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1.
Alexis Petit Alessandro Rossi Elisa Maria Alessi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(12):4177-4192
The Earth orbital environment is drastically changing due to an intensification of the space activities. In particular, several projects of large constellations, proposed for the next years for communications purpose like global internet access, Internet of Things, or for Earth observations, will lead to the deployment of several thousands of new satellites at an unprecedented rate. It is a crucial challenge for space traffic management, which will deal with a great number of satellite conjunctions, potentially causing a collision with damaging consequences for the constellation itself and the space environment sustainability.In this paper, we investigate the close approach frequency and the cumulative collision probability for each referenced constellation. For this purpose, we compute the orbital evolution of satellites in different constellations during the lifecycle, from the deployment to the decommissioning, and we apply the CUBE algorithm and the Foster method to assess the collision probability with the background space debris population assuming a constant uncertainty in position. We show the variation of risk defined by the close approach frequency and the cumulative collision probability as a function of the proposed configuration. In particular, satellites of the Iridium and Kuiper constellation, but also satellite of the Telesat constellation on polar orbits are the most exposed at a collision. Moreover, the decommissioning phase contribute for a major part to the final cumulative collision probability. 相似文献
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航空发动机熄火预测是重要关键问题之一,湍流和化学反应的非线性相互作用使预测非常困难。本文采用大涡模拟(LES)对湍流进行高精度模拟,采用概率密度函数输运方程湍流燃烧模型(TPDF)耦合JL4、Z66和H73三种化学反应机理,对预混丙烷钝体熄火现象和规律进行研究。JL4的反应机理最简单,反应释热快,局部放热高,火焰宽度大,火焰两侧温度梯度大,燃烧更加趋于稳定,无法模拟出熄火状态。H73机理绝热火焰温度低,火焰温度低,回流区中部OH含量高;在近熄火状态,大量CO被氧化,释放热量过高导致无法模拟出熄火现象。Z66机理可以模拟出火焰正常状态,在低当量比下也可以模拟出熄火状态。本文算例中,局部Da数大于1的区域超过35%则会发生熄火。 相似文献
3.
《中国航空学报》2020,33(2):634-663
The determination of optimal aerial transport networks and their associated flight frequencies is crucial for the strategic planning of airlines, as well as for carrying out market research, to establish target markets, and for aircraft and crew rostering. In addition, optimum airplane types for the selected networks are crucial to improve revenue and to provide reduced operating costs. The present study proposes an innovative approach to determine the optimal aerial transport network simultaneously with the determination of the optimum fleet for that network, composed of three types of airplanes (network and vehicle integrated design). The network profit is maximized. The passenger’s demands between the airports are determined via a gravitational model. An embedded linear programming solution is responsible for obtaining potential optimal network configurations. The optimum fleet combination is determined from a database of candidate aircraft designs via genetic algorithm. A truly realistic airplane representation is made possible thanks to accurate surrogate models for engine and aerodynamics is adopted. An accurate engine deck encompassing a compression map and an innovative engine weight calculation besides an aerodynamical artificial neural network module enable a high degree of accuracy for the mission analysis. The proposed methodology is applied to obtain the optimum network comprised of twenty main Brazilian airports and corresponding fleet. 相似文献
4.
对无动力J—7LP动力学缩比模型进行了遥控试飞,以研究其失速尾旋特性,全偏平尾和方向舵可使模型进八尾旋,舵面全回中即可从各种尾旋中改出。偏转副翼对尾旋特性有明显的影响。 相似文献
5.
The architecture of digital sheet metal manufacturing system is proposed based on the classification of sheet metal manufacturing information.The essence of digital manufacturing is the definition,management and transfer of information,and the key technologies are brought forward and described.It is pointed out that knowledge-based manufacturing elements design is necessary to make digital technology efficient.The management of all kinds of sheet metal manufacturing element information is to build single source of manufacturing data.Multi-state model-based digital transfer and coordination method is designed to provide a foundation for digital manufacturing of aircraft sheet metal part.The application of digital sheet metal manufacturing is exemplified with an aircraft sheet metal part.The application result is compared to that of the traditional analog transfer technology.It is shown that the developed technology can improve part quality,shorten manufacturing time and lower manufacturing cost. 相似文献
6.
分析了目前国内一些飞机基于三点温度控制方案的逆升压电子设备冷却系统的缺陷 ,提出了一种新的系统控制方案 ,即基于飞行速度和高度的逆升压电子设备冷却系统的控制方案。这一方案不需要人工干预 ,可实现全自动化。 相似文献
7.
基于冯·卡门模型,选择中心挠度为摄动参数,利用摄动方法将正交异性矩形薄板大挠问题的非线性偏微分方程组逐级线性化,导出了各级摄动对应的几个线性偏微分方程组,然后再借助变分法求解,得到了均布载荷作用下正交异性矩形薄板的载荷-挠度曲线。 相似文献
8.
空间站大型伸展机构的运动稳定性分析 总被引:4,自引:0,他引:4
从空间站大型伸展机构的运动特点和系统动力学方程出发,着重分析了该系统的稳定性判据。这一问题又可分为五个方面:姿态-伸展-振动耦合系统的分析方法,复杂大系统的分解集结方法,时滞系统和滞后系统的稳定性问题,Stick-Ship运动对系统对系统稳定性的影响,非线性非定常系数稳定性的一般解。其中还对接触、摩擦、碰撞问题,变拓扑系统,非光滑动力学系统等进行了专门的研究,分析了Lyapunov指数方法在这些特殊系统中的适应性。本文对空间站大型伸展机构的稳定性问题进行了较全面的分析,指出了目前在处理这类复杂大系统时存在的一些难点问题,为其设计和研制工作提出了理论基础。 相似文献
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