aeroelastic load simulations and aerodynamic and ... load simulations and aerodynamic and structural...
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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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 4
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 5
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]
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 6
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 7
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 8
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 9
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 10
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 11
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 12
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)
=
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 13
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 14
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 15
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 16
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)
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 17
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
]
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 18
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 19
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)
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 20
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)
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 21
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.
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 22
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 23
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 24
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
]
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 25
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
SIMPACK Conference: Wind and Drivetrain, 17 June 2010 26
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)