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VOCO, a real time multibody software for guided systems dynamics

Contact :

  • Michel Sébès

Other contributors :

  • Hugues CHOLLET
  • Jean-Louis MAUPU
  • Jean-Bernard AYASSE (retired)



This multibody software is based on a 30-year experience in wheel rail contact models and stability simulation. INRETS researchers have proposed a first multibody simulator arround 1997 for stability simulations of non linear freight bogies (Y25 familly) using dry friction dampers and other non-linearities.

Under the name VOCO, the application has been extended to curve studies and to other railway vehicles including tramways (street cars), metros, locomotives, passenger cars, high speed trains.

VOCO stands for : VOitures en COurbes : Vehicles in curves.

Today, VOCO includes functionalities like:

  • real time non Hertzian contact;
  • periodic cyclic track structures;
  • dynamic track structures with non linear elements;
  • switch panels with variable rail profile;
  • flexible bodies.

Special vehicles like tamping machines, long trains, flexible structures, can be developped in this environnement.



The VOCO codes are using a specific geometric environment to describe small displacements relatively to the track layout. Simulations of loopings, very high cant, very low speed - a more difficult challenge than high speed in fact - can be managed by the code.

Vehicle models

The major part of the connections between bodies are non linear. The dry fricition elements, a basis of the code, are particularly stable and fast. Specific suspensions like air cushion and pendular elements can be managed. Additional forces like air drag, vibrators, compression, can be added.

Recent developpments

The bodies are not necessary rigid. Starting from a CAD drawing, Craig Bampton based formulation allows fast simulations of structures. Complex suspension elements can be managed through a matlab interface.

Vehicle-track interaction

The wheel rail contact element is one of the most developped among multibody tools. It allows to manage non-Hertzian contact including various measured profiles along the track : in curves, switch and crossings. Large derailments can be managed, as well as a different wheel profiles for each wheel. A simplified formulation can be used to accelerate the simulation.

*Special elements are used to simulate various tramways (TVR, Translohr) rolling on tyres and guided by steel rollers, buses and metro on tyres (RATP types).

*A road-tyre interaction element is available to simulate some road vehicles.

Track models

From a simple elastic following foundation, to a complete *finite element formulation (FEM, with ANSYS, under validation), passing by a DEM formulation (Discrete elements model, non linear) 4 different flexible track solutions can be managed.The DEM formulation allows to realisticaly simulate track shift in extreme conditions.

Real time simulations

Simulations on the simplest track model can be real time for a few connected vehicles. Of course, using flexible bodies, long trains, and DEM or FEM track models slow down the application.


VOCO is an executable usable under Windows and Linux, inputs and outputs are managed through a Matlab environment where the user can develop himself his own tools.

This interface includes a vehicle modeler, as well as a set of generic vehicles, generic wheel and rail profiles, a wheel-rail contact toolbox, a track modeler, different tools in order to define new rails or analytical track defects.

A set of predefined UIC tests is proposed : derailment and stability studies are the main application of this environment.

Tools to analyse contact stresses, UIC criteria on forces like NADAL, PRUDHOMME, video animation of the vehicle and contact etc... are proposed.


A standard railway end user licence on a single PC is proposed for 2500 € HT (does not include the Matlab licence). 

The standard licence does not include non-railways and advanced application (marked by * above), nor a permanent hotline.