Did you know that ... Part 2

1. Digital Imaging received this years Nobel Prize in Physics. Willard
Boyle and George Smith received their recognition for work on Charge
Couple Devices (CCD) used in range of scientific instruments including the telescope.

2. There have been many Nobel Prize awarded to people who used imaging as one of their tools of investigation

3. Hough Transform used in the detection of geometrical shapes was initially patented by Paul Hough in 1962

4. NASA Aerogel was used to collect the interstellar and comet particles. The aerogel slows the particles otherwise traveling at high velocity to a halt without heating. NASA collected images of these tracks along which the particle translated and requested help from public in determining the location of them.

5. Open shot is a free non-linear movie editor under Linux. You can clip, resize and trim movies, add transition between scenes, change speed of clips and even "Ken Burns effect".

Matlab alternatives

Matlab is a powerful programming language for scientific computing. The popularity of Matlab stems from the fact that it is a high level programming language focusing more on faster development and less on syntax. It also has many tool boxes that extend the functionality that is offered by basic Matlab on to other scientific and engineering domains. In spite of all these advantage, it comes with a price, the fact that we need to pay for purchasing, installing and maintaining it. Although the price we pay might be easily offset by the benefits, many Matlab like software are in existence and perform similar even if not the same set of functionality. In this blog, we will look at some of the alternatives. In all these alternatives, the program written to be run on Matlab can be run directly, within the constrains of functionality offered by that particular software.

FreeMat
FreeMat is a open source software released under GPL. It is available for most of the common OS like Windows, Linux and Mac. Installing the software on a Windows machine was a piece of cake. Its repertoire of functionality is large but does not have many of the toolboxes offered by Matlab.

Octave
Octave is another software available under GPL. The syntax of Octave commands are similar to Matlab (and not the same) and is also highly extensible using C, C++ and Fortran. Unlike FreeMat, Octave comes with many toolboxes for Image processing, Signal processing, Statistics etc. Installing the software on a Windows machine using cygwin is easy but installing from source on Linux machine requires expertise due to many dependencies.

Numpy and Scipy
Numpy and Scipy are Python modules that can be used to perform high level scientific computation like Matlab. Since these modules are based in python, their syntax is not similar to Matlab but due to its focus on high level programming, the syntax is generally simple. With installation of dependencies like python imaging library (PIL), we can perform image and signal processing. Scipy can also be used to perform optimization and statistics. Prebuilt binary packages are easy to install but installation from source is cumbersome due to its dependencies.

Python and Abaqus

Recently I had the opportunity to work with a student who needed to perform a Finite Element Analysis on roughly 400 files using Abaqus. Processing such large number of images using the graphical user interface would have been impractical. We were happy to learn that Abaqus has a python scripting module which could help us with the automation.

We set about writing the python program from the individual function calls given in their manuals. But considering the scope of the software and its complexity, the approach quickly became difficult. Instead, we resorted to creating "macros" and modifying it to our purpose.

Creating Macros

The macros in Abaqus lets you perform a series of operations and record them as python scripts. The scripts by default are stored in "abaqusMacros.py" with each macro recorded as a function. Since the macro was created for a particular model, we modified the names in the function " Entire_Work_Flow" to be generic so that other models can be loaded. We then added other functions that will call the function created using macro.

The other function created were "getvalues" that obtains the relavant von mises stress values from the ODB file. The main function reads each of the solid model (.sat file) in a given directory and passes the filename to the macro function. It then calls getvalues function and stores the result in a CSV file for further analysis.

To run the script, type "abaqus cae -noGUI scriptname.py".

The Entire_Work_Flow has been trimmed to show only the relevant lines that corresponds to creation of the name of parts, instance and job name.


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