27,792 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
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
Liu Kang
No full textLiu Kang: Essays on Art and Culture is a testament to the inexorable passion of an artist who knew no boundaries. This collection of essays, which Liu Kang wrote over 44 years, offers an insight into the artist’s myriad interests as well as his contributions as a first generation Nanyang artist and art educator. Translated into English for this volume, Liu Kang’s essays are accompanied by commentaries and photographs of the artist-author and his subjects
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
Accretion with two-phase gas supply and its application in black hole X-ray binaries
No full textAccretion in black hole X-ray binaries is commonly believed to be supplied by the Roche lobe overflow or the stellar wind. The former is thought to form a geometrically thin disc while the diffuse wind could form a geometrically thick hot accretion flow. In this paper, we instead consider a more generalised case, i.e., accretion with both cold and hot gas supplies, which feed a disc and a corona respectively. We investigate the interaction of disc and corona by analysing the energy coupling and matter exchange, i.e. corona condensation/disc evaporation, with a semi-analytical method. It is found that the accretion geometry in the radial direction and the resultant emission spectrum depend strongly on both the total gas supply rate and the ratio of cold and hot gases. For gas supply rates of a few percent of the Eddington value, diverse geometries and spectral shapes are possible, depending on the fraction of cold gas supply. This provides an interpretation for the various spectra observed in intermediate states. However, at higher accretion rates, regardless of the form of the feeding gas, the inner accretion flow is always disc-dominated, implying an inevitable transition to the soft state, while at very low gas supply rates, hard state spectrum dominated by the hot flow is expected. We also present the predicted hardness-intensity correlation of Cygnus X-1, and constrain the value of the viscosity parameter of the accretion flow to the range of 0.25--0.35 by comparing our results with MAXI observations.This work is supported by the National Natural Science Foundation of China (grants 12333004 and 12433005). This research has made use of the MAXI data provided by RIKEN, JAXA and the MAXI team.Peer reviewe
Alteration of the damiao anorthosite complex in the northern North China Craton: implications for high-grade iron mineralization
No full textAbstract not availableHoumin Li, Lixing Li, Zhaochong Zhang, M.Santosh, Mingjun Liu, Yanhe Cui, Xiuqing Yang, Jing Chen, Tong Ya
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