Framework for Evaluation of Silent Installation Technologies

Abstract

As offshore wind turbines grow in size, the installation of monopile foundations faces increasing technical, operational, and environmental challenges. A key concern is underwater noise pollution generated during pile driving, which poses risks to marine life and must comply with increasingly strict environmental regulations. While conventional impact piling is still the most commonly used technique, it often requires extensive mitigation measures to reduce noise levels. As turbine dimensions, and consequently the required driving energy, continue to increase, these mitigation measures may no longer be sufficient to ensure compliance with noise limits. This has led to growing interest in alternative installation techniques, such as vibropiling and vibrojetting, which are expected to operate more quietly but introduce technical uncertainties, particularly regarding drivability.

This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.

The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.

The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.

The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...