#105: How to remove offsets defined on shell and beams?
Method 1: Properties > Modify > GLOBAL
Method 2: Utility > Property > Property Editor
Property Words to Change: 4111 Plate Offset, Only Process If Exists: Check, Action: =, Value: 0
Offsets should not be used for the beam and plate elements in a buckling or nonlinear analysis (or any solution developing differential stiffness). The offset is internally using rigid which makes the differential stiffness wrong (same for plates). However, the action taken for the beam and plate element with offsets is inconsistent. In the case of a beam element, the job terminates with UFM 6174. However, in the case of the plate element, the job continues without any messages. If the offset is much less than the thickness of the plate. In short no offsets are allowed as 1) bad KDIFF, 2) no update.
In case of CBEAMs the offset could be very large and it is difficult in differential stiffness calculation. In QRG under remark 7, its mentioned that “Offset vectors are treated like rigid elements and are therefore subject to
the same limitations.
– Offset vectors are not affected by thermal loads.
– The specification of offset vectors is not recommended in solution sequences that compute differential stiffness because the offset vector remains parallel to its original orientation.
(Differential stiffness is computed in buckling analysis provided in SOLs 105 and 200; SOLs 103 and 107 through 112 with the STATSUB command; and also in nonlinear analysis provided in SOLs 106, 129, 153, and 159 with PARAM,LGDISP,1).
For Composite layers:
The use of PCOMP with Z0 in buckling analysis is not recommended.
Please refer the remark 12 of PCOMP entry in QRG.
“An unsymmetric layup or the use of Z0 to specify an unsymmetric layup, is not recommended in buckling analysis or the calculation of differential stiffness.”
Possible workarounds would be to Avoid Z0 by moving elements and using RBEs. However, if you are using MD Nastran R4 this feature is also included in sol 105 and For nonlinear analysis, the new offset method would be available in SOL 400 only.
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