François Pétrélis’s research while affiliated with French National Centre for Scientific Research and other places

... Our understanding of such complex oscillatory flows and the development of theoretical models of the QBO is based on assumptions of how individual, weakly nonlinear, vertically propagating internal waves interact and energise a zonally symmetric zonal flow. It is somewhat surprising, therefore, that until recently, experimental investigations of this kind of phenomenon have tended to explore rather complicated configurations of wave forcing that are spatially inhomogeneous and/or complex in time [57,86,87] The reasons for this are partly historical in that experiments were typically motivated by a desire to reproduce an analogue of a complex geophysical phenomenon, such as the QBO itself (see also [88,89]). But one of the particular strengths of an experimental approach is the possibility of isolating particular fundamental processes in a real fluid and exploring their sensitivity to and dependence upon different experimental conditions. ...

Reference:

Eddy-driven Zonal Jet Flows in the Laboratory

... At critical shear stiffness of the fault loading system, modeling by Rice and Ruina (1983) and Perfettini et al. (2001) suggest a resonant phenomenon, where the shear stress change and slip velocity are strongly amplified at a specific oscillation frequency. Except for the mechanical behaviors, results of triaxial experiments conducted by Colledge et al. (2023) suggest a linear relationship between the amplitude of confining pressure oscillation and the response amplitude of acoustic events. For a fault producing stick slip under quasistatic loading, the degree of correlation between the fault failure time and the phase of NSO depends on both NSO amplitude and frequency (Beeler & Lockner, 2003). ...

Reference:

Effects of Periodic Normal Stress Oscillations on Frictional Properties of Simulated Natural Fault Gouges Under In Situ P‐T Conditions

... The one-dimensional model for earthquakes considered in [34] is a chain of sliders connected by springs, pulled by a force: the system alternates between periods where no slider moves (due to friction, the "stress" accumulates) and earthquake events when a slider moves and possibly makes other sliders move with it. One is led to consider the "stress" profile, which somehow describes in space the intensity of the constraint between tectonic plates (see Figure 1): physicists then argue that during an earthquake, the local displacement variation is a function of the stress. ...

Reference:

Some topics in random walks

... This led to the investigation of this type of random process in simplified stochastic dynamical systems, where a new type of intermittency was identified (distinct from the dissipative intermittency of 3D turbulence mentioned in Sec. II), so-called Lévy on-off intermittency, 113,114 namely, stochastic dynamics near a phase transition subject to multiplicative power-law noise. In particular, this theory predicts a distinct power-law behavior of the 3D energy ...

Reference:

Phase transitions in anisotropic turbulence

... the magnetic field). Then, this study seems in line with previous dynamo studies underlining the benefic action of inhomogeneous materials [10][11][12][13][14]. However, from a theoretical point of view, the anisotropic dynamo only relies on anisotropy, and not on inhomogeneity. ...

Reference:

Three-body anisotropic dynamo: the rotor, the gap and the stator

... All these observations are difficult to interpret due to differences between studies, with significant changes in tectonic contexts, fault geometry, and oscillation frequency and amplitude. Theoretical and numerical studies have attempted to unify all these observations, invoking nucleation times relative to the period of the stress oscillations as one of the factors differentiating a stress controlled regime from a stressing rate controlled regime (Ader & Avouac, 2013;Beeler & Lockner, 2003;Dublanchet, 2022;Heimisson & Avouac, 2020;Perfettini et al., 2001), or suggesting magnitude-dependent and oscillation-geometry-dependent modulation (Pétrélis et al., 2021). Experimental studies focused on the links between stress oscillations and seismicity have investigated the increased synchronization of the temporal distribution of AEs with periodic stress oscillations prior to macroscopic failure (Chanard et al., 2019;Noël, Pimienta, & Violay, 2019) and either the triggering or the induced clock-advance of stick-slips (Bartlow et al., 2012;Chelidze et al., 2010;P. ...

Reference:

Susceptibility of Microseismic Triggering to Small Sinusoidal Stress Perturbations at the Laboratory Scale

... with β 2 observed to be greater than one. 69,98 In fact, in the regime H ≪ ℓ f , it has been rigorously proven 69,99,100 that all 3D fluctuations are damped out by viscosity and the flow becomes exactly 2D, such that one recovers the properties described in Sec. II B. ...

Reference:

Phase transitions in anisotropic turbulence

... Some vibration experiments of granular materials have also been conducted, and it has been found that large vibration amplitude, lower frequency and longer duration are more likely to trigger sliding (Denies & Holeyman, 2017;Hu et al., 2022;Richards et al., 1990;Taslagyan et al., 2015;Youd, 1970). Some experiments show the promoting effect of large amplitude and long period vibration on instability under long-term creep (Chanard et al., 2019;Noël, Pimienta, & Violay, 2019). In addition, some experiments studied the effect of vibration on granular materials at background shear velocity, indicating the complex influence of amplitude and frequency on unstable slip (Colledge et al., 2023;Lockner & Beeler, 1999;Noël, Passelègue, et al., 2019;Savage & Marone, 2007;van der Elst & Savage, 2015). ...

Reference:

JGR Solid Earth - 2024 - Luo - Phase‐Transition Variations in Granular Materials Under Multi‐Period Vibrations

... Our understanding of such complex oscillatory flows and the development of theoretical models of the QBO is based on assumptions of how individual, weakly nonlinear, vertically propagating internal waves interact and energise a zonally symmetric zonal flow. It is somewhat surprising, therefore, that until recently, experimental investigations of this kind of phenomenon have tended to explore rather complicated configurations of wave forcing that are spatially inhomogeneous and/or complex in time [57,86,87] The reasons for this are partly historical in that experiments were typically motivated by a desire to reproduce an analogue of a complex geophysical phenomenon, such as the QBO itself (see also [88,89]). But one of the particular strengths of an experimental approach is the possibility of isolating particular fundamental processes in a real fluid and exploring their sensitivity to and dependence upon different experimental conditions. ...

Reference:

Eddy-driven Zonal Jet Flows in the Laboratory

... Thus, the moments are not the correct indicator for stability in the system (1) with γ = 0 and one needs to be careful when concluding stability based on them. However, as discussed in [106], the limit of µ c (n) as n → 0 does indicate the correct threshold, namely µ = 0. This is because that limit is related to the growth of log(X(t)) , which weighs large-X contributions less strongly. ...

Reference:

Lévy on-off intermittency