gravitational potential is positive *and* negative?
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Gareth Few
May 16, 2019, 4:15:27 AM5/16/19
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Dear Ramsers,
I am having a little trouble understanding the gravitational potential output by Ramses. This is output in the gravity files for the grid and the particle files also.
My question is, why does the potential have positive and negative values? And is there some conversion to recover, say, gravitational potential energy?
Or have I perhaps fallen foul of something and should be getting positive and negative values at all?
Thanks in advance for any help!
Cheers,
Gareth
I am having a little trouble understanding the gravitational potential output by Ramses. This is output in the gravity files for the grid and the particle files also.
My question is, why does the potential have positive and negative values? And is there some conversion to recover, say, gravitational potential energy?
Or have I perhaps fallen foul of something and should be getting positive and negative values at all?
Thanks in advance for any help!
Cheers,
Gareth
Romain Teyssier
May 16, 2019, 4:21:21 AM5/16/19
to Gareth Few, ramses...@googlegroups.com
Hi Gareth,
What kind of simulations are you considering here ?
Romain
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What kind of simulations are you considering here ?
Romain
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Gareth Few
May 16, 2019, 4:23:42 AM5/16/19
to Romain Teyssier, ramses...@googlegroups.com
Hi Romain,
Cosmological periodic volumes. Dark matter, stars, and hydrodynamics are all used. Is there anything else that would make a difference?
Cheers,
Gareth
Twitter: @galaxy_gareth
E.A. Milne Centre for Astrophysics
School of Mathematics & Physical Sciences
University of Hull
Hull, HU6 7RX, United Kingdom
E.A. Milne Centre for Astrophysics
School of Mathematics & Physical Sciences
University of Hull
Hull, HU6 7RX, United Kingdom
Romain Teyssier
May 16, 2019, 4:25:34 AM5/16/19
to Gareth Few, ramses...@googlegroups.com
If you are using periodic boundary conditions, then it is normal to have the potential changing sign.
The average is zero over the box.
Dense regions are the ones with the most negative values, while voids have positive values.
Romain
Gareth Few
May 16, 2019, 4:37:11 AM5/16/19
to Romain Teyssier, ramses...@googlegroups.com
Thank you, that is reassuring!
Is there some way to recover the gravitational potential energy from that?
It seems like a simple shift in the zero-point is all that is needed but I don’t see how to calculate that. It must be a different baseline at each timestep, and presumably it isn’t just subtracting the largest value.
Cheers,
Gareth
Twitter: @galaxy_gareth
E.A. Milne Centre for Astrophysics
School of Mathematics & Physical Sciences
University of Hull
Hull, HU6 7RX, United Kingdom
E.A. Milne Centre for Astrophysics
School of Mathematics & Physical Sciences
University of Hull
Hull, HU6 7RX, United Kingdom
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