Lifting analysis with Ansys Mechanical

[Mateus_R]

Hi everyone.

To perform a lifting analysis of an equipment using Ansys Mechanical, I know two different approaches and I would like your opinion about them:

1) I simulate the cables that will lift the structure as spring elements (body-reference), including the axial stiffness of the designed cable that will be used in this operation. If I have a 4 lifting set, I connect the body side of the spring in the lifting padeye and the reference side of the spring where the masterlink/cranehook is located (considering the design angles).
In my opinion, this approach provides a good understanding about the real operation, but a problem arise when I want to understand the elastic deformations that the structure suffer. Since my "spring cables" can deform, I can't exclude this effect of the simulation and I can't evaluate only the deformations of the structure.
Anyone knows how to exclude the cable deformation effect?

2) Simulate the lifting condition using remote points. In this case I can create a local coordinate system where the masterlink/cranehook is located and attach a Remote Point on it. I'll constrain the model using a remote displacement, selecting the holes of the lifting padeyes as geometry and defining the local coordinate system where the remote point is attached. Later on I can set as free the rotations, limit the translations...
I'm not familiar with the use of Remote Points and how they'll affect the model (I imagine they can affect the stiffness of the elements) and the results. In this case, I can observe only the deformation on the structure and it solves my problem.

What do you think about these 2 approaches? Any pro/cons about them?

Thank you in advance.

 

[FEA way]

You can easily hide and show selected parts/elements using named selections or Hide Body option.

 

[Mateus_R]

I already try to hide the elements, but it doesn't change the overall result of the analysis.

If the cable deforms 10mm and the structure 1mm, in the Total Deformation Plot, the max. deformation will be 10mm, hiding or not the cables/springs.

 

[ldeem]

I suggest being careful about relying on computer results for rigging design. I agree it is very useful and necessary to analyze the item being lifted but consider in a 4 point lift only two slings are likely to carry most of the weight. This is because actual sling lengths in the field will never be exactly the same. Therefore the analysis should be done with only two lift points.

I am not familiar with Ansys but keep in mind wire rope E is not the same as steel. There are many references you can consult but one I use a lot is the old USS manual.

 

[JStephen]

ideem's comment is what I was thinking. You can assume theoretically exact lengths for the slings and get forces associated with their deflections, but that doesn't allow for actual variations in sling length, and details at connecting hardware.

 

[Mateus_R]

Yes, I'm aware of this problem. The point here is to understand which approach could be better --> cables as springs x Remote Points.
Once I understand this, I can perform the analysis considering 2 cables or changing the axial stiffness of one diagonal cable to obtain a higher/lower force at this diagonal... for example.