Determination of the modular elliptic function in problems of free-flow filtration

The calculated dependences in elementary functions for determining the modular elliptic function lambda(tau) =lambda(1) + i lambda(2) obtained on the basis of consecutive (six) conformal mappings of a curvilinear triangle to a complex half-plane are presented. Comparison of the values of lambda(tau) from the proposed dependences with the results of the Hamel-Gunter exact analytical solution for the boundary contour of the curvilinear triangle, i.e., the real axis of the complex half-plane, gives a very close coincidence (with the largest error of aecurrency sign1%). The use of the complex values of the function lambda(tau) for the entire internal region of the curvilinear triangle makes it possible to solve one of the most difficult problems of the theory of filtration (filtration through a rectangular dam) in the direct formulation and, for the first time, to construct the pattern of an equal filtration-rate field (the family of isotaches) over the entire internal region of the dam. In this case, the boundary values of filtration rates for special cases (along the sides and along the base of the dam) completely coincide with the results of the Masket exact analytical calculations.