Simulation time issue

[fabriziorosichini]

Hello everyone,

I would like to share an issue I am experiencing with a dynamic simulation for my master thesis. I am using an external PID controller (connected to DWSIM through the OPC UA Client plugin) to control a temperature by manipulating the heat input to a heater. I saw that using a large integration step the temperature set point is reached but the heat input stabilyzes on a value that is different from the steady state one. Reducing the integration step, the heat input converges closer to the steady state valiue. My issue is that, due to the communication with the external PID controller, the simulation becomes very slow : 10 minutes of real timer are required to simulate 1 minute of process time.

I would want to ask:

• is there a way to reach the steady state even using a larger integration timne step?
• is there a way to make the OPC-simulation faster?

Any suggestions would be greatly aprreciated,
Fabrizio

[DanWBR]

@fabriziorosichini what takes more time, data transfer or the flowsheet solver?

[fabriziorosichini]

the flowsheet solver because tags via OPC are continuously uploaded. I also tried to use the PID controller already implemented in DWSIM and the simulation is faster.

[DanWBR]

@fabriziorosichini maybe you could delay the flowsheet calculation a little bit using a python script, disabling automatic calculation after the data is retrieved via OPC

[DanWBR]

or change the auto update interval in the plugin

[fabriziorosichini]

Hello, increasing the auto update interval the situation improves, so thank you! Sometimes the simulation crashes, and the error reported "object reference not set an instance to an object" , everytime to a different flowsheet object. There is a way to avoid it?

[DanWBR]

can you see more details of the error if you click on it?

[fabriziorosichini]

"This error was raised during the calculation of a Unit Operation or Material Stream.

System.NullReferenceException: Object reference not set to an instance of an object.
at DWSIM.Thermodynamics.PropertyPackages.PropertyPackage.RET_VNAMES() in C:\Users\danie\source\repos\DanWBR\dwsim\DWSIM.Thermodynamics\PropertyPackages\PropertyPackage.vb:line 8739
at DWSIM."

This is the errore refered to a material stream. It often appears during steady state period

[DanWBR]

this may happen if an invalid temperature and/or pressure was given

[fabriziorosichini]

I don't understand how it is possible, since the initial flowsheet state is the same but the error appears at different simulation times and in different objects.

[DanWBR]

@fabriziorosichini I'll see what I can do about it

[fabriziorosichini]

Thank you