Hydrodynamic Stability

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 following conclusion could be drawn from the analysis:

  • The anchor provides a good stability margin. An initial disturbance with an angular pitch velocity of 0.175 rad/sec (10 º/sec) will be fully damped within a distance of 20 meters from initial drop position. A usual requirement for good penetration is to minimize yaw (or pitch) angles.
  • Hydrodynamic drag is less important at elevation less than 50 meters, but is crucial for the terminal velocity. For a 75 ton anchor, the terminal velocity is estimated to be between 32 m/sec and 35 m/sec for total drag coefficient varying from 0.7 down to 0.6, respectively