ANSYS Mechanical-APDL Harmonic Analysis Example and Comparison to ANSYS Mechanical ...

23 Pages·2017·0.65 MB·English

by  David Johnson

ANSYS Mechanical-APDL Harmonic
Analysis Example and Comparison
to ANSYS Mechanical results
Dave Johnson
Penn 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
• 1421 SHELL 181 elements
• Modulus = 200,000 Mpa
• Poisson’s 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
9/11/2017 2
Hand calc for verification and
validation of modal analysis results
Reference: 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:
Where:
• E = elastic modulus (N/mm2)
• r = plate radius (mm)
• g = gravity acceleration (mm/s2)
• ν = Poisson’s ratio
• t = plate thickness (mm)
9/11/2017 3
Hand calc for verification and
validation of modal analysis results
*** FREQUENCIES FROM BLOCK LANCZOS ITERATION ***
MODE FREQUENCY (HERTZ)
FREQUENCY RANGE REQUESTED= 0.00 500.00
1 31.02836452595
2 31.15668930275
3 53.41778877860
4 79.03494598450
~3.2% difference
5 79.04406402341
Hand calc vs. FEA
9/11/2017 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
In the frequency
8 298.3216528279
9 322.7271830757 range of interest, we
10 322.8378280898
observe 14 modes:
11 336.4477549042
12 336.9226420643 31 < f < 497 Hz
n
13 496.8088338095
14 497.0594794059
9/11/2017 5
Harmonic Analysis Setup
• Method: Mode Superposition
• Load (1 N) on keypoint in z-direction at edge (at
3 o’clock 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 Results
Z-deformation at
node where the
harmonic load
is applied
– Linear vs. Log ?
Note: the Mode Superposition Solution
used 14 modes (in range 0 – 500 Hz), and
max. amplitude (27.59 mm) occurred @ 30 Hz
9/11/2017 7
Harmonic Analysis Results - 2
Use modes from twice the range of interest,
i.e., 0 – 1000 Hz (26 modes were found)
Note: the Mode Superposition Solution
used 26 modes (in range 0 – 500 Hz), and
max. amplitude (27.62 mm) occured @ 30 Hz
9/11/2017 8
Harmonic Analysis Results - 3
Used the FULL Method, not Mode Superposition
Note: the FULL Method Solution, maximum
amplitude (33.07 mm) occurred @ 30 Hz
9/11/2017 9
ANSYS Mechanical Comparison
Modal linked to Harmonic (B-C) vs. Harmonic (D & E)
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]
9/11/2017 10