Institut Pprime

The accumulation of cohesive sediments is one of the most prominent issues in many tidal estuaries, as it has major implications on estuarine morphodynamics and on water quality and dredging strategies to support harbor activities. The work presented here focuses on the Gironde estuary, and more specifically on the Cadillac site located 40 km upstream of Bordeaux, where sediments were taken from the banks at low tide.The first step was to characterise the physical properties of these materials by means of a granulometric analysis and rheological tests. Granulometric analysis (Mastersizer 3000, Malvern) is used to ensure the homogeneity of the sediments taken during the various campaigns. These reworked materials are then studied from a rheological point of view (HR2, TA Instruments) in order to identify in particular their yield stress for setting in motion. To do this, flow tests were carried out in a coaxial disc geometry in order to define the corresponding rheogram. The Hershel-Bulkley behaviour law is then applied to the descent curve to identify the yield stress. Once the protocol has been established, the effect of concentration is measured by diluting the sediments taken and the concentration is measured a posteriori by weighing the samples before and after drying. In this way, the law governing the evolution of yield stress as a function of concentration can be established.Erosion tests were then carried out in a laboratory channel. The sediments were placed in the space left free between two ramps placed at the bottom of the channel. Initially, the threshold stress for setting the various samples in motion was established by gradually increasing the flow rate in the channel for a given height of water. The flow rate at which movement starts to occur on the sediment surface is noted. This flow rate is then translated into parietal stress on the bottom using PIV calibration on a rigid surface. It is assumed that the friction stress on the rigid bottom is equal to the minimum stress required to set the sediment in motion. These tests are repeated for different sediment concentrations. In a second phase, flows greater than the minimum flow are applied for 45 minutes and the quantity of sediment eroded is obtained by a double weighing method and by optical measurement using a 3D camera. In this way, the erosion rate, defined by the change in mass over time on a given reference surface, can be established and its evolution as a function of flow parameters and rheological properties can be determined. The final aim is to be able to propose an erosion law corresponding to the sediments of the Gironde estuary, which could then be used in numerical modelling.This work was supported by the French National Agency for Research in the context of EMPHASE project (ANR-19-FQSM-0003).This work pertains to the French Government program “Investissements d’Avenir” EUR INTREE, reference ANR-18-EURE-0010.

International audience

ABSTRACTBackground and AimThis study aims to retrospectively assess the point‐light display (PLD) action observation methodology, in order to explore the effect of action observation treatment (AOT) for locomotion rehabilitation in aged patients at risk of falling.MethodsThe results of 30 patients were assessed with 10 patients benefiting from conventional rehabilitation program, 10 patients receiving an AOT program involving the observation of PLD representing a young actor, and 10 patients receiving an AOT program involving the observation of PLD representing an old actor (PLD‐O).ResultsThe analysis revealed more progress for patients who benefited from AOT observation compared to conventional therapy on standardized tests measuring daily life actions (Bartel index) and disability in the lower limbs (Short Physical Performance Battery) but only when PLD represented an old actor.DiscussionThese results suggest that an AOT program involving the observation of PLDs is a promising approach for rehabilitating patients at risk of falling in a clinical context but matching the motor repertoire seems a crucial factor for optimizing the effects.

Purpose In the field of 4D printing, shape memory polymers are gaining more and more interest, thanks to their large deformability and ease of manufacturing, compared to their metallic alloy counterparts. However, they are still rarely adopted for industrial applications, often limited by the poor time and space accuracy of their recovery behaviour. In this paper, the aim is to use an electroconductive shape memory polymer to design a hinge for the self-deployment of space structures. Design/methodology/approach Fused filament fabrication and composite material made of bio-sourced polylactic acid filled with carbon black particles are used. First, the hinge is conceived as the answer to an inverse design problem: its geometry integrates an electrical circuit and the influence of the printing parameters is considered to perform the shape memory behaviour. The deployment of the hinge is filmed and tracked thanks to a multi-instrumented setup to calculate its recovery ratio and kinetics and evaluate its performance. One to ten deployments are considered to study their behaviour under repeated use. Furthermore, the force deployed is measured and compared between the first and the tenth cycles to evaluate its durability. Findings Results show that the hinge is able to recover up to 80% of its initial shape and deploy the same force through the cycles. Originality/value This paper highlights the ability of training the shape memory effect to obtain targeted results and the capacity of the device to maintain the force deployed throughout the cycles. A novel multi-instrumented setup is presented to measure four different properties (electrical, thermal, mechanical and force).

This work presents wavepacket models for supersonic round twin jets operating at perfectly expanded conditions, computed via plane-marching parabolised stability equations based on mean flows obtained from the compressible Reynolds-averaged Navier–Stokes (RANS) equations. High-speed schlieren visualisations and non-time-resolved PIV measurements are performed to obtain experimental datasets for validating the modelling strategy. The RANS solutions are found to be in good quantitative agreement with the particle image velocimetry (PIV) mean-flow measurements, confirming the ability of the approach to capture the interaction between jets at the mean-flow level. The obtained wavepackets consist of toroidal and flapping fluctuations of the twin-jet system, and show similarities with those of single axisymmetric jets. However, for the case of closely spaced jets, they exhibit deviations in the phase speed of structures travelling in the outer mixing layer and those travelling in the inner one, leading to different non-axisymmetric behaviours. In particular, toroidal twin-jet wavepackets feature tilted ring-like structures with respect to the jet axis, while flapping twin-jet wavepackets are distorted and lose the clean chequerboard pattern typically observed in $m = 1$ modes in axisymmetric jets. A quantitative comparison of the modelled wavepackets with experimentally educed coherent structures is performed in terms of their structural agreement measured through an alignment coefficient, providing a first validation of the modelling strategy. Alignment coefficients are found to be particularly high in the intermediate range of studied frequencies.

Insertion of crystal defects (dislocations, point defects and lattice distortion) plays a crucial role in thermoelectric/optical properties and can be controlled in thin films of the narrow-band-gap semiconductor ScN.