最新刊期
卷 49 ， 期 8 ， 2015
- 摘要：A new algorithm to calculate the system damping ratio and natural frequency using frequency spectrum correction of exponentially decaying sinusoidal signals is proposed to solve the problem that time domain methods are easy to cause subjective errors and there exists the accuracy limit problem in frequency domain methods in traditional methods to calculate natural frequencies and damping ratios of mechanical systems. The interpolation spectrum correcting method based on Hanning-window is used to obtain frequency deviations and damped factors. Then the natural frequency is calculated by combining similarity relations between damping free vibration responses and exponentially decaying sinusoidal signals, and the system damping ratio and damped natural frequency are obtained. The undamped natural frequency is finally calculated. Both a traditional time domain method and the proposed frequency domain method are respectively used to calculate the natural frequency and damping ratio of a piezoelectric cantilever beam. The results show that the proposed algorithm has a higher calculation accuracy and better adaption of signal to noise ratio. Comparisons with the traditional frequency fitting method show that the new algorithm is simpler and its computational efficiency is higher.关键词：damped signal;frequency spectrum correction;natural frequency;damping ratio;piezoelectric cantilever1978|4|3更新时间：2025-07-09
- 摘要：Metal tips with low melting point suffer from sublimation during field emission. A layer of graphene in-situ on a submicron copper tip is synthesized to suppress the sublimation and to improve the field emission stability. A copper wire is etched in ferric trichloride solution to get a copper tip with submicron radius. Then a graphene layer is successfully synthesized on the copper tip by chemical vapor deposition. The copper tip is tested pre and after graphene growth. The field emission tests show that after the graphene growth, the turn-on field of the copper tip reduces from 4 V/μm to 2.5 V/μm while the current stability is improved. The results reported here is valuable for both the growth of graphene on a copper surface of sub-micron area and the improvement of field emission of graphene decorated metal tips.536|4|1更新时间：2025-07-09
- 摘要：A method to extract dielectric parameters of PCB board in a wide band is proposed to focus on the problem that rough conductor surfaces of small-scale printed circuit board in high-speed transmission/interconnection structures increase their impact on transmission loss and phase constant. Surface impedance for conductors with smooth surface and rough surface is respectively calculated based on a stripline model and then propagation constants of the stripline model with rough conductors are obtained. A differential extrapolation method is proposed to separate the dielectric loss from the total loss so that dielectric parameters such as permittivity and loss tangent are extracted in a wide frequency band. Simulation results from DC to 20 GHz with eliminating the effects of conductor surface roughness and comparisons with the actual FR4 material parameters show that the extracted permittivity and loss tangent have errors of 2% and 5% respectively at 1MHz and both the maximum errors reach to 1% and 8.6% respectively in a high frequency band from 10 GHz to 20 GHz. The proposed method is based on the equivalent surface impedance theory, and can save computing resources effectively without decreasing accuracy, and it is suitable for extracting dielectric parameters of PCB board in wide band.关键词：printed circuit board;rough surface;surface impedance;differential extrapolation;dielectric parameters22914|8|1更新时间：2025-07-09
- 摘要：A novel multi-parameter joint estimation algorithm based on spatial polarimetric time-frequency distributions(SPTFD)for frequency-hopping(FH)signals is proposed to sort frequency-hopping network, identifying and to track signals effectively via the two dimensional direction of arrival(2D-DOA)and polarization of FH signals in underdetermined conditions. Both the time and the frequency features of FH signals are used to derive a data model for its polarization sensitive array based on the modeling method for manifold matrices of arrays; Then a SPTFD matrix for each hop is generated by the combined time-frequency distribution. The 2D-DOA and the polarization information are then de-coupled in the light of rank reduction theory, and the elevation angle is estimated via ESPRIT algorithm. Both the azimuth and the polarization are estimated through one-dimensional search and equation solution, respectively, and the joint estimation of both the 2D-DOA and the polarization of FH signals is completed. The proposed algorithm has good estimate precision without multi parameters optimization or pair-matching. Simulation results show that the proposed algorithm accurately estimates the 2D-DOA and the polarization of FH signals in underdetermined conditions and that the RMSE of all parameters for five FH signals is less than one degree when there are 4 sensors and the SNR is bigger than 6 dB.关键词：frequency hopping;polarization;time-frequency distribution;parameter estimation793|4|6更新时间：2025-07-09
- 摘要：A maximum likelihood time delay estimation algorithm using Monte Carlo method(MCML)is proposed to solve the problems that the maximum likelihood delay algorithm has high computational complexity due to peak searching and is easy to fall into local convergence. A likelihood function is constructed by using the channel response estimation vector in frequency domain. Then the MCML translates the time delay estimation into the expectation of a random variable, and a standardization probability density function is built from the index likelihood function to approximate an impulse function, and to make the variance of the random variable approach zero. Finally, the random variable is sampled using the Monte Carlo method, and the time delay is estimated from sampling mean. Compared with the traditional methods, the MCML avoids the grid search, reduces the computational complexity, and ensures the global convergence and estimation accuracy. Simulation results show that the MCML is always close to Cramer-Rao bound, and the time delay estimation range of the MCML is 34% of the MCMC's range when the signal to noise ratio is from 0 dB to 25 dB.关键词：maximum likelihood;Monte Carlo;time delay estimation;Cramer-Rao bound584|4|3更新时间：2025-07-09
- 摘要：A joint beamforming method of information and noise is proposed to reduce the power consumption of conventional zero-forcing beamforming method for full duplex secure communication systems. An information beamforming vector is designed for down-link communication of a full-duplex base-station(FD-BS)in a Gaussian channel model, and a noise beamforming vector is designed to jam the eavesdropper and to protect the information of both uplink and downlink for FD-BS. Then the joint beamforming problem, that is NP hard, is converted to a convex optimization problem which can be efficiently solved, and the optimal information beamforming vector and noise beamforming vector are derived from the optimal solutions. Simulation results show that when both the uplink and the downlink secret rates are set to 3 b/(s·Hz), the proposed algorithm effectively reduces the power consumption of FD-BS. A comparison with the conventional zero-forcing beamforming method show that the power saved by the proposed algorithm is 18%.关键词：physical layer security;full duplex communications;beamforming;convex optimization803|4|1更新时间：2025-07-09
- 摘要：To effectively evaluate the source number of mechanical systems from the measured mixed signals, and solve the calculating difficulty of BIC for large data points, three information criterion-based source number estimation methods, Akaike information criterion(AIC), minimum description length(MDL), and Bayesian information criterion(BIC), are comparatively studied and an improved BIC, named IBIC, is proposed following an exponential function modification, which transforms the multi-parameter exponential calculating to multiplications. Without decreasing the accuracy, IBIC obviously improves the calculating efficiency and engineering application performances. The numerical case study results show that AIC and MDL obtain the similar performances on source number estimation, and they are both very sensitive to the nonlinear modulation effects. In respect to signal energy ratios, the proposed method has a robustness tolerance on nonlinear modulation effects for 5.15%, which is higher than that of AIC(0.07%)and MDL(0.08%). The results of source number estimation for acoustical signals of a test bed with shell structures show that all the three methods are effective for the given acoustical signals. This work benefits model order selection, complexity analysis of a system, and applications of source separation to mechanical systems for the condition monitoring and fault diagnosis purposes.关键词：source number estimation;information criteria;Akaike information criterion;minimum description length;Bayesian information criterion585|4|5更新时间：2025-07-09
- 摘要：Harmonic force of linear motor acts directly on the drive element, which reduces the motion stability of the feed system. The servo drive circuit and the nonlinear of motor structure are considering. With the equivalent magnetizing current method and Maxwell equations, the analytic expression of ripple force, cogging force, end effect force, coupling force and inductance asymmetry force are obtained. In the computation process, the coupling effect between multiple harmonic factor is considered, which makes up for the former single factor analysis of harmonic force. The results show that the thrust in the linear motor contains multiple harmonic force, influenced by the servo drive circuit and the nonlinear of motor structure, and each harmonic component gets mutually coupled. These harmonic force acts directly on the mechanical system to lead to the displacement wave of feed system. The effect of the harmonic force rises with the increasing speed. Near the speed of 5, 20 and 33 m/min, the harmonic force results in system resonance to seriously weaken motion stability of the feed system. The amplitude of ripple force declines with the decreasing amplitude of the harmonic current. The ratio between pole pitch and tooth space pitch and ratio between tooth space opening and pitch exert an important influence on the harmonic frequency and amplitude of cogging force, especially, the cogging force disappears in the ratio of tooth space opening and pitch of 0.625.关键词：linear motor;harmonic force;motion stability;system resonance722|4|1更新时间：2025-07-09
- 摘要：A nonlinear bi-stable energy harvester from the human motion is proposed to solve the problem that the frequency bandwidth of traditional linear piezoelectric energy harvesters is narrow and it is hard to match with human motions. The harvester considers the characteristics of the human leg's motion and improves the energy harvesting efficiency by using the acceleration caused by leg swings and their impacts on the ground. An electromechanical model of nonlinear energy harvesters is derived based on the Hamilton principle and human motion signals. A portable nonlinear energy harvesting device is designed based on the characteristics of the human motion, and dynamic characteristics of linear, nonlinear mono-stable and bi-stable oscillators are realized by adjusting the position of magnets. Numerical simulations based on real human leg's vibration data show that the proposed harvester achieves the large amplitude inter-well oscillation and generates more energy from the human motion. Experimental results under various motion speeds verify the great advantage of the nonlinear bi-stable energy capture technology, and the efficiency of the proposed electromechanical model. The average output power of the bi-stable system reaches a maximum value of 23.2 μW when the motion speed is 8 km/h.关键词：energy harvesting;nonlinear;bi-stable;human motion;piezoelectric cantilever629|4|5更新时间：2025-07-09
- 摘要：To predict the temperature field of spindle-bearing system more accurately and monitor the temperature rise of key parts, a transient thermal network model with the coupling of the temperature field and deformation was established. The radial compound stress-deformation equation under the initial assembly stress, centrifugal stress and thermal stress was derived following thermo-elasticity theory. The key system components were picked out as the heat nodes according to thermal network optimization. Taking both temperature-viscosity effect and radial compound stress-deformation into account, several key thermal parameters, such as heat source and thermal boundary conditions, were modified in real time. The coupled temperature field and deformation of spindle-bearing system were analyzed. The transient temperature curves of bearings under different conditions and the transient properties of key thermal parameters were obtained numerically. The results shows that the higher of the spindle speed, the higher of the equilibrium temperature, and the shorter of the equilibrium time. The iterative step can only affect the equilibrium time but not the equilibrium temperature. A comparison with a set of experiments indicates that the transient thermal network model enables to reduce errors remarkably in predicting the temperature field of spindle-bearing system.关键词：spindle-bearing system;thermo-deformation coupling;transient thermal properties;thermal network method723|6|5更新时间：2025-07-09
- 摘要：A theoretical-experimental method is used to study the shape, forming mechanism of flow-rate characteristic curves and some existing problems of test methods specified in ISO6358. It is found out that the cut-off point of the flow-rate in characteristic curve is obviously different from the transitional point of airflow velocity in pneumatic components by studying the relationship between two different methods to calculate critical back-pressure ratios. Moreover, it is proposed that it is necessary to compensate the measured upstream and downstream pressures of components under test. The experimental results show that the difference between critical back-pressure ratios obtained from the two methods is about 0.15, and the fallen section of the flow-rate characteristic curve includes not only the state of subsonic but also a change process from supersonic to sonic. Furthermore, the subsonic index m≈0.5, that is, the fallen section of the curve is an approximate elliptic curve. It is also found out that a 15% error appears when the influence of pressure compensation is ignored.关键词：flow-rate characteristic curve;forming mechanism;critical back-pressure ratio611|4|1更新时间：2025-07-09
- 摘要：A resource license scheduling method using resource allocation is proposed to improve the poor performance caused by different computing capacities of nodes and mixed workload in cloud computing. The method improves the performance through reducing the resources wasting or overload. It collects resource information and estimates resource requirements of workloads and allocates computing resources dynamically according to available resources and resource requirements of workloads. Licenses uncoupled with resources are used to launch tasks and to adjust the number of parallel tasks to adapt the cloud environment by controlling the number of licenses. The method is evaluated in the national high performance computing center(Xi'an). Results show that the completion times of single job workloads of the proposed method are better than those of the FAIR scheduler in competitive environments. Moreover, the completion times of mixed workloads of the method in three environments reduce 27.5%, 37.1% and 50.98% respectively on average, that is, the performance of the method has a significant improvement. It can be concluded from the results that the proposed method adapts the complex environment and solve the performance problem in cloud computing.关键词：cloud computing;Hadoop;resource allocation;job scheduling;mixed workload726|4|0更新时间：2025-07-09
- 摘要：A new leg-paddle coupling crablike robot is developed based on the bionic prototype of portunus trituberculatus. The construction with three pairs of walking legs and one pair of swimming legs is adapted for the robot. By the composite propulsion of waking legs and flapping hydrofoil, the robot is endowed with the ability of walking and swimming under water to indicates the characteristics of morphological and functional bionics. Numerical simulations and water tunnel experiments are carried out to obtain the hydrodynamic performance of swimming legs. It is found that both the upstroke and downstroke phases generate propulsive load to lead to much higher propulsive efficiency when the hydrofoil is in the lift-based swimming mode. The average thrust and propulsive efficiency decreases apparently with the increasing flapping amplitude. The relationships between the propulsive efficiency and flapping frequency are like a parabola. The maximum propulsive efficiency of the lift-based swimming mode is achieved at Strouhal number of 0.4-0.6, and the propulsive efficiency reaches the maximum value at Strouhal number of 0.8-1.0 for the drag-based swimming mode. The wake structures of the two modes are characterized by reverse Karman vortex street. Furthermore, the effects of hydrofoil thickness of swimming leg on hydrodynamic performance are investigated, and the results show that the average thrust of much thinner hydrofoil is higher as well as less energy consumption, indicating that thinner hydrofoil is favorable for propulsion performance.关键词：crablike robot;swimming leg;hydrodynamic performance;swimming mode878|4|6更新时间：2025-07-09
- 摘要：An ensemble classification model for Trojan traffic detection is proposed to solve the problem that traditional ensemble learning methods overly depend on training samples, have low classification precision and poor generalization ability when they are applied to the detection of Trojan traffic. Traffic statistics features between Trojan communication and normal communication are distinguished and then extracted to build training sets. Equalization method is introduced to improve the principal component transform of rotation forest algorithm, and the updated rotation forest algorithm is used to rotate original training samples. Then, base classifiers are constructed by using three classification algorithms: Naive Bayes, C4.5 decision tree and Support Vector Machine. Integration is realized and the Trojan traffic detection rules are eventually established by using a weighted voting strategy based on the dynamic choice of instance. Experimental results show that the model makes full use of the diversity of different training sets and the complementarity of heterogeneous classifiers, and that a 96.30% detection rate is reached while the false positive rate is not higher than 4.21%, that is, both the accuracy and the generalization ability of Trojan traffic detection are improved.关键词：Trojan traffic;ensemble learning;rotation forest;heterogeneous classifier;weighted voting792|4|3更新时间：2025-07-09
- 摘要：An optimization method based on simulated annealing(SA)approach for the energy management of the compound-type hybrid power source(CHPS)is proposed to focus on the operating modes of CHPS and the optimization of power distributions in different operating modes. The operating modes of the CHPS are divided into different layers, and loss models of different components are established for the energy management system. Energy management strategies are designed for different layers. The SA approach is used to reduce the system loss on the basis of the energy management strategies in different layers. A simulation model and an experimental platform of the CHPS are constructed. Experimental results and comparisons with the hysteresis-logic threshold control strategy show that the total system loss of the CHPS using the proposed method reduces 0.8% and 1.1%, respectively, in the NYCC and EUDC drive cycles. It can be concluded that the proposed energy management system of the CHPS reduces the system loss and realizes the optimization of power distributions. Moreover, the CHPS can respond to the power demands, provide or absorb peak powers by ultracapacitor(UC), and ensures the safety of batteries.关键词：electric vehicle;hybrid power source;simulated annealing approach;energy management system633|4|7更新时间：2025-07-09
- 摘要：Noises of an electric vehicle(EV)at different speeds are sampled as the evaluation objects. An objective evaluation parameter, sensitive frequency-band energy ratio(SFBER), is established by combining with the human auditory system characteristics. The subjective evaluation test of sound quality annoyance is carried out by using the grading method. Several objective psychoacoustical parameters are calculated, and for each sample and a subjective evaluation model describing the correlation between subjective annoyance evaluations and psychoacoustical objective parameters is established through analyses of linear correlation and multi linear regression. The results show that the noise energy of traditional cars is concentrated in low frequency band and the maximum reaches 37% when the central frequency is the frequency band of 200 Hz, while the noise energy of electric vehicles is concentrated on the frequency band with its center frequency above 1 kHz and the peak value reaches 30%. The correlation between SFBER and annoyance is 0.958 and is better than the other psychoacoustical parameters. The EV sound quality annoyance is affected mainly by three psychoacoustical parameters, i.e. roughness, fluctuation and SFBER.关键词：electric vehicle;noise sound quality;subjective evaluation;psychoacoustics888|5|9更新时间：2025-07-09
- 摘要：A multi-objective optimization method for the composite leaf spring of a type of buses is described to optimize the performance of the composite leaf spring. A multi-objective optimization model is established in the genetic algorithm toolbox of Matlab software by using the weighting coefficient transformation method and the hybrid method in genetic algorithms. The variables of the model are parameters of the layer scheme and the stiffness, the strength ratio and the mass of the composite leaf spring are sub-goals of the model. A Matlab program is coded to calculate the performance of the composite leaf spring. The results show that the width of the composite leaf spring should be maximized and the thickness of the composite leaf spring parabolically increases from the end of the layer region with gradient length towards the bump structure. The prototypes of the optimal design scheme are manufactured and a bench test is performed. The test results show that the mass and the fatigue life of the composite leaf spring are 40% and three times of those of the steel leaf spring, respectively. Moreover, the stiffness and the strength of the composite leaf spring also meet the requirements of this type of buses.关键词：bus;leaf spring;composite material;genetic algorithm;multi-objective optimization933|4|10更新时间：2025-07-09
- 摘要：Aiming at alleviating conflicts at signalized intersection, a new approach to organize non-motor vehicles is proposed following the analysis of right-turn vehicles and straight non-motor vehicle behavior. Based on the traditional non-motor vehicle stop line preposed design, a stop line and a signal light behind the first stop line are added in this strategy, thus two stop areas for non-motor vehicles are formed. By staggering signal lights, non-motor vehicles in two areas pass through in turn, and in this way, right-turn vehicles pass through the conflict area at interval between two groups appearing. As an example, intersection of Quyang road and Dalianxi road is investigated. The strategy is verified to be rational by Vissim simulation. The result indicates that this strategy is suitable for the approaches having a large sum of right-turn vehicles and straight non-motor vehicles. When non-motor vehicle volume reaches above 500 per hour, this strategy enables to reduce traffic conflicts and heighten safety reliability and traffic efficiency in right-turn area.关键词：traffic safety;traffic organization;traffic conflicts;signalized intersection;non-motor vehicle;Vissim simulation865|5|0更新时间：2025-07-09
- 摘要：A heat source distribution model in grinding zone is established with probability statistical method to reveal the residual stress field induced by the coupling of grinding force and grinding heat following grain trajectory analysis and grain contact analysis. Heat partition analysis in grinding zone is performed in the modeling of heat source distribution. Heat source profile was always assumed to be rectangular or triangular in the previous studies, however rectangular or triangular heat source can not describe the heat source profile accurately. On the assumption of uniform heat partition ratio in grinding zone and without providing profile of total heat source in advance, the heat source distribution model enables to obtain the heat source profile in grinding zone. Finite element method is used to simulate grinding temperature field. An infrared thermal imager is used to measure grinding temperature field. A comparison indicates that the simulations coincide well with the measurements of grinding temperature field, and the errors of the maximum temperature in grinding zone range from 2.24% to 15.3%. The heat source distribution in grinding zone approaches the profile of quartic polynomial curve.关键词：heat source distribution;heat source profile;heat partition ratio;grinding temperature field773|4|6更新时间：2025-07-09
- 摘要：Effects of welding parameters on fracture behaviors of refill friction stir spot welding(RFSSW)welds are investigated. RFSSW is used to weld LY12 aluminum alloys with different thicknesses by changing the sleeve plunge depth. The fracture mechanisms of the welds are investigated from the aspects of material flow, atomic diffusion and softening, and are verified by the cross section, microstructure and hardness of the weld. Results show that the crack propagates along the interface of lap weld with lower joining strength and forms a shear fracture mode when the plunge depth is smaller than the thickness of upper plate, the hook defect is flat and thicknesses of bonding ligament in the weld are almost the same, and the crack is more easily to propagate along the withdrawing path with shorter atom diffusion time and results in the shear-plug fracture. When the sleeve penetrates into the lower plate thickness of 15%, the hook defect bends upwards and the crack defect appears at the sleeve withdrawing path. When the sleeve further plunges into the lower plate thickness of 35% and the hook defects present along a downward bending direction, the crack grows downwards along the withdrawing path of sleeve. When the crack reaches the bottom of lower plate, the plug fracture of RFSSW weld completed. These results show that the fracture morphologies are in agreement with analytical results of the fracture features.关键词：refill friction stir spot welding;fracture behavior;aluminum alloy;plunge depth818|6|3更新时间：2025-07-09
- 摘要：A fractional impedance model based on the electrochemical impedance spectroscopy of lithium batteries is proposed to focus on the charge state estimation problem of the EV power lithium-ion batteries. A relatively simple equivalent circuit is derived from EIS analysis under different frequency and the introduction of fractional order modeling, and a fractional Kalman filter is designed according to the fractional impedance model. Parameters of the model are identified from the HPPC test data. The software SIMULINK is used to simulate the working voltage and charge state of the lithium battery and the simulation results are compared with test results. Comparison results show that the proposed model accurately predicts the working voltage, and its error range is within 0.05 V, and the charge state estimation has an error range of 2%. Results show that the fractional impedance model can accurately predict charge state of lithium batteries, and provides effective state estimations for EV power battery management system.关键词：lithium battery state of charge;fractional impedance model;fractional Kalman filter812|4|5更新时间：2025-07-09
- 摘要：The current 10 kV distribution transformers in rural area can hardly satisfy the gradually increasing power demand due to the aging-failure. Facing this challenge, a novel decision approach for the replacement of aged transformers is developed with life cycle cost theory and risk assessment. The proposed approach considers the impacts of operating time, supply reliability and heavy load to transformer economic life, which remedies the limitation of the conventional approach. Furthermore, the methodology based on risk assessment is also utilized in the final investment strategy. A replacement order for nine aged transformers of a rural distribution network in southern Shaanxi is arranged. The numerical results indicate that the proposed approach enables to make a more reasonable investment decision and to reflect the adverse impacts of poor reliability and heavy load on the economic life of transformers. This approach improves the cost-effectiveness of transformer replacement by reducing 2.93% of the total cost.关键词：life cycle cost;distribution network;transformer replacement;investing risk assessment;power supply reliability797|5|4更新时间：2025-07-09
- 摘要：Focusing on the low efficiency, lager cell damage and low forming accuracy of circular channel in soft tissue scaffolds construction by 3D printing technology, a novel method is presented to fabricate scaffolds by combining imprinting with 3D printing techniques. The imprinting technique is combined with light crosslinking method to make single-layer soft tissue scaffold with flow channel structure. Then, gelatin, a kind of temperature-sensitive material, is injected along the flow channel by printing technique to cure in the low temperature environment to support the upper layers. A stereoscopic structure is formed via the layer-by-layer accumulation. The gelatin is finally melted in the flow channel by temperature control to form pipelines. An automatic fabrication device is developed to realize the strategy. The results demonstrate that the light uniformity reaches the maximum when the scanning interval reaches 51 mm, and that the arc-type flow channel structure is clearly visible and interlinked. The approach is beneficial to accurate manufacture of soft tissue scaffolds, and it can be expected to improve cell survival rate and forming efficiency in cell printing.关键词：channel structure;imprinting/printing;layer-by-layer fabrication;soft tissue engineering607|4|0更新时间：2025-07-09
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