EUROPLEXUS: a reference code for fast transient dynamics and fluid-structure interaction

What is Europlexus?

Europlexus is a computational software jointly developed since 1999 by the French CEA (DES/ISAS/DM2S) and the European Commission (Joint Research Center, Ispra, IPSC). It merges two earlier codes CASTEM-PLEXUS from CEA and PLEXIS-3C from the Commission and is maintained by a consortium including EDF, ONERA, and Framatome.

It is a general-purpose tool for fast dynamics simulations in 1D, 2D, or 3D, capable of modeling structures and fluids, with or without fluid-structure interaction. Europlexus handles large deformations and displacements, making it suitable for a wide range of applications such as:

  • Mechanical integrity of nuclear reactor components under dynamic loads
  • Transient analysis of piping systems
  • Impact and shock effects on structures
  • Perforation and explosion scenarios
  • Water hammer
  • Structural resistance to various aggressions
  • Articulated mechanical systems modeling

The main spatial discretization methods used are the Finite Element Method and the Finite Volume Method (FVM). Its explicit time integration suits rapid transients, and it handles geometric and material nonlinearities (e.g., plasticity, damage, hyperelasticity). Parallel computing is enabled via MPI.

Europlexus uses Lagrange multipliers by default for boundary conditions, contact, and fluid-structure interaction. Other methods are also available such as the penalty method. It has become a reference tool for industrial and nuclear safety, with growing interest from sectors beyond nuclear due to its ability to simulate complex physical phenomena. Continuous development ensures adaptability and regular monitoring.

Capabilities

⚙️ Core Capabilities of Europlexus

  • Explicit Dynamics Simulation: Specialized in transient, high-speed phenomena involving structures and fluids.
  • Multiphysics Modeling: Solid mechanics, Fluid mechanics, and others if using a coupling interface with EPX.
  • Advanced Discretization Methods:
    • Finite Element Method (FEM)
    • Finite Volume Method (FVM)
    • Smooth Particle Hydrodynamics (SPH)
    • Discrete Element Method (DEM)
  • Fluid-Structure Interaction (FSI):
    • ALE (Arbitrary Lagrangian-Eulerian) for congruent meshes
    • Immersed boundary techniques for complex geometries
    • Mediating Body Method (MBM)
  • Material Behavior Modeling:
    • Nonlinearities: plasticity, damage, …
    • Material-specific models (concrete, wood, …)
  • High-Performance Computing:
    • Parallel execution via MPI
    • Adaptive mesh refinement (AMR)
    • Temporal partitioning and mapping tools

🏭 Major Application Areas (examples)

  • Piping Systems:
    • Transient thermohydraulic analysis in pressurized circuits
    • Primary coolant loss (LOCA) scenarios
    • Pipe whipping and water hammer effects
    • Coupled 1D/3D modeling of flexible piping and dynamic rupture
  • Explosions:
    • Hydrogen and TNT blast simulations
    • Reactive flows and detonation modeling
    • Structural impact analysis using fine mesh and FSI
  • Concrete Impact Modeling:
    • High-speed impact on reinforced concrete structures
    • Concrete-rebar links
  • Fluid-Structure Interaction:
    • ALE for precise coupling
    • Immersed boundary / MBM methods for complex or rupturing geometries
  • Multiphysics Coupling:
    • EPX as a solver within a partitioned coupling framework
    • Example: modeling prompt criticality accidents in molten salt reactors (fast dynamics / neutronics)

More details here:

Structural dynamics Strongly coupled dynamics Fast transient fluid dynamics

✅ Validation Report

To ensure the reliability and predictive accuracy of the simulations, every Europlexus release comes with a validation campaign.

Validation_EPX_2026.0Download