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SAMC
o
T • Annual report 2012
Since Farid-Afshin began his PhD work in August
2012, he has studied the topic through taking relevant
courses, shaped the initial scope of his research through
meetings with industry professionals, and conducted
a literature review. This work resulted in two project
reports, which serve as the basis for the core of his
research, theoretical studies of the alternative methods
of uncertainty quantification.
In addition, he has initiated a study to address the failure
probability of a particular icemanagement operation as a
result of environmental uncertainties and ship manoeu
vrability restrictions. Failure in this context relates to
the possibility of the protected vessel (PV) or offshore
installation to drift away and fall off the managed ice
channel or to larger outgoing ice floe sizes than antici
pated. Farid-Afshin is developing a toolbox to address
these concerns. The developed toolbox builds upon
superposed kinematics of icebreakers and a global ice
plate or floes at each discretized time increment during
the total duration of an operation. However, some effort
is also put into understanding and deriving the physics
of the problem in closed form rather than sticking to the
typically more convenient numerical solution (see Fig.
24 below where trajectory and ice channel functions
ψ
and
Φ
as illustrated are derived under varying ice drift
heading and speeds, linear and nonlinear change). The
relationship for estimating the maximum outgoing floe
size of a particular ice management operation is also
deducted. The toolbox is under progress and additional
features are being incorporated.
He is additionally planning to implement a structural
analysis toolbox to evaluate the response of moored
floaters in level and broken ice. This will serve as a
vehicle to investigate various mathematical methods of
uncertainty quantification.
Modelling of Iceberg Drift and Towing
In the Arctic Ocean, collisions between and iceberg and
an offshore structure can produce extreme loads on the
impacted structure. To estimate probability of impact by
an iceberg, an accurate forecast of the iceberg’s drift is
a prerequisite. Once a collision is designated unavoid
able, operators must then decide either to disconnect
and temporarily relocate the structure or to apply physi
cal iceberg management, e.g., iceberg towing.
Considering iceberg drift models are normally highly
sensitive to weather forecasts and sea current, the
simulation results are only as reliable as the weather
forecasts themselves. The computational time is also
important, as an iceberg can travel up to 2.7 km per
hour. This relatively rapid drift means that the calcu
lation procedures to determine the path of the iceberg
must be fast enough to make a reliable prediction within
a limited time.
Iceberg drift involves many different physical processes
that make drift simulation a complex task. Bothmechan
ical and thermodynamic effects influence not only the
iceberg itself but also the ice floes and water around
it. Iceberg drift simulation is usually
based on equation of motion, which
includes several terms corresponding
to different forces acting on an iceberg
simultaneously. Such models treat
an iceberg as a point mass with zero
moment of inertia but having surface
area as a numerical property. This
simplification is useful in prediction
of an iceberg drift in open water under
1. Schematic of the trajectory of the global drifting ice plate or floes (ψ), together with the broken ice
ement channel (φ). The exterior rectangle illustrates the global boundary of the ice plate. The dashed orange
ustrates the region where the protected vessel is located and the ice management operation is established.
Fig. 24. Schematic of the trajectory of
the global drifting ice plate or floes (
ψ
),
together with the broken ice manage-
ment channel (
φ
). The exterior rectangle
illustrates the global boundary of the
ice plate. The dashed orange area illus-
trates the region where the protected
vessel is located and the ice manage-
ment operation is established.