2000 , Volume 5, № 3, p.21-28

Within the framework of the nonlinear theory the initially-boundary problem about periodic oscillations of the circular cylinder in three-layer fluid is considered. A liquid in each stratum is ideal, incompressible, heavy and homogeneous. The cylinder is completely located in a low layer. The system of integro-differential equations of a problem is obtained, expressing kinematic and dynamic conditions on the interface of liquid mediums, and also condition of equality to zero of a velocity normal component in points of a contour. These equations contain unknown function, that appropriate to intensities of vortex sheets, located along the liquid boundaries, and sources, simulating contour. The solution of given system is based on two iterative processes, one of which is connected to an integration on time under the fifth order Runge-Kutta-Fehlberg scheme, and other - with a solution of a system of the linear algebraic equations, obtained by discretization of integral equations on each time step with the help of high order panel method. For a diminution of the computing costs, caused by a plenty of collocation points on the boundaries, the method of areas decomposition is used. The horizontal and vertical oscillations of circular cylinder in threelayer fluid (salty, fresh water and air medium) and in a twolayer fluid (water-air medium) are considered. Outcomes of accounts of the form of the fluids interfaces and total hydrodynamic performances of circular cylinder are indicated. For parameters considered in work, essential influence of an additional stratum to performances of fluids it is not revealed.

*65N55 Multigrid methods; domain decomposition

65R20 Integral equations

76B55 Internal waves

76B70 Stratification effects in inviscid fluids