Browsing by Author "Zhang, Baihai"
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Item Embargo Convex–concave optimization for a launch vehicle ascent trajectory with chance constraints(Elsevier, 2024-04-18) Sun, Xin; Chai, Senchun; Chai, Runqi; Zhang, Baihai; Felicetti, Leonard; Tsourdos, AntoniosThe objective of this paper is to present a convex–concave optimization approach for solving the problem of a multistage launch vehicle ascent trajectory. The proposed method combines convex–concave decomposition and successive linearization techniques to generate a new sequence of convex subproblems to replace the original non-convex problem. Bernstein approximation is used to transform the chance constraints into convex ones. A hp-adaptive pseudospectral scheme is employed to discretize the optimal control problem into a nonlinear programming problem with less computation cost. The performance of the proposed strategy is compared against other typical techniques in a selection of test case scenarios. Numerical results demonstrate the viability of the method and show pros and cons of the proposed technique.Item Open Access A novel industrial intrusion detection method based on threshold-optimized CNN-BiLSTM-attention using ROC curve(IEEE, 2020-09-09) Lan, Mindi; Luo, Jun; Chai, Senchun; Chai, Ruiqi; Zhang, Chen; Zhang, BaihaiIn recent years, many researchers have proposed many intrusion detection methods to protect the industrial network. However, there are two existing problems among them: one is that they only consider the overall accuracy rate (AC) while ignoring the problem of class imbalance; another one is that they have considered the problem of class imbalance, but the detection rate (DR) is low and false positive rate (FR) is high for minority classes. In order to improve AC and DR of minority classes, we propose a method called threshold-optimized CNN-BiLSTM-Attention that combines CNN-BiLSTM-Attention model, with threshold modification method based on receiver operating characteristic (ROC) curve. In this method, we use CNN-BiLSTM-Attention model as a classifier and modify threshold of the classifier through ROC curve. To evaluate the proposed method, we have performed experiments on the standard industrial data set. And the experimental results show that the proposed method can improve AC and the DR of minority classes at low FR, which is better than other intrusion detection methods.Item Open Access Stability of a class of multi-agent tracking systems with unstable subsystems(IEEE, 2016-06-30) Dong, Lijing; Chai, Senchun; Zhang, Baihai; Nguang, S. K.; Savvaris, AlIn this work, we pre-deploy a large number of smart agents to monitor an area of interest. This area could be divided into many Voronoi cells by using the knowledge of Voronoi diagram and every Voronoi site agent is responsible for monitoring and tracking the target in its cell. Then, a cooperative relay tracking strategy is proposed such that during the tracking process, when a target enters a new Voronoi cell, this event triggers the switching of both tracking agents and communication topology. This is significantly different from the traditional switching topologies. In addition, during the tracking process, the topology and tracking agents switch, which may lead the tracking system to be stable or unstable. The system switches either among consecutive stable subsystems and consecutive unstable subsystems or between stable and unstable subsystems. The objective of this paper is to design a tracking strategy guaranteeing overall successful tracking despite the existence of unstable subsystems. We also address extended discussions on the case where the dynamics of agents are subject to disturbances and the disturbance attenuation level is achieved. Finally, the proposed tracking strategy is verified by a set of simulations.Item Open Access UAV trajectory optimization using chance-constrained second-order cone programming(Elsevier, 2021-12-23) Sun, Xin; Zhang, Baihai; Chai, Runqi; Tsourdos, Antonios; Chai, SenchunIt is challenging to generate optimal trajectories for nonlinear dynamic systems under external disturbances. In this brief, we present a novel approach for planning safe trajectories of the chance-constrained trajectory optimization problems with nonconvex constraints. First, the chance constraints are handled by deterministic ones which show its availability. We derive an iterative convex optimization method to solve the optimal control problem. Then the chance-constrained optimal control (CCOCP) problem is reformed to be a nonlinear programming problem (NLP) through the hp-adaptive pseudospectral method. An iterative successive linearization algorithm is detailed to convex the NLP to be a convex optimization one which described as a second-order cone programming problem. We demonstrate the proposed approach on a 3-DoF of unmanned aerial vehicle system under chance-constrained. The simulation results show reliable solutions for the UAV chance-constrained trajectory optimization problem.