tag:blogger.com,1999:blog-1675184707067447729.post6292029886621805604..comments2023-07-12T07:12:04.697-07:00Comments on The RAS Solution: Mixed Flow Regime Options – LPI MethodChris G.http://www.blogger.com/profile/00354834185663924786noreply@blogger.comBlogger20125tag:blogger.com,1999:blog-1675184707067447729.post-44354453920413682282019-05-15T20:42:35.712-07:002019-05-15T20:42:35.712-07:00Hi Ioannis-
I don't know about the TVD solver ...Hi Ioannis-<br />I don't know about the TVD solver in Flood Modeller, but the LPI reduction factor dampens the "hyperactive" acceleration terms in the St Venant equation when you are close to critical depth. It is nearly always needed for dam breach modeling. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-15858429985700488572019-05-11T03:16:44.310-07:002019-05-11T03:16:44.310-07:00Hello Chris.
I would like to make a question just...Hello Chris.<br /><br />I would like to make a question just for clarification. Is the LPI in Hec-Ras the method for shock wave capturing (like for instance the TVD solver in Flood Modeller software)? Does Ras has any specific solver for this occasions (e.g. Dam Breach)?<br /><br />Thank you so much Chris in advance. Keep on teaching us!! : )<br /><br />Regards,<br />IoannisAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-4846833349950018302018-02-21T08:59:34.280-08:002018-02-21T08:59:34.280-08:00Lots of close cross sections, lots of resolution w...Lots of close cross sections, lots of resolution with your bridge htabs, try exploring other bridge modeling approaches. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-13315431811804802592018-02-19T23:41:26.733-08:002018-02-19T23:41:26.733-08:00Hello, I need to simulate flood in steep river (sl...Hello, I need to simulate flood in steep river (slope 15%) in 2D. 2D is not problem, but there are some bridges in the area. I wanted to simulate bridges in 1D and then use rating curves for 2D model to simulate these bridges. Problem is that there is a lot of warnings in 1D model and it is not computing right. I think it is caused by steep slope. Solution could be 2D model with bridges modeled as a gates, but there is no data for calibration of bridges flow. So what do you recommend to simulate bridges in steep rivers please?Michalnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-81820390259037308632017-03-08T08:10:35.516-08:002017-03-08T08:10:35.516-08:00If steady flow, and you're not sure of the reg...If steady flow, and you're not sure of the regime, try mixed flow. If it is indeed all sub critical, then you'll see that. Note that for unsteady flow, RAS will compute mixed flow automatically, whether you check the mixed flow box or not. Checking the mixed flow box for unsteady just adds stability to the computations when you are near or transitioning through critical depth.Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-81208319381701806722017-03-08T05:02:24.544-08:002017-03-08T05:02:24.544-08:00Hello i simulate a canal there is a box culvert in...Hello i simulate a canal there is a box culvert in the mont of the canal when I put the flow and run the simulation the canal and the culvret are submerged and there is a problem of flood so my question wich regim of flow i should use if Subcrit. Supercrit, mixed please help meAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-84552083100334791402017-03-03T08:05:46.256-08:002017-03-03T08:05:46.256-08:00A couple things about supercritical flow. First, ...A couple things about supercritical flow. First, you typically need much closer spaced cross sections. I would try doing even more interpolation. Also, make sure you are using the suggested contraction and expansion coefficients for supercritical flow (0.01 and 0.03 as opposed to 0.1 and 0.3 for subcritical). Finally, at the contraction and expansion, make sure you have your ineffective flow areas properly defined. If you believe there will be flow separation as flow contracts and expands, there needs to be ineffective flow areas. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-72441425601260608242017-03-03T06:23:04.908-08:002017-03-03T06:23:04.908-08:00Hello,
I have a question that concerns the mixed f...Hello,<br />I have a question that concerns the mixed flow regime for a steady flow analysis. I'm modeling a steep channel which contains a very narrow and flat section in the middle. A hydraulic jump occurs right before that section and a few meters downstream the flow changes back to supercritical. Now the computation works fine for all of the cross sections (interpolated or not) except for the one cross section where the flow changes from subcritical to supercritical. There I get the warning that the energy equation could not be balanced and that the program defaulted to critical depth. When i modified the Manning's values so the change of flow would take place at another cross section that type of warning now appeared for the other xs. So I don't think that my cross section data is bad and I'm sure I interpolated properly.<br />Is there something I could do?<br />Thanking you in anticipation, greetings from GermanyRaphaelnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-81256689608821050342016-10-03T08:48:16.351-07:002016-10-03T08:48:16.351-07:00This can happen if you do some manual changes the ...This can happen if you do some manual changes the the invert of one or more cross sections. Easy to fix. Go the the HTAB Param. button in the geometry editor. Make sure you have All River selected. Then highlight the entire column with the header "Starting El". Then click the button at the top that says "Copy Invert". That should fix it.<br />Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-55456790060926241022016-10-03T02:06:08.428-07:002016-10-03T02:06:08.428-07:00Hi, when i running unsteady flow, i've some pr...Hi, when i running unsteady flow, i've some problem like "HTab Parameter for starting elevation is lower than lowest elevation in the cross section main channel". what should i do ?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-73769104472694329422015-05-13T14:21:38.527-07:002015-05-13T14:21:38.527-07:00Thanks Chris, i couldnt believe it, but sediment t...Thanks Chris, i couldnt believe it, but sediment transport does not support supercritical flow. The version 5 beta neither...Anonymoushttps://www.blogger.com/profile/06135376448726112630noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-51953430393399624592015-05-01T09:54:47.275-07:002015-05-01T09:54:47.275-07:00I believe that sediment transport does not support...I believe that sediment transport does not support supercritical flow in the current version. Where you see Froude Number equal to 1 is likely a place where it wants to be supercritical, but since RAS will not compute a supercritical result for sediment computations, it defaults to critical depth (Froude number = 1). Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-51308635769002644952015-04-30T08:55:02.453-07:002015-04-30T08:55:02.453-07:00Hello, I have a question...
I’m modelling sediment...Hello, I have a question...<br />I’m modelling sediment transport (quasi-steady flow)<br />After running the model the Froude Number is equal or less than 1 in all the river, there is not super-critical flow. <br />In Sediment transport simulation there is not the MIXED FLOW option. You know something about this?<br /><br />I performed the steady and unsteady flow too, the results show that in these points the river has supercritical flow (froude number>>1). I don't understand why in quasi-steady froude are equal or less than 1.<br /><br />Thanks...Anonymoushttps://www.blogger.com/profile/06135376448726112630noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-73780638605569849972014-07-02T14:32:32.500-07:002014-07-02T14:32:32.500-07:00Thanks for the fast response Chris, the report is ...Thanks for the fast response Chris, the report is on it's way!Gerinchttps://www.blogger.com/profile/03446052517637543902noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-83691892287360321532014-07-02T14:19:50.434-07:002014-07-02T14:19:50.434-07:00Hey Gergely, Send me a debug report zip file of yo...Hey Gergely, Send me a debug report zip file of your model data files (go to this link if you don't know how to do that). http://hecrasmodel.blogspot.com/2008/12/hec-ras-debug-report.html<br /><br />I'll take a quick look to see if I can figure it out.<br />cgoodell@westconsultants.com <br />Chris G.https://www.blogger.com/profile/00354834185663924786noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-74216861621409257192014-07-02T14:14:37.282-07:002014-07-02T14:14:37.282-07:00Hi,
I'm now modelling a channel, which's b...Hi,<br />I'm now modelling a channel, which's bed slope is mostly big, and in some parts covered. The steady analysis gave a well solution, via mixed flow calculation, but I can't stabilize the same model for unsteady calculations. I followed tips from Your posts, which worked well before, but now the unstable state of the calculation stays incredibly huge. I interpolated the x's within the whole reach, the lower boundary is normal depth in both calculations, the upper one is flow, and flow hydrograph. I tried to follow Your advice here by changing the reduction factor and FT, but the ammount of errors in the calculation hardly changed, whatever I tried to change. What else could I do, or had forgot?<br />Thanks,<br />GergelyGerinchttps://www.blogger.com/profile/03446052517637543902noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-50712570516308585952011-12-12T10:21:58.675-08:002011-12-12T10:21:58.675-08:00Mr. Ali-
What kind of help are you looking for? ...Mr. Ali-<br /><br />What kind of help are you looking for? You can email me at cgoodell@westconsultants.com if you'd like a more efficient line of communication.<br /><br />ChrisChris G.https://www.blogger.com/profile/00354834185663924786noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-4417294579397598182011-12-11T08:59:02.363-08:002011-12-11T08:59:02.363-08:00Hi.I am Urban Planner & GIS expert by professi...Hi.I am Urban Planner & GIS expert by profession..My boss assigned project regarding Glacial lake outburst floods & use of HECRAS to show its effects onn near settlements...I am came up with BREACH model for such cases & HECRAS..can any one assist me, b/c it will help many poor people to cope with climate change & its impacts..<br /><br />Masood Ali from GilgitAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-59233345527461618782011-04-22T08:35:27.056-07:002011-04-22T08:35:27.056-07:00Hi Sarah-
When you turn on the mixed flow option,...Hi Sarah-<br /><br />When you turn on the mixed flow option, it is applied everywhere and at every timestep in your model. However, there will be minimal to no affect when and where Froude Numbers are low, depending on how you set your LPI controls. <br /><br />It could be an HTAB parameter problem. Make sure that in your steep reach, your HTAB computations start at the invert of each cross section and that there is good resolution (i.e. a lot of computation points). See this blog post for more info on HTAB parameters:<br /><br />http://hecrasmodel.blogspot.com/2011/03/more-on-htab-parameters.htmlChris G.https://www.blogger.com/profile/00354834185663924786noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-13443798481811836842011-04-21T16:33:28.916-07:002011-04-21T16:33:28.916-07:00Hi,
Is it possible to apply the mixed flow option...Hi, <br />Is it possible to apply the mixed flow option to some reaches and not to others? I am currently modelling a dam breach that flows from a steep small channel and into a large river that is relatively flat. When the mixed flow options are turned off the flat large river produces nice results but the steep channel's flow is not correct. When it is turned on (default), the steep channel produces good results. Playing around with the LPI does not seem to be helping. <br />Any thoughts? <br /><br />Thanks, <br />SarahUnknownhttps://www.blogger.com/profile/15368834537008694225noreply@blogger.com