Improving the fidelity of numerical simulations using available test data is an important activity in the overall process of model verification and validation. While model updating or calibration of linear elastodynamic behaviors has been extensively studied for both academic and industrial applications over the past three decades, methodologies capable of treating nonlinear dynamics remain relatively immature. The authors propose a novel strategy for updating an important subclass of nonlinear models characterized by globally linear stiffness and damping behaviors in the presence of local nonlinear effects. Existing nonlinear updating strategies are based on the Response Force Surface (RSF), Proper Orthogonal Decomposition (POD), or first-order Harmonic Balance (HB) methods. With the exception of the RFS approach, these methods introduce some form of linearization and this naturally limits their application to relatively weak nonlinear effects. As for the RFS approach, its major weakness lies in the fact that it requires that the structural responses be measured on all model degrees-of-freedom where significant nonlinear effects are present. In this paper, a novel methodology is presented which effectively combines two well-known methods for structural dynamic analysis: the Multi-harmonic Balance method for calculating the periodic response of a nonlinear system and the Extended Constitutive Relation Error method for establishing a well-behaved metric for modeling and test-analysis errors. The proposed methodology neither requires any linear approximation nor the observation of all nonlinear degrees-of-freedom. The advantages and limitations of the proposed nonlinear updating strategy will be illustrated based on an academic example.
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