Coupled Atmosphere-Wave-Ocean Modeling to Characterize Hurricane Load Cases for Offshore Wind Turbines

Abstract

We report on work in progress that is seeking to define hurricane load cases for the design of offshore wind turbines. A software tool, CHAISE (Coupled Hydro-Aerodynamic Interface for Storm Environments), is being developed that will integrate a fully coupled atmospheric-wave-ocean model, referred to as the University of Miami Coupled Model (UMCM), with downscaling using computational fluid dynamics (CFD) tools and, ultimately, with turbine aeroelastic loads computation. The goal is to simulate turbine rotor, tower, and support structure loads on an offshore wind turbine throughout the evolution of a hurricane. We present various elements of this end-to-end simulation capability that is under development. I. INTRODUCTION In order to assess the risks to potential U.S. offshore wind farms from the destructive wind, wave, and current conditions induced by hurricanes in the Gulf of Mexico and the Eastern seaboard, a state-of-theart numerical simulation tool, CHAISE (Coupled Hydro-Aerodynamic Interface for Storm Environments), is under development. The principal objective of CHAISE is to provide accurate estimates of hurricaneinduced forces on offshore wind turbine structures at high temporal and spatial resolution; its capabilities are expected to exceed the reliability and applicability afforded by today’s design standards. The CHAISE software is composed of several geophysical modeling components that simulate the environment at various scales. The University of Miami Coupled Model (UMCM) is a fully coupled atmosphere-wave-ocean model that is used to simulate the storm and associated environmental fields at spatial and temporal resolutions of the order of 1 kilometer and several seconds, respectively; the model is able to represent relevant physical processes at the air-sea interface at those scales. The UMCM output is used as input to a Large-Eddy Simulation (LES) model (OpenFOAM and WRF-LES) that will achieve the needed downscaling and solve the Naiver-Stokes equations at 5-10 meter spatial scales. Finally, these finely scaled fields will be used as input to FAST, an established wind turbine design tool, that provides accurate estimates of loads on the offshore wind turbine structure of interest. A schematic diagram describing CHAISE is shown on Figure 1. We describe the methodology, application, and some results of the work in progress that uses the CHAISE tool.