ANSYS Mechanical-APDL Harmonic Analysis Example engr.bd.psu.edu/ansysug/ANSYS M-APDL...

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  • ANSYS Mechanical-APDL Harmonic Analysis Example and Comparison

    to ANSYS Mechanical results

    Dave JohnsonPenn State Erie

    9/11/2017 1

  • Disk modal and harmonic analyses Steel disk - 75 mm radius and 3mm radius

    center hole, and 0.34 mm thickness

    9/11/2017

    1421 SHELL 181 elements Modulus = 200,000 Mpa Poissons Ratio = 0.3 Density = 7.85E-9 tonnes/mm3

    TOTAL MASS: 0.471E-04 (tonne)

    Support: simply-supported, (no translation: UX = UY = UZ = 0) at the edge of the hole

    2

  • Hand calc for verification and validation of modal analysis results

    Reference: Marks 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) = Poissons 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= 0.00 500.001 31.028364525952 31.156689302753 53.417788778604 79.034945984505 79.04406402341

    9/11/2017

    ~3.2% differenceHand calc vs. FEA

    4

  • Modal Analysis Results*** FREQUENCIES FROM BLOCK LANCZOS ITERATION ***

    MODE FREQUENCY (HERTZ)

    FREQUENCY RANGE REQUESTED= 0.00000 500.000

    1 31.02836452595

    2 31.15668930275

    3 53.41778877860

    4 79.03494598450

    5 79.04406402341

    6 183.3880216411

    7 183.4157944991

    8 298.3216528279

    9 322.7271830757

    10 322.8378280898

    11 336.4477549042

    12 336.9226420643

    13 496.8088338095

    14 497.05947940599/11/2017

    In the frequency range of interest, we observe 14 modes: 31 < fn < 497 Hz

    5

  • Harmonic Analysis Setup Method: Mode Superposition Load (1 N) on keypoint in z-direction at edge (at

    3 oclock position) use all (14) modes from 0 to 500 Hz,

    solve 100 substeps 0.03 damping ratio

    (minimal, structural value) perform an expansion

    pass after the harmonic analysis solution

    9/11/2017 6

  • Harmonic Analysis ResultsZ-deformation at

    node where the harmonic load is applied Linear vs. Log ?

    9/11/2017 7

    Note: the Mode Superposition Solutionused 14 modes (in range 0 500 Hz), and

    max. amplitude (27.59 mm) occurred @ 30 Hz

  • Harmonic Analysis Results - 2Use modes from twice the range of interest,

    i.e., 0 1000 Hz (26 modes were found)

    9/11/2017 8

    Note: the Mode Superposition Solutionused 26 modes (in range 0 500 Hz), and

    max. amplitude (27.62 mm) occured @ 30 Hz

  • Harmonic Analysis Results - 3Used the FULL Method, not Mode Superposition

    9/11/2017 9

    Note: the FULL Method Solution, maximumamplitude (33.07 mm) occurred @ 30 Hz

  • ANSYS Mechanical ComparisonModal linked to Harmonic (B-C) vs. Harmonic (D & E)

    9/11/2017

    Structural Steel properties from WB library

    Same geometry, constraint, and loading

    Similar mesh: 1433/1422 SHELL181 elements

    TOTAL MASS = 0.47072E-04 (tonne)

    [same as ANSYS Mechanical APDL model]

    10

  • ANSYS Mechanical Comparison

    9/11/2017

    Modal linked to Harmonic (B-C) vs. Harmonic (D & E)

    11

    (Split to make vertex for loading)

  • ANSYS Mechanical ComparisonModal linked to Harmonic (Schematic Objects B-C)

    9/11/2017 12

    Compared to ANSYS Mechanical APDL Results:*** FREQUENCIES FROM BLOCK LANCZOS ITERATION ***

    MODE FREQUENCY (HERTZ)

    FREQUENCY RANGE REQUESTED= 0.00 500.0

    1 31.02836452595

    2 31.15668930275

    3 53.41778877860

    4 79.03494598450

    5 79.04406402341

    6 183.3880216411

    7 183.4157944991

    8 298.3216528279

    9 322.7271830757

    10 322.8378280898

    11 336.4477549042

    12 336.9226420643

    13 496.8088338095

    14 497.0594794059

  • ANSYS Mechanical ComparisonModal linked to Harmonic (Schematic Objects B-C)

    9/11/2017 13

    Note: (default) uses log scale for Amplitude,Solution used 14 modes (in range 0 500 Hz),and max. amplitude (18 mm) occurs @ 30 Hz

  • ANSYS Mechanical ComparisonHarmonic without Modal (Schematic Object D)

    9/11/2017 14

    Note: (default) uses log scale for Amplitude,Solution used 26 modes (in range 0 1000 Hz),and max. amplitude (26 mm) occurs @ 35 Hz

  • ANSYS Mechanical ComparisonHarmonic without Modal (Schematic Object E)

    using FULL Method

    9/11/2017 15

    NOTE: different damping input under Analysis Settings ( = 11 and = 2e-5) see next slide, and max. amplitude (18.2 mm) occurs @ 30 Hz

  • Full Harmonic, Damping Input

    For this example:

    9/11/2017 16

    From ANSYS Help > Mechanical APDL >Structural Analysis Guide > 1.2.1 Alpha & Beta Damping (Rayleigh Damping)

  • Comparing Results

    9/11/2017 17

  • Comparing Results

    9/11/2017 18

  • Comparing ResultsMaximum Response occurs at 30 or 35 Hz and

    the Next Highest Response occurs at 80 Hz

    9/11/2017 19

  • Conclusions/Observations Mechanical (WB) default method for Harmonic

    Analysis is Mode Superposition. The ANSYS default method is Full

    Mechanical (WB), Harmonic Analysis without linked Modal Analysis, uses 2x the user-requested frequency range, i.e., 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)

    9/11/2017 20

  • 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 ?

    9/11/2017 21

  • finish

    /clear

    /PREP7

    ET,1,SHELL181 ! use 3D 4-node thin shell element

    !*

    MPTEMP,,,,,,,,

    MPTEMP,1,0

    MPDATA,EX,1,,200000 ! modulus in MPa

    MPDATA,PRXY,1,,0.3 ! Poisson's ratio

    MPTEMP,,,,,,,,

    MPTEMP,1,0

    MPDATA,DENS,1,,7.85e-9 ! density in tonnes/mm^3

    sect,1,shell,,

    secdata, 0.34,1,0.0,3 ! shell thickness 0.34 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

    !*

    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,0.03, ! 3% damping ratio

    DMPSTR,0,

    MDAMP,1, , , , , , ,

    !*

    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

    ANSYS M-APDL Harmonic Analysis Example and Comparison to WBANSYS Mechanical-APDL Harmonic Analysis Example and Comparison to ANSYS Mechanical resultsDisk modal and harmonic analysesHand calc for verification and validation of modal analysis resultsHand calc for verification and validation of modal analysis resultsModal Analysis ResultsHarmonic Analysis SetupHarmonic Analysis ResultsHarmonic Analysis Results - 2Harmonic Analysis Results - 3ANSYS Mechanical ComparisonANSYS Mechanical ComparisonANSYS Mechanical ComparisonANSYS Mechanical ComparisonANSYS Mechanical ComparisonANSYS Mechanical ComparisonFull Harmonic, Damping InputComparing ResultsComparing ResultsComparing ResultsMaximum Response occurs at 30 or 35 Hz and the Next Highest Response occurs at 80 HzConclusions/ObservationsConclusions/Observations

    Disk_Input