## Beam definition

@BEAM_DEFINITION {
@BEAM_NAME {BeamName} {
@EDGE_NAME {EdgeName}
@BEAM_PROPERTY_NAME {BldPropName}
@INITIAL_COORDINATE {si}
@SHAPE_NAME {ShapeName}
@GRAPHICAL_PARAMETERS_NAME {GrfParamName}
}
}

### 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. An external shape, ShapeName, can be optionally defined for the beam. This external shape is exclusively used in the visualization post-processor and has no effect on the analysis procedure. Beam shapes must be of the CURVE type.
5. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

### Graphical parameters

The appearance of the beam during the visualization phase of the analysis can be controlled by associating graphical parameters, GrfParamName, to the element. The following representations are valid for beam elements: RepresentationType = CURVE, LINE, MESH, or SURFACE. 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; CURVE 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. Default value: SURFACE if a ShapeName is defined, LINE otherwise. The following vector fields are valid for beam elements: VfdType = ANGULAR_VELOCITIES, CURVATURES, FORCES, MOMENTS, STRAINS or VELOCITIES.

### 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, EIGEN_FORCES_CENTER, FORCES, FORCES_CENTER, 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_FORCES_CENTER, EIGEN_STRAINS, FORCES, FORCES_CENTER, POSITIONS, STRAINS, VELOCITIES. (Default value: DISPLACEMENTS).

### Maps

Maps can be defined to extract information about beams.

1. The following MapType are allowed for beam elements.
• DISPLACEMENTS. Evaluates displacements within the beam. Three displacement components and three rotation components are evaluated. ChannelNumber = 1, 2, or 3 correspond to displacement components along axes e1, e2 or e3, respectively; ChannelNumber = 4, 5 or 6 correspond to rotation components about axes e1, e2 or e3, respectively.
• FORCES. Evaluates the forces within the beam. Three force components and three moment components are evaluated. ChannelNumber 1, 2 or 3 correspond to force components along axes e1, e2 or e3, respectively; ChannelNumber 4, 5 or 6 correspond to moment components about axes e1, e2 or e3, respectively.
• FORCES_CENTER. Evaluates the forces within the beam. Three force components and three moment components are evaluated. With this option, the torque, M1k, is computed with respect to the shear center and the bending moments, M2c and M3c, with respect to the centroid.
• STRAINS. Evaluates strains within the beam. Three strain components and three curvature components are evaluated. ChannelNumber 1, 2 or 3 correspond to strain components along axes e1, e2 or e3, respectively; ChannelNumber 4, 5 or 6 correspond to curvature components about axes e1, e2 or e3, respectively.
• VELOCITIES. Evaluates velocities within the beam. Three linear velocity components and three angular velocity components are evaluated. ChannelNumber 1, 2 or 3 correspond to velocity components along axes e1, e2 or e3, respectively; ChannelNumber 4, 5 or 6 correspond to angular velocity components about axes e1, e2 or e3, respectively.
2. These various option are compatible with various FrameName as detailed in table 2. For beams, the local axis system (FrameName = LOCAL) is defined by the curve triads.
FrameName
INERTIAL
FrameName
LOCAL

FrameName
DISPLACEMENTS YES ♠ NO YES
FORCES YES YES ♠ YES
FORCES_CENTER YES YES ♠ YES
STRAINS YES YES ♠ YES
VELOCITIES YES ♠ YES YES
Table 1. Available options for the MapType and FrameName.
♣ indicates the default option for MapType.
♠ indicates the default option for FrameName.