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The geometric and kinematic properties of the element are described, along with development of the matrices and vectors which characterize the element. The necessity for considering small deviations from element planeness is discussed, and the approach taken to account for these deviations is described. The improved accuracy over the existing quadr

Autor: NASA Technical Reports Server (NTRS)

Fuente: https://archive.org/


Introducción



AN ISOPARA,bBTRIC QUADRILATERAL MEBBRANE ELESIENT FOR NASTRAN BY Howard M.
Adelman, Joseph E.
Walz, and James L.
Rogers, Jr. NASA Langley Research Center SUMMARY T h i s paper describes t h e implementation of an improved quadrilateral membrane element i n NASTRELN. Descriptions of t h e geometrical and kinematic properties of t h e element a r e included along w i t h development of t h e matrices and vectors which characterize t h e element. The necessity for considering small deviations from planeness of t h e element i s discussed and the approach taken t o account f o r these deviations f o r the new element i s described. The improved accuracy available from t h e element over t h e e x i s t i n g quadrilateral membrane i s indicated by a sample calculation for which an a n a l y t i c a l solution i s available from beam theory. For t h e same f i n i t e element idealization, t h e errors i n maximum displacement and s t r e s s were s i g n i f i c a n t l y reduced by t h e use of t h e new element. INTRODUCTION One of the more frequently used elements i n t h e NASTRAN library i s t h e quadrilateral membrane element (CQDMEM) . T h i s element i s used t o represent portions of structures f o r which membrane action constitutes t h e predominant contribution t o t h e s t r a i n energy. the s k i n of a i r c r a f t wings. An example of one such application i s t o In addition, t h e quadrilateral membrane element i s also used i n conjunction w i t h t h e quadrilateral bending element (CQDPLT) t o form the membrane-bending elements CQUADl and CQUAD2 needed t o represent more general deformation behavior. The quadrilateral membrane element currently available i n NASTRAN i s composed of overlapping constant strain t r i a n g l e s as described i n reference 1.
It has been reported t h a t the CQDMEM element does not accurately represent problems involving high stress gradients, suggesting t h a t t h e current element needs impr...






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