[FLASH-USERS] Question about total mass in ZPinch example

[Hansen, Eddie]

Hello,

The total mass of the ‘vacuum’ region should increase and that is by construction. As the liner and fuel move inwards, the vacuum region becomes larger. The BC along with a density floor effectively fills in the increased vacuum region with more low-density vacuum material. We do this because otherwise there would be even lower densities in the vacuum that would result in very fast Alfven speeds, which would make the time steps too small to complete a simulation in a reasonable amount of time.

The important thing is for the vacuum ro remain at low enough densities to not impart any momentum onto the liner. The total masses of the fuel and liner should remain constant, and you can check this using the species mass fractions.

--
Eddie Hansen
Applications Group Leader
Flash Center for Computational Science


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Alvaro Sanchez <alvaro.sanchez at greentownsbyfusion.com>
Date: Friday, October 27, 2023 at 5:52 AM
To: flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: [FLASH-USERS] Question about total mass in ZPinch example
Hello dear Flash users,

I have a concern about the ZPinch example, we have calculated total mass in a lot of variations of this example and we arrived at the conclusion that compression increases the total mass within the domain.

In our experiments this happens when there are no outflow boundary, so the domain is closed. In the original ZPinch example this is not the case (since it has outlfow), but still it can be observed the mass increasing by a factor of ten (show in attached picture)

We also calculated total mass in the Orszang-Tang example, and we also observed a weird increase in mass of 40%

Do you know what's happening here?

Thank you very much for your answer 🙂
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