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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Modeling Hydro-Bio-Chemo-Mechanical Mechanisms in Granular Soils

Bista, Hemanta 23 December 2014 (has links)
No description available.
242

Shoreline Mapping with Integrated HSI-DEM using Active Contour Method

Sukcharoenpong, Anuchit 30 December 2014 (has links)
No description available.
243

Morphology-Based Identification of Surface Features to Support Landslide Hazard Detection Using Airborne LiDAR Data

Mora, Omar Ernesto 29 May 2015 (has links)
No description available.
244

Rigorous Model of Panoramic Cameras

Shin, Sung Woong 31 March 2003 (has links)
No description available.
245

Att leva i en blandad kultur : En Kvalitativ Studie Om Hur Andra Generationens Invandrare Upplever Mellanförskap / Living in a Mixed Culture : A Qualitative Study of how Second-generation Immigrants Experience Inbetweenship

Daabas, Donja January 2022 (has links)
The purpose of this study is to investigate how people living with a mixed culture experience the integration process in Sweden. The overall point of the essay is to create a greater understanding of how my interviewees, who belong to the second generation of immigrants, experience that their identity is shaped by the fact that they live in mixed cultures at the same time. The motive is also to create an understanding of their experiences of inbetweenship. To achieve the goal of the study, I will interview six different people who belong to the second generation of immigrants. The results of the study showed that their social interactions and the environment affect their identity development and the feeling of inbetweenship. I have come to the conclusion that not all my informants experience inbetweenship
246

Uppdatering av nationella höjdmodellen över begränsade områden med hjälp av UAS

Hedqvist, Emma, Jakobsson, Daniel January 2016 (has links)
I det här examensarbetet undersöks möjligheten att använda UAS över begränsade områden när den nationella höjdmodellen skapad av Lantmäteriet ska uppdateras. Ämnet var ett förslag från Lantmäteriet och huvudsyftet var att testa om UAS kan användas som komplettering till traditionell flygfotografering. Det blir allt vanligare att använda UAS inom till exempel geomatiken, eftersom det är ett bra verktyg när ett snabbt och effektivt resultat krävs. Lantmäteriet använder flygburen laserskanning vid genereringen av nationella höjdmodellen och den uppdateras med traditionell flygfotografering. Andra aspekter som undersökts i detta examensarbete var vilken mätosäkerhet kan uppnås med UAS vid framställandet av en DHM, vilken skillnad i lägesosäkerhet finns mellan studiens punktmoln jämfört med nationella höjdmodellen, samt mot punktmolnet genererat från traditionell flygfotografering och den ekonomiska aspekten vid användning av UAS. Detta utfördes genom att samla in data med hjälp av UAS över Furuvik, Gävle. Flyghöjden var 88 m över ett område på ca 1 ha. Därefter skapades en höjdmodell som kontrollerades enligt den tekniska specifikationen SIS-TS 21144:2013. I examensarbetet jämfördes punktmolnet som genererades från flygfoton tagna med UAS mot nationella höjdmodellen. Osäkerheten för den genererade höjdmodellen vid användandet av UAS visade ett bra resultat i höjd med en standardosäkerhet på 0,015 m. Punktmolnet genererat från Lantmäteriets bildmatchning låg 0,315-0,392 m under studiens punktmoln medan punktmolnet från laserskanningen låg 0,014-0,155 m över. Resultatet visade att användning av UAS är väldigt kostnadseffektivt när den nationella höjdmodellen över begränsade områden ska uppdateras. Det rekommenderas därför för Lantmäteriet att använda UAS för detta ändamål. Det blir mer än väl godkänt resultat och kostnaden är liten med tanke på resultatet, d.v.s. en metod för att verkligen kunna ajourhålla nationella höjdmodellen och komplettera traditionell flygfotografering över begränsade områden. Med denna metod slipper de vänta på att den traditionella flygfotograferingen ska ske. Tekniken går hela tiden framåt och inom en snar framtid kommer även laserskanning kunna ske med UAS. Det skulle vara intressant att se resultat av den metoden. Intressant skulle även vara att se om det i framtiden går att utesluta flygsignalering och verkligen kunna använda direkt georeferering för att spara tid ute i fält. / In this thesis we are going to investigate possibility of using UAS, over small areas, for updating national elevation model produced by the National Land Survey of Sweden. The subject of the thesis was proposed by the National Land Survey of Sweden. One of the main objectives of the study was to test if UAS can be used as a complement to traditional aerial photo. The use of UAS has increased over the years within for example geomatics, because it is a great tool when quick and effective results are required. The National Land Survey of Sweden uses airborne laser scanning to generate the national elevation model. The elevation model is then updated by traditional aerial photogrammetry. Other objectives that have been investigated in this study are what uncertainty can be expected with UAS when generating a DEM, the differences in uncertainty between the point cloud generated in this study to the national height model and to the point cloud generated from the traditional photogrammetry and the economic aspects when using UAS. For this purpose data was collected by UAS in Furuvik, Gävle. The flight height was 88 m over the area of about 1 ha. Then a DEM was created and controlled according to the technical specification SIS-TS 21144:2013. In this thesis a comparison between the point cloud generated in this study and the national elevation model has been performed. Uncertainty of the produced DEM using UAS showed very good result in height with a standard deviation of 0.015 m. The point cloud generated from the traditional photogrammetry was 0.315-0.392 m below the point cloud generated in this study, while the point cloud from laser scanning was 0.014-0.155 m above. The results showed that using UAS are very cost-effective to update the national elevation model. It is advisable for the National Land Survey of Sweden to update the national height model over small areas with this method. There will be more than efficient and the costs are small considering the result. In other word this method is to recommend when updating the national elevation model and can be used as a complement to traditional photogrammetry within limited areas. With this method, they will not have to wait for the traditional aerial photography to take place. The technology is constantly moving forward and in the near future laser scanning with UAS will occur. It would be interesting to see the results of that method. It would also be interesting to see if it is possible to exclude the ground control points, and really be able to use direct georeferencing to save time in the field.
247

DEM simulation of a single screw granulator: The effect of liquid binder on granule properties

Arthur, Tony B., Sekyi, Nana, Rahmanian, Nejat 25 January 2024 (has links)
Yes / The Caleva UK single-screw Variable Density Extruder (VDE) is a continuous powder processing equipment known for spheronization and extrusion. Its suitability for granulation remains uncertain, a common challenge in powder processing industries that deal with granules, pellets, and tablets. This study investigates the VDE's potential for granulation, using 65 µm CaCO3 powder and PEG 4000 as a liquid binder. In order to replicate several experimental setups with varying binder concentrations and liquid-to-solid ratios (L/S) of 0.1 and 0.15, eight DEM simulations were run. Our results indicate that higher binder concentrations yield more consistent products with fewer fines, while lower concentrations result in inconsistent products with increased fines. Low L/S ratios produce fragile, fine-sized products with a broad particle size distribution (PSD). DEM simulations reveal a direct relationship between liquid binder content and contact forces. Analysis of bonds formed, and particle counts in simulations corroborates experimental observations of fines production. Additionally, granule strength appears to be directly proportional to contact force. / Special gratitude is given to Ghana Scholarship Secretariat for providing the necessary funding for this research. / The full-text of this article will be released for public view at the end of the publisher embargo on 23 Jan 2025.
248

Development and Validation of a DEM-based Model for Predicting Grain Damage

Zhengpu Chen (7036694) 20 May 2024 (has links)
<p dir="ltr">During agricultural production, grain damage is a persistent problem that reduces grain quality. The goal of this study is to develop mechanics-based models that can accurately predict grain damage caused by mechanical handling processes and validate the models with lab-scale and industrial-scale test systems.</p><p dir="ltr">A discrete element method (DEM) simulation was developed to predict the impact damage of corn kernels in a Stein breakage tester. The DEM model relied on an empirically generated, three-parameter Weibull distribution describing the damage probability of repeated impacts. It was found that the DEM model was able to give good predictions on the kernel damage fraction for different sample sizes and operating times. The root-mean-square deviation between the damage fractions acquired from the simulation and experiment is 0.05. A sensitivity analysis was performed to study the effects of material and interaction properties on damage fraction. It was found that damage resistance parameters, coefficients of restitution, and particle shape representation had a significant effect on damage fraction. The statistics of the number of contacts and impact velocity were collected in the simulation to interpret the results of sensitivity analysis at the contact level. The locations where the damage occurs on the particle and in the operating device were also predicted by the model.</p><p dir="ltr">In addition to impact damage, another major type of grain damage is compression damage caused by mechanical harvesting and handling processes. A mechanistic model was developed to predict the compression damage of corn kernels using the DEM. The critical model input parameters were determined using a combination of single kernel direct measurements and bulk kernel calibration tests. The Young's modulus was measured with a single kernel compression test and verified with a bulk kernel compression test. An innovative approach was proposed to calibrate the average failure stress using a bulk kernel compression test. After implementation of the model, a validation test was performed using a Victoria mill. Comparing the simulation and the experimental results demonstrated that the simulation gave a good prediction of the damage fraction and the location of the damage when the von Mises stress damage criterion with a variable damage threshold was used. A sensitivity analysis was conducted to study the effects of selected model input parameters, including particle shape, Young's modulus, particle-particle coefficient of friction, particle-boundary coefficient of friction, particle-boundary coefficient of restitution, and damage criterion.</p><p dir="ltr">An industrial-scale handling system was designed and built to validate the DEM-based grain impact damage model. The low moisture content corn and soybean samples were handled through the system at three impeller speed levels and two feed rate levels, and the amount of damage caused by handling was evaluated. DEM simulations with the impact damage model were constructed and run under the corresponding test conditions. The experimental results showed that grain damage increased with increasing impeller speed and decreasing feed rate, which aligned with the model predictions. The simulated damage fraction values were larger than the experimental measurements when the experimentally-measured DEM input parameters were used. The simulation predictions can be significantly improved by decreasing the particle-boundary coefficient of restitution (PB COR). The mean absolute error between the simulation and experimental results decreased from 0.14 to 0.02 for the corn tests and from 0.05 to 0.01 for the soybean tests after the reduction of PB COR.</p><p dir="ltr">The developed damage models can accurately predict the amount of grain damage and the locations where the damage occur within a grain handling system. The models are expected to be useful in providing guidance on designing and operating grain handling processes to minimize kernel damage and, thus, improve grain quality. To further improve the performance of the model, the methods that accurately and efficiently determine the model input parameters need to be explored. In addition, in this work, the models were only applied to corn and soybeans at specific conditions. The applicability of the model to other types of grain, such as rice, or other grain conditions, such as wet corn, should be investigated.</p>
249

Comparison of Two Algorithms for Removing Depressions and Delineating Flow Networks From Grid Digital Elevation Models

Srivastava, Anurag 03 August 2000 (has links)
Digital elevation models (DEMs) and their derivatives such as slope, flow direction and flow accumulation maps, are used frequently as inputs to hydrologic and nonpoint source modeling. The depressions which are frequently present in DEMs may represent the actual topography, but are often the result of errors. Creating a depression-free surface is commonly required prior to deriving flow direction, flow accumulation, flow network, and watershed boundary maps. The objectives of this study were: 1) characterize the occurrence of depressions in 30m USGS DEMs and assess correlations to watershed topographic characteristics, and 2) compare the performance of two algorithms used to remove depressions and delineate flow networks from DEMs. Sixty-six watersheds were selected to represent a range of topographic conditions characteristic of the Piedmont and Mountain and Valley regions of Virginia. Analysis was based on USGS 30m DEMs with elevations in integer meters. With few exceptions watersheds fell on single 7.5minute USGS quadrangle sheets, ranged in size from 450 to 3000 hectares, and had average slopes ranging from 3 to 20 percent. ArcView (3.1) with the Spatial Analyst (1.1) extension was used to summarize characteristics of each watershed including slope, elevation range, elevation standard deviation, curvature, channel slope, and drainage density. TOPAZ (ver 1.2) and ArcView were each used to generate a depression-free surface, flow network and watershed area. Characteristics of the areas 'cut' and 'filled' by the algorithms were compared to topographic characteristics of the watersheds. Blue line streams were digitized from scanned USGS 7.5minute topographic maps (DRGs) then rasterized at 30 m for analysis of distance from the derived flow networks. The removal of depressions resulted in changes in elevation values in 0 - 11% of the cells in the watersheds. The percentage of area changed was higher in flatter watersheds. Changed elevation cells resulted in changes in two to three times as many cells in derivative flow direction, flow accumulation and slope grids. Mean fill depth by watershed ranged from 0 to 10 m, with maximum fill depths up to 40 m. In comparison with ArcView, TOPAZ, on average affected 30% fewer cells with less change in elevation. The significance of the difference between ArcView and TOPAZ decreased as watershed slope increased. A spatial assessment of the modified elevation and slope cells showed that depressions in the DEMs occur predominantly on or along the flow network. Flow networks derived by ArcView and TOPAZ were not significantly different from blue line streams digitized from the USGS quadrangles as indicated by a paired t test. Watershed area delineated by ArcView and TOPAZ was different for almost all watersheds, but was generally within 1%. Conclusions from this study are: 1) The depressions in 30 m DEMs can make up a significant portion of the area especially for flatter watersheds; 2) The TOPAZ algorithm performed better than ArcView in minimizing the area modified in the process of creating a depressionless surface, particularly in flatter topography; 3) Areas affected by removing depressions are predominantly adjacent to the stream network; 4) For every elevation cell changed, slopes are changed for two to three cells, on average; and 5) ArcView and TOPAZ derived flow networks closely matched the blue line streams. / Master of Science
250

Use of Multi-Temporal LiDAR-derived DEMs for Landslide Detection in the Klarälven Region, Sweden

Renard, Salomé January 2024 (has links)
Landslides are one of the most widespread, yet difficult to predict, geohazards in the world. Theyrepresent a major threat to society, which is why it is so important to understand and study them.Landslide detection is one of the approaches that help scientists to gain a better knowledge of landslides,how they form and the characteristics they hold. In this work, a new landslide detection technique istested in the Klarälven Region, Sweden. The method involves using multi-temporal DEMs generatedfrom LiDAR point clouds from 2010 and 2020. Once two respective DEMs are generated from theoriginal point cloud data sets, a DEM of Difference (DoD) is obtained by subtracting the 2010 DEMfrom the 2020 DEM. The DoD highlights areas of vertical change over the ten-year period. In order todetect potential landslides, a Level of detection (LoD) threshold is applied, as well as a second upperthreshold filtering out elevation difference resulting from anthropogenic activities. Lastly, a spatialthreshold is applied to eliminate any remaining potential errors clusters that are too small to belandslides. Once this stage is completed, the study area is surveyed, focusing on certain areacharacterised by particular slope angles and soil types most likely to exhibit mass movement. Thishelped in the analysis and interpretation of the data. In order to discuss the results as fully as possible,four types of region were studied in more detail using four representative examples. Since a few doubtfulcases were found, potential sources of error are also being explored. Despite minor inaccuracies, themethod appears to be a relevant technique for detecting differences in altitude, even if it also considersunnatural mass movements.

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