Simpack Wind 2010 Swe Loadsimulations

Aeroelastic Load Simulations

and Aerodynamic and Structural

Modeling Effects

Stefan Hauptmann Denis Matha Thomas Hecquet

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

W

in

d

Energy Specif

ic

standards and Guidelines

Standards, Guidelines Guideline Environmental Conditions Loads States of Operation Wind Field

Dynamic Simulation of the System „Wind Turbine“

Hydro-dynamics Aero-dynamics Structural Dynamics 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 Damping Displacements

Serviceability Analysis

(geometry, resonance, dynamic stability)

Common Standards and Guidelines

Validation via

Measure-ments

[Fig.: R. Gasch, Windkraftanlagen]

Major modules of a wind turbine simulation tool 1. wind field

2. rotor aerodynamics

3. structural dynamics including electro-mechanical system 4. control unit and actuators

5. 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:

major minor

[Fig.: M. Kühn]

Model with 28 modal

degrees of freedom (dof)

Foundation:

6 dof‘s

3 translational (1, 2, 4) 3 rotational (3, 5, 6)

Rotor blade (each):

4 dof‘s 2 flapwise (e.g. 16, 17) 2 edgewise (e.g. 18, 19) Tower: 5 dof‘s 2 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

R N K F, T 16, 17 18, 19 20-23 24-27 28 1 2 3 4 5 6 7, 8 9, 10 11 12 13 14 15 x y z flexural beam Wind [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 simulation approach More sophisticated aerodynamic approaches Solution Solution

Modular Integrated Simulation: SIMPACK - Wind

SIMPACK

Wind Turbine MBS Model Rotoraerodynamics v₁ v₂ v3 S BEM Wind Field Lifting Line-Method CFD Generator, Converter AS-Läufer Filter ~ = DC = ~ Trafo PLäufer zum Netz ///PStänder,, fNetz fLäufer Ständer /// [Fig. SWE, ECN, IAG, SIMPACK AG ] 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_Gearbox

1 DOF 1 DOF

, , Shaft torsion, bending

3 DOF LSS_Hub 0 DOF HSS LSS_Hub Blade_ Connect 1 0 DOF (pitch) 0 DOF (pitch) 0 DOF Blade_

Connect 2 Connect 3Blade_

generator Drive Train

Tower (Flexible Body) 4DOF

brake

Blades (Flexible Body) 4DOF/blade Foundation Hub C14-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 Kinematic

Measurement FE-143 Connector and

Fct 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. power P_rated Pitch a ngle [ o ] Wind speed

V_in Vrated Vcut out

Rot. speed

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 PT2 Control system PT1 PT1 Losses M_set x + M_geno W_gen W_gen P_el Electric system dead time Low pass Drivetrain filter Converter delays Electro-technical inertia Electrical & mechanical Losses (look-up table)

W_gen Look-up table Mgeno

AS-Läufer Filter ~ = DC = ~ Trafo P_Läufer zum Netz /// PStänder,, fNetz fLäufer Ständer /// MatSIM • Modeled in Matlab/SIMULINK • Exported to SIMPACK • Using MatSIM

Blade Element Momentum Theory

Basic 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 seperation and at the blade tip)

3. No tangential variation within the annuli

(but empirical correction for finite number of blades)

Loads derived from the global 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 Project

Activities

Objectives

The IEA

O

ffshore

C

ode

C

omparison

C

ollaboration (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

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)

AWSM – Non-linear Lifting Line Vortex Wake Theory

• Developed at ECN, NL

• Blade representation: Lifting line

• Near Wake representation:

Free surface of shed vortices

Coupled Simulations: SIMPACK - AWSM

Simulation time: 12sec Mean Wind speed: 5 m/s Gust: 9m/s for 0.2 sec

Vorticity of rotor blade 1

• Start-up procedure • Occurring wind gust • Aeroelastic effects because of gust t t = 0s t = 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

Fast Individual Pitch Action

Change of pitch angle for blade 1

(+7.3° for 10 seconds)

• Tip deflection blade 1 • Tip deflection blade 3

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+2 Qn Qn+2 Qn tn _tn+1 _tn+2 1 2

Blade surface SIMPACK beam model

SIMPACK blade model with deformation

SIMPACK

FLOWer

Loads calculation _{Loads on element nodes} (principle of virtual disp.) load projection on

beam elements

Conversion of deformations

to quarter chord line Calculation of deformation Grid deformation

SIMPACK WEA model

AeroDyn + SIMPACK FLOWer + SIMPACK AeroDyn + SIMPACK FLOWer + SIMPACK Rotor mo m ent [Nm] Roto th rust [N]

Time-accurate aeroelastic simulation of the start-up phase

(FLOWer + SIMPACK)

Offshore Application I

• Adding capability of SIMPACK to model Offshore Wind Turbines

(Floating & Monopile)

• Coupling of HydroDyn

and SIMPACK

• Hydrodynamic Forces

calculated with HydroDyn

• HydroDyn developed by NREL • Participation in OC4

SIMPACK

HydroDyn

[J on km an, N R E L /T P -500 -41958 ]

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

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)