1/20

Numerical and Theoretical Study on the Wind Response of Wind Turbine

June 11th, 2005The University of TokyoPham Van Phuc

2/20Wind turbine (WT)

• Wind turbines are getting bigger• Turbine rotor size increases• Hub height increases• Tower are getting higher

Time

Scale

Tower

NacelleBlade

Hub

Rotor

Wind turbine

3/20The largest wind turbine• 5000kW Wind turbine

– Manufacturer ： Repower (Germany)– Rotor diameter ：126m– Tower height ：120m

4/20WT transportations

5/20WT constructions (1)

6/20WT constructions (2)

7/20Wind energy development

• Wind energy:– pure, clean, and inexhaustible.

• Installed turbines (in 2003)– All of the world: 40000 turbines.

– Germany : 12000.– USA : 4600– Spain : 3550– Denmark : 2880– Japan : 600

• Target by 2010– Japan: 3000 turbines. Wind farm at Tomamae, Hokaido, northern of Japan

8/20Damages of wind turbine in Japan

The damage of turbines in the Okinawa Island by typhoon Maemi in 2003

• Many damages of WT tower, blades have been reported consecutively.

• . It is strongly required to enhance the wind resistant design of wind turbines.

Collapsed due to foundation destruction

Blades broken Blades broken

Collapsed due to the buckling of the tower

9/20Wind turbine design & problems• Concepts of WT design (IEC61400-1)

– Controlled by adjusting the pitch angle of blade (Fig.1) and direction of nacelle (Fig.2)

• to get maximum wind power during their operations

• to minimize the wind load during the strong wind

(Fig.1)

(Fig.2)

• Japan has various types of typhoons and complex mountains– Control system becomes ineffective especially during

blackout which often occurs during typhoon– Control system is insensitive especially in the site with a large

turbulence.

Wind resistant design is required to consider the critical wind load

10/20Objectives of study

• Carrying out a field investigation and measurement to obtain structural data and characteristics of wind turbine.

• Numerical study– Constructing the wind turbine model of beam element. Comparing

the eigenfrequencies of analytical model with measured natural frequencies.

– Developing a FEM code to simulate the wind load. The performance of code is compared with field measurement results.

• Theoretical study– Proposing an equivalent static load formulas that can estimate

the wind load. The performance of formula is compared with the results from FEM.

11/20Field Investigation

Cutting

Blade

Cut and measure sections

Wind turbine model

Blade

HubNacelle

Tower

Investigate the collapsed turbines in the Okinawa I l d

12/20Field measurements

Modem

② ③

①⑥

Strain gaugeInternet

ISP

Mail server

amplifier

Tel. line

Monitoring PC

The Tokyo University, Bridge Lab.

A/D TransformNTT

Tel. line

Anemometer Accelerometer

• Measurement Period ： Jan. 16th 2004～Mar. 16th 2004 ( 2 months)• Sampling frequency ：20Hz• Record time ： every 10-minute

Measure the survived turbine in

the Okinawa Island

13/20Wind turbine model contribution

10-2

10-1

100

101

102

103

0 2 4 6 8 10

nS(n)/σ2

n(Hz)

0.81Hz6.4Hz

4.6Hz

5.6Hz

7.6Hz

2.4Hz

6.9Hz

X

Y

X

Y

23m

10-2

10-1

100

101

102

103

0 2 4 6 8 10

X DirectionY Direction

nS(n)/σ2

n(Hz)

0.81Hz

2.4Hz4.6Hz

7.6Hz

7.6 (Y)

6.9 (X)

6.4 (Y)

5.6 (X)

5.6 (Y)

4.6 (Y)

-

-

2.4 (X)

0.81 (X)

0.81 (Y)

Measurements

Frequencies (Hz)

WT model

7.6 (Y)11

6.3 (X)10

6.2 (Y)9

5.7 (X)8

5.3 (Y)7

4.5 (Y)6

2.6 (X)5

2.5 (X)4

2.4 (X)3

0.81 (X)2

0.81 (Y)1

No

Power Spectral density of accelerations

Good agreement between the eigenfrequencies of WT model and measured natural frequencies of WT

35m

Wind turbine target

Eigenvalues analysis for WT model

14/20Development of wind response analysis

• Aerodynamic force

• Motion of equation

– [K]: stiffness matrix– [M]: Mass matrix– F: Aerodynamic force vector– [C]: Rayleigh damping

MX CX KX F+ + =&& &

Node i

Node j

Wind load

Load[K]

Mi

M j

Load

Discretiations

X−uur&

Vur

Uur

Wind Vel.：Element Vel.Relative Vel.

FLFD

FM

θ

U

VX&

( ) ( )20.5 fF AC U Xρ θ= × −uurur&

Quasi-steady aerodynamic theory

15/20Wind response simulation

Y, My

X, Mx

12/17

Tower coordinateSimulation results show a good agreement with measurement

-600

0

600

1200

0 200 400 600

Mx My

Moment(kNm)

Time(s)

-600

0

600

1200

0 200 400 600

Mx My

Moment(kNm)

Time(s)

10

100

1000

1 10 100

Max(Obs.)

Ave(Obs.)

Sdev(Obs.)

Max(Cal.)

Ave(Cal.)

Dev(Cal.)

Moment Mx(kN・m)

Velocity(m/s)

10

100

1000

1 10 100

Moment My(kN・m)

Velocity(m/s)

Measured bending moment time series Simulation bending moment time series

Bending moments against Wind speed

16/20

• Proposed formula – Wind loads of along-wind direction and across-wind direction

– Considering Freq.（n）、Damping（ξ）to present the characteristic of wind load on WT. Where θ：wind direction

( )max , ,fM M G n ξ θ= ×

Proposed equivalent static load formula

• Old formula by Building Standard Law of Japan

– Gf is constant

max fM M G= × （Mean×Gust effect coef.）

17/20Combinations of wind loads

( ) 2 2, ,,DL D Max L MaxMaxM M Mθ = +

ML,Max

MD,Max

MDL,Max

Wind θ

Along-wind load

Across-wind load

Flapwise

Edgewise

(Combined load)

• Blade case– Vibrating only in flapwise

( ) ( )

( )

22, ,,

22, ,

,DL D Max L Mean LMax

L Max D Mean D

M Max M M

M M

θ σ

σ

⎛= + +⎜⎝

⎞+ + ⎟⎠

Wind θ

My

Mx

(Along-wind load)(Across-wind load)

ML,Max MD,Max

MDL,Max

(Combined load)

• Tower case

18/20The Results of the Proposed equivalent static load

0 100

3 102

6 102

-180 -90 0 90 180

MDL,max

(数値解析)

MDL,max

(本提案式)

MDL,max

(建築基準法)

Moment (kNm)

Wind directionθ(deg)

0 100

6 103

1.2 104

-180 -90 0 90 180

MDL,max

(数値解析)

MDL,max

(本提案式)

MDL,max

(建築基準法)

Moment (kNm)

Wind directionθ(deg)

(Simulation)(Formula)(Old Formula)

(Simulation)(Formula)

(Old Formula)

• Blade case • Tower case

Proposed formula results show a good agreement with simulation results

19/20Further study

The interaction among typical criteria of Japan– Complex terrain criteria– Seismic criteria

to determine the relative importance of each aspect and to further assess structural optimization of wind turbine in Japan.

20/20

Thank you!