bentley water hammer

Question

I have made a model on water hammer software , whole layout I have plotted. pressure and head output I got correctly but HGL line shows equal levels, i don't know why it's done Ithink something I missed while putting input. 
 Anybody please say me what data need to put for getting accurate HGL (hydraullic gredient line), so I can compared with my input data. Please give me solution as early as possible. 
 THANK YOU.....

Johan Olivier · Accepted Answer

Hi Sanket, 
 Your model looks ok. For the pipe diameter and flow you have the friction is very low, that's why the HGL (steady state) seems to be horizontal. If you look carefully the HGL at the pump discharge is 340.27 and at the end reservoir 340. Therefore the friction is only 0.27 m which is correct. For this flow scenario the pipe is too big (not sure if you have other flow scenarios too).

Scott Kampa · Answer

Hello Sanket, 
 I am assuming that you were able to successfully compute the transient solver. Based on that, what kind of transient event are you model? Events like a pump shut down or valve closure should show some change in hydraulic grade. If you are not modeling a transient event, you may see no change in the hydraulic grade over time. Further details on what you are seeing would be useful. 
 I would make sure that you are animating the transient profile , as that will show you how the hydraulic grade or pressure is changing over time. 
 Regards, Scott

Scott Kampa · Answer

To add to the reply above, you will want to make sure you are working with a calibrated model. If the flow is accurate but pressures at the downstream nodes are not what you expect, you can adjust the pipe roughnesses to assure accurate input. This will also make sure your transient results are accurate. 
 The low headloss also means that that transient pressure results are slow to diminish. You may want to try computing the transient run for longer to gauge how long it will take for the pressure wave to reach a new equilibrium after the pump shut down. This link has some additional information on this. 
 Regards, 
 Scott

Jesse Dringoli · Answer

I took a quick look at the model and wanted to add a few more points: 
 
 If you want to see what happens during the transient event (not just the flat HGL from the initial conditions), be sure to use the Transient Results Viewer (see link previously provided by Scott) to animate the results to see the HGL change after the pump shutdown event. The Transient Results Viewer will also show you the minimum and maximum HGL "envelope" for your profile. 
 In your model, I see a downsurge wave in the transient profile animation, which causes some vapor pockets on the downstream end (due to the low initial pressure at those points). You may need to ensure that your junctions are using pipe elevation instead of ground , and possibly consider a PSV or top-fill tank at the downstream end via a D2A (assuming "res2" represents a tank), to prevent the initially low pressures and subsequent vapor pockets during the transient event.. 
 Regarding inputting the "HGL data" manually - you can indeed manually enter the initial conditions by choosing "true" for the "Specify initial conditions" transient calculation option, but if the initial conditions HGL computed by the initial conditions solver is not what you expect, then it is probably best to determine the cause of the discrepancy and amend the model so that the results match your expectations.

Scott Kampa · Answer

Hello Sanket, 
 Some input was already provided. Is there something in particular you are concerned about? 
 Regarding the ground and hydraulic grade profile, do you mean the profile in the Transient Results Viewer? The profile in the Transient Results Viewer will show a few things by default. At the initial time step, it will show the ground elevation, the initial HGL, the maximum HGL and the minimum HGL. This link has more information on these: What do the different colored lines a Transient Results Viewer profile represent? 
 As mentioned above, animating the profile will show you how the hydraulic grade will change over time. Some of our observations after doing this can be found above. 
 You can also view Time History graphs. These are graphs of results (such as hydraulic grade, flow, and air/vapor volume) at select points in the model. You have some of these selected. If there are key areas of concern, you can include these as well. This information can be useful to see what is happening at a given point in the model. 
 Regards, 
 Scott

Scott Kampa · Answer

Hello Sanket, 
 Here is a link related to air valves and how they work in HAMMER: Modeling Reference - Air Valves 
 For the zero-velocity valve, do you mean a check valve? If so, this link has information. You can find general information on model valves in HAMMER here: Modeling Reference - Valves . 
 Regards, Scott

Jesse Dringoli · Answer

Hello Sanket, 
 For the model you provided, there are several different scenarios with labels that suggest different air valve types, yet all the air valves seem to have the same type in these four scenarios. The first one on the left is set to triple acting (with invalid transition volume and outflow orifice sizes), the next one is set to double acting, and the last two on the right are set to slow closing. Did you intend to have all four air valves set the same way, and make them different types in the different scenarios? 
 I see that you have assigned different transient alternatives, and that is where the air valve type (double acting, triple acting, etc) is stored. When you change the air valve type, ensure that you change the current scenario (select from the dropdown or right click > make current). 
 As a side note - for new questions in the future, it is best to start a new forum thread.

bentley water hammer

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