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Radioss Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
LS-DYNA Input
This manual provides a list of LS-DYNA input files available in Radioss.
*ELEMENT
*ELEMENT_SPH
LS-DYNA Input Interface KeywordDefines a Smooth Particle Hydrodynamic (SPH).

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.
- LS-DYNA Input
  This manual provides a list of LS-DYNA input files available in Radioss.
  - *AIRBAG
  - *BOUNDARY
  - *CONSTRAINED
  - *CONTACT
  - *CONTROL
  - *DAMPING
  - *DATABASE
  - *DEFINE
  - *ELEMENT
    - *ELEMENT_BEAM
      LS-DYNA Input Interface KeywordDefines a beam, discrete beam, or a truss element.
    - *ELEMENT_DISCRETE
      LS-DYNA Input Interface KeywordDefines a 1 degree of freedom spring element.
    - *ELEMENT_MASS
      LS-DYNA Input Interface KeywordThis keyword defines mass added to nodes or node sets.
    - *ELEMENT_MASS_PART
      LS-DYNA Input Interface KeywordThis keyword defines mass added to parts or part sets.
    - *ELEMENT_PLOTEL
      LS-DYNA Input Interface KeywordDefines a spring element without any stiffness for visualization.
    - *ELEMENT_SEATBELT
      LS-DYNA Input Interface KeywordDefines a 1D seat belt element.
    - *ELEMENT_SEATBELT_ACCELEROMETER
      LS-DYNA Input Interface KeywordThis keyword defines an accelerometer.
    - *ELEMENT_SEATBELT_PRETENSIONER
      LS-DYNA Input Interface KeywordDefines a 1D seat belt pretensioner element.
    - *ELEMENT_SEATBELT_RETRACTOR
      LS-DYNA Input Interface KeywordDefines a 1D seat belt retractor element.
    - *ELEMENT_SEATBELT_SENSOR
      LS-DYNA Input Interface KeywordDefines a seat belt sensor.
    - *ELEMENT_SEATBELT_SLIPRING
      LS-DYNA Input Interface KeywordDefines a 1D or 2D seat belt slipring.
    - *ELEMENT_SHELL
      LS-DYNA Input Interface KeywordDefines a shell element with 3 or 4 nodes.
    - *ELEMENT_SOLID
      LS-DYNA Input Interface KeywordDefines 3-dimensional solid elements.
    - *ELEMENT_SPH
      LS-DYNA Input Interface KeywordDefines a Smooth Particle Hydrodynamic (SPH).
    - *ELEMENT_TSHELL
      LS-DYNA Input Interface KeywordDefines 3-dimensional thick shell elements.
  - *EOS
  - *HOURGLASS
    LS-DYNA Input Interface KeywordDefine solid and hourglass formulation for 8-node solid elements.
  - *INCLUDE
  - *INITIAL
  - *INTEGRATION_SHELL
    LS-DYNA Input Interface KeywordDefine user-defined through the thickness integration rules for the composite shell element.
  - *INTERFACE_SPRINGBACK
    LS-DYNA Input Interface KeywordDescribes the variables to output in an initial state file or DYNAIN file at the end of the analysis.
  - *KEYWORD
    LS-DYNA Input Interface KeywordThis keyword should always be the first card of the input file. Optionally used with *CONTROL_UNITS card to specify model units.
  - *LOAD
  - *MAT
  - *NODE
    LS-DYNA Input Interface KeywordDefines a node number and nodal coordinates in the global coordinate system.
  - *PART
    LS-DYNA Input Interface KeywordDefines a part, which combines material and property information.
  - *RIGIDWALL
  - *SECTION
  - *SET
- 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.

*ELEMENT_SPH

LS-DYNA Input Interface KeywordDefines a Smooth Particle Hydrodynamic (SPH).

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
*ELEMENT_SPH_{OPTION}
`Node_ID`	`part_ID`	`Mass`		`NEND`

Definition


Field	Contents	SI Unit Example
`OPTION`	= <blank> The mass value is understood as mass if positive and volume if negative. = VOLUME The mass value is understood as volume. The mass is computed with the density defined in the associated material.
`Node_ID`	Node identifier. (Integer)
`part_ID`	Part identifier. (Integer)
`Mass`	Mass or volume value. < 0 Volume value. > 0 Mass value. (Real)	$[kg]$ or $[m m^{3}]$
`NEND`	(Optional) Final node identifier for SPH generation. Particles are generated between `Node_ID` to `NEND` using current `PID` and `MASS` data. (Integer)

Comments

This keyword maps to /SPHCEL.