Engineering topics

Vandegrift, R. E.

Publications and source records attributed to Vandegrift, R. E..

3 records

NASA NTRS1986

Improved isoparametric solid and membrane elements

Improvements that were made to the COSMIC NASTRAN elements CIHEX1 and QDMEM1 are described. These elements are isoparametric representations of solid and membrane elastic behavior. Recent papers by the authors have shown the official COSMIC versions of these elements to be inferior to those available in the MacNeal-Schwendler Corporation (MSC) version of NASTRAN in that they are overly stiff for some loadings. Modifications were made to these elements which reduce the order of integration for shear terms and, for the eight-mode solid element, add additional strain functions. The resulting element formulations give behavior similar to that of the MSC elements. The changes made in the element formulations are discussed and results of test problems are compared with results from the official COSMIC elements and with the MSC elements.

Case, W. R.↗

NASA NTRS1985

Improved accuracy in solid isoparametric elements using selectively reduced integration

Currently COSMIC NASTRAN uses the same Gaussian integration order for every term in the stiffness matrix of the solid isoparametric elements. This results in overly stiff elements under some conditions. A modification to the CIHEXI, CIHEX2 and CIHEX3 elements is described which provides the user with the capability of controlling the order of integration for selected terms in the stiffness matrix. Examples of improved accuracy using selectively reduced integration be provided are provided.

Case, W. R.↗

NASA NTRS1984

Accuracy of Three Dimensional Solid Finite Elements

The results of a study to determine the accuracy of the three dimensional solid elements available in NASTRAN for predicting displacements is presented. Of particular interest in the study is determining how to effectively use solid elements in analyzing thick optical mirrors, as might exist in a large telescope. Surface deformations due to thermal and gravity loading can be significant contributors to the determination of the overall optical quality of a telescope. The study investigates most of the solid elements currently available in either COSMIC or MSC NASTRAN. Error bounds as a function of mesh refinement and element aspect ratios are addressed. It is shown that the MSC solid elements are, in general, more accurate than their COSMIC NASTRAN counterparts due to the specialized numerical integration used. In addition, the MSC elements appear to be more economical to use on the DEC VAX 11/780 computer.

Case, W. R.↗