Nastran is an Autodesk Inventor add-on that provides powerful simulation functionality for multi-disciplinary structural analysis. The heat transfer characteristics of structures and mechanical components, linear and nonlinear stress and dynamic effects can be analysed. 

When you purchase a licence for Autodesk Nastran 2018, you also have the right to use the 2015 version. This is the only way, in the new licensing structure, to "buy" Nastran 2015 (further information on licensing).