Clarification regarding platform Inertia (Ptfm[R,P,I]Iner) values in "ElastoDyn.dat" input file for 15MW UMaine VolturnUS-S Reference platform

Wind & Water Computer-Aided Engineering Software Tools
1

Hi,
Before posting this question I was able to read Dr. @Jason.Jonkman’s post (5MW Semisubmersible OC4 DeepWind Model) regarding the platfrom inertia values and my understanding is:

Regarding platform inertia values, platform steel, tower interface, tower and RNA shall be included except water ballast and mooring. Kindly let me know if I am missing something here.

  1. But, 15 MW UMaine semi has both fixed concrete ballast and water ballast. While calculating platform inertia values for Elastodyn.dat input, shall I include concrete ballast into this mass model?

  2. About which point these inertia values are to be calculated?

For information, I am using SOLIDWORKS for calculation of inertia values.

Kind regards,
Touhid

2

Dear @Touhidul.Islam,

Regarding (1), water ballast can be modeled in HydroDyn, but if you are modeling the floating platform as single rigid body, you could also lump the water ballast in with the other masses when defining the platform mass, center of mass, and inertias in ElastoDyn. And I would lump the concrete ballast in with the other masses when defining the platform mass, center of mass, and inertias in ElastoDyn. What matters is that the total (including any ballast) mass, center of mass, and inertias of the platform is correct within the model.

Regarding (2), the platform inertias in ElastoDyn are defined about the platform center of mass specified in ElastoDyn.

FYI: The platform is typically modeled independently from the tower and RNA, an so, the platform inertias should be specified without the tower and RNA.

Best regards,

3

Dear Dr. @Jason.Jonkman,

Many thanks for your quick reply and clarification.

Touhid