A METHOD FOR BOTTOM SCANTLINGS CALCULATIONS FOR SHIPS PERFORMING ICEBREAKING IN SHALLOW WATERS

摘要

In IACS UR I "Polar Class Requirements", which has been introduced in the Rules of all Classification Societies participating in IACS, there is no special consideration for the icebreaking in shallow waters where grounding on the ice can occur. Areas where we can have this problem are rivers or the Caspian Sea, where the mean depth is about 5 meters. The Caspian Sea is an area rich in oil and in recent years several Offshore Sen ice Vessels have been built for operation in this area, under the supervision of Bureau Veritas. In this paper we investigate the influence of shallow waters on the bottom scantlings of icebreaking ships. While these ships are performing icebreaking operations in shallow waters, which are defined as less than 2 meters keel clearance, we can have grounding on pieces of ice which are trapped below the ship. Due to this, additional forces are applied to the bottom structure from the ice trapped below. During normal icebreaking (not aggressive operation) we can assume that the angle of the longitudinal inclination of the ship is not greater than 5 degrees. Taking into account the kinetic energy of the ship at the vertical direction due to grounding on the ice and applying energy and force balance on this direction, we can come to a formula which gives us the force applied to the bottom. In the energy and force balance we take into consideration the variations of the kinetic and dynamic energy of the ship, the work of buoyancy and the work due to vertical ice crushing. We can come to the same formula by applying Lagrange formulation on the vertical movement of the ship. The above formula has been introduced in Bureau Veritas Rules and can be used for the bottom scantlings calculations of ships performing icebreaking in shallow waters.