Learning Forum

[eagleaero1]

I am modelling a case of a load that is shared between two marine jib cranes (load is being transfered from port to hatch on boat). Up to know I have I modelled load using a remote point/force half way between both jibs using the two geometrical surfaces where the wire swivel will be located on the end of each jibs. However, my concern is that does this consider any side loading effects from wire tension, and only considers a vertical load. To this end, I have evaluated potential wire tension loads for certain angles and modelled this as two force boundary conditions at each jib end with component vectors. However, I think this could be over conservative. Can someone please tell me what is the best way to connect the remote load (half way between both jibs) between both jib ends, can I use two longitudinal spring contacts to model the marine wire rope and input appropriate stiffness? I have done this already and results seem reasonable, but is this a sound approach or is there a better way to do this? Thanks 

 

[peteroznewman]

Please reply with an image of the jib cranes, the cargo and lines to show all the wires.

[eagleaero1]

 

 

See attached, there are two more wires going to each winch on the underside of each jib, and likely more depending upon how end user attaches load. I have modelled these using APDL interface separately with link180 elements. But what I am interested in here is the interaction between the load and the sides of both jibs through the wire at the mid point. This is a worst case, in reality the smaller jib is able to swing around towards larger jib before load transfer. What I want to know is this approach transfering the wire tension through the springs to the side of the jibs valid? Deflection seems to indicate so, yet the stress results I get from this approach are much less as opposed to when I model the loads at the jib ends with directional components from hand calculations.

 

 

[peteroznewman]

Stiff springs are a good way to transfer load from one point to another, but two springs meeting at a single node is an unstable configuration since the stiffness for the single node to move laterally in the plane of the two springs is practically zero. If you had three non-coplanar springs, that would be a stable configuration.  You can artificially add stability by adding a Displacement BC to that one node to set the lateral deformation to 0. You may need to create a Coordinate System to define the lateral direction.

The title of that analysis in the image above mentions that Large Deflection is On, which is a requirement to get accurate forces in the springs.