Troubleshooting Tools for Unstable 2D HEC-RAS Models

so i'm working on 2d razz model here and as you can see it is not super stable um i'm going to the max iterations at pretty much every time step and we're going to have to troubleshoot this model a little bit and there are a number of helpful tools that can help us troubleshoot that this model that have been added to the latest version of raz so let's go over to mapper and take a look at them but before we go over there i'm gonna pause this model and take a look at you know what are some of the uh cells that are actually causing us the most trouble you can see that this like seven seven two eight two nine region is causing us trouble so let's go over to the results and take a look at that and so here we are back over in ras mapper and here we're looking at the result and the first thing we can do is we kind of turn on the velocity and see you know what's uh what's this model doing and this model is actually going through a series of gates here it's a detention basin and uh we've got pretty high velocities both upstream and downstream not not surprising that we're having some stability problems right out of the gate but the you know the first thing that we can do here is we can actually go look at the cell that is causing us trouble and the kind of the easiest way to do that is to go here and click on the 2d flow area then press ctrl f and ctrl f is kind of a new feature in mapper you can find almost anything with ctrl f depending on what you click on over here but here it you press ctrl f and you get the cell the face or the face point and if we recall you know what was giving us trouble well it was cell 7728 and 7729 so i'm going to come over here and type those in and press the arrow button it'll take us right to 728 or seven seven two nine and you can see that you know these are the cells that are pretty much surrounding this rapid flow of the gates which is not surprising okay so that tells us kind of what is happening at an independent time step but one of the problems with this output is that it only actually tells us the cell with the maximum error there could actually be a number of cells that are problematic and they're being masked by this one cell you could go through and kind of maybe look and create a list but that's pretty tedious and so what the raz team has actually done is they've added coverage there's different layers that can help you identify which cells are giving you problem at kind of the model scale and so let's go take a look at those because those are really helpful so we right click on the result and go to create a new results map you know just like you're going to add shear stress or new velocity field or something like that you come here under additional 2d variables this is where the magic is this is where you can select cumulative iterations which will tell you the number of times that you exceed that 20 iterations at each cell and then maximum water surface error and so i'll just add those both i'll add them one at a time and so now i have these two options over here and so now if i turn off the velocity you can see that i have this cumulative iterations and this maps by default from 0 to one and so you know if it goes more than one you know that that's actually not as helpful as it could be so let's right click on that and go to layers and actually let's say let's go from zero to one hundred and create a ramp okay and what you can immediately see is that actually it is really right through this structure if i turn on the i have this 2d i have this 2d connection this internal connection which is essentially my spillway with these gates in it and you can see that actually iterations are lining up with the flow through those gates pretty well and you if you hover over them you can see that you know right where the flow is happening through the gates that's really where i'm having the trouble you know i'm going to 400 iterations there that that's that's problematic but you can also see other places where this is problematic where i have large slope changes or if you go upstream to the boundary condition we've got some issues with the boundary condition this is a good way of kind of overviewing even if like these cells don't emerge as the maximum cell ever they are going to maximum iterations and you can come up with a relative differentiation of which ones are problematic the other really helpful thing is the maximum water surface the maximum water service error tells you exactly that like um throughout the model was the biggest water service error that was computed the cell and if it's like smaller than 0.01 well then it didn't even register and then we consider that convergence but i think greater than that you know the model will keep a memory of that okay so those are just a couple of new layers that we put in razz that can help you troubleshoot the model kind of at the like whole model scale and help you identify regions or cells that are problematic without kind of fixing one re-running it and then seeing the error message again my name is stanford gibson i'm the cinnamon transport specialist on the razz team and this in this video was funded by the hhnc set program

Channel: Stanford Gibson

Views: 7,337

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Id: tKB0gNTUd_A

Length: 5min 3sec (303 seconds)

Published: Tue May 17 2022