Health Monitoring of Offshore Wind Turbine

Structures: Lessons Learned

Presented by Jens Krieger

Offshoretage, 01.03.2018 bis 02.03.2018,

Warnemünde

Offshore Track Record

System implementation, concepts, data evaluation, structural health assessment, consultancy in the Offshore Wind Industry (Monitoring):

• OWF alpha ventus

• OWF Borkum West II

• OWF Nordsee 1

• OSS Baltic 2

• OWF Meerwind Süd/Ost

• OWF Butendiek

• OWF Baltic 2

• OWF Nordsee 1

• OWF Wikinger

• OWF Nordergründe

• OWF Hohe See

2

SHM Authority Requirements

BSH Standard 2007 vs. 2015

2007 2015

…Representation of the

planned inspection of

the support structure by

a condition inspection

system (CMS) for at

least 1/10 of the offshore

wind turbines…

…In order to monitor

the overall behaviour of

the foundation

elements during the

operating

phase, parameters,

such as shifting,

deformation,

component stress and

frequencies, shall be

measured and recorded

(monitoring) in the area

of the foundation

elements at

representative

offshore wind turbine

sites…Source: BSH Standard Design, 2015

3

SHM Standards

VDI 4551 in progress: ‚Strukturüberwachung und Beurteilung von Windenergieanlagen und Plattformen‘

Vorsitz: Prof. Dr.-Ing. Werner Rücker

Content (preliminary):

• Aims and Tasks of SHM

• Inspection Strategy and Life Time Prognosis

• Support Structures and Modelling

• Periodic Inspections

• Loads

• Design Verification, Condition Monitoring, Damage Assessment

• Measurement Concept

• SHM Requirements

4

SHM – Example Concept

Global Monitoring Concept

• Global monitoring for robust structures

• Ambient Vibration Monitoring (proven technology)

• Model Based Observer for data interpretation

• Few sensors only

• Accessible positions

• Lower operational costs

The one monitoring concept does not exist. Implementation depends on monitoring aims.

acceleration

acceleration

inclination

5

Example Data: Correlations

Correlations give data plausibility and turbine behaviour

Wind Inclination

6

Example: Turbine Comparison, Finding the

‘Odd’ Behaviour

Three distance sensors monitor vertical

displacement in the grout connection

7

Similar structures in a wind farm

show similar behaviour

Example Data: Threshold Monitoring

Generation of alarms

Grout displacement Inclination

8

Example: Lifetime

9

Wind farm

comissioning

20 years. End of

planned lifetime

Start lifetime assessment early:

- Monitoring system is in good state and working

- No information about structure or measurement system is lost

- Original structure designer is still available

5 years

End of warranty

Lifetime

prolongation

Load Cycle Matrix Accumulated Fatigue Damage Lifetime Prognosis

Example: Hidden Reserves

10

Comparison of predicted fatigue damage

profile (design) and actual fatigue damage

of a TP (measured) for a period of 2 years of

offshore operation.

Example: Deviations from Design

Eigenfrequencies are used for design verification and damage

detection

11

Example: Machine Behaviour

Anomalies usually show in several parameters

Pitch algorithm adapted

8 12

Example: Periodic Inspection Support

Sensors can replace or supplement periodic

inspection tasks

13

Automatically

measured data

Data taken

manually

During periodic

inspection

Example: Oberservation Method (EC7)

• Structure inclination is used as indirect

parameter

• Data processing is used for

compensation of statistical loads and

environmental influences

• The use of a high quality inclinometer

allows the monitoring of extremely

small permanent deformations in the

soil

14

Picture source: BSH Standard

Design, 2015

20mm

0,03°

Monitoring of permanent deformation within the soil

Lessons Learned: Clear Aims Necessary

A focus on few aims lead to reduced sensor numbers and lower maintenance costs!

• Structure condition

• Structure integrity / safety

• Loadmonitoring (ULS, FLS, usability)

• Fullfill Authortity Requirements

• Reduce Periodical Inspection Effort

• Data for O&M / Asset Management

• Lifetime prolongation

• Hot Spot Monitoring

• Feedback for designer

15

Lessons Learned: Target Areas

16

Picture source: BSH Standard Design,

2015

BSH requires foundation soil

interaction to be monitored

Application of Observation Method

(EC7)

Grouted connections are subject to

ZiE procedure

Foundation-Tower is an important

contractual interface

Design limits of structure

For maximum project benefit the focus of SHM needs to be on technical

and contractual interfaces

Lessons Learned: SHM Timeline

Planning Installation O&M

17

Wind farm

commissioning

End of warranty

period

Change of

ownershipDecommissioning

Wind Farm Lifecycle

SHM Activities

BSH requirement, ZiE,

Observation Method EC7

Lifetime Assessment

Periodic Inspection

suppport

As built status, current

status

Hidden defects

Contractual interfaces define the SHM activities timeline

Lessons Learned: Structural Integrity

Life time prolongation ispossible

The structures do deviate from

design

18

Lessons Learned: Soil-Structure

Interaction

With high accuracy

inclinometers and

compensation algorithms

for statistical loads and

environmental influences,

it is possible to detect

permanent foundation

displacements of few mm.

Application:

Observation Method (EC7)

Fullfill BSH requirements

19

Picture source: BSH Standard Design, 2015

20mm

0,03°

Lessons Learned: SHM and periodic

Inspection

Periodic inspection supportis possible

Under water inspection is

expensive and dangerous.

BSH allows flexible

inspection concepts utilizing

SHM systems. Proven

concepts (e.g. risk based

inspection from offshore oil

and gas) can be adapted.

This is still rare.

20

Source: API RP 581, 2008

Lessons Learned

21

SHM needs to be part of Asset Management