Aeroelastic Load Simulations and Aerodynamic and ... Load Simulations and Aerodynamic and Structural Modeling Effects Stefan Hauptmann Denis Matha Thomas Hecquet Hamburg, 17 June 2010

Aeroelastic Load Simulations and Aerodynamic and Structural

Modeling Effects

Stefan HauptmannDenis Matha

Thomas Hecquet

Hamburg, 17 June 2010

SIMPACK Conference: Wind and Drivetrain

SIMPACK Conference: Wind and Drivetrain, 17 June 2010 2

Contents

• Dynamic Simulations in the WT Design Process

• Wind Turbine Modeling in SIMPACK

• Wind Turbine Aerodynamics in SIMPACK– Blade element Momentum Theory (BEM)– Non-linear Lifting Line Vortex Wake Model – Computational Fluid Dynamics (CFD)

• Simulation Results– Offshore Code Comparison Collaboration (OC3)– Evaluation of Lifting Line Vortex Wake Model– Validation of CFD Approach for Aeroelastic Simulations

• Offshore Applications

• Conclusions

SIMPACK Conference: Wind and Drivetrain, 17 June 2010 3W

ind

Ener

gy S

peci

fic

stan

dard

s an

d G

uide

lines

Standards, Guidelines

GuidelineEnvironmental

Conditions Loads States of Operation

Wind Field

Dynamic Simulation of the System „Wind Turbine“

Hydro-dynamics

Aero-dynamics

StructuralDynamics

Electr.System

Control,Operation

Structural Loads (time series or spectra, extreme values,

load collectives)

Site WT-Type

(Static) Mechan. Component model(FEM, analytical oder empirical)

Ultimate Strength Analysis(fracture, buckling, fatigue)

Natural Frequencies and

DampingDisplacements

Serviceability Analysis(geometry, resonance, dynamic stability)

Com

mon

Sta

ndar

ds

and

Gui

delin

es

Validation via

Measure-ments

[Fig.: R. Gasch, Windkraftanlagen]

Dynamic simulations in the WT design process


Major modules of a wind turbine simulation tool1. wind field2. rotor aerodynamics3. structural dynamics including electro-mechanical system4. control unit and actuators5. Hydrodynamics (Offshore turbines)

Wind field

Wave field, currents, ice

Soil

Aero-dynamics

Hydro-dynamics

Soil-dynamics

Rotor

Support structure (Tower &

Foundation)

Grid

Environment Loads Support structure Consumption

Electro-mech. System

Control

Offshore Wind Turbine

Dynamic interactions:

majorminor

[Fig.: M. Kühn]

Integrated system model


Model with 28 modal degrees of freedom (dof)Foundation:6 dof‘s3 translational (1, 2, 4)3 rotational (3, 5, 6)

Rotor blade (each):4 dof‘s2 flapwise (e.g. 16, 17)2 edgewise (e.g. 18, 19)

Tower:5 dof‘s2 fore-aft (7, 8)2 lateral (9, 10)1 torsional (11)

Additionals dof‘s:nacelle tilt (12)rotor rotation (13)main shaft bending (14, 15)drive train torsion (28)

Traditional dynamic model for aeroelastic simulation

RN

K

F, T

16, 17 18, 19

20-23

24-27

28

1

2

3

45

6

7, 8

9, 10

11

1213

1415

x

yz

flexural beam

Win

d

[Fig.: Vestas]


Motivation - Improvements needed

Limitations of the traditional dynamic model• Structure: Fixed number of only few modal degrees of Freedom• Aerodynamics: Simplified representation of rotor aerodynamics by BEM theory• Problem: Coupling effects are NOT considered

Improvements for Structural dynamics• Flexible levels of detail for the wind turbine models• More accurate models for rotor blades, drive train etc.

Improvements for Aerodynamics• New engineering models for BEM ? • Codes, based on more advanced theories than

BEM are needed to consider some aeroelastic effects

Multibody simulationapproach

More sophisticated aerodynamic approaches

Solution

Solution


Modular Integrated Simulation: SIMPACK - Wind7

SIMPACKWind Turbine MBS Model

Rotoraerodynamics

v1

v2v3

S

BEM

Wind Field

Lifting Line-Method

CFDGenerator, Converter

AS-Läufer

Filter~=

DC~

=Trafo

PLäufer

zum Netz///

PStänder,, fNetz

fLäufer

Ständer

///

[Fig

. SW

E, E

CN

, IA

G, S

IMP

AC

K A

G ]

Controller Interface


Dynamic wind turbine model in SIMPACK

• “Traditional Dynamic Model”

• 28 Degrees of Freedom

• Used for a large number of load simulations

Foundation_Ground

,yaw), (tilt)2 DOF

UF22 Aerodyn

x, y, z, , ,6 DOF

0 DOF

Foundation

0 DOF

0 DOF

Bedplate_Connect

Drive train / base plate

LSS_Gearbox1 DOF1 DOF

, ,Shaft torsion, bending

3 DOF

LSS_Hub

0 DOF

HSSLSS_Hub

Blade_Connect 1

0 DOF

(pitch)

0 DOF

(pitch)

0 DOF

Blade_Connect 2

Blade_Connect 3

generator

Drive Train

Tower (Flexible Body)4DOF

brake

Blades (Flexible Body)4DOF/blade

Foundation

HubC14-Gearbox

Gearratio (constraint)

Tower

Pitch_Reference_1

(pitch)

Pitch_Reference_2

Pitch_Reference_3

0 DOF 0 DOF 0 DOF

FE-43 Bushing

FE-13 Spring Rot

FE-110 Proportional Actuator Cmp

FE-165 KinematicMeasurement

FE-143 Connector andFct generators

FE-43 Bushing


Rotor Blade Models

Automatic generation of 2 different kinds of rotor blade models

• Euler-Bernoulli or Timoshenko beam elements

• Modal Reduction

• Geometric stiffening

• Simple rotor blade– Only bending modes are considered

• Sophisticated rotor blade– Bending and Torsional Modes are considered– Coupling effects are included


The Control System Interface

• DLL – interface

• Bladed compatible

• Baseline controller– Variable speed below rated– Collective pitch control above

rated power

• Advanced control algorithms– Individual pitch control– (Tower-) Feedback controller– Etc.

El. p

ower

Prated

Pitc

han

gle

[o ]

Wind speedVin Vrated Vcut out

Rot

. spe

ed

90o


Generator Models (Variable Speed Generator)

– Static look-up table

– Simulation of generator/converter system dynamics

– Detailed electrical model of the coupled generator, converter and grid

FiFo PT2Controlsystem PT1PT1

Losses

Msetx

+Mgeno

WgenWgen

Pel

Electricsystem

dead time

Low passDrivetrain

filterConverter

delays

Electro-technical

inertia

Electrical &mechanical

Losses(look-up table)

Wgen Look-up tableMgeno

AS-Läufer

Filter~=

DC~

=Trafo

PLäufer

zum Netz///

PStänder,, fNetz

fLäufer

Ständer

///

MatSIM

• Modeled in Matlab/SIMULINK• Exported to SIMPACK • Using MatSIM


Blade Element Momentum TheoryBasic approach: Load equilibrium in axial and radial direction

=> Iterative derivation of induced velocities

Important assumptions:1. Stream Tube theory and

splitting in isolated annuli (no radial interdependency)

2. No radial flow along the blades(problematic in combination with flow seperationand at the blade tip)

3. No tangential variation within the annuli(but empirical correction for finite number of blades)

Loads derived from theglobal momentum balance(depending on the induced velocities)

Loads at the local blade element(depending on the induced velocities)

=


AeroDyn - Blade Element Momentum Theory

• Developed at the National Renewable Energy Laboratory, USA

• Empirical correction models:– Tip-Loss Model: Prandtl– Hub-Loss Model: Prandtl– Turbulent wake state: Glauert Correction– Dynamic stall model: Beddoes-Leishman– Skewed Wake Correction: Pitt and Peters


The OC3 ProjectA

ctiv

ities

Obj

ectiv

esThe IEA Offshore Code Comparison Collaboration (OC3) is an

international forum for OWT dynamics code verification

• Discuss modeling strategies• Develop suite of benchmark models & simulations• Run simulations & process results• Compare & discuss results

• Assess simulation accuracy & reliability• Train new analysts how to run codes correctly• Investigate capabilities of implemented theories• Refine applied analysis methods• Identify further R&D needs


OC3 Participants & Codes• 3Dfloat• ADAMS-AeroDyn-HydroDyn• ADAMS-AeroDyn-WaveLoads• ADCoS-Offshore• ADCoS-Offshore-ASAS• ANSYS-WaveLoads• BHawC• Bladed• Bladed Multibody• DeepC• FAST-AeroDyn-HydroDyn• FAST-AeroDyn-NASTRAN• FLEX5• FLEX5-Poseidon• HAWC• HAWC2• SESAM• SIMPACK-AeroDyn• Simo


Exemplary SIMPACK/AeroDyn Result in OC3

0,0

20000,0

40000,0

60000,0

80000,0

100000,0

120000,0

NREL FAST (kN·m)

GH Bladed (kN·m)

SWE FLEX5 (kN·m)

NREL ADAMS (kN·m)

Risoe HAWC2 (kN·m)

SWE SIMPACK (kN·m)

Model Results for Tower Base Bending Moment (OC3 Phase 1 DLC 3.2)


AWSM – Non-linear Lifting Line Vortex Wake Theory

• Developed at ECN, NL

• Blade representation: Lifting line

• Near Wake representation: Free surface of shed vortices

[Fig

.: E

CN

]


Coupled Simulations: SIMPACK - AWSM

Simulation time: 12secMean Wind speed: 5 m/sGust: 9m/s for 0.2 sec

Vorticity of rotor blade 1

• Start-up procedure

• Occurring wind gust

• Aeroelastic effects because of gust

t

t = 0st = 6s

t = 12s WRotor


Demonstration Simulation

Turbine:• 1,5 MW NREL generic wind turbine• 8 m/s wind speed

Modeling approach• Only the rotor (hub and three rotor blades) is modeled• Flexible rotor blades

– Sophisticated model– Coupling effects are considered

Aerodynamics• AWSM• AeroDyn (with empirical correction models activated)


Fast Individual Pitch Action

Change of pitch angle for blade 1(+7.3° for 10 seconds)• Tip deflection blade 1 • Tip deflection blade 3• Tip deflection blade 3 (detail view)


FLOWer – A RANS solver

• Developed to solve the three-dimensional, compressible, unsteady Euler or Reynolds averaged Navier-Stokes (RANS) equations

• Analyses the flow field around rotors (primarily for helicopters, adapted to wind turbines)

• Different turbulence models are available(but the k-ω SST turbulence model is the sole model used in this project)

• FLOWer features the Chimera technique allowing for arbitrary relative motion of aerodynamic bodies.


Fluid

Structure

Qn+1

Qn+1 Qn+2Qn

Qn+2Qn

tn tn+1 tn+2

1

2

Blade surface SIMPACK beam model

SIMPACK blade modelwith deformation

SIMPACKFLOWer

Loads calculation Loads on element nodes(principle of virtual disp.)

load projection onbeam elements

Conversion of deformations

to quarter chord line Calculation of deformationGrid deformation

SIMPACK WEA model

Time-Accurate Fluid-Structure Coupling of Wind Rotors


AeroDyn + SIMPACKFLOWer + SIMPACK

AeroDyn + SIMPACKFLOWer + SIMPACK

Rot

or m

omen

t[N

m]

Rot

oth

rust

[N]

Time-accurate aeroelastic simulation of the start-up phase

(FLOWer + SIMPACK)

Validation of Fluid-Structure Coupling


Offshore Application I

• Adding capability of SIMPACK to model Offshore Wind Turbines(Floating & Monopile)

• Coupling of HydroDynand SIMPACK

• Hydrodynamic Forcescalculated with HydroDyn

• HydroDyndevelopedby NREL

• Participationin OC4

SIMPACK

HydroDyn

[Jon

kman

, NR

EL/T

P-50

0-41

958

]


Offshore Application II

• Mooring Lines are an important component for Floating WT Dynamics

• Currently mainly quasi static and linear models• Introduction of a nonlinear multi-body mooring system

model• Improvement of load predictions by considering line

dynamics, hydrodynamics, line-seabed interaction, nonlinear effects & anchor system

• Goal: Detailed modeling of floating WT in SIMPACK


Conclusions

• The traditional approach for load simulations has limitations:– The number of degrees of freedom for dynamic models is fixed– The rotor aerodynamics is modeled using simplistic BEM theory

• SIMPACK offers advantages for load simulations– MBS models with a variable level of detail can be generated– Different aerodynamic modules can be coupled to SIMPACK to consider

aeroelastic effects with the needed accuracy

• SIMPACK Interfaces to several aerodynamic codes have been developed– AeroDyn (Blade Element Momentum Theory)– AWSM (Non-linear Lifting Line Vortex Wake Theory)– FLOWer (RANS solver)

Documents

Aeroelastic Load Simulations and Aerodynamic and ... Load Simulations and Aerodynamic and Structural Modeling Effects Stefan Hauptmann Denis Matha Thomas Hecquet Hamburg, 17 June 2010