Numerical and experimental study of forced heave of two-dimensional section in ice

Abstract

A two-dimensional study of a ship section forced to heave in open water and surrounded by plates representing ice have been performed. The setting is a ship moored in ice infested waters. The ice is modeled as a stiff rigid body and is not allowed to move or bend in any degrees of freedom nor modes. The distance between the ship section and ice have been varied and added mass and damping have been calculated in a frequency range including resonance. The investigation is carried out by means of model tests as well by a linear wave tank based on the boundary element method.

In the study it was found that around resonance with ice present an abrupt and steep change in added mass occurs. In the numerical results for the case with two ice-floes the maximum values for added mass it is seen that it becomes larger from b = 0.01 m before it becomes smaller after b = 0.02 m. For the experiments with the same geometric set up the maximum values show a similar trend. The maximum values for added mass shows a growing trend from b = 0.01 m and peaks at b = 0.08 m and get a smaller value for b = 0.10 m. For the case with one ice-floe  the same maximum values decrease a the ship section gets further away from the ice. The model tests show an discrepancy of when resonance occurs compared to the numerical simulation and difference in the maximum and minimum values. In general the numerical program predicts a higher added mass and damping compared to the model tests when ice is present. For the tests without ice present the numerical and experimental results correlate well.