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Construction of complex potentials for multiply connected domain

Ivanshin Pyotr N.

Journal of Applied Analysis

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2021

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Vol. 27, nr 2

209--217

EN

The method of reduction of a Fredholm integral equation to the linear system is generalized to construction of a complex potential - an analytic function in an unbounded multiply connected domain with a simple pole at infinity which maps the domain onto a plane with horizontal slits. We consider a locally sourceless, locally irrotational flow on an arbitrary given n-connected unbounded domain with impermeable boundary. The complex potential has the form of a Cauchy integral with one linear and n logarithmic summands. The method is easily computable.

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On approximate conformal mapping of a disk and an annulus with radial and circular slits onto multiply connected domains

Ivanshin Pyotr N., Shirokova Elena A.

Journal of Applied Mathematics and Computational Mechanics

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2020

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Vol. 19, nr 2

73--84

EN

The method of boundary curve reparametrization is generalized to the case of multiply connected domains. We construct the approximate analytical conformal mapping of the unit disk with m circular slits and n-m radial slits and an annulus with (m-1) circular slits and n-m radial slits onto an arbitrary given (n+1) multiply connected finite domain with a smooth boundary. The method is based on extension of the Lichtenstein-Gershgorin equation to a multiply connected domain. The proposed method is reduced to the solution of a linear system with unknown Fourier coefficients. The approximate mapping function has the form of a Cauchy integral. Numerical examples demonstrate that the proposed method is effective in computations.

3

An approximate method for estimation of fluid motion in a lake containing islands

Klonowska-Prosnak M. E., Prosnak W. J., Cześnik P. P.

Archives of Hydro-Engineering and Environmental Mechanics

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2005

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Vol. 52, nr 4

335-349

EN

The physical phenomenon considered in the paper deals with flow in a lake, which contains one or several islands. The flow is generated by rivers, their inlets and outlets being distributed on the shoreline of the lake. The problem to be solved consists in determination of the velocity field - in the domain bounded by the shorelines of the lake and the islands. In fact, it is attempted to arrive solely at an estimation of the field. Consequently, a rather simple physical model of the phenomenon, as well as its simple mathematical description has been applied. In particular, plane, irrotational and steady flow of ideal liquid has been introduced, the inlets and outlets of the rivers being simulated by sources and sinks. Hence, the problem reduces to determination of a complex function, representing the complex velocity field, which satisfies the impermeability condition on all contours representing the shorelines, the field being generated by the singularities already mentioned. Unfortunately, the so formulated problem is "overconditioned" or "too stiff", what means that the impermeability condition on the outer contour cannot be satisfied. Nevertheless, we arrived at a simple method for circumventing this obstacle, the payoff consisting in some modification of this contour. We had this particular modification in mind, applying the word "approximate" in the title of the paper. The paper contains results - in the form of streamline patterns - for lakes containing from 1 to 3 islands. In the relevant figures the distances between the given and the modified exterior contours can be seen distinctly - allowing the reader to draw conclusions, whether the errors due to the modifications are admissible or not. Of course, it depends anyway on the point of view of the user of the results.