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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3305-3315页

作者： junhui Peng Huiren Hu junhui zhang National Engineering Research Center of Highway Maintenance Technology Changsha University of Science and TechnologyChangsha410114China

The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.

关键词： Subgrade soil Soil–water characteristic curve(SWCC) Overburden stress Degree of compaction Prediction mode

An improved creep model for unsaturated reticulated red clay

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第11期16卷 4754-4768页

作者： Chuang zhang junhui zhang Jianzhong Li Key Laboratory of Special Environment Road Engineering of Hunan Province Changsha University of Science and TechnologyChangsha410114China School of Traffic and Transportation Engineering Changsha University of Science and TechnologyChangsha410114China Department of Architecture and Civil Engineering City University of Hong KongChina School of Geosciences and Info-Physics Central South UniversityChangsha410083China

Establishment of a creep model is an important method to analyze the relationship between soil creep deformation and time,and the element model is widely used for studying soil ***,the element creep model is employed for fitting saturated soil,and the mechanical element model is generally linear,which cannot well fit the nonlinear deformation of the soil with time in *** creep process of the soil is not only time-dependent,but also related to the deviatoric stress ***,the fractional calculus theory and a parameter n reflecting the effect of deviatoric stress level on the creep properties of the soil were introduced into the element model,and the fractional qBurgers creep model was established by using the fractional Koeller dashpot and Caputo fractional *** proposed model was used to fit the triaxial test data of reticulated red clay under different net confining pressures and matric suctions by unsaturated triaxial *** proposed model can well describe the nonlinearity of unsaturated reticulated red clay,has memory and global correlation to the creep development process of unsaturated reticulated red clay,and has clear physical *** functional relationships of the model parameters with the matric suction,net confining pressure and deviatoric stress level were deduced,so that the creep curves of unsaturated reticulated red clay can be obtained for any conditions,which is of great value for the study of unsaturated soils.

关键词： Fractional calculus Creep model Burgers Parameter study Unsaturated reticulated red clay

Impact of Typical Steady-state Conditions and Transient Conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

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Chinese Journal of Mechanical Engineering 2015年第5期28卷 1012-1022页

作者： XU Bing HU Min zhang junhui State Key Laboratory of Fluid Power Transmission and Control Zhejiang University

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy o

关键词： axial piston pump flow ripple test accuracy steady-state condition transient condition wide operating ranges

Structural dynamic responses of a stripped solar sail subjected to solar radiation pressure

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Chinese Journal of Aeronautics 2020年第8期33卷 2204-2211页

作者： junhui zhang Na WU An TONG Yinghua LIU School of Civil Engineering North China University of TechnologyBeijing 100144China School of Aerospace Engineering Tsinghua UniversityBeijing 100144China

The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural *** this paper,the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in *** the coupling effects between booms and membrane strips,an exact and semianalytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is *** case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic *** prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic *** thickness of the boom will benefit to stability of the sail and reduce the resonant *** proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail.

关键词： Distributed transfer function method Frequency response Solar radiation pressure Solar sail Structural dynamic response

Analysis of the cylinder block tilting inertia moment and its effect on the performance of high-speed electro-hydrostatic actuator pumps of aircraft

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Chinese Journal of Aeronautics 2018年第1期31卷 169-177页

作者： junhui zhang Qun CHAO Bing XU State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University

Electro-hydrostatic actuator （EHA） pumps are usually characterized as high speed and small displacement. The tilting inertia moment on the cylinder block produced by the inertia forces of piston/slipper assemblies cannot be ignored when analyzing the cylinder block balance. A large tilting inertia moment will make the cylinder block tilt away from the valve plate, resulting in severe wear and significantly increased leakage. This paper presents an analytical expression for the tilting inertia moment on the cylinder block by means of vector analysis. In addition, a high-speed test rig was built up, and experiments on an EHA pump prototype were carried out at high speeds of up to 10,000 r/min. The predicted nature of the cylinder block tilt at high speeds corresponds closely to the witness marks on the dismantled EHA pump prototype, It is suggested that more attention should be given to the tilting inertia moment acting on the cylinder block of an EHA pump since both wear and leakage flow between the cylinder block and the valve plate are very much dependent on this tilting moment.

关键词： Aircraft pump Cylinder block High speed Inertia moment Leakage Wear

Investigation on the Radial Micro-motion about Piston of Axial Piston Pump

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Chinese Journal of Mechanical Engineering 2013年第2期26卷 325-333页

作者： XU Bing zhang junhui YANG Huayong zhang Bin State Key Laboratory of Fluid Power Transmission and Control Zhejiang University

The limit working parameters and service life of axial piston pump are determined by the carrying ability and lubrication characteristic of its key friction pairs. Therefore, the design and optimization of the key friction pairs are always a key and difficult problem in the research on axial piston pump. In the traditional research on piston/cylinder pair, the assembly relationship of piston and cylinder bore is simplified into ideal cylindrical pair, which can not be used to analyze the influences of radial micro-motion of piston on the distribution characteristics of oil-film thickness and pressure in details. In this paper, based on the lubrication theory of the oil film, a numerical simulation model is built, taking the influences of roughness, elastic deformation of piston and pressure-viscosity effect into consideration. With the simulation model, the dynamic characteristics of the radial micro-motion and pressure distribution are analyzed, and the relationships between radial micro-motion and carrying ability, lubrication condition, and abrasion are discussed. Furthermore, a model pump for pressure distribution measurement of oil film between piston and cylinder bore is designed. The comparison of simulation and experimental results of pressure distribution shows that the simulation model has high accuracy. The experiment and simulation results demonstrate that the pressure distribution has peak values that are much higher than the boundary pressure in the piston chamber due to the radial micro-motion, and the abrasion of piston takes place mainly on the hand close to piston ball. In addition, improvement of manufacturing roundness and straightness of piston and cylinder bore is helpful to improve the carrying ability of piston/cylinder pair. The proposed research provides references for designing piston/cylinder pair, and helps to prolong the service life of axial piston pump.

关键词： axial piston pump piston/cylinder pair micro motion carrying ability

Influence of Piston Number on Churning Losses in Axial Piston Pumps

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Chinese Journal of Mechanical Engineering 2022年第5期35卷 194-207页

作者： Ying Li Xing Chen Hao Luo junhui zhang Jin zhang School of Mechanical Engineering Yanshan UniversityQinhuangdao 066004China State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027China

Raising the rotational speed of an axial piston pump is useful for improving its power density;however,the churning losses of the piston increase significantly with increasing speed,and this reduces the performance and efficiency of the axial piston ***,there has been some research on the churning losses of pistons;however,it has rarely been analyzed from the perspective of the piston *** improve the performance and efficiency of the axial piston pump,a computational fluid dynamics(CFD)simulation model of the churning loss was established,and the effect of piston number on the churning loss was studied in *** simulation analysis results revealed that the churning losses initially increased as the number of pistons increased;however,when the number of pistons increased from six to nine,the torque of the churning losses decreased because of the hydrodynamic shadowing *** addition,in the analysis of cavitation results,it was determined that the cavitation area of the axial piston pump was mainly concentrated around the piston,and the cavitation became increasingly severe as the speed *** comparing the simulation results with and without the cavitation model,it was observed that the cavitation phenomenon is beneficial for the reduction of churning *** this study,a piston churning loss test rig that can eliminate other friction losses was established to verify the accuracy of the simulation results.A comparative analysis indicated that the simulation results were consistent with the actual *** addition,this study also conducted a simulation study on seven and nine piston pumps with the same *** simulation results revealed that churning losses of the seven pistons were generally greater than those of the nine pistons under the same *** addition,regarding the same piston number and displacement,reducing the pitch circle radius of piston bores is effective in reducing the churning *** resea

关键词： Axial piston pumps Churning losses Pistons CFD simulations Experimental study

Investigation on structural optimization of anti-overturning slipper of axial piston pump

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Science China(Technological Sciences) 2012年第11期55卷 3010-3018页

作者： XU Bing zhang junhui YANG HuaYong State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027China

Improving the carrying ability of oil film between slipper and swash plate and reducing the partial abrasion of slipper are important to improve the service life and reliability of axial piston *** this paper,a numerical simulation model was developed for slipper/swash-plate friction pair based on the elastohydrodynamic *** dynamic micro-motion and pressure distribution of slipper were analyzed and it was pointed out that the tilt of slipper was the main reason for its partial *** simulations about the slippers with different slopes on the outer edge of the sealing belt showed that the partial abrasion could reduce the carrying ability and increase the leakage of the slipper/swash-plate *** proper slope on the inner edge helped to improve the carrying ability and reduce the leakage of *** experimental tests were in accord with the simulation results to a great extent,showing that the simulation model had a high accuracy and could be applied to the design and optimization of slipper,and that the slipper with optimal inner slope provided an encouraging method to improve the efficiency and reliability of axial piston pump.

关键词： axial piston pump slipper anti-overturning partial abrasion

Synoptic-Scale Analysis on Development and Maintenance of the 19–21 July 2021 Extreme Heavy Rainfall in Henan,Central China

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Journal of Meteorological Research 2023年第2期37卷 174-191页

作者： Dorina CHYI Xiuming WANG Xiaoding YU junhui zhang China Meteorological Administration Training Centre China Meteorological AdministrationBeijing 100081 Department of Meteorology Service Yantai International AirportYantai 265617

In this paper,synoptic-scale analyses of frontogenesis,moisture budget,and tropospheric diabatic heating are performed to reveal the development and maintenance mechanisms for the extreme heavy rainfall in Henan Province of central China from 19 to 21 July 2021,based on station observations and the ECMWF Reanalysis version 5(ERA5)*** results demonstrate that owing to the blocking effect of local topography,low-level wind convergence in Henan appeared underneath high-level divergence,conducive to development and maintenance of a midtropospheric low-pressure system saddled by the Asian continental high and the western Pacific subtropical high(WPSH),during the extreme heavy *** the lower troposphere,frontogenesis occurred in the θ_(se) intensive region,as a result of the divergence and horizontal deformation(which play equally important roles),generating frontal secondary circulation with strong vertical motion favorable to heavy *** budget analysis reveals that 1)with the continuous strengthening of the easterly wind from the north side of Typhoon In-Fa(2106),strong wind shear and orographic uplift led to abnormally strong convergence of water vapor flux in the boundary layer in Henan;2)there occurred extremely strong net inflow of moisture in the boundary layer from the ***,both the apparent heat source and the moisture sink coincided with the area of heavy rainfall;vertically,however,Q_(1)exhibited a single peak with the heating center in the middle and upper troposphere,while large Q_(2)values evenly resided over 850–400 hPa;and Q_(1)(Q_(2))was dominated by vertical(horizontal)transport of potential temperature(moisture).These indicate that the latent heat release from condensation of initial heavy rainfall provided a positive feedback,leading to increasingly heavy *** these synoptic settings sustained the extreme rainfall process.

关键词： extreme heavy rainfall frontogenesis apparent heat source moisture sink water vapor budget

Piecewise model-based adaptive compensation control for high-speed trains with unknown actuator failures

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Transportation Safety and Environment 2023年第4期5卷 172-181页

作者： Chang Tan junhui zhang Hui Yang Leilei zhang School of Electrical and Automation Engineering East China Jiaotong UniversityNanchangJiangxi 330013China State Key Laboratory of Performance Monitoring and Protecting of Rail Transit Infrastructure NanchangJiangxi 330013China

In order to deal with the uncertainties caused by different operation conditions and unknown actuator failures of high-speedtrains,an adaptive failures compensation control scheme is designed based on the piecewise model.A piecewise constant model is introduced to describe the variable system parameters caused by the variable operation environments,and a multiple-particle plecewise model of high-speed trains,with unknown actuator failures,is then *** adaptive failure compensation controller is developed for the multiple-particle piecewise constant model,by using a direct model refering to the adaptive control *** an adaptive controller can not only compensate the uncertainties from unknown actuator failures,but also effectively deal with the uncertainties caused by different operating ***,a CRH380A high-speed train model is taken as the controlled object for the simulation *** simulation results show that the proposed controller ensures the desired system performance in the presence of unknown actuator failures and uncertain operation conditions.

关键词： actuator failures adaptive compensation piecewise model high-speed train multiple-particle model