| 1. |
- Hansson, Klas, et al.
(författare)
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Equifinality and sensitivity in freezing and thawing simulations of laboratory and in situ data
- 2006
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 44:1, s. 20-37
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Hansson, Klas, et al.
(författare)
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Modeling water flow patterns in flexible pavement
- 2005
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Ingår i: TRB 2005 Annual Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Most road design models do not explicitly account for moisture transport mechanisms in roads even though it is well known that water content plays an important role in the deterioration of roads. The Swedish National Road Administration aims to improve the current situation by supporting the development of models that eventually can provide a better and more complete description of the road/environment system. The water transport model used in this manuscript is one such model. The objective of this study was to investigate the applicability of hydrological theories and methods to the road/environment system. Particular attention was paid to flow patterns inside the road as affected by capillary barriers, and generated by mechanisms of surface runoff followed by infiltration into cracks and the embankment. The effect of rain intensity, precipitated amount, and/or fracture conductivity on the flow patterns was investigated using numerical particle tracking. Changes in rain intensity had a small effect on flow patterns but velocities were higher for larger rain intensities. Both changes in precipitated amount and fracture conductivity controlled the appearance of the flow patterns while capillary barrier effects were limited. The numerical code used proved to be appropriate in describing the relevant processes.
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| 3. |
- Hansson, Klas, et al.
(författare)
-
Modeling water flow patterns in flexible pavements
- 2005
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Ingår i: Transportation Research Record. - Washington D.C. : Transportation Research Board of the National Academies. - 0361-1981 .- 2169-4052. ; 1936, s. 133-141, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- Most road design models do not explicitly account for moisture transport mechanisms in roads, even though it is well known that water content plays an important part in the deterioration of roads. The Swedish National Road Administration aims to improve the current situation by supporting the development of models that eventually can provide a better and more complete description of the road and environment system. The applicability of hydrological theories and methods to the road and environment system was investigated. Particular attention was paid to flow patterns inside the road as affected by capillary barriers and generated by mechanisms of surface runoff, followed by infiltration into cracks, and the embankment. Particle tracking was used to investigate the effect of rain intensity, precipitated amount, or fracture conductivity on the flow patterns. Changes in rain intensity had a small effect on flow patterns, but velocities were higher for larger rain intensities. Both changes in precipitated amount and fracture conductivity controlled the appearance of the flow patterns, but capillary barrier effects were limited. The numerical code used proved to be mostly appropriate in describing the relevant processes.
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| 4. |
- Hansson, Klas, 1972-
(författare)
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Water and Heat Transport in Road Structures : Development of Mechanistic Models
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The coupled transport of water and heat, involving freezing and thawing, in the road structure and its immediate environment is important to consider for optimal design and maintenance of roads and when assessing solute transport, of e.g. de-icing salt, from roads. The objective of this study was to develop mechanistic models, and measurement techniques, suitable to describe and understand water flow and heat flux in road structures exposed to a cold climate. Freezing and thawing was accounted for by implementing new routines in two numerical models (HYDRUS1D/2D). The sensitivity of the model output to changes in parameter values and operational hydrological data was investigated by uncertainty and sensitivity analyses. The effect of rainfall event characteristics and asphalt fractures on the subsurface flow pattern was investigated by scenario modelling. The performance of water content reflectometers (WCR), measuring water content, was evaluated using measurements in two road structure materials. A numerical model was used to simulate WCR sensor response. The freezing/thawing routines were stable and provided results in agreement with laboratory measurements. Frost depth, thawing period, and freezing-induced water redistribution in a model road was greatly affected by groundwater level and type of subgrade. The simulated subsurface flow patterns corresponded well with published field observations. A new method was successful in enabling the application of time domain reflectometer (TDR) calibration equations to WCR output. The observed distortion in sampling volume for one of the road materials could be explained by the WCR sensor numerical model. Soil physical, hydrological, and hydraulic modules proved successful in simulating the coupled transport of water and heat in and on the road structure. It was demonstrated in this thesis that numerical models can improve the interpretation and explanation of measurements. The HYDRUS model was an accurate and pedagogical tool, clearly useful in road design and management.
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| 5. |
- Hansson, Klas, et al.
(författare)
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Water content reflectometer application to construction materials and its relation to time domain reflectometry
- 2006
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 5:1, s. 459-468
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Tidskriftsartikel (refereegranskat)abstract
- Moisture content measurements using time domain reflectometry (TDR) or water content reflectometry (WCR) are basic in many research areas. The goals of this study were to establish a relation between apparent dielectric number and WCR sensor output, to compare TDR and WCR calibration equations for two coarse road construction materials, and to investigate the influence of sampling volume for horizontally installed sensors. Measurements were performed in fluids of known dielectric number and in two incrementally saturated coarse materials. The effect of sampling volume was evaluated using an electrostatic finite-element model. A two-parameter equation was determined relating the apparent dielectric number to Campbell CS616 ( Campbell Scientific, Logan, UT) WCR output (r(2) > 0.99). A simple calibration can adapt the equation to individual CS616, or similar, sensors. For the finer, coarse material, a three-phase mixing model proved best, while for the coarser material no equation adequately described the measurements. Numerical simulations indicated that limited capillary rise, creating a rapid transition from wet to dry close to saturation, was the explanation, warranting caution when interpreting measurements in nearly saturated coarse materials.
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| 6. |
- Hoiom, Veronica, et al.
(författare)
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MC1R variation and melanoma risk in the Swedish population in relation to clinical and pathological parameters
- 2009
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Ingår i: Pigment Cell & Melanoma Research. - 1755-148X .- 1755-1471. ; 22:2, s. 196-204
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Tidskriftsartikel (refereegranskat)abstract
- The genetic background of cutaneous malignant melanoma (CMM) includes both germ line aberrations in high-penetrance genes, like CDKN2A, and allelic variation in low-penetrance genes like the melanocortin-1 receptor gene, MC1R. Red-hair colour associated MC1R alleles (RHC) have been associated with red hair, fair skin and risk of CMM. We investigated MC1R and CDKN2A variation in relation to phenotype, clinical factors and CMM risk in the Swedish population. The study cohort consisted of sporadic primary melanoma patients, familial melanoma patients and a control group. An allele-dose dependent increase in melanoma risk for carriers of variant MC1R alleles (after adjusting for phenotype), with an elevated risk among familial CMM patients, was observed. This elevated risk was found to be significantly associated with an increased frequency of dysplastic nevi (DN) among familial patients compared to sporadic patients. MC1R variation was found to be less frequent among acral lentiginous melanomas (ALM) and dependent on tumour localisation. No association was found between CDKN2A gene variants and general melanoma risk. Two new variants in the POMC gene were identified in red haired individuals without RHC alleles.
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