LS-DYNA隐式分析算网壳结构振动模态，结果对比分享

本文以一个球面网壳结构为例，介绍基于LS-DYNA的隐式分析实现结构模态计算的过程。

球面网壳结构球面半径为20.0m，跨度约35m，矢跨比1：3.5，如图1所示。结构所有杆件均采用Φ114.0×4.0的Q235圆形钢管。球面网壳结构的质量应按重力荷载代表值计算，除了结构自重由程序自动计算外，还需要包括其他永久荷载及可变荷载组合值，本例中这部分质量按水平投影面积100kg/m2计算，平均分配到网壳的全部内部节点（共计91个），每个内部节点大约分配附加质量1000kg。约束情况为约束底部周边节点的线位移自由度。

图1 球面网壳的俯视图

可以在Mechanical APDL中采用直接法创建有限元模型，涉及到的单元类型包括BEAM161以及MASS166，具体建模过程从略，建模完成后写出K文件。创建完成后的模型及约束情况如图2所示。

图2 球面网壳计算模型及周边支撑情况

打开关键字文件，在其中添加隐式分析与特征值分析相关的如下关键字：

*CONTROL_TERMINATION

*CONTROL_IMPLICIT_GENERAL

*CONTROL_IMPLICIT_EIGENVALUE

关键字文件修改完成后，递交LS-DYNA求解器进行计算。完成求解后打开计算输出的eigout文件，特征值计算结果（CYCLES列为频率）如图3所示。

图3 特征值计算结果

打开LS-Prepost，按下Ctrl+B快捷键，指向计算路径下的d3eigv文件并打开，按“+”号即可观察各阶振型，每一节振型可通过向前动画播放按钮动画显示和观察。各阶振型的前视图如图4、图5所示。

图4网壳结构振型

图5网壳结构振型（后三阶）

附：本文关键字文件Modal_DYNA.k（单元、节点信息有删减）

*KEYWORD

*TITLE

$

*DATABASE_FORMAT

0

$

$

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ NODE DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*NODE

1 1.732050808E+04 0.000000000E+00 1.000000000E+04 0 0

2 1.627595363E+04 5.923962655E+03 1.000000000E+04 0 0

3 1.326827896E+04 1.113340798E+04 1.000000000E+04 0 0

......

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ SECTION DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*SECTION_BEAM

1 5 1.0000 2.0 1.0

114. 114. 106. 106. 0.00 0.00

$

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ MATERIAL DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

*MAT_ELASTIC

1 0.785E-08 0.206E+06 0.300000 0.0 0.0 0.0

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ PARTS DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

*PART

Part 1 for Mat 1 and Elem Type 1

1 1 1 0 0 0 0

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ ELEMENT DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

*ELEMENT_BEAM

1 1 1 2 200

2 1 2 3 200

3 1 3 4 200

......

*ELEMENT_MASS

307 19 1.000000000E+00

308 20 1.000000000E+00

309 21 1.000000000E+00

......

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ BOUNDARY DEFINITIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*SET_NODE_LIST

1 0.000 0.000 0.000 0.000

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18

*BOUNDARY_SPC_SET

1 0 1 1 1 0 0 0

$

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ CONTROL OPTIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*CONTROL_TERMINATION

0.500E-01 0 0.00000 0.00000 0.00000

*CONTROL_IMPLICIT_GENERAL

1,0.05,2,,2,

*CONTROL_IMPLICIT_EIGENVALUE

6

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ TIME HISTORY $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*DATABASE_BINARY_D3PLOT

0.5000E-03

*DATABASE_BINARY_D3THDT

0.5000E-04

$

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$ DATABASE OPTIONS $

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

$

*DATABASE_EXTENT_BINARY

0 0 3 1 0 0 0 0

0 0 4 0 0 0

*END

作者：尚晓江  仿真秀优秀讲师

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