Skip to main content

Defining Ansys Superelement SUB File Manually

Photo by  James Owen  on  Unsplash A surprisingly popular blog-post written here is Exporting Stiffness Matrix from Ansys . A sensible follow up question is what can one do with the exported stiffness matrix? In a recent Xansys Forum post, a question was raised on how we can edit the stiffness matrix of a superelement and use it for our model.  An approach presented below is to first create a superelement that has the same number of DOF and nodal location that will serve as a template. An APDL script can then be written to edit the stiffness matrix entries as desired before exporting to a new superelement *.SUB file for use in future models. The self-contained script below demonstrates this.  /prep7 et ,1, 185 mp , ex, 1, 200e3 mp , prxy, 1, 0.33 w = 0.1 ! single element (note nodal locations) n , 1, w, -w, -w n , 2, w, w, -w n , 3, -w, w, -w n , 4, -w, -w, -w n , 5, w, -w, w n , 6, w, w, w n , 7, -w, w, w n , 8, -w, -w, w e , 1, 2, 3, 4, 5, 6, 7, 8 /solu antype , substr     ! analy

Harmonic MSUP Using the Multiple SOLVE Method

Triangle Wave by Fourier Series*

In the Ansys APDL documentation of Mode-Superposition Harmonic Analysis and other Verification Manual documentation (e.g. VM76VM149), only load step file method was described. Personally, I favor Multiple Solve Method instead because you can vary the loads for different frequencies. This could come in handy for different loads at various engine orders or rotating unbalance force. Or say if you have the Fourier coefficients of the periodic force of irregular form (e.g. triangle wave), the steady state response can be computed.

The APDL script below replicates VM183 but uses the Multiple Solve Method. Do let me know if you could recommend ways to improve the script.

Script
!!   Modified from VM183 to use Multiple SOLVE Method
!!   Results should be identical to VM183
! Author: Sze Kwan (Jason) Cheah
! Modified: August 27, 2017
! Disclaimer: Use at own risk!

/PREP7
ANTYPE, MODAL        ! MODE - FREQUENCY ANALYSIS
MODOPT, LANB,2,,,     
ET,1,COMBIN40,,,2    ! UY DOF
R,1,6,,2             ! K1=6 N/M     M1=2 KG
R,2,16,,2            ! K2=16 N/M    M2=2 KG
N,1
N,2,0,1
N,3,0,2
REAL,1
E,1,2
REAL,2
E,2,3
OUTPR,,ALL
D,3,ALL
FINISH

/SOLU    
SOLVE
FINISH

/SOLU
ANTYPE, HARMIC  ! HARMONIC ANALYSIS
HROPT, MSUP     ! MODE SUPERPOSITION
*do, ct, 1, 50
   fnow = 0.1+(1-0.1)/50*ct ! referencing array is alternative
   HARFRQ, fnow
   F, 1, FY, 50 ! force function can be frequency dependent
    ! e.g.  F,1,FY,m*e*(2*3.14159*fnow)**2
   KBC, 1                
   SOLVE
*enddo
FINISH

/SOLU
allsel
expass, on      ! EXPANSION PASS
numexp, all
solve
finish

Comments