Journal of Vibroengineering
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A method for analyzing the revolute joint wear of planar multibody systems and its application in unbalance loading working condition
Get PDFThis paper develops an efficient method to describe the evolution of the revolute joint wear during the process of the mechanism movement. In the framework of multibody systems formulation, the prediction method of the revolute joint wear in different motion time interval is established by considering the wear ranges between the pin and the bushing on the basis of the Archard’s wear model. Then a typical non-planar mechanism with unbalancing loads acting on single non-ideal revolute joint is used to illustrate the application of the method. Moreover, the corresponding experimental mechanism is tested to validate the predicting results of the proposed method. The analysis shows that the method proposed is of high efficiency and can guarantee enough predicting accuracy when the predicted wear depth is not big. Therefore, the method is practical to a certain degree in engineering
A study on vibration of Setar: stringed Persian musical instrument
Get PDFKnowing how a musical instrument vibrates can benefit the tonal characteristics shaping of the instrument. In this research, an approach for investigating the mode shapes and natural frequencies of Setar body is addressed. First, mechanical properties of wood used in the production of Setar are analyzed experimentally. Then a numerical modal test is performed to find the mode shapes and natural frequencies of Setar structure. To validate the results obtained by the numerical method, experimental modal testing is also done for the structure, and it is found that the results of both the methods are in good consistency. As the vibration pattern of plates is of utmost importance in the production of musical instruments, vibration patterns of a Setar plate are experimentally extracted and the results are compared with finite element analysis
Vibration measurement of long-span floors in high-speed railway station
Get PDFHigh-speed rail stations have long-span floor structures stretching over rail tracks and platforms. These long-span floor structures are prone to vibration caused by large crowds. Current floor vibration design guidelines lack specific provisions addressing this type of structures. There is a need to study the crowd excitation and the vibration performance of the long-span floor structures. A field testing study was recently conducted in China’s newly constructed Xi’an North Railway Station, and results of the study is discussed in this paper. The output-only method was used for modal testing, where vertical accelerations were recorded at a grid of fifty locations on the floor panels and analyzed to obtain the natural frequencies, mode shapes, and damping ratios of structural vibration modes. Vibration measurements were taken and analyzed at a variety of load cases, which included operating cases at the floor sections in use to assess vibration performance of the floor structure, and several experimental cases at the floor sections not yet in use to investigate the effects of crowd size and walking and jumping frequency on floor vibration. It was found that under most operating conditions, the floor structural vibration didn’t exceed the commonly accepted design limits. Thus, the vibration control design of the floor structure is deemed satisfactory. Under certain coordinated crowd movements (e.g., walking and jumping at certain frequencies), resonance occurred, and vibration levels exceeded the threshold for acceptance. The crowd excitation frequency has a greater influence than the crowd size on floor vibration responses
Assessment of noise and vibration hazards generated by hybrid PEM-FC personal power supply
Get PDFThe paper presents a part of ongoing research into the use of a proton exchange membrane fuel cell (PEM-FC) to power military installations and personal power supply of soldier or rescuer. Construction of this type device use elements, which generate vibration, noise and heat. Emitting these types of pollution worsens the detection of military installations as well as operator’s safety. The presented research includes the assessment of noise and vibration hazards generated by 20 Watt PEM-FC personal power supply which was created by Polish Naval Academy in consortium with Central Laboratory of Batteries and Cells in Poznan and Impact Clean Power Technology S.A. in Warsaw. Measurements of noise and vibration levels were performed in an anechoic chamber at AGH University of Science and Technology during nominal operation of the device. The vibration parameters transferred to external cover as well sound power level and the insulation effectiveness of device cover were determined
An improved extreme-point symmetric mode decomposition method and its application to rolling bearing fault diagnosis
Get PDFHHT (Hilbert-Huang Transform) which consist of EMD (Empirical Mode Decomposition) and HT (Hilbert Transform) now is the most widely used time-frequency analysis technique for rolling element bearing fault diagnosis, however, its fault characteristic information extraction accuracy is usually limited due to the problem of mode mixing in EMD. ESMD (Extreme-point symmetric mode decomposition) is a novel development of HHT which is promising to alleviate this limitation and it has been applied to some fields successfully, but its application for rolling bearing fault diagnosis has rarely been seen in the literature. In this paper, ESMD is applied to extract the bearing fault characteristics for rolling bearing fault detection, and the results proved that ESMD can have a better fault diagnose effect than EMD and HT. What’s more, for further improving bearing fault characteristic extraction accuracy of rolling bearing vibration signals, the sifting scheme is proposed for selecting the sensitive fault-related IMFs (intrinsic mode functions) generated by ESMD, in which a weighted kurtosis index is introduced for automatic selection and reconstruction of the fault-related IMFs, and then the original and reconstructed bearing fault vibration signal after performing Hilbert transform as the results to diagnose the incipient rolling bearing fault. ESMD combined with the proposed sifting scheme are applied to diagnose the simulated and experimental signals, and the results confirmed that the sifting scheme based ESMD is superior to the other conventional method in rolling bearings fault diagnosis
A roller bearing fault diagnosis method using interval support vector deterministic optimization based on nested PSO
Get PDFAn interval support vector deterministic optimization model (ISVD) is proposed for the fault classification problem of uncertainty samples in this paper. Firstly, based on the order relation theory, support vector machines using interval samples is transformed into ISVD, which is a two-objective optimization problem, with the midpoint and the radius optimized at the same time. Then, ISVD is converted into a single objective optimization model by the linear combination. The single objective optimization model includes Lagrange multiplier vector and interval sample vectors, both of which are nested. Thus, the nested particle swarm optimization (PSO) based on dynamic decreasing inertia weight is applied to select the optimal Lagrange multiplier vector of this model. Lastly, the effectiveness of the proposed method is proved by the data set of University of California Irvine (UCI) and the roller bearing fault experiments. The experimental results show: ISVD owns outstanding generalization ability with the help of the structured risk minimization and global optimization. The accuracy of the proposed ISVD is better than that of the native Bayes uncertain classification method 1 (NBU1), native Bayes uncertain classification method 2 (NBU2) and the formula-based Bayes classifier (FBC)
Optimization design of semi-active controller for in-wheel motors suspension
Get PDFOwing to significant influences of in-wheel motors on the performance of suspension, a modified GPSO-LQG controller is proposed for one-quarter vehicle suspension with the purpose of optimizing suspension performance for entire speed ranges. After the introduction of one-quarter vehicle suspension model, road surface excitation model and magneto-rheological damper model, the GPSO-LQG controller is investigated with three weighted coefficients optimized by utilizing the Genetic Particle Swarm Optimization (GPSO). With the intension of meeting the requirements across the speed range, the weighted coefficients are presented as functions of speed in a modified GPSO-LQG controller while constraint values α,β are given in the optimization of the weighted coefficients. Subsequently, simulation models are constructed with two working conditions. In the end, simulation results indicate that the modified GPSO-LQG controller reduces body acceleration by 8.37 % at a low speed and decreases the tire dynamic load by 8.55 % at a high speed, as compared with a GPSO-LQG controller. In terms of its outstanding advantages in improving the performance of suspension, the modified GPSO-LQG controller is more suitable for in-wheel motors suspension
Study on kinetic characteristics of a reciprocating mechanism with clearances
Get PDFClearances in mechanism are inevitable due to the errors from assembly, manufacture and wear. To study the kinetic characteristics of a typical automatic mechanism and the influence of clearances, an experimental device based on a reciprocating mechanism with clearances was set up, and a high speed camera system (HSCS) was used to record the mechanism motions. While the kinetic characteristics were analyzed based on the experimental data from HSCS, a coefficient of initial pressure of gas chamber used to characterize the randomness of the gunpowder gas force was proposed and its distribution was obtained. Meanwhile, the stiffness coefficient and damping coefficient of counterrecoil spring were identified. The virtual prototype model of this automatic mechanism was established. It’s found that the kinetic characteristics from the simulation and the experimental results of stochastic parameters and identification parameters are coincident approximately. Finally, the influence of guide rail’s clearances on kinetic characteristics based on the virtual prototype model was studied
Impacts of the weight coefficient and modal assurance criterion of large structures on observation station selection and optimization
Get PDFConsidering the shortcomings of the modal assurance criterion in the observation station selection and optimization algorithm for the structural modal testing experiment, this paper proposed a new criterion on the basis of the rule that the vibration mode is weighted-orthogonal to the mass. Since the vibration distributions of modes for large-scale structures vary from one another, the contribution of the high-order modes to the modal strain energy cannot be neglected. Therefore, a weight coefficient representing the contribution ratio of the high-order modal was introduced to modify the modal matrix. In addition to that, a hybrid optimization algorithm based on effective independence method and the weighted average modal strain energy coefficient method based on the effective independence method were proposed. Calculations guided by two-degree freedom system equal mass and non-equal-mass theories were initiated and comparisons and contrasts were made for the above-mentioned two methods, the average mode strain energy coefficient method based on the effective independence method and the weighted average modal strain energy coefficient method based on effective independence method through Garteur simulation tests to examine the differences in their resultant observation station arrangements. Results have shown that the traditional mode assurance criterion could not be used to judge whether the modes are weighted orthogonally or not when various nodes differ in their masses, but the new criterion involved in this paper could. The introduction of the weight coefficient effectively averted the aggregation of observation stations, best ensured the contributions of all the modal strain energy and fulfilled what’s required by a preferred observation station arrangement. Model tests were also conducted by employing the Garteur plane to test the weighted average mode energy coefficient method based on the effective independence method with the new modal assurance criterion proposed. It was found that the new modal mode assurance criterion guaranteed the completeness and linear independence of the monitoring mode, and that the weight coefficient introduced effectively magnified the contributions of the high-order modes to the modal strain energy, improved the accuracy of the test results. In the final analysis, the new assurance criterion is of great practical value to the observation station optimization and large-scale structure distribution. The method proposed in this paper has been applied to the modal test of a large carrier rocket and an observation station layout optimization software of large structural modes has been developed based on MATLAB language. It has been validated that this algorithm has faithfully guaranteed the integrity and linear independence of the modes monitored and that it can ensure the optimization and arrangement of observation stations in the modal test of large and complex structures
Cantilever model with curvature nonlinearity and longitudinal inertia excited by lateral basal moments being Gaussian white noise
Get PDFA slender in-extensional cantilever model excited by this transverse pedestal moments with the form of the Gaussian white noise was studied. The purpose of this paper was to explore how the geometrical nonlinearity influence the responses of the model excited by the Gaussian white noise. The curvature nonlinearity and inertia nonlinearity problems were addressed emphatically. The standard stochastic averaging method was applied to simplify the system into the Ito functions of amplitude and phase. Stationary probability density function (PDF) of amplitude, the joint PDF of the displacement and velocity together with the reliability function and the probability density of the first passage failure time were studied theoretically and numerically. The theoretical approximations coincide with the digital results very well when noise density is not too large. When the noise is stronger, a prediction-correction method was proposed to improve the predicting performance. Numerical simulations verified the effectiveness of this approach