Small angle assumption violated in SUBROUTINE

[ashwing1407]

Hello Yang,
I have 2 structures and already set the value of IndexTwrStr = 2 (id of structure) but I am getting this warning, what does it mean, and how to rectify it?
I also tried it with a smaller timestep but it's not working.

[yang7857854]

Hi, This warning comes from the subroutine of FAST in which a small angle assumption (<15 degree) is made for platform, blade and tower, etc. This warning will be output to notice the users when the actual rotation of platform exceeds 15 degrees. This warning very frequently happens for a high wind speed condition. In your case, I think, maybe the platform motion is a little bit large. But your simulation terminates normally, indicating it is fine and you can ignore this warning. Kind regards Yang | | Yang Yang Ningbo University - Associate Professor +86-0574-87604348 ***@***.*** 169 South Qixing Road, Ningbo Postcode: 315832 Web: hyxy.nbu.edu.cn/info/1178/10531.htm | ---- Replied Message ---- | From | ***@***.***> | | Date | 2/28/2023 17:25 | | To | ***@***.***> | | Cc | ***@***.***> | | Subject | [yang7857854/F2A] Small angle assumption violated in SUBROUTINE (Issue #3) | Hello Yang, I have 2 structures and already set the value of IndexTwrStr = 2 (id of structure) but I am getting this warning, what does it mean, and how to rectify it? I also tried it with a smaller timestep but it's not working. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[ashwing1407]

simulation is terminated here normally but when I open the LIS file it is not completed i.e. it initializes perfectly but after a few time steps a sudden increase in velocity and acceleration is observed and due to this the tower base forces are very very large as compared to to the normal operating condition which may be one of the reasons for small angle violation.

I have one more question. In the inputfileforFAST2AQWA.txt when CouplingFlag is set to FALSE the above error is disappeared and also the tower base loads(from .out files ) are imported to the LIS file as an external force. But in the user manual, it is mentioned for coupled analysis CouplingFlag should be set to True. So I am confused about what exactly is happening here ?

[yang7857854]

Hi, Yes, CouplingFlag must be set to true so that the platform motions will affect the aerodynamics for a coupled analysis. You need to check about the TowerIndex that has been set correctly in the inputfileforFAST2AQWA.txt. This value corresponds to the ID of the structure connecting to the tower in AQWA. I suppose you are running a simulation of wind-wave energy system. This needs to be correct. If it is another case (multi-body floater), you need to check about the platform design. Maybe the restoring is not large enough. | | Yang Yang Ningbo University - Associate Professor +86-0574-87604348 ***@***.*** 169 South Qixing Road, Ningbo Postcode: 315832 Web: hyxy.nbu.edu.cn/info/1178/10531.htm | ---- Replied Message ---- | From | ***@***.***> | | Date | 2/28/2023 23:19 | | To | ***@***.***> | | Cc | Yang ***@***.***> , ***@***.***> | | Subject | Re: [yang7857854/F2A] Small angle assumption violated in SUBROUTINE (Issue #3) | simulation is terminated here normally but when I open the LIS file it is not completed i.e. it initializes perfectly but after a few time steps a sudden increase in velocity and acceleration is observed and due to this the tower base forces are very very large as compared to to the normal operating condition which may be one of the reasons for small angle violation. I have one more question. In the inputfileforFAST2AQWA.txt when CouplingFlag is set to FALSE the above error is disappeared and also the tower base loads(from .out files ) are imported to the LIS file as an external force. But in the user manual, it is mentioned for coupled analysis CouplingFlag should be set to True. So I am confused about what exactly is happening here ? — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you commented.Message ID: ***@***.***>