Delay Conveyor

[ESC]

Just a quick simple question:

Is it possible, if one is using a delay conveyor function to somehow specify the following:

- at time t take out a given amount of material (leak) from a given point in a conveyor.

From what I read in the manual, the leakage rate is constant and it occurs all along the conveyor. It's also a percentage, so it's painful to formulate it as take 100 units out as opposed to take 5%.

Now the variable leakage rate (so it's different at a given point in time) I can imagine by simply making the rate a variable and using some function to alter it (or a lookup), but that will affect elements along the whole of the conveyor as opposed to a smaller section, which is what I want :\

[bob@vensim.com]

To target a quantity leakage just use that quantity divided by the stock to get a fraction.

To target leakage at certain points you need to move to different formulation. Generally a series of levels cascaded using SHIFT_IF_TRUE will be the easiest to manage. Then you can target any individual cohort for adjustment.

[Edited on 10-2-2005 by bob@vensim.com]

[LAUJJL]

I do not think that it is possible in a standard way to have the leakage work on a specific point on the conveyor.
I think that if you want to have something specific it is better to construct your own model with levels and subscripts.
You can try too the queue functions that work nearly the same as the conveyor.
All these functions are very tricky to use.
I have a model that works with queue functions, and I would prefer that I had used levels and subscripts for the sake of clarity. One of the queuing function has 9 parameters and is a horrible black box.
you can go to the Powersim site (Powersim.com). They explain how you can use levels to construct queuing models. You can then easily transpose the method to the Vensim environment.
Regards.
J.J. Laublé

[ESC]

Thanks a lot, that's more or less settled then. One surprising finding though was that if I increase the leakage rate, the amount leaving the conveyor drops but the amount on it actually increases, keeping everything else constant. That strikes me as somewhat counterintuitive.

[Edited on 10-2-2005 by ESC]

[LAUJJL]

There is may be an error in the way you calculate what is on the conveyor.
I think that there is an example on how to calculate what is on the conveyor in the Vensim doc.
Regards.
J.J.L

[ESC]

I thought what is inside the stock is actually what is on the conveyor. The way it's designed are a stock, an inflow and the outflow. The outflow is a delay conveyor of the inflow, so I assumed the outflow to be the finished items and the stock to be what is on there.

Lee, did I understand that correctly from our course? :dunno

[bob@vensim.com]

Not quite - the leakage also needs to be subtracted - this is actually the hard part. See CONVEY3.mdl in mguid\9discret to see the details of the computation.

[Lee Jones]

Originally posted by ESC
Lee, did I understand that correctly from our course? :dunno

Bob's right, I have had another look at your model and there needs to be a flow out if the stock to account for the leakage. (we used convey4.mdl as an example on the course)

Lee

[ESC]

Actually it makes perfect sense. Thanks a lot