Environmental Engineering Reference
In-Depth Information
Safety coefficient can be introduced to choose the suitable mooring line or towing
device attached to the boom. The safety coefficient to be applied for a numerical
result on boom tension varies from 1.8 to 7. This large amplitude illustrates the
difficulty to quantify the uncertainty in the forcing conditions during a maritime or
coastal operation.
The reaction force along the vertical at a node belonging to
∂ˉ
c
on the sea surface
is interpreted as the local buoyancy force of the boom. Under normal boom usage,
without the observation of swimming, surfing or splashing behaviours, the vertical
reaction permits a model validation. The local reaction can be interpreted as the
linear mass density of the boom. Depending of boom size and design the linear
density varies from 4 to 12kg/m. The numerical result on the vertical reaction can
be interpreted in another way. The nodal reaction differs significantly from the boom
linear density can be interpreted as a wrong implementation of the boom under the
given conditions.
When the current velocity is higher than a threshold value of a barrier efficiency,
a dynamic recovery of oil by using a towed barrier can be proposed. Based on the
above static model a pseudo dynamic model for a towed barrier can be defined. Let us
consider a towing along a line parallel to a uniform sea current and a boat moored at
each boom end-parts. The sea water velocity along the barrier becomes the velocity
V
b
of the boat. At each time step, the equilibrium geometry is moved according
to the updated towing boat position. The Dirichlet boundary conditions are applied
to both updated end-parts of the barrier. The mooring line tensions can be used to
limit the velocity
V
b
and thus to avoid structural damage. Velocities interpolation and
composition aswell as geometry updating, duringmore general towing circumstances
with non-straight route, using two boats and under a non-uniform sea current are not
detailed here.
7.3.5 Statement
The principal drawback of the 3D membrane model usage is the difficulty to ensure
in any case the convergence of the Newton-Raphson method. Initialization with a
2D model result allows to increase the robustness of the approach. With the verti-
cal component, a principal advantage of the 3D model is to give the skirt motion
throughout boom section. As a consequence, a fluid flow study of the sea water and
oil pollutant can be based on a realistic boom geometry.
Search WWH ::
Custom Search