ABSTRACT:

The paper deals with the problems of offshore structure analysis subjected to cyclic ice forces. The existing estimation methods are compared. It is concluded that the process under study is defined by the conditions in the ice-structure contact zone not depending on the accepted method. The relationship of the authors to the description of ice force fluctuations is presented in the domain. The results of offshore flexible structure analysis depending on the cyclic ice force are given. A new approach to the offshore structure analysis depending on the dynamic ice force is discussed.

INTRODUCTION

The characteristic feature of offshore construction today is the large water depth of structure location. It refers both to harbor structures where the depth increase is connected, mainly, with the ship draughts up to 20 - 25 m and to offshore structures with the depth up to 350 m. These conditions and the necessity to reduce the ice and wave forces led to the construction of offshore structures with one or several pile supports at large height with relatively small cross sectional dimension. It increased the structure flexibility and in the case at cyclic nature at load caused the offshore structure vibrations. Under certain conditions this phenomenon may give rise to the considerable inertial forces which are ignored now in the offshore structure analysis (Code, 1983) or to the structure fatigue resistance. The governing equations to describe the time-dependent ice force behavior and the numerical procedure for a single mass elastic system under the cyclic loadings are given in this paper.

MATHEMATICAL MODEL OF THE ICE-STRUCTURE INTERACTION

A t present there are three main approaches to the problem at cyclic ice force actions on the behaviour at offshore structure. The third approach takes into account auto-vibrational processes in the ice-structure system.

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