Fri, 30/10/2009 - 09:17 — Elemer
HI!.
I need some help related to the nature of flow's direction. I am trying to simulate with a boolean expresion (if) for the direction of a flow depending on concentrations of substrtate between compartments: i.e. If comp A=10 and compB= 20 the flow goes from B to A; else if comp A=20 and B=10 then flow is reversed, from A to B.
My question: Can I have a reverse flow on the same flow arrow, and how to build the expresion ( i tried putting a negative symbol depending on how I wanted it, but it didn't work), or, must I just draw a different arrow for the condition?. I atatch a simple example below.
I appreciatte every input I might receive,
Elemer Briceño, PhD. Forestry
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Reporter:
Elemer
Created:
Fri, 30/10/2009 - 09:17
Updated:
Wed, 16/06/2010 - 19:21
Comments
#1
Hi,
Flows and compartments both may be negative. An arrows direction (tail to head) shows which direction is represented by positive numbers. So if the flow value is negative then the flow will be from the arrow head to the tail.
Taking your example above using compartments A and B, and calling the flow, F.
If the flow arrow is drawn from A to B, a postive value for F will be a flow from A to B and if F is negative the flow will be from B to A
Now to the flow equation:
F = A - B
would give the results you want
first case:
If comp A=10 and B= 20 the flow goes from B to A
so substituting values for the compartments
F = 10 - 20
= -10
F is negative and the flow will be in the reverse direction compartment, B to A
second case:
comp A=20 and B=10 then flow is reversed, from A to B.
so substituting values for the compartments
F = 20 - 10
= 10
F is positive and the flow will be in the forward direction, ie compartment A to compartment B.
I guess introducing boolean expressions complicates things rather than letting the maths do the work.
I hope that helps.
Jonathan
#2
I would add that there appears to be a bug in your model, in that the flow 'dedo' is set positive no matter which end is larger, and this causes its end compartments to diverge to very large values. I am thinking it should be like 'dodi' which becomes negative when the destination compartment is larger.
Cheers
Jasper
#3