
1990, Safetec 1999, Gucma&Przywarty 2007,
Nyman 2009). The limitations of this approach and
its weak areas were pointed out by
Michel&Winslow (1999) and Eide et al (2007),
where the main concern about historical data was
that they are not necessarily representative to today’s
accident scenarios, mostly due to changes in ship
construction or layout of the tanks.
Another method, included in the IMO guidelines
for approval of alternative tanker designs (IMO
1995, IMO 2003), contains a probabilistic-based
procedure for estimating oil outflow performance.
Probability density functions describing the location,
extent and penetration of side and bottom damage
are applied to a vessel's compartmentation,
generating the probability of occurrence and
collection of damaged compartments associated with
each possible damage incident. All oil is assumed to
outflow from tanks penetrated in collisions, whereas
outflow from bottom damage is based on pressure
balance calculations. This method sounds, however,
more reliable than the previous it still lacks the time
component. The method does not provide this vital
information on the rate of the spill nor the time
needed for tank to be released. From the
preparedness and response point of view this
parameter is essential, as the bunker spills occur in a
close vicinity of a shore and the response time is
usually very limited.
Recently a methodology has been introduced
based on the analytical calculations and time domain
simulations in order to calculate the volume of oil
outflow and outflow rate versus time (Tavakoli et al.
2008, Tavakoli et al. 2010). The method addresses
accidental cargo spills from tankers.
In this paper a method for bunker spill estimation
in spatial-temporal domain is presented. The
methodology takes into account the fluid dynamics,
the size of a tank rupture is estimated with the use of
the IMO methodology. However the damaged tank
is assumed not to be a subject to longitudinal and
transverse motions.
2 BUNKER OIL SPILL MODELING BY 3-D
CFD METHODS
The technique for oil spill modeling applied in the
paper makes use of Computational Fluid Dynamics.
Authors propose the methodology aiming at
estimation a quantity of the bunker spill, a rate of
such a spill and time for the bunker to release. The
method can contribute some information to the
probabilistic approach utilized in previously
mentioned IMO methodology. CFD based solution
seems to be useful for better understanding the oil
outflow process and its duration.
The proposed methodology has a wide range of
applications and is free of the constraints typical for
IMO statistical approach. In the paper a model for
bunker spill estimation is put forward and finally a
case study is presented, which is assumed as an
exemplary grounding accident.
The 3-dimentional simulations of oil trickling and
disseminating in water phenomenon were performed
by the use of the commercial code “Fluent”. The
software is an universal and flexible tool designed
for modeling of liquids dynamics. Most commercial
CFD codes use the finite-volume or finite-element
methods which are well suited for modeling flow
past complex geometries (Bhaskaran&Collins). The
Fluent code uses the finite-volume method (FVM),
and uses the volume of fluid (VOF) method for free
surface problems (Dongming&Pengzhi 2008, Fluent
2006).
The numerical simulations of the oil dispersing in
water phenomenon were performed for a number of
damage extend configuration (Fig.4) and tank
geometry corresponding to the relevant parameters
of the selected bulk carrier. The cross section of a
vessel and the location of a damaged double bottom
tank is shown in Figure 2.
Figure 2. The cross section of a ship and her double bottom
tank to be ruptured
In the course of the study a typical double bottom
bunker tank of an exemplary bulk carrier is
considered. The characteristic dimensions of the
damaged tank are as follows:
− length – 40.0 m;
− breadth – 9.6 m;
− double bottom height – 1.9 m.
The shape of the double bottom bunker tank is
presented in Figure 3.
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