TiAl系金属间化合物球型预合金粉末制备及粉末冶金工艺研究

成功制备了Ti-46Al-2Cr-2Nb-0．2B-0．1W（原子分数）球型预合金粉末，并对粉末的特性进行了研究。在随后的粉末冶金技术研究中，运用热等静压技术得到了组织细小、均匀的粉末TiAl系金属间化合物，但材料的伸长率很低。经热处理后，材料的伸长率达到了2．5％。     

球形贮箱中三维液体大幅晃动数值模拟

提出一种新颖有效的网格移动算法,使用任意拉格朗日-欧拉（ALE）有限元方法对球形贮箱中三维液体大幅晃动问题进行数值模拟。对接触线网格及自由液面网格指定其运动轨道,对湿壁面网格采用代数更新算法,对域内网格采用Laplace方程对网格速度进行平滑。同时采用基于特征线的时间分裂（CBS）格式来处理对流效应引起的数值振荡。数值计算结果与已有试验数据进行了对比,两者吻合良好,证明了网格移动算法与计算格式的可行性与准确性。     

Lunar gravity field modeling critical analysis and challenges

This paper summarizes and provides a critical analysis of the historical developments of lunar gravitational models from the earliest use of ground based tracking systems of the Lunar Orbiter to the Lunar Prospector mission. This encompasses a comprehensive and critical analysis of the various methods used in the estimation of the gravity coefficients and the processing of large batches of diverse measurements and data types. It has been shown that weakness exists in the current models of the lunar gravity field, which is primarily due to the lack of far side lunar tracking data information, which makes the lunar potential modeling difficult but expected to be overcome as data from SELENE satellite-to-satellite tracking becomes available. Comparisons of various lunar models reveal an agreement in the low order coefficients of the spherical harmonics. However, substantial differences in the models exist in the higher-order harmonics. A numerical comparison has been presented showing the performance of all the contemporary lunar gravitational models used within the astrodynamics community and available in public domain. Improvements to the current models are part of a continuing process and the recent model improvements and future possibilities in lunar gravity modeling are discussed. A brief review of the recent missions has been presented. It is hoped that this critical review will benefit the researchers by presenting the historical as well as state of the art in this field.     

复合材料帽型加筋舱门结构 RF 成型工艺研究

舱门属于飞机上次承力结构,但由于其是运动部件,承受较大的气动载荷,必须要考虑到强度、刚度、气密、可靠性、表面质量等因素,在此基础上,还要求舱门质量尽可能轻。复合材料帽型加筋结构壁板因其刚度大,。结构整体性好等优点,使其在飞机舱门结构上得到应用。文中采用自动缝合RF 工艺,完成缝合预成型体制备、RFI 工艺树脂流道设计等关键技术,实现了帽型加筋舱门结构件的一次整体成型。     

HASDM修正方法分析与评估

分析Jacchia70（J70）热层模式原理、美国空军高精度卫星拖曳模型（HASDM）的修正方法及选取球面调和函数的原因.推导模式密度对球谐系数（SH）的偏导数,给出利用模式密度泰勒展开进行线性化处理、迭代求解球谐系数的具体过程.针对2003年10月29日大磁暴事件,基于CHAMP和GRACE A/B卫星加速度计实测密度,进行修正方法的性能评估.统计相对误差的均值及标准差变化：改进前分别为-81.7%,74.4%;改进后分别为-5.9%,53.1%,验证了改进算法的有效性.从热层上下边界温度角度,详细分析了热层模式动态修正原理,研究结果为类HASDM修正模式的工程应用提供了理论基础.     

Negative VTEC with spherical harmonic expansion model under different solar activity conditions

The Earth’s ionosphere can be described by a spherical harmonic (SH) expansion up to a specific degree. However, there exist negative vertical total electron content (VTEC) values in the global ionosphere map (GIM) with the SH expansion model. In this contribution, we specifically investigated the negative VTEC values that are induced by the SH expansion model and validated the performance of the inequality-constrained least squares (ICLS) method in eliminating the negative VTEC values. The GPS data from 2004 to 2017 was selected to cover one solar cycle and the experiments under different solar activity conditions were analyzed. The results in our work show that the occurrence of the negative VTEC values is attributed to the deficiency of the SH expansion model when the VTEC itself is small instead of the unevenly distribution of the GNSS stations. The negative VTEC values appear periodically in the temporal domain, showing apparently one year and half year periods. During one year, two peaks in June and December can be observed in the time series of the negative VTEC values. The number of negative VTEC values in June is obvious larger than that in December. During one solar cycle, the number of negative VTEC values under quiet solar activity condition is obvious larger than that under strong solar activity condition. In the spatial domain, the appearance of the negative VTEC values is strongly related with the movement of the subsolar point. In the latitude of the subsolar point has the largest magnitude, the negative values will appear on the opposite hemisphere and the further from the subsolar point the more negative values. The maximum number of the negative VTEC values in the southern hemisphere appears in June, while the peak value in the northern hemisphere appears in December. The maximum number of negative VTEC values in the southern hemisphere is generally larger than that in the northern hemisphere. In addition, the negative VTEC values are distributed both at middle latitude and high latitude in the southern hemisphere, while they are mainly distributed at high latitude in the northern hemisphere. When the ICLS method is used, the negative VTEC values can be eliminated efficiently and it has nearly no influence on the positive VTEC values. The ICLS method can also improve the receiver’s differential code bias (DCB) and significantly decrease the unreasonable negative slant TEC (STEC) values along the lines of sight. Using the final GIM product of the Jet Propulsion Laboratory (JPLG) as a reference, the root mean square (RMS) of the ICLS solution shows maximum 25%, 20% and 45% improvement relative to the least squares (LS) solution at northern high latitude, southern middle latitude and southern high latitude, respectively.