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SAMC
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T • Annual report 2012
Fig. 30. Left: The test setup used for the novel forced vibration experiments at HSVA. An actuator was used to force the
test structure into a harmonic motion. While being pushed through the ice, ice forces were measured. Results will be
used in further analysis. Right: Example of new results obtained with the test. The added damping of the ice load was
calculated, showing to be negative over a range of velocities. This result could contain the explanation of the frequency
lock-in occurrence. More data points are needed to draw further conclusions.
VIV Analogy
In the search for a physical explanation of the observed
phenomena that occurs during ice-structure interac
tion, analogies with different fields of dynamic flow-
structure interaction have been pursued. In 2012, a
comparison of the similarity between vortex-induced-
vibrations (VIV), a phenomenon well known in the field
of fluid-structure interaction, and ice-induced vibra
tions (Fig. 29) was completed. In fluid-structure inter
action, steady-state vibrations occur at a specific range
of flow velocities for cylindrical submerged pipes. When
ice interacts with a structure, an interaction occurs that
seems to have characteristics similar to the range of
velocities during which frequency lock-in is obtained.
In the field of VIV, use has been made of forced vibration
experiments to obtain characteristic information about
interaction forces. During the large ice basin tests at
HSVA in 2011, forced vibration tests were applied for the
first time for ice-structure interaction (Fig. 30).
The results of these tests revealed new information
about the interaction process and largely contributed to
increasing the knowledge on how these types of tests
and the analogies with the VIV process could be used
to decipher the ice induced vibrations phenomenon. In
2013, the team will continue to follow this path with a
proposal for a new test campaign.
Structural and Ice Load Identification
The main activity in this topic was to study the veloc
ity effects of ice-induced vibrations based on the data
provided from the DIIV test campaign. Fig. 31 shows
the set-up. The ice force was not measured directly and
a main challenge in the analysis of the DIIV tests is to
identify the forces.
The ice force and response of the structure changed with
increasing velocity. Fig. 32 shows detailed plotting of
how the derived ice force developed and the structure’s
response in one of the tests. At certain velocities, the
forces are significantly increased. We can also observe
that the structural response frequencies change. The
horizontal red lines indicate the natural frequencies of
the structure, so that any indication of vibrations at those
frequencies could be investigated more thoroughly.