功能梯度热释电材料平板柱形弯曲问题的精确解

采用状态空间法，假定材料常数沿厚度方向均按同一指数函数规律变化，获得了功能梯度热释电材料平板柱形弯曲问题的精确解。通过算例，分析了在机械荷载、电荷载和热荷载分别作用下，材料性质的不同梯度变化对平板结构响应的影响。     

壁湍流扩展的自相似标度律的实验研究

对风洞中零压力梯度平板湍流边界层进行了实验研究，用热线风速仪测量了不同法向位置的脉动速度，研究了湍流边界层不同法向位置速度结构函数的扩展的自相似标度律。     

复合材料层压板低速冲击响应尺度效应数值模拟研究

为了研究尺度效应对于复合材料层压板在低速冲击作用下的动态响应和冲击损伤的影响,基于相似理论,建立了三种不同尺寸的层压板受冲击的三维有限元模型。在该模型中,针对层压板的面内损伤,采用改进的Chang-Chang准则进行预测;针对层压板内层间分层损伤,则使用Cohesive界面单元进行模拟。一旦复合材料层压板在低速冲击作用下产生损伤,则对出现损伤的区域进行材料参数退化。采用该模型对三种不同尺寸的层压板的冲击过程进行有限元分析,并将不同冲击速度下的冲击响应进行比较,得出了如下结论：在层压板内未发生冲击损伤时,冲击产生的挠度和冲击力与相似理论解十分吻合,一旦出现冲击损伤,则冲击力的变化与相似理论解有所差别;如果两个缩放模型的冲击速度之比等于缩放比例的平方根,则两个模型中的相对分层尺寸基本是相同的,这个结果与已有的实验结果吻合;而对冲击后面内损伤的分析表明,其损伤尺寸不符合这一相似规律。     

沿垂等温平板的自然对流问题的近似解析解

本文用加权残值得到了沿垂等温平板的自然对流问题的近似解析解。和已有准确解的比较表明，在平板表面附近，近似解有很好的精度，而且速度场的精度比温度场更好一些。文末还对配域法的准收敛问题作了说明。     

运动激波扫过运动平板的非定常传热问题

本文研究运动激波扫过平板边界层后边界层随时间的演化。首先将霍华斯变换推广到非定常情形并引入相似参数将非定常问题化为有两个前缘的边界层问题。这时抛物型方程是奇异的。在激波附近用奇异摄动法求出级数解,然后用逆风格式数值积分将解延拓到平板前缘。     

钻进速度对钻杆扭矩影响的理论分析与试验研究

利用钻杆扭矩法预测冲击地压等煤矿动力灾害时,钻进速度是影响钻杆扭矩的一个重要因素。研究钻进速度对钻杆扭矩的影响可以减少预测指标的误差,提高预测准确性。利用自主研发的钻杆扭矩测试装置,对预制煤体相似材料试件进行了不同钻进速度下的钻孔试验,研究了不同钻进速度对钻杆扭矩变化的影响规律。试验结果表明:钻进速度对钻杆扭矩影响很大。同种煤岩体材料,相同压力条件下,钻进速度越快,钻杆扭矩越大,反之,钻杆扭矩越小。上述研究成果可用于减少预测指标误差。     

平行平板间Couette流起动过程的运算微积解

 求解平行平板间Couette流的起动过程通常使用分离变量法，得到的速度分布在平板间距 趋于无穷时难以逼近Stokes第一问题的解，而两者在物理上却是完全一致的. 本文利用运 算微积法和Heaviside算子进行求解，不但解决了这一问题，而且具有运算简单的 特点.     

楔形体入水时域解的复边界元数值分析

基于速度势理论,利用复数变量边界元法对二维楔形体常速入水冲击的时域解进行了数值研究。 以相似解作为数值计算的初始条件,采用时域解射流线性近似处理方法,利用复数变量边界元法进行求解,以 减少计算量和数值误差。深入讨论了扩展坐标系求时域解、射流处理、网格划分和网格更新等关键技术。最 后数值计算了不同斜升角楔形体入水时的自由液面隆起、射流飞溅和压力分布,经与相似解结果作比较,自由 液面隆起轮廓基本吻合,而压力分布更符合实际情况,从而证明了模型及分析方法的正确性。     

不同厚度及冲击角度对复合材料平板抗冲击能力的影响

为了考核叶片飞脱碎片撞击机匣的抗包容能力,采取钛合金方块作为弹体撞击复合材料平板机匣进行等效模拟。通过获取弹体不同冲击角度撞击不同厚度平板时的抗冲击临界速度,得到复合材料机匣在不同工况下的抗冲击能力极限。基于试验所获得的物理参数,进一步分析了抗冲击临界速度、应变响应、位移响应等关键物理量随平板厚度及撞击角度变化的规律。结果表明,复材平板抗冲击能力对厚度较为敏感,但呈非线性变化趋势;复材表面压应力会抑制表面裂纹的扩展,且厚度越大,这种效应越明显;机织复合材料结构抗冲击能力和裂纹扩展速度与其内部经纬纱编织角度有密切关系,且呈非单调关系。本文提出的等效考核机匣结构抗包容能力的试验方法和获得的试验数据可为真实机匣包容性试验的顺利完成提供支撑,降低适航试验取证的风险。     

含孔平板弹性波散射问题的复变函数方法

本文采用平板弯曲波动理论及复变函数方法，对平板开孔弹性波的散射及动应力集中问题进行了分析研究，得到了传播急剧记波时此种平板弯曲波动问题的分析解。若同时采用保角射技术，就为主解平板任意形状开孔弹性波的散射及动应力集中问题提供了一种统一规范的方法。作为算例，本文给出了平板开圆孔和椭圆孔附近的动应力集中系数的数值结果，并对其进行了讨论。     

强吸气旋转圆筒壁面湍流边界层建模及计算

提出了湍流边界层的一种简单、快速计算方法, 用以求解强吸气作用下旋转圆筒表面边界层流动. 首先, 理论分析了同心圆筒间的旋转流体运动, 外筒静止、内筒旋转且为多孔吸气条件. 强吸气情况下旋转流动主要表现为内筒壁面附近的边界层流动, 基于这一事实得到了周向速度分布的解析表达式. 其次, 通过引入新参数扩展Cebeci-Smith代数湍流模型, 使其能考虑流线曲率、壁面吸气、低Reynolds数效应等因素. 针对这些因素的综合影响, 采用解析修正和经验参数对模型进行调整. 同时, 基于Reynolds应力湍流模型的仿真结果, 校准代数湍流模型中的经验参数. 最后, 给出基于广义Cebeci-Smith湍流模型的旋转壁面边界层流动的迭代算法, 该算法适用于需要特殊迭代过程的轴向及周向流动均匀情况. 计算了不同旋转速度和吸气强度组合工况下的边界层流动, 其周向速度和湍流强度分布与基于Reynolds应力湍流模型的计算结果非常接近. 并且表明, 当Reynolds应力湍流模型数值模拟预测内筒边界层为稳定层流时, 该方法也再现了相同初始条件下的层流边界层.      

MODELLING AND CALCULATION OF THE TURBULENT BOUNDARY LAYER ON A ROTATING CYLINDER SURFACE WITH STRONG SUCTION 1)

提出了湍流边界层的一种简单、快速计算方法, 用以求解强吸气作用下旋转圆筒表面边界层流动. 首先, 理论分析了同心圆筒间的旋转流体运动, 外筒静止、内筒旋转且为多孔吸气条件. 强吸气情况下旋转流动主要表现为内筒壁面附近的边界层流动, 基于这一事实得到了周向速度分布的解析表达式. 其次, 通过引入新参数扩展Cebeci-Smith代数湍流模型, 使其能考虑流线曲率、壁面吸气、低Reynolds数效应等因素. 针对这些因素的综合影响, 采用解析修正和经验参数对模型进行调整. 同时, 基于Reynolds应力湍流模型的仿真结果, 校准代数湍流模型中的经验参数. 最后, 给出基于广义Cebeci-Smith湍流模型的旋转壁面边界层流动的迭代算法, 该算法适用于需要特殊迭代过程的轴向及周向流动均匀情况. 计算了不同旋转速度和吸气强度组合工况下的边界层流动, 其周向速度和湍流强度分布与基于Reynolds应力湍流模型的计算结果非常接近. 并且表明, 当Reynolds应力湍流模型数值模拟预测内筒边界层为稳定层流时, 该方法也再现了相同初始条件下的层流边界层.     

On the impulsive motion of a flat plate with suction

Summary The impulsive motion of a flat plate through a viscous incompressible fluid with time-dependent suction applied normally at the plate is considered. An approximate solution is obtained which describes the motion of the fluid during the initial stage of the motion of the plate, and also one which describes the motion at later stages when the suction velocity is large. The particular case when the suction velocity depends linearly on the time is considered in detail.     

非饱和土吸力的温度性质

根据热力学理论，讨论非饱和土中的土吸力随温度变化的情况，得到在一般情况下非饱和土中的土吸力随着温度增加而线性减小的规律．     

湍流壁函数的一般形式

本文给出了一般形式的湍流壁函数。该壁函数适用于具有壁面引射的湍流计算。广为应用的无引射的湍流壁函数是该壁函数的特例。     

Three-dimensional laminar boundary layer on a permeable surface in the neighborhood of a symmetry plane

Analytical and numerical methods are used to investigate a three-dimensional laminar boundary layer near symmetry planes of blunt bodies in supersonic gas flows. In the first approximation of an integral method of successive approximation an analytic solution to the problem is obtained that is valid for an impermeable surface, for small values of the blowing parameter, and arbitrary values of the suction parameter. An asymptotic solution is obtained for large values of the blowing or suction parameters in the case when the velocity vector of the blown gas makes an acute angle with the velocity vector of the external flow on the surface of the body. Some results are given of the numerical solution of the problem for bodies of different shapes and a wide range of angles of attack and blowing and suction parameters. The analytic and numerical solutions are compared and the region of applicability of the analytic expressions is estimated. On the basis of the solutions obtained in the present work and that of other authors, a formula is proposed for calculating the heat fluxes to a perfectly catalytic surface at a symmetry plane of blunt bodies in a supersonic flow of dissociated and ionized air at different angles of attack. Flow near symmetry planes on an impermeable surface or for weak blowing was considered earlier in the framework of the theory of a laminar boundary layer in [1–4]. An asymptotic solution to the equations of a three-dimensional boundary layer in the case of strong normal blowing or suction is given in [5, 6].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 37–48, September–October, 1980.     

Some Steady MHD Flows of the Second Order Fluid

The exact analytic solutions of two problems of a second order fluid in presence of a uniform transverse magnetic field are investigated. The governing equation is of fourth order ordinary differential equation and is solved using perturbation method. In the first problem we discuss the flow of a second order fluid due to non-coaxial rotations of a porous disk and a fluid at infinity. In second problem the flow of a second order conducting fluid between two infinite plates rotating about the same axis is investigated, with suction or blowing along the axial direction. For second order conducting fluid it is observed that asymptotic solution exists for the velocity both in the case of suction and blowing.     

Minimization of the Wing Airfoil Drag Coefficient Using the Optimal Control Method

The problem of designing a wing airfoil starting from the surface velocity (or pressure) distribution, given in multi-parameter form, is considered. In the diffuser region, the velocity decrease law is determined from the conditions of minimum drag and separationless flow for a given Reynolds number. The case of boundary layer suction for the purpose of improving the aerodynamic characteristics of the airfoil is studied. A solution is obtained using optimal control theory.     

Series solution for steady flow of a third grade fluid through porous space

In this paper steady flow of a third grade fluid through porous space is considered. Modified Darcy’s law for third grade fluid in a porous space has been introduced. The governing non-linear equation is first modelled and then solved using homotopy analysis method (HAM). The convergence of the obtained series solution is discussed. The effects of the emerging parameters on the velocity field are seen. It is noted that meaningful solution exists only in the case of suction.     

An analytical solution for the laminar flow over a flat plate with similarity preserving suction

An exact analytical solution is presented for the laminar boundary-layer flow over a semi-infinite flat plate subjected to a type of similarity preserving suction. The solution is developed for the case of a plate immersed in either a uniform compressible stream with viscosity proportional to temperature or a uniform incompressible stream with constant viscosity. The problem is formulated in Crocco's variables. It is described by a second-order, non-linear, ordinary differential (and singular) boundary-value problem for the shear stress as a function of the velocity in the boundary layer. A unique solution is shown to exist and to possess a power series representation for all magnitudes of suction. The series is constructed explicitly and provides a transcendental equation for the shear stress at the plate (the important skin friction) which can be solved to any desired accuracy. Examples of upper and lower bounds for the wall shear are presented for several magnitudes of suction and confirm the reasonable accuracy of results obtained heretofore only by numerical solutions of the problem. In addition to the intrinsic value of the technique developed, it can be the basis of accurate checks for the numerical solution of more complex problems.