Beer game reflection

First, if you haven't played the beer game, I suggest you don't read my blog yet. Finish it first, and it is fun to play both the researchers and students.

Here is my log (actions + reflections)
Objective -
1. maintain a stable inventory at 20 cases
2. Keep total expenditures for 20 week period under 300.

How it works:
sell when I have stock
lead time = 2 weeks
4 x carrying cost = out of stock cost

Seems like I have only ONE input variable - how many cases to order.

my notes: I rather write down the objectives to help me keep focus; also I translate the game rules into my langauge. I had inventory management experience, so I am kind of an expert. But, i still try to not using my knowledge at the beginning (try not to invoke any prior inventory model that I know of; but I know my general mental model should be invoked anyway - let's see)

My first question: what is the demand function? (too bad, my previous knowledge kicks in, but it is also a normal question to ask. We got to know the demand before we stock). Then, I found that the informatino is located at the left (given by the problem).

What i have now =
20 cases
Cases order per week 4

I start with 8 cases, because the lead time is 2 weeks, and the demand is 4 per week. Then, I run (try not to think too much at this time because I don't want to invoke any inventory model that I know of at this time).

Week number and number of cases ordered are listed below:
1 - 8
2 - 2 => I found out the price for each case $3.2??
3 - 4
4 - 4
5 - 8 => customer demand 8 => I reacted with more order.
6 - 8
7 - 8 => I still order 8, since I think I am still OK with 15 on my shelves (and my order from warehouse is getting in).
8 - 8
9 - 12 => because the objective is keeping the inventory at 20. So, I order 12 to push up my inventory now (actually, I don't think we need 20 safty stock).
10 - 9 => still adding a little bit more to keep the inventory at 20 (and, seems like I cank keep the target expenditure in range)
11 - 8
12 - 4 - we are over the target.
13 - 8 - The demand is keeping at 8. So, I order 8 (assuming we already balance our inventory)
14 - 8
15 - 8
16 - 8
17 - 8
18 - 8
19 - 8
20 - 8

I keep my inventory at 20, and cost at 245.88.

Can I do it better. Yes, with a spreadsheet. where I have initial inventory, demand, and supply, where initial inventory(t) = initial inventory (t-1) - demand (t-1) + supply (t-2). => this is my model

I still order 8 in the first week. Instead of order something on the second week, I order nothing. But, for some reason, my supply is below target when the demand jump from 4 to 8.
I keep my inventory at 20, and cost at 223.88

Then, I look at the model which is very similar to the mathematical model that I created.

I did almost the same thing, but keep the inventory closer to 20 most of the time.

Actually, the math model is abstract and it is not easy for students to create such a model (maybe my math model is off a little bit, too). I think the stock and flow diagram should be a lot more intuitive for the students to learn the concept.

Again, I took inventory management classes over my academic career. I think this is a better way for the students to experience the different issues of inventory management. Actually, the two key issues are (which I know before I play the game) are demand uncertainty and lead time uncertainty. I haven't played the advance game, but I guess the game will introduce the lead time uncertainty (or minimize the cost) to the equation. No matter what, I believe it is a better way to provide the students the key concepts. Then, mathematical models can be introduced to "solve the problem" because we do have mathematical models to solve the problems accurately. The instructional question is when and how to introduce the math models. In other words, how to use the simulation AND the math models to achieve academic goal? In this case, learning the inventory management concepts.

Victor