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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.
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.
Time Step Control Methods
The time step can often be increased using some of these time step control methods.
Advanced Mass Scaling (AMS)
Increase Computation Speed and Maintain Accuracy
AMS (Advanced Mass Scaling) saves significant computation time by increasing the time step of the model for an explicit computation. This is similar to traditional mass scaling, except that the added mass does not increase the translational kinetic energy of the system.
Engine

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.
    - Element Time Step
      The default time step calculation used by Radioss is the element time step.
    - Nodal Time Step
      The nodal time step calculates the time step based on the nodal mass and nodal stiffness in the model.
    - Global Time Step
      The global time step (GTS) method can be used to calculate the time step of a model based on the natural frequency of the model.
    - Contact Interface Time Step
      The contact interface time step is calculated in two different ways. First, based on stiffness and second, based on the velocity of the secondary nodes.
    - Time Step Output from a Model
      The time step of the initial model is output to the Starter output file. Whereas the time step of a running model can be output to the animation files.
    - Time Step Control Methods
      The time step can often be increased using some of these time step control methods.
      - Nodal Time Step Control
      - Element Time Step Control
      - Contact Interface Time Step Control
      - Advanced Mass Scaling (AMS)
        Increase Computation Speed and Maintain Accuracy
        AMS (Advanced Mass Scaling) saves significant computation time by increasing the time step of the model for an explicit computation. This is similar to traditional mass scaling, except that the added mass does not increase the translational kinetic energy of the system.
        Starter
        Engine
        Capabilities and Limitations
        Recommended Checklist
        Example: Automotive Application
        Metal Forming Application Example
        1.out File Examples
    - Time Step Scale Factor
      The theoretical stable time step for both elements and nodes is an approximation and may change during the following time increment.
    - General Recommendations
      Every time step control method has advantages and limitations.
  - 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.
  - 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.

View All Altair HyperWorks Help

Engine

Only Keyword: only /DT/AMS must be present in order to invoke AMS with the targeted increased elementary time step (Radioss Engine Input).

CAUTION: /AMS is mandatory in the Radioss Starter Input in order to designate the selected parts or the entire model on which AMS is applied.

In /DT/AMS/Iflag if I_flag= 1, the tolerance for AMS convergence, Tol_AMS, must be provided. If I_flag is ignored, the default value (1E-3) for Tol_AMS is applied. It is not recommended to modify AMS tolerance, if it is not needed. Note that Tol_AMS was 1E-4 in 12.0.210.

In /DT/AMS/Iflag, if I_flag = 2, the display of the number of AMS iterations may help in debugging or monitoring convergence at no extra CPU cost. Maximum allowed iterations before sending a divergence message is 1000 by default. It is advised to NOT change this value. Anything above this maximum value, Radioss stops with the following error message:

** ERROR ** AMS IS LIKELY DIVERGING

Monitoring the number of iterations per cycle can help to understand the resulting AMS performance:
75 to 100 iterations is a sign of a really bad convergence 50 iterations may not provide any speedup 30 iterations or less is considered a good convergence.

It is advised to use 0.67 as the scale factor, $Δ T_{s c a}$ , rather than 0.9 (as well as in traditional nodal mass scaling /DT/NODA/CST, especially if it is used for comparison with the AMS results).

Target a minimum time step, $Δ T_{\min}$ , from 10 to 20 times than the one used in /DT/NODA/CST, that is, start with 10 times, then check how far to go by verifying the numerical convergence, the gain of elapsed time, and the results quality.

/DT/AMS will not modify the global mass, therefore:

The global momentum of the related nodes is conserved.
A comparison with traditional mass scaling requires a minor added mass along the /DT/NODA/CST computation, if used as a reference.

/DT/Eltyp/Keyword3 is compatible with /DT/AMS, except /DT/INTER/CST (refer to Capabilities and Limitations for further details).

Use /DT/INTER/DEL as a workaround for slow convergence, or possible divergence, when invoking a nonlinear penalty stiffness with contact interfaces TYPE7, TYPE11, and TYPE19.

/ANIM/NODA/NDMAS may be added in order to output non-diagonal mass variation.

/ANIM/NODA/DINER may be added in order to output added inertia per nodes.