Semi-Active Adaptive Control Of Helicopter Ground Resonance

The semi-active control of helicopter ground resonance by using magneto-rheological (MR) damper has been investigated in this thesis. A helicopter can be damaged severely once the ground resonance happens. It must be solved during the design of a helicopter. The semi-active control is an ideal method for control of ground resonance with the advantage of lower power required and wider suitability for working condition.The investigation in this thesis was conducted along with two lines. One is in application of MR dampers including the MR damper's modeling, control and design. The other is in control of the ground resonance including the linear and nonlinear stability analysis, the determination of expects damping function, the loop of semi-active control, and so on. The creation of the investigation is mainly as follows.1. With the concept of least mean square (LMS) equivalent force, the damping force of MR damper under any current control and velocity excitation was decomposed into a linear combination with two damping forces which controlled by two different constant control currents and the same velocity excitation. With the LMS equivalent force and the linear combination, a new modeling method for MR damper has been developed to simplify the model of MR damper by selecting a base model and a fitting process.2. The inverse of MR damper which is defined as the control variable calculated by output damping force of MR damper under same excitation state was investigated. The existing region and condition of the inverse were analyzed. With the strategy of adaptive inverse control, the output performance of MR damper has been changed. Thus, the MR damper can become an intelligent device which can supply the damping force by using the excitation and expect output as input, actual output to track expecting output.3. The flux equation of MR fluid, magnet field function and structure limitation equation of MR damper were described. The structure parameters of MR damper were determined by using the optimization algorithm. A principle specimen of helicopter MR lag damper was designed and manufactured. The performance of the specimen was tested by using the MTS machine.4. The ground resonance has been studied by using the classical model containing two degrees of fuselage freedom in-plane and rigid blades to determine the critical stability boundary of the linear system of ground resonance. The effect of nonlinear damping force on the stability of ground resonance was investigated. A desired model of damping force to guarantee the stability of ground resonance has been presented.5. To use the controlled MR lag damper to suppress the ground resonance, a semi-active control loop of ground resonance with nonlinear damping was built. The adjusting algorithm of the desired damping force model was presented. The numerical simulation of the nonlinear ground resonance control with MR lag damper has been conducted.