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Methods for analyzing the structural-acoustic power efficiency of active structures are developed. For this work we define the power efficiency as the ratio of the sound power radiated by a structure to the maximum possible radiated sound power. An active structure is defined as one that has electromechanical actuators distributed over its surface for the purpose of structural-acoustic excitation. The power efficiency of planar, baffled structures with arbitrary boundary conditions is examined using a combination of methods based on numerical integration, variational principles, and finite element analysis. The fundamental result of this work is that computing the power efficiency of an active structure reduces to the solution of two eigenvalue problems. The maximum possible sound power radiated by a planar, baffled structure is shown to be equivalent to the largest eigenvalue of the acoustic power transfer matrix. The structural-acoustic power efficiency is the solution of a separate generalized eigenvalue problem whose parameters include the location of the electromechanical actuators and the type of electromechanical actuation. The advantage of this metric over other measures of radiation efficiency is that 0 and 1 bound the structural-acoustic power efficiency. Furthermore, solving for the power efficiency as a function of frequency yields a measure of the bandwidth of the structural-acoustic actuator. Power efficiency is analyzed for point force actuation and distributed moment actuation. Numerical simulations demonstrate that maximizing the power efficiency requires that the magnitude and phase of the structural modal velocity vector be matched to that of the eigenvector that corresponds to the maximum eigenvalue of the acoustic power transfer matrix. Matching the modal velocity to the maximizing eigenvector produces a vibration shape that maximizes the sound power radiation of the structure. Individual actuators are not able to achieve high efficiency over a broad frequency range for both types of electromechanical actuation. Multiple-actuator arrays are able to achieve higher average efficiency at the expense of increased number of actuators. An optimization problem is then posed to maximize the structural-acoustic power efficiency by varying the location and size of distributed moment actuators. We demonstrate that an average efficiency on the order of 0.85 is possible over a large bandwidth through optimal placement and sizing of a set of four distributed moment actuators. Experimental results on a baffled plate demonstrate that correct phasing of the actuators results in velocity distributions that correlate well with predicted results. / Ph. D.

The main focus of this study is on the active and semi-active control of civil engineering structures subjected to seismic excitations. Among different candidate control strategies, the sliding mode control approach emerges as a convenient alternative, because of its superb robustness under parametric and input uncertainties. The analytical developments and numerical results presented in this dissertation are directed to investigate the feasibility of application of the sliding mode control approach to civil structures. In the first part of this study, a unified treatment of active and semi-active sliding mode controllers for civil structures is presented. A systematic procedure, based on a special state transformation, is also presented to obtain the regular form of the state equations which facilitates the design of the control system. The conditions under which this can be achieved in the general case of control redundancy are also defined. The importance of the regular form resides in the fact that it allows to separate the design process in two basic steps: (a) selection of a target sliding surface and (b) determination of the corresponding control actions. Several controllers are proposed and extensive numerical results are presented to investigate the performance of both active and semi-active schemes, examining in particular the feasibility of application to real size civil structures. These numerical studies show that the selection of the sliding surface constitutes a crucial step in the implementation of an efficient control design. To improve this design process, a generalized sliding surface definition is used which is based on the incorporation of two auxiliary dynamical systems. Numerical simulations show that this definition renders a controller design which is more flexible, facilitating its tuning to meet different performance specifications. This study also considers the situation in which not all the state information is available for control purposes. In practical situations, only a subset of the physical variables, such as displacements and velocities, can be directly measured. A general approach is formulated to eliminate the explicit effect of the unmeasured states on the design of the sliding surface and the associated controller. This approach, based on a modified regular form transformation, permits the utilization of arbitrary combinations of measured and unmeasured states. The resulting sliding surface design problem is discussed within the framework of the classical optimal output feedback theory, and an efficient algorithm is proposed to solve the corresponding matrix nonlinear equations. A continuous active controller is proposed based only on bounding values of the unmeasured states and the input ground motion. Both active and semi-active schemes are evaluated by numerical simulations, which show the applicability and performance of the proposed approach. / Ph. D.

Sustainable Built Environments Senior Capstone Project / Tucson is a reflection of the inefficient transportation system of the United States. The city’s auto centric emphasis is resulting in a collection of unhealthy citizens, endlessly investing into constructing unaccommodating infrastructure and contributes to the degradation of the natural environment. In order to correct these issues facing Tucson, the city must encourage more active transportation. By using case studies of other American cities- Portland, Minneapolis, and Austin- Tucson can learn some strategies that have been successful. Portland, Minneapolis and Austin have all effectively created active transportation systems utilizing various techniques. Creating a safe built environment, constructing a connected network and introducing equity amongst all forms of transportation can encourage more participation of active transportation in Tucson. By adopting the strategies used by Portland, Minneapolis and Austin, Tucson can produce a successful active transportation system and furthermore, create a healthier population, an efficient economy, and reduce the degrading environmental behavior that all exist today.

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