OFEM or Open FEM is a personal project of mine in my journey of studying FEM for structural engineering. It's a practical C++ implementation from textbook FEM derivations found in textbooks, which are purely mathematical/theoretical on their own.
OFEM doesn't reinvent the wheel. It uses the Eigen library for underlying linear algebra calculations and sparse matrices implementation. SFML, specifically SF::Graphics is used as a 2D graphics library for some basic drawing and interaction with mesh. This is to avoid getting into the hassle of learning OpenGL to write a 2D graphics engine from scratch and is not the purpose of OFEM.
Currently, I've had time to implement only 2D plane-strain 3-noded triangle elements during the COVID19 lockdown. Multi-noded plane strain elements, 2D truss, and beam elements should be added in the near future as these are relatively simple, and I need the free time to do so. Future goals include implementing 2D plate/shell elements and possibly non-linear large deformations. Also, migrating from SFML to a more mainstream option such as QTwidgets since SFML is not cross-platform friendly and feature-rich as QT.
OFEM.exe <inputfile> <outputfile>
Input files must be in format of:
<poisson's ration> <modulus of elasticity>
<number of nodes>
<node x cord> <node y cord>
<number of elements>
<first node #> <second node #> <third node #>
<number of supports>
<node #> <2 for x constraint, 3 for both x&y constraints>
<number of loads>
<node #> <load in x> <load in y>
Node numbering must start from 0, i.e., the first node has to have a 0 index when defining elements
Sample input files are included in the repository. As it is evident from input parameters, OFEM does not have a meshing algorithm. You can draw whatever polygon you'd like analyzed on AutoCAD, export nodes coordinates and lines starting x and ys and ending x and ys into excel, format them into .node and .poly files and use them as inputs for a meshing tool such as Triangles then use the output .node output and .ele files as input to OFEM after reformatting them.
This is obviously a gigantic hassle and will be changed in future releases.
The output file contains the displacement vector. The model displays the original and displaced mesh along with a color contour of element stresses in the x-direction. This is for debugging only, and you can customize whatever output you want to see written to file by looking into engine.cpp and controlling what output window displays by modifying the call to the display instance.
Use the middle mouse button to pan and zoom across the drawing space.