Learning Forum

[John Miller]

Hello,

I*m trying to model radiation in an AM process in Workbench thermal transient module.

The scripting of the element birth for AM modelling is easy and doesn't make any problems, but the use of surf152 elements for adding radition effect puzzles me a bit.

I'm generating a component of nodes wich are only on the surface (only exterior nodes) of the generated material (red part in the image)

I would like to use this component as basis for the creation of SURF152 Elements:

 cm,external,node

For the creation of surface elements I need to go the /prep7 create the elements and after this go back to /solu

*do,...

....

other code

....

solve

     /prep7
     /GOPR

   *get,nmax,etyp,,num,max
     eakt=nmax+1
    *get,mmax,node,,num,max
     nakt=mmax+1

     et,eakt,surf152       !Surf152 Element
     keyopt,eakt,5,1      !Extra node
     keyopt,eakt,9,1      !Radiation with form factor reale konstant
     keyopt,eakt,11,1    !Node DOF-TTOP
     r,eakt,1,5.8e-8       !Stefan Boltzman konstant
     mp,emis,?,0.5   !Emissivity coefficient
     mat,eakt               !Material
     type,eakt               !Type
     real,eakt

     esel,s,type,,?
     esurf,nakt
     d,nakt,temp,tamb
     alls
     toffst,273
     /solu
     nropt,full

....

...further processing

....

*enddo

I'm struggeling to create the surf152 on top of the exterior nodes, maybe some has a clue to break down this obstacle

 

Greetings

John M.

 

[dlooman]

You need to select the nodes on the surface prior to the esurf, not elements.  A possible way would be to use a named selection for the faces you want to apply the surf152 elements to.  Then cmsel,s,named_selection would select those nodes prior to the esurf command.  The radiation capability in Mechanical would seem to be a better way to model radiation though.  

[John Miller]

Happy New Year,

@Dave Looman, thanks for your answer.

 

I define in the load loop a component, which includes the currently active external nodes of the extruded material:

cm,external,node

 

I’m struggling still with the esurf command:

ESURF, XNODE, Tlab, Shape
Generates elements overlaid on the free faces of selected nodes.

The XNODE definition is not really clear to me.

With your suggestion, I would script the radiation as follows:

*do,…

…

Load

…

/prep7

/GOPR

*get,nmax,etyp,,num,max

     eakt=nmax+1

*get,mmax,node,,num,max

     nakt=mmax+1

 

et,eakt,surf152       !Surf152 Elements

keyopt,eakt,5,1      !Extra nodes

keyopt,eakt,9,1      !Radiation with form factor real constant

keyopt,eakt,11,1    !Nodes DOF-TTOP

r,eakt,1,5.8e-8        !Stefan Boltzman constant

mp,emis,eakt,0.5   !Emissivity coefficient

mat,eakt                  !Material assignment

type,eakt                 !Type assignment

real,eakt

 

cmsel,s,external

esurf,nakt

 

d,nakt,temp,tamb

alls

toffst,273

/solu

nropt,full

…

Load or something else

…

*enddo

 

Is the radiation with this code applied or is something else necessary in the load stage(/solu) after leaving the /prep7 ?

 

Greetings

John M.

[John Miller]

 

 

 

 

[dlooman]

Hi John,  You have have to create the extra node.  Its physical location doesn't matter so it can be at the origin:  n,nakt,0,0,0.  I think if you do that this script will work.  

 

Dave

[John Miller]

 

Hi Dave,

thanks for your support. I added an extra node and some code to delete the surf152 elements of the last step.

I also changed the node selection a little bit to:

cmsel,s,external,nodes     ! Select nodes for esurf
esel,all                               ! Select elements for esurf (including the “external” nodes)
esurf                                  ! Creation of surface elements

it differs from the former version:

cmsel,s,external
esurf,nakt

 

I’m not sure if my current version of nodal and element selection previous to esurf is doing the right thing.

 

The whole script would look like this:

/prep7                                  ! Pre processor
/GOPR

*get,nmax,etyp,,num,max   ! nmax=name of resulting parameter, Entity=etyp aka Element typ,ENTNUM=blank, Item1=num,IT1NUM=max aka maximum number, Item2=blank,IT2NUM=blank
     eakt=nmax+1                 ! maximum element typ number +1
*get,mmax,node,,num,max   ! mmax=name of resulting parameter, Entity=node,ENTNUM=blank, Item1=num,IT1NUM=max aka maximum number, Item2=blank,IT2NUM=blank
     nakt=mmax+1                  ! maximum node number +1

n,nakt,0,0,0                         ! Creation of extra node
et,eakt,surf152                    ! Surf152 Elements
keyopt,eakt,5,1                   ! Extra nodes
keyopt,eakt,9,1                   ! Radiation with form factor real constant
keyopt,eakt,11,1                 ! Nodes DOF-TTOP
r,eakt,1,5.8e-8                    ! Stefan Boltzman constant
mp,emis,eakt,epsilon         ! Emissivity coefficient
mat,eakt                             ! Material assignment
type,eakt                            ! Type assignment
real,eakt                             ! Real constant

esel,s,ename,,surf152       ! Element selection of surf152 elements
cm,ELsurf152,elements     ! Create a component which includes surf152 elements
edele,ELsurf152                ! Deletion of former surf152 elements

cmsel,s,external,nodes     ! Select nodes for esurf
esel,all                               ! Select elements for esurf
esurf                                  ! Creation of surface elements

d,nakt,temp,tamb              ! Temperature of the the extra/space node, Temperature=ambient Temperature
alls
toffst,273                          ! Specifies the temperature offset from absolute zero to zero, 273 for the Celsius system
/solu                                 ! Re-entering the solution

Greetings

John M.

 

[dlooman]

esurf,nakt was correct.  You shouldn't have changed that.  You want esurf to create the surf152 with nakt as their extra node to radiate to.

[John Miller]

 

 

Hi Dave,

thank you very much for your hint regarding esurf command.

With that I would state the radiation like this:

 

*do,…

…

Element ealive

Load application

/prep7

…

esel,s,ename,,surf152        ! Element selection of surf152 elements
cm,ELsurf152,elements     ! Create a component which includes surf152 elements
edele,ELsurf152                ! Deletion of former surf152 elements

 

Does it make sense to erase the surf152 elements? I’m not sure about it.

In every step ot the do loop, elements were activated and thermal load is applied.

Therefore, the external Nodes for radiation application is constantly changing. I would guess that deletion of former surf152 elements is necessary.

Is the position right or should be "outside" in the /solu part of the loop?

 

cmsel,s,external,nodes     ! Select nodes for esurf
esel,all                               ! Select elements for esurf
esurf,nakt                           ! Creation of surface elements

d,nakt,temp,tamb                ! Temperature of the the extra/space node, Temperature=ambient Temperature
alls
toffst,273                             ! Specifies the temperature offset from absolute zero to zero, 273 for the Celsius system

/solu

nropt,full

…

*enddo

 

How can I prove that the script is working? 

Is there a way to visualise the radiation with the aid of /post ?

 

Greetings

John M.

 

 

[dlooman]

A way in APDL POST1 would be to retrieve the heat flow to the space node.  Check the APDL element documentation for other ways to postprocess surf152 results.

/post1

set,last

nsel,s,,,natk

prrsol