Learning Forum

[HollyFart]

Hello, I try to implement a moving pressure load with a circle shaped area, which is moving along the Y direction
I failed to take the circle equation into account regarding the apdl script
Is it possible to implement the mentioned restrictions?

[Rohith Patchigolla]

Hi Hollyfart, 

Please clarify, 

Is the pressure within the circle constant (i.e. F/A) or varying based on the X and Y coordinates (i.e. according to the function) based on a co-ordinate system located at the center of circle? Let us ignore the time factor for now. 

Best regards,

Rohith

 

[HollyFart]

Hi rgpatchi,

the pressure within the circle area should be uniform.

It’s simple P=F/A and not dependant on X and Y coordinates.

Best regards

HF

[Rohith Patchigolla]

Hello Holly, 

Thanks for your reply. 

In that case, function approach is not feasible. 

Try the below steps:

0. Create SURF154 elements on the face where you would like to apply this pressure.

1. Divide your simulation into number of load steps, say 10 (more number of load steps --> more resolution of the moving pressure load)

2. At each load step, 

• Create a local cylindrical co-ordinate system at a center of the current circles position. 


• select the SURF154 elements and nodes attached to these elements


• Re-elect nodes in the created cyl co-ordinate system within radius of the circle, using X co-ordinate (radial)


• Re-select SURF154 elements attached to the selected nodes


• Apply Pressure value (calculated based on your equation) to the selected elements 


• Go to next load step

I have pasted a simple script for step 2, you can use for this purpose (to demonstrate the steps - please customize according to your need).

wpcs,-1,0		! WP @ GLOBAL ORIGIN
wpof,,6			! OFFSET WP ALONG ITS Y AXIS (i.e. provide current position of center of circle along Y axis)
cswp,11,1		! DEFINE Cylindrical COORDINATE SYSTEM @ WP ORIGIN
esel,s,ename,,154       ! Select SURF154 elements 
sfed,all,,pres          ! Delete old pressures if any
nsle                    ! Select nodes attached to selected SURF elements
nsel,r,loc,x,0,3        ! Select nodes within radius of circle, say 3 mm
csys,0                  ! Set CSYS back to global
esln,r                  ! Select SURF elements attached to the nodes within the circle
sfe,all,,pres,,1        ! Apply pressure based on your calculation at the said time. You can automate this by some more commands
allsel,all
outres,all,all

Hope this helps. 

Please let me know if you have any other questions. 

Best regards,

Rohith

[HollyFart]

Hallo Rohith,

thank you very much for your solution post.

It’s really helpful!, but I’m not really sure how to implement SURF154 Elements on the part surface.

Can it be done by defining named component or should I use an APDL snippet to achieve this?

Like:

et,matid,154

Best regards,

HF

[Rohith Patchigolla]

Hi Holly, 

Are you using Workbench or ANSYS Classic?

Best regards,

Rohith

[HollyFart]

Hi Rohith,

I use Ansys Workbench 16 and I'm quite familiar with the use of APDL command snippets.

Best regards

 

HF

[Rohith Patchigolla]

Hi Holly, 

Thanks for the clarification. 

You can ofcourse create SURF154 elements on a surface, by selecting nodes of the surface (by selecting the face named selection via CMSEL command) and use ESURF command to create the elements. 

But, easier option would be to simply, create a dummy pressure load via GUI in Mechanical on the face, with a very low pressure value, say 1e-8. 

This will create the elements for you, and then you can simply select these elements in the script I suggested. 

Also, when you have multiple pressure loads in your model, multiple SURF154 (with different type numbers) will be created. So, care is to be taken to select correct set of SURF154 elements via Type number, i.e. ESEL,S,TYPE,, instead of ESEL,S,NAME,,154 as I suggested before.

Hope this helps. 

Best regards,

Rohith

[HollyFart]

Hi Rohith,

 

I'm making progress but it's still not working

I’m struggling with the ESURF command

Best regards,

HF.

 

[Rohith Patchigolla]

Hi Holly, 

Please try below commands in the command object, corresponding only to Step 1. 

/prep7                          ! Enter into /prep7 as ET and ESURF are valid only in /PREP7
et,100,154                      ! Create a new element type for SURF154     			
cmsel,s,surface1		! Select nodes on a face via Face named selection
type,100                        ! Set the element type as 100
esurf                           ! Create surface effect elements on the selected nodes
allsel,all                      ! Select everything back  
/solu                           ! Re-enter /SOLU

Hope this helps. 

Best regards,
Rohith

[HollyFart]

Hi Rohith,

thank you very much for your help. It’s perfectly working.

Best regards,

HF

[HollyFart]

Hi Rohith,

I’m trying to implement the pressure load via do loop.

Something isn’t working, I’m missing something.

The command script is:

total_time = 10                   ! Total simulation time in seconds

time_steps = 100                  ! Total amount of steps

time_inc = total_time/time_steps  ! Time increment in seconds

V_p = 0.01                        ! m/s Load velocity

Radius = 0.005                    ! m   Radius of the load area

PV = 1E04                         ! Pa  Load value

X_GESAMT= 0.1                     ! m  Workpiece length                        

 

*do,i,1,time_steps,1

 

 nsub,1

 time=i*time_inc

 

 wpcs,-1,0               ! WP @ GLOBAL ORIGIN

 wpof,,V_p*time          ! OFFSET WP ALONG ITS Y AXIS (i.e. provide current position of center of circle along Y axis)

 cswp,11,1               ! DEFINE Cylindrical COORDINATE SYSTEM @ WP ORIGIN

 esel,s,ename,,154       ! Select SURF154 elements 

 sfed,all,,pres          ! Delete old pressures if any

 nsle                    ! Select nodes attached to selected SURF elements

 nsel,r,loc,x,Radius     ! Select nodes within radius of circle, 0.005m

 csys,0                  ! Set CSYS back to global

 esln,r                  ! Select SURF elements attached to the nodes within the circle

 sfe,all,,pres,,PV       ! Apply pressure based on your calculation at the said time. 

 allsel,all

 outres,all,all

 

*if,i,EQ,1,THEN

 

 /prep7                          ! Enter into /prep7 as ET and ESURF are valid only in /PREP7

 et,100,154                      ! Create a new element type for SURF154                

 cmsel,s,surface1                ! Select nodes on a face via Face named selection

 type,100                        ! Set the element type as 100

 esurf                           ! Create surface effect elements on the selected nodes

 allsel,all                      ! Select everything back  

 /solu     

 

 nsub,1

 time=i*time_inc

 

 wpcs,-1,0               ! WP @ GLOBAL ORIGIN

 wpof,,V_p*time          ! OFFSET WP ALONG ITS Y AXIS (i.e. provide current position of center of circle along Y axis)

 cswp,11,1               ! DEFINE Cylindrical COORDINATE SYSTEM @ WP ORIGIN

 esel,s,ename,,154       ! Select SURF154 elements 

 sfed,all,,pres          ! Delete old pressures if any

 nsle                    ! Select nodes attached to selected SURF elements

 nsel,r,loc,x,Radius     ! Select nodes within radius of circle, 0.005m

 csys,0                  ! Set CSYS back to global

 esln,r                  ! Select SURF elements attached to the nodes within the circle

 sfe,all,,pres,,PV       ! Apply pressure based on your calculation at the said time. 

 allsel,all

 outres,all,all

 

*else

 

 nsub,1

 time=i*time_inc

 

 wpcs,-1,0               ! WP @ GLOBAL ORIGIN

 wpof,,V_p*time          ! OFFSET WP ALONG ITS Y AXIS (i.e. provide current position of center of circle along Y axis)

 cswp,11,1               ! DEFINE Cylindrical COORDINATE SYSTEM @ WP ORIGIN

 esel,s,ename,,154       ! Select SURF154 elements 

 sfed,all,,pres          ! Delete old pressures if any

 nsle                    ! Select nodes attached to selected SURF elements

 nsel,r,loc,x,Radius     ! Select nodes within radius of circle, 0.005m

 csys,0                  ! Set CSYS back to global

 esln,r                  ! Select SURF elements attached to the nodes within the circle

 sfe,all,,pres,,PV       ! Apply pressure based on your calculation at the said time. 

 allsel,all

 outres,all,all

 

*endif

*enddo

 

Best regards,

HF

[SteBir]

You can find a very helpful tutorial, which explains everything in detail.

https://www.youtube.com/watch?v=dteRMtuXjdk