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Welcome
What's New
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
  - 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.
    - Rigid Bodies
      Block Format Keyword
    - Boundary Conditions and Constraints
      Block Format Keyword
      - /BCS
        Block Format Keyword Defines boundary conditions on node groups for translational and rotational motion.
      - /BCS/CYCLIC
        Block Format Keyword Defines a cyclic boundary condition on a structure in a fixed cylindrical coordinate system.
      - /BCS/LAGMUL
        Block Format Keyword Defines boundary conditions on node groups using Lagrange multipliers. This keyword is not available for SPMD computation.
      - /BCS/WALL
        Block Format Keyword Defines the sliding wall boundary condition with collocated scheme (FVM).
      - /IMPACC
        Block Format Keyword Defines imposed accelerations on a group of nodes.
      - /IMPDISP
        Block Format Keyword Defines imposed displacements on a group of nodes.
      - /IMPDISP/FGEO
        Block Format Keyword Describes the final position of a set of N nodes, input by coordinates.
      - /IMPTEMP
        Block Format Keyword Defines imposed temperatures on a group of nodes.
      - /IMPVEL
        Block Format Keyword Defines imposed velocities on a group of nodes.
      - /IMPVEL/FGEO
        Block Format Keyword Describes the final position of a set of N nodes. The final position is provided by a node number. The node may eventually move.
      - /IMPVEL/LAGMUL
        Block Format Keyword Defines imposed velocities on node groups using Lagrange multiplier method.
      - /NBCS
        Block Format Keyword Defines boundary conditions on node groups for translational and rotational motion.
    - Rigid Link
      Block Format Keyword
    - Rigid Walls
      Block Format Keyword
    - Joints
      Block Format Keyword
    - Tied Contact
      Block Format Keyword
    - Flexible Body
      Block Format Keyword
    - Other Constraints
      Block Format Keyword
  - 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.

View All Altair HyperWorks Help

/IMPACC

Block Format Keyword Defines imposed accelerations on a group of nodes.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/IMPACC/`impacc_ID`/`unit_ID`
`impacc_title`
`fct_ID`_T	`Dir`	`Skew_ID`	`sens_ID`	`grnd_ID`
`Ascale`_x		`Fscale`_Y		`T`_start		`T`_stop

Definition


Field	Contents	SI Unit Example
`impacc_ID`	Imposed acceleration block identifier. (Integer, maximum 10 digits)
`unit_ID`	Unit identifier. (Integer, maximum 10 digits)
`impacc_title`	Imposed acceleration block title. (Character, maximum 100 characters)
`fct_ID`_T	Time function identifier. (Integer)
`Dir`	Direction: X, Y, and Z in translation; XX, YY, and ZZ in rotation. (Text)
`Skew_ID`	Skew identifier. (Integer)
`sens_ID`	Sensor identifier. ≠ 0 (sensor activated) The imposed acceleration is applied at the time of sensor activation and the time versus acceleration function are shifted in time. (Integer)
`grnd_ID`	Node group on which the imposed acceleration is applied. (Integer)
`Ascale`_x	Abscissa (time) scale factor for `fct_ID`_T. Default = 1.0 (Real)	$[s]$
`Fscale`_Y	Ordinate (acceleration) scale factor for `fct_ID`_T. Default = 1.0 (Real)	$[\frac{m}{s^{2}}]$ or $[\frac{r a d}{s^{2}}]$
`T`_start	Start time. (Real)	$[s]$
`T`_stop	Stop time. Default = 10³⁰ (Real)	$[s]$

Comments

The acceleration direction must be right justified in the ten characters of field number 2.
If T_start and T_stop are specified, the acceleration is imposed between these times, but the time versus acceleration function is not shifted to begin at T_start.
When a sensor is defined sens_ID, the imposed acceleration is applied at the time of sensor activation and the function is shifted by the sensor activation time.
When a sensor sens_ID is used with T_start and T_stop, the imposed acceleration will only occur if the sensor activation time occurs between T_start and T_stop.
The Ascale_X and Fscale_Y are used to scale the abscissa (time) and ordinate (translational or angular acceleration).
The actual load function value is calculated as:
$a (t) = F s c a l e_{y} \cdot f_{T} (\frac{t}{A s c a l e_{x}})$
Where, $f_{T}$ is the function of fct_ID_T.
Unlike /GRAV, this keyword is a kinematic condition which is applied to a set of nodes. The node will always be moving with the specified acceleration.