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Assessment of Modelling Approaches for the Development of the Ocean Energy Sector

Eider Robles & Pablo Ruiz-Minguela, TECNALIA

Technology qualification basic steps and key questions associated with a WEC hybrid testing programme

Reliability testing is a recurrent issue in wave energy. At early development stages (low TRLs), there are many uncertainties and design decisions that need to be explored, and this is commonly perceived as a costly investment. However, relegating this activity to later development stages (high TRLs), when a full prototype is manufactured and ready for experimental testing, also has negative implications: the design may be too rigid to make significant changes and the associated costs can be prohibitive.

Here is where the VALID project can do its part, developing a novel test methodology based on accelerated hybrid testing techniques. Accelerated hybrid testing allows developers to integrate knowledge from a real environment (ocean, uncontrolled testing), a simplified lab environment (physical test rigs, controlled testing) and a virtually enhanced environment (numerical models, controlled testing). The combination of modelling approaches at a suitable scale plays a pivotal role in increasing understanding of the key requirements for the robust design of a WEC at early stages.

Once implemented, accelerated hybrid testing will offer a higher fidelity approach in the development and design of critical sub-systems. It will enable the industry to scale up simulated lab conditions and test a virtual model of the existing structure, therefore reducing uncertainties, increasing confidence in results, empowering informed decision-making, and largely assisting in the design and development process of WECs, especially at low TRLs.

Currently the team is establishing the overall framework for the development of the VALID Hybrid Testing Platform (VHTP) at the core of the VALID project. The aim is to provide guidance for the entire ocean energy sector identifying the critical components / subsystems, that will be addressed theoretically, numerically or physically.

Partners have completed, and documented in a public report, a comprehensive review of the different modelling approaches to be considered in the VALID project to address the design and accelerated testing of critical components and subsystems for WECs:

  • Theoretical models, which are simplified and schematic representations of the theory applicable to WECs, focusing the environmental characterisation, wave-structure interaction, affecting effects and deterioration and, reliability and survivability.

  • Numerical modelling methods most typically applied in WEC and WEC sub-system design have been presented. Basic formulations covering the range of most common approaches used to date (for example frequency-domain solvers; time-domain solvers), a brief introduction of the concept of design situations and design load cases and, a qualitative ranking of numerical modelling methods as a function of specific design situations have been described. Recent representative examples of WEC numerical models and models for critical sub-systems of WECs have also been overviewed.

  • Experimental modelling or physical testing cover experimental models for hydrodynamic interaction, energy transformation and, degradation and failure.

This report also discusses the limitations, impact and practicalities associated with the implementation of these modelling approaches in the future VALID testing framework.

This initial analysis has led to the classification and description of the models, test rigs and testing platforms that are currently available for its use in the VALID project within the partnership. User cases are now analysing the upgrade needs for the future steps of the project. Learnings from the initial application of the hybrid testing framework in the user cases will inform the re-contextualisation of the final methodology, promoting wider adoption in the wave energy community.

Graphical representation of hybrid testing approaches in the three User Cases.

User Case #1: Dynamic seals (CorPower)

User Case #2: Generator failure (IDOM)

User Case #3: Hydraulic pump seals & glider pads (WavePiston)

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