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

[Hansen, Eddie]

Are you looking at total mass from the  .dat file that is being outputted? For the default flash.par file for ZPinch, the file gets named ZPinch_2D.dat. Total mass should be the 2nd column.

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


From: Alvaro Sanchez <alvaro.sanchez at greentownsbyfusion.com>
Date: Monday, October 30, 2023 at 10:21 AM
To: Hansen, Eddie <ehansen at pas.rochester.edu>, flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: [EXT] Re: Question about total mass in ZPinch example
Hello dear Eddie, firs of all thank you very much for your quick response, really appreciate it.

I understand what you say about the vacuum but it is still too much of a raise (x10 as seen in picture) to be that the cause maybe?
If it is low density vacuum filling the domain left by the liner moving inward mass, then it should not raise that much, I think.

We performed the same calculation for the Orszang-Tang test (we just modified the runtime, attached is total mass of the O-T test) and we still get weird results for total mass. We also created a version of the Z-pinch where no vacuum is entering and we get similar results, with the mass increasing as compression happens.

How can we check the species mass fractions? I am not finding them in the user's guide, probably this is all a mistake in our calculations, and we are doing something wrong, but we have checked a lot of times and found no errors yet.

Thank you very much for your help, we are quite lost at the moment so everything is appreciated.

Alvaro 🙂     
________________________________
From: Hansen, Eddie <ehansen at pas.rochester.edu>
Sent: Friday, October 27, 2023 2:46 PM
To: Alvaro Sanchez <alvaro.sanchez at greentownsbyfusion.com>; flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: Re: Question about total mass in ZPinch example


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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