Search Results (8)

Existing buckling stiffness tests usually load the ski boot in a manner that changes with the buckling angle of the boot cuff. As a result, the direction of the applied force changes as the cuff bends, which can cause a deviation between the measured force and the actual acting force and can influence the test result. In this study, a new buckling stiffness test device was designed and constructed. By introducing a translational-rod loading structure, the device keeps the loading force perpendicular to the prosthetic-foot loading rod throughout the test. Tests were conducted at a room temperature of 15 °C, with a fixed force-arm length of L = 0.31 m and a standard binding tension of F = 40 N, thereby improving the consistency of load-angle measurement. A binding-force adjustment unit was also designed through computer-aided design, and the standard binding force was determined through subjective comfort tests involving 20 skiers, enabling consistent control of the tightness state of the ski boot. Theoretically, the expression for ski-boot buckling stiffness was established using an equivalent torsional-spring model. Under small-angle and quasi-static conditions, the equivalent buckling stiffness was represented as a linear relationship between the applied load and the normalized deflection angle. The experimental results show that, within the loading range of 60–260 N, the relationship between load and deformation exhibited good linearity, with coefficients of determination of 0.986–0.996. Repeatability tests showed that the coefficients of variation of load and deflection-angle measurements were controlled within 0.40–1.48% and 6.92–8.26%, respectively, and the relative expanded uncertainty of equivalent buckling stiffness was 7.33–11.93%. These results indicate that the device has good stability. Although the fitted curves showed slight nonzero intercepts, these mainly originated from clamping error, contact effects, and sensor zero drift, and did not affect stiffness identification. Overall, the device can provide stable and reliable buckling stiffness measurement and offers an effective method for evaluating ski-boot performance. Full article

Skiing technique, and performance are impacted by the interplay between ski and snow. The resulting deformation characteristics of the ski, both temporally and segmentally, are indicative of the unique multi-faceted nature of this process. Recently, a PyzoFlex^® ski prototype was presented for measuring the local ski curvature ($w^{″}$), demonstrating high reliability and validity. The value of $w^{″}$ increases as a result of enlargement of the roll angle ($RA$) and the radial force ($RF$) and consequently minimizes the radius of the turn, preventing skidding. This study aims to analyze segmental $w^{″}$ differences along the ski, as well as to investigate the relationship among segmental $w^{″}$, $RA$, and $RF$ for both the inner and outer skis and for different skiing techniques (carving and parallel ski steering). A skier performed 24 carving and 24 parallel ski steering turns, during which a sensor insole was placed in the boot to determine $RA$ and $RF$, and six PyzoFlex^® sensors were used to measure the $w^{″}$ progression along the left ski ($w_{1-6}^{″}$). All data were time normalized over a left-right turn combination. Correlation analysis using Pearson’s correlation coefficient ($r$) was conducted on the mean values of $RA$, $RF$, and segmental $w_{1-6}^{″}$ for different turn phases [initiation, center of mass direction change I (COM DC I), center of mass direction change II (COM DC II), completion]. The results of the study indicate that, regardless of the skiing technique, the correlation between the two rear sensors ($L_2$ vs. $L_3$) and the three front sensors ($L_4$ vs. $L_5$, $L_4$ vs. $L_6$, $L_5$ vs. $L_6$) was mostly high ($r$ > 0.50) to very high ($r$ > 0.70). During carving turns, the correlation between $w^{″}$ of the rear ($w_{1-3}^{″}$) and that of front sensors ($w_{4-6}^{″}$) of the outer ski was low (ranging between −0.21 and 0.22) with the exception of high correlations during COM DC II ($r$ = 0.51–0.54). In contrast, for parallel ski steering, the $r$ between the $w^{″}$ of the front and rear sensors was mostly high to very high, especially for COM DC I and II ($r$ = 0.48–0.85). Further, a high to very high correlation ($r$ ranging between 0.55 and 0.83) among $RF$, $RA$, and $w^{″}$ of the two sensors located behind the binding ($w_2^{″},w_3^{″}$) in COM DC I and II for the outer ski during carving was found. However, the values of $r$ were low to moderate ($r$ = 0.04–0.47) during parallel ski steering. It can be concluded that homogeneous ski deflection along the ski is an oversimplified picture, as the $w^{″}$ pattern differs not only temporally but also segmentally, depending on the employed technique and turn phase. In carving, the rear segment of the outer ski is considered to have a pivotal role for creating a clean and precise turn on the edge. Full article

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 (v_slow, v_medium, v_fast) 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 v_slow, v_medium, and v_fast and between pairs of velocity (v_slow vs. v_medium and v_slow vs. v_fast) 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. Full article

This research is aimed at evaluating the effect of low-cycle fatigue on a newly designed hybrid sandwich ski structure to determine the changes that may occur due to cyclic loading and thus affect its use. This is primarily concerned with the fatigue behavior of the tested ski over different time intervals simulating its seasonal use and its effect on the mechanical properties of the ski, i.e., the durability and integrity of the individual layers of the sandwich ski structure. The ski was subjected to 70,000 deflections by moving the crossbar by 60 mm according to the ski deflection calculation in the arch. The results of the cyclic tests of the engineered ski design showed no significant changes in the ski during loading. The average force required to achieve deflection in the first 10,000 cycles was 514.0 ± 4.2 N. Thereafter, a secondary hardening of the structure occurred during relaxation and the force required increased slightly to 543.6 ± 1.7 N. The required force fluctuated slightly during the measurements and in the last series the value was 540.4 ± 0.8 N. Low-cycle fatigue did not have a significant effect on the mechanical properties of the ski; there was no change in shape or visual delamination of the individual layers of the structure. From the cross-section, local delamination was demonstrated by image analysis, especially between the Wood core and the composite layers E-Glass biaxial and Carbon triaxial. Full article

The ski deflection with the associated temporal and segmental curvature variation can be considered as a performance-relevant factor in alpine skiing. Although some work on recording ski deflection is available, the segmental curvature among the ski and temporal aspects have not yet been made an object of observation. Therefore, the goal of this study was to develop a novel ski demonstrator and to conceptualize and validate an empirical curvature model. Twenty-four PyzoFlex^® technology-based sensor foils were attached to the upper surface of an alpine ski. A self-developed instrument simultaneously measuring sixteen sensors was used as a data acquisition device. After calibration with a standardized bending test, using an empirical curvature model, the sensors were applied to analyze the segmental curvature characteristic (m⁻¹) of the ski in a quasi-static bending situation at five different load levels between 100 N and 230 N. The derived curvature data were compared with values obtained from a high-precision laser measurement system. For the reliability assessment, successive pairs of trials were evaluated at different load levels by calculating the change in mean (CIM), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. A high reliability of CIM −1.41–0.50%, max CV 1.45%, and ICC 3.1 > 0.961 was found for the different load levels. Additionally, the criterion validity based on the Pearson correlation coefficient was R² = 0.993 and the limits of agreement, expressed by the accuracy (systematic bias) and the precision (SD), was between +9.45 × 10⁻³ m⁻¹ and −6.78 × 10⁻³ m⁻¹ for all load levels. The new measuring system offers both good accuracy (1.33 × 10⁻³ m⁻¹) and high precision (4.14 × 10⁻³ m⁻¹). However, the results are based on quasi-static ski deformations, which means that a transfer into the field is only allowed to a limited extent since the scope of the curvature model has not yet been definitely determined. The high laboratory-related reliability and validity of our novel ski prototype featuring PyzoFlex^® technology make it a potential candidate for on-snow application such as smart skiing equipment. Full article

Red-headed Buntings (Emberiza bruniceps) perform long-distance migrations within their southerly overwintering grounds and breeding areas in the northern hemisphere. Long-distance migration demands essential orientation mechanisms. The earth’s magnetic field, celestial cues, and memorization of geographical cues en route provide birds with compass knowledge during migration. Birds were tested during spring migration for orientation under natural clear skies, simulated overcast skies at natural day length and temperature, simulated overcast at 22 °C and 38 °C temperatures, and in the deflected (−120°) magnetic field. Under clear skies, the Red-headed Buntings were oriented NNW (north–northwest); simulated overcast testing resulted in a northerly mean direction at local temperatures as well as at 22 °C and 38 °C. The Buntings reacted strongly in favor of the rotated magnetic field under the simulated overcast sky, demonstrating the use of a magnetic compass for migrating in a specific direction. Full article

Recently, the number of alpine ski junior players in Japan has drastically decreased. The causes include a decrease in ski areas and instructors, along with difficulty of early childhood alpine ski guidance. The alpine ski competition is not simply a glide on a slope. It requires understanding of ski deflection and skier posture mechanics. Therefore, a passive ski robot without an actuator was developed for junior racers of the alpine ski competition to facilitate understanding of the turn mechanism. Using this robot can elucidate factors affecting ski turns, such as the position of the center of gravity (COG) and the ski shape. Furthermore, a mechanism for changing the COG height, the edge angle and the ski deflection is added to the passive turn type ski robot. The developed ski robot can freely control the turn by changing those parameters during sliding. Full article

Spillway outlet design is a major issue in hydraulic engineering with high head and large discharge conditions. A new type of design for a streamwise-lateral spillway is proposed for ski-jump flow discharge and energy dissipation in hydraulic engineering. The water in the spillway outlet is constrained by three solid walls with an inclined floor, a horizontal floor on the bottom and a deflected side wall in the lateral direction. The water flow releases in a lateral direction into the plunge pool along the streamwise direction. It generates a free jet in the shape of “∩” in a limited area, causing the water to fully diffuse and stretch in the air simultaneously, and drop into the plunge pool to avoid excessive impact in the plunge pool. The formation mechanism for the flow pattern is analyzed, and the results show that the optimum inclination is an angle range of 30°~45° for a good performance of free ski-jump jet diffusion shape. Full article