In the today world context of strong attention about energy resources and global sustainability, Offshore Wind Turbines (OWT) reached a main consensus about effectiveness. The Symposium is concerned about all the features related with these complex challenging structural systems, covering both design aspects and analysis problems, with special attention on interaction mechanisms and multidisciplinary studies, with demanding technological characteristics and experimental activities.

1. 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
BASIS KNOWLEDGE
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
STRUCTURAL
MODELING

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Global / Local Structural Aspects
LOCAL
STRUCTURAL
MODELING

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MACRO-LEVEL MESO-LEVEL MICRO-LEVEL
DESIGN
VARIABLES
PERFORMANCE
LEVELS
MACRO-LEVELMESO-LEVELMICRO-LEVEL
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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BASIC
LOAD#1

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BASIC
LOAD#2

15. MODEL

16. MESH

17. LOADS &
RESTRAINTS

18. SHELL
MODEL

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FRAME
MODEL

20. 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
ZONE
EXCHANGE
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 SPECIFIC
REQUIREMENTS
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 stability
...
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
Requirement
loop
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 product
and process solutions
Requirements Analysis
- Analyze missions and enviroments
- Identify functional requirements
- Define performance and design
constraint requirement
System
Modeling
And
Analysis
SYSTEM DESIGN

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