HPC Model Review: Difference between revisions

Check for any unusually high velocities in the maximum and temporal output. Review of velocity vectors can also be useful when styled Scaled to Magnitude in a GIS package.

 

Look for “bumps” or “monds” in the maximum water level surface. One way to do this is by generating water level contours at, say, 0.1m intervals and panning around looking for any bumps. Alternatively, appropriate shading settings will also work. As the maximum surface values are being tracked every timestep, if there is a numerical bounce, it will be recorded and propagate away from the location creating the bump or mound. Typically Classic, with its fixed timestep, nearly always goes unstable if a bounce occurs and the simulation stops with error. However, HPC with its adaptive timestepping can recover from the bounce and continue simulating. Thus a sudden, change in timestepping (not associated with approaching an output interval) is evidence of a possible bounce. But by far, the best way of reviewing (for any 2D software) is to check there are no bumps or mounds across the maximum water level surface as a result of a bounce, especially for adaptive timestepping solutions due to their ability to recover and not go unstable. Checking the water level surfaces at instants in time is also an option noting that a bounce may have occurred between map output times. <br>

If bumps or mounds are evident then try using smaller timestepping. Sensitivity run can be done by reducing timestepping interval using Control Number Factor == 0.8. This reduces the timestep (as dictated by the three control numbers) by the factor 0.8, making the simulation to take roughly 20% longer. If comparing the two maximum water surfaces shows negligible differences it is a strong indicator of no bounces. If there are areas with significant differences, these are likely to be areas of numerical bounces. To be extra sure re-run with Control Number Factor 0.5.