SHEN Zhi-peng, DAI Chang-sheng, ZHANG Ning. Trajectory tracking control of underactuated ship based on adaptive iterative sliding mode[J]. Journal of Traffic and Transportation Engineering, 2017, 17(6): 125-134.
Citation: SHEN Zhi-peng, DAI Chang-sheng, ZHANG Ning. Trajectory tracking control of underactuated ship based on adaptive iterative sliding mode[J]. Journal of Traffic and Transportation Engineering, 2017, 17(6): 125-134.

Trajectory tracking control of underactuated ship based on adaptive iterative sliding mode

More Information
  • Author Bio:

    SHEN Zhi-peng(1977-), male, professor, PhD, shenbert@dlmu.edu.cn

  • Received Date: 2017-07-21
  • Publish Date: 2017-12-25
  • Aiming at the trajectory tracking control problem of underactuated ship, the unknown parameters and external disturbances of ship system were considered, and a control method with reinforcement learning based on neural network adaptive iterative sliding mode was put forward.The nonlinear iterative sliding mode functions were constructed based on the horizontal and vertical deviations of tracking trajectory, and the neural network iterative sliding mode controllers of diesel engine speed and rudder angle were designed, respectively.According to the real-time measurement values of diesel engine speed and rudder angle, the reinforcement learning signals reflecting the chattering states of control quantities were calculated, and the neural networks' constructions and parameters were optimized online to restrain control the chattering states and enhance the control system's adaptability.The mathematical model of 5446 TEU container ship was established, and the trajectory tracking controls of circular and sinusoidal trajectories werecarried out, respectively.Simulation result shows that when the circular trajectory is tracked under the disturbances of wind and sea wave, the tracking time of target trajectory is about 250 s with the proposed control strategy, and the tracking speed is about 1 time higher than the value with iterative sliding mode control strategy.The maximum tracking yaw distance is 250 m, and the error reduces by about 30%.The control rudder angle is basically stable after 400 s, and its chattering amplitude is about 2°.The chattering amplitudes of rudder angle and diesel engine speed reduce by more than 50%.The control parameters of diesel engine speed and rudder angle are adaptively adjusted between 38-45 and 3.3-3.9, respectively.When the sinusoidal trajectory is tracked, the proposed control strategy is compared with the fuzzy iterative sliding mode control strategy, and the average vertical tracking error is less than 20 mand reduces by more than 50%.The average chattering amplitude of rudder angle is less than 10°and reduces by more than 60%.The control parameters of diesel engine speed and rudder angle are adaptively adjusted between5.7-5.8 and 0.8-2.5, respectively.

     

  • FullText

    Disclaimer: The English version of this article is automatically generated by Baidu Translation and only for reference. We therefore are not responsible for its reasonableness, correctness and completeness, and will not bear any commercial and legal responsibilities for the relevant consequences arising from the English translation.

    At present, most single propeller and single rudder ships sailing at sea are typical underactuated system ships, in which the rudder device controls the ship's bow turning motion, the main engine propeller controls the ship's speed, and the ship lacks a driving device in the transverse direction[1]When ships are carrying out specific tasks such as laying pipelines, laying mines, and maneuvering, they need to accurately track the path according to the set route, and the trajectory tracking of the ship also requires the target ship to track the preset path at regular intervals according to time parameters[2]It is difficult to track the trajectory of underactuated ships using conventional control methods, and exploring new adaptive nonlinear control strategies has attracted widespread attention from scholars at home and abroad.

    In recent years, there have been many research achievements on ship trajectory tracking control problems[3-4]Wondergen et al. designed an output feedback controller based on a 1:70 actual model to achieve real-time tracking of ship trajectories[5]Ashrafiuon et al. used sliding mode method to track the trajectory of underactuated ships, solving the problem of parameter uncertainty[6-7]Jia Heming et al. designed an adaptive inversion control strategy to effectively track the trajectory of underactuated underwater robots[8]Liao Yulei et al. proposed a sliding mode control method for underactuated unmanned boat trajectory tracking, ensuring asymptotic stability of the tracking error signal[9]Xing Dodge et al. designed an exponentially convergent sliding mode controller that uses coordinate transformation to transform the nonlinear ship model into a chain form[10]Xu Jian et al. designed an inverse dynamic sliding mode controller for 3D trajectory tracking of underactuated UUVs[11]Liao Yulei et al. combined inversion adaptive and sliding mode methods to achieve exponential asymptotic stability of underactuated ship path tracking error[12].

    Currently, Fossen ship motion model is used to study ship trajectory tracking control[5, 8, 10-11]The calculation output usually consists of three control variables: longitudinal and transverse thrust and turning torque of the ship. For conventional single propeller and single rudder underactuated ships, these three control variables need to be converted into the set speed of the diesel engine and the commanded rudder angle of the servo. Therefore, compared with practical applications of ship control, the control variables designed using the Fossen model cannot be directly used. To be consistent with practical engineering applications, this paper will design a controller based on the MMG separation model, directly obtaining control variables such as diesel engine speed and rudder angle. The MMG model for underactuated ship horizontal motion can be represented as

    In the formula:uFor the longitudinal velocity of the vessel;vFor the lateral velocity of the vessel;rShake the angular velocity of the bow;xyThe vertical and horizontal positions of the ship's center of gravity in a fixed coordinate system;ψFor heading angle;X1Y1N1The longitudinal and transverse forces, as well as the rotational moment, generated by the fluid dynamics of the bare hull;X2Y2N2They are the longitudinal and transverse forces and rotational torque of the propeller, respectively;X3Y3N3They are the longitudinal and transverse forces and rotational torque of the rudder;X4Y4N4The longitudinal and transverse forces, as well as the rotational moment, generated by the wind;X5Y5N5The longitudinal and transverse forces and rotational moments generated by waves respectively;mFor the quality of ships;mxmyThey are the vertical and horizontal components of the additional mass of water in the attached coordinate system;IJShip hull pairs in inertial coordinate system and attached coordinate system respectivelyzThe moment of inertia of the vertical axis.

    Figure  1.  Ship trajectory tracking errors

    System controller design objective: To design an adaptive trajectory tracking controller for the ship trajectory tracking mathematical model defined by equation (1) and the ship trajectory tracking error defined by equation (2), ensuring that all signals in the system converge asymptotically while allowing underactuated ships to track the preset trajectory within a limited time.

    in compliance withFigure 2As shown, this paper proposes an adaptive iterative sliding mode trajectory tracking control method for underactuated ship neural networks with reinforcement learning. The output of the control system isxyandψEnter as the set trajectory. The system first calculates the trajectory error and obtainsxeandyeThen, longitudinal error iterative sliding surface 1 and lateral error iterative sliding surface 2 are designed, and the diesel engine command speed is calculated separately through sliding surface feedback controlnAnd command rudder angleδThus driving the executing mechanism toxeandyeTowards zero, ultimately achieving the goal of ship trajectory tracking.

    To effectively suppress the chattering output of the control rudder angle and the main engine speed, and enhance the adaptability of the controller,Figure 2Two parameter optimizers for diesel engine speed and rudder angle control were also designed in the middle. The parameter optimizer calculates the error separatelyxeandyeConstruct RBF neural network as input and output as control parametersk15andk25At the same time, to optimize the output parametersk15andk25According to the speed of the diesel enginenAnd rudder angleδConstruct a reinforcement signal based on the vibration measurement values and adjust the RBF neural network structure online. Under different operating conditions, through adaptive optimization of parameters, the controller can effectively reduce the oscillation of control rudder angle and main engine speed, and improve the overall control performance of the system.

    Figure  2.  Neural network adaptive iterative sliding mode control structure

    To reduce longitudinal errorsxeConvergence, design diesel engine speed iterative sliding mode controller as

    In the formula:σ11σ12They are the first and second order sliding mode surfaces for diesel engine speed control;k11k12respectivelyσ11Convergence speed and input domain control parameters;k13k14respectivelyσ12Convergence speed and input domain control parameters;k15k16They are the convergence law of sliding mode surface feedback control and the zero domain convergence parameter.

    From equation (3), it can be concluded that whenσ12At 0:00, there isσ11→ 0, and then obtainxe→ 0, therefore, the control objective becomes how to adjust the speednachieveσ12Converge and remain calm.

    answerσ12Expand to obtain

    In the formula:tFor time.

    When the ship is sailing normally, the lateral thrust generated by the propeller is small and its influence can be ignored, so the above equation can be approximated as

    During normal navigation, ships generally do not track their trajectory laterally or backwards, meaning that the error between the actual heading and the expected direction is usually less than 90 °. Additionally, the relationship between propeller thrust and diesel engine speed is a monotonically increasing function

    According to equation (4), if the designed ship trajectory is smooth enough and the diesel engine speed system is controllable, there are parameters presentk11k12k13k14R+And expected rotational speedn*∈[-nmax, nmax], makingσ12→0, nmaxFor the forward speed threshold. According to the literature[24]The asymptotic stability theorem of nonlinear scalar systems can be obtained, and the diesel engine speed control law designed by equation (3) can makeσ12Asymptotically converge to zero, and then combineσ11The definition of longitudinal trajectory tracking error is knownxeIt will also converge asymptotically.

    Utilize lateral erroryeAnd heading errorψe=ψ-ψrThe iterative sliding surface for designing a ship rudder angle controller is

    In the formula:σ21σ22σ23σ24They are the first to fourth order sliding surfaces for rudder angle control;k21k22k23k24R+The convergence speed parameters for the four sliding surfaces are respectively, andk23< k24.

    Designing a fourth-order sliding surface is to make the highest order sliding surfaceσ24There is a heading error in the middleψeThe second derivative term of, thus obtainingσ24With rudder angleδThe functional relationship.

    Figure  3.  Circular trajectory tracking curves
    Figure  4.  Lateral error curves of circular trajectory
    Figure  5.  Vertical error curves of circular trajectory
    Figure  6.  Rudder angle curves of circular trajectory
    Figure  7.  Diesel engine speed curves of circular trajectory
    Figure  8.  Ship velocity curves of circular trajectory
    Figure  9.  Speed control parameter k15curve of circular trajectory
    Figure  10.  Ruder angel control parameter k25curve of circular trajectory
    Figure  11.  Sinusoidal trajectory tracking curves
    Figure  12.  Lateral error curves of sinusoidal trajectory
    Figure  13.  Vertical error curves of sinusoidal trajectory
    Figure  14.  Rudder angle curves of sinusoidal trajectory
    Figure  15.  Diesel engine speed curves of sinusoidal trajectory
    Figure  16.  Ship velocity curves of sinusoidal trajectory
    Figure  17.  Diesel engine speed control parameter k15curve of sinusoidal trajectory
    Figure  18.  Ruder angel control parameter k25curve of sinusoidal trajectory
  • [1]
    GUO Chen, WANG Yang, SUN Fu-chun, et al. Survey for motion control of underactuated surface vessels[J]. Control and Decision, 2009, 24 (3): 321-329. (in Chinese). doi: 10.3321/j.issn:1001-0920.2009.03.001
    [2]
    YANG Yang, DU Jia-lu, LIU Hong-bo, et al. A trajectory tracking robust controller of surface vessels with disturbance uncertainties[J]. IEEE Transactions on Control Systems Technology, 2014, 22 (4): 1511-1518. doi: 10.1109/TCST.2013.2281936
    [3]
    DUAN Hai-qing, ZHU Qi-dan. Trajectory tracking control of ships based on an adaptive backstepping neural network[J]. CAAI Transactions on Intelligent Systems, 2012, 7 (3): 259-264. (in Chinese). doi: 10.3969/j.issn.1673-4785.201205056
    [4]
    ZHANG Wei, TENG Yan-bin, WEI Shi-lin, et al. Underactuated UUV tracking control of adaptive RBF neural network and backstepping method[J]. Journal of Harbin Engineering University, 2018, 39 (1): 93-99. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-HEBG201801015.htm
    [5]
    WONDERGEN M, LEFEBER E, PETTERSEN K, et al. Output feedback tracking of ships[J]. IEEE Transactions on Control Systems Technology, 2011, 19 (2): 442-448. doi: 10.1109/TCST.2010.2045654
    [6]
    ASHRAFIUON H, MUSKE K R, MCNINCH L C, et al. Sliding-mode tracking control of surface vessels[J]. IEEE Transactions on Industrial Electronics, 2008, 55 (11): 4004-4012. doi: 10.1109/TIE.2008.2005933
    [7]
    YU Rui-ting, ZHU Qi-dan, XIA Gui-lin, et al. Sliding mode tracking control of an underactuated surface vessel[J]. IET Control Theory and Applications, 2012, 6 (3): 461-466. doi: 10.1049/iet-cta.2011.0176
    [8]
    JIA He-ming, CHENG Xiang-qin, ZHANG Li-jun, et al. Three-dimensional path tracking control for underactuated AUV based on adaptive backstepping[J]. Control and Decision, 2012, 27 (5): 652-657, 664. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-KZYC201205005.htm
    [9]
    LAO Yu-lei, ZHUANG Jia-yuan, LI Ye, et al. Sliding-mode trajectory tacking control for underactuated autonomous surface vehicle[J]. Journal of Applied Sciences, 2011, 29 (4): 428-434. (in Chinese). doi: 10.3969/j.issn.0255-8297.2011.04.016
    [10]
    XING Dao-qi, ZHANG Liang-xin. Sliding-model control for trajectory tracking of surface vessels[J]. Ship and Boat, 2011, 22 (5): 10-14. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-CBZZ201105005.htm
    [11]
    XU Jian, WANG Man, QIAO Lei, et al. Backstepping dynamical sliding mode controller for three-dimensional trajectory tracking of underactuated UUV[J]. Journal of Huazhong University of Science and Technology: Natural Science Edition, 2015, 43 (8): 107-113. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-HZLG201508023.htm
    [12]
    LIAO Yu-lei, WAN Lei, ZHUANG Jia-yuan. Backstepping adaptive dynamical sliding mode control method for path following of underactuated surface vessel[J]. Journal of Central South University: Science and Technology, 2012, 43 (7): 2655-2661. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD201207029.htm
    [13]
    ELMOKADEM T, ZRIBI M, YOUCEF-TOUMI K. Trajectory tracking sliding mode control of underactuated AUVs[J]. Nonlinear Dynamics, 2016, 84 (2): 1079-1091.
    [14]
    HWANG C L, CHIANG C C, YEH Y W. Adaptive fuzzy hierarchical sliding-mode control for the trajectory tracking of uncertain underactuated nonlinear dynamic systems[J]. IEEE Transactions on Fuzzy Systems, 2014, 22 (2): 286-299.
    [15]
    RAYGOSA-BARHONA R, PARRA-VEGA V, OLGUIN-DIAZ E, et al. A model-freebackstepping with integral sliding mode control for underactuated ROVs[C]//IEEE. 8th International Conference on Electrical Engineering, Computing Science and Automatic Control. New York: IEEE, 2011: 1-7.
    [16]
    LIU Chun-mei, YEH Chih-ping, CHEN Wen. Robust iterative learning control for output tracking via chatteringfree sliding mode control technique[C]//IEEE. 8th IEEE International Conference on Control and Automation. New York: IEEE, 2010: 241-246.
    [17]
    ZHAO Guo-liang, ZHAO Can, WANG De-gang. Tensor product model transformation based integral sliding mode control with reinforcement learning strategy[C]//IEEE. Proceedings of the 33rd Chinese Control Conference. New York: IEEE, 2014: 77-82.
    [18]
    HE Xiong-xiong, ZHUANG Hua-liang, ZHUANG Duan, et al. Pulse neural network-based adaptive iterative learning control for uncertain robots[J]. Neural Computing and Applications, 2013, 23 (7/8): 1885-1890.
    [19]
    HUANG Zheng-yu, EDWARDS R M, LEE K Y. Fuzzyadapted recursive sliding-mode controller design for a nuclear power plant control[J]. IEEE Transactions on Nuclear Science, 2004, 51 (1): 256-266.
    [20]
    JIA He-ming, ZHANG Li-jun, CHENG Xiang-qin, et al. Three-dimensional path following control for an underactuated UUV based on nonlinear iterative sliding mode[J]. Acta Automatica Sinica, 2012, 38 (2): 308-314. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-MOTO201202019.htm
    [21]
    BU Ren-xiang, LIU Zheng-jiang, LI Tie-shan. Iterative sliding mode based increment feedback control and its application to ship autopilot[J]. Journal of Harbin Engineering University, 2007, 28 (3): 268-272. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-HEBG200703004.htm
    [22]
    BIAN Xin-qian, CHENG Xiang-qin, JIA He-ming, et al. A bottom-following controller for underactuated AUV based on iterative sliding and increment feedback[J]. Control and Decision, 2011, 26 (2): 289-292, 296. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-KZYC201102025.htm
    [23]
    SHEN Zhi-peng, JIANG Zhong-hao, WANG Guo-feng, et al. Fuzzy-adapted iterative sliding mode control for sail-assisted ship motion[J]. Journal of Harbin Engineering University, 2016, 37 (5): 634-639. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-HEBG201605002.htm
    [24]
    SHEN Zhi-peng, DAI Chang-sheng. Iterative sliding mode control based on reinforced learning and used for path tracking of under-actuated ship[J]. Journal of Harbin Engineering University, 2017, 38 (5): 697-704. (in Chinese). https://www.cnki.com.cn/Article/CJFDTOTAL-HEBG201705007.htm
    [25]
    SHEN Zhi-peng, GUO Chen, ZHANG Ning. A general fuzzified CMAC based reinforcement learning control for ship steering using recursive least-squares algorithm[J]. Neurocomputing, 2010, 73 (4-6): 700-706.
  • Relative Articles

    [1]QIAN Kun, SHEN Zheng-hua, TAN Jing, LIU Ke, DUAN Ji-ying, DU Xi-kang, ZHAO Jian. Review on evaluation of sound quality in high-speed trains[J]. Journal of Traffic and Transportation Engineering, 2024, 24(5): 154-172. doi: 10.19818/j.cnki.1671-1637.2024.05.011
    [2]JIANG Ling-li, LI Shu-hui, LI Xue-jun, WANG Guang-bin, GAO Lian-bin. Health assessment method of traction motor bearing based on transfer learning and convolutional neural network[J]. Journal of Traffic and Transportation Engineering, 2023, 23(3): 162-172. doi: 10.19818/j.cnki.1671-1637.2023.03.012
    [3]ZHANG Wen-jing, RUAN Yu-xin, GAO Ya-ping, CHEN Yu-feng, YUE Qiang, XU Hong-ze. Sliding mode periodic adaptive learning control method for medium-speed maglev trains[J]. Journal of Traffic and Transportation Engineering, 2023, 23(2): 264-272. doi: 10.19818/j.cnki.1671-1637.2023.02.019
    [4]CHEN Li-jia, WANG Kai, WEI Tian-ming, HAO Guo-zhu. Virtual port modeling method based on dynamic fluid field data[J]. Journal of Traffic and Transportation Engineering, 2022, 22(2): 287-297. doi: 10.19818/j.cnki.1671-1637.2022.02.023
    [5]WU Chao-zhong, LENG Yao, CHEN Zhi-jun, LUO Peng. Human-machine integration method for steering decision-making of intelligent vehicle based on reinforcement learning[J]. Journal of Traffic and Transportation Engineering, 2022, 22(3): 55-67. doi: 10.19818/j.cnki.1671-1637.2022.03.004
    [6]XUE Han, SHAO Zhe-ping, PAN Jia-cai, FANG Qiong-lin. Sliding mode control for ship dynamic positioning based on linear matrix inequality[J]. Journal of Traffic and Transportation Engineering, 2018, 18(5): 119-129. doi: 10.19818/j.cnki.1671-1637.2018.05.012
    [7]DUAN Zun-lei, REN Guang, ZHANG Jun-dong, CAO Hui. Intelligent assessment for collaborative simulation training in ship engine room[J]. Journal of Traffic and Transportation Engineering, 2016, 16(6): 82-90.
    [8]LIU Yang, GUO Chen, LIU Zheng-jiang, FAN Yun-sheng. Control method of underactuated surface ship formation based on stable adaptive neural network control law[J]. Journal of Traffic and Transportation Engineering, 2014, 14(3): 120-126.
    [9]WANG Xing-ju, GAO Gui-feng, MIYAGI T. RLRM control method of single entrance ramp for highway[J]. Journal of Traffic and Transportation Engineering, 2012, 12(3): 101-107. doi: 10.19818/j.cnki.1671-1637.2012.03.015
    [10]HAO Ru-ru, ZHAO Xiang-mo, MA Jian, XU Zhi-gang. A novel detection system of automobile ABS[J]. Journal of Traffic and Transportation Engineering, 2011, 11(5): 69-75. doi: 10.19818/j.cnki.1671-1637.2011.05.011
    [11]WANG Wei, YANG Zhao-sheng, ZHAO Ding-xuan. Control model of variable speed limit based on finite horizon Markov decision-making[J]. Journal of Traffic and Transportation Engineering, 2011, 11(5): 109-114. doi: 10.19818/j.cnki.1671-1637.2011.05.017
    [12]NIE Pei-lin, YU Zhi, HE Zhao-cheng. Constrained Kalman filter combined predictor for short-term traffic flow[J]. Journal of Traffic and Transportation Engineering, 2008, 8(5): 86-90.
    [13]Peng Xiao-yun, Ye Wan-jun, She Xue-sen, Zhao Juan, Liu Zhao. Settlement prediction model of wettest-soft loess subgrade in ravine regions[J]. Journal of Traffic and Transportation Engineering, 2007, 7(2): 70-75.
    [14]Bu Ren-xiang, Liu Zheng-jiang, Hu Jiang-qiang. Berthing controller of underactuated ship with nonlinear sliding mode[J]. Journal of Traffic and Transportation Engineering, 2007, 7(4): 24-29.
    [15]BU Ren-xiang, LIU Zheng-jiang, LI Tie-shan. Increment feedback control algorithm of ship track based on nonlinear sliding mode[J]. Journal of Traffic and Transportation Engineering, 2006, 6(4): 75-79.
    [16]XIAO Jian-mei, WANG Xi-huai, LI Shun-lin. Dynamic Identification of Ship Diesel Engine Based on T-S Fuzzy Model[J]. Journal of Traffic and Transportation Engineering, 2006, 6(1): 80-83.
    [17]YIN Zi-bin, WU Gui-tao, SUN Pei-ting. Calculation method of brake NOx emission from marine diesel engine[J]. Journal of Traffic and Transportation Engineering, 2005, 5(4): 67-71.
    [18]WU Hao-zhong, WANG Kai-wen. Fault diagnosis using wavelet packet and neural network in tilting control system of tilting train[J]. Journal of Traffic and Transportation Engineering, 2003, 3(2): 27-30.
    [19]WANG Yun-song, CHU Fu-lei, LIU Ya-dong. Fault diagnosis of diesel engine based on neural network[J]. Journal of Traffic and Transportation Engineering, 2003, 3(4): 44-47.
    [20]HU Yan-ping, YAN Li, ZHU Xin-he, YAN Zhi-jun. Application of Neuro-net in Maintenace Decision for Ship Diesel Engine[J]. Journal of Traffic and Transportation Engineering, 2001, 1(3): 69-73.
  • Cited by

    Periodical cited type(6)

    1. 余荣臻,袁剑平,李俊益. 基于蝗虫优化算法的大型运输船舶自适应控制. 中国舰船研究. 2023(03): 66-74 .
    2. 李宗宣,卜仁祥,邹韵. 结合状态观测与遗传算法的船舶路径预测控制. 船舶工程. 2022(03): 110-117 .
    3. 李宗宣,卜仁祥,章沪淦. 结合改进RBF与虚拟圆弧的船舶路径滑模控制. 西北工业大学学报. 2021(01): 216-223 .
    4. 章沪淦,卜仁祥,于镓铭. 船舶路径跟踪RBF神经网络滑模控制. 上海海事大学学报. 2021(04): 7-11 .
    5. 薛晗,邵哲平,方琼林,马峰. 具有输入时滞的二轮自平衡车自适应滑模控制. 交通运输工程学报. 2020(02): 219-228 . 本站查看
    6. 白昀,郭巍,张鹏. 欠驱动多轴机械节能控制系统误差时域分析. 计算机测量与控制. 2018(11): 129-132 .

    Other cited types(22)

Catalog

    Figures(18)

    Article Metrics

    Article views (724) PDF downloads(364) Cited by(28)
    Related

    /

    DownLoad:  Full-Size Img  PowerPoint
    Return
    Return