Learning Forum

[Caterina Azais]

Hi everyone! I am new to ansys and I am trying to simulate a piezoelectric material by applying some pressure and wanting to see the output voltage in mechanical padl. the following is my code but when I get to /POST1 part and try to display the deformed structure using PLDISP1, it will output the following command "The degree of freedom solution is not available. The PLDISP command is ignored." I dont really know how to fix this. Could someone please help me figure out how to solve this and if there are any other issues in my code? thank you very much !

! Geometry
l = 5e-3 ! beam length, m
w = 5e-3 ! electrode width, m
t = 100e-6 ! thickness, m

!Loading
PRES= 1 !pressure loading, Pa

! Material properties
Y = 140e9 ! Young modulus, Pa
mu=0.358 ! Poisson ratio (nearly incompressible rubber)
eps=8.17 ! electrical permittivity, relative
eps0=8.854e-12 ! free-space permittivity, F/m

/VUP,1,z
/VIEW,1,1,1,1


/PREP7
ET, 1, 5, 3

! == Material parameters
! -- Elastic coefficients, MPa
c11 = 209.71e9
c12 = 121.14e9
c13 = 105.36e9
c33 = 210.9e9
c44 = 42.5e9
c66 = 44.28e9

tb,ANEL,1
tbdata, 1, c11, c12, c13
tbdata, 7, c11, c13
tbdata, 12, c33
tbdata, 16, c66
tbdata, 19, c44
tbdata, 21, c44

! -- Piezoelectric coefficients, pC/um2
e13 = -0.61
e33 = 1.14
e15 = -0.59

tb,PIEZ,1
tbdata, 3, e13
tbdata, 6, e13
tbdata, 9, e33
tbdata,14, e15
tbdata,16, e15

! -- Dielectric constants
emunit,EPZRO,8.854e-6 ! pF/um
mp,PERx,1, 7.57
mp,PERy,1, 7.57
mp,PERz,1, 8.31

! -- model and mesh block
block,-l/2,l/2,-w/2,w/2,0,t

! Set the merging tolerance (adjust as needed)
KETOL = 1.0e-5
SMRTSIZE, 8
vmesh,1


! Structural BC - fix the displacement of bottom face
nsel,r,loc,z,0
d,all,uz,0
nsel,all

! Electrical BC
nsel,s,loc,z,0
cp,1,pres,all
ng=ndnext(0) ! ground node

nsel,all
nsel,s,loc,z,t
cp,2,pres,all
nl=ndnext(0) ! load node
nsel,all

/SOLU
antype,static
cnvtol,f,1,1.e-6
cnvtol,amps,1,1.e-6
cnvtol,volts,1,1.e-6

nsel,all
nsel,s,loc,z,t
sfe, all,6,pres ! APPLY PRESSURE LOAD
solve
fini

/POST1
nsel,all
pldisp,1 ! display deformed/undeformed shape
andscl ! animate deformed/undeformed shape
nsel,s,loc,x,l/2
nd=ndnext(0) ! pick node for display
nsel,r,node,,nd
prnsol,epel ! print strain
prnsol,volt ! print voltage
nsel,all
fini

[Erik Kostson]

 

 

 

 

 

Hi

This does not solve that is why.

Before the solve command add (nodes are unselected):

allsel,all,all

Also it is able to move in x and y so add some bc to prevent this movement (u only have BC in z).

For the voltage you need to use volt dof not pres:

! Electrical BC

nsel,s,loc,z,0

cp,1,volt,all

ng=ndnext(0) ! ground node

d,ng,volt,0

 

nsel,all

nsel,s,loc,z,t

cp,2,volt,all

nl=ndnext(0) ! load node

nsel,all

For the load (please see the help manual for all commands):

remove your sfe command and add this instead

sf,all,pres,6E5

Finally I would suggest using Workbench (coupled field static) where the newer solid226 elements are used.

For an example in apdl see :

2.3. Piezoelectric Analysis (ansys.com)

and an example:

VM237 Input Listing (ansys.com)

If you are not able to open the links, refer to this forum discussion: How to access the ANSYS Online Help

Guidelines for Posting on Ansys Learning Forum

Hope that helps

 

 

All the best

Erik

 

 

 

 

 

[Caterina Azais]

Dear Erik,

Thank you so much for your help, I have modified the boundary conditions to look as follows

! Structural BC

nsel,s,loc,z,0

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

d, all, uz, 0

d, all, uy, 0

d, all, ux, 0

nsel,all

 

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

d, all, uy, 0

d, all, ux, 0

nsel,all

 

! Electrical BC

nsel,s,loc,z,0

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

cp,1,volt,all

ng=ndnext(0) ! ground node

d,ng,volt,0

 

nsel,all

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

cp,2,volt,all

nl=ndnext(0) ! load node

nsel,all

 

/SOLU

antype,static

cnvtol,f,1,1.e-6

cnvtol,amps,1,1.e-6

cnvtol,volts,1,1.e-6

 

nsel,all

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

sf,all,PRES,0 ! APPLY PRESSURE LOAD

and added the comment you suggested before the /solve, however I am still unable to solve the problem. I will paste below the whole code. I am still unable to display the pldisp,1 command. Where do you think I am going wrong? Thank youuuuuuu :) 

! Geometry

l=5e-3 ! beam length, m

w=5e-3 ! electrode width, m

t=100e-9 ! thickness, m

 

!Loading

PRES=1 !pressure loading, Pa 

 

! Material properties

Y=140e9 ! Young modulus, Pa

mu=0.358 ! Poisson ratio (nearly incompressible rubber)

eps=8.17 ! electrical permittivity, relative

eps0=8.854e-12 ! free-space permittivity, F/m

 

/VUP,1,z

/VIEW,1,1,1,1

 

 

/PREP7

ET, 1, 5, 3

 

! == Material parameters

! -- Elastic coefficients, MPa

c11 = 209.71e9

c12 = 121.14e9

c13 = 105.36e9

c33 = 210.9e9

c44 = 42.5e9

c66 = 44.28e9

 

tb,ANEL,1

tbdata, 1, c11, c12, c13

tbdata, 7, c11, c13

tbdata, 12, c33

tbdata, 16, c66

tbdata, 19, c44

tbdata, 21, c44

 

! -- Piezoelectric coefficients, pC/um2

e13 = -0.61

e33 = 1.14

e15 = -0.59

 

tb,PIEZ,1

tbdata, 3, e13

tbdata, 6, e13

tbdata, 9, e33

tbdata,14, e15

tbdata,16, e15

 

! -- Dielectric constants

emunit,EPZRO,8.854e-6 ! pF/um

mp,PERx,1, 7.57

mp,PERy,1, 7.57

mp,PERz,1, 8.31

 

! -- model and mesh block

block,-l/2,l/2,-w/2,w/2,0,t

smrtsize, 8

vmesh,1

 

! Structural BC

nsel,s,loc,z,0

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

d, all, uz, 0

d, all, uy, 0

d, all, ux, 0

nsel,all

 

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

d, all, uy, 0

d, all, ux, 0

nsel,all

 

! Electrical BC

nsel,s,loc,z,0

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

cp,1,volt,all

ng=ndnext(0) ! ground node

d,ng,volt,0

 

nsel,all

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

cp,2,volt,all

nl=ndnext(0) ! load node

nsel,all

 

/SOLU

antype,static

cnvtol,f,1,1.e-6

cnvtol,amps,1,1.e-6

cnvtol,volts,1,1.e-6

 

nsel,all

nsel,s,loc,z,t

nsel,r,loc,x,-l/2,l/2

nsel,r,loc,y,-w/2,w/2

sf,all,PRES,0 ! APPLY PRESSURE LOAD

 

sfe, all,6,pres 

solve

fini

 

allsel,all,all

/SOLVE

OUTPR,,LAST

/OUT,SCRATCH

SOLVE

FINISH

 

/POST1 

pldisp,1 ! display deformed/undeformed shape

andscl ! animate deformed/undeformed shape

nsel,s,loc,x,l/2

nd=ndnext(0) ! pick node for display

nsel,r,node,,nd

prnsol,epel ! print strain

prnsol,volt ! print voltage 

nsel,all

fini

 

 

[Caterina Azais]

sorry the allsel, all, all command was added right after the sfe, all, 6, pres but it is still not working. Also I am getting a warning saying that node 256, 267, 258 are both in couple 1 and 2 but i dont know how that is possible ...