28 June 2022, Volume 56 Issue 6 Previous Issue   
New Type Power System and the Integrated Energy
An Identification Method for DC-Link Capacitor Capacitance of Grid Connected Inverter
ZHU Chenghao, WANG Han, SUN Guoqi, WEI Xiaobin, WANG Fuwen, CAI Xu
2022, 56 (6):  693-700.  doi: 10.16183/j.cnki.jsjtu.2021.515
Abstract ( 259 )   HTML ( 318 )   PDF (5050KB) ( 410 )  

DC-link for the capacitor is one of the most vulnerable components of the grid connected converter, whose capacitance identification will help to improve the system reliability by finding and replacing the aging capacitor in time. An identification method for the DC-link capacitor capacitance of the grid connected inverter based on pre-charging circuit is proposed. By analyzing the relationship between the capacitance and the charging current, charging voltage during pre-charging process, and combining the historical operating data, the set of capacitance state feature vector is built. The support vector regression (SVR) model is trained and the regression prediction relationship between the state value and the capacitance is set. The model is optimized by using the particle swarm optimization (PSO) algorithm, which can be used for capacitance identification of the DC-link capacitor. Simulation and experiments results show that the proposed method can implement the accurate capacitance identification of the DC-link capacitor of the grid connected inverter, with an identification error of less than 0.95%. This method does not need to add hardware circuit and change the control algorithm, and has a certain practical value.

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Calculation Method of Uplift Capacity of Pile-Anchor Composite Foundation and Influence of Parameters
SUN Yizhou, SUN Honglei, CAI Yuanqiang
2022, 56 (6):  701-709.  doi: 10.16183/j.cnki.jsjtu.2021.366
Abstract ( 84 )   HTML ( 202 )   PDF (3967KB) ( 45 )  

In view of the extensive geology of overlying soil and underlying rock in mountainous areas, a pile-anchor composite foundation has been used in transmission line tower engineering. To reveal the uplift bearing mechanism and supplement the calculation method of the uplift capacity and the bearing exertion coefficient k, the verification model of field test case was established by using the PLAXIS 3D finite element software to study this problem. Parameter studies were conducted on this foundation. The influence of elastic modulus and cohesion of rock and soil and foundation condition on coefficient k was studied. The results show that there is asynchronism of ultimate uplift limit state of upper and lower parts of the pile-anchor foundation. The bearing ratio and coefficient k of the upper and lower parts of the foundation are related to geology and foundation structure. In combination with the parameter study and the relevant analytical solution of the relationship between the uplift load and the displacement, a theoretical calculation method of the coefficient k considering the foundation weight was proposed. Three test cases were used to perform confirmatory calculations for this method. By comparing with field tests and numerical calculation results, the correctness of this method has been verified. This method provides a theoretical reference for the design and application of this type of new foundation.

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Naval Architecture, Ocean and Civil Engineering
Application of Plane Elements and Shell Elements in Imitating Ribs of Members in Compound Strip Method
HOU Yanguo, LI Zhanjie, GONG Jinghai
2022, 56 (6):  710-721.  doi: 10.16183/j.cnki.jsjtu.2021.071
Abstract ( 100 )   HTML ( 202 )   PDF (10465KB) ( 237 )  

Finite strip method (FSM) is a classical method to analyze the buckling of thin-walled members. The traditional FSM adopting trigonometric functions longitudinally can hardly analyze the members with spaced ribs along the longitudinal direction, while the compound strip method (CSM) can compensate for this shortcoming. Based on the CSM, the influence of utilizing plane elements and shell elements to respectively imitate stiffeners on buckling is investigated. Compared with the shell-element ribs, the plane-element ribs are prone to assembling the stiffener matrices with fewer degrees of freedom. But the shell-element ribs are more comprehensive as the out-plane displacement of ribs are taken into consideration. It is found that plane element ribs and shell element ribs have little difference on the buckling capacity of members. The buckling capacity has a small difference of mean absolute error (MAE) underneath 0.75% between the two types of CSMs, and the buckling capacity and modes are in good agreement with the finite element results. The buckling loads of the two types of CSMs are close to the FEM with a MEA less than 5%. The accuracy of the plane elements satisfies the predicted requirements, which helps to reduce the program computation and simplify the analysis complexity. The efficiency of analysis can be dramatically improved for fine meshing elements.

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Interaction Mechanisms of Synchronously Performed Adjacent Excavations
YANG Qirun, LI Mingguang, CHEN Jinjian, WU Hang
2022, 56 (6):  722-729.  doi: 10.16183/j.cnki.jsjtu.2021.149
Abstract ( 56 )   HTML ( 6 )   PDF (1386KB) ( 44 )  

An adjacent excavation model based on the hardening soil-small strain (HSS) constitutive model was established by using the numerical method, which was compared with the single excavation model and the adjacent excavation model without considering the wall-soil friction. The stress deformation characteristics of adjacent excavation implemented simultaneously were obtained, and the interaction mechanism of adjacent excavations were revealed. The results show that two kinds of arching effects exist in the confined soil. One is the arching effect caused by uneven deformation of walls, and the other is the arching effect caused by the wall-soil friction, both of which affect the lateral earth pressure acting on the retaining walls. With the decrease of the excavation spacing, the former is weakened, resulting in the weakening of the transfer of lateral earth pressure between the soil near the excavation face to bracing soil, while the latter is enhanced, leading to the decrease of magnitude of the lateral earth pressure acting on adjacent retaining walls. Under the action of the arching effects, the curve of lateral earth pressure develops from an R-shaped distribution to a linear distribution and then returns to an R-shaped distribution with the decrease of the spacing. The maximum horizontal displacement of non-adjacent walls increases, and the maximum horizontal displacement of adjacent walls increases primarily and then decreases.

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A Numerical Model for Analysing Response of Membrane Surface Under Ponding Load
WANG Shasha, ZHANG Xiangyu, QIU Guozhi, GONG Jinghai
2022, 56 (6):  730-738.  doi: 10.16183/j.cnki.jsjtu.2021.152
Abstract ( 60 )   HTML ( 7 )   PDF (20233KB) ( 206 )  

A numerical model to analyze the response of the membrane surface under ponding load is propesed which combines the smoothed particle hydrodynamics (SPH) method and the non-linear constitutive model of the membrane material. According to the stress-strain response surface of the membrane material based on the biaxial tensile test with different stress ratios, a nonlinear constitutive model is established. SPH particles are used to simulate water, and a numerical model of the fluid-solid coupling between the membrane surface and ponding load is established. The mesh size adopted in this paper is determined by verifying the mesh convergence, and the influence of the loading time on the calculation results is analyzed. At the same time, the distribution law of stress and strain of the membrane surface are analyzed. The results show that the loading process becomes increasingly stable with the increase of the loading time, and 100 s can meet the analysis requirements.The numerical simulation results are compared with those of the flat membrane ponding test. It is found that the maximum vertical deformation of the membrane surface is in good agreement, which verifies the reliability of the method proposed in this paper.

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Slope Stability Considering the Effects of Air Pressure and Seepage Under Heavy Rainfall Conditions
YAO Maohong, CHEN Tielin, FAN Rong, YANG Zili, SHI Ye
2022, 56 (6):  739-745.  doi: 10.16183/j.cnki.jsjtu.2021.302
Abstract ( 68 )   HTML ( 7 )   PDF (1020KB) ( 49 )  

Rainfall infiltration analysis is one of the important methods for predicting engineering disasters. In order to effectively analyze the infiltration process of slope under heavy rainfall, based on the classical Green-Ampt model, a slope rainfall infiltration model considering the effect of saturated zone seepage and air pressure under the condition of non-uniform distribution of initial water content was established, and the corresponding expression of landslide stability coefficient was derived. The results show that the influence of slope size on rainfall infiltration is obvious. On the one hand, the expansion rate of wetting front increases with the increase of slope length, on the other hand, when considering the effect of air pressure, the smaller the slope length, the longer it takes to reach the same wet front. When the slope length increases to a certain extent, the difference is not obvious. In addition, the influence of seepage force on slope stability is greater than that of air pressure. Because the former gradually increases during the rainfall process while the latter is basically unchanged, the influence of seepage force increases, and the influence of air pressure decreases.

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Quasi-Steady State Time Model of Fire Smoke Transmission in Long-Narrow Spaces
WANG Jinhui, HUANG Yijun, CUI Xin, ZHANG Shaogang, ZHANG Ruiqing
2022, 56 (6):  746-753.  doi: 10.16183/j.cnki.jsjtu.2021.062
Abstract ( 55 )   HTML ( 6 )   PDF (1102KB) ( 27 )  

Transport time lag is a crucial characteristic of fire spreading in fire early stage, which determines the activation time of the fire detector. To clarify the quantitative relationship between the delay behavior and the quasi-steady state of smoke transmission in a long-narrow space, a time-varying spreadsheet is theoretically proposed to calculate the delay time of fire smoke transmission based on the theory of weak plume and the existing achievements concerned. Moreover, a theoretical model concerning the critical time for quasi-steady state assumption applicability is developed, where the method of calculating the critical time is also presented. The results of the case study show that due to the difference of smoke spreading velocity in long-narrow spaces and unconfined spaces for a case with the same conditions, the critical time for the smoke transmission to reach the quasi-steady state at a given radial distance on the ceiling in a long-narrow space is larger than that in the open space. For the open case, the thin ceiling plume, the small volume of entrained air, and the relatively high velocity of smoke lead to the longer delay time of smoke transmission in a long-narrow space than that in the open space under the same situations.

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Calculation Method of Bearing Capacity of Screw Pile Based on Unified Strength Theory
MA Jiakuan, LUO Lijuan, REN Xiang, SHI Hang, YIN Yimo
2022, 56 (6):  754-763.  doi: 10.16183/j.cnki.jsjtu.2021.077
Abstract ( 49 )   HTML ( 9 )   PDF (1180KB) ( 56 )  

Based on the unified strength theory and the Terzaghi limit equilibrium theory, the ultimate bearing capacity of screw pile has been deduced. The method to determine the critical pitch and calculate the ultimate bearing capacity of the screw pile in two failure modes including the independent bearing failure mode and the cylinder shear failure mode has been proposed. The influence of the unified strength theoretical parameter b and the key parameters of concrete screw pile on the ultimate bearing capacity has been analyzed. The results show that the ultimate bearing capacity of the screw pile is 1.5—2 times that of the round pile with the same outer diameter. The ultimate bearing capacity of the screw teeth is mainly determined by the cohesion, the internal friction angle, and the buried depth of the soil. As b increases from 0 to 1, the theoretical value of the ultimate bearing capacity of the screw pile increases by nearly 48%. As the influence of the medium principal stress on the soil strength is considered, the theoretical calculation results of the bearing capacity of the concrete screw pile will be more accurate. Of the parameters of the concrete screw pile, the screw height bh has the greatest influence on the ultimate bearing capacity, while the screw thickness t has little influence on the bearing capacity. When designing threaded pile, the height of screw can be increased to some extent to improve the ultimate bearing capacity of the screw pile.

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Sound Scattering Characteristics of Oxygen Cylinder for Open Breathing Diver
ZHANG Peizhen, LIN Fang
2022, 56 (6):  764-771.  doi: 10.16183/j.cnki.jsjtu.2021.078
Abstract ( 52 )   HTML ( 7 )   PDF (8690KB) ( 26 )  

This paper aims to solve the problem of the oxygen cylinder contribution to the overall scattering intensity of the open breathing diver, which is the basis for mastering the accurate prediction and identification of the diver. A two-dimensional finite element axisymmetric model of 3D-object with non-axisymmetric excitation is constructed. The numerical solution to the far-field frequency characteristics of the acoustic scattering by the object with different azimuths is obtained by using the acoustic-solid coupling multi-physical interface in frequency domain. The reason and the estimation formula of the bright fringe at the resonance frequency are given. Under the assumption of the linear acoustics, the numerical solution to finite element method (FEM) is taken as the system function, and the linear frequency modulation signal with the same bandwidth is taken as the input signal of the system. The echo simulation in time domain can be obtained based on the convolution theorem. Combining the bright spot model and the elastic circumferential wave theory, the precise prediction model of the distance-angle echo in time domain is proposed. The results show that the main factors that affect the strength of the echo include the mirror reflection and the angular reflection. The additional bright spots and circumferential waves generated by the fine structures such as valves and spherical cap have a non-negligible influence on the frequency response characteristics in different azimuths. The validity of the echo prediction and resonance frequency characteristics is verified by the lake experiment in monostatic mode.

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Mechanical Engineering
Mechanism and Influencing Factors of Frictional Energy Dissipation in Multilayer Ultrasonic Welding
MA Zunnong, ZHANG Yansong, ZHAO Yixi
2022, 56 (6):  772-783.  doi: 10.16183/j.cnki.jsjtu.2020.423
Abstract ( 69 )   HTML ( 8 )   PDF (6855KB) ( 35 )  

In multilayer ultrasonic welding, the sonotrode presses on metal sheets and drives the sheets to produce ultrasonic vibration. Then, each contact interface generates heat, produces plastic deformation, and forms solid-state bonding. However, the load distributes unevenly in each sheet, which results in the uneven friction state and inconsistent welding quality. Hence, it is necessary to reveal the mechanism of frictional state and energy dissipation based on the load distribution in each sheet. A finite element model of 5-layer copper sheets is established using Abaqus and considering the Cattaneo-Mindlin contact theory. The clamping force and ultrasonic vibration in each interface is simulated. The slip-stick state of each interface is obtained and the effect of the clamping force are analyzed. The frictional energy dissipation and proportion of each interface are calculated, the influencing factors of frictional energy dissipation are summarized, and the optimization of input clamping force is discovered, which can provide theoretical guidance for the improvement of multilayer ultrasonic welding.

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Cryogenic Minimal Quantity Lubrication Assisted Cutting Process for Polyimide Materials
CAO Zheng, LEI Xuelin, ZHANG Hang, CAI Xiaojiang
2022, 56 (6):  784-793.  doi: 10.16183/j.cnki.jsjtu.2021.173
Abstract ( 162 )   HTML ( 7 )   PDF (21845KB) ( 295 )  

The cutting performance of the porous polyimide material assisted by cold air trace lubrication was investigated, and the influence law of cutting process parameters on the cutting effect (cutting force, surface finish quality, and oil content) of the porous material was explored. The results show that compared with dry cutting and low-temperature cold air cutting, the cutting temperature and the machined surface roughness of cold air micro-lubrication cutting are the lowest, and the damage to the porous runner is the smallest. The depth of cut and the feed volume are the factors that have the greatest influence on milling force and surface roughness, respectively. Defects such as chip burrs and tears are the main factors that lead to the increase in surface roughness. The existence of drawing, micro-crack, stacking, and tiny debris on the workpiece surface are the main causes for the decrease in the oil content and oil delivery rate of the material. The optimal machining parameters of the porous polyimide material in the orthogonal experiment with the aid of cold air trace lubrication are vc=(100±2) mm/min, fz=(0.3±0.01) mm/r, ap=(0.8±0.1) mm (vc is the cutting speed, fz is the feeding rate, and ap is the cutting depth). With the assist of the cryogenic minimal quantity lubrication technology, the low damage processing, high oil content, and high oil delivery rate of cage products can be obtained.

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Fast 3D Pose Estimation Method for High Speed GMAW of Large Box Girders
LI Gaoyang, JIA Aiting, HONG Bo, LI Xiangwen, GAO Jiapeng
2022, 56 (6):  794-800.  doi: 10.16183/j.cnki.jsjtu.2020.362
Abstract ( 57 )   HTML ( 10 )   PDF (10448KB) ( 221 )  

In the process of high speed gas metal arc welding (GMAW), large box girder has many complex working conditions, such as positioning weld, low assembly accuracy, difficulty in strictly ensuring the pose of workpiece through tooling, real-time change of 3D pose of weld, etc. The vision based weld recognition method has a large amount of calculation and is not aimed at the workpiece with positioning weld, making it difficult to obtain the 3D pose of large box girders quickly. Aimed at this problem, a fast 3D pose estimation method for large box girder based on laser displacement sensing and point cloud clustering was proposed. Using this method, the vertical plane and flat plane of the welding seam of large box girders were obtained by fast segmentation of point cloud. Then, the pose information of welding seam was calculated. A pose information estimation test was conducted for welds with different poses. The results show that when the welding speed is up to 1200 mm/min, the pose error of the weld is less than 0.25 mm and 1.8°respectively. The robustness of the automatic welding of large box girders to complex conditions of positioning weld and low assembly accuracy is enhanced, which greatly improves the welding quality.

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A Novel Prediction Model for Fatigue Strength
DUAN Hongyan, TANG Guoxin, SHENG Jie, CAO Mengjie, PEI Lei, TIAN Hongwei
2022, 56 (6):  801-808.  doi: 10.16183/j.cnki.jsjtu.2021.051
Abstract ( 276 )   HTML ( 7 )   PDF (1208KB) ( 199 )  

Fatigue failure is one of the most important reasons for the failure of engineering application components. However, due to the high cost of fatigue experiments, it is necessary to use mechanical properties to predict fatigue strength. Based on the true stress-strain curves, a novel model for fatigue strength prediction is established and is used to calculate the fatigue strength. The strength predicted is compared with that calculated by the staircase method and the Basquin equation. The results show that the model could obtain the fatigue strength of the materials only by using tensile strength and work-hardening strength, and it is suitable for other steels, which greatly saves costs and increases accuracy.

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Design and Realization of Continuum Manipulator Based on Coupling of Double Parallel Mechanism
WU Guanlun, SHI Guanglin
2022, 56 (6):  809-817.  doi: 10.16183/j.cnki.jsjtu.2021.060
Abstract ( 72 )   HTML ( 11 )   PDF (14846KB) ( 185 )  

A 5-degree-of-freedom continuum manipulator is designed and implemented to improve the flexible positioning ability of the continuum mechanism in applications such as interactivity operations, light object grabbing, and human-machine collaboration. In the design process, by introducing a two-segment constant curvature model, the distribution of degrees of freedom on the mechanism is explained geometrically by the method of twist. Coupling two stretchable parallel modules in series, a two-segment structure is formed for curving and each segment has two degrees of freedom in bending and one degree of freedom in stretching, thereby giving 5 degrees of freedom to the end-effector. Concentrating on the dynamic performance of the manipulator, an electromechanical system platform is built as a prototype. The experiments show that the structure realizes the control of the end-effector during large deformation of the manipulator, and is able to achieve extreme pose in 2 s with an approximation positioning error of 2% of the nominal arm length.

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Chemistry and Chemical Engineering
Effect of Copper-Ammonia Complex on the Oxygen Removal and Corrosion Inhibition Performance of Diethylhydroxylamine
WEI Xiaojing, ZHAI Shuangling, SHI Xin, GAO Duolong, WEN Xiaohu, LIU Dongmei, REN Tianhui
2022, 56 (6):  818-826.  doi: 10.16183/j.cnki.jsjtu.2021.171
Abstract ( 58 )   HTML ( 11 )   PDF (17293KB) ( 86 )  

The catalytic effect of copper-ammonia complex on the deoxygenation efficiency of diethylhydroxylamine (DEHA) and the corrosion protection ability of the compound on carbon steel are studied. The effects of the addition of catalyst, and the pH and temperature of water on the deoxygenation performance of DEHA are investigated. The results of the deoxygenation test show that the deoxygenation rate of DEHA increases with the increase of the pH and temperature of water. The deoxygenation effect is greatly improved after the addition of catalyst. The optimal concentration of copper ammonia complex is 8 mg/L. Under these conditions, when the water pH≥7 or the water temperature is in the range of 30 ℃ and 70 ℃, the oxygen removal rate can reach more than 95%. The corrosion inhibition test results show that the copper-ammonia complex can significantly improve the corrosion protection ability of DEHA to carbon steel, and the corrosion inhibition rate can reach 96.2% with a long-term effect. Therefore, the compound has a good deoxygenation and corrosion inhibition performance, which has broad application prospects in the field of deoxygenation of industrial water and corrosion protection of industrial carbon steel equipment.

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