Applies To Product(s): Bentley StormCAD, Bentley CivilStorm, Bentley SewerGEMS Version(s): 08.11.03.77+ Environment: N/A Area: Calculations Subarea: Original Author: Jesse Dringoli, Bentley Technical Support Group Problem Description Why do I see different hydraulic results between using a value less than 30 versus a value higher than 30 for the Maximum Network Traversals calculation option? Shouldn't the results be the same as long as they are converging? This applies to StormCAD as well as the GVF Rational numerical solver in CivilStorm and SewerGEMS. Reason Starting the SELECTseries 3 (a patch for 08.11.03.77, automatically included in later builds) a convergence enhancement is included and invoked when setting the Maximum Network Traversals to a value of 30 or greater. For any models where the Max traversals option is set to a value below 30, there should be no change in the results. The main reason why this enhancement was made was because some models had trouble converging with pipes flowing near the crown, in the 'instability zone'. This is the range of depths just below the pipe crown of a circular pipe, where there are two conjugate depths for the same flow. (yn and yn' in the below illustration of normal depth vs flow). As a side note, this problem occurs even with the simplified Capacity analysis option, because of the Actual Uniform Flow Velocity method. The velocity calculated from this method is always based on uniform flow, so the velocity is the same in both the Capacity and Backwater analysis methods (since the flow and physical properties stay the same.) One of our assumptions in this situation was causing an increased likelihood for the solver to have trouble converging. When using the uniform flow velocity method, if the pipe's depth corresponds to a surcharged condition (both start and stop depth above crown), the full flow velocity method is used (V=Q/A). This assumption causes instability in the case of pipes flowing near full, due to the velocity change occuring between the surcharged depth and non-surcharged depth condition. Basically the abrupt change could cause the solver to bounce back and forth between these states (surcharged depth/full flow velocity and non-surcharged depth / uniform flow velocity), leading to convergence issues. To fix this (with traversals set to 30 or higher), we changed the assumption here, so that it aligns with the normal depth assumption with the uniform flow velocity method. We removed the aforementioned depth check, so that the solver will only compare the pipe's flow to the "QMax" (typically about 15% higher than the "full capacity", which is the flow with normal depth equal to the crown) to determine when to use the full flow velocity method (V=Q/A). This is more consistent with the uniform flow assumption and is more stable. In short, the default should be left as 5 traversals (and default flow tolerance of 0.001) and if a model has trouble converging, try increasing the max traversals option. Between a value of 20 and 29 for maxtraversals, a relaxation algorithm will be applied. In difficult cases where pipes are flowing near the top, increasing it to 30 or higher should help, by eliminating the depth check as explained above. See Also My scenario is not converging on a solution. Convergence NOT achieved in StormCAD
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Wiki Page: Different results when changing Maximum Network Traversals
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Forum Post: RE: Convergence NOT Achieved
This question has always been on my mind because my company likes to archive files. When I want to archive or post files to share, which file formats do I need to archive/share a model?
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Forum Post: RE: Convergence NOT Achieved
In the latest version of the software the files that you need are the .STSW, .STSW.SQLLITE and the .STSW.DWH files, although the .DWH file is not really necessary unless you have a lot of color coding and annotations that you would like to retain. In older versions it would be the .STC, .STC.MDB, and the .STC.DWH files. If you go older than that then you'd only need the .STM file.
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Forum Post: RE: Help With setting up a VSP or VFD with 4 pumps.
Got it! i mean the priority part. I think I have a real issue on my hand. First of all I am analyzing power failure at a LS (an example of the specific LS is attached to the model. My goal is to be able to identify the first MH to overflow within the LS catchment. I have define all the controls as part of the failure analysis but I do not seem to be getting a reasonable results which reflects what you will typically see (See graph). Per the results I am getting, it takes about 15 mins for the LS to reach its highest HFL (19.65ft) after the power failure which is too short of a time. Don’t forget I have a 30 inch inlet pipe to the lift station connected to other 36inch pipes on the upstream end of the LS. I believe it should take the system some considerable amount of time for pipes downstream of the LS to surcharge, overflow before the water starts backing up. It’s taking my model only 15 mins to go through all these phases before overflow occurs. Something must be wrong and I need the experts. Thanks..
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Forum Post: RE: Convergence NOT Achieved
Hi, I uploaded two models using the Secure Sharefile method. One model is dated 14_0925 and the other model is dated 14_1002. The 14_0925 is an earlier model version of 14_1002, but both are largely the same to each other. Both models I uploaded currently converges. Note the results at the outfalls pipe (rational flow, velocity, etc.). ----- The pipes I am trying to revise are pipes P-A-3L-1 and P-A-3. I have profiles for these pipes set up in the model named "O Street - Earl - Outfall". Both pipes are surcharged. In general, I am trying to maintain a minimum 2' of freeboard between the HGL and finished grade. ----- For the 14_0925 Model: Based on the HGL/finished grade profile, I can downsize pipe P-A-3L-1. For pipe P-A-3L-1, I am trying to downsize the pipe from 54" to 48". The model converges after this change. Based on the HGL/finished grade profile I can also downsize pipe P-A-3. For pipe P-A-3, I am trying to downsize the pipe from 60" to 54". The model converges after this change. ----- For the 10_1002 Mode, which is largely the same as the 14_0925 Model: Based on the HGL/finished grade profile, I can downsize pipe P-A-3L-1. For pipe P-A-3L-1, I am trying to downsize the pipe from 54" to 48". The model does not converge after this change. Based on the HGL/finished grade profile I can also downsize pipe P-A-3. For pipe P-A-3, I am trying to downsize the pipe from 60" to 54". The model does not converges after this change. If I increase the Maximum Network Traversals, it converges, but the results are nothing similar to either before the change or the 14_0925. It also blows up the results of the other outfalls and storm drain systems. What's going on with this model? The pipes are also considerably surcharged; why is model having difficulty converging? Why do I need to even touch the maximum network traversals in the 14_1002 model if changing the pipe size was working fine in the 14_0925 model? Thanks
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Forum Post: RE: Help With setting up a VSP or VFD with 4 pumps.
Model uploaded. Thanks Jesse.
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Forum Post: RE: Help With setting up a VSP or VFD with 4 pumps.
Wait a second. This is a whole different problem. The GVF convex solver is great for most collection systems, especially those with significant pressure flow. In the gravity subnetworks, they work by routing flow to the flow to the wet well and then doing a backwater curve at each time step. This isn't the most accurate way to study filling a system. Instead, you should be using a full St. Venant equation solver, such as the implicit or explicit solvers in SewerGEMS. These would do a more accurate job in modeling the filling of a system. The network model should translate readily but the controls would be different. If you want to learn more about how the solvers work, check out the SewerGEMS help. For even more, look at the chapter on Unsteady Gravity Flow in our Wastewater Collection System Modeling and Design book or sign up for Bentley's on demand training. Best wishes, Tom
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Wiki Page: My scenario is not converging on a solution. Convergence NOT achieved in StormCAD
Applies To Product(s): Bentley StormCAD Version(s): 08.11.XX.XX Environment: N/A Area: Output and Reporting Subarea: Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem Description My scenario is not converging on a solution when once computed. I am getting a message in the calculation summary that Convergence is NOT achieved. Reason The calculation solver was not able to converge on a solution given the number of traversals of the network and/or other unresolved user notifications Steps to Resolve Make sure you have the latest patch set installed The latest patch set can be downloaded by following these instructions: http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/8175.aspx Try to resolve all user notifications that are pertinent to the network functioning properly In the user notifications dialog box you can double click on each notification and if it relates to a single element you will be brought directly to that element in the drawing pane. Read the user notification carefully and make the necessary changes to the element properties based on the notification details Increase the number of network traversals in the calculation options Open the calculation options for the current scenario (Analysis Calculation Options) Try increasing the number of network traversals. Start with a large number like 100. If that doesn't work try 1,000. If that doesn't work then you should probably post on the forums about the issue or create a service request for the issue, so you can get more help. If 100 does work then increase the number until you find the lowest number that still allows the model to converge. See Also Different results when changing Maximum Network Traversals
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Wiki Page: Can a different liquid be modeled in WaterGEMS/WaterCAD/HAMMER?
Applies To Product(s): Bentley WaterCAD, Bentley WaterGEMS, Bentley HAMMER Version(s): 08.11.xx.xx Environment: N/A Area: Layout and Data Input Subarea: Original Author: Scott Kampa, Bentley Technical Support Group Problem Description Can a different model besides water be modeled in WaterGEMS, WaterCAD, and HAMMER? Steps to Resolve WaterGEMS, WaterCAD, and HAMMER are designed to model any Newtonian, single phase fluid. Keep in mind that you may need to change the viscosity and specific gravity depending on the fluid To change this, go to Analysis Calculation Options. Double-click the active calculation under the "Steady State/EPS Solver" section to open the properties window. Next, find attribute "Liquid Label". You can click the ellipsis ("...") button to open the enigineering libraries of available liquids that come with the program. To select one of the available liquids, you can highlight the item and click the "Select" button. If you do not see the liquid you want among the available liquids, you can add new items to the engineering library. Steps to add items to the engineering library can be found at the following link: http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/modifying-and-adding-entries-to-engineering-libraries.aspx If you want to manually change the liquid or the liquid properties, without going through the engineering libraries. Simply change the values in the calculation options for liquid label, kinematic viscosity, and specific gravity. Note: HAMMER has been used successfully in the past for analyzing certain mining slurries. You need to change the fluid specific gravity and viscosity, and also use a friction factor that is appropriate for the slurry. If it isn’t Newtonian then HAMMER’s standard friction models don’t work very well. This is more of an issue after the initial transient occurs and the resulting pressure waves are being dampened by friction (although it is also a factor to consider when computing the steady state). HAMMER was developed with Water in mind, so the further you deviate from 1.0 specific gravity, the more the user would have to rely on his expertise in transient analysis to assess the results. See Also Related Discussion on crude oil What is the difference between pressure head and pressure? When the user changes the fluid, why doesn't the calculated pump head change?
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Forum Post: RE: Fire flow in dedicated fire main
Hello, The below Support Solution may be of interest to you: communities.bentley.com/.../9293.modeling-a-connection-to-an-existing-system.aspx This talks about the suggested approach to modeling the connection point to the existing system based on hydrant tests. You can then use the automated fire flow routine (see quick start lesson #5 in the Help) or manually add a demand of 1000 gpm to the hydrant in question (you may want to set up a separate scenario for this). There's also some good information on this in our Advanced Water Distribution Modeling and Management book, especially Chapter 8.4, Extending a System to New Customers: pages.info.bentley.com/books
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Forum Post: Gravity Notifications (Sewer Cad)
Dear All, What this notification means? "Manhole" "7199" "MH-969_581-C05" (N/A) "There should be only one non-diversion type conduit out of a gravity junction." Hydraulics Validation Best Regards, June
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Forum Post: PondPack - How to change rainfall depth for different storms?
We're using the SCS Type-II distribution for various storm events. PondPack will not let us input the rainfall depth for a specific design storm using the SCS methodology. I've used a lot of software over the years and have never run into this issue. Does anyone know how to deal with this? This should be a simple issue to address and it's not. Thank you,
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Forum Post: RE: PondPack - How to change rainfall depth for different storms?
Hello, Are you using PondPack V8i? PondPack does support applying rainfall depths to the SCS distributions. Section 2 of Quick Start Lesson 1 in the Help (Specify Temporal Rainfall Distribution Data ) should guide you through this process. There is also an entry on this in the following FAQ: communities.bentley.com/.../3055.whats-new-in-pondpack-v8i-faq.aspx How can I apply a rainfall depth to a dimensionless curve to create a storm event? First go to Components Storm Data. Click the new button and select "Time-Depth" or "Time-Intensity" and provide a name for your storm event group (equivalent to the "Design Storm" in previous versions). On the right side, click the new button and select "Add return event from dimensionless curve". In the window that appears, expand the library of choice and select your dimensionless rainfall curve. If you need to create a custom one first, you can do so under Components Engineering libraries. In the "generate storm event" window that appears next, provide a label, return frequency, total depth, etc and click OK. Your time-depth or time-intensity event will be constructed based on the entered depth and dimensionless distribution. If this does not help, please elaborate on the steps that you are taking and where you are getting stuck. If you need to send a model, you can use the process below: http://communities.bentley.com/p/bentleysecurefilesupload.aspx
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Forum Post: RE: Gravity Notifications (Sewer Cad)
June, It sounds like you have a flow split in your model at manhole "7199". Meaning, there is more than one pipe leaving the manhole. In SewerCAD, you will need to use the diversion feature to model this flow split. One of the outgoing pipes should be flagged as a diversion by setting "is diversion?" to "true". You can read more about diversions in the below Support Solution: communities.bentley.com/.../8582.aspx
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Forum Post: RE: Convergence NOT Achieved
Anyone have any luck with figuring out why changing the sizes of surcharged pipes would lead to the model NOT converging, when an earlier version converged after changing the pipe sizes?
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Forum Post: RE: Convergence NOT Achieved
In the 14_0925 model as you sent it, the max traversals option is set to 1000 In the 14_1002 model, it was set to 10. If you change the max traversals in the 14_0925 model to 10, to match the other model, it also has difficulty converging when downsizing one of those pipes. StormCAD is typically used to size pipes so they do not surcharge. Having numerous surcharging, near surcharging and/or flooding conditions in a StormCAD model is difficult to solve and can be sensitive as you have seen. As mentioned earlier, setting the max traversals option to a value of 30 or greater changes the way the model calculates in a surcharges condition. This can lead to more stable results, but can also lead to differences in results, which could be more noticable for certain models such as this one where a large portion is surcharged (due to the changes in velocity for these pipes which changes the system flow time which changes the flow). For this very sensitive model, try changing the average velocity method to Weighted Average Velocity. The outfall results are pretty close. Here's a comparison. Note that I used the latest version of StormCAD, 08.11.04.54.
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Wiki Page: Demand calculation with Continuous patterns and EPS Snapshot (Solution 500000059856)
Applies To Product(s): Bentley WaterGEMS, Bentley WaterCAD Version(s): 08.11.XX.XX Environment: N\A Area: Calculations Subarea: N\A Original Author: Jesse Dringoli, Bentley Technical Support Group Problem When using the EPS Snapshot calculation option, why is the calculated demand not equal to the base demand times the multiplier for that same timestep in that demand's pattern, when using the "continuous" pattern format? Problem number 33025 Solution Below is an explanation of the fields in the calculation options when "Is EPS Snapshot?" is set to "True", which is followed by an example for a better understanding: With a continuous pattern the calculated demand at a particular timestep is equal to the average of the calculated demand for that timestep and the next one. The "Equivalent Hydraulic Time Step" field is used in order to make sure that the pattern multipliers used in an EPS Snapshot run exactly match those in an equivalent EPS run. You need to specify the hydraulic time step of the EPS run that you wish to match. (The hydraulic time step is the time interval used between hydraulic calculations assuming that no intermediate time steps are required for controls.) The "Start Time" field in the calculation options is where you set the time that you want to run the EPS snapshot for. For example, let's assume the base demand on a given junction is 500gpm, the equivalent hydraulic time timestep in the calculation options is set to 1 hour, the pattern multiplier for timestep 8 is 1.0 and for time step 9 is 1.945, and the Start Time field would be 8 am (assuming the simulation was started at 12 am). The total calculated demand at the junction shown for timestep 8 will be (500 * 1) + (500 * 1.945) / 2 = 736.25. For the continuous pattern, if you want to achieve a demand that is very close to the one specified in the pattern you could set the "Equivalent hydraulic Time Step" field to a very small number like .5 minutes or .1 minutes. This should result in a calculated demand that is very close to 100% of the demand for a given junction for the specific start time that you selected. With stepwise, as long as the hydraulic timestep is less than or equal to the pattern timestep, the multipliers used for a certain timestep are taken directly from the pattern, with no averaging being done. However, if the hydraulic timestep is bigger than the stepwise pattern timestep, averaging is done. See Also
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Wiki Page: Demand during EPS not equal to base demand times pattern multiplier (Solution 500000059857)
Applies To Product(s): Bentley WaterGEMS, Bentley WaterCAD Version(s): 08.XX.XX.XX Environment: N\A Area: Calculations Subarea: N\A Original Author: James Falconer, Bentley Technical Support Group Problem When I use a demand pattern, why is the calculated demand at a junction not exactly the base demand times the pattern multiplier? The numbers seem to be close, but not exact. Solution In WaterCAD and WaterGEMS, the demand value at a specific element at a specific time, when using a continuous demand pattern format, uses special volume smoothing logic such that the resultant pattern is modified whilst preserving the total volume of the demand pattern for the known hydraulic time step and simulation duration. So, the demand value at a particular timestep will be the average of the demand at that specific timestep and the next timestep. For example: Base demand is 500 at Junction 101. Hour 8: Demand pattern is 1 Hour 9: Demand pattern is 1.945 Average demand at Junction 101 is (500 + 972.5) /2 = 736.25 When you check demand at hour 8 at Junction 101 the demand is 736.25. See Also
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Forum Post: TREX
I recently utilized a XML file to assign elevations to the nodes in a model through the TREX tool. Today, I added around 10 new nodes to the model. I planned to create a selection set of the new nodes and utilize TREX and the same XML to assign elevations to the new nodes. However, when I began the process, over half of the new nodes already had elevations assigned. I am puzzled as to how they got there. Is there a new feature of WaterCAD that stores the XML data and automatically assigns to new nodes? A nice feature if so, however, why would it assign some and not others? Could it be that the software interpolated between existing node values when I split pipes and I got no assigned elevation when drawing a new node in an area with no existing lines.
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Forum Post: RE: Gravity Notifications (Sewer Cad)
Jesse, What if I don't have Sewer Gems and Civil Storm? What can I do to approximate the diversion rating curve? What Im thinking right now, is that, If Sewer Cad cant do that, Is it possible that I can just represent them via one (1) pipe? Do the hydraulics of the upstream pressure lines will be affected? (Base on my observations its not?) The only affected is that the conduit having all the flow (instead of they are 2) it will be only one (1).? Do my observations are correct? Thanks again Jesse. Best Regards, June
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