国际机械系统动力学学报(英文)最新文献

In this paper, according to the fractional factor derivative method, we study the Lie symmetry theory of fractional nonconservative singular Lagrange systems in a configuration space. First, fractional calculus is calculated by using the fractional factor, and the fractional equations of motion are derived by using the differential variational principle. Second, the determining equations and the limiting equations of Lie symmetry under an infinitesimal group transformation are obtained. Furthermore, the fractional conserved quantity form of singular Lagrange systems caused by Lie symmetry is obtained by constructing a gauge-generating function that fulfills the structural equation, which conforms to the Noether criterion equation. Finally, we present an example of a calculation. The results show that the Lie symmetry condition of nonconservative singular Lagrange systems is more strict than conservative singular systems, but because of increased invariance restriction, the nonconservative forces do not change the form of conserved quantity; meanwhile, the fractional factor method has high natural consistency with the integral calculus, so the theory of integer-order singular systems can be easily extended to fractional singular Lagrange systems.

Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications, such as aerospace, architecture, automotive, and marine construction, due to their attractive mechanical properties. Constructing lattice materials from fiber-reinforced composites is an efficient approach for developing ultra-lightweight structural systems with superior mechanical properties and multifunctional benefits. In contrast to corrugated, foam, and honeycomb core materials, composite lattice materials can be manufactured with various architectural designs, such as woven, grid, and truss cores. Moreover, lattice materials with open-cell topology provide multifunctional advantages over conventional closed-cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems, hypersonic vehicles, long-range rockets and missiles, ship and naval structures, and protective systems. The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.

Displacement is a critical indicator for mechanical systems and civil structures. Conventional vision-based displacement recognition methods mainly focus on the sparse identification of limited measurement points, and the motion representation of an entire structure is very challenging. This study proposes a novel Nodes2STRNet for structural dense displacement recognition using a handful of structural control nodes based on a deformable structural three-dimensional mesh model, which consists of control node estimation subnetwork (NodesEstimate) and pose parameter recognition subnetwork (Nodes2PoseNet). NodesEstimate calculates the dense optical flow field based on FlowNet 2.0 and generates structural control node coordinates. Nodes2PoseNet uses structural control node coordinates as input and regresses structural pose parameters by a multilayer perceptron. A self-supervised learning strategy is designed with a mean square error loss and L₂ regularization to train Nodes2PoseNet. The effectiveness and accuracy of dense displacement recognition and robustness to light condition variations are validated by seismic shaking table tests of a four-story-building model. Comparative studies with image-segmentation-based Structure-PoseNet show that the proposed Nodes2STRNet can achieve higher accuracy and better robustness against light condition variations. In addition, NodesEstimate does not require retraining when faced with new scenarios, and Nodes2PoseNet has high self-supervised training efficiency with only a few control nodes instead of fully supervised pixel-level segmentation.

In this paper, we develop an exhaustive numerical simulator for the dynamic visualization and behavior prediction of the tether-net system during the whole space debris capture phases, including spread, contact, and close. First of all, to perform its geometrically nonlinear deformation, discrete different geometry theory is applied to model the mechanical response of a flexible net. Based on the discretization of the whole structure into multiple vertexes and lines, the internal force and associated Hession are derived in a closed form to solve a series of nonlinear dynamic equations of motion. The spread and deployment of a packaged net can be realized using this well-established net solver. Next, a multidimensional incremental potential formulation is selected to achieve the intersection-free boundary nonlinear contact and collision between the deformable net and rigid debris. Finally, for the closing mechanism analysis, a log-like barrier functional is derived to achieve the nondeviation condition between the ring–rod linkage system. The $��C^2�$ continuous log barrier functionals constructed for both the contact model and the linkage system are smooth and differentiable, and, therefore, the nonlinear net capture dynamic system can be efficiently solved through a fully implicit time integrator. Overall, as a demonstration, the whole capture process of a defunct satellite using a hexagon net is simulated through our well-established numerical framework. We believe that our comprehensive numerical methods could provide new insight into the optimal design of active debris removal systems and promote further development of the online control of tether tugging systems.

Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices. However, nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes; thus, the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes. Due to diffraction limits of optical imaging, the obtained optical image has insufficient spatial resolution. Therefore, electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research, and numerous breakthroughs have been achieved in recent years. In this review, we cover three typical ultrafast electron beam imaging techniques, namely, time-resolved photoemission electron microscopy, scanning ultrafast electron microscopy, and ultrafast transmission electron microscopy, in addition to the principles and characteristics of these three techniques. Some outstanding results related to photon–electron interactions, charge carrier transport and relaxation, electron–lattice coupling, and lattice oscillation are also reviewed. In summary, ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental understanding of physics, chemistry, and optics, as well as guide the development of advanced semiconductors and electronics.

An analytical solution was used to investigate the elastic response of a sandwich beam with a graphene-reinforced aluminum-based composite (GRAC) on an elastic foundation using copper as the face layer of the functionally graded composite beam and a simply supported boundary condition. Mantari's higher-order shear deformation theory was utilized to derive the equations, which were solved in Laplace space and then converted into space–time using Laplace inversion. The exact response of the GRAC sandwich beam was obtained by considering the displacement at the mid-span of the sandwich beam. Two moving loads with different speed ratios were applied at a single point, and the effect of various parameters, including the spring constant, the speed ratio, the percentage of graphene, the moving load speed, and the distribution pattern, was investigated. This study aimed to eliminate any overlap and improve the accuracy of the results. The exact solving method presented has not been reported in other articles so far. Additionally, due to the difficulty of solving mathematical equations, this method is only applicable to simple boundary conditions.

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The mission of IJMSD is to provide cutting-edge scientific and technology research in the area of mechanical system dynamics, with the goal of enhancing modern industrial research and development capabilities to improve the performance of mechanical systems. The research published in the journal highlights the crucial role of mechanical system dynamics throughout the entire lifecycle of modern and complex engineering products. The journal covers a wide range of topics, including theories, modeling, computation, analysis, software, design, control, manufacturing, testing, and evaluation of mechanical system dynamics. Since IJMSD's launch in July 2021, three volumes, eight issues, and 64 papers have been published. All these papers are open-access and available at https://onlinelibrary.wiley.com/loi/27671402.

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This short communication uses numerical continuation to highlight the existence of an isola in a simple one-degree-of-freedom harmonically forced feedback system with actuator rate limiting as its only nonlinear element. It was found that the isola (1) contains only rate-limited responses, (2) merges with the main branch when the forcing amplitude is sufficiently large, and (3) includes stable solutions that create a second attractor in regions where rate limiting is not expected. Furthermore, the isola is composed of two solutions for a given forcing frequency. These solutions have the same amplitudes in the state (pitch rate) projection; however, they have distinct phases, and their amplitudes are also distinct when projected onto the integrator state in the controller. The rich dynamics observed in such a simple example underlines the impact of rate limiting on feedback systems. Specifically, the combination of feedback and rate limiting can create detrimental dynamics that is hard to predict and requires careful analysis.

This paper presents a new analytical solution for the vibration response of a beam-stiffened Mindlin plate having a completely free boundary condition by utilizing a finite cosine integral transform. In the solution, the unknown coupling force and moments at the beam/plate interface and the unknown modal constants from the integral transform are determined by the continuity and compatibility conditions at the interface as well as the boundary conditions. It provides an easily implemented tool for exploring complex edge value problems for a class of higher-order partial differential equations represented by fully free-stiffened Mindlin thick plates. The validity of the model is evaluated by comparing the calculated free and forced vibration responses of the beam-stiffened plate with those calculated using a beam-stiffened thin plate and those from finite element analysis.

Microscopic roughness is inevitable on the gear meshing surface, which is also a key parameter affecting the dynamic response. The surface roughness exhibits self-affine characteristics across multiscales. To explore the influence of surface fractal topography on the vibration amplitude of the gear system under different rotational speeds and loads, an experimental setup of spur gear transmission is devised. The fractal dimension and fractal roughness of the meshing surface are calculated by the power spectral density method. The relationships between gear response and fractal parameters are revealed experimentally. Results indicate that a rougher tooth surface, that is, a smaller fractal dimension or larger fractal roughness, corresponds to an intense vibration amplitude. The sensitivity of dynamic response to the tooth surface topography varies at different rotational speeds and loads. Under low speed and light load conditions, the fractal dimension and fractal roughness have a more obvious influence on the dynamic response of the gear transmission system. With the increase of speed and load, the macroworking conditions gradually become the main factor attributed to vibration amplitude.