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Sequential batch processes in Simulink

Asked by Bastian Andersen on 22 Oct 2018
Latest activity Answered by TAB
on 23 Oct 2018
Hi,
I have the following system with 3 sequential batch reactors. Each batch reactor consists of a system of ODEs which are solved. Several 'subtraction' blocks are illustrated, however they would be slightly more complicated units, I just haven't figured out what they should be yet. The process flow is as follows:
  • The initial input (Start) to reactor 1 is known.
  • Reactor 1 runs for X hours with the initial input along with an estimated output from reactor 3.
  • The output from reactor 1 is used for reactor 2 along with the estimated output from reactor 3 which runs for Y hours.
  • The output from reactor 2 is used as input for reactor 3, which runs for Z hours.
  • Everything is updated and all reactors are recalculated with the new initial values, untill a steady state is obtained.
I do have a single reactor running atm. The problems are, that I don't know how to set reactor 1 to start at t=0, then reactor 2 at t = X and reactor 3 at t = X+Y, which all increases for the next loop. I do not have the package 'stateflow'.
How do I get the simulation to stop, when the simulation is close enough to steady state? Do I have to specify a simulation time prior to simulation?
BR Bastian

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1 Answer

Answer by TAB
on 23 Oct 2018

In Simulink, you can not start different subsystems at different time. When you start simulation at t=0, all block in the model will be executed based on their sorted order and will produce some output which will be input to succeeding blocks.
You can only control the output of the subsystem using Enabled Subsystem or Triggered Subsystem.
For example, place your reactor 2 in an Enabled subsystem and activate the enable input from t=X time (using Clock and Compare blocks). Until subsystem is disabled (before t=X) its outputs will have reset values defined in outports. When subsystem is enabled (from t=X) its internal logic will be executed and outputs will have calculated values.

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