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28 October 2020, Volume 54 Issue 10 Previous Issue    Next Issue

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Modelling of Spatial Pose of Ortho-SUV Frame and Mathematical Solution FU Chao, FAN Jiacheng, WANG Shigang, LIANG Qinghua 2020, 54 (10):  1007-1014.  doi: 10.16183/j.cnki.jsjtu.2019.017 Abstract ( 814 )   PDF (7461KB) ( 409 )   Save The Ortho-SUV frame, as an innovative parallel mechanism with variable hinge joints, can flexibly and conveniently treat limb deformities and fractures. In order to achieve orthopedic treatment, the spatial pose of the Ortho-SUV frame needs to be adjusted according to the fracture or deformity of different patients. Its kinematic analysis is therefore required. The pose of the Ortho-SUV frame was described by six spatial pose parameters, and its mathematical model was established. Based on its special structure, the nonlinear and high-coupled equations with trigonometric functions were transformed into ordinary non-linear equations without trigonometric functions, and the efficient and fast solution methods for the forward and inverse solutions of the spatial pose model were given. The correctness and the accuracy of the model were proved by checking calculation and simulated orthopedic experiment of tibial fracture, which provides a theoretical basis for the Ortho-SUV frame to be used in orthopedic treatment. References | Related Articles | Metrics

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Preparation and Thermal Storage Properties of Sodium Acetate Trihydrate-Expanded Graphite as Phase Change Composite LI Wenchen, CAI Yifan, YAN Taisen, LI Tingxian, WANG Ruzhu 2020, 54 (10):  1015-1023.  doi: 10.16183/j.cnki.jsjtu.2019.108 Abstract ( 1267 )   PDF (4092KB) ( 501 )   Save Salt hydrate as an energy storage material has the problems of low thermal conductivity, phase separation, and large supercooling. In this paper, a composite phase change material (CPCM) with sodium acetate trihydrate (SAT) as the main body is fabricated by melting blending. Expanded graphite (EG) is used as a high heat conduction additive to enhance the thermal conductivity, and as a nucleating agent to decrease supercooling degree simultaneously. Xanthan gum (XG) is used as a thickening agent to suppress the phase separation of the composite phase change material. The phase change properties, thermal stability and, thermal conductivity of the composite phase change materials are studied. A high energy-density heat storage device is built by using the composite phase change material (SAT/EG/XG) and its thermal property is analyzed by heating at 85℃ and cooling at 20℃. The results show that the addition of EG can obviously enhance the heat conductivity and eliminate the supercooling. With the addition of 2%—4% (mass fraction)expanded graphite, the thermal conductivity of CPCM reaches to 1.12—1.81W/(m·K), which is 2—3 times of the pure SAT. Besides, the addition of 0.5%—1.2% (mass fraction)XG can significantly inhibit phase separation. The composite phase change material has a good thermal stability. After 50 cycles, the melting temperature is kept at about 58.0℃, the solidification temperature is stable at about 57.6℃, there is no obvious supercooling, and the phase change enthalpy is 250—255kJ/kg. Moreover, the thermal storage device filled with composite phase change material has a heat storage density of 442.70kJ/L, which is 1.7 times that of the traditional water tank, and its heat storage and release efficiency reaches to 96.4%, which shows obvious advantages. References | Related Articles | Metrics

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Blade Optimization Design for Expanding Stable Operating Range of High Bypass Ratio Fan ZHANG Ke, WU Yadong 2020, 54 (10):  1024-1034.  doi: 10.16183/j.cnki.jsjtu.2019.130 Abstract ( 932 )   PDF (4795KB) ( 449 )   Save An aerodynamic optimization design method for high bypass ratio fan blades based on the Kriging surrogate model was constructed, which integrated parametric modeling, TurboGrid meshing, and computational fluid dynamics (CFD) combined optimization technology. The optimization method was implemented for airfoils at several spans of a fan blade and redesign of airfoils from blade setting angle rotating and maximum-thickness position moving. The mass flow at stall points was chosen as target function to evaluate and optimize the stable operating range of fan blade. Compared with prototype design, the stable operating range of the blade optimized was expanded by 10.1%, among which the aerodynamic performance was also enhanced, with a maximum increment of 2.63% for efficiency and 9.27% for pressure coefficient. The results show that the optimization design system has broadened the stable operating range of fan blade effectively, and has also substantially improved efficiency and total pressure rise. References | Related Articles | Metrics

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Analysis of Factors Affecting Tribo-Dynamics of Guide Shoe of Marine Diesel Engine LI Rui,MENG Xianghui 2020, 54 (10):  1035-1044.  doi: 10.16183/j.cnki.jsjtu.2020.99.004 Abstract ( 968 )   PDF (2215KB) ( 394 )   Save Based on the tribo-dynamics model established and numerical solution method for the guide shoe-guide friction pair in low-speed marine diesel engines, the effects of guide shoe-guide clearance, lubricating area, guide shoe profile, crankshaft offset, and crosshead pin offset on the tribo-dynamics of guide shoe are analyzed. The results show that increasing the clearance between guide shoe and guide plate can reduce the loss of friction. However, it can significantly increase the maximum slap energy of guide shoe, which exacerbates the engine vibration and noise. Offsetting the crankshaft axis towards the main thrust side reduces the side force after top dead center and the friction loss of guide shoe. The maximum slap energy in a working cycle can also be reduced. However, offsetting the crosshead pin to the main thrust side increases side force after top dead center and the friction loss of guide shoe. References | Related Articles | Metrics

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The Sensitivity Analysis of Energy System Parameters of Solar Powered Unmanned Aerial Vehicle YANG Yudan,ZHU Bingjie,GUO Zheng,YANG Xixiang 2020, 54 (10):  1045-1052.  doi: 10.16183/j.cnki.jsjtu.2020.99.005 Abstract ( 795 )   PDF (1083KB) ( 405 )   Save Through analysis of the characteristics of four typical flight stages of solar powered unmanned aerial vehicle (UAV) in the air, the power models required are summarized in this paper. Based on these models, it is concluded that the power required is closely related to total mass, power factor, and aspect ratio. The influence of these factors on energy system and overall design are analyzed. By studying the relationship between power factor and angle of attack, the range of angle of attack which meets the flight energy requirements is obtained. Considering the energy balance, the models of each subpart mass and total mass of solar powered UAV are established. Besides, the influence of wingspan and aspect ratio on mass is examined. Simultaneously, the relationships among the mass of battery, solar cells, and power demands are discussed. Based on the analysis, it is concluded that with the increase in wingspan, the power required of solar powered UAV increases. When the wingspan is constant, the power required decreases as the aspect ratio increases. References | Related Articles | Metrics

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Pore Structure and Pore Scale Simulation of Permeability of Micro-Porous Layer in PEM Fuel Cell HE Yusong,BAI Minli,HAO Liang 2020, 54 (10):  1053-1064.  doi: 10.16183/j.cnki.jsjtu.2019.143 Abstract ( 913 )   PDF (2814KB) ( 358 )   Save Numerical reconstructions of the micro-porous layer (MPL) have been performed by using the sphere-based simulated annealing method and the dynamic particle-packing model, of which, the former is more accurate to reflect the pore structures of the porous media. The single-phase flow inside the MPL reconstructed is simulated by using the lattice Boltzmann method (LBM) with multi-relaxation time (MRT) and multi-reflection (MR) solid boundary. The effects of carbon volume fraction, polytetrafluoroethylene (PTFE) loading, porosity, and PTFE distribution on the pore structure and permeability of the MPL are studied. The results show that the MPL permeability decreases with the increase in carbon volume fraction and PTFE loading, and the pore structure and permeability of MPL are also influenced by the distribution of PTFE. The Kozeny-Carman (KC) equation underestimates the permeability of MPL and a modified correlation to predict the permeability coefficient of MPL is proposed. The relative error between the results predicted by this correlation and the pore scale simulations is less than 12%. References | Related Articles | Metrics

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Parallel Resonance Mechanism Analysis and Suppression Method for LCL Type Grid-Connected Inverter TAO Haijun,ZHOU Yousong,ZHANG Guopeng,ZHENG Zheng 2020, 54 (10):  1065-1073.  doi: 10.16183/j.cnki.jsjtu.2019.046 Abstract ( 1326 )   PDF (1634KB) ( 683 )   Save For the parallel system of two grid-connected inverters, the effect of each inverter on the grid-connected current is analyzed by using the superposition theorem, and the grid-connected current is decomposed. Besides, the mechanism of resonance generated by the interaction current and the common current is studied, and the resonance frequency point characteristics of parallel systems with multiple grid-connected inverters of the same and different capacities are compared and analyzed. Moreover, based on the resonant frequency point generated by the interactive current in the parallel system, a digital notch filter is designed and introduced into the traditional capacitive current feedback active damping control to realize the static-free control of the fundamental signal, which meets grid-connected requirements of such systems. Furthermore, the models of parallel systems of inverters with the same and different capacities are built. The simulation results verify the correctness and effectiveness of the proposed strategy. References | Related Articles | Metrics

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Tensile Damage Evolution of Plain Weave SiC/SiC Composites Based on In-situ X-Ray CT Tests LIU Hailong，ZHANG Daxu，QI Heyin，WU Haihui，GUO Hongbao，HONG Zhiliang，CHEN Chao，ZHANG Yi 2020, 54 (10):  1074-1083.  doi: 10.16183/j.cnki.jsjtu.2019.274 Abstract ( 1284 )   PDF (8739KB) ( 848 )   Save Plain weave SiC/SiC composites were manufactured by the chemical vapor infiltration process，and X-ray computed tomography non-destructive testing technology was used to investigate the damage evolution and failure mechanism of textile ceramic matrix composites. Besides the third generation SiC fiber toughened plain weave laminated SiC/SiC dog bone test pieces were prepared. In addition, a CT in-situ tensile tester was developped, the nano in-situ X-ray CT tensile tests were completed, and the three-dimensional reconstruction images and scanning electron microscope photos of CT scans were analyzed. The results show that nano X-ray CT in-situ tests can reveal the evolution of tensile damage of materials. The uniaxial tensile stress-strain curve of plain weave SiC/SiC composites exhibits obvious nonlinear characteristics, with damage initiating in the stage of nonlinear changes. First, lateral cracking of the substrate occurs and gradually expands with increasing tensile force. Next, interlayer matrix cracking and fiber bundle matrix cracking occur longitudinally and gradually expand to the fiber bundle width. Finally, the fiber in the tensile direction breaks and the material fails. Most of the substrates have transverse cracks closed, but the longitudinal fiber bundles and the matrix between the bundles are severely separated, the fractures are uneven, and there are obvious fiber pull-outs. References | Related Articles | Metrics

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Numerical Analysis and Design Method of Cold-Formed Thin-Walled C-Section Steel Perforated Member REN Chong,LIU Qiuting,WANG Binhua,DAI Liusi 2020, 54 (10):  1084-1093.  doi: 10.16183/j.cnki.jsjtu.2019.023 Abstract ( 850 )   PDF (3759KB) ( 344 )   Save Cold-formed thin-walled steel structure is widely used because of its light weight, high strength, and easy construction. C-section member with web perforate is commonly used as a load-bearing member in cold-formed thin-walled steel structures. To investigate the influence of various buckling modes, i.e., local, distortional, global buckling and their interactions, on the behaviour of cold-formed steel beam-columns, a numerical study was undertaken to analyze the elasticity and elastoplasticity of cold-formed thin-walled C-section steel perforated member and investigate the influences of hole size, position and form on the member performance. Based on the numerical study, the direct strength method (DSM) curve for the compression member without holes was modified. The results show that the numerical model is verified by the existing test data. The holes will have a certain impact on the critical load of the member, and will reduce the bearing capacity. This study proposes the associated DSM design curve in cold-formed thin-walled C-section steel perforated member, and reveals the associated distortional and global buckling mode interactions. References | Related Articles | Metrics

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Influence of Dewatering in Confined Aquifers on Wall Deformation and Ground Settlements in Deep Excavation ZHENG Qiyu,XIA Xiaohe,LI Mingguang,ZHANG Yangqing 2020, 54 (10):  1094-1100.  doi: 10.16183/j.cnki.jsjtu.2019.157 Abstract ( 876 )   PDF (1231KB) ( 378 )   Save A numerical method considering the fluid-mechanical interaction is used to study the wall deformation and the ground settlements caused by dewatering in a confined aquifer in deep excavation. In the simulation of project example, the fluid-mechanical interaction methods based on the Biot’s consolidation theory are used to calculate the variation of settlements in deep excavation. Mechanics and seepage are iterated alternately to solve the deformation under combined effect of unloading and dewatering. The rationality of this method is verified by comparing with observed data. The three-dimensional numerical models of deep excavation are established. And the situations with or without dewatering are made direct comparison in terms of dewatering-induced wall deformations and ground surface settlements. By stripping the correlation curve of dewatering-induced additional settlements outside the pit, this paper focus on its discrepancies and mechanism with the comparison of one-dimensional consolidation theory based on the same pore pressure change. The results show that dewatering in the confined aquifer has less effects on wall deformation, but intensifies the magnitude and the influence range of total ground surface settlements. The dewatering-induced additional ground surface settlements outside 1.5 times of excavation depth of the pit match well with the settlements of one-dimensional consolidation theory, while the settlements discrepancy within 1.5 times of excavation depth behind the wall is mainly attributed to the soil-wall interaction. References | Related Articles | Metrics

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Multi-Objective Optimization Model for Expansion Method of Three-Dimensional Curved Hull Plate LAN Hongkai,LIU Cungen,NIE Xin 2020, 54 (10):  1101-1107.  doi: 10.16183/j.cnki.jsjtu.2019.159 Abstract ( 792 )   PDF (1850KB) ( 373 )   Save In order to effectively improve the management of ship building process, an optimization model for expansion of three-dimensional curved hull plate is proposed based on an expansion method with a constant unit length, taking the steel plate cutting and plate conforming technology into full consideration. The error of area, linear degree of borders, and mean strain energy are taken as objective functions. The multi-objective memetic algorithm (MOMA) with heuristic operator is adopted to solve the optimization model of three-dimensional curved plate expansion of ship hull. Based on the analytic hierarchy process(AHP) method, multiple solutions are selected to obtain the final expansion surface. By comparing with the geodesic expansion results, the effectiveness of the optimization algorithm is verified. Besides, the effectiveness of local search operator and heuristic operator in the algorithm is further verified. References | Related Articles | Metrics

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Performance of Automotive Ultra-Low Temperature Economized Vapor Injection Heat Pump Air Conditioning Using R1234yf Refrigerant LIU Yusheng,LI Wanyong,ZHANG Li,SHI Junye,CHEN Jiangping 2020, 54 (10):  1108-1116.  doi: 10.16183/j.cnki.jsjtu.2019.244 Abstract ( 1279 )   PDF (1873KB) ( 562 )   Save In this paper, an automotive ultra-low temperature heat pump air conditioning system based on the economized vapor injection (EVI) technology is proposed. The new low-global warming potential (GWP) R1234yf is used as the refrigerant. Besides, the comparative performance test in R134a and system optimization are conducted. In the ultra-low temperature environment of -20℃, the heating performance and coefficient of performance (COP) of this system can reach 2kW and 2.0, which is 30% and 14% higher than those of the traditional heat pump. Thus, the system can meet the heating requirements of crew cabin in a low temperature environment. The heating capacity of the R1234yf system is a little bit lower but pretty much the same as R134a. Moreover, the effect of EVI for R1234yf refrigerant is better than that of R134a. Increasing the inner-condenser area and optimizing components, such as outdoor heat exchanger and compressor, can significantly improve heat pump air conditioning system performance and its energy efficiency. References | Related Articles | Metrics