Quantification and design of jumping-ski characteristics

Gim, Jinsu; Jeon, Joohyeong; Kim, Bongju; Jeong, Taejoon; Jeon, Kyeonghyeon; Rhee, Byong-Duk

doi:10.1177/1754337117721831

Cited by 5 publications

(3 citation statements)

References 26 publications

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“…The first natural frequencies of the forebody and afterbody of jumping skis are lower than 10 Hz. The second and third natural frequencies are about 25-35 and 70-90 Hz [10]. Videos from the present measurements show no steady frequencies for the vibration.…”

Section: Discussioncontrasting

confidence: 50%

Aerodynamics of an isolated ski jumping ski

Virmavirta

Kivekäs

2019

Sports Eng

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A single isolated ski was suspended from a six-component wind tunnel balance and three angles, the angle of attack, the yaw angle and the edge angle were adjustable during the test. Increasing yaw angle from 0 to 15° increased the lift coefficient C L from 0.42 to 0.90 at edge angle 0° and from 0.70 to 0.87 at edge angle 10°, respectively. Increasing yaw angle also increased the sensitivity of the ski to changes in edge angle, i.e., increasing the edge angle (20°-45°) decreased the C L and the ratio C 2 L ∕C D with large yaw angles. However, to maximize the lift-to-drag ratio with a typical angle of attack of 30° in ski jumping, it may be reasonable to have an edge angle of 5°-10° on skis as the ratio C 2 L ∕C D increased from 1.24 to 1.35 when edge angle increased from 0° to 10°.

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Section: Discussioncontrasting

confidence: 50%

Aerodynamics of an isolated ski jumping ski

Virmavirta

Kivekäs

2019

Sports Eng

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“…As a practical application, various ski-specific deformations of Alpine skis (e.g., simulation of ski bending during a carved turn) in three-dimensional space can be systematically analyzed in the laboratory. In addition to Alpine skis [ 23 , 24 ], other measurement objects such as snowboards [ 29 ], cross-country skis and poles [ 30 ] or jumping skis [ 31 ] can also be utilized. Furthermore, an OMS can be used to calibrate bending sensors in both static and dynamic settings, eliminating the need for a complex and difficult-to-adjust laser measurement system in the tree-dimensional space.…”

Section: Discussionmentioning

confidence: 99%

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

Thorwartl

Stöggl

Teufl

et al. 2021

Sensors

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So far, no studies of material deformations (e.g., bending of sports equipment) have been performed to measure the curvature (w″) using an optoelectronic measurement system OMS. To test the accuracy of the w″ measurement with an OMS (Qualisys), a calibration profile which allowed to: (i) differentiates between three w″ (0.13˙ m−1, 0.2 m−1, and 0.4 m−1) and (ii) to explore the influence of the chosen infrared marker distances (50 mm, 110 mm, and 170 mm) was used. The profile was moved three-dimensional at three different mean velocities (vzero = 0 ms−1, vslow = 0.2 ms−1, vfast = 0.4 ms−1) by an industrial robot. For the accuracy assessment, the average difference between the known w″ of the calibration profile and the detected w″ from the OMS system, the associated standard deviation (SD) and the measuring point with the largest difference compared to the defined w″ (=maximum error) were calculated. It was demonstrated that no valid w″ can be measured at marker distances of 50 mm and only to a limited extent at 110 mm. For the 170 mm marker distance, the average difference (±SD) between defined and detected w″ was less than 1.1 ± 0.1 mm−1 in the static and not greater than −3.8 ± 13.1 mm−1 in the dynamic situations. The maximum error in the static situation was small (4.0 mm−1), while in the dynamic situations there were single interfering peaks causing the maximum error to be larger (−30.2 mm−1 at a known w″ of 0.4 m−1). However, the Qualisys system measures sufficiently accurately to detect curvatures up to 0.13˙ m−1 at a marker distance of 170 mm, but signal fluctuations due to marker overlapping can occur depending on the direction of movement of the robot arm, which have to be taken into account.

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“…6 Although generally accepted, this standard seems to have little relevance to the real-life responses of a multilayered ski, and it does not allow consideration of nonlinear effects. 7,8…”

Section: Introductionmentioning

confidence: 99%

An experimental study on granular dissipation for the vibration attenuation of skis

Bajkowski

Dyniewicz

Bajer

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part P:

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Due to the continuous deformations and irregularities of the surface of snow, alpine skis exhibit dynamic excitation, leading to drastic vibrations and decreased manoeuvrability. Therefore, attenuating these unwanted vibrations, while ensuring that the ski experience is not compromised, is an important challenge. The possibility of using granular material in a damping device is studied in this paper. A container that was partially filled with loose granules was fixed at the tip of an alpine ski to suppress vibrations by dissipating energy through collisions. The performance was verified experimentally by studying the transient response of a ski mounted in a horizontal cantilever orientation. Moreover, on-snow tests were performed. Different numbers of plastic granules were used as a dissipating material. To identify the nonlinear damping characteristics of the system, a Hilbert transform was used. In the laboratory test, the displacement amplitude decay was up to 16 percentage points higher when a granular dissipator was attached to the ski than without the damper. During field testing, acceleration amplitudes were 9% lower compared to the ski without the dissipator. This solution could possibly be adapted to other boardsports on a wide variety of terrain, including ground, water and snow.

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Quantification and design of jumping-ski characteristics

Cited by 5 publications

References 26 publications

Aerodynamics of an isolated ski jumping ski

Aerodynamics of an isolated ski jumping ski

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

An experimental study on granular dissipation for the vibration attenuation of skis

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