求助：悬索模态分析中出现的问题！ - A1. 索膜 - 中华钢结构论坛 China Structure Forum

积分 14
帖子 25

2005-4-20 17:40

我正在做一水平悬索的模态分析。由于我做的悬索上有集中质量点，不加集中质量点时，运行结果正确，可加了集中质量，就出了问题，出现如下错误：
DOF (e.g. Displacement) limit exceeded at time 1
  (load step 1 substep 1 equilibrium iteration 1)
  Max.absolute value= 4.6048E+16 (limit= 1000000) at UY of node 7 .
   May be due to an unrestrained or unstable model.

LSSOLVE looping is stopped because of a solution error.

我是先建link8单元的索模型，再用mass21单元建集中质量点，两者间我用过耦合，刚化，结果都出现如上错误，请高手们指点一下，不胜感激！

Leanfee

积分 14
帖子 25

2005-4-20 17:46

模型中，悬索一段全约束，一段受水平拉力，索中间有集中质量，在模态分析前先进行有预应力的静力分析，此时出现上述错误，请高手们指点一下！

命令流有点乱，我做过很多次了，不过还是附上。
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! /EXIT,NOSAV
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CM,_CERGCM,NODE
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!*
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CMSEL,S,_CERGCM
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CERIG,91,ALL,ALL, , , ,
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!*
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!*
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SAVE
FINISH
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!*
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!*
/GO
DK,P51X, ,0, ,0,ALL, , , , , ,
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!*
/GO
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/COM,ANSYS RELEASE  6.1 UP20020321    15:44:58 04/20/2005
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LSSOLVE,1,3,1,
FINISH
/BATCH
/COM,ANSYS RELEASE  6.1 UP20020321    15:58:12 04/20/2005
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RESUME,3,db,E:\linfei\ansysmulu\jiechuxian\,0,0

bjliu

积分 194
帖子 162

2005-5-6 07:22

  阁下的命令流确实有点乱，我看不了。不过根据你描述的过程，我认为求解出错的原因在于静力分析过程求解不收敛造成的。因为在未加集中质量时，阁下的模型初应力与外载（如自重）自相平衡，结构处于稳定状态，静力求解收敛；而加上集中质量后（计入自重的话），该点出现位移突变超限，造成分析不收敛。要解决该问题，可以这样处理：（1）避免加集中质量的节点位移突变，可以只计入质量，而不将质量产生的重量加在该点（不在该点计入重力），可以在附近区域以加力的方式代替集中质量产生的重力。（2）改变迭代收敛方式，细分荷载步缓慢加载等方式帮助收敛。
  在模态分析中只计入应力刚度即可，不应该会有什么问题。
       mass21可以直接定义在索节点上，不采用耦合，因为耦合中的设置可能会影响模态分析，如BEAM4就有此问题。

Leanfee

积分 14
帖子 25

2005-5-10 10:09

谢谢bjliu兄的帮助！受益匪浅