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Vibration characteristics of stators of bearingless switched reluctance motors
Get PDFThe vibration characteristics of stators of bearingless switched reluctance motors (BSRMs) are analyzed based on finite-element method (FEM) in this paper. Aiming at to overcome the limitations of the previous modal analysis in which the influence of stator windings on the natural frequencies of switched reluctance motors (SRMs) stators is treated simply as an additional mass, the finite-element (FE) model of a 12/8-pole BSRM stator which takes torque windings and suspension windings in account is constructed based on its real structural model. In this paper, a kind of method is proposed to connect the windings and stator core as well as torque windings and suspension windings through the contact whose type is bonded. The validity of the connection method is proved by three-dimension (3D) finite-element analysis (FEA) and experimental modal analysis results of the SRM prototype
Reanalysis of the structural dynamic characteristics based on double coordinate free-interface mode synthesis and matrix perturbation method
Get PDFThe design of key parts of civil engineering structures often undergo several modifications to ensure that the usability of entire structure meets the requirements. Dynamic characteristics are important parameters to evaluate the performance of structure, so it is necessary to calculate dynamic characteristics after each modification. This paper proposes a new method to calculate the dynamic characteristics of the structures rapidly after each modification. According to this method, the structure is decomposed into relatively simple substructures, and the dynamic characteristics of the whole structure can be obtained by the modal synthesis method (MSM). When a substructure has been modified, its dynamic characteristics can be calculated by using the matrix perturbation method (MPM). The proposed method is applied to the numerical calculation of a Y-shape continuous beam bridge, and the results show that the method is correct and efficient
Rolling bearing fault diagnosis using modified K-means cluster analysis
Get PDFRolling bearing is essential component of most rotating machinery, fault diagnosis of rolling bearing is significant for enhance the reliability of mechanical device. It is becoming a hot research topic recent years. There are some disadvantages for existing methods, like computing complex, long spending time and so on. In order to overcome these shortcomings of existing methods, this paper present a modified K-means cluster analysis which is used to bearing fault diagnostics. And the data of Case Western Reserve University are used to validate effectiveness of the proposed method
A remaining useful life prediction and maintenance decision optimal model based on Gamma process
Get PDFAiming at the practical problem of maintenance decision-making, the remaining useful life (RUL) prediction method and the maintenance decision optimization model are studied emphatically. Firstly, the condition space model based on Gamma degradation process is established, according to the characteristics of the degradation process of the equipment condition. Then the RUL expectancy is predicted by this model, and the RUL probability density function of the equipment can be got. Finally, this model is validated by the data obtained from the roller bearing life test. The maintenance decision model is established with the minimum cost as the objective, the maintenance decision is optimized, and the RUL prediction and maintenance decision are realized. the example proves the validity and feasibility of this model
The effect of vibration inside the Constantine’s tramway on the comfort of passengers
Get PDFNowadays the tramway is a means of transport that is frequently used in Constantine city, the tramway of Constantine took its place in the landscape and improved the offer of public transportation in Constantine city with its capacity to transporting 6000 travelers per hour. This means of transport is experiencing a gain of interest for its qualities: ability, comfort, speed, and improving accessibility to the city center. Despite these advantages there are some problems related to users’ comfort like the noise and vibration caused during the operation, track rail, engine blocks and other traction equipment are among the main sources of vibration. On this paper, we present the type of tram used and the level of vibration caused by the traction elements and by rail track inside the tramway Alstom Citadis 402. We also made a survey based on the opinion of users of the Constantine’s tramway about the discomfort level caused by the vibration and how it effects on the comfort of passengers, this is in order to improve furthermore the comfort in the conception of tram extensions to other urban areas in the city
Experimental research and numerical simulation of influence of pre-stress values on the natural vibration frequency of concrete simply supported beams
Get PDFTo study the relationship between the fundamental frequencies and pre-stress values, based on experiments and numerical simulation, the simply supported was excited under different pre-stress values through using the hammering method. The collected acceleration signals in the mid-span of the beam were processed and analyzed to obtain the relationship between the fundamental frequency and pre-stress values. As shown from the analyzed result, the relationship between the fundamental frequency and pre-stress values could not be explained better based on the traditional “Euler-Bernoulli Beam Equation” theory. The fundamental frequency of the pre-stressed beam with the hammering method would be increased with the increasing pre-stress value. When the hammering method was introduced into the numerical simulation, its analysis result and the experimental result were very approximate and presented a small error, which indicated the feasibility and accuracy of the analyzed method. When the pre-stress value was a constant, the fundamental frequency of the beam would be increased with the increasing eccentric distance of the pre-stressing tendon. When other conditions were constant, the fundamental frequency of the beam presented a decreasing trend with the counterweight at the upper part of the beam
Dynamic characteristic analysis of two-stage quasi-zero stiffness vibration isolation system
Get PDFA novel two-stage quasi-zero stiffness (QZS) vibration isolator was proposed for the purpose of low-frequency vibration isolation. Firstly, the dynamic model of the vibration isolation system was established; furthermore, the force transmissibility of the system under harmonic force excitation was derived by the averaging method; finally, the effects on the vibration isolation performance caused by excitation amplitude, mass ratio and damping ratio were discussed. Results show that, compared with the corresponding two-stage linear system, two-stage QZS system not only has better isolation performance, but also possesses a wider range of isolation frequency provided that the excitation amplitude, mass ratio and damping ratio is appropriate
Experimental research and numerical simulation on vibration characteristics of a rectangular plate structure in fast time-varying thermal environments
Get PDFPlate attitude control structures such as rudders and vertical tails of high-speed aircraft are faced with the compound effect of fast time-varying thermal environments and vibration during the high maneuvering flight. In this paper, a thermal/vibration test system was established by combining a transient aerodynamic heating simulation system with a vibration test system. A rectangular plate structure made of nickel-based stainless steel was tested at different heating rates and its modal frequencies in fast time-varying thermal environments were obtained. Numerical calculation was performed accordingly. The calculated results coincide well with the experimental results, verifying the credibility and effectiveness of the experimental methods. The research results can provide an important test method and reference basis for the dynamic performance analysis and safety design for the plate-like structures of high-speed aircraft in fast time-varying thermal environments
Improvement of the durability of rolling bearings in high-speed drive systems
Get PDFAt present, in many high-speed machines (e.g. appliances) bearing systems based on ball bearings. These solutions are used because of the low cost of production. However, in the process of operation, it appears that the use of this type of bearings has low durability of the system associated with its underload. In these systems, the output shaft rotates at a very high speed (20 thousand RPM), so even slight imbalance causes very high inertia forces aggravating bearings with dynamic reactions. These reactions rotate with the shaft, and their rotation frequency is equal to the frequency of the shaft rotation. Clearances in the bearing lead to the situation where the shaft together with the inner ring vibrates. These vibrations cause the slip between the balls and the cage of the bearing. As a result, the cage is a subject to accelerated damage because of sliding and collisions with the balls. Another factor affecting the durability of the bearing system is work at temperatures exceeding permissible limits. The article compares two design solutions and their impact on the life of the bearings used. In the original construction very fast wear of bearings takes place, and thus the damage of the whole device. In a second experiment there was examined the durability of the system with the use of tension of the bearings with axial spring. The initial effects of changes in structure of the system have led to a change of bearing lubrication. The final result of the re-search was a proposal to change such a structure eliminating the problem of accelerated wear of the bearings
A novel method for detecting bearing defects based on EMD and fractal dimension
Get PDFBearings are widely used in rotating machines. Its health status is a significant index to indicate whether machines run continually or not. Detecting the bearing defects timely is very important for the maintenance decision making. In this paper, a novel bearing defects detection method based on EMD and Fractal Dimension is developed. The original data is decomposed into a set of intrinsic mode functions (IMFs) using EMD, and the fractal dimension of IMFs which contains bearing fault characteristic information are calculated, and these characteristic parameters are used to identify bearing fault types. The effectiveness of this methodology is demonstrated using experimental data