The magnetorheology and dispersion stability of bidisperse magnetic particles (BMP)-based magnetorheological (MR) fluids were improved by applying a novel functional coating composed of gelatin and graphite oxide (GO) to the surfaces of the micron-sized carbonyl iron (CI) and nanoparticles Fe₃O₄. Gelatin acted as a grafting agent to reduce the aggregation and sedimentation of CI particles and prevent nanoparticles Fe₃O₄ from oxidation. In addition, a dense GO network on the surface of gelatin-coated BMP was synthesized by self-assembly to possess a better MR performance and redispersibility. The rheological properties of MR fluids containing dual-coated BMP were measured by a rotational rheometer under the presence of magnetic field and their dispersion stability was examined through sedimentation tests. The results showed that CI@Fe₃O₄@Gelatin@GO (CI@Fe₃O₄@G@GO) particles possessed enhanced MR properties and dispersion stability. In addition, the nanoparticle-enhancing effects on the dispersion stability of BMP-based MR fluids were investigated using Monte Carlo simulations.

In this paper, a modified Fourier series method is presented for the free vibration of moderately thick orthotropic functionally graded plates with general boundary restraints based on the first-order shear deformation theory. Regardless of boundary restraints, displacements and rotations of each plate are described as an improved form of double Fourier cosine series and several closed-form auxiliary functions to eliminate all the boundary discontinuities and jumps. Exact solutions are obtained by the energy functions of the plates based on Rayleigh-Ritz method. The convergence and reliability of the current method and the corresponding theoretical formulations are verified by comparing the present results with those available in the literature, and numerous new results for orthotropic functionally graded (OFG) plates with general boundary restraints are presented. In addition, the effects of gradient index, volume fraction and geometric parameters on frequencies with general boundary restraints are illustrated.

In dynamic structure test, the specimen of hydraulic servo shaking table contains not only inertia load but also elastic load. The specimen herein is simplified as a spring‐mass‐damping system, and the mathematical model of the hydraulic servo shaking table is established by theoretical analysis. The coupling between specimen’s elastic load and shaking table itself produces resonance phenomenon in the required bandwidth when the elastic load is not negligible, which deteriorates the system’s dynamic performance and even leads to the instability of the control system. Also, the time‐varying resonance frequency further aggravates the control performance of the system in the shaking test. In this paper, an adaptive notch filter based on least mean square (LMS) error principle is employed to identify the resonance frequencies online and real‐time adjust the parameters of the notch filter. Simulation and experiment results show the effectiveness of frequency identification and resonance mode suppression. Compared with the existing resonance suppression scheme, the proposed method can suppress the appeared resonance mode adaptively.

Recently, bio-inspired artificial muscles based on ionic polymers have shown a bright perspective in engineering and medical research, but the inherent tremor behavior can cause instability of output response. In this paper, dynamic additional grey catastrophe prediction (DAGCP) is proposed to forecast the occurrence time of tremor behavior, providing adequate preparation time for the suppression of the chitosan-based artificial muscles. DAGCP constructs various dimensions of time subsequence models under different starting points based on the threshold of tremor occurrence times and peak-to-peak values in unit time. Next, the appropriate subsequence is selected according to grey correlation degree and prediction accuracy, then it is updated with the newly generated values to achieve a real-time forecast of forthcoming tremor time. Compared with conventional grey catastrophe prediction (GCP), the proposed method has the following advantages: (1) the degradation of prediction accuracy caused by the immobilization of original parameters is prevented; (2) the dynamic input, real-time update and gradual forecast of time sequence are incorporated into the model. The experiment results show that the novel DAGCP can predict forthcoming tremor time earlier and more accurately than the conventional GCP. The generation mechanism of tremor behavior is illustrated as well.

Hydraulic shaking table is mainly used to stimulate the desired vibration environment and evaluate the shock resistance of structure. However, due to the inherent nonlinearities of the hydraulic shaking table, the acceleration response displays amplitude attenuation and phase delay for sinusoidal excitation signal. The distorted response degrades the control performance and even leads to an increase in system instability. In this paper, the water cycle algorithm (WCA), a recently developed metaheuristic method, is developed to estimate the harmonic information such as amplitude and phase. The basic idea of the proposed algorithm is inspired from nature and based on the observation of water cycle process and how rivers and streams flow to the sea in the nature world. The estimation process based on WCA is sequentially updating the weight vector of the signal. The amplitude and phase of fundamental as well as each harmonic can be achieved when the objective function is minimized. Simulation and experimental results demonstrate that the proposed harmonic estimation algorithm has good real‐time performance, fast convergence, and excellent accuracy.

In this investigation, an exact method based on the first‐order shear deformation shallow shell theory (FSDSST) is performed for the free vibration of functionally graded sandwich shallow shells (FGSSS) on Winkler and Pasternak foundations with general boundary restraints. Vibration characteristics of the FGSSS have been obtained by the energy function represented in the orthogonal coordinates, in which the displacement and rotation components consisted of standard double Fourier cosine series and several closed‐form supplementary functions are introduced to eliminate the potential jumps and boundary discontinuities. Then, the expansion coefficients are determined by using Rayleigh‐Ritz method. The proposed method shows good accuracy and reliability by comprehensive investigation concerning free vibration of the FGSSS. Numerous new vibration results for FGSSS on Winkler and Pasternak foundations with various curvature types, geometrical parameters, and boundary restraints are provided, which may serve as benchmark solutions for future research. In addition, the effects of the inertia, shear deformation, and foundation coefficients on free vibration characteristic of FGSSS are illustrated.