file type for simulation

hellow , i have a question;

 I have to make a fluid dynamics simulation to a formula sae car, but for the machine files I have a file solidworks 'assembly'.

if I create a file .iges  this is very heavy because I have a lot of machine components, if i create a file .stl this export  only lines and create complex surface in hypermesh is not simple.

How can I fix the problem ?

I have to change the file type? 

can i use some program that allows me to make my geometry suited to a simulation ?

Thanks /emoticons/default_biggrin.png' srcset='/emoticons/biggrin@2x.png 2x' title=':D' width='20'>