Dynamic analysis of a floating vertical axis wind turbine under emergencyturbine under emergency shutdown using hydrodynamic brakeKai Wang, Martin O.L. Hansen and Torgeir MoanKai Wang, Martin O.L. Hansen and Torgeir MoanWP6 of NOWITECHCentre for Ships and Ocean Structures (CeSOS)p ( )The Norwegian University of Science and Technology (NTNU)

EERA DeepWind’ 2014 ,Trondheim, January 22, 2014EERA DeepWind 2014 ,Trondheim, January 22, 2014

Outline

►Background and objective►Modeling and simulation tool►Torque estimation of the hydrodynamic brake►Torque estimation of the hydrodynamic brake►Analysis results of emergency shutdown by using

the hydrodynamic brakethe hydrodynamic brake►Concluding remarks►Future work

Background► Increasing interest in floating vertical axis wind turbines

• DeepWind Concept• VertiWind Concept• Aerogenerator X Concept

3

Vertical floating concepts

Courtesy of Wind Power Limited & Grimshaw Courtesy of DeepWind Project Courtesy of Marc Cahay

► DeepWind Concept 5 MW European project

► VertiWind Concept 2 MW in France

► Aerogenerator X Concept 10 MW in UK 5 MW, European project -

FP7 Rotor Height 129.56 m Rotor Radius 63 77 m

2 MW in France Rotor Height 105 m

10 MW in UK Maximum Height 130 m

4 Rotor Radius 63.77 m

Background► Increasing interest in floating vertical axis wind turbines

• DeepWind ConceptV tiWi d C t• VertiWind Concept

• Aerogenerator X Concept• Novel concept proposed in OMAE 2013Novel concept proposed in OMAE 2013

A novel concept:• 5-MW VAWT • Darrieus rotor • Semi-submersible floater

M i li• Mooring lines

Wang, K., Moan, T., and Hansen, M.O.L. A method for modeling of floating vertical axis wind turbine. in Proceedings of the 32th International Conference on Ocean, Offshore and Arctic Engineering. 2013. Nantes, France: paper no: OMAE2013-10289.

5g g p p

Background► Increasing interest in floating vertical axis wind turbines►Distinctive features of FVAWT compared with FHAWT

HAWT Components1. Blade Pitch system

Insensitive to wind direction Sensitive to wind direction

y2. Yaw system3. Gear box4. Generator

VAWT Components1 Gear box1. Gear box2. Generator

Difficult access to drivetrainIncrease O&M cost

Easy access to drivetrainReduce O&M costs

6Increase O&M costReduce O&M costs

Background► Increasing interest in floating vertical axis wind turbines ►Distinctive features of FVAWTs compared with FHAWTs►Distinctive features of FVAWTs compared with FHAWTs►Drawbacks of the FVAWTs Aerodynamic torque ripple resulting in cyclic loading on Aerodynamic torque ripple resulting in cyclic loading on

drive train and structures Emergency shutdown situation Emergency shutdown situation

Scenario: grid loss, loss of generator torque, failure of mechanical brake (possible happen in cold weather), (p pp ),stormy weather

Measure: aerobrake (Spoilers)

7

Background► Increasing interest in floating vertical axis wind turbines ►Distinctive features of FVAWTs compared with FHAWTs►Distinctive features of FVAWTs compared with FHAWTs►Drawbacks of the FVAWTs Aerodynamic torque ripple resulting in cyclic loading on Aerodynamic torque ripple resulting in cyclic loading on

drive train and structures Emergency shutdown situation Emergency shutdown situation

Scenario: grid loss, loss of generator torque, failure of mechanical brake (possible happen in cold weather), (p pp ),stormy weather

Measure: aerobrake (Spoilers)►An economic and efficient braking system is preferred

8

Objectivesj►Propose a novel hydrodynamic brake

►Establish a numerical model of the hydrodynamic brake

► Integrate the brake model with the coupled model of the floating vertical axis floating turbinefloating vertical axis floating turbine

►Evaluate the effect of the hydrodynamic brake►Evaluate the effect of the hydrodynamic brake

►D namic anal sis of the floating ertical a is ind t rbine►Dynamic analysis of the floating vertical axis wind turbine with the hydrodynamic brake during shutdown situation

9

A floating vertical axis wind turbine with hydrodynamic brakehydrodynamic brake

5 MW D Wi d5 MW DeepWindrotor

OC4 semi submersibleOC4 semi-submersible

Hydrodynamic brake:f fl l h dfour flat plates attached

to the centre column

Modeling of the floating vertical axis wind turbineturbine

windRIFLEX wind turbineStructural analysis of slender, flexible beams (Mooring lines tower and blades) A d i(Mooring lines, tower and blades)

SIMOMotion analysis of floating structure (rigid floater )

Aerodynamic loads

y g ( g )

waveHydrodynamic loads

Aerodynamic loads provided through Dynamic Link Library (DLL)

wave loads

F ll l d d lFully coupled model

11

Modeling of the hydrodynamic brake Preliminary design of hydrodynamic brake

Modeling as a slender beam

Hydrodynamic coefficients

Determination of the torque from drag force on the plate

Modeling of the hydrodynamic brake Preliminary design of hydrodynamic brake

Modeling as a slender beam

Hydrodynamic coefficients

Determination of the torque from drag force on the plate

Modeling of the hydrodynamic brake (1)

Preliminary design of hydrodynamic brake

Modeling as a slender beam

Hydrodynamic coefficients

Determination of the torque from drag force on the plate

Added mass

Drag coefficientDrag coefficient

Det Norske Veritas, ENVIRONMENTAL CONDITIONS AND ENVIRONMENTAL LOADS,Tech. Rep., DNV-RP-C205 (2007).

Cd= 1.9Tech. Rep., DNV RP C205 (2007).

Modeling of the hydrodynamic brake (1)

Preliminary design of hydrodynamic brake

Modeling as a slender beam Modeling as a slender beam

Hydrodynamic coefficients

Determination of the torque from drag force on the plate

CFD simulation: 2D sliding mesh model first-order upwind absolute velocity formulationy renormalized Group (RNG) k-ɛ turbulence model standard wall function for near-wall treatment grid mesh Brake I grid mesh

135900 inner region 24640 outer region

time step 0 1 s

Brake I

Brake II time step 0.1 s

Simulation tool: Simo-Riflex-DMSForces/ moments/ rotor power

Displacement/

Turbsim DMS Interface Riflex/SimoWind field

Dynamics of fully coupled model Aerodynamics

Displacement/ velocity

AerodynamicsDouble Multiple-Streamtube model (DMS) and BL dynamic stall model. Structural dynamicsThe structural dynamics of the rotor mooring lines and brake is calculated by the nonlinearThe structural dynamics of the rotor, mooring lines and brake is calculated by the nonlinearfinite element solver in RIFLEX (developed by MARINTEK). HydrodynamicsThe floater motion is simulated according to linear hydrodynamic theory plus viscous termThe floater motion is simulated according to linear hydrodynamic theory plus viscous termof the Morison formula in SIMO.Wind turbine controlA PI controller is designed for generator torque.g g q

Environmental and shutdown conditions

A) The original FVAWT without hydrodynamic brake and no fault happenB) The FVAWT with hydrodynamic brake I and no fault happenC) The FVAWT with hydrodynamic brake I and fault happen followed by free rotationD) The FVAWT with hydrodynamic brake II and fault happen followed by shutdown

The accidence of grid loss was assumed to happen at time TF = 1200 sThe accidence of grid loss was assumed to happen at time TF = 1200 s The hydrodynamic brake was connected to the rotating shaft to initiate the shutdown process by a short time delay TD = 1 s.

Effect of the hydrodynamic brake IA selection of results: Surge motion Roll motion Pitch motion

15

20

25

m2 s

LC1ALC1B

8 m/s0.12

0.14

0.16

0.18

0.2

eg2 s

LC1ALC1B

2.5

3

3.5

4

eg2 s

LC1ALC1B

5

10 S(

1), m

0.02

0.04

0.06

0.08

0.1

S(

4), de

0.5

1

1.5

2

S(

5), d

0 0.5 1 1.5 2 2.5 30

, rad/s

20

25 LC3ALC3B

14 /

0 0.5 1 1.5 2 2.5 30

, rad/s

0.7

0.8 LC3ALC3B

0 0.5 1 1.5 2 2.5 30

, rad/s

2.5

3 LC3ALC3B

10

15

20

S( 1),

m2 s

14 m/s

0 3

0.4

0.5

0.6

S( 4),

deg2 s

1.5

2

S( 5),

deg2 s

0 0.5 1 1.5 2 2.5 30

5

S

0 0.5 1 1.5 2 2.5 3

0

0.1

0.2

0.3 S

0 0.5 1 1.5 2 2.5 30

0.5

1 S

, rad/s , rad/s , rad/s

Effect of the hydrodynamic brake IA selection of results:

Mooring line tensionMooring line tension

2500

3000

3500

sion

, kN

2 s

LC2ALC2B

4000

5000

6000

nsio

n, k

N2 s

LC6ALC6B10 m/s 25 m/s

1000

1500

2000

Moo

ring

line

1 te

n

2000

3000

4000

oorin

g lin

e 1

te

0 0.5 1 1.5 2 2.5 30

500

1000

rad/s

PS

D o

f M

0 0.5 1 1.5 2 2.5 3

0

1000

d/

PS

D o

f Mo

• The brake could significantly reduce the mooring tension response from the wind excitation, whereas it makes larger peak at higher frequencies. • Besides the peak at the 2P frequency another peak at the higher frequency was found

, rad/s , rad/s

• Besides the peak at the 2P frequency, another peak at the higher frequency was found and it should be induced by the eigenfrequency of the blade. • With the increase of wind speed, the peak induced by structural eigenfrequecy is more apparentapparent.

Analysis of emergency shutdown by using the hydrodynamic brake Iusing the hydrodynamic brake I

Time history of rotational speed for different wind speed after fault occurs at TF=1200 s by using brake I

0.7

0.8

0.9 wind 8 m/swind 10 m/swind 14 m/swind 18 m/s

Fault Time

occurs at TF 1200 s by using brake I

0.4

0.5

0.6

nal s

peed

, rad

/s wind 22 m/swind 25 m/s

0.1

0.2

0.3

Rot

atio

n

• Once the hydrodynamic brake takes effect to counter the aerodynamic torque, the rotation 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 28000

0.1

Time, s

speed varies depending on the balance of aerodynamic torque and hydrodynamic torque• The brake I does not give enough torque to stop the rotation, but it could avoid the overspeedof the rotor.

Analysis of emergency shutdown by using the hydrodynamic brake Iusing the hydrodynamic brake I

Global motion fault configuration B vs. fault configuration Cg g

10

15

urge

, m

-0.5

0

0.5

Sw

ay, m

0 1

-0.05

0

eave

, m

Load case 1-6 BLoad case 1-6 C Different wind speeds

810 14 18 22250

5

Wind speed, m/s

Mea

n su

810 14 18 2225-2

-1.5

-1

Wind speed, m/s

Mea

n S

810 14 18 2225-0.2

-0.15

-0.1

Wind speed, m/s

Mea

n he

p , p , p ,

0

0.5

roll,

deg

4

6

pitc

h, d

eg

-4

-2

0

yaw

, deg

810 14 18 2225-1

-0.5

Wind speed, m/s

Mea

n

810 14 18 22250

2

Wind speed, m/s

Mea

n p

810 14 18 2225-8

-6

Wind speed, m/sM

ean

• The global motion of the platform shows better performance, which contributed from the decreasing rotational speed after the hydrodynamic brake initiates. • Surge and pitch motion can get much more advantages while the sway and roll motions have got both good and bad effects from different load case.

Analysis of emergency shutdown by using the hydrodynamic brake Ithe hydrodynamic brake I

• The less wind speed, the more pitch 3.5

4 LC1BLC1C 2 5

3 LC3BLC3C

Pitch motion

motion reduced. • The peak at the 2P frequency was still presented, but the 2P frequency was reduced to a lower value1.5

2

2.5

3

S( 5),

deg2 s

LC1C

1

1.5

2

2.5

S( 5),

deg2 s

LC3C

0 0.5 1 1.5 2 2.5 30

0.5

1

, rad/s

S

0 0.5 1 1.5 2 2.5 3

0

0.5

1

, rad/s

S

15x 10

9

ent,

kNm2 /s

LC3BLC3C 14

16x 10

9en

t, kN

m2 /s LC3BLC3C

Fore-aft and Side-side bending moment of shaft base

The initiation of the brake with the

10

Base

Ben

ding

Mom

e

6

8

10

12

Bas

e B

endi

ng M

ome

rotating shaft of the wind turbine together could mitigate the 2P effect and then the wave frequency excitation dominates the response of

0 0.5 1 1.5 2 2.5 30

5

PSD

of F

A To

wer

B

0 0.5 1 1.5 2 2.5 3

0

2

4

6

PSD

of S

S To

wer

B

pFA tower base bending moment

0 0 5 5 5 3, rad/s

0 0 5 5 5 3, rad/s

Shutdown process by using the hydrodynamic brake II and mechanical brakebrake II and mechanical brake

Global platform motion, bending moment and mooring line tension0.8 8 4

0 2

0.4

0.6

, r

ad/s

2

4

6

1, m

1

2

3

5, d

eg

Fault Time

MechanicalBrake Load case 2D

1000 1500 2000 25000

0.2

Time, s1000 1500 2000 2500

-2

0

Time, s1000 1500 2000 2500

-1

0

Time, sx 10

5, kN

m

kN

V=10 m/s

-2

0

2

6, deg

0

1

2

3x 10

ndin

g M

omen

t FASS

1200

1400

1600

1800

Moo

ring

lines

, k Mooring 1Mooring 2Mooring 3

1000 1500 2000 2500-6

-4

Time, s

1000 1500 2000 2500-2

-1

0

Time, sower

bas

e B

en

1000 1500 2000 2500

800

1000

1200

Time, sTens

ion

of M

Fault occurs at TF=1200 s followed by using brake II and by using mechanical brake at 1400s

T

Concluding remarks►An integrated model of a floating vertical axis wind with a

hydrodynamic brake was established to carry out the non-li i d i i l ilinear time domain simulation

►The effect of the hydrodynamic brake on the FVAWT was l t d b i th FVAWT ith th h d d ievaluated by comparing the FVAWT with the hydrodynamic

brake I to the original FVAWT►A series of promising results indicate the merit of the►A series of promising results indicate the merit of the

hydrodynamic brake used during emergency shutdown►Combing a mechanical brake with a larger hydrodynamic►Combing a mechanical brake with a larger hydrodynamic

brake, the shutdown could be successfully achieved.►The application of hydrodynamic brake is expected to be pp y y p

efficient and promising for the emergency shutdown and reduce the platform motion and structural loads.

Future workA more efficient brake is more attractive and promising.

http://www.cd3wd.com/cd3wd_40/ap/Optimization_and_CFD_analysis_of_wind-powered_water_pump_system.html

Th k f tt ti !Thank you for your attention!