Hi, I think I've discovered an issue in your implementation of initial data.

The best way to describe it is with an example:

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[li]Model whichever plant you want. Be sure it contains: a) constant influent (so Dynamic simulation is just as steady as the Steady State one. b) at least one PI controler (as example: one to get a constant DO measure in an ASU tank with link between DO and Kla). I say [i]"at least one PI controler"[/i] because I know this is one of the conflictive blocks, I don't know if other blocks are affected.[/li]

[li]Run the Steady simulation till it's currently steady. I mean till all the graphs of whichever variable you want are flat lines forever.[/li]

[li]Switch to Dynamic and run the simulation. As the influent is fully constant and Dynamic start point is the ending of Steady State simulation, those very same flat lines are expected in every single variable of the plant.[/li]

[li]But look what you are getting. [b][u]There's some kind of unexpected transient at the beginning of the Dynamic run[/u][/b]. (It is much more prominent in some variables than in other ones).[/li]

[li]The culprit, ([u]or one of the culprits[/u]), is that PI block. If you graph Kla in the ASU tank, you'll see how it ALWAYS start at 0, because that PI block always wrongly starts at 0. There's no way to insert an initial value in its output [b]u[/b] variable (in fact, a value which should have been copied from the Steady State run...) Therefore the ASU aeration is wrongly switched off at the beginning of the Dynamic run.[/li]

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I really think you should revise this way of modelling blocks. C(X_S) in ASU Tanks, or actually M(X_S), is as needed as initial condition as the previous stored integral part in a PI controler is. If you do not properly initialize ALL the needed variables thorough the model, (not only direct ASMxx concentration/masses), you are going to generate unexpected wrong transients at the beginning of each subsequent run.