Modeling a system with two arrival lists for a server

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Martiny
Posts: 3
Joined: Thursday 08 January, 2015 - 17:46

Modeling a system with two arrival lists for a server

Post by Martiny »

Hi!
I need help with a task and it's quite urgent. Here's the task:

One unit of raw material makes one unit of finished inventory. The production process performing this transformation takes an uncertain time per unit characterized by a TRIANGULAR(1,2,3) distribution (in hours); thus the average time to convert one unit from raw to finished state is 2 hours. You can only work on producing one unit at a time.

We store the raw material in a facility with a capacity of 60 units. When the raw material inventory level reaches 25 units, we order an additional 35 units. The lead time for the raw material is characterized by a TRIANGULAR(24,36,48) distribution (in hours).

Simulate 10,000 hours of operation of this system. What fraction of the time the server isn't working because there is no raw material?


I have created an Arrival list that creates 60 products, connected it to a Queue and connected that to a Server, followed by a Sink. Underneath, I've created another Arrival list that creates 1 product, followed by a Queue. After it there is a Server that transforms 1 unit of raw material into a batch of 35. The server is connected to the first Queue.

Unfortunately, I don't know how to program the triggers on the Queues so everything works properly. I've been told I need the Initialize atom but i don't know how to use it.

Please help.
Thank you.
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HarryBunnik
Posts: 362
Joined: Monday 07 February, 2011 - 11:22

Re: Modeling a system with two arrival lists for a server

Post by HarryBunnik »

Ha Martiny,

It is possible to build some controls to make it do what you want, but I was wondering if, when you use a normal source (instead of the arrival list) and a reservoir (instead of a queue), your problem wouldn't be solved? A reservoir has a lot of the things you require already build in (upper level, lower level etc) and it can stop the source once the upper level is reached and open it again once the lower level is reached.

I hope this helps you, otherwise we have to look a bit further.

Cheers,

Harry
Martiny
Posts: 3
Joined: Thursday 08 January, 2015 - 17:46

Re: Modeling a system with two arrival lists for a server

Post by Martiny »

The Reservoir thing didn't work.

I've written a trigger on exit on the 1st queue "if(And(Content(c)<=25, Content(AtomByname([Server7], Model))=0), OpenOutput(AtomByName([Queue6], Model)))".
Also I've written a trigger on entry on the second queue "CloseOutput(c)".

Everything works except, at first, a product goes straight to the server from the second ArrivalList (it doesn't wait for the conditions). Afterwards everything works fine. I thought I might use the Initialize atom but I don't know how.
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HarryBunnik
Posts: 362
Joined: Monday 07 February, 2011 - 11:22

Re: Modeling a system with two arrival lists for a server

Post by HarryBunnik »

Strange, but ok. Out of interest, what is not working with it?

To me it sounds as if you should use just one queue, one source and the server. Then you can control all from that single queue. At the moment I have the impression from your explanation that it is all one product and since you're trying to control all with code on the queue(s), you're complicating it by using "Arrival lists" and more than one queues.

Cheers,

Harry
Martiny
Posts: 3
Joined: Thursday 08 January, 2015 - 17:46

Re: Modeling a system with two arrival lists for a server

Post by Martiny »

I found the solution.

I've written a new trigger on exit for the first Queue: "if(And(Content(c)=25, time>10), OpenOutput(AtomByName([Queue6], Model)))". The thing is, there was <=25 units of raw material in the first queue from the start because the raw material gets in one by one, even though it takes only a fraction of a second for all 60 units come in. That's why I added time>10.

Your solution is probably better but I didn't even know there was a Reservoir atom in ED. I'm a newbie when it comes to ED.

Thank you for your help anyway Harry.
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