Laboratory Tank Research Articles

Performance evaluation of the Hydroluis drainpipe-envelope system in a saline-sodic soil

Subsurface drains, when installed in non-cohesive soil, are typically covered with an envelope to tackle problems of clogging and siltation. Selecting a suitable envelope material, however, is complicated and depends primarily on soil characteristics in the area where the drains are to be installed. A new promising drainpipe-envelope concept, Hydroluis, has been developed which the designers claim works in a wide range of soils. The Hydroluis drainpipe consists of a corrugated inner pipe with three rows of perforations at the top and an unperforated outer pipe that covers the top two thirds of the inner pipe. We analysed the hydraulic and filter functions of this new drainpipe in a soil tank laboratory model with a saline-sodic problem soil from south-western Iran and compared Hydroluis performance with that of a locally-manufactured synthetic envelope material (PP450). The silty clay soil used in this study was 40 % clay, with a plasticity index (IP) of 16.9 and an exchangeable sodium percentage (ESP) of 60.4 %. The Hydroluis drainpipe clogged during the first two weeks of the test due to invasion of the test soil into the space between the inner and outer pipes. Of the substantial volume of sediment that entered the Hydroluis inner pipe, 38 % removed from the pipe in the first day. In contrast, the PP450 drainpipe showed good hydraulic and filter functions, entering very little sediment to drainpipe during the entire test period and stabilizing at drainage rate of 28 mm/day and entrance resistance of 55 days/m, at around day 50. Our analyses suggest that the clogging and poor drainage function of the Hydroluis drainpipe was caused by the higher flow velocity (21.5 times higher) at the soil-envelope interface of the drainpipe, in addition to the lower Hydroluis drainpipe’s soil retention capacity (18 times lower) compared to the PP450 drainpipe. Assuming Stokes’ Law governs filter function, the results of Hydroluis design evaluation also suggest that in stable soils, very fine sand or coarser soil particles (D > 0.05 mm) place no serious limitations for Hydroluis drainpipe application, whereas the current design is unsuitable for filtering fine silt particles (0.002 < D < 0.02 mm). In conclusion, we suppose the Hydroluis drainpipe does not perform well in silty saline-sodic soils, such as those found in south-western Khuzestan Province, Iran.

Normal and Tangential Drag Forces of Nylon Nets, Clean and with Fouling, in Fish Farming. An Experimental Study

Experiments in a laboratory tank have provided measurements of the normal and tangential drag forces exerted on flat nets for different flow conditions. From those forces, normal and tangential drag coefficients of the nets have been obtained as functions of the Reynolds number and the solidity index. The experiments used two types of nets employed in the operation of a cultivation center: the fish net and the sea lion net, for the clean situation and for real operating conditions, with fouling adhered to the nets. Polyethylene ropes were used to characterize the presence of fouling in the nets. The experiments were carried out to determine equations for the normal and tangential drag coefficients. For the normal drag coefficient, the equations are linear with the Reynolds number, and the coefficients of the equations are linear with the solidity index. The equations are not so accurate for the tangential drag coefficient. The Reynolds number is not a relevant parameter for this coefficient and neither is the solidity index for the fish net, but the coefficient grows slightly with it for single and double sea lion nets with fouling. The literature review on the drag forces of nets reports that the tangential drag force is around 30% of the normal drag force. This value is approximately an average value of the ratio for the sea lion net and is higher for the clean fish net in this article.

Evaluating the Euler-Euler approach for predicting a strongly 3D bubble-induced recirculatory flow with OpenFOAM

Wastewater treatment plants use bubbly flows to promote grit removal from the plant’s influent. Computational fluid dynamics is an attractive tool to virtually prototype grit-chamber designs. This study assesses a two-phase unsteady Reynolds-averaged Euler-Euler (uRANS-EE) approach to predict bubble induced recirculatory flow in a laboratory tank of similar complexity to that expected in a full-scale grit-chamber. Numerical results are validated against a comprehensive experimental data set consisting of a 3D reconstruction of the flow field using a multi-plane stereoscopic particle image velocimetry technique, void fraction profiles using an optical probe and bubble rise-velocities using high-speed video. Depending on the combination of modeling parameters the predicted volumetric fluid flux returning towards the diffuser varied between 60 and 97% of the experimental flux. Predicted rise velocities exceeded measured values by a factor between 1.15 to 1.75 and near bed velocities were underpredicted by upwards of 25%. The principal 3D flow field features were predicted to a sufficient accuracy to support the use of the uRANS-EE approach for numerical grit-chamber prototyping.

A vision system for pose estimation of an underwater robot

This paper presents a vision system designed for an underwater robot to facilitate measuring the distance to an inspected surface and its orientation with respect to the robot. The system uses a set of laser modules to project a rectangular dot pattern on the inspected surface. The vision system is used to measure the dots’ locations in the 3D space and calculate the distance to the surface, together with the pitch angle and the yaw angle of the camera. A novel calibration procedure is presented, which allows for constructing high resolution camera-laser systems, without requiring a perfect alignment of laser beams and camera optical axis. An underwater vision system simulation environment, based on open-source software, is also introduced and extensively used to test the developed algorithms. The experimental results, obtained in a laboratory tank and a pool, confirm high performance of the system.

Combined Plate-Pile Foundations Settlement Calculation Under Cyclic Loading

The purpose of the study is to develop a method for calculating the settlement of a combined plate-pile foundation, with taking into account the effect from the repetitive cyclic loads in the process of construction and operation of buildings and structures. Experimental researches on plate-pile foundations were conducted in laboratory tanks and the field in order to find basic laws of such foundations behavior at cyclic loading. A method has been developed for calculating the estimated subsidence of the soil base of slabs-piles, taking into account the complex stress-strain state in the system of “plate grillage-ground between the piles-ground base” under cyclic loading. The improved method for calculating the settlement of plate-pile foundations under the cyclic load action allows to increase reliability, design bearing capacity, reduce the settlement, and as a result to obtain more cost-effective design solutions by saving materials and time during the construction of this type foundations.

Heart rate bio-loggers as welfare indicators in Atlantic salmon (Salmo salar) aquaculture

In this study, 12 farmed Atlantic salmon (~1200 g) were tagged with commercially available heart rate (HR) bio-loggers and maintained in a controlled fish tank laboratory environment at 9 °C on a 12 h day/night cycle for 13 weeks. Apart from one fish that had obtained severe wounds on the tail region in the beginning, the remaining fish survived the entire test period and displayed consistent and similar HR in response to the day/night cycles with peak HR midday during feeding. At the end of the experiment, untagged conspecifics had significantly higher weights, fork lengths and conditions factors, showing the bio-logger may have a long term negative impact on growth. However, tagged fish still gained weight during the trial. Resting HR, as measured at night and early morning, decreased significantly over the first 2–3 weeks, and remained stable at ~25 beats min−1 between week 3 and 10, highlighting that substantial time is required for complete recovery following implantation of the bio-logger. At the start of week 11, 12 and 13, crowding stress trials of 30 min were performed which elevated HR to 55.7 beats min−1, whereafter it took 24 h to recover normal HR. Emerging bio-logger technologies can provide otherwise unobtainable information on the physiology and behaviour in free swimming individual fish over long periods and has great potential as welfare assessment tools in aquaculture. However, the impact of the tag must be considered with regards to the general representativeness of untagged counterparts when interpreting data.

Instability and cross-boundary-layer transport by shoaling internal waves over realistic slopes

Internal solitary and solitary-like waves (ISW) play an important role in mixing and sediment resuspension in naturally occurring stratified fluids, primarily through various instabilities and wave-breaking mechanisms. When shoaling into shallow waters, waves of depression may either fission into a packet of waves of elevation over mild slopes or break over steep slopes. The fissioning process is generally considered a less efficient transport and resuspension mechanism, compared to wave breaking, since very little turbulent mixing or energy dissipation occurs during this process. In the present work, however, we found that this is not always the case, at least in the particular context of ISW boundary-layer interaction. Using high-resolution numerical simulations performed in a domain representing a tilted laboratory tank, we found that boundary-layer instability in the form of a separation bubble consistently occurs during the fissioning process. The separation bubble is generated beneath the wave of elevation that emerges from the fissioning process, and is vitally influenced by currents induced by the leading wave of depression. As the waves shoal further, the growth and breakdown of the separation bubble leads to significant cross-boundary-layer transport. The results suggest that the fissioning process, which occurs over a considerable geographical region in the ocean, can be as efficient as wave breaking when it comes to cross-boundary-layer transport.

Assessment of sea urchin spawning induction and oocyte conservation applied to ecotoxicological assays

Abstract Marine toxicity tests using sea urchin embryos and larvae are characterized by physicochemical induction for the release of gametes by adult organisms and by the production of excess gamic material after induction. Evaluating the effects of mortality that inducers cause on organisms, and the improvement in oocyte maintenance techniques for subsequent use, are actions of interest in the conservation of species and the sustainable use of this type of biological model. For this study, adults of the sea urchin species Lytechinus variegatus and Echinometra lucunter were obtained from the field for inductions and tests with their gametes in the laboratory. The species L. variegatus was used in maintenance experiments to assess health after induction (longline outdoor and indoor tanks) and mortality rates after induction by potassium chloride (KCl) and a mixture of potassium chloride with calcium chloride (CaCl2), and to evaluate bacterial growth as well as antibiograms of seawater resulting from induced spawning and in vitro fertilization. For the species E. lucunter, experiments with the same chemical inducers on mortality rates were carried out, as well as the conservation of oocytes in artificial seawater with antibiotics selected for their efficiency and toxicity for later use. Maintenance in the laboratory tanks, filled with seawater in a closed system, showed the lowest mortality rates in the group of non-induced organisms (control). The mixture of KCl and CaCl2 resulted in the lowest mortality rates of the adult organisms after spawning induction. The antibiotics Chloramphenicol and Gentamicin showed moderate efficiency in inhibiting bacterial growth, but with low toxicity, demonstrating the ability to maintain the integrity of sea urchin oocytes for up to 14 days under refrigeration.

Optimization of Drag Reducing Shark Inspired Blade-Shape Riblet Surfaces in External Flow

The main goal of this research is to study the drag reduction capabilities of blade-shape riblet surfaces in external flows. For this purpose, the ability of riblet surfaces for drag reduction of an underwater hydrodynamic model has been investigated. The surface geometry has been modified by applying shark skin inspired blade-shape riblets on the surface. These riblets have been modeled in various dimensions and applied on the exterior surface of an underwater hydrodynamic model, and their effects on the exerted drag force, at different flow velocities, have been studied numerically. For validating the numerical solution, the simulation results have been compared with the experimental data obtained by testing an underwater hydrodynamic model in a towing tank laboratory; and the validity of the numerical solution results has been confirmed. The results indicated that, riblet spacing has a significant effect on the reduction of drag force. Furthermore, by increasing the riblet spacing, the drag force is increased rather than decreased. Also, as the velocity increases, the performance of riblets in reducing the drag force is enhanced. In order to minimize the drag force applied on the underwater hydrodynamic model, by analyzing the numerical results, the most optimum riblet spacing has been obtained; at which the drag force is reduced by 7%. The achieved distance is a limit value; and at distances smaller or larger than this optimal distance, the effectiveness of the blade-shape riblet surface in reducing the drag force diminishes.

Descriptions of spawning of the pouched lamprey (Geotria australis) in tanks and of morphological changes leading up to and following spawning

The anadromous Geotria australis, one of only three lamprey species representing the early agnathan (jawless) stage of vertebrate evolution in Australia and New Zealand, is declining in abundance. Its adults were caught soon after they had entered rivers on their non-trophic upstream migration and maintained in laboratory tanks for 13–15 months through to spawning. As adult G. australis are susceptible to haemorrhagic septicaemia, they were treated prophylactically and maintained in 3-m3 aquaria supplied with a flow-through charcoal filtration system and UV steriliser. Air temperature and the light:dark regime were constantly adjusted to parallel those in the environment. Males developed the very large suctorial disc and gular pouch characteristic of maturity and both sexes matured at the same time as in the wild. While males frequently showed aggressive behaviour towards each other, the same male and female mated on several occasions. The male coiled around the female and, with his urogenital papilla close to the female’s cloaca, twisted and vibrated, leading to egg release. These eggs formed coagulated clusters as in the wild, with many progressing through to the eight-cell stage. Remarkably, numerous G. australis were still alive 95–392 days after the end of the short spawning period, and one male after a further 119 days. Postspawning survival would be facilitated inter alia by extensive proteolysis, reflected in a shortening of the body. The data in this paper emphasise that G. australis is a highly atypical lamprey and provides invaluable information for conserving this declining species.

A Multi-Function Sensor for Eddy Correlation Measurements of Benthic Flux.

Eddy Correlation (EC) is a technique that can be used to measure transport of substances in aquatic ecosystems between bottom sediments and the overlying water (i.e. benthic fluxes). Based on high-speed, simultaneous, and co-located velocity and concentration measurements, EC has been successfully used in a variety of freshwater and marine settings to determine benthic fluxes of dissolved oxygen. Application to a larger range of compounds is limited, however, by the lack of suitable chemical sensors. Here, we describe FACT, a novel, high-speed, multi-function sensor created to expand the range of benthic fluxes that can be measured with EC. An optical fiber spectrofluorometer with a proximally located conductivity cell and thermistor, FACT enables benthic flux measurements of fluorescing compounds, such as fluorescent dissolved organic matter, as well as of heat and salinity which can be used as tracers for submarine groundwater discharge. The high bandwidth and open-beam geometry of the fluorescence sensor are particularly beneficial for EC measurements. FACT was integrated with a velocity sensor into a full EC system capable of simultaneous benthic flux measurements of fluorescing compounds, heat, and salinity. Tested in a laboratory tank, fluxes measured by all three sensors were found to track each other as well as compare favorably with expected values. Furthermore, the ability to measure fluxes of multiple substances both extends the applicability of EC to a wider range of natural sites, and can provide insight into issues of sensing volume and time responses as they affect the application of EC to natural waters.

Tertiary Waves Measured during 2017 Pohang Earthquake Using an Underwater Glider

An underwater glider equipped with a hydrophone observed the acoustic sounds of an earthquake that occurred on 15 November 2017 05:29:32 (UTC) in the Pohang area. The underwater glider observed the earthquake sounds after 19 s (05:29:51) at approximately 140 km from the Pohang epicenter. In order to distinguish the earthquake sound from the glider’s operation noise, the noise sources and Sound Pressure Level (SPL) of the underwater glider were analyzed and measured at laboratory tank and sea. The earthquake acoustic signal was distinguished from glider’s self-noises of fin, pumped Conductivity-Temperature-Depth profiler (CTD) and altimeter which exist over 100 Hz. The dominant frequencies of the earthquake acoustic signals due to the earthquake were 10 Hz. Frequencies at which the spectra had dropped 60 dB were 50 Hz. By analysis of time correlation with seismic waves detected by five seismic land stations and the earthquake acoustic signal, it is clearly shown that the seismic waves converted to Tertiary waves and then detected by the underwater glider. The results allow constraining the acoustic sound level of the earthquake and suggest that the glider provides an effective platform for enhancing the earth seismic observation systems and monitoring natural and anthropogenic ocean sounds.

О численном моделировании поверхностных волн в бассейне с подвижными непроницаемыми границами

Представлены результаты, связанные с разработкой вычислительного алгоритма для изучения поверхностных волн в областях с подвижными непроницаемыми границами (подвижные боковые стенки бассейна, подвижные фрагменты дна). Алгоритм основан на конечноразностной аппроксимации на подвижных сетках двумерной модели потенциальных течений несжимаемой жидкости со свободной границей. Предложены новые начальные данные для задачи о движении уединенной волны, неотражающие условия, способ задания нулевого итерационного приближения для расчета потенциала скорости и результаты исследования устойчивости численного метода. Показано, что поверхностные волны, вызванные подводным оползнем, существенно влияют на процесс наката на берег одиночной волны и могут увеличить ее максимальный заплеск. In numerical simulation of fluid flows with a free surface, the most difficult problems are those in which not only the free boundary is mobile, but also some other parts of the boundary of the region occupied by the liquid. For example, these are the problems of surface waves caused by underwater and coastal landslides, the generation of waves by wavemakers in laboratory flumes and tanks, the problem of waves runup on the shore, the interaction of waves with moving wave protection walls and problems addressed moving semisubmerged or fully immersed objects. The purpose of this paper is to analyze the properties and evaluate the capabilities of the computational algorithm based on the finitedifference approximation of the equations of potential fluid flows with a free boundary and designed to study surface waves in a confined basin, part of the impermeable boundary of which can be mobile. The algorithm relies on the use of curvilinear grids that adapt to all parts of the boundary, both moving and stationary. New initial data are proposed for the problem of motion of a solitary or a single wave, consistent with the initial data for the shallow water equations of the second longwave approximation. New nonreflecting conditions have been developed that allow waves to be emitted across the boundary of a flow region with very little reflection. A new initial approximation is proposed for the iterative process of calculating the potential of the velocity vector. By using this approach we significantly reduce the number of iterations at each time step. The original stability condition of the linearized difference scheme is derived. The reasons for the appearance of two peaks in the chronograms of pressure when the long waves of large amplitude roll onto a vertical wall are discussed. The capabilities of the numerical algorithm are demonstrated on the problem of generating waves by a moving wall travelling in the initial part of the flume. The results of the calculations well reproduce the experimental data, in particular, the decrease in the length and increase in the amplitude of the wave when it moves towards the shallow part of the flume, as well as the formation of a dispersion tail as the waves reverse motion after reflection from the vertical wall installed at the end of the flume. The developed algorithm was used to study the process of generation for surface waves by an underwater landslide moving along an uneven bottom, and the interaction of these landslide waves with a single surface wave moving towards the shore. It is shown that the surface waves caused by an underwater landslide significantly affect the process of rolling of a single wave on the shore and it could increase its maximum splash.

Measurements and modeling of acoustic propagation in a scale model canyon.

Two scale-model acoustic propagation experiments were conducted in a laboratory tank to investigate three-dimensional (3D) propagation effects induced by range-dependent bathymetry. The model bathymetry, patterned after measured bathymetric data, represents a portion of the Hudson Canyon at 1:7500 scale. The bottom condition in the scale model is nearly pressure release, and as a result, the bottom reflection and backscattering are stronger than that of the real ocean environment. Measurements are presented for propagation paths oriented along and across the axis of the canyon. The measured data are interpreted using both 3D adiabatic-mode and 3D ray models. For propagation along the canyon axis, horizontal focusing is observed, and the out-of-plane arrivals are identified using the vertical mode/horizontal ray analogy to determine which wall or walls of the canyon refracted the sound. For the across-canyon propagation, out-of-plane arrivals are observed for both forward scattered and backward scattered sound. Using the 3D ray model, an investigation of the horizontal and vertical launch angles is used to identify features on the canyon walls responsible for the measured out-of-plane propagation. For both the along- and across-canyon experiments, the 3D ray model produced a solution that was more accurate and less computationally intensive.

Sound production mechanism in the Brazilian spiny lobsters (Family Palinuridae)

Strident lobsters of the Palinuridae family emit sounds in the presence of predators that can be used in the acoustic monitoring of such species. This study aims to identify sound emission and describe the structures of sound mechanism in red (Panulirus meripurpuratus) and green (Panulirus laevicauda) Brazilian spiny lobsters. The lobsters were collected in the environment, and recordings were performed in laboratory tanks with submerged hydrophones. The animals were stimulated to emit sound by the presence of an artificial octopus in the tank. The sounds emitted by the lobsters were analyzed by means of the waveform, and the structures involved (plectrum and file) were observed using scanning electron microscopy (SEM). Both species emitted a rasp sound composed of several pulses, with a rate varying from 125 to 265 pulses per second. The SEM showed that the file is similar between the species and it is covered by microscopic plates (shingles) measuring between 12.6 and 12.9 μm of medial–lateral width and 6.2 μm and 7.1 μm of anteroposterior length. This analysis also revealed for the first time the presence of pores (< 1 μm in diameter) with vestiges of cuticular setae in-between the shingles, which could be involved in the mechanosensory control of sound production in lobsters. The results of this study corroborate the morphological pattern of sound emission structure described for other lobsters of the genus Panulirus.

Time-domain hydroelastic analysis of nonlinear motions and loads on a large bow-flare ship advancing in high irregular seas

This paper investigates the nonlinear hydroelastic motion and load responses on a large flexible ship advancing in harsh irregular waves. A 3D time-domain nonlinear hydroelasticity theory for the prediction of ship motions, deformations and wave loads in long-crested irregular waves is presented. The nonlinear Froude–Krylov force and hydrostatic restoring force are calculated on the instantaneous wetted hull surface while the linear diffraction force and radiation force are estimated on the static mean wetted surface. The radiation forces are estimated by retardation function method to take account of the wave memory effects and forward speed effects. The slamming loads that were derived by momentum impact theory are also included in the ship motion equation to investigate the whipping responses. The hydrodynamic and structural responses are fully coupled by modal superposition principle to consider the hydroelastic effects including springing and whipping responses. The numerical results are well validated by the experimental data of a segmented model with large flare-bow tested in an ultra-long laboratory tank. The numerical and experimental data of ship responses in different irregular wave conditions are systemically analyzed and compared by time series analysis, spectral analysis, and probability statistics analysis methods.

Rising bubbles enhance the gelatinous nature of the air–sea interface

AbstractBubbles rising through the water column are known to scavenge organic material and microorganisms, and transport them through the air–sea interface after bursting. This mechanism has important implications for air–sea exchange processes. However, little is known about how bubbles influence the chemical and biological properties of the sea‐surface microlayer (SML), a gelatinous film at the air–sea interface. We used floating mesocosms in the coastal Baltic Sea and a laboratory tank filled with seawater from the North Sea to study the effect of bubbling on the gelatinous nature of the SML. Bubbling was found to always increase concentrations of transparent exopolymer particles (TEP) in the SML. In the field, TEP in the SML already increased after 2 min (53% ± 63%) and 10 min (19% ± 12%) bubbling, respectively. During the tank experiment, TEP enriched in the SML by 312% (± 244%) after &gt; 3 h of bubbling. Therefore, bubbling is a highly efficient mechanism for TEP enrichment in the SML. Bubbling caused enrichment and depletion of microbial abundances (prokaryotes, flagellates, eukaryotes) in the SML. However, the incorporation of 3H‐thymidine (i.e., bacterial carbon production) was consistently stimulated after 10 min of bubbling in the field experiment, indicating a bubble‐induced import of unstressed bacteria and fresh organic substrates into the SML. Overall, our results suggest that the gelatinous matrix of the SML is re‐formed within min after disruption by bursting bubbles, and, thus, highlights the importance of biogeochemical interactions within the air–sea interface.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ТРЕХМЕРНЫХ ВОЛНОВЫХ АТТРАКТОРОВ

Internal and inertial waves obey very specific dispersion relation, which defines the direction of wave propagation with respect to the gravity or axis of rotation, but which does no define the wavelength. Particular cases of scale effects are described in (Brouzet et al., 2017). In closed geometrics the presence of a monochromatic wavemaker can produce wave beams, which after multiple reflections from the boundaries may approach a closed loop – the wave attractor. In ideal fluids the concentration of energy on the wave attractor can grow without any limits. In viscous stratified or rotating fluids the concentration will be balanced with dissipation due to viscosity, which results in appearance of wave attractors of finite width. The characterization of the flow with the Reynolds number based on the boundary conditions is questionable in this case, since on the attractor the velocity can be several times magnified. When the wave beam is reflected from an inclined plane, the horizontal component of velocity rotates, as was first described by O. Phillips, while preserving the angle with the gravity or axis of rotation. With the help of ray tracing it can be shown that due to this effect the three-dimensional accumulation of wave energy can occur. First qualitative and quantitative correspondence of laboratory and numerical simulation of wave attractors in the pseudo-2D laboratory tank with trapezoidal section was described in (Brouzet et al., 2016), and importance of dissipation on the lateral boundaries was shown (F. Beckebanze et al., 2018). For high Schdmidt number there appear the folded structures, which can interact with the background wave motion (Sibgatullin, Kalugin 2016). In (Brouzet et al., 2016b), (Dauxois et al., 2018) cascade of triadic resonances in (1,1) produced by a wave attractor was demonstrated. Three-dimensional accumulation of wave energy in trapezoidal frustum with a localized wavemaker was investigated in (Pillet et al., 2018). Numerical simulations of the present work had showed the importance of phase shift in transversal direction. An attractor can have the same form as the 2D attractor in any given longitudinal cut, but the phase of oscillation can change up to counter-phase. Interplay of 3D concentration of waves beams, dissipation and phase shifting impact the final energy distribution in transversal direction. First three-dimensional simulations (Sibgatullin et al., 2017) of tidal and symmetric forcing on the rotating layer of fluid with inclined walls showed three-dimensional twisted structure of waves attractors for precession of one boundary of the layer in opposite direction to the rotation of the layer. With growth of the amplitude of the external forcing the the instability of triadic resonance appears, but in contrast to the internal wave attractors, triadic resonances take place in azimuthal (transversal to the trapeze) section. The turbulent regimes generated by the background wave attractors are studied, with analysis of full power income and total dissipation. The research was supported by the Program of Fundamental Research of the Presidium of the Russian Academy of Sciences No. 26

Electrochemical investigation of chalcopyrite (bio)leaching residues

Chalcopyrite is the most abundant but also the most recalcitrant copper sulfide mineral in leaching processes. The reasons for its refractory character are passivation and/or its semi-conductive properties. In our study chalcopyrite was hydrometallurgically processed via chemical leaching, electrochemical leaching, bioleaching and electrobioleaching in 2 l stirred tank laboratory experiments. Both biotic leaching treatments were more successful than both abiotic leaching experiments, however, overall the copper recovery was low due to the recalcitrant character of chalcopyrite. Various electrochemical techniques such as cyclic voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy were applied to investigate the differences in surface properties of the residues. Potentiodynamic polarization and cyclic voltammetric studies showed that any kind of leaching resulted in increased dissolution resistance and surficial redox inactivation compared to unprocessed chalcopyrite. However, if chalcopyrite was continuously in direct contact to the cathodic working electrode its surface was activated and showed even the highest oxidation currents which implicates increased leachability. Thus, at the surface of such chalcopyrite particles the mineral was converted into readier leachable minerals such as chalcocite. Additionally, electrochemical impedance spectroscopy (EIS) was carried out in the presence of ferrous and ferric iron. It turned out that surface activation via ferrous iron was not observed. In contrast, ferric iron led to successive passivation over time. The charge transfer resistance was the lowest for unprocessed and surface reduced chalcopyrite and the highest for chemically and electrochemically leached sulfide mineral. The findings of this comparative, electrochemical study support that passivation takes place to larger extend during abiotic leaching (chemical and electrochemical leaching) compared to biotic leaching (bioleaching and electrobioleaching).

Impacts of Artificial Regulation on Karst Spring Hydrograph in Northern China: Laboratory Study and Numerical Simulations

Karst aquifers produce the world’s largest springs and supply the water resources to about a quarter of the global population while being influenced by high-intensity human activities. Knowledge about spring discharge hydrographs driven by the effects of artificial regulation is essential to develop practical strategies for the management of karst groundwater. Based on hydrogeological conditions of the karst aquifer in Jinan, a two-dimensional laboratory tank was constructed, and a corresponding numerical simulation model was developed to explore how artificial regulation drives spring hydrographs in northern China. The results showed that the spring hydrographs were significantly changed under the effects of artificial regulation. The recession coefficient increased with pumping and decreased with increasing injection rates. The late sub-recession of spring discharge did not obey the exponential recession under the influence of injection. Pumping and injection in conduit zones showed more obvious effects on the recession coefficient in the late sub-recession curves. Groundwater exchange between conduits and fissure zones differed totally for different artificial regulation modes. With continuing rainfall, the flow fields were gradually controlled by rainfall. There was a time lag in the flow fields caused by rainfall. Under the stress of exploitation at different positions, stagnation points appeared at different locations in fissure zones, and locations of stagnation points were highly dependent on the positions of pumping wells. These findings are essential for better management of karst groundwater and karst spring protection.