We propose an optimization method for a semi-active shock absorber for use in aircraft landing gear using Carroll’s FORTRAN Genetic Algorithm (GA) Driver. This method is compared with Powell’s conjugate direction method, a nonlinear programming (NP) approach, which uses not gradients, but only function values. In these optimizations, we handle variations in the maximum vertical acceleration of an aircraft during landing caused by the variation of the aircraft mass due to variations in the number of passengers and the amounts of cargo and fuel. The maximum vertical acceleration of an aircraft is set as an objective function to be minimized. Design variables searched in the first step of this optimization are discrete orifice areas formed by the outer surface of a hollow metering pin and a hole in the semi-active shock absorber. The design variable searched in the second step is an orifice area which is controlled based on the mass variation. For the GA runs, the ratio of the total number of optimum and near-optimum solutions to the total number of runs was greater than that for the NP runs. In addition, for the total GA runs, the total number of function evaluations per total number of optimum and near-optimum solutions was greater than that for the total NP runs. The optimum semi-active shock absorber is compared to the optimum passive shock absorber with respect to the variation of the acceleration of the aircraft mass. The ratio of maximum acceleration in the semi-active shock absorber to that in the passive shock absorber is 0.79 when the mass ratio is 0.65 maximum mass and is 0.58 when the mass ratio is 0.31 maximum mass.

We propose an optimization method for a semi-active shock absorber for use in aircraft landing gear, in order to handle variations in the maximum vertical acceleration of an aircraft during landing caused by the variation of the aircraft mass due to the variations in the number of passengers, and the amounts of cargo and fuel. In this optimization, the maximum vertical acceleration of an aircraft is set as an objective function to be minimized. Design variables searched in the first step of this optimization are discrete orifice areas formed by the outer surface of a hollow metering pin and a hole in the semi-active shock absorber. The design variable searched in the second step is a compensating orifice area which is controlled based on the mass variation. Using the optimum target orifice area obtained in the second step, we optimally determine a practical orifice area that is controlled by a stepping motor. The optimizations for a passive shock absorber and for semi-active shock absorbers with target and practical orifice areas indicate that the semi-active shock absorbers can handle aircraft mass variation much better than the optimum passive shock absorber. Furthermore, the robustness of the optimum practical orifice area controlled by a stepping motor is shown via simulation.

This paper describes the modeling of a semi-active shock absorber that uses magnetorheological (MR) fluid, which is a material that responds to an applied magnetic field and changes its apparent viscosity. We propose a dynamic system in which the friction of a falling body is taken into consideration, and a model in which the shearing resisting force depends on the velocity of flow. The validity of this model and a Bingham model is verified by comparison of the experiment with a simulation. This study clarifies that resisting forces obtained by the simulation corresponded to those obtained by the experiment, and that the current model is effective in predicting the behavior of a MR shock absorber.

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