Das Model des Flankengleitens der Carvingschier

In the paper a mathematical model of side skidding for carving skis is presented. The authors have demonstrated in their previous work that carving skis generate generally lower vibrations during the parallel ski turn in comparison to the skis with the classical side cut. However, carving skis can provoke excessive vibration in the case of side skidding. This phenomena have been explained by applying a heuristic model of side skidding for carving skis. The model was verified with measurements on the ski slope and with a simulation using an industrial robot.Die Arbeit stellt ein mathematisches Modell des Flankengleitens der Carvingschier dar. Vorher haben die Autoren gezeigt, wie die Carvingschier bei den Parallelkurven meistens weniger Vibrationen als die Schier mit dem klasischen Flankenprofil verursachen. Andererseits können die Carvingschier beim Flankengleiten übermäßige Vibrationen erregen. Um dieses Phänomen zu erklären, haben wir ein heuristisches Model des Flankengleitens der Carvingschier benutzt. Das Model ist durch die Messungen auf den Schispuren sowie durch die Simulation mittels eines industriellen Robots verifiziert worden

Das Model des Flankengleitens der Carvingschier

In the paper a mathematical model of side skidding for carving skis is presented. The authors have demonstrated in their previous work that carving skis generate generally lower vibrations during the parallel ski turn in comparison to the skis with the classical side cut. However, carving skis can provoke excessive vibration in the case of side skidding. This phenomena have been explained by applying a heuristic model of side skidding for carving skis. The model was verified with measurements on the ski slope and with a simulation using an industrial robot.Die Arbeit stellt ein mathematisches Modell des Flankengleitens der Carvingschier dar. Vorher haben die Autoren gezeigt, wie die Carvingschier bei den Parallelkurven meistens weniger Vibrationen als die Schier mit dem klasischen Flankenprofil verursachen. Andererseits können die Carvingschier beim Flankengleiten übermäßige Vibrationen erregen. Um dieses Phänomen zu erklären, haben wir ein heuristisches Model des Flankengleitens der Carvingschier benutzt. Das Model ist durch die Messungen auf den Schispuren sowie durch die Simulation mittels eines industriellen Robots verifiziert worden

Physics of Skiing: The Ideal-Carving Equation and Its Applications

Ideal carving occurs when a snowboarder or skier, equipped with a snowboard or carving skis, describes a perfect carved turn in which the edges of the ski alone, not the ski surface, describe the trajectory followed by the skier, without any slipping or skidding. In this article, we derive the "ideal-carving" equation which describes the physics of a carved turn under ideal conditions. The laws of Newtonian classical mechanics are applied. The parameters of the ideal-carving equation are the inclination of the ski slope, the acceleration of gravity, and the sidecut radius of the ski. The variables of the ideal-carving equation are the velocity of the skier, the angle between the trajectory of the skier and the horizontal, and the instantaneous curvature radius of the skier's trajectory. Relations between the slope inclination and the velocity range suited for nearly ideal carving are discussed, as well as implications for the design of carving skis and snowboards.Comment: 13 pages, 9 figures, LaTeX; to appear in Can. J. Phy

Virtual Skiing as an Art Installation

The Virtual Skiing game allows the user to immerse himself into the skiing sensation without using any obvious hardware interfaces. To achieve the movement down the virtual skiing slope the skier who stands on a pair of skis attached to the floor performs the same movements as on real skis, in particular this is the case on carving skis: tilting the body to the left initiates a left turn, tilting the body to the right initiates a right turn, by lowering the body, the speed is increased. The skier observes his progress down the virtual slope projected on the wall in front of him. The skier’s movements are recorded using a video camera placed in front of him and processed on a PC in real time to drive the projected animation of the virtual slope

ANALYSIS OF VIBRATIONS AND SHOCKS DURING THE PARALLEL TURN IN ALPINE SKIING

INTRODUCTION: In downhill skiing a skier is exposed to shocks and vibrations caused by the interaction of skis and snow (Muller and Hautz, 1991; Hull and Mote, 1978; Wunderley et al., 1988). This interaction is directed by the controlled and reflex action of a skier’s muscles. In this paper we present results on measurements of forces normal to the ski during downhill skiing and evaluate their effect on skiing safety. The main goal of the research is to the develop a tool for the evaluation of vibration isolators inserted between skis and ski bindings. METHODS: Forces during downhill skiing on well packed snow using parallel technique were measured. Forces were measured at the contact point between the ski boot sole and the ski, using four force transducers per each leg (Nemec, 1997). Forces on both skis were measured simultaneously at the rate of 50 measurements per second. Force measurement was synchronized with the video image. Filtered data, using a low-pass filter with the cut-off frequency at 20 Hz, were then analyzed using power spectrum density in the frequency domain

Complementing mass customization toolkits with user communities: How peer input improves customer self-design

In this article, the authors propose that the canonical customer-toolkit dyad in mass customization (MC) should be complemented with user communities. Many companies in various industries have begun to offer their customers the opportunity to design their own products online. The companies provide web-based MC toolkits which allow customers who prefer individualized products to tailor items such as sneakers, PCs, cars, kitchens, cereals, or skis to their specific preferences. Most existing MC toolkits are based on the underlying concept of an isolated, dyadic interaction process between the individual customer and the MC toolkit. Information from external sources is not provided. As a result, most academic research on MC toolkits has focused on this dyadic perspective. The main premise of this article is that novice MC toolkit users in particular might largely benefit from information given by other customers. The pioneering research conducted by Jeppesen (2005), Jeppesen and Frederiksen (2006), and Jeppesen and Molin (2003) has shown that customers in the computer gaming and digital music instruments industries are willing to support each other for the sake of efficient toolkit use (e.g., how certain toolkit functions work). Expanding on their work, this article provides evidence that peer assistance appears also extremely useful in the two other major phases of the customer's individual self-design process, namely the development of an initial idea and the evaluation of a preliminary design solution. Two controlled experiments were conducted in which 191 subjects used an MC toolkit in order to design their own individual skis. The authors find that during the phase of developing an initial idea, having access to other users' designs as potential starting points stimulates the integration of existing solution chunks into the problem-solving process, which indicates more systematic problem-solving behavior. Peer customer input also turned out to have positive effects on the evaluation of preliminary design solutions. Providing other customers' opinions on interim design solutions stimulated favorable problem-solving behavior, namely the integration of external feedback. The use of these two problem-solving heuristics in turn leads to an improved process outcome, that is, self-designed products which meet the preferences of the customers more effectively (measured in terms of perceived preference fit, purchase intention, and willingness to pay). These findings have important theoretical and managerial implications. (author's abstract

Modellierung und Computersimulation zweier Slalomtechniken beim Wettbewerb

The new geometry of skis highly affects skiing and consequently the slalom technique. A new improved slalom technique with a single movement has been recently presented. This study deals with the biomechanical modelling and computer simulation of the new technique and the old technique with double movement. The simulation is set to enable a comparison of forces and force distributions. It was found that the behaviour of the force is of vital importance because of the skier’s movement. Due to the movement, the force causes an increase and decrease in the total ground reaction force. The consequence of the different movements is a higher presence of the highest and strongest ground reaction forces acting in skiing when the double movement technique is applied. Furthermore, a much better steering of the skis can be achieved as a consequence of better contact with the snow, especially during the transfer of weight using the single movement technique. In addition to that, much lower knee momentums act around the gate in the single movement technique as a result of a more stretched body position. The final conclusion relating to the forces point of view achieved with computer simulation is that the new technique with a single movement is much more appropriate for the new skis. The conclusion is consistent with the measurement of forces and times presented in previous articles.Uvod Nova, poboljšana slalomska tehnika s jednim pokretom tek je nedavno predstavljena javnosti. U radu će biti prikazane razlike i prednosti poboljšane tehnike uz pomoć simulacije u laboratorijskim uvjetima, gdje su svi remeteći faktori i promjenjivi uvjeti prirodne okoline uklonjeni. Temelj računalnog modela slalomske tehnike jesu četiri zavoja. Trajektorija skijanja generira se pomoću sinusoidnog zavoja i pretpostavlja da skijaš izvodi karving zavoj. Simulirana skijaševa brzina sve vrijeme iznosi 13 m/s, a nagib padine je konstantan i iznosi 20°. Model skijaša je kruto tijelo s masom skupljenom u centar težišta tijela. Zatim je dodan pokret koji, po glavnoj osi tijela, oponaša pokrete opružanja i sagibanja. Skijaševo težište tijela pokreće se samo po površini, protegnuto preko normalnih i binormalnih vektora trajektorija gibanja, što je optimalan ravnotežni položaj skijaša. Metoda Uspoređuju se dvije slalomske tehnike. U oba se slučaja skijaševi pokreti modeliraju po glavnoj vertikalnoj osi tijela i uvijek se okreću u smjeru skijaševa nagiba, što za posljedicu ima održavanje tijela u ravnoteži. U slučaju tehnike jednog pokreta, amplituda pokreta obuhvaća 20 cm, a tijekom zavoja skijaš se uspravlja 40% vremena, a sagiba 60% od ukupnog vremena. Simulacija pokreta sadrži dva sinusoidna zavoja koja su spojena pri vrhu. Tehnika dvostrukog pokreta modelirana je sinusoidnom krivuljom dvostrukog zavoja frekvencije i amplitude 15 cm (slika 1). Za vrijeme tehnike jednog pokreta skijaš je u najnižoj poziciji za vrijeme prijenosa težine nakon čega se uspravlja. Najuspravniji je ispred vrata, a potom se sagiba. Za vrijeme izvođenja tehnike dvostrukog pokreta skijaš nije maksimalno pognut za vrijeme prijenosa težine, već tek nakon toga, kada već čvrsto premjesti skiju na rubnik. U tom se trenutku počinje kretati prema dolje i zauzima najniži položaj ubrzo nakon vrata. Potom slijedi odguravanje i uspravljanje, pokretanje težišta tijela bliže skiji počinje kada skijaš ponovno priprema prijenos težine. Rezultati Dijagrami na slici 3 i 4 prikazuju silu generiranu za vrijeme simulirane izvedbe prve i druge tehnike. Može se utvrditi da zakretna sila determinira glavni oblik sile reakcije podloge. Najveće je djelovanje gravitacije u blizini prijenosa težine, a mnogo manje u blizini vrata. Ponašanje sile zbog skijaševa kretanja je iznimno važno. U slučaju tehnike dvostrukog pokreta sila uzrokuje da skijaš ima područje vrlo niske minimalne sile u vrijeme prijenosa težine. Suprotno tome maksimum sile jest ispod štapa, kada se svi doprinosi sila zbrajaju. Rezultat je tipičan zavoj s dvostrukim vrhom. Tehnika jednog pokreta pokazuje potpuno različitu sliku, reakcija podloge se smanjuje u vrijeme djelovanja maksimalne sile i povećava u području vrlo niskih minimalnih sila. Rasprava i zaključak Može se utvrditi da je u modeliranju skijaša kao krutog tijela u jednoj točki (‘skijanje bez kretanja’) raspodjela sila reakcija podloge ograničena na donji rub, nešto manje nego Fg na gornjem rubu, do približno 3*Fg (vidi sliku 4). Distribucija doseže vrh u blizini sile skijaševe težine. Tehnika dvostrukog pokreta značajno proširuje distribuciju sila (slika 5). Prvo, postoji veća koncentracija sila u blizini nule, što znači da skijaš teško može manevrirati skijama. Glavni vrh je mnogo niži i širi zbog širine raspodjele. Drugi nedostatak ove tehnike je također veća prisutnost najviše i najjače sile (do 2700 N). U praksi, najviša sila znači više kočenja i teže uvjete skijanja. Slika tehnike jednog pokreta potpuno je različita, vrh distribucije je slično pomaknut višom kolonom, do otprilike 1.5*Fg, ali je bitno uži (vidi sliku 6). Raspodjela nije rastegnuta, naprotiv čak se sužava i završava otprilike 300 N niže od skijaševa modela u jednoj točki, ili otprilike 600 N niže nego u tehnici dvostrukog pokreta. Pomoću ove tehnike skijaš umanjuje najvišu silu i njezinu prisutnost. U slučaju tehnike jednog pokreta područje sila nije vidljivo u blizini 0 N, što znači da skijaš cijelo vrijeme ima dobar kontakt s podlogom. Važna je još jedna činjenica koja proizlazi iz ovog modela. U tehnici dvostrukog pokreta skijaš je pognut u području visokih sila, što poveća-a snagu mišića zbog poluga u zglobovima (vidi slike 2 i 4). Situacija je upravo suprotna u tehnici jednog pokreta; skijaš je prilično opružen u području djelovanja većih sila, koje su u ovom slučaju prilično niske (slike 2 i 3). Konačni zaključak sa stajališta djelovanja sila, utvrđen računalnom simulacijom, jest da je nova tehnika jednog pokreta znatno prikladnija za novo skijanje kada skijaš izvodi karving zavoj. Zaključak je sukladan mjerenju sila i vremena predstavljenima u prethodnom članku.Die neue Beschaffenheit von Skiern hat einen starken Einfluss auf das Skifahren und als Folge dessen auf die Slalomtechnik. Eine neue verbesserte Slalomtechnik mit einer Bewegung wurde neulich vorgestellt. Dieses Projekt befasst sich mit der biomechanischen Modellierung und Computersimulation der neuen und der alten Technik mit doppelter Bewegung. Die Simulation sollte einen Kräftevergleich vemitteln, sowie einen Einblick in die Distribution der Kräfte gewähren. Es wurde festgestellt, dass, was die Bewegung des Skifahrers betrifft, das Benehmen der Kraft von größter Wichtigkeit ist. Abhängig von der Bewegung verursacht die Kraft entweder eine Zu- oder Abnahme der gesamten Bodenreaktionskraft. Die Folge verschiedener Bewegungen ist eine höhere Anwesenheit der höchsten und stärksten Bodenreaktionskräfte, wenn die Doppelbewegungstechnik angewendet wird. Außerdem kann man eine weit bessere Skierführung erreichen, als Folge besseren Schneekontakts, besonders während der Gewichtsverlagerung bei der Einzelbewegungstechnik. Zudem macht der Skifahrer weit kürzere Schwünge um das Tor in der Einzelbewegungstechnik, als Folge einer ausgestreckteren Körperposition. Ensprechend der Computersimulation lässt sich folgern, im Bezug auf die mittels Computersimulation erhaltenen Kräfte, dass die neue Einzelbewegungstechnik für die neuen Skier angemessener ist. Das ist auch im Einklang mit den Messungen von Kräften und Zeit, die in vorhergehenden Artikeln beschrieben wurden

Balance as a Risk Factor for Injury Occurrence in Recreative Skiing

The objective of this study was to determine the efficiency of intervention based on the analysis of the static and dynamic balance status in order to reduce the probability of skiing injuries in adult beginners. In addition, we also analyzed the incidence of injury during initial training in alpine skiing. The subjects were recreational skiers aged from 20 to 25 years (287 subjects; 214 men and 73 women). The experimental group (E) consisted of 146 subjects out of whom 104 were men and 42 women. The control group (C) was made up of 110 men and 31 women, a total of 141 subjects. Independent variables included data on basic anthropometric measures and balance status parameters that were obtained using the Biodex Balance System. The dependent variables in the study included injury incidence or more specifically: number (frequency) of injuries, injury location (region of the body), and injury severity (mild, severe…). Both groups had a 6-day ski training program. Prior to the program, the E-Group was tested for balance, and the subjects with a relative balance insufficiency were identified. These subjects attended a special ski training program with reduced volume and work intensity (20–30% less intensive than other subjects). The data about subjects’ injuries were prospectively obtained. The χ2 test for independent samples was used for the analysis of the differences in the injury incidence between the E and C-Group, 18.5% of subjects from the E-Group suffered minor injuries as well as 24.8% of subjects from the C-Group. In the E-Group, 1.3% of them suffered serious injuries same as 2.8% of subjects from the C-Group, (p < 0.05). Contusions account for the largest number of injuries and they are followed by strains (sprains) and front knee pain. A total of one fracture was recorded in each Group, followed by three dislocations, four lacerations and one brain concussion. Hips/the gluteal region was the most frequently injured locality in minor injuries. There was one fracture of the fist, and in one case a rupture occurred. Dislocations were recorded in the shoulder, and twice in the fingers. The injury incidence is lower than that reported so far (2 to 2.5 injuries in 1000 skiing days). The main reason for this difference is to be found in the level of training, proper equipment control and in the methodological advantages of the study. The data suggest that the experimental program had a significant effect on the reduction of injuries during ski training. The conducted intervention was especially efficient in terms of the reduction of serious injuries. The effects, however, relatively failed to occur in terms of the differential effect of gender of the subjects. The study points to the importance of a precise, complete and quality training in recreational skiing

Izrazi za sneg in smuči v slovenski smučarski terminologiji

Snow and skis are the fundamental terms of skiing terminology. In the past a significant share of the terms in both concept groups thrived in dialects. From there they passed into the standard language, where they are now indispensable units of Slovenian skiing terminology. The vitality of this terminology is also evident in its responsiveness to new technological achievements (carving skis).Sneg in smuči sta temeljna termina smučarske terminologije. Pomemben delež izrazov iz obeh pojmovnih skupin je v preteklosti živel v narečjih. Od tu so prešli v knjižni jezik in so sedaj nepogrešljive enote slovenske smučarske terminologije. Živost le-te se izkazuje tudi v izraznem odzivanju na nove tehnološke dosežke (smuči karving)