Lifecycle

[hakani]

I am trying to develop system dynamic model about dairy cow lifecycle. Cow number growing exponentially but when calf grow , heifer should inceace , number of calf shoud be decreace. I'm adding model that I made.
I'm waiting for your suggestion
Thank you

[Administrator]

I'd start by adding units to all the variables in your model.

[hakani]

]Thank you i have added all to units
And i worked for control only 1 year
Result

hata 1.png (13.54 KiB) Viewed 8630 times

but it have to this

hatayok.png (8.18 KiB) Viewed 8630 times

For example number of calf have to decrace later 6 mounts and number of heifer 6-12 have to increace

[tomfid]

I think your first step should be to adopt standard stock-flow notation in your diagram.

Currently you have no flows, so your are integrating earlier age categories directly into later age categories, like

Code: Select all

Bull= INTEG (
    -Bull+"Bullock 12-18",
        0)
Units: number

**************************************************************
"Bullock 12-18"= INTEG (
    "Bullock 6-12",
        0)
Units: number

**************************************************************

This won't work, and produces the unit errors reported.

[tomfid]

For inspiration, you might look to
C:\Users\Public\Vensim\Models\Sample\EXTRA\COMMOD.MDL
which installs with Vensim.

[hakani]

Thank you very much. i update to my model. i have 2 problem for now

1- i"d like first female calf and first male calf come about at 25 mounths but later other female and male calf come about once every 12 mounts.

2-Since the number of cows cannot be a number with a decimal(1,05 ), is there any way to solve this?

[tomfid]

1 - the PULSE TRAIN function might work

2 - you can solve this, but it may not be the best choice - https://metasd.com/2017/01/forrester-on ... ous-flows/

[hakani]

i set up my dynamic system with yearly units.
but first move time will be 26 mounth so i have to fix units ?

when i use time private variate , how can l use formula?

[hakani]

(Cow*Birth Rate)-(Cow*Death Birth Rate)-(Cow*Female Birth Rate)

how is formula for work above formula ?
So if time is 26< dont work
if time =26 formula work and it will work every 12 month ?
i did not solve