Advanced Topics in Offshore Wind Turbines Design

Franco Bontempi, Ph.D., P.E.,

Professor of Structural Analysis and Design

School of Engineering

University of Rome La Sapienza

ITALY

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INDEX OF TOPICS

• Evolutive / Innovative Design

• System Complexity

1) Structural Systems Decomposition

2) Enlarged Structural System

(Actions Decomposition)

3) System Performance Decomposition

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NEW KNOWLEDGE

REQUIRED BY

AN INNOVATIVE

DESIGN

ACTUAL

KNOWLEDGE

BASISKNOWLEDGE

REQUIRED

BY AN EVOLUTIVE

DESIGN

Evolutive / Innovative Designs (1)

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Evolutive / Innovative Designs (2)

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STRUCTURAL SYSTEM

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Wind / Wave Interaction

DESIGN ENVIRONMENT

MODELING

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Soil / Structure Interaction

GLOBAL

STRUCTURALMODELING

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Global / Local Structural Aspects

LOCAL

STRUCTURALMODELING

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MACRO-LEVEL MESO-LEVEL MICRO-LEVEL

DESIGN

VARIABLES

PE

RF

OR

MA

NC

E

LE

VE

LS

MA

CR

O-L

EV

EL

ME

SO

-LE

VE

LM

ICR

O-L

EV

EL

Structural System Decomposition

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jacket:

vertical element

base:

diagonal element

base:

horizontal element

bucket – pile guide

pile

jacket:

diagonal element

jacket:

horizontal element

tower

special junction

zone

Traditional Concepts

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Scheme of strutted support structures for OWT positioned in sea with water level ranging

from 20 to 35 m

Innovative Concepts

FLEXIBILITY OF CONFIGURATION

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BA

SIC

L

OA

D #

1

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BA

SIC

L

OA

D #

2

MODEL

MESH

LOADS & RESTRAINTS

SHELL MODEL

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FRAME MODEL

SHELL MODEL

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ENVIRONMENT ZONE

Structure

Non

environmental

solicitations

EXCHANGE ZONE

Wind and wave flow

Structural (non-

environmental)

system

Site-specific

environment

Wind site basic

parameters

Other

environmental

agents

Wave site basic

parameters

Wind, wave and

sea current

actions

Aerodynamic and

Aeroelastic

phenomena

Hydrodynamic

phenomena

Enlarged Structural System

ENVIRONMENT

ZONEEXCHANGE

ZONE

STRUCTURE

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SYSTEM PERFORMANCE

DEFINITION OF PRINCIPAL FUNCTIONS /

GLOBAL PARTS

DEFINITION OF INTERFACE VARIABLES /

COMPONENTS

DEFINITION OF DETAILED FUNCTIONS /

LOCAL ELEMENTS

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Performance decomposition

STRUCTURAL

SYSTEM

PERFORMANCE

INTRINSIC

TO THE

STRUCTURAL

SYSTEM

REFERRED

TO SPECIFICREQUIREMENTS

i.e. LIMIT STATES

DYNAMIC

CHARACTERIZATION

STRUCTURAL

ROBUSTNESS

SERVICEABILITY

LIMIT STATES

ACCIDENTAL /

EXTREME

LIMIT STATES

ULTIMATE

LIMIT STATES

deformation limits

connection decompression / slippage

natural frequencies

...

strength of the parts, elements, connections

strength of the whole structure

global / local stabil ity

...

survivability of the structural system in

presence of extreme and/or

unforeseen, situations

compatibility of the intrinsic vibration characteristics of the structural system with those of

the acting forces and loads and

compatibility for the movement and the accelerations

of the support system for the functionality of the

turbine

decrease in the load bearing capacity proportional

to the damage

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STRUCTURE

Main structure

Nacelle

Rotor–nacelle assembly

Operation

Maintenance

Emergency

Support structure

ACTIONS/LOADSENVIRONMENT

Junctions/bearings

Rotor

Junctions/bearings

Blades

Junctions/bearings

Tower

Junctions

Substructure

Junctions

Foundations

Junctions

Secondary structure

Energy production

Energy transfer

Auxiliary structure

Gravitational / Inertial

Gravity

Braking

Aviation

Seismic activity

Aerodynamic

Hydrodynamic

Actuation

Other

Wave

Current

Torque control

Mechanical breaking loads

Yaw and pitch actuator loads

Tsunami

Impact loads

Wake loads

Wind conditions

Marine conditions

Seabed movement and scour

Other conditions

Normal wind conditions

Extreme wind conditions

Waves

Sea currents

Water level

Marine growth

Air temperature

Humidity

Solar radiation

Rain, hail, snow, ice

Chemically active substances

Mechanically active substances

Environmental aggressiveness

Lighting

Seismicity

Water density

Water temperature

Maritime traffic

Normal wave conditions

Extreme wave conditions

Serviceability Safety Reliability Robustness

Service Limit States – SLS Ultimate Limit States – ULS_1 Accidental Limit States – ALSUltimate Limit States – ULS_2

Fatigue Limit States – FLS

Deflections/Displacements

Vibrations Strain limit

Stress limit Degradation effects

Buckling Fire

Impact

Explosion

PERFORMANCE

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Functional Analysis/

Resources Allocation- Decomposition to lower-level function- Allocate performance- Define functional interfaces- Define functional architecture

Requirementloop

Design loop

PROCESS

INPUT

Historic Analyses

Evolutive / Innovative

Design

Risk Management

PROCESS

OUTPUT

Synthesis- Transform architecture- Define alternative product concepts- Define physical interfaces- Define alternative productand process solutions

Requirements Analysis- Analyze missions and enviroments- Identify functional requirements- Define performance and designconstraint requirement

System

Modeling

And

Analysis

SYSTEM DESIGN

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