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A spacecraft is subjected to dynamic and static loads during launch. These loads are deterministic and of random nature and cannot be tested under the real conditions due to cost considerations. The spacecraft must therefore sustain certain mechanical loads without permanent deformation with a certain safety factor due to the uncertainties in the actual loading values during launch. The applicable mechanical test requirements and load combination have been first determined for the structure of interest: the SEAM CubeSat. These requirements are found to be steady-state accelerations, random vibration and shock response spectrum loadings. They have been simulated onto the structure globally and locally in order to extract stress values, amend design features when necessary and determine adequate material properties in order for the final design to fulfill the mechanical requirements during launch. / En satellit utsätts för dynamiska och statiska belastningar under uppskjutningen. Dessa laster är av deterministisk och av slumpmässig natur och kan inte testas under verkliga förhållanden på grund av kostnadsskäl. Satellitens konstruktion måste därför klara att utsättas för utan permanent deformation med en viss säkerhetsfaktor på grund av osäkerheter i de faktiska belastningarna under uppskjutningen. Mekaniska provningskrav och lastkombinationer har bestämts för en utvald struktur: SEAM CubeSat. Dessa krav visar sig vara accelerationer, slumpmässiga vibrationer och stötar. Strukturen har simulerats globalt och lokalt för att få fram de mekaniska belastningarna. Baserat på resultat från simuleringarna har konstruktionen modifierats och lämpliga material egenskaper har bestämts för att den slutliga konstruktionen ska uppfylla de mekaniska kraven under uppskjutningen.

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CubeSats, specially the 6U standard, is nowadays the tendency where many developers point towards. The upscaling size of the standard and payloads entail the increase of the satellite overall mass. Composite materials have demonstrated the ability to fulfill expectations like reducing structural masses, having been applied to different types of spacecraft, including small satellites. This Thesis is focused on designing, manufacturing, and dynamic testing of a 6U CubeSat made of carbon fiber, fiberglass, and aluminum. The main objective of this study was obtaining a mass reduction of a 6U CubeSat structure, maintaining the stiffness and strength. Considering the thermal effects of the used materials an outgassing test of the used materials was performed and the experimental results are presented. The CubeSat structure was entirely manufactured and tested at Cal Poly Aerospace Engineering Department facilities. A mechanical shock test and random vibration test were performed using a shock table and a shake table respectively. Results of both tests are presented. A correlation between the Experimental data and the Finite Element Model of the satellite was carried out. Finally, a comparison between 6U structure studied and aluminum 6U structures available in the market is presented.

No / The causal and physically realizable Biot hysteretic model proves to be the simplest linear model able to describe the nearly rate-independent behaviour of engineering materials. In this paper, the performance of the Biot hysteretic model is analysed and compared with those of the ideal and causal hysteretic models. The Laguerre polynomial approximation (LPA) method, recently proposed for the time-domain analysis of linear viscoelastic systems, is then summarized and applied to the prediction of the dynamic response of linear hysteretic systems to deterministic and random excitations. The parameters of the LPA model generally need to be computed through numerical integrals; however, when this model is used to approximate the Biot hysteretic model, closed-form expressions can be found. Effective step-by-step procedures are also provided in the paper, which prove to be accurate also for high levels of damping. Finally, the method is applied to the dynamic analysis of a highway embankment excited by deterministic and random ground motions. The results show that in some cases the inaccuracy associated with the use of an equivalent viscous damping model is too large.

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There is a need to investigate and improve upon existing methods to predict response of sensors due to flow-induced vibrations in a pipe flow. The aim was to develop a tool which would enable an engineer to quickly evaluate the suitability of a particular design for a certain pipe flow application, without sacrificing fidelity. The primary methods, found in guides published by the American Society of Mechanical Engineers (ASME), of simple response prediction of sensors were found to be lacking in several key areas, which prompted development of the tool described herein. A particular limitation of the existing guidelines deals with complex stochastic stationary and non-stationary modeling and required much further study, therefore providing direction for the second portion of this body of work. A tool for response prediction of fluid-induced vibrations of sensors was developed which allowed for analysis of low aspect ratio sensors. Results from the tool were compared to experimental lift and drag data, recorded for a range of flow velocities. The model was found to perform well over the majority of the velocity range showing superiority in prediction of response as compared to ASME guidelines. The tool was then applied to a design problem given by an industrial partner, showing several of their designs to be inadequate for the proposed flow regime. This immediate identification of unsuitable designs no doubt saved significant time in the product development process. Work to investigate stochastic modeling in structural dynamics was undertaken to understand the reasons for the limitations found in fluid-structure interaction models. A particular weakness, non-stationary forcing, was found to be the most lacking in terms of use in the design stage of structures. A method was developed using the Karhunen Loeve expansion as its base to close the gap between prohibitively simple (stationary only) models and those which require too much computation time. Models were developed from SDOF through continuous systems and shown to perform well at each stage. Further work is needed in this area to bring this work full circle such that the lessons learned can improve design level turbulent response calculations. / Ph. D.

Accelerated durability testing of automotive components has become a major interest as it may predict the life characteristics of the vehicle by testing fatigue failure at higher stress level within a shorter period of time. In this work, a specially designed sub-scaled experimental testing bed with the rigid and elastic supports of a simply supported beam was designed and built to compare the effects of the elastic foundation on the change of modal parameters of the tested structure which was later used to tune the FE model. Afterwards, the accelerated loading profiles of both sine sweep and random vibration were applied on the FE model to compare the deviation of the cumulative fatigue damage between the elastic and rigid supports. This work reveals a significant amount of inaccuracy in the current laboratory testing system where the dynamic properties of the tested structure are not maintained close to the real situation. / October 2016

L’étude analytique proposée porte sur le comportement en vibration de nanotubes de carbone et de nanoplaques de graphène. Pour ce faire, il s’agira dans un premier temps d’étudier les traditionnelles théories de Bresse-Timoshenko pour les poutres et de Uflyand-Mindlin pour les plaques. Des modèles de cisaillement alternatifs sont développés, notamment basés sur des approches asymptotiques issues du milieu élastique tri-dimensionnel. Les interactions interatomiques, ne pouvant pas être négligées à une échelle nanoscopique, seront ensuite prises en compte dans les modèles à travers la présence de paramètres non locaux. Ainsi, différentes approches continues seront considérées : phénoménologiques, asymptotiques et continualisées. Ce dernier type d’approche est récent et est basé sur le développement de modèles continus à partir des équations discrètes de poutres et plaques épaisses et de l’utilisation des approximants de Padé et des développements en séries de Taylor. Pour chaque modèle développé au cours de cette étude, les fréquences propres seront déterminées pour différentes conditions aux limites. Il s’agira ainsi de définir le meilleur cadre pour l’utilisation de chaque modèle et de déterminer l’éventuelle supériorité d’un modèle sur les autres. / This thesis deals with the analytical study of vibration of carbon nanotubes and graphene plates. First, a brief overview of the traditional Bresse-Timoshenko models for thick beams and Uflyand- Mindlin models for thick plates will be conducted. It has been shown in the literature that the conventionally utilized mechanical models models overcorrect the shear effect and that of rotary inertia. To improve the situation, two alternative versions of theories of beams and plates are proposed. The first one is derived through the use of equilibrium equations and leads to a truncated governing differential equation in displacement. It is shown, by considering a power series expansion of the displacement, that this is asymptotically consistent at the second order. The second theory is based on slope inertia and results in the truncated equation with an additional sixth order derivative term. Then, these theories will be extended in order to take into account some scale effects such as interatomic interactions that cannot be neglected for nanomaterials. Thus, different approaches will be considered: phenomenological, asymptotic and continualized. The basic principle of continualized models is to build continuous equations starting from discrete equations and by using Taylor series expansions or Padé approximants. For each of the different models derived in this study, the natural frequencies will be determined, analytically when the closed-form solution is available, numerically when the solution is given through a characteristic equation. The objective of this work is to compare the models and to establish the eventual superiority of a model on others.

Neste trabalho, é apresentado um modelo aperfeiçoado para gerar carregamentos dinâmicos pseudo-aleatórios para modelos estruturais sob excitação sísmica e de vento. Este é baseado no modelo de vento sintético proposto por Franco, diferindo pelo fato que usa a transformada de wavelet harmônica ao invés da série de Fourier, pois tem como objetivo descrever um comportamento não estacionário com a ajuda de uma função temporal. Para testar a qualidade do sinal desenvolvido neste trabalho, este foi comparado com sinais verdadeiro, das acelerações de sismos ocorrido na cidade de Hachinohe, no Japão e em El-centro, na Califórnia, e com um sinal gerado pelo modelo do sismo sintético de Corbani, este também baseado no modelo de vento sintético, com o uso de séries de Fourier. Em todas as análises feitas, foi mostrando que embora a geração de carregamentos com transformadas de wavelet harmônica seja mais complexa, esta possui um bom potencial para gerar carregamentos mais próximos da realidade do que métodos usuais baseados em carregamentos estacionários. / In this work is intruduced a improve model to create random loads to use in structural models under sismic and wind disturbance. The model is based on synthetic wind model intends by Franco, differing by the fact that applies harmonic wavelet transform instead of Fourier series, because it has the goal to describe a non stationary behavior with temporal function support. To test the quality from the signal developed in this work, it has been analyzed against true seismic acceleration signal that occurs from Hachinohe city in Japan and El-centro city in California, and with the synthetic seismic model developed by Corbani, that one descending on synthetic wind model, with Fourier series application. In all analysis, although loading creation with harmonic wavelet transform have been more sophisticated, that one has a great potencial to creat loading closer to the fact than usual methods based in stationary loading.