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failure. The first-order reliability assessment of Ship A under its single and double hull configurations
is performed using the hybrid approach in PULSTR. A comparison of PDFs of applied moment (Mopp)
and hull capacity (Mu,,) is shown in Figure 5. Based on 250,000 simulations, a curve-fit CDF model is
developed and used as the user-defined probability distribution of Mu/, in UPCDF (see Fig. 4). Using
PULSTR’s FORM solution module, both the failure probability (Pf) and the reliability index (p, of
Ship A are computed and given by

P, =4.4317xlO-’; p=4.915(SingleHull)
P, = 5.441 7 x IO-’; p= 5.31 13 (Double Hull)

Since the PDF curve of hull capacity of the double hull is shifted along the positive x-axis (see Fig. S),
the resulting probability of failure (P,) is about 8 times less than Pf of the corresponding single hull of
Ship A. The computational efliciency of the hybrid approach can be demonstrated through comparison
of the number of simulations (250,000) used with the number of simulations (3.482E+10) that would
have been required if the direct MCSs were performed to compute the Pf with the same accuracy.

CONCLUSIONS
An overview of two probabilistic analysis and design tools, SIMLAB and PULSTR, has been given
along with their applications to surface ships subjected to both extreme dynamic and seaway loading.

ACKNOWLEDGEMENT

The authors gratefully acknowledge the support of Dr. Roshdy Barsoum at Office of Naval Research
and Dr. Jeff Beach at the Structures and Composites Department of Naval Surface Warfare Center of
Carderock Division.

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