Need help on stock and flow

amatriciana85 · Post by **amatriciana85** » Tue Nov 23, 2010 3:15 pm

I have to study the project of developing a new product, the main goal for the organization is to make a profit, but the product life cycle is short. Only three years after the start of the product development project, the product is obsolete and no customer will buy the product anymore. This means that the number of weeks that the product is actually sold to customers is equal to 3 years minus the development time. I must therefore be able to balance the right number of employees to be taken in order to maximize profits by reducing the development time to have more time to sell the product, but taking account of development costs.
In the book of Business Dynamic the five steps of the modeling process are given. I have already the first step (problem articulation).

-Scheduled Development Time (SDT) = 60 weeks

-Planned Team Size (PTS) = 10 persons

- Planned Product Performance (PP) = 1.45 (in which 0.5 ≤ PP ≤ 2)
PP = 1 means that the product is similar to products that are already on the market. So the higher the PP, the better the product is compared to products of the competition, and the more potential customers (PC) the company can interest in buying the product. This relationship is reflected in the following equation:
Initial Potential Customers = PC(0) = 10000*PP

-Besides PC, also the sales price (sp) is dependent on the PP. The higher PP, the higher the sales price customers will be willing to pay for the product. This is reflected in the following equation: sp = 41.72 * PP [euro/product]

-The labor costs of Rookie Engineers is 750 [euro/person/week]

-The labor costs of Experienced Engineers is 950 [euro/person/week]

-The time that an experienced engineer requires on average to develop 1 task is 4.18 [weeks/task/person]

- A rookie engineer needs on average 67% more time to do a task.

-Each rookie needs to be supervised by one experienced engineer. This supervision costs the experienced engineer 20% of his time (for each rookie). So, 1 experienced engineer can supervise a maximum of 5 rookies.

-The project uncertainty (pu) is 33%. This means that at the start of the project 33% of the final workload is not yet discovered. The number of tasks that are discovered (Project Tasks in Execution (TE) in the beginning is: TE(0) = (1-pu) * 100 * PP. The number of project tasks that are undiscovered (UT) in the beginning is: UT(0) = pu * 100 * PP. These undiscovered tasks are gradually discovered during the project. The average discovery delay of these undiscovered tasks is 12 weeks.

-When project tasks are executed, they flow to the state Project Tasks Finished (TF). As soon as > 99% of all tasks (= 100 * PP) are finished, the project is considered to be complete and the developed product can be sold to customers that are ready to buy the product.

Someone can help me to make a project on vensim.
Because I've tried, but I would like to compare my work with that of some expert in the field!
Thank you all for your cooperation
NB:If you need I can attach my job ...

Post by **Administrator** » Tue Nov 23, 2010 4:56 pm

It might be an idea to break your questions up into smaller chunks (and post the model here as well so we have something to look at).

Tony.

karankhosla · Post by **karankhosla** » Thu Nov 25, 2010 6:21 am

Hi amatriciana85, Please attach your file, I can take a look.

Karan

amatriciana85 · Post by **amatriciana85** » Thu Nov 25, 2010 1:42 pm

this is the part where i developed a complete stocks and flows structure.
-The product development process.You can assume that product development tasks are in one of the following three states: undiscovered project tasks , project tasks in execution , and project tasks finished . You can also assume that all tasks that are developed are correct, no rework.
-The human resource process. You can assume that when team members are hired, they are rookies and after they will become experienced.

I must now make a part that represents the customer ordering process. You can assume that customers are in one of the following four states: potential customers , customers that are ready to buy , actual customers , lost customers .
If the project is not finished by the time customers are ready to buy the product, these customers immediately move to the state lose customers. Otherwise, they buy the product, become actual customers.

For the part I posted, I have not yet determined the equations

Thanks

LAUJJL · Post by **LAUJJL** » Thu Nov 25, 2010 3:00 pm

I cannot download the model. Try uploadkng the model, and try to download it to see if it works.
Regards.
JJ

amatriciana85 · Post by **amatriciana85** » Thu Nov 25, 2010 3:21 pm

Yes it's working

LAUJJL · Post by **LAUJJL** » Thu Nov 25, 2010 3:50 pm

When I donwload the model, I get a text version that is not directly read into Vensim and appears as an ordinary text file. It I copy that file into a new Vensim blank text model it shows errors if I want to display it as sketch probalby because there are errors in the original model. I should then correct the errors in the text model which is not easy. What should I do, Mister adminastrators?
Regards.
JJ

Post by **Administrator** » Thu Nov 25, 2010 5:05 pm

I can download the model fine, but it is just a diagram, none of the parameters have any equations.

JJ, try renaming the downloaded file as model.mdl, hopefully it will then open up for you.

Tony.

amatriciana85 · Post by **amatriciana85** » Thu Nov 25, 2010 8:45 pm

test by right-clicking and save link as.....What do you think about it?

LAUJJL · Post by **LAUJJL** » Thu Nov 25, 2010 9:59 pm

saved the file as text and named it something.mdl. I could then open it with Vensim as text and could switch to sketch. It is ok now.
JJ

Post by **tomfid** » Fri Nov 26, 2010 7:24 pm

Seems like the MIME types for .mdl have gone wrong, because links open in a browser window rather than prompting for download.

Post by **Administrator** » Fri Nov 26, 2010 8:14 pm

I've added the mime type for mdl. Let me know if it downloads ok now.

Tony.

Post by **tomfid** » Fri Nov 26, 2010 10:35 pm

Still tries to open in a browser window for me, though I haven't tried other browsers so it could be me.

On models.metasd.com I have .mdl set to text/plain;charset=\"UTF-8\" although I recall that it used to take application/octet-stream to force a download.

Tom

Post by **Administrator** » Sat Nov 27, 2010 12:21 am

I've tried again.

Post by **tomfid** » Sat Nov 27, 2010 12:30 am

Still doesn't work for me - in Firefox, launches in a new tab. In ie, creates a new window. Neither triggers a Save dialog. Right-click & Save Link As... works fine though.

[Edited on 11-27-2010 by tomfid]

LAUJJL · Post by **LAUJJL** » Sat Nov 27, 2010 10:11 am

It still does not work for me either.

Go to the thread
http://www.ventanasystems.co.uk/forum/v ... php?t=4281

and download the first model posted by Nadia. it works fine.

The second file correcting the model posted by Nadia and posted by Raphael does not work!

JJ

Post by **Administrator** » Sat Nov 27, 2010 1:15 pm

I've opened a support ticket with our ISP, hopefully it will get fixed soon.

Tony.

Post by **tomfid** » Sat Nov 27, 2010 3:00 pm

The 1st model in Nadia's thread triggers the download dialog, with MIME application/octet-stream, but the filename prompt is wrong (just "stock" instead of "stock oscillation.mdl"). The second file opens into a browser tab as text. Strange.

Post by **Administrator** » Sat Nov 27, 2010 6:24 pm

It seems to be a forum software problem. I'm looking into it.

Tony.

amatriciana85 · Post by **amatriciana85** » Sun Nov 28, 2010 7:27 pm

ok. someone can help me or not!

Post by **tomfid** » Mon Nov 29, 2010 12:16 am

I took a look at NPD_Vensim.mdl - it seems like a good start. I'd recommend writing the equations, checking units and getting things running before adding the customer sector. It's usually easier to proceed in small working chunks, rather than trying to get everything working at once. I'd even consider running the two existing pieces separately: first test your workforce sector, then run your task sector with an exogenous (constant) workforce, then connect the two.

One question: why is Undiscovered Tasks downstream from Tasks Remaining?

There are several project models in the samples that install with Vensim.

Tom

amatriciana85 · Post by **amatriciana85** » Tue Nov 30, 2010 2:00 pm

Because of all the remaining tasks to be performed, are a percentage is processed immediately while the remainder is discovered after a delay of 12 weeks and sent running.
.....Now someone can help me for improve this model about the equation e draw the customer sector....thanks

Post by **tomfid** » Wed Dec 01, 2010 6:51 pm

As I read your diagram, there's an initial stock of work in the project definition. There's some kind of initial process ("workflow phase 1") that translates the definition into tasks remaining (what does this flow represent?). Those tasks are then either assigned to "tasks in execution" or "undiscovered tasks" by "workflow phase 2". "Undiscovered tasks" are subsequently discovered and moved to "tasks in execution". The part that doesn't make sense to me. What is actually happening in "workflow phase 2" and what is the rationale for the split between execution and undiscovered? The proposed structure seems to imply that tasks aren't undiscovered until they pass through the "workflow phase 2" process.

Again, I'd encourage you to get these two pieces running separately before creating the 3rd customer sector.

Post by **tomfid** » Wed Dec 01, 2010 7:10 pm

Also, take a look at Chapter 3 of the modeling guide (in the Vensim help system, or at http://www.vensim.com/documentation/ind ... ?mgu03.htm ), which is a project model. The models are usually in C:\Documents and Settings\All Users\Vensim\models\mguide\3PROJ or C:\Program Files\Vensim\models\mguide\3PROJ

LAUJJL · Post by **LAUJJL** » Thu Dec 02, 2010 10:24 am

Amatriciana

With such a problem and having nearly 9 years of SD modelling experience, I would still start with an extremely simplified definition of the problem and build a very simple model that I would use until I have perfectly understood how it works. I would then choose to add another characteristic to the definition, improve the model and use it etc.. repeating the process. If you are a new comer how do you expect to avoid that process?
Additionnally it will make it much easier for anyone to help you.

Coyle in his book gives the following advice:

''The key to successful modelling is ot keep one's understanding of the model and what it says about the problem ahead of its size "

Regards.

JJ

[Edited on 2-12-2010 by LAUJJL]