Redha Taiar

Analysis of the effect of swimmer's head position on swimming performance using computational fluid dynamics.

The aim of this numerical work is to analyze the effect of the position of the swimmers head on the hydrodynamic performances in swimming. In this initial study, the problem was modeled as 2D and in steady hydrodynamic state. The geometry is generated by the CAD software CATIA and the numerical simulation is carried out by the use of the CFD Fluent code. The standard k-epsilon turbulence model is used with a specific wall law. Three positions of the head were studied, for a range of Reynolds numbers about 10(6). The obtained numerical results revealed that the position of the head had a noticeable effect on the hydrodynamic performances, strongly modifying the wake around the swimmer. The analysis of these results made it possible to propose an optimal position of the head of a swimmer in underwater swimming.

Turbulence model choice for the calculation of drag forces when using the CFD method

The aim of this work is to specify which model of turbulence is the most adapted in order to predict the drag forces that a swimmer encounters during his movement in the fluid environment. For this, a Computational Fluid Dynamics (CFD) analysis has been undertaken with a commercial CFD code (Fluent). The problem was modelled as 3D and in steady hydrodynamic state. The 3D geometry of the swimmer was created by means of a complete laser scanning of the swimmers body contour. Two turbulence models were tested, namely the standard k-epsilon model with a specific treatment of the fluid flow area near the swimmers body contour, and the standard k-omega model. The comparison of numerical results with experimental measurements of drag forces shows that the standard k-omega model accurately predicts the drag forces while the standard k-epsilon model underestimates their values. The standard k-omega model also enabled to capture the vortex structures developing at the swimmers back and buttocks in underwater swimming; the same vortices had been visualized by flow visualization experiments carried out at the INSEP (National Institute for Sport and Physical Education in Paris) with the French national swimming team.

Visualizations of the flow around a swimmer in turbulent regime

Graphical abstract

Vestibular rehabilitation therapy.

Dizziness and balance disorders are frequent complaints in the general population. Vestibular rehabilitation exercises have been shown to be efficient in controlled studies, provided that a precise, individual diagnosis has previously been made. Depending on the pathology, a subject with a peripheral vestibular pathology can benefit from manoeuvres aiming at dislodging or repositioning otoliths, from non-specific muscles strengthening techniques, from techniques for vestibular-ocular or vestibular-cervical stabilisation of gaze, or from physical exercises aimed at strengthening proprioceptive afferents, inhibiting a sensory predominance, or improving spatial orientation and navigation. These analytical exercises should then be implemented in an ecological context in order to favour transfer to daily-living activities. These physical exercises can enable the development of compensation strategies following vestibular damage (habituation, adaptation and substitution).

Infrared Thermography in Sports Activity

The origin of infrared thermography comes in 1800 when William Herschel discovered thermal radiation, the invisible light later called infrared, but only in the mid-sixties infrared thermography became a technique of temperature cartography. He proved that this radiation, called infrared, followed the same law as visible light. Later, this phenomenon was connected with the laws of Planck and Stefan. The first detectors for this type of radiation, based on the principle of the thermocouple and thermopile called, were developed around 1830. In 1970, the first cameras appeared for commercial. The first models were made up of a technology-based pyroelectric tube with an optical IR instead of the classical elements. Today, these concepts have been improved with new technologies in electronics and computing. Infrared acquisition systems can arrive at very high frame rates. The major argument is whether infrared thermography can determine thermal variations to enable sufficient quantitative analyses. The creation of computerized systems using complex statistical data analysis, which ensure high quality results, and the enhancement of thermal sensitivity have increased the development of technology of infrared thermography.

Influence of a postural change of the swimmer's head in hydrodynamic performances using 3D CFD

This study deals with recent researches undertaken by the authors in the field of hydrodynamics of human swimming. The aim of this numerical study was to investigate the flow around the entire swimmers body. The results presented in this article focus on the combination of a 3D computational fluid dynamics code and the use of the k–ω turbulence model, in the range of Reynolds numbers representative of a swimming level varying from national to international competition. Emphasis is placed on the influence of a postural change of the swimmers head in hydrodynamic performances, which is directly related to the reduction of overall drag. These results confirm and complete those, less accurate, of a preliminary 2D study recently published by the authors and allow the authors to optimise the swimmers head position in underwater swimming.

Aerodynamic study of time-trial helmets in cycling racing using CFD analysis

The aerodynamic drag of three different time-trial cycling helmets was analyzed numerically for two different cyclist head positions. Computational Fluid Dynamics (CFD) methods were used to investigate the detailed airflow patterns around the cyclist for a constant velocity of 15 m/s without wind. The CFD simulations have focused on the aerodynamic drag effects in terms of wall shear stress maps and pressure coefficient distributions on the cyclist/helmet system. For a given head position, the helmet shape, by itself, obtained a weak effect on a cyclists aerodynamic performance (<1.5%). However, by varying head position, a cyclist significantly influences aerodynamic performance; the maximum difference between both positions being about 6.4%. CFD results have also shown that both helmet shape and head position significantly influence drag forces, pressure and wall shear stress distributions on the whole cyclists body due to the change in the near-wake behavior and in location of corresponding separation and attachment areas around the cyclist.

Medical Infrared Thermography assistance in the surgical treatment of axillary Hidradenitis Suppurativa: A case report

Highlights • We used a Medical Infrared Thermography tool to assist the surgeon in the surgical treatment of Hidradenitis Suppurativa inflammatory disease.• The advantage of the medical infrared thermography is to allow the optimization of the presurgical mapping of lesion with adequate free margins.• The advantage of medical infrared thermography is to be used like a control tool after excision surgery if all the affected tissues are removed.• This study was therefore conducted as an effort to fill this knowledge gap.• We suggest that medical infrared thermography assessment be better performed with more case surgery.

Preliminary numerical investigation in open currents-water swimming

The drafting in swimming is a sports practice usually used during the open water race of triathlon. Indeed, it is well known that swimming drafting behind or close to the lead swimmer induces a reduction in drag, once the draft swimmer is located in the low pressure field of the lead swimmers wake. For this purpose, in order to determine the best position for the draft swimmer, a preliminary perfect knowledge of the lead swimmers wake is necessary in presence or not of currents. The present preliminary study focuses this point before developing further analyses on reducing drag and enhancing performance in drafting by considering both lead and draft swimmers. In this work, the computational fluid dynamics (CFD) method was used in order to evaluate the hydrodynamic drag during the swimmers displacement in presence of currents. The standard k-ω turbulence model was chosen to predict the resistance forces with currents-negative (α=0°: aligned position of the swimmers body relative to the main flow direction) and cross-currents (angle of incidence of the swimmers body relative to the main flow direction, respectively 10 and 20°). The analysis of the CFD results have shown that the best position for a draft swimmer was found to be directly behind the lead swimmer (close to the toes) and very close to the side of the lead swimmer when drafters head is between shoulders and hip level of the leader.

Theoretical modeling of time-dependent skin temperature and heat losses during whole-body cryotherapy: A pilot study

This article establishes the basics of a theoretical model for the constitutive law that describes the skin temperature and thermolysis heat losses undergone by a subject during a session of whole-body cryotherapy (WBC). This study focuses on the few minutes during which the human body is subjected to a thermal shock. The relationship between skin temperature and thermolysis heat losses during this period is still unknown and have not yet been studied in the context of the whole human body. The analytical approach here is based on the hypothesis that the skin thermal shock during a WBC session can be thermally modelled by the sum of both radiative and free convective heat transfer functions. The validation of this scientific approach and the derivation of temporal evolution thermal laws, both on skin temperature and dissipated thermal power during the thermal shock open many avenues of large scale studies with the aim of proposing individualized cryotherapy protocols as well as protocols intended for target populations. Furthermore, this study shows quantitatively the substantial imbalance between human metabolism and thermolysis during WBC, the explanation of which remains an open question.