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1.
In an experiment conducted on a space shuttle flight, contact angle hysteresis was observed for the water-glass system. Surface heterogeneities have usually been taken as the cause of the observed hysteresis. In order to examine if other factors such as adsorption could be the cause of the observed hysteresis, contact angles on homogenous, smooth surfaces of glass were examined in ground-based experiments. Ten glass cylinders with different inside diameters were constructed with a capillary tube in the centre of each cylinder. The cylinders were filled with prepared water and the meniscus heights inside the capillary tube and in the glass cylinder were measured. Using the values of these parameters, the pressure in the vapour and the contact angle at the three-phase line of each interface were calculated from the equilibrium conditions. In each of the cylinders, a difference in the contact angle at the three-phase line of the capillary and the three-phase line of the cylinder was observed. This contact angle hysteresis cannot be explained by surface heterogeneity or line tension effect. The observed contact angle hysteresis is predicted to be the result of the pressure profile in the system. This suggests adsorption and its extraordinary sensitivity to vapour-phase pressure as the source of the contact angle hysteresis.  相似文献   

2.
Surface displacements at the end of a semi-infinite, circular cylinder due to an axisymmetric ring of forces on the end are examined. The solution which has been found may then be used to find surface displacements for general axisymmetric loadings by convolution. The solution, in tabular form, is given as corrections to the counter-part half-space solution. The method of solution involves a three step superposition process. First, the displacement due to a ring of forces on a half-space is found by using the Boussinesq solution. Then, the excess tractions on the half-space, over that of the cylinder, are removed. This is done in two parts. The problem of an infinite cylinder with linearly varying pressure and shear over a short length of the lateral surface is solved by using Fourier integrals. This is used for the removal of the pressure and shear on the lateral surface of the cylinder by convolution. Next, the stresses at the mid-section of the infinite cylinder are removed. This is done by finding a set of boundary conditions for the end which yields zero tractions on the lateral surface. Then a series of these boundary conditions is used to approximate the tractions which must be removed. With the solution thus obtained, two sample problems are shown: 1. an elastic cylinder in contact with a half-space; 2. a rigid punch in contact with an elastic cylinder.  相似文献   

3.
地震波、冲击波、环境振动激励会通过地基基础传递到拱上,致使拱发生动力失稳失去承载能力。为深入研究拱在基础竖向激励下的动力稳定性,该文基于能量法,建立了基础竖向激励下圆弧拱平面内动力稳定能量方程,利用哈密顿原理得到了拱面内径向和切向振动的耦合控制方程,求解了圆弧拱平面内失稳前的动轴力与动弯矩解析解。引入拱轴线不可压缩假设,解决了圆弧拱平面内动力控制方程的解耦问题。利用伽辽金法建立了基础竖向多频激励下圆弧拱平面内二阶常微分动力稳定方程,运用多尺度法推导了基础竖向多频激励下圆弧拱平面内动力失稳的临界激励频率解析公式,得到了圆弧拱同时发生一阶反对称参数共振和二阶正对称共振失稳的动力不稳定域,并利用有限元数值分析验证了理论解析解的正确性。进一步分析了拱矢跨比、长细比和圆心角对动力不稳定域的影响。  相似文献   

4.
We consider the torsional deformation of a non-homogeneous infinite elastic cylinder slackened by an external circular cut. The shear modulus of the material of the cylinder is assumed to vary with the radial coordinate by a power law. It is assumed that the lateral surface of the cylinder as well as the surface of the cut are free of stress. The main object of this study is to establish the effect of the non-homogeneity on the stress intensity factor at the tip of the cut. The problem leads to a pair of dual series relations, the solution of which is governed by a Fredholm integral equation of the second kind with a symmetric kernel. This equation is solved numerically by reducing it to an algebraic system. It is concluded that for any degree of non-homogeneity and for D, the relative depth of the cut, greater than 0.6, the cylinder may be replaced by a half-space. However, as the non-homogeneity increases, D decreases.  相似文献   

5.
The frequencies of free oscillation of a fluid in a rectangular tank are reduced by the introduction of a rigid internal structure. This paper gives general, approximate methods for the calculation of the oscillation frequencies when the structure is a cylinder of arbitrary cross section spanning the tank, and with generators normal to one pair of vertical faces. Particular results are given for submerged, circular cylinders and both vertical and horizontal thin baffles.  相似文献   

6.
The exact solution to a screw dislocation oscillating about an arbitrary position in a circular cylinder is obtained. The resonant radiation phenomenon due to asymmetric dislocations is found to be considerably different from the symmetric case previously investigated. Results show that the resonance phenomenon inherent to the system must be taken into account in order to interpret correctly signals produced by acoustic emission.  相似文献   

7.
Stokes波在铅垂圆柱上绕射的二阶分析   总被引:1,自引:0,他引:1  
贺五洲  陈炜 《工程力学》2004,21(6):177-182
在势流假设下,利用摄动原理,求解Stokes波中铅垂圆柱的二阶绕射势,得到完整的二阶波浪压力和波浪力.根据铅垂圆柱的几何特性,采用两种求解方法.一是直接利用外场解析表达式求解;二是设置控制面,外场用解析表达式,内场用简单Green函数方法求解.两种方法得到的结果吻合良好,验证了计算方法的有效性,可为求解任意三维物体的二阶绕射问题提供参考.  相似文献   

8.
This paper presents two applications of the double-shearing theory for flow of granular materials under gravitational forces for axially symmetric flow. In the first the material is contained in a vertical circular cylinder which compresses the material by contracting radially. Exact solutions for the stress and velocity fields are derived, under the boundary conditions that the cylinder wall is either `perfectly rough' or subject to Coulomb friction. In the second problem the material flows under gravity through a tube with circular cross-section of radius that decreases slowly with depth. For this problem an approximate solution is derived that is accurate to first order in the slope of the tube wall relative to the vertical. It is also shown that an alternative theory, in which it is postulated that the principal axes of the stress and rate-of-strain tensors are coincident, leads to the prediction of unacceptable singularities in the flow field in the interior of the material.  相似文献   

9.
Capillary driven surface oscillations of liquid argon (Tsat = 87.3 K at 1,013 hPa) have been investigated in a partly filled right circular cylinder under non-isothermal boundary conditions. The oscillations take place during the reorientation from the normal gravity surface position towards a new position upon step reduction of gravity. The situation is similar to the end of thrust in a rocket tank when the cold propellant moves along the warmer tank wall driven by capillary forces. The aim was to investigate the influence of the temperature difference between the slightly subcooled cryogenic liquid and the superheated cylinder wall on the oscillations and their characteristics in a single-component, two-phase system. Axial wall temperature gradients of averaged 0.15 K/mm ? 1.93 K/mm above the normal gravity surface position were implemented. A general dependence of the reorientation behavior on the gradient value was observed, concerning the apparent contact line behavior, the frequency and damping of the oscillations of the free surface center point, and the apparent contact angle. The behavior of the ullage pressure was found to follow the behavior of the contact line.  相似文献   

10.
In this paper the contact and the crack problems for an elastic wedge of arbitrary angle are considered. The problem is reduced to a singular integral equation which, in the general case, may have a generalized Cauchy kernel. The singularities under the stamp as well as at the wedge apex are studied and the relevant stress intensity factors are defined. The problem is solved for various wedge geometries and loading conditions. The results may be applicable to certain foundation problems and to crack problems in symmetrically loaded wedges in which cracks may initiate from the apex.  相似文献   

11.
The boundary-layer flow induced by a permeable sheet stretching with general polynomial velocity distribution is considered. This generalizes the work of Kumaran and Ramanaiah (Acta Mech. 116: 229–233, 1996) who were the first to observe that a Crane-type solution exists for wall motion composed of arbitrary linear and quadratic stretching terms, as long as an appropriate lateral transpiration is applied. We solve explicitly the problem to an arbitrarily high degree of the polynomial stretching. This motivates the second part of our study which provides explicit boundary-layer solutions for arbitrary wall stretching, with suitable transpiration. These solutions describe generalized Crane flows whose reciprocal (dimensionless) thicknesses always coincide with the negative of their (dimensionless) entrainment velocities. The associated heat transfer problem is solved explicitly for arbitrary stretching when an appropriate surface temperature distribution is prescribed.  相似文献   

12.
The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample.  相似文献   

13.
Mishchenko MI 《Applied optics》2000,39(6):1026-1031
General equations are derived for computing the amplitude matrix for a nonspherical particle in an arbitrary orientation and for arbitrary illumination and scattering directions with respect to the laboratory reference frame, provided that the scattering problem can be solved with respect to the particle reference frame. These equations are used along with the T-matrix method to provide benchmark results for homogeneous, dielectric, rotationally symmetric particles. The computer code is publicly available on the World-Wide Web at http://www.giss.nasa.gov/~crmim.  相似文献   

14.
This paper is concerned with the elastostatic contact problem of a semi-infinite cylinder compressed against a layer lying on a rigid foundation. It is assumed that all the contacting surfaces are frictionless and that only compressive normal tractions can be transmitted through the interfaces. Upon loading the contact along the layer-foundation interface shrinks to a circular area whose radius is unknown. The analysis leads to a system of singular integral equations of the second kind. The integral equations are solved numerically and the contact pressures, extent of the contact area between the layer and the foundation, and the stress intensity factor round the edge of the cylinder are calculated for various material pairs.  相似文献   

15.
We analytically investigate the contribution of arbitrarily varied surface elasticity to the Saint-Venant torsion problem of a circular cylinder containing a radial crack. The varied surface elasticity is incorporated by using a modified version of the continuum-based surface/interface model of Gurtin and Murdoch. In our discussion, the surface shear modulus is assumed to be arbitrarily varied along the crack surfaces. Both internal and edge cracks are studied. By using Green's function method, the boundary value problem is reduced to the Cauchy singular integro-differential equation of first order, which can be numerically solved by using the Gauss–Chebyshev integration formula, the Chebyshev polynomials, and the collocation method. The torsion problem of a cylinder containing two symmetric collinear radial cracks of equal length with symmetrically varied surface elasticity is also solved by using a similar method. Our numerical results indicate that the variation of the surface elasticity exerts a significant influence on the strengths of the logarithmic stress singularity at the crack tips, the torsional rigidity, and the jump in warping function.  相似文献   

16.
The axially symmetric problem of a finite circular plate loaded at its center by a smooth, rigid punch is solved by superposing an infinite layer elasticity solution with a pure bending plate theory solution. The problem is reduced to dual integral equations, which are further reduced to a single Fredholm integral equation of the second kind. The Fredholm equation is numerically solved and the results are used to compute contact stresses under the indenter as well as the overall load-deflection behavior. The problem is formulated to model a partially fixed edge around the plate's perimeter, and calculations are carried out for the limiting cases of simple supports and complete fixity. Various ratios of plate diameter to plate thickness are studied, and the results are compared to both Hertzian contact theory and standard plate theory.  相似文献   

17.
The problem of misfit (interference or clearance) pin in a large orthotropic plate was solved earlier by the authors for biaxial loading in the principal directions of orthotropy. Here, a more general case of arbitrarily oriented loading is considered. The most important aspect of the problem studied is the partial contact at the pin-hole interface. The solution is obtained by extending the use of ‘inverse technique’ which was successfully applied earlier by the authors to problems of pins in isotropic and orthotropic domains. The loss of symmetry because of the arbitrary orientation of loading makes the problem more complex. Additional parameters are then involved in the inversion of the problem for the solution. Numerical results are presented primarily for a smooth interference fit pin in a typical orthotropic plate.  相似文献   

18.
A dynamic problem for an elastic hollow cylinder whose surfaces are subjected to the action of arbitrary forces is solved by a new method based on the use of finite differences only with respect to time [12]. The numerical analyses of the time dependences of stress concentration are carried out for hollow cylinders of different thickness under impact loading. The proposed method is tested by solving a problem of circular hole in an infinite body subjected to the action of impact loads over the entire surface. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 7–13, January–February, 2008.  相似文献   

19.
The InxGa1?xN epitaxial layers, with indium (x) concentration changes between 0.16 and 1.00 (InN), were grown on GaN template/(0001) Al2O3 substrate by metal organic chemical vapour deposition. The indium content (x), lattice parameters and strain values in the InGaN layers were calculated from the reciprocal lattice mapping around symmetric (0002) and asymmetric (10–15) reflection of the GaN and InGaN layers. The characteristics of mosaic structures, such as lateral and vertical coherence lengths, tilt and twist angle and heterogeneous strain and dislocation densities (edge and screw dislocations) of the InGaN epilayers and GaN template layers were investigated by using high-resolution X-ray diffraction (HR-XRD) measurements. With a combination of Williamson–Hall (W-H) measurements and the fitting of twist angles, it was found that the indium content in the InGaN epilayers did not strongly effect the mosaic structures’ parameters, lateral and vertical coherence lengths, tilt and twist angle, or heterogeneous strain of the InGaN epilayers.  相似文献   

20.
Stability of viscous flow past a circular cylinder   总被引:1,自引:0,他引:1  
A spectral method which employs trigonometric functions and Chebyshev polynomials is used to compute the steady, incompressible laminar flow past a circular cylinder. Linear stability methods are used to formulate a pair of decoupled generalized eigenvalue problems for the growth of symmetric and asymmetric (about the dividing streamline) perturbations. We show that, while the symmetric disturbances are stable, the asymmetric perturbations become unstable at a Reynolds number about 40 with a Strouhal number about 0.12. The critical conditions are found to depend on the size of the computational domain in a manner similar to that observed in the laboratory.  相似文献   

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