Review and Assessment of Model Updating for Nonlinear, Transient Dynamics

The purpose of this publication is to motivate the need of validating numerical models based on time-domain data for nonlinear, transient, structural dynamics and to discuss some of the challenges faced by this technology. Our approach is two-fold. First, several numerical and experimental testbeds are presented that span a wide variety of applications (from nonlinear vibrations to shock response) and difficulty (from a single-degree of freedom system with localized nonlinearity to a 3D, multiple-component assembly featuring nonlinear material response and contact mechanics). These testbeds have been developed at Los Alamos National Laboratory (LANL) in support of the advanced strategic computing initiative and our code validation and verification program. Conventional, modal-based updating techniques are shown to produce erroneous models although the discrepancy between test and analysis modal responses can be bridged. This conclusion offers a clear justification that metrics based on modal parameters are not well suited to the resolution of inverse, nonlinear problems. In the second part of this work, the state-of-the-art in the area of model updating for nonlinear, transient dynamics is reviewed. The techniques identified as the most promising are assessed using data from our numerical or experimental testbeds. Several difficulties of formulating and solving inverse problems for nonlinear dynamics are identified. Among them, we cite the formulation of adequate metrics based on time series and the need to propagate variability throughout the optimization of the model’s parameters. Another important issue is the necessity to satisfy continuity of the response when several finite element optimizations are successively carried out. The publication concludes with a brief description of the framework developed at LANL for the probabilistic validation and verification of nonlinear structural models. This discussion is illustrated with results obtained when parameters of a model are optimized such that acceleration signals become statistically consistent with measurements obtained during a series of impact tests. 1 Technical Staff Member, ESA-EA, [email protected] , 505-665-7955 (Voice), 505-665-2137 (Fax). 2 Technical Staff Member, ESA-EA, [email protected] , 505-667-6950 (Voice), 505-665-2137 (Fax). F.M. HEMEZ AND S.W. DOEBLING Authorized for unlimited, public release on December XX, 1999. LA-UR-99-XXXX. Unclassified. 2