Some questions about PreComp

Dear Jason,
I have encountered some doubts when using PreComp in order to find sectional properties of an own blade design for the first time. I will number them in order to make it easier for you to answer:

  1. Regarding the ply concept, as I am not a native speaker, I dont know if I understand it well. Each lamina is composed by one or more plies, which are some kind of sub laminas? (i.e. a lamina formed by 5 plies, with a thickness of ply of 1 mm will make a lamina thickness of 5 mm ?). If this is correct, I do not understand why in the sample internal structure data input file (Figure 5) in PreComp user guide, the ply number assigned to the material “balsa” (Mat_id=5) is set to 0. Wouldn`t it mean that this lamina is not existing for the program? (as nº of plies * ply thickness = 0)

2.1) With respect to the material table in the sample file (Figure 9 in PreComp user guide ), in those materials that have the same Young’s Modulus in both 1 and 2 directions (E1=E2), the classic equation of 2G(1+ν)=E does not need to be fullfilled? I found that it does not work for them.

2.2) Also regarding materials, do you have some information or reference about where the data (or commercil datasheet) was taken from? Which king of materials are the “gelcoat” and the “nexus”? As the nexus has the same moduli than the double-bias FRP with a bit lower density, I guess it is also a reinforced polimer.

  1. Do you know if the sample file layout reproduces a real blade layout, or at least, if it is consistent with real blades’ ? As I find it difficult to find information about material layouts, I have thought to calculate and average chord of the blade considered in the sample file, and scale the thickness of those FRP laminas taking into account my own blade average chord, which is a bit smaller. Do you think it will work for academic purpose, in order to calculate loads with FAST after the mechanical modelling of the blade?

Thank you very much in advance for your help.
Best regards,
Alvaro Olcoz Alonso
Public University of Navarre

I work with precomp software and I have a question
When we define a lamina in the file related to the internal structure, does that lamina contain single and dry fibers or is the resin also with it?


Hello Ali and Alvaro,

Our apologies for the 2.5-year delay Alvaro, I hope you’ve answered your doubts yourself by now. Still, it’s useful to answer your questions for future reference.

Ali: these are laminate-level properties, so the properties of the infused composite


  1. If the number of plies is zero, then the lamina has zero thickness and is not modeled by PreComp. The example in the manual is somewhat misleading, although from a coding side this can be useful to maintain the same list of laminae and corresponding ply thicknesses and simply vary with the number of plies along the stations
  2. I don’t know where these material properties come from, and they might not be 100% realistic. You can find more realistic material properties in the IEA Wind Task 37 reference wind turbines I’m also not familiar with the material “nexus”, whereas gelcoat is the material used in the external coating of the blades to protect them against UV, rain, ice, soiling, etc
  3. I’d recommend referring to the IEA Wind Task 37 reference wind turbines and disregard blade models that are 15+ years old

I hope this helps.

Best regards,
Pietro Bortolotti