velocity increasing problem

General scientific issues regarding ROMS

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WY0116
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Joined: Sat Oct 10, 2015 1:04 am
Location: UCL

velocity increasing problem

#1 Unread post by WY0116 »

Hi all,
I want to get a stable velocity field of the South China Sea, and I tried the below scheme: I used the SODA data (u,v,t,s,sla) as initial field; the boundary is set to time-invariable for 0:1:29(days); the forcing is also set to time-invariable (0:1:29).
with the above scheme, I wanted to get a stable velocity field for about 30 days. However, the velocity seems to increase monotonously and become much larger than the initial value.
Could anyone give me suggestions?
Thanks

best,
Yan
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kate
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Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: velocity increasing problem

#2 Unread post by kate »

You show before and after. What you need is a timeseries of total energy to see if you are approaching a steady-state. I'm not surprised that your ROMS grid supports sharper fronts than what came from SODA. What I don't know is the spin-up time for getting to steady-state. Or perhaps it will go unstable and get to an unsteady equilibrium.

WY0116
Posts: 16
Joined: Sat Oct 10, 2015 1:04 am
Location: UCL

Re: velocity increasing problem

#3 Unread post by WY0116 »

kate wrote:You show before and after. What you need is a timeseries of total energy to see if you are approaching a steady-state. I'm not surprised that your ROMS grid supports sharper fronts than what came from SODA. What I don't know is the spin-up time for getting to steady-state. Or perhaps it will go unstable and get to an unsteady equilibrium.
Hi kate,
Thanks for your kind reply. I have got the velocity field for the ninth month. I think it has gone unstable and unsteady with excessive eddies. any suggestions to reduce the excessive eddies?
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kate
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Re: velocity increasing problem

#4 Unread post by kate »

The eddying nature of your solution is to be expected at your resolution. If you go to 1 degree or coarser, the eddies should go away. Or you can crank up the viscosity to the point where it will damp out those eddies.

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