Journal of Vibroengineering
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Cogging force reduction for tubular permanent magnet linear motor by slots with different sizes
Get PDFReduction of cogging force is one of the main concerns of tubular permanent magnet linear motor (TPMLM). In this paper, an analytical calculation of air-gap magnetic density is derived. In addition, an analytical calculation of cogging force is deduced by the energy method. The impact of slots with different sizes on the Fourier coefficients of relative air-gap permanence function is demonstrated. When the nz/4p is the integer, it will produce the cogging force. Therefore, it is practical to reduce the cogging force by changing the Fourier coefficient smaller. The effectiveness of the theoretical analysis is validated by experimental results
The semi-analytical method for damping of tubular transition layer damping structure
Get PDFTo solve the limited vibration consumption of the traditional tubular damping structure (TTDS), the tubular transition layer damping structure (TTLDS) is proposed; Based on viscoelastic materials and theories of thin cylindrical shells, the governing equation, the first order matrix differential equation describing vibration of TTLDS under harmonic excitation, is derived by considering the interaction between all layers and the dissipation caused by the shear deformation for transition layer and damping layer. By using the extended homogeneous capacity precision integration method to solve the control equation, a semi-analytical method for studying the vibration and damping characteristics of TTLDS is given. By way of comparison, the correctness of the method provided in paper is verified. At last, the influence of thickness, material and location of transition layer on damping effect is analyzed. The results show that the change for the thickness or material of the transition layer can make the structural damping effect change greatly, while the change for location of the transition layer plays only a few roles on the structural damping effect
Active vibration suppression of a nonlinear electromechanical oscillator system with simultaneous resonance
Get PDFIn this paper, we explored the nonlinear dynamics behavior and vibration suppression of a nonlinear electromechanical oscillator system under harmonic and parametric excitation. The model comprises of an electrical part coupled to mechanical part and displayed by a coupled nonlinear ordinary differential equations. The analytical up to second order approximate solutions are sought applying the method of multiple scales method. We utilized the time-series and method of averaging to analyze the response and stability of the solutions at the worst resonance cases. We checked the results of perturbation solution through numerical simulations and the effects of different system parameters have been reported. Comparison between analytical and numerical solutions is obtained. Also, the numerical results are obtained using MAPLE and MATLAB algorisms
Structural state inspection using dual-tree quaternion wavelet transform
Get PDFThe dual-tree quaternion wavelet transform (QWT) was used in conjunction with quaternion-based three-channel joint transmissibility (QTJT) for state inspection. Multiple QTJTs from the same structural state were used to construct a state matrix, which was considered as a feature image. Then QWT coefficients of the feature image were calculated. It supported one magnitude and three phases, in particular, the low-frequency magnitude-phase was set as state feature index. Ultimately, the difference of the state feature indexes were utilized as the state indicator. This method reduced the influence on state inspection caused by measurement uncertainty of single testing sample, because it took overall consideration of multiple testing samples and described the similarity from multiple directions. The availability of suggested method was demonstrated by a real experiment, in which the state changing was realized by loosening fasteners and altering the longitudinal force of rail. This method was also compared with method based on Karhunen-Loeve Transform (K-LT) and artificial neural network (ANN). Experimental result indicated that the suggested method was integrated optimal, moreover, the resolution of the longitudinal force of rail was less than 10 MPa which was equivalent to temperature change of 1.75 °C for full-lock rail
A method based on multiscale base-scale entropy and random forests for roller bearings faults diagnosis
Get PDFA method based on multiscale base-scale entropy (MBSE) and random forests (RF) for roller bearings faults diagnosis is presented in this study. Firstly, the roller bearings vibration signals were decomposed into base-scale entropy (BSE), sample entropy (SE) and permutation entropy (PE) values by using MBSE, multiscale sample entropy (MSE) and multiscale permutation entropy (MPE) under different scales. Then the computation time of the MBSE/MSE/MPE methods were compared. Secondly, the entropy values of BSE, SE, and PE under different scales were regarded as the input of RF and SVM optimized by particle swarm ion (PSO) and genetic algorithm (GA) algorithms for fulfilling the fault identification, and the classification accuracy was utilized to verify the effect of the MBSE/MSE/MPE methods by using RF/PSO/GA-SVM models. Finally, the experiment result shows that the computational efficiency and classification accuracy of MBSE method are superior to MSE and MPE with RF and SVM
Buffeting performance of long-span suspension bridge based on measured wind data in a mountainous region
Get PDFLong-span suspension bridge increases rapidly in size as a result of bridge construction in a mountainous region, in addition, more and more long-span suspension bridges are in process of preparation. The bridge stiffness decreases with the increase of bridge span length, and hence the buffeting performance of bridge is sensitive to external factors. In this paper, the Cuntan Yangze Bridge located in a mountainous region is taken as the background to study the effect of different power spectrums on the buffeting performance. A three-dimensional finite element model is set up on the ANSYS platform. The fitted power spectrum of extreme strong wind is recorded and taken as the sample to analyze the buffeting performance. The results are compared with the specified power spectrum in the time and frequency domains. Different from existing studies, buffeting performances with the fitted power spectrum are larger than those with the specified power spectrum on the whole. Two kinds of power spectrum are coincidental in the overall tendency in the frequency domain and are distinct in the low frequency region. Structure performance of long-span suspension bridge in the mountainous region should be the subject of specially paid attention
The undamped control for PWM rectifier based on LCL filter
Get PDFLCL filter is applied in PWM rectifier with the better filtering effect. Its inductor also plays a role in inhibiting the current impact, which not only has a good dynamic performance, but also reduces the system cost. However, LCL filter can cause resonance in certain frequency that affects system performance, as well as the parameters of LCL filter are hard to design. With analysis on the theory and characters of the fixed switching frequency control strategy, an undamped control strategy of three-phase voltage PWM rectifier based on LCL filtering is proposed for the resonance of LCL filter. The delay of system and the fixed switching frequency are used to control the damp. PI regulator’s sampling time is adjusted to achieve the system stability. The structure of system is optimized by the design of simplified capacitance sensor. The simulation results show that this method has better dynamic performance, the current harmonic of grid side has reduced sharply, and the resonance of LCL filter has been inhibited effectively
On crack detection in curved beams using change of natural frequency
Get PDFIn this study, an inverse method for the purpose of identifying the parameters of a single-edge crack in a curved beam is investigated. This method requires both numerical and experimental natural frequencies. The differential quadrature element method (DQEM) is introduced to get the numerical ones. For the purpose of implementing the DQEM the beam is divided into some elements and the governing equations, the continuity and the boundary conditions, are exerted on these elements to create an eigenvalue problem which is solved to obtain the required frequencies. A rotational spring whose stiffness is a function of crack depth is used to model the crack. An objective function with the variables of crack location and depth which is the weighted mean squared error between experimental and numerical frequencies is defined. The artificial bee colony algorithm (ABC) an optimization algorithm inspired by the natural foraging behavior of honeybees is used to minimize the aforementioned objective function and obtain crack parameters. To investigate the accuracy of this non-destructive, fast and easy method, an experimental modal analysis test is conducted on a cracked beam. The results indicate that the position and depth of the crack can be determined successfully using this method. This test is done five times with a different crack depth each time, to show the efficiency of the method for all cracks even small ones. A brief investigation is also done on the effect of crack location and depth on the natural frequencies
Monitoring of blast-induced ground vibration using WSN and prediction with an ANN approach of ACC dungri limestone mine, India
Get PDFBlast-induced ground vibration (BIGV) is an undesirable environmental issue in and around mines. Usage of a high amount of explosive causes ground vibrations that are harmful to the nearby habitats and dwellings. In this paper, an attempt has been made to monitor the BIGV with low-cost wireless sensor network (WSN) and prediction of peak particle velocity (PPV) using an artificial neural network (ANN) technique at ACC Dungri limestone mine, Bargarh, Odisha, India. Eleven blasts PPV were recorded at different locations using wireless sensor network prototype system. The data has been transmitted by ZigBee (IEEE 802.15.4) protocol. The results are very promising and the recorded PPV varies from 0.191 mm/s to 8.60 mm/s. A three-layer, feed-forward back propagation neural network consists of 6 input parameters, 5 hidden neurons, and one output parameters were trained. Obtained results were compared based on correlation of determination (R2) and standard error between recorded and predicted values of PPV
Study on unsteady aerodynamic characteristics of two trains passing by each other in the open air
Get PDFBased on three-dimensional, non-steady, compressive and unsteady control equations and k-ε turbulence model, the paper adopts the finite volume method and moving grid technologies to conduct a numerical simulation analysis on pressure waves and aerodynamic forces (force moments) of two meeting trains in the open air. The simulation model has been validated by experimental test. Computational results show that during the meeting, the damage of the lateral window glass during the meeting is caused by that the window glass will be sucked out by negative pressures rather than be hit by positive pressures; both head wave pressure amplitude and tail wave pressure amplitude are in direct ratios to the square of the running speed; resistance values of the head and tail train experienced several changes, but the changing rules of the head train are opposed to those of the tail train; the lift force of the head train is downward all the time, the lift force is more than that of other train bodies, and lift force directions of the middle train and the tail train change alternately; the head train has the largest lateral force, the tail train ranks the second position, and the middle train ranks the last position; each train experiences 6 shaking force moment impacts including outward, inward, outward, inward, outward and inward impacts in succession; each train experiences 6 nodding force moment impacts, including downward, upward, downward, upward, downward and upward impacts, in succession