Enrico Remigi WEST Product Owner

You can use a Timer (e.g. "21" that is: 2 phases and 1 signal):
[list]
[li]set the 1st period (T1) to 5 min and the 1st signal (u11) so as to feed your tank (e.g. u could be linked to a pump in a buffer tank, so u11 should be the desired feed flow)[/li]
[li]set the 2nd period (T2) to 23h55min and the 2nd signal (u21) to zero[/li]
[/list]
Mind that such "hard-switch" (u changes istantaneously from non-zero to zero) may slow down the simulation considerably - also because you may need to use a non-adaptive stepsize algorithm.
You could insert a ResponseTime model (DataTreatment block) downstream to the Timer in order to smoothen the signal (order 2 is generally fine).

I agree with you: we should probably not remove anything from ASM1, it is such a reference. For quite some applications the soluble organic nitrogen is not negligible and it is quite easy to estimate the soluble nitrogen fraction with a TKNsol analysis.

Would you be able to suggest a modification to the current ASM1_AN implementation?

Then it is ".[NameOfQuantity]" only, as a Calculator Variable is some kind of top-level object

What kind of variable do you need? I assume it's a plain algebraic expression - with no articulated statement, right?
If so, it is most likely that you have typed it in incorrectly. Remember:
[list]
[li]the code is case-sensitive (e.g. if a block is called "ASU_1", the string ".asu_1.Vol" is going to fire that error message)
[/li][li]the syntax is: .[NameOfBlock].[NameOfQuantity] (remark the 'dot' in front of the block name and in front of the quantity name)[/li]
[/list]

Section 2.6.10 of the User Guide

This error has nothing to do with your specific set up or influent file.
It looks like the project folded or some file may be in use outside of WEST - hence access is denied.

[quote author=Zoi link=topic=2526.msg5920#msg5920 date=1437138318]
Dear all,
.. but I cannot run it because I get error that the [b]buffer is empty [/b] and [b]error while executing simulation[/b] ..
[/quote]
Difficult to say based on the log file you provided, because it contains a lot of extra information from previous attempts.

When sending the WEST log file, [b]is always best to first [u]clear[/u] the Logging pane and then execute the action that may cause the error[/b]. In this way, the log file will only contain essential information.

Anyway, in your case it seems to be due to the influent file (incorrect format, missing rows - probably the first one at time zero, ..) or influent specs.
How do you provide the influent characterisation? do you use one file? multiple files that are to be merged by WEST?
Do you modify the list of "components" (i.e. measurements) in the General page of the Influent Tool - and the default fractionation model?

[quote author=Zoi link=topic=2526.msg5920#msg5920 date=1437138318]
.. which of the two fractionation type (custom or standard) is best to use and which information should the input files should include[/quote]

There's no best way to do it: it depends on what type of influent specs you can provide.
Generally, one does not measure all the ASM- components (cf Standard) but a certain set of conventional, lumped, quantities (e.g. COD, TSS, ..).
As to which information should the influent specs include: it does not really matter, as long as, based on your limited set of measured quantities, you can provide all the state components of the selected category/instance (in your case, ASM2).
So you could use flow rate, COD, BOD, TSS, T(K)N, TP; or flow rate, COD, BOD, TSS, NHx, NOx, PO4, TP; or .. any combination [b]as long as you can "map" all the ASM2 components[/b].

Hello Hector,
ok I see: you used the [b]MBRIdeal[/b] model (I thought we were dealing with fouling and backwashing too): so your layout is correct (cf image "MBR_Layout"). Interesting application by the way: [b]retrofitting an existing facility[/b] with the addition of an MBR unit.

I see only one issue: you're starting at an incorrect initial volume (at time 0), 1000 m3. This is the library default value which, I will agree with you, is kind of hidden ...
If you reset it to 50 (or 40) m3, the initial transient is reduced to a bare minimum and the simulation runs smoothly.
To do so - and this is the 'hidden' part, you need to [b][u]reset the initial mass of water[/u][/b] (M[H2O] which is a derived state variable of the MBR).

Then it's all correct - except that you cannot use an adaptive step size integrator (like RK4ASC) nor VODE, essentially because you have a couple of timer blocks in your layout and the MBR has also got phases.
These are a couple of runs I've done:
[list]
[li]RK4, step size 1E-5; communication interval for plots 0.01 -> 5 days in SS take 88"[/li]
[li]RK4, step size 1E-4; communication interval for plots 0.01 -> 5 days in SS take 17"[/li]
[li]RK4, step size 1E-4; communication interval for plots 0.005 -> 5 days in SS take 21"[/li]
[li][u][b]RK4[/b][/u], [u][b]step size 1E-4[/b][/u]; [u][b]communication interval for plots 0.005[/b][/u] -> 100 days in SS take 2'14"[/li]
[/list]
Steady-state is reached after approximately 30 days (cf image "MBR_Simul").

I already see a significant improvement: there's no negative volume or flow rate.
Anyway, I guess the only way to gain a better view on your set up is that you share 1) your [b]WEST layout[/b]; and 2) the settings for the following [b]parameters[/b]:
[list]
[li]average QIn to your system and desired QWaste[/li]
[li]filtration and backwashing periods (relaxation are less relevant, can be zero)[/li]
[li]filtration and backwashing fluxes[/li]
[/list]

Alternatively - it may be faster, you can send your project to 'mike' then we can post the working settings here.

Hello Hector,
indeed, it may not be easy to pin-point specific issues that may have got to do with parameter settings.
However, in your current set up, I believe the main problem is with the volume ('min' and 'tank'): it is not advisable that they have the same value as it would make a test like IF ((V > Vmin) & (V < Vtank)) THEN fail. And, as a consequence, the solver to become unstable.

Rather use the Vmin as some lower bound (not zero, but one order of magnitude smaller that the maximum should do); and Vtank as the actual, desired tank volume.
See how the simulation outputs improve.

Also, carefully set the integrator and integrator settings, as you have phases in the MBR model.

I cannot judge from the snapshot, but I see a negative quantity (flow rate or volume): what is it? why does it happen?