bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation on the vibration characteristics of circular saw blade with different slots
Authors: Feng Wei , Zhang Jinsheng , Zhou Haoren , Di Hao
Published: September 2020

Irregular vibration of circular saw blade caused by complex forces in the process of cutting harms the operators, product quality and the life of circular saw blade. In this paper, the modal analysis of circular saw blades with different slot length and four kinds of unequal slot length saw blades are carried out based on the finite element theory. The vibration characteristics of circular saw blades with different slot length is studied. The results show that the natural frequency and the maximum deformation increase with the increasing slot length. In the case of higher order after the 5th order, the phenomenon is even more obvious. The effects of slot length, slot depth and diamond segment on natural frequency are compared. The results show that slot length has the greatest effect on natural frequency. Circular saw blades of different structures with unequal slot length can be selected to avoid resonance during operation.
Nonlinear forced vibration of the magnetic gear system with the internal resonance
Authors: Hao Xiuhong , Hao Wenbin , Pan Deng
Published: September 2020

Considering the nonlinear magnetic coupling stiffness among components of the magnetic gear with intersecting axes and a straight SP (MGIASS), the nonlinear dynamic model and differential equations of the MGIASS system are established. Then, the expression of the forced response is obtained when the excited frequency is close to the torsional mode frequency of the input rotor. The forced responses analysis of the example system shows that: the response frequencies include the excited frequency and the double frequency. Multiple proximity between the natural frequencies directly affects the stability and resonance amplitude.
Optimization design of gas sand deflector for reverse circulation drilling
Authors: Liu Biao , Wang Lei , Chen Shukai , Zhang Dongsen , Wang Caibao , Wang Hao , Zhou Yufan
Published: September 2020

Gas reverse circulation drilling which has a wide application prospect in complex strata of deep and ultra-deep wells can effectively improve drilling speed, protect the environment, reduce costs, and reduce downhole accidents, but its string structure is different from that of conventional drilling. In this paper, the design of integral and splitter head-in to side-out rotary sand deflecting device consists of rotating inner tube and non-rotating outer deflecting chamber, so that it can be effectively connected to the double-wall drill pipe system to ensure the normal sand deflecting of the gas reverse circulation drilling system. At the same time, the test well was verified and analyzed, and the sand-carrying efficiency was close to 92.53%. After drilling, there was no sand-settling at the bottom of the well. The average carrying rock diameter is about 10-15mm, and the maximum can be up to 30-40mm, indicating that the top-injection side-exit gas sand guide can be used for gas reverse-circulation drilling.
The system design based on long-wave uncooled infrared detector
Authors: Feng Shuyi , Xie Baorong , Liu Yanli , Wang Yang , Mu Wentao
Published: September 2020

According to the requirement of high-definition surveillance of the status of space targets in low illuminance, a high SNR (Signal to Noise Ratio) uncooled long-wave infrared system is designed. Based on the detector of UL04371 with 640 × 480 array, the system scheme, acquisition system and real-time image processing algorithms are realized. On the basis of system implementation, the paper mainly focuses on how to reduce the noises from the aspect of hardware circuits and how to realize the real-time processing in the way of specified infrared image algorithms. Finally, the paper gives the test result which shows that the system has achieved a relatively good SNR characteristic with the average NETD (Noise Equivalent Temperature Difference) value of 220mK under the condition of the integration time of 64us and the radiation of 300K black body.
Analysis and optimization of electromagnetic scattering characteristics of two-dimensional metal airfoil covered with metamaterial
Authors: Liu Ji , Yan Zhaowen , Ji Jinzu , Chang Qi , Song Hang
Published: September 2020

Airfoil is one of the strong scattering sources of aircraft, so it is of great significance to study the stealth characteristics of airfoil for the reduction of the radar cross section of the whole aircraft. As is known, the airfoil of aircraft is the main component that generates lift. Shaping the airfoil will reduce the aerodynamic performance of the aircraft. However, the emergence of metamaterials allows aircraft designers to achieve a good balance between stealth and aerodynamics. Considering the high cost of stealth test, numerical simulation is proposed to guide the design of metamaterial stealth. Then, the bistatic radar cross section (RCS) of airfoil covered with metamaterial is researched in this paper. We employ the 2-D auxiliary differential equation finite-difference time-domain (ADE-FDTD) to simulate the airfoil’s stealth characteristics. The two-dimensional situation can be regarded as a special approximate when electromagnetic waves are perpendicularly incident on the three-dimensional infinitely long airfoil. The tuning parameters including coating thickness, Drude frequency and collision frequency are considered on the airfoil’s bistatic RCS. The calculation program verified its correctness by simulating the perfect lens characteristics of electromagnetic waves propagating in the metamaterial plate. The numerical experiments show that the meta-material Drude frequency and collision frequency mechanism are more complicated than the coating thickness. The dual-station RCS increases at some angles and decreases at other angles than metal airfoils. But by choosing appropriate metamaterial parameters, airfoils with excellent stealth effect can be obtained.
Simulation analysis of autofretted barrel strength based on ABAQUS
Authors: Yang Yuliang , Sun Yezun , Li Yue
Published: September 2020

Autofretted technology is used generally by high-pressure guns to enhance the strength of barrels. Mechanical properties of the autofretted barrel were studied based on the finite element software ABAQUS. For the open autofretted process, a simulation model of gun barrel was established and its accuracy was verified by comparing the simulation results with theoretical results. Various stress of autofretted gun in the firing process was simulated, and the best autofretted pressure was found. For the closed autofretted process, autofretted pressure was affected by the gap amount between the mold and the barrel.
Research on obtaining method of rotor moment of inertia of synchronous generator set suitable for different rated speed
Authors: Wen Libin
Published: September 2020

Aiming at the problem that the moment of inertia of the rotor of the generator set is different from that of the generator set under different load rejection, according to the energy conversion characteristics of the generator set during the rotor rotation, the energy conversion balance equation of the rotor rotation process is put forward, which is applied to the load rejection process of the generator set under different load and calculated and analyzed, and the accurate moment of inertia of the rotor of the generator set is obtained, this method improves the accuracy of kinetic energy of generator, which is one of the parameters of generator model in power grid stability analysis.
Verification of the numerical analysis using a collocated grid system directly solving the quasi-inviscid incompressible flow around a symmetric airfoil
Authors: Suzuki Hiroki , Watanabe Masaya , Hasegawa Yutaka , Mochizuki Shinsuke
Published: September 2020

The present study describes the results of validating a high-quality computational scheme of kinetic energy conservation characteristics under a collocated grid system. In the present study, the pseudo-inviscid incompressible flow around the Kármán-Trefftz airfoil is analyzed. In this analysis, the kinetic energy conservation error is reduced by temporally evolving the governing equation using pressure increments in fractional steps. This sufficient conservation of kinetic energy is validated using an inviscid homogeneous isotropic fluctuation field. The velocity field obtained by this analysis is compared to that of the potential flow obtained using the Kármán-Trefftz airfoil. The numerical analysis is also validated using the lift coefficient profile as a function of a small angle of attack.
Model of thermal power plant considering water spray desuperheater for power system analysis
Authors: Wen Libin
Published: September 2020

It is of great significance to build a model of the water spray temperature reduction system that is more suitable for electrical simulation, and apply it to the existing thermal power plant model for the simulation analysis of today’s complex thermal power plants. Based on reasonable thermodynamic assumptions, the law of conservation of energy and the law of conservation of mass, a transfer function model of a water-jet cooling system suitable for the simulation of a thermal power plant is established by using mechanism modeling. The relationship between these variables and the effect of each variable on the output variables verified the correctness of the model. A steam turbine system considering the influence of the boiler was further established, and a simulation analysis of the operating characteristics was performed, which verified that the influence of the boiler on the dynamic response of the unit is necessary in the long-term stability analysis. Finally, combined with the model established in this paper, a dynamic model of thermal power unit with water spray temperature reduction device was established. The model is simulated with the step disturbance of velocity, the disturbance of cooling water flow and the disturbance of opening door. Based on the simulation results, the action response characteristics in the process are analyzed. It is verified that the model can accurately describe the main steam parameters and power regulation when applied to large-scale power grid transient simulation.
Grab application of remote operation service robot
Authors: Wang Xia , Zhao Tong , Wang Ding
Published: September 2020

The remote operation service robot can realize remote wireless control through the handle to help people with inconvenient movement to grasp objects. In this paper, based on the robot, the kinematic analysis is carried out to obtain the coordinate transformation of the mechanical fingers relative to the ground, and the dynamic analysis is carried out to obtain the driving torque required by each motor. The inverse kinematics of the manipulator is solved by MATLAB to obtain the joint parameters of the manipulator. Raspberry PI is used as the main control board, the handle sends out instructions, Raspberry PI judge instructions, and communicates with C8051F040 development board located in the manipulator through CAN bus. The mechanical finger realizes open-loop control through micro stepping motor, and finally realizes the remote operation of the service robot to grab objects.
Development and design of Bluetooth intelligent car
Authors: Wang Yongjie
Published: September 2020

Bluetooth is a kind of radio technology that supports short distance communication (usually within 10m). It can exchange wireless information among many devices, including mobile phones, PDAs, wireless headphones, laptops, and related peripherals. Using “Bluetooth” technology can effectively simplify the communication between mobile communication terminal devices, and also can successfully simplify the communication between devices and the Internet, so that the data transmission becomes more rapid and efficient, and broaden the way for wireless communication. This paper starts from the mechanical design and electrical control design of the intelligent car, designs the software and hardware of the Bluetooth intelligent car, mainly involving several technologies: wireless transmission technology; AVR single-chip technology; pulse width speed regulation and other related technologies. Realize the function of controlling the car forward, backward, left, right, acceleration and deceleration with Bluetooth.
Application of highly deviated well injection technology in Huabei Oilfield
Authors: Wang Yao , Han Mingzhe , Chen Junzheng , Li Ran , Zhang Xu , Liu Zhijuan , Wang Shuangyan , Wei Yuhao , Cheng Xiangfa , Xiong Wei , Liu Dayong , Huang Bohua , Li Xueying
Published: September 2020

With the deepening of oilfield development, the amount of highly deviated (≥30°) layered water injection wells have increased year by year. In order to solve the technical bottlenecks such as poor sealing of the columns and short effective period of dispensing. The self-supporting step-by-step releasable packers with the outer diameter of 114mm and the highly deviated well ball seat are developed. The packer integrates the function of centering-righting, ball centering, spiral righting and stepping unblocking and the ball seat has self-locking function and able to meet the requirements of pipe string used in highly deviated wells within 60°. Through the field application, a highly deviated well-dispensing process technology suitable for the characteristics of Huabei Oilfield has been formed, it has a strong popularization and application value.
Design and analysis of energy supplement system of waterfowl-type unmanned vessel platform
Authors: Fang Zifan , Hong Junpeng , Qin Lin , Liu Jin , Xie Zhiheng , Xie Zheyu
Published: September 2020

For the marine unmanned vessel platform’s long-distance navigation, a waterfowl-type unmanned vessel platform energy supplement system consisting of a wave energy collecting mechanism and a hydraulic conversion system was presented. A four-link acquisition mechanism and an energy conversion system are designed. The wave force on the float and the vertical wave force on the unmanned vessel platform were calculated by Matlab software. Based on the energy flow conversion process, the Adams and AMESim co-simulation model of the system was established. The energy conversion efficiency of the system under different sea conditions was calculated. The research shows that it can realize the continuous energy supplement and provides a reference solution for solving the problem of continuous energy supply in marine unmanned vessel platforms.
Numerical modeling of Vickers indentation on polycrystalline alumina
Authors: Liu Zhonglei , Wang Chao , Chen Zhanying , Rong Yiming , Li Xuekun
Published: September 2020

Indentation techniques are usually simple and effective methods to characterize ceramics properties. This article establishes a numerical model of Vickers indentation by using the general exponent Drucker-Prager model, which is suitable for materials whose compressive yield strength is much higher than tensile strength. In addition, a standard method for calculating the diagonal length of indentation is also proposed. Using this FE model, several numerical simulations of Vickers indentation process are conducted. Then, through measuring the indentation morphology with the proposed method, the Vickers hardness is calculated, which has excellent agreement with the experiment results. The comparison results of simulation and experiment show that the proposed numerical model is robust and effective. It is very promising in modeling the indentation process.
Error analysis and kinematic calibration of a new 3-PRS parallel mechanism
Authors: Sun Fuwei , Chen Guoqiang , Chen Shuisheng , Li Yongsheng , Yuan Jingshuai , Zhang Qin
Published: September 2020

Taking a new 3-PRS parallel mechanism as the research object, error analysis and kinematics calibration are carried out. Combining with inverse kinematics, the parameter error of the mechanism is analyzed comprehensively. a calibration method of inverse kinematics based on structural parameters and genetic algorithm is proposed, and the error calibration model of 3-PRS parallel mechanism is deduced. The calculation by MATLAB shows that the reverse motion error calculated by nominal machine tool structural parameters is larger than that obtained by calibrated structural parameters. The position of the three cylindrical and spherical hinges after calibration is closer to the nominal position. It shows that the error calibration can correct the machine tool structure and guide the subsequent installation and debugging of the machine tool.
Modelling and analysis of fuel temperature during fuel injection process of electronically controlled injector
Authors: Wang Jun , Liu Yanbin , Jin Yi , Zhang Youtong
Published: September 2020

In order to explore fuel temperature variation during the process of fuel injection, mathematical model of the fuel heat-temperature in electronic controlled injector (ECI) is founded, fine thermal simulation modelling of ECI is fulfilled by software AMEsim, fuel temperature change of different place in ECI is analysed. The analysis results show that injection pressure and initial fuel temperature have a great effect on the fuel temperature of the needle chamber and the control room, injection duration has little influence on the fuel temperature of the needle chamber, the fuel density decreases with the increase of fuel temperature under a certain pressure.
Study on strength reliability of actuator piston parts
Authors: Li Wending , Shi Guanglin , Dong Wenyong , Qiu Haihui
Published: September 2020

On the basis of the stress–strength interference model and reliability perturbation theory, this study applies the second-order distance method to analyze the reliability of actuator parts under the normal distribution of random parameters with ring as the dangerous section. The method of equivalent normalization of non-normal distribution parameters is also implemented in the reliability analysis of the tensile strength of ring sections. The design method described in this paper is applied to the design process of the piston rod of a carrier rocket servo mechanism. The influence curve of random parameters on reliability is drawn. A calculation software is established. This study provides theoretical support and practical method for the design of axial bearing parts with circular section.
Design and analysis of a lower extremity exoskeleton with the humanoid knee joint
Authors: Li Tingting , Li Jian , Han Zhonghua , Yang Jiechao , Li Qiang
Published: September 2020

Exoskeletons should have certain capabilities and characteristics such as human performance enhancement, low impedance and comfortable. In this paper we present a lower extremity exoskeleton. In order to achieve the characteristics of exoskeletons mentioned above we choose the Series Elastic Actuator (SEA) as its driver. A novel humanoid knee joint is introduced into the exoskeleton to improve the coordination between exoskeleton and human body during work progress. A stable control method is proposed to achieve the exoskeleton joint following motion. Finally, the feasibility of control algorithm is verified by simulation.
Analysis on screw preload condition of acoustic beacon in high water pressure environment
Authors: Chen Yang , Dong Shichao , He Junbo , Xiao Haitao , Sun Jialu
Published: September 2020

The acoustic beacon is mainly assembled by using screw thread couplings between caps and shell. The products are always affected by heavy loads when operating under high water pressure. In this paper, to investigate the influence of screw thread couplings on acoustic beacon strength under deep water condition, the structural stresses and the distributions of the acoustic beacon with different pre-tightening torque of screw thread under particular water pressure is analysed by using finite element method. The variations of stresses which is relative to the pre-tightening torque of screw thread are also analysed and proposed as the form of line chart. The results indicate that the acoustic beacon strength can be improved by increasing the pre-tightening torque of screw thread, and the line chart can be used to determine the most suitable pre-tightening torque while assembling the products.
Modal analysis of monorail rocket sled and its cabin connections
Authors: Hu Bing , Xia Hongli , Hao Fenfen , Li Hui
Published: September 2020

Structural stiffness is an important dynamic parameter for the rocket sled. In this paper, both modal test and finite element modal analysis are carried out on the certain monorail sled and its two different cabin connection kinds which are bolt and thread. By comparing the natural frequencies and modal shapes obtained by test and simulation methods respectively, it is found that the stiffness of bolted cabins is consistent with the simulation results, while the threaded cabins performs a severe stiffness degradation due to the thread clearance, which also causes the natural frequencies of the completed sled to be reduced and the modal shapes to be inconsistent with the simulation results. The finite element model of threaded connections is modified by giving anisotropic material properties to the connected elements, and the simulation deviation is reduced. According to the analysis results of two different kinds of cabin connections, threaded cabins on the final assembled rocket sled are strengthened by welding. The modal test results of the reinforced threaded cabin connection indicate that negative influence of the threaded connections is eliminated and the natural frequency and vibration mode are very close to the simulation results.
Influence of wheel-diameter difference of the same locomotive on ride quality of locomotive
Authors: Zhao Bin , Liu Fei , Li Ruiyu , Wang Jianming , Liang Lin , Luo Ailing
Published: September 2020

The existence of wheel-diameter difference of track locomotive will directly affect the motion performance of locomotive. In this paper, the creep force of coaxial wheel-diameter difference is analysed, and the dynamic model of 2-axle bogie locomotive is established by SIMPACK software. Based on the study of two typical wheel-diameter difference of the same bogie, 10 special working conditions of wheel-diameter differences of the same locomotive are put forward. The effects of different working conditions and different wheel-diameter differences of the same working condition on the straight line motion performance of locomotive are analysed. The results show that, the lateral displacement and lateral ride quality index of locomotive body increase with the increase of wheel-diameter difference under the same working condition, and they do not exceed the safety limit. The change of wheel-diameter difference has little effect on the vertical ride quality index of locomotive body. According to the lateral displacement of the locomotive body, the 10 working conditions are divided into three grades. The third grade (working condition 4, working condition 5, working condition 8 and working condition 11) is more conducive to the safe and stable motion of the locomotive. Therefore, in the wheel matching installation and repairing process, priority should be given to the arrangement of wheel-diameter difference of the same locomotive in the third grade. This will provide a reference and basis for the scheme of locomotive wheel economic repairing.
Simulation analysis of the fertilizer ejecting device of corn fertilizer applicator based on EDEM
Authors: He Yakai , Li Cuiling , Zhao Xueguan , Gao Yuanyuan , Li Si , Wang Xiu
Published: September 2020

In order to improve the fertilization efficiency of corn fertilizer applicator in the Huang-Huai-Hai area, according to the requirements of the wide-row crop fertilizer requirements, a centralized type fertilizer ejecting device was designed. Straight outer groove-wheel was regarded as research objects in this paper. The simulation model of fertilizer ejecting device was established and the simulation analysis of fertilizer ejecting was carried out by using the discrete element simulation software (EDEM). In the simulation environment, the requirement of fertilizer ejecting amount was 300kg·hm-2, the forward speed of fertilizer ejecting device was set to 5.4km·h-1, and the working height of fertilizer axis was 250mm. The effect of different working lengths of fertilizer ejecting wheels on the fertilizer performance was analyzed. The simulation results showed that when the working length of fertilizer ejecting wheel was 28mm, the uniformity variation coefficient of fertilizer ejecting was 14.62%, and the accuracy rate of fertilizer ejecting was 95.95%, which indicated that performance of fertilizer ejecting was better. This research results can provide references for the subsequent development of corn fertilizer applicator.
Second-order kinetic energy-conservative analysis of incompressible turbulence under a collocated grid system
Authors: Suzuki Hiroki , Hasegawa Yutaka , Watanabe Masaya , Tatsuo Ushijima , Mochizuki Shinsuke
Published: September 2020

The study presented in this paper investigates the second-order conservation error of kinetic energy of an incompressible flow under a collocated grid. A collocated grid is often used to numerically analyse the flow around an aerofoil. The kinetic energy conservation error under a collocated grid is often greater than that under a staggered grid. The results of analysis based on coarse computational grids, such as LES analysis, are considerably affected by the kinetic energy conservation error. This study shows the results of numerical analysis in which the kinetic energy has a second-order conservation error under the collocated grid. This higher-order kinetic energy is strictly validated using inviscid flow. Furthermore, the results of conservation errors of higher-order statistics of kinetic energy are discussed in this study. The numerical analysis is then validated using a turbulent channel flow. The statistics obtained by this analysis agree well with those of previous studies in turbulent channel flows.
Design and performance analysis of pneumatic disc brake of a new energy commercial vehicle
Authors: Fu Shichao , Sun Haiming
Published: September 2020

The brake is the key mechanism of automobile braking system, which makes the vehicle reach the expected driving state by outputting braking force to the wheel. SolidWorks was used to model the pneumatic disc brake of EQ1180GEVJ new energy commercial vehicle. The finite element software ANSYS workbench was used to conduct the finite element analysis of the brake disc, brake clamp and bracket, and the stress cloud diagram under the braking condition, as well as the first 10 natural frequencies and the main vibration pattern diagram were obtained. The results show that the maximum deformation of the brake disc is in the lower position on both sides of the brake disc, and the maximum stress is in the position connected with the wheel hub. The maximum stress of the brake clamp is at the connection between the connecting arm and the brake chamber. The maximum stress of the support is at the connection between the support and the suspension. The first ten natural frequencies of the three parts are between 240Hz and 3000Hz. By analysing the mode, we can obtain the position where the mode which is prone to sudden vibration frequency change and the system may generate the maximum vibration amplitude when resonance occurs. The results provide some references for further optimization of disc brake.
Research on the simulation technology of the combined effects of transient thermal shock and a triaxial 6-DOF
Authors: Yao Zemin , Huang Xiaokai , Huang Shouqing , Liu Shouwen
Published: September 2020

During the reentry of a spacecraft, it will encounter extreme environment of transient thermal shock and a triaxial 6-DOF. Currently, there is a lack of experimental verification means. Taking a second power supply as an example, the finite element simulation model is established, and the model is verified by the heat balance test and random vibration modal test. The thermal response distribution of rapid temperature change, low-temperature holding and high-temperature holding phrases is obtained through the transient thermal shock simulation; Based on the multi-stress simulation of the workbench, the stress-strain response distribution under the triaxial 6-DOF random vibration is obtained. According to the principle of stress coupling, the thermal response distribution matrix and stress-strain response distribution matrix are applied to the finite element model of electronic products at the same time, and then the transient thermal shock and the triaxial 6-DOF coupling simulation is realized, which provides a theoretical guidance for test verification of the extreme environment during the reentry of a spacecraft.
Analysis of vibration resistance reliability of directional probe framework for MWD logging system
Authors: Liu Qing , Wu Junjie
Published: September 2020

This paper discusses the failure mode of structure under complex working conditions of oil drilling. The method of selecting the main failure mode of directional probe framework under the condition of vibration is deduced. The calculation of the vibration resistance reliability for the framework of directional probe is simplified. The anti-vibration reliability index of directional probe framework is calculated by an example in this paper. The influence of machining error and additional quality on the vibration resistance reliability of directional probe framework are also analyzed. The results show that the main failure modes of the directional probe framework are different with different additional mass. Therefore, the research results have certain design guidance significance.
The study on lashing ware location of vibration reduction model of detuned blade disc structure
Authors: Wang Lijuan , Yang Guohui
Published: September 2020

The studies on vibration localization of periodic structure are mainly based on displacement modes at present, while the strain modes have not been applied to the research of vibration localization. Consequently, it was imagined to apply the strain modes to vibration localization based on a finite element model of bladed disk with shrouds, and the vibration localization factors based on strain modes and displacement modes were compared with the condition that the bladed disk is mistuning. The result shows that the vibration localization based on strain modes is much more sensitive to stiffness mistuning than the vibration localization based on displacement modes; what’s more, the strain mode shapes are different with the displacement modes at the same mode order. The result is important to the design of periodic structure with snubbing mechanism.
Numerical simulation, verification and experiment validation on hydrodynamic performance and radiated noise properties of skewed propeller
Authors: Ma Fuqiang , Liu Yansen , Mu Lin , Jia Bing
Published: September 2020

Numerical simulation of hydrodynamic performance and radiated noise properties of the standard propeller is carried out by computational fluid dynamics (CFD) approach and acoustic analogy equation, and verifying and validating the numerical result by experiments in cavitation tunnel. Taking Potsdam Propeller Test Case (PPTC) propeller as an example, the geometric model, grid model and numerical simulation boundary conditions are established. The comparison between numerical calculation and experimental results of open water characteristics of propeller, including thrust coefficient, torque coefficient and efficiency shows that the numerical model is reliable. Under the condition of good agreement between numerical simulation and experimental results of unsteady hydrodynamic characteristics, which contains the pressure distribution of blades, cavitation properties, the wake vortex distribution of the propeller, the numerical calculation and characteristic analysis of propeller radiated noise are carried out. The results show that the relation between the radiated noise of the propeller and the inherent structure and the motion state is correlated. The research can provide a theoretical basis for the target detection and recognition based on such characteristics.
Research on the influence of pulse parameters on surface charge of epoxy resin
Authors: Lin Haofan , Tao Ruixiang , Zhou Luyao , Yang Yong , Yu Bing , Liu Shuang
Published: September 2020

The dynamic characteristic of the surface charge on insulating material is an important electrical characteristic, which can effectively reflect the insulation performance of materials. The phenomenon of surface charge accumulation leads to surface discharge and surface flashover. In this paper, the surface charge accumulation and dissipation of epoxy resin under different pulse parameters were studied. The experimental results showed that the increase of pulse frequency intensified the phenomenon of surface charge accumulation and inhibited the process of charge dissipation. Meanwhile, the increase of the number of pulses led to the increase of surface charge accumulation first and then saturation. At the same time, it inhibited the process of surface charge dissipation.
Investigation on the transient stability of hydro generator working with power grid
Authors: Sun Fuchun , Wang Andong , Wang Jihao , Xu Dai , Zhuang Xu
Published: September 2020

Huge hydro-generator is the inevitable development trend of hydro-generator for utilization of water resources. It is very necessary to research the technical issues for 1000MW hydro-generator. Whether the short-circuit faults locate at the generator terminal or the end of transmission line, the transient stability of hydro-generator is calculated and analyzed based on the field-circuit coupling model. Short-circuit fault must be cleared immediately in order that the power system and generator can maintain stable operation, in this paper, fault clearing time limit under different conditions is obtained by mass of simulation. The results obtained in this paper can provide valuable reference for the actual operation of 1000MW hydro-generator, and it is also useful and valuable for the design of protection devices, the dispatching of power grid and the debugging of generator when be connected to power grid.
Partial discharge identification of DC cross-linked polyethylene cables based on GA-BP algorithm
Authors: Wang Luliang , Yang Xu , Jiang Yi , Zhang Jing , Yao Yuhang , Wu Qian
Published: September 2020

In this paper, XLPE DC cables were used to construct three kinds of defects of inner semiconducting layer breakage, internal air gap defect, and insulating surface scratching defect. And their DC PD characteristics were tested under different voltage amplitudes and polarities. The study found that these three defects exhibit different DC partial discharge characteristics and change with voltage amplitude and polarity. Subsequently, two methods were used to identify the type of defect. The recognition rate of the traditional defect type identification method reached 97.1%, and the recognition rate of the optimized defect type identification method based on GA-BP was increased to 98.9%, which solved the problem that the traditional method was affected by the voltage level and polarity, and improved the recognition rate.
Defect simulation and state characteristic analysis of cable joints with tip defects
Authors: Jiang Hang , Cao Junping , Wang Shuyang , Tong Li , Zhou Weijie , Yang Yong
Published: September 2020

In recent years, the breakdown of the body and accessories of high voltage cables has increased gradually. Taking the tip defect of 110 kV high voltage cable joint as an example to carry out electric field simulation analysis, the distribution and change law of electric field under this defect are put forward. Based on full working condition detection platform of high voltage cable, the simulation test of the defect is carried out. The effectiveness of various charged detection methods and on-line monitoring methods has been studied, and the variation rules of cable state under different working conditions have been obtained. The results show that, when tip defect is between stress cone silicon rubber and main insulation of cable body, electric field distortion around the tip shows discharge, and the breakdown potential is 83 kV. The high frequency partial discharge detection method and ultrasonic partial discharge detection method can detect the defects effectively, among which anti-interference ability of high frequency partial discharge detection at the capacitive arm is the best, and detection sensitivity of the grounding current is higher in the on-line monitoring. The thermal efficiency of load current has little effect on development of tip defects. But with the increase of test voltage, the high frequency emission volume increases obviously and breakdown occurs easily at higher voltage.
Research on motion characteristics and stability of 500kV fast mechanical switch
Authors: Huang Leichao , Fang Chun’en , Li Wei , Tang Xiaoyu , Zhang Ning , Chen Junping
Published: September 2020

The key component of fast mechanical switch (FMS) is electromagnetic repulsion mechanism (ERM), and the stability of ERM has an important influence on fault breaking time and breaking performance of hybrid DC circuit breaker (DCCB). In this paper, a FMS based on ERM is designed. In order to improve the stability of the FMS, the key factors affecting the stability of the excitation coil resistance, the inductance of the excitation coil, the capacitance of the energy storage capacitor, the charging voltage and the ambient temperature are analyzed. Then, 2D ERM simulation model is set up and study the above parameters deviation and the change of environmental temperature on the repulsive force driving characteristics. In order to ensure that the ERM moves to 10mm in 2ms, and the time dispersion is less than ±0.2ms. The reasonable variation ranges of each parameter required for the stable action of the ERM and the appropriate working environment temperature are determined. Finally, the developed FMS prototype was tested for opening, temperature rise and consistency, and the test results were consistent with the simulation results.
Simulation study on parameters of steam turbine governing system based on power grid stability analysis
Authors: Wen Libin
Published: September 2020

Limited to the general software model of power grid stability analysis can not be changed and added, the parameter setting of steam turbine regulating system is improper, and it will be difficult to model and simulate if it does not conform to the relevant software model; moreover, improper parameter setting of steam turbine regulating system will also cause large fluctuation of generator output power in the process of unit primary frequency regulation, which will affect the stable operation of power grid. In this paper, through the simulation analysis and experimental research of the turbine governing system, the relevant control parameters are changed and optimized, so that the actual unit governing system model is consistent with the general calculation software model of power grid stability, so as to meet the technical requirements of power grid stability analysis and generator unit access to the grid; at the same time, the stability and rapidity of the unit participation in power grid primary frequency regulation are improved.
Open-circuit fault diagnosis of traction inverter based on improved convolutional neural network
Authors: Liu Jun , Wang Junnian , Yu Wenxin , Wang Zhenheng , Zhong Guang’an
Published: September 2020

In the traction system of high-speed EMUs, the inverter’s Insulated Gate Bipolar Transistor (IGBT) often occurs open-circuit (OC) faults. However, traditional fault diagnosis relies mainly on signal processing to extract fault features, which is susceptible to environmental interference, resulting in poor generalization ability of the model. Aiming at this problem, a fault diagnosis method based on an improved convolutional neural network is proposed. Firstly, the three-phase stator current signal is preprocessed by wavelet domain denoising. Secondly, fault features are independently learned through a convolutional network. Finally, a fully-connected layer is used for fault diagnosis. The experimental results show that this method could resolve the OC fault diagnosis problem of the inverter’s IGBT effectively, and also achieve higher accuracy under the interference of noise, and the diagnosis can be made at 0.01s after the fault occurs.
Research on mppt control method of doubly-fed wind power system based on sliding mode control
Authors: Huang Yong , Jiang Dongmei , Pan Lin
Published: September 2020

In order to solve the problem of maximum wind energy tracking wind speed measurement of wind turbine at present, a new wind energy control algorithm, sliding mode control algorithm, is proposed, which adjusts the speed of fan by sliding mode control, avoids the problem of real-time wind speed measurement in wind speed tracking control, and can respond quickly to the sudden change of wind speed and solve the problem of uncertain inherent parameters of wind speed. The proposed algorithm is compared with the PI control algorithm and the analog 660KW generator, and the effectiveness of the algorithm is verified. Results: the sliding mode control algorithm has good track tracking performance, can shorten the delay time between the actual value and the reference value, and has good performance.
Study on electro-hydraulic control system of advanced support in large section roadway
Authors: Wang Qi , Shi Tao
Published: September 2020

Taking the large cross-section return air roadway of 4201 working face in No.2 panel of Liuzhuang Coal Mine as engineering background, the engineering geological conditions and supporting conditions of roadway were analyzed, and the 3×ZQL2×5200/23/45WD split advanced support was used to support the roadway in the advance support area. On this basis, the design schemes of support pressure monitoring system, automatic deviation adjustment system, environmental monitoring system, remote control system and software control system were analyzed, the subsystems with different functions constitute the electro-hydraulic control system of advanced support. The advanced support has good application effect and can meet the requirements of advanced support and automation control of large cross-section roadway.
Power system reserve scheduling with wind farm integration considering robust security constraints
Authors: Dou Fei , Cheng Jinmin , Wang Weiyuan , Yu Xuan , Xia Kai , Xu Yiqing , Wan Zhendong
Published: September 2020

The fluctuation of real-time wind power output and the capacity limits of transmission network have been identified as bottlenecks to integrate wind power in power system operation. This paper proposes a novel model of robust linear optimization for the reserve scheduling considering the secondary frequency the power network security constraints. In this model, the linearization decision rule is introduced to describe the allocation of the secondary frequency control reserves; the mean value and unsymmetrical interval bound instead of the probability distribution are used to describe the wind power uncertainty. The stochastic robust linear optimization model is converted into a deterministic linear programming, thus achieving the tractability. Case studies are carried out to verify the effectiveness of the proposed method.
Speed optimal method of intelligent network vehicles passing through signalized intersection
Authors: Chen Zhenglong , Chen Jing , Xiao Chun , Li Zhihua
Published: September 2020

Aiming at the problem that the frequent stops and changes of intelligent network vehicles passing through the signalized intersections, speed Optimal method of intelligent network vehicles passing through signalized intersection is proposed in the paper. The position and speed of the intelligent network vehicles are detected by the RSU (Road Side Unit) in real time, the distance of ahead vehicles is controlled by the method. The frequent deceleration of the vehicles passing through the signal intersection is solved effectively, at the same time reducing the vehicles fuel consumption in the running.
Performance comparison of switching losses of SiC DMOS vs Si IGBT
Authors: Bukhari Syed Arslan , Zhang Hongjuan , Bukhari Syed Humza , Iqbal Muhammad Yousaf
Published: September 2020

Silicon Carbide Double Diffused Metal Oxide Semiconductor (SiC-DMOS), having a more comprehensive bandgap, fast switching and low power losses, has been rapidly developed and applied. This paper elaborates a detailed analysis of switching losses by comparing Si IGBT and SiC DMOS under the same voltage parameters and identical conditions. The switch’s characteristics are evaluated and contrasted in various gate resistances. In addition, a gate driver is designed to calculate the switching losses of IGBT and SiC DMOS at different frequencies. Then they are respectively used in the buck converter. The experimental platform is built to test and validate that the SiC DMOS buck converter achieves faster dynamic performance and higher efficiency than Si IGBT.
Fuzzy comprehensive evaluation method of variable weight for power distribution equipment group
Authors: Liu Chenlong
Published: September 2020

The evaluation of equipment group status has some reference value for maintenance strategy optimization and distribution network reliability evaluation. In this paper, the fuzzy evaluation method of variable weight is applied to evaluate the equipment group of power distribution network hierarchically. The importance degree of individual equipment in the evaluation of equipment group is determined by the load size and the importance degree of load borne by the equipment, the network equivalent method is applied to calculate the weight of individual equipment, and the conjoint analysis optimization algorithm is applied to realize dynamic weight variation. A set of transformer winding and casing and a partial 10kV line are taken as examples to verify the effectiveness of the proposed method.
A new discrimination of stator single-phase grounding fault based on multi-dimensional fusion for Powerformer
Authors: Fang Tao , Zhou Yue , Liao Weiping , Su Jue , Xie Wuchao , Xu Jianxiong , Li Huahui , Li Yun , Chen Xinquan , Su Hailin
Published: September 2020

Some existing fusion discriminations are used to identify whether a stator single-phase grounding fault occurs in parallel Powerformers. However, such methods are complicated to operate and require a large amount of training data as support. Therefore, a new discrimination of stator single-phase grounding fault based on multi-dimensional fusion for Powerformer is proposed. Firstly, the faulty Manhattan distance and the sound Manhattan distance about each Powerformer are calculated by the fusion formula of Manhattan distance base on the four features extracted in Powerformer. Then, the sizes of the faulty and sound Manhattan distances about each Powerformer are compared. If the faulty Manhattan distance of the Powerformer is less than the sound Manhattan distance, the Powerformer can be judged as the fault, otherwise, it can be judged as the sound Powerformer. The simulation experiment show that this method does not need a large number of data as support, nor does need to set the threshold value artificially, so it improves the practicability and applicability of the method.
Application of improved wavelet denoising method in low-frequency oscillation analysis of power system
Authors: Liu Mosi , Sun Zhiyuan , Li Mingpo
Published: September 2020

The Prony algorithm has been widely used in low-frequency oscillation analysis of power system due to its good mathematical characteristics. However, the Prony algorithm is very sensitive to noise and requires a high level of input signal. This paper overcomes the shortcomings of traditional soft and hard threshold denoising methods by improving the threshold and threshold function of wavelet denoising. Using the improved wavelet threshold denoising method to preprocess the sampled signal can effectively improve the anti-interference ability of the Prony algorithm. The simulation experiment is performed with MATLAB and the experimental results show the effectiveness of the improved method.