AssumptionsThe Devils in the Details

Where do you stand?Where do you stand in the spectrum between maximum

assumptions and maximum details?We are going to examine the simulation efforts of Team Alpha

and Team BetaPay attention to your initial feelings and reaction to the team

and their: Approach Work Results

Alpha vs Beta - Problem Warehouse needs to increase throughput to meet future demand Current State:

Items are placed in the racks to distribute the demand evenly Picking routes take an average of 10 min Pick containers are then sent to a packing station to be broken out into individual orders

Future State: Storage will be broken into two sections

• The high demand section will contain the SKUs that make up 80% of their throughput• The low demand section will contain the SKUs that make up the remaining 20%

High demand packing will work the same as current• Orders with low demand will go to another packing station that will pull the required product from a

low demand picking container

Alpha vs Beta – Setup (same) The model begins with pick orders generated by a source

Inter-arrival and SKU distributions obtained through analysis of past/current data SKU demand is evenly distributed throughout the associated storage area.

i.e. HD SKU demand is evenly distributed throughout the HD storage area Packing stations

HD stations are represented by a small group of objects that accurately represent the current state.

Orders with HD SKUs exit the model as complete Orders with LD SKUs are then sent to an LD packing station

• The LD packing station picked is the station where the associated LD container was sent• After all the LD SKUs have been placed the order exits the model as complete

Alpha vs Beta – Setup (different)

Alpha Team - Detailed Storage areas

Racks were used to represent the storage system

Network Nodes were used for the operator travel path

Operators Load and Unload time distributions were

obtained from past/current data

Beta Team - Assumptions Order picking simulated with

processers Pick Times

Distribution shapes were based on analysis of past/current state pick times

Average Pick Times (distribution locations) will be tested to determine system sensitivity and maximum possible values

Alpha vs Beta - Results

Alpha Team - Detailed Simulation project took 3 weeks

The actual model build took 2 weeks• 1 week for the storage areas

Results The proposed storage upgrades will be

able to meet the projected demand for the next 5 years

The average pick times• HD area 5 min 34 sec• LD area 7 min 46 sec

Beta Team - Assumptions Simulation project took 2 weeks

The actual model build took 1 week• <1 day for the storage areas

Results The proposed storage upgrades should be able to

meet the projected demand based on our assumed pick times

The maximum pick times that can meet the projected demand• HD area 6 min 20 sec• LD area 8 min 39 sec

Estimated achievable pick times• HD area 6 min• LD area 7 min

Question 1 – Next Step

Alpha Team As part of this team what would you

recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

As a reviewer of this project what would you recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

Beta Team As part of this team what would you

recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

As a reviewer of this project what would you recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

Question 2 - PreferenceYou are a manager in charge of both teamsDid one team impress you as having a superior:

Method / approach to the problem Quality of work Work Ethic

Which team produced the most valuable/usable results?Which team do you turn to first for your next project?

The ProblemDetails are seen as indicators of:

Time and Effort Accuracy Validity

Assumptions are seen as indicators of: Corner Cutting Inaccuracy Increased Risk

Is this simply painting over rust?

ExampleAssuming you have a family with small childrenIs it safer to have them around an open fire or a kitchen?

Potential Risks

Fire Pit Burns

Open access to fire Property

Things thrown into the fire

Kitchen Burns

Stove Top / Oven Cuts

Knives Disposal

Falls Counter Tops

Poisoning Cooking Ingredients Cleaners

Electrocution Electrical outlets Appliances + water

Water Damage Sink Water dispenser on Fridge

Risk Mitigation

Fire Pit Fire

Limit access Put it out

Kitchen Stove / Oven

May be able to child proof buttons and knobs Knives

Put in locked drawers Appliances

Leave unplugged Outlets

Child proof inserts or covers Cleaners and Ingredients

Put child proof locks on all cabinets and drawers Fridge

Lockout water dispenser

Take awayThe actual risk of a situation can be greatly different from the

initial risk that we perceive.Being unaware of or ignoring a potential threat increases the

overall risk of the situation.The obviousness of a risk is not correlated with the cost to

mitigate the risk.

Simulation?We can apply the prior example to simulation if we consider

the following: Every assumption that is made carries with it some level of

uncertainty That uncertainty is a risk to a model’s results and conclusions

The likely hood of a successful project is dependent on two things: Identifying assumptions Reducing the risk associated with each one

AssumptionsThere are more than you will initially perceiveLogical assumptions can be hard to spot when they are buried in code.Every variable entered is based on an underlying assumptionAdding detail to eliminate a large assumption increases the number of

variables This simply exchanges one large obvious assumption for many smaller non-

obvious ones Increasing the number of assumptions can potentially increase the risk

for failure (inaccuracy)

Alpha vs Beta – Assumptions

Alpha Team Rack Layout Network Paths

Routing Passing Congestion

Operators (Spd, Acc, Dec) Pick and Place Times Pick Routes

Beta Team Total pick time could be represented

by a single distribution

Take II

Question 1 – Next Step As part of each team what would you

recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

As a reviewer of each project what would you recommend as the next step? Scrap the project Further Investigation

• Where? Implementation

Question 2 - Preference You are a manager in charge of both

teams Did one team impress you as having a

superior: Method / approach to the problem Quality of work Work Ethic

Which team produced the most valuable/usable results?

Which team do you turn to first for your next project?

Steps for more Accuracy Stick to the question at hand

Build the model to answer the question that was asked not the questions that may or may not be asked later

Identify Look through the model and identify assumptions (variables and logic)

• Specifically assumptions that have a low certainty level

Test Test the models sensitivity to assumptions

• If not all of the assumptions then at least the assumptions with low levels of certainty

Increase Accuracy Assumptions that the model is sensitive to need to have higher levels of certainty

(accuracy)

SummaryAssumptions are everywhere

Increase in number as detail increasesThe level of detail in a model should be limited to:

The level necessary to answer the question at hand The level to which you can acquire data

Identifying and testing assumptions is key to model accuracy

So what!?Why such a big deal over a small topic?I want to change how simulation is approachedProcess Library

To model “processes” The “process” of building a model

Scalable -> Sequential -> Successful