Metamaterial source mitigation for underwater noise from vibratory offshore pile driving

The rapid expansion of offshore wind energy intensifies the need to further reduce underwater noise and seabed vibration generated during turbine installation and decommissioning. Vibratory pile driving is already substantially quieter than conventional impact piling, yet its characteristic harmonic-rich signature can still cause ecological disturbance, particularly at super-harmonics of the driving frequency. Existing mitigation measures—such as bubble curtains—remain costly, logistically complex, and can diminish the advantages of vibratory installation if they are still required. This work introduces a metamaterial-based mitigation at the source, designed to suppress harmful super-harmonic frequencies while preserving the energy at the fundamental driving frequency that is essential for effective installation. A tailored finite element model is developed to capture the key soil–fluid–structure–metamaterial interactions governing this behaviour. A parametric and optimisation-based framework is developed to identify unit-cell geometries capable of producing broad and tunable bandgaps that encompass multiple super-harmonics relevant to the vibratory installation processes. Special attention is given to exploring nonlinear and locally resonant mechanisms that enable attenuation over wider bandwidths than classical designs. This study lays the theoretical groundwork for a scalable, source-integrated mitigation strategy that has the potential to reduce ecological impact, facilitate regulatory compliance, and support sustainable offshore wind development.