Abstract
This project has investigated the use of computer simulations, in the form of finite element analysis to assess fish mortality from impacts with tidal turbine blades at various flow speeds and turbine operating conditions. In order to perform these analyses, an idealized fish finite element model was developed using previous research on the mechanical properties of fish and calibrated using laboratory tests to obtain strain data from fish impacts on a flat aluminum plate.
A further objective of the project was to assess the suitability of strain gauges as a method to monitor fish impacts with a tidal turbine.
Laboratory tests were performed in the Dalhousie University Flume tank over the summer of 2017 using fish selected for their relevance to the high energy sites of the Minas Passage in Nova Scotia. Analysis of the test data was completed in October 2017. Results from the laboratory tests showed that it was possible to differentiate when an object hits the plate from the background “noise” of the flow and turbulence of the environment, however “noise” obscured several of the smaller fish impact tests and strain gauge measurements would likely be problematic in real turbine operating conditions.
Finite element models were developed and analyzed through the winter of 2017/18. The initial analyses focused on simulating laboratory tests in order to calibrate the fish finite element model which was developed based on the properties of a striped bass. The comparison of finite element analysis results to strain data collected in the laboratory was favorable and allowed the project to progress to the finite element analysis of tidal turbine blade and fish interactions which were conducted in early 2018.
The results from the finite element analyses of the fish impact with a tidal turbine blade showed that in all but the slowest impact speed (fish impacting the blade at 2 m/s) with no blade rotation, a significant quantity of finite elements in the fish model exceeded the strain or stress failure criteria. As a result it was concluded that there is a high probability of fish mortality in the event that it impacts an operational turbine blade.
Recommendations for related future work include testing of strain gauge measurement of impacts in real turbine operating conditions, research into technology and techniques to improve analysis of strain gauge data in “noisy” flow environments, investigation into whether strain data from fish impacts can be distinguished from impacts of other objects, refinement of finite element techniques to analyze larger biological object impacts and investigation into the use of finite element analysis to assess effects of impacts on the turbine blades themselves.