Table of Content

25 January 2019, Volume 47 Issue 1

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Mechanical Engineering

Resonant Soft Switching Plasma Power Supply Based on SiC MOSFET

WANG Zhenmin WU Jianwen FAN Wenyan YE Chunxian

2019, 47(1):  1-6.  doi:10.12141/j.issn.1000-565x.180311

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SiC MOSFET can simplify circuit topology and improve power density and efficiency of power supply． A full bridge resonant converter using a new SiC power device was proposed to promote the upgrading of high-power plasma power supply． The main circuit of the resonant converter adopts LLC Zero Voltage Switching ( ZVS) topology，which can enlarge the frequency range of resonant commutation to 260 ～ 310 kHz． The rated output power of the designed full bridge LLC ZVS resonant converter prototype is 8kW and the output voltage is 270V． The driving performance，commutation process，temperature rise and efficiency of the 8kW SiC MOSFET full-bridge LLC ZVS resonant converter prototype were tested． The results show that the developed resonant soft-switching plasma power supply is of good performance and high reliability，and both its efficiency and power density are better than those of the traditional LLC resonant converter using Si MOSFET． 

Friction Behavior of Carbon Fiber Forged Composite

 

LU Longsheng FANG-HE Zhengzi XIE Yingxi SUN Jiawei WAN Zhenping

2019, 47(1):  7-13.  doi:10.12141/j.issn.1000-565x.180331

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Carbon fibre forged composite ( CFFC) with epoxy matrix was prepared with moulding pressing technology． The friction performance of the CFFC under dry and water-lubricated friction conditions were comparatively investigated． The variations of the friction coefficient under these two friction conditions were studied，and the micro wear mechanism of the CFFC was analyzed． Ｒesults show that the friction process of CFFC exhibits different trends under these two conditions． The friction process in dry friction can be divided into three stages，including an initial stability stage，a transfer film formation stage and a stabilization stage，during which an iron-containing transfer film possesses a self-lubricating effect． While in water-lubricated friction，the friction behaviour of CFFC is dominated by a water-lubricated film，which could help its friction process rapidly develop into the stabilization stage． A smaller friction coefficient and a lower and more stable wear rate of CFFC are obtained under the water-lubricated friction condition． In addition，the reduction rates of friction coefficient are basically the same under two friction conditions． 

Current Ｒesearch on the Application of Slip Line Field Theory in the Orthogonal Cutting Process

 

SHI Hongyan ZHAO Xianfeng JIANG Xueting

2019, 47(1):  14-31.  doi:10.12141/j.issn.1000-565x.180133

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 Cutting is a complex process involving many mechanical phenomena such as elastic deformation，plastic deformation，fracture，shear，impact and thermal field etc． Slip-line field theory is an effective mechanical tool for analyzing orthogonal cutting process． So far，many classical slip-line field models of orthogonal cutting at low and medium speeds have been established by scholars at home and abroad． Those models provide theoretical support for optimizing the cutting process parameters and guiding the cutting process． But with the development of high-speed cutting and micro-cutting，the current models cannot fully explain many physical phenomena in the cutting process． Therefore，the slip-line field models of orthogonal cutting in the past 70 years were reviewed，and the preconditions and applications of the models were analyzed and compared． The characteristics and disadvantages of various models were summarized． The slip line field models including uniform slip line field，non-uniform slip line field，free contact slip line field，restricted contact slip line field，slip line field in the transition zone between chip and work piece，blunt and circular slip line field of cutter，edge wear ( negative chamfering) slip line field，etc． were summarized． The future development of orthogonal cutting slip line field model was discussed， and laid a foundation for establishing orthogonal cutting slip line field model under the high speed cutting and micro cutting conditions． 

Design and Manufacturing Technology of Flexspline's Spatial Tooth Profile in Harmonic Drive

 

WU Shangsheng SUN Hanlei YANG Qi

2019, 47(1):  32-38,85.  doi:10.12141/j.issn.1000-565x.180309

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After the analysis of the defects of traditional conjugate tooth profile design method，the traditional spatial tooth profile design method was optimized and improved in order to eliminate the disadvantageous effect of“cup opening angle”on harmonic drive after flexspline assembly，and the design method of the inclined adjustment of the wall thickness of the flexspline gear ring was put forward． For the design method of the inward inclination adjustment of the wall thickness of the flexspline gear ring，the manufacturing technology scheme of continuous cutting of flexspline tooth profile was put forward，the special fixture was designed，and the experimental trial production was made． The results show that，compared with the conventional flexspline tooth profile design model，the flexspline of the new spatial tooth profile does not interfere with the rigid wheel after assembly． The assembly stress is reduced by 50. 2% and the meshing area is increased by 7. 6%，the maximum process deviation of tooth profile is far less than the machining accuracy of the equipment． The experimental results are consistent with the theoretical analysis，so the feasibility of the method is verified． 

Architecture & Civil Engineering

Simulation Analysis of Shaft Space's Influence on Hospital Building Ventilation

 

GUO Haoxu YI Changwen DENG Mengren

2019, 47(1):  39-47.  doi:10.12141/j.issn.1000-565x.180152

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Hospital buildings require better indoor air quality and greater fresh air volume compared to other types of public buildings． Andmechanical ventilation needs large energy consumption． For Lingnan area，the indoor natural ventilation of shaft space can be well utilized by hospital buildings． The method is both environmental and energy saving． Taking hospital buildings in Lingnan for example，a computing model based on the layout of the shaft space set was built，and the wind environment during transitional seasons was analyzed by using CFD technology． The results show that the rational spatial orientation and the relative position relations of the shaft setting can improve the ventilation comfort and uniformity of hospital buildings． Even without mechanical ventilation，it can help keep human body comfortable in ventilated environment． Proper shaft space setting can effectively shorten the medical streamline，and make full use of the building land． The reasonable implantation of shaft space is also conducive to shading，which is an effective means to solve the ventilation and lighting problems between new and old buildings in the process of expansion． 

Static Tensile Behavior of Half Grout Sleeve Splicing of Rebars Under High Temperature

 

ZHANG Wangxi DENG Xi HE Chao

2019, 47(1):  48-55.  doi:10.12141/j.issn.1000-565x.180107

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 The static tensile test was carried out for 12 half grout sleeve splicing of rebars specimens under high temperature，and 12 steel bars in the same batch were tested as control group under the same conditions． The influence of the temperature on the specimens and the mechanical property difference between the specimens and the steel bars under high temperature were studied． The test results show that the ultimate tensile strength of the specimens is similar to that of the steel bar under high temperature，and the failure modes of the specimens are the tensile rupture of rebars and the pulling-out of rebars． The tensile behaviors of the specimens are similar to the constitutive relations of uniaxial tension of the steel bars at temperatures of 200℃ and below，while the mechanical properties of the specimens is different from those of the steel rebars at temperatures of 400℃ and above． The failure modes of the specimens at room temperature and 400℃ are both tensile rupture of rebars． At 600℃，the rebars of the specimens may be pulled out first，rather than be ruptured． 

Reliability Verification for Seismic Capacity Utilization Factors of Structure

 

ZENG Fanliang HUANG Yansheng ZHOU Jing

2019, 47(1):  56-63.  doi:10.12141/j.issn.1000-565x.170496

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The seismic performance design of Guangdong local code Technical Specification for Concrete Structures of Tall Building ( DBJ15-92—2013) was improved based on current national earthquake resistant design code． The elements' bearing capacity was designed according to the earthquake force of inter-mediate earthquake and the ductility of elements measured by the capacity utilization factors． First-order Second-moment Method ( FOSM) was employed to verify the reliability of the new earthquake resistant capacity equation． And the influence of many factors，such as the ratio of load ( the ratio of seismic force to gravity) ，performance levels，and precautionary intensity and element types，on the reliability were evaluated． The results show that under the same performance level， the reliability index and the reliable probability of elements conform to the rule: compression members ＞ shear members ＞ flexural members ＞ tension members． This rule satisfies the“strong shear weak bending”design conception． The ratio of load and the index of component importance coefficient have a great impact on the reliability， but the fortification intensity has a small influence． 

Fragility Analysis of High-pier and Long-span Continuous Rigid Frame Bridge Based on Double Effects of the Actual Site and Collision

 

ZHAO Jingang JIA Hongyu LI Xi ZHAN Yulin LI Lanping

2019, 47(1):  64-74.  doi:10.12141/j.issn.1000-565x.180166

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The influence of the double effects of actual site and collision on the fragility of high-pier and long-span continuous rigid frame bridge was studied． A real high-pier and long-span continuous rigid frame bridge was taken as the research object，and some finite element models of the bridge were built for the various separation distances between deck and abutment based on the OpenSees software． And the bedrock seismic waves were converted into surface seismic waves according to the filtration of actual soil characteristics at the bridge location for incremental dynamic analysis ( multi-support excitation) ． The results were compared with the structural responses which do not consider the effect of actual soil filtration ( uniform excitation) ． The results show that with the increase of the width of expansion joint，the damage probability of Pier 2# ( second highest pier) under the uniform excitation is gradually becoming larger than that of multi-support excitation with the maximum difference of 0. 28． The collision effect reduces the damage probability of Pier 3# ( the highest pier) ，and the uniform excitation method underestimates the damage probability of Pier 3# in each damage stage，with an underestimation up to 0. 35． With the increase of peak acceleration of bedrock seismic wave，the probability demand value of displacement ductility coefficient of Pier 2# under the uniform excitation is gradually growing larger than that of the multi-support excitation，while the probability demand values of displacement ductility coefficient of Pier 3# under multi-support excitation are all larger than those of uniform excitation． The influence of the double effect of actual site and collision on the fragility of bridge structures depends on the heights of piers of long-span continuous rigid-frame bridge，so it should be considered synthetically in seismic design of bridge． 

Experimental Study on the Bending Capacity of Castellated Composite Beam Under Negative Moment

 

MA Hongwei LIU Weiya LIN Lang YUAN Jialiang

2019, 47(1):  75-85.  doi:10.12141/j.issn.1000-565x.180125

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Castellated composite beam can decrease the floor height of buildings． In order to investigate the bending capacity of castellated composite beam under negative moment，two cantilever beam specimens were designed and tested by applying static loads． The influences of the expansion ratio and location of first web opening on beam mechanical behavior were studied． The results show that bending failures of the specimens occur near the beam support section or the first web opening section for the specimens with the expansion ratio no larger than 1. 3． When the expansion ratio of specimens is maintained unchanged，the location of the first web opening mainly affects on the failure mode of the beam． For both the beam support section and the first web opening section being the strength control section，the expansion ratio of specimens have greatly effect on the strength and stiffness of the beam． Considering both the failure modes and the flexural capacity of two control sections，the method calculating the nominal bending capacity of the castellated composite beam near the support section were presented，and the calculated values fit well with the experimental ones． 

Power & Electrical Engineering

Performance Study of Free Piston Expander-linear Generator

 

ZHANG Hongguang ZHANG Mengru HOU Xiaochen XU Yonghong ZHAO Tenglong LI Jian

2019, 47(1):  86-94.  doi:10.12141/j.issn.1000-565x.180223

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 A new free piston expander-linear generator ( FPE-LG) prototype for small-scale organic Ｒankine cycle ( OＲC) waste heat recovery system was developed，and a new valve train was designed to control the intake and exhaust process of working fluid． The motion characteristics，output performance and indicated efficiency of the FPE-LG were investigated based on a compressed air test rig． The results show that the intake duration and exhaust duration have a great influence on the motion characteristics and output performance of the FPE-LG． The stroke and velocity of free piston assembly increase with the increase of the intake duration，and decrease with the decrease of the exhaust duration． the valve timing optimization can significantly improve the output power of linear generator． The maximum value of voltage is 13 V and the maximum value of peak power is 18. 6 W when the intake angle is 60°and the exhaust angle is 180°，and the intake pressure，operating frequency and the external load resistance are 1. 9 ×105 Pa、2 Hz and 9 Ω，respectively． The velocity and stroke of the free piston assembly show an increasing tendency，and higher peak voltage and power output，when the external load resistance increases． The indicated efficiency shows a downward tendency when the external load resistance increases． The indicated efficiency is 66. 2% when the external load resistance，operating frequency and the intake pressure are 3 Ω、3 Hz and 1. 9 ×105 Pa，respectively． 

Hybrid Hydro-mechanical Continuously Variable Transmission Technology for Wind Power System

 

HUANG Guoqin LUO Shaqi HU Bo YU Jin

2019, 47(1):  95-102.  doi:10.12141/j.issn.1000-565x.180237

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A wind power generation system design based on power-split type Hydro-mechanical continuously variable transmission ( HMCVT) was proposed，aiming at the problem of variable speed constant frequency ( VSCF) in wind power generation system． The system combines high-power density and stepless speed regulation in hydraulic circuit and high efficiency in mechanical circuit by means of power-split． Firstly，the static speed regulation and efficiency characteristics were analyzed theoretically on the premise of variable speed input and constant speed output． Secondly，modeling，dynamic simulation and analysis were carried out for the HMCVT wind power system by Matlab/Simulink，combining with the practical working conditions． Additionally，the controller based on fuzzy PID was established，which enabled it to control the output speed rapidly and accurately． Finally，the speed regulation characteristics of the transmission prototype was investigated on the comprehensive test platform． The simulation and experimental results show that the HMCVT technology provides a solution to VSCF problem for wind power generation system between the wind speed range of cut-in and cut-out． Moreover，it has swift dynamic property with the efficiency around 87%． 

Research and Implementation of Micro-grid's Dynamic Reconfiguration Strategy

 

CHEN Yuanrui LIN Wei WANG Qiaoqiao LIU Junfeng ZENG Jun

2019, 47(1):  103-111.  doi:10.12141/j.issn.1000-565x.180227

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 Micro-grid is an advanced application to utilize distributed renewable energy． Due to the randomness and intermittency of renewable energy and the environmental uncertainty，it is important to seek an effective dynamic reconfiguration strategy to ensure the efficient and stable operation of micro-grid． To solve the problem of micro-grid energy management，a dynamic reconfiguration strategy was proposed for micro-grid architecture based on the multi-agent system ( MAS) technology． Firstly，the mathematic model of micro-grid aiming at a maximum economic benefit is built based on the analysis of the excitation conditions and basic characteristics of micro-grid's reconfiguration． Secondly，the micro-grid energy management system ( MEMS) based on MAS and the potential game algorithm introduced as the core optimization algorithm is built based on the self-benefit maximization of distributed power supply． It realized the dynamic reconfiguration of micro-grid through the interaction of each agent． Potential game has excellent distributed characteristics that realize absolute distributed dynamic reconfiguration by combining topology with core optimization algorithm． Finally，simulation verification was carried out by an example of islanded micro-grid． Simulation results show that micro-grid can realize effectivelly dynamic reconfiguration while ensuring that individuals have sufficient autonomy and independent decision-making ability． Simulation results also verify the validity of the proposed methods． 

Modeling and Performance Testing of Aluminum Non-contact Thermal Resistance Condensers

 

WAN Rui WANG Yichun Revaz Kavtaradze JIA Runze

2019, 47(1):  112-119.  doi:10.12141/j.issn.1000-565x.180135

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 The steady state calculation model of aluminum non-contact thermal resistance condensers for air conditioning system was established by using distributed parameter method，and the performance of the all-aluminum non-contact thermal resistance condensers was tested with air enthalpy method． The calculation accuracy of the numerical model is verified by comparison with the experimental results． The results show that，under the same working conditions，the maximum error of heat exchange of the condenser is 4. 8%，and the maximum error of air side pressure drop is 6. 7%． The influence of condenser structure on its heat exchange performance and pressure drop was analyzed，and the comprehensive performance factor ε was employed to study the influence both of the heat exchange and the pressure drop of the air side on the performance of the condenser． The results show that the heat exchange capacity of the aluminum condenser decreases with the increase of the inner flow channel width b'; the heat exchange capacity of the aluminum condenser increases with the increase of the finned tube number n; the heat exchange capacity of the aluminum condenser increases with the increase of the finned tube width a; when the finned tube width a is 40 mm，the finned tube number n is 22，and the inner flow channel width b' is 1. 4 mm，the condenser's heat exchange reaches the maximum，3423. 2W，and the air pressure drop is 19. 15Pa; the heat exchange coefficient of the aluminum condenser increases first and then decreases with the increase of the finned tube width a，and the maximum value is obtained when the finned tube width a is 38 mm; the heat exchange coefficient increases with the increase of finned tube number n; the overall performance factor ε of the condenser increases first and then decreases with the increase of the finned tube width a，and increases with the increase of the finned tube number n． 

Heat Dissipation Characteristics of Plate-fin Heat Exchanger with Internal Flow Channel

 

CAI Huikun WENG Zeju LIAO Yidai SU Lijun

2019, 47(1):  120-126,144.  doi:10.12141/j.issn.1000-565x.180386

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Currently，little study has been carried out on the plate-fin heat exchanger with internal flow channel， and its heat dissipation power cannot be calculated accurately as its boundary conditions are be over-simplified． Therefore，a simulation analysis model of plate-fin heat exchanger with internal flow channel and a small wind tunnel experimental system was developed based on the interactions of cooling air，hot fluid and heat exchanger． The results show that，under the cooling conditions of 1m/s air speed and 25℃air inlet temperature，the heat dissipation power increases with mass volume of hot fluid，and will be stable after the mass volume reaches 3 L/min． The maximum deviation between the numerical analysis results and the experimental results is less than 5%． After validation，the effect of flow channel level on heat dissipation performance was investigated． The result shows that the heat exchanger with four-level internal flow channel is of best efficiency and temperature uniformity，but its highest temperature in internal flow channel is still lower than that of hot fluid inlet temperature 22 K，which demonstrates the necessity to take the interactions of cooling air，hot fluid and heat exchanger into consideration in simulation analysis． 

Behavioral Characteristics of Bubble Collision with Different Extremely Humid Surfaces

 

JI Xianbing DAI Chao WANG Ye Xu Jinliang

2019, 47(1):  127-134.  doi:10.12141/j.issn.1000-565x.180069

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Three types of surfaces，namely superhydrophilic，low adhesive superhydrophobic and high adhesive superhydrophobic surfaces，were prepared to improve the functionality of the extremely humid surfaces． The behavioral characteristics of bubble collision with different extremely humid surfaces under different rising heights were studied by using high-speed camera． The bubble diameters are 2. 16，2. 59 and 3. 32 mm，respectively． The results show that surface wettability，bubble rising height ( L) and bubble diameter ( D) have important influences on bubble's behavioral characteristics． The bubble stable state is mainly affected by microstructure and surface tension． When bubbles collide with low adhesive surface，bubbles will initially vibrate or bounce，then spread and form a layer of gas film on the surface at last． When bubbles collide with superhydrophilic and high adhesive surfaces，bubbles will also firstly vibrate or bounce，and finally stay on the surfaces with a ball-lacking shape． As bubble collision velocity is large，the bubble can all rebound on the three types of surfaces． With the increasing L， the initial jump height ( h1) increases first and then decreases on three types of surfaces，and they reach the maximum value at L =13. 6 mm，which are 6. 05，5. 53 and 4. 37 mm，respectively． As to the low adhesive superhydrophobic surface，due to the energy dissipation of bubble increases during the collision process，both h1 and the time of bubble spreading decrease with the increasing D． 

Energy-saving Optimization Operation of Central Air-conditioning System Based on Double-DQN Algorithm

 

YAN Junwei HUANG Qi ZHOU Xuan

2019, 47(1):  135-144.  doi:10.12141/j.issn.1000-565x.180330

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A method about energy-saving optimization operation of central air-conditioning system based on adaptive modeling and self-learning was proposed to solve the difficulties of mechanism modeling and parameters identification． The Markov decision process model of air-conditioning system was designed and the reinforcement learning algorithm with dual neural network structure was used to solve the curse of dimensionality and overestimation of value function during the learning process． A TＲNSYS simulation platform based on the central air-conditioning system of an office building in Guangzhou was built and the effectiveness of the algorithm was validated． The simulation results show that under the premise of meeting the indoor thermal comfort requirement，the energy-saving optimization operation of the system is realized with the goal of minimizing the energy consumption． Compared with PID control and single neural network reinforcement learning control，the total energy consumption of the system is reduced by 5. 36% and 1. 64%，the proportion of total uncomfortable time is decreased by 2. 32% and 1. 37%，respectively． The reinforcement learning controller proposed can effectively solve the overestimation problem． It has good robustness，self-adaption optimization capability and better energy-saving effect，and it can provide new ideas for building energy efficiency．