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- Hansson, Klas, et al.
(author)
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Equifinality and sensitivity in freezing and thawing simulations of laboratory and in situ data
- 2006
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In: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 44:1, s. 20-37
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Journal article (peer-reviewed)abstract
- Numerical models of soil freezing and thawing are being increasingly used in, e.g., agriculture, forestry, ecology and civil engineering. This study was conducted to 1) elucidate the sensitivity in simulation output to the variability of model parameters for the hydrodynamic model Hydrus-1D and 2) investigate how two operational considerations in the model setup, groundwater level and subgrade material (soil texture), affect indicators of road accessibility in northern Sweden. The analysis was carried out by applying the generalized likelihood uncertainty estimation (GLUE) procedure when simulating laboratory measurements of freezing cylinders and by a more conventional sensitivity analysis, varying one parameter at a time, using road surface temperatures measured during nearly 1 year as upper boundary condition. For the simulation of the laboratory experiment, it was found that, although the thermal conductivity scaling factor, λf, and the convective heat transfer coefficient, hc, most strongly affected the output, no parameter was redundant for the given problem. The frost depth was most sensitive to changes in λf and hc, while the water content in the unfrozen zone was most sensitive to changes in the hydraulic conductivity impedence parameter Ω. For the 1-year road simulation, the frost depth was larger for sand than for the loam and silt subgrades; the thawing period was shortest for sand and longest for the silt subgrade; and the silt subgrade allowed for the largest frost-induced upward water flow. Thus, among the subgrades studied, roads built on silt show the potential of being most frost-susceptible as a consequence of having the largest elevated water content in combination with the longest time of thawing. The study performed indicates that the model can provide information of interest from an operational perspective, allowing for local predictions important in the road construction and maintenance process.
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| 3. |
- Nohr, Christian, 1966, et al.
(author)
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A dynamic sea ice model based on the formation direction of leads
- 2009
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In: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 58:02-jan, s. 36-46
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Journal article (peer-reviewed)abstract
- A dynamic ice model is presented using a novel approach where the memory of weak directions in the ice cover is stored. The model computes ice motion, ice deformation and the associated dynamic ice production without the need of a full two dimensional computation. The ice dynamics is based on a viscous-plastic approach in a marginal ice zone with both compressive and shear stresses. The method is very computational efficient but is likely restricted to basin scales of semi size with relatively coherent wind forcing over the basin. The model is applied to the Bothnian Bay of the Baltic Sea and coupled with an ocean model. The results show good agreement when compared against measurements of ice velocity from an upward looking ADCP deployed in the center of the Bothnian Bay and observations from ice charts. As a model application, the dynamic ice production that occurs in addition to the pure thermodynamic growth in a deforming ice cover has been computed over the period 1991-2004. The results show that the dynamic ice production typically increases the ice volume with 80% over the simulation period.
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- Skogsberg, Kjell, et al.
(author)
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Wood chips as thermal insulation of snow
- 2005
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In: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 43:3, s. 207-218
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Journal article (peer-reviewed)abstract
- Snow (and ice) cooling is in some areas an alternative cooling technique to chillers. However, to utilise snow cooling during the summer, storage is needed. Snow storages were traditionally insulated by sawdust. A large demonstration plant has been in operation since 2000 for cooling the regional hospital in Sundsvall, Sweden. This storage is thermally insulated by larger wood chips. This paper summarizes laboratory testing of some key factors that influence the functioning of cutter shavings (another kind of wood chips) as thermal insulation. The melt rate significantly increased with increased wind velocity, light intensity (from spotlight bulbs), air temperature, and air humidity. A 1 cm thicker layer of cutter shavings decreased the melt rate about 0.097 kg m- 2 h- 1, within the studied layer limits of 2.5 to 7.5 cm. The melt rate with initially wet cutter shavings was about the same as for initially dry cutter shavings. This was explained by the increased evaporation which balanced increased thermal conductivity. Evaporation was found to be an important part of the energy balance and reduced the melt rate. Solar light reflectivity of new cutter shavings was measured in a separate outdoor experiment, found to be about 20%.
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