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Annual Report 2016
SAMCoT
Nord’s research at SAMCoT and his adjunct associate
professor position at the University Centre in Svalbard
(UNIS) has enabled him to supervise Niek Heijkoop, an
MSc student from Delft University of Technology (TU
Delft), who has attended courses at UNIS, Longyearbyen,
during the winter of 2016. Heijkoop focussed on resear-
ching ice that has cyclic (regular) stresses applied to it.
The goal is to figure out how ice affects built structures
(and vice versa) under the very harsh conditions
frequently encountered in the Arctic. Wind turbines in
the Baltic Sea are present-day examples of the kind
of structures Heijkoop is considering in his research.
Understanding how ice reacts around fixed and floating
installations under different conditions is key to the
work done within SAMCoT.
Ice can surround a fixed structure in the far north for
much of the year. A structure like this will vibrate, affect
the ice and in turn be affected by it. Relatively steady
wave action will cause these movements to repeat
themselves again and again.Heijkoop and Nord want to
study how such repetitive waves affect ice. The pressure
that arises in the ice from these movements can be si-
mulated in the lab at UNIS. Sea ice strength is sensitive
to how fast loads are applied. This is also the case when
applying cyclic stresses to the ice. Waves, for example,
Uniaxial cyclic testing of a small sample of saline ice at
the UNIS laboratory. These tests mimic the repeated wave
action on an ice cover. a) Cycles of stress versus strain of
a laboratory grown saline ice sample. b) Stress and strain
as a function of time for a cyclic compression test on a
vertical sample.
Cyclic behaviour of laboratory grown sea ice
are a natural load for sea ice that repeats cyclically and
with a specific frequency. It is important to examine the
strength properties of sea ice for such loads. Structures
can also move with a particular frequency as a result of
ice being forced and crushed against the structure. In
this case it helps to understand how the cyclical load
applied from the structure affects the ice strength.
The challenge is to obtain results that can be compared.
This means that the ice samples that are subjected to
pressure must be similar enough so that the results
from different tests can provide real answers. Going
outdoors to fetch a random block of ice is not sufficient.
Therefore, the researchers make their own ice in the
UNIS lab, in order for it to be as consistent as possible
from test to test.
Heijkoop’s work was also supervised by associate pro-
fessor Jeroen Hoving from TU Delft. Heijkoop’s testing
involved huge practical difficulties. David M. Cole from
the Cold Regions Research and Engineering Laboratory
of the US Army Corps of Engineers, a group with broad
experience in laboratory testing, visited Heijkoop and
Nord during the experiment and helped them solve a
number of challenges related to the tests. The results
will have direct influence on how we interpret and model
ice that is subject to periodic loads.
In the first and second quarter of 2016, PhD candidate
Hayo Hendrikse from TU Delft worked on a paper on
ice-induced vibrations and ice buckling which was pu-
blished in November the journal in Cold Regions Science
and Technology. The aim was to investigate the limiting
effect of flexural deformation and bending failure resul-
ting from buckling with respect to ice-induced vibrations.
The numerical model developed earlier for the prediction
of ice-induced vibrations has been expanded to include
this type of failure and has been shown to be applicable
to the thin ice conditions often found in model-scale
testing. This work was presented to the SAMCoT partners
at the annual PhD Scientific Seminar in May. During the
summer, Hayo finished his PhD thesis and defended it
Cum Laude in Delft on the 20th January 2017.
A summary of the results and potential for additional
work within Ice Induced Vibrations was presented to
ICE-INDUCED VIBRATIONS MODEL
SAMCoT partners at a dedicated ice-induced vibrations
workshop in Trondheim in October. Following this
workshop, and due to the relevance of Hendrikse’s work,
the SAMCoT board decided in November 2016, during the
review/approval of the Cost Time and Resources (CTRs)
plans for 2017, to allocate additional funds to continue
the work on model validation for the 2017-2019 period.
Hendrikse continued his advisory work in the SAMCoT
associated project Ice-Induced Vibrations of Offshore
Structures (IVOS) and visited HSVA in December for
experiments and discussion. At the same time Cody
Owen, an MSc student with the European Wind Energy
Master (EWEM) program in the Offshore Engineering
Track at TU Delft, started his research at the ice lab at
HSVA. Owen’s topic of research is the comparison of
cylindrical and flat vertically-sided indenters subjected
to ice-induced vibrations in the frequency lock-in regime.
He will be using data collected during the IVOS tests for
his research under the supervision of both Hendrikse
and Gesa Ziemer, the IVOS project leader. The work on
ice-induced vibrations is gaining increasing interest from
the wind power industry and new contacts have been
made with Siemens Windpower.
After his PhD defence, Hendrikse will stay on as
assistant professor in Delft and will remain part of the
SAMCoT team focussing on validation of the developed
model with existing full-scale data together with the
data obtained from the IVOS campaign.
In addition to the activities previously described, Nord
and Hendrikse are working together using Hendrikse’s
model to compare simulations with full-scale mea-
surements at the Norströmsgrund lighthouse. Nord is
dedicated to the analysis of the data that will be used for
their study throughout 2017.
a
b