2 - Dependability of Offshore Wind Turbines - Arangio

DEPENDABILITY OF OFFSHOREDEPENDABILITY OF OFFSHORE

WIND TURBINESWIND TURBINES

Franco Bontempi, Marcello Ciampoli, Stefania Arangio

University of Rome University of Rome ““La SapienzaLa Sapienza””

Department of Department of

Structural and Geotechnical EngineeringStructural and Geotechnical Engineering

Honolulu, March 17th 2010

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Conclusions

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System approach for structural engineering applications

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The concept of dependabilityPart

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Application to an offshore wind turbine support structure

Bontempi F., Ciampoli M., Arangio S. – Dependability of offshore wind turbines

Definition of structure

Stefania Arangio - Structural integrity monitoring of long span bridges using adaptive models

“device for channeling loads that results from the use and/or presence of the building to the ground”

STRUCTURE

This definition does not consider some important aspects:

INTERACTION AMONG

DIFFERENT

STRUCTURAL PARTS

INTERACTION

BETWEEN THE

WHOLE STRUCTURES

AND THE DESIGN

ENVIRONMENT

Interactions are

characterized by

nonlinearities and

uncertainties

COMPLEXITY

Structure vs. Structural System

STRUCTURE

SYSTEM APPROACH

STRUCTURAL

SYSTEM

“a set of interrelated

components working

towards a common

purpose”

INTERACTION AMONG

DIFFERENT

STRUCTURAL PARTS

INTERACTION

BETWEEN THE

WHOLE STRUCTURES

AND THE DESIGN

ENVIRONMENT

Interactions are

characterized by

nonlinearities and

uncertainties

COMPLEXITY


NASA System complexity


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Structure vs. Structural System


STRUCTURAL

DECOMPOSITION


SYSTEM APPROACH

STRUCTURAL

SYSTEM

INTERACTION AMONG

DIFFERENT

STRUCTURAL PARTS

INTERACTION

BETWEEN THE

WHOLE STRUCTURES

AND THE DESIGN

ENVIRONMENT

Interactions are

characterized by

nonlinearities and

uncertainties

COMPLEXITY

Structural decomposition


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OWT Structural decomposition

SCALE

DETAIL

LEVEL

FINITE

ELEM.

SYSTEM LEVEL MACRO LEVEL MESO-LEVEL MICRO-LEVEL

Wind farm Single turbine Single turbineIndividual

components

Idealized model

components

Approximate

shape of the

components

Detailed

shape of the

components

Detailed shape of

the connections

BLOCK elements BEAM elements SHELL and

SOLID elementsSHELL and

SOLID elements

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How is possible to define (and measure ) the quality of complex structural

systems as the OWT farms?

We need a concept able to take properly into account the different aspects

related to conceptual and structural design, construction and maintenance

during the whole lifetime.

DEPENDABILITY

It is a global concept that describes the aspects assumed as relevant with

regards to the quality performance and its influencing factors (Bentley,1993)

In rigorous terms, the dependability of a system reflects the user’s degree of

trust in that system, i.e. the user’s confidence that the system will operate as

expected and will not “fail” in normal use (Sommerville, 2000): the system

shall give the expected performance during the whole lifetime

Dependability (1)


Dependability (2)

DEPENDABILITY

OF STRUCTURAL

SYSTEMS

MEANS

THREATS

ATTRIBUTESObjective measure of the

dependability

Things that can undermine

the dependability

Ways to improve the

dependability


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Availability

Integrity

Safety

Reliability

Maintainability

Security

High level/ Activeperformance

Low level/ Passive performance

Attributes of the dependability

ATTRIBUTES


ReliabilityReliability: the system capacity of failure-free operation over a

specified time in a given environment for a given performance

(can be expressed quantitatively by a probability … )

AvailabilityAvailability: the system capacity (or readiness) at a point in time

of being operational and able to perform as required (can be

expressed quantitatively by a probability … )

MaintainabilityMaintainability: the system attribute concerned with the ease of

repairing the system after a failure has been discovered or

improving the system to include new features

Active performance


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IntegrityIntegrity: absence of alterations of structural response (related to

the completeness and consistency of the structural configuration)

SafetySafety: is a property of the system that reflects its ability to

operate, normally or abnormally, without danger of causing

human injury or death and without damage to the system’s

environment (safety-related prescriptions usually exclude undesirable situations, rather than specify required

performances)

SecuritySecurity: The system property that reflects the system’s ability to protect itself from accidental or deliberate external attack

(robustnessrobustness)

Passive performance


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Reliability and safety are related but distinct

o In general, reliability (and availability) is necessary but not sufficient

condition for system safety

o Reliability is concerned with conformance to a given specification for a

given performance

o Safety is concerned with ensuring system cannot cause damage

irrespective of whether or not it conforms to its specification

ReliabilityReliability SafetySafety

SecuritySecurity

It is an essential pre-requisite for availability, reliability and safety.


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Failure

Fault

Error

Permanent interruption of the system

ability to perform a required function

under assigned operating conditions

THREATS The system is in an incorrect state: it

may or may not cause failure

Defect that represents a potential

cause of error, active or dormant

Fault managing

Fault detection

Fault diagnosis

MEANS

Fault tolerant design

Inverse problems

ATTRIBUTES

THREATS

MEANS

RELIABILITY

FAILURE

ERROR

FAULT

FAULT TOLERANT

DESIGN

FAULT DETECTION

FAULT DIAGNOSIS

FAULT MANAGING

DEPENDABILITY

of

STRUCTURAL

SYSTEMS

AVAILABILITY

SAFETY

MAINTAINABILITY

permanent interruption of a system ability

to perform a required function

under specified operating conditions

the system is in an incorrect state:

it may or may not cause failure

it is a defect and represents a

potential cause of error, active or dormant

INTEGRITY

ways to increase

the dependability of a system

An understanding of the things

that can affect the dependability

of a system

A way to assess


the trustworthiness

of a system which allows

reliance to be justifiably placed

on the service it delivers

SECURITY

High level / active

performance

Low level / passive

performance

ATTRIBUTES

THREATS

MEANSMEANS

RELIABILITYRELIABILITY

FAILURE

ERROR

FAULT

FAULT TOLERANT

DESIGN

FAULT TOLERANT

DESIGN

FAULT DETECTIONFAULT DETECTION

FAULT DIAGNOSISFAULT DIAGNOSIS

FAULT MANAGINGFAULT MANAGING

DEPENDABILITY

of

STRUCTURAL

SYSTEMS

AVAILABILITY

SAFETY

MAINTAINABILITY

permanent interruption of a system ability

to perform a required function

under specified operating conditions

the system is in an incorrect state:

it may or may not cause failure

it is a defect and represents a

potential cause of error, active or dormant

INTEGRITY

ways to increase


An understanding of the things

that can affect the dependability

of a system

A way to assess


the trustworthiness

of a system which allows

reliance to be justifiably placed

on the service it delivers

SECURITY

High level / active

performance

Low level / passive

performance

Dependability


Analysis and design of complex structural systems


STRUCTURAL

SYSTEM

INTERACTION AMONG

DIFFERENT

STRUCTURAL PARTS

INTERACTION

BETWEEN THE WHOLE

STRUCTURE AND THE

DESIGN ENVIRONMENT

Interactions are

characterized by strong

character, nonlinearity

and uncertainty

COMPLEXITYDECOMPOSITION

STRATEGY

SYSTEM

APPROACH

QUALITY

ON THE WHOLE

FOR THE

STRUCTURAL

SYSTEM:

DEPENDABILITY

ATTRIBUTES

THREATS

MEANS

STRUCTURAL INTEGRITY

PERFORMANCE

BASED DESIGN

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Progressive loss of structural integrity

105 m

35 m

• Water level: 35 m

• Heigth of the structure

above water level:

105 m

• Pile length under sea bed

• Steel 355

•Turbine 5/6 MW

For wind farms with a lot of structures it is interesting to investigate the ability of the system to sustain further levels of demand after the ULS up to extreme loading conditions


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Description of the analysis (1)

The survivability of the system is investigated allowing large damage developing

inside the structural system: the spread of the plasticity is allowed until the last

configuration of equilibrium is reached

Non linear analysis:

-Material plasticity

-Large displacements

Integer structure (ULS) Loss of structural integrity

λ = 1.00λ = 1.44

Increase of damage from the reference baseline ULS configuration to

the last equilibrium configuration

λ = 1.44λ = 1.00 λ = 1.32λ = 1.10

Description of the analysis (2)


Measuring the loss of integrity

1st freq

2nd freq

3rd freqA quantitative measure can

be obtained considering the

modal behavior

Load multiplier

Fre

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Conclusions

Offshore wind turbines (OWT) are complex structural systemsTheir complexity is related to:

- nonlinearities- uncertainties

- interaction between the parts- interaction between the whole structure and the environmental

design

University of Rome “La Sapienza”

A global concept is needed to the define the quality of the OWT

in a comprehensive wayDEPENDABILITY

Conclusions (2)

The concept of dependability has been applied to OWT support

structures to investigate the survivability of the system in

presence of extreme actions

University of Rome “La Sapienza”

λ = 1.44λ = 1.00

The increasing of damage from

the reference ULS configuration

has been considered by means of the load multiplier and considering

the modal behavior of the structure

Design

2 - Dependability of Offshore Wind Turbines - Arangio