jason jonkmansandy butterfield marshall buhlgunjit bir pat moriartyalan wright neil kellybonnie...

Jason JonkmanJason Jonkman Sandy ButterfieldSandy Butterfield

Marshall BuhlMarshall Buhl Gunjit BirGunjit Bir

Pat MoriartyPat Moriarty Alan WrightAlan Wright

Neil KellyNeil Kelly Bonnie JonkmanBonnie Jonkman

2006 Wind Program Peer Review2006 Wind Program Peer Review

May 10, 2006May 10, 2006

Design CodesDesign Codes

22006 Wind Program Peer Review

Outline of Presentation

Introduction & Background

State of the Art Modeling & Limitations

Program Contributions

Current & Future Work


Introduction & BackgroundThe Big Picture

Knowledge AreasWind-Inflow

Waves

Aerodynamics

Aeroacoustics

Hydrodynamics

Elasticity

Controls

Power Generation

Design Standards

wind energy knowledge istransferred to the industry

through design codes

Application AreasConceptual Design

Rotor Performance

Turbine Design

Controller Design

Loads Analysis

Certification

Training

Testing Support

Benchmarking

the advancement of windenergy technology is limited

by design code capability

Design Codes


Introduction & BackgroundModeling Requirements

Fully coupled aero-hydro-servo-elastic interaction

Wind-Inflow:–discrete events–turbulence

Waves:–regular–irregular

Aerodynamics:–induction–rotational augmentation–skewed wake–dynamic stall

Hydrodynamics:–scattering–radiation–hydrostatics

Structural dynamics:–gravity / inertia–elasticity–foundations/moorings

Control system:–yaw, torque, pitch


State of the Art Modeling & LimitationsWind-Inflow

Rotor Performance: steady/uniform

Design: IEC-specified deterministic,discrete inflows and an idealistic neutral turbulence simulation (supported by TurbSim)

Research: TurbSim now provides a variety of specific operatingenvironments including flowsover flat, homogenous terrain, in and near multi-row wind farms,the NWTC Test Site (complex terrain), and the Great Plains with and without the presence of a low-level jet stream


State of the Art Modeling & LimitationsWind-Inflow (cont)

Current Limitations– The Great Plains simulation provides low-level jet wind

speed and direction profiles up to 490 m but the turbulence scaling has been extrapolated with validated data from 120 to 230 m (the top of a future 10MW turbine rotor). Data is needed within this height range for validation.

– The wind farm simulations are only based on validated data up to a height of 50 m, data is needed to expand and validate this capability for modern wind farms consisting of multi-megawatt turbines for both onshore and offshore installations.

– Detailed turbulence measurements and updated models are needed for a range of climatic types in order to better assess potential operating environments and aid in improving siting and turbine reliability.


State of the Art Modeling & Limitations Aerodynamics & Aeroacoustics

THIS SLIDE TO BE EDITED BY PAT

Rotor Performance: BEM (WT_Perf)

Design: GDW, interaction with elasticity

(AeroPrep, AeroDyn)

Research: Vortex, CFD

Current Limitations:– mention what can and cannot be done– corrections for:

• rotational augmentation,• dynamic stall,• unsteady wake,• etc.


State of the Art Modeling & Limitations Aerodynamics & Aeroacoustics (cont)

THIS SLIDE TO BE EDITED BY PAT


State of the Art Modeling & Limitations Offshore Waves & Hydrodynamics

Fixed-Bottom Design: Linear & nonlinear waves + Morison

Floating Design: Linear wave + potential flow (floating)

Research: CFD

Current Limitations:– mention what can and cannot be done– no steep/breaking waves– no 2nd order slow-drift/sum-frequency effects– no sea current/VIV– no sea ice


State of the Art Modeling & Limitations Offshore Waves & Hydrodynamics


State of the Art Modeling & Limitations Structural Dynamics

Design: external geometrymaterial lay-ups

Loads Analysis: Modal (PreComp, BModes, FAST)

Research: Multibody, FEM (ADAMS, RCAS)

Furling - DWT

Current Limitations:– mention what can and cannot be done– No coupled modes– No flap/twist coupling– No precurve/presweep


State of the Art Modeling & Limitations Structural Dynamics (cont)


Program ContributionsUsers & Certification

ADAMS FASTUS Academic 7 18US Government 9 10US Industry 15 25International 9 21

Total 40 74

University of MassachusettsUniversity of Massachusetts


Program ContributionsWhy Develop Design Codes In-House?

Other codes:– Bladed, FLEX5, DHAT, Phatas, HAWC2

Flexibility:– custom design for our unique requirements

Full system Vs. Component level

Support U.S. wind industry:– workshops


Current & Future WorkWind-Inflow Current work:

– Document the development of TurbSim – Use the TurbSim Great Plains Low-Level Jet Spectral Model to

excite the 5MW Reference Turbine to assess and document the effects of these jets on LWST turbines

– Analyze the available Lamar LIDAR data to obtain further validating information of Great Plains LLJ spectral model simulations

– Planning for a workshop on inflow turbulence issues and training in the use of TurbSim

Future plans (2 years out):– Plan field experiment to collect data on turbulence within large,

multi-megawatt wind farms

Future opportunities:– Form a multi-discipline, synergistic effort to understand the role of

coherent inflow turbulence on turbine drive train dynamics and fatigue


Current & Future WorkAerodynamics & Aeroacoustics THIS SLIDE TO BE EDITED BY PAT

Current work:– improved fidelity of GDW– tower influence

Future plans (2 years out):– Rewrite AeroDyn – make modular, provide hooks for other

aero models

Future Opportunities:– Wind tunnel tests/NASA Ames data:

• improve engineering aero modules

– Aerodynamics:• add vortex aero module• Add CFD aero modules


Current & Future WorkOffshore Waves & Hydrodynamics

Current work:– Fixed-bottom– Offshore foundations: p-y, t-z – Floating: WAMIT– Mooring dynamics: Lines – OC3 benchmarking

Future plans (2 years out):– ???

Future opportunities:– breaking waves– 2nd order potential flow


Straight bladeexternal shape

Internalcomposite

materials lay-up

PreComp(analysis)

Coupledstructuralproperties

BModes(isotropic material)

FAST(uncoupled EoM)

Coupled modes

Blade: rotorspeed, pitch,precone, etc.

Uncoupledstructuralproperties

Tower:guy wires

Future Plans(next 2 years)


Internalcomposite

materials lay-up

PreComp(analysis)

Design loads

PreComp(inverse design)



FAST(uncoupled EoM)

Coupled modes


Curved bladeexternal shape

Tower:guy wires

BModes(anisotropic material)

FAST(coupled EoM)

FutureOpportunities

Current & Future WorkStructural Dynamics


Internalcomposite

materials lay-up

PreComp(analysis)



Coupled modes



Tower:guy wires


Current & Future WorkNew Horizons

Gearbox dynamics:– Gearbox housing deflection?– Missing internal gearbox loads?

Tower shadow

Controls/stability analysis

Code validation

FEM


Introduction & BackgroundWhat are Design Codes Used For?

R&D knowledge feeds into codes:– Aero– Hydro– Controls– Etc.

----------------

Preliminary design:– Rotor performance– Material lay-ups

Detailed design:– Loads– Certification

Controller design (see Alan’s presentation)

Research:– new concepts– Benchmarking

Designers are limited by code capability


Introduction & BackgroundDesign / Certification Process

Explain how codes fit into the design/certification process– Preliminary design– Detailed design– research

Load cases– Quantity– type (extreme, fatigue)– Justify need for engineering models, as opposed to straight-

up CFD/FEM



Internalcomposite

materials lay-up

PreComp(analysis)



Coupled modes



Tower:guy wires




Internalcomposite

materials lay-up

PreComp(analysis)



FAST(uncoupled EoM)

Coupled modes



Tower:guy wires

Future Plans(next 2 years)




Internalcomposite

materials lay-up

PreComp(analysis)

Design loads

PreComp(inverse design)



FAST(uncoupled EoM)

Coupled modes


Curved bladeexternal shape

Tower:guy wires

BModes(anisotropic material)

FAST(coupled EoM)

FutureOpportunities



Outline of Presentation

Introduction & Background

Model Development

Sample Results

Conclusions

Future Work

Acknowledgements


Introduction & BackgroundThe Big Picture

Some wind turbines have been installed in shallow water; none in deepwater

A vast deepwater offshore wind resource represents a potential to power much of the world using floating wind turbines

Numerous platform concepts are possible

Simulation tools capable of modeling the dynamic responses are needed

GE Wind Energy 3.6 MW Turbine


Introduction & BackgroundModeling Requirements for Floating Turbines

Turbulent winds

Irregular waves

Gravity / inertia

Aerodynamics:– induction– skewed wake– dynamic stall

Hydrodynamics:– scattering– radiation– hydrostatics

Elasticity

Mooring dynamics

Control system

Fully coupled

0.001

0.010

0.100

1.000

10.000

100.000

0.01 0.10 1.00 10.00Omega (rad/s)

P-M (m^2/(rad/s))

JONSWAP (m^2/(rad/s))

Kaimal ((m/s)^2/(rad/s))

Wind and Wave Spectra

0.001

0.010

0.100

1.000

10.000

100.000

0.01 0.10 1.00 10.00Omega (rad/s)

P-M (m^2/(rad/s))





Model DevelopmentOnshore Wind Turbine SimulatorsFAST Fatigue, Aerodynamics,

Structures, and Turbulence Developed by NREL/NWTC

– Originated from Oregon State University

Wind turbine specific (HAWT) Structural dynamics and controls Combined modal & multibody rep.

(modal for blades and tower) Up to 24 structural DOFs Preprocessor for MSC.ADAMS

MSC.ADAMS® Automatic Dynamic Analysis of

Mechanical Systems Commercial

(MSC.Software Corporation)

General purpose Structural dynamics and controls Multibody dynamics

representation Virtually unlimited structural DOFs Datasets created by FAST

Both use AeroDyn aerodynamics Equilibrium inflow or generalized dynamic wake Steady or unsteady aerodynamics Aeroelastic interaction with structural DOFs


Model DevelopmentOffshore O&G Platform Simulators

Hydrodynamic simulators for offshore platforms developed by the Center for Ocean Engineering, Massachusetts Institute of Technology (MIT)

SML SWIM – treatment of linear and second-order

frequency-domain hydrodynamics MOTION – solutions of the large-amplitude time-

domain slow-drift responses LINES – determines the nonlinear mooring-line /

tether / riser effects upon the platformSML Developed for Offshore Platforms

Wave Analysis @ MIT (WAMIT) solves wave interaction problem

using numerical panel method


Measurements(power, loads, accel., wind)

Aerodynamics(AeroDyn)

StructuralDynamics

(FAST, ADAMS)

Controls(user-defined)

Wind Field(TurbSim, fieldexprmnt., etc.)

Actuator Inputs(blade pitch, gen. torque, yaw)

Aerodynamic Loads(lift, drag, pitch mom.)

Blade Motions(blade pitch, element pos. & vel.)

Wind-Inflow

Time Series Loads(forces, moments)

Time Series Motions(defl., vel., accel.)

OutputHydro-

dynamics Hydrodynamic Loads(radiation, scattering)

Platform Motions(disp., vel., time)



StructuralDynamics

(FAST, ADAMS)


Wind Field(TurbSim, fieldexprmnt., etc.)




Wind-Inflow



Output

Model DevelopmentCoupling Hydrodynamics with Aeroelastics

FAST and the ADAMS processor upgraded to add:– support platform DOFs

– platform loading

SML and WAMIT used where applicable

Add support platform kinematics & kinetics here

Add hydrodynamic loading and mooring system dynamics here


Model DevelopmentSupport Platform Kinematics & Kinetics

Introduce support platform DOFs to FAST and the ADAMS preprocessor:– translational: surge, sway, heave– rotational: roll, pitch, yaw

(assume small rotations)

Include dynamic couplings between motions of platform and turbine:– all position, velocity, and acceleration

expressions are now affected by the platform DOFs

– the wind turbine’s response to wind and wave excitation is fully coupled through the structural dynamics

ZY

X

Heave

Yaw

Roll Surge

Sway

Pitch

Wind

ZY

X

Heave

Yaw

Roll Surge

Sway

Pitch

Wind

Support Platform DOFs


Model DevelopmentSupport Platform Kinematics & Kinetics (cont) The equations of motion (EoMs) in FAST are derived

and implemented using Kane’s Dynamics:– complete, nonlinear aeroelastic EoM:

Total external load on the support platform:– hydrodynamic added mass important since ρwater ≈ ρstructure

(aerodynamic added mass not important since ρair « ρstructure)

– to avoid making the EoM implicit, separate out the added mass components from the rest of the load:

ij j iM q,u,t q f q,q,u,t

Platformi ij j iF = A q f


+ +


Model DevelopmentHydrodynamic Loading—Possible Realizations

Model Advantages Disadvantages Application

Linear Frequency Domain

Many codes available from offshore O&G industry

Results presented in summary form (RAOs or statistics)

Rigid payloadNo nonlinear dynamic characteristics

No transient events

Morison’s Equation Time Domain

Easy to implementEasy to incorporate nonlinear / breaking waves

Diffraction term only valid for slender base

No wave radiation or free surface memory

No added mass-induced coupling between modes

True Linear Time Domain

Satisfy linearized governing BVPs exactly, without restriction on platform size, shape, or manner of motion

Frequency domain solution used as input

Linear waves onlyNo 2nd order effects


Model DevelopmentHydrodynamic Loading (cont)—Assumptions

Assume – Potential Flow:– incompressible and inviscid fluid– irrotational flow– subject only to conservative body forces

Assume – Linearization of Hydrodynamics Problem:– wave amplitudes are much smaller than wavelengths– translational motions of platform are small relative to its size– application of superposition

Limitations:– no nonlinear wave kinematics– no 2nd order slow-drift excitation– no 2nd order sum-frequency effect– no sea current or vortex-induced vibrations (VIVs)– ignore potential loading from floating debris or sea ice


Model DevelopmentHydrodynamic Loading (cont)—Overview

Aij and fi must be defined in:

Problem is split into separate and simpler problems:– Scattering: seek loads on platform when it is fixed and

incident waves are present Froude-Kriloff, diffraction – Hydrostatics: seek loads on platform when it is in equilibrium

and there are no waves present buoyancy– Radiation: seek loads on platform when it oscillates in its

various modes of motion with no incident waves present, but waves radiate away added mass, radiation damping


tWaves Hydrostatic

i i 0 i3 ij j ij j0

f F gV C q K t q d


Waves 2-Sided j t

i i

-

1F t = W 2 S X , e d

2

2-Sided j t

-

1t = W 2 S e d

2

= wave spectrum 2-SidedS W = FFT of White Gaussian Noise = complex wave excitation force per unit wave amplitude, depending on:– geometric shape of platform– frequency and direction of incident wave– proximity to seabed, free surface, etc.– sea current / forward speed– solution to the frequency domain problem

iX ,


tWaves Hydrostatic

i i 0 i3 ij j ij j0

f F gV C q K t q d

Model DevelopmentHydrodynamic Loading (cont)—Scattering

Wave excitation:

Wave elevation:

0.001

0.010

0.100

1.000

10.000

100.000

0.01 0.10 1.00 10.00Omega (rad/s)

P-M (m^2/(rad/s))




-4-3-2-101234

Probability-4-3-2-101234

Time

White Guassian Noise


tWaves Hydrostatic

i i 0 i3 ij j ij j0

f F gV C q K t q d Platformi ij j iF = A q f

= static buoyancy from Archimede’s Principle:– generally cancels with the weight of the floating body and the weight

in water of the mooring lines; separated out due to turbine flexibility

= change in hydrostatic load from the effects of:– waterplane area changes in displaced volume– center-of-buoyancy vector cross product moments

Model DevelopmentHydrodynamic Loading (cont)—Hydrostatics

Hydrostaticij jC q

0 i3gV


Aij and = impulsive added mass and radiation kernel, determined from solution to frequency domain problem:

and = added mass and damping, depending on:– geometric shape of platform – proximity to seabed, free surface, etc.

Wave radiation damping loads exhibit memory effects, meaning they depend on the history of platform motion:– = ith component of load at t due to unit impulse in speed of DOF j

and or

tWaves Hydrostatic

i i 0 i3 ij j ij j0

f F gV C q K t q d Platformi ij j iF = A q f

Model DevelopmentHydrodynamic Loading (cont)—Radiation

ij ij ij

0

2K t = A A sin t d

ij ij

0

2K t = B cos t d

ij ijA = A

ijA ijB

ijK t

ijK t

– frequency of oscillation– sea current / forward speed


Model DevelopmentMooring System Dynamics

A mooring system restrains a support platform with cable tension, depending on:– excess buoyancy of platform– platform location / motion– cable weight in water– hydrodynamic loading– seabed friction– geometrical layout of cables

If the mooring compliance was linear:

Mooring dynamics introduced in FAST and ADAMS by interfacing with LINES module:– ignores effects of bending stiffness

Lines Lines,0 Linesi i ij jF = F C q

Oil Rig TLP


Model DevelopmentCalculation Procedure Summary

Platform Pos. ( )

Wave Spectrumand Direction

Damping(Radiation Kernel)

Incident WaveExcitation

Moorings(Lines)

Platform Motions( , , )

Frequency Domain Hydrodynamics Preprocessor(Swim, WAMIT, etc.)

Mooring Loads

ijA

ijA

ijB

jq jq t

ijA ifHydrodynamic Loads

( , )

Structural Dynamics(FAST, ADAMS)

Added Mass(Radiation Problem)

Damping(Radiation Problem)

Added Mass(Infinite Frequency Limit)

jq

ij ij

0

2K t = B cos t d

iX ,

Seed forRNG

Lines Lines,0 Linesi i ij jF = F C q if linear

Restoring(Buoyancy)

Incident Wave Excitation(Scattering Problem)

WhiteNoise

W

WaveEnvironment

1-SidedS ,


Time Domain Hydrodynamics Routine , ij ijA = A

Hydrostatic0 ijV ,C

Waves Viscous Linesi i i i

tHydrostatic

0 i3 ij j ij j

0

f F F F

gV C q K t q d

Waves 2-Sided j t

i i

-

1F t = W 2 S X , e d

2


Sample ResultsBaseline Wind Turbine & Platform Properties

Wind turbine:– NREL baseline– 5MW rating– 126m diameter– 90m hub height– 700,000kg mass

Baseline WindTurbine with TLP

0E+0

2E+6

4E+6

6E+6

8E+6

0 1 2 3Omega (rad/s)

A11 (kg)

B11 (kg/s)

Added Mass and Dampingin Surge

-2E+6

0E+0

2E+6

0 5 10 15Time (s)

K11 (kg/s^2)

Radiation Kernel in Surge

Platform:– MIT design– TLP– 19m diameter– 17m draft– 134,000kg mass

0E+0

1E+6

2E+6

3E+6

4E+6

0 1 2 3Omega (rad/s)

-180

-90

0

90

180

Wave Excitation in X-Direction

MAG(X1) (kg/s^2)

ANG(X1) (deg)


Sample ResultsMSC.ADAMS Simulation


-5

0

5

10

0 10 20 30 40 50 60Time (sec)

Oo

PD

efl

1 (

m)

-5

0

5

10

15

0 10 20 30 40 50 60Time (sec)

BlP

itc

h1

(d

eg

)

-20

-10

0

10

20

0 10 20 30 40 50 60Time (sec)

Ptf

mS

urg

e (

m)

Sample ResultsFAST & ADAMS Verification

FASTADAMS

FASTADAMS

FASTADAMS


Sample ResultsMSC.ADAMS Simulation


Conclusions

Developed simulation tools capable of modeling a variety of floating wind turbines:– started with FAST and ADAMS preprocessor– added support platform DOFs:

• surge, sway, heave

• roll, pitch, yaw

– added hydrodynamic loading:• scattering

• hydrostatics

• radiation

– added mooring system dynamics (Lines)

Established critical capability to help the US wind industry evaluate design options for deepwater wind development

use SML or WAMIT as preprocessor


Future Work

Using simulation capability:– characterize dynamic response and identify

critical loads and instabilities– assess the role of wind turbine control to provide

platform stability and loads mitigation

New model development:– 2nd order effects– sea current and VIVs– loading from sea ice– fixed-bottom support bases and breaking waves– blade torsion DOF and coupled modes

Model validation and refinement


Acknowledgements

Walt Musial & Sandy Butterfield of NREL for leading US offshore wind research program

Erik Withee of US Navy for initiating study at MIT

Kwang Lee of MIT for verifying output of SWIM

Libby Wayman of MIT for modifying SWIM

My Ph.D. Committee at CU, UW, NREL, & MIT for evaluating the project


Introduction & BackgroundContrasting Modeling Requirements

Onshore Wind Turbines Flexible and dynamically active Turbulent winds in analysis Nonlinear time domain

analysis Controllable

Offshore Floating Wind Turbines Compliant support structure Significant coupling between

turbine and platform motions Response and wave spectra

coalescence Deepwater / linear waves

Offshore Oil & Gas Platforms Rigid and static Steady winds in analysis Linear frequency domain

analysis Passive

Offshore Fixed-Bottom Turbines Rigid support structure Little coupling between turbine

and support structure motions Separation of dynamic

response and wave spectra Shallow water / breaking

waves


Model DevelopmentHydrodynamic Loading—Assumptions Assume – Potential Flow:

– incompressible and inviscid fluid; irrotational flow– subject only to conservative body forces

Assume – Linearization of Hydrodynamics Problem:– wave amplitudes are much smaller than wavelengths– translational motions of platform are small relative to its size– application of superposition

• problem is split into 3 separate and simpler problems: (scattering, hydrostatics, radiation)

Limitations:– no nonlinear wave kinematics– no 2nd order slow-drift excitation– no 2nd order sum-frequency effect– no sea current or vortex-induced vibrations– ignore potential loading from floating debris or sea ice


Model DevelopmentHydrodynamic Loading—Scattering

Scattering: seek loads on platform when it is fixed and incident waves are present

Found by IFFT of the product of wave spectrum, normalized complex wave excitation force, and FFT of White Gaussian Noise

Froude-Kriloff, diffraction loads depend on:– amplitude, frequency, direction of

incident waves– geometric shape of platform– proximity to seabed, free surface, etc.– sea current / forward speed– solution to frequency domain problem

0.001

0.010

0.100

1.000

10.000

100.000

0.01 0.10 1.00 10.00Omega (rad/s)

P-M (m^2/(rad/s))





Model DevelopmentHydrodynamic Loading—Hydrostatics

Hydrostatics: seek loads on platform when it is in equilibrium and there are no waves present

Found by summing static buoyancy and its change with platform displacement

Buoyancy load depends on:– waterplane area– loacation of center-of-buoyancy


Model DevelopmentHydrodynamic Loading—Radiation

Radiation: seek loads on platform when it oscillates in its various modes of motion with no incident waves present, but waves radiate away

Found by convolution of platform velocity and radiation kernel

Radiation kernel found by sin- or cosine-transform of added mass or damping matrices

Added mass, radiation damping loads depend on:– history of platform motion (memory effect)– geometric shape of platform– proximity to seabed, free surface, etc.– sea current / forward speed– solution to frequency domain problem


A mooring system restrains a support platform with cable tension, depending on:– excess buoyancy of platform– platform location / motion– cable weight in water– hydrodynamic loading– seabed friction– geometrical layout of cables

Mooring dynamics introduced in FAST and ADAMS by interfacing with LINES module:– ignores effects of bending stiffness

Model DevelopmentMooring System Dynamics

Oil Rig TLP


Model DevelopmentCalculation Procedure Summary

Measurements(power, loads, etc.)


StructuralDynamics

(FAST, ADAMS)


Wind Field(TurbSim, field

exp., etc.)




Wind-Inflow



Output

Moorings(Lines)

Hydrodynamic Loads(added mass, damping)

Platform Motions(defl., vel., accel.)Time-Domain

Hydrodynamics(Motion)

Wave Env.(Motion, field

exp., etc.)

Freq. To Time(Motion)

Wave Spectrum

Wave History

Freq.-DomainHydrodynamics

(Swim)

Added Mass &Damping Matrices

Mooring Loads(restoring)

Platform Pos.

MODIFY THIS TO INDICATE WHERE SWIM/WAMIT and LINES ARE!!!


Introduction and BackgroundPrevious Studies—Fixed-Bottom

Several wind turbine simulators have been expanded to model fixed-bottom offshore support structures:– use linear wave theory for irregular sea and nonlinear

Stream Function theory for regular sea wave kinematics– use Morison’s equation for hydrodynamic loading:

DUWECS Fixed-Bottom Offshore Turbine

Viscous

i

2 2Platformi A i A i

D i i

dF t

D DdF t = C dz q 1 C dz a t

4 4

1C Ddz v t q v t q

2


Introduction and BackgroundPrevious Studies (cont)—Floating

A few simulators have been developed for the preliminary analysis of floating support structures:– frequency domain:

• Bulder et al — found RAOs and amplitude standard deviations of the 6 rigid body modes

for a tri floater design

• Lee — performed similar analysis for TLP and Spar Buoy designs

• Results — natural frequencies of platform can be designed away from peak of wave spectrum

– time domain:• Henderson — used RAOs to prescribe platform motion in state

domain

• Withee — hydrodynamic loading via Morison’s eq. for a TLP

• Fultan et al — hydrodynamic loading via Morison’s eq. for a TLP

• Results — platform motions have little effect on power performance and rotor loads, but a large effect on nacelle and tower loads

Frequency

RA

O

Frequency

RA

O

Response AmplitudeOperator (RAO)


Introduction and BackgroundPrevious Studies (cont)—Onshore Controls

Disturbance Accommodating Control (DAC) has been used to design multiple-input, multiple-output (MIMO) controllers to mitigate loads and stabilize flexible modes of onshore wind turbines

References:– Stol and Balas

– Hand and Balas

– Wright and Balas

Composite Estimator

Plant State Estimator

Plant

Disturbance Generator

Disturbance Estimator

Du

u

y

x

yy ˆ

Dz

Du

Generator Torque

Nacelle Yaw

Blade Pitch

Control Actions

o

DD

xx

Cxy

uBBuAxx

)0(

0)0(

ˆ

DD

DD

DD

zz

zFz

zu

DG

XG

0)0(ˆ

)ˆ(ˆˆ

ˆˆ

D

DDD

DD

z

yyKzFz

zu

0)0(ˆ

ˆˆ

)ˆ(

ˆˆˆ

x

xCy

yyK

uBBuxAx

X

DD


Thesis Statement and ObjectivesLimitations of Previous Studies

Developed dynamics models are limited in capability:– do not permit multiple platform and mooring configurations– frequency domain models ignore turbine flexibility, nonlinear

dynamic characteristics, and transient events– time domain models ignore the effects of:

• platform size in the diffraction problem

• wave radiation damping and free surface memory

• added mass-induced coupling between modes of motion

Load results are demonstrated through few simulations:– must be verified through a rigorous loads analysis

No attempt to mitigate the increased loads through the application of simple or advanced control theory


Thesis Statement and ObjectivesGoals of Work

To develop simulation tools capable of modeling the fully coupled aeroelastic and hydrodynamic responses of a variety of floating offshore wind turbines

To identify critical loads and/or instabilities that are brought about by the dynamic couplings between and within the turbine and platform in the presence of combined wind and wave loading

To design, simulate, and assess the effectiveness of an advanced controller to mitigate unwanted loads and/or instabilities using generator torque, blade pitch, and/or nacelle yaw


Rating 5MWWind Regime IEC 61400-3 (Offshore) Class 1B / Class 6 windsRotor Orientation UpwindControl Variable Speed, Collective PitchRotor Diameter / Hub Diameter 126m / 3mHub Height 90mMaximum Rotor / Generator Speed 12.1rpm / 1,173.7rpmMaximum Tip Speed 80m/sOverhang / Shaft Tilt / Precone 5m / 5º / -2.5º Rotor Mass 110,000kgNacelle Mass 240,000kgTower Mass 347,460kgReference Site National Data Buoy Center (NDBC) Buoy 44008

Overall c.g. location:(xt,yt,zt) = (-0.2m,0.0m,64.0m)


Approach and MethodsDesign Loads Analysis

Involves verifying structural integrity by running a series of design load cases (DLCs)

IEC 61400-1 for onshore or IEC 61400-3 for offshoreDesign Situation DLC Wind

ConditionWave

ConditionDirectionality Other

ConditionsType of

AnalysisPower production 1.x

Power production plus occurrence of fault

2.x

Start up 3.x

Normal shut down 4.x

Emergency shut down 5.x

Parked 6.x

Parked with fault 7.x

Transport, assembly, and maintenance

8.x

Load Case MatrixCritical Locations


Approach and MethodsDesign Loads Analysis (cont)

Using FAST, I will compare load case simulation results between the onshore and offshore configurations:– use NREL’s baseline wind turbine and reference site– pick one candidate support platform concept and subset of DLCs– Identify critical loads and/or instabilities brought about by the

dynamic couplings and combined wind and wave loading

Q: Is power performance degraded?

Q: Where and by how much are loads increased?

Q: What are the dominant instabilities?

0

1

2

3

Off

sho

re L

oad

÷ O

nsh

ore

Lo

ad

Blade Root Shaft Yaw Bearing Tower Base


Approach and MethodsControls Design

I will use DAC to design MIMO state-space controllers to mitigate detrimental loads and/or instabilities:– pick one or two of the critical loads and/or instabilities– extend linearization capability of FAST to include states and

disturbances associated with platform motion and wave loading

– implement and test controller in FAST/Simulink interface

Q: Can independent pitch, torque, or yaw be used to control combinations of wind and wave loading?

– including side-to-side loading?

Q: Are actuators other than pitch, torque, and yaw required for controllability?

Q: What measurements are needed for observability?– blade root & shaft strain gages, nacelle accelerations, etc.?


Approach and MethodsProject Scope

ControlsDesign

Design LoadsAnalysis

Simulation Capability

Floating Platform Concepts

As I get deeper in depth,

I narrow my focus




StructuralDynamics

(FAST, ADAMS)

Controls


exp., etc.)




Wind-Inflow



OutputHydro-



Recent ProgressSupport Platform Kinematics & Kinetics

Add support platform kinematics & kinetics here


Recent ProgressSupport Platform Kinematics & Kinetics (cont)

Assume small rotations:– rotation order doesn’t matter– use linearized Euler transformation:

3 2

3 1

2 1

x 1 X

y 1 Y

z 1 Z

2 2 2 2 2 2 2 2 2 2 2 22 2 2 2 2 2

3 1 2 3 1 2 1 2 3 2 1 2 3 1 3 1 2 31 1 2 3 2 3

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 21 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

2 2 23 1 2 3 1 2 1

1 1 1 11

1 1 1

x 1y

z

2 2 2 2 2 2 2 2 22 2 2 2 2 2

2 3 1 1 2 3 2 3 1 2 31 2 1 2 3 3

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 21 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

2 2 2 2 2 22 1 2 3 1 3 1 2 3 1

2 2 2 2 2 21 2 3 1 2 3

1 1 11

1 1 1

1 1

1

2 2 2 2 2 22 2 2 2 2 2

1 2 3 2 3 1 2 31 2 3 1 2 3

2 2 2 2 2 2 2 2 2 2 2 21 2 3 1 2 3 1 2 3 1 2 3

X

Y

Z

1 1 1

1 1

The closest orthonormal matrix in the Frobenius norm sense is [U][V]T where [U] and [V] are the matrices of eigenvectors inherent in the Singular Value Decomposition (SVD) of the matrix

Orthogonal Rotations

1

2

3

1

23

1

12

131

X

Y

Z

x

y

z

Not an orthonormal transformation

:. use a correction



Aerodynamics(AeroDyn )

StructuralDynamics

(FAST, ADAMS )

Controls


exp., etc. )




Wind-Inflow



OutputHydro-



Recent ProgressHydrodynamic Loading

Add hydrodynamic loading and mooring system dynamics here


Work Plan

1. Review Background Literature September 2005 Learn fundamentals of marine hydrodynamics Identify computational methodologies used by other

simulation tools developed for offshore wind turbines Examine requirements for determining design loads Learn about design process for advanced controls

2. Develop Simulator December 2005 Add support platform DOFs to FAST Develop a support platform hydrodynamics loading model

and interface it to FAST and ADAMS Interface LINES module to FAST and ADAMS Verify response predictions between FAST and ADAMS

and frequency domain results Publish AIAA paper on model development activities


Work Plan (cont)

3. Establish Baseline Turbine & Site February 2006 Identify baseline turbine rating and reference site location Establish aerodynamic and structural properties Define a baseline control system Create FAST and ADAMS models Identify and design candidate support platform concepts Establish a design basis at the reference offshore site

4. Perform Design Loads Analysis October 2006 Pick one of the candidate support platform concepts for

subsequent analysis Identify a subset of DLCs to run Run DLCs to determine on- and offshore design loads Compare results to identify critical loads and/or instabilities Publish conference paper on modeling results


Work Plan (cont)

5. Controls Design March 2007 Pick one or two critical loads and/or instabilities for

subsequent analysis Design an advanced torque, pitch, and/or yaw controller to

mitigate the unwanted loads and/or instabilities Implement and simulate the controller in FAST Assess the effectiveness of the controller

6. Complete Requirements of Ph.D. May 2007


Thesis Contributions

Develop simulation tools capable of modeling a variety of floating offshore wind turbines

Characterize the dynamic response and identify critical loads and instabilities

Assess the role of wind turbine control to provide platform stability and loads mitigation

Establish a critical capability to help the US wind industry evaluate design options for deepwater wind development


Introduction and BackgroundWind Turbine Fundamentals

WindTurbine

Wind Speed

Po

we

r

1 2 3

Rated

Cut-InCut-Out

Generator Torque

Nacelle Yaw

Blade Pitch

Control Actions


Introduction and BackgroundWhy Offshore?

Higher-quality wind resource:– less turbulence, smaller shear– stronger, more consistent winds

Economies of scale:– avoid logistical constraints on size

Proximity to loads:– many demand centers near coastline

Increased transmission options:– access to less heavily loaded lines

Potential for reducing land use, noise, and aesthetic concerns

GE Wind Energy 3.6 MW Turbine


Introduction and BackgroundWhy Floating?

Region 0 - 30 30 - 60 60 - 900 > 900New England 10.3 43.5 130.6 0.0Mid-Atlantic 64.3 126.2 45.3 30.0Great Lakes 15.5 11.6 193.6 0.0California 0.0 0.3 47.8 168.0Pacific Northwest 0.0 1.6 100.4 68.2Total 90.1 183.2 517.7 266.2

GW by Depth (m)


Model DevelopmentHydrodynamic Loading—Possible Realizations Frequency Domain Representation

– find Response Amplitude Operators (RAOs)

– ignore turbine flexibility

– ignore nonlinear dynamic characteristics

– ignore transient events

Morison’s Representation– valid for slender, vertical, surface-piercing cylinders

– Easily incorporate nonlinear and breaking waves

– ignore effects of platform size in diffraction problem

– ignore wave radiation damping and free surface memory

– ignore added mass-induced coupling between modes of motion

True Linear Hydrodynamic Representation in the Time Domain:– satisfy the linearized governing BVPs exactly without restriction on

platform size, shape, or manner of motion

Frequency

RA

O

Frequency

RA

O

Response AmplitudeOperator (RAO)


Thesis Statement and ObjectivesLimitations of Previous Studies Developed dynamics models are limited in capability:

– do not permit multiple platform and mooring configurations important to have for configuration trade-off studies

– the frequency domain models ignore turbine flexibility, nonlinear dynamic characteristics, and transient events important considerations for wind turbines

– the time domain models ignore the effects of:• platform size in the diffraction problem important for large platforms• wave radiation damping and free surface memory important for

platforms with compliance• added mass-induced coupling between modes of motion important for

platforms that are not axisymmetric

Load results are demonstrated through few simulations:– must be verified through a rigorous loads analysis important to

characterize the dynamic response and identify design-driving loads

No attempt to mitigate the increased loads through the application of simple or advanced control theory important to minimize cost


Thesis Statement and ObjectivesHypothesis

Existing aeroelastic models can be expanded to include the important loading and responses representative of floating offshore wind turbines

and will demonstrate that the increased dynamic complexity produces detrimental loads and/or instabilities,

which can then be mitigated through the development of advanced controls

This work is critical to determining the most technically attractive and economically feasible floating wind turbine design


Codes for Component and Full System Level Analysis

Component Level

– Determine design integrity of individual components based on specified loads

– Single-physics model

– Not industry-specific

– Commercial products available (ANSYS, etc.)

Full System Level

– Determine loads throughout full system for component level analysis

– Multi-physics model

– Industry-specific

– Developed for particular application (FAST, etc.)


Model Fidelity for Multi-Physics Simulation Tools

• Numerical Panel Method

• Vortex Method

• Computational Fluid Dynamics

• Finite Element Method

Research

• Analytical Time Domain

• Dynamic Inflow• Modal

• Multi-BodyDetailed Design

• Freq. Domain• Blade Element / Momentum

• None

Preliminary Design

Platform

Hydrodynamics

Rotor

Aerodynamics

Structural Dynamics

• Numerical Panel Method

• Vortex Method

• Computational Fluid Dynamics

• Finite Element Method

Research

• Analytical Time Domain

• Dynamic Inflow• Modal

• Multi-BodyDetailed Design

• Freq. Domain• Blade Element / Momentum

• None

Preliminary Design

Platform

Hydrodynamics

Rotor

Aerodynamics

Structural Dynamics

1st mode2nd mode1st mode2nd mode

Frequency

RA

O

Frequency

RA

O

Inc

reas

ing

Co

mp

lexi

tyIn

cre

asin

g C

om

ple

xity


Approach and MethodsDevelopment of a Coupled Simulator (cont)

24 degrees of freedom (DOFs) available for 3-bladed, 22 DOFs available for 2-bladed turbine:– blade flexibility: 2 flap and 1 edge mode DOF per blade– tower flexibility: 2 fore-aft and 2 side-to-side mode DOFs

– drivetrain: 1 variable generator speed DOF and 1 shaft torsion DOF

– nacelle yaw: 1 yaw hinge DOF

– rotor teeter: 1 rotor teeter hinge DOF with optional 3 (for 2-bladed rotor only)

– rotor-furl: 1 furl hinge DOF of arbitrary orientation and location between the nacelle and rotor

– tail-furl: 1 furl hinge DOF of arbitrary orientation and location between the nacelle and

tail

– platform: 3 translation (surge, sway, and heave) and 3 rotation (roll, pitch, and yaw) DOFs

1st mode2nd mode

ModalRepresentation


Users and Certification

ADAMS FASTUS Academic 7 18US Government 9 10US Industry 15 25International 9 21

Total 40 74

University of MassachusettsUniversity of Massachusetts


FAST, ADAMS & AeroDyn Interaction

Linearization(exe only)

SystemProperties

FASTInput Files

FAST

Time-SeriesData

Periodic StateMatrices

ADAMSAeroDyn

ADAMSDatasets

Simulation(exe or

Simulink DLL)

AeroDyn

FAST-to-ADAMSPreprocessor

(exe only)

Time-SeriesData

Simulation(ADAMS Solver)

AeroDynInput Files

User-DefinedRoutines

User-DefinedRoutines


Recent ProgressSupport Platform Kinematics & Kinetics (cont) The equations of motion (EoMs) in FAST are derived

and implemented using Kane’s Dynamics

*r rF F 0 r 1,2, ,NDOF

i i i i i iN N N N N NE E E EH I α ω I ω

NDOF

rr 1

q,q,t q,t q q,t

i i iN N NE E E

r tω ω ω

NDOF

rr 1

q,q,t q,t q q,t

i i iX X XE E E

r tv v v

Kane’s EoM for holonomic system:

Generalized active forces: Generalized inertia forces:

w

ri 1

F

r 1,2, ,NDOF

i i i iX X N NE Er rv F ω M

i

wN*

ri 1

F m

r 1,2, ,NDOF

i i i iX X N NE E E Er rv a ω H

Partial angular velocities:

Partial linear velocities: iN

iX

w = # of rigid bodies

= rigid body i

= mass center of rigid body i


Platform Concepts: Analysis Capabilities

Tri Floater

Monopile

Tripod Lattice

Tension Leg Platform

(TLP)

Taut Leg Spar Buoy

Disk Buoy with Catenary Moorings

Wind Turbine On

Boat

X X

X X


Future Offshore Code Development Direction

Modeling of fixed bottom support structures– monopiles– multiple-member support structure– P-y foundations– shallow water (breaking) waves

2nd order mean (wave drift), difference-frequency (slow drift), and sum-frequency wave loading

Sea current / forward speed effects

Model validation and refinement

jason jonkmansandy butterfield marshall buhlgunjit bir pat moriartyalan wright neil kellybonnie...

Documents

wind program peer review

pat slide

modern wind farms

pitch slide

wind farm simulations

multirow wind farms

cfd current limitations

lowlevel jet wind speed