Structural Monitoring on Germanys Offshore Research ...videos.rennes.inria.fr/ConferenceEWSHM/20140701_EWSHM2014-N… · European Workshop on Structural Health Monitoring 2014 July

Structural Monitoring on Germanys Offshore Research Platform FINO3

A. Jeromin B. Boesche H. Jacobsen

R. Patz B. Lehmann-Matthaei

J. Bachmann

European Workshop on Structural Health Monitoring 2014

July 11, 2014, Nantes, France

Overview

• The FINO platforms

• Structural health monitoring system

– Motivation

– Setup of the system

– Measurement

– Models

– Results

• Summary

Structural Monitoring on Germanys Offshore Research Platform FINO3 2

FuE Zentrum GmbH – General company information

• Stockholder: University of Applied Sciences Kiel (72%)

Förde Sparkasse (13%)

FuE-Zentrum FH Kiel GmbH (15%)

• Employees: approx. 100 in projects; 6 in administration

• Projects: approx. 140 per year

• Enterprise purposes according to company guidelines – Support of the technology transfer between university and industries

– Improvement of the teaching quality and practice

– Support of the personnel qualification by offering employment possibilities for graduates

– Know-how marketing of the UAS Kiel and other universities

The glue between industries and university


FINO – German Offshore Research platforms in North sea & Baltic sea


Alpha Ventus On Jackets

DanTysk (under constr.) On Monopiles

Baltic sea

Baltic II On Jackets

& Monopiles

Research applications on FINO3

• Meteorological measurements

• Sea waves, tides and sea currents

• Salinity and water temperature gradient

• Construction, foundation and durability issues

• Biological research (bird migration & porpoises)


Why structural health monitoring on offshore structures?

• Environmental influences on structure

regular service loads and extreme events (storms)

• Design rules only for extreme events

• Endurance coarsely checked by empirical formulas when the design is finished

• What must be done to extend the life time of offshore structures?

• How to reduce cost in construction?

Measure real loads/stresses during life!


Setup of structural health monitoring system on FINO3

• Four steps in health monitoring system

• Each step covers a special field of work

• Step 1 & 2 are universal

• Step 3 & 4 focus on critical parts

• 3 & 4 are replaceable depending on part under consideration

1 • Measurement of accelerations

2 • Convert accelerations to

displacements

3

• Convert displacements to stresses at critical parts

• Apply FEM models

4

• Compute suffered fatigue from stresses

• Predict remaining endurance


Boundary conditions for monitoring system


• Special conditions offshore: – Subsequent installation (Platform

exists since 2009)

– Limited access (under water / under ground)

– Protective coating must not be harmed

– Structure in permanent movement

– No fixed reference available for measurement of displacement

• Eigenmodes Measurements at multiple heights

Accelerations

1

Modular measurements of accelerations

• Consisting of: – Central command and

supply unit

– 4 sensing modules

– Electric supply and data link

• Advantages: – Easy installation

– Customizable

– Easy maintenance

• 1.5 GB of data every day


Control

AccUnit

AccUnit AccUnit

AccUnit

link1 link2

1

Placement of sensors


1

Automated conversion of accelerations to displacements

• Acceleration data must be processed (1.5 GB/day)

• Processing steps: – Correction of z- and x-axis

– Spectral analysis of acceleration

– Integration of acceleration to displacement

• Issues with integration: – Unknown starting values

– Filtering of integration constants

stable filters

– Reduction of sampling rates by integration method

higher sampling rate for accelerations


2

Apply a model to compute stresses from displacements


• Simple bending beam

• Lots of simplifications – Fixed mount instead of elastic soil

– Material parameters kept constant

– Only first eigenmode

• More complex models (FEM)

3

Estimating fatigue and remaining life time

Estimating fatigue

• Create the load collectives for critical details

• Use common counting algorithm (rainflow)

• Use fatigue curve for few details or structures to monitor

• Use damage equivalent load range for many details or structures

Remaining life time

• Difference of experienced counts and permitted counts of loads

• Estimate future load cycles from past data

• Needs long term monitoring


4

Results: Spectral properties and Eigenfrequencies


North – South

Eigen-frequency

Modal analysis during design 1)

Measure-ments

f1 0,363 Hz 0,422 Hz

f2 0,802 Hz 0,983 Hz

f3 1,627 Hz 1,756 Hz

f4 1,880 Hz 1) Designbasis FINO3, Ed. Züblin AG, 2007

Frequency f [Hz]

N O

S W

Am

plit

ud

e (

a/2

)² [

m²/

s4]

Results: Excitation through waves is visible in spectrum

Schwingungsmessungen auf der Offshore-Forschungsplattform FINO3 15

Type of wave:

Originating effects:

Relative amplitude:

Lower Graph: wikipedia.de (http://commons.wikimedia.org/wiki/File:Munk_ICCE_1950_Fig1_de.svg); Ref.: Munk „Origin and generation of waves“, Coastal Eng. Proc.(1), 2010

Classification of sea waves

(Munk) Frequency f [Hz]

Am

plit

ud

e (

a/2

)² [m

²/s4

]

http://commons.wikimedia.org/wiki/File:Munk_ICCE_1950_Fig1_de.svg





Results: Stresses in monopile at sea floor level


N O

S W

Conclusions

• Project start was in November 2012

• Sensors installed on FINO3 at the end of August 2013

• Continuous monitoring since September 2013

• Automated data processing determines displacement

• Models provide load collectives for critical details

• Estimates for fatigue and remaining life time

• FINO3 provides non-commercial platform for testing and validation

• Estimation of external load sources possible by linking results from other measurement projects


Thank you for your attention!

Acknowledgements

We also thank Arne Neumann and Matthias Riedel of UAS Kiel as well as Marko Cerina for technical support in the lab and many fruitful discussions. 18

Structural Monitoring on Germanys Offshore Research ...videos.rennes.inria.fr/ConferenceEWSHM/20140701_EWSHM2014-N… · European Workshop on Structural Health Monitoring 2014 July

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