This study presents a finite-time spatial path following control method for a robotic underactuated airship subject to model uncertainties and external disturbances. A finite-time path following ...approach is proposed by combining the backstepping approach with the terminal sliding mode control technique, and the upper bounds of model uncertainties and external disturbances are estimated by the designed adaptive laws. Compared with existing works on the path following control of airships, the algorithm presented in this study can guarantee the airship track a spatial predefined path in finite time in the presence of model uncertainties and external disturbances. Simulations are given to illustrate the effectiveness of the proposed path following control method.
An effective path-following controller is a guarantee for stable sailing of underactuated unmanned surface vehicles (USVs). This paper proposes an event-triggered robust control approach considering ...an unknown model nonlinearity, external disturbance, and event-triggered mechanism. The proposed method consists of guidance and dynamic control subsystems. Based on the tracking error dynamics equations, the guidance subsystem is designed to achieve the guidance law. For the dynamic control subsystem, the radial basis function neural networks (RBFNNs) are designed to approximate the unknown model nonlinearity and external disturbances to improve the robustness of the proposed method. In addition, an event-triggered mechanism is constructed to reduce the triggering times. The closed-loop system is proven to be stable, and the effectiveness of the proposed method is illustrated through simulation results.
Wood wool cement board is made of Portland cement as a cross-linking agent, wood fiber as a fiber reinforcement material, and some additives. The precast WWCB-filled concrete floor slabs are a new ...type of hollow slab. This structure formed by pouring the bottom layer of concrete, laying the WWCB, then pouring the top layer of concrete, and finally curing. And this type of floor slabs is composed of double-layer reinforcement mesh, including top and bottom reinforcement which connected by triangular contact bars. In order to study the mechanical properties of the precast WWCB-filled concrete slabs themselves, this paper conducted four-point bending loading tests on 9 precast WWCB-filled concrete slabs of different sizes to analyze the effect of penetration type and cavity size on the flexural performance of the slabs. The results of the experimental study show that: the ultimate load-bearing capacity of precast WWCB-filled concrete slabs is higher than 100-mm-thick solid slabs, and their deflection of them is similar to that of ordinary solid slabs, with good plasticity and flexibility; the overall flexural resistance of the precast WWCB-filled concrete slabs is good, the crack distribution is uniform, and the damage pattern is better than that of cast-in-situ slabs.
Multipactor is a common discharge phenomenon occurring in space microwave systems. The surface microstructure has been verified to be effective in mitigating multipactor. In this work, we design a ...square coaxial low-pass filter (SCLPF) with dielectric sheets loaded to check the multipactor dependence on the structure parameters of the loaded dielectric sheets, and further model groove structures on the sensitive area surface to lower the risk of multipactor. Simulation results indicate that the SCLPF loaded with alumina and PTFE exhibits favorable operational characteristics, and the multipactor threshold is significantly improved after introducing the surface grooves. Then, we investigate the effects of three typical groove parameters, groove depth, groove number, and aspect ratio, on the multipactor threshold of the SCLPF device. The results show that the multipactor threshold rises at first as the groove number and groove depth increase, and then the threshold reaches a saturation status. For a deeper analysis of multipactor, we discuss how the grooves shelter the secondary electrons, and further mitigate the electron avalanche. Furthermore, the mechanisms of threshold saturation under the effect of groove parameters are analyzed in detail, and a contour map for the multipactor threshold of PTFE-loaded SCLPFs is given, which makes significant sense for predicting the multipactor threshold of the devices with its sensitive surface being grooved. The regularity of modulating the multipactor threshold by the groove structures obtained in this study is of engineering significance for suppressing multipactor in microwave devices in practical applications.
This article investigates the problem of path following for the underactuated unmanned surface vehicles (USVs) subject to state constraints. A useful control algorithm is proposed by combining the ...backstepping technique, adaptive dynamic programming (ADP), and the event-triggered mechanism. The presented approach consists of three modules: guidance law, dynamic controller, and event triggering. First, to deal with the "singularity" problem, the guidance-based path-following (GBPF) principle is introduced in the guidance law loop. In contrast to the traditional barrier Lyapunov function (BLF) method, this article converts the USV's constraint model to a class of nonlinear systems without state constraints by introducing a nonlinear mapping. The control signal generated by the dynamic controller module consists of a backstepping-based feedforward control signal and an ADP-based approximate optimal feedback control signal. Therefore, the presented scheme can guarantee the approximate optimal performance. To approximate the cost function and its partial derivative, a critic neural network (NN) is constructed. By considering the event-triggered condition, the dynamic controller is further improved. Compared with traditional time-triggered control methods, the proposed approach can greatly reduce communication and computational burdens. This article proves that the closed-loop system is stable, and the simulation results and experimental validation are given to illustrate the effectiveness of the proposed approach.
In recent years, the control synthesis and analysis of networked control systems (NCSs) have attracted increasing attention from both industrial and scientific communities, and many contributions ...have been published. With the development of advanced control theories, it has become a trend to combine networks with control systems. As a specific nonlinear control method, due to its complete robustness on the sliding mode surface, sliding mode control (SMC) becomes an effective means to solve the uncertainties and nonlinear characteristics in NCSs. In this paper, a review of the recent advances and challenges of SMC in NCSs is given. Firstly, a brief introduction to NCSs is given and the essential technical constraints are also summarized. Then, the results of the SMC applied to NCSs with basic constraints, including packet dropouts, time delays and signal quantization are given in details. Finally, some concluding remarks are made and several potential future research topics are discussed.
In this article, the formation control of unmanned surface vehicles (USVs) is addressed considering actuator saturation and unknown nonlinear items. The algorithm can be divided into two parts, ...steering the leader USV to trace along the desired path and steering the follower USV to follow the leader in the desired formation. In the proposed formation control framework, a virtual USV is first constructed so that the leader USV can be guided to the desired path. To solve the input constraint problem, an auxiliary is introduced, and the adaptive fuzzy method is used to estimate unknown nonlinear items in the USV. To maintain the desired formation, the desired velocities of follower USVs are deduced using geometry and Lyapunov stability theories; the stability of the closed-loop system is also proved. Finally, the effectiveness of the proposed approach is demonstrated by the simulation and experimental results.
This paper presents a reliable intelligent path following control method for a robotic airship subject to sensor faults. First, an adaptive backstepping sliding mode controller is designed based on ...the six degrees of freedom model of airship, where the backstepping technique is used to obtain the desired velocities, and the adaptive sliding mode method is adopted to deal with the unknown model uncertainties. The stabilization of the whole path following control system is studied based on Lyapunov stability theory. Specially, since the measured data in the airship control system are interrelated, a data-driven soft sensor based on adaptive neuro-fuzzy inference system is designed to detect and isolate the sensor fault. Based on the developed detection and isolation mechanism, the airship control system still work well in the presence of sensor fault. Finally, simulations are given to demonstrate the effectiveness of the proposed path following strategy.
Graphdiyne nanoribbons with high chemical precision are of great significance for further understanding of the intrinsic properties of graphdiyne and the relationship between structure and ...properties. However, the reliable synthesis of graphdiyne nanoribbons with chemical precision remains a significant challenge. A facile method is now presented for fabrication of graphdiyne nanoribbons with uniform width through stepwise inter‐ and intramolecular Glaser–Hay coupling reaction of ethynyl groups. The synthetic ribbons were interwoven into nanotextiles by π–π stacking and were applied for protective coating of Li‐electrode in Li‐ion batteries, which efficiently suppressed the growth of the Li dendrites during cycling and prolonged the life span of Li‐metal batteries.
Stack a nanoribbon: A facile method for atomically precise graphdiyne nanoribbons has been developed. The method featured inter‐ and intramolecular stepwise Glaser–Hay coupling strategy to reduce random intermolecular polymerization of the ethynyl groups.
This studies the dynamic collision avoidance (CA) problem of unmanned surface vehicle (USV) under the International Regulations for Preventing Collisions at Sea (COLREGs, short for Collision ...Regulations). A more realistic virtual spatial velocity field and two-stage CA area are proposed to reflect the movement of the target ship (TS), and the heading state of the USV is divided into a safe state and an emergency state. A decision model of ship steering for CA by analyzing the obligatory behavior of giving way to ships in the COLREGs is proposed. First, in the safe state, a novel of CA algorithm is proposed by using particle swarm optimization (PSO) and the problems of avoiding the TS and sailing to the destination are considered simultaneously. Second, in the emergency state, a new CA algorithm is developed by combining the decision model of ship steering for CA with the artificial potential field (APF) method, when considering avoiding the TS. Finally, the effectiveness of the algorithms are proved by simulation.
•The paper investigates the dynamic collision avoidance problem of USV based on new two-stage collision avoidance algorithm.•The decision model of ship steering for collision avoidance that meet COLREGs requirements are proposed.•The virtual spatial velocity field is improved to reflect the movement state of target ship.
