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Experimental Investigation of Dynamic Force on The Performance of Wet Snow Shedding
International Journal of Mechanical Engineering and Mechatronics, 2012
Wet snow can create serious electrical and mechanical problems to power transmission networks due to its high adherence to materials. In this study, both adherence of wet snow to cables and wet snow shedding following the application of periodic loads were investigated in small-scale experiments. Wet snow was obtained from fresh dry snow collected from the top layer of snow accumulated outdoors. The collected dry snow was exposed to warm air for periods of time long enough to obtain the desired liquid water content (LWC) values. Wet snow sleeves were manually prepared after being compressed around the cable. The room temperature, snow sleeve length, cable diameter, and cable length were kept constant for each experiment. Dynamic load on the cable was simulated by a periodic excitation applied at one end of the cable, while the other end was fixed. Since fading adhesion is a condition for snow shedding, and since LWC is a critical factor influencing adhesion, the effects of excitation frequency and amplitude were investigated for different LWC values. LWC was examined for values from 10 to 40%. When free water began to increase, snow at this stage was wet and it adhered stronger to the cable than low LWC, where there is no enough water to stick on the cable or high LWC where snow is transparent. The LWC range was found experimentally between 20 to 30% (Hefny R. et al., 2009). Different snow shedding scenarios were studied, for which the shedding sequence and acceleration were observed at the excitation point, also cable tension at the fixed end and vertical displacement at the mid-point of the span were measured.
Evidence that abrasion can govern snow kinetic friction
Journal of Glaciology
ABSTRACTThe long-accepted theory to explain why snow is slippery postulates self-lubrication: frictional heat from sliding melts and thereby lubricates the contacting snow grains. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. Here we provide additional observational and theoretical evidence that abrasion can govern snow kinetic friction. We obtained coordinated infrared, visible-light and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area, and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests...
Microstructural resistance of snow following first wetting
Cold Regions Science and Technology, 2011
One of the main causes for the formation of wet snow avalanches is the decrease in strength following the introduction of liquid water. The influence of liquid water on initially dry snow was investigated in twelve field experiments in the Eastern Swiss Alps. For this, a variety of different snow types were artificially wetted and liquid water content (using the Snow Fork), microstructural penetration resistance (Snow Micro Penetrometer, SMP) and snow density were measured. Measurements were repeated up to eight times resulting in a total 1100 liquid water content, 355 penetration resistance, and 737 snow density measurements. Following wetting, microstructural penetration resistance decreased in layers consisting of faceted crystals or depth hoar at low liquid water content. Layers consisting of precipitation particles or small round grains, on the other hand, showed no significant trend at a similar water content. The results indicate that first wetting of faceted crystals and depth hoar layers has an impact on snow strength, and consequently contributes to a decrease in snow stability.
An infield study of road snow properties related to snow-car adhesion and snow smoke
Cold Regions Science and Technology, 2018
This article analyzes the properties of snow on the road related to the formation of snow smoke and contamination of the car. The increased usage of sensors for active safety in modern cars increases the importance of understanding contamination of the car body. The analysis characterizes snow in terms of shape, size, and adhesiveness. The data is related to changing weather conditions and experienced car contamination. Several different sampling positions were chosen both on the road and on the car. The temperatures during the days of measurements ranged from − 4°C to −12°C, which gave cold and dry snow. Data on size and shape was obtained via microscope analysis. An infield adhesion tester for snow adhesion measurements was built. The microscope analysis showed that the shape of the snow particles in the tire tracks and on the car body generally had a rounded structure. Even soon after a fresh snow fall, the rounded shapes remained in these positions. This structure was found to change to a more edgy hexagonal shape during hoar formation on the existing snow. The particle size distributions from tire tracks, from suspended snow smoke, and from different positions on the car were analyzed. It was found that smaller particles travel higher and are more prone to enter the wake behind the car to stick to the back parts of the vehicle. The adhesion test gave little distinction between the different snow types and samples. The adhesion force was found to range from 2 to 12 dyne.
Simulation of Snow Adhesion on Real-Scale Lines
International Journal of Mechanical Engineering and Mechatronics, 2012
Wet snow shedding from overhead power transmission cables due to periodically repeated impacts was simulated using the finite element software ADINA. It was simulated by point loads whose mass depended on the snow load on the cable. The adhesion between snow and cable was modeled by vertical springs whose stiffness was determined so that the spring force simulates tensile adhesion. Failure criterion for snow detachment from the cable was defined based on the acceleration of the snow-covered cable. This model was applied on a real scale cable with span length of 470 m. Time history of displacement at the excitation point was the input to the model, where varying impacts lead to different accelerations of the cable. The results showed the effects of increasing impact loads on cable jump and, consequently, on the rate of shedding.
Sixth International Symposium on Snow Removal and Ice Control Technology
2000
tudies to identify specific causes of winter crashes in Wyoming indicated that the majority of crashes were associated with icy road conditions and that blowing snow was the dominant cause of icy roads in wind-exposed areas. The finding that 74% of all crashes over a 5-year period were associated with icy road conditions on a segment of Interstate 80 was illustrative and typical.
Relationship between snow microstructure and physical and chemical processes
Atmospheric Chemistry and Physics Discussions, 2012
Ice and snow in the environment are important because they not only act as a host to rich chemistry but also provide a matrix for physical exchanges of contaminants within the ecosystem. This review discusses how the structure of snow influences both chemical reactivity and physical processes, which thereby makes snow a unique medium for 5 study. The focus is placed on impacts of the presence of liquid and surface disorder using many experimental studies, simulations, and field observations from the molecular to the micro-scale.
International Snow Science Workshop 2014 Proceedings Banff Canada, 2014
Of critical importance to avalanche forecasting is the ability to draw meaningful conclusions from potentially only a small handful of field observations. With this in mind, our research focuses on the development of a new field metric for estimating the likelihood and rate at which new ice crystal growth and kinetic snow metamorphism may be occurring on or near a buried ice lens or crust that is based solely on the thickness of the ice lens and the field-measurable temperature gradient. While both previous literature and theory predict that the presence of an ice lens can act both as a natural barrier to the diffusion of water vapor in the snowpack and as an interface of differential thermal conductivities, no such direct measurements have ever been successfully made in order to characterize or quantify this presumed effect. Presented here, we have developed a laboratory technique that has allowed us to show via in-situ measurements that a super-temperature gradient of several factors greater than the bulk temperature gradient does indeed exist within a millimeter above and below the surface of an artificially created ice lens when placed between two layers of natural snow and held under a controlled temperature gradient. Additionally, we have also investigated the type of new ice crystal growth and kinetic snow metamorphism that has occurred as a result of such a super-temperature gradient existing near the ice lens/snow interface. For this portion of the research, we have utilized Scanning Electron Microscopy for the characterization of ice crystal type and time-lapse X-ray Micro-Computed Tomography to quantify the rates of change in the parameters of interest related to kinetic snow metamorphism, such as the specific surface area and mean grain diameter.