Статьи журнала - Вестник Южно-Уральского государственного университета. Серия: Математическое моделирование и программирование
Все статьи: 729
Stationary electrochemical machining simulation applying to precision technologies
Статья научная
The modification of statement of electrochemical formation problem is offered for mathematical modelling of the precision technologies. As an example the process of cutting with a plate electrode-tool is considered. For the description of the technologies with high localization of the processes a stepwise function of current efficiency is used. It realizes for simulation of the anode dissolution process in passivating electrolytes under short impulse current. This function determines the movement rate of the anode boundary in the areas of an active electrochemical dissolution and also it defines the boundaries of the areas where dissolution is absent. The stationary and limiting-stationary machining problems are formulated and solved on the base of the offered model. The limiting model describes the maximum localization process. The stationary problem is characterized by the presence of anode surface part, on which the current density is equal to a critical value. Investigations in the whole range of ratio of the maximal and critical values of electrical field strength on the anode surface are carried out.
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Stationary solutions for the Cahn - Hilliard equation coupled with Neumann boundary conditions
Статья научная
The structure of stationary states of the one-dimensional Cahn - Hilliard equation coupled with the Neumann boundary conditions has been studied. Here the free energy is given by a fourth order polynomial. The bifurcation diagram for existence and uniqueness of monotone solutions for this problem has been constructed. Namely, we find the length of the interval on which the solution monotonically increases or decreases and has one zero for some fixed values of physical parameters. Under the non-uniqueness we understand a possibility of existence of more than one monotone solutions for the same values of physical parameters.
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Statistical analysis module for weight design of aircraft elements
Статья научная
The concept of a statistical analysis module for weight design of aircraft elements (for predicting weight characteristics of one or another aircraft elements) is proposed. Models, methods to construct single-point estimates of the predicted characteristic, quality criteria of constructed models are considered. Two approaches to the confidence estimation of the predicted characteristic are proposed. First approach is based on the assumption that errors at predicting are caused by inaccurate identification of the deterministic part of the predicted characteristic behavior. The second one is based on the assumption that the deterministic part of the predicted characteristic behavior is identified correctly and errors at predicting are caused by inaccuracy in the measurements. The structure, goals of each component of the software package that implements the statistical analysis module is considered in details. Based on the real data the problem of predicting the take-off mass of an empty equipped airliner depending on maximum pay load and the maximum flight distance at maximum pay load is given. By this problem applicability of considered models and methods is demonstrated.
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Statistical analysis of the functional status of the students
Статья научная
The South Ural is one of the most advanced industrial regions in Russia. It has huge industrial potential (metal industry, mechanical engineering, chemical process industry, oil-extracting industry, mineral resource industry) which predetermines negative ecological trends in the region. Levels of air pollution with salts of heavy metals, phenol and CO2 are 2-4 times higher than national air quality standards. Moreover, natural background radiation in the region is increased. Under the stated conditions, low levels of motor activity lead to hypoxia and cumulative disorders of the locomotor system as well as to respiratory, gastric, oncological, allergic and other diseases. Poor environmental background significantly affects demographic rates including the life expectancy which is 72 in average for the region: 60 years for men, and 75 years for women. The paper studies how the main anthropometric and physiological parameters in the local residents who are divided into three groups according to their health status and motor activity (so called health groups) influence the physical fitness. Social-biological and medical aspect of the study - to find out the correlation between parameters in the examined people from different groups - may also be of interest for specialists working on optimization of physical education practice and student's health promotion.
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Stochastic Leontief type equations with impulse actions
Статья научная
By a stochastic Leontief type equation we mean a special class of stochastic differential equations in the Ito form, in which there is a degenerate constant linear operator in the left-hand side and a non-degenerate constant linear operator in the right-hand side. In addition, in the right-hand side there is a deterministic term that depends only on time, as well as impulse effects. It is assumed that the diffusion coefficient of this system is given by a square matrix, which depends only on time. To study the equations under consideration, it is required to consider derivatives of sufficiently high orders from the free terms, including the Wiener process. In connection with this, to differentiate the Wiener process, we apply the machinery of Nelson mean derivatives of random processes, which makes it possible to avoid using the theory of generalized functions to the study of equations. As a result, analytical formulas are obtained for solving the equation in terms of mean derivatives of random processes.
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Stochastic Leontieff type equations and mean derivatives of stochastic processes
Статья научная
We understand the Leontieff type stochastic differential equations as a special sort of Ito stochastic differential equations, in which the left-hand side contains a degenerate constant linear operator and the right-hand side has a non-degenerate constant linear operator. In the right-hand side there is also a summand with a term depending only on time. Its physical meaning is the incoming signal into the device described by the operators mentioned above. In the papers by A.L. Shestakov and G.A. Sviridyuk the dynamical distortion of signals is described by such equations. Transition to stochastic differential equations arise where it is necessary to take into account the interference (noise). Note that the investigation of solutions of such equations requires the use of derivatives of the incoming signal and the noise of any order. In this paper for differentiation of noise we apply the machinery of the so-called Nelson's mean derivatives of stochastic processes. This allows us to avoid using the machinery of the theory of generalized functions. We present a brief introduction to the theory of mean derivatives, investigate the transformation of the equations to canonical form and find formulae for solutions in terms of Nelson's mean derivatives of Wiener process.
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Stochastic Leontieff type equations in terms of current velocities of the solution II
Статья научная
In papers by A.L. Shestakov and G.A. Sviridyuk a new model of the description of dynamically distorted signals in some radio devices is suggested in terms of so-called Leontieff type equations (a particular case of algebraic-differential equations). In that model the influence of noise is taken into account in terms of the so-called symmetric mean derivatives of the Wiener process instead of using white noise. This allows the authors to avoid using the generalized function. It should be pointed out that by physical meaning, the current velocity is a direct analog of physical velocity for the deterministic processes. Note that the use of current velocity of the Wiener process means that in the construction of mean derivatives the σ-algebra "present" for the Wiener process is under consideration while there is also another possibility: to deal with the σ-algebra "present" of the solution as it is usually done in the theory of stochastic differential equation with mean derivatives. This approach was previously suggested by the authors under the assumption that the matrix pencil, that determines the equation, satisfies the so-called "rank-degree" condition. In this paper we consider stochastic Leontieff type equation given in terms of current velocities of the solution without this assumption.
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Stochastic Leontieff-type equations with multiplicative effect in spaces of complex-valued «noises»
Статья научная
We consider a Leontieff-type stochastic equation, that is, a system of differential equations implicit with respect to the time derivative in the spaces of random processes. The concepts previously introduced for the spaces of differentiable «noise» using the Nelson-Gliklikh derivative carry over to the case of complex-valued «noise»; in addition, the right-hand side of the equation is subject to multiplicative effect of a special form. We construct a solution to the Showalter-Sidorov problem for Leontieff-type equations with multiplicative effect of a complex-valued process of special form. Aside from the introduction and references, the article consists of two parts. In the first part we carry over various concepts of the space of real-valued differentiable «noise» to the complex-valued case. In the second part we construct a Showalter-Sidorov solution to a Leontieff-type equation with multiplicative effect of a complex-valued process of special form. The list of references is not intended to be complete and reflects only the authors'' personal preferences.
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Stochastic inclusions with forward mean derivatives having decomposable right-hand sides
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In this paper, we prove a theorem on the existence of solutions for stochastic differential inclusions given in terms of the forward mean derivatives and the quadratic mean derivatives. These derivatives present information on the drift and the diffusion coefficient, respectively. The forward mean derivatives were introduced by E. Nelson for the needs of the so-called stochastic mechanics (a version of quantum mechanics), while the quadratic mean derivatives were introduced by Yu.E. Gliklich and S.V. Azarina. In the case of both the forward mean derivatives and the quadratic mean derivatives, we assume that the right-hand side is set-valued and lower semi-continuous, but not necessarily convex. Instead of this, we assume that the right-hand side is decomposable. Such inclusions naturally arise in many models of physical processes.
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Stochastic mathematical model of internal waves
Статья научная
The paper studies a mathematical model of internal gravitational waves with additive "white noise'', which models the fluctuations and random heterogeneity of the medium. The mathematical model is based on the Sobolev stochastic equation, Dirichlet boundary conditions and the initial Cauchy condition. The Sobolev equation is obtained from the assumption of the propagation of waves in a uniform incompressible rotation with a constant angular velocity of the fluid. The solution to this problem is called the inertial (gyroscopic) wave, since it arises due to the Archimedes's law and under the influence of inertia forces. By "white noise'' we mean the Nelson-Gliklikh derivative of the Wiener process. The study was conducted in the framework of the theory of relatively bounded operators, the theory of stochastic equations of Sobolev type and the theory of (semi) groups of operators. It is shown that the relative spectrum of the operator is bounded, and the solution of the Cauchy-Dirichlet problem for the Sobolev stochastic equation is constructed in the operator form.
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Stochastic model of optimal dynamic measurements
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Under consideration is the stochastic model of optimal dynamic measurements. To solve this problem, the theory of optimal dynamic measurements which has actively been developing for the deterministic problems is extended to the stochastic case. The main purpose of the model is to restore a dynamically distorted input signal from a given observation using methods of the theory of dynamic measurements and the optimal control theory for Leontief type systems. Based on the results obtained by the authors earlier it is shown that optimal dynamic measurement as a minimum point of the cost functional doesn't depend on stochastic interference such as resonances in chains and random interference at the output of measuring transducer.
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Strongly continuous operator semigroups. Alternative approach
Статья научная
Inheriting and continuing the tradition, dating back to the Hill-Iosida-Feller-Phillips-Miyadera theorem, the new way of construction of the approximations for strongly continuous operator semigroups with kernels is suggested in this paper in the framework of the Sobolev type equations theory, which experiences an epoch of blossoming. We introduce the concept of relatively radial operator, containing condition in the form of estimates for the derivatives of the relative resolvent, the existence of C 0-semigroup on some subspace of the original space is shown, the sufficient conditions of its coincidence with the whole space are given. The results are very useful in numerical study of different nonclassical mathematical models considered in the framework of the theory of the first order Sobolev type equations, and also to spread the ideas and methods to the higher order Sobolev type equations.
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Structural parametric modelling of an information-analytical system
Статья научная
We develop a method for studying relations between interior and exterior characteristics of an information-analytical system. As interior characteristics, we use the balance estimates accounting for conflict interactions among the elements. We solve the problem on assuming that the interior and exterior characteristics of the system are related. We justify the expediency of using the least squares method to find an explicit functional dependence among the characteristics. We develop a method for calculating the functional dependence in the case of a matrix representation of the values of characteristics basing on pseudoinverse matrices. A numerical example illustrates how the proposed method works in the structure parametric modeling of an information-analytical system in an internal affairs department.
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Studying the model of air and water filtration in a melting or freezing snowpack
Статья научная
The article is devoted to a theoretical study of a non-stationary problem on thermomechanical processes in snow taking into account the effects of melting and freezing. Snow is modeled as a continuous medium consisting of water, air and porous ice skeleton. The governing equations of snow are based on the fundamental conservation laws of continuum mechanics. For the one-dimensional setting, the Rothe scheme is constructed as an approximation of the considered problem and the Rothe method is formally justified, i.e., convergence of approximate solutions to the solution of the considered problem is established under some additional regularity requirements.
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Статья научная
In this paper we prove some new results on Sturm - Liouville abstract problems of the second order differential equations of elliptic type in a new non-commutative framework. We study the case when the second member belongs to a Sobolov space. Existence, uniqueness and optimal regularity of the strict solution are proved. This paper is naturally the continuation of the ones studied by Cheggag et al in the commutative case. We also give an example to which our theory applies.
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Supercomputer simulation of oil spills in the Azov Sea
Статья научная
We present the research on microbiological destruction of oil pollution in shallow water. In order to conduct the research, we use a multiprocessor computer system with distributed memory. The research takes into account the oil fractional composition as well as hydrodynamic and chemical-biological features of water. In order to simulate the dynamics of hydrocarbon microbiological degradation in the Azov Sea, we propose the complex of interrelated precision models. For model discretization, we use the space splitting schemes taking into account the partial filling cells of computational domain. Therefore, the computational accuracy significantly increases, while the computational time decreases. On supercomputer, we implement an experimental software for predictive modelling the ecological situation under oil and other pollution conditioned by natural and industrial challenges in shallow water.
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Synthesis of surface h-polarized currents on an unclosed cylindrical surface
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The article describes the inverse problem of diffraction of electromagnetic waves, finding surface H-polarized currents on an unclosed cylindrical surface according to a given radiation pattern. The work is based on modelling an operator equation with a small parameter. The operator is represented as the sum of a positive-definite, continuously invertible operator and a compact positive operator. The positive-definite operator exactly coincides with the main operator of the corresponding direct problem of diffraction of electromagnetic waves. Due to this fact, the solution to the simulated equation satisfies the necessary boundary conditions. And this is the novelty and difference of the approach developed in this work from the methods known in the scientific literature. We develop a theory of an operator equation with a small parameter and a numerical method based on Chebyshev polynomials with weights that take into account the behavior at the boundary. The efficiency of the numerical method is shown.
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System analysis of classification of prime knots and links in thickened surfaces of genus 1 and 2
Статья научная
In this paper, we present a system analysis of approaches to classification of prime knots and links in thickened surfaces of genus 1 and 2 obtained by the author in collaboration with S.V. Matveev and V.V. Tarkaev in 2012 - 2020. The algorithm of the classification forms structure of the present paper. The results of classification are considered within system analysis of the main ideas of key steps of the algorithm. First, we construct prime projections. To this end, we define a prime link projection, enumerate graphs of special type which embedding in the surface can be a prime projection, enumerate projections in the surface, and show that all obtained projections are prime and not equivalent using some invariants of projections. Second, we construct prime links. To this end, we define a prime link, construct a preliminary set of diagrams, use invariants of links to form equivalence classes of the obtained diagrams and show that the resulting diagrams are not equivalent, and prove primality of the obtained links. At that, at each step, the used methods and the introduced objects are characterized from viewpoints of two cases (genus 1 and 2), and we distinguish properties that are common for both cases or characteristics of only one of two cases. Note consolidated tables, which systematize the classified projections with respect to their properties: generative graph, genus, number of components and crossings, existence and absence of bigon that simplifies the further work with the proposed classification of projections and links.
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