2,058 research outputs found
Adaptive fault tolerant control and thruster fault reconstruction for autonomous underwater vehicle
No full textThis paper investigates adaptive fault tolerant control and fault reconstruction problem for AUV subject to ocean current disturbance and modelling uncertainty. At first, a virtual closed-loop system based adaptive fault tolerant control method is developed. In this method, the constructed virtual closed-loop system is mainly used to deal with the influence of the initial tracking error in an ideal environment and avoid the serious chattering phenomenon in control output. Then with respect to fault reconstruction in the framework of fault tolerant control, an improved second-order sliding mode observer is constructed to estimate the thruster fault effect. The feedback of the developed observer consists of different functions of the estimation errors, including fractional function, signature function and integral function etc. Furthermore, the stability analysis is given based on Lyapunov theory. Finally, a series of simulations are performed on an over-actuated AUV for different desired trajectories and different types of thruster faults under the condition of the simulated ocean current environment. The comparative simulation results demonstrate the effectiveness and feasibility of the new design.</p
Trajectory tracking control for autonomous underwater vehicles based on fuzzy re-planning of a local desired trajectory
No full textThis paper investigates the trajectory tracking control problem for autonomous underwater vehicles whose initial starting position differs substantially from that specified by the desired trajectory. This scenario is very likely to cause serious chattering in the control output, especially in the early stages, when the large tracking error is the input to the controller. A novel trajectory tracking control strategy is developed based on fuzzy re-planning of a local desired trajectory. At each time instant, a local desired trajectory is reconstructed based on the AUV's current position and that specified by the original desired trajectory at a future time. Also the control effort is computed based on the local desired trajectory, rather than the original one. Moreover, the interval between each time instant is determined by a new single-input fuzzy model, where the input is determined by the distance between AUV's current and desired trajectories and the change in the distance. Finally, the effectiveness of the new control strategy is verified by simulation-based case studies using an actual vehicle model as a necessary step prior to experimental validation.</p
Puleicaofu.
No full text高爾基 ; 費明君譯.三幕劇.本電子書乃根據《香港版權條例(第528章)》而複製, 並只可在大學圖書館系統內的獨立電子書系統上使用.Gao'erji ; Fei Mingjun yi.Ben dian zi shu nai gen ju "Xianggang ban quan tiao li (Di 528 zhang)" er fu zhi, bing zhi ke zai da xue tu shu guan xi tong nei de du li dian zi shu xi tong shang shi yong.Detailed notes in vernacular field only
A sphere region tracking control scheme for underwater vehicles
No full textThe concept of region tracking control has advantages for underwater vehicles for some special missions, such as pipeline tracking. This article develops a sphere region tracking control scheme based on barrier Lyapunov functions, where an observer is used to estimate the effects of external disturbances and modeling uncertainty. It is shown that the distance between the vehicle's position and the corresponding point on the desired trajectory is always kept within the prescribed boundaries. Simultaneously, the absolute value of each attitude-tracking error is less than another defined boundary. Finally, the new control scheme is applied to a fully actuated underwater vehicle, and the advantages of this strategy are validated compared to other region-tracking control schemes.</p
Supplemental Material - 3D-printed Tortuous Vessels with Photodissociable and Morphology-controllable Ink
No full textSupplemental Material for 3D-printed Tortuous Vessels with Photodissociable and Morphology-controllable Ink by Biling Wang, Pengcheng Zhao, Peng Zhang, Jun Hu, Yande Liu, Mingjun Xie and Yong He in Journal of Biomaterials Applications</p
Terminal sliding mode‐based tracking control with error transformation for underwater vehicles
No full textOcean currents and waves can cause the initial position of an underwater vehicle to deviate from the initial state of the desired trajectory. For such cases, this paper investigates the finite-time tracking control problem for a vehicle in the presence of large initial tracking errors and external disturbances. A continuous finite-time tracking control scheme is developed for this scenario based on an improved nonsingular terminal sliding mode surface modified by a piecewise function. Compared to the alternative approaches, a method based on error transformation is added to the sliding mode surface, resulting in improved tracking accuracy in the steady state. Then, to reduce the effect of large initial tracking error on the control input signals, an exponential decay function about the initial location of the vehicle is developed to obtain the control law by combining it with a strictly generalized saturation function. In contrast to alternative approaches, a nonlinear structure is used to counteract the approximation error of the neural network used in the modeling of the dynamics. Moreover, it is shown that the tracking error converges to a small neighborhood of zero in a fixed time. Finally, the new control scheme's effectiveness is verified by simulation studies on an underwater vehicle model and the results compared to other existing control designs
Spatial distribution of grassland and sparsely vegetated land in Central Asia from 2000 to 2014.
No full textSpatial distribution of grassland and sparsely vegetated land in Central Asia from 2000 to 2014. Raster data was done for Exacerbated grassland degradation and desertification in Central Asia during 2000–2014 study. The data was generated by using standard deviation of Enhanced Vegetation Index (EVI) during thermal growing season (EVITGS). The resolution is 463 m, and the coordinate system is Sinusoidal, projected to WGS84. 0 and 1 mean grassland and sparsely vegetated land, respectively
Fan ti zi he jian ti zi du zhe zai yue du zhong de cha yi
No full textZhai, Mingjun.Thesis M.Phil. Chinese University of Hong Kong 2014.Includes bibliographical references (leaves 64-68).Abstracts also in Chinese.Title from PDF title page (viewed on 30, September, 2016).Zhai, Mingjun
Design and experimental validation of an adaptive sliding mode observer-based fault-tolerant control for underwater vehicles
No full textCost and other practically related reasons can mean that velocity sensors are not available on an underwater vehicle. For such cases, the results in this brief are developed on an observer-based fault-tolerant control for underwater vehicles in the presence of external disturbances and unknown thruster faults. An adaptive sliding mode observer is developed to achieve finite-time convergence where, in comparison to a high-gain-based design for the observer, a nonlinear feedback is constructed based on the position estimation error. Unlike alternatives, a discontinuity term in the developed fault tolerant controller is avoided, and the stability of the controlled dynamics is characterized using the Lyapunov theory. Finally, these new results are supported by both a simulation-based study and experimental verification.</p
sj-docx-1-hol-10.1177_09596836241236344 – Supplemental material for The evolution of river systems under the influence of climate change and human activities in the endorheic zones during the Holocene
No full textSupplemental material, sj-docx-1-hol-10.1177_09596836241236344 for The evolution of river systems under the influence of climate change and human activities in the endorheic zones during the Holocene by Mingjun Gao, Yu Li, Zhansen Zhang, Junjie Duan, Yaxin Xue, Simin Peng, Hao Shang and Shiyu Liu in The Holocene</p
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