If you call the buildModel() command, it returns the path of the executable. If you run Linux, you can run that without changing any environment variables.
For a model M, there is also a file M_input.xml which is read before initialisation. You can write a GUI that read the parameters from that file, allows users to make changes, and then sends an override file on the command-line when calling the executable.

Ok thanks for the quick answer so far.
So now as my next step I tried a bit with OMShell and got the model built and simulated. However I can't get the results plotted.
Ok, so this is my model (testdatei.mo):

model test
  Real x;
  Real y;
equation
  x = 1;
  y = x;
end test;




in OMShell(after loading):

>>simulate(test)
record SimulationResult
    resultFile = "test_res.mat",
    messages = ""
end SimulationResult;

now i try to plot results:

>>plot({x,y})
{"_omc_PlotResult","C:/Users/wohlera/AppData/Local/Temp/OpenModelica/test_res.mat","Plot by OpenModelica","true","true","plot","false","false","time","","0.0","0.0","0.0","0.0","x","y"}

no window opens, also no "true" appears as should on success (https://build.openmodelica.org/Document … plot.html), I also tried opening it by giving the filename but still no success.
On this screenshot http://www.ida.liu.se/labs/pelab/modeli … enshot.jpg I saw, that they use a plt-file instead. I changed the filetype in the simulate command but I still couldn't open it.
What am I doing wrong?

Works fine for me. It is probably an omc session shared with OMNotebook (which overrides some plotting functionality).

Ok thanks again. You were right with the session of OMShell. I've tried a few things so far.
Now I have a problem with a model that was created using Wolfram System Modeler. I can load in OMEdit and the check and instantiation works without problems. Only the view is a bit corrupted, but think that shouldn't matter for simulation.
When I try to simulate either in OMEdit or in the shell ( simulate() or buildModel() ), it crashes, without an error. In WSM the model and simulation works fine.
Do you know anything about compability between WSM and OpenModelica?
I also tried to export the simulationname.exe from WSM (which comes with a file named simulationname.sim (simular to the simulationname.xml from OpenModelica, but different) but since I dont have the xml, I can't get it to run (I tried using the "system()" command).
Is there any possibility to load the .exe or the c-code file without this file? Or is it possible to create this file using OpenModelica without buildModel() or simulate() (since this leads to a crash) . Or do you have an idea what the problem at compiling might be?

I know nothing about WSM other than they use an older OpenModelica frontend. The backend and executables files are different, so you can probably not use them together with OpenModelica.

What crashes? OMShell or the simulation executable. If it's the executable, you found a bug somewhere and a bug report is in order (preferably with the model provided). You could also run it through gdb to find out where it crashes, but since you are using Windows, I will just assume that is too much to ask