LICENGINEERING short intro Founded 1985 located in Denmark. 50% - PowerPoint PPT Presentation

D IGITAL G UARDIAN Health monitoring and lifetime extension of OWF structures

LICENGINEERING – short intro • Founded 1985 – located in Denmark. • 50% Offshore Oil & Gas – 50 % Offshore Renewables • OWF since 1998, selected detailed design - Blyth: MP drill – grout - Scroby Sands: MP fixed Flange – TP less – Outer cage - North Hoyle: MP – TP grouted with shear keys - NorthWind: MP – TP grouted with shear keys - Rampion: MP fixed flange grouted skirt – TP - Dafeng/SPIC: MP fixed flange - Kriegers Flak: MP – TP fixed flange secondary structure. - Vesterhav N&S: MP – TP fixed flange, secondary structure - New concept: TP-less solution, inner and outer cage.

INTRODUCTION This presentation outlines a health monitoring system aimed at offshore support structures within the oil&gas and wind industry, that provides an accurate estimate of the true fatigue life of these assets in order to unlock potential fatigue life and ultimately extend the life of assets. Data from a few strategically placed sensors is decomposed into modal parameters by means of Operational Modal Analysis (OMA). The modal parameters are expanded to a high-resolution stress field solution (MDE) via a calibrated FE-model (Digital Twin) representing the considered asset. The concept offers a compelling and cost-effective method for offshore assets that are facing life time extension beyond what current methodologies can provide. The concept is currently being implemented on a platform in the UK continental shelf of a supermajor oil company.

D IGITAL G UARDIAN The Digital Guardain concept = Digital Twin updated high resolution RB-FEA model of asset + Structural Integrity Monitoring SIM system based on e.g. OMA

Digital Guardian LICengineering A/S has in cooperation with Akselos SAS developed a Digital Guardian System. The project started in 2016 and funded by Eurostar. Reduced based FE solver, based on a MIT R&D project and continued in the start up company Akselos located in Switzerland and Boston. RB-FEA ~1000 times faster than conventional FE-solvers, gives you the ability to model high resolution details and get all structural analysis in One-Model. LIC developed the plug-ins to the Akselos solver making a design package software for Design of offshore Foundations. LIC developed the SIM sensor system based on Operational Model Analysis theory in combination with accelerometers and data logging system. The system include postprocessing module for health monitoring and has been tested on a 8-legged offshore platform in the North Sea.

W HY IS CONDITION BASED MODELLING IMPORTANT ? • Few structural failures and most are non- critical. • Today: ~38% of European oil platforms have exceeded original design life. • 2029: This number will increase to ~80%. Same picture for for OWF foundations in the future but the numbers will be much larger.

What is known prior to application of SIM system Four governing parameters control the motion of any structure: mass, damping, stiffness and load. In numerical models, there are significant uncertainties for these parameters which often results in overly conservative prediction of fatigue life. } Mass Damping 𝑁 ሷ 𝑣 ∙ 𝐷 ሶ 𝑣 ∙ 𝐿𝑣 = 𝐺 Stiffness Equation of motion Loading

Flow of SIM System • The SIM system measures the accelerations ( ሷ 𝑣 ) directly • Through (double) integration and filtering of the accelerations the derived parts, i.e. velocities ( ሶ 𝑣 ) and displacements (u), are known. Thus responses from environmental loads. • Analyzing the measured accelerations through OMA gives the global stiffness (K) and damping (C) of the asset • The high-resolution model is updated to fit with the quantities identified by OMA (eigen frequencies, mode shapes) based on engineering judgement • Sea States are measured by wave bouy or similar, usually measured during lifetime from start to end • Combining the structural response of the Digital Twin will allow for a correlation between sea-states and structural response - leading to retrospective fatigue calculation of asset

SOLUTION TIER 1 – yellow line High-resolution modelling of asset (RB-FEA). Accurate modelling of complex structural details has been shown to significantly reduce fatigue damage. TIER 2 – blue line Update model to reflect real-world conditions (Digital Twin). Modal differences due to changes in mass or significant damages will be identified. TIER 3 – red line Fatigue calculation based on continuous monitoring and real measured responses. “On - line” fatigue calculation gives a real -time and accurate look into the health and condition of the asset. TIER 4 – green line Statistical correlation between sea states and fatigue damage → Retrospective fatigue calculation. If a statistical basis that forms the relation between sea states and responses is established, retrospective fatigue calculation is a possibility.

Validation of the system The concept has been validated via experiments under laboratory conditions. The concept has recently been implemented on a platform in the UK continental shelf of a supermajor oil company. The concept is now validated under real-world conditions.

Validation • Lattice structure with two sensor clusters. • Accelerometers used for analysis. • Displacements sensors used for validation. • Solenoid for excitation.

Validation • Measured accelerations. • Tuned numerical model using modal parameters from Operational Modal Analysis. • Determine displacement at any location using Modal Decomposition and Expansion. • Compare calculated displacements with measure displacements

REAL-WORLD IMPLEMENTATION • Implementation on 8-legged jacket in the North Sea. • 8 accelerometers on two levels. • Operational for about 2 months, ongoing.

REAL-WORLD IMPLEMENTATION • Significant deviations between initial numerical estimates of natural frequencies and measured natural frequencies. • Likely due bridge modelling and soil stiffness. • Conclusion: large differences between numerical condition and real- world condition. • Update of model in Digital Twin, re-analyses of model shows the fatigue life is extended more than the predicted life of asset > 25 x Relative Eigenmode difference 1 1.45 2 1.44 3 1.36

BENEFITS The Digital Guardian concept gives you following benefits: • Significantly increase the predicted fatigue life of assets compared to current methodologies. • More accurate prediction of your assets true behavior. • Information of stiffness, frequencies, damping, modes and responses. • Identify hot spots • Basis for inspection planning and risk based inspektion. • Use for due diligence as farms often are sold between operators. Small investment for the SIM system. Same Investment for the RB-FEA as for conventional FE tools.

N EXT APPLICATION Anholt Test Centre LIC design Anholt Test center for DHRTC. Here the system will be used to improve knowledge about breaking waves and structural responses. Danish Oil & Gas Centre – sponsored by TOTAL. 16

ISOPE 2019

CONTACT INFORMATION Hans Jørgen Riber LICengineering A/S hjr@liceng.dk