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1.
  • Murekatete, Rachel Mundeli, 1981- (författare)
  • Sensitivity, Variation, and Application of Least-Cost Path Models in Landscape Connectivity Analysis and Corridor Planning
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In recent decades, Rwanda has been affected by the loss and fragmentation of natural habitats for native species of animals and plants. As a consequence, landscape connectivity—i.e., the degree to which a landscape facilitates or impedes the movement of organisms between resource patches—has considerably weakened or is even completely lost, causing detrimental effects on biodiversity, notably the reduction of populations of key native species. In order to counter this problem, one potential solution currently being explored by local planners in Rwanda consists of establishing conservation corridors for organisms to move safely between their habitat remnants. Specifically, this thesis was inspired by a project initiated by the Dian Fossey Gorilla Fund International, a conservation non-governmental organization (NGO) based in Rwanda, which consists of establishing a conservation corridor for pollinators.For their capabilities of storing, processing, and visualizing landscape data, geographic information systems (GIS) have been increasingly popular among conservation biologists and practitioners. Of particular relevance to connectivity analysis and corridor planning is the least-cost path model. A typical use of this model is such that one first estimates the cost for a certain action (e.g., movement by an organism or acquisition by a government) at each location of a given landscape and represents the results in the form of a raster surface, and then measures the degrees of connectivity between patches of interest in terms of effective distances, which are equated with least-cost path distances over the raster cost surface. While the least-cost path model is easy to use and available in virtually any commercial raster-based GIS, we observe that users of it often overlook some important assumptions, the violation of which might greatly affect the validity of the model’s outcome.The goal of this thesis is to provide a scientific contribution to landscape connectivity analysis and conservation corridor planning by 1) investigating the potential misuse or abuse of the conventional least-cost path model when sufficient information is not available on the underlying cost surface, 2) proposing an alternative model under such a circumstance and 3) demonstrating its relevance to conservation practice. More specifically, for the model to work, it is explicitly or implicitly assumed that, the optimality of a path is evaluated as the sum of the cost-weighted lengths of all its segments—cost-weighted, i.e., multiplied by their underlying cost values. The validity of this assumption must be questioned, however, if cost values are measured on a scale—e.g., an ordinal scale of measurement in Stevens’s typology—that does not permit arithmetic operations. In a typical practice of landscape connectivity analysis and corridor planning, the raster cost surface is created by transforming one or more sets of values (e.g., land cover type, land ownership, and elevation) attributed to cells into another set of such values (representing cost) through a function reflecting one or more criteria. A question arises: how certain can one be about the correctness of such a cost estimation function?There are at least four issues in the application of the least-cost path model to landscape connectivity analysis and corridor planning under uncertainty. First, while it is generally anticipated that different cost estimation functions lead to different least-cost paths (hence to different effective distances or different corridor locations), little is known on how such differences arise (or do not arise). Second, while it is generally recognized that the location and length of a least-cost path are both sensitive to the spatial resolution of the raster cost surface, little is known if they are always sensitive in the same way and to the same degree and if not, what makes them more (or less) sensitive. Third, when it is difficult to establish a fully connected corridor between target habitat areas (e.g., because of surrounding anthropogenic activities), the least-cost path (which is by definition fully connected) may not be useful at least in its original form. Lastly, even if the conventional least-cost path model may have inconsistent results in theory, it may well be continued to be used in practice, unless there is a sound alternative to it.The issues raised above are addressed through four studies corresponding to four respective papers which are appended to this thesis. While the first three studies use artificial landscape data generated by computers with varying spatial and non-spatial characteristics, the fourth study uses data on a real landscape. The first study (Paper 1) evaluates how the locations and lengths of least-cost paths (the latter of which are referred to as least-cost distances) vary with change in cost estimation parameters. This is done through a series of computational experiments, in which each of the artificial landscapes is converted into different cost surfaces by systematically varying parameters of a cost-estimation function, on which least-cost paths are generated. The locations and lengths of those paths are statistically analyzed to find sources of their variation. The second study (Paper 2) investigates how the least-cost distance is affected by the spatial resolution of the corresponding cost surface. This is also done through a series of computational experiments, in which each of the artificial landscapes is converted into a cost surface, which is, in turn, converted into different cost surfaces (different, i.e., only in their spatial resolutions) by systematically aggregating grid cells. Then, the statistical behavior of the ratio of the least-cost distance measured on a lower-resolution cost surface to that measured on a higher-resolution cost surface is analyzed. The third study (Paper 3) proposes the mini-max path model as an alternative to the least-cost path model. Unlike the conventional model (in which the optimality of a path is based on the sum of its length multiplied by the underlying cost values), the alternative model determines the optimality of a path using the length of a segment(s) of the path that intersects the cells having the maximum cost value (with a special tie-breaking rule). The performances of the two models are tested in one of the following two assumptions at a time: the cost values are measured on an ordinal scale or on a ratio scale. The fourth study (Paper 4) applies the model proposed in the third study to an ongoing conservation project of the Dian Fossey Gorilla Fund International that plans to design a ‘stepping-stone’ corridor—which is not fully connected but takes the form of a sequence of fragmented forest patches—between two core habitat areas of pollinator birds between two protected areas in Rwanda. The project does not have complete information on the study area and the target species and thus the project staff can only rank land cover types in terms of their suitability/cost for being part of the corridor. The utility of the model is tested with different assumptions on the behavior of the birds (e.g., minimum stepping stone size) as well as on the cost associated with the implementation of the corridor (e.g., cost for planting shrubs along the corridor to encourage the birds to use it).The first study finds that the same pair of terminal cells may well be connected by different least-cost paths on different cost surfaces though derived from the same landscape data. The variation among those paths is highly sensitive to the forms of spatial and non-spatial distributions of landscape elements (which cannot be controlled by users of the least-cost path model) as well as by those of cost values derived from them (which may be, at least indirectly, controlled by users of the model). The second study finds that least-cost distances measured on lower-resolution cost surfaces are generally highly correlated with—and useful predictors of—effective distances measured on higher-resolution cost surfaces. This relationship tends to be weakened when linear barriers to connectivity (e.g., roads and rivers) exist, but strengthened as distances increase and/or when linear barriers (if any) are detected by other presumably more accessible and affordable sources such as vector line data. The third study confirms the effectiveness of the conventional least-cost path model on ratio-scaled cost surfaces but finds that the alternative mini-max path model is mathematically sounder if the cost values are measured on an ordinal scale and practically useful if the problem is concerned not with the minimization of cost but with the maximization of some desirable condition such as suitability. The fourth study demonstrates the utility of the mini-max path model by effectively casting the stepping stone corridor problem as a special case of it. The model allows for a rapid first delineation of candidate routes for stepping stone corridors and facilitates the early exploratory stages of conservation projects.Major implications of this thesis to the research and practice in landscape connectivity analysis and conservation corridor planning with raster-based GIS are summarized as follows.When sufficient information is available for quantification of cost values, the conventional least-cost path model is a reasonable approach to use.However, it is worth trying or at least acknowledging alternatives that do not rely on the quantitative-cost assumption if the value of each cell only indicates the ordinal category of cost of intersecting that cell. Note in particular that information used for cost estimation in practice (e.g., expert opinions or public surveys) are often of subjective and qualitative nature.The highest-resolution data may not always be most effective—much less, most cost-effective—for the task being undertaken. The choice of spatial resolution of th
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2.
  • Nickman, Alireza (författare)
  • Road disasters? Modeling and assessment of Swedish roads within crucial climate conditions
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • An efficient maintenance of roads to ensure high accessibility and durability of the transport capacity requires an understanding of how the hydrological response depends on both the road and the landscape characteristics. New methods and data were used to identify and explain interaction between roads and surrounding environment and their influence on hydrologic responses both in watershed scale and road-section scale. In the watershed scale, flood hazard probability was made with reference to the most influential physical catchment descriptors and road characteristics. Additionally, a physical based model was used to estimate the effect of road topography on the hydrological responses of 20 watersheds to storms with different intensities. A simple method was developed and discussed to address flood risk probability in the road-stream crossings concerning the correlation between the quantities of the physical catchment descriptors and occurrence/absence of flooding. The most influential factors in describing the probability of flooding along the roads were topographic wetness index, soil properties, road density and channel slopes. A detailed study of simulated flow duration curves showed differences between the 20 watersheds for three different storms based on topography with and without roads. An increase in peak flow and reduced time to pick occurred with existence of roads and increased storm intensity.In the road-section scale, an uncertainty-based simulation approach was used to identify the most influencing processes in controlling the dynamics of the groundwater level. A model (CoupModel) set up with four different geological stratifications was made to model two positions in a slope upstream of a road with drainage pipes and ditches. Results from the simulations indicate the significance of precipitation rate, road drainage and position in hillslope, and soil properties and stratifications in controlling groundwater levels. The same model was also applied to simulate soil moisture and temperature dynamics in two road sections by using groundwater and climate data. Porous media properties were obtained as statistical distribution function that provided the best performance of moisture and temperature dynamic in the road layers and underlying soil.
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3.
  • Acuña, José, 1982- (författare)
  • Distributed thermal response tests : New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes
  • 2013
  • Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
    • U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO2 as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO2 may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N2, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.
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5.
  • Nickman, Alireza (författare)
  • Modeling moisture and temperature dynamics in road structure during winter conditions
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Excess moisture significantly impact durability and sustainability of road components especially in cold regions. To improve understanding of moisture dynamics in roads with drainage system, hourly measured moisture content, soil temperature and groundwater level data during a 3-year period from a test site in Växjö, Sothern Sweden were utilized. Seasonal and manipulated changes in the groundwater level and moisture dynamics were observed that describe extreme conditions providing extra moisture to the upper layers of road. CoupModel was used to estimate mass and heat balance in four depths of two spots of the road section. Good performances of the model were achieved in calculation of the soil moisture in different depths. Soil water retention curve parameters were sensitive to constrain criteria which demonstrate importance of soil texture in controlling moisture dynamics. Model could properly capture temperature dynamic during winter time but simulated excess evaporation from soil layers reduced performance of model in the estimation of temperature during summer The combined monitoring and modelling of physical conditions in the road structure will be highly relevant to help decision makers and road engineers to avoid moisture in road structures and to also identify crucial events from meteorological data.
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6.
  • Nickman, Alireza (författare)
  • Uncertainty based approach to simulate groundwater levels in a hillslope upstream of a road
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Knowledge of the processes governing groundwater dynamics in the areas close to roads is important for sustainable road infrastructure in the face of a changing climate. This study established an uncertainty based approach to simulate groundwater oscillations in a hillslope upstream of a road by using a process based model. Four different soil configurations were analyzed in CoupModel to simulate groundwater dynamics in presence of a road drainage system by implementation of meteorological data as driving factors. An approach similar to GLUE method was applied to analyze the statistical performance of the simulated groundwater level versus high resolution measured groundwater level dynamics. Results of the simulations indicate deviations in simulated results due to different soil stratifications. Uncertainties resulted from the lack of precise information about the geological structure of the site are important contributors to deviated simulation results. Different scenarios showed different model performances in which a simpler soil profile describes better the groundwater dynamics when it is closer to the road drainage system while a more complicated soil profile better describes groundwater dynamics in undisturbed soils. Correlation between hydraulic conductivity of each layer and the model performance was discussed. The results also indicate significance of variables such as physical drainage characteristics of the road in governing level of saturations also the position of the road structure in a hillslope. Texture (hydraulic conductivity) of the soil layers that fluctuation of groundwater occurs in those layers and types of modifications that have been done due to road construction are important driving factors. These factors are suggested as suitable indicators for designing an early warning system based on physical characteristics of a road site.
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7.
  • Nickman, Alireza (författare)
  • Uncertainty based approach to simulate groundwater levels in a hillslope upstream of a road
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Knowledge of the processes governing groundwater dynamics in the areas close to roads is important for sustainable road infrastructure in the face of a changing climate. This study established an uncertainty based approach to simulate groundwater oscillations in a hillslope upstream of a road by using a process based model. Four different soil configurations were analyzed in CoupModel to simulate groundwater dynamics in presence of a road drainage system by implementation of meteorological data as driving factors. An approach similar to GLUE method was applied to analyze the statistical performance of the simulated groundwater level versus high resolution measured groundwater level dynamics. Results of the simulations indicate deviations in simulated results due to different soil stratifications. Uncertainties resulted from the lack of precise information about the geological structure of the site are important contributors to deviated simulation results. Different scenarios showed different model performances in which a simpler soil profile describes better the groundwater dynamics when it is closer to the road drainage system while a more complicated soil profile better describes groundwater dynamics in undisturbed soils. Correlation between hydraulic conductivity of each layer and the model performance was discussed. The results also indicate significance of variables such as physical drainage characteristics of the road in governing level of saturations also the position of the road structure in a hillslope. Texture (hydraulic conductivity) of the soil layers that fluctuation of groundwater occurs in those layers and types of modifications that have been done due to road construction are important driving factors. These factors are suggested as suitable indicators for designing an early warning system based on physical characteristics of a road site.
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8.
  • Paul, Seema, et al. (författare)
  • Hydrodynamic wind induce model influencing inner Murchison Bay flow circulation
  • 2019
  • Konferensbidrag (populärvet., debatt m.m.)abstract
    • Wind stress is exerted by the wind on the lake surface may be important for lake flow analysis and the Inner Murchison Bay is strongly influenced by urban pollution from Uganda Capital Kampala and bay is highly eutrophic cause of back and forth nutrient movement. The rapid population growth, growing commercial activities and industrialization in Kampala, Uganda coupled with inadequate provision of waste management services which have led to increase volume of urban waste entering the North-Western part of Lake Victoria. The Murchison Bay (MB) is in the Northern part of Lake Victoria in Uganda which has for decades received a daily wastewater load of 0.2 % of its volume from Kampala City of Uganda, through the Nakivubo channel [1]. Kampala City people habitants 1.7 million. The uncontrolled solid waste seen along roadsides and storm water drains enter the Nakivubo Channel. The Nakivubo channel is ended in a papyrus swamp in Uganda that retained a large portion of water pollution before it reached in the inner Murchison Bay [2]. In addition, the channel is widened in 2001-2003 to improve the city drainage which has increased the potential loading of nutrients to the bay. The partially treated effluent from treatment plants are mixed with the water in channel and it contribute a high significant pollution load, and is the most polluted system by organic matter in solid waste and wastewater discharged from slums and un-sewered areas, Luzira Prison and small & large scale industries [3]. There are urgent need to resolve the problem. Nowadays, the inner Murchison Bay (MB) water quality are destroying by several complex mixture processes, Ex.: pollution and nutrients loading, river inflows, un-sewered water, wetland management and flora and fauna populations. Present study is focusing on inner Murchison Bay (MB) water pollution behaviour by using wind speed hydrodynamic model. The model processes are determining the fate and transport of pollutant that are vertically mixing (wind force) and horizontal flow (advection-dispersion) analysis. Vertically transport of wind flow that is forcing on the lake water surface are analysed by the vertically integrated Shallow Water Equation model. Horizontally transport of pollution of water and its flow and speed are analyzing by advectiondispersion and diffusion model. Result shows that the horizontal mixing is continuing with lake nutrients and the vertically wind flow from MB into lake is also determine the mixing of lake water which is not much affecting the lake nutrients. 
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9.
  • Paul, Seema (författare)
  • Lake Hydrodynamics and Pollution Transport under Climate Change : The Case of Lake Victoria
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • A very small part of the total earth’s water is freshwater (only 2.5 %). Unfortunately, due to climate change and pervasive manmade activities, surface freshwater quality in many places of the world has become degraded. This is manifested in the Rift Valley lakes, a series of lakes in Eastern Africa that runs from Ethiopia in the north to Malawi in the south. Water quality degradation in the Rift Valley lakes is driven by various factors, including water quantity and scarcity, pollution and contamination, nutrients loading, and general water use by industry and society. In particular, Lake Victoria, the world’s second-largest freshwater body and the largest tropical lake, has seriously polluted near lakeshore areas, which is a great regional development problem causing misfortune for millions of people.This dissertation contributes new insights into lake hydrodynamic processes and pollution transport in shallow lakes through developing more accurate models to understand the complex processes of water quality degradation. Based on empirical data this thesis developed systematic methods to consider lake bathymetry, lake flow, water level verification, water balance, hydro-climatological processes, transport and dispersion of pollutants and nutrient particles. The data-driven hydrological model of Lake Victoria that is developed in the thesis considers hydro-meteorological and climatological data, river discharges and outflow, wind speed and direction, atmospheric deposition, nutrient loading, concentration of pollutants and nutrients, and remote sensing satellite data. The thesis illustrates the power of numerical and hydrodynamic methods that uses one- and two-dimensional mathematical equations (1D and 2D) to model the three-dimensional (3D) behaviour of shallow lakes over time. The results indicate that the lake hydrodynamics of Lake Victoria are heavily influenced by lake bathymetry and regional weather patterns and are thus connected to increasing climate variation. The hydro-meteorological processes, verified by empirical data on precipitation, lake flow and lake water levels, show that extreme weather events are responsible for changing the characteristics of lake water balance, changing seasonal variations, and exhibiting strong correlations among water level and hydro-meteorological data. The model of the movement of pollutants and nutrient particles shows how pollutants and nutrients travel within Lake Victoria and where they concentrate in the lake and its sediments. The wind hydrodynamic modelling shows that the wind, along with hydrodynamic stability, plays an important role in pollution flow patterns and that pollutants can be transported from shallow parts, when they leave rivers and shorelines, to deeper lake areas. The hydro-climatological model demonstrates the crucial interdependence between hydrodynamic processes and climatological factors at the catchment scale of Lake Victoria. The numerical models and calculation methods that have been developed in this dissertation represent additional contributions to hydrodynamic research and can be used to investigate hydrodynamic processes in other lakes. The thesis contributes to UN Sustainable Development Goals related to water security, drinking water, food, and health. A potential area of application lies in supporting analysis and mitigation of pollution and climate change effects and more generally aid in the natural resource governance of this vital African lake.
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10.
  • Zou, Liangchao, 1987-, et al. (författare)
  • Impact of normal stress-induced closure on laboratory-scale solute transport in a natural rock fracture
  • 2020
  • Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Chinese Academy of Sciences. - 1674-7755.
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study. The fracture is created from a measured surface of a granite rock sample. The Bandis model is used to calculate the fracture closure due to normal stress, and the fluid flow is simulated by solving the Reynold equation. The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture. The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures. It causes fracture closure and creates asperity contact areas, which significantly reduces the effective hydraulic aperture and enhances flow channeling. Consequently, the reduced aperture and enhanced channeling affect travel time distributions. In particular, the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport. The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time. The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures. 
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11.
  • Eliasson, Åsa, 1993, et al. (författare)
  • Efficient heat integration of industrial CO2 capture and district heating supply
  • 2022
  • Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 118
  • Tidskriftsartikel (refereegranskat)abstract
    • Excess heat from industrial processes can be used for carbon capture and storage (CCS) as well as providing heat to a district heating network, leading to increased energy efficiency and reduction of on-site and/or off-site CO2 emissions. In this work, both options are assessed with respect to economic performance and potential reduction of CO2 emissions. The work includes a generic study based on five heat load curves for each of which three CO2 capture plant configurations were evaluated. The economic assessment indicates that the specific cost of capture ranges from 47-134 €/t CO2 depending on heat profile and capture plant configuration. Having excess heat available during a long period of the year, or having a high peak amount of heat, were shown to lead to low specific capture costs. The paper also includes results of a case study in which the methodology was applied to actual seasonal variations of excess heat for an integrated steel mill located in northern Sweden. Specific capture costs were estimated to 27-44 €/t CO2, and a 36% reduction of direct plant emissions can be achieved if the CO2 capture plant is prioritized for usage of the available excess heat
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12.
  • Elyouncha, Anis, 1978, et al. (författare)
  • Wind-wave effect on ATI-SAR measurements of ocean surface currents in the Baltic Sea
  • 2016
  • Ingår i: 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. ; 2016-November, s. 3982-3985
  • Konferensbidrag (refereegranskat)abstract
    • Along-Track Interferometric (ATI) SAR has demonstrated through several studies a capability to detect ocean surface currents. One of the most challenging problems in ocean surface current retrieval using SAR is the removal of the wind-wave contribution. The phase difference provided by ATI-SAR technique is directly related to the radial velocity of the moving ocean surface. In order to infer the current-only velocity from the total phase the wind-wave contribution need to be removed. This is achieved by simulation of SAR Doppler spectra from given wind fields. This paper investigates the effect of the local wind on ATI-SAR phase. A study case, where the backscatter modulation is dominated by the wind variation, is illustrated using TanDEM-X data over the Baltic Sea. It is shown that retrieving high resolution winds from SAR data using an empirical wind model and using the retrieved winds as input to the SAR imaging model improves the simulated SAR signatures.
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13.
  • Löfgren, Johan, 1983, et al. (författare)
  • Sea level time series and ocean tide analysis from multipath signals at five GPS sites in different parts of the world
  • 2014
  • Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 80, s. 66-80
  • Tidskriftsartikel (refereegranskat)abstract
    • We present sea level observations derived from the analysis of signal-to-noise ratio (SNR) data recorded by five coastal GPS stations. These stations are located in different regions around the world, both in the northern and in the southern hemisphere, in different multipath environments, from rural coastal areas to busy harbors, and experience different tidal ranges.The recorded SNR data show periodic variations that originate from multipath, i.e. the interference of direct and reflected signals. The general assumption is that for satellite arcs facing the open sea, the rapid SNR variations are due to reflections off the sea surface. The SNR data recorded from these azimuth intervals were analyzed by spectral analysis with two methods: a standard analysis method assuming a static sea level during a satellite arc and an extended analysis method assuming a time dependent sea level during a satellite arc.The GPS-derived sea level results are compared to sea level records from co-located traditional tide gauges, both in the time and in the frequency domain. The sea level time series are highly correlated with correlation coefficients to the order of 0.89–0.99. The root-mean-square (RMS) difference is 6.2 cm for the station with the lowest tidal range of 165 cm and 43 cm for the station with the highest tidal range of 772 cm. The relative accuracy, defined as the ratio of RMS and tidal range, is between 2.4% and 10.0% for all stations.Comparing the standard analysis method and the extended analysis method, the results based on theextended analysis method agree better with the independent tide gauge records for the stations with a high tidal range. For the station with the highest tidal range (772 cm), the RMS is reduced by 47% when using the extended analysis method. Furthermore, the results also indicate that the standard analysis method, assuming a static sea level, can be used for stations with a tidal range of up to about 270 cm, without performing significantly worse than the extended analysis method.Tidal amplitudes and phases are derived by harmonic analysis of the sea level records. Again, a high level of agreement is observed between the tide gauge and the GPS-derived results. Comparing the GPS-derived results, the results based on the extended analysis method show a higher degree of agreement with the traditional tide gauge results for stations with larger tidal ranges. Spectral analysis of the residuals after the harmonic analysis reveals remaining signal power at multiples of the draconitic day. This indicates that the observed SNR data are to some level disturbed by additional multipath signals, in particular for GPS stations that are located in harbors.
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14.
  • Saberi, Azim, et al. (författare)
  • Accuracy assessment and improvement of SRTM, ASTER, FABDEM, and MERIT DEMs by polynomial and optimization algorithm : A case study (Khuzestan Province, Iran)
  • 2023
  • Ingår i: Open Geosciences. - : De Gruyter Open. - 2391-5447. ; 15:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Satellite digital elevation models (DEMs) are used for decision-making in various fields. Therefore, evaluating and improving vertical accuracy of DEM can increase the quality of end products. This article aimed to increase the vertical accuracy of most popular satellite DEMs (i.e., the ASTER, Shuttle Radar Topography Mission [SRTM], Forest And Buildings removed Copernicus DEM [FABDEM], and Multi-Error-Removed Improved-Terrain [MERIT]) using the particle swarm optimization (PSO) algorithm. For this purpose, at first, the vertical error of DEMs was estimated via ground truth data. Next, a second-order polynomial was applied to model the vertical error in the study area. To select the polynomial with the highest accuracy, employed for vertical error modeling, the coefficients of the polynomial have been optimized using the PSO algorithm. Finally, the efficiency of the proposed algorithm has been evaluated by other ground truth data and in situ observations. The results show that the mean absolute error (MAE) of SRTM DEM is 4.83 m while this factor for ASTER DEM is 5.35 m, for FABDEM is 4.28, and for MERIT is 3.87. The obtained results indicated that the proposed model could improve the MAE of vertical accuracy of SRTM, ASTER, FABDEM, and MERIT DEMs to 0.83, 0.51, 0.37, and 0.29 m, respectively. 
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15.
  • Andrén, A., et al. (författare)
  • Frost shattering and ice problems in rock tunnels from a maintenance perspective
  • 2012
  • Ingår i: ISRM International Symposium - EUROCK 2012.
  • Konferensbidrag (refereegranskat)abstract
    • Every winter a number of railway tunnels in Sweden are affected by problems with ice. When ice is allowed to form in the rock fracture network and interface between the rock and shotcrete, degradation of both materials occur which can cause fall-outs of rock debris and shotcrete. To reduce maintenance costs it is necessary to improve knowledge of frost penetration along tunnels and the effect of frost shattering on the load bearing structures. Temperature measurements in Swedish railway tunnels have shown that frost penetrates much deeper into tunnels than previously assumed. By field observations it has been confirmed that ice problems often occur throughout the entire tunnel, even for longer tunnels (>1.5 km). If the load bearing structures are subjected to alternating freezing and thawing the shotcrete can be exposed to frost shattering. In a similar manner as frost action in soil, water tends to migrate in rock and cause ice bodies to grow inside pores and cracks. Laboratory tests show that when a rock/shotcrete sample has access to water during the freezing process, degradation occurs that affects adhesion between the materials. Therefore the load bearing structures exposed to water leakage should be designed for freezing temperatures along the entire length of the tunnel.
  •  
16.
  • Arvidson, Sebastian, 1981, et al. (författare)
  • Grey-area mitigation using commutation terms at the interfaces in hybrid RANS-LES modeling
  • 2018
  • Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer International Publishing. - 1612-2909 .- 1860-0824. ; 137, s. 113-124
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2018, Springer International Publishing AG. With the aim to mitigate the grey area at the RANS-LES interface, the effect of commutation terms is investigated. Simulations of fully developed channel flow and spatially developing boundary layer flow are presented using the commutation terms at the RANS-LES interfaces. The commutation terms are added as source terms in the k, ω and momentum equations of a zonal RANS-LES model. It is concluded that as an inlet in embedded LES of the developing boundary layer flow, the use of the proposed commutation terms are needed for the LES simulated flow to accurately predict the skin friction. However, it is demonstrated for flows where the RANS-LES interface aligns with the mean flow direction that the effect of the proposed interface methodology is weak.
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17.
  • Bonitz, Sabine, 1985, et al. (författare)
  • Experimental Investigation of the Near Wall Flow Downstream of a Passenger Car Wheel Arch
  • 2018
  • Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 11:1, s. 22-34
  • Tidskriftsartikel (refereegranskat)abstract
    • The flow around and downstream of the front wheels of passenger cars is highly complex and characterized by flow structure interactions between the external flow, fluid exiting through the wheelhouse, flow from the engine bay and the underbody. In the present paper the near wall flow downstream of the front wheel house is analyzed, combining two traditional methods. A tuft visualization method is used to obtain the limiting streamline pattern and information about the near wall flow direction. Additionally, time resolved surface pressure measurements are used to study the pressure distribution and the standard deviation. The propagation of the occurring flow structures is investigated by cross correlations of the pressure signal and a spectral analysis provides the characteristic frequencies of the investigated flow. It is found that two main flow phenomena can be observed: one originates from flow exiting the upper wheelhouse and a second one resulting from a separation on the lower wheel house edge. The frequency spectrum reveals a dominant Strouhal number of 0.2. As the observed flow structures are attributed to the wheel-wheelhouse interaction, a closed wheelhouse configuration is also investigated and the results confirm that the fluctuations and observed flow structures are created by the flow interaction between the wheel, wheelhouse and the rotation of the wheel.
  •  
18.
  • Di Donna, Alice, et al. (författare)
  • The contribution of swelling to self-sealing of claystone studied through x-ray tomography
  • 2022
  • Ingår i: Physics and Chemistry of the Earth. - : Elsevier BV. - 1474-7065. ; 127
  • Tidskriftsartikel (refereegranskat)abstract
    • Many countries, as among others France, Belgium and Switzerland, are facing the issue of finding a proper solution to store radioactive waste coming from nuclear power plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets RAdioactifs) selected the Callovo-Oxfordian clay rock situated in the Meuse/Haute Marne site between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. The factures will be then gradually re-saturated by the underground water coming from the surrounding rock and they are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing, i.e. closing of fractures after water contact and possibly restoring of permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. The physical mechanisms driving this phenomenon are mainly the swelling and de-structuration of the clay matrix present in the claystone. In this work, the self-sealing response of COx was investigated through x-ray tomography at multi-micrometre and sub-micrometre voxel size. The objective was to study the influence of mineralogy, size of the discontinuity, hydraulic paths, mutual orientation of the bedding plane and fractures. The size of the discontinuity is of primary importance in determining the percentage of closure. Fractures parallel to the bedding plane are more likely to seal as swelling is anisotropic and occurs mainly perpendicular to the bedding plane. The main novelty is represented by the direct and local observation of the physical process of self-sealing down to a scale lower than 1 μm.
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19.
  • Ericsson, Lars O, 1949, et al. (författare)
  • Comparison between blasting and wire sawing regarding hydraulic properties of the excavated damaged zone in a Tunnel – Experiences from crystalline rock at the Äspö hard rock laboratory, Sweden
  • 2018
  • Ingår i: 52nd U.S. Rock Mechanics/Geomechanics Symposium.
  • Konferensbidrag (refereegranskat)abstract
    • In tunneling with blasting, the tunnel periphery could be damaged (the EDZ, "Excavated Damaged Zone") with altered mechanical, hydraulic properties and reoriented stresses. In recent underground infrastructure projects, diamond wire cutting is used as an alternative excavation method. At the Äspö Hard Rock Laboratory in Sweden investigations have been conducted to determine hydraulic properties of the EDZ at water saturated conditions. Comprehensive hydraulic testing (hundreds of injection tests), in the floor of a blasted as well as a wire sawn tunnel section has made it possible to quantitatively compare hydraulic properties of the different excavation methods. Diamond wire cutting, as expected, greatly reduces the EDZ permeability compared to blasting.
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20.
  • Fransson, Åsa, 1971, et al. (författare)
  • Geological and hydrogeological reference conditions for rock engineering: An example for grouting design at äspö hard rock laboratory, Sweden
  • 2017
  • Ingår i: ISRM AfriRock - Rock Mechanics for Africa. ; 2017-October, s. 983-994
  • Konferensbidrag (refereegranskat)abstract
    • © 2017 International Society for Rock Mechanics. All Rights Reserved. The observational method includes the idea that rock engineering design can be modified as construction progresses, and that identification (confirmation or rejection and updating) of e.g. rock classes can be used in order to choose from predefined design classes. To facilitate rock engineering design, we suggest that geological and hydrogeological reference conditions are used as a basis. Fundamental to a reference condition approach is the identification and sampling of reference sites. Attributes, in this case geological and hydrogeological attributes, are selected and used to define the reference conditions. The reference conditions should be defined and described early on in a project, using relevant engineering parameters, and grouped together into rock classes with similar engineering characteristics. The reference conditions are subsequently used to define e.g. grouting design classes, to adapt to project-specific flow requirements. In this paper we suggest and give examples of geological and hydrogeological reference conditions for grouting, and present an example where reference conditions were used to define the grouting design for a site in crystalline rock, located at a depth of 400 m at the Äspö Hard Rock Laboratory, Sweden.
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21.
  • Hernqvist, Lisa, 1968 (författare)
  • Characterization of rock in 2D and 3D for grouting
  • 2012
  • Ingår i: ISRM International Symposium - EUROCK 2012.
  • Konferensbidrag (refereegranskat)abstract
    • © BeFo and ISRM, 2012. In tunnel construction in hard rock, a common method to reduce water inflow is to perform pre-grouting. The grouting design should be adapted to the current rock mass conditions, as well as to the stated inflow requirement for the tunnel project. One step in the grouting design process is to make a prediction of the expected inflow into the tunnel. The objectives of the research reported in this paper were to increase the understanding of fractures in 3D for grouting, to improve an existing method of inflow prediction so that hydrogeological aspects such as 3D fracture systems can be captured, and to increase the understanding of how grouting design should be adapted to the fracture system. It was concluded that a relevant conceptual model of the rock mass is good basis for grouting design and for inflow prediction. Conceptual models which describe different types of fracture systems are presented: 2D systems, 3D systems, fracture zones, flow dominated by 1D, and combinations of 2D-1D flow. Awareness of anisotropy is important: identification of the most water-bearing fracture set is essential both for inflow prediction and for grouting design. To illustrate the findings, data from case study tunnels have been analyzed.
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22.
  • Kannan, Ananda Subramani, 1989, et al. (författare)
  • A hydrodynamic basis for off-axis Brownian diffusion under intermediate confinements in micro-channels
  • 2021
  • Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 143
  • Tidskriftsartikel (refereegranskat)abstract
    • The mobility of a Brownian particle diffusing in a micro-channel is heterogeneous and spatially dependent on the surrounding hydrodynamic resistance fields. The positional asymmetry of such a diffusing particle leads to anisotropies in the observed diffusive behavior. In this paper, we probe such directionally varying diffusive behavior of a spherical nanoparticle diffusing at a location off-set from the centerline of a square micro-channel in a quiescent fluid. This investigation is carried out over varying degrees of intermediate hydrodynamic confinements. A coupled Langevin-immersed boundary method is used for these assessments. We observe that the co-axial diffusivity may be slightly enhanced during off-axis hindered diffusion when compared with a corresponding centerline diffusive behavior. We attribute this increased particle diffusivity to a reduced co-axial fluid resistance through a hydrodynamic basis derived using steady-state CFD solutions to the corresponding Stokes problem. For co-axial motion, the particle creates a recirculating flow pattern around itself when moving along the centerline, whereas it drags along the fluid in between itself and the wall when in close proximity to the latter. These contrasting flow behaviors are responsible for the unexpected enhancement of the co-axial diffusivity for some off-axis positions under intermediate hydrodynamic confinements.
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23.
  • Pazmiño, Sebastián A., et al. (författare)
  • A generalized 3DLS-DEM scheme for grain breakage
  • 2022
  • Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 399
  • Tidskriftsartikel (refereegranskat)abstract
    • We introduce a new generalized 3DLS-DEM (3D Level Set Discrete Element Method) scheme that incorporates grain breakage, taking an important step towards realistic modeling at the micro-scale with DEM. For the first time, simulating thousands of real 3D grains that are able to break, which was possible due to the algorithm used for grain breakage. The presented scheme is not only capable of efficiently simulating grains with real shapes but also preserving mass and grains morphology with high fidelity when breakage occurs. Hence, with this approach, further works within the original 3DLS-DEM scheme could take into account other physical phenomena at the grain-scale such as electrostatic induced cohesion, heat transfer, or the presence of a fluid, etc. On the other hand, the breakage process modified grain size and roundness distributions, which, in turn, might change the strength and critical state of the sample. Withal, the overall process seems to suggest that grain breakage may be a sufficient condition to exacerbate the prevalence of shear banding within the sample. Finally, our model is able to perform breakage on several real 3D grains of a sample consisting of thousands of grains in a generalized 3DLS-DEM scheme.
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24.
  • Rao, Anirudh Narayan, 1985, et al. (författare)
  • Investigation of the near-wake flow topology of a simplified heavy vehicle using PANS simulations
  • 2018
  • Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 183, s. 243-272
  • Tidskriftsartikel (refereegranskat)abstract
    • The near-wake flow topology of a ground transportation system (GTS) is investigated using partially-averaged Navier–Stokes (PANS) simulations at Re=2.7×104. Recent numerical investigations for the GTS model using large eddy simulations (LES) showed an anti-symmetric flow topology (flow state II) in the vertical midplane compared to that observed in previous experimental studies (flow state I). The geometrical configuration of the GTS permits bi-stable behaviour, and the realisation of each of the two flow states, which are characterised by an asymmetrical flow topology, is achieved by varying the differencing scheme for the convective flux in the PANS simulations; AVL SMART schemes predict flow state I, while central differencing scheme (CDS) predicts flow state II. When the GTS model was placed away from the ground plane, the AVL SMART scheme fails to predict the flow asymmetry resulting in a pair of symmetrical vortices in the vertical midplane, while flow state II topology is observed when CDS is used. The switch from flow state I (II) to flow state II (I) is achieved by changing the numerical scheme from AVL SMART (CDS) to CDS (AVL SMART), with an intermediate transient-symmetric (TS) state being observed during the switching process. The numerical scheme in the PANS simulations thus plays a critical role in determining the initial flow topology in the near wake of the GTS.
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25.
  • Sundberg, Jan, 1953 (författare)
  • Thermal properties and experiment at Äspö HRL
  • 2017
  • Ingår i: Rock Mechanics and Engineering: Volume 2: Laboratory and Field Testing. - : CRC Press. ; , s. 499-530
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • The underground hard rock laboratory at Äspö (Äspö HRL), situated north of Oskarshamn, Sweden, is where much of the research about the final repository for spent nuclear fuel is taking place. The Äspö HRL is a unique research facility situated 450 meters underground. One part of the investigations at Äspö HRL, and the adjacent Simpevarp and Laxemar areas, has focused on thermal transport properties in the rock. The thermal properties of the rock have large influence on the thermal design of an underground repository for spent fuel. Temperature requirements on the canister or the surrounding buffer influence the distances between canisters and tunnels. The relevant scale for the thermal processes is of importance. This chapter discusses influences on thermal transport properties in crystalline rock with respect of e.g. scale, mineral composition and anisotropy. Primarily these processes are discussed according to methods for determination of thermal conductivity, from laboratory measurements to large scale experiments. The chapter also discusses indirect methods that make it possible to calculate the thermal conductivity from mineral composition and from the density log, including the theoretical base. Results on thermal conductivity and heat capacity from common rock types are reported. The development of prediction methods in different scales are exemplified with large scale thermal response test and inverse modeling at the prototype repository. Finally the strategy is outlined for the site descriptive thermal modeling in the Swedish site investigation program for nuclear waste disposal.
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26.
  • Wang, Benxin, 1991, et al. (författare)
  • Fracture characteristics and the damage constitutive model of 3D printing undulating joint samples based on DIC
  • 2022
  • Ingår i: Gongcheng Kexue Xuebao/Chinese Journal of Engineering. - 2095-9389. ; 44:12, s. 2029-2039
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to the influence of geological structures, various forms of joint structural planes are present in rock mass engineering. The undulating structural planes, such as a torsional fold surface, are unique geological structures. These structures affect the stability of rock masses and cause potential hazards to rock mass engineering. Because of their shape complexity, the research on the fracture and damage constitutive law of rock mass with undulating joints is not thoroughly conducted. Undulating joints with various dip angles were fabricated using three-dimensional printing technology. The uniaxial compression test and digital image correlation (DIC) technology were used to study the mechanical and fracture characteristics of undulating joint specimens. Based on the principle of fracture mechanics, an idea was proposed to use the DIC displacement field for solving the stress intensity factor (SIF: type one KI and type two KII) at the joint tips and to study the damage constitutive law. The results show that the upper limit of undulating joint damage to specimens is determined with 46.6% through the minimum strength analysis. The sensitivity of uniaxial strength to a joint dip angle of undulating joint specimen is greater than that of a straight joint specimen. The fracture initiation occurs near peak stress. The fracture process can be divided into the initiation and synchronous penetration of microcracks on the fracture path. Additionally, the fracture mode shows a combination of multiple tension and shear fractures. The SIF increases with loading at the prepeak stage, and the cracks propagate in shear fracture at the joint left and right tips in the postpeak stage because KII>KI under the same stress. The undulating joint damage to the specimen with the dip angle is in a sinusoidal curve form. The relationships between the total damage coupled by joint and load with strain are all “S” curves.
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27.
  • Wang, Benxin, 1991, et al. (författare)
  • Study on mechanical and fracture characteristics of rock-like specimens with rough non-persistent joints by YADE DEM simulation
  • 2023
  • Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 158
  • Tidskriftsartikel (refereegranskat)abstract
    • Rough non-persistent joints exist widely in natural rock mass. The roughness of joints influences its mechanical and fracture characteristics. However, the research on rough non-persistent jointed rock mass is inadequate. To investigate the effects of joint angle, rock bridge angle and roughness of rough non-persistent joints, the rough non-persistent joints were truncated and their JRC was calibrated based on the Barton typical roughness profiles. A series of DEM numerical uniaxial compression tests were conducted based on the laboratory tests of rock-like specimens with 3D printed non-persistent joints. By the investigation of mechanical behaviour, crack coalescence types, crack evolution law, fracture modes presented by the strain field, and micro-fracture mechanism revealed by the displacement vectors, it was verified that YADE is suitable to simulate the fracture of rough non-persistent jointed specimens; the six types of coalescence of rough non-persistent joints were concluded, and the relation between micro-crack and macro-fracture was established by the four types of micro-cracks causing macro-fractures.
  •  
28.
  • Wang, Benxin, 1991, et al. (författare)
  • The Strength and Macro-mesoscopic Fracture Characteristics of 3D-printed Rock-like Specimens with Internal Parallel Joints
  • 2022
  • Ingår i: Geotechnical and Geological Engineering. - : Springer Science and Business Media LLC. - 0960-3182 .- 1573-1529. ; 40:6, s. 3307-3324
  • Tidskriftsartikel (refereegranskat)abstract
    • The internal parallel joints weaken the rock mass and they are more difficult to be studied than the exposed joints. The intact specimen and internal parallel four joints (IPFJ) specimen were prepared by 3D printing for the uniaxial compression. According to the macro-mechanical parameters of the intact specimen, the apparent fractures, and internal 3D fracture modes obtained by computerized tomography technology, the Particle Flow Code 3D (PFC3D) was used to study the strength properties, 3D fracture modes, and macro-meso evolution mechanism of specimens with IPFJ under uniaxial compression. It was found that the apparent macro fractures are initiated at the yield point of about 90% of the peak stress in 3D similar to 2D. However, the stress of inner initial fracture is approximately 30% of the peak stress due to the strike discontinuity of joints in 3D. The stress intensity factors at the inner and outer edges of the joints are influenced by the adjacent joints leading to four fracture modes. Finally, a small number of tensile micro-cracks on the propagation path cause a large number of shear micro-cracks based on the force chain analysis.
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29.
  • Yu, R., et al. (författare)
  • Assessment of an Evolution Equation for the Displacement Speed of a Constant-Density Reactive Scalar Field
  • 2020
  • Ingår i: Flow Turbulence and Combustion. - : Springer. - 1386-6184 .- 1573-1987.
  • Tidskriftsartikel (refereegranskat)abstract
    • The displacement speed that characterises the self-propagation of isosurfaces of a reaction progress variable is of key importance for turbulent premixed reacting flow. The evolution equation for the displacement speed was derived in a recent work of Yu and Lipatnikov (Phys Rev E 100:013107, 2019a) for the case where the flame is described by a transport equation for single reaction progress variable assuming simple transport and one-step chemistry. This equation represents interaction of a number of complex coupled mechanisms related to straining by the velocity field, surface curvature and the scalar gradient. The aim of the current work is to provide detailed physical explanations of the displacement speed equation and its various terms, and to provide a new perspective to understand the mechanisms responsible for observed variations in the displacement speed. The equation is then used to analyze the propagation of a statistically planar reaction wave in homogeneous isotropic constant-density turbulence using direct numerical simulations. Additional emphasis is put on retracting surface segments that have a negative displacement speed, a phenomenon that commonly occurs at high Karlovitz numbers. 
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30.
  • Abrahamsson, Per, 1985, et al. (författare)
  • Analysis of mesoscale effects in high-shear granulation through a computational fluid dynamics–population balance coupled compartment model
  • 2018
  • Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 36, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a need for mesoscale resolution and coupling between flow-field information and the evolution of particle properties in high-shear granulation. We have developed a modelling framework that compartmentalizes the high-shear granulation process based on relevant process parameters in time and space. The model comprises a coupled-flow-field and population-balance solver and is used to resolve and analyze the effects of mesoscales on the evolution of particle properties. A Diosna high-shear mixer was modelled with microcrystalline cellulose powder as the granulation material. An analysis of the flow-field solution and compartmentalization allows for a resolution of the stress and collision peak at the impeller blades. Different compartmentalizations showed the importance of resolving the impeller region, for aggregating systems and systems with breakage. An independent study investigated the time evolution of the flow field by changing the particle properties in three discrete steps that represent powder mixing, the initial granulation stage mixing and the late stage granular mixing. The results of the temporal resolution study show clear changes in collision behavior, especially from powder to granular mixing, which indicates the importance of resolving mesoscale phenomena in time and space.
  •  
31.
  • Ahmadi, H., et al. (författare)
  • Experimental Research on Variation of Pore Water Pressure in Constant Rate of Strain Consolidation Test
  • 2014
  • Ingår i: Acta Geotechnica Slovenica. - 1854-0171. ; 11:2, s. 46-57
  • Tidskriftsartikel (refereegranskat)abstract
    • Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure.
  •  
32.
  • Al-Yaarubi, A. H., et al. (författare)
  • Navier-Stokes Simulations of Fluid Flow Through a Rock Fracture
  • 2013
  • Ingår i: Dynamic Fluids and Transport Through in Fractured Rock. - : American Geophysical Union (AGU). - 9781118666173 ; , s. 55-64
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • A surface profilometer was used to measure fracture profiles every 10 microns over the surfaces of a replica of a fracture in a red Permian sandstone, to within an accuracy of a few microns. These surface data were used as input to two finite element codes that solve the Navier-Stokes equations and the Reynolds equation, respectively. Numerical simulations of flow through these measured aperture fields were carried out at different values of the mean aperture, corresponding to different values of the relative roughness. Flow experiments were also conducted in casts of two regions of the fracture. At low Reynolds numbers, the Navier-Stokes simulations yielded transmissivities for the two fracture regions that were closer to the experimental values than were the values predicted by the lubrication model. In general, the lubrication model overestimated the transmissivity by an amount that varied as a function of the relative roughness, defined as the standard deviation of the aperture divided by the mean aperture. The initial deviations from linearity, for Reynolds numbers in the range 1-10, were consistent with the "weak inertia" model developed by Mei and Auriault for porous media, and with the results obtained computationally by Skjetne et al in 1999 on a two-dimensional self-affine fracture. In the regime 10 < Re < 40, both the computed and measured transmissivities could be fit very well to a Forchheimer-type equation, in which the additional pressure drop varies quadratically with the Reynolds number.
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33.
  • Allen, Matthew S., et al. (författare)
  • Model reduction concepts and substructuring approaches for linear systems
  • 2020
  • Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 25-73
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • In this chapter, we give an overview of some of the most common reduction techniques based on substructuring. Although all techniques follow a similar approach, the main difference between the methods lies into the basis vectors used in the approximation subspace to represent the dynamics of each substructure and the manner in which the substructures are a couple.
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34.
  • Andersson, Johan Vium (författare)
  • Undifferenced GPS for Deformation Monitoring
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis contains the development of a deformation monitoring software based on undifferenced GPS observations. Software like this can be used in alarm systems placed in areas where the earth is unstable. Systems like this can be used in areas where people are in risk of getting hurt, like in earthquake zones or in land slide areas, but they can also be useful when monitoring the movements in buildings, bridges and other artefacts. The main hypotheses that are tested are whether it is possible to detect deformations with undifferenced observations and if it is possible to reach the same accuracy in this mode as when working in a traditional mode where the observations are differenced. The development of a deformation monitoring software based on undifferenced GPS observations is presented. A complete mathematical model is given as well as implementation details. The software is developed in Matlab together with a GPS observation simulator. The simulator is mainly used for debugging purposes. The developed software is tested with both simulated and real observations. Results from tests with simulated observations show that it is possible to detect deformations in the order of a few millimetres with the software. Calculations with real observations give the same results. Further, the result from calculations in static mode indicates that the commercial software and the undifferenced software diverge a few millimetres, which probably depends on different implementations of the tropospheric corrections. In kinematic mode the standard deviation is about 1 millimetre larger in the undifferenced mode than in the double differenced mode. An initial test with different observation weighting procedures indicates that there is a lot of potential to improve the result by applying correct weights to the observations. This is one of the aims in the future work within this project. This thesis are sponsored by the Swedish Research Council for Enviroment, Agricultural Sciences and Spatial Planning, FORMAS within the framework “Monitoring of construction and detection of movements by GPS ref no. 2002-1257"
  •  
35.
  • Arosemena, Arturo A., et al. (författare)
  • Effects of shear-thinning rheology on near-wall turbulent structures
  • 2021
  • Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 925
  • Tidskriftsartikel (refereegranskat)abstract
    • Turbulent channel flow simulation of a shear-thinning fluid is considered - see Arosemena et al. (J. Fluid Mech., vol. 908, 2021, p. A43) - and compared with a Newtonian base case to reveal the effects of the shear-dependent rheology on the near-wall structures. Analyses of different flow statistics revealed that, for the shear-thinning fluid case, the streamwise vortices appear to grow in size, depart from the wall and present a lessening in their intensity. Information regarding variations in the quasi-longitudinal vortices is also obtained from three-dimensional structures identified through a normalized -criterion. With shear-thinning rheology, it is shown that the structures are comprised of wall-attached and -detached families which are taller than for a Newtonian fluid. Also, for a given height, the structures appear to be longer, with approximately the same width and overall larger volume for the shear-thinning fluid case; albeit their fractal dimension remains the same when compared to the Newtonian base case. Moreover, it is observed that the number density of vortical structures decreases with shear-thinning fluid behaviour. These observations, in conjunction with the known changes to the longitudinal velocity structures which appear to be less streaky, more spanwise separated and thickened with shear-thinning rheology, strongly suggest that the near-wall self-sustaining process has been disrupted. As we move slightly away from the wall and with shear-thinning behaviour, the local increase in viscosity seems to lead to less energetic vortices whereas the streaks are provided with an additional source of energy due to fluctuations in viscosity.
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36.
  • Axelsson, Magnus, 1974, et al. (författare)
  • A robust method to determine the shear strength of cement-based injection grouts in the field
  • 2006
  • Ingår i: Tunnelling and Underground Space Technology. ; 21:5, s. 499-503
  • Tidskriftsartikel (refereegranskat)abstract
    • There is no standardised method to directly determine the shear strength of grouts in the field. Determining the shear strength would make it possible to calculate the penetration length of cement-based grouts and hence establish a design of the grouting procedure. By developing a new robust method that consists of a stick sinking in the grout, a direct measurement of the shear strength can be made, using the same set up as the separation test. The sink of the stick depends on the shear force interaction between the grout and the stick, and hence the shear strength of the grout can be determined. To verify the results, the shear strengths obtained with the stick are compared with measurements of the shear strength made with a rotational rheometer in the laboratory. The comparison shows good agreement; hence the stick can be used in the field to determine the yield strength of cement-based grouts.
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37.
  •  
38.
  • Axelsson, Magnus, 1974 (författare)
  • Mechanical tests on a new non-cementitious grout , silica sol: A laboratory study of the material characteristics
  • 2006
  • Ingår i: Tunnelling and Underground Space Technology. ; 21:5, s. 554-560
  • Tidskriftsartikel (refereegranskat)abstract
    • This introductory study on mechanical properties aims to characterize silica sol and to improve knowledge of the suitability of silica sol as grout. Silica sol is a non-cementitious grout that consists of spherical particles of amorphous silica, with a diameter of 5100 nm. For a testing period of six months, specimens of silica sol were kept at 8 °C with three relative humidities: 75%, 95% and 100%. During the test period measurements of the drying shrinkage, compressive strength, modulus of elasticity (Youngs modulus), shear strength and flexural strength were made. The results show that the strength of silica sol continues to increase for a long time and during the test period of six months the strength kept increasing. The increase of strength depends on the humidity to which silica sol is exposed but the humidity also affects the drying shrinkage. A lower humidity results in a faster increase in strength but also a larger shrinkage.
  •  
39.
  • Axelsson, Magnus, 1974, et al. (författare)
  • Stop mechanism for cementitious grouts at different water-to-cement ratios
  • 2009
  • Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 24:4, s. 390-397
  • Tidskriftsartikel (refereegranskat)abstract
    • Cementitious grouts are the most commonly used grouting material in the world. The general concept of grouting is to propagate the grout in a sufficiently large volume in the grouted medium and hence to have a controlled penetration. This study has been performed in order to determine and test the different mechanisms that result in stoppage of the penetration of cementitious grouts. This is performed as sand column tests in a laboratory study, coupled with grouting in the field. The result shows that three different stop mechanisms can be identified depending on the ratio between the grain size of the grout and the available opening. At an opening up to three times the size of the largest grout grains, penetration does not occur due to clogging of the grains. For an opening larger than five times the largest grain the penetration is unrestricted and stoppage occurs due to equilibrium between the driving and resistance forces. Between these ratios, a transition area exists where the water content determines the penetrability and the stoppage is governed by a filtration process for the grout grains. This implies that grouting with higher water-to-cement ratios results in a larger penetration area and hence by applying the mixture-thickening method during grouting an increased sealing efficiency can be obtained. (c) 2008 Elsevier Ltd. All rights reserved.
  •  
40.
  • Axelsson, Magnus, 1974 (författare)
  • Strength Criteria on Grouting Agents for Hard Rock- Laboratory studies performed on gelling liquid and cementitious grout
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Grouting is usually successful in excavations at moderate depths and groundwater inflow. At great depths, in post-grouting or in rock with a large inflow of water, grouting is more problematic due to the forces from groundwater. The thesis aims to increase the understanding of the groundwater forces that act on grouting agents in rock and characterisation of the required grout strength to withstand the forces. The outcome is a better understanding of the strength demands, thus providing an opportunity to perform more successful grouting. The strength of a gelling liquid for grouting in hard rock, silica sol, has been investigated. The strength of silica sol increases over a long time and the rate is depending on the humidity. In low humidities, silica sol shrinks but immersed in water, no shrinkage occurs. Further, a new robust method for determining the yield stress of cementitious grout in the field, termed the Yield stick, was developed. The method consists of a stick that sinks into the grout and the yield strength of the grout is determined by the sink depth. Good agreement was found between the Yield stick and reference tests made with rheometer. A study of the erosion process was performed where a Bingham fluid was injected into a pipe with flowing water. The study showed that the most important factor for the erosion process was the flow regime of water. To relate the conclusions with field conditions, grouting should always be done with shear strength of the grout that is higher than the shear stress from water, the grouting time should be sufficiently long and the grouting pressure should be resolute.
  •  
41.
  • Back, Pär-Erik, 1961, et al. (författare)
  • Value of information analysis for site investigation programs accounting for variability, uncertainty and scale effects with the Aspo HRL prototype repository as an example
  • 2009
  • Ingår i: International Journal of Rock Mechanics and Minings Sciences. - : Elsevier BV. - 1365-1609. ; 46:5, s. 896-904
  • Tidskriftsartikel (refereegranskat)abstract
    • An important feature of underground projects is the early site investigations, performed as a means to identify and quantify hazards. A methodology is presented for identifying the most cost-effective investigation program among a set of alternatives. Methodologies are presented for both investigation of thermal conductivity in hard rock and collection of rock mechanic data for stress induced spalling problems. The cost-effectiveness of an investigation program is estimated by means of value of information analysis (VOIA). Each investigation program of thermal conductivity is associated with uncertainty due to natural variability and lack of knowledge. These uncertainties are taken into account in a simulation model with the aim to estimate the distribution of thermal conductivity values at different scales. The output is a set of thermal conductivity values from which a design parameter can be estimated. The simplest measure of the value of a site investigation is the expected reduction of uncertaintyofthedesignparameter. The methodology is demonstrated with a case study for the prototype nuclear waste repository at Aspo Hard Rock Laboratory, Sweden. A set of four investigation programs for thermal conductivity were evaluated, and the most effective one identified. The application illustrates that an investigation program may supply very different value to a project, depending on how the objective of the investigation is defined. This is demonstrated by using two different objectives and comparing the results. Practical applications of the methodology on both thermal properties and rock mechanics are discussed, with emphasis on site investigations performed by the Swedish Nuclear Fuel and Waste Management (SKB). (C) 2009 Elsevier Ltd. All rights reserved.
  •  
42.
  • Bakyayita, Grace Kizito, et al. (författare)
  • Assessment of Levels, Speciation, and Toxicity of Trace Metal Contaminants in Selected Shallow Groundwater Sources, Surface Runoff, Wastewater, and Surface Water from Designated Streams in Lake Victoria Basin, Uganda
  • 2019
  • Ingår i: Journal of Environmental and Public health. - : Hindawi Publishing Corporation. - 1687-9805 .- 1687-9813.
  • Tidskriftsartikel (refereegranskat)abstract
    • The levels, speciation of elements, and toxicity of selected trace metals as well as other parameters in selected surface water, shallow groundwater sources, landfill leachate, and associated surface runoff in the Lake Victoria basin, Uganda, were studied. The WHO guidelines, Ugandan standards, Canadian guidelines and Swedish EPA were used for assessment. The shallow groundwater was acidic with pH values below 6.5. The pH, dissolved organic carbon, flouride, and sulphate levels for all springs were below the guideline values although 52.8% was contaminated with nitrates while 39% was contaminated with chloride ions. Some surface water samples had levels of major elements, such as iron, chromium, aluminium, and manganese, above the guideline values. Speciation studies showed that 74% of the metal ions was bound to dissolved organic matter in surface water, whereas in landfill leachates, the dominant ionic species was metal hydroxides or fulvic acid bound. Risk analysis based on the Swedish EPA showed varied risks of negative effects in 30%-76% of the sample sites ranging from high to increased risk in surface water, whereas the results from modelling sorption data using the Bio-met tool showed potential risk to toxicity effects of Cu2+, Ni2+, Zn2+, and Pb2+ in 15.3%-30.8% surface water samples and 8.3%-62.5% groundwater samples.
  •  
43.
  • Bazargan, Mohsen, et al. (författare)
  • Numerical, predictive and experimental study on elastic wave propagation in crystalline rocks
  • 2021
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Calculating anisotropy and better understanding this physical effect is one of the main challenges in geophysics, whether in the size of the field or micro scale. one of the very common methods of calculating seismic anisotropy is to take into account the bulk properties of the material, in a micro-scale, this is based on the average value of Crystallographic preferred orientation measurements by using, for example, Scanning Electron Microscopy to operate - Electron backscatter diffraction method.
  •  
44.
  • Berndtsson, Ronny, et al. (författare)
  • Spatial variability of infiltration in a semi-arid environment
  • 1987
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 90:1-2, s. 117-133
  • Tidskriftsartikel (refereegranskat)abstract
    • Fifty-two double-ring infiltrometer tests, performed in a small, partly urbanized catchment in northern Tunisia are analyzed. Spatial variability is characterized by use of cross-correlation functions. Spatial patterns of infiltration properties are shown to be governed by geomorphology and occurring vegetation. Different geomorphological zones and zones with equal density of vegetation tend to be oriented in a parallel pattern in relation to the wadi. Statistical properties of infiltration capacities depending on geomorphological zone are presented.
  •  
45.
  • Biermann, Max, 1989 (författare)
  • Partial CO2 capture to facilitate cost-efficient deployment of carbon capture and storage in process industries - Deliberations on process design, heat integration, and carbon allocation
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Climate change requires that all energy-related sectors reduce drastically their greenhouse gas (GHG) emissions, at a global rate of 1–2 GtCO2 per year, starting now. Process industries, such as the iron and steel, cement, petrochemical, and oil-refining industries, are inherently carbon-intensive, and carbon capture and storage (CCS) is one of the few options available to achieve the required deep reductions in carbon dioxide (CO2) emissions. Despite being technologically mature, CCS has so far not been implemented at the required rates. This is due inter alia to the low value created by CCS for process industries, which is attributed to uncertainties related to carbon pricing and the considerable investments required for CO2 capture installations. This thesis explores the concept of partial carbon capture as an opportunity for the process industry, as part of its transition, to operate in a net-zero emissions framework by the middle of this century. Partial capture is governed by market and site conditions, and aims to capture a designated share of the CO2 emissions from an industrial site, thereby lowering the absolute and specific costs (in€/tCO2) for CO2 capture, as compared to a conventional full-capture system. The thesis elaborates the relevant technical, economic, and policy-related aspects related to facilitating the near-term implementation of carbon capture at industrial sites. These aspects include: 1) the energy- and cost-effective design of solvent-based processes for partial capture, which can lead to capture cost savings of up to 10% for gases with a high CO2 content (>17 vol.%wet); 2) the efficient use of residual heat and existing capacities on-site to power partial capture, which in case studies of an oil refinery and an integrated steel mill, are shown to confer cost savings along the entire CCS chain of 17%–24%; 3) the incorporation of site realities, such as temporal variations in heat availability, into techno-economic assessments; 4) the adaption of policies that address the allocation of carbon emissions reductions to low-carbon products, so that investments in mitigation technologies are incentivized with respect to the ambition level; and 5), the recognition of the rather narrow window of opportunity for partial capture with regard to the lifetime of the existing infrastructure, alternative production and (co-)mitigation technologies, as well as the regional energy and CO2 transport and storage systems. As the title image indicates, the share of carbon extracted from the earth that is sequestered needs to reach 100% by mid-century, in order to limit global warming in line with the targets of the Paris Agreement (i.e., 1.5°C or well below 2°C). Thus, partial capture is only a short-term solution for kick-starting CCS, and it will eventually have to lead to full capture, alternatively full mitigation (e.g., via carbon-free production), or be combined with renewable feedstocks if used in the longer term. Therefore, it is timely for the process industry to apply partial capture and, thereby, ramp up widespread adoption of CCS, so to build up the infrastructure for direct removal of carbon from the atmosphere, which will be required on the gigatonne scale in the second half of the 21st Century.
  •  
46.
  • Birkholzer, Jens T., et al. (författare)
  • 25 years of DECOVALEX - Scientific advances and lessons learned from an international research collaboration in coupled subsurface processes
  • 2019
  • Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1365-1609 .- 1873-4545. ; 122
  • Forskningsöversikt (refereegranskat)abstract
    • This paper provides an overview of an international research collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems. The creation of the international DECOVALEX Project, now running for over 25 years, was initially motivated by the recognition that prediction of these coupled effects is an essential part of the performance and safety assessment of geologic disposal systems for radioactive waste and spent nuclear fuel. Later it was realized that these processes also play a critical role in other subsurface engineering activities, such as storage of CO2, exploration of enhanced geothermal systems, and unconventional oil and gas production through hydraulic fracturing. Research teams from radioactive waste management organizations, national research institutes, regulatory agencies, universities, as well as industry and consulting groups have participated in the DECOVALEX Project, providing a wide range of perspectives and solutions to these complex problems. Analysis and comparative modeling of state-of-the-art field and laboratory experiments has been at the core of the collaborative work, with an increasing focus on characterizing uncertainty and blind prediction of experimental results. Over these 25 years, many of the major advances in this field of research have been made through DECOVALEX, as evidenced by three books, seven journal special issues, and a good number of seminal papers that have emerged from the DECOVALEX modeling work. Examples of specific research advances will be presented in this paper to illustrate the significant impact of DECOVALEX on the current state-of-the-art of understanding and modeling coupled THMC processes. These examples range from the modeling of large-scale in situ heater tests representing mock-ups of nuclear waste disposal tunnels, to studies of fluid flow and chemical-mechanical coupling in heterogeneous fractures, and to the numerical analysis of controlled-injection meso-scale fault slip experiments.
  •  
47.
  • Boano, F., et al. (författare)
  • Hyporheic flow and transport processes : Mechanisms, models, and biogeochemical implications
  • 2014
  • Ingår i: Reviews of geophysics. - 8755-1209 .- 1944-9208. ; 52:4, s. 603-679
  • Forskningsöversikt (refereegranskat)abstract
    • Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.
  •  
48.
  • Bonitz, Sabine, 1985, et al. (författare)
  • Numerical investigation of crossflow separation on the a-pillar of a passenger car
  • 2018
  • Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 140:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The flow around passenger cars is characterized by many different separation structures, typically leading to vortices and areas of reversed flow. The flow phenomena in these patches show a strong interaction and the evolution of flow structures is difficult to understand from a physical point of view. Analyzing surface properties, such as pressure, vorticity, or shear stress, helps to identify different phenomena, but still it is not well understood how these are created. This paper investigates the crossflow separation (CFS) on the A-pillar of a passenger car using numerical simulations. It is discussed how the CFS and the resulting A-pillar vortex can be identified as well as how it is created. Additionally, the vortex strength is determined by its circulation to understand and discuss how the vortex preserves until it merges with the rear wake of the vehicle.
  •  
49.
  • Breton, Simon-Philippe, et al. (författare)
  • Validation of the actuator disc and actuator line techniques for yawed rotor flows using the New MEXICO experimental data
  • 2017
  • Konferensbidrag (refereegranskat)abstract
    • Experimental data acquired in the New MEXICO experiment on a yawed 4.5m diameter rotor model turbine are used here to validate the actuator line (AL) and actuator disc (AD) models implemented in the Large Eddy Simulation code EllipSys3D in terms of loadingand velocity field. Even without modelling the geometry of the hub and nacelle, the AL and AD models produce similar results that are generally in good agreement with the experimental data under the various configurations considered. As expected, the AL model does better at capturing the induction effects from the individual blade tip vortices, while the AD model can reproduce the averaged features of the flow. The importance of using high quality airfoil data (including 3D corrections) as well as a fine grid resolution is highlighted by the results obtained. Overall, it is found that both models can satisfactorily predict the 3D velocity field and blade loading of the New MEXICO rotor under yawed inflow.
  •  
50.
  • Butron, Christian, 1978, et al. (författare)
  • A Swedish grouting design concept: Grouting with silica sol in the Nygård and Törnskog tunnels
  • 2012
  • Ingår i: Geotechnical Special Publication. - Reston, VA : American Society of Civil Engineers. - 0895-0563. - 9780784412350 ; :228 GSP, s. 826-835
  • Konferensbidrag (refereegranskat)abstract
    • The scope of this paper is to present two tunnel grouting design case studies where the waterproofing aimed not only to reduce the water inflow to a specified level, but to minimize the number of dripping spots by means of pre-excavation grouting. Every grouted section of around one hundred meters in both tunnels used relevant parameters from the rock and the grout material properties to develop an adequate, pre-excavation grouting design. Both tunnels, constructed in crystalline rock, used silica sol as the main grouting material and were evaluated later by means of control boreholes and dripping characterization. Control boreholes showed a decrease in the transmissivity in these sections, and the dripping characterization showed a reduction in the number of dripping spots compared to the rest of the tunnel, where this pre-excavation grouting concept was not used. This led to minimization of the number of drains used, which was clearly visible in the Nygård case, suggesting that the designs were successful and confirming that an understanding of the rock and grout properties is crucial to the design concept.
  •  
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