This article studies the decoupling control strategies for a quasi-linearised vehicle model consisting of three degrees of freedom. The key feature of the model is that it preserves strong non-linearities and inherent coupling effects between longitudinal acceleration/braking force, steering angles and state variables of the vehicle, based on which two kinds of decoupling controllers are presented. Firstly, a control law for approximate decoupling of longitudinal, lateral and yaw motions is derived, which requires small control magnitude. Next, by selecting the virtual control inputs, a new inputoutput map is built, and the input-output decoupling controller is proposed. Furthermore, according to the characteristics of the vehicle model, an exponentially stable observer is designed. Several simulations are included to illustrate the proposed control scheme.
The microscopic fluid dynamics of a wire screen bound to a slit resonator excited by incident sound waves of different intensity are investigated numerically. The microscopic flow features help in understanding the acoustic behavior. A normal impedance-tube model is used in this investigation, and the wire mesh is modeled as an array of eight identical tiny circular cylinders arranged in parallel. Tonal waves of different sound pressure levels and frequencies are introduced from the termination of the tube through a non-reflecting boundary condition. Direct numerical simulations are carried out to solve for the flow and acoustic fields simultaneously, and the velocity and vorticity fields around the resonator are resolved. Upon closer inspection, the tiny cylinders suppress the vortex shedding from the slit excited by high-intensity incident sound waves, thereby retarding the nonlinear acoustic behavior of the slit. Furthermore, the wire mesh contributes greatly to the absorption of acoustic energy through scrubbing loss and flow separation. The acoustic impedance and absorption coefficient are derived using a two-microphone method. The numerical results show that the wire mesh increases the resistance of the resonator significantly while hardly affecting its reactance.
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