GPS卫星信标信噪比的统计分析

GPS卫星信标信噪比(SNR)受到卫星上的发射机增益、地面站的接收机增益、卫星与接收机之间的几何距离、接收机处的仰角、信标传播路径上电离层介质衰减等因素的共同影响.首先提出了一种从SNR观测数据中分离出SNR在电离层中衰减的算法,并应用于MANA接收站(273.751°E,12.149°N)2003年的观测数据,得到了一个电离层介质引起的对L波段信标SNR衰减日变化的平均情况.通过与IRI模式计算的电波垂直穿过电离层时衰减的SNR比较发现,由我们得到的SNR在电波垂直穿过电离层时的衰减与IRI模式计算的衰减随地方时的变化符合得比较好.      

基于循环平稳性的噪声调频干扰高分辨测向方法

根据噪声调频信号循环平稳特性分析,提出了基于阵列接收信号循环均值-空域处理的波达方向(DOA)估计算法。仿真结果表明:该算法的角度估计性能明显高于比幅比相单脉冲测角法,且在高信噪比环境中,该法的估计性能更好、运算量较小。     

非开普勒轨道下卫星交会变轨决策研究

针对卫星在非开普勒轨道下的运动特征,提出了研究卫星交会变轨决策的方法。首先,在Hill坐标下,采用比例导引方法求解卫星进行变轨机动时所需要的速度增量。然后,再通过Lagrange插值算法解出卫星在任意特征点上变轨机动所需要的速度增量,根据数字仿真得出大量的仿真数据并画出满足变轨决策条件的决策曲面。最后,对决策曲面的涵义做出分析,说明了该方法对于研究非开普勒轨道下卫星变轨决策问题具有一定的意义。     

自然通风和蒸发冷却在新疆建筑应用的数值分析

为了使新疆和田地区夏季在经济性合理前提下使室内通风环境满足人体热舒适要求。利用蒸发冷却技术将室外空气处理后送入室内，通过数值模拟分析得出在夏季室内负荷最大时刻采用机械辅助式自然通风，使得室温能够雏持在26-8℃，风速为0．6m/s，基本满足人体热舒适要求。在室外温度适宜的过渡季节采用Trombe墙和太阳能烟囱复合的自然通风系统，建筑太阳能烟囱的经济高度为10m。     

风扇进口噪声预测模型的改进

针对Heidmann模型对风扇进口低频噪声(1k Hz)预测结果偏低的情况,通过引入风扇叶尖弦长雷诺数和相关几何参数改进了Heidmann模型中风扇进口宽频噪声的频谱修正函数,确定了其中频谱修正系数为0.085。对比改进模型和Heidmann模型的风扇进口噪声预测结果发现:在亚声速工况下,改进的模型很好地改善了风扇进口低频噪声的预测结果,改进幅值可以达到约45d B;而在超声速工况下,由于风扇进口产生的组合单音噪声成为风扇进口噪声的主要组成部分,除了在小于100Hz的频域内,改进的模型与Heidmann模型的预测结果差别不大。     

Noise analysis of continuous GPS coordinate time series for CMONOC

The Crustal Movement Observation Network of China (CMONOC) is one of the major scientific infrastructures, mainly using Global Positioning System (GPS) measurements, to monitor crustal deformation in the Chinese mainland. In this paper, decade-long coordinate time series of 26 continuous GPS sites of CMONOC are analyzed for their noise content using maximum likelihood estimation (MLE). We study the noise properties of continuous GPS time series of CMONOC for the unfiltered, filtered solutions and also the common mode signals in terms of power law plus white noise model. In the spatial filtering, we remove for every time series a common mode error that was estimated from a modified stacking of position residuals from other sites within ∼1000 km of the selected site. We find that the common mode signal in our network has a combination of spatially correlated flicker noise and a common white noise with large spatial extent. We demonstrate that for the unfiltered solutions of CMONOC continuous GPS sites the main colored noise is a flicker process, with a mean spectral index of ∼1. For the filtered solutions, the main colored noise is a general power law process, indicating that a major number of the filtered regional solutions have a combination of noise sources or local effects. The velocity uncertainties from CMONOC continuous GPS coordinate time series may be underestimated by factors of 8–16 if a pure white noise model is assumed. In addition, using a white plus flicker noise model, the median values of velocity errors for the unfiltered solutions are 0.16 (north), 0.17 (east) and 0.58 (vertical) mm/yr, and the median values for the filtered solutions are 0.09 (north), 0.10 (east) and 0.40 (vertical) mm/yr.     

Performance of a small and low-cost chamber to simulate lunar surface environment

The performance of a small and low-cost metal chamber built to simulate the pressure and temperature conditions of lunar surface was assessed and the results are presented. This chamber is intended for studying the physical properties of lunar surface and subsurface (using soil simulants) and also to validate the technology readiness of certain newly developed payloads planned for future lunar surface missions (Lander/Rover). It is possible to reach down to ∼10⁻⁷ Pa under specific conditions and maintain the temperature of the sample under investigation to lunar day and night temperatures. The designed system has been subjected to various tests to evaluate its performance and suitability for carrying out experiments in a simulated lunar environment.     

A systematic approach to nonlinear rotorcraft model identification

The development of a powerful parameter estimation routine and its integration into the simulation environment HOST is described. With this tool approaches are being made towards new strategies of mathematical modeling, aimed at providing highly accurate and nevertheless run-time efficient simulation models. The identification routine is capable of optimizing parameterized models in both dynamic time domain simulation and static (e.g. trim state variation) conditions. Examples of both cases are presented to emphasize the improvement in the system response prediction and to demonstrate the abilities of the identification techniques in combination with the nonlinear simulation platform. This article reviews the activities and achievements accomplished by the DLR Institute of Flight Research and the ONERA Systems Control and Flight Dynamics Department during the last few years in the research on rotorcraft flight dynamics modeling and model identification. Future activities that require extensive high fidelity modeling are in the scope of the current and coming modeling activities that include the use of the presented methods and software technologies.     

槽对超声速混压式进气道性能及附面层的影响

为了提高定几何超 声速混压式轴对称进气道的性能，应用在进气道不同位置开槽的方法 ，研究了在各级锥体上、锥体的折角处开槽时锥体上的附面层变化；研究了多工况下开槽对进气道的总压恢复系数、流量系数、冲压比和起动性能产生的影响。结果表明开槽将改变超声速进气道头锥上的波系分布，使槽后附面层厚度增加。折角处开槽槽后附面层厚度比原型进气道增加16.7%，锥体上开槽比原型进气道增加33.3%。开槽使高马赫数下的总压恢复系数有所增加，其增加量随来流马赫数的变化而变化。在马赫数为4.0的设计状态下，折角处开槽可使进气道的总压恢复系数提高1.8%，锥体上开槽可以提高4.3%。之外，锥体折角处开槽对流量系数影响不大，还可以改善进气道的起动性能，降低起动马赫数。     

An artificial neural network approach for aerodynamic performance retention in airframe noise reduction design of a 3D swept wing model

With the progress of high-bypass turbofan and the innovation of silencing nacelle in engine noise reduction, airframe noise has now become another important sound source besides the engine noise. Thus, reducing airframe noise makes a great contribution to the overall noise reduction of a civil aircraft. However, reducing airframe noise often leads to aerodynamic perfor-mance loss in the meantime. In this case, an approach based on artificial neural network is intro-duced. An established database serves as a basis and the training sample of a back propagation (BP) artificial neural network, which uses confidence coefficient reasoning method for optimization later on. Then the most satisfactory configuration is selected for validating computations through the trained BP network. On the basis of the artificial neural network approach, an optimization pro-cess of slat cove filler (SCF) for high lift devices (HLD) on the Trap Wing is presented. Aerody-namic performance of both the baseline and optimized configurations is investigated through unsteady detached eddy simulations (DES), and a hybrid method, which combines unsteady DES method with acoustic analogy theory, is employed to validate the noise reduction effect. The numerical results indicate not merely a significant airframe noise reduction effect but also excel-lent aerodynamic performance retention simultaneously.