Hello,
Apologies if this issue has been dealt with before. I’m trying to model a full lattice tower all the way up to the yaw bearing with SubDyn.
In the ElastoDyn file, I have switched off the Tower’s degree’s of freedom and have moved the platform reference point to the Yaw bearing, but I don’t know how to make the tower completely disappear. When running FAST, it still tries to read in the TOWER section in the ElastoDyn file and aborts.
Also in the ElastoDyn file should the variables ‘TowerHt’ and ‘TowerBsHt’ be set to 0?
Thanks,
Anish
Dear Anish,
To model a full lattice tower up to the yaw bearing in SubDyn within FAST, you should set TowerHt, TowerBsHt, PtfmCMzt, and PtfmRefzt in ElastoDyn all equal to the height of the yaw bearing (effectively reducing the tower length to zero). You should also disable all tower DOFs in ElastoDyn (TwFADOF1 = TwFADOF2 = TwSSDOF1 = TwSSDOF2 = False). You must still include a tower file in ElastoDyn, but effectively the data specified within it will be unused.
I hope that helps.
Best regards,
Hi Jason,
Thanks for the reply. I tried that and the error I get is: “TowerBsHt must be less than TowerHt”.
(Full message is: FAST_InitializeAll:ED_Init:ED_ValidateInput:ValidatePrimaryData:TowerBsHt must be less than TowerHt.)
Anything else I could be missing here? A setting or a switch in some other file perhaps?
Hi Anish,
ElastoDyn is simply checking for possible errors in the input parameters. You can get around this error by setting TowerHt ever so slightly higher (e.g. epsilon higher) than TowerBsHt, which would make the flexible tower in ElastoDyn epsilon long. For example, if you want the yaw bearing at 90 m, you could set TowerHt = 90 and TowerBsHt = 89.9999 m, reducing the flexible tower length to 0.0001 m
Best regards,
Hi Jason,
It seems to work as I now have a new error at the ‘Internal Modal Eigenvectors’ calculation . " forrt1: severe (170): Program Exception - stack overflow ". (Additional information… Routine:MAIN__, Line:80, Source:FAST_Prog.f90…if this helps). I suspect this is due to my model, where I have members whose length is small compared to their diameter. Could this be a reason?
Anyway, as a test, I replaced the ElastoDyn Tower of the OC4Jacket with a SubDyn Tower, using the modifications discussed below and FAST seems to run, so it works. I set TowerHt epsilon higher than TowerBsHt so I didn’t have to modify PtfmCMzt and PtfmRefzt. I also had to change it in the Tower AeroDyn file.
Thanks again.
Anish
Dear Anish,
OK, I’m glad it is working.
Yes, I would guess the error you are receiving is resulting from a numerical problem in SubDyn e.g. due to the use of elements that are too small.
Best regards,