Table of Content

28 September 2018, Volume 52 Issue 9 Previous Issue    Next Issue

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Numerical Simulations of Impact Loads and Structural Responses of Bottom Decks of Platforms Caused by Nonlinear Freak Waves QIN Hao,TANG Wenyong,XUE Hongxiang 2018, 52 (9):  1009-1016.  doi: 10.16183/j.cnki.jsjtu.2018.09.001 Abstract ( 732 )   Save In order to study the impact on offshore platforms caused by nonlinear freak waves, a numerical wave tank is built, in which the incompressible Navier-Stokes equations are solved, with the free surfaces reconstructed using a VOF method. Nonlinear freak waves based on the Peregrine breather solution are generated. A fluid-structure interaction (FSI) algorithm is used to calculate the structural response of the bottom deck, which is discretized with the finite element method (FEM). The impact loads underneath a platform model are calculated and compared with the ones caused by the 2nd-order regular waves with the same wave lengths and heights to reveal the unique features of the impact caused by nonlinear freak waves. The structural response of the bottom deck is calculated using the FSI algorithm and processed with an FFT method to analyze the wetted vibration. Additionally, the influence of the vertical initial velocity is considered during the structural response simulations. References | Related Articles | Metrics

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Lateral Failure Analysis of Unbonded Flexible Risers Under Axial Compression Force LIU Xiaoyuan,XUE Hongxiang,TANG Wenyong 2018, 52 (9):  1017-1022.  doi: 10.16183/j.cnki.jsjtu.2018.09.002 Abstract ( 34 )   Save Nonlinear finite element method is used to study the failure characters of flexible riser under axial compression force. The tensile armor layer, structural tape and outer sheath are modeled by solid elements. Material nonlinearity, geometrical large deformation, complex contact and friction are considered in this article. The effects of number of helix bands in armor layer, friction coefficient, thickness of outer sheath on the failure modes and axial compression force of flexible risers are studied. The results show that the failure process of all steel helix bands model is more complex than the simplified model which only contains partial helix bands. And the axial compression force exhibits a multiple peak phenomenon. Friction coefficient has a great influence on failure mode. It’s a lateral failure when the friction coefficient is small, otherwise a radial failure when the friction coefficient is large. The thickness of the outer sheath has limited influence on the maximum axial compression force of lateral failure. References | Related Articles | Metrics

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Pulse Width Modulation Rectifier Based Electromagnetic Transmitter ZHANG Jialin,ZHANG Yiming,DING Jianzhi,GAO Junxia 2018, 52 (9):  1023-1030.  doi: 10.16183/j.cnki.jsjtu.2018.09.003 Abstract ( 44 )   Save In order to improve the power factor and power density of electromagnetic transmitter, and make the transmitter small in size and light in weight, a novel electromagnetic transmitter circuit based on pulse width modulation (PWM) rectifier is presented in this paper. Parameters for the permanent synchronous generator (PMSG) PWM rectifier in the transmitter are designed. First, the mathematical model of the PMSG PWM rectifier is established, and then based on the flux oriented control theory in motor speed control system, a double closed loop control strategy, which consists of a decoupling current controller and an outer voltage controller is proposed. The active and reactive current decoupling control is obtained. To improve the dynamic performance and stability of the PMSG PWM rectifier, parameters in the PI controller are designed. Simulation and experimental results show that the proposed transmitter can not only meet the needs of geophysical exploration, but also has the advantages of simple structure, high power factor and low current harmonics. The proposed design method of controller can effectively determine the PI parameters and simplify control system. References | Related Articles | Metrics

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Optimal Design of Wireless Power Transfer System for Gastrointestinal Robots LI Dawei,JIANG Pingping,KE Quan,YAN Guozheng 2018, 52 (9):  1031-1037.  doi: 10.16183/j.cnki.jsjtu.2018.09.004 Abstract ( 22 )   Save This paper proposed an analytical model and optimal design for wireless power transmitting system used for gastrointestinal robots. Based on the phase-shift PWM controller UCC3895, a wireless power transmitting circuit which is suitable for large-sized coils and large driving current conditions was designed. The system has the characteristics of stable operation, adjustable frequency and power. We optimized the number of turns of a single-layer transmitting coil with a diameter of 69cm according to the analytical model and the feasible region analysis of the coil. The results show that at the operating frequency of 218kHz, the power transmitting system can provide up to 650mW for endoscopic robots with a transmission efficiency of 3.60%. References | Related Articles | Metrics

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Gaseous Flow and Heat Transfer Characteristic in a Microchannel with Different Thermal Boundary Conditions GU Juan,HUANG Rongzong,LIU Zhenyu,WU Huiying 2018, 52 (9):  1038-1043.  doi: 10.16183/j.cnki.jsjtu.2018.09.005 Abstract ( 27 )   Save The micro total-energy-based double-distribution-function lattice Boltzmann (LB) model with viscous dissipation and compression work was developed to simulate the gaseous flow and heat transfer in a microchannel with uniform wall temperature boundary condition and uniform heat flux boundary condition. The rarefaction effect on gaseous flow and heat transfer characteristic was studied intensively for different uniform Knudsen numbers. The numerical results show that the rarefaction effects on gaseous flow with these two thermal boundary conditions are similar，which can increase the gaseous flow velocity and reduce the friction coefficient. However, due to the different temperature distributions caused by different boundary conditions, the rarefaction effect will have different influences on the heat transfer characteristics. The heat transfer process is enhanced with uniform wall temperature boundary condition and deteriorated with uniform heat flux boundary condition, respectively. References | Related Articles | Metrics

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Dynamic Mode Decomposition of Unsteady Flow Filed in a Volute of Centrifugal Compressor HU Chenxing,DING Jie,ZHU Xiaocheng,DU Zhaohui 2018, 52 (9):  1044-1049.  doi: 10.16183/j.cnki.jsjtu.2018.09.006 Abstract ( 30 )   Save Unsteady numerical simulations of the centrifugal compressor with and without volute were carried out to investigate the effect of vaneless diffuser and volute on compressor instability. Combined with dynamic mode decomposition (DMD) method, the three-dimensional flow field of the volute is decomposed and reconstructed under design and stall condition. It is shown that the dominating perturbation of volute under design condition is the one induced by main blade passing, while the perturbation with higher frequency due to main and splitter blades is suppressed by the volute. The occurrence of stall in the compressor is delayed by the volute compared with the compressor without volute. A standing wave comes into being in the volute during stall, and the flow filed of volute fluctuates along the tangential direction. The occurrence of volute stall indicates that the volute loses the ability to suppress the instability perturbation, and the compressor is occupied by stall. The application of DMD method on volute provides the detailed flow information under specific perturbation frequency before and after stall. References | Related Articles | Metrics

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Large Eddy Simulation on the Turbulence Flow in Three-Dimensional Randomly Pellet Packed Beds LIU Hongsheng,JIANG Linsong,WU Dan,XIE Maozhao 2018, 52 (9):  1050-1057.  doi: 10.16183/j.cnki.jsjtu.2018.09.007 Abstract ( 36 )   Save A three-dimensional random structure model of pellet packed bed for porous media is built based on the discrete element software of LIGGGHTS. The effectiveness of the random model has been verified by the calculation of the macroscopic flow resistance coefficient and the local porosity. A comparative study on the turbulence characteristics and vortex distribution within the porous structure has been carried out employing large eddy simulation (LES) and the conventional k-ε turbulence model. Simulation results show that the random structure model could predict the local porosity and the macroscopic resistance coefficient of the porous medium effectively. For the complex turbulent flow inside the porous structure, LES could give detailed information of the small vortices with diameter of 0.4-2.0mm within the porous structure and demonstrate the complex vortex structure in large pores of the porous medium. Besides, LES could also record the generation and development of the small vortex, and the process of stretching, splitting and disappearing of the large vortex within the local pores in detail, and the results are more consistent with the reality and the basic theory of turbulence. The LES study on turbulence characteristics in the random pellet packed bed in this paper will lay the foundation for the future simulation of filtration combustion. References | Related Articles | Metrics

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Sliding-Mode Control of Current for Wind Power Grid-Connected Converter Under Unbalanced Grid Voltage HAN Gang,CAI Xu 2018, 52 (9):  1065-1071.  doi: 10.16183/j.cnki.jsjtu.2018.09.009 Abstract ( 16 )   Save In order to strengthen the ability in adopting unbalanced grid voltage, a sliding-mode control strategy of current for grid-connected converter with an LCL filter was proposed, and the sliding-mode governing equations of inner current loop and outer voltage loop were established, respectively. Dynamic quality and chattering effect of the designed sliding-mode controller were improved by using exponential rate control method. The referenced current was generated based on extended instantaneous power theory, and the objective of three-phase sinusoidal current was achieved while the second frequency fluctuation in both active and extended reactive power were eliminated. Finally, hardware-in-loop experimental platform based on RT-LAB was built. Results of comparative experiment demonstrated the correctness of proposed algorithm, as well as the excellent properties in dynamic response speed and parameter robustness. References | Related Articles | Metrics

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Expansible Modeling and Applied Strategies Based on Semantic Web for Expert System of AC-DC Intelligent Substation SONG Jie,ZHOU Jian,BAO Wei,HUANG Wentao,GAO Xiang 2018, 52 (9):  1072-1080.  doi: 10.16183/j.cnki.jsjtu.2018.09.010 Abstract ( 31 )   Save In order to realize the modeling of the C language integrated production system (CLIPS) expert system, this paper analyzes the basic conception and function of semantic web. The strategies and rules of the expert system for smart breaker unit and voltage unit, voltage unit, smart breaker unit and hybrid AC-DC stability control unit are devised. By adding the semantic web conception to the structure, the expert system knowledge-base is more systematic and it does help to improve the logic and uniformity among different concepts of the knowledge-base. The final goal is to improve the expansibility of the expert system knowledge-base and improve the reuse rate of the rules in expert system rule-base. References | Related Articles | Metrics

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Aluminum Foil Forming Limitation Test and Numerical Simulation CHEN Weiye,ZOU Tianxia,TANG Ding,GUO Feipeng,LI Dayong 2018, 52 (9):  1081-1085.  doi: 10.16183/j.cnki.jsjtu.2018.09.011 Abstract ( 47 )   Save Thinner aluminum foil brings bigger challenge to its forming performance, so in this paper, no-damage UV printing technology was applied to marking grid in specimens, and an FLD test for 0.11 mm 8011-H22 aluminum foils was successfully launched. Because aluminum foil deformed very little in the width direction under the big width-thickness ratio and the effect of friction, only the right part of FLD could be obtained. Then the finite element simulation of rigid model bulging test was established, and the left part of FLD could be further completed based on the “strain acceleration” failure criteria. A complete FLD was then finally established. References | Related Articles | Metrics

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Simulation of Hydrogen Diffusion in Duplex Stainless Steel TAO Ping,WANG Yanfei,GONG Jianming,WU Weijie,LIANG Tao 2018, 52 (9):  1086-1091.  doi: 10.16183/j.cnki.jsjtu.2018.09.012 Abstract ( 24 )   Save Duplex stainless steels (DSS) are subjected to a deleterious effect known as hydrogen embrittlement. Due to the difference of the ratio of various alloying elements and the influence of processing technology, the volume fraction of austenite phase (φγ) will be changed. Hydrogen diffusion models with different φγ were established based on transient finite element mass diffusion in program—Abaqus. In addition, the discrepancies of hydrogen diffusion in both transverse and longitudinal microstructure were implemented. After the simulation analysis, the apparent diffusion coefficients (Dapp) of the models were calculated. The results show that Dapp decreased with the increase of φγ, and there is a linear relationship between ln Dapp and φγ; the values of hydrogen diffusion coefficient are greater when the elongated austenite is orientated parallel with the direction of hydrogen flux, i.e. the transverse samples are more susceptible to hydrogen embrittlement than longitudinal samples. References | Related Articles | Metrics

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Formability of AZ31B Magnesium Alloy Sheet Under Different Die Temperatures WANG Zimin,LIU Qi,GU Ruiying,WANG Wurong,WEI Xicheng 2018, 52 (9):  1092-1097.  doi: 10.16183/j.cnki.jsjtu.2018.09.013 Abstract ( 28 )   Save To investigate the effect of die temperature on formability of AZ31B magnesium alloy sheet in stamping, forming limit curve (FLC) of AZ31B magnesium alloy sheet was obtained through Nakazima semispherical drawing under different die temperatures. Thermo-mechanical coupling effect under heat transfer between AZ31B magnesium alloy sheet and die was analyzed based on temperature fields of biaxial tension specimens obtained by thermo-mechanical coupled simulation using finite element method. Effect of die temperature on forming limit of AZ31B alloy sheet in working condition was finally verified in a tryout stamping of hinge cover. The results show that temperature gradient distribution of AZ31B magnesium alloy is highly changed with the decline of die temperature, forming limit is thus decreased and fracture position is also affected. The FLCs under different die temperatures are proved to be in good agreement with actual stamping of AZ31B alloy sheet. References | Related Articles | Metrics

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A Design of Low Power Audio Noise Reduction Processor for Smart Microphone CHEN Liming，CHEN Chengying，YANG Jun 2018, 52 (9):  1098-1103.  doi: 10.16183/j.cnki.jsjtu.2018.09.014 Abstract ( 20 )   Save A low power noise reduction processor is developed to improve SNR of microphone. The processor consists of ASIP (application specific instruction-set processor) and hardware accelerators, achieving a great tradeoff of power, efficiency and flexibility. The ASIP has 24-bit width, multi-step pipeline, dual Harvard memory architecture. Acceleration instructions are developed to improve computation efficiency. The reconfigurable accelerators are introduced for high density computing tasks, such as the transformation between time and frequency domain. The processor is implemented on SMIC 130 nm technology, and results show that the processor reduces the noise by 10 dB, consuming about 206 μA current on average. References | Related Articles | Metrics

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Energy Saving Strategy Based on Lightpath Holding Time Aware for Elastic Optical Network Lü Yi,SHI Jin,YANG Yaya 2018, 52 (9):  1104-1111.  doi: 10.16183/j.cnki.jsjtu.2018.09.015 Abstract ( 24 )   Save To effectively reduce the energy consumption for elastic optical network, an energy saving strategy based on software defined networking is proposed. The strategy is designed to reduce the huge switching power of lightpath termination and re-establishment. Firstly, the software defined networking technology and back propagation neural network model are used to predict the traffic situation of each lightpath in the network. Then, for the lightpath on which the traffic transmission has been completed and is about to be removed, a holding time is set according to the prediction result. Setting the holding time for the idle lightpath can avoid the re-establishment of the lightpath between the same source destination node pairs and eliminat the switching power consumption. The simulation results show that the proposed strategy can reduce the total energy consumption by 45% while maintaining a bandwidth blocking ratio at levels comparable to strategies which do not consider the switching power. References | Related Articles | Metrics

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Fault Diagnosis of Terminal Guidance Radar Based on Attribute Granulation Clustering and Echo State Network LU Cheng,XU Tingxue,WANG Hong 2018, 52 (9):  1112-1119.  doi: 10.16183/j.cnki.jsjtu.2018.09.016 Abstract ( 27 )   Save In order to improve the efficiency and precision of terminal guidance radar fault diagnosis, a fault diagnosis method based on attribute granulation clustering and echo state network (ESN) was proposed. Firstly, an attribute distinguishing ability index was defined by attribute value influence degree. As the basis of similarity measure, a number of attribute granules of similar distinguish are obtained through affinity propagation clustering algorithm, and then fault attribute reduction was completed by selecting clustering center attributes. In order to improve the dynamic adaptability of ESN reservoir to samples, Bienenstock-Cooper-Munro (BCM) rule was introduced into the reservoir construction to train the connection weight matrix. Meanwhile, the L1/2-norm penalty term was added to the objective function in order to improve the sparsification efficiency, solving a numerical oscillation problem by using a smoothing L1/2 regularizer, the model was solved by using the half threshold iteration method at last. The effectiveness and superiority of the proposed method are verified by a fault diagnosis example of terminal guidance radar signal processing module. The training time of the simulation experiment is only 8.98s, and the diagnostic accuracy can reach 95.2%. References | Related Articles | Metrics

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Autonomous Localisation Method Based on Linear Feature for Robots YANG Jingdong,PENG Kun,GU Haonan,SHI Yanwei 2018, 52 (9):  1120-1124.  doi: 10.16183/j.cnki.jsjtu.2018.09.017 Abstract ( 31 )   Save The convergence for iterative closest point (ICP) algorithm depends much on the inputs, which often results in local optimum. And normal distribution transform (NDT) algorithm usually acquires more scans in scan matching, and the large angular deviation occurs during long-term autonomous navigation for robots. An improved ICP self-localization algorithm based on line feature is proposed in the paper. We derive functional relations of covariance matrix between matching scans and their fitting lines to scan and match line features rapidly. And the robot updates global poses in terms of closed form correlations. We test the reliability of CICP algorithm in indoor locating experiments. The experiments show that CICP algorithm, compared with ICP or NDT, owns higher real-time and location accuracy, and can reduce matrix computation and improve self-localization precision efficiently. References | Related Articles | Metrics

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An Examination Method of Dense Skeleton Type Resisting Rutting Gradation Based on Fractal Theory LI Limin,ZHANG Guoxiang,JIANG Jianqing 2018, 52 (9):  1125.  doi: 10.16183/j.cnki.jsjtu.2018.09.018 Abstract ( 34 )   Save To solve the anti-rutting gradation design problem, based on fractal theory and many experiments and calculations, a new resisting rutting gradation examination method is put forward. Based on empirical formulas of dynamic stability for asphalt mixture between asphalt penetration and gradation fractal dimension D, which is put forward, by means of binary variables curve regression through self-made MATLAB program, the method applies fractal theory to examining the aggregate gradation, by using the indices such as the fractal dimension of coarse and fine aggregate particle size distribution, the fractal void ratio of coarse aggregate, the fractal volume of fine aggregate in coarse aggregate, etc. The method solves the design blindness of mixture gradation effectively, with simple process of calculation and examination. References | Related Articles | Metrics