Effcts of smooth divergence-free flows on tracer gradients and spectra: Eulerian prognosis description

Ocean eddies play an important role in the transport of heat, salt, nutrients or pollutants. During a finite-time advection, the gradients of these tracers can increase or decrease, depending on a growth rate and the angle between flow gradients and initial tracer gradients. The growth rate is directly related to finite-time Lyapunov exponents. Numerous studies on mixing and/or tracer downscaling methods rely on satellite altimeter-derived ocean velocities. Filtering most oceanic small-scale eddies, the resulting smooth Eulerian velocities are often stationary during the characteristic time of tracer gradient growth. While smooth, these velocity fields are still locally misaligned, and thus uncorrelated, to many coarse-scale tracers observations amendable to downscaling (e.g. SST, SSS). Using finite-time advections, the averaged squared norm of tracer gradients can then only increase, with local growth rate independent of the initial coarse-scale tracer distribution. The key mixing processes are then only governed by locally uniform shears and foldings around stationary convective cells. To predict the tracer deformations and the evolution of their 2nd-order statistics, an effcient proxy is proposed. Applied to a single velocity snapshot, this proxy extends the Okubo-Weiss criterion. For the Lagrangian-advection-based downscaling methods, it further successfully predicts the evolution of tracer spectral energy density after a finite time, and the optimal time to stop the downscaling operation. A practical estimation can then be proposed to define an effective parameterization of the horizontal eddy diffusivity.

Extended Lattice Boltzmann Model

Conventional lattice Boltzmann models for the simulation of fluid dynamics are restricted by an error in the stress tensor that is negligible only for small flow velocity and at a singular value of the temperature. To that end, we propose a unified formulation that restores Galilean invariance and the isotropy of the stress tensor by introducing an extended equilibrium. This modification extends lattice Boltzmann models to simulations with higher values of the flow velocity and can be used at temperatures that are higher than the lattice reference temperature, which enhances computational efficiency by decreasing the number of required time steps. Furthermore, the extended model also remains valid for stretched lattices, which are useful when flow gradients are predominant in one direction. The model is validated by simulations of two- and three-dimensional benchmark problems, including the double shear layer flow, the decay of homogeneous isotropic turbulence, the laminar boundary layer over a flat plate and the turbulent channel flow.

The study results of the filtration process in the ground dams body and its chemical effect on piezometers

The article describes the definition of filtration flow gradients in the dam's body on the example of the Kattakurgan reservoir, the analysis of the reasons for their change in cross-section. Evaluation of the aggressiveness of the filtration flow in the dam's body plays an important role in ensuring the stability of the reservoir dam and its parts. To assess the aggressiveness of the filtration flow in the dam's body, it is necessary to know the action pattern of the filtration water in the reservoir dam and its effect on the elements of the dam. In addition, the chemical composition of the water in the piezometers was analyzed in the laboratory to determine the aggressive effect of sulfate elements on the piezometers and their corrosion. Measures on the observations of systemic piezometers were also mentioned.

Digitalization of hydrogeological processes in mining industry

The groundwater monitoring reconstruction and hydrogeological digitalization are discussed on the ground of the past and modern mine flooding protection technologies and geo-information technologies. According to the authors, it is of the current concern to advance digitalization technologies for hydrogeological processes in the mining industry to be focused on: – operative and episodic control and display of water condition at the control point in the x, y, z, t coordinates, including pore pressure, temperature, mineralization, flow rate of drainage water intake devices, productivity of pumping equipment of mine and quarry drainage, water-development in pit walls, in underground mines, in the influence zone of mining production; – creation of permanent hydrogeological models of groundwater flow, pore pressure distribution, flow gradients and transport of pollutants within the framework of conceptual and numerical models of subsoil, mining facilities, terrain, natural environment and anthropogenic activity in the influence zone of mining. The article discusses the working cycles of digitalization of operational and occasional monitoring data on the status of groundwater at the control points and 3D representations of groundwater flow, distribution of pore pressure, pressure gradients and movement of pollutants using constantly operating models to ensure safe and competitive development of flooded mineral deposits in modern conditions. The relevance of the digitalization technologies for hydrogeological processes based on the latest achievements in the field of geoinformatics and automation of hydrogeological work is substantiated.

Turning Water Pollution Sources Into Assets: Exploring Innovative Options Of Using Abandoned Mines For Generating And Storing Renewable Energy

Through moving large volumes of rock for decades or even centuries from geological underground to surface, industrial scale mining invariably alters the natural local and regional hydrological conditions. Consequences include irreversible changes of flow gradients and water quality in aquifers and streams effected through dewatering, ground subsidence, acid mine drainage, etc. During their lifetime mines spent significant resources and energy on maintaining an ever-increasing diversion from natural hydraulic equilibria through pumping rising volumes of ingress water from ever greater depths, especially if operating below water-rich formations (karst) or in humid climates. Associated pumping costs may even lead to premature mine closure. In cases where complete flooding of closed mines is not an option (e.g. to protect water resources or infrastructure) such costs remain well after mines closed for as long as flooding restrictions apply. In large and densely populated regions in South Africa or Germany, for example, where mining succeeded in triggering urbanisation and self-sustaining economic development it is (currently) assumed that pumping will be needed forever. Accordingly, postclosure water management is no longer only a long-term liability but indeed a perpetual burden placed on future generations that had little direct benefits from earlier mining. This paper focuses specifically on possible ways of reducing perpetual postclosure water management costs specifically of using abandoned mines for generating and storing renewable energy. It discusses successful examples already implemented, concepts investigated but not yet realised as well as technologies that received little, if any, attention to date. The latter range from using mines (included flooded ones) for the storage of electrical energy via different technologies, harvesting geothermal energy from mine water and voids to different ways of transforming chemical energy contained in mine water into electricity.

First experience of using NVT Allegra system for transcatheter implantation of aortic valve and prospects for routine interventions on aortic valve in Ukraine

The aim – to present the first experience in Ukraine of using the NVT Allegra device for the procedure of transcatheter implantation of the aortic valve prosthesis to patients with high surgical risk with severe aortic stenosis. Materials and methods. The presented clinical cases included two patients of age 90 and 80 years with severe aortic stenosis, mean transaortic blood flow gradients of 32 and 76 mm Hg and aortic valve areas of 0.4 and 0.6 cm2, respectively. Both patients were recognized as high surgical risk patients. Results and discussion. Both patients underwent transcatheter implantation of the aortic valve prosthesis through transfemoral access. After implantation, the average gradients of the transaortic blood flow were 13 and 8 mm Hg respectively. Residual paravalvular insufficiency was mild in both cases. Second patient was implanted permanent pacemaker due to persistent complete AV block. Conclusions. The NVT Allegra system for transcatheter implantation of the aortic valve prosthesis is a third generation device that enables successful and safe intervention of the aortic valve.

Regulation Principles of Power Flow Gradients to Multiple Characteristic Independent Variables in UPFC Embedded Power System

The power flows in the unified power flow controller (UPFC) embedded system is mainly regulated by the two variables containing the magnitude and the phase angle of the output series inserted voltage (OSIV) of UPFC. Different value combinations of the two variables can form multiple regulation modes of OSIV, and the regulation principles and efficiencies for power flows are distinct by different regulation modes. This paper dedicates to research the regulation principles of active and reactive power flow gradients (PFG) to multiple characteristic independent variables (CIVs) at several selected critical points (SCP) of the system in different operation conditions. The CIVs contains the magnitude of OSIV, the phase angle of OSIV, and the phase difference of the system. First, multiple power flow regulation modes of OSIV are designed, the mathematical models of the PFG to each CIV at each SCP are established, and the theoretical principles for the PFG to each CIV at each SCP are analyzed and compared. Next, four typical operation conditions of the system and four regulation scenarios are assumed and case studies for the PFG to each CIV at different SCP are carried out. The test results at each SCP are analyzed both in the two-dimensional planes and three-dimensional spaces. The regulation principles and efficiencies of PFG to each CIV at different SCP are compared with each other and summarized, which can offer useful references for practical engineering and applications of UPFC.

Hydrodynamic simulation of urban stormwater drain (Delhi city, India) using iRIC Model

Flooding in urban areas takes place mainly due to increased urbanization, decrease in infiltration rate and poor infrastructure for stormwater drainage network. Nays2DFlood is a recently developed solver by iRIC for the simulation of river flow regime. The number of input data requirement is few which makes this solver superior to other models but has been rarely applied to urban catchments. In this paper, a hydrodynamic model was developed to assess the model’s feasibility to simulate urban stormwater drainage system of Delhi, capital city of India for mapping inundation extents using Nays2DFlood solver. The data used in this model is a DEM (5 × 5 m resolution) and daily discharge data of the drains. The simulated drainage is analysed keeping in mind the constraints which were observed during the collection of field data; the storm-water drains are choked, the drains have improper flow gradient or damaged flow gradients. Based on the simulated results, the water depth and velocity profiles were analysed for the drain. The model identified four critical locations where the problem like zig-zag bed slope of the drain, undersized cross-section of the drain and last but not the least the backflow problem which were in close agreement with the observed field data. The flood propagation exactly predicting the inundated area. Thus, Nays2DFlood solver model can also be applied to urban catchments for identifying the flood extent.

Material stability and instability in non-local continuum models for dense granular materials

A class of common and successful continuum models for steady, dense granular flows is based on the$\unicode[STIX]{x1D707}(I)$model for viscoplastic grain-inertial rheology. Recent work has shown that under certain conditions,$\unicode[STIX]{x1D707}(I)$-based models display a linear instability in which short-wavelength perturbations grow at an unbounded rate – i.e. a Hadamard instability. This observation indicates that$\unicode[STIX]{x1D707}(I)$models will predict strain localization arising due to material instability in dense granular materials; however, it also raises concerns regarding the robustness of numerical solutions obtained using these models. Several approaches to regularizing this instability have been suggested in the literature. Among these, it has been shown that the inclusion of higher-order velocity gradients into the constitutive equations can suppress the Hadamard instability, while not precluding the modelling of strain localization into diffuse shear bands. In our recent work (Henann & Kamrin,Proc. Natl Acad. Sci. USA, vol. 110, 2013, pp. 6730–6735), we have proposed a non-local model – called the non-local granular fluidity (NGF) model – which also involves higher-order flow gradients and has been shown to quantitatively describe a wide variety of steady, dense flows. In this work, we show that the NGF model also successfully regularizes the Hadamard instability of the$\unicode[STIX]{x1D707}(I)$model. We further apply the NGF model to the problem of strain localization in quasi-static plane-strain compression using nonlinear finite-element simulations in order to demonstrate that the model is capable of describing diffuse strain localization in a mesh-independent manner. Finally, we consider the linear stability of an alternative gradient–viscoplastic model (Bouzidet al.,Phys. Rev. Lett., vol. 111, 2013, 238301) and show that the inclusion of higher-order gradients does not guarantee the suppression of the Hadamard instability.