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cameronParticipant
It is generally best to have a survey cross-section on both the upstream and downstream of a bridge, but could make a copy of the upstream cross-section and set it at the downstream end of the bridge. You would probably need to lower the elevations on the copied cross-section though.
If there is no constriction you don’t need to add ineffective areas, but you would still need multiple cross-sections upstream and downstream of a bridge to model it correctly.
May 17, 2017 at 6:29 am in reply to: Depth Peak at the beginning of a simple channel – 2D Modeling #10538cameronParticipantYou need to follow the Courant criteria when selecting a time step. A 30 min timestep is way to high. It should be on the order of seconds genearally and with a 2m grid it would be 1 second or smaller most likely.
cameronParticipantare you trying to save the velocities as a raster or something else? You can set HEC-RAS to save out the Vx and Vy and each cell node and use that data in GIS or other software.
May 16, 2017 at 5:55 am in reply to: Depth Peak at the beginning of a simple channel – 2D Modeling #10536cameronParticipantwhat is your timestep? If you switch to Full Momentum and the model crashes, your timestep is too high. Do you need to use a cell of 2m or can you use a larger value?
May 15, 2017 at 6:43 am in reply to: Depth Peak at the beginning of a simple channel – 2D Modeling #10534cameronParticipantWhat is your timestep and what slope did you enter for the upstream boundary condition? Are you using the Full Momentum Solver?
cameronParticipantDoes the slope change or ineffective area change near that cross-section?
cameronParticipantIf you have a 2m cell then the velocities need to be around 2 m/s or less for a 1 second time step or you would start to get interesting results. The 20 second time step is to large and probably breaks the Courant Criteria. You can get a smaller timestep than 0.1 seconds which can be done in the Unsteady Plan Options for 2D meshes using a multiplier.
The pulsing waves is due to too high of a timestep.
The diffusion wave solver is very stable and will run with high timesteps, but give poor results.
cameronParticipantI would not use the supercritical results for bridge design unless I had a really strong compelling reason. If debris ever accumulated on the bridge piers, it would cause a backwater and a hydraulic jump most likely.
Your cross-sections and bridge look very skewed to the direction of flow based on the placement of the other other cross-sections, are you accounting for the Skew? Is the bridge opening aligned with the flow or is it skewed as well? It also appears that the internal cross-sections are the same elevation as cross-section 2 and 3 which can impact the super critical results as it is not a continuous slope through the bridge.
Since this is for a design and you need freeboard, you could just model it as cross-sections (no HEC-RAS bridge) adding blocked obstructions or editing the cross-section to include the piers.
The other option is to switch to a 2D model in HEC-RAS or another such as SRH-2D to develop the required freeboard.
cameronParticipantFirst I would update to the 5.0.3 version of HEC-RAS to see if that fixes the problem. HDF is the new file format for HEC-RAS and results get stored in the *.01p.hdf. This issue could have to do with writing to the hdf file and you may need to delete the hdf file and have HEC-RAS recreate it. Are these files located on your local machine or from a network? I would also trying running the model on a different machine and see if the error is still there.
cameronParticipantThere are many company’s that do training. WEST Consultants provides training for RAS 2D. I have done training in the past as well on RAS 1D and 2D, but would probably need to recreate most of the training material.
cameronParticipantI do not believe pumps work in 2D yet.
cameronParticipantDid you check under View| Sediment Output? You may need to adjust the output level in the Sediment Output Options Window to level 6. page 17-73 of user manual.
cameronParticipantI took a quick look and here are my initial thoughts. Your cross-sections are too far apart at a lot of locations especially near the many drop structures you have. The HEC-RAS manual has guidance on how far about cross-sections are supposed to be. I interpolated cross-sections every couple hundred meters and tested it the model and it appears the drop structures are giving the model a hard time. I would also think about changing the HTAB parameters so that it starts at your invert and have a decent elevation change of .1 meters or someting better than 0.3 or higher.
I would say a 2D model would be more stable, but the model is long and your hydrograph is for a very long time so run times might not be worth it.
cameronParticipantWould need some more information to help.
cameronParticipantHave you tried adjusting the time step? Basically the model crashed for some reason causing it to calculate a very high water surface elevation that is not real which then produces the extrapolation error.
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