No Brasil é comum a utilização de barras tubulares com extremidades estampadas na confecção das treliças metálicas espaciais, uma vez que representam uma significativa redução de custos, quando comparado a sistemas mais elaborados, devido a sua simplicidade de fabricação e montagem, entretanto trata-se aparentemente de um sistema precário do ponto de vista estrutural, merecendo estudos que estabeleçam critérios para uma utilização segura. Neste trabalho são apresentadas análises teóricas e experimentais destas estruturas, onde foi analisada a situação construtiva usual de treliça com nós típicos (extremidade das barras estampadas, sobrepostas e unidas por um único parafuso), e com nós de aço (sistema de conexão formado por uma peça com aletas de aço soldadas). Os resultados experimentais foram obtidos em ensaios de quatro protótipos que simulam um trecho de treliça espacial, constituídos por uma malha quadrada sobre quadrada, composta de nove módulos piramidais de 2,5 x 2,5 x 1,5 (m), totalizando uma estrutura com dimensões iguais a 7,5 x 7,5 x 1,5 (m), apoiada por colunas nos vértices, permitindo comparar a rigidez, o modo de falha e a resistência entre estes protótipos. A análise teórica dos protótipos foi feita admitindo-se os casos de linearidade e também de não linearidade física e geométrica, levando-se em consideração a variação de inércia das barras junto aos nós. / In Brazil the use of tubular bars with stamping extremities is common in space steel structures, as it means a significant reduction of cost, when caompared with more elaborete system, due to its simplicity of manufacture and assembly. However it is apparently an uncertain system from a structural point of view, which requires studies establishing safe utilization criteria. This paper presents theorical and experimental analysis of this structures. The usual constructive situation of space structure with \'nós típicos\' (bars with flattened ends, superposed and connected by a unique bolt), and \'nós de aço\' (connection system formed by a piece with steel fin welded) was studied. The experimental results were obtained in tests of four prototypes which simulated a section of space structure composed of a mesh squareon- square, with nine 2.5 x 2.5 x 1.5 (m) pyramidal modules, totaliing a structure with 7.5 x 7.5 x 1.5 (m) dimensions, supported by columns in their vertices, permiting to compare the stiffness, the failure manner and the resistance of this prototypes. The theorical analysis of prototypes was carried out by assuming the cases of linearity and physical and geometric non-linearity, taking into consideration the variation of stiffness of the bars next to the nodes.

MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / Includes bibliographical references. / by Jeffrey Hastings Lang. / Ph.D.

No Brasil é comum a utilização de barras tubulares com extremidades estampadas na confecção das treliças metálicas espaciais, uma vez que representam uma significativa redução de custos, quando comparado a sistemas mais elaborados, devido a sua simplicidade de fabricação e montagem, entretanto trata-se aparentemente de um sistema precário do ponto de vista estrutural, merecendo estudos que estabeleçam critérios para uma utilização segura. Neste trabalho são apresentadas análises teóricas e experimentais destas estruturas, onde foi analisada a situação construtiva usual de treliça com nós típicos (extremidade das barras estampadas, sobrepostas e unidas por um único parafuso), e com nós de aço (sistema de conexão formado por uma peça com aletas de aço soldadas). Os resultados experimentais foram obtidos em ensaios de quatro protótipos que simulam um trecho de treliça espacial, constituídos por uma malha quadrada sobre quadrada, composta de nove módulos piramidais de 2,5 x 2,5 x 1,5 (m), totalizando uma estrutura com dimensões iguais a 7,5 x 7,5 x 1,5 (m), apoiada por colunas nos vértices, permitindo comparar a rigidez, o modo de falha e a resistência entre estes protótipos. A análise teórica dos protótipos foi feita admitindo-se os casos de linearidade e também de não linearidade física e geométrica, levando-se em consideração a variação de inércia das barras junto aos nós. / In Brazil the use of tubular bars with stamping extremities is common in space steel structures, as it means a significant reduction of cost, when caompared with more elaborete system, due to its simplicity of manufacture and assembly. However it is apparently an uncertain system from a structural point of view, which requires studies establishing safe utilization criteria. This paper presents theorical and experimental analysis of this structures. The usual constructive situation of space structure with \'nós típicos\' (bars with flattened ends, superposed and connected by a unique bolt), and \'nós de aço\' (connection system formed by a piece with steel fin welded) was studied. The experimental results were obtained in tests of four prototypes which simulated a section of space structure composed of a mesh squareon- square, with nine 2.5 x 2.5 x 1.5 (m) pyramidal modules, totaliing a structure with 7.5 x 7.5 x 1.5 (m) dimensions, supported by columns in their vertices, permiting to compare the stiffness, the failure manner and the resistance of this prototypes. The theorical analysis of prototypes was carried out by assuming the cases of linearity and physical and geometric non-linearity, taking into consideration the variation of stiffness of the bars next to the nodes.

Made available in DSpace on 2016-04-16T00:15:22Z (GMT). No. of bitstreams: 7 Andre Luiz Ribeiro1.pdf: 2358539 bytes, checksum: 96b1600fbc289e03678f8980b8a90e1f (MD5) Andre Luiz Ribeiro2.pdf: 2257374 bytes, checksum: ec3d0b885fe685d218d41626070c7b77 (MD5) Andre Luiz Ribeiro3.pdf: 2676248 bytes, checksum: e640f67173bf7beed608261d65377cd8 (MD5) Andre Luiz Ribeiro4.pdf: 1669145 bytes, checksum: 0d233fd7c37ca8df5b6114d3752e4f2d (MD5) Andre Luiz Ribeiro5.pdf: 3180282 bytes, checksum: 3865a968b4f37d30ab444b820362e76d (MD5) Andre Luiz Ribeiro6.pdf: 1438158 bytes, checksum: f1c2cc81f218be303f39012ee96ef593 (MD5) Andre Luiz Ribeiro7.pdf: 2533571 bytes, checksum: 012d63a228d283086ec6eecc361dcce1 (MD5) Previous issue date: 2009-02-17 / Fundo Mackenzie de Pesquisa / The university campus is a space that has great importance in the development of the society. The formation of the knowledge in the university space is intrinsically related to all the set of elements in it: from the physical structure, to the knowledge and the people. The well understanding of what it means the physical structure of the campus will contribute strongly for this formation. The structures that compose the university campus and its own evolution passed through historical process analyses which are instruments of the process comprehension and relevance from its contribution in the society formation. This research analyzes campi from its characteristics applied in the monachal structures yet scholastic, the formation of the first universities and colleges in the Occidental Europe. Then, in the research s development, it slowly evaluates the campi of University of Virginia made by Jefferson, the Illinois Institute of Technology made by Mies van der Rohe and finally the Architecture s College of Porto in Porto University made by Alvaro Siza. The understanding of these structures will be certainty important in the project of new campi to be produced in XXI century. / O Campus universitário é um espaço que tem grande importância no desenvolvimento da sociedade. A formação do conhecimento no espaço universitário está intrinsecamente relacionada com todo o conjunto de elementos presentes nele: da estrutura física, ao conhecimento e as pessoas. O bom entendimento do que significa a estrutura física do campus contribuirá fortemente para esta formação. A análise do processo histórico pelo qual passam as estruturas espaciais que geram o campus universitário e a própria evolução do campus como tal são instrumentos de compreensão do processo e da relevância de sua contribuição na formação da sociedade. Este trabalho analisa os campi desde suas características presentes nas estruturas espaciais monacais ainda escolásticas, a formação das primeiras universidades e colleges na Europa Ocidental. Na seqüência avalia detidamente os campi da Universidade de Virginia de Jefferson, o Instituto Illinois de Tecnologia de Mies van der Rohe e finalmente a Faculdade de Arquitetura do Porto na Universidade do Porto de Álvaro Siza. A compreensão destas estruturas espaciais com certeza será importante no projeto dos novos campi a serem produzidos no século XXI.

The emergence of freeform architecture provides interesting geometric challenges with regards to the design and manufacturing of large-scale structures. To design these architectural structures, we have to consider two types of constraints. First, aesthetic constraints are important because the buildings have to be visually impressive. Sec- ond, functional constraints are important for the performance of a building and its e cient construction. This thesis contributes to the area of architectural geometry. Specifically, we are interested in the geometric rationalization of freeform architec- ture with the goal of combining aesthetic and functional constraints and construction requirements. Aesthetic requirements typically come from designers and architects. To obtain visually pleasing structures, they favor smoothness of the building shape, but also smoothness of the visible patterns on the surface. Functional requirements typically come from the engineers involved in the construction process. For exam- ple, covering freeform structures using planar panels is much cheaper than using non-planar ones. Further, constructed buildings have to be stable and should not collapse. In this thesis, we explore the geometric rationalization of freeform archi- tecture using four specific example problems inspired by real life applications. We achieve our results by developing optimization algorithms and a theoretical study of the underlying geometrical structure of the problems. The four example problems are the following: (1) The design of shading and lighting systems which are torsion-free structures with planar beams based on quad meshes. They satisfy the functionality requirements of preventing light from going inside a building as shad- ing systems or reflecting light into a building as lighting systems. (2) The Design of freeform honeycomb structures that are constructed based on hex-dominant meshes with a planar beam mounted along each edge. The beams intersect without torsion at each node and create identical angles between any two neighbors. (3) The design of polyhedral patterns on freeform surfaces, which are aesthetic designs created by planar panels. (4) The design of space frame structures that are statically-sound and material-e cient structures constructed by connected beams. Rationalization of cross sections of beams aims at minimizing production cost and ensuring force equilibrium as a functional constraint.

This dissertation is concerned with developing new time-optimal control techniques for higher-order linear and weakly nonlinear systems. As an application, we consider the simultaneous slewing and vibration suppression of a flexible beam, possibly with a tip mass. This application arises in the design of large space structures and flexible lightweight and accurate robotic arms. The solution of the soft-constrained time-optimal control problem is expressed in terms of the controllability Grammian. The properties of the open-loop solution are studied. A closed-loop control algorithm, which takes into account the mUltiplicity of extremal solutions, is then developed. The algorithm is based on the concept of continuation and reduces the computational complexity by as much as two orders of magnitude when compared to the brute-force approach. The amplitude of the soft-constrained time-optimal control is found to saturate as the state norm becomes large, thus suggesting a simpler but suboptimal feedback implementation. We develop and discuss the concept of saturating controls for linear systems, and we develop a design approach that generates a family of saturating control laws in which the speed of the response and amount of available control action can be explicitly traded off. The soft-constrained time-optimal cheap-control problem is formulated and solved using singular-perturbation theory. The solution procedures are illustrated with an example solved using the MACSYMA symbolic manipulation language. Regular-perturbation theory is then used to find the open-loop hard-constrained time-optimal control for a class of weakly nonlinear systems. The control is found by solving a nonlinear two-point boundary value problem (TPBVP) characterizing the control of the linearized system, and a second linear TPBVP. / Ph. D.

The digital transformation of engineering design processes is essential for the aerospace industry to remain competitive in the global market. Multidisciplinary design optimization (MDO) frameworks play a crucial role in this transformation by integrating various engineering disciplines and enabling the optimization of complex spacecraft structures. Since the design team consists of multiple entities from different domains working together to build the final product, the design and analysis tools must be readily available and compatible. An integrated approach is required to handle the problem's complexity efficiently. Additionally, most aerospace structures are made from composite panels. It is challenging to optimize such panels as they require the satisfaction of constraints where the design ply thicknesses and orientations can only take discrete values prescribed by the manufacturers. Heuristics such as particle swarm or genetic algorithms are inefficient because they provide sub-optimal solutions when the number of design variables is large. They also are computationally expensive in handling the combinatorial nature of the problem. To overcome these challenges, this work proposes a two-fold solution that integrates multiple disciplines and efficiently optimizes composite spacecraft structures by building a rapid design framework. The proposed model-based design framework for spacecraft structures integrates commercially available software from Siemens packages such as NX and HEEDS and open-source Python libraries. The framework can handle multiple objectives, constraint non-linearities, and discrete design variables efficiently using a combination of black-box global optimization algorithms and Mixed Integer Programming (MIP)-based optimization techniques developed in this work. Lamination parameters and MIP are adopted to optimize composite panels efficiently. The framework integrates structural, thermal and acoustic analysis to optimize the spacecraft's overall performance while satisfying multiple design constraints. Its capabilities are demonstrated in optimizing a small spacecraft structure for required structural performance under various static and dynamic loading conditions when the spacecraft is inside the launch vehicle or operating in orbit. / Doctor of Philosophy / The design of new spacecraft takes several years and requires significant resources. The primary design objective is to minimize spacecraft mass/cost while satisfying the mission requirements. This is done by altering the structure's geometric and material properties. Most spacecraft panels are made from composite materials where the orientations of fiber paths and the thickness of the panel determine its strength and stiffness. Finding the best values for these parameters cannot be done efficiently using existing optimization algorithms, as several combinations of orientations can give a similar performance which can be subpar. In this dissertation, mathematical programming is adopted for fast evaluation of optimum panel properties, thereby saving a significant amount of resources compared to conventional techniques. Moreover, the requirements that govern the design process are handled one at a time in an organization. This leads to discrepancies in the various teams' designs that satisfy all requirements. A framework is built to integrate all requirements to account for their conflicting nature and quickly give the best possible spacecraft structural design configuration.

The design of feedback control laws for discrete models of flexible structures is addressed. Two strategies are proposed. First, a parameter optimization method is used, in which the behavior of the controller is described by a performance measure and numerically optimized. A second method, based on continuation maps, allows several performance criterion to be met. These performance measures are quite general in nature; they may be functions of eigenvalues, eigenvectors, sensitivities, and other mission specific quantities. A model of a cantilevered flexible beam is developed and used to demonstrate capabilities and problems with the design methods. / M.S.

This thesis reports a study in the area of active vibration damping focused primarily on reconfiguration of control actuators following failure of one or more components. Several related issues concerning practical implementation were considered, and these also were discussed. These subjects were studied with reference to a particular laboratory structure, a hanging plane grid in the Spacecraft Controls Branch at NASA Langley Research Center. The structure had dynamics representative in many respects of a large, highly flexible space structure (LSS), and this study was intended to contribute toward the development of vibration control for LSS. A numerical analysis of the reconfiguration by computer simulation is presented. The possible future experimental validation of this numerical analysis motivated examination of some auxiliary problems related to implementation of vibration control with real, nonideal hardware. One of these problems is the effect of the dynamics of real sensors, actuators, and filters on a vibration control system. An experimental analysis of this problem was conducted, and the results presented here include hardware induced performance degradation and system instability. Another problem considered is prediction of response for use in feedback control by a digital controller that introduces a significant computational delay. A prediction technique is described, and some results of open-loop experimental evaluation of this technique are presented. Also, a computer simulation of closed-loop application of this technique was conducted, and the results, which include system instabilities, are presented. / M.S.

During the past decade, researchers have shown much interest in control and identification of Large Space Structures (LSS). Our inability to model these LSS accurately has generated extensive research into robust controllers capable of maintaining stability in the presence of large structural uncertainties as well as changing structural characteristics. In this work the performance of Model Reference Adaptive Control - (MRAC) is studied in numerical simulations and verified experimentally, to understand how differences between the plant and the reference model affect the control effort. MRAC is applied analytically and experimentally to a single-degree-of-freedom system and analytically to a multi-degree-of-freedom system with multi-inputs and multi-outputs. Good experimental and analytical agreement is demonstrated in control experiments and it is shown that MRAC does an excellent job of controlling the structures and achieving the desired performance even when large differences between the plant and ideal reference model exist. However, it is shown that reasonable differences between the reference model and the plant significantly increase the required control effort. The effects of increased damping in the reference model are considered, and it is shown that requiring the controller to provide increased damping actually decreases the required control effort when differences between the plant and reference model exist. This result is very useful because one of the first attempts to counteract the increased control effort due to differences between the plant and reference model might be to require less damping, however, this would actually increase the control effort. The use of optimization to successfully improve performance and reduce control effort is shown to be limited, because the actual control-structure system can not realize all the performance improvements of the analytical optimal system. Finally, it is shown that very large sampling rates may be required to accurately implement MRAC. / Ph. D.