The Computational Structural Mechanics Testbed Structural Element Processor ES5: STAGS Shell Element

摘要

The purpose of this manual is to document the theory behind the CSM Testbed structural finite element processor ES5 for the STAGS shell element. This report is intended both for CSM Testbed users, who would like theoretical background on element types before selecting them for an analysis, as well as for element researchers who are attempting to improve existing elements or to develop entirely new formulations.nProcessor ES5 contains the displacement-based 4-node quadrilateral shell element used as the "workhorse" element in the STAGS code). This C1 element is intended for modeling thin shells for which transverse-shear deformation is not important. The element employs an incompatible displacement field, which features a high-order (cubic) bending field and a semi-lower-order (linear/cubic) membrane field. For many problems with regular geometry, the STAGS 410 element in ES5, called E410, provides rapid convergence not possible with the same number of freedoms in an element where inter-element compatibility is rigidly enforced. However, it does exhibit distortion sensitivity, especially due to in-plane distortion. Sensitivity to out-of-plane distortion (i.e., warping) is largely eliminated by the generic corotational projection operator built-in to the ES processor shell.nThe E410 is a quadrilateral shell element with 3 translational and 3 rotational freedoms per node. This element also has "drilling" rotational stiffness, which proves to be an advantage for problems with intersecting geometries. Hence, no suppression is required for the drilling (i.e., 6th) degree of freedom - even for flat plates - because all 6 nodal freedoms have stiffness.