光子晶体热控结构防护性能研究

光子晶体在红外波段同时具有高反射率和高辐射率,可作为高超声速飞行器的防热材料。文章利用FLUENT软件和辐射模型中的离散坐标算法对有/无光子晶体防热层结构进行了气动加热数值模拟计算,得到了在不同热流密度条件下基体的温度分布;通过计算结果的对比发现,采用光子晶体防热层结构使基体温度下降约360～515 K,具有良好的热控性能。光子晶体是一种具有广阔应用前景的热防护材料,作为高超声速飞行器的防热层结构的可行性与有效性还有待深入研究。     

Shannon 采样定理的由来和一些数学方面的发展

阐述Ｓｈａｎｎｏｎ采样定理在插值理论上的含义和对Ｓｈａｎｎｏｎ采样定理作进一步研究的必要性。对广义采样定理,特别是多分辨率空间中的采样定理作了介绍,并对二种非带限信号的采样定理作了总结和概况。     

抗核电磁脉冲设计中的屏蔽理论——带有孔缝屏蔽体屏效的计算

本文对形状规则的屏蔽体提出了一种新的计算方法,采用并矢格林函数法求解矢量波动方程,得到屏蔽体内的场分布,再利用小孔耦合理论得到屏蔽等效源,从而利用镜象原理求得泄漏场,最后求得屏效,并举例说明。     

玻璃纤维对CYD-128/ GA-327 体系固化特性的影响

研究了CYD-128/GA-327环氧树脂体系在纯树脂和有玻璃纤维存在下的固化特性.结果表明:玻璃纤维加入后使复合材料体系的表观活化能、指前因子、反应级数和反应速率常数有小幅增加;固化放热峰面积和反应热明显下降,且下降幅度随纤维质量含量的增加而增大.纤维的加入,使得复合材料体系在相同升温速率下的最大固化反应速率降低,固化起始温度提前,达到最大固化反应速率的时间延长,固化反应完成所需的时间变长.在170℃以前,纤维的加入对树脂体系的固化反应具有催化作用,170℃以后,纤维的加入对树脂体系的固化反应具有缓聚作用.     

推进剂中新型聚醚聚氨酯粘合剂的热分解行为

采用ＳＤＣ和ＴＧ两种热分析方法研究了推进剂中两种新型聚醚粘合剂及经不同增塑剂增塑后的聚氨酯弹性的热分解行为。研究表明环氧乙烷／四氢呋喃共聚醚具有较好的热稳定性, 热分解大约从２２０°Ｃ开始; 用Ｎ－１００ 固化和加入抗氧剂均能显著提高其稳定性。聚氨酯弹性体的热失重分阶段进行, 首先是增塑剂的挥发和分解, 然后是聚氨酯网络的裂解。以聚乙二醇（ＰＥＧ）为聚醚二元醇的聚氨酯比共聚醚聚氨酯具有较低的热稳定性, 但经硝酸酯增塑后,ＰＥＧ体系比共聚醚体系表现出较高的稳定性。     

大型客机涡扇发动机动力特性模拟

机体/发动机干扰问题是现代大型客机设计中必须考虑和解决的核心问题之一。长期以来,商用和in-house计算流体力学（CFD）软件,都是通过在发动机进气口设置质量流量比,排气口和外涵道设置总温比/总压比,建立动力特性模型来等效模拟机体/发动机干扰流场。在现有动力特性模型基础上,借鉴特征边界思想,将外涵道指定为特征边界,建立了一种新的发动机动力特性模型。采用轴对称超高涵道比涡扇发动机模型、轴对称涡轮动力模型以及某型客机带发动机模型对两种动力特性模型进行了系统的验证和确认,结果表明：两种发动机动力特性模型均能很好地模拟涡扇发动机动力效应,且计算结果与试验数据吻合较好,说明了两种动力特性模型的正确性、可靠性以及工程适用性。此外,所建立的新动力特性模型特别适合于大涵道比涡扇发动机的动力效应模拟,且可以在外涵道总温比、总压比等参数未知的情形下,评估发动机的动力特性,在实际工程中应用更广泛。     

旋转叶片尾缘通道的换热特性

用实验的方法研究了旋转和静止状态下带交错肋和柱肋的涡轮叶片尾缘通道的换热特性.通道截面为楔形,交错肋段上下表面肋错开布置,节距比约为7,柱肋段包含大小两排扰流柱.在实验雷诺数为6 100~33 000,旋转数0~0.6的工况下对比分析了尾缘通道交错肋段和柱肋段的旋转静止换热特性.研究结果表明:静态下,交错肋段前后缘面存在换热差异,且该差异沿程减小;在交错肋充分发展段,旋转增强了后缘面的换热,削弱了前缘面的换热;交错肋段前后缘面叶间处换热旋转下均得到增强;旋转下柱肋段的过渡段尺度减小,换热最强点向低半径处偏移.     

飞机重心允许范围设计准则

基于稳定气动布局飞机的操纵性和稳定性要求，提出飞机重心允许范围的确定需要考虑的一些准则。以某型机为例，用综合提出的设计准则及相关数据对该机的重心允许范围进行了详细计算。结果表明，按照提出的设计准则确定的重心允许范围与按经验估计的结果接近．说明所提出的设计准则是可行的。     

Using only observation station data for PPP ambiguity resolution by UPD estimation

This article proposes a new method for uncalibrated phase delay (UPD) estimation to improve the accuracy of precise point positioning (PPP), which uses only observation station data. This means that the station used to generate the UPDs is the same station to which they are applied. First, dual-frequency observation equations based on a raw PPP model are developed. Then, the UPDs are calculated from integer linear combinations of float ambiguities. Third, with the UPD corrections, the least-squares ambiguity decorrelation adjustment (LAMBDA) method is utilized to obtain the integer ambiguities. Since only observation station data are used for UPD estimation, the partial ambiguity resolution (PAR) method is adopted to increase the possibility of finding a subset of integer ambiguities. The UPD estimation and ambiguity resolution are performed in each epoch. To obtain the correct integer ambiguity, the ratio test and success rate (bootstrapping) are used to evaluate the estimated integer ambiguity. Finally, by treating the integer ambiguities as constants, fixed solutions can be obtained. Quality control is also applied throughout the entire data processing procedure to obtain high quality float and fixed solutions. Data from 22 stations of the International Global Navigation Satellite System (GNSS) Service (IGS) in East Asia on day of year (DOY) 206, 2017, are used to verify the feasibility of this method. The experimental results show that compared with the float solution, the proposed method can significantly improve the accuracy in the east, north and up directions by 24%, 21% and 18% for static PPP and 36%, 18% and 34% for dynamic PPP, respectively. However, the accuracy of the proposed method is still lower than that of the fixed solutions obtained by the PRIDE-PPPAR software, in which the fractional cycle bias is computed based on reference network data. These findings sufficiently show that the proposed method can offer better solution accuracy than the float solution. However, the quality of the UPDs estimated only from observation station data is not as good as that of the estimates obtained based on reference network data.