Sling / Grommet Node

Sling / Grommet Node#

A Sling / Grommet node (SlingGrommet) can be used to conveniently model slings or grommets from typical properties.

Slings / Grommets are created between circle nodes. Between the endpoints it can run over other circle or roundbar nodes.

To create a sling or grommet,

  1. select the circle nodes that will act as endpoints. Hold shift when selecting a node to add nodes to the selection.

  2. select image-20231106150947456from the quick-actions.

Hint: Sometimes it can be difficult to see the the circles. In that case switching to x-ray-mode can help.

Physical properties#

Once a sling or grommet node is created it is time to define its physical properties.

Property

Meaning

#ID and optional remarks

This is for reporting only. The part followed by # is the ID and the rest of the text is comments. For example #3.1.12 re-used will show up as 3.1.12 as ID and re-used as comment.

Type

Either Sling or Grommet

Material

The material that the item is made off. For Steel IWRC and Cable-laid the wire properties can be estimated. For other types this estimation is not available

Length

The length can be specified as Ultimate, Nominal or Circumferential length. Whatever is most convenient or available.
See Wire properties

Rope properties

Diameter, Weight per length, EA and MBL are all inter-related. For Steel IWRC and Cable laid wires DAVE can estimate these if at least one of the values is provided.
See Wire properties

Total properties

Weight per length and Stiffness can also be defined as “total” properties. These are “derived” properties and will change when the length of the item chages. Weight per length and EA are “leading”

Sling specific#

For slings the length of the eyes and splices have to be defined.

Routing and connections#

Adding intermediate connections to a sling or grommet is done in the same way as for cables. Refer to the cable node for details.

The SlingGrommet node can be used to model a Sling or Grommet and allows easy switching between the two types.

For slings the connections are as for Cable nodes.

image-20230914174213309

For grommets there are two ways in which the connections can be interpreted: Line mode and Circle mode. Both are illustrated below:

image-20230914174345793

For line mode (left) the grommet follows the same way back running over the intermediate connections in opposite (reversed) direction. For circle mode the grommet automatically routes back directly to the first connection.

Friction#

Friction between the rope and the connections can be defined by pressing the “advanced” button. Note that the friction that is defined here will be overwritten when running a Rigging Analysis Report.

For slings or grommets in “circle” mode the friction is defined in the same way as for a cable.

Line mode#

For grommets in “line” mode the definition. If not all friction is No then:

  • At least one of the connections shall be set to “Position”

  • The position on the cable is the fraction [0..1] of the of the length measured from end A.

  • If position is only defined on one of the ends, then no value needs to be provided for the position.

  • If position is defined on any intermediate connection, then the position shall be 0 < position < 1 (else no length is left for the rest of the cable)

  • If position is defined on end A, then the position on the cable shall be 0

In line mode the friction on the intermediate connections (connection 2 in the figure) controls the friction for both times that the grommet passes this point. A positive friction factor means that the tension on the A (1) side is higher than on the B (3) side of the line.

Furthermore at least one point needs to be fixed. In this case position B is fixed at L=1.

Note that the position at B can not be more than 1. In this case this translates half the cable length. If a position beyond half the cable length is needed then this is not possible. A simple work-around in that case it use symmetry and fix a point the same distance before half the cable length instead.

image-20230914204921514

Connection coupled properties#

The following properties can be defined per connection:

  1. Friction properties

  2. Maximum winding

  3. Offset

  4. Reversed

Sling

Grommet Line mode

Grommet circle mode

Friction

only intermediate

All connections

All connections (note auto-loop)

Max-winding

all connections (first and last not used)

all connections

all connections

Offset

all connections

all connection

all connections

Reversed

all connections

all connections

all connections
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