Este trabalho apresenta um estudo sobre as estruturas espaciais em forma de cúpulas abordando os seguintes aspectos: histórico, desenvolvimento, descrição dos tipos mais utilizados, comportamento, análise e alguns aspectos de projeto e execução. Enfatizam-se as cúpulas constituídas por elementos tubulares com seção transversal circular e, em particular, as que necessitam da estampagem da extremidade de seus elementos para confecção do sistema de ligação. Descrevem-se vários sistemas de ligação utilizados em vários países e os utilizados no Brasil. A influência da variação de inércia causada pela estampagem das barras foi estudada via método dos elementos finitos com a devida modelagem da região afetada. A região modelada foi inserida em uma treliça espacial plana e seus resultados comparados com resultados experimentais desta estrutura. Apresentam-se também, os procedimentos básicos para elaboração do projeto de uma cúpula considerando as hipóteses utilizadas nos escritório de projeto, ou seja, comportamento elástico linear e nós rotulados. Para a mesma estrutura, um breve estudo sobre ruína progressiva, é apresentado. / This research presents a study about dome space structures about the following aspects: history, development, description of the more utilized types, behavior, analysis and some project and design aspects. It\'s emphasized the tubular element domes with circular section, particularly, those which need stamping at the end to wake the joint system. It\'s described many joint systems which are utilized in several countries and also in Brazil. The variable stiffness influence caused by the stamping on the bar ends was studied using the Finite Element Method by a suitable model of the affected region. The modeled region was inserted into a plane space truss and the analysis results were compared to the experimental values. It\'s also presented the basic procedures to dome project development, considering linear-static behavior. For the same model, a short study about failure downfall is presented.

As estruturas metálicas espaciais de cobertura apresentam aspectos diferenciados de projeto. Existem diversos arranjos geométricos possíveis para estas estruturas, cuja escolha está associada, entre outros fatores, às formas e dimensões do contorno, aos pontos de apoio e aos sistemas de conexões empregadas. Neste trabalho, foi analisado o projeto destas estruturas, abordando aspectos históricos, os sistemas de ligação, o comportamento estrutural, as particularidades de projeto, e realizando uma análise numérica de diferentes arranjos geométricos. Foram analisados 27 arranjos geométricos quadrados (66 m x 66 m) e 6 arranjos geométricos retangulares (186 m x 66 m), todos os vãos centrais de 60 m, e com variações na quantidade e posicionamento dos apoios, na disposição das barras do reticulado, na altura e nas dimensões dos módulos. Adotou-se o modelo de treliça ideal em análise elástica linear (teoria de primeira ordem). Com os resultados dos processamentos, realizou-se uma comparação entre os modelos, abrangendo os seguintes aspectos: quantidade de nós e barras, consumo de material, deslocamentos máximos, reações de apoio máximas e esforços internos máximos. O fator que causou maior influência no comportamento dos arranjos analisados foi a disposição dos apoios. / The roofing space steel structures have differentiated aspects of design. There are many types of arrangements to these structures, and the choice is associate, among other factors, with the shapes e dimensions of the boundary, with the points of support and with the connection systems employed. In this work was analysed the design of these structures, including the historical aspects, the connection systems, the structural behaviour, the particulars aspects of the design, and a numerical analysis of differents arrangements. Twenty seven square structures (66 m x 66 m) and six rectangular structures (186 m x 66 m) were analysed, all them with 60 m span, and variations in the amount and position of supports, in the member arrangement, in the depth and in the node spacing. These structures were analysed adopting the ideal truss model with elastic linear behaviour. With the results were made a comparison between the arrangements that reports these aspects: amount of nodes and members, material consumption, displacements, support reactions and internal forces. The factor that caused the biggest influence in the behaviour of the space structures analysed was the amount and position of supports.

Modern design methodologies for control systems create controllers with dynamics which are of a similar order to the physical system being controlled. When these are implemented digitally as Infinite Impulse Response (HR) filters the processing requirements are extensive, in particular when high sample rates are necessary to minimise the detrimental effects of sample delay. The aim of the research was to apply signal processing techniques to facilitate the implementation of control algorithms in digital form, with the principal objective of maximising the computational efficiency, either to achieve the highest possible sample rates using a given processor, or to minimise the processor complexity for a given requirement. One of the approaches is to design a fixed point processor whose architecture is optimised to meet the computational requirements of signal processing for control, thereby maximising what can be achieved with a single processor. Hence the aim of the research was to head towards a processor architecture optimised for Control System Processing. The design of this processor is based on a unified structural form and it will be shown that controllers, represented either in state space form or as transfer functions, can be implemented using this unified structure. The structure is based on the σ-operator, which has been shown to be robust to changes in coefficients and hence require shorter coefficient wordlength to achieve a comparable performance to traditional z-operator based structures. Additionally, the σ-operator structures are also shown to have lower wordlength requirements for the internal variables. Also presented is a possible architecture for a Control System Processor and a model for the processor is developed and constructed using VHDL. This is simulated on a test bench, also designed in VHDL. The results of implementing a phase advance controller on the processor are then compared with those obtained from a MATLAB simulation.

In order to satisfy the mechanical requirements for space structures, achieving lightweight designs is of the greatest significance. The primary focus of this study is the utilization of Kelvin cell core in the design of sandwich structures for space applications. The research encompasses a variety of production techniques, analyzes, and tests related to the design of sandwich structures with Kelvin cells as the core material. While a variety of configurations are evaluated in a general sense, particular configurations are examined in greater extensive detail. In this context, the structure's bending stiffness, compression stiffness, and vibration characteristics are analyzed. The analytical procedure begins with a simplified structure analysis, followed by the modeling of the actual geometry. According to applicable standards, stiffness values are calculated based on the deflection results of the analyzes. However, it is important to note that the tests performed on the modeled structures are conducted in a laboratory environment using additively manufactured samples. This permits a comparison between the obtained test results and the findings of the analyzes, shedding light on the effect of the manufacturing method. This study demonstrates that the honeycomb sandwich structure is superior in terms of overall stiffness. In addition, a specially designed reinforced Kelvin Cell structure possesses exceptional bending rigidity properties. In light of these findings, it is clear that the combination of Kelvin Cell core and specific reinforcement strategies has the potential to improve the mechanical performance of sandwich structures. In addition, the deformation results revealed by the analyzes showed that the structure can be deformed in large amounts in directions other than the direction of the force it is exposed to. This situation is of great importance for damping in space applications. As a result of vibration analyzes and tests, the effect of stiffness and mass increase in a certain direction on natural frequencies has been revealed, and with 3-point bending tests, the facing elastic modulus and core shear modulus values of the structure have been determined separately and its effect on the sandwich structure has been shown. Accordingly, this study examined and evaluated many aspects of the possible role of the Kelvin Cell in space applications. / För att tillgodose de mekaniska kraven på rymdkonstruktioner är det av största vikt att uppnå lätta konstruktioner. Det primära fokuset för denna studie är utnyttjandet av Kelvin-Cellkärna vid design av sandwichstrukturer för rymdtillämpningar. Forskningen omfattar en mängd olika produktionstekniker, analyser och tester relaterade till design av sandwichstrukturer med Kelvin-Celler som kärnmaterial. En mängd olika konfigurationer utvärderas generellt, medan vissa specifika konfigurationer undersöks mer utförligt på detaljnivå. I detta sammanhang analyseras strukturens böjstyvhet, kompressionsstyvhet och vibrationsegenskaper. Den analytiska proceduren börjar med en förenklad strukturanalys, följt av modellering av den faktiska geometrin. Enligt gällande standarder beräknas styvhetsvärdena baserat på strukturanalysens resultat. Det är dock viktigt att notera att de tester som utförs på de modellerade strukturerna utförs i en laboratoriemiljö med hjälp av additivt tillverkade prover. Detta möjliggör en jämförelse mellan de erhållna testresultaten och resultaten av analysen, vilket belyser effekten av tillverkningsmetoden. Denna studie visar att sandwichstrukturen honeycomb är bäst när det gäller total styvhet. Dessutom har en specialdesignad förstärkt Kelvin-Cellstruktur exceptionella böjstyvhetsegenskaper. I ljuset av dessa fynd är det tydligt att kombinationen av Kelvin-Cellkärna och specifika förstärkningsstrategier har potential att förbättra den mekaniska prestandan hos sandwichstrukturer. Dessutom visade deformationsresultaten från analyserna att strukturen kan deformeras till hög grad i andra riktningar än den kraft som den utsätts för. Denna iaktagelse är av stor betydelse för dämpning i rymdapplikationer. Som ett resultat av vibrationsanalyser och tester har effekten av styvhet och massökning i en viss riktning på naturliga frekvenser upptäckts, och med 3-punkts böjtester har konstruktionens elasticitetsmodul och skjuvmodulsvärden bestämts separat och dess effekt på sandwichstrukturen har visats. Följaktligen undersökte och utvärderade denna studie många aspekter av Kelvin-Cellens möjliga roll i rymdtillämpningar.

Space structures are inevitable while covering large spans. Space structures are skeletal structures, which are lighter for the same stiffness when compared with RCC roofs. Till now, space structures, like any other metal structures have been designed assuming the joints as rigid, although there have been several publications about semi rigid joints. Of course, the publications mostly deal with 2D structures and there are very few reports on 3D structures. Space structures, by their nature fall into the latter category. The joints in a space structure are popularly called as "nodes". Generally, nodes, which ensure concentricity of member axes, are either solid or hollow. These are either cast or forged. There are other proprietary types, which do not come under the above classification, and have not been considered in this thesis. Hollow nodes are obviously more economical than solid nodes, but also more flexible. While it is prudent to prefer hollow nodes, it is equally necessary to assess their flexibility, because of its influence on the behaviour of the structure. The hollow spherical node is very popular because of its simplicity and adaptability to various forms of space frames. Double layer grids, which are the most popular forms for roofing applications, are being increasingly implemented. While the hollow spherical node is well suited for double layer grids, an evolutionary development has been what is called as the hollow octahedral node (this node is simply referred to as the 'Octa ' node in this thesis). Chapter 1 introduces space frames and double layer grids in particular, with the advantages of using double-layer grids. Jointing systems available around the world are briefed and the node connector used in the present study is introduced with a brief write-up on its advantages and disadvantages. This chapter also explores the available literature and, the scope and objectives of the thesis are mentioned. Chapter 2 introduces 3D finite element models of the hollow spherical and octahedral nodes. The stiffness matrixes of these nodes have been derived by conducting analyses on the computer for six sizes each of the Octa and spherical nodes. Using the stiffness matrix of the node, a new method of incorporating this into the regular analysis of a space truss has been developed. The new method proposed yields realistic values for the forces in the members and takes into account the elastic deflections in the node under the action of member forces. Implementation of the proposed method has been carried out by writing a custom program using state-of-the-art object oriented programming techniques. A sample problem has been analyzed using this program to demonstrate the effect of including joint flexibility. The effect of flexibility of nodes on the effective length of compression members in double-layer grids has been evaluated. The effect of compliance on the dynamic characteristics of a space frame has also been evaluated for the sample space frame with flexible joints. The analysis program has been modified to evaluate the natural frequencies of the system using rigid or flexible nodes. The study of the Octanode and spherical node under the action of uniaxial compression and tension dominates the contents of Chapter 3. The two types of nodes have been analyzed using commercially available finite element software considering material nonlinearity. The stress patterns from the analyses have been examined thoroughly. Two consistent methods for fixing the load at yield in both uniaxial compression and tension have been proposed using the load-displacement curve. Yield loads for all the nodes have been evaluated using both the methods and the results agree well between the two methods. Three material yield values have been selected for each of the node size for evaluating the yield values viz. 240,320 and 415 MPa. The members of a double layer grid are connected to the nodes by bolts and holes are drilled in the nodes for this purpose. The bolthole patterns differ between two popular types of double-layer grids. Both these bolthole patterns have been modeled separately in the above exercise and the results for these two have been shown to be approximately the same. The effect of varying diameters of the boltholes on the response of the nodes has been examined. Relationships between the yield load, diameter, thickness and material yield have been developed using the method of least squares. The differences in the behaviour of the nodes under uniaxial compression and tension have been discussed. Ramberg Osgood type of relationships have been worked out for all the load-displacement curves obtained from the analyses. The simulation of non-linear behaviour of nodes with cracks with plastic crack closing forces have been carried out with useful insights into the behaviour of the two types of nodes in uniaxial compression and tension. Chapter 4 is devoted largely for studying the two types of nodes under the influence of biaxial load combinations. The combinations studied are dual compression, dual tension and compression-tension. In all cases equal loads are applied along two orthogonal; directions in the horizontal plane. Stress patterns have been examined for each type of load combination and yield values for each case have been obtained using one of the methods proposed in chapter 3. These have been compared with the corresponding uniaxial values in both compression and tension. Some useful inferences have been possible by studying the behaviour of the nodes under the various biaxial load combinations. In each case, relationships between the biaxial yield load, uniaxial yield load, diameter of node, thickness of node and material yield of node have been obtained using the method of least squares. The nodes have been analyzed under some selected Multi-axial loading and combinations of load which cause yield based on the second method proposed in Chapter 3 have been obtained and tabulated. However, a proper and thorough study of the nodes under multi-axial loading proved to be beyond the scope of this thesis. Chapter 5 contains the contributions made towards developing new methods and algorithms for obtaining the several results of chapters 2, 3 and 4, using object oriented programming (OOP) techniques. The contributions have been in Object Pascal, the underlying language of Delphi, a popular RAD tool developed by Borland/Inprise of USA. Several new modules have been developed to reliably handle the large amounts of data generated by the hundreds of analyses detailed in chapters 2,3 and 4. The ease with which new methods were possible to be incorporated into existing software using OOP has been demonstrated, with source code examples. Comparisons with other types of tools available and die advantages of using OOP have also been demonstrated using the experience during the preparation of this thesis. A strong case for OOP as an indispensable tool for the researcher has been made. Chapter 6: Several important conclusions and suggestions for future work have been made. Appendix 1 contains a brief note on the Method of Least Squares. Appendix 2 contains a small write-up on Delphi and OOP. Concepts of OOP have been briefly described and comparisons between three popular OOP languages have been attempted. A brief description of the features in Delphi's Object Pascal has also been provided. Appendix 3 contains the listing of Unit Arrays, which is a general purpose unit developed to make handling of large arrays easy. Several matrix calculations have been implemented which make the unit extremely useful for programmers. Appendix 4 contains the full listing of program FormK, which has been developed for chapter 2 to derive the fall stiffness matrix of a space frame node. The program picks up results from several analyses, forms a few columns of the stiffness matrix and then fills up the rest using the cyclic symmetry present in the space frame node. This program is given in full, with the intention that other researchers may find it useful to use it as-is or use after making small alterations to suit their circumstances. OOP is known for fast, reliable and easy ways of implementing modifications to existing code. Appendix 5 provides the full listing of the Object Pascal program for extracting Eigenvalues of a space truss with rigid joints or flexible joints. The incorporation of flexibility of the joints proposed in chapter 2 has been implemented. Descriptions of the program's implementations have been provided in chapter 5. Bibliography contains the alphabetical list of references.

This thesis project has been conducted during a five-month research exchange visit to the Space Structure Dynamics and Control research group at University College Dublin. This report presents the design, development, and validation of a nanosatellite attitude control testbed. The testbed was designed to replicate the microgravity conditions of space by utilising an air bearing, enabling single-axis rotational motion for a 1U CubeSat-sized nanosatellite. The novel aspect of this research is the inclusion of two-degree-of-freedom, lumped-mass flexible appendages on either side of the nanosatellite, emulating a lightweight, flexible space structure. These flexible appendages were designed based on the stiffness characteristics of a deployable CubeSat solar array system found in existing literature, with exaggerated motion to amplify the measurable effects of various control approaches. The central focus of this project was the development of an avionics stack closely resembling CubeSat attitude control boards. The stack uses an STM32 microcontroller as the primary attitude control computer, and a suite of off the shelf breakout boards for sensors and wireless telemetry systems. Power, serial and I2C buses connect the attitude control board and the onboard computer board. A reaction wheel actuator controls the Euler heading attitude. The testbed was designed as an experimental platform for validating control algorithms developed through a model-based approach. Integration with the Simulink Embedded Coder toolbox allows for the compilation of Simulink models into C code, facilitating direct execution on the testbed. The testbed’s physical construction involves 3D printed ABS components, with the inclusion of load cells to measure disturbance torques from the excited flexible appendages. Results from validation experiments show that a simple PID controller causes significant excitation in the flexible appendages during a slew manoeuvre. However, the introduction of an input shaped attitude profile tailored to the natural frequency of the appendages successfully reduced the measured appendage excitation by 50%. Conversely, the force impedance wave based control approach did not show a reduction in appendage excitation, but shows promise for further developments in future work. In conclusion, the testbed has successfully achieved its predefined project objectives, albeit requiring further refinement, particularly in the telemetry down-link system. It is recommended that future work focuses on enhancement of the telemetry system, and validation of a model based approach to controller design. / Detta examensarbete har utförts under ett fem månaders forskningsutbyte vid forskningsgruppen Space Structure Dynamics and Control vid University College Dublin. Denna rapport presenterar design, utveckling och validering av en testbädd för attitydstyrning av en nanosatellit. Testbädden utformades för att efterlikna mikrogravitationsförhållandena i rymden genom att använda ett luftbärande lager, vilket möjliggör rotationsrörelse kring en axel för en nanosatellit av storleken 1U CubeSat. En unik aspekt av detta arbete är inkluderingen av två-frihet-graders, sammansatta flexibla påhängen på vardera sidan av nanosatelliten, vilket efterliknar en lätt, flexibel rymdstruktur. Dessa flexibla påhängen utformades med utgångspunkt från styvhetsegenskaperna hos ett utskjutbart CubeSat-solcellssystem som finns i befintlig litteratur, med överdriven rörelse för att förstärka de mätbara effekterna av olika styrmetoder. Det centrala fokuset för detta projekt var utvecklingen av en avionikstack som nära liknar CubeSat-attitydregleringkort. Stacken använder en STM32-mikrokontroller som primär dator för attitydkontroll och ett urval färdiga breakout-kort för sensorer och trådlös telemetri. Strömförsörjning, serie- och I2C-bussar ansluter attitydregleringkortet och omborddatorn med en reaktionshjulsaktuator som styr Euler-attityd. Testbädden utformades som en experimentell plattform för att validera styralgoritmer som utvecklats med hjälp av en modellbaserad metod. Integration med Simulink Embedded Coder möjliggör kompilering av Simulink-modeller till C-kod, vilket underlättar direkt exekvering på testbädden. Testbäddens fysiska konstruktion innefattar 3D-utskrivna ABS-komponenter med inkludering av lastceller för att mäta störningsmoment från de exciterade flexibla påhängen. Resultaten från valideringsexperiment visar att en enkel PID-regulator orsakar betydande excitation i de flexibla påhängena under en vridningsmanöver. Dock lyckades en input-formad attitydprofil som anpassats till de flexibla påhängenas naturliga frekvens framgångsrikt minska den uppmätta excitationen med 50%. Omvänt visade den kraftimpedansvågbaserade styrmetoden inte någon minskning i excitation, men visar potential för vidare utvecklingar i framtida arbete. Sammanfattningsvis har testbädden framgångsrikt uppnått sina fördefinierade projektmål, om än med behov av ytterligare förfining, särskilt i telemetrisystemet. Det rekommenderas att framtida arbete fokuserar på förbättring av telemetrisystemet och validering av en modellbaserad ansats till styrdesign.