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 Matt September 1, 2004 14:22

Moving Body Grid Question

Can anyone offer me any insight as to the strengths and weaknesses of using either an unstructured overset grid method vs. local grid remeshing while performing moving body flight performance calculations?

matt

 ag September 1, 2004 16:48

Re: Moving Body Grid Question

For ease of use and coding overset is better. The only argument that I know of that favors local remeshing is that you don't have to use interpolation boundary conditions as you do at the submerged boundaries of overset grids, which can have some impact on global conservation (although the effect is in my experience very small if good practice is followed). However you still have to develop some scheme to distribute the information from one step to the next in a remeshing, which usually involves essentially the same work that goes into hole-cutting and donor-searching for an overset approach. But - if the idea of having a "non-conservative" boundary (such as in an overset approach) bothers you then you should go with local remeshing.

 versi September 2, 2004 06:00

Re: Moving Body Grid Question

I was bothered by why one still resort to Overset grid when already using a "versatile" unstructured grid. The unstructured grid is adaptive enough to cope with multi-object gridding problem, which have to use Overset grid for block structured mesh.

 Matt September 2, 2004 08:22

Re: Moving Body Grid Question

Now that is my general feeling in the whole situation also. It seems that using a unstructured overset method is just a way of not having to deal with any of the local remeshing issues, but algorithms and schemes for doing local remeshing of multi-object dynamic simulations have been done before.

thanks,

matt

 ag September 2, 2004 09:18

Re: Moving Body Grid Question

Overset methods are a very practical way of handling moving-body, relative motion problems. It is fairly easy to take an existing code and make it overset-capable. Overset methods allow the application engineer to create one set of meshes that work for the calculation and not have to worry about the quality of the mesh later in the calculation. Lastly, automatic unstructured grid generation for viscous calculations about complex geometries is still not as developed as some areas need, and the use of overset grids allows simpler grids to be generated to fill the domain. For more information I would recommend searching for the reports out of the most recent Overset Grid Symposia.

This is not to dismiss the use of local remeshing. I have seen work done by Whitfield, et. al. (formerly of Miss. State, now at UTC) using stretch-and-break that is very impressive. It may well be the way of the future. But I would not discount overset methods yet.

 Edmond Young September 13, 2004 00:45

Re: Moving Body Grid Question

Can anyone recommend some papers on good interpolation methods for transferring info from grid to grid that has good global conservation properties?? I've seen some that involve very complicated cut-cell methods; are there other less cumbersome methods that do a similarly good job of conservation?