Session: 06-02-02 Coastal Engineering - II

Submission Number: 181837

Numerical Validation of a Floating Breakwater Using Moodymarine 

Demand for resilient coastal defenses is increasing due to sea level rise and more frequent extreme events such as storm surges. In this context, floating breakwaters (FBs) have several advantages over conventional breakwaters, since these systems can be deployed in larger water depths and can dynamically adjust to the sea level. Combining FBs with wave energy converters (WECs) potentially increases the versatility and efficiency of such a combined protection–energy system. In contrast to their bottom fixed counterpart, FBs require mooring systems or station keeping. Such mooring systems can be designed as catenary or taut mooring. Previous literature has shown that the hydrodynamic performance of taut moored breakwaters offers an enhanced wave transmission capacity and reduced radiated wave field close to the FB; however, resulting in increased mooring stiffness and, thus, mooring line cost, in comparison to catenary systems.

While catenary-moored FBs have been extensively studied in literature, experimental and numerical studies concerning taut-moored FBs remain scarce, despite the potential for enhanced performance. To advance the understanding of taut mooring configurations, particularly under longer waves at large scale, an experimental campaign was carried out in the framework of the marTech project (BMEW, Grant number 0324196B). The experimental campaign focused on collecting benchmark data on the effect of the spreading angle of the mooring lines and line pretension on reflection/transmission coefficients, mooring loads, and the FB’s motion response both with and without consideration of attached oscillating water column WECs. This reliable experimental data is valuable not only for fundamental understanding but also for validating efficient and accurate numerical models. As documented in the literature, an inaccurate characterization of the mooring line properties during the experiments can critically impact the numerical model validation by modifying the numerical model FB natural frequencies and mispredicting mooring loads.

Numerical modeling of catenary-moored FBs is typically done using mooring solvers based on the lumped mass approach. However, to model taut moored FBs where dynamic tension response and shock wave propagation play a major role on the mooring line behaviour, higher order locally conservative methods are recommended. In this study, a subset of the experimental data (FB without WECs) was used to validate MoodyMarine, a weakly nonlinear potential flow solver with a high order cable dynamics numerical model. MoodyMarine employs the frequency domain hydrodynamics coefficients from, e.g., NEMOH and models the body dynamics using the Cummins equation of motion. Cable dynamics are solved using a high-order discontinuous Galerkin method, and the surrounding wave field is derived using incident, diffracted, and radiated wave potentials. The validation objective is two-fold: first, to assess MoodyMarine's capability to provide reliable and fast numerical results, and second to investigate how the characterization of the mooring line experimental parameters can impact the final numerical predictions.

Presenting Author: Gael Verao Fernández Technische Universität Braunschweig

Presenting Author Biography: Gael Verao Fernández graduated from A Coruña University with a B.Sc in Civil Engineering (2013) and obtained a M.Sc. in Marine Renewable Energy (2014) from Plymouth University. In 2019, Gael received a PhD from Ghent University, with a thesis focused on numerical modelling of wave energy converters arrays. Later Gael worked on the MSCA-IF project ISLINGTON studying cable trenching of floating offshore wind turbines. Currently, Gael works as the project coordinator of the INF4INiTY project.

Authors:

Gael Verao Fernández Technische Universität Braunschweig
Christian Windt Technische Universität Braunschweig
Constantin Schweiger Technische Universität Braunschweig
Johannes Palm Sigma Energy & Marine AB
Claes Eskilsson RISE - Research Institutes of Sweden
Lorenzo Cappietti UNIVERSITÀ DEGLI STUDI DI FIRENZE
Nils Goseberg Technische Universität Braunschweig