CFD Based Study of Steep Irregular Waves for Extreme Wave Spectra

Abstract

Offshore structures are exposed to irregular sea states. It consists of breaking and non-breaking waves. They experience extreme wave loads perpetually after being installed in the open ocean. Thus, the study of steep waves is an important factor in the design of offshore structures. In the present study, a numerical investigation is performed to study steep irregular waves in deep water. The irregular waves are generated using the Torsethaugen spectrum which is a double-peaked spectrum defined for a locally fully developed sea. The Torsethaugen spectrum takes both the sea and swell waves into account. Thus, the generated waves can be very steep. The numerical investigation of such steep waves is quite challenging due to their high wave steepness and wave-wave interaction. The present investigation is performed using the open-source computational fluid dynamics (CFD) model. The wave generation and propagation of steep irregular waves in the numerical model is validated by comparing the numerical wave spectrum with the experimental input wave spectrum. The numerical results are in a good agreement with experimental results. The changes in the spectral wave density during the wave propagation are studied. Further, the double-hinged flap wavemaker is also tested and validated by comparing the numerical and experimental free surface elevation over time. The time and the frequency domain analysis is also performed to investigate the changes in the free surface horizontal velocity. Complex flow features during the wave propagation are well captured by the CFD model.