Simulation Software development on VB 2012 (& FORTRAN)

Hi,
I have been working on a chemical process simulation software that was built on Visual Basic 6 and FORTRAN. The user can define the input variables using the VB interface and then the software performs the simulation using the FORTRAN executable (numerical integration of the complex process equations). Results are shown using the VB interface. I was a beginner in Visual Basic when I started 9 months back to upgrade the software. I am still working on upgrading the VB 6 codes to VB 2012.

My projects eventual goal is to build/upgrade the software so that it can handle a change in input variable i.e. simulate with recycle stream. Let me explain it in detail. Right now the software can simulate for example a process container behavior with respect to time and distance of the container. The software writes the output result data’s (i.e. concentration, pH etc.) in comma separated variable (.csv). As per my project goal, I want to use these output result data’s and process in a way so that it can be fed back into the input file for continuous simulation (restarting the simulation, may be). As I understand, I will need to change the FORTRAN executable as well because it involves solving the differential equation.

I am posting this problem in the visual basic forum to get some ideas about what kind feature of visual basic (2012) can I use to solve this problem? Can it be done without stopping the simulator as input values are changed which means change in the constants that are used to solve the differential equations? Feel free to share and discuss your ideas. I am looking for any kind of guideline i.e. books, online articles, forum posts that include this kind of problem.

I hope you don’t mind reading a long problem description as I wanted to make it clear what I am looking for. Thank you very much for reading and replying.

Rafi