For a typical example of a Steel suction-pile structure interacting with soil, one can define orthotropic friction that is a function of sliding distance. Check TBFIELD command in Ansys/Help for more details at, https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v192/ans_cmd/Hlp_C_TBFIELD.html?q=TBFIELD . This can be added with Command Snippet using APDL Commands in Mechanical. Above example is suitable if the user wants nonlinear relationship of force-deflection to mimic the soil interaction. On the other hand, if the Steel suction-pile is dragging on the seabed and has nonlinear relationship of coefficient of friction with respect to sliding distance, this is treated differently via TBFIELD and contact. For more details on Pile Structure and Soil modeling please refer the following link to a Technology Demonstration Guide: https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v194/ans_tec/tecsuction.html