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7/27/2019 Pauls Clavo Unos

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Deep Water Floater Concepts for

Offshore Wind Turbines.

Design, Modeling and Testing

Paul D. Sclavounos

Department of Ocean Engineering

Massachusetts Institute of Technology


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Benefits of Offshore Wind Energy

Wind speeds higher and less variable due to the absence of

obstacles (e.g. terrain, buildings, forests)

Environmental restrictions more lax at offshore sites

removed from densely populated areas (e.g. visual effects,

noise, interference with electromagnetic waves)

Large coastal and open seas areas available for exploration

at lower real estate costs relative to areas of comparable

size onshore

Proven Deep Water Floater technologies available from

Offshore Industry


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Challenges of Offshore Wind Energy

Large and variable water depths

Severe weather conditions

Development of reliable and flexible turbine,

electric generator and floater technologies

Cost of Development and Operation


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Floating Wind Turbines

Floating support structure increases the flexibility in locatingthe turbine in water depths of up to 200 meters

Turbines can be located closer to major population centersand into deeper waters instead of up a coast

Less of a problem for ocean front property owners andcoastal fishing / boating

Bottom features are not as large of a hindrance since

mooring lines or tethers are used instead of concrete bases

Individual Floaters Allow the Deployment of Large andVariable Number of Units


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Offshore Industry Floater Concepts

Gravity Tower

Semi-Submersible

Moored SPAR Buoy

Mini Tension Leg Platform


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Semi Submersible Platform


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Tension Leg Platform


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Swim-Motion-Lines (SML)

Floater Response Simulation Model

Wave-Floater Interaction by Frequency Domain Methods(Swim)

Slow-Drift Response Simulation by Time Domain Method(Motion)

Frequency-to-Time-Domain Force Record Simulation byLinear and Quadratic FFT Methods (Motion)

Full Coupling with Nonlinear Mooring-Tether-Riser ModuleLines (Lines)

Fully Coupled Response Simulations in Random Waves

Response Statistics by Direct Analysis of Time-DomainRecords


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Spar and TLP SML Simulation Models


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Design I: Tethered Buoy

Water Depth 100-200m


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Design II: Spread Moored Buoy

Water Depth 100-200m


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Analysis Requirements

Wind Turbine Power/Thrust Determination

Linear and Nonlinear Hydrodynamic and Response

Analysis

Full Coupling of Wind Turbine and Floater Responses

Optimization of Floater Given Wind and Wave Loading

Extreme Responses Fatigue Analysis


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Simulation using ADAMSAerodynamic

Properties

of Wind Turbine

AERODYN

Module

Generator/Turbine

Control Module

Floater and Wave Parameters(Floater Input File)

ADAMS Solver

ADAMS

Control File

ADAMSModel File

FloaterLoading Module

ADAMS

Output Files

Floater SpecificOutput Files


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Floater Loading Module

Wave Characteristics

and Floater Dimensions

(Floater Input File)

Initial Calculation

Wave Spectrum

Added Masses

Wave Spectrum

and Elevation Output

ADAMS Marker

Number and Motions

Position, Velocities,and Accelerations

(from ADAMS)

Inertia Forces

Drag Forces

Forces

And Moments

for each frequency

band are summed

together.

Component

Loading Output

(returned to Adams)

Roll, Pitch, and

Yaw MomentsLoading Output File


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Above-Waterline Structure

Above waterline structure(tower and tower-top)

based on the WindPACT1.5-MW turbine*

Shaft height = 84.00 m

Tower height = 82.39 m Rotor diameter = 70.00 m

* All data for the 1.5-MW turbine are takenfrom input files for the FAST (Fatigue,

Aerodynamics, Structures, andTurbulence) code developed at theNational Renewable Energy Laboratory(NREL) National Wind TechnologyCenter (NWTC)


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General Description ofDesign 1

Cylindrical floating platformof draft T= 30 m and radius

r= 6 m Tension-leg mooring system

with 3 tendons

Radial distance of tendons

from the vertical axis of theplatform = 36 m

Water depth = 100 m

Unstretched length of lines =

69.940 m

Anchor Tension = 289.3 kips


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Design 1 (continued)

Natural frequencies

1

2

3

4

5

6

0.05 rad/s

0.05 rad/s

4.41 rad/s4.27 rad/s

4.27 rad/s

0.97 rad/s

=

=

=

=

=

=


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General Description ofDesign 2

SPAR floating platform of draftT= 30 m and radius r= 6 m

Taut-leg mooring system withfairlead locations at zF

= -30.0m and zF= 30.0 m (above thewaterline)

Radial distance of anchorsfrom the vertical axis of theplatform = 206 m

Water depth = 100 m

Unstretched length of top lines

= 240.10 m; unstretched lengthof bottom lines = 211.90 m

Anchor Tension = 550.8 kips


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Design 2(continued)

Natural frequencies

1

2

3

4

5

6

1.30 rad/s

1.30 rad/s

1.19 rad/s

1.77 rad/s

1.77 rad/s

0.68 rad/s

=

=

=

=

=

=


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Design I: Fully Coupled Response Simulations

Wind Speed 15 m/s, Sea State 6, Water Depth 100m


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Response Statistics in States 1 and 2

State 1: U= 22 knots, H1/3 = 3.0 m, and Tp = 8.69 s

State 2: U= 26 knots, H1/3 = 4.6 m, and Tp = 10.76 s

Response Standard Deviation

Env. State: 1 2 1 2

1 (m) 0.243 0.482 0.447 0.6022 (m) 0.246 0.484 0.446 0.565

3 (m) 0.020 0.053 0.067 0.134

4 (deg) 0.006 0.007 0.652 0.852

5 (deg) 0.007 0.008 0.556 0.647

6 (deg) 0.034 0.020 1.010 1.510

Design 1 Design 2


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Planned Work

Comparative Evaluation of Floater I & II Concepts in

Water Depths 100-200m

Determination of Optimum Floater Configuration in

given Weather Environment

Establish Analysis Steps for Floater-Turbine

System Certification

Perform Wind Farm Optimization Analysis

Perform Wind Farm Lifetime Economic Analysis


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Method Validation

Perform On Site Wind and Wave

Measurements

On Site Measurements on Floating Wind

Turbine Prototype

Prototype Instrumentation and Response

Measurement

Validation of Simulations with Measured and

Design Wind and Wave Conditions

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