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If you use the Modelica Language for simulation it's basically a rite of passage to at least try out OpenModelica, although your mileage on various operating systems and versions thereof can vary wildly (you can always ask for the money back that you didn't pay).
If you can do the work you wish with OpenModelica, by all means stick with it, but you can't expect to get the same power as from the Modelica-based tools from the big commercial players such as MapleSim and Wolfram SystemModeler that have the advantage of optionally integrating with their extremely powerful Maple and Mathematica symbolic algebra platforms.