Triangle Wave by Fourier Series*

In the Ansys APDL documentation of Mode-Superposition Harmonic Analysis and other Verification Manual documentation (e.g. VM76 & VM149), 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

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