Development of a Digital Twin for the Mutriku Oscillating Water Column Plant

Abstract

The Mutriku wave energy plant, operational since 2011, integrates 16 Oscillating Water Columns (OWCs) into a breakwater and has delivered over 3 GWh to the grid, making it one of the most established examples of commercial wave energy technology. Despite its success, challenges persist in optimizing performance under highly variable sea states and ensuring long-term reliability. Within the MAR+ project, a digital twin is being developed to replicate the plant's operational dynamics, combining advanced wave modelling and system simulations. This innovative tool aims to enhance both the current performance of the plant and the development of next-generation OWC systems.

A core component of the digital twin is the wave-to-wire numerical model, which operates in the time domain and couples the hydrodynamic, aerodynamic, and control subsystems of the plant. The hydrodynamic foundation is derived from frequency-domain analyses based on linear potential flow theory. These analyses provide critical parameters—such as added mass, hydrodynamic damping, and excitation forces—that are then integrated into a time-domain framework using the Cummins equation to capture transient system responses. The aerodynamic model simulates compression and expansion processes within the air chamber, assuming ideal gas behaviour and incorporating non-linear effects, such as viscous losses and dynamic interactions. The turbine is preliminarily modelled using Buckingham’s turbine theory, providing a foundation for future integration of advanced control strategies to enhance system performance.

A key feature of this digital twin is its integration with real-time wave data provided by an operational application. This web-based tool offers hindcast, nowcast and forecast information of the complete wave spectrum at the breakwater, enabling the digital twin to simulate realistic wave inputs under both historical and predictive scenarios. This capability not only bridges the gap between wave resource characterization and plant performance modelling but also ensures the robustness of the digital twin under variable wave climates.

Validation of the wave-to-wire framework employs a combination of experimental and field data. Laboratory-scale tests focus on single-chamber hydrodynamics, providing high-resolution data for numerical refinement. Simultaneously, field measurements at Mutriku capture the dynamic interactions between multiple chambers, validating the model’s ability to replicate real-world conditions. Preliminary results demonstrate the model's capacity to accurately represent chamber pressure dynamics, chamber pressure and free surface dynamics, and turbine behaviour, confirming its suitability for optimization studies.

The digital twin facilitates advanced optimization strategies, such as adaptive control systems for varying wave climates, and supports scalability for multi-chamber configurations. Moreover, it provides a robust platform for assessing system reliability and long-term performance under operational conditions, addressing key challenges for OWC systems.

Future work will integrate refined turbine control strategies, additional physical phenomena, and further validation steps to enhance predictive accuracy. This research establishes a replicable framework for incorporating real-time wave modelling and digital twins into marine renewable energy projects, contributing to cleaner and more sustainable energy systems globally.