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基于离散Fourier模态有限和生成的随机大气湍流场,采用修正波形参数方法,开展了均匀各向同性大气湍流对典型超声速客机声爆传播特性的影响分析。计算采用的超声速客机模型为自行生成的简化超声速公务机模型。首先,应用航空工业空气动力研究院自主研制的CFD软件ARI_Overset在三维空间求解Navier-Stokes方程,得到作为声爆远场传播初始值的近场空间压力分布;其次,基于Von Karman能量谱,采用离散Fourier模态有限和形式生成随机均匀各向同性大气湍流场;最后,采用修正波形参数方法模拟了声爆信号在随机速度湍流场中的传播过程。数值结果表明:各向同性大气湍流对于地面声爆特征有重要影响。与无湍流状态相比,均匀各向同性大气湍流使得地面声爆特征增强的概率约为55%,使得地面声爆特征减弱的概率约为45%,故总体而言大气湍流效应更倾向于增强地面声爆特征;均匀各向同性大气湍流对于声爆传播路径影响相对较小,但是这一变化仍会导致地面信号接收点的不确定性。 相似文献
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将等参梯度有限元法应用于非线性功能梯度材料,推导了2种受力情况下指数体积分数变化的功能梯度材料的应力分布解析解。通过不同的单元划分形式,对等参梯度元数值解、均匀单元数值解及解析解三者进行比较分析,得出等参梯度有限元方法对非线性梯度材料同样适用,为等参梯度有限元的推广应用提供了证据。 相似文献
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In the present work, the coefficients of thermal expansion(CTEs) of unidirectional(UD)fiber-reinforced composites are studied. First, an attempt is made to propose a model to predict both longitudinal and transverse CTEs of UD composites by means of thermo-elastic mechanics analysis. The proposed model is supposed to be a concentric cylinder with a transversely isotropic fiber embedded in an isotropic matrix, and it is subjected to a uniform temperature change. Then a concise and explicit formula is offered for each CTE. Finally, some finite element(FE) models are created by a finite element program MSC. Patran according to different material systems and fiber volume fractions. In addition, the available experimental data and results of other analytical solutions of CTEs are presented. Comparisons are made among the results of the cylinder model,the finite element method(FEM), experiments, and other solutions, which show that the predicted CTEs by the new model are in good agreement with the experimental data. In particular, transverse CTEs generally offer better agreements than those predicted by most of other solutions. 相似文献
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LI Tong-qi HU Zi-jun WANG Jun-shan GUO Yu-ming WANG Cheng-yang 《中国航空学报》2006,19(B12):187-191
Mesocarbon microbeads (MCMB) and super fine mesophase powder (SFMP) were prepared firstly from a coal tar pitch and then hot-condensed into high-density isotropic carbon (HDIC) bulks under 160 MPa and finally sintered at 1 000 ℃. By analyzing the thermogravimetric behavior of the MCMB and SFMP powders, their volume shrinkage and weight loss during sintering and the bulk density and flexural strengths of their sintered bulks, it was found that the smaller sizes and the richer β-resin contents of SFMP ha)re facilitated formation of sintered bulks with more compact isotropic structure and higher flexural strengths than MCMB. Because of the filling and bonding effects of SFMP on MCMB bulks, addition of SFMP, albeit a little, can greatly increase the flexural strengths of sintered bulks of MCMB. However, adding MCMB, even a slight amount, into SFMP can severely impair the flexural strength of sintered bulks. This might be attributed to both the crack initiation along the boundaries between MCMB and SFMP and the formation of layered texture of MCMB sphere. 相似文献
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利用直接积分方法,求解了横观各向同性热弹材料在力-热载荷作用下的三维半平面问题.其中,材料的各向同性对称面与半无限平面平行.本文将原始热弹方程简化为仅含应力张量的控制方程,且考虑了远端应力有限性等条件已确保控制方程的正确性.计算结果显式地呈现了机械和热学载荷对热弹体的影响并满足固体连续性条件.本文给出的求解方法适用于各... 相似文献
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板和加筋板结构的稳定性特性,是设计人员十分关注的一个问题。本文首次采用新近提出的微分求积单元法分析了各向同性加筋板的稳定性问题,建立了微分求积梁单元和板单元,并给出了详细的分析过程。通过与现有结果的对比验证了所建立的分析过程和程序的正确性。计算结果表明:微分求积单元法具有简单、收敛速度快、计算量少和精度高等优点。 相似文献
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平方主剪应力屈服准则 总被引:3,自引:0,他引:3
石寒 《南京航空航天大学学报》1994,26(5):589-593
对各向同性材料在复杂应力状态下的屈服现象提出一新的物理解释。以菱形十二面体力滑移模型,即三组主剪应力的十二个作用面构成的应力单力体,并考虑到它的两个较小的主剪应力以反静力应力对材料屈服的影响,这一解释可称为平方主剪应力屈服准则。该准则认为当两个较小的主剪应力之平方和达到材料的某一极限值时,材料将开始屈服,而此极限值一般与静水应力成非线性关系。在三维主应力空间中,该准则在π-平面上的极限迹线满足Drucker公设关于屈服面的外凸性条件,而极限速线的面积比Tresca屈服准则,Mises屈服准则和双剪应力屈服准则要大。 相似文献