Deterministic and Stochastic Modeling of Water Entry and Drop of an Arbitrary Three-Dimensional Body

A reliable and accurate prediction of the motion of a body impacting the water surface and then falling through the water is of significance to the success of mine burial predictions, as it provides the necessary input on the motion of the body to the mine penetration models. Owing to the limit of understanding of the dynamic processes involved, a robust and quantitatively accurate model for water entry and drop prediction of a general three-dimensional bluff body is not available yet.

The goal of this study is to develop a robust and accurate physics-based model for predicting water entry and subsequent drop of a mine-shaped three-dimensional body. Specifically, we develop: (i) theoretical and computational predictions of the (translational and rotational) motion of a mine-shaped (bluff) object impacting the water surface at arbitrary entry velocity and angle; and (ii) a dynamical model for the simulation of the six degree-of-freedom motion of the body as it falls through the water to the bottom including the drag associated with cavitation, vortex shedding and flow separation as well as the effects due to surface waves, shallow water and currents. To properly account for the vortex shedding and flow separation effects, scaled laboratory tests are conducted to establish a data base of the drag coefficients of different mines at various velocities and orientations in the water tunnel of MIT. For validation/calibration of the water entry and drop models, we compare the models against tank and field drop tests which are conducted by the ONR mine burial prediction research program. The main output of this research is to provide the necessary deterministic/stochastic transfer functions for water entry and drop which are essential input to the stochastic mine burial prediction model.