Hi Jed, Thanks for the answer, sorry for the long delay here, I got knocked out by the flu. Oh well.
>Fra: Jed Brown [[email protected]] >Sendt: 22. februar 2014 01:50 >Til: Åsmund Ervik; [email protected] >Emne: Re: [petsc-users] Using DM for a refined level-set grid > > >Is this 2D or 3D, what fraction of the domain is likely to be within >5*dxCoarse of the interface, and how large do you intend your subdomains >to be? This is 3D. Of the global domain only a small fraction would be within 5*dxCoarse of the interface; we're not studying atomization or anything extreme like that. I guess it's a little tricky to say how large the subdomains will be, but I'd say around 300 subdomains would be a reasonable guess at the number of them. Then the size would be roughly 1/7th of the global domain in each dimension, so for a typical case around 100*dxCoarse in each dimension. So still the subdomains should not be nearly-full refined. >My worry is that even if you implement the dynamic algorithm you're >thinking of (which is nontrivial to do well), some subdomains will have >nearly-full refined sections which will limit your max problem size and >performance. If you can't load balance dynamically (in terms of peak >memory and time) at the needed granularity, there is no point trying to >save some storage in benign regions of your domain. This is a good point. It's probably worth it to implement just a plain refined grid (without any "sparse allocation") and see if that will be sufficiently fast. Should be quick to do. >What sort of methods will you be using for your CFD? Does it involve >assembled matrices? We're solving a pressure Poisson equation, so yes, it involves assembled matrices. >From your questions I now realize that perhaps the worst-scaling part of our >code will be velocity extrapolation for level-set advection. This takes some >time (not as much as the Poisson equation, maybe 5% of that) and only happens >in a band around the interface. I guess we should look into alternatives to >velocity extrapolation. Regards, Åsmund
