Date of Award
Spring 5-5-2023
Level of Access Assigned by Author
Open-Access Thesis
Degree Name
Master of Science in Mechanical Engineering (MSME)
Department
Mechanical Engineering
Advisor
Richard Kimball
Second Committee Member
Andrew Goupee
Third Committee Member
Babak Hejrati
Abstract
This work presents the development, verification and resulting performance of active mooring simulators used for scale model testing of floating offshore wind turbines (FOWTs) at 1:56.7 and 1:70 scale. Synthetic mooring designs being proposed for full scale FOWTS can reduce mooring scope and overall cost of FOWTs. Proposed synthetic materials, such as nylon and polyester have highly nonlinear, viscoelastic material properties making accurate scale representations infeasible. Scale model testing is a necessary step for design validation and performance verification before full scale construction. To scale moorings for basin testing, truncation of the system or linearization is common. Active hybrid tests have been used to represent nonlinear mooring behavior and have been found to accurately represent nonlinear mooring behavior at scale.
The development of two mooring simulators is outlined. The simulators presented represent the entire mooring line to allow for fast and efficient transition between different mooring configurations during basin testing. The first simulator proved to be a viable way to model nonlinear mooring behaviors of an 11MW FOWT at 1:56.7 scale for the New England Aqua Ventus (NEAV) Phase 2 test campaign. At 1:56.7 scale, the developed system is versatile and allows for two mooring configurations, catenary and polyester semi-taut mooring, to be tested rapidly. The second iteration simulator, utilizing a linear actuator, aimed to represent nonlinear mooring behavior of a 15MW FOWT at 1:70 scale for the New York State Energy Research and Development Authority (NYSERDA). It was found that a geared rotary-motor was unsuitable.
The control system developed for both mooring simulators uses closed-loop, force control and linear interpolation of a look-up table to generate force setpoints. The lookup table values are representative of the desired nonlinear force displacement mooring response. The process to generate a force-displacement lookup table of synthetic semi-taut systems using a combination of OrcaFlex and synthetic rope theory is outlined.
Simulator verification for the initial system was performed in-basin against a traditional spring mooring system prior to the full test campaign. Additionally, benchtop verifications are also presented. Benchtop verification for iteration two of the simulator revealed how valuable accurately representing hull inertia, and FOWT interactions are to a successful mooring simulator.
NEAV test campaign results using the active mooring simulator system in irregular sea states are compared to numerical simulations. The numerical simulations are performed using tuned OrcaFlex for the 1:56.7 scale FOWTs. FOWT surge motion is compared to the results of three mooring configurations: the linearized spring mooring, the actuated nonlinear catenary mooring, and the nonlinear actuated polyester semi-taut mooring. Additionally, lead mooring line tension is compared to numerical simulation of the catenary and polyester mooring experimental results. Final recommendations on motor and control scheme are presented based on numerical results as well as ease of use throughout the testing process.
Recommended Citation
McGlynn, Alyssa, "Development, Verification and Use of Active Mooring Simulators for Scale Model Testing of Floating Offshore Wind Turbines at 1:56.7 and 1:70 Scale." (2023). Electronic Theses and Dissertations. 3770.
https://digitalcommons.library.umaine.edu/etd/3770