Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Drag force of non-tabular icebergs during towing
Konstantin A. Kornishin1, Yaroslav O. Efimov1, Petr A. Tarasov1, Alexey V. Chernov2, Ivan A. Svistunov2,Igor V. Buzin2, Dmitriy V. Nikushchenko3, Dmitriy S. Khmara3, Nikita V. Tryaskin3
1R&D Department, Arctic Research Centre, Moscow, Russia
2Arctic and Antarctic Research Institute (AARI), St. Petersburg, Russia
3State Marine Technical University (SMTU), St. Petersburg, Russia

trajectory is the most cost-effective method for ensuring iceberg safety.
The main method to deflect icebergs from their original trajectory is totow them with one vessel. Depending on the size of the iceberg, thisoperation can be performed either with a synthetic rope (medium andlarge icebergs) or with a specially designed net (iceberg fragments,
small and medium icebergs). The process of iceberg towing iscomplicated by a number of features caused by the colossal mass oficebergs and different environmental conditions, correct determinationof which is impossible without experimental trials and subsequent
research. At the same time, for the correct experimental set up, it isnecessary to assess the force of water resistance to the movement of theiceberg, which primarily affects the required towing force.

ABSTRACTThe article presents analytical dependencies for calculating the water
resistance force acting on a non-tabular iceberg under tow, that dependon geometric dimensions of the iceberg and the speed of it’s movement.
During 2016-2017 iceberg towing trials in the Barents and Kara Seas
15 full-scale experiments on towing non-tabular icebergs of various
sizes were conducted in open water conditions. After further
processing, 39 pairs of values “Towing force - Iceberg speed” instationary towing regime were analyzed, with known geometricparameters of the iceberg above-water part. Based on the obtained data,
Reyonolds diagrams were constructed; the drag coefficient of icebergs
was determined by two different methods; it is shown that the main size
influencing on the resistance force of an iceberg is it’s length (thelargest linear size). As a result of the performed regression analysis,
formulas for calculating the towing force of an iceberg with a known
length and speed are proposed; these formulas are recommended
primarily for icebergs/bergy bits up to 50 thousand tons and for towing
forces and up to 1000 kN. Deviation of the obtained analyticaldependences from the quadratic law of resistance, which is usually usedin the calculations of towing of various objects, is also discussed. The
article presents hydrodynamic drag coefficients of a non-tabular
iceberg of about 1 million tons, the underwater part of which wasstudied by with an echo sounder and the shape of which can be used ascharacteristic of large non-tabular icebergs.

INTRODUCTION

According to the international classification (WMO Sea Ice
Nomenclature, 2014), icebergs are divided into the following types:
tabular, dome-shaped, sloping, pinnacled, dry-docked, blocky,
weathered or glacier bergs. At the same time, tabular icebergs areformed in the zones of the current and nearest upfloat of producing
glaciers, while other types of icebergs are the result of deformation or
destruction of tabular icebergs, or appear outside the zones of glacier
upfloat, in the process of ice crushing on their front. In this case, thedrag coefficients significantly depend on the shape of the iceberg’s
underwater part; it is possible to consider the drag coefficients oftabular (including the “tabular” and “block” types) and non-tabular(including all other types) icebergs separately. It should be noted that
the International Ice Patrol (IIP) and the Canadian Ice Service (CIS)
already use such a classification. In the IIP classification, two types oficebergs are distinguished: tabular and non-tabular, divided intosubtypes, which are considered independent in the WMO classification.

Iceberg towing is one of the technologies of safe and efficientdevelopment of offshore projects in iceberg waters that makes it
possible to change the drift trajectory of icebergs in order to prevent
their collision with offshore facilities. If it’s impossible to move theiceberg away from the offshore structure, it is necessary to either
suspend all technological operations and move the facility away fromthe work site (for mobile units), or allow the possibility of collision with
the iceberg (for fixed units). However, this scenario must be anticipatedin advance, and certainly will significantly increase the cost of thestructure. Since both of these cases are emergency and complicate theplanned realization of the offshore projects, changing the iceberg

This article deals with issues related to the experimental and model
determination of the water resistance force to the movement of nontabular icebergs; similar research on tabular icebergs is described in thearticle (Tryaskin et al., 2022). Unlike tabular icebergs, the underwater
shape of which can be estimated from the shape of the above water part,
determination of the underwater shape of non-tabular icebergs isimpossible without instrumental surveys (for example, by means ofecho sounding from a boat or by means of a specialized AUV). For
convenience of presentation and the possibility of deriving empiricaldependencies, non-tabular icebergs are divided into two groups:
weighing up to 50 thousand tons (including bergy bits and fragments)

KEY WORDS: iceberg; towing; ice defense; modelling.

1251