How to deal with the blow-up at boundaries due to high wind?

Discussion of how to use ROMS on different regional and basin scale applications.

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jayasankar
Posts: 15
Joined: Fri Sep 20, 2013 1:09 pm
Location: India

How to deal with the blow-up at boundaries due to high wind?

Hello All,

My simulations are getting terminated due to blow-up at boundaries, To be specific node like (1,2),(2,2),(1,4) etc...

The wind velocities are very high in this region, around 12±5 m/s.
Grid Resolution is 0.2 to 0.25 degrees, I have tried time steps 1800 sec and 1200 sec.

Thank you, Jayasankar

kate
Posts: 3803
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: How to deal with the blow-up at boundaries due to high w

I would keep trying shorter timesteps to see if that solves the problem or if there's something else going on. If you go for half the timestep and the model runs for twice as many steps, there's something else going on.

jayasankar
Posts: 15
Joined: Fri Sep 20, 2013 1:09 pm
Location: India

Re: How to deal with the blow-up at boundaries due to high w

Hi Kate,

thank you for the suggestion ,

I am trying with time step....

Could you give me an idea about time steps used in various model in general?

Is it normal to use time steps of 600 sec for a model with 0.25 degree grid resolution and maximum depth 5000m.

Also, I'm kind of thinking about editing wind velocities by reducing them along strips of say 2 degrees, along the boundary, would that be an acceptable practice?

Thank you, Jayasankar

kate
Posts: 3803
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: How to deal with the blow-up at boundaries due to high w

Is it normal to use time steps of 600 sec for a model with 0.25 degree grid resolution and maximum depth 5000m.
It depends on more than that, including your vertical grid structure. We have a domain at 11 km resolution in which we started with 42 vertical levels, then went to 60, then back to 50. The timestep for the latter is now 360, with an option to go shorter as needed. Many of my domains have a default timestep (say 100 sec) and a commented out shorter step (80 sec) to get through the rough spots.

Are there other models for which you could use a longer timestep? I expect so, including Sasha's version of the code.

I have been too lazy to fuss with the winds in the manner you suggest. Easier to just use a short timestep.

jayasankar
Posts: 15
Joined: Fri Sep 20, 2013 1:09 pm
Location: India

Re: How to deal with the blow-up at boundaries due to high w

Hi,

I am trying not to compromise on the speed, hence i thought about reducing the wind velocities along the boundaries.

I am wondering if anyone had tried this way before, or if this would make noticeable variations in the model predictions in the entire domain.

Thank you.