# * Error* there is at least 1 small equation solver pivot term (eg. VOLT DOF of node 575)

Member Posts: 10
edited April 2021

Greetings,

Facing the error while doing the analysis

Analysis - The copper plate and a magnet are placed adjacent to each other with a certain gap. A velocity is given to the plate (-0.1m/s) and the magnet remains stationary. So, as the plate move, the plate will see a change in a magnetic field by which eddy current will be generated in the plate and due to this current a magnetic field will be generated of opposite polarity as that of the magnet. Due to this generated magnetic field, the magnet experiences a force. I FMAGBC the copper plate and parallel flux as a boundary condition.

In this analysis I have to calculate the eddy current generated in the copper plate and magnetic field generate the magnetic field due eddy current .

Model -

Marcos of the analysis.

fini

/cle

/PREP7

C*************************************************

!Element Table

ET,1,SOLID97

!*

ET,2,SOLID97

!*

KEYOPT,1,1,1

KEYOPT,1,2,1

KEYOPT,1,5,0

!*

KEYOPT,1,1,1

ET,3,SOLID97

!*

KEYOPT,3,1,0

KEYOPT,3,2,0

KEYOPT,3,5,0

!*

!*

KEYOPT,1,1,1

KEYOPT,1,2,1

KEYOPT,1,5,2

!*

KEYOPT,1,1,1

KEYOPT,2,1,0

KEYOPT,2,2,0

KEYOPT,2,5,2

!Real Constant Value

R,1,

RMORE, , , , ,0.1, ,

RMORE, , , , , ,

C**************************************************

!Material Properties

MPTEMP,,,,,,,,

MPTEMP,1,0

MPDATA,MURX,1,,1.2289  ! Permeability of magnet

MPTEMP,,,,,,,,

MPTEMP,1,0

MPDATA,MGXX,1,,

MPDATA,MGYY,1,,

MPDATA,MGZZ,1,,9.26e5  !coercive force of magnet

MPTEMP,,,,,,,,

MPTEMP,1,0

MPDATA,MURX,2,,0.999  ! Permeability of copper plate

MPTEMP,,,,,,,,

MPTEMP,1,0

MPDATA,RSVX,2,,1.72e-8 ! Resistivity of copper plate

MPTEMP,,,,,,,,

MPTEMP,1,0

MPDATA,MURX,3,,1  ! Permeability of air

C************************************************************************************

! Geometry

BLOCK,-0.013,0.013,-0.013,0.013,-0.0025,0.0025, ! copper plate

CYLIND,0.013, ,0.0055,0.0355,0,360,  ! magnet

BLOCK,-0.05,0.05,-0.05,0.05,-0.05,0.05, ! enclosed area

C*********************************************************************

! Overlap, Glue and Numbering Comp operation

FLST,2,3,6,ORDE,2

FITEM,2,1

FITEM,2,-3

VOVLAP,P51X

FLST,2,3,6,ORDE,3

FITEM,2,1

FITEM,2,-2

FITEM,2,4

VGLUE,P51X

NUMCMP,VOLU

C************************************************************************

!Meshing

TYPE,  1

MAT,    2

REAL,    1

ESYS,    0

SECNUM,

!*

MSHAPE,1,3D

MSHKEY,0

!*

CM,_Y,VOLU

VSEL, , , ,    1

CM,_Y1,VOLU

CHKMSH,'VOLU'

CMSEL,S,_Y

!*

VMESH,_Y1

!*

CMDELE,_Y

CMDELE,_Y1

CMDELE,_Y2

!*

TYPE,  2

MAT,    1

REAL,    1

ESYS,    0

SECNUM,

!*

CM,_Y,VOLU

VSEL, , , ,    2

CM,_Y1,VOLU

CHKMSH,'VOLU'

CMSEL,S,_Y

!*

VMESH,_Y1

!*

CMDELE,_Y

CMDELE,_Y1

CMDELE,_Y2

!*

TYPE,  3

MAT,    3

REAL,    1

ESYS,    0

SECNUM,

!*

CM,_Y,VOLU

VSEL, , , ,    3

CM,_Y1,VOLU

CHKMSH,'VOLU'

CMSEL,S,_Y

!*

VMESH,_Y1

!*

CMDELE,_Y

CMDELE,_Y1

CMDELE,_Y2

!*

C****************************************

!Flag copper plate

ALLSEL,ALL

VSEL,S, , ,    1

ESLV,S

CM,A,ELEM

!*

!*

FMAGBC,'A'

FLST,2,6,5,ORDE,2

FITEM,2,11

FITEM,2,-16

DA,P51X,ASYM

ALLSEL,ALL

FINISH

C***********************************************

! Transient Solution

/SOL

!*

ANTYPE,4

!*

TRNOPT,FULL

!*

DELTIM,0.002,0,0

OUTRES,ERASE

OUTRES,ALL,ALL

KBC,0

TIME,0.01

/STATUS,SOLU

SOLVE

Attaching the elements used in the analysis

Element ref 1 - for copper

Element ref 2 - for permanent magnet

Element ref 3 - for air

Error

Note - Some suggested to use SOLID236 element, but there are some papers which have calculated the results by using the SOLID97 even with more complicated model than this (Ex - https://www.scielo.br/scielo.php?pid=S1679-78252016001101997&script=sci_arttext). This is hypothetical model just to calculate the the various parameters, later use this concept for complicated models .

As per the my understanding the problem might in the elements types option or loading

Please suggest if any constrained is not defined or if any change required in the model.

Tagged:

• Posts: 74Ansys Employee

Hi,

See if turning off pivot checking helps. To do this, use the PIVC,OFF command prior to the SOLVE command. I have yet to see a case in which disabling pivot checking causes an erroneous emag solution, so chances are very good it should be OK to do this.

Strictly speaking, the modeled representation of the moving electrically conductive domain (in your case the plate) is supposed to be continuous in the direction of motion for the velocity effect to be valid:

Your modeled representation of the plate appears to have a finite length. If you need it to remain so, try to find a way to validate the results you obtain (e.g., see if the induced eddy currents are normal to the plate boundaries).

Also, depending of the velocity and electrical resistivity of the conductor, the mesh may need to be refined so that the resulting magnetic Reynold's number isn't too high:

Lastly, the nodal based MVP (magnetic vector potential) formulation used by legacy SOLID97 element type can produce erroneously calculated fields on material interfaces between domains that have very different magnetic permeabilities (e.g., "iron" and air). This is due to the fact that the MVP forces the tangential component of B to be continuous on the interface. Physically, there is a discontinuous "jump" in the tangential component of B at such an interface. The edge-flux formulation used by the new technology SOLID236/237 properly addresses the field at such interfaces. If the PM is Neodymium, then it has a permeability that is quite close to that of free space and the error might be acceptably small. If the permeability of the PM is high, you should probably consider using new technology SOLID236/237.

Oh, one additional thing. When using the FMAGSUM command to get the plate force, the forces determined by the virtual displacement method are typically more accurate than those obtained using the Maxwell stress tensor. But more accurate than either of these (as long as the conductive body is not permeable, as is the case for Copper) is a summation of the Lorentz forces. You can select the plate elements and read in the x, y, and z components of FMAG into the element table (these should be the volumetrically distributed Lorentz forces in the plate at element centroids) and use the SSUM command to obtain total values for the selected elements.

I hope this helps,

Best,

Bill

• Posts: 22Member

@wrbulat Thank you! for your guidance .