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Annual Report 2016
SAMCoT
FIXED STRUCTURES IN ICE
The opening of previously ice-infested waters, the dwindling supply of non-renewable
resources and the demand for alternative sources of renewable clean energy have all contri-
buted to increased economic interest in the Arctic and its natural resources in recent years.
This increased interest is reflected in the construction of numerous types of offshore stru-
ctures, such as oil rigs and wind farms, within the Arctic and sub-Arctic Oceans including
the Baltic Sea. Sea ice is dynamic, and when driven by winds or ocean currents it can pose
a formidable hazard to these offshore structures.
If the effect of ice loads is ignored in the structural design, an ice-structure collision may
result in material failure. This poses financial risk to commercial interests in the vicinity,
as well as potential environmental risks to marine ecosystems and local communities. It is
therefore in the interest of multiple parties to maximise understanding of the mechanical
properties of sea ice and its interaction with offshore structures.
IDENTIFYING THE DYNAMIC PROPERTIES OF A STRUCTURE
Since the beginning of 2016, postdoc Torodd Nord has
worked on analysing data from the Norströmsgrund
lighthouse. The objectives of the research were twofold.
Nord aimed to assess how modern methods in operati-
onal modal analysis work for structures in ice-infested
waters and to further investigate how a system changes
during ice actions.
Operational modal analysis quantifies the dynamic
properties of a civil structure during operational condi-
tions by using response measurements. The measured
dynamic properties can be used to track differences
between the predicted behaviour of the structure (e.g.
from design) and the real behaviour. Some structures,
for example wind turbines, have installations with
operational requirements that rely on low disturbance
from the structure. If the dynamic properties of a wind
turbine structure change due to the presence of ice,
these changes must be tracked to judge whether the
turbine will be able to operate or not. Currently it is not
known for which types of ice conditions we can expect
operational modal analysis to be applicable and able to
track system changes.
For his research, Nord has used an automated
operational modal analysis routine on 190 time series of
various types of ice actions against the Norströmsgrund
lighthouse. The same methodology, now tested on the
Norströmsgrund lighthouse, was first successfully
applied to floating pontoon bridges. Nord will present
his results at the EURODYN Conference in 2017.