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I am creating a dynamic inventory model follows continuous review policy. My objective of this project as I have to maintain inventory fill rate as 99%, suppose whenever the fill rate get falls below 99% "Adjust to S" has to trigger the model to order quantities from the supplier. My i am confused how to set the trigger value i browsed various models but i couldnt understand can any help me with this model? I have attached the screenshot and model for your reference. Let me know if you need any other inputs Hoping expecting feedback from this vensim experts

The model you uploaded does not simulate. Do you have a version that does?

Administrator wrote:The model you uploaded does not simulate. Do you have a version that does?

Yes,one of the Phd scholar did the same scenerio in VENSIM. Kindly please guide, More over I got this adotped from Edx website from Supply chain Dynamics course taught by MIT. Why do you think this models doesnt simulate

If you have access to a copy of Business Dynamics, that has a whole chapter on inventory control & ordering, as I recall.

tomfid wrote:If you have access to a copy of Business Dynamics, that has a whole chapter on inventory control & ordering, as I recall.

Can you please tell me why my model is wrong here???I am struck with right and of the model. My modle automatically want to trigger the order quantity when ever the service rate falls below 90% can you please guide me?

HI

IF you hit the CTRL T key Vensim will tell you that there is a simultaneous error.

I join a model that is corrected and that works in Vensim PLE and DSS. In DSS you can optimize

the PLE version is in .mdl format and the DSS in vpm published format with an optimized file, searching to optimize the net profit cumulated.

you should correct the units and probably start with a simpler model that will be easier to analyse.

Regards.

JJ

Thank you so much Laujj. I really appreciate your help. Once I check and make sure whether i got the expect result i will let you know. I really appreciate your help Thanks a lot

HI

there are quite a lot of errors corrected in the two added models.

the last one has been greatly simplified and has units corrected.

Regards.

JJ

Here's a minor update that makes the feedback a little clearer. I also calculate an average fill rate, which could be used to endogenously adjust the inventory goal to achieve a desired service level.

tomfid wrote:Here's a minor update that makes the feedback a little clearer. I also calculate an average fill rate, which could be used to endogenously adjust the inventory goal to achieve a desired service level.
Vensim inventory_5.mdl

hello sir, I have attached the pdf file for your reference. this is the model exactly what i want to model in VENSIM. Only difference is the author modelled it in Arena, but i want to model it in VENSIm. The main objective is i want to compare the two inventory policy, continuous review policy and periodic review policy at the select which one is best the constraint is 99% fill rate. Kindly please guide me. if not, atleast i want to model only one policy either continuous or periodic review policy in Vensim. thank you for your help. i really appreciate your help

LAUJJL wrote:HI

there are quite a lot of errors corrected in the two added models.

the last one has been greatly simplified and has units corrected.

Regards.

JJ

Thank you

LAUJJL wrote:HI

there are quite a lot of errors corrected in the two added models.

the last one has been greatly simplified and has units corrected.

Regards.

JJ

hello sir, I have attached the pdf file for your reference. this is the model exactly what i want to model in VENSIM. Only difference is the author modelled it in Arena, but i want to model it in VENSIm. The main objective is i want to compare the two inventory policy, continuous review policy and periodic review policy at the select which one is best the constraint is 99% fill rate. Kindly please guide me. if not, atleast i want to model only one policy either continuous or periodic review policy in Vensim. thank you for your help. i really appreciate your help

lakshkrish153 wrote:

tomfid wrote:Here's a minor update that makes the feedback a little clearer. I also calculate an average fill rate, which could be used to endogenously adjust the inventory goal to achieve a desired service level.
Vensim inventory_5.mdl

Thank you

Since the policies you're after have some discrete event attributes, you might take a look at this:
http://vensim.com/discrete-stochastic/

I'd note that the policy in the paper is not very general, because it doesn't directly account for expected sales, and it would be challenging to account for other features like shipping delays.

Hi

In the Vensim inventory_4 model, there is an error about using the smoothed sales. instead of using it, one should use the past smoothed sales, because at the moment when order is decided one does not know the sales of the period and then not the smoothed sales. One is obliged to use the past smoothed sales which is known.

Regards.

JJ

If you want to replicate the arena model, it is better to simplify the problem to its utmost limit, build a simplistic model first, test it and use it extensively and once that the model has no more secret for you, add only one factor and repeat the process. A good idea is to start with one level and one feedback loop. Each version should not have more than one level or feedback loop more than the presious one. This will take a lot of time (it could take several months) but wil generate a quality model, well used, tested and especially understood (Something rate in the SD community).

Regards.

JJ.