Use ACDC for linearization

Wind & Water Computer-Aided Engineering Software Tools
1

Dear Jason,

I am currently using ACDC to linearize wind turbine generators and have encountered the following issues:

  1. If I use ACDC for linearization, do I first calculate the steady-state rotational speed corresponding to each wind speed in the time domain, then substitute it into ACDC, and finally perform linearization using ACDC? If so, ACDC should automatically disable GenDoF. Is my understanding of ACDC linearization correct?

2. If I skip ACDC and linearize solely by fixing wind speed and enabling GenDoF, this approach seems equally convenient compared to my described ACDC method. Where exactly does ACDC offer advantages? Is it merely for easier Campbell diagram plotting and mode shape visualization? However, modifying Campbell diagrams isn’t particularly convenient within ACDC.

3. Currently, I wish to study the aeroelastic stability of wind turbine blades. I lack familiarity with the principles of linearizing BEM theory and beam models. Could you recommend relevant research papers for my study?
Many thanks beforehand,
regards,

Translated with DeepL.com (free version)

2

Dear @Hua.Li,

Here are my responses to your questions:

  1. ACDC can compute Campbell diagrams with or without aerodynamics. Either way, you need to specify what rotor speeds to linearize about. With aerodynamics enabled, for a given turbine, you would likely already know what the steady-state rotor speed is as a function of wind speed (this information is published if you are using one of the OpenFAST reference models, such as the NREL 5-MW baseline turbine or the IEA Wind 15-MW RWT). But if not, you can compute these separately from OpenFAST at different wind speeds before running ACDC. ACDC does not require that GenDOF be disabled, and if it is enabled, ACDC will use OpenFAST’s trim solution to figure out the appropriate generator torque (below rated) or blade-pitch angle (above rated) that will give the desired rotor speed at each wind speed at the steady-state condition.
  2. ACDC automates the process of setting up the OpenFAST input files for each operating point, running OpenFAST to compute the steady state plus linearized solution, applying the multi-blade coordinate transformation (MBC3), plotting the Campbell diagram, and visualizing the mode shapes. You could certainly do some of these steps by hand, but it should be easier to use ACDC for all steps.
  3. Here are few papers that describe the linearization capability available in OpenFAST:

(Other papers have been published on the linearization of offshore capability, but you didn’t ask about that.)

Best regards,