Blade crack modeling in NREL 5-MW baseline wind turbine, modifying EdgeStff

Hello everyone.
I am working on a project about blade crack modeling in OpenFAST. I am modeling it on the NREL 5-MW baseline Onshore wind turbine. For the modeling, it is necessary to reduce the blade stiffness. For this, I am modifying the stiffness only in Edge, that is, only EdgeStff from the Blade.dat file, which is called from ElastoDyn. When I make modifications, I encounter problems in the simulations. The issue I have is that in certain sections out of the 49 in the blade parameterization file, if I change the original value (regardless of whether it is higher, lower, or extreme values), when comparing the final simulation with the healthy blade, the simulations are exactly the same. In other words, it is as if the value had not been changed, and the blade remains healthy.

  1. Do you know why this phenomenon occurs? What is the cause?

At the end of the message, I have attached capturas of the blade.dat file, where I modified the EdgStff value on line 27, corresponding to the length 1.495·10^-1 (14.95%). I have problems with this specific line, but not with the next one for example.

I found in this forum that the modification of the EdgStff values must be done simultaneously with the modification of the BLADE MODE SHAPES coefficients. That is, the most realistic modeling involves modifying both EdgeStff and the BLADE MODE SHAPES coefficients. don’t know what the relationship is between the two. I don’t know in what proportion the coefficients change depending on the change in EdgeStff. So here are my questions.

  1. What is the relationship between the two?
  2. How do I modify these coefficients?
  3. Is there any article or document that talks about this topic?

There is a variable, CalcBMode, which does not appear in my Blade.dat file and gives me an error if I add it to my file. If I don’t want to calculate the coefficients:

  1. Should I implement this variable?
  2. How do I implement it?

Thank you all very much.

Best regards,

Borja Velázquez

Captures off the blade.dat code:

Dear @Borja.Velazquez,

Here are my responses:

1 . The distributed blade mass and stiffness specified in the ElastoDyn blade file get interpolated to the structural analysis nodes specified within ElastoDyn. In the case of the NREL 5-MW baseline wind turbine, there are many more stations in the blade file (NBlInpSt = 49) than there are analysis nodes (BldNodes = 17), so, effectively not all of the data specified in the blade file is used in the interpolation. You could always increase BldNodes (which will slow down the simulation) or reduce NblInpSt to resolve this issue.

2-4. The blade mode shapes are intrinsically tied to the distributed mass and stiffness, so, if you change one, you should change the other. You can use tools such as the old Modes or BModes software provided by NREL or other preprocessors to calculate the mode shapes. Modes and BModes have been discussed in many topics on this forum.

5-6. CalcBMode was proposed at one point, but never implemented. You cannot enable this feature.

Best regards,