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In the present work an implementation of the Back and Forth Error Compensation and Correction (BFECC) algorithm specially suited for running on General-Purpose Graphics Processing Units (GPGPUs) through Nvidia's Compute Unified Device Architecture (CUDA) is analyzed in order to solve transient pure advection equations. The objective is to compare it to a previous explicit version used in a Navier-Stokes solver fully written in CUDA. It turns out that BFECC could be implemented with unconditional stable stability using Semi-Lagrangian time integration allowing larger time steps than Eulerian ones. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we introduce and describe an efficient thread-safe matrix library for computing element/cell residuals and Jacobians in Finite Elements and Finite Volume-like codes. The library provides a wide range of multi-index tensor operations that are normally used in scientific numerical computations. The library implements an algorithm for choosing the optimal computation order when a product of several tensors is performed (i.e., the so-called ‘multi-product’ operation). Another key-point of the FastMat approach is that some computations (for instance the optimal order in the multi-product operation mentioned before) are computed in the first iteration of the loop body and stored in a cache object, so that in the second and subsequent executions these computations are retrieved from the cache, and then not recomputed. The library is open source and freely available within the multi-physics parallel FEM code PETSc-FEM http://www.cimec.org.ar/petscfem and it can be exploited on distributed and shared memory architectures as well as in hybrid approaches. We studied the performance of the library in the context of typical FEM tensor contractions. [Copyright &y& Elsevier]

Shock waves and contact discontinuities usually appear in compressible flows, requiring a fine mesh in order to achieve an acceptable accuracy of the numerical solution. The usage of a mesh adaptation strategy is convenient as uniform refinement of the whole mesh becomes prohibitive in three-dimensional (3D) problems. An unsteady h-adaptive strategy for unstructured finite element meshes is introduced. Non-conformity of the refined mesh and a bounded decrease in the geometrical quality of the elements are some features of the refinement algorithm. A 3D extension of the well-known refinement constraint for 2D meshes is used to enforce a smooth size transition among neighbour elements with different levels of refinement. A density-based gradient indicator is used to track discontinuities. The solution procedure is partially parallelised, i.e. the inviscid flow equations are solved in parallel with a finite element SUPG formulation with shock capturing terms while the adaptation of the mesh is sequentially performed. Results are presented for a spherical blast wave driven by a point-like explosion with an initial pressure jump of 105 atmospheres. The adapted solution is compared to that computed on a fixed mesh. Also, the results provided by the theory of self-similar solutions are considered for the analysis. In this particular problem, adapting the mesh to the solution accounts for approximately 4% of the total simulation time and the refinement algorithm scales almost linearly with the size of the problem. [ABSTRACT FROM AUTHOR]

In this paper some results on the convergence of the Gauss–Seidel iteration when solving fluid/structure interaction problems with strong coupling via fixed point iteration are presented. The flow-induced vibration of a flat plate aligned with the flow direction at supersonic Mach number is studied. The precision of different predictor schemes and the influence of the partitioned strong coupling on stability is discussed. [Copyright &y& Elsevier]

Abstract: The number and type of boundary conditions to be used in the numerical modeling of fluid mechanics problems is normally chosen according to a simplified analysis of the characteristics, and also from the experience of the modeler. The problem is harder at inflow/outflow boundaries which are, in most cases, artificial boundaries, so that a bad decision about the boundary conditions to be imposed may affect the precision and stability of the whole computation. For inviscid flows, the analysis of the sense of propagation in the normal direction to the boundaries gives the number of conditions to be imposed and, in addition, the conditions that are “absorbing” for the waves impinging normally to the boundary. In practice, it amounts to counting the number of positive and negative eigenvalues of the advective flux Jacobian projected onto the normal. The problem is even harder when the number of incoming characteristics varies during the computation, and the correct treatment of these cases poses both mathematical and practical problems. One example considered here is a compressible flow where the flow regime at a certain part of an inlet/outlet boundary can change from subsonic to supersonic and the flow can revert. In this work the technique for dynamically imposing the correct number of boundary conditions along the computation, using Lagrange multipliers and penalization, is discussed and several numerical examples are presented. [Copyright &y& Elsevier]

The aim of this paper is to describe the methodology followed in order to determine the viscous effects of a uniform wind on the blades of small horizontal-axis wind turbines that rotate at a constant angular speed. The numerical calculation of the development of the three-dimensional boundary layer on the surface of the blades is carried out under laminar conditions and considering flow rotation, airfoil curvature and blade twist effects. The adopted geometry for the twisted blades is given by cambered thin blade sections conformed by circular are airfoils with constant chords. The blade is working under stationary conditions at a given tip speed ratio, so that an extensive laminar boundary layer without flow separation is expected. The boundary layer growth is determined on a non-orthogonal curvilinear coordinate system related to the geometry of the blade surface. Since the thickness of the boundary layer grows from the leading edge of the blade and also from the tip to the blade root, a domain transformation is proposed in order to solve the discretized equations in a regular computational 3D domain. The non-linear system of partial differential coupled equations that governs the boundary layer development is numerically solved applying a finite difference technique using the Krause zig-zag scheme. The resulting coupled equations of motion are linearized, leading to a tridiagonal system of equations that is iteratively solved for the velocity components inside the viscous layer applying the Thomas algorithm, procedure that allows the subsequent numerical determination of the shear stress distribution on the blade surface. [ABSTRACT FROM AUTHOR]

This work describes a formulation for the treatment of submerged rigid solids within the framework of the finite volume method. The proposal consists in considering the solid as a porous region and the hydrodynamic forces that arise from the Darcy terms. The methodology is implemented in an open code that allows large-scale calculations. In the present work, we present the methodology and its verification using cases of study, to demonstrate spatio-temporal numerical convergence and the accuracy of the imposition of boundary conditions. For this purpose, cases that have an analytical solution are analyzed, such as the Pouiseuille flow, the first and second Stokes problems, and immersed walls that move with imposed movement generating different pressures between both faces. A moving cylinder analysis is shown to validate the numerical technique in comparison with cases reported in the literature. The analysis leads to stability conditions against external parameters such as permeability. The ability of the method to represent moving walls and immersed bodies with imposed movement is established. • An embedded finite volume formulation is proposed for rigid solids interacting with fluids. • Boundary conditions varying in space and time are easily imposed. • Simple and precise calculation of the hydrodynamic forces. • Satisfactory validation of the hydrodynamic coefficients. • Optimal relation between model parameter and time step and mesh size to obtain convergence. [ABSTRACT FROM AUTHOR]

A novel approach using an algebraic-based Chimera type domain composition method in the context of the finite element method for non-matching overlapping unstructured grids is proposed in this work. The scheme is based on both the transfer of information across each grid interface via Dirichlet boundary conditions and a high-order interpolation algorithm to obtain one global solution of the system. The solution can be obtained iteratively, with a convergence rate that is similar to that obtained with an analogous conformal mesh, and the matrix–vector operator can be computed with completely decoupled operations on both meshes. Furthermore, the scheme can be set as a linear operator that can be fed to a matrix-free efficient iterative solver, such as the BiConjugate Gradient Stabilized method. Several numerical examples using non-matching unstructured grids that are partially and completely overlapped with different element sizes are presented, assessing the precision and convergence rate of the method. [ABSTRACT FROM AUTHOR]

The purpose of this work is twofold: to present a computational strategy to simulate the dynamics of a rigid sphere during water sloshing and to validate the model with original experimental data. The numerical solution is obtained through the coupling between a two-fluid Navier-Stokes solver and a rigid solid dynamics solver, based on a Newton scheme. A settling sphere case reported in the literature is first analyzed to validate the numerical strategy by ascertaining the settling velocity. In addition, an experiment is carried out based on a sphere submerged into a communicating vessel subjected to sloshing. Experimental data are captured using image processing and statistically treated to provide sphere dynamics quantitative information. The effects of different classical models used to describe drag coefficients, added mass, and wall effects are considered in the study to evaluate their influence on the results. The numerical model provides results that are consistent with the physical data, and the trajectory analysis shows good agreement between the simulations and the experiments. [ABSTRACT FROM AUTHOR]

This work encompasses numerical and experimental studies of three-dimensional (3D) sloshing problems. The two-fluid viscous flow, which is solved within a stabilized finite element context, involves liquid and gaseous phases. The free surface is captured with a level set (LS) method, including the bounded renormalization with continuous penalization technique, to avoid the well-known spreading of the marker function. Specifically, this technique is improved with a volume-preserving algorithm for long-term analyses. To verify the numerical model, the responses of free-sloshing cases are compared with analytical solutions and other results computed using a Lagrangian technique. These simulations assess the influence of considering two-dimensional (2D) and 3D analyses, as well as the effects of depth and viscosity. This work presents data obtained from a forced sloshing experiment that is specifically devoted to 3D free surface behaviour. Free surface evolution measurements are used to validate the numerical method. Moreover, the effect of the initial conditions used to promote 3D behaviour in the modelling is evaluated. [ABSTRACT FROM AUTHOR]

The efficient dissipation of energy losses in electrical power transformers is crucial to prevent overheating of their windings and ensure proper functioning. In this study, we investigate the thermal design of a 30 [MVA], 132/34.5/13.8 [kV] power transformer radiator operating in Oil Natural-Air Natural mode by using Computational Fluid Dynamics (CFD) simulations. We introduce artificial body forces in the momentum Navier-Stokes equation to analyze the thermo-fluid dynamic performance of secondary transverse flows. Additionally, we propose a numerical scheme to solve the thermal equation with periodic boundary conditions using a reduced length of the oil channel, allowing for the decoupling of the thermal and fluid dynamic problems. To enhance the heat transfer, we propose the use of turbulators and wall indentation arrangements. Through our simulations, we analyze the effects of these enhancements on the cooling capacity of the transformer radiator. Our results demonstrate that these modifications increase the heat transfer coefficient and improve the cooling capacity of the radiator. Furthermore, we propose manufacturing considerations for the turbulators and wall indentation arrangements to ensure their practicality. Our findings provide valuable insights into the thermal design of power transformer radiators and demonstrate the effectiveness of turbulators and wall indentation arrangements in enhancing their cooling capacity. • Body forces are strategically employed to induce secondary flow without the need for remeshing. • Implementation of periodic boundary conditions for both fluid and thermal dynamics minimizing computational costs. • Automated scheme that decouples heat and flow physics, executed within the open-source software Code Saturne. • Triangular-prismal shaped indenters remarkably elevate thermo-fluid dynamic performance by 36%. [ABSTRACT FROM AUTHOR]

In this work we present an efficient implementation of Eulerian TVD methods. We apply parallelization strategies based entirely on GPU for the solution of the 2D transport equation in heterogeneous porous media. Additionally, a parallel strategy is proposed for the generation of exponentially correlated lognormally distributed permeability fields in GPU. The programs are developed using C++/CUDA. The implemented methods are used to solve advective dominant problems, in a context of Monte Carlo type simulations to numerically determine the longitudinal and transversal macrodispersion coefficients averaging over 100 simulations for permeability fields for a large range of variances. The following types of transport are considered for testing: pure advection, advection-diffusion and advection-dispersion. The performance in terms of the computation time of explicit and implicit methods are compared. We show that the implemented algorithms allow to efficiently solve problems in computational domains of up to 134.5 million cells in a single GPU. [ABSTRACT FROM AUTHOR]

Finite element computation and experimental validation of sloshing in rectangular tanks near the primary and secondary resonance modes are presented. In particular, 2D free-surface evolution is studied. The computational analysis is based on solving the Navier-Stokes equations of incompressible flows with a monolithic solver that includes a stabilized formulation and a Lagrangian tracking technique for updating the free surface. The time-dependent behavior of the numerical and experimental wave heights at different control points are compared, where the experimental data is collected using ultrasonic sensors and a shake table that controls the motion of the rectangular container. [ABSTRACT FROM AUTHOR]

Abstract: MPI for Python provides bindings of the message passing interface (MPI) standard for the Python programming language and allows any Python program to exploit multiple processors. In its first release, MPI for Python was constructed on top of the MPI-1 specification defining an object-oriented interface that closely followed the MPI-2 bindings, and provided support for communications of general Python objects. In the latest release, this package is improved to enable direct blocking/non-blocking communication of numeric arrays, and to support almost all MPI-2 features. Improvements in communication performance have been tested in a Beowulf class cluster. Results showed a negligible overhead in comparison to compiled C code. MPI for Python is open source and available for download on the web (http://mpi4py.scipy.org/). [Copyright &y& Elsevier]

Axisymmetric inertial waves of a viscous fluid that fill a perturbed rotating spherical container are numerically simulated by finite elements. A laminar flow of an incompressible viscous fluid of Newtonian type is assumed in the numerical simulations. A monolithic computational code is employed, which is based on stabilized finite elements by means of a Streamline Upwind Petrov Galerkin (SUPG) and Pressure Stabilized Petrov Galerkin (PSPG) composed scheme. The Reynolds number is fixed as 50,000, while the ranges of the Rossby and Ekman numbers are [image omitted] and [image omitted] respectively. Some flow visualizations are performed. The pressure coefficient spectrum at the centre of the sphere is plotted as a function of the frequency ratio and some resonant frequencies are identified. The position of these resonant frequencies are in good agreement with previous experimental and analytical ones in the inviscid limit. [ABSTRACT FROM AUTHOR]

In this work, transient free surface flows of a viscous incompressible fluid are numerically solved through parallel computation. Transient free surface flows are boundary-value problems of the moving type that involve geometrical nonlinearities, hi contrast to more conventional computational fluid dynamics problems, the computational flow domain is partially bounded by a free surface which is not known a priori, since its shape must be computed as part of the solution. In steady flow the free surface is obtained by an iterative process, but when the free surface evolves with time the problem is more difficult as it generates large distortions in the computational flow domain. The incompressible Navier-Stokes numerical solver is based on the finite element method with equal order elements for pressure and velocity (linear elements), and it uses a streamline upwind/ Petrov-Galerkin (SUPG) scheme (Hughes, T. J. R., and Brooks, A. N., 1979, "A Multidimensional Upwind Scheme With no Crosswind Diffusion," in Finite Element Methods for Convection Dominated Flows, ASME ed., 34. AMD, New York, pp. 19-35, and Brooks, A. N., and Hughes, T J. R., 1982, "Streamline Upwind/Petrov--Galerkin Formulations for Convection Dominated Flows With Particular Emphasis on the Incompressible Navier-Stokes Equations," Comput. Methods Appl. Mech. Eng., 32, pp. 199-259) combined with a Pressure-Stabilizing/Petrov-Galerkin (PSPG) one (Tezduyar, T. E., 1992, "Stablized Finite Element Formulations for Incompressible Flow Computations," Adv. Appl. Mech., 28, pp. 1-44, and Tezduyar, T. E., Mittal, S., Ray, S. E., and Shih, R., 1992, "Incompressible Flow Computations With Stabilized Bilinear and Lihear Equal Order Interpolation Velocity-Pressure Elements," Comput. Methods Appl. Mech. Eng., 95, pp. 221-242). At each time step, the fluid equations are solved with constant pressure and null viscous traction conditions at the free surface and the velocities obtained in this way are used for updating the positions of the surface nodes. Then, a pseudo elastic problem is solved in the fluid domain in order to relocate the interior nodes so as to keep mesh distortion controlled. This has been implemented in the PETSc-FEM code (PETSc-FEM: a general purpose, parallel, multi-physics FEM program. GNU general public license (GPL), http://www.cimec.org.ar/petscfem) by running two parallel instances of the code and exchanging information between them. Some numerical examples are presented. [ABSTRACT FROM AUTHOR]

Abstract: MPI for Python provides bindings of the Message Passing Interface (MPI) standard for the Python programming language and allows any Python program to exploit multiple processors. This package is constructed on top of the MPI-1 specification and defines an object-oriented interface which closely follows MPI-2 C++bindings. It supports point-to-point (sends, receives) and collective (broadcasts, scatters, gathers) communications of general Python objects. Efficiency has been tested in a Beowulf class cluster and satisfying results were obtained. MPI for Python is open source and available for download on the web ( http://www.cimec.org.ar/python ). [Copyright &y& Elsevier]

Improving gas turbine performance depends almost exclusively on the maximum temperature of the combustion gases. This temperature is limited by the thermomechanical strength of the turbine vanes. In this work, a Chimera approach for overlapping grids in the finite element method (FEM) context is proposed to optimize the arrangement of several cooling passages within the vane to minimize its average temperature, thereby improving the thermal transfer efficiency. The scheme is based on a fixed background mesh covering the entire domain, while finer meshes surrounding the coolant passages can move around over the airfoil while searching for the best configuration of the cooling system. Information is exchanged between meshes through a high-order interpolation algorithm. The optimization strategy is developed based on the use of the population-based augmented Lagrangian particle swarm optimizer (ALPSO) to approach a probable global minimum, and then a refinement of the solution is performed using the gradient-based sequential least squares quadratic programming (SLSQP) algorithm. Both the gradient, for the gradient-based optimizer, and the function evaluations, for the population-based optimizer, are solved in parallel to speed up the solution. • A Chimera approach in the FEM context to address optimization problems is presented. • The refrigeration system of a gas turbine vane is enhanced. • Large displacements of the cooling passages are allowed without remeshing the domain. • Good speed up is obtained when using the parallel capabilities of pyOpt. • We provide a tool to efficiently enhance the thermal performance of engineering parts. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a three-dimensional numerical simulation is used to analyze the performance of delta-wing vortex generators for enhancing the heat exchange in panel type radiators, which are widely used in electric power transformers. The study is focused on natural convection and buoyancy-driven flows, which are common working conditions for this type of heat exchanger. First, the performance of a single delta wing between parallel vertical plates is analyzed to establish the best combination of characteristic parameters to obtain the highest thermal enhancement factor. It is found that separating the vortex generator from the surface of the panel has positive effects in this sense. Then, with the selected configuration, a set of delta-wing arrays is placed on the surface of the heat exchanger, and the resulting thermo-fluid dynamic is analyzed. The total heat flux and local/global heat exchange coefficients are reported. Using these passive devices, the overall heat transfer improves by 12%. [ABSTRACT FROM AUTHOR]

The interest in synthetic methods relies in the fact that reliability of methodologies such as large eddy simulations (LES) or direct numerical simulations strongly depends on how well the developed turbulence is characterized, which generally leads to computationally expensive simulations. Turbulence generation methods allow the initialization and up-keeping of the velocity fluctuations field to promote the observed/needed turbulence in the flow. In this work the methodology known as ‘modified discretizing and synthesizing random flow generation’ (MDSRFG) jointly with a LES method is analyzed for its use in the study of tall building aerodynamics. A comparison with other generation techniques, that are closely related by their features and their conceptual origins, is presented with particular emphasis on the correct representation of the coherence of the velocity field. Particularly, an expression for the coherency function for the MDSRFG is derived. After an analysis and revision of these generation methodologies, the turbulent air flow around a rectangular prismatic model is computationally simulated. A comparison of the results obtained from different methods is performed. The resulting wind loads on the model, along with the statistical characteristics of the flow, show that the MDSRFG technique allows to represent a field of spatially correlated velocities correctly. [ABSTRACT FROM AUTHOR]

Problems with moving sources and moving inner boundaries in transient regime are of high interest in many research fields and engineering applications. One approach to properly tackle such problems is based on the Chimera method for non-matching grids, where each moving object is defined on a fine mesh that moves across the fixed coarse background. In this way, the high gradients around moving sources or boundaries are captured by the fine mesh without need of globally fine fixed meshes or adaptive refinement. In this work, Chimera is implemented in the framework of the finite element method, following an arbitrary Lagrangian–Eulerian formulation for the moving meshes and a standard Eulerian formulation for the fixed background mesh. Further, in case of convection-dominated problems, the scheme is stabilized using the streamline upwind Petrov–Galerkin method. The coupling between the moving fine meshes and the coarse fixed one is achieved via Dirichlet boundary conditions and a high-order interpolation algorithm. The performance of the proposed methodology in terms of accuracy and stability is assessed by means of numerical tests to be compared with equivalent problems solved using fixed meshes. Further tests serve to highlight the good performance of the proposed Chimera-based finite element method to address both convection-dominated problems with multiple moving boundaries and sources, and three-dimensional arc welding processes. • An algebraic-based Chimera-FEM scheme for unsteady problems is proposed. • Remeshing is avoided for large movements of heat sources and boundaries. • Advective-dominant problems can be addressed with Chimera-FEM and SUPG. • Good accuracy is obtained compared to conventional one-domain approaches. • The scheme is suitable to be used on 3D welding process simulations. [ABSTRACT FROM AUTHOR]

This research work evaluates the performance of a Fluid–Structure Interaction (FSI) solver, which is created using a generic interface to couple two independent software packages. The basic idea is to combine the advantages of the two independent codes to create a powerful FSI solver for two and three dimensional FSI analysis using the concept of modular programming. A detailed description about the implementation of an interface to couple a three-field system involved in the analysis is given, and this developed interface can be generalized to others codes. Since solving complex FSI problems is very time consuming, the focus of this work is placed on the performance of the coupled solver, for which a FSI benchmark will be solved on a computer cluster in order to measure speed up and efficiency. [ABSTRACT FROM AUTHOR]

A Navier–Stokes solver based on Cartesian structured finite volume discretization with embedded bodies is presented. Fluid structure interaction with solid bodies is performed with an explicit partitioned strategy. The Navier–Stokes equations are solved in the whole domain via a Semi-Implicit Method for Pressure Linked Equations (SIMPLE) using a colocated finite volume scheme, stabilized via the Rhie–Chow discretization. As uniform Cartesian grids are used, the solid interface usually do not coincide with the mesh, and then a second order Immersed Boundary Method is proposed, in order to avoid the loss of precision due to the staircase representation of the surface. This fact also affects the computation of fluid forces on the solid wall and, accordingly, the results in the fluid–structure analysis. In the present work, first and second order approximations for computing the fluid forces at the interface are studied and compared. The solver is specially oriented to General Purpose Graphic Processing Units (GPGPU) hardware and the efficiency is discussed. Moreover, a novel submerged buoy experiment is also reported. The experiment consists of a sphere with positive buoyancy fully submerged in a cubic tank, subject to harmonic displacements imposed by a shake table. The sphere is attached to the bottom of the tank with a string. The position of the buoy is determined from video records with a Motion Capture algorithm. The obtained amplitude and phase curves allow a precise determination of the added mass and drag forces. Due to this aspect the experimental data can be of interest for comparison with other fluid–structure interaction codes. Finally, the numerical results are compared with the experiments, and allow the confirmation of the numerically predicted drag and added mass of the body. [ABSTRACT FROM AUTHOR]

Validation of three-dimensional (3D) sloshing models is a relevant task in order to guarantee the correctness of numerical predictions. In this work, attention is focused on assessing the 3D free surface (FS) evolution when an Arbitrary Lagrangian–Eulerian method is applied to solve sloshing problems. The computational scheme consists of three stages: (i) solve the incompressible Navier–Stokes equations over a single fluid domain with a FS; (ii) determine the FS displacements from the velocity field computed at (i); and (iii) update the mesh with a computational mesh dynamic problem. The study aims to evaluate the global mass-conservation strategy reported in this work for long term simulations. The forced sloshing cases present moderate FS displacements with complex wave pattern behaviours. Specifically, sloshing in a tank with a stepped shape in the bottom and two sloshing cases of a rectangular tank are presented. The numerical results are compared with experimental data to evaluate the performance of the proposed model. • 3D one-phase mass-preserving stabilized ALE technique. • Mesh dynamics based on minimal distortion principle is extended to free surfaces. • Report of the sloshing in a tank with a stepped-shape bottom. • Experimental validation of the model. [ABSTRACT FROM AUTHOR]

Power transformers are the first devices used to transfer the electrical energy produced in power plants to the grid to supply the industrial and individual receivers with electricity. The heat generation in windings and core, being an effect of the power losses, is usually dissipated in large units by using mineral oils, which are harmful to the environment. Nowadays, the industry and global society seek environmentally-friendly alternatives. One of the most promising substitute for their high biodegradability, safety in operation, and favourable thermo-physical properties are natural ester oils. For this reason, a numerical study of 8.5 MVA disk-type power transformer cooled using conventional mineral oil and a commercially used rapeseed ester oil is presented in this paper. Moreover, due to different thermal behaviour of the considered oils, the comparison was made for the unit working in different seasons of hot and moderate climate zones (Argentina and Poland). In the numerical approach, electromagnetic (EMAG) and computational fluid dynamics (CFD) models were used for a detailed study of the selected device. In particular, a novel and very efficient EMAG–CFD–CFD coupling procedure was developed to assess the cooling of the large power transformer. Such a coupled computational procedure allowed for the detailed investigation of the power loss, oil flow characteristics, and temperatures with a satisfying computational effort. The results showed that the average windings temperatures are higher by 2–9 K when the ester oil is used, dependent on the ambient conditions. The hotspot temperature in the low voltage windings increased by up to 9 K and up to 18 K in the high voltage windings using ester oil. According to the results, the oil duct construction requires modification in the high voltage region for transformers cooled using mineral oil in cold climate conditions. • Coupled electromagnetic and thermo-fluid model of disk-type transformer was developed. • Advanced coupling approach allowed to perform a detailed CFD simulation efficiently. • Separate detailed CFD sub-models of windings and transformer tank were coupled. • Biodegradable ester oil was compared with mineral oil for the transformer cooling. • Power transformer cooling in Polish and Argentinian climate-zones was compared. [ABSTRACT FROM AUTHOR]

Abstract: This article discusses high performance numerical simulations of electrokinetic flow and transport phenomena in microfluidic chips. Modeling grounds on conservation equations of mass, momentum and electric charge in the framework of continuum mechanics. Two examples of interest in microfluidics are considered as study cases. Three dimension effects and whole chip geometries are taking into account. All numerical simulations presented are performed with PETSc-FEM within a Python programming environment employing parallel computing. Computation time and parallel efficiency are measured in order to study additive Schwarz method performance as domain decomposition technique in solving common ill-conditioned microfluidics problems. [Copyright &y& Elsevier]