Current Issue : January-March Volume : 2024 Issue Number : 1 Articles : 5 Articles
For the problem of spacecraft attitude actuator failure, an adaptive terminal sliding mode fault-tolerant controller (ATSMFTC) based on the differential manifold SO(3) modelling is designed in this paper. First, SO(3) is used to provide a global and unique description of the spacecraft attitude dynamic model. This modelling method not only avoids the problems of singularity and unwinding that exist in traditional modelling methods but also the SO(3) modelling has a simple formulation of the dynamic equations. Then a left attitude error descriptor function is constructed on SO(3) to design an ATSMFTC. This controller is capable of fast and accurate tracking of the time-varying desired attitude. At the same time, it can react quickly to maintain system stability in case of spacecraft attitude actuator failure. The controller designed based on the left attitude error description system of SO(3) has the features of small computational effort and simple design process. Finally, the numerical simulation of the attitude tracking error verifies the feasibility and high efficiency of the controller designed in this paper....
With the steady increase of air traffic column, an auxiliary decision tool is required to compensate the operation redundancy deficiency of more sectors of air traffic control. To solve the problem of nonconflict high-density departure and arrival traffic flow, this method is expected to rapidly establish and maintain safe separation with more flexible changing strategies for aircraft heading and speed. This paper proposes an improved reinforcement learning framework to achieve conflict detection and resolution. The proposed framework includes the first development of an air traffic flow model based on a multiagent Markov decision process. The goal reward function was then maximized by improved Monte-Carlo tree search combined with an upper confidence bound tree. Three simulation scenarios were designed for illustrating the improvements of the proposed algorithm, with the results indicating that the algorithm could establish and maintain safe separation between 20 agents in the simplified hexagon-shaped airspace of Huadong, China. Furthermore, the proposed method was demonstrated to reduce the number of conflicts between aircraft agents by up to 26.32% compared to previous research....
Recently, flow control using vortex generators (VGs) and a Gurney flap (GF) has received considerable attention, but independently. The purpose of this study is to perform a numerical investigation into the lift augmentation effects of a tiltrotor wing with the combination of VGs and GF. The numerical results were obtained with the Reynolds-averaged Navier-Stokes (RANS) equations, and the turbulence was solved by the Spalart-Allmaras one-equation turbulence model. The separate and joint performances of these two control devices at different angles of attack are determined. It is shown that the combined configuration can provide greater lift augmentation than either device individually. Compared with the baseline wing, the implementation of both devices increases the stall angle of attack from 10° to 22°, and the maximum lift coefficient is improved by 82.33%....
This paper studies the multiple geosynchronous spacecraft refueling problem (MGSRP) with multiple servicing spacecraft (Ssc) and fuel depots (FDs). In the mission scenario, multiple Ssc and FDs are parked in the geosynchronous Earth orbit (GEO) initially. Ssc start from FDs and maneuver to visit and refuel multiple GEO targets with known demands. These capacitated Ssc are expected to rendezvous with fuel-deficient GEO targets and FDs for the purpose of delivering the fuel stored in FDs to GEO targets. The objective is to find a set of Pareto-optimal solutions with minimum fuel cost and mission duration. The MGSRP is a much more complex variant of multidepot vehicle routing problems mixing discrete and continuous variables. A two-nested optimization model is built. We propose a new multiobjective hybrid particle swarm optimization to solve the outer-loop problem, and the design variables are the refueling sequence, task assignment, time distribution, and locations of FDs. In the inner-loop problem, branch and bound method is used to find the optimal decision variable for a given outer-loop solution. Finally, numerical simulations are presented to illustrate the effectiveness and validity of the proposed approach....
Bleeding is an effective method to improve the starting performance of the inlet, and the conventional method often adopts the bleeding to longitudinal direction. This article proposes the use of transversal bleeding method to explore the influence on starting capacity by changing the bleeding direction. The paper designs 6 bleeding inlets. By calculating the starting performance, it is found that the projected bleeding rate of the inlet, which is the direct factor influencing the starting performance, would change due to the direction change of bleeding, although designed with the same entrance. For the inlet designed with longitudinal slots and bleeding, it could reach the starting state at Mach 3.6, but it showed the unstart state when they are transversal direction. The same entrance, when inlet is designed by transversal bleeding with longitudinal slots, the starting Mach number would decrease to 3.8. For the changes of aerodynamic capabilities, there would be the “point jump” tendency when reaching starting state, but the same inlets would keep the similar performance when they get the starting state....
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