Abstract
The effect of whipping vibration on the fatigue life was estimated for larger ship safety. Miner’s law and Fatigue crack propagation analysis were applied for the fatigue life estimation. The delay phenomenon occurring fatigue crack growth according to over loading caused by whipping were simulated by using non-linear fatigue crack propagation program. The simulated stress acting on deck structure of the actual post-panamax container ship were applied to numerical program, the whipping effect was evaluated by comparing with the superimposing vibration stress (RAW) and without vibration stress (LF).
It was found that the effect is about 30% in Miner’s law and 10-55% in Fatigue crack propagation analysis assuming a long-term storm of 25 years in North Atlantic. The effect became smaller than those reported in the previous report (abt.50%), where a maximum storm was assumed. And, it was estimated that the effect of delay phenomenon is same level of the whipping effect. Furthermore, as an example of probabilistic approaches for fatigue life evaluation, structural reliability analysis in Monte Carlo simulation was performed in the parameters with the ship speed, wave direction, and the rank of storms. The effect of operating condition was quantitatively indicated by the reliability index and the failure probability. It was indicated that the effect of whipping on fatigue life can be canceled by operational effect of ship speed reduction in severe sea.
