Development of Methodologies for the Estimation of Thermal Properties Associated with Aerospace Vehicles

A thermal stress analysis is an important aspect in the design of aerospace structures and vehicles such as the High Speed Civil Transport (HSCT) at the National Aeronautics and Space Administration Langley Research Center (NASA-LaRC). These structures are complex and are often composed of numerous components fabricated from a variety of different materials. The thermal loads on these structures induce temperature variations within the structure, which in turn result in the development of thermal stresses. Therefore, a thermal stress analysis requires knowledge of the temperature distributions within the structures which consequently necessitates the need for accurate knowledge of the thermal properties, boundary conditions and thermal interface conditions associated with the structural materials. The goal of this proposed multi-year research effort was to develop estimation methodologies for the determination of the thermal properties and interface conditions associated with aerospace vehicles. Specific objectives focused on the development and implementation of optimal experimental design strategies and methodologies for the estimation of thermal properties associated with simple composite and honeycomb structures. The strategy used in this multi-year research effort was to first develop methodologies for relatively simple systems and then systematically modify these methodologies to analyze complex structures. This can be thought of as a building block approach. This strategy was intended to promote maximum usability of the resulting estimation procedure by NASA-LARC researchers through the design of in-house experimentation procedures and through the use of an existing general purpose finite element software

A Comparative Analysis of Darwinian Asexual and Sexual Reproduction in Evolutionary Robotics

Evolutionary Robotics systems draw inspiration from natural evolution to solve the problem of robot design. A key moment in the evolutionary process is reproduction, when the genotype of one or more parents is inherited by their offspring. Existent approaches have used both sexual and asexual reproduction but a comparison between the two is still missing. In this work, we study the effects of sexual and asexual reproduction on the controllers of an Evolutionary Robotics system. In our system, both morphologies and controllers are jointly evolved to solve two separate tasks. We adopt the Triangle of Life framework, in which the controllers go through a phase of learning before reproduction. Using extensive simulations we show that sexual reproduction of the robots' brains is preferable over asexual reproduction as it obtains better robots in terms of fitness. Moreover, we show that sexually reproducing robots present different morphologies and behaviors than the asexually reproducing ones, even though the reproduction mechanism only affects their brains. Finally, we study the effects of the reproduction mechanism on the robots' learning capabilities. By measuring the difference between the inherited and the learned brain we find that robots that evolved using sexual reproduction have better inherited brains and are also better learners

Projeto ótimo de neutralizadores dinâmicos com múlitplos graus de liberdade considerando os parâmetros físicos, localização e material viscoelástico

Orientador: Prof. Dr. Carlos Alberto BavastriTese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Mecânica. Defesa : Curitiba, 10/04/2019Inclui referências: p. 131-142Área de concentração: Mecânica dos Sólidos e VibraçõesResumo: Neutralizadores dinâmicos de vibração, também chamados de absorvedores dinâmicos de vibração, são dispositivos ressonantes que, ao serem fixados em uma estrutura mecânica, conseguem reduzir as vibrações. O projeto desse tipo de dispositivo, utilizando materiais viscoelásticos, é de baixo custo, fácil construção e produz excelentes resultados na redução dos níveis de vibração devido à capacidade daqueles materiais em armazenar e dissipar a energia de vibração. Entretanto, projetá-lo de maneira adequada indicará o seu sucesso no controle da vibração. Nos últimos 20 anos, o grupo de pesquisa GVIBS da UFPR/CNPq tem trabalhado no projeto ótimo de neutralizadores simples, aplicados no controle de vibração em banda estreita e banda larga de frequências. Neste contexto, o presente estudo visa desenvolver uma metodologia de projeto ótimo de neutralizadores dinâmicos viscoelásticos de um e de múltiplos graus de liberdade considerando os parâmetros físicos, a posição do dispositivo na estrutura e o material viscoelástico ótimo como variáveis a serem otimizadas, para uma dada temperatura de trabalho e para uma determinada banda de frequências. A configuração ótima é obtida através de Algoritmos Genéticos (AG) considerando variáveis contínuas e discretas no mesmo vetor de projeto. Inicialmente, a metodologia de projeto ótimo de neutralizadores é implementada para o modelo de neutralizador simples e aplicada no controle de vibração, em banda larga de frequências, de uma placa de aço apoiada em seus quatro cantos. Os resultados mostram que esta metodologia é interessante e robusta para o controle de vibração de estruturas geometricamente complexas. Agregando a esta metodologia o projeto ótimo de um neutralizador de múltiplos graus de liberdade, as propriedades dinâmicas do neutralizador passam a ser descritas por matrizes de tamanhos consideráveis, que estão associadas ao número de graus de liberdade considerados na modelagem do neutralizador. A obtenção dessas matrizes é realizada utilizando o método dos elementos finitos via software ANSYS e as características dinâmicas do material viscoelástico são introduzidas no modelo através de uma metodologia própria utilizando o software Matlab. Para validar a metodologia proposta, uma análise numérica é aplicada para o controle de uma viga de aço engastada-livre. Com os parâmetros de projeto ótimos fornecidos pelo algoritmo, o neutralizador pode ser construído e inserido na viga para a realização do experimento. O resultado mostra que o modelo numérico é muito semelhante ao experimental, logo esta metodologia pode ser reproduzida fisicamente. O presente estudo apresenta três modelos de neutralizadores de múltiplos graus de liberdade: viga sanduíche, viga sanduíche com massa de sintonização na extremidade livre modelada por elementos finitos, e viga sanduíche com massa concentrada na extremidade livre. Os resultados numéricos para o controle da viga de aço engastada livre são comparados com o modelo de um grau de liberdade, mostrando que os três modelos de neutralizadores de múltiplos graus de liberdade reduzem a vibração da viga de forma mais eficiente que o neutralizador simples. Os resultados apresentados mostram que a metodologia proposta é promissora para o controle passivo de vibração de estruturas, especialmente quando muitos modos estão presentes. Palavras-chave: Controle passivo de vibrações. Neutralizadores dinâmicos. viscoelásticos de múltiplos graus de liberdade. Otimização. Algoritmos genéticos.Abstract: Dynamic vibration neutralizers, also called dynamic vibration absorbers, are mechanical devices attached to a structure aiming at controlling or reducing vibration levels. Designing such devices using viscoelastic materials result in low costs, easy construction, and produce excellent results in the vibration reduction levels due to their ability to dissipate vibration energy. However, their suitable design will indicate their success in the vibration control. In the last 20 years, the research group GVIBS from the UFPR/CNPq, has been working in the optimal design of simple neutralizers, applied to vibration control in both narrow and broad bands of frequency. In this context, the present study aims at developing a methodology for an optimal design of DVNs with one and multiple degrees-of-freedom considering the physical parameters, the positions to attach them onto the structure, and the viscoelastic materials as variables to be optimized, for a given working temperature and for a determined frequency band. The optimal configuration is obtained through Genetic Algorithms (GA) considering continuous and discrete variables in the same design vector. Initially, the methodology of optimal design of the neutralizers is implemented to a simple neutralizer model applied to vibration control, in a broadband of frequency, of a simplysupported steel plate its four corners. The results show that this methodology is interesting and robust to handle the vibration control of geometrically complex structures. Adding to this methodology the optimal design of a multi-degrees-offreedom neutralizer, the dynamic properties of the neutralizer are described by matrices of considerable sizes, which are associated to the number of degrees-offreedom considered in the neutralizer modeling. The obtaining of those matrices for the metallic part is carried out using the finite element method through the ANSYS software and the dynamic characteristics of the viscoelastic material are introduced to the model through an own methodology using the Matlab software. To validate the methodology of optimal design of multi-degree-of-freedom viscoelastic neutralizers, a numerical analysis is applied to the control a clamped steel beam. With the parameters of optimal design provided by the algorithm, the neutralizer can be built and attached to the beam for the experiment. The results show that the numerical model is very similar to the experimental one, thus this methodology can be reproduced physically. The present study shows three models of multi-degree-of-freedom neutralizers: sandwich beam, sandwich beam with a tuning mass modeled by finite elements and sandwich beam with a concentrated mass in the free end. Both models are able to handle the vibration control and the numerical results to the clamped steel beam control are compared with those of the one degree-of-freedom model, showing that all the three models of multi-degree-of-freedom neutralizers reduce the beam vibration more efficiently than the simple neutralizer. The results also show that the methodology is promising for passive vibration control of structures, especially when many modes are present. Keywords: Passive vibration control. Multi-degrees-of-freedom dynamic viscoelastic neutralizers. Optimization. Genetic algorithms