| 1. |
- Al-Chalabi, Hussan S., et al.
(författare)
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Downtime analysis of drilling machines and suggestions for improvements
- 2014
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Ingår i: Journal of Quality in Maintenance Engineering. - 1355-2511 .- 1758-7832. ; 20:4, s. 306-332
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Tidskriftsartikel (refereegranskat)abstract
- Purpose– The purpose of this paper is to analyse and compare the downtime of four drilling machines used in two underground mines in Sweden. The downtime of these machines was compared to show what problems affect downtime and which strategies should be applied to reduce it.Design/methodology/approach– The study collects failure data from a two-year period for four drilling machines and performs reliability analysis. It also performs downtime analysis utilising a log-log diagram with a confidence interval.Findings– There are notable differences in the downtime of most of the studied components for all machines. The hoses and feeder have relatively high downtime. Depending on their downtime, the significant components can be ranked in three groups. The downtime of the studied components is due to reliability problems. The study suggests the need to improve the reliability of critical components to reduce the downtime of drilling machines.Originality/value– The method of analysing the downtime, identifying dominant factors and the interval estimation for the downtime, has never been studied on drilling machines. The research proposed in this paper provides a general method to link downtime analysis with potential component improvement. To increase the statistical accuracy; four case studies was performed in two different mines with completely different working environment and ore properties. Using the above method showed which components need to be improved and suggestions for improvement was proposed and will be implemented accordingly.
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| 2. |
- Grelle, A., et al.
(författare)
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Evaporation components of a boreal forest : variations during the growing season
- 1997
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Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 197:1-4, s. 70-87
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Tidskriftsartikel (refereegranskat)abstract
- To improve the understanding of interactions between the boreal forest and the climate system as a key issue for global climate change, the water budget of a mixed pine and spruce forest in central Sweden was estimated by measurements of the water flux components and the total evaporation flux during the period 16 May-31 October 1995. Total evaporation was measured using eddy correlation and the components were obtained using measurements of precipitation, throughfall, tree transpiration, and forest floor evaporation. On a daily basis, tree transpiration was the dominant evaporation component during the vegetation period. However, it could be efficiently blocked by a wet canopy associated with large interception evaporation. The accumulated total evaporation was 399 mm, transpiration was 243 mm, forest floor evaporation was 56 mm and interception evaporation was 74 mm. The accumulated sum of interception, transpiration, and floor evaporation was 51 mm larger than the actual measured total evaporation. This difference was mainly attributed to the fact that transpiration was measured in a rather dense 50-year-old stand while total evaporation represented the average conditions of older, roughly 100-year-old stands. To compare eddy-correlation measurements with small-scale measurements of evaporation components, a source area analysis was made to select the flux data that give the best representation of the investigated stand. Especially under stable atmospheric conditions the requirements for surface homogeneity were very high and extreme care had to be taken to be aware of the flux source areas. Canopy water storage was determined by two methods: by the water balance of the canopy, which gave a result of 3.3 mm; and by the so-called minimum method based on plots of throughfall versus precipitation, which gave a much lower value of 1.5 mm. Seasonal interception evaporation constituted 30% of the precipitation.
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| 3. |
- Kløve, Bjørn, et al.
(författare)
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Groundwater surface water interaction in GDE
- 2012
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Rapport (populärvet., debatt m.m.)abstract
- This report reviews and discussed the interaction of groundwaterin GDEs. The report presents and integrates past and new results.Different methods used to measure groundwater interaction withecosystems are presented. Various GENESIS case studies acrossEurope to demonstrate the variable and complex role ofgroundwater in GDEs. The basis for developing conceptual for GDEsis presented. Various methods to model GDEs are discussed.
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| 4. |
- Lundberg, Angela, et al.
(författare)
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Evaporation of intercepted snow : analysis of governing factors
- 1994
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 30:9, s. 2587-2598
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Tidskriftsartikel (refereegranskat)abstract
- Insufficient understanding of winter hydrology conditions still hampers progress in predicting springtime discharge. The least known term in the winter water balance is evaporation, particularly of intercepted snow. Recent studies have shown that the evaporation from intercepted snow can be important. This paper elaborates factors governing evaporation of intercepted snow. Measurements with a cut tree-weighing device combined with a method to measure throughfall and drip gave a maximum evaporation rate of 0.3 +/- 0.06 mm/h or 3.3 +/- 0.06 mm/24 hours from a 6-m-high spruce. Calculations of evaporation with a combination equation and different ways to calculate the aerodynamic resistance and the evaporation from a snow-intercepted canopy during melt and sleet events showed that the most important factors for calculating the evaporation were the relative humidity, the aerodynamic resistance, the wind speed, and the intercepted mass. Less important factors were the energy to melt the intercepted snow, the method for calculating reduction in evaporation caused by a partly snow-covered canopy, accuracy in measurement of wind speed, air temperature, and net radiation.
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| 5. |
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| 6. |
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| 7. |
- Lundberg, Magnus, et al.
(författare)
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Spatial modeling of occlusion patterns applied to the detection of surface-laid mines
- 2004
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Ingår i: Detection and Remediation Technologies for Mines and Minelike Targets IX. - : SPIE. ; , s. 799-810
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Konferensbidrag (refereegranskat)abstract
- Images recorded in ground areas potentially containing surface laid land mines are considered. The first hypothesis is that the image is of clutter (grass) only, while the alternative is that the image contains a partially occluded (covered) land mine in addition to the clutter. In such a scenario, the occlusion pattern is unknown and has to be treated as a nuisance parameter. In a previous paper it was shown that deterministic treatment of the unknown occlusion pattern, in companion with the applied model, renders a substantial increase in detector performance as compared to employment of the traditional additive model. However, a deterministic assumption ignores possible correlation and additional gains could be possible by taking the spatial properties into account. In order to incorporate knowledge regarding the occlusion, the spatial distribution is characterized in terms of an underlying Markov Random Field (MRF) model. A major concern with MRF models is their complexity. Therefore, in addition to this, a less computationally demanding technique to accommodate the occlusion behavior is also proposed. The main purpose of this paper is to investigate if significant gains are possible by acknowledging the spatial dependence. Evaluation on data using real occluded targets however indicates that the gain seem to be marginal.
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| 8. |
- Lundin, Lars-Christer, et al.
(författare)
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Continuous long-term measurements of soil-plant-atmosphere variables at a forest site
- 1999
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Ingår i: Agricultural and Forest Meteorology. - 0168-1923 .- 1873-2240. ; 98-99, s. 53-73
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Tidskriftsartikel (refereegranskat)abstract
- It is a major challenge in modem science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetation-atmosphere-transfer (SVAT) system. Continuous, long-term data are needed in order to correctly quantify balances of water, energy and CO2 in this system and to correctly model it. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from a forested site under almost all environmental conditions. The Central Tower Site (CTS) system was set up in 1993-1994 in a 25 m high boreal forest growing on a highly heterogeneous till soil with a high content of stones and blocks. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of temperature, water vapour, CO2, short-and long-wave radiation, heat storage in soil and trees, sap-dow and a variety of ecophysiological properties, soil-water contents and tensions, and groundwater levels, rainfall and throughfall. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation include e.g., budgets for energy, water and CO2, information on important but rarely occurring events such as evaporation from snow-covered canopies, and reactions of the forest to extreme drought. The carbon budget shows that the forest may be a sink of carbon although it is still growing. The completeness of the data has made it possible to test the internal consistency of SVAT models. The pioneering set-up at the CTS has been adopted by a large number of SVAT-monitoring sites around the world. Questions concerning tower maintenance, long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual research-funding agencies. The full value of data generated by the CTS system can best be appreciated after a decade or more of continuous operation. Main uses of the data would be to evaluate how SVAT models handle the natural variability of climate conditions, quantification of water. carbon and energy budgets during various weather conditions, rind development of new parameterisation schemes in global and regional climate models.
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| 9. |
- Mensah, Rhoda Afriyie, et al.
(författare)
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The effect of infill density on the fire properties of polylactic acid 3D printed parts: A short communication
- 2022
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Ingår i: Polymer testing. - : Elsevier. - 0142-9418 .- 1873-2348. ; 111
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Tidskriftsartikel (refereegranskat)abstract
- The use of 3D printing technology for manufacturing construction materials is gaining popularity, however, only a few studies have reported the fire behavior of such parts. In this research, the fire properties of 3D printed polylactide acid (PLA) parts with varying infill densities along with the tensile properties were analysed. The results from the fire tests showed that increasing the infill density increased the fuel load, which sustained combustion. Hence, the peak heat release rate and total heat release increased with an increment in infill density percentage. It was also observed that the increasing infill density had no effect on the flammability rating of the parts due to the constant shell thickness used for all the parts. In addition, the tensile strength and ductility of the parts increased with density as a porous part is more susceptible to failure than a solid homogeneous part.
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| 10. |
- Peterson, Jim A., et al.
(författare)
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Landforms from the Quaternary glaciation of Papua New Guinea: an overview of ice extent during the Last Glacial Maximum
- 2004
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Ingår i: Developments in Quaternary Science. - 1571-0866. ; 2:Part C, s. 313-319
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Tidskriftsartikel (refereegranskat)abstract
- Documentation of glacial landforms of Papua New Guinea is dominated by accounts of landscapes that are supported by chronologies assembled during biostratigraphical studies of peat cores showing that glacial landscape reconstruction will refer to the Last Glacial Stage. The steep terrain ensured that the scale of the air photographs used in these studies would vary all over the stereographic models formed for landscape interpretation. Here, in the form of annotated ortho-rectified (i.e. scale-consistent) satellite images, a summary of the maps found in the literature is presented, together with the results of simple spatial query designed to refine the accuracy of previously-estimated Last Glacial Maximum (LGM) ice extents
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