Table of Content

    28 April 2021, Volume 55 Issue 4 Previous Issue    Next Issue
    Wind Vibration and Vibration Reduction of a H-Rotor Type Three-Bladed Vertical Axis Wind Turbine
    YANG Mengyao, MAO Lulu, HAN Zhaolong, ZHOU Dai, LEI Hang, CAO Yu
    2021, 55 (4):  347-356.  doi: 10.16183/j.cnki.jsjtu.2020.054
    Abstract ( 947 )   HTML ( 743 )   PDF (4944KB) ( 614 )   Save

    Aimed at the wind-induced response and vibration reduction of an H-rotor type three-bladed vertical axis wind turbine (VAWT), and based on computational fluid dynamics (CFD) method, a numerical simulation is conducted to obtain the blade wind pressure distribution during the rotation period. Then, the wind pressure obtained is applied to the surface of the blades to analyze the wind vibration response of the VAWT. Dampers are arranged at different positions of the VAWT to simulate the vibration reduction capacity. The results show that applying the damper at the connection between the main shaft and the support rod of VAWT could reduce the displacement response of the structure to a certain extent and the maximum drop would reach 44%. Furthermore, the displacement reduction rate of the structure is related to the position of the damper. If a damper is arranged near the top end of the blade, the maximum displacement of the structure would occur at the bottom of the blade. However, if a damper is arranged near the bottom end of the blade, the maximum displacement of the structure would occur at the top of the blade and the maximum drop would reach 40.7%. The results would provide technical reference for research on the vibration reduction of VAWT structures.

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    Progressive Collapse Resistance Analysis of Precast Concrete Frames with Infill Walls
    ZHANG Jingbo, YANG Jian, WANG Feiliang
    2021, 55 (4):  357-364.  doi: 10.16183/j.cnki.jsjtu.2019.286
    Abstract ( 671 )   HTML ( 12 )   PDF (3705KB) ( 376 )   Save

    The infill wall has a significant influence on the progressive collapse resistance of the precast concrete (PC) frame, and there is no corresponding design method at present. In order to obtain a reliable calculation method for progressive collapse, a numerical and analytical analysis of progressive collapse resistance of PC frames with infill walls was conducted. According to the 3∶1 scale test of PC frames with and without infill walls after removing middle column, and considering the displacement of middle column under the asymmetric distribution of infill walls, a mechanical model based on equivalent strut was established by introducing asymmetry coefficient. Based on the finite element (FE), numerical models of the sub frames with the asymmetric infill walls were established, and displacement-load curves of the middle column were obtained, based on which, the analytical solutions were compared with the test results of bare, double, and single infill wall PC frames, and the results were found in good agreement. A comparison of the calculation results with the recommended values in current codes indicates that the displacement of PC frames under the peak load of catenary is increased when considering the infill wall. The recommended value of the displacement, whose middle column is 0.2 times of the span, is suitable for the bare PC frames, but conservative for the PC frames with infill walls. The results provide a basis for the calculation of the progressive collapse resistance of PC frames with infill walls.

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    Wave Flume Simulation Experiment on Influence of Wave Load on Bearing Capacity of Monopile
    JIN Xiaokai, CHEN Jinjian, LIAO Chencong
    2021, 55 (4):  365-371.  doi: 10.16183/j.cnki.jsjtu.2019.268
    Abstract ( 736 )   HTML ( 11 )   PDF (3396KB) ( 438 )   Save

    For the foundation of the monopile in the shallow water environment,a scale model of sand-monopile-wave was adopted in the wave flume simulation experiment, and the static load test of the monopile under wave action was explored. The pore water pressure of the soil around the monopile and the settlement of the monopile at different wave loads were examined. Based on the static load test results, the interaction mechanism between sand and the monopile subjected to wave load, the characteristics of load settlement curve,and the influence of excess pore water pressure (ps) on the vertical bearing capacity of the monopile with various pile diameters were analyzed. The results show that due to the presence of the monopile, the ps of the soil around the pile increases whereas the ps at the bottom of the monopile decreases. However, the ps around the pile increases with increasing pile diameter. The bearing capacity of the monopile under the influence of wave load is less than that without wave load. At the same load, the pile settlement increases remarkably and the increase is more obvious in the case of larger pile diameter. The experiment shows that the effect of wave load on the pile foundation bearing capacity should be monitored during the design process.

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    Development of K0 Coefficient Measurement and Stress Path Test Function of Triaxial Apparatus
    PAN Shang, LIU Jinhao, ZHANG Qi, YE Guanlin
    2021, 55 (4):  372-379.  doi: 10.16183/j.cnki.jsjtu.2019.296
    Abstract ( 773 )   HTML ( 7 )   PDF (1433KB) ( 342 )   Save

    The high accuracy small strain triaxial apparatus (hereinafter inferred to as the new triaxial apparatus) developed and assembled by Shanghai Jiao Tong University adopts a built-in pressure chamber by integrating the stress and strain loading function automatically controlled by the program and the linear variable differential transformer (LVDT) function of measuring small strain. In this paper, the new triaxial apparatus is further expanded. Now it has the function of measuring K0 coefficient of undisturbed soil sample and performing stress path loading along any direction of q-p (q is the deviatoric stress and p is the average principal stress) stress space. First, the development history of the new triaxial apparatus is briefly introduced and the control program algorithm of K0 coefficient measurement and stress path test for the two new functions are described in detail. Then, the K0 coefficient measurement and stress path test for deep soft clay in Shanghai are conducted, and the results are analyzed to verify the reliability of the new functions. The experience of the new triaxial apparatus can provide reference for the development of geotechnical instruments.

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    Prediction of Ultimate Bearing Capacity of Long-Term Loaded Piles
    LI Jingpei, XU Zihan
    2021, 55 (4):  380-386.  doi: 10.16183/j.cnki.jsjtu.2019.348
    Abstract ( 691 )   HTML ( 5 )   PDF (761KB) ( 274 )   Save

    To predict the ultimate bearing capacity of long-term loaded piles, the shortcomings of current empirical formulas of pile bearing capacity considering time effect are discussed. Based on the current research of the bearing capacity of static bearing piles in natural saturated clay, factors for the bearing capacity of long-term loaded old piles are analyzed. Then, based on analysis of the data from pile foundation bearing tests, the formula for calculating the ultimate bearing capacity of jacked piles considering the time effect and the current pile foundation technical code is proposed, in which the pile side resistance aging coefficient of pile side resistance is proposed, and some factors for the aging coefficient are discussed. Based on the experimental data, a method for calculating the parameters in the formula by using soil properties is proposed. The accuracy of the proposed method is verified by a field test. The results show that this pile side resistance aging coefficient can predict the bearing capacity of single pile under current code, increase the design value of the bearing capacity of old piles while ensuring safety. By using the undrained shear strength and plasticity index, the pile side resistance aging coefficient can be predicted.

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    Test of Uniaxial Tensile Mechanical Properties of ECTFE Foils at Various Temperatures
    LIU Changjiang, ZHAO Bing, CHEN Wujun
    2021, 55 (4):  387-393.  doi: 10.16183/j.cnki.jsjtu.2019.317
    Abstract ( 753 )   HTML ( 5 )   PDF (1601KB) ( 439 )   Save

    Uniaxial tensile tests of ethylene-chloro-tri-fluoro-ethylene (ECTFE) foils were conducted at a thickness of 250 μm and various low and high temperatures (-50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50, 60, 70, and 80 ℃). The specimens were fabricated according to the machine direction (MD). The tensile stress-strain curves of the foils at various temperatures were obtained. According to the variation discipline with temperature, several parameters such as elastic modulus, yield stress, yield strain, cold drawing stress, tensile strength, and tensile strain at break were subsequently analyzed and calculated. The results show that with the elevation of the stress-strain curves, the yield strength, tensile strength, cold drawing stress, and elastic modulus increase, but the strain at break and toughness decrease when the temperature decreases. At a wide range of temperatures from -50 ℃ to 80 ℃, the difference of elastic modulus can increase up to 93%, with a yield stress of 89%, which reflects the great sensitivity of ECTFE to temperatures. The fitting formulas of main mechanical parameters are also obtained, which can be used to predict the mechanical properties of ECTFE foils at various temperatures.

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    Simulation Study of Aluminum Alloy Ribbed Member Spinning with Ultrasonic Vibration
    LI Xiaokai, ZHAO Yixi, YU Zhongqi, ZHU Baohang, CUI Junhui
    2021, 55 (4):  394-402.  doi: 10.16183/j.cnki.jsjtu.2019.263
    Abstract ( 576 )   HTML ( 5 )   PDF (14149KB) ( 348 )   Save

    Flow spinning process is beneficial to realizing the integral forming of the ribbed members, but the height of the inner rib that can be formed is limited. Therefore, an ultrasonic assisted method was introduced into the flow spinning process to increase the height of the inner rib. Uniaxial tensile and compression tests with ultrasonic vibration were conducted to establish the hardening equation of the 2219-O aluminum alloy considering the acoustic softening effect. The friction reduction effect after ultrasonic loading was analyzed. A simulation model of aluminum alloy ribbed member spinning with ultrasonic vibration was established using the Abaqus software. The simulation results show that the ultrasonic vibration can reduce the deformation resistance of the material, improve the material flow of the ribs in different directions, guide the material flowing into the rib grooves, and thereby improve the filling height of the ribs. When the amplitude reaches 12μm, the rib height can be increased by 1/3.

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    Shear Layer and Wake Characteristics of Square Cylinder in Transonic Flow
    XU Changyue, ZHENG Jing, WANG Zhe, WANG Bin
    2021, 55 (4):  403-411.  doi: 10.16183/j.cnki.jsjtu.2019.299
    Abstract ( 618 )   HTML ( 6 )   PDF (8876KB) ( 343 )   Save

    The transonic flow around a square cylinder at Ma= 0.71 and Re= 4×105 has been studied by using the scale-adaptive simulation (SAS) method, and the characteristics of separated shear layer and wake have been analyzed in depth. To validate the SAS approach, the SAS results are compared with the existing numerical and experimental results. In the present transonic flow, the convective Mach number inside the shear layer is about 0.6. This indicates that the initial evolution of the separated shear layer is dominated by Kelvin-Helmholtz instability, and the roller spanwise eddies in the initial stage of the shear layer can be observed. In the regions near the shear layer and the wake, the doubling frequencies can be obtained indicative of the harmonic phenomenon inside the separated shear layer, which is closely related to the obvious merging of the vortices in the shear layer. Proper orthogonal decomposition of the pressure field shows that the transonic flow field of square cylinder is dominated by the antisymmetric mode, which is associated with the vortex shedding in the wake and the propagation of compression waves induced by the shear layer.

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    Effect of Linearly Stratified Environment and Submerged Vegetation on Hydrodynamic Characteristics of Downslope Gravity Currents
    LIU Yayu, LIN Yingtien, YUAN Yeping, HE Zhiguo
    2021, 55 (4):  412-420.  doi: 10.16183/j.cnki.jsjtu.2019.228
    Abstract ( 630 )   HTML ( 3 )   PDF (3512KB) ( 255 )   Save

    A series of lock-exchange experiments of slope gravity currents were conducted to analyze the development and evolution characteristics of rigid vegetations in uniform and linear stratified environments. The development of gravity currents was recorded by using a digital camera, and the local flow field structure was obtained by particle image velocimetry (PIV). The results show that the head velocity of gravity currents with submerge vegetation experience the processes of acceleration, deceleration, second acceleration, and second deceleration. As the stratification degree increases, the transition points among the four stages move ahead, but the vegetation density does not significantly impact that point. In the stratified environments with the submerged vegetation patches, the phenomena of “first separated then advanced and finally separated from the slope” is observed. Vegetation can restrain the development of vorticity fields of gravity currents. When the vegetation densens, the vorticity of gravity currents will decrease more significantly. Both stratified environments and submerged vegetation patches can inhibit the development of vorticity fields of gravity currents, and the stratified water environment plays a more important role in this inhibition.

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    Review of Movement and Accumulation Characteristics of Granular Column Collapse
    LAI Zhiqiang, JIANG Enhui, ZHAO Lianjun, ZHOU Wei, TIAN Wenxiang, MA Gang
    2021, 55 (4):  421-433.  doi: 10.16183/j.cnki.jsjtu.2019.329
    Abstract ( 850 )   HTML ( 10 )   PDF (1839KB) ( 478 )   Save

    Domestic and foreign relevant literatures of granular column collapse movement models are concluded to analyze the effects of initial spatial characteristics, essential physical properties of particles, boundaries, and environment conditions of model on the movement and accumulation characteristics of granular columns. Besides, the related mechanisms of movement and accumulation characteristics of granular columns are also analyzed. Remarkable linear and power relationships exist between the movement distance and the aspect ratios of initial height to initial width. Similarly, remarkable linear and power relationships exist between accumulation height and aspect ratio of initial height to initial width. The movement patterns and energy consumption mechanisms for granular columns with large aspect ratios are significantly different from those with small aspect ratios. A consensus has basically been reached concerning the effect of particle size, particle stiffness, particle breakage, and wet particles on the movement and accumulation characteristics of granular columns. Some preliminary research achievements of the effects of different wall constraints, fluidization phenomenon due to the gas mixing and water condition on the movement and accumulation characteristics of granular column are obtained. However, there still exist disagreements in the conclusions about the influences of initial porosity of granular column, particle friction, and wall friction on the movement and accumulation characteristics of granular column. A review of the current research indicate that the research in the future will be focused on the relationship between forces acted on particles and movement regimes. The mechanisms of the effect of complex particle shape, surface, particle density, and water movement conditions on the movement and accumulation characteristics of granular column collapse will also be focused on in the future.

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    A Hybrid Compression-Absorption High Temperature Heat Pump Cycles for Industrial Waste Heat Recovery
    AN Meiyan, ZHAO Xinrui, XU Zhenyuan, WANG Ruzhu
    2021, 55 (4):  434-443.  doi: 10.16183/j.cnki.jsjtu.2020.023
    Abstract ( 962 )   HTML ( 10 )   PDF (1257KB) ( 563 )   Save

    Aimed at the problem that the conventional absorption heat pumps and compression heat pumps cannot take into account the temperature rise and efficiency, this paper proposes the use of a thermally-coupled hybrid compression-absorption heat pump to achieve high-efficiency and high-temperature output. To meet the demands of different scenarios, a large-temperature-lift cycle and a high-temperature-output cycle are constructed. R245fa and lithium bromide aqueous solution are used as working substance. For output temperature above 100℃, Aspen Plus software is used to establish a mathematical model to predict the cycle performance for calculation. The results show that the optimized coefficient of performance(COP) can be 2.58 or higher when the large-temperature-lift cycle is used to recover the waste heat at 30-40℃. When the high-temperature-output cycle is used to recycle waste heat at 60-70℃, the optimized COP of the cycle can reach 2.83. The cycles proposed are more advantageous than the R245fa compression cycle on temperature lift, output temperature, and efficiency.

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    Simulation and Performance Reliability of Boiler Load Raising Process Considering Leakage of Feed Water
    NI He, QIN Haibo, ZHENG Yiyang
    2021, 55 (4):  444-454.  doi: 10.16183/j.cnki.jsjtu.2020.033
    Abstract ( 583 )   HTML ( 6 )   PDF (1696KB) ( 350 )   Save

    In response to the problems of boiler low water level and pump cavitation caused by the leakage of feedwater unloading pipeline in the process of boiler load raising of the conventional steam power system, the relational model of water-lift, mass flow, revs of booster pump, and each impeller of the feedwater pump are identified by using a differential evolution algorithm based on residual correction. The relational model of mass flow and resistance of feedwater pipelines and valves, the calculational model of working fluid parameters in feedwater system, and the performance degradation model of feedwater unloading control valve are established by using be mechanism modeling method. On this basis, the process of boiler load raising is simulated, and the main parameters of feedwater system are obtained at different feedwater unloading flow rates. It is found that the performance degradation of the control valve of the feedwater unloading pipeline is one of the main causes for boiler water low level and pump cavitation in the process of boiler load raising. In order to further clarify the degradation rule of the performance reliability of the feedwater system with the working time, a simulation method integrating the mathematical model and Monte Carlo random sampling is adopted to the performance reliability simulation of a certain type of marine water supply system in the process of boiler load raising. Thus the whole performance reliability changes of this boiler and the performance reliability life of this feedwater unloading control valve are obtained. The research results reveal the mechanism and degeneration rule of a unique fault of the steam power system, which has certain theoretical and engineering application value.

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    Motion Characteristics of Vibrated Droplets on Micropillared Surface with Gradient Energy
    XIONG Xuejiao, JIA Zhihai, DENG Yong, FEI Yuanyuan
    2021, 55 (4):  455-461.  doi: 10.16183/j.cnki.jsjtu.2020.079
    Abstract ( 681 )   HTML ( 4 )   PDF (3138KB) ( 374 )   Save

    A gradient energy surface with micropillared structures is prepared by photolithography using polydimethylsiloxane (PDMS) as the substrate. The dynamic characteristics of vibrated droplets on the gradient energy surface with micropillared structures are studied by a high-speed camera. The influence of geometric parameters of the gradient energy surface with micropillared structures on the motion characteristics of vibrated droplets is analyzed. It is found that the droplets begin to wriggle when a certain vibration frequency is exerted on the gradient energy surface with micropillared structures and the vibration amplitude reaches a certain threshold. With the increase of the amplitude, the droplets move from the larger area fraction to the smaller area fraction. At the same vibration frequency, the acceleration of droplets gradually decreases as the amplitude increases. At the same time, compared to the region with a smaller area fraction, the acceleration of droplets motion is smaller in the region with a larger area fraction. In the region with a large area fraction, the range of wet contact diameter has a greater variation than the region with a small area fraction. A model is established using the mechanics and surface physical chemistry theory, and the influence of the surface microstructure on droplet motion characteristics is analyzed.

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    Gas-Fired Flame Stability Based on Optical Flow Method and Deep Learning
    WANG Yu, YU Yuefeng, ZHU Xiaolei, ZHANG Zhongxiao
    2021, 55 (4):  462-470.  doi: 10.16183/j.cnki.jsjtu.2020.111
    Abstract ( 734 )   HTML ( 11 )   PDF (8629KB) ( 534 )   Save

    The stability of gas-fired flame is studied by combining the optical flow method and deep learning. The optical flow vector of the flame image is directly calculated by using the optical flow method. The pulsation of the flame in the two-dimensional image is observed, and an optical flow pulsation evaluation model is proposed to evaluate the stability of the flame. In addition, a deep convolutional neural network based on VGG-Nets is built and fine adjustments are made on ImageNet pre-training weights. Combining the static and dynamic characteristics of flames, the classification and recognition of five typical combustion states are achieved. The results show that this method has a good judgment ability for different combustion states of flames and a high recognition rate for unstable combustion flames.

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    Test of Thermo-Physical Property Parameters of Solid Material Based on Laser Point Heat Source Unsteady-State Heat Transfer Model
    CHEN Qinghua, GAO Wei, SU Guoyong, GUAN Weijuan, QIN Ruxiang, JI Jiadong, MA Yangbin
    2021, 55 (4):  471-479.  doi: 10.16183/j.cnki.jsjtu.2020.99.013
    Abstract ( 746 )   HTML ( 10 )   PDF (1402KB) ( 408 )   Save

    Based on the laser point heat source unsteady state transfer model, a novel method to gain thermo-physical parameters of isotropic solid materials is proposed. The enantiomorphous heat-source theory is introduced to calibrate the influence of adiabatic boundary on temperature rise of the measuring points, and a mathematical model is established. The thermal conductivity and thermal diffusivity of the material are calculated by numerical solution combined with computer programming, and a thermo-physical testing system is developed. The low vacuum environment in the sample container is obtained by using a vacuum pump. The laser generator emits a laser beam to heat a corner of the sample, and the variation of temperature on the upper surface of the sample measured by the temperature sensor is monitored by the wireless signal transmitting unit. The thermophysical properties of borosilicate glass (Pyrex7740), marble, diatomite firebrick, silica brick, and zirconium brick are comprehensively tested. The results show that the relative deviation between the test values of the first four samples with a relatively low thermal conductivity and the reference value is not more than 2.76%, and the test accuracy is higher. The relative deviation between the test values of the zirconium brick with a relatively large thermal conductivity and the reference value reaches 6.38%, and the test accuracy is lower. Uncertainty analysis of the test system shows that as the thermal conductivity of the tested sample increases, the credibility between the test value and the true value decreases, indicating that the device is more suitable for solid materials with a thermal conductivity less than 3.0W/(m·K).

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    Imperfect Maintenance Policy for a Two-Machine One-Buffer System Based on Markov Decision Process
    TIAN Xueyan, WANG Mengya, PAN Ershun
    2021, 55 (4):  480-488.  doi: 10.16183/j.cnki.jsjtu.2019.270
    Abstract ( 707 )   HTML ( 13 )   PDF (1019KB) ( 288 )   Save

    To solve the problem of machine maintenance optimization of degraded systems, the preventive maintenance policy of a two-machine one-buffer production system is studied. First, random degradations of both machines are considered. For imperfect minimal repair and preventive maintenance, a Markov process is used to describe the system state. Then, a profit model for the production system is established based on cost and income. Finally, preventive maintenance decisions in different system states are determined by maximizing long-term expected profits. The model is solved by value iteration, and numerical analysis results show that the maintenance decision of the machine depends not only on its own state, but also on the state of other machines and the amount of the buffer.

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