Development and validation of a procedure for numerical vibration analysis of an oscillating wave surge converter

Pál Schmitt,Christian Windt,Jonathan Nicholson,Björn Elsässer

doi:10.1016/j.euromechflu.2016.02.005

Abstract

During extreme sea states so called impact events can be observed on the wave energy converter Oyster. In small scale experimental tests these impact events cause high frequency signals in the measured load which decrease confidence in the data obtained. These loads depend on the structural dynamics of the model. Amplification of the loads can occur and is transferred through the structure from the point of impact to the load cell located in the foundation. Since the determination of design data and load cases for Wave Energy Converters originate from scale experiments, this lack of confidence has a direct effect on the development.Numerical vibration analysis is a valuable tool in the research of the structural load response of Oyster to impact events, but must take into account the effect of the surrounding water. This can be done efficiently by adding an added mass distribution, computed with a linearised potential boundary element method. This paper presents the development and validation of a numerical procedure, which couples the OpenSource boundary element code NEMOH with the Finite Element Analysis tool CodeAster. Numerical results of the natural frequencies and mode shapes of the structure under the influence of added mass due to specific structural modes are compared with experimental results.

Highlights

Wave Energy remains one of the largest unexploited renewable energy resources and has led to many conceptual developments of Wave Energy Converters (WECs) [1]
During extreme sea states so called impact events can be observed on the wave energy converter Oyster
Since the determination of design data and load cases for Wave Energy Converters originate from scale experiments, this lack of confidence has a direct effect on the development

Summary

Introduction

Wave Energy remains one of the largest unexploited renewable energy resources and has led to many conceptual developments of Wave Energy Converters (WECs) [1]. One such type and most advanced concept is the Oscillating Wave Energy Converter (OWSC) Oyster [2], developed by Aquamarine Power Limited (cf Fig. 1). The Oyster OWSC consists of a buoyant hinged flap, which pitches back and forth in the near shore environment pumping water onshore to generate electricity in a conventional hydro power station [3]. It can be shown that diffraction governs the motion of Oyster, leading to a difference in water level on the seaward and landward faces of the flap. The resulting differential in hydrostatic pressure (cf. Fig. 2) creates an exciting torque around the hinge axis [4]

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Conclusion