Recent Hydrodynamic Modeling Enhancements in OpenFAST

Lu Wang, Jason Jonkman, Greg Hayman, Andy Platt, Bonnie Jonkman, Amy Robertson

Research output: Contribution to conferencePaperpeer-review

2 Scopus Citations

Abstract

To improve the hydrodynamic modeling capabilities of the offshore wind design and modeling tool OpenFAST, a restructuring of the HydroDyn hydrodynamics module was undertaken with several new features implemented. The generation of the wave field is now separated from HydroDyn into a new module called SeaState. Unlike previous versions of HydroDyn, which precomputed the wave kinematics at the undisplaced positions of the hydrodynamic nodes, the new SeaState module computes the complete time history of the wave field at the vertices of a user-defined wave grid. During the simulation, the wave kinematics at any point within the grid can be efficiently interpolated, allowing the strip-theory wave loads to be evaluated based on the wave kinematics at the displaced structure position. A phase correction was also implemented for the potential-flow wave-exciting loads to account for large structure displacements. Several wave-stretching methods were implemented for the strip-theory solution along with a wave-load redistribution method that ensures smooth variation of the nodal loads as the nodes of a discrete hydrodynamic mesh enter and exit the water. The load smoothing is included to avoid the excitation of unphysical high-frequency structural vibration during hydroelastic simulations. The MacCamy-Fuchs diffraction correction for the strip-theory solution and the capability to insert a constrained NewWave into extreme stochastic sea states with directional spreading were also added. The present article documents the formulations of the new improvements to HydroDyn with example applications and numerical results.

Original languageAmerican English
Number of pages12
DOIs
StatePublished - 2023
EventASME 2022 4th International Offshore Wind Technical Conference, IOWTC2022 - Boston, United States
Duration: 7 Dec 20228 Dec 2022

Conference

ConferenceASME 2022 4th International Offshore Wind Technical Conference, IOWTC2022
Country/TerritoryUnited States
CityBoston
Period7/12/228/12/22

Bibliographical note

See NREL/CP-5000-83679 for preprint

NREL Publication Number

  • NREL/CP-5000-85494

Keywords

  • constrained wave
  • HydroDyn
  • instantaneous position
  • MacCamy-Fuchs
  • nonlinear
  • OpenFAST
  • wave stretching

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