疲劳开裂结构等效分析谱构造方法

为了解决外场疲劳裂纹排故中结构疲劳载荷谱数据不全或过于复杂的问题,提出了一种适用于飞机外场疲劳开裂结构的等效分析谱构造方法。该方法以细节疲劳额定值(DFR)法和结构细节有限元分析为基础,构建地—空—地最大应力与结构疲劳寿命的变化曲线,进而通过寿命反推,获取适用的地—空—地损伤比,以此构建等效分析谱,谱型为等幅谱。通过应用实例,将该方法构造的载荷谱与实测谱进行了对比,确认了该方法的正确性和有效性。     

运载火箭尾段防热/承载一体化热防护系统设计及性能分析

先进热防护技术是可重复使用运载火箭研制的关键技术之一,具有高结构效率的防热/承载一体化热防护系统是运载火箭极具潜力的备选热防护方案。本文系统地总结了可重复使用运载火箭尾舱段防热和承载两方面的设计要求,设计了一种全复合材料防隔热/承载一体化热防护系统。开展了运载火箭尾段一体化热防护系统设计,进行了代表性单胞结构的高温环境地面试验,揭示了复合材料一体化热防护系统的防隔热机理。同时施加力学和热流载荷,利用有限元方法对运载火箭尾段进行了热力耦合分析,获得了尾段结构的温度场、应变场和应力场。结果表明:在典型载荷工况下一体化热防护系统内壁温度保持在89.2℃以下,内部最大应力不超过9.53 MPa,安全系数达到1.89。     

基于图剖分的多块结构网格负载平衡方法

负载平衡是影响并行计算性能的重要因素。针对多块结构网格,给出了一种改进的多层次图剖分负载平衡方法。该方法设计了新的网格剖分算法,采用改进的子块分裂方法与图剖分算法的循环调用实现结构对接网格剖分,并通过建立不同物体重叠网格间的连接关系,实现了结构重叠网格的负载平衡。采用2个典型算例对方法进行了对比验证,数值结果表明,子块分裂方法对剖分结果具有重要影响,采用循环调用算法及改进的子块分裂方法能有效地实现计算负载均衡及通信量优化,同时显著减少了网格块数及因虚网格导致的内存需求,有利于提高并行效率。该负载平衡方法与网格拓扑无关,适用于多块结构对接网格及重叠网格,且整体型剖分方式对于多块结构重叠网格具有更好的剖分效果。     

萧山国际商务中心风载风洞试验研究

本文介绍了杭州萧山国际商务中心双塔楼的表面风压风洞试验及主要试验结果,分析讨论了该双塔楼沿高度变化的体型系数、对结构的顺风向、横风向风载以及扭矩,为整体结构和表面玻璃幕墙设计提供了合理的风载荷参数.     

Space science education in Egypt and the 2006 solar eclipse

The space science research has been started in Egypt since 1910 by measuring the solar constant as indication of solar radiation at Helwan Observatory. The solar sunspot studies and its influence on the Nile flooding was erected and operated at Helwan as a first solar station in Egypt during 1957. Zeiss-Coude’ refractor was installed in 1964. Astronomy and space science educations started in Egypt at the university level since 1936 at Department of Astronomy and Meteorology of Cairo University. Undergraduate and graduate education in Egypt will be discussed in this work.     

考虑前屈曲几何非线性影响的结构稳定性分析

本文采用有限元法分析考虑前屈曲几何非线性影响的结构稳定性。应用伴有线性搜索和各种牛顿型解法的组合弧长法可以顺利地描述包含有极值点的载荷一位移曲线,与此同时,若在加载点处计算结构刚度矩阵的行列式值、临界载荷因子和特性刚度参数等值,则可根据稳定准则,通过插值确定临界点的位置。从而为研究复杂结构稳定性提供简便而有效的方法。     

舰载机壁板剪切后屈曲承载能力预测与试验验证

舰载机着舰撞击对机翼盒段产生巨大的扭矩，蒙皮以剪切形式承受扭矩，这是机翼壁板的重要设计工况。为准确预测加筋壁板剪切后屈曲承载能力，采用MSC.NASTRAN软件MRIKS弧长法，将线性屈曲分析的一致模态缺陷位移作为扰动引入后屈曲分析。考虑材料和几何双重非线性，对整体加筋壁板剪切试验件的后屈曲破坏过程进行模拟、对承载能力进行预测。根据剪切试验结果，进行对比分析。结果表明：有限元模拟的加筋板初始屈曲发生在蒙皮上，长桁足够大的相对刚度使得长桁与蒙皮连接线上出现屈曲节点，随着载荷增大，加筋壁板整体"坍塌"，与试验现象一致。有限元分析（FEA）得到的初始屈曲载荷与试验结果的误差为1.25%，预测的极限承载载荷与试验破坏载荷的误差为2.4%。表明引入缺陷后的MSC.NASTRAN弧长法非线性后屈曲计算能够准确预测加筋壁板剪切后屈曲承载能力，为加筋壁板剪切试验和强度设计提供了分析方法。     

Using sunshine for elementary space science education: A model for IHY scientist–teacher partnerships

An elementary science education professional development partnership between Culver City Unified School District teachers and UCLA has been formed. The project was designed to assist teachers to comfortably present introductory space science concepts, to support them in their efforts, and to aid them in encouraging their students to develop inquiry skills related to space sciences. The project encourages teacher use of observational science techniques in their classrooms, the use of NASA solar mission images and enhanced use of astronomical observation to facilitate discovery learning. The integrated approach of the project has fostered collegial learning activities among the participating teachers and offered them opportunities for continued renewal and professional development of teacher competencies in astronomy and space science. The activities used in the classroom were developed by others, classroom tested, and specifically address National Science Education and California Science Content Standards. These activities have been sustained through on-going collaboration between the scientist and the teachers, a summer Research Experience for Teachers program, and on-going, grade-specific, district-sponsored workshops. Assessment of the value of the program is done by the school district and is used to continuously improve each workshop and program component. Culver City (California) Unified School District is a small urban school district located on the Westside of Los Angeles. This paper describes the program and the plans for incorporating IHY-themed science into the classroom.     

高速加工HSK工具系统的力学模型

根据HSK工具系统的结构和工作机理建立了HSK工具系统的力学模型,分析了影响工具系统刚度的主要因素和载荷与加工质量之间的关系,揭示出HSK工具系统刚度变化的基本规律,理论分析结果与实验结果吻合.在此基础上,提出评估工具系统的性能不仅要考虑工具系统的静刚度,而且要进一步考虑工具系统的动刚度.最后,给出了HSK工具系统型号的选择原则,并建立了相应的优化操作条件.     

基于概率的航空发动机飞行换算率改进算法

针对斯贝MK202发动机应力标准对零部件工作寿命评定中未包含各种随机因素的影响,考虑零部件疲劳性能参数的分散性和发动机整机载荷谱的随机性,将实测数据统计分析、零部件应力有限元分析以及蒙特卡罗模拟分析有机结合,提出了基于概率的航空发动机飞行换算率改进算法,以解释航空发动机零部件实际工作寿命存在的差异.经范例验证表明:确定性寿命评定方法的飞行换算率计算结果与改进算法下的平均值相当;对于单次飞行换算率,改进算法的单次飞行换算率平均值比确定性方法的计算结果小2%;对于综合飞行换算率,改进算法的综合飞行换算率平均值比确定性方法的结果小1%;且在改进算法下单次飞行换算率和综合飞行换算率服从正态分布.