Improved experimental impedance modeling techniques for updating finite element models.

摘要

In the design and optimization of a structure or machine, an accurate finite element model is often necessary to predict the structure's noise and vibration behavior. This dissertation investigates some important aspects of experimental impedance modeling techniques and proposes the improved techniques for updating finite element models.; An SVD/QR based model error indicator function is proposed to improve the error localizing procedure. A singular value decomposition is first used to select the meaningful portion of a least squares problem data matrix. Then, a QR permutation pivoting decomposition is applied on the selected matrix to find out the parameters that correspond to the dominant model errors. This method is efficient since both SVD and QR decomposition methods have a good ability to condense large data matrices and is effective since the meaningless portion of the data matrix is discarded.; The experimentally measured data contains damping, while damping is generally not available in the finite element model. An improved finite element model updating procedure is proposed to handle this inconsistency. In the improved algorithm, the dominating elements in a finite element damping matrix are eliminated by matrix multiplication operations. The improved procedure is used successfully for heavily damped structures. Three strategic methods are proposed for three specific application cases respectively.; Large differences exist among the updated results from different updating methods. This is because of insufficient information about the test structure in the measured data. A Perturbed Boundary Condition (PBC) updating procedure is proposed which utilizes the data from more than one structural configuration. The use of properly selected PBC configurations generally leads to more accurate updated models and so provides better predictions of the structural dynamic properties.; Numerous simulations as well as an experimental examples are used to demonstrate the concepts evaluated in the course of this research. A combined application of all of the proposed techniques are made to update the finite element model of an H-frame structure, emphasizing on the rotational stiffness properties of the joints between box beams. Practical considerations in applying the new methods are addressed.