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February 16, 2017 at 7:12 pm in reply to: Does HecRas use previous run files when doing an unsteady run? #10409cameronParticipant
Not unless you specify it to use a previous run. Did you set up the initial conditions in the flow editor the same?
cameronParticipantDo the cross-sections overlap or is there a big difference between how wide the cross-sections are at that location?
cameronParticipantWhen you tried the 1D/2D model, did you have the 1D/2D iterator set to 20 (or any value)?
In your case, I would probably go to 2D only route with a 25 ft spacing, but do a sensitivity on the the time step. The rule of thumb most people use is to follow the Courant criteria which in your case would be less than 1 sec and gradual increase it to see how the results change. If you go too low with a time step HEC-RAS may give velocities that are too small and higher depths (this generally only occurs in areas with high velocities).
When you say velocity and depths are 1 fps and 0.7 ft different, different to what (30 fps, 10 ft of depth)? How different is the time to peak, or flood wave arrival time, or the deflood time, or peak discharge?
One thing you may try is to adjust the cell faces so that they are perpendicular to the direction of flow.
How important is it that you model the steep channel area? you have a breach hydrograph and could just place it near the area where it begins to expand.
cameronParticipantIf you export out the raster results for each timestep in HEC-RAS you could load them into a raster catalog in ArcMap and create a animation. Another option may be to try the SMS 12.2 beta software as it is adding back in the HEC-RAS functionality.
cameronParticipantI have done many dam breach models where I had to use very small spacing to get it to be stable. Samuel’s Eqn and the USACE documents are just guidance. If you are getting a good answer with smaller stationing, that is fine.
cameronParticipantThe value entered in that box is the discharge for the model.
January 29, 2017 at 10:00 am in reply to: Re: Dam Breach Model using 2D in HEC-RAS 5.0.3: 1D/2D Flow Error Message #10357cameronParticipantFor dam breach simulations, you can usually get away with larger grid cells as long as you include breaklines. By using larger grid cells, this should help with the run times.
3 to 5 hours is normal for 2D modeling depending on the size of models. Most models I run require 10-20 hours if not more as they require either a large area or lots of detail. Not sure what type of machine you have, but more cores is not always better. I seen models where a few cores is faster than over 20, but it all depends on the project.
January 29, 2017 at 9:53 am in reply to: Re: Dam Breach Model using 2D in HEC-RAS 5.0.3: 1D/2D Flow Error Message #10360cameronParticipantthe 1D/2D connection needs to occur where you will have a uniform water surface elevation (same elevation across entire connection) as 1D only can have a constant elevation. The multiple iterations are due to the 2D domain and 1D domain not being able to get a constant wse.
Since you are modeling the bridge as a culvert with a weir, why not model the entire thin in 2D and include the culvert inside the 2D domain?
cameronParticipantdid you recompute the tables for the 2D area? Are there any problems with your mesh?
cameronParticipant1D models require to have flow in the channel no matter what or the model will go unstable. 2D models do not require this.
cameronParticipantIt should export the horizontal results when you have it generate the stored rasters, unless they changed something with the latest version of HEC-RAS.
cameronParticipantYou could do it by brute force. You can specify a water surface elevation for each cross-section in the steady flow editor under “set internal changes in WS and EG”. In your case, it would be the EG, rerun the model, and then you could export it out with the energy grade from either the export GIS data or Mapper.
January 23, 2017 at 9:47 am in reply to: Mapper freezes while computing XS interpolation surfaces #10331cameronParticipantMultiple people have reported this problem and there does not seem to be a simple answer to fix it. Generally people have recreated the cross-section layers by exporting and then importing into a new geometry. I would recommend checking the cross-sections that none are overlapping or changes between to cross-sections is not to great.
cameronParticipantcan you elaborate what you mean by SVSQ iterations?
cameronParticipantManning’s roughness is a subject people have some strong opinions on. I say look at the HEC-RAS 2D manual or the ARR (http://arr.ga.gov.au/revision-projects/project-list/projects/project-15) manuals. You could also look at the FLO-2D manual.
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