With the development of manufacturing techniques such as the Electron Beam Free Form Fabrication (EBF3), a metal deposition technique which deposits metal in complex shapes on a metallic base plate, it has become easy to manufacture complex shapes such as panels with curvilinear stiffeners. Designing and optimizing stiffened panels with predefined structural and acoustic response is the focus of this dissertation. Researchers have dealt with sizing optimization of panels with straight/curvilinear stiffeners for many years and it has been proven that in some cases the mass of a panel with curvilinear stiffeners is lesser than the mass of a panel with straight stiffeners for a complex loading such as bi-axial compression with shear and transverse pressure. The research work in this dissertation addresses the sizing as well as placement optimization of panel with straight and curvilinear stiffeners for desired structural as well as acoustic response. For acoustic optimization, point-excited stiffened panels are designed for minimal sound radiation given the constraint on total mass of the structure. To reduce the computational expense of structural-acoustic optimization, a new methodology for the objective function evaluation is also proposed and optimal design for minimum radiated acoustic power is discussed. The developed framework, named EBF3PanelOpt for structural acoustic optimization of point excited stiffened panels is extended to multi point excitation to capture the realistic excitations such as turbulent boundary layer (TBL) pressure fluctuations. The Corcos model of representing TBL is used to capture correlation of TBL pressure excitation. Validation of the approach using Corcos TBL model, implemented in EBF3PanelOpt is performed using fast multi-pole boundary element method in FastBEM and a conventional boundary element code, HELM3D. The optimal designs are obtained for a panel with two and four stiffeners, respectively. The minimization of both, the mass and the acoustic response during structural-acoustic optimization is conflicting in nature. Therefore, a multi-objective design optimization using non-dominated sorting genetic algorithm-II (NSGA-II) is performed. The Pareto optimal designs, obtained using multi-objective design optimization approach has reduced the acoustic response significantly with a minor mass penalty of the structure when compared to a baseline design while meeting all the constraints such as buckling eigenvalue, von Mises, and crippling stresses. A multi-objective design optimization framework is also developed for design optimization of diffuse field excited panels with straight and curvilinear stiffeners. The Pareto optimal designs of panel with six stiffeners are obtained using developed framework and a comparative study is performed with a baseline design with six straight stiffeners. The developed framework is also extended to perform multi-objective design optimization of point excited complex structures such as curved panels with straight or curvilinear stiffeners. A fast multi-pole boundary element method is used to calculate the acoustic response of the curved panel with stiffeners and design optimization results of a curved panel with two and four stiffeners are discussed. Experiments are also performed at Sound and Acoustic Load Transmission (SALT) facility of Langley Research Center to measure the sound radiation and transmission loss for two panels with straight and curvilinear stiffeners, respectively. The stiffened test panels with six stiffeners have been designed using multi-objective design optimization framework for TBL excitation. / Ph. D.

A crescente demanda por reduções nos níveis de ruído gerados por veículos, e, mais recentemente, pela melhoria na qualidade sonora, aliada às penalidades associadas ao espaço e peso das soluções passivas, sugerem o uso de técnicas de controle ativo de ruído. O projeto de sistemas ativos deve fazer parte do desenvolvimento de produto desde sua fase de concepção para que tais soluções sejam aplicadas em nível industrial. Portanto, propõem-se metodologias de simulação para o projeto de sistemas de controle de ruído. Modelos vibroacústicos em elementos finitos são reduzidos e formulados em espaço de estados para permitir a simulação do sistema em malha fechada. Os modelos envolvidos permitem a inclusão da dinâmica de sensores e atuadores para que o desempenho seja previsto de forma acurada. As vantagens do uso de simulação de sistema de controle de ruído, além da redução de custo e tempo de projeto, permite o desenvolvimento de sistemas ativos onde estrutura e controle são desenvolvidos de forma simultânea. O procedimento de simulação é validado experimentalmente, tanto para malha aberta quanto para malha fechada, com o uso de uma geometria simplificada de veículo. Graças à redução dos modelos originais, é possível utilizar técnicas de otimização, onde a interação entre a estrutura e o controle são considerados de forma simultânea, resultando em um sistema ativo com desempenho superior a sistemas desenvolvidos separadamente. Através dos resultados obtidos com a otimização observam-se os parâmetros conflitantes e as decisões de compromisso envolvendo o controle de transmissão de ruído em veículos. Demonstra-se, que um sistema de controle estrutural, descentralizado, de alimentação de velocidade, oferece praticidade de implementação e desempenho satisfatório. Finalmente, o impacto do controle ativo na percepção dos ocupantes é avaliado por meio de métricas objetivas de qualidade sonora, como tonalidade e nível de pressão sonora. / The demands for improvement in sound quality and noise reduction generated by vehicles are steadily increasing, as are the penalties for space and weight of passive control solutions. This scenario suggests the use of active noise control. In order to bring active solutions to industrial level applications, the design of such systems should be part of the product development cycle. Therefore, methodologies for simulating and designing such active solutions are proposed. These models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustical, and even sensor/actuator models in the controller algorithm simulation. The proposed modelling procedure coupe with this challenge, and besides the advantages on the cost and time reduction in the development phase, it allows the development of active systems with structure and controllers being designed concurrently. An experimental validation is performed using data obtained from simplified car geometry. Thanks to the reduced models, it is possible to run optimization routines in which the interaction of structure and control is considered, thus resulting in an improved system when compared to conventional stepwise procedure. The optimization results presented give some insights on the problem of designing active noise controllers for transmission loss in vehicles. It is shown that, a purely structural decentralized velocity feedback controller can offer both, easy practical implementation and satisfactory noise reduction. Also, the impact of the active control on the perceived noise reduction is evaluated with objective sound quality metrics, such as sound pressure level and specific loudness.

A crescente demanda por reduções nos níveis de ruído gerados por veículos, e, mais recentemente, pela melhoria na qualidade sonora, aliada às penalidades associadas ao espaço e peso das soluções passivas, sugerem o uso de técnicas de controle ativo de ruído. O projeto de sistemas ativos deve fazer parte do desenvolvimento de produto desde sua fase de concepção para que tais soluções sejam aplicadas em nível industrial. Portanto, propõem-se metodologias de simulação para o projeto de sistemas de controle de ruído. Modelos vibroacústicos em elementos finitos são reduzidos e formulados em espaço de estados para permitir a simulação do sistema em malha fechada. Os modelos envolvidos permitem a inclusão da dinâmica de sensores e atuadores para que o desempenho seja previsto de forma acurada. As vantagens do uso de simulação de sistema de controle de ruído, além da redução de custo e tempo de projeto, permite o desenvolvimento de sistemas ativos onde estrutura e controle são desenvolvidos de forma simultânea. O procedimento de simulação é validado experimentalmente, tanto para malha aberta quanto para malha fechada, com o uso de uma geometria simplificada de veículo. Graças à redução dos modelos originais, é possível utilizar técnicas de otimização, onde a interação entre a estrutura e o controle são considerados de forma simultânea, resultando em um sistema ativo com desempenho superior a sistemas desenvolvidos separadamente. Através dos resultados obtidos com a otimização observam-se os parâmetros conflitantes e as decisões de compromisso envolvendo o controle de transmissão de ruído em veículos. Demonstra-se, que um sistema de controle estrutural, descentralizado, de alimentação de velocidade, oferece praticidade de implementação e desempenho satisfatório. Finalmente, o impacto do controle ativo na percepção dos ocupantes é avaliado por meio de métricas objetivas de qualidade sonora, como tonalidade e nível de pressão sonora. / The demands for improvement in sound quality and noise reduction generated by vehicles are steadily increasing, as are the penalties for space and weight of passive control solutions. This scenario suggests the use of active noise control. In order to bring active solutions to industrial level applications, the design of such systems should be part of the product development cycle. Therefore, methodologies for simulating and designing such active solutions are proposed. These models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustical, and even sensor/actuator models in the controller algorithm simulation. The proposed modelling procedure coupe with this challenge, and besides the advantages on the cost and time reduction in the development phase, it allows the development of active systems with structure and controllers being designed concurrently. An experimental validation is performed using data obtained from simplified car geometry. Thanks to the reduced models, it is possible to run optimization routines in which the interaction of structure and control is considered, thus resulting in an improved system when compared to conventional stepwise procedure. The optimization results presented give some insights on the problem of designing active noise controllers for transmission loss in vehicles. It is shown that, a purely structural decentralized velocity feedback controller can offer both, easy practical implementation and satisfactory noise reduction. Also, the impact of the active control on the perceived noise reduction is evaluated with objective sound quality metrics, such as sound pressure level and specific loudness.

Low frequency noise caused by vibrating panels can pose problems for vehicles from noise, vibration and harshness (NVH) standpoint. In order to reduce interior noise levels in cars, some structural modifications are required on the car body. Structural modifications studied in this work are stiffeners welded on the walls of enclosed structure to change vibration characteristics. In this thesis, interaction between acoustic domain inside closed structures and their vibrating enclosing boundaries are analyzed. Analysis of vibro-acoustic behavior includes frequency response analysis of structure by Finite Element Method (FEM) and sound pressure level (SPL) prediction of the cabin interior by Boundary Element Method (BEM). The standard parts of the analyses are performed using available CAE (Computer Aided Engineering) software. It is demonstrated that the structural modification technique integrated with the vibro-acoustic model of the system reduces the computational effort considerably. The frequency response functions of a structure for each modification can easily be obtained in a fast and efficient way by using the structural modification technique. Thus, effects of design changes in the structure body on noise levels due to vibration of the structure can be very handily and efficiently studied. In the case studies presented, the effects of various different stiffeners applied on a simple closed structure are studied in detail.

New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro- and visco-elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco-elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode-matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro-elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three-dimensional problem is split up into several, much smaller, two- dimensional ones, radically decreasing the computational load.Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.

La caractérisation expérimentale de la réponse vibro-acoustique de panneaux excités par des champs de pression aléatoires est d'un grand intérêt autant en recherche que pour des applications industrielles. Deux excitations sont particulièrement étudiées: le champ acoustique diffus les pressions fluctuantes induites par une couche limite turbulente. Les moyens d’essais associés à ces excitations (chambre réverbérante, soufflerie, essais in situ) peuvent être très coûteux, difficilement contrôlables et rarement comparables entre laboratoires ou centre d’essais (installations de différentes dimensions ou mises en œuvres). La reproductibilité des mesures peut alors être remise en cause, ce qui rend difficile la comparaison entre différentes solutions technologiques. Il y a donc un fort intérêt à disposer d'un outil de laboratoire permettant de reproduire l’effet de ces excitations aléatoires dans un environnement contrôlé. Dans ce contexte, cette thèse propose de développer une méthode expérimentale permettant de caractériser le comportement vibro-acoustique de panneaux sous un champ de pression aléatoire en s’affranchissant des moyens d’essais usuels. Les approches que l’on étudie se basent sur la formulation mathématique du problème dans le domaine des nombres d'onde. Celle-ci met en évidence une séparation explicite des contributions de l'excitation (via l’interspectre de pression pariétale), de celles du comportement vibro-acoustique du panneau (via les fonctions de sensibilité). A partir de la connaissance de l'interspectre de pression pariétale, il suffit alors de déterminer expérimentalement les fonctions de sensibilité du panneau afin de déterminer par post-traitement sa réponse à l'excitation considérée. Deux méthodes permettant de déterminer les fonctions de sensibilité sont étudiées numériquement et validées expérimentalement : la méthode dite de l’antenne synthétique et une méthode basée sur des principes de réciprocité. Pour étudier la validité de ces méthodes, on compare leurs résultats à ceux obtenus par des moyens standards pour deux types de panneaux et les deux types d’excitations évoqués précédemment. / Abstract: The experimental vibro-acoustic characterization of panels submitted to random pressure fields is of great interest in the industry as well as in research laboratories. For the transport sector, this type of excitation can be found when a turbulent flow develops at the wall of a moving vehicle for example. The pressure fluctuations induced by the turbulent boundary layer excite the panels which radiate a noise inside the cabin. The experimental reproduction of those pressure fluctuations requires test means which can be very costly (i.e., wind tunnel, in situ tests) and whose physical parameters can hardly be controlled. The repeatability of measurements can thereby be questioned which makes it hard to compare different technological solutions. A second example of random pressure field is the diffuse acoustic field. This latter is usually reproduced in a reverberant room which is often coupled with an anechoic chamber by means of the panel whose acoustic insulation is to be tested. A pressure field is assumed to be diffuse if the acoustic energy comes from every direction with an equiprobable intensity of the incident waves. This assumption is never fully reached in practice (lack of grazing incident waves, strong modal behavior of the room at low frequencies, etc.). A laboratory tool which allows reproducing the effect of those random excitations in a controlled environment is therefore of great interest. In this context, this thesis aims at developing an experimental method to characterize the vibro-acoustic behavior of panels under random pressure fields without using the common test means (wind tunnel, reverberant room, in situ tests, etc.). For relevance sake, this approach must compensate for the previously stated issues. The approaches studied in this work are based on the mathematical formulation of the problem in the wavenumber domain. This latter allows an explicit separation of the contributions of the excitation via the wall-pressure cross-spectrum, from those of the vibro-acoustic behavior of the panel via so-called ‘sensitivity functions’. Assuming the wall-pressure cross-spectrum of the excitation is known, it is only required to experimentally determine those sensitivity functions, on the panel or in the acoustic medium, to determine the response of the panel to the considered excitation by post-processing. Two methods aiming at determining the sensitivity functions will be numerically and experimentally studied: the source scanning technique and the method based on the reciprocity principle. Results obtained with those method are compared to measurements using standard test means to attest the validity of those methods. Several vibro-acoustic indicators will be confronted while considering the two previously mentioned excitations and for two types of panels: an academic panel and a ‘complex’ from the aeronautic sector. This latter shows the applicability of the method in an industrial context.

An annoying tonal noise is produced by modern electrical trains duringacceleration and deceleration. This noise is caused by electromagneticforces generating structural vibrations, especially from the traction motors.The electromagnetic noise is dominant at low train speeds and affectsboth the passengers on the train and on platforms, as well as peopleliving near the track. The focus on this issue has increased the last years,both regarding legislation, contractual requirements and also because ofexpectations from citizens and travelers. To be able to design low noiseelectric drive systems, a thorough understanding of the cause and thepossibility to predict the electromagnetic noise is needed. This thesisdescribes the modelling and simulation of an complete multi-physicsreal-time environment for prediction and analysis of the electromagneticnoise. The simulation results are validated against measurements of thestructural vibration and acoustic response of a real traction motor fed bya power converter running in the entire operational range. / <p>QC 20161118</p>

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