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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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正武际可教授的新书《伟大的实验与观察——力学发展的基础》(高等教育出版社2018年10月出版)(图1),讲述了在力学中最基础的、并对力学发展起过重要作用的15个实验故事:阿基米德的杠杆,斯蒂文的尖劈,第谷的观测与开普勒的行星运动定律,伽利略的斜面上下落实验,碰撞问题,玻义耳的抽气筒,惠更斯的摆钟,郑玄的弓和胡克的弹簧,丹尼尔伯努利的流体动力学,焦耳的热动当量实验,卡文迪什的万有引力实验,雷诺的湍流实验,傅科摆,金属疲劳实验,沃尔夫定律。 相似文献
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设定了圆丝辊拔或辊挤球坐标系的连续速度场,以曲线积分方法求得摩擦功率,按上界定理求得辊拔或辊挤力解析解。该解与以弦代弧得到的辊拔或辊挤力解析解进行比较,两者相当吻合。 相似文献
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应用同伦分析法研究了Mathieu-Duffing振子的周期解,展示了Mathieu-Duffing振子的周期1和周期2解的求解过程,通过求解构造的非线性代数方程组而获得周期解,应用Floquet理论判别了周期解的稳定性。比较了同伦分析方法得到的周期解和数值方法得到的周期解,结果表明两者具有一致性。 相似文献
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On the computation of the main eigen-pairs of the continuous-time linear quadratic control problem 总被引:3,自引:0,他引:3
The degeneration of the eigenvalue equation of the discrete-time linear quadraticcontrol problem to the continuous-time one when△t→0?is given first.When thecontinuous-time n-dimensional eigenvalue equation,which has all the eigenvalues located inthe left half plane,has been reduced from the original2n-dimensional one,the present paperproposes that several of the eigenvalues nearest to the imaginary axis be obtained by thematrix transformation A_e=e~A.All the eigenvalues of A_e are in the unit circle,with theeigenvectors unchanged and the original eigenvaiues can be obtained by a logarithmoperation.And several of the eigenvalues of A_e nearest to the unit circle can be calculated bythe dual subspace iteration method. 相似文献
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Alan Jeffrey 《Wave Motion》1982,4(4):381-389
The random choice (RC) method due to Glimm [1], subsequently modified by Chorin [2] and Sod [3], is applied to the shallow water equations of Stoker [4], in order to determine the free-surface profile of water, as a function of position and time, when a dam wall suddenly collapses. The numerical results obtained by this method are compared with the analytical results due to Stoker for this classical problem [5], and with numerical results obtained by a further modification of the Glimm-Chorin scheme involving a smoothing operation. The improvement brought about by the smoothing, and the generally close agreement with the exact result that is then obtained, is a feature of this modified approach. 相似文献
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In this paper, the transient response of an infinite reservoir is analyzed using the dual-reciprocity boundary element method.
A vertical and an inclined-face rigid dam are analyzed under a transient loading. Sharan-type boundary-condition transmission
is implemented in the formulation. The results are compared with the exact solution and those obtained by using the finite
element method. It is seen that the application of the dual-reciprocity boundary element method is simpler and the results
are in very good agreement with the exact solution and those obtained by using the finite element method. 相似文献
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In the case of the slip flow regime expressions both for the mass velocity of a rarefied molecular gas entrained by a rotating
sphere and for the moment of the friction forces exerted on the sphere by the gas are obtained with allowance for the second-order
correction with respect to the Knudsen number. It is demonstrated that these quantities depend on the Prandtl number and the
accommodation coefficients of the tangential impulse of the gas molecules and its flux toward the sphere surface. The results
are compared with analogous results obtained in the case of diffuse reflection of the gas molecules by the sphere surface. 相似文献
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A number of problems for the interaction of laser radiation with a heat-conducting half-space and a layer are considered. The obtained solutions are compared with each other and with the solutions of the classic heat equation and the wave equation. A laser impulse is modelled by defining the heat flux at the boundary for the opaque medium, or by defining the distribution of heat sources in the volume for the semitransparent medium. The power of the laser pulse depends on time as the Dirac delta function or as the Heaviside function do. It allows for the simulation of instant and continuous laser exposure on the medium. Temperature distributions are obtained by using Green’s functions for a half-space and a layer with the Dirichlet and Neumann boundary conditions. 相似文献
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N. I. Shishkin 《Journal of Applied Mechanics and Technical Physics》2011,52(6):849-856
Formulas for the diameter and depth of an explosion crater are obtained which take into account the energy and impulse of
the explosion products, rock strength, burial depth of the explosive charge, and gravity. Using the explosive-shock analogy,
the obtained relations are extended to the case of meteorite (impactor) impact on the planet’s crust (target). It is shown
that in the gravity cratering regime, the influence of the impulse of the impactor is significant and increases with increasing
its size. In the strength cratering regime, the impulse has little effect on crater dimensions. It is established that crater
dimensions are determined mainly by the kinetic energy of the impactor and, to a lesser degree, by its impulse. 相似文献
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应用INSTRON5544对110甲基乙烯基硅橡胶材料进行了单轴大变形压缩的力学特性测试。本文根据已有的Mooney-Rivilin模型和Yeoh模型的本构关系,采用泰勒级数展开的办法获得了基于小变形的本构关系表达式。利用本文所得本构关系,将实验数据进行了非线性拟合处理,得到了相应的Mooney-Rivilin模型和Yeoh模型的材料参数。拟合所得的名义应力-应变曲线与实测的名义应力-应变曲线吻合较好。利用非线性拟合所得的Mooney-Rivilin模型和Yeoh模型的材料参数,应用ABAQUS软件进行有限元分析计算。通过有限元的分析计算,验证了Mooney-Rivilin模型和Yeoh模型材料参数的正确性与可行性。 相似文献