MBBR slows down simulation

Hello,
I am trying to model a WWTP which uses an MBBR reactor.
With the default values int the MBBR block the software is able to finish the computation in few minutes, but just by changing the parameter "f_solid" (5%) into the real value (23%) it's impossible to end a 100 days simulation in reasonable time.

I was thinking about reducing the number of layers with which the MBBR block works to speed up the run. It is now set on 10 layer. Is it possible to decrease it? I cannot find anything like that with the model editor.
Do you have suggestions?

Thanks for the attention,
Simone

Hi Simone,
reducing the number of layers may indeed speed up the simulation, but the reason why the simulation slows down when changing the "f_solid" is something different.

So yes, you can certainly vary the number of layers: [b]NrOfLayers[/b] is a global variable (a [b]Setting[/b]) and can be changed, at the project level, from the Miscellaneous / Block Library Setup dialog.

But I would also recommend that you monitor the Logging while executing the simulation with your "f_solid": you will hopefully get a warning (or a set of warnings) that will help you identify the underlying issue.

Hi guys,

I'm also working on a biofilm progress by utilizing MBBR. In my case the f_solid value is at least 0.7 in the real field. However, the default f_solid value is 0.05 for MBBR. When I enter some value higher than 0.45-0.50 for f_solid, the simulation doesn't lunch and gives me error.
Do you know any suggestion in order to avoid the error, either by editing another parameter or by changing some configuration on the layout?

Thanks.

Hi,
such a behaviour has usually got to do with some numerical issue - impossible to say what goes wrong without taking a closer look to the actual expeirment set-up.
I suggest you carefully inspect the Logging:
- Does the simulation not start at all? If so: do you get an error message?
- Does the simulation start and end in an instant? in this case too, one usually gets an error message of some sort ..
- Does the simulation start but progress extremely slowly? you probably get a constant flow of warning messages: can you pause/stop the simulation and check those warnings? do they point to any specific variable being negative, extremely small or infinite (NAN)?

Depending on the value that I enter for "[b]f_solid[/b]"; sometimes the simulation doesn not start at all or even if it starts it stops in an instant, either in steady state or dynamic simulation by telling me the error as below:

[u]System error: Error while executing simulation experiment, reading input file, or evaluating lower and upper bounds.
[/u]
Until the simulation gives error and stops, the velocity of simulation is not slow. It has a reasonable speed.

And at this moment, the variables under MBBR block details "[b]V (volume of the bulk liquid phase)[/b]" and "[b]V_ASU (Volume measurement data)[/b]" drops in negative values, which as indicated with red font.

Thanks.

If you say that the volumes become negative, this is precisely what the error message points at:
[quote author=astroneer link=topic=16094.msg20654#msg20654 date=1477402747]
[u]System error: Error [..] or evaluating lower and upper bounds.
[/u]
[/quote]
because the data type "Volume" is limited within the range [0 +INF].

The key now is to find out WHY does this occur: which quantity (or set of quantities) brings the volume below zero ?

Can you please send your project folder to the tech support (mikebydhi@dhigroup.com) ?