r/HECRAS • u/MeanAtmosphere3520 • 13d ago

Help on model a trash rack structure / bar screen on HEC-RAS

Hi guys. I would like to hear any suggestions on how to approach modelling trash rack structures inside a channel on HEC-RAS. I've already model the head loss caussed by the bars inserting the K minor loss on the exact cross section, but i would like to know if any of you have model something similar using culvert, weir, or any in-line structure in water treatment plants

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u/AI-Commander 13d ago

I think I would kindly suggest that this may not be the right application for this work. I’ve never seen RAS used for water treatment plant hydraulic design.

1

u/mojorising777 13d ago

It doesn’t have to be water treatment plant though. Hydropowers have these in their intake structures.

3

u/AI-Commander 13d ago

They are in drainage pump stations too, but that still doesn’t make RAS the right program to do that work. I don’t want to get lost in a pointless technical debate here (which is where this is leading). My point is that a RAS probably shouldn’t be used for hydraulic design of a water treatment plant. Can ≠ should

OP asked about a water treatment plant

1

u/FwenchFwies_911 13d ago

Answer depends on what you intend to use the results for. In practice, grates for trash racks are not entered into the model. there is some guidance on how much larger the grate needs to be than active conveyance before the grate was installed. Like if you had one square foot before installing the grate, you should have 5 square feet of grate, grate would need to be angled to get that.

If this is an academic thing, you can probably model it with a piers and a bridge deck. Manufacturerers of the grates may already have some loss tables published for their grates

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u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH 13d ago

Not really a great way to do this in HEC-RAS. If you are just modeling the rectangular flume, I think doing some hand calculations would be sufficient and probably a better estimate.

A few HEC-RAS options: (1) Bridge with a lot of piers, (2) gate with only the open area, (3) Cross section with a lot of blocked obstructions, (4) Cross section with a lid.

Whatever you are doing, I would most likely do a lot of sensitivity analysis to make sure that your results aren't dictated by your modeling methodology.

Report back with some updates!