国际机械系统动力学学报(英文)最新文献

Due to the large error of the traditional battery theoretical model during large-rate discharge for electromagnetic launch, the Shepherd derivative model considering the factors of the pulse cycle condition, temperature, and life is proposed by the Naval University of Engineering. The discharge rate of traditional lithium-ion batteries does not exceed 10C, while that for electromagnetic launch reaches 60C. The continuous pulse cycle condition of ultra-large discharging rate causes many unique electrochemical reactions inside the cells. The traditional model cannot accurately describe the discharge characteristics of the battery. The accurate battery theoretical model is an important basis for system efficiency calculation, precise discharge control, and remaining capacity prediction. To this purpose, an experimental platform for electromagnetic launch is built, and discharge characteristics of the battery under different rate, temperature, and life decay are measured. Through the experimental test and analysis, the reason that the traditional model cannot accurately characterize the large-rate discharge process is analyzed. And a novel battery theoretical model is designed with the help of genetic algorithm, which is integrated with the electromagnetic launch topology. Numerical simulation is compared with the experimental results, which verifies the modeling accuracy for the large-rate discharge. On this basis, a variety of discharge conditions are applied to test the applicability of the model, resulting in better results. Finally, with the continuous cycle-pulse condition in the electromagnetic launch system, the stability and accuracy of the model are confirmed.

A generalized solution scheme using implicit time integrators for piecewise linear and nonlinear systems is developed. The piecewise linear characteristic has been well-discussed in previous studies, in which the original problem has been transformed into linear complementarity problems (LCPs) and then solved via the Lemke algorithm for each time step. The proposed scheme, instead, uses the projection function to describe the discontinuity in the dynamics equations, and solves for each step the nonlinear equations obtained from the implicit integrator by the semismooth Newton iteration. Compared with the LCP-based scheme, the new scheme offers a more general choice by allowing other nonlinearities in the governing equations. To assess its performances, several illustrative examples are solved. The numerical solutions demonstrate that the new scheme can not only predict satisfactory results for piecewise nonlinear systems, but also exhibits substantial efficiency advantages over the LCP-based scheme when applied to piecewise linear systems.

As one of the most advanced and precise equipment in the world, a photolithography scanner is able to fabricate nanometer-scale devices on a chip. To realize such a small dimension, the optical system is the fundamental, but the mechanical system often becomes the bottleneck. In the photolithography, the exposure is a dynamic process. The accuracy and precision of the movement are determined by the mechanical system, which is even more difficult to control compared with the optical system. In the mechanical system, there are four crucial components: the reticle and wafer stages, the linear motor, the metrology system, and the control system. They work together to secure the reticle and substrate locating at the correct position, which determines the overlay and alignment performance in the lithography. In this paper, the principles of these components are reviewed, and the development history of the mechanical system is introduced.

Dozens of hyperelastic models have been formulated and have been extremely handy in understanding the complex mechanical behavior of materials that exhibit hyperelastic behavior (characterized by large nonlinear elastic deformations that are completely recoverable) such as elastomers, polymers, and even biological tissues. These models are indispensable in the design of complex engineering components such as engine mounts and structural bearings in the automotive and aerospace industries and vibration isolators and shock absorbers in mechanical systems. Particularly, the problem of vibration control in mechanical system dynamics is extremely important and, therefore, knowledge of accurate hyperelastic models facilitates optimum designs and the development of three-dimensional finite element system dynamics for studying the large and nonlinear deformation behavior. This review work intends to enhance the knowledge of 15 of the most commonly used hyperelastic models and consequently help design engineers and scientists make informed decisions on the right ones to use. For each of the models, expressions for the strain-energy function and the Cauchy stress for both arbitrary loading assuming compressibility and each of the three loading modes (uniaxial tension, equibiaxial tension, and pure shear) assuming incompressibility are provided. Furthermore, the stress–strain or stress–stretch plots of the model's predictions in each of the loading modes are compared with that of the classical experimental data of Treloar and the coefficient of determination is utilized as a measure of the model's predictive ability. Lastly, a ranking scheme is proposed based on the model's ability to predict each of the loading modes with minimum deviations and the overall coefficient of determination.

Recent developments in the fields of materials science and engineering technology (mechanical, electrical, biomedical) lay the foundation to design flexible bioelectronics with dynamic interfaces, widely used in biomedical/clinical monitoring, stimulation, and characterization. Examples of this technology include body motion and physiological signal monitoring through soft wearable devices, mechanical characterization of biological tissues, skin stimulation using dynamic actuators, and energy harvesting in biomedical implants. Typically, these bioelectronic systems feature thin form factors for enhanced flexibility and soft elastomeric encapsulations that provide skin-compliant mechanics for seamless integration with biological tissues. This review examines the rapid and continuous progress of bioelectronics in the context of design strategies including materials, mechanics, and structure to achieve high performance dynamic interfaces in biomedicine. It concludes with a concise summary and insights into the ongoing opportunities and challenges facing developments of bioelectronics with dynamic interfaces for future applications.

An improved variable cross-section cantilever beam model for evaluating the time-varying mesh stiffness (TVMS) of the perfect gear tooth is developed in which the tooth number of driving gear is less than 42 and that of driven is more than 42. The TVMS obtained by the proposed method is compared with the result without considering the misalignment between the base circle and gear root. Four types of root crack models and changes in TVMS of 13-crack levels are presented. The fault vibration characteristic of a single-stage spur gear reducer with root crack is analyzed and the correctness is qualitatively verified by the vibration signals of an experimental gearbox with crack or missing failure. The results presented in this paper are of great significance for a deep understanding of the possible causes of vibration and noise of gears and provide a theoretical foundation for the fault diagnosis of the gearbox.

For linear mechanical systems, the transfer matrix method is one of the most efficient modeling and analysis methods. However, in contrast to classical modeling strategies, the final eigenvalue problem is based on a matrix which is a highly nonlinear function of the eigenvalues. Therefore, classical strategies for sensitivity analysis of eigenvalues w.r.t. system parameters cannot be applied. The paper develops two specific strategies for this situation, a direct differentiation strategy and an adjoint variable method, where especially the latter is easy to use and applicable to arbitrarily complex chain or branched multibody systems. Like the system analysis itself, it is able to break down the sensitivity analysis of the overall system to analytically determinable derivatives of element transfer matrices and recursive formula which can be applied along the transfer path of the topology figure. Several examples of different complexity validate the proposed approach by comparing results to analytical calculations and numerical differentiation. The obtained procedure may support gradient-based optimization and robust design by delivering exact sensitivities.

The dynamic dashpot models are widely used in EDEM commercial software. However, most dashpot models suffer from a serious numerical issue in calculating the granular chain because the denominator of damping force includes the initial impact velocity. Moreover, the existing dynamic dashpot models extended from the original Hertz contact law overestimated the contact stiffness in the elastoplastic contact phase. These two reasons above result in most dynamic dashpot models confronting some issues in calculating the multiple collision of the granular chain. Therefore, this investigation aims to propose a new composite dynamic dashpot model for the dynamic simulation of granular matters. First, the entire contact process is divided into three different phases: elastic, elastoplastic, and full plastic phases. The Hertz contact stiffness is still used in the elastic contact phase when the contact comes into the elastoplastic or full plastic phase. Hertz contact stiffness in the dynamic dashpot model is replaced by linearizing the contact stiffness from the Ma-Liu (ML) model in each time step. Second, the whole contact behavior is treated as a linear mass-spring-damper model, and the damping factor is obtained by solving the single-degree-freedom underdamped vibration equation. The new dynamic dashpot model is proposed by combining the contact stiffnesses in different contact phases and corresponding damping factors, which not only removes the initial impact velocity from the denominator of damping force but also updates the contact stiffness based on the constitutive relation of the contact body when the contact comes into the elastoplastic or full plastic phase. Finally, a granular chain is treated as numerical examples to check the reasonability and effectiveness of the new dynamic dashpot model by comparing it to the experimental data. The simulation shows that the solitary waves obtained using the new dashpot model are more accurate than the dashpot model used in EDEM software.

Flutter is a self-excited vibration under the interaction of the inertial force, aerodynamic force, and elastic force of the structure. After the flutter occurs, the aircraft structures will exhibit limit cycle oscillation, which will cause catastrophic accidents or fatigue damage to the structures. Therefore, it is of great theoretical and practical significance to study the aeroelastic characteristics and flutter control for improving the aeroelastic stability of aircraft structures. This paper reviews the recent advances in aeroelastic analysis and flutter control of wings and panel structures. The mechanism of aeroelastic flutter of wings and panels is presented. The research methods of aeroelastic flutter for different structures developed in recent years are briefly summarized. Various control strategies including the linear and nonlinear control algorithms as well as the active flutter control results of wings and panels are presented. Finally, the paper ends with conclusions, which highlight challenges of the development in aeroelastic analysis and flutter control, and provide a brief outlook on the future investigations. This study aims to present a comprehensive understanding of aeroelastic analysis and flutter control. It can also provide guidance on the design of new wings and panel structures for improving their aeroelastic stability.

This study aims to show an approach for the dynamic simulation of a synchronous machine. The magnetic forces in the air gap are calculated efficiently using simplified approaches without neglecting important effects. For the modeling of the magnetic forces, an equivalent magnetic circuit is constructed in which the magnetic saturation and the leakage flux are taken into account and coupled with the electrical circuit at the end. The calculated magnetic forces are then passed to a mechanical model of the motor. Together with a predefinable load torque, the resulting motor rotation and the forces in the bearings are identified. The presented model is then investigated in a small example. This novel approach is intended to provide a method of calculating dynamically the forces transmitted from the shaft to the motor housing and to create the basis for evaluating electric motors for vibrations, noise, and harshness under varying loads and input voltages.