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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.
Finite Elements
Springs
Spring TYPE12 - Pulley (/PROP/SPR_PUL)
Spring TYPE12 is used to model a pulley. When used in a seat belt model, it is defined with three nodes.

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Radioss^® is a leading explicit finite element solver for crash and impact simulation.
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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
    - Solid Elements (/PROP/SOLID)
      Solids hexahedron and tetrahedron with linear and quadratic interpolation functions are available in Radioss.
    - Solid-Shell Elements (/PROP/TSHELL)
      The elements HA8, HEPH and BRICK20 can be transformed to solid-shell elements by setting constant the normal stress through the thickness.
    - Shell Elements
    - Beam Elements (/PROP/BEAM, /PROP/INT_BEAM)
      The two beam elements available in Radioss are used on one-dimensional structures and frames. It carries axial loads, shear forces, bending and torsion moments (contrary to the truss that supports only axial loads).
    - Springs
      - Stiffness Formulation
        The stiffness of the spring can be defined multiple ways with each degree of freedom defined differently.
      - Spring Failure
      - Spring Hardening
        Isotropic, kinematic or uncoupled spring hardening options can be defined by the hardening flag $H$ .
      - Spring Coordinate System
      - Spring TYPE4 - 1 DOF Spring (/PROP/SPRING)
        Spring TYPE4 is a simple physical spring, physical dashpot or parallel spring and dashpot.
      - General TYPE8 Spring (/PROP/SPR_GENE)
        Spring TYPE8 is a six degrees of freedom spring: three translations and three rotations.
      - Spring TYPE12 - Pulley (/PROP/SPR_PUL)
        Spring TYPE12 is used to model a pulley. When used in a seat belt model, it is defined with three nodes.
      - Beam TYPE13 Spring (/PROP/SPR_BEAM)
      - Kinematic Joint TYPE33 (/PROP/KJOINT)
        Kinematic joints are declared by /PROP/KJOINT. Joints are defined by a spring and two local coordinate axes, which belong to connected bodies.
      - Spring Joint TYPE45 (/PROP/KJOINT2)
        In Radioss, property TYPE45 is the joint type spring.
      - Axisymmetric Spring TYPE25 (/PROP/SPR_AXI)
        This spring is a simplification of spring TYPE13; in which the properties of the spring cross-section are considered to be invariable with respect to Y and Z.
    - Mesh Recommendations
      Mesh recommendations in crash worthiness and in Implicit Analysis are covered.
    - Hourglass Formulations
      Under-integrated elements are very familiar in crash worthiness. In these elements, a reduced number of integration points are used to decrease the computation time. This simplification generates zero energy deformation modes, called hourglass modes.
    - Stress-Strain Computation Options (/PROP)
    - Radioss Coordinate System
  - 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.

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Spring TYPE12 - Pulley (/PROP/SPR_PUL)

Spring TYPE12 is used to model a pulley. When used in a seat belt model, it is defined with three nodes.

Node 2 is located at the pulley, and a deformable rope is joining the three nodes (Figure 1). The spring mass is distributed on the three nodes with ¼ at node 1 and node 3 and ½ at node 2.

A Coulomb friction can be applied at node 2, taking into account the angle between the two strands. Without friction, forces are computed as:

| F_{1} | = | F_{2} | = K δ

With,

$δ$: Total rope elongation
$K$: Stiffness

If the Coulomb friction is used, forces are computed as:

F_{f r} = \min {| Δ F |, \max [0, (| F_{1} | + | F_{2} |) \cdot \tanh (\frac{β \cdot μ}{2})]} \cdot s i g (Δ F)

Where,

$μ = f_{f r} (\frac{Δ F}{X s c a l e_F}) \cdot Y s c a l e_F$
$β$: Angle (radians unit)
$f_{f r}$: Function of fct_ID_fr

I_fr =0 (symmetrical behavior)
$Δ F = | F_{1} - F_{2} |$
I_fr =1 (non-symmetrical behavior)
$Δ F = F_{1} - F_{2}$

δ_{1}

is the elongation of strand 1-2 and

δ_{2}

of strand 2-3.

Figure 1. Spring TYPE12, Pulley

Time step is computed with the same equation that for spring TYPE4, but the stiffness is replaced with twice the stiffness to ensure stability with high friction coefficients.

Note: The two strands have to be long enough to avoid node 1, or node 3 slides up to node 2. Nodes 1 and 3 will be stopped at node 2, if there is a knot at nodes 1 and 3.

Figure 2. Spring TYPE12, Locking

For further information, refer to the Radioss Theory Manual.