Table of Content

    28 August 2021, Volume 55 Issue 8 Previous Issue    Next Issue
    Hydrodynamics Study of Riser with Helical Strakes Oscillating in Flow
    LI Ang, SUN Ren
    2021, 55 (8):  907-915.  doi: 10.16183/j.cnki.jsjtu.2020.234
    Abstract ( 739 )   HTML ( 510 )   PDF (4486KB) ( 545 )   Save

    To reduce the vibration damage to the riser, hydrodynamic parameters of a smooth riser and a riser with triple symmetrically distributed helical strakes are evaluated in an experiment. The wave and current in natural environment are conceptualized to the experimental condition of the oscillatory flow and the uniform flow. Experiment cases are divided into the static flow and the uniform flow, while the risers oscillate along the in-line, the transverse, and the diagonal direction. The added mass coefficient Cm and the drag coefficient Cd are calculated from experimental data by using the Morison equation. The results of the riser with strakes indicate that Cm is independent of the Keulegan-Carpenter (KC) number and the oscillating direction. Cd is found to be in inverse proportion to the ratio of 1/3 power of the KC number and the maximum flow speed to oscillatory velocity. This finding is consistent with the format of Morison parameters of a flat plate in oscillatory flow, which endows the classical theory with novel validation and implication in the design of a riser. Under the same condition, the Cd of the helical strake riser is promoted over 273% than the bare riser, which indicates that the helical strakes efficiently reduce the influence of oscillation under complex conditions. The results provide a new solution for vibration reduction of offshore structures, which is of high value in ocean engineering.

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    Propagation Evolution Characteristics of Weakly Nonlinear Internal Solitary Waves on Slopes
    ZHI Changhong, CHEN Ke, YOU Yunxiang
    2021, 55 (8):  916-923.  doi: 10.16183/j.cnki.jsjtu.2020.125
    Abstract ( 746 )   HTML ( 10 )   PDF (6862KB) ( 313 )   Save

    The propagation equation of variable-coefficient internal solitary waves was used to describe the propagation and evolution of weakly nonlinear internal solitary waves (ISWs)on slopes with different slopes. The results show that weakly nonlinear ISWs suffer from fission during the climbing process and split into the prominent wave and the trailing wave train. The ISWs are mainly influenced by the shoaling effect and the energy dissipation caused by terrain induction. For the ISWs with weak nonlinearity, the shoaling effect caused by topography is dominant, and causes the increase in wave amplitude and the decrease in wave speed. The wave amplitude and the wave speed, meanwhile, tend to be stable. Under the same terrain condition, as the initial wave amplitude increases, the increase in wave amplitude decreases, and the decrease in wave speed increases. As the slope increases, the energy dissipation effect of the nonlinear internal solitary wave in the propagation process is gradually greater than the shoaling effect, which makes the wave amplitude of the internal solitary wave increase first and then decrease in the propagation process. The ISWs change from concave to convex as the wave passes over the turning point (where the depth of the upper layer is the same as that of the lower layer).

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    Shear Layer Instability of Flow Around a Circular Cylinder Based on Large Eddy Simulation
    GUO Zhiyuan, YU Peixiang, OUYANG Hua
    2021, 55 (8):  924-933.  doi: 10.16183/j.cnki.jsjtu.2019.266
    Abstract ( 827 )   HTML ( 19 )   PDF (8100KB) ( 556 )   Save

    The flow around a cylinder is a common research object of fluid mechanics. As the Reynolds number (Re) increases, the Kelvin-Helmholtz instability of the shear layer will occur in the wake behind the cylinder. Using the large eddy simulation method to investigate the problem numerically in a medium range of Re (Re=2000, 3900, 5000), the refined flow field behind the cylinder can be obtained, and an in-depth study of the instability of the shear layer can be conducted. To get the characteristic frequency of the shear layer instability, two methods, i.e., the traditional analysis of monitoring points and the dynamic mode decomposition method on the local flow field, are used. The results show that the frequencies obtained by the two methods are basically the same. However, compared with the traditional method, the dynamic mode decomposition method can overcome the random error caused by the artificial selection of monitoring points, and can give the characteristic frequency of shear layer instability more conveniently. In addition, it can further analyze the influence of different Re values on the instability characteristics of the shear layer based on different flow field modes.

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    Variation Characteristics of Formation and Development of Ventilated Supercavity at Low Froude Numbers
    XU Haiyu, LUO Kai, HUANG Chuang, ZUO Zhenhao, GU Jianxiao
    2021, 55 (8):  934-941.  doi: 10.16183/j.cnki.jsjtu.2020.128
    Abstract ( 592 )   HTML ( 6 )   PDF (8083KB) ( 492 )   Save

    To study the variation characteristic of supercavity shape and gas-leaking mode in the initial generation and development process of a ventilated supercavity, a 3-D numerical model considering the compressibility of the ventilated gas and gravity effect was adopted to simulate the supercavitation flow by using the inhomogeneous multiphase flow model and the SST turbulence model, which is verified and validated by the experimental results. The process of initial generation and development of the ventilated supercavity were investigated over a wide range of air entrainment coefficients and Froude numbers. The results show that the development of the re-entrant jet supercavity is very unstable. The initial generation of the supercavity is accompanied by the cavity collapse and cavity shedding, the phenomenon of air-water mixture reversely flowing occurs in the devolopment of the supercavity, and the supercavity shape is difficult to be estimated. The twin vortex supercavity is initially developed by the re-entrant jet closure mode. Then, the supercavity closure mode transfers to the twin vortex after the supercavity is fully developed, and the supercavity shape and the internal pressure are relatively stable. When approaching the criteria for the formation of the twin vortex and re-entrant jet closure, the supercavity mode changes between the twin vortex and the re-entrant jet, resulting in a more complex variation of supercavitation flow and supercavity shape.

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    Experimental Study of Supersonic Boundary Layer Transition Induced by Cylindrical Roughness Elements
    JIN Long, YI Shihe, HUO Junjie, LIU Xiaolin, NIU Haibo
    2021, 55 (8):  942-948.  doi: 10.16183/j.cnki.jsjtu.2020.221
    Abstract ( 555 )   HTML ( 6 )   PDF (9494KB) ( 274 )   Save

    The boundary layer transition process induced by different heights and quantities of the cylindrical roughness elements at Mach 3.0 is investigated experimentally by using the nano-tracer-based planar laser scattering (NPLS) technique. Fine structures of the boundary layers of both streamwise and spanwise induced by the cylindrical roughness elements in the supersonic flow are obtained, and the development of the boundary layer in the roughness element wakes is observed. The boundary layer after reattachment will keep the laminar state within a certain distance, meanwhile hairpin vortexes can be observed clearly during the development of the boundary layer. The fractal theory is used to quantitatively analyze the NPLS images of the boundary layer. This method can achieve the positions of the boundary layer transition in several cases. The research results show that the interaction between multiple roughness elements can inhibit the boundary layer transition and the evolution of hairpin vortexes. However, when the roughness elements on both sides are higher than those in the middle, the interaction between roughness elements has no obvious inhibitory effects on the development of the boundary layer.

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    One-Layer Particle Level Set Method
    MU Kailong, ZHAO Lanhao, MAO Jia
    2021, 55 (8):  949-957.  doi: 10.16183/j.cnki.jsjtu.2020.368
    Abstract ( 623 )   HTML ( 6 )   PDF (6576KB) ( 493 )   Save

    A one-layer particle level set method in which Lagrangian particles are employed to track the interface features is proposed and utilized to capture the interface. First, the interface is captured by utilizing the level set method. Then, the interface is corrected based on the position information of Lagrangian particles and the smooth and accurate interface is obtained. The defect of poor volume conservation properties of the level set method is overcome, which greatly improves the accuracy of the moving interface. After that, a simple and effective particle reallocation strategy is presented, including the addition and deletion of particles, so that the method can accurately handle complex topological changes such as the interface merging and separation. Finally, the method proposed is verified by several benchmark examples, which can be used to accurately describe the moving interface.

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    Propagation Characteristics of Low Frequency Sound Energy in Range-Dependent Shallow Water Waveguides
    ZHU Hanhao, XIAO Rui, ZHU Jun, TANG Jun
    2021, 55 (8):  958-967.  doi: 10.16183/j.cnki.jsjtu.2019.237
    Abstract ( 593 )   HTML ( 6 )   PDF (20149KB) ( 336 )   Save

    In view of the low-frequency sound energy propagation in range-dependent waveguides in shallow water, in cylindrical coordinates, the sound energy flux is used as the study object based on the finite element method (FEM). The influence laws and the corresponding mechanisms of three types of complex seabed topographies, wedye-shaped seabed, seamount, and trench on sound energy propagation characteristics in sound field are discussed combined with specific simulation examples. The simulation results reveal that the FEM can accurately calculate sound field distribution in any seabed topography. For the up-sloping wedge-shaped seabed, the greater the inclination angle is, the stronger the sound energy leaks to the bottom, the more rapid the sound energy attenuates in water. But for the down-sloping wedge-shaped seabed the opposite is true. A small seamount enhances the sound energy above it, but hinders the reception of the sound energy behind it. The influence laws of small trenches are related to the grazing angle of sound energy. Only when the horizontal angle of the trench is smaller than the grazing angle of each normal mode in waveguide, would the sound energy be influenced in propagation.

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    Structural Impact Dynamic Response Characteristics of Offshore Platform Blast Wall in High Temperature Environment
    WANG Rui, XUE Hongxiang, YUAN Yuchao, TANG Wenyong
    2021, 55 (8):  968-975.  doi: 10.16183/j.cnki.jsjtu.2019.249
    Abstract ( 550 )   HTML ( 7 )   PDF (7696KB) ( 284 )   Save

    The blast wall is an important protection facility for offshore platforms, whose anti-explosion performance needs to be focused on. Based on the nonlinear finite element method, the structural dynamic response of the blast wall under the explosion at normal temperature was studied. The applicability of the quasi-static and dynamic algorithms was compared with the experimental data, and the structural impact deformation forms at room temperature were analyzed. Considering the effects of high temperature on materials and structures, the structural dynamic response characteristics of the blast wall were analyzed. The study shows that the high temperature has a significant aggravating effect on structural response. That is, given the load level, the maximum displacement can reach 5 times of that at normal temperature. Under the impact of normal temperature load, the structural strain is elastic with no permanent deformation or with small deformation, but it may aggravate to huge permanent deformation at a high temperature. The effect of high temperature will change the response pattern of the structure. This research can provide reference for the design of blast wall.

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    Numerical Simulation of Propeller Cavitation in Non-Uniform Flow
    LIU Heng, WU Rui, SUN Shuo
    2021, 55 (8):  976-983.  doi: 10.16183/j.cnki.jsjtu.2020.211
    Abstract ( 673 )   HTML ( 10 )   PDF (20891KB) ( 530 )   Save

    Taking a certain oil tanker propeller as the research object, and using Schnerr-Sauer cavitation model based on Rayleigh-Plesset equation and the realizable k-ε two-layer turbulence model, the cavitation pattern around the propeller in non-uniform flow conditions is simulated by using the computational fluid dynamics (CFD) software STAR-CCM+. Through effective and reasonable mesh densification of the propeller blade tip area, the tip vortex cavitation is successfully captured with a small number of meshes. The comparison between numerical calculation and test results shows that the whole process of cavitation inception, development, and collapse in wake flow can be accurately reproduced. The back-sheet cavitation pattern at each phase angle is in good agreement with the test results and the difference of cavitation area between calculation and the experiment is within 5%. Although the numerical method can capture the tip vortex cavitation, it cannot accurately predict the unsteady characteristics and spatial structure of the tip vortex cavitation. Based on the above results, it can be concluded this numerical methodology is suitable for simulating cavitation flows around propeller in non-uniform flow.

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    Extreme Response Analysis of Parametric Roll of C11 Container Ship
    ZHOU Xiaoyu, LI Hongxia, HUANG Yi
    2021, 55 (8):  984-989.  doi: 10.16183/j.cnki.jsjtu.2020.085
    Abstract ( 620 )   HTML ( 8 )   PDF (830KB) ( 399 )   Save

    Based on the narrow-band stochastic processes theory and Hermite transform, this paper proposed a method to study the extreme dynamic response of the parametric roll of ships. Taking the C11 container ship as an example, the average extremum of the stochastic parametric roll of the ship was estimated. A comparison of the results of Monte Carlo simulation indicates that the estimation error is lower than 1%, which proves that the proposed method is valid. Meanwhile, the prediction accuracy of the proposed method in this paper by using 20 time history samples is the same as that of the Monte Carlo method by using 104 time history samples, which proves the efficiency of the proposed method. Then, the conventional Gumbel model was used to estimate the extremum of the C11 parametric roll. A comparison of the results shows that the estimation error of the conventional Gumbel model is quite large, proving that the conventional Gumbel model is not appropriate to estimate the extreme responses of strong non-linear motions, such as the parametric roll of ships. However, even if the proposed method is used to predict extreme values, there is a certain deviation from the model test results. The analysis indicates that this prediction error is caused by ignoring the correlation between the maximum values.

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    Influence of Free-State Ice Size and Initial Position on Coupled Hydrodynamic Performance of Ice Propeller
    WANG Chao, LIU Zheng, LI Xing, WANG Chunhui, XU Pei
    2021, 55 (8):  990-1000.  doi: 10.16183/j.cnki.jsjtu.2019.262
    Abstract ( 518 )   HTML ( 5 )   PDF (10307KB) ( 327 )   Save

    In order to simulate the effect of free-moving ice on the hydrodynamic performance of the propeller, a non-contact model of ice-impeller interaction was established by using the overlapping grid method. In the calculation process, the hexahedral mesh was used to conduct mesh division of the computational domain, and the dynamic fluid body interaction (DFBI) method was used to simulate the motion of ice blocks under the propeller suction effect. The accuracy of the numerical method is verified by the experimental study on the action of the ice under the influence of the ice propeller. On this basis, the influences of different parameters such as ice size, the initial radial position of ice, and the initial axial position on the hydrodynamic performance of the propeller are obtained. The results show that there are a certain accelerating area and a certain blocking area behind the moving ice block. The size of ice block has a direct influence on the hydrodynamic performance of the propeller.

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    Principal Polynomial Nonlinear Process Fault Detection Based on Neighborhood Preserving Embedding
    LI Yuan, YAO Zongyu
    2021, 55 (8):  1001-1008.  doi: 10.16183/j.cnki.jsjtu.2020.295
    Abstract ( 453 )   HTML ( 8 )   PDF (1341KB) ( 379 )   Save

    Aimed at the problem of high dimension and nonlinearity of variable data in chemical process, a process fault detection algorithm based on neighborhood preserving embedding(NPE )-principal polynomial analysis (PPA) is proposed in this paper. The NPE algorithm is used to extract low dimensional submanifolds of high dimensional data, which overcomes the problem that the traditional linear dimensionality reduction algorithm cannot extract local structure information, so as to reduce the dimensions. The PPA method is used to describe data by a set of flexible principal polynomial components, which can effectively capture the inherent nonlinear structure of process data. The principal polynomial analysis is conducted in the reduced manifold space, and Hotelling’s T2 and square prediction error statistical models are established to determine the control limit for fault detection. Finally, compared with the traditional kernel principal component analysis and the PPA method, a group of nonlinear numerical examples and Tennessee Eastman chemical process data experiments are performed to verify the effectiveness and superiority of the NPE-PPA algorithm.

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    Online Motion Planning for Two Space Rigid Bodies with Rolling Constraints
    REN Shufeng, YANG Dan, YU Haidong, Wang Hao
    2021, 55 (8):  1009-1017.  doi: 10.16183/j.cnki.jsjtu.2019.261
    Abstract ( 581 )   HTML ( 10 )   PDF (2429KB) ( 345 )   Save

    The rolling restraint system between two space rigid bodies is a typical non-holonomic system. The incomplete characteristics can be used to simplify the mechanical structure and improve the reliability of the system. Aimed at the problems that the state variables of the pure rolling constraint non-holonomic system are difficult to control, the existing control methods are limited to specific models, and there is a lack of online control research, a solution method suitable for the online motion planning of the general rolling constraint system is established based on the rolling constraint first-order motion model. First, the offline motion planning is achieved by using the collocation method to obtain the reference trajectory. Then, the sequential action control (SAC) algorithm is used in real-time control combined with the rolling optimization framework to realize the online motion planning of the rolling system. The algorithm is applied to the real-time motion planning of the ball-plane rolling model and the rolling model between two spheres. The simulation results show that the method has a practical application value in broadening the control of the spherical robot and the operation of the dexterous manipulator.

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    Dynamics Analysis of Flexible Manipulator Driven by SMA Spring
    TENG Yajun, CHEN Wujun, YANG Tianyang, JING Zhongliang, LIU Wuji
    2021, 55 (8):  1018-1026.  doi: 10.16183/j.cnki.jsjtu.2020.207
    Abstract ( 772 )   HTML ( 15 )   PDF (4217KB) ( 656 )   Save

    Combining the flexible robot driven by intelligent materials with the octahedral variable geometry truss system, and based on the theory of octahedral variable geometry truss system, a single flexible unit is designed and driven by parallel shape memory alloy (SMA) spring. The kinematic model is established by utilizing the geometric method. The kinetic energy, the elastic potential energy, and the gravitational potential energy of the flexible manipulator are analysed. The general dynamics equation is established based on the Lagrangian dynamics. The driving force of a single flexible element of SMA spring is calculated by utilizing MATLAB. Adams simulation is performed, and the calculation results are in good agreement with the theoretical calculation results. Finally, a prototype of the flexible control arm is built and the rotation angles at different currents are measured. Modeling and simulation methods are useful references for other types of robots.

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    Stackelberg-Game-Based Intelligent Vehicle Decision Method for Merging Scenarios
    HU Yikai, ZHUANG Hanyang, WANG Chunxiang, YANG Ming
    2021, 55 (8):  1027-1034.  doi: 10.16183/j.cnki.jsjtu.2020.319
    Abstract ( 818 )   HTML ( 21 )   PDF (3724KB) ( 498 )   Save

    Existing decision-making methods for intelligent vehicles do not consider factors such as the right of way information, polite driving of the vehicle, and limited perception range of the vehicle, which may easily lead to safety hazards in merging scenarios. Aimed at these problems, a Stackelberg-game-based decision-making method is proposed. This method constructs a game model combining the right of way and conducts parametric modeling of the merging scenarios. Then, the cooperation factor is introduced to design the corresponding profit function. Finally, the vehicle decision-making solution framework is designed to achieve the maximum value of decision-making benefits in this scenario. The experimental results illustrate that the proposed method can effectively improve the accuracy of vehicle decision-making behavior prediction on the datasets and the decision-making robustness in a high traffic density environment.

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    Expert Forum
    Decision-Making Method of Intelligent Vehicles: A Survey
    HU Yikai, WANG Chunxiang, YANG Ming
    2021, 55 (8):  1035-1048.  doi: 10.16183/j.cnki.jsjtu.2020.387
    Abstract ( 1001 )   HTML ( 31 )   PDF (1687KB) ( 978 )   Save

    Combined with the current research status of the intelligent vehicle decision-making methods at home and abroad, this paper classifies and summarizes decision-making methods from four aspects: decision input and output, environment interaction, and algorithm types. Besides, it analyzes their advantages and disadvantages, and evaluates applicable scenarios. Moreover, it surveyes the common data sets and current evaluation standards which are used for decision-making researches. Furthermore it discusses the technical difficulties faced by current decision-making methods and future development trends.

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