ABAQUS AC3D8 Element Quality Assessment
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Transcript ABAQUS AC3D8 Element Quality Assessment
ABAQUS AC3D8R Element
Quality Assessment
By Michael Hubenthal
ABAQUS AC3D8R Element Quality Assessment
Background
AC3D8R is an acoustic element used for
modeling wave propagation in Abaqus Explicit
It can be used to model fluid-structure interaction
behavior
The accuracy of the structural response is
dependent on the accuracy of the fluid mesh
The AC3D8R accuracy can vary with element
shape
Relevant Geometric Characteristics
Element Size
Aspect Ratio
Skew
Orientation
ABAQUS BENCHMARKS MANUAL
Element Verification Concept
Abaqus verification tests look at the first node in a
mesh of ideally shaped elements
This project will perform verification of the AC3D8R
element for geometry that is less than ideal
This project will develop a baseline comparison
using ideal geometry and a known wave
This project will compare the geometric
characteristics to the baseline results
Methodology
Calculate theoretical wave speed in water
Set up the baseline model and develop a known wave to
propagate through the model (triangle wave)
Build and test a fluid mesh with varying aspect ratio
…Methodology
Build and test a fluid mesh with varying mesh density
Build and test a fluid mesh with varying element skew
Build and test a fluid mesh with varying element orientation relative
to wave
Compare results from all the cases
Element Size
1 meter length of fluid
Cube shaped elements
Vary element size only
Element Size Results
Element Size (t=0.00068165sec)
500.00
theoretical
element size 1/4 of baseline
400.00
element size 1/2 of baseline
baseline
element size 2x baseline
Pressure (N/m^2)
300.00
element size 3x baseline
element size 4x baseline
element size 10x baseline
200.00
100.00
0.00
0
0.1
0.2
0.3
0.4
0.5
-100.00
distance (m)
0.6
0.7
0.8
0.9
1
Element Density
1 meter length of fluid
Cube shaped elements
Constant volume
Compare to element size test to consider if multiple elements
affect the results
Element Density Results
(0.0025in x 0.0025in x 0.0025in) elements
(0.005in x 0.005in x 0.005in) elements
5.00E+02
500
density 2x2
4.00E+02
element size 1/2 of
baseline
300
pressure (N/m^2)
pressure (N/m^2)
400
density 4x4
element size 1/4 of baseline
200
100
0
3.00E+02
2.00E+02
1.00E+02
0.00E+00
0.5
0.6
0.7
0.8
-100
0.9
1
0.5
0.6
0.7
0.8
-1.00E+02
distance (in)
distance (in)
0.9
1
Aspect Ratio
1 meter length of fluid
Constant volume
Vary element aspect ratio
Aspect Ratio Results
Aspect Ratio
500
400
Pressure (N/m^2)
300
aspect 1 to 4
aspect 1 to 3
aspect 1 to 2
aspect 2 to 1
aspect 4 to 1
baseline
Theoretical
200
100
0
0
0.1
0.2
0.3
0.4
0.5
-100
distance (m)
0.6
0.7
0.8
0.9
1
Element Skew
1 meter length of fluid
Same number of elements as baseline
Compare to baseline to consider if element skew affects the
results
Element Skew Results
Element Skew (t=0.00068165sec)
500
400
Pressure (N/m^2)
300
5 deg. Skew
15 deg. Skew
30 deg. Skew
45 deg. Skew
Theoretical
baseline
200
100
0
0
0.1
0.2
0.3
0.4
0.5
-100
distance (in)
0.6
0.7
0.8
0.9
1
Element Orientation
1 meter length of fluid
Same number of cube elements as baseline
Compare to baseline to consider if element orientation affects
the results
Element Orientation Results
Element Orientation (t=0.00068165sec)
500.00
theoretical
baseline
orientation
400.00
Pressure (N/m^2)
300.00
200.00
100.00
0.00
0
0.1
0.2
0.3
0.4
0.5
-100.00
distance (m)
0.6
0.7
0.8
0.9
1
Propagation Length
10 meter length of fluid
Same element edge lengths as element size test models
Compare to element size test to consider if element
propagation length affects the results
1 meter
10 meter
Propagation Length Results
Extended Length Propagation (t=0.0068165sec)
500.00
Theoretical
1/2 size baseline-long
1/4 size baseline-long
baseline_long
400.00
Pressure (N/m^2)
300.00
200.00
100.00
0.00
9
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
10
-100.00
Distance (m)
1 meter length
10 meter length
Model
Maximum
Pressure
Accuracy
Maximum
Pressure
Accuracy
Baseline
480.80
96.2%
456.02
91.2%
½ baseline element size
488.30
97.7%
475.46
95.1%
¼ baseline element size
492.67
98.5%
484.52
96.9%
Conclusions
Element length in the direction of wave propagation is the
most important geometric element characteristic
The modeled fluid extent should be minimized to prevent
losses