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In aerospace engineering, structural modifications play an essential role in design of structures. In some cases, it is necessary to guarantee that a specific natural frequency of the structure remains unchanged when additional masses are attached. The methods based on the Sherman-Morrison formula are proposed in this paper, called the optimal selection method and the absolute value method, to maintain the specific natural frequency. The methods are both implemented by installing a spring on the system and can eliminate the effect of the additional mass on the specific frequency. The proposed methods were verified to be effective and accurate through numerical simulations. Results show that the optimal selection method has similar applicability as the existing real value method, and both methods are applicable only in cases of small damping. In addition, the absolute value method has extensive applicability in systems with either small or large damping. [ABSTRACT FROM AUTHOR]

Substructure method has been widely applied in dynamic analysis of complex structures due to high computational efficiency. On the basis of Residual flexibility mixed-boundary (RFMB) substructure method, a model updating approach is proposed in this paper. Four major steps of the RFMB model updating method are summarized as: 1) Substructuring: Dividing the whole structure into residual part and reduced part according to the junction surface; 2) reduction: Using the RFMB component mode synthesis approach to reduce the order of each substructures; 3) assembly: Residual structure analysis by using the reduced assemble matrix; 4) updating: Model updating by solving the optimization problem. Numerical simulation is conducted to verify the effectiveness by adopting a cantilever plate in case I. In case II, the proposed method is applied to identify the elastic parameter of interface of a bolted joint structure using experimental data. After parameter identification, the maximum error between numerical results and the experimental data decreases to 2.44 %. And three component mode synthesis model updating methods: Craig-Bampton (CB), Mixed-boundary (MB) without considering residual flexibility and RFMB model updating approach, are applied to update the same bolted joint structure for comparing the accuracy. For comparing the computational efficiency, the RFMB model updating approach is applied to the complicated aero-engine casing structure. In case III, the average time-consuming of the Whole finite element model (WFEM) is 5.15 times to the Residual finite element model (RFEM) in the single updating iteration. Results show that the proposed approach has better performance in the finite element model updating. [ABSTRACT FROM AUTHOR]

Design optimization of dynamic properties, for example, modal frequencies, can be of much importance when structures are exposed to the shock and/or vibration environments. A modal strain based method is proposed for fast design of natural frequencies of plate-like structures. The basic theory of modal strains of thin plates is reviewed. The capability of determining the highly sensitive elements by means of modal strain analysis is theoretically demonstrated. Finite element models were constructed in numerical simulations. Firstly, the application of the proposed method is conducted on a central-massed flat plate which was topologically optimized by the Reference. The results of modal strain analysis at the first mode have good agreement with the results from the topology optimization. Furthermore, some features of the strain mode shapes (SMSs) of the flat plate are investigated. Finally, the SMSs are applied to the optimization of a stiffened plate. Attention is focused on the distributions of the SMSs of the stiffeners, which also shows good agreement with the results from the topology optimization in the previous study. Several higher orders of SMSs are extracted, which can visualize the most sensitive elements to the corresponding modal frequency. In summary, both the theory and simulations validate the correctness and convenience of applying SMSs to dynamic design of plate-like structures. [ABSTRACT FROM AUTHOR]

Assembling sandwich serpentine structures with soft functional materials creates an effective way to high-performance stretchable devices. In order to achieve better design criteria for the application of serpentine-shaped stretchable systems, this paper explores the mechanics governing the deformation mechanisms of the sandwich serpentine structures. Firstly, detailed three-dimensional (3-D) numerical simulations were conducted to well capture the deformation modes. Secondly, a theoretical model was developed within the simplified 1-D formulation. Numerical and theoretical investigations reveal the important features of the underlying materials (including the representative low-modulus elastomers) and mechanics aspects of the polymer/metal/polymer sandwich serpentine interconnects system with strain-isolating layers, and their dependence on key design variables (including the material selection and thickness of both the isolation layer and the serpentine clad). Three distinct deformation modes of the sandwich serpentine structures were observed and discussed: 1) Global buckling; 2) Local wrinkling; and 3) Planar bending. By theoretically analyzing the wrinkling wavelengths, we propose a simple design criterion for the strain-isolating layers that indicates a transition from local wrinkling to global buckling, with the increasing thickness of the isolation layer. Results will be useful to mechanical design of stretchable systems with high levels of the elastic stretchability. • Systematic simulations were conducted for sandwich serpentine structures mounted on soft substrates with isolating layers. • Three deformation modes were differentiated by various designs: 1) Local wrinkling, 2) Global buckling, 3) Planar bending. • The wrinkling/buckling transition point obtained from FEA results agrees well with the wavelengths by theoretical analysis. • We proposed a useful design criterion to improve the stretchability of sandwich serpentine interconnects. [ABSTRACT FROM AUTHOR]

In the modal test of lightweight structures, the measured data is easily polluted by mass loading effects of transducers. A method is proposed to eliminate the influence of sensors for accurately estimating the frequency response functions (FRFs) of structures. Considering the situation that the multiple accelerometers lead to changes in the dynamic stiffness matrix, the corrected FRFs are derived from the original measured signals based on the Sherman-Morrison-Woodbury formula. The salient feature of the proposed strategy is that the adverse effects of sensors can be eliminated in only one step. Numerical simulations are conducted by employing a six-degrees of freedom spring-mass system, modal frequencies and mode shapes with high accuracy are obtained by measured signals. Experimental investigation is undertaken by using a laboratory solar panel. Results show that the effects of multi-transducers mass can be removed efficiently and the corrected FRFs are in good agreement with the targeted values. The excitation and measurement points are regarded as active coordinates, and the computational efficiency can be significantly improved when the presented method is applied on active coordinates. [ABSTRACT FROM AUTHOR]