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Studies on novel composite structures that can decrease floor height and improve constructional efficiency in order to increase spatial efficiency and lease revenue have been actively conducted. An innovative fire-proof, lightweight, absorbed, shallow, and hybrid (iFLASH) system was developed to solve construction site issues, such as improving constructability, reducing construction time, and attaining structural efficiency by reducing the weight of the building structure. This system can shorten the construction duration and decrease the floor height and structural weight, owing to features such as a low thickness and light weight. However, studies on the vibration characteristics of this new floor system have not been performed yet. As the general thickness of the iFLASH system ranges from 25 to 30 mm, it must have a sufficient floor vibration performance in order to be utilized. To evaluate the floor vibration performance of the iFLASH system, an experiment was performed in two buildings where the system was applied. This paper presents the results of the dynamic characteristics and serviceability testing as basic data for the vibration characteristics of the iFLASH system.

This paper aims to reveal the coupling relationship between surface topography and wear and introduce a new coupling failure dynamic model of tooth surface topography and wear. Based on the fractal theory, the theoretical model of gear rough surface and the prediction model of wear are established and reveal the relationship between tooth surface roughness, wear depth, and meshing position. In particular, we analyze rough tooth surfaces’ time-varying meshing stiffness and system dynamic characteristics. The greater the contact surface roughness level, the more severe the wear behavior, and the greater the contact deformation of the gear; the vibration response and amplitude growth rate are highly related to the surface roughness. The results of coupled vibration characteristics show that the topography of the contact surface causes the system noise and shock to increase from the two aspects of stiffness excitation and error excitation. The multi-state coupled dynamic model of the contact surface can provide a theoretical basis for optimizing gear systems.

The electromagnetic vibration of the motor and the mechanical vibration of the transmission mechanism are highly coupled in an electric drive system for an electric vehicle, complicating the positioning of the vibration source and suppress vibrations. To study the electromechanical coupling dynamic characteristics of the electric drive system under steady state, variable speed, and variable load operating conditions, a dynamic modeling method for a permanent magnet synchronous motor considering non-ideal factors was proposed, and a comprehensive electromechanical coupling nonlinear dynamic model of the electric drive system considering the electromagnetic nonlinearity of the permanent magnet synchronous motor, output nonlinearity of the control system, and meshing nonlinear factors of the gear transmission system was established. The dynamic response and electromechanical coupling dynamic characteristics of the electric drive system under steady-state, impact, and acceleration conditions were analyzed. The research results confirm that under the joint action of time current harmonics and space magnetic field harmonics, the frequency characteristics of the electromagnetic torque are more complex, and under steady-state conditions, electromagnetic and mechanical vibration excitations are further aggravated by the electromechanical coupling effect. In the phase current, there are clear electromechanical coupling frequency characteristics kf g 1  ±  f e and kf g 2  ±  f e ( k  = 1,2,3…); in the transient impact stage, the excitation system generates free vibration dominated by the 1st, 5th, and 12th modes; under acceleration conditions, the internal dynamic excitation of the gear system can easily excite the resonance of the high-frequency components of the system. Finally, compared with the motor-phase current test data, the accuracy of the mathematical modeling and dynamic characteristics were verified, providing a theoretical reference for mathematical modeling and dynamic characteristics research on electric vehicle drive systems.

To investigate the multifield coupled vibration properties of electric-drive systems of electric vehicles, an improved equivalent magnetic network model of a permanent magnet synchronous motor suitable for variable speed/load and other non-stationary conditions is established by considering the nonlinear factors such as stator slotting, pole distribution, and magnetic saturation. On this basis, a machine-electric–magnetic multi-field coupling dynamics model of the electric drive system is established by comprehensively considering the gear transmission error, time-varying meshing stiffness, etc. The laws affecting the dynamic properties of the electric drive system under excitation of the internal nonlinear factors and external load are investigated. Research shows that electromagnetic excitation exacerbates the vibration amplitude of the gear. Mechanical excitation modulates the current frequency. The system vibration response amplitude trend is consistent with the current low-frequency harmonic components that can be used to monitor the system vibration state. External shock loads have the greatest impact on the vibration of the first-stage active gear and secondary-stage driven gear. The coupling effect of the motor and gear can effectively suppress the shock oscillation caused by a sudden change in the load.

The term “over-skidding” indicates that the cage rotational speed ratio exceeds the theoretical value as ball purely rolls on the raceway. Different from the skidding phenomenon that occurs in low-load and high-speed bearing, over-skidding usually occurs in large-size angular contact bearings, and it is still difficult to suppress under high load conditions. The main forms of damage to the raceway by over-skidding are spinning and gyro slip. To further explore the vibration characteristics and thermal effects of this phenomenon, a set of over-skidding tests of an angular contact bearing with a bore diameter of 220 mm were conducted on an industrial-size test bench. Through the experiment, the influence of axial load, rotational speed, and lubrication conditions on the occurrence of over-skidding were determined. Based on a previous dynamics model, the heat generation and thermal network models were integrated in the present study to predict the over-skidding and its thermal behavior. The model was validated in terms of the measured degree of over-skidding and temperature rise. The results showed that the degree of over-skidding reaches up to 12% of the theoretical value, and the friction power loss of the ball-pocket accounts for 30% of the total power loss. The analysis of the vibration signal showed a strong correlation between the bearing vibration characteristics and over-skidding behavior, thereby providing a way to indirectly measure the degree of over-skidding.

With the development of compressors toward high speed and multiple columns, the torsional vibration phenomenon has become a major factor affecting the service life and reliability of the shaft system. Therefore, this paper considers the influence of friction between piston and cylinder on the instantaneous inertia of the crank connecting rod mechanism, establishes a nonlinear torsional vibration mechanics model of shale gas compressor shaft system, solves the natural frequency of the shaft system under undamped and damped conditions using the eigenvector method, and investigates the influence of the friction coefficient between piston and cylinder and the operating speed on the torsional vibration response of the shaft system under the self-excitation of the shaft system and the action of and excitation moment by the Runge–Kutta methods. The results show that after considering the friction between the piston and the cylinder, the second-order natural frequency of the shaft system shows a \"high-low–high\" fluctuation pattern. As the friction coefficient increases, the amplitude of the shaft system and the peak vibration speed show a rising trend. Meanwhile, when the speed increases, the vibration of the shaft system changes from chaotic \\ period to the proposed periodic state, but the amplitude shows a decreasing trend. The research in this paper aims to improve the theory of nonlinear dynamics of compressor shaft systems, and the determined nonlinear parameters can be used to guide the operation and maintenance of compressors in engineering.

Gear cracks may occur during the operation of planetary driveline, leading to a huge safety hazard. However, few studies have been conducted to investigate the influence mechanism of planetary driveline vibration with crack extension. In order to simulate the actual working conditions, a damage dynamics model of the planetary gear train is constructed. Firstly, the system dynamics differential equations are established based on the dynamics model and solved to obtain the bifurcation diagram, time-domain diagram, phase diagram, three-dimensional wavelet diagram, three-dimensional spectrogram, and meshing force diagram of the system to investigate the effects of the excitation frequency and the degree of cracking of the gears on the vibration characteristics of the system. Then, the global bifurcation diagram of the system is constructed by using the cell mapping method, and the evolution mechanism of the global vibration characteristics of the system is explored according to the coexisting states of the system. In addition, the proposed dynamics model is verified by planetary gear train failure simulation experiments. The results show that the system has similar global characteristics under healthy operating conditions and cracked faults, and the system instability increases with the gear crack extension. Therefore, it is valuable to predict the planetary gear life by analysing the global vibration characteristics of the system.

Vibration characteristics are important reference indicators for reflecting the overall performance of RV reducers. At present, there is no factory testing standard for vibration characteristics applicable to production enterprises in the industry. This study conducted vibration characteristic tests on RV40E reducers at different speed ratios. Through a large number of sample comparisons, suitable vibration characteristic factory testing standards for production enterprises were provided. Detailed on-site inspection standards have been developed based on research and analysis results for defective products such as eccentricity, gear defects, and detection errors. This standard can cover 90% of defect types within the factory. The samples are specific and executable. This study solves the problem of the lack of clear vibration detection standards in the industry. For the first time, such a detailed sample set of internal data within a company has been provided. It has extremely practical engineering application value and provides data reference for the development of RV reducer industry.

To address severe equipment vibration and large load fluctuations during hard-rock excavation, this study proposes mechanical pre-cracking as a preparatory treatment. A hard-rock model containing pre-cracked holes is developed using the discrete element method; the crack initiation and propagation induced by a hydraulic cracker are simulated. The rock models before and after pre-cracking and a rigid–flexible coupling model of the roadheader are then analysed jointly via DEM–MFBD two-way coupling, and the cutting loads and vibration responses are systematically examined. Results indicate that the three-way average load on the cutting head is reduced by 8.2% and the load fluctuation coefficient decreases from 0.0242 to 0.0213 following rock pre-cracking, effectively mitigating impact loads. Frequency-domain analysis shows that, within the principal vibration band of 20–30 Hz, the vibration-acceleration amplitudes of the cutting head, cutting arm and slewing table are reduced by 14.7%, 8.7% and 3.6%, respectively, demonstrating a “near-loaded component” vibration response. This reveals an attenuation law along the transmission path: components closer to the load exhibit superior vibration damping compared with remote elements. The study confirms that mechanical pre-cracking achieves effective vibration attenuation at the source by reducing the overall stiffness of the rock mass and altering the rock-breaking pattern, thereby providing a theoretical basis and engineering reference for improving the efficiency and reliability of hard-rock tunnelling equipment.

The coupling of various modes in centrifugal pumps renders the process of modal parameter identification through frequency response functions both time-consuming and labour-intensive. To accurately identify modal parameters, current modal testing typically requires the deployment of numerous measurements or excitation points. However, certain modal parameters may suffer from low SNR, leading to distorted modal shapes that deviate from reality. This study employs a semi-empirical approach to ingeniously design the excitation vector by leveraging the relationships among the centre of mass, inertial axes, and excitation points. During modal testing experiments, specific modes of the centrifugal pump are decoupled, significantly improving the SNR for the targeted modes. Experimental validation demonstrates that the proposed method markedly enhances the accuracy of modal parameters identification, thereby facilitating the analysis of its vibration characteristics. The findings enable rapid identification of modal parameters related to vibration issues in engineering applications, contributing to the swift localization and resolution of vibration problems.