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Dropped object onto mesh

Dropped object onto mesh

Dropped object onto mesh

(OP)
Hi,
Im trying to design a dropped object protection platform for a drillers cabin, on an offshore drilling platform. Ive been told to assume a 2kg object, 200mmx200m area could be dropped onto it from a height of approx 25m. The proposal is to design the frame out of angle sections, with a mesh "pancake" on top - 8mm dia steel bars at 50mm c/c, both directions. My proposal is to determine an impact force and apply this evenly between the 25 No. nodes (50mm c/c over 200mmx200mm = 25 nodes). I will then check the frame as per AISC code checks in STAAD and the i will check the max stress in the mesh; allowing the mesh to go right up to yield. This is a "sacrificial" structure. However, im having trouble ascertaining the impact force the object exerts. I have calculated the potential energy, just before impact in kJ=kNm and i know i shoul then divide this by the deformation in the dropped object and mesh, to turn this into a force?!? The other way i thought i could approach this problem was to determine a plate thickness which is equivalent to the mesh and carry out the dropped object assessment on that eg strain energy, plugging etc?

Any help would be greatly appreciated.

Thanks
Neil

RE: Dropped object onto mesh

If the item being dropped is heavier and/or stiffer than the target, then the equivilent load method is valid. Apply a static load to the item being dropped until the strain energy in your target structure equals the kinetic energy of the dropped object. Using Ansys? Then:

ecount=elmiqr(0,14)
*dim,edata,,ecount,1
esel,s,,,,,,, ! select the target sructure
etable,sene,sene
*vget,edata(1),elem,0,etab,sene
*vscfun,totalse,sum,edata(1)

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