Journal of Vibroengineering
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A frequency slice wavelet transform based on wavelet de-noising using neighboring coefficients method and its application in feature extraction of rolling bearing’ early weak fault
Get PDFExtracting the characteristics of rolling bearings in early weak failure stage before the occurring of complete failure has important safety and economic significance in engineering application. The wavelet transform (WT) is the commonly used and effective time-frequency method for fault feature extraction of rotating machinery due to that it could reflect the fault feature in time and frequency domains synchronously. However, WT would not work effectively when the impulsive fault signal is buried by strong background noise, and the situation is particularly serious in the early weak fault stage of rolling bearing. A frequency slice wavelet transform based on wavelet de-noising using neighboring coefficients method is proposed in the paper by combing frequency slice wavelet transform with wavelet de-noising using neighboring coefficient to solve the above problem: Firstly, the vibration signal of rolling bearing is de-noised by wavelet de-noising using the neighboring coefficients method. Then the frequency slice wavelet transform is applied on the de-noised signal, and satisfactory analysis results could be obtained. The effectiveness of the proposed method is verified by the vibration data of rolling bearing accelerated fatigue test. Besides, the analysis result of the same vibration data of rolling bearing accelerated fatigue test using Kurtogram method is also presented in the paper to verify the advantage of the proposed method
Electrolytic capacitor life time calculation under varying operating conditions
Get PDFA fair evaluation of an electrolytic capacitor time to failure is important for the design and development of electronic devices. In practice, it is required to consider variable operating conditions, for example, weather temperature fluctuations or load variations. Based on the principle of Miner’s fatigue accumulation and reasonable approximations, the general formulas are derived that take into account weather temperature changes. The outdoor air temperature was modeled by the sum of components like averaged seasonal changes, averaged daily temperature changes and random temperature fluctuations. An Easy-to-use analytical formulas for the electrolytic capacitor life time estimation were obtained, in which the contribution of each individual temperature phenomenon can be evaluated. The impact of these components on the non-linear estimation formula by the Miner's principle has been clarified for some example climatic regions. Also, the capacitor life time estimation formula under particularly scheduled variable load was derived for example. The resulting formulas are useful for engineering calculations of the reliability of electronic devices exposed to weather temperature changes
Optimizing SVM’s parameters based on backtracking search optimization algorithm for gear fault diagnosis
Get PDFThe accuracy of a support vector machine (SVM) classifier is decided by the selection of optimal parameters for the SVM. The Backtracking Search Optimization Algorithm (BSA) is often applied to resolve the global optimization problem and adapted to optimize SVM parameters. In this research, a SVM parameter optimization method based on BSA (BSA-SVM) is proposed, and the BSA-SVM is applied to diagnose gear faults. Firstly, a gear vibration signal can be decomposed into several intrinsic scale components (ISCs) by means of the Local Characteristics-Scale Decomposition (LCD). Secondly, the MPE can extract the fault feature vectors from the first few ISCs. Thirdly, the fault feature vectors are taken as the input vectors of the BSA-SVM classifier. The analysis results of BSA-SVM classifier show that this method has higher accuracy than GA (Genetic Algorithm) or PSO (Particles Swarm Algorithm) algorithms combined with SVM. In short, the BSA-SVM based on the MPE-LCD is suitable to diagnose the state of health gear
Research of multi-point adaptive control strategy based on electromagnetic active vibration absorber
Get PDFIn order to improve the signal natural frequency of dynamic vibration absorber and eliminate the influence of nonlinear output force to the adaptive vibration absorption system. A new type of electromagnetic active vibration absorber is designed in this article. The internal magnetic circuit structure is changed through the electromagnet placed on the upper and lower, produce the electromagnetic force in two directions. Reaction force of upper mass is used to eliminate the target vibration. The effective frequency range of the vibration absorption increases, output force is basically linear. Aimed at multiple-point adaptive control strategy, a distributed multi-channel adaptive control algorithm is proposed, in which coupling between channels can be compensated on each control loop. Influence of secondary path on active control is analyzed, put forward the improved least mean square algorithm to identify the secondary. Active vibration control experiment platform is structured to verify the output force of absorber, and engineering application of the distributed multi-channel adaptive control algorithm. The results show that the distributed multi-channel adaptive control algorithm system has about 15 dB noise reduction, effect is obvious; new type of electromagnetic active vibration absorber is not limited to the natural frequency, output force can adaptive keep pace with the excitation frequency
Optimal fuzzy iterative learning control based on artificial bee colony for vibration control of piezoelectric smart structures
Get PDFCombining P-type iterative learning (IL) control, fuzzy logic control and artificial bee colony (ABC) algorithm, a new optimal fuzzy IL controller is designed for active vibration control of piezoelectric smart structures. In order to accelerate the learning speed of feedback gain, the fuzzy logic controller is integrated into the ANSYS finite element (FE) models by using APDL (ANSYS Parameter Design Language) approach to adjust adaptively the learning gain of P-type IL control. For improving the performance and robustness of the fuzzy logic controller as well as diminishing human intervention in the operation process, ABC algorithm is used to automatically identify the optimal configurations for values in fuzzy query table, fuzzification parameters and defuzzification parameters, and the main program of ABC algorithm is operated in MATLAB. The active vibration equations are driven from the FE equations for the dynamic response of a linear elastic piezoelectric smart structure. Considering the vibrations generated by various external disturbances, the optimal fuzzy IL controller is numerically investigated for a clamped piezoelectric smart plate. Results demonstrate that the proposed control approach makes the feedback gain has a fast learning speed and performs excellent in vibration suppression. This is demonstrated in the results by comparing the new control approach with the P-type IL control
The effectiveness of nonlinear integral positive position feedback control on a duffing oscillator system based on primary and super harmonic resonances
Get PDFIn this paper, we applied three different control methods; Positive Position Feedback (PPF), Integral Resonance Control (IRC) and Nonlinear Integrated Positive Position Feedback (NIPPF) added to a Duffing oscillator system subjected to harmonic force. An analytic solution is introduced using the multiple scales perturbation technique (MSPT) to solve the nonlinear differential equations, which simulate the system with NIPPF controller. Before and after control at the primary and superharmonic resonances, the nonlinear systems’ steady-state amplitude and stability are studied and examined. The influences of various parameters of the system after being connected to NIPPF are illustrated. Optimum working conditions for the NIPPF controller are obtained at internal resonance ratio 1:1. A Comparison is also made to validate the closeness between the numerical solution and the analytical perturbative one at time-history and frequency response curves (FRC). Finally, a comparison with the available results in the literature is presented. From this comparison, we find that the best control to the system is via the NIPPF controller
Aerodynamic admittance influence on buffeting performance of suspension bridge with streamlined deck
Get PDFBuffeting performance is growing sensitive to external and internal factors with increasing span of bridge. Aerodynamic admittance is an essential parameter in analyzing buffeting performance. In this paper, aerodynamic admittance in different conditions were conducted in wind tunnel tests by section model. Three kinds of aerodynamic admittance functions were used to calculating buffeting performance respectively. It is found that the aerodynamic admittance of streamlined deck is closely related to wind attack angle, and has a small difference at different wind speeds. However, the influence of aerodynamic admittance on buffeting performance is affected by the wind speed significantly. Under given conditions, adopting the Sears function as the admittance function of a similar streamlined box girder is reasonable, while the buffeting performance result obtained by adopting an admittance function as 1.0 is very conservative
Study on the optimum penetration depth by two TBM cutters under different cutter spacings
Get PDFThis paper investigates the optimum penetration depth and the synergistic effect of TBM (Tunnel Boring Machine) rock breaking under the different cutter spacings. Indentation tests, using two TBM cutters, were conducted on sandstone specimens based on an improved uniaxial testing. Afterwards, morphological measurement was performed to analyze the change of the groove volume, using a surface profilometer. Based on the evaluations of typical chips and cracks propagation, the fragmentation modes of the rock between two cutters under different penetration depths were proposed. In addition, the TBM rock breaking efficiency was studied. As the increase of the penetration depth, when the cutter spacing was constant, the results show that: (1) The rock fragmentation modes gradually changed from shear failure and shear-tensile failure to tensile failure. (2) Though penetration energy gradually increased, the groove volumes also increased, thus, the TBM rock breaking efficiency rises. (3) Specific energy decreased first and then gradually increased. It indicates that the optimum penetration depth was existent for different preset penetration depths. With the increase in cutter spacing, the optimum penetration depth also rised. According to the derivation and verification of the analytical formula, the internal relationship between the penetration depth and the fracture toughness was obtained, which was in line with the linear relationship between penetration depth and penetration energy. From a microscopic point of view, the sharp increase of penetration energy with increase of penetration depth can be explained
Acceleration and displacement dynamic response laws of a shallow-buried bifurcated tunnel
Get PDFIn order to obtain the seismic dynamic laws of the acceleration and displacement of a shallow-buried bifurcated tunnel, the analysis of the numerical simulation was carried out by MIDAS-GTS/NX software. The results of the numerical simulation were verified by a shaking table model test. The results show that: (1) the numerical simulation and shaking table test coincide with each other in terms of variation law and peak value. The results of the numerical simulation are credible. (2) For different tunnel cross-section, the response of acceleration and displacement are significant difference. (3) The seismic response of the small distance tunnel (Section 6) is intense. The seismic response laws of the small distance tunnel are significant difference from other type tunnels. The seismic response of the measuring point at the middle rock column is intense. (4) Along the axis of the tunnel, the displacement of the tunnel firstly increases and then decreases. The displacement of the measuring point at the middle rock column is intense, which is in accordance with the law of the acceleration response. The seismic response laws of the tunnel are significantly affected by the middle rock column. The section structure size has a significant effect on the dynamic response of the tunnel
Survey on roof movement of the gangue backfill working face
Get PDFThis paper studied the roof movement characteristics of LW1302N-1 with gangue backfill mining in Shandong Xinjulong Company of China. The monitoring of roof subsidence of the gob and bearing stress of filled gangue was carried out by using the roof subsidence and gangue loading monitoring system. From data analysis, the result shows that: (1) Gob roof subsidence can be divided into six stages including slow subsidence, fast subsidence, very fast subsidence, subsidence slowing down, subsidence speeding up and subsidence becoming slow. (2) Filled gangue loading period can be divided into four stages including slow increasing resistance, fast increasing strength, strengthening and continuing increasing resistance, Similarly, the gob roof movement consists of four steps such as immediate roof caving, central roof flexure, main roof fracturing, and high strata flexure. (3) The immediate roof is 3.1 times the thickness of equal mining height, and the main roof is 2.7 times the thickness of equal mining height. The research results provide a reference to the analysis of the characteristics of overlying strata structure and roof movement for gangue backfill mining in deep coal mines