Prediction of Attainable Ship Speed in Brash Ice Using Empirical Formula

Kim, Hyun Soo. (Inha Technical College) | Han, Donghwa. (Inha University) | Go, Bumsu. (Inha University) | Jeong, Seong-Yeob. (Korea Research Institute of Ships & Ocean Engineering (KRISO))

OnePetro 

ABSTRACT

While operating on the Arctic route, ships may face various issues. The ice environment, such as level ice, pre-sawn, pack ice, ice ridge and brash ice, is one of the sources of those issues. Prediction of ship resistance in brash ice is very important for safe operation. There are three ways to estimate the ice resistance: using a mathematical model, numerical simulation, and using empirical formula. In this paper, empirical formulas are used. The main aim of the study is to develop a computer program (I-RES) for prediction of attainable speed in brash ice and for ice resistance estimation. To achieve this goal, first, the brash ice environmental characteristics were analyzed. The results of I-RES were evaluated by comparing with the model test results of brash ice. The accuracy of I-RES calculations was found to be around 5%.

INTRODUCTION

As global warming reduces Arctic sea ice, Russia's Arctic resource development is taking place in earnest. In recent years, Russia has successfully built up Yamal LNG vessels. Interest in the Arctic route has been increasing as a result of the use of the Arctic Sea as a means of shipping and transportation, which saves time and money compared to the existing Suez Canal. Ships operating on the Arctic route are exposed to various ice conditions such as collision with ice and friction. For this reason, it is important to determine the engine power at the initial stage of the ship design, because the ship operating at the Arctic route has a larger hull resistance. For this purpose, research is being conducted in various ways including analytical methods and model tests. The Arctic sea routes have various types of sea ice such as brash ice, which is formed by overlapping small ice, level ice which is frozen flat in a large area, pack ice where ice pieces of different sizes float, ice ridge which is formed by overlapping ice and flat ice. Since ice resistance has a very different value depending on the type of ice, it is important to establish a method for estimating the ice resistance accordingly. The method of estimating the ice resistance includes a mathematical model, a method using a simulation, and use of empirical formulas. The method of using a mathematical model and the method using simulation has an advantage that relatively accurate results can be obtained and the result analysis is also easy. However, these methods are time-consuming to define the shape and characteristics of ships and ice. Therefore, in this study, an empirical formula that can estimate ice resistance in a short time (Kim et al., 2015) was used to estimate ice resistance. The purpose of this study is to expand the application range of ice resistance and to adopt the safe speed estimation program for the brash ice, which was first developed for the level ice. The process of determination of the attainable speed from the estimated ice resistance and calculated engine power was summarized. Engine power was determined from the characteristic curve derived from the relationship between the engine and the propeller. To verify the accuracy and validity of the results of previous studies, we compared the model test results in level ice, pre-sawn, pack ice environment with the I-RES program results. The ice resistance estimation of brash ice developed ice resistance estimation algorithm through the environmental characteristics analysis. Also, the velocity estimation algorithm of brash ice using empirical equation is verified by comparing with the model test. The I-RES program, which has been supplemented with the proven algorithm, can be used to determine the maximum engine power of a ship working at the Arctic route.