旋翼尾流对空空导弹的气动干扰研究

直升机发射导弹时,旋翼尾流对导弹产生很强的气动干扰,研究旋翼尾流对导弹的气动干扰对于改进机载导弹发射技术具有重要意义。结合动量理论和涡流理论,推导了桨叶环量方程,用广义尾流模型计算了旋翼下洗流场。并在此基础上用工程方法计算了有旋翼尾流干扰和无旋翼尾流干扰两种条件下的某空空导弹气动特性,揭示了旋翼尾流对导弹的气动干扰规律,为直升机载导弹的发射控制提供了参考依据。     

射频识别技术在仓储物流系统中的应用

射频识别技术在仓储物流系统中的应用,能记录从生产、配送到仓储管理的全过程,能进行成批的读写操作.文中通过介绍射频识别技术,及其相关硬件设备电子标签和读写器的组成和工作原理,分析出射频识别技术在仓储物流系统中应用的方法和工作流程,并给出应用这一技术的仓储物流管理系统的组装、工作流程图和实验模型图.同时简要介绍了选用美国德州仪器生产的最新一代射频系列＂Tag-it＂的优势.     

某型飞机进气道地面涡畸变流动特性

以配装大涵道比涡扇发动机的某型运输机在未铺装跑道静止开车、滑行等实战使用环境为背景,建立了全尺寸三维仿真计算模型,通过数值仿真,分析研究了风速、风向以及滑跑速度对该型飞机进气道地面涡的流动特性及发动机进口畸变特性的影响。结果表明:该型运输机270°侧风条件下,随着风速的增加,地面涡强度呈现先增加后减小的规律,风速为2~4 m/s时强度最大,风速在6 m/s以上地面涡特性消失;风速为3m/s时,在风向为210°左右地面涡强度达到最大,外物吸入能力最高,其导致的进气道出口周向压力畸变最强。该型运输机滑行状态相对于其静止、逆风环境,地面涡的范围、强度均较小,对进气道出口流场品质也影响较弱。      

非对称交变应力下疲劳强度条件的探讨

对当前广泛应用于机械设计的非对称循环下构件的疲劳强度条件进行分析,求导合理的疲劳强度条件.由材料力学可知,在简化的构件持久极限图上,同一循环特征下,构件的工作安全系数是由同一射线上的两点得到的.但由于构件的综合影响系数只对应力幅值(纵坐标)有影响,因此材料的持久极限与构件的持久极限一般不会落在同一射线上.由此可知,当前通用的非对称交变应力的疲劳强度条件是不正确的.通过对构件持久极限图的分析,进行了推导,得出了构件工作安全系数的正确表达式,并分析了两者之间的误差.结论指出,按原有的疲劳强度条件进行设计有时会造成较大的浪费.     

低轨卫星的北斗反射信号海洋覆盖分析

北斗系统作为我国自行研制的导航系统，具有独特的混合星座特性，其反射事件在海洋上的空间分布和覆盖性能的研究成果较少。针对上述问题，模拟了北斗三号（Beidou System 3，BDS3）以及全球定位系统（Global Positioning System，GPS）空间星座，模拟不同性能参数的低轨接收卫星，在此仿真系统的基础上，计算反射事件在各仿真场景下的海洋覆盖率以及同时发生反射事件的卫星数量。结果表明：BDS3与GPS相比具有更大的反射事件海洋覆盖率，覆盖性能更优；仿真周期7天与1天相比,前者卫星产生的反射事件海洋覆盖率约为后者5倍；低轨道卫星（Low Earth Orbit,LEO）轨道高度越高，天线波束角度越大，反射事件海洋覆盖率越大；3颗LEO卫星下同时发生反射事件卫星数的平均值约为单颗LEO卫星的3倍。可通过设计多星组网来提高反射事件海洋覆盖率。研究结果对星载反射技术海洋遥感应用方面有一定的参考价值。     

High-performance altimeter Doppler processing for measuring sea level height under varying sea state conditions

This paper describes an innovative method for processing nadir altimeter data acquired in Synthetic Aperture Radar (SAR) mode, enhancing the system performances over open ocean. Similarly to the current SAR data processing scheme, the so-called LR-RMC (Low Resolution with Range Migration Correction) method, originally designed by Phalippou and Demeester (2011), includes Doppler beam forming, Doppler shift correction and range correction. In LR-RMC, however, an alternative and less complex averaging (stacking) operation is used so that all the Doppler beams produced in a radar cycle (4 bursts of 64 beams for the open-burst Sentinel-3-mode altimeter) are incoherently combined to form a multi-beam echo. In that manner, contrarily to the narrow-band SAR technique, the LR-RMC processing enlarges the effective footprint to average out the effects of surface waves and particularly those from small sub-mesoscale structures (<1 km) that are known to impact SAR-mode performances. On the other hand, the number of averaged beams is as high as in current SAR-mode processing, thus providing a noise reduction at least equally good. The LR-RMC method has the added benefit of reducing the incoherent integration time with respect to the SAR-mode processing (50 ms compared to 2.5 s) limiting possible surface movement effects. By processing one year of Sentinel-3A SRAL SAR-mode data using the LR-RMC method, it is shown that the swell impact on the SAR altimeter performances is totally removed and that an improvement of 10–50% is obtained in the measurement noise of the sea surface height and significant wave height with respect to SAR mode. Additionally, observational capabilities over the middle scales are enhanced potentially allowing the ocean mesoscale features to be retrieved and observations assimilated more usefully in ocean models.     

Application of satellite observations to study the changes of hypoxic conditions in near-bottom water in the western part of Peter the Great Bay (the Sea of Japan)

In this paper we explore the possibilities of applying satellite ocean colour (OC) observations and SST to study the changes in the conditions of hypoxia in the near-bottom water in the western part of Peter the Great Bay. Near-bottom water hypoxia occurs in water bodies with increased organic matter influx when the dissolved oxygen (DO) consumed at its oxidation is not restored. Consumption of most DO is usually attributed to the oxidation of organic matter formed as a result of increased algae growth during water eutrophication. Satellite data on indicators of phytoplankton (chlorophyll-a concentration (Chl) and fluorescence (FLH)) allow to analyze the spatial-temporal changes of this substation. Coloured dissolved organic matter (CDOM), non-algal particles (NAP) influence on satellite Chl estimates and also on near-bottom water hypoxia formation. This study analyzes daily, seasonal, and inter-annual changes in the distributions of indicators (Chl, FLH, the coefficients of light absorption by coloured detrital matter (a_CDM) and light backscattering by suspended particles (b_bp)), based on the instant satellite OC data from MODIS-Aqua. Data on the Chl, the sea surface temperature (SST) from the MODIS-Aqua, the precipitation from the TRMM satellite and the hydrometeorological stations (HMSs), the wind speed and direction from HMS “Vladivostok” are used to study the influence of hydrometeorological conditions on the Chl values. These distributions were compared with the literary information based on field observations of the hypoxia cases in the same area and with the changes in the vertical DO, Chl, temperature, salinity distribution obtained by coastal expeditions in October-November 2010 and February-March 2011. Significant interrelations within 95% confidence level between the satellite Chl, FLH values calculated at the MUMM atmospheric correction and in situ Chl values obtained in the autumn of 2010 were reached separately for the cases with winds of northern and southern directions with the correlation coefficients of 0.71, 0.48 and 0.49, 0.71, respectively. Significant dependences of Chl on SST and Chl on wind speed explained by the influence of continental runoff and water ventilation were obtained. Therefore, the changes of Chl reflect the changes of hypoxic conditions in the near-bottom water. In Amursky Bay the onset of hypoxia was at the Chl and SST values equal to 4 mg m^?3 and 13 °C (↑ – at increasing SST); near Furugelm Island it was at 1.6 mg m^?3 and 25 °C (↑), 1 mg m^?3 and 21 °C (↓). The difference in the Chl values was reflected in the hypoxia onset timings that were the beginning of June (2011), August (2013), and September (2014), respectively. The water flow from the eastern coast of Amursky Bay in early August of 2013 recorded from the OC and SST satellite imagers appeared in an additional hypoxic zone. Decreased OC characteristics in the runoff of the Razdolnaya River in August-September of 2014 were a sign of hypoxia at its mouth. Near Furugelm Island the hypoxia destruction (increase in the DO level from 1 to 4.5 ml L^?1) was observed at the Chl of 0.9 mg m^?3 and SST = 18 °C (↓). At the autumn maximum of Chl equal to 1.7 mg m^?3 and SST = 4 °C (↓) in mid-November the DO level here increased to 8 ml L^?1. In Amursky Bay, short-term destructions/weakening of hypoxia manifested themselves in sharp increases of Chl. At that, the ratio between the Chl value and the approximation level was equal to 2 and higher for SST equal to 22–25 °C (↑), to 0.9 and higher for SST equal to 5–13 °C (↓). With the water stratification destruction in temperature and the noticeable weakening of the stratification in salinity (mid-November), the hypoxia destructed (the DO level increased from 2 to 6 ml L^?1). In this case, Chl and SST were about 3 mg m^?3 and 5 °C (↓).     

Preliminary gravity recovery from CryoSat-2 data in the Baffin Bay

A number of geophysical phenomenons in the open ocean are still unresolved by conventional altimetry, but could be resolved through the potential improvements offered by Synthetic Aperture Radar (SAR), also called Delay-Doppler, altimetry. The SAR altimeter offers the following benefits with respect to conventional satellite altimetry: factor of 20 improvements in the along-track resolution, the along-track footprint length which does not vary with wave height (sea state), and improved precision in sea surface height measurements or sea surface slope measurements.     

前缘下垂结合内吹式襟翼失速特性研究

内吹式襟翼具有高效的增升能力,但失速迎角在较高的吹气动量系数下下降明显,为改善其失速特性,研究内吹式襟翼加装前缘下垂后的失速特性。对前缘下垂结合无缝襟翼的亚声速翼型在环量控制作用下的流场进行数值模拟,研究吹气动量系数对失速特性的影响规律,前缘刚性偏转、弯度变化和厚度变化对失速特性的改善作用,以及改变襟翼偏角研究前缘下垂...     

A simple model for the interhemispheric coupling of the middle atmosphere circulation

The interhemispheric coupling of the middle atmosphere general circulation is characterized by a global anomaly pattern of the zonal-mean temperature. This pattern reflects an anomalous stratospheric and mesospheric residual circulation, in which a weaker (stronger) stratospheric winter circulation is linked to an upward (downward) shift of its upper mesospheric branch reaching from the summer to the winter pole. This phenomenon is robust in observational data and several middle atmosphere general circulation models. In the present study, the recently proposed mechanism of the interhemispheric coupling is unequivocally proven within the framework of a zonally symmetric model that excludes any additional effects due to resolved waves and non-zonally propagating gravity waves. Two simulations are conducted that differ in the strength of the polar vortex. A weaker polar vortex results in a downward shift of the winter mesospheric gravity wave drag. This leads to changes also in the summer upper mesosphere via a feedback solely between gravity wave breaking and the zonal-mean state. The accompanying temperature anomaly reproduces the pattern of the interhemispheric coupling.