ANSYS Mechanical-APDL Harmonic Analysis Example and ...

1 ANSYS Mechanical-APDL Harmonic Analysis Example and Comparison to ANSYS Mechanical resultsDave JohnsonPenn State Erie9/11/20171 Disk modal and Harmonic analyses Steel disk - 75 mm radius and 3mm radius center hole, and mm thickness9/11/2017 1421 SHELL 181 elements Modulus = 200,000 Mpa Poisson s Ratio = Density = tonnes/mm3 TOTAL MASS: (tonne) Support: simply-supported, (no translation: UX = UY = UZ = 0) at the edge of the hole2 Hand calc for verification and validation of modal Analysis resultsReference: Mark s Standard Handbook for Mechanical Engineers, 8th ed., p. 5-75 For a flat circular plate constrained at the center, the umbrella mode (zero nodal diameters) is predicted by:9/11/2017 Where: E = elastic modulus (N/mm2) r = plate radius (mm) g = gravity acceleration (mm/s2) = Poisson s ratio t = plate thickness (mm)3 Hand calc for verification and validation of modal Analysis results** FREQUENCIES FROM BLOCK LANCZOS ITERATION **MODE FREQUENCY (HERTZ)FREQUENCY RANGE REQUESTED= ~ differenceHand calc vs.

2 FEA4 Modal Analysis Results** FREQUENCIES FROM BLOCK LANCZOS ITERATION **MODE FREQUENCY (HERTZ)FREQUENCY RANGE REQUESTED= the frequency range of interest, we observe 14 modes: 31 < fn< 497 Hz5 Harmonic Analysis Setup Method: Mode Superposition Load (1 N) on keypointin z-direction at edge (at 3 o clock position) use all (14) modes from 0 to 500 Hz,solve 100 substeps damping ratio (minimal, structural value) perform an expansionpass after the Harmonic Analysis solution9/11/20176 Harmonic Analysis ResultsZ-deformation at node where the Harmonic load is applied Linear vs.

3 Log ?9/11/20177 Note: the Mode Superposition Solutionused 14 modes (in range 0 500 Hz), andmax. amplitude ( mm) occurred @ 30 HzHarmonic Analysis Results -2 Use modes from twicethe range of interest, , 0 1000 Hz (26 modes were found)9/11/20178 Note: the Mode Superposition Solutionused 26 modes (in range 0 500 Hz), andmax. amplitude ( mm) occured@ 30 HzHarmonic Analysis Results -3 Used the FULL Method, not Mode Superposition9/11/20179 Note: the FULL Method Solution, maximumamplitude ( mm) occurred @ 30 HzANSYS Mechanical ComparisonModal linked to Harmonic (B-C) vs. Harmonic (D & E)9/11/2017 Structural Steel properties from WB librarySame geometry, constraint, and loadingSimilar mesh: 1433/1422 SHELL181 elementsTOTAL MASS = (tonne)[same as ANSYS Mechanical APDL model]10 ANSYS Mechanical Comparison9/11/2017 Modal linked to Harmonic (B-C) vs.

4 Harmonic (D & E)11(Split to make vertex for loading) ANSYS Mechanical ComparisonModal linked to Harmonic (Schematic Objects B-C)9/11/201712 Compared to ANSYS Mechanical APDL Results:** FREQUENCIES FROM BLOCK LANCZOS ITERATION **MODE FREQUENCY (HERTZ)FREQUENCY RANGE REQUESTED= Mechanical ComparisonModal linked to Harmonic (Schematic Objects B-C)9/11/201713 Note: (default) uses log scale for Amplitude,Solution used 14 modes (in range 0 500 Hz),and max. amplitude (18 mm) occurs @ 30 HzANSYS Mechanical ComparisonHarmonic without Modal (Schematic Object D)9/11/201714 Note: (default) uses log scale for Amplitude,Solution used 26 modes (in range 0 1000 Hz),and max.

5 Amplitude (26 mm) occurs @ 35 HzANSYS Mechanical ComparisonHarmonic without Modal (Schematic Object E) using FULL Method9/11/201715 NOTE: different damping input under Analysis Settings ( = 11 and = 2e-5) see next slide, and max. amplitude ( mm) occurs @ 30 HzFull Harmonic , Damping InputFor this Example :9/11/201716 From ANSYS Help > Mechanical APDL >Structural Analysis Guide > Alpha & Beta Damping (Rayleigh Damping)Comparing Results9/11/201717 Comparing Results9/11/201718 Comparing ResultsMaximum Response occurs at 30 or 35 Hz and the Next Highest Response occurs at 80 Hz9/11/201719 Conclusions/Observations Mechanical (WB) default method for Harmonic Analysis is Mode Superposition.

6 The ANSYS default method is Full Mechanical (WB), Harmonic Analysis without linked Modal Analysis , uses 2x the user-requested frequency range, , requested 0 500 Hz, and WB used modes from 0 1000 Hz Mechanical (WB), default Frequency Response plot format uses a log scale for the y-axis (for the Amplitude)9/11/201720 Conclusions/ObservationsWhy ? Does the Full Method show higher max. values, in general ? Is Mechanical MSUP-26 max. value at 35 Hz ? Should we care about variations at higher frequencies where the amplitude is much less ?9/11/201721finish /clear /PREP7 ET,1,SHELL181 ! use 3D 4-node thin shell element !* MPTEMP,,,,,,,, MPTEMP,1,0 MPDATA,EX,1,,200000 !

7 Modulus in MPa MPDATA,PRXY,1,, ! Poisson's ratio MPTEMP,,,,,,,, MPTEMP,1,0 MPDATA,DENS,1,, ! density in tonnes/mm^3 sect,1,shell,, secdata, ,1, ,3 ! shell thickness mm secoffset,MID seccontrol,,,, , , , PCIRC,75,3,0,360, ! 75 mm outer radius, 3 mm radius center hole SMRT,6 ! Smart size for meshing ESIZE,5,0, ! Global element size MSHAPE,0,2D ! MSHKEY,0 ! allow "free" meshing !* AMESH,all ! create the mesh FINISH /SOLU ANTYPE,2 ! Modal Analysis MODOPT,LANB,50 ! use (default) Block Lanczos method EQSLV,SPAR MXPAND,50, , ,0 ! extract & expand up to 50 modes LUMPM,0 PSTRES,0 !

8 * MODOPT,LANB,50,0,500, ,OFFbv ! frequency range 0 - 500 Hz lsel,s,,,5,8,1 DL,all, ,UX, ! constraints on edge of hole DL,all, ,UY, DL,all, ,UZ, lsel,all solve save,disk_modal,db finish /POST1 set,list finish /SOLU ANTYPE,3 ! Harmonic Analysis !* HROPT,MSUP, , ,0 ! Mode Superposition Method HROUT,ON LUMPM,0 !* HROPT,MSUP,14,1,0 ! use (all) 14 modes from modal Analysis HROUT,ON,OFF,0 !* FK,1,FZ,1, ! Harmonic load amplitude HARFRQ,0,500, ! Frequency range NSUBST,100, ! substep thru freq range KBC,1 ! step change boundary conditions !* ALPHAD,0, BETAD,0, DMPRAT, , ! 3% damping ratio DMPSTR,0, MDAMP,1, , , , , , , !

9 * solve finish save,disk_harmonic,db /SOLU !* EXPASS,1 ! Harmonic Analysis Expansion Pass NUMEXP,ALL,0,500,1 ! Frequency range HREXP,ALL, !* SOLVE /POST26 ! Time History Postprocessor *GET,nn,KP,1,ATTR,NODE NSOL,2,nn,U,Z, !* LINES,200 PRCPLX,1 ! print Amplitude/Phase vs. Real/Imaginary results /AXLAB,Y,UZ Deformation (mm) /title, disk Harmonic Analysis - w/linear y-axis (default) plvar,2 prvar,2 /GROPT,LOGY,ON /title, disk Harmonic Analysis - w/log y-axis to match WB plvar,2