SAMCoT - Annual Report 2015

SAMC

• ANNUAL REPORT 2015

Iceberg drift observations and iceberg towing

in broken ice

Iceberg towing in ice still has not been performed in full-

scale. Model-scale experiments on iceberg towing in ice

are represented by only one experiment in the Hamburg

Ship Model Basin (HSVA). A validation study based on these

very limited data has been run by PhD candidate Renat

Yulmetov for his numerical model of iceberg towing in ice.

The model was developed further to address the impulse-

to-force conversion and now uses a relationship between

the impact impulse and peak force measured in different

experiments. In addition, the position stabilization has been

improved by switching from the Baumgarte stabilization to

a position projection method with pseudo velocities.

The average forces when compared between the experi-

ment and simulation are in fairly good agreement. However,

they are different from the ice resistance expressed by

existing analytical estimates that has been derived for

icebergs. The main source of error is the confinement

in the experiment, which results in higher values for the

resistance. A draft of a paper has been prepared ready for

journal submission.

At the same time a deeper analysis of iceberg and ice track-

ing data from the OATRC 12/13 campaigns has been made.

The statistical velocity distributions have been obtained.

It was found that drift speed and direction distributions

are very different for objects drifting in the shear zone

compared to those in the central pack. Therefore, icebergs

and ice show different drift characteristics in different

regions.

In addition, the yawing of icebergs has been measured,

analysed andmodelled. Themodel is based on the equations

of motion for a cylinder in an unbounded fluid. Themodelling

results demonstrated good agreement with the measured

rotation. The yawing of icebergs is very important during

towing operations, because large rotations may result in

unbalanced tension in tow lines which can put the iceberg

management operation at risk. The model in this case is

directly relevant and helps to predict possible rotations. A

paper about iceberg observations off North East Greenland

has been submitted to the Ocean Engineering journal and is

now under revision. Yulmetov will defend his thesis soon.

WP5_Fig. 2: The mean ice resistance compared for the experiment, model and existing analytical approximations.

At the same time deeper analysis of iceberg and ice tracking data from OATRC’12/13 campaigns has

been made. The statistical velocity distributions have been obtained. It was found that drift speed

and direction distributions are very different for the objects drifting in the shear zone and in the

central pack. Therefore, icebergs and ice express various drift characteristics in different regions.

Figure WP5_2 The mean ice resistance compared for the

experiment, model an existing analytical approximations.

WP5_Fig. 4: Measured and simulated yaw of icebergs. Strong wind suspends the rotation caused by the rotating ocean

currents.

Renat Yulmetov is on his way towards the defense, already working on the thesis. As soon as the

validation paper is submitted and the thesis is prepared, he will apply for the defense.

Allision risk models for harsh environments

Author: Martin Hassel

Figure WP5_3 Measured and simulated yaw of icebergs. Strong wind suspends the rotation caused by the rotating ocean currents.