Figure 6: Overlay of the displacement response from reference and predicted solution using first six modes for expansion; (a) response location on the top plate, (d) response location inside the rib. The full-field displacements obtained from using first six modes are used for obtaining dynamic strain solution. This predicted dynamic strain solution (Y normal strain) is shown in comparison with reference strain solution in Figures 7a & 7b with response location at the tip of the box-beam and in the rib of the box-beam respectively. Recall that the force pulse primarily excites the first four modes of the system. Only 14 y (vertical) direction points of a total of 434 finite element model nodes were used as sensor locations measuring vibration displacement response. The strain response is shown for a sample time period of 0.05 seconds. Although the full-field displacements obtained using first six modes provided excellent correlation with reference displacement solution, the full-field strain results obtained after incorporating the six-mode fullfield displacement solution is not as good as expected (Figures 7a &b) because the strain solution is more sensitive than the displacement solution due to the contribution from higher modes. However when the full-field displacement solution obtained from using first ten modes is used to obtain the full-field dynamic stress-strain solution then excellent correlation is seen with reference strain solution as seen in Figures 8a & b. This trend is more prominent for higher strain regions (strain in the rib) as seen from Figures 7b & 8b. Figure 7: Overlay of strain response of box-beam at (a) tip and (b) interior location; predicted solution used first 6 modes in expansion process. 194
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