Use Of Ice Model Basins To Simulate And Predict Full Scale Ice-Structure Interactions

Abstract

Modeling the behavior of offshore drilling platforms, ships, and other hydraulic structures in ice covered waters is relatively new in the Western Hemisphere. The recent emphasis on developing such a capability is primarily a result of oil, gas, and mineral discoveries in Alaska and the Canadian Arctic Archipelago. The need for model testing arises from the fact that model data can be obtained in a timely and economical manner as compared to the conduct of full scale experiments in the hostile arctic environment. The purpose of the paper is to present the techniques and modeling procedures for simulating the interactions of structures and ice and expanding the force data from model to full scale. A brief history of simulating ice sheets and the methods of ice model testing are reviewed including early Soviet work and current United States efforts. The characteristics of the Soviet, Finnish, German, United Kingdom, and American ice model basins are compared including a description of methods used to grow model ice sheets and control ice properties. A test facility which uses saline ice for simulating the ice cover has been in operation in the United States for over a year. Some results of icebreaking model tests from this facility and full scale icebreaking tests are discussed and compared. The comparison shows that good correlation exists between model and full scale icebreaking ship resistances when saline model ice is used. Having established a satisfactory correlation with full scale tests variations in structural design parameters to determine changes in ice resistance can be made merely by changing model shapes. Several model tests of offshore structures in ice fields are also described. A variety of different ice conditions can be modeled in the basin. They include: uniform ice sheets, pressure ridges, pressure in the ice sheet, hummock ice fields, broken ice in a channel, refrozen clogged channels, and brash ice. Modeling other than continuous icebreaking could include ramming capability of ships, dual ship operations, moving loads on the ice surface, moving vehicle just below the ice surface, dynamic response of structures due to unsteady ice forces, heat of fusion tests, and tests involving creep of long term loads on ice sheets. INTRODUCTION The recent discovery of large oil, gas, and mineral resources in Alaska and the Canadian archipelago has stimulated significant activity in the development of transportation systems and offshore structures which must be capable of continuous, reliable, and safe operation in ice covered waters. Past knowledge in these fields has been relatively scarce as demands for technology were very low-keyed and operating experience was limited. Operations in the arctic and Antarctic were conducted during summer months with few attempts to collect performance data as the impetus to expand missions and improve the technology was lacking. The impetus came after the statehood of Alaska and the desire by the United States Coast Guard in 1966 to start the development of a program to replace the aging icebreaker fleet of WIND Class icebreakers.