Song Bifeng

A Direct Simulation Method for Calculating Multiple-hit Vulnerability of Aircraft with Overlapping Components

Abstract When components overlap, the aircraft multiple-hit vulnerability analysis usually consists of two steps. The first is to determine the aircraft unique existent states using vulnerable area decomposition method, and the second is to calculate the aircraft cumulated probability of kill using Markov chain method for exact solution or Monte Carlo method for solving the combinatorial explosion problem. This article proposes a direct simulation method for calculating the aircraft multiple-hit vulnerability in order to avoid the complex vulnerable area decomposition issue. In this method, random method is adopted to produce the multiple-hit locations and Bernoulli trial is used to determine the kill or no kill of each component hit by one shot line, and kill tree is checked to determine aircraft existent states during one simulation. When the number of times of simulation is large enough, the aircraft multiple-hit vulnerability can be statistically obtained. Analysis shows that the proposed direct simulation method can provide good accuracy compared with Markov chain method and avoid the combinatorial explosion problem, and does not need the complex vulnerable area decomposition and can directly calculate the aircraft multiple-hit vulnerability. Another important finding is the binomial or Poisson simplified approach is sometimes very poor in accuracy, and should be used cautiously.

Shot Line Geometric Description Method for Aircraft Vulnerability Calculation

Abstract This article, firstly, categorizes aircrafts presented area in a particular hit aspect into non-vulnerable region, non-overlapping vulnerable region and overlapping vulnerable region. Then, the aircrafts unique existing states are divided into kill states, intermediate states and no kill states. The parameters pertinent to aircrafts existing states in the above-mentioned regions are analyzed by using the shot line scanning method. Finally, the method provides two kinds of shot line geometric descriptive data: components vulnerable area and presented area in each region, which can be used to calculate the components single-hit vulnerability and aircrafts unique existing states and the areas corresponding to each state, which can be used to calculate the aircrafts single-hit and multi-hit vulnerability. Examples show that the proposed method can provide the parameters of the aircrafts or its components area under threat being hit through tracing the shot line path thereby enabling the vulnerability calculated results to conform with reality to larger extent. In addition, the method solves the generality problem in dealing with overlapping components.

Reliability simulation analysis for complex mechanism based on support vector machine

In order to deal with the issues of implicit limit state function and high computational cost in the mechanism reliability analysis, the methodology for predicting the failure probability of mechanism by combining simulation technology and support vector machine (SVM) based reliability analysis is introduced. Then, two strategies of mechanism reliability analysis using support vector machine are proposed, and the different sample methods are adopted for the corresponding strategy. According to the two proposed strategies, an integrated platform combining with the commercial software for mechanism reliability simulation analysis is developed. Finally, a lock mechanism is utilized to illustrate the feasibility and efficiency of the proposed methods. The obtained results show that the computational costs of the proposed methods are much less than the computational costs of Monte Carlo Simulation (MCS). Therefore, the proposed methods might be efficient and valuable for the reliability analysis of complex mechanism.

仿鸟型扑翼飞行器气动/结构/飞行力学耦合研究进展

仿鸟型扑翼飞行器在飞行机动性和飞行效率上有巨大发展潜力，是一种具有较高研究价值和应用前景的微型飞行器。由于仿鸟型扑翼飞行器的柔性扑动翼在扑动过程中会产生较大结构变形，同时扑动翼的扑动运动与机体的刚体运动会产生高度耦合，因此需要从气动、结构与飞行力学多学科耦合的角度对该类飞行器的气动特性和飞行稳定性进行分析。针对该类飞行器的气动机理、气动/结构耦合研究、飞行稳定性分析方法以及扑动翼的柔性对飞行稳定性的影响等方面进行了国内外现状的分析和总结。目前仿鸟型扑翼飞行器的发展还面临着诸多难题，尤其在非定常气动机理、气动/结构耦合的尺度律以及气动/结构/飞行力学的耦合方法等方面亟需进一步的突破和发展。

Effects of propeller thrust trimming on tailless unmanned aerial vehicle performance

Flight performance and longitudinal static stability are two contradictory requirements for aircraft. This is especially true for a tailless configuration, whose flight performance is traded for static stability. A new tailless gull wing configuration with propeller thrust trimming is proposed in this paper. It is expected that the propeller thrust can help to provide a nose-up pitching moment and improve the flight performance. In the present configuration, a cambered airfoil is used to increase the lift-to-drag ratio as well as the maximum lift coefficient. Two approaches are adopted to obtain the nose-up pitching moment. Firstly, the thrust line is shifted below the center of gravity to make a positive contribution to the pitching moment. Secondly, the thrust vectoring is employed to trim longitudinally instead of elevon deflection. The wind-tunnel data indicate that the lift-to-drag ratio and maximum lift coefficient increase notably with the help of propeller thrust trimming. To determine the performance benefits of the gull wing with propeller thrust trimming, a conceptual design environment of the electric-powered unmanned aerial vehicle is developed by integrating the modules of the conceptual parameters, aerodynamics, stability, propulsion, weight, performance, as well as optimization. The optimization results suggest that, compared with the two other conventional tailless configurations, the gull wing with propeller thrust trimming results in 20 and 34% endurance increase. Flight tests of a 2.5 kg built aircraft demonstrate the aerodynamic feasibility of the gull wing with propeller thrust trimming concept.