Effect of flexural stiffness distribution of a ski on the ski–snow contact pressure in a carved turn

Yoneyama, T.; Kagawa, Hiroyuki; Tatsuno, Daichi; Kitade, Motoki; Osada, Kazutaka; Shigehara, Satoshi

doi:10.1007/s12283-020-00339-6

Cited by 5 publications

(1 citation statement)

References 18 publications

(24 reference statements)

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“…The most common method to measure ski deflection under standardized laboratory conditions is the three-point bending test [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. For analyzing the ski deflection in the field, only strain gauges [ 6 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] have been used. The strain gauge-based approaches have not been tested for reliability or validity from a scientific point of view, and consequently the studies are limited for proof-of-concept investigations.…”

Section: Introductionmentioning

confidence: 99%

Validation of a Sensor-Based Dynamic Ski Deflection Measurement in the Lab and Proof-of-Concept Field Investigation

Thorwartl

Kröll

Tschepp

et al. 2022

Sensors

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Introduction: Ski deflection is a performance-relevant factor in alpine skiing and the segmental and temporal curvature characteristics (m−1) along the ski have lately received particular attention. Recently, we introduced a PyzoFlex® ski deflection measurement prototype that demonstrated high reliability and validity in a quasi-static setting. The aim of the present work is to test the performance of an enhanced version of the prototype in a dynamic setting both in a skiing-like bending simulation as well as in a field proof-of-concept measurement. Material and methods: A total of twelve sensor foils were implemented on the upper surface of the ski. The ski sensors were calibrated with an empirical curvature model and then deformed on a programmable bending robot with the following program: 20 times at three different deformation velocities (vslow, vmedium, vfast) with (1) central bending, (2) front bending, (3) back bending, (4) edging left, and (5) edging right. For reliability assessment, pairs of bending cycles (cycle 1 vs. cycle 10 and cycle 10 vs. cycle 20) at vslow, vmedium, and vfast and between pairs of velocity (vslow vs. vmedium and vslow vs. vfast) were evaluated by calculating the change in the mean (CIM), coefficient of variation (CV) and intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. For validity assessment, the calculated segment-wise mean signals were compared with the values that were determined by 36 infrared markers that were attached to the ski using an optoelectrical measuring system (Qualisys). Results: High reliability was found for pairs of bending cycles (CIM −0.69–0.24%, max CV 0.28%, ICC 3.1 > 0.999) and pairs of velocities (max CIM = 3.03%, max CV = 3.05%, ICC 3.1 = 0.997). The criterion validity based on the Pearson correlation coefficient was r = 0.98. The accuracy (systematic bias) and precision (standard deviation), were −0.003 m−1 and 0.047 m−1, respectively. Conclusions: The proof-of-concept field measurement has shown that the prototype is stable, robust, and waterproof and provides characteristic curvature progressions with plausible values. Combined with the high laboratory-based reliability and validity of the PyzoFlex® prototype, this is a potential candidate for smart ski equipment.

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Section: Introductionmentioning

confidence: 99%

Validation of a Sensor-Based Dynamic Ski Deflection Measurement in the Lab and Proof-of-Concept Field Investigation

Thorwartl

Kröll

Tschepp

et al. 2022

Sensors

View full text Add to dashboard Cite

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Shape optimization of a snowboard sidecut geometry

Caillaud

Gerstmayr

2022

Sports Eng

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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.

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