Positive normal definition for conventional shell elements

(常規殼單元正法向定義)

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.（在有限元分析中確定單元正法向十分重要，基礎弱的初學者難以準確確定各種單元的正法向，本文梳理了三維傳統殼單元及軸對稱殼單元正法向的確定方法，旨在為讀者提供便利，更進一步亦可以此為基礎可確定單元局部坐標系。）

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.(傳統殼單元的“頂”面是正法線方向的表面，在接觸定義中稱為正(SPOS)面。“底部”表面是沿著法線的負方向，在接觸定義中被稱為負(SNEG)面。指定參考面與殼體中間面的偏移時，正負也用于指定頂面和底面。)

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.(正法線方向定義了通過殼體厚度變化的壓力載荷應用和輸出量的慣例。施加在殼單元上的正壓力載荷產生的載荷作用方向為正法線.)

Three-dimensional conventional shells(三維傳統的殼)

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.(對于空間中的殼層，正法線由右手規則給出，按照元素定義中指定的順序圍繞元素的節點。)

(Positive normals for three-dimensional conventional shells.)

Axisymmetric conventional shells(傳統軸對稱殼)

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.(對于軸對稱的傳統殼體(包括允許非對稱變形的SAXA1n和SAXA2n單元)，正法線方向由從節點1到節點2的方向逆時針旋轉90°定義。)

(Positive normal for conventional axisymmetric shells.)