国际机械系统动力学学报(英文)最新文献

Incipient faults of gears and rolling bearings in rotating machineries are very difficult to identify using traditional envelope analysis methods. To address this challenge, this paper proposes an effective local spectrum enhancement-based diagnostic method that can identify weak fault frequencies in the original complicated raw signals. For this purpose, a traversal frequency band segmentation technique is first proposed for dividing the raw signal into a series of subfrequency bands. Then, the proposed synthetic quantitative index is constructed for selecting the most informative local frequency band (ILFB) containing fault features from the divided subfrequency bands. Furthermore, an improved grasshopper optimization algorithm-based stochastic resonance (SR) system is developed for enhancing weak fault features contained in the selected most ILFB with less computation cost. Finally, the enhanced weak fault frequencies are extracted from the output of the SR system using a common spectrum analysis. Two experiments on a laboratory planetary gearbox and an open bearing data set are used to verify the effectuality of the proposed method. The diagnostic results demonstrate that the proposed method can identify incipient faults of gears and bearings in an effective and accurate manner. Furthermore, the advantages of the proposed method are highlighted by comparison with other methods.

This paper aims to examine the influence of gravity on a thermoelastic micro-elongated layer when a piezoelectric layer is above it, utilizing the theory of Lord–Shulman (L–S) and also the model of dual-phase-lag (DPL). A partial differential equation was transformed into an ordinary differential equation using the normal mode analysis. Aluminum epoxy numerical computations are carried out, and the results are presented in graphical format. The L–S theory and the model of DPL are compared in the presence and absence of gravity and it is found that gravity has quite a massive influence on all the physical quantities.

Thermal metamaterials based on transformation theory offer a practical design for controlling heat flow by engineering spatial distributions of material parameters, implementing interesting functions such as cloaking, concentrating, and rotating. However, most existing designs are limited to serving a single target function within a given physical domain. Here, we analytically prove the form invariance of thermoelectric (TE) governing equations, ensuring precise controls of the thermal flux and electric current. Then, we propose a dual-function metamaterial that can concentrate (or cloak) and rotate the TE field simultaneously. In addition, we introduce two practical control methods to realize corresponding functions: one is a temperature-switching TE rotating concentrator cloak that can switch between cloaking and concentrating; the other is an electrically controlled TE rotating concentrator that can handle the temperature field precisely by adjusting external voltages. The theoretical predictions and finite-element simulations agree well with each other. This work provides a unified framework for manipulating the direction and density of the TE field simultaneously and may contribute to the study of thermal management, such as thermal rectification and thermal diodes.

High-speed Maglev is a cutting-edge technology brought back into the focus of research by plans of the Chinese government for the development of a new 600 km/h Maglev train. A Chinese-German cooperation with industrial and academic partners has been established to pursue this ambitious goal and bring together experts from multiple disciplines. This contribution presents the joint work and achievements of CRRC Qingdao Sifang, thyssenkrupp Transrapid, CDFEB, and the ITM of the University of Stuttgart, regarding research and development in the field of high-speed Maglev systems. Furthermore, an overview is given of the historical development of the Transrapid in Germany, the associated development of dynamical simulation models, and recent developments regarding high-speed Maglev trains in China.

In this paper, we investigate the impact of coronary artery dynamics on the wall shear stress (WSS) vector field topology by comparing fluid–structure interaction (FSI) and computational fluid dynamics (CFD) techniques. As one of the most common causes of death globally, coronary artery disease (CAD) is a significant economic burden; however, novel approaches are still needed to improve our ability to predict its progression. FSI can include the unique dynamical factors present in the coronary vasculature. To investigate the impact of these dynamical factors, we study an idealized artery model with sequential stenosis. The transient simulations made use of the hyperelastic artery and lipid constitutive equations, non-Newtonian blood viscosity, and the characteristic out-of-phase pressure and velocity distribution of the left anterior descending coronary artery. We compare changes to established metrics of time-averaged WSS (TAWSS) and the oscillatory shear index (OSI) to changes in the emerging WSS divergence, calculated here in a modified version to handle the deforming mesh of FSI simulations. Results suggest that the motion of the artery can impact downstream patterns in both divergence and OSI. WSS magnitude is also decreased by up to 57% due to motion in some regions. WSS divergence patterns varied most significantly between simulations over the systolic period, the time of the largest displacements. This investigation highlights that coronary dynamics could impact markers of potential CAD progression and warrants further detailed investigations in more diverse geometries and patient cases.

This study proposes a spider-web elastic metamaterial to suppress vibrations in space slender structures, such as flexible space tethers. The metamaterial consists of unit cells that are periodically distributed on the space tether to obtain band gaps. The finite element model of the unit cell is established by employing the absolute nodal coordinate formulation (ANCF) due to the large deformation of the structure. The eigenfrequencies and corresponding vibration modes of the unit cell are obtained by ANCF. Moreover, the band gap of the unit cell is calculated based on the phonon crystal theory. The relationship between the vibration modes and the band gaps is analyzed. Finally, an experiment is conducted to verify the vibration transmission characteristics of finite period cells. The results show the effectiveness of the spider-web elastic metamaterial for vibration suppression of a flexible tether. This study provides insights into the use of elastic metamaterials for vibration isolation in space tether systems.

The stochastic response of a multi-degree-of-freedom nonlinear dynamical system is determined based on the recently developed Wiener path integral (WPI) technique. The system can be construed as a representative model of electrostatically coupled arrays of micromechanical oscillators, and relates to an experiment performed by Buks and Roukes. Compared to alternative modeling and solution treatments in the literature, the paper exhibits the following novelties. First, typically adopted linear, or higher-order polynomial, approximations of the nonlinear electrostatic forces are circumvented. Second, for the first time, stochastic modeling is employed by considering a random excitation component representing the effect of diverse noise sources on the system dynamics. Third, the resulting high-dimensional, nonlinear system of coupled stochastic differential equations governing the dynamics of the micromechanical array is solved based on the WPI technique for determining the response joint probability density function. Comparisons with pertinent Monte Carlo simulation data demonstrate a quite high degree of accuracy and computational efficiency exhibited by the WPI technique. Further, it is shown that the proposed model can capture, at least in a qualitative manner, the salient aspects of the frequency domain response of the associated experimental setup.

A stall diagnosis method based on the entropy feature extraction algorithm is developed in axial compressors. The reliability of the proposed method is determined and a parametric sensitivity analysis is experimentally conducted for two different types of compressor stall diagnoses. A collection of time-resolved pressure sensors is mounted circumferentially and along the chord direction to measure the dynamic pressure on the casing. Results show that the stall and prestall precursor embedded in the dynamic pressures are identified through nonlinear feature perturbation extraction using the entropy feature extraction algorithm. Further analysis demonstrates that the prestall precursor with the peak entropy value is related to the unsteady tip leakage flow for the spike-type stall diagnosis. The modal wave inception with increasing amplitude is identified by the considerable increase of the entropy value. The flow field in the tip region indicates that the modal wave corresponds to the flow separation in the suction side of the rotor blade. The warning time is 100–300 rotor revolutions for both types of stall diagnoses, which is beneficial for stall control in different axial compressors. Moreover, a parametric study of the embedding dimension m, similar tolerance n, similar radius r, and data length N in the fuzzy entropy method is conducted to determine the optimal parameter setting for stall diagnosis. The stall warning based on the entropy feature extraction algorithm provides a new stall diagnosis approach in the axial compressor with different stall types. This stall warning can also be adopted as an online stability monitoring index when using the concept of active stall control.

Dynamic characteristics of large permanent magnet direct-drive generators (PMDGs) considering electromagnetic–structural coupling effects are analyzed in this study. Using the conformal mapping method, the scalar magnetic potential of the air gap magnetic field considering the slot effect is calculated. On the basis of the discrete current element and magnetic equivalent circuit model, the local magnetic saturation effect of the stator and rotor is quantitatively simulated and the air gap magnetic field intensity distribution is obtained via numerical simulation. A series of uniformly distributed equivalent electromagnetic springs are introduced to develop an electromagnetic–structural coupling finite element PMDG model. The proposed air gap field analysis method is verified by the finite element analysis results. On the basis of the test platform for the Goldwind 1.5 MW PMDG, both modal and dynamic response tests for the stator/rotor coupling system are conducted, and the results are compared with the natural frequencies, mode shapes, and vibration responses obtained using the numerical model. The effects of the air gap length and rotor speed on the natural frequencies of the coupling system are analyzed. The proposed model has the potential to accurately evaluate the PMDG vibration energy, avoiding resonance points, and maintaining stable operations of the unit.

This paper presents an analytical solution for the free vibration of functionally graded material (FGM) sandwich plates in a thermal environment. An equivalent-single-layer (ESL) plate theory with four variables is used to obtain the solution. Two types of sandwich plates are examined in this study: one with FGM face sheets and a homogeneous core and the other with an FGM core and homogeneous face sheets. The governing equations of motion are derived based on Hamilton's principle and then solved using the Navier method. The results of natural frequencies of simply supported FGM sandwich plates are compared with the available solutions in the literature. The effects of volume fraction distribution, geometrical parameters, and temperature increments on the free vibration characteristics are discussed in detail.