【作者】 张逸凡；

【导师】 薛明德；

【作者基本信息】 清华大学 ， 力学， 2005， 硕士

【摘要】 热屈曲是航天器设计中经常遇到的问题,对于含开口薄壁杆件的大型空间柔性结构来说,热屈曲问题尤为严重。目前热引起结构弯扭耦合屈曲的机理尚未得到充分的阐明。而本文的工作说明,在研究这个问题时开口薄壁杆件本身的特性是必须加以考虑的因素。本文发展了一种包含翘曲自由度的二节点开口薄壁杆单元。该单元可以综合考虑约束扭转与弯扭耦合的影响,并在大变形分析的几何刚度阵中考虑了热应力的影响。在此基础上,本文将该新型单元与其它传统梁单元相结合,发展了一种计算含开口薄壁杆件的大型空间杆系结构热变形以及热屈曲的有限元方法。对于热变形计算,可以考虑杆件截面内非均匀分布的温度场所产生的热力矩以及热双力矩的作用;对于热屈曲分析,给出了复杂结构在一定温度场下的热屈曲问题提法。上述方法已经被编成了相应的有限元计算程序,并且进行了若干计算。对简单梁模型算例,用本文方法所求得的各阶屈曲特征值和屈曲模态与ANSYS二维薄壳有限元解吻合甚好。这表明该开口薄壁杆单元具有良好的适用性。计算结果同时表明在考虑开口薄壁杆的特性之后,杆件的弯扭耦合热屈曲将先于弯曲型屈曲发生。本文进一步对哈勃太空望远镜太阳帆板的简化模型进行了大变形与屈曲分析。用本文的程序计算所得的变形以及预应力屈曲临界值和前人使用解析方法所得到的近似解基本符合,从而进一步验证了本文计算方案的正确性。最后本文利用相同的方法对哈勃太空望远镜太阳能帆板进行了热屈曲分析,成功地解释了热使该太阳帆板发生扭转屈曲的原因。更多还原

【Abstract】 Thermal buckling is a common problem for space structure design. Thisproblem is especially dominative for large flexible space structures, whichconsist of thin-walled open section beams. However, the mechanism ofthermal buckling with coupled bending-torsional mode has not beencompletely clarified. This paper illustrates that the characteristic of thethin-walled open section beam must be considered to study this problem.A kind of two nodes thin-walled open section beam element with warpingdegree of freedom is developed in this paper. This element is capable ofanalyzing the restricted torsion and the coupled bending-torsional deformation.Moreover, in the large deformation analysis, the thermal stress is consideredin the geometric stiffness matrix.Combining this element and other traditional beam elements, a FiniteElement (FE) scheme is developed to compute the thermal-inducedbending-torsional deformation and the thermal buckling of large space trussstructures. The thermal deformation analysis considers the thermal-inducedmoment and bi-moment, which are caused by the non-uniform temperaturefield on the cross-section of the beam;while the thermal buckling analysis isbased on a given mode of temperature field. The above methods have beencoded into a FE program, and several numerical computations are conducted.Firstly, a simple example with one beam is computed. The resultingcritical temperature and the buckling modes are in good agreement with thesolutions of ANSYS. This illustrates that this element is suitable and reliablefor this kind of applications. This example also reveals that the thermalbending-torsional mode will occur earlier than the bending mode. This is dueto the characteristic of thin-walled open section beam.Further more, the large deformation and buckling analysis are conductedfor a simplified model of the solar array on the Hubble Space Telescope(HST). The displacement and the critical prestress obtained by the presentnumerical method are approximately coincident with the ones from thetheoretical method mentioned in the references. This further illustrates thevalidity of the present FE scheme. Finally, the cause of the torsional bucklingobserved on the HST solar arrays is explained based on the thermal bucklinganalysis using the same process.更多还原