## Beam definition

@BEAM_DEFINITION {
@BEAM_NAME {BeamName} {
@EDGE_NAME {EdgeName}
@BEAM_PROPERTY_NAME {BldPropName}
@INITIAL_COORDINATE {si}
@SHAPE_NAME {ShapeName}
@VISUALIZATION_PARAMETERS_NAME {VizPrmName}
}
}

### Introduction

A beam is defined as a structure having one of its dimensions much larger than the other two, as depicted in fig. 1. The axis of the beam is defined along that longer dimension and its cross-section is normal to this axis. The cross-section's geometric and physical properties are assumed to vary smoothly along the beam's span. The beam associated with edge, EdgeName, used for the representation of multibody systems.  ##### Figure 1. Configuration of a beam. Figure 2. Geometry of the beam.

The geometry of the beam is inherited from edge, EdgeName, which must have an associated curve, CurveName. The end points of the curve must match the points associated with the vertices of the edge. The finite element discretization of the beam is controlled by the curve mesh parameters, which must be associated with this curve.

As shown in fig. 2, the reference axis of the beam coincides with the curve which must have an associated triad field, E (η) = (e1, e2, e3). The plane of the cross section is determined by the triad field associated with the curve. Unit vector e1 must be tangent to the curve; unit vectors e2 and e3 are in the plane normal to the curve and define the plane of the cross-section of the beam. If the triad field of the curve is defined by an orientation distribution, it is possible to define the triad field by means of a twist angle. This option automatically selects e1 to be normal to the curve. The structural mass and stiffness properties of the beam are defined with respect to the local triad E.

### NOTES

1. The finite element discretization of the beam is controlled by the curve mesh parameters, which must be associated with curve, CurveName.
2. The structural mass and stiffness properties of the beam are specified by the beam properties, BldPropName.
3. The beam properties, BldPropName, are defined at a number of stations along the curve that defines the geometry of the beam. Various parameterizations of the curve can be used, including η-coordinate, the curvilinear coordinate, s, or the axial coordinate, x. In these latter two cases, the initial value of the coordinate will be s = si or x = si if curvilinear or axial coordinates, respectively, are used to define the beam properties. When using this option, different beams are allowed to refer the same beam property table, typically using adjacent portions of the table.
4. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

### Visualization parameters

Reference
Configuration
Deformed
Configuration
Representation LINE LINE
Color CHOCOLATE CHOCOLATE
Point size HUGE THICK
Line Size THICK THICK
##### Table 1. Default visualization parameters for the beam element. Default font type: HELVETICA_18, Default color: RED.

The appearance of beams during the visualization phase of the analysis can be controlled by visualization parameters. The default values of the visualization parameters are summarized in table 1. If those default parameters are not adequate, suitable values can be specified by associating visualization parameters, VizPrmName, with the element.

For beams, the following representations are valid. The LINE representation depicts the beam as a line along curve CurveName that defines the beam element. The other three representations are allowed only if a shape, ShapeName, is defined for the beam. The CURVE representation shows the shape as a set of sectional curves at the beam nodes, MESH depicts the shape as an orthogonal mesh of curves, and SURFACE as an external surface.

The definition of an external shape is used in the visualization post-processor exclusively and has no effect on the analysis procedure. Beam shapes must be of the CURVE type.

### Sensors

Sensors can be defined to extract information about beams. The following SensorType values and associated FrameName specifications are allowed for beams: ACCELERATIONS, DISPLACEMENTS, EIGEN_DISPLACEMENTS, EIGEN_FORCES, FORCES, POSITIONS, STRAINS, and VELOCITIES. (Default value: DISPLACEMENTS).

The location of the sensor within the beam element is determined by a single u value (0 ≤ u ≤ 1) that corresponds to the η value along the curve defining the beam element. No v value value is accepted for the beam element.

### Surveys

Surveys can be defined to extract information about beams. The following SurveyType values and associated FrameName specifications are allowed for beams: ACCELERATIONS, DISPLACEMENTS, EIGEN_DISPLACEMENTS, EIGEN_FORCES, EIGEN_STRAINS, FORCES, POSITIONS, STRAINS, VELOCITIES. (Default value: DISPLACEMENTS).

FrameName
INERTIAL
FrameName
LOCAL

FrameName
DISPLACEMENTS YES ♠ NO YES
FORCES YES YES ♠ YES
STRAINS YES YES ♠ YES
VELOCITIES YES ♠ YES YES
.