[pinobartali]

I am using Ansys Mechanical to solve an expensive static structural analysis. I am performing this calculation on following machine:

• 12th Gen Intel(R) Core(TM) i9-12900K 3.20 GHz
• Installed RAM 64.0 GB
• GPU NVIDIA GeForce RTX 3080 Ti
• Windows 11 HOME

However, when performing the very same calculation on a modest machine, it takes about two hours. On the former instead, it takes ages. Wondering around performance and resource usage, I found out that only 4% of CPU is being exploited.
In Ansys, I set the calculation as "serial" instead of "parallel", as my licence does not allow the latter yet. I will soon start using the parallel modality, but I feel this is not the main issue.
Attached you will find a screenshot of the allocated resources during such a calculation.
Thank you very much for your help,
Pino

[flotus1]

Your CPU has a total of 24 threads.
One thread running at 100% load will indeed report as ~4% load in Windows task manager.
If you switch the view in task manager to individual threads, you should see one thread running at 100% load.

I will soon start using the parallel modality, but I feel this is not the main issue.

It sure is. In an ideal world, running parallel on e.g. 8 threads will be 8 times faster than running serial.
One of the few other possible issues for low performance: the 64GB of RAM in your new computer is not enough, and the one you are comparing to had more system memory.

By the way, we can't see your attached screenshot. You could upload it to an image sharing site like imgur, and put the link here.