Session: 09-03-02 Tidal Energy: Hydrodynamics

Paper Number: 128251

128251 - High and Mid-Fidelity Modeling Comparison for a Floating Marine Turbine System 

Marine current energy is an abundant renewable resource that can boost grid resiliency and reduce infrastructure vulnerability, but its cost is still not competitive relative to other renewable resources like wind and solar. One driver of this high cost is over-built designs resulting from the complex, coupled loads caused by extreme operating environments. These loads are difficult to model and often not fully predicted. Improved understanding of the relevant physical phenomenon and the ability to efficiently estimate the loads with reduced uncertainty can help designers improve the economics of current energy devices while maintaining reliability. There is a lack of suitable numerical tools, particularly open-source tools, that can be used for designing and optimizing marine turbine systems. The National Renewable Energy Laboratory (NREL) has added features to their widely used mid-fidelity wind turbine modeling code, OpenFAST, to enable modeling of axial flow marine turbines. This necessitated the addition of several physical effects relevant to marine turbine that can be neglected for wind turbines. These include buoyant loads, added mass loads, wave-current coupling, and changes to the coordinate systems. This updated version of OpenFAST allows for the modeling of both fixed and floating marine turbine systems at a speed comparable to real time. While efficient for long simulations, large sets of load cases, and design studies, mid-fidelity codes cannot capture all of the potentially important physical phenomenon impacting marine turbine systems. High-fidelity computational fluid dynamics (CFD) simulations can capture more flow effects with fewer assumptions and provide detailed body pressure mapping and flow-field information. It is important to compare predictions between mid-fidelity and high-fidelity codes, both to verify the models and to understand the limitations. A floating marine turbine system designed by NREL was modeled both with OpenFAST and with the commercial CFD code, STARCCM+. The CFD model used a 3-D unsteady Reynolds-averaged Navier-Stokes solver for a volume-of-fluid numerical wave and current tank. The blade-resolved simulations used the sliding-interface technique for the spinning rotor and an overset grid to accommodate the rigid-body motion of the floating system. The mooring system was modelled with a custom coupling of the CFD solver with the open-source code, MoorDyn. This improves upon the existing quasi-static catenary solver in STARCCM+, which lacks seabed contact or line-to-line connections. Spatial and temporal convergence studies were conducted. The simulation results for a combined current and wave condition are compared between OpenFAST and CFD, highlighting the capabilities of the mid-fidelity code and identifying the areas where a high-fidelity approach is needed.

Presenting Author: Thanh Toan Tran NA

Presenting Author Biography: Thanh Toan Tran received a Ph.D. in Aerospace Engineering from Gyeongsang National University, South Korea, in 2016. His graduate research has focused on high-fidelity fluid-structure interaction simulation of floating offshore wind turbines considering the influence of aero-hydrodynamic coupling.
Prior to NREL, he was a Postdoctoral Researcher at UC Berkeley and has developed a high-fidelity simulation of wave energy converters. At NREL, he is working on a combination of marine energy (ME) and offshore wind (OSW) projects. On the ME side, he is involved in the development of numerical tools for both marine hydrokinetic turbine and wave energy converter devices.

Authors:

Thanh Toan Tran NA
Hannah Ross National Renewable Energy Laboratory
Will Wiley National Renewable Energy Laboratory
Lu Wang National Renewable Energy Laboratory
Senu Sirnivas NREL