Design Optimization of Aircraft Engine-Mount Systems

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Abstract
Design optimization of aircraft engine-mount systems for vibration isolation is presented. The engine is modeled as a rigid body connected to a flexible base representing the nacelle. The base (nacelle) is modeled with mass and stiffness matrices and structural damping using finite element modeling. The mounts are modeled as three-dimensional springs with hysteresis damping. The objective is to select the stiffness coefficients and orientation angles of the individual mounts in order to minimize the transmitted forces from the engine to the nacelle. Meanwhile, the mounts have to be stiff enough not to allow the engine deflection to exceed its limits under static and low frequency loadings. It is shown that with an optimal system the transmitted forces may be reduced significantly particularly when orientation angles are also treated as design variables. The optimization problems are solved using a constraint variable metric approach. The closed form derivatives of the engine vibrational amplitudes with respect to design variables are derived in order to determine the objective function gradients and consequently a more effective optimization search technique.

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