The local system that I am running ansys electronics desktop on, have 128 GB of RAM capacity (4*32 GB). I thought hf3d cannot work in parallel might be to the RAM issues. So I went back to the two simple design (which I provided the table) that I created and increased the meshing density in multiple steps. In everythin I run I didn't ask to save the fields

1- In the highest meshing density: With HPC set to 1 core (auto or manual) : using direct solver it used 95 GB of Ram to solved the problem and frequency sweep just fine. Also for iterative solver it used 30 ish GB of RAM and solved the the probem and frequency sweep just fine.

2- In the medium density meshing: with HPC set to 1 core (auto or manual): everything works fine. With HPC auto up to 4 cores and 95% of RAM direct solvers started solving the adaptive meshing at 60 GB RAM capacity and transitioned to 1 frequency at a time for solving sweep frequency. The iterative solver, solves the adaptive frequency with at 20 GB and went to for solving frequency sweep with 4 cores in parallel. I was following the pid of 4 hf3d created on my machine. They started to utilize RAM up to 9 GB each and then the error code 149 appeared.

3- Low density is provided by the table above.

Having said that, Now I am confused. On one hand each core can access to almost whole RAM capacity (case 1, direct solver used 95 GB). On the other hand when 4 cores supposed to access around 80 GB (4*20 GB) it failed and gave me that error. 

looking forward for your reply.