Align Cells with Flow Direction: HEC-RAS 2D Mesh

[@konefadjiguiabdoulaye8921]

Thank you very much for this very useful video, from Cote d'Ivoire (Ivory Coast)

[@mp31389]

Great video Stan! Your videos keep improving. Keep it up! Also, if there is a lot of diagonal flow one could use a hexagonal mesh. Ups your run time but it's a quick and easy method.

[@vojtechkouba9367]

Thank you for this video, greetings from Prague

[@cornedbeef-b1d]

Thank you Stan, looking forward to more videos on best management practices!

[@JALAJDARPAN]

thank you Dr.Gibson

[@wenkaiqin]

Thank you for your instructions!

[@davidedimauro4804]

Thanks Stan! Quality as usual!

[@usgsalcsarmiento9578]

Excelente video gracias por compartir su conocimiento ing. Me gustaría aprender de dónde lo obtienes ese Dem. ??????

[@sunnytheuetianable]

Hey Stan, please make a comprehensive video on Calibration of Sediment Transport !

[@amt19696]

very good video thank you.

[@rockb78]

This makes intuitive sense. However, do you or HEC have any comparative studies? I ask because you start the video by saying RAS can still handle it, but then say this will improve accuracy. Again, I understand why one would expect this to be better, but wondering if you have comparative data.

[@stanfordgibson]

Early on the team did careful comparative studies with simplified meshes at different orientations and saw no difference. But when the meshes got more complex, we started to see time and accuracy improvements with aligned cells. It is anecdotal at this point, but we see a lot of models, so there are a lot of anecdotes. Documenting this in a comparative study would be worth doing...but the to do list is long. This turns out to be particularly important for 2D sediment models.

[@rajeevshrestha6175]

@@stanfordgibson I haven't done a detailed comparative study. However, when I aligned my unstructured grids to the direction of flow, I got a very good result. The R2 value improved greatly. Water levels got more closer to observed values. 2D sediment result improved too. It definitely improved my model. Is there any articles or documents where I can study more about what happens behind the scene?

[@babakiani]

Thank you very much Sir! Very informative! Looks like having cells aligned with the flow is more important than the using fine cells. Is it a correct statement? Thanks

[@stanfordgibson]

That is tough to say as a general rule...but I think its a pretty good principle. Because of the subgrid control, you can generally get away with larger cell sizes in RAS (and shorter run times). But you have to make sure you use break lines to set the cell faces along the high ground and inflection points. I think its fair to say that if you align your cells you can use coarser cell sizes (and lager time steps).

[@zaydwaheed3584]

Hi Stan. I was wondering if you knew of ways to mitigate fragmented inunndation when performing these sediment models on a more steep gradient ? I seem to be having it occur as a repeated problem that as far as the forums go dosent seem to have a solution ?