2015 12-02-optiwind-offshore-wind-turbine-modelling-lms-samsef-siemens
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Emilio Di Lorenzo – Research engineer – Siemens Industry Software nv PhD candidate at KU Leuven and University of Naples "Federico II" emilio.dilorenzo@siemens.com
OFFSHORE WIND TURBINE MODELLING IN LMS SAMCEF TO DERIVE AND VALIDATE NEW PROCESSING APPROACHES
Optiwind Open Project Meeting, Leuven, Belgium 02/12/2015
E. Di Lorenzo, S. Manzato
Agenda
1. Introduction
2. Rotor analysis
1. MBC transformation
2. HPS method
3. Validation cases
4. Conclusions
3. Gearbox analysis
1. Operational Modal Analysis
2. Order-Based Modal Analysis
3. Validation cases
4. Conclusions
Objectives
• Understand the problems and limitations of applying Operational Modal Analysis (OMA) techniques to wind turbines in operation
Deal with the time-variant nature of the structure Deal with presence of harmonics components
• Development of methodologies for automated data
processing for online structural health monitoring (SHM) applications
Operational Modal Analysis - OMA
• Identification of modal parameters (natural frequencies, damping ratios, mode shapes) from response data measured in operating conditions
• Operational Modal Analysis = identifying H without knowing U (white noise assumption) based on Y
Unkown input Structure Measured output
U H
Y
310.000.00 s
0.34
-0.36
Rea
lg
1.00
0.00
Ampl
itude
OMA: Limitations and solutions
Agenda
1. Introduction
2. Rotor analysis
1. MBC transformation
2. HPS method
3. Validation cases
4. Conclusions
3. Gearbox analysis
1. Operational Modal Analysis
2. Order-Based Modal Analysis
3. Validation cases
4. Conclusions
Rotor analysis
• Analyze the modal behaviour of Linear Time Periodic (LTP) systems.
• Analyze data with an harmonic dominance which masks the structural dynamics.
• Find modal parameters sensitive to small structural damages for SHM purposes.
Multi-Blade coordinate transformation - MBC
• Method to describe the motions of individual blades in the same coordinate system as the structure supporting the rotor
• Offers physical insight into rotor dynamics and how rotor interacts with fixed-system entities
• Fundamental assumption: rotor must be isotropic
• Filters out all periodic terms except those which are integral multiples of ΩN, where Ω is the rotor angular speed and N is the number of blades G.S.Bir – Multiblade Coordinate Transformation and
its Application to Wind Turbine Analysis
Multi-Blade coordinate transformation - MBC
∑=
=N
bibi q
Nq
1,,0
1
( )b
N
bibic nq
Nq ψ∑
=
=1
,, cos2
)(sin21
,, b
N
bibis nq
Nq ψ∑
=
=
Mode animation
Mode shapes in physical coordinates
Inverse MBC transformation
OMA
Mode shapes in multiblade coordinates
Modal frequencies & damping ratios
Accelerations in multiblade coordinates
MBC transformation
Accelerations of points on the
blades
Data from measurement campaign/aeroelastic code
Accelerations of points on the tower/nacelle
RESULTS
)sin()cos( ,,,0, bisbiciib qqqq ψψ ++=
• Input at a single frequency will cause output at a single frequency
𝑢 𝑡 = 𝑢0 sin 𝜔𝑡
y 𝑡 = 𝑦0 sin 𝜔𝑡 − 𝜙
Harmonic Power Spectrum - HPS
Linear Time Invariant (LTI) system �̇� = 𝑨𝑥 + 𝑩𝑢 𝑦 = 𝑪𝑥 + 𝑫𝑢
Linear Time Periodic (LTP) systems �̇� = 𝑨(𝑡 + 𝑇𝐴)𝑥 + 𝑩(𝑡 + 𝑇𝐴)𝑢
𝑦 = 𝑪(𝑡 + 𝑇𝐴)𝑥 + 𝑫(𝑡 + 𝑇𝐴)𝑢
• Input at a single frequency will cause output at an infinite number of frequencies
𝑢 𝑡 = 𝑢0 sin 𝜔𝑡
y 𝑡 = 𝑦0 sin 𝜔𝑡 − 𝜙 + 𝑦1 sin (𝜔 + 𝜔𝐴𝑡) − 𝜙 + ⋯
𝜔𝐴 =2𝜋𝑇𝐴
Harmonic Power Spectrum - HPS
Linear Time Invariant (LTI) system �̇� = 𝑨𝑥 + 𝑩𝑢 𝑦 = 𝑪𝑥 + 𝑫𝑢
Linear Time Periodic (LTP) systems �̇� = 𝑨(𝑡 + 𝑇𝐴)𝑥 + 𝑩(𝑡 + 𝑇𝐴)𝑢
𝑦 = 𝑪(𝑡 + 𝑇𝐴)𝑥 + 𝑫(𝑡 + 𝑇𝐴)𝑢
𝑢 𝑡 = 𝑢0 sin 𝜔𝑡
y 𝑡 = 𝑦0 sin 𝜔𝑡 − 𝜙 + 𝑦1 sin (𝜔 + 𝜔𝐴)𝑡 − 𝜙 + ⋯ y 𝑡 = 𝑦0 sin 𝜔𝑡 − 𝜙
u𝑛 𝑡 = � 𝑢(𝑡)𝑒 𝑖𝜔+𝑖𝑛𝜔𝐴 𝑡𝑑𝑡∞
−∞
y𝑛 𝑡 = � 𝑦(𝑡)𝑒 𝑖𝜔+𝑖𝑛𝜔𝐴 𝑡𝑑𝑡∞
−∞
Power Spectrum (LTI system) Harmonic Power Spectrum (LTP system)
𝑢 𝑡 = 𝑢0 sin 𝜔𝑡
M. S. Allen et al. – Output-Only Modal Analysis of Linear Time Periodic Systems with Application to Wind Turbine Simulation Data
EMP
Harmonic Power Spectrum - HPS
Mode animation
Time periodic mode shapes
Harmonic Power
Spectrum (HPS)
Modal frequencies & damping ratios
Exponentially Modulated
Periodic (EMP) signal
Accelerations of points on the wind turbine under random
excitation
Data from measurement campaign/aeroelastic code
RESULTS
OMA
Summation over the
harmonics
Mode shapes at different harmonics
Reference wind turbines
NREL 5-MW WIND TURBINE Rated rotor speed 12.1 rpm Generator rated power 5 MW Tower Height 87.6 m Tower Mass 347*103 kg Nacelle Mass 240*103 kg
NREL 5-MW Wind Turbine
DTU 10-MW WIND TURBINE Rated rotor speed 9.6 rpm Generator rated power 10 MW Tower Height 119 m Tower Mass 628*103 kg Nacelle Mass 446*103 kg
DTU 10-MW Wind Turbine
2D WIND TURBINE m1 = m2 = m3 41,7*103 kg mT 446*103 kg k1 = k2 = k3 2,006*108 Nm/rad kH 2,6*106 N/m kV 5,2*108 N/m
2D Wind Turbine
2D Wind Turbine
1.500.00 Hz
0.01e-3
1.00e-12Lo
g
g2
180.00
-180.00
°
Before MBC - bladeAfter MBC - bladeTower
1.500.00 Hz
0.01e-3
0.10e-12
Log
g2
180.00
-180.00
°
Before MBC - bladeAfter MBC - bladeTower
• Crosspower comparison before and after MBC transformation • Isotropic rotor vs. Anisotropic rotor (k3=0.85*k1) • Same considerations can be done by applying HPS method • Very good match between MBC and HPS results has been found
Isotropic rotor Anisotropic rotor
2D Wind Turbine
No transformation
• White noise input • Extract displacement from the model and
apply OMA technique • Estimate modal parameters by means of
Operational Polymax
MBC transformation
HPS method
MBC AutoMAC HPS AutoMAC
MAC: (MBC) vs. (HPS selection)
Mode #
Freq [Hz]
S2S 0,37
B_as 0,84
B_coll 0,84
B_as 0,92
Mode #
Freq [Hz]
S2S 0,37
B_bw 0,74
B_coll 0,86
B_fw 1,06
Parked Operating (Ω=0.16 Hz)
2D Wind Turbine
Tower S2S mode Collective Edge mode
Backward Whirling
mode
Forward Whirling
mode
Backward Whirling Mode
f=0.37 f=0.74 f=0.86 f=1.06
2D Wind Turbine
Backward Whirling Mode
k1= 0.98*k1
• Isotropic conditions: Backward and forward whirling mode shapes have a constant amplitude for each blade and the phase lag between the blades is equal to 120°
• Anisotropic conditions: These properties are lost. The damaged blade amplitude is higher than the others. The phase lag is not anymore equal to 120°
DTU 10-MW wind turbine
10 MW HAWT vs
Antonov An-225 Mriya
Rotor Diameter 178.3 m vs
Wing Span 88.4 m
DTU 10-MW wind turbine: modeling
TOWER • 10 – segments tower • Steel S355 • Diameters linearly variable from the base to the top • Thickness constant in each segment.
BLADES • Bladed rotor concept • Distributed properties assigned along the blades.
DRIVETRAIN • A rigid drivetrain has been written in Samcef code • The rigid connection can be exchanged with a flexible one • Several kinematic chains have been investigated.
CONTROLLER Generator Torque Law • Below rated conditions
• Gain speed to reach the rated speed. • Above rated conditions
• Keep the power produced constant. Pitch controller law • Pitch to feather • Pitch to stall
FFA – W3 – xxx
NACA 0015 cylinder
DTU 10-MW wind turbine: OMA in parked conditions
Turbulence: Kaimal Model Turbine class: 1A Wind speed: 10 m/s
Turbine instrumented with virtual accelerometers
Mode DTU [Hz]
SWT [Hz]
Error [%]
1st Tower FA 0.249 0.247 < 1 %
1st Tower S2S 0.251 0.251 < 1 %
1st flap with yaw 0.547 0.549 < 1 %
1st flap with tilt 0.590 0.598 1.3 %
1st collective flap 0.634 0.636 < 1 %
1st edge with tilt 0.922 0.942 2.2 %
1st edge with yaw 0.936 0.959 2.4 %
2nd flap with yaw 1.376 1.413 2.7 %
2nd flap with tilt 1.550 1.573 1.5 %
2nd collective flap 1.763 1.812 2.7 %
DTU 10-MW wind turbine: OMA in parked conditions
Ice density
Ice but one Germanischer Lloyd WindEnergie GmbH: Guideline for the Certification of Wind Turbines, Edition 2010
5.000.08 Hz
-40.00
-100.00
dBg2
no iceice
5.000.00 Hz
-40.00
-100.00
dBg2
no iceice
5.000.00 Hz
-40.00
-90.00
dBg2
no iceice
DTU 10-MW wind turbine: OMA in power production
1st Backward Whirling Mode 1st Forward Whirling Mode 1st Tower modes
2nd Backward Whirling Mode
2nd Forward Whirling Mode
ROTATING – MBC
1st Flap Yaw
DTU 10-MW wind turbine: OMA in power production
3.500.00 Hz
0.01
0.01e-6
Log
g2
0.16
OperatingParked
1.400.10 Hz
3.36e-3
1.98e-6
Log
g23p 6p0.80 1.12
F Before MBCF After MBC
• Crosspower comparison: parked vs operating conditions • All pairs of asymmetric rotor edgewise modes in parked conditions become pairs of
rotor whirling modes owing to the rotation
Conclusions
Two methods for taking into account the time varying nature of the wind turbine have been implemented and applied to different test cases:
Multi-Blade Coordinate transformation (MBC) Harmonic Power Spectrum method (HPS)
Conventional OMA techniques can be applied to estimate the modal parameters
FUTURE DIRECTIONS • Further studies will be done regarding SHM techniques for wind turbine
blades • Applicability of the implemented methods will be tested in case of real
experimental data
Emilio Di Lorenzo – Research engineer – Siemens Industry Software nv PhD candidate at KU Leuven and University of Naples "Federico II" emilio.dilorenzo@siemens.com
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