from r&d to an industrial application · 01.11.2012 to 31.10.2015 qs-m grout quality assurance...

Offshore foundation monitoring – from R&D to an industrial application Andreas Nuber, Herbert Friedmann, Moritz Häckell, Bernd Wölfel, Peter Kraemer

We are experts in this world. It is our home. We support our customers with engineering services and products for the analysis, prognosis and solution of tasks in the fields of vibrations and noise. Vibrations and noise are almost always unwanted. Their reduction provides safety, prevents damage and avoids unnecessary costs.

Welcome to the world of vibrations, structural mechanics and acoustics

In which industries are we currently active?

Introduction

Extremely high operational demands due to a complex superposition of cyclic and stochastic dynamic loading from

• wind

• waves

• operation

Impact on

• Global stability

• Welding seams

• Failure of foundation is possible

• Regulations of BSH (German maritime authority)

• Support structures (Tower, foundation) have to be revised with respect to corrosion, cracks, scouring etc.

• Every tenth plant must be equipped with a SHM system (2007), frequent inspections are required (2015)

Due to costs a reduction of inspection effort is necessary!

UnderwaterINSPECT

Structural Health Monitoring of offshore foundations

01.11.2012 to 31.10.2015

QS-M Grout

Quality assurance and SHM of grouted joints on underwater supporting structures of OWT

01.11.2014 to 30.10.2017

UnderwaterINSPECT was funded by a grant of the German Federal Ministry of Economic Affairs, contract number 03SX345A

QS-M Grout is funded by a grant of the German Federal Ministry of Economic Affairs, contract number 03SX372A

Mode of Operation of a vibration based SHM system

Basic principle of the SHM system is the analysis of the structural response due to operational and environmental vibrations.

The linearized structural behavior can be described by the equation of motion:

Mass , Damping and Stiffness govern the dynamic behavior of the foundation.

Structural vibrations are an indicator of

• Stability,

• Stiffness,

• Wind- and wave loads,

• Operational loads,

• Mode of operation of a turbine.

The structural response can be measured in the form of deformations, vibration velocities or accelerations.

However, the frequency changes are very small: 0,5 % - 1 % 0.005 Hz - 0.01 Hz

Measurement of the structural response of a rotor blade

The Method

Damage Indicators

Stochastic Mathematics: Two Stochastic Subspace Identification (SSI) algorithms:

Covariance-driven Stochastic Subspace Identification algorithm, SSI-COV

Use in conjunction with output-only modal analysis or operational modal analysis, OMA Low order stochastic state space models derived from measured time histories. Changes comply with changes in the modes of vibration.

Null Space-based Fault Detection algorithm, NSFD

High order stochastic state space models derived from measured time histories.

NSFD method is more sensitive to structural changes as SSI-COV, but at the same time also to changes in the EOC. Therefore the compensation of the ambient conditions is even more challenging than in SSI COV.

Experiments in TTH, Test center for foundations in Hannover

Test of measurement technique basis for the following system development

Measurement data from

• Undamaged foundation,

• Operational loads,

• Peak loads,

• Changes in environmental conditions,

• damages

serve as a basis for the development of automatically operating algorithms for damage detection, for the compensation of EOC and for determining the sensitivity of the method. The following measurements were performed:

• Reference measurements, at the same time observations to soil degradation,

• Load variations, changes in the EOC,

• Loss of stiffness of the supporting structure, damage,

• Influence of marine fowling, changes in the EOC,

• Scouring, damage

• Misalignment by extreme loads, damage.

Experimental setup

Reference measurement and soil degradation

• Excitation by a Shaker

• Remote control of the experiment

• Force: 400 N 350 N 250 N RMS

• Power spectral density Structural response due to excitation with white noise from 2 to 50 Hz

Soil degradation

Reference measurement shows significant changes in the first natural frequency of the pile at 4,3 Hz.

M. Link 2015: Hardening of the sediment; however piles are rammed!

Soil behavior is specific to the experimental set-up

Initial soil degradation

• Monopile installation by vibrations,

• No time for settlement,

• No water pressure,

• Incomplete water saturation of the sediment

• Higher Frequencies

Sensitivity with regard to stability of the foundation

Soil degradation and scouring obscured all other changes in the signals

For compensation specific signal analysis methods are necessary

Loss of Stiffness with the Pile

Reproducible structural damage is modelled by a flange with 20 screws between pile and tower:

Loosening of 2, 4 and 6 screws,

SSI-COV is based on the analysis of 4 natural frequencies; safe detection of 4 and 6 loosened screws.

NSFD is able to detect all damage levels with 2, 4 and 6 screws.

NSFD-based Indicator

SSI-COV based Indicator

Fouling

Restricted possibilities to simulate fouling with an experimental set-up like in TTH!

Special case: fouling in the tidal reach with low water.

Bio mass is hanging in the air additional mass of 4, 20 and 30 kg on a structure with a mass of about 1 t

SSI-COV is not able to detect such small changes of the mass satisfactorily

NSFD-Indicator is able to detect all changes

Additional mass of 4, 20 or 30 kg

NSFD-Indicator

Scouring

Scouring changes the depth of embedding into the sediment; the contact region between pile and sediment is reduced; experiments with 30, 60 and 80 cm depth of the scour.

Changings of the boundary conditions of a cantilever beam have a significant influence to natural frequencies

Initial soil degradation

Scouring of 5 cm depth can be detected!

Both indicators SSI-COV and NSFD are able to detect scouring very well

Problem: Obscuring other changes in the signals

NSFD-Indicator

SSI-COV-Indicator

Depth of scour 30 cm

Misalignment

Hydraulic forces for the simulation of maximum loads like gusts or waves with a 50 year recurrence period

Changings within the mechanical system is detected by SHM

It is possible to detect a misalignment of the pile using accelerometers;

however it is easier to use an inclinometer

UnderwaterINSPECT

Structural Health Monitoring of offshore foundations

01.11.2012 to 31.10.2015

QS-M Grout

Quality assurance and SHM of grouted joints on underwater supporting structures of OWT

01.11.2014 to 30.10.2017

UnderwaterINSPECT was funded by a grant of the German Federal Ministry of Economic Affairs, contract number 03SX345A

QS-M Grout is funded by a grant of the German Federal Ministry of Economic Affairs, contract number 03SX372A

QS-M Grout: Measurement setup and sensor positions

• Intended measurement levels

• Level 0 – below flange foundation pile

• Level 1 – above flange grout bottom

• Level 2 – In grout area

• Level 3 – below flange grout top

• Level 4 – above flange tower bottom

• Level 5 – above clamp

• Level 6 – below flange tower top

• Instrumentation has to be movable between test pit and test bed (level 1-6)

• Clamp for loading must be mounted during complete experiment

shaker

clamp for loading

test pit

6x (3x2) SG Wölfel (15x)

1x 2D-inclinometer

15x (5x3) acceleration sensors

3x surface microphone

Level 0

Level 3

Level 2

Level 1

Level 4

Level 5

Level 6

test bed

Installation of sensors

Industrial application of R&D results: Monitoring of offshore foundations

Wölfel CMS – communication concept

Wölfel Structural health monitoring – modular data analysis

Wölfel Structural health monitoring – online web portal

WEA-01

WEA-04

WEA-05

WEA-06

WEA-07

WEA-08

WEA-02

WEA-03

Wölfel Structural health monitoring – hardware (example)

Transition Piece

acceleration &

inclination

Platform 3

acceleration

Platform 5

acceleration &

inclination

Overview Close-Up Position 145°

acceleration

sensor

inclination sensor

acceleration sensor 22.5°

acceleration and

inclination sensor 202.5°

Selection of references

Experiences in the field of foundation and blade SHM

ALPHA VENTUS Foundation-CMS (Jacket, Tripod)

EnBW /SIEMENS CMS for dynamical behavior of offshore wind turbines

RWE / SENVION Foundation and Grout-CMS

IBERDROLA / ADWEN Foundation (Monopile, Jacket) and Grout-CMS

TENNET Monitoring Converter Platform

E.ON Continuous Condition Validation of offshore turbines

NORDEX Lifetime monitoring tower; Blade monitoring

ENERCON Blade monitoring

References Offshore Wind

Wölfel-Group Max-Planck-Str.15 97204 Höchberg, Germany Phone: +49 931 49708-600 Fax: +49 931 49708-650 E-Mail: info@woelfel.de www.woelfel.de

Dr. Andreas Nuber Phone: +49 931 49708-365 E-Mail: nuber@woelfel.de

Thank you for your attention!

from r&d to an industrial application · 01.11.2012 to 31.10.2015 qs-m grout quality assurance...

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