Adding new components and turning them on/off?

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Charles Ikenberry

• January 02, 2018 01:05

I'm trying to figure out the "best" way (or maybe several good ways) to add components (a group of elements to represent a process or feature) to a single model with the ability to turn them on and off.  For example, I have a water and nutrient mass balance model of a lake.  I'd like to add a routine to simulate the removal of nutrients from the inflow (via a constructed wetland).  I've already built the wetland routine using a Pool element and some accompanying Expression elements.  I'd like to turn the wetland on and off in order to compared nutrient concentrations in the lake before and after construction of the wetland.  Ideally, I would do this in one model, vs. building a "wetland" version of the model, which would then require comparing outputs of two different models, which can become confusing as multiple water quality improvement alternatives are added.

Perhaps I can simply have an on/off "switch" in the form of a Data element with input value of "0" to ignore the wetland and "1" to simulate the wetland (in conjunction with a Selector or Conditional Function element or Status Event element).   That would allow me to utilize the scenario manager to compare results.  I have multiple improvement alternatives I'd like to add to the model - the wetland is just one example.  I'd appreciate anyone's experience/thoughts on this.  It would be acceptable to turn elements on and off and then run and save output (rather than comparing using the Scenario Manager) if the Scenario Manager is limiting in some way.

Any experienced thoughts appreciated.  Thanks in advance.

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  Rick Kossik

  • January 02, 2018 17:34

  Charles,

  You have the right idea. Doing what you describe will require two things: 

  1) First, put the parts of the model that may or may not be turned off in a conditional Container.  Use a Data element (defined as a Condition, and named something like Model_Wetland") to turn it on or off at the beginning of the simulation.  

  2) That conditional Container will still have outputs.  If it is turned off, you obviously do not want to use them (they will output their initial value since by definition the elements in the conditional Container will not have been updated at all during the simulation).  Hence, you then use an If statement (or Selector) utilizing the same Data element to deal with those outputs appropriately (e.g., set to zero, or reference some other output).

  And of course, the Data element can be set to True or False when defining scenarios.

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  Charles Ikenberry

  • January 02, 2018 21:33

  Thanks, Rick.  That makes sense.  The trick may be keeping the components I don't want turned off out of the conditional Container.  In other words, making sure elements that reflect or calculate a flux in or out of the wetland must be outside the conditional "wetland" Container so the pathways I'm simulating are not affected.  As is nearly always the case with models, it's seeing the end from the beginning and organizing accordingly from the outset.  Easy to say, tougher to do.  Thanks again!

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