A scientific perspective on reducing ski-snow friction to improve performance in Olympic Cross-Country Skiing, the Biathlon and Nordic Combined

Of the medals awarded at the 2022 Winter Olympics in Beijing, 24% were for events involving cross-country skiing, the biathlon and Nordic combined. Although much research has focused on physiological and biomechanical characteristics that determine success in these sports, considerably less is yet known about the resistive forces. Here, we specifically describe what is presently known about ski-snow friction, one of the major resistive forces. Today, elite ski races take place on natural and/or machine-made snow. Prior to each race, several pairs of skis with different grinding and waxing of the base are tested against one another with respect to key parameters, such as how rapidly and for how long the ski glides, which is dependent on ski-snow friction. This friction arises from a combination of factors, including compaction, plowing, adhesion, viscous drag, and water bridging, as well as contaminants and dirt on the surface of and within the snow. In this context the stiffness of the ski, shape of its camber, and material composition and topography of the base exert a major influence. An understanding of the interactions between these factors, in combination with information concerning the temperature and humidity of both the air and snow, as well as the nature of the snow, provides a basis for designing specific strategies to minimize ski-snow friction. In conclusion, although performance on "narrow skis" has improved considerably in recent decades, future insights into how best to reduce ski-snow friction offer great promise for even further advances

Snow storage in Piteå 2012

Godkänd; 2012; 20130830 (ninlin

Mechanical properties of artificial snow

Mechanical properties of snow have been a subject of research since the mid-20th century. Theresearch done is based on natural snow. During the last decades the winter business industryhas been growing and also the interest for constructing buildings and artwork of snow. Suchconstructions are generally built using artificial snow, i.e. snow produced by snow guns. Up tothe present constructions of snow are designed based on knowledge by experience. Only minorscientific studies on artificial snow and its properties has been published. Hence it is ofimportance to investigate material properties for artificial snow.A survey of current state of the art knowledge of properties for natural snow was done andbasic material properties for different qualities of artificial snow were investigated. Strengthand deformation properties for artificial snow were evaluated through uniaxial compressivetests where cylindrical test specimens were subjected to different constant deformation rates.The results show that artificial snow at low deformation rates will have a plastic deformationbehavior where the initial deformation will cause a hardening of the snow structure. At higherdeformation rates brittle failure may occur. For artificial snow with a homogeneous and finegrained structure the deformation behavior was found to change from plasticity to brittleness ata certain critical deformation rate. Artificial snow with coarse grained structure was found to bebrittle giving unstructured results independent of the load level.Four point loading was applied on beams of artificial snow to study creep deformation, bendingstrength and to determine the ultimate load for the different snow qualities. The results showedcoarse grained artificial snow underwent relatively small creep deformations. Both the creepbehavior and the ultimate strength varied randomly at the same applied load. Large plasticdeformations were observed with the fine grained artificial without any failure of the beams.The ultimate load was relatively high and repeatable results were achieved for all test.Previous presumptions that coarse grained artificial snow with high density would have highstrength and were not confirmed by the experiments performed on different qualities ofartificial snow. The performed tests indicate that fine grained artificial snow of lower densityhave more predictable strength properties of equally high or higher magnitude as for coarsegrained artificial snow. The plastic deformations were however higher for the fine grainedartificial snow. High deformations are not favorable for structures which should maintain theshape during the winter season. When designing constructions of snow both strength anddeformation properties should be taken into account.Godkänd; 2013; 20131002 (ninlin); Tillkännagivande licentiatseminarium 2013-10-23 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Nina Lintzén Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Uppsats: Mechanical Properties of Artificial Snow Examinator: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Tekn. lic. Lars Vikström, LKAB, Luleå Tid: Fredag den 15 november 2013 kl 10.00 Plats: F1031, Luleå tekniska universite

Properties of snow with applications related to climate change and skiing

Snow has been a subject of research since the mid-20th century. Research on mechanical properties of snow started as an off-shoot of soil mechanics, where methods, tools and instruments used often are the same. However, during the last decades the winter business industry has been growing requiring a number of new fields of research. The aim with this PhD thesis is to investigate and contribute to solutions of some of the new research problems appearing in this area. Machine-made snow is commonly used for buildings and artwork of snow. Only minor scientific studies of machine-made snow and its properties have been published. Therefore, mechanical properties of machine-made snow were investigated. Strength and deformation properties were evaluated through uniaxial compressive tests where cylindrical test specimens were subjected to different constant deformation rates. Creep deformation, bending strength and ultimate load were also evaluated through beam tests. The results showed that the deformation rate is crucial if the snow will deform plastically or if brittle failure will occur. The grain size and structure of the snow had a strong influence on the strength properties. Snow is a constantly changing material with a large variety of grain sizes and shapes. Therefore it is of importance to classify snow. Classication of snow can be done using different methods depending on the property that is to be investigated. Several non-contact detection methods to evaluate snow properties exist. In this thesis, spectral reflectance measurements were performed to investigate liquid water content in snow using two different systems, a spectrometer and an optical sensor called Road Eye. The Road Eye sensor was also used to classify snow in cross-country ski tracks. This method enables a fast classication of a complete track where different types of snow can be distinguished. The properties of a ski track and the characteristics of the snow determine the type of skis that should be selected for optimum sliding properties. Cross-country skis have different mechanical properties, which to a large extent can be evaluated from the span curve of the ski. Depending on the skiing style, the skier's skills, terrain and track conditions different ski properties are required, which is particularly important for competitive skiing. Span curves of cross-country skis were measured using a digital instrument called Skiselector. Results from the investigations showed that skis within the same pair may have signicantly different properties. Moreover, temperature influences the span curve and thus the mechanical properties of the skis. Therefore, skis should be measured at a temperature close to where they are aimed to be used. Field tests of skis with similar span curves but different ski base topography were tested during wet and cold snow conditions. The results indicate that different topographies are preferable during different snow conditions. Due to the climate change, winters have become shorter and warmer with less natural snow. To compensate for the lack of natural snow, ski resorts and other stakeholders produce machinemade snow in order to run their business. Storing snow in insulated piles is an alternative and sometimes a complement to snow production. Studies on stored snow show that the surface area of the pile should be minimized in order to reduce the melt rate. Furthermore, the pileshould be covered with a suciently thick insulating layer, preferably with good evaporation properties. Theoretical calculations can be used to estimate the amount of snow that melts and to predict the efficiency of different materials as thermal insulation on snow. These calculations coincide well with experiments performed in northern Sweden where snow melt was measured. This PhD thesis consists of five publications and an introduction to this area which in particular puts these publications into a more general frame

Compressive strength of snow : Experimental mesaurements at ICEHOTEL, April 2012

Godkänd; 2012; 20130830 (ninlin

Snowmaking and snowstorage

Godkänd; 2012; 20130830 (ninlin

Mechanical properties of artificial snow

Mechanical properties of snow have been a subject of research since the mid-20th century. Theresearch done is based on natural snow. During the last decades the winter business industryhas been growing and also the interest for constructing buildings and artwork of snow. Suchconstructions are generally built using artificial snow, i.e. snow produced by snow guns. Up tothe present constructions of snow are designed based on knowledge by experience. Only minorscientific studies on artificial snow and its properties has been published. Hence it is ofimportance to investigate material properties for artificial snow.A survey of current state of the art knowledge of properties for natural snow was done andbasic material properties for different qualities of artificial snow were investigated. Strengthand deformation properties for artificial snow were evaluated through uniaxial compressivetests where cylindrical test specimens were subjected to different constant deformation rates.The results show that artificial snow at low deformation rates will have a plastic deformationbehavior where the initial deformation will cause a hardening of the snow structure. At higherdeformation rates brittle failure may occur. For artificial snow with a homogeneous and finegrained structure the deformation behavior was found to change from plasticity to brittleness ata certain critical deformation rate. Artificial snow with coarse grained structure was found to bebrittle giving unstructured results independent of the load level.Four point loading was applied on beams of artificial snow to study creep deformation, bendingstrength and to determine the ultimate load for the different snow qualities. The results showedcoarse grained artificial snow underwent relatively small creep deformations. Both the creepbehavior and the ultimate strength varied randomly at the same applied load. Large plasticdeformations were observed with the fine grained artificial without any failure of the beams.The ultimate load was relatively high and repeatable results were achieved for all test.Previous presumptions that coarse grained artificial snow with high density would have highstrength and were not confirmed by the experiments performed on different qualities ofartificial snow. The performed tests indicate that fine grained artificial snow of lower densityhave more predictable strength properties of equally high or higher magnitude as for coarsegrained artificial snow. The plastic deformations were however higher for the fine grainedartificial snow. High deformations are not favorable for structures which should maintain theshape during the winter season. When designing constructions of snow both strength anddeformation properties should be taken into account.Godkänd; 2013; 20131002 (ninlin); Tillkännagivande licentiatseminarium 2013-10-23 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Nina Lintzén Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Uppsats: Mechanical Properties of Artificial Snow Examinator: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Tekn. lic. Lars Vikström, LKAB, Luleå Tid: Fredag den 15 november 2013 kl 10.00 Plats: F1031, Luleå tekniska universite

Properties of snow with applications related to climate change and skiing

Snow has been a subject of research since the mid-20th century. Research on mechanical properties of snow started as an off-shoot of soil mechanics, where methods, tools and instruments used often are the same. However, during the last decades the winter business industry has been growing requiring a number of new fields of research. The aim with this PhD thesis is to investigate and contribute to solutions of some of the new research problems appearing in this area. Machine-made snow is commonly used for buildings and artwork of snow. Only minor scientific studies of machine-made snow and its properties have been published. Therefore, mechanical properties of machine-made snow were investigated. Strength and deformation properties were evaluated through uniaxial compressive tests where cylindrical test specimens were subjected to different constant deformation rates. Creep deformation, bending strength and ultimate load were also evaluated through beam tests. The results showed that the deformation rate is crucial if the snow will deform plastically or if brittle failure will occur. The grain size and structure of the snow had a strong influence on the strength properties. Snow is a constantly changing material with a large variety of grain sizes and shapes. Therefore it is of importance to classify snow. Classication of snow can be done using different methods depending on the property that is to be investigated. Several non-contact detection methods to evaluate snow properties exist. In this thesis, spectral reflectance measurements were performed to investigate liquid water content in snow using two different systems, a spectrometer and an optical sensor called Road Eye. The Road Eye sensor was also used to classify snow in cross-country ski tracks. This method enables a fast classication of a complete track where different types of snow can be distinguished. The properties of a ski track and the characteristics of the snow determine the type of skis that should be selected for optimum sliding properties. Cross-country skis have different mechanical properties, which to a large extent can be evaluated from the span curve of the ski. Depending on the skiing style, the skier's skills, terrain and track conditions different ski properties are required, which is particularly important for competitive skiing. Span curves of cross-country skis were measured using a digital instrument called Skiselector. Results from the investigations showed that skis within the same pair may have signicantly different properties. Moreover, temperature influences the span curve and thus the mechanical properties of the skis. Therefore, skis should be measured at a temperature close to where they are aimed to be used. Field tests of skis with similar span curves but different ski base topography were tested during wet and cold snow conditions. The results indicate that different topographies are preferable during different snow conditions. Due to the climate change, winters have become shorter and warmer with less natural snow. To compensate for the lack of natural snow, ski resorts and other stakeholders produce machinemade snow in order to run their business. Storing snow in insulated piles is an alternative and sometimes a complement to snow production. Studies on stored snow show that the surface area of the pile should be minimized in order to reduce the melt rate. Furthermore, the pileshould be covered with a suciently thick insulating layer, preferably with good evaporation properties. Theoretical calculations can be used to estimate the amount of snow that melts and to predict the efficiency of different materials as thermal insulation on snow. These calculations coincide well with experiments performed in northern Sweden where snow melt was measured. This PhD thesis consists of five publications and an introduction to this area which in particular puts these publications into a more general frame

Uniaxial Strength and Deformation Properties of Machine-Made Snow

Snow as a construction material has been used for centuries, with igloos among the first examples. Each winter, snow and ice villages, buildings, and artwork are built in many places around the world. Machine-made snow manufactured by snow guns is commonly used for constructions made of snow. However, only a few basic studies on machine-made snow have been published. Knowledge based on experience and studies on natural snow constitute the basis for constructions made using snow and ice. Through material tests on machine-made snow used for construction, data on important physical and mechanical properties have been established that aim to improve and optimize safe constructions made from snow. Strength tests have been performed using two different qualities of machine-made snow. Specimens used for testing were cut out from one block of snow that had a coarse-grained structure with clusters of ice in the snow and from one block of snow with a fine-grained and homogeneous structure. The density for each tested snow sample was measured and strength tests were performed at different deformation rates to investigate the relationship between mechanical properties and deformation rate or strain rate. The load response curves achieved from the strength tests were used to evaluate compressive strength, Young’s modulus, and the residual modulus. The results show that compressive strength increases with increasing density. Increasing compressive strength with an increasing strain rate was also observed for fine-grained snow quality specimens, whereas no similar tendency was observed for coarse-grained snow. The residual modulus increased with an increasing strain rate up to a certain critical value for the fine-grained machine-made snow specimens. Regression analysis was used to investigate whether any dependence was observed between the calculated mechanical properties; no further relationship between the mechanical and the physical properties was noticedValiderad; 2015; Nivå 2; 20150109 (ninlin

Study on basic material properties of artificial snow

For buildings and constructions made by snow, like for example the ICEHOTEL in Jukkasjärvi, generally artificial snow is used. Both for safety reasons and for design purposes it is hence of importance to understand the material behaviour of artificial snow. Many buildings and structures made by snow and ice are constructed using knowledge obtained by experience.When subjected to a load snow undergoes an immediate elastic deformation and a time-dependent irreversible deformation, known as snow creep, which constitutes the considerably highest part of the total deformation. The magnitude of the snow creep deformation is the dominating deformation mechanism for snow structures but it is poorly investigated and not well understood.To study material parameters and mechanical behaviour of artificial snow unconfined compression test and deformation tests to observe the creep behaviour have been performed. Results from experimental tests have been analyzed and compared with theoretical calculations and finite element simulations. The density and viscosity have shown to be important parameters for the deformation behaviour and will have a direct influence on the creep rate. The investigation indicates that the artificial snow used for the tests have higher density, compression strength and creep strength compared to natural snow used in other studies.Validerad; 2012; 20120607 (ysko)</p