Modelling, Seeing, Imagining & Photography

I believe that to understand a model we need to experience it, feel it even if it is in some very different way…. The more we experiment the more we can imagine and this is probably our way of modelling what we don’t know through our life inputs or the data we collect. Photography is all about the experimentation and imagination that make us build imaginary portraits that we materialize through a shot. My first photo experiment that I place here was the bokeh effect.

Bokeh effect
Bokeh effect

Round and creamy a mixture of color that gives a yummy taste on the nightly environment full of color and sparkling lights. Why are night shots so captivating that we forget everything around us?

4 leg chair the chalenge

Continuing my divagation through chair design and analysing the previous chair/seat post.

4 Led Table Front view
4 Led Table Front view

The purpose of this design is to serve as a support for objects. All 4 legs are tilted in a square fashion pattern at the bottom and are closer to each other near the table surface.

Tilted table
Tilted table

It’s not my intention to replicate the design of the table completely so my first simplification is the junction of the legs to the table.

4 Led Table Bottom view
4 Led Table Bottom view

Every design has it’s strengths and weaknesses. It’s purpose and function. This design is particularly sensitive to edge force since leg is supporting the table center. For a table this size the table will work comfortably with the objects we place on top, however as a seat considering an average weight of 80Kg.

So here starts the challenge:

  • Withstand 80 Kg to 120Kg
  • Use a clean, light design

Everyone probably already has an idea and the first one that comes up my mind is a straight leg chair (the simplest form of this design).

So why do we bother inventing new ideas??? The answer is that not all people are made equal. Some like simple chairs, others like edge design chairs, some others are in between and the rest probably don’t care.

Looking for over the edge designs, challenge our notion of possible or not possible. And maybe let us feel in some way better either for simplicity or because of blending in room design…

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).

NGSolve/NetGen mesh in windows
NGSolve/NetGen mesh in windows

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

NetGen Close up mesh
NetGen Close up 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.

Gmsh pin mesh
Gmsh pin mesh

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.

Mac 3D STEP viewer

For me the best so far free STEP file viewer is LSTC LSPrepost for mac. This software is a simulation pre and post processor for LS-Dyna and basically works on system. Rendering quality is great.

This software also provides a good image exporting feature to produce great quality step figures.

4 leg seat in LSPP
4 leg seat in LSPP


Improving Rendering in DS Mechanical 2.0

Some time ago I was noticing some rendering quality degradation on my screen. I noticed that maybe my customization values had change. In order to have nice graphics one just needs to change on the options menu the following.

Improving Rendering In Design Spark
Improving Rendering In Design Spark

Fracture Mechanics

I had an interesting problem to solve last week. It was concerning fatigue failure. A simple element after sucessive stress solicitations breaks apart (nothing new). It starts with a small scratch/crack and after a few million cycles and voilá the part breaks.

I initially made the traditional fatigue analysis but discovered that it is possible to go one step ahead! Using crack analysis directly in my model. Well I know this is around since at least 2014 so says Ansys.

My traditional approach involved a two way analysis where I calculated my maximum stresses for a dynamic input load measured through lab tests. After this I used standard fatigue analysis techniques to calculate the fatigue strenght. To do this I also required a wohler curve.

An alternative way is to include the crack into the finite element model and calculate what happens after a few cycles. Some software packages allow this type of calculation making our lives simpler.

I will go more indeph on fracture mechanics and fatigue in the future but for now I just want to give some good references to get started fast in this subject.

A good example of what to do, to give you a guide for your first steps on fracture mechanics can be seen in the following link.

A good example of a fatigue fracture can be seen in the Wikipedia

Dificult to find a CAD software that’s free to use

From time to time I make an effort to know what’s out there regarding simulation and CAD applications.

Free software are allways evolving and it is good practice from time to time to see what’s available out there.
This time around my quest was for a good (suficient) CAD editor and STP viewer. I found a list of many packages in the link bellow however after reviewing each of the links I got a little disapointed with what I learned.
From start major packages were disqualified: Solidworks, Catia, Siemens NX, Creo, Autodesk Inventor, Spaceclaim, Solid Edge and AutoCAD. All major software packages that I could remember off.
On the list I noticed a mixture of DWG and 2D CAD files with 3D models files like .STEP, .IGES. The 2D versions were also disqualified leaving only a few candidates.

The list shows many projects and might have something useful, though not for my purposes.

But to be honest I could not use effectivelly any of the offereings.

What I really like to use and edit CAD files:

• Free CAD (Any use)

• SketchUp (Personal use)

• Design Spark Mechanical (Any use) My preference

Unfortunatelly aside from Free CAD I could not find any good software for a mac system which is free. I wish DS Mechanical would come in Mac version.
The good thing here is that DS Mechanical is Spaceclaim but more simplified. It’s Enough to work with and produces great results. So my recomendation is to use Desgin Spark Mechanical.

• Easy to model and learn (Push and Pull interface)

• Good rendering

• Easy 2D sketch

Design Spark Mechanical
Design Spark Mechanical

Scissors, needles and little clip pins

This weekend I dedicated my time stitching. Basically me and my wife are preparing some things for my new born which is on his way. We spent some fun time building things together. One of them was a pacifier holder.


What took my attention was the purple and pink clip pins.

Clip pins
Clip pins

There are two sets of pins. The male and the female each are fixed on opposite sides. The fixation process looks like riveting but with plastic. The rivet pin is pressed and fixes the male or female part to the cloth.

Pacifier with mini clips
Pacifier with mini clips

Who is out there consulting

I was searching the web for CAE serviçes companies and made a listing of the top ranking companies in this field. I still think I am missing a few specific areas that are not in the typical mechanical engineering field. Please feal free to recomend more to my list, will add them gratefully.

• CadFem (
• Enterfea (
• Simuleon (
• PADT (
• FS Dynamics (
• CAE (
• CAELynx (
• Optimal (
• CAE Automotive GMbH (
• Dynamore (
• CAE SIM SOL ( *Bio
• BETA simulation Solutions ( *Bio
• AMET ( *Bio

The list is still incomplete…