Journal of Vibroengineering
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Bending shape curvature as dynamic criterion for the structural health control
Get PDFThe paper describes a constructive system parameter – Bending shape curvature, as a dynamic criterion for assessing the technical state of structures. Previous studies of various dynamic criteria for structural health control have revealed a lack of accuracy. Analysis of a constructive system dynamic work based on internal response only is limited by a variety of external force factors, the determination of which is difficult. A constructive system can be deformed due to a change in cross-section stiffness at one of its elements because of a defect or damage and that affects displacements at its control points. It makes it difficult to determine bending stiffness only by constructive system displacements. As a result, the development of structure test methods with a control impact force is relevant. The article presents the methods of calculating bending shape curvature over controlled displacements. It is suggested to use an artificial impact on a structural system for getting the elements response to the bending moment. The advantage of bending shape curvature calculating for assessing the stiffness of a structure system is explained. It is shown the results of defect size influence on bending shape curvature during static tests and stiffness assessment results of the metal frame during dynamic tests. The necessity of taking into account the stiffness of structures joints has been revealed, as well as a high dependence of method’s relative error on the value of dynamic shaker force and the distance between registration sensors
Operating state prediction for wind turbine generator bearing based on ULSSVM and QPSO
Get PDFAiming at the problem of operating state prediction of generator bearing, a prediction method based on quantum particle swarm optimization (QPSO) and united least squares support vector machine (ULSSVM) is proposed. Firstly, the time least squares support vector machine (TLSSVM) model is established in accordance with the change law of characteristic parameters over time. Space least squares support vector machine (SLSSVM) model is established in accordance with the law of mutual influence between characteristic parameters. Secondly, the QPSO algorithm is used to optimize the parameters of each least squares support vector machine (LSSVM) model. When the difference between the predicted value and the measured value reaches the minimum, the optimal LSSVM parameter set is output. Then the improved Dempster-Shafer (D-S) theory is used to determine the weights of TLSSVM and SLSSVM. A united model of time LSSVM and space LSSVM is established. The characteristic parameters are predicted. The prediction results and the reference matrix are fused and reduced in dimension. Finally, the generator bearing operating status is predicted based on the location of the prediction results. The results show that the proposed method is helpful to realize the operating state prediction of the wind turbine bearing
Blasting vibration monitoring scheme and its application
Get PDFAccording to BET project of High-level radioactive waste geological disposal, the smooth blasting parameters and the corresponding blasting vibration monitoring scheme are designed separately. Combining with the blasting vibration monitoring scheme, the blasting vibration monitoring was carried out with the blasting test simultaneously. It was found that the maximum vibration velocity was controlled within a reasonable range. Furthermore, the vibration attenuation law was obvious after analysis, which indicated that the blasting parameters design and vibration monitoring scheme were reasonable. It illuminated that the blasting parameters designed were proved to be reasonable and desirable. Moreover, the vibration reduction measurements for this project have been put forward. This study can provide the corresponding experimental data and theoretical support for the High-level radioactive waste geological disposal. The result and the theoretical knowledge could be applied to the blasting and excavation of the deep geo-engineering and the HLW geo-disposal
Study on torsional vibration of a harmonic driver based on time-varying stiffness caused by manufacturing error
Get PDFThe torsional vibration of Harmonic reducer is concerned with the positioning accuracy and trajectory accuracy of industrial robots. A study on the parametric torsional vibration based on time-varying stiffness will improve the mechanical performance of Harmonic reducer. In this paper, the phenomenon of time-varying stiffness caused by manufacturing error is investigated on a Harmonic driver through mechanism analysis and experimental investigation. Meanwhile, a model of forced parametric vibration is set up for the Harmonic driver transmission system with an inertia load. The parametric vibration response is simulated by the Runge-Kutta method, and the issue of bi-spectra, combined harmonic group, and the envelope of system sweeping frequency response are analyzed in detail. The influence of double periodic time-varying stiffness on vibration is emphasized with simulation data. To observe the characteristic of parametric vibration in Harmonic driver, a test device has been developed for the measurement of torsional vibration. The dynamic characteristics can be confirmed through signal processing on torsional vibration. An engineering example is given to illustrate that the manufacturing defect can be on-line diagnosed in Harmonic driver by using the characteristic of bi-spectra. As a result, the magnitude of torsional vibration is eliminated to one half of the original case through the reassembly process, and one of the mechanical performances, i.e., the property of torsional vibration-speed, is improved obviously. The dynamic characteristics caused by time-varying stiffness, i.e., bi-spectra, can be used as a new clue of manufacturing quality assurance for Harmonic driver
Modelling of transient and steady-state modes of a vertical rotor with an automatic balancing device
Get PDFThe authors of the study work out the differential equations of motion of a vertical rotor model on an elastic-dissipative suspension, balanced by a ball-type automatic balancing device. Often, the cross-section of the cavity of the body of the automatic balancing device is rectangular and during rolling the balls have two points of contact, in one of which the balls slide along the surface of the cavity. To prevent the balls from sliding, the inner surface of the cavity of the automatic balancing device is made in the shape of a torus, which provides one point of contact. The forces of gravity and the forces of resistance to the movement of the correcting weights are taken into account, and the model is drawn up for both viscous and dry friction forces inside the body of the automatic balancing device. The obtained mathematical model of the rotor makes it possible to study the transient and steady-state modes of motion of the rotor system
Impact coefficient analysis on long-span beam bridge
Get PDFThis paper presents a numerical study on the impact coefficient calculation of a straight-line π-shaped composite beam and a curved box girder beam. A numerical model of vehicle-bridge coupling system is established, where the random irregularity of bridge surface is considered in the model. The effect of lane numbers, bridge surface flatness, vehicle speed, vehicle weight and primary beam stiffness on the impact coefficient are considered. The results indicate that the lane numbers have certain influence on the impact coefficient; the impact coefficient presents nonlinear increment as the bridge surface flatness becomes from grade A to grade D; the vehicle-bridge coupling system can resonate at both low speed and high speed; the vehicle weight has little influence on the impact coefficient; whilst the displacement impact coefficient is decreased with an increment in the primary beam stiffness. Besides, the local and global impact coefficients, the displacement, moment and shear force impact coefficients are also comprehensively discussed
Toltén Bridge’s response under extreme conditions analysis through numerical models
Get PDFThis article presents the structural health analysis of a full-scale vehicular bridge, using a twin model calibrated with experimental information. This structure consists of concrete arches, built more than 80 years ago, and reinforced in the 1990s with a steel structure. Different load combinations were evaluated in this model to determine the strength of the structure according to current design standards. Finally, it was found that several of its components do not meet the current design requirements, putting the structure in a vulnerable condition to seismic hazards and restricting its service to traffic loads
The seismic analysis and performance of steel frame with additional low-yield-point steel dampers
Get PDFThis paper describes the seismic performance of a steel frame with additional LYP steel dampers. LYP steel dampers provides passive energy dissipation device in a structure, it also reduces the lateral forces in efficient way which is produced by seismic wave. The seismic performance of structures is needed in the design of structure, especially in countries where seismic activities occur. This analysis is accomplished with the FEM and software called SAP2000. The steel frame is only analyzed using numerical simulation. This paper describes two steel frames, the first steel frame is a two story steel frame without LYP steel dampers while the second steel frame has with LYP steel dampers. The seismic mechanism analysis was accomplished with the help of nonlinear time history analysis technique and the results for inter-story drift, steel frames, base shear, the displacement of the top story and the stress of the dampers was obtained. The time history analysis was taken out with three different earthquake waves according to the Chinese code for the seismic design of buildings; the earthquake waves were divided into the three different earthquake levels in China which include the frequent, moderate and rare earthquake level. The seismic mechanism analysis was accomplished on the three different earthquakes and three different earthquake levels in China. The modal analysis was taken to obtain the frequency and the period of the steel frames. The steel frames were examined under the different load combination which is also described in the code for the seismic design of buildings to obtain the internal forces of the members of the steel frame which include the axial force, shear force and bending moment. The different load combinations are used to get the stress of the dampers. We notice that the addition of LYP steel dampers increases the seismic resistance of the steel frame as we can observe by a reduction in the displacement of the top story, base shear, and inter-story drift angle by the addition of LYP steel dampers on the steel frame. We can be able to observe the behavior of the frames under the different earthquake levels in China using the pushover analysis
A study on the diagnosis of compound faults in rolling bearings based on ITD-SVD
Get PDFConsidering the difficulty in the diagnosis of compound faults in rolling bearings, the paper combines Intrinsic Time-scale Decomposition (ITD) and Singular Value Decomposition (SVD) for extracting the characteristics of compound faults from rolling bearings. Rotational components obtained from ITD decomposition are denoised according to Singular Value Decomposition algorithm; signal is reconstructed by denoised rotational components; at last, characteristics of compound faults of rolling bearings are extracted by Hilbert spectrum envelope of reconstructed signal. In validation, the paper has made a comparative study on the proposed ITD-SVD method and conventional one based on ITD algorithm and PCA method, and the result shows that ITD-SVD method works better on noise control and thereby provides more precise extraction of characteristic frequency of compound faults from rolling bearings of aero-engine
Dynamic analysis of multi point winding hoisting system under non synchronous movements of wire ropes in deep well
Get PDFTaking the multi point winding hoisting system with depth of 1000 m, drum radius of 0.4 m, drum radius difference of 0.1 mm as the research background, a model of multi point winding hoisting system under non synchronous movement of wire ropes is established, and the mathematical model is deduced by Lagrange equation. Then the dynamic characteristic of super deep multi point winding hoisting system under non synchronous movements of wire ropes is analyzed. The results show that: the rotational displacement of mass block is 5°, the rotational velocity is 0.07 °/s in the stage of constant speed. The rope length difference reaches 0.07 m, the tension of each wire rope changes 333 N, accounted for about 7 % of the average tension. And with the length difference increasing 35 mm, the force differences increasing 320 N, which indicates that the length difference has great impact on the tension difference of wire ropes. Finally, the mathematical model is verified through experiment