Thesis (M.S.)--Ohio University, November, 1987. / Title from PDF t.p.

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 108-113).

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017. / The aim of this thesis is to investigate the applications of multifunctional compos- ite (MFC) technology to nano-satellite structures and to produce a working concept design, which can be implemented on future Cube-Satellites (CubeSats). MFC tech- nologies can be used to optimise the performance of the satellite structure in terms of mass, volume and the protection it provides. The optimisation of the structure will allow further room for other sub-systems to be expanded and greater payload allowance. An extensive literature view of existing applications of MFC materials has been conducted, along with the analysis of a MFC CubeSat structural design account- ing for the environmental conditions in space and well-known design practices used in the space industry. Numerical analysis data has been supported by empirical analysis that was done where possible on the concept material and structure. The ndings indicate that the MFC technology shows an improvement over the conventional alu- minium structures that are currently being used. Improvements in rigidity, mass and internal volume were observed. Additional functions that the MFC structure o ers include electrical circuitry and connections through the material itself, as well as an increase electromagnetic shielding capability through the use of carbon- bre composite materials. Empirical data collected on the MFC samples also show good support for the numerical analysis results. The main conclusion to be drawn from this work is that multifunctional composite materials can indeed be used for nano-satellite structures and in the same light, can be tailor-made to the speci c mission requirements of the satellite. The technology is in its infancy still and has vast room for improvement and technological development beyond this work and well into the future. Further improvements and additional functions can be added through the inclusion of various other materials.

In this investigation, the elasto-plastic behavior and the seismic performance of concrete reinforced frame structures reinforced are evaluated by applying the Pushover method. This evaluation is done on several cases: with high ductility steel (Grade 40), conventional steel (Grade 60) and high strength steel (Grade 75). For the previous, the capacity curve graph obtained from the displacement coefficient method was used to measure the capacity of the structure. In addition, the performance of the structure for different levels of seismic design are evaluated with the resulting values of ductility and rigidity of each case. The results showed that reinforcing a structure with a Grade 40 reinforcing steel increases the energy dissipation capacity, and if reinforced with a Grade 75 reinforcing steel increases the strength capacity in the structure. Finally, the comparative result of the various cases are presented to demonstrate the influence of reinforcing steel on the plastic behavior of concrete reinforced frame structures.

The partial differential equations of motion for an uncontrolled distributed structure can be transformed into a set of independent modal equations by means of the system eigenfunctions. In vibration analysis, the modal coordinates are referred to as natural coordinates. Active control forces generally recouple the modal equations so that the natural coordinates for the open-loop (uncontrolled) system cease to be natural coordinates for the closedloop (controlled) system. Control of this form is known as coupled control. In contrast, it is shown that a method known as the independent modal-space control method is a natural control method; i.e., the natural coordinates of the open-loop system and of the closed-loop system are identical. Furthermore, it is shown that natural control provides a unique and globally optimal closed-form solution to the linear optimal control problem for the distributed structure. The optimal control forces are ideally distributed. If implementation of distributed control is not feasible, then the distributed control forces can be approximated by finite-dimensional control forces. The class of self-adjoint systems are first considered following a treatment of non-self-adjoint systems. Numerical examples of a beam, a membrane and a whirling shaft are presented. In general, the eigenquantities for a distributed structure cannot be computed in closed-form, so that spatial discretization of the differential eigenvalue problem is necessary. A common discretization method is the finite element method leading to a discrete eigenvalue problem. Two bracketing theorems characterizing convergence of the discrete eigenvalue problem derived by the finite element method to the differential eigenvalue problem are formulated. The independent modal-space control method requires as many actuators as controlled modes. In contrast, coupled control is capable of controlling any number of modes using a single actuator, provided controllability is ensured. However, coupled control is sensitive to errors in the system parameters. As a compromise between coupled control and independent mbdal-space control, a block-independent control method is developed in which blocks of modes are controlled independently. The performances of independent modal-space control, coupled control and block-independent control are compared. / Ph. D.

The objectives of this experimentally and to simulate study were to implement theoretically a method of active vibration control, known as modal-space control, on a relatively simple beam-cable structure. The control was implemented in analog form and provided modal viscous damping in each of the three modes of the structure. Transient response to initial conditions was analyzed experimentally and theoretically. Control hardware included permanent magnet-coil systems for the three control force actuators and the single velocity sensor, and an analog controller built around integrated circuit operational amplifiers. This thesis compares open-loop experimental response and closed-loop experimental and theoretical response on the basis of Fast Fourier Transforms of transient time data. / M.S.

Interest in large flexible space structures has grown considerably over the last decade. These distributed parameter systems exhibit vibration characteristics such as low, closely spaced natural frequencies and light damping, which, when coupled with the stringent pointing accuracy and vibration control requirements imposed on these systems, bring about interesting control problems. Addressing these problems has called for the use of active vibration control. Up to now, two of the most popular means for active vibration control of large space structures have been proof mass and reaction wheel actuators. These actuators are inertial-type actuators in that they operate by applying forces or moments to masses whose reaction forces, imposed on the structure, act to dampen the vibrations of the structure. A new class of actuators, variable geometry trusses (VGT's), has been recently introduced. These actuators are actually built into the structure, and they operate by varying their link lengths to apply forces to the structure or to change the shape of the structure itself. This study compared the effectiveness of four actuators in controlling the planar vibrations of a cantilevered truss-beam. The actuators chosen for the study were a proof mass actuator, a reaction wheel actuator, and two VGT's, the planar truss actuator, and the planar truss proof mass actuator (a combination VGT/inertial type actuator). Numerical simulations of each beam/actuator system were performed in response to initial condition inputs. A full-state, LQR optimal feedback control law was used with each system. These simulations provided information such as time response of the closed-loop system, damping provided to the beam, and power required by each actuator. This information can be used to determine the "best" actuator for a given purpose. The results of these simulations show that the VGT's are preferable in terms of damping added to the beam. The proof mass actuator is more efficient as far as power required to do the control, however, the efficiencies for all actuators are very similar. / Master of Science

Ever since the advent of the Moment-Distribution procedure (1) for analyzing continuous frames, it has been possible to solve many problems conveniently which previously had required laborious solutions. Indeed, the current literature of the engineering profession finds the Cross method being adopted in new fields and being applied to new problems. The classical methods of analysis, while still retaining some measure of their former utility, are being superseded by this and other methods involving less time and labor. Yet, even with this new impetus to the field of structural analysis, the rigid space frame has received far less attention than seems justified. Here is a class of structure devoid of practically any analytical investigation and even less experimental research. The desired characteristic of all current designs has been continuity, and yet there exists this paradoxical neglect of the third dimension, without which all structures would be non-existent. The reasons for this apparent indifference are not difficult to ascertain. Practicing engineers are practical men and as such require reasonably accurate results, obtained with a minimum of effort. Economy has dictated that refinements of analysis be saved for the classroom. A two-plane analysis is generally substituted for the more complex three-dimensional case. The write feels that the interaction of members in different planes of certain structures may be quite important in some cases and that a complete, convenient analysis is justified to determine the extent of such action. / Master of Science

The control problem of a large-order flexible system in the form of a beam-lattice is presented using the Independent Modal-Space Control (IMSC) method. The method is based on a transformation of the system equations of motion to modal space, yielding internally independent modal equations of motion. The control laws are designed in the modal space, permitting independent control of each mode, providing complete decoupling of the equations of motion. Linear optimal control with quadratic performance index is designed to control the response of the elastic as well as the rigid body modes, using the IMSC method. Actuators placement is of fundamental importance in the control of two-dimensional domains if IMSC is used. A method is presented as to the selection of actuators configuration in order to avoid singularity in the mode participation matrix, guaranteeing system controllability. The minimum-fuel problem is a very important one in the design of various space structures. Solution of the minimum-fuel problem is feasible in a coupled form for a fourth order system at most, but will be of insurmountable computational difficulty in the control of a flexible structure, since the model of such system will require a large number of degrees of freedom. A reformulation of the problem in the framework of "Modal Minimum-Fuel Problem" is presented, using the IMSC method. By this method, the complexity inherent in a high-order system is reduced, thus treatment of the coupled high-order system is avoided. Numerical examples for linear optimal control, with quadratic performance index, as well as for the minimum-fuel problem, are presented. / Ph. D.

In this thesis, we examine the Linear DC Motor in a configuration such that it provides the forces necessary to damp vibrations in a large flexible structure. The design is broken down into three steps where in each step, a feedback loop is placed around the actuator and/or the structure. The first loop is a motor compensation loop which effectively decouples the motor model from the structure model by removing the effect of the velocity of the structure on the motor's performance. The second loop stabilizes the relative position response of the combined actuator/structure model. This loop also shapes the magnitude response of the system, thus determining the bandwidth of the actuator. Two designs are developed: a narrow bandwidth design and a wide bandwidth design. The third loop is the vibration suppression design loop and can be designed a number of ways. In this thesis, we develop two decentralized designs and a centralized design. The final system is simulated to check design results. The various nonlinearities of the proof mass actuator are considered and their effect on results noted. These nonlinearites, the stroke and current limits, determine the effectiveness of each vibration suppression design. The linear model is checked for robustness to parameter uncertainty. Results for the various designs are tabulated and discussed. / M.S.