ABSTRACT
This chapter explains recommended damping methods, which may be applied to hull monitoring systems on board for continuous recording of damping values. Several damping methods have been applied to reveal which method is more reliable. The damping of the wave induced vibration of the steel hull girder is generally low, but could vary with an order of magnitude example varying from 0.5% of the critical damping to 10% depending on the ship type and vibration mode. Low damping, which is more relevant for blunt ships, tends to affect both the extreme loading and fatigue damage more than on slender ships like container ships with higher damping. The Stochastic Subspace Identification is a more complex mathematical method that can identify mode shapes, natural frequencies and damping coefficients. Realistic damping values and natural frequencies were considered based on time series with realistic duration and sampling frequency frequently used on hull monitoring systems. The damping estimation methods have their individual advantages and weaknesses.
