Moving Least Squares Shape Functions Research Articles

On a Galerkin boundary node method for potential problems

A Galerkin boundary node method (GBNM), for boundary only analysis of partial differential equations, is discussed in this paper. The GBNM combines an equivalent variational form of a boundary integral equation with the moving least-squares (MLS) approximations for generating the trial and test functions of the variational formulation. In this approach, only a nodal data structure on the boundary of a domain is required, and boundary conditions can be implemented directly and easily despite of the fact that the MLS shape functions lack the delta function property. Formulations of the GBNM using boundary singular integral equations of the second kind for potential problems are developed. The theoretical analysis and numerical results indicate that it is an efficient and accurate numerical method.

The meshless Galerkin boundary node method for Stokes problems in three dimensions

AbstractThe Galerkin boundary node method (GBNM) is a boundary only meshless method that combines an equivalent variational formulation of boundary integral equations for governing equations and the moving least‐squares (MLS) approximations for generating the trial and test functions. In this approach, boundary conditions can be implemented directly and easily despite of the fact that the MLS shape functions lack the delta function property. Besides, the resulting formulation inherits the symmetry and positive definiteness of the variational problems. The GBNM is developed in this paper for solving three‐dimensional stationary incompressible Stokes flows in primitive variables. The numerical scheme is based on variational formulations for the first‐kind integral equations, which are valid for both interior and exterior problems simultaneously. A rigorous error analysis and convergence study of the method for both the velocity and the pressure is presented in Sobolev spaces. The capability of the method is also illustrated and assessed through some selected numerical examples. Copyright © 2011 John Wiley & Sons, Ltd.

An integral meshless‐based approach in electromagnetic scattering

PurposeThe purpose of this paper is to solve the electromagnetic scattering problem through a new integral‐based approach that uses the moving least squares (MLS) meshless method to generate its shape functions.Design/methodology/approachThe electric field integral equation and its magnetic counterpart (MFIE) are discretized via special shape functions built numerically through the MLS procedure. This approach is applied to the particular problem concerning the scattering of a TM plane wave by an infinite conductor cylinder. An error norm is established in order to verify the quality of the obtained results.FindingsResults show that the discretization process which employs MLS shape functions presents very good precision and fast convergence to the solution, when compared to results provided by another numerical method, the method of moments.Originality/valueMLS shape functions occur in meshless methods intended to solve problems based on differential formulation. This paper shows that these shape functions can also be applied successfully to problems coming from an integral formulation.

Meshless analysis of two-dimensional Stokes flows with the Galerkin boundary node method

In this paper, the Galerkin boundary node method (GBNM) is developed for the solution of stationary Stokes problems in two dimensions. The GBNM is a boundary only meshless method that combines a variational form of boundary integral formulations for governing equations with the moving least-squares (MLS) approximations for construction of the trial and test functions. Boundary conditions in this approach are included into the variational form, thus they can be applied directly and easily despite the MLS shape functions lack the property of a delta function. Besides, the GBNM keeps the symmetry and positive definiteness of the variational problems. Convergence analysis results of both the velocity and the pressure are given. Some selected numerical tests are also presented to demonstrate the efficiency of the method.

A Galerkin boundary node method and its convergence analysis

The boundary node method (BNM) exploits the dimensionality of the boundary integral equation (BIE) and the meshless attribute of the moving least-square (MLS) approximations. However, since MLS shape functions lack the property of a delta function, it is difficult to exactly satisfy boundary conditions in BNM. Besides, the system matrices of BNM are non-symmetric. A Galerkin boundary node method (GBNM) is proposed in this paper for solving boundary value problems. In this approach, an equivalent variational form of a BIE is used for representing the governing equation, and the trial and test functions of the variational formulation are generated by the MLS approximation. As a result, boundary conditions can be implemented accurately and the system matrices are symmetric. Total details of numerical implementation and error analysis are given for a general BIE. Taking the Dirichlet problem of Laplace equation as an example, we set up a framework for error estimates of GBNM. Some numerical examples are also given to demonstrate the efficacity of the method.

Galerkin-based meshless methods for photon transport in the biological tissue

As an important small animal imaging technique, optical imaging has attracted increasing attention in recent years. However, the photon propagation process is extremely complicated for highly scattering property of the biological tissue. Furthermore, the light transport simulation in tissue has a significant influence on inverse source reconstruction. In this contribution, we present two Galerkin-based meshless methods (GBMM) to determine the light exitance on the surface of the diffusive tissue. The two methods are both based on moving least squares (MLS) approximation which requires only a series of nodes in the region of interest, so complicated meshing task can be avoided compared with the finite element method (FEM). Moreover, MLS shape functions are further modified to satisfy the delta function property in one method, which can simplify the processing of boundary conditions in comparison with the other. Finally, the performance of the proposed methods is demonstrated with numerical and physical phantom experiments.

An improved meshless collocation method for elastostatic and elastodynamic problems

AbstractMeshless methods for solving differential equations have become a promising alternative to the finite element and boundary element methods. In this paper, an improved meshless collocation method is presented for use with either moving least square (MLS) or compactly supported radial basis functions (RBFs). A new technique referred to as an indirect derivative method is developed and compared with the direct derivative technique used for evaluation of second‐order derivatives and higher‐order derivatives of the MLS and RBF shape functions at the field point. As the derivatives are obtained from a local approximation (MLS or compact support RBFs), the new method is computationally economical and efficient. Neither the connectivity of mesh in the domain/boundary nor integrations with fundamental/particular solutions is required in this approach. The accuracy of the two techniques to determine the second‐order derivative of shape function is assessed. The applications of meshless method to two‐dimensional elastostatic and elastodynamic problems have been presented and comparisons have been made with benchmark analytical solutions. Copyright © 2007 John Wiley & Sons, Ltd.

A MLPG(LBIE) numerical method for solving 2D incompressible and nearly incompressible elastostatic problems

AbstractA new meshless local Petrov–Galerkin (MLPG) method, based on local boundary integral equation (LBIE) considerations, is proposed here for the solution of 2D, incompressible and nearly incompressible elastostatic problems. The method utilizes, for its meshless implementation, nodal points spread over the analysed domain and employs the moving least squares (MLS) approximation for the interpolation of the interior and boundary variables. On the local and global boundaries, traction vectors are treated in a way so that no derivatives of the utilized MLS shape functions are required. Both displacement and hydrostatic pressure, at all the considered nodal points, are evaluated with the aid of local integral representations valid for incompressible and nearly incompressible solids. Since displacements and stresses are treated as independed variables, the boundary conditions are imposed directly without any problem via the integrals defined on the global boundary of the analysed body. Singular and hypersingular integrals are evaluated directly with high accuracy through advanced integration techniques. Three numerical examples illustrate the proposed methodology and demonstrates its accuracy. Copyright © 2006 John Wiley & Sons, Ltd.

Efficient cubature formulae for MLPG and related methods

AbstractThe paper introduces four kinds of compact, simple to implement Gaussian cubature formulae for approximating the domain integrals arising in the discrete local weak form (DLWF) of a governing partial differential equation solved by means of the meshless local Petrov–Galerkin method of type MLPG1. The integral weight functions are fixed to be the quartic‐spline weight function of the moving least squares (MLS) method and the function's gradient. The integration domain is a circle in 2D or a sphere in 3D. The fact that the DLWF test functions are directly incorporated into the formulae increases both their exactness degree and their computational efficiency.A number of numerical tests are carried out in order to asses the accuracy of the cubature formulae. For integrands involving MLS shape functions, the main factor controlling the integration accuracy is found to be the accuracy of the MLS‐approximation. Only a small number of cubature points is thus required to match that accuracy without a need for domain partitioning. The recommended approach for increasing the overall accuracy is by adding more MLS nodes and taking advantage of the computationally inexpensive cubature formulae. Copyright © 2005 John Wiley & Sons, Ltd.

A new singular/hypersingular MLPG (LBIE) method for 2D elastostatics

A new meshless local Petrov-Galerkin (MLPG) type method based on local boundary integral equation (LBIE) considerations is proposed for the solution of elastostatic problems. It is called singular/hypersingular MLPG (LBIE) method since the representation of the displacement field at the internal points of the considered structure is accomplished with the aid of the displacement local boundary integral equation, while for the boundary nodes both the displacement and the corresponding traction local boundary integral equations are employed. Nodal points spread over the analyzed domain are considered and the moving least squares (MLS) interpolation scheme for the approximation of the interior and boundary variables is employed. The essential boundary conditions are satisfied via the free terms of the singular and hypersingular LBIEs, respectively. This means that, for any distribution of nodal points, displacements and tractions can be treated as independed variables, avoiding thus derivatives of the MLS shape functions. On the local boundaries of the hypersingular LBIEs, tractions are avoided with the aid of an auxiliary local integral equation explicitly derived in the present work. Strongly singular and hypersingular integrals are evaluated directly and with high accuracy by means of advanced integration techniques. Two representative numerical examples that demostrate the achieved accuracy of the proposed singular/hypersingular MLPG (LBIE) method are provided.

Moving Least-Squares Differential Quadrature Method for Free Vibration of Antisymmetric Laminates

In this paper, the moving least-squares differential quadrature (MLSDQ) method is employed for free vibration of thick antisymmetric laminates based on the first-order shear deformation theory. The generalized displacements of the laminates are independently approximated with the centered moving least-squares (MLS) technique within each domain of influence. The MLS nodal shape functions and their partial derivatives are computed quickly through back-substitutions after only one LU decomposition. Subsequently, the weighting coefficients in the MLSDQ discretization are determined with the nodal partial derivatives of the MLS shape functions. The MLSDQ method combines the merits of both the differential quadrature and meshless methods which can be conveniently applied to complex domains and irregular discretizations without loss of implementation efficiency and numerical accuracy. The natural frequencies of the laminates with various edge conditions, ply angles, and shapes are calculated and compared with the existing solutions to study the numerical accuracy and stability of the MLSDQ method. Effects of support size, order of completeness of basis functions, and node irregularity on the numerical accuracy are investigated in detail.

Vibration analysis of symmetrically laminated plates based on FSDT using the moving least squares differential quadrature method

In this paper, we adopt the first-order shear deformation theory in the moving least squares differential quadrature (MLSDQ) procedure for predicting the free vibration behavior of moderately thick symmetrically laminated composite plates. The transverse deflection and two rotations of the laminate are independently approximated with the moving least squares (MLS) approximation. The weighting coefficients used in the MLSDQ approximation are obtained through the fast computation of the MLS shape functions and their partial derivatives. The natural frequencies of vibration are computed for various laminated plates and compared with the available published results. Through numerical experiments, the capability and efficiency of the MLSDQ method for eigenvalue problems are demonstrated, and the numerical accuracy and convergence are thoughtfully examined. Effects of the size of support, order of completeness of the basis functions and node irregularity on the numerical accuracy are also investigated.

Bending and buckling of thick symmetric rectangular laminates using the moving least-squares differential quadrature method

In this paper, the moving least-squares differential quadrature (MLSDQ) method is applied to the bending and buckling analyses of moderately thick symmetric laminates based on the first-order shear deformation theory (FSDT). The transverse deflection and two rotations of the laminate are independently assumed with the moving least-squares (MLS) approximation. The weighting coefficients used in the MLSDQ approximation are obtained through a fast computation of the MLS shape functions and their partial derivatives. Numerical examples are illustrated to study the accuracy, stability and convergence of the MLSDQ method. The typical displacements, stresses and critical buckling loads of various laminated plates are presented and compared with the analytical values. Effects of support size, order of the complete basis functions and node irregularity on the numerical accuracy are investigated.

On elimination of shear locking in the element‐free Galerkin method

AbstractIn this study, a method for completely eliminating the presence of transverse shear locking in the application of the element‐free Galerkin method (EFGM) to shear‐deformable beams and plates is presented. The matching approximation fields concept of Donning and Liu has shown that shear locking effects may be prevented if the approximate rotation fields are constructed with the innate ability to match the approximate slope (first derivative of displacement) fields and is adopted. Implementation of the matching fields concept requires the computation of the second derivative of the shape functions. Thus, the shape functions for displacement fields, and therefore the moving least‐squares (MLS) weight function, must be at least C1 continuous. Additionally, the MLS weight functions must be chosen such that successive derivatives of the MLS shape function have the ability to exactly reproduce the functions from which they were derived. To satisfy these requirements, the quartic spline weight function possessing C2 continuity is used in this study. To our knowledge, this work is the first attempt to address the root cause of shear locking phenomenon within the framework of the element‐free Galerkin method. Several numerical examples confirm that bending analyses of thick and thin beams and plates, based on the matching approximation fields concept, do not exhibit shear locking and provide a high degree of accuracy for both displacement and stress fields. Copyright © 2001 John Wiley & Sons, Ltd.

A three‐dimensional element‐free Galerkin elastic and elastoplastic formulation

A small strain, three-dimensional, elastic and elastoplastic Element-Free Galerkin (EFG) formulation is developed. Singular weight functions are utilized in the Moving-Least-Squares (MLS) determination of shape functions and shape function derivatives allowing accurate, direct nodal imposition of essential boundary conditions. A variable domain of influence EFG method is introduced leading to increased efficiency in computing the MLS shape functions and their derivatives. The elastoplastic formulations are based on the consistent tangent operator approach and closely follow the incremental formulations for non-linear analysis using finite elements. Several linear elastic and small strain elastoplastic numerical examples are presented to verify the accuracy of the numerical formulations. Copyright © 1999 John Wiley & Sons, Ltd.

A three-dimensional element-free Galerkin elastic and elastoplastic formulation

A small strain, three-dimensional, elastic and elastoplastic Element-Free Galerkin (EFG) formulation is developed. Singular weight functions are utilized in the Moving-Least-Squares (MLS) determination of shape functions and shape function derivatives allowing accurate, direct nodal imposition of essential boundary conditions. A variable domain of influence EFG method is introduced leading to increased efficiency in computing the MLS shape functions and their derivatives. The elastoplastic formulations are based on the consistent tangent operator approach and closely follow the incremental formulations for non-linear analysis using finite elements. Several linear elastic and small strain elastoplastic numerical examples are presented to verify the accuracy of the numerical formulations. Copyright © 1999 John Wiley & Sons, Ltd.