Carrefour Develops WITNESS Analysis and Operations Tool

The Carrefour Group is the second biggest large-scale distribution organization in the world, with more than 2 billion customers a year and 9,000 shops in 31 countries across 3 continents. Its turnover for the year 2000 was 64.8 billion Euros.

Background

Carrefour built a new textiles distribution center in the Paris area. This center handles very important daily streams, with peaks that can reach up to 1.7 times the normal stream.

Activity at this particular Carrefour center has, by definition, clearly defined seasonal phases, but must also meet variations in demand that are hard to anticipate. The distribution center must be able to respond to these demands with the highest level of service possible.

In order to be able to study the way in which the center could react to any set of circumstances, Carrefour wanted to use a very detailed computer model of its center. This tool allowed:

• Anticipation of the means to be used (adapting numbers to workload),
• Anticipation of problems in high-risk areas
• Understanding of the limitations of the system
• Exploration of the available options when critical levels are reached
• Identification and testing of the sensitivity of parameters that are stipulated by Carrefour, such as : schedules of lorry arrivals and departures, flow allocation
• Validation of stock capacity, especially for the main automated warehouse
• Experience of what happens when a line changes before going live
• Overall vision of the center
• In short, to test the ability of the center to handle the necessary streams and to provide a solution before problems are discovered in the real-life system.

The distribution centre is based on a very modern concept. It is highly mechanised and automated, which entails rigorous control of the streams of physical items as well as data, as the two areas are interdependent.

Interface with the model
The model is controlled by an Excel interface.This application consists of a main screen that allows the user to control scenarios and as many scenario screens that you want to create.

Each scenario consists of about ten screens that contain the information required for performing a simulation. WITNESS writes the results dynamically to a corresponding number of Excel screens.

WITNESS reads the data from the selected scenario file. This allows you to change the data by using a simple Micosoft Excel screen. The use of Excel allows users who are not familiar with WITNESS to get to grips with the tool quickly. It is a user-friendly interface that lends itself well to experimentation. Also, the choice of Microsoft Excel makes applications of this type easier to maintain.

Although a new scenario contains several hundred items of data, it only takes a few seconds to create the scenario; most of the data stays the same.

Results
During the simulation or experiment, WITNESS records the results on the various screens belonging to the current scenario file.

These screens are presented as tables and show the following information:

• Monitoring of work units in approximately sixty places
• Monitoring equipment and personnel
• Detailed monitoring of loading for inward goods bays
• Detailed monitoring of loading sorting chutes
• Detailed monitoring of loading of the warehouse stocking equipment
• Monitoring of the shipping preparation batch
• A summary sheet, using several key statistics to show operational activity

Initial results
The first scenarios have enabled an understanding of the limits for accommodating incoming lorries, as well as the sensitivity of the sorting mechanism at reception to the combination of parameters such as control constraints.

When overloaded, the architecture of the sorting mechanism can result in a blockage. The dynamic visualization of this in the model generates ideas for solutions to implement as well as mistakes to avoid.

Optimization
The objective is to study several configurations and to analyse the sensitivity of the system to certain criteria. Therefore we ran the model in WITNESS Optimizer to execute several scenarios automatically.

Some key figures
The simulation model includes around 20,300 WITNESS elements, of which there are:

• 17,000 variables
• 260 kilometers of conveyors, for carrying parts
• Over a hundred people (varying according to the scenario)
• Over 50 "vehicles" (varying according to the scenario)
• 350 "tracks" or alleys, representing several kilometers of cart circuits.

Deliverables
The application can be installed on all versions of Windows and consists of:

• The model, developed using the latest version of WITNESS
• The Microsoft Excel interface for running the scenario
• A default scenario
• A user manual, printed in color.