Browsing by Author "Shahidi, R."
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Item Active Vibration Damping by Parametric Control(1994) Shahidi, R.; Shayman, M.; ISRIn recent years, smart composites have been introduced in the market that open up new possibilities for controlling or sensing flexible structures. Internal properties of these composite materials which are either embedded into the structure or bonded to the surface of the structure can be manipulated, through application of magnetic field (in magneto-strictive material), voltage (in piezoelectric material), or heat (in Shape Memory Alloys).This dissertation is primarily concerned with those composites with variable stiffness or modulus of elasticity. The objective is to control the stiffness of the structure to achieve stability. A lumped parameter model of a non-shearable and inextensible beam is derived as an approximation to the continuum model with attached composites. Due to the ability to manipulate the modulus of elasticity of the composite, the spring constants of the finite dimensional model of the beam are identified as the control variables. We design nonlinear feedback control laws to damp vibrations in the resultant simple Hamiltonian control system while satisfying the input constraints. Then, the analysis is specialized to a class of bilinear system which is the state linearized version of the original system. Optimality of the proposed controller is studied and under special conditions a discontinuous control law is proposed which achieves a faster dissipation of the energy than the continuous one for some simulated cases.
Item Mobile Robot Navigation Using Potential Functions(1989) Shahidi, R.; Shayman, M.; Krishnaprasad, P.S.; ISRThis thesis presents a method to construct a smooth obstacle free path for a mobile robot on which to navigate. The first step is to assign potential functions to each obstacle and the goal. Then, the gradient system constructed by the gradient of the sum of the above functions generates the desired path. The construction is analytically proven to produce obstacle free paths to the goal for an environment whose obstacles can be approximated by disks. The procedure does not require complete information on the position of the obstacles beforehand, as long as they can be detected and approximated by disks. The algorithm presented shows a computationally simple way to construct paths and a systematic method to encode the geometric data about the environment into a smooth vector field, which is used for mobile robot navigation.