locally increasing grid resolution using seagrid

[hiphop]

Hi all,

I am facing this specific problem how to locally increase the grid resolution using seagrid. I am running ROMS in a large area but focus on a local bay. If I adjust the control points on both edges to increase it, it will generate 2 intersected bands with high grid resolution. I only need the bay area be incresed, rather than other area. Anyone has some experience on this problem?

Thanks.

Li

[kate]

A picture might help. In general, the constraint that our grids be orthogonal is quite limiting compared to unstructured grid models. That's why there's attempts at off-line nesting, on-line nesting, and a development effort to run with patched grids.

[hiphop]

I am trying to increase the grid resolution inside the red circle marked in the picture (attached jpg). Can it be done with structured griding (seagrid)?

[fragoso]

You can certainly increase the resolution with seagrid, but since it is a structured grid you´ll have a strip of high resolution all along your grid from east to west and from north to south. Then you´ll have an area (for example in your eastern border) with high resolution and deep bathymetry, which implies that youl´ll must have a very small time step to fulfill CFL condition. This by its turn will affect computational performance. Maybe as Kate pointed out, it would be better to do a nesting in your case.

Regards,
Mauricio.
PROOCEANO - Brazil

[kate]

Another thing you have going on is a non-orthogonal grid. The equations of motion were formulated assuming that the grids would be orthogonal, so you will get some errors from that.

Our recent grids have been rectangles plopped down over the region of interest, many on a conformal conic projection. That way you know the grid is well-behaved. I think you would be well served by nesting in the region of the red circle.

[hiphop]

Yes, maybe a nesting method would be better for this.

[sak007]

One can do a lot (but not everything) by using multi-corner grids. Generally, it is fairly easy to get required resolution in elongated channels and bays; it may be not so easy or impossible to do that in open areas.You may see some grid examples here: http://code.google.com/p/gridgen-c/downloads/list