In sewerGEM while running continuous simulation (SCS methodology), flow transition do occur. It means flow will vary from supercritical flow to subcritical based on water levels and flow controls within the network. Certain portion of the network might be under surcharge condition during the simulation hence it tells that those pipes are operating under pressure.
↧
Forum Post: RE: SewerGEMS notification
↧
Wiki Page: Tips for finding answers to Haestad product questions
Applies To Product(s): Bentley WaterGEMS, Bentley SewerGEMS, Bentley CivilStorm, Bentley StormCAD, Bentley PondPack, Bentley StormCAD, Bentley HAMMER, Bentley WaterCAD Version(s): XX.XX.XX.XX Area: Other Original Author: Mark Pachlhofer, Bentley Technical Support Group This article explains how to best search for content on Bentley Communities Background Bentley Communities is our website where you can connect, communicate, and learn from those around the world who contribute to global sustainability through infrastructure projects. This is where you can get technical support for Bentley products, receive Bentley product information and announcements, interact with peers, experts, Be MVPs, and Bentley colleagues, join an industry community, and share best practices and solutions, among other things. With Be Communities, you can be the best by connecting with the best in the industry. Bentley Communities also offers a search function that allows you to quickly find answers to any question you have related to any Bentley products. This makes the site a great tool to use for finding out what a certain messages in a application might mean, finding help on specific elements, or just for finding general information. We hope Communities can help to answer your questions more easily, facilitate discussions on important subject matters, and assist us in understanding more uses and needs for our software, so we can improve it in future releases. Steps to Accomplish Option 1 - Use keywords related to what you are looking for 1) First locate the search box at the top of the page you are on. 2) Start typing in a keyword of what you are looking for. A list of topics will appear and will change as you enter more data. For example, if you were looking for information on how to sort flextables you might type in "flextable sorting" as your search term. You would get results that look like this: Note that if you are in the Wiki section, the results will default to just the items in the Wiki. If you are searching from the forums, the results will default to just items in the Forum. However, you can also select to look at all of the Hydraulics and Hydrology section or the entirety of Bentley Communities as well. In addition, if you enter key words and then hit the Enter key on your keyboard, the search results will be for all of Bentley Communities. For best results when search for Haestad topics, it is best to use the dynamic list of the topics and not hit the Enter key. Option 2 - Use your favorite search engine 1) Use the same search structure as step 2 in option 1 with your favorite search engine and look for Bentley Communities entries.
↧
↧
Wiki Page: "Is variable speed drive?" vs "Is variable speed pump?"
Applies To Product(s): Bentley WaterGEMS, WaterCAD Version(s): 08.XX.XX.XX Area: Layout and Data Input Original Author: Jesse Dringoli, Bentley Technical Support Group Problem What is the difference between the "Is variable speed drive?" check box in the "motor" tab of a pump definition, and the "Is variable speed pump?" property of a pump node element? Problem ID#: 44136 Solution The "variable speed drive" check box in the pump properties is used to for energy cost analysis only. With a constant speed pump (Non-VSP) the motor speed, and thus the motor efficiency, is constant. However with a VSP, the motor speed changes, so the user must account for the different motor efficiency for various motor speeds. This check box allows you to enter a table of speed (relative speed factor) and motor efficiency. For a pump that is a VSP, that check box should be checked, since the speed (relative speed factor) will very likely not be constant (1.00). The "is variable speed pump" option in the pump properties allows you to choose if the pump can actually operate as a variable speed pump, where the motor speed can change over the course of the simulation. See Also
↧
Forum Post: RE: Finding Water Deceleration in Pipeline - Check Valve Slam Analysis
Manfredi, I consulted with my colleagues on this. Credit for the below answer goes to Mal Sharkey. This is a good reference: www.valmatic.com/.../DynamicCharacteristicsCheckValves11-2-11.pdf It’s not the closing time that causes high reverse velocities, it’s the deceleration. The deceleration also impacts the closing time. So, for higher system decelerations, the closure time is fast (because the reversing water helps push the valve closed). But, because deceleration is so quick, the reverse velocity is still high (even with a short closing time) and therefore likely to cause surge issues.
↧
Wiki Page: How can I find water deceleration in a pipeline with a check valve?
Applies To Product(s): Bentley HAMMER Version(s): 08.11.xx.xx Area: Output and Reporting Original Author: Jesse Dringoli, Bentley Technical Support Group Problem How can I find water deceleration in a pipeline with a check valve? Solution First, run the Initial Condition analysis and record the velocity in the pipe downstream of the check valve. Let's assume it is 4 ft/second. Next, run the transient simulation and open the Transient Results Viewer. Plot a time history graph of flow in the pipe downstream of the check valve and measure the time from when the pump turns off until the flow curve crosses the x-axis (i.e. when flow reaches zero). Let's assume it is 2 seconds. So the deceleration of the water column is 4 ft/second / 2 seconds = 2 ft/s^2. This is an average deceleration rate, which is typically what valve manufacturers provide. See Also Finding Water Deceleration in Pipeline - Check Valve Slam Analysis Reverse Velocity vs. Deceleration curves for a check valve
↧
↧
Wiki Page: Reverse Velocity vs. Deceleration curves for a check valve
Applies To Product(s): Bentley HAMMER Version(s): 08.11.XX.XX Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Question How can you input Reverse Velocity vs. Deceleration curves from the check valve manufacturer, into the check valve element in HAMMER? (to model different types of check valves that react differently) Answer HAMMER currently does not have a way to enter dynamic characteristic curves for check valves. That type of analysis requires a bit of judgement and interpretation. The reverse velocity vs. deceleration curves from the valve manufacturer don't typically tell you much about the relationship between flow and headloss in the check valve, or the rate the valve is closing (is it a linear closure, or does it start closing slowly and then accelerate?). What they do give engineers is a flow velocity 'delta' to use in Joukowsky's Equation, dH = dV . a / g (where dH is change in head, dV is change in velocity, a is wave speed and g is gravitational constant - see Bentley's Advanced Water Distribution Modeling & Management book, section 13.3 for details) so you can do a quick check of the change in head in the pipe as the check valve slams shut. So, these curves are a bit more of a 'rule of thumb' than actual physical valve parameters and should be used with appropriate caution - but they are usually the best information available from manufacturers on dynamic behavior of check valves. By default, the check valve node and check valve pipe attribute close instantly upon sensing reverse flow (i.e. reverse velocity = 0.) If the reverse velocity is not high, then it should be ok to model them as regular check valves that close instantly. However, in version 08.11.XX.XX+, you can utilize the new slow-closing feature of the check valve nodal element. This allows you to specify a check valve closure time and opening time (over which the check valve is assumed to close linearly.) With this feature, you would set different closing times, run the model, then review the results and look at the flow through the valve as it shuts. You might need to iterate a couple of times until the reverse flow corresponds to your reverse velocity for the valve. In the future, we will look into the possibility of enhancing HAMMER to allow entry of dynamic characteristic curves (Enhancement #202422). In the meantime, a conservative assumption may be best. A note on closing time vs. deceleration vs reverse velocity System deceleration causes high reverse velocities, not the closing time. So, for higher system decelerations, the closure time is fast (because the reversing water helps push the valve closed). But, because deceleration is so quick, the reverse velocity is still high (even with a short closing time) and therefore likely to cause surge issues. See Also Finding Water Deceleration in Pipeline - Check Valve Slam Analysis How can I find water deceleration in a pipeline with a check valve?
↧
Blog Post: Building and maintaining a GIS model with WaterGEMS/SewerGEMS/HAMMER for ArcMap
A question that comes up every now and again when I talk to users is how do I prepare my GIS data for use in WaterGEMS or SewerGEMS for ArcMap? I find the question usually arises from a need to figure out how to keep GIS data in sync for building a model or updating a model using ModelBuilder. Below are steps that outline a good process to use in order to 1) Familiarize yourself with WaterGEMS or SewerGEMS properties and how they work 2) Learn how ModelBuilder works for different data types when building and maintaining a model. 1) In WaterGEMS or SewerGEMS write down the field names that you want to add to your shapefile or feature class, which are going to be used in ModelBuilder to import/export data. If you're updating a field that is dependent upon another field being set to a Boolean value, for example, “Has User Defined Length?”, make note of it and about setting up fields to work with in ModelBuilder. 2) Understand how to use GIS-ID's as your unique identifiers for an element . GIS-ID's can be used to maintain a one to one link between your GIS file and the software property element, a one to many link, or a many to one link. There is more information about how this works found in the help documentation under the search term ‘GIS-ID’. Some specific help document names are 'GIS-ID's' and 'Preparing to Use Modelbuilder'. If you plan on maintaining your GIS system and hydrologic model over a long period it’s worth researching and setting this up. 3) Create shapefiles or feature classes with the snapping feature on to assure all elements are linked together. This will prevent gaps in connections between elements and your connectivity will be intact the way it was originally connected in the GIS shapefile or feature class instead of allowing the possibility for a misconnection. If the shapefiles or feature classes are already created, make sure to edit your data so the features are very close together or are snapped. The smaller the gap the smaller the tolerance must be set during an import with ModelBuilder. 4) When creating your shapefile make sure to snap all the lines(pipes) to end points (junctions, pumps, catch basins, manholes, etc …). If you snap the lines to mid-points when Modelbuilder builds your network it will create a junction on the end of a pipe that is attached to the mid-point of the other pipe, but the pipe won't be attached. When this occurs, you'll have to use the batch pipe split tool (Tools > Batch PIpe Split) to connect the lines, which would add additional work. For example, if polyline P-1 connects to P-3 below in your GIS shapefile (feature class) at a mid-point as shown in the screen shot below, when constructed in Modelbuilder the junction that is created at the end of P-1 will appear to be attached to P-3, but it will not have split the pipe. Instead of having two pipes, say P-4 on the left side of where P-1 splits the pipe and P-5 on the right side, you just have one single pipe, P-3. In the diagram below the junction that is created after running Modelbuilder does NOT split pipe P3, therefore, you would have to perform a batch pipe split. The best approach to build your polylines file along with your points features in your GIS and make sure to snap all the elements together at endpoints. If you do this you'll have no trouble creating your network model with Modelbuilder 5) After your shapefiles or feature classes have the fields that you need to keep track of your GIS data run a test using ModelBuilder on a small amount of data. This makes it easier to understand how the ModelBuilder process works.
↧
Wiki Page: Customizing FlexTables for viewing and reporting data -- Moving, adding, and removing columns
Applies To Product(s): Bentley WaterGEMS, Bentley WaterCAD, Bentley SewerGEMS, Bentley SewerCAD, Bentley CivilStorm, Bentley StormCAD, Bentley HAMMER, Bentley PondPack Version(s): 08.11.xx.xx Area: Output and Reporting Original Author: Jesse Dringoli, Bentley Technical Support Group Problem How can I add or remove columns from my FlexTable? How can I customize FlexTable reports? Solution To customize a FlexTable, click Edit button at the top of the FlexTable to choose which fields you would like to be displayed. This will open the dialog below, which will show the available columns on the left and the columns that are already in the FlexTable on the right. You can now add columns by selecting the property from the Available column and click the Add button (">"). To remove unnecessary or unneeded columns, highlight the property from the Selected column and click the Remove button (" Report Options. If the appearance of the FlexTable report is still unsatisfactory, you have two options. First, you could copy the entire FflexTable to clipboard by clicking the gray cell at the top left corner and then click the copy button and select Control+C on your keyboard. You can then paste in an external application such as Microsoft Excel and format and print from there. In addition, you can export the file as a .CSV file by clicking the Export to File button in the upper left of the FlexTable. The .CSV file type can be opened in Excel as well. The other option, which is available in versions 08.11.01.xx and greater, is XML reporting. In the FlexTable, when clicking the report button, choose "Report in XML". You can then apply a custom style sheet and thus have better control over the FlexTable printout. See Also How to duplicate FlexTables
↧
Wiki Page: Preparing GIS data for use in the hydraulics and hydrology products
Applies To Product(s): Bentley WaterGEMS, Bentley SewerGEMS, Bentley CivilStorm, Bentley StormCAD, Bentley PondPack, Bentley SewerCAD, Bentley HAMMER, Bentley WaterCAD Version(s): 08.11.XX.XX Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem I'm using GIS data to construct a model that is going to be used to build a water or storm sewer model. What's the best way to prepare the data to make it easy to use with the software's element properties design? Solution 1) Familiarize yourself with the ModelBuilder field mapping step (step 5) and the properties of the elements that you'll be importing in your model. Write down the field names that you want to add to your shapefile or feature class. If you're updating a field that is dependent upon another field being set to a Boolean value make note of it and read the following wiki article . 2) Understand how to use GIS-ID's as your unique identifiers for an element . GIS-ID's can be used to maintain a one to one link between your GIS file and the software property element, a one to many link, or a many to one link. There is more information about how this works found in the help documentation under the search term GIS-ID. Some specific help document names are 'GIS-ID's' and 'Preparing to Use Modelbuilder'. 3) Create shapefiles or feature classes with the snapping feature on to assure all elements are linked together. This will prevent gaps in connections between elements and your connectivity will be intact the way it was originally connected in the GIS shapefile or feature class instead of allowing the possibility for a misconnection. When creating your shapefile make sure to snap all the lines(pipes) to end points. If you snap the lines to mid-points when Modelbuilder builds your network it will create a junction on the end point of a pipe that is attached to the mid-point of the other pipe, but the pipe won't be attached. When this occurs you'll have to use the batch pipe split tool (Tools > Batch PIpe Split) to connect the lines. For example, if polyline P-1 connects to P-3 below in your GIS shapefile (feature class) at a mid-point as shown in the screen shot below, when constructed in Modelbuilder the junction that is created at the end of P-1 will appear to be attached to P-3, but it will not have actually split the pipe. Instead of having two pipes, say P-4 on the left side of where P-1 splits the pipe and P-5 on the right side you just have one single pipe, P-3. In the diagram below the junction that is created after running Modelbuilder does NOT split pipe P3, therefore, you would have to perform a batch pipe split. The best approach to build your polylines file along with your points features in your GIS and make sure to snap all the elements together at endpoints. If you do this you'll have no trouble creating your network model with Modelbuilder 4) Run a test using ModelBuilder on a small amount of data to understand how the process works. This will allow you to understand which fields you'll need to add to specific shapefiles. For example, elevation invert fields that you want to import for conduits/pipes should be added to the conduit/pipe shapefile. if you plan on manually setting the invert (start) and invert (stop) instead of allowing the fields to automatically be populated by the manhole inverts. If you are automatically allowing the invert (start) and invert (stop) to be populated by the software you can omit this field from the conduits/pipes and enter it in the manhole shapefile. You can read more about this in the wiki article linked to above about using Boolean values in ModelBuilder. See Also Converting your model elements to shapefiles Building a model using ModelBuilder WaterGEMS for ArcGIS FAQs SewerGEMS for ArcGIS FAQs
↧
↧
Forum Post: SewerCAD "Property Connection" not showing up under Layout
SewerCAD "Property Connection" not showing up under Layout. Version: SewerCAD V8i (SELECTseries 5) Any suggestions? Wrong software version? Is there a work around? Thanks in advance.
↧
Forum Post: Setting a pump Pattern
Ref: http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/118468 Hello Jesse, Could you please elaborate how I can assign the pump pattern to a pump? I have explored and so far, I could find the only possible method to be a. declaring the pump as variable speed pump b. Set VSP type as Pattern based and c. set the pump pattern as relative speed pattern. However, my pump is not of VSP type and it is not following the pattern in EPS run. What I am trying to achieve here is, two lift pumps to a tank operating in tandem for a certain period. So, when one pump is switched off, other is pumping to the tank. Thanks for your insight. Regards, Imtiaz
↧
Forum Post: RE: How can I model a 48 hr pump Pattern using water cad
Hello Imtiaz, The method you describe is correct - choose True for Is VSP, choose Pattern as the type and set up the pattern of time vs. relative speed factor. Even though your pump is not a VSP, you can use this method to have a pattern of 1 for on and 0 for off. Make sure to select the pattern in the pump properties after setting it up. If this does not work in your model, please send a copy for review per the below instructions: communities.bentley.com/.../32100.sharing-hydraulic-model-files-on-our-forum
↧
Forum Post: RE: SewerCAD "Property Connection" not showing up under Layout
Hello Grae, The Property Connection element was added in the CONNECT Edition, so you will need to upgrade in order to take advantage of it. More on that here: What's new in SewerCAD CONNECT Edition Property Connections Introducing individual Property Connections to your model
↧
↧
Wiki Page: Changing the width of the border lines of catchments or other polygon elements
Applies To Product(s): CivilStorm, SewerGEMS, StormCAD Version(s): 08.11.xx.xx Area: Modeling Original Author: Scott Kampa, Bentley Technical Support Group Problem Is there a way to change the width of the border for the catchment? Solution There is no direct way of doing this, but it can be done by adding a color coding feature. Under the Catchment section of Element Symbology, create a new color coding for some attribute, such as "Area". Under the Color Maps section, change the Options to "Size". When you initialize, change the multipliers all to the same number greater than 1 (which is the default). Then choose "Apply" and "Okay". The border on the catchment should now be wider.
↧
Wiki Page: Notifications about conduits operating under pressure or being in the Preissmann slot
Applies To Product(s): SewerGEMS, CivilStorm Version(s): 08.11.XX.XX, 10.XX.XX.XX Area: Modeling Original Author: Scott Kampa, Bentley Technical Support Group Problem What does the following user notification mean: "One or more junctions are pressurizing all conduits; or conduits are in Preissmann slot at this location for this time-step." "Conduit is operating under pressure." OR How does the implicit solver (SewerGEMS) transition from pressure flow to gravity flow and vice versa? Problem ID#: 67974 Solution This message is generated when a pipe's HGL is above the top elevation. The numerical solver does not distinguish between conduits and pressure pipes in the model, so this message may be generated when pressure pipes exist in the system. You can view profiles of the system to see the HGL across the system, as a way to see any gravity pipes in the model are surcharging. For more information on Preissmann slot method used in this situation, there are topics about this in the Help documentation. Search for the term "Preissmann slot" or "Pressurized Flow".
↧
Forum Post: RE: SewerGEMS notification
To supplement Sarat's good answer: "A supercritical to subcritical transition is occuring for this element." - this is telling you that a hydraulic jump may be occuring, which you might want to be aware of. "Froude number is greater than 1 for sections in this element." - This is telling you that supercritical flow occurs in the pipe at some point, which you might want to be aware of. "Conduit is operating under pressure" - This means the HGL is above the top of the pipe (surcharged), which you may want to be aware of. See more here: Notifications about conduits operating under pressure or being in the Preissmann slot
↧
Wiki Page: Troubleshooting unstable SewerGEMS and CivilStorm results using the implicit solver
Applies To Product(s): SewerGEMS, CivilStorm Version(s): 08.11.XX.XX, 10.XX.XX.XX Area: Modeling Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem How do you troubleshoot SewerGEMS or CivilStorm results using the implicit solver? Solution If your hydraulic model provides unexpected results or high continuity error (mass balance), try the following steps: 1. Check the model for data entry problems: Use the Validate command and look at the warnings and/or errors that are reported. Fix as many as you can while keeping in mind the goal of the model is to make it resemble what you have in the field as closely as possible. When you Calculate the model, validation routines are performed that are not included during a Validate operation. Review the warnings and/or errors that are returned after calculating the model too. Examine Graphs and Profiles. Create Flow plots at splits and at pump discharge areas and look for jagged peaks in the plot. Common data problems: Conduits or Channels: I ncorrect channel or conduit slopes : Reasonable slopes are generally small and rarely negative. You can view slopes along a reach visually by using the Profiles feature. You can find unusually large or negative slopes through User Notifications and FlexTable reports. You can Color Code link elements by Slope and look for excessive values. If the model has parallel conduits connected by a flat (slope value of 0) conduit, try making that conduit Inactive. I nc orrect Channel or Conduit size : Look for unusual size changes along a reach. Color code drawing by Diameter to look for this type of discrepancy and or create numerous profiles for an even better visual of your pipe sizes. This will help you locate bottlenecks in the system that could be causing calculation problems. You will also see user notifications if the diameter decreases as you move downstream. A mix of very long and very small pipes . Eliminate or combine short pipes because their effect on routing is small. Break exceptionally long pipes into mutliple pipes that are each roughly the same length as other pipes in the network. Very low flows : If flows are less than 0.01 cfs (0.001 m3/s), depths may fall below accuracy tolerances. Consider omitting dry pipes from the model (or combine/skeletonize them out) Pumps and pressure pipes: Pumps operating at or near the shutoff point defined on the pump curve When pumps operate at or near the shutoff head point on their curve review downstream results for accuracy. In the past there have been cases where graphs of the hydraulic grade would show large jumps that were out of the range of the normal pump operating points. To resolve this adjust the pump curve by reducing the flow or head accordingly to produce a curve that operates near the point the pump is running at in the model. The new pump curve can be tested using the SewerCAD (GVF-Convex solver) because the pump calculations are done using the pressure solver, which is more stable for pump calculations than the implicit solver. Pumps using a multiple point pump curves that have large differences between flow or head values on the pump curve. Pumps that cycle on and off very quickly - check the on/off elevations and wetwell size/operating range. Make sure the pump curve is sized appropriately for the wetwell size. Use a small calculation timestep if fast pump cycling is needed. Manifolded pumps (pressure pipes combining together). This may require a small calculation timestep. The Implicit solver tends to be better than the Explicit (SWMM) solver with this. Unnecessary check valves on pressure pipes. Users commonly use the option to have a check valve on pressure pipes that are directly downstream of a pump, but this is unnecessary because pumps already have built in check valves. Keeping them can cause unnecessary difficulty for the solver. Parallel pumps - the short pipes adjacent to the pump may need to be designated as Virtual. Try toggling the "is virtual?" setting. Ponds and pond outlet structure s: Flow control structures on relatively small storage nodes (ponds, wet-wells). Consider combining ponds, modeling as manhole storage or using a very small calculation timestep. Unusually small ponds compared to their inflow. Consider modeling as a manhole with downstream conduit start control structure, or use a very small calculation timestep. Significant backwater/tailwater effects against an upstream pond outlet structure. If a backup occurs and acts as tailwater for an upstream pond outlet, this can be extremely challenging to solve. A very small calculation timestep may be necessary, the Explicit (SWMM) solver may need to be used (with a very small Routing Step). Or, consider changing the model layout or otherwise resolving the downstream backup to prevent this challenging situation. Conduit control structures : Using a start control structure tends to be more stable than a stop control structure Use a smaller calculation timestep in cases where a large change in flow can occur with a small change in head, such as when using a weir. Significant backwater/tailwater effect against a conduit control structure can be challenging to solve. A very small calculation timestep may be necessary, the Explicit (SWMM) solver may need to be used (with a very small Routing Step). Consider using an approximate pond (representing the ponded area upstream of the control) with pond outlet structure, which might work better in some situations Storm Data: Make sure the storm data entered has labels and the data entered is correct. Verify data input in the following other challenging situations Flow splits at weirs and orifices that are dry at certain points during an extended period simulation. Hydrograph rapidly changes within a short time (minutes). Very sharp flood waves - check catchment runoff hydrographs to make sure they are correct. Near-critical slopes. Significant and abrupt changes in the conduit size, shape and/or slope. Looped networks. Significant backwater conditions. System inflows vastly exceeding the system capacity resulting in mass flooding. 2. Simplify where possible Dynamic solvers tend to be complex, and little changes can sometimes make a big difference. What you should keep in mind when creating a dynamic model is to keep things as simple as possible and only model what you really need to study. In other words, if there are some conduits that can be left out because they won't have a significant effect on what you are studying or don't provide a lot of flow (near-dry) don't put them in the model or take the flow they would produce and add it to another node element as an inflow. With dynamic modeling less is better than more. If you're working with a very large model, you may have a much easier time splitting it into smaller subsections if possible. Then, work on the sections one by one. Trying to troubleshoot results in a very large model can be cumbersome and overwhelming. Examples 1) Parallel conduits with the exact same physical properties . Instead of putting both conduits in the model you might model this as one conduit with 2 barrels. 2) A pond with an outlet structure. Let's say the outlet structure was made up of a 24 inch orifice and a weir at the very berm of the pond. After going through the outlet structure the water goes into a 24 inch conduit. Assuming the water never gets up to the level of the weir what you could do to simply this situation is set the Pond Outlet Structure property for "Has control structure?" = 'No'. In this situation, this can be done because the conduit was the same size as the orifice, so the conduit will act as the controlling structure for incoming water. 3) A wet well with a sanitary load. Remove the sanitary load that is directly on the wet well and add it to a manhole upstream of the wet well or create a dummy manhole directly upstream and connect it to the wet well. Before: After: 3. Adjust the calculation options to reduce the continuity error Default values for calculation options will work for the majority of cases, but some systems need small adjustments to converge. When the calculation is moving very slowly (you can observe that the model is stuck at certain times) or the results show apparent instabilities, it is an indication that the model is experiencing difficulties in converging to a stable and robust result. Try adjusting calc options in the order below. This is an iterative process and only one option should be adjusted at a time to see whether it gives better results or worse results. If the choice provides better results see if you can adjust it again more in the same direction to provide even better results than the first choice. For example, if changing the computational distance at 50 ft provides a continuity error of 25% and adjusting to 10 feet provides a continuity error or 15% then try to adjust it further to 5 feet to see if you can reduce the continuity even more. The goal with this is to get the continuity for the model under 5% and the lower the error the more accurate your results. Initial conditions: Options include warm start or transitional start. Try both and see if one gives better results for your system. Calculation Option Suggested Range of Values Computational Distance 5 ft - 75 ft Calculation Time Step 0.005 hr - 0.025 hr NR Weighting Coefficient 0.7 - 0.990 Relaxation Weighting Coefficient 0.6 - 0.990 NR Iterations 5 - 20 LPI Coefficient 1.0 - 15.0 Most of the time you can get the continuity error under 5% using the 4 options above. If you still need to adjust things after that continue in the order below. Try an NR Weighting Coefficient value of between 0.9 and 0.99 with the default Computational Distance and Calculation Time Step. Set NR back to default and try reducing the Computational Distance value. Set Computational Distance back to default and try reducing the Calculation Time Step value. Keep the Calculation Time Step the same and repeat the above steps. Try increasing the the NR Iterations to 20. Try increasing the LPI Coefficient to a value over 5.0. You do not need to go higher than 15. Note: There is no absolute rule on whether the time step, LPI Coefficient, or the NR weighting coefficient should be changed or to what specific value; normally you should reduce the time step and increase the NR coefficient but sometimes the opposite can also help. 4. Isolate problems areas: Isolate the problem area by incrementally deleting small sections of your model and re-computing. This may help you narrow down the source data that the engine has trouble with. It may expose data entry issues or areas that are exhibiting common modeling difficulties. 5. Determine at what time step the problem occurs. Look for what is happening at that time. Is a weir beginning to overflow? Is it the first time a large pump comes on? Sometimes it's easiest to look at your user notifications for the time or locate the problem on a profile and slide the time browser bar to that location before examining the model. 6. Switch to using the Explicit (SWMM) numerical solver (Analysis > Calculation Options > Click on the active option to open the properties). If there are problems when using the SWMM engine, try changing the Routing Method from Dynamic Wave (default) to Kinematic Wave or Uniform Flow. These methods do not handle backups as accurately as dynamic wave, but they tend to be more stable. If the results are still not stable with the SWMM solver (as seen in the summary output text report), try reducing the Routing Time Step calculation option. Suggested value range: 1.0 sec - 30 sec. Smaller values tend to yield more stable results. Note: Headlosses at nodes are ignored during periods of supercritical flow. Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver See Also
↧
↧
Wiki Page: Transient pressure wave not dampening or unexpected lack of headloss
Applies To Product(s): Bentley HAMMER Version(s): 08.11.xx.xx Area: Calculations Original Author: Scott Kampa, Jesse Dringoli, Bentley Technical Support Group Problem Description Symptom A - waves not dampening No matter how long I run the transient simulation in HAMMER, the surge waves (such as the pressure or HGL over time) never dampen or settle down to a final steady state condition. For example the pressure oscillated back and forth forever. Sympmtom B - unexpected lack of headloss across a pipe or Orifice-Between-Pipes When viewing a profile across a pipe or across a Orifice Between Pipes node element, no headloss is observed. Solution For pipes that start with a positive flow and end with zero flow If you have flow in the pipe in question during the initial conditions, but then close it off during the transient simulation (such as from a valve closure), most likely you are not seeing the surge waves dampen (reach a final steady state) or are seeing a lack of headloss, due to the lack of flow. Without flow, there is no headloss, and no dampening of surge waves, so the hydraulic grade will oscillate back and forth without settling down. If the pipe is connected to a reservoir or tank, you can have a small amount of water movement that can slightly dampening the waves. Also if you have a small demand anywhere and the pressure is positive at that location, the outflow can induce a flow that can dampen the pressure wave. You can try adjusting the Transient Friction Method in the transient calculation options as mentioned in the below article, but that may not necessarily help. You might consider simply accepting this behavior. For example if you need to design the system based on the max or min pressure, you may already have the information you need to proceed. "Unsteady" vs. "Unsteady - Vitkovsky" transient friction methods in HAMMER You can also observe this in the "sample1.wtg" file that ships with HAMMER, located in the "Samples" subfolder - the pipe in this model has no headloss, so attenuation doesn't occur. If you reduce the stop HGL of that pipe and re-run, the wave will be attenuated due to friction. For pipes that start with zero initial flow This situation can sometimes occur in pipes that have zero flow in the initial conditions. The likely cause of this is the value calculated for the pipe's Darcy-Weisbach friction factor, f. If the friction factor is zero, you'll have no headloss, and thus nothing to dampening the pressure wave over time. The HAMMER transient solver uses the Darcy-Weisbach friction factor, f, for the frictional losses in a model. In pipes with non-zero initial flow, the Darcy Weisbach coefficient is calculated based on the headloss across the pipe. In pipes that have zero flow in the initial conditions (which may occur for many pipes when simulating a pump startup event), the Darcy Weisbach coefficient will be computed based on the entered Hazen-Williams, Darcy-Weisbach, or Manning's coefficient, using the the Von Karman equation to calculate the Darcy-Weisbach friction factor, based on the Roughness height and diameter: DW f = (1.0 / (2.0 * Log10(Diameter / roughness height) + 1.14)^2 However, calculation 'noise' can sometimes occur in the initial conditions, causing the flow in a pipe to be near-zero instead of exactly zero. In your transient calculation options, you will see the tolerance that HAMMER uses to determine pipes that have zero flow, to account for this situation. In some cases, you may need to either make the "accuracy" value smaller in your steady state calculation options, or increase the flow tolerance value in the transient calculation options. Similar to a valve discharge coefficient, if the flows are near zero but above the flow tolerance, the coefficient that HAMMER computes to use for that pipe may be unreasonable (since it's based on a tiny headloss), especially when higher flows occur when the pumps are on. This situation can happen even if your pipe has a 'real', non-zero flow that is relatively small. To check HAMMER's computed friction coefficients, open the "Output log" under Report > Transient Analysis Reports, and scroll down to the section titled "Pipe Information". The flow tolerance determines if a pipe is considered as having zero flow or not. The best value to use for the Flow Tolerance field in the transient calculation options depends on the modeling situation. If you have pipes whose flow is zero in the initial conditions (such as near a pump that is off or a closed valve), you will need to make sure the flow tolerance is higher than the flow seen in those pipes. There's always going to be a little bit of calculation noise, so pipes whose flows should be zero might be something like 0.0004567. So, be sure to change the decimal precision on both the flow tolerance field and the computed flow field and compare the two. If all of the pipes in your model have positive flows, you don't need to worry about what to set the flow tolerance to. Please note, if you have zero flow in conduits, there is no friction and no headloss, and the minor loss coefficient is ignored. When the flow in a pipe in the initial conditions is less than the tolerance, it will be considered as having exactly zero flow during the transient simulation, which changes the method by which HAMMER computes the Darcy-Weisbahc friction factor to use for those pipes. The flow tolerance should be small enough so that pipes with positive flow aren't considered as having zero flow, but large enough so that pipes that do have zero flow are considered as such. So, if you have a pipe that basically has zero flow in the initial conditions, yet some numerical noise causes it to be slightly above the tolerance, the friction factor will not be accurate. If the Darcy-Weisbach friction factor is calculated as zero, this will basically mean that the pipe is frictionless and you will see oscillating flow in the system with dampening. In such cases, you may need to review the Steady State/EPS solver Accuracy value and the Transient solver Flow Tolerance setting so that the friction factor is correctly calculated. This situation can also happen with the Orifice Between Pipes element; if the flow through it is less than the tolerance, it will use the entered nominal head and flow value to calculate headloss, but if the flow is higher than the tolerance, it will try to use that flow along with the head drop to calculate the coefficient used to calculate change in headloss during the transient simulation. So, if the flow through it is higher than the tolerance but yields a headloss of zero, it will use a zero discharge coefficient and thus you'll see zero headloss.
↧
Wiki Page: Modeling An Initially Partially Closed Valve [TN]
Applies To Product(s): Bentley HAMMER Version(s): CONNECT Editioni and V8i Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Overview This technote explains how to set up an initially partially closed valve that changes positions during the transient simulation. An example model is provided for demonstration, and version 08.11.01.32 of HAMMER is assumed. Background In previous versions of HAMMER, all valves (including TCV, GPV, PRV, etc) were assumed to be either fully open or fully closed in the initial conditions. So, the transient operating rule (which describes when and how fast a valve closes during the transient simulation) was required to begin with either 100% (fully closed) or 0% (fully open). However, as of HAMMER V8i SELECTseries 1, you can now model a valve that is initially partially closed. The process by which this can be done is described below. Establish the Initial and Fully-Open Conditions The first thing you will need to do is enter the head loss or discharge coefficient that describes the hydraulics of the valve during the initial conditions. You must also enter the coefficient for the fully-open position of that valve, so that HAMMER can determine the relative discharge coefficient at certain positions of the valve (discussed later on in this technote.) 1. In the properties of the TCV, select "Discharge Coefficient" as the "Coefficient Type", then set the initial status to active. Enter the discharge coefficient representing your valve's initial position. 2. For the "Discharge Coefficient (Fully Open)" field, enter the discharge coefficient representing the valve in its fully open position: How can I Determine the Discharge Coefficient? Most valve manufacturer can provide a table of discharge coefficient for a range of valve positions. The discharge coefficient is sometimes referred to as "Cv" and describes the flow for a unit pressure (such as gpm/psi 0.5 ). So, the discharge coefficient for a certain desired initial closure position can be looked up on the table. For example, consider the below table: In this case, the fully open discharge coefficient would be set to 10.0. If you know the valve is initially 20% closed, the initial discharge coefficient would be set to 5.0. What if I'm not using a TCV? Note: skip this section if you are using a TCV As of version 08.11.01.32 of HAMMER, only the Throttle Control Valve (TCV) supports initial partial closure. If you're using a FCV, PRV, PSV, PBV or GPV, you'll need to convert it to an equivalent TCV first, using the below steps. Note: when computing initial conditions with any valve type, there will be one single specific head loss across the valve for that steady state condition. HAMMER converts this head loss into a discharge coefficient to be used in the transient calculations. 1. First, compute initial conditions to see the head loss through your valve. The below example uses a GPV: This head loss will be based on the type of valve you choose. For example for this GPV, the head loss was based on the GPV head loss curve. In another example, the head loss through a FCV would be the head loss necessary to achieve the desired FCV flow rate. To derive the discharge coefficient, you can use the following formula: Cv = { (39.693 * D 4 ) / [Hl / (V^2 / 2g) ] } 0.5 Where Cv is the discharge coefficient (cfs/(ft H2O)^0.5), D is the diameter (ft), V is the velocity (ft/s) and Hl is the head loss (ft). However, a shortcut can be employed to find the discharge coefficient… 2. Go to Analysis > Calculation Options and open the transient calculation option set associated with the current scenario. In the properties of the calculation options, choose "True" for "specify initial conditions?" 3. Go to Tools > Copy Initial Conditions. Choose the desired timestep (0.000 hours for steady state) and click OK. This will copy the discharge coefficient to a special field in the valve properties, which you can view under the "Transient (Physical)" section: 4. Next, morph the valve into a TCV, by selecting the TCV from the layout toolbar and clicking directly on top of the valve: 5. Now, enter the discharge coefficient found in step 3 as the initial discharge coefficient for the TCV. The fully open discharge coefficient will also still need to be entered. One way to find this would be to compute initial conditions with the original valve (GPV, FCV, PRV, PSV or PBV) set to "inactive". In this case, the initial conditions solver will use the "minor loss coefficient" that you entered, which represents the fully open condition. You would then use steps 2-4 above to find the discharge coefficient, then enter it as the TCV's fully open discharge coefficient. 6. Choose "false" for "specify initial conditions" in the transient calculation options, compute initial conditions, then verify that the computed head loss is the same as it was with your other valve type: What if I only know the head loss coefficient? It is always preferable to describe your valve with a discharge coefficient, since HAMMER always uses discharge coefficients in the transient calculations. As of HAMMER version 08.11.01.32, is it not recommended to use the "headloss coefficient" coefficient type for a TCV, if you need to model it in an initially partially closed position. To determine the equivalent discharge coefficient, either computer initial conditions and look at the calculated discharge coefficient in the Results section of the TCV properties, or use the following formula: Cv = ((39.693 * D 4 ) / H) 0.5 Where D is the diameter (ft), H is the headloss coefficient and Cv is the discharge coefficient (cfs/(ft H2O) Note: the "Minor Loss Coefficient" should be converted to the "Discharge Coefficient (fully open)". What if I Want to Use the Valve Characteristics Curve Coefficient Type? There are three options available for the "coefficient type" for a TCV: Discharge coefficient, headloss coefficient and Valve Characteristics curve. The latter option lets you enter the initial valve setting in terms of relative closure percentage, instead of a head loss or discharge coefficient. For example if you know your valve is 20% open in the initial conditions, you would simply enter 20%. However, some extra work is necessary with this option. Essentially you will need to relate relative closure percentages to discharge coefficients, in order to be able to refer to positions in terms of percent. This is done using the Valve Characteristics selection, described in the next section. For example if you enter 20% as the "Relative Closure (initial)", HAMMER needs to look that percentage up in the valve characteristics curve, to find the corresponding relative discharge coefficient. Then, based on the fully open discharge coefficient, it knows the discharge coefficient corresponding to 20%. Establish the Valve Characteristics The next step in the process of modeling an initially partially closed TCV is to select or define the valve characteristics curve. This is basically a table of relative closure versus relative discharge coefficient, which HAMMER uses to translate a percent open to a discharge coefficient . Basically when you model a valve closure in HAMMER, you are entering a table of time versus relative closure. This is done under Components > Patterns and is selected in the TCV properties under the Transient Operating Rule. In order for HAMMER to understand what these percentages really mean, it needs to translate them into a discharge coefficient. Every valve behaves a bit differently as it closes, so for example a value of 90% closed in your operating rule might not necessarily mean that the valve's open area is 10% of the fully open area. Therefore, the Valve Characteristics table is used to define this relationship. By default, several standard valve types are available, in the "valve type" field (such as butterfly, globe, needle). The table of relative closure versus relative discharge coefficient is not visible to the user for these predefined valves, but is defined based on the following equations: Note: the X axis represents relative closure and the Y axis represented relative discharge coefficient. The two equations on the right side can be used to derive tabular values from which the curves were constructed. For example, let's say you wanted to use the "butterfly" valve characteristics selection, and you want the valve to be initially 25% closed, with a fully open discharge coefficient of 10.0 cfs/ft H2O 0.5 . In this case, we can determine from the above diagram that the 25% relative closure translates to a relative discharge coefficient of 58.7%, which means a discharge coefficient of 0.587 X 10.0 = 5.87 cfs/ft H2O 0.5 . Note: The relative discharge coefficient values are relative to the value entered for "Discharge Coefficient (fully open)". You can also define a user defined table of relative closure versus relative discharge coefficient, by selecting "user defined" as the valve type. This exposes the "Valve Characteristics" attribute, which is where you would enter the table of relative closure versus relative discharge coefficient to define the characteristics of your valve. Note: remember that HAMMER uses relative closure, so 0% means fully open and 100% means fully closed. Other places may use relative opening, where the opposite is true. Establish the Transient Operating Rule The last step needed to model the closure of an initially partially closed valve is to tell HAMMER when the valve closes (or opens) during the transient simulation and how fast it occurs. This is done by establishing a table of time versus relative closure, called the Operating Rule. First, go to Components > Patterns and create a new pattern under "Operational (transient, valve)". Here you can enter the table of relative closure over time. Next, select the name of the pattern you just created in the "Operating Rule" field in the TCV properties. Intuitively, the "Starting relative closure" field in the pattern must match the initial relative closure, which you can see in the "results" section of the properties of the TCV: Putting it All Together To summarize what we've done, let's consider the following example valve: From the Operating Rule, the valve is initially 20% closed. From the Valve Characteristics table, a 20% relative closure translates to a 50% relative discharge coefficient. The "fully open" discharge coefficient is 10.0, so the initial discharge coefficient must be 10.0 X 50% = 5.0. 5.0 is entered as the initial discharge coefficient, so when the initial conditions are calculated, the computed relative closure (in the results section of the properties) is 20%. Let's say you wanted to run another scenario where the valve starts at 90% closed. First, you would modify or create a new operating rule, with the "Starting Multiplier" set to 90%. Next you would need to match up the initial discharge coefficient to the 90% by looking at the characteristics curve. A 90% relative closure translates to a 5% relative discharge coefficient. 5% of the fully open discharge coefficient of 10.0 is 0.5. So, the initial discharge coefficient would be set to 0.5. Troubleshooting What does the following message mean? "The valve's Initial Closure percent does not match the initial closure percent in the valve's referenced Operating Rule. The Operating Rule will be used as specified, but should be modified in order to get the expected results." This means that the Starting Relative Closure in your transient operating rule is not in agreement with the initial conditions of the valve. Check the "Relative Closure (Calculated)" field in the "Results" section of the properties of the TCV, to see what the initial relative closure is (which is calculated based on the initial discharge coefficient, fully open discharge coefficient and valve characteristic curve). You'll need to adjust the initial discharge coefficient so that the initial relative closure matches your pattern, or adjust the starting multiplier in your transient operating rule so that it matches the computed initial relative closure. If you're using a FCV, PRV, PSV, PBV or GPV, you will need to convert it to an equivalent TCV, using the method described further above in this technote. Example Model Click to Download Note: the above model is for example purposes only. It can be opened in version 08.11.01.32 or greater. See Also Product TechNotes and FAQs Haestad Methods Product Tech Notes And FAQs Protective Equipment FAQ General HAMMER V8i FAQ External Links Hydraulics and Hydrology Forum Bentley SELECTservices Bentley LEARN Server
↧
Wiki Page: How do I select columns in flextables, conduit catalogs, graph data tables, alternatives, etc...?
Applies To Product(s): WaterGEMS, SewerGEMS, CivilStorm, StormCAD, SewerCAD, HAMMER, WaterCAD Version(s): 08.11.05.XX+ for Storm and Sewer and 08.11.06.XX+ for Water Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem How do I select columns in Flextables, Conduit Catalogs, the Data tab of Graphs, the Data tab of a profile in HAMMER's Transient Results Viewer, etc...? How do I select columns so I can copy the data from alternatives? Solution There are a few ways to select columns in the latest versions of the software, so they can be copied. Select one column In order to select one column can right click on that column header and choose "Select Column" Select multiple columns 1. Left click the cell in the upper left corner of the table (Please visit the site to view this video) Left click and hold on a cell in the table and drag to the right. See video below: (Please visit the site to view this video) See Also What are the new flextable features and how do I use them for the Water Select Series 6 products?
↧