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An interactive computer program has been developed to design aircraft engine mounting systems used for vibration isolation. Mount design is largely driven by two competing criteria. Mounts must be soft enough to provide vibration isolation, yet stiff enough to support the engine without excessive motions. The constrained variable metric optimization technique is used to determine the mount design parameters which minimize the transmitted forces in the mounts, subject to constraints on the maximum allowable deflection of the engine to static forces. The design parameters are the stiffness and orientation of each individual engine mount. The aircraft engine is modeled as a rigid body that is mounted to a rigid base representing the nacelle. An example is used to show that the optimization technique is effective in designing engine mounting system.

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Vibration normal modes and static correction modes have been previously used to model flexible bodies for dynamic analysis of mechanical systems. The efficiency and accuracy of using these modes to model a system depends on both the flexibility of each body and the applied loads. This paper develops a generalized method for the generation of a set of Ritz vectors to be used in addition to vibration normal modes to form the modal basis to model flexible bodies for dynamic analysis of multibody mechanical systems. The Ritz vectors are generated using special distribution of the D’Alembert force and the kinematic constraint forces due to gross-body motion of a flexible body. Combined with vibration normal modes, they form more efficient vector bases for the modeling of flexible bodies comparing to using vibration normal modes alone or using the combination of static correction modes and vibration normal modes. Ritz vectors can be regenerated when the system undergoes significant changes of its configuration and the regeneration procedure is inexpensive. The effectiveness of using the combination of vibration normal modes and the proposed Ritz vectors is demonstrated using a planar slider-crank mechanism.

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