Ship squat prediction using a potential flow Rankine source method

A numerical method has been developed for predicting ship squat, with the goal of providing guidance to ship operators for avoidance of grounding in shallow water. The method assumes potential flow, and computations are sufficiently fast to allow evaluation for large numbers of conditions within practical time scales. Boundary conditions on the hull, free surface, and canal walls are satisfied using planar Rankine sources on solid boundaries and point Rankine sources placed a nominal distance above the calm waterline or free surface. Four different models of the free surface boundary condition have been implemented, ranging from a nominally flat free surface to fully nonlinear. For ships with a transom stem, the influence of flow separation is modelled using a virtual stem, which extends afterward from the transom to a location with zero width. The numerical method is generally robust, except for in the vicinity of critical flow conditions. Validation with model tests has been used to develop an envelope for over-prediction of bottom clearance, which can be considered when developing guidance for ship operators.