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Typical seismic sway braces (SSBs) are composed of several bolted steel components. As the connecting bolts become loose, the stiffness and bearing capacity of SSBs decline from which their seismic performance degrades significantly. Based on the vibration response of the brace components, a framework of a vibration-based pre-alarming method for the bolt looseness of SSBs is created and established. Four damage indexes were constructed based on the methods of Fast Fourier Transform (FFT), Wavelet Packet (WP), Intrinsic Mode Function (IMF) and Hilbert-Huang Transform (HHT). Having tested and verified their sensitivity to the bolting torque of bolts, a multi-index hierarchical early warning system (MHES) was established by associating the four damage indexes with the tightening torque of the bolts, by which the threshold of the yellow (slightly damaged) and red (severely damaged) warnings were defined and confirmed. By means of the application in an actual project, the validation of the MHES was finally verified and confirmed according to its stability and accuracy. [ABSTRACT FROM AUTHOR]

Typical seismic sway braces (SSBs) are composed of several bolted steel components. As the connecting bolts become loose, the stiffness and bearing capacity of SSBs decline from which their seismic performance degrades significantly. Based on the vibration response of the brace components, a framework of a vibration-based pre-alarming method for the bolt looseness of SSBs is created and established. Four damage indexes were constructed based on the methods of Fast Fourier Transform (FFT), Wavelet Packet (WP), Intrinsic Mode Function (IMF) and Hilbert-Huang Transform (HHT). Having tested and verified their sensitivity to the bolting torque of bolts, a multi-index hierarchical early warning system (MHES) was established by associating the four damage indexes with the tightening torque of the bolts, by which the threshold of the yellow (slightly damaged) and red (severely damaged) warnings were defined and confirmed. By means of the application in an actual project, the validation of the MHES was finally verified and confirmed according to its stability and accuracy.

• A coupled hydraulic-mechanical-electrical-structural model for hydroelectric generating system is proposed. • The hydraulic-mechanical-electrical transient process is connected with shafting system. • The dynamic response from shafting system at different stages attached to start-up process are scrutinized. • The kinetic property of structure is illuminated compared with motion trait for system under steady operating condition. The operating parameters of hydroelectric generating system vary constantly in the course of transition, meanwhile, the coupled correlations among hydraulic, mechanical, electrical and structural subsystems are convoluted, which makes the vibration of shafting system prominent, as well as affects the safe and stable operation for hydropower station. In this paper, a coupled hydraulic-mechanical-electrical-structural model for hydroelectric generating system is proposed, while the start-up transient process is incorporated into the investigation system, and the dynamic response from shafting system at different stages attached to start-up process is scrutinized numerically, making allowance for the effect of unbalanced magnetic pull with static and dynamic eccentricity. The kinetic property of structure over the start-up process is illuminated, by means of the comparison with motion trait for system under steady-state operating condition. The results indicate that the dynamic feature of rotor and runner is significantly contrasting in different stages affiliated to the start-up scenario, especially for the voltage building-up subdivision. In addition, the response peculiarity from rotor covering the trajectory, vibration amplitude and frequency components, etc., is markedly altered, due to the participation of static, dynamic eccentricity as well as the matching variation on electromagnetic excitation. The trajectory of rotor evolves from a regular circle to a butterfly-shaped curve, and the associated transient displacement intensifies immensely, besides, the 2x frequency component emerges and corresponding dominant role gradually strengthens, accompanied by a developmental amplitude of 1x frequency in spectrum diagram. Relevant research results can provide profitable reference for the analysis of dynamic characteristic on hydropower station through transient conditions. [ABSTRACT FROM AUTHOR]

Epoxy resins used in engineering applications are commonly exposed to wet environment during intended service life, which causes vibration property degradation and increasing risk of structural failure. In this work, vibration properties of epoxy resin plate under different moisture conditions are predicted with various sizes and boundary conditions using developed machine learning (ML) models. The dataset of epoxy vibration is established first, where values in the dataset are calculated with five moisture contents using previously developed meshless model. The dataset from meshless simulation is used to train ML models of epoxy vibration using six different algorithms, including support vector machine, decision tree, random forest, gradient boosting decision tree, extreme gradient boosting, and artificial neural network. It is found that the prediction model developed using extreme gradient boosting algorithm shows the highest accuracy of 99.9% and strong reliability. Using this model, vibration properties of epoxy resin with a series of sizes and boundary conditions are predicted under various moisture contents from dry case to saturated case, which deepens the understanding of the effects of wet environments on the vibration responses of epoxy resins. The results could be used for analysis of durability of epoxy resin, and the developed ML prediction models contribute to investigating vibration property of epoxy resin under different moisture conditions, which is crucial for ensuring durability of epoxy resin in wet environment. [Display omitted] • Machine learning method is employed to explore the vibration property. • Prediction model possesses high accuracy of 99.9%. • Moisture content is the most important factor of epoxy vibration. • Epoxy resin processes an enhanced vibration property with 1.0 wt% moisture. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effects of key factors on the powertrain loading dynamic characteristics and fatigue damage. First, the engine and the transmission output shaft torque of a multi-axle vehicle powertrain system were measured by proving grounds (PG) testing and analyzed with a conclusion that the powertrain loading changes were mainly related to three key factors: the mean engine torque, the harmonic engine torque, and the vibration properties of the system. Subsequently, a dynamic model considering the three factors was built and validated by the test data. Finally, fatigue damage of shaft parts and gear parts were calculated to investigate the influence degrees of the three factors. The results show that, the harmonic engine torque and the vibration properties of the powertrain system have a great influence on the fatigue damage of shaft parts, and the mean engine torque is the main factor causing the fatigue damage of gear parts. [ABSTRACT FROM AUTHOR]

In order to control yarn vibration and improve carpet quality, it is essential to research the fluctuation of yarn tension and its influences during tufting process. Assuming the polypropylene yarn has linear elasticity with a circular cross-section, we take the dynamic tension as the output and the friction acted on yarn by Jacquard roller as the input. At the moment of clutch operation and release, the tension fluctuation of polypropylene yarn during transmission from pulling roller to Jacquard roller was theoretically analyzed. A mathematical model describing yarn tension fluctuation was derived based on the moment of momentum theorem and mass conservation. The dynamic tension was obtained by applying Laplace’s transformation, providing the input-breaking moment as a step response. The result shows that tension fluctuation has an important influence on the carpet quality; therefore, it is necessary to carefully design the Jacquard roller and the control friction plate of clutch. Moreover, the effects of the yarn length between Jacquard rollers and pulling rollers on natural frequency and damping coefficient of yarn tension fluctuation were analyzed. [ABSTRACT FROM PUBLISHER]

Abstract: Vibration properties are investigated in the stable suspension between a permanent magnet (PM) and a bulk YBaCuO magnet at 77K. The bulk YBaCuO is magnetized by a controllable electromagnet. Experiments and analyses show that a PM can just suspend under the YBaCuO magnet at certain magnetization conditions of a high-temperature superconductor (HTSC). In this paper, the stable suspension happens when the ratio is set as 0.1–0.29 between the maximum trapped field and the maximum field of the PM. The resonance frequency increases with the increment of the trapped field, that is, a “stronger” HTS magnet results in a higher resonance frequency as well as larger dynamic stiffness. However, transmissibility dependence on the trapped field of an HTSC magnet goes to an inflexion of 41.37dB at 0.065T maximum trapped field in the HTS magnet, which brings a small damping and instability. These relationships are helpful in improving the mechanical and levitation performance of some high-temperature superconducting magnetic levitation systems. [Copyright &y& Elsevier]

Longitudinal sawn wood are usually selected as samples in the study of sound properties of a musical instrument board. But in real production, radial sawn timber are cut and are also widely used as vibration component. Therefore, it is very important to evaluate the vibration properties of the board in the round, especially for the sound radiation characteristic of radial sawn timber and its relationship to longitudinal sawn timber. However, for the national and international experts, researches on radial sawn timber and its role and function in sound emission have not yet been developed. This paper describes a study of seven important spruces that grow up in the Sichuan and Heilongjiang provinces of China, and one Picea sitchensis specimen from North America. Under the high bending vibration mode, resonance frequency and other parameters of longitudinal and radial wood were tested. Analysis result disclosed the relationship between longitudinal and radial wood vibration property. An important conclusion of wood for musical instruments with proper anisotropy, fine toughness, and weak shear of longitudinal and radial vibration was inducted. [ABSTRACT FROM AUTHOR]

Abstract: Shape memory alloy (SMA) is commercially available for a variety of actuator and damping materials. Recently, SMA wires have also become commercially available for the design of smart composite structures because SMA wires with a small diameter can be easily produced. In this work, two types of SMA-based composites are presented for investigating the vibration characteristics. First, laminated composite plates containing unidirectional fine SMA wires are fabricated. By measuring the vibration mode of a clamped cantilever, the influence of both SMA arrangement and temperature on the vibration characteristics is made clear. Next, laminated composite plates with embedded woven SMA layer are fabricated. The stiffness tuning capability is evaluated by impact vibration tests with different temperatures. It is found that the stiffness tuning capability may be improved by increasing the volume fraction of SMAs and by controlling accurately the internal stress according to the phase transformation temperature of SMAs from martensite to austenite. The theoretical prediction on the natural frequency considering the SMAs behavior and laminated structures is proposed and their results agree reasonably with experimental ones. [Copyright &y& Elsevier]