Water-entry and-exit of a horizontal circular cylinder

Abstract

The strongly non-linear free-surface deformations and inviscid fluid loadings which occur during the constant velocity water entry and exit of a horizontal circular cylinder are here calculated by the numerical method of Vinje and Brevig1. Comparison with the loading predicted by conventional slamming theory (here called added-mass theory) shows fair agreement in some cases. However, a wide and fascinating diversity of free-surface flows is calculated for various starting positions and values of Froude number and this precludes the use of added-mass theory in general. Interesting effects calculated by the numerical scheme are supported by photographs of experiments. For entry these effects include inflow over the top of the cylinder, cavity formation, jet formation and combinations of these. For exit the calculations predict the lifting of the water above the cylinder and subsequent formation of thin layers; the draw-down and rush-up of the free surface beneath the cylinder, the rush-up terminating in localised breaking clearly seen in the experiments; the fluid motion after complete cylinder exit; and, perhaps most interestingly, the formation of large regions of strongly negative pressure on the cylinder surface during late stages of exit which explains the occurrence of the “spontaneous” breaking of the free surface seen in experiments.