| 1. |
- Dai, Xu, et al.
(författare)
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An engineering CFD model for fire spread on wood cribs for travelling fires
- 2022
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Ingår i: Advances in Engineering Software. - : Elsevier Ltd. - 0965-9978 .- 1873-5339. ; 173
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Tidskriftsartikel (refereegranskat)abstract
- The temperature heterogeneity due to fire in large open-plan office compartments is closely associated with fire spread behaviour and has been historically limited to experimental investigations using timber cribs. This study explores the ability of Computational Fluid Dynamics (CFD) models, specifically the Fire Dynamics Simulator (FDS), to reproduce the results of full-scale tests involving fire spread over timber cribs for continuous fuel-beds. Mesh schemes are studied, with a fine mesh over the crib and 2 × 2 cells in the wood stick cross-section by default, this being relaxed in the surrounding regions to enhance computational efficiency. The simple pyrolysis model considers the charring phase and moisture. In application to the TRAFIR-Liège LB7 test, this calibrated “stick-by-stick” representation shows a good agreement for interrelated parameters of heat release rate, fire spread, gas phase temperature, and burn-away, a set of agreements which has not been demonstrated in previous studies. Fire spread shows relatively high sensitivities to: heat of combustion, ignition temperature, thermal inertia, radiation fraction, heat release rate per unit area, and the fuel load density. An approximately linear regression was found between the different fire modes and the thermal exposures, with “travelling” (and decaying) fires characterised by heat fluxes associated with the fire plume, while the growing fires were associated with proportionally higher heat fluxes on the horizontal surfaces of the sticks, in conditions where these receive more pre-heating. The trends in the overall HRR are more dependent on the fire spread rates than variations in the stick burning rates. © 2022 The Author(s)
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| 2. |
- Persson, Andreas, et al.
(författare)
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Spatial Influence of Topographical Factors on Yield of Potato (Solanum Tuberosum L.) in Central Sweden
- 2005
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Ingår i: Precision Agriculture. - : Springer Science and Business Media LLC. - 1385-2256 .- 1573-1618. ; 6:4, s. 341-357
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Tidskriftsartikel (refereegranskat)abstract
- This study has evaluated the sampling density for creation of high-resolution digital elevation models (DEMs) for precision agriculture purposes. The relationships between yield and topographical factors were investigated in a study area located in the central Sweden province of Dalarna. The DEM data sampling was carried out with a RTK-GPS system. A dense sampling scheme was employed and data was divided into two for both interpolation and validation. Kriging interpolation was used for DEM generation. From the DEM, topographical parameters were extracted and topographical indices were estimated. The indices were calculated with slope length and its vertical and horizontal components. The drainage area for a point of interest and the relationship of this area to the total drainage area were also estimated. The relationship of yield and the topographical parameters and indices was investigated usingboth circular and spatial statistics. A spatial regression was used to calculate a model for the relationship. Up to 20% of the yield could be explained in the final model for one of the fields.
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| 3. |
- Pilesjö, Petter, et al.
(författare)
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Digital elevation data for estimation of potential wetness in ridged fields - Comparison of two different methods
- 2006
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Ingår i: Agricultural Water Management. - : Elsevier BV. - 1873-2283 .- 0378-3774. ; 79:3, s. 225-247
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to develop, adjust and test two different methods for the estimation of drainage area and potential wetness in ridged fields. The methods were applied to a gridded digital elevation model (DEM) of a potato field in central Sweden. Elevation data were registered by a global positioning system (GPS) receiver. A high-precision real time kinematic (RTK) system was used to record positions both horizontally and vertically. The study can be divided into four parts. First, we present the two different methods of estimating the drainage area and potential wetness. The potential wetness index used is 1n(a/tan beta), which is directly related to drainage area. Second, we constructed a high-accuracy DEM based on GPS-measured elevation points. We then modelled the GPS errors and the sampling errors in the DEM. Finally, we used a Monte Carlo simulation to test differences between the two methods of estimating the drainage area and potential wetness. The wetness index for the new method, which takes ridges into account, differs both statistically and visually from the first method, which does not incorporate ridges. The new method, incorporating ridges, is thus strongly recommended for hydrological modelling in ridged agricultural fields. (c) 2005 Elsevier B.V. All rights reserved.
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| 4. |
- Pilesjö, Petter, et al.
(författare)
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Topographical data for delineation of agricultural management zones.
- 2005
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Ingår i: Proceedings of the Fifth European Conference on Precision Agriculture. ; , s. 819-826, s. 819-826
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to delineate management zones by using topographical data, and to investigate how these management zones relate to soil parameters and yield. Elevation, as well as soil and yield data, were sampled in the field. Digital elevation models have been created, and the topographical parameters of slope, aspect and drainage area, estimated. Management zones have been delineated by the use of threshold values and filtering. Significant differences between the zones with respect to organic matter, clay content, phosphorus, pH, potassium, magnesium and yield have been found. The results indicate that topographical data can be used delineate agricultural management zones in central Sweden.
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| 5. |
- Wiens, R. C., et al.
(författare)
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Compositionally and density stratified igneous terrain in Jezero crater, Mars
- 2022
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Ingår i: Science Advances. - : NLM (Medline). - 2375-2548. ; 8:34
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Tidskriftsartikel (refereegranskat)abstract
- Before Perseverance, Jezero crater's floor was variably hypothesized to have a lacustrine, lava, volcanic airfall, or aeolian origin. SuperCam observations in the first 286 Mars days on Mars revealed a volcanic and intrusive terrain with compositional and density stratification. The dominant lithology along the traverse is basaltic, with plagioclase enrichment in stratigraphically higher locations. Stratigraphically lower, layered rocks are richer in normative pyroxene. The lowest observed unit has the highest inferred density and is olivine-rich with coarse (1.5 millimeters) euhedral, relatively unweathered grains, suggesting a cumulate origin. This is the first martian cumulate and shows similarities to martian meteorites, which also express olivine disequilibrium. Alteration materials including carbonates, sulfates, perchlorates, hydrated silicates, and iron oxides are pervasive but low in abundance, suggesting relatively brief lacustrine conditions. Orbital observations link the Jezero floor lithology to the broader Nili-Syrtis region, suggesting that density-driven compositional stratification is a regional characteristic.
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