The present study investigates experimentally the laminar mixing and heat transfer of a range of helical ribbon and anchor impellers for both Newtonian and inelastic non-Newtonian fluids. The work also correlates the experimental data empirically in the form of dimensionless groups. In order to estimate the relative importance and the effect of all the geometrical parameters on the mixing power and heat transfer, data from the published literature sources will be utilized and combined with the results from this study. Thus, reliable empirical correlations will be obtained which are applicable over the widest range of operating conditions. The study also investigates the ablity of the various impellers to level out temerature distributions. The measurement of these temperature gradients and the impeller power requirements gives a measure of the mixing efficiency of the impeller used.

The present study investigates experimentally the laminar mixing and heat transfer of a range of helical ribbon and anchor impellers for both Newtonian and inelastic non-Newtonian fluids. The work also correlates the experimental data empirically in the form of dimensionless groups. In order to estimate the relative importance and the effect of all the geometrical parameters on the mixing power and heat transfer, data from the published literature sources will be utilized and combined with the results from this study. Thus, reliable empirical correlations will be obtained which are applicable over the widest range of operating conditions. The study also investigates the ablity of the various impellers to level out temerature distributions. The measurement of these temperature gradients and the impeller power requirements gives a measure of the mixing efficiency of the impeller used. / Science Research Council

Environmental noise has for decades been a well known problem, especially in urban areas. As noise requirements for vehicles are sharpened, noise reducing concepts are needed in early design stages requiring accurate simulations to support the design. Specifically for optimization of noise treatments, the absorber performance must be simulated correctly. So called noise encapsulations are placed below the powertrain on heavy vehicles to enclose the engine and reduce noise radiation. The attenuation of the absorbers on these shields must be represented correctly in simulations, even in environments with complex sound field, cooling flow and high temperature variations which may affect the absorber performance. This thesis studies the performance variation due to different absorber representations and due to these factors and how to include this in simulations. It is shown that the material representation significantly affects the attenuation performance in the simulations. Assuming locally reacting absorbers neglects the full interaction between the sound field and the material, which was shown to affect the noise reduction considerably. A measurement method to determine the angular dependent surface impedance was evaluated. It was shown sensitive to small samples and a method to improve accuracy was suggested. Including the angular dependence, either by full resolution or an angular dependent impedance, the field-absorber interaction is included in the simulations and more accurate results are obtained. The influence of flow and temperature fields on the absorber performance was also investigated. A method to include these effects was developed and the attenuation performance shown significant, especially for materials with bulk reaction. In conclusion, thorough knowledge of the material behavior and the field in the applications is required to choose appropriate material representation to enable reliable simulation results.​ / <p>QC 20160311</p>

Esta tese apresenta soluções para o gerenciamento e otimização de temperatura para sistemas de codificação de vídeo baseados nas características da aplicação e no conteúdo dos vídeos digitais. Diferente dos trabalhos estado-da-arte, as soluções propostas nesta tese focam em técnicas de gerenciamento de temperatura no nível da aplicação e características da aplicação codificação de vídeo e as propriedades dos vídeos digitais são explorados para desenvolver soluções termais para a codificação de vídeo com baixas perdas na qualidade de serviço das aplicações. Diversas análises são realizadas considerando a aplicação de codificação de vídeo para entender o comportamento da temperatura durante o processo de codificação para diferentes sequências de vídeo. Com base nos resultados das análises, soluções com diferentes abordagens são propostas para atenuar os efeitos da temperatura nos sistemas de codificação de vídeo. Gerenciamento de temperatura baseado nas características da aplicação para o padrão de codificação HEVC usa uma técnica de seleção de configuração em tempo de execução para manter a temperatura abaixo dos limites seguros de operação com bons resultados de qualidade de vídeo. Otimização de temperatura baseado em computação imprecisa usa aproximações baseadas em conteúdo para reduzir a temperatura de chips executando o HEVC. Um escalonador de tarefas que usa características da aplicação para guiar o escalonamento de threads focando na redução dos gradientes espaciais de temperatura que são resultantes do desbalanceamento natural de cargas entre as threads da aplicação. As soluções propostas são capazes de reduzir em até 10 ºC a temperatura do chip com perdas insignificantes na eficiência de compressão. Os resultados de qualidade objetiva (medida usando PSNR) são de 12 dBs até 20 dBs maiores quando comparados com trabalhos da literatura. Além disso, o escalonador de tarefas proposto é capaz de eliminar os gradientes espaciais de temperatura maiores que 5 ºC para arquitetura multi-cores. Como principal conclusão, esta tese demonstra que as técnicas de gerenciamento de temperatura que usam o conhecimento da aplicação de maneira conjunta com as propriedades dos vídeos digitais tem um alto potencial para melhorar os resultados de temperatura de sistemas de codificação de vídeo mantendo bons resultados de qualidade visual dos vídeos codificados. / This thesis presents application-driven temperature-aware solutions for next generation video coding systems, such as the High Efficiency Video Coding (HEVC). Different from state-of-the-art works, the proposed solutions raise the abstraction of temperature management to the application-level, where video coding characteristics and video content properties are used to leverage thermal-aware solutions for video coding with low QoS (Quality of Service) degradation. Several video coding and temperature analyses are performed to understand the behavior of temperature when encoding different video sequences. Based on the analyses results, different approaches are proposed to mitigate the temperature effects on video coding systems. Application-driven temperature management for HEVC uses run-time encoder configuration selection to keep temperature under safe operational state while providing good visual quality results. Temperature optimization using approximate computing uses content-driven approximations to reduce the on-chip temperature of HEVC encoding. Application-driven temperature-aware scheduler leverages application-specific knowledge to guide a scheduling technique targeting reducing the spatial temperature gradients that are resulted from the unbalance workload nature of multi-threaded video coding application. The proposed solutions are able to provide up to 10 °C of chip temperature reduction with negligible compression efficiency loss. Besides, when compared with previous works the resulted objective video quality (PSNR) is from 12 dB up to 20 dB higher. Moreover, the proposed scheduler eliminates spatial temperature gradients greater than 5 ºC of multi-core architectures. As conclusion, this thesis demonstrates that leveraging application-specific knowledge and video content properties has a significant potential to improve temperature profiles of video coding systems while still keeping good quality results.

Une zone de constriction dans un micro-canal fluidique peut générer, si le débit est suffisant, un écoulement bi-phasique. Ceci est l’origine de la cavitation hydrodynamique. Les échanges de chaleur latente générés par l’apparition et l’implosion des bulles impliquent une variabilité importante de la température dans les zones au-delà de la constriction. En ajoutant des sondes de température nanométriques dans le fluide et en utilisant un microscope confocal on peut déterminer la température en un point. Ainsi on a pu établir des cartographies thermiques en 2 et 3 dimensions à l’intérieur d’un écoulement stationnaire bi-phasique. La technique permet en outre d’avoir accès à la quantité de gaz ce qui permet de corréler les gradients de température avec les zones de transitions de phases. Des zones de très forts refroidissements sont observées après la constriction, là où les bulles apparaissent. Par contre on n’observe pas les zones d’échauffement attendu à cause de la condensation. Une méthode complémentaire, moins sensible, utilisant la spectroscopie Raman a aussi été utilisée pour confirmer ce résultat. Par ailleurs une nouvelle classe de matériaux luminescents sensible à la température et la pression a été étudiée. Enfin une étude de la production de radicaux lors de l’implosion des bulles a été menée en utilisant la chimiluminescence du luminol. La technique utilisée par comptage de photons a permis de quantifier cette production et une cartographie de l’émission du luminol a permis d’associer celle-ci avec la zone d’implosion des bulles / A constriction in the microchannel can be used to establish a two-phase flow, when a sufficient liquid flux is introduced. This is known as hydrodynamic cavitation. The latent heat resulting from the growing and collapsing vapor bubbles makes it interesting to observe the temperature conditions in the flow downstream of the constriction. Using fluorescence microscopy, with the addition of temperature sensitive nano probes into the working fluid, we can determine the temperature at a single point, averaged over the integration time. Coupled with a confocal microscope, we were able to produce two and three dimensional temperature maps of the steady state flow in the microchannel by the use of ratiometric intensity measurements. This technic allows us to observe temperature gradients in two-phase flow as well yielding the void fraction information. Areas of substantial cooling are observed downstream the constriction in the two-phase flow, linked to the bubble growth, while heating regions due to condensations are missing. A complementary, yet less sensitive probe-less technique using the inherent Raman scattering signal of the liquid, was used to confirm the findings. A separate study evaluating a new group of luminescent materials for optical temperature and pressure probes is performed and discussed herein. Finally, the luminol chemiluminescent reaction with radicals produced by the cavitating flow, is used to obtain a corresponding photon yield. By counting the photons produced, an estimate on the radical yield can be obtained. Additionally, rudimentary mapping of the chemiluminescence signal allows the localization of the bubble collapse regions

Many cutting-edge computer and electronic products are powered by advanced Systems-on-Chip (SoC). Advanced SoCs encompass superb performance together with large number of functions. This is achieved by efficient integration of huge number of transistors. Such very large scale integration is enabled by a core-based design paradigm as well as deep-submicron and 3D-stacked-IC technologies. These technologies are susceptible to reliability and testing complications caused by thermal issues. Three crucial thermal issues related to temperature variations, temperature gradients, and temperature cycling are addressed in this thesis. Existing test scheduling techniques rely on temperature simulations to generate schedules that meet thermal constraints such as overheating prevention. The difference between the simulated temperatures and the actual temperatures is called temperature error. This error, for past technologies, is negligible. However, advanced SoCs experience large errors due to large process variations. Such large errors have costly consequences, such as overheating, and must be taken care of. This thesis presents an adaptive approach to generate test schedules that handle such temperature errors. Advanced SoCs manufactured as 3D stacked ICs experience large temperature gradients. Temperature gradients accelerate certain early-life defect mechanisms. These mechanisms can be artificially accelerated using gradient-based, burn-in like, operations so that the defects are detected before shipping. Moreover, temperature gradients exacerbate some delay-related defects. In order to detect such defects, testing must be performed when appropriate temperature-gradients are enforced. A schedule-based technique that enforces the temperature-gradients for burn-in like operations is proposed in this thesis. This technique is further developed to support testing for delay-related defects while appropriate gradients are enforced. The last thermal issue addressed by this thesis is related to temperature cycling. Temperature cycling test procedures are usually applied to safety-critical applications to detect cycling-related early-life failures. Such failures affect advanced SoCs, particularly through-silicon-via structures in 3D-stacked-ICs. An efficient schedule-based cycling-test technique that combines cycling acceleration with testing is proposed in this thesis. The proposed technique fits into existing 3D testing procedures and does not require temperature chambers. Therefore, the overall cycling acceleration and testing cost can be drastically reduced. All the proposed techniques have been implemented and evaluated with extensive experiments based on ITC’02 benchmarks as well as a number of 3D stacked ICs. Experiments show that the proposed techniques work effectively and reduce the costs, in particular the costs related to addressing thermal issues and early-life failures. We have also developed a fast temperature simulation technique based on a closed-form solution for the temperature equations. Experiments demonstrate that the proposed simulation technique reduces the schedule generation time by more than half.

Esta tese apresenta soluções para o gerenciamento e otimização de temperatura para sistemas de codificação de vídeo baseados nas características da aplicação e no conteúdo dos vídeos digitais. Diferente dos trabalhos estado-da-arte, as soluções propostas nesta tese focam em técnicas de gerenciamento de temperatura no nível da aplicação e características da aplicação codificação de vídeo e as propriedades dos vídeos digitais são explorados para desenvolver soluções termais para a codificação de vídeo com baixas perdas na qualidade de serviço das aplicações. Diversas análises são realizadas considerando a aplicação de codificação de vídeo para entender o comportamento da temperatura durante o processo de codificação para diferentes sequências de vídeo. Com base nos resultados das análises, soluções com diferentes abordagens são propostas para atenuar os efeitos da temperatura nos sistemas de codificação de vídeo. Gerenciamento de temperatura baseado nas características da aplicação para o padrão de codificação HEVC usa uma técnica de seleção de configuração em tempo de execução para manter a temperatura abaixo dos limites seguros de operação com bons resultados de qualidade de vídeo. Otimização de temperatura baseado em computação imprecisa usa aproximações baseadas em conteúdo para reduzir a temperatura de chips executando o HEVC. Um escalonador de tarefas que usa características da aplicação para guiar o escalonamento de threads focando na redução dos gradientes espaciais de temperatura que são resultantes do desbalanceamento natural de cargas entre as threads da aplicação. As soluções propostas são capazes de reduzir em até 10 ºC a temperatura do chip com perdas insignificantes na eficiência de compressão. Os resultados de qualidade objetiva (medida usando PSNR) são de 12 dBs até 20 dBs maiores quando comparados com trabalhos da literatura. Além disso, o escalonador de tarefas proposto é capaz de eliminar os gradientes espaciais de temperatura maiores que 5 ºC para arquitetura multi-cores. Como principal conclusão, esta tese demonstra que as técnicas de gerenciamento de temperatura que usam o conhecimento da aplicação de maneira conjunta com as propriedades dos vídeos digitais tem um alto potencial para melhorar os resultados de temperatura de sistemas de codificação de vídeo mantendo bons resultados de qualidade visual dos vídeos codificados. / This thesis presents application-driven temperature-aware solutions for next generation video coding systems, such as the High Efficiency Video Coding (HEVC). Different from state-of-the-art works, the proposed solutions raise the abstraction of temperature management to the application-level, where video coding characteristics and video content properties are used to leverage thermal-aware solutions for video coding with low QoS (Quality of Service) degradation. Several video coding and temperature analyses are performed to understand the behavior of temperature when encoding different video sequences. Based on the analyses results, different approaches are proposed to mitigate the temperature effects on video coding systems. Application-driven temperature management for HEVC uses run-time encoder configuration selection to keep temperature under safe operational state while providing good visual quality results. Temperature optimization using approximate computing uses content-driven approximations to reduce the on-chip temperature of HEVC encoding. Application-driven temperature-aware scheduler leverages application-specific knowledge to guide a scheduling technique targeting reducing the spatial temperature gradients that are resulted from the unbalance workload nature of multi-threaded video coding application. The proposed solutions are able to provide up to 10 °C of chip temperature reduction with negligible compression efficiency loss. Besides, when compared with previous works the resulted objective video quality (PSNR) is from 12 dB up to 20 dB higher. Moreover, the proposed scheduler eliminates spatial temperature gradients greater than 5 ºC of multi-core architectures. As conclusion, this thesis demonstrates that leveraging application-specific knowledge and video content properties has a significant potential to improve temperature profiles of video coding systems while still keeping good quality results.

Esta tese apresenta soluções para o gerenciamento e otimização de temperatura para sistemas de codificação de vídeo baseados nas características da aplicação e no conteúdo dos vídeos digitais. Diferente dos trabalhos estado-da-arte, as soluções propostas nesta tese focam em técnicas de gerenciamento de temperatura no nível da aplicação e características da aplicação codificação de vídeo e as propriedades dos vídeos digitais são explorados para desenvolver soluções termais para a codificação de vídeo com baixas perdas na qualidade de serviço das aplicações. Diversas análises são realizadas considerando a aplicação de codificação de vídeo para entender o comportamento da temperatura durante o processo de codificação para diferentes sequências de vídeo. Com base nos resultados das análises, soluções com diferentes abordagens são propostas para atenuar os efeitos da temperatura nos sistemas de codificação de vídeo. Gerenciamento de temperatura baseado nas características da aplicação para o padrão de codificação HEVC usa uma técnica de seleção de configuração em tempo de execução para manter a temperatura abaixo dos limites seguros de operação com bons resultados de qualidade de vídeo. Otimização de temperatura baseado em computação imprecisa usa aproximações baseadas em conteúdo para reduzir a temperatura de chips executando o HEVC. Um escalonador de tarefas que usa características da aplicação para guiar o escalonamento de threads focando na redução dos gradientes espaciais de temperatura que são resultantes do desbalanceamento natural de cargas entre as threads da aplicação. As soluções propostas são capazes de reduzir em até 10 ºC a temperatura do chip com perdas insignificantes na eficiência de compressão. Os resultados de qualidade objetiva (medida usando PSNR) são de 12 dBs até 20 dBs maiores quando comparados com trabalhos da literatura. Além disso, o escalonador de tarefas proposto é capaz de eliminar os gradientes espaciais de temperatura maiores que 5 ºC para arquitetura multi-cores. Como principal conclusão, esta tese demonstra que as técnicas de gerenciamento de temperatura que usam o conhecimento da aplicação de maneira conjunta com as propriedades dos vídeos digitais tem um alto potencial para melhorar os resultados de temperatura de sistemas de codificação de vídeo mantendo bons resultados de qualidade visual dos vídeos codificados. / This thesis presents application-driven temperature-aware solutions for next generation video coding systems, such as the High Efficiency Video Coding (HEVC). Different from state-of-the-art works, the proposed solutions raise the abstraction of temperature management to the application-level, where video coding characteristics and video content properties are used to leverage thermal-aware solutions for video coding with low QoS (Quality of Service) degradation. Several video coding and temperature analyses are performed to understand the behavior of temperature when encoding different video sequences. Based on the analyses results, different approaches are proposed to mitigate the temperature effects on video coding systems. Application-driven temperature management for HEVC uses run-time encoder configuration selection to keep temperature under safe operational state while providing good visual quality results. Temperature optimization using approximate computing uses content-driven approximations to reduce the on-chip temperature of HEVC encoding. Application-driven temperature-aware scheduler leverages application-specific knowledge to guide a scheduling technique targeting reducing the spatial temperature gradients that are resulted from the unbalance workload nature of multi-threaded video coding application. The proposed solutions are able to provide up to 10 °C of chip temperature reduction with negligible compression efficiency loss. Besides, when compared with previous works the resulted objective video quality (PSNR) is from 12 dB up to 20 dB higher. Moreover, the proposed scheduler eliminates spatial temperature gradients greater than 5 ºC of multi-core architectures. As conclusion, this thesis demonstrates that leveraging application-specific knowledge and video content properties has a significant potential to improve temperature profiles of video coding systems while still keeping good quality results.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-27T17:30:21Z No. of bitstreams: 1 JAILSON ALVES DA NÓBREGA - DISSERTAÇÃO PPGEM 2014..pdf: 8059019 bytes, checksum: 3342c79a6597e27674ae52970211493c (MD5) / Made available in DSpace on 2018-04-27T17:30:21Z (GMT). No. of bitstreams: 1 JAILSON ALVES DA NÓBREGA - DISSERTAÇÃO PPGEM 2014..pdf: 8059019 bytes, checksum: 3342c79a6597e27674ae52970211493c (MD5) Previous issue date: 2014-12-03 / Capes / Muitas são as variações metalúrgicas sofridas pelo material quando o mesmo é submetido a um ciclo térmico de soldagem, exercendo uma considerável influência sobre as suas propriedades mecânicas e mais especificamente sobre os níveis de tensões residuais. Na fase de projeto, uma dessas alternativas para a avaliação dos ciclos térmicos e tensões residuais de soldagem é o emprego de simulação via métodos computacionais. A partir disto, neste trabalho foi desenvolvida uma metodologia numérica para determinar o campo de temperatura e tensões residuais transversais em juntas soldadas. As simulações numéricas foram realizadas por meio de um software comercial, ABAQUS®, baseado no Método de Elementos Finitos (MEF). Foram considerados fenômenos que fazem a modelagem matemática do processo de soldagem de forma a torná-la mais robusta. Foi utilizada a fonte de calor analítica proposta por Goldak, capaz de modelar a entrada de calor. Foram avaliados os parâmetros de entrada, tais como: Corrente, voltagem, velocidade de soldagem e temperatura inicial da chapa virtual. Para validação dos resultados térmicos, foi utilizada uma chapa virtual do aço API 5L X70 soldada pelo processo FCAW. Nas demais simulações térmicas e mecânicas foram utilizadas uma chapa virtual do aço API 5L X80 soldadas pelos processos GTAW e SMAW. Foi possível observar neste estudo a influência da temperatura de pré-aquecimento e de interpasse sobre os gradientes térmicos e ciclos térmicos na junta soldada, além das mudanças nos valores das temperaturas de pico e do tempo de resfriamento entre 800 e 500 °C (∆t8/5) quando avaliados em diferentes regiões da junta soldada. Com relação às tensões residuais transversais, verificaram-se mudanças no perfil destas tensões quando aplicado mais de um passe da soldagem virtual podendo o modelo servir de base para trabalhos futuros. / Many are the metallurgical variations suffered by the material when it is subjected to a weld thermal cycle, which promote a considerable influence on mechanical properties, and specifically on the welded joint residual stresses. In the project phase, one of these alternatives is the use of computational methods via simulation. So, in this work a numerical methodology to determine the temperature field and transverse residual stresses was developed. The numerical simulations were implemented using a commercial software ABAQUS® based on finite element method (FEM). In addition, a source of heat proposed by Goldak, able to model the heat input value was used. Input parameters, such as: Current, voltage, speed and initial temperature of the virtual plate were also evaluated. To validate the thermal results and the other thermal and mechanical simulations a virtual plate of API 5L X70 and API 5L X-80 steel welded by the FCAW and GTAW and SMAW processes respectively was used. The results showed that it was possible to evaluate the influence of preheat and interpass temperature on the weld thermal gradients and thermal cycling, as well as the change in peak temperature and cooling time between 800 and 500 (∆t8/5) values in different regions of the welded joint. In relation to the transverse residual stresses, it was showed that there were changes in its profile when it was applied more than one weld pass which can serve as base model for future work in this area.

[EN] This Thesis is focused on the development and implementation of efficient numerical methods for the acoustic modelling and design of noise control devices in the exhaust system of combustion engines. Special attention is paid to automotive perforated dissipative silencers, in which significant differences are likely to appear in their acoustic behaviour, depending on the temperature variations within the absorbent material. Also, material heterogeneities can alter the silencer attenuation performance. Therefore, numerical techniques considering all these features are required to guarantee the accuracy of the results. A literature review is carried out, mainly related to one-dimensional models, as well as to acoustic models for absorbent materials and perforated surfaces. However, plane wave model limitations make indispensable using alternative multidimensional methods. In addition, the possibility of using new acoustic elements is explored. These elements have as an objective being a potential alternative to the fibrous absorbent materials, which can have a negative impact on health. The Thesis considers the use of microperforated and sintered surfaces. The latter have, in some cases, a nearly constant acoustic impedance, whose value depends, among others, on the thickness and porosity of the plates. To avoid the limitations of plane wave models, a finite element (FE) approach is proposed for the acoustic analysis of dissipative silencers including a perforated duct with uniform axial mean flow and an outer chamber with a heterogeneous distribution of the absorbent material. On the other hand, property variations can be also produced by temperature gradients. In this case, a hybrid FE model has been derived for perforated dissipative silencers including: (1) Thermal gradients in the central duct and the chamber; (2) A perforated passage carrying non-uniform axial mean flow. A FE approach has been implemented to solve the pressure-based wave equation for a non-moving heterogeneous medium, associated with the chamber. Also, the governing equation in the central duct has been written and solved in terms of an acoustic velocity potential to allow the presence of an axially inhomogeneous flow. The coupling between both regions has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects. It has been found that the presence of non-homogeneities can have a significant influence on the acoustic attenuation of a silencer and should be included in the theoretical models. Optimization techniques for industrial noise control devices are relevant, since they lead to the production of elements with better characteristics. Evolutionary algorithms are emergent techniques able to obtain a solution, even in those problems in which the traditional optimization have difficulties. Optimization techniques are combined with the FE method to achieve the maximum attenuation in the frequency range of interest. A multichamber silencer optimization problem is defined and several analyses are carried out to obtain the most suitable configuration for each application. Under certain assumptions of axial uniformity, several techniques have been considered to reduce the computational effort of a full 3D FE analysis for dissipative silencers with temperature gradients and mean flow. These are based on a decomposition of the acoustic field into transversal and axial modes within each silencer subdomain, and a matching procedure of the modal expansions at the silencer area changes through the continuity conditions of the acoustic fields. The relative computational efficiency and accuracy of predictions for the matching techniques are studied, including point collocation at nodes and Gauss points and also mode-matching with weighted integration. All of them provide accurate predictions of the attenuation and improve the computational cost of a FE calculation / [ES] Esta Tesis se centra en el desarrollo e implementación de métodos numéricos eficientes para el diseño y modelado de componentes de la línea de escape en motores de combustión interna. Merecen especial atención los silenciadores disipativos perforados de automóviles, ya que su comportamiento acústico puede sufrir variaciones importantes debidas a las variaciones de temperatura en el material absorbente, así como a las heterogeneidades de la fibra. Por tanto, se requieren técnicas numéricas que consideren estos casos para garantizar la precisión de los resultados. Se lleva a cabo una revisión bibliográfica que recoge los modelos de onda unidimensionales, así como modelos acústicos de materiales absorbentes y superficies perforadas. Sin embargo, las limitaciones de los primeros hacen indispensable el uso de modelos multidimensionales. Además se explora la posibilidad de usar nuevos elementos acústicos, cuyo objetivo es ser una alternativa potencial a los materiales absorbentes, que pueden tener un efecto negativo sobre la salud. La Tesis considera el uso de superficies microperforadas y sinterizadas. Estas últimas en algunos casos presentan una impedancia casi constante, cuyo valor depende, entre otras cosas, del espesor y la porosidad de las placas. Para evitar las limitaciones de los modelos de onda plana, se propone un enfoque en elementos finitos (EF) para el análisis acústico de silenciadores disipativos que incluyen un conducto con flujo medio axial uniforme y una cámara externa con una distribución heterogénea de material absorbente. Por otro lado, la variación de las propiedades también puede producirse por gradientes térmicos. En este caso, se propone una formulación híbrida de EF para silenciadores disipativos perforados que incluye: (1) Gradientes térmicos en el conducto central y la cámara; (2) Un conducto perforado que canaliza flujo medio axial no uniforme. Se ha implementado una formulación de EF para resolver la ecuación de ondas en términos de presión para el medio estacionario heterogéneo asociado a la cámara. Además, la ecuación asociada al conducto central, expresada en términos de potencial de velocidad acústica, permite la presencia de flujo axial no uniforme. El acoplamiento entre ambas regiones se ha realizado mediante un conducto perforado y su impedancia acústica y se ha adaptado para incluir la citada falta de homogeneidad. Se ha visto que las heterogeneidades pueden influir notablemente en la atenuación acústica de un silenciador, debiéndose incluir en los modelos teóricos. Las técnicas de optimización para componentes industriales de control de ruido son importantes, ya que producen elementos con mejores características. Los algoritmos evolutivos son técnicas emergentes capaces de obtener una solución, incluso cuando la optimización tradicional tiene dificultades. Las técnicas de optimización se combinan con el MEF para conseguir la máxima atenuación posible en el rango de frecuencias de interés. Se ha definido un problema de optimización de un silenciador multicámara y se han llevado a cabo varios análisis para obtener la configuración más adecuada para cada caso. Bajo ciertas hipótesis de uniformidad axial, se han considerado varias técnicas para reducir el coste computacional de un análisis 3D completo para silenciadores disipativos con gradientes de temperatura y flujo medio. Éstas se basan en la descomposición del campo acústico en modos axiales y transversales dentro de cada subdominio, y un procedimiento de acoplamiento de las expansiones modales en los cambios de sección del silenciador mediante las condiciones de continuidad de los campos acústicos. Se estudia la eficiencia computacional y precisión de las predicciones de las técnicas de acoplamiento, incluyendo colocación puntual en nodos y puntos de Gauss, así como ajuste modal. Todos ellos proporcionan predicciones precisas de la atenuación mejorando el coste / [CAT] Aquesta Tesi es centra en el desenvolupament i implementació de mètodes numèrics eficients per al disseny i modelatge de components de la línia d'escapament en motors de combustió interna. Mereixen especial atenció els silenciadors dissipatius perforats d'automòbils, ja que el seu comportament acústic pot patir variacions importants degudes a les variacions de temperatura en el material absorbent, així com a les heterogeneïtats de la fibra. Per tant, es requereixen tècniques numèriques que considerin aquests casos per garantir la precisió dels resultats. Es porta a terme una revisió bibliogràfica que recull els models d'ona unidimensionals, així com models acústics de materials absorbents i superfícies perforades. No obstant això, les limitacions dels primers fan indispensable l'ús de models multidimensionals. A més s'explora la possibilitat d'usar nous elements acústics amb l'objectiu que siguen una alternativa potencial als materials absorbents, que poden tenir un efecte negatiu sobre la salut. La Tesi considera l'ús de superfícies microperforades i sinteritzades. Aquestes últimes en alguns casos presenten una impedància gairebé constant. El seu valor depèn, entre altres coses, del gruix i la porositat de les plaques. Per evitar les limitacions dels models d'ona plana, es proposa un enfocament amb elements finits (EF) per a l'anàlisi acústic de silenciadors dissipatius que inclouen un conducte amb flux mig axial uniforme i una càmera externa amb una distribució heterogènia de material absorbent. D'altra banda, la variació de les propietats també es pot produir per gradients tèrmics. En aquest cas, es proposa una formulació híbrida d'EF per silenciadors dissipatius perforats que inclou: (1) Gradients tèrmics en el conducte central i la càmera; (2) Un conducte perforat que canalitza flux mig axial no uniforme. S'ha implementat una formulació d'EF per resoldre l'equació d'ones en termes de pressió per al medi estacionari heterogeni associat a la càmera. A més, l'equació associada al conducte central, expressada en termes de potencial de velocitat acústica, permet la presència de flux axial no uniforme. L'acoblament entre les dues regions s'ha realitzat mitjançant un conducte perforat i la seva impedància acústica i s'ha adaptat per incloure la esmentada falta d'homogeneïtat. S'ha vist que les heterogeneïtats poden influir notablement en l'atenuació acústica d'un silenciador i s'han d'incloure en els models teòrics. Les tècniques d'optimització per a components industrials de control de soroll són importants, ja que produeixen elements amb millors característiques. Els algoritmes evolutius són tècniques emergents capaces d'obtenir una solució, fins i tot quan l'optimització tradicional té dificultats. Les tècniques d'optimització es combinen amb el mètode d'elements finits (MEF) per aconseguir la màxima atenuació possible en el rang de freqüències d'interès. S'ha definit un problema d'optimització d'un silenciador multicàmera i s'han dut a terme diverses anàlisis per obtenir la configuració més adequada per a cada cas. Sota certes hipòtesis d'uniformitat axial, s'han considerat diverses tècniques per reduir el cost computacional d'una anàlisi 3D complet per silenciadors dissipatius amb gradients de temperatura i flux mig. Aquestes es basen en la descomposició del camp acústic en modes axials i transversals dins de cada subdomini, i un procediment d'acoblament de les expansions modals en els canvis de secció del silenciador mitjançant les condicions de continuïtat dels camps acústics. S'estudia l'eficiència computacional i precisió de les prediccions de les tècniques d'acoblament, incloent col·locació puntual en nodes i punts de Gauss, així com ajust modal. Tots ells proporcionen prediccions precises de l'atenuació millorant el cost computacional d'EF. / Sánchez Orgaz, EM. (2016). Advanced numerical techniques for the acoustic modelling of materials and noise control devices in the exhaust system of internal combustion engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/64090 / TESIS