DWSIM Development Blog

I just finished the Utilities Plugin system for DWSIM. What follows is a little Q&A to help clarify your minds:

Q) What is this plugin system?
A) It is nothing more than an interface definition for add-in classes in DWSIM. You can develop a class library in any .NET language which implements the interface, compile it as a .NET DLL and copy the generated file to the plugins folder. Next time you start DWSIM, it will detect the plugin and make it available as an utility in any simulation.

Q) What information from the simulation will be available to the plugin?
A) You will have the entire DWSIM Namespace available - since you're adding a reference to it - and also a reference to the active simulation and all its objects (streams, unit operations, settings, etc.). You will be able to, for example, instantiate new thermodynamic classes to do calculations, but nothing stops you from using your own class libraries, even if they are in separate assemblies (files).

Q) Ok, so what do I need to do to build a working plugin?
A) The basic steps to create a plugin for DWSIM are:
1 - Create a new .NET project in your IDE of choice (Visual Studio, SharpDevelop or MonoDevelop), in any .NET language;
2 - Add a reference to DWSIM.exe, and set the CopyLocal property to False (you don't have to copy the entire DWSIM application to create the plugin, just add the reference);
3 - Create a class that implements the Interface IUtilityPlugin located in the DWSIM.Interfaces Namespace;
4 - Implement the required methods;
5 - Compile your project as a .NET DLL;
6 - Copy the generated DLL to the plugins folder in the DWSIM application folder;
7 - Start DWSIM and create a new/open an existing simulation;
8 - Your plugin will be available in the "Plugins" menu item.

To test the system I created an example plugin which shows some information about itself and a list of GUIDs of the objects in the active simulation. It is really easy and all you will need is some guidance on how to use DWSIM methods and access flowsheet objects and their properties.

Download here.

If you have any suggestion for other video tutorials, please leave a message in the comments section.

/Daniel

Just minor fixes and a gift: The Lee-Kesler-Plöcker Property Package. Changelog:

- [NEW] Lee-Kesler-Plöcker Property Package
- [FIX] Fixed K-value calculation call in the Sum Rates method for solving Absorption Columns
- [FIX] Fixed IO Flash calculation in single phase region
- [FIX] Fixed Critical Point calculation with PR and SRK Equations of State
- [FIX] Fixed portions of GUI language that were not being set on the first run

Click here to go to the downloads page.

Regarding the new PP, I would like to count on your help to test it against other simulators.

I just tried a different approach to solve the single phase temperature problem with the IO flash and it seems to be faster and equally reliable as the nested loops one. I did some benchmarking and here are the results (numbers represent execution time in seconds):

	IO old	IO new	NL
cavett16	52.424	7.952	8.93
ngpu	N/D	42.124	22.94
extrdist	4.62	3.19	2.7
Single PH Flash	5.796	1.67	2.14

That's definitely an improvement, except when the IO flash is used to calculate bubble and dew points without proper initialization, which is the case when we solve columns with no initial temperature estimates.

I also finally found the error in the triple sum routine for critical point calculation. It was, in fact, an error in the equation on the paper (by Michelsen and Heidemann, "Calculation of Critical Points from Cubic Two-Constant Equations of State"). They wrote an "alpha" were it should be an "a". I found another paper with the correct expression, and now the calculated critical points seem to be consistent:

Pretty nice, eh?

The original IO algorithm is intended to work only in the VLE region, that is, it was not meant to use in single-phase scenarios. That's why you'll see DWSIM slowing down when calculating PH/PS flashes in the single-phase region with the IO algorithm.

I'm still trying to find a way to tune the parameters and make the algorithm at least as fast as the nested loop one but, for now, be advised. If you would like to test it, try to run the Cavett simulation with the IO method and check the compressor calculation time - it is very slow because it is only gas, and there is a PS flash and a PH one right after.

Also, the critical point calculation is not behaving as expected. The problem is in the "triple sum" calculation, because the stability curve is being calculated correctly. I'll try to find another paper with the formulation for the PR EOS and check against the one I used to make the code. This only affects the phase envelope and critical point utilities, but it is important for you to know that this is a known bug.