Table of Content

25 February 2021, Volume 49 Issue 2

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Contents



2021, 49(2):  0. 

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Energy, Power & Electrical Engineering

State Switching Control Method for Direct-Drive Wave Power Generation System 



YANG Jinming HUANG Wei

2021, 49(2):  1-8.  doi:10.12141/j.issn.1000-565X.190833

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Based on the research of the power capture optimization method for the direct-drive wave power generation system，a state switching control method based on a linear generator was proposed in this paper． Based on the characteristic that the speed of the linear generator in the no-load state is higher than that in the power generation state，the linear generator is controlled to switch between the no-load state and the power generation state，thereby increasing the speed of the linear generator in the power generation state． Therefore，the captured power is further improved． The results show that，compared with other power capture optimization methods，the proposed method has excellent performance in power capture．

Study on MILD Combustion of MSW Pyrolysis Gas Based on FLUENT



LIAO Yanfen, ZHANG Manyu, CHEN Shunkai, et al

2021, 49(2):  9-16.  doi:10.12141/j.issn.1000-565X.200309

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With the development of social economy，the production of all kinds of garbage is increasing rapidly， and the research on efficient and clean utilization of pyrolysis gas of garbage is gradually carried out． This study used FLUENT software to simulate the MILD combustion of MSW pyrolysis gas in the burner，and the effects of fuel nozzle diameter，air nozzle diameter，distance between fuel nozzle and air nozzle，air nozzle distribution and thermal value fluctuation on the combustion and NO emission in the burner were explored． The results show that the change of jet velocity indicated by the change of air nozzle diameter has the most significant effect on combustion， and the increase of jet velocity can achieve better MILD combustion effect by turbulence and entrainment． And there is an optimal value of 8mm of air nozzle diameter in this study． The increase of fuel jet velocity has less effect on combustion effect，the high speed of fuel jet is conducive to fuel jet rigidity and combustion zone extension，and there is an optimal value of 8 mm of fuel nozzle diameter in this study． The diffusion process and the size of return area can be influenced by the distance between air and fuel nozzle，which can be matched with the aperture to obtain an optimal value when the nozzle spacing is 15mm． The uniformity of the air jet distribution affects the combustion effect，but has little effect on NO emission，so 4 air nozzles are suitable． The burner can satisfy the MILD combustion with the calorific value of the pyrolysis gas fluctuating at 20% ．

Concentration Closed-Loop Control of Dry Electrostatic Precipitator in a 1 000 MW Coal-Fired Unit



HAO Yongsheng, WANG Zhongwei, ZHU Xiaojin, et al

2021, 49(2):  17-24,67.  doi:10.12141/j.issn.1000-565X.200341

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Closed-loop control method of electrostatic precipitator outlet dust concentration was studied to solve the problems of high energy consumption of dry electrostatic precipitator in 1000 MW coal-fired units and the failure to achieve closed-loop control of concentration． Firstly，for dry electrostatic precipitator with a five-field structure，a concentration control method combining feedforward control of the first three-stage electric fields and closed-loop control of the last two-stage electric field was proposed． The IMC-PID parameter setting method was used to set the PID ( Proportional Integral Derivative) controller parameters，and a disturbance observer was added to the PID controller to enhance the anti-disturbance ability of the system． Finally，the method of fuzzy weighted switching was used to achieve smooth switching between the control functions of each load point model． The simulation and experimental results show that the proposed control method can realize the fixed value control of electrostatic precipitator outlet dust concentration and has good performance．

Application of Vapor Chamber in the Thermal Management of Proton Exchange Membrane Fuel Cell Stack#br#



BAI Xingying, JIAN Qifei, LUO Lizhong, et al

2021, 49(2):  25-32.  doi:10.12141/j.issn.1000-565X.200345

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Too low or too high operating temperature and excessive temperature fluctuations will adversely affect the output performance and durability of proton exchange membrane fuel cells． Therefore，effective thermal management is the essential to the stable and efficient output of proton exchange membrane fuel cells． In this study，a 1. 5mmthick vapor chamber was used as a heat dissipation structure in the thermal management of a proton exchange membrane fuel cell stack，and 80 thermocouples were installed on a cathode graphite plate with 5 single cells to obtain the internal surface temperature of cells，so as to explore the temperature distribution characteristics of the stack under different load currents． It’s found that，during the loading process of 0 ～ 8A，the maximum temperature difference of the cathodic side within each single cell is less than 1. 0 ℃，and local temperature fluctuation only occurs at inlet ports． In addition，the temperature distribution uniformity of the stack with vapor chamber is better than that of the ordinary water-cooled stack under the same operating condition．

Numerical Investigation of Heat Transfer Performance of Molten Salt-Based Nanofluids for Internal Flow#br#



HE Boshu, YING Zhaoping, SU Liangbin, et al

2021, 49(2):  33-39.  doi:10.12141/j.issn.1000-565X.190865

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To study the flow heat transfer characteristics of Al2O3-HITEC molten salt-based nanofluids in heating tubes with constant heat flux，a computational fluid dynamics ( CFD) simulation was carried out with the singlephase thermal dispersion model． The effects of nanoparticle additions with different mass fractions on the heat transfer performance of molten salt were analyzed，and the heat transfer performance variations were discussed from the respect of the thermal physical properties of the fluid． Comparisons of results show that the thermal dispersion model can be used to simulate the heat transfer performance of molten salt-based nanofluids． Simulations show that the temperature inside the tube with various nanofluids is lower than that with pure molten salt，and the temperature drop is the most obvious with the particle concentration of 0. 063% ． The temperature distributions at the four sections show that under the wall heat flux boundary，the temperature of molten salt with or without nanoparticles increases radially，while the temperature of molten salt-based nanofluids is lower than that of the pure molten salt，indicating nanofluids absorb and take away more heat energy． Moreover，compared with that of pure molten salt，the heat transfer performance of molten salt-based nanofluids increases，proving that the nanoparticle additions can improve the heat transfer performance of molten salt． However，the improvement is not proportional to the increase of nanoparticle concentration． Instead，the nanofluids with a mass fraction of 0. 063% show the greatest heat transfer enhancement，and the heat transfer coefficient in the fully developed region is 6. 5% higher than that of pure molten salt． Finally，the drastic change of specific heat capacity is found playing a key role in the change of heat transfer performance through analyzing the physical properties of molten salt and molten salt-based nanofluids．

Speed Fluctuation Suppression Based on Adaptive Periodic Disturbance Observer for Inverter Compressor



MENG Fankun WEN Xiaoqin YOU Linru

2021, 49(2):  40-49.  doi:10.12141/j.issn.1000-565X.200323

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Inverter compressor operating in low frequency range shows apparent speed fluctuation． It is the periodic load torque disturbance that brings about speed offset． The poor performance of periodic load disturbance is caused by the small gain of disturbance observation ( DOB) ． To solve this problem，a periodic disturbance observer ( PDOB) was proposed to estimate load disturbance and compensate current in this paper and attenuate speed deviation in low frequency range． Load disturbance is compensated by PDOB based on internal model theorem，including fundamental and related harmonic components． Adaptive notch filter based on Steiglitz-McBride method was constructed to estimate the fundamental frequency of periodic disturbance． Experiments were carried out on inverter compressor platform and results show that speed fluctuation of can be effectively suppressed by the proposed method comparing with general DOB．

Traffic & Transportation Engineering

Analysis on the Degree of Support for Urban Central System from the Job-Housing Density in Ｒailroad Station Areas



WU Jiaorong XIE Jinhong LIU Mengyao

2021, 49(2):  50-58.  doi:10.12141/j.issn.1000-565X.200310

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As an important node that directly links the rail transit system to the urban space，the railroad station gathers the resident population and the employment in the surrounding area of the railroad station ( referred to as the station area) to support the optimization of urban spatial structure． This study used Shanghai data to analyze the gathering level of residential population and employment in rail station areas at different ring layers of the city and classified rail station areas into 2 major types ( the employment type and the residential type) ，8 small classes based on job-housing density levels． Considering the urban activity center system planning，urban main center—urban sub-center—regional center，in“Shanghai Urban Master Plan ( 2016-2035) ”，the degree of support for urban central system was proposed based on the job-housing density of the railroad station areas and the spatial coupling relationship between the railroad station and the urban central system． It is concluded that the gathering level of employment and residential population to suburban railroad stations is still in its infancy and the average job-housing density of the railroad station areas at several levels of city center is significantly different: urban main center ( 43 thousand per square meter) ＞ urban sub-center ( 15 thousand per square meter) ＞ regional center ( 13 thousand per square meter) ． Besides，38 sub-centers and regional centers with low supporting degree that need attention in subsequent urban renewal were identified． This study will provide a reference for the sustainable development of railroad station areas in the urban sub-center and regional center of the suburbs，and for the rationalization of suburban job-housing spatial relationship．

Study on a Simplified Activity-Based Model Framework Based on Stability of Travelers



CHEN Xianlong CHEN Xiaohong

2021, 49(2):  59-67.  doi:10.12141/j.issn.1000-565X.200259

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From the review of the transport model development trend in China and other countries，the limitations of both traditional four-step model and activity-based model，especially the shortcomings of the current transport models in explicating and extracting the stability properties of travelers to promote the accuracy of transport model， were summarized． Based on the opportunities and challenges brought with big data to transport model，the feasibility to solve these problems by using location-based services data was discussed． Considering that travel behaviors have stable endpoints-purpose property，this paper defined trip purpose classification which is different from the home-based or none home-based in the traditional four-step model，and developed a simplified activity-based model considering the fact that travelers have fixed house location，job locations ( school locations) and other basic daily live locations and the difference between stable trips and occasional trips． Furthermore，a new four-step model structure combined with trip generation and trip distribution was developed． Taking Huadu District of Guangzhou as an example，the results among a new simplified activity-based model，a traditional optimization model ( i. e. ，the standard gravity model) and a gravity model with K factors was comparatively analyzed． The results show that the optimization model can not reveal the stability attributes of the city，while the simplified activity-based model based on travelers’stability fits urban reality better． Besides，this paper sheds light on the possibility of more stability factors of travelers being introduced to the transport model in the future

Variation Laws and Influencing Factors of Heating Characteristics of Concrete Pavement with Wave Absorbing and Ice Melting



FAN Zhenyang, CHEN Bing, WANG Xuancang, et al

2021, 49(2):  68-78.  doi:10.12141/j.issn.1000-565X.200369

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In order to analyze the microwave ice melting rate，the properties of various kinds of absorbing aggregates and powders were analyzed to determine the concrete mix ratio of different materials and structures． Microwave heating test was carried out on various prepared concrete specimens of absorbing channel surface structure． By measuring the temperature change on the surface of the concrete specimen，the regularity of the influence of different factors on the temperature rise was analyzed，and the structure of the absorbing channel surface based on the law of the surface temperature rise was proposed． The results show that，the reduction of the waveguide opening distance can increase the temperature rise rate of the concrete specimen surface to a certain extent; the temperature rise rate of the bottom screen and free state wave-absorbing concrete specimens is significantly higher than that of the side screen and full screen state; the increase in the thickness of the part will cause the surface heating rate to decrease; the concrete surface absorbing heating rate decreases with the increase of the concrete moisture content; the absorbing surface structure has more efficient ice melting than the layered thin layer structure． Finally，3 typical absorber surface structures were recommended based on the surface heating characteristics．

Quantitative Analysis of the Diffusion Behavior of Ｒejuvenator in Aged Asphalt



MAO Yu, LI Ping, NIAN Tengfei, et al

2021, 49(2):  79-87.  doi:10.12141/j.issn.1000-565X.200359

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Ｒejuvenator adjusts the components of the aged asphalt through diffusion and miscibility，so as to restore its road performance and make it meet the application requirements． Therefore，the diffusion of rejuvenator is the main technical problem influencing the regeneration effect of aging asphalt． Firstly，an analysis method of rejuvenator diffusion coefficient was established by using Fourier transform infrared spectroscopy technique and taking the characteristic absorption peak area as the measurement standard． Then，using CTBN as a tracer，a self-designed diffusion test was used to quantitatively analyze the diffusion amount of the rejuvenator with the characteristic absorption peak intensity，and calculate the rejuvenator diffusion coefficient． The results show that the characteristic peak at 1739cm － 1 of the infrared spectrum of the rejuvenator change significantly after CTBN labeling，and the peak area shows a linear relationship with the change of CTBN content． The diffusion amount of rejuvenator in aged asphalt can be effectively reflected by establishing a standard curve． Taking the peak area ratio D1739 /D1458 as the measurement standard，the established theoretical analysis method of the rejuvenator diffusion coefficient has certain reliability． The diffusion coefficient is closely related to the concentration change，and can effectively reflect the degree of aging asphalt regeneration． The diffusion coefficient and the cumulative diffusion amount are proportional to the temperature change，and the growth rate of the two is basically the same． The diffusion rate at the same temperature shows a decreasing trend with the increase of the vertical depth． It is consistent with the change trend of the rejuvenator diffusion amount，and is in compliance with Fick’s second law．

Fluid Power & Electromechanical Control Engineering

Application and Technology Prospects of Hydrodynamic-Magnetic Compound Support for Axial Piston Pump



JIANG Jihai DU Boran ZHANG Jian

2021, 49(2):  88-98,109.  doi:10.12141/j.issn.1000-565X.200428

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Firstly，the development background and research significance of axial piston pump were described，and friction pair was pointed out as the key factor to restrict the development of axial piston pump． Then the research status of friction pair of axial piston pump at home and broad and the problems in current research were summarized． After that，the technical background，principle，development and application prospect of hydrodynamic-magnetic compound support ( HMCS) applied in axial piston pump was introduced． It was showed that the successful application of HMCS in axial piston pump can solve the difficult problems in traditional piston pump technology． Finally，the key technologies and research difficulties faced by the realization of the hydrodynamic-magnetic compound support were prospected，and the relevant research achievements that are helpful to conquer the key technologies were summarized． The hydrodynamic-magnetic compound support is of great theoretical significance and practical application value for the axial piston pump with high reliability and low viscosity medium using．

Modeling and Analysis of Oil Film Lubrication Characteristics of Valve-Plate Pair in Axial Piston Motor



HOU Liang, LAI Weiqun, CUI Kai, et al

2021, 49(2):  99-109,139.  doi:10.12141/j.issn.1000-565X.200636

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The working performance and stability of the axial piston motor are significantly affected by the frictional lubrication characteristics of the valve-plate pair． Considering the oil film pressure distribution and moment action of the auxiliary support belt with surface veins，this study established the oil film dynamic model of the valve-plate pair，and analyzed the change rules of the flow leakage and friction loss of the valve-plate pair under different working pressure，working speed and swash plate angle． The research results show that the leakage flow of the valveplate pair of the axial piston motor increases approximately linearly with the increase of speed，and the increase rate decreases with the increase of pressure． At the same time，the viscous-friction torque of oil film increases with the increase of the rotational speed and pressure，and there is an approximate linear relationship between the friction torque and the rotating speed． The leakage flow and the thickness of the central film decrease with the increase of the inclined angle of the swash plate，while the friction torque increases with the increase of the inclined angle．

Fault Diagnosis Method of Piston Pump in Construction Machinery under Variable Load Condition



TANG Hongbin, FU Zheng, DENG Xishu, et al

2021, 49(2):  110-119.  doi:10.12141/j.issn.1000-565X.200448

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Piston pump is the power source and key component of hydraulic system in construction machinery． Its working status and service performance directly affect the construction quality and operation safety of the construction machinery． Aiming at the harsh working environment and the variable load working condition of the piston pump，different severity levels of loose slipper faults were simulated based on the virtual prototype model of piston pump． The dynamic responses of the piston pump under different loading and structural health conditions were investigated through simulated analysis． And a fault diagnosis method of piston pump in construction machinery under variable load condition was proposed in this paper． According to the method，the axial vibration signal of piston pump is collected at first． Then the vibration signal is divided into several equal parts and the ＲMS of each segmented signal is calculated． At last，the loose slipper failure can be detected based on the gradient of the ＲMS trend line． The experimental results show that the proposed method can effectively detect the loose slipper of piston pump in construction machinery under variable load working condition．

Experiment and Numerical Analysis of Temperature Distribution of Hydraulic Valve Orifice Based on Embedded Miniature Thermocouple



CHEN Qianpeng, JI Hong, ZHAO Jing, et al

2021, 49(2):  120-130.  doi:10.12141/j.issn.1000-565X.200610

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Viscous heating of valve orifice not only wastes energy but also causes thermal deformation． It increases the risk of spool clamping and exerts a strong impact on the stability and safety of hydraulic machines． A deep research on the temperature distribution of valve orifice is the foundation of accuracy prediction of thermal deformation，so a temperature measurement method was put forward by embedding miniature thermocouples in different locations of the planar valve orifice． The experiments were conducted with the valve opening x ranges from 1 mm to 3 mm and inlet pressure pin ranges from 0. 5MPa to 3MPa． The results show that the valve orifice temperature rises with the increase of the inlet pressure; the heating rate can reach 0. 79 ℃ /min when x = 2 mm and pin = 3. 0 MPa; the temperature of valve orifice caused by viscous heating distributes unevenly，and the temperature gradient seems more sensitive to pressure drop under a small orifice． The maximum temperature difference of valve orifice can reach 7. 86 ℃ when x = 1 mm and pin = 3. 0MPa． In most cases，the sharp edge of the valve orifice is likely to generate a higher temperature，which can reach 72. 9 ℃ after heating 110 min under 3. 0 MPa． However，a higher temperature will also appear along the vertical edge under a larger valve opening or a higher pressure drop． To analyze the phenomenon，a comprehensive analysis was carried out by combining fluid-solid-heat coupling module and mixture multiphase flow model in ANSYS Fluent software． The results show that the vortex and cavitation have a strong impact on the temperature distribution in the wall of the valve orifice．

Cooperative Optimization Design of Pilot Valve Parameters for CDC Shock Absorber



XIE Fangwei, XU Chunjie, WAN Kuaidi, et al

2021, 49(2):  131-139.  doi:10.12141/j.issn.1000-565X.200599

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The mathematical model of electromagnetic field and electromagnetic force of the continuous damping control shock absorber’s pilot valve was established on the basis of electromagnetic theory． The appropriate pilot valve material was selected based on the magnetic circuit analysis，and the rationality of the material selection was verified by the magnetic field distribution of the pilot valve which was obtained through simulation． The influence of various structural parameters on the electromagnetic force was analyzed by simulation，and the structural parameters of the pilot valve with greater influence on electromagnetic force were obtained by variance analysis method． Furthermore，the optimized parameter combination scheme was obtained through collaborative optimization for the selected parameters which was carried out with the orthogonal experiment method． The results show that the electromagnet has better constant force characteristics when D2 = 12. 6 mm，δ4 = 0. 25 mm，L2 = 4 mm．

Performance of Magnetorheological Damper with Shear-Extrusion Hybrid Mode



CHEN Shumei, TANG Hongjan, HUANG Hui, et al

2021, 49(2):  140-150.  doi:10.12141/j.issn.1000-565X.200620

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The magnetorheological damper is a kind of intelligent semi-active vibration damping device with good prospects，but the current magnetorheological dampers mostly use shear valves as the working mode． The vibration damping effect of this type of damper is poor when used in hydraulic mechanical legs，press leveling and other areas due to the insufficient output force caused by the size of the structure． In this paper，a shear-extrusion hybrid mode magnetorheological damper was designed to solve the problem，and a full-channel magnetic circuit structure was used to replace the traditional magnetic circuit structure to increase the maximum output and dynamic range． This research carried out the structure design and principle analysis of the new magnetorheological damper，established the mechanical model，simulated the magnetic field，and made optimization on the structure． The superiority of the new magnetorheological damper was proved by the prototype test． The above tests and simulations show that the damping force of the new magnetorheological damper can be up to 1065N in the shear valve type and 4939N in the squeeze type． Especially，when the piston coil is fed with reverse current，the magnetic induction intensity of the new damper in the piston damping channel is all above 0. 2 T，while the magnetic induction intensity of the traditional damper only nearly 40% reaches 0. 2 T． When set the current in the same direction，the magnetic induction intensity of the new damper more than 80% can reaches 0. 3T，while the damping channel of the traditional damper only nearly 40% reach 0. 3T． Compared with the traditional magnetorheological damper，the shear-extrusion hybrid mode magnetorheological damper has a larger output value and a higher dynamic adjustable coefficient．

Design and Experiments of Spherical Magnetic Actuated Ｒobot Based on Magnetorheological Fluid 



HUA Dezheng, LIU Xinhua, ZHAO Xin, et al

2021, 49(2):  151-160.  doi:10.12141/j.issn.1000-565X.200608

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For the problem that NdFeB permanent magnet is brittle and has moulding difficulties in making micro structure，magnetorheological fluid was used as the actuated material for the micro magnetic robot，and a spherical robot for targeted drug delivery in human stomach was designed． According to the rheological principle of magnetorheological fluid，the mechanical relationship of magnetic particles in magnetic field was analyzed，and the dynamic model of spherical robot was established and simulated． The magnetic robot motion image acquisition system was built and robot displacement was calculated with Hough transform circle detection algorithm． Finally，a prototype robot was made and its motion characteristics were tested on an experimental platform with space magnetic field． Ｒesults show that the spherical actuated robot based on magnetorheological fluid is easy to control and its motion is stable and reliable.