Analysis of the Skeleton Sled Sliding Motion Induced Vibrations with Different Runner Stiffness’s on an Inclined Ice Track

Abstract

The skeleton is one of the winter Olympics games sports and it is the only sport where is possible to alter the degree of contact with ice by altering the runner stiffness. Stiffness increased by compressing the ends of the runners resulting in less contact with the ice. Beginners prefer a runner setting with a lower stiffness for greater stability. Experienced winter athletes will select a higher stiffness for higher speeds, but this comes at the cost of less control of slider motion on the ice. Sliding motion induced vibrations are not very obvious but can play a quite positive role in reducing the sliding friction. The purpose of this research is to identify skeleton sled vibrations that are characterized by natural frequencies of the structure and which are characterizing sliding motion friction forces and compare them with different runner stiffness. Analyzing the effect of structural vibrations from the sliding motion on the ice surface first is clarified how the sliding object responds on forced oscillations. Using CAD Simulation software the first natural frequencies were detected for skeleton sled and runners. Values were compared with laboratory measuring equipment data. Practical experiments were performed in ice track at the bobsled push-start facility in Sigulda, Latvia and it was conducted on a straight 23.7 m long ice track angled at α = 12°. The sliding time was measured with optical sensors at the top and bottom of the incline after the skeleton starts from sliding from a stationary position. This sliding time was used to calibrate the accelerometer data. Measurements were made with portable accelerometer, it was fixed to the base plate of skeleton. Data was processed by spectral analysis. Then motion and structure characterizing frequencies were obtained. The results were analyzed by comparing computer calculations and simulations with practical experiments. The acceleration data analysis confirmed that the natural frequency of skeleton sleigh structure does not change as the sleigh’s runner stiffness changes. 3D modeling certified that the change was minimal if the connection type was not altered. The created mathematical model for determining natural frequencies allows to quickly and accurately determine the first modes of the oscillations of the structure.KeywordsWinter sportsSkeletonStructural vibrationsInduced vibrationsSliding motion