Modelling hydraulic jump using the bubbly two-phase flow method

Hydraulic jumps have complex flow structures, characterised by strong turbulence and large air contents. It is difficult to numerically predict the flows. It is necessary to bolster the existing computer models to emphasise the gas phase in hydraulic jumps, and avoid the pitfall of treating the phenomenon as a single-phase water flow. This paper aims to improve predictions of hydraulic jumps as bubbly two-phase flow. We allow for airflow above the free surface and air mass entrained across it. We use the Reynolds-averaged Navier–Stokes equations to describe fluid motion, the volume of fluid method to track the interface, and the k–ε model for turbulence closure. A shear layer is shown to form between the bottom jet flow and the upper recirculation flow. The key to success in predicting the jet flow lies in formulating appropriate bottom boundary conditions. The majority of entrained air bubbles are advected downstream through the shear layer. Predictions of the recirculation region’s length and air volume fraction within the layer are validated by available measurements. The predictions show a linear growth of the shear layer. There is strong turbulence at the impingement, and the bulk of the turbulence kinetic energy is advected to the recirculation region via the shear layer. The predicted bottom-shear-stress distribution, with a peak value upstream of the toe of the jump and a decaying trend downstream, is realistic. This paper reveals a significant transient bottom shear stress associated with temporal fluctuations of mainly flow velocity in the jump. The prediction method discussed is useful for modelling hydraulic jumps and advancing the understanding of the complex flow phenomenon.     

Part I : <Emphasis Type="Italic">a priori</Emphasis> study of erosion and deposition with large eddy simulation of turbulent flow over multiple 2D sandy Gaussian hills

The micro-scale prediction of sand trapping or take-off over hilly terrains is a crucial issue in semi-arid regions for soil depletion. In this context, large eddy simulations around one or several hills are performed in order to provide statistical parameters to characterize the flow at micro-scales and provide data for mesoscale modelling. We focus on the determination of recirculation zones since they play an important role in solid particle erosion or entrapment. A new wall modeling adapted from Huang et al. (J Turbul 17:1–24, 2016) for rough boundary layers is found to improve the prediction of the recirculation zone length downstream of an isolated hill and is used for all the numerical cases presented here. A geometrical parameterization of the recirculation zones is proposed. When the recirculation region is assumed to have an ellipsoidal shape, the total surface of the recirculation can be obtained from this new parameterization and easily extrapolated to more general dune configurations. Numerical results are compared with experiments performed in our laboratory (Simoëns et al. in Procedia IUTAM 17:110–118, 2015) and good agreement is achieved. We explore general aerodynamic cases deduced from the urban canopy scheme of Oke (Energy Build 11:103–113, 1988). In this scheme the momentum and mass exchange between the upper layer and the space between hills is sorted according to the streamwise hill spacing within three basic cases of skimming, wake or isolated flow. The study of the recirculation zones, the mean velocity and Reynolds stress profiles around an isolated or two consecutive hills with different distances shows that the double hill configuration with 3H separation behaves as much as a whole to the upcoming flow. The vortex formed between the crests does not strongly affect the overall evolution of the outer flow. By an a priori prediction of the preferential zones of erosion and accumulation of fictive particles, it is shown that isolated dunes present more deposition and less erosion than two-hill configurations. The results presented in this study will be discussed in the presence of Lagrangian transport of sand particles above 2D Gaussian hills in future work.     

Status,source identification,and health risks of potentially toxic element concentrations in road dust in a medium-sized city in a developing country

This study aims to determine the status of potentially toxic element concentrations of road dust in a medium-sized city (Rawang, Malaysia). This study adopts source identification via enrichment factor, Pearson correlation analysis, and Fourier spectral analysis to identify sources of potentially toxic element concentrations in road dust in Rawang City, Malaysia. Health risk assessment was conducted to determine potential health risks (carcinogenic and non-carcinogenic risks) among adults and children via multiple pathways (i.e., ingestion, dermal contact, and inhalation). Mean of potentially toxic element concentrations were found in the order of Pb > Zn > Cr(IV) > Cu > Ni > Cd > As > Co. Source identification revealed that Cu, Cd, Pb, Zn, Ni, and Cr(IV) are associated with anthropogenic sources in industrial and highly populated areas in northern and southern Rawang, cement factories in southern Rawang, as well as the rapid development and population growth in northwestern Rawang, which have resulted in high traffic congestion. Cobalt, Fe, and As are related to geological background and lithologies in Rawang. Pathway orders for both carcinogenic and non-carcinogenic risks are ingestion, dermal contact, and inhalation, involving adults and children. Non-carcinogenic health risks in adults were attributed to Cr(IV), Pb, and Cd, whereas Cu, Cd, Cr(IV), Pb, and Zn were found to have non-carcinogenic health risks for children. Cd, Cr(IV), Pb, and As may induce carcinogenic risks in adults and children, and the total lifetime cancer risk values exceeded incremental lifetime.     

Geochemical fractionation of metals and metalloids in tailings and appraisal of environmental pollution in the abandoned Musina Copper Mine,South Africa

The economic benefits of mining industry have often overshadowed the serious challenges posed to the environments through huge volume of tailings generated and disposed in tailings dumps. Some of these challenges include the surface and groundwater contamination, dust, and inability to utilize the land for developmental purposes. The abandoned copper mine tailings in Musina (Limpopo province, South Africa) was investigated for particle size distribution, mineralogy, physicochemical properties using arrays of granulometric, X-ray diffraction, and X-ray fluorescence analyses. A modified Community Bureau of Reference (BCR) sequential chemical extraction method followed by inductively coupled plasma mass spectrometry/atomic emission spectrometry (ICP-MS/AES) technique was employed to assess bioavailability of metals. Principal component analysis was performed on the sequential extraction data to reveal different loadings and mobilities of metals in samples collected at various depths. The pH ranged between 7.5 and 8.5 (average?≈?8.0) indicating alkaline medium. Samples composed mostly of poorly grated sands (i.e. 50% fine sand) with an average permeability of about 387.6 m/s. Samples have SiO₂/Al₂O₃ and Na₂O/(Al₂O₃?+?SiO₂) ratios and low plastic index (i.e. PI?≈?2.79) suggesting non-plastic and very low dry strength. Major minerals were comprised of quartz, epidote, and chlorite while the order of relative abundance of minerals in minor quantities is plagioclase?>?muscovite?>?hornblende?>?calcite?>?haematite. The largest percentage of elements such as As, Cd and Cr was strongly bound to less extractable fractions. Results showed high concentration and easily extractable Cu in the Musina Copper Mine tailings, which indicates bioavailability and poses environmental risk and potential health risk of human exposure. Principal component analysis revealed Fe-oxide/hydroxides, carbonate and clay components, and copper ore process are controlling the elements distribution.     

Coastal dwellers-power against climate change: a place-based perspective on individual and collective engagement in North Frisia

Climate change induces non-linear and unevenly distributed changes, such rising sea levels and extreme weather events that materialise on the regional level and considerably contribute to changes in the social fabric of regions, communities and places. Because of the need for societal responses, an in-depth understanding of individual and collective forms of engagement with climate change is of growing relevance. To contribute to close this gap, this paper applies a place-based approach for investigating how people’s place attachments and meanings inform individual and collective engagement with climate change. As a case study, the district of North Frisia (Germany) was chosen, a region between climate-change vulnerability and renewable-energy potential. Qualitative interviews and a household survey with coastal dwellers of the municipality of Reußenköge have been conducted, a group discussion with the Country Youth (Landjugend) and further interviews with experts from government, companies and associations spread over North Frisia and in Kiel. The results reveal two main findings: firstly, place-dependent attachments and meanings play a pivotal role for understanding people’s engagement with climate change, and secondly, the behavioural dimension of engagement involves diverse adaptation and mitigation measures adopted on individual and collective level. In sum, the findings conceptually and empirically reveal the importance of memories, experiences, knowledge and creativity for how people engage with climate change, but also exhibit the importance of policies mobilising community-based actions.     

High-resolution geological cartography and coastal evolution assessment at Armação de Pêra – Galé sector: a prototype for a national coastal mapping

Portuguese coastal areas are of current major concern due to the continuous expansion of a strong urbanization, accentuated development of economic activities, resilient land use and general population growth. A particular attention has been given to the shoreline evolution, pointing out evidences of critical coastal sectors that are prone to suffer adverse consequences of climate changes direct impacts. Areas where climate change and sea-level rise effects will be stronger include, among others, coastal sectors associated to soft rocky or mobile substrate shores and/or low morphological shores with recognized marked erosion trend. Within this context, the knowledge of the geological setting is imperative as different lithologies have distinct resistance and behavior against marine erosion. The available digital geological Portuguese cartography at 1:25000 scale is not suitable to well characterize the geology within the context of small geographic areas or within the perspective of costal management. Hence, the National Laboratory of Energy and Geology (LNEG) developed a prototype to evaluate the potential of the integrated “geological and coastal hazard mapping” at a 1:3000 resolution scale. The combination of detailed geology and historical coastline displacement information, in a single map, constitute a new and valuable cartographic product to support coastal managers and general users of littoral regions. The application of the prototype to the entire Portuguese coastal areas will be carried out by LNEG and digital information will be available at LNEG GeoPortal (http://geoportal.lneg.pt/).     

Elements of fishing community resilience to climate change in the coastal zone of Bangladesh

Resilience has been conceptualized in various ways by anthropologists, ecologists, systems scientists and engineers; the boundaries of resilience are subjective and context dependent. Consequently, choosing the standards and metrics for assessing resilience remains key challenges for policy makers. In this study, using multicriteria evaluation of 40 basic criteria of human, physical, financial, natural and social assets, we have identified several elements, such as experienced fishermen, natural abundance of hilsa (Tenualosa ilisha), ability to assert decision on fish selling, nets and boats ownership, social harmony and capacity of buying food as essential livelihood assets for the fishermen at Hatiya Island, Bangladesh. These assets may enhance the relative resilience of the fishing community of the island to climate change by as much as 20–40%. The results of this study will improve our understanding of the elements that lead to resilience at the community level.     

Effects of nanoparticles on Daphnia magna population dynamics

Spherical TiO₂ nanoparticles (npTiO₂) were prepared by controlled hydrolysis of tetraethoxy orthotitanate under a nitrogen atmosphere. ZnO nanoparticles (npZnO) were prepared using hydrothermal methods. The crystal structure, chemical, thermal and morphological properties of npZnO and npTiO₂ were characterised using Fourier Transform Infrared Spectrometer, enery-dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscope techniques. The short- and long-term experiments were started with neonates taken from the same culture and laboratory condition. In the acute experiments, npTiO₂, npZnO, and cocktail concentrations were applied. 96h-LC₅₀ values were 1.8, 0.7, and 0.1?mg?L^?1, respectively (p?<?.05). For the chronic experiments, different npTiO₂ concentrations were performed. 21d-LC₅₀ value was 1.0?mgL^?1 (p?<?.05). Morphometry became progressively worse in concentrations of more than 1?mgL^?1 npTiO₂. Neonate and young individuals were more sensitive to death because of their low tolerance. This result was affected by population progeny and growth rates (p?<?.05). While control and 0.5?mgL^?1 npTiO₂ groups were determined as growing population, 1.5 and 2?mgL^?1 npTiO₂ groups had decreased population size as R₀ values. Consequently, the relationships between nanoparticle accumulation within Daphnia magna and its population structure and body morphometry for each concentration were important indicators. Its tolerance level to nanoparticles under laboratory conditions reflected its replacement and behaviour in the ecosystem.     

Unexpected behavior of Zn,Cd, Cu,and Pb in soils contaminated by ore processing after 70 years of burial

Environmental Chemistry Letters - Heavy metals in contaminated ore processing areas present a risk of contamination of waters and life. Therefore, the most mobile fractions of metals, which can be...