US-Egypt Cooperative Research: Application of the Saturation- Based Controller to Self-Excited Oscillators and Systems with Limited Energy Sources

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0322101 NayfehDescription: This award supports a cooperative research project between Professor AliNayfeh, Department of Engineering Sciences and Mechanics, Virginia Polytechnic Institute and State University (Virginia Tech.), Blacksburg, Virginia and Dr. Ayman El-Badawy, Department of Mechanical Engineering, Al-Azhar University, Cairo, Egypt. They plan to study the suppression of the large-amplitude vibrations of self-excited systems and systems with limited power supplies. The control strategy will be based on the saturation phenomenon exhibited by multi-degree-of-freedom systems with quadratic nonlinearities possessing a two-to-one autoparametric resonance. The strategy consists of introducing a second-order controller, and coupling it to the plant through a sensor and an actuator, where both the feedback and control signals are quadratic. Therefore, the desired nonlinearities can be introduced into the complete plant/control system even when the plant does not exhibit any nonlinear behavior. When the plant is forced near resonance, its response saturates at a small value, and the remaining oscillatory energy is channeled and absorbed by the actuator. The investigators will implement the technique by using a digital signal processing board and a modeling software. They will develop an adaptive control strategy using an effective frequency-tuning mechanism to maintain the two-to-one internal-resonance condition. Adaptive control makes it possible for the system (or structure) to adapt to a variable environment in the interest of continuously optimizing its performance. The investigators will examine the use of a logic gate with Schmitt-trigger action on the input to measure the system frequency because of its accuracy and because it is immune to noise disturbances.Scope: The project involves analytical and experimental approaches, and combines the complementary expertise of the US and Egyptian scientists. The self-excited oscillations are encountered in a number of important engineering systems, and the suppression of these oscillations, especially under the constraint of limited power supplies, is an important problem. The development of the active nonlinear feedback control will have many applications. The project will support an Egyptian scientist to work at Virginia Tech and will include interaction of students at both universities.