Add MixerSplitter UnitOperation

[schmoelder]

This is my first try at anything C++. Please be gentle! ;-)

As mentioned in #40, the goal is to implement a Unit that has zero volume but can be used to mix and reconnect streams between UnitOperations.

I took the OutletModel as a template and

• enabled outlets
• added setFlowRates() function from StirredTankModel

What works

• It compiles!
• Simulations work if there is only one ingoing stream active at the time.
• The stream can (dynamically) be separated into different outgoing streams (also with fractional flow rates)

What does not work

• Having more than one active input at a time leads to a TimeOut.

I guess I forgot to implement something related to the flow rates.

[sleweke]

Unfortunately, this unit operation is not going to work in the current simulator. There's a shortcut for consistent initialization of the underlying DAE system. This shortcut is based on the assumption that the outlet concentration of a unit operation does not change (immediately) if its inlet concentration is changed. Or, more mathematically, the outlet port is a differential state variable. This assumption is true for all models implemented so far.

The proposed mixer/splitter unit breaks this assumption since the signale at the inlet is immediately propagated to the outlet (outlet ports are algebraic states). Thus, consistent initialization is not going to work and the system will not simulate.

[schmoelder]

I understand. Could this alternatively somehow be added in the ModelSystem?

[schmoelder]

FYI, I pushed some other changes for completeness sake that I still had not published. Due to the mentioned underlying problem explained by @sleweke, it obviously still does not run correctly...

[schmoelder]

Closing since this approach is not working with the current architecture of CADET. Must be implemented on switch level.