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  1. peto24ap

    Curved (degenerated) shell elements

    Hi, I have written a code for analysis of curved shell structures using Ahmed/Irons/Zienkiewicz degenerated shell element. Now I would like to connect it to a more complex structure with beams and trusses. Degenerated shell elements have 5 degrees of freedom in node (3 translations wrt global...
  2. peto24ap

    Shell structure buckling analysis

    Many thanks for your advice. This book looks pretty interesting - only positive customer reviews on Amazon. But I would appreciate a little less expensive answer for my non-profit project :)
  3. peto24ap

    Shell structure buckling analysis

    Hello, I would like to perform a buckling analysis of a thin concrete doubly curved shell structure (architectural / structural). I am writing my own code and as a shell element I am using a combination of a plane stress triangle (for membrane forces) and DKT triangle (for plate part of the...
  4. peto24ap

    Tangent stiffness matrix

    Hi friends, I am looking for an advice. I am constructing tangent stiffness matrix of an arbitrary element for stability or nonlinear analysis. When I am transforming the stiffness matrix from local to global coordinate system, which approach is correct: (1) K = Tt * Ke * T + Kg (2) K = Tt * (...
  5. peto24ap

    FEA / FEM coding

    Thank you for you suggestions gentleman, bkal: until present day I was using Matlab, but my current work deals with form finding, nonlinear analysis and structural optimization of shell and tensile membrane structures. I need quiet strong pre-processor for that, so I decided to build a Python...
  6. peto24ap

    FEA / FEM coding

    Hi all, I am looking for some textbook, lecture notes or online resource about how to efficiently organize FEM code (from the programming point of view). I have already wrote some small FEM codes for specific problems, but this time I need to make it bigger (coupling different element types -...
  7. peto24ap

    8-node brick element load vector

    Thank you for your opinion, I also often do it like this - I analyse my problem in ceftified FEA soft, and then tune my theory. But this time I cant move from a place, no matter the results :) So I am looking for somebody experienced to discuss my problem. But still - thank you.
  8. peto24ap

    8-node brick element load vector

    Professional structural engineer, but new to FEA (self-learning)..
  9. peto24ap

    8-node brick element load vector

    Hi friends, I am trying to calculate 8-node brick element load vecotr. Top face consist from points 1-2-3-4, bottom face from points 5-6-7-8. When I am calculating self weight (body forces) I am using 8-node brick shape functions (8 shape functions). When I have a surface load perpendicular to...
  10. peto24ap

    I need some guides to write a code for solution of geometrically nonlinear problems

    Hi Dirnad, ==== For my question ==== in case of truss element F_int = Integral (Bt * sigma) dV, results in: epsilon = (u2 - u1)/L (what is correct for small displacement), but in case of large displacements (and rotations) the other directions are not negligable so you have use epsilon =...
  11. peto24ap

    I need some guides to write a code for solution of geometrically nonlinear problems

    Thank you for your reply, In the meantime I have done it exactly the way you have wrote and it converges to the exact solution. Even more complex geometries converges. I know Bathe very well, I have gone thru Finite element procedures as well as his OCR MIT lectures, but I still have a...
  12. peto24ap

    I need some guides to write a code for solution of geometrically nonlinear problems

    Hi all, I am trying to follow Ansys theory manual for Newton Raphson analysis of geometrically nonlinear problems. There is: Kt * dU = (F_int - F_ext) (1) u = u + dU (2) Kt = Ke + Kg dU = incrmenet of deformations (this is what we are looking for) F_ext = vector of applied...
  13. peto24ap

    Geometrically nonlinear analysis

    Thanks for your guess, I am updating coordinates within step (2) in stiffness matrix calculation. Kt is computed from the coordinates after the deformation from each step. I think there is a problem in calculating internal forces vector. In this step I am using tangent stiffness matrix which...
  14. peto24ap

    Geometrically nonlinear analysis

    Hi everybody, I am trying to write my own code for geometric nonlinear analysis of mixed cable, truss and beam structure. I am trying to follow Newton-Raphson procedure (non incremental) from Ansys theory manual, but I cant achieve convergence. Here is my flow: ==== Linear analysis ==== u(1)...

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