Aerospace Science and Technology最新文献

This study presents an innovative approach to mitigate vibrations induced by external shock on composite structures through the application of an intelligent controller. Leveraging the first-order shear deformation panel theory, a sophisticated controller scheme is developed, integrating methodologies such as the differential quadrature approach and Laplace transform. Furthermore, deep neural network (DNN) and support vector regression (SVR) techniques are employed to enhance prediction accuracy and control efficiency. Additionally, two optimized hybrid models are proposed, incorporating Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) algorithms, to further refine the controller's performance. The proposed methodology aims to address the challenges associated with vibrations in composite structures by providing a comprehensive and adaptive control solution. By utilizing advanced optimization algorithms and machine learning techniques, the controller can effectively adapt to dynamic changes in external shock conditions, thereby minimizing vibrations and ensuring structural integrity. The integration of ANN and SVR enhances the controller's predictive capabilities, enabling it to anticipate and respond to varying shock scenarios with precision. Through theoretical analysis and numerical simulations, the effectiveness of the proposed intelligent controller is demonstrated in reducing vibrations and enhancing the structural stability of composite systems. The optimized hybrid models, employing PSO and GWO algorithms, further improve the controller's performance by fine-tuning its parameters for optimal control efficiency. Overall, this research contributes to the development of robust control strategies for mitigating vibrations in composite structures subjected to external shock, with potential applications in aerospace, automotive, and civil engineering industries.

On-orbit assembly is a highly effective technique for building large space structures. This paper presents the dynamics and control of an on-orbit assembly of a large space structure based on a heterogenous spacecraft cluster comprising both rigid and flexible spacecraft. The topology of the large space structure is inspired by the Vicsek fractal. A distributed assembly strategy is proposed for the spacecraft team. Radial Basis Function neural networks (RBFNNs) are utilized to approximate the bounded uncertain terms in translational and attitude dynamics. To avoid collisions during the pre-assembly phase, a neural network (NN)-based controller with collision avoidance force is designed for relative position motion. During the assembly phase, only proportional-derivative (PD) law is employed for relative position control. In addition, an NN-based controller is designed for relative attitude control for both rigid and flexible spacecraft. To estimate the unmeasured flexible vibrations, modal coordinate observers are introduced for the flexible spacecraft. The stability of the closed-loop system is proved via Lyapunov functions. Moreover, numerical results are presented to validate the effectiveness of the proposed controllers and assembly strategy.

In this study, a new analytical framework for free vibration solutions of rectangular plates with various internal discontinuities is developed. The discontinuities caused by a line hinge, a rigid line support, or a step change in thickness are under consideration. All such discontinuities are bypassed via the domain decomposition technique, which divides the entire plate into sub-plates, and then the symplectic superposition is leveraged to analytically address the free vibration of the sub-plates. Specifically, the governing free vibration equations are elegantly reformulated in the Hamiltonian system and rigorously solved by the three mathematical treatments, i.e., separation of variables, eigen expansion, and superposition. This innovative framework, developed through the integration of the domain decomposition and the symplectic superposition, is particularly notable for its ability to simplify the mathematical challenges in obtaining analytical solutions of plates with internal discontinuities. The obtained analytical solutions are well validated by other methods and are thus capable of serving as benchmarks for future studies. These solutions also reveal distinct vibration characteristics of plates with different internal discontinuities. In comparison to continuous plates, plates with a line hinge exhibit lower natural frequencies due to increased flexibility, whereas plates with a rigid line support demonstrate higher natural frequencies due to restricted deflection at the support location. Furthermore, the design of stepped plates with thickened sub-plates effectively suppresses vibration, hence achieving higher natural frequencies. In view of the wide usage of plate assemblies in engineering, the present framework is expected to facilitate their early-stage design and parametric optimization.

In this study, the effect of combustion chamber length on the hypergolic combustion instability of hydrogen peroxide-based propellants was investigated. Twenty-four hot-firing tests were conducted using a combination of 95 wt.% hydrogen peroxide and amine-based fuel with a drop test ignition delay of 5.65 ms and an adjustable length hypergolic thruster. When the chamber length was changed from 80 mm to 120 mm, the root mean square (RMS) combustion instability decreased drastically from 24 % to 9 %. The measured high-frequency instability was considerably consistent with the longitudinal resonance mode of each combustion chamber geometry. Low-frequency instability, that is, the rate of popping, occurred predominantly in all hot-firing tests. Within the 245–418 Hz range, its frequency increased as the chamber length decreased or the chamber pressure increased. The high-speed camera image of the exhaust plume coincided with the period of low-frequency instability, which was confirmed by the periodic popping of the propellant. Combustion instability was analyzed in depth by performing power spectral density (PSD), wavelet synchro squeezed transform (WSST), dynamic mode decomposition (DMD), and image intensity analyses using the chamber pressure and exhaust plume images. DMD decomposed the plume behavior into one expansion mode and three plume decay modes, and it also matched the low-frequency instability of the chamber pressure with an error of less than 5 %.

Application of rotating detonation combustion can significantly enhance gas turbine performance, but the limited flow capacity caused by normally aspirated characteristic of rotating detonation combustor (RDC) severely constrains the operating range of gas turbine. In this paper, the detailed investigation was carried out for the influence of RDC passage area on cycle characteristic parameters for a 25MW single shaft gas turbine. The results demonstrated that changes of RDC passage area had a significant impact on operating range of rotating detonation gas turbine. As RDC passage area increased, operating range of gas turbine moved to the higher power, with the slight increases for cycle efficiency, cycle efficiency increment and net power increment compared to traditional gas turbine at identical net power. For the process when RDC passage area decreased from 0.0272 m² to 0.0240 m², the lower working limit of rotating detonation gas turbine decreased to 53.3 % of rated power, in which equivalence ratio of RDC replaced turbine efficiency as the greatest influence factor on cycle efficiency increment.

This paper proposed a resilient guidance strategy for planar pursuit evasion, in which the homing guidance problem is formulated as a Stackelberg game. As is known, the most salient challenge for pursuit evasion guidance is how to ensure an interception despite both players (i.e., missile and target) actively optimize their own interest with preferably incomplete information. Toward this, we introduce a game-theoretic guidance strategy that effectively integrates incentive feedback strategy into pursuit evasion game. In particular, the proposed resilient guidance law takes the form of Stackelberg game conjecture with missile/interceptor as the designated leader, and rigorously proves that leader's interest can be best served with a properly designed feedback gain, and an interception can be made possible in spite of incomplete knowledge on target's intentions (i.e., performance index). Simulation results verify the performance of the proposed strategy.

Under the background of energy conservation and emission reduction in the aviation industry, blends of ethanol with aviation kerosene have been widely accepted as a potential alternative fuel. Investigating its evaporation process is essential for comprehensively understanding the mechanisms of spray combustion process, which provides significant insights for improving the utilization of aviation fuel. Therefore, in this study, the effects of initial droplet size, ambient temperature and pressure on the micro-explosion and evaporation characteristics of RP70E30 droplets (70% RP-3 aviation kerosene and 30% ethanol by mass) are experimentally investigated. The evolutions of droplet temperature and size are simultaneously obtained by a suspended thermocouple and a high-speed video camera. The results indicate that in the cases without micro-explosion, RP70E30 droplet evaporation undergoes two stages, namely: transient heating and equilibrium evaporation stages. While the evaporation process of RP70E30 droplet with micro-explosion could be separated into three stages: transient heating, fluctuation evaporation and equilibrium evaporation stages. The sequential order of fluctuation evaporation stage and equilibrium evaporation stage is determined by the occurrence time of micro-explosion. RP70E30 droplets only exhibit weak rupture phenomena: weak micro-explosion and puffing. For all test conditions, a continuous increase in droplet temperature is observed throughout the entire evaporation process, and its trend exhibits a three-stage characteristic, including a rapid rise, a slow rise and then another rapid rise stages. At 400 °C and 1 bar, increasing initial droplet diameter (from 0.746 to 1.258 mm) can promote the heating and evaporation of RP70E30 droplet. While at 1 bar and 600 °C, the droplet with an initial diameter of 1.156 mm evaporates at a slower rate than droplet with an initial diameter of 1.030 mm in the early evaporation process. This is because weak micro-explosion somewhat suppresses the evaporation of PR70E30 droplet, which is attributed to the formation of bubbles increasing the heat transfer resistance inside the droplet. The droplets having similar initial diameters (from 0.95 to 1.05 mm) were selected to investigate the effects of ambient pressure and temperature on evaporation. At all the studied temperatures (400–600 °C) and pressures (1–20 bar), increasing ambient pressure and temperature both have a promoting effect on the heating and evaporation of RP70E30 droplet. Moreover, at 1 bar, high temperature can increase the possibility of micro-explosion. At 5–20 bar, no micro-explosion occurs.

The driving mechanism of the vibration of aerostatic bearings is still unclear. Although there are several interpretations, none of them is conclusive. The difficulty lies in the complicated information concealed beneath the turbulence flow. To this end, the proper orthogonal decomposition (POD) method was systematically implemented in the aerostatic bearing flow field analysis in the present study, and some new findings have been proposed. First, the accuracy of our large eddy simulation (LES) has been validated through quantitative comparisons with the experimental references in terms of pressure distribution. Then, the mode decomposition has been conducted at a circumferential symmetry plane and bottom surface and the influence of supply pressure has been uncovered. It turns out that the vortices within the recess dominate the flowfield when the supply energy Ps=3atm, which could be recognized as the driving mechanisms of vibrations. The convection and shearing process in the vicinity of the recess inlet becomes intense and corresponding vortices become predominant in the cases of Ps=4atm and 5atm. Eventually, the influences of film thickness have also been discussed when Ps=4atm. Different from the case of h = 10 μm, the low-frequency vortices near the recess outlet could be detected when the film thickness is increased to 20 µm. The control of corresponding flow structures might be helpful for the vibration suppression.

Experimental studies were performed to compare the effects of porous coating, downstream porous plate and their combination on the pressure drag, turbulence velocity, wall pressure fluctuation and aerodynamic noise associated with flow around a cylinder. The studies utilized metal foams as porous materials. The results suggest that the downstream porous plate is superior to the porous coating in reducing pressure drag, but the porous coating has advantages in suppressing the wall pressure fluctuations and radiated noise levels. Moreover, the downstream porous plate and the porous coating have opposite effects on the wake velocity fluctuations, with the former decreasing but the latter increasing the velocity fluctuations compared with the original cylinder. The porous materials have both positive and negative effects on the noise level. They can suppress wall pressure fluctuation, which is positive, but also form additional sources, which is negative. The positive effect dominates in the low-frequency range but gradually decreases as the frequency increases. Conversely, the negative effect gradually increases with an increase in the frequency. Therefore, the noise reduction level is usually significant in the low-frequency range but gradually decreases with an increase in the frequency. The experimental data also indicate that the linear addition property is inadequate for reducing pressure drag and aerodynamic noise with the porous coating and downstream porous plate.

The space vehicle total temperature simulation device introduces the actual gas total temperature signal into the vehicle development process. It enables the simulation of flight environments, reduces development time, and decreases overall costs. The uniform and stable temperature signal is paramount in accurately simulate the vehicle's real flight speed and altitude. However, the existing ground test facilities for space vehicles, characterized by their large scale, face significant challenges including insufficient uniformity in gas mixing and inadequate simulation accuracy. The Tesla-type flow channel (TFC) is widely applied for its excellent mixing capabilities in gas and liquid mixing across various domains. In this paper, from the working principle of the total temperature simulation device of space vehicle, according to the characteristics of TFC, a high mixing efficiency optimization design method of TFC is proposed by using RBF neural network response surface and NSGA-II algorithm. The optimized TFC is implemented in the mixing chamber of the total temperature simulation device to enhance the mixing efficiency. This improvement ultimately leads to enhanced accuracy in simulating the flight environment of space vehicles during semi-physical simulations. By utilizing the Pareto optimal solution, the optimal pressure drop is 985.50 Pa, while the standard deviation of temperature is 39.37 K. The results demonstrate a significant improvement in mixing efficiency within the total temperature simulation device due to the introduction of the TFC. This study serves as a valuable reference for enhancing the mixing performance of the total temperature simulation device for space vehicles, while also addressing the need for total temperature simulation in smaller laboratory environments.