Development of an experimental methodology for appraising the dynamic response of tethered tidal turbines

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Ordonez Sanchez, Stephanie Eugenia and Johnstone, Cameron and Grant, Andrew (2013) Development of an experimental methodology for appraising the dynamic response of tethered tidal turbines. PhD thesis, University Of Strathclyde.

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Abstract

This thesis makes a comparison of different station keeping structures to support tidal energy converters. It was observed that the use of flexibly tethered turbines would be beneficial due to low material costs and the capability to permit the turbine’s self alignment to the flow regime. However, because of the uncertainties over their dynamic behaviour, it was considered that an analysis of response in a range of conditions was essential before they could be considered as practical station keeping system. Firstly, a static analysis was carried out for both rigid and flexible foundations. Thereafter, the thesis presents the development of an experimental methodology to study the dynamic response of tethered tidal energy converters. In this methodology, the alignment and oscillations of the three main rotational angles (i.e. roll, pitch and yaw), estimated over a period of time, were taken as the fundamental metrics of system behaviour. The analysis was extended into the frequency domain in order to estimate the intensity of the parameters that affect the turbine and its condition (e.g. blade failure, excessive backlash or misalignment, vortex shedding, etc.) Within the methodology development a series of steps were specified, based on established protocols related to similar concepts (for example EquiMar) where parameters such as the selection of test facilities, blockage ratio limits or safety factors in applied loads were discussed. Instruments to measure the dynamic motion of turbines were specified, along with other instruments to measure power, thrust, angular velocity and flow speed. The final steps in the methodology denoted methods to analyse the acquired signals. In order to verify the feasibility of the methodology, a series of experiments were carried out at various turbine models scales. Firstly, small turbine models were installed on a zero turbulence tow tank and a flume tank with significant levels of turbulence, under controlled conditions and at similar flow velocities. To compare the dynamic responses, studies were undertaken for a larger turbine deployed in the natural turbulence of an open tidal site and in a turbulent river stream affected by marine traffic. This thesis concludes that the methodology proposed is suitable to characterise the dynamic response of tethered devices at various model scales. The results presented showed the advantages and disadvantages of using various turbine configurations. Therefore, this methodology can be used develop and validate analytical models that predict the dynamic response of flexibly moored turbines.

ORCID iDs

Ordonez Sanchez, Stephanie Eugenia ORCID logoORCID: https://orcid.org/0000-0002-7253-6299, Johnstone, Cameron and Grant, Andrew;
CORE (COnnecting REpositories)