Dynamical Model Updating Based on Modal Tests with Changed Structure

A new approach to modifying the stiffness and mass matrices of finite element models is presented to improve the calculation precision. By measuring the mode frequencies and shapes of both of the original and the new structures with changed stiffness and mass, the stiffness and mass matrices of the finite element model can be updated through matrices calculation and solving algebra equations. Taking a multi-freedom model as an example, the relation between the number of the modes and the correction precision of stiffness and mass matrix elements is researched. The facility and precision of the method are totally confirmed especially when the modeling error is known limited to a definite local range. The feasibility of the approach is proven by an effective engineering application to the model updating of a wing piece used in flutter test.     

直升机燃油系统增压转自吸供油动特性

通过某型燃油系统增压供油转自吸供油试验,研究了发动机入口处的流量历程。在试验研究和直升机燃油系统增压转自吸供油机理基础上,利用Flowmaster软件建立了某典型直升机燃油系统仿真模型,仿真结果与试验结果吻合较好,验证了模型的正确性。在此基础上,研究了直升机燃油系统增压转自吸供油动特性。结合仿真结果,分析了增压泵出口单向阀的弹簧预紧力、弹簧刚度对发动机入口燃油流量、压力的影响,为燃油系统零部件选型及参数确定提供参考。     

我国通用航空应急管理体系构建

低空空域开放是助力我国通用航空迅速发展的重大战略性举措,同时将对通用航空在作业过程中的应急管理带来挑战。文章给出通用航空突发事件的定义,对引起通用航空突发事件的致灾因素从通用航空器、通用航空作业环境、通用航空服务保障情况做一分析。阐述了通用航空应急管理的定义。最后提出了基于应急管理平台的通用航空应急管理体系。     

Experimental study of a flush wall scramjet combustor equipped with strut/wall fuel injection

In this study a flush wall scramjet combustor is tested in a supersonic incoming air flow with the Mach number of 3 which is generated by an air vitiation heater producing the stagnation temperature of 1505 K. Using liquid kerosene as the fuel, the flame is stabilized by means of a centrally mounted O₂ pilot strut after being ignited by a plasma torch. During experimental measurements, the fuel is injected with a constant equivalence ratio of 0.8 according to specified strut/wall injection ratios, i.e., a portion of the fuel amount is injected from the strut while the rest is injected from the wall. The strut and wall injectors are arranged at the same axial position. The combustion performance and wall temperature gradients are evaluated with various fuel feeding ratios between the wall and the strut. Experimental results show, when the equivalence ratio is constant and the axial injection position is fixed, the combustion characteristics vary significantly with the strut/wall fuel feeding ratio, especially when this ratio is close to its lowest and highest limits. Among the four fuel feeding ratios examined, the strut only injection mode and the average distributed strut/wall injection mode show the best combustion performance. However, the strut/wall injection mode produces a smaller wall temperature gradient compared to the strut only injection mode, which is due to the significant film cooling effect caused by the wall injected liquid kerosene.     

摄影测量技术及其在航天器变形测量中的应用

文章介绍了摄影测量技术的测量原理,系统调研了近年来摄影测量技术在国内外航天器变形测量领域的发展概况,分析总结了该技术的发展趋势和关键技术,并结合我国的具体国情提出了当前变形测量技术发展的建议,为我国在航天器大型复杂部件微变形测量技术的发展提供借鉴和参考。     

航天器着陆碰撞动力学CUDA并行计算技术

航天器着陆接触碰撞过程中的瞬态响应计算,涉及到几何非线性、接触非线性和材料非线性,计算过程复杂,计算量大。为此,文章将统一计算架构(CUDA)技术应用到接触碰撞问题的并行显式积分计算,研究了质量矩阵和刚度矩阵的并行生成方法,并将基于中心差分法的求解过程并行化实施。仿真算例表明:并行算法计算结果准确,较大地提高了计算仿真分析的效率,可为航天器着陆过程中冲击动力学计算的快速和高精度实现奠定基础。     

Intra-annual variations of the thermospheric density at 400 km altitude from 1996 to 2006

We investigate the intra-annual variations of globally averaged thermospheric density at 400 km altitude from 1996 to 2006 by using Artificial Neural Network Method (ANNM). The results indicate that thermospheric density is governed by solar activity, and the absolute error of our model is 13.67%, less than NRLMSISE-00 model. Fourier representation can catch the intra-annual variations more accurately than NRLMSISE-00 model and JB2008 model especially during 2002. We find that the Autumn maximum is slightly greater than Spring maximum during solar minimum, while the reverse is correct during solar maximum. There is a strong linear relation between solar activity and the amplitude of annual/semiannual variations, and the correlation coefficients are 0.9534 and 0.9424, respectively. Moreover, the amplitude ratio of the annual to semiannual variation is about 1.3 averaged, and changes in different years, but it has little relation with solar activity. Besides that, the amplitude of annual variation is larger than semiannual variation during 1996 and 2006 except 1998 and 2000. The relative error of NRLMSISE-00 model is 14.95%, decreasing to 12.49% after revising, and the correlation coefficients between this empirical model and its improved results and the observation are 0.8185 and 0.9210, respectively. Finally, we suggest the revised version of MSIS series of model should use the Fourier representation to express the intra-annual variations.     

Dynamics and control of spacecraft hovering using the geomagnetic Lorentz force

To achieve hovering, a spacecraft thrusts continuously to induce an equilibrium state at a desired position. Due to the constraints on the quantity of propellant onboard, long-time hovering around low-Earth orbits (LEO) is hardly achievable using traditional chemical propulsion. The Lorentz force, acting on an electrostatically charged spacecraft as it moves through a planetary magnetic field, provides a new propellantless method for orbital maneuvers. This paper investigates the feasibility of using the induced Lorentz force as an auxiliary means of propulsion for spacecraft hovering. Assuming that the Earth’s magnetic field is a dipole that rotates with the Earth, a dynamical model that characterizes the relative motion of Lorentz spacecraft is derived to analyze the required open-loop control acceleration for hovering. Based on this dynamical model, we first present the hovering configurations that could achieve propellantless hovering and the corresponding required specific charge of a Lorentz spacecraft. For other configurations, optimal open-loop control laws that minimize the control energy consumption are designed. Likewise, the optimal trajectories of required specific charge and control acceleration are both presented. The effect of orbital inclination on the expenditure of control energy is also analyzed. Further, we also develop a closed-loop control approach for propellantless hovering. Numerical results prove the validity of proposed control methods for hovering and show that hovering around low-Earth orbits would be achievable if the required specific charge of a Lorentz spacecraft becomes feasible in the future. Typically, hovering radially several kilometers above a target in LEO requires specific charges on the order of 0.1 C/kg.     

虚警影响下的备件库存优化

在虚警存在时完好的零部件被误诊为故障件而对维修站点发出备件需求,从而会对备件的需求率高估,所以需要引入虚警率修正备件需求率使之更为精确.证明了当虚警率服从指数分布时,考虑虚警的外场故障发生数仍然符合泊松分布.根据多层可修件库存控制理论,建立考虑虚警率的需求数和期望备件短缺数（EBO,Expected BackOrder）的函数关系,以期望备件短缺数为优化目标,对目标函数进行凸分析,建立面向系统虚警的备件配置凸优化算法,保证所选库存方案在系统发生虚警的情况下提高系统效能,并构建了某型飞机的应用验证案例,给出了最优的备件配置方案.      

弹道相机水平投影交会测量法的改进及精度分析

介绍弹道相机数据处理的水平投影交会测量法,提出了加权平均水平投影交会测量法,并分析了两种方法的交会精度,得出加权平均水平投影法可显著提高交会精度的结论。