Positive normal definition for conventional shell

Positive normal definition for conventional shell elements

(常规壳单元正法向定义)

In finite element analysis, it is very important to determine the unit the teachings to the weak foundation of difficult to accurately determine the various units of the teachings to the beginners, this article combed the traditional three-dimensional shell element and axisymmetric shell element, and a method for determining the teachings to the aim to provide convenience for readers, further can be based on local coordinate system can be set for unit.（在有限元分析中确定单元正法向十分重要，基础弱的初学者难以准确确定各种单元的正法向，本文梳理了三维传统壳单元及轴对称壳单元正法向的确定方法，旨在为读者提供便利，更进一步亦可以此为基础可确定单元局部坐标系。）

The “top” surface of a conventional shell element is the surface in the positive normal direction and is referred to as the positive (SPOS) face for contact definition. The “bottom” surface is in the negative direction along the normal and is referred to as the negative (SNEG) face for contact definition. Positive and negative are also used to designate top and bottom surfaces when specifying offsets of the reference surface from the shell's midsurface.(传统壳单元的“顶”面是正法线方向的表面，在接触定义中称为正(SPOS)面。“底部”表面是沿着法线的负方向，在接触定义中被称为负(SNEG)面。指定参考面与壳体中间面的偏移时，正负也用于指定顶面和底面。)

The positive normal direction defines the convention for pressure load application and output of quantities that vary through the thickness of the shell. A positive pressure load applied to a shell element produces a load that acts in the direction of the positive normal.(正法线方向定义了通过壳体厚度变化的压力载荷应用和输出量的惯例。施加在壳单元上的正压力载荷产生的载荷作用方向为正法线.)

Three-dimensional conventional shells(三维传统的壳)

For shells in space the positive normal is given by the right-hand rule going around the nodes of the element in the order that they are specified in the element definition.(对于空间中的壳层，正法线由右手规则给出，按照元素定义中指定的顺序围绕元素的节点。)

(Positive normals for three-dimensional conventional shells.)

Axisymmetric conventional shells(传统轴对称壳)

For axisymmetric conventional shells (including the SAXA1n and SAXA2n elements that allow for nonsymmetric deformation) the positive normal direction is defined by a 90° counterclockwise rotation from the direction going from node 1 to node 2.(对于轴对称的传统壳体(包括允许非对称变形的SAXA1n和SAXA2n单元)，正法线方向由从节点1到节点2的方向逆时针旋转90°定义。)

(Positive normal for conventional axisymmetric shells.)