ansys 热分析中材料温度为什么会先下降？

cat_Tom

最近作一个矩形容器石英坩锅的瞬态升温分析，从室温20度升至出炉温度1100度。接下来想计算它的热膨胀伸长。
单元用solid70，参考温度20度，计算时间30秒，步长0。4秒，结果发现在部分地方材料温度是先下降的，很奇怪。在材料内部和拐角处尤其明显。
后来计算了300秒，材料温度都升上去了，但拐角处仍明显偏低。
请问这是怎么回事？

cat_Tom

!石英坩锅的热分析，从室温20度升至出炉温度1100度
finish
/clear
!
! Part1---predefined scalar parameters计算参数定义
!
! parameters for geometrical dimension
top_width=0.849              !上口外缘边长
top_wall_thickness=0.018           !上口壁厚
bottom_width=0.889           !下口外缘边长
bottom_wall_thickness=0.024        !下口壁厚
height=0.500                 !坩锅高
bottom_thickness=0.021        !坩锅底厚度
inner_wall_radius=0.016       !内缘墙角倒脚半径
outer_wall_radius=0.023       !外缘墙角倒脚半径
inner_bottom_radius=0.017     !内缘底部四周倒脚半径
outer_bottom_wedge=0.014      !外缘底部四周斜倒脚契子尺寸
element_size=0.008
! paramters for material properties
modulus=80e9               !elastic modulus Pa
c_heat=744                 !specific heat   J/kg/K
air_convection=2.5         ! BTU/hr./ft.^2/F
heat_conduct=0.5           !千卡/米/时/K
heat_expansion=0.55e-6       ! /K
density=2.1e3              !Kg/m^3
! paramters for temperatures
prev_temp=1100  !开始温度
room_temp=20    !室温
!
! Part2----preprocessor建立实体模型
!
/PREP7
!***** building keypoints of top
K,1,top_width/2, 0,height
K,2,top_width/2, top_width/2,height
K,3,0, top_width/2,height
K,4,0, (top_width/2-top_wall_thickness),height
K,5,(top_width/2-top_wall_thickness), (top_width/2-top_wall_thickness),height
K,6,(top_width/2-top_wall_thickness), 0,height
!***** building keypoints of inner bottom
K,7,(bottom_width/2-bottom_wall_thickness), 0,bottom_thickness
K,8,(bottom_width/2-bottom_wall_thickness), (bottom_width/2-bottom_wall_thickness),bottom_thickness
K,9,0, (bottom_width/2-bottom_wall_thickness),bottom_thickness
K,10,0, 0,bottom_thickness
!***** building keypoints of outer bottom
K,11,0, 0,0
K,12,0, (bottom_width/2),0
K,13,(bottom_width/2), (bottom_width/2),0
K,14,(bottom_width/2), 0,0
!*****building vertical surface areas that hold the volume
A,5,6,7,8
A,2,3,12,13
A,4,5,8,9
A,1,2,13,14
A,11,10,9,12
A,11,10,7,14
A,1,6,7,14
A,3,4,9,12
!*****building area fillets on inner wall corners
AFILLT, 1, 3, inner_wall_radius
!*****building area fillets on 4 outer wall corners
AFILLT, 2,4, outer_wall_radius
!*****building horizontal surface areas that hold the volume
LSTR,23,27
LSTR,25,29
AL,4,30,23,41
AL,3,4,25,5
AL,5,33,22,44
AL,24,42,16,19,34
AL,1,31,18,21,45
!*****building area fillets on 2 inner floor corners
AFILLT, 11, 14, inner_bottom_radius
AFILLT, 9, 18,inner_bottom_radius
!****画出内缘的空间倒角
!**作辅助面，以便画出空间倒角
K,1001,(bottom_width/2), (bottom_width/2),inner_bottom_radius+bottom_thickness
A,1001,22,34
A,22,28,36
!**形成内缘墙倒角面与水平面的交线，并将倒角面在交线处截止
ASBA, 10, 9
ASBA, 17, 18
ADELE,9,,,1
ADELE,20,,,1
AL,9,11,26
ADELE,5,8,,1
ADELE,1,,,0
ADELE,3,,,0
ADELE,12,,,0
ADELE,15,,,0
!*****生成外缘地板处的斜倒角
KL,-21,(bottom_width/2-outer_bottom_wedge)/(bottom_width/2),37
KL,-18,(bottom_width/2-outer_bottom_wedge)/(bottom_width/2),38
*GET, lenth, line, 14, LENG
KL,-14,(lenth-outer_bottom_wedge)/lenth,39
KL,6,(lenth-outer_bottom_wedge)/lenth,40
KL,43,(lenth-outer_bottom_wedge)/lenth,41
KL,32,(lenth-outer_bottom_wedge)/lenth,42
K,43,kx(41)-outer_bottom_wedge,ky(41),0
K,44,kx(42),ky(42)-outer_bottom_wedge,0
LSTR,37,43
LSTR,38,44
LSTR,39,41
LSTR,40,42
LARC,44,43,37,(outer_wall_radius-outer_bottom_wedge)
LARC,41,42,39,outer_wall_radius
!*****生成地板处的角落
K,45,kx(35),ky(35),0
K,46,kx(36),ky(36),0
K,47,kx(32),ky(32),0
LSTR,45,46
LSTR,46,47
LDELE,6,,,1
LDELE,18,,,1
LDELE,14,,,1
LDELE,21,,,1
LDELE,43,,,1
LDELE,32,,,1
LDELE,45,,,1
LDELE,1,,,1
LDELE,31,,,1
K,11,0,0,0
LSTR,10,11
LSTR,11,45
LSTR,11,47
LSTR,45,37
LSTR,47,38
LSTR,38,40
LSTR,37,39
LSTR,40,3
LSTR,39,1
LSTR,36,46
LSTR,35,45
LSTR,32,47
LSTR,29,41
LSTR,23,42
LSTR,22,42
LSTR,34,41
LSTR,20,39
LSTR,19,40
LSTR,41,43
LSTR,42,44
LSTR,44,46
LSTR,22,44
LSTR,34,43
LSTR,43,46
!*****生成包络体积的面
AL,1,40,35,14
AL,1,6,32,54
AL,18,24,45,10,32
AL,29,22,34,45
AL,20,21,46,7,35
AL,46,28,23,27
AL,29,44,38,12
AL,13,27,30,39
AL,31,17,32,53
AL,31,55,35,19
AL,16,39,3,38
AL,42,26,43,16
AL,37,46,13,42
AL,43,50,45,12
AL,12,47,2,24
AL,13,48,8,21
AL,16,48,15,47
AL,57,2,18,17
AL,17,6,14,19
AL,4,39,42,36
AL,5,38,43,49
AL,51,8,20,19
AL,42,48,52
AL,51,52,11,31
AL,56,43,47
AL,9,56,57,31
AL,15,51,57
!*****生成底板实体
VA,19,3,1,18,17,29
VA,16,2,8,23,30,15
VA,11,13,6,24,31,12
VA,4,20,30,21,31,22
VA,7,26,32,18,10,23,33,34
VA,35,36,24,14,17,28,25,5
VA,9,33,34,36,35,22,27,37
!*  
! element definition
!ET,1,SOLID226,11,1   !**耦合场分析单元
ET,1,SOLID70,0,,0
!*  
! material properties
MPTEMP,,,,,,,,  
MPTEMP,1,0,200,400,600,800,1000
MPTEMP,7,1200  
MPDATA,EX,1,,77.8e9,82.5e9,83e9,84e9,85e9,85e9
MPDATA,EX,1,7,85e9
MP,PRXY,1,0.17   
UIMP,1,REFT,,,room_temp  
MP,ALPX,1,heat_expansion
MP,DENS,1,density
MPDATA,C,1,,0.213*4.2*1000,0.213*4.2*1000,0.23*4.2*1000,0.24*4.2*1000,0.26*4.2*1000,0.273*4.2*1000
MPDATA,C,1,7,0.28*4.2*1000
MPDATA,KXX,1,,0.331*4.2,0.394*4.2,0.367*4.2,0.447*4.2,0.484*4.2,0.514*4.2,0.547*4.2
MPDATA,KXX,1,7,0.581*4.2
ALLSEL,ALL

!*****网格划分
*get,lenth,line,1,leng
LSEL,,,,37
LSEL,A,,,12,13
LSEL,A,,,55
LSEL,A,,,8
LSEL,A,,,19
LSEL,A,,,50
LSEL,A,,,53
LSEL,A,,,17
LSEL,A,,,2
LESIZE,all,,,60
allsel,all
TYPE,1
MAT,1
mshape,0,3D
vmesh,1,4
VADD,5,6,7
TYPE,1
mshape,1,3D
!vmesh,5,7
VMESH,8
!*go,:10
!*****求解
/SOLU
ANTYPE,trans
!*****施加对称边界条件
ASEL,,,,3
ASEL,A,,,5,6
DA,all,SYMM
allsel,all
ASEL,,,,1
ASEL,A,,,7,8
DA,all,SYMM
allsel,all
!*****求解时间步长
TIME,30
DELTIM,0.4,0.4,3
AUTOTS,on
OUTRES,,all
TUNIF,20  !** 起点温度20度
!*****定义对流传热系数
ASEL,,,,9,16
ASEL,A,,,19,21
ASEL,A,,,25,29
ASEL,A,,,32
ASEL,A,,,2
ASEL,A,,,4
ASEL,A,,,37
NSLA,
SF,all,CONV,650,1100
!D,all,TEMP,1100
allsel,all
solve
finish
/POST1
PLNSOL,temp
:10
FINISH

cat_Tom

如何贴图片？

cat_Tom

因对称性，只取了1/4进行分析。图中为30秒的计算结果

panda1981

降温可能是因为对流比生热要快吧，命令太长没看，猜的

cat_Tom

原帖由 panda1981 于 2009-2-9 14:09 发表
降温可能是因为对流比生热要快吧，命令太长没看，猜的

降温是违反常识的，因为周围对流的流体温度是1100度，坩锅的初始温度是20度，怎么可能会降至－20度的低温呢？

xiaoan

从你的命令流看，材料参数随温度变化，产生非线性。非线性求解应该要做一些设置。命令流并无体现。这应该是问题的根源。我也遇到过这种情况。

cat_Tom

问题已经解决。
主要是对流加载加到了节点上，实际上应加到面上。还有就是加载面漏掉了拐角处的3个面。
希望能对其他有类似问题的人提供帮助。

scanzhizhi

问题已经解决。
主要是对流加载加到了节点上，实际上应加到面上。还有就是加载面漏掉了拐角处的3个面。
希望能对其他有类似问题的人提供帮助。
cat_Tom 发表于 2009-2-14 11:27

可是对流加载到面上和节点上有什么区别呢
理论上如何解释？

jiang.yanyuan

有什么区别？