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| 2. |
- Bahaloohoreh, Hassan, 1983-, et al.
(författare)
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Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size
- 2022
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 131:2
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Tidskriftsartikel (refereegranskat)abstract
- We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.
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| 3. |
- Eidevåg, Tobias, 1987, et al.
(författare)
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Angle of repose of snow: An experimental study on cohesive properties
- 2022
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- The angle of repose is a measure reflecting the internal friction and cohesion properties of a granular material. In this paper, we present an experimental setup and measurements for the angle of repose of snow for seven different snow samples over a large range of temperatures. The results show that the angle of repose is dependent on the fall height, the temperature, and the grain size of the snow. These variables are quantified, and their interdependencies are separately studied. With increased snow temperature, the angle of repose increases, and this can be explained by the presence of a liquid layer on ice that can be thermodynamically stable at temperatures below the melting point of water. With decreasing grain size the angle of repose also increases which is expected since the cohesive energy decreases more slowly than the grain mass. For increasing fall height, the snow grains generally accelerate to larger collisional velocities, yielding a smaller angle of repose. In general, the dimensionless cohesion number was found to largely reflect the dependencies of the variables and is therefore useful for understanding what affects the angle of repose. The results demonstrate that the drag force and collision dynamics of ice grains are important for understanding how snow accumulates on a surface, for example if one desires predicting snow accretion by simulating a dispersed cloud of snow. © 2021
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| 4. |
- Eidevåg, Tobias, 1987, et al.
(författare)
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Collisional damping of spherical ice particles
- 2021
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 383, s. 318-327
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental values for the coefficient of restitution (e(n)) for millimeter-sized ice particles colliding with massive walls at different temperatures. Three different wall materials are tested: hardened glass, ice and Acrylonitrile butadiene styrene (ABS) polymer. The results show a high sensitivity to impact velocity V-i, where e(n) decreases rapidly with increasing V-i. The results also show a decrease in e(n) with increasing temperature T. A novel model that predicts e(n) based on the assumption of collisional melting and viscous damping caused by an increased premelted liquid-layer, is proposed. The model predicts both the velocity and the temperature trends seen in the experiments. The difference obtained in experiments between wall materials is also captured by the new model. A generalized regime map for ice particle collisions is proposed to combine the new model with previous work. (C) 2021 The Author(s).
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| 5. |
- Eidevåg, Tobias, 1987, et al.
(författare)
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Modeling of dry snow adhesion during normal impact with surfaces
- 2020
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 361, s. 1081-1092
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Tidskriftsartikel (refereegranskat)abstract
- Contamination due to dry snow smoke adhesion is an evident danger for sensor blinding on future autonomous driving cars under winter road conditions. This paper examines at what velocities ice particles and agglomerates, representing dry snow, adhere to surfaces of various materials. Contact models for normal direction, tangential sliding, and tangential rolling that account for the adhesive interaction of spherical particles due to Van der Waals forces are used in the study. Three different scenarios of impacts are presented i) single particle impact, ii) small agglomerate impacts, and iii) large agglomerate impacts. It is shown that by increasing the number of particles in an agglomerate, the velocity at which the agglomerate sticks to the impact wall increases, i.e. the agglomerate is more likely to stick to a surface. It is also shown how material properties influence the tendency of dry road snow to adhere to a surface.
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| 6. |
- Eidevåg, Tobias, 1987
(författare)
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Snow Contamination of Cars: Adhesive Particle Collisions with Exterior Surfaces
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An ongoing challenge regarding autonomous vehicles is the obstruction of sensors by contaminants on exterior surfaces. This often occurs when driving in harsh weather conditions, where the contaminant can be, for example, water spray, dirt, or snow. Certain regions on a vehicle can have higher rates of deposition compared to others and it is therefore crucial when developing an autonomous vehicle to choose sensor locations that avoid contamination. The present research has aimed to increase the knowledge regarding snow deposition when a vehicle is driving on a snow-covered road. Mathematical models for the cohesive properties of snow and ice have been developed to predict and understand snow deposition on exterior vehicles surfaces. The models were solved analytically or numerically for ice particle collisions with exterior surfaces. Multiple experimental studies were conducted ranging from small-scale experiments on millimeter-sized single ice particle collisions to large-scale climate wind tunnel experiments on bluff bodies. The cohesive properties of snow were measured using an experimental setup for the angle of repose of snow. In summary, this thesis presents results for single ice particle collisions, the angle of repose of snow, and snow contamination on bluff bodies. A regime map for ice particle collisions was developed that predicts a nonlinear dependency between impact velocity and collisional damping. The angle of repose of snow was shown to strongly correlate with temperature, but also with particle size and fall height. Experimental results for the snow contamination of bluff bodies show that snow tends to deposit near aerodynamic wake regions and reattachment regions where the airflow velocities are expected to be low. A numerical model was proposed for the transport of ice particles in a turbulent flow. Simulations that replicate the experiments, show that the numerical model captures the main characteristics of the snow deposition obtained in the experiments.
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| 7. |
- Eidevåg, Tobias, 1987
(författare)
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Snow contamination of cars: Collisions of ice particles with surfaces
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Seasonal snow cover on roads causes car accidents that lead to human suffering and economic loss. Snow cover decreases visibility and road-tire friction. Advanced active safety systems have been developed to cope with sudden changes in driving conditions and have been engineered to act as quickly as possible. These systems are heavily reliant on sensors on the exterior of the car that can detect these changes. Snow, however, has a tendency to accumulate and cause sensor blockage, and consequently, the sensors might not be available when they are most needed. The physics of how snow and ice adhere to surfaces must be understood in order to develop measures that avoid snow accumulation. Snow and ice during normal winter temperatures in the northern hemisphere (0 °C to ~-30 °C) are close to the melting point of ice and are therefore thermodynamically active. This fact in combined with small grain sizes causes ice and snow to easily adhere to surfaces. Mathematical models for snow adhesion are developed in this work by studying collisions of ice particles with walls. Based on a general theory for adhesive-elastic interactions, the threshold velocities for ice particles are calculated so that particles that collide with surfaces at velocities below this threshold will adhere to the surface they collide with. Experimental measurements are also conducted on ice particles that collide with different massive walls, and from these measurements, a collisional melting model is proposed to model the abrupt increase in energy loss observed. The two different modeling approaches are combined as a generalized velocity-dependent collision model for ice particles.
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| 8. |
- Eidevåg, Tobias, 1987, et al.
(författare)
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Snow Contamination of Simplified Automotive Bluff Bodies: A Comparison between Wind Tunnel Experiments and Numerical Modeling
- 2022
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 2641-9637 .- 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- We describe experiments and numerical modeling of snow surface contamination on two simplified automotive bluff bodies: The Ahmed body and a wedge. The purpose was twofold: 1) To obtain well defined experimental results of snow contamination on simple geometries; 2) To propose a numerical modeling approach for snow contamination. The experiments were performed in a climatic wind tunnel using a snow cannon at −15 °C and the results show that the snow accumulation depends on the aerodynamics of the studied bluff bodies. Snow accumulates on surfaces in proximity to the aerodynamic wakes of the bodies and characteristic snow patterns are obtained on side surfaces. The numerical modeling approach consisted of an aerodynamic setup coupled with Lagrangian particle tracking. Particles were determined to adhere or rebound depending on an adhesion model combined with a resuspension criterion. The adhesion model was based on adhesive-elastic contact theory and the resuspension criterion is derived from the balance between the aerodynamic forces acting on a particle and the critical force for onset of resuspension. The results show that the numerical method can predict certain characteristic snow patterns obtained from the experiments and we also highlight deviations obtained between experimental and simulation results. The simulation results show that the snow accumulation patterns on a bluff body will depend on the smallest ice particles in a snow sample which implies that samples with larger ice particle (for example natural snow) could produce different snow patterns than the fine machine-made snow used in this study.
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