Hello Nalaka, I would tend to say that you would use the model to answer that question, by running a few scenarios varying the parameter (initial water level or certain time of an EPS) and observing the sensitivity. There may not necessarily be a rule-of-thumb for this, as there are many factors that influence the transient response. When the initial wetwell level is lowered, the pump head may be higher, but the pump discharge HGL might actually be lower. This is because the reduced pump flow (from shifting on its curve) reduces headloss. Because the discharge HGL is lower before the transient begins, This means that the initial HGL downstream of the pump The lower pump discharge HGL means a lower starting head before the transient event. It could be in some cases that this reduction in the initial head is more significant than the reduction in fluid momentum from the reduction in pump flow (and velocity) Also, a slight change in results (either flow or head) could impact multiple factors, including the timing of how transient waves combine. I strongly recommend animating a few profile paths in the Transient Results Viewer, which can sometimes reveal some interesting insights. Here's a related post on our blog about this: communities.bentley.com/.../using-profile-animation-to-better-understand-transient-results-in-hammer

Product(s): SewerGEMS Version(s): 10.00.00.40 Environment: N\A Area: N/A Overview The CONNECT Edition release of SewerGEMS introduces numerous improvements and features to help you be more successful. Let's explore each of these in detail. List of Topics Compatibility Supported Operating Systems Compatible Platforms Interface Ribbon Interface File and Help Menus Layout & Data Input Background Images View and edit the path for background images Improved background layer performance World file support for background images New Element Property Connection Automated Catchment Delineation Calculations Pump Energy Costs SWMM Enhancements Updated EPA SWMM Version New SWMM Climatology Monthly Adjustments Table New SWMM Calculation Executive Summary New SWMM Calculation Options SWMM Culvert Support New Roadway Weir LID (Low Impact Development) Enhancements Outfall to a catchment Improved Performance Structure Headloss Calculations Tractive Stress Results Graphs QuickGraph More meaningful steady state graph "Select in drawing" in graphs and graph manager Profiles Engineering Profile Annotation Table Profiles no longer save automatically Customizable Reports Record AVI video from time results Usability Enhancements Duplicate Prototypes Open on selection from within FlexTable Double-click on dropdown list to toggle through values Option to auto-close the Calculation Summary dialog after computing a model New alternative features (recently added to FlexTables) Excel export option available in all platforms Inroads IDF Importer Ability to use Wetwell %full as a condition with SewerCAD controls Maximum depth/rise property added to conduits to identify flooding/surcharging CONNECT Integration View Changes Toggle tap node dashed line display Added support for DGN files in ModelBuilder New Queries Display contour lines in plan view Compatibility [ Top of Page ] Supported Operating Systems Windows 10 (32-bit or 64-bit) Windows 8 (32-bit or 64-bit) Windows 7 (32-bit or 64-bit) Compatible Platforms SewerGEMS CONNECT Edition standalone version does not require any CAD or GIS software to work. However, it can be integrated with the following platforms: MicroStation V8i SELECTseries 4 (Note: MicroStation CONNECT Edition integration is not yet supported with this release) AutoCAD 2016, or 2017 ArcGIS 10.2, 10.2.2, 10.3.1, or 10.4 See: Wiki Platform Compatibility Wiki SewerGEMS CONNECT Edition (10.00.00.40) Readme Interface [ Top of Page ] Ribbon Interface A new ribbon user interface has been added to the stand-alone products. A button has been added to the welcome dialog to provide quick access to the ribbon interface help documentation. The application menus match the platform the program is integrated with. MicroStation V8i and ArcGIS do not use a ribbon user interface. Therefore this release of the Storm and Sewer products will not use the ribbon interface when integrated with MicroStation or ArcGIS. The following article provides an in-depth look at the new ribbon menu. Ribbon Interface for Storm and Sewer CONNECT Edition products File and Help Menus When the File tab is selected, the entire program dialog switches to display the File menu (ie. "backstage"). The Help menu and Database Utilities have been moved to the File menu. Layout & Data Input [ Top of Page ] Background Images View and edit the path for background images The Image Properties dialog now displays the image's filename and includes a Browse button to edit the field. Improved background layer performance Background layers are now loaded more efficiently so that less memory is consumed. This improvement is especially helpful when using multiple large files for background images. World file support for background images The following background image formats are now supported. Bentley Drawing Files (*.idgndb, *.imodel, *.dgn) World Files Some image formats support associated world files. When attaching a background image file that has an associated world file present, the image will be spatially located automatically (ie. georeferenced). The following file formats support an associated world file. bmp jpg jpeg jpe jfif tif tiff png Gif The World file extension is based on the image's extension. One convention is to use the first and last letter of the image's extension and add a "w" (eg. .jpg>.jgw). Another convention is to append the image's extension with a "w" (eg. .jpg>.jpgw). When opening the file, the Image Properties dialog will automatically enter the coordinates from the World file in the editable (Drawing) fields. New Elements This release includes a new element type; property connection. Property Connection Property connection elements are used to load sewer models based on data at the level of individual properties. This is useful when you have loading data provided for customers/properties based on metering, number of occupants/fixture units, or simply flow per property. Including all property connections in your hydraulic model is useful when there is a need to have a closer (one-to-one) match with your GIS. Being able to see all property connections in the hydraulic model allows you to get a more detailed view of where the individual loading occurs, rather than lumping many loads into one manhole. Property connections are used for sanitary loading in the Implicit, Explicit and GVF Convex solvers, but not the GVF Rational solver. Property connections support hydrograph, pattern, and unit loads. They can also directly accept runoff as the outlet of a catchment. For the GVF Rational Solver, flow through a Property Connection must come from a Catchment. (Property Connection designated as the Outflow Element.) Inflow/loading from a property connection element would typically enter your network via a Lateral link that connects to a conduit via a tap node. See: Wiki Property Connections Help "Property Connections" LoadBuilder can be used to assign isolated Property Connection elements to the nearest element by creating a tap and lateral connection. Isolated Property Connections are those elements that are not connected to any lateral element. Laterals are automatically placed between the source element and the hydraulic network when using LoadBuilder and selecting Property Connection Load Data as the Available LoadBuilder Method. When this data source is used, it is assumed that that load data is already available in the Property Connection. See: Wiki Using LoadBuilder to assign Property Connections to the nearest element and create taps and laterals Help "LoadBuilder Wizard" The query "Property Connections not connected to Nearest Link" is now included in the Network Review Predefined Queries. Automated Catchment Delineation The new Catchment Delineation tool is a terrain model analysis system designed to find the catchment area with runoff flow path ending at a low point or passing through an inlet surface area. It automatically finds catchment boundary points for inlets, calculates catchment properties, and derives gutter network and gutter properties. Note: Bentley terrain model and its functions are used in running catchment delineation. When the Run Catchment Delineation is selected from the Terrain Modeling Manager, the button for Catchment Delineation will be placed in the depressed position. At this time, whenever a catch basin is added or moved within the Digital Terrain Model (DTM) the catchment is identified or updated. Selecting Catchment Delineation Settings from the Terrain manager opens the following dialog where the user can adjust parameters that control the catchment delineation tool behavior. See: Help "Catchment Delineation" Help "Catchment Delineation Settings" Calculations [ Top of Page ] Pump Energy Costs This release introduces a new Energy Cost tool which optimizes pump operations. With this tool you can now analyze the cost of operating pumps (by the energy used) during a single extended period simulation scenario. The scenario energy cost analysis determines the energy cost by pump for all pumps selected by the user. Pricing for energy cost is set up in the Pricing button in the energy costing manager. Price functions are assigned to individual pumps in energy costing. This tool works with all solvers that support pumps: Explicit (SWMM Solvers) Implicit (SewerGEMS Dynamic Wave) This solver always assumes the Relative Speed Factor = 1 if the pump is on. GVF-Convex (SewerCAD) Results can be viewed in tabular format or graphed. Depending on the selection, results can show data for a single pump or a pump station. SWMM Enhancements Updated EPA SWMM Version This release uses EPA SWMM version 5.1.010. See: Wiki EPA SWMM solver versions used by SewerGEMS and CivilStorm New SWMM Climatology Monthly Adjustments Table The SWMM extension Climatology now includes the "Adjustments" tab. Checking the Apply Climate Adjustments box enables the Monthly Adjustments table, where you can define Temperature Constant, Evaporation Constant, Rainfall Multiplier, and Soil Conductivity Multiplier adjustments by month. New SWMM Calculation Executive Summary In previous versions, after successfully computing a model with the SWMM solver a large text file would be created and opened with an external text editor, such as Notepad. Starting with this release, an internal dialog provides the SWMM Calculation Executive Summary. This makes it much easier to browse or find results. This dialog displays values using the hydraulic model's units. In prior versions, the results were displayed in US Customary units regardless of the hydraulic model's defined units. New SWMM Calculation Options The Explicit default Routing Time Step was reduced from 30 seconds to 5 seconds for better stability. The default value for Use Variable Time Step is now True. The following two calculation options for the Explicit solver were introduced in this release. The Minimum Variable Time Step is the smallest time step allowed when variable time steps are used. The default is 0.5 seconds. Smaller steps may be warranted, but they can lead to longer simulation runs without much improvement in solution quality. The Number of Threads is the number of parallel computing threads to use on machines equipped with multi-core processors. The default is 1. The SWMM Default Infiltration Method has the new option "Green and Ampt (Modified)". This modified version of the original Green and Ampt method no longer redistributes upper zone moisture deficit during low rainfall events. The original authors of SWMM's Green-Ampt model have endorsed this modified version. It will produce more infiltration for storm events that begin with low rainfall intensities, such as the SCS design storm distributions. SWMM Culvert Support Culverts can now be modeled by the Explicit (SWMM) solver. When exporting a model to SWMM the culverts in the engineering libraries will now be converted with their associated SWMM culvert codes. This allows the culvert to be recognized when the model is opened in SWMM. The Section "SWMM Solver" has been added to the Culvert Catalog dialog. You can either enter the "SWMM culvert code" or you can click the ">" button to select the culvert from a menu. New Roadway Weir A new type of weir, a ROADWAY weir, has been added. It models roadway overtopping using the FHWA HDS-5 method and would typically be used in parallel with a culvert conduit to route bypass to the downstream node. This is available for the Explicit (SWMM) solver; with the Implicit solver, you can use the roadway overtopping weir option in the conduit properties when setting the conduit as a culvert. The fields Road Width and Surface Type are specific to the Roadway weir type. LID (Low Impact Development) Enhancements New LID Underdrain Target option The LID (Low Impact Development) element has the new field "Underdrain Outflow Element" which lets you specify an element that will accept underdrain flow from the LID. New LID Control Type Low Impact Development Control type now includes the option Roof Top Disconnection. New Soil fields for Porous Pavement type LID control A Soil section has been added to the LID control type Porous Pavement as shown below. This allows you to model a sand filter or bedding layer beneath the pavement. Outfall to a catchment The field "Route to Catchment" is now available for the outfall element when using the Explicit solver. This field allows you to specify the catchment to which flow will be routed from the outlet. The following outfall Boundary Condition Types are supported. Free Outfall Normal Tidal Time-Elevation Curve User Defined Tailwater Improved Performance Other general improvements have been implemented to reduce the computation time when using the SWMM Solver. Structure Headloss Calculations Starting with this release, the Explicit (SWMM) solver supports structure headloss calculations. Structures can now use the headloss methods “HEC-22 Energy (Third Edition)” and “Standard”. Tractive Stress When conduits and channels have sufficient tractive stress they are essentially self-cleaning in that particles will either not settle or they will be re-suspended if they do. Conduit tractive shear stress is now calculated when using the following solvers. GVF-Convex Explicit Implicit (Dynamic Wave) Note: Previously, tractive stress was only supported by the GVF-Convex solver. Starting in this release, tractive stress is included in constraint based design. See: Help "Tractive Force Design" Wiki Tractive Stress (aka Tractive Force, Shear Stress) Calculations and Design Results [ Top of Page ] Graphs QuickGraph The new Quick Graph feature provides a fast way to view a graph of a single element in the drawing. The Quick Graph automatically updates to display data for the selected element. More meaningful steady state graph If the current scenario is steady-state (available with the GVF Convex/SewerCAD solver), the default graph is a bar chart for the selected elements. Elements from different scenarios can also be added in the Series Options dialog. The Series Options dialog can be used to customize the information displayed in the graph (scenarios, elements, and fields). "Select in drawing" in graphs and graph manager In the graphs manager you now have an additional option "Select in Drawing" which is to the right of "Add to Graph". When a saved graph is selected and you click this button it will select the elements that are part of the saved graph. Any existing selection will first be cleared. Only elements that are checked in the graph options will be selected in the drawing. Profiles Engineering Profile Annotation Table Engineering profiles now have the option to include an annotation table which is drawn similar to the analysis profile. However, the displayed fields and field order can be edited in the engineering profile which makes it more customizable. To toggle the annotation table display, click on the down arrow next to the Chart Settings icon and select "Show Profile Annotation Table" from the dropdown menu. The annotation table options can be edited by selecting "Profile Annotation Table Options…" from this dropdown menu. Profiles no longer save automatically Profiles created with the context menu (right-click>Create Profile) are now temporary. When you close the profile viewer for a temporary profile, you are asked if you want to save it. When you select Yes to this prompt you will have the chance to enter a label for the profile. Customizable Reports A new Custom Report tool has been added to the Report tab. This tool allows you to quickly assemble a customized report which can contain user input, results, graphs, etc. You can now define the template interactively instead of modifying an XML file manually (which can still be done). The reports can be exported to the following formats PDF HTML MHT RTF Excel CSV Text Image The Report Options dialog can be accessed by clicking the icon below the Custom Report icon. This dialog allows you to control how reports are displayed (eg. font, header, footer, margins). See: Help "Custom Reports" Help "Report Options" Record AVI video from time results The AVI Screen capture enhancement allows you to record videos of scenario animations. You can select which portion of the screen will be recorded. The screen capture utility will capture and record all the frames of the animation within the bounds you specify and produce an AVI video file which is sharable outside of the storm and sewer products. An internal video player allows you to watch the video after it is done recording. See: Help "Recording Scenario Animations" Usability Enhancements [ Top of Page ] Duplicate Prototypes The Prototypes Manager now includes the option to duplicate prototypes. Open on selection from within FlexTable When you have a FlexTable open, i.e. Junction FlexTable, you can now select the rows in the table based on the current selection. To use the feature: Select some elements. Open a FlexTable for one of the selected elements and click the drop-down arrow for the “Select in Drawing” button. Click the last item, “Select from Drawing”. If there are any elements for the type of table you currently have open, it will select the rows for the elements selected. You can then filter down the contents of the table by right-clicking the row header and clicking on “Open on Selection”. Double-click on dropdown list to toggle through values When editing data in the property grid you can double-click the label to change the value. This applies to Boolean fields (those that show true/false values); reference fields (i.e. zone); and enumerated fields (i.e. Status (Initial)). When you double-click any of these field types it will cycle through the available values in the drop-down list. Commands like “Edit” for reference fields are excluded during the cycling. Option to auto-close the Calculation Summary dialog after computing a model The Calculation Executive Summary dialog box opens after you compute a model. You now have the option to not automatically open the dialog after a compute by unchecking “Show this dialog after Compute”. This option applies to all available solvers for the product. This is a global option and once unchecked applies to all projects opened in the product. The post-calculation summary dialog now allows you to choose if it displays after computing a model as seen in the image below. This dialog can also be accessed by clicking on the Home tab and selecting the Calculation Summary icon. New alternative features (recently added to FlexTables) Some features that were recently added to FlexTables are now available for alternatives. You can now quickly zoom to an element within an Alternative dialog by either right-clicking on the row header and selecting "Zoom To", or by double-clicking on the row header. When a row is highlighted, pressing enter will select the next row. Excel export option available in all platforms FlexTables can be exported to an Excel file in multiple products (SewerGEMS, SewerCAD, StormCAD, and CivilStorm) and for all integrated platforms (MicroStation, AutoCAD, ArcMap, and stand alone). See: Can I easily export my results to an Excel spreadsheet? Inroads IDF Importer InRoads IDF files can now be imported into an engineering library storm event group which can then be used by SewerGEMS, StormCAD, CivilStorm, or PondPack. This can be done as a batch process with an external tool or individually using the Storm Data dialog. Ability to use Wetwell %full as a condition with SewerCAD controls Wet well control conditions now include the storage attribute "Percent Full". Note: Controls only apply to the "GVF-Convex (SewerCAD)" numerical solver. If using the "Explicit (SWMM Solvers)" or "Implicit (SewerGEMS Dynamic Wave)" numerical solver, pump controls must be defined in the properties of the pump. Controls do not apply to the "GVF-RationaI (StormCAD)" numerical solver. Maximum depth/rise property added to conduits to identify flooding/surcharging Conduits now have the property "Depth (Maximum) / Rise (%)" which displays the ratio of maximum calculated average depth (average between start and stop) to the rise of the conduit. CONNECT Integration This release requires the latest version of CONNECTION client. If it isn't already on the computer, it will be downloaded and installed during the product's installation. After the product installation completes, a CONNECTION client slideshow will display. This provides an introduction to the CONNECTION client, allows you to enter your login information, or create a new account if you don't already have one. There is a new CONNECTED Project association dialog which allows the default behavior to be set. If you don't want the dialog to appear in the future, then select "Do not notify me again". View Changes The view can be quickly set to Zoom Extents by double-clicking the middle button on your mouse. For some, this may be done with the scroll-wheel button. Toggle tap node dashed line display When a tap is placed, a dashed line appears to show which link the tap is associated with. The tap element symbology properties now include a "Show Associated Link Decorations" field to control if this dashed line is displayed. Added support for DGN files in ModelBuilder ModelBuilder now supports Bentley Drawing File formats (*.idgndb, *.imodel, *.dgn). New Queries The following Queries have been added. Network Review Property Connections not connected to Nearest Link Inlets In Sag With Bypass Gutters Inlets On Grade Without Bypass Gutters Catch Basins Without a Catchment Network Trace Find Adjacent Nodes Find Adjacent Links Find Adjacent Start Nodes Find Adjacent Stop Nodes Display contour lines in plan view Terrain Models can now display contour lines. The terrain model edit dialog allows you to define the minor interval and the amount of lines per major interval. The major interval will be calculated based off of those inputs. You can also customize the colors of the major and minor interval contour lines. See Also [ Top of Page ] SewerGEMS CONNECT Edition (10.00.00.40) Readme Ribbon Interface for Storm and Sewer CONNECT Edition products Product TechNotes and FAQs Haestad Methods Product TechNotes And FAQs SewerGEMS and CivilStorm TechNotes and FAQs Downloading Haestad / Hydraulics and Hydrology Software Software installation order Cumulative patch set information Set up notifications for new versions and patch set releases Original Author: Craig Calvin

Hello Lindle, Take a look at the following wikis, which may be of some use to you: communities.bentley.com/.../modeling-reference-_2D00_-hydropneumatic-tanks communities.bentley.com/.../8387.hammer-hydropneumatic-tank-user-notifications-the-bladder-type-hydropneumatic-tank-fills-its-containing-tank If they do not help with the issue, we will likely need to see a copy of the model files. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded. communities.bentley.com/.../7079.be-communities-secure-file-upload If you upload the files to Sharefile, please post here with the name of the files so that we know they are available. Regards, Scott

Product(s): Bentley WaterGEMS, Bentley WaterCAD, Bentley HAMMER Version(s): 08.11.ss.ss Environment: N\A Area: Output and Reporting Subarea: N\A Problem The following error message is generated when computing or validating an error message: System.FormatException: Input string was not in a correct format. However, the name model will compute on a different computer. Problem ID#: 52307 Solution First, make sure that you are using the most up-to-date version of the software. You can download the latest version of the products using the steps in this link . Otherwise, this issue has been known to occur because of regional settings on the computer. Check the regional settings and compare it with another computer where the product is working. Most of the time, there is a field that is not defined correctly in the Control Panel under Regional Settings > Customize

Product(s): Bentley StormCAD, Bentley SewerCAD, Bentley SewerGEMS, Bentley CivilStorm Version(s): 08.11.xx.xx, 10.00.xx.xx Environment: N\A Area: Modeling Subarea: N\A Problem What structure headloss methods are available in StormCAD V8 XM and V8i? Problem ID#: 67086 Solution Structure losses For structure head losses (headloss through a manhole or catch basin), there are a number of methods available: 1) Absolute - The user will enter the exact head loss in feet or meters. 2) Standard - The user will enter the standard headloss coefficient K. The headloss will then be calculated based on the formula: headloss = K*V^2/2g 3) Generic - The generic method computes the structure headloss by multiplying the velocity head of the exit pipe by the user-entered downstream coefficient and then subtracting the velocity head of the governing upstream pipe multiplied by the user-entered upstream coefficient. 4) HEC-22 Energy (2nd Edition) and HEC-22 Energy (3rd Edition) - this is the standard HEC-22 headloss method, which correlates structure headloss to the velocity head in the outlet pipe using a coefficient, which accounts for several factors such as benching, plunging, diameter, etc. This method was changed between the two latest editions of the HEC-22 manual. Note that the HEC-22 (3rd Edition) is not available in SewerGEMS or CivilStorm. 5) AASHTO - this is based on power-loss methodologies, which accounts for contractions, expansions and bends. This method is only available in StormCAD and SewerCAD 6) Flow-Headloss curve - this method allows you to enter a rating table of flow versus headloss across the structure. This method is only available in StormCAD and SewerCAD. For more information on the above headloss methods, please see the Help documentation Pipe losses Conduit and pressure pipe losses are available using four methods: Mannings, Hazen-Williams, Darcy-Weisbach and Kutters. See Also Can I set a minimum structure headloss value to be used in my model? Original Author: Bentley Technical Support

Andrew, The pump relative speed factor is increasing beyond 1.0 because the pump cannot deliver ~1600 gpm of flow at a head of ~140 ft. The pump definition would allow for about 1600 gpm at around 70 ft. of head and the shut off point for the pump is 0 flow at 133 ft. of head. The pump needs to operate off it's curve because at certain points in your simulation the flow demanded is more than the flow supplied or the demand has a spike in it's pattern that causes an increase the pump can't meet. For example, if you look at the pattern labeled "April 1-7, 2015-D-3" you'll see the spikes in the pattern of over 1.00 as a multiplier and the times of these spikes correspond to the spikes you're seeing from your pump flow. Possible solutions for you would be to check your demand pattern data to make sure that it's correct or increase the size of your East Park Booster pumps. Regards, Mark

Mark and Jesse 1- The load is NOT dropping to zero INSTANTLY (in Load Rejection), since the generator itself IS a kind of load and it uses the torque which turbine generates. But in 'Instant Load Rejection' it assumes that the shaft between turbine and generator is broken and no any load remains on the turbine and the speed of the turbine must drop to zero INSTANTLY. Am I right? If so, then have a look at patterns which are defined in the model. In both Load Rejection and Instant Load Rejection, 10 seconds must elapse until Gate Opening becomes zero. As I can interpret, gate opening must drops to zero instantly (in Instant Load rejection pattern) and gate opening must NOT drops to zero (in Load Rejection), since the generator itself has load and uses the turbine's torque. 2- What is the role of 'Spherical valve' here? Does it prevent hammer to reach the turbine by closing itself? Is it something like Check Valve for Pumps? What is it good for? 3- Regarding the aforementioned article, the initial condition for Load rejection and Instant Load rejection and Load Variation is 100% gate open (fully open). Initial condition for Load Acceptance is 0% gate open (fully closed). Are these true? 4- more about relation between speed and wicket gate opening in Load variation pattern: when electrical load decreases, governor orders to wicket gate to close to avoid entering water into turbine. When entering water decreases, the turbine's speed DECREASES logically. Is not it? but in Load Variation pattern -as you see- speed is fixed while the wicket gate opening is vary. H.

Hello, Jesse Dringoli Really helped me to understand, many thanks

Hello All, I am trying to simulate check valve in the water hammer, but I have a problem when inserting the check valve just upstream the vessel. it results into a vacuum pressure upstream the check valve. is this simulation is real, and the vacuum pressure will occur? is it is the case an additional protection device is required? or there i a mistake in the simulation. Fig 1 presents the output when check valve is inserted, while fig 2 shows the results without introducing the check valve, while

I'm going to start by assuming that you are modeling an emergency pump shutdown event, that you have a check valve node element with time to open and close configured, that the check valve is directly downstream of the pump and that the "vessel" is a hydropneumatic tank just downstream of the check valve. Please confirm and clarify the setting of your elements. If this is the case, then check valve "slam" is common with this modeling situation. When the pump shuts down, it takes some time for the downstream tank's hydraulic grade to drop (which helps protect against low pressure downstream of the pump/check valve), so there is quickly a point at which the water column has stopped moving forward (flow through the pump is zero) and the tank HGL is greater than the pump upstream HGL, which causes a reverse flow situation. Depending on the check valve used, some reverse velocity can occur before the valve is able to fully close, which can cause a surge. I strongly recommend animating your profile path in the Transient Results Viewer (you may also want to create an additional profile, focusing on the area of interest), as this will help you understand how the actions that ocur during the transient event influence results like min and max HGL and vapor pockets. You'll need to make sure that the calculation timestep and reporting timestep are small enough so that you can see important changes, which can happen within a few hundredths of a second. A smaller timestep is also often needed if the pipes between the pump, check valve and tank are short. More information can be found in these article: Understanding length/wave speed adjustments and their impact on results How do you select only certain report points in the transient calculation options? "The period between path histories has been increased by a factor of..." Since the water column starts to move in reverse, if the check valve slams, a positive, "upsurge" wave will travel toward the tank and a "downsurge" will travel toward the pump. So, in your case, this downsurge wave may be occurring and is severe enough to cause the vapor pressure limit to be exceeded, forming the vapor pocket. If the downsurge wave didn't cause this to happen right away, it could have occurred due to how that wave interacted with another wave heading in the opposite direction at the time. Again, profile animation is best for understanding this. It is also very important to note that the results you see can also be influenced by data input such as elevations and settings of the pump, tank and check valve. So, you'll need to make sure that the input is correct and that you have a firm understanding of the assumptions used by the program first, as they can influence this result. If you're using a check valve without an open or close delay (such as the pump's built in check valve or a check valve on the pipe), then the part above about the reverse velocity does not apply, but the closure could still cause a disturbance that eventually causes the vapor pocket to form. Here is an article with more information on the built-in valve with the "shut after time delay" transient pump type: Modeling a pump shut down transient event If you check the input and are confident that everything is set up correctly and that your timestep and report increment are appropriate, then you might conclude that careful selection may be necessary for the type of check valve. You will likely find some papers on this subject (check valve slam from pump shutdown with hydropneumatic tank) which may help further. I believe I have also seen several check valve manufacturers with "anti-slam" check valves that specifically mention this type of situation. I did a quick search on YouTube and found this one . I believe the subject has also been discussed before on the forum, so you could try a few searches. In summary: The vapor pocket you see is quite small and may not end up being a concern, but there's a chance that you may need to address the situation The result you see is likely "real", but can be influenced by a number of different factors in the model that you will need to double check

My imbedded response are in green: 1- The load is NOT dropping to zero INSTANTLY (in Load Rejection), since the generator itself IS a kind of load and it uses the torque which turbine generates. [Jesse] With instant load rejection the electrical load drops to zero instantly, but with Load rejection, you define the electrical torque over time, which represents the resistance from the electrical load. The situation is similar but could be considered not as conservative since the electrical load does not drop instantly. But in 'Instant Load Rejection' it assumes that the shaft between turbine and generator is broken and no any load remains on the turbine and the speed of the turbine must drop to zero INSTANTLY. Am I right? [Jesse] No - see the article and Help topic on Turbines. With both load rejection and instant load rejection, the program simulates a drop in the resistance from the electrical load (from the distribution grid). The turbine impeller is still present and starts to spin faster since the hydraulic torque from the water moving through it is greater than the resistance from the distribution grid (electrical torque). The idea is that you want to close the wicket gates to prevent the impeller from reaching "runaway" speed which can be destructive. If the wicket gates are closed too quickly, this can cause a transient (upsurge), which is why you may want to analyze the situation with HAMMER. If so, then have a look at patterns which are defined in the model. In both Load Rejection and Instant Load Rejection, 10 seconds must elapse until Gate Opening becomes zero. As I can interpret, gate opening must drops to zero instantly (in Instant Load rejection pattern) and gate opening must NOT drops to zero (in Load Rejection), since the generator itself has load and uses the turbine's torque. [Jesse] See above; if the gate slammed closed, it could cause a destructive transient. You want to close it slowly enough to not cause this, but also fast enough to prevent runaway speed. 2- What is the role of 'Spherical valve' here? Does it prevent hammer to reach the turbine by closing itself? Is it something like Check Valve for Pumps? What is it good for? [Jesse] If you're not sure about the spherical valve, then most likely the turbine you are modeling does not have one. It is an additional valve (just a straight valve, not a check valve) that HAMMER can simulate in a case where your turbine is equipped with one and you have a need to operate its closure. 3- Regarding the aforementioned article, the initial condition for Load rejection and Instant Load rejection and Load Variation is 100% gate open (fully open). Initial condition for Load Acceptance is 0% gate open (fully closed). Are these true? [Jesse] Correct. Load rejection, instant load rejection and load variation all simulate a turbine that starts in the open and operating condition, whereas load acceptance models a turbine that starts in the closed condition and opens up during the transient simulation. 4- more about relation between speed and wicket gate opening in Load variation pattern: when electrical load decreases, governor orders to wicket gate to close to avoid entering water into turbine. When entering water decreases, the turbine's speed DECREASES logically. Is not it? but in Load Variation pattern -as you see- speed is fixed while the wicket gate opening is vary. [Jesse] see my previous response - with load variation, the assumption is that the wicket gate pattern represents the change in wicket gate position necessary to match changes in electrical load (to keep the turbine at synchronous speed).

Hi, Which option in darwin calibrator represents the number of assessment ? Thank you in advance. yours faithfull fariba

Hello Fariba, Could you please explain a bit, what exactly are you looking for? Are you looking for the software to give the total number of field data sets imported through Calibrator? You can see the total number of field data sets imported in the observed target table, at the end. If that is not the case, then please provide further details.

Good afternoon, I'm working on a project of a fire network in Hammer V8i, where the goal is to calculate the surge vessel required to ensure that in case of power failure of the pumps, the pressure in the network don’t pass down from -5 M.C.A. I considered the fire hydrants as discharges to atmosphere (valve type), in order to be possible to consider them initially open or closed. The system is composed by two different pumps operating simultaneously: the 1st pump starts operation when the pressure in the network goes down from 9.5 bar and stops when the pressure reaches 10.5 bar; and the 2nd pump starts operation when the pressure in the network goes down from 9.0 bar. My question is, how can I set in the software these limits for operation of the pumps? I considered them Variable Speed Pumps, selecting as a control node the point with the highest elevation of the network, for both. For the 1st pump I considered the target pressure of 9.5 bar and for the 2nd pump 9.0 bar. With this setting, when I ran the software it gave the following message: "Different target heads for the same control node are not allowed." Faced with this message, I selected a control node different for the 2nd pump, but with the same elevation. This time the message was: "Cannot solve network hydraulic equations". I have read some of the posts that exist here in Bentley Communities about this subject, including this: “ How do I model parallel fixed head (target head) variable speed pumps that are controlled by flow in a downstream pipe? ”. I followed the steps, that is, I added 5 points after the pumps and I set the fifth point as a control node. However, I still cannot guarantee the minimum pressure in the network of 9.0 bar. What is the solution to simulate in the best way, the operation of the pumps? Is there a way to simulate more simply the network and the operating conditions? Thanks.

Hello all, I have been searching available literature on Dawin designer for a research project am working on.It has not been clear to me whether it is a single objective optimization tool or it can also perform Multi-objective optimization. Kind regards, Simon

i have two reservoirs ,junctions and one pump delivered water from R1 to R2 levels of it as flowing junctions levels Label Elevation (m) J-1 110.00 J-2 120.00 J-3 130.00 J-4 120.00 J-5 115.00 reservoirs levels Label Elevation (m) R-1 100.00 R-2 110.00 pumps levels Label Elevation (m) PMP-1 99.50 when i make run and open pump system curve i found water gems calculate when Q=0 H = 10 its difference between two reservoirs but H must me static head in water line calculated as ( max level in system - pump level ) in this example must be when Q=0 H=130-99.50=30.50 m system curve is very important in hydraulic analysis as its control flow in pipe and delivered head from pump

The system head curve is the difference in head across the pump required to move water at the corresponding flow rate. In the case when Q=0, the system head across the pump is 110 - 100 = 10 m. See any hydraulics book for an explanation of this. It's page 45 of out Advanced Water Distribution System Modeling and Management book. The elevation of the pump makes no difference in determining the system head curve (as long as you have adequate NPSH).

Product(s): Bentley SewerCAD, WaterCAD, WaterGEMS Version(s): 08.11.XX.XX Environment: N\A Area: Modeling Subarea: N\A Problem How can I view the static head of a pump, especially when there's an intermediate high point that may see part-full flow? Problem ID#: 87875 Solution First, ensure that you have an air valve node element at the high point(s) that you expect to see part full flow, and ensure that the "Treat as junction?" property is set to "false". Next, turn the pump(s) off and compute a steady state simulation. The pump head (or the difference in upstream/downstream HGL) should be the static head. You can also right click on the pump and choose "system head curve", then look at the zero flow point. See Also System Head Curves in WaterGEMS and WaterCAD Modeling Air Valves At High Points in WaterCAD or WaterGEMS

Regarding the high point at 130 m - you may need to insert an air valve there, and select "false" for "treat as junction". More on air valves here: communities.bentley.com/.../23896.system-head-curve-with-intermediate-high-point communities.bentley.com/.../2662.modeling-air-valves-at-high-points-in-watercad-or-watergems-tn More on System Head Curves here: communities.bentley.com/.../24627.system-head-curves-in-watergems-and-watercad

Just to clarify what happens when you have a intermediate high point. The downward sloping part of the pipe will generally be empty when you start the pump. You should calculate the system head curve from the suction reservoir to the high point (assuming you have an air release valve there which you should). Once the pipe is full, you calculate the system head curve for the entire pipeline. There are some exceptions. In some cases, the downward sloping pipe is so large and steep that it never runs full and the system head curve is always to the high point. The other case is the one where you don't have a air valve and the HGL at the high point drops below the vapor pressure of the fluid, which then vaporizes. You don't; want to have that happen. You need to make the downward pipe so small that it easily flows full or so large that it always flows partly full.