Derivation of conditions of complete contact for a beam on a tensionless Winkler elastic foundation with Mathematica

The classical problem of a beam on a tensionless Winkler elastic foundation is reconsidered for the derivation of the conditions of complete contact between the beam and the foundation. This is achieved through the application of modern quantifier elimination software included in the computer algebra system Mathematica together with Taylor–Maclaurin series approximations to the deflection of the beam. Four particular beam problems have been considered in detail and the related QFFs (quantifier-free formulae) have been obtained for several values of the order in the series approximations. Additional approximation possibilities have also been investigated with an emphasis put on the use of the Galerkin method based on weighted residuals. The present results seem to constitute one more interesting application of modern quantifier elimination algorithms and the related software (here in Mathematica) to applied and engineering mechanics.     

Winkler地基上薄板问题的准格林函数方法

将准格林函数方法应用到Ｗｉｎｋｌｅｒ地基上的薄板理论中,得到了一个第二类Ｆｒｅｄｈｏｌｍ积分方程。通过边界方程的适当选择,积分方程 奇异性被克服了。算例表明,本文采用的方法具有较高的精度。     

Stability and optimization of a clamped beam elastically restrained against translation on one end resting on Winkler foundation

In this study, stability and bimodal optimization of clamped beam elastically restrained against translation on one end subjected to a constant axially load are analyzed. The beam is positioned on elastic Winkler type foundation. The Euler method of adjacent equilibrium configuration is used in deriving the nonlinear governing equations. The critical load parameters, axial force and stiffness of foundation, are obtained for beam with the unit cross-sectional area.The shape of the beam stable against buckling that has minimal volume is determined by using Pontryagin’s maximum principle. The optimality conditions for the case of bimodal optimization are derived. The cross-sectional area for optimally designed beam is found from the solution of a nonlinear boundary value problem. New numerical results are obtained. A first integral (Hamiltonian) is used to monitor accuracy of integration. It is shown that there is the saving in material for the same buckling force.     

Nonlinear free vibration of a beam on Winkler foundation with consideration of soil mass motion of finite depth

Nonlinear Dynamics - Nonlinear free vibration characteristics of a beam on elastic foundation are investigated. Considering the effect of soil–structure interaction on the nonlinear dynamic...     

非均匀Winkler弹性地基上变厚度矩形板自由振动的DTM求解

针对非均匀Winkler弹性地基上变厚度矩形板的自由振动问题,通过一种有效的数值求解方法——微分变换法（DTM）,研究其无量纲固有频率特性。已知变厚度矩形板对边为简支边界条件,其他两边的边界条件为简支、固定或自由任意组合。采用DTM将非均匀Winkler弹性地基上变厚度矩形板无量纲化的自由振动控制微分方程及其边界条件变换为等价的代数方程,得到含有无量纲固有频率的特征方程。数值结果退化为均匀Winker弹性地基上矩形板以及变厚度矩形板的情形,并与已有文献采用的不同求解方法进行比较,结果表明,DTM具有非常高的精度和很强的适用性。最后,在不同边界条件下分析地基变化参数、厚度变化参数和长宽比对矩形板无量纲固有频率的影响,并给出了非均匀Winkler弹性地基上对边简支对边固定变厚度矩形板的前六阶振型。     

基于敏度分析的拉压不同模量桁架问题的数值分析

利用光滑函数技术,提出光滑化的拉压不同弹性模量问题的应力应变关系,与有限元方法相结合,建立了拉压不同模量一维连续体与桁架结构的数值求解模型,推导了敏度计算公式,采用Newton-Raphson算法进行求解.数值结果表明,本文算法具有较高的计算精度和收敛速度.     

Symplectic system based analytical solution for bending of rectangular orthotropic plates on Winkler elastic foundation

This paper analyses the bending of rectangular orthotropic plates on a Winkler elastic foundation.Appropriate definition of symplectic inner product and symplectic space formed by generalized displacements establish dual variables and dual equations in the symplectic space.The operator matrix of the equation set is proven to be a Hamilton operator matrix.Separation of variables and eigenfunction expansion creates a basis for analyzing the bending of rectangular orthotropic plates on Winkler elastic foundation and obtaining solutions for plates having any boundary condition.There is discussion of symplectic eigenvalue problems of orthotropic plates under two typical boundary conditions,with opposite sides simply supported and opposite sides clamped.Transcendental equations of eigenvalues and symplectic eigenvectors in analytical form given.Analytical solutions using two examples are presented to show the use of the new methods described in this paper.To verify the accuracy and convergence,a fully simply supported plate that is fully and simply supported under uniformly distributed load is used to compare the classical Navier method,the Levy method and the new method.Results show that the new technique has good accuracy and better convergence speed than other methods,especially in relation to internal forces.A fully clamped rectangular plate on Winkler foundation is solved to validate application of the new methods,with solutions compared to those produced by the Galerkin method.     

Dynamics of thin periodic plates resting on a periodically inhomogeneous Winkler foundation

Summary The aim of the paper is to investigate the dynamic response of thin elastic plates having periodic substructure in planes parallel to the plates midplane and interacting with a Winkler foundation. The main goal of the analysis is to describe the effect of substructure size on the plates dynamics. For this purpose, the method proposed in [4, 5] is used. Two special cases are analysed: a plate band with a constant thickness interacting with a periodically inhomogeneous Winkler foundation, and a plate band with a periodically variable thickness interacting with a homogeneous Winkler foundation. The physical correctness conditions of the model are also discussed. Received 14 July 1998; accepted for publication 7 January 1999     

Beam on viscoelastic foundation: an extension of Winkler’s model

Models in the field of Applied Mechanics originate less from thought experiments but rather from technical problems. So does the so-called Winkler model: elastic beam on deformable foundation. It stems from the then (1870) High Technology the railway system. The question was: What is the stress state in a continuously bedded beam, the sleeper, loaded by singular rail loads? Winkler came up with a convincing closed form solution by linearising the behaviour of the subgrade which consists of a compressed layer of stones. The Winkler model is time-independent. The extension is to make the subgrade time dependent, in the simplest case to make it viscous. This also applies to the problem of a wheel set consisting of a beam ring, a rigid disc, and in between a pre-stressed rubber sheet. Such wheel sets are or have been in use in nowadays tram and railway systems. In this paper an analysis of such a rotating wheel set under a singular load is given. It is shown that the stress state in the ring beam depending on rotational speed decreases linearly with increasing rotational speed.     

Static analysis of an infinite beam resting on a tensionless Pasternak foundation

This paper addresses the static response of an infinite beam supported on a unilateral (tensionless) two-parameter Pasternak foundation and subjected to complex transverse loads, including self weight. The transfer displacement function method (TDFM) is employed to determine the initially unknown lengths that remain in contact. In contrast to a Winkler Foundation System (WFS), the lift-off points in a PFS (Pasternak Foundation System) are not necessarily at zero displacement but may be determined sequentially through considering the compatibility conditions at the junctions of contact and non-contact segments. After the response of the whole system including the beam and foundation is expressed through the displacement constants of the initial segment, the contact problem is reduced to two nonlinear algebraic equations with two unknowns. The foundation reactions and the internal actions of the beam may also be determined from the displacement response of the system. Two simple cases are solved to illustrate the influence of the foundation stiffness factors and finally, a third example of a beam with several contact segments is presented to demonstrate the application of the TDFM.     

Bending of rectangular thin plates with free edges laid on tensionless Winkler foundation

In this paper, the bending problem of rectangular thin plates with free edges laid on tensionless Winkler foundation has been solved by employing Fourier series with supplementary terms. By assuming proper form of series for deflection, the basic differential equation with given boundary conditions can be transformed into a set of infinite algebraic equations. Because the boundary of contact region cannot be determined in advance, these equations are weak nonlinear ones. They can be solved by using iterative procedures.Doctor candidate in Civil Engineering Department of Qinghua University at present.     

Dual reciprocity hybrid radial boundary node method for Winkler and Pasternak foundation thin plate

An efficient dual reciprocity hybrid radial boundary node method is developed for the analysis of Winkler and Pasternak foundation thin plate, in which a hybrid displacement variational principle, radial point interpolation method (RPIM) and dual reciprocity method (DRM) are combined. Firstly, the hybrid displacement variational principle is developed, in which the domain variables are interpolated by two groups of symmetric fundamental solutions, while the boundary variables are interpolated by RPIM instead of the traditional moving least square, and the shape function obtained by RPIM satisfies the delta function property, so boundary conditions can be applied directly. Besides, DRM is exploited to evaluate the particular solutions of inhomogeneous terms, which can be used to transform the domain integrals arising from the inhomogeneous term into equivalent boundary integrals. Finally, some additional equations based on the DRM theory are proposed to overcome the problem that the boundary integral equations are not enough to solve all variables. This method has the advantages of both no element mesh of meshless method and dimensionality reduction of boundary element method. Numerical examples of Winkler and Pasternak foundation plates are given to illustrate that the present method is effective, accurate and it can be further expanded into practical engineering.     

Vibrations of nonhomogeneous orthotropic rectangular plates with bilinear thickness variation resting on Winkler foundation

Free transverse vibrations of nonhomogeneous orthotropic rectangular plates with bilinear thickness variation resting on Winkler foundation are presented here using two dimensional boundary characteristic orthogonal polynomials in the Rayleigh-Ritz method on the basis of classical plate theory. Gram-Schmidt process has been used to generate orthogonal polynomials. The nonhomogeneity of the plate is assumed to arise due to linear variations in elastic properties and density of the plate material with the in-plane coordinates. The two dimensional thickness variation is taken as the Cartesian product of linear variations along the two concurrent edges of the plate. Effect of nonhomogeneity parameters, aspect ratio and thickness variation together with foundation parameter on the natural frequencies has been illustrated for the first three modes of vibration for four different combinations of clamped, simply supported and free edges correct to four decimal places. Three dimensional mode shapes for specified plate for all the four boundary conditions have been plotted. A comparison of results in special cases with published one has been presented.     

Winkler地基模型上功能梯度材料涂层的摩擦接触问题

研究Winker地基模型上功能梯度材料涂层在一刚性圆柱形冲头作用下的摩擦接触问题。功能梯度材料涂层表面作用有法线向和切线向集中作用力。假设材料非均匀参数呈指数形式变化,泊松比为常量,利用Fourier积分变换技术将求解模型的接触问题转化为奇异积分方程组,再利用切比雪夫多项式对所得奇异积分方程组进行数值求解。最后,给出了功能梯度材料非均匀参数、摩擦系数、Winker地基模型刚度系数及冲头曲率半径对接触应力分布和接触区宽度的影响情况。     

考虑接缝传荷的文克勒地基上矩形薄板的级数解

应用双重正弦级数展开的方法,推演得到了文克勒地基上计入两块矩形板间接缝传荷效应的级数解。假设接缝传递剪力与板间挠度差成正比、传递弯矩与板间转角差成正比,进而分析了单轮和单轴荷载作用在纵缝边缘中部时,接缝传荷效应对板边最大挠度和最大应力的影响规律;通过引入接缝传荷效应系数和接缝极限传荷的两个挠度比及两个应力比,建立了计入接缝传荷效应的板边最大挠度和最大应力的一般式,总结了不同板尺寸、荷载面积尺寸和类型及板材料泊松比对四个接缝影响系数和四个接缝极限传荷的挠度比及应力比的影响规律。结果表明:不同荷载面积下,受荷板接缝边缘最大挠度、最大应力均随弯矩或剪力传荷刚度系数的增大而减小,且应力的变化幅度相较挠度要小。影响系数fV^w(ξV)、fM^w(ξM)、fM^σ(ξM)与荷载圆相对半径(a/l)、相对板长(L/l)和相对板宽(B/l)无关,且单轮荷载与双轮荷载规律相同;而影响系数fV^σ(ξV)与荷载圆相对半径(a/l)有关,与相对板长(L/l)和相对板宽(B/l)无关;挠度比λV^w与荷载圆相对半径、板尺寸(L/l,B/l)及泊松比v无关,恒等于0.5,而λM^w、λV^σ、λM^σ均与荷载相对半径(a/l)、板尺寸(L/l,B/l)及泊松比v有关,且影响因素中荷载面积尺寸的影响最为显著。     

Large amplitude free vibrations of irregular plates placed on an elastic foundation

A unified method for determining the lowest natural frequency of large amplitude free vibrations of thin elastic plates of any shape and placed on elastic foundation is given. The conformal mapping technique is introduced and Galerkin's method is used to calculate approximate values of the lowest natural frequency. Time periods for circular, square and cornered plates placed on elastic foundation have been determined for simply supported and clamped edge boundary conditions. Practical values have also been determined experimentally. The results are presented in the form of graphs and they are compared with other known results.     

Free vibration analysis of general stepped circular plates with internal elastic ring support resting on Winkler foundation by green function method

Natural frequencies are important dynamic characteristics of a structure. Therefore, the exact solution pertaining to free vibration of stepped circular plate elastically restrained against rotation, translation, and internal elastic ring support resting on an arbitrary variable elastic foundation using Green Function is presented in this paper. Thus, an accurate and direct modeling technique is introduced for modeling stepped circular plate on an arbitrary variable elastic foundation with arbitrary boundary conditions and internal elastic ring support. The effect of the translational along with rotational support flexibilities, as well as, the elastic coefficient of Winkler foundation and other parameters are assessed. Finally, some numerical examples are shown in order to present the efficiency and simplicity of the Green Function in the new formulation.     

A new method for the non-linear deflection analysis of an infinite beam resting on a non-linear elastic foundation

The aim of this paper is to develop a new method of analyzing the non-linear deflection behavior of an infinite beam on a non-linear elastic foundation. Non-linear beam problems have traditionally been dealt with by semi-analytical approaches that involve small perturbations or by numerical methods, such as the non-linear finite element method. In this paper, in contrast, a transformed non-linear integral equation that governs non-linear beam deflection behavior is formulated to develop a new method for non-linear solutions. The proposed method requires an iteration to solve non-linear problems, but is fairly simple and straightforward to apply. It also converges quickly, whereas traditional non-linear solution procedures are generally quite complex in application. Mathematical analysis of the proposed method is performed. In addition, illustrative examples are presented to demonstrate the validity of the method developed in the present study.     

自然单元法在Winkler地基薄板计算中的应用

自然单元法是一种基于Voronoi图及Delaunay三角形剖分图,以自然邻接点插值为试函数的一种无网格数值方法.本文以目前该方法中自然邻接点的Laplace插值形函数为基础,求出了其一阶及二阶导函数,建立了Winkler地基上薄板弯曲挠度的自然单元法求解控制方程,并编制了相应的计算程序,通过算例分析表明了本文方法的可行性和有效性.