Estimation of Soil Physico-chemical Properties by On-the-go Measurement of Soil Electrical Conductivity

For modern crop management practices, like precision farming, is crucial information about detailed spatial distribution of soil properties. A study was conducted to evaluate the on-the-go measurement of soil electrical conductivity for mapping of agronomical relevant soil properties. The experimental work was carried out on the eight fields of Rostenice a.s. farm enterprise, located in the South Moravia region of Czech Republic. The measurement of apparent electrical conductivity of soil was done by using CMD-1 and CMD-6L instruments (GF Instruments, Czech Republic) in 2013 (117 ha) and 2016 (359 ha). Soil properties were obtained by soil sampling in irregular grid with the density of 1 sample per 3 ha. Soil samples were taken from the depth of 30 cm and analyzed for soil texture (percentage of clay, silt and sand particles), content of available nutrients (P, K, Mg, Ca) and soil organic matter (SOM) content. The results of correlation analysis showed differences in main sensitivity of EMI to the soil properties across observed fields. Most frequent correlation was found in the percentage of clay particles smaller than 0.002 mm (r = 0.598). The correlation between EMI and nutrients content in soil and pH value was significant only for few fields. These results were obtained for individual fields, the aggregated evaluation showed lower relationships to EC. These outcomes showed, that rather than predictor of soil properties could be on-the-go measurement of soil EC used for identification of main zones within the fields at high spatial level

Estimation of Soil Physico-chemical Properties by On-the-go Measurement of Soil Electrical Conductivity

For modern crop management practices, like precision farming, is crucial information about detailed spatial distribution of soil properties. A study was conducted to evaluate the on-the-go measurement of soil electrical conductivity for mapping of agronomical relevant soil properties. The experimental work was carried out on the eight fields of Rostenice a.s. farm enterprise, located in the South Moravia region of Czech Republic. The measurement of apparent electrical conductivity of soil was done by using CMD-1 and CMD-6L instruments (GF Instruments, Czech Republic) in 2013 (117 ha) and 2016 (359 ha). Soil properties were obtained by soil sampling in irregular grid with the density of 1 sample per 3 ha. Soil samples were taken from the depth of 30 cm and analyzed for soil texture (percentage of clay, silt and sand particles), content of available nutrients (P, K, Mg, Ca) and soil organic matter (SOM) content. The results of correlation analysis showed differences in main sensitivity of EMI to the soil properties across observed fields. Most frequent correlation was found in the percentage of clay particles smaller than 0.002 mm (r = 0.598). The correlation between EMI and nutrients content in soil and pH value was significant only for few fields. These results were obtained for individual fields, the aggregated evaluation showed lower relationships to EC. These outcomes showed, that rather than predictor of soil properties could be on-the-go measurement of soil EC used for identification of main zones within the fields at high spatial level

Dynamics in European exports in times of crisis: the impact on growth at home and abroad

While the financial crisis of 2008-2009 led to the great collapse of international trade, the European debt crisis in 2010-2013 did not have such a drastic impact on trade. The collapse has been studied a lot in recent empirical literature, but the European debt crisis has not been investigated thoroughly yet. This paper looks into the impact of economic growth in European exporters and in their export destination markets on export performance as reflected in total export growth and growth in various export margins. Our findings point to an important role for both demand and supply side factors

Dinamika Taylorjevega mehurja v protitočnem turbulentnem toku

This thesis presents an in-depth investigation of Taylor bubbles in counter-current flows, employing a dual approach of high-fidelity numerical simulations and state-of-the-art experimental techniques. Taylor bubble is one of the manifestations of two-phase slug flow in a pipe. It consists of large gas bubbles separated from each other by slugs of the liquid phase. The dynamics of Taylor bubbles in air-water mixture were examined in two different regimes - the transitional flow regime with Reynolds number $Re = 1400$ and the fully turbulent flow with $Re = 5600$. The study focused on bubbles of various lengths in stagnant conditions, where buoyancy is counterbalanced by inertial drag in the downward turbulent flow. The experimental study focuses on three main aspects: the analysis of bubble disintegration, the detailed analysis of the bubble interface dynamics and measurement of velocity fields using Particle Image Velocimetry (PIV) technique. By developing specialized algorithms for interface reconstruction from the obtained high-speed camera images, the research identified asymmetric, bullet-train-like shapes of Taylor bubbles in fully turbulent flow, but axi-symmetric bubbles in transitional liquid flow. This was a significant finding, demonstrating also the presence of disturbance waves along the bubble interface, which were tracked with high sensitivity. These waves exhibited correlated movements across the bubble surface, adding new understanding to the behavior of such flows. The numerical study focused on the bubble behavior and breakup mechanisms, highlighting the limitations of the numerical methods. Using the OpenFOAM framework, the research implemented a high-order Runge-Kutta time-integration scheme combined with the Volume-Of-Fluid (VOF) method and the geometric reconstruction of bubble interfaces. The study concentrated on the transitional flow regime with a liquid $Re=1400$, comparing algebraic and geometric capturing techniques. The results highlighted the superiority of geometric reconstruction in capturing the nuances of Taylor bubble breakup. A novel discovery was also the emergence of a secondary vortex in the turbulent wake of the Taylor bubble, particularly noticeable at finer mesh resolutions. This thesis contributes to the field of nuclear engineering and fluid dynamics by providing a more comprehensive understanding of Taylor bubble behavior in counter-current flows. The combination of experimental observations and numerical simulations offers a holistic view, paving the way for improved designs and operations in various engineering fields where such flow phenomena are encountered.Taylorjev mehur je ena od manifestacij dvofaznega čepastega toka v cevi, ki se pojavlja v številnih industrijskih procesih in napravah. Sestavljajo ga veliki plinski mehurji, ločeni drug od drugega s čepi kapljevine. Doktorsko delo se osredotoča na obnašanje Taylorjevega mehurja v protitoku kapljevine, pri čemer smo uporabili numerične simulacije visoke ločljivosti in najsodobnejše eksperimentalne metode za podrobno analizo hitrostnih polj, dinamike medfazne površine in razpada mehurja. Z uporabo hitrotekoče kamere je bila dinamika Taylorjevih mehurjev v mešanicah zrak-voda natančno raziskana v dveh različnih režimih – prehodnem režimu toka z Reynoldsovim številom $Re = 1400$ in turbulentnem toku z $Re = 5600$. Študija se je osredotočila na mehurje dolžine $2-10D_h$, pri katerih je vzgon uravnotežen z vztrajnostnim uporom v padajočem turbulentnem toku. Z razvojem algoritma za prepoznavo medfazne površine na posnetih slikah je analiza identificirala asimetrične oblike mehurjev, podobne obliki hitrih vlakov. To je pomembna ugotovitev, ki je pokazala tudi prisotnost majhnih vzbujenih valov vzdolž površine mehurjev, ki smo jim z omenjenim algoritmom sledili z visoko občutljivostjo. Ti valovi so pokazali korelirana gibanja po površini mehurja, kar je dodalo novo razumevanje o obnašanju tovrstnih tokov. Pri uporabi orodja za računsko dinamiko tekočin OpenFOAM je bila implementirana Runge-Kutta shema časovne integracije visokega reda v kombinaciji z metodo VOF in geometrično rekonstrukcijo medfazne površine. Študija se je osredotočila na režim prehodnega toka s kapljevinastim $Re=1400$ ter primerjala algebraične in geometrične tehnike zajemanja medfazne površine. Rezultati so pokazali prednost geometričnega zajemanja pri simulacijah razpada Taylorjevega mehurja. Novo odkritje je tudi pojav sekundarnega vrtinca za Taylorjevim mehurjem, v t.i. sledi Taylorjevega mehurja, ki je še posebej opazen pri gostejših ločljivostih mreže, potrdili pa smo ga tudi z eksperimenti. Doktorsko delo prispeva k področju jedrske tehnike in dinamike tekočin s celovitejšim razumevanjem obnašanja čepastih tokov v protitočnih turbulentnih tokovih, ki se lahko pojavijo tudi v primarni zanki tlačnovodnih jedrskih elektrarn. Kombinacija eksperimentalnov in numeričnih simulacij ponuja bolj celostni pogled ter utira pot izboljšanemu načrtovanju na različnih inženirskih področjih, kjer se pojavljajo tovrstni pretočni pojavi

Large Eddy Simulations of turbulent heat transfer near heated foil

Na Odseku za reaktorsko tehniko Inštituta Jožef Stefan se postavlja nov eksperiment v Laboratoriju za termohidravliko večfaznih tokov (THELMA). Namen eksperimenta je študija temperaturnih fluktuacij na greti kovinski foliji, ki je hlajena s turbulentnim tokom. Načrtovanje eksperimenta temelji na numeričnih simulacijah, v katerih smo analizirali vpliv različnih aproksimacij na temperaturne fluktuacije na greti foliji. To delo opisuje rezultate simulacij. Tok in prenos toplote v novem eksperimentu smo napovedali s simulacijami z metodo velikih vrtincev (ang. Large Eddy Simulation) s pomočjo računalniškega programa OpenFOAM. Prevajanja toplote v foliji nismo modelirali. Folijo smo opisali z idealiziranim robnim pogojem konstantnega toplotnega toka. Simulacije so predpostavljale nestisljiv, polno razvit turbulentni tok Newtonske tekočine z Reynoldsovim številom 10000. V prvih simulacijah je bila dodana temperatura kot pasivni skalar, torej brez povratne zanke na enačbo za ohranitev gibalne količine. Drugi del simulacij pa je upošteval spreminjanje viskoznosti vode s temperaturo ter vzgonske sile. Določili smo ustrezno toplotno moč folije v eksperimentu ter moč, pri kateri je mogoče zanemariti vpliv temperature na materialne lastnosti vode. Posebej nas je zanimala porazdelitev temperature na vroči foliji v turbulentnem režimu. Z analizo koherentnih termičnih struktur v simulacijah smo uspeli določiti potrebno resolucijo in frekvenco visokohitrostne termične kamere pri danemu Reynoldsovemu in Prandtlovemu številu. V zaključku je predstavljena kratka primerjava naših simulacij s preliminarnimi meritvami temperaturnih fluktuacij na greti foliji.At Reactor Engineering Division of Jožef Stefan Institute a new experiment is being designed in the THELMA laboratory to study temperature fluctuations at the heated foil cooled by turbulent flow. Detailed design of the experiment is based on Computational Fluid Dynamics (CFD) studies which are described in the present work. The flow and heat transfer in the new experiment predicted with a wall-resolved Large Eddy Simulation (LES) using a wall-adapting local eddy-viscosity (WALE) model in OpenFOAM computer code. Foil was modeled with approximation of the constant heat flux. Simulations assumed incompressible, fully developed turbulent flow of Newtonian fluids with Reynolds number of 10000. In the first part of the study, heat transfer has been included to the study using temperature as a passive scalar, so there is no feedback loop on mass and momentum conservation equation. The second part of the simulations took into account the influence of the temperature on the water viscosity and density. We have identified the power of the foil in the experiment and the maximum foil temperatures at which the water temperature can be described with the passive scalar approximation. The most relevant result of our simulations were temperature fluctuations on the foil. With observation and analysis of coherent thermal structures in simulations we have predicted the required resolution and frequency needed by thermographic high-speed camera at given Reynolds and Prandtl numbers. In the Conclusions we present the comparison of our simulations with the preliminary measurements

Dynamics in European Exports in Times of Crisis: The Impact on Growth at Home and Abroad

While the financial crisis of 2008-2009 led to the great collapse of international trade, the European debt crisis in 2010-2013 did not have such a drastic impact on trade. The collapse has been studied a lot in recent empirical literature, but the European debt crisis has not been investigated thoroughly yet. This paper looks into the impact of economic growth in European exporters and in their export destination markets on export performance as reflected in total export growth and growth in various export margins. Our findings point to an important role for both demand and supply side factors