BeamDyn : compute cross-sections properties with PreComp

Wind & Water Structural Analysis
1

Hello,

I am trying to model a composite sandwich blade, in order to simulate a wind turbine with FAST v8.

First, I am using the stand-alone version of BeamDyn, and Precomp as a pre-processor.

As I read in the documentation, the inputs for the cross-sections of the beam are a 6x6 stiffness matrix and a 6x6 mass matrix. I have some trouble to well fill the stiffness matrix.

Without coupling effects, the stiffness is as given in the BeamDyn manual :

Img1_StiffnessMatrixBeamdyn.jpg
Img1_StiffnessMatrixBeamdyn.jpg879×351 32.8 KB

However, the coupling effects are not negligible in my case. Precomp give me coupling terms for the cross sections :

Img2_OutputPrecomp.jpg
Img2_OutputPrecomp.jpg1022×269 65.8 KB

My questions are :

  • How to fill the stiffness matrix with these terms ?
  • Which are the effects neglicted by Precomp, compared with other preprocessor (BECAS for instance) ?
  • I read transverse shearing is neglicted. For isotropic material blade in the BeamDyn stiffness matrix, I give KShrFlp = KShrEdg = GS. Negligible shear transverse does it mean that Precomp cannot give me results for KShrFlp and KShrEdg ?

Thanks fo your help,

Damien Caous

2

Dear Damien,

Yes, PreComp neglects the effects of transverse shear (for Timoshenko-like beam models), and so, cannot compute K_ShrFlp or K_ShrEdg.

In my response, I’ve made the following nomenclature changes to what you copied from the PreComp manual:

S_f → S_fe (coupled flap-edge stiffness)
S_airfoil → S_af (couled axial-flap stiffness)
S_al → S_ae (coupled axial-edge stiffness)
S_lt → S_et (coupled edge-torsion stiffness)

Assuming you’ve chosen your blade reference axis in BeamDyn to coincide with the X_E-Y_E frame in PreComp, PreComp can be used to populate the following portion of the 6x6 stiffness matrix required by BeamDyn:

[ 0 0 0 0 0 0;
0 0 0 0 0 0;
0 0 EA S_ae S_af S_at;
0 0 S_ae EI_Edg S_fe S_et;
0 0 S_af S_fe EI_Flp S_ft;
0 0 S_at S_et S_ft GJ ]

Sectional analysis tools such as VABS, BECAS, or NuMAD/BPE can be used to populate the complete 6x6 mass and stiffness matrices needed by BeamDyn.

I hope that helps.

Best regards,