Robust Semi-active Control of Aircraft Landing Gear System Equipped with Magnetorheological Dampers

Landing is the most critical operational phase of an aircraft since it directly affects the passenger safety and comfort. The factors such as the undesirable wind and ground effects, runway unevenness, excessive sink speeds and approach speeds and pilot errors can deteriorate the landing performance of an aircraft several times during its entire lifetime. When an aircraft lands, large amplitude vibrations get transmitted to the fuselage from the runway thereby causing safety and comfort problems and hence need to be suppressed quickly. Landing gear is an essential assembly that prevents the aircraft fuselage from the ground loads. A shock absorber which is considered as the heart of the landing gear assembly plays an important role in this process by absorbing the vibrations during landing. The existing Oleo-pneumatic shock absorbers are the most efficient in absorbing the vibrations during each aircraft operation. However, they are unable to provide the continuously variable damping required during the landing phase which might reduce their efficiency. Moreover, to account for the uncertainties during landing, a damper capable of providing the variable damping effect can play a vital role in increasing the passenger safety. A semi-active control system of a landing gear suspension can solve the problem of excessive vibrations effectively by providing a variable damping during each operational phase. Magnetorheological (MR) dampers are one of the most efficient and attractive solutions that can provide the continuously variable damping required depending on a control command. This thesis focuses on the concept of the semi-active aircraft suspension system using the MR damper with the implementation of robust control strategy. Initially, the dynamic behavior of the MR damper is studied using the parametric modeling approach. Spencer dynamic model is adopted for simulating the dynamic behavior of the MR damper. This is followed by the analysis of the energy dissipation patterns of the MR damper for different excitation inputs. A semi-active suspension system is developed for a three degree-of-freedom (3 DOF) aircraft model considering a tri-cycle landing gear configuration. A switching technique is developed in the simulation of the landing procedure which enables the system to switch from the single degree of freedom to three degrees of freedom system in order to simulate the sequential touching of the two wheels of the main landing gears and the nose landing gear wheel with the ground. For developing the semi-active MR suspension system, two different controller approaches, namely, the Linear Quadratic Regulator (LQR) and the H∞ control are adopted. The results of the designed controllers are compared for a particular landing scenario for studying the performance of the controllers in reducing the overshoot of the bounce response as well as the bounce rate response. The simulation results confirmed the improved performance of the robust controller compared to the optimal control strategy when the aircraft is subjected to the disturbances during landing. Finally, implementing the robust control approach, the landing performance of an aircraft embedded with the semi-active suspension system is simulated and analyzed for different sink velocities considering the disturbances

New dynamic modeling and pratical control design for MacPherson suspension system

The ride quality, handling, and stability are three main issues in vehicle suspension design. Different suspension systems have been designed in the past to fulfil these conflicting requirements. One of the popular suspension systems integrated in small and midsize passenger cars is MacPherson suspension system. A suspension system is either passive if a conventional damper is incorporated or is semi-active with a variable damper. A new control oriented dynamic model of the MacPherson suspension system is developed in this thesis to consider the effects of the suspension structure on the dynamic response and a new kinematic model is proposed to investigate those suspension kinematic parameters affecting both handling performance and stability of the vehicle. The performance of MacPherson suspension system under alternative hybrid semi-active controls is evaluated. It is shown that the contribution of different control strategies on the ride quality enhancement of the vehicle could be similar whereas their effectiveness on the performance of suspension kinematc parameters is completely different. Using the H {592} robust control theory, a full state feedback controller is designed to improve MacPherson suspension specifications. The gain of the controller is optimized so that the trade-off between the requirements is achieved. To be more practical and to reduce the design cost, H, output feedback control theory is employed to design a controller with the minimal cost design. To optimize the controller gain, the LMI and Genetic Algorithm optimization tools are used. It is shown that the output controller can improve the suspension performance close to that of a full state feedback controller. A magnetorheological damper with continuously variable damping is considered as the actuator to the system. In order to tune the current signal of the damper so as to track the desired force calculated from the controller unit, a mathematical dynamic model of the damper is required. For modelling the damper, the MR damper is characterized by a piece-wise polynomial model which is identified by using the data acquired from various tests in the laboratory. The dynamic behaviour of the MR damper on control performance is investigated. The Hardware-in-the-Loop Simulation is made and the effectiveness of the controllers is evaluated through experiments

Calculating the Lyapunov exponents of a piecewise smooth soft impacting system with a time-delayed feedback controller

This is the final version. Available on open access from Elsevier via the DOI in this record.Lyapunov exponent is a widely used tool for studying dynamical systems. When calculating Lyapunov exponents for piecewise smooth systems with time delayed arguments one faces two difficulties: a high dimension of the discretized state space and a lack of continuity of the variational problem. This paper shows how to build a variational equation for the efficient construction of Jacobians along trajectories of the delayed nonsmooth system. Trajectories of a piecewise smooth system may encounter the so-called grazing events, where the trajectory approaches discontinuity surfaces in the state space in a non-transversal manner. For these events we develop a grazing point estimation algorithm to ensure the accuracy of trajectories for the nonlinear and the variational equations. We show that the eigenvalues of the Jacobian matrices computed by the algorithm converge with an order consistent with the order of the numerical integration method. Finally, we demonstrate the proposed method for a periodically forced impacting oscillator under a time-delayed feedback control, which exhibits grazing and crossing of the impact surface.EPSRCEuropean Union