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# Restrains for Nonlinear Spring or Axial / Lateral Friction

## Restrains for Nonlinear Spring or Axial / Lateral Friction

(OP)
To model subsea pipeline on seabed, I use restrain type +Y with given friction coefficient (Mu) (to model pipe and soil friction) and static soil stiffness (Stif) (to model pipe settlement in the seabed.) Any comment on this type of modeling is welcomed.
However, to near the model to reality for better precision I would like to model in one of the following ways:
1)Define distinct friction coefficient in axial and lateral directions
2)The lateral behavior of pipe on the soil to be the same as a nonlinear spring (i.e. lateral resistance as function of lateral displacement) (ref DNV-RP-F109 sec 3.4.6) (NB, X2 restrain is only bilinear)
Can somebody kindly advise, to model the above what restrains (or combination of restrains) can be used (i.e. restrains to define both axial and lateral friction coefficients ; and/or restrains to define nonlinear spring)?

### RE: Restrains for Nonlinear Spring or Axial / Lateral Friction

You can define "mu" when you define a restraint.  CAESAR II does not provide non-linear springs.  The closest you can come to this is the "bi-linear restraint", as you have noted.

Richard Ay

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