Question about model with Queue, Delay and capacity contrain

[Mattes_01]

Dear all,

I got another question about a model which gives me weired results. See the model attached.

Actually I am doing some research about this queueing problem, discussed earlier.

I thought I should be able to combine the queue with a delay fixed or delay3. By this it should be possible to model a process using a continuous delay but also taking the effect with a increasing queue when driving the model near the contraints with random variation in the arrival process.

My question to the model is what I might have done wrong:

I am having a contrained WIP.
Before putting materials into the WIP I check if the WIP has capacity (WIP+finishing<WIP capacity).
I check, too, if the queue infront of the WIP stock is non zero and put either the actual availiable WIP capacity or the available widgets in the queue into the WIP/into my process.

The weired thing is that the WIP is much higher than it should be, based on the contraints.

Why is that the case?

Thank you and best regards
Mattes

[Mattes_01]

I found the problem:

Have a look at "to actual WIP". There is the flow "finishing" taken into account. And I have taken this flow as a stock, this was the problem. Its fixed now (just use instead of "finishing" "finishing*TIME STEP".

Sorry for this topic.

[bob@vensim.com]

Units check - always a good idea