ABSTRACT

This paper presents a theoretical method for calculation of dynamic loads and average ice forces on sloping structures and ships in ice of uniform thickness. The method is used for estimation of ice loads on inclined structures, resistance of ice transiting vessels and ice force distribution on ships maneuvering in level ice. The calculations are compared with results from full scale measurements.

INTRODUCTION

The interaction between a sloping structure and a floating ice sheet has been the subject of both theoretical and experimental investigations during recent years. This contact problem is of special interest because the inclination of the structure will considerably reduce the ice forces. This is due to the vertical component of the reaction, which will cause bending failure in the ice sheet at some distance from the structure. Consequently, slopedshapes are commonly used in the waterline area of offshore structures and icebreaking ships.

Based on investigations mentioned above, methods for estimation of ice loads on offshore structures and ice resistance on ships have been developed. Unfortunately, most of the theoretical models are based on the static solution of an elastic plate on an elastic foundation, although the importance of the dynamic behaviour of the ice sheet has been stated.

Varsta1 and Jeberaj et al2 have treated the dynamic interaction between a landing craft bow and an ice sheet by the finite elementmethod. The maximum ice force seems to increase with the relative velocity between the ice and the structure while the impact duration and the size of the broken ice piece decrease. When estimating the average forces acting on ships and offshore structures, all these three parameters are of equal importance.

The use of the finite element method in a general mathematical model is not very convenient. A solution to this problem is given by S?rensen 3 in his work "Interaction betweenFloating Ice Sheets and Sloping Structures", where he treats the problem analytically. The method presented in this paper is partly based on S?rensen's work mentioned above.

THEORY AND DEFINITIONS