考虑剪切变形的矩形截面薄壁杆件畸变分析

在以往不考虑剪切变形的畸变分析理论基础上，假设翘曲位移及切向位移的分布函数，考虑剪切变形的影响，利用最小势能原理建立单位均布畸变荷载作用下的畸变角微分方程。采用一般解法对该畸变角微分方程进行求解，并推导求解的初参数法。随之，通过实例验证了本文理论的正确性，结果表明考虑剪切变形的影响大大提高了考虑畸变效应的计算精度。     

三维含裂纹有限大体剪切型应力强度因子能量释放率方法的封闭解

本文利用能量释放率法,导出三维含裂纹有限大体剪切型应力强度因子的封闭解。这种方法非常节省机时,可获得大量K_Ⅱ和K_Ⅲ的有用结果,所得结果与现有少量结果基本吻合。     

Homoclinic bifurcation at resonant eigenvalues

We consider a bifurcation of homoclinic orbits, which is an analogue of period doubling in the limit of infinite period. This bifurcation can occur in generic two parameter vector fields when a homoclinic orbit is attached to a stationary point with resonant eigenvalues. The resonance condition requires the eigenvalues with positive/negative real part closest to zero to be real, simple, and equidistant to zero. Under an additional global twist condition, an exponentially flat bifurcation of double homoclinic orbits from the primary homoclinic branch is established rigorously. Moreover, associated period doublings of periodic orbits with almost infinite period are detected. If the global twist condition is violated, a resonant side switching occurs. This corresponds to an exponentially flat bifurcation of periodic saddle-node orbits from the homoclinic branch.Partially supported by DARPA and NSF.Partially supported by the Deutsche Forschungsgemeinschaft and by Konrad-Zuse-Zentrum für Informationstechnik Berlin.     

A Trigger of Coupled Singularities

By using example of nonlinear dynamics of a pair of coupled gears, the phenomenon of appearance and disappearance of a trigger of coupled singularities and homoclinic orbits in the form of number eight in the phase portrait in the phase plane is investigated. That phenomenon is an accompanying phenomenon of loss of stability of the local unique equilibrium position. For a generalized case under certain conditions, a theorem of the appearance of a trigger of coupled singularities in a nonlinear dynamical conservative system, the first derivative of the system potential energy which is a product of two periodic functions with different periods, and one bifurcation parameter, which is the cause for the appearance of new roots of these two functions, is defined.     

Assessment of High Speed Imaging Systems for 2D and 3D Deformation Measurements: Methodology Development and Validation

Ultra high-speed and moderate speed image acquisition platforms have been characterized, with special emphasis on the variability and accuracy of the measurements obtained when employed in either 2D or 3D computer vision systems for deformation and shape measurements. Specifically, the type of image distortions present in both single channel cameras (HS-CMOS) and multi-channel image intensified cameras (UHS-ICCD) are quantified as part of the overall study, and their effect on the accuracy of experimental measurements obtained using digital image correlation have been determined. Results indicate that established methods for noise suppression and recently developed models for distortion correction can be used effectively in situations where the primary intensity noise components are characterized by minimal cross-talk and stationary spatial distortions. Baseline uniaxial tension experiments demonstrate that image correlation measurements using high speed imaging systems are unbiased and consistent with independent deformation measurements over the same length scale, with point-to-point strain variations that are similar to results obtained from translation experiments. In this study, the point-to-point variability in strain using the image intensified system is on the order of 0.001, whereas the non-intensified system had variability of 0.0001. Results confirm that high speed imaging systems can be utilized for full field two and three-dimensional measurements using digital image correlation methods.

裂纹转子的振动响应研究

本文研究了裂纹转子的振动响应。文章首先通过应力强度因子积分得到含裂纹轴单元的刚度矩阵；建立了裂纹转子的运动微分方程。进而研究了裂纹转子的振动响应，得出了裂纹转子的振动响应随裂纹位置和深度的变化关系。为工程上早期诊断微小裂纹提供了理论根据。     

移动接触下求解二维闭合裂纹的双重迭代边界元法

使用子域边界元法对受移动接触弹性体作用下的二维闭合裂纹问题进行了数值计算。由于两弹性体的接触界面和裂纹表面的接触范围的大小和接触状态事先是未知的 ,对此 ,在两个接触表面同时采用迭代的方法进行了求解。在裂纹的每个裂尖上都采用了四分之一的奇异单元以保证裂尖位移场和应力场奇异性的满足。用我们编制的二维裂纹问题程序对一些中心裂纹问题进行了计算 ,计算结果与经典断裂力学的理论值比较吻合。在无摩擦的条件下 ,对一些具有不同角度且受移动接触弹性体作用下的闭合裂纹问题进行了数值计算 ,得到了一些耦合作用下的应力强度因子的计算结果     

Semianalytic Finite-Element Method in Problems of Nonlinear Continuum Mechanics

A technique for solving problems of nonlinear continuum mechanics associated with contact interaction, plastic distortion, and continuous and discrete fracture of spatial bodies is developed based on the semianalytic finite-element method generalized to noncanonical bodies. Solutions are obtained to new applied problems in various branches of technology. Compared with the traditional FEM, the technique is highly efficient—the amount of computation needed to solve spatial problems reduces by several orders of magnitude     

Response of flexure–torsion coupled composite thin-walled beams with closed cross-sections to random loads

A study of the flexure–torsion coupled random response of the composite beams with solid or thin-walled closed-sections subjected to various types of concentrated and distributed random excitations is dealt with in this paper. The effects of flexure–torsion coupling, shear deformation and rotary inertia are included in the present formulations. The random excitations are assumed to be stationary, ergodic and Gaussian. Analytical expressions for the displacement response of the composite beams are obtained by using normal mode superposition method combined with frequency response function method. The present method can produce the effective solutions for the composite Timoshenko beams with circumferentially antisymmetric (CAS) configuration and more general beam assemblages of connected beams. The influences of flexure–torsion coupling, shear deformation and rotary inertia on the random response of an appropriately chosen composite beam from the literature are demonstrated and discussed.     

火箭剩余推进剂排放过程的分析与模拟

为了减少空间碎片的产生,星箭分离后,需要在轨排放火箭末级贮箱内的剩余推进剂,分析表明,排放条件下的推进剂射流进入太空后,立即失稳破碎为大量液滴;液滴在高真空环境下扩散,它们的表面不断有气体分子蒸发,逐渐在箭体周围形成了一个由液滴和蒸气分子组成的羽流场.采取Lagrange方法追踪该流场中每个液滴的运动轨迹以及表面蒸发冷凝过程,利用直接模拟Monte Carlo方法计算蒸气分子的运动和碰撞,然后通过微观量的统计平均获得感兴趣的宏观流场、箭体表面的压力和剪应力分布等.为了检验稀薄蒸气算法、模型和程序,模拟了真空水射流周围水蒸气羽流场,获得的径向Pitot压力分布与Fuchs和Legge的实验数据的符合。在此基础上,分别模拟了CZ-4B火箭末级剩余燃料偏二甲肼在不同排放方式下的三维稀薄蒸气与液滴羽流场。计算表明:原排放方式的扰动力矩相当大,超出了火箭姿控范围,新排放方式的扰动力矩很小,处于火箭姿控范围之内。这些预测得到了飞行遥测数据的支持。