RELIABILITY ANALYSIS OF CRACK GROWTH OCCURRENCE FOR A SECONDARY STRUCTURAL COMPONENT DUE TO VIBRATION EXCITATION

Ship hull vibration is a significant contributor to fatigue crack growth and the major sources of vibrations are found to be the main engine vibration excitation, the wave-induced springing and whipping loads, and the action of the propeller. In the midship region, wave-induced loads and the main engine are the major contributors, whereas propeller excitation dominates in the aft region of the ship hull. The vibration problems onboard a ship are very complex and are found at both global and local levels. No general method exists to solve all kinds of vibration problems and hence they need to be evaluated through a cost-by-case approach. The complex and uncertain aspects of hull vibration and fatigue crack growth motivate the need for a reliability-based scheme for assessing the resulting fatigue crack propagation of secondary components and structural details. In the present paper, a probabilistic formulation for the failure probability of the occurrence of crack propagation of a secondary hull component is outlined. A generic cargo hold model is analyzed with engine excitation and wave-induced loading as vibration sources, and a stochastic model for vibration response is obtained based on this. The limit state is presented as the possible occurrence of crack growth. The secondary structural component considered is a pipe stack support, and different initial crack sizes are evaluated. The adequacy of the applied stochastic model for vibration response is evaluated and the accuracy of the estimated failure probability is assessed.