Rigid beam elements and connector element

The Abaqus element type RB3D2 is a two-node, three-dimensional rigid beam element used to model components that do not deform. 

It is frequently used in Abaqus/Standard, particularly in the modeling of offshore structures, because it can transmit Abaqus/Aqua loads (such as fluid drag and buoyancy). It can also serve as a rigid link between different nodes or deformable bodies.

In Abaqus, RNODE3D is not a standard element type in the core element library like RB3D2, R3D3, or C3D8R. Instead, it is the name often used in specific analyses, reports, or custom scripts to refer to the rigid body reference node in a three-dimensional model.

In Abaqus, ARSC is a special element type that stands for Analytic Rigid Surface (Cylindrical). 

• It is a non-deformable element used in the software to define a perfectly rigid cylindrical surface for contact interactions.

• These "special elements" appear in the output database and are used for visualization and query purposes, rather than being part of the meshed geometry itself.

In Abaqus, for the CONN3D2 connector element, the output variables CTF1, CTF2, CTF3 and CTM1, CTM2, CTM3 refer to the total force and total moment components in the local connector element coordinate system. 

Here is a breakdown of what each output variable represents:

Total Force Components (CTF)

These variables provide the total force transmitted by the connector element along its local axes:

• CTF1: Total force component in the connector's local 1-direction (translational degree of freedom 1).

• CTF2: Total force component in the connector's local 2-direction (translational degree of freedom 2).

• CTF3: Total force component in the connector's local 3-direction (translational degree of freedom 3). 

Total Moment Components (CTM)

These variables provide the total moment transmitted by the connector element about its local axes:

• CTM1: Total moment component about the connector's local 1-direction (rotational degree of freedom 4).

• CTM2: Total moment component about the connector's local 2-direction (rotational degree of freedom 5).

• CTM3: Total moment component about the connector's local 3-direction (rotational degree of freedom 6). 

The specific direction of these local axes depends on how you defined the connector's orientation in your Abaqus model. The total force and moment values are a summation of forces from various sources, including elastic behavior, viscous damping, friction, stops, and applied loads.

*CONNECTOR SECTION, ELSET=BTEN
TRANSLATOR
my_local_csys,

*CONNECTOR BEHAVIOR, NAME=spring_behavior
*CONNECTOR ELASTICITY, COMPONENT=1
 100.0,                               ! Stiffness value (Force/length)

*ORIENTATION, NAME=my_local_csys, SYSTEM=RECTANGULAR
 1.0, 0.0, 0.0,  0.0, 1.0, 0.0      ! Coordinates of point a and point b
 0.0, 0.0, 0.0                      ! Coordinates of point c (origin) - optional, defaults to global origin

• The first line of data defines point 'a' and point 'b'. The vector from the origin (point 'c') to point 'a' defines the local 1-axis.

• The second line of data defines the origin, point 'c'.