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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.
Tools
Block Format Keyword In this group, tools like transformation, frames, skews, and curve are introduced.
Sensors
Block Format Keyword Describes the sensors which are used to activate or deactivate an object according to the defined characteristics.
/SENSOR/USER1, /SENSOR/USER2 or /SENSOR/USER3
Block Format Keyword Defines a user sensor.

Welcome
What's New
View new features for Radioss 2025.1.
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
  - 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.
    - Transforms
      Block Format Keyword Transformation types and their description.
    - Frames
      Block Format Keyword
    - Skews
      Block Format Keyword
    - Seatbelts
      Block Format Keyword
    - Curves
      Block Format Keyword
    - SPH
      Block Format Keyword
    - Sensors
      Block Format Keyword Describes the sensors which are used to activate or deactivate an object according to the defined characteristics.
      - /SENSOR/ACCE
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to accelerometer.
      - /SENSOR/AND_OR
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to Boolean of another sensors.
      - /SENSOR/DIST
        Block Format Keyword Describes a sensor which is used to activate or deactivate an object according to distance.
      - /SENSOR/DIST_SURF
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to the shortest distance from a reference node to a plane or a surface.
      - /SENSOR/ENERGY
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to energy.
      - /SENSOR/GAUGE
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to pressure gauge.
      - /SENSOR/HIC
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to Head Injury Criteria (HIC).
      - /SENSOR/INTER
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to interface force.
      - /SENSOR/NIC_NIJ
        Block Format Keyword Describes the sensors based on Neck Injury Criteria (NIC), which are used to activate or deactivate an object according to the defined characteristics.
      - /SENSOR/NOT
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to Boolean NOT of another sensor.
      - /SENSOR/PYTHON
        Block Format Keyword Describes a sensor defined Python script and used to activate or deactivate an object.
      - /SENSOR/RBODY
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to rigid body force.
      - /SENSOR/RWALL
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to rigid wall force.
      - /SENSOR/SECT
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to section force.
      - /SENSOR/SENS
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to another sensor.
      - /SENSOR/TEMP
        Block Format Keyword Describes a sensor activated when the temperature in a group of nodes reaches one of the prescribed limit values during a minimum time duration.
      - /SENSOR/TIME
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to time delay.
      - /SENSOR/USER1, /SENSOR/USER2 or /SENSOR/USER3
        Block Format Keyword Defines a user sensor.
      - /SENSOR/VEL
        Block Format Keyword Describes the sensor activated when the velocity of the chosen node reaches the prescribed limit value.
      - /SENSOR/WORK
        Block Format Keyword Describes the sensors used to activate or deactivate an object according to work.
    - Other Tools
      Block Format Keyword
  - 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.

/SENSOR/USER1, /SENSOR/USER2 or /SENSOR/USER3

Block Format Keyword Defines a user sensor.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/SENSOR/USER1/`sens_ID`, /SENSOR/USER2/`sens_ID` or /SENSOR/USER3/`sens_ID`
`sens_title`
`T`_delay
User input

Definition


Field	Contents	SI Unit Example
`sens_ID`	Sensor identifier. (Integer, maximum 10 digits)
`sens_title`	Sensor title. (Character, maximum 100 characters)
`T`_delay	Time delay. Default = 0.0 (Real)	$[s]$

Comments

For additional information about the user window, refer to User Sensors in the User Subroutines Manual.