Effect of edged snow contact on the vibration of alpine skis

Abstract

When skiing, excessive ski vibrations can affect comfort, control and performance. Through the years, much efforts have been invested in understanding and reducing these ski vibrations. However, the vibration response of skis is still poorly understood as most laboratory measurements do not correlate with the on-snow response. This paper aims to understand the differences between ski vibrations measured in a laboratory setting and the actual in-use response. To that end, a miniature custom data-logging system was developed to measure the on-snow vibration response of an alpine ski during a turn and its associated operational deflection shapes. The operational deflection shapes of two fore-body resonant frequencies (22 Hz and 66 Hz) and one aft-body resonant frequency (37 Hz) were measured using that system and their frequencies agree with previously documented on-snow measurements. These operational deflection shapes also show that the ski's first three resonances are coupled in bending and torsion, and that the ski fore-body and aft-body are coupled in torsion. New tools were also developed to facilitate quantitative vibration testing of skis, including a custom test bench for controlled skidding and a ski simulation that include a simple snow interaction model. The operational deflection shapes obtained with these tools showed differences in resonance frequencies and amplitudes. Nevertheless, the results showed good overall agreement with on-snow measurements and confirmed that the observed vibration response and deflection shapes were the result of coupling between bending and torsion caused by the ski being on edge.

Technique-Dependent Relationship between Local Ski Bending Curvature, Roll Angle and Radial Force in Alpine Skiing

“…However, it is remarkable that, especially in carving, there are only low relationships between the front and rear w of the ski, except for the COM DC II phase. This finding reflects the ski's inhomogeneous w pattern and the corresponding decoupling of front and rear segment bending caused by the binding [37]. The prediction that the w" of the ski increases with larger RA and larger RF is predominantly valid for the rear sensors L 2 and L 3 of the outer ski during carving in the COM DC I and COM DC II phases.…”

Distributed IMU Sensors for In-Field Dynamic Measurements on an Alpine Ski

“…Ref. [ 34 ] suggests that the IMUs may experience upwards of 150 G in terms of acceleration, which means that conventional MEMS devices may not be feasible. The use of more advanced inertial sensors with greater measurement ranges would make this project prohibitively expensive.…”

“…Contrarily, Ref. [ 31 ] reported acceleration values well below what [ 34 ] hypothesize to be maximum acceleration values, indicating that conventional MEMS accelerometers may indeed be suitable to measure the structural dynamics of a ski during in-field testing. Typical measurement ranges of MEMS gyroscopes are within the range of angular rates expected from the ski’s structural dynamics and our results never saturate the sensors, supporting [ 34 ]’s hypothesis.…”

“…[ 33 ] used two or more accelerometers attached to the ski shovel to measure both the bending and twisting motion during in-field runs. A set of nine distributed IMUs were placed on the upper surface of an alpine ski by [ 34 ], who performed limited in-field testing and mainly focused on laboratory vibration testing on an ice bank. The three goals of our research are to develop a sensing tool that has distributed inertial sensing of the structural dynamics of an alpine ski; can collect data at a high rate; and is robust to the harsh conditions experienced during in-field testing.…”

Wood in Sport Equipment - Heritage, Present, Perspective

“…In this regard there seems to be the indication that the optimal compromise regarding mass for a ski with good performance has been achieved throughout the past decades (Truong et al, 2020). As mentioned, a ski in use is subjected to a variety of forces, particularly the inherent stiffness that is acting as a dampened mass-spring system and can be set into oscillatory motion through the wind resistance at the curved tips or lateral skidding over the snow (Gosselin et al, 2021). Cheaper foam cores typically prove to be inferior and experience fatigue earlier, especially at lower temperatures (Lackner, 2003).…”