Jim Cowie wrote: > Hi Miguel, thanks for your response. Julie Prestopnik provided me with some > additional details on this issue since she first noticed it a couple years > ago. > > Perhaps there is no absolute fix for this, but I want to be sure that > something > else is not happening either. As you said, if you increase the concrete depth, > METRo is stable and produces a forecast. However, we are already using a value > that is larger than the minimum mentioned in the bug report (0.25m). We are > using 0.275m, and it still fails. This seems rather thick to me, and is > surprising that it cannot resolve enough layers here. > > Second, if we leave the concrete at 0.275m, but reduce the depth of the > overlaying asphalt layer, it also produces a forecast. If the issue is > resolving enough layers in the concrete, how does reducing the asphalt > thickness suddenly cause it to work? > > Thanks for you help,
Hi Jim, The observation you did is based on the fact that METRo have more layers of resolution at the surface than it has at the bottom. You can look in the METRo paper at the page 2028 for equation (7) for more detail. I copy here the most pertinent part: "The resolution for the uniform grid is 0.01 m; for the variable grid, the constants a and b in (7) are chosen to give a maximum resolution of 0.01 m at the surface and about 0.05 m at a depth of 0.5 m; the bottom of the variable grid is at 1.4 m, and 24 out of its 29 levels lie above 0.5 m. The number of levels for the uniform grid depends on the thickness of the bridge." In case of a bridge, a uniform grid is used. We are currently discussing about a road configuration, so equation (7) is used (E = a ln(1 + bz)). When you reduce the thickness of the top layer, all the layer below it have more levels in it, even if they keep the same thickness. Be sure that if you see this error, it is exactly what is happening. This message is very in deep in the METRo physical model and it looks at a negative sign in an exponential in the iterative method for differential equation solving. I doubt that it can be generated by something else. Regards, Miguel -- Miguel Tremblay Physicien - Physicist Centre météorologique canadien - Canadian meteorological centre (CMC) Environnement Canada - Environment Canada http://www.ec.gc.ca/ 2121 Trans-Canada N. Suite 228 Téléphone/Phone: 514-421-4729 Dorval, Québec Fax: 514-421-4679 CANADA H9P 1J3 courriel/email: [email protected] _______________________________________________ METRo-developers mailing list [email protected] https://mail.gna.org/listinfo/metro-developers
