An algorithm to separate wind tunnel background noise from turbulent boundary layer excitation

Wall pressure fluctuations generated by Turbulent Boundary Layers(TBL) provide a significant contribution in reducing the structural vibration and the aircraft cabin noise. However,it is difficult to evaluate these fluctuations accurately through a wind tunnel test because of the pollution caused by the background noise generated by the jet or the valve of the wind tunnel. In this study, a new technology named Subsection Approaching Method(SAM) is proposed to separate the wall pressure fluctuations from the background noise induced by the jet or the valve for a transonic wind tunnel test. The SAM demonstrates good performance on separating the background noise from the total pressure compared to the other method in this study. The investigation considers the effects of the sound intensity and the decay factor on the sound-source separation. The results show that the SAM can derive wall pressure fluctuations effectively even when the level of background noise is considerably higher than the level of the wall pressure fluctuations caused by the TBL. In addition, the computational precision is also analyzed based on the broad band noise tested in the wind tunnel. Two methods to improve the precision of the computation with the SAM are also suggested: decreasing the loop gain and increasing the sensors for the signal analysis.     

某型飞机护板作动筒自动开锁故障分析及改进

针对某型飞机护板在飞行中自动打开的故障,对护板收放作动筒工作原理、结构组成进行了研究,在开锁试验验证和故障件分解检查后,确定了作动筒自动开锁的原因是由于弹簧力过小,使得作动筒开锁压力小于瞬时回油压力所致.通过改进作动筒内部零件弹簧的安装方式,增大了开锁压力,提高了开锁压力的稳定性,排除了故障,为飞机飞行安全提供了保障.     

Sailing with solar and planetary radiation pressure

Literature on solar sailing has thus far mostly considered solar radiation pressure (SRP) as the only contribution to sail force. However, considering a sail in a planetary mission scenario, a new contribution can be added. Since the planet itself emits radiation, this generates a radial planetary radiation pressure (PRP) that is also exerted on the sail. Hence, this work studies the combined effects of both SRP and PRP on a sail for two case studies, i.e. Earth and Venus. In proximity of the Earth, the effect of PRP can be significant under specific conditions. Around Venus, instead, PRP is by far the dominating contribution. These combined effects have been studied for single- and double-sided reflective coating and including eclipse. Results show potential increase in the net acceleration and a change in the optimal attitude to maximise the acceleration in a given direction. Moreover, an increasing semi-major axis manoeuvre is shown with and without PRP, to quantify the difference on a real-case scenario.     

Geocenter coordinates estimated from GNSS data as viewed by perturbation theory

Time series of geocenter coordinates were determined with data of two global navigation satellite systems (GNSSs), namely the U.S. GPS (Global Positioning System) and the Russian GLONASS (Global’naya Nawigatsionnaya Sputnikowaya Sistema). The data was recorded in the years 2008–2011 by a global network of 92 permanently observing GPS/GLONASS receivers. Two types of daily solutions were generated independently for each GNSS, one including the estimation of geocenter coordinates and one without these parameters.     

复杂群塔风荷载试验研究

介绍了一复杂群塔结构节段刚性测压试验概况和主要试验结果,讨论了结构典型部位风压分布的基本特征和结构风压分布的基本规律.试验结果表明,由于该结构由多个单体高耸塔结构组成,相互干扰严重,风压的分布相当复杂.根据风压试验结果得到了风力沿各塔高度的分布,并讨论了分布规律,进一步得出基底剪力系数和基底弯矩系数,分析了最危险风向,给出了用于结构设计的荷载建议.     

Plants survive rapid decompression: Implications for bioregenerative life support

Radish (Raphanus sativus), lettuce (Latuca sativa), and wheat (Triticum aestivum) plants were grown at either 98 kPa (ambient) or 33 kPa atmospheric pressure with constant 21 kPa oxygen and 0.12 kPa carbon dioxide in atmospherically closed pressure chambers. All plants were grown rockwool using recirculating hydroponics with a complete nutrient solution. At 20 days after planting, chamber pressures were pumped down as rapidly as possible, reaching 5 kPa after about 5 min and ∼1.5 kPa after about 10 min. The plants were held at 1.5 kPa for 30 min and then pressures were restored to their original settings. Temperature (22 °C) and humidity (65% RH) controls were engaged throughout the depressurization, although temperatures dropped to near 16 °C for a brief period. CO₂ and O₂ were not detectable at the low pressure, suggesting that most of the 1.5 kPa atmosphere consisted of water vapor. Following re-pressurization, plants were grown for another 7 days at the original pressures and then harvested. The lettuce, radish, and wheat plants showed no visible effects from the rapid decompression, and there were no differences in fresh or dry mass when compared to control plants maintained continuously at 33 or 98 kPa. But radish storage root fresh mass and lettuce head fresh and dry masses were less at 33 kPa compared to 98 kPa for both the controls and decompression treatment. The results suggest that plants are extremely resilient to rapid decompression, provided they do not freeze (from evaporative cooling) or desiccate. The water of the hydroponic system was below the boiling pressure during these tests and this may have protected the plants by preventing pressures from dropping below 1.5 kPa and maintaining humidity near 1.5 kPa. Further testing is needed to determine how long plants can withstand such low pressure, but the results suggest there are at least 30 min to respond to catastrophic pressure losses in a plant production chamber that might be used for life support in space.     

纤维缠绕金属内衬压力容器的设计和分析技术

介绍了纤维缠绕金属内衬压力容器的工艺特点、性能优势和爆破前先泄漏(LBB)的安全失效模式，以及一般设计原则、构形、材料和工艺要求。分析了金属内衬的厚度、过渡区、焊接区和纤维缠绕层。以及输入输出极孔的设计技术。阐明了用于静力分析的解析法和数值法，以及用于循环寿命预测的断裂力学分析法。最后概述了一些新技术、新材料的应用情况，并指出了压力容器设计的发展趋势。     

空气动压探头的动态响应研究

本文采用动力类比法对用于核爆炸测量的空气动压探头的动态响应进行了理论分析,并对探头的三个压力量程计算了总压边和静压边进气管道中的阻尼孔直径和动压波形的上升时间。分析计算表明,在探头的三个系统中,电学系统对动态响应的影响可忽略不计;力学系统的影响也是较小的;对动态响应起主要作用的是声学系统(即管道空腔系统)。在直径为130mm 激波管中进行了全尺寸探头的动态响应实验。实验表明,阻尼孔直径和波形上升时间的实验值与计算值符合较好。此探头曾多次用于我国大气层核试验测试中。从核爆炸和激波管实验中测得的空气动压波形可看出,它们的前沿都是很好的,这反映出此探头具有良好的动态响应特性。     

低密实度基础月壤的钻进压力建模及试验验证

基于钻采过程中月壤颗粒的运动规律提出了一种钻具与月壤相互作用区域的等效方法,并由此从宏观角度建立了一种新型月壤钻进压力解析模型.通过70％密实度基础月壤地面钻采试验验证了该模型对低密实度月壤钻进压力的预测能力,得到了相关修正系数与钻进比之间的关系并分析了模型的可扩展性.该建模方法为复杂工况下钻具-土体相互作用建模提供了...     

Influence of Earth’s shadowing effects on space debris stability

Solar radiation pressure affects the evolution of high area-to-mass geostationary space debris. In this work, we extend the stability study of Valk et al. (2009) by considering the influence of Earth’s shadows on the short- and long-term time evolutions of space debris. To assess the orbits stability, we use the Mean Exponential Growth factor of Nearby Orbits (MEGNO), which is an efficient numerical tool to distinguish between regular and chaotic behaviors. To reliably compute long-term space debris motion, we resort to the Global Symplectic Integrator (GSI) of Libert et al. (2011) which consists in the symplectic integration of both Hamiltonian equations of motion and variational equations. We show how to efficiently compute the MEGNO indicator in a complete symplectic framework, and we also discuss the choice of a symplectic integrator, since propagators adapted to the structure of the Hamiltonian equations of motion are not necessarily suited for the associated variational equations. The performances of our method are illustrated and validated through the study of the Arnold diffusion problem. We then analyze the effects of Earth’s shadows, using the adapted conical and cylindrical Earth’s shadowing models introduced by Hubaux et al. (2012) as the smooth shadow function deriving from these models can be easily included into the variational equations. Our stability study shows that Earth’s shadows greatly affect the global behaviour of space debris orbits by increasing the size of chaotic regions around the geostationary altitude. We also emphasize the differences in the results given by conical or cylindrical Earth’s shadowing models. Finally, such results are compared with a non-symplectic integration scheme.