Franck Schoefs

University of Nantes | UNIV Nantes · Institute for Civil and Mechanical Engineering Research

Several studies have been performed in the last two decades to assess the impacts of marine biofouling on offshore wind turbines (OWTs) substructures. Marine biofouling generally refers to the settlement and growth of aquatic organisms on human-made structures situated in marine and estuarine environments. OWTs continue to demonstrate significant e...

The objective of this paper is to propose tools for the lifecycle management of infrastructure by showing the slow degradation processes for which inspection data are accessible, especially the data obtained from non-destructive testing (NDT) and structural health monitoring (SHM). One major characteristic of these degradation processes is their mu...

AB). Abstract Several studies have been performed in the last two decades to assess the impacts of marine biofouling on offshore wind turbines (OWTs) substructures. Marine biofouling generally refers to the settlement and growth of aquatic organisms on human-made structures situated in marine and estuarine environments. OWTs continue to demonstrate...

In recent years, several studies have been performed to assess the damages caused by marine biofouling. Marine biofouling (or marine growth) generally refers to the settlement and growth of unwanted aquatic organisms on human-made structures situated in marine and estuarine environments. Regarding the continued demonstration of energy resource pote...

Offshore wind substations are subjected to uncertain loads from waves, wind and currents. Sea states are composed of irregular waves which statistics are usually characterized. Irregular loads may induce fatigue failure of some structural components of the structures. By combining fatigue damage computed through numerical simulations for each sea s...

The presence of marine growth increases submarine structures diameter and roughness and thus the hydrodynamic loading due to wave and current excitation. In this paper, two kinds of hard roughness (mussels and corals) are studied experimentally. In order to cover a wide range of the dimensionless numbers (Reynolds number, Keulegan–Carpenter number...

Lifetime performance requirements for safety and operations of wind turbines is very important for its competitiveness and further uptake. While significant novelties are observed around the development of new turbines, we are also grappling with challenges related to lifetime performance. On the other hand, new materials, sensors, and analysis met...

This paper presents two approaches to tackle the issue of discretization error in the reliability assessment of structures. The first method (AGSK-MCS for Adaptive Guaranteed State Kriging Monte Carlo Sampling) uses discretization error bounds to guarantee the state safe or failed of the points used to build the Kriging metamodel of the limit state...

One major issue when considering the effects of climate change is to understand, qualify and quantify how the changing climate will likely impact infrastructure assets and services as it strongly depends on current and future climate variability, location, asset design life, function and condition. Expected changes to local climatic conditions may...

How sea and littoral Institure gathers the Academic Strength in Region pays de la Loire France to adress localy the needs of the industry and citizens about Offshore Wind.

Prise en compte de l'historique de chargement pour l'estimation du dommage au sein d'une structure en acier sollicitée en fatigue Résumé : Pour les structures soumises à des chargements d'origine environnementale la fatigue polycyclique est l'une des principales sources des défaillances d'origine mécanique, il est donc primordial de considérer ce p...

The changing climate with resulting more extreme weather events will likely impact infrastructure assets and services. This phenomenon can present direct threats to the assets as well as significant indirect effects for those relying on the services those assets deliver. Such threats are path-dependent and place-specific, as they strongly depend on...

Le rapport a été présenté dans l'hémicycle de l'Hotel de Région, en séance de l'Assemblé des Territoires et en présence de Mme la Présidente de la Région pays de la Loire le 24 juin 2022.

With 80% of European trade exchange and a key role for European defence, harbours play a major socio-economic role. Inspection of wharves is very expensive due to the difficult access to some components. Reinforced Concrete (RC) structures in harbours are designed for a long service life (50 to 70 years). For RC structures exposed to marine environ...

Wind energy is expected to play a significant role in meeting emission targets over the next 20 years. Offshore wind turbines in deep water (>150 m) must be developed due to resource quality, environmental, and activity constraints. Floating offshore wind turbines (FOWT) will be the best technology for reaching these targets. The dynamic submarine...

Novel attempts to optimize the design and requalification of offshore structures draws attention to the importance of updating information about the environmental forces. One of the important steps to design or re-assess offshore structures is the re-evaluation/evaluation of bio-colonization’s effects. This paper presents a review of studies that c...

This presentation is about classification of in air and underwater images of biofouling for the specific use of Marien Renewable Energies.

Onshore pipelines are usually subjected to a corrosion attack. Regular inspections known as In-Line inspections (ILI) are commonly used with magnetic (MFL) or ultrasonic (UT) tools to prevent any failure. New defects will appear between consecutive inspections due to the aggressiveness of the surroundings and the detection thresholds associated wit...

The main objective of this Collaborative Innovation Group (CIG) of the Ocean Power Innovation Network (OPIN) project,was to identify one or several future R&D collaboration opportunities within the CIG members (all or a subset) and start preparing the basis for associated grant applications. A state-of-the-art report has been prepared to support th...

Marine growth is a known problem for oceanic infrastructure and has been shown to negatively impact the reliability of bottom-fixed or floating offshore structures submitted to fatigue or extreme loading. Among other effects, it has been shown to change drag forces by increasing member diameters and modifying the roughness. Bio-colonization being h...

Hard marine growth is an important process that affects the design and maintenance of floating offshore wind turbines. A key parameter of hard biofouling is roughness since it considerably changes the level of drag forces. Assessment of roughness from on-site inspection is required to improve updating of hydrodynamic forces. Image processing is rap...

Corrosion monitoring is currently not yet implemented by default and many questions remain as to the available technology, but also the potential gains of implementing corrosion monitoring. Within the framework of the OPIN project, a Collaborative Innovation Group (CIG) on Corrosion Monitoring was established. The CIG consists of a consortium of co...

Submarine cables such as electrical umbilical power cables for floating wind turbines are subject to biofouling which can have an important effect on their dynamical behaviour under wave and current conditions by drastically increasing their size and mass. The impact of biofouling on the dynamic behaviour of an underwater power cable characterized...

After a few weeks, underwater components of offshore structures are colonized by marine species and after few years this marine growth can be significant. It has been shown that it affects the hydrodynamic loading of cylinder components such as legs and braces for jackets, risers and mooring lines for floating units. Over a decade, the development...

In structural reliability, the Markovian cumulative damage approaches such as Gamma process seem promising to model a nonreversible deterioration that involves gradually over time with small time increments. However, in many degradation phenomena, its evolution depends on the level of the degradation rather than the increments of time. Further, the...

Manufacturing of structures is usually achieved through building processes involving periodic or at least regular actions: rotating machines for steel rolling, vibration of concrete, etc. After several years of operation, these same structures are subjected to non-homogeneous degradation processes due to loading or biochemical effects (for example,...

Obtaining a precise estimation of the probability of failure for a given structure is critical when doing its reliability analysis. The Monte-Carlo estimator is easily implemented, non-intrusive to the simulations and un-biased [5]. However, it requires to simulate the structure for a large number of realizations of input random variables. Each sim...

This project was selected by the Région Pays de la Loire for the "Exhibition of Region pays de la Loire for the 30th Anniversary of Interreg Projects in Atlantic Area. Floods are climate change phenomena that affect a considerable number of people in the Atlantic Area, as increasingly intense rains overflow rivers and create runoffs in urban areas....

p>One major issue when considering the effects of climate change is to understand, qualify and quantify how natural hazards and the changing climate will likely impact infrastructure assets and services as it strongly depends on current and future climate variability, location, asset design life, function and condition. So far, there is no well-def...

https://www.weamec.fr/en/technologies/biocolmar/

Inspection by non-destructive testing (NDT) techniques is an effective way for assessing structures’ condition state, their pathologies and locating potential critical areas. However, establishing accurate diagnoses requires numerous measurements while available budget is limited. Nevertheless, determining the spatial variability of the material pr...

Link to the conference: https://www.youtube.com/watch?v=OxGBZdDvG-E&feature=youtu.be EU Strategy from time: 2 hours 26 mn

United States on the innovation potential of floating offshore wind energy technology and to discuss and identify the key issues that can lead to lower costs of energy and increased public acceptance. The workshop featured 120 participants from academia, industry and government with expertise in engineering, social science, economics, financing, pu...

The unit influence line of a structure reflects its behaviour and changes in response to damage that may occur. An iterative algorithm is presented in this paper to obtain the shape of the instantaneous influence line of a bridge together with the relative axle loads of trucks passing overhead. One great advantage of this approach is that the need...

This work focuses on predicting corrosion onset induced by concrete carbonation or chloride ingress when using analytical predictive models. The paper proposes a procedure that helps building and infrastructure managers to select an appropriate model depending on the available information and the means granted to auscultation campaigns. The approac...

This paper presents an approach to build a multi‐fidelity kriging metamodel from finite element computations on different meshes for stuctural reliability assessment. The proposed method takes advantage of the computation of bounds on the discretization error, which enables to guarantee the state (safe or failure) of each computation of the perform...

This paper investigates the role that virtual environments can play in assisting engineers and divers when performing subsea inspections. We outline the current state of research and technology that is relevant to the development of effective virtual environments. Three case studies are presented demonstrating how the inspection process can be enha...

In this paper damage indicators are presented for bridges based on measured data collected underuncontrolled traffic conditions.The test bridge considered is a small stiff concrete culvert with low dynamics, making it sub-optimal for monitoring with accelerometers.Largely static strain responses are measured, with the variability in the vehicle wei...

Due to both wave and wind fluctuations, the steel foundations of offshore wind turbines are highly submitted to fatigue. To date, current methods of fatigue design proposed in the regulations are not devoted to structural optimization and to the consideration of time-variant hazards. We propose hence an incremental two-scale model of damage in orde...

Bio-colonisation affects the ageing of materials and the behaviour of offshore structures. Mooring systems and umbilicals belong to the family of slender bodies which are components sensitive to bio-colonisation because of a change of dynamic behaviour due to shape, roughness and mass modifications. However, this stochastic process in time and spac...

Optimization of maintenance and design of coastal steel infrastructure needs for long-term predictive degradation models. The phenomenon of corrosion in the offshore and coastal environment is very complex due to the stochastic and changing nature of the environment (temperature, water chemical properties) and the multiple involved processes in com...

Offshore Wind Energy is one of the most promising offshore renewable energies. Bottom fixed offshore wind turbines have reduced step by step their Levelized Cost of Energy. It relies both on CAPEX and OPEX reduction by optimizing the design. One of the key issues is a better assessment of the risks and reliability. As a consequence, the accuracy of...

Large structures are systems composed by a significant number of components with parallel or series distributions. How these components fail and interact, aggravate the complexity of the main structure reliability calculation. Some methods commonly proposed to reduce this complexity by dividing the system into segments of similar properties using d...

Nowadays, the service life monitoring of mooring lines attracts more and more attention from the marine renewable energy (MRE) industry where developers desire to have a closer look on the safety margin. Besides, current standards are also being improved in order to ensure safe and cost-effective design for MRE devices. In the present study, we bel...

Corrosion defects affect the structural integrity of onshore pipelines making them prone to a Loss of Containment (LOC). LOCs may trigger significant consequences over the surrounding people and environment. Therefore, In-Line (ILI) inspections are commonly implemented to measure indicators of the metal loss along the pipe due to corrosion to suppo...

In marine environments structures are subjected to a variety of environmental conditions which govern the degradation processes. For reinforced concrete structures these degradation processes (chloride ingress and corrosion) are driven by the availability of oxygen and humidity. Due to the random process of tidal movements it is difficult to determ...

In this paper a methodology is presented to update estimated level of corrosion damage using routine short-term health monitoring measurement data. The case study bridge is a reinforced concrete (RC) slab. It is subject to traffic loading from a weigh-in-motion database and time-dependent deterioration is modelled through corrosion. Different damag...

Characterising spatial variability, which is of utter importance in inspection and maintenance strategies, requires comprehensive spatially distributed databases. However, in real practice, spatially distributed inspection is costly and could damage the structure if a large number of destructive tests are carried out. Therefore, the first objective...

Chloride ingress is the main chemical process that induces corrosion in reinforced concrete structures exposed to marine environment. It can either be assessed with chlorides titration on core samples, or quickly evaluated with resistivity measurements. However, whatever the technique, one of the major concern of stakeholders is the accuracy of the...

Nowadays, the service life monitoring of mooring lines attracts more and more attention from the offshore industry. This is especially more vital for the Marine Renewable Energy (MRE) sector where developers desire to have a closer look on the safety margin in order to reduce the structure cost, then the electricity producing price. In this study,...

The present paper deals with the stochastic modeling of bio-colonization for the computation of stochastic hydrodynamic loading on jacket-type offshore structures. It relies on a multidisciplinary study gathering biological and physical research fields that accounts for uncertainties at all the levels. Indeed, bio-colonization of offshore structure...

The subject of damage localization is an important issue for Structural Health Monitoring (SHM) particularly in mechanical or civil structures under ambient excitation. In this paper, the statistical subspace based damage localization method has been applied on a benchmark application, namely a 1/200 scale model of the Saint-Nazaire Bridge, which i...

Optimal placement of Non-destructive Testing sensors is essential for structure diagnosis as it allows to get maximum information about degradation at minimum cost. Latest optimization methods consider spatial variability of quantities of interest and thus strongly rely on correlation lengths assessment. However, this estimation is usually done wit...

Marine growth (or macro-biofouling) is well known to colonized the immersed part of marine structures after only few weeks. Among various effects, behavior of Floating Offshore Wind Turbines is mostly affected by the added mass, the increase in mooring and umbilicals diameter and the change in hydrodynamic forces. Surface roughness is highlighted t...

The present paper deals with the stochastic modeling of bio-colonization for the computation of stochastic hydrodynamic loading on jacket-type offshore structures. It relies on a multidisciplinary study gathering biological and physical research fields that accounts of uncertainties at all the levels. Indeed, bio-colonization of offshore structures...