Conventional shell versus continuum shell

Conventional shell versus continuum shell

Shell elements are used to model structures in which one dimension, the thickness, is significantly smaller than the other dimensions. Conventional shell elements use this condition to discretize a body by defining the geometry at a reference surface. In this case the thickness is defined through the section property definition. Conventional shell elements have displacement and rotational degrees of freedom.( 使用壳单元常常来模拟结构，其中一个维度，即厚度，明显小于其他维度。传统的壳单元利用这个条件，通过在参考面上定义几何形状来离散一个物体。在这种情况下，厚度是通过截面属性定义的。传统的壳体有位移和转动自由度。)

In contrast, continuum shell elements discretize an entire three-dimensional body. The thickness is determined from the element nodal geometry. Continuum shell elements have only displacement degrees of freedom. From a modeling point of view continuum shell elements look like three-dimensional continuum solids, but their kinematic and constitutive behavior is similar to conventional shell elements.( 相反，连续壳单元离散整个三维体。厚度由单元节点几何形状确定。连续壳单元只有位移自由度。从建模的角度看，连续壳单元类似于三维连续体，但其运动学和本构特性与常规壳单元相似。)

The following picture illustrates the differences between a conventional shell and a continuum shell element. 下图说明了传统壳单元和连续壳单元之间的区别。

What calls for special attention is that In large-deformation (geometrically nonlinear) analysis these local directions rotate with the average rotation of the surface at that point.( 需要特别注意的是，在大变形(几何非线性)分析中，这些局部方向随该点表面的平均旋转而旋转)