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HAMMER - engine Calculation Failed

I am modeling a pump station and transfer line with a very high elevation point in the middle of the line in HAMMER. Different pipe sizes are used in the model for the pump station and transfer line (a range of 6" to 24")

In the initial conditions run I get the message of low pressure points in the model.

When I compute the transient it shows the Engine Error Message as attached.

So, I removed the pipeline after the high elevation point and the error of low pressure points and Engine calculation failure are removed.

But How Can I solve the model for water hammer with keeping the whole line?

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  • Hi Hoda,

    After the "Engine Error Message", did your user notification list indicate that the problem was due to an initial pressure being less than vapor pressure? If so, this is not allowed because it would mean that there would be a vapor pocket formed even before the transient simulation began. 

    Most likely this is happening at that high point, which may be indicating that an air valve at the high point would actually be open during normal operating conditions. Pumps will not "see" high points and add more head to overcome them unless you use the air valve element as described here: Modeling Air Valves At High Points in WaterCAD or WaterGEMS

    First, create a profile covering the whole pipeline and look at the initial conditions profile plot. If you have demands at the downstream end, the pump will add the head corresponding to the flow equal to the sum of those demands and the HGL along the profile will be based on that in conjunction with pipe headlosses. If you modeled the end of the system as a reservoir (known HGL), the pump will add enough head to "lift" the water to that downstream known HGL, regardless of the elevations of the junctions at the high point.

    If you do find that the pump would need to add more head to overcome the high point, you may be tempted to use the air valve element there. This will resolve the initial low pressure problem because the pump would see the high point as a boundary condition and the pump would add more head to overcome the high point, but the transient simulation would not work well because there would essentially be an air gap at the high point with part-full flow. If this is indeed the situation in your case, it may be best to stop the model at the high point (remove the pipeline downstream of it) and model the high point as a Discharge-to-Atmosphere element configured to model the flow that "spills" into the part-full portion of the pipeline at the high point. The downstream section would not necessarily need to be modeled in this case because of the air gap, where a transient wave would not pass. See the section called "Transient Simulation Implications in HAMMER" in the above article for more details and illustrations to explain this.

    If you find that you did not expect to have low pressure or part-full flow (open air valve) at the high point and expected it to all be under pressure in the initial conditions, you may need to adjust the model to enable the pump to add more head. Check for data entry errors by examining a profile for example.

    If this does not help, please provide more details on the user notification, a screenshot of the profile view of the initial conditions, and/or a copy of the model for review: Sharing Hydraulic Model Files on the OpenFlows Forum


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • Hi Jesse,

    Thanks so much for replying to my question.

    Removing the pipeline after the high point solves the issue. But about designing a surge prevention device in the highest point of the pipeline how can we use HAMMER software? Should we go with another type of software?

    Thanks,

    Hoda

  • As mentioned in my previous post, you can run a transient simulation of this system if you end it at the high point using the D2A element. This enables you to model the portion of the network that would remain pressurized during the transient simulation. Meaning, HAMMER can model the pressure waves that would travel to and stop at the high point (due to the air gap).

    First ensure that  you do expect part-full flow at the high point (with air entering an air valve). As mentioned if you expect the pipeline to remain under pressure even at the high point, there could be a data entry error that you'll need to fix so that you can run the full model (both the initial conditions and the transient simulation).


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

Reply
  • As mentioned in my previous post, you can run a transient simulation of this system if you end it at the high point using the D2A element. This enables you to model the portion of the network that would remain pressurized during the transient simulation. Meaning, HAMMER can model the pressure waves that would travel to and stop at the high point (due to the air gap).

    First ensure that  you do expect part-full flow at the high point (with air entering an air valve). As mentioned if you expect the pipeline to remain under pressure even at the high point, there could be a data entry error that you'll need to fix so that you can run the full model (both the initial conditions and the transient simulation).


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

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