Vol 27, No 2 (2021)

The article is a continuation of the authors’ work «On decoding algorithms for generalized Reed — Solomon codes with errors and erasures». In this work, another modification of the Gao algorithm and the Berlekamp — Massey algorithm is given. The first of these algorithms is a syndrome-free decoding algorithm, the second is a syndrome decoding algorithm. The relevance of these algorithms is that they are applicable for decoding Goppa codes, which are the basis of some promising post-quantum cryptosystems.

It is shown that the presence of a lower p - estimate with constant 1 in the symmetric space E is sufficient for the condition of equivalence of convergence in norm and in measure on the subspace H of the space E to be satisfied if and only if the numerical characteristic ηE(H) < 1. The last criterion is also valid for symmetric spaces ”close ”to L1, more precisely, for which an analog of the Dunford - Pettis criterion of weak compactness is valid. In particular, it is shown that spaces ”close” to L1, have the binary property: the characteristic ηE(H) takes only two values, 0 and 1. This gives an example of binary Orlicz spaces different from the spaces Lp.

Modern mechanical engineering sets the tasks of calculating thin-walled structures that combine lightness and economy on the one hand and high strength and reliability on the other. In this regard, the use of anisotropic materials and plastics seems justified. The problems of the theory of plates and shells belong to the class of boundary value problems, the analytical solution of which, due to various circumstances (nonlinearity of differential equations, complexity of geometry and boundary conditions, etc.), cannot be determined. Numerical methods help to solve this problem. Among numerical methods, undeservedly little attention is paid to the boundary element method. In this regard, the further development of indirect method of compensating loads for solving problems of the anisotropic plates and shells theory based on the application of exact fundamental solutions is relevant. The paper considers the application of the indirect boundary element method for solving of an anisotropic plates and shells nonlinear deformation problem. Since the kernels of the system of singular integral equations to which the solution of the problem is reduced are expressed in terms of the fundamental solution and its derivatives, first of all, the article provides a method for determining the fundamental solutions to the problem of bending and the plane stress state of an anisotropic plate. The displacement vector is determined from the solution of linear equations system describing the bending and plane stress state of an anisotropic plate. The solution of the system is performed by the method of compensating loads, according to which the area representing the plan of the shallow shell is supplemented to an infinite plane, and on the contour that limits the area, compensating loads are applied to the infinite plate. Integral equations of indirect BEM are given. In this paper, the study of nonlinear deformation of anisotropic plates and shallow shells is carried out using the “deflection – load” dependencies. The deflection at a given point on the median surface of the shell was taken as the leading parameter.

The problem of natural oscillations of a liquid column in a tubing string, arising after a sudden opening or closing of a vertical well (water hammer), is considered. For this, a mathematical model has been built that describes the dynamics of the fluid column in the well and the filtration flow in the bottomhole zone, analytical solutions of the system of equations have been obtained. To determine the frequency, period, coefficient and decrement of damping of oscillations, a characteristic equation is found. The impact of such parameters as the length of the open section, the perforation zones of the well, the length of the tubing string, the permeability coefficient on the dynamic nature of natural pressure fluctuations has been analyzed.