|
用轴对称单元计算振动模态,不是所有的轴对称单元都能用的,可以参考 ANSYS 帮助中的以下内容:
Axisymmetric Elements with Nonaxisymmetric Loads - 说明又哪些轴对称单元可以进行非轴对称分析及如何进行;
Mode 命令 - 定义用轴对称单元进行非轴对称分析时的轴向谐波数
shell61 - 用于进行非轴对称分析的轴对称简谐壳体单元 (实际上是一个线单元)
VM151 - 一个简支圆盘非轴对称振动的算例,使用 shell61进行计算。
关于 VM151:
其中提供了一个简支圆盘非轴对称振动的算例,使用 shell61进行计算。
圆盘厚度.05, 半径3,弹性模量 30e6, 泊松比 0.3, 密度 0.00073
此例我也算了一下,并使用 shell93 实际算了一个圆盘的例子,两种模型的计算结果列出如下:
按 shell61 计算的频率结果:
轴对称解 (前三阶) 267.67, 1611.5, 4018.9
1个谐波的解 (前三阶) 753.74, 2628.1, 5568.1
2个谐波的解 (前三阶) 1388.9, 3800.2, 7273.5
3个谐波的解 (前三阶) 2166.3, 5122.9, 9131.8
4个谐波的解 (前三阶) 3081.2, 6592.1
5个谐波的解 (前三阶) 4129.7, 8204.3
排列以后,前 6 阶频率为:
267.67, 753.74, 1388.9, 1611.5, 2166.3, 2628.1
按 shell93 计算,前10 阶频率为:
267.60, 752.66, 752.66, 1385.0, 1385.0, 1610.2, 2158.9, 2158.9, 2624.2, 2624.2
二者比较,去掉重复的频率后,显然基本一致。
由此可见,用轴对称单元计算振动模态是完全可以的,只是需要掌握有关的技巧。
不过,我不太主张用轴对称单元计算振动模态,原因是对于非轴对称振动频率,全面的振型显示不出来,不知是否有更好的办法显示。
VM151的命令流如下:
VM151 (Nonaxisymmetric Vibration of a Circular Plate) Input Listing
- /VERIFY,VM151
- /PREP7
- JPGPRF,500,100,1 ! MACRO TO SET PREFS FOR JPEG PLOTS
- /SHOW,JPEG
- /TITLE, VM151, NONAXISYMMETRIC VIBRATION OF A CIRCULAR PLATE
- C*** FORMULAS FOR NATURAL FREQUENCY AND MODE SHAPE, BLEVINS, PAGE 240
- ET,1,SHELL61
- R,1,.05 ! THICKNESS OF PLATE
- MP,EX,1,30E6
- MP,DENS,1,.00073
- MP,PRXY,1,0.3
- K,1
- K,2,3
- L,1,2
- LESIZE,1,,,9
- LMESH,1
- M,ALL,UY
- NSEL,S,LOC,X,0
- D,ALL,UX
- NSEL,S,LOC,X,3 ! SELECT NODE AT R=3 AND CONSTRAIN
- D,ALL,UX,,,,,UY
- NSEL,ALL
- D,ALL,UZ ! CONSTRAIN TORSIONAL DOF'S
- FINISH
- /SOLU
- ANTYPE,MODAL ! MODE FREQUENCY ANALYSIS
- MXPAND,3 ! EXPAND FIRST 3 MODE SHAPES
- MODOPT,REDUC
- OUTPR,BASIC,ALL
- MODE,0 ! ZERO HARMONIC MODE
- SOLVE
- FINISH
- /POST1
- /WINDOW,1,LTOP
- SET,1,1
- PLDISP,1
- /NOERASE
- /WINDOW,1,OFF
- *GET,F1,MODE,0,FREQ
- FINISH
- /SOLU
- MODE,1 ! FIRST HARMONIC MODE
- SOLVE
- FINISH
- /POST1
- /WINDOW,2,RTOP
- SET,1,1
- PLDISP,1
- /WINDOW,2,OFF
- *GET,F2,MODE,1,FREQ
- FINISH
- /SOLU
- MODE,2 ! SECOND HARMONIC MODE
- SOLVE
- FINISH
- /POST1
- /WINDOW,3,BOT
- SET,1,1
- PLDISP,1
- *GET,F3,MODE,1,FREQ
- *STATUS
- *DIM,LABEL,CHAR,3,2
- *DIM,VALUE,,3,3
- LABEL(1,1) = 'F(0,1) ','F(1,1) ','F(1,2) '
- LABEL(1,2) = 'Hz ','Hz ','Hz '
- *VFILL,VALUE(1,1),DATA,269.96,756.13,1391.3
- *VFILL,VALUE(1,2),DATA,F1,F2,F3
- *VFILL,VALUE(1,3),DATA,ABS(F1/269.96),ABS(F2/756.13),ABS(F3/1391.3)
- /COM
- /OUT,vm151,vrt
- /COM,------------------- VM151 RESULTS COMPARISON -------------
- /COM,
- /COM, | TARGET | ANSYS | RATIO
- /COM,
- *VWRITE,LABEL(1,1),LABEL(1,2),VALUE(1,1),VALUE(1,2),VALUE(1,3)
- (1X,A8,A8,' ',F11.2,' ',F11.2,' ',1F6.3)
- /COM,----------------------------------------------------------
- /OUT
- FINISH
- *LIST,vm151,vrt
- ! 整个圆盘计算的命令流
- finish
- /clear,start
- ! /COM,ANSYS RELEASE 5.7 UP20001208 13:28:34 07/18/2003
- /PREP7
- !*
- !*
- ET,1,SHELL93
- !*
- KEYOPT,1,4,0
- KEYOPT,1,5,2
- KEYOPT,1,6,0
- !*
- R,1,0.05,0,0,
- !*
- MPTEMP,,,,,,,,
- MPTEMP,1,0
- MPDATA,EX,1,,30e6
- MPDATA,PRXY,1,,0.3
- MPDATA,DENS,1,,0.00073
- !*
- CYL4, , ,3
- !*
- wpro,,90.000000,
- ASBW, 1
- !*
- wpro,,,-90.000000
- ! o,,-90.000000,
- ! o,,-90.000000,
- !*
- FLST,2,2,5,ORDE,2
- FITEM,2,2
- FITEM,2,-3
- ASBW,P51X
- !*
- LESIZE,ALL,0.25, , , ,1, , ,1,
- !*
- FLST,5,4,5,ORDE,3
- FITEM,5,1
- FITEM,5,4
- FITEM,5,-6
- CM,_Y,AREA
- ASEL, , , ,P51X
- CM,_Y1,AREA
- CHKMSH,'AREA'
- CMSEL,S,_Y
- !*
- MSHKEY,1
- AMESH,_Y1
- MSHKEY,0
- !*
- CMDELE,_Y
- CMDELE,_Y1
- CMDELE,_Y2
- !*
- CSYS,1
- !*
- NROTAT,all
- !*
- FLST,2,160,1,ORDE,8
- FITEM,2,1
- FITEM,2,-41
- FITEM,2,962
- FITEM,2,-1001
- FITEM,2,1882
- FITEM,2,-1921
- FITEM,2,2802
- FITEM,2,-2840
- !*
- /GO
- D,P51X, , , , , ,UX,UY,UZ, , ,
- !*
- D,all, , , , , ,ROTZ, , , , ,
- !*
- FINISH
- /SOLU
- !*
- ANTYPE,MODAL ! MODE FREQUENCY ANALYSIS
- MODOPT,LANB,10
- EQSLV,SPAR
- LUMPM,0
- PSTRES,0
- !*
- MODOPT,LANB,10,0,10000, ,OFF, ,2
- !*
- SOLVE
- !*
- FINISH
- /POST1
- !*
- SET,LIST
- !*
复制代码
|
|