Date of Award

Summer 7-8-2016

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Advisor

Andrew Goupee

Second Committee Member

Krish P. Thiagarajan

Third Committee Member

Senthil S. Vel

Additional Committee Members

Habib J. Dagher

Jason M. Jonkman

Abstract

Hybrid modeling combining physical tests and numerical simulations in real time opens new opportunities in floating wind turbine research. Wave basin testing is an important validation step for floating support structure design, but current methods are limited by scaling problems in the aerodynamic loadings. Actuating wind turbine loads from a simulation that responds to the basin test in real time offers a way to avoid scaling problems and make floating wind turbine design validation in realistic coupled conditions more accessible to researchers. This thesis describes the development, realization, and demonstration of an approach for hybrid modeling of floating wind turbines.

Possible coupling arrangements for hybrid modeling were considered and simulated numerically to determine performance requirements for the mechatronic system needed to connect the physical and numerical sub-models. The sensitivity of floating wind turbine response to errors in the coupling system was quantified, leading to actuation accuracy specifications. The results suggest that achieving accurate hybrid modeling is feasible.

To provide the numerical sub-model, modifications were made to a widely-used floating wind turbine simulator to allow coupling with external dynamics models. Also, a new dynamic mooring line model was developed and validated which provides important accuracy improvements over previously-standard approaches with minimal computational cost. It has been integrated into a variety of simulation tools and is also well-suited for use in hybrid modeling involving simulated moorings.

An approach for the hybrid coupling system using cable-based actuation was developed. Feedforward and feedback control elements take input from motion tracking equipment and cable tension measurements to provide responsive actuation of forces on a moving floating platform. A prototype two-cable system was built and bench tested to refine the control approach and measure performance.

Finally, the system was applied to 1:50-scale testing of a floating wind turbine in a wind-wave basin. Results using the hybrid model agree closely with conventional wind-wave tests, experimentally validating the hybrid approach. Additional tests with the hybrid system incorporating true-to-scale aerodynamics and also the presence of wind turbulence in the numerical sub-model demonstrate significant changes in response, indicating the value of a hybrid model approach in floating wind turbine basin testing.

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