Christof Devriendt

Christof Devriendt
Vrije Universiteit Brussel | VUB · Department of Mechanical Engineering (MECH)

PhD (Doctor in the engineering sciences)

About

115
Publications
28,559
Reads
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2,092
Citations
Citations since 2016
48 Research Items
1580 Citations
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Introduction
The main research interests of Christof Devriendt are situated in the field of system identification, modal analysis and structural health monitoring. Currenlty he is coordinating the Brussels Wind Energy Research Institute, BruWind (www.bruwind.eu). He is also the scientific coordinator of “ The Offshore Wind Infrastructure Lab” or OWI-lab (www.owi-lab.eu).
Additional affiliations
January 2011 - present
Offshore Wind Infrastructure Lab
Position
  • Scientific coordinator offshore wind infrastructure lab (http://www.owi-lab.be//)
Description
  • Analyzing the integration of Condition Monitoring Systems (CMS), Structural Health Monitoring Systems (SHM) and new Operation & Maintenance (O&M) strategies for offshore windturbines in Flanders
October 2010 - present
Vrije Universiteit Brussel
Position
  • PostDoc Position
Description
  • Research into the analysis of the dynamic behavior of structures and their health monitoring during operational use (such as aircraft during flight, offshore wind turbines, bridges)

Publications

Publications (115)
Chapter
In recent years there has been an increased interest of the offshore wind industry to use structural health monitoring (SHM) data in the assessment of consumed lifetime and lifetime extension for an entire wind farm. In order for operators, certifying bodies, insurance entities and government agencies to agree on a lifetime extension, a commonly ac...
Chapter
Full-text available
Structural Health Monitoring (SHM) represents the course of action of implementing a damage assessment strategy for engineering infrastructures. SHM systems can provide substantial aid towards the improvement of Offshore Wind turbines (OWTs) reliability, sustainability, and profitability. Usually, SHM system development is affected by three major c...
Preprint
Full-text available
Offshore wind structures are subject to deterioration mechanisms throughout their operational lifetime. Even if the deterioration evolution of structural elements can be estimated through physics-based deterioration models, the uncertainties involved in the process hurdle the selection of lifecycle management decisions. In this scenario, the collec...
Article
Full-text available
In the present contribution, data from a measurement campaign on XL monopiles (with 9.5 MW turbines and water depths of up to 36 m) is presented. This campaign is based on data collected by three types of sensors: strain gauges (installed at the TP-tower interface), accelerations (taken at bottom, mid and upper levels of the tower) and SCADA data,...
Article
Full-text available
Structural Health Monitoring (SHM) has seen an explosion in data gathering in the last few years. This is illustrated in the offshore wind industry through an increase in the amount of placed offshore wind turbines (OWT), a higher rate of SHM instrumented OWTs and an increase in the sampling rate. The growing data gathering has led to the interest...
Article
Offshore wind turbines (OWTs) are sensitive, dynamic structures that require accurate estimation of the natural frequency of the support structure. This requires an integrated analysis of the wind turbine structure, including a realistic representation of the foundation response. This paper studies how the natural frequency analysis is influenced b...
Article
To date, despite advancements in the design of offshore wind turbines, the as-designed and identified as-built natural frequencies of offshore wind turbines still show discrepancies. These discrepancies are partially rooted in modelling uncertainties, as well as uncertain input parameters, related to e.g. aero-, fluid- or soil-structure interaction...
Article
Full-text available
The mutual and simultaneous action of external variable forces on (offshore) wind support structures causes fatigue. Fatigue analysis in this context relies on 10-minute-long strain signals. Cycle-counting allows capturing the fatigue cycles nested within these signals but inevitably leaves some open loops called half-cycles or residuals. Some othe...
Article
Full-text available
Offshore wind turbines founded on monopiles are highly dynamic structures in which the stiffness of the soil adjacent to the monopile controls the natural frequency of the structure. As the loading regime and ground conditions surrounding the foundation are subject to considerable uncertainty, adaptable digital twins of the offshore structures are...
Article
Full-text available
The sustained development over the past decades of the offshore wind industry has seen older wind farms beginning to reach their design lifetime. This has led to a greater interest in wind turbine fatigue, the remaining useful lifetime and lifetime extensions. In an attempt to quantify the progression of fatigue life for offshore wind turbines, als...
Chapter
Full-text available
The contribution of soil damping to the overall damping of offshore wind turbine structures has proven to be elusive. The strain-dependent soil stiffness and material damping can be quantified from small-scale element tests but applying the results from these tests in an integrated structural model requires a realistic assessment of the shear strai...
Conference Paper
Full-text available
In this contribution we present a physics-informed neural net-work (PINN) approach for wind turbine fatigue estimation. This PINN in-corporates physical information of the structure’s fatigue profile in its loss function, referred to as Minkowski logarithmic error (MLE) - an extension of the log loss for any given Lp space. The function is mathemat...
Article
Full-text available
Strain measurements using fibre Bragg grating (FBG) optical sensors are becoming ever more commonplace. However, in some cases, these measurements can become corrupted by sudden jumps in the signal, which manifest as spikes or step-like offsets in the data. These jumps are caused by a defect in the FBG itself, which is referred to as peak-splitting...
Article
Full-text available
The design of monopile foundations for offshore wind turbines is most often driven by fatigue. With the foundation price contributing to the total price of a turbine structure by more than 30%, wind farm operators seek to gain knowledge about the amount of consumed fatigue. Monitoring concepts are developed to uncover structural reserves coming fro...
Preprint
Full-text available
The sustained development over the past decades of the offshore wind industry has seen older wind farms beginning to reach their design lifetime. This has led to a greater interest in wind turbine fatigue, the remaining useful lifetime and lifetime extensions. In an attempt to quantify the progression of fatigue life for offshore wind turbines, als...
Article
Offshore wind turbines are subjected to cyclic loads from wind and waves, ultimately resulting in a fatigue-driven design. These cyclic loads result in cyclic shell forces above the bolted ring flange and ultimately into the cyclic loading of the bolt tension forces. To model the transfer of the shell forces into the bolt, Load Transfer Functions (...
Conference Paper
Full-text available
As older wind farms begin to reach their design lifetime, topics such as wind turbine fatigue, the remaining useful lifetime and lifetime extensions also start to be discussed with greater frequency. It is in this context that wind turbine fatigue assessment appears as crucial contribution. Its accurate portrayal can enable informed decisions regar...
Presentation
Full-text available
The OWI-Lab Soiltwin project’s objective is to improve the fatigue design of offshore monopiles through better modelling the soil-pile interaction. The project aims to update these models based on in-situ measurements over an entire fleet of OWTs on monopile foundations. Therefore, the project aims to create an updatable ‘digital twin’ FE model for...
Conference Paper
Full-text available
In this contribution SCADA data and thrust attained through strain measurements are used to train a neural network model which predicts the thrust load of an offshore wind turbine. The model is subsequently cross-validated for different turbines with SCADA data outside of the training period as input and the thrust load from strain measurements as...
Article
Full-text available
As the older wind farms are slowly reaching their design lifetime, topics like fatigue and lifetime assessment gain importance. To decide on a possible lifetime extension of the turbine and its foundation, an accurate fatigue assessment for every wind turbine in the farm is needed. As the installation of specific sensors needed for a fatigue assess...
Article
Structural fatigue is a design driver for offshore wind turbines (OWT). In particular, the substructures, like jackets, are strongly affected by fatigue. Monitoring the fatigue progression in the welds is vital for the maintenance and a potential lifetime extension. However, inspections of critical locations are costly due to the limited accessibil...
Article
Reassessing the remaining fatigue life of the wind turbine support structures becomes more and more crucial for operation, maintenance, and life extension when they are reaching the end of their design service life. By using measured oceanographic and strain data, each year, remaining fatigue life can be updated to adapt the operation to real loadi...
Article
Full-text available
Fatigue damage is a design-driving phenomenon for substructures of offshore wind turbines. However, fatigue design based on numerical simulations is quite uncertain. One main reason for this uncertainty is scattering offshore conditions combined with a limited number of simulations (samples). According to current standards, environmental conditions...
Conference Paper
Full-text available
An accurate stress or strain history at fatigue critical locations is often needed for a fatigue assessment. Unfortunately it is not feasible to install strain gauges as these fatigue hotspots. This contribution compares two techniques to obtain a reliable stress history at any location of the turbine structure, one is based on modal decomposition...
Conference Paper
Full-text available
Ice throw from the blades of operational wind turbines is a safety concern when wind turbines are installed in a densely built environment. While several commercial solutions exist to detect icing or prevent ice build up altogether, there is still a desire for a more effective low-cost solution. In this contribution a previously instrumented onshor...
Article
Full-text available
Measuring on offshore wind turbines is a challenging and cost intensive work especially when aiming for poorly accessible parts of the structure. While it is desirable to replace these measurements by indirect methods uncertainty exists about the necessary assumptions in environmental properties (e.g. soil conditions) and the structural dynamics. T...
Article
Full-text available
While substructures of offshore wind turbines become older and begin to reach their design lifetimes, the relevance of measurement based lifetime extension increases. To make well-founded decisions on possible lifetime extensions, damage extrapolations based on measurements are needed. However, although for all substructures, fatigue damage calcula...
Article
Full-text available
A reliable load history is crucial for a fatigue assessment of wind turbines. However, installing strain sensors on every wind turbine is not economically feasible. In this paper, a technique is proposed to reconstruct the thrust load history of a wind turbine based on high-frequency Supervisory Control and Data Acquisition (SCADA) data. Strain mea...
Article
Full-text available
In 2011 a first vibration monitoring system was installed on a single Belgian offshore wind turbine to research the possibility to monitor the structural integrity of the wind turbines substructure using accelerometers. From 2011 to 2017 four more wind turbines have been equipped with a similar setup. A combined total of 15 years of vibration measu...
Article
Full-text available
A reliable load history is crucial for a fatigue assessment of wind turbines. However, installing strain sensors on every wind turbine is economically not feasible. In this paper, a technique is proposed to reconstruct the thrust load history of a wind turbine based on high frequent SCADA data. Strain measurements recorded during a short period of...
Conference Paper
Full-text available
Maintenance costs are a main cost driver for offshore wind energy. Prediction of failure and particularly failure understanding can help to bring these costs down significantly. Since the wind turbine is subjected to a large number of dynamic events it is important to fully understand the turbine response to these events. Pattern mining has been us...
Conference Paper
The effects of operational wave loads and wind loads on offshore monopile wind turbines are well understood. For most sites, however, the water depth is such that steep and/or breaking waves will occur causing impulsive excitation of the monopile and consequently considerable stresses, displacements and accelerations in the monopile, tower and turb...
Poster
Full-text available
Since 2011 OWI-lab has been conducting acceleration measurements on an offshore wind turbine with a monopile substructure at the Belwind wind farm. A site with layers of clay and sand. The main goal of the campaign was to validate the design with in-situ measurements on the operational turbine. Initial results confirmed that the actual resonance fr...
Poster
Full-text available
Damping remains a hot topic in design of offshore wind turbines as turbine and monopile sizes grow. For these new designs the contribution of fatigue loads in parked conditions have increased. In addition the larger impact of wave loads on XL monopiles has given wind wave misalignment a bigger role in fatigue in the cross-wind direction. Both fatig...
Article
Full-text available
An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling noise, vibration, and harshness (NVH) issue...
Chapter
Offshore Wind Turbine (OWT) is complex structure that consists of different parts (e.g. foundation, tower, drivetrain, blades, …). The last decade there is a continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling NVH issues and validating complex simulation models it is o...
Article
Offshore wind turbines (OWTs) are subjected to both quasi-static loads originating from variations in the thrust force and dynamic loads linked to turbulence, waves and turbine dynamics. Both types of loads contribute to fatigue life progression and thus define the turbine's age. As a structural health monitoring solution, one could thus directly m...
Article
There is a trend towards large wind farms clustering a significant amount of turbines, aiming at continuously optimizing design and maintenance costs and thus reducing the overall cost of energy. Advanced control algorithms and maintenance optimizations may affect the lifetime of the turbines. Therefore it is necessary to actively monitor turbine b...
Article
Performance monitoring of offshore wind turbines is an essential first step in the condition monitoring process. This paper provides three novelties regarding power curve modeling. The first consists of illustrating that univariate power curve modeling can be improved by the use of non-parametric methods such as stochastic gradient boosted regressi...
Article
Full-text available
The present contribution is part of the ongoing development of a fatigue assessment strategy driven purely on in-situ measurements on operational wind turbines. The primary objective is to estimate the remaining life time of existing wind farms and individual turbines by instrumenting part of the farm with a load monitoring setup. This load monitor...
Article
Full-text available
As offshore wind farms (OWFs) grow older, the optimal use of the actual fatigue lifetime of an offshore wind turbine (OWT) and predominantly its foundation will get more important. In case of OWTs, both quasi-static wind/thrust loads and dynamic loads, as induced by turbulence, waves and the turbine's dynamics, contribute to its fatigue life progre...
Conference Paper
Fatigue life is often a design driver for the foundations of offshore wind turbines (OWTs). Moreover, conservatism in earlier designs might allow for future life time extension and re-use of existing foundations. Monitoring the consumption of fatigue life is thus an essential part in a full-scope structural health monitoring strategy for OWTs. To a...
Article
Offshore wind turbines are exposed to continuous wind and wave excitation. The monitoring of high periodic strains at critical locations is important to assess the remaining lifetime of the structure. At some critical locations below the water level, direct measurements of the strains are not feasible. Response estimation techniques can then be use...
Article
This paper experimentally investigates a grid loss event on the Gearbox Reliability Collaborative drivetrain mounted on the NREL nacelle testrig. It is shown that during the grid loss event the system vibration is driven by a counter phase rotation of the rotor and generator rotor about the drivetrain flexibility. This behavior results in significa...
Chapter
This paper presents two applications of joint input-state estimation in structural dynamics. The considered joint input-state estimation algorithm relies upon a limited set of response measurements and a system model, and can be applied for online input and state estimation on structures. In the first case, the algorithm is applied for force identi...
Chapter
Fatigue life is a design driver for the foundations of offshore wind turbines (OWT’s). A full-scope structural health monitoring strategy for OWT’s needs to consider the continuous monitoring of the consumption of fatigue life as an essential part. To do so, the actual stress distribution along the entire length of the structure and predominantly a...
Chapter
Fatigue life is a design driver for the foundations of offshore wind turbines (OWT’s). A full-scope structural health monitoring strategy for OWT’s needs to consider the continuous monitoring of the consumption of fatigue life as an essential part. To do so, the actual stress distribution along the entire length of the structure and predominantly a...
Conference Paper
Since fatigue life is a design driver for the foundations, the continuous monitoring for life-time assessment of an offshore wind turbine during its wide range of operational states can serve as a valuable tool for maintenance, end-of-life decisions and feedback into design for optimization of future substructures. For the offshore wind turbine, th...
Conference Paper
Fatigue life is often a design driver for the foundations of offshore wind turbines. A continuously monitored fatigue life can thus serve an important role in deciding over wind farm inspections, repowering or lifetime extension. As such it should be an integral part of any structural health monitoring system on offshore wind turbines’ foundations....
Article
Structural health monitoring of wind turbines is usually performed by collecting real-time operating data on a limited number of accessible locations using traditional sensors such as accelerometers and strain-gauges. When dealing with offshore wind turbines (OWT) though, most of the fatigue sensitive spots are inaccessible for direct measurements,...
Article
Full-text available
The monitoring of the condition of the offshore wind turbine during its operational states offers the possibility of performing accurate assessments of the remaining life-time as well as supporting maintenance decisions during its entire life. The efficacy of structural monitoring in the case of the offshore wind turbine, though, is undermined by t...
Conference Paper
Offshore wind turbines are exposed to continuous wind and wave excitation. The continuous monitoring of high periodic strains at critical locations is important to assess the remaining lifetime of the structure. Some of the critical locations are not accessible for direct strain measurements, e.g. at the mud-line, 30 meter below the water level. Re...
Article
Full-text available
In this contribution, first, the results in the development of a structural health monitoring approach for the foundations of an offshore wind turbine based on its resonance frequencies will be presented. Key problems are the operational and environmental variability of the resonance frequencies of the turbine that potentially conceal any structura...
Conference Paper
Full-text available
This contribution summarizes over two years of applied automated operational modal analysis on an operational offshore wind turbine. It discusses the applied automated Operational Modal Analysis (OMA) algorithm and the challenges of applying OMA to operational offshore wind turbines, ranging from the strong presence of rotor-harmonics to the sensit...
Conference Paper
Full-text available
Fatigue life is often a design driver for offshore wind turbines. A better understanding on the mech- anisms behind fatigue can improve design and thus reduce the initial cost of future substructures. This contribution aims to improve the understanding of fatigue life progression through monitoring. Mea- surements on an existing structure allow lin...
Poster
Full-text available
Health and condition monitoring is increasingly popular for offshore wind turbines due to the need for condition based rather than fault driven maintenance strategies and insurance requirements. The traditional health and condition monitoring approaches consider each monitoring source as a separate entity, which has its own dedicated measurement sy...