HEC RAS Debris Flow Speed Run

[@edwinamaya6334]

Thank you, excellent tutorial. I have a question: how can I estimate my CV through HMS? and what information would you need to feed that model? Thank you

[@rahmadeenk3362]

Dear Prof. Gibson, I've trouble and error : Unsteady Input Summary: 2D Unsteady Diffusion Wave Equation Set (fastest) 2D number of Solver Cores: 12 HDF_ERROR trying to use HDF output file Subroutine HDF_SET_COMPRESSION HDF_ERROR trying to close HDF output file: HDF5-DIAG: Error detected in HDF5 (1.8.11) thread 0: #000: ..\..\src\H5Pdcpl.c line 869 in H5Pset_chunk(): all chunk dimensions must be less than 2^32 major: Invalid arguments to routine minor: Out of range Error starting unsteady simulation - Stopping compute process What is the solution for this case, Thanks before

[@TheBalticSun]

Very useful, thanks for the lesson! I'm working with this Bingham model in my master thesis. I have a question about the non newtonian Cv parameter: If I set the Cv = 60% and select the "Do Not Bulk" option, then the simulation doesn't take into account the volume concentration? Or is it actually taken into account but its assumed that it is included in the flow hydrograph? (and if so, how does the bulking factor work in this case?) I have been running the model all this time with "do not bulk" option, does this mean I am modeling clear water?

[@stanfordgibson]

The bulking option assumes your boundary condition is a clear water hydrograph and RAS is adding your solids to it. "Do not bulk" assumes that your boundary hydrograph is a time series of the whole mixture volume.

[@stanfordgibson]

But, if you use the O'Brian or exponential rheology equations, those use Cv, so you can choose "do not bulk" and still have effects from Cv. If you choose user specified parameters and "do not bulk" the model will be insensitive to your Cv...assuming that you already included it in your boundary hydrograph. HMS includes both options, a bulk mixture hydrograph, or a clear water hydrograph and a Cv time series.

[@TheBalticSun]

@@stanfordgibson thank you so much for answering! a last question is about the downstream boundary condition (DSBC), is it not mandatory to set de normal depth as the DSBC? can I only run the model with the upstream boundary condition? or does it depend on whether the flow passes through the mesh downstream?

[@stanfordgibson]

@@TheBalticSun Because NN can "run out" (e.g. come to rest) before it reaches the "downstream boundary" you don't really need a downstream boundary if the flow doesn't reach the domain boundary. But if the flow does reach the domain boundary, you will need a normal depth or something.

[@TheBalticSun]

@@stanfordgibson I got it, thanks again!

[@pierre-louisligier1845]

Interesting! A quick question: how does RAS account for the fluid density of the debris flow mixture, and how to specify the material’s specific grain density? Density is often twice as large as clear water and can have significant impact on flow dynamics. Thanks in advance!

[@stanfordgibson]

We compute fluid density based on the concentration by volume (CV) in the non-Newtonian fixed bed model, which means that for now we assume the solid phase has a specific gravity of 2.65. I suppose you could estimate higher density material with some sort of "apparent Cv" that converts mass in to volume...but I'd need to think/read more about that. Overall, though, most of the density effects are in the empirical parameters, not the physics, anyway, so I don't think it matters too much. In the mobile-bed sediment transport model you can edit the specific gravity of each grain class and simulate multiple grain density transport....but that is a much bigger effort.

[@stanfordgibson]

I am going to post a video on Binham parameters in a couple months...if you would like to preview a rough draft, reach out ot me on linkedin and I can give you a link

[@TheofficialPr0]

Hello, i have written to you before. I'm working on my bachelors thesis on HEC-RAS sediment moddeling and have run into an issue while hydraulicaly calibraing my model. I have 6 gates in a SA/2D connections opening based on the rules i've set but based on my previous runs it seems like they dont follow the rules at all in fact most of the gates dont open at all. This has left me and all my professors confused since we do not see any problem with my model. Would you please help me because i have been trying to resolve this issue for over a month now and I'm at my wits end. Thank you very much.

[@stanfordgibson]

I don't think I've tested connections with rules in a 2D sediment model. There is a chance that that particular confluence of features has a bug. If you believe there is a bug, please send the files to the RAS inbox www.hec.usace.army.mil/contact/

[@TheofficialPr0]

@@stanfordgibson I have not tried adding any sediment data yet because I can't calibrate the model hydraulicaly. I semt an email to the email you have send. I've run more tests and the gates just do not work...