Invariant imbedding and the identification of aquifer parameters

The technique of invariant imbedding is applied to the problem of identifying the parameters in an unconfined aquifer system. This new technique is shown to be a very effective way of converting field observations based upon pumping tests into the desired aquifer parameters. The procedure is straightforward as it requires neither curve plotting nor graphical matching. The parameters to be identified are the hydraulic conductivity and specific storage in an extensive unconfined aquifer system. Results and numerical experiments are presented.Identification is an inverse process whereby the parameters embedded in a differential equation are determined from observations of systems input and output along with appropriate initial and boundary conditions. These parameters are usually noy physically measurable. In general, the governing equation is nonlinear with no closed-form solution.In this paper, this inverse problem is solved by invariant imbedding and quasilinearization. A comparison is made between these methods. The problem of convergence and stability is discussed and demonstrated by numerical experimentation.     

Reconstruction of boundary regimes in the inverse problem of thermal convection of a high-viscosity fluid

A problem of reconstruction of boundary regimes in a model for free convection of a high-viscosity fluid is considered. A variational method and a quasi-inversion method are suggested for solving the problem in question. The variational method is based on the reduction of the original inverse problem to some equivalent variational minimum problem for an appropriate objective functional and solving this problem by a gradient method. When realizing the gradient method for finding a minimizing element of the objective functional, an iterative process actually reducing the original problem to a series of direct well-posed problems is organized. For the quasi-inversion method, the original differential model is modified by means of introducing special additional differential terms of higher order with small parameters as coefficients. The new perturbed problem is well-posed; this allows one to solve this problem by standard methods. An appropriate choice of small parameters gives an opportunity to obtain acceptable qualitative and quantitative results in solving the inverse problem. A comparison of the methods suggested for solving the inverse problem is made with the use of model examples.     

The question of embedding theorems in domains of the space En

The problem of formulating embedding theorems for main spaces of differentiable functions defined in a domain of the Euclidean space Eⁿ is connected to the problem of finding an extremal (in a certain sense) n -dimensional vector satisfying a number of linear constraints determined by three groups of parameters: parameters of the original class of functions, parameters characterizing the embedding, and parameters characterizing some properties of the domain of the functions. Determination of the extremal vector is reduced to a linear programming problem. The vector thus obtained determines the form of the inequalities which determine the embedding under given relations between parameters. In those cases where this vector does not coincide with the extremal vector found for the same values of parameters of the original class of functions but for the domain G=Eⁿ there is a kind of saturation of properties of the type of embedding theorems. An example is given, in which the linear programming problem is solved by the simplex method.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 124, pp. 164–199, 1983.     

Inverse problem of hydrodynamics for doubly connected domain

We consider an inverse problem of hydrodynamics for flow past pair of aerofoils. We find a general form of its solution. The key part of problem’s solving is to determine numerical parameters defining flow domain and complex velocity in it up to conformal mapping (the parameters problem). The solvability of parameters problem is proved for various flow schemes. For that we essentially use the interpretation of the problem in terms of Riemann surface and the Riemann surfaces theory.     

Inverse analysis of an internal reforming solid oxide fuel cell system using simplex search method

An inverse problem is solved for estimating fuel cell operating parameters such as current density, pressure and fuel flow rate (FFR) separately and then simultaneously two parameters in an internal reforming solid oxide fuel cell (IRSOFC). Initially, a mathematical model for the forward problem is developed to simulate the IRSOFC steady state operation and its performance in terms of power output and then an inverse problem is solved for recovering the above parameters using a simplex search minimization algorithm. The objective function (IRSOFC power) and the estimation accuracy are studied for the effects of initial guess values of the operating parameters and the number of iterations required for retrieval of these parameters. The objective function is represented by the sum of square of the error between a given IRSOFC power and the power evaluated based on some arbitrary guessed values of the unknowns which is then regularized in an iterative manner for solution of the inverse fuel cell problem. The study reveals that a multiple combinations of parameters (current density, operating pressure and FFR) exist which provides guidelines for selecting feasible combinations of these parameters required for meeting a given power requirement. The results show relatively good agreement between the inverse and exact solutions.     

哈明距离下圈图上1-重心问题的反问题

主要讨论哈明距离下圈图上1-重心问题的反问题.1-重心问题的反问题主要研究如何尽可能少地改变网络中的参数值,使得给定的顶点到其它顶点的加权距离之和不超过一个给定的上界.通过将该问题转化为0-1背包问题,证明了在哈明距离下该问题是NP困难的,并运用动态规划的思想,在考虑改变边的长度的情况下,对圈图进行了求解.     

Optimization of loading places and load response functions for stationary systems

The problem of optimizing loading places and corresponding load response functions with respect to objects described by systems of loaded ordinary differential equations is solved numerically. Analytical formulas for the gradient of the functional with respect to the optimized load parameters are derived to solve the problem by applying first-order numerical methods. Results of numerical experiments are presented. The approach proposed can also be used to optimize load parameters in distributed systems described by partial differential equations, which are reduced to the considered problem by applying the method of lines.     

Mathematical modeling and study of the process of solidification in metal casting

The process of melting and solidification in metal casting is considered. The process is modeled by a three-dimensional two-phase initial-boundary value problem of the Stefan type. The mathematical formulation of the problem and its finite-difference approximation are given. A numerical algorithm is presented for solving the direct problem. The results are described and analyzed in detail. Primary attention is given to the evolution of the solidification front and to how it is affected by the parameters of the problem. Some of the results are illustrated by plots.     

A penalty method for grid matching in the mixed Herrmann-Miyoshi scheme

A penalty method for mixed finite element methods is formulated and studied. The Herrmann-Miyoshi scheme for the biharmonic equation is considered. The main idea is to build a perturbed problem with two parameters playing the role of penalties. The perturbed problem is constructed by replacing principal conditions in the mixed variational formulation at the interface by natural conditions containing parameters. Discretization of the perturbed problem is effected by a finite element method. Estimates for the norm of the difference between the solutions of a discrete perturbed problem and of an initial value problem are derived depending on the mesh size and penalties. Recommendations are given as to how to choose penalties so as to fit a mesh size.     

A method of solving a nonlinear boundary value problem with a parameter for a loaded differential equation

A nonlinear loaded differential equation with a parameter on a finite interval is studied. The interval is partitioned by the load points, at which the values of the solution to the equation are set as additional parameters. A nonlinear boundary value problem for the considered equation is reduced to a nonlinear multipoint boundary value problem for the system of nonlinear ordinary differential equations with parameters. For fixed parameters, we obtain the Cauchy problems for ordinary differential equations on the subintervals. Substituting the values of the solutions to these problems into the boundary condition and continuity conditions at the partition points, we compose a system of nonlinear algebraic equations in parameters. A method of solving the boundary value problem with a parameter is proposed. The method is based on finding the solution to the system of nonlinear algebraic equations composed.     

基于多分类支持向量机的评估模型研究

支持向量机中的参数直接影响其推广能力,针对参数选取的主观性,提出基于改进的遗传算法优化其参数,并将其应用于银行个人信用的五等级分类问题中,针对多分类问题,设计了3个二值分类器,不同分类的参数不同,通过实验证实可以达到更精细的分类效果.     

Stability sets of multiparameter Hamiltonian systems

A real linear Hamiltonian system with constant coefficients that depend on several real parameters is considered. A method is proposed for calculating the sets of all values of the parameters for which the stationary solution of this system is stable for fixed values of the parameters (that is, the stability sets). The application of the method is demonstrated for a gyroscopic problem described by a Hamiltonian system with four degrees of freedom and three parameters. Computer algebra, in particular, a Gröbner basis and a Power Geometry are used. It is shown that the four-parameter generalization of this problem does not contain fundamentally new difficulties.     

Theoretical framework of an identification problem for an elliptic variational inequality with bilateral restrictions

An identification problem associated to an elliptic variational inequation subject to a bilateral restriction is considered. The whole of the parameters involved in the inequation as well as the parameters defining the restriction are to be identified. The continuous dependence of the direct problem solution on these parameters is proved. As a consequence the well-posedness of the identification problem follows.     

The impedance boundary-value problem of diffraction by a strip

We consider the impedance boundary-value problem for the Helmholtz equation originated by the problem of wave diffraction by an infinite strip with imperfect conductivity. The two possible different situations of real and complex wave numbers are considered. Bessel potential spaces are used to deal with the problem, and the identification of corresponding operators of single and double layer potentials allow a reformulation of the problem into a system of integral equations. The well-posedness of the problem is obtained for a set of impedance parameters (and wave numbers), after the incorporation of some compatibility conditions on the data. At the end, an improvement of the regularity of the solution is derived for the same set of parameters previously considered.     

Concerning an approach to identifying the Lamé parameters of an elastic functionally graded cylinder

Based on the general linear elasticity relations, an axisymmetric problem on the steady-state oscillations of a functionally graded hollow cylinder is formulated. The Lamé parameters are considered variable in radial coordinate. Oscillations are caused by the distributed load applied to the outer part of the cylinder boundary. Using the variable separation method, the direct problem on determining the radial and longitudinal components of the displacement field is investigated. The influence of the laws of variation for the Lamé parameters on acoustic characteristics is analysed. The inverse coefficient problem on the identification of the variable Lamé parameters from the data on the amplitude-frequency characteristic is stated. Based on the weak formulation of the problem for an elastic inhomogeneous body, a general linearised relation for the desired and given characteristics is obtained. A system of the Fredholm integral equations of the first kind is formulated with respect to two unknown corrections to the restored laws of the Lamé parameters change. The solution is built by means of an iterative process. A reconstruction of various laws of changing the Lamé parameters is carried out. The accuracy of the presented algorithm is estimated, and recommendations for the most efficient implementation of the reconstruction procedure are proposed.     

The penalty method for grid matching in mixed finite element methods

In this paper we prove the possibility of the use of the penalty method for grid matching in mixed finite element methods. We consider the Hermann-Johnson scheme for biharmonic equation. The main idea is to construct a perturbed problem with two parameters which play roles of penalties. The perturbed problem is built by the replacement of essential conditions on the interface in the mixed variational statement with natural conditions that contain parameters. The perturbed problem is discretized by the finite element method. We estimate the norm of the difference between a solution of the discrete perturbed problem and a solution of the initial problem; the obtained estimates depend on the step and the penalties. We give recommendations for the choice of penalties depending on the step.     

同伦分析法求解非线性多孔收缩表面上黏性磁流体的流动

研究在非线性多孔收缩表面上黏性磁流体(MHD)的流动.先用相似变换简化其控制方程,然后用同伦分析法(HAM)求解该简化问题.用图表的形式对问题的相关参数进行讨论,发现在有磁流体时,收缩解存在.同时得到,在不同参数下f″(0)的解是收敛的.     

A refinement of Sharkovskii's theorem on orbit types characterized by two parameters

The so-called type problem or forcing problem is considered as a way to generalize Sharkovskii's theorem. In this paper, by focusing on certain types of orbits, we obtain a solution of the type problem, which gives a refinement of Sharkovskii's theorem on orbit types characterized by two parameters.     

Monte Carlo study of time asymptotics of the polarized radiation intensity

The parameters of time asymptotics of the polarized radiation intensity are estimated. Precision Monte Carlo estimates of these parameters are derived for finite medium layers by iterating the resolvent of the corresponding transfer operator with a given scattering matrix and by evaluating parametric time derivatives. The computations are performed for two versions of the problem: with a Rayleigh scattering matrix and an aerosol scattering matrix. It is shown that the asymptotics of the radiation intensity are affected by polarization, except for the spatially homogeneous problem, for which the results are obtained analytically.     

一类两参数非线性奇摄动边值问题解的渐近性态

本文研究了一类两参数非线性奇摄动边值问题的基本模型.利用奇摄动方法,对该问题解的结构在两个小参数相互关联的三种不同情形下作了讨论,得到了该问题的渐近解并证明了在三种情形下不同的解的结构与渐近性态.