Dropped object onto mesh

[neilthom]

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

 

[rickfischer51]

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)