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Dissertation
Final work : Modal and Acoustic simulation and testing in Aftertreatment system
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Year: 2018 Publisher: Liège Université de Liège (ULiège)

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Abstract

Limiting the loudness of machines has always been a challenge to engineers. Loudness becomes even more crucial for vehicles due to their continuous proximity to humans and thus being capable of having adverse effect on health and quality of life. The exhaust system of vehicles is one of the major sound sources mounted on the chassis. Although the flow and exhaust noise have been characterized in detail by the vehicle industry, the capability to simulate shell noise remains relatively unexplored. In order to develop a reliable shell noise simulation model, it is required to characterize the structural behavior of the silencer jacket plates and the excitation sources present on an operating vehicle. Current thesis focused on development of a testing and simulation method which could complement each other and thus verify the accuracy and robustness of the simulation results. The comparison of acoustic properties of jacket plates was done by measuring the acoustic radiation efficiency of these plates and then obtaining the same from simulation results. Although radiation efficiency provides a comparison of loudness between different structures, it fails to generate physically relevant data as radiation efficiency is undefined for flow generated sound. Physical impact of radiated sound is better characterized by Sound power levels as these can be coupled with sound power from various other sources to estimate the overall sound emitted by a vehicle.&#13;The reciprocity method of acoustic measurements provides a reliable way to measure radiation efficiency of structures and at the same time allows the measurement of sound power. This was used to obtain measurement data for three samples of three different plates. Further a hybrid FEM – BEM model was developed. An initial comparison of eigenfrequencies and radiation efficiency indicated a deviation in the range of 3 – 8%. The measurement process was then optimized by averaging radiation efficiency over three measurement points. For the simulation model, the variation of plate thickness due to the stamping process involved in manufacturing was taken into account to update the model. As a result the deviation was reduced to <2% in the frequency range up to 1000Hz. This incites a need to develop a more accurate simulation for the manufacturing process so that the plate topologies and prestress can be accounted for. Acoustic radiation efficiency measurement is based on the acceleration response to excitation force ratio which is indicated by the measured FRF. However, it was found that much accurate results are obtained if auto – power is used to calculate the response to input ration instead of the measured FRF. &#13;This thesis was successfully able to develop a simulation model in COMSOL Multiphysics to predict shell noise emitted by free boundary plates and can be used for further investigation by imposing suitable boundary conditions and excitations to develop a full model.


Book
Innovative Composite Materials for Sound Absorption and Insulation
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Year: 2021 Publisher: Basel, Switzerland MDPI - Multidisciplinary Digital Publishing Institute

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Materials with sound-absorbing or sound-insulating properties have been rapidly evolving in recent years for several reasons. On one side, there is the ever-increasing awareness of the adverse effects that noise and lack of acoustic comfort may have on human health. On the other, the availability of more sophisticated fabrication techniques, calculation methods, and new materials, has stimulated researchers and, more and more frequently, industry to develop customized materials with improved properties.This book collects contributions from different researchers covering several topics. A group of papers investigated the use of 3D printing to obtain perforated panels with extended frequency response, as well as to ideally design an optimized cell distribution to print (when fabrication techniques will make it possible) a porous material with a broader sound absorption. The role of the geometrical and microstructural properties of granular molecular sieves is investigated by another paper. A second group of papers focused its attention on the use of natural or recycled components to create a skeleton of porous materials with good sound-absorbing properties and low environmental impact. Cigarette butts, recycled textile waste, and almond skins have been investigated by different authors.Finally, the last batch of papers included a review of sound insulation properties of innovative concretes and two research papers focussing on a numerical and experimental analysis of wood plastic composite (WPC) panels and on the potential of semi-active solutions employing compressible constrained layer damping (CCLD).


Book
Innovative Composite Materials for Sound Absorption and Insulation
Author:
Year: 2021 Publisher: Basel, Switzerland MDPI - Multidisciplinary Digital Publishing Institute

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Abstract

Materials with sound-absorbing or sound-insulating properties have been rapidly evolving in recent years for several reasons. On one side, there is the ever-increasing awareness of the adverse effects that noise and lack of acoustic comfort may have on human health. On the other, the availability of more sophisticated fabrication techniques, calculation methods, and new materials, has stimulated researchers and, more and more frequently, industry to develop customized materials with improved properties.This book collects contributions from different researchers covering several topics. A group of papers investigated the use of 3D printing to obtain perforated panels with extended frequency response, as well as to ideally design an optimized cell distribution to print (when fabrication techniques will make it possible) a porous material with a broader sound absorption. The role of the geometrical and microstructural properties of granular molecular sieves is investigated by another paper. A second group of papers focused its attention on the use of natural or recycled components to create a skeleton of porous materials with good sound-absorbing properties and low environmental impact. Cigarette butts, recycled textile waste, and almond skins have been investigated by different authors.Finally, the last batch of papers included a review of sound insulation properties of innovative concretes and two research papers focussing on a numerical and experimental analysis of wood plastic composite (WPC) panels and on the potential of semi-active solutions employing compressible constrained layer damping (CCLD).


Book
Innovative Composite Materials for Sound Absorption and Insulation
Author:
Year: 2021 Publisher: Basel, Switzerland MDPI - Multidisciplinary Digital Publishing Institute

Loading...
Export citation

Choose an application

Bookmark

Abstract

Materials with sound-absorbing or sound-insulating properties have been rapidly evolving in recent years for several reasons. On one side, there is the ever-increasing awareness of the adverse effects that noise and lack of acoustic comfort may have on human health. On the other, the availability of more sophisticated fabrication techniques, calculation methods, and new materials, has stimulated researchers and, more and more frequently, industry to develop customized materials with improved properties.This book collects contributions from different researchers covering several topics. A group of papers investigated the use of 3D printing to obtain perforated panels with extended frequency response, as well as to ideally design an optimized cell distribution to print (when fabrication techniques will make it possible) a porous material with a broader sound absorption. The role of the geometrical and microstructural properties of granular molecular sieves is investigated by another paper. A second group of papers focused its attention on the use of natural or recycled components to create a skeleton of porous materials with good sound-absorbing properties and low environmental impact. Cigarette butts, recycled textile waste, and almond skins have been investigated by different authors.Finally, the last batch of papers included a review of sound insulation properties of innovative concretes and two research papers focussing on a numerical and experimental analysis of wood plastic composite (WPC) panels and on the potential of semi-active solutions employing compressible constrained layer damping (CCLD).

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