An analytical and experimental investigation into the position and vibration control of beam-like structures within a gravity field using only root actuation was performed. Two methods were used to linearize the system's equations of motion. This, in turn, allowed for the use of powerful Modern Control Theory pole-location techniques to determine proper feedback-control gains. The control law was implemented on an IBM PC capable of analog/digital conversion. A DC servo motor served as the control actuator. Gains were computed for a continuous controller rather than for one having a sampled-data nature. Both simulation and experimental response were good, and were seen to correspond well with computed system-eigenvalues. If gains were chosen to cause more negative eigenvalues, the system's response speed increased, as it should. If eigenvalues are forced to become too negative, however, the system becomes too fast for the controller, and response deteriorated. / M.S.

The purpose of this study was to review the history of financing public school facilities in Virginia with primary emphasis on the period of the public schools, 1870 through 1987. An ancillary purpose of the study was to review alternative methods of financing public school capital facilities in Virginia in 1987 and certain considerations in the determination of school plant needs and implementation of a capital improvements plan. A combination topical-chronological synthesis research plan was employed within time frames of twenty-six to thirty-year periods from 1870-1987. As a result of this study, the following findings and conclusions were made: / Ph. D.

The use of active control actuators integral to a structure's construction has been suggested in large space structure technology. A 3-D active truss is presented and analyzed and control of the actuators to reduce the vibration of a flexible rod attached to the structure is discussed. A state feedback control law is used. Experiments are performed using digital control implementation. Some experimental results are acceptable compared to expected theoretical analysis. Conclusions and recommendations are made for future research. / M.S.

M.S.

This dissertation concentrates on the three principal problems facing experimentalists during their attempts to identify and control lightly damped, large space structures (LSS). The problems are low damping, high modal density, and low natural frequencies of oscillation. They present a blend of difficulties which lead the experimentalist to turn to multiple-input multiple-output (MIMO) identification techniques and high performance compensators. Presented here are two MIMO modal identification techniques: Polyreference, and the Eigensystem Realization Algorithm, as well as two types of compensator-based controllers: Linear Quadratic Gaussian, and Independent Modal Space Control. The various techniques are described in the context of controlling lightly damped LSS. Because the research in this dissertation is primarily applications oriented, problems which experimentalists encounter in the laboratory are addressed as well as the performance of the different identification and control techniques on the test articles. Polyreference and ERA are both shown to perform very well in identifying modal frequencies while overestimating model damping ratios. Simulations show that high modal density combined with noisy data results in standard deviations that increase linearly with respect to mode separation. Pseudo- Inverse IMSC is shown to be robust with respect to system uncertainties. Block Independent Control is shown to possess minor coupling between blocks and provides a powerful control approach to overcome actuator bandwidth limitations. / Ph. D.

In this study three types of optimized controllers are developed and tested on two laboratory structures. The two structures represented a progression in complexity and challenge to the controllers. The first structure was simple enough to be accurately modeled so the analytical frequencies and mode shapes agreed with the experimental measurements. The second structure being more complex was more difficult to model so differences between the analytical results and experimental measurements were present. These differences required the application a correction method to the reduced models developed for the second structure. The correction method was shown to work with good results on one reduced model and with poor results on the second reduced model. Two direct rate feedback control laws and a linear quadratic regulator with state estimation (LQG controller) were designed and implemented on both structures. It was shown that the performance of the LQG controller can be approached with a much simpler direct rate feedback controller with better analytical-experimental agreement. The best analytical-experimental agreement occurred with the simplest controller applied analytically to the corrected reduced model demonstrating the validity of the correction method as well as giving a strong reason to use simpler controller designs. / Ph. D.

CubeSat or Cubic Satellite is an effective method to study the space aroundthe Earth thanks to its low cost, easy maintenance and short lead time. However, a great challenge of small satellites lies in achieving technicaland scientific requirements during the design stage. In the present workprimary focus is given to dynamic characterization of the deployable tapespringboom in order to verify and study the boom deployment dynamiceffects on the satellite. The deployed boom dynamic characteristics werestudied through simulations and experimental testing. The gravity offloadingsystem was used to simulate weightlessness environment in theexperimental testing and simulations showed that the deployment of thesystem influence the results in a different way depending on the vibrationmode shape. / En CubeSat eller kubisk satellit är effektivt för att studera rymden runtjorden på grund av dess låga kostnad, enkla underhåll och korta ledtid. Enstor utmaningen i utformningen av små satelliter är att uppnå de tekniskaoch vetenskapliga kraven. Detta arbete har analyserat de dynamiska egenskapernahos en utfällbar band-fjäder bom i syfte att verifera och för attstudera bommens utfällningsdynamiska effekter på satellitens bana och attityd.Den utfällda bommens dynamiska egenskaper har studerats genomsimuleringar och experimentella tester. Ett tyngdkraftskompenserande systemhar använts för att simulera tyngdlöshet i de experimentella testernaoch simuleringar visar att utformningen av detta system påverkar resultatenolika beroende på svängingsmodens form.

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.

Stiff, ultra-lightweight thermal-formed polyimide panels considered in this dissertation are examples of next generation gossamer structures that resolve some of the technology barriers of previous, membrane-dominated gossamer designs while maintaining their low mass and low stowage volume characteristics. The research involved statically and dynamically characterizing and modeling several of these panels to develop validated computer models which can be used to determine the effects of changing manufacturing parameters and scalability. Static characterization showed substantial local nonlinear behavior that was replicated by new physics-based finite element models, and global linear bending behavior that was modeled using classical shell finite elements incorporating effective properties in place of bulk material properties to represent the unique stiffening structure of these panels. Dynamic characterization was performed on individual panels using standard impact hammer and accelerometer testing, enabling successful extraction of several structural natural frequencies and mode shapes. Additionally, the three dimensional time history of the surface of the panels was rendered from video data, and temporal filters were applied to the data to examine the frequency content. These data were also correlated to the shell element numerical models. Overall, the research contributes to the total knowledge base of gossamer technologies, advances stiff panel-based structures toward space qualification, and demonstrates their potential for use in apertures and other spacecraft.

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.