最新刊期
卷 51 ， 期 6 ， 2017
- 摘要：Aiming at accurately and rapidly recognizing bearing fault pattern and performance degradation, a bearing fault detection and diagnosis method based on principal component analysis and hidden Markov model is proposed. The mixed domain fault feature set of bearing vibration signal, which corresponds to different bearing conditions, is extracted with principal component analysis to reduce the dimension of the feature set, then hidden Markov models are trained with part of the reduced feature set. The performances of trained models are verified with the remaining parts in this feature set. The bearing fault patterns are recognized and bearing performance degradation is assessed by comparing the logarithmic likelihood probability value of the hidden Markov models. Experiments under different bearing conditions are carried out, vibration signals are collected, and the correct classification rate of the proposed method reaches 100%. Compared with the compensation distance evaluation based feature dimension reducing technique and hidden Markov model, the classification dispersion of the proposed method is increased by 123.74%. In the bearing performance degradation monitoring, the proposed method exhibits better effectiveness and accuracy for early bearing degradation warning.关键词：mixed domain fault feature set;principal component analysis;hidden Markov model;bearing fault detection and diagnosis1086|6|0更新时间：2025-07-09
- 摘要：A fault severity assessment method is proposed to solve the problem that early fault signals of rolling bearings are weak and difficult to be quantitatively measured, and the method uses Hilbert vibration decomposition(HVD)combined with Lempel-Ziv complexity(LZC). HVD is adopted to decompose fault signals of rolling bearings into initial HVD components ordered from large to small and with different instantaneous frequencies. The best initial HVD component is selected based on the kurtosis index analysis, and then the component is used to reconstruct the fault signals. The normalized LZC index of the reconstructed signals is calculated using the mean symbolic method. The mirror extension method is adopted to deal with endpoint effect of HVD. Simulation results show that the mirror extension method effectively improves the endpoint effect of HVD, and the decomposition accuracy is obviously increased. The HVD-LZC method is used to analyze fault signals of the inner and outer rings of rolling bearings with different level of defect severity, and the results show that the method eliminates the non-stationary and non-linear interferences. As a result, the main fault vibration modes are extracted and the HVD-LZC characteristic intervals for different damage state are estimated; The characteristics of HVD-LZC for three kinds of fault severities of rolling bearing are modeled using the GA-SVM based on RBF kernel. Experimental results show that the HVD-LZC method recognizes different levels of fault severity of the inner and outer rings of rolling bearings. Hence, this study provides an effective fault severity assessment method for rolling bearings.关键词：rolling bearing;damage severity assessment;Hilbert vibration decomposition;Lempel-Ziv complexity708|6|2更新时间：2025-07-09
- 摘要：Considering the blind hyper parameters selection in least squares support vector machine(LSSVM)modeling, a new improved fruit fly optimization algorithm(IFOA)for hyper parameter optimization is proposed based on the conventional FOA. This algorithm selects the different step size formula to realize the adaptive update of the search step by judging the relation between the optimal value obtained by contemporary optimization and the previous generation optimal value, which improves the optimization precision and global optimization ability of the IFOA with fewer parameters and quick calculation rate. The simulation and mill load softsensing application show that the prediction model based on IFOA, compared with those based on grid search method, particle swarm optimization algorithm and FOA, significantly improves the mill load forecast precision and more accurately reveals the change rule of mill load.关键词：improved fruit fly optimization algorithm;least squares support vector machine;mill load593|5|7更新时间：2025-07-09
- 摘要：To solve the difficulty that the observed signals on aircraft engine case are generally a mixture of multiple vibration sources, a blind source separation algorithm is proposed based on the characteristics of aircraft engine vibration sources, where the spectral characteristics of the rotating shaft vibration signal of aircraft engine are aimed at. The vibration spectrum of shaft fault signals of rotating machinery usually includes fundamental frequency, harmonic components and sub-harmonic components, corresponding to such as misalignment, rubbing and crack. The observed signals from different channels are decomposed by continuous wavelet transform, the main vibration sources and the corresponding fundamental frequencies are determined according to the spectral peak analysis, and the harmonics and subharmonic components of each vibration source are extracted from each observed signal with time synchronous averaging method, thus an image of each source can be extracted from each observation channel, and several image signals are obtained for the same source. The optimal estimation is determined by comparing the 2-norm of image signals of each source. The proposed algorithm is validated by numerical simulation signal and measured aerodynamic acceleration signal from aircraft engine case. The results show that the algorithm can estimate the number of main vibration sources inside the engine and extract the main components of each source signal in the case of a certain priori knowledge of the engine speed.关键词：aircraft engine;blind source separation;signal feature;vibration signal679|5|4更新时间：2025-07-09
- 摘要：A novel composite model predictive control method based on neural network is proposed for a constrained hypersonic vehicle(HV)in the presence of external persistent disturbances and restriction of asymmetric constraints. Firstly, a stable polyhedral invariant set is constructed based on multiple discrete points of velocity and height of HV, and the ability of the set to deal with asymmetric constraint is used to limit asymmetric constraints of control signals and angle of attack. A nominal predictive controller for the nominal longitudinal theoretical model of HV without external persistent disturbances is designed. Secondly, an adaptive neural network disturbance observer is designed, and the observer is used to estimate the disturbances in loops of velocity, angle of attack and pitch rate. An auxiliary compensation controller of the nominal predictive controller is appended to effectively attenuate the influences of external persistent disturbances. Simulation results show that when HV is affected by persistent disturbances and limitation of asymmetric constraints, the proposed method guarantees the tracking errors for altitude and velocity to converge into sufficiently small ranges of 10-4 km and 10-4 km/s, respectively, while the tracking errors from the uncompensated control methods are oscillating in large amplitude.关键词：hypersonic vehicle;predictive control;neural network;polyhedral invariant set628|6|0更新时间：2025-07-09
- 摘要：A 4D chaotic oscillator controlled by a single voltage input is proposed to solve the problem that the security in chaotic secret communication is reduced because the chaotic mappings of traditional chaotic oscillators are easy to predict. The chaotic oscillator is controlled by a DC voltage and it can be kept in motion state of period, period-doubling, chaos or even hyper-chaos through regulating the control voltage. Because the oscillator's attractors are hidden attractors in chaotic state and the locations of these attractors cannot be calculated through choosing points in the neighborhood of line equilibrium, the unpredictability of these chaotic oscillator's dynamic behaviors and the security of secret communication are improved. Hardware experiment shows that when the voltage is controlled within the interval of [2.80, 3.40] V, the chaotic oscillator is the most sensitive to external disturbance, the unpredictability of its chaotic motion is the highest, and the security of chaotic secret communication achieves the best.关键词：secret communication;chaotic oscillator;line equilibrium422|5|1更新时间：2025-07-09
- 摘要：A novel optimal route evaluation method based on principal component analysis(OREPCA)is proposed to solve the transmission route sequencing problem appeared in the optimality evaluation process of wireless sensor networks. Sample routes information is firstly collected in a discrete time domain by using an ant colony algorithm. Then, a relevant evaluation index system of routes is constructed based on the deployment environment of the network, and a positive dimensionless method is given and is applied to the indicators of the set. The priority of all indicators is used to score each sample route and to obtain a vector of evaluation indicators. Finally, a correlation coefficient matrix among different indicators in the vector is calculated, and the principal component approach is used to obtain a route evaluation function and the weighting factor of each evaluation indicator in the function. The algorithm avoids the problem of subjective randomness caused by manually selecting weighting factors based on experience. Moreover, the evaluation function generated by the proposed method achieves the diversified evaluation and prompts dynamic server load balance in different monitoring environments. Comparisons with the multi-objective routing algorithm and the cluster based route optimisation and load balancing protocol, OREPCA can increase the lifetime of network by 14% and put down the delay of communication notably.关键词：route evaluation;principal component analysis;ant colony algorithm;wireless sensor network690|5|1更新时间：2025-07-09
- 摘要：A soft decision based blind recognition(SDBR)method for primitive BCH codes is proposed to solve the problem that existing recognition methods have low error-resilient capabilities. Firstly, bit sequences as well as the corresponding reliability information are obtained by soft demodulation of the intercepted data, then code words are divided and a reliability coefficient of code roots is established with the reliability information to calculate the occurrence probability of code roots, and code length is estimated by using Kullback-Leibler divergence. Secondly, reliability statistics of common code roots are defined and a binary hypothesis test is built, then common code roots are verified under different primitive polynomials. Finally, the right primitive polynomial is recognized by using the continuous distribution characteristics of common code roots, and a generator polynomial is calculated from all these code roots. Simulation results show that the SDBR method effectively recognizes the commonly used primitive BCH codes when the signal-to-noise ratio is above 7 dB. A comparison with the roots information dispersion entropy based method shows that the SDBR method improves the error-resilient performance by 1.8 dB.关键词：BCH codes;blind recognition;soft decision;Kullback-Leibler divergence;hypothesis test474|5|5更新时间：2025-07-09
- 摘要：A novel topology construction incentive algorithm(TCI)using reputation is proposed to solve the service migration oriented node incentive problem in wireless ubiquitous environment. First, a hierarchical selection model is established to select the optimal service migration cell and relay for a demand node. Then, an improved method is proposed to accurately calculate the reputation of each cooperation node. Finally, the topology construction algorithm is used to adaptively adjust the topology of the entire network and to effectively promote the node cooperation. Simulation results and comparisons with the random probability selection based incentive algorithm and the shortest distance selection based incentive algorithm show that the service migration rate of TCI improves respectively by 43% and 106%. Comparisons with the direct reputation based incentive algorithm and the integrated reputation based incentive algorithm show that TCI motivates noncooperation nodes to change their attitudes before the 3rd period. These results indicate that TCI performs outstandingly in terms of service migration and node incentive.关键词：wireless ubiquitous environment;service migration;reputation;node cooperation;node incentive467|5|1更新时间：2025-07-09
- 摘要：An incremental analog-to-digital converter(I-ADC)with chopper stabilization(CHS)and self-calibration techniques is presented to meet the requirements of high resolution, low power consumption and small area for measuring devices of ultra-low-frequency signals. The I-ADC has the function of reset operation to avoid pattern noise caused by ultra-low-frequency signals. A first-order architecture is adopted for the I-ADC to reduce power consumption and chip area, and to achieve 14-bit resolution by increasing certain conversion time. The chopper stabilization technique is employed to eliminate the influence of amplifier's low-frequency noise and offset on the I-ADC's precision, and power-on self-calibration is employed to eliminate the systematic offset of the I-ADC. The circuit of the I-ADC and the layout of the modulator are designed with the DongBu 0.5 μm BCD technology. Simulation results in an input range of -156.25～156.25 mV show that the maximum absolute conversion error of the I-ADC is 21 μV, the maximum errors of differential nonlinearity and integral nonlinearity are 0.12 and 0.21 bit, respectively, and the average current consumption of the modulator is only 20 μA. The modulator occupies a chip area of only 150 μm×310 μm. The proposed I-ADC achieves 14 bit resolution, which is required by ultra-low-frequency signal measuring systems, such as lithium-ion battery coulometer, and has significant advantages of low power consumption and small area.关键词：ultra-low-frequency;incremental;analog-to-digital converter;chopper stabilization;self-calibration694|7|6更新时间：2025-07-09
- 摘要：A novel feature extraction method called three-structure descriptor(TSD)used in HSV color space is proposed to address the problem that the image description methods based on texton pay undue attention to the color description so reduce the performance of image retrieval due to directly extracting other features in color space. The proposed method extracts color and texture information in HSV color space and the same importance of both the color and texture is taken into account while the excessive interference of color information is avoided. TSD uses the information change among pixels to represent the local spatial structure information in texture feature extraction, which solves the problem that the traditional local pattern methods disregard the spatial correlation in local structure and captures more information regarding to spatial structure information. Experimental results show that the retrieval precisions of the proposed method reach 78.08%, 38.12% and 52.12% on the Corel-1000, Corel-5000 and Corel-10000 databases respectively, and its retrieval precisions are higher than those of existing methods based on texton.关键词：HSV color space;three-structure descriptor;texture descriptor;image retrieval604|5|1更新时间：2025-07-09
- 摘要：Large number of nonlinear equations in the existing ball bearing models lead to a lower calculation efficiency. Following Jones-Harris model, the contact angels of ball bearing are chosen as the iterative variables, and the partial equilibrium equations of balls are further deduced and simplified, which facilitates decreasing the number of nonlinear equations to significantly reduce the computing task. The contact angle is taken as the most important dynamic parameter of high-speed angular contact ball bearings, and the influencing rules of various factors on it are analyzed. The results show that the new model has high computing efficiency, and the uneven distribution of contact angle due to radial load can be eliminated by applying an appropriate moment.关键词：angular contact ball bearing;quick calculation;contact angle;combined loads924|7|2更新时间：2025-07-09
- 摘要：Widely deployed applications in cloud computing with many-to-one communication pattern may cause TCP incast congestion problem, resulting in throughput collapse. Mice flows are easily influenced by elephant flows to miss the application deadline. To address these problems, we propose the differentiated flow transmission control protocol(DFTCP). The DFTCP adopts active queue management scheme and delivers the network congestion information through explicit congestion notifications. DFTCP reduces the number of discarding bursty small packets by controlling the queue length of switches to solve TCP incast problem. TCP flows are classified by DFTCP at the end-servers. When network congestion happens, DFTCP adjusts TCP congestion windows based on network states and classified flow information. Elephant flows have larger back-off time compared with mice flows. Simulation shows that DFTCP can effectively avoid TCP incast congestion compared with the traditional TCP, and it can reduce the completion time of mice flows compared with DCTCP. In addition, DFTCP can make multiple elephant flows converge quickly to guarantee the fairness of link sharing.关键词：cloud computing;data center network;TCP incast;congestion control;congestion window479|5|1更新时间：2025-07-09
- 摘要：Machining precision is attenuated by thermal factors. Making use of neural network's strong self-learning and data fitting ability, a novel method based on improved BP-neural network algorithm is proposed for comprehensive error compensation of multi-axis machine tools. An improved algorithm introducing steepness factor and amplification factor is presented to improve the convergence efficiency affected by slow decline of neurons error surface, and to predict and compensate machining precision of motion axes. The measured data of the temperature of each key heat source and displacement errors of motion axis of the large A/B double-pendulum angle gantry milling machine are respectively regarded as input and output. A machining precision error prediction model of machine tool is established and trained by the improved BP-neural network. The nonlinear relationship between temperature and displacement errors is obtained. Cutter location data file of workpiece is modified accordingly and machining precision is improved. Simulation and experiments indicate that this method reduces the prediction errors and computing period compared with the conventional BP-neural network. It is unnecessary to greatly reform the existing machine tools for application of the comprehensive error compensation system.关键词：BP-neural network;steepness factor;amplification factor;error compensation809|5|5更新时间：2025-07-09
- 摘要：An evaporation model of single moving liquid nitrogen droplet in high-speed gas flow is developed based on the classical evaporation model to reveal the evaporation of whole liquid nitrogen spray. The droplet evaporation rate, diameter and velocity are obtained in the evaporation process by adjusting ambient temperature, ambient pressure and gas flow velocity. The results show that for those parameters, the ambient temperature has greater influence on the droplet evaporation rate, which grows with temperature. Within the falling distance of two meters, with the ambient temperature riseing by every 100 K in the range from 100 to 300 K, the relative evaporation increases about 18%. The higher the gas flow speed reaches, the higher the droplet evaporation rate gets at equal time due to the stronger convection heat transfer, but the evaporation capacity decreases because of limited evaporation distance. Under above conditions, the relative evaporation is 5%～6% within the flow speed range of 10～30 m/s. Bigger droplet has bigger absolute evaporation capacity but smaller relative evaporation capacity, and the droplet evaporation rate rises with the ambient pressure.关键词：spray cooling;droplet evaporation;liquid nitrogen;movement characteristics750|5|10更新时间：2025-07-09
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0