Craig Bampton Reductions

Wind & Water Computer-Aided Engineering Software Tools
1

I am attempting to run OpenFAST, version github.com/HaymanConsulting/OpenFAST.git with a floating wind turbine platform. I have modeled some members as rigid in SubDyn, and also want to perform the Craig-Bampton reductions. Is this possible?

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-Dana

2

Dear Dana,

Glosten reported the same exact error earlier today via e-mail. Are you working together? Emmanuel Branlard is communicating with Glosten about this issue via e-mail. Let’s move this conversation their.

Best regards,

3

Dear Jason,

I am working in the same topic. My goal is to study the OC4 Semi with SubDyn module on, I’ve create my own input file with the members, joints and sections properties. Apparently it seems to work, however I get the same error as Dana. How can I solve this issue?

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4

Dear Raul,

I would guess there is something incorrectly specified in your SubDyn input file. Are all joints interconnected by members? Do you have any noncantilevered joints (such as pin, universal, or ball) or any members that are not beams (such as rigid links or pretensioned cable elements)?

Best regards,

5

Dear Jason,

I have checked my SubDyn input file and all joints are interconnected by members, all the joints are cantilever and all the members are beams. Could exist conflict in one joint with two or more members?

Here are somo screenshoots of my input file. All the data I take are from the HydroDyn input file of the OC4 Semi (r-test/NRELOffshrBsline5MW_OC4DeepCwindSemi_HydroDyn.dat at main · OpenFAST/r-test · GitHub).

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Thanks for your quick reply!

6

Dear Raul,

Can you share your complete SubDyn input file?

For the member cross-sectional properties, have you set any mass exceptionally low or any stiffness exceptionally high to mimic rigid or mass-less elements that could cause numerical difficulties with the eigensolver?

I see that you’ve used NDiv = 6, which will subdivide each member, creating many beam elements. Does the problem go away if you reduce NDiv to 1?

Best regards,

7

Dear Jonkman,

I share you via private message.

Properties are the same from OC4 Semi in HydroDyn, they look logical. I use NDiv=1 and still get the same error.

Best regards,
Raúl.

8

Dear Raul,

I took a closer look at your SubDyn input file. Joint 2 is the interface joint (connected to the platform reference point in ElastoDyn). You have a member connecting joints 1 and 2, which appears to be a central column below the tower, but no other members connect to these joints. All members should be interconnected and connect to this central column.

Best regards,