Abstract
This manual details a low-cost method for measuring turbulence at tidal energy sites. The critical issue with measuring tidal turbulence is positioning a sufficiently accurate velocity sensor at the height of interest to tidal devices (hub height). In the wind industry, sonic anemometers mounted on meterological towers provide high-fidelity turbulence velocity measurements that are needed to drive device design tools and for inflow experiments; however, towers are extremely costly to install and maintain in the oceanic environment.
This work introduces a method for measuring turbulence velocity from compliant moorings. These moorings serve as a platform that position acoustic Doppler velocimeters (ADVs) at turbine hub heights (the ADV is the oceanographer’s sonic anemometer). These ADVs are equipped with inertial motion units (IMUs) that measure mooring motion. These independent measurements of mooring motion are then removed from the ADV-measured velocity signal in post-processing to produce stationary/earth frame estimates of turbulence velocity time series. These time series are critical for producing realistic performance and loads estimates from device simulation tools such as HydroFAST and Tidal bladed.
This manual details mooring design, instrument configuration, data processing steps, and analysis guidelines for quantifying turbulence at tidal energy sites. Because turbulence is known to reduce turbine performance and lifetime, this information is critical to classifying tidal energy sites, and performing device simulations with realistic estimates of device performance and lifetime.
This manual is intended to provide site and device developers with a complete guide for performing turbulence assessments at tidal energy sites. It includes:
- Hardware requirements and recommendations
- Instrumentation configuration details
- Guidelines for deployment and recovery planning
- Data processing and analysis details.
The key innovations described in this work are:
- The use of moorings to position ADVs at tidal turbine hub heights
- The use of IMU measurements to remove mooring motion from the measured velocity signal.