Author: Yu, Xiang
Title: Modeling, analysis, and optimization of complex vibroacoustic systems with micro-perforates
Advisors: Cheng, Li (ME)
Degree: Ph.D.
Year: 2016
Subject: Structural dynamics.
Hong Kong Polytechnic University -- Dissertations
Department: Department of Mechanical Engineering
Pages: xxiii, 199 pages : color illustrations
Language: English
Abstract: Vibroacoustic modeling of complex systems is a challenging task. Their in-depth analyses are essential for the development of advanced noise control solutions. In this thesis, a package of efficient numerical modeling tools is developed based on the sub-structuring approach, in order to deal with complex structural-acoustical couplings among various subsystem components in a wide range of applications. A Compound Interface-Patch Transfer Function (CI-PTF) approach is proposed, highlighting its ability in handling mixed separations, such as those composed of rigid or flexible structures and apertures. Typical structural and acoustical subsystems are characterized as a few versatile subsystem modules, serving as the building blocks for constructing complex system configurations. The convergence, accuracy, and efficiency of the developed numerical tools are thoroughly validated. As an important non-fibrous sound absorbing material, micro-perforated panels (MPPs) and their in-situ sound absorption in coupled vibroacoustic systems are investigated. The MPP is modeled as an integral component of the system using the proposed CI-PTF approach. Numerical studies show that the actual sound absorption performance of the MPPs strongly depends on the surrounding environment, which unequivocally demonstrates that MPP cannot be simply considered as a locally reactive element in a complex vibroacoustic environment.
For sound transmission control inside a duct, acoustic silencers are considered whose modeling is systematically tackled by the proposed numerical tools. Reactive silencers with rigid internal partitions are studied for their parametric influences and noise attenuation mechanisms. With the introduction of MPPs as dissipative elements, a unit cell treatment is proposed to model the complex side-branch configuration, and investigations reveal the hybrid attenuation mechanism of such device, which combines the reflection and absorption effects. Benefiting from the modular nature of the sub-structuring approach, the size of the perforated hole and the perforation ratio can be optimized to strike a balance between the dissipative and reactive effect, for ultimately achieving a desired Transmission Loss (TL) within a prescribed frequency range. The calculation accuracy for both reactive and hybrid MPP silencers using the proposed approach have been confirmed with finite element method (FEM) simulations and experiments.For the tuning and optimization of a silencer, the broadband TL performance realized by a number of cascade-connected sub-chambers is investigated. A theoretical basis for the description of the overall system TL is presented. The characteristics of the sub-chambers, along with the understandings of influences of the parameters, provide guidelines for their optimizations, and a desired broadband performance is achieved by connecting sub-chambers with optimized TLs to tackle different frequency regions. Based on the sub-chamber strategy, a multi-level approach for the design, analysis and optimization of acoustic silencers with cascaded sub-chambers is proposed. Through numerical case studies and a retrofitted design of a mining truck muffler, the effectiveness of the proposed methodology is demonstrated, which greatly reduces the design variables and computational costs compared with global design and optimization.
Rights: All rights reserved
Access: open access

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