最新刊期
卷 47 ， 期 1 ， 2013
- 摘要：Since traditional solutions like frequency hopping spread spectrum technique not only are technically difficult to implement but also make the frequency resources shortage even more critical, researches on signal's energy distribution over space are conducted to achieve secure wireless communications. The results indicate that space spectrum varies from location to location in multi-antenna transceiver wireless communications systems, which implies that plentiful space spectrum resources rather than frequency spectrum resources can be taken into account in secure wireless communications. Based on this point of view, a distributed multi-antenna space hopping transceiver technique—0/1 space hopping technique is proposed. In correspondence to the space hopping pattern at the transmitter, weights are obtained at the receiver via training, so that a regular constellation can be obtained at the receiver without either to know a prior the array manifold or to solve the sophisticated multichannel. Some simulation results are presented and analyzed to evaluate the performance of the proposed technique.关键词：wireless communications;space spectrum;space hopping technique;multi-antenna;frequency hopping spread spectrum;security2518|4|15更新时间：2025-07-09
- 摘要：Dust devil is a short-life and small-scale surface-heated whirlwind system in nature. Sustainable dust devil-like whirlwind possesses potential of wind power generation. Analogous to the induced conditions of dust devil, a new wind energy concept of swirling buoyant jet driven by low-temperature solar energy was proposed by using artifical solar-concentrating shed and air inflow prerotation technologies. This kind of swirling buoyant jet is an interdisciplinary concept, relating to atmospheric physics, fluid mechanics and thermophysics. The theory of stable swirling buoyant jet and the key technologies of the heating design of solar-concentrating shed and the air inflow prerotation part were initially put forward for the development of such a new wind system of low-temperature solar-powered whirlwind.关键词：swirling buoyant jet;wind energy;low-temperature solar energy2014|4|1更新时间：2025-07-09
- 摘要：To accurately calibrate the lens distortion in linear array cameras, a simplified distortion model for the actual application is proposed, and a new corresponding calibration method is suggested to guarantee the stability of calibration results. The imaging characteristic of equidistant collinear feature points is used to calculate the distortion and nonlinear optimization is used to calibrate the distortion parameters. The experiments show that the calibration results of the simplified model are consistent with ones of the normal model. In the calibrated image, the distribution of feature points gets uniform, the maximum distortion is not more than 0.5 pixels and the correction accuracy is not lower than 9 μm. Compared with the traditional calibrations, the newly introduced method has better robustness.关键词：lens distortion;linear array camera;nonlinear optimization1880|4|12更新时间：2025-07-09
- 摘要：A numerical investigation on full-three-dimensional steady viscous flow fields in the last three stages and low pressure exhaust hood(LPEH)of a steam turbine was conducted using the commercial computational flow dynamics software CFX. The flow fields in the last three stages were analyzed in detail. The results show that a separation caused by the adverse pressure gradient occurs at the hub section near the trailing edge of the last stage rotor at 40% of the design mass flow rate. Moreover, a separation caused by the negative attack angle occurs at the tip section near the leading edge of the last stage rotor at 30% of the design mass flow rate. A separation also caused by the negative attack angle occurs near the leading edge of the last stage stator at 10% of the design mass flow rate. In addition, the absolute outlet flow angle of the last stage rotor at the tip section increases with the decrease in volume flow rate, and the radial location of the reverse flow can be determined by the turning point of the absolute outlet flow angle in the blade radial direction.关键词：steam turbine;last three stages;volume flow rate;numerical research;flow characteristics2057|5|3更新时间：2025-07-09
- 摘要：The computational fluid dynamics software CFX was applied and the thermodynamic phase change characteristics of the cylinder head cooling water were considered. The calculation model of sub-cooled boiling heat transfer for gas-liquid two-phase flow was used for the fluid-solid coupling heat transfer system which is composed by the diesel engine cylinder head and the cooling water jacket with the method of discretizing and solving for the entire domain. The cylinder head temperature field distribution was obtained under the different influence factor conditions and validated by the experimental data. The results show that, compared with the single-phase flow without considering the boiling heat transfer, the sub-cooled boiling heat transfer of gas-liquid two-phase flow can effectively reduce the highest temperature of the cylinder head flame-face, and increase the inlet speed of cooling water and lower the inlet temperature. In addition, the cooling system pressure drops appropriately which further reduces the cylinder head flame-face temperature, thus lowering the heat load of the cylinder head flame-face.关键词：cylinder head;cooling water jacket;gas-liquid two-phase flow;sub-cooled boiling heat transfer;simulation research2129|4|6更新时间：2025-07-09
- 摘要：The two-phase flow coefficient of a V-cone meter was proposed to correct the “over-reading” produced by measuring the wet gas using the V-cone meter. The experiment was conducted with the V-cone meter with a diameter ratio of 0.75 for air and water. The test pressure ranged from 0.10 MPa to 0.22 MPa, and the gas and liquid mass flow rates were from 100 m3·h-1 to 300 m3·h-1 and from 0 to 0.08 m3·h-1, respectively. The effects of the Lockhart-Martinelli parameter, the operating pressure and the gas densiometric Froude number on the two-phase flow coefficient were investigated. The results show that the two-phase flow coefficient increased linearly with the Lockhart-Martinelli parameter, and the slope of the two-phase flow coefficient vs. the Lockhart-Martinelli parameter was affected by the gas densiometric Froude number and the pressure. The correlation between the two-phase flow coefficient and the Lockhart-Martinelli parameter, the gas densiometric Froude number and the pressure was obtained. On the basis of the two-phase flow coefficient, the wet gas model was developed. The relative error of the gas mass flow rate predicted by the model is within ±5.0% at the 95% confidence level.关键词：wet gas;V-cone;two-phase flow coefficient;flow measurement2153|4|4更新时间：2025-07-09
- 摘要：The aerodynamic optimization design method was extended to turbulent flow environment, and a discrete adjoint solver applicable to the turbulent flow environment was implemented. On the basis of the solver, an aerodynamic optimization design platform was established by coupling the parameterization technology, grid generation technology, an in-house flow solver, the discrete adjoint solver and optimization technology. A typical transonic two-dimensional cascade was optimized based on the platform with the entropy generation being taken as the optimization function. Moreover, a mass flow ratio constraint was added to the objective function by using the penalty function method to keep the mass flow ratio constant. The optimization results show that the entropy generation of the optimized cascade decreases by 17.7% compared with that of the baseline cascade, demonstrating the correctness and effectiveness of the discrete adjoint solver developed.关键词：discrete adjoint theory;turbulent flow;turbine cascade;aerodynamic optimization2260|4|4更新时间：2025-07-09
- 摘要：Boil-off gas(BOG)compressors operate at low suction temperature and suffer from great temperature change when the working condition changes. In this study, the FEM simulation of heat transfer in a BOG compressor was performed, and the static and periodic transient temperature fields and their changes were obtained during the compressor starting both under ambient condition and precooling conditions. The results show that, when the BOG compressor operates steadily, the average temperatures in the suction chamber and the discharge chamber of the cylinder are -97 ℃ and -21 ℃, respectively, and the amplitude of temperature fluctuation is less than 0.1 ℃ in the periodic transient temperature field. In addition, the maximum temperature difference in the cylinder is 53.5 ℃ when the compressor starts at -30 ℃ while it is 87.1 ℃ when the compressor starts under the ambient condition(at 30 ℃).关键词：boil-off gas compressor;cylinder;temperature field;finite analysis2095|4|2更新时间：2025-07-09
- 摘要：This article puts forward a collaborative method based on flow-passage-force to deal the conflicts and coupling problems between high-energy and low-vibration design of high-parameter rotor system, and verifies the method based on typical engineering units. The collaborative design model was established through the research of flow-passage-force concept and its characterization methods. New model which has advantage of strong pertinence and high reliability reduces the number of variables and the complexity and randomness of design compared with the traditional model. Taking the 1 000 MW unit as typical case and taking rotor characteristic diameter and characteristic rotational speed as core collaborative variables, collaborative design method improves the efficiency of high-pressure cylinder and the critical speed meets requirements. Collaborative design solves the main design contradictions of high-pressure rotor effectively which proves that collaborative design based on flow-passage-force can solve co-design problems of actual units effectively.关键词：high-parameter rotor;flow-passage force;collaborative design2218|4|1更新时间：2025-07-09
- 摘要：Focusing on the nonlinearly changed dynamic stiffness of bearings with working speed, a numerical approach is presented to calculate the dynamic stiffness of a single bearing and a bearing group based on the ball bearing quasi-static model, the dynamic equation is established according to the finite element model of the rotor-ball bearing system,the eigenvalues then are obtained by numerical iteration and the critical speed is sought out. Due to the influence of speed on dynamic stiffness of bearings, the finite element model ought to be updated according to the calculated dynamic stiffness by last iteration. Combining the optimization toolbox of Matlab,the inner diameter of rotor and the bearing span are optimized by simplex method. The analysis results show that the stiffness of spindle bearings is obviously influenced by the working speed and inner ring centrifugation, which should be taken into consideration during the dynamic analysis of a high-speed rotor-ball bearing system, and the first critical speed of the rotor-ball bearing system increases by 7.65% after optimization.关键词：high-speed rotor-ball bearing system;angular contact ball bearing;dynamic stiffness;critical speed2305|5|1更新时间：2025-07-09
- 摘要：To investigate the structures of high speed train side walls applicable to different running speeds and operation conditions, a multi-objective optimization design is carried out following structure topology optimization. The weight of sandwich plate, static compliance and maximum deformation are defined as the objectives, the thickness of face panels and cores in five parts of the side wall as the variables while the changing air pressure gradient in compartments as the constraint. The surrogate model techniques are implemented for constructing the response surfaces of objective and constraint functions. Then a multi-objective optimization is performed with NSGA-II to generate a Pareto solution set. The structure performance in Pareto set is greatly improved by 8.21% to 33.58% than that from topology structure, besides, the Pareto solution set provides many alternative Pareto-optimal solutions for optimization design of the sandwich plate section in high-speed trains.关键词：sandwich plate;surrogate model;NSGA-Ⅱ algorithm;multi-objective optimization;Pareto optimal solution set2205|4|6更新时间：2025-07-09
- 摘要：The traditional anti-windup compensator is difficult to adapt to a strongly nonlinear systems by fixed feedback coefficients, a new anti-windup compensator from fuzzy idea is thus proposed. Conditional integral and anti-reset windup are utilized, whose feedback coefficient is fuzzily adjusted. Hardware description language is adopted to realize the algorithm, and the multiplication and division operations are optimized and implemented into the field programmable gate array to finally achieve hardware implementation for the compensator. The experiments indicate that the new compensator enables to improve the accuracy and reduce the occupancy resources significantly in the direct drive rotary valve control, the maximum overshoot of the spool step response gets less than 3%, and the needed equivalent gates decrease by 41% compared with that in usual cases.关键词：anti-windup;fuzzy idea;field programmable gate array;rotary valve1958|4|0更新时间：2025-07-09
- 摘要：To rapidly and accurately detect the geometric precision of large horizontal lathe, a multi-pointed and time-sharing measurement with laser tracker is proposed. A virtual axis is set between principal axis and tailstock, then precision of the guide rail and other parts is adjusted up to the virtual axis standard. Two axis lines are obtained by cylindrical fitting, then adjusted to coaxial to establish the new standard. In the simulation and experiments, only one laser tracker is necessary to detect the geometric precision of large horizontal lathe in four hours, and an auxiliary measuring service of axis line is designed to solve light barrier.关键词：laser tracker;virtual axis;cylindrical fitting;auxiliary measuring1949|4|1更新时间：2025-07-09
- 摘要：To improve the convenience of the relaxation based particle tracking velocimetry(RM-PTV)in obtaining the instantaneous flow structure, a centroid Delaunay triangulation(DT)based technique was proposed to determine candidate particles for the target particles in the matching process, and typical self-defined particle images and standard particle images were analyzed to test the validity of the new method. The results show that the centroid DT method can select the candidate particles effectively and conveniently. Moreover, consideration is given to balance accuracy and efficiency, and the previous estimation of the flow field can be avoided, which makes the application of RM-PTV more independent, especially for the complicated flow situation and inexperienced users.关键词：relaxation based particle tracking velocimetry;candidate particles;settled threshold;Delaunay triangulation1909|4|1更新时间：2025-07-09
- 摘要：A novel modal identification for dynamic system following locally linear embedding is proposed. Regarding manifold learning as the theory foundation, and starting from the structural geometry or inherent characteristics extraction, the modal parameters of the system structure can be identified only by analyzing the response data. The principal idea is to consider the response data as a high-dimensional data set and the modals of the structure as the essential structure and the inherent characteristics of the high-dimensional data set. Then the modal parameter identification problem is transformed into a low dimensional embedding problem of the data set. The numerical simulation results of a cylindrical shell show that this locally linear embedding based method is effective in modal identification, and with the increase of the damping coefficient, it gets superior to the principal component analysis based method in identification of the modals with larger contribution.关键词：modal identification;locally linear embedding;manifold learning2101|4|11更新时间：2025-07-09
- 摘要：The FTO glass coated with ZnO seed layer was prepared by spin-coating, and it was further placed in growth solution to form messy and neat ZnO nanowires(NWs)via hydrothermal growth. By repeating the procedure, branched ZnO NWs were obtained. X-ray diffraction, UV-visible spectrophotometer, and photoelectric conversion test system were employed to analyzed the influences of growth conditions on the morphology and crystal structure of ZnO NWs, and on dye adsorption ratio and conversion efficiency. The results show that the addition of polyethylenimine to the growth solution facilitates the growth of ZnO seed along the optimal crystal face. ZnO NWs are of hexagonal wurtzite structure with good crystallinity. The key factors affecting the formation of branched ZnO NWs are the number of hanging seeds and the heating rate of crystallization heat treatment. Compared with bare ZnO NWs, branched ZnO NWs show higher dye adsorption ratio and conversion efficiency.关键词：ZnO nanowire;hydrothermal growth;dye adsorption ratio;conversion efficiency2226|4|5更新时间：2025-07-09
- 摘要：Particle image velocimetry(PIV)was employed to measure the flow field quantitatively at the transitional Reynolds number to investigate the large scale structure in channel flow at transitional state. The intermittent instantaneous velocity field was captured, and the large-scale structure in stripe shape was extracted from the flow field reconstructed on the basis of the Taylor's hypothesis. The results show that there is an angle of about 25°-30° between the borderline of the high velocity stripe and the low velocity stripe and the flow direction. The absolute values of the skewness factor and the flatness factor decrease with the decrease in Reynolds number, indicating that the turbulent events become fewer and the flow state tends to be laminar. In addition, the flow state changes dramatically at Reynolds number from 1 300 to 1 600 according to the flow field and the high-order statistics.关键词：transitional flow;particle image velocimetry;intermittency;large-scale structure1863|5|0更新时间：2025-07-09
- 摘要：An evaluation function of overlapping community is proposed to solve overlapping community detection of complex networks. A chaos quantum discrete particle swarm algorithm is presented to detect overlapping community structure based on the proposed function. The quantum coding and the logistic mapping are used to generate an initial particle population, and the particle swarm speed changing method is used to update the size of the corner. It is shown that the algorithm converges with probability 1. Experimental results show that the algorithm has higher detection accuracy and can better reflect the real situation of the community divided.关键词：complex networks;community detection;overlapping community;discrete particle swarm algorithm2118|4|4更新时间：2025-07-09
- 摘要：To automatically grind and polish welded seam, a binocular stereo is constructed by connecting double CCD and laser with grinding and polishing robot. On the dependency between the robot and structured light on welded seam, a dynamic region of interest(ROI)is composed, and an algorithm for quick-extracting typical line is proposed as well. This proposed algorithm enables to narrow the image processing region to 1.49% of the original one, to significantly improve the efficiency. Analyzing the image within dynamic ROI, the preprocessing is optimized according to the characteristic of quick-extracting image, and the threshold computing during binarization also improved by histogram smoothed by a dynamic Gaussian mask. Then the typical lines of structured light band are extracted and experimentally investigated. It indicates that the visual system is endowed with good reliability and stability, and the algorithm is able to quickly locate dynamic ROI and precisely extract laser featured line.关键词：image processing;structured light;welded seam grinding and polishing2029|4|7更新时间：2025-07-09
- 摘要：An unsupervised topic and sentiment unification model, UTSU model for short, is proposed based on the LDA-Col model. Unlike the ASUM model and the JST model that sample sentiments and topics from the same plate, the UTSU model imposes the constraint that all words in a sentence are generated from one sentiment and each word in the sentence is generated from one topic. The constraint accords with the sentiment expression of language and will not limit the topic relation of words. The experiments of sentiment classification show that the result of the UTSU model is close to the results of supervised classification methods and outperforms other topic and sentiment unification models. Comparisons with the ASUM and JST models show that the UTSU model improves the F1 value of sentiment classification by about 3% and 17%, respectively.关键词：text sentiment classification;unsupervised learning;unification model2146|4|1更新时间：2025-07-09
- 摘要：The orthogonal experiment design was performed to investigate the effects of the jet velocity, the jet angle, the jet slot width, the commutated plate area and the range hood flow rate on the performance of the range hood and the kitchen environment for the range hood with a jet air curtain and a commutated plate. The optimum design parameters of the air curtain were obtained. The results show that, coupled with the commutated plate, the air curtain with the optimum parameters can effectively control the movement of the high temperature air with oil fume in the kitchen. The range hood flow rate has a significant influence on the temperature distribution and the oil fumes concentration. For the range hood studied, the optimum value of the flow rate, the commutated plate area, the jet velocity, the jet angle, and the jet slot width are 10.5 m3/min, 0.22 m2,1.5 m/s,-5°, and 4 mm, respectively.关键词：jet air curtain;range hood;kitchen environment;design of experiment;parametric study2041|4|1更新时间：2025-07-09
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