•Rainfall partitioning is the most influenced by amount of rainfall and its intensity.•Drop diameter and velocity significantly influenced rainfall partitioning.•Affecting variables differ among ...vegetation periods and tree species.
Rainfall partitioning is an important part of the ecohydrological cycle, influenced by numerous variables. Rainfall partitioning for pine (Pinus nigra Arnold) and birch (Betula pendula Roth.) trees was measured from January 2014 to June 2017 in an urban area of Ljubljana, Slovenia. 180 events from more than three years of observations were analyzed, focusing on 13 meteorological variables, including the number of raindrops, their diameter, and velocity. Regression tree and boosted regression tree analyses were performed to evaluate the influence of the variables on rainfall interception loss, throughfall, and stemflow in different phenoseasons. The amount of rainfall was recognized as the most influential variable, followed by rainfall intensity and the number of raindrops. Higher rainfall amount, intensity, and the number of drops decreased percentage of rainfall interception loss. Rainfall amount and intensity were the most influential on interception loss by birch and pine trees during the leafed and leafless periods, respectively. Lower wind speed was found to increase throughfall, whereas wind direction had no significant influence. Consideration of drop size spectrum properties proved to be important, since the number of drops, drop diameter, and median volume diameter were often recognized as important influential variables.
•Experimental characterization of droplet velocity emerging from gas-focused micro-jet breakup.•Validation of the numerical model of micro-jet in terms of its velocity and shape.•Improved capability ...in virtual design of micro-nozzles for sample delivery in femtosecond crystallography.
Compressible multiphase numerical simulations of gas-focused micro-jets are compared with the experimental data obtained with the dual pulse imaging laser-induced fluorescence drop velocimetry. Such jets, originating from a 3D printed gas dynamic virtual nozzle into a low-vacuum (150 Pa) environment, are increasingly being used for sample delivery in serial femtosecond crystallography. The distance traveled by a detaching drop from the jet is measured between the two consecutive illumination pulses with a known time delay at the positions 200 µm and 450 µm from the nozzle. Additionally, the high-speed camera images are used to analyze the shape of the jet. An axisymmetric, compressible, Newtonian two-phase helium-water mixture model is numerically solved within the framework of the volume of fluid and the finite volume method. The experimental and the computational studies are performed with a constant volumetric liquid flow rate of 14 μl/min and the gas mass flow rate in the range from 4.6 mg/min to 20 mg/min. The related jet Reynolds number ranges from 120 to 220 and Weber number from 30 to 150. The maximum difference between the measurements and the results of the numerical model in terms of the droplet velocity and jet diameter is within 10 %. The study provides new information on the jet velocities for micron-sized gas-focused nozzles. The validated numerical model can be used as a design tool for the nozzles dedicated to the specific needs of the femtosecond crystallography experiments.
In the pneumatic conveying process, particles move to the bend under the influence of inertia to form a particle rope, which will cause serious wear between the particles and the pipe wall, and then ...the dune model is designed and installed in the 90° bend to reduce energy consumption and wear in this study. Firstly, the minimum pressure drop velocity of particles transported by different size dune models was obtained through experimental study. Then the energy saving mechanism of the dune model is studied by CFD-DEM coupling. The experimental results show that the installation of the dune model reduces the minimum pressure drop velocity. The numerical simulation results show that the number of collisions between the particles and the tube wall in the vertical tube decreases after the installation of the dune model, which reduces the energy loss. Moreover, the increasing of tail size of the dune model is beneficial to the diffusion and acceleration of the particles in the vertical tube.
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•Dune model is installed in a 90° bend to change flow pattern of particles in bend-vertical pipe.•Increasing tail size of dune model facilitates particle dispersion in vertical tube.•Dune model reduces the friction between particles and pipe wall.•Installation of a dune model reduces mutation mode in velocity of gas and particle phases.
Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall ...simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions, which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection.
The artificially generated rainfall of the simulators used at the Universities Basel, La Rioja, Malaga, Trier, Tübingen, Valencia, Wageningen, Zaragoza, and at different CSIC (Spanish Scientific Research Council) institutes (Almeria, Cordoba, Granada, Murcia and Zaragoza) was measured with the same methods (Laser Precipitation Monitor for drop spectra and rain collectors for spatial distribution). Data are very beneficial for improvements of simulators and comparison of simulators and results. Furthermore, they can be used for comparative studies, e.g. with measured natural rainfall spectra. A broad range of rainfall data was measured (e.g. intensity: 37–360mmh−1; Christiansen Coefficient for spatial rainfall distribution: 61–98%; median volumetric drop diameter: 0.375–6.5mm; mean kinetic energy expenditure: 25–1322Jm−2h−1; mean kinetic energy per unit area and unit depth of rainfall: 0.77–50Jm−2mm−1). Similarities among the simulators could be found e.g. concerning drop size distributions (maximum drop numbers are reached within the smallest drop classes <1mm) and low fall velocities of bigger drops due to a general physical restriction. The comparison represents a good data-base for improvements and provides a consistent picture of the different parameters of the simulators that were tested.
•Small portable rainfall simulators in soil erosion and soil hydrology studies•Detailed investigation of simulated rainfall characteristics•Comparison of artificial rainfall generated by 13 rainfall simulators based in Europe•Identical methods in all simulations to ensure comparability•Methods: Laser Precipitation Monitor and rain collectors
The size of the drops determines soil erosion and runoff rates, and then the fate of ecosystems. Various raindrop measurement techniques and tools have been developed to determine natural and ...simulated raindrop size distributions and mean drop size. There is a need to improve the procedure to determine the raindrop properties, and this is why we develop a new technique to analyze drop size distribution and fall velocity. For this purpose a rainfall simulator with two oscillating Veejet 80100 nozzles in laboratory condition, and high speed imaging technique and edge detection approach in image processing was applied to identify and measure drop size and calculate drop velocity. The results showed that the rainfall simulator was able to create drops with diameter in the range from 0.2 to 9.9 mm. Fall velocity ranged from 0.8 to 9.2 m/s for different diameter classes in the height of 0.5 m above the ground. The results indicate that the low-cost technique developed in this paper had high ability to automatically and rapidly identify raindrops characteristics with high accuracy. This technique can help to calibrate other rainfall simulators, but also to characterize natural rainfall events in different regions, which is a worldwide need due to the lack of information, and the importance of the raindrop characteristic to characterize and model the soil erosion processes.
•Raindrop properties determine soil detachment and soil transport.•It is necessary to find easy-to-apply and accurate techniques to measure raindrop properties.•Simulated raindrops were used to test a new method.•A high speed imaging technique and edge detection in image processing was applied.•Fall velocity and raindrop size were accurately measured.
► A high accuracy, portable rainfall simulator for field rainfall simulations was developed. ► It generates drops that nearly reach their terminal velocity. ► The energy flux of the simulated rain is ...76% of the energy flux applied by the expected natural rainfall. ► It produces homogenous water distribution in varied rain intensities. ► This rainfall simulator can be a powerful tool for field infiltration, soil crusting and soil erosion experiments.
Rain simulators (RSs) are used in soil crusting and soil erosion laboratory and field studies. The energy flux produced by RSs is usually high in respect to the intensity of the application. The high energy flux applied on the soil surface by these RSs becomes a crucial disadvantage when low intensity rainfall is considered. Moreover, crust formation under natural field conditions is very different from crusting in disturbed soil samples.
The main purpose of this study was the design and the construction of a portable RS to be used in the field for simulating rainfalls that induce soil crusting and thus lead to the generation of runoff and eventually soil erosion. A high accuracy portable RS for field rainfall simulations was designed and built. The D50 of the drops is 1.5mm with a ground hitting velocity that nearly matches the theoretical terminal velocity without the necessity of a tower (Barros et al., 2008). The energy flux of the simulated rain is 76% of the energy flux expected for a natural rainfall of the same intensity. The spatial distribution of water is homogenous for a wide range of rain intensities. This RS can be a powerful tool for field infiltration, soil crusting and soil erosion field trials.
Bloodstain pattern analysis (BPA) provides significant evidentiary value in crime scene interpretation and reconstruction. In this work, we develop a quantitative methodology using digital image ...analysis techniques to differentiate impact bloodstain patterns. The bloodstain patterns were digitally imaged and analyzed using image analysis algorithms. Our analysis of 72 unique bloodstain patterns, comprising more than 490,000 individual droplet stains, indicates that the mean drop size in a gunshot spatter pattern is at most 30% smaller than the mean drop stain size in blunt instrument patterns. In contrast, we demonstrate that the spatial distribution of the droplet stains—their density as a function of position in the pattern—significantly differs between gunshot and blunt instrument patterns, with densities as much as 400% larger for gunshot impacts. Thus, quantitative metrics involving the spatial distribution of droplet stains within a bloodstain pattern can be useful for objective differentiation between blunt instrument and gunshot bloodstain patterns.
Part of precipitation is intercepted by forest canopies, while the rest reaches the ground as throughfall or stemflow. This process is influenced by various meteorological variables, of which we have ...mainly focused on drop diameter and velocity. Rainfall in the open and throughfall under birch and pine trees have both been measured since 2014 in Ljubljana, Slovenia. The results demonstrate that the total throughfall during 3.5 years was 73% and 53% of rainfall under birch and pine trees, respectively. During the 236 analysed events, the median volume diameter was 1.8 mm (±1.7 mm), and kinetic energy between 0.01 mJ/cm2 and 23.3 mJ/cm2 was recorded. We closely analysed the effect of rainfall microstructure on throughfall under pine and birch trees during three specific rainfall events. The increase in drop diameter and fall velocity during a rainfall event instantaneously increased throughfall under pine trees between 25% and 47%, whereas no such changes were observed under birch trees. This may be the consequence of different tree properties of the two species. Additionally, in the case of a saturated canopy, throughfall under pine trees exceeded rainfall in the open after an onset of larger and faster drops.
It is known that damages to the subsea cables used for electric power transmission between islands and countries, including renewable energy from offshore wind power, current, tides, etc., cost much ...to restore, which causes social and economic losses. Various types of fishing rigs and anchors have been reported to be the greatest hazards to subsea cables. It is possible to design and construct a suitable protection facility for a subsea cable by precisely estimating the underwater behavior of such hazardous apparatuses. In this study, numerical simulations of the underwater behaviors of various hazardous apparatuses were carried out using fluid-structure interaction (FSI) analysis as a basic study to simulate the actual behavior phenomena of hazardous apparatuses in relation to a subsea cable. In addition, the underwater drop characteristics according to the types of hazardous apparatuses were compared. In order to verify the accuracy of the FSI analysis method used in this study, we compared the test results for underwater drops of a steel ball bearing. Stock anchors, stockless anchors, and rocket piles, which were actually reported to be the cases of damage to subsea cables along the southwest coast of Korea, were considered as the hazardous apparatuses for the numerical simulations. Each hazardous apparatus was generated by a Lagrangian model and coupled with the fluid domain idealized by the Eulerian equation to construct the three-dimensional FSI analysis model. The accuracy of the numerical simulation results was verified by comparing them with the analytical solutions, and the underwater drop characteristics according to the types of hazard apparatuses were compared.
The control rod assembly controls reactor power by adjusting its position during normal operation and shuts down chain reactions by its free drop under scram conditions. Therefore, the drop ...performance of the control rod assembly is important for the safety of a nuclear reactor. In this study, the drop performance of the conceptually designed control rod assembly for the prototype generation IV sodium-cooled fast reactor that is being developed at the Korea Atomic Energy Research Institute as a next-generation nuclear reactor was experimentally investigated. For the performance test, the test facility and test procedure were established first, and several free drop performance tests of the control rod assembly under different flow rate conditions were then carried out. Moreover, performance tests under several types and magnitudes of seismic loading conditions were also conducted to investigate the effects of seismic loading on the drop performance of the control rod assembly. The drop time of the conceptually designed control rod assembly for 0% of the tentatively designed flow rate was measured to be 1.527 seconds, and this agrees well with the analytically calculated drop time. It was also observed that the effect of seismic loading on the drop time was not significant.
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