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An investigation of vibration isolation systems using active, semi-active and tunable passive mechanisms, with applications to vehicle suspensions

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  • Mathematics


In this dissertation, an analytical investigation on active, semi-active and passive vibration control mechanisms is presented in order to achieve improved shock and vibration isolation of mechanical systems, especially ground vehicle applications. A hybrid active vibration isolation system, incorporating an electro-magnetic force generator along with passive damping and spring elements, is mathematically modeled based on fundamental physical laws and taking into account the generator dynamics. Complete vibration isolation characteristics of the hybrid active control system are evaluated for various feedback variables and control schemes, using numerical simulations. Influence of the force generator dynamics on vibration isolation performance is illustrated through the simulation results. A concept of tunable pressure limiting modulation is proposed in hydraulic damper systems. A hydraulic orifice damper is modified by using the proposed tunable pressure limiting modulation to achieve variable damping in vibration isolation systems, without requiring any external energy source, sophisticated control devices and feedback instrumentation that are essential for active and semi-active isolators. The fluid flow equations are employed to develop the nonlinear mathematical model of the hydraulic damper, incorporating the fluid and mechanical compliance, and the dynamics of the pressure limiting mechanism. The computer simulation reveals that the shock and vibration isolation performance of the tunable pressure limited hydraulic damper systems is comparable to that of the semi-active 'on-off' vibration control systems. A generalized harmonic linearization technique, based on a principle of energy similarity of dynamic elements, is proposed to derive equivalent linear representations of both nonlinear damping and spring elements, in the frequency domain. An analysis of the nonlinear in-plane vehicle model, with air-springs, orifice damping and pressure limiting modulation due to tunable hydraulic shock absorbers, is carried out to establish the stochastic response to random road inputs in terms of power spectral density, and to illustrate the improved vehicle ride performance due to tunable shock absorbers. An interconnected hydro-pneumatic suspension with tunable pressure limiting mechanism is presented to achieve improved vehicle ride and handling performance. Analysis of a roll plane model of a vehicle employing the tunable interconnected suspension shows that the connections of fluid flow within the interconnected suspension provide an enhanced static roll stability; while the tunable pressure limiting modulation between the strut and the accumulator of each suspension unit offers an improved vehicle ride performance

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