基于小波理论的岩体质量声波多参数分级方法

文章在传统的超声波速分级基础上,通过对超声信号的小波变换及频谱分析,提取不同频段的超声波动力学参数,综合考虑超声波运动学和动力学特征,采用系统聚类和逐步回归法确定分级因素、归一化后的多元线性回归法确定分级模式,建立了基于小波理论的岩体质量声波多参数分级方法.经过对比分析,证明新方法可提高声波岩体质量评价方法的可靠性和准确性.     

织物-多种相变微胶囊复合材料热特性数值模拟

为了研究添加相变微胶囊织物的热特性,基于织物热湿耦舍模型,本文发展了一个新的数学模型.模型考虑了多种相变微胶囊与织物的热传递,纤维的吸湿性/放湿性以及热湿耦合作用.模型方程采用控制体积法进行了求解.数值解与实验结果进行了对比,表明了该模型具有满意精度.模拟了相变材料总合量相同,但相变材料布置方式不同的织物在加热过程中的热特性.结果表明,相变微胶囊及其混合物在织物中的布置方式不同,对织物热特性有重要影响.     

虚拟质量法在运载火箭模态分析中的应用

针对液体燃料对火箭结构的模态影响,提出采用虚拟质量法进行模态分析。首先建立了一个贮箱模型,分析了液体对结构模态的影响;然后利用该方法对一个带有液体推进剂的助推器进行了模态分析,并与集中质量法计算结果进行了比较。计算结果显示,采用虚拟质量法计算时由于液体的存在结构的频率会降低,而且虚拟质量法和集中质量法在模拟液体推进剂对结构横向一阶频率的影响时有较好的一致性,结果证明虚拟质量法作为一种模态分析方法可以为设计人员提供参考。     

翼伞-载荷系统多体动力学仿真分析

翼伞具有良好的滑翔性、操纵性和稳定性,广泛应用于航天器精确着陆和定点回收。为进行归航控制算法设计,需对翼伞系统动力学特性进行深入研究。以一般翼伞-载荷系统为研究对象,采用拉格朗日乘子法建立了两体8自由度动力学仿真模型,对3个飞行工况进行了仿真分析,结果与相应的空投试验数据基本吻合,验证了仿真模型的有效性。     

基础激励结构的试验模态分析

阐述了基础激励结构的试验模态分析理论和原理,引进了结构响应和界面力方程。给出了结构约束状态和自由状态下的结构响应与基础激励之间的关系式。讨论了界面力的直接和间接测量方法。用一个四自由度集中参数模型对两种方法进行了原理性试验验证。     

Experiments on film cooling with sonic injection into a supersonic flow

Film cooling experiments with sonic injection were conducted to investigate the effects of the number of the injection holes, the mass flow ratio, and the hole spacing on the film cooling effectiveness. The mainstream was obtained by the hydrogen-oxygen combustion, entering the experimental section at a Mach number of 2.0. The nitrogen with ambient temperature was injected into the experimental section at a sonic speed. The measured mainstream recovery temperature was approximately 910K. The mass flow ratio was regulated by varying the nitrogen injection pressure. The experimental results show that for the investigated cooling surface, the cooling effectiveness increases with the increase in the number of the injection holes with other parameters held constant. For a fixed cooling configuration, the cooling effectiveness increases with the increase in the mass flow ratio. Different from the subsonic film cooling, the optimal mass flow ratio is not observed. When the hole spacing is less than 4, no obvious difference is observed on the cooling effectiveness and lateral uniformity. With the mass flow ratio increasing further, this difference becomes much smaller. The shock wave also has an effect on the cooling effectiveness. Downstream the incident point of the shock wave, the cooling effectiveness is lower than that in the case without the shock wave.     

冰风洞试验中水滴的传热传质计算研究

进行冰风洞试验时,出口过冷水滴的参数往往使用风洞来流空气参数进行计算,忽略了真实情况下水滴与空气的传热传质过程,致使试验数据产生偏差,并影响测试结果的可靠性.通过对冰风洞试验中水滴的运动过程进行研究,考察了水滴与空气主流间的传热与传质现象,建立了水滴运动过程中参数变化的控制方程.基于该方程编制了冰风洞水滴粒径温度变化分析软件,计算分析了过冷水滴在行进过程中相关参数的变化曲线,比较了不同初始条件及各参数对水滴温度、直径和速度的影响.结果表明:不同环境下水滴在运动过程中温度、尺寸和速度变化受来流温度、速度、相对湿度和水滴初始温度的影响,呈现出不同的特点,不能忽略水滴状态参数在冰风洞内的变化.     

Interplanetary Physics Research in China During 2004 - 2005

This brief report summarized the latest advances of the interplanetary physics research in China during the period of 2004-2005, made independently by Chinese space physicists and through international collaboration. The report covers all aspects of the interplanetary physics, including theoretical studies, numerical simulation and data analysis.     

Acceleration of Solar-Energetic Particles by Shocks

Our current understanding of the acceleration of solar-energetic particles is reviewed. The emphasis in this paper is on analytic theory and numerical modeling of the physics of diffusive shock acceleration. This mechanism naturally produces an energy spectrum that is a power law over a given energy interval that is below a characteristic energy where the spectrum has a break, or a rollover. This power law is a common feature in the observations of all types of solar-energetic particles, and not necessarily just those associated with shock waves (e.g. events associated with impulsive solar flares which are often described in terms of resonant stochastic acceleration). Moreover, the spectral index is observed to have remarkably little variability from one event to the next (about 50%). Any successful acceleration mechanism must be able to produce this feature naturally and have a resulting power-law index that does not depend on physical parameters that are expected to vary considerably. Currently, only diffusive shock acceleration does this.     

Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko

Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time, impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production rate of 67P/C–G are those of a fairly typical comet.