Computational Fluid Dynamics
CFD
analyses have been performed with the objective to compute anchor
performance with respect to drag, terminal velocity and hydrodynamic
stability. A finite volume technique was applied for solving the 3D
non-viscous Euler equations. This method predicts the pressure and
velocity components at any given point in the flow field surrounding
the anchor. Hence the drag force can be computed by integrating the
pressure forces acting on the anchor surface. The skin friction drag
is added by use of empirical formulas.
The numerical grid (top figure) consists of 12 structured blocks with a total of approximately one million nodes. | 
Numerical grid - CFD norway |
| Results
from the analysis are visualized by the velocity and pressure
distributions on the surface as shown in the figures (right). | 
Velocity distribution - CFD norway |
| At
the cut-off trailing edge the flow separates resulting in a
low-pressure wake. This yields a large contribution to the total drag
and may be reduced by streamlining the trailing edges and boat-tailing
the cylindrical center body or so-called shank. | 
Pressure distribution - CFD norway |
| Simulation
of the trajectory after release is presented as velocity as a
function of distance. After travelled 10m the computed velocity is
13m/sec and after 25m 18m/sec. To investigate the sensitivity of the
computed hydrodynamic drag, CD values from 0.55 to 0.75 were included i.e. a variation of ±15%
for comparison. As observed in the figure for velocity vs travel
distance, drag becomes more and more important at higher velocities (as
expected) and is crucial when determining the terminal velocity. The
terminal velocity of the anchor was estimated to 37m/sec with an
average CD equal to 0.65. |  |
| The
hydrodynamic stability of the anchor was investigated by giving the
anchor an initial angular pitch velocity of 0.175 rad/sec (10o/sec).
As observed from the bottom figure, the pitch movement will be fully
damped within a distance of 20 meters assuming a 75ton 13m long anchor.
This has been documented through the 1:3 scale tests. See the animation
under Development. |  |
