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Lagrangian particle movement - Model catalogue -

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Lagrangian particle movement

Model : lagrangian1
Simile version : 3.1+
Date added : 2003-06-20
Keywords : Movement ; Individual-based ;


This is a (small) modification of a basic individual-based movement model. In this case, particles are being continuously created and destroyed, the random movement is rather less - particles tend to move in straight lines - and an impermeable 'barrier' has been introduced. Those particles above it are not affected, but those that would hit it change direction as they approach it and flow around it.

The original context for this model was the simulation of large numbers of CO2 molecules moving from the soil up through the forest canopy into the atmosphere above. The 'barrier' could thus represent a leaf that the moleculs need to move around. An extension of the model could then involve providing stomata that some molecules could enter, and then participate in photosynthesis.


Model file

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Equations in PREDATOR
  X:    initial value=80
  Dir:  initial value=rand(0,6.28)
  Y:    initial value=rand(10,90)

  xchange    = if outside==1 then speed*cos(dir+3.14)else speed*cos(dir)
  dirchange  = if outside==1 then 3.14/dt(1)else(if (x>30,x<50,y<70)then 0.4*(1.57-fmod(abs(dir),6.28))else 0.4*(3.14-fmod(abs(dir),6.28))+rand(-0.15,0.15)/dt(1))
  ychange    = if outside==1 then speed*sin(dir+3.14)else speed*sin(dir)

  speed      = 5
  size       = 1
  outside    = if max(abs(50-x),abs(50-y))>50 then 1 else 0
  im1        = 10
  loss1      = X<0



When the model is run, and the behaviour presented using the 'lollipop' diagram, you see particles being created along the right-hand side of the area and flowing across to the left. The ones moving along the bottom then flow up and over the barrier.