3D Numerical Simulations Research Articles

Pore-scale modeling of coupled thermal and solutal dispersion in double diffusive-advective flows through porous media

In double diffusive-advective flows through porous media, the combined effects of fluid and solid properties, pore space geometry, and flow conditions on the transport rates and distribution of the thermal and solutal fronts can be characterized by dispersion coefficients. In this study, conjugate heat and solute transport in the process of miscible displacement through porous media is studied through pore-scale numerical simulations in 2D and 3D digital representations of the unconsolidated sandpacks. The temperature and solute concentration distributions during both viscously stable and unstable displacements are obtained by solving the point equations of flow and transport on the discretized computational domains. Next, the longitudinal components of the solute and thermal dispersion coefficients are determined by fitting the effluent profiles to the analytical solutions of the advection-diffusion equations for the transport of mass and heat, respectively. The length scales of the solutal and thermal transition zones are also measured along the principal direction of the flow and then correlated with the displacement time. In stable displacements, different dispersion regimes are identified based on the magnitude of the solutal and thermal Peclet numbers. It is observed that the onset of convective spreading is different in the 2D and 3D simulation runs. In unstable displacements, the results indicate that solutal dispersion is more affected by thermo-solutal viscous fingering compared to thermal dispersion. Moreover, as the viscosity contrast across the thermal and solutal fronts increases, the dynamics of the mixing length growth gradually changes from dispersion-dominated toward fingering-dominated. Finally, the results show that two-dimensional simulation runs may not completely characterize the dispersion-related phenomena that occurs during heat and solute transfer in a real porous medium. Therefore, it is essential to conduct three-dimensional runs to capture all the underlying mechanisms contributing to the mixing and dispersion in porous media. The outcomes of this study can pave the way for an optimal design and implementation of an efficient non-isothermal miscible displacement in porous media.

Optimization of radio-frequency plasma parameters for spheroidization of zirconium oxide powders

Based on numerical 3D simulation of induction coupled plasma, optimal conditions are found for spheroidization of “difficult to process” ceramic powders. Yttria-stabilized zirconium oxide powder, widely used for thermal barrier coatings, was chosen as an example. Transparent and matt type of spherical particles are obtained as a result of the plasma processing. An interpretation is given for the observed phenomenon. The processed powders were tested and compared with alternatives by means of their arc plasma deposition to create a barrier coating.

Analytical and numerical prediction of mechanical properties of heterogeneous materials with expansive inclusions: Application to waste cementation

In this paper, we are concerned with the analytical and numerical study of the effective properties of heterogeneous microstructures resulting from nuclear waste cementation processes. In certain cases, the presence of free-water in the cement matrix pores causes corrosion of metal inclusions that are immobilized, and which transform progressively into an expansive metal oxide layer. Such expansions may lead to high stress/strain levels able to generate micro-cracks in the cement matrix, and to affect the integrity of the waste containers. A homogenization model is then developed to estimate the effective properties of a composite material including spherical inclusions surrounded by a corrosion product layer seen as an expansive phase. The differential scheme is applied, allowing to extend the model to different types of inclusions with high volume fraction, and an interaction coefficient is introduced that relates macroscopic behavior and expansions at microscale. Finally, numerical 3D simulations are performed to determine the effective properties of representative elementary volumes generated with different shapes and volume fractions of inclusions, some of them exhibiting a layer of expansive phase. A comparison between numerical and analytical results shows a good agreement, which confirms the relevance of the model.

Numerical 3D simulation of wire deposition process to predict distortion of parts

In the work, on the basis of the analysis of publications, existing approaches to the numerical modeling of additive processes of product formation are shown. The work itself is devoted to the study of the influence of parameters of the process of surfacing wire materials on the formation of residual deformations in parts. A mathematical formulation of the non-stationary thermomechanical problem is presented, and algorithms for solving the problem using the technology of birth and death of finite elements in the ANSYS package are described. Verification of the model created by the finite element was carried out on the basis of data from the experiment on surfacing a multilayer sample. The effect on the level of residual warping of the following process parameters was studied: the exposure time before the next layer was deposited; the motion path of the burner; ambient temperature. It is shown that the change in ambient temperature is the most effective way to reduce the residual distortions of the form.

Nonlinear Coda Wave Interferometry: Sensitivity to wave-induced material property changes analyzed via numerical simulations in 2D

The numerical studies conducted in this paper are based on our previous research (Chen et al., 2017); through use of the spectral element method, parametric sensitivity studies of Nonlinear Coda Wave Interferometry (NCWI) are established here and divided into two parts. In the first part, CWI observables are found to be proportional to the product of the changes in elastic modulus within the Effective Damaged Zone (EDZ) and the EDZ surface area. The modifications to intrinsic properties are quantified via an overall wave velocity variation, as probed by a reverberated coda wave. However, for high-level changes, CWI may fail due to meaningless decorrelation values. In this context, parametric studies are conducted to yield a maximum range for EDZ contrast and area. To further validate these observations using a more realistic numerical model, instead of introducing a homogeneous EDZ model, the second part of this paper adds random cracks with random orientations into the EDZ of a material sample. The influence of a strong pump wave on localized nonlinear damage is reestablished; results show that the cracks added into the EDZ reduce the property changes required to match the previous experimental dataset.

Star-planet interaction through spectral lines

AbstractThe growth of spectroscopic observations of exoplanetary systems allows the possibility of testing theoretical models and studying the interaction that exoplanetary atmospheres have with the wind and the energetic photons from the star. In this work, we present a set of numerical 3D simulations of HD 209458b for which spectral lines observations of their evaporative atmosphere are available. The different simulations aim to reproduce different scenarios for the star-planet interaction. With our models, we reconstruct the Lyα line during transit and compare with observations. The results allows us to analyse the shape of the line profile under these different scenarios and the comparison with the observations suggest that HD209458b may have a magnetic field off less than 1 G. We also explore the behaviour of the magnesium lines for models with and without magnetic fields.

Optimized finite difference method with artificial dissipation for under-resolved unsteady incompressible flow computations using kinetically reduced local Navier-Stokes equations

Under-resolved unsteady incompressible flow computations employed on coarser grids are presented. Kinetically Reduced Local Navier-Stokes (KRLNS) equations is a newly method to deal with unsteady incompressible flows, which is applicable to the unsteady incompressible flows without the need for sub-iterations and is capable of capturing the correct transient behavior. To stabilize the computations and achieve high accuracy, the KRLNS equations is discretized with higher order standard and optimized types of central finite difference method (FDM) together with artificial dissipation or spatial filter and is integrated by using 4-stage Runge-Kutta method. Numerical simulations of 2D doubly periodic shear layers are carried out on coarser regular grids and the computed solutions are compared with those obtained on finer grids. The parallel computations are implemented on multiple GPU (Tesla K40) system with 4 GPUs, based on the domain decomposition method and the acceleration is investigated. It is found that the solution obtained by optimized type of FDM is more accurate than that of standard one especially for much coarser grids, and that the proposed approach is easy to perform the parallel computations and obtain a large acceleration according to the number of GPUs used.

Numerical simulation of gas-particle dense flow with LES/VFDF/SC model

A velocity filtered density function (VFDF) transport equation is derived to solve the interaction between the gas and solid particles, in which the sub-grid scale turbulence encountered by the particles is included. The stochastic collision (SC) model is developed to deal with collision between particles based on the kinetic theory, in which the instantaneous collision rate at every time interval is obtained. Together with the large eddy simulation (LES) which is used to model the fluid flow, the LES/VFDF/SC model is developed for dense gas-particle flows. It is for the first time to consider both the SGS effect and the influence of particle collision on the particle motion in LES of dense gas-particle. Numerical simulations of 2D and 3D fluidized beds are carried out with the developed model, in which the CFD software FLUENT is applied to simulate the flow field with the LES, and the VFDF/SC model is implemented in the self-developed code with the tool of user-defined functions (UDFs) in FLUENT. Comparisons between the numerical results and the experimental data show that the dense gas-particle flow in present cases can be well predicted with the developed model.

Sensitivity analysis for 3D Maxwell's equations and its use in the resolution of an inverse medium problem at fixed frequency

ABSTRACTThis paper deals with the reconstruction of small-amplitude perturbations in the electric properties (permittivity and conductivity) of a medium from boundary measurements of the electric field at a fixed frequency. The underlying model is the three-dimensional time-harmonic Maxwell equations in the electric field. Sensitivity analysis with respect to the parameters is performed, and explicit relations between the boundary measurements and the characteristics of the perturbations are found from an appropriate integral equation and extensive numerical simulations in 3D. The resulting non-iterative algorithm allows to retrieve efficiently the centre and volume of the perturbations in various situations from the simple sphere to a realistic model of the human head.

Conductor losses calculation in two-dimensional simulations of H-plane rectangular waveguides

ABSTRACTThis paper presents a novel numerical approach to simulate H-plane rectangular-waveguide microwave circuits considering a reduced quasi-2D simulation domain with benefits for computational cost and time. With the aim to evaluate the attenuation of the full height 3D component, we propose a modified expression for the waveguide top/bottom wall conductivity. Numerical 2D simulations are validated against results from full wave 3-D commercial electromagnetic simulator. After a benchmark on a simple straight waveguide model, the method has been successfully applied to an asymmetric un-balanced power splitter, where an accurate power loss prediction is mandatory. Simulation time and memory consumption can be reduced by a factor ten and seven respectively, in comparison with complete 3D geometries. Finally, we show that, also for quasi-2D E-bend waveguide, a case where the translational H-plane symmetry is broken, the error on conductor losses computation is mitigated by our approach since the method remains still valid in a first approximation.

The Dynamic Three-Dimensional Localization of Fields in Active Percolating Systems

We study a dynamic three-dimensional (3D) field localized states in a medium with percolation disorder, where the percolation cluster is filled by the active nanoemitters. In such a system, the incipient percolating cluster generates a fractal radiating structure in which the field is radiated and scattered by the anisotropic inhomogeneity. Our numerical 3D simulations show that such a nonlinear system with noninteger fractal dimension has well-defined localized solutions for fields (3D speckles). The statistics of speckles is studied too.

Numerical 3D simulation of developing turbulent stratified gas-liquid flow in curved pipes consisting of entrained particles through this type of flow

Predicting multiphase flows in curved pipes is of great importance in industrial equipment. In the present study, a computational model for predicting the velocity profile is developed and used to study the developing turbulent gas-liquid- solid three dimension flow in curved pipes. In order to discretize and solve the three-dimensional steady-state momentum equations, the finite volume scheme on staggered grids besides central difference and QUICK scheme have been used. Moreover, the k-e model is employed to reflect the nature of turbulence in the flow. In order to address the needs for sooner convergence and convenient mapping of the physical domain, the computations have been performed in an extended toroidal coordinate system. Particle tracking has been done using Lagrangian approach in which two-way coupling regime is considered. In terms of validation, the numerical simulation results for the straight duct (infinite curvature), have been compared with the analytical solution and previous experimental results. Moreover, injection of particles through the flow indicates that, in each section of the bend, trade-off between centrifugal and pressure gradient forces plays a key role on particles motion. In last section, the effects of particle diameter and bend curvature on particle motion have been examined.

Development and validation of a meshless 3D material point method for simulating the micro-milling process

A meshless generalized interpolation material point method for simulating the micro-milling process was developed. This method has several advantages over well-established approaches (such as finite elements) when it comes to large plastic strains and deformations, since it inherently does not suffer from tensile instability problems. The feasibility of the developed material point model for simulating micro-milling is verified against finite element simulations and experimental data. The model is able to successfully predict experimentally measured cutting forces and determine chip temperatures in agreement with conventional finite element simulations. After having verified the approach, the model was applied to perform extensive numerical 3D simulations of the micro-milling process. The goal is to evaluate the response of the micro-milling cutting forces as function of the hardening behavior of the micro-milled material. The meshless 3D simulations reveal a dependency of tool force slopes (with respect to the uncut chip thickness) on the hardening parameters. Based on these findings, a new approach is outlined to determine hardening parameters directly from two micro-milling experiments with distinct, sufficiently large uncut chip thicknesses.

Simulation of acoustic and flexural-gravity waves in ice-covered oceans

We introduce a provably stable, high-order-accurate finite difference method for simulation of acoustic and flexural gravity waves in compressible, inviscid fluids partially covered by a thin elastic layer. Such waves arise when studying ocean wave interactions with floating ice shelves, sea ice, and floating structures. Particular emphasis is on a well-posed interface treatment of the fluid-ice coupling. To ensure numerical stability and efficiency, finite difference approximations based on the summation-by-parts (SBP) framework are combined with a penalty technique (simultaneous approximation term, SAT) to impose the boundary and interface conditions. The resulting SBP-SAT approximations are time integrated with an unconditionally stable finite difference method. Numerical simulations in 2D corroborate the predicted efficiency and stability behaviors. The method can be used in its current form to study transmission of ocean waves and tsunamis through ice shelves, and upon coupling to an elastic half-space beneath the ice and water, to study ice motions associated with long-period seismic surface waves.

Numerical 3D simulations of seepage and the seepage stability of the right-bank dam of the Dry Flood Control Reservoir in Racibórz

Abstract This article presents the results of numerical simulations of seepage through the body of the dam and the reservoir bed. The purpose of this study was to analyse the seepage stability during a flood as well as the impact on seepage stability of the diaphragm wall and gravel columns, on which the dam body is founded in selected segments. Simulations were conducted for three different locations, and the following 3D models of the dum were prepared: – a model containing the front and right-bank part of the dam, for which no diaphragm wall, gravel columns and drainage ditch were provided for – a model of a segment of the right-bank dam including a diaphragm wall, drainage ditch and gravel columns under the dam (two variants with differing diaphragm wall lengths) – a model of the water dam segment accounting for gravel columns and a drainage ditch, but without a diaphragm wall. In the case of founding on gravel columns, the base was modelled as an anisotropic medium in terms of seepage properties, macroscopically equivalent to the actual soil medium. The numerical model utilises the finite element method. The geometry of the dam and geological substrate was defined in the GIS tools in the form of a 3D model of the terrain and geology of the substrate.

Finite-Volume Discretisations for Flow in Fractured Porous Media

Over the last decades, finite-volume discretisations for flow in porous media have been extended to handle situations where fractures dominate the flow. Successful discretisations have been based on the discrete fracture-matrix models to yield mass conservative methods capable of explicitly incorporating the impact of fractures and their geometry. When combined with a hybrid-dimensional formulation, two central concerns are the restrictions arising from small cell sizes at fracture intersections and the coupling between fractures and matrix. Focusing on these aspects, we demonstrate how finite-volume methods can be efficiently extended to handle fractures, providing generalisations of previous work. We address the finite-volume methods applying a general hierarchical formulation, facilitating implementation with extensive code reuse and providing a natural framework for coupling of different subdomains. Furthermore, we demonstrate how a Schur complement technique may be used to obtain a robust and versatile method for fracture intersection cell elimination. We investigate the accuracy of the proposed elimination method through a series of numerical simulations in 3D and 2D. The simulations, performed on fractured domains containing permeability heterogeneity and anisotropy, also demonstrate the flexibility of the hierarchical framework.

Mechanical characterization and numerical simulation of a subcutaneous implantable 3D printed cell encapsulation system

Cell transplantation in bioengineered scaffolds and encapsulation systems has shown great promise in regenerative medicine. Depending on the site of implantation, type of cells and their expected function, these systems are designed to provide cells with a physiological-like environment while providing mechanical support and promoting long-term viability and function of the graft. A minimally invasive 3D printed system termed neovascularized implantable cell homing and encapsulation (NICHE) was developed in polylactic acid for subcutaneous transplantation of endocrine cells, including pancreatic islets. The suitability of the NICHE for long term in vivo deployment is investigated by assessing mechanical behavior of both fresh devices under simulated subcutaneous conditions and NICHE retrieved from subcutaneous implantation in pigs. Both experimental and numerical studies were performed with a focus on validating the constitutive material model used in the numerical analysis for accuracy and reliability. Notably, homogeneous isotropic constitutive material model calibrated by means of uniaxial testing well suited experimental results. The results highlight the long term durability for in vivo applications and the potential applicability of the model to predict the mechanical behavior of similar devices in various physiological settings.

Antiskeletal Morphology of Crystals as a Possible Result of Their Regeneration

This paper presents a possible mechanism forming crystals with antiskeletal morphology due to their regeneration after partial dissolution. Consideration is carried out by numerical 2D-simulation of the coordinate zone evolution of a single crystal ball using the kinematic model of regeneration crystal surface growth. According to this model, the genetic predecessors of subindividuals on the regenerated crystal are protrusions formed on its surface during the partial dissolution stage. It has been shown that the main parameter responsible for the antiskeletal morphology of regenerated crystals is the ratio of depression depths (l) between adjacent protrusions and protrusion radii (r), 0 0.6, there is a ball with a rough surface covered by flat areas on the most slowly growing faces. The crystal with the antiskeletal morphology grows at intermediate values of l/r.

Multi-GPU parallel computation of unsteady incompressible flows using kinetically reduced local Navier–Stokes equations

Numerical simulations of 2D doubly periodic shear layers and 3D decaying homogeneous isotropic turbulence are presented using Kinetically Reduced Local Navier–Stokes (KRLNS) equations that is applicable to the unsteady incompressible flows without the need for sub-iterations and is capable of capturing the correct transient behavior. To achieve high accuracy, the KRLNS equations is discretized with higher order central difference approximations and 4-stage Runge–Kutta method. The results are compared with the solutions obtained by Lattice Boltzmann method (LBM) and pseudo-spectral method (PSM), which is the standard approach for this problem. Parallel computations are carried out on multiple GPUs (Tesla K40), maximum 4 GPUs available, based on the domain decomposition method and the speedup of the KRLNS equations is investigated. It is found that all three methods can capture the transient flow fields of unsteady incompressible flow and a large speedup for the KRLNS equations is obtained.

Compressive experiment and numerical simulation of 3D carbon/carbon composite open-hole plates

Experiments and finite element analysis were carried out for the problem of open-hole sensitivity of 3D carbon/carbon composite material plates. Finite element models of the representative volume element and open-hole plates of 3D carbon/carbon composite were established. Transition method between macro-level stress and meso-level stress was given, and numerical simulation on the compressive failure of open-hole plates was implemented based on this method. By uniaxial compressive tests of 3D carbon/carbon composite open-hole plates, good agreement between numerical results and experiments was observed. In addition, the influence of width-to-diameter ratio (WTDR) on the compressive strength was analyzed. The results show that the compressive strength of the WTDR-6 open-hole plate is larger than that of the WTDR-4 open-hole plate. It can be considered that the carbon/carbon composite plate is insensitive to the opening hole when the WTDR reaches to 6. And the result of the investigation provides insight into the design of carbon/carbon composite open-hole plates.