2024铝合金预拉伸板喷丸强化前后疲劳寿命的分布及可靠度模型研究

为了研究喷丸强化对2024铝合金预拉伸板疲劳特性的影响以及喷丸强化前后疲劳寿命的数学分布及可靠度模型,对铸钢丸喷丸强化前后的2024铝合金预拉伸板进行疲劳对比试验。结果表明:喷丸强化能明显提高2024铝合金预拉伸板的疲劳寿命。对喷丸强化前后的疲劳寿命分布进行拟合优度检验发现:喷丸强化前疲劳寿命服从威布尔分布,而喷丸强化后的疲劳寿命服从对数正态分布。建立了2024铝合金预拉伸板喷丸强化前后疲劳寿命的分布模型和可靠度模型。     

Optimal assimilation for ionospheric weather – Theoretical aspect

Observation, specification and prediction of ionospheric weather are the key scientific pursuits of space physicists, which largely based on an optimal assimilation system. The optimal assimilation system, or commonly called data assimilation system, consists of dynamic process, observation system and optimal estimation procedure. We attempt to give a complete framework in this paper under which the data assimilation procedure carries through. We discuss some crucial issues of data assimilation as follows: modeling a dynamic system for ionospheric weather; state estimation for static or steady system in sense of optimization and likelihood; state and its uncertainty estimation for dynamic process. Meanwhile we also discuss briefly the observability of an observation system; system parameter identification. Some data assimilation procedures existed at present are reviewed in the framework of this paper. As an example, a second order dynamic system is discussed in more detail to illustrate the specific optimal assimilation procedure, ranging from modeling the system, state and its uncertainty calculation, to the quantitatively integration of dynamic law, measurement to significantly reduce the estimation error. The analysis shows that the optimal assimilation model, with mathematical core of optimal estimation, differs from the theoretical, empirical and semi-empirical models in assimilating measured data, being constrained by physical law and being optimized respectively. The data assimilation technique, due to its optimization and integration feature, could obtain better accurate results than those obtained by dynamic process, measurement or their statistical analysis alone. The model based on optimal assimilation meets well with the criterion of the model or algorithm assessment by ‘space weather metrics’. More attention for optimal assimilation procedure creation should be paid to transition matrix finding, which is usually not easy for practical space weather system. High performance computing hardware and software studies should be promoted further so as to meet the requirement of large storage and extensive computation in the optimal estimation. The discussion in this paper is appropriate for the static or steady state or transition process of dynamic system. Many phenomena in space environment are unstable and chaos. So space environment study should include and integrate these two branches of learning. This revised version was published online in August 2006 with corrections to the Cover Date.     

Beacon Monitoring: Reducing the Cost of Nominal Spacecraft Operations

Beacon monitoring is an architecture for augmenting on-board health assessment software with the following elements: a transmitter that periodically broadcasts this health assessment to the ground, a network of globally distributed low-cost monitoring stations that relays the health assessment to mission control, and an automated mission control system for notifying on-call operators and initiating appropriate response actions. While beacon monitoring is often cited as a means of lowering nominal monitoring costs for particular missions, these claims have typically been qualitative and undiscriminating in nature. This study introduces modeling and experimentation as means of providing a more fundamental validation of the cost-effectiveness of beacon monitoring. Results include simple quantitative estimates of first-order performance metrics, experimental data that verifies predicted performance and validates the use of beacon monitoring for a test mission, and a method for assessing the value of beacon monitoring for general satellites missions.     

无线传感网中能量优化的异常检测算法

基于网内数据处理技术和网络动态分簇技术,提出一种能量优化的异常检测算法。算法首先利用节点协作计算获取相关性信息,然后根据节点相关性和节点能量信息进行动态网络分簇,最后利用簇内相关与簇间相关性进行能量有效性的异常检测。相关测试结果表明,本文算法既保证了传感网异常检测精度又提高了网络能量利用效率。     

磁探仪应召搜潜建模与仿真

依据经典的磁探仪应召搜潜方法,以某型反潜巡逻机为背景,建立了反潜巡逻机利用磁探仪执行平行航线、扩展矩形和螺旋形搜潜模型.对3种方法的搜潜概率进行分析,仿真了相同潜艇运动模型条件下,潜艇初始位置散布、初始距离、潜艇经济航速和海洋环境磁噪声对搜潜概率的影响.实验结果表明:相同条件下,螺旋形搜潜效能最高;潜艇只进行航速机动时...     

归因于空间环境的航天器故障与异常

天然空间环境对航天器设计、研制和运行的影响是NASA马歇尔空间飞行中心系统分析和集成实验室电磁与航空宇宙环境部组织编写的一系列NASA RP报告的主题。其中,NASA RP-1390详细概述了天然空间环境7个主要环境因素,包括它们的简单定义、相关的型号计划事项以及对各种航天器分系统的影响。该报告提供100多个从1974～1994年间发生的归因于天然空间环境的航天器故障和异常的案例,统计分析天然空间环境及其对航天器的影响。文章是对这篇报告的介绍与点评。     

飞艇续航时间论证方法研究

由于飞艇续航时间受飞行速度、重力浮力配平方式、载油量变化、风场条件等多种因素的影响,飞机续航时间计算方法并不适用于飞艇,因此提出了一种新的基于试验设计和统计分析方法的飞艇续航时间论证方法。分析了工作高度的风场速度分布规律,分别给出完全靠发动机推力矢量平衡和完全靠动升力平衡两种不同情况下飞艇续航时间计算方法,以某大型对流层飞艇为研究对象,计算了初始方案在不同平均巡航速度、配平重量和配平方式下的平均燃油消耗率和最大续航时间,对经过减阻、减重、减少耗油率等技术改进后优化方案能达到的续航时间和概率进行了分析和论证。研究表明,某飞艇初始方案在使用区域风场条件下基本能满足留空时间72h的指标要求,经技术改进后,指标仍有较大的提升的空间。方法考虑了飞艇续航时间的多种影响因素、取值变化和交互影响,比较适宜在飞艇这类涉及重浮力配平和任务耗油率变化的浮空器上使用。     

Vertical TEC variations and model during low solar activity at a low latitude station,Xiamen

GPS-derived vertical TEC recorded at Xiamen (24.5°N, 118.1°E, geomagnetic latitude 13.2°N), China, during year 2006 is analyzed for the first time and compared to that predicted by ionosphere model SPIM recommend by ISO. A manifest seasonal anomaly is found with the high value during equinoctial season and low value during summer and winter season. Relative standard deviation for VTEC shows high value at around midnight and before sunrise. The correlation analysis exhibits that the variation of VTEC has a very weak relation with geomagnetic and solar activities (Dst, AP, SSN and F10.7). Comparative results reveal that the SPIM overestimates the observed VTEC at most of the time.     

IRI-2007预测TEC在广州地区的适用性分析

利用广州站(23.2°N, 113.3°E) GPS双频接收机监测的电离层TEC数据和IRI-2007模型不同电离层输入参数计算得到的TEC预测值, 对比分析了太阳活动低年(2008年)广州地区TEC的变化特征. 结果表明, TEC观测值周日变化在16:00LT左右达到最大值, 而IRI-TEC最大值出现时间较GPS-TEC提前1h左右. TEC季节变化在春秋分较高, 两至季节较低, 表现出明显的半年特性和季节依赖性, 并出现冬季异常现象. IRI-TEC与GPS-TEC在白天具有较好的一致性, 夜间偏差较大. 不同电离层输入参数得到的TEC预测值也相差较大, 选用顶部电子密度参数NeQuick、底部厚度参数B0 Table并用URSI系数计算F₂层峰值参数时, 能较好地反映TEC观测值的变化特征. 在对磁暴的响应上, 预测值无明显变化, 观测值则有比较明显的表现. 通过对比, 初步分析了利用IRI-2007模型预测TEC在广州地区的适用性, 并给出了合理的参数选择方案.