In this thesis, experiments and simulations are performed to study the deployment dynamics of space webs and space booms, focusing on the deployment and stabilization phases of the space web and the behavior of the bi-stable tape spring booms after long-term stowage. The space web, Suaineadh, was launched onboard the sounding rocket REXUS-12 from the Swedish launch base Esrange in Kiruna on 19 March 2012. It served as a technology demonstrator for a space web. A reaction wheel was used to actively control the deployment and stabilization states of the 2×2 m2 space web. After ejection from the rocket, the web was deployed but entanglements occurred since the web did not start to deploy at the specified angular velocity. The deployment dynamics was reconstructed by simulations from the information recorded by inertial measurement units and cameras. Simulations show that if the web would have started to deploy at the specified angular velocity, the web would most likely have been deployed and stabilized in space by the motor, reaction wheel and controller used in the experiment. A modified control method was developed to stabilize the out-of-plane motions before or during deployment. New web arms with tape springs were proposed to avoid entanglements. A deployable booms assembly composed of four 1-m long bi-stable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The deployment dynamics and reliability of the SEAM boom design after long-term stowage were tested by on-ground experiments. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic strain energy relaxation, and other factors that act to decrease the deployment force. In order to mitigate the viscoelastic effects and thus ensure self-deployment, different tape springs were designed, manufactured and tested. A numerical model was used to assess the long-term stowage effects on the deployment capability of bi-stable tape springs including the friction, nonlinear-elastic and viscoelastic effects. A finite element method was used to model a meter-class fully coiled bi-stable tape spring boom and verified by analytical models. / <p>QC 20170508</p> / SEAM

Foldable and deployable space structures refer to a broad category of pre-fabricated structures that can be transformed from a compact folded configuration to a predetermined expanded configuration. Such deployable structures are stable and can carry loads. These structures are also mechanisms with one degree of freedom in their entire transformation stages whether in the initial folded form or in the final expanded configuration. Usually, pantograph mechanisms or a scissor-like elements (SLEs) are part of such deployable structures. A new analysis tool to study kinematic and static analyses of foldable and deployable space structures /mechanisms, containing SLEs, has been developed in this thesis. The Cartesian coordinates are used to study the kinematics of large deployable structures. For many deployable structures the degree of freedom derived using the standard Grubler-Kutzback criteria, is found to be less than one even though the deployable structure /mechanism can clearly move. In this work the dimension of nullspace of the derivatives of the constraint equations are used to obtain the correct degrees of freedom of deployable structure. A numerical algorithm has been developed to identify the redundant joints /links in the deployable structure /mast which results in the incorrect degrees of freedom obtained by using the Grubler-Kutzback criteria. The effectiveness of the algorithm has been illustrated with several examples consisting of triangular, box shaped SLE mast and an eighteen-sided SLE ring with revolute joints. Further more the constraint Jacobian matrix is also used to evaluate the global degrees of freedom of deployable masts/structures. Closed-form kinematic solutions have been obtained for the triangular and box type masts and finally, as a generalization, extended to a general n-sided SLE based ring structure. The constraint Jacobian matrix based approach has also been extended to obtain the load carrying characteristics of deployable structures with SLEs in terms of deriving the stiffness matrix of the structure. The stiffness matrix has been obtained in the symbolic form and it matches results obtained from other commonly used techniques such as force and displacement methods. It is shown that the approach developed in this thesis is applicable for all types of practical masts with revolute joints where the revolute joint constraints are made to satisfy through the method of Lagrange multipliers and a penalty formulation. To demonstrate the effectiveness of the new method, the procedure is applied to solving (i) a simple hexagonal SLE mast, and (ii) a complex assembly of four hexagonal masts and the results are presented. In summary, a complete analysis tool to study masts with SLEs has been developed. It is shown that the new tool is effective in evaluating the redundant links /joints there by over coming the problems associated with the well –known Grubler-Kutzback criteria. Closed-form kinematic solutions of triangular and box SLE masts as well as a general n-sided SLE ring with revolute joints has been obtained. Finally, the constraint Jacobian based method is used to evaluate the stiffness matrix for the SLE masts. The theory and algorithms presented in this thesis can be extended to masts of different shapes and for the stacked masts.

Antennas play a crucial role in communication systems since they are the transmitting/receiving elements that transition information from guided transmission to open-space propagation. Antennas are used in many different applications such as aerospace communications, mobile phones, TVs and radios. Since the dimensions of antennas are usually physically proportional to the wavelength at their operating frequencies, it is important to develop large antennas and arrays that can be stowed compactly and easily deployed. Also, it is important to minimize the number of antennas on a platform by developing multifunctional antennas. The first aim of this research is to develop new deployable, collapsible, light-weight and robust reconfigurable antennas based on origami principles. All designs will be validated through simulations and measurements. Paper as well as other substrates, such as, Kapton and fabric, will be used to develop our origami antennas. The second aim of this research is to derive integrated analytical and simulation models for designing optimal origami antennas for various applications, such as, satellite or ground communications. This dissertation presents research on origami antennas for novel reconfigurable communication systems. New designs of reconfigurable monofilar, bifilar and quadrifilar antennas based on origami cylinders are developed and validated. Novel fabrication methods of origami antennas are presented with detailed geometrical analysis. Furthermore, multi-radii origami antennas are proposed, analyzed, fabricated and validated and they exhibit improved circular polarization performance and wide bandwidths. An actuation mechanism is designed for these antennas. For the first time, a low-cost and lightweight reconfigurable origami antenna with a reflector is developed here. In addition, an array is developed using this antenna as its element. Finally, a kresling conical spiral antenna and a spherical helical antenna are designed with mode reconfigurabilities.

This thesis study addresses the problem of overconstraint via introduction of conformal polyhedral linkages comprising revolute joints only and investigation of special geometric properties for the mobility of such overconstrained linkages. These linkages are of particular interest as deployable structures. First, planar case is issued and conditions for assembling irregular conformal polygonal linkages composed of regular and angulated scissor elements are derived. These planar assemblies are implemented into faces of polyhedral shapes and radially intersecting planes to obtain two different kind of polyhedral linkages. Rest of the thesis work relates to spatial linkages. Identical isosceles Bennett loops are assembled to obtain regular polygonal linkages and many such linkages are assembled to form polyhedral linkages. Then, Fulleroid-like linkages are presented. After these seemingly independent linkage types, Jitterbug-like linkages are introduced. Based on some observations on present linkages in the literature a definition for Jitterbug-like linkages is given first, and then a set of critical properties of these linkages are revealed. This special type of polyhedral linkages is further classified as being homothetic and non-homothetic, and geometric conditions to obtain mobile homothetic Jitterbug-like polyhedral linkages are investigated. Homohedral linkages, linkages with polyhedral supports with 3- and 4-valent vertices only, tangential polyhedral linkages are detailed as special cases and the degenerate case where all faces are coplanar is discussed. Two types of modifications on Jitterbug-like linkages are presented by addition of links on the faces and radial planes of Jitterbug-like linkages. Finally, a special class of Jitterbug-like linkages - modified Wren platforms are introduced as potential deployable structures.

Planar bar-and-joint mechanisms with one degree-of-freedom are widely used in deployable structures and machines. Such mechanisms are designed to undergo a specific motion, which can be described mathematically by plotting out the compatibility conditions, resulting in a curve called compatibility path. It has been observed that compatibility paths can develop singularities similar to that of equilibrium paths of elastic structures. This dissertation studies singularities occurring in compatibility paths with the aid of knowledge in the theory of structural stability. An analogy is set up between the equilibrium path of elastic structures and the compatibility path of mechanisms with a single degree-of-freedom incorporating the different types of bifurcation, effects of imperfections and detection of singularities. It is shown that the fundamentally distinct critical points such as limit points and bifurcation points can also appear in compatibility path. Methods used to singularities for compatibility conditions of mechanisms and equilibrium of structures are unified so that they can be used for both cases. A formulation of potential energy for mechanisms is also proposed in analogy with the potential energy function used in structural analysis. Further analysis of the mechanisms is carried out to demonstrate that singularities of compatibility paths can also be dealt with by the elementary catastrophe theory similar to the stability theory. A relationship is established between the mathematical formulation of different compatibility bifurcations and the canonical forms of catastrophe types. Examples of mechanisms demonstrating the existence of cuspoids of the compatibility conditions are given. An overall classification of the compatibility paths is also proposed.

This dissertation concerns the structural design of medical stent grafts. A new type of an innovative stent graft has been developed. Unlike the conventional stent grafts which consist of a wire mesh and a covering membrane, the proposed stent graft can be made from a single folded sheet of material. Firstly, a detailed symmetric design of a foldable cylindrical tube for the new stent graft has been presented. Folding is achieved by dividing the structure into a series of identical elements with hill and valley folds as in origami (Japanese art of paper folding). The folding patterns allow the stent graft to be folded and expanded both radially and longitudinally. The relationships among the design of the elements, the number of elements in the circumferential and longitudinal directions and the folded dimensions of the stent graft have been derived. It has been found that compact folding in the radial direction can be achieved by increasing the number of circumferential elements. A geometric mismatch during deployment has also been identified. The elements have to deform when the structure is expanded. Optimum designs which minimise the deformation have been found. Secondly, a new stent graft with helical folds has also been designed to improve radial strength and ease the deployment process. Helical folds are introduced by adjusting the joining position of the two edges of a sheet that had been symmetrically jointed in the symmetric design. The relationships among the number of elements in one complete circumference of a helix, the helical angle and the radius of the helical type stent graft have been established. The locations for the helical folds are optimised for easy folding by considering both geometric aspects of folding and the buckling patterns of a thin-walled tube under torsion, which are found analytically. Thirdly, using numerical analysis of the finite element method (FEM) the strain level and overall deformation of the stent graft during deployment has been calculated. Finally, the stent graft has been manufactured to verify the concept. A number of prototypes of the stent graft, which are the same size as standard oesophageal and aortal stent grafts, have been produced successfully using the same materials as current stent grafts of stainless steel and shape memory alloy (SMA) sheets. The patterns of folds on the materials are produced by photochemical etching. It has also been demonstrated that the SMA stent grafts self-expand smoothly and gradually by a near body temperature.

abstract: CubeSats offer a compelling pathway towards lowering the cost of interplanetary exploration missions thanks to their low mass and volume. This has been possible due to miniaturization of electronics and sensors and increased efficiency of photovoltaics. Interplanetary communication using radio signals requires large parabolic antennas on the spacecraft and this often exceeds the total volume of CubeSat spacecraft. Mechanical deployable antennas have been proposed that would unfurl to form a large parabolic dish. These antennas much like an umbrella has many mechanical moving parts, are complex and are prone to jamming. An alternative are inflatables, due to their tenfold savings in mass, large surface area and very high packing efficiency of 20:1. The present work describes the process of designing and building inflatable parabolic reflectors for small satellite radio communications in the X band. Tests show these inflatable reflectors to provide significantly higher gain characteristics as compared to conventional antennas. This would lead to much higher data rates from low earth orbits and would provide enabling communication capabilities for small satellites in deeper space. This technology is critical to lowering costs of small satellites while enhancing their capabilities. Principle design challenges with inflatable membranes are maintaining accurate desired shape, reliable deployment mechanism and outer space environment protection. The present work tackles each of the mentioned challenges and provides an understanding towards future work. In the course of our experimentation we have been able to address these challenges using building techniques that evolved out of a matured understanding of the inflation process. Our design is based on low cost chemical sublimates as inflation substances that use a simple mechanism for inflation. To improve the reliability of the inflated shape, we use UV radiation hardened polymer support structures. The novelty of the design lies in its simplicity, low cost and high reliability. The design and development work provides an understanding towards extending these concepts to much larger deployable structures such as solar sails, inflatable truss structures for orbit servicing and large surface area inflatables for deceleration from hypersonic speeds when re-entering the atmosphere. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2015

Over the last decade there has been a worldwide increase in the use of retractable roofs for stadia. This increase has been based on the flexibility and better economic performance offered by venues featuring retractable roofs compared to those with traditional fixed roofs. With this increased interest an evolution in retractable roof systems has followed. This dissertation is concerned with the development of concepts for retractable roof systems. A review is carried out to establish the current state-of-the-art of retractable roof design. A second review of deployable structures is used to identify a suitable retractable structure for further development. The structure chosen is formed by a two-dimensional ring of pantographic bar elements interconnected through simple revolute hinges. A concept for retractable roofs is then proposed by covering the bar elements with rigid cover plates. To prevent the cover plates from inhibiting the motion of the structure a theorem governing the shape of these plate elements is developed through a geometrical study of the retractable mechanism. Applying the theorem it is found that retractable structures of any plan shape can be formed from plate elements only. To prove the concept a 1.3 meter diameter model is designed and built. To increase the structural efficiency of the proposed retractable roof concept it is investigated if the original plan shape can be adapted to a spherical surface. The investigation reveals that it is not possible to adapt the mechanism but the shape of the rigid cover plates can be adapted to a spherical surface. Three novel retractable mechanisms are then developed to allow opening and closing of a structure formed by such spherical plate elements. Two mechanisms are based on a spherical motion for the plate elements. It is shown that the spherical structure can be opened and closed by simply rotating the individual plates about fixed points. Hence a simple structure is proposed where each plate is rotated individually in a synchronous motion. To eliminate the need for mechanical synchronisation of the motion, a mechanism based on a reciprocal arrangement of the plates is developed. The plate elements are interconnected through sliding connections allowing them mutually to support each other, hence forming a self-supporting structure in which the motion of all plates is synchronised. To simplify the structure further, an investigation into whether the plate elements can be interconnected solely through simple revolute joints is carried out. This is not found to be possible for a spherical motion. However, a spatial mechanism is developed in which the plate elements are interconnected through bars and spherical joints. Geometrical optimisation of the motion path and connection points is used to eliminate the internal strains that occur in the initial design of this structure so a single degree-of-freedom mechanism is obtained. The research presented in this dissertation has hence led to the development of a series of novel concepts for retractable roof systems.

[pt] Pontes transportáveis para uso em caso de desastres naturais são geralmente estruturas pesadas, com altos custos de fabricação e exigem mão de obra qualificada para montagem, limitando o alcance de seu uso, especialmente em locais carentes de recursos. Dessa forma, este trabalho tem como objetivo desenvolver uma solução de ponte dobrável leve, fácil de construir, transportar e montar, sendo feita, principalmente, de bambu, um material com elevada relação resistência/peso e sustentável. O trabalho discute aspectos relevantes sobre o comportamento de estruturas pantográficas existentes, bem como sobre as principais características mecânicas e físicas do bambu, especificamente da espécie Guadua Angustifolia Kunth utilizada na pesquisa. Em uma primeira etapa, a fim de se avaliar a viabilidade do material escolhido, um programa experimental incluindo ensaios de flexão, fluência e dois diferentes tipos de ensaios de compressão foi conduzido. Ensaios feitos após ciclos de imersão e secagem com o intuito de avaliar o efeito de chuvas reincidentes sobre o material também foram realizados. Ensaios para determinação de coeficiente de atrito entre cordas de nylon e o bambu também foram realizados para estabelecer parâmetros adequados para avaliação da resistência das ligações amarradas. Num segundo estágio, o projeto da estrutura é apresentado e discutido, destacando o comportamento das ligações nas fases de desdobramento, protensão e final. Por fim, análises estruturais estáticas e dinâmicas foram realizadas com auxílio de modelos computacionais para as diferentes fases de montagem, apontando para a viabilidade da ponte proposta. / [en] Transportable bridges for natural disaster relief are usually heavy, have higher fabrication costs and demand qualified professionals for assembly. These disadvantages limit the reach of their benefits, especially in places with little available resources. The objective of this work is to develop a bridge designed to be lightweight, easy-to-build, -transport and –assembly and also mainly made of bamboo, a cheap sustainable material with high strength/weight ratio. This work discusses relevant aspects regarding the mechanics of existing pantographic structures, as well as the main mechanical and physical properties of bamboo, more specifically the species Guadua Angustifolia Kunth used in this research. At first, to evaluate the viability of the chosen material, an experimental program including bending, creep and two different types of compression tests was carried out. Tests after wet-and-dry cycles, considering the possible effects of repeated rain to exposed bamboo, were also performed. Tests to determine the friction coefficient between nylon ropes and bamboo were also carried to obtain parameters necessary to assess the strength of tied bamboo joints. After that, the structural design is presented and discussed, exploring the mechanics of the proposed connections and their behavior at the deployment stage, pre-stressing stage and final stage. At last, static and dynamic structural analysis were made with numeric models to all development stages, confirming the viability of the proposed bridge.

Origami has been extensively studied by engineers for its unique motions and ability to collapse to small volumes. Techniques have been studied for replicating origami-like folding motion in thick materials, but limited practical applications of these techniques have been demonstrated. Developable mechanisms are a new mechanism type that has a similar ability to collapse to a low profile. The cylindrical developable mechanism has the ability to emerge from and conform to a cylindrical surface. In this work, a few practical applications of devices with novel expanding motions are presented. The design and testing of an origami-inspired deployable ballistic barrier, which was designed by combining and modifying existing thickness accommodation techniques, is discussed. The properties of cylindrical developable mechanisms are examined and two devices designed for use with minimally invasive surgical tooling are presented. Various hinge options for small-scale cylindrical developable mechanisms are then reviewed and discussed. A planar modeling assumption for curved lamina emergent torsional joints in thin-walled cylinders is then analytically and empirically validated. Conclusions are drawn and recommendations for future work are given.