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Table of Content

    01 January 2021, Volume 55 Issue 1 Previous Issue    Next Issue
    Numerical Wave Simulation Using Geometrical VOF Method Based on OpenFOAM
    TIAN Kang, ZHANG Yao, LI Jinlong, ZHANG Xinshu, YOU Yunxiang
    2021, 55 (1):  1-10.  doi: 10.16183/j.cnki.jsjtu.2020.99.015
    Abstract ( 1582 )   HTML ( 441 )   PDF (2416KB) ( 671 )   Save

    Numerical wave simulation is a significant research topic. In this paper, the open source computational fluid dynamics (CFD) platform, OpenFOAM, is utilized to simulate Stokes fifth-order waves. Since geometrical volume-of-fluid (VOF) could better capture free surface due to its geometrical reconstruction step, the free surface simulations are accomplished by applying OpenFOAM built-in geometrical VOF method-isoAdvector, and the relaxation zone scheme is introduced through secondary development for wave absorption. The mesh density and Courant number convergence analyses with geometrical VOF are conducted. The simulation shows that satisfactory results could be obtained with a large Courant number. The algebraic and geometrical VOF simulated data with respect to wave elevation and phase at varied wave steepnesses and frequencies are recorded and compared with the theoretical value of Stokes fifth-order waves, which demonstrates that geometrical VOF is better than algebraic VOF in the prediction of wave elevation. Finally, the lengths and weights of the wave absorption zone are discussed, and the results imply that the best practice for the wave absorption is assigning the wave absorption zone length at least two times of the wave length along with applying exponential weight distribution.

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    Multi-Objective Optimization of Three-Column Semi-Submersible Platforms Based on Surrogate Models
    QIU Wenzhen, SONG Xingyu, ZHANG Xinshu
    2021, 55 (1):  11-20.  doi: 10.16183/j.cnki.jsjtu.2019.087
    Abstract ( 911 )   HTML ( 8 )   PDF (5962KB) ( 473 )   Save

    In the initial design stage of a semi-submersible platform, the main particulars of the platform are the key factor affecting the hydrodynamic performance and construction cost. Therefore, multi-objective optimization of the main particulars of the semi-submersible platform is of great engineering significance. First, the design variables of each platform and sample database are determined by design of experiments. Then, the hydrodynamic performances of the semi-submersible platform are analyzed by using the panel method and Morison’s equation. The distribution of probes for estimating the wave elevations on the calm water surface is arranged, and the airgap can be computed. Based on the database obtained by numerical simulation, the surrogate models based on radial basis function (RBF) are established. Next, the formal parameters in RBF are obtained by using the leave-one-out cross validation method. The surrogate model can greatly improve the optimization efficiency. Finally, by using the multi-objective particle swarm optimization (MOPSO) method, taking safety and economy of offshore platforms as two optimization objectives, and taking platform stability, airgap and horizontal motion performance as constraints, the optimization program for the semi-submersible platform can be obtained. Through the detailed analyses of the optimization program for the semi-submersible platform, the most efficient design strategy for the three-column semi-submersible platform is proposed.

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    Coupled Dynamic Response on a 6 MW Spar-Type Floating Offshore Wind Turbine Under Extreme Conditions
    YANG Jie, HE Yanping, MENG Long, ZHAO Yongsheng, WU Haoyu
    2021, 55 (1):  21-31.  doi: 10.16183/j.cnki.jsjtu.2019.140
    Abstract ( 1013 )   HTML ( 10 )   PDF (3907KB) ( 469 )   Save

    To realize the practical scale application of the spar-type floating offshore wind turbine (FOWT) in the medium depth sea areas, a novel 6 MW spar-type floating offshore wind turbine is analyzed by model test and numerical simulation under extreme conditions. The response of main freedom degrees, the mooring tense and the stress at the danger point are explored by a 1∶65.3 scale model at the State Key Laboratory of Ocean Engineering in Shanghai JiaoTong University. Coupled motion response of the spar-type floating wind turbine is calculated by using numerical simulation software in time domain. The results of the numerical simulation and model test are compared and analyzed in time and frequency domain. The maximum deviation between numerical simulation and model test is less than 12%, which shows that the numerical simulation results are in good agreement with the model test results. The dynamic response energy of the FOWT is mainly concentrated at low frequency and wave frequency. Moreover, the whole FOWT system has an excellent survivability under extreme conditions. Finally, the ultimate load of the wind turbine is predicted, which provides the necessary theoretical basis and calculation parameters for the structural strength calculation.

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    Envelope Features of Response Amplitude of Hanging Underwater Slender Bodies in Upper End Horizontal Periodical Motion
    CONG Shanxue, XU Xuesong
    2021, 55 (1):  32-39.  doi: 10.16183/j.cnki.jsjtu.2019.225
    Abstract ( 640 )   HTML ( 0 )   PDF (3237KB) ( 247 )   Save

    To improve the safety and operating efficiency of underwater slender bodies, the hanging underwater slender body is divided into several micro segments for analysis. The equilibrium equations of each segment are listed according to the mechanical equilibrium and deformation coordination conditions. Then, the equilibrium equations are solved with MATLAB programming. When the upper end moves horizontally and periodically, the upper end motion amplitude, upper end motion period, and lower end weight are changed separately to obtain the amplitude envelope of hanging underwater slender bodies. Based on the results of numerical calculations, the response envelope characteristics of hanging underwater slender bodies are analyzed. The maximum amplitude point on the amplitude envelope of the slender body is generally at the upper end. As the parameters change, it can be converted to the lower end. Changing the amplitude and period of upper end motion has a greater impact on the minimum amplitude point. The lower end weight has a small influence on the minimum amplitude point. By adjusting the ranges of these parameters, the positions of maximum amplitude point and minimum amplitude point on the amplitude envelope of slender body can be controlled.

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    Modeling and Sliding Mode Control for Chaotic Yawing Phenomenon of Large Oil Tanker
    ZHANG Xianku, HAN Xu
    2021, 55 (1):  40-47.  doi: 10.16183/j.cnki.jsjtu.2019.104
    Abstract ( 718 )   HTML ( 2 )   PDF (1255KB) ( 652 )   Save

    In order to explain and control the unexpected yawing phenomenon of large oil tankers, a pilot model is used to replace the original proportional model and is combined with the nonlinear ship responding model to construct a model of the whole closed-loop maneuvering system, which is found to be similar to the chaotic Duffing equation, and to be able to have a positive Lyapunov exponent after parameter adjustment, indicating that the chaotic theory can be used to explain this unexpected yawing phenomenon. In order to realize course keeping control with robustness to parameter uncertainty, based on the model built and the backstepping method, a sliding mode control scheme is proposed. The simulation illustrates that the static state rudder angle is smaller than 5° and course deviation is smaller than 0.07° when the chaotic yawing is at the theoretical maximum. Chaotic yawing is eliminated. The idea of establishing man-in-the-loop chaotic system is novel, and the method of solving backstepping parameter uncertainty through sliding mode is easy and effective.

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    Optimization of Subgrade Structure Parameters of Ballasted Track Passenger Dedicated Line
    WANG Wei, LU Sikui, YANG Chengzhong, FENG Qingsong
    2021, 55 (1):  48-55.  doi: 10.16183/j.cnki.jsjtu.2019.235
    Abstract ( 719 )   HTML ( 1 )   PDF (1643KB) ( 315 )   Save

    In order to improve the force condition of ballasted railway subgrade structure and reduce maintenance cost, it is necessary to study the influence of subgrade structure parameters on subgrade dynamic response under train load. Orthogonal test was designed and used to analyze the sensitive relationship between dynamic response of railway subgrade structure and parameters of each structural layer, and the optimal parameter combination of subgrade structure of ballasted railway was determined by combining analytic hierarchy process (AHP) and linear evaluation index. The parameters include elastic modulus of ballast bed, elastic modulus of surface and bottom layer of subgrade bed, thickness of ballast bed, thickness of surface and bottom layer of subgrade bed, and elastic modulus of foundation. The results show that the thickness of track bed is the main factor that affects dynamic stress of ballast bed, dynamic stress and vibration acceleration of surface layer of subgrade bed. The elastic modulus of foundation is the main factor that affects the vertical displacement of the sleeper. The mechanical optimum parameter combination of ballast track structure parameters is determined as the elastic modulus ballast bed is 250 MPa, elastic moduli of surface and bottom layer of subgrade bed are 120 MPa and 115 MPa, the thickness of ballast bed is 0.35 m, the thickness of surface and bottom layer of subgrade bed are 1.1 m and 2.3 m, and the elastic modulus of foundation is 70 MPa.

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    Design and Test of a Magneto-Rheological Mount Applied to Start/Stop Mode of Vehicle Powertrains
    DENG Zhaoxue, YANG Qinghua, CAI Qiang, LIU Tianqin
    2021, 55 (1):  56-66.  doi: 10.16183/j.cnki.jsjtu.2019.192
    Abstract ( 869 )   HTML ( 4 )   PDF (6695KB) ( 425 )   Save

    In order to overcome the disadvantage of vehicle ride comfort caused by large vibration and torque excitation of vehicle engine in start/stop mode, a flow mode magneto-rheological (MR) mount is designed for low frequency working conditions. Based on the analysis on the influence of exciting current on the viscosity of the MR fluid (MRF) and the relationship between the fluid resistance effect and the flow rate in the damping channel, the magnetic circuit and the damping performance of the MR mount model are analyzed. According to the mathematical model of the MR mount damping force, the multi-objective optimization function of the magnetic circuit is established. The co-simulation optimal platform is developed by using the Isight and ANSYS software. The non-dominated sorting genetic algorithm II (NSGA-II) is used to optimize magnetic circuit design. The dynamic performance test of the MR mount monomer and the vibration isolation performance test of the whole vehicle in start/stop mode are conducted respectively. The results show that the controllable damping force of the optimized MR mount increases by 111.71% and the restoring force increases by 21.99% compared with those before. When the vehicle is in start/stop mode and the excitation current is 1.0A, the peak vibration acceleration of the passive side (the side connected to the body) with the optimized MR mount decreases by 33.3% compared with that before. Besides, the peak vibration acceleration of driver’s seat rail decreases by 21.6%, which significantly improves the ride comfort of the vehicle.

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    Experimental Investigation on Motion Hydrodynamics of Water Entry for Inclined Cylinders
    XIA Weixue, WANG Cong, LI Jiachuan, HOU Dongbo
    2021, 55 (1):  67-76.  doi: 10.16183/j.cnki.jsjtu.2019.116
    Abstract ( 827 )   HTML ( 1 )   PDF (2031KB) ( 483 )   Save

    Experiments of vertical water entry for a cylinder with different inclined angles are performed at a low Froude number to investigate the cavity evolution and hydrodynamics. Unique phenomena of double cavities and separated cavity are observed. The accurate trajectories and attitude angles for the inclined cylinders are proposed, which are extracted by utilizing the method of digital image correlation from the image sequence recorded by a high-speed camera. The raw data of trajectory and attitude angle are fitted using the method of quintic smoothing spline, with which, the velocity and acceleration of the cylinders during water entry are estimated, and the cylinder characteristics of motion and hydrodynamic force are studied. The experimental results demonstrate that the unique cavity phenomena are observed for the inclined cylinder during water entry, such as cavity separation and double cavities. The acceleration increases quickly after the cylinder penetrates into water and achieves the maximum value after cavity separation occurs. After that, the acceleration decreases quickly and tends to zero. The vertical velocity of the cylinder with a large initial inclined angle decreases faster than that with a small inclined angle, while the corresponding horizontal velocity increases rapidly. The trajectories of the cylinder with different initial inclined angles generally present the characteristics of first moving in the upstream direction and then in the downstream direction. With respect to the properties of inclined angle, the angular acceleration responds very quickly to the hydrodynamic force, and it generally first increases and then decreases. In addition, the angular speed of cylinder for a large initial inclined angle increases faster than that for a small inclined angle. The inclined angle shows the same trend as well. The cylinder drag and lift coefficients rapidly increase after the cylinder enters the water, and then slowly increase after the cavity pinches off. Moreover, the force coefficients increase more quickly for the cylinder with a large initial inclined angle.

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    Entrainment and Turbulence Characteristics of Continuous-Flux Release Gravity Current over Rough Beds
    HAN Dongrui, YU Junyang, YUAN Yeping, HE Zhiguo, WANG Yuhang, LIN Yingdian
    2021, 55 (1):  77-87.  doi: 10.16183/j.cnki.jsjtu.2019.110
    Abstract ( 675 )   HTML ( 0 )   PDF (4226KB) ( 426 )   Save

    In both the natural environment and hydraulic engineering, there widely exists the phenomenon of gravity current. In practical conditions, most beds are covered with gravel and sediment particles of different sizes, which can be regarded as rough bed conditions. Therefore, it is of practical scientific significance and engineering application value to study the dynamic characteristics of gravity current flowing over rough beds. By conducting flume experiments for continuous-flux gravity current, and considering the bed roughness and the current initial mass fraction comprehensively, the propagation characteristics such as head position, head velocity, and entrainment coefficient of gravity current are analyzed, the turbulence characteristics such as the turbulence intensity and Reynolds stress at different cross-sections are studied, and the bed shear stress is calculated by using the Reynolds stress method and the turbulent kinetic energy method. The results show that the velocity of the gravity current head is negatively correlated with the bed roughness, but positively correlated with the current initial mass fraction. In the experimental runs of conspicuous roughness and high initial mass fraction, the former is the dominant factor for the kinematic characteristics of gravity currents. When the bed roughness increases to a certain extent, the "lifting phenomenon" of the averaged longitudinal velocity profiles occurs in the gravity current body. One minimum and two maximun values are presented in the turbulence intensity profile of gravity current, and the longitudinal turbulence intensity is the main controlling factor for the current turbulent structure. Besides, the vertical turbulence intensity over rough beds increases significantly compared with that of smooth beds. Near the bed, the Reynolds shear stress is positive, whereas far away from the bed, the Reynolds shear stress is negative. The bed shear stress calculated by using the Reynolds stress method is higher than that by using the turbulent kinetic energy method at identical bed roughness. At the same bulk Richardson number, the entrainment coefficient of gravity current is positively correlated with the bed roughness. It can be concluded that the influence of rough beds on gravity current is mainly as follows: increasing friction resistance, reinforcing mixing effect, redistributing current density near the bed, thickening turbulent boundary layer, and "lifting phenomenon" of the averaged longitudinal velocity profiles.

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    Prediction of Energy Transmission Spectrum of Layered Periodic Structures by Neural Networks
    LIU Chenxu, YU Guilan
    2021, 55 (1):  88-95.  doi: 10.16183/j.cnki.jsjtu.2019.242
    Abstract ( 707 )   HTML ( 3 )   PDF (1494KB) ( 608 )   Save

    In this paper, the prediction of the energy transmission spectrum for layered periodic structures is studied. By considering three cases of geometric parameters and physical parameters changing individually or simultaneously, a deep back propagation (BP) neural network is constructed to realize accurate prediction of the energy transmission spectrum of layered periodic structure. A comparison of the predicted results with those obtained by the radial basis function (RBF) neural network verifies the effectiveness of the proposed method.

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    Copper Surface Treatment in Metal-Polymer Direct Molding Technology
    GUO Rongsheng, HU Guanghong, RONG Jian, WANG Yuanlong
    2021, 55 (1):  96-102.  doi: 10.16183/j.cnki.jsjtu.2019.185
    Abstract ( 900 )   HTML ( 5 )   PDF (6924KB) ( 530 )   Save

    The preparation technology of micro-nano structure on copper surface is studied and optimized. Aqueous solution containing sodium carbonate and sodium molybdate is used as electrolyte, and the copper sample is anodized at a constant voltage to form a layer of oxidation on the copper surface. Then, the copper surface is treated with aqueous solution containing phosphate and sodium dihydrogen phosphate as corrosion solution to obtain a micro-nano structure on the copper. The surface is observed by using a scanning electron microscope. Finally, the analysis software is used to analyze the scanning electron microscope image to calculate the micro-nano structure pores on the copper surface. The results show that when the anodizing voltage is 15 V, the anodizing time is 20 min, the phosphoric acid mass fraction is 20%, and the corrosion time is 30 min, the copper surface is relatively smooth, and the porosity reaches 25.77%. Orthogonal experiments demonstrate that the type, concentration of the corrosive solution, and etching time have a great effect, while the anodizing electrolyte, voltage and electrolysis have no significant effect on the porosity. Using a combination of anodic oxidation and chemical corrosion, micro and nano junctions with uniform and high porosity can be prepared on the copper surface.

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    A Single Machine Scheduling Problem Considering Machine Availability Constraints
    WANG Jinfeng, CHEN Lu, YANG Wenhui
    2021, 55 (1):  103-110.  doi: 10.16183/j.cnki.jsjtu.2019.173
    Abstract ( 744 )   HTML ( 3 )   PDF (949KB) ( 390 )   Save

    The study described in this paper is derived from a real rotor production workshop where low reliability leads to poor quality of workpieces. A single machine scheduling problem considering machine availability constraints is addressed. The availability is defined by the machine reliability, which can be restored by preventive maintenance. Preventive maintenance with different improvement factors is defined in the mathematical model to minimize the total tardiness. A genetic algorithm is designed to solve the problem. Numerical results show that the proposed approach can effectively deal with the impact of machine availability constraints on production scheduling. Sensitivity analyses provide valuable managerial insights for real workshop scheduling.

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