## help in modelling transport

Use this forum to discuss any issues relating to Systems Dynamics and Systems Thinking.
KarthikThilak
Member
Posts: 21
Joined: Mon May 29, 2017 9:25 am
Vensim version: PLE

### help in modelling transport

Hello,

My aim is to reduce the freight cost of shipping parcels(cartons) having a certain volume either by using means of pallet or parcel shipping.This is decided on SAP by the parameter Volume(volume per order).I am aiming to alter this volume parameter in my model.

Every order has a certain number of parcels(cartons) to be shipped with a certain volume.Also,the pallet capacity is not an important factor and generally 1 pallet is used for shipping these parcels(cartons).

Here are the challenges I am facing during modelling:

1.If then else("Volume per order<=0.9,Parcel shipping method,Pallet shipping method)
I want input the same relation to the model.

2.The freight cost for parcels are calculated by multiplying the number of parcels(cartons) with a constant price for a parcel(carton).But,I have a lookup table of volume per order shipped and freight cost incurred for the pallet shipping method(using historical data).I need to input this lookup table into the model to calculate the cost incurred by shipping pallets.

Then,my final idea is to find the min of the two freight costs associated with Parcel/pallet shipping ways.

KarthikThilak
Member
Posts: 21
Joined: Mon May 29, 2017 9:25 am
Vensim version: PLE

### Re: help in modelling transport

If you could please provide a little insight into above problem.

Thanks,

Posts: 3041
Joined: Wed Mar 05, 2003 3:10 am

### Re: help in modelling transport

KarthikThilak wrote:1.If then else("Volume per order<=0.9,Parcel shipping method,Pallet shipping method)
You need two parameters, one to calculate the number of parcels, and one to calculate the number of pallets.
number of parcels = If then else(Volume per order<=0.9 , 1 , 0)
number of pallets = If then else(Volume per order>0.9 , 0 , 1)

This is exactly what I did for you in a demo model,
viewtopic.php?f=15&t=6715#p24259
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559

KarthikThilak
Member
Posts: 21
Joined: Mon May 29, 2017 9:25 am
Vensim version: PLE

### Re: help in modelling transport

Hello,

Thank you very much for your input.

I have managed to complete the model.

But I find no difference in the minimum(cost) when I change the volume per order(in the pallet or parcel equation) from 0.5 to 0.6 or to 0.7 or even 0.9 as well.The minimum(cost)graph remains the same for all.

Is the model fundamentallly correct.

1.Why am I not getting different cost minimum curves for different volumes?
2. Can I make the volume per order and number of cartons per order random for each iteration?
Attachments
SHIPPING1- draft.mdl
Last edited by KarthikThilak on Tue Jul 25, 2017 9:04 am, edited 1 time in total.

Posts: 3041
Joined: Wed Mar 05, 2003 3:10 am

### Re: help in modelling transport

They are the same calculation, in
This
pallet shipping method = IF THEN ELSE(volume per order>0.6, lookup of freight cost ,cartons per order*2.84)

Is exactly the same as this
parcel shipping method = IF THEN ELSE(volume per order<=0.6,cartons per order,lookup of freight cost)
freight cost parcel = COST PER PARCEL*parcel shipping method

I'd suggest putting units in your model and checking continually, this error shows up very quickly as you've embedded "2.84" in the pallet shipping method equation.
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559

KarthikThilak
Member
Posts: 21
Joined: Mon May 29, 2017 9:25 am
Vensim version: PLE

### Re: help in modelling transport

So should i frame the equations differently.

I tried reframing the equation for
pallet shipping method = IF THEN ELSE(volume per order>0.6, lookup of freight cost ,cartons per order*2.84)

and removed the parcel shipping method from the model.

Now there is only one equation.But still the problem exists.

will assigning units to the variables really solve the issue?

Posts: 3041
Joined: Wed Mar 05, 2003 3:10 am

### Re: help in modelling transport

KarthikThilak wrote:will assigning units to the variables really solve the issue?
No, but it will highlight any obvious errors.
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559

KarthikThilak
Member
Posts: 21
Joined: Mon May 29, 2017 9:25 am
Vensim version: PLE

### Re: help in modelling transport

Hello,

I would like to validate my output graphs obtained.

Is there any way to export these graphs and analyse the result in MSexcel or any other tool?