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Recent content by gantovnik

  1. gantovnik

    Fitting factor and casting factor

    I will add this description of the fitting factor from JSC 65828. Contrary to the description given by the FAA (14 CFR § 27.625 - Fitting factors), it contains a very good rationale for the fitting factors (and it is more modern than the description by Peery, D.J., Aircraft Structures...
  2. gantovnik

    Fitting factor and casting factor

    No, no! This is just an assumption about the bad supplier and two errors. I don't know if that part has geometrical defects (covered by FF) and property defects (voids) covered by CF. But these two errors could happen at the same time! And instead of applying CF=1.25 on material properties and...
  3. gantovnik

    Fitting factor and casting factor

    Thank you, guys. Of course, I know the current practice in our industry, and we use only one (largest) factor, CF. But... let's see the origin/background of these factors FF and CF: Origin of FF: "Many uncertainties exist concerning the stress distribution in fittings. Manufacturing tolerances...
  4. gantovnik

    Buckling of Composite Plates

    Try to write email to Prof. Kollar: https://scholar.google.com/citations?user=l_sYNdgAAAAJ&hl=en https://epito.bme.hu/kollar-laszlo? email: kollar.laszlo@emk.bme.hu May be, he will answer all your questions. Ask him about reference to those equations, may be, they have a paper. How do you...
  5. gantovnik

    Fitting factor and casting factor

    Follow to the discussion from Link Fitting factor FF = 1.15 In [14 CFR § 25.625 - Fitting factors] we can read. "No fitting factor need be used with respect to any bearing surface for which a larger special factor is used." Assume, I have casting factor CF=1.25, because the part is made by...
  6. gantovnik

    Example of bat file to run Nastran for every *.dat file in the current folder

    This is example of Windows bat file to run Nastran for every *.dat file in the current folder. It also calculates the total Nastran execution time. Of course, you should change path to nastran.exe. The nice thing here is that script uses variable set MyPath=%cd%, so you don't need to enter path...
  7. gantovnik

    Sign convention of CBUSH forces

    Useful link about CBUSH elements: Link
  8. gantovnik

    Torsion shear stress using patran free-body tool

    I have non-symmetrical beam cross-section, where centroid does not coincide with shear center. I extracted free-body forces and moments at the centroid: Fx,Fy,Fz,Mx,My,Mz, where Mz is torsion moment. I want to calculate torsion shear stress by the formula: fs=T*n/J, where J=(1/3)*sum^n_{i=1}b_i...
  9. gantovnik

    DOE role in optistruct MDO

    You can use DOE for selection of most significant design variables. Run DOE before optimization, evaluate your variables, and turn off some of them, because they don't have any significant effect on the solution. The size of you problem and its complexity will be reduced. Another way is to use...
  10. gantovnik

    fatigue analysis

    Now Nastran can do it :) Fatigue Analysis Integrated into MSC Nastran 2013 http://www.deskeng.com/articles/aabkmb.htm
  11. gantovnik

    How to Use the Optimization Tool

    Since you did not mention ply orientation angle, I assume that you speak about composite laminate with isotropic layers. If it is simple plate with isotropic layers you can quickly write your own code based on classical lamination theory. Why Nastran? Even Excel now include genetic algorithm.
  12. gantovnik

    Cross-sectional properties using Patran Beam Library

    I don't need hand calculation. I need automatically generated Patran report file with coordinates of all points, all moments of inertia, area, etc. I want to use this report file as an input to other code, so any hand calculation is not an option.
  13. gantovnik

    Cross-sectional properties using Patran Beam Library

    Dummy element? I try to connect two surfaces by line, and I tried to create a new surface combining two initial surfaces. It did not work. See image with two surfaces. There is a hole in the plate, and I want to get information about this cross-section. Hmmmm! Catia can find everything in this...
  14. gantovnik

    Cross-sectional properties using Patran Beam Library

    How to get cross-sectional properties (moments of inertia, area, etc) if the cross-section consists of several separate parts? I usually get cross-section properties in Patran from Beam Library using Arbitrary Shape option. But in this case (several disjoint areas) it does not work. Thank you!
  15. gantovnik

    Stress result in particular point

    Dear friends! How to get stress result in particular point inside solid (I have geometrical coordinates xyz)? Should I cut solid and use mesh seeds? It should be another way, right? Thank you! Vlad
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