A Simple Noise Analysis Example

The following figure shows the parametric Abaqus/CAE model of a cantilever boss structure. This example (BossNoisy6.9-1.cae) is located in the following directory: <Isight_install_directory>\<operating_system>\examples\models\components\noiseanalysis\

The structure is fixed at the four holes on the vertical plate and is subject to a downward force near the tip of the horizontal plate.

Under this loading condition, as the span of the cantilever is increased, you would expect the maximum stress and displacement in the structure to also increase. However, consider the two line graphs in the following figure showing a noisy response to span increases by maximum stress and displacement outputs. These results put into doubt the validity of this finite element model.

Subsequent analysis of the model reveals that it was created using default C3D4 tetrahedral elements as well as a default mesh seed. It is known that a coarse mesh comprised of C3D4 elements is not suitable for bending loads like those present in this model. If the model is modified to use higher order tetrahedral elements like C3D10 or element types like C3D8I hex elements (which behave well for bending loads), and mesh seeds are refined to provide a sufficient number of elements through the thickness, a more accurate and robust model can be created that eliminates the noise. The corrected model for this example is generated using C3D8I elements with a fine mesh through the thickness.

The maximum stress and displacement versus span for the corrected model is displayed in the following figure. This example (BossCorrect6.9-1.cae) is located in the same directory.

Optimizations using the BossCorrect6.9-1.cae file will perform well, whereas optimizations using the inaccurate BossNoisy6.9-1.cae file could easily become trapped in a local minimum.