Pre-test Predictions of Next-Level Assembly Using Calibrated Nonlinear Subcomponent Model 5 3.1 Fixture-Pylon Finite Element Model A detailed finite element model (FEM) of the fixture-pylon assembly was used to create an initially linear HCB model. The mesh of the finite element model was generated using CUBIT [13], and the Sierra Structural Dynamics codes [11] were used for the eigenvalue analysis and HCB reduction. An eigenvalue analysis was performed on the fixture-pylon assembly with a fixed base to determine the linear natural frequencies and mode shapes, such as the first mode shown in Fig. 3b. This f rist mode is the “swinging pendulum” mode of the pylon, with a natural frequency of 7.3 Hz. This was the target mode for the experiments conducted in Ligeikis et al. [5] and was used to characterize the nonlinearity between the thin beam and block. The linear ROM was generated from an HCB reduction with 16 fixed-interface modes and retained seven physical DOFs (drive point, accelerometer s1, accelerometer s2, and four virtual nodes). To account for the nonlinearity, a whole joint modeling approach [14] was used to constrain the finite element nodes along the contact edge of the block to a single, virtual node as shown in Fig. 4; an analogous whole joint is created along a node line along the thin beam. The nonlinearity localized within the pylon block was modeled as a 1-D constitutive element between the virtual node pairs, resulting in the nonlinear HCBmodel. (a) Mode 1 (fn = 7.3 Hz) (b) Fig. 3 Fixture-pylon CAD assembly; (a) general view; (b) natural frequency and mode shape for mode 1 2 1 3 4 Virtual nodes Virtual nodes Fig. 4 Nonlinear element in pylon block
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