I have a fair amount of experience using Blender, Maya, and 3DS Max, three of the most popular 3D programs, and all allow you to set gravity to any value, including zero, for physics simulations. I believe that most of the Autodesk/AutoCAD software allows you the same freedom, though I can't speak from experience there.
However, a vast majority of 3D ...
Most 3D modelling packages let you define forces - I wasn't aware Blender had gravity turned on by default, but you can turn it off.
Generally though, modelling is unlikely to require it unless you are doing detailed stress analysis, in which case I'm not sure Blender would be up to the job.
Those two graphs are not showing the same thing. The lecture slide is misleadingly labeled, but the original paper makes clear that the table is only showing neutrons, mostly produced by shield spallation. That does go up with added shielding (no shielding means no spallation) but the overall dose including other sources goes down.
See figure 7 in the ...
3D Modeling Programs:
SolidWorks - Used almost universally for quick spacecraft design and development. Commonly used for SmallSat/CubeSat development, however for higher fidelity design it's common practice to use Siemens NX due to the wide verity of modeling tools and how the software can handle large complex spacecrafts.
Siemens NX - ...
Maybe Systems Tool Kit could be helpful:
It's a powerful tool, and there is also the possibility to have a free license, although it does not include all capabilities.
I have used it on Windows 10, but I cannot tell about Windows 8.
The level of detail you seem to want probably requires the use numerical radiation software. I would recommend the free SPENVIS package made available by the European Space Agency or SRIM software. SRIM has to be purchased though, so it may not be ideal for your usage. I have used both, SRIM focuses on the effectiveness of a material as shielding given some ...
SaVi runs under Windows. It can be run under the Windows Linux Subsystem, under Cygwin, or under VirtualBox. And how to get it running is fully documented.
And SaVi includes GPS and GNSS simulations.