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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.
Materials
Equation of State
Used by Radioss to compute the hydrodynamic pressure.
/EOS/EXPONENTIAL
Block Format Keyword This equation of state provides an exponential time-dependent pressure model. The pressure is defined as $P (t) = P_{0} e^{α t}$ .

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View new features for Radioss 2025.
Overview
Radioss^® is a leading explicit finite element solver for crash and impact simulation.
Tutorials
Discover Radioss functionality with interactive tutorials.
User Guide
This manual provides details on the features, functionality, and simulation methods available in Altair 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 2025
  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
    - Material Compatibility
      Block Format Keyword The following tables list the compatibility options for each of the material laws.
    - Elasto-plastic Materials
      These materials can be used to represent elasto-plastic materials.
    - Hyper and Visco-elastic Materials
      These materials can be used to represent hyper and visco-elastic materials.
    - Composite and Fabric Materials
      These materials can be used to represent composite and fabric materials.
    - Multiscale Materials
    - Concrete and Rock Materials
      In Radioss these materials can be used to represent rock or concrete materials.
    - Honeycomb Materials
      These materials can be used to represent honeycomb materials.
    - Connection Materials
      These materials can be used to represent connection materials.
    - Other Materials
      These materials can be used to represent other materials.
    - Multi-Material, Fluid and Explosive Materials
      These materials can be used to represent multi-material, fluid and explosive materials.
    - ALE and CFD Options
      Block Format Keyword ALE and CFD options used to activate ALE formulation or Eulerian formulation for a given material law.
    - Viscosity Option
    - Leakage Option
    - Thermal Option
    - Equation of State
      Used by Radioss to compute the hydrodynamic pressure.
      - /EOS/COMPACTION
        Block Format Keyword Describes pressure for a porous media such as soil or foam which can be compacted and unloaded.
      - /EOS/EXPONENTIAL
        Block Format Keyword This equation of state provides an exponential time-dependent pressure model. The pressure is defined as $P (t) = P_{0} e^{α t}$ .
      - /EOS/GRUNEISEN
        Block Format Keyword Describes the Gruneisen equation of state.
      - /EOS/IDEAL-GAS or /EOS/IDEAL-GAS-VE
        Block Format Keyword Describes the ideal gas equation of state $P = (γ - 1) (1 + μ) E$ .
      - /EOS/IDEAL-GAS-VT
        Block Format Keyword Describes the equation of state for ideal gas (volume - temperature).
      - /EOS/LINEAR
        Block Format Keyword Describes the linear equation of state $P (μ) = P_{0} + B μ$ with initial pressure and bulk modulus.
      - /EOS/LSZK
        Block Format Keyword Describes the Landau-Stanyukovich-Zeldovich-Kompaneets EOS for detonation products.
      - /EOS/MURNAGHAN
        Block Format Keyword Describes the Murnaghan equation of state.
      - /EOS/NASG
        Block Format Keyword Describes the NASG (Noble-Abel-Stiffened-Gas) equation of state.
      - /EOS/NOBLE-ABEL
        Block Format Keyword Describes the co-volume equation of state $P (v - b) = R T$ .
      - /EOS/OSBORNE
        Block Format Keyword Describes the Osborne Equation of State from R.K. Osborne, also called the “quadratic EOS”.
      - /EOS/POLYNOMIAL
        Block Format Keyword Describes the linear polynomial equation of state $P (ρ, E)$ .
      - /EOS/PUFF
        Block Format Keyword Describes the linear polynomial equation of state $P (ρ, E)$ .
      - /EOS/SESAME
        Block Format Keyword Describes the SESAME table equation of state.
      - /EOS/STIFF-GAS
        Block Format Keyword Describes the ideal gas equation of state for stiffed gas $P (μ, E) = (γ - 1) (1 + μ) E - γ P^{*}$ .
      - /EOS/TABULATED
        Block Format Keyword Describes the tabulated equation of state $P = A (µ) + B (µ) E$ .
      - /EOS/TILLOTSON
        Block Format Keyword Describes the Tillotson equation of state.
    - Failure Models
      The supported failure models in Radioss.
  - 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.
- 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
Example Guide
This manual presents examples solved using Radioss with regard to common problem types.
Verification Problems
This manual presents solved verification models.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding Radioss.
Theory Manual
This manual provides detailed information about the theory used in the Altair Radioss Solver.
User Subroutines
This manual describes the interface between Altair Radioss and user subroutines.

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/EOS/EXPONENTIAL

Block Format Keyword This equation of state provides an exponential time-dependent pressure model. The pressure is defined as $P (t) = P_{0} e^{α t}$ .

This equation of state does not have any real physical meaning. It is a model for verification and validation purposes.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/EOS/EXPONENTIAL`mat_ID`/`unit_ID`
`eos_title`
$P_{0}$		$α$		$P_{s h}$

Definition


Field	Contents	SI Unit Example
`mat_ID`	Material identifier. (Integer, maximum 10 digits)
`unit_ID`	(Optional) Unit identifier. (Integer, maximum 10 digits)
`eos_title`	EOS title. (Character, maximum 100 characters)
$P_{0}$	Initial parameter. (Real)	$[Pa]$
$α$	EOS parameter. (Real)	$[Hz]$
$P_{s h}$	Pressure shift. (Real)	$[Pa]$

Example

#RADIOSS STARTER
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/UNIT/1
                   g                  mm                  ms
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/EOS/EXPONENTIAL/7/1
artificial EoS
#                 P0               Alpha                 PSH
               100.0                 1.0                90.0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA
/END
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

Comments

Pressure shift is introduced as:
$P (t) = P_{0} e^{α t} - P_{s h}$
As the thermodynamics for this equation of state plays no role, the speed of sound is null. Therefore, time step is 1e20. As a result, the /DTIX card should be used to impose a timestep in case only material using this equation of state is used.