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Hi @bnret Mike |
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Hello everyone,
currently, I am having trouble sufficiently constraining a model of mine that consists of a large number of bodies. My thought was to use spring elements to slowly transition from a fully fixed support for each body to the bodies just being held by their interactions. Unfortunately, I seem to have misunderstood this concept completely, as I am failing to conduct such an analysis for single tetrahedral element. As far as I understand it, if each node of the element is connected to two grounded nodes with spring elements (and those nodes are not coincidental), rigid body motion should be prevented. This is not the result of my algorithm, as the static analysis fails with a pivot error and the modal analysis shows 0 as the lowest two modal frequencies, thus pointing at rigid body motion. I am very confused by this and I do not see at which point I misunderstood the concept of those spring elements. I am glad for any help/support provided here!
This would be a minimal (not) working example of my problem:
from ansys.mapdl.core import launch_mapdl
mapdl = launch_mapdl(print_com=True)
mapdl.clear()
mapdl.prep7()
mapdl.et(1, 187) # solid
mapdl.mp("EX", 1, 10)
mapdl.mp("NUXY", 1, 0)
mapdl.mp("DENS", 1, 1000)
pos = [[-0.118498779833,0.0674275234342,0.0222713090479],
[-0.120090339784,0.0670430315701,0.0226928617557],
[-0.118498779833,0.0674275234342,0.0237713092938],
[-0.118498779833,0.0684275254607,0.0232713092119],
[-0.119294559809,0.0672352775021,0.0224820854018],
[-0.119294559809,0.0672352775021,0.0232320855248],
[-0.118498779833,0.0674275234342,0.0230213091709],
[-0.118498779833,0.0679275244474,0.0227713091299],
[-0.119294559809,0.0677352785154,0.0229820854838],
[-0.118498779833,0.0679275244474,0.0235213092528]]
for i,p in enumerate(pos):
mapdl.n(i+1,p[0],p[1],p[2])
mapdl.e(1,2,3,4,5,6,7,8)
mapdl.emore(9,10)
mapdl.et(2, "COMBIN14", kop2=0, kop3=0)
mapdl.r(2, 5)
mapdl.type(2)
mapdl.real(2)
for i,p in enumerate(pos):
mapdl.n(11+i,p[0],p[1],p[2]+0.1)
mapdl.d(11+i,"all",0)
mapdl.e(i+1,i+11)
mapdl.allsel()
mapdl.finish()
mapdl.slashsolu()
mapdl.antype("MODAL")
mapdl.modopt("LANB", 6)
#mapdl.mxpand(6, "", "Yes")
mapdl.solve()
mapdl.finish()
mapdl.post1()
output = mapdl.set("LIST")
print(output)
mapdl.exit()
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