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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.
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.
Reference State
Block Format Keyword
/REFSTA
Block Format Keyword Describes the reference state for elements belonging to a part, using given nodal coordinates.

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.
    - Initial Conditions
      Block Format Keyword
    - Load
      Block Format Keyword
    - Thermal
      Block Format Keyword
    - Reference State
      Block Format Keyword
      - /EREF
        Block Format Keyword Describes the reference state for elements belonging to a part using given element and node identifier.
      - /REFSTA
        Block Format Keyword Describes the reference state for elements belonging to a part, using given nodal coordinates.
      - /XREF
        Block Format Keyword Describes the reference state for elements belonging to a part, using given nodal coordinates.
    - Defense
      Block Format Keyword
    - ALE Elementary Boundary Conditions
      Block Format Keyword
    - ALE and CFD Constraints
      Block Format Keyword
    - SPH Constraints
      Block Format Keyword
  - 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.
- 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.

View All Altair HyperWorks Help

/REFSTA

Block Format Keyword Describes the reference state for elements belonging to a part, using given nodal coordinates.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/REFSTA
`rs_name`
`Nitrs`	`RSO`_FMT

Definition


Field	Contents	SI Unit Example
`rs_name`	File name for reference state. (Character, maximum 100 characters)
`Nitrs`	Number of steps from reference to initial state. Default = 100 (Integer)
`RSO`_FMT	RS0 file format. = 0 (Default) The RS0 file read is a version 5 or later Radioss file (Integer on 10 digits, Real on 20 digits). = 1 The RS0 file read is a version 4 Radioss file (Integer on 8 digits, Real on 16 digits). (Integer)

Comments

The default (blank line) reference state file name is RunnameRS0.
A reference state file contains the reference coordinates of the nodes (input format is the same as for node coordinates in /NODE option; lines starting with # are comment lines).
A reference state file does not necessarily contain the coordinates of all nodes in the model. If no coordinates are given for a node, initial coordinates are used instead.
Enhanced reciprocity will be obtained if Nitrs is increased.
Reference state is available:
- for shells using /MAT/LAW1 (ELAST), /MAT/LAW19 (FABRI) or /MAT/LAW58 (FABR_A)
- 4-node tetrahedron elements using I_frame =2 (co-rotational formulation)
- 8-node bricks using I_solid =1, 2 or 24 and I_frame =2
- material laws /MAT/LAW35 (FOAM_VISC), /MAT/LAW38 (VISC_TAB), /MAT/LAW42 (OGDEN), /MAT/LAW70 (FOAM_TAB) or /MAT/LAW90