45 / 2025-04-24 12:55:12

Flow amplification in the cable touch down zone of monopile foundations – CFD investigations

This paper presents and discusses recent computational fluid dynamic (CFD) simulations of wave and current induced flow amplification and reductions in the cable touchdown zone of scour protections at monopile foundations.

Fatigue and abrasion failure of cable protection systems (CPS) at offshore wind farm foundations have led to an industry wide practice of rock berm stabilisation of the CPS. The rock installation works are costly in their own right and can be on the critical path of the offshore construction timeline. A driving element in CPS mechanical design is the temporary period prior to rock berm stabilization. The presented CFD results aim to improve the understanding of the hydrodynamic conditions driving the response of the CPS in this interim period.

From potential flow theory it is recognized that current flow speed amplifies at the sides of cylinders due to flow contraction. In the case of waves, the paper presents CFD simulations that confirm that flow amplification of wave motion in the vicinity of a monopile foundation can be described well with the potential flow theory of MacCamy and Fuchs (1954) for the investigated conditions. The present paper argues that such amplification of wave induced flow is part of the overall hydrodynamic loading of a CPS system. There are indications, that when located oblique to the waves and current, the CPS loading may be reduced compared to undisturbed conditions.

The paper investigates the extent to which having the cable touchdown zone as a corridor within the scour protection can provide partial shelter against wave and current loading. It is found that some sheltering can be provided for currents. For waves the sheltering appears minimal albeit presence of the trench reduces overall wave motion amplification. Apart from above modelling objectives, general observations of the CFD model are highlighted.