Beam188
3维线性有限应变梁单元
Beam188单元描述
Beam188单元适合于分析从细长到中等粗短的梁结构，该单元基于铁木辛哥梁结构理论，并考虑了剪切变形的影响。
Beam188是三维线性（2节点）或者二次梁单元。每个节点有六个或者七个自由度，自由度的个数取决于KEYOPT(1)的值。当KEYOPT(1)＝0（缺省）时，每个节点有六个自由度；节点坐标系的x、y、z方向的平动和绕x、y、z轴的转动。当KEYOPT(1)=1时，每个节点有七个自由度，这时引入了第七个自由度（横截面的翘曲）。这个单元非常适合线性、大角度转动和/并非线性大应变问题。
当NLGEOM打开的时候，beam188的应力刚化，在任何分析中都是缺省项。应力强化选项使本单元能分析弯曲、横向及扭转稳定问题（用弧长法）分析特征值屈曲和塌陷）。
Beam188/beam189可以采用sectype、secdata、secoffset、secwrite及secread定义横截面。本单元支持弹性、蠕变及素性模型（不考虑横截面子模型）。这种单元类型的截面可以是不同材料组成的组和截面。
Beam188从6.0版本开始忽略任何实参数，参考seccontrols命令来定义横向剪切刚度和附加质量。
单元坐标系统（/psymb，esys）与beam188单元无关。
下图是单元几何示意图：
BEAM188输入数据
The geometry, node locations, and coordinate system for this element are shown in Figure 188.1: "BEAM188 Geometry". BEAM188 is defined by nodes I and J in the global coordinate system.
该单元的几何形状、节点位置、坐标体系如图“BEAM Geometry”所示，beam188由整体坐标系的节点i和j定义。
Node K is a preferred way to define the orientation of the element. For information about orientation nodes and beam meshing, see Generating a Beam Mesh With Orientation Nodes in the ANSYS Modeling and Meshing Guide. See the LMESH and LATT command descriptions for details on generating the K node automatically.
节点K是定义单元方向的所选方式，有关方向节点和梁的网格划分的信息可以参见ANSYS Modeling and Meshing Guide中的Generating a Beam Mesh With Orientation Nodes。参考lmesh和latt命令描述可以得到k节点自动生成的详细资料。
BEAM188 may also be defined without the orientation node. In this case, the element x-axis is oriented from node I (end 1) toward node J (end 2). For the two-node option, the default orientation of the element y-axis is automatically calculated to be parallel to the global X-Y plane. For the case where the element is parallel to the global Z-axis (or within a 0.01 percent slope of it), the element y-axis is oriented parallel to the global Y-axis (as shown). For user control of the element orientation about the element x-axis, use the third node option. If both are defined, the third node option takes precedence. The third node (K), if used, defines a plane (with I and J) containing the element x and z-axes (as shown). If this element is used in a large deflection analysis, it should be noted that the location of the third node (K) is used only to initially orient the element.
Beam188可以在没有方向节点的情况下被定义。在这种情况下，单元的x轴方向为i节点指向j节点。对于两节点的情况，默认的y轴方向按平行x－y平面自动计算。对于单元平行与z轴的情况（或者斜度在0.01％以内），单元的y轴的方向平行与整体坐标的y轴（如图）。用第三个节点的选项，用户可以定义单元的x轴方向。如果两者都定义了，那么第三节点的选项优先考虑。第三个节点（K），如果采用的话，将和i、j节点一起定义包含单元x轴和z轴的平面(如图)。如果该单元采用大变形分析，需要注意这个第三号节点紧紧在定义初始单元方向的时候有效。
The beam elements are one-dimensional line elements in space. The cross-section details are provided separately using the SECTYPE and SECDATA commands (see Beam Analysis and Cross Sections in the ANSYS Structural Analysis Guide for details). A section is associated with the
