Error running FAST

Hi, I am trying to generate some wind turbine blade loads using Aerodyn with geometry/structural information I generated with the PreComp-to-FAST tool in NuMad. I haven’t been able to get FAST working with my blade information yet.
I can get the CertTest examples to run correctly, and I have been gradually modifying the Test01 files. I have modified the elastodyn and blade properties files, and now I’m modifying the aerodyn file. Everything was ok up until the point that I changed the blade geometry information in the aerodyn file. I am getting the following error:

FAST_InitializeAll:CheckRComp: TipRadius must be equal to HubRadius + SUM( P%Blade%DR(:slight_smile: ).

I am assuming that TipRadius and HubRadius refer to TipRad and HubRad from the aerodyn file, and that SUM( P%Blade%DR(:slight_smile: ) is the sum of the DRNodes values in the aerodyn file. In my case I have a 30m blade with 20 equally spaced elements of 1.5m length each. HubRad is 1 and TipRad is 31. HubRadius (1) + (20 x 1.5) = 31, so it seems to me that everything adds up. I checked this interpretation against the Test01 example, and it all seems consistent to me.

I would be grateful if someone would help me figure out what is going on. I thought there might be a different TipRadius and HubRadius in another input somewhere, but I can’t find anything.
I haven’t changed the airfoil data or wind files yet, but I can’t see any relevant parameters in those files that would be causing this problem.

Dear Rosemary,

Actually, TipRad and HubRad in FAST v8.10 are specified in the ElastoDyn primary input file, not AeroDyn. Your question is actually one from our FAQ–see the answer here:

Best regards,

Thanks for getting back to me so quickly Jason. Yes, you’re right I meant that those two variables are in my Elastodyn file, not Aerodyn. Sorry about that little mistake.
But the problem I’m having is not with the spacing, as far as I can tell. I did have that problem at first because originally my segments were not equally spaced. But I adjusted the spacing and stopped getting that message. I am now using a blade model with equally spaced segments just to make extra sure that that is not what is causing my problem.

So I currently have a 1m hub radius, then the first segment goes from 1m to 2.5m with the node at the centre: RNode is 1.75m. The subsequent segments/ nodes are at 1.5m intervals (3.25, 4.75, … 30.25). DRnodes in each case is 1.5m. In the elastodyn file, TipRad is 31 and HubRad is 1.

My error message is:
TipRadius must be equal to HubRadius + SUM( P%Blade%DR(:slight_smile: ).

I don’t see how that FAQ discussion about node spacing will help me to fix my problem, unless I am totally misunderstanding the FAQ and your response (which is possible). Could you provide any further guidance?


Dear Rosemary,

I agree with your approach according to your description–there should not be a problem in the case you describe. Have you double checked each entry in RNodes and DRNodes? Have you tried running your model through a debugger (requires a compiler) to identify the problem? Please upload your FAST input files so that we can take a quick look to.

Best regards,

Hi again, thanks for confirming my approach was correct. I started over from scratch with my aerodyn file and now it is working. Still no idea what was wrong in the original file as I just pasted the same values in again from my spreadsheet, but now it is all working so that’s the main thing.
Thanks a lot for your help,

Hi Jason,

I have a similar problem (same error: TipRadius must be equal to hubradius + SUM< P%Blade%DR<:> >) however the blade nodes are not equally distributed.
My blade length is 73.5m with 1.5m hub radius.
So Tiprad=73.5 and Hubrad=1.5
My distribution is the following:
RNodes AeroTwst DRNodes Chord NFoil PrnElm
4.32 13.308 5.6400 3.542 1 NOPRINT
8.64 13.308 3.0000 3.854 1 NOPRINT
12.96 13.308 5.6400 4.167 2 NOPRINT
17.28 13.308 3.0000 4.557 3 NOPRINT
21.6 11.480 5.6400 4.652 4 NOPRINT
25.92 10.162 3.0000 4.458 4 NOPRINT
30.24 9.011 5.6400 4.249 5 NOPRINT
34.56 7.795 3.0000 4.007 6 NOPRINT
38.88 6.544 5.6400 3.748 6 NOPRINT
43.20 5.361 3.0000 3.502 7 NOPRINT
47.52 4.188 5.6400 3.256 7 NOPRINT
51.84 3.125 3.0000 3.010 8 NOPRINT
56.16 2.319 5.6400 2.764 8 NOPRINT
60.48 1.526 3.0000 2.518 8 NOPRINT
64.8 0.863 5.6400 2.313 8 NOPRINT
69.12 0.370 3.0000 2.086 8 NOPRINT
73.5 0.106 5.7600 1.419 8 NOPRINT

What does the error message exactly mean?


Dear Kan,

The error means that the sum of all element lengths must equal the total blade length. I haven’t checked all of your data, but I see that the location of the most-outboard node is at the blade tip (73.5 m), which cannot be correct because the node locations must be at the element centers and the most-outboard element has a length of 5.76 m. See the FAQ linked above for more information.

Best regards,