Hydrodynamic interaction of a squat submarine towed by a marine vessel: Experimental investigation

Abstract

This research investigates the short-distance hydrodynamic interaction of a squat submarine towed by a marine vessel. A one-tenth scaled captive model of a 0.625-m squat submarine is constructed along with a 1.5-m Fridsma ship to perform 69 unique experiments in a 4 × 6 × 400-m3 water tank located in a towing tank center. The submarine model is a new mini-submersible, Apam-Napat SMSD type, with an L/D ratio below four. The cable is specified, regarding its weight per unit length, using a scaling method introduced in this paper. The submarine-cable-ship system is tested for nine various relative lengths and depths at short-distance conditions. In each case, drag and heave forces are recorded and presented for the vessels using resistance tests at velocities of 0.5, 1.0, and 1.5-m/s. Finally, outputs are extended to develop 2-dimensional contours to estimate the interactional forces in the full domain. The results show a critical zone behind the ship around a depth of 0.75D where ship drag forces are increased by up to 177% compared to free-running conditions. In addition, comparing the towing mechanism to self-propelling operations shows that the towing effect dominates vessel interaction, increasing the drag forces by up to 240% when the ship tows the submarine.