| 1. |
- Abrahamsson, Per, 1985, et al.
(författare)
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An infield study of road snow properties related to snow-car adhesion and snow smoke
- 2018
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X. ; 145, s. 32-39
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Elsevier B.V. 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.
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Eng, Matthias, 1983, et al.
(författare)
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Analysis of Particle Cloud Height Dynamics in a Stirred Tank
- 2016
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 62:1, s. 338-348
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Tidskriftsartikel (refereegranskat)abstract
- Local and temporal variations of the particle cloud formed in a cylindrical mixing vessel were investigated experimentally. Different particle sizes (0.5, 1, and 2 mm) and volumetric concentration up to 20 vol % were evaluated at different impeller speeds. The time-averaged cloud height was linear with impeller frequency and with volume concentration. Suspensions with larger particles had a lower average cloud height, while the standard deviation for the temporal cloud height variation was larger. Two strong periodic phenomena were identified to be dominating the particle cloud height variations. The frequencies were linear with impeller speed, resulting in dimensionless frequencies of S-1 = 0.02-0.03 and S-2 = 0.05-0.06. The frequencies were affected by neither the particle size nor the volumetric concentration. The amplitude showed no dependency on the particle size, but the S-2 amplitude significantly decreases and S-1 increases with increasing solid concentration. The results were compared to LES/discrete element method simulations and showed a fair agreement.
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| 6. |
- Eng, Matthias, 1983, et al.
(författare)
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Influence of solids on macro-instabilities in a stirred tank
- 2012
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 90:8, s. 1052-1062
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Tidskriftsartikel (refereegranskat)abstract
- Measurements were conducted in a cylindrical tank stirred with a PBT in order to study the effect of varying amounts of suspended solids, up to 11.8% by volume, on the frequency and amplitude of macro-instabilities (MI). Solid glass particles of three different sizes were used in order to investigate the influence of the particle Stokes number. Measurements were made at 18 different locations in the vessel using laser Doppler anemometry (LDA) and were evaluated with the Lomb algorithm to obtain the frequency spectrum of the liquid flow. The results showed that the MI frequency is not influenced by the addition of solids. However, the MI amplitude was reduced by the addition of the solid phase although still detectable up to the highest concentration measured (11.8 vol.%). In the studied system there seems to be a difference dependent on the particle Stokes number.
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| 7. |
- Eng, Matthias, 1983, et al.
(författare)
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Large Eddy Simulation of the influence of solids on macro instability frequency in a stirred tank
- 2015
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 259, s. 900-910
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Tidskriftsartikel (refereegranskat)abstract
- The mixing flow in a cylindrical tank stirred with a PBT was simulated with a LES model with Eulerian–Lagrangian approach, in order to study the effect of varying amounts of suspended solids on the frequency and amplitude of macro instabilities (MI). The dispersed phase was reassembled solid glass particles of two different sizes (1 mm, 2 mm) and varying concentrations (up to 3% by volume). The continuous phase velocities were sampled at 18 different locations and were evaluated with the Lomb algorithm to obtain frequency spectra of the flow. The results showed that the MI could be detected in all suspensions and that the frequency is not influenced by the addition of solids. However, the MI became less prominent with increasing number of particles. A periodic fluctuation of the baffle jet could be observed with identical frequency. All results compare fairly well to previously obtained experimental data.
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| 8. |
- Eng, Matthias, 1983, et al.
(författare)
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Measurement of Continuous Phase Velocities in a Confined Solid-Liquid Jet Using LDV
- 2014
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Ingår i: Chemical Engineering Communications. - : Informa UK Limited. - 0098-6445 .- 1563-5201. ; 201:11, s. 1497-1513
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Tidskriftsartikel (refereegranskat)abstract
- A two-component LDV was used to investigate how flow structures in a liquid jet are influenced by the presence of solid particles. Solid glass spheres with a density of 2.5 kg/dm(3) and three different sizes (0.5 mm, 1 mm, and 2mm) at different solids loading (0-6.2 vol.%) were used as particles, while water served as continuous phase. No significant influence of the solid particles on the rate of decrease in the centerline liquid velocity or the jet expansion ratio could be observed. Two flow regimes were identified: a stable jet characterized by a symmetric shear layer close to the nozzle, and a flow dominated by large-scale instabilities farther from the nozzle. The spreading of particles was dominated by interparticle collisions in the region close to the nozzle and by jet instability in the region farther from the nozzle. With increased solids loading increased liquid RMS values in the region close to the nozzle could be found. The effect on RMS values was larger with larger particles. For the 1mm particles the RMS increased in this region, but decreased in the region farther from the nozzle. The presence of 2mm particles acted to stabilize the jet, and the instability moved farther downstream. Suspensions with smaller particles had no effect on the instability, strength, or location.
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| 9. |
- Isaksson, Magnus, 1969-, et al.
(författare)
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A Study of a Variable-Capacitance Drain Network's Influence on Dynamic Behavioral Modeling of an RF PA
- 2007
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Ingår i: 69th ARFTG Microwave measurement conference, Honolulu, HI, USA. ; , s. 112-116, s. 5456336-
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Konferensbidrag (refereegranskat)abstract
- An investigation of the complex-valued parameters of two different dynamic behavioral models due to changes in the drain decoupling network of a PA has been performed. The study is based on complex-envelope measurements on a real PA. The complex coefficients of the parallel Hammerstein (PH) and the optimal pole placements of the Kautz-Volterra (KV) models are analyzed. It is concluded that the parameters follow smooth, predictable functions and that the KV poles give a robust description of the PA's memory effects compared with the PH model.
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| 10. |
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