A Comparative Study of the Nonlinear and Linear Performance of Vehicle Air Cushion Suspensions Using Bond Graph Models

A nonlinear analytical model for the dominant low-frequency dynamic behavior of flexible-skirt air cushion suspensions is developed using bond graph notation. The model includes nonlinear fluid source and orifice characteristics, and modulation of cushion fluid capacitance and sealing gap fluid resistance by changes in geometry and cushion pressure. Bond graphs are presented for the fully nonlinear cushion and for the linearized small perturbation case. Both the nonlinear and linearized equations for the heave dynamics of an air cushion vehicle are developed and solved by machine computation for a realistic range of operating conditions. By comparing the linear and nonlinear solutions, it is concluded that the linear model is suitable for the preliminary design and optimization of air cushion vehicle suspensions. The full nonlinear simulation is prudent, however, to check a tentative design for the effects of unusually large guideway irregularities or external load disturbances.