油盘火热释放率影响细水雾灭火特性试验

为了研究细水雾针对不同热释放率条件下的灭火特性及规律,采用7种不同尺寸油盘火模型和正庚烷燃料,在4.6m×3.2m×4m的空间内,进行了单喷头和四喷头灭火试验,试验过程中采用热电偶树和气体分析仪对火焰温度及火场氧浓度进行了测量,得到了不同热释放率条件下的细水雾灭火特性规律和灭火过程中火场温度场的变化规律,为细水雾灭火系统设计、检验标准制定及细水雾灭火产品开发提供了相应的试验依据.      

Development of a GNSS water vapour tomography system using algebraic reconstruction techniques

A GNSS water vapour tomography system developed to reconstruct spatially resolved humidity fields in the troposphere is described. The tomography system was designed to process the slant path delays of about 270 German GNSS stations in near real-time with a temporal resolution of 30 min, a horizontal resolution of 40 km and a vertical resolution of 500 m or better. After a short introduction to the GPS slant delay processing the framework of the GNSS tomography is described in detail. Different implementations of the iterative algebraic reconstruction techniques (ART) used to invert the linear inverse problem are discussed. It was found that the multiplicative techniques (MART) provide the best results with least processing time, i.e., a tomographic reconstruction of about 26,000 slant delays on a 8280 cell grid can be obtained in less than 10 min. Different iterative reconstruction techniques are compared with respect to their convergence behaviour and some numerical parameters. The inversion can be considerably stabilized by using additional non-GNSS observations and implementing various constraints. Different strategies for initialising the tomography and utilizing extra information are discussed. At last an example of a reconstructed field of the wet refractivity is presented and compared to the corresponding distribution of the integrated water vapour, an analysis of a numerical weather model (COSMO-DE) and some radiosonde profiles.     

GPS sensing of precipitable water vapour during the March 2010 Melbourne storm

The March 2010 Melbourne storm is used as a case study to examine the potential of using Global Positioning System (GPS) observations for studying the precipitable water vapour (PWV) field. The Victorian statewide GPS infrastructure network, i.e. GPSnet, was used in this study. GPSnet is currently the only statewide and densest GPS infrastructure network in Australia, which provides an excellent opportunity to examine the distribution of water vapour as the severe weather system passed over the state. Data from 15 GPSnet stations were processed over a one-week period, i.e. a few days prior to and after the storm passage, during which the course of the storm extended from the west to the southeast corner of the state. In addition, data from two radiosonde sites of the Australian Bureau of Meteorology Upper Air Network were used to compare and validate the GPS derived PWV measurements. The findings demonstrate that there is strong spatial and temporal correlation between variations of the ground-based GPS-PWV estimates and the passage of the storm over the state. This is encouraging as the ground-based GPS water vapour sensing technique can be considered as a supplemental meteorological sensor in studying severe weather events. The advantage of using ground-based GPS-PWV technique is that it is capable of providing continuous observation of the storm passage with high temporal resolution. The spatial resolution of the distribution of water vapour is dependent on the geographical location and density of the GPS stations.     

Report of the COSPAR mars special regions colloquium

In this paper we present the findings of a COSPAR Mars Special Regions Colloquium held in Rome in 2007. We review and discuss the definition of Mars Special Regions, the physical parameters used to define Mars Special Regions, and physical features on Mars that can be interpreted as Mars Special Regions. We conclude that any region experiencing temperatures > −25 °C for a few hours a year and a water activity > 0.5 can potentially allow the replication of terrestrial microorganisms. Physical features on Mars that can be interpreted as meeting these conditions constitute a Mars Special Region. Based on current knowledge of the martian environment and the conservative nature of planetary protection, the following features constitute Mars Special regions: Gullies and bright streaks associated with them, pasted-on terrain, deep subsurface, dark streaks only on a case-by-case basis, others to be determined. The parameter definition and the associated list of physical features should be re-evaluated on a regular basis.     

海上薄雾条件下退化图像的快速Retinex增强算法

目前基于Retinex 理论的各种算法对海上薄雾条件下拍摄到的退化图像有很 好的增强效果,但是这些算法主要是采用在RGB 色空间对3 个颜色通道进行高斯卷积方 法,导致处理较大尺寸图像速度慢,现针对上述现象,提出一种改进的Retinex 快速增强 算法来处理海上薄雾条件下的退化图像,此方法改变了传统Retinex 算法利用二维高斯核 进行卷积的办法, 并且考虑到HSV 空间更适于人眼视觉特征, 先将RGB 色空间转换到 HSV 空间,再将二维高斯函数简化成一维迭代高斯函数,然后应用一维迭代高斯函数对 亮度V 分量进行卷积,并对饱和度S 做相应的拉伸。根据时间复杂度理论对改进的方法 进行了分析,并经过实验验证,此算法的处理速度有明显的提高,去雾效果较明显,图 像质量得到了改善,为视觉导航系统后续的工作提供了保证。     

弱可压缩流体与可压缩流体模型的管路水击研究

为提升液体推进系统模型对可压缩流体的仿真能力,针对供应管路的瞬变流动,采用一维有限体积法,使用Modelica语言基于MWorks平台分别开发了适用于补燃循环发动机仿真模型库的弱可压缩流体与可压缩流体的管路模型,不同于控制方程中显含声速的弱可压缩流体模型,可压缩流体模型通过将守恒方程与真实流体的SRK型状态方程耦合求解来计算压力波的传播。在管路供应系统中,分别以液氢、液氧及液甲烷为工质进行关阀水击的仿真研究,结果表明:使用SRK状态方程避免了可压缩流体模型对内能拟合公式的依赖,减轻了建模难度;可压缩流体模型对液氧及液甲烷的仿真结果较为准确,最大误差不超过2%,对液氢的最大计算误差约9%;相对于可压缩流体模型,弱可压缩流体模型计算得到的水击压力在振幅及频率上均偏大;可压缩流体模型计算得到的流体密度波动不超过3%,因此工程实践中处理水击问题时将液体假设为弱可压具有一定的合理性。     

TBCC发动机涡轮进气道喷水冷却特性数值研究

对涡轮基组合循环(Turbine Based Combined Cycle, TBCC)发动机涡轮进气道进行喷水冷却是解决TBCC发动机推力不连续问题的有效方式之一。本文基于实际流场条件选取某型TBCC发动机涡轮进气道结构,对进气道内喷水冷却特性进行了数值仿真,研究飞行器不同工况下水滴的蒸发特性及喷水对来流高温空气的预冷效果。结果表明,来流空气温度降幅随水气比提高而增大,最高温降可达152.4K。水气比提高后水滴蒸发率逐渐降低,但蒸发总量仍会继续上升。相同水气比条件下,飞行马赫数越高,喷水冷却效果越明显。在Ma3.5飞行速度和水气比0.03条件下有最高蒸发率,达83.05%。喷水冷却有效扩展了涡轮模态飞行马赫数,最高能使飞行速度提升至Ma2.84,即喷水冷却扩展了TBCC从涡轮模态向超燃冲压模态转换的衔接速域。     

水雾对火箭点火超压抑制效果的参数化研究

为研究水雾对火箭点火超压的抑制效果,采用平面波跨介质传播理论分析水雾对点火超压的抑制机理,得到了影响水雾抑制点火超压效果的主要因子。进而,数值研究各因子对抑制效果的影响规律,分析了在满足火箭安全发射条件下各因子的取值范围。最后,利用均匀试验设计方法设计数值计算的参数水平,采用回归分析方法得到了抑制效果与影响因子之间的参数化模型,并进行了抑制效果的优化研究。结果表明影响点火超压抑制效果的主要因子有:水滴直径、水雾体积分数和水雾层厚度。受水滴直径影响,水雾对点火超压有2种不同的抑制机理。此外,当影响因子在一定阈值内变化时,点火超压抑制效果与影响因子之间存在参数化模型,且置信概率不小于95%。      

水冷温度对TC4钛合金组织演变的影响

水冷温度影响TC4钛合金的组织形态与力学性能的变化.TC4钛合金固溶后缓慢冷却到3种不同温度.水冷后组织形态与力学性能的变化结果表明:当由900℃开始水冷时,α相在晶界形核,原始的β晶粒出现;当温度继续降低达700℃然后再水冷时,析出α相相对均匀细小,试样抗拉强度和硬度分别达到了最高值867MPa和HV5218;随着冷却温度的继续下降,β相逐渐析出α相,水冷温度越低,α相呈现为粗大的片层状,试样强度和硬度降低.     

选择性激光烧结尼龙材料及其挡水板制件性能研究

采用SLS尼龙12设计并成形了某箭体低承载挡水板薄壁结构,重点就SLS尼龙12及其碳纤维增强材料的力学、热学、断口微观形貌以及制件SLS工艺参数进行了研究。研究表明,选用牌号X1556尼龙12作为挡水板材料,其无缺口冲击强度81.2 kJ/m^2,断裂伸长率26.9%,烧结窗口温度差26.0℃,材料具备良好的抗冲击强度、断裂韧性和较宽的烧结窗口温度范围。优化设置成形工艺参数,如预铺粉起始温度为155℃,预铺粉保持温度168℃,加工温度169℃,填充速度4 000 mm/s,成形的挡水板制件外观良好,并且该制件通过了防水及耐热试验考核验证,为SLS尼龙成形技术在航天领域中的拓展应用打下基础。