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Failure Modes
ICE ACTIONS
Interaction Geometry
Ice Features Ice Properties Limiting Mech.
Crystallography
Rubble
Temperature
Salinity
Porosity
Surface tension
Limit stress
Ridge
Rafted
Level
Limit momentum
Limit force
Single
Multi-leg
Out- of-plane shape
Water depth
Waterline shape
Creep
Bending
Buckling
Splitting
Crushing
Spalling
First/multi-year
Dimensions
Coverage
Strength
Adhesion
Compressive
Flexure
Tensile
Shearing
Material
Roughness
Iceberg
Friction
Limit splitting
Pressure/conf.
Velocity
7
SAMC
o
T • Annual report 2012
Floating Structures in Ice
Offshore drilling and production activities in ice-covered
waters date back to the 1960s, when offshore platforms
were deployed in Cook Inlet, Alaska. There, the sea
surface routinely froze for a couple of months each
winter. Gradually, this offshore drilling and produc
tion activity expanded to waters with more severe ice
conditions, such as the Beaufort Sea. The latest drilling
and production developments extend even further into
deeper waters, where floating structures are a must.
SAMCoT has a strong focus on floating structures
in ice. Its research focuses on establishing a better
understanding of the interaction processes between
structures and ice. This research includes studies and
modelling of waterline processes on the upstream side
of the structure, bending failure, ventilation and backfill
effects. Further, this research entails multibody dynam
ics and hydrodynamic effects on the interaction process.
Also, accidental collisions with ice masses are focused
upon. The work on this topic has also included friction
studies between sea ice and steel and sea ice on sea ice,
as well as ice actions on a floating jetty in moving ice.
Each of these fundamental research topics are studied
at SAMCoT based on development of novel theory,
numerical modelling, and model and full-scale data.
Ice Management and Design Philosophy
To ensure station-keeping of floating structures in
ice, whether by mooring or dynamic positioning (DP),
ice management may be needed. Ice management is
defined as the sum of all activities where the objective is
to reduce or avoid actions from any kind of ice features.
Here, the research at SAMCoT is directed towards
establishing a design philosophy for floating structures
protected by ice management, which ensures the fulfil
ment of standard design requirements without being
overly conservative.
In this context, SAMCoT researchers are exploring a
number of methods to quantify the safety of offshore
structures protected by ice management. In particu
lar, probabilistic and non-probabilistic methods (e.g.,
conventional reliability analyses and formal measures
of possibility) are being investigated. The ultimate goal is
to develop a mathematical tool capable of assisting the
concept selection for Arctic offshore field developments.
Iceberg drift and iceberg towing, especially in pack
ice, are also important research topics at SAMCoT.
Considerable amounts of full-scale data, useful for
these topics, were collected by SAMCoT researchers
during the research surveys off northeast Greenland
and in the Barents Sea. Two PhD candidates are actively
working on analysing the data, understanding the physi
cal processes and developing numerical models for
iceberg drift and towing in scattered ice.
Ice-Induced Vibrations
It is well known that bottom founded offshore structures
occasionally experience sustained ice-induced vibra
tions. This vibration causes operational problems and
may be a risk for structural safety. The ice-induced vibra
tion research at SAMCoT
concerns
developing
an understanding of the
processes that cause
these vibrations. From
these data, it should be
possible to generate
designs that mitigate
these problems.
In 2011, SAMCoT perfor
med experiments in
the Hamburg Ice Basin
(HSVA)
to
provoke
ice-induced vibrations.
A major effort in 2012
was to carefully analyse
these data and use it as
one of several inputs for
Fig. 1: Major factors that affect
Ice Actions on offshore and
coastal structures.