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The subject of this study is the Warrior armoured personnel carrier rotary suspension damper. This is a simple passive device where energy is dissipated by the resistance to oil flowing through an orifice. In principle the mechanism of this damper is simple, but the requirement for a compact unit that can withstand high dynamic loads means that the design is complex in detail. Because of this complexity it is possible for air to remain in the oil chambers if care is not taken when priming the device. Measurements show that the nonlinear response of the damper is primarily due to turbulent oil flow through the orifice and the compression of entrapped air, but that friction is negligible. The most appropriate model for this system in multi-body dynamic simulations is to represent the damper as two discrete components: a non-linear dashpot (representing oil flow through the orifice) and a non-linear spring (representing the compression of entrapped air). From measurements, a splined curve is determined that describes the non-linear torque-velocity relationship due to orifice flow characteristics. By applying Henry's law and assuming isothermal compression, a function is derived that describes the compression of air in oil. This modelling method closely reproduces the measured response of the damper.
Allen et al. (2006) studied this question.