In this chapter
you will find the modeling of the forces on the fluke, the shank and the
mooring line. Cutting theory of Miedema is still valid for the fluke part of
the anchor forces. For determining the forces on the shank and the mooring line
we will use the strip footing theory as discussed in Verruijt.
Phase 4
The soil layer
properties can be interpreted in a same way as described in phase 3. So this
way the function for G is still valid.
Forces on the anchor and mooring line
To determine the
forces on the anchor for this situation the theory as discussed in phase 3 is
valid. For the mooring line forces we will also use the Brinch Hansen theory.
Forces on the anchor
The penetration
of the mooring line causes resistance perpendicular to this line (penetration
resistance).
This effect is
noticeable in all soil conditions. The type of mooring line will determine the
value of this resistance. Think of a wire rope mooring line which penetrates
deeper (less resistance) than a chain mooring line.
During the penetration process of the anchor, the resistance increases when
depth increases, which is related to the position of the anchor.
The mooring line
penetration can be described by the following geometry:
Forces on the mooring line
With:
M= resistance on mooring line
C= Catenary force
T= Anchor pull force
When looking at
the point where the anchor becomes stable, a force and moment balance can be
made out of all the forces on the anchor and mooring line. In fact this is the
moment were the anchor reaches his maximum holding capacity.
Vertical equilibrium of forces:
Horizontal equilibrium of forces:
Moment balance to point A: