dimensional consistency

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bahri
Senior Member
Posts: 61
Joined: Wed May 11, 2016 4:43 am
Vensim version: DSS

dimensional consistency

Post by bahri »

Hi,

I have a model with time unit is "monthly".
So, I put monthly water consumption (m^3) as "a stock" and then
later, I need annual water consumption.

If I create a stock of annual water consumption,
there will be an awkward situation as a "monthly water consumption"
will be a flow for a stock of annual water consumption.

Any advice to resolve this issue?
Administrator
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Joined: Wed Mar 05, 2003 3:10 am

Re: dimensional consistency

Post by Administrator »

Create a parameter in your model called "months per year".

months per year = 12
Units : month/year

Divide the value you have that is measured in "months" by "months per year" and it will give you a value measured in years.
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bahri
Senior Member
Posts: 61
Joined: Wed May 11, 2016 4:43 am
Vensim version: DSS

Re: dimensional consistency

Post by bahri »

Considering your advice,
could you please give me an example of Vensim model?
A simple model would be fine

Cheers
Administrator
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Joined: Wed Mar 05, 2003 3:10 am

Re: dimensional consistency

Post by Administrator »

This is very easy,

Months per year = 12
Units : month/year

a rate measured in widget per year = 10
Units : widget/year

the same rate measured in widgets per month = a rate measured in widget per year / months per year
Units : widget/month
Advice to posters seeking help (it really helps us to help you)
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bahri
Senior Member
Posts: 61
Joined: Wed May 11, 2016 4:43 am
Vensim version: DSS

Re: dimensional consistency

Post by bahri »

Hi,
I think there is misunderstood.
So, I reproduce my first question and give more info as follows:


I have a model with time unit is "monthly".
So, I put monthly water consumption (m^3) as "a stock" and then
later, I need annual water consumption.

If I create a stock of annual water consumption,
there will be an awkward situation as a "monthly water consumption"
will be a flow for a stock of annual water consumption.



More info:
monthly water consumption ( a stock) will have a dimension: m^3 or litres.
Now, that I want to measure annual water consumption, so I use
monthly water consumption as a flow.
Classifying monthly water consumption as a flow to measure annual water
consumption will be an awkward situation.

Any advice to resolve this issue?
Administrator
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Joined: Wed Mar 05, 2003 3:10 am

Re: dimensional consistency

Post by Administrator »

Can you upload your model and explain using variable names? I don't understand what you are trying to do.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559
bahri
Senior Member
Posts: 61
Joined: Wed May 11, 2016 4:43 am
Vensim version: DSS

Re: dimensional consistency

Post by bahri »

Please find attached model.

The time unit is monthly and I want to measure
annual water consumption so I create a stock named "annual water consumption".
But, there is an awkward situation as a flow has a dimension "m^3" instead of "m^3/month".
Attachments
benidorm_model_sent.mdl
(7 KiB) Downloaded 188 times
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: dimensional consistency

Post by Administrator »

I think your logic is slightly wrong. Have a look at the attached model.
benidorm_model_sent_modified.mdl
(6.67 KiB) Downloaded 243 times
Advice to posters seeking help (it really helps us to help you)
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Units are important!
http://www.bbc.co.uk/news/magazine-27509559
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