Page 23 - Annual Report 2012 - SAMCoT

23 SAMCoT • Annual report 2012
tion concept and methodology for a floater in ice cou­
pled fluid-solid system.
In Tsarau’s model, a floating structure and ice pieces are
assumed to be rigid bodies with six degrees of freedom.
The fluid medium is modelled under the assumptions
of potential flow theory. A boundary element method is
employed to calculate water flow induced by the hull and
moving ice. Rigid-body equations of motion are solved
using the fourth-order Runge-Kutta integration method.
Numerical methods for FSI usually combine computa­
tional fluid dynamics (CFD) and computational struc­
tural dynamics, considering both problems together.
Regarding FSI in ice-related problems, many authors
admit the importance of the hydrodynamic effect of wa­
ter on ice and floaters dynamics, e.g. the phenomena
shown in Figs. 13 and 14.
In such situations, the motion of the floater and the ice
floe will determine the unsteady flow pattern in the vicin­
ity of the hull, accelerating the water around it and thus
increasing the added mass effect on the ice dynamics.
Some representative values of the size of the zone sur­
rounding the floater, where the fluid inertia force can be
dominant, were obtained using the developed numerical
model for a conical structure in broken ice (Fig. 15).
The implemented potential flow method provides a hy­
drodynamic coupling between all the bodies in the ice-
floater system and can be used in a wide range of practi­
cal problems related to operations in ice covered waters
for dynamic simulations and further analysis. However,
for accurate rubble transport predictions, especially
when the propeller flow is considered, the mathematical
model has to account for the viscosity effects also.
In many cases such as DP or ice washing processes,
the induced water flow is often strongly unsteady and
thus empirical formulas for the viscous drag are hardly
applicable in such cases. The current research is aimed
to overcome these difficulties in order to generalize the
approach.
Accidental Collisions with Ice Masses
Arctic conditions will challenge the limits of technology.
Accidents cannot be completely avoided and absolute
safety does not exist. The possibility of accidental col­
lision between potential ice features and ships or off­
shore installations has drawn considerable attention
since the RMS Titanic struck an iceberg and sank on
April 15th 1912.
Although the topic of iceberg/structure collision is not
novel and has been investigated by many researchers,
challenges still remain. Focus has to a large extent
been concentrated on load assessment, used with Ul­
timate Limit State (ULS) design methods.
Damage-tolerant design procedures (Accidental Limit
State, ALS) should be used to perform a safe design for
vessels with low ice classes. With a ULS approach, op­
erational conditions that minimize serious damage to
the vessel could be established.
With an ALS approach, adequate precautions against
scenarios outside of the ice class requirements can be
provided for both ships and offshore structures, i.e. en­
sure that the consequences of an accidental event does
not lead to progressive collapse or severe environmen­
tal damages.
Fig. 15. Model of a conical floater in a randomly generated
ice field.