This TechNote describes the step-by-step process used to model a pump starting up (as opposed to shutting down) in Bentley HAMMER V8 XM Edition.
Note that Bentley HAMMER V8i offers an automated way of modeling this. The steps below are only for users of Bentley HAMMER V8 XM. For V8i, see this article.
In most cases, the transient-inducing effects of a pump are modeled by having that pump shut down. In Bentley HAMMER, the "shut after time delay" transient pump type is used to do this. However, in some cases, an engineer may want to model the effects of a pump turning on (a pump start-up event.) In this case, HAMMER does not offer a direct way to do this; there is currently no "start after time delay" transient pump type. This is primarily due to the fact that the nominal operating point of the pump after it turns on is not known by the transient simulation, if the initial conditions describe the pump being off. So, a few extra steps are required to model this case.
Before performing these steps, ensure that the demands, physical properties, and other settings in the model describe the condition that you would like to represent. Meaning, if you would like to see the transient effects of the pump turning on during high demands and low tank level, ensure that the demands and tank level are adjusted as such.
This walkthrough also assumes a steady-state analysis for the initial conditions and that you have storage downstream of the pump in question, or other pumps, either of which could supply the demands you have entered when the pump in question is off.
Note that if you do not have an active valve in your model, you can skip steps 6, 7 and 11.
Now that the transient simulation has been provided the correct initial conditions, we need to specify a few extra key pieces of information: the nominal operating point and discharge coefficient that describe the conditions of the pump and valve(s) when the pump is on. This is why the above steps were performed.
At this point, the model is correctly configured for a pump startup event and you can compute the transient simulation via Analysis > Compute.
The results of this model can be viewed just like any other transient simulation. Go to Analysis > Transient Results Viewer. To view a graph of head and flow for the pump, you may want to select a time history for the pipe end adjacent to the pump:
As you can see, when the pump starts up, a transient occurs. After about 40 seconds, the head/flow stabilize to the nominal conditions.
Note that in many cases, you may not see flow start to occur through the pump until the speed has increased enough so that the downstream head can be overcome.
You can also select a transient profile and click the "Animation" button:
As you can see, there are some problems with vapor pockets forming upstream of the pump when it starts up. A surge tank may be required in this case.
Note that you can also view extended data specific to the pump by entering a number for the "Report Period" attribute of its properties. For example, "10" would mean that extended data will be reported every 10 timesteps. You can view this report by going to Report > Transient Analysis Reports > Transient Analysis Detailed Report. At the very bottom of this text report, you will see the table of flow, speed, upstream head, and downstream head:
Yes. HAMMER V8i introduced a new transient pump type called "Pump start". This exposes the rated head/flow values without having to specify initial conditions. So, all you would need to do is turn the pump on first to obtain the rated head/flow and then turn it off and enter those values for in the "pump start" pump.
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