Welcome

This is my home in the virtual world, where I write about things that I want to share. The freely available software that I've written as well as some of the photographs I've taken over the years can also be found here. Please use the navigation links on the right if you are looking for something.

Recent articles

1. Why can’t a piece of software be finished?

   It is rare to see a piece of software considered “done”. The TeX typesetting engine in one of the few examples I could name. Why isn’t this more common?

2. Decoding temperature data logger files

   At work, we recently bought an EBI 40 TC-01 6-channel temperature logger. It saves data in a file with the ed3 extension. It comes with a ms-windows program to show the data and export to CSV and ms-excel.

   However, I want to be able to use the data on my FreeBSD workstation. So I have to figure out the data format of the ed3 files.

3. Building an epub from a single ReStructuredText file

   The sphinx documentation generator is a an excellent tool. It was written to generate documentation for Python, but is used by many other projects as well. Its source format is ReStructuredText.

   These webpages are written in ReStructuredText as well, and I also use this format for other bits and pieces. On occasion, I want to convert a single ReStructuredText file to an epub. This article documents how to do that.

4. Continuum properties of aluminium honeycomb

   Honeycomb cores are often used in composite structures as an alternative core material to e.g. polymeric foams or end-grain balsa.

   In FEA we want to be able to treat honeycomb as a continuous material instead of having to model individual cells. Otherwise even simple FEA models involving honeycomb would become unmanageably large.

5. Switching to SSH keys for github

   This article covers some aspects of using SSH keys with github that are left out of the original documentation on github.

   It assumes that you’ve been using HTTPS with a password for remote access to github.

6. Making ringtones with open source tools

   Most smartphones come with a range of ringtones.

   But if you don’t like those, you can make them yourself from music that you are allowed to use.

   All software that is used here is open source. They should work on all recent UNIX-like operating systems. In my case, I installed all of these programs using the FreeBSD ports system.

7. Automating CalculiX with make(1)

   The make program is a staple UNIX development tool. In this article I will show how it can be used to automate and simplify the usage of CalculiX.

   My CalculiX projects are all kept in their own directories. In each of those directories there exists a Makefile. This contains instructions for the make program.

   By default, invoking make in this directory runs the pre-processor and the solver. But there are also specific sub-commands, for example:

   • “make mesh” shows the mesh used in the FEA.
   • “make disp” shows the deformed product in the post-processor.
   • “make stress” shows the stresses in the product in the post-processor.

8. Mooney-Rivlin rubber data for CalculiX

   Recently I was looking for material data for 60 Shore A rubber for a simulation. This article describes what I found and how I transformed that to material data.

9. FEA with Calculix (3)

   This is the third installment of a series of articles about how to analyze sandwich structures with FEA.

   It might be a good idea to read part 1 and part 2 first.

   In this part we will look at a simplified simulation of a three-point bending test of a sandwich panel.

10. FEA with Calculix (2)

    This is the second part in a series how to analyse sandwich structures with FEA. The first part is here. If you haven’t done so, you should probably read that first.

    In that part we built and analyzed a sandwich where the core and skins shared nodes. We saw how that leads to incorrect stress distribution images because of nodal averaging. In this article, we’re going to fix that by using *TIE constraints.