## So what’s out there again?

I always get confused with the quantity of file types there are. FreeCAD, Salome, Code_Aster, Salome Meca, Calculix, Elmer, Gmsh, NetGen, ParaView, Python, OpenFOAM, … So how can one understand how each of these work and connect to each other?

We divide the file types in 5 categories:
• Geometry
• Mesh / Model
• Boundary Conditions + Model
• Solver
• Solution

Since these softwares can do a mixture of these 5 elements it’s not that easy to keep up with so many software and so many interconnections.

• Gemetry
○ Salome
○ Salome Meca
○ Gmsh
○ Elmer

• Mesh/Model
○ Salome
○ Salome Meca
○ Gmsh
○ NetGen
○ Elmer

• Boundary Conditions
○ Salome-Meca
○ Gmsh
○ Elmer

• Solver
○ Code_Aster
○ Calculix
○ OpenFOAM
○ Elmer

• Solution
○ Salome
○ Salome Meca
○ ParaViewer
○ Elmer

## Straight leg seat design for a bit of fun

Remembering when I was small, where i played countless hours with lego. Built many interesting constructions and tested the strength of many designs. That was a form of modeling the behaviour of a bridge, house or any structural  analysis that I could think of at that time. We all model things every day since we need to live in this world and figure out even if very basically the behaviour of objects. Think that when you hold an object you use the right force to hold it. Some how we know exactly the necessary configuration to execute physical task even without any though what so ever. When we look at a design and it challenges our notation that it will work it is because our underlaying protective system already is calculating and giving us feedback that it is dangerous to use. However this feeling can be wrong and the structure can be very safe, however most of the time our body is wright :).

I tested two designs on the simple table to understand what would happen.

This design present complete load transfer to the legs. The connection between table and leg is compress. Very little to none torsion is present. This design looks very stable, simple and is the classic, maybe the only simpler alternative is to use a solid cylinder instead, but that would make the seat very heavy. This design probably will hold as much as what the material used (wood, iron) can handle.

Comparing one design with another we can see that the behaviour to pressure  is completely different. The straight legs approach is stronger and would deal better with increased weight on top.

## Why NetGen Why!!

This time around I am presenting a alternative mesher to gmsh. The application is called NGSolve/NetGen it’s installable both in Mac and Windows which made me very happy at the beginning. Afterwards I opened a step file with no issues and generated a default mesh (on the windows version).

I really liked the visual display and the mesh quality. This is a default mesh.

The close up rendering mesh shows good image detail and the mesh elements geometry look more uniform and the circular shape looks well represented through the mesh.

At a first view the mesh seems much better compared to gmsh. There is however a problem. I could not open step and iges files through my mac. This was a frustration…. It seems that the windows version already has a binary file for open cascade which is the library that allows the NetGen software to understand these formats. On the other hand there is no easy way to install the open cascade library on a mac neither it seems to have been tested in detail with netgen.

This is a big frustration point for me.

## Free simulation package Gmsh

Free simulation package Gmsh – Geometry – Mesh – Result

I have posted previously a list with many comercial simulation packages. These packages have numerous features, are very robust and have active development, however they are expensive and their source code is closed. A free alternative is growing day by day, although the user interface isn’t as user friendly and are feature reach as comercial packages they allow for some level of calculations or the same but with an added patience requirement to understand how they work. Many packages developed so far tend to solve individually each simulation requirement from geometry creation to mesh generation, a solver to calculate results and finally a display environment to view the calculated results. Gmsh tries to combine all in one in order to work in a similar fashion as Ansys APDL or LSPrePost. It still has a long way to go but the ideia is there and with time the user interface will grow to be even better. Just wish it was easier to work with.

The image above is a slightly refined mesh. I did’t play much with the meshing parameters.

The good thing was that I could run it with Windows and Mac with no installing issues.