What static and dynamic properties should slalom skis possess? Judgments by advanced and expert skiers

Flexural and torsional rigidity are important properties of skis. However, the flexural and torsional rigidity that lead to optimal performance remain to be established. In the present study, four pairs of slalom skis that differed in flexural and torsional rigidity were tested by advanced and expert skiers. Using a 10-item questionnaire, different aspects of the skis’ performance were rated on a 9-point scale. For each pair of skis, physical measurements were compared with the ratings of the two groups of skiers. Correlations (Spearman) were then determined between (i) different mechanical properties of the skis (static and dynamic), (ii) subjective assessments of the participants, and (iii) properties of the skis and the participants’ assessments. The latter showed that expert skiers rate the aspects of the skis more accurately than advanced skiers. Importantly, expert skiers are particularly sensitive to torsion of the skis. These results suggest that such highly rated elements should be addressed in future ski designs

DETERMINATION OF TURNING PARAMETERS IN CARVED SKIING AND APPLICATION TO A NUMERICAL SKI-BINDING MODEL

Skiing has regained in popularity after the introduction of the caNing technique. The biomechanics of caNing have been investigated in numerous studies. However, a comprehensive study of the behaviour of the ski/binding system taking into account the interactions between athlete, skiing equipment, and snow is still missing. In a first phase of the current study, the forces acting between skier and ski equipment and the evolution of the edging angle during caNing were determined using video analysis and force measurements. Next, the passive snow resistance to a penetrating ski was determined using two specially designed tools. Finally, the determined quantities seNed as boundary conditions for a finite-element simulation of the ski/binding system in the caNing situation. Calculated ski shapes were compared against measured turn radii and good agreement was found. The implemented model is intended to help in the development of improved ski equipment. As such, it can for example be used to study the effect of different skier's actions on the equipment behaviour

FT-IR analysis of aerosols in microgravity

International audienceAerosol evolution is a major challenge in climatology. Many questions remain unanswered, especially in the field of cloud microphysics. The aerosols studied here consist of micrometric water droplets formed from a mixture of water-saturated air and HFE7100, and are studied using a set-up that combines optical microtomography and Fourier transform infrared spectrophotometry (FT-IR). Parabolic flight experiments were performed with different concentrations of HFE. About 500 droplets are tracked over time. During the microgravity phase (about 22 s), as they move slowly, a high degree of coherence is achieved between successive microtomographic images. This makes it possible to follow each individual droplet and thus to study the overall dynamics of evaporation. FT-IR analysis provides a time-resolved measurement of the evolution of the chemical composition of the gas phase. This work demonstrates the possibility of analyzing aerosols under microgravity conditions using optical microtomography and FT-IR analysis simultaneously. The combination of these two techniques provides access to both the chemical composition and the size distribution of the droplets, opening up interesting prospects for the description of droplet nucleation and evaporation in gas mixture

FT-IR Analysis Of Aerosols In Microgravity

International audienceThis work demonstrates the possibility of analyzing aerosols under microgravity conditions using optical microtomography and FT-IR analysis simultaneously. The combination of these two techniques provides access to both the chemical composition and the size distribution of the droplets, opening up interesting prospects for the description of droplet nucleation and evaporation in gas mixtures

A new experimental set-up for aerosol stability investigations in microgravity conditions

The temporal and spatial evolution of dispersed media is a fundamental problem in a wide range of physicochemical systems, such as emulsions, suspensions and aerosols. These systems are multiphasic and involve compounds of different densities. They are therefore subject to the influence of gravity which determines the sedimentation rate of their dispersed phase. This effect can be dominant and prevent a detailed study of the phenomena occurring between the constituents themselves, such as the coalescence of drops in emulsions, the evaporation of droplets or the flocculation in suspensions. In this context, the Centre National d'Etudes Spatiales (CNES) has recently supported the development of a new instrument to produce populations of droplets, a few micrometers in radius, under controlled conditions with the objective of allowing a detailed study of their properties in microgravity conditions. The principle of this instrument is to generate, by a fast compression/expansion of air, populations of water droplets and to track their evolution by optical scanning tomography in transmission mode within a volume of approximately 2 mm 3. Parabolic flight experiments have shown the possibility to generate and accurately follow the evolution of populations of several hundred droplets for more than 20 seconds. The first experimental results show that it is possible to study their evaporation kinetics or their motion when imposing Von Karman swirling flows. This work is part of the AEROSOL project of DECLIC-EVO supported by CNES and aims to help the understanding of cloud microphysics which remains a critical open problem in the context of global warming