Water Losses During Technical Snow Production: Results From Field Experiments

Alpine as well as Nordic skiing tourism strongly depend on the production of machine-made snow for the timely opening of the winter season. However, it is likely that sublimation, evaporation, wind drift, and the discharge of unfrozen water to the ground will result in the loss of significant parts of the water used. The relation between these water losses and the ambient meteorological conditions is poorly understood. We present results from a series of 12 detailed snow-making field tests performed in a ski resort near Davos, Switzerland. Water inflows, measured at the snow machine, are related to the mass of snow deposited on the ground. Snow amounts are calculated from accumulated volumes, measured with terrestrial laser scanning (TLS), and manually sampled snow densities. Additionally, samples of liquid water contents (LWCs) of the produced snow are presented. We find that 7 to 35 ± 7% (mean 21%) of the consumed water was lost during snow-making and that the loss is strongly related to the ambient meteorological conditions. Linear regression analysis shows that water losses increase with air temperature (TA). Combining our data with observations from earlier field measurements shows similar correlations

Towards more valid simulations of slopestyle and big air jumps: Aerodynamics during in-run and flight phase

Objectives: This study aimed to investigate air drag and lift during the in-run and flight phase of ski and snowboard slopestyle and big air, to allow more valid modeling of jumps and hence reduce injury risk. Design: We present an experimental, multiple single athlete study based on wind tunnel measurements of 4 skiers and 3 snowboarders. Methods: Measurements were carried out in a closed loop wind tunnel, measuring airflow speed and 3D forces acting on the athletes. Athletes performed trials in typical postures at 35, 60 and 85 km/h wearing slim-, regular- and wide fit apparel. Drag and lift area (cDA; cLA) were calculated and analyzed using linear and multiple regression to describe their dependencies on posture, apparel and speed. Results: cDA values were higher than earlier assumed and ranged from 0.3 to 0.95 m2 for skiers and from 0.35 to 0.55 m2 for snowboarders, primarily dominated by posture, and followed by apparel. cLA ranged from −0.1 to 0.45 m2 for skiers and from 0.04 to 0.17 m2 for snowboarders. To facilitate more valid jump modeling posture- and apparel-dependent formulations for air drag coefficients were provided and the consequences of sport specific differences on modeling were highlighted. Conclusions: Applying the air drag coefficients and relationships determined in this study will help to improve validity of jump modeling in big air and slopestyle. The variability in aerodynamic forces in slopestyle and big air is caused by differences between sports, posture and apparel

The snow-friction of freestyle skis and snowboards predicted from snow physical quantities

Previous research has shown that friction between ski and snow can vary substantially due to changes in snow conditions. The variation of friction affects the speed a freestyle skier or snowboarder (athlete) reaches during the in-run of a jump. Athletes risk severe injuries if their take-off speed is not within the right margin to land in the “sweet spot” zone. To reduce the risk of injury, snow park designers and competition managers need to calculate the speed athletes reach during the in-run. However, despite multiple attempts over the last decades, to date no model can predict ski-snow friction from snow physical quantities. Hence, simulations of in-run speeds suffer from insufficient validity. For the first time, this work combines kinematic athlete data and comprehensive snow surface measurements to infer the coefficient of friction of freestyle skis and snowboards across a wide range of snow conditions. Athletes’ point mass kinematics were recorded at more than 200 straight gliding runs with differential global navigation satellite systems. The subjects’ air drag and lift were deployed from wind tunnel measurements. Along with the kinematic data and data from wind measurements, a mechanical model of the athlete was established to solve the equation of motion for the coefficient of friction between ski/snowboard and snow. The friction coefficients for ski (snowboard) ranged from 0.023 ± 0.006 (0.026 ± 0.008) to 0.139 ± 0.018 (0.143 ± 0.017) and could be explained well (Radj2 = 0.77) from the measured snow parameters using a multivariate statistical model. Our results provide a new quantitative tool for practitioners to predict the friction of skis and snowboard on snow of various conditions, which aims to increase athletes’ safety in slopestyle and big air

The snow-friction of freestyle skis and snowboards predicted from snow physical quantities

Previous research has shown that friction between ski and snow can vary substantially due to changes in snow conditions. The variation of friction affects the speed a freestyle skier or snowboarder (athlete) reaches during the in-run of a jump. Athletes risk severe injuries if their take-off speed is not within the right margin to land in the “sweet spot” zone. To reduce the risk of injury, snow park designers and competition managers need to calculate the speed athletes reach during the in-run. However, despite multiple attempts over the last decades, to date no model can predict ski-snow friction from snow physical quantities. Hence, simulations of in-run speeds suffer from insufficient validity. For the first time, this work combines kinematic athlete data and comprehensive snow surface measurements to infer the coefficient of friction of freestyle skis and snowboards across a wide range of snow conditions. Athletes’ point mass kinematics were recorded at more than 200 straight gliding runs with differential global navigation satellite systems. The subjects’ air drag and lift were deployed from wind tunnel measurements. Along with the kinematic data and data from wind measurements, a mechanical model of the athlete was established to solve the equation of motion for the coefficient of friction between ski/snowboard and snow. The friction coefficients for ski (snowboard) ranged from 0.023 ± 0.006 (0.026 ± 0.008) to 0.139 ± 0.018 (0.143 ± 0.017) and could be explained well (Radj2 = 0.77) from the measured snow parameters using a multivariate statistical model. Our results provide a new quantitative tool for practitioners to predict the friction of skis and snowboard on snow of various conditions, which aims to increase athletes’ safety in slopestyle and big air

Design parameters and landing impacts of snow park jumps in Switzerland

Objectives: Design parameters and landing impacts for selected snow park jumps in Switzerland were compared with the parameters recommended to increase the jumps’ safety by the Swiss Council for Accident Prevention (BFU). High impact zones were identified to help snow park shapers optimize the design of their jumps. A rough estimate of the influence of snow hardness on landing impacts was also provided. Design: During the 2020/2021 winter season three-dimensional geometries of 23 jumps were captured using differential global navigation satellite system and terrestrial laser scanning. A point mass model was used to numerically calculate trajectories. The equivalent fall height (eFH) was used to quantify landing impacts and an empiric snow-deformation function was applied to take the effect of snow hardness into consideration. Workshops were held to discuss results and transfer findings. Methods: 2D-profiles of the jumps were estimated by projecting the captured 3D position data onto the longitudinal cross-section plane. Table and landing geometry were smoothed and interpolated to a spatial resolution of 0.1 ​m, while the kicker was fitted with a 2nd order polynomial. Trajectories were numerically calculated for take-off speeds from 6 to 17.6 ​m ​s−1 including aerodynamic forces using the Runge-Kutta method. The calculated eFH at the landing points were used to divide the landing into low-impact, medium-impact, and high-impact zones. Results: Medium sized jumps had a low-impact zone of sufficient length (>6 ​m) and eFH smaller than 1.5 ​m throughout the entire table meeting the BFU recommendations. Nevertheless, critical eFH larger than 1.5 ​m, were obtained when take-off speeds increased by only 1.14 ​m ​s−1. Large jumps had low-impact zone lengths in accord with the recommendations (>9 ​m), but high eFH (2.3–3.4 ​m) occurred for table landings. 10 of the 13 XL-jumps had long low-impact zones of approximately 12–15 ​m. Besides the risk of high impact landings towards the end of the landing area, as found similarly for the smaller jumps, portions of XL-jumps had very high eFH (2.6–4.6 ​m) for table landings. Conclusions: The study confirmed the existing BFU recommendations of size categories, design parameters and landing impacts limits as prevalent and practicable and provided knowledge for future safety recommendations. Modifying table geometries and taking measures to limit the in-run speeds would help reduce landing impacts, and the hazard due to hard snow conditions should also be considered