82 D. Day et al. Fig. 8.7 Cantilever beam: effect of density change on stress-acceleration error relation, selected points and maximum Fig. 8.8 Cantilever beam: effect of length change on stress-acceleration error relation, selected points and maximum at 1374 Hz starts to increase well beyond the input level. These two factors suggest that the changing error relationship in the Point 2 plot of Fig. 8.8 is caused by the influence of the new mode and the increased response of an existing mode. This significant change in modes and frequencies disrupts the initially linear error relation. On the other hand, the response ASD for the modulus perturbations shown in the second plot of Fig. 8.9 demonstrates consistency in the modes and small changes across all 20 simulations, leading to the error relation shown previously in Fig. 8.6. A summary of the range of stress-acceleration error and the error ratios is given in Table 8.1. The range of stress values is also listed for reference. The data presented in the table is for the error in the maximum value at any point in the model. This is distinct from the maximum error for a single point in model, but similar values can also be found at the individual points.
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