Дополнительные граничные условия в задачах теплопроводности с неоднородными граничными условиями

Abstract

Using additional boundary conditions (ABC) and an additional sought function (ASF), a solution to the heat conduction problem with non-homogeneous boundary conditions has been obtained. ABC allows satisfying the differential equation at the boundaries, leading to its fulfillment both inside the domain and without resorting to integration over Cartesian coordinates. ASF reduces the original partial differential equation to a temporal ordinary equation, from which the eigenvalues of the boundary value problem are determined, as formulated in the classical methods of the Sturm-Liouville problem, stated in spatial variables. Thus, this work considers an alternative way of determining eigenvalues. The integration constants are found from the initial condition using the least squares method, which allows their values to be determined with a given accuracy. The solution obtained based on ABC and ASF approximates n → ∞ the exact analytical solution in the form of an infinite series, including trigonometric coordinate functions with coefficients that stabilize exponentially in time. In this case, the eigenvalues determined from the solution of the temporal ordinary differential equation regarding the additional sought function coincide with their exact values at any approximation. The accuracy of the integration constants, determined by the method of least squares, is controlled by the number of approximation points in the range of the auxiliary variable's variation. It should be noted that the additional boundary conditions considered in this work hold true for any other method of obtaining a solution to the problem under consideration, including the exact method, as can be verified by direct substitution. Therefore, their introduction does not distort the original mathematical formulation of the problem but only significantly simplifies the process of obtaining its analytical solution.