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Increase of Wave Drift Forces in Severe Seastates Due to Wave Frequency Viscous Damping

Abstract

Calculation of wave drift forces in the context of mooring analysis is usually performed by potential flow boundary element methods. For monohulls with large waterplane area, such as floating, production, storage and offloading vessels (FPSOs), the assumption is that heave and pitch damping is dominated by inviscid radiation of waves. The present study investigates the effects of heave and pitch wave frequency viscous damping on the horizontal wave drift forces of a FPSO. Experimental evidence indicates the presence of non-negligible viscous damping in case of moderate and severe seastates. Such observation is confirmed by computational fluid dynamic (CFD) simulations of forced harmonic motions with different periods and amplitudes. On a second step, a numerical analysis shows that the surge wave drift forces increase significantly at the low frequency range when realistic heave and pitch viscous damping is considered. The frequency range where standard potential flow calculations appear to underestimate wave drift forces coincides with the range where design seastates have most of the energy. Finally, the wave drift coefficients calculated with realistic additional viscous damping are compared with empirical coefficients identified from model test data. The identification procedure follows a second order signal analysis technique known as cross bi spectral analysis.

Category

Academic chapter

Language

English

Affiliation

  • SINTEF Ocean / Energi og transport
  • SINTEF Ocean / Skip og havkonstruksjoner

Year

2022

Publisher

The American Society of Mechanical Engineers (ASME)

Book

ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering Volume 1: Offshore Technology

ISBN

9780791885857

View this publication at Norwegian Research Information Repository