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    28 June 2021, Volume 55 Issue 6 Previous Issue    Next Issue
    Numerical Analysis of Local Scour and Protection of a Single Pile Around a Seabed Under Solitary Wave and Current
    LI Weijie, ZHANG Qi, LIAO Chencong, ZHOU Xianglian, LIU Chenchen
    2021, 55 (6):  631-637.  doi: 10.16183/j.cnki.jsjtu.2020.108
    Abstract ( 753 )   HTML ( 653 )   PDF (6015KB) ( 440 )   Save

    A numerical simulation is conducted to investigate the local scour of the seabed around the pile under the actions of both solitary waves and currents. By solving the N-S equations enclosed by the RNG k-ε turbulence model, the change of the flow field around the pile is simulated accurately. The sediment transport model considers all the sediment transport processes including entrainment, suspended load transport, deposition, and bed-load transport. For the slope seabed, the influence of gravity on the sediment particles is considered, and the shields parameter is modified. The accuracy of the model is verified by comparing the numerical results with the experimental data. Besides, the process of scour development at different wave heights is investigated in detail. The effect of pile foundation protection layer on scour is preliminarily studied. The results show that the combined solitary wave-current conditions have a significant effect on the scour depth around the pile than the current-only or wave-only. The scour depth around the pile on the inclined seabed is larger than that of the horizontal seabed. The setting of protection layer can effectively reduce the local scour depth around the pile. In addition, the particle size of the protective layer has a great influence on the protective effect.

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    Dynamic Response of Pile at Waterwave Load and Seismic Load
    LIU Chenchen, ZHANG Qi, LI Mingguang, ZHOU Xianglian, LI Weijie
    2021, 55 (6):  638-644.  doi: 10.16183/j.cnki.jsjtu.2020.142
    Abstract ( 797 )   HTML ( 14 )   PDF (1262KB) ( 452 )   Save

    The pile foundation of offshore wind turbines is not only subjected to the cyclic action of wave load, but also the threat of seismic load. Therefore, the environment of pile in the ocean is complex. However, most theoretical investigations have often focused on the seabed response at water wave load or seismic load respectively. In this paper, a wave-seismic-pile-seabed coupling model is constructed by using the finite element method. The numerical analysis is based on the implicit dynamic analysis in Abaqus. Morison’s equations are used to simulate the effect of water wave on pile foundation. The Mohr-Coulomb model is adopted to simulate the seabed while the pile is considered as an elastic medium. The earthquake is applied on the bottom of the model as acceleration. The dynamic response of the pile embedded in seabed are studied, such as acceleration, displacement, shear force, and bending moment. The results show that seismic load has an important influence on the single pile foundation of offshore wind turbine. Under the action of earthquake load, the acceleration and displacement response of the pile are amplified to a certain extent. The properties of the soil and the parameters of the pile are crucial to the design of the single pile foundation for offshore wind turbines.

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    Particle-Fluid Coupling Algorithm Considering Dynamic Fluid Mesh
    HE Jinhui, LI Mingguang, CHEN Jinjian, XIA Xiaohe
    2021, 55 (6):  645-651.  doi: 10.16183/j.cnki.jsjtu.2020.317
    Abstract ( 774 )   HTML ( 6 )   PDF (1573KB) ( 366 )   Save

    It is generally difficult to consider the fluid dynamic boundary problem in the traditional particle-fluid coupling algorithm, causing calculation errors owing to the mismatching of the fluid-solid boundary and affecting the accuracy of the results in the modeling of large deformation issues. In view of this problem, the dynamic updating method of fluid mesh is introduced and Darcy’s seepage equation and the particle-fluid interaction equation in dynamic mesh are derived. Based on the discrete element commercial software PFC2D, the particle-fluid coupling algorithm considering dynamic fluid mesh is developed. The proposed algorithm is applied to simulate the undrained shear biaxial test of saturated soil. The comparison result with the constant volume method verifies the effectiveness of the developed algorithm. Finally, the algorithm is used to simulate the undrained biaxial tests at different confining pressures. The law of the calculated results agrees well with that of the laboratory tests. By considering the problem of fluid dynamic boundary, the developed algorithm can obtain the fluid-solid boundary matching in the simulation of triaxial compression test and one-dimensional consolidation test or other cases in large deformations, which can help to improve the simulation accuracy and offer a theoretical reference for similar studies.

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    Analytical Analysis of Influence of Dewatering on Adjacent Pipelines Based on Pasternak Foundation
    XU Changjie, ZENG Yiting, TIAN Wei, CHEN Ming
    2021, 55 (6):  652-662.  doi: 10.16183/j.cnki.jsjtu.2020.007
    Abstract ( 559 )   HTML ( 6 )   PDF (2959KB) ( 308 )   Save

    Based on the Pasternak model of elastic foundation beams, and combining the effective stress principle of soil and Dupuit hypothesis, the analytical solution of adjacent pipeline deformation in sandy soil caused by single well dewatering is derived. The example calculation results are in good agreement with the results of pumping test and numerical simulation, which verifies the applicability. The law of stress and deformation for the pipeline is studied by parameter analysis. The results show that the influence of soil shear stiffness should not be ignored in the study of soil-pipeline interaction and the pipeline deformation range is approximately equal to the influence radius of dewatering. Pipeline deformation and stress are greatly influenced by dewatering depth and the distance between the pipeline and the dewatering well. Before reaching the critical drawdown, the maximum value of pipeline deformation and bending moments are at the center of pipeline, increasing with the increase of dewatering depth. When the dewatering depth exceeds the critical drawdown, the maximum bending moment will shift outward from the center with the increase of the dewatering depth, resulting in two peak bending moments which are at the intersection of the water level line and at the pipeline. The research results can provide reference for pipeline protection in relevant projects.

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    Dynamic Responses of Saturated Soil Foundation Subjected to Plane Wave Based on Nonlocal-Biot Theory
    WANG Ning, DING Haibin, TONG Lihong, JIANG Yalong
    2021, 55 (6):  663-671.  doi: 10.16183/j.cnki.jsjtu.2020.149
    Abstract ( 491 )   HTML ( 4 )   PDF (1484KB) ( 328 )   Save

    To investigate the influence of pore size effect on dynamic response of saturated soil foundation, a model for predicting the dynamic response of the ground surface of the saturated soil foundation under incident P wave and SV wave is proposed based on the nonlocal-Biot theory. The analytical solution is obtained using the wave function expansion method. The influence of pore size described by nonlocal parameter, input frequency, and the incident angle on the dynamic response of displacement and stress is discussed in detail. The results show that at low frequencies, the calculation results of the nonlocal-Biot theory are basically the same as those of the classical Biot theory. At high frequencies, the surface displacement and stress change significantly with nonlocal parameters, that is, at high frequencies, the effect of pore size on the surface response cannot be ignored. The influence of incident wave frequency on the ground-surface response is related to pore size, that is, the larger the pore size, the more significant the frequency effect. The influence of SV wave on the dynamic response of ground surface is larger than that of P wave. Besides, the total reflection phenomenon is observed at an incident angle of 45° for the incident of SV wave. The results obtained in this work can provide reference for studying the problem of wave propagation in half-space saturated soil foundation.

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    Time-Domain Calculation Method of an Equivalent Viscous Damping Model Based on Complex Damping Model
    SUN Panxu, YANG Hong, ZHAO Zhiming, LIU Qinglin
    2021, 55 (6):  672-680.  doi: 10.16183/j.cnki.jsjtu.2020.031
    Abstract ( 600 )   HTML ( 5 )   PDF (1139KB) ( 322 )   Save

    The damping matrix of the complex damping model is easy to be constructed, which only depends on the material loss factor and the structural stiffness matrix. However, the complex damping model has some shortcomings, such as time-domain divergence and causality. Structural inherent characteristics are constant, so that the equivalent relationship between material loss factor and structural damping ratio is deduced and the viscous damping model which is equivalent to complex damping model is obtained. The proposed damping model overcomes the shortcoming of the complex damping model. Besides, the convenience that the complex damping model is directly dependent on material loss factor is retained. According to the equivalent relationship between the material loss factor and structural modal damping ratio, the real mode superposition method based on the proposed damping model is suggested for the proportional damping system. For the non-proportional damping system, according to the equivalent relationship between the material loss factor and modal damping ratio of the substructure, the complex mode superposition method based on the proposed damping model is proposed by the aid of Rayleigh damping and the state space method. The example analysis proves the feasibility and correctness of the proposed method.

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    Simulation of Influence of End Anchorage Degradation of Stirrups Caused by Alkali Aggregate Reaction on Shear Performance of Reinforced Concrete Beams
    ZHAO Pengfei, XUE Xin, YANG Cheng
    2021, 55 (6):  681-688.  doi: 10.16183/j.cnki.jsjtu.2020.094
    Abstract ( 592 )   HTML ( 3 )   PDF (1890KB) ( 298 )   Save

    This paper conducted a three-point loading experiment and analytical investigations on the shear performance of reinforced concrete (RC) beams with anchor defect at the lower end of stirrups. In the experiment, artificial methods were used to simulate the anchor degradation of the lower end of the stirrup caused by the alkali-aggregate reaction (AAR). The results show that, compared with the sound beams, the anchorage degradation of stirrups reduces the shear capacity of RC beams, and the degree of reduction becomes more pronounced with the increase of the local bond degradation area. The decrease in shear capacity is thought to be attributed to the reduction of the shear contribution by the stirrups and the reduction of the shear resistance by interlock action of coarse aggregate between diagonal cracks. The quantitative evaluation of shear contribution based on the computed stirrup strains confirms that the anchorage defect at the lower end of the stirrup reduces both the shear contribution Vc by concrete and Vs by stirrups, and the reduction of Vs is more significant than Vc.

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    Numerical Calculation Method for Crack Dynamic Propagation Based on Newmark Implicit Time Integration Scheme
    GUO Deping, LI Zheng, PENG Senlin, ZENG Zhikai, WU Daifeng
    2021, 55 (6):  689-697.  doi: 10.16183/j.cnki.jsjtu.2020.021
    Abstract ( 759 )   HTML ( 8 )   PDF (1724KB) ( 320 )   Save

    Extended finite element method (XFEM) is based on the idea of unit decomposition. The jump function that can reflect the discontinuity of the crack surface and the progressive displacement field function of the crack tip is added to the conventional finite element displacement mode, which avoids the inconvenience of remeshing the crack tip and the heavy calculation. Then the conventional finite element method calculates the fracture problem, and the crack propagation is independent of the mesh. When the standard finite element deals with time integration, the degree of freedom of the overall stiffness matrix will continue to increase in the process of crack propagation, which makes iterative calculation impossible. This paper proposes a novel Newmark implicit time integration scheme based on the XFEM to simulate dynamic crack growth. This method enriches all the nodes with the Heaviside function and the asymptotic displacement field function at the crack tip, that is, each node has 12 degrees of freedom, so that the overall stiffness matrix is consistent without making iterative calculation impossible. At the same time, a sparse matrix technology is proposed to solve the problems of large memory and long calculation time occupied by the matrix.

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    Deformation of a Collinear Tunnel Induced by Overlying Long-Distance Excavation
    CHEN Shuan, WU Huaina, CHEN Renpeng, SHEN Shuilong, LIU Yuan
    2021, 55 (6):  698-706.  doi: 10.16183/j.cnki.jsjtu.2020.026
    Abstract ( 556 )   HTML ( 6 )   PDF (1463KB) ( 428 )   Save

    Overlying excavation will inevitably cause uplift of the existing tunnel due to the stress relief and rebound of soil, and the impact will be more significant when the long-distance is in line. Based on the Timoshenko simplified model of tunnel which considers the shearing dislocation between rings, and combining with the Winkler foundation model, an analytical model for soil-tunnel interaction analysis of overlying excavation was established. Based on the superposition principle, the model proposed was applied to a case study of tunnel deformation induced by overlying long-distance collinear excavation. By comparing the calculated results with the measured data, the accuracy of the proposed model was verified. The analysis results show that after the construction of the upper main structure, the uplift deformation of the tunnel has significantly decreased, but the local differential settlement increases, resulting in a significant increase in the internal force of the tunnel and the deformation of the annular joint. The groundwater leakage generally occurrs not at the location with the maximum uplift of tunnel, but between the location with the maximum opening of joint and the location with the maximum shearing dislocation. As a result, not only the total deformation but also the opening and dislocation deformation of joints caused by differential settlement should be concerned in practice. Although the shear deformation generally accounts for about 21.41% of tunnel deformation, the induced shearing dislocation is significant compared with the opening caused by bending, which can be more important for waterproof in joints. The analytic model should not neglect the shearing deformation of the tunnel.

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    Consolidation Characteristics and Bearing Behavior of Sand Pile Composite Foundation in Caisson Heightening
    CHEN Peishuai, PAN Yazhou, LIANG Fayun, LI Dejie
    2021, 55 (6):  707-715.  doi: 10.16183/j.cnki.jsjtu.2020.058
    Abstract ( 598 )   HTML ( 7 )   PDF (2208KB) ( 321 )   Save

    To study the influence of consolidation on the bearing capacity of the composite foundation in the process of caisson heightening, the consolidation characteristics of the sand pile composite foundation in the process of caisson heightening are discussed based on the sand pile composite foundation engineering of a large-scale onshore caisson foundation. The influence of loading duration and replacement rate of the sand pile are analyzed. Based on the area ratio method of pile-soil and the pile-soil stress ratio method, the formula of the ultimate bearing capacity of the sand pile composite foundation considering the consolidation effect is derived, which is compared with the measured value of the ultimate bearing capacity of the foundation. The results show that the time history curves of the bearing capacity of the composite foundation based on the two methods are close, and the initial bearing capacity is less than the measured value of bearing capacity, while the bearing capacity after consolidation is 68% and 80% higher than the natural strength of the composite foundation. This method considers the influence of consolidation on the bearing capacity of the foundation in the process of caisson heightening. It can avoid the problem of stagnant sinking of open caisson as it underestimates the actual bearing capacity of the foundation, and provides suggestions for calculation of ultimate bearing capacity of the composite foundation considering the influence of consolidation and formulating the reasonable construction scheme of open caisson.

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    A Combined Residual Detection Method of Reaction Wheel for Fault Detection
    HE Xiawei, CAI Yunze, YAN Lingling
    2021, 55 (6):  716-728.  doi: 10.16183/j.cnki.jsjtu.2019.254
    Abstract ( 562 )   HTML ( 4 )   PDF (7000KB) ( 315 )   Save

    A fault detection method of combined residual is proposed to effectively master the health state of the reaction wheels of in-orbit satellite according to the telemetry data. Based on the characteristics of in-orbit telemetry data, in the proposed method, the XGBoost regression model is used to predict the rotation speed and generate residual with available data of the closed-loop controlled reaction wheel. The sensitivity of viscous friction coefficient to the sudden change of friction torque is also combined with the method. In addition, the fault detection method is verified in view of the incomplete telemetry data in orbit. The result shows that the proposed method has an excellent detection effect on common reaction wheel faults. The combined residual fault detection method does not rely on fault samples and has low requirements for samples, so it has a certain application value in practical fault detection system.

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    Design and 3D Printing Simulation of a Lattice Compressor Impeller
    ZHANG Yuan, LI Fanchun, JIA Dejun
    2021, 55 (6):  729-740.  doi: 10.16183/j.cnki.jsjtu.2020.034
    Abstract ( 812 )   HTML ( 9 )   PDF (25454KB) ( 455 )   Save

    Taking the compressor impeller as the research object, and based on the octagonal truss lattice structure, a novel lightweight lattice compressor impeller is designed, and its machinability is verified by using a SLM280 3D printer. In order to understand its 3D printing performance, the 3D printing process of the lattice impeller is simulated based on the finite element method (FEM). Based on the feasibility of using the numerical method to study the 3D printing process, the printing process of the lattice impeller at different power values is analyzed and compared with the solid compressor impeller under the same working condition. The results show that the layer deformation of the lattice impeller and the solid impeller is a process that increases layer by layer. Under the 7 working conditions studied in this paper, the maximum residual deformation and residual stress of the lattice impeller after printing are less than those of the solid impeller. The maximum residual deformation of the lattice impeller can be 20.19% smaller than that of the solid impeller, and the maximum residual stress can be 10.69% smaller than that of the solid impeller. This means that the lattice impeller is not only lighter, but also has a better printing performance than the solid impeller.

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    Online Measurement of Machining Tool Wear Based on Machine Vision
    ZHOU Junjie, YU Jianbo
    2021, 55 (6):  741-749.  doi: 10.16183/j.cnki.jsjtu.2020.083
    Abstract ( 872 )   HTML ( 14 )   PDF (4784KB) ( 641 )   Save

    In order to solve the problems of tool wear measurement in actual production, such as manual operation and shutdown detection, a machining tool wear measurement system based on machine vision is developed in this paper. First, the Otsu segmentation algorithm based on Laplacian edge information is proposed to binarize the images. Then, through rough positioning by morphology-based Canny operator edge detection and image registration, the tool wear area is extracted effectively. Finally, sub-pixel edge detection based on Zernike moment is used to improve the measurement accuracy while the principal curve method is used to fit sub-pixel edge points so as to obtain the smooth edge curve and realize the online measurement of tool wear. In real machining process, the tool wear test results show that the system has a high degree of automation and a rapid running speed. Moreover, its measurement accuracy can reach micron level. This system can be effectively applied to real-time monitoring of tool wear in industry.

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    Surface Micro-Texture and Cutting Characteristics of Milling Cutter for Die-Casting Aluminum Alloy
    HE Lihua, PAN Jianfeng, NI Jing, FENG Kai, CUI Zhi
    2021, 55 (6):  750-756.  doi: 10.16183/j.cnki.jsjtu.2020.195
    Abstract ( 689 )   HTML ( 10 )   PDF (13249KB) ( 431 )   Save

    Aimed at the problems of low processing accuracy and surface quality of die-casting aluminum alloy under the influence of cutting force, a method of using surface micro-textured milling cutter with groove and V-shaped arrays on the rake face was proposed. The variations of milling forces were monitored and analyzed by using tri-direction-force transducer, and the spectrum characteristics of the y-direction milling force (Fy) was emphatically analyzed. The spectrum analysis diagrams of Fy of three different milling cutters were obtained by fast Fourier transform. The milling performance of the micro-textured milling cutters was evaluated by surface topography and surface roughness. The results show that compared with the average values in the x, y, and z directions of the conventional milling cutter, the values of the groove micro-structured milling cutter are reduced by 3.8%, 0.29%, and 11.7%, while those of the V-shaped micro-structured milling cutter are reduced by 8.5%, 14.3%, and 12.4%. The relationship between high frequency amplitudes of Fy at 6 times spindle frequency are proposed as conventional milling cutter>groove arrays milling cutter>V-shaped arrays milling cutter. Compared with the conventional milling cutter, the surface roughness is decreased when using micro-textured milling cutters, and the surface quality of the workpiece processed by the V-array milling cutter is the best. This paper will provide a theoretical basis for precision milling of die-cast aluminum alloys.

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    Weld Seam Profile Identification with T-Joints Based on Intensity Mutation and Density Feature Detection for Thick Plate Welding Process
    HE Yinshui, LI Daize, ZHAO Ziyu, QIAN Weixu
    2021, 55 (6):  757-763.  doi: 10.16183/j.cnki.jsjtu.2020.068
    Abstract ( 537 )   HTML ( 4 )   PDF (2687KB) ( 415 )   Save

    There is a need for the effective weld seam profile extraction method to realize the automatic and intelligent welding process with thick steel plates based on laser vision sensing. In this paper, a method was proposed to identify the variable weld seam profiles from the strong arc background based on intensity mutation and density feature detection for the thick plate welding process with T-joints. First, an improved Canny algorithm was used to magnify the weld seam profile and restrain interference. Next, an intensity mutation detection method was proposed to further strengthen the weld seam profile because there exists intensity mutation in the local region surrounding the weld seam profile. Finally, an algorithm based on the band-width and density feature scanning method was proposed to further eliminate the interference data after the strengthened image was binarized with the Otsu algorithm. The weld seam profile was identified as clusters with their spatial scale features after the nearest neighbor clustering was dealt with. The results show that this method can identify over 95% of the weld seam profiles from the arc interference background whose area is about 20% of the image. It provides valuable reference for promoting the automatic and intelligent welding process with different joints.

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    Topology Optimization Strategy of Structural Strength Based on Variable Density Method
    DING Mao, GENG Da, ZHOU Mingdong, LAI Xinmin
    2021, 55 (6):  764-773.  doi: 10.16183/j.cnki.jsjtu.2019.301
    Abstract ( 1113 )   HTML ( 15 )   PDF (15908KB) ( 517 )   Save

    In structural strength topology optimization based on the variable density method, there are gray cells in the optimization result, making it difficult to accurately predict the structural stress which changes greatly before and after post-processing. This paper uses a filter-projection-based structural parameterization method to achieve a continuous decrease in the proportion of structural intermediate density units during the iterative optimization process. By studying the influence of the main optimization parameters of the structural ratio strength problem on the optimization process and structural strength optimization, a novel optimization strategy of structural topology optimization followed by approximate shape optimization is proposed, which realizes the accurate control of the change of structural stress during the optimization process, achieveing structural strength optimization while improving the stability of the optimization process. Typical optimization examples verify the rationality and practicability of the proposed optimization method.

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    A Compressor Power Soft-Sensing Method Based on Interpretable Neural Network Model
    WANG Yulin, ZHOU Dengji, HAO Jiarui, HUANG Dawen
    2021, 55 (6):  774-780.  doi: 10.16183/j.cnki.jsjtu.2020.086
    Abstract ( 546 )   HTML ( 8 )   PDF (1586KB) ( 390 )   Save

    In order to ensure the accuracy and efficiency of measurement, and reduce the dependence of the soft sensing on dataset, a soft-sensing method of compressor power based on interpretable neural network is proposed. When training on a dataset with good generalization in the experiment, the root mean squared error(RMSE) of the interpretable neural network model on the test set is 0.0094, which is 1.1% lower than that of the back propagation(BP) neural network model. When training on a dataset with poor generalization, the RMSE of the interpretable neural network model on the test set is 0.0128, which is 79.8% lower than that of the BP neural network model. The experimental results show that the soft-sensing method based on interpretable neural network not only has a high accuracy rate, but also can maintain a good measurement performance when training on a dataset with poor generalization.

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