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• ANNUAL REPORT 2013
first to quantify uncertainties related to applications of
the model and, second to aid in defining the applicabil-
ity of the model for integrated (coupled) finite element
analysis of ice-structure interaction problems in which
local deformations of the structure and ice crushing
are considered. Improvements (modifications) to the ice
material model are also suggested. Figure 9 presents
a comparison between the calculated contact pressure
distribution (Figure 9a) and measured values (Figure
9b).
To improve the ice model, several modifications have
been suggested including the generalized version of
a strain-based, pressure-dependent (or triaxiality-
dependent) failure criterion, and a combination of a
nonlinear finite element method and smooth parti-
cle hydrodynamics (FEM-SPH) for modelling the ice
fragmentation and contact-pressure patterns (Figure
10). An interpretation of the model parameters was also
suggested.
Figure 10. Stages of FEM-SPH simulation of the ice
crushing process.
The model was validated against experimental data and
semi-empirical considerations, highlighting its accuracy
and capability of properly describing the main features
of the ice crushing process such as process pressure
area relationship and spatial pressure distribution and
energy absorption during crushing. An advantage of
the ice model is that it is rather simple and does not
require sophisticated tests for validation of the material
parameters. The model is a good candidate for predict-
ing structural damage due to ice crushing.
Operational safety of ice-reinforced vessels
around non-reinforced platforms
PhD candidate Martin Storheim is studying the opera-
tional safety of ice-reinforced vessels. Due to the
prospects of large amounts of natural resources being
available in the Arctic, there is an increasing demand for
units (platforms and ships) that are capable of operat-
ing in light to difficult ice conditions. With short Arctic
operating seasons, these platforms and vessels are
often required to operate in normal offshore areas
during the winter months in order to be cost effective.
Offshore platforms are designed with collision safety in
mind, and are required to withstand certain minimum
impact scenarios with given kinetic energy. When
using ice-reinforced vessels around non-reinforced
platforms, this will increase the overall risk level for the
platform. The probability of collision is similar to when
using non-reinforced vessels, but the consequences
of an impact can be far more severe as the relative
strength between the two impacting bodies is changed.
Non-linear FEM analysis was used to investigate this.
(a) Low type film
(b) Medium type
(c) High type film
ATION
be determined to proceedto
lue of each tested pressure
ramatically increase if pixel
ring a resolution of pressure
PRESSURE DISTRIBUTION MAP PLOTTING
Pressure value was calculated by regression equation,and only the
maximum pressure value was sorted out to plot pressure distribution
map at each step. Figure 10 shows an example of scanned image of
each type of films and pressure distribution map.
It could be seen that distributed pressure pattern between tested
pressure measurement film and pressure distribution map matches well.
(a) Low film (b) Medium film (c) High film
(d) Pressure distribution map
Figure 10. Pressure distribution map plotting
SPATIAL PRESSURE-AREA CURVE PLOTTING
There is no specific method to plot spatial pressure-area curves. Daley
(2003) plotted spatial pressure-are curves using the measurement data
from the ‘Polar Sea Trial’. The main concept of Daley’s spatial
pressure-area plot was the starting point of the curve was the largest
value from measured data, and points were added at the next large
value maintaining a continuous area.
If there is only one peak of measured pressure or force, the method
mentioned above might be the simplest ways to plot the spatial
pressure-area curve.However, if there aremultiple locations,which show
the peak pressure in pressure measurement film as indicated in Figure
Figure 9. Contour plots of the contact pressure distribution
envelope (MPa): (a) scattering of pressures from numeri-
cal simulations; (b) scattering of contact pressures from
cone crushing experiments obtained using a pressure-
measurement film.
a)
b)