Can anyone help me solve this simulation problem

This forum is for discussion of topics related to System Dynamics. You must be logged in to post but anyone who has registered on the System Dynamics web portal may post. Note that there may be a delay of a working day or two after registering before you can post anything.
Post Reply
Abhyank Srinet
Posts: 4
Joined: Mon Jun 22, 2015 4:07 am
Location: Paris
Contact:

Can anyone help me solve this simulation problem

Post by Abhyank Srinet » Wed Jul 29, 2015 4:16 am

Hi Everyone,

I was trying to simulate a production process, and wanted to factor in efficiency losses. I have tried playing around with different designs but i somehow cannot arrive at the right answer.

The problem statement: Building a very simple model in which a certain amount of inventory is needed to be maintained as buffer stock, this value is dependent on the order rate. The manufacturing rate is calculated by adding the smoothed out order rate and the gap. Now not all material manufactured goes into inventory, there are efficiency losses of 10%. I am basically in a fix on how to properly simulate these losses.
Here are 2 methods i tried

1) if i take one stock as inventory and multiply the manufacturing rate with the efficiency (as in model 1 attached below) there is always a gap related to efficiency losses. Now i know i have to create a feedback to account for these looses, i just am not getting how to account the formulation for it. Should i add another flow which accounts for losses in efficiency or is there a better way?

2) Another model i tried in which i took 2 stocks, one "work in progress inventory" and another "Normal inventory", i accounted for efficiency losses in a flow called conversion rate. This model gave me sustained oscillations around the buffer inventory figure. Now because of the two stocks i am getting sustained oscillations but this is not real world behavior and is in no way getting me close to the final buffer inventory value. Plus i feel i am missing something in this approach.


I feel i am missing a key point here.
I hope some of the much more experienced in this forum can help me out. It will be very much appreciated.

Regards,
Abhyank Srinet
Attachments
model 2.mdl
Model with 2 stocks
(6.57 KiB) Downloaded 221 times
MODEL 1.mdl
Model with a single stock
(5.61 KiB) Downloaded 209 times

Richard Dudley
Posts: 65
Joined: Sun Jan 11, 2009 1:17 pm
Location: Etna, New York, USA
Contact:

Re: Can anyone help me solve this simulation problem

Post by Richard Dudley » Fri Jul 31, 2015 9:49 am

I haven't looked carefully, but one thing that you should do (in model 2) first is decrease the time step. The oscillations will disappear (although such a model can have oscillations).

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest