fcFEM integration with FEM work bench

About the development of the FEM module/workbench.

Moderator: bernd

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HarryvL
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fcFEM integration with FEM work bench

Postby HarryvL » Wed Jul 03, 2019 10:26 am

Further to https://forum.freecadweb.org/viewtopic. ... 70#p308524 here some notes for comment:

Objective
Provide practical finite element analysis capabilities within the FreeCAD framework that are easily maintained and extended.

Characteristics
  • Robust, automated solution procedures
  • Capturing the essence of structural/mechanical behavior (no more, no less)
  • Capability to perform a staged analysis, e.g.:
    1. Excavate deep cavern for water storage in a hydro-electric power generation scheme. stage 1: apply weight for initial stress state, stage 2: excavate, stage 3: apply hydrostatic load.
    2. Elastic-plastic buckling of a slender structure/component. stage 1: initial imperfection from linear buckling analysis, stage 2: elasto-plastic collapse analysis
    3. Machining of a cold-formed metal component: stage 1: elasto-plastic loading of the component, stage 2: elasto-plastic unloading of the component, stage 3: remove material.
  • Efficient specification of material and analysis control parameters from within the FC UI.
  • Output in tabulated form (by node or by integration point) and the VTK pipeline
  • Restart possible from any intermediate load steps at any stage.
  • Option for (limited) user defined post processing of results through Python calculator.
  • Modular approach (with output from any load step in any stage calculated by one module available as initial conditions for another stage in another module).
Step-wise development approach
Generic modules
  1. Analysis control input
  2. Extraction of relevant information from FC data structures for specification of finite element geometry, material and boundary conditions.
  3. Bandwidth reduction
  4. FE matrix generation
  5. FE “load vector” generation
  6. Application of FE displacement boundary conditions
  7. Decomposition of FE matrix
  8. Automatic load stepping and arc length control
  9. Eigenvalue solver
  10. On-screen analysis progress reporting
  11. Storage of (user specified) step results (including VTK) and information
Specific modules
  1. Volume elements
  2. Interface elements
  3. Shell/plate elements
  4. Material-specific stress return routines for plasticity
  5. Etc.
Basic functionality can be achieved by implementing modules 1-8, A and D.

First steps
The functionality for the basic modules is currently available in the development version of fcFEM, but requires modularizing and optimizing, as well as seamless integration with FreeCAD
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bernd
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Re: fcFEM integration with FEM work bench

Postby bernd » Fri Jul 05, 2019 10:53 pm

YEAH we should start to integrate your work in FEM :D

Basically adding a new solver which uses a binary and text input file as well as vtk output file still follows the oofem implementation. See branch https://github.com/berndhahnebach/FreeC ... s/femoofem It has a very clean commit history. The commit history is like a tutorial How to add a new solver.

Yours is a bit different. I need to run fcFEM to get an overview but I am just full of other work ATM. Since the reinforced material code has been merged it has not stooped in finding new bugs which needs to be fixed. Some where new some where years old ... Tons of fixes since June 19th https://github.com/FreeCAD/FreeCAD/comm ... dhahnebach This will slow down soon hopefully. Next will be fcFEM, means some more patience :mrgreen:
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Kunda1
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Re: fcFEM integration with FEM work bench

Postby Kunda1 » Wed Aug 14, 2019 5:55 pm

has fcFEM been integrated yet ?
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HarryvL
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Re: fcFEM integration with FEM work bench

Postby HarryvL » Thu Aug 15, 2019 4:32 am

@Kunda1, I have not made much progress since early July. Partly because I am busy with other things and partly because I have focused on the first objective mentioned above, i.e. “Robust, automated solution procedures”. My solution procedures are very robust for metal and soil plasticity, but for concrete require many small load steps (as evidenced by the examples I posted). In trying to improve this I found myself catching up on 30 years of theoretical research and coming to the conclusion that what I want is not readily available for the plasticity model I propose for concrete (Drucker Prager plasticity with tension cut off on principal stress). I am therefore developing a solution procedure of my own that is not available in literature. I think this is worth the wait, because having a robust model for concrete would add much value to the workflow already in place for concrete conceptual design.

So the answer to your question is no. It is not even clear to me yet that the proposal I describe above is the best way to go. Rather than go for a general purpose integration of fcFEM (which would mean a complete overhaul of FEM work bench), perhaps it is better to develop application-specific capabilities, like a toolkit for concrete design, a toolkit for excavation and cutting (or the reverse: staged construction and additive manufacturing), etc etc. It would mean duplication of functionality, but be more focused and less intrusive and draw on the procedures developed and tested off line in fcFEM.
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Kunda1
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Re: fcFEM integration with FEM work bench

Postby Kunda1 » Thu Aug 15, 2019 12:47 pm

HarryvL wrote:
Thu Aug 15, 2019 4:32 am
Thanks for the update!
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