彩色PDP运动图像动态假轮廓的评测方法--动态积分法

采用ADS方法来实现灰度显示的等离子体显示器 (PDP) ,在显示运动图像时会出现动态假轮廓现象 ;定量评测动态假轮廓的方法很少 ,而且现有的方法还存在着缺陷。本文根据动态假轮廓的产生原因以及人眼的积分特性提出动态积分评测方法 ;对图像子场进行积分 ,计算出反应到人眼中的灰度 ,并与实际显示的灰度进行比较 ,得到一个量化的动态假轮廓     

A SIMPLE PATH-INDEPENDENT INTEGRAL FOR CALCULATING MIXED-MODE STRESS INTENSITY FACTORS

A path-independent integral is introduced for calculating stress intensity factors. The derivation of the integral is based on the application of the known Bueckner's fundamental field solution for a crack in an infinite body and on the reciprocal theorem. The method was applied to two-dimensional linear elastic mixed-mode crack problems. The key advantage of the present path-independent integral is that the stress intensity factor components for any irregular cracked geometry under any kind of loading can be easily obtained by a contour integral around the crack tip. The method is simple to implement and only the far field displacements and tractions along the contour must be known. The required stress analysis can be made by using any analytical or numerical method, e.g. the finite element method, without special consideration of the modelling of crack tip singularity. The application of this integral is also independent of the crack type, that is, there is no difference between an edge crack and an embedded crack, provided that the crack tip asymptotic behaviour exists.     

Evaluation of fracture parameters in continuously nonhomogeneous piezoelectric solids

A contour integral method is developed for computation of stress intensity and electric intensity factors for cracks in continuously nonhomogeneous piezoelectric body under a transient dynamic load. It is shown that the asymptotic fields in the crack-tip vicinity in a continuously nonhomogeneos medium is the same as in a homogeneous one. A meshless method based on the local Petrov-Galerkin approach is applied for computation of physical fields occurring in the contour integral expressions of intensity factors. A unit step function is used as the test functions in the local weak-form. This leads to local integral equations (LBIEs) involving only contour-integrals on the surfaces of subdomains. The moving least-squares (MLS) method is adopted for approximating the physical quantities in the LBIEs. The accuracy of the present method for computing the stress intensity factors (SIF) and electrical displacement intensity factors (EDIF) are discussed by comparison with available analytical or numerical solutions.     

Null-field approach for the antiplane problem with elliptical holes and/or inclusions

In this paper, we extend the successful experience of solving an infinite medium containing circular holes and/or inclusions subject to remote shears to deal with the problem containing elliptical holes and/or inclusions. Arbitrary location, different orientation, various size and any number of elliptical holes and/or inclusions can be considered. By fully employing the elliptical geometry, fundamental solutions were expanded into the degenerate kernel by using an addition theorem in terms of the elliptic coordinates and boundary densities are described by using the eigenfunction expansion. The difference between the proposed method and the conventional boundary integral equation method is that the location point can be exactly distributed on the real boundary without facing the singular integral and calculating principal value. Besides, the boundary stress can be easily calculated free of the Hadamard principal values. It is worthy of noting that the Jacobian terms exist in the degenerate kernel, boundary density and contour integral; however, these Jacobian terms would cancel each other out and the orthogonal property is preserved in the process of contour integral. This method belongs to one kind of meshless methods since only collocation points on the real boundary are required. In addition, the solution is regarded as semi-analytical form because error purely attributes to the number of truncation term of eigenfunction. An exact solution for a single elliptical inclusion is also derived by using the proposed approach and the results agree well with Smith’s solutions by using the method of complex variables. Several examples are revisited to demonstrate the validity of our method.     

A boundary diffraction wave in the Fresnel-Kirchhoff theory

A method for transformation of the Fresnel-Kirchhoff diffraction surface integral into an integral over the contour bounding this surface is proposed for an observation point in the Fresnel zone. An expression for the boundary wave field is obtained for a parametric representation of the contour. Examples of application of the obtained relations are given. Calculated dependences are compared to the experimental results.     

Computational simulation of crack problems by means of the contour element method

The article discusses a contour element method applied to numerical simulations of crack problems in elastic structures. Because the boundary integral equation degenerates for a body with two crack-surfaces occupying the same location, one of the forms of the displacement discontinuity method is implemented. According to the implemented method, resultant forces and dislocation densities, which are placed at mid-nodes of contour segments on one of the crack surfaces, are characterized by the indirect boundary integral equation. Contrarily to internal crack problems, for edge crack problems an edge-discontinuous element is used at the intersection between a crack and an edge to avoid a common node at the intersection. New numerical formulations that are built up on analytical integration are implemented. Therefore, all regular and singular integrals are evaluated only analytically. Tractions and resultant forces at a mid-node of any contour segment are regularized by a nonlocal characterization function. Hence, values of their components are obtained from the modified form of Somigliana’s identity that embraces nonlocal elements and standard elements of kernel matrices used in the boundary element analysis.     

The traction boundary contour method for linear elasticity

This paper presents a further development of the boundary contour method. The boundary contour method is extended to cover the traction boundary integral equation. A traction boundary contour method is proposed for linear elastostatics. The formulation of traction boundary contour method is regular for points except the ends of the boundary element and corners. The present approach only requires line integrals for three‐dimensional problems and function evaluations at the ends of boundary elements for two‐dimensional cases. The implementation of the traction boundary contour method with quadratic boundary elements is presented for two‐dimensional problems. Numerical results are given for some two‐dimensional examples, and these are compared with analytical solutions. This method is shown to give excellent results for illustrative examples. Copyright © 1999 John Wiley & Sons, Ltd.     

Extraction of stress intensity factors from generalized finite element solutions

The performance of several superconvergent techniques to extract stress intensity factors (SIFs) from numerical solutions computed with the generalized finite element method is investigated. The contour integral, the cutoff function and the J-integral methods are considered. An implementation of the extraction techniques based on a sequence of mappings that are independent of the underlying solution method or discretization is proposed. It is shown that this approach is suitable for virtually any mesh-free or mesh-based solution method. Several numerical examples demonstrating the convergence of the computed SIF and the flexibility of the proposed implementation are presented. The path independence of the extraction methods is also investigated. Numerical experiments demonstrate that the contour integral and the cutoff function methods are more robust than the J–integral method with the CFM being the most accurate.     

Modified diffraction theory of Kirchhoff

The diffraction theory of Kirchhoff is reinterpreted and a new form of a surface diffraction integral is developed by using the axioms of the modified theory of physical optics, which leads to the exact scattered fields by conducting bodies. The new integral is arranged according to the interpretation of Young, and the diffracted waves are expressed in terms of a line integral. The method is applied to the diffraction problem by a semi-infinite edge contour.     

Coupled FE–BE method for eigenvalue analysis of elastic structures submerged in an infinite fluid domain

For thin elastic structures submerged in heavy fluid, e.g., water, a strong interaction between the structural domain and the fluid domain occurs and significantly alters the eigenfrequencies. Therefore, the eigenanalysis of the fluid–structure interaction system is necessary. In this paper, a coupled finite element and boundary element (FE–BE) method is developed for the numerical eigenanalysis of the fluid–structure interaction problems. The structure is modeled by the finite element method. The compressibility of the fluid is taken into consideration, and hence the Helmholtz equation is employed as the governing equation and solved by the boundary element method (BEM). The resulting nonlinear eigenvalue problem is converted into a small linear one by applying a contour integral method. Adequate modifications are suggested to improve the efficiency of the contour integral method and avoid missing the eigenvalues of interest. The Burton–Miller formulation is applied to tackle the fictitious eigenfrequency problem of the BEM, and the optimal choice of its coupling parameter is investigated for the coupled FE–BE method. Numerical examples are given and discussed to demonstrate the effectiveness and accuracy of the developed FE–BE method. Copyright © 2016 John Wiley & Sons, Ltd.     

A note on the kernel approximation in a certain axially symmetric temperature problem

A contour integral technique and the second mean value theorem of integral calculus are used to obtain an approximation to the kernel of the integral equation associated with a certain axially symmetric temperature problem. The method of derivation also provides the scheme by which the approximation can be improved to any desired degree of accuracy. Numerical results are obtained to demonstrate the effectiveness of the scheme.     

五轴联动数控展成电解磨床原理与控制

为解决整体叶轮叶片型面的精加工难题,进行了五轴联动数控展成电解磨削整体叶轮的基础研究。根据数控展成电解磨削整体叶轮叶片型面这一加工方法的特点,在分析了数控展成电解磨削整体叶轮原理的基础上,对磨削系统的结构与运动进行了总体设计,提出了经济型多轴数控系统及其联动控制方法,建立了电解磨削非平行直纹展成曲面的数学模型,开发了五轴联动数控展成电解磨削自动数控编程系统,对航空发动机整体叶轮的叶片型面进行了电解磨削。五轴联动数控展成电解磨削技术为整体叶轮叶片型面的精加工提供了一种新的加工手段。     

An Interaction Integral Method for Computing Fracture Parameters in Functionally Graded Magnetoelectroelastic Composites

A contour integral method is developed for the computation of stress intensity, electric and magnetic intensity factors for cracks in continuously nonhomogeneous magnetoelectroelastic solids under a transient dynamic load. It is shown that the asymptotic fields in the crack-tip vicinity in a continuously nonhomogeneos medium are the same as in a homogeneous one. A meshless method based on the local Petrov-Galerkin approach is applied for the computation of the physical fields occurring in the contour integral expressions of intensity factors. A unit step function is used as the test functions in the local weak-form. This leads to local integral equations (LIEs) involving only contour-integrals on the surfaces of subdomains. The moving least-squares (MLS) method is adopted for approximating the physical quantities in the LIEs. The accuracy of the present method for computing the stress intensity factors (SIF), electrical displacement intensity factors (EDIF) and magnetic induction intensity factors (MIIF) are discussed by comparison with numerical solutions for homogeneous materials.     

Evaluation of T-stresses and stress intensity factors in stationary thermoelasticity by the coservation integral method

New methods for determining T-stresses and stress intensity factors in two-dimensional stationary thermoelasticity are presented. The methods utilize the path independence of J^-integral. The mutual M-integral expressed through J^-integrals provides sufficient information for determining T-stresses. The M-integral is composed of contour and domain integrals. Their integrands include the thermomechanical fields under consideration and mechanical fields corresponding to an auxiliary solution. The thermomechanical fields along the integration path and in the enclosed domain are obtained by the boundary element method. Stress intensity factors are calculated using the path independent J^-integral technique. This integral is expressed in a pure contour integral form. Numerical results for a cracked rectangular plate and thick-walled tube with internal cracks are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stress analysis with arbitrary body force by boundary element method

Linear stress analysis without body force can be easily carried out by means of the boundary element method. Some cases of linear stress analysis with body force can also be solved without the domain integral. However domain integrals are generally necessary to solve the linear stress problems with complicated body forces. This paper shows that the linear stress problems with complicated body forces can be solved approximately without the domain integral. In order to solve these problems, the domain is divided into small areas using contour lines of body force. In these areas, the distributions of body force are assumed approximately to satisfy the Laplace equation.     

Contour integral method for stress intensity factors of interface crack

A general Betti's reciprocal work theorem with interface cracks of a bimaterial is established in this paper, and a path independent contour integral method for the stress intensity factor (SIF) of the interface crack was obtained. When the stress and displacement fields in a specimen are calculated by the finite element method, the SIF K _I and K _II of interface cracks can be obtained immediately by a contour integral. Some solutions of interesting examples, such as two collinear interface cracks, are also given.Presented at the Far East Fracture Group (FEFG) International Symposium on Fracture and Strength of Solids, 4–7 July 1994 in Xi'an China.     

Application of the Jk integral to mixed mode crack problems for anisotropic composite laminates

The J_k integral method for determining mixed mode stress intensity factors separately in the cracked anisotropic plate is developed. Stress intensity factors are indirectly determined from the value of J₁ and J₂. The J₂ integral can be evaluated efficiently from a finite element solution, neglecting the contribution from the portion of the integration contour along the crack faces, by selecting the integration contour in the vicinity of the crack tip. Using functions of a complex variable, the complete relations between J₁, J₂ and K_I, K_II for anisotropic materials are derived conveniently by selecting narrow rectangular contours shrinking to the crack tip. Compared to the existing path independent integral methods, the present method does not involve calculating the auxiliary solution and hence numerical procedures become quite simple. Numerical results to various propblems are given and demonstrate the accuracy, stability and versatility of the method.     

A new look at energy release rates for quasistatically propagating cracks in inelastic materials

A mapping technique is used to derive an integral expression for the energy release rate for a quasistatically propagating crack. The derivation does not depend on any assumptions in regard to the contitutive behavior of the material. It leads to a contour integral around the crack tip, plus an area integral over the region enclosed by this contour. Only the stress and displacement fields appear in the integrands. Although for stationary crack solutions known to the authors the area integral is not convergent, for propagating crack solutions in elastoplastic material, the integrals are convergent, and lead to zero energy release rate. This confirms conclusions by Rice from an independent point of view.     

Boundary integral equation method to solve embedded planar crack problems under shear loading

The solution of three-dimensional planar cracks under shear loading are investigated by the boundary integral equation method. A system of two hypersingular integral equations of a three-dimensional elastic solid with an embedded planar crack are given. The solution of the boundary integral equations is succeeded taking into consideration an appropriate Gauss quadrature rule for finite part integrals which is suitable for the numerical treatment of any plane crack without a polygonal contour shape and permit the fast convergence for the results. The stress intensity factors at the crack front are calculated in the case of a circular and an elliptic crack and are compared with the analytical solution.     

The Bueckner work conjugate integral for a permeable crack in piezoelectric materials

Summary The Bueckner work conjugate integral for cracked piezoelectric materials is studied. The analysis is based on the permeable crack model to avoid the unphysically impermeable crack assumption. It is proved that the values of the Bueckner integrals are dependent on the normal electric displacement component on the crack surfaces and the coordinates of the starting point and the end point of the integral contour on the lower and upper crack faces, respectively. This means that, strictly speaking, the Bueckner integral for the permeable crack model is path-dependent unless a special condition is satisfied, i.e., the horizontal coordinates of the starting point and the end points of the integral contour are the same. The present conclusions are quite different from those derived from the impermeable crack model, where the Bueckner integral is strictly path-independent. The universal relation between the Bueckner integral and the J-integral existing in the impermeable crack model is also proved not to be always valid for the present permeable model unless the special integral contour is taken. This implies that the crack electric boundary condition in piezoelectric materials yields some significant influence on the properties of the Bueckner work conjugate integral.