There is a lot one can imagine that can happen with a tomato. We can eat it using it to prepare a delicious meal or we can throw it as what happens in Spain on a special event “the tomatina” festival. Here the tomato is munition and we all are the targets. Basically a tomato splat party but on a huge village scale. Now more seriously dropping a tomato will yield an impact test, more known as a drop test. But how could I model this explicit behavior? Looks like an interesting subject, a drop test on a open source application. No LS-Dyna.
Also the drop test will destroy the tomato a a deformable body. These look like interesting subjects for future discussion.
Was strolling about my garden and found a wonderful flower. It looked like it was hugging the sun, trying to reach it pushing the lower petals down and the pulling the fluffy pink part up. So beautiful…
Units play a major role on any simulation software. What are units? Which units are present in specific physics problems and the various types of units that exist for the same physics are a small list of this world. Some times units can be a big headache when we want to send data from one system to another. A good example where I have struggled with this was in combining Ansys with LS-Dyna; fortunately today interchanging k files is a breeze but this was not so in the past.
Learning bit of photography gave me more sensitivity about what my eyes are seeing. The way light touches objects, involving them, bouncing back shedding a shadow giving texture and form. Is a illusion? Maybe yes. But still lighting is a pathway to our senses and mood expression. I know there are out there rendering software that intends to simulate lighting effects but maybe still lacks the warmth real light gives to photography.
When using FreeCAD 0.17 it is not that difficult to make a simulation of something pressuring a cube that is fixed to the ground. I’t a simple case where we follow the typical simulation procedure… Make drawing, define boundary conditions, generate mesh, solve and get results.
I can understand that I need boundary conditions since these are the essence of the problem. But the mesh seems out of place. Or not… It is the building block of the finite element method where we describe a complex geometry into multiple small connected elements. The mesher will transform the solid in building blocks that represent the geometry we wish to study. We can use a mirrad of element types (block shapes) and the mathematical formulations they hold. NetGen should not be any different it can have tetrahedrons, hexahedrons, … and each specific nodes required…
But a question which came to my mind was how would the element shape originator and the element formulation originator work. Are they the same?Why I make this question? In freeCAD I generate a mesh with NetGen or Gmsh, however I solve it with Calculix and not the solver from NGSolve or Gmsh.
Before attempting a solution, a mesh is generated and thus the shape of the elements is defined and from the images they look tetrahedrons.
I found an answer to my questions in a paper written by one of the Authors of NetGen: Joachim Schöberl: An advancing front 2D/3D-mesh generator based on abstract rules.
The mesh is generated according to a specific sequence from a geometry. First special points are gathered on the corners of the target geometry, next edges have to be detected to then create a surface mesh that follows specific element shape rules; the final step is to create a volume mesh from the surface mesh and another specific rules necessary for element quality.
The output should be a cloud of nodes, elements and their connectivity to each other. From the paper it looks like it is purely connected to the geometry but then what connects to the differential equations we wish to solve? For instance how do I say a line is a beam? Or how do I create a body shell which basically is a shell with thickness.
Here comes the solver part. In case of calculix with NetGen used in this example all tetrahedrons should have a specific element type which will define the physics involved being structural, thermal, electric. In this case structural.
Indirectly the program gives a hint of the element type suggesting structural loads and forces in the boundary conditions or for a thermal case (not this one), the appropriate thermal boundary conditions.
As an example I am picking a Cube made in FreeCAD using NetGen mesher and Calculix solver. Before entering the solving process I generated the .inp file which contains the mesh, the boundary conditions and the material data to perform the simulation.
Somewhere in the .inp file you will find the following:
A simple apple resting on top of a table. The apple could simply be a pressure point on top of the table. But what if instead of having a rigid support the apple was resting on top of an elastic surface? Depending if we want to know the transient between oscillation (transient) to final static resting position (static structural). I know that can try my luck with FreeCAD and Calculix to study stationary problems but what about explicit methods for transient analysis?