Session: 01-03-02 Hydrodynamics-2

Submission Number: 182194

Experimental Investigation of a Full-Scale Flexible Cable Riser Subjected to Combined Wave and Current Effects for Floating Renewables Applications 

Floating offshore renewables, such as offshore wind or offshore photovoltaics (FPV), represent an emerging energy technology with substantial potential for large-scale deployment. To ensure a consistent power transmission from offshore floaters to shore , dynamic subsea cables are required, which connect the floating platforms to the transmission infrastructure. Experience from offshore wind farms has revealed that cable failure remains one of the main causes of unplanned downtime and repair costs. Such failures are often linked to limited understanding of the complex hydrodynamic forcing acting on cables in offshore flow environments during the design process.  While the characteristics of VIV in uniform currents are well understood, the combined effects of irregular surface waves, mean currents, and near-bed turbulence, caused by bathymetric variability, introduce nonlinear excitation mechanisms that are not yet fully understood for floating offshore configurations.

The present work experimentally investigates the dynamic response of a subsea power cable under combined wave–current conditions representative for nearshore floating offshore deployments. The data from this experiment form a unique addition to the existing state-of-the-art literature, because (i) the experiment was taken at (near to) prototype scale and (ii) motions of cables in the combination of current and waves have not been investigated before. The cable specimen has a total length of 4.7 m, a mass of 1600 kg, and a bending stiffness of 5 kNm. The model was subjected to regular and irregular wave conditions with (significant) heights up to 1.4 m and peak periods between 2.8 s and 9 s, combined with opposing and following currents up to 1.0 m/s in increments of 0.25 m/s. These conditions correspond to the range of flow velocities, typically observed over a tidal cycle in the North Sea. In total, 51 unique tests were conducted covering cases of current-only, wave-only, and combined wave–current excitation.

Results from this study contribute to a better understanding of the fundamental response mechanisms governing cable integrity in floating solar applications. The results show that in case of the waves becomes non-linear, the cables locks in to a multiple of the wave frequency close to the eigen frequency of the cable. The dominance of current over wave orbital velocities highly affect this trend and can cause a broader response spectrum near the eigen frequency that may indicate vortex-induced vibrations. A more in-depth investigation is required into the data to present this at the conference.

Presenting Author: Martin Van Der Eijk Deltares

Presenting Author Biography: Martin van der Eijk is a researcher in hydrodynamics at Deltares in the Netherlands. He obtained his PhD (cum laude) in Maritime Technology from Delft University of Technology (TU Delft) in 2023. His doctoral research focused on the effects of entrained air in wave impacts on marine and offshore structures, combining numerical modelling, laboratory experiments, and analytical approaches to improve understanding of short-duration, high-intensity hydrodynamic loads.

Since joining Deltares, Martin has developed a strong affinity with complex fluid–structure interaction (FSI) phenomena, including the dynamic behaviour of flexible and moveable components such as power cables and floating structures exposed to waves and currents. His work integrates advanced two-way coupled computational fluid dynamics (CFD), two-phase and compressible flow modelling, and experimental validation to enhance the design and resilience of offshore and coastal systems.

His research interests include:
– Fluid–structure interaction
– Multiphase, free-surface, and compressible flows
– Hydrodynamics
– Numerical modelling
– Short-duration wave loading
– Underwater explosions

Martin’s overarching goal is to improve the physical understanding and predictive capability of models describing offshore and coastal structures under complex environmental conditions, supporting the development of safer and more reliable marine infrastructure. Building the future of offshore innovation through the three pillars of science: analytical, numerical, and experimental hydrodynamics.

Authors:

Martin Van Der Eijk Deltares
Christian Van Nieuwenhuizen Deltares
Maarten Van Poppelen Oceans of Energy
Peter Wellens University of Technology Delft