Measurement of ski snow-pressure profiles

Shape optimization of a snowboard sidecut geometry

The distribution of the contact pressure occurring under the edge of a snowboard during a carved turn is a key factor influencing the riding behaviour. These interface loads are determined by the structural design, and in particular by the sidecut geometry of the edge line. In this study, the following inverse problem was set under investigation: if a certain interface pressure distribution is wished, how can the corresponding initial geometry of the snowboard be determined? A structural optimization strategy was presented, involving parametric B-spline representation of the sidecut geometry, finite element modeling of the composite structure deforming against a rigid surface, frictional contact formulation and derivative-free algorithm. A sidecut geometry leading to a contact pressure uniformly distributed along the sidecut line was sought, to illustrate the capabilities of the method. An actual snowboard prototype was made according to the outcome of the optimization, and an experimental validation was conducted to measure the physical pressure distribution and assess the accuracy of the numerical predictions. With the proposed method, the design can be controlled by the state variables of the deformed structure rather than the initial design variables, thus providing an alternative shortcut to the classical trial and error development strategies.

The effect of foot setting on kinematic and kinetic skiing parameters during giant slalom: A single subject study on a Paralympic gold medalist sit skier

OBJECTIVES

Aim was to study the effect of monoski foot adjustment on kinematic and kinetic skiing parameters expressing sit skier's technique.

DESIGN

Independent variable was skier position with respect to bindings, acting on position of monoski foot sole clamp. Front (F), Mid (M) and Rear (R) settings changed with intervals of 20mm. Course time, skiing speed, Ground Reaction Forces (GRFs) magnitude and point of application and damper stroke were dependent variables.

METHOD

A Paralympic monoski was equipped with a dynamometric binding plate measuring GRFs, roll and pitch moments. A Paralympic gold medalist (LW10-1) was involved. Skier trajectory and gates location were measured by a differential global navigation satellite system (GNSS) in steep and medium steep slope portions. The athlete performed two giant slalom runs for each foot setting the same day.

RESULTS

GRFs, center of pressure (COP) and variations with foot settings were measured. Peaks values up to 3.36 times the total weight and damper speed of 675mm/s in compression were found. Fastest runs, highest peak loads and best subjective ratings were recorded with F setting. COP mean values were influenced by foot adjustments. GRFs in left turns were 54% larger than in the right turns with F setting on steep slope.

CONCLUSIONS

The monoski foot adjustment influenced kinematic and kinetic skiing, with F setting showing best results. A skier asymmetric behavior between right and left turning was discovered. Findings can support the design of monoskis for a wider dissemination of Paralympic alpine sit skiing.

Application of Inertial Motion Unit-Based Kinematics to Assess the Effect of Boot Modifications on Ski Jump Landings-A Methodological Study

Biomechanical studies of winter sports are challenging due to environmental conditions which cannot be mimicked in a laboratory. In this study, a methodological approach was developed merging 2D video recordings with sensor-based motion capture to investigate ski jump landings. A reference measurement was carried out in a laboratory, and subsequently, the method was exemplified in a field study by assessing the effect of a ski boot modification on landing kinematics. Landings of four expert skiers were filmed under field conditions in the jump plane, and full body kinematics were measured with an inertial motion unit (IMU) -based motion capture suit. This exemplary study revealed that the combination of video and IMU data is viable. However, only one skier was able to make use of the added boot flexibility, likely due to an extended training time with the modified boot. In this case, maximum knee flexion changed by 36° and maximum ankle flexion by 13°, whereas the other three skiers changed only marginally. The results confirm that 2D video merged with IMU data are suitable for jump analyses in winter sports, and that the modified boot will allow for alterations in landing technique provided that enough time for training is given.

Potential of IMU Sensors in Performance Analysis of Professional Alpine Skiers

In this paper, we present an analysis to identify a sensor location for an inertial measurement unit (IMU) on the body of a skier and propose the best location to capture turn motions for training. We also validate the manner in which the data from the IMU sensor on the proposed location can characterize ski turns and performance with a series of statistical analyses, including a comparison with data collected from foot pressure sensors. The goal of the study is to logically identify the ideal location on the skier’s body to attach the IMU sensor and the best use of the data collected for the skier. The statistical analyses and the hierarchical clustering method indicate that the pelvis is the best location for attachment of an IMU, and numerical validation shows that the data collected from this location can effectively estimate the performance and characteristics of the skier. Moreover, placement of the sensor at this location does not distract the skier’s motion, and the sensor can be easily attached and detached. The findings of this study can be used for the development of a wearable device for the routine training of professional skiers.

A parameter optimization method to determine ski stiffness properties from ski deformation data

The deformation of skis and the contact pressure between skis and snow are crucial factors for carved turns in alpine skiing. The purpose of the current study was to develop and to evaluate an optimization method to determine the bending and torsional stiffness that lead to a given bending and torsional deflection of the ski. Euler-Bernoulli beam theory and classical torsion theory were applied to model the deformation of the ski. Bending and torsional stiffness were approximated as linear combinations of B-splines. To compute the unknown coefficients, a parameter optimization problem was formulated and successfully solved by multiple shooting and least squares data fitting. The proposed optimization method was evaluated based on ski stiffness data and ski deformation data taken from a recently published simulation study. The ski deformation data were used as input data to the optimization method. The optimization method was capable of successfully reproducing the shape of the original bending and torsional stiffness data of the ski with a root mean square error below 1 N m2. In conclusion, the proposed computational method offers the possibility to calculate ski stiffness properties with respect to a given ski deformation.