Overview of the HydroDyn Hydrodynamics Module

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

NREL Wind Turbine Modeling Workshop March 2, 2012 NREL – Golden, CO Jason Jonkman, Ph.D. Senior Engineer, NREL

Wind Turbine Modeling Workshop 2 National Renewable Energy Laboratory

Outline

• Overview: – HydroDyn – What Is It?

• Monopiles: – Waves, Currents, & Hydrodynamic Loads

• Floating Platforms: – Combining Computational Methodologies – Waves, Currents, & Hydrodynamic Loads – Mooring Systems

• Current & Planned Work • Future Opportunities

• Yet-to-be documented hydrodynamics routines for offshore wind turbines: – Currently an undocumented feature in FAST & A2AD – Input settings contained in FAST’s platform input file – Source code included in FAST

v7.00.01a-bjj & newer – Interfaced to MSC.ADAMS via

A2AD v13.00.00a-bjj & newer

• Support-structure types: – Monopiles – Floating platforms

• Theory Manual: – Jonkman Ph.D. Dissertation (2007) – Jonkman, Wind Energy (2009)

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Overview HydroDyn – What Is It?

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Monopiles Waves, Currents, & Hydrodynamic Loads

• Wave kinematics: – Linear regular (periodic) – Linear irregular (stochastic):

• Pierson-Moskowitz, JONSWAP, or user-defined spectrum

– With optional stretching: • Vertical, extrapolation, or Wheeler

– Arbitrary choice of wave direction, but no spreading – Or routine to read in externally generated wave data:

• Nonlinear wave option available

• Steady sea currents: – IEC-style sub-surface, near-surface, &

depth-independent – Or user-defined

• Hydrodynamic loads: – Relative form of Morison’s equation – Calculated at each structural node along tower

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Floating Platforms Combining Computation Methodologies

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Floating Platforms Waves & Currents

• Wave kinematics: – Linear regular (periodic) – Linear irregular (stochastic):

• Pierson-Moskowitz, JONSWAP, or user-defined spectrum

– Arbitrary choice of wave direction, but no spreading

• Steady sea currents: – IEC-style sub-surface, near-surface, & depth-

independent – Or user-defined

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Floating Platforms Hydrodynamic Loads

• Hydrodynamic loads: – Wave-body interaction with rigid platform – Arbitrary platform geometry – Linear frequency-domain radiation & diffraction

solutions imported from WAMIT or equivalent: • Internal frequency-to-time domain conversion

– Radiation “memory effect” accounted for by direct time-domain convolution

– Linear hydrostatic restoring – Applied as 6-component (lumped) load on

platform at reference point – 2nd-order (mean-drift, slow-drift, sum-

frequency) effects neglected – Damping in surge, sway, roll, & pitch

augmented with nonlinear viscous drag term from relative form of Morison’s equation: • Distributed along platform analysis nodes

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Floating Platforms Hydrodynamics Calculation Procedure

Time-Domain Hydrodynamics (H ydroDyn)

Wave Spectrum& Direction

Radiation Kernel

Incident-WaveExcitation

Plat formMot ions

Hydrod ynamic For cing Lo ads

Added-Ma ss Matrix(Radiation Problem)

Damping Matrix(Radiation Problem)

Impu lsiveAdded Mass

Restoring Matrix (Hydrostatic Problem)

Wave-Excitation Force(Diffraction Problem)

White G aussianNo ise

Infinite-Freq.Limit

Cosine Transform

Inverse FFT

Box-MullerMethod

Seed forRNG

PlatformGeometry

SeaCurrent

Time Convolution

BuoyancyCalculation

Sum Forces

MemoryEffect

Buoy ancy

Morison’s Equation

ViscousDrag

Frequency-Domain Radiation / DiffractionHydrodynamics Preprocessor (SWIM or WAMIT)

Incid ent-WaveKin ematics

Wind Turbine Modeling Workshop 9 National Renewable Energy Laboratory

Floating Platforms Mooring Systems – Overview

• Continuous quasi-static mooring system module implemented within HydroDyn: – Solves analytical catenary equations – Fairlead tensions applied as reaction forces on

platform • Accounts for:

– Array of homogenous taut or catenary lines – Apparent weight of line in fluid – Elastic stretching – Seabed friction – Nonlinear geometric restoring

• Neglects: – Line bending stiffness – Mooring system inertia – Mooring system damping Dutch Tri-Floater

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Floating Platforms Mooring Systems – Calculation Procedure

Mooring Lin e Properties( , , , )

Quasi-Static Mooring-System Module (Calculations Shown for Each Line)

Newton-Raphson Iteration to Find Fairlead TensionGlobal-to-Local

Transformation

Compute Anchor Tension

Compute Configuration of,& Tensions Within, Line

Fairlead Location Relativeto Anchor ( , )

Fairlead Tension ( , )

Local-to-Global Transformation &

Sum Tensions

Platform Position

Mooring Restoring

Anchor Tension( , )

Configu ration of, & Tensions Within, Line

[ , , ]

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Current & Planned Work • Extend to space-frame support structures:

– Features: • Multiple members & intersecting members at joints

– Accurate calculation of overlap of intersecting members • Inclined & tapered members • Flooded members • Marine growth

– Hydrodynamic loads: • Distributed inertia, added mass, & viscous drag (Morison) • Distributed static buoyancy & dynamic pressure • Concentrated loads at member ends & joints

– Applicable to: • Fixed-bottom tripod or jacket • Thin members (e.g., braces/spokes) of floating platforms

– Verification under IEA Wind Task 30 (OC4) & against CFD – Upcoming OTC & OMAE papers

Jacket with Regular &

Super Members

Regular Member

Super Member

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Current & Planned Work (cont)

• Develop improved interface: – Making HydroDyn—including inputs—standalone,

like AeroDyn • Write HydroDyn user & theory manual & publically

release • Verify recent FAST-OrcaFlex coupling • Further verify under IEA Wind Task 30 (OC4) • Calibrate & validate floating functionality through:

– DeepCwind – 1/50th-scale of 5-MW atop spar buoy, TLP, & semisubmersible

– Hywind – Siemens 2.3-MW atop Statoil spar buoy – SWAY – 1/5th-scale of 5-MW downwind turbine atop a

TLS – WindFloat – Vestas V80 2-MW atop a PPI

semisubmersible

DeepCwind Test

Hywind Prototype

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Current & Planned Work (cont) • Numerically improve how the stretched wave kinematics are interpolated at

the free surface for fixed-bottom • Assess & add 2nd-order hydrodynamic effects:

– Add 2nd-order irregular waves for fixed-bottom (with UT-Austin) – Assess magnitude of mean-draft, slow-drift, & sum-frequency hydrodynamic

loads for floaters (with ETH Zürich) – Add mean-draft, slow-drift, & sum-frequency hydrodynamic loads for floaters

Sea-Surface Elevation (η) from the Combining of 1st- (η1) & 2nd- (η2) Order Waves

P. Agarwal (2008)

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Current & Planned Work (cont) & Future Opportunities

• Current & Planned Work (cont): – Add linear state-space-based radiation

formulation – Interface FAST to an MIT-developed

module with nonlinear fluid-impulse theory – Interface FAST to the TAMU-developed

CHARM3D dynamic mooring code – Develop a standalone dynamic mooring

system module (MAP) • Future Opportunities:

– Add nonlinear regular wave kinematics models for fixed-bottom

– Add ability to prescribe wave time history for floaters

– Floating platform hydro-elastics – Additional/improved nonlinear terms

( ) ( ) ( )t

0

u y t K t u d y

x Ax Buu y

y Cx Du

τ τ τ= −

= += +

∫

Reformulation of Radiation Convolution to Linear

State-Space Form

Questions?

Jason Jonkman, Ph.D. +1 (303) 384 – 7026 jason.jonkman@nrel.gov

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.