INLET TEST: Why are initial wave directions 81 deg?

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

Moderators: arango, robertson

Post Reply
Message
Author
txu68
Posts: 27
Joined: Wed Nov 11, 2015 4:49 pm
Location: Georgia Institute of Technology

INLET TEST: Why are initial wave directions 81 deg?

#1 Post by txu68 » Thu Nov 19, 2015 2:30 am

Hello,

I have successfully compiled and run the INLET_TEST case using the 2015 COAWST system. But when I looked at the output of Dwave, it seems to me that the initial wave directions along the boundaries except the north boundary are always 81 degrees. This problem doesn't exist in the 2010 COAWST system.

In my project, I also need to compile SWAN and ROMS and use the periodic boundary conditions on east and west boundaries. Since the initial wave directions along the boundaries are set to be 81 degrees, this causes inconsistent results from ROMS and SWAN when periodic boundaries are implemented. Can anyone enlighten me how to solve this issue?

Thank you in advance.

Amy

jcwarner
Posts: 823
Joined: Wed Dec 31, 2003 6:16 pm
Location: USGS, USA

Re: INLET TEST: Why are initial wave directions 81 deg?

#2 Post by jcwarner » Thu Nov 19, 2015 3:01 pm

Amy-

To run the inlet_test, we set the init conditions for SWAN to be Hwave=0. This case does not have any wind forcing, so there is really no 'real' init conditions for Dwave. The value of DWAVE=81 is computed by SWAN, but there are really no waves present at start so this is just some value that really has no significance. SWAN is forced with a wave imposed at the northern edge that propagates southward into the domain. After a short time, the DWAVE throughout the domain becomes close to 360 (from N), with variations due to current interactions.

For Periodic, SWAN (I believe) can only do E-W periodic and this is only for very idealized cases. Because of this, I don't think the coupling would work for periodic conditions for SWAN. A way to get around this is to use different grids for roms and swan. The Inlet_test/Diffgrid is an example of that.

thanks
john

txu68
Posts: 27
Joined: Wed Nov 11, 2015 4:49 pm
Location: Georgia Institute of Technology

Re: INLET TEST: Why are initial wave directions 81 deg?

#3 Post by txu68 » Thu Nov 19, 2015 4:15 pm

Hello John,

Thank you for your help.

In my project, I actually need E-W periodic boundaries. I know this can be tricky. So after I ran the INLET_TEST case, I replaced the bathymetry to a plane beach without changing any other parameters. That is to say, the east and west boundaries were set to be the gradient. When I looked at the results, SWAN set the initial Dir at the east and west boundaries to be NaN. But when I looked at the results from ROMS, the initial Dwave along the east and west boundaries were set to be 81 degree. Although this causes no problems in the INLET_TEST case or in the plane beach case with gradient boundaries along east and west, it does cause the inconsistent results between SWAN and ROMS when I try to run the plane beach with the periodic boundaries along east and west. The 81 degree line is shifted to somewhere in the middle and becomes a straight line with an angle smaller than 90 degree.

I tried to run the periodic boundaries in the 2010 COAWST system, which gave me some errors like grid size is inconsistent as soon as I started to run the coawstM. So I think this is a great news to me that the periodic boundaries can be implemented in the 2015 COAWST system. But when I ran the plane beach with the same boundaries as the INLET_TEST case in 2010 COAWST, the 81 degree did not show up in the initial Dwave in ROMS output. I really hope this can be fixed.

Amy

Post Reply