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Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
Starter Input
This manual provides a list of all the model definition keywords and options available in Radioss.
Output Database
Block Format Keyword Time histories output for different element groups, section output, or gauge output are described in this group.
Other Output Databases
Block Format Keyword Describes the specific features for time history post-processing, like accelerometer or section force.

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.
  - 2D and 3D Analysis Options
  - Starter Keywords Syntax
    Block Format Keyword
  - Smooth Particle Hydrodynamics (SPH)
    The Smooth Particle Hydrodynamics method formulation is used to solve the equations of mechanics, when particles are free from a meshing grid.
  - Computational Fluid Dynamics (CFD)
  - General Controls
    Block Format Keyword In this group, keywords are used to set default value, global parameter, analysis type, input/output print, damping and ALE and CFD treatment for the whole model. For default value, it is still possible to overwrite in each specific keywords.
  - Nodes
    Block Format Keyword In Radioss, two node types are available. They use Cartesian coordinate to describe the position of each node.
  - Elements
    Block Format Keyword
  - Component and Parts Organization
    Block Format Keyword In this group, keywords are used to combine material and property information (/PART), assemble model (/SUBSET) or define a separate model (//SUBMODEL).
  - Interfaces
    Block Format Keyword Interfaces solve the contact and impact conditions between two parts of a model. Several interface types are available in Radioss and use different contact treatments.
  - Materials
  - Properties
    Block Format Keyword
  - Monitored Volumes (Airbags)
    Block Format Keyword Monitored volumes can be used to model an airbag, tire, tank, or any closed volume.
  - Constraints
    Block Format Keyword Radioss supports several different kinematic constraints, which are mainly used to impose acceleration, velocity, displacement or temperature in structure or constraint the moving of structure. They are mutually exclusive for each degree-of-freedom (DOF). Two kinematic conditions applied to the same node may be incompatible.
  - Load Cases
    Block Format Keyword In Radioss the following load cases are available. Stress/strain as initial state could be considered by modeling, as well as pressure, gravity, and thermal load.
  - Tools
    Block Format Keyword In this group, tools like transformation, frames, skews, and curve are introduced.
  - Groups(Sets)
    Block Format Keyword Keywords in this group are used to define how to select a group of node, part, elements, lines, or surfaces.
  - Adaptive Meshings
    Block Format Keyword Adaptive Meshing is used in metal forming to divide the element to better describe the geometry. /ADMESH/GLOBAL and /ADMESH/SET are not available for SPMD computation.
  - Output Database
    Block Format Keyword Time histories output for different element groups, section output, or gauge output are described in this group.
    - Time Histories
      Block Format Keyword Describes the time history output request.
    - Time Histories (Part definitions)
      Block Format Keyword Describes the time history output request for set of elements.
    - Other Output Databases
      Block Format Keyword Describes the specific features for time history post-processing, like accelerometer or section force.
      - /ACCEL
        Block Format Keyword Defines accelerometers using a node and skew system.
      - /CLUSTER
        Block Format Keyword Describes an assembly of brick or spring elements for post-processing and failure control.
      - /GAUGE
        Block Format Keyword Defines gauges.
      - /GAUGE/POINT
        Block Format Keyword Defines gauges. Gauge can be used to save the pressure, density and specific energy histories at a fixed position.
      - /GAUGE/SPH
        Block Format Keyword Defines SPH gauges.
      - /INTER/SUB
        Block Format Keyword Defines a sub-interface. A sub-interface is a portion of (may include all of) an existing interface and is defined in order to output the forces applied by nodes of a specified node group on the segments of a specified surface (refer to Time Histories output for interfaces).
      - /SECT
        Block Format Keyword Sections are used to output the force and moment of a cross section defined by a group of nodes and groups of elements.
      - /SECT/CIRCLE
        Block Format Keyword A circle section is used to output the force and moment of a cross section defined by a circular disc.
      - /SECT/PARAL
        Block Format Keyword A parallelogram section is used to output the force and moment of a cross section defined by a parallelogram.
- Engine Input
  This manual provides a list of all the solution definition keywords and options available in Radioss.
- 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.

Other Output Databases

Block Format Keyword Describes the specific features for time history post-processing, like accelerometer or section force.

Below is an alphabetical list of Other Output Databases keywords.