PSI - Issue 19

Giovanni M. Teixeira et al. / Procedia Structural Integrity 19 (2019) 175–193 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The steady state dynamic analysis produces the frequency responses (generalized displacements) shown on Fig. 25. These signals are combined with the modal stresses and input PSDs (Fig. 17-19) in order to obtain the stress PSDs at every node in the structure, followed by the calculation of the spectral moments and the parameters that compose the probability density functions (Dirlik in this case). The integration of the probability density functions result in damage and life as described on section 4.

Fig. 25. Generalized displacements for the first 10 vibration modes from the steady state dynamics analysis (frequency domain).

The Fatigue lives for the two most critical weld lines (here named Weld1 and Weld2) are shown on Fig. 26. The left contour plot shows the fatigue results from the time domain analysis. The right contour plot shows the fatigue results from the frequency domain analysis. The differences in the results for critical nodes on Weld1 and Weld2 are 10.1% and 4.5% respectively. The number of repeats presented below refers to the number of times the loading block can be repeated until cracks are nucleated at the shown locations. The duration of the loading block is 81.92s.

Fig. 26. Fatigue Life Results from (a) Time Domain and (b) Frequency Domain.