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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.
Initial Conditions
Block Format Keyword
/INIVEL/FVM
Block Format Keyword Defines initial material velocities on a group of elements (bricks, quad or triangles) for the Finite Volume solver.

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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
      - /INIBEAM
      - /INIBRI
        Describes the different initial state for a brick. The initial state for brick may be defined by more than one block.
      - /INICRACK
        Block Format Keyword Definition of the initial crack.
      - /INIGRAV
        Block Format Keyword Defines initial state from hydrostatic pressure due to gravity loading.
      - /INIMAP1D
        Block Format Keyword Map 1D velocities and thermodynamic values into 2D or 3D space using spherical, cylindrical, or planar mapping methods. The mapped results are used with /ALE/EULER materials.
      - /INIMAP1D/FILE
        Block Format Keyword Map 1D velocities and thermodynamic values into 2D or 3D space using spherical, cylindrical, or planar mapping methods. The mapped results are used with /ALE/EULER materials.
      - /INIMAP2D
        Block Format Keyword Map 2D velocity and thermodynamic values into a 3D axi-symmetric space for use with /ALE/EULER materials.
      - /INIMAP2D/FILE
        Block Format Keyword Map 2D velocity and thermodynamic values into a 3D axi-symmetric space for use with /ALE/EULER materials.
      - /INIQUA
        Block Format Keyword Describes the different initial state for a quad element.
      - /INISHE or /INISH3
      - /INISPHCEL/FULL
        Block Format Keyword Describes the initial state for a Smooth Particle Hydrodynamic (SPH).
      - /INISPRI/FULL
        Block Format Keyword Describes the initial state for spring elements. All values defined in this card will be applied at the beginning on the computation.
      - /INISTA
        Block Format Keyword Describes the initial state file.
      - /INITEMP
        Block Format Keyword Describes the initial nodal temperature.
      - /INITRUSS/FULL
        Block Format Keyword Describes the initial state for truss elements. All values defined in this card will be applied at the beginning on the computation.
      - /INIVEL
        Block Format Keyword Defines initial velocity on a group of nodes.
      - /INIVEL/AXIS
        Block Format Keyword Initialize both translational and rotational velocities on a group of nodes in a given coordinate system.
      - /INIVEL/FVM
        Block Format Keyword Defines initial material velocities on a group of elements (bricks, quad or triangles) for the Finite Volume solver.
      - /INIVEL/NODE
        Block Format Keyword Initialize translational and rotational velocities on each node in the global or in a given coordinate system.
      - /INIVOL
        Block Format Keyword For multi-material ALE modeling, this initial condition defines the initial volumetric fractions on a side of a defined surface.
      - /STATE/STR_FILE
        Block Format Keyword Allows to read an initial state (blocks /INISHE, /INISH3, and /INIBRI) by specifying the name of a stress file possibly compressed using GZIP.
    - Load
      Block Format Keyword
    - Thermal
      Block Format Keyword
    - Reference State
      Block Format Keyword
    - 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.

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/INIVEL/FVM

Block Format Keyword Defines initial material velocities on a group of elements (bricks, quad or triangles) for the Finite Volume solver.

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/INIVEL/FVM/`inivel_ID`/`unit_ID`
`inivel_title`
`V`_X_.		`V`_Y_.		`V`_Z		`grbric_ID`	`grqd_ID`	`grtria_ID`	`skew_ID`
`T`_start		`sens_ID`

Definition


Field	Contents	SI Unit Example
`inivel_ID`	Initial velocity block identifier. (Integer, maximum 10 digits)
`unit_ID`	(Optional) Unit identifier. (Integer, maximum 10 digits)
`inivel_title`	Initial velocity block title. (Character, maximum 100 characters)
`V`_X	X velocity. (Real)	$[\frac{m}{s}]$
`V`_Y	Y velocity. (Real)	$[\frac{m}{s}]$
`V`_Z	Z velocity. (Real)	$[\frac{m}{s}]$
`grbric_ID`	Brick group on which specific initial velocities are applied. (Integer)
`grqd_ID`	Quad groups on which specific initial velocities are applied. (Integer)
`grtria_ID`	Tria groups on which specific initial velocities are applied. (Integer)
`skew_ID`	Skew identifier. (Integer)
`T`_start	Start time. Default = 0.0 (Real)	$[s]$
`sens_ID`	Sensor property identifier. = 0 No sensor is used. (Integer)

Comments

At least one group ID must be provided.
/INIVEL/FVM is used to initialize velocities in solid elements for the Finite Volume solver of /MAT/LAW151 (MULTIFLUID).
Initial velocity is applied when time T_start is reached or when the sensor is activated.