Intro HEC-RAS Sediment Demo (Part 1 of 3 - Quasi-Unsteady Flow)
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- เผยแพร่เมื่อ 28 ก.ค. 2024
- In part one of this video series we create a quasi-unsteady flow file for an HEC-RAS sediment transport model.
Files are available at:
drive.google.com/open?id=1vO9...
The HEC-RAS sediment user manual is now online:
www.hec.usace.army.mil/conflu...
Hi Dr. Gibson, when I run my model, this error messages popup. I checked all my input data - flow duration and computation increment, all data is more than 0. Can help to clarify why this error keeps happening?
Sediment Transport Analysis HEC-RAS 6.x
An error occurred with sediment boundary data.
The Boundary duration data and Computation Increment
Must both be greater than 0.0
Please check your data.
Hello, Thanks for the video. I'd like to know the HEC-RAS limitations. When we simulate sediment transport, usually we have rivers with steep slopes ( greather than 4%). Which is the max bed slope of the channel that HEC-RAS could handle? could you help me with this question please?
how to determine the computation increments for various flow?thanks
A convergence test is often the way to go. Reduce the computation increment until the answer doesn't change. Sometimes the mixing methods complicate this approach, but it is often the best way to go.
sory sir, i got the problem. how if the data input on simulation time is not day to day (4:05) but hourly (cz of my flow data is hourly). so, what sud i fill on flow duration (hrs) column? am i right if i write 1 hour for all simulation time?
That's right. If you have hourly data, make your duration 1 hour for all rows. Then you can sub-divide those into sub-hour Computation Increments if you need to.
can anyone give me sediment transport data for simulation?
Hi, is it possible to modelize sediment transport with Steady flow ? Thank you by advance for your response
Kind of. A steady flow model has no time component, so you cannot "route" sediment or compare capacity to load. But the Hydraulic Design Tools in HEC-RAS allow you to compute sediment transport capacity for each flow in a steady flow plan with the main suite of transport functions. Go to Run-->Hydraulic Design Functions and then in the HD menu, go to Type-->Sediment transport Capacity. It will probably be some time before i do a video on this, so check out the user manual.
Alternately, you could run a constant flow in quasi-unsteady until it reaches an equilibrium.
Can i input hydrograf 24 hours?
Yes. You can use any regular or irregular time step to input your hydrograph. Use the length of the hydrograph time step as the "Duration" in hours. Then you can subdivide this into computational time steps with the "Computation Increment"
how to choose study area for sediment transport modelling?
I often chose my study area based on a couple criteria...1) where do i have data and 2) is there a relatively stable portion of the river to set a boundary. I often start the sediment model (upstream) where i have a flow and/or sediment gage. And I try to place model boundaries on less morphological active parts of the channel.
But similar principles apply to sediment models as hydraulic models. Get the boundaries away from the area of interest so the model has time to adjust for boundary effects before it gets to the river reach where the results matter.
can anyone give me sediment transport data for simulation?
Sir please explain computational increment in simple language
The computational increment is THE time step the model uses for the simulation. Flow duration is just specifies how long the flow lasts. It is not used in the computations
Can I add piles and collar in piers data in Hec ras?
Piles and structures are not really 1D features. You need at least 2D to study their effects, and preferably 3D or physical models. If you are just interested in removing the conveyance and adding wetted perimeters you could add blocked obstructions. But - in general - 1D sediment transport is not great for structures that only span part of the cross section.
@@stanfordgibson sir but when we do local Scour analysis for quasi unsteady flow at bridge pier ( not including subsurface structure because HEC-RAS don't have its facilities) so will it give wrong interpretation or result for intermediate cross section ( if sediment transportation happens)?
My question is when we can do local Scour analysis so why we can't do sediment transport at different cross section?
@@ushagupta3204 I'm not sure I totally understand, but we do not use the Federal Highway equations in the mobile bed sediment transport equations. To compute Bridge Scour you must go to the Bridge Scour calculator in the Hydraulic Design editor. www.hec.usace.army.mil/confluence/rasdocs/rasum/latest/hydraulic-design-hd-calculators/computing-scour-at-bridges
I have detailed information about the limitations and approaches to bridges in the mobile-bed quasi-unsteady/unsteady sediment model in the user manual: www.hec.usace.army.mil/confluence/rasdocs/rassed1d/1d-sediment-transport-user-s-manual/geometric-considerations-for-a-sediment-transport-model/modeling-bridges-in-a-sediment-simulation
@@stanfordgibson thanks sir..but I will kind request to you make one video on this topic..Your way of explanation is very impressive and quite easy to understand for beginners.
How to solve this problem in hec ras ?,it said like this No flow in channel at river/station
Kulfo Chamo 2864.181
(channel may have overfilled with sediment).if I run the sediment transport.please help me every body if you have idea about it?
There are several issues that can cause this error:
1. The most common is that your "computational increment" is too large. Particularly during high flows. If too much bed change happens in one time step, the model can go unstable and artificially fill the channel.
2. If the channel fills so that an overbank area is lower than the talweg, it can drain the main channel (you can fix this with ineffective flow areas or allowing deposition outside your movable bed limits).
3. If it is the upstream cross section, your boundary load is too large or too coarse. One common mistake is to use the bed gradation to partition the boundary load...but the upstream flux is usually MUCH finer than bed samples.
4. If your bed gradation is too fine, the model can scour too much sediment in one XS, and deposit it in the other. Because RAS can handle a deeper channel, but can't model one that is full, the secondary cause will generate the error.
can anyone give me sediment transport data for simulation?
@@NadeemKhan-bu5cr Data for all the demos are here : drive.google.com/open?id=19cKMTZeJ0Sq7VKjr2WeCgb1nS2sPv_dw
@@stanfordgibson Sir how can a simulation be done with any arbitrary data for any general river section?
@@NadeemKhan-bu5cr I'm not sure I understand your question. Sediment data are extremely site specific. Data from one river cannot be applied to another.
si estuviera en espanol fuera genial
Lo siento, you hablo un poco...muy poco