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User Guide
This manual provides details on the features, functionality, and simulation methods available in Altair Radioss.
Explicit Structural Finite Element Analysis
In this section, available explicit features for different explicit analyses are presented.
Airbag Modeling
Airbags are modeled as monitored volumes /MONVOL in several different ways.
FVMBAG1 Airbag Modeling Guidelines
Elimination of Bad Volume

Welcome
What's New
View new features for Radioss 2024.1.
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.
- Run Radioss
  The Radioss solver can be executed using different methods described here.
- Explicit Structural Finite Element Analysis
  In this section, available explicit features for different explicit analyses are presented.
  - Time Step
    An explicit is solved by calculating results in small time increments or time steps. The size of the time step depends on many factors but is automatically calculated by Radioss.
  - Finite Elements
  - Modeling Tools
  - Materials
    Different material tests could result in different material mechanic character.
  - Failure
  - Composites
    Composite materials consist of two or more materials combined each other. Most composites consist of two materials, binder (matrix) and reinforcement. Reinforcements come in three forms, particulate, discontinuous fiber, and continuous fiber.
  - Connections
  - Kinematic Constraints
    In Radioss, a kinematic condition is a nodal constraint applied to a set of nodes.
  - Interfaces
    Several interfaces are available in Radioss, this section deals with contact interfaces only. Each interface is distinguished with a type number.
  - Loads
  - Airbag Modeling
    Airbags are modeled as monitored volumes /MONVOL in several different ways.
    - Monitored Volume (/MONVOL)
      A monitored volume is defined with one or more shell (3-node or 4-node) parts.
    - Monitored Volume Time Step
      An "AIRBAG1" time step is estimated into the Engine, but this time step will never control the time step during the run. If that is the case, it means there is a non-physical airbag definition in the input deck.
    - FVMBAG1 Airbag Modeling Guidelines
      - Application Field
        Present guidelines define modeling and validation requirements for numerical airbag models in Radioss with Finite Volume Method (FVM).
      - General Airbag Model Requirements
        Airbag numerical models are created for the numerical simulation of crash events related to occupant safety problems. Airbag models may differ in the amount of detail and accuracy depending on their intended application.
      - Meshing and Folding
      - Reference Geometry
        Reference geometry should be represented as flat node based (/XREF) or element based (/EREF) geometry.
      - Gas Generator
        The gas generator model should represent all details available in CAD data: gas generator, injector openings, and retainers.
      - Initial Air inside of Airbag
        Material for the air inside of the airbag should be specified either through /MAT/GAS/MASS, /MAT/GAS/MOLE or /MAT/GAS/PREDEF.
      - Airbag Fabric Material
        The nonlinear anisotropic material LAW58 used be used as the airbag material.
      - Finite Volume Method Airbag Modeling
        In Radioss the standard method for airbag calculation is the Finite Volume Method (FVM).
      - Vent Holes
        Each vent hole should be represented as a separate component in the same position as in the CAD geometry.
      - Airbag Fabric Porosity
        Porosity of airbag material is modeled by the addition of a porosity card /LEAK/MAT to /MAT/LAW58 card.
      - Venting and Fabric Porosity Activation
      - Airbag Internal Contacts
        External and internal airbag components including inter-chamber voids and void components used for vents should not have any geometrical intersections.
      - Airbag Housing
        The airbag housing should represent all details available in CAD data.
      - Stability Run
        A folded airbag model with the correct material, property, contact definition, and specified reference geometry should not move before activation of injector.
      - Uniform Pressure Run
        A uniform pressure run should be performed to make sure that gas dynamic data, injector input, fabric materials, and contacts give physical results.
      - Standalone Run of FVM Airbag
      - Elimination of Bad Volume
      - Checklist
    - Tank Test
      By using data from a tank test output, it is possible to obtain the temperature and the mass flow of the gas supplied, which can be used as input to Radioss.
    - Airbag Setup Recommendation
    - Airbag Deployment Debugging
      The objective here is to provide some guidelines on how to troubleshoot a simulation where the airbag does not deploy properly or crashes because of the airbag.
  - Debugging Guidelines
  - Appendix
- Implicit Structural Finite Element Analysis
- Fluid and Fluid-Structure Simulation
  In this section, fluid and fluid-structure simulation is presented.
- 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.
- Multi-Domain Technique
  The objective of the Multi-Domain technique (also referred to as RAD2RAD) is to optimize the computing performances of large scale Radioss models.
- Design Optimization
  Optimization in Radioss was introduced in version 13.0. It is implemented by invoking the optimization capabilities of OptiStruct and simultaneously using the Radioss solver for analysis.
- Error Message Database
  This section is comprised of error messages in ascending numerical order.
- Engine Error Messages
- Warning Message Database
  This section is comprised of warning messages in ascending numerical order.
Reference Guide
This manual provides a detailed list of all the input keywords and options available in Radioss.
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.

Elimination of Bad Volume

Initial tetra shape is not very important for FVM calculation. The volumes are merged with neighbors according to Cmerge global merging parameters and Tscale parameter I for FVM time step definition.