NREL OC3 Monopile Questions.

Wind & Water Structural Analysis
39

Dear @Yangyang.Li,

I’ll just clarify a couple points regarding the modeling of a monopile in OpenFAST:

  • The structural dynamics of the support structure are solved by splitting the support structure into a tower solved in ElastoDyn and the monopile solved in SubDyn. PtfmRefzt in ElastoDyn is the transition point between the two modules. In this case, the ElastoDyn platform is given zero mass (because the tower mass is represented as the tower in ElastoDyn and the monopile mass is represented in SubDyn), so, the setting of PtfmCMzt does not really matter and is simply set equal to PtfmRefzt to avoid ElastoDyn triggering an error.
  • A monopile with a deep penetration into the seabed does not have buoyancy because there is no horizontal surface area where hydrostatic water pressure may act upon. The hydrostatic pressure acting normal to the centerline of the monopile cancels out around its circumference and does not contribute to buoyancy.

Best regards,