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Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
Engine Input
This manual provides a list of all the solution definition keywords and options available in Radioss.
General Controls
Engine Keyword In this group keywords are used to generally define the output style, control of computation, damping and ALE setup during the computation.
ALE
ALE/GRID
/ALE/GRID/FLOW-TRACKING
Engine Keyword With this keyword it is possible to switch to flow tracking grid control or to change the parameters. ALE mesh motion and deformation based on mass-weighted average velocity of the material flow inside the ALE mesh.

Welcome
What's New
View new features for Radioss 2026.
Radioss Overview
Radioss is a leading explicit finite element solver for crash and impact simulation.
Tutorials
Discover Radioss functionality with interactive tutorials.
Radioss User Guide
This manual provides details on the features, functionality, and simulation methods available in Altair Radioss.
Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
- File Extensions and Formats
  Current Radioss format uses the 12x extension format.
- Single File Input
  This format allows running either Starter or Engine with the same file.
- New Keywords in 2026
  New and modified features in Radioss.
- Starter Input
  This manual provides a list of all the model definition keywords and options available in Radioss.
- Engine Input
  This manual provides a list of all the solution definition keywords and options available in Radioss.
  - Engine Keywords Syntax
  - General Controls
    Engine Keyword In this group keywords are used to generally define the output style, control of computation, damping and ALE setup during the computation.
    - Formats
    - Computation
    - Input/Output
    - Damping
    - ALE
      - ALE/GRID
        /ALE/GRID/DISP
        Engine Keyword With this keyword it is possible to modify grid formulation parameters, which initially was set in Starter keyword /ALE/GRID/DISP. (Altair average displacement grid formulation).
        /ALE/GRID/DONEA
        Engine Keyword With this keyword it is possible to modify grid formulation parameters, which initially were set in Starter keyword /ALE/GRID/DONEA.
        /ALE/GRID/FLOW-TRACKING
        Engine Keyword With this keyword it is possible to switch to flow tracking grid control or to change the parameters. ALE mesh motion and deformation based on mass-weighted average velocity of the material flow inside the ALE mesh.
        /ALE/GRID/LAGRANGE
        Engine Keyword With this keyword it is possible to switch to Lagrangian framework (grid velocity set to material velocity). The material velocity is used to update the grid.
        /ALE/GRID/LAPLACIAN
        Engine Keyword With this keyword it is possible to switch to Laplacian grid control or to change the parameters. ALE grid smoothing using the Laplacian smoothing method for 2D and 3D elements.
        /ALE/GRID/SPRING
        Engine Keyword With this keyword it is possible to modify grid formulation parameters which initially be set in Starter keyword /ALE/GRID/SPRING. (Altair bar method for grid velocity computation).
        /ALE/GRID/STANDARD
        Engine Keyword With this keyword it is possible to modify grid formulation parameters, which initially were set in Starter keyword /ALE/GRID/STANDARD. (Altair standard method for grid velocity computation).
        /ALE/GRID/VOLUME
        Engine Keyword With this keyword it is possible to switch to smoothing formulation grid control is based on volume. Each ALE node position is computed as the average position of the centroids of the elements to which it is connected.
        /ALE/GRID/ZERO
        Engine Keyword No grid calculation is performed when this keyword is used. Grid does not move, unless constrained otherwise.
      - /ALE/LINK/OFF
        Engine Keyword An ALE link definition /ALE/LINK/VEL (Starter) can be deactivated.
      - /ALE/LINK/ON
        Engine Keyword An ALE link definition /ALE/LINK/VEL (Starter) which was deactivated during a previous Engine run can be activated again with this keyword.
      - /ALE/LINK/VEL
        Engine Keyword With ALE links on grid velocities, given nodes are linked to the given main grid velocities. You can specify the direction or a combination of directions. This definition is only taken into account during the current run.
      - /ALE/MUSCL/OFF
        Engine Keyword The MUSCL scheme is enabled by default. This option disables it and leads to first order precision.
      - /ALE/OFF
        Engine Keyword Deactivates the ALE / EULER parts that are listed.
      - /ALE/ON
        Engine Keyword Activates the ALE / EULER parts that are listed.
      - /ALE/SOLVER/FINT
        Engine Keyword This option defines the numerical method for internal force integration. This is relevant only for brick element and the ALE legacy solver (momentum equation solved with FEM).
      - /ALE/SUPG/OFF
        Engine Keyword Disable the SUPG formulation for momentum advection (ALE and EULER).
  - Deletion/Input Modifications
    Engine Keyword In this group, keywords are used for modification (deletion or add options) in Engine.
  - Animation and Post-processing Output Files
    Generates animation files containing results according to the keywords specified. The keywords are specified in the topics within Animation and Post-processing Output Files.
  - Implicit Solution
    Engine Keyword In this group keywords are used for implicit solution. Different implicit solver methods (linear, nonlinear, buckling or quasi-static), different options to control the implicit computation, different implicit time step method and implicit output messages are introduced.
  - Kinematics and Loading
    Engine Keyword In this group, keywords are used to define the kinematic condition (constrain/release rotation or translation DOF) and initial condition (rotational/translational velocity).
  - Time Step
    Engine Keyword In this group, keywords are used to define different time step control (STOP, KILL, CST or DEL, and so on) for different entities (shell, brick, beam, airbag, interface, and so on) during the computation.
  - Initial State
    Engine Keyword In this group, keywords are used to output different info (like stress, strain, orthotropy direction, temperature, and so on) in a state file (STA-File).
- LS-DYNA Input
  This manual provides a list of LS-DYNA input files available in Radioss.
- Multi-Domain
  This manual contains the description of the keywords for the Radioss Multi-Domain.
- Obsolete Keywords
  Keywords that are still supported, but no longer maintained (*) are considered obsolete.
- Other Files
- Definition
Radioss Example Guide
This manual presents examples solved using Radioss with regard to common problem types.
Radioss Verification Problems
This manual presents solved verification models.
Radioss Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding Radioss.
Radioss Theory Manual
This manual provides detailed information about the theory used in the Altair Radioss Solver.
Radioss User Subroutines
This manual describes the interface between Altair Radioss and user subroutines.

/ALE/GRID/FLOW-TRACKING

Engine Keyword With this keyword it is possible to switch to flow tracking grid control or to change the parameters. ALE mesh motion and deformation based on mass-weighted average velocity of the material flow inside the ALE mesh.

Format

I_def scale_def

I_rot scale_rot

Comments

For more details, refer to ALE Grid Calculation in the User Guide and /ALE/GRID/FLOW-TRACKING in the Reference Guide.
This option is not available when /ALE/GRID/ZERO is initially set in the model.