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A wealth of practical cases indicates that the fatigue failure of subway bogies primarily stems from the modal resonance of the structure. If the modal characteristics of the entire vehicle, including equipment and bogies, are mismatched, rail vehicles may experience abnormal vibrations and noise. Therefore, it is imperative to conduct modal analysis and matching design for subway vehicle bogies to ensure smooth operation, reduce structural vibrations and noise, and enhance vehicle safety and ride comfort. Modal identification methods under the ambient l excitations during vehicle operation were employed to identify the modal parameters of the bogie structure before and after wheel reprofiling and under different load conditions. According to the test results, wheel reprofiling has minimal impact on the modal parameters of the structure, but with an increase in load, the modal frequencies of each order generally increase. This is associated with boundary constraint states, such as the increased stiffness of the bogie air spring with an increase in vehicle load. By comparing the test results with simulation analysis results of the bogie structure under free and constrained states, it is evident that simulating realistic boundary constraint conditions is crucial to ensure the accuracy of the finite element model. Based on frequency isolation criteria and vibration isolation theory, a frequency planning basis for the bogie structure was established. The study found that as the vehicle load increases, changes in the boundary conditions of the bogie affecting the elastic modal frequencies of the structure may have a certain impact on matching design, and may even better comply with the requirements of frequency management equations. This provides a new direction for subsequent scholars researching modal matching design. [ABSTRACT FROM AUTHOR]

Gantry five-axis machine tools have garnered acclaim for their robustness, cost-effectiveness, and accuracy in fabricating intricate workpieces. In the era of Industry 4.0, these tools necessitate heightened flexibility, precision, and cognitive capabilities to meet contemporary industrial requisites and accommodate escalating processing demands. This study delved into a comprehensive analysis of a gantry five-axis machine tool via the finite element method, encompassing static, modal, spatial accuracy analysis, and topological optimization, to grasp the structural attributes of the entire apparatus. Modal experiments were conducted to validate the numerical findings, with experimental and analytical errors falling within an acceptable range, ranging from 11 to 2.5% respectively. The analysis outcomes facilitated the identification of structural vulnerabilities and resonance frequencies, enabling the avoidance of these frequencies during machining, thereby enhancing machining precision and work piece value. Utilizing ANSYS mechanical, topology optimization of the column was executed, achieving objectives such as weight reduction, augmented rigidity, and enhanced natural frequencies in contrast to the original design. Lattice optimization was applied to the spindle, aiming to elevate the fundamental frequency and diminish mass. This approach yielded a notable frequency increase from 580 to 736 Hz and nearly halved the mass. Spatial accuracy analysis facilitated the detection of component errors at various machine positions, enabling input to the machine tool's controller for error compensation, thereby enhancing precision. This comprehensive investigation underscores the significance of advanced analytical techniques and optimization strategies in fortifying the performance and efficacy of gantry five-axis machine tools in modern industrial settings. [ABSTRACT FROM AUTHOR]

Measurement of thermal forces is an important process that aids in reducing the maintenance cost of continuous welded rails (CWRs). But it is still a very challenging problem. Axial force can be measured through vibration modal changes, and vibration measurement methods have several merits compared to conventional measurement methods using piles, strain sensors, magnetoelastic and acoustoelastic effect sensors, and X-rays. Vibration measurement methods have the ability to measure the absolute thermal force in a local interval and are robust against abrasion, surface residual stress, and material grains. However, they are affected by both axial force and track parameters, thereby restricting their engineering applications. To address these limitations, this study proposes a novel method called 'modal utilization method of periodic structure' (MUMPS). Its novelty lies in proving that variations in frequency constitute a random sequence satisfying the constraints of Chebyshev's law of large numbers. It can determine the influence of track parameters on the vibration modes by averaging across different eigenfrequencies without investigating what they correspond to respectively. First, MUMPS is introduced through a hypothesis that the mean value of the natural frequency variations caused by the track parameter variations approaches a stable value. Second, MUMPS is validated using finite element simulation results, which show that the probability density function of the measurement error of the neutral temperature obey N(0.5,2.6). Finally, the accuracy of MUMPS is investigated through experiments, the results are compared with the strain-gauge method results, and they show good agreement. The experimental results show that as the number of the eigenfrequencies reaches 12, the mean value becomes stable, and the measurement error of neutral temperature is less than 4 ∘ C . Engineering applicability of MUMPS is demonstrated by conducting real-time measurements on railway tracks. The results show that the proposed method is simple, as sophisticated instruments are not employed to determine the axial forces on railway tracks. [ABSTRACT FROM AUTHOR]

Composite sandwich structures with a grid-stiffened core (SSGSC) are one of the new structural configurations employed in advanced industries, and therefore the knowledge of their dynamic characteristics is very important. Hence, in the present study, three composite SSGSC samples of glass/epoxy and carbon/epoxy were fabricated by the hand lay-up method using a silicon rubber die. Also, two metallic samples — a monolithic one and a SSGSC, made of Aluminum 1050, were fabricated. The core of the aluminum SSGSC was produced using the wire cutting process, and the face sheets were attached using a high-grade adhesive. Modal experiments were carried out on all the samples using B&K vibration equipment. The frequency, mode shape, and damping coefficients were obtained from each experiment. Finally, a numerical modal analysis was performed, and good agreement between experimental and numerical results was obtained. [ABSTRACT FROM AUTHOR]

To improve the dynamic performance and reduce the weight of the planet carrier in wind turbine gearbox, a multi-objective optimization method, which is driven by the maximum deformation, the maximum stress and the minimum mass of the studied part, is proposed by combining the response surface method and genetic algorithms in this paper. Firstly, the design points' distribution for the design variables of the planet carrier is established with the central composite design (CCD) method. Then, based on the computing results of finite element analysis (FEA), the response surface analysis is conducted to find out the proper sets of design variable values. And a multi-objective genetic algorithm (MOGA) is applied to determine the direction of optimization. As well, this method is applied to design and optimize the planet carrier in a 1.5MW wind turbine gearbox, the results of which are validated by an experimental modal test. Compared with the original design, the mass and the stress of the optimized planet carrier are respectively reduced by 9.3% and 40%. Consequently, the cost of planet carrier is greatly reduced and its stability is also improved. [ABSTRACT FROM AUTHOR]

Because of the limited space of the launch rockets, deployable mechanisms are always used to solve the phenomenon. One dimensional deployable mast can deploy and support antenna, solar sail and space optical camera. Tape-spring hyperelastic hinges can be folded and extended into a rod like configuration. It utilizes the strain energy to realize self-deploying and drive the other structures. One kind of triangular prism mast with tape-spring hyperelastic hinges is proposed and developed. Stretching and compression stiffness theoretical model are established with considering the tape-spring hyperelastic hinges based on static theory. The finite element model of ten-module triangular prism mast is set up by ABAQUS with the tape-spring hyperelastic hinge and parameter study is performed to investigate the influence of thickness, section angle and radius. Two-module TPM is processed and tested the compression stiffness by the laser displacement sensor, deploying repeat accuracy by the high speed camera, modal shape and fundamental frequency at cantilever position by LMS multi-channel vibration test and analysis system, which are used to verify precision of the theoretical and finite element models of ten-module triangular prism mast with the tape-spring hyperelastic hinges. This research proposes an innovative one dimensional triangular prism with tape-spring hyperelastic hinge which has great application value to the space deployable mechanisms. [ABSTRACT FROM AUTHOR]