How do we define a logistic system?

• It is a geographical territory composed of urban areas and of logistic structures.
• These structures support organised flows of goods which mainly move between the urban areas, forming the logistic corridor.
• The goods enter and leave the system through well-known access nodes.
• Different constraints (spatial, economical, political, or ecological) act over the system.
• There are numerous and heterogeneous actors (importers, exporters, freight forwarders, logistic providers,...). Their behaviours and interactions with each other allow to organise the flows of goods. They are auto-organised.

Problematic

• We want to understand how actors with different goals, are organised around all the logistic infrastructures to manage flows of goods despite all the constraints of the system.
• We are looking for an individual-based model which can reproduce the working of a logistic system thanks to the simulation.
• And then we could test different scenarios on this simulation to understand how the local decisions impact the system.

A Complex System Approach

We can perceive logistic systems as complex and we will use the concepts of the complexity science to model such a system.

• A Multi-agent approach : we model the numerous and heterogeneous actors and infrastructures by agents with their own local behaviours and properties.
• A multi-scale approach : we want to observe how the macro properties of the system emerge from these local properties and behaviours.

A model in two main parts

• Each actors and logistic structures from the reality are modelled as reactive agents (individual-based model) :
  • They have defined rules about how they can interact with each other and how they must behave.
  • Agents bring flexibility since they can be adapted to different logistic system.
  • A dynamic graph represents the interactions between the agents.
• The transportation network :
  • It is made of dynamic sub-graphs in order to integrate multi-modality.
  • Vehicles move over the network and leave a dynamic trace on their way in order to represent the traffic's evolution.

The implementation

• We implemented the model as a step-by-step simulation into the agent-based simulation platform GAMA.
• We use real data on the Seine axis to check its validity and to make measures.
• The Seine axis is mostly represented by the road (around 90% of the traffic is by road).
• The implemented agents:
  • Final consignees: consume stocks and choose logistic providers.
  • Logistic providers: build and manage supply chain to outsource stocks.
  • Warehouses: spread over territory, they provide storage surface.
  • Providers: they play the role of access nodes to the territory.

Configuration and analysis

How to configure the simulation?

• The input data: the transportation network, the position and properties of each agent,...
• We can set locally the consumption of the population.
• We can set the restock strategy of logistics providers.
• Logistics providers can use different strategies to build supply chains.
• ...

What can be analysed?

• Observe the effects of disrupting events (such as road accidents).
• Highlight paths with the highest values of traffic.
• Detection of spatial cluster (logistic areas) thanks to neighbourhood graphs.
• Measure accessibility of agents thanks to Schimbel's index.
• Measures of logistics performances: time to deliver goods and number of stock shortages. These measures can be computed for each agent, for regions, or for the whole system.
• ...

How do restock strategies affect stocks shortages?

How do best strategies emerge from local decisions?

To sum up

• Logistic systems can be seen as complex systems.
• We used an agent based model and dynamic graphs to represent such a system.
• It brings the possibility to represent the dynamics of such a system and the adaptability to different logistic systems.

• The model has been implemented on GAMA and we can experiment it on the Seine axis.
• We can observe the effect of different strategies adopted by agents and how the best ones emerge from local decisions.

Perspectives

• We would like to implement new measures of logistic performance based on cost in order to observe the competition between Le Havre and Antwerp.
• We want to implement new disrupting events in order to observe how the agents restructure their organisation.
• We want to study the interaction network in order to detect special communities of actors.