"In rough seas, the ship’s bow and stern may occasionally emerge from a wave and re-enter the wave with a heavy impact or slam as the hull structure comes in contact with the water. A ship with such excessive motions is subject to very rapidly developed hydrodynamic loads. The ship will experience impulse loads with high-pressure peaks during the impact between the ship hull and water. Of interest are the impact loads such as bowflare slamming, bottom slamming, stern slamming, green water, and bow impact loads. These impact loads are of a transient nature and can cause severe structural damages. Impact loads can cause local structural damage due to high impact pressure. They can also induce hull girder vibration mainly in the fundamental 2-node mode. This hull girder vibration is referred to as “whipping”, as shown in Section 1, Figure 1. The vibratory hull girder bending stress, or whipping stress, is of much higher frequency than the wave-induced stress, and is effectively superimposed on it. The period of the fundamental mode of whipping is usually in the range from 0.5 to 2 sec.
Whipping has been observed in full scale measurements and can result in an increase of the extreme value of the hull girder bending moment and fatigue damage to structures. "
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