Experimental Study on the Resistance of a Transport Ship Navigating in Level Ice

This study investigates the resistance of a transport ship navigating in level ice by conducting a series of model tests in an ice tank at Tianjin University. The laboratory-scale model ship was mounted on a rigid carriage using a one-directional load cell and then towed through an ice sheet at different speeds. We observed the ice-breaking process at different parts of the ship and motion of the ice floes and measured the resistances under different speeds to determine the relationship between the ice-breaking process and ice resistance. The bending failure at the shoulder area was found to cause maximum resistance. Furthermore, we introduced the analytical method of Lindqvist （1989） for estimating ice resistance and then compared these calculated results with those from our model tests. The results indicate that the calculated total resistances are higher than those we determined in the model tests.

Ice Resistance Assessment for a Large Size Vessel Running in a Narrow Ice Channel Behind an Icebreaker

Large size vessels sailing in continuous level ice and broken ice of high concentration are mostly assisted by icebreakers.This is done in order to provide for fast transportation through the North Sea Route and safe operation in extreme ice conditions.Currently,new large size gas and oil carriers and container ships are being designed and built with beams much greater than the beams of existing icebreakers.At the same time,no mathematical description exists for the breaking mechanism of ice channel edges,when such vessels move under icebreaker escort.This paper suggests a simple method for assessment of the ice resistance in the case of a large ship running in an icebreaker channel;the method is based on modification of well-known semi-empirical methods for calculation of the ice resistance to ships in level and broken ice.The main feature of the proposed calculation scheme consists in that different methods are applied to estimate the ice resistance in broken ice and due to breaking of level ice edges.The combination of these methods gives a deliverable ice resistance of a large size vessel moving under icebreaker assistance in a newly made ice channel.In general,proposed method allows to define the speed of a carrier moving in an ice channel behind a modern linear icebreaker and could be applied at the ship design stage and during development of the marine transportation system.The paper also discusses the ways for further refinement of the assessment procedure suggested.

The Shielding Effect of Multi-Pile Structures on Ice Force

The shielding effect of the front pile-row on the ice force acting on the back pile-row is studied by ice force model tests. In the tests, the front pile-row is designed to model jacket legs and the back pile-row to model the water resisting pipe-phalanx within the jacket. The shielding factor for ice force corresponding to different conditions are given in this paper. The research indicates that there are many factors, including the longitudinal and lateral spacing between the front and back pile-row, ice attacking angle and the ratio of pile diameter to ice thickness, that influence the shielding effect on ice force.

Modification Method of Longitudinal Bow Structure for Ice-Strengthened Merchant Ship

:Merchant ships,which are quite different from icebreakers,usually require the light ice-strengthened bow under the floe-ice condition.According to ice-class B,requirements of China Classification Society(CCS),intermediate frames and thick hull plates are necessary for the ice belt area to resist floe-ice impact.However,due to the limited space,it is not practical to set so many intermediate longitudinals from manufacture point of view.In this paper,a modification method is proposed to solve the problem by maintaining the frame spacing and increasing the plate thickness.The aim is to make sure that the bow owns the equivalent ice-bearing capacity with the original frame spacing.At first,a bulk carrier with ice-class B is used for case study.According to the requirements of the ice class rule,a designed ice thickness is used to calculate the ice load acting on the bow area due to the impact of ice floe.Two structural models are presented to perform the strength analysis under ice load,including the out-shell plate model and the longitudinal model.The results show that increasing the plate thickness is helpful to remove the negative effect induced by enlarging the spacing of the longitudinal.A reasonable curve is presented to modify the bow for the ice-strengthened merchant ship,which shows the relationship between the increase of plate thickness and the spacing of longitudinal.Moreover,a model test of floe-ice–ship interaction is conducted to measure the dynamic ice load,based on which nonlinear dynamic FE analysis is used to verify the presented plate-thickness–longitudinal spacing curve.The results show that the proposed method can be used to improve the ice-strengthened bow structure effectively,which provides theoretical foundation to modify the requirement of CCS’s ice class rule.