Introduction

A brief review of the various types of “dynamic” loads acting on marine structures is given. In general, the intensity of loads varies in both space and time. The description needs to address this variability.

There are multiple ways to classify loads. Usually, account is made of what kind of physical phenomenon causes them, the uncertainty of the loads (this will affect the safety (load) factor that is to be applied), etc. Design codes contain a load classification. The following list covers major types of loads for marine structures, which could have dynamic structural effects:

• Functional loads due to the operation of machinery to extract energy (wave and wind) and the operation of cranes

• Environmental loads due to wind, wave, current, ice, and earthquakes

Environmental phenomena vary over time. If the variation of the corresponding environmental load over time synchronizes with a natural period of the structure, dynamic amplification of the response may occur. Typical natural periods of oscillation are a few seconds for bottom-supported structures and up to 300 seconds for moored floating structures. Load fluctuations with time may, hence, be separated into (see, e.g., (Larrabee and Cornell, 1979)):

• Macro-scale variations, which do not affect the structural response

• Micro-scale variations, which may directly influence the structural response

Macro-scale description may, for instance, be

• average wind velocity over a 10-minute period

• tidal current

• significant wave height and peak period of a wave spectrum

• peak ground acceleration of an earthquake motion