ABSTRACT
Although a triangle is the simplest of all shapes available for approximating a two-dimensional region, a quadrilateral is, in some ways, a more natural shape. For example, a network of quadrilaterals is generated automatically, at least implicitly, with definition of any x–y coordinate system. An increase in analysis effort, including a discussion of a novel coordinate transformation, is required, but the benefits of a quadrilateral element are well worth the effort as demonstrated in subsequent developments. A square element would be severely limited in applications. When the element shape functions are chosen to be the same as the element interpolation functions, the result is called an isoparametric element. An apparent advantage to an isoparametric formulation is that the shape functions are immediately known, once the interpolation functions are computed. There is no need for additional computation.
