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1.
任意截面的弯曲进气道内流场的近似计算 总被引:1,自引:0,他引:1
本文应用摄动法给出了任意截面的弯曲进气道内流场的近似计算方法.进气道内的气体假设是可压缩的无粘性有势流动.进气道的轴线假设是任意的平面曲线,而且截面的形状也可以是任意的.同时还要求进气道的几何形状是细长的,即横截面方向的尺度要比其轴线的曲率半径小得多,而且截面积的大小及形状沿轴线方向的变化是缓慢的.近似解的结果表明,截面积形心处的轴向速度等于按一元流关系算出的值,而非形心处的轴向速度则和该点至轴线曲率中心处的距离成反比.横截面上的速度分量可分解为代表截面积的大小变化和形状变化的两部分,其中代表面积大小变化部分的速度分量由文中的简单公式给出,求形状变化部分的速度分量相当于求解一个平面调和函数的Neumann边值问题. 相似文献
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本文从四十多年前遇到并解决的三个与固体力学和结构力学相关的机械强度与振动的问题谈起。当时在分析与解决这些问题的方法时,思考并领悟到如何从结构的构形与几何约束、结构承受的外载的性质和结构材料的秉性与行为着眼,实质上就是从以牛顿力学体系的外载(F)、质点质量(m)和物体运动的加速度(a)(即物体的位移、速度、加速度等运动表现的力学运动的几何量)的运动行为作为三个最基本的视点并描述它们之间的联系,在拓广后给出可变形固体力学分析的基本框架。进而刻画出在20世纪70年代、90年代和21世纪初的固体力学的基本框架及其框架内每个不同构元的联系与演进,并以图1,2,3表示。随着现代科技的发展,这一框架下的分析方法近些年已经扩展到更广泛的科技疆域,并在与其他学科的交缘的过程中揭示新的交缘变量的演化方程。人们还期望进入更小和更大尺度时空,研究更广泛的物质包括信息的生成与传递、有生命物质的运动和各种“极端”的力学环境条件下的力学现象,这些新的疆域将是明天的力学工作者耕耘的新天地。 相似文献
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本文从四十多年前遇到并解决的三个与固体力学和结构力学相关的机械强度与振动的问题谈起。当时在分析与解决这些问题的方法时,思考并领悟到如何从结构的构形与几何约束、结构承受的外载的性质和结构材料的秉性与行为着眼,实质上就是从以牛顿力学体系的外载(F)、质点质量(m)和物体运动的加速度(a)(即物体的位移、速度、加速度等运动表现的力学运动的几何量)的运动行为作为三个最基本的视点并描述它们之间的联系,在拓广后给出可变形固体力学分析的基本框架。进而刻画出在20世纪70年代、90年代和21世纪初的固体力学的基本框架及其框架内每个不同构元的联系与演进,并以图1,2,3表示。随着现代科技的发展,这一框架下的分析方法近些年已经扩展到更广泛的科技疆域,并在与其他学科的交缘的过程中揭示新的交缘变量的演化方程。人们还期望进入更小和更大尺度时空,研究更广泛的物质包括信息的生成与传递、有生命物质的运动和各种"极端"的力学环境条件下的力学现象,这些新的疆域将是明天的力学工作者耕耘的新天地。 相似文献
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对摩擦部件材料的要求 现代机器制造业和运输业的发展是与摩擦部件的运转速度和载荷容量的提高联系在一起的。对抗摩材料的要求是由它的工作条件决定的,并在广阔的范围内变化着。但是,存在着一系列对所有抗摩材料都必须共同具备的要求,这些共同的要求就是:尽可能低的摩擦系数和高的耐磨性;最优化的整体和表面强度,这种强度使表面层的高强度与能够有效磨合相结合;足够高的韧性以尽可能排除脆性破坏;高的抗疲劳强度;在材料的工作表面上形成能防止咬粘的二次结构层的能力;相当高的导热性和最佳的热胀系数; 相似文献
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构造了带有补充项的双重正弦傅里叶级数通解来求解各种边界条件的多层正交各向异性矩形薄板的弯曲、振动和稳定问题.将坐标轴取在中性面上,求出用挠度表示的应力表达式,然后由横截面上每单位宽度的应力合成板的内力;再将层合板的内力代入板的平衡方程中得到板的控制方程,将多层板的物理参数折算为等价的单层板物理参数;最后联立控制方程与边界条件,求得未知量的系数并代入本文的通解中.本文的通解不需要叠加即可求解各种边界条件的板的弯曲、振动和稳定问题;现有的对于单层板的研究都可以用本文的方法拓展到多层板领域;对于复杂边界条件的板,也可以使用该通解分析. 相似文献
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本文对于由线性应变硬化刚塑性材料构成的矩形截面简支梁在中央集中载荷作用下的载荷-挠度关系进行了研究.文中不仅考虑了应变硬化效应使梁的极限弯矩增大的作用,而且还考虑了由于应变硬化而引起的塑性区的扩展所致的挠度改变对于梁的承载能力的影响.研究表明:不仅仅材料的应变硬化特性对于梁在屈服后的承载能力有显著的影响,梁的几何特征细长比也对梁在屈服后承载能力有很显著的影响。 相似文献
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P.W. Doyle 《International Journal of Non》1998,33(6):83
Newton equations are dynamical systems on the space of fields. The solutions of a given equation which are curves of characteristic fields for its force are planar and have constant angular momentum. Separable solutions are characteristic with angular momentum equal to zero. A Newton equation is separable if and only if its characteristic equation is homogeneous. Separable equations correspond to invariants of homogeneous ordinary differential equations, and those associated with a given homogenous equation correspond to its generalized dilation symmetries. A Newton equation is compatible with the characteristic condition if and only if its characteristic equation is linear. Such equations correspond to invariants of linear ordinary differential equations. Those associated with a given linear equation correspond to the central force problems on its solution space. Regardless of compatibility, any Newton equation with a plane of characteristic fields has non-separable characteristic solutions. 相似文献
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研究了中心力场中的一类刚-弹耦合系统的平面运动动力学,模型是带有一悬臂
梁的刚体. 综合考虑了系统轨道运动与姿态运动,在Lagrange力学体系下给出了系统的运
动方程,在保守系统和考虑梁的材料黏滞阻尼两种情况下,利用能量-动量方法给出了一类
相对平衡点稳定性的充分条件. 相似文献
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Integrals of motion for the two-body problem with drag are obtained by operating on the second-order vector differential equation describing the motion. The force field consists of an inverse-square gravitational attraction and a drag force proportional to the velocity vector and inversely proportional to the square of the distance to the attracting center. The developed integrals are the analogs of the Keplerian scalar energy, the vector angular momentum, and the Laplace vector. 相似文献
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The motion of a heavy bead on the surface of a parabolic bowl rotating at a constant angular velocity about its axis, which coincides with the vertical, is considered. It is assumed that the dry friction force acts between the bead and the bowl. The sets of nonisolated relative equilibria of the bead on the bowl are determined, and their dependence on the problem parameters is studied. The results are illustrated in the form of bifurcation diagrams. 相似文献
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给出了匀质圆轮受力偶或水平力作用在水平地面上作纯滚动时, 其静摩擦力方向的确定方
法. 只受力偶作用作纯滚动的圆轮, 其摩擦力的方向仅取决于外力偶矩的转向, 判断依据为
摩擦力在该圆轮的平面运动中起阻碍圆轮的转动和为圆轮的平移提供主动力两相对的作用.
当圆轮只受水平力作用作纯滚动时, 用刚体平面运动微分方程和动能定理两种方法对摩擦力
方向进行了推导判定, 摩擦力的方向不仅与水平力的作用位置相关, 还与圆轮的大小和相对
质心的惯性半径等因素相关. 相似文献
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We consider the dynamics of a tower crane: a point mass suspended by a light cable (itself assumed massless) from a horizontally moving support. We derive general equations of motion, and analyse two cases in detail: the linearly accelerating support, and the support describing a circle at constant speed. We show that the former system remains completely integrable, in spite of the fact that energy is no longer conserved. In the second case, while a Hamiltonian is conserved, there is no analogue of angular momentum conservation and the system appears to be non-integrable. We find steadily rotating solutions, discuss their stability and bifurcations, and provide a partial characterisation of global orbit structures. 相似文献
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T.-L. Zhu 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(4):479-494
Free vibration analysis of a rotating double-tapered Timoshenko beam undergoing flapwise transverse vibration is presented.
Using an assumed mode method, the governing equations of motion are derived from the kinetic and potential energy expressions
which are derived from a set of hybrid deformation variables. These equations of motion are then transformed into dimensionless
forms using a set of dimensionless parameters, such as the hub radius ratio, the dimensionless angular speed ratio, the slenderness
ratio, and the height and width taper ratios, etc. The natural frequencies and mode shapes are then determined from these
dimensionless equations of motion. The effects of the dimensionless parameters on the natural frequencies and modal characteristics
of a rotating double-tapered Timoshenko beam are numerically studied through numerical examples. The tuned angular speed of
the rotating double-tapered Timoshenko beam is then investigated. 相似文献
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For strain sufficiently small such that Hooke's Law is valid, it is shown that only a linear model for axial deformation of rotating rods can be derived. As discussed in the literature, this linear model exhibits an instability when the angular speed reaches a certain critical value. However, unless this linear model is valid for large strain, it is impossible to determine whether this instability really exists; because, as the angular speed is increased, the strain becomes large well short of the critical speed. Next, axial deformation of rotating rods is analyzed using two strain energy functions to model non-linear elastic behavior. The first of these functions is the usual quadratic strain energy function augmented with a cubic term. With this model it is shown that no instability exists if the non-linearity is stiffening (i.e. if the coefficient of the cubic term is positive), although the strain can become large. If the non-linearity is of the softening variety, then the critical angular speed drops as the degree of softening increases. Still, the strains are large enough that, except for rubber-like materials, a non-linear elastic model is not likely to be appropriate. The second strain energy function is based on the square of the logarithmic strain and yields a softening model. It quite accurately models the behavior of certain rubber rods which exhibit the instability within the validated range of elongation. 相似文献
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The main features of the unsteady outflow of a fluid from a cylindrical vessel rotating together with it at a constant angular velocity through a central drain hole in the bottom are studied. The software package STAR-CD tested on the results of experiments with water in the absence of rotation is used. Certain important features of the phenomenon under consideration related with the formation of vortex funnels in the fluid are established. The effect of the main control parameters of the problem, namely, angular velocity, viscosity, initial depth, etc., is analyzed. 相似文献