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lifting the construction

93 REPLIES 93
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Message 1 of 94
mortel09
6062 Views, 93 Replies

lifting the construction

How can i simulate that the construction is getting lifted in robot. The construction i have build is going to be lifted onto an oil rig. how do i simulate this in robot?

93 REPLIES 93
Message 41 of 94
mortel09
in reply to: Artur.Kosakowski

Iam not sure if its okei or not. You can look at the file that i attached earlier. 

Message 42 of 94
Artur.Kosakowski
in reply to: mortel09

I would say that something has to be corrected

 

displ and rot.PNG

 

 

 



Artur Kosakowski
Message 43 of 94
mortel09
in reply to: Artur.Kosakowski

yeah, I see it now. Whats your opinion of what i should do? If i added a Support in node 1 (RX, RY and RZ) i get as good as zero. Would this be the proper way of doing it?

Message 44 of 94
Rafacascudo
in reply to: mortel09

RX,RY and RZ support on node 1 will give significant MX and MY moment reactions on this support. Try putting very soft Ux and Uy springs, like 0.01kN/m on the 4 botton nodes of your model.This will eliminate the instabilities. This solution will be as good as you get closer to ZERO on these X,Y reactions. To achieve that ,your lifting point coordinates (node 71) should be as precise as the CG of the loads on your lifting load case/combination. The lifting case should match this criteria. model attached


Rafael Medeiros
Robot Structural Analysis

Message 45 of 94
thomoh08
in reply to: Rafacascudo

After we put the soft springs in each of the four corners we still get a wierd reading in the displacements bar under node properties. 

 

See attachment.

Message 46 of 94
mortel09
in reply to: thomoh08

I put the springs to 100 kN/m and got rid of the displacements, dont know if thats the best solution. The reactions in the springs is still very low..

Message 47 of 94
Rafacascudo
in reply to: mortel09

as I said before " your lifting point coordinates (node 71) should be as precise as the CG of the loads on your lifting load case/combination"

   This will not work with several load cases.For each load case you should have a unique lifting support type(UX + coordinates) according to the lifting point coordinates.

If the lifting point coordinates doesn´t match the Loads CG , the sum of the cables horizontal components will not be zero and as consequence you´ll get horizontal reactions on the XY supports and large displacements on the structure nodes



Rafael Medeiros
Robot Structural Analysis

Message 48 of 94
ingolfurj
in reply to: mortel09

Hei guys. Just read this thread and found him quite interesting. Now that the problem is probably solved my comment is perheps as useless as a ear on an elbow. But I will shoot anyway.
I just wonderd if modelling the cables, lifting the construction, would work but only modelling them half way to there meeting point ( center of gravity) or so and placing a support there for every cable. Then you would get 4 pin supports, and realistic force distribution in your structure with x, y and z forces acting on the corners....
Message 49 of 94
tony.ridley
in reply to: ingolfurj

hmmmmm my suggestion:

 

download Mortels' model from this thread and try!  Post the results.

 

Tony

Message 50 of 94
ingolfurj
in reply to: tony.ridley

Hei!

Just downloaded the model and playd with it a little.  I did have to place fixed supports at the end og the cables, forcing them to get some moments but placed an release at the connection to the main struture so that the moments wont travel further into the structure.  I have not been using Robot for a long time so this may be total fail but this way I think the axial forces from the cables with there angle towards center of gravity will be taken into account without playing with supports at each corner

Message 51 of 94
ingolfurj
in reply to: ingolfurj

Why am I not able to sent attachements?

Message 52 of 94
mortel09
in reply to: ingolfurj

Have you ziped the file? right click on it and 7-zip it to "filename.zip" Smiley Happy

Message 53 of 94
ingolfurj
in reply to: ingolfurj

Its not working....arrrgggg....I did compress it to .rar file, attached it and when I click on "post" the attachment dissapears and no post sent.  Any Idea what might be the problem?

Message 54 of 94
mortel09
in reply to: ingolfurj

It dos'nt support .rar file. You need to make it a .zip file or any of the other file type that this forum support, see the attachment

 

Message 55 of 94
ingolfurj
in reply to: ingolfurj

Sorry but I still cant send the file.  Maby its the security insallation on my computer.  I will send my model tomorrow. 

But despite of me not being able to send the model, my instict tellls me that modelling the cables instead of manipulatin the supports is the right thing to do.  Why??  because it will take a long time predicing how to define the supports.  How can you place a support in these corners knowing how they will react in reality?????   

 

Message 56 of 94
mortel09
in reply to: ingolfurj

Do you need to modell the cabels? Editing a support dos'nt take much time. adding a support in each corner with only Ux checked i think is the right way. 

Message 57 of 94
ingolfurj
in reply to: mortel09

As I understand this problem, due to angle that the cables will form from the support to senter of gravity there will be axial forces acting on the frames.  Applying a support that only Ux checked you wont be taking these forces into the calculations. And you get warning of unstable constuction.....

So there for I think modelling the cables gives you the correct picture of how this modell will react. 

Message 58 of 94
Jummybear
in reply to: mortel09

The tipoc is still unsolved? I need to calculate similar structure... : )

Message 59 of 94

I have made a test model and tried to iterate the position of the support till the moment the values of bending moments is small enough to be neglected. Basically I started with step a and then I adjusted the support position moving it according to the values obtained from the reactions:

 

x movement = MY / FZ

y movement = MX/ FZ

 

You may want to exclude rods from self-weight loads.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 60 of 94
jo2ny
in reply to: Artur.Kosakowski

Here is a similar lifting problem, but with 2 levels of slings.

Check it out and comment it if you like.

The above suggested approach was used: moved the top support (pinned), then calculation, again moving, again calculation and so on, until minimum dispacements found.

On the base there are 2 UX and 2 UY blocked.

The load case intended for verification is DWNet.

DWLift is DWNet x 2

The other load cases don't quite work, because the loads they apply move the center of gravity somewhere else.

So it would be another equilibrium geometry for each of them.

 

 How close to reality do you consider this model to be?

Download if from here http://www.fileshare.ro/e29427221

Thanks

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