Monday, April 29, 2013

A Preview of RAS2D, two-dimensional modeling in HEC-RAS

Written by Aaron A. Lee | WEST Consultants
Copyright © RASModel.com. 2013.  All rights reserved.

UPDATEHEC has asked that I no longer distribute HEC-RAS 4.2 with 2D Alpha.  Their purpose for releasing this alpha version is to get constructive feedback so that they can improve its functionality and efficiency; and to minimize bugs before the offical beta release-not to be critically compared to other established 2D software packages...yet.  So far, they have received no comments from anyone I have distributed the software to, which is very disappointing.  Please keep your eye out for the official beta release, which is due out early next calendar year some time.  You will be very impressed with its capabilities!  In the meantime, if you have been given a copy of the alpha version of RAS2D, please take a brief moment and provide some comments and/or suggestions to HEC.  User feedback is very important to their product development. 
Sorry for any inconvenience.  Chris    @RASModel

ANOTHER UPDATE.  The release of RAS2D beta is now projected to be end of February, 2014.  I'll post updates as I get them.   Chris    @RASModel

UPDATE #3.  RAS2D will now be released as a new feature in HEC-RAS Version 5.0.  There will be no official release of RAS2D under version 4.2.  The Beta version of HEC-RAS 5.0 is due to be released in the March/April 2014 timeframe. 
UPDATE #4.  Latest indications are Version 5.0 beta will be released at the end of April, and the full version will  be released at the end of the summer.
UPDATE #5 (as of May 11, 2014).  Latest indications are Version 5.0 beta will be released in 2 to 3 weeks, putting it at the end of May, early June time frame.  
UPDATE #6 (as of May 23, 2014).  Version 5.0 beta is out!!! Go get it at http://hecrasmodel.blogspot.com/2014/06/update-to-hec-ras-50-beta.html




I’ve gotten a chance to play around with the alpha version of HEC-RAS 4.2 and check out the program’s new two-dimensional (2D) modeling capabilities. From what I’ve seen this will be a really useful feature! Being the alpha version of RAS2D there are still features in development, and is bound to be a bit “buggy”, but it is definitely worth looking forward to. What is it?
The new build of RAS will allow users to connect 2D flow elements to a 1D river system. You will now be able to model overland areas as dynamic, 2 dimensional grids, rather than level pool storage areas. The figure below shows the 1D and 2D features together in the geometry window. clip_image002
  • The 2D area can be drawn in as a polygon (much like a storage area)
  • The grid cells are automatically generated at a user-specified size within the 2D area
  • Cells can be added, removed, or edited manually
How does it work? The 2D mesh and the 1D system are tightly coupled during an unsteady simulation. This means that water surface elevation is calculated at each XS and each grid cell for every timestep, allowing direct feedback at the connections. 2D flow areas can be linked to the 1D system the same way storage areas are. The Figure shown below is a schematic of how the 2D mesh is built, and how RAS routes flow from cell to cell. clip_image004 Upon creating the 2D mesh, you need to load a digital terrain file (.flt format). Both the pre- and post-processing steps for the 2D flow area are done through RAS Mapper.
  • RAS pre-processes the 2D mesh separately from the 1D system. During this process RAS creates an elevation-storage curve for each cell, and calculates hydraulic properties for each cell face. These hydraulic properties are similar to the cross section hydraulic properties (HTAB curves).
  • The Cell Center is where water surface elevation is computed for the whole cell.
  • Cell Faces control flow between cells by acting as a detailed XS. Station/elevation data is captured directly from the underlying terrain file.
  • Cell Face Points are used for stationing to connect to a lateral structure. They also represent the ends of cell faces.
  • Manning’s n-values for each cell will be assigned by a spatially varied polygon or manually entered.
Computationally, RAS will allow the user to choose between using 2D Diffusion Wave equations (default), or the full 2D Dynamic Wave equations. Most flood applications should be adequately modeled using the Diffusion Wave equations. What are the advantages?Besides computing in 2-dimensions, the main advantage is the program’s ability to maintain computational robustness while preserving the details of the underlying terrain. Smaller features (i.e. drainage ditches) that run through large cells will be captured in the hydraulic properties of the cell faces. Therefore, these features will be preserved and accounted for both computationally and visually, even though they are smaller than the grid cell size, as demonstrated in the RAS2D output displayed in the figure below. Traditionally, many 2D models require cell size to be consistent with the size of the features to be included. Not the case with RAS2D. clip_image006 Additional advantages include:
  • Cells can be any size and shape. This allows the user to model odd-shaped features within the 2D flow area as well as provide more computational detail around areas of interest.
  • Faster computation times. RAS uses an implicit scheme to calculate water surface and flow at each XS and cell simultaneously. The implicit scheme is also more stable, which allows for larger cell sizes.
  • Detailed mapping. RAS Mapper will be able to post-process results to map depth and velocity grids on detailed terrain.
  • RAS2D will be able to utilize multiple processors (if available).












41 comments:

  1. My cousin recommended this blog and she was totally right keep up the fantastic work!




    Temperature calibration

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  2. G Day,

    How we can download RAS2D?

    Cheers,

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    1. Keep your eye out for the beta release of HEC-RAS with RAS2D. It is due out by the end of the calendar year. You'll be able to download it from www.hec.usace.army.mil. Right now, only the alpha version is out with limited release.

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    2. Is it possible to get hold of the Alpha version?

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    3. HEC wants to know who is testing the Alpha version. If you send me your contact info, and some information about the types of projects you'll be testing it for, I can get you an Alpha version. Just realize it is not for commercial use and HEC expects to get feedback from its Alpha testers. cgoodell@westconsultants.com

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  3. which method is used to solve the equations of motion?

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    1. For 2-dimensional flow areas, RAS uses an implicit finite volume solution of the 2-d Diffusive Wave form of the St. Venant equations by default, with the option to run the full dynamic form if so desired. HEC feels that for most applications, the diffusive wave form will be adequate.

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  4. kindly give me download link for ras2d I want to test it for my own learning

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    1. Please include your email address and I'll send you instructions.

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  5. In 2011, I had an experience with HECRAS and GIS to see if it was possible to model such scenarios. I had built a network with full square mesh connected by overflow. As I am French, the note is written in ... French! Sorry. I can send it to you if you are interested especially in patterns and images.

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    1. Hi Stephane-

      That would be great. Thanks. If you format it like the blog posts, I'll included it as it's own blog post.

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    2. I have put the file there :
      https://www.dropbox.com/s/6jk9r82amx9ln3i/Les%20mod%C3%A8les%20hydrauliques%20%C3%A0%20mailles%20-v2.doc

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    3. I'm also interrested in testing the new version ...

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  6. Thank you for the summary, Chris. Will RAS-2D be able to evaluate culvert systems along with river systems?

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    1. RAS2D will handle culverts the same way it has in the past, to my knowledge. I'm not sure what you mean by culvert systems, but you can have culverts in streams, in lateral structures, and in storage area connections. Those methods for modeling culverts should all still be available to you in RAS2D.

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    2. Chris, my apologies. I wrote in haste. I meant storm drain networks. I was curious if RAS2D will be able to model floodplain areas that also have underground SD.

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  7. When Hec-Ras 2D is available?. Is it going to release soon?

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    1. The latest info I have is that the beta version will be released to the public around the end of the calendar year. Please stay tuned

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  8. when 2-d will be available? is this 2 -D version available now?

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  9. Latest intel says end of January for the beta release...

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  10. *Fingers crossed for end of January!*

    By the way Chris, where do you get your intel from? This is the only site I am able to find with any information pertaining to RAS2D..

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    1. Better uncross those fingers:). Looks like the latest projection is end of February now. My intel comes directly from the HEC-RAS development team at HEC. They're a great group of guys and are always forthcoming with me about the latest and greatest RAS news.

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    2. Ah shucks. Better to cross my fingers than hold my breath I suppose.

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    3. Haha. Definately. Hang in there. We'll all be 2D modeling in no time...

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  11. Its middle of March, any update yet regarding release of Version 5.0

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    1. Latest indications are Version 5.0 beta will be released at the end of April, and the full version will be released at the end of the summer.

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  12. Are you aware if we can use this version to complete a 2D analysis of flow in a river? Are 1D cross sections needed to run the 2D part of the model?

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    1. Yes, when version 5.0 comes out towards the end of this month, you'll be able to do a 2D analysis of flow in a river. I think (though I'm not sure) you'll still need some cross sections. You can always set up "dummy" cross sections to fulfill this need.

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    2. In the Alpha version (August 2013) you needed to have dummy cross-sections, but I was told they were thinking about removing that requirement as some point.

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  13. Thank you for the reply. I am interested in Version 5.0's capability to model the change in velocity vectors and shear stress around flow deflection structures. Does 5.0 allow for different sized cells (smaller near structures, larger cells away) and how many cells can be allowed? I'm trying to figure out how to create an .flt file out of Civil 3D and am interested in what is 5.0's capacity for cell size and number so I know how big a surface I can make in 3D.

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    1. Version 5.0 will allow you to have different sized (and different shaped) cells to get more resolution around areas of interest. I'm not sure what the cell size/number limitations will be in 5.0, but I'm sure you won't have a problem for most applications.

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  14. any updates for the release date of ras 5.0 beta? thx

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    1. latest out of HEC is 2 to 3 weeks from now. Expect end of June.

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  15. Am working in a paper on flood plain mapping of Detchatu river in Dire Dawa , Ethiopia .
    I believe the beta version will help me and I will have help full comments for its improvement since am gone use it in depth.
    Would you please help me how to get beta version ?
    Many thanks

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    1. Please follow the directions on this post to get the beta version of HEC-RAS 5.0. http://hecrasmodel.blogspot.com/2014/06/update-to-hec-ras-50-beta.html

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  16. Great, I will try it. I hope the engine can be run from command prompt.

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