Figure 5: Multi-Segmented Shell Structure The new reduction strategy is applied to this 6480 DOF shell finite element model by application of unit body loads (following equation 13) at each of the individual “ring” stations. An interesting result of the selected unit load patterns is a reduction of displacement DOFs to centerline grid points (following equation 16) as illustrated in Figure 6. The reduced model consisting of 27 centerline DOFs, with a fixed base, may serve as a test-analysis model (TAM). Also depicted in Figure 6 are (a) a typical accelerometer arrangement that may be employed to construct an effective centerline 6 DOF displacement array, and (b) the (consistent) rigid body mass matrix associated with the reduced model. Figure 6: Reduced Centerline Shell Structure Model with Related TAM Information Computed modes for both the exact and reduced shell models, summarized in Figure 7, indicate several key features associated with the new reduction method (when it is applied to shell structural dynamics), namely (a) overall body mode frequency and mode shapes of the reduced model are essentially exact, and (b) shell breathing modes are automatically not computed by the reduced model. Figure 7: Exact and Reduced Model Modes of the Shell Structure 365
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