最新刊期
卷 56 ， 期 6 ， 2022
- 摘要：To quickly calculate the inductance of the central converging region and reveal the laws of the power and energy transmission efficiency of the high current Z-pinch driver, an analytical method is established to calculate the central inductance by an approximation of the structure of the central converging region, providing the approximate calculation formulas of inductance of insulator stacks, vacuum flare, vacuum magnetically insulated transmission lines and post-hole convolute. The quantitative relation between the central inductance and the electric(peak voltage of insulator stack)and structural parameters(radius and number of levels of the central confluence region, vacuum magnetically insulated transmission lines)was discussed. The simplified circuit of the typical Z-pinch driver was modeled on this basis, and the self-consistent circuit model of the structural parameters → electric parameters → load current was set up. Finally, the influence of the level and radius of the stack on the short-circuit load current of the driver is obtained. The results show that the maximum error between the inductance obtained by the method proposed and values given in the literature of the international typical Z-pinch drivers is 3.3%. The central inductance decreases with the increase of the number of levels of the central region, decreases first with the radius and then increases, and there is an optimization radius that minimizes the central inductance. This method proposed can provide a theoretical reference for the design of the same type of Z-pinch drivers.关键词：Z-pinch;central converging region;inductance calculation;insulator stack;magnetically-insulated-transmission-line428|5|0更新时间：2025-04-27
- 摘要：To meet the requirements of the safety and reliability for de-carbonization of gas turbine power systems, the performance changes and hydrogen admixture limits of the dry low emission(DLE)lean premixed(LP)combustor fueled with natural gas when switching to hydrogen fuel was numerically studied. The F-class heavy-duty gas turbine combustor for power generation was selected as the study object. Details of the actual combustor geometry were included in the simulations. The effects of different hydrogen admixture ratios of natural gas(6 working conditions of volume content for 0-100% H2)on the combustion and emission performance of the gas turbine combustor are numerically studied. Potential problems in the combustion chamber during fuel switching are analyzed. The results have shown that there is a huge risk of flashback when significant amounts of hydrogen are added to fuel mixtures in the LP combustor fueled with natural gas. When the hydrogen content reaches 40%, the high temperature area of the burner nozzle caused by the flashback is obvious. With a higher hydrogen content, the head parts of the combustion chamber is at risk of being burned down and the high temperature flame may propagates upstream along the pipeline, which brings huge safety problems to the system. There is no risk of flashback in the diffusion flame hold in the center pilot burners. The content of CO and CO2 in the product decrease and the content of H2O increase with the increase of the hydrogen mixing ratio. NOx levels in the combustor outlet show an increasing trend with the increase of the hydrogen content, but the rate of increase is not significant.关键词：hydrogen gas turbine;combustion performance;combustor;fuel flexibility212|6|0更新时间：2025-04-27
- 摘要：For the practical application of the underwater robot cluster communication platform, there are the problems of the Doppler effect and bit errors generated due to susceptibility to water quality and obstacles. In this paper, an underwater bionic electric field communication system based on the perception mechanism of weak electric fish is proposed. According to the principle of bionic current field communication, the communication system transmits signals through two pairs of transmitting and receiving electrodes. A set of digital-analog hybrid circuit using field programmable gate arrays(FPGA)based on the principle of amplitude shift keying is designed. At first, to achieve a miniaturized system with low power consumption, the analog circuit is reasonably selected by the component model. Circuits are placed, routed and patterned. The specific transmitting circuit includes an amplitude shift keying modulation circuit and a half-bridge drive amplifier circuit. The potential difference between the two ends of the receiving electrode is extracted by using a low-zero-drift high-precision instrumentation amplifier. Secondly, in order to improve the stability of the communication system when the communication distance of the underwater robot cluster changes in real time, the programmable amplifier is controlled by gain control digital circuit in the FPGA to realize the adaptive multiple amplification. Then this system uses analog-to-digital conversion digital drive circuit in FPGA to drive the analog-to-digital conversion chip to convert analog signals into digital signals. Finally, after the signal is rectified by the rectification filter digital circuit, the amplitude shift keying non-coherent demodulation digital circuit is designed to output the binary demodulation data. The signal is transmitted to the Raspberry Pi through the serial port circuit for processing. The influence of obstacles of different sizes and different shapes on underwater electric field communication is simulated and analyzed, and the underwater communication experiment is carried out. The results show that the underwater electric field communication system can transmit information with a bit error rate of 0 when the communication distance is 2.4 m under the condition of conductivity of 4.87×10-4 S/cm in fresh water. When the transmitting and receiving electrodes of underwater electric field communication are parallel, the communication performance is the best.关键词：underwater robot;underwater communication;digital communication system;FPGA144|7|0更新时间：2025-04-27
- 摘要：The fuel capsule of cryogenic ICF target is generally filled through a micro tube. In order to generate the required smooth and uniform low-temperature layers, the capsule needs to be cooled and heated repeatedly with a residue of fuel ice in the gas filling tube until the crystal seed is formed and grows to a single-crystal layer. Based on Boussinesq assumption and the discrete coordinate radiation model, a three-dimensional simulation model is established to investigate the influence of the gas filling tube residual ice on the temperature control of fuel capsule, in detail, the influence of the length of the gas filling tube residual ice on the capsule temperature uniformity and stability in the standard steady-state, shimming heating and rapid cooling processes. Results show that in the standard steady-state process, the maximum temperature difference on the capsule surface lowers and then rises with the increase of the gas filling tube residual ice length, and when the ice end is flush to the outer surface of the capsule(optimal ice length of 0.09 mm), the maximum temperature difference reaches the lowest level, lowered by 31.5% compared with the none ice residue condition. During the transient process of shimming heating, the maximum temperature difference on the capsule surface rises and then lowers with time, finally staying stable, and the capsule temperature uniformity is less deteriorated when the ice length in the gas filling tube is shorter than or equal to 0.09 mm. Moreover, the capsule with an ice length of 0.09 mm maintains the best temperature stability(during cooling)and uniformity(at the end of cooling)when it is linearly cooled at a rate of 6 K/min, thus ensuring relatively good temperature control performance.关键词：gas filling tube;residual fuel ice;cryogenic target;temperature control;uniformity59|7|0更新时间：2025-04-27
- 摘要：In terms of problems of unstable transmission and inaccurate rotational position for a drive shaft when an on-load tap-changer realizes switching operations, a closed-loop feedback disturbance rejection control strategy is proposed with the rotational position for the drive shaft of the on-load tap-changer taken as the controlled variable. Firstly, according to rotational position requirements of the drive shaft for the on-load tap-changer under actions of an electric mechanism, an error dynamic control system is established for the desired position of the drive shaft. Secondly, two tracking differentiators are designed to calculate smooth tracking signals of drive shaft position signals, and then transition processes of the drive shaft position trajectory can be controlled by adjusting parameters in tracking differentiators Then, two extended state observers are designed to estimate state values in the error dynamic control system and the total disturbance caused by load change, switching direction change and other factors for the on-load tap-changer during operation. Finally, a nonlinear feedback controller is designed by using the position error signal of the drive shaft and state estimation values of the error dynamic control system, and the total disturbance value estimated by the extended state observer is compensated in the nonlinear feedback controller to achieve effects of disturbance rejection control. The Matlab simulation software is used to verify the proposed control strategy. Simulation results show that the proposed control strategy can realize the desired position control of the drive shaft for the on-load tap-changer. Compared with the traditional PID control strategy, the proposed disturbance rejection control strategy reduces the position error of the drive shaft for the on-load tap-changer under closed-loop feedback control by 85%.关键词：on-load tap-changer;error dynamic control system;active disturbance rejection control;extended state observer;closed loop feedback control47|5|0更新时间：2025-04-27
- 摘要：An adaptive speed compensation control method with coefficient self-tuning is proposed to improve the anti-torque disturbance performance of the permanent magnet synchronous motor(PMSM)speed servo system. Firstly, a reduced order state observer of PMSM is designed using the state space representation method to realize real time identification and estimation of load torque. Then, the torque identification value is compensated to the output of the PMSM speed controller as the compensation input of the current controller, which realizes the adaptive speed compensation and improves the torque disturbance resistance. In terms of the problem that the torque identification is affected by the change of rotational inertia, the influence law of the time-varying characteristics of inertia on the torque observation results is analyzed, and a self-tuning control method of compensation coefficient based on the sigmoid function is proposed. According to the electromagnetic torque and torque identification value, the self-tuning sigmoid function is used to adjust the compensation coefficient online and in real time, so the parameter self-tuning of adaptive speed compensation is realized. Experimental results show that speed recovery time of the proposed coefficient self-tuning control method is faster. Compared with the conventional fixed coefficient control method, the speed adjustment time is reduced from 120 ms to 100 ms. This method can reduce the impulse and oscillation caused by speed compensation when torque identification overshoot or deviation occurs due to the deviation of inertia from its true value, and improve the speed control performance of PMSM servo system effectively.关键词：permanent magnet synchronous motor;torque identification;speed compensation;coefficient self-tuning101|6|0更新时间：2025-04-27
- 摘要：Aiming at the problems of difficult quantitative supply of the lubricant in artificial joint, resulting in serious wear of prosthesis surface a method for supplying and preserving joint lubricant by using hydrogel to simulate the structure of articular capsule is proposed, experimental exploration and theoretical verification are carried out. Firstly, the hyaluronic acid agar hydrogel is prepared, and the unconfined compression creep release test is carried out in the saline immersion environment. The relationship curves between creep volume, medium release and pressure are obtained, and the conversion formula between creep volume and medium release is obtained. Then, based on the structure and properties of hydrogels, a constitutive model of coupled diffusion and large deformation theory is established, under the given pressure condition, the creep curve of hydrogel can be obtained through the model. Finally, the release rate of gel medium can be deduced from the transformation formula obtained from the experiment. A finite element inverse method technology combining the test results with the finite element modeling and optimization method is used to obtain the material parameters of the experimental sample, which are used to simulate the creep behavior under different pressures, the results show that the creep release volume of hyaluronic acid agar hydrogel under constant pressure is proportional to the creep volume. Under the given pressure and action time, the coupled diffusion and large deformation theoretical models can quantitatively predict the release quantity of hyaluronic acid agar hydrogel within the permissible range of error. The research results can provide references for future hydrogel as artificial joint capsule for quantitative lubrication of artificial joints.关键词：artificial joint;lubricant fluid;creep release of hydrogel;finite element method42|8|0更新时间：2025-04-27
- 摘要：To reveal the coupling mechanism of metal impurities eroding the epoxy mica insulation layer of the stator bar in the whole working condition of large generators, the dielectric loss of metal impurity particles and stator insulation layer under high strain was subject to electromagnetic-mechanical-temperature multi-field finite element simulation and experimental analysis. Firstly, the electromagnetic-mechanical parametric model of bar and core slot containing spherical metal impurities is constructed under the swirl field of vector magnetic potential, and the characteristic element type and air domain odd symmetry boundary conditions are assigned. Then, the force density value and nonlinear transient force application behavior of the model are analyzed by the interactive sequence coupling method such as the matrix method. By studying the phase transition and microscopic loss increment of the epoxy insulating layer at the end of the stator bar, the characteristic value range of stress and deformation of the metal impurity grinding insulating layer are obtained. Furthermore, an electromagnetic-temperature model containing spherical metal impurities is established and the thermal erosion calculation is carried out by using the unidirectional magneto-thermal coupling method. Based on this model, the temperature field range of the impurity contact surface is rigorously analyzed. Finally, the metal grinding experiment under the alternating magnetic field is conducted on the insulating layer of the bar section for simulated force application verification and the samples were observed by the scanning electron microscope in detail. The experimental and simulation results show that the abnormal temperature rise caused by joule loss of metal impurities is not enough to cause short-term thermal erosion of the epoxy insulation layer, and the mechanical process of sheet mica's defect being aggravated due to the breakage of the epoxy molecular chain ground and eroded by impurities is the main cause of insulation deterioration of the stator bar. The conclusion provides a reference for the state monitoring and fault diagnosis of the main insulation of generator stator bars.关键词：large generator;stator bar;insulation deterioration;finite element analysis;scanning electron microscope44|6|0更新时间：2025-04-27
- 摘要：In terms of the problems of the standard test block method, such as the high cost of making the standard test block, the complicated measurement process, and the inability to adapt to the change of the refractive index of the thermal barrier coating after service, a thermal barrier coating thickness measurement method based on terahertz time-domain spectroscopy is proposed. Firstly, according to the propagation characteristics of terahertz waves in thermal barrier coatings, a terahertz wave propagation model of thermal barrier coatings is established, and the relationship between the number of echoes and the phase of echoes of terahertz detection signals can be obtained through the model. Then, a refractive index calculation model is established according to Fresnel's law and the interaction between the first three echoes of the terahertz detection signal. Finally, according to the obtained refractive index and the time interval between two adjacent echoes, the time-of-flight method is used to calculate the thickness of the thermal barrier coating. The feasibility and accuracy of the proposed method to measure the thickness of thermal barrier coatings are investigated by several groups of experiments. The results show that compared with the standard test block method, the proposed method does not need the making of a standard test block, and the refractive index and thickness of the thermal barrier coating can be calculated at the same time based on the terahertz detection signal, thus realizing the efficient and high-precision thickness measurement of the thermal barrier coating. The relative error of the proposed method can reach 1.15%, which is 42.5% lower than that of the standard test block method.关键词：thickness measurement of thermal barrier coating;no standard test block;terahertz time-domain spectroscopy;time of flight method72|5|0更新时间：2025-04-27
- 摘要：Most of the existing multi-view point set registration methods based on point-to-point measurement cannot obtain the accurate overlap of the individual points due to the discretization of object surface, resulting in the problems of slow convergence and low registration accuracy. To solve this problem, this paper proposed a multi-view point set registration method based on point-to-plane measurement. To achieve the multi-view registration, the proposed method uses the stepwise refinement strategy to break down the multi-view registration problem into several point-to-plane pair-wise registration problems. In the pair-wise registration process, first of all, a new objective function is given which uses the point-to-plane error to replace the point-to-point distance error; Secondly, an effective normal vector transformation strategy is proposed to reduce the times of solving the plane normal vector in each iteration of the multi-view point set registration. Then, in the process of solving the objective function, the linear least square method is used to approximate the nonlinear optimization problem, so as to minimize the point-to-plane error. Finally, the proposed method is tested on Stanford data sets, and the experimental results show that: compared with four other multi-view registration methods, the proposed method reduces the rotation error by more than 38.9% in terms of different data sets, and the translation error by more than 16.6%, thus effectively achieving accurate and reliable multi-view point sets registration.关键词：multi-view registration;point-to-plane;linear least squares;normal vector63|5|0更新时间：2025-04-27
- 摘要：To ensure the stable operation of T/R components of high-power phased-array antennas for a long time, this paper proposes a thermal management strategy using the phase change energy storage and flat heat pipe, in which the phase change material and the flat heat pipe play the roles of heat storage and thermal diffusion, respectively. In this paper, the thermal diffusion features between the aluminum flat heat pipe and the aluminum alloy plate are compared, and their thermal management performance resulting from the combination with phase change materials are experimentally investigated. The experimental results show that the aluminum flat heat pipe depicts much better heat transfer performance than the same-size aluminum alloy plate, since the maximum temperature difference at the condensing side is 3.2 ℃ at 40 W and the equivalent thermal resistance can be maintained below 0.35 K/W. When the heat source is shifted to the side, the thermal performance of the flat heat pipe rapidly drops due to the longer vapor diffusion and liquid reflux paths compared to the case at the middle position. Meanwhile, compared with the local overheating phenomenon when aluminum alloy is used as the bottom substrate of the heat storage container, the thermal control design of the flat heat pipe with phase change energy storage can diffuse the heat from the heat source evenly and reduce the heat flow density thus demonstrating better temperature uniformity, and then heat is absorbed by means of phase change energy storage, which can ensure that the junction temperature of the antenna product is controlled at 70 ℃ when it works continuously for 90 min. For the channel type flat heat pipe with a high aspect ratio, the capillary structure of the channel needs to be further improved to reduce the influence of the difference of vapor diffusion and liquid reflux paths on the thermal diffusion performance.关键词：high power antenna products;thermal control design;flat plate heat pipe;phase change energy storage63|6|0更新时间：2025-04-27
- 摘要：To investigate the difference of the cooling characteristics of film cooling when moist air and dry air are used as cooling medium respectively, the experimental and numerical studies are carried and the effects of blowing ratio and humidity ratio of moist air on the film cooling performance of a flat plate are analyzed in detail. In the experimental test, the infrared camera was used to measure the temperature of the target surface. The effects of different blowing ratios and humidity ratios on the film-cooling performance were taken into consideration and the variation of film cooling efficiency with respect to blowing ratio and humidity ratio was obtained. In the numerical analysis, a film cooling model with a single film-cooling hole with periodical boundary conditions was established, and the commercial software ANSYS CFX is used to investigate the influences of the blowing ratio and the humidity ratio on film cooling performance under high temperature and high pressure condition. The experimental results show that when the blowing ratio is 0.7, the cooling performance of film cooling of the target surface improves with the increasing humidity ratio, and when the humidity is 188.9 g/kg, the average cooling efficiency of the whole target surface improves 4.8% compared to dry air cooling. The numerical study results are consistent with the experimental results. The results also show that when the blowing ratio is 0.7, the cooling performance of film cooling is optimal, and the cooling performance of film cooling of the target surface improves with the increasing humidity ratio when the blowing ratio is between 0.3 and 0.7, while the film-cooling efficiency shows a reverse trend when blowing ratio is higher than 0.7. Based on the experimental and numerical results, a correlation of film-cooling performance of the target surface in terms of the blowing ratio and the humidity ratio was proposed. The correlation has a relative error within ±2%.关键词：film cooling;moist air;blowing ratio;humidity ratio57|5|0更新时间：2025-04-27
- 摘要：In order to improve the aerodynamic performance of the centrifugal compressor to meet the demand of the fuel cell system, this paper takes a fuel cell centrifugal compressor impeller as the study object, selects the key configuration parameters such as the impeller inlet inclination angle, number of blades, radial flow path and other profile control points and blade mounting angle distribution control points as optimization variables, then uses the numerical calculation method to simulate and optimize the aerodynamic performance of the centrifugal impeller. Based on the Latin hypercube sampling and the BP neural network, this paper mapped the relationship between the impeller configuration parameters and the aerodynamic performance, then uses the maximum isentropic efficiency of the impeller as the optimization target, and takes the total pressure ratio and power as constraints. The genetic algorithm was used to optimize the key configuration parameters of the impeller, and the aerodynamic performance and internal flow characteristics of the impeller before and after optimization were compared and analyzed. The results show that the isentropic efficiency of the optimized impeller increases by 3.90%, its total pressure ratio is 1.742, and its power is 8.53 kW under the design conditions, which satisfies the design requirements. At the same time, the range of stable operating conditions of the impeller becomes wider, and the isentropic efficiency of the impeller is also improved in the whole range of operating conditions. The flow field analysis shows that the high entropy area on the cover side of the impeller is reduced after optimization, the velocity distribution in the pressure surface and outlet section of the blade is more uniform, the area of the low-speed gas mass is reduced in multiple directions, and the flow separation in the impeller channel is suppressed. The above verifies the effectiveness of the multi-parameter optimization design method of the centrifugal impeller in this paper.关键词：centrifugal compressor;impeller;fuel cell;aerodynamic performance;multi-parameter optimization85|6|0更新时间：2025-04-27
- 摘要：To meet the demand of low power small cryogenic pump for fluid circulation in aerospace and biomedical applications, a small volume cryogenic centrifugal pump with a flow rate of 10 L/min and a power of less than one hundred watts was developed, of which the impeller and inducer structures were designed by numerical simulation and 3D printing impeller iterative optimization method. A set of closed-loop performance testing system for small cryogenic pumps was built, and the performance tests of the cryogenic pump using liquid nitrogen as the medium were completed. The external characteristic curves of the cryopump with a rotation speed of 4 500-8 000 r/min was obtained, and the influence of the fluid pressure(gauge pressure 140-800 kPa)in front of the pump on the head of the cryopump was studied. The study results showed that the small cryogenic centrifugal pump ran stably under a small flow and a small head. As the flow rate increased, the power first increased approximately linearly, and then the rate of increase gradually decreased. When the speed increased, the slope of the power linear growth area became larger and the efficiency curve began to peak. The higher the speed, the more the best efficiency operating point shifted to the large flow area. At the rated speed of 6 500 r/min, the best efficiency operating point was 10 L/min with a flow rate of 10 L/min and a head of 7.12 m. When the inlet pressure was higher than 200 kPa, the head of the cryopump was not sensitive to pressure changes. This paper can provide a reference for solutions to low flow cryogenic fluid drive applications.关键词：centrifugal pump;low power;small flow rate;performance testing;cryogenic fluid87|5|0更新时间：2025-04-27
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