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Deal all,
For many of our project we have "sealed" manholes. What is the best way of modelling seals?
I've used breaks to resemble the seal, which seems to work fine. However I do get a warning "Headloss type is inappropriate for this object". Could this have an effect on the calculation? please refer to attached documentation for reference.
Attachment 524Attachment 525Attachment 526Attachment 527
Thanks and regards,
Sebastiaan
Hi Sebastiaan,
I recommend that you use an ordinary manhole with a flood type of 'sealed'. This means that you'll be able to specify the dimensions of the manholes as they exist in the ground. If the manhole floods, it'll represent the pressure head which would exist in reality, with an equivalent elevation head, but no water will be lost from the manhole.
Break nodes have zero volume and should only be used to represent changes in cross section, gradient or direction in fully pressurised systems such as forcemains / rising mains.
Mike,
Thanks for your reply.
So it is not possible to simulate the headloss introduced by the seal (the elbows in the piping)? I should model only the Pipe as if the seal is not present? To me this feels inaccurate.
Thanks.
Hi, I assume we're talking here about changes in say gradient of pipes in a gravity system, which exist below the ground, i.e. with no manhole present. Is that correct? If that's the case, we need a node to represent this, but that node would have a zero volume. For changes in direction, we can use pipe bends, but I agree that in both situations, there is a danger we will under represent the headlosses which occur.
Going back to the warning message you received "Headloss type is inappropriate for this object", I think that's because you are using the default 'normal' headloss, which represents the transition from a pipe to a manhole and then back to the pipe, whereas when we use a break node in a pressurised system there is no manhole and a 'fixed' headloss is more appropriate. This warning should disappear if you switch to an ordinary manhole with a sealed flood type.
My recommendation would be a add up all the headlosses and apply them to the upstream end of the pipe. Like many aspects of modelling, this is a compromise because we are combining the headlosses which occur in the pipe / manhole transitions and those which occur due to bends / changes in gradient etc. This compromise is better than using break nodes in gravity systems, which often lead to instabilities.
Hi, Yes correct. An underground piping empty running gravity type system, where all connections to pits (manholes and catch basins) are sealed by means of two 45 degree elbows. Using a sealed inlet is common practice on an empty running gravity type system in the petrochemical industry. Please refer to the snapshot of the standard drawing attached to my first post. Note there also other type of seals used in the industry.
Having the seal in place will have an effect on the calculation (not having it will also introduce a discrepancy in manhole chamber floor level), therefore I am looking for a way to do it properly. As I understand now, there is not really an accurate way of modeling what is required. Adding the headloss to the US end will not fix the discrepancy in manhole chamber elevation right? Are there any other recommendations you could give us?
We have been struggling with this issue for some time now, often resulting in using other calculation methods. We would however prefer to use InfoWorks or any Innovyze software actually, to do our (dynamic) calculations because of the accuracy.
Regards
No doubt this is a tough one, taking InfoWorks outside the area it was originally intended for. I guess the two main issues are what type of manholes should be used up and downstream of the rocker pipe and what type of headloss should be used for them. I stand by the original advice that break nodes tend to cause instabilities, but you may want to try them first and in locations with instabilities, switch to a very small manhole, say 0.1m2, or whatever will achieve stability. With regard to the headloss type I guess you are most interested in the situation where the pipe is in surcharge and therefore I would used the fixed headloss type.
The manhole chamber elevation shouldn't be an issue, just set it lower than the incoming and outgoing pipes as you have done.
Dear Mike, Since today the calculations, Runs, all fail if there a Warning for "Headloss Type is unappropriated for this object.". Any clue if there has been an upgrade causing this? Thanks.
Hi - the most likely thing is that you are using the 'normal' headloss, which is only appropriate for gravity systems. Hence this is a warning, rather than an error.
Note that for specific support questions like this, it's best to use our support process, such as emailing support@innovyze.com.
Ok. Thanks for your prompt reply. The weird thing is, the calc always was running fine. Now it stops...