Environmental Engineering Reference
In-Depth Information
The oil effective containment is defined by a post-treatment based on the current
velocity giving the oil normal velocity to the boom. The threshold normal velocity
generally considered is 0.35m/s
v
(
s
)
·
N
(
s
)
≤
0
.
35m/s
∀
s
(7.10)
for boom efficiency to contain oils.
The oil leakage can be based on the current velocity
v
)
to the boom and the oil properties. As a consequence the oil containment efficiency
of the barrier can vary during time in term of the current velocity and the boom
geometry. We use the Lee criteria [
10
] to define the oil leakage at any curvilinear
coordinate of the domain. A Boolean value is defined by using the comparison of
v
(
s
)
the normal vector
N
(
s
(
s
)
·
N
(
s
)
with a threshold velocity depending of the oil density
ˁ
oil
, the oil-water
interfacial tension
ˁ
w
and the boom draught.
The hydrodynamic friction (tangential viscous drag) has not been considered.
This force can occur for example during the towing of a barrier. The friction is
defined by using the tangent velocity
v
˃
ow
,
to the boom. The friction coefficient
of the boundary layer of the fluid in the vicinity of the boom is not detailed here.
The non-smooth geometry of a barrier (Fig.
7.2
) and the smoother geometry of a
curtain, suggest that the friction during towing is lower for curtain than for barrier,
considering same boom draught and length.
Generally, the ratio between the boom section length
L
and the end-points distance
belongs to
(
s
)
·
T
(
s
)
[
.
,
.
]
. It permits to avoid boom over-tension. The model results
can be used for a preliminary evaluation of the barrier length installed between the
mooring points.
1
07
1
10
7.2.5 Others Notions
The boom model uses as input the velocity of the surface of the water domain. The
velocity map of the coastal water is a time-dependent function which can be solu-
tion of an hydrodynamic model. Such data may depend on local ocean-atmosphere
interaction and river-estuarine morphology of the coastal region studied.
The mooring lines connected to the boom end-points have not been studied here.
The end-points are supposed fixed. The hypothesis made permits to reduce consid-
erably the computation time, for example when the current direction reverses at high
and low tides. The drawback of this hypothesis is the avoidance of the swinging
radius prediction of the moored device.
This section presents a curvilinear numerical model for a floating boom in the
horizontal plane of the water surface. The next section will describe a 3D membrane
model including a vertical motion of the boom. The 2D result initializes the 3D fine
grid solution with a similarity to the injection used in a multi-grid V-cycle [
8
].
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