62. Clamped cable connections

The identification tag for this tutorial is PDS-ABS. Pregenerated input files for this tutorial are found in the folder named PDS-ABS in the provided tutorial input files.

62.1. Tutorial overview

This tutorial covers:

Creating a clamped cable connection with a RigidBody

Fig. 62.1 Clamped cable

62.2. Simulation setup

Create a Cable DObject.
Set the Cable node 0 position to be (0,0,5) m and the Cable Node N position to be (10,0,5) m. Set the number of cable elements to 10 and the length to 10 m.
Adjust the default DCableSegment feature properties for the newly created cable: increase $Density to 2000 kg/m³, increase $Diameter to 0.25 m and increase the bending stiffness ($EI1 and $EI2) to 10000 Nm².

Note

This will make the cable heavier and more stiff, such that it will deflect under its own self weight. The larger cable diameter will assist with visualization.

Create a RigidBody DObject.
Set the RigidBody position to be (0,0,5) m.
To fix the RigidBody in space set the $Kinematic property to 1 in the RigidBody input file.
Add a RigidBodyCuboid feature named myCube to the Library, use the default properties. Associate the cuboid feature with the RigidBody created using the $Cuboid property:

// Mass properties
$Ix 1
$Iy 1
$Iz 1
$Ixy 0
$Ixz 0
$Iyz 0
$DefineInertiaAboutCG 0
$CGPosition 0 0 0
$Mass 1

// Numerical
$Kinematic 1

$Cuboid myCube -0.5 0 0 0 0 0

62.3. Create a pinned and clamped connection

Add a Point connection between RigidBody and the Cable, accepting the default connection properties.
Run a 10 second simulation and view the results. Notice that the cable swings down below the cube. Due to the point connection, the cable will act like a pendulum.

Note

To model a rigid connection between the stiff cable that has been created and the RigidBody, a clamped connection must be used. Clamped connections are useful for simulating bend stiffeners and pipe flanges.
The tangent direction, $p_3$, of a cable at node 0 and node N of a cable is defined by the $p_1$ and $p_2$ unit vectors as shown in Fig. 62.2. To make a clamped cable connection with a RigidBody, $p_1$ and $p_2$ are defined in terms of the RigidBody reference frame within the cable connection. By defining these directions, the cable is constrained in torsion and bending.

Fig. 62.2 Relationship between $p_1$ and $p_2$ vectors and cable tangent definition at node 0 and node N

To clamp the connection between the RigidBody and cable, add the $DCableFollowerClamped property to the RigidBodyDCablePointConnection that was created earlier. Additionally, one must define the $p_1$ and $p_2$ vectors:

// Mechanical
$DCableFollowerNodeN 0
$DCableFollowerLocation 0 0 0

$DCableFollowerClamped 1
$DCableFollowerP2 0 0 1
$DCableFollowerP1 0 1 0

Run the simulation again for 10 seconds and view the results.
When loading the simulation results into PostPDS, in the Specify Load Options dialog, increase the number of radial elements to display to 12 to better visualize the results; compare how the cable looks in PostPDS when this value is set to 6.
To examine the bending radius, select Stress (Flexural) as the plotted variable (as shown in Fig. 62.1).

Note

For clamped connections between node N and a RigidBody, note that the tangent vector $p_3$ comes out of the end of the cable, whereas at node 0, $p_3$ goes into the cable.