On the determination of optimal transition profile of a stepped bar in tension or in torsion by BEM

The objective is to have uniformly distributed tangential stresses on the transition profile of a stepped bar subjected to tensile and torsional loading using an axisymmetric boundary element formulation. The transition curve is represented by the Langragian interpolation polynomial with progressive degrees to avoid shape distortion during the optimization procedure. The calculated result is compared with that obtained by fluid dynamics given in the literature. It is seen that the transition curve obtained in this paper is reasonable.     

横观各向同性功能梯度圆板弯曲问题的精确解

对周边为弹性支承边界条件下的横观各向同性功能梯度材料圆板轴对称弯曲问题进行了分析.将位移函数写成傅里叶-贝塞尔级数的形式,根据横观各向同性功能梯度材料基本方程,并针对指数函数形式的梯度分布情况,对功能梯度圆板轴对称弯曲问题的位移和应力进行了精确分析.并通过具体算例,分析了在圆板上、下表面荷载作用下,材料性质的不同梯度变化对圆板结构响应的影响.分析结果表明,材料性质的梯度变化对圆板的力学性能有显著影响.     

超高速弹丸膛口流场结构分析

为了计算和分析超高速弹丸膛口流场的分布状况,建立了超高速弹丸从膛底飞离出炮口整个过程的膛口流场二维轴对称数值仿真模型.基于有限体积法,采用分块网格划分的整体运动处理方法,结合结构动网格技术及Realizable k-ε湍流模型,耦合内弹道及后效期过程,利用六自由度运动方程控制弹丸运动,以300 mm平衡炮为例,研究了1 730 m/s发射速度下的超高速膛口流场特性.计算结果表明:超高速运动的弹丸在距膛口3.3 m远处便形成了清晰的初始流场,弹前激波到达炮口处压力达到了3.8 MPa左右.喷射出的火药燃气速度达到2 500 m/s,但火药燃气仍未能追赶并包围弹丸,因此膛口流场对超高速弹丸运动的影响不同于对中低速弹丸运动的影响;膛口形成了由冠状冲击波、弹底激波、反射激波、马赫盘构成的多层次激波、间断面相互叠加的完整波系,该发射条件下的膛口流场异常强烈,波系结构更加明显.     

The inception cavitating flows over an axisymmetric body with a blunt head-form

The inception cavitating flows around a blunt body are studied based on flow visualizations and velocity field measurements. The main purpose of the present work is to study the incipient cavity evolution and the interplay between the inception cavitation and the local turbulent flows. A high-speed video camera is used to visualize the cavitating flow structures, and the particle image velocimetry(PIV) technique is used to measure the velocity field, the vorticity, and the Reynolds stresses under non-cavitating and inception cavitating flow conditions. It is found that the appearance of visible cavities is preceded by the formation of a cluster of micro-bubbles not attached to the body surface and in a hairpin-shaped vortex structure. During its evolution, the cavity moves downstream with a lower speed. The effect of the incipient cavity is significant on the local vortical structures but slight on the timeaveraged velocity distribution. The mean Reynolds stress distributions in the turbulent shear flow can be substantially altered by the incipient cavities. The presence of the incipient cavities can lead to the production of turbulent fluctuations.     

Research in the Development of Finite Element Software for Creep Damage Analysis

This paper reports the development of finite element software for creep damage analysis. Creep damage deformation and failure of high temperature structure is a serious problem for power generation and it is even more technically demanding under the current increasing demand of power and economic and sustainability pressure. This paper primarily consists of three parts： （1） the need and the justification of the development of in-house software; （2） the techniques in developing such software for creep damage analysis; （3） the validation of the finite element software conducted under plane stress, plane strain, axisymmetric, and 3 dimensional cases. This paper contributes to the computational creep damage mechanics in general.     

不确定噪声下基于轴对称盒空间滤波的非线性系统状态估计

针对不确定噪声下的非线性系统状态估计问题, 本文提出了一种基于轴对称盒空间滤波的状态估计方法. 首先, 利用轴对称盒空间包裹线性化过程带来的误差项, 将状态函数线性化误差轴对称盒空间与噪声轴对称盒空间求取闵可夫斯基和, 得到干扰误差轴对称盒空间; 随后, 利用状态量、线性误差和测量噪声的轴对称盒空间的闵可夫斯基和, 得到系统状态预测集; 进而, 利用轴对称盒空间边界正交的性质, 将盒空间拆分为多组超平面, 构造测量更新的约束条件并得到集员包裹. 本文所提方法相比传统的椭球滤波方法而言, 降低了算法的复杂度, 减少了包裹状态可行集和线性化过程带来的余, 获得了更加紧致精确的系统状态集. 最后, 采用非线性弹簧–质量–阻尼器系统验证了本文所提算法的有效性.     

有限大障板上轴对称扬声器声压级的近似计算方法

扬声器声压级测试一般是将扬声器安装在矩形标准障板上进行的,而要通过仿真分析方法准确计算该扬声器在这种声场条件下的声压级,以往只能采用3D模型,其计算量非常大。提出了一种近似计算方法,将有限大障板近似为很多个扇形障板块的组合,再利用2D轴对称模型的仿真分析方法计算每个扇形障板块影响下的声压,进而得到轴对称扬声器安装在该有限大障板上的声压级。这种方法使仿真分析模型与实际测试相符合,同时也避免了规模庞大的3D仿真计算。     

Analysis for twinning and slip in face-centered cubic crystals under axisymmetric co-deformation

The maximum work principle of Bishop-Hill was developed to analyze the axisymmetric co-deformation in face-centered cubic crystals (f.c.c.) for twinning on {111} 112 and slip on {111} 110 systems. The influence of ξ , the ratio of critical re- solved shear stress for twinning to slip, on the yield stress states and corresponding active slip or/and twinning systems for orientations in the standard stereographic triangle of cubic crystal was investigated systematically. The Taylor factors and the anisotropy of yield strength for three important orientations [100], [110] and [111] in orientation space were analyzed. It is found that the yield strength asymmetry for the case of axisymmetric de- formation of tension and compression can be explained based on the microscopic theory of crystal plasticity. The concept of orientation factor for twinning ability was proposed and the deformation mechanism map in the orientation space was established for the case of axisymmetric deformation. The deformation texture formation and development of f.c.c. crystals with low stacking fault energy for axisymmetric tension can be explained qualita- tively on the basis of analyzed results.     

轴对称射流研究进展

综述了轴对称射流的实验测试方法、理论分析和数值模拟。提出应加强对喷嘴前流体湍动程度对射流发展的影响，喷孔形状、喷孔孔长、喷孔孔径以及喷孔分布方式对射流发展的影响；以及固—液、气—液、气—固等混合体系的轴对称射流等问题的研究。     

用边界元法计算轴对称弹性体内部点位移、应力和边界应力

采用边界元法推导出了具有轴对称问题的弹性体内部点位移、应力和边界应力的计算公式，并且给出了算例。