Advanced Solver Settings : Raft

There are times when it may be difficult to achieve convergence, particularly where the soil stiffness varies significantly over the site. Adjusting the damping and stiffness parameters may help achieve convergence.

Definition

Damping Coefficient

The damping coefficient relates to damping of the numeric solution, and is where the proportion of the old spring stiffness that is to be retained is specified. For a damping coefficient d the new stiffness will be

$$k_{i+1}= d \cdot k_i+(1-d)\frac{f}{x}$$

Initial Support Stiffness

Raft analysis needs an initial stiffness for the soil. The closer this is to the actual soil stiffness the more rapid the convergence is likely to be. At the start of the analysis an initial support stiffness is assigned to the all soil interaction nodes that do not have support stiffness explicitly defined.