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To excite sufficient vibrations of bridges for more effective modal experiments to take place, traveling vehicles were utilized in many bridge field inspection campaigns in history. However, the dynamics of a bridge subjected to the traveling vehicles are of changed resonant properties compared with those of the same structure with the ambient excitation in nature. Therefore, the field modal experiments employing vehicle excitations might unfavorably lead to shifted measurement results of low-order natural frequencies for long-span bridges of large mass. Using Xinjiang Bridge (a single-tower pre-stressed concrete cable-stayed bridge with spans 40m + 150m + 150m + 40m) as the engineering background, this paper validates this technical notion based on reliable physical experiments and numerical simulations and seeks a practical approach to deal with the issue. It is found that the maximum deviation between the low-order modal frequencies measured on Xinjiang Bridge for the vehicle excitation case and those measured for the ambient excitation case (the accurate values) reaches 0.65Hz, and the deviation between the lower limit of the usual vehicle excitation’s energy band and the modal frequency measured (factor 1) and the traveling vehicles’ speed (factor 2) are the two key factors influencing the modal frequency shifts. An empirical model to compensate for modal frequencies’ deviations is formulated considering the two key factors accordingly, which is of high-practical significance in future applications of the modal experiments using vehicle excitations to other long-span bridges. [ABSTRACT FROM AUTHOR]

Abstract In addressing the finite element model and actual structural error of the sprayer boom truss, this study aims to achieve high-precision dynamic characteristics, enhance simulation credibility, make informed optimization decisions, and reduce testing costs. The research investigates the dynamic behavior of the sprayer boom truss through modal experiments and finite element simulations. Initially, modal parameters of the sprayer boom are obtained through experimental testing, validating their reasonableness and reliability. Subsequently, Ansys Workbench18.0 simulation software was employed to analyze the finite element model of the sprayer boom, revealing a maximum relative error of 11.93% compared to experimental results. To improve accuracy, a kriging-based response surface model was constructed, and multi-objective parameter adjustments using the MOGA algorithm reduce the maximum relative error to 4.6%. Sensitivity analysis further refines the model by optimizing target parameters, resulting in a maximum relative error of 4.96%. These findings demonstrate the effective enhancement of the corrected finite element model’s precision, with the response surface method outperforming sensitivity analysis the maximum relative error between the updated finite element model and experimental results was within the engineering allowable range, confirming the effectiveness of the updated model.

Abstract 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.

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]

As the core component of electronic equipment, vibration load has an important effect on the reliability of circuit boards. However, construction machinery has high requirements for construction efficiency and safety performance, and also has high maintenance costs. In this paper, a vibration reliability analysis and structural optimization of the control circuit board of a drilling rig are conducted. First, Failure Mode, Effects and Criticality Analysis (FMECA) and Fault Tree Analysis (FTA) qualitative and quantitative analysis were used to find the weak links in the circuit board. The quantitative and qualitative analysis results of FMECA and FTA show that the critical probability importance values of the chip inductor and TVS diode short circuit are the highest, at 0.249 and 0.173, respectively. They are up to 0.239 higher than those of the other components. Then, according to the analysis results, a precise simplified model is established for the core components, including the weak links, and modal simulations and modal tests are carried out. The key influencing parameters are obtained through comparative analysis and research on natural frequency and frequency response curves. Finally, the position of the stress–strain sensitive source in the real working environment is determined by a dynamic simulation analysis of the random vibration performance of the finite element model. The results can provide an optimization basis for an anti-vibration design of circuit boards. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The double stator high-temperature superconducting field modulated (DS-HTS-FM) machine with a dual-stator configuration and high-temperature superconducting materials includes numerous cryogenic components that establish the required operating temperature for superconducting magnets. This abundance of cryogenic elements introduces complexity to the process of conducting a modal analysis of the entire machine. However, the conventional trial-and-error approach employed to achieve precise modal analysis results for the entire-machine suffers from the drawback of lacking a clear direction for adjustment elastic modulus which has a great influence on the modal analysis results. Therefore, it is difficult to obtain accurate modal analysis results of the entire-machine. In response to this challenge, this study focuses on a 10 kW DS-HTS-FM machine as its subject and presents an elastic modulus adjustment method based on the entire-machine modal analysis, aiming to obtain accurate finite element (FE) modal analysis results of the entire-machine. Initially, the FE method is used to find the components that have a great influence on the outer stator modals while the components that have less influence on the outer stator modal are equivalent to the front and rear end cover in the form of additional mass, thus establishing an entire-machine equivalent model for elastic modulus adjustment. Subsequently, an examination is conducted to ascertain the relative impact proportions of the elastic modulus associated with the outer stator, casing, end cover, and armature windings on the natural frequencies of the outer stator, which can lead to a precise determination of the optimal direction for adjusting the elastic modulus parameters. Lastly, based on the entire-machine modal experiment, the elastic modulus of the equivalent model is modified in a definite direction. Consequently, the elastic modulus values for various components of the DS-HTS-FM machine can be accurately identified. Experimental outcomes affirm the efficacy of this approach in attaining precise FE modal results for the DS-HTS-FM machine and reducing the computational time required for FE analysis.

This paper proposes a novel method to design the internal stiffeners layout of the supporting parts of a machine tool. This method skillfully adopts the natural growth law of leaf veins. Firstly, the similarity between the growth law of leaf veins and the layout of stiffeners in the supporting parts is dealt with in detail. The mechanical properties of different growth types of leaf veins are compared and analyzed by the finite element simulation. In addition, the optimality of the adaptive growth law of leaf veins is also analyzed. Then, a parameter optimization method of stiffeners layout based on a variable cross-section structure is proposed. Distinct from the traditional design of stiffeners layout, the method proposed in this paper not only adopts the idea of a variable cross-section structure, but also simulates the adaptive growth law of leaf veins through a parametric method. In the process of establishing a meta model, three modeling methods are compared, and the excellent performance of the genetic algorithm and BP neural network (GABPNN) method in meta model accuracy is determined. And a marine predator algorithm is implemented to optimize the meta model. Finally, the method proposed in this paper is applied to the design of the column part of a machine tool, and the effectiveness of the proposed method is verified by simulation and experiments, which provides a good idea for the design of stiffeners layout of the supporting parts of a machine tool. [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]

Considering the current heavy mining and light digging in coal mines, limitations of the structural design of the fully mechanized excavation equipment, backward tunneling technology and other problems lead to inefficient tunneling. mining ratio is out of balance, at the same time, the comprehensive excavation equipment of the coal mine underground roadway is huge, the downhole environment is complicated, and the equipment is difficult to disassemble and assemble. It is difficult to analyze the mechanical properties of key components and cut efficiency improvement experiments under laboratory conditions. A method of active excitation assisted cutting is researched, this method is based on similarity theory, a similar model test bench with a ratio of 1:3 is established, modal experiments were performed firstly, the natural frequencies of the first six orders and the modal shapes of each order are obtained, the feasibility of the active vibration-assisted cutting experimental bench is verified, perform cutting experiments on the test bench separately with or without active excitation. With or without active excitation, the cutting contact force and cutting current change of the pick are measured. The experimental results show that during the same time period, when there is active excitation, the initial time for increasing contact force is 0.07 s earlier than when there is no excitation, longer duration, contact force is reduced by 0.12 kN compared with no excitation, after excitation, the average cutting current decreased by 1.12 A.Through the test bench based on Similarity theory, the active excitation vibration experiment and test can be carried out on the cutting arm of the road-header under limited laboratory conditions. Which provides a theoretical reference for selecting the best excitation-assisted cutting parameters. At the same time, it has opened up new ideas and new methods for the energy-saving and efficient work of the cutting machine cutting mechanism from the perspective of external excitation.

Accurate calculation of the mode shape and natural frequency of the motor stator is the basis for reducing motor noise and vibration. At present, scholars have disputes about the setting of stator core and winding material property parameters. In this paper, the modal simulation analysis and experimental test of a 2.2 kW permanent magnet brushless DC motor stator system are carried out. First, to give the stator core and the winding materials, The finite element software is used to analyze the relationship between the motor modal frequency and the parameters of the anisotropic materials. According to the modal frequency variation law, a method for correcting the parameters of the anisotropic materials based on the modal frequency is proposed. The method can complete the finite element model parameter correction of the stator. Secondly, the modal experiment is carried out by hammering method to verify the accuracy of the finite element model and determine the effectiveness of the method for correcting the equivalent material parameters. And by this method, the stator material parameters of the stator can be quickly determined. The error of this experiment and simulation is within 3%, achieving the purpose of experiment and simulation benchmarking.

Taking RV-40E reducer as the object，the dynamic characteristics of RV reducer under free mode are studied by combining modal simulation and modal analysis experiment. Firstly，the RV reducer is modeled and simulated based on Ansys，and the simulation results of natural frequency and mode shape are obtained. After comparing the experimental modalities of the domestic and Nabtesco RV-40E reducer，the test results show that the first-order modal of domestic RV-40E reducer is generally lower than that of Nabtesco，with a maximum difference of 11.1%. At the same time，the simulation and experimental results are compared. The largest domestic difference in the first-order mode is -5.8%，and that of Nabtesco is +5.9%. The above research provides effective data and methods for the structural optimization design and modal performance analysis of the RV reducer.

The vibration problem during the operation of rice transplanter is the most common phenomenon. In order that the static and dynamic characteristics of the rice transplanter chassis can meet the requirements of more stable operation, the research took the 2ZG-6DK rice transplanter as the research object to carry out a vibration reduction optimization study. In the research, the Pro/Engineer 5.0 software was first used to model the chassis of the rice transplanter. The constructed finite element model was revised by using the structural parameter revision method and the mixed penalty function method. The model was imported into ANSYS Workbench to solve the modal frequency and vibration shape of the rice transplanter chassis. Based on the MAC (modal assurance criterion) criterion, modal tests were carried out to verify the accuracy of the finite element theoretical analysis. Through the analysis of the characteristics of the external excitation frequency, the chassis is structurally optimized to avoid resonance caused by the natural frequency of the chassis falling within the road excitation frequency range. The final optimization results showed that the first four orders of modal frequencies of the chassis were adjusted to 32.083 Hz, 33.751 Hz, 42.517 Hz, and 50.362 Hz, respectively, in the case that the chassis mass was increased by 6.714 kg (8.8%). They all avoid the range of road excitation frequency (10-30 Hz) so that the rice transplanter can effectively avoid the resonance phenomenon during operation. This study can provide a reference for the design and optimization of chassis structure of transplanter. [ABSTRACT FROM AUTHOR]

Copyright of Journal of National University of Defense Technology / Guofang Keji Daxue Xuebao is the property of NUDT Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The inaccurate prediction of vibrations in blade-disk structures leads to frequent occurrences of failures in rotating machinery, such as air-engines. Existing methods often empirically treat the contact parameters of interfaces as globally constant and rarely consider manufacturing and assembly deviations, resulting in a deviation of prediction models from reality. This work presents a model for complex assembly structures that includes non-uniform distributions of normal contact stiffness and tangential friction coefficients at rough interfaces, while also introducing experimentally measured geometric deviations to enhance alignment with real-world conditions. Taking fir-tree blade-disk structure as an example, the accuracy of the proposed method is comprehensively verified by four measurement experiments and one modal experiment. Subsequently, the combined influence of rough interfaces and three experimentally measured geometric deviations on the overall modal characteristics of blade-disk structure are investigated, and their influencing mechanisms are revealed. The results indicate that ignoring the interface roughness and geometric deviations may significantly affect the prediction accuracy of the modal characteristics. The proposed method has great potential in the field of predicting the modal characteristics for complex assembly structures and optimizing the design of their machining and assembly processes. [Display omitted] • A model including distributions of stiffness and friction coefficient is proposed. • Various experiments are carried out to verify the proposed model. • Combined influence of contact parameters between rough interfaces is obtained. • The necessity of experimentally measuring geometric deviations is explored. • Influence mechanisms of roughness and geometric deviations on the mode are revealed. [ABSTRACT FROM AUTHOR]

Rods fastened rotor system are widely used in heavy-duty gas turbines. The contact nonlinearity and discontinuity induced by bolted rotor structures, make it difficult to design a scaled rotor system accurately. Thus, a dynamic scaling design strategy for discontinuous bolted rotor systems is proposed in this paper. An improved continuous modeling method considering rods deformation based on equivalent material layer (EML) is introduced to reflect the weakening effect of the rotor stiffness with bolted structure, and the parameter mapping relationships between the continuous and the discontinuous structure are constructed. The scaling factors of each element of the rotor system are derived by the similarity theory. Through this approach, a discontinuous rotor system can be scaled, demonstrating a high level of consistency with the prototype in terms of natural frequencies, critical speeds as well as frequency response. In addition, modal experiments under different preloads and dynamic acceleration experiment are carried out to verify of the proposed modeling method for discontinuous rotor structures. The testing and simulation results prove that the introduced equivalent material layer reflects the contact effect of prototype accurately. Compared with the experimental results, the maximum deviation of the first two natural frequencies is 4.06%, and the maximum deviation of the critical speeds is 1.36%, demonstrating the potential of small size, low-cost scaled models for predicting the complex dynamic characteristics of the prototype rotor system. Overall, the proposed scaling design strategy provides practical guidance for the design and manufacture of the discontinuous scaled rotor systems, which has broad application in testing, fault prediction and dynamic design of prototypes. [ABSTRACT FROM AUTHOR]