Francois Schmitt

CNRS LOG · Laboratory of Oceanology and Geosciences

We study the statistical properties of scalar fields undergoing reversible chemical reactions in a turbulent environment by means of numerical simulations. To produce strong chemical fluctuations in a wide region of the domain, an original flow configuration has been proposed, where the species are supplied from buffer boundaries with adjustable th...

Annual phytoplankton succession is a key ecological phenomenon that drives marine species’ life cycles and energy flows within marine ecosystems. Identifying processes that control annual succession is critical to anticipate climate-induced environmental perturbations of this phenomenon and the consequences upon ecosystem functioning. Here, we demo...

Copepods of the species Acartia tonsa have been placed in a laboratory generated turbulent flow system, called Agiturb, characterized by Taylor-scale-based Reynolds numbers from 130 to 360. Trajectories of alive and dead copepods, and of polystyrene spherical particles of size 600 μm, have been measured in the dark with infrared lights, using a hig...

The discrete SIR (Susceptible–Infected–Recovered) model is used in many studies to model the evolution of epidemics. Here, we consider one of its dynamics—the exponential decrease in infected cases I(t). By considering only the I(t) dynamics, we extract three parameters: the exponent of the initial exponential increase \(\gamma \); the maximum valu...

We study the three-dimensional turbulent Kolmogorov flow, i.e., the Navier–Stokes equations forced by a single-low-wave-number sinusoidal force in a periodic domain, by means of direct numerical simulations. This classical model system is a realization of anisotropic and non-homogeneous hydrodynamic turbulence. Boussinesq's eddy viscosity linear re...

The nocturnal low-level jet (LLJ) and orographic (gravity) waves play an important role in the generation of turbulence and pollutant dispersion and can affect the energy production by wind turbines. Additionally, gravity waves have an influence on the local mixing and turbulence within the surface layer and the vertical flux of mass into the lower...

The time scales of a catchment hydrologic response in a human impacted intra-Apennine basin, was assessed by a power spectral analysis. Turbidity and streamflow data, at high resolution (10 minutes) have been considered during four years. The turbidity and streamflow have heavy tails that follow approximately Pareto distributions. Both also display...

Barred macrotidal beaches are affected by continuous horizontal displacements of different hydrodynamic zones associated with wave transformation (shoaling, breaker and surf zones) due to significant tide-induced water level changes. A series of wave and current meters, complemented by a video imagery system, were deployed on a barred beach of nort...

Turbulence or turbulence‐like phenomena are ubiquitous in nature, often showing a power‐law behavior of the fluctuations in either spatial or temporal domains. This power‐law behavior is due to interactions among different scales of motion, and to the absence of characteristic scale. In this work, we consider the multiscale dynamics of China France...

Observations of the interstellar medium (ISM) show a complex density and velocity structure, which is in part attributed to turbulence. Consequently, the multifractal formalism should be applied to observation maps of the ISM in order to characterize its turbulent and multiplicative cascade properties. However, the multifractal formalism, even in i...

We study the three-dimensional turbulent Kolmogorov flow, i.e. the Navier-Stokes equations forced by a low-single-wave-number sinusoidal force in a periodic domain, by means of direct numerical simulations. This classical model system is a realization of anisotropic and non-homogeneous hydrodynamic turbulence. Boussinesq's eddy viscosity linear rel...

This book contains an introduction to turbulence and statistical methods, with a chapter on turbulence and plankton, animal and vegetal. A chapter also discusses biogeochemistry and the role of turbulence for benthic organisms, which live on the seabed. It has many examples and illustrations. It is aimed at a public of doctoral students and researc...

Observations of the interstellar medium (ISM) show a complex density and velocity structure which is in part attributed to turbulence. We here present a self-contained introduction to the multifractal formalism in a microcanonical version which allows us for the first time to compute precise turbulence characteristic parameters from a single observ...

Dans le cadre d’un projet intitulé « Quel littoral dans cinquante ans ? Co-construction de stratégies d’adaptation au changement climatique en Côte d’Opale », une équipe de chercheurs d’horizons divers, géographes, sociologue et physicien, a travaillé pendant trois ans (2016-2019) sur les évolutions passée et à venir du rivage de deux communes du d...

In aquatic ecosystems, anthropogenic activities disrupt nutrient fluxes, thereby promoting harmful algal blooms that could directly impact economies and human health. Within this framework, the forecasting of the proxy of chlorophyll a in coastal areas is the first step to managing these algal blooms. The primary goal was to analyze how phytoplankt...

The statistical properties of species undergoing chemical reactions in a turbulent environment are studied. We focus on the case of reversible multicomponent reactions of second and higher orders, in a condition close to chemical equilibrium sustained by random large-scale reactant sources, while the turbulent flow is highly developed. In such a st...

The statistical properties of species undergoing chemical reactions in a turbulent environment are studied. We focus on the case of reversible multi-component reactions of second and higher orders, in a condition close to chemical equilibrium sustained by random large-scale reactant sources, while the turbulent flow is highly developed. In such a s...

Ruz, M.-H.; Rufin-Soler, C.; Héquette, A.; Révillon, R.; Hellequin, A.-P.; Deboudt, P.; Herbert, V.; Cohen, O.; Lebreton, F.; Le Goff, L.; Schmitt, F.G., and Marin, D., 2020. Climate change and risk perceptions in two French coastal communities. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Speci...

Sea breeze (SB) phenomena may strongly influence air quality and lead to important effects on human health. In order to study the impact of SB dynamics on the properties and toxicity of aerosols, an atmospheric mobile unit was deployed during a field campaign performed in an urbanized and industrialized coastal area in Northern France. This unit co...

An experiment was performed to study the power production by a Darrieus type turbine of the Dutch company Water2Energy in a tidal estuary. Advanced instrumentation packages, including mechanical sensors, acoustic Doppler current profiler (ADCP), and velocimeter (ADV), were implemented to measure the tidal current velocities in the approaching flow,...

The intermittency of wind turbine power is an important issue limiting the massive development of this renewable energy. To address this issue, we consider the theoretical framework of multifractal energy cascades, which is a classical framework for describing and characterizing the fluctuations in the turbulent wind input. The multi-scaling statis...

The temporal statistics of incompressible fluid velocity and passive scalar fields in developed turbulent conditions is investigated by means of direct numerical simulations along the trajectories of self-propelled pointlike probes drifting in a flow. Such probes are characterized by a propulsion velocity which is fixed in intensity and direction;...

Topography presents, as many geophysical fields, important fluctuations over a large range of scales. On the Earth, theses fluctuations are controlled by various geological processes over which, tectonics (and isostasy) is a first order one. Indeed, it generates surfaces which are scale invariant over many scales. Here we are interested in a multi-...

Coastal flooding due to surge events represents natural hazards with huge potential consequences for coastal regions. Sea level time series display variations on a large range of timescales, with a deterministic component associated with tidal variations and a stochastic component primarily associated with meteorological forcing, the non-tidal resi...

The temporal statistics of incompressible fluid velocity and passive scalar fields in developed turbulent conditions is investigated by means of direct numerical simulations along the trajectories of self-propelled point-like probes drifting in a flow. Such probes are characterised by a propulsion velocity which is fixed in intensity and direction;...

A key ecological parameter for planktonic copepod studies is their encounter rates within the same population as well as with other species. The encounter rate is partly determined by copepod’s swimming behaviour and is strongly influenced by turbulence of the surrounding environment. A distinctive feature of copepods’ motility is their ability to...

A vertical axis tidal turbine (VATT) of the Dutch company "Water2Energy", mounted on a surface platform , was tested during several weeks in real sea conditions in a tidal estuary-the Sea Scheldt, Belgium. Velocity measurements were performed to estimate the major turbulent properties of the tidal flow at the experimental site, to evaluate the tida...

This study is the first in situ work comparing Rapid Light Curves (RLC) and Non Sequential Steady-State Light Curves (N-SSLC) in their efficiency to characterize phytoplankton photosynthetic activity and acclimation status. Measurements were carried out at two time scales (daily and annual) using the Pulse Amplitude Modulated fluorometry on samples...

In recent years several local extrema-based methodologies have been proposed to investigate either the nonlinear or the nonstationary time series for scaling analysis. In the present work, we study systematically the distribution of the local extrema for both synthesized scaling processes and turbulent velocity data from experiments. The results sh...

We consider here the works of French, British, and German researchers in fluid mechanics from 1870 to the beginning of the twentieth century. Our aim is to understand how the term “turbulence” introduced by William Thomson in 1887, which was not used by the main researchers of the time, including Joseph Boussinesq, Osborne Reynolds, Lord Rayleigh,...

The correlation between the flow turbulence and the performances of a ma- rine current turbine is studied. First, the incoming flow encountered in the flume tank is characterized in the framework of fully developed turbulent cascades in the inertial range. The Reynolds number, the Kolmogorov dissipation scale and the integral scale, are estimated f...

The CASES-99 experimental data are used to analyze turbulence behaviour under a range of stable conditions using an adaptive method based on Hilbert spectral analysis. The characteristic scales of intrinsic mode functions vary between different stratifications. The second-order Hilbert marginal spectra display clear separation between fine-scale tu...

The massive integration of sustainable energies into electrical grids (non-interconnected or connected) is a major problem due to their stochastic character revealed by strong fluctuations at all scales. In this paper, the scaling behaviour or power law correlations and the nature of scaling behaviour of sustainable resource data such as flow veloc...

A series of tidal turbine tests were conducted in a tidal estuary (the Sea Scheldt, Belgium). Two in-stream vertical axis tidal turbines were tested in real conditions during several weeks in winter 2014 and late summer 2015. Tidal current velocity variations were continuously recorded by one ADCP, operating at 1 Hz and two ADV operating at 16 and...

Turbulent characteristics in the atmospheric surface layer are investigated using a data-driven method, Hilbert spectral analysis. The results from empirical mode decomposition display a set of intrinsic mode functions whose characteristic scales suggest a dyadic filter-bank property. It can be concluded from the joint probability density function...

Geophysical fields possess large fluctuations over many spatial and temporal scales. Satellite successive images provide interesting sampling of this spatio-temporal multiscale variability. Here we propose to consider such variability by performing satellite time series analysis, pixel by pixel, using Empirical Mode Decomposition (EMD). EMD is a ti...

The growing demand of energy and a new conscience in environmental issues are the basis for a emergent sustainable energetic model. The wind energy has in this context a special focus on its improving performance. The ongoing efforts to develop more efficient wind turbines faces the discontinuity problem of the electric power. These large fluctuati...

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It was hypothesized that the Malabar grouper Ephinephelus malabaricus larvae have developed search patterns adapted to the distribution of their prey to maximise their net energy intake per unit time. Analysis of the swimming behaviour of E. malabaricus larvae in both the presence and absence of Artemia sp. nauplii is presented to test this hypothe...

High-frequency temperature fluctuations recorded in the English Channel are compared using two long-term autonomous underwater monitoring stations at less than 20-min time resolution. Measurements were taken from 2005 to 2011 from two systems 460 km apart in the western and eastern parts of the English Channel. Spectral analysis reveals similar sta...

Renewable resources such as atmospheric wind speed and global horizontal irradiance, possess huge fluctuations over a large range of spatial and temporal scales, indicating their nonlinear and nonstationary properties. In this study, the multiple scale dynamics and the correlations between simultaneous time series are analyzed using EMD (Empirical...

Planktonic copepods are small crustaceans that have the ability to swim by quick powerful jumps. Such an aptness is used to escape from high shear regions, which may be caused either by flow per- turbations, produced by a large predator (i.e. fish larvae), or by the inherent highly turbulent dynamics of the ocean. Through a combined experimental an...

We consider Lagrangian velocity differences of zooplankters swimming in still water and in turbulence. Using cumulants, we quantify the intermittency properties of their motion recorded using three-dimensional particle tracking velocimetry. Copepods swimming in still water display an intermittent behaviour characterized by a high probability of sma...

The Taylor power law (or temporal fluctuation scaling), is a scaling relationship of the form σ ~ (P)λ where !! is the standard deviation and hPi the mean value of a sample of a time series has been observed for power output data sampled at 5 min and 1 s and from five wind farms and a single wind turbine, located at different places. Furthermore, a...

Marine coastal processes are highly variable over different space scales and timescales. In this paper we analyse the intermittency properties of particle size distribution (PSD) recorded every second using a LISST instrument (Laser In-Situ Scattering and Transmissometry). The particle concentrations have been recorded over 32 size classes from 2.5...

There is growing efforts for the development of wind energy. Yet, as for other renewable resources, a basic characteristic of wind energy is to deliver intermittent power. In this paper, we consider this topic by analyzing data provided by the wind industry. We discuss first the spectral properties of the data and the corresponding power curve. We...

We consider here some scaling and intermittency properties of oceanic turbulence, with a general aim of considering the impact of turbulence on the bio-optical dynamics. For that purpose, we tried two different approaches, using in situ and satellite data. For the in situ study we adopted one dimensional and for the satellite two dimensional approa...

Multifractal time series, characterized by a scale invariance and large fluctuations at all scales, are found in many fields of natural and applied sciences. Here we consider a quite general type of multifractal time series, called multifractal random walk, as non stationary stochastic processes with intermittent stationary increments. We first qui...

Marine coastal processes are highly variable over different space and time scales. In this paper we analyse the intermittency properties of particle size distribution (PSD) recorded every second using a LISST instrument (Laser In-Situ Scattering and Transmissometry). The particle concentrations have been recorded over 32 size classes from 2.5 to 50...

Satellite remote sensing observations allow the ocean surface to be sampled synoptically over large spatio-temporal scales. The images provided from visible and thermal infrared satellite observations are widely used in physical, biological, and ecological oceanography. The present work proposes a method to understand the multi-scaling properties o...

The temporal variability in phytoplankton photosynthetic activity was studied in the coastal waters of the Strait of Dover and related to environmental conditions. Phytoplankton photosynthetic activity data collected from October 2008 and August 2010 at different time scales (hourly to interannual) using a nested sampling design are presented. Phot...

Satellite remote sensing observation allow the ocean surface to be sampled synoptically over large spatio-temporal scales. The images provided by ocean colour satellites are widely used in physical, biological and ecological oceanography. The present work proposes a method for understanding the multi-scaling properties of satellite ocean colour pro...

Satellite remote sensing observation allow the ocean surface to be sampled synoptically over large spatio-temporal scales. The images provided by ocean colour satellites are widely used in physical, biological and ecological oceanography. The present work proposes a method for understanding the multi-scaling properties of satellite ocean colour pro...

Satellite remote sensing is a powerful tool for understanding many of oceanic processes synoptically. The images provided by the ocean colour satellites are widely used in physical, biological and ecological aspects of oceanography, but the scaling properties of satellite images are too rarely studied. In the present work we aim to understand the s...