|Title:||Multi-objective optimization of active constrained layer damping treatment for shape control application|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Structural control (Engineering)
|Department:||Department of Mechanical Engineering|
|Pages:||xvi, 166 leaves : ill. ; 30 cm|
|Abstract:||Vibration and shape control of structures are common subjects among the engineering community. In vibration control, suppressing the structural vibrations is of primary concern, while shape control means commanding the structure to take a desired shape when both subjected to changes of environment or load conditions. The science and technology developed in the latter topic has found applications in many areas; examples are in the re-adjustment of the focal point of antenna reflectors, and the improvement of aerodynamic and hydrodynamic performances of airfoils and blades respectively. This thesis presents a study conducted to explore the feasibility of utilizing Active Constrained Layer Damping (ACLD) treatment for shape control of flexible structures. The key idea is to reduce the complexity and enhance the stability of the control system, since ACLD patches can not only change the shapes of flexible structures but also introduce passive damping. The present study deals with the dynamic modeling, analysis and optimization of an ACLD flexible beam for shape control. First of all, the dynamic model of a flexible beam with distributed ACLD patches is formulated by means of the Finite Element Method (FEM). The Golla-Hughes-McTavish (GHM) model is employed to capture the frequency-dependent characteristic of the viscoelastic materials. With this model, a parametric study of the ACLD flexible beam is conducted by computer simulations to understand the effects of treatment length and location, the layer physical and geometrical properties, and control gain values on the damping characteristic of the flexible beam. The optimal performance of the system in this application is defined by several objective functions. Both open and closed-loop performances are taken into account. With respect to open-loop control, certain amount of passive damping is necessary for stability and fail-safe consideration. Meanwhile, a heavy structure is undesirable. For closed-loop control, the minimization of the error between the desired and achieved shapes should be another concern. Based on the previous parametric study, specific design variables in addition to the control gains can be chosen and the inequalities can be set up for the respective constraints. Instead of aggregating the objectives with a weighting function, the Multi-Objective Genetic Algorithm (MOGA) is employed, and a computer code is developed to solve this multi-objective optimization problem. Pareto solutions are successfully obtained. A clear tradeoff between the total treatment weight and passive damping is found. Transient behavior is analyzed by numerical simulations. Results show the feasibility of using ACLD patches for the shape control of structures. Effects of external disturbances on the shape control system are also examined by applying different types of loadings to the system. It is demonstrated that for the loads under consideration, closed-loop control can regulate the actuator voltages to correct the destroyed shapes. Comparison is also made between open and closed-loop controls. Simulation results confirm that the closed-loop control outperforms the open-loop one in terms of disturbance-rejection ability as well as settling time.|
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