A Study on the Design of Bottom Vents for the Buoyancy-control Type Ballast-free-Ship

Abstract

Ballast water discharged at each port is accounted to help spreading marine organisms and to cause damage to the marine ecological system. At present, the International Maritime Organization is preparing to take effect 'International Convention for the control and management of Ships'Ballast Water and Sediments, 2004' to solve this issue. Responding to the convention various type of ballast water treatment systems are under developing worldwide. The present ballast-free system is based on a completely different concept compared to those ballast water treatment systems. The present system utilizes the flow around a moving ship to generate water circulation inside the ship's tanks. Thus the water inside the tanks is always exchanged with the sea water outside the ship to keep the contents of water inside the tank to be identical to those of the sea water outside the ship. In order to design suitable vent shapes that can generate effective water circulation in the tanks numerical simulations and model tests were carried out to analyze the flow around the vents and estimate the increase of the ship resistance.