Page 22 - Annual Report 2012 - SAMCoT

22 SAMCoT • Annual report 2012
Fig. 12. Different submergence stages of a broken ice floe
simulation.
study, Lu stressed the importance of rubble accumu­
lation to influence the whole interaction mechanism.
These influences include ice bending failure, secondary
ice breaking and ventilation effects.
Ventilation and Backfill Effects
After the initial bending failure of level ice, the result­
ing broken ice is pushed downward below the water­
line. Conventionally, when considering this process, the
‘full ventilation’ or ‘no ventilation’ assumptions are usu­
ally considered. However, depending on the interaction
speed and ice concentration, the ventilation effect to­
gether with the so-called backfill effect compete to add
additional ice rotating load to the global ice resistance.
Lu investigated this process with the Coupled Eulerian
and Lagrangian (CEL) method (Fig. 12).
The CEL method allows simulating of the fluid’s back­
fill process during submergence of the ice floe. When
integrating the pressures on the upper and lower sur­
faces of the rotating ice floe, the net force required is
available in different speed ranges in contrast with the
traditional assumptions of ‘full ventilation’ and ‘no ven­
tilation’.
This research result highlights the importance of tak­
ing into account the backfill effect at the specified inter­
action speed range (i.e. floating structure in ice).
Ice-structure and Fluid-structure
Interaction Processes
Operations in icy waters produce different physical
processes due to the simultaneous interaction between
water with ice, hulls, risers, mooring lines, propellers,
rudders and other marine systems.
Numerical modelling of the interaction between broken­
ice and floating offshore structures requires new
and efficient methods capable of predicting both ice-
structure and fluid-structure interaction processes. In
general­, fluid-structure interaction (FSI) problems are
extremely complex and cannot be solved analytically
but often can be analyzed by means of experiments or
numerical simulations. Furthermore, state-of-the-art
FSI techniques become hardly applicable to multi-body
systems when contact interactions are involved and the
computational time is of importance. Doctoral candi­
date Andrei Tsarau is developing a numerical simula­
Fig. 13. Bird’s-eye view of the icebreaker Oden and the
transport of broken ice, indicated by yellow arrows.
Fig. 14. Subsurface transport of broken floes and rubble
along the hull.