弹簧质点的初始位移带来的自由振动

molen

一个应该是非常简单的模型和问题。

两个弹簧两个质点，只有水平自由度，左边固定，右边自由。现在要给右边质点一个初始位移，然后求此位移释放以后的自由振动。

想用direct integration, 怎么做都不行，不收敛？ 还是别的常识错误？ 谁能帮忙看看呢？

*HEADING
** two masses connected by springs in serie.
*NODE, NSET=ALLNodes
1,   0.0,    0, 0
2,   6.0,    0, 0
3,  12.0,   0, 0
*ELEMENT, TYPE=SPRINGA, ELSET=SL
1, 1, 2
*ELEMENT, TYPE=SPRINGA, ELSET=SR
2, 2, 3
*SPRING, ELSET=SL

10000
*SPRING, ELSET=SR

1
*ELEMENT, TYPE=MASS, ELSET=MASS_EL
3, 2
4, 3
*MASS , ELSET=MASS_EL
1
*ELSET, ELSET=ALLSpring
1,2
*BOUNDARY
ALLNodes, 2, 3
1, 1
******************************
**Modal decomposition step
*STEP
*FREQUENCY
2,
*EL PRINT, ELSET=ALLSpring, FREQUENCY=1
S11,E11
*EL FILE, ELSET=ALLSpring
ELEN,
*NODE PRINT, NSET=AllNodes, FREQUENCY=0
U
*OUTPUT,FIELD
*ELEMENT OUTPUT, ELSET=ALLSpring
ELEN,
*NODE OUTPUT, NSET=AllNodes
U
*END STEP
**********************************
**Apply initial displacement step
*STEP, PERTURBATION
*STATIC
*EL PRINT, ELSET=ALLSpring, FREQUENCY=1
S,E
*BOUNDARY, OP=NEW
3, 1, ,  10
*NODE PRINT
U,
RF,
*NODE FILE,NSET=ALLNodes,FREQUENCY=1
U,RF
*OUTPUT,FIELD, FREQUENCY=1
*ELEMENT OUTPUT, ELSET=ALLSpring
ELEN,
ENER,
S,E
*NODE OUTPUT,NSET=ALLNodes
U,
RF,
*OUTPUT,HISTORY,FREQUENCY=1
*NODE OUTPUT,NSET=ALLNodes
U,RF
*END STEP
******************************
*STEP, INC=300
** RELEASE The Displacement, must use CONTINUES=YES for initial

displacement
*DYNAMIC, ALPHA=-0.3, DIRECT
.01,30
*PRINT,FREQUENCY=100
*NODE PRINT,NSET=ALLNodes,FREQUENCY=100
U,
*NODE FILE,NSET=ALLNodes,FREQUENCY=100
U,V,A,RF
*EL FILE,ELSET=ALLSpring,FREQUENCY=100
S,
*EL PRINT,ELSET=ALLSpring,FREQUENCY=100
S,
*OUTPUT,FIELD,FREQUENCY=100
*NODE OUTPUT,NSET=ALLNodes
U,V,A,RF
*ELEMENT OUTPUT,ELSET=ALLSpring
S,
*OUTPUT,HISTORY,FREQUENCY=100
*NODE OUTPUT,NSET=ALLNodes
U,V,A,RF
*ELEMENT OUTPUT,ELSET=ALLSpring
S,
*END STEP

后面是用模态叠加法，似乎正确了，至少似乎成功。能检查一下麽？  大家看direct integration, HHT algorithm, 如何修改呢？  谢谢

*HEADING
** two masses connected by springs in serie.
*NODE, NSET=ALLNodes
1,   0.0,    0, 0
2,   6.0,    0, 0
3,  12.0,   0, 0
*ELEMENT, TYPE=SPRINGA, ELSET=SL
1, 1, 2
*ELEMENT, TYPE=SPRINGA, ELSET=SR
2, 2, 3
*SPRING, ELSET=SL

10000
*SPRING, ELSET=SR

1
*ELEMENT, TYPE=MASS, ELSET=MASS_EL
3, 2
4, 3
*MASS , ELSET=MASS_EL
1
*ELSET, ELSET=ALLSpring
1,2
*BOUNDARY
ALLNodes, 2, 3
1, 1
******************************
**Modal decomposition step
*STEP
*FREQUENCY
2,
*EL PRINT, ELSET=ALLSpring, FREQUENCY=1
S11,E11
*EL FILE, ELSET=ALLSpring
ELEN,
*NODE PRINT, NSET=AllNodes, FREQUENCY=0
U
*OUTPUT,FIELD
*ELEMENT OUTPUT, ELSET=ALLSpring
ELEN,
*NODE OUTPUT, NSET=AllNodes
U
*END STEP
**********************************
**Apply initial displacement step
*STEP, PERTURBATION
*STATIC
*EL PRINT, ELSET=ALLSpring, FREQUENCY=1
S,E
*BOUNDARY, OP=NEW
3, 1, ,  10
*NODE PRINT
U,
RF,
*NODE FILE,NSET=ALLNodes,FREQUENCY=1
U,RF
*OUTPUT,FIELD, FREQUENCY=1
*ELEMENT OUTPUT, ELSET=ALLSpring
ELEN,
ENER,
S,E
*NODE OUTPUT,NSET=ALLNodes
U,
RF,
*OUTPUT,HISTORY,FREQUENCY=1
*NODE OUTPUT,NSET=ALLNodes
U,RF
*END STEP
******************************
*STEP
** RELEASE The Displacement, must use CONTINUES=YES for initial displacement
*MODAL DYNAMIC, CONTINUE=YES
0.02,100.0
*SELECT EIGENMODES, GENERATE
1,2,1
*PRINT,FREQUENCY=100
*NODE PRINT,NSET=ALLNodes,FREQUENCY=100
U,
*NODE FILE,NSET=ALLNodes,FREQUENCY=100
U,V,A,RF
*EL FILE,ELSET=ALLSpring,FREQUENCY=100
S,
*EL PRINT,ELSET=ALLSpring,FREQUENCY=100
S,
*OUTPUT,FIELD,FREQUENCY=100
*NODE OUTPUT,NSET=ALLNodes
U,V,A,RF
*ELEMENT OUTPUT,ELSET=ALLSpring
S,
*OUTPUT,HISTORY,FREQUENCY=100
*NODE OUTPUT,NSET=ALLNodes
U,V,A,RF
*ELEMENT OUTPUT,ELSET=ALLSpring
S,
*END STEP

molen

就是初始位移释放后的自由振动

谁能指点？

如何加初始位移？

我的方法对不对？

为何步收敛？

谢谢