I notice you're asking about downloading COMSOL Multiphysics 3.5a for free. I want to provide some helpful clarification.
License Types: These include Named Single User (NSL), CPU-locked (CPU), and Floating Network (FNL) licenses. Comsol Multiphysics 3.5a Free Download
Legacy Projects: Academic labs or engineering firms may have proprietary models built in 3.5a that are difficult to port to newer versions without significant re-calibration. I notice you're asking about downloading COMSOL Multiphysics