An ecologically aware modification of the Morison’s equation for long term marine growth effects

Abstract

The Morison’s equation continues to be an important approximation of the load effect of waves on structures. However, such forces can evolve with time due to marine growth and the evolution of long term growth within the Morison equation is challenging. Incorporation of long term marine growth gives rise to two timescales associated with the Morison equation. A short time scale is associated with the period of a wave, while a long time scale is associated with the change in geometry of the structure due to marine growth. This paper proposes a new modification of the Morison’s equation where these multiple time scales of change are addressed. The proposed method allows for a better understanding of how the force predicted by the Morison equation changes over time. The approach allows considering marine growth as an integral part of the Morison equation, expanding the capability to handle a significantly wider range of conditions related to lifetime performance of marine infrastructure, like wind turbines. The proposed approach is compatible with ecological processes and consequently the sampling of randomness over time is physically and biologically viable. The proposed approach allows incorporation of changes in the geometry of these structures through simple biological sampling and subsequently provides a way of updating Morison’s equation to provide more accurate force estimates. This ecologically compatible geometry allows for forces estimates closer to reality, departing from the existing and simplistic smooth and rough regimes which are typically used as binary parameters.