Coupling of a Boundary Element Method With a Boundary Layer Method for Accurate Rudder Force Calculation Within the Early Design Stage

During the early design stage, it is essential to produce quick and reliable results. Regarding the calculation of forces acting on a rudder in the propeller slipstream, potential flow solvers are often used for this purpose due to their low computational effort. The drawback of these solvers is that viscous effects as drag or flow separation cannot be calculated. To overcome this drawback, the coupling of an inviscid three dimensional boundary element method with a viscous two dimensional boundary layer method is presented. The inflow from the propeller and the propeller rudder interaction is calculated using a lifting line approach. The inviscid calculation of the rudder forces is done with a boundary element method and the viscous rudder forces are calculated with the boundary layer method. Two different approaches are presented for the coupling. The results calculated with the implemented methods are compared to reverse open water model tests.

Оscillations of a three-layer viscous fluid in a stationary tank

Due to the continued research into chemistry, biology, pharmaceutics and rocket space technology, interest in the study of the dynamics of layered fluids has increased significantly. The paper focuses on oscillations of a three-layer viscous fluid, gives the formulation of the viscous fluid free oscillations problem. Within the research, we determined natural frequencies and damping coefficients of oscillations of the three-layer viscous fluid in a cylindrical vessel by means of the boundary layer method and a mechanical analog. Oscillations of the three-layer viscous fluid were considered as joint oscillations of two partial hydrodynamic systems, one of which corresponds to oscillations of the upper and middle viscous fluids, and the other one - to oscillations of the middle and lower fluids. Then, we determined the coefficients of viscous resistance in partial hydrodynamic systems of a two-layer viscous fluid. Using the mechanical analog of oscillations of the three-layer liquid, we derived the characteristic equation for determining natural frequencies of the hydrodynamic system under consideration. Next, we calculated the dependency of natural frequencies and liquid-liquid interface damping coefficients on the height of the middle layer and the density of the upper fluid. Finally, we analyzed and compared theoretical calculations with the results obtained by other researchers and experimental investigation. The paper gives the results of experimental studies of oscillations of the three-layer fluid in a stationary cylindrical tank.