Stuttgart Wind Energy @ Institute of Aircraft Design Load Simulation of Offshore Wind Turbines - Modeling Techniques and Validation by Measurements SIMPACK Wind and Drivetrain Conference 2015 Hamburg, Germany October 7 th , 2015 Dipl.-Ing. Friedemann Beyer Dipl.-Ing. Matthias Arnold, Dipl.-Ing. Birger Luhmann, Dipl.-Ing. Matthias Kretschmer, Prof. Dr. Po Wen Cheng
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Load Simulation of Offshore Wind Turbines - Modeling ... Wind Energy @ Institute of Aircraft Design Load Simulation of Offshore Wind Turbines - Modeling Techniques and Validation by
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sender: collecting local data & transfer to common storage
receiver: distributing coupling data & synchronization of time
moderator: communication procedure & convergence control
CF
D:
CF
X
MB
S:
SIM
PA
CK
Tra
nsla
tor
Sender
(loads)
Receiver
(motion)
Tra
nsla
tor
Sender
(motion)
Receiver
(loads)
Transfer memory
Moderator
12
Advantages:
integrated analysis: aero-, hydro, structural dynamics, control system
inclusion of flexible bodies with reasonable computational effort
Damping Characteristics
16
Heave Damping:
entrapped water in the pool
piston like in- and outflow during floater motion
shedding of large 3D vortices at the skirt and inner hull
colormap: velocity colormap: velocity
floater bow floater stern
Floater Motion: Surge and Heave
Surge:
drift loads acting on the
floater
mean surge position after
transients
good correlation (period,
mean, extreme values)
Heave:
little transients
high heave damping
very good correlation
(period, mean, extreme
values)
19
Ongoing Scale Testing and Validation
20
Froude-scaled rotor thrust
Redesigned blades
Low wind speeds
Ducted fan
Real-time controlled (HIL)
No wind generator necessary
Figs. INNWIND.EU; Politecnico di Milano; University of Stuttgart
Computational Fluid
Dynamics:
very advanced,
very high comp time
finite volume, RANS
equation, structured
and unstructured grids
VOF approach for free
surface
fully implicit, transients
ANSYS CFX
Potential Flow:
more advanced,
medium comp time
potential flow theory,
viscous drag from ME
non-transparent structures
diffraction dominated
HydroDyn, AQWA (Pre), WAMIT (Pre)
Range of hydro dynamic models
21
Morison Equation:
simple, fast
semi-empiric
slender cylindrical
bodies, D/λ<0.2
inertia, drag dominated
flow separation
HydroDyn
Project: IEA Wind Task 30 Extension - OC5
Overview:
OC5 = Offshore Code Comparison Collaboration,
Continued, with Correlation
validation of design codes through code‐to‐data comparisons
Phase II:
semi, tank testing
Jun 2015 – May 2016
Phase III:
jacket/tripod, open ocean
Jun 2016 – May 2017
[IN
RE
L]
[DO
TI]
22
Phase I:
monopile, tank testing
Jan 2014 – Nov 2015
[ID
TU
, D
HI]
OC5 Phase Ib: Model Properties, Measurements
23
[ID
TU
, D
HI]
Property model scale (1:80) full scale
cylinder diameter 0.075 m 6.0 m
cylinder height 2.0 m 160.0 m
wall thickness 1.8 mm 144.0 mm
density 0.64 kg/m 4200.0 kg/m
natural frequency, f1 2.5 Hz 0.28 Hz
natural frequency, f2 18.0 Hz 2.0 Hz
Measurements:
wave elevation at cylinder
total wave force on cylinder at bottom
cylinder acceleration along length
Load Cases:
regular wave case:
H = 0.118 m, T = 1.5655 s
irregular wave case:
Hs = 0.14 m, Tp = 1.55 s
water depth d = 0.51 m
OC5 Phase Ib: 2nd Order Loads
26
non-linear waves:
higher peaks, smaller
troughs
2nd order wave
theory required to
capture higher order
wave loads
recommendation:
check validity of
applied wave theory,
use Simpack 9.9
(HydroDyn 2.02.02)
for large waves/small
depths
Range of aerodynamic models
32
Computational Fluid
Dynamics:
very advanced,
very high comp time
finite volume, RANS,
LES, structured and
unstructured grids
use for calculation of
airfoil tables possible
ANSYS CFX,
FLOWER, SOWFA
Blade Element
Momentum:
simple, fast
momentum balance
industry standard
airfoil table required
ECN Aeromodule,
AeroDyn
v1
v2
v3
S
[Univ
ers
ity o
f S
tutt
ga
rt,
IAG
]
Free Vortex Wake:
more advanced, medium
comp time
potential flow, viscous
vortex core models
rotor-wake-interaction
wind farm simulation
airfoil table required
ECN AeroModule, WInDS
Applied Simulation Method
33
[DO
TI]
Wind turbine model:
NREL 5MW reference wind turbine
structural: MBS (Simpack)
aerodynamics: Free vortex (WInDS)
control: Pitch and torque
hydrodynamics/foundation: none
Load case:
wind: steady, w/ and w/o shear at 12 m/s
half wake condition (50% shadowing)
AV4 AV5
tower: rigid flexible
blade: rigid flexible
control: fixed pitch, speed enabled AV
4/5
mo
de
lled
by N
RE
L 5
MW
,
dis
tan
ce
ba
se
d o
n A
V p
ark
la
yo
ut
Jonkm
an
, J. M
., B
utt
erf
ield
, S
., M
usia
l, W
., S
cott
, G
. (2
009).
Defin
itio
n o
f a 5
-MW
Refe
rence W
ind T
urb
ine f
or
Off
shore
Syste
m D
evelo
pm
ent.
Gold
en,
CO
.
Basics of Free Vortex Methods
34
Free Vortex Methods:
potential flow approach
velocity induction via Biot-Savart law
viscosity via vortex core models
vortex filaments convect and deform
freely, account for flow unsteadiness
and spanwise variation in lift
lifting-line model: lift distribution related
to strengths of vortex filaments
[Katz
, P
lotk
in]
Wake Induced Dynamic Simulator
(WInDS):
Matlab® based
GPU accelerated
implicit and explicit coupling to
Simpack
[DO
TI]
Sebastian, T. (2010). Understanding the Unsteady Aerodynamics and Near Wake of an Offshore Floating Horizontal Axis Wind Turbine. Dissertation. Amherst, MA.
Lenz, D., Beyer, F., Luhmann, B., Cheng, P. W. (2014). Untersuchung instationärer aerodynamischer Effekte an Windenergieanlagen mittels Free Vortex Methoden, Bachelor
Thesis. Universität Stuttgart.
Results: System Behaviour, Blade Loads
36
vhub = 12 m/s
steady, uniform
Summary and Conclusions
Simpack and CFX:
successfully applied for wave impact on floating offshore wind
turbine foundation
good correlation for global floater motion
save model tests to assess impact loads, design
optimisation
Simpack and HydroDyn:
ongoing validation study within OC5 and INNWIND.EU
project
good correlation for wave kinematics, structural loads and
motion
use 2nd order wave theory (Simpack 9.9) for extreme conditions
Simpack and WInds:
effects of wakes on structural loads and system behavior in a
wind farm
validation by Lidar and load measurements within 2016/2017
37
Acknowledgements
38
The presented work is funded partially by the European Community’s
Seventh Framework Programme (FP7) under grant agreement number
295977 (FLOATGEN) and Voith Hydro Ocean Current Technologies
GmbH & Co. KG. The presented work is supported by Simpack AG and
Ansys Germany GmbH.
Stuttgart Wind Energy
@ Institute of Aircraft Design
Thank you for your attention!
Contact:
Dipl.-Ing. Friedemann Beyer
Team Leader Conceptual Design and System Simulation