Phase 4


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.


Fluke, shank and mooring line in the soil

 

Phase 4

 

Forces on the soil layer

 

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 fluke, shank and mooring line





















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: