BeamDyn questions

Wind & Water Structural Analysis
1

Dear @Jason.Jonkman

I have been using BeamDyn for structural analysis of blades and have observed some phenomena. The details are as follows:

Under gravity-free conditions, applying only a RootVel to the blade results in very small deformation.

图片
图片508×289 30.4 KB
图片
图片508×289 32.4 KB

图片
图片508×289 16.1 KB

Under conditions of no rotation and no gravity, applying a distributed moment in the z-direction of the local coordinate system produces zero translational deformation in the x- and y-directions, and only a torsional deformation in the z-direction that decays over time.

图片
图片508×289 3.91 KB
图片
图片508×289 3.92 KB

图片
图片508×289 13.7 KB

However, when both a root rotational velocity and the same z-direction distributed moment are applied simultaneously, a significant periodic deformation occurs, with a period matching the rotational period.

图片
图片508×289 23.8 KB
图片
图片508×289 26.6 KB

图片
图片497×288 18.8 KB

Is the structural solution computed in the blade’s local coordinate system? If so, the externally applied loads should theoretically be transformed from the global coordinate system to the local coordinate system. However, while reviewing the code, I noticed that the SetRefFramefunction does not seem to function as expected in calculating the rotation matrix—the rotation matrix remains consistent with the settings in the input file throughout the computation, without any changes. Does this imply that the solution is actually computed in the fixed initial blade local coordinate system?

I observed that the external loads are assembled in the blade’s local coordinate system at the initial time step. What variables are affected by rotation that cause this periodic response in the results? Could it be that I haven’t identified the correct location where the load transformation takes place?

Is the rotational period observed in the deformation results due to the loads being dead loads , leading to periodic variations in the rotating local coordinate system)?

I aim to use BeamDyn to input external loads in the blade’s body-fixed coordinate system and solve for the resulting deformations. I would greatly appreciate your suggestions or guidance on how to correctly achieve this objective and how to interpret the phenomena described above.

Thank you for taking the time to read this email. I look forward to your response.

Best regards,

2

Dear @Min.Li,

Can you clarify which version of OpenFAST you are running the BeamDyn driver from? There have been many improvements and bug fixes made to BeamDyn over the years. If you are not already, I suggest upgrading to the newest version of OpenFAST (currently v4.1.2).

Are you using a BeamDyn model provided by NLR or is this a custom-made model?

Regarding your case with blade rotation without applied loads, which vector are you rotating about?

Regarding your case with blade rotation and distributed loads, are you specifying the load through the driver input file or by customization of the source code? The BeamDyn driver documentation (4.6.3. Input Files — OpenFAST v4.1.2 documentation) mentions that the loads specified through the input file do not follow the blade rotation, and summarizes how the source code can be customized for your application.

Another option to address your use case is to simulate BeamDyn using OpenFAST as the driver (with all DOFs disabled in ElastoDyn) and apply prescribed loads that follow the blade as it rotates and deflects through the Structural Control (StC) submodel of ServoDyn.

Best regards,