Narrow Results

This paper demonstrates that a sandwich beam with the continuous harmonic distribution of geometrical and physical parameters can be adjusted to yield the desired response. The facial layer thickness and core layer modulus of the sandwich beam are considered as the harmonic distribution. The frequency responses and response spectral densities of the finite harmonic sandwich beam with supported mass under stochastic support motion excitations are studied for improving the performance. The partial differential equations for the horizontal and vertical coupling motions of the harmonic sandwich beam are derived and converted into the ordinary differential equations for the multi-mode coupling vibration. The modal stiffness, mass and excitation coefficients are functions of the harmonic distribution parameters (HDPs). The vibration responses including resonances and anti-resonances can be adjusted by the harmonic parameter wave numbers and amplitudes. The frequency responses and response spectral densities of the harmonic sandwich beam are obtained. The single and two-mode vibrations are analyzed to demonstrate that the response resonance and anti-resonance can be adjusted via the HDPs of the beam. The substantially improved vibration response characteristics and the influence of the HDPs on the response spectral densities are illustrated with numerical results.

This study presents two hybrid methods, the full combination method and the simplified expression, for evaluating the fatigue life of linear structures with uncertain-but-bounded parameters subjected to stochastic excitations. First, approximate expressions of the spectral moments and spectral bandwidth parameters are derived based on the improved interval analysis via extra unitary interval and the interval Taylor expansion. Then, the lower and upper bounds of the interval expected fatigue damage rate and fatigue life are evaluated by fully or properly combining the two bounds of the spectral moments and spectral bandwidth parameters by the Tovo–Benasciutti method. Through the numerical study, the full combination method is recommended for the accurate assessment of the interval fatigue life, and the simplified expression is recommended for rapid evaluation of the two bounds of the interval fatigue life using the explicit expression. Finally, three numerical examples are adopted to illustrate the accuracy and efficiency of the proposed methods via comparison of the present results with the exact ones.

Friction pendulum systems (FPSs) are increasingly being used for bridge seismic isolation, and the isolated response is generally achieved at the expense of inducing large bearing displacements. Setting up a tuned inerter damper (TID) is an approach for improving seismic performance. Nevertheless, the optimization and performance enhancement of multiple TIDs to mitigate the seismic responses of bridges isolated with the FPSs are limited. In this study, the stochastic optimization of multiple TIDs for controlling stochastically excited bridges with FPS bearings was pursued. By describing the hysteretic characteristics of the FPS using the Bouc–Wen model, augmented systems of the bridge model, FPS bearings, and TIDs were formulated and combined with the modeling of stochastic excitation as filtered Gaussian white noise. A stochastic optimization procedure of multiple TIDs for controlling the bridge response considering the nonlinearity of the FPS bearings is proposed and illustrated using examples of continuous bridges. The effects of FPS friction on the optimization and robustness of the TID parameters were identified. A parametric study was performed to determine the mechanism of TID performance enhancement depending on the number of TIDs, multiple modes of tuning, and inertance distribution. Numerical results indicate that the TIDs designed via stationary-stochastic-global (SSG) optimization significantly reduced the responses of the isolated bridge, and the performance was improved by increasing the TID number. Considering the multi-mode contributions to the transversal responses, the performance of spatially distributed TIDs can be substantially enhanced by adding the TID inertance as a design parameter.

The lumbar disc has complex structure and material properties, and if it develops disease, it cannot heal itself. Therefore, prevention of lumbar disc herniation is very important. In this paper, the model of lumbar disc is built, and the nonlinear dynamic response of the system is researched. A modified Van der Pol model is imported to describe the stress–strain curves of the lumbar disc. The system’s dynamic model is set up, and harmonic balance method is applied to revise the natural frequency of the system. The product of numerical simulation reveals that the lumbar disc has complex dynamic characteristics, including balance point, limit cycle bifurcation and stochastic Hopf bifurcation. By changing the parameters, we can avoid large-scale periodic movement of the lumbar disc which causes lumbar disc herniation. These results contribute to the prevention of lumbar disc herniation.

For severe patients with new coronavirus pneumonia, the use and stability of the ventilator are important. In this paper, we proposed a new type of shock-absorbing structure that can be used to improve the stability of the ventilator’s gas pipeline, thereby reducing the risk of the gas pipeline falling due to external interference. The film shape memory alloy (SMA) compared with bulk SMA is more suitable for gas pipeline shock absorption due to its large volume ratio and extremely high energy density. In order to optimize the performance of actuator and enhance the utilization rate of SMA, the nonlinear characteristics of Ti-Ni thin film actuator are researched and the effect of SMA film position on the system are investigated. The van der Pol term is introduced to fit the hysteresis loop of shape memory materials. Thus, the nonlinear dynamic response of SMA thin film actuator under stochastic excitation is studied. The numerical and experiment results show that the position of SMA can change the system’s stability, the proposed structure can reduce the system’s vibration to the maximum extent. The results indicate that the new proposed polymer/SMA composite film micro-actuator exhibits high energy dissipation ability, and the utilization rate of smart material is enhanced. Therefore, the new damping structure proposed in this paper is of great significance to the damping of gas pipelines.

The Bouc model describes the behavior of hysteretic materials using three-coupled differential equations. Under white noise excitation, the probability density of the state variables can be approximated using closure methods. Here, a new closure approach is presented that utilizes the beta distribution for hysteretic softening together with a nonlinear mapping using the inverse hyperbolic tangent. The beta distribution properly models the distribution of the force-proportional displacement, the required nonlinear relation between displacement, velocity, and force-proportional displacement is, however, not entirely captured for large excitation levels leading to deviations from the Monte-Carlo simulations.