ABSTRACT

Regarding the development of offshore natural gas field near Sakhaltn Island which is an ice-infested area, in this paper the design ice load and dynamic responses of a slender Arctic structure upon continuous ice movement are studied. A simpltfied ice-structure interaction model for the system of slender Arctic offshore structure and drifting ice floe is proposed. The nonlinear interaction model incorporates the floating ice features such as crushing strength, thickness, incoming velocity of ice floes. Crushing after a certain elastic deformation is assumed as a primary failure mechanism at the contact zone between semi-infinite level ice edge and the face of structure. Interaction forces are calculated using a modified Korzhavin's equation and a computer program based on two-dimensional finite difference numerical scheme is developed. For verification of the numerical model, calculation is performed for one of the Baltic Sea channel markers whose response patterns were previously observed.

INTRODUCTION

Unlike the ordinary sea conditions where waves and winds are the primary sources of environmental load, ice force is the most important external load for designing offshore structures to be used in ice-covered sea. Hence it is necessary to accurately evaluate the design ice load on Arctic offshore structures with sufficient safety and economic advantage. The primary topic in ice engineering may be an estimation of the maximum ice forces, but sometimes this is not sufficient. In fact, offshore structures in ice-covered sea need to resist dynamic as well as static interaction with surrounding ice features. In the dynamic analysis. ice force has to be described at all instants of interaction. Ice is an extraordinary material which exhibit brittle as well as ductile behaviors at various conditions. Indentation tests show that ice fails in several different modes, such as creep, crushing or crack formation, depending on the loading rate, ice thickness and indentor width. For all these failure modes, ice-induced vibrations have been observed for different types of structures.

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