Hello,
I am trying to use BModes to obtain the tower mode shapes for use in Elastodyn. I am a bit confused on some of the parameters and I hope you can help answer them.
The total length of my monopile and tower is 150m. The monopile from z = 0 (mudline) to 50m (transition-piece top), which leaves the total length of my tower to be 100m. The SWL is at z = 30m.
In subdyn, I construct the monopile support structure with a 6x6 stiffness matrix representing soil-structure interaction. I then use the mass and stiffness matrices at the transition-piece obtained from subdyn in BModes (hydro_M, hydro_K) with tow_support = 1 and hub_con = 2. I am using the BModes_JJ version.
Since in elastoDyn, we just need the tower coefficients, I am not sure how to set radius, hubRad, and draft. Since I re-created the substructure in subDyn and represent that as a stiffness and mass matrix in BModes, I would assume radius would be the tower height (100m) and draft and hubRad be 0. But I would appreciate some clarity on this.
Thank you,
Jacob
Dear @Jacob.Fontaine,
When using BModes_JJ to compute tower mode shapes for an OpenFAST model with the tower in ElastoDyn and the substructure in SubDyn, the beam properties specified in BModes should characterize only the tower and the monopile should be represented through the additional tower support. Thus, for your case, I would say in BModes:
radius = 120 m (corresponding to the tower top above MSL)
hub_rad = 0 m (no extra rigid tower about the additional tower support)
draft = -20 m (corresponding to the tower base above MSL)
Best regards,
Hi Dr. Jonkman,
Thank you for your reply. Is this still the case if the entire substructure up to the tower base is modeled in subdyn and I am using the 6x6 mass and stiffness matrix from the top of the subdyn structure at z = 50m.
It is still a bit confusing to me that if I am representing the entire support structure as a 6x6 element at the turbine towers base, why the radius would be set to 120m, and the draft as -20m. I understand that radius+draft would be the total tower length, but I am still a bit confused.
I appreciate any clarification,
Jacob
Dear @Jacob.Fontaine,
Yes, my explanation assumed that the monopile is modeled in SubDyn and the tower is modeled in ElastoDyn. With the inputs I specified, BModes will understand that the tower extends from 20- to 120-m above the MSL (100-m length total) with the monopile represented by 6x6 mass and stiffness matrices located at 20-m above MSL.
Best regards,
Dr. Jonkman,
Great, thank you so much for your time.
Best,
Jacob