Adaptive Stretching of Dynamic Pressure Distribution in Long- and Short-Crested Sea States

Abstract

During their lifetime, marine structures and ships are frequently exposed to severe weather and rough, sometimes extreme sea states. To ensure survival, the precise knowledge of global and local loads is an inevitable integral prerequisite for the design of safe offshore structures and marine vessels. Wave-structure interaction and the associated pressure induced wave loads are key parameters for the definition of design load cases. Once the complete surrounding sea state for the identified load condition is known, the pressure induced loads can be computed by calculating the pressure distribution along the hull, using an appropriate wave theory. As 1st-order AIRY-Theory as well as 2nd- and 3rd-order STOKES-Theory excessively overestimate the dynamic pressure above still water level, especially in high wave crests, a variety of stretching terms has been applied to common wave theories to correct the pressure distribution. This paper presents a second-order stretching approach to describe the distribution of the dynamic pressure in regular wave crests. In combination with FFT (Fast Fourier Transformation), the applicability of this method can be extended to irregular sea states and even extreme waves. Calculations for several regular and irregular sea states are shown and compared to calculations with existing stretching methods. The results are validated by measurements conducted in a wave tank at the Technical University Berlin. The paper concludes with an example for the calculation of the wave induced pressure field along a ship hull operating in a short-crested, multidirectional sea state.