Previously, superlement in Finite Element Analysis is described and a Normal Mode Analysis for a BIW Body-In-White (BIW) Model without superelements is performed and the results are studied. Now Normal Mode Analysis of BIW Model ran with using superelements and the results are compared.
Generation of Superelement:
In this BIW model, say we are interested only to design the center floor component, we can reduce the rest of the model to a super element in GENESIS®. Craig-Bampton modes will be calculated relative to an A-set interface of the BIW model without the center floor. The C-B modes along with statically condensed Constraint modes will be assembled into Matrices [KAA] and [MAA] for the BIW without the center floor. The superelement data will be used for the substructured setup to perform the normal mode analysis. The figure 1 below shows the model to be reduced to a superelement along with the A-set interface grids.
Figure 1. Non designable model for superelement reduction
Normal Mode Analysis of BIW w/Superelement Reduction:
The analysis is performed for the first 15 frequency modes, targeting the frequency range 0-50 Hz on the center floor substructure with the remaining model as a superelement. The figures 2 shows the comparison of tenth mode frequency of the Normal Mode Analysis with & without superlement reduction. Also, the displacement result is same as the analysis without superelement.
Figure 2. Comparison of Tenth mode of car BIW – w/o & w/Superelement reduction
The tables 1 & 2 show the comparison of results & computational time respectively. The results are in good agreement while the analysis computational time is reduced by 12x times.
Table 1. Comparison between BIW and BIW w/Superelement for Normal Mode Analysis
| Table 1. Comparison between BIW and BIW w/Superelement for Normal Mode Analysis | |||
| Mode | Mode BIW (Hz) | Mode BIW w/Superelement (Hz) | Difference |
| 1 | 23.05 | 23.09 | 0.17% |
| 2 | 27.70 | 27.71 | 0.03% |
| 3 | 33.01 | 33.06 | 0.15% |
| 4 | 33.13 | 33.20 | 0.20% |
| 5 | 35.60 | 35.70 | 0.27% |
| 6 | 36.40 | 36.41 | 0.02% |
| 7 | 37.04 | 37.06 | 0.05% |
| 8 | 37.20 | 37.31 | 0.30% |
| 9 | 37.95 | 37.97 | 0.06% |
| 10 | 39.30 | 39.44 | 0.34% |
| 11 | 44.85 | 45.12 | 0.61% |
| 12 | 46.05 | 46.16 | 0.23% |
| 13 | 46.87 | 46.89 | 0.05% |
| 14 | 48.12 | 48.24 | 0.25% |
| 15 | 52.65 | 52.70 | 0.08% |
Table 2. Comparison of Normal Mode Analysis computational time
| BIW Normal Mode Analysis | BIW Normal Mode Analysis w/Superelement | |
| Computational Time (Second) | 24 Seconds | 2 Seconds |
Conclusion: GENESIS® allows easy and quick creation of superelements to perform accurate and faster analysis of large models. The results showed 12x improvement in the analysis time.
Note: Please refer to Genesis® Design Studio example problems SEDSG001- SEDSG005 for detailed steps on creation and usage of superelements for engineering analysis.
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