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• A novel non-intrusive sensitivity-based nonlinear finite element model updating method is proposed. • The nonlinear response sensitivity is computed using real and imaginary perturbation synchronously. • The nonlinear finite element model is updated using time history responses. • A cantilever beam with steel slice is conducted to illustrate the experimental application of the proposed method. This paper presents a novel non-intrusive sensitivity-based nonlinear finite element model updating method in which the local nonlinearity of structure is considered. The sensitivity analysis is conducted to determine the sensitivity of a dynamic response with respect to different nonlinear parameters using the real and imaginary perturbation method in one single calculation. The use of the imaginary perturbation is capable of second-order accuracy in imaginary perturbation sensitivity analysis of the nonlinear finite element model updating procedure. The nonlinear parameters in the finite element model are estimated by using the improved sensitivity-based optimization algorithm. A nonlinear multi-degree-of-freedom oscillator and a cantilever beam with multiple nonlinear supports are studied to verify the accuracy of the proposed method. The effects of measurement noise and initial parameters on the performance of the presented approach are further investigated. Then, the proposed approach is verified by an experimental test of a cantilever beam with a steel slice. The updated nonlinear finite element model is further evaluated by the structure subjected to new excitations. Results show that the proposed method can effectively update the nonlinear finite element model even in the presence of contaminated measurement data and different initial parameters in the finite element model. [ABSTRACT FROM AUTHOR]

The effective numerical model of stitched sandwich composite plays crucial role in dynamics analysis and structural design. A sensitivity-based multistage model updating method is proposed for modeling of the stitched sandwich panel using the experimental modal frequencies. Based on applying the periodic boundary condition, the initial equivalent finite element model of a stitched sandwich composite is constructed; the measured frequencies are obtained from the modal test. According to relative sensitivity analysis of modal frequencies with respect to updating parameters, the different well-conditioned groups of parameters are selected to be updated. This method is applied to a stitched sandwich panel with established configuration of the stitches. Results show that the proposed method with the smallest condition number of relative sensitivity matrix has a better performance than the multistage method using type-based parameter group selection and the traditional model updating approach. [ABSTRACT FROM AUTHOR]

• A dynamic sensitivity-based nonlinear finite element model updating method is proposed. • The direct differential method is presented for calculating the nonlinear dynamic responses and its sensitivities synchronously. • A scheme for responses points selection and its effect on the updating accuracy are analyzed. To obtain the numerical model for predicting the nonlinear dynamic responses with high accuracy, a dynamic sensitivity-based model updating approach by using the time-domain responses is proposed in this paper. The sensitivity analysis of time-domain response is derived by using the direct differentiation method. The objective function of the nonlinear model updating is constructed by minimizing the discrepancy between the measured and the calculated time-domain responses. The time-domain responses and the corresponding dynamic sensitivities are calculated synchronously. The repeated nonlinear dynamic analysis can be avoided to obtain dynamic sensitivity, which is independent of the perturbation step. Numerical examples of a Duffing-Van der Pol oscillator, a magnetometer boom, and a cantilever plate with multiple nonlinear supports are adopted to verify the method. Crucial issues about the measured noise and the selection of the targeted responses are also considered and discussed. The validation results show that the proposed method is effectively applied to model updating of nonlinear structure using time-domain response with good anti-noise performance, and the scheme for response points selection is reliable for guaranteeing the accuracy. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The honeycomb sandwich composite material has been widely applied in engineering due to its excellent mechanical performance. The elastic properties of honeycomb core is of crucial importance in efficient mechanical analysis. An approach on determining the equivalent elastic modulus of honeycomb core using experimental modal data is proposed in this paper. Based on analytically predicted elastic constants of the pure core, the initial finite element model of a honeycomb panel is constructed using a three-layer sandwich theory; according to errors that exist in analytically estimated equivalent parameters and the sensitivity analysis of modal frequencies with respect to system parameters, the out-of-plane shear moduli G cxz and G cyz are selected to be determined. Consequently, the two parameters are determined by minimizing an objective function which is formulated with vibration test and numerical modal data. Comparative investigations are conducted to illustrate that the initial values of the parameters with physical significance play an important role in the identification procedure. The presented method can provide accurate and reliable predictions of material constitutive parameters of honeycomb core. [ABSTRACT FROM AUTHOR]

The unsteady vortex-lattice method provides a medium-fidelity tool for calculation of low-speed aerodynamic loads based on the potential-flow theory. It has long been favored in research on the aeroelasticity and flight dynamics for flexible aircraft with high aspect ratios. However, the unsteady vortex-lattice method is established in the discrete time domain which brings difficulties to modeling aeroelastic system for stability analysis. An analytical aerodynamic sensitivity calculation scheme is developed in this paper to formulate the aeroelastic equations of motion with UVLM aerodynamics. A free wake model is used to simulate accurate vortex shedding and subsequent wake propagation. Using a small perturbation method, the aerodynamic governing equations are linearized around the equilibrium condition, where the analytical sensitivities can be derived. The surface spline interpolation algorithm is adopted to implement the structure-aerodynamic coupling. Both aerodynamic sensitivities with respect to structural motions and circulation strengths of vortices are obtained. In numerical studies, a time-marching transient response analysis scheme is used to obtain the distributed aerodynamic loads and structural deformations. Analytical sensitivity results are validated by the finite difference method. The proposed analytical sensitivity calculation framework is demonstrated to be applicable to commonly used beam-based flexible wing models, as well as the shell-based finite element models with higher fidelity. The derived sensitivity formulations and related numerical implementations can build the foundation for further studies on aeroelastic optimization and stability analysis. [ABSTRACT FROM AUTHOR]