Aishwarya Kumar (2010102002)Bhargavi Ganesh (2010102014)Deepika Ramesh (2010102018)

•Offshore Wind Technology

•Objectives of Project

•Methodology

•Design of Structure

•Results

•Conclusion

• Introduction

• Global Scenario

• Potential and Application in India

To conduct the structural analysis of

possible supporting structures for an

offshore wind turbine

To design a suitable supporting structure in

accordance with the specific site conditions

•Introduction

•Software Used

•Schematic Diagram of Methodology

•*Load Estimation & Load Cases

•*Input parameters

•Power Production at Site

Capacity of selected turbine: 1.5 MW

Location of Site: Off the coast of Rameshwaram

Steps involved:

STAGE I: Load Estimation

STAGE II: Soil Structure Interaction

STAGE III: Structural Analysis & Design

STAGE IV: Power Production at Site

Software Used:

1) FAST (developed by NREL)

2) USFOS (developed by SINTEF marintek & NTNU)

Stage Code/ Theory based onSoftware

Used

I. Load Estimation

Aerodynamic Loads on turbine IEC 61400 – Part 1 (2005) FAST

Hydrodynamic Loads on tower Airy’s Theory, Morrison Equation

USFOS

Wind Loads on tower IS 875 – Part 3 (1987) USFOS

II. Soil Structure Interaction API RP 2A-WSD (2007) USFOS

III. Structural Analysis & Design IEC 61400 – Part 3 (2009),API RP 2A-WSD (2007)

USFOS

STAGE I: Load Estimation

•Aerodynamic•Hydrodynamic•Wind

STAGE II: Soil Structure Interaction•Foundation: Monopile•Modeled as springs in axial and lateral direction at every 5 m

STAGE III: Structural Analysis & Design

•Safety criteria: Displacement & Interaction Ratio•Designed such that criteria were met

Data obtained: Wind speeds at

10 m & 20 m above MSL from

September 1991 to August 1993

Collected at site in Rameshwaram

(09°13’40”N, 79°20’35”E)

Power Law used to extrapolate

speeds at different elevations

Power curve generated for site

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30

Pow

er (k

W)

Wind Speed (m/s)

Power Curve

Turbine Parameters

Capacity of Turbine 1.5MW

Wind Turbine Class Class 2

Turbulence Category B

Cut-in Speed 5.0 m/s

Rated Speed 11.5 m/s

Cut-out Speed 25.0 m/s

Rotor Diameter 70.0 m

Hub Height84.3 m (from MSL to hub

of turbine)

Tower Parameters

Tower Height 80.0 m

Diameter of Tower 4.0 m

Thickness of Tower 0.05 m

Material of Tower Steel

Pile Parameters

Type of Foundation Monopile

Diameter of Pile 3.5 m

Thickness of Pile 0.085 m

Length of Monopile 30.0 m (below mudline)

Length of Monopole 15.0 m (above mudline)

Material of Pile Steel

Young’s Modulus of Steel 200,000 MPa

Yield Strength of Steel 250 MPa

Turbine parameters are defined by the manufacturer – This study uses the properties defined by NREL (inbuilt in FAST)

Design of Structure

Tower Height = 80 m

Hub Height = 85 m

Monopile Length= 30 m

Monopole Length = 15

m

Depth of Water = 10 m

Total Height of

structure above mudline

= 95 m

Turbine

Tower

Monopole

Monopile

30 m

15 m

80

m

10 m

85

mMSL

Mudline

•Displacement & Interaction Ratio

•Capacity of Tower

•Bending Moment & Shear Force Diagrams

•Simulation on USFOS

•Power Production

DISPLACEMENT

According to Nicholson (2011):

Limiting value: 1.25% of height of structure above mudline

(i.e. 95 m) (=1.1875)

INTERACTION RATIO

According to API RP 2A-WSD (2007):

Limiting value: 1

Maximum Value Corresponding Case

Displacement 1.16789 m ECD-R+2

Interaction Ratio 0.5979 EWM50

ECD-R+2: Extreme Coherent Gust with Direction Change when wind velocity at hub = Rated speed + 2 m/sEWM50 : Extreme Wind Speed Model with recurrence period of 50 years

Displacement & Interaction Ratio

•The highest value of

displacement obtained

was for Case No. 6. (ECD-

R+2). It occurred at a time

instant of 53.1 s.

•For Extreme Wind speed

Models (EWM), the rotor

stops rotating because the

cut-out speed is reached in

such extreme conditions.

Thus, displacements in

these cases are not

considered for analysis.

0

100

200

300

400

500

600

700

800

374 376 378 380 382 384 386

Ba

se S

he

ar

(KN

)

Time (sec)

TIME-HISTORY RESPONSE OF BASE SHEAR

Maximum Base Shear

0

10000

20000

30000

40000

50000

60000

68 70 72 74 76 78 80 82

Ove

rtu

rn M

om

en

t (K

Nm

)

Time (sec)

TIME-HISTORY RESPONSE OF OVERTURN MOMENT

Maximum Overturn Moment

Parameter Value

Maximum Base Shear 726.735 kN (at 380.1 s)

Maximum Overturn Moment 5.01 x 104 kNm (at 75.1 s)

Maximum Total Axial Load 5.11 x 103 kN

Factored Pile Axial Capacity 1.19 x 104 kN

Factor of Safety 2.5

All the aforementioned maximum values were found to be for the loading case ECD-R+2. Pile capacity was calculated as per API RP 2A-WSD.

B

B) Shear Force Diagram for the

Tower under ECD-R+2 loading

condition at the 53.1 s

A) Bending Moment Diagram for the

Tower under ECD-R+2 loading

condition at the 53.1 s

A

*Maximum Displacement occurred for this case at 53.1 s

*Maximum Displacement occurred for this case at 53.1 s

0.00

5.00

10.00

15.00

20.00

25.00

09/91 12/91 04/92 07/92 10/92 01/93 05/93 08/93

Win

d S

pp

ed

(m

/s)

Time (MM/YY)

Wind Speed (Hub Level)

0.00

500.00

1000.00

1500.00

09/91 12/91 04/92 07/92 10/92 01/93 05/93 08/93

Po

we

r P

rod

uct

ion

(k

W)

Time (MM/YY)

Power Production - 1.5 MW

726

1345

2306

2734

30032836

2389

1411

605

14839 2 00

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 16-18 18-20 20-22 22-24 24-26

FREQUENCY DISTRIBUTION

OF WIND SPEEDS AT

HUB

Fre

qu

en

cy

Wind Speed at Hub Height (m/s)

For the Rameshwaram site (using

Power Curve generated):

•Average wind speed = 9.14 m/s

•Standard deviation of wind speed

= 4.12

•Avg. power generated = 0.781 MW

• Plant Load Factor = 0.52

India has potential to support Offshore Wind

Technology

A 1.5 MW capacity turbine gives a PLF of 0.52 at

the Rameshwaram site

Based on analysis, the proposed design is

structurally feasible – further studies are

needed for cost analysis