Conversion from IGS to Nastran is not supported yet :(

An IGS extension (Initial Graphics Exchange) is a 2D or 3D CAD vector file that can store wireframes, surfaces, solids, etc. IGS is mainly used for exchanging CAD drawings based on the Initial IGES (Graphics Exchange Specification) format.

The IGS file structure is based on the ASCII text-based format, which is used in numerous CAD software applications for delivering high-end graphics.

Among CAD applications that support IGS extension are Autodesk 3ds Max, Autodesk Fusion 360, Dassault Systemes CATIA, and Autodesk Inventor.

MSC Nastran is a multidisciplinary structural analysis application used by engineers to perform static, dynamic, and thermal analysis across the linear and nonlinear domains, complemented with automated structural optimization and award winning embedded fatigue analysis technologies, all enabled by high performance computing.

Engineers use MSC Nastran to ensure structural systems have the necessary strength, stiffness, and life to preclude failure (excess stresses, resonance, buckling, or detrimental deformations) that may compromise structural function and safety. MSC Nastran is also used to improve the economy and passenger comfort of structural designs