【作者】 赵阳；

【导师】 王博；

【作者基本信息】 大连理工大学 ， 工程力学， 2017， 硕士

【摘要】 半硬壳结构因其具有较高的比强度和比刚度而广泛应用于火箭结构当中,在进行有限元计算时,火箭全箭模型的复杂性往往导致计算工作量异常庞大,因此对其进行模型简化工作具有重要的实际意义。在静力学方面,针对蒙皮桁条结构和网格加筋结构,本文分别提出了基于刚度等效的优化定解法和基于渐进均匀化思想的等效性能法。在大直径蒙皮桁条结构简化为梁-壳模型后,会出现刚度不匹配的情况,采用尺寸优化的方法,可进行模型刚度修正,确定简化模型的几何尺寸;对于周期性网格加筋结构,采用改进的渐进均匀化方法,获取结构单胞的刚度信息,进而可建立与精细模型性能一致的光筒模型。采用两种方法得到的静力学简化模型可在降低计算量的同时具有较高精度的拉压、弯曲和扭转刚度特性。在动力学方面,针对实体建模的细长半硬壳结构,本文对基于梁平截面假设的模型简化方法进行了改进,提出了多点凝聚法。基于梁理论中的平截面假设,将结构每个截面上的有限元节点通过位移转换矩阵凝聚到该截面形心,会导致结构整体刚度过大,通过增加每个截面的凝聚点个数来增加自由度数,进而建立用于模型降阶的减缩基向量,可减小因简化模型结构过刚而导致的计算误差,使得最终得到的简化模型既可提升动力学计算效率,又能保证较高的频率计算精度。此外,该方法还可应用于运载火箭液体推进剂的模拟当中,获取结构的低阶模态信息。经验证,采用本文提出的方法不但可以提升计算效率,而且得到的静力学简化模型与精细模型的位移误差可保证在5%以内,动力学简化模型与精细模型的低阶频率误差可保证在10%以内,方法有效可行。更多还原

【Abstract】 Semirigid shell structures have been widely used in launch vehicles for their high specific strength and specific rigidity.The complexity of the launch vehicle model often leads to excessive calculationtime,therefore,it is of great importance to simplify the model.For static analysis,with regard to skin-stringer structures and grid stiffened structures,an optimization method based on equivalent stiffness and a property equivalent method based on asymptotic homogenization theory are proposed respectively.Stiffness error will appear when large diameter skin-stringer structures are converted into beam-shell mixed structures.Adopting size optimization method,not only can the model be updated,but also geometry sizes of the simplified model will be settled.As for periodic grid stiffened structures,the stiffness matrixes of unit cells can be obtained by using improved asymptotic homogenization method(NIAH),using that a simplified model which has the same mechanical properties as the original model’s can be got.The static simplified models obtained by the two methods can reduce the computation amount,in the meantime,they have high precision tensile,compressive,bending and torsional stiffness properties.Fordynamic analysis,the dynamic model simplification method which is suitable for slender structures has been improved when applied to solid models.Based on the plane section assumption of the beam theory,it will cause stiffness changes when the displacement of FEM nodes in each cross section is approximated by the motion of centroid of the cross section through the displacement transformation matrix.The model’s degrees of freedom will increase by adding the number of cohesion points for each cross section so that the calculation error of the simplified model got by the localized base vectorscan be reduced.Consequently,the simplified model may have high computational efficiency as well as frequency accuracy.In addition,it offers a way to simulate the liquid propellant in a rocket tank’s dynamic model.Results of illustrative examples indicate that,while improving the computational efficiency,the displacement error is within 5% and the maximum frequency error is less than 10% between models.The results verifythe effectiveness of thesemethods.更多还原