细观力学有限元法预测复合材料宏观有效弹性模量

基于能量等效原理提出了复合材料有效弹性模量的定义，并指出了该定义的基础及前提条件。为从理论上计算复合材料宏观有效弹性模量，建立了通过细观力学有限元法计算复合材料有效弹性模量的方法。复合材料宏观弹性模量，是通过对复合材料细观结构代表性体积元的力学响应的计算来得到，在该计算方法中，给出了施加简便的边界载荷以及恰当的边界变形约束条件的方法。数值计算结果与部分试验结果具有较好的一致性，表明所提出的方法能够较好地计算复合材料的宏观有效弹性模量。     

带气膜阻尼结构振动特性的理论研究

针对航空发动机气膜阻尼的结构设计需求,基于挤压间隙流理论和能量方程建立气膜阻尼的力学模型,由此获得气膜阻尼结构的等效刚度系数和等效阻尼系数,通过振动方程的理论推导获得放大因子的表达式.结果表明:气腔厚度、气腔初始压强、吸振薄板模态频率和安装位置是影响减振效果的关键参数.气腔最优厚度主要由附面层厚度和实际振动频率决定,需结合实际情况确定气腔厚度,以最大程度降低振动响应;气腔初始压强越高,阻尼系数越大;吸振薄板的固有频率应尽可能与叶片本体接近,并且安装在本体振动响应最大位置,以取得最好的减振效果.      

含缺陷结构非概率可靠性分析方法研究

将基于分段描述的结构非概率可靠性模型引入含缺陷结构的可靠性分析,结合断裂判据,并用分段描述模型刻画未确知变量,实现了非概率的断裂力学分析,克服了概率断裂力学方法对原始数据要求高的局限和未确知信息区间均匀分布模型过于保守的缺陷,有效解决了含裂纹结构在小样本、贫信息场合的可靠性评定问题.通过算例,对文中方法的可行性和有效性...     

某型飞机纵向平衡速度的调整

通过对影响飞机纵向平衡速度的结构特性和气动原理的分析,指出了飞机纵向平衡速度调整中存在的问题,给出了不同飞机有效调整纵向平衡速度的方法。     

一种遥感图像建筑物检测新方法

遥感图像中的建筑物检测对于土地规划和地图绘制等具有重要意义。文章针对高分辨率全色遥感图像植被覆盖中隐蔽建筑物检测问题,提出了一种结合屋顶结构信息和纹理信息的快速房屋检测方法。首先利用屋顶边缘的几何关系寻找具有矩形屋顶的建筑物;然后使用形态学方法提取屋顶较亮的建筑物;最后利用局部二值模式（Local Binary Pattern,LBP）描述屋顶的纹理特征,并利用支持向量机（Support Vector Machine,SVM）排除误检区域。通过在全色遥感图像集上的试验证明,所提方法对高分辨率遥感图像植被覆盖区域中的建筑物目标具有较高检测率和较低误检率。     

结合损伤力学与有限元方法预估铆接结构疲劳寿命

利用飞机铆接试验件疲劳试验数据,结合损伤力学与有限元方法,通过MATLAB调用ABAQUS进行损伤演化方程参数的遗传优化反演。将反演得到的损伤演化方程用于飞机结构疲劳寿命预估中,对机翼蒙皮锪窝形式的铆接结构进行了寿命计算和分析,并与试验数据作对比,证明了方法的可行性。     

Modelling of grinding mechanics: A review

Grinding is one of the most widely used material removal methods at the end of many process chains. Grinding force is related to almost all grinding parameters, which has a great influence on material removal rate, dimensional and shape accuracy, surface and subsurface integrity, thermodynamics, dynamics, wheel durability, and machining system deformation. Considering that grinding force is related to almost all grinding parameters, grinding force can be used to detect grinding wheel wear, energy calculation, chatter suppression, force control and grinding process simulation. Accurate prediction of grinding forces is important for optimizing grinding parameters and the structure of grinding machines and fixtures. Although there are substantial research papers on grinding mechanics, a comprehensive review on the modeling of grinding mechanics is still absent from the literature. To fill this gap, this work reviews and introduces theoretical methods and applications of mechanics in grinding from the aspects of modeling principles, limitations and possible future trendencies.     

环型与线型聚能装药射流成型机理对比

环型聚能装药药型罩2侧在挤压汇聚形成射流过程中存在不对称性,不能完全套用线型聚能装药射流成型的现有理论。利用DYNA3D软件对相同剖面结构的环型、线型聚能装药射流成型过程进行数值模拟,通过比较分析得出了环型聚能装药形成杵体及射流参数的分布特性,为进一步理论研究及工程应用提供参考。     

Statistical study of the time delay of ionospheric TEC storms to geomagnetic storms in Taoyuan,Taiwan

We have studied the time delay of ionospheric storms to geomagnetic storms at a low latitude station Taoyuan (25.02°N, 121.21°E), Taiwan using the Dst and TEC data during 126 geomagnetic storms from the year 2002 to 2014. In addition to the known local time dependence of the time delay, the statistics show that the time delay has significant seasonal characteristics, which can be explained within the framework of the seasonal characteristics of the ionospheric TEC. The data also show that there is no correlation between the time delay and the intensity of magnetic storms. As for the solar activity dependence of the time delay, the results show that there is no relationship between the time delay of positive storms and the solar activity, whereas the time delay of negative storms has weakly negative dependence on the solar activity, with correlation coefficient −0.41. Especially, there are two kinds of extreme events: pre-storm response events and long-time delay events. All of the pre-storm response events occurred during 15–20 LT, manifesting the Equator Ionospheric Anomaly (EIA) feature at Taoyuan. Moreover, the common features of the pre-storm response events suggest the storm sudden commencement (SSC) and weak geomagnetic disturbance before the main phase onset (MPO) of magnetic storms are two main possible causes of the pre-storm response events. By analyzing the geomagnetic indices during the events with long-time delay, we infer that this kind of events may not be caused by magnetic storms, and they might belong to ionospheric Q-disturbances.     

Determination of an instantaneous Laplace plane for Mercury’s rotation

Mercury is the target of two space missions: MESSENGER, which carried out its first and second flybys of Mercury on January 14, 2008 and October 6, 2008, and the ESA/JAXA space mission BepiColombo, scheduled to arrive at Mercury in 2020. The preparation of these missions requires a good knowledge of the rotation of Mercury.