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Determination warm up period, run length, number of replications

Builder
Builder

Dear all,

 

I have a question concerning the determination of the warm up period, run length, and the number of replications. I have experience in determining this for a system in which only one product was produced. Here, I could just use the mean flow time of this product as input information. However, in the system that I`m modeling now, 76 products are produced.

 

My question now is how to determine the proper values for the warm up period, run length, and number of replications, while 76 products are present.

 

Many thanks in advance.

 

Kind regards.

37 REPLIES 37

Re: Determination warm up period, run length, number of replications

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

There are several posts on this topic, so you should consult thiose anyway.

 

The multi-product case is not fundamentally different from a single-product case. In general, there is no exact and single best answer, what matters is that you make the choices explicit. What specific concerns would you have?


Gert Nomden
Senior Consultant | Tecnomatix Product Manager
cardsplmsolutions.com

Re: Determination warm up period, run length, number of replications

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

if you need an answer for your professor, then please have a look into the literature...

 

from the practical view you need three "numbers"

 

- statistics reset (eventcontroller - start stat):  let the simulation run and wait for the point in time, when the model starts to create a stable output (model fill); these state will cause failures in the statistics, so we reset the satistics at this time

 

- due to the random influences, your model will take time to create stable outputs e.g. parts per hour (e.g. depend on the failures) - you may plot one of your key figures and wait until it stops "flickering"; the time you need to create stable values is your warm up period; add some days/week/years and you get the length of the simulation run, you you need to set in the eventController

 

- if you run your model with different random number variants, the output can/should be different, to get a mean value, you need to run several experiments with different random variants. The number of experiments depends on the fluctuation of your results. How to calculate the right number of experiments, you can easily find in the literature.

My experience is, if you need more then 10 replications (because your results are quite different after each experiment), then 

a) your model behavior is worng

b) but mostly the simulation time is much to short

Steffen Bangsow
freelance simulation specialist  
web: www.bangsow.eu
mail: steffen@bangsow.net

Re: Determination warm up period, run length, number of replications

Builder
Builder

Dear @Steffen_B, @Nomden,

 

Thanks for your replies! I need this from a practical point of view, so not for a professor.

 

I know how to determine the warm up period in case one product flows through a system (based on the mean throughput time). However, I have some doubts on how to determine a sufficient warm up period in case 76 products flow through the system. Should I just select a product then, with the longest total processing time for instance?

 

Many thanks in advance.

 

Kind regards.

Re: Determination warm up period, run length, number of replications

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

how many drains do you use?

Steffen Bangsow
freelance simulation specialist  
web: www.bangsow.eu
mail: steffen@bangsow.net

Re: Determination warm up period, run length, number of replications

Builder
Builder

Dear @Steffen_B,

 

I use one drain.

Re: Determination warm up period, run length, number of replications

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

then you could plot drain.statThroughputPerHour to see when it starts to become stable

 

Steffen Bangsow
freelance simulation specialist  
web: www.bangsow.eu
mail: steffen@bangsow.net

Re: Determination warm up period, run length, number of replications

Builder
Builder

Dear @Steffen_B,

 

Thanks for your suggestion! As I`m quite inexperienced in Plant Simulation I did not plot anything at all, so can you give me some short stepwise plan to implement this?

 

Many thanks in advance.

Re: Determination warm up period, run length, number of replications

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

- add a chart object into your frame

- drag the drain onto the chart

- select occupancy from the drop-down list

- open the chart (doubleclick)

- change mode to Sample Inverval e.g. 10 minutes

- click on data - input channels --> change the input channel to drain.statThroughputPerhour

-change display to Plotter

 

you may need to change the Axis (20000 number of values, x-axis: 100 days)...

 

jph.png

 

 

Steffen Bangsow
freelance simulation specialist  
web: www.bangsow.eu
mail: steffen@bangsow.net

Highlighted

Re: Determination warm up period, run length, number of replications

Builder
Builder

Dear @Steffen_B,

 

Please find attached my model and my chart settings as suggested by you. Nevertheless, I cannot manage to set proper X-axis settings. I tried "0 ... 100:00:00:00" but after pressing "Apply" it changes to "1:00" again.

 

Do you kno what`s going wrong here?

 

Many thanks in advance.

 

Kind regards.