Factorization method for solving nonlocal boundary value problems in Banach space

This article deals with the factorization and solution of nonlocal boundary value problems in a Banach space of the abstract form B1 u = A u - S Φ( u )- G Ψ(A0 u) = f, u ∈ D (B1) , where A, A0 are linear abstract operators, S, G are vectors of functions, Φ, Ψ are vectors of linear bounded functionals, and u, f are functions. It is shown that the operator B1 under certain conditions can be factorized into a product of two simpler lower order operators as B 1 = BB0. Then the solvability and the unique solution of the equation B1 u = f easily follow from the solvability conditions and the unique solutions of the equations Bv = f and B0 u = v. The universal technique proposed here is essentially different from other factorization methods in the respect that it involves decomposition of both the equation and boundary conditions and delivers the solution in closed form. The method is implemented to solve ordinary and partial Fredholm integro-differential equations

Factorization method for solving nonlocal boundary value problems in Banach space

This article deals with the factorization and solution of nonlocal boundary value problems in a Banach space of the abstract form B1u = Au − SΦ(u) − GΨ(A0u) = f, u ∈ D(B1),where A, A0 are linear abstract operators, S, G are vectors of functions, Φ, Ψ are vectors of linear bounded functionals, and u, f are functions. It is shown that the operator B1 under certain conditions can be factorized into a product of two simpler lower order operators as B1 = BB0. Then the solvability and the unique solution of the equation B1u = f easily follow from the solvability conditions and the unique solutions of the equations Bv = f and B0u = v. The universal technique proposed here is essentially different from other factorization methods in the respect that it involves decomposition of both the equation and boundary conditions and delivers the solution in closed form. The method is implemented to solve ordinary and partial Fredholm integro-differential equations

Multiscale analysis of materials with anisotropic microstructure as micropolar continua

Multiscale procedures are often adopted for the continuum modeling of materials composed of a specific micro-structure. Generally, in mechanics of materials only two-scales are linked. In this work the original (fine) micro-scale description, thought as a composite material made of matrix and fibers/particles/crystals which can interact among them, and a scale-dependent continuum (coarse) macro-scale are linked via an energy equivalence criterion. In particular the multiscale strategy is proposed for deriving the constitutive relations of anisotropic composites with periodic microstructure and allows us to reduce the typically high computational cost of fully microscopic numerical analyses. At the microscopic level the material is described as a lattice system while at the macroscopic level the continuum is a micropolar continuum, whose material particles are endowed with orientation besides position. The derived constitutive relations account for shape, texture and orientation of inclusions as well as internal scale parameters, which account for size effects even in the elastic regime in the presence of geometrical and/or load singularities. Applications of this procedure concern polycrystals, wherein an important descriptor of the underlying microstructure gives the orientation of the crystal lattice of each grain, fiber reinforced composites, as well as masonry-like materials. In order to investigate the effects of micropolar constants in the presence of material non central symmetries, some numerical finite element simulations, with elements specifically formulated for micropolar media, are presented. The performed simulations, which extend several parametric analyses earlier performed [1], involve two-dimensional media, in the linear framework, subjected to compression loads distributed in a small portion of the medium

A unified formulation of analytical and numerical methods for solving linear fredholm integral equations

This article is concerned with the construction of approximate analytic solutions to linear Fredholm integral equations of the second kind with general continuous kernels. A unified treatment of some classes of analytical and numerical classical methods, such as the Direct Computational Method (DCM), the Degenerate Kernel Methods (DKM), the Quadrature Methods (QM) and the Projection Methods (PM), is proposed. The problem is formulated as an abstract equation in a Banach space and a solution formula is derived. Then, several approximating schemes are discussed. In all cases, the method yields an explicit, albeit approximate, solution. Several examples are solved to illustrate the performance of the technique. © 2021 by the author. Licensee MDPI, Basel, Switzerland

Approximate Solution of Fredholm Integral and Integro-Differential Equations with Non-Separable Kernels

This chapter deals with the approximate solution of Fredholm integral equations and a type of integro-differential equations having non-separable kernels, as they appear in many applications. The procedure proposed consists of firstly approximating the non-separable kernel by a finite partial sum of a power series and then constructing the solution of the degenerate equation explicitly by a direct matrix method. The method, which is easily programmable in a computer algebra system, is explained and tested by solving several examples from the literature. © 2022, Springer Nature Switzerland AG

Factorization and Solution of Linear and Nonlinear Second Order Differential Equations with Variable Coefficients and Mixed Conditions

This chapter deals with the factorization and solution of initial and boundary value problems for a class of linear and nonlinear second order differential equations with variable coefficients subject to mixed conditions. The technique for nonlinear differential equations is based on their decomposition into linear components of the same or lower order and the factorization of the associated second order linear differential operators. The implementation and efficiency of the procedure is shown by solving several examples. © 2021, Springer Nature Switzerland AG

Exact Solution to Systems of Linear First-Order Integro-Differential Equations with Multipoint and Integral Conditions

This paper is devoted to the study of nonhomogeneous systems of linear first-order ordinary integro-differential equations of Fredholm type with multipoint and integral boundary constraints. Sufficient conditions for the solvability and correctness of the problem are established and the unique solution is provided in closed-form. The approach followed is based on the extension theory of operators. © 2019, Springer Nature Switzerland AG

On the Solution of Boundary Value Problems for Loaded Ordinary Differential Equations

This chapter is devoted to the solution of the so-called loaded ordinary differential equations which arise in applications in sciences and engineering. We propose a direct operator method for examining existence and uniqueness and constructing the solution in closed form to a class of boundary value problems for loaded nth-order ordinary differential equations with multipoint and integral boundary conditions. © 2021, Springer Nature Switzerland AG

A procedure for factoring and solving nonlocal boundary value problems for a type of linear integro-differential equations

The aim of this article is to present a procedure for the factorization and exact solution of boundary value problems for a class of n-th order linear Fredholm integro-differential equations with multipoint and integral boundary conditions. We use the theory of the extensions of linear operators in Banach spaces and establish conditions for the decomposition of the integro-differential operator into two lower-order integro-differential operators. We also create solvability criteria and derive the unique solution in closed form. Two example problems for an ordinary and a partial intergro-differential equation respectively are solved. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

An assessment of two fundamental flat triangular shell elements with drilling rotations

An approach for adding drilling rotations to the constant strain triangle, such that the added rotation stiffness contributes a minimum to the strain energy of the triangle is presented. The element is combined with a bending triangle to produce a flat shell element having six-degrees-of-freedom per node. Allman's triangle with true drilling rotations is also combined with the same bending element. These two facet shell elements are examined for their capacity to accurately simulate inextensional bending of general thin shells. A novel eigenvalue procedure and specially designed inextensional bending patch tests for thin shells are applied. Selected practical thin shell problems are also solved. (C) 2000 Elsevier Science Ltd. All rights reserved