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- Bogren, Jörgen, 1961, et al.
(författare)
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Klimat och väder
- 2008
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Bok (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Hu, Yumei, et al.
(författare)
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Modeling Road Surface Temperature from Air Temperature and Geographical Parameters-Implication for the Application of Floating Car Data in a Road Weather Forecast Model
- 2019
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Ingår i: Journal of Applied Meteorology and Climatology. - : American Meteorological Society. - 1558-8424 .- 1558-8432. ; 58:5, s. 1023-1038
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Tidskriftsartikel (refereegranskat)abstract
- Precise forecasts of road surface temperature (RST) and road conditions allow winter roads to be maintained efficiently. The upcoming "big data" application known as "floating car data" (FCD) provides the opportunity to improve road weather forecasts with measurements of air temperature T-a from in-car sensors. The research thus far with regard to thermal mapping has mainly focused on clear and calm nights, which occur rarely and during low traffic intensity. It is expected that more than 99% of the FCD will be collected during conditions other than clear and calm nights. Utilizing 32 runs of thermal mapping and controlled T-a surveys carried out on mostly busy roads over one winter season, it was possible to simulate the use of T-a and geographical parameters to reflect the variation of RST. The results show that the examined route had several repeatable thermal fingerprints during times of relatively high traffic intensity and with different weather patterns. The measurement time, real-time weather pattern, and previous weather patterns influenced the spatial pattern of thermal fingerprints. The influence of urban density and altitude on RST can be partly seen in their relationship with T-a, whereas the influence of shading and sky-view factor was only seen for RST. The regression models with T-a included explained up to 82% of the RST distribution and outperformed models that are based only on the geographical parameters by as much as 30%. The performance of the models denotes the possible utility of T-a from FCD, but further investigation is needed before moving from controlled T-a measurements to T-a from FCD.
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| 11. |
- Hu, Yumei, et al.
(författare)
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The use of screening effects in modelling route-based daytime road surface temperature
- 2016
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 125:1, s. 303-319
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Tidskriftsartikel (refereegranskat)abstract
- © 2015 The Author(s) Winter road maintenance is essential for road safety. Accurate predictions of the road surface temperature (RST) and conditions can enhance the efficiency of winter road maintenance. Screening effects, which encompass shading effects and the influence of the sky-view factor (ψs), influence RST distributions because they affect road surface radiation fluxes. In this work, light detection and ranging (Lidar) data are used to derive shadow patterns and ψs values, and the resulting shadow patterns are used to model route-based RST distributions along two stretches of road in Sweden. The shading patterns and road surface radiation fluxes calculated from the Lidar data generally agreed well with measured RST values. Variation in land use types and the angle between the road direction and solar azimuth may introduce uncertainties, and accounting for these factors may improve the results obtained in certain cases. A simple shading model that only accounts for the direct radiation at the instant of measurement is often sufficient to provide reasonably accurate RST estimates. However, in certain cases, such as those involving measurements close to sunset, it is important to consider the radiation accumulated over several hours. The inclusion of ψs improves the model performance even more in such cases. Overall, RST models based on the accumulated direct shortwave radiation offered an optimal balance of simplicity and accuracy. General radiation models were built for country road and highway environments, explaining up to 70 and 65 %, respectively, of the observed variation in RST along the corresponding stretches of road.
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| 12. |
- Hu, Yumei, et al.
(författare)
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Winter hoar frost conditions on Swedish roads in a warming climate
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:12, s. 4345-4354
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Tidskriftsartikel (refereegranskat)abstract
- As one of the most common reasons for slippery roads in wintertime, hoar frost can reduce surface friction and affect traffic safety. The risk of winter road hoar frost is subjected to changes in the warming climate. A better understanding of these changes could lead to improved forecasting of hoar frost risk and provide information to policymakers in making climate adaptation strategies. In this work, the decadal variation in winter road hoar frost risk between 2000 and 2016 in Sweden was examined by using in situ observations from 244 stations in the Swedish Road Weather Information System. Results show that hoar frost risks have decreased in the south of Sweden (south of 59 degrees N), whilst increasing in central Sweden (approximately 59 degrees-65 degrees N). Hoar frost risk tends to increase (decrease) in regions where there is a relatively high (low) mean number of hoar frost risk days. Further analysis indicates that the strengthened winter North Atlantic Oscillation (NAO) over the last few decades, which resulted in warmer and wetter winters in Sweden, is the main cause of the changes. During strong positive NAO winters, the frequency of blocking anticyclones centred to the south-west of Sweden significantly decreased and led to more warm and moist air from south-west being transported to Sweden. The reduction in hoar frost risk in the southern part of Sweden is mainly due to an increase in road surface temperature, while the increasing hoar frost risk in central Sweden is dominated by the increase in relative humidity, which favours the occurrence of hoar frost.
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| 13. |
- Nordin, Lina, 1981, et al.
(författare)
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Road Surface Wetness Variations: Measurements and Effects for Winter Road Maintenance
- 2013
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Ingår i: Journal of Transportation Engineering. - : American Society of Civil Engineers (ASCE). - 0733-947X .- 1943-5436. ; 139:8, s. 787-796
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Tidskriftsartikel (refereegranskat)abstract
- Road wetness is a critical parameter when it comes to preventing road slipperiness. It has so far been difficult to measure, but new measurement techniques on the market make it useful to investigate the savings opportunities within road maintenance operations. The present study tests a new sensor mounted on a road maintenance vehicle run in a maintenance district in central Sweden. The sensor that measures road surface water depth is connected to a global positioning system (GPS) system and a global system for mobile communications (GSM) phone modem. Potential savings are calculated based on the measured road surface water depth and on the amount of applied salt needed to lower the freezing point to a certain degree. The results indicate variations in water depth along the measured roads, which implies that the salt concentrations along the roads could also vary. Though the variations were smaller along the tested highway, the calculated savings could still be up to 22%. Despite the many assumptions made in the calculations, considerable savings could potentially be realized by applying such wetness measurements. (C) 2013 American Society of Civil Engineers.
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- Riehm, Mats, et al.
(författare)
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Ice formation detection on road surfaces using infrared thermometry
- 2012
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 83-84, s. 71-76
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Tidskriftsartikel (refereegranskat)abstract
- Ice formation on roads causes hazardous conditions due to reduction of road surface friction. Forecasting, detecting and preventing ice formation are therefore of high importance for winter road maintenance personnel. Advanced sensors for detecting road ice exist, but there is a demand for more cost-effective technologies. A method for detection of road surface ice formation based on remote temperature measurements with infrared thermometers is presented. Freezing events were detected based on the temperature dynamics that result from the exothermic reaction as water freezes. Experimental measurements in a climate chamber and in field conditions showed that ice formation often causes a distinct temperature pattern, which could easily be identified and distinguished from other temperature fluctuations. The method is promising as a cost-effective technique suitable for several applications in cold regions where detection of ice formation is important. (C) 2012 Elsevier B.V. All rights reserved.
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| 17. |
- Önnheim, Magnus, 1985, et al.
(författare)
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Ergodic, primal convergence in dual subgradient schemes for convex programming, II: the case of inconsistent primal problems
- 2017
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Ingår i: Mathematical programming. - : Springer Science and Business Media LLC. - 0025-5610 .- 1436-4646. ; 163:1, s. 57-84
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Tidskriftsartikel (refereegranskat)abstract
- Consider the utilization of a Lagrangian dual method which is convergent for consistent optimization problems. When it is used to solve an infeasible optimization problem, its inconsistency will then manifest itself through the divergence of the sequence of dual iterates. Will then the sequence of primal subproblem solutions still yield relevant information regarding the primal program? We answer this question in the affirmative for a convex program and an associated subgradient algorithm for its Lagrange dual. We show that the primal–dual pair of programs corresponding to an associated homogeneous dual function is in turn associated with a saddle-point problem, in which—in the inconsistent case—the primal part amounts to finding a solution in the primal space such that the Euclidean norm of the infeasibility in the relaxed constraints is minimized; the dual part amounts to identifying a feasible steepest ascent direction for the Lagrangian dual function. We present convergence results for a conditional ε-subgradient optimization algorithm applied to the Lagrangian dual problem, and the construction of an ergodic sequence of primal subproblem solutions; this composite algorithm yields convergence of the primal–dual sequence to the set of saddle-points of the associated homogeneous Lagrangian function; for linear programs, convergence to the subset in which the primal objective is at minimum is also achieved.
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