation of two-dimensional metamaterial plates is investigated and compared with periodic metammaterial plates.
Abstract: This paper investigates the influences of nonperiodic rainbow resonators on the vibration attenuation of two-dimensional metamaterial plates. Rainbow metamaterial plates composed of thin host plates and nonperiodic stepped resonators are considered and compared with periodic metamaterial plates. The metamaterial plates are modelled with the finite element modelling method and verified by the plane wave expansion method. It was found that the rainbow metamaterial plates with spatially varying resonators possess broader vibration attenuation bands than the periodic metamaterial plate with the same host plates and total mass. The extension of attenuation bands was found not to be attributed to the extended bandgaps for the two-dimensional metamaterial plates, as is generally believed for a one-dimensional metamaterial beam. The complete local resonance bandgap of the metamaterial plates is separated to discrete bandgaps by the modes of nonperiodic resonators. Although the additional modes stop the formation of integrated bandgaps, the vibration of the plate is much smaller than that of resonators at these modal frequencies, the rainbow metamaterial plates could have a distinct vibration attenuation at these modal frequencies and achieve broader integrated attenuation bands as a result. The present paper could offer a new idea for the development of plate structures with broadband vibration attenuation by introducing non-periodicity.
7 citations
TL;DR: In this paper, the free vibration of a tapered beam modeling non-uniform single-walled carbon nanotubes was considered, and the differential quadrature method (DQM) was applied to compute the natural frequencies.
Abstract: Here, we consider the free vibration of a tapered beam modeling nonuniform single-walled carbon nanotubes, i.e., nanocones. The beam is clamped at one end and elastically restrained at the other, where a concentrated mass is also located. The equation of motion and relevant boundary conditions are written considering nonlocal effects. To compute the natural frequencies, the differential quadrature method (DQM) is applied. The influence of the small-scale parameter, taper ratio coefficient, and added mass on the first natural frequency is investigated and discussed. Some numerical examples are provided to verify the accuracy and validity of the proposed method, and numerical results are compared to those obtained from exact solution. Since the numerical results are in excellent agreement with the exact solution, we argue that DQM provides a simple and powerful tool that can also be used for the free vibration analysis of carbon nanocones with general boundary conditions for which closed-form solutions are not available in the literature.
6 citations
References
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TL;DR: In this article, the directivity of acoustic radiation from a rectangular piston arbitrarily located on a rigid prolate spheroidal baffle is formulated in terms of a modal series representation in sphero-al eigenfunctions.
Abstract: The directivity of acoustic radiation from a rectangular piston arbitrarily located on a rigid prolate spheroidal baffle is formulated. The piston is assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wave functions are obtained using computer programs that have been recently developed to provide accurate values of the wave functions at high frequencies. Results are presented in the form of far-field polar directivity patterns for various piston/spheroid acoustic sizes, piston locations on the spheroid, and spheroidal shapes.
8 citations
TL;DR: In this paper, a hybrid actuator was proposed to improve the low frequency transmission loss at low frequencies without altering the passive attenuation, which was tested in a plane wave acoustic tube setup with different kinds of SISO feedforward control implementations.
2 citations