Effects of a radially varying electrical conductivity on 3D numerical dynamos
Gomez-Perez, Natalia; Wicht, Johannes; 10.1016/j.pepi.2010.03.006
2010-01-01
The transition from liquid metal to silicate rock in the cores of the terrestrial planets is likely to be accompanied by a gradient in the composition of the outer core liquid. The electrical conductivity of a volatile enriched liquid alloy can be substantially lower than a light-element-depleted fluid found close to the inner core boundary. In this paper, we investigate the effect of radially variable electrical conductivity on planetary dynamo action using an electrical conductivity that decreases exponentially as a function of radius. We find that numerical solutions with continuous, radially outward decreasing electrical conductivity profiles result in strongly modified flow and magnetic field dynamics, compared to solutions with homogeneous electrical conductivity. The force balances at the top of the simulated fluid determine the overall character of the flow. The relationship between Coriolis and Lorentz forces near the outer boundary controls the flow and magnetic field intensity and morphology of the...
3D Babcock-Leighton Solar Dynamo Models
Miesch, Mark S.; Hazra, Gopal; Karak, Bidya Binay; Teweldebirhan, Kinfe; Upton, Lisa
2016-05-01
We present results from the new STABLE (Surface flux Transport and Babcock Leighton) Dynamo Model. STABLE is a 3D Babcock-Leighton/Flux Transport dynamo model in which the source of poloidal field is the explicit emergence, distortion, and dispersal of bipolar magnetic regions (BMRs). In this talk I will discuss initial results with axisymmetric flow fields, focusing on the operation of the model, the general features of the cyclic solutions, and the challenge of achieving supercritical dynamo solutions using only the Babcock-Leighton source term. Then I will present dynamo simulations that include 3D convective flow fields based on the observed velocity power spectrum inferred from photospheric Dopplergrams. I'll use these simulations to assess how the explicit transport and amplification of fields by surface convection influences the operation of the dynamo. I will also discuss the role of surface magnetic fields in regulating the subsurface toroidal flux budget.
A 3D Babcock-Leighton Solar Dynamo Model
Miesch, Mark S
2014-01-01
We present a 3D kinematic solar dynamo model in which poloidal field is generated by the emergence and dispersal of tilted sunspot pairs (more generally Bipolar Magnetic Regions, or BMRs). The axisymmetric component of this model functions similarly to previous 2D Babcock-Leighton (BL) dynamo models that employ a double-ring prescription for poloidal field generation but we generalize this prescription into a 3D flux emergence algorithm that places BMRs on the surface in response to the dynamo-generated toroidal field. In this way, the model can be regarded as a unification of BL dynamo models (2D in radius/latitude) and surface flux transport models (2D in latitude/longitude) into a more self-consistent framework that captures the full 3D structure of the evolving magnetic field. The model reproduces some basic features of the solar cycle including an 11-yr periodicity, equatorward migration of toroidal flux in the deep convection zone, and poleward propagation of poloidal flux at the surface. The poleward-p...
Numerical dynamo action in cylindrical containers
Nore, Caroline; Castanon Quiroz, Daniel; Guermond, Jean-Luc; Léorat, Jacques; Luddens, Francky
2015-06-01
The purpose of this paper is to present results from numerical simulations of dynamo action in relation with two magnetohydrodynamics (MHD) experiments using liquid sodium in cylindrical containers. The first one is the von Kármán sodium (VKS) experiment from Cadarache (France), the second one is a precession-driven dynamo experiment from the DREsden sodium facility for DYNamo and thermohydraulic studies (DRESDYN). Contribution to the topical issue "Electrical Engineering Symposium (SGE 2014) - Elected submissions", edited by Adel Razek
Numerical Simulations of Boundary-Driven Dynamos
White, K.; Brummell, N.; Glatzmaier, G. A.
2012-12-01
An important topic of physics research is how magnetic fields are generated and maintained in the many astrophysical bodies where they are ubiquitously observed. Of particular interest, are reversals of magnetic fields of planets and stars, especially those of the Earth and the Sun. In an attempt to provide intuition on this problem, numerous physical dynamo experiments have been performed in different configurations. Recently, a tremendous breakthrough was made in the Von Karman sodium (VKS) experiments in France when the most realistic laboratory fluid dynamo to date was produced by driving an unconstrained flow in a cylinder of liquid sodium (Monchaux et al, 2007, PRL). One of the curiosities of the VKS experiment however is the effect of the composition of the impellers that drive the flow. Steel blades failed to produce a dynamo, but soft iron impellers, which have much higher magnetic permeability, succeeded. The role of the magnetic properties of the boundaries in boundary-driven dynamos is therefore clearly of interest. Kinematic and laminar numerical dynamo simulations (Giesecke et al, 2010, PRL & Gissinger et al, 2008 EPL) have shed some light but turbulent, nonlinear simulations are necessary. Roberts, Glatzmaier & Clune 2010 created a simplified model of the VKS setup by using three-dimensional numerical simulations in a spherical geometry with differential zonal motions of the boundary replacing the driving impellers of the VKS experiment. We have extended these numerical simulations further towards a more complete understanding of such boundary-forced dynamos. In particular, we have examined the effect of the magnetic boundary conditions - changes in the wall thickness, the magnetic permeability, and the electrical conductivity - on the mechanisms responsible for dynamo generation. Enhanced permeability, conductivity and wall thickness all help dynamo action to different degrees. We are further extending our investigations to asymmetric forcing to
Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations
Amit, Hagay; Leonhardt, Roman; Wicht, Johannes
2010-08-01
Recent advances in the study of geomagnetic field reversals are reviewed. These include studies of the transitional field during the last geomagnetic reversal and the last geomagnetic excursion based on paleomagnetic observations, and analysis of reversals in self-consistent 3D numerical dynamo simulations. Field models inferred from observations estimate reversal duration in the range of 1-10 kyr (depending on site location). The transitional fields during both the Matuyama/Brunhes reversal and the Laschamp excursion are characterized by low-latitude reversed flux formation and subsequent poleward migration. During both events the dipole as well as the non-dipole field energies decrease. However, while the non-dipole energy dominates the dipole energy for a period of 2 kyr in the reversal, the non-dipole energy merely exceeds the dipole energy for a very brief period during the excursion. Numerical dynamo simulations show that stronger convection, slower rotation, and lower electrical conductivity provide more favorable conditions for reversals. A non-dimensional number that depends on the typical length scale of the flow and represents the relative importance of inertial effects, termed the local Rossby number, seems to determine whether a dynamo will reverse or not. Stable polarity periods in numerical dynamos may last about 1 Myr, whereas reversals may last about 10 kyr. Numerical dynamo reversals often involve prolonged dipole collapse followed by shorter directional instability of the dipole axis, with advective processes governing the field variation. Magnetic upwellings from the equatorial inner-core boundary that produce reversed flux patches at low-latitudes of the core-mantle boundary could be significant in triggering reversals. Inferences from the observational and modeling sides are compared. We summarize with an outlook on some open questions and future prospects.
Numerical simulation of 3D breaking waves
Fraunie, Philippe; Golay, Frederic
2015-04-01
Numerical methods dealing with two phase flows basically can be classified in two ways : the "interface tracking" methods when the two phases are resolved separately including boundary conditions fixed at the interface and the "interface capturing" methods when a single flow is considered with variable density. Physical and numerical properties of the two approaches are discussed, based on some numerical experiments performed concerning 3D breaking waves. Acknowledgements : This research was supported by the Modtercom program of Region PACA.
Numerical simulation of Martian historical dynamo: Impact of the Rayleigh number on the dynamo state
WANG TianYuan; KUANG WeiJia; MA ShiZhuang
2009-01-01
The observed Mars remnant magnetism suggests that there was an active dynamo in the Martian core.We use the MoSST core dynamics model to simulate the Martian historical dynamo,focusing on the variation of the dynamo states with the Rayleigh number Ra (a non-dimensional parameter describing the buoyancy force in the core).Our numerical results show that the mean field length scale does not vary monotonically with the Rayleigh number,and the field morphology at the core mantle boundary changes with Rayleigh number.In particular,it drifts westward with a speed decreasing with Rayleigh number.
Cosmic dynamo analogue and decay of magnetic fields in 3D Ricci flows
de Andrade, Garcia
2009-01-01
Magnetic curvature effects, investigated by Barrow and Tsagas (BT) [Phys Rev D \\textbf{77},(2008)],as a mechanism for magnetic field decay in open Friedmann universes (${\\Lambda}<0$), are applied to dynamo geometric Ricci flows in 3D curved substrate in laboratory. By simple derivation, a covariant three-dimensional magnetic self-induced equation, presence of these curvature effects, indicates that de Sitter cosmological constant (${\\Lambda}\\ge{0}$), leads to enhancement in the fast kinematic dynamo action which adds to stretching of plasma flows. From the magnetic growth rate, the strong shear case, anti-de Sitter case (${\\Lambda}<0$) BT magnetic decaying fields are possible while for weak shear, fast dynamos are possible. The self-induced equation in Ricci flows is similar to the equation derived by BT in $(3+1)$-spacetime continuum. Lyapunov-de Sitter metric is obtained from Ricci flow eigenvalue problem. In de Sitter analogue there is a decay rate of ${\\gamma}\\approx{-{\\Lambda}}\\approx{-10^{-35}s^{-...
Numerical solution of 3D Stokes problems
Preconditions conjugate gradient algorithms for solving 3D Stokes problems by stable piecewise discontinuous pressure finite elements are presented. The emphasis is on the preconditioning schemes and their numerical implementation for use with Hermitian-based discontinuous pressure elements. For the piecewise constant discontinuous pressure elements, a variant implementation of the preconditioner proposed by Cahouet and Chabard for the continuous pressure elements is employed. For the piecewise linear discontinuous pressure elements, a new preconditioner is presented. Numerical examples are presented for the cubic lid driven cavity problem with two representative elements (i.e., the Q2-P0 and the Q2-P1 brick elements). Numerical results show that the preconditioning schemes are very effective in reducing the number of pressure iterations at very reasonable costs. It is also shown that they are insensitive to the mesh Reynolds number, except for nearly steady flows (Rem → 0), and are almost independent of mesh sizes. It is demonstrated that the schemes performed reasonably well on nonuniform meshes. 15 refs., 6 figs., 1 tab
Determining role of Krein signature for 3D Arnold tongues of oscillatory dynamos
Kirillov, Oleg N; Stefani, Frank
2008-01-01
Using a homotopic family of boundary eigenvalue problems for the mean-field $\\alpha^2$-dynamo with helical turbulence parameter $\\alpha(r)=\\alpha_0+\\gamma\\Delta\\alpha(r)$ and homotopy parameter $\\beta \\in [0,1]$, we show that the underlying network of diabolical points for Dirichlet (idealized, $\\beta=0$) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, $\\beta=1$) boundary conditions. In the $(\\alpha_0,\\beta,\\gamma)-$space the Arnold tongues of oscillatory solutions at $\\beta=1$ end up at the diabolical points for $\\beta=0$. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding $\\alpha$-profiles leading to spectral exceptional...
Numerical demonstration of fluctuation dynamo at low magnetic Prandtl numbers
Iskakov, A B; Cowley, S C; McWilliams, J C; Proctor, M R E
2007-01-01
Direct numerical simulations of incompressible nonhelical randomly forced MHD turbulence are used to demonstrate for the first time that the fluctuation dynamo exists in the limit of large magnetic Reynolds number Rm>>1 and small magnetic Prandtl number Pm6000 compared to Rm_c~60 for Pm>1. Is is not as yet possible to determine numerically whether the growth rate of the magnetic energy is ~Rm^{1/2} in the limit Rm->infinity, as should be the case if the dynamo is driven by the inertial-range motions at the resistive scale.
Numerical Simulations of Dynamos Generated in Spherical Couette Flows
Guervilly, Céline; 10.1080/03091920903550955
2010-01-01
We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculi...
Šimkanin, Ján; Hejda, Pavel
2009-01-01
Roč. 53, č. 1 (2009), s. 99-110. ISSN 0039-3169 R&D Projects: GA AV ČR IAA300120704 Institutional research plan: CEZ:AV0Z30120515 Keywords : hydromagnetic dynamos * control volume method * numerical dynamo benchmark * efficiency of parallelization Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.000, year: 2009
Radiative Transfer in 3D Numerical Simulations
Stein, R; Stein, Robert; Nordlund, Aake
2002-01-01
We simulate convection near the solar surface, where the continuum optical depth is of order unity. Hence, to determine the radiative heating and cooling in the energy conservation equation, we must solve the radiative transfer equation (instead of using the diffusion or optically thin cooling approximations). A method efficient enough to calculate the radiation for thousands of time steps is needed. We assume LTE and a non-gray opacity grouped into 4 bins according to strength. We perform a formal solution of the Feautrier equation along a vertical and four straight, slanted, rays (at four azimuthal angles which are rotated 15 deg. every time step). We present details of our method. We also give some results: comparing simulated and observed line profiles for the Sun, showing the importance of 3D transfer for the structure of the mean atmosphere and the eigenfrequencies of p-modes, illustrating Stokes profiles for micropores, and analyzing the effect of radiation on p-mode asymmetries.
Numerical 3-D Modelling of Overflows
Larsen, Torben; Nielsen, L.; Jensen, B.; Christensen, E. D.
2008-01-01
-dimensional so-called Volume of Fluid Models (VOF-models) based on the full Navier-Stokes equations (named NS3 and developed by DHI Water & Environment) As a general conclusion, the two numerical models show excellent results when compared with measurements. However, considerable errors occur when......The present study uses laboratory experiments to evaluate the reliability of two types of numerical models of sewers systems: - 1-dimensional model based on the extended Saint-Venant equation including the term for curvature of the water surface (the so-called Boussinesq approximation) - 2- and 3...
Numerical experiments on dynamo action in sheared and rotating turbulence
Yousef, T A; Rincon, F; Schekochihin, A A; Kleeorin, N; Rogachevskii, I; Cowley, S C; McWilliams, J C
2008-01-01
Numerical simulations of forced turbulence in elongated shearing boxes are carried out to demonstrate that a nonhelical turbulence in conjunction with a linear shear can give rise to a mean-field dynamo. Exponential growth of magnetic field at scales larger than the outer (forcing) scale of the turbulence is found. Over a range of values of the shearing rate S spanning approximately two orders of magnitude, the growth rate of the magnetic field is proportional to the imposed shear, gamma ~ S, while the characteristic spatial scale of the field is l_b ~ S^(-1/2). The effect is quite general: earlier results for the nonrotating case by Yousef et al. 2008 (PRL 100, 184501) are extended to shearing boxes with Keplerian rotation; it is also shown that the shear dynamo mechanism operates both below and above the threshold for the fluctuation dynamo. The apparently generic nature of the shear dynamo effect makes it an attractive object of study for the purpose of understanding thegeneration of magnetic fields in ast...
Dipole collapse and reversal precursors in a numerical dynamo
Olson, Peter; Driscoll, Peter; Amit, Hagay
2009-03-01
Precursors to extreme geomagnetic field changes are examined in a numerical dynamo with a reversing dipolar magnetic field. A dynamo model with compositional convection in a rotating spherical shell produces a strongly dipolar external magnetic field over 6 Myr of simulated paleomagnetic time, with stable polarity epochs and occasional dipole collapses, some of which result in polarity reversals or dipole axis excursions. We analyze the model behavior during two dipole collapses, one that leads to a polarity reversal and one that does not, focusing on observable precursors. Reversed magnetic field induced in the dynamo interior by intermittent convective variability is the primary cause of dipole collapse. Spots of reversed magnetic flux emerge on the outer boundary at an early stage, then re-emerge with greater intensity at the height of the collapse. The energy in the external field cascades to higher harmonics as these reversed patches appear. Butterfly diagrams showing the reversed and normal flux contributions to the axial dipole reveal poleward migration of the patches during dipole collapse. Axial dipole reduction by precursory reversed flux is several times larger in the reversing case, compared to the non-reversing case. A butterfly diagram of the geomagnetic field since 1840 shows high latitude reversed flux emerging on the core-mantle boundary. Although the reversed geomagnetic flux is presently too weak to be labeled a reversal precursor, it is consistent with early stage dipole collapse in the dynamo model.
3D numerical design of tunnel hood
Uystepruyst, David; Monnoyer, François
2015-01-01
This paper relates to the parametric study of tunnel hoods in order to reduce the shape, i.e the temporal gradient, of the pressure wave generated by the entry of a High speed train in tunnel. This is achieved by using an in-house three-dimensional numerical solver which solves the Eulerian equations on a Cartesian and unstructured mesh. The efficiency of the numerical methodology is demonstrated through comparisons with both experimental data and empirical formula. For the tunnel hood design, three parameters, that can influence the wave shape, are considered: the shape, the section and the length of the hood. The numerical results show, (i) that a constant section hood is the most efficient shape when compared to progressive (elliptic or conical) section hoods, (ii) an optimal ratio between hood's section and tunnel section where the temporal gradient of the pressure wave can be reduced by half, (iii) a significant efficiency of the hood's length in the range of 2 to 8 times the length of the train nose. Fi...
3 D Numerical Field Analysis at NAC
The NAC [1] was established in 1977 as a multi-disciplinary research centre to provide particle beams for basic and applied physics research, for advanced particle radiotherapy and for supplying accelerator-produced radioisotopes for nuclear medicine and research. The finite differences computer programs VEPO 2 and POFEL 3 were developed from the early 1970's over more than one decade for electromagnetic field analysis at NAC[2]. They were successfully used in the design of the sector magnets of our 200 MeV separated-sector cyclotron [3]. In the late 80's NAC implemented the more user-friendly software package Poisson/Super Fish [4], for two-dimensional numerical field analysis
Numerical studies of dynamo action in a turbulent shear flow
Singh, Nishant K
2013-01-01
We perform numerical experiments to study the shear dynamo problem where we look for the growth of large-scale magnetic field due to non-helical stirring at small scales in a background linear shear flow, in previously unexplored parameter regimes. We demonstrate the large-scale dynamo action in the limit when the fluid Reynolds number (Re) is below unity whereas the magnetic Reynolds number (Rem) is above unity; the exponential growth rate scales linearly with shear, which is consistent with earlier numerical works. The limit of low Re is particularly interesting, as seeing the dynamo action in this limit would provide enough motivation for further theoretical investigations, which may focus the attention to this analytically more tractable limit of Re 1. We also perform simulations in the limits when, (i) both (Re, Rem) 1 & Rem < 1, and compute all components of the turbulent transport coefficients (\\alpha_{ij} and \\eta_{ij}) using the test-field method. A reasonably good agreement is seen between ...
Numerical Relativity Towards Simulations of 3D Black Hole Coalescence
Seidel, E
1998-01-01
I review recent developments in numerical relativity, focussing on progress made in 3D black hole evolution. Progress in development of black hole initial data, apparent horizon boundary conditions, adaptive mesh refinement, and characteristic evolution is highlighted, as well as full 3D simulations of colliding and distorted black holes. For true 3D distorted holes, with Cauchy evolution techniques, it is now possible to extract highly accurate, nonaxisymmetric waveforms from fully nonlinear simulations, which are verified by comparison to pertubration theory, and with characteristic techniques extremely long term evolutions of 3D black holes are now possible. I also discuss a new code designed for 3D numerical relativity, called Cactus, that will be made public.
Numerical analysis of 3-D potential flow in centrifugal turbomachines
Daiguji, H.
1983-09-01
A numerical method is developed for analysing a three-dimensional steady incompressible potential flow through an impeller in centrifugal turbomachines. The method is the same as the previous method which was developed for the axial flow turbomachines, except for some treatments in the downstream region. In order to clarify the validity and limitation of the method, a comparison with the existing experimental data and numerical results is made for radial flow compressor impellers. The calculated blade surface pressure distributions almost coincide with the quasi-3-D calculation by Krimerman and Adler (1978), but are different partly from the quasi-3-D calculation using one meridional flow analysis. It is suggested from this comparison that the flow through an impeller with high efficiency near the design point can be predicted by this fully 3-D numerical method.
Solar dynamo models with alpha-effect and turbulent pumping from local 3D convection calculations
Käpylä, P J; Tuominen, I
2006-01-01
(abridged) Results from kinematic solar dynamo models employing alpha-effect and turbulent pumping from local convection calculations are presented. We estimate the magnitude of these effects to be around 2-3 m/s. The rotation profile of the Sun as obtained from helioseismology is applied. We obtain an estimate of the ratio of the two induction effects, C_alpha/C_Omega \\approx 10^-3, which we keep fixed in all models. We also include a one-cell meridional circulation pattern having a magnitude of 10-20 m/s near the surface and 1-2 m/s at the bottom of the convection zone. The model essentially represents a distributed turbulent dynamo, as the alpha-effect is nonzero throughout the convection zone, although it concentrates near the bottom of the convection zone obtaining a maximum around 30 degrees of latitude. Turbulent pumping of the mean fields is predominantly down- and equatorward. We find that, when all these effects are included in the model, it is possible to correctly reproduce many features of the so...
Numerical modeling of wave processes in 3D fractured media
Golubev V.; Petrov I.
2014-01-01
Seismic response from the cluster of vertical oriented cracks is simulated using grid-characteristic method on parallelepiped structured meshes. Synthetic seismograms and wave fields are calculated. The structure of the response including dependency on type of saturator (gas, fluid) is analyzed. Numerical experiments showed the effect of high-frequency daisy-chain wave’s generation from 3D periodic structures.
Finding Apparent Horizons in Dynamic 3D Numerical Spacetimes
Anninos, P.; Camarda, K.; Libson, J.; Masso, J.; Seidel, E; Suen, W.
1996-01-01
We have developed a general method for finding apparent horizons in 3D numerical relativity. Instead of solving for the partial differential equation describing the location of the apparent horizons, we expand the closed 2D surfaces in terms of symmetric trace--free tensors and solve for the expansion coefficients using a minimization procedure. Our method is applied to a number of different spacetimes, including numerically constructed spacetimes containing highly distorted axisymmetric blac...
Direct numerical simulation of 3D transitional fluid flows
Full text: For the numerical simulation of the 2D-3D transitional homogeneous and stratified incompressible viscous fluid flows, characterizing by the full Navier-Stokes equations, the splitting on physical factors method is used. The explicit hybrid finite difference scheme of the method has the following behaviors: the second order of accuracy in space, minimum scheme viscosity and dispersion, workable in wide range of Reynolds and Froude numbers and monotonicity. The efficiency of the developed numerical method and the advanced performance of the supercomputers allowed simulating 2D-3D transitional uncompressible viscous fluid flows around the bluff bodies in particular around a cylinder. By the numerical simulation of the fluid flows around 3D circular cylinder it was found that the transition to 3D regime arrives at Re>200. At 200< Re<300 the mode A with wavelength 3.5 d<λ<4.0 d (where d is the diameter of the cylinder) for 3D structures along the axis of a cylinder was observed. At 300< Re<400 the mode B with wavelength 0.8 d<λ<0.9 d was observed. At Re=300 the both modes A and B were observed simultaneously. The regime with large dislocations previously discovered experimentally was first obtained numerically at 210< Re<260. This regime is characterized by flow phase dislocation along the axis of the cylinder and as the effect by the amplitude fall of the lift force coefficient and the variations in the drag coefficient. There was simulated numerically the initiation of the attached internal waves behind the circular cylinder and upstream disturbance area at low Froude and moderate Reynolds numbers. (author)
3-D MHD Numerical Simulations of Cloud-Wind Interactions
Gregori, G.; Miniati, Francesco; Ryu, Dongsu; Jones, T. W.
2000-01-01
We present results from three-dimensional (3-D) numerical simulations investigating the magnetohydrodynamics of cloud-wind interactions. The initial cloud is spherical while the magnetic field is uniform and transverse to the cloud motion. A simplified analytical model that describes the magnetic energy evolution in front of the cloud is developed and compared with simulation results. In addition, it is found the interaction of the cloud with a magnetized interstellar medium (ISM) results in ...
Magnetic field stretching at the top of the shell of numerical dynamos
Peña, Diego; Amit, Hagay; Pinheiro, Katia J.
2016-05-01
The process of magnetic field stretching transfers kinetic energy to magnetic energy and by that maintains dynamos against Ohmic dissipation. Stretching at the top of the outer core may play an important role at specific regions. High-latitude intense magnetic flux patches may be concentrated by flow convergence. Reversed flux patches may emerge due to expulsion of toroidal field advected to the core-mantle boundary by fluid upwelling. Here we analyze snapshots from self-consistent 3D numerical dynamos to unravel the nature of field-flow interactions that induces stretching secular variation at the top of the core. We find that stretching at the top of the shell has a significant influence on the secular variation despite the relatively weak poloidal flow. In addition, locally stretching is often more effective than advection in particular at regions of significant field-aligned flow. Magnetic flux patches are concentrated by fluid downwelling and dispersed by fluid upwelling. Stretching is more efficient than advection in intensifying magnetic flux patches. Both stretching and the poloidal flow mostly depend on the magnetic Prandtl number Pm. Decreasing Pm gives smaller poloidal flow but stronger stretching. Accounting for field-flow interactions in both the advection and stretching terms suggests that the magnetic Reynolds number overestimates the actual ratio of magnetic advection to diffusion by ˜50 %. Morphological resemblance between local stretching in our dynamo models and local observed geomagnetic secular variation may suggest the presence of stretching at the top of the Earth's core. Our results shed light on the kinematic origin of intense geomagnetic flux patches and may have implications to the convective state of the upper outer core.
Using 3-D Numerical Weather Data in Piloted Simulations
Daniels, Taumi S.
2016-01-01
This report describes the process of acquiring and using 3-D numerical model weather data sets in NASA Langley's Research Flight Deck (RFD). A set of software tools implement the process and can be used for other purposes as well. Given time and location information of a weather phenomenon of interest, the user can download associated numerical weather model data. These data are created by the National Oceanic and Atmospheric Administration (NOAA) High Resolution Rapid Refresh (HRRR) model, and are then processed using a set of Mathworks' Matlab(TradeMark) scripts to create the usable 3-D weather data sets. Each data set includes radar re ectivity, water vapor, component winds, temperature, supercooled liquid water, turbulence, pressure, altitude, land elevation, relative humidity, and water phases. An open-source data processing program, wgrib2, is available from NOAA online, and is used along with Matlab scripts. These scripts are described with sucient detail to make future modi cations. These software tools have been used to generate 3-D weather data for various RFD experiments.
Numerical Investigation of 3D Flow Around Two Tandem Cylinders
Kalvig, Ragnhild Birgitte Hidle
2015-01-01
Circular cylinders in tandem arrangement are used in many marine applications like dual pipelines and dual risers. Turbulent flow in 3D around two tandem cylinders is simulated numerically using Large Eddy Simulation (LES) with a Smagorinsky subgrid scale model. The Reynolds number based on the cylinder diameter of 1 meter and free stream velocity of $U=1.31$ m/s is 13100, which is in the subcritical flow regime. The center-to-center spacing between the cylinders is $S/D=5$. The software used...
3D numerical simulation and analysis of railgun gouging mechanism
Jin-guo Wu
2016-04-01
Full Text Available A gouging phenomenon with a hypervelocity sliding electrical contact in railgun not only shortens the rail lifetime but also affects the interior ballistic performance. In this paper, a 3-D numerical model was introduced to simulate and analyze the generation mechanism and evolution of the rail gouging phenomenon. The results show that a rail surface bulge is an important factor to induce gouging. High density and high pressure material flow on the contact surface, obliquely extruded into the rail when accelerating the armature to a high velocity, can produce gouging. Both controlling the bulge size to a certain range and selecting suitable materials for rail surface coating will suppress the formation of gouging. The numerical simulation had a good agreement with experiments, which validated the computing model and methodology are reliable.
Evolutions in 3D numerical relativity using fixed mesh refinement
Schnetter, E; Hawke, I; Schnetter, Erik; Hawley, Scott H.; Hawke, Ian
2004-01-01
We present results of 3D numerical simulations using a finite difference code featuring fixed mesh refinement (FMR), in which a subset of the computational domain is refined in space and time. We apply this code to a series of test cases including a robust stability test, a nonlinear gauge wave and an excised Schwarzschild black hole in an evolving gauge. We find that the mesh refinement results are comparable in accuracy, stability and convergence to unigrid simulations with the same effective resolution. At the same time, the use of FMR reduces the computational resources needed to obtain a given accuracy. Particular care must be taken at the interfaces between coarse and fine grids to avoid a loss of convergence at high resolutions. This FMR system, "Carpet", is a driver module in the freely available Cactus computational infrastructure, and is able to endow existing Cactus simulation modules ("thorns") with FMR with little or no extra effort.
Towards an experimental von Karman dynamo: numerical studies for an optimized design
Ravelet, Florent; Chiffaudel, Arnaud; Daviaud, François; Léorat, Jacques
2004-01-01
Numerical studies of a kinematic dynamo based on von Karman type flows between two counterrotating disks in a finite cylinder are reported. The flow has been optimized using a water model experiment, varying the driving impellers configuration. A solution leading to dynamo action for the mean flow has been found. This solution may be achieved in VKS2, the new sodium experiment to be performed in Cadarache, France. The optimization process is described and discussed, then the effects of adding...
Bayliss, R A; Nornberg, M D; Terry, P W
2006-01-01
The role of turbulence in current generation and self-excitation of magnetic fields has been studied in the geometry of a mechanically driven, spherical dynamo experiment, using a three dimensional numerical computation. A simple impeller model drives a flow which can generate a growing magnetic field, depending upon the magnetic Reynolds number, Rm, and the fluid Reynolds number. When the flow is laminar, the dynamo transition is governed by a simple threshold in Rm, above which a growing magnetic eigenmode is observed. The eigenmode is primarily a dipole field tranverse to axis of symmetry of the flow. In saturation the Lorentz force slows the flow such that the magnetic eigenmode becomes marginally stable. For turbulent flow, the dynamo eigenmode is suppressed. The mechanism of suppression is due to a combination of a time varying large-scale field and the presence of fluctuation driven currents which effectively enhance the magnetic diffusivity. For higher Rm a dynamo reappears, however the structure of t...
3-D MHD Numerical Simulations of Cloud-Wind Interactions
Gregori, G; Ryu, D; Jones, T W; Miniati, Francesco; Ryu, Dongsu
2000-01-01
We present results from three-dimensional (3-D) numerical simulations investigating the magnetohydrodynamics of cloud-wind interactions. The initial cloud is spherical while the magnetic field is uniform and transverse to the cloud motion. A simplified analytical model that describes the magnetic energy evolution in front of the cloud is developed and compared with simulation results. In addition, it is found the interaction of the cloud with a magnetized interstellar medium (ISM) results in the formation of a highly structured magnetotail. The magnetic flux in the wake of the cloud organizes into flux ropes and a reconnection, current sheet is developed, as field lines of opposite polarity are brought close together near the symmetry axis. At the same time, magnetic pressure is strongly enhanced at the leading edge of the cloud from the stretching of the field lines that occurs there. This has an important dynamical effect on the subsequent evolution of the cloud, since some unstable modes tend to be strongl...
Evolutions in 3D numerical relativity using fixed mesh refinement
We present results of 3D numerical simulations using a finite difference code featuring fixed mesh refinement (FMR), in which a subset of the computational domain is refined in space and time. We apply this code to a series of test cases including a robust stability test, a nonlinear gauge wave and an excised Schwarzschild black hole in an evolving gauge. We find that the mesh refinement results are comparable in accuracy, stability and convergence to unigrid simulations with the same effective resolution. At the same time, the use of FMR reduces the computational resources needed to obtain a given accuracy. Particular care must be taken at the interfaces between coarse and fine grids to avoid a loss of convergence at higher resolutions, and we introduce the use of 'buffer zones' as one resolution of this issue. We also introduce a new method for initial data generation, which enables higher order interpolation in time even from the initial time slice. This FMR system, 'Carpet', is a driver module in the freely available Cactus computational infrastructure, and is able to endow generic existing Cactus simulation modules ('thorns') with FMR with little or no extra effort
3-D NUMERICAL SIMULATIONS OF FLOW LOSS IN HELICAL CHANNEL
ZHAO Ling-zhi; PENG Yan; LU Fang; LI Jian; LI Ran; LIU Bao-lin
2012-01-01
The flow loss of a helical channel Magnetohydrodynamic (MHD) thruster without MHD effect was numerically studied with 3-D simulations,and a flow loss coefficient ξ was defined to quantify the flow loss and its influencing factors were studied.The results show that ξ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number,and it declines slowly when t / T ＞ 0.2 and Re ＞ 105,a flow guide makes the flow more smooth and uniform,especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly,by about 30％ with the averaged value of ξ from 0.0385to 0.027,a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions,thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4％ from 0.0385 to 0.037,and ξ decreases with a rectifier's axial length when Re ＞ 105.
3D numerical modeling of India-Asia-like collision
-Erika Püsök, Adina; Kaus, Boris; Popov, Anton
2013-04-01
above a strong mantle lithosphere - the jelly sandwich model (Burov and Watts, 2006). 3D models are thus needed to investigate these hypotheses. However, fully 3D models of the dynamics of continent collision zones have only been developed very recently, and presently most research groups have relied on certain explicit assumptions for their codes. Here, we employ the parallel 3D code LaMEM (Lithosphere and Mantle Evolution Model), with a finite difference staggered grid solver, which is capable of simulating lithospheric deformation while simultaneously taking mantle flow and a free surface into account. We here report on first lithospheric and upper-mantle scale simulations in which the Indian lithosphere is indented into Asia. Acknowledgements. Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on JUQUEEN of the Jülich high-performance computing center. • Beaumont, C., Jamieson, R.A., Nguyen, M.H., Medvedev, S.E., 2004. Crustal channel flows: 1. Numerical models with applications to the tectonics of the Himalayan-Tibetan orogeny. J. Geophys. Res. 109, B06406. • Burov, E. & Watts, W.S., 2006. The long-term strength of continental lithosphere: "jelly sandwich" or "crème brûlée"?. GSA Today, 16, doi: 10.1130/1052-5173(2006)10161132.1130.CO;1132. • England P., Houseman, G., 1986. Finite strain calculations of continental deformation. 2. Comparison with the India-Asia collision zone. J. Geophys. Res.- Solid Earth and Planets 91 (B3), 3664-3676. • Jackson, J., 2002. Strength of the continental lithosphere: time to abandon the jelly sandwich?. GSA Today, September, 4-10. • Lechmann, S.M., May, D.A., Kaus, B.J.P., Schmalholz, S.M., 2011. Comparing thin-sheet models with 3D multilayer models for continental collision. Geophy. Int. J. doi: 10.1111/j.1365-246X.2011.05164.x • Royden, L.H., Burchfiel, B.C., King, R
3-D numerical modelling of flow around a groin
Miller, R.; Roulund, A.; Sumer, B. Mutlu;
2003-01-01
A 3-D flow code, EllipSys3D, has been implemented to simulate the 3-D flow around a groin in steady current. The k turbulence model has been used for closure. Two kinds of groins are considered: (1) A vertical-wall groin, and (2) A groin with a side slope. Steady-flow simulations were conducted....... The paper reports early results of the investigation. The simulations capture main features of the flow around the groin. The horseshoe vortex in front of the vertical-wall groin is resolved. The vortex shedding at the head is not resolved because no transient flow simulations have been conducted at...
3D Printing device adaptable to Computer Numerical Control (CNC)
Gardan, Julien; DANESI, Frédéric; Roucoules, Lionel; Schneider, A
2014-01-01
This article presents the development of a 3D printing device for the additive manufacturing adapted to a CNC machining. The application involves the integration of a specific printing head. Additive manufacturing technology is most commonly used for modeling, prototyping, tooling through an exclusive machine or 3D printer. A global review and analysis of technologies show the additive manufacturing presents little independent solutions [6][9]. The problem studied especially the additive manu...
Numerical modelling of 3D woven preform deformations
Green, S D; Long, A.C.; El Said, B. S. F.; Hallett, S. R.
2014-01-01
In order to accurately predict the performance of 3D woven composites, it is necessary that realistic textile geometry is considered, since failure typically initiates at regions of high deformation or resin pockets. This paper presents the development of a finite element model based on the multi-chain digital element technique, as applied to simulate weaving and compaction of an orthogonal 3D woven composite. The model was reduced to the scale of the unit cell facilitating high fidelity resu...
Numerical Results of 3-D Modeling of Moon Accumulation
Khachay, Yurie; Anfilogov, Vsevolod; Antipin, Alexandr
2014-05-01
For the last time for the model of the Moon usually had been used the model of mega impact in which the forming of the Earth and its sputnik had been the consequence of the Earth's collision with the body of Mercurial mass. But all dynamical models of the Earth's accumulation and the estimations after the Pb-Pb system, lead to the conclusion that the duration of the planet accumulation was about 1 milliard years. But isotopic results after the W-Hf system testify about a very early (5-10) million years, dividing of the geochemical reservoirs of the core and mantle. In [1,2] it is shown, that the account of energy dissipating by the decay of short living radioactive elements and first of all Al26,it is sufficient for heating even small bodies with dimensions about (50-100) km up to the iron melting temperature and can be realized a principal new differentiation mechanism. The inner parts of the melted preplanets can join and they are mainly of iron content, but the cold silicate fragments return to the supply zone and additionally change the content of Moon forming to silicates. Only after the increasing of the gravitational radius of the Earth, the growing area of the future Earth's core can save also the silicate envelope fragments [3]. For understanding the further system Earth-Moon evolution it is significant to trace the origin and evolution of heterogeneities, which occur on its accumulation stage.In that paper we are modeling the changing of temperature,pressure,velocity of matter flowing in a block of 3d spherical body with a growing radius. The boundary problem is solved by the finite-difference method for the system of equations, which include equations which describe the process of accumulation, the Safronov equation, the equation of impulse balance, equation Navier-Stocks, equation for above litho static pressure and heat conductivity in velocity-pressure variables using the Businesque approach.The numerical algorithm of the problem solution in velocity
Towards a von Karman dynamo: numerical studies based on experimental flows
Ravelet, F; Daviaud, F; Leorat, J; Chiffaudel, Arnaud; Daviaud, Francois; Leorat, Jacques; Ravelet, Florent; ccsd-00003337, ccsd
2004-01-01
Numerical studies of a kinematic dynamo based on von K{\\'a}rm{\\'a}n type flows between two counterrotating disks in a finite cylinder are reported. The flow has been optimized using a water model experiment, varying the driving impellers configuration. A solution leading to dynamo action for the mean flow has been found. This solution may be achieved in VKS2, the new sodium experiment to be performed in Cadarache, France. The optimization process is briefly described and discussed, then the effects of adding a stationary conducting layer around the flow on the threshold, on the shape of the neutral mode and on the magnetic energy balance are studied. Finally, the possible processes involved into kinematic dynamo action in a von Karman flow are reviewed and discussed. Among the possible processes we highlight the joint effect of the boundary-layer radial velocity shear and of the Ohmic dissipation localized at the flow/outer-shell boundary.
Numerical Results of Earth's Core Accumulation 3-D Modelling
Khachay, Yurie; Anfilogov, Vsevolod
2013-04-01
For a long time as a most convenient had been the model of mega impact in which the early forming of the Earth's core and mantle had been the consequence of formed protoplanet collision with the body of Mercurial mass. But all dynamical models of the Earth's accumulation and the estimations after the Pb-Pb system, lead to the conclusion that the duration of the planet accumulation was about 1 milliard years. But isotopic results after the W-Hf system testify about a very early (5-10) million years, dividing of the geochemical reservoirs of the core and mantle. In [1,3] it is shown, that the account of energy dissipating by the decay of short living radioactive elements and first of all Al,it is sufficient for heating even small bodies with dimensions about (50-100) km up to the iron melting temperature and can be realized a principal new differentiation mechanism. The inner parts of the melted preplanets can join and they are mainly of iron content, but the cold silicate fragments return to the supply zone. Only after the increasing of the gravitational radius, the growing area of the future core can save also the silicate envelope fragments. All existing dynamical accumulation models are constructed by using a spherical-symmetrical model. Hence for understanding the further planet evolution it is significant to trace the origin and evolution of heterogeneities, which occur on the planet accumulation stage. In that paper we are modeling distributions of temperature, pressure, velocity of matter flowing in a block of 3D- spherical body with a growing radius. The boundary problem is solved by the finite-difference method for the system of equations, which include equations which describe the process of accumulation, the Safronov equation, the equation of impulse balance, equation Navier-Stocks, equation for above litho static pressure and heat conductivity in velocity-pressure variables using the Businesque approach. The numerical algorithm of the problem solution in
3-D numerical modeling of methane hydrate deposits
Pinero, Elena; W. Rottke; Fuchs, T.; Hensen, Christian; Haeckel, Matthias; Wallmann, Klaus
2011-01-01
Within the German gas hydrate initiative SUGAR, we have developed a new tool for predicting the formation of sub-seafloor gas hydrate deposits. For this purpose, a new 2D/3D module simulating the biogenic generation of methane from organic material and the formation of gas hydrates has been added to the petroleum systems modeling software package PetroMod®. T ypically, PetroMod® simulates the thermogenic generation of multiple hydrocarbon components including oil and gas, their migration t...
Simulation of Fully Nonlinear 3-D Numerical Wave Tank
张晓兔; 滕斌; 宁德志
2004-01-01
A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simply Rankine source, the resulting boundary integral equation is repeatedly solved at each time step and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A smooth technique is also adopted in order to eliminate the possible saw-tooth numerical instabilities. The incident wave at the uptank is given as theoretical wave in this paper. The outgoing waves are absorbed inside a damping zone by spatially varying artificial damping on the free surface at the wave tank end. The numerical results show that the NWT developed by these approaches has a high accuracy and good numerical stability.
Numerical study of 3-D constraint effects in ferritic steels
The presentation reviews the results of a numerical investigation, in which single-edge cracked bars in three point bend SE(B) specimens, with different relative crack lengths and thickness, were systematically studied via detailed three-dimensional finite element analyses
3D numerical modeling of YSO accretion shocks
Matsakos T.
2014-01-01
Full Text Available The dynamics of YSO accretion shocks is determined by radiative processes as well as the strength and structure of the magnetic field. A quasi-periodic emission signature is theoretically expected to be observed, but observations do not confirm any such pattern. In this work, we assume a uniform background field, in the regime of optically thin energy losses, and we study the multi-dimensional shock evolution in the presence of perturbations, i.e. clumps in the stream and an acoustic energy flux flowing at the base of the chromosphere. We perform 3D MHD simulations using the PLUTO code, modelling locally the impact of the infalling gas onto the chromosphere. We find that the structure and dynamics of the post-shock region is strongly dependent on the plasma-beta (thermal over magnetic pressure, different values of which may give distinguishable emission signatures, relevant for observations. In particular, a strong magnetic field effectively confines the plasma inside its flux tubes and leads to the formation of quasi-independent fibrils. The fibrils may oscillate out of phase and hence the sum of their contributions in the emission results in a smooth overall profile. On the contrary, a weak magnetic field is not found to have any significant effect on the shocked plasma and the turbulent hot slab that forms is found to retain its periodic signature.
Gravitational collapse of gravitational waves in 3D numerical relativity.
Alcubierre, M.; Allen, G; Brügmann, B.; Lanfermann, G.; Seidel, E; Suen, W; Tobias, M
2000-01-01
We demonstrate that evolutions of three-dimensional, strongly non-linear gravitational waves can be followed in numerical relativity, hence allowing many interesting studies of both fundamental and observational consequences. We study the evolution of time-symmetric, axisymmetric and non-axisymmetric Brill waves, including waves so strong that they collapse to form black holes under their own self-gravity. An estimate for the critical amplitude for black hole formation in a particular interpo...
3-D Numerical Simulations of Twisted Stacked Tape Cables
Krüger, Philipp A. C.; Zermeño, Victor M. R.; Takayasu, Makoto; Grilli, Francesco
2014-01-01
Different magnet applications require compact high current cables. Among the proposed solutions, the Twisted Stacked Tape Cable (TSTC) is easy to manufacture and has very high tape length usage efficiency. In this kind of cables the tapes are closely packed, so that their electromagnetic interaction is very strong and determines the overall performance of the cable. Numerical models are necessary tools to precisely evaluate this interaction and to predict the cable's behavior, e.g. in terms o...
Numerical simulation of 3D flows in atmospheric boundary layer
Šimonek, Jiří; Kozel, K.; Jaňour, Zbyněk
Praha : Ústav termomechaniky AV ČR, v. v. i, 2012 - (Šimurda, D.; Kozel, K.), s. 93-96 ISBN 978-80-87012-40-6. [Topical Problems of Fluid Mechanics 2012 . Praha (CZ), 15.02. 2012 -17.02. 2012 ] R&D Projects: GA ČR GAP101/12/1271 Institutional research plan: CEZ:AV0Z20760514 Keywords : numerical solution * atmospheric boundary layer * Navier-Stokes equation s Subject RIV: DG - Athmosphere Sciences, Meteorology
NUMERICAL STUDY OF 3D EXPLOSION BUBBLES ADJACENT TO STRUCTURES
无
2002-01-01
The bejavior of a bubble near a rigid structure was considered by using the local surface fitting method and the "jet prediction" method. The convergence difficulty caused by the abnormality of the elements was overcome. The flow was numerically simulated by using the boundary-integral method on the assumption that the water was inviscid and incompressible, and the bubble gas obeyed the isoentropic rule. The evolution of the bubble was investigated by means of the mixed Euler-Lagrange method, and the Runge-Kutta method. The important behavior of the bubble, such as migration and jetting, was analyzed in several examples. And the solution of one period of the explosion bubble was obtained.
3D numerical simulations of vesicle and inextensible capsule dynamics
Farutin, Alexander; Biben, Thierry; Misbah, Chaouqi
2014-10-01
Vesicles are locally-inextensible fluid membranes, capsules are endowed with in-plane shear elasticity mimicking the cytoskeleton of red blood cells (RBCs), but are extensible, while RBCs are inextensible. We use boundary integral (BI) methods based on the Green function techniques to model and solve numerically their dynamics. We regularize the single layer integral by subtraction of exact identities for the terms involving the normal and the tangential components of the force. The stability and precision of BI calculation is enhanced by taking advantage of additional quadrature nodes located in vertices of an auxiliary mesh, constructed by a standard refinement procedure from the main mesh. We extend the partition of unity technique to boundary integral calculation on triangular meshes. The proposed algorithm offers the same treatment of near-singular integration regardless whether the source and the target points belong to the same surface or not. Bending forces are calculated by using expressions derived from differential geometry. Membrane incompressibility is handled by using two penalization parameters per suspended entity: one for deviation of the global area from prescribed value and another for the sum of squares of local strains defined on each vertex. Extensible or inextensible capsules, a model of RBC, are studied by storing the position in the reference configuration for each vertex. The elastic force is then calculated by direct variation of the elastic energy. Various nonequilibrium physical examples on vesicles and capsules will be presented and the convergence and precision tests highlighted. Overall, a good convergence is observed with numerical error inversely proportional to the number of vertices used for surface discretization, the highest order of convergence allowed by piece-wise linear interpolation of the surface.
Numerical modelling of gravel unconstrained flow experiments with the DAN3D and RASH3D codes
Sauthier, Claire; Pirulli, Marina; Pisani, Gabriele; Scavia, Claudio; Labiouse, Vincent
2015-12-01
Landslide continuum dynamic models have improved considerably in the last years, but a consensus on the best method of calibrating the input resistance parameter values for predictive analyses has not yet emerged. In the present paper, numerical simulations of a series of laboratory experiments performed at the Laboratory for Rock Mechanics of the EPF Lausanne were undertaken with the RASH3D and DAN3D numerical codes. They aimed at analysing the possibility to use calibrated ranges of parameters (1) in a code different from that they were obtained from and (2) to simulate potential-events made of a material with the same characteristics as back-analysed past-events, but involving a different volume and propagation path. For this purpose, one of the four benchmark laboratory tests was used as past-event to calibrate the dynamic basal friction angle assuming a Coulomb-type behaviour of the sliding mass, and this back-analysed value was then used to simulate the three other experiments, assumed as potential-events. The computational findings show good correspondence with experimental results in terms of characteristics of the final deposits (i.e., runout, length and width). Furthermore, the obtained best fit values of the dynamic basal friction angle for the two codes turn out to be close to each other and within the range of values measured with pseudo-dynamic tilting tests.
A fully covariant mean-field dynamo closure for numerical 3+1 resistive GRMHD
Bucciantini, N
2012-01-01
The powerful high-energy phenomena typically encountered in astrophysics invariably involve physical engines, like neutron stars and black hole accretion disks, characterized by a combination of highly magnetized plasmas, strong gravitational fields, and relativistic motions. In recent years numerical schemes for General Relativistic MHD (GRMHD) have been developed to model the multidimensional dynamics of such systems, including the possibility of an evolving spacetime. Such schemes have been also extended beyond the ideal limit including the effects of resistivity, in an attempt to model dissipative physical processes acting on small scales (sub-grid effects) over the global dynamics. Along the same lines, magnetic fields could be amplified by the presence of turbulent dynamo processes, as often invoked to explain the high values of magnetization required in accretion disks and neutron stars. Here we present, for the first time, a further extension to include the possibility of a mean-field dynamo action wi...
Single-sided sheet-to-tube spot welding investigated by 3D numerical simulations
Nielsen, Chris Valentin; Chergui, Azeddine; Zhang, Wenqi
The single-sided resistance spot welding process is analyzed by a 3D numerical study of sheet-to-tube joining. Finite element simulations are carried out in SORPAS® 3D. Two levels of electrode force and five levels of welding current are simulated. The overall effects of changing current and forc...
Numerical simulation of laminar plasma dynamos in a cylindrical von K\\'arm\\'an flow
Khalzov, I V; Ebrahimi, F; Schnack, D D; Forest, C B; 10.1063/1.3559472
2011-01-01
The results of a numerical study of the magnetic dynamo effect in cylindrical von K\\'arm\\'an plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model.We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von K\\'arm\\'an flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field ...
Interplay between experimental and numerical approaches in the fluid dynamo problem
Léorat, Jacques; Nore, Caroline
2008-09-01
After years of purely analytical and numerical investigations, the dynamo fluid problem has advanced to a phase of experimental study. We present an outline of the numerical steps that have accompanied the Von Kármán Sodium (VKS) experiment at Cadarache for the past ten years. We show how various numerical studies contributed progressively to the optimization of the experimental facility. The recent success of the VKS2 experiment of September 2006 in achieving dynamo action has prompted an extension of the numerical code. Modeling of the electromotive force induced in the volume of the impellers shows that an axial dipole is excited, as observed in the experiment. We infer from these results that the observed value of the critical magnetic Reynolds number may be linked to the soft iron of the impellers and not to turbulence which occurs for any choice of materials. We conclude with proposals for further lines of numerical development. To cite this article: J. Léorat, C. Nore, C. R. Physique 9 (2008).
Interpreting geomagnetic reversal frequency using numerical dynamos (Invited)
Olson, P.; Amit, H.
2013-12-01
We derive scaling relationships for the frequency of polarity reversals in numerical geodynamo models powered by thermochemical convection for comparison with the geomagnetic polarity record. We find that the average number of reversals per unit of time scales with the local Rossby number of the convection. For uniform core-mantle boundary conditions, polarity reversals are absent below a critical value of the local Rossby number near 0.05, beyond which reversal frequency increases approximately linearly with that parameter. The relative standard deviation of the dipole intensity fluctuations increases with reversal frequency and the local Rossby number. For tomographic boundary conditions that model the observed large-scale seismic heterogeneity in the Earth's lower mantle, reversal frequency also exhibits linear dependence on the local Rossby number, and in addition, increases approximately as the square root of the amplitude of the boundary heterogeneity. Applied to the history of the geodynamo, our results indicate that outer core convection was relatively weak and homogeneous with small local Rossby number during geomagnetic superchrons and relatively vigorous with larger local Rossby number at times when geomagnetic reversals were frequent. Translated into core energetics, we find that the difference between the present-day geomagnetic reversal frequency and superchron conditions requires a 25% change in the total heat flux across the core-mantle boundary, or alternatively, a 75% change in the amplitude of the boundary heterogeneity. Our results also indicate that polarity reversals were likely throughout Earth history and may also have been commonplace in the early history of other terrestrial planets.
Numerical simulation of 3D backward facing step flows at various Reynolds numbers
Louda Petr
2015-01-01
Full Text Available The work deals with the numerical simulation of 3D turbulent flow over backward facing step in a narrow channel. The mathematical model is based on the RANS equations with an explicit algebraic Reynolds stress model (EARSM. The numerical method uses implicit finite volume upwind discretization. While the eddy viscosity models fail in predicting complex 3D flows, the EARSM model is shown to provide results which agree well with experimental PIV data. The reference experimental data provide the 3D flow field. The simulations are compared with experiment for 3 values of Reynolds number.
Study of 3-D Numerical Simulation for Gas Transfer in the Goaf of the Coal Mining
WU Zheng-yan; JIANG Shu-guang; HE Xin-jian; WANG Lan-yun; LIN Bai-quan
2007-01-01
In order to simulate field distribution rules, mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established, based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode, surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally, a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.
Numerical stability of coupling schemes in the 3d/0d modelling ofairflows and blood flows
Fouchet-Incaux, Justine; Grandmont, Céline; Martin, Sebastien
2014-01-01
We consider models which are classically used in the simulation of airflows and blood flows andinvestigate the numerical stability of some discretization strategies. The geometrical complexity of the networksin which air/blood flows leads to a classical decomposition of two areas: a truncated 3D geometry correspondingto the largest contribution of the domain and a 0D part connected to the 3D part, modelling air/blood flowsin smaller airways/vessels. The resulting Navier-Stokes system in the 3...
A simple stochastic model for dipole moment fluctuations in numerical dynamo simulations
Domenico G. eMeduri
2016-04-01
Full Text Available Earth's axial dipole field changes in a complex fashion on many differenttime scales ranging from less than a year to tens of million years.Documenting, analysing, and replicating this intricate signalis a challenge for data acquisition, theoretical interpretation,and dynamo modelling alike. Here we explore whether axial dipole variationscan be described by the superposition of a slow deterministic driftand fast stochastic fluctuations, i.e. by a Langevin-type system.The drift term describes the time averaged behaviour of the axial dipole variations,whereas the stochastic part mimics complex flow interactions over convective time scales.The statistical behaviour of the system is described by a Fokker-Planck equation whichallows useful predictions, including the average rates of dipole reversals and excursions.We analyse several numerical dynamo simulations, most of which havebeen integrated particularly long in time, and also the palaeomagneticmodel PADM2M which covers the past 2 Myr.The results show that the Langevin description provides a viable statistical modelof the axial dipole variations on time scales longer than about 1 kyr.For example, the axial dipole probability distribution and the average reversalrate are successfully predicted.The exception is PADM2M where the stochastic model reversal rate seems too low.The dependence of the drift on the axial dipolemoment reveals the nonlinear interactions that establish thedynamo balance. A separate analysis of inductive and diffusive magnetic effectsin three dynamo simulations suggests that the classical quadraticquenching of induction predicted by mean-field theory seems at work.
Application of 3-D numerical simulation software SRIFCAST to produce ductile iron castings
无
2005-01-01
Based on a method using numerical simulation equations and their solution schemes for liquid metal flows and heat transfer during mold filling and the solidification process of casting, 3-D numerical simulation software SRIFCAST was created. This includes enmeshment of casting; velocity and temperature fields calculation; displaying iso-temperature lines;velocity vectors and 3-D temperature fields on a Windows 9x operating system. SRIFCAST was applied to produce sound castings of automobile and diesel engines, and also to connect with microstructure simulation for ductile iron castings.
GENETIC ALGORITHM IN REDUCTION OF NUMERICAL DISPERSION OF 3-D ADI-FDTD METHOD
Zhang Yan; Lǖ Shanwei; Gao Wenjun
2007-01-01
A new method to reduce the numerical dispersion of the three-dimensional Alternating Direction Implicit Finite-Difference Time-Domain(3-D ADI-FDTD)method is proposed.Firstly,the numerical formulations of the 3-D ADI-FDTD method are modified with the artificial anisotropy,and the new numerical dispersion relation is derived.Secondly,the relative permittivity tensor of the artificial anisotropy can be obtained by the Adaptive Genetic Algorithm(AGA).In order to demonstrate the accuracy and efficiency of this new method,a monopole antenna is simulated as an example.And the numerical results and the computational requirements of the proposed method are cornpared with those of the conventional ADI-FDTD method and the measured data.In addition the reduction of the numerical dispersion is investigated as the objective function of the AGA.It is found that this new method is accurate and efficient by choosing proper objective function.
Amit, Hagay; Deschamps, Frédéric; Choblet, Gaël
2015-11-01
Mantle control on the geodynamo is often simulated using numerical dynamos with imposed outer boundary heat flux inferred from lower mantle tomography, assuming that seismic and thermal anomalies in the lowermost mantle are highly correlated. However, non-thermal effects might perturb this idealized linear seismic-thermal mapping. Here we use a probabilistic tomography model to isolate the thermal part of the seismic anomaly in order to impose a more realistic core-mantle boundary heat flux pattern on the outer boundary of numerical dynamo simulations. We demonstrate that on time average these dynamo models have more low-latitude convective and magnetic activity than corresponding models with conventional tomographic heat flux. In addition, the low-latitude magnetic flux and kinetic energy contributions are more time-dependent in the dynamo models with a probabilistic tomography heat flux, and thus may recover the observed latitudinal distribution of geomagnetic flux on the core-mantle boundary, which we propose as a morphological criterion for Earth-like dynamo models.
Amit, Hagay; Deschamps, Frédéric; Choblet, Gaël
2015-04-01
Mantle control on the geodynamo is often simulated using numerical dynamos with imposed outer boundary heat flux inferred from lower mantle tomography, assuming that seismic and thermal anomalies in the lowermost mantle are highly correlated. However, non-thermal effects might perturb this idealized linear seismic-thermal mapping. Here we use a probabilistic tomography model to isolate the thermal part of the seismic anomaly in order to impose a more realistic core-mantle boundary heat flux pattern on the outer boundary of numerical dynamo simulations. We demonstrate that on time-average these dynamo models have more low-latitudes convective and magnetic activity than corresponding models with conventional tomographic heat flux. In addition, the low-latitudes magnetic flux and kinetic energy contributions are more time-dependent in the dynamo models with a probabilistic tomography heat flux, and thus may recover the observed latitudinal distribution of geomagnetic flux on the core-mantle boundary, which we propose as a morphological criterion for Earth-like dynamo models.
3D numerical analysis of crack propagation of heterogeneous notched rock under uniaxial tension
Wang, S. Y.; Sloan, S. W.; Sheng, D. C.; Tang, C. A.
2016-05-01
Macroscopic notches play an important role in evaluating the fracture process zone (FPZ) and the strengths of a heterogeneous rock mass. Crack initiation, propagation and coalescence for unnotched, single-notched and double-notched rock specimens are numerically simulated in a 3-D numerical model (RFPA3D). A feature of the code RFPA3D is that it can numerically simulate the evolution of cracks in three-dimensional space, as well as the heterogeneity of the rock mass. For the unnotched case, special attention is given to the complete stress-strain curve and the corresponding AE events for the failure process of rock specimen. By comparing with published experimental results, the simulation results from RFPA3D are found to be satisfactory. For the single-notched case, the effect of the length and the depth of the single notch and the thickness of the specimen on the failure mode and peak stress are evaluated. The 3D FPZ is very different from that in two dimensions. For the double-notched case, the effects of the separation distance and overlap distance of the double notches, as well as influence of the homogeneity index (m) are also investigated. As the overlap distance increases, the direction of the principal tensile stress at each notch-end changes from a perpendicular direction (tensile stress field) to a nearly parallel direction (compressive stress field), which affects the evolution of the cracks from the two notches.
New results on an equipartition dynamo
Dorch, S. B. F.; Archontis, V.
2006-01-01
linear and non-linear saturation regimes. The means were 3-d non-linear MHD simulations and visualization using the high resolution numerical scheme by Nordlund, Galsgaard and others. We have found that the dynamo has a high growth rate in the linear regime, and that it can saturate at a level...
Calculation of residual stresses by means of a 3D numerical weld simulation
Nicak, Tomas; Huemmer, Matthias [AREVA NP GmbH, Postfach 1109 (Germany)
2008-07-01
The numerical weld simulation has developed very fast in recent years. The problem complexity has increased from simple 2D models to full 3D models, which can describe the entire welding process more realistically. As recent research projects indicate, a quantitative assessment of the residual stresses by means of a 3D analysis is possible. The structure integrity can be assessed based on the weld simulation results superimposed with the operating load. Moreover, to support the qualification of welded components parametric studies for optimization of the residual stress distribution in the weld region can be performed. In this paper a full 3D numerical weld simulation for a man-hole drainage nozzle in a steam generator will be presented. The residual stresses are calculated by means of an uncoupled transient thermal and mechanical FE analysis. The paper will present a robust procedure allowing reasonable predictions of the residual stresses for complex structures in industrial practice. (authors)
Improvements to the RELAP5-3D Nearly-Implicit Numerical Scheme
The RELAP5-3D computer program has been improved with regard to its nearly-implicit numerical scheme for two phase flow and single-phase flow. Changes were made to the nearly-implicit numerical scheme finite difference momentum equations as follows: (1) added the velocity flip-flop mass/energy error mitigation logic, (2) added the modified Henry-Fauske choking model, (3) used the new time void fraction in the horizontal stratification force terms and gravity head, and (4) used an implicit form of the artificial viscosity. The code modifications allow the nearly-implicit numerical scheme to be more implicit and lead to enhanced numerical stability
Improvements to the RELAP5-3D Nearly-Implicit Numerical Scheme
Richard A. Riemke; Walter L. Weaver; RIchard R. Schultz
2005-05-01
The RELAP5-3D computer program has been improved with regard to its nearly-implicit numerical scheme for twophase flow and single-phase flow. Changes were made to the nearly-implicit numerical scheme finite difference momentum equations as follows: (1) added the velocity flip-flop mass/energy error mitigation logic, (2) added the modified Henry-Fauske choking model, (3) used the new time void fraction in the horizontal stratification force terms and gravity head, and (4) used an implicit form of the artificial viscosity. The code modifications allow the nearly-implicit numerical scheme to be more implicit and lead to enhanced numerical stability.
Experimental validation of a numerical simulation on a ballscrew system by 3D photoelasticity
Germaneau A.
2010-06-01
Full Text Available The Trimmable Horizontal Stabilizer Actuator (THSA system equips the whole airbus line. One component of this system is a ball-screw system on which spalling problems appear on the balls. This phenomenon is mostly due to local high pressures and reduces the service life of the system. 3D numerical simulations are usually used to tackle this kind of problems but are subjected to assumptions. As the aim of the project is to build a numerical model able to predict pressure distribution, these assumptions need to be experimentally assessed to be perfectly relevant of the real load distribution in the ball screw system. Due to the 3D geometry of the specimen, a 3D measurement technique, Scattered Light Photoelasticity (SLP, has been chosen to perform experimental measurements,. Because of complexity of the geometry, the study is divided in three steps; the present paper is dealing with the second one where a demonstrator ball-screw system is manufactured in casted epoxy to perform the SLP. This technique gives information on 3D stress fields inside the epoxy specimen from the analysis of photoelastic fringes. They are compared to numerical ones and indicate whether numerical boundary conditions are relevant of the experimental ball-screw system behaviour.
Slab detachment in laterally varying subduction zones: 3-D numerical modeling
Duretz, T.; Gerya, T.V.; Spakman, W.
2014-01-01
Understanding the three-dimensional (3-D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench variations. High-resolution thermomechanical numerical models, encompass
Sheyko, A.A.; Finlay, Chris; Marti, P.;
We present a set of numerical dynamo models with the convection strength varied by a factor of 30 and the ratio of magnetic to viscous diffusivities by a factor of 20 at rapid rotation rates (E =nu/(2 Omega d^2 ) = 10-6 and 10-7 ) using a heat flux outer BC. This regime has been little explored...... (aside from a pioneering study by Sakuraba and Roberts 2009) due to the significant computing resources required. Our simulations are carried out using a discretisation of degree and order 256 in spherical harmonics, and 516 finite difference points in radius and parallelized on 516 cores. We report on...
3-D NUMERICAL SIMULATION OF FLOW THROUGH AN ORIFICE SPILL-WAY TUNNEL
无
2002-01-01
A Large Eddy Simulation (LES) approachbased on the weakly compressible hydrodynamic equation with a single-plase fluid model for the cavitation flow has been de-veloped and employed in simulating 3-D unsteady viscous flowthrough an orifice type spillwy tunnel. The finite volume ap-proach in space and the predictor-corrector method in timehave been used to the numerical discretization, and the "Lawof wall" is applied at the solid boundary. The velocity, pres-sure fields and the cavitation phenomenon are obtained, thecomputational results show that 3-D LES approach can givemore realistic flow field prediction of the orifice type spillwaytunnel.
Numerical investigation of the 3D Hubbard model on a Linux cluster
We investigate numerically the magnetic properties of the 3D Isotropic and Anisotropic Hubbard model at half-filling on a Linux cluster. The behavior of the transition temperature as a function of the anisotropic hopping parameter is qualitatively described. In the Isotropic model we measure the scaling properties of the susceptibility finding agreement with the magnetic critical exponents of the 3D Heisenberg model. We describe several particularities concerning the implementation of our simulation in a cluster of personal computers paying special attention to the issues related with the parallelization of the algorithm
3D numerical simulation analysis of passive drag near free surface in swimming
Zhan, Jie-min; Li, Tian-zeng; Chen, Xue-bin; Li, Yok-sheung; Wai, Wing-hong Onyx
2015-04-01
The aim of this work is to build a 3D numerical model to study the characteristics of passive drag on competitive swimmers taking into account the impact of the free surface. This model solves the 3D incompressible Navier-Stokes equations using RNG k- ɛ turbulence closure. The volume of fluid (VOF) method is used to locate the free surface. The 3D virtual model is created by Computer Aided Industrial Design (CAID) software, Rhinoceros. Firstly, a specific posture of swimming is studied. The simulation results are in good agreement with the data from mannequin towing experiments. The effects of a swimmer's arms and legs positions on swimming performance are then studied. Finally, it is demonstrated that the present method is capable of simulating gliding near the free surface.
3D flow past transonic turbine cascade SE 1050 — Experiment and numerical simulations
Šimurda, D.; Fürst, J.; Luxa, M.
2013-08-01
This paper is concerned with experimental and numerical research on 3D flow past prismatic turbine cascade SE1050 (known in QNET network as open test case SE1050). The primary goal was to assess the influence of the inlet velocity profile on the flow structures in the interblade channel and on the flow field parameters at the cascade exit and to compare these findings to results of numerical simulations. Investigations of 3D flow past the cascade with non-uniform inlet velocity profile were carried out both experimentally and numerically at subsonic ( M 2is = 0.8) and at transonic ( M 2is = 1.2) regime at design angle of incidence. Experimental data was obtained using a traversing device with a five-hole conical probe. Numerically, the 3D flow was simulated by open source code OpenFOAM and in-house code. Analyses of experimental data and CFD simulations have revealed the development of distinctive vortex structures resulting from non-uniform inlet velocity profile. Origin of these structures results in increased loss of kinetic energy and spanwise shift of kinetic energy loss coefficient distribution. Differences found between the subsonic and the transonic case confirm earlier findings available in the literature. Results of CFD and experiments agree reasonably well.
2D/1D approximations to the 3D neutron transport equation. II: Numerical comparisons
In a companion paper [1], (i) several new '2D/1D equations' are introduced as accurate approximations to the 3D Boltzmann transport equation, (ii) the simplest of these approximate equations is systematically discretized, and (iii) a theoretically stable iteration scheme is developed to solve the discrete equations. In this paper, numerical results are presented that confirm the theoretical predictions made in [1]. (authors)
3D-Workbench : Design and Development of a 3-Dimension Computer Numerical Controlled Machine
Sandru, Andrei
2015-01-01
The purpose of this thesis was to examine and develop a multipurpose Computer Numerical Controlled (CNC) device which would satisfy industrial requirements, but could also be implemented at universities for students to improve and apply their knowledge in different scopes. The topic was specifically chosen because of its close relation to a summer job at a metal factory the author completed and his personal fascination with 3D printers. The project presented in this thesis was commissioned...
3-D NUMERICAL STUDY AND COMPARISON OF ECCENTRIC AND CONCENTRIC ANNULAR-FINNED TUBE HEAT EXCHANGERS
FAROUK TAHROUR; ABDELMOUMENE HAKIM BENMACHICHE; MOUNIR AKSAS; CHERIF BOUGRIOU
2015-01-01
The use of 3-D computational fluid dynamics (CFD) is proposed to simulate the conjugate conduction-convection of heat transfer problems in eccentric annularfinned tube heat exchangers. The numerical simulation results allow us to evaluate the heat transfer coefficient over fin surfaces, the fin efficiency and the pressure drop. The aim of the present paper is to determine the optimum tube position in the circular fin that maximizes heat dissipation and minimizes pressure drop. In addition, th...
Numerical Calculation of the Flow Inside Pump Impellers Using 3D Euler Equations
SARIOĞLU, Kemal; Ayder, Erkan
1999-01-01
The flow pattern inside an impeller should be determined for maximum efficiency and performance. The effects of the design parameters on the pump performance can be determined using numerical calculations instead of empirical equations. Incompressible 3D time-dependent Euler equations, written in a conservative form, are used. An artificial pressure term is added to preserve the hyperbolic character of the equations. A finite-volume technique is used for space discretization. A fou...
3D Nonlinear Numerical Simulation of Intact and Debonded Reinforced Concrete Beams
Chen Quan(陈权); Marcus L.
2004-01-01
To study the behaviour of reinforced concrete (RC) structures with sections of concrete removed and the reinforcement exposed, 3D nonlinear numerical analysis was performed upon both intact and debonded RC beams by using finite element techniques. The deformational characteristics and the ultimate loads were obtained through numerical models, as well as crack and stress distributions. The failure modes can also be deduced from computational results. Compared with intact beams, the normal assumptions of plane section behaviour is not hold true and the patterns of stress and strain are different in debonded RC beams. The numerical results show good consistency with experimental data. This kind of numerical simulation is a supplement to existing codes.
Jompob WAEWSAK
2014-12-01
Full Text Available This paper presents a 3-D numerical modeling of heat transport phenomena in soil due to a change of sensible and latent heat, under the ambient conditions of southern Thailand. The vertical soil temperature profile within 3 m was predicted based on energy balance and 3 modes of heat transfer mechanisms, i.e., conduction, convection, and radiation. Mathematical models for estimation of solar radiation intensity, ambient and sky temperatures, relative humidity, and surface wind velocity were used as model inputs. 3-D numerical implicit finite difference schemes, i.e., forward time, and forward, center, and backward spaces were used for discretizing the set of governing, initial, and boundary condition equations. The set of pseudo-linear equations were then solved using the single step Gauss-Seidel iteration method. Computer code was developed by using MATLAB computer software. The soil physical effects; density, thermal conductivity, emissivity, absorptivity, and latent heat on amplitude of soil temperature variation were investigated. Numerical results were validated in comparison to the experimental results. It was found that 3-D numerical modeling could predict the soil temperature to almost the same degree as results that were obtained by experimentation, especially at a depth of 1 m. The root mean square error at ground surface and at depths of 0.5, 1, 1.5, 2, 2.5 and 3 m were 0.169, 0.153, 0.097, 0.116, 0.120, 0.115, and 0.098, respectively. Furthermore, it was found that variation of soil temperature occurred within 0.75 m only.
Young, R. P.; Collins, D.; Hazzard, J.; Heath, A. [Department of Earth Sciences, Liverpool University, 4 Brownlow street, UK-0 L69 3GP Liverpool (United Kingdom); Pettitt, W.; Baker, C. [Applied Seismology Consultants LTD, 10 Belmont, Shropshire, UK-S41 ITE Shrewsbury (United Kingdom); Billaux, D.; Cundall, P.; Potyondy, D.; Dedecker, F. [Itasca Consultants S.A., Centre Scientifique A. Moiroux, 64, chemin des Mouilles, F69130 Ecully (France); Svemar, C. [Svensk Karnbranslemantering AB, SKB, Aspo Hard Rock Laboratory, PL 300, S-57295 Figeholm (Sweden); Lebon, P. [ANDRA, Parc de la Croix Blanche, 7, rue Jean Monnet, F-92298 Chatenay-Malabry (France)
2004-07-01
This paper presents current results from work performed within the European Commission project SAFETI. The main objective of SAFETI is to develop and test an innovative 3D numerical modelling procedure that will enable the 3-D simulation of nuclear waste repositories in rock. The modelling code is called AC/DC (Adaptive Continuum/ Dis-Continuum) and is partially based on Itasca Consulting Group's Particle Flow Code (PFC). Results are presented from the laboratory validation study where algorithms and procedures have been developed and tested to allow accurate 'Models for Rock' to be produced. Preliminary results are also presented on the use of AC/DC with parallel processors and adaptive logic. During the final year of the project a detailed model of the Prototype Repository Experiment at SKB's Hard Rock Laboratory will be produced using up to 128 processors on the parallel super computing facility at Liverpool University. (authors)
Numerical simulations of self-propelled swimming of 3D bionic fish school
无
2009-01-01
Numerical simulations of self-propelled swimming of a three dimensional bionic fish and fish school in a viscous fluid are carried out. This is done with the assistance of a parallel software package produced for 3D moving boundary problems. This computational fluid dynamics package combines the adaptive multi-grid finite volume method, the immersed boundary method and VOF (volume of fluid) method. By using the package results of the self-propelled swimming of a 3D bionic fish and fish school in a vis- cous fluid are obtained. With comparison to the existing experimental measurements of living fishes, the predicted structure of vortical wakes is in good agreement with the measurements.
Numerical simulations of self-propelled swimming of 3D bionic fish school
WU ChuiJie; WANG Liang
2009-01-01
Numerical simulations of self-propelled swimming of a three dimensional bionic fish and fish school in a viscous fluid are carried out. This is done with the assistance of a parallel software package producedfor 3D moving boundary problems. This computational fluid dynamics package combines the adaptive multi-grid finite volume method, the immersed boundary method and VOF (volume of fluid) method. By using the package results of the self-propelled swimming of a 3D bionic fish and fish school in a vis cous fluid are obtained. With comparison to the existing experimental measurements of living fishes, the predicted structure of vortical wakes is in good agreement with the measurements.
Twisting Rolls. Heuristic Model and 3D Numerical Simulation of Vortex Patterns
Bouali, S
2003-01-01
We connect an appropriate feedback loop to a model of 2D vertical eddy of airflow which unfolds a wide range of vorticity behavior. Computational fluid dynamics of the twisted roll display a class of long lifespan 3D vortices. On the one hand, the infinitely stable columnar vortex simulated describes waterspouts and tornadoes with extended lifetime. On the other hand, a light modification of the retroaction exhibits strong similarities to tropical cyclones. Moreover, we investigate the outcome of the twisting process vertically shifted. This modelisation leads to the simulation of simultaneous vortices associated to this other class of 3D vortices with short lifespan. Our heuristic dynamical systems lay the foundations of a comprehensive modelisation of vortices since it joins numerical simulations and theory.
This paper presents current results from work performed within the European Commission project SAFETI. The main objective of SAFETI is to develop and test an innovative 3D numerical modelling procedure that will enable the 3-D simulation of nuclear waste repositories in rock. The modelling code is called AC/DC (Adaptive Continuum/ Dis-Continuum) and is partially based on Itasca Consulting Group's Particle Flow Code (PFC). Results are presented from the laboratory validation study where algorithms and procedures have been developed and tested to allow accurate 'Models for Rock' to be produced. Preliminary results are also presented on the use of AC/DC with parallel processors and adaptive logic. During the final year of the project a detailed model of the Prototype Repository Experiment at SKB's Hard Rock Laboratory will be produced using up to 128 processors on the parallel super computing facility at Liverpool University. (authors)
Numerical solution of 3-D magnetotelluric using vector finite element method
Prihantoro, Rudy; Sutarno, Doddy; Nurhasan
2015-09-01
Magnetotelluric (MT) is a passive electromagnetic (EM) method which measure natural variations of electric and magnetic vector fields at the Earth surface to map subsurface electrical conductivity/resistivity structure. In this study, we obtained numerical solution of three-dimensional (3-D) MT using vector finite element method by solving second order Maxwell differential equation describing diffusion of plane wave through the conductive earth. Rather than the nodes of the element, the edges of the element is used as a vector basis to overcome the occurrence of nonphysical solutions that usually faced by scalar (node based) finite element method. Electric vector fields formulation was used and the resulting system of equation was solved using direct solution method to obtain the electric vector field distribution throughout the earth resistivity model structure. The resulting MT response functions was verified with 1-D layered Earth and 3-D2 COMMEMI outcropping structure. Good agreement is achieved for both structure models.
Stone, James
2011-04-01
Numerical methods have proved crucial for the study of the nonlinear regime of the magnetorotational instability (MRI) and resulting dynamo action. After a brief introduction to the methods, a variety of results from new simulations of the MRI in both local (shearing box approximation) and global domains will be presented. Previous work on the saturation level and numerical convergence in both stratified and unstratified domains with no net flux (both with and without explicit dissipation) will be described, and the connection to dynamo theory will be mentioned. Results from several groups in which the size of the computational domain, and the vertical boundary conditions, are varied will be discussed. Finally, new work on the direct comparison between high-resolution global and shearing box simulations will be presented, and new studies of stratified disks with radiative transfer will be introduced.
Numerical methods for 3D tokamak simulations using a flux-surface independent grid
A numerical approach for 3D tokamak simulations using a flux surface independent grid is presented. The grid consists of few poloidal planes with a Cartesian Isotropic grid within each poloidal plane. Perpendicular operators can be discretised within a poloidal plane using standard second order finite difference methods. The discretisation of parallel operators is achieved with a field line following map and an interpolation. The application of the support operator method to the parallel diffusion operator conserves the self-adjointness of the operator on the discrete level and keeps the numerical decay rate at a low level. The developed numerical methods can be applied to geometries where an X-point is present.
Numerical modelling of pollution dispersion in 3D atmospheric boundary layer
Benes, L.; Bodnar, T.; Kozel, K. [Czech Technical Univ. of Prague (Czech Republic). Dept. of Technical Mathematics; Fraunie, Ph. [Univ. de Toulon et du Var, La Garde (France). Lab. de Sondages Electromagnetiques et Environnemental Terrestre
2002-07-01
The main goal of this work is to present the applicable models and numerical methods for solution of flow and pollution dispersion in 3D atmospheric boundary layer (ABL). Mathematical models are based on the system of Reynolds averaged Navier-Stokes equations and its simplifications. The sets of governing equations are completed by the transport equations for passive impurities and potential temperature. A simple algebraic turbulent closure model is used. The thermal stability phenomenon is taken into account. For each mathematical model a numerical scheme based on finite-difference or finite-volume discretization is proposed and discussed. Some results of numerical tests are presented for pollution dispersion from point sources and flows over simple geometries. (orig.)
2D and 3D numerical models on compositionally buoyant diapirs in the mantle wedge
Hasenclever, Jörg; Morgan, Jason Phipps; Hort, Matthias; Rüpke, Lars H.
2011-11-01
We present 2D and 3D numerical model calculations that focus on the physics of compositionally buoyant diapirs rising within a mantle wedge corner flow. Compositional buoyancy is assumed to arise from slab dehydration during which water-rich volatiles enter the mantle wedge and form a wet, less dense boundary layer on top of the slab. Slab dehydration is prescribed to occur in the 80-180 km deep slab interval, and the water transport is treated as a diffusion-like process. In this study, the mantle's rheology is modeled as being isoviscous for the benefit of easier-to-interpret feedbacks between water migration and buoyant viscous flow of the mantle. We use a simple subduction geometry that does not change during the numerical calculation. In a large set of 2D calculations we have identified that five different flow regimes can form, in which the position, number, and formation time of the diapirs vary as a function of four parameters: subduction angle, subduction rate, water diffusivity (mobility), and mantle viscosity. Using the same numerical method and numerical resolution we also conducted a suite of 3D calculations for 16 selected parameter combinations. Comparing the 2D and 3D results for the same model parameters reveals that the 2D models can only give limited insights into the inherently 3D problem of mantle wedge diapirism. While often correctly predicting the position and onset time of the first diapir(s), the 2D models fail to capture the dynamics of diapir ascent as well as the formation of secondary diapirs that result from boundary layer perturbations caused by previous diapirs. Of greatest importance for physically correct results is the numerical resolution in the region where diapirs nucleate, which must be high enough to accurately capture the growth of the thin wet boundary layer on top of the slab and, subsequently, the formation, morphology, and ascent of diapirs. Here 2D models can be very useful to quantify the required resolution, which we
3-D numerical modelling of stresses around a longwall panel with top coal caving
Yasitli, N.E.; Unver, B. [University of Hacettepe, Ankara (Turkey). Dept. of Mining Engineering
2005-06-01
There is a considerable amount of lignite reserve in the form of thick seams in Turkey. It is rather complicated to predict the characteristics of strata response to mining operation in thick seams. However, a comprehensive evaluation of ground behaviour is a prerequisite for maintaining an efficient production, especially when top coal winning by means of caving behind the face is applied. A comprehensive modelling of deformations and induced stresses is vital for the selection of optimum production strategy. In this study, numerical modelling and analysis of a longwall panel at Omerler underground coalmine have been carried out by using the software called FLAC(3D) developed based on the finite difference technique. Firstly, a 3-D numerical model of the M3 panel has been prepared. Secondly, induced stresses formed around the longwall face have been determined as a function of face advance where the face was located at the bottom of thick coal-seam. Results obtained from modelling studies have revealed that the front abutment vertical stress was maximum at 7 metres in front of the face and magnitude of front abutment stress was found to increase up to a distance of 200 metres away from the face start line. As the face was further advanced after 200 m from the face start line, there was not any significant change in the characteristics of front abutment stresses. Results of numerical analysis of the panel were in good agreement with in situ observations.
Numerical and experimental investigation of the 3D free surface flow in a model Pelton turbine
This investigation focuses on the numerical and experimental analysis of the 3D free surface flow in a Pelton turbine. In particular, two typical flow conditions occurring in a full scale Pelton turbine - a configuration with a straight inlet as well as a configuration with a 90 degree elbow upstream of the nozzle - are considered. Thereby, the effect of secondary flow due to the 90 degree bending of the upstream pipe on the characteristics of the jet is explored. The hybrid flow field consists of pure liquid flow within the conduit and free surface two component flow of the liquid jet emerging out of the nozzle into air. The numerical results are validated against experimental investigations performed in the laboratory of the Institute of Fluid Mechanics (FLM). For the numerical simulation of the flow the in-house unstructured fully parallelized finite volume solver solver3D is utilized. An advanced interface capturing model based on the classic Volume of Fluid method is applied. In order to ensure sharp interface resolution an additional convection term is added to the transport equation of the volume fraction. A collocated variable arrangement is used and the set of non-linear equations, containing fluid conservation equations and model equations for turbulence and volume fraction, are solved in a segregated manner. For pressure-velocity coupling the SIMPLE and PISO algorithms are implemented. Detailed analysis of the observed flow patterns in the jet and of the jet geometry are presented.
Numerical simulation of a 3-D flow within a storage area hexagonal modular pavement systems
This numerical study has been performed to predict the flow patterns and characteristics within a storage area Hexagonal Modular Pavement Systems. Throughout the design and planning period for future construction are increasingly integrating computational fluid dynamics (CFD) into the process. A commercially known software, FLOW-3D, is applied to numerically solve the Navier-stokes equations for solution domains which are separated into three regions with overlapping boundaries to efficiently accommodate the grid resolutions, namely the honeycomb shaped modular, gravel and combined honeycomb shaped modular with gravel fill. The filtration of the fluid within the interstices of a permeable pavement is evaluated by integrating the Reynolds Averaged Navier-Stokes equations (RANS) inside the voids rather than making use of the widespread porous media approach. In conclusion, the results from numerical simulation are generally well agreed with the existing data and flow information such as flow patterns at increased flow, discharge rate and pressure is obtained to be used for engineering design purpose. Overall, the potential for FLOW-3D to model various geometries and configurations appears great. It should be noted that CFD should not be considered a complete replacement for physical modelling; however, it can definitely be used as a supplementary tool throughout the pavement design process.
Metallic foams represent one of the most exciting materials introduced in the manufacturing scenario in the last years. In the study here addressed, the experimental and numerical investigations on the forging process of a simple foam billet shaped into complex sculptured parts were carried out. In particular, the deformation behavior of metallic foams and the development of density gradients were investigated through a series of experimental forging tests in order to produce a selected portion of a hip prosthesis. The human bone replacement was chosen as case study due to its industrial demand and for its particular 3D complex shape. A finite element code (Deform 3D) was utilized for modeling the foam behavior during the forging process and an accurate material rheology description was used based on a porous material model which includes the measured local density. Once the effectiveness of the utilized Finite Element model was verified through the comparison with the experimental evidences, a numerical study of the influence of the foam density was investigated. The obtained numerical results shown as the initial billet density plays an important role on the prediction of the final shape, the optimization of the flash as well as the estimation of the punch load
Numerical modeling of 3-D Position Reconstruction from 3-Axial Planar Spiral Coil Sensor Sensitivity
Sanjaya, Edi; Viridi, Sparisoma
2011-01-01
A sensitivity profile of a planar spiral coil sensor (PSCS) is proposed and use to generate the relation of 3-D position of object observed using three (PSCS)-s, one in each x, y, and z axis to the sensors response. A numerical procedure using self consistent field-like method to reconstruct the real position of observed object from sensor sensitivity is presented and the results are discussed. Unfortunately, the procedure fails to approach the desired results due to the existence of quadratic terms.
The Numerical Investigation on Vortex Flow Behavior Using FLOW-3D
Jafar Chapokpour
2012-01-01
Full Text Available In this paper a numerical investigation is given for a Rankine type vortex flow inside the cylindrical vortex chamber using FLOW-3D. The FLOW-3D is a general purpose computational fluid dynamics (CFD package. The fluid motion is described with non-linear, transient, second-order differential equations. Additionally the free surface also exists in many simulations carried out with FLOW-3D because flow parameters and materials properties, such as density, velocity and pressure experience a discontinuity at it. After analysis of the vortex by mentioned details, the finding of time-averaged velocity components, turbulent components, turbulence dissipation, in the 2D briefed sections of chamber were depicted. It was found that there are different flow patterns like clockwise/anticlockwise vortices and some sink points combined with each other in different time intervals, decaying and generating along the time. Also the turbulence intensity and dissipations around the boundary conditions of chamber like central flushing discharge are higher than the flow body. It was also found that this CFD package was not able to simulate thoroughly the central air core of chamber after filling of chamber. This analysis is validated by comparison with previous experimental data that was measured in vortex settling basin.
Numerical investigation of band gaps in 3D printed cantilever-in-mass metamaterials
Qureshi, Awais; Li, Bing; Tan, K. T.
2016-06-01
In this research, the negative effective mass behavior of elastic/mechanical metamaterials is exhibited by a cantilever-in-mass structure as a proposed design for creating frequency stopping band gaps, based on local resonance of the internal structure. The mass-in-mass unit cell model is transformed into a cantilever-in-mass model using the Bernoulli-Euler beam theory. An analytical model of the cantilever-in-mass structure is derived and the effects of geometrical dimensions and material parameters to create frequency band gaps are examined. A two-dimensional finite element model is created to validate the analytical results, and excellent agreement is achieved. The analytical model establishes an easily tunable metamaterial design to realize wave attenuation based on locally resonant frequency. To demonstrate feasibility for 3D printing, the analytical model is employed to design and fabricate 3D printable mechanical metamaterial. A three-dimensional numerical experiment is performed using COMSOL Multiphysics to validate the wave attenuation performance. Results show that the cantilever-in-mass metamaterial is capable of mitigating stress waves at the desired resonance frequency. Our study successfully presents the use of one constituent material to create a 3D printed cantilever-in-mass metamaterial with negative effective mass density for stress wave mitigation purposes.
Numerical investigation of band gaps in 3D printed cantilever-in-mass metamaterials
Qureshi, Awais; Li, Bing; Tan, K. T.
2016-01-01
In this research, the negative effective mass behavior of elastic/mechanical metamaterials is exhibited by a cantilever-in-mass structure as a proposed design for creating frequency stopping band gaps, based on local resonance of the internal structure. The mass-in-mass unit cell model is transformed into a cantilever-in-mass model using the Bernoulli-Euler beam theory. An analytical model of the cantilever-in-mass structure is derived and the effects of geometrical dimensions and material parameters to create frequency band gaps are examined. A two-dimensional finite element model is created to validate the analytical results, and excellent agreement is achieved. The analytical model establishes an easily tunable metamaterial design to realize wave attenuation based on locally resonant frequency. To demonstrate feasibility for 3D printing, the analytical model is employed to design and fabricate 3D printable mechanical metamaterial. A three-dimensional numerical experiment is performed using COMSOL Multiphysics to validate the wave attenuation performance. Results show that the cantilever-in-mass metamaterial is capable of mitigating stress waves at the desired resonance frequency. Our study successfully presents the use of one constituent material to create a 3D printed cantilever-in-mass metamaterial with negative effective mass density for stress wave mitigation purposes. PMID:27329828
3-D-geomechanical-numerical model of the contemporary crustal stress state in the Alberta Basin
K. Reiter
2014-08-01
Full Text Available In the context of examining the potential usage of safe and sustainable geothermal energy in the Alberta Basin whether in deep sediments or crystalline rock, the understanding of the in-situ stress state is crucial. It is a key challenge to estimate the 3-D stress state at an arbitrary chosen point in the crust, based on sparsely distributed in-situ stress data. To address this challenge, we present a large-scale 3-D geomechanical-numerical model (700 km × 1200 km × 80 km from a large portion of the Alberta Basin, to provide a 3-D continuous quantification of the contemporary stress orientations and stress magnitudes. To calibrate the model, we use a large database of in-situ stress orientation (321 SHmax as well as stress magnitude data (981 SV, 1720 SHmin and 2 (+11 SHmax from the Alberta Basin. To find the best-fit model we vary the material properties and primarily the kinematic boundary conditions of the model. This study focusses in detail on the statistical calibration procedure, because of the large amount of available data, the diversity of data types, and the importance of the order of data tests. The best-fit model provides the total 3-D stress tensor for nearly the whole Alberta Basin and allows estimation of stress orientation and stress magnitudes in advance of any well. First order implications for the well design and configuration of enhanced geothermal systems are revealed. Systematic deviations of the modelled stress from in-situ data are found for stress orientations in the Peace River- and the Bow Island Arch as well as for leak-off-test magnitudes.
吴开腾; 宁建国
2003-01-01
A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves produced by an explosive source. These numerical results indicate that the code MMIC3D has the ability in computing cases such as 3D shock waves produced by air explosion, vortex region of the shock wave, the Mach wave, and reflected waves behind rigid boundaries.
A numerical solution of 3D inviscid rotational flow in turbines and ducts
Oktay, Erdal; Akmandor, Sinan; Üçer, Ahmet
1998-04-01
The numerical solutions of inviscid rotational (Euler) flows were obtained using an explicit hexahedral unstructured cell vertex finite volume method. A second-order-accurate, one-step Lax-Wendroff scheme was used to solve the unsteady governing equations discretized in conservative form. The transonic circular bump, in which the location and the strength of the captured shock are well predicted, was used as the first test case. The nozzle guide vanes of the VKI low-speed turbine facility were used to validate the Euler code in highly 3D environment. Despite the high turning and the secondary flows which develop, close agreements have been obtained with experimental and numerical results associated with these test cases.
Parareal in time 3D numerical solver for the LWR Benchmark neutron diffusion transient model
In this paper we present a time-parallel algorithm for the 3D neutrons calculation of a transient model in a nuclear reactor core. The neutrons calculation consists in numerically solving the time dependent diffusion approximation equation, which is a simplified transport equation. The numerical resolution is done with finite elements method based on a tetrahedral meshing of the computational domain, representing the reactor core, and time discretization is achieved using a θ-scheme. The transient model presents moving control rods during the time of the reaction. Therefore, cross-sections (piecewise constants) are taken into account by interpolations with respect to the velocity of the control rods. The parallelism across the time is achieved by an adequate use of the parareal in time algorithm to the handled problem. This parallel method is a predictor corrector scheme that iteratively combines the use of two kinds of numerical propagators, one coarse and one fine. Our method is made efficient by means of a coarse solver defined with large time step and fixed position control rods model, while the fine propagator is assumed to be a high order numerical approximation of the full model. The parallel implementation of our method provides a good scalability of the algorithm. Numerical results show the efficiency of the parareal method on large light water reactor transient model corresponding to the Langenbuch–Maurer–Werner benchmark
Parareal in time 3D numerical solver for the LWR Benchmark neutron diffusion transient model
Baudron, Anne-Marie, E-mail: anne-marie.baudron@cea.fr [Laboratoire de Recherche Conventionné MANON, CEA/DEN/DANS/DM2S and UPMC-CNRS/LJLL (France); CEA-DRN/DMT/SERMA, CEN-Saclay, 91191 Gif sur Yvette Cedex (France); Lautard, Jean-Jacques, E-mail: jean-jacques.lautard@cea.fr [Laboratoire de Recherche Conventionné MANON, CEA/DEN/DANS/DM2S and UPMC-CNRS/LJLL (France); CEA-DRN/DMT/SERMA, CEN-Saclay, 91191 Gif sur Yvette Cedex (France); Maday, Yvon, E-mail: maday@ann.jussieu.fr [Sorbonne Universités, UPMC Univ Paris 06, UMR 7598, Laboratoire Jacques-Louis Lions and Institut Universitaire de France, F-75005, Paris (France); Laboratoire de Recherche Conventionné MANON, CEA/DEN/DANS/DM2S and UPMC-CNRS/LJLL (France); Brown Univ, Division of Applied Maths, Providence, RI (United States); Riahi, Mohamed Kamel, E-mail: riahi@cmap.polytechnique.fr [Laboratoire de Recherche Conventionné MANON, CEA/DEN/DANS/DM2S and UPMC-CNRS/LJLL (France); CMAP, Inria-Saclay and X-Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex (France); Salomon, Julien, E-mail: salomon@ceremade.dauphine.fr [CEREMADE, Univ Paris-Dauphine, Pl. du Mal. de Lattre de Tassigny, F-75016, Paris (France)
2014-12-15
In this paper we present a time-parallel algorithm for the 3D neutrons calculation of a transient model in a nuclear reactor core. The neutrons calculation consists in numerically solving the time dependent diffusion approximation equation, which is a simplified transport equation. The numerical resolution is done with finite elements method based on a tetrahedral meshing of the computational domain, representing the reactor core, and time discretization is achieved using a θ-scheme. The transient model presents moving control rods during the time of the reaction. Therefore, cross-sections (piecewise constants) are taken into account by interpolations with respect to the velocity of the control rods. The parallelism across the time is achieved by an adequate use of the parareal in time algorithm to the handled problem. This parallel method is a predictor corrector scheme that iteratively combines the use of two kinds of numerical propagators, one coarse and one fine. Our method is made efficient by means of a coarse solver defined with large time step and fixed position control rods model, while the fine propagator is assumed to be a high order numerical approximation of the full model. The parallel implementation of our method provides a good scalability of the algorithm. Numerical results show the efficiency of the parareal method on large light water reactor transient model corresponding to the Langenbuch–Maurer–Werner benchmark.
Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis
Ha-Minh, Cuong; Boussu, François; Kanit, Toufik; Crépin, David; Imad, Abdellatif
2012-06-01
3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2® fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.
Negara, Ardiansyah
2013-01-01
Anisotropy of hydraulic properties of subsurface geologic formations is an essential feature that has been established as a consequence of the different geologic processes that they undergo during the longer geologic time scale. With respect to petroleum reservoirs, in many cases, anisotropy plays significant role in dictating the direction of flow that becomes no longer dependent only on the pressure gradient direction but also on the principal directions of anisotropy. Furthermore, in complex systems involving the flow of multiphase fluids in which the gravity and the capillarity play an important role, anisotropy can also have important influences. Therefore, there has been great deal of motivation to consider anisotropy when solving the governing conservation laws numerically. Unfortunately, the two-point flux approximation of finite difference approach is not capable of handling full tensor permeability fields. Lately, however, it has been possible to adapt the multipoint flux approximation that can handle anisotropy to the framework of finite difference schemes. In multipoint flux approximation method, the stencil of approximation is more involved, i.e., it requires the involvement of 9-point stencil for the 2-D model and 27-point stencil for the 3-D model. This is apparently challenging and cumbersome when making the global system of equations. In this work, we apply the equation-type approach, which is the experimenting pressure field approach that enables the solution of the global problem breaks into the solution of multitude of local problems that significantly reduce the complexity without affecting the accuracy of numerical solution. This approach also leads in reducing the computational cost during the simulation. We have applied this technique to a variety of anisotropy scenarios of 3-D subsurface flow problems and the numerical results demonstrate that the experimenting pressure field technique fits very well with the multipoint flux approximation
Wang, Z; Barnes, C W; Barnes, D C; Wang, Zhehui; Pariev, Vladimir I.; Barnes, Cris W.; Barnes, Daniel C.
2002-01-01
A new kind of dynamo utilizing flowing laboratory plasmas has been identified. Conversion of plasma kinetic energy to magnetic energy is verified numerically by kinematic dynamo simulations for magnetic Reynolds numbers above 210. As opposed to intrinsically-turbulent liquid-sodium dynamos, the proposed plasma dynamos correspond to laminar flow topology. Modest plasma parameters, 1-20 eV temperatures, 10^{19}-10^{20} m^{-3} densities in 0.3-1.0 m scale-lengths driven by velocities on the order of the Alfven Critical Ionization Velocity (CIV), self-consistently satisfy the conditions needed for the magnetic field amplication. Growth rates for the plasma dynamos are obtained numerically with different geometry and magnetic Reynolds numbers. Magnetic-field-free coaxial plasma guns can be used to sustain the plasma flow and the dynamo.
Implementation of a 3d numerical model of a folded multilayer carbonate aquifer
Di Salvo, Cristina; Guyennon, Nicolas; Romano, Emanuele; Bruna Petrangeli, Anna; Preziosi, Elisabetta
2016-04-01
The main objective of this research is to present a case study of the numerical model implementation of a complex carbonate, structurally folded aquifer, with a finite difference, porous equivalent model. The case study aquifer (which extends over 235 km2 in the Apennine chain, Central Italy) provides a long term average of 3.5 m3/s of good quality groundwater to the surface river network, sustaining the minimum vital flow, and it is planned to be exploited in the next years for public water supply. In the downstream part of the river in the study area, a "Site of Community Importance" include the Nera River for its valuable aquatic fauna. However, the possible negative effects of the foreseen exploitation on groundwater dependent ecosystems are a great concern and model grounded scenarios are needed. This multilayer aquifer was conceptualized as five hydrostratigraphic units: three main aquifers (the uppermost unconfined, the central and the deepest partly confined), are separated by two locally discontinuous aquitards. The Nera river cuts through the two upper aquifers and acts as the main natural sink for groundwater. An equivalent porous medium approach was chosen. The complex tectonic structure of the aquifer requires several steps in defining the conceptual model; the presence of strongly dipping layers with very heterogeneous hydraulic conductivity, results in different thicknesses of saturated portions. Aquifers can have both unconfined or confined zones; drying and rewetting must be allowed when considering recharge/discharge cycles. All these characteristics can be included in the conceptual and numerical model; however, being the number of flow and head target scarce, the over-parametrization of the model must be avoided. Following the principle of parsimony, three steady state numerical models were developed, starting from a simple model, and then adding complexity: 2D (single layer), QUASI -3D (with leackage term simulating flow through aquitards) and
Coolability of a 3D homogeneous debris bed, experimental and numerical investigations
Within the framework of nuclear safety analysis, we present here experimental and numerical results in the field of debris bed coolability. Experimental data are provided by the SILFIDE 3D experimental facility in which the debris bed is heated by induction, at Electricite de France (EDF). Numerical computations are obtained with MC3D-REPO which is a 3-phase and 3D code developed by the Commissariat a l'Energie Atomique (CEA). The uniform debris bed consists of 2 and 3,17 mm diameter steel beads contained in a 50 cm x 60 cm x 10 cm vessel. Water is used as a coolant and can be introduced either by the top or the bottom of the bed at a determined temperature. Due to heterogeneous power distribution within the bed, two definitions for the critical heat flux are proposed: the classical mean value and the local flux (much higher). Even in the first case, the measured dryout heat flux is higher than the Lipinsky 1-D flux. Temperature curve analyses show that the dryout phenomenon is very local, therefore one should be careful about the right flux definition to use. As the injected power is being increased stepwise, steady temperature stages above saturation temperature before dryout can be observed. A discussion is proposed. For some very high values of the induction power, some spheres melted together, leading to a bigger non-porous region. Even if the local temperature went over 1300 C, the bed was still coolable and the critical heat flux value was not impacted. Some parametric studies led to the following conclusions: bottom coolant injection leads to a twice time higher critical flux than by top injection, the influence of the height of the water pool above debris bed is negligible, a sub-cooled liquid injection has no influence on the coolability. Fluidization of surface particles is also discussed. The MC3D-REPO model assumes a thermal equilibrium between the three phases, which gives results in agreement with experiments until dryout occurs. (author)
Terascale direct numerical simulations of turbulent combustion using S3D
Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air coflow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory
Terascale direct numerical simulations of turbulent combustion using S3D
Chen, J. H.; Choudhary, A.; de Supinski, B.; DeVries, M.; Hawkes, E. R.; Klasky, S.; Liao, W. K.; Ma, K. L.; Mellor-Crummey, J.; Podhorszki, N.; Sankaran, R.; Shende, S.; Yoo, C. S.
2009-01-01
Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air coflow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory
Generating Irregular Models for 3D Spherical-Particle-Based Numerical Methods
Gang-Hai Huang
2013-01-01
Full Text Available The realistic representation of an irregular geological body is essential to the construction of a particle simulation model. A three-dimensional (3D sphere generator for an irregular model (SGIM, which is based on the platform of Microsoft Foundation Classes (MFC in VC++, is developed to accurately simulate the inherent discontinuities in geological bodies. OpenGL is employed to visualize the modeling in the SGIM. Three key functions, namely, the basic-model-setup function, the excavating function, and the cutting function, are implemented. An open-pit slope is simulated using the proposed model. The results demonstrate that an extremely irregular 3D model of a geological body can be generated using the SGIM and that various types of discontinuities can be inserted to cut the model. The data structure of the model that is generated by the SGIM is versatile and can be easily modified to match various numerical calculation tools. This can be helpful in the application of particle simulation methods to large-scale geoengineering projects.
3D numerical investigation of turbulent flow through lateral intake in open channel
The flow at a channel bifurcation is turbulent, highly three-dimensional (3D) and has many complex features. There is transverse motion accompanying the main flow and an extensive separation zone that develops in the branch channel. This zone causes hydraulic and sedimentation problems that must be known before designing the system. This necessitates a deeper insight into the flow patterns and shear stress distributions near the solid boundaries. This paper reports a 3D numerical investigation of flow pattern and shear stress distribution at a lateral intake in an open channel. Simulations are done on rectangular channel geometry, with smooth bed and sidewalls. The CFD model uses the standard k-ε and k-ω model of Wilcox turbulence closure schemes as implemented in the FLUENT code. The simulation results were compared with available experimental data. It was found that both turbulence models used accurately predicted velocity profiles in the main channel but in the branch channel, the k-ω model is performed better than the k-ε turbulence model. (author)
3D printing device for numerical control machine and wood deposition
Julien Gardan
2014-12-01
Full Text Available The paper presents the development of a new sustainable approach in additive manufacturing adapted on a Numerical Control (NC machining. Wood has several advantages that are transferable to various derivatives allowing the introduction of sustainable material into the product lifecycle. The application involves the integration of wood pulp into rapid prototyping solutions. Wood is the main material studied for its ecological aspect. The primary goal was to create reconstituted wood objects through a rapid manufacturing. Additive manufacturing technology is most commonly used for modeling, prototyping, tooling through an exclusive machine or 3D printer. An overall review and an analysis of technologies show that the additive manufacturing presents some little independent solutions [9] [12]. The problem studied especially the additive manufacturing limits to produce an ecological product with materials from biomass. The study developed a 3d printing head as solution for shaping wood pulp or powder materials. Some technological problematic require enslavement to the NC controller, the programming building of model, and the realization of wood pulp. This work also presents a wood pulping process characterized by adding wood flour and starch. A machine implementation and some application examples used for its development are presented.
3D numerical simulation of the transport of chemical signature compounds from buried landmines
Irrazabal, Maik; Borrero, Ernesto; Briano, Julio G.; Castro, Miguel; Hernandez, Samuel P.
2005-06-01
The transport of the chemical signature compounds from buried landmines in a three-dimensional (3D) array has been numerically modeled using the finite-volume technique. Compounds such as trinitrotoluene, dinitrotoluene, and their degradation products, are semi volatile and somewhat soluble in water. Furthermore, they can strongly adsorb to the soil and undergo chemical and biological degradation. Consequently, the spatial and temporal concentration distributions of such chemicals depend on the mobility of the water and gaseous phases, their molecular and mechanical diffusion, adsorption characteristics, soil water content, compaction, and environmental factors. A 3D framework is required since two-dimensional (2D) symmetry may easily fade due to terrain topography: non-flat surfaces, soil heterogeneity, or underground fractures. The spatial and temporal distribution of the chemical-signature-compounds, in an inclined grid has been obtained. The fact that the chemicals may migrate horizontally, giving higher surface concentrations at positions not directly on top of the objects, emphasizes the need for understanding the transport mechanism when a chemical detector is used. Deformation in the concentration contours after rainfall is observed in the inclined surface and is attributed to both: the advective flux, and to the water flux at the surface caused by the slope. The analysis of the displacements in the position of the maximum concentrations at the surface, respect to the actual location of the mine, in an inclined system, is presented.
Direct numerical simulation of the axial dipolar dynamo in the Von Kármán Sodium experiment
Nore, C.; Castanon Quiroz, D.; Cappanera, L.; Guermond, J.-L.
2016-06-01
For the first time, a direct numerical simulation of the incompressible, fully nonlinear, magnetohydrodynamic (MHD) equations for the Von Kármán Sodium (VKS) experiment is presented with the two counter-rotating impellers realistically represented. Dynamo thresholds are obtained for various magnetic permeabilities of the impellers and it is observed that the threshold decreases as the magnetic permeability increases. Hydrodynamic results compare well with experimental data in the same range of kinetic Reynolds numbers: at small impeller rotation frequency, the flow is steady; at larger frequency, the fluctuating flow is characterized by small scales and helical vortices localized between the blades. MHD computations show that two distinct magnetic families compete at small kinetic Reynolds number and these two families merge at larger kinetic Reynolds number. In both cases, using ferromagnetic material for the impellers decreases the dynamo threshold and enhances the axisymmetric component of the magnetic field: the resulting dynamo is a mostly axisymmetric axial dipole with an azimuthal component concentrated in the impellers as observed in the VKS experiment.
Volatile transport on inhomogeneous surfaces: II. Numerical calculations (VT3D)
Young, Leslie A
2015-01-01
Several distant icy worlds have atmospheres that are in vapor-pressure equilibrium with their surface volatiles, including Pluto, Triton, and, probably, several large KBOs near perihelion. Studies of the volatile and thermal evolution of these have been limited by computational speed, especially for models that treat surfaces that vary with both latitude and longitude. In order to expedite such work, I present a new numerical model for the seasonal behavior of Pluto and Triton which (i) uses initial conditions that improve convergence, (ii) uses an expedient method for handling the transition between global and non-global atmospheres, (iii) includes local conservation of energy and global conservation of mass to partition energy between heating, conduction, and sublimation or condensation, (iv) uses time-stepping algorithms that ensure stability while allowing larger timesteps, and (v) can include longitudinal variability. This model, called VT3D, has been used in Young (2012), Young (2013), Olkin et al. (201...
3D numerical investigation on landslide generated tsunamis around a conical island
Montagna, Francesca; Bellotti, Giorgio
2010-05-01
This paper presents numerical computations of tsunamis generated by subaerial and submerged landslides falling along the flank of a conical island. The study is inspired by the tsunamis that on 30th December 2002 attacked the coast of the volcanic island of Stromboli (South Tyrrhenian sea, Italy). In particular this paper analyzes the important feature of the lateral spreading of landside generated tsunamis and the associated flooding hazard. The numerical model used in this study is the full three dimensional commercial code FLOW-3D. The model has already been successfully used (Choi et al., 2007; 2008; Chopakatla et al, 2008) to study the interaction of waves and structures. In the simulations carried out in this work a particular feature of the code has been employed: the GMO (General Moving Object) algorithm. It allows to reproduce the interaction between moving objects, as a landslide, and the water. FLOW-3D has been firstly validated using available 3D experiments reproducing tsunamis generated by landslides at the flank of a conical island. The experiments have been carried out in the LIC laboratory of the Polytechnic of Bari, Italy (Di Risio et al., 2009). Numerical and experimental time series of run-up and sea level recorded at gauges located at the flanks of the island and offshore have been successfully compared. This analysis shows that the model can accurately represent the generation, the propagation and the inundation of landslide generated tsunamis and suggests the use of the numerical model as a tool for preparing inundation maps. At the conference we will present the validation of the model and parametric analyses aimed to investigate how wave properties depend on the landslide kinematic and on further parameters such as the landslide volume and shape, as well as the radius of the island. The expected final results of the research are precomputed inundation maps that depend on the characteristics of the landslide and of the island. Finally we
3-D NUMERICAL SIMULATION OF CONVOY-GENERATED WAVES IN A RESTRICTED WATERWAY
JI Sheng Cheng; OUAHSINE Abdellatif; SMAOUI Hassan; SERGENT Philippe
2012-01-01
We consider waves generated by the passing of convoys in a restricted waterway.The magnitude of these waves depends mainly on the geometrical and kinematical parameters of the convoy,such as the speed and the hull geometry.The objective of this study is to predict the relationship between these geometrical and kinematical parameters and the amplitude of ship-generated waves as well as the water plane drawdown.Numerical simulations are conducted by solving the 3-D Navier-Stokes equations along with the standard k-ε model for turbulent processes.The results are compared first with the empirical model and second with experimental measurements performed by the French company Compagnie National du Rh(o)ne (CNR).
A NUMERICAL SIMULATION OF 3-D INNER FLOW IN UP-STREAM PUMPING MECHANICAL SEAL
ZHANG Jin-feng; YUAN Shou-qi; FU Yong-hong; FANG Yu-jian
2006-01-01
Numerical simulation of 3-D inner flow between Up-stream Pumping Mechanical Face Seals (UPMFS) faces was initially done by CFD software, which made the flow visualization come true.Simulation results directly discover the action of hydrodynamic lubrication, and by comparison with that of Conventional Mechanic Face Seals (CMFS), the advantage over bigger bearing capability, less friction and much less leakage are explained clearly.Otherwise there are also some different ideas and results from precedent analysis and computational research results: dynamic and static pressure profiles can be obtained respectively instead of the analytic total pressure distribution only, pressure distribution is nonlinear, while always be solved as linear, lower pressure is observed at the area of inner diameter caused by the grooves, but its possible cavitations effects to the performance of UPMFS still need further study.
Slab detachment in laterally varying subduction zones: 3-D numerical modeling
Duretz, T.; Gerya, T. V.; Spakman, W.
2014-03-01
Understanding the three-dimensional (3-D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench variations. High-resolution thermomechanical numerical models, encompassing experimentally derived flow laws and a pseudo free surface, are employed to unravel lithospheric and topographic evolutions. First, we consider coeval subduction of adjacent continental and oceanic lithospheres (SCO). This configuration yields to two-stage slab detachment during collision, topographic buildup and extrusion, variable along-trench convergence rates, and associated trench deformation. The second setting considers a convergent margin, which is laterally limited by a transform boundary (STB). Such collisional system is affected by a single slab detachment, little trench deformation, and moderately confined upper plate topography. The effect of initial thermal slab age on SCO and STB models are explored. Similarities with natural analogs along the Arabia-Eurasia collision are discussed.
Numerical determination of OPE coefficients in the 3D Ising model from off-critical correlators
Caselle, M; Magnoli, N
2015-01-01
We propose a general method for the numerical evaluation of OPE coefficients in three dimensional Conformal Field Theories based on the study of the conformal perturbation of two point functions in the vicinity of the critical point. We test our proposal in the three dimensional Ising Model, looking at the magnetic perturbation of the $$, $$ and $$ correlators from which we extract the values of $C^{\\sigma}_{\\sigma\\epsilon}=1.07(3)$ and $C^{\\epsilon}_{\\epsilon\\epsilon}=1.45(30)$. Our estimate for $C^{\\sigma}_{\\sigma\\epsilon}$ agrees with those recently obtained using conformal bootstrap methods, while $C^{\\epsilon}_{\\epsilon\\epsilon}$, as far as we know, is new and could be used to further constrain conformal bootstrap analyses of the 3d Ising universality class.
Full 3-D numerical modeling of borehole electric image logging and the evaluation model of fracture
2008-01-01
A full 3-D finite element method numerical modeling program is written based on the principle and technical specification of borehole electric image well logging tool. The response of well logging is computed in the formation media model with a single fracture. The effect of changing fracture aperture and resistivity ratio to the logging response is discussed. The identification ability for two parallel fractures is also present. A quantitative evaluation formula of fracture aperture from borehole electric image logging data is set up. A case study of the model well is done to verify the accuracy of the for-mula. The result indicates that the formula is more accurate than the foreign one.
Temperature distributions in the laser-heated diamond anvil cell from 3-D numerical modeling
We present TempDAC, a 3-D numerical model for calculating the steady-state temperature distribution for continuous wave laser-heated experiments in the diamond anvil cell. TempDAC solves the steady heat conduction equation in three dimensions over the sample chamber, gasket, and diamond anvils and includes material-, temperature-, and direction-dependent thermal conductivity, while allowing for flexible sample geometries, laser beam intensity profile, and laser absorption properties. The model has been validated against an axisymmetric analytic solution for the temperature distribution within a laser-heated sample. Example calculations illustrate the importance of considering heat flow in three dimensions for the laser-heated diamond anvil cell. In particular, we show that a “flat top” input laser beam profile does not lead to a more uniform temperature distribution or flatter temperature gradients than a wide Gaussian laser beam
ZHANG AMan; YAO XiongLiang; LI Jia; GUO Jun
2008-01-01
Based on the potential flow theory,the vortex ring is introduced to simulate the toroidal bubble,and the boundary element method is applied to simulate the evo-lution of the bubble.Elastic-plasticity of structure being taken into account,the interaction between the bubble and the elastic-plastic structure is computed by combining the boundary element method (BEM) and the finite element method (FEM),and a corresponding 3D computing program is developed.This program is used to simulate the three-dimensional bubble dynamics in free field,near wall and near the elastic-plastic structure,and the numerical results are compared with the existing experimental results.The error is within 10%.The effects of different boundaries upon the bubble dynamics are presented by studying the bubble dy-namics near different boundaries.
Numerical modeling of time domain 3-D problems in accelerator physics
Time domain analysis is relevant in particle accelerators to study the electromagnetic field interaction of a moving source particle on a lagging test particle as the particles pass an accelerating cavity or some other structure. These fields are called wake fields. The travelling beam inside a beam pipe may undergo more complicated interactions with its environment due to the presence of other irregularities like wires, thin slots, joints and other types of obstacles. Analytical solutions of such problems is impossible and one has to resort to a numerical method. In this paper we present results of our first attempt to model these problems in 3-D using our finite difference time domain (FDTD) code. 10 refs., 9 figs
2008-01-01
Based on the potential flow theory, the vortex ring is introduced to simulate the toroidal bubble, and the boundary element method is applied to simulate the evo- lution of the bubble. Elastic-plasticity of structure being taken into account, the interaction between the bubble and the elastic-plastic structure is computed by combining the boundary element method (BEM) and the finite element method (FEM), and a corresponding 3D computing program is developed. This program is used to simulate the three-dimensional bubble dynamics in free field, near wall and near the elastic-plastic structure, and the numerical results are compared with the existing experimental results. The error is within 10%. The effects of different boundaries upon the bubble dynamics are presented by studying the bubble dy- namics near different boundaries.
Numerical Investigation of Nozzle Geometry Effect on Turbulent 3-D Water Offset Jet Flows
Negar Mohammad Aliha
2016-01-01
Full Text Available Using the Yang-Shih low Reynolds k-ε turbulence model, the mean flow field of a turbulent offset jet issuing from a long circular pipe was numerically investigated. The experimental results were used to verify the numerical results such as decay rate of streamwise velocity, locus of maximum streamwise velocity, jet half width in the wall normal and lateral directions, and jet velocity profiles. The present study focused attention on the influence of nozzle geometry on the evolution of a 3D incompressible turbulent offset jet. Circular, square-shaped, and rectangular nozzles were considered here. A comparison between the mean flow characteristics of offset jets issuing from circular and square-shaped nozzles, which had equal area and mean exit velocity, were made numerically. Moreover, the effect of aspect ratio of rectangular nozzles on the main features of the flow was investigated. It was shown that the spread rate, flow entrainment, and mixing rate of an offset jet issuing from circular nozzle are lower than square-shaped one. In addition, it was demonstrated that the aspect ratio of the rectangular nozzles only affects the mean flow field of the offset jet in the near field (up to 15 times greater than equivalent diameter of the nozzles. Furthermore, other parameters including the wall shear stress, flow entrainment and the length of potential core were also investigated.
Crosta, G.; Imposimato, S.; Roddeman, D.; Frattini, P.
2012-04-01
Fast moving landslides can be originated along slopes in mountainous terrains with natural and artificial lakes, or fjords at the slope foot. This landslides can reach extremely high speed and the impact with the immobile reservoir water can be influenced by the local topography and the landslide mass profile. The impact can generate large impulse waves and landslide tsunami. Initiation, propagation and runup are the three phases that need to be considered. The landslide evolution and the consequent wave can be controlled by the initial mass position (subaerial, partially or completely submerged), the landslide speed, the type of material, the subaerial and subaqueous slope geometry, the landslide depth and length at the impact, and the water depth. Extreme events have been caused by subaerial landslides: the 1963 Vajont rockslide (Italy), the 1958 Lituya Bay event (Alaska), the Tafjord and the Loen multiple events event (Norway), also from volcanic collapses (Hawaii and Canary islands). Various researchers completed a systematic experimental work on 2D and 3D wave generation and propagation (Kamphuis and Bowering, 1970; Huber, 1980; Müller, 1995; Huber and Hager, 1997; Fritz, 2002; Zweifel, 2004; Panizzo et al., 2005; Heller, 2007; Heller and Kinnear, 2010; Sælevik et al., 2009), using both rigid blocks and deformable granular" masses. Model data and results have been used to calibrate and validate numerical modelling tools (Harbitz, 1992; Jiang and LeBlond, 1993; Grilli et al., 2002; Grilli and Watts, 2005; Lynett and Liu, 2005; Tinti et al., 2006; Abadie et al., 2010) generally considering simplified rheologies (e.g. viscous rheologies) for subaerial subaqueous spreading. We use a FEM code (Roddeman, 2011; Crosta et al., 2006, 2009, 2010, 2011) adopting an Eulerian-Lagrangian approach to give accurate results for large deformations. We model both 2D and fully 3D events considering different settings. The material is considered as a fully deformable elasto
Wang, Zhehui; Pariev, Vladimir I.; Barnes, Cris W.; Barnes, Daniel C.
2002-01-01
A new kind of dynamo utilizing flowing laboratory plasmas has been identified. Conversion of plasma kinetic energy to magnetic energy is verified numerically by kinematic dynamo simulations for magnetic Reynolds numbers above 210. As opposed to intrinsically-turbulent liquid-sodium dynamos, the proposed plasma dynamos correspond to laminar flow topology. Modest plasma parameters, 1-20 eV temperatures, 10^{19}-10^{20} m^{-3} densities in 0.3-1.0 m scale-lengths driven by velocities on the orde...
Reiter, Karsten; Heidbach, Oliver; Moeck, Inga
2013-04-01
For the assessment and exploration of a potential geothermal reservoir, the contemporary in-situ stress is of key importance in terms of well stability and orientation of possible fluid pathways. However, available data, e.g. Heidbach et al. (2009) or Zang et al. (2012), deliver only point wise information of parts of the six independent components of the stress tensor. Moreover most measurements of the stress orientation and magnitude are done for hydrocarbon industry obvious in shallow depth. Interpolation across long distances or extrapolation into depth is unfavourable, because this would ignore structural features, inhomogeneity's in the crust or other local effects like topography. For this reasons geomechanical numerical modelling is the favourable method to quantify orientations and magnitudes of the 3D stress field for a geothermal reservoir. A geomechanical-numerical modelling, estimating the 3D absolute stress state, requires the initial stress state as model constraints. But in-situ stress measurements within or close by a potential reservoir are rare. For that reason a larger regional geomechanical-numerical model is necessary, which derive boundary conditions for the wanted local reservoir model. Such a large scale model has to be tested against in-situ stress measurements, orientations and magnitudes. Other suitable and available data, like GPS measurements or fault slip rates are useful to constrain kinematic boundary conditions. This stepwise approach from regional to local scale takes all stress field factors into account, from first over second up to third order. As an example we present a large scale crustal and upper mantle 3D-geomechanical-numerical model of the Alberta Basin and the surroundings, which is constructed to describe continuously the full stress tensor. In-situ stress measurements are the most likely data, because they deliver the most direct information's of the stress field and they provide insights into different depths, a
3D numerical model of the Omega Nebula (M17): simulated thermal X-ray emission
Reyes-Iturbide, J; Rosado, M; Rodríguez-Gónzalez, A; González, R F; Esquivel, A
2009-01-01
We present 3D hydrodynamical simulations of the superbubble M17, also known as the Omega nebula, carried out with the adaptive grid code yguazu'-a, which includes radiative cooling. The superbubble is modelled considering the winds of 11 individual stars from the open cluster inside the nebula (NGC 6618), for which there are estimates of the mass loss rates and terminal velocities based on their spectral types. These stars are located inside a dense interstellar medium, and they are bounded by two dense molecular clouds. We carried out three numerical models of this scenario, considering different line of sight positions of the stars (the position in the plane of the sky is known, thus fixed). Synthetic thermal X-ray emission maps are calculated from the numerical models and compared with ROSAT observations of this astrophysical object. Our models reproduce successfully both the observed X-ray morphology and the total X-ray luminosity, without taking into account thermal conduction effects.
The Making of FR Is I. Numerical Hydrodynamic 3D Simulations of Low Power Jets
Massaglia, S; Rossi, P; Capetti, S; Mignone, A
2016-01-01
Extragalactic radiosources have been classified in two classes, Fanaroff-Riley I and II, which differ in morphology and radio power. Strongly emitting sources belong to the edge brightened FR II class while the weak ones to the edge darkened FR I class. The origin of this dichotomy is not yet fully understood. Numerical simulations are successful in generating FR~II morphologies but they fail to reproduce the diffuse structure of FR Is. By means of hydro-dynamical 3D simulations of supersonic jets, we investigate how the displayed morphologies depend on the jet parameters. Bow shocks and Mach disks at the jet's head, likely responsible for the presence of hot spots in the FR II sources, disappear for a jet kinetic power less than 10^43 erg/s. This threshold compares favorably with the luminosity at which the FR~I/FR~II transition is observed. The problem is addressed by numerical means carrying out three-dimensional HD simulations of supersonic jets that propagate in a non homogeneous medium with the ambient ...
A parametric study of mucociliary transport by numerical simulations of 3D non-homogeneous mucus.
Chatelin, Robin; Poncet, Philippe
2016-06-14
Mucociliary clearance is the natural flow of the mucus which covers and protects the lung from the outer world. Pathologies, like cystic fibrosis, highly change the biological parameters of the mucus flow leading to stagnation situations and pathogens proliferation. As the lung exhibits a complex dyadic structure, in-vivo experimental study of mucociliary clearance is almost impossible and numerical simulations can bring important knowledge about this biological flow. This paper brings a detailed study of the biological parameters influence on the mucociliary clearance, in particular for pathological situations such as cystic fibrosis. Using recent suitable numerical methods, a non-homogeneous mucus flow (including non-linearities) can be simulated efficiently in 3D, allowing the identification of the meaningful parameters involved in this biological flow. Among these parameters, it is shown that the mucus viscosity, the stiffness transition between pericilliary fluid and mucus, the pericilliary fluid height as well as both cilia length and beating frequency have a great influence on the mucociliary transport. PMID:27126985
Mochalskyy, S.; Wünderlich, D.; Ruf, B.; Franzen, P.; Fantz, U.; Minea, T.
2014-02-01
Decreasing the co-extracted electron current while simultaneously keeping negative ion (NI) current sufficiently high is a crucial issue on the development plasma source system for ITER Neutral Beam Injector. To support finding the best extraction conditions the 3D Particle-in-Cell Monte Carlo Collision electrostatic code ONIX (Orsay Negative Ion eXtraction) has been developed. Close collaboration with experiments and other numerical models allows performing realistic simulations with relevant input parameters: plasma properties, geometry of the extraction aperture, full 3D magnetic field map, etc. For the first time ONIX has been benchmarked with commercial positive ions tracing code KOBRA3D. A very good agreement in terms of the meniscus position and depth has been found. Simulation of NI extraction with different e/NI ratio in bulk plasma shows high relevance of the direct negative ion extraction from the surface produced NI in order to obtain extracted NI current as in the experimental results from BATMAN testbed.
Optimising GPR modelling: A practical, multi-threaded approach to 3D FDTD numerical modelling
Millington, T. M.; Cassidy, N. J.
2010-09-01
The demand for advanced interpretational tools has lead to the development of highly sophisticated, computationally demanding, 3D GPR processing and modelling techniques. Many of these methods solve very large problems with stepwise methods that utilise numerically similar functions within iterative computational loops. Problems of this nature are readily parallelised by splitting the computational domain into smaller, independent chunks for direct use on cluster-style, multi-processor supercomputers. Unfortunately, the implications of running such facilities, as well as time investment needed to develop the parallel codes, means that for most researchers, the use of these advanced methods is too impractical. In this paper, we propose an alternative method of parallelisation which exploits the capabilities of the modern multi-core processors (upon which today's desktop PCs are built) by multi-threading the calculation of a problem's individual sub-solutions. To illustrate the approach, we have applied it to an advanced, 3D, finite-difference time-domain (FDTD) GPR modelling tool in which the calculation of the individual vector field components is multi-threaded. To be of practical use, the FDTD scheme must be able to deliver accurate results with short execution times and we, therefore, show that the performance benefits of our approach can deliver runtimes less than half those of the more conventional, serial programming techniques. We evaluate implementations of the technique using different programming languages (e.g., Matlab, Java, C++), which will facilitate the construction of a flexible modelling tool for use in future GPR research. The implementations are compared on a variety of typical hardware platforms, having between one and eight processing cores available, and also a modern Graphical Processing Unit (GPU)-based computer. Our results show that a multi-threaded xyz modelling approach is easy to implement and delivers excellent results when implemented
Shrestha, Bishwo Vijaya
2012-01-01
This study is about 3D Numerical Investigation of Settling basin layout by using numerical modeling program SSIIM. This study is carried out by using SSIIM windows version 1 (SSIIM 1.0). SSIIM is numerical modeling software, developed at NTNU by Professor Nils Reidar B. Olsen. This program has been used for investigation numerical modeling of hydraulic and sediment transport for different layouts geometry of settling basin.In this study a case study has carried out on settling basin layout of...
Shrestha, Bishwo Vijaya
2012-01-01
This study is about 3D Numerical Investigation of Settling basin layout by using numerical modeling program SSIIM. This study is carried out by using SSIIM windows version 1 (SSIIM 1.0). SSIIM is numerical modeling software, developed at NTNU by Professor Nils Reidar B. Olsen. This program has been used for investigation numerical modeling of hydraulic and sediment transport for different layouts geometry of settling basin.In this study a case study has carried out on settling basin layout of...
Comparison of 3-D finite element model of ashlar masonry with 2-D numerical models of ashlar masonry
Beran, Pavel
2016-06-01
3-D state of stress in heterogeneous ashlar masonry can be also computed by several suitable chosen 2-D numerical models of ashlar masonry. The results obtained from 2-D numerical models well correspond to the results obtained from 3-D numerical model. The character of thermal stress is the same. While using 2-D models the computational time is reduced more than hundredfold and therefore this method could be used for computation of thermal stresses during long time periods with 10 000 of steps.
Numerical 3D models support two distinct hydrothermal circulation systems at fast spreading ridges
Hasenclever, Jörg; Theissen-Krah, Sonja; Rüpke, Lars
2013-04-01
We present 3D numerical calculations of hydrothermal fluid flow at fast spreading ridges. The setup of the 3D models is based our previous 2D studies, in which we have coupled numerical models for crustal accretion and hydrothermal fluid flow. One result of these calculations is a crustal permeability field that leads to a thermal structure in the crust that matches seismic tomography data of the East Pacific Rise (EPR). The 1000°C isotherm obtained from the 2D results is now used as the lower boundary of the 3D model domain, while the upper boundary is a smoothed bathymetry of the EPR. The same permeability field as in the 2D models is used, with the highest permeability at the ridge axis and a decrease with both depth and distance to the ridge. Permeability is also reduced linearly between 600 and 1000°C. Using a newly developed parallel finite element code written in Matlab that solves for thermal evolution, fluid pressure and Darcy flow, we simulate the flow patterns of hydrothermal circulation in a segment of 5000m along-axis, 10000m across-axis and up to 5000m depth. We observe two distinct hydrothermal circulation systems: An on-axis system forming a series of vents with a spacing ranging from 100 to 500m that is recharged by nearby (100-200m) downflows on both sides of the ridge axis. Simultaneously a second system with much broader extensions both laterally and vertically exists off-axis. It is recharged by fluids intruding between 1500m to 5000m off-axis and sampling both upper and lower crust. These fluids are channeled in the deepest and hottest regions with high permeability and migrate up-slope following the 600°C isotherm until reaching the edge of the melt lens. Depending on the width of the melt lens these off-axis fluids either merge with the on-axis hydrothermal system or form separate vents. We observe separate off-axis vent fields if the magma lens half-width exceeds 1000m and confluence of both systems for half-widths smaller than 500m. For
Numerical Calculations of 3-D High-Lift Flows and Comparison with Experiment
Compton, William B, III
2015-01-01
Solutions were obtained with the Navier-Stokes CFD code TLNS3D to predict the flow about the NASA Trapezoidal Wing, a high-lift wing composed of three elements: the main-wing element, a deployed leading-edge slat, and a deployed trailing-edge flap. Turbulence was modeled by the Spalart-Allmaras one-equation turbulence model. One case with massive separation was repeated using Menter's two-equation SST (Menter's Shear Stress Transport) k-omega turbulence model in an attempt to improve the agreement with experiment. The investigation was conducted at a free stream Mach number of 0.2, and at angles of attack ranging from 10.004 degrees to 34.858 degrees. The Reynolds number based on the mean aerodynamic chord of the wing was 4.3 x 10 (sup 6). Compared to experiment, the numerical procedure predicted the surface pressures very well at angles of attack in the linear range of the lift. However, computed maximum lift was 5% low. Drag was mainly under predicted. The procedure correctly predicted several well-known trends and features of high-lift flows, such as off-body separation. The two turbulence models yielded significantly different solutions for the repeated case.
Numerical investigation of wave attenuation by vegetation using a 3D RANS model
Marsooli, Reza; Wu, Weiming
2014-12-01
Vegetation has been recognized as an important natural shoreline protection against storm surges and waves. Understanding of wave-vegetation interaction is essential for assessing the ability of vegetation patches, such as wetlands, to mitigate storm damages. In this study the wave attenuation by vegetation is investigated numerically using a 3-D model which solves the Reynolds-Averaged Navier-Stokes equations (RANS) by means of a finite-volume method based on collocated hexahedron mesh. A mixing length model is used for turbulence closure of the RANS equations. The water surface boundary is tracked using the Volume-of-Fluid (VOF) method with the Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) to solve the VOF advection equation. The presence of vegetation is taken into account by adding the vegetation drag and inertia forces to the momentum equations. The model is validated by several laboratory experiments of short wave propagation through vegetation over flat and sloping beds. The comparisons show good agreement between the measured data and calculated results, but the swaying motion of flexible vegetation which is neglected in this study can influence the accuracy of the wave height predictions. The model is then applied to one of the validation tests with different vegetation properties, revealing that the wave height attenuation by vegetation depends not only on the wave conditions, but also the vegetation characteristics such as vegetation height and density.
High resolution 3D hydraulic numerical modelling for WEP environmental approval and engineering
Fissel, D.B.; Jiang, J. [ASL Environmental Sciences Inc., Sidney, BC (Canada)
2009-07-01
This paper discussed biophysical analyses conducted to determine the impacts of a new powerhouse at the Waneta Dam on the Pen d'Oreille River. A hydraulic 3-D numerical model with a high resolution was calibrated and validated using data from field studies of river velocities, water levels, temperatures. Pre-and post-project river velocities and temperatures were compared in order to determine their impacts on the deepwater habitat of the Waneta. The aim of the study was to determine the effects of the Waneta Expansion Project (WEP) on the sub-population of white sturgeon in the confluence waters. The model assessed the impacts of various factors on sturgeon egg deposition areas in late summer water temperatures. It was concluded that the analyses will serve as a useful guide for the WEP diversion channel design and excavation, and will help determine measures for preventing bottom sediment contaminants from being re-suspended during the construction of the channel. 19 refs., 1 tab., 10 figs.
Numerical simulation of the 3D behavior of thermal buoyant airflows in pentahedral spaces
Ridouane, El Hassan [Department of Mechanical Engineering, University of Vermont, 33 Colchester Avenue, 201 Votey Building, Burlington, VT 05405 (United States)], E-mail: eridouan@uvm.edu; Campo, Antonio [Department of Mechanical Engineering, University of Vermont, 33 Colchester Avenue, 201 Votey Building, Burlington, VT 05405 (United States)
2008-10-15
A numerical study of three-dimensional natural convection in an attic space with heated horizontal base and cooled upper walls is presented. Every previous study pertinent to this subject as of today has assumed that the flow in attics is two-dimensional and restricted to triangular cavities. This problem is examined for fixed aspect ratios holding width to height of 2 and depth to height of 3.33 and Rayleigh numbers ranging from 10{sup 4} to 8 x 10{sup 5}. The coupled system of conservation equations, subject to the proper boundary conditions, along with the equation of state assuming the air behaves as a perfect gas are solved with the finite volume method. In the conservation equations, the second-order-accurate QUICK scheme was used for the discretization of the convective terms and the SIMPLE scheme for the pressure-velocity coupling. It is categorically found that the flow in the attic is 3D. From the physics of the problem, two steady-state solutions are possible. The symmetrical solution prevails for relatively low Rayleigh numbers. However, as the Ra is gradually increased, a transition occurs at a critical value Ra{sub C}. Above this value of Ra{sub C}, an asymmetrical solution exhibiting a pitchfork bifurcation arises and eventually becomes steady. Results are presented detailing the occurrence of the pitchfork bifurcation and the resulting flow patterns are described.
Numerical study of elastic turbulence in a 3D curvilinear micro-channel
Zhang, Hongna; Kunugi, Tomoaki; Li, Fengchen
2012-11-01
Elastic turbulence is an intriguing phenomenon of viscoelastic fluid flow, and dominated by the strong nonlinear elasticity due to the existence of flexible microstructures. It implies the possibility to generate a turbulent state (so-called an elastic turbulence) in the micro-scale devices by introducing the viscoelastic fluids, which could significantly enhance the mixing efficiency therein. Several experiments have been carried out to study its characteristics and underlying physics. However, the difficulty in measuring the flow information and behaviors of the microstructures, especially in the cross section normal to the mean flow direction, limits our current understanding and controlling. In the present study, the nondimensionalization method in which the characteristic velocity is defined as the ratio of the solution viscosity to the width of the channel was adopted to simulate the elastic turbulence in the micro-scale devices. And the elastic turbulent flow was obtained numerically in the 3D curvilinear micro-channel. Therein, the characteristics of the velocity field and polymer's behavior are discussed. Moreover, the energy transfer between the kinetic energy and the polymer's elastic energy is also investigated to understand its physical mechanism. Supported by the Japan Society for the Promotion of Science research fellowship and the Ministry of Education, Culture, Sports, Science and Technology via `Energy Science in the Age of Global Warming' of Global Center of Excellence (G-COE) program (J-051).
Analytic and numerical demonstration of quantum self-correction in the 3D Cubic Code
Bravyi, Sergey
2011-01-01
A big open question in the quantum information theory concerns feasibility of a self-correcting quantum memory. A quantum state recorded in such memory can be stored reliably for a macroscopic time without need for active error correction if the memory is put in contact with a cold enough thermal bath. In this paper we derive a rigorous lower bound on the memory time $T_{mem}$ of the 3D Cubic Code model which was recently conjectured to have a self-correcting behavior. Assuming that dynamics of the memory system can be described by a Markovian master equation of Davies form, we prove that $T_{mem}\\ge L^{c\\beta}$ for some constant $c>0$, where $L$ is the lattice size and $\\beta$ is the inverse temperature of the bath. However, this bound applies only if the lattice size does not exceed certain critical value $L^*\\sim e^{\\beta/3}$. We also report a numerical Monte Carlo simulation of the studied memory indicating that our analytic bounds on $T_{mem}$ are tight up to constant coefficients. In order to model the ...
Method of internal 3D flow field numerical simulation for hydrodynamic torque converter
Tao SHANG; Dingxuan ZHAO; Yuankun ZHANG; Xiangen GUO; Xiangzhong SHI
2008-01-01
To enhance the performance of a hydrody-namic torque converter and thoroughly understand the trait of inside flow, a numerical simulation method of internal 3D flow for the three-element centrifugal hydrodynamic torque converter was systematically researched and expatiated in this paper. First, the internal flow field of each impeller was calculated. The curves that illustrate the relationships between the pressure differences of the inlet and outlet versus flux were drawn. Second, the concurrent working point of each impeller was approximately estimated. Finally, a calculation was performed considering the influence on each impeller. The flow field of a working point was solved by multiple calculations and the actual working condition was gradually determined. The pressure and velocity distributions of the flow field were proposed. The performance parameters of the hydrodynamic torque converter were predicted. The calculation method, and the proposed pressure and velocity distribution of the flow field, have practical significance for the design and improvement of a hydrodynamic torque converter.
A novel code for numerical 3-D MHD studies of CME expansion
J. Kleimann
2009-03-01
Full Text Available A recent third-order, essentially non-oscillatory central scheme to advance the equations of single-fluid magnetohydrodynamics (MHD in time has been implemented into a new numerical code. This code operates on a 3-D Cartesian, non-staggered grid, and is able to handle shock-like gradients without producing spurious oscillations.
To demonstrate the suitability of our code for the simulation of coronal mass ejections (CMEs and similar heliospheric transients, we present selected results from test cases and perform studies of the solar wind expansion during phases of minimum solar activity. We can demonstrate convergence of the system into a stable Parker-like steady state for both hydrodynamic and MHD winds. The model is subsequently applied to expansion studies of CME-like plasma bubbles, and their evolution is monitored until a stationary state similar to the initial one is achieved. In spite of the model's (current simplicity, we can confirm the CME's nearly self-similar evolution close to the Sun, thus highlighting the importance of detailed modelling especially at small heliospheric radii.
Additionally, alternative methods to implement boundary conditions at the coronal base, as well as strategies to ensure a solenoidal magnetic field, are discussed and evaluated.
Saleh, Mohamed Nasr
2016-01-08
Damage initiation and evolution of three-dimensional (3D) orthogonal woven carbon fibre composite (3DOWC) is investigated experimentally and numerically. Meso-scale homogenisation of the representative volume element (RVE) is utilised to predict the elastic properties, simulate damage initiation and evolution when loaded in tension. The effect of intra-yarns transverse cracking and shear diffused damage on the in-plane transverse modulus and shear modulus is investigated while one failure criterion is introduced to simulate the matrix damage. The proposed model is based on two major assumptions. First, the effect of the binder yarns, on the in-plane properties, is neglected, so the 3DOWC unit cell can be approximated as a (0o/90o) cross-ply laminate. Second, a micro-mechanics based damage approach is used at the meso-scale, so damage indicators can be correlated, explicitly, to the density of cracks within the material. Results from the simulated RVE are validated against experimental results along the warp (0o direction) and weft (90o direction). This approach paves the road for more predictive models as damage evolution laws are obtained from micro mechanical considerations and rely on few well-defined material parameters. This largely differs from classical damage mechanics approaches in which the evolution law is obtained by retrofitting experimental observations.
Influence of aggregate shapes on drying and carbonation phenomena in 3D concrete numerical samples
This study aims at generating numerical 3D samples of concrete so as to study the effects of the granular inclusions shape on the macroscopic kinetics of reactive transport phenomena. Two types of meso-structure configurations are considered: the first one is composed of a matrix of mortar in which are randomly distributed inclusions corresponding to the concrete coarse aggregates, and the second one also includes a steel rebar. The choice of a mesoscopic modeling for the mortar matrix is based on the need to obtain numerical structures of reasonable size. In particular, the Interfacial Transition Zones (ITZs) are assumed to be incorporated into the homogenized mortar properties. This study is applied to the case of drying and atmospheric carbonation by using simplified models solved by the finite element code Cast3M. The purpose is to quantify the influence of the aggregate shape on the kinetics of macroscopic transfer and the iso-value lines for some physical variables representative of the reactive transport problems: saturation degree for drying, and porosity, calcite and portlandite concentrations for carbonation. Basic aggregates shapes are studied (spheres, cubes), as well as more complex ones (Voronoi particles) which are supposed to be more representative of real aggregates. The effects of 'non-isotropic' shapes (oblate and prolate ones) are also investigated. It is shown that the influence of the aggregate shapes appears negligibly small on macroscopic indicators, except for oblate shapes with aspect ratios of 3. This latter case also exhibits substantial local delayed effects and a more important variability, which may have some importance for a precise description and estimation of degradation processes related to steel rebar corrosion. (authors)
Simulations of astrophysical dynamos
Brandenburg, Axel
2010-01-01
Numerical aspects of dynamos in periodic domains are discussed. Modifications of the solutions by numerically motivated alterations of the equations are being reviewed using the examples of magnetic hyperdiffusion and artificial diffusion when advancing the magnetic field in its Euler potential representation. The importance of using integral kernel formulations in mean-field dynamo theory is emphasized in cases where the dynamo growth rate becomes comparable with the inverse turnover time. Finally, the significance of microscopic magnetic Prandtl number in controlling the conversion from kinetic to magnetic energy is highlighted.
Geodynamic background of the 2008 Wenchuan earthquake based on 3D visco-elastic numerical modelling
Liu, Chang; Zhu, Bojing; Yang, Xiaolin; Shi, Yaolin
2016-03-01
The 2008 Wenchuan earthquake (Mw7.9) occurred in the Longmen Shan fault zone. The stress change and crustal deformation during the accumulation period is computed using 3D finite element modelling assuming visco-elastic rheology. Our results support that the eastward movement of the Tibetan Plateau resulting from the India-Eurasia collision is obstructed at the Longmen Shan fault zone by the strong Yangtze craton. In response, the Tibetan ductile crust thickens and accumulates at the contact between the Tibetan Plateau and the Sichuan Basin. This process implies a strong uplift with the rate of about 1.8 mm/a of the upper crust and induces a stress concentration nearly at the bottom of the Longmen Shan fault zone. We believe that the stress concentration in the Longmen Shan fault zone provides a very important geodynamic background of the 2008 Wenchuan earthquake. Using numerical experiments we find that the key factor controlling this stress concentration process is the large viscosity contrast in the middle and lower crusts between the Tibetan Plateau and the Sichuan Basin. The results show that large viscosity contrast in the middle and lower crusts accelerates the stress concentration in the Longmen Shan fault zone. Fast moving lower crustal flow accelerates this stress accumulation process. During the inter-seismic period, spatially the maximum stress accumulation rate of the eastern margin of the Tibetan Plateau is located nearly at the bottom of the brittle upper crust of the Longmen Shan fault zone. The spatial distribution of the stress accumulation along the strike of the Longmen Shan fault zone is as follows: the normal stress decreases while the shear stress increases from southwest to northeast along the Longmen Shan fault zone. This stress distribution explains the thrust motion in the SW and strike-slip motion in the NE during the 2008 Wenchuan earthquake.
Cédric, Guyonnet-Benaize; Fabrice, Hollender; Maria, Manakou; Alexandros, Savvaidis; Elena, Zargli; Cécile, Cornou; Nikolaos, Veranis; Dimitrios, Raptakis; Artemios, Atzemoglou; Pierre-Yves, Bard; Nikolaos, Theodulidis; Kyriazis, Pitilakis; Emmanuelle, Chaljub
2013-04-01
The Mygdonian basin, located 30 km E-NE close to Thessaloniki, is a typical active tectonic basin, trending E-NW, filled by sediments 200 to 400 m thick. This basin has been chosen as a European experimental site since 1993 (European Commission research projects - EUROSEISTEST). It has been investigated for experimental and theoretical studies on site effects. The Mygdonian basin is currently covered by a permanent seismological network and has been mainly characterized in 2D and 3D with geophysical and geotechnical studies (Bastani et al, 2011; Cadet and Savvaidis, 2011; Gurk et al, 2007; Manakou et al, 2007; Manakou et al, 2010; Pitilakis et al, 1999; Raptakis et al, 2000; Raptakis et al, 2005). All these studies allowed understanding the influence of geological structures and local site conditions on seismic site response. For these reasons, this site has been chosen for a verification exercise for numerical simulations in the framework of an ongoing international collaborative research project (Euroseistest Verification and Validation Project - E2VP). The verification phase has been made using a first 3D geophysical and geotechnical model (Manakou, 2007) about 5 km wide and 15 km long, centered on the Euroseistest site. After this verification phase, it has been decided to update, optimize and extend this model in order to obtain a more detailed model of the 3D geometry of the entire basin, especially the bedrock 3D geometry which can affect drastically the results of numerical simulations for site effect studies. In our study, we build a 3D geological model of the present-day structure of the entire Mygdonian basin. This "precise" model is 12 km wide, 65 km long and is 400 m deep in average. It has been built using geophysical, geotechnical and geological data. The database is heterogeneous and composed of hydrogeological boreholes, seismic refraction surveys, array microtremor measurements, electrical and geotechnical surveys. We propose an integrated
罗志强; 陈志敏
2013-01-01
A three-dimensional (3D) predictor-corrector finite difference method for standing wave is developed. It is applied to solve the 3D nonlinear potential flow equa-tions with a free surface. The 3D irregular tank is mapped onto a fixed cubic tank through the proper coordinate transform schemes. The cubic tank is distributed by the staggered meshgrid, and the staggered meshgrid is used to denote the variables of the flow field. The predictor-corrector finite difference method is given to develop the difference equa-tions of the dynamic boundary equation and kinematic boundary equation. Experimental results show that, using the finite difference method of the predictor-corrector scheme, the numerical solutions agree well with the published results. The wave profiles of the standing wave with different amplitudes and wave lengths are studied. The numerical solutions are also analyzed and presented graphically.
Analytical and Numerical Study of the Aharonov--Bohm Effect in 3D and 4D Abelian Higgs Model
Chernodub, M. N.; Gubarev, F. V.; Polikarpov, M.I.
1996-01-01
We discuss the Aharonov--Bohm effect in three and four dimensional non--compact lattice Abelian Higgs model. We show analytically that this effect leads to the long--range Coulomb interaction of the charged particles, which is confining in three dimensions. The Aharonov--Bohm effect is found in numerical calculations in 3D Abelian Higgs model.
Krasņikovs, A; Khabaz, A; Teļnova, I; Machanovsky, A; Klavinsh, J
2010-01-01
In the paper short glass and carbon fiber micro-mechanics in concrete matrix is under consideration. In present work was performed pull-out 3D numerical modeling. Numerical results were compared with realized experiments for single and few (fibre bundle) AR glass and carbon fibers pulling out of concrete matrix. Investigated were one fiber pull-out dynamics as well micro-stresses in the material. During performed single fiber pull out experiments were established such process mains steps: a) ...
Experimental and numerical investigation of 3D aerofoil characteristics on a MW wind turbine
Troldborg, Niels; Bak, Christian; Sørensen, Niels N.; Aagaard Madsen, Helge; Réthoré, Pierre-Elouan; Zahle, Frederik; Guntur, Srinivas
2013-01-01
3D aerofoil characteristics on a MW wind turbine is investigated through a combination of field measurements, wind tunnel tests and computational fluid dynamics (CFD). Surface pressuremeasurements as well as the integrated force coefficients for selected aerofoil sections on a blade of the turbine...... resolved 3D computations on the wind turbine as well as 2D aerofoil simulations....... is compared to wind tunnel measurements on the same aerofoil sections in order to reveal the difference in performance of aerofoils on full scale rotors in atmospheric conditions and aerofoils in wind tunnels. The findings of the measurements are backed up by analogous CFD analysis involving fully...
3D wake dynamics of the VAWT: experimental and numerical investigation
Ferreira, C.; Hofemann, C.; Dixon, K.; Kuik, G. A. M.; Van Bussel, G.J.W.
2010-01-01
The Vertical Axis Wind Turbine, in its 2D form, is characterized by a complex unsteady aerodynamic flow, including dynamic stall and blade vortex interaction. Adding to this complexity, the 3D flow causes spanwise effects and the presence of trailing vorticity and tip vortices. The objective of the current paper is to bring insight into the 3D development of the near wake of a H-VAWT, understanding: • The spanwise blade load distribution in the upwind and the downwind blade passages. • The tr...
Kim, Jungkwun; Yoon, Yong-Kyu; Allen, Mark G.
2016-03-01
This paper presents a computer-numerical-controlled ultraviolet light-emitting diode (CNC UV-LED) lithography scheme for three-dimensional (3D) microfabrication. The CNC lithography scheme utilizes sequential multi-angled UV light exposures along with a synchronized switchable UV light source to create arbitrary 3D light traces, which are transferred into the photosensitive resist. The system comprises a switchable, movable UV-LED array as a light source, a motorized tilt-rotational sample holder, and a computer-control unit. System operation is such that the tilt-rotational sample holder moves in a pre-programmed routine, and the UV-LED is illuminated only at desired positions of the sample holder during the desired time period, enabling the formation of complex 3D microstructures. This facilitates easy fabrication of complex 3D structures, which otherwise would have required multiple manual exposure steps as in the previous multidirectional 3D UV lithography approach. Since it is batch processed, processing time is far less than that of the 3D printing approach at the expense of some reduction in the degree of achievable 3D structure complexity. In order to produce uniform light intensity from the arrayed LED light source, the UV-LED array stage has been kept rotating during exposure. UV-LED 3D fabrication capability was demonstrated through a plurality of complex structures such as V-shaped micropillars, micropanels, a micro-‘hi’ structure, a micro-‘cat’s claw,’ a micro-‘horn,’ a micro-‘calla lily,’ a micro-‘cowboy’s hat,’ and a micro-‘table napkin’ array.
This paper presents a computer-numerical-controlled ultraviolet light-emitting diode (CNC UV-LED) lithography scheme for three-dimensional (3D) microfabrication. The CNC lithography scheme utilizes sequential multi-angled UV light exposures along with a synchronized switchable UV light source to create arbitrary 3D light traces, which are transferred into the photosensitive resist. The system comprises a switchable, movable UV-LED array as a light source, a motorized tilt-rotational sample holder, and a computer-control unit. System operation is such that the tilt-rotational sample holder moves in a pre-programmed routine, and the UV-LED is illuminated only at desired positions of the sample holder during the desired time period, enabling the formation of complex 3D microstructures. This facilitates easy fabrication of complex 3D structures, which otherwise would have required multiple manual exposure steps as in the previous multidirectional 3D UV lithography approach. Since it is batch processed, processing time is far less than that of the 3D printing approach at the expense of some reduction in the degree of achievable 3D structure complexity. In order to produce uniform light intensity from the arrayed LED light source, the UV-LED array stage has been kept rotating during exposure. UV-LED 3D fabrication capability was demonstrated through a plurality of complex structures such as V-shaped micropillars, micropanels, a micro-‘hi’ structure, a micro-‘cat’s claw,’ a micro-‘horn,’ a micro-‘calla lily,’ a micro-‘cowboy’s hat,’ and a micro-‘table napkin’ array. (paper)
Some Methods of Applied Numerical Analysis to 3d Facial Reconstruction Software
Roşu, Şerban; Ianeş, Emilia; Roşu, Doina
2010-09-01
This paper deals with the collective work performed by medical doctors from the University Of Medicine and Pharmacy Timisoara and engineers from the Politechnical Institute Timisoara in the effort to create the first Romanian 3d reconstruction software based on CT or MRI scans and to test the created software in clinical practice.
Mechanical Modelling of Pultrusion Process: 2D and 3D Numerical Approaches
Baran, Ismet; Hattel, Jesper Henri; Akkerman, Remko;
2015-01-01
mechanical analysis should be performed. In the present work, the two dimensional (2D) quasi-static plane strain mechanical model for the pultrusion of a thick square profile developed by the authors is further improved using generalized plane strain elements. In addition to that, a more advanced 3D thermo...
Numerical Simulation of Injection Molding Cooling Process Based on 3D Surface Model
CUIShu-biao; ZHOUHua-min; LIDe-qun
2004-01-01
The design of the coohng system of injection molds directly affects both productivity and the quality of the final part. Using the cooling process CAE system to instruct the mold design, the efficiency and quality of design can be improved greatly. At the same time, it is helpful to confirm the cooling system structure and optimize the process conditions. In this paper, the 3D surface model of mold cavity is used to replace the middle-plane model in the simulation by Boundary Element Method, which break the bottleneck of the application of the injection molding simulation softwares base on the middle-plane model. With the improvements of this paper, a practical and commercial simulation software of injection molding cooling process named as HsCAE3D6.0 is developed.
Numerical simulation of the filling stage in injection molding based on a 3D model
GENG Tie; LI De-qun; ZHOU Hua-min
2005-01-01
Most injection molded parts are three-dimensional, with complex geometrical configurations and thick/thin wall sections. The change of the thickness of parts has significant influence on flow during injection molding. This paper presents a 3D finite element model to deal with the three-dimensional flow, which can more accurately predict the filling process than a 2. 5D model. In this model, equal-order velocity-pressure interpolation method is successfully employed and the relation between velocity and pressure is obtained from the discretized momentum equation in order to derive the pressure equation. A 3D control volume scheme is employed to track the flow front. The validity of the model has been tested through the analysis of the flow in a cavity.
Cross-Wire Calibration for Freehand 3D Ultrasonography: Measurement and Numerical Issues
J. Jan
2005-06-01
Full Text Available 3D freehand ultrasound is an imaging technique, which is graduallyfinding clinical applications. A position sensor is attached to aconventional ultrasound probe, so that B-scans are acquired along withtheir relative locations. This allows the B-scans to be inserted into a3D regular voxel array, which can then be visualized usingarbitrary-plane slicing, and volume or surface rendering. A keyrequirement for correct reconstruction is the calibration: determiningthe position and orientation of the B-scans with respect to theposition sensor's receiver. Following calibration, interpolation in theset of irregularly spaced B-scans is required to reconstruct aregular-voxel array. This text describes a freehand measurement of 2Dultrasonic data, an approach to the calibration problem and severalnumerical issues concerned with the calibration and reconstruction.
Twisting Rolls. An Heuristic Model and 3D Numerical Simulations of Vortex Patterns
Bouali, Safieddine
2003-01-01
We connect an appropriate feedback loop to a model of 2D vertical eddy of airflow which unfolds a wide range of vorticity behavior. Computational fluid dynamics of the twisted roll display a class of long lifespan 3D vortices. On the one hand, the infinitely stable columnar vortex simulated describes waterspouts and tornadoes with extended lifetime. On the other hand, a light modification of the retroaction exhibits strong similarities to tropical cyclones. Moreover, we investigate the outcom...
Soil-structure interaction during tunnelling in urban area: observations and 3D numerical modelling
Fargnoli, Valentina
2015-01-01
This work illustrates a soil-tunnel-structure interaction study performed by an integrated,geotechnical and structural,approach based on 3D finite element analyses and validated against experimental observations.The study aims at analysing the response of reinforced concrete framed buildings on discrete foundations in interaction with metro lines.It refers to the case of the twin tunnels of the Milan (Italy) metro line 5,recently built in coarse grained materials using EPB machines,for which ...
Comment on "Numerical Study on Aging Dynamics in the 3D Ising Spin Glass Model"
Marinari, Enzo; Parisi, Giorgio; Ruiz-Lorenzo, Juan J.
1999-01-01
We show that the dynamical behavior of the 3D Ising spin glass with Gaussian couplings is not compatible with a droplet dynamics. We show that this is implied from the data of reference cond-mat/9904143, that, when analyzed in an accurate way, give multiple evidences of this fact. Our study is based on the analysis of the overlap-overlap correlation function, at different values of the separation r and of the time t.
Mandumpala Devassy, B.; Edelbauer, W.; Greif, D.
2015-12-01
Cavitation and its effect on spray formation and its dispersion play a crucial role in proper engine combustion and controlled emission. This study focuses on these effects in a typical common rail 6-hole diesel injector accounting for 3D needle movement and flow compressibility effects. Coupled numerical simulations using 1D and 3D CFD codes are used for this investigation. Previous studies in this direction have already presented a detailed structure of the adopted methodology. Compared to the previous analysis, the present study investigates the effect of 3D needle movement and cavitation on the spray formation for pilot and main injection events for a typical diesel engine operating point. The present setup performs a 3D compressible multiphase simulation coupled with a standalone 1D high pressure flow simulation. The simulation proceeds by the mutual communication between 1D and 3D solvers. In this work a typical common rail injector with a mini-sac nozzle is studied. The lateral and radial movement of the needle and its effect on the cavitation generation and the subsequent spray penetration are analyzed. The result indicates the effect of compressibility of the liquid on damping the needle forces, and also the difference in the spray penetration levels due to the asymmetrical flow field. Therefore, this work intends to provide an efficient and user-friendly engineering tool for simulating a complete fuel injector including spray propagation.
3D Numerical Simulation on the Sloshing Waves Excited by the Seismic Shacking
Zhang, Lin; Wu, Tso-Ren
2016-04-01
In the event of 2015 Nepal earthquake, a video clip broadcasted worldwide showed a violent water spilling in a hotel swimming pool. This sloshing phenomenon indicates a potential water loss in the sensitive facilities, e.g. the spent fuel pools in nuclear power plant, has to be taken into account carefully under the consideration of seismic-induced ground acceleration. In the previous studies, the simulation of sloshing mainly focused on the pressure force on the structure by using a simplified Spring-Mass Method developed in the field of solid mechanics. However, restricted by the assumptions of plane water surface and limited wave height, significant error will be made in evaluating the amount of water loss in the tank. In this paper, the computational fluid dynamical model, Splash3D, was adopted for studying the sloshing problem accurately. Splash3D solved 3D Navier-Stokes Equation directly with Large-Eddy Simulation (LES) turbulent closure. The Volume-of-fluid (VOF) method with piecewise linear interface calculation (PLIC) was used to track the complex breaking water surface. The time series acceleration of a design seismic was loaded to excite the water. With few restrictions from the assumptions, the accuracy of the simulation results were improved dramatically. A series model validations were conducted by compared to a 2D theoretical solution, and a 3D experimental data. Good comparisons can be seen. After the validation, we performed the simulation for considering a sloshing case in a rectangular water tank with a dimension of 12 m long, 8 m wide, 8 m deep, which contained water with 7 m in depth. The seismic movement was imported by considering time-series acceleration in three dimensions, which were about 0.5 g to 1.2 g in the horizontal directions, and 0.3 g to 1 g in the vertical direction. We focused the discussions on the kinematics of the water surface, wave breaking, velocity field, pressure field, water force on the side walls, and, most
A hybrid experimental-numerical technique for determining 3D velocity fields from planar 2D PIV data
Eden, A.; Sigurdson, M.; Mezić, I.; Meinhart, C. D.
2016-09-01
Knowledge of 3D, three component velocity fields is central to the understanding and development of effective microfluidic devices for lab-on-chip mixing applications. In this paper we present a hybrid experimental-numerical method for the generation of 3D flow information from 2D particle image velocimetry (PIV) experimental data and finite element simulations of an alternating current electrothermal (ACET) micromixer. A numerical least-squares optimization algorithm is applied to a theory-based 3D multiphysics simulation in conjunction with 2D PIV data to generate an improved estimation of the steady state velocity field. This 3D velocity field can be used to assess mixing phenomena more accurately than would be possible through simulation alone. Our technique can also be used to estimate uncertain quantities in experimental situations by fitting the gathered field data to a simulated physical model. The optimization algorithm reduced the root-mean-squared difference between the experimental and simulated velocity fields in the target region by more than a factor of 4, resulting in an average error less than 12% of the average velocity magnitude.
Numerical Simulation and Experimental Investigation of 3-D Separated Flow Field around a Blunt Body
无
1999-01-01
@@Motivated by re-designing a fuselage in engineering application, the numerical and experimental investigation of the separated flow field around a special blunt body is described in this thesis. The aerodynamic response of the blunt body is successively studied. The thesis consists of four parts: the numerical simulation of the flow field around a two-dimensional blunt body; the numerical simulation of the flow field around a three-dimensional blunt body; the flow
Numerical simulation of complex 3D compressible viscous flows through rotating blade passage
Despotović M.; Babić Milun; Milovanović D.; Šušteršič Vanja
2003-01-01
This paper describes a three-dimensional compressible Navier-Stokes code, which has been developed for analysis of turbocompressor blade rows and other internal flows. Despite numerous numerical techniques and statement that Computational Fluid Dynamics has reached state of the art, issues related to successful simulations represent valuable database of how particular technique behave for a specifie problem. This paper deals with rapid numerical method accurate enough to be used as a design ...
Numerical Simulations of High-Frequency Respiratory Flows in 2D and 3D Lung Bifurcation Models
Chen, Zixi; Parameswaran, Shamini; Hu, Yingying; He, Zhaoming; Raj, Rishi; Parameswaran, Siva
2014-07-01
To better understand the human pulmonary system and optimize the high-frequency oscillatory ventilation (HFOV) design, numerical simulations were conducted under normal breathing frequency and HFOV condition using a CFD code Ansys Fluent and its user-defined C programs. 2D and 3D double bifurcating lung models were created, and the geometry corresponds to fifth to seventh generations of airways with the dimensions based on the Weibel's pulmonary model. Computations were carried out for different Reynolds numbers (Re = 400 and 1000) and Womersley numbers (α = 4 and 16) to study the air flow fields, gas transportation, and wall shear stresses in the lung airways. Flow structure was compared with experimental results. Both 2D and 3D numerical models successfully reproduced many results observed in the experiment. The oxygen concentration distribution in the lung model was investigated to analyze the influence of flow oscillation on gas transport inside the lung model.
Melnikov N. N.
2016-03-01
Full Text Available The paper presents results on 3D numerical calculation of a thermal task related to assessing a thawing area when placing modules with reactor and steam-turbine facility of a small nuclear power plant in thickness of permafrost rocks. The paper discusses influence of the coefficient of thermal conductivity for large-scaled underground excavations lining and cryolithic area porosity on thawing depth and front movement velocity under different spatial directions
Rincon, F; Schekochihin, A A; Valentini, F
2015-01-01
Magnetic fields pervade the entire Universe and, through their dynamical interactions with matter, affect the formation and evolution of astrophysical systems from cosmological to planetary scales. How primordial cosmological seed fields arose and were further amplified to $\\mu$Gauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions and on scales of at least tens of kiloparsecs, is a major theoretical puzzle still largely unconstrained by observations. Extragalactic plasmas are weakly collisional (as opposed to collisional magnetohydrodynamic fluids), and whether magnetic-field growth and its sustainment through an efficient dynamo instability driven by chaotic motions is possible in such plasmas is not known. Fully kinetic numerical simulations of the Vlasov equation in a six-dimensional phase space necessary to answer this question have until recently remained beyond computational capabilities. Here, we show by means of such simulations that magnetic-field a...
NUMERICAL SIMULATION OF 3-D FLOW FIELD IN ARCIFORM PLUNGE POOL
无
2002-01-01
The 3-D complex turbulent flow fields in aplunge pool with arciform bottom are simulated by using thek-ε model in body-fitted coordinates. The calculated results re-veal the flow characteristics in the arciform plunge pool underthe different flood discharge conditions, which can not be easi-ly obtained in the physical model test because the measure-ment of the complex velocity is very difficult. The calculatedflow fields are helpful to understand in depth the hydrauliccharacteristics of plunge pool. The calculated and the meas-ured pressure distributions on the pool bottom are comparedand in good agreement.
Numerical computation of critical properties and atomic basins from 3D grid electron densities
Katan, C; Lecomte, C; Guezo, M; Oison, V; Souhassou, M
2003-01-01
InteGriTy is a software package that performs topological analysis following AIM approach on electron densities given on 3D grids. Use of tricubic interpolation is made to get the density, its gradient and hessian matrix at any required position. Critical points and integrated atomic properties have been derived from theoretical densities calculated for the compounds NaCl and TTF-2,5Cl2BQ, thus covering the different kinds of chemical bonds: ionic, covalent, hydrogen bonds and other intermolecular contacts.
Sofronov, I.D.; Voronin, B.L.; Butnev, O.I. [VNIIEF (Russian Federation)] [and others
1997-12-31
The aim of the work performed is to develop a 3D parallel program for numerical calculation of gas dynamics problem with heat conductivity on distributed memory computational systems (CS), satisfying the condition of numerical result independence from the number of processors involved. Two basically different approaches to the structure of massive parallel computations have been developed. The first approach uses the 3D data matrix decomposition reconstructed at temporal cycle and is a development of parallelization algorithms for multiprocessor CS with shareable memory. The second approach is based on using a 3D data matrix decomposition not reconstructed during a temporal cycle. The program was developed on 8-processor CS MP-3 made in VNIIEF and was adapted to a massive parallel CS Meiko-2 in LLNL by joint efforts of VNIIEF and LLNL staffs. A large number of numerical experiments has been carried out with different number of processors up to 256 and the efficiency of parallelization has been evaluated in dependence on processor number and their parameters.
3D Numerical Simulation of Overbank Flow in Non-Orthogonal Curvilinear Coordinates
ZHANG Ming-liang; SHEN Yong-ming; WU Xiu-guang
2005-01-01
The velocity field in meandering compound channels with overbank flow is highly three dimensional. To date, its features have been investigated experimentally and little research has been undertaken to investigate the feasibility of reproducing these velocity fields with computer models. If computer modeling were to prove successful in this context, it could become a useful prediction technique and research tool to enhance our understanding of natural river dynamics. A 3-D k-ε turbulence hydrodynamic model in curvilinear coordinates is established to simulate the overbank flow. The body-fitted coordinate is adopted in the horizontal plane, the part grid is adopted in the vertical direction, and the wall-function method is employed to simulate the bed resistance. The model is applied to the simulation of the meandering channel with straight flood plain banks, and the main velocities and secondary velocities for both the longitudinal and cross sections are presented. Comparison and analysis show that the results of simulation are fit to reflect the results of experiment. These results show the application value of the model to 3D overbank flow.
Numerical and Experimental Verification of a 3D Quasi-Optical System
Zejian Lu
2015-01-01
Full Text Available A modular and efficient Gaussian beam (GB analysis method, incorporating frame-based Gabor transformation, GB reflection, and a 3D GB diffraction technique, was developed to analyze both the reflectors and frequency selective surface (FSS in quasi-optical (QO system. To validate this analysis method, a 3D dual-channel QO system operating at 183 and 325 GHz was designed and tested. The proposed QO system employs two-layer structure with a FSS of perforated hexagonal array transmitting the 325 GHz signal on the top layer while diverting the 183 GHz signal to the bottom layer. Measured results of the system demonstrate that the agreement can be achieved down to −30 dB signal level for both channels in the far field pattern. The discrepancy between the calculation and measurement is within 2 dB in the main beam region (2.5 times −3 dB beamwidth, verifying the effectiveness and accuracy of the proposed method.
Analytical and numerical aspects in solving the controlled 3D Gross-Pitaevskii equation
The results of recently developed investigations, that have been carried out within the framework of the controlling potential method (CPM), are reviewed. This method allows one to decompose a three dimensional (3D) Gross-Pitaevskii equation (GPE) into the pair of coupled Schroedinger-type equations. Under suitable mathematical conditions, the solutions of the 3D controlled GPE can be constructed from the solutions of a 2D linear Schroedinger equation (the transverse component of the GPE) coupled with a 1D nonlinear Schroedinger equation (the longitudinal component of the GPE). Such decomposition allows one to cast the solutions in the form of the product of the solutions of the transverse and the longitudinal components of the GPE. The coupling between these two equations is the functional of both the transverse and the longitudinal profiles. It is shown that the CPM can be used to obtain a new class of three-dimensional solitary waves solutions of the GPE, which governs the dynamics of Bose-Einstein condensates. By imposing an external controlling potential, the desired time-dependent shape of the localized BECs is obtained. The stability of the exact solutions was checked with direct simulations of the time -dependent, three-dimensional GPE. Our simulations show that the localized condensates are stable with respect to perturbed initial conditions.
Ash3d: A finite-volume, conservative numerical model for ash transport and tephra deposition
Schwaiger, Hans F.; Denlinger, Roger P.; Mastin, Larry G.
2012-01-01
We develop a transient, 3-D Eulerian model (Ash3d) to predict airborne volcanic ash concentration and tephra deposition during volcanic eruptions. This model simulates downwind advection, turbulent diffusion, and settling of ash injected into the atmosphere by a volcanic eruption column. Ash advection is calculated using time-varying pre-existing wind data and a robust, high-order, finite-volume method. Our routine is mass-conservative and uses the coordinate system of the wind data, either a Cartesian system local to the volcano or a global spherical system for the Earth. Volcanic ash is specified with an arbitrary number of grain sizes, which affects the fall velocity, distribution and duration of transport. Above the source volcano, the vertical mass distribution with elevation is calculated using a Suzuki distribution for a given plume height, eruptive volume, and eruption duration. Multiple eruptions separated in time may be included in a single simulation. We test the model using analytical solutions for transport. Comparisons of the predicted and observed ash distributions for the 18 August 1992 eruption of Mt. Spurr in Alaska demonstrate to the efficacy and efficiency of the routine.
Strong Field Spherical Dynamos
Dormy, Emmanuel
2014-01-01
Numerical models of the geodynamo are usually classified in two categories: those denominated dipolar modes, observed when the inertial term is small enough, and multipolar fluctuating dynamos, for stronger forcing. I show that a third dynamo branch corresponding to a dominant force balance between the Coriolis force and the Lorentz force can be produced numerically. This force balance is usually referred to as the strong field limit. This solution co-exists with the often described viscous branch. Direct numerical simulations exhibit a transition from a weak-field dynamo branch, in which viscous effects set the dominant length scale, and the strong field branch in which viscous and inertial effects are largely negligible. These results indicate that a distinguished limit needs to be sought to produce numerical models relevant to the geodynamo and that the usual approach of minimizing the magnetic Prandtl number (ratio of the fluid kinematic viscosity to its magnetic diffusivity) at a given Ekman number is mi...
Numerical simulation of complex 3D compressible viscous flows through rotating blade passage
Despotović M.
2003-01-01
Full Text Available This paper describes a three-dimensional compressible Navier-Stokes code, which has been developed for analysis of turbocompressor blade rows and other internal flows. Despite numerous numerical techniques and statement that Computational Fluid Dynamics has reached state of the art, issues related to successful simulations represent valuable database of how particular technique behave for a specifie problem. This paper deals with rapid numerical method accurate enough to be used as a design tool. The mathematical model is based on System of Favre averaged Navier-Stokes equations that are written in relative frame of reference, which rotates with constant angular velocity around axis of rotation. The governing equations are solved using finite volume method applied on structured grids. The numerical procedure is based on the explicit multistage Runge-Kutta scheme that is coupled with modem numerical procedures for convergence acceleration. To demonstrate the accuracy of the described numerical method developed software is applied to numerical analysis of flow through impeller of axial turbocompressor, and obtained results are compared with available experimental data.
Discrete 3D model as complimentary numerical testing for anisotropic damage
DELAPLACE, Arnaud; Desmorat, Rodrigue
2008-01-01
It is proposed to use a discrete particle model as a complimentary “numerical testing machine” to identify the hydrostatic elasticity-damage coupling and the corresponding sensitivity to hydrostatic stresses parameter. Experimental tri-axial tensile testing is difficult to perform on concrete material, and numerical testing proves then its efficiency. The discrete model used for this purpose is based on a Voronoi assembly that naturally takes into account heterogeneity. Tri-tension tests on a...
NUMERICAL MODELING FOR POSITIVE AND INVERSE PROBLEMS OF 3-D SEEPAGE IN DOUBLE FRACTURED MEDIA
ZHOU Zhi-fang; GUO Geng-xin
2005-01-01
Three-dimensional seepage in double fractured media was modeled in this paper.The determination of hydraulic conductivity tensor of rock mass is a vital problem for the sea water intrusion or sea water encroachment and seepage of fissured medium.According to the geological and hydrogeological conditions for the 2nd-stage construction of the Three Gorges Project (TGP), the physical and mathematical models for the groundwater movement through the 3D double fractured media of rock mass during construction were established in this paper.Based on discontinuity-control inverse theory, some related parameters of double fractured media were inversed with flux being the known quantity and calibration of water table the objective function.Synchronously, the seepage field of the construction region was systematically analyzed and simulated, the results of which exhibit that the double fractured media model of fracture water can comprehensively and correctly describe the geological and hydrogeological conditions in the construction region.
Mechanism of local dynamo action on the Sun
Kitiashvili, I N; Mansour, N N; Wray, A A
2013-01-01
In the quiet Sun, magnetic fields are usually observed as small-scale magnetic elements, `salt and pepper', covering the entire solar surface. By using 3D radiative MHD numerical simulations we demonstrate that these fields are a result of local dynamo action in the top layers of the convection zone, where extremely weak `seed' magnetic fields can locally grow above the mean equipartition field (e.g., from a $10^{-6}$ G `seed' field to more than 1000 G magnetic structures). We find that the local dynamo action takes place only in a shallow, about 500 km deep, subsurface layer, from which the generated field is transported into deeper layers by convection downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and the horizontal fields above the photosphere can be explained by multi-scale magnetic loops produced by the dynamo.
Internal wave attractors examined using laboratory experiments and 3D numerical simulations
Brouzet, Christophe; Scolan, H; Ermanyuk, E V; Dauxois, Thierry
2016-01-01
In the present paper, we combine numerical and experimental approaches to study the dynamics of stable and unstable internal wave attractors. The problem is considered in a classic trapezoidal setup filled with a uniformly stratified fluid. Energy is injected into the system at global scale by the small-amplitude motion of a vertical wall. Wave motion in the test tank is measured with the help of conventional synthetic schlieren and PIV techniques. The numerical setup closely reproduces the experimental one in terms of geometry and the operational range of the Reynolds and Schmidt numbers. The spectral element method is used as a numerical tool to simulate the nonlinear dynamics of a viscous salt-stratified fluid. We show that the results of three-dimensional calculations are in excellent qualitative and quantitative agreement with the experimental data, including the spatial and temporal parameters of the secondary waves produced by triadic resonance instability. Further, we explore experimentally and numeri...
NUMERICAL SIMULATION OF 3-D TURBULENT FLOW IN THE MULTI- INTAKES SUMP OF THE PUMP STATION
CHEN Hong-xun; GUO Jia-hong
2007-01-01
In this article, a numerical model for three-dimensional turbulent flow in the sump of the pump station was presented. A reasonable boundary condition for the flow in the sump with several water intakes at different flow rates was proposed. The finite volume method was employed to solve the governing equations with the body fitted grid generated by the multi-block grid technique. By using the Fluent software, the fluid flow in a model sump of the pump station was calculated. Compared with the experimental result, the numerical result of the example is fairly good.
NUMERICAL SIMULATION OF 3-D REAERATION IN BODY-FITTED COORDINATE SYSTEM
Fang Xiang-wei; Chen Gang; Shen Chun-ni; Chen Zheng-han; Li Jian-zhong
2003-01-01
A three-dimensional numerical model was developed to simulate reaeration using a body-fitted coordinate system. The model was designed to calculate the velocity and oxygen concentration separately, called,"no pairing resolution". The velocity was calculated by SIMPLEC algorithm in the body-fitted coordinate system. The considerably proposed model was checked by a reaeration experiment couducted in an open channel. The computed results agree considerably well with the experimental data. The model was also used to predict the reaeration in an S-shaped channel, and the numerical results are discussed.
Decker, J.; Peysson, Y
2004-12-01
A new original code for solving the 3-D relativistic and bounce-averaged electron drift kinetic equation is presented. It designed for the current drive problem in tokamak with an arbitrary magnetic equilibrium. This tool allows self-consistent calculations of the bootstrap current in presence of other external current sources. RF current drive for arbitrary type of waves may be used. Several moments of the electron distribution function are determined, like the exact and effective fractions of trapped electrons, the plasma current, absorbed RF power, runaway and magnetic ripple loss rates and non-thermal Bremsstrahlung. Advanced numerical techniques have been used to make it the first fully implicit (reverse time) 3-D solver, particularly well designed for implementation in a chain of code for realistic current drive calculations in high {beta}{sub p} plasmas. All the details of the physics background and the numerical scheme are presented, as well a some examples to illustrate main code capabilities. Several important numerical points are addressed concerning code stability and potential numerical and physical limitations. (authors)
Rusanov, A.V.; Yershov, S.V. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1997-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
A new original code for solving the 3-D relativistic and bounce-averaged electron drift kinetic equation is presented. It designed for the current drive problem in tokamak with an arbitrary magnetic equilibrium. This tool allows self-consistent calculations of the bootstrap current in presence of other external current sources. RF current drive for arbitrary type of waves may be used. Several moments of the electron distribution function are determined, like the exact and effective fractions of trapped electrons, the plasma current, absorbed RF power, runaway and magnetic ripple loss rates and non-thermal Bremsstrahlung. Advanced numerical techniques have been used to make it the first fully implicit (reverse time) 3-D solver, particularly well designed for implementation in a chain of code for realistic current drive calculations in high βp plasmas. All the details of the physics background and the numerical scheme are presented, as well a some examples to illustrate main code capabilities. Several important numerical points are addressed concerning code stability and potential numerical and physical limitations. (authors)
A Direct Numerical Reconstruction Algorithm for the 3D Calderón Problem
Delbary, Fabrice; Hansen, Per Christian; Knudsen, Kim
2011-01-01
In three dimensions Calderón's problem was addressed and solved in theory in the 1980s in a series of papers, but only recently the numerical implementation of the algorithm was initiated. The main ingredients in the solution of the problem are complex geometrical optics solutions to the conducti...
A numerical study of the 3D random interchange and random loop models
Barp, Alessandro; Barp, Edoardo Gabriele; Briol, François-Xavier; Ueltschi, Daniel
2015-08-01
We have studied numerically the random interchange model and related loop models on the three-dimensional cubic lattice. We have determined the transition time for the occurrence of long loops. The joint distribution of the lengths of long loops is Poisson-Dirichlet with parameter 1 or \\frac{1}{2}.
Numerical scheme for riser motion calculation during 3-D VIV simulation
Huang, Kevin; Chen, Hamn-Ching; Chen, Chia-Rong
2011-10-01
This paper presents a numerical scheme for riser motion calculation and its application to riser VIV simulations. The discretisation of the governing differential equation is studied first. The top tensioned risers are simplified as tensioned beams. A centered space and forward time finite difference scheme is derived from the governing equations of motion. Then an implicit method is adopted for better numerical stability. The method meets von Neumann criteria and is shown to be unconditionally stable. The discretized linear algebraic equations are solved using a LU decomposition method. This approach is then applied to a series of benchmark cases with known solutions. The comparisons show good agreement. Finally the method is applied to practical riser VIV simulations. The studied cases cover a wide range of riser VIV problems, i.e. different riser outer diameter, length, tensioning conditions, and current profiles. Reasonable agreement is obtained between the numerical simulations and experimental data on riser motions and cross-flow VIV a/D . These validations and comparisons confirm that the present numerical scheme for riser motion calculation is valid and effective for long riser VIV simulation.
Research on the Inner Water Flow Field in a Hydrocyclone by the Method of 3D Numerical Simulation
Hui Li
2013-01-01
Full Text Available The inner water flow field in a hydrocyclone was simulated by the software of computational fluid dynamics-FLUENT, using RSM turbulent model. The air core, 3D velocity field distribution and pressure field distribution were simulated and contrasted with experimental results. The results indicated that the air core was through from the inlet to the outlet. The simulated 3D velocity field distribution was consistent with the results obtained by the experiments. The axial symmetry of pressure field distribution was quite good and the pressure gradient was very large. All these results tested the reliability of the method of numerical simulation and provided a reference for the further research of solid-liquid separation and the optimizing design of the hydrocyclone.
3D micromanipulation at low numerical aperture with a single light beam: the focused-Bessel trap.
Ayala, Yareni A; Arzola, Alejandro V; Volke-Sepúlveda, Karen
2016-02-01
Full-three-dimensional (3D) manipulation of individual glass beads with radii in the range of 2-8 μm is experimentally demonstrated by using a single Bessel light beam focused through a low-numerical-aperture lens (NA=0.40). Although we have a weight-assisted trap with the beam propagating upward, we obtain a stable equilibrium position well away from the walls of the sample cell, and we are able to move the particle across the entire cell in three dimensions. A theoretical analysis for the optical field and trapping forces along the lateral and axial directions is presented for the focused-Bessel trap. This trap offers advantages for 3D manipulation, such as an extended working distance, a large field of view, and reduced aberrations. PMID:26907437
Robustness of numerical TIG welding simulation of 3D structures in stainless steel 316L
The numerical welding simulation is considered to be one of those mechanical problems that have the great level of nonlinearity and which requires a good knowledge in various scientific fields. The 'Robustness Analysis' is a suitable tool to control the quality and guarantee the reliability of numerical welding results. The robustness of a numerical simulation of welding is related to the sensitivity of the modelling assumptions on the input parameters. A simulation is known as robust if the result that it produces is not very sensitive to uncertainties of the input data. The term 'Robust' was coined in statistics by G.E.P. Box in 1953. Various definitions of greater or lesser mathematical rigor are possible for the term, but in general, referring to a statistical estimator, it means 'insensitive to small deviation from the idealized assumptions for which the estimator is optimized. In order to evaluate the robustness of numerical welding simulation, sensitivity analyses on thermomechanical models and parameters have been conducted. At the first step, we research a reference solution which gives the best agreement with the thermal and mechanical experimental results. The second step consists in determining through numerical simulations which parameters have the largest influence on residual stresses induced by the welding process. The residual stresses were predicted using finite element method performed with Code-Aster of EDF and SYSWELD of ESI-GROUP. An analysis of robustness can prove to be heavy and expensive making it an unjustifiable route. However, only with development such tool of analysis can predictive methods become a useful tool for industry. (author)
Numerical simulation on the evolution of cloud particles in 3-D convective cloud
LIU XiaoLi; NIU ShengJie
2009-01-01
A 3-D convective cloud model with compressible non-hydrostatic dynamics and the spectral bin microphysics of a 2-D slab-symmetric model has been used to simulate an observed supercell storm occurring on 29 June, 2000 near Bird City, Kansas, USA. The main objective of this paper is to study the evolution of particles in this convective storm with bin spectral microphysics scheme. Graupels form and grow through two mechanisms, deposition and riming, with the riming process dominant on top of the inflow and in the upper portion of main updraft. Over the outflow and during the developing and mature stages of the storm, graupel particles mainly grow through deposition with dominant unimodal spectra. Most fall out after growing up. Reducing initial relative humidity disturbance (increasing initial potential temperature disturbance) has negative impact on the formation and growth of graupels over the inflow (outflow). This study shows that large graupel and hail could be suppressed by altering the deposition and coalescence process over the inflow and main updraft. At different locations of the convective cells and with different initial humidity and potential temperature disturbance, the graupel formation and growth mechanisms are different, so as to the feasible hail suppression locations and methods.
Spent Fuel Ratio Estimates from Numerical Models in ALE3D
Margraf, J. D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Dunn, T. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-08-02
Potential threat of intentional sabotage of spent nuclear fuel storage facilities is of significant importance to national security. Paramount is the study of focused energy attacks on these materials and the potential release of aerosolized hazardous particulates into the environment. Depleted uranium oxide (DUO_{2}) is often chosen as a surrogate material for testing due to the unreasonable cost and safety demands for conducting full-scale tests with real spent nuclear fuel. To account for differences in mechanical response resulting in changes to particle distribution it is necessary to scale the DUO_{2} results to get a proper measure for spent fuel. This is accomplished with the spent fuel ratio (SFR), the ratio of respirable aerosol mass released due to identical damage conditions between a spent fuel and a surrogate material like depleted uranium oxide (DUO_{2}). A very limited number of full-scale experiments have been carried out to capture this data, and the oft questioned validity of the results typically leads to overly-conservative risk estimates. In the present work, the ALE3D hydrocode is used to simulate DUO_{2} and spent nuclear fuel pellets impacted by metal jets. The results demonstrate an alternative approach to estimate the respirable release fraction of fragmented nuclear fuel.
3D Numerical Simulations of AGN Outflows in Clusters and Groups
Gaspari, M; Brighenti, F; D'Ercole, A
2009-01-01
We compute 3D gasdynamical models of jet outflows from the central AGN, that carry mass as well as energy to the hot gas in galaxy clusters and groups. These flows have many attractive attributes for solving the cooling flow problem: why the hot gas temperature and density profiles resemble cooling flows but show no spectral evidence of cooling to low temperatures. Subrelativistic jets, described by a few parameters, are assumed to be activated when gas flows toward or cools near a central SMBH. Using approximate models for a rich cluster (A1795), a poor cluster (2A 0336+096) and a group (NGC 5044), we show that mass-carrying jets with intermediate mechanical efficiencies ($\\sim10^{-3}$) can reduce for many Gyr the global cooling rate to or below the low values implied by X-spectra, while maintaining $T$ and $\\rho$ profiles similar to those observed, at least in clusters. Groups are much more sensitive to AGN heating and present extreme time variability in both profiles. Finally, the intermittency of the feed...
RFX first wall thermal power handling: 3D numerical models and experimental validations
One of the emerging issues for future thermonuclear devices is the non-uniform power deposition on the first wall or divertor surfaces. The localized peaks of power are detrimental both for the lifetime of the plasma facing components and for plasma heating and confinement. The thermal monitoring of the first wall can be done with temperature measurements acquired during the experiments by means of thermocouples and/or infrared camera images. If the measurement system is integrated with analytical or numerical models, it is possible to estimate the applied thermal loads and to obtain a thorough knowledge of the thermal behaviour of the first wall and vacuum vessel system. The numerical model developed for the RFX machine is hereby described and validated by means of comparisons with IR camera and thermocouple temperature measurements
GeoFlow: 3D numerical simulation of supercritical thermal convective states
Futterer, B; Egbers, C [Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus, Siemens-Halske-Ring 14, 03046 Cottbus (Germany); Hollerbach, R [Department of Applied Mathematics, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT (United Kingdom)], E-mail: futterer@tu-cottbus.de
2008-11-01
'GeoFlow' is a thermal convection experiment in rotating spherical shell geometry, which is going to take place in microgravity environment of International Space Station. We present numerical preliminary studies of the spherical Rayleigh-Benard problem under an artificial central force field. Numerical simulation is done with a pseudospectral method. Special focus here is the simulation of flow states at selected parameter points of Rayleigh and Taylor number of a defined plan for experimental runs on ISS. One loop will contain thermal convection without rotation, i.e. rising temperature gradient between inner and outer sphere. Another loop investigates convection superimposed by rotation, i.e. fixing temperature gradient and then rising rotation rate. In such cases different transitions are expected to be observed. Just rising Rayleigh number shows different stable states depending on initial conditions. Fixing Rayleigh number and then rising up Taylor number leads to traverse of different convective states showing rich dynamics of the system.
2D and 3D numerical modeling of seismic waves from explosion sources
Over the last decade, nonlinear and linear 2D axisymmetric finite difference codes have been used in conjunction with far-field seismic Green's functions to simulate seismic waves from a variety of sources. In this paper we briefly review some of the results and conclusions that have resulted from numerical simulations and explosion modeling in support of treaty verification research at S-CUBED in the last decade. We then describe in more detail the results from two recent projects. Our goal is to provide a flavor for the kinds of problems that can be examined with numerical methods for modeling excitation of seismic waves from explosions. Two classes of problems have been addressed; nonlinear and linear near-source interactions. In both classes of problems displacements and tractions are saved on a closed surface in the linear region and the representation theorem is used to propagate the seismic waves to the far-field
3D FEM Numerical Simulation of Seismic Pile-supported Bridge Structure Reaction in Liquefying Ground
Ling XianZhang, Tang Liang and Xu Pengju
2011-04-01
Full Text Available This study examines the establishment of liquefied ground pile-soil-bridge seismic interaction analysis of three-dimensional finite element analysis method for the simulation of liquefied ground shaking table test of pile-soil seismic interaction analysis, undertake OpenSees finite element based numerical simulation platform, for the shaking table test based on two-phase saturated porous media, Comparative numerical and experimental results, detailed test pile dynamic response of bridge structure and dynamic properties, especially liquefaction pore pressure, liquefaction of pile foundation and the dynamic response of the free field. Finite element method can reasonably predict the site of pore pressure, dynamic response; despite the conventional beam element simulation of pile, pile dynamic response can still accurately simulated.
Wavelet-based adaptive numerical simulation of unsteady 3D flow around a bluff body
de Stefano, Giuliano; Vasilyev, Oleg
2012-11-01
The unsteady three-dimensional flow past a two-dimensional bluff body is numerically simulated using a wavelet-based method. The body is modeled by exploiting the Brinkman volume-penalization method, which results in modifying the governing equations with the addition of an appropriate forcing term inside the spatial region occupied by the obstacle. The volume-penalized incompressible Navier-Stokes equations are numerically solved by means of the adaptive wavelet collocation method, where the non-uniform spatial grid is dynamically adapted to the flow evolution. The combined approach is successfully applied to the simulation of vortex shedding flow behind a stationary prism with square cross-section. The computation is conducted at transitional Reynolds numbers, where fundamental unstable three-dimensional vortical structures exist, by well-predicting the unsteady forces arising from fluid-structure interaction.
On the numerical modfeling of 3D-atmospheric boundary layer flow
Beneš, Luděk; Sládek, Ivo; Jaňour, Zbyněk
Karlsruhe : Forshungszentrum Karrlsruhe GmbH, 2004 - (Suppan, P.), s. 340-344 ISBN 3-923704-44-5. [Harmonisation within atmospheric Dispersion modeling for regulatory purposes. Garmisch-Partenkirchen (DE), 01.06.2004-04.06.2004] R&D Projects: GA MŠk OC 715.10 Institutional research plan: CEZ:AV0Z2076919 Keywords : atmosphere * pollution * numerical simulation Subject RIV: BA - General Mathematics
3D printing device for numerical control machine and wood deposition
Julien Gardan; Lionel Roucoules
2014-01-01
The paper presents the development of a new sustainable approach in additive manufacturing adapted on a Numerical Control (NC) machining. Wood has several advantages that are transferable to various derivatives allowing the introduction of sustainable material into the product lifecycle. The application involves the integration of wood pulp into rapid prototyping solutions. Wood is the main material studied for its ecological aspect. The primary goal was to create reconstituted wo...
Parareal in time 3D numerical solver for the LWR Benchmark neutron diffusion transient model
Baudron, Anne-Marie A -M; Maday, Yvon; Riahi, Mohamed Kamel; Salomon, Julien
2014-01-01
We present a parareal in time algorithm for the simulation of neutron diffusion transient model. The method is made efficient by means of a coarse solver defined with large time steps and steady control rods model. Using finite element for the space discretization, our implementation provides a good scalability of the algorithm. Numerical results show the efficiency of the parareal method on large light water reactor transient model corresponding to the Langenbuch-Maurer-Werner (LMW) benchmark [1].
I-Simpa, a graphical user interface devoted to host 3D sound propagation numerical codes
PICAUT, Judicaël; Fortin, Nicolas
2012-01-01
Whatever for indoor noise applications (room acoustics, noise in vehicles...) or sound propagation in the environment (open field, urban areas...), many numerical codes have been developed by researchers. Most of them have many common aspects, like the definition of the domain geometry and the materials (boundary conditions, impedance...), the definition of sound sources and of receivers (position, spectrum, directivity...). Moreover, they all have the same objective that is to predict the so...
Virial theorem analysis of 3D numerical simulations of MHD self-gravitating turbulence
Shadmehri, Mohsen; Vazquez-Semadeni, Enrique; Ballesteros-Paredes, Javier
2001-01-01
We discuss the virial balance of all members of a cloud ensemble in numerical simulations of self-gravitating MHD turbulence. We first discuss the choice of reference frame for evaluating the terms entering the virial theorem (VT), concluding that the balance of each cloud should be measured in its own reference frame. We then report preliminary results suggesting that a) the clouds are far from virial equilibrium, with the ``geometric'' (time derivative) terms dominating the VT. b) The surfa...
Guo, Wei; Kang, Hai-gui; Chen, Bing; Xie, Yu; Wang, Yin
2016-03-01
Vertical axis tidal current turbine is a promising device to extract energy from ocean current. One of the important components of the turbine is the connecting arm, which can bring about a significant effect on the pressure distribution along the span of the turbine blade, herein we call it 3D effect. However, so far the effect is rarely reported in the research, moreover, in numerical simulation. In the present study, a 3D numerical model of the turbine with the connecting arm was developed by using FLUENT software compiling the UDF (User Defined Function) command. The simulation results show that the pressure distribution along the span of blade with the connecting arm model is significantly different from those without the connecting arm. To facilitate the validation of numerical model, the laboratory experiment has been carried out by using three different types of NACA aerofoil connecting arm and circle section connecting arm. And results show that the turbine with NACA0012 connecting arm has the best start-up performance which is 0.346 m/s and the peak point of power conversion coefficient is around 0.33. A further study has been performed and a conclusion is drawn that the aerofoil and thickness of connecting arm are the most important factors on the power conversion coefficient of the vertical axis tidal current turbine.
Efficient 3D Acoustic Numerical modeling in the Logarithmic-grid using the Expanding Domain Method
Hong, B. R.; Chung, W.; Ko, H.; Bae, H. S.
2015-12-01
In the numerical modeling of seismic wave propagation by the use of a discrete computing domain, dispersion analysis is preceded by the determination of the spatial grid spacings in order to ensure accurate modeling results. Grid spacing is a function of wavelength, and the wavelength depends on the minimum velocity and maximum source frequency. Therefore, as the frequency increases, the number of grids increase and this leads to computational overburden. In order to reduce the computing complexity, coordinate transformation techniques such as Riemannian coordinates and logarithmic grid sets are proposed. Riemannian wave-field extrapolation is a way to reformulate the wave-field by expressing it in Riemannian coordinates. In the logarithmic grid, grid spacing changes logarithmically, so this enables us to reduce the number of grids compared to a conventional grid set. Furthermore, this could completely remove boundary reflections by extending the model dimensions. However, numerical modeling in the logarithmic grid is still inefficient because it is performed for whole model at every individual time step. In this study we applied the expanding domain method to the logarithmic modeling in order to improve computational efficiency. This method, based on amplitude comparison, excludes computations for zero wave-fields by considering a non-zero domain boundary. Numerical examples demonstrated that our new modeling method enhances computational efficiency maintaining accuracy compared with conventional modeling methods. In wider and higher-order dimensions, particularly, the efficiency of our modeling method increased. Our new modeling technique could also be applied to the generation of underwater target echo signals requiring high frequency analysis.
Visual numerical steering in 3D AGENT code system for advanced nuclear reactor modeling and design
Highlights: ► Numerical steering framework developed for deterministic neutron transport code AGENT to speed up the solution. ► Resulting speed up is on the order of 50%. ► Use of the steering framework is demonstrated modeling a TRIGA reactor. ► Numerical steering framework showed to be well suited for the deterministic neutron transport methods. - Abstract: The AGENT simulation system is used for detailed three-dimensional modeling of neutron transport and corresponding properties of nuclear reactors of any design. Numerical solution to the neutron transport equation in the AGENT system is based on the Method of Characteristics (MOCs) and the theory of R-functions. The latter of which is used for accurately describing current and future heterogeneous lattices of reactor core configurations. The AGENT code has been extensively verified to assure a high degree of accuracy for predicting neutron three-dimensional point-wise flux spatial distributions, power peaking factors, reaction rates, and eigenvalues. In this paper, a new AGENT code feature, a computational steering, is presented. This new feature provides a novel way for using deterministic codes for fast evaluation of reactor core parameters, at no loss to accuracy. The computational steering framework as developed at the Technische Universität München is smoothly integrated into the AGENT solver. This framework allows for an arbitrary interruption of AGENT simulation, allowing the solver to restart with updated parameters. One possible use of this is to accelerate the convergence of the final values resulting in significantly reduced simulation times. Using this computational steering in the AGENT system, coarse MOC resolution parameters can initially be selected and later update them – while the simulation is actively running – into fine resolution parameters. The utility of the steering framework is demonstrated using the geometry of a research reactor at the University of Utah: this new
Code and Solution Verification of 3D Numerical Modeling of Flow in the Gust Erosion Chamber
Yuen, A.; Bombardelli, F. A.
2014-12-01
Erosion microcosms are devices commonly used to investigate the erosion and transport characteristics of sediments at the bed of rivers, lakes, or estuaries. In order to understand the results these devices provide, the bed shear stress and flow field need to be accurately described. In this research, the UMCES Gust Erosion Microcosm System (U-GEMS) is numerically modeled using Finite Volume Method. The primary aims are to simulate the bed shear stress distribution at the surface of the sediment core/bottom of the microcosm, and to validate the U-GEMS produces uniform bed shear stress at the bottom of the microcosm. The mathematical model equations are solved by on a Cartesian non-uniform grid. Multiple numerical runs were developed with different input conditions and configurations. Prior to developing the U-GEMS model, the General Moving Objects (GMO) model and different momentum algorithms in the code were verified. Code verification of these solvers was done via simulating the flow inside the top wall driven square cavity on different mesh sizes to obtain order of convergence. The GMO model was used to simulate the top wall in the top wall driven square cavity as well as the rotating disk in the U-GEMS. Components simulated with the GMO model were rigid bodies that could have any type of motion. In addition cross-verification was conducted as results were compared with numerical results by Ghia et al. (1982), and good agreement was found. Next, CFD results were validated by simulating the flow within the conventional microcosm system without suction and injection. Good agreement was found when the experimental results by Khalili et al. (2008) were compared. After the ability of the CFD solver was proved through the above code verification steps. The model was utilized to simulate the U-GEMS. The solution was verified via classic mesh convergence study on four consecutive mesh sizes, in addition to that Grid Convergence Index (GCI) was calculated and based on
Improvement of the 3D numerical model of the spherical particle saltation
Lukerchenko, Nikolay; Piatsevich, Siarhei; Chára, Zdeněk; Vlasák, Pavel
Tbilisi : Agricultural University of Wroclaw, Poland, 2006 - (Gochitashvili, T.; Sobota, J.), s. 177-186 ISBN 83-60574-00-6. [International Conference on Transport and Sedimentation of Solid Particles /13./. Tbilisi (GE), 18.09.2006-20.09.2006] R&D Projects: GA ČR GA103/06/1487 Institutional research plan: CEZ:AV0Z20600510 Keywords : particle saltation, * particle-bed collision * Magnus force * contact zone * numerical simulation * deviation angle * relative concentration Subject RIV: BK - Fluid Dynamics
3-D numerical simulation on the vibration of liquid sodium's free surface in sodium pool of FBR
This paper succeeds in simulating three-dimensional incompressible flows with free surface, complicated in-flow and out-flow boundary conditions and internal obstacles, and also can treat these fluid flows in arbitrary shape vessel using a partial cell. According to all kinds of the element influencing the free surface's vibration in sodium pool it may give the various wave's form, the highest and lowest position, and the amount of the vibration. This paper introduces the brief principle of VOF numerical method, develops the computational program based on NASA-VOF3D, provides some results about the free surface's vibration in sodium pool of FBR
Montant, S; Marre, G; Blanchot, N; Rouyer, C; Videau, L; Sauteret, C
2006-12-11
An important issue, mosaic grating compressor, is studied to recompress pulses for multiPetawatt, high energy laser systems. Alignment of the mosaic elements is crucial to control the focal spot and thus the intensity on target. No theoretical approach analyses the influence of compressor misalignment on spatial and temporal profiles in the focal plane. We describe a simple 3D numerical model giving access to the focal plane view after a compressor. This model is computationally inexpensive since it needs only 1D Fourier transforms to access to the temporal profile. We present simulations of monolithic and mosaic grating compressors. PMID:19529688
Ferrara, P; Ciofini, M; Esposito, L; Hostaša, J; Labate, L; Lapucci, A; Pirri, A; Toci, G; Vannini, M; Gizzi, L A
2014-03-10
We present a study of Yb:YAG active media slabs, based on a ceramic layered structure with different doping levels. We developed a procedure allowing 3D numerical analysis of the slab optical properties as a consequence of the thermal load induced by the pump process. The simulations are compared with a set of experimental results in order to validate the procedure. These structured ceramics appear promising in appropriate geometrical configurations, and thus are intended to be applied in the construction of High Energy Diode Pumped Solid State Laser (DPSSL) systems working in high repetition-rate pulsed regimes. PMID:24663877
Numerical simulation of 3D unsteady flow in a rotating pump by dynamic mesh technique
In this paper, the numerical simulation of unsteady flow for three kinds of typical rotating pumps, roots blower, roto-jet pump and centrifugal pump, were performed using the three-dimensional Dynamic Mesh technique. In the unsteady simulation, all the computational domains, as stationary, were set in one inertial reference frame. The motions of the solid boundaries were defined by the Profile file in FLUENT commercial code, in which the rotational orientation and speed of the rotors were specified. Three methods (Spring-based Smoothing, Dynamic Layering and Local Re-meshing) were used to achieve mesh deformation and re-meshing. The unsteady solutions of flow field and pressure distribution were solved. After a start-up stage, the flow parameters exhibit time-periodic behaviour corresponding to blade passing frequency of rotor. This work shows that Dynamic Mesh technique could achieve numerical simulation of three-dimensional unsteady flow field in various kinds of rotating pumps and have a strong versatility and broad application prospects
3D numerical simulation and structural optimization of the rod baffle heat exchanger
YAN Liang-wen; PAN Lei; KAN Shu-lin
2009-01-01
Because of the complexities of fluid dynamics equations and the structure of heat exchangers, few theoretical solutions have been acquired to specify the shell side characteristics of the rod baffle heat exchanger (RBHE). Based on the platform of PHEONICS version 3.5.1, a three-dimensionai numerical method for predicting the turbulent fluid flow behavior in the shell side of the rod baffle heat exchangers is developed in this paper. With this method, modeling of the tube bundle is carried out based on the porous media concept using volumetric porosities and applicable flow resistance correlations. Turbulence effects are modeled using a standard κ-ε model. It is shown that the simulation results and experimental results are in good agreement in the shell side. The maximum absolute deviation value of pressure drops is less than 5%, and that of the heat transfer coefficients is less than 8%. Furthermore, the numerical model is used to optimize the structure of the RBHE and improves its performance.
A Numerical Study on the Thermal Conductivity of 3D Woven C/C Composites at High Temperature
Shigang, Ai; Rujie, He; Yongmao, Pei
2015-12-01
Experimental data for Carbon/Carbon (C/C) constituent materials are combined with a three dimensional steady state heat transfer finite element analysis to demonstrate the average in-plane and out-of-plane thermal conductivities (TCs) of C/C composites. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibres and (b) a meso scale comparable with the carbon fibre yarns. Micro-scale model calculate the TCs at the fibre yarn scale in the three orthogonal directions ( x, y and z). The output results from the micro-scale model are then incorporated in the meso-scale model to obtain the global TCs of the 3D C/C composite. The simulation results are quite consistent with the theoretical and experimental counterparts reported in references. Based on the numerical approach, TCs of the 3D C/C composite are calculated from 300 to 2500 K. Particular attention is given in elucidating the variations of the TCs with temperature. The multi-scale models provide an efficient approach to predict the TCs of 3D textile materials, which is helpful for the thermodynamic property analysis and structure design of the C/C composites.
Beretta, S.; Moia, F.; Guandalini, R.; Cappelletti, F.
2012-04-01
The research activities carried out by the Environment and Sustainable Development Department of RSE S.p.A. aim to evaluate the feasibility of CO2 geological sequestration in Italy, with particular reference to the storage into saline aquifers. The identification and geological characterization of the Italian potential storage sites, together with the study of the temporal and spatial evolution of the CO2 plume within the caprock-reservoir system, are performed using different modelling tools available in the Integrated Analysis Modelling System (SIAM) entirely powered in RSE. The numerical modelling approach is the only one that allows to investigate the behaviour of the injected CO2 regarding the fluid dynamic, geochemical and geomechanical aspects and effects due to its spread, in order to verify the safety of the process. The SIAM tools allow: - Selection of potential Italian storage sites through geological and geophysical data collected in the GIS-CO2 web database; - Characterization of caprock and aquifer parameters, seismic risk and environmental link for the selected site; - Creation of the 3D simulation model for the selected domain, using the modeller METHODRdS powered by RSE and the mesh generator GMSH; - Simulation of the injection and the displacement of CO2: multiphase fluid 3D dynamics is based on the modified version of TOUGH2 model; - Evaluation of geochemical reaction effects; - Evaluation of geomechanic effects, using the coupled 3D CANT-SD finite elements code; - Detailed local analysis through the use of open source auxiliary tools, such as SHEMAT and FEHM. - 3D graphic analysis of the results. These numerical tools have been successfully used for simulating the injection and the spread of CO2 into several real Italian reservoirs and have allowed to achieve accurate results in terms of effective storage capacity and safety analysis. The 3D geological models represent the high geological complexity of the Italian subsoil, where reservoirs are
3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes
Daiffallah, K; Bendib, A; Cameron, R; Gizon, L
2010-01-01
Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave was found to consist primarily of m=0 (axisymmetric) and m=1 modes. It was found that the ratio of the amplitude of these two modes is strongly dependant on the radius of the flux tube: The kink mode is the dominant mode excited in tubes with a small radius while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient and robust way to start understanding the seismic signature of flux tubes, which have recently began to be observed.
3D numerical simulations of THz generation by two-color laser filaments
Tera-hertz (THz) radiation produced by the filamentation of two-color pulses over long distances in argon is numerically investigated using a comprehensive model in full space-time-resolved geometry. We show that the dominant physical mechanism for THz generation in the filamentation regime at clamping intensity is based on quasi-dc plasma currents. The calculated THz spectra for different pump pulse energies and pulse durations are in agreement with previously reported experimental observations. For the same pulse parameters, near-infrared pump pulses at 2 μm are shown to generate a more than 1 order of magnitude greater THz yield than pumps centered at 800 nm. (authors)
NUMERICAL SIMULATION OF 3D KIRLOSKER TV-1 MODEL ENGINE CYLINDER FOR COLD FLOW
S. SIVA
2013-12-01
Full Text Available The definition of an efficient optimization methodology for internal combustion engine design using computational fluid dynamic simulation models is presented. This paper aims at validating the fundamental numerical and computational fluid dynamic aspects which can lead to the definition of following models. The models used for analysis of Standard k-ε model, Realizable k-ε model, V2F k-ε model, AKN k-ε model, and Standard k-ω (Wilcox model. For these reasons, both single-and multi-objective problems will be addressed, where the former are still of relevant interest (i.e. optimization of engine performances, while the later have a much wider range of applications and are often characterized by conflicting objectives.Modeling of the KIRLOSKER OIL ENGINE TV1 will be done using GAMBIT. Flow inside the engine is to be the analysis and validation various turbulence models using STARCD. This is used to find the model which predicts the engine performance better.
A continuous flow microfluidic calorimeter: 3-D numerical modeling with aqueous reactants
Sen, Mehmet A., E-mail: mehmet.sen@mathworks.com [Northeastern University, Department of Mechanical and Industrial Engineering, 360 Hungtington Avenue, 334 Snell Engineering Center, Boston, MA 02115 (United States); Kowalski, Gregory J., E-mail: gkowal@coe.neu.edu [Northeastern University, Department of Mechanical and Industrial Engineering, 360 Hungtington Avenue, 334 Snell Engineering Center, Boston, MA 02115 (United States); Fiering, Jason, E-mail: jfiering@draper.com [Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139 (United States); Larson, Dale, E-mail: dlarson@draper.com [Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139 (United States)
2015-03-10
Highlights: • A co-flow microreactor is modeled in flow, reaction/diffusion, and thermal domains. • Analysis shows how arrayed temperature sensors can provide enthalpy of reaction. • Optical plasmonic temperature sensors could be arrayed suitably for calorimetry. • The reactor studied has a volume of 25 nL. - Abstract: A computational analysis of the reacting flow field, species diffusion and heat transfer processes with thermal boundary layer effects in a microchannel reactor with a coflow configuration was performed. Two parallel adjacent streams of aqueous reactants flow along a wide, shallow, enclosed channel in contact with a substrate, which is affixed to a temperature controlled plate. The Fluent computational fluid dynamics package solved the Navier–Stokes, mass transport and energy equations. The energy model, including the enthalpy of reaction as a nonuniform heat source, was validated by calculating the energy balance at several control volumes in the microchannel. Analysis reveals that the temperature is nearly uniform across the channel thickness, in the direction normal to the substrate surface; hence, measurements made by sensors at or near the surface are representative of the average temperature. Additionally, modeling the channel with a glass substrate and a silicone cover shows that heat transfer is predominantly due to the glass substrate. Finally, using the numerical results, we suggest that a microcalorimeter could be based on this configuration, and that temperature sensors such as optical nanohole array sensors could have sufficient spatial resolution to determine enthalpy of reaction.
Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine
ZHAO Qingjun; WANG Huishe; ZHAO Xiaolu; XU Jianzhong
2007-01-01
To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT),a threedimensional,viscous,unsteady computational fluid dynamics (CFD) analysis was performed.The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained.The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT.The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface.The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven.The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span.The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction.A similar result can also be obtained in the outlet of a low pressure turbine rotor.This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives.
LUO Zu-jiang; WANG Yan
2012-01-01
In order to correctly evaluate the exploitable groundwater resource in regional complex,thick Quaternary unconsolidated sediments,the whole Quaternary unconsolidated sediments are considered as a unified hydrogeological unit and a 3-D unsteady groundwater flow numerical model is adopted.Meanwhile,with the consideration of the dynamic changes of the porosity,the hydraulic conductivity and the specific storage with the groundwater level dropping during the exploitation process,an improved composite element seepage matrix adjustment method is applied to solve the unsteady flow problem of free surface.In order to evaluate the exploitable groundwater resource in Cangzhou,Hebei Province,the hydrogeological conceptual model of Cangzhou is generalized to establish,a 3-D variable parameter numerical model of Cangzhou.Based on the prediction of the present groundwater exploitation,and by adjusting the groundwater exploitation layout,the exploitable groundwater resource is predicted.The model enjoys features like good convergence,good stability and high precision.
3D NUMERICAL STUDY ON LAMINAR FORCED CONVECTION IN V-BAFFLED SQUARE CHANNEL
Amnart Boonloi
2013-01-01
Full Text Available The article presents a mathematical study of fully developed periodic laminar flow visualization and heat transfer characteristics in an isothermal wall square-channel fitted with V-shaped baffles on one wall. The computations based on the finite volume method together with the SIMPLE algorithm have been performed. The investigation covers a range of Re based on the hydraulic diameter of the channel, Re = 100-1200. To create a pair of main streamwise vortex flows through the tested section, the V-baffles with the attack angle of 30Â° with the main flow direction are mounted in tandem and pointing downstream on the lower channel wall only. Effects of different baffle heights and pitches on heat transfer and pressure drop in the channel are examined and the results obtained are compared with smooth channel with no baffle. The numerical result shows that the presence of the V-baffle yields a significant heat transfer enhancement compared with the smooth channel. It is visible that the main vortex flows, a pair of streamwise twisted vortex (P-vortex can induce impingement flows on the walls leading to a drastic increase in heat transfer rate over the channel. In addition, the increase in the baffle height leads to the rise in the heat transfer and pressure loss while that in the baffle pitch provides the opposite trend. The predicted results expose that the maximum thermal enhancement factors for the V-baffles with BR = 0.3, 0.3 and 0.4; and PR = 1, 1.5 and 2 are, respectively, about 2.44, 2.29 and 2.37 at higher Re.
A numerical study of the transition to oscillatory flow in 3D lid-driven cubic cavity flows
Chiu, Shang-Huan; He, Jiwen; Guo, Aixia; Glowinski, Roland
2016-01-01
In this article, three dimensional (3D) lid-driven cubic cavity flows have been studied numerically for various values of Reynolds number ($Re$). The numerical solution of the Navier-Stokes equations modeling incompressible viscous fluid flow in a cubic cavity is obtained via a methodology combining a first order accurate operator-splitting, $L^2$-projection Stokes solver, a wave-like equation treatment of the advection and finite element methods. The numerical results obtained for Re$=$400, 1000, and 3200 show a good agreement with available numerical and experimental results in literature. Simulation results predict that the critical Re$_{cr}$ for the transition from steady flow to oscillatory (a Hopf bifurcation) is somewhere in [1870, 1875] for the mesh size $h=1/96$. Via studying the flow field distortion of fluid flow at Re before and after Re$_{cr}$, the occurrence of the first pair of Taylor-G\\"ortler-like vortices is connected to the flow field distortion at the transition from steady flow to oscilla...
Malapaka, Shiva Kumar; Mueller, Wolf-Christian [Max-Planck Institute for Plasma Physics, Boltzmannstrasse 2, D-85748 Garching bei Muenchen (Germany)
2013-09-01
Statistical properties of the Sun's photospheric turbulent magnetic field, especially those of the active regions (ARs), have been studied using the line-of-sight data from magnetograms taken by the Solar and Heliospheric Observatory and several other instruments. This includes structure functions and their exponents, flatness curves, and correlation functions. In these works, the dependence of structure function exponents ({zeta}{sub p}) of the order of the structure functions (p) was modeled using a non-intermittent K41 model. It is now well known that the ARs are highly turbulent and are associated with strong intermittent events. In this paper, we compare some of the observations from Abramenko et al. with the log-Poisson model used for modeling intermittent MHD turbulent flows. Next, we analyze the structure function data obtained from the direct numerical simulations (DNS) of homogeneous, incompressible 3D-MHD turbulence in three cases: sustained by forcing, freely decaying, and a flow initially driven and later allowed to decay (case 3). The respective DNS replicate the properties seen in the plots of {zeta}{sub p} against p of ARs. We also reproduce the trends and changes observed in intermittency in flatness and correlation functions of ARs. It is suggested from this analysis that an AR in the onset phase of a flare can be treated as a forced 3D-MHD turbulent system in its simplest form and that the flaring stage is representative of decaying 3D-MHD turbulence. It is also inferred that significant changes in intermittency from the initial onset phase of a flare to its final peak flaring phase are related to the time taken by the system to reach the initial onset phase.
Statistical properties of the Sun's photospheric turbulent magnetic field, especially those of the active regions (ARs), have been studied using the line-of-sight data from magnetograms taken by the Solar and Heliospheric Observatory and several other instruments. This includes structure functions and their exponents, flatness curves, and correlation functions. In these works, the dependence of structure function exponents (ζp) of the order of the structure functions (p) was modeled using a non-intermittent K41 model. It is now well known that the ARs are highly turbulent and are associated with strong intermittent events. In this paper, we compare some of the observations from Abramenko et al. with the log-Poisson model used for modeling intermittent MHD turbulent flows. Next, we analyze the structure function data obtained from the direct numerical simulations (DNS) of homogeneous, incompressible 3D-MHD turbulence in three cases: sustained by forcing, freely decaying, and a flow initially driven and later allowed to decay (case 3). The respective DNS replicate the properties seen in the plots of ζp against p of ARs. We also reproduce the trends and changes observed in intermittency in flatness and correlation functions of ARs. It is suggested from this analysis that an AR in the onset phase of a flare can be treated as a forced 3D-MHD turbulent system in its simplest form and that the flaring stage is representative of decaying 3D-MHD turbulence. It is also inferred that significant changes in intermittency from the initial onset phase of a flare to its final peak flaring phase are related to the time taken by the system to reach the initial onset phase
Cameron, R H; Brandenburg, A
2016-01-01
A brief summary of the various observations and constraints that underlie solar dynamo research are presented. The arguments that indicate that the solar dynamo is an alpha-omega dynamo of the Babcock-Leighton type are then shortly reviewed. The main open questions that remain are concerned with the subsurface dynamics, including why sunspots emerge at preferred latitudes as seen in the familiar butterfly wings, why the cycle is about 11 years long, and why the sunspot groups emerge tilted with respect to the equator (Joy's law). Next, we turn to magnetic helicity, whose conservation property has been identified with the decline of large-scale magnetic fields found in direct numerical simulations at large magnetic Reynolds numbers. However, magnetic helicity fluxes through the solar surface can alleviate this problem and connect theory with observations, as will be discussed.
Cameron, R. H.; Dikpati, M.; Brandenburg, A.
2016-02-01
A brief summary of the various observations and constraints that underlie solar dynamo research are presented. The arguments that indicate that the solar dynamo is an alpha-omega dynamo of the Babcock-Leighton type are then shortly reviewed. The main open questions that remain are concerned with the subsurface dynamics, including why sunspots emerge at preferred latitudes as seen in the familiar butterfly wings, why the cycle is about 11 years long, and why the sunspot groups emerge tilted with respect to the equator (Joy's law). Next, we turn to magnetic helicity, whose conservation property has been identified with the decline of large-scale magnetic fields found in direct numerical simulations at large magnetic Reynolds numbers. However, magnetic helicity fluxes through the solar surface can alleviate this problem and connect theory with observations, as will be discussed.
A-man ZHANG; Shao-fei REN; Qing LI; Jia LI
2012-01-01
In the underwater-shock environment,cavitation occurs near the structural surface.The dynamic response of fluid-structure interactions is influenced seriously by the cavitation effects.It is also the difficulty in the field of underwater explosion.With the traditional boundary element method and the finite element method (FEM),it is difficult to solve the nonlinear problem with cavitation effects subjected to the underwater explosion.To solve this problem,under the consideration of the cavitation effects and fluid compressibility,with fluid viscidity being neglected,a 3D numerical model of transient nonlinear fluid-structure interaction subjected to the underwater explosion is built.The fluid spectral element method (SEM) and the FEM are adopted to solve this model.After comparison with the FEM,it is shown that the SEM is more precise than the FEM,and the SEM results are in good coincidence with benchmark results and experiment results.Based on this,combined with ABAQUS,the transient fluid-structure interaction mechanism of the 3D submerged spherical shell and ship stiffened plates subjected to the underwater explosion is discussed,and the cavitation region and its influence on the structural dynamic responses are presented.The paper aims at providing references for relevant research on transient fluid-structure interaction of ship structures subjected to the underwater explosion.
Yu.V. STARODUBTSEV; I.G. GOGOLEV; V.G. SOLODOV
2005-01-01
@@ The paper describes 3D numerical Reynolds Averaged Navier-Stokes (RANS) model and approximate sector approach for viscous turbulent flow through flow path of one stage axial supercharge gas turbine of marine diesel engine. Computational data are tested by comparison with experimental data. The back step flow path opening and tip clearance jet are taken into account.This approach could be applied for variety of turbine theory and design tasks: for offer optimal design in order to minimize kinetic energy stage losses; for solution of partial supply problem; for analysis of flow pattern in near extraction stages; for estimation of rotational frequency variable forces on blades; for sector vane adjustment (with thin leading edges mainly), for direct flow modeling in the turbine etc. The development of this work could be seen in the direction of unsteady stage model application.
Magnetic fields end-face effect investigation of HTS bulk over PMG with 3D-modeling numerical method
Qin, Yujie; Lu, Yiyun
2015-09-01
In this paper, the magnetic fields end-face effect of high temperature superconducting (HTS) bulk over a permanent magnetic guideway (PMG) is researched with 3D-modeling numerical method. The electromagnetic behavior of the bulk is simulated using finite element method (FEM). The framework is formulated by the magnetic field vector method (H-method). A superconducting levitation system composed of one rectangular HTS bulk and one infinite long PMG is successfully investigated using the proposed method. The simulation results show that for finite geometrical HTS bulk, even the applied magnetic field is only distributed in x-y plane, the magnetic field component Hz which is along the z-axis can be observed interior the HTS bulk.
Zarzo, Manuel
2015-06-01
Many authors have proposed different schemes of odor classification, which are useful to aid the complex task of describing smells. However, reaching a consensus on a particular classification seems difficult because our psychophysical space of odor description is a continuum and is not clustered into well-defined categories. An alternative approach is to describe the perceptual space of odors as a low-dimensional coordinate system. This idea was first proposed by Crocker and Henderson in 1927, who suggested using numeric profiles based on 4 dimensions: "fragrant," "acid," "burnt," and "caprylic." In the present work, the odor profiles of 144 aroma chemicals were compared by means of statistical regression with comparable numeric odor profiles obtained from 2 databases, enabling a plausible interpretation of the 4 dimensions. Based on the results and taking into account comparable 2D sensory maps of odor descriptors from the literature, a 3D sensory map (odor cube) has been drawn up to improve understanding of the similarities and dissimilarities of the odor descriptors most frequently used in fragrance chemistry. PMID:25847969
Amir Hossein Haghi
2013-06-01
Full Text Available Ground settlement is often the most serious concern when tunneling under an old city with numerous historic monuments. A successful engineering design under these conditions would require getting the most out of the ground strength parameters and avoiding any weakening maneuver throughout the operation. Knowing that surface settlement is highly affected by tunneling parameters in EPB shield tunneling lead us to estimate the optimum values for the machine heading pressure with the lower amount of the ground settlement in fragile structure of the old city for the Esfahan Subway Project. Tunnels were dug underneath some of the most prominent historical sites along the path of the project. To improve precision and efficiency in tunneling operation, at the first step, tunnel heading confinement pressure is calculated by using an advanced 3D mathematical approach based on the limit equilibrium theory. Then, a promoted 3D finite element model is developed, taking into account the tunneling procedures and the designed heading confinement pressure from the first step. Settlements were pre-calculated and the surface displacement was checked at all sensitive locations. At the third step, settlement is estimated by exerting executed face supporting pressure to the tunnel face and the concluded amounts for displacement are compared with the outputs of extensometers. This comparison leads us to check the reliability of calculated settlements and the accuracy of the designed tunnel heading confinement pressure. Furthermore, evaluating the relation between extensometer outputs and executed tunnel face pressure at the points of extensometers stations validates the assumption that the safe face supporting pressure causes least surface displacement. Although the minimum pressure occurred in short term fluctuations, this approach confirms the sensibility of settlement with the least executed face supporting pressure.. It is also found that higher executed face
ZHU Zi-qiang; LIU Qun-yi; ZENG Fan-he; QING Du-gan
2009-01-01
To study the grouting reinforcement mechanism in jointed rock slope, first, the theoretical deduction was done to calculate the critical length of slipping if the slope angle is larger than that of joint inclination; Second, the numerical calculation model was founded by FLAG3D, so as to find the stress and deformation responses of rock mass in the state before and after grouting, the analysis results show that the range between the boundary of critical slipping block and the joint plane that passes the slope toe is the effective grouting area (EGA). After excavation, large deformation occurs along the joint plane. After grouting, the displacements of rock particles become uniform and continuous, and large deformations along the joint plane are controlled; the dynamic displacement can reflect the deformation response of slope during excavation in the state before and after grouting, as well as the shear location of potential slip plane. After grouting, the dynamic displacement of each monitoring point reaches the peak value with very few time steps,which indicate that the parameters of the joint plane, such as strength and stiffness, are improved; the stress field becomes uniform. Tensile area reduces gradually; whole stability of the slope and its ability to resist tensile and shear stress are improved greatly.
3D experimental and numerical study of fatigue of a slanted crack path in a thin sheet
Propagation of fatigue cracks in 7075-T6 aluminum and S355 steel were experimentally characterized in air and in a corrosive solution in a CCP specimen. A technique of crack front marking, coupled with a 3D topographic reconstruction of the crack, allowed to characterize the three-dimensional crack path and the crack growth rate at any point of the crack front. Transverse and longitudinal profiles at different propagation stages were used to calculate the twist and tilt angle. In an elastic XFEM framework, stress intensity factors I, II and III, were calculated. While the correlation of experimental crack growth rate with ΔKI is unsatisfactory, the correlation is correct with ΔKeq emphasizing the major contribution of shear modes to the crack driving force. A finite element analysis in elasto plasticity coupled with the application of a local fatigue criterion, which depend on the equivalent plastic strain ahead of the crack front, was qualitatively able to predict the shear lips growth. A modification of the XFEM method is proposed to improve computations with cyclic plasticity. This part is based on an analytical study which suggests to replace the discontinuous 'Heaviside' enrichment by a new continuous enrichment in the elements cut by the crack. The sub-division of the elements cut by the crack, inducing a field projection of the internal variables which introduces an error in the numerical computations, is thus avoided. Convergence test cases show the potentiality of this method. (author)
Pathak, Himanshu; Singh, Akhilendra; Singh, Indra Vir
2016-06-01
In this work, finite element method (FEM) and element free Galerkin method (EFGM) are coupled for solving 3D crack domains subjected to cyclic thermal load of constant amplitude. Crack growth contours and fatigue life have been obtained for each of the considered numerical examples. Thermo-elastic problems are decoupled into thermal and elastic problems . Firstly, the unknown temperature field is obtained by solving heat conduction equation, then, it is used as the input load in the elastic problem to calculate the displacement and stress fields. The geometrical discontinuity across crack surface is modelled by extrinsically enriched EFGM and the remaining part of the domain is approximated by standard finite element method. At the crack interface, a ramp function based interpolation scheme has been implemented. This coupled approach combines the advantages of both EFGM and FEM. A linear successive crack increment approach is used to model crack growth. The growing crack surface is traced by level set function. Standard Paris law is used for life estimation of the three-dimensional crack models. Different cases of planar and non-planar crack problems have been solved and their results are compared with the results obtained using extended finite element method to check accuracy, efficiency and robustness of the coupled FE-EFG approach implemented in this study.
Koldan, Jelena
2013-01-01
The growing significance, technical development and employment of electromagnetic (EM) methods in exploration geophysics have led to the increasing need for reliable and fast techniques of interpretation of 3-D EM data sets acquired in complex geological environments. The first and most important step to creating an inversion method is the development of a solver for the forward problem. In order to create an efficient, reliable and practical 3-D EM inversion, it is necessary to have a 3-D EM...
Wei Lu; Qingchun Yang; Jordi D Martín; Ricardo Juncosa
2013-04-01
During the 1990s, groundwater overexploitation has resulted in seawater intrusion in the coastal aquifer of the Shenzhen city, China. Although water supply facilities have been improved and alleviated seawater intrusion in recent years, groundwater overexploitation is still of great concern in some local areas. In this work we present a three-dimensional density-dependent numerical model developed with the FEFLOW code, which is aimed at simulating the extent of seawater intrusion while including tidal effects and different groundwater pumping scenarios. Model calibration, using waterheads and reported chloride concentration, has been performed based on the data from 14 boreholes, which were monitored from May 2008 to December 2009. A fairly good fitness between the observed and computed values was obtained by a manual trial-and-error method. Model prediction has been carried out forward 3 years with the calibrated model taking into account high, medium and low tide levels and different groundwater exploitation schemes. The model results show that tide-induced seawater intrusion significantly affects the groundwater levels and concentrations near the estuarine of the Dasha river, which implies that an important hydraulic connection exists between this river and groundwater, even considering that some anti-seepage measures were taken in the river bed. Two pumping scenarios were considered in the calibrated model in order to predict the future changes in the water levels and chloride concentration. The numerical results reveal a decreased tendency of seawater intrusion if groundwater exploitation does not reach an upper bound of about 1.32 × 104 m3/d. The model results provide also insights for controlling seawater intrusion in such coastal aquifer systems.
Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin
2016-04-01
The entrainment of single grains and, hence, their erosion characteristics are dependent on fluid forcing, grain size and density, but also shape variations. To quantitatively describe and capture the hydrodynamic conditions around individual grains, researchers commonly use empirical approaches such as laboratory flume tanks. Nonetheless, it is difficult with such physical experiments to measure the flow velocities in the direct vicinity or within the pore spaces of sediments, at a sufficient resolution and in a non-invasive way. As a result, the hydrodynamic conditions in the water column, at the fluid-porous interface and within pore spaces of a granular medium of various grain shapes is not yet fully understood. For that reason, there is a strong need for numerical models, since these are capable of quantifying fluid speeds within a granular medium. A 3D-SPH (Smooth Particle Hydrodynamics) numerical wave tank model was set up to provide quantitative evidence on the flow velocities in the direct vicinity and in the interior of granular beds composed of two shapes as a complementary method to the difficult task of in situ measurement. On the basis of previous successful numerical wave tank models with SPH, the model geometry was chosen in dimensions of X=2.68 [m], Y=0.48 [m], and Z=0.8 [m]. Three suites of experiments were designed with a range of particle shape models: (1) ellipsoids with the long axis oriented in the across-stream direction, (2) ellipsoids with the long axis oriented in the along-stream direction, and (3) spheres. Particle diameters ranged from 0.04 [m] to 0.08 [m]. A wave was introduced by a vertical paddle that accelerated to 0.8 [m/s] perpendicular to the granular bed. Flow measurements showed that the flow velocity values into the beds were highest when the grains were oriented across the stream direction and lowest in case when the grains were oriented parallel to the stream, indicating that the model was capable to simulate simultaneously
Moroni, L.; Poort, G.; Keulen, van F.; Wijn, de J.R.; Blitterswijk, van C.A.
2006-01-01
Mechanical properties of three-dimensional (3D) scaffolds can be appropriately modulated through novel fabrication techniques like 3D fiber deposition (3DF), by varying scaffold's pore size and shape. Dynamic stiffness, in particular, can be considered as an important property to optimize the scaffo
Magnetic Helicity Conservation and Astrophysical Dynamos
Vishniac, Ethan T.; Cho, Jungyeon
2000-01-01
We construct a magnetic helicity conserving dynamo theory which incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries in the second derivative of the velocity correlation function, closely related to the `twist and fold' dynamo model. The turbulent damping term is, as expected, almost unchanged. Numerical simulations ...
Hu, Bin; Kieweg, Sarah
2010-11-01
Gravity-driven thin film flow down an incline is studied for optimal design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. We develop a 3D FEM model using non-Newtonian mechanics to model the flow of gels in response to gravity, surface tension and shear-thinning. Constant volume setup is applied within the lubrication approximation scope. The lengthwise profiles of the 3D model agree with our previous 2D finite difference model, while the transverse contact line patterns of the 3D model are compared to the experiments. With incorporation of surface tension, capillary ridges are observed at the leading front in both 2D and 3D models. Previously published studies show that capillary ridge can amplify the fingering instabilities in transverse direction. Sensitivity studies (2D & 3D) and experiments are carried out to describe the influence of surface tension and shear-thinning on capillary ridge and fingering instabilities.
Castaldo, Raffaele; De Novellis, Vincenzo; Lollino, Piernicola; Manunta, Michele; Tizzani, Pietro
2015-04-01
The new challenge that the research in slopes instabilities phenomena is going to tackle is the effective integration and joint exploitation of remote sensing measurements with in situ data and observations to study and understand the sub-surface interactions, the triggering causes, and, in general, the long term behaviour of the investigated landslide phenomenon. In this context, a very promising approach is represented by Finite Element (FE) techniques, which allow us to consider the intrinsic complexity of the mass movement phenomena and to effectively benefit from multi source observations and data. In this context, we perform a three dimensional (3D) numerical model of the Ivancich (Assisi, Central Italy) instability phenomenon. In particular, we apply an inverse FE method based on a Genetic Algorithm optimization procedure, benefitting from advanced DInSAR measurements, retrieved through the full resolution Small Baseline Subset (SBAS) technique, and an inclinometric array distribution. To this purpose we consider the SAR images acquired from descending orbit by the COSMO-SkyMed (CSK) X-band radar constellation, from December 2009 to February 2012. Moreover the optimization input dataset is completed by an array of eleven inclinometer measurements, from 1999 to 2006, distributed along the unstable mass. The landslide body is formed of debris material sliding on a arenaceous marl substratum, with a thin shear band detected using borehole and inclinometric data, at depth ranging from 20 to 60 m. Specifically, we consider the active role of this shear band in the control of the landslide evolution process. A large field monitoring dataset of the landslide process, including at-depth piezometric and geological borehole observations, were available. The integration of these datasets allows us to develop a 3D structural geological model of the considered slope. To investigate the dynamic evolution of a landslide, various physical approaches can be considered
Jones, C. A.
2001-12-01
There has been significant progress in the development of numerical geodynamo models over the last eight years. Advances in computer technology have made it possible to perform three-dimensional simulations, with thermal or compositional convection as the driving mechanism. These numerical simulations give reasonable results for the morphology and strength of the field at the core-mantle boundary, and the models are also capable of giving reversals and excursions which can be compared with paleomagnetic observations. Some useful constraints are obtained by considering the entropy balance and the ohmic dissipation. However, recent studies of plane layer dynamos suggest that the current generation of dynamo models have not yet reached the correct dynamical regime. A rather severe test of how well we understand the geodynamo comes when we try to apply the theory to the magnetic fields of stars and other planets. It becomes clear that not all dynamos are in the same dynamical regime. Some, like the Earth, are in magnetostrophic balance; others like the Sun, are not. Some are in a strong field regime with Elsasser number of order one, others (including some planetary dynamos) are not. Even within late type stars, the rotation rate strongly affects the dynamical regime that the dynamo operates in. The prospects for classifying the various type of convection driven dynamo, by elucidating the possible dynamical regimes, will be reviewed.
裴吉; 袁寿其; 李晓俊; 袁建平
2014-01-01
Numerical simulation and 3-D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition. The pressure fluctuation intensity coefficient (PFIC) based on the standard deviation method, the time-averaged velocity unsteadi-ness intensity coefficient (VUIC) and the time-averaged turbulence intensity coefficient (TIC) are defined by averaging the results at each grid node for an entire impeller revolution period. Therefore, the strength distributions of the periodic flow unsteadiness based on the unsteady Reynolds-averaged Navier-Stokes (URANS) equations can be analyzed directly and in detail. It is shown that under the des.0.6Q condition, the pressure fluctuation intensity is larger near the blade pressure side than near the suction side, and a high fluctuation intensity can be observed at the beginning section of the spiral of the volute. The flow velocity unsteadiness intensity is larger near the blade suction side than near the pressure side. A strong turbulence intensity can be found near the blade suction side, the impeller shroud side as well as in the side chamber. The leakage flow has a significant effect on the inflow of the impeller, and can increase both the flow velocity unsteadiness intensity and the turbulence intensity near the wall. The accumulative flow unstea-diness results of an impeller revolution can be an important aspect to be considered in the centrifugal pump optimum design for ob-taining a more stable inner flow of the pump and reducing the flow-induced vibration and noise in certain components.
Bagaiev, Andrii; Ivanov, Vitaliy
2014-05-01
The Black Sea north-western shelf plays a key role in economics of the developing countries such as Ukraine due to food supply, invaluable recreational potential and variety of the relevant maritime shipping routes. On the other hand, a shallow flat shelf is mostly affected by anthropogenic pollution, eutrophication, hypoxia and harmful algae blooms. The research is focused on modeling the transport and transformation of PCBs (PolyChlorinated Biphenyls) because they are exceedingly toxic and highly resistant to degradation, hence cumulatively affect marine ecosystems. Being lipophilic compounds, PCBs demonstrate the distinguishing sorption/desorption activity taking part in the biogeochemical fluxes via the organic matter particles and sediments. In the framework of the research, the coastal in-situ data on PCB concentration in the water column and sediments are processed, visualized and analyzed. It is concluded that the main sources of PCBs are related to the Danube discharge and resuspension from the shallow-water sediments. Developed 3D numerical model is aimed at simulation of PCB contamination of the water column and sediment. The model integrates the full physics hydrodynamic block as well as modules, which describe detritus transport and transformation and PCB dynamics. Three state variables are simulated in PCB transport module: concentration in solute, on the settling particles of detritus and in the top layer of sediments. PCB adsorption/desorption on detritus; the reversible PCB fluxes at the water-sediment boundary; destruction of detritus are taken into consideration. Formalization of PCB deposition/resuspension in the sediments is adapted from Van Rijn's model of the suspended sediment transport. The model was spun up to reconstruct the short term scenario of the instantaneous PCB release from the St. George Arm of Danube. It has been shown that PCB transport on sinking detritus represents the natural buffer mechanism damping the spreading PCB
Alfv\\'en-dynamo balance and magnetic excess in MHD turbulence
Grappin, Roland; Verdini, Andrea
2016-01-01
3D Magnetohydrodynamic (MHD) turbulent flows with initially magnetic and kinetic energies at equipartition spontaneously develop a magnetic excess (or residual energy), as well in numerical simulations and in the solar wind. Closure equations obtained in 1983 describe the residual spectrum as being produced by a dynamo source proportional to the total energy spectrum, balanced by a linear Alfv\\'en damping term. A good agreement was found in 2005 with incompressible simulations; however, recent solar wind measurements disagree with these results. The previous dynamo-Alfv\\'en theory is generalized to a family of models, leading to simple relations between residual and total energy spectra. We want to assess these models in detail against MHD simulations and solar wind data. The family of models is tested against compressible decaying MHD simulations with low Mach number, low cross-helicity, zero mean magnetic field, without or with expansion terms (EBM or expanding box model). A single dynamo-Alfv\\'en model is ...
Turbulent dynamo with advective magnetic helicity flux
Del Sordo, Fabio; Brandenburg, Axel
2012-01-01
Many astrophysical bodies harbor magnetic fields that are thought to be sustained by dynamo processes. However, it has been argued that the production of large-scale magnetic fields by a mean-field dynamo is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of magnetic helicity. This phenomenon is known as catastrophic quenching. Advection of magnetic field toward the outer boundaries and away from the dynamo is expected to alleviate such quenching. Examples are stellar and galactic winds. Such advection might be able to overcome the constraint imposed by the conservation of magnetic helicity, transporting a fraction of it outside the domain in which the dynamo operates. We study how the dynamo process is affected by advection. In particular, we study the relative roles played by advective and diffusive fluxes of magnetic helicity. We do this by performing direct numerical simulations of a turbulent dynamo of alpha^2 type driven by forced turbulence in a Cartesian domain in the ...
Zanini, A.; Tanda, M.
2007-12-01
The groundwater in Italy plays an important role as drinking water; in fact it covers about the 30% of the national demand (70% in Northern Italy). The mineral water distribution in Italy is an important business with an increasing demand from abroad countries. The mineral water Companies have a great interest in order to increase the water extraction, but for the delicate and complex geology of the subsoil, where such very high quality waters are contained, a particular attention must be paid in order to avoid an excessive lowering of the groundwater reservoirs or great changes in the groundwater flow directions. A big water Company asked our University to set up a numerical model of the groundwater basin, in order to obtain a useful tool which allows to evaluate the strength of the aquifer and to design new extraction wells. The study area is located along Appennini Mountains and it covers a surface of about 18 km2; the topography ranges from 200 to 600 m a.s.l.. In ancient times only a spring with naturally sparkling water was known in the area, but at present the mineral water is extracted from deep pumping wells. The area is characterized by a very complex geology: the subsoil structure is described by a sequence of layers of silt-clay, marl-clay, travertine and alluvial deposit. Different groundwater layers are present and the one with best quality flows in the travertine layer; the natural flow rate seems to be not subjected to seasonal variations. The water age analysis revealed a very old water which means that the mineral aquifers are not directly connected with the meteoric recharge. The Geologists of the Company suggest that the water supply of the mineral aquifers comes from a carbonated unit located in the deep layers of the mountains bordering the spring area. The valley is crossed by a river that does not present connections to the mineral aquifers. Inside the area there are about 30 pumping wells that extract water at different depths. We built a 3
Bartzke, Gerhard; Rogers, Benedict D.; Fourtakas, Georgios; Mokos, Athanasios; Huhn, Katrin
2016-04-01
The processes that cause the creation of a variety of sediment morphological features, e.g. laminated beds, ripples, or dunes, are based on the initial motion of individual sediment grains. However, with experimental techniques it is difficult to measure the flow characteristics, i.e., the velocity of the pore water flow in sediments, at a sufficient resolution and in a non-intrusive way. As a result, the role of fluid infiltration at the surface and in the interior affecting the initiation of motion of a sediment bed is not yet fully understood. Consequently, there is a strong need for numerical models, since these are capable of quantifying fluid driven sediment transport processes of complex sediment beds composed of irregular shapes. The numerical method Smoothed Particle Hydrodynamics (SPH) satisfies this need. As a meshless and Lagrangian technique, SPH is ideally suited to simulating flows in sediment beds composed of various grain shapes, but also flow around single grains at a high temporal and spatial resolution. The solver chosen is DualSPHysics (www.dual.sphysics.org) since this is validated for a range of flow conditions. For the present investigation a 3-D numerical flume model was generated using SPH with a length of 4.0 cm, a width of 0.05 cm and a height of 0.2 cm where mobile sediment particles were deposited in a recess. An experimental setup was designed to test sediment configurations composed of irregular grain shapes (grain diameter, D50=1000 μm). Each bed consisted of 3500 mobile objects. After the bed generation process, the entire domain was flooded with 18 million fluid particles. To drive the flow, an oscillating motion perpendicular to the bed was applied to the fluid, reaching a peak value of 0.3 cm/s, simulating 4 seconds of real time. The model results showed that flow speeds decreased logarithmically from the top of the domain towards the surface of the beds, indicating a fully developed boundary layer. Analysis of the fluid
Numerical simulation of X-wing type biplane flapping wings in 3D using the immersed boundary method.
Tay, W B; van Oudheusden, B W; Bijl, H
2014-09-01
The numerical simulation of an insect-sized 'X-wing' type biplane flapping wing configuration is performed in 3D using an immersed boundary method solver at Reynolds numbers equal to 1000 (1 k) and 5 k, based on the wing's root chord length. This X-wing type flapping configuration draws its inspiration from Delfly, a bio-inspired ornithopter MAV which has two pairs of wings flapping in anti-phase in a biplane configuration. The objective of the present investigation is to assess the aerodynamic performance when the original Delfly flapping wing micro-aerial vehicle (FMAV) is reduced to the size of an insect. Results show that the X-wing configuration gives more than twice the average thrust compared with only flapping the upper pair of wings of the X-wing. However, the X-wing's average thrust is only 40% that of the upper wing flapping at twice the stroke angle. Despite this, the increased stability which results from the smaller lift and moment variation of the X-wing configuration makes it more suited for sharp image capture and recognition. These advantages make the X-wing configuration an attractive alternative design for insect-sized FMAVS compared to the single wing configuration. In the Reynolds number comparison, the vorticity iso-surface plot at a Reynolds number of 5 k revealed smaller, finer vortical structures compared to the simulation at 1 k, due to vortices' breakup. In comparison, the force output difference is much smaller between Re = 1 k and 5 k. Increasing the body inclination angle generates a uniform leading edge vortex instead of a conical one along the wingspan, giving higher lift. Understanding the force variation as the body inclination angle increases will allow FMAV designers to optimize the thrust and lift ratio for higher efficiency under different operational requirements. Lastly, increasing the spanwise flexibility of the wings increases the thrust slightly but decreases the efficiency. The thrust result is similar to one of the
Numerical simulation of X-wing type biplane flapping wings in 3D using the immersed boundary method
The numerical simulation of an insect-sized ‘X-wing’ type biplane flapping wing configuration is performed in 3D using an immersed boundary method solver at Reynolds numbers equal to 1000 (1 k) and 5 k, based on the wing's root chord length. This X-wing type flapping configuration draws its inspiration from Delfly, a bio-inspired ornithopter MAV which has two pairs of wings flapping in anti-phase in a biplane configuration. The objective of the present investigation is to assess the aerodynamic performance when the original Delfly flapping wing micro-aerial vehicle (FMAV) is reduced to the size of an insect. Results show that the X-wing configuration gives more than twice the average thrust compared with only flapping the upper pair of wings of the X-wing. However, the X-wing's average thrust is only 40% that of the upper wing flapping at twice the stroke angle. Despite this, the increased stability which results from the smaller lift and moment variation of the X-wing configuration makes it more suited for sharp image capture and recognition. These advantages make the X-wing configuration an attractive alternative design for insect-sized FMAVS compared to the single wing configuration. In the Reynolds number comparison, the vorticity iso-surface plot at a Reynolds number of 5 k revealed smaller, finer vortical structures compared to the simulation at 1 k, due to vortices’ breakup. In comparison, the force output difference is much smaller between Re = 1 k and 5 k. Increasing the body inclination angle generates a uniform leading edge vortex instead of a conical one along the wingspan, giving higher lift. Understanding the force variation as the body inclination angle increases will allow FMAV designers to optimize the thrust and lift ratio for higher efficiency under different operational requirements. Lastly, increasing the spanwise flexibility of the wings increases the thrust slightly but decreases the efficiency. The thrust result is similar
David Boutelier; M. Rosenau; T. Ziegenhagen; Frank Neumann; O. Oncken; A. Cruden
2011-01-01
The influence of plate boundary curvature on the large-scale stress and strain patterns in an overriding plate is explored using 2D numerical and 3D thermo-mechanical analogue experiments. Numerical experiments reveal that trench-parallel compression is produced near the symmetry axis of a seaward-concave plate boundary if in- terplate friction is high and/or the subducting lithosphere has a low flexural rigidity. In contrast, trench-parallel compression is reduced along the obliq...
Heat flux modulation in domino dynamo model
Reshetnyak, Maxim
2012-01-01
Using domino dynamo model we show how variations of the heat flux at the core-mantle boundary change frequency of geomagnetic field reversals. In fact, we are able to demonstrate effect known from the modern 3D planetary dynamo models using ensemble of the interacting spins, which obey equations of the Langevin-type with a random force. We also consider applications to the giant- planets and offer explanations of some specific episodes of the geomagnetic field in the past.
Experimental realization of dynamo action: present status and prospects
Giesecke, Andre; Gundrum, Thomas; Gerbeth, Gunter; Nore, Caroline; Leorat, Jacques
2012-01-01
In the last decades, the experimental study of dynamo action has made great progress. However, after the dynamo experiments in Karlsruhe and Riga, the von-Karman-Sodium (VKS) dynamo is only the third facility that has been able to demonstrate fluid flow driven self-generation of magnetic fields in a laboratory experiment. Further progress in the experimental examination of dynamo action is expected from the planned precession driven dynamo experiment that will be designed in the framework of the liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies). In this paper, we briefly present numerical models of the VKS dynamo that demonstrate the close relation between the axisymmetric field observed in that experiment and the soft iron material used for the flow driving impellers. We further show recent results of preparatory water experiments and design studies related to the precession dynamo and delineate the scientific prospects for the final set-up.
3D numerical model of the spherical particle saltation in a channel with a rough fixed bed
Lukerchenko, Nikolay; Piatsevich, Siarhei; Chára, Zdeněk; Vlasák, Pavel
2009-01-01
Roč. 57, č. 2 (2009), s. 100-112. ISSN 0042-790X R&D Projects: GA ČR GA103/06/1487 Institutional research plan: CEZ:AV0Z20600510 Keywords : 3D Saltation Model * Bed-Load Transport * Particle-Bed Collision * Particle Rotation * Particle Lateral Dispersion Subject RIV: BK - Fluid Dynamics Impact factor: 1.000, year: 2009
A Three-Dimensional Babcock-Leighton Solar Dynamo Model: Initial Results with Axisymmetric Flows
Miesch, Mark S
2015-01-01
The main objective of this paper is to introduce the STABLE (Surface flux Transport And Babcock-LEighton) solar dynamo model. STABLE is a 3D Babcock-Leighton/Flux Transport dynamo model in which the source of poloidal field is the explicit emergence, distortion, and dispersal of bipolar magnetic regions (BMRs). Here we describe the STABLE model in more detail than we have previously and we verify it by reproducing a 2D mean-field benchmark. We also present some representative dynamo simulations, focusing on the special case of kinematic magnetic induction and axisymmetric flow fields. Not all solutions are supercritical; it can be a challenge for the BL mechanism to sustain the dynamo when the turbulent diffusion near the surface is $\\geq 10^{12}$ cm$^2$ s$^{-1}$. However, if BMRs are sufficiently large, deep, and numerous, then sustained, cyclic, dynamo solutions can be found that exhibit solar-like features. Furthermore, we find that the shearing of radial magnetic flux by the surface differential rotation ...
Brown, Andrew
2014-08-01
Full Text Available This paper presents a prototype Stereolithography (STL file format slicing and tool-path generation algorithm, which serves as a data front-end for a Rapid Prototyping (RP entry- level three-dimensional (3-D printer. Used mainly in Additive Manufacturing (AM, 3-D printers are devices that apply plastic, ceramic, and metal, layer by layer, in all three dimensions on a flat surface (X, Y, and Z axis. 3-D printers, unfortunately, cannot print an object without a special algorithm that is required to create the Computer Numerical Control (CNC instructions for printing. An STL algorithm therefore forms a critical component for Layered Manufacturing (LM, also referred to as RP. The purpose of this study was to develop an algorithm that is capable of processing and slicing an STL file or multiple files, resulting in a tool-path, and finally compiling a CNC file for an entry-level 3- D printer. The prototype algorithm was implemented for an entry-level 3-D printer that utilises the Fused Deposition Modelling (FDM process or Solid Freeform Fabrication (SFF process; an AM technology. Following an experimental method, the full data flow path for the prototype algorithm was developed, starting with STL data files, and then processing the STL data file into a G-code file format by slicing the model and creating a tool-path. This layering method is used by most 3-D printers to turn a 2-D object into a 3-D object. The STL algorithm developed in this study presents innovative opportunities for LM, since it allows engineers and architects to transform their ideas easily into a solid model in a fast, simple, and cheap way. This is accomplished by allowing STL models to be sliced rapidly, effectively, and without error, and finally to be processed and prepared into a G-code print file.
Zhou, F.; Miorali, M.; Slob, E. C.; Arts, R.
2011-12-01
Smart wells, a new generation of wells used in oil production, combine down-hole monitoring and control of the reservoir flow. Smart technology allows the implementation of proactive strategies that can mitigate potential problems, such as the approach of undesired fluids, before they impact production from the well. The effectiveness of the proactive strategies depends on the ability of monitoring the near-well region. We propose that borehole radar is a promising technology for this purpose. We couple 3D reservoir flow modeling with 3D radar modeling. The time-lapse analysis of the electromagnetic simulations confirms that radar can map the movement of the oil-water contact in a range of 1-10 m from the well. The comparison of the 3D reflected signals with the 2D show a good correlation, which allows cheaper simulation for a large-scale reservoir model. We use the radar results to implement a proactive control strategy in a realistic reservoir scenario. The NPV(Net Present Value) has improved by controlling the production according to the modeled radar measurements. We suggest borehole radar as a promising application in oil production optimization if an effective smart well control strategy is combined.
Numerical investigation of 3-D constraint effects on brittle fracture in SE(B) and C(T) specimens
This investigation employs 3-D nonlinear finite element analyses to conduct an extensive parametric evaluation of crack front stress triaxiality for deep notch SE(B) and C(T) specimens and shallow notch SE(B) specimens, with and without side grooves. Crack front conditions are characterized in terms of J-Q trajectories and the constraint scaling model for cleavage fracture toughness proposed previously by Dodds and Anderson. The 3-D computational results imply that a significantly less strict size/deformation limit, relative to the limits indicated by previous plane-strain computations, is needed to maintain small-scale yielding conditions at fracture by a stress- controlled, cleavage mechanism in deep notch SE(B) and C(T) specimens. Additional new results made available from the 3-D analyses also include revised η-plastic factors for use in experimental studies to convert measured work quantities to thickness average and maximum (local) J-values over the crack front
V.I. GNESIN; L.V. KOLODYAZHNAYA; R. RZADKOWSKI
2005-01-01
Fiszera st., 14, Gdansk, 80 952 PolandIn this study presented the algorithm proposed involves the coupled solution of 3-D unsteady flow through a turbine stage and the dynamics problem for rotor-blade motion by the action of aerodynamic forces, without separating the outer and inner flow fluctuations. The partially integrated method involves the solution of the fluid and structural equations separately, but information is exchanged at each time step, so that solution from one domain is used as a boundary condition for the other domain. 3-D transonic gas flow through the stator and rotor blades in relative motion with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of GodunovKolgan. The structural analysis uses the modal approach and a 3-D finite element model of a blade. A calculation has been done for the last stage of the steam turbine, under design and off-design regimes. It is shown that the amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to the rotor moving past one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow nonunifonnity downstream from the blade row; moreover, the spectrum involves the harmonics which are not multiples of the rotation frequency.
Huber, E.; Huggenberger, P.
2012-12-01
Accurate predictions on groundwater flow and transport behavior within fluvial and glaciofluvial sediments, but also interaction with surface water bodies, rely on knowledge of distributed aquifer properties. The complexity of the depositional and erosional processes in fluvial systems leads to highly heterogeneous distributions of hydrogeological parameters. The system dynamics, such as aggradation rates and channel mobility of alluvial systems; its influence on the preservation potential of the key depositional elements in the geological record; and its influence on the heterogeneity scales and the relevance for groundwater hydraulics is topic of the presentation. The aims of our work are to find a relation between surface morphological structures and the sedimentary structures in vertical profiles (i.e. gravel pits or GPR sections) and to derive rules for the interpretation of horizontal time-slices from 3D GPR data. Based on these data we set-up conceptual models of the structures of coarse alluvial systems at different scales which can be tested by stochastic methods. Relevant depositional elements and a hierarchy or genetic relationship of such elements will be defined based on the knowledge of depositional processes in alluvial systems inferred from: field observations after major flood events; 2D and 3D GPR data; and from existing data derived from laboratory flumes. Extensive geophysical field experiments within the Tagliamento alluvial system gave new insights to the sedimentary structures developing at high flows. Owing to the fact that rivers often destroy at least part of their bed during or shortly after large floods and subsequently rebuild, it is not easy to establish a simple relationship between surface morphology and the sedimentary structures found in vertical sections of many alluvial outcrops. According to these findings we suppose that surface or near-surface structures will not catch the essence of heterogeneity of alluvial aquifers
Lavergne, Francis; Sab, Karam; Sanahuja, Julien; Bornert, Michel; Toulemonde, Charles
2015-01-01
Glass reinforced plastics based on polyvinyl chloride (PVC) is a material of choice for construction applications, such as pipes. The lifetime of pipes may be limited by creep failure and polymers exhibit a viscoelastic response that depends on the time of loading. In this paper, homogenization methods are designed to upscale the viscoelastic properties of a composite material made of chopped glass fibers with random orientations and PVC. The estimates of the Mori?Tanaka scheme and 3D numeric...
In the paper a successful automatisation of advanced air pollution dispersion modelling is presented. Air pollution dispersion modelling is an important part of dose projection procedures. At Krsko NPP modelling consists of 3D wind and turbulence field reconstruction and numerical Lagrangean particle model air pollution dispersion simulation. Input data collection and modelling calculations are done every half hour totally automatically. Results are automatically available for dose calculation system. (author)
Baocheng Shi; Jinjia Wei
2014-01-01
For numerically simulating 3D solid-liquid turbulent flow in low specific speed centrifugal pumps, there exist several problems including how to design geometrical shape of the calculation model to represent the real pump and how to predict pump performance accurately to guide the design of pump. To solve these problems, four kinds of geometric models were designed. The performance of a low specific speed solid-liquid centrifugal pump was predicted, and the results showed that the improved pr...
Petry, H.; Ebel, A.; Franzkowiak, V.; Hendricks, J.; Lippert, E.; Moellhoff, M. [Koeln Univ. (Germany). Inst. fuer Geophysik und Meteorologie
1997-12-31
The impact of aircraft emissions released in the tropopause region on atmospheric trace gases as O{sub 3} or HNO{sub 3} is investigated by means of model studies. Special emphasis is drawn on seasonal effects. A box model is applied as well as a 3-D mesoscale chemistry transport model. These model studies show that the impact of aircraft emissions on ozone in the tropopause region is much stronger in summer than in late autumn with a difference of one order of magnitude. (author) 14 refs.
Gabl, R.; Seibl, J.; Gems, B.; Aufleger, M.
2015-12-01
The impact of an avalanche in a reservoir induces impulse waves, which pose a threat to population and infrastructure. For a good approximation of the generated wave height and length as well as the resulting overtopping volume over structures and dams, formulas, which are based on different simplifying assumptions, can be used. Further project-specific investigations by means of a scale model test or numerical simulations are advisable for complex reservoirs as well as the inclusion of hydraulic structures such as spillways. This paper presents a new approach for a 3-D numerical simulation of the avalanche impact in a reservoir. In this model concept the energy and mass of the avalanche are represented by accelerated water on the actual hill slope. Instead of snow, only water and air are used to simulate the moving avalanche with the software FLOW-3D. A significant advantage of this assumption is the self-adaptation of the model avalanche onto the terrain. In order to reach good comparability of the results with existing research at ETH Zürich, a simplified reservoir geometry is investigated. Thus, a reference case has been analysed including a variation of three geometry parameters (still water depth in the reservoir, freeboard of the dam and reservoir width). There was a good agreement of the overtopping volume at the dam between the presented 3-D numerical approach and the literature equations. Nevertheless, an extended parameter variation as well as a comparison with natural data should be considered as further research topics.
The Supercritical-Water-Cooled Reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal-hydraulics in rod bundles of the core. The experimental conditions of mockup tests, however, have to be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique which can extrapolate experimental data to various design conditions of the reactor. JAEA (Japan Atomic Energy Agency) have been improved the three-dimensional two-fluid model analysis code ACE-3D, which has been developed originally for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water at supercritical region. In the present paper, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which simulates the core flow around a fuel rod, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was confirmed that the calculated wall surface temperature agreed with the measured results and the code is applicable to prediction of heat transfer of supercritical water in the system that simulates the SCWR core. (author)
Magnetic Helicity Conservation and Astrophysical Dynamos
Vishniac, E T; Vishniac, Ethan T.; Cho, Jungyeon
2000-01-01
We construct a magnetic helicity conserving dynamo theory which incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries in the second derivative of the velocity correlation function, closely related to the `twist and fold' dynamo model. The turbulent damping term is, as expected, almost unchanged. Numerical simulations with a spatially constant fluid helicity and vanishing resistivity are not expected to generate large scale fields in equipartition with the turbulent energy density. In fact, there seems to be little prospect for driving a fast dynamo in a closed box containing homogeneous turbulence. On the other hand, there is an efficient analog to the $\\alpha-\\Omega$ dynamo. Systems whose turbulence is driven by some anisotropic local instability in shearing flow, like real stars and accretion disks, and some computer simulations, ma...
Luquet, David; Marchiano, Régis; Coulouvrat, François, E-mail: francois.coulouvrat@upmc.fr [Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d’Alembert, F-75005, Paris (France)
2015-10-28
Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D
Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D
Luquet, David; Marchiano, Régis; Coulouvrat, François
2015-10-01
Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D
Progress in the Peeling-Ballooning Model of ELMs: Numerical Studies of 3D Nonlinear ELM Dynamics
Snyder, P B; Wilson, H R; Xu, X Q
2004-12-13
Nonlinear simulations with the 3D electromagnetic two-fluid BOUT code are employed to study the dynamics of edge localized modes (ELMs) driven by intermediate wavelength peeling-ballooning modes. It is found that the early behavior of the modes is similar to expectations from linear, ideal peeling-ballooning mode theory, with the modes growing linearly at a fraction of the Alfven frequency. In the non-linear phase, the modes grow explosively, forming a number of extended filaments which propagate rapidly from the outer closed flux region into the open flux region toward the outer wall. Similarities to non-linear linear ballooning theory, as well as additional complexities are observed. Comparison to observations reveals a number of similarities. Implications of the simulations and proposals for the dynamics of the full ELM crash are discussed.
PROGRESS IN THE PEELING-BALLOONING MODEL OF ELMS: NUMERICAL STUDIES OF 3D NONLINEAR ELM DYNAMICS
SNYDER,P.B; WILSON,H.R; XU,X.Q
2004-11-01
Nonlinear simulations with the 3D electromagnetic two-fluid BOUT code are employed to study the dynamics of edge localized modes (ELMs) driven by intermediate wavelength peeling-ballooning modes. It is found that the early behavior of the modes is similar to expectations from linear, ideal peeling-ballooning mode theory, with the modes growing linearly at a fraction of the Alfven frequency. In the nonlinear phase, the modes grow explosively, forming a number of extended filaments which propagate rapidly from the outer closed flux region into the open flux region toward the outboard wall. Similarities to non-linear ballooning theory, as well as additional complexities are observed. Comparison to observations reveals a number of similarities. Implications of the simulations and proposals for the dynamics of the full ELM crash are discussed.
PROGRESS IN THE PEELING-BALLOONING MODEL OF ELMS: NUMERICAL STUDIES OF 3D NONLINEAR ELM DYNAMICS
Nonlinear simulations with the 3D electromagnetic two-fluid BOUT code are employed to study the dynamics of edge localized modes (ELMs) driven by intermediate wavelength peeling-ballooning modes. It is found that the early behavior of the modes is similar to expectations from linear, ideal peeling-ballooning mode theory, with the modes growing linearly at a fraction of the Alfven frequency. In the nonlinear phase, the modes grow explosively, forming a number of extended filaments which propagate rapidly from the outer closed flux region into the open flux region toward the outboard wall. Similarities to non-linear ballooning theory, as well as additional complexities are observed. Comparison to observations reveals a number of similarities. Implications of the simulations and proposals for the dynamics of the full ELM crash are discussed
Menant, Armel; Sternai, Pietro; Jolivet, Laurent; Guillou-Frottier, Laurent; Gerya, Taras
2016-05-01
Interactions between subduction dynamics and magma genesis have been intensely investigated, resulting in several conceptual models derived from geological, geochemical and geophysical data. To provide physico-chemical constraints on these conceptual models, self-consistent numerical simulations containing testable thermo-mechanical parameters are required, especially considering the three-dimensional (3D) natural complexity of subduction systems. Here, we use a 3D high-resolution petrological and thermo-mechanical numerical model to quantify the relative contribution of oceanic and continental subduction/collision, slab roll-back and tearing to magma genesis and transport processes. Our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3D slab dynamics and related asthenospheric flow. Moreover, the decrease of the bulk lithospheric strength induced by mantle- and crust-derived magmas promotes the propagation of strike-slip and extensional fault zones through the overriding crust as response to slab roll-back and continental collision. Reduction of the lithosphere/asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust. Similarities between our modeling results and the late Cenozoic tectonic and magmatic evolution across the eastern Mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region, which in turn promotes lithospheric deformation by mantle drag via melt-induced weakening effects.
Hou-de Han; Xin Wen
2003-01-01
We consider the numerical approximations of the three-dimensional steady potential flow around a body moving in a liquid of finite constant depth at constant speed and distance below a free surface in a channel. One vertical side is introduced as the upstream artificial boundary and two vertical sides are introduced as the downstream artificial boundaries. On the artificial boundaries, a sequence of high-order global artificial boundary conditions are given. Then the original problem is reduced to a problem defined on a finite computational domain, which is equivalent to a variational problem. After solving the variational problem by the finite element method, we obtain the numerical approximation of the original problem. The numerical examples show that the artificial boundary conditions given in this paper are very effective.
Haji Mohammadi, M.; Kang, S.; Sotiropoulos, F.
2011-12-01
It is well-known that meander bends impose local losses of energy to the flow in rivers. These local losses should be added together with friction loss to get the total loss of energy. In this work, we strive to develop a framework that considers the effect of bends in meandering rivers for one-dimensional (1-D) homogenous equations of flow. Our objective is to develop a simple, yet physically sound, and efficient model for carrying out engineering computations of flow through meander bends. We consider several approaches for calculating 1-D hydraulic properties of meandering rivers such as friction factor and Manning coefficient. The method of Kasper et al. (2005), which is based on channel top width, aspect ratio and radius of curvature, is adopted for further calculations. In this method, a correction is implemented in terms of local energy loss, due to helical motion and secondary currents of fluid particles driven by centrifugal force, in meanders. To validate the model, several test cases are simulated and the computed results are compared with the reported data in the literature in terms of water surface elevation, shear velocity, etc. For all cases the computed results are in reasonable agreement with the experimental data. 3-D RANS turbulent flow simulations are also carried out, using the method of Kang et al. (Adv. In Water Res., vol. 34, 2011), for different geometrical parameters of Kinoshita Rivers to determine the spatial distribution of shear stress on river bed and banks, which is the key factor in scour/deposition patterns. The 3-D solutions are then cross-sectionally averaged and compared with the respective solutions from the 1-D model. The comparisons show that the improved 1D model, which incorporates the effect of local bend loss, captures key flow parameters with reasonable accuracy. Our results also underscore the range of validity and limitations of 1D models for meander bend simulations. This work was supported by NSF Grants (as part of
Bentzen, Thomas Ruby
2009-01-01
The paper presents results from an experimental and numerical study of flows and transport of primarily particle bound pollutants in highway wet detention ponds. The study presented here is part of a general investigation on road runoff and pollution in respect to wet detention ponds. The objecti...
Thermally driven hydromagnetic dynamos
There are still many challenges to be overcome before we can claim to have a full understanding of the generation of the Earth's magnetic field. From a mathematical point of view, the governing equations are nonlinear and must be solved in fully three dimensions, meaning that a numerical method must be employed, although this would probably also be the case for a two-dimensional problem. However, it is only relatively recently that the computer technology has become available to make this possible. Obtaining these solutions remains a highly computationally intensive task, making it difficult to find solutions for a range of parameter values. This is extremely important as a great deal of uncertainty still surrounds the present (and past) geophysical values of the main parameters in the governing equations. Our aim is to try and further understanding of the effect of varying some of these key parameters in simplified, but fully self-consistent hydromagnetic dynamo models. These models will allow us to examine the effect of including the full inertial term to the equations, which has in the past been neglected due to the small geophysical value of the parameter which controls its effect. Further physical insight into the magnetic field generation mechanism will be provided, and we will examine some key issues in numerical dynamo modelling
Vizman, D.; Dadzis, K.; Friedrich, J.
2013-10-01
The role of various growth and process conditions (Lorentz force, temperature gradients in the melt and the crystal, steady-state crystallization velocity) in directional solidification of multicrystalline silicon in a traveling magnetic field is analyzed for a research-scale furnace (melt size of 22×22×11 cm3). The influence on the melt flow pattern, the typical melt flow velocity, the oscillation amplitude of the velocity and the temperature, the shape of the crystallization interface is determined using three-dimensional (3D) numerical calculations with the STHAMAS3D software and a local quasi steady-state model. It was found that both the interface shape and the melt flow are sensitive to the variation of the considered growth and process parameters.
Erlekampf, J.; Seebeck, J.; Savva, P.; Meissner, E.; Friedrich, J.; Alt, N. S. A.; Schlücker, E.; Frey, L.
2014-10-01
A numerical analysis of an ammonothermal synthesis process for the bulk growth of nitride crystals was performed. The analysis includes the development of a thermal model for a lab-scale ammonothermal autoclave, which was validated by in situ temperature measurements and applied to tailor the temperature field inside the autoclave. Based on the results of the global thermal 2D simulations, a local 3D model was used to include convective phenomena in the analysis. Moreover, the influence of the baffle and different baffle shapes on the flow velocity was investigated. Fluctuations of the temperature as well as the flow velocities occur, indicating that 3D considerations are essential to accurately investigate the heat and mass transport in ammonothermal systems.
Sangermano, J. J.; Zhou, Z.; Hsu, T.
2012-12-01
When a tsunami wave propagates toward the coast, the interactions of the waves, shoreline, and coastal hard structures can cause the generation of large coherent structures (vortices). These coherent structures are shown to last for a long time through Boussinesq wave modeling (Son et al. 2011, Ocean Modeling, 38) and are believed to cause damage to vessels and coastal structures. Here, we investigate the generation, evolution, and dissipation of these coherent structures using a 3D large eddy simulation approach with a dynamic Smagorinsky closure, and a volume of fluid scheme for free surface tracking. The open-source CFD library OpenFOAM model is validated by lab experiments conducted on solitary waves by Synolakis (1987, Journal of Fluid Mechanics, 185) and Ting (2006, Coastal Engineering, 53). The model predicts wave shoaling, run up, ensemble-averaged velocity, and turbulence fields in agreement with laboratory observations. Analysis of simulation results focusses on the generation and evolution of turbulent coherent structures and their interaction with the seabed. Implications for sediment transport are investigated through nondimensional bottom stress (Shields parameter) and flow acceleration (Sleath parameter) as these are critical parameters for the initiation of sheet flow and plug flow. We pay special attention during the deceleration and drawdown stage of the simulation because large turbulence and bottom stress is known to occur according to prior literature. Preliminary results on the generation and evolution of horizontal coherent structures in shallow water due to solitary wave interaction with hard structures will also be presented.
Numerical modeling of the Linac4 negative ion source extraction region by 3D PIC-MCC code ONIX
Mochalskyy, S; Minea, T; Lifschitz, AF; Schmitzer, C; Midttun, O; Steyaert, D
2013-01-01
At CERN, a high performance negative ion (NI) source is required for the 160 MeV H- linear accelerator Linac4. The source is planned to produce 80 mA of H- with an emittance of 0.25 mm mradN-RMS which is technically and scientifically very challenging. The optimization of the NI source requires a deep understanding of the underling physics concerning the production and extraction of the negative ions. The extraction mechanism from the negative ion source is complex involving a magnetic filter in order to cool down electrons’ temperature. The ONIX (Orsay Negative Ion eXtraction) code is used to address this problem. The ONIX is a selfconsistent 3D electrostatic code using Particles-in-Cell Monte Carlo Collisions (PIC-MCC) approach. It was written to handle the complex boundary conditions between plasma, source walls, and beam formation at the extraction hole. Both, the positive extraction potential (25kV) and the magnetic field map are taken from the experimental set-up, in construction at CERN. This contrib...
On the role of meridional flows in flux transport dynamo models
Jouve, L
2007-01-01
The Sun is a magnetic star whose magnetism and cyclic activity is linked to the existence of an internal dynamo. We aim to understand the establishment of the solar magnetic 22-yr cycle, its associated butterfly diagram and field parity selection through numerical simulations of the solar global dynamo. Inspired by recent observations and 3D simulations that both exhibit multicellular flows in the solar convection zone, we seek to characterise the influence of various profiles of circulation on the behaviour of solar mean-field dynamo models. We are using 2-D mean field flux transport Babcock-Leighton numerical models in which we test several types of meridional flows: 1 large single cell, 2 cells in radius and 4 cells per hemisphere. We confirm that adding cells in latitude tends to speed up the dynamo cycle whereas adding cells in radius more than triples the period. We find that the cycle period in the four cells model is less sensitive to the flow speed than in the other simpler meridional circulation pro...
K. Majidi
2000-01-01
Full Text Available The flow field in volute and circular casings interacting with a centrifugal impeller is obtained by numerical analysis. In the present study, effects of the volute and circular casings on the flow pattern have been investigated by successively combining a volute casing and a circular casing with a single centrifugal impeller. The numerical calculations are carried out with a multiple frame of reference to predict the flow field inside the entire impeller and casings. The impeller flow field is solved in a rotating frame and the flow field in the casings in a stationary frame. The static pressure and velocity in the casing and impeller, and the static pressures and secondary velocity vectors at several cross-sectional planes of the casings are calculated. The calculations show that the curvature of the casings creates pressure gradients that cause vortices at cross-sectional planes of the casings.
Castillo-Reyes, Octavio; de la Puente, Josep; Puzyrev, Vladimir; Cela, José M.
2015-01-01
This paper deals with the most relevant parallel and numerical issues that arise when applying the Edge Element Method in the solution of electromagnetic problems in exploration geophysics. In this sense, in recent years the application of land and marine controlled-source electromagnetic (CSEM) surveys has gained tremendous interest among the offshore exploration community. This method is especially significant in detecting hydrocarbon in shallow/deep waters. On the other hand, in Finite Ele...
Sun Yongle; Li Q.M.; Withers P.J.
2015-01-01
Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band) of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi) may not be sufficiently representative to capture t...
Yang, Jianfeng; Kaus, Boris
2016-04-01
The mechanism of intraplate deformation remains incompletely understood by plate tectonics theory. The India-Asia collision zone is the largest present-day example of continental collision, which makes it an ideal location to study the processes of continental deformation. Existing models of lithospheric deformation are typically quasi two-dimensional and often assume that the lithosphere is a thin viscous sheet, which deforms homogeneously as a result of the collision, or flows above a partially molten lower crust, which explains the exhumation of Himalayan units and lateral spreading of Tibetan plateau. An opposing view is that most deformation localize in shear zones separating less deformed blocks, requiring the lithosphere to have an elasto-plastic rather than a viscous rheology. In order to distinguish which model best fits the observations we develop a 3-D visco-elasto-plastic model, which can model both distributed and highly localized deformation. In our preliminary result, most of the large-scale strike-slips faults including Altyn-Tagh fault, Xianshuihe fault, Red-River fault, Sagaing fault and Jiali fault can be simulated. The topography is consistent with observations that flat plateau in central Tibet and steep, abrupt margins adjacent to Sichuan basin, and gradual topography in southeast Tibet. These models suggest that the localized large-scale strike-slip faults accommodate the continental deformation. These results show the importance of a weak lower crust and topographic effects, as well as the effect of rheology and temperature structure of the lithosphere on the deformation patterns.
Wu, Dongwei
In recent years, Mainland China, and in particular the industrial hotbed of the Pearl River Delta (PRD) has experienced an increasingly serious problem of high concentrations of airborne particulate matter. Following the tightening-up of China's air quality policies in recent years, and with especially fine particles now added to a new air quality objective, the identification of major source regions and major types of pollutants has become critically important. In this study, a source-oriented method (Particulate Source Apportionment Technology: PSAT) implemented in 3-D Comprehensive Air Quality Model (CAMx), has been applied to analyze how different emission activities impact fine particle concentration in the PRD region. By using this method, a detailed source region and emission category contribution matrix is derived for all regions within the Hong Kong/PRD region. Source appointment results shows that, in summer and spring time, emissions inside PRD region are the major fine particle sources, contribution 70.7% (11.2 mug/m3) and 52.5% (13.1 mug/m3) to the total figure. Super-regional transports are found to be significant in autumn and winter, contribution 58.5% (20.2 mug/m3) and 64.6% (27.8 mug/m3) of the total fine particles in PRD and Hong Kong region. Another important cause of high PM levels has been the transport of fine particles between cities within the PRD region, with three different regions selected for detailed analysis. Results show that mobile vehicle and industry emission are the two major sources for fine particles. Meanwhile, over the same period in Hong Kong, marine proved to be another very significant source of particle pollutant in addition to the significant impact from motor vehicle. Results show that for the Hong Kong/PRD region local reduction of mobile sources and collaboration between different areas could have succeeded in alleviating the air pollution problem.
Rodrigues, Dario B.; Maccarini, Paolo F.; Salahi, Sara; Colebeck, Erin; Topsakal, Erdem; Pereira, Pedro J. S.; Limão-Vieira, Paulo; Stauffer, Paul R.
2013-02-01
Background: Brown adipose tissue (BAT) plays an important role in whole body metabolism and could potentially mediate weight gain and insulin sensitivity. Although some imaging techniques allow BAT detection, there are currently no viable methods for continuous acquisition of BAT energy expenditure. We present a non-invasive technique for long term monitoring of BAT metabolism using microwave radiometry. Methods: A multilayer 3D computational model was created in HFSSTM with 1.5 mm skin, 3-10 mm subcutaneous fat, 200 mm muscle and a BAT region (2-6 cm3) located between fat and muscle. Based on this model, a log-spiral antenna was designed and optimized to maximize reception of thermal emissions from the target (BAT). The power absorption patterns calculated in HFSSTM were combined with simulated thermal distributions computed in COMSOL® to predict radiometric signal measured from an ultra-low-noise microwave radiometer. The power received by the antenna was characterized as a function of different levels of BAT metabolism under cold and noradrenergic stimulation. Results: The optimized frequency band was 1.5-2.2 GHz, with averaged antenna efficiency of 19%. The simulated power received by the radiometric antenna increased 2-9 mdBm (noradrenergic stimulus) and 4-15 mdBm (cold stimulus) corresponding to increased 15-fold BAT metabolism. Conclusions: Results demonstrated the ability to detect thermal radiation from small volumes (2-6 cm3) of BAT located up to 12 mm deep and to monitor small changes (0.5 °C) in BAT metabolism. As such, the developed miniature radiometric antenna sensor appears suitable for non-invasive long term monitoring of BAT metabolism.
Kwak, D.
1994-01-01
INS3D computes steady-state solutions to the incompressible Navier-Stokes equations. The INS3D approach utilizes pseudo-compressibility combined with an approximate factorization scheme. This computational fluid dynamics (CFD) code has been verified on problems such as flow through a channel, flow over a backwardfacing step and flow over a circular cylinder. Three dimensional cases include flow over an ogive cylinder, flow through a rectangular duct, wind tunnel inlet flow, cylinder-wall juncture flow and flow through multiple posts mounted between two plates. INS3D uses a pseudo-compressibility approach in which a time derivative of pressure is added to the continuity equation, which together with the momentum equations form a set of four equations with pressure and velocity as the dependent variables. The equations' coordinates are transformed for general three dimensional applications. The equations are advanced in time by the implicit, non-iterative, approximately-factored, finite-difference scheme of Beam and Warming. The numerical stability of the scheme depends on the use of higher-order smoothing terms to damp out higher-frequency oscillations caused by second-order central differencing. The artificial compressibility introduces pressure (sound) waves of finite speed (whereas the speed of sound would be infinite in an incompressible fluid). As the solution converges, these pressure waves die out, causing the derivation of pressure with respect to time to approach zero. Thus, continuity is satisfied for the incompressible fluid in the steady state. Computational efficiency is achieved using a diagonal algorithm. A block tri-diagonal option is also available. When a steady-state solution is reached, the modified continuity equation will satisfy the divergence-free velocity field condition. INS3D is capable of handling several different types of boundaries encountered in numerical simulations, including solid-surface, inflow and outflow, and far
Colloquium: Laboratory experiments on hydromagnetic dynamos
Cosmic magnetic fields, including the fields of planets, stars, and galaxies, are believed to be caused by dynamo action in moving electrically conducting fluids. While the theory and numerics of hydromagnetic dynamos have flourished during recent decades, an experimental validation of the effect was missing until recently. We sketch the long history towards a working laboratory dynamo. We report on the first successful experiments at the sodium facilities in Riga and Karlsruhe, and on other experiments which are carried out or planned at various places in the world
Magnetic Cycles and Buoyant Loops in Convective Dynamos
Nelson, Nicholas J.
2013-01-01
Solar-type stars display a rich spectrum of magnetic activity. Seeking to explore convective dynamo action in solar-like stars with the anelastic spherical harmonic (ASH) code, we have carried out a series of global 3-D MHD simulations. Here we report on the dynamo mechanisms realized in a series of numerical models of a sun-like star which explore the effects of decreasing diffusion. While these models nominally rotate at three times the current solar rate (3Ω), the results may be more widely applicable as both these simulations and the solar convection zone achieve similar levels of rotationally constrained convection. Previous simulations at 3Ω have shown that convective dynamos can build persistent wreath-like structures of strong toroidal magnetic field in the convection zone (Brown et al. 2010). Here we find that magnetic reversals and cycles can be realized at 3Ω by decreasing the explicit diffusion and thereby making the resolved flows more turbulent. In these more turbulent models, diffusive processes no longer play a primary role in the key dynamical balances which maintain differential rotation and generate the global-scale wreaths. With reduced resistive diffusion of magnetic fields, the axisymmetric poloidal fields can no longer achieve a steady state and this triggers reversals in global magnetic polarity. Additionally, the enhanced levels of turbulence lead to greater intermittency in the toroidal magnetic wreaths, which can create buoyant magnetic loops that rise from the deep interior to the upper regions of our simulated domain. Turbulence-enabled magnetic buoyancy in our most turbulent simulation yields large numbers of buoyant loops, enabling us to examine the distribution of the characteristics of buoyant magnetic loops, such as twist, tilt angle, and relation to axisymmetric fields. These models provide a pathway towards linking convective dynamo models and the emergence of magnetic flux in the Sun and sun-like stars.
The possibilities for applying the Finite Element Method (FEM) with gauged magnetic vector potential and the Edge Element Method (EEM) for three-dimensional numerical analysis of magnetostatic systems are analyzed. It is established that the EEM ensures sufficient accuracy for engineering calculations but in some cases its use results in bad convergence. The use of the FEM with gauged magnetic vector potential instead of the EEM is recommended for preliminary calculations of devices with complex geometry and large air gaps between the ferromagnetic parts. (Author)
Cho, Jae Ho; Cho, Kwang Hwan; Keum, Ki Chang; Han, Yong Yih; Kim, Yong Bae; Chu, Sung Sil; Suh, Chang Ok [College of Medicine, Yonsei Univ., Seoul (Korea, Republic of)
2003-03-01
To reduce the irradiation dose to the lungs and heart in the case of chest wall irradiation using an oppositional electron beam, we used an individualized custom bolus, which was precisely designed to compensate for the differences in chest wall thickness. The benefits were evaluated by comparing the normal tissue complication probabilities (NTCPs) and dose statistics both with and without boluses Boluses were made, and their effects evaluated in ten patients treated using the reverse hockey-stick technique. The electron beam energy was determined so as to administer 80% of the irradiation prescription dose to the deepest lung-chest wall border, which was usually located at the internal mammary lymph node chain. An individualized custom bolus was prepared to compensate for a chest wall thinner than the prescription depth by meticulously measuring the chest wall thickness at 1 cm{sup 2} intervals on the planning CT images. A second planning CT was obtained overlying the individualized custom bolus for each patient's chest wall. 3-D treatment planning was performed using ADAC-Pinnacle{sup 3} for all patients with and without bolus, NTCPs based on 'the Lyman-Kutcher' model were analyzed and the mean, maximum, minimum doses, V{sub 50} and V{sub 95} for the heart and lungs were computed. The average NTCPs in the ipsilateral lung showed a statistically significant reduction (p<0.01), from 80.2{+-}3.43% to 47.7{+-}4.61%, with the use of the individualized custom boluses. The mean lung irradiation dose to the ipsilateral lung was also significantly reduced by about 430 cGy from 2757 cGy to 2,327 cGy (p<0.01). The V{sub 50} and V{sub 95} in the ipsilateral lung markedly decreased from the averages of 54.5 and 17.4% to 45.3 and 11.0%, respectively. The V{sub 50} and V{sub 95} in the heart also decreased from the averages of 16.8 and 6.1% to 9.8% and 2.2%, respectively. The NTCP in the contralateral lung and the heart were 0%, even for the cases with no bolus
Numerical modelling and simulation provide an efficient tool for analysis and optimization of device structure design. In this paper we present the analysis and the geometry optimization of the power module with high power pin diode structure supported by the advanced 2-D/3-D mixed-mode electro-thermal device simulation. The structure under investigation is P+NN+ power diode device designed for high reverse voltages and very high forward currents, with a maximum forward surge current up to 2.7 kA.
Vergara, Christian; Lange, Matthias; Palamara, Simone; Lassila, Toni; Frangi, Alejandro F.; Quarteroni, Alfio
2016-03-01
We present a model for the electrophysiology in the heart to handle the electrical propagation through the Purkinje system and in the myocardium, with two-way coupling at the Purkinje-muscle junctions. In both the subproblems the monodomain model is considered, whereas at the junctions a resistor element is included that induces an orthodromic propagation delay from the Purkinje network towards the heart muscle. We prove a sufficient condition for convergence of a fixed-point iterative algorithm to the numerical solution of the coupled problem. Numerical comparison of activation patterns is made with two different combinations of models for the coupled Purkinje network/myocardium system, the eikonal/eikonal and the monodomain/monodomain models. Test cases are investigated for both physiological and pathological activation of a model left ventricle. Finally, we prove the reliability of the monodomain/monodomain coupling on a realistic scenario. Our results underlie the importance of using physiologically realistic Purkinje-trees with propagation solved using the monodomain model for simulating cardiac activation.
Document available in extended abstract form only. Plans are made in France in order to assess the feasibility of constructing a repository for radioactive waste at depth within a clay-stone layer. In this framework, the potential damage that may occur in the clay-stone surrounding a disposal gallery is of concern. First, it has been observed that excavation in such a material produces a pattern of fractures. Second, it is clear that the lining of any cavity built to store radioactive waste will eventually fail, albeit after a long period. The creep-prone clay-stone surrounding the cavity may then experience some damage. While the initial fractures have been effectively observed, the long term behavior or the liner-clay-stone pair is both important and difficult to assess, one major question being: how do the excavation-induced fractures affect the long term behavior? A 3D model is built using the distinct element approach. The 4.5 m - radius gallery is oriented along the major principal in-situ stress. The concrete - lined gallery is filled by a series of parallelepiped-shaped canisters, leaving specified voids between canisters and liner. The excavation - induced fractures are explicitly reproduced in the model, as observed, near the gallery. The model reproduces the behavior of the clay-stone subjected to different unloading paths, depending on the damage scenario for the liner, over a creep duration of 100 000 years. The instant response of the material is represented by a hardening-softening Hoek-Brown law, where damage before peak strength is simulated by hardening in the framework of plasticity theory, while post-peak behavior is classically produced by softening. Time - dependant behavior is produced using a modified Lemaitre model, including a creep threshold and variation of the creep velocity with damage. The liner and the canisters are considered as a Mohr-Coulomb material with fairly brittle softening. Steel reinforcement is not modeled. Since the
Yoshida, Hiroyuki; Misawa, Takeharu; Takase, Kazuyuki
Two-fluid model can simulate two-phase flow by computational cost less than detailed two-phase flow simulation method such as interface tracking method or particle interaction method. Therefore, two-fluid model is useful for thermal hydraulic analysis in large-scale domain such as a rod bundle. Japan Atomic Energy Agency (JAEA) develops three dimensional two-fluid model analysis code ACE-3D that adopts boundary fitted coordinate system in order to simulate complex shape flow channel. In this paper, boiling two-phase flow analysis in a tight-lattice rod bundle was performed by ACE-3D code. The parallel computation using 126 CPUs was applied to this analysis. In the results, the void fraction, which distributes in outermost region of rod bundle, is lower than that in center region of rod bundle. The tendency of void fraction distribution agreed with the measurement results by neutron radiography qualitatively. To evaluate effects of two-phase flow model used in ACE-3D code, numerical simulation of boiling two-phase in tight-lattice rod bundle with no lift force model was also performed. From the comparison of calculated results, it was concluded that the effects of lift force model were not so large for overall void fraction distribution of tight-lattice rod bundle. However, the lift force model is important for local void fraction distribution of fuel bundles.
Two-fluid model can simulate two-phase flow by computational cost less than detailed two-phase flow simulation method such as interface tracking method or particle interaction method. Therefore, two-fluid model is useful for thermal hydraulic analysis in large-scale domain such as a rod bundle. Japan Atomic Energy Agency (JAEA) develops three dimensional two-fluid model analysis code ACE-3D that adopts boundary fitted coordinate system in order to simulate complex shape flow channel. In this paper, boiling two-phase flow analysis in a tight-lattice rod bundle was performed by ACE-3D code. The parallel computation using 126 CPUs was applied to this analysis. In the results, the void fraction, which distributes in outermost region of rod bundle, is lower than that in center region of rod bundle. The tendency of void fraction distribution agreed with the measurement results by neutron radiography qualitatively. To evaluate effects of two-phase flow model used in ACE-3D code, numerical simulation of boiling two-phase in tight-lattice rod bundle with no lift force model was also performed. From the comparison of calculated results, it was concluded that the effects of lift force model were not so large for overall void fraction distribution of tight-lattice rod bundle. However, the lift force model is important for local void fraction distribution of fuel bundles. (author)
Castellanza, Riccardo; Fernandez Merodo, Josè Antonio; di Prisco, Claudio; Frigerio, Gabriele; Crosta, Giovanni B.; Orlandi, Gianmarco
2013-04-01
Aim of the study is the assessment of stability conditions for an abandoned gypsum mine (Bologna , Italy). Mining was carried out til the end of the 70s by the room and pillar method. During mining a karst cave was crossed karstic waters flowed into the mine. As a consequence, the lower level of the mining is completely flooded and portions of the mining levels show critical conditions and are structurally prone to instability. Buildings and infrastructures are located above the first and second level and a large portion of the area below the mine area, and just above of the Savena river, is urbanised. Gypsum geomechanical properties change over time; water, or even air humidity, dissolves or weaken gypsum pillars, leading progressively to collapse. The mine is located in macro-crystalline gypsum beds belonging to the Messinian Gessoso Solfifera Formation. Selenitic gypsum beds are interlayered with by centimetre to meter thick shales layers. In order to evaluate the risk related to the collapse of the flooded level (level 3) a deterministic approach based on 3D numerical analyses has been considered. The entire abandoned mine system up to the ground surface has been generated in 3D. The considered critical scenario implies the collapse of the pillars and roof of the flooded level 3. In a first step, a sequential collapse starting from the most critical pillar has been simulated by means of a 3D Finite Element code. This allowed the definition of the subsidence basin at the ground surface and the interaction with the buildings in terms of ground displacements. 3D numerical analyses have been performed with an elasto-perfectly plastic constitutive model. In a second step, the effect of a simultaneous collapse of the entire level 3 has been considered in order to evaluate the risk of a flooding due to the water outflow from the mine system. Using a 3D CFD (Continuum Fluid Dynamics) finite element code the collapse of the level 3 has been simulated and the volume of
Zemskova, Varvara; Deal, Morgan; Vauclair, Sylvie
2014-01-01
Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature and detailed structure can affect the excitation process of various stellar pulsation modes, and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, and its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection, and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (2013), and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. (2...
The Comet Rendezvous and Asteroid Flyby Mission (CRAF) will include, as one of its complement of thirteen scientific instruments, a plasma electron analyzer capable of providing 3-dimensional measurements of the energy and angular distribution of electrons in the solar wind, asteroidal and cometary environments. After initial instrument selection, mission planners at JPL suggested that an instrument capable of performing angular scanning electronically rather than mechanically be investigated. This paper describes the computer design of the new CRAF plasma electron detector, consisting of an electronic scanning component, called the 'elevation analyzer', and an energy analyzing component based on the Soft Particle Spectrometer (SPS) and its successor, the Spectrographic Particle Imager (SPI). Numerical simulation of each component's operation - consisting of ray-tracing particles through the electrostatic field of each analyzer and collecting statistics on those particles successfully transmitted - is used to determine the energy and angular response functions of each component and the design dimensions that optimize these responses. (orig.)
Spitz, Richard; Schmalholz, Stefan; Kaus, Boris
2016-04-01
The Helvetic nappe system of the European Alps is generally described as a complex of fold and thrust belts. While the overall geology of the system has been studied in detail, the understanding of the tectonic development and mechanical interconnection between overthrusting and folding is still incomplete. One clue comes from the mechanical stratigraphy and the corresponding lateral transition from overthrusting to folding, which is characteristic for the Helvetic nappe system. We employ a three-dimensional numerical model with linear and non-linear viscous rheology to investigate the control of the lateral variation in the thickness of a weak detachment horizon on the transition from folding to overthrusting during continental shortening. The model configuration is based on published work based on 2D numerical simulations. The simulations are conducted with the three-dimensional staggered-grid finite difference code LaMEM (Lithosphere and Mantle Evolution Model), which allows for coupled nonlinear thermo-mechanical modeling of lithospheric deformation with visco-elasto-plastic rheology and computation on massive parallel machines. Our model configuration consists of a stiff viscous layer, with a pre-existing weak zone, resting within a weaker viscous matrix. The reference viscosity ratio μL/μM (for the same strain rate) between the layer and matrix ranges from 10 to 200. The simulations were run with several distinct initial geometries by altering the thickness of the detachment horizon below the stiff layer across the configurations. Shortening with a constant bulk rate is induced by the prescription of a horizontal velocity on one side of the model. The first results of our simulations highlight the general importance of the initial geometry on the lateral transition from overthrusting to folding. Additionally, models with a stepwise lateral variation of the detachment horizon indicate a fold development orthogonal to the main compressional axis.
Sun Yongle
2015-01-01
Full Text Available Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi may not be sufficiently representative to capture the actual structural effect. To overcome these limitations, the strain-rate sensitivity of the compressive and tensile properties of closed-cell aluminium Alporas foam is investigated in this study by means of meso-scale realistic finite element (FE simulations. The FE modelling method based on X-ray computed tomography (CT image is introduced first, as well as its applications to foam materials. Then the compression and tension of Alporas foam at a wide variety of applied nominal strain-rates are simulated using FE model constructed from the actual cell geometry obtained from the CT image. The stain-rate sensitivity of compressive strength (collapse stress and tensile strength (0.2% offset yield point are evaluated when considering different cell-wall material properties. The numerical results show that the rate dependence of cell-wall material is the main cause of the strain-rate hardening of the compressive and tensile strengths at low and intermediate strain-rates. When the strain-rate is sufficiently high, shock compression is initiated, which significantly enhances the stress at the loading end and has complicated effect on the stress at the supporting end. The plastic tensile wave effect is evident at high strain-rates, but shock tension cannot develop in Alporas foam due to the softening associated with single fracture process zone occurring in tensile response. In all cases the micro inertia of individual cell walls subjected to localised deformation
Sun, Yongle; Li, Q. M.; Withers, P. J.
2015-09-01
Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band) of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi) may not be sufficiently representative to capture the actual structural effect. To overcome these limitations, the strain-rate sensitivity of the compressive and tensile properties of closed-cell aluminium Alporas foam is investigated in this study by means of meso-scale realistic finite element (FE) simulations. The FE modelling method based on X-ray computed tomography (CT) image is introduced first, as well as its applications to foam materials. Then the compression and tension of Alporas foam at a wide variety of applied nominal strain-rates are simulated using FE model constructed from the actual cell geometry obtained from the CT image. The stain-rate sensitivity of compressive strength (collapse stress) and tensile strength (0.2% offset yield point) are evaluated when considering different cell-wall material properties. The numerical results show that the rate dependence of cell-wall material is the main cause of the strain-rate hardening of the compressive and tensile strengths at low and intermediate strain-rates. When the strain-rate is sufficiently high, shock compression is initiated, which significantly enhances the stress at the loading end and has complicated effect on the stress at the supporting end. The plastic tensile wave effect is evident at high strain-rates, but shock tension cannot develop in Alporas foam due to the softening associated with single fracture process zone occurring in tensile response. In all cases the micro inertia of individual cell walls subjected to localised deformation is found to
Naoto Miyama; Kazuaki Inaba; Makoto Yamamoto
2008-01-01
In these years, a lot of environmental problems such as air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. Considering these backgrounds, jet engines with hydrogen-fueled combustion within a turbine blade passage have been studied. Although some studies have been made on injecting and burning hydrogen fuel from a stator surface, little is known about the interaction between a tip leakage vortex near the suction side of a rotor tip and hydrogen-fueled combustion.The purpose of this study is to clarify the influence of the tip leakage vortex on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ε turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is numerically visualized, and the three-dimensional turbulent flow fields with hydrogen combustion and the structure of the tip leakage vortex are investigated.
Miyama, Naoto; Inaba, Kazuaki; Yamamoto, Makoto
2008-06-01
In these years, a lot of environmental problems such as air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. Considering these backgrounds, jet engines with hydrogen-fueled combustion within a turbine blade passage have been studied. Although some studies have been made on injecting and burning hydrogen fuel from a stator surface, little is known about the interaction between a tip leakage vortex near the suction side of a rotor tip and hydrogen-fueled combustion. The purpose of this study is to clarify the influence of the tip leakage vortex on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ɛ turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is numerically visualized, and the three-dimensional turbulent flow fields with hydrogen combustion and the structure of the tip leakage vortex are investigated.
Chaljub, Emmanuel; Maufroy, Emeline; Moczo, Peter; Kristek, Jozef; Priolo, Enrico; Klin, Peter; De Martin, Florent; Zhang, Zenghuo; Hollender, Fabrice; Bard, Pierre-Yves
2013-04-01
Numerical simulation is playing a role of increasing importance in the field of seismic hazard by providing quantitative estimates of earthquake ground motion, its variability, and its sensitivity to geometrical and mechanical properties of the medium. Continuous efforts to develop accurate and computationally efficient numerical methods, combined with increasing computational power have made it technically feasible to calculate seismograms in 3D realistic configurations and for frequencies of interest in seismic design applications. Now, in order to foster the use of numerical simulations in practical prediction of earthquake ground motion, it is important to evaluate the accuracy of current numerical methods when applied to realistic 3D sites. This process of verification is a necessary prerequisite to confrontation of numerical predictions and observations. Through the ongoing Euroseistest Verification and Validation Project (E2VP), which focuses on the Mygdonian basin (northern Greece), we investigated the capability of numerical methods to predict earthquake ground motion for frequencies up to 4 Hz. Numerical predictions obtained by several teams using a wide variety of methods were compared using quantitative goodness-of-fit criteria. In order to better understand the cause of misfits between different simulations, initially performed for the realistic geometry of the Mygdonian basin, we defined five stringent canonical configurations. The canonical models allow for identifying sources of misfits and quantify their importance. Detailed quantitative comparison of simulations in relation to dominant features of the models shows that even relatively simple heterogeneous models must be treated with maximum care in order to achieve sufficient level of accuracy. One important conclusion is that the numerical representation of models with strong variations (e.g. discontinuities) may considerably vary from one method to the other, and may become a dominant source of
This work addresses a numerical investigation of the crack front fields and effects of crack-tip constraint in conventional fracture specimens with prescribed transverse delamination cracks. One purpose of this study is to conduct a systematic evaluation of delamination effects in side-grooved and plane-sided C(T) and clamped SE(T) fracture specimens, which are commonly utilized in fracture toughness testing of pipeline steels. Another is to quantify the potential coupling influence of specimen geometry and delamination size on crack-tip constraint by means of the J−Q theory thereby providing valuable insight into the effect of delamination cracks on macroscopic fracture behavior in conventional fracture specimens. Laboratory testing of an API 5L X70 steel at room temperature provides the mechanical properties used in the numerical analysis incorporating delamination cracks with varying sizes. Nonlinear finite element analyses of very detailed 3-D finite element models of C(T) and clamped SE(T) fracture specimens for the API X70 pipeline steel enable assessing the effects of prescribed delamination cracks on the crack front fields and constraint with increased deformation levels as characterized by the J-integral. Overall, the present analyses reveal important features of 3-D crack front fields in fracture specimens with a crack-divider delamination that have a direct bearing on the often observed toughness increase in fracture testing of materials with through-thickness anisotropy in mechanical properties. - Highlights: • Extensive 3-D FE analysis of fracture specimens with crack-divider delamination cracks. • Formation of a crack-divider drastically changes the distribution of J over the crack front. • Even a small delamination crack promotes a pronounced stress redistribution. • Side-grooves do not change significantly delamination cracking effects on fracture behavior. • Delamination cracking effects in clamped SE(T) and C(T) geometries are
Nonlinear MHD dynamo operating at equipartition
Archontis, V.; Dorch, Bertil; Nordlund, Åke
2007-01-01
Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy-equipartition a......Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy......-equipartition and a turbulent state. The generation and evolution of such strong magnetic fields is relevant for the understanding of dynamo action that occurs in stars and other astrophysical objects. Aims.We study the mode of operation of this dynamo, in the linear and non-linear saturation regimes. We also consider...... the effect of varying the magnetic and fluid Reymolds number on the non-linear behaviour of the system. Methods.We perform three-dimensional non-linear MHD simulations and visualization using a high resolution numerical scheme. Results.We find that this dynamo has a high growth rate in the linear regime...
Zemskova, Varvara [Department of Marine Sciences, University of North Carolina at Chapel Hill, 3202 Venable Hall, CB 3300, Chapel Hill, NC 27599-3300 (United States); Garaud, Pascale [Department of Applied Mathematics and Statistics, Baskin School of Engineering, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Deal, Morgan; Vauclair, Sylvie [Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, Université de Toulouse, F-31400-Toulouse (France)
2014-11-10
Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature, and detailed structure can affect the excitation process of various stellar pulsation modes and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, as well as its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection (which neglect radiative transfer and complex opacity effects) and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (within the scope of the aforementioned approximation) and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. prescription in the Toulouse-Geneva Evolution Code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Théado et al., that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases it ultimately triggers dynamical convection. The direct effects of radiative acceleration on the dynamics of fingering convection (especially in the
Stretch-Twist-Fold and slow filamentary dynamos in liquid sodium Madison Dynamo Experiments
de Andrade, Garcia
2009-01-01
Recently Ricca and Maggione [MHD (2008)] have presented a very simple and interesting model of stretch-twist-fold dynamo in diffusive media based on numerical simulations of Riemannian flux tubes. In this paper we present a yet simpler way of analytically obtaining fast and slow dynamo, generated by by the curvature energy of magnetic filaments in diffusive media. geometrical model for the galactic or accretion disk dynamo in shear flows is presented. In the fast dynamo case it is shown that the absence of stretching leads to the absence of fast dynamos and when torsion of filaments vanishes the dynamo action cannot be support as well. This is the Cowling-Zeldovich theorem for planar flows. Isotropy of the magnetic fields hypothesis is used to compute the fast nature of dynamo. A similar result using non-holonomic Frenet frame has been recently obtained for filamentary dynamos [Garcia de Andrade, AN (2008)]. The stretch-twist-fold (STF) filamented models discussed here may serve to formulate future experiment...
Subcritical dynamo bifurcation in the Taylor Green flow
Ponty, Yannick; Dubrulle, Berengere; Daviaud, François; Pinton, Jean-François
2007-01-01
We report direct numerical simulations of dynamo generation for flow generated using a Taylor-Green forcing. We find that the bifurcation is subcritical, and show its bifurcation diagram. We connect the associated hysteretic behavior with hydrodynamics changes induced by the action of the Lorentz force. We show the geometry of the dynamo magnetic field and discuss how the dynamo transition can be induced when an external field is applied to the flow.
Subcritical dynamo bifurcation in the Taylor Green flow
Ponty, Yannick; Laval, Jean-Phillipe; Dubrulle, Berengere; Daviaud, François; Pinton, Jean-François
2007-01-01
4 pages We report direct numerical simulations of dynamo generation for flow generated using a Taylor-Green forcing. We find that the bifurcation is subcritical, and show its bifurcation diagram. We connect the associated hysteretic behavior with hydrodynamics changes induced by the action of the Lorentz force. We show the geometry of the dynamo magnetic field and discuss how the dynamo transition can be induced when an external field is applied to the flow.
Period doubling route to chaos in Taylor-Green dynamo
Yadav, R; Verma, M K; Paul, S; Wahi, P
2010-01-01
We perform spectral simulations of dynamo for magnetic Prandtl number of one with Taylor-Green forcing. We observe dynamo transition through a supercritical pitchfork bifurcation. Beyond the transition, the numerical simulations reveal complex dynamo states with windows of constant, periodic, quasiperiodic, and chaotic magnetic field configurations. For some forcing amplitudes, multiple attractors were obtained for different initial conditions. We show that one of the chaotic windows follows the period-doubling route to chaos.
Dynamo generated by the centrifugal instability
Marcotte, Florence
2016-01-01
We present a new scenario for magnetic field amplification where an electrically conducting fluid is confined in a differentially rotating, spherical shell with thin aspect-ratio. When the angular momentum sufficiently decreases outwards, an hydrodynamic instability develops in the equatorial region, characterised by pairs of counter-rotating toroidal vortices similar to those observed in cylindrical Couette flow. These spherical Taylor-Couette vortices generate a subcritical dynamo magnetic field dominated by non-axisymmetric components. We show that the critical magnetic Reynolds number seems to reach a constant value at large Reynolds number and that the global rotation can strongly decrease the dynamo onset. Our numerical results are understood within the framework of a simple dynamical system, and we propose a low-dimensional model for subcritical dynamo bifurcations. Implications for both laboratory dynamos and astrophysical magnetic fields are finally discussed.
Fast dynamos in weakly ionized gases
Heitsch, Ellen G Zweibel Fabian
2008-01-01
The turnover of interstellar gas on $\\sim 10^9$yr timescales argues for the continuous operation of a galactic dynamo. The conductivity of interstellar gas is so high that the dynamo must be "fast" - i.e. the magnetic field must be amplified at a rate nearly independent of the magnetic diffusivity. Yet, all the fast dynamos so far known - and all direct numerical simulations of interstellar dynamos - yield magnetic power spectra that peak at the resistive scale, while galactic magnetic fields have substantial power on large scales. In this paper we show that in weakly ionized gas the limiting scale may be the ion-neutral decoupling scale, which although still small is many orders of magnitude larger than the resistive scale.
Castellanza, R.; Orlandi, G. M.; di Prisco, C.; Frigerio, G.; Flessati, L.; Fernandez Merodo, J. A.; Agliardi, F.; Grisi, S.; Crosta, G. B.
2015-09-01
After the abandonment occurred in the '70s, the mining system (rooms and pillars) located in S. Lazzaro di Savena (BO, Italy), grown on three levels with the method rooms and pillars, has been progressively more and more affected by degradation processes due to water infiltration. The mine is located underneath a residential area causing significant concern to the local municipality. On the basis of in situ surveys, laboratory and in situ geomechanical tests, some critical scenarios were adopted in the analyses to simulate the progressive collapse of pillars and of roofs in the most critical sectors of the mine. A first set of numerical analyses using 3D geotechnical FEM codes were performed to predict the extension of the subsidence area and its interaction with buildings. Secondly 3D CFD analyses were used to evaluated the amount of water that could be eventually ejected outside the mine and eventually flooding the downstream village. The predicted extension of the subsidence area together with the predicted amount of the ejected water have been used to design possible remedial measurements.
Saturation of Zeldovich Stretch-Twist-Fold Map Dynamos
Seta, Amit; Subramanian, Kandaswamy
2014-01-01
Zeldovich's stretch-twist fold (STF) dynamo provided a breakthrough in conceptual understanding of fast dynamos, including fluctuation or small scale dynamos. We study the evolution and saturation behaviour of two types of Baker's map dynamos, which have been used to model Zeldovich's STF dynamo process. Using such maps allows one to analyze dynamos at much higher magnetic Reynolds numbers $R_M$ as compared to direct numerical simulations. In the 2-strip map dynamo there is constant constructive folding while the 4-strip map dynamo also allows the possibility of field reversal. Incorporating a diffusive step parameterised by $R_M$, we find that the magnetic field $B(x)$ is amplified only above a critical $R_M=R_{crit} \\sim 4$ for both types of dynamos. We explore the saturation of these dynamos in 3 ways; by a renormalized decrease of the effective $R_M$ (Case I) or due to a decrease in the efficiency of field amplification by stretching (Case II), or a combination of both effects (Case III). For Case I, we s...
Convective Dynamo Simulation with a Grand Minimum
Augustson, Kyle C.; Brun, A. S.; Miesch, Mark; Toomre, Juri
2015-01-01
The global-scale dynamo action achieved in a simulation of a Sun-like star rotating at thrice the solar rate is assessed. The 3-D MHD Anelastic Spherical Harmonic (ASH) code, augmented with a viscosity minimization scheme, is employed to capture convection and dynamo processes in this G-type star. The simulation is carried out in a spherical shell that encompasses 3.8 density scale heights of the solar convection zone. It is found that dynamo action with a high degree of time variation occurs, with many periodic polarity reversals occurring roughly every 6.2 years. The magnetic energy also rises and falls with a regular period. The magnetic energy cycles arise from a Lorentz-force feedback on the differential rotation, whereas the processes leading to polarity reversals are more complex, appearing to arise from the interaction of convection with the mean toroidal fields. Moreover, an equatorial migration of toroidal field is found, which is linked to the changing differential rotation, and potentially to a nonlinear dynamo wave. This simulation also enters a grand minimum lasting roughly 20 years, after which the dynamo recovers its regular polarity cycles.
Biggin, A. J.; Suttie, N.; Paterson, G. A.; Aubert, J.; Hurst, E.; Clarke, A.
2013-12-01
address challenge 2, we take an approach using the outputs of numerical dynamo simulations. This involves subsampling synthetic global time series of full-vector magnetic field data, converting these datasets into virtual (axial) dipole moments, and comparing these to the entire distribution to ascertain how well secular variation is averaged and characterised. Finally, the two approaches will be combined. Datasets of real dipole moment estimates, filtered by QPI, will be compared to the synthetic distributions in order to present more robust characterisations of geomagnetic behaviour in different time intervals than has previously been possible.
Benmansour, Abdelkrim; Liazid, Abdelkrim; Logerais, Pierre-Olivier; Durastanti, Jean-Félix
2016-02-01
Cryogenic propellants LOx/H2 are used at very high pressure in rocket engine combustion. The description of the combustion process in such application is very complex due essentially to the supercritical regime. Ideal gas law becomes invalid. In order to try to capture the average characteristics of this combustion process, numerical computations are performed using a model based on a one-phase multi-component approach. Such work requires fluid properties and a correct definition of the mixture behavior generally described by cubic equations of state with appropriated thermodynamic relations validated against the NIST data. In this study we consider an alternative way to get the effect of real gas by testing the volume-weighted-mixing-law with association of the component transport properties using directly the NIST library data fitting including the supercritical regime range. The numerical simulations are carried out using 3D RANS approach associated with two tested turbulence models, the standard k-Epsilon model and the realizable k-Epsilon one. The combustion model is also associated with two chemical reaction mechanisms. The first one is a one-step generic chemical reaction and the second one is a two-step chemical reaction. The obtained results like temperature profiles, recirculation zones, visible flame lengths and distributions of OH species are discussed.
Towards a precession driven dynamo experiment
Stefani, F; Gerbeth, G; Giesecke, A; Gundrum, T; Herault, J; Nore, C; Steglich, C
2014-01-01
The most ambitious project within the DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is the set-up of a precession-driven dynamo experiment. After discussing the scientific background and some results of water pre-experiments and numerical predictions, we focus on the numerous structural and design problems of the machine. We also outline the progress of the building's construction, and the status of some other experiments that are planned in the framework of DRESDYN.
Magnetorotational Turbulence and Dynamo in a Collisionless Plasma
Kunz, Matthew W; Quataert, Eliot
2016-01-01
We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disc. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatio-temporally variable. Energy spectra suggest an Alfv\\'en-wave cascade at large scales and a kinetic-Alfv\\'en-wave cascade at small scales, with strong small-scale density fluctuations and weak non-axisymmetric density waves. Ions undergo n...
Realistic modeling of local dynamo processes on the Sun
Kitiashvili, I N; Mansour, N N; Wray, A A
2015-01-01
Magnetic fields are usually observed in the quiet Sun as small-scale elements that cover the entire solar surface (the `salt and pepper' patterns in line-of-sight magnetograms). By using 3D radiative MHD numerical simulations we find that these fields result from a local dynamo action in the top layers of the convection zone, where extremely weak 'seed' magnetic fields (e.g., from a $10^{-6}$ G) can locally grow above the mean equipartition field, to a stronger than 2000~G field localized in magnetic structures. Our results reveal that the magnetic flux is predominantly generated in regions of small-scale helical downflows. We find that the local dynamo action takes place mostly in a shallow, about 500~km deep, subsurface layer, from which the generated field is transported into the deeper layers by convective downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and horizontal fields above the photosphere can be explained by small-scale magnetic loops produced ...
Lin, C. W.; Wu, T. R.; Chuang, M. H.; Tsai, Y. L.
2015-12-01
The wind in Taiwan Strait is strong and stable which offers an opportunity to build offshore wind farms. However, frequently visited typhoons and strong ocean current require more attentions on the wave force and local scour around the foundation of the turbine piles. In this paper, we introduce an in-house, multi-phase CFD model, Splash3D, for solving the flow field with breaking wave, strong turbulent, and scour phenomena. Splash3D solves Navier-Stokes Equation with Large-Eddy Simulation (LES) for the fluid domain, and uses volume of fluid (VOF) with piecewise linear interface reconstruction (PLIC) method to describe the break free-surface. The waves were generated inside the computational domain by internal wave maker with a mass-source function. This function is designed to adequately simulate the wave condition under observed extreme events based on JONSWAP spectrum and dispersion relationship. Dirichlet velocity boundary condition is assigned at the upper stream boundary to induce the ocean current. At the downstream face, the sponge-layer method combined with pressure Dirichlet boundary condition is specified for dissipating waves and conducting current out of the domain. Numerical pressure gauges are uniformly set on the structure surface to obtain the force distribution on the structure. As for the local scour around the foundation, we developed Discontinuous Bi-viscous Model (DBM) for the development of the scour hole. Model validations were presented as well. The force distribution under observed irregular wave condition was extracted by the irregular-surface force extraction (ISFE) method, which provides a fast and elegant way to integrate the force acting on the surface of irregular structure. From the Simulation results, we found that the total force is mainly induced by the impinging waves, and the force from the ocean current is about 2 order of magnitude smaller than the wave force. We also found the dynamic pressure, wave height, and the
Dynamos and anti-dynamos as thin magnetic flux ropes in Riemannian spaces
de Andrade, L Garcia
2007-01-01
Two examples of magnetic anti-dynamos in magnetohydrodynamics (MHD) are given. The first is a 3D metric conformally related to Arnold cat fast dynamo metric: ${ds_{A}}^{2}=e^{-{\\lambda}z}dp^{2}+e^{{\\lambda}z}dq^{2}+dz^{2}$ is shown to present a behaviour of non-dynamos where the magnetic field exponentially decay in time. The curvature decay as z-coordinates increases without bounds. Some of the Riemann curvature components such as $R_{pzpz}$ also undergoes dissipation while component $R_{qzqz}$ increases without bounds. The remaining curvature component $R_{pqpq}$ is constant on the torus surface. The other anti-dynamo which may be useful in plasma astrophysics is the thin magnetic flux rope or twisted magnetic thin flux tube which also behaves as anti-dynamo since it also decays with time. This model is based on the Riemannian metric of the magnetic twisted flux tube where the axis possesses Frenet curvature and torsion. Since in this last example the Frenet torsion of the axis of the rope is almost zero, o...
Mahendra K Verma; Bidya Binay Karak; Rohit Kumar
2013-12-01
In this paper, we estimate the magnetic Reynolds number of a typical protostar before and after deuterium burning, and claim for the existence of dynamo process in both the phases, because the magnetic Reynolds number of the protostar far exceeds the critical magnetic Reynolds number for dynamo action. Using the equipartition of kinetic and magnetic energies, we estimate the steady-state magnetic field of the protostar to be of the order of kilogauss, which is in good agreement with observations.
Brandenburg, Axel; Tuominen, Ilkka
The traditional -dynamo as a model for the solar cycle has been successful in explaining the butterfly diagram, phase relations between poloidal and toroidal field, and polar branch migration features. Observational and theoretical achievements in recent years have however shaken this picture. The current trend is towards dynamos operating in the overshoot region of the convection zone. Nevertheless, there are many open questions and a consistent picture has not been established. In this paper we compare recent approaches and discuss remaining problems.
El-Ahmar, W
2007-04-15
The numerical welding simulation is considered to be one of those mechanical problems that have the great level of nonlinearity and which requires a good knowledge in various scientific fields. The 'Robustness Analysis' is a suitable tool to control the quality and guarantee the reliability of numerical welding results. The robustness of a numerical simulation of welding is related to the sensitivity of the modelling assumptions on the input parameters. A simulation is known as robust if the result that it produces is not very sensitive to uncertainties of the input data. The term 'Robust' was coined in statistics by G.E.P. Box in 1953. Various definitions of greater or lesser mathematical rigor are possible for the term, but in general, referring to a statistical estimator, it means 'insensitive to small deviation from the idealized assumptions for which the estimator is optimized. In order to evaluate the robustness of numerical welding simulation, sensitivity analyses on thermomechanical models and parameters have been conducted. At the first step, we research a reference solution which gives the best agreement with the thermal and mechanical experimental results. The second step consists in determining through numerical simulations which parameters have the largest influence on residual stresses induced by the welding process. The residual stresses were predicted using finite element method performed with Code-Aster of EDF and SYSWELD of ESI-GROUP. An analysis of robustness can prove to be heavy and expensive making it an unjustifiable route. However, only with development such tool of analysis can predictive methods become a useful tool for industry. (author)
Turbulent dynamo in a collisionless plasma
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-04-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
Current helicity constraints in solar dynamo models
Sokoloff, D; Moss, D; Kleeorin, N; Kuzanyan, K; Rogachevski, I; Gao, Yu; Xu, H
2012-01-01
We investigate to what extent the current helicity distribution observed in solar active regions is compatible with solar dynamo models. We use an advanced 2D mean-field dynamo model with dynamo action largely concentrated near the bottom of the convective zone, and dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic 2D mean-field dynamo model with simple algebraic alpha quenching only. Using these numerical models we obtain butterfly diagrams for both the small-scale current helicity and the large-scale magnetic helicity, and compare them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by $-A \\cdot B$ evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation....
Brown, Andrew; De Beer, Deon; Conradie, Pieter
2014-01-01
This paper presents a prototype Stereolithography (STL) file format slicing and tool-path generation algorithm, which serves as a data front-end for a Rapid Prototyping (RP) entry- level three-dimensional (3-D) printer. Used mainly in Additive Manufacturing (AM), 3-D printers are devices that apply plastic, ceramic, and metal, layer by layer, in all three dimensions on a flat surface (X, Y, and Z axis). 3-D printers, unfortunately, cannot print an object without a special algorithm that is re...
Dynamos and MHD theory of turbulence suppression
Characteristics of electrically-conducting media are reviewed from the macroscopic viewpoint based on the mean-field magnetohydrodynamics, while being compared with the methodology and knowledge in fluid mechanics. The themes covered in this review range from the generation mechanism of stellar magnetic fields (dynamo) to transport properties in fusion. The primary concern here is to see the characteristics common to these apparently different phenomena, within the framework of the mean-field theory. Owing to the intrinsic limitation of the approach, the present discussions are limited more or less to specific aspects of phenomena. They are supplemented with the reference to theoretical, numerical, and observational approaches intrinsic to each theme. In the description of dynamo phenomena, an emphasis is put on the cross-helicity dynamo. Features common to the stellar magnetic-field generation and the rotational-motion drive in toroidal plasmas are illustrated on this basis. (author)
Could giant basin-forming impacts have killed Martian dynamo?
Kuang, W.; Jiang, W.; Roberts, J.; Frey, H. V.
2014-11-01
The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30° of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16° polar reorientation is needed if Utopia is the dynamo killer.
Could Giant Basin-Forming Impacts Have Killed Martian Dynamo?
Kuang, W.; Jiang, W.; Roberts, J.; Frey, H. V.
2014-01-01
The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30 deg of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16 deg polar reorientation is needed if Utopia is the dynamo killer.
Photopolymers in 3D printing applications
Pandey, Ramji
2014-01-01
3D printing is an emerging technology with applications in several areas. The flexibility of the 3D printing system to use variety of materials and create any object makes it an attractive technology. Photopolymers are one of the materials used in 3D printing with potential to make products with better properties. Due to numerous applications of photopolymers and 3D printing technologies, this thesis is written to provide information about the various 3D printing technologies with particul...
Fortier, R.; Allard, M.; Gagnon, O.
2002-12-01
survey aims at providing information on the geological and geotechnical characteristics of permafrost. Thermistor cables in deep boreholes, meteorological stations, dataloggers for the measurement of surface temperature, and thermal probes have been also installed in the valley. Air photographs will be used to produce a digital terrain model of the valley. This integrated multi-technique approach is essential for properly assessing the permafrost conditions in the valley. The study will provide the data needed for the development of a 3D model of permafrost conditions in the valley. A 3D numerical simulation of the geothermal field of permafrost in the valley will be then undertaken. This simulation is a major challenge giving the size of the thermal field and the variability in permafrost conditions. The impacts of climate warming on the thermal field of permafrost will be simulated and predicted by forcing the surface temperature to increase following different scenarios of climate warming. It is planned to combine the geotechnical properties and the simulation of the geothermal field of permafrost in order to define threshold values of permafrost strength and slope instability and set a pre-warning scheme of permafrost temperature in case of further warming in the coming years. The monitoring of permafrost temperature will be continued in the future. If the scheme is reached, actions can be then undertaken to mitigate the impacts of climate warming on the infrastructures and protect the population of Salluit.
3D flow numerical simulation of ball valve based on CFD%基于CFD的球阀三维流场数值模拟
张生昌; 张玉林; 方志明; 柯愈龙
2013-01-01
为了探索新型转子式油气混输泵出口球阀内流场规律,建立球阀流场的三维模型,利用Fluent软件,将标准k-ε湍流模型与多相流技术相结合,采用SIMPLE算法,对新型转子式油气混输泵出口球阀内的三维气液两相流场进行数值模拟.在容积含气率为25％,50％,75％的不同工况下,通过对球阀开启高度分别为3,5,7 mm时的速度场、压力场与气液相分布的分析,探讨在气液混输过程中阀的开启高度及不同气液比对阀内流场的影响规律.模拟结果表明:球阀开启高度越大,阀球上下压差越小；阀隙流速随着开启高度的增大而减小.在气液混输过程中气相介质主要靠近阀球壁流动,同一开启高度下气液比对阀隙流速的影响较小.研究结果直观展现了球阀内流场形态,在一定程度上揭示了气液两相介质在阀内的流动规律,为新型转子式油气混输泵出口球阀的设计与优化提供理论指导.%To explore the flow field law of the outlet ball valve of the new rotor oil-gas mixed pump, a 3D model of ball valve flow field was established. Using Fluent software, combining standard turbulent model and multiphase flow technology together, adopting SIMPLE algorithm, a 3D gas-liquid double-phase flow field in outlet ball valve of new rotor oil-gas mixed pump was numerically simulated. With gas fraction of 25% , 50% and 75% and valve's opening height at 3, 5 and 7 mm respectively, velocity field, pressure field and the distribution of liquid and gas was analyzed. The law of valve's opening height and different gas-liquid ratio's effect on outlet ball valves in the process of gas-liquid mixing was discussed. The simulation results show that, the greater the opening height, the smaller the pressure difference between ball valves: The gap flow velocity decreases as the open height increases. Gas mainly flows in the vicinity of the valve ball in the process of gas-liquid mixing. At the same
Lucas, Laurent; Loscos, Céline
2013-01-01
While 3D vision has existed for many years, the use of 3D cameras and video-based modeling by the film industry has induced an explosion of interest for 3D acquisition technology, 3D content and 3D displays. As such, 3D video has become one of the new technology trends of this century.The chapters in this book cover a large spectrum of areas connected to 3D video, which are presented both theoretically and technologically, while taking into account both physiological and perceptual aspects. Stepping away from traditional 3D vision, the authors, all currently involved in these areas, provide th
Beane, Andy
2012-01-01
The essential fundamentals of 3D animation for aspiring 3D artists 3D is everywhere--video games, movie and television special effects, mobile devices, etc. Many aspiring artists and animators have grown up with 3D and computers, and naturally gravitate to this field as their area of interest. Bringing a blend of studio and classroom experience to offer you thorough coverage of the 3D animation industry, this must-have book shows you what it takes to create compelling and realistic 3D imagery. Serves as the first step to understanding the language of 3D and computer graphics (CG)Covers 3D anim
Filina, Irina Y.; Blankenship, Donald D.; Thoma, Malte; Lukin, Valery V.; Masolov, Valery N.; Sen, Mrinal K.
2008-11-01
A new distribution of water and unconsolidated sediments in subglacial Lake Vostok, East Antarctica was developed via inversion of airborne gravity data constrained by 60 seismic soundings. A model was developed for host rock with a density of 2550 kg/m 3 that was inferred from prior 2D modeling. Our 3D bathymetry model of Lake Vostok corresponds better with seismic data (RMS of 125 m) than two previous models based on the same gravity dataset. The good match in both water and sediment thicknesses between the gravity model and seismic measurements confirms two major facts about Lake Vostok: (1) the lake is hosted by sedimentary rocks, and (2) the bottom of the lake is covered with a layer of unconsolidated sediments that does not exceed 300 m in the southern basin and thickens almost to 400 m in the northern basin. Our new bathymetry model suggests much shallower water thicknesses (up to twice the previous estimates) in the middle and northern parts of the lake, while the water layer is thicker in the southern basin. Numerical modeling of the internal processes in the lake reveals the relevance of our new bathymetry model to the basal mass balance. A significant decrease in transport is observed in the shallower northern basin, as well as a decrease of 33% in the turbulent kinetic energy. However, only minor differences were observed in the distribution of the calculated freezing and melting zones compared to previous models. Estimates for the sedimentation rates for six possible mechanisms were made. Possible sedimentation mechanisms are: (1) fluvial and periglacial, i.e. those that are active prior to the establishment of a large subglacial lake; (2) deposition due to overlying ice sheet, including melting out of the ice, as well as bulldozering by the overriding ice; and (3) suspended sediments from subglacial water flow including those deposited by periodical subglacial outbursts. The estimates for these mechanisms show that unconsolidated sediments of the
Magnetic Wreaths and Cycles in Convective Dynamos
Nelson, Nicholas J; Brun, A Sacha; Miesch, Mark S; Toomre, Juri
2012-01-01
Solar-type stars exhibit a rich variety of magnetic activity. Seeking to explore the convective origins of this activity, we have carried out a series of global 3D magnetohydrodynamic (MHD) simulations with the anelastic spherical harmonic (ASH) code. Here we report on the dynamo mechanisms achieved as the effects of artificial diffusion are systematically decreased. The simulations are carried out at a nominal rotation rate of three times the solar value (3$\\Omega_\\odot$), but similar dynamics may also apply to the Sun. Our previous simulations demonstrated that convective dynamos can build persistent toroidal flux structures (magnetic wreaths) in the midst of a turbulent convection zone and that high rotation rates promote the cyclic reversal of these wreaths. Here we demonstrate that magnetic cycles can also be achieved by reducing the diffusion, thus increasing the Reynolds and magnetic Reynolds numbers. In these more turbulent models, diffusive processes no longer play a significant role in the key dynam...
Stochastic flux freezing and magnetic dynamo
Magnetic flux conservation in turbulent plasmas at high magnetic Reynolds numbers is argued neither to hold in the conventional sense nor to be entirely broken, but instead to be valid in a statistical sense associated to the ''spontaneous stochasticity'' of Lagrangian particle trajectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. Empirical evidence is presented for spontaneous stochasticity, including numerical results. A Lagrangian path-integral approach is then exploited to establish stochastic flux freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux conservation must remain stochastic at infinite magnetic Reynolds number. An important application of these results is the kinematic, fluctuation dynamo in nonhelical, incompressible turbulence at magnetic Prandtl number (Prm) equal to unity. Numerical results on the Lagrangian dynamo mechanisms by a stochastic particle method demonstrate a strong similarity between the Prm=1 and 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. Finally, some consequences for nonlinear magnetohydrodynamic turbulence, dynamo, and reconnection are briefly considered.
The effects of vertical outflows on disk dynamos
Bardou, A.; Rekowski, B. v.; Dobler, W.; Brandenburg, A.; Shukurov, A.
2000-01-01
We consider the effect of vertical outflows on the mean-field dynamo in a thin disk. These outflows could be due to winds or magnetic buoyancy. We analyse both two-dimensional finite-difference numerical solutions of the axisymmetric dynamo equations and a free-decay mode expansion using the thin-disk approximation. Contrary to expectations, a vertical velocity can enhance dynamo action, provided it is not too strong. In the nonlinear regime this can lead to super-exponential growth of the ma...
3-dimensional simulation of dynamo effect of reversed field pinch
A non-linear numerical simulation of the dynamo effect of a reversed field pinch (RFP) with finite beta is presented. It is shown that the m=-1, n=(9,10,11,....,19) modes cause the dynamo effect and sustain the field reversed configuration. The role of the m=0 modes on the dynamo effect is carefully examined. Our simulation shows that the magnetic field fluctuation level scales as S-0.2 or S-0.3 in the range of 103 5, while Nebel, Caramana and Schnack obtained the fluctuation level is independent of S for a pressureless RFP plasma. (author)
Alfvén-dynamo balance and magnetic excess in magnetohydrodynamic turbulence
Grappin, Roland; Müller, Wolf-Christian; Verdini, Andrea
2016-05-01
Context. Three-dimensional magnetohydrodynamic (3D MHD) turbulent flows with initially magnetic and kinetic energies at equipartition spontaneously develop a magnetic excess (or residual energy) in both numerical simulations and the solar wind. Closure equations obtained in 1983 describe the residual spectrum as resulting from a balance between a dynamo source proportional to the total energy spectrum and a linear Alfvén damping term. A good agreement was found in 2005 with incompressible simulations; however, recent solar wind measurements disagree with these results. Aims: The previous dynamo-Alfvén theory is generalized to a family of models, leading to simple relations between residual and total energy spectra. We want to assess these models in detail against MHD simulations and solar wind data. Methods: We tested the family of models against compressible decaying MHD simulations with a low Mach number, low cross-helicity, and zero-mean magnetic field with or without expansion terms (EBM; expanding box model). Results: A single dynamo-Alfvén model is found to describe correctly both solar wind scalings and compressible simulations without or with expansion. This model is equivalent to the 1983-2005 closure equation, but it incorporates the critical balance of nonlinear turnover and linear Alfvén times, while the dynamo source term remains unchanged. We elucidate the discrepancy with previous incompressible simulations. The model predicts a linear relation between the spectral slopes of total and residual energies mR = -1/2 + 3/2mT. By examining previous solar wind data, our relation is found to be valid for any cross-helicity, and is even better at high cross-helicity with the total energy slope varying from 1.7 to 1.55.
von Tscharner, M.; Schmalholz, S. M.; Epard, J.-L.
2016-05-01
The Helvetic nappe system exhibits three-dimensional (3-D) features such as the lateral variation in geometry between the Morcles and Doldenhorn fold nappes or the Rawil depression. We perform 3-D finite element simulations of linear and power-law viscous flow to investigate fold nappe formation during shortening of a half graben with laterally varying thickness. 3-D ellipsoids and corresponding 2-D intersection ellipses are used to quantify finite strain. Fold nappes which formed above a thicker graben have (i) larger amplitudes, (ii) a less sheared and thinned overturned limb, and (iii) a larger thickness than fold nappes formed above a thinner graben. These results agree with observations for the Morcles and Doldenhorn nappes. We also perform 3-D simulations for a tectonic scenario suggested for the evolution of the Rawil depression. The basement is shortened and extended laterally and includes a graben which is oblique to the shortening direction and acts as mechanical weak zone. The graben causes laterally varying basement uplift generating a depression whose amplitude depends on the graben orientation and the stress exponent of basement and sediments. The axial plunge of the depression is smaller (approximately 10°) than the observed plunge (approximately 30°) indicating that additional processes are required to explain the geometry of the Rawil depression.
Mechanically-forced dynamos (Invited)
Le Bars, M.
2013-12-01
It is a commonly accepted hypothesis that convection is responsible for planetary dynamos. However, the validity of the convective dynamo model can be questioned in various planets and moons as well as in asteroids, where the constraints from thermal evolution and compositional core models are sometimes difficult to reconcile with available data from paleomagnetism and in situ measurements. Over the last few years, researches have thus been pursued to find alternative mechanisms for sustaining intense three-dimensional motions in liquid cores, a necessary ingredient for planetary dynamo. In particular, mechanical forcings driven by libration, precession, nutation and tides, have received a renewed interest, following the first studies by Malkus in the 60's. A huge reservoir of energy is available in the rotational and orbital motions of all planetary systems. If planetary bodies were completely rigid and rotating at a constant spin rate, their fluid layers in the absence of convection would also behave rigidly and follow the spin of their boundaries. But small periodic perturbations of the shape of the core/mantle boundary (i.e. dynamic tides) and/or small periodic perturbations of the direction of the spin vector (i.e. precession and nutation) and/or small periodic perturbations of the spin rate (i.e. libration) systematically perturb this rigid state. Then, each of these small perturbations is capable of triggering instabilities in fluid layers, conveying energy from the spin and orbital motions to drive intense three-dimensional flows in the liquid cores. With the view to establish a general framework for planetary applications, I will present here the basic physical ingredients of these instabilities, which involve a resonance between the considered mechanical forcing and two inertial waves of the core. I will then review the numerical and experimental validations of this generic principle, and the few magnetohydrodynamic validations of their dynamo capacity
Magnetic flux concentrations from dynamo-generated fields
Jabbari, Sarah; Losada, Illa R; Kleeorin, Nathan; Rogachevskii, Igor
2014-01-01
The mean-field theory of magnetized stellar convection gives rise to the two possibility of distinct instabilities: the large-scale dynamo instability, operating in the bulk of the convection zone, and a negative effective magnetic pressure instability (NEMPI) operating in the strongly stratified surface layers. The latter might be important in connection with magnetic spot formation, but the growth rate of NEMPI is suppressed with increasing rotation rates, although recent direct numerical simulations (DNS) have shown a subsequent increase in the growth rate. We examine quantitatively whether this increase in the growth rate of NEMPI can be explained by an alpha squared mean-field dynamo, and whether both NEMPI and the dynamo instability can operate at the same time. We use both DNS and mean-field simulations (MFS) to solve the underlying equations numerically either with or without an imposed horizontal field. We use the test-field method to compute relevant dynamo coefficients. DNS show that magnetic flux ...
3D Computations and Experiments
Couch, R; Faux, D; Goto, D; Nikkel, D
2004-04-05
This project consists of two activities. Task A, Simulations and Measurements, combines all the material model development and associated numerical work with the materials-oriented experimental activities. The goal of this effort is to provide an improved understanding of dynamic material properties and to provide accurate numerical representations of those properties for use in analysis codes. Task B, ALE3D Development, involves general development activities in the ALE3D code with the focus of improving simulation capabilities for problems of mutual interest to DoD and DOE. Emphasis is on problems involving multi-phase flow, blast loading of structures and system safety/vulnerability studies.
Wichura, Henry; Quinteros, Javier; Melnick, Daniel; Brune, Sascha; Schwanghart, Wolfgang; Strecker, Manfred R.
2015-04-01
Over the last four years sedimentologic and thermochronologic studies in the western and eastern branches of the Cenozoic East African Rift System (EARS) have supported the notion of a broadly contemporaneous onset of normal faulting and rift-basin formation in both segments. These studies support previous interpretations based on geophysical investigations from which an onset of rifting during the Paleogene had been postulated. In light of these studies we explore the evolution of the Lake Victoria basin, a shallow, unfaulted sedimentary basin centered between both branches of the EARS and located in the interior of the East African Plateau (EAP). We quantify the fluvial catchment evolution of the Lake Victoria basin and assess the topographic response of African crust to the onset of rifting in both branches. Furthermore, we evaluate and localize the nature of strain and flexural rift-flank uplift in both branches. We use a 3D numerical forward model that includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology. The model is able to reproduce the flexural response of variably thick lithosphere to rift-related deformation processes such as lithospheric thinning and asthenospheric upwelling. The model domain covers the entire EAP and integrates extensional processes in a heterogeneous, yet cold and thick cratonic block (Archean Tanzania craton), which is surrounded by mechanically weaker Proterozoic mobile belts, which are characterized by thinner lithosphere ("thin spots"). The lower limits of the craton (170 km) and the mobile belts (120 km) are simulated by different depths of the 1300 °C lithosphere-asthenosphere boundary. We assume a constant extension rate of 4 mm/a throughout the entire simulation of 30 Ma and neglect the effect of dynamic topography and magmatism. Even though the model setup is very simple and the resolution is not high enough to calculate realistic rift-flank uplift, it intriguingly reveals important topographic
Conserved quantities in kinematic dynamo theory
Using a Lagrangian approach to the magnetic induction equation in an infinite medium, it is demonstrated that there exist seven conserved quantities which, by analogy with classical mechanics, labeled as ''energy,'' ''momentum,'' and ''angular momentum.'' For prescribed fluid motions the detailed conservation equations are spelled out. For a fluid motion which is turbulent one also gives the average conserved quantities. In a pragmatic sense it is expected that these conservation laws will be of use in attempts to obtain numerically accurate solutions to the turbulent kinematic dynamo equations. Since the magnetic induction equation is not self-adjoint, numerical attempts to date have to impose some extraneous ad hoc ''criteria of goodness'' at any given level of numerical truncation. The conserved quantities given provide an internal check of the accuracy of any numerical calculation without the necessity for arbitrarily imposed external criteria of accuracy. As such they should be a powerful tool in rapidly increasing the accuracy of numerical solutions to the kinematic dynamo equations. It is also pointed out that the conserved quantities can be used to indicate the possibility of kinematic dynamo activity ahead of any detailed calculations
D. Pletinckx
2012-09-01
Full Text Available The current 3D hype creates a lot of interest in 3D. People go to 3D movies, but are we ready to use 3D in our homes, in our offices, in our communication? Are we ready to deliver real 3D to a general public and use interactive 3D in a meaningful way to enjoy, learn, communicate? The CARARE project is realising this for the moment in the domain of monuments and archaeology, so that real 3D of archaeological sites and European monuments will be available to the general public by 2012. There are several aspects to this endeavour. First of all is the technical aspect of flawlessly delivering 3D content over all platforms and operating systems, without installing software. We have currently a working solution in PDF, but HTML5 will probably be the future. Secondly, there is still little knowledge on how to create 3D learning objects, 3D tourist information or 3D scholarly communication. We are still in a prototype phase when it comes to integrate 3D objects in physical or virtual museums. Nevertheless, Europeana has a tremendous potential as a multi-facetted virtual museum. Finally, 3D has a large potential to act as a hub of information, linking to related 2D imagery, texts, video, sound. We describe how to create such rich, explorable 3D objects that can be used intuitively by the generic Europeana user and what metadata is needed to support the semantic linking.
Yang, Xu; Zhang, Yong; Yang, Chenghua; Xu, Lu; Wang, Qiang; Zhao, Yuan
2016-06-01
Conventional three dimensional (3D) ghost imaging measures range of target based on pulse fight time measurement method. Due to the limit of data acquisition system sampling rate, range resolution of the conventional 3D ghost imaging is usually low. In order to take off the effect of sampling rate to range resolution of 3D ghost imaging, a heterodyne 3D ghost imaging (HGI) system is presented in this study. The source of HGI is a continuous wave laser instead of pulse laser. Temporal correlation and spatial correlation of light are both utilized to obtain the range image of target. Through theory analysis and numerical simulations, it is demonstrated that HGI can obtain high range resolution image with low sampling rate.
This book explains modeling of solid works 3D and application of 3D CAD/CAM. The contents of this book are outline of modeling such as CAD and 2D and 3D, solid works composition, method of sketch, writing measurement fixing, selecting projection, choosing condition of restriction, practice of sketch, making parts, reforming parts, modeling 3D, revising 3D modeling, using pattern function, modeling necessaries, assembling, floor plan, 3D modeling method, practice floor plans for industrial engineer data aided manufacturing, processing of CAD/CAM interface.
The New Mexico alpha-omega Dynamo Experiment Modeling Astrophysical Dynamos
Colgate, S A; Beckley, H F; Ferrel, R; Romero, V D; Weatherall, J C
2001-01-01
A magnetic dynamo experiment is under construction at the New Mexico Institute of Mining and Technology. The experiment is designed to demonstrate in the laboratory the alpha-omega magnetic dynamo, which is believed to operate in many rotating and conducting astrophysical objects. The experiment uses the Couette flow of liquid sodium between two cylinders rotating with different angular velocities to model the omega-effect. The alpha-effect is created by the rising and expanding jets of liquid sodium driven through a pair of orifices in the end plates of the cylindrical vessel, presumably simulating plumes driven by buoyancy in astrophysical objects. The water analog of the dynamo device has been constructed and the flow necessary for the dynamo has been demonstrated. Results of the numerical simulations of the kinematic dynamo are presented. The toroidal field produced by the omega-effect is predicted to be B_{\\phi} \\simeq (R_m/2\\pi) B_{poloidal}\\simeq 20 \\times B_{poloidal} for the expected magnetic Reynold...
The manifold zoology of anelastic dynamos with variable conductivity
Dietrich, Wieland; Jones, Chris
2015-04-01
Whereas the dynamo processes in terrestrial planets is strongly influenced by the overlying rocky mantle, the induction of global magnetic fields in gas giants is mainly affected by internal properties, such as the rapid outward decay of static density, pressure and temperature throughout the gaseous shell. Further for Jupiter and Saturn it is well known that the transition from metallic to molecular hydrogen leads to a steep decrease in the electrical conductivity. This drop-off radius is closer to the surface for heavy Jupiter (at 90% of its respective radius), but much deeper for the less massive Saturn (65%). From the modelling perspective this leads to an inner conducting shell where the magnetic fields dominate the dynamics, and outer hydro dynamic shell where the strong Coriolis force reigns. Within this study we parametrise the conductivity drop-off radius and investigate the interaction between these shells, such as the emergence of differential rotation and induction of magnetic fields. Remarkably, we could identify numerous rather different self-consistent dynamo solutions. E.g., hemispherical dynamos, quadrupolar dynamos, octupolar dynamos, dipolar dynamo waves or many mixed modes, such as solutions where the quadrupole is stable in time and the dipole periodically reverses. In summary, our results suggest anelastic dynamo models with variable conductivity yield manifold different solutions in close poriximity in the parameter space. Unfortunately for Saturn-like models with deep conductivity drop-off, Saturn-like magnetic field (stable, strongly dipolar) seemed rather unlikely.
Azimuthal dynamo wave in spherical shell convection
Cole, Elizabeth; Mantere, Maarit J; Brandenburg, Axel
2013-01-01
We report the finding of an azimuthal dynamo wave of a low-order (m=1) mode in direct numerical simulations (DNS) of turbulent convection in spherical shells. Such waves are predicted by mean field dynamo theory and have been obtained previously in mean-field models. Observational results both from photometry and Doppler imaging have revealed persistent drifts of spots for several rapidly rotating stars, but, although an azimuthal dynamo wave has been proposed as a possible mechanism responsible for this behavior, it has been judged as unlikely, as practical evidence for such waves from DNS has been lacking. The large-scale magnetic field in our DNS, which is due to self-consistent dynamo action, is dominated by a retrograde m=1 mode. Its pattern speed is nearly independent of latitude and does not reflect the speed of the differential rotation at any depth. The extrema of magnetic m=1 structures coincide reasonably with the maxima of m=2 structures of the temperature. These results provide direct support for...
Boufaida, Zakariya; André, Stéphane; Farge, Laurent
2016-01-01
In the study presented in this paper, we analyzed the mechanical response of a glass fiber plain weave/polymer composite at the fabric millimetric mesoscale. The detail of the stress and strain fields in a fabric repeating unit cell was numerically calculated using CraFT (Composite response and Fourier Transforms), a code specifically conceived for simulating the mechanical behaviour of materials with complex microstructure. The local strain fields obtained by simulation were found to be in very good agreement with measurements carried out using 3D Digital Image Correlation (3D DIC). From numerical stress fields calculated with the CraFT solver, we also highlighted the subregions inside the periodic mesostructure where there is maximum stress. Furthermore, with X-ray tomography post mortem measurements, we were able to confirm that certain damage modes were well initiated in these microstructure subregions of stress concentration.
Felician ALECU
2010-01-01
Full Text Available Many professionals and 3D artists consider Blender as being the best open source solution for 3D computer graphics. The main features are related to modeling, rendering, shading, imaging, compositing, animation, physics and particles and realtime 3D/game creation.
Convective Dynamo Simulation with a Grand Minimum
Augustson, Kyle; Miesch, Mark; Toomre, Juri
2015-01-01
The global-scale dynamo action achieved in a simulation of a Sun-like star rotating at thrice the solar rate is assessed. The 3-D MHD Anelastic Spherical Harmonic (ASH) code, augmented with a viscosity minimization scheme, is employed to capture convection and dynamo processes in this G-type star. The simulation is carried out in a spherical shell that encompasses 3.8 density scale heights of the solar convection zone. It is found that dynamo action with a high degree of time variation occurs, with many periodic polarity reversals occurring roughly every 6.2 years. The magnetic energy also rises and falls with a regular period. The magnetic energy cycles arise from a Lorentz-force feedback on the differential rotation, whereas the processes leading to polarity reversals are more complex, appearing to arise from the interaction of convection with the mean toroidal fields. Moreover, an equatorial migration of toroidal field is found, which is linked to the changing differential rotation, and potentially to a no...
压电复合材料三维壳体简化数值建模研究%Simplified numerical modeling of 3D piezoelectric composite shells
钟轶峰; YU Wenbin
2011-01-01
为有效分析三维压电复合材料壳体结构非线性、单向耦合压电弹性问题,基于变分渐近方法(VAM)建立了壳体结构在机械和电场作用下的简化模型.推导了基于旋转张量分解概念的压电复合材料三维壳体能量表达式;利用变分渐近法将三维壳体严格拆分为二维壳体线性分析和沿法线方向的一维非线性分析;进行了降维后近似能量推导及Reissner-Mindlin形式转换;提供了三维场重构关系以得到沿厚度方向的准确应力分布.通过对由4层压电复合材料构成的壳体柱形弯曲算例分析表明:基于该理论和重构过程开发的变分渐近程序VAYAS重构生成的三维应力场精确性较一阶剪切变形理论和古典层合理论更好,与三维有限元精确解相吻合,表明该压电复合材料壳体模型的有效性.%Based on the variational asymptotic method (VAM), an engineering model for piezoelectric composite shell under mechanical and electronic loads was established in order to efficient analyze the nonlinear, one-way coupled piezoelectric problem. The 3D energy expressions based on the decomposition of rotation tensor (DRT) were deduced. The 3D shell model was decomposed into a 2D, nonlinear shell analysis and a linear analysis through the normal direction based on VAM. The approximate energy after dimensionality reduction was deduced and converted to a form of Reissner - Mindlin model. The 3D field recovery relations were provided to obtain accurate stress distribution through the thickness. The cylindrical bending example of 4-layer piezoelectric composite shell shows that the 3D stress field recovered by the variational asymptotic plate and shell analysis program (VAPAS) based on this theory agrees better with the exact results than those of first-order shear deformation theory (FOSDT) and classic laminated theory (CLT), indicating the validity of this model.
3d-3d correspondence revisited
Chung, Hee-Joong; Dimofte, Tudor; Gukov, Sergei; Sułkowski, Piotr
2016-04-01
In fivebrane compactifications on 3-manifolds, we point out the importance of all flat connections in the proper definition of the effective 3d {N}=2 theory. The Lagrangians of some theories with the desired properties can be constructed with the help of homological knot invariants that categorify colored Jones polynomials. Higgsing the full 3d theories constructed this way recovers theories found previously by Dimofte-Gaiotto-Gukov. We also consider the cutting and gluing of 3-manifolds along smooth boundaries and the role played by all flat connections in this operation.
Brdnik, Lovro
2015-01-01
Diplomsko delo analizira trenutno stanje 3D tiskalnikov na trgu. Prikazan je razvoj in principi delovanja 3D tiskalnikov. Predstavljeni so tipi 3D tiskalnikov, njihove prednosti in slabosti. Podrobneje je predstavljena zgradba in delovanje koračnih motorjev. Opravljene so meritve koračnih motorjev. Opisana je programska oprema za rokovanje s 3D tiskalniki in komponente, ki jih potrebujemo za izdelavo. Diploma se oklepa vprašanja, ali je izdelava 3D tiskalnika bolj ekonomična kot pa naložba v ...
Wave-driven dynamo action in spherical MHD systems
Reuter, K; Tilgner, A; Forest, C B
2009-01-01
Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of non-orthogonal eigenstates of the time dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.
Energy transfers in dynamos with small magnetic Prandtl numbers
Kumar, Rohit
2015-06-25
We perform numerical simulation of dynamo with magnetic Prandtl number Pm = 0.2 on 10243 grid, and compute the energy fluxes and the shell-to-shell energy transfers. These computations indicate that the magnetic energy growth takes place mainly due to the energy transfers from large-scale velocity field to large-scale magnetic field and that the magnetic energy flux is forward. The steady-state magnetic energy is much smaller than the kinetic energy, rather than equipartition; this is because the magnetic Reynolds number is near the dynamo transition regime. We also contrast our results with those for dynamo with Pm = 20 and decaying dynamo. © 2015 Taylor & Francis.
Non-linear Galactic Dynamos and The Magnetic Pitch Angle
Chamandy, Luke
2015-01-01
Pitch angles $p$ of the large-scale magnetic fields $\\overline{\\bf{\\it{B}}}$ of spiral galaxies have previously been inferred from observations to be systematically larger in magnitude than predicted by standard mean-field dynamo theory. This discrepancy is more pronounced if dynamo growth has saturated, which is reasonable to assume given that such fields are generally inferred to be close to energy equipartition with the interstellar turbulence. This 'pitch angle problem' is explored using local numerical mean-field dynamo solutions as well as asymptotic analytical solutions. It is first shown that solutions in the saturated or kinematic regimes depend on only 5 dynamo parameters, two of which are tightly constrained by observations of galaxy rotation curves. The remaining 3-dimensional (dimensionless) parameter space can be constrained to some extent using theoretical arguments. Predicted values of $|p|$ can be as large as $\\sim40^\\circ$, which is similar to the largest values inferred from observations, b...
Resistive and ferritic-wall plasma dynamos in a sphere
We numerically study the effects of varying electric conductivity and magnetic permeability of the bounding wall on a kinematic dynamo in a sphere for parameters relevant to Madison plasma dynamo experiment. The dynamo is excited by a laminar, axisymmetric flow of von Kármán type. The flow is obtained as a solution to the Navier-Stokes equation for an isothermal fluid with a velocity profile specified at the sphere's boundary. The properties of the wall are taken into account as thin-wall boundary conditions imposed on the magnetic field. It is found that an increase in the permeability of the wall reduces the critical magnetic Reynolds number Rmcr. An increase in the conductivity of the wall leaves Rmcr unaffected but reduces the dynamo growth rate.
Sharp magnetic structures from dynamos with density stratification
Jabbari, Sarah; Kleeorin, Nathan; Rogachevskii, Igor
2016-01-01
Recent direct numerical simulations (DNS) of large-scale turbulent dynamos in strongly stratified layers have resulted in surprisingly sharp bipolar structures at the surface. Here we present new DNS of helically and non-helically forced turbulence with and without rotation and compare with corresponding mean-field simulations (MFS) to show that these structures are a generic outcome of a broader class of dynamos in density-stratified layers. The MFS agree qualitatively with the DNS, but the period of oscillations tends to be longer in the DNS. In both DNS and MFS, the sharp structures are produced by converging flows at the surface and are driven by the Lorentz force associated with the large-scale dynamo-driven magnetic field if the dynamo number is at least 5 times supercritical.
Tidally Driven Dynamos in a Rotating Sphere
Cébron, D.; Hollerbach, R.
2014-07-01
Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star τ-boo, Mars, or the early Moon. By simulating a small local patch of a rotating fluid, Barker & Lithwick have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested in the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results and numerical results obtained in a truly deformed ellipsoid, which confirms the presence of elliptical instability. We then perform magnetohydrodynamic simulations and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating a dipole-dominated large-scale magnetic field in global simulations of a fluid rotating sphere.
TIDALLY DRIVEN DYNAMOS IN A ROTATING SPHERE
Cébron, D.; Hollerbach, R., E-mail: david.cebron@ujf-grenoble.fr, E-mail: r.hollerbach@leeds.ac.uk [Institut für Geophysik, Sonneggstrasse 5, ETH Zürich, Zürich CH-8092 (Switzerland)
2014-07-01
Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star τ-boo, Mars, or the early Moon. By simulating a small local patch of a rotating fluid, Barker and Lithwick have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested in the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results and numerical results obtained in a truly deformed ellipsoid, which confirms the presence of elliptical instability. We then perform magnetohydrodynamic simulations and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating a dipole-dominated large-scale magnetic field in global simulations of a fluid rotating sphere.
Clay-stone rock masses are a reasonable alternative to e.g. salt rock masses as a host rock for underground radioactive waste repositories because of their very low permeability as well as their radionuclide retention capacity. Though clay-stone has been explored for many years, there is still a need for further research on its hydro-mechanical behaviour. Convergence measurements over a 4-year period in the tunnel system of the argillaceous Tournemire site in France yielded the presence of a time-dependent deformation behaviour in indurated clay. Moreover, a mine-by test was carried out with extensometer measurements capturing the rock mass deformation during the excavation process of a new gallery in 2003.This work focuses on the validation of a constitutive model by means of a three-dimensional (3D) simulation of the mine-by test. The utilised constitutive model Hou/Lux-T is based on the viscous constitutive model Lubby2 with which time-dependent deformation behaviour of salt rock can appropriately be simulated. It has been adapted to clay-stone by considering anisotropy effects, and in addition it features a strain-dependent fracture and failure criterion. The results of the mine-by-test simulation show that the calculated stresses and deformations in the rock mass seem to behave reasonably under this constitutive model with respect to time-dependency. A comparison of the 3D results to the results of a simplified two-dimensional (2D) simulation confirms the adequacy of using a 2D model with the constitutive model Hou/Lux-T for the setting at hand, described in the text (material parameters, time scale), in order to assess load-bearing capacity and deformability of the gallery near field away from heading face and tunnel crossing. Finally, a comparison of the 3D simulation results to the extensometer measurement results yields the principal ability of the used constitutive model to describe time-dependent evolutions of stresses and deformations during a three
Meulien Ohlmann, Odile
2013-02-01
Today the industry offers a chain of 3D products. Learning to "read" and to "create in 3D" becomes an issue of education of primary importance. 25 years professional experience in France, the United States and Germany, Odile Meulien set up a personal method of initiation to 3D creation that entails the spatial/temporal experience of the holographic visual. She will present some different tools and techniques used for this learning, their advantages and disadvantages, programs and issues of educational policies, constraints and expectations related to the development of new techniques for 3D imaging. Although the creation of display holograms is very much reduced compared to the creation of the 90ies, the holographic concept is spreading in all scientific, social, and artistic activities of our present time. She will also raise many questions: What means 3D? Is it communication? Is it perception? How the seeing and none seeing is interferes? What else has to be taken in consideration to communicate in 3D? How to handle the non visible relations of moving objects with subjects? Does this transform our model of exchange with others? What kind of interaction this has with our everyday life? Then come more practical questions: How to learn creating 3D visualization, to learn 3D grammar, 3D language, 3D thinking? What for? At what level? In which matter? for whom?
The Magnetic Furnace: Intense Core Dynamos in B-stars
Augustson, Kyle C; Toomre, Juri
2016-01-01
The dynamo action achieved in the convective cores of main-sequence massive stars is explored here through 3-D global simulations of convective core dynamos operating within a young 10$M_{\\mathrm{sun}}$ B-type star, using the anelastic spherical harmonic (ASH) code. These simulations capture the inner 65% of this star by radius, encompassing the convective nuclear-burning core (about 23% by radius) and a portion of the overlying radiative envelope. Eight rotation rates are considered, ranging from 0.05% to 16% of the surface breakup velocity, thereby capturing both convection barely sensing the effects of rotation to others in which the Coriolis forces are prominent. The vigorous dynamo action realized within all of these turbulent convective cores builds magnetic fields with peak strengths exceeding a megagauss, with the overall magnetic energy (ME) in the faster rotators reaching super-equipartition levels compared to the convective kinetic energy (KE). The core convection typically involves turbulent colum...
McWilliams, James C
2011-01-01
A quasi-linear theory is presented for how randomly forced, barotropic velocity fluctuations cause an exponentially-growing, large-scale (mean) magnetic dynamo in the presence of a uniform shear flow, $\\vec{U} = S x \\vec{e}_y$. It is a "kinematic" theory for the growth of the mean magnetic energy from a small initial seed, neglecting the saturation effects of the Lorentz force. The quasi-linear approximation is most broadly justifiable by its correspondence with computational solutions of nonlinear magneto-hydrodynamics, and it is rigorously derived in the limit of large resistivity, $\\eta \\rightarrow \\infty$. Dynamo action occurs even without mean helicity in the forcing or flow, but random helicity variance is then essential. In a sufficiently large domain and with small wavenumber $k_z$ in the direction perpendicular to the mean shearing plane, a positive exponential growth rate $\\gamma$ can occur for arbitrary values of $\\eta$, the viscosity $\
Turbulent Dynamos and Magnetic Helicity
Ji, H
1999-01-01
It is shown that the turbulent dynamo $\\alpha$-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is electrostatic or due to the electron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity except for resistive effects and a small battery effect. Implications for astrophysical situations, especially for the solar dynamo, are discussed.
Parker's dynamo and geomagnetic reversals
Reshetnyak, M
2011-01-01
Fluctuations of the alpha-effect which break equatorial symmetry of the flow in the kinematic Parker's dynamo are considered. We show, that even small (a few percents) fluctuation can leed to the substantial assymmetry of the magnetic field in the hemispheres as well as the propagation of the dynamo wave through the equator plane. We also consider how change of the dynamo number can be used to explain different regimes of magnetic field generation in geodynamo.
F. H. Busse; Simitev, R.
2009-01-01
Possibilities and difficulties of applying the theory of magnetic field generation by convection flows in rotating spherical fluid shells to the Giant Planets are outlined. Recent progress in the understanding of the distribution of electrical conductivity in the Giant Planets suggests that the dynamo process occurs predominantly in regions of semiconductivity. In contrast to the geodynamo the magnetic field generation in the Giant Planets is thus characterized by strong radial conductivity v...
Cattaneo, F.
2000-05-01
Magnetic activity on the Sun presents us with an interesting dichotomy. On large spatial and temporal scales the solar magnetic field displays a remarkable degree of organization. The 11 years cadence of the solar cycle, Hales' polarity law, and the systematic drift of the regions of emergence of active regions towards the equator throughout the solar cycle are all indicative of a powerful organizing process. On small spatial and temporal scales, the Solar magnetic field appears random and chaotic. It is interesting that recent advances in dynamo theory provide us with a unified approach to solar magnetic activity whereby both large and small scales emerge naturally as dynamo processes associated with rotationally constrained and unconstrained scales of motions in the convection zone (or directly below it). According to this view all coherent scales of motions produce magnetic structures of comparable coherence length. Those that are further endowed with lack of reflectional symmetry by virtue of being rotationally constrained are further associated with inverse cascades that can generate magnetic structures on larger scales still. The picture that emerges is one in which dynamo action proceeds on different time scales all over the convection zone. But only in very special regions, like for instance the solar tachocline, is the magnetic field organized on large scales. This idea provides a natural explanation for the origin of active regions, ephemeral regions, and intra--network fields.
Fluid Dynamics Prize Lecture: Homogeneous Dynamos in Planets and in the Laboratory
Busse, F. H.
2000-11-01
Numerical simulations of the dynamo problem of the generation of magnetic fields by convection flows in rotating spherical fluid shells have been extended to a sufficiently large parameter regime such that extrapolation to the condition of planetary cores have become feasible. Besides dipolar fields, hemispherical and quadrupolar fields are preferred in various regimes of the parameter space. In the latter two cases oscillating time dependances are always found inspite of the chaotic nature of the dynamos. Subcritical dynamo states are typical and multiple dynamo states are possible. On the experimental side the homogeneous dynamo process has recently been demonstrated without the use of ferromagnetic material in Riga and Karlsruhe. Further experiments at other laboratories are expected to realize dynamos under conditions of strong turbulence.
Austenitic welds and dissimilar welds are extensively used in primary circuit pipes and pressure vessels in nuclear power plants, chemical industries and fossil fuelled power plants because of their high fracture toughness, resistance to corrosion and creep at elevated temperatures. However, cracks may initiate in these weld materials during fabrication process or stress operations in service. Thus, it is very important to evaluate the structural integrity of these materials using highly reliable non-destructive testing (NDT) methods. Ultrasonic non-destructive inspection of austenitic welds and dissimilar weld components is complicated because of anisotropic columnar grain structure leading to beam splitting and beam deflection. Simulation tools play an important role in developing advanced reliable ultrasonic testing (UT) techniques and optimizing experimental parameters for inspection of austenitic welds and dissimilar weld components. The main aim of the thesis is to develop a 3D ray tracing model for quantitative evaluation of ultrasonic wave propagation in an inhomogeneous anisotropic austenitic weld material. Inhomogenity in the anisotropic weld material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The influence of anisotropy on ultrasonic reflection and transmission behaviour in an anisotropic austenitic weld material are quantitatively analyzed in three dimensions. The ultrasonic beam directivity in columnar grained austenitic steel material is determined three dimensionally using Lamb's reciprocity theorem. The developed ray tracing model evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase
Audigane, Pascal; Chiaberge, Christophe; Mathurin, Frédéric; Lions, Julie; Picot-Colbeaux, Géraldine
2011-04-01
This paper is addressed to the TOUGH2 user community. It presents a new tool for handling simulations run with the TOUGH2 code with specific application to CO 2 geological storage. This tool is composed of separate FORTRAN subroutines (or modules) that can be run independently, using input and output files in ASCII format for TOUGH2. These modules have been developed specifically for modeling of carbon dioxide geological storage and their use with TOUGH2 and the Equation of State module ECO2N, dedicated to CO 2-water-salt mixture systems, with TOUGHREACT, which is an adaptation of TOUGH2 with ECO2N and geochemical fluid-rock interactions, and with TOUGH2 and the EOS7C module dedicated to CO 2-CH 4 gas mixture is described. The objective is to save time for the pre-processing, execution and visualization of complex geometry for geological system representation. The workflow is rapid and user-friendly and future implementation to other TOUGH2 EOS modules for other contexts (e.g. nuclear waste disposal, geothermal production) is straightforward. Three examples are shown for validation: (i) leakage of CO 2 up through an abandoned well; (ii) 3D reactive transport modeling of CO 2 in a sandy aquifer formation in the Sleipner gas Field, (North Sea, Norway); and (iii) an estimation of enhanced gas recovery technology using CO 2 as the injected and stored gas to produce methane in the K12B Gas Field (North Sea, Denmark).
Hunter, Kendall; Zhang, Yanhang; Lanning, Craig
2005-11-01
Insight into the progression of pulmonary hypertension may be obtained from thorough study of vascular flow during reactivity testing, an invasive diagnostic procedure which can dramatically alter vascular hemodynamics. Diagnostic imaging methods, however, are limited in their ability to provide extensive data. Here we present detailed flow and wall deformation results from simulations of pulmonary arteries undergoing this procedure. Patient-specific 3-D geometric reconstructions of the first four branches of the pulmonary vasculature were obtained clinically and meshed for use with computational software. Transient simulations in normal and reactive states were obtained from four such models were completed with patient-specific velocity inlet conditions and flow impedance exit conditions. A microstructurally based orthotropic hyperelastic model that simulates pulmonary artery mechanics under normotensive and hypoxic hypertensive conditions treated wall constitutive changes due to pressure reactivity and arterial remodeling. Pressure gradients, velocity fields, arterial deformation, and complete topography of shear stress were obtained. These models provide richer detail of hemodynamics than can be obtained from current imaging techniques, and should allow maximum characterization of vascular function in the clinical situation.
Yiyun Lu
2012-01-01
Full Text Available Magnetic forces of a cylinder shape bulk high-temperature superconductor (HTS over a permanent magnet guideway (PMG are studied mathematically. One cylindrical bulk HTS with a diameter of 30 mm and 15 mm in height is used. Two types of PMG are employed for external magnetic fields consideration. The relationship of magnetic forces of bulk HTS under different lateral offsets over PMG is studied with 3D-model finite element method (FEM. The calculation results show that the maximum magnetic levitation force of bulk HTS over PMG is tightly related to the applied magnetic field distribution. For the symmetrical PMG, the maximum magnetic levitation force decreases linearly with the increase of lateral offset of the bulk sample. For the Halbach PMG, when lateral offset changes from 0 mm to 25 mm, the maximum magnetic levitation force increases with the increase of lateral offset of the bulk HTS. When the lateral offset exceeds the center of the Halbach by 25 mm, the maximum levitation force decreases rapidly with the increase of the lateral offset of the bulk sample.
Consistent scaling laws in anelastic spherical shell dynamos
Yadav, Rakesh K; Christensen, Ulrich R; Duarte, Lúcia D V
2013-01-01
Numerical dynamo models always employ parameter values that differ by orders of magnitude from the values expected in natural objects. However, such models have been successful in qualitatively reproducing properties of planetary and stellar dynamos. This qualitative agreement fuels the idea that both numerical models and astrophysical objects may operate in the same asymptotic regime of dynamics. This can be tested by exploring the scaling behavior of the models. For convection-driven incompressible spherical shell dynamos with constant material properties, scaling laws had been established previously that relate flow velocity and magnetic field strength to the available power. Here we analyze 272 direct numerical simulations using the anelastic approximation, involving also cases with radius-dependent magnetic, thermal and viscous diffusivities. These better represent conditions in gas giant planets and low-mass stars compared to Boussinesq models. Our study provides strong support for the hypothesis that b...
Tournay, Bruno; Rüdiger, Bjarne
2006-01-01
3d digital model af Arkitektskolens gård med virtuel udstilling af afgangsprojekter fra afgangen sommer 2006. 10 s.......3d digital model af Arkitektskolens gård med virtuel udstilling af afgangsprojekter fra afgangen sommer 2006. 10 s....
Hassam, Adil [Univ. of Maryland, College Park, MD (United States)
2015-09-21
We studied the feasibility of resonantly driving GAMs in tokamaks. A numerical simulation was carried out and showed the essential features and limitations. It was shown further that GAMs can damp by phase-mixing, from temperature gradients, or nonlinear detuning, thus broadening the resonance. Experimental implications of this were quantified. Theoretical support was provided for the Maryland Centrifugal Experiment, funded in a separate grant by DOE. Plasma diamagnetism from supersonic rotation was established. A theoretical model was built to match the data. Additional support to the experiment in terms of numerical simulation of the interchange turbulence was provided. Spectra from residual turbulence on account of velocity shear suppression were obtained and compared favorably to experiment. A new drift wave, driven solely by the thermal force, was identified.
Hase, M.
2005-07-01
In the present work a method for the direct numerical simulation (DNS) of heat and mass transfer with evaporation in two-phase flow is developed. DNS of two-phase flow means that the interface is tracked exactly and all conservation equations are solved without additional models. With the so-called one-field formulation the two-phase flow is described by the equation system of a one-phase flow with different properties and an additional source term for the surface tension force. The distribution of the phases is got with the volume-of-fluid (VOF) method. With the VOF-method the fluid properties and the surface tension force can be computed. With an accurate comparison between numerical and experimental results the new implemented method is validated. Both the numerically obtained mass transfer with evaporation and the heat transfer show a good to very good agreement with experimental/analytical data. Simulations for the heat transfer on strongly deformed droplets are performed with the new implemented method. The dependency of the heat transfer also from the Weber number is shown for the droplet deformation due to an approaching flow. This flow condition agrees with the flow for the secondary break-up. The dependency of the heat transfer grows with increasing Reynolds number. For an initially deformed droplet the dependency of the heat transfer on the oscillation period is shown. (orig.)
Roberto Rinaldi
2014-12-01
Full Text Available After an experimental phase of many years, 3D filming is now effective and successful. Improvements are still possible, but the film industry achieved memorable success on 3D movie’s box offices due to the overall quality of its products. Special environments such as space (“Gravity” and the underwater realm look perfect to be reproduced in 3D. “Filming in space” was possible in “Gravity” using special effects and computer graphic. The underwater realm is still difficult to be handled. Underwater filming in 3D was not that easy and effective as filming in 2D, since not long ago. After almost 3 years of research, a French, Austrian and Italian team realized a perfect tool to film underwater, in 3D, without any constrains. This allows filmmakers to bring the audience deep inside an environment where they most probably will never have the chance to be.
Jin, BoCheng
2011-12-01
Organic and inorganic fiber reinforced composites with innumerable fiber orientation distributions and fiber geometries are abundantly available in several natural and synthetic structures. Inorganic glass fiber composites have been introduced to numerous applications due to their economical fabrication and tailored structural properties. Numerical characterization of such composite material systems is necessitated due to their intrinsic statistical nature, which renders extensive experimentation prohibitively time consuming and costly. To predict various mechanical behavior and characterizations of Uni-Directional Fiber Composites (UDFC) and Random Fiber Composites (RaFC), we numerically developed Representative Volume Elements (RVE) with high accuracy and efficiency and with complex fiber geometric representations encountered in uni-directional and random fiber networks. In this thesis, the numerical simulations of unidirectional RaFC fiber strand RVE models (VF>70%) are first presented by programming in ABAQUS PYTHON. Secondly, when the cross sectional aspect ratios (AR) of the second phase fiber inclusions are not necessarily one, various types of RVE models with different cross sectional shape fibers are simulated and discussed. A modified random sequential absorption algorithm is applied to enhance the volume fraction number (VF) of the RVE, which the mechanical properties represents the composite material. Thirdly, based on a Spatial Segment Shortest Distance (SSSD) algorithm, a 3-Dimentional RaFC material RVE model is simulated in ABAQUS PYTHON with randomly oriented and distributed straight fibers of high fiber aspect ratio (AR=100:1) and volume fraction (VF=31.8%). Fourthly, the piecewise multi-segments fiber geometry is obtained in MATLAB environment by a modified SSSD algorithm. Finally, numerical methods including the polynomial curve fitting and piecewise quadratic and cubic B-spline interpolation are applied to optimize the RaFC fiber geometries
Magnetized Turbulent Dynamo in Protogalaxies
Leonid Malyshkin; Russell M. Kulsrud
2002-01-28
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached.
Magnetized Turbulent Dynamo in Protogalaxies
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached
Ge, Liang; Sotiropoulos, Fotis
2007-08-01
A novel numerical method is developed that integrates boundary-conforming grids with a sharp interface, immersed boundary methodology. The method is intended for simulating internal flows containing complex, moving immersed boundaries such as those encountered in several cardiovascular applications. The background domain (e.g the empty aorta) is discretized efficiently with a curvilinear boundary-fitted mesh while the complex moving immersed boundary (say a prosthetic heart valve) is treated with the sharp-interface, hybrid Cartesian/immersed-boundary approach of Gilmanov and Sotiropoulos [1]. To facilitate the implementation of this novel modeling paradigm in complex flow simulations, an accurate and efficient numerical method is developed for solving the unsteady, incompressible Navier-Stokes equations in generalized curvilinear coordinates. The method employs a novel, fully-curvilinear staggered grid discretization approach, which does not require either the explicit evaluation of the Christoffel symbols or the discretization of all three momentum equations at cell interfaces as done in previous formulations. The equations are integrated in time using an efficient, second-order accurate fractional step methodology coupled with a Jacobian-free, Newton-Krylov solver for the momentum equations and a GMRES solver enhanced with multigrid as preconditioner for the Poisson equation. Several numerical experiments are carried out on fine computational meshes to demonstrate the accuracy and efficiency of the proposed method for standard benchmark problems as well as for unsteady, pulsatile flow through a curved, pipe bend. To demonstrate the ability of the method to simulate flows with complex, moving immersed boundaries we apply it to calculate pulsatile, physiological flow through a mechanical, bileaflet heart valve mounted in a model straight aorta with an anatomical-like triple sinus. PMID:19194533
3D laptop for defense applications
Edmondson, Richard; Chenault, David
2012-06-01
Polaris Sensor Technologies has developed numerous 3D display systems using a US Army patented approach. These displays have been developed as prototypes for handheld controllers for robotic systems and closed hatch driving, and as part of a TALON robot upgrade for 3D vision, providing depth perception for the operator for improved manipulation and hazard avoidance. In this paper we discuss the prototype rugged 3D laptop computer and its applications to defense missions. The prototype 3D laptop combines full temporal and spatial resolution display with the rugged Amrel laptop computer. The display is viewed through protective passive polarized eyewear, and allows combined 2D and 3D content. Uses include robot tele-operation with live 3D video or synthetically rendered scenery, mission planning and rehearsal, enhanced 3D data interpretation, and simulation.
Rubber Impact on 3D Textile Composites
Heimbs, Sebastian; Van Den Broucke, Björn; DUPLESSIS KERGOMARD, Yann; Dau, Frédéric; MALHERBE, Benoit
2012-01-01
A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic o...
Valenza, Enrico
2015-01-01
This book is aimed at the professionals that already have good 3D CGI experience with commercial packages and have now decided to try the open source Blender and want to experiment with something more complex than the average tutorials on the web. However, it's also aimed at the intermediate Blender users who simply want to go some steps further.It's taken for granted that you already know how to move inside the Blender interface, that you already have 3D modeling knowledge, and also that of basic 3D modeling and rendering concepts, for example, edge-loops, n-gons, or samples. In any case, it'
Mcwilliams, James C.
2011-01-01
A quasi-linear theory is presented for how randomly forced, barotropic velocity fluctuations cause an exponentially-growing, large-scale (mean) magnetic dynamo in the presence of a uniform shear flow, $\\vec{U} = S x \\vec{e}_y$. It is a "kinematic" theory for the growth of the mean magnetic energy from a small initial seed, neglecting the saturation effects of the Lorentz force. The quasi-linear approximation is most broadly justifiable by its correspondence with computational solutions of non...
Boerstoel, J. W.
1988-01-01
The current status of a computer program system for the numerical simulation of Euler flows is presented. Preliminary test calculation results are shown. They concern the three-dimensional flow around a wing-nacelle-propeller-outlet configuration. The system is constructed to execute four major tasks: block decomposition of the flow domain around given, possibly complex, three-dimensional aerodynamic surfaces; grid generation on the blocked flow domain; Euler-flow simulation on the blocked grid; and graphical visualization of the computed flow on the blocked grid, and postprocessing. The system consists of about 20 codes interfaced by files. Most of the required tasks can be executed. The geometry of complex aerodynamic surfaces in three-dimensional space can be handled. The validation test showed that the system must be improved to increase the speed of the grid generation process.
Hundebøl, Jesper
wave of new building information modelling tools demands further investigation, not least because of industry representatives' somewhat coarse parlance: Now the word is spreading -3D digital modelling is nothing less than a revolution, a shift of paradigm, a new alphabet... Research qeustions. Based...... on empirical probes (interviews, observations, written inscriptions) within the Danish construction industry this paper explores the organizational and managerial dynamics of 3D Digital Modelling. The paper intends to - Illustrate how the network of (non-)human actors engaged in the promotion (and arrest) of 3......D Modelling (in Denmark) stabilizes - Examine how 3D Modelling manifests itself in the early design phases of a construction project with a view to discuss the effects hereof for i.a. the management of the building process. Structure. The paper introduces a few, basic methodological concepts...
Turbulent 2.5 dimensional dynamos
Seshasayanan, K
2015-01-01
We study the dynamo instability driven by a turbulent two dimensional flow with three components of the form (u(x, y, t), v(x, y, t), w(x, y, t)) sometimes referred to as a 2.5 dimensional flow. This type of flows provides an approximation to very fast rotating flows often observed in nature. The low dimensionality of the system allows the investigation of a wide range of fluid Reynolds number Re, magnetic Reynolds number Rm and forcing length scales relative to the domain size that is still prohibited for full three dimensional numerical simulations. We were thus able to determine the properties of the dynamo onset as a function of Re and and the asymptotic behavior of the most unstable mode in the large Rm limit. In particular it has been shown that: In a non-helical flow in an infinite domain the critical magnetic Reynolds number Rmc becomes a constant in the large Re limit. A helical flow always results in dynamo in agreement with mean field predictions. For thin layers for both helical and nonhelical flo...
Lively, Michael
2010-01-01
Professional Papervision3D describes how Papervision3D works and how real world applications are built, with a clear look at essential topics such as building websites and games, creating virtual tours, and Adobe's Flash 10. Readers learn important techniques through hands-on applications, and build on those skills as the book progresses. The companion website contains all code examples, video step-by-step explanations, and a collada repository.
The Kinematic Theory of Solar Dynamo
无
2003-01-01
Generation of the Sun's magnetic fields by self-inductive processes inthe solar electrically conducting interior, the solar dynamo theory, is a fundamen-tally important subject in astrophysics. The kinematic dynamo theory concernshow the magnetic fields are produced by kinematically possible flows without beingconstrained by the dynamic equation. We review a number of basic aspects of thekinematic dynamo theory, including the magnetohydrodynamic approximation forthe dynamo equation, the impossibility of dynamo action with the solar differentialrotation, the Cowling's anti-dynamo theorem in the solar context, the turbulent al-pha effect and recently constructed three-dimensional interface dynamos controlledby the solar tachocline at the base of the convection zone.
Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models
Jouve, L; Lesur, G
2010-01-01
The Sun is a magnetic star whose cyclic activity is thought to be linked to internal dynamo mechanisms. A combination of numerical modelling with various levels of complexity is an efficient and accurate tool to investigate such intricate dynamical processes. We investigate the role of the magnetic buoyancy process in 2D Babcock-Leighton dynamo models, by modelling more accurately the surface source term for poloidal field. Methods. To do so, we reintroduce in mean-field models the results of full 3D MHD calculations of the non-linear evolution of a rising flux tube in a convective shell. More specifically, the Babcock-Leighton source term is modified to take into account the delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. We find that the time delays introduced in the equations produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. Aperiodic modulations of the solar cy...
Cartalade, Alain; Plapp, Mathis
2016-01-01
A lattice-Boltzmann (LB) scheme, based on the Bhatnagar-Gross-Krook (BGK) collision rules is developed for a phase-field model of alloy solidification in order to simulate the growth of dendrites. The solidification of a binary alloy is considered, taking into account diffusive transport of heat and solute, as well as the anisotropy of the solid-liquid interfacial free energy. The anisotropic terms in the phase-field evolution equation, the phenomenological anti-trapping current (introduced in the solute evolution equation to avoid spurious solute trapping), and the variation of the solute diffusion coefficient between phases, make it necessary to modify the equilibrium distribution functions of the LB scheme with respect to the one used in the standard method for the solution of advection-diffusion equations. The effects of grid anisotropy are removed by using the lattices D3Q15 and D3Q19 instead of D3Q7. The method is validated by direct comparison of the simulation results with a numerical code that uses t...
3-D Relativistic MHD Simulations
Nishikawa, K.-I.; Frank, J.; Koide, S.; Sakai, J.-I.; Christodoulou, D. M.; Sol, H.; Mutel, R. L.
1998-12-01
We present 3-D numerical simulations of moderately hot, supersonic jets propagating initially along or obliquely to the field lines of a denser magnetized background medium with Lorentz factors of W = 4.56 and evolving in a four-dimensional spacetime. The new results are understood as follows: Relativistic simulations have consistently shown that these jets are effectively heavy and so they do not suffer substantial momentum losses and are not decelerated as efficiently as their nonrelativistic counterparts. In addition, the ambient magnetic field, however strong, can be pushed aside with relative ease by the beam, provided that the degrees of freedom associated with all three spatial dimensions are followed self-consistently in the simulations. This effect is analogous to pushing Japanese ``noren'' or vertical Venetian blinds out of the way while the slats are allowed to bend in 3-D space rather than as a 2-D slab structure.
3D Spectroscopic Instrumentation
Bershady, Matthew A
2009-01-01
In this Chapter we review the challenges of, and opportunities for, 3D spectroscopy, and how these have lead to new and different approaches to sampling astronomical information. We describe and categorize existing instruments on 4m and 10m telescopes. Our primary focus is on grating-dispersed spectrographs. We discuss how to optimize dispersive elements, such as VPH gratings, to achieve adequate spectral resolution, high throughput, and efficient data packing to maximize spatial sampling for 3D spectroscopy. We review and compare the various coupling methods that make these spectrographs ``3D,'' including fibers, lenslets, slicers, and filtered multi-slits. We also describe Fabry-Perot and spatial-heterodyne interferometers, pointing out their advantages as field-widened systems relative to conventional, grating-dispersed spectrographs. We explore the parameter space all these instruments sample, highlighting regimes open for exploitation. Present instruments provide a foil for future development. We give an...
Halskov, Kim; Johansen, Stine Liv; Bach Mikkelsen, Michelle
2014-01-01
Three-dimensional projection installations are particular kinds of augmented spaces in which a digital 3-D model is projected onto a physical three-dimensional object, thereby fusing the digital content and the physical object. Based on interaction design research and media studies, this article...... contributes to the understanding of the distinctive characteristics of such a new medium, and identifies three strategies for designing 3-D projection installations: establishing space; interplay between the digital and the physical; and transformation of materiality. The principal empirical case, From...... Fingerplan to Loop City, is a 3-D projection installation presenting the history and future of city planning for the Copenhagen area in Denmark. The installation was presented as part of the 12th Architecture Biennale in Venice in 2010....
Francisco R. Feito Higueruela
2010-04-01
Full Text Available Applications of Geographical Information Systems on several Archeology fields have been increasing during the last years. Recent avances in these technologies make possible to work with more realistic 3D models. In this paper we introduce a new paradigm for this system, the GIS Thetrahedron, in which we define the fundamental elements of GIS, in order to provide a better understanding of their capabilities. At the same time the basic 3D characteristics of some comercial and open source software are described, as well as the application to some samples on archeological researchs
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-01
We study the conformal bootstrap for a 4-point function of fermions in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
Villaume, René Domine; Ørstrup, Finn Rude
2002-01-01
Projektet undersøger potentialet for interaktiv 3D design via Internettet. Arkitekt Jørn Utzons projekt til Espansiva blev udviklet som et byggesystem med det mål, at kunne skabe mangfoldige planmuligheder og mangfoldige facade- og rumudformninger. Systemets bygningskomponenter er digitaliseret som...... 3D elementer og gjort tilgængelige. Via Internettet er det nu muligt at sammenstille og afprøve en uendelig række bygningstyper som systemet blev tænkt og udviklet til....
Kotek, L.
2015-01-01
This paper is about 3D scan of plaster dental casts. The main aim of the work is a hardware and software proposition of 3D scan system for scanning of dental casts. There were used camera, projector and rotate table for this scanning system. Surface triangulation was used, taking benefits of projections of structured light on object, which is being scanned. The rotate table is controlled by PC. The camera, projector and rotate table are synchronized by PC. Controlling of stepper motor is prov...
Ms. Swapnali R. Ghadge
2013-01-01
In today’s ever-shifting media landscape, it can be a complex task to find effective ways to reach your desired audience. As traditional media such as television continue to lose audience share, one venue in particular stands out for its ability to attract highly motivated audiences and for its tremendous growth potential the 3D Internet. The concept of '3D Internet' has recently come into the spotlight in the R&D arena, catching the attention of many people, and leading to a lot o...
无
2002-01-01
A new dynamo model based on the polarization of plasma is presented in this paper.From the Maxwell equations in a moving medium, a magnetization vector can be causedwith Rongon current. The steady solar magnetic field is solved from the equations. Onthe assumption that the meridianal flow is ignored, the distribution of magnetic field isput out. In the model, there is no additional parameter considered. The intensity ofmagnetic field inside the sun ranges from 1-6T. The surface magnetic field around thepole is in the order of 1×10-3T, at low latitude the calculated surface magnetic fieldhas the order of 1×10-2 T. The maximum magnetic field is around 30° in latitude.
Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
2016-05-01
We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within ~10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacremento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales.
DYNA3D2000*, Explicit 3-D Hydrodynamic FEM Program
1 - Description of program or function: DYNA3D2000 is a nonlinear explicit finite element code for analyzing 3-D structures and solid continuum. The code is vectorized and available on several computer platforms. The element library includes continuum, shell, beam, truss and spring/damper elements to allow maximum flexibility in modeling physical problems. Many materials are available to represent a wide range of material behavior, including elasticity, plasticity, composites, thermal effects and rate dependence. In addition, DYNA3D has a sophisticated contact interface capability, including frictional sliding, single surface contact and automatic contact generation. 2 - Method of solution: Discretization of a continuous model transforms partial differential equations into algebraic equations. A numerical solution is then obtained by solving these algebraic equations through a direct time marching scheme. 3 - Restrictions on the complexity of the problem: Recent software improvements have eliminated most of the user identified limitations with dynamic memory allocation and a very large format description that has pushed potential problem sizes beyond the reach of most users. The dominant restrictions remain in code execution speed and robustness, which the developers constantly strive to improve
Solar and stellar dynamos -- latest developments
Brandenburg, A; Brandenburg, Axel; Dobler, Wolfgang
2002-01-01
Recent progress in the theory of solar and stellar dynamos is reviewed. Particular emphasis is placed on the mean-field theory which tries to describe the collective behavior of the magnetic field. In order to understand solar and stellar activity, a quantitatively reliable theory is necessary. Much of the new developments center around magnetic helicity conservation which is seen to be important in numerical simulations. Only a dynamical, explicitly time dependent theory of alpha-quenching is able to describe this behavior correctly.
Effects of Penetrative Convection on Solar Dynamo
Masada, Youhei; Kageyama, Akira
2013-01-01
Spherical solar dynamo simulations are performed. Self-consistent, fully compressible magnetohydrodynamic system with a stably stratified layer below the convection zone are numerically solved with a newly developed simulation code based on the Yin-Yang grid. The effects of penetrative convection are studied by comparing two models with and without the stable layer. A solar-like differential rotation profile is established when the penetrative convection is taken into account without assuming any forcing. A large-scale magnetic field is also spontaneously organized in the underlying stable layer. The embedded field has a dipole symmetry about the equator and it shows polarity reversals in time.
Scaling laws of turbulent dynamos
Fauve, Stephan; Petrelis, Francois
2007-01-01
We consider magnetic fields generated by homogeneous isotropic and parity invariant turbulent flows. We show that simple scaling laws for dynamo threshold, magnetic energy and Ohmic dissipation can be obtained depending on the value of the magnetic Prandtl number.
Hejlesen, Aske K.; Ovesen, Nis
2012-01-01
This paper presents an experimental approach to teaching 3D modelling techniques in an Industrial Design programme. The approach includes the use of tangible free form models as tools for improving the overall learning. The paper is based on lecturer and student experiences obtained through...
Stenholt, Rasmus; Madsen, Claus B.
2011-01-01
Enabling users to shape 3-D boxes in immersive virtual environments is a non-trivial problem. In this paper, a new family of techniques for creating rectangular boxes of arbitrary position, orientation, and size is presented and evaluated. These new techniques are based solely on position data...
M.M. Voormolen
2007-01-01
textabstractThree dimensional (3D) echocardiography has recently developed from an experimental technique in the â€™90 towards an imaging modality for the daily clinical practice. This dissertation describes the considerations, implementation, validation and clinical application of a unique
Shear dynamo, turbulence, and the magnetorotational instability
Squire, Jonathan
The formation, evolution, and detailed structure of accretion disks remain poorly understood, with wide implications across a variety of astrophysical disciplines. While the most pressing question --- what causes the high angular momentum fluxes that are necessary to explain observations? --- is nicely answered by the idea that the disk is turbulent, a more complete grasp of the fundamental processes is necessary to capture the wide variety of behaviors observed in the night sky. This thesis studies the turbulence in ionized accretion disks from a theoretical standpoint, in particular focusing on the generation of magnetic fields in these processes, known as dynamo. Such fields are expected to be enormously important, both by enabling the magnetorotational instability (which evolves into virulent turbulence), and through large-scale structure formation, which may transport angular momentum in different ways and be fundamental for the formation of jets. The central result of this thesis is the suggestion of a new large-scale dynamo mechanism in shear flows --- the "magnetic shear-current effect" --- which relies on a positive feedback from small-scale magnetic fields. As well as being a very promising candidate for driving field generation in the central regions of accretion disks, this effect is interesting because small-scale magnetic fields have historically been considered to have a negative effect on the large-scale dynamo, damping growth and leading to dire predictions for final saturation amplitudes. Given that small-scale fields are ubiquitous in plasma turbulence above moderate Reynolds numbers, the finding that they could instead have a positive effect in some situations is interesting from a theoretical and practical standpoint. The effect is studied using direct numerical simulation, analytic techniques, and novel statistical simulation methods. In addition to the dynamo, much attention is given to the linear physics of disks and its relevance to
Can a Sinking Metallic Diapir Generate a Dynamo?
Schaeffer, N.; Monteux, J.; Amit, H.; Cardin, P.
2012-12-01
Metallic diapirs may have strongly contributed to core formations during the first million years of planetary evolutions. The length-scales of these diapirs can range from several centimetres to several hundred kilometres. The aim of this study is to determine whether the dynamics enhanced by the diapir sinking can drive a dynamo and to characterize the required conditions on the size of the diapir, the mantle viscosity and the planetary latitude at which the diapir sinks. We impose a classical Hadamard flow solution for the motion at the interface between a sinking diapir and a viscous mantle on dynamical simulations that account for rotational and inertial effects in order to model the flow within the diapir. The flows are confined to a velocity layer with a thickness that decreases with increasing rotation rate. This decrease depends on the initial latitude of the diapir. This 3D flow is then used as input for kinematic dynamo simulations to determine the critical magnetic Reynolds number for dynamo onset. Our results demonstrate that the flow pattern occurring inside a diapir sinking through a partially molten mantle within a rotating planet can generate a magnetic field. This dynamo generation is more favourable for a large diapir sinking from the equator than from the planet's rotational pole.
THE TURBULENT DYNAMO IN HIGHLY COMPRESSIBLE SUPERSONIC PLASMAS
The turbulent dynamo may explain the origin of cosmic magnetism. While the exponential amplification of magnetic fields has been studied for incompressible gases, little is known about dynamo action in highly compressible, supersonic plasmas, such as the interstellar medium of galaxies and the early universe. Here we perform the first quantitative comparison of theoretical models of the dynamo growth rate and saturation level with three-dimensional magnetohydrodynamical simulations of supersonic turbulence with grid resolutions of up to 10243 cells. We obtain numerical convergence and find that dynamo action occurs for both low and high magnetic Prandtl numbers Pm = ν/η = 0.1-10 (the ratio of viscous to magnetic dissipation), which had so far only been seen for Pm ≥ 1 in supersonic turbulence. We measure the critical magnetic Reynolds number, Rmcrit=129−31+43, showing that the compressible dynamo is almost as efficient as in incompressible gas. Considering the physical conditions of the present and early universe, we conclude that magnetic fields need to be taken into account during structure formation from the early to the present cosmic ages, because they suppress gas fragmentation and drive powerful jets and outflows, both greatly affecting the initial mass function of stars
THE TURBULENT DYNAMO IN HIGHLY COMPRESSIBLE SUPERSONIC PLASMAS
Federrath, Christoph [Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 (Australia); Schober, Jennifer [Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Strasse 2, D-69120 Heidelberg (Germany); Bovino, Stefano; Schleicher, Dominik R. G., E-mail: christoph.federrath@anu.edu.au [Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany)
2014-12-20
The turbulent dynamo may explain the origin of cosmic magnetism. While the exponential amplification of magnetic fields has been studied for incompressible gases, little is known about dynamo action in highly compressible, supersonic plasmas, such as the interstellar medium of galaxies and the early universe. Here we perform the first quantitative comparison of theoretical models of the dynamo growth rate and saturation level with three-dimensional magnetohydrodynamical simulations of supersonic turbulence with grid resolutions of up to 1024{sup 3} cells. We obtain numerical convergence and find that dynamo action occurs for both low and high magnetic Prandtl numbers Pm = ν/η = 0.1-10 (the ratio of viscous to magnetic dissipation), which had so far only been seen for Pm ≥ 1 in supersonic turbulence. We measure the critical magnetic Reynolds number, Rm{sub crit}=129{sub −31}{sup +43}, showing that the compressible dynamo is almost as efficient as in incompressible gas. Considering the physical conditions of the present and early universe, we conclude that magnetic fields need to be taken into account during structure formation from the early to the present cosmic ages, because they suppress gas fragmentation and drive powerful jets and outflows, both greatly affecting the initial mass function of stars.
Buoyant Magnetic Loops in a Global Dynamo Simulation of a Young Sun
Nelson, Nicholas J; Brun, Allan Sacha; Miesch, Mark S; Toomre, Juri
2011-01-01
The current dynamo paradigm for the Sun and sun-like stars places the generation site for strong toroidal magnetic structures deep in the solar interior. Sunspots and star-spots on sun-like stars are believed to arise when sections of these magnetic structures become buoyantly unstable and rise from the deep interior to the photosphere. Here we present the first 3-D global magnetohydrodynamic (MHD) simulation in which turbulent convection, stratification, and rotation combine to yield a dynamo that self-consistently generates buoyant magnetic loops. We simulate stellar convection and dynamo action in a spherical shell with solar stratification, but rotating three times faster than the current solar rate. Strong wreaths of toroidal magnetic field are realized by dynamo action in the convection zone. By turning to a dynamic Smagorinsky model for subgrid-scale turbulence, we here attain considerably reduced diffusion in our simulation. This permits the regions of strongest magnetic field in these wreaths to rise...
A hemispherical dynamo model : Implications for the Martian crustal magnetization
Dietrich, Wieland
2014-01-01
Mars Global Surveyor measurements revealed that the Martian crust is strongly magnetized in the southern hemisphere while the northern hemisphere is virtually void of magnetization. Two possible reasons have been suggested for this dichotomy: A once more or less homogeneously magnetization may have been destroyed in the northern hemisphere by, for example, resurfacing or impacts. The alternative theory we further explore here assumes that the dynamo itself produced a hemispherical field. We use numerical dynamo simulations to study under which conditions a spatial variation of the heat flux through the core-mantle boundary (CMB) may yield a strongly hemispherical surface field. We assume that the early Martian dynamo was exclusively driven by secular cooling and we mostly concentrate on a cosine CMB heat flux pattern with a minimum at the north pole, possibly caused by the impacts responsible for the northern lowlands. This pattern consistently triggers a convective mode which is dominated by equatorially ant...
Suppression of a kinematic dynamo by large shear
Sood, Aditi; Kim, Eun-jin
2016-01-01
We numerically solve the magnetic induction equation in a spherical shell geometry, with a kinematically prescribed axisymmetric flow that consists of a superposition of a small-scale helical flow and a large-scale shear flow. The small-scale flow is chosen to be a local analog of the classical Roberts cells, consisting of strongly helical vortex rolls. The large-scale flow is a shearing motion in either the radial or the latitudinal directions. In the absence of large-scale shear, the small-scale flow is an efficient dynamo, in agreement with previous results. Adding increasingly large shear flows strongly suppresses the dynamo efficiency, indicating that shear is not always a favourable ingredient in dynamo action.
Spherical single-roll dynamos at large magnetic Reynolds numbers
Latter, Henrik
2010-01-01
This paper concerns kinematic helical dynamos in a spherical fluid body surrounded by an insulator. In particular, we examine their behaviour in the regime of large magnetic Reynolds number $\\Rm$, for which dynamo action is usually concentrated upon a simple resonant stream-surface. The dynamo eigensolutions are computed numerically for two representative single-roll flows using a compact spherical harmonic decomposition and fourth-order finite-differences in radius. These solutions are then compared with the growth rates and eigenfunctions of the Gilbert and Ponty (2000) large $\\Rm$ asymptotic theory. We find good agreement between the growth rates when $\\Rm>10^4$, and between the eigenfunctions when $\\Rm>10^5$.
Highlights: • Design of the test section for investigation of heat transfer in the first wall is presented. • Manufacturing details and providing of operational ready mock-up are given. • Corresponding 3D CFD model of the test section is described. - Abstract: This paper deals with cooling of the first wall of Helium-Cooled-Pebble-Bed Test Blanket Module (HCPB TBM) for ITER. The first wall cooling is an important investigation issue due to an extreme asymmetry of heat loads: heat flux on the plasma facing side is several times stronger than the one on the side which faces breeding units. Our preliminary 3D CFD analysis revealed that under such conditions the heat transfer coefficient is significantly lower than predicted by common heat transfer correlations (see Ilić et al., 2006). For an experimental validation of these results HETRA (HEat TRAnsfer) test section has been designed and built at the Institute for Neutron Physics and Reactor Technology in Karlsruhe Institute of Technology. The HETRA test section involves in full scale one U-pass of the cooling channel in the first wall of HCPB TBM Version 1.1 (see Meyder et al., 2005). The HCPB TBM relevant experimental conditions have been provided: test channel made of Eurofer steel, helium coolant at pressure of 8 MPa and inlet temperature of 300 °C and heat flux of 270 kW/m2 at the channel surface representing plasma facing side of the first wall. Test channels with hydraulically smooth and with hydraulically rough walls have been built. At each test channel the temperature of Eurofer walls has been measured at ∼60 positions. For numerical investigations the 3D CFD modelling with the code STAR CD has been applied. This paper is the first report on this study and presents the development of the test section and of the 3D CFD model. The analyses of the obtained experimental and computational results are presented in the second report (see Ilić et al., 2014)
Fast magnetic and electric dynamos in flat Klein bottle plasma flows
de Andrade, L C Garcia
2009-01-01
Recently Shukurov et al [Phys Rev \\textbf{E} (2008)] presented a numerical solution of a Moebius strip dynamo flow, to investigate its use in modelling dynamo flows in Perm torus of liquid sodium dynamo experiments. Here, by analogy one presents an electric dynamo on a twisted torus or Klein bottle topology. An exact solution in the form of flat Klein bottle dynamo flow is obtained. It is shown that even in the absence of magnetic dynamos initial electric fields can be amplified in distinct points of the Klein bottle. In this case diffusion is taken as ${\\eta}\\approx{5.0{\\times}10^{-3}{\\Omega}-m}$ the electric potential is obtained. The difference of electric fields at the beginning of plasma flow profile is ${\\Delta}E_{Dyn}\\approx{468\\frac{V}{m}}$, which is stronger than the electric dynamo field obtained in the magnetic axis of spheromaks, which is of the order of $E_{Dyn}\\approx{200\\frac{V}{m}}$. The potential of the dynamo at the surface of the Earth computed by Boozer [Phys Fluids \\textbf{B} (1993)] of $...
Klusoň, Jindřich
2010-01-01
Computer animation has a growing importance and application in the world. With expansion of technologies increases quality of the final animation as well as number of 3D animation software. This thesis is currently mapped animation software for creating animation in film, television industry and video games which are advisable users requirements. Of them were selected according to criteria the best - Autodesk Maya 2011. This animation software is unique with tools for creating special effects...
Millan Barrera, Cecia; Ramirez Leon, Hermilo [Instituto Mexicano de Tecnologia del Agua, Jiutepec, Morelos (Mexico)
2001-12-01
A numerical analysis is applied to a flow in an open channel and deformed by a three dimensional obstacle. The proposed model solves the 3-D Navier-Stokes equations, to which a {kappa}-{epsilon} turbulence model is coupled. The numerical analysis was constructed using a finite difference formulation for time evaluation purposed and staggered cells for space evaluation. The main goal of the present work was to study the turbulent structures and patterns of the flow due to an obstacle at the bottom of the channel plate. Our results are according to those found in the related literature. Flow patterns allow establishing the generation of turbulent structures by means of a comparison between this study and a most recent related work that evaluates the vorticity of the flow. [Spanish] Se reportan los resultados obtenidos, mediante simulaciones numericas, del movimiento del flujo en un canal con superficie libre y un obstaculo en el fondo. El sistema ecuaciones utilizado resuelve las ecuaciones de Navier-Stokes en tres dimensiones, al cual se le acoplo un modelo de turbulencia tipo {kappa}-{epsilon}. La solucion se obtiene numericamente utilizando un esquema en diferencias finitas para la evaluacion temporal de las variables y una celda escalonada para la evaluacion espacial de las mismas. El objetivo del modelo es estudiar los patrones de flujo y las estructuras turbulentas que se generan debido a la presencia del obstaculo. El estudio se realizo para un flujo en tres dimensiones. Los resultados son satisfactorios, ya que muestran concordancia con otros estudios numericos y experimentales encontrados en la literatura.
Terajets produced by 3D dielectric cuboids
Pacheco-Peña, V; Minin, I V; Minin, O V
2014-01-01
The capability of generating terajets using 3D dielectric cuboids working at terahertz (THz) frequencies (as analogues of nanojets in the infrared band) are introduced and studied numerically. The focusing performance of the terajets are evaluated in terms of the transversal full width at half maximum along x- and y- directions using different refractive indexes for a 3D dielectric cuboid with a fixed geometry, obtaining a quasi-symmetric terajet with a subwavelength resolution of ~0.46{\\lambda}0 when the refractive index is n = 1.41. Moreover, the backscattering enhancement produced when metal particles are introduced in the terajet region is demonstrated for a 3D dielectric cuboid and compared with its 2D counterpart. The results of the jet generated for the 3D case are experimentally validated at sub-THz waves, demonstrating the ability to produce terajets using 3D cuboids.
Tsunami: ocean dynamo generator.
Sugioka, Hiroko; Hamano, Yozo; Baba, Kiyoshi; Kasaya, Takafumi; Tada, Noriko; Suetsugu, Daisuke
2014-01-01
Secondary magnetic fields are induced by the flow of electrically conducting seawater through the Earth's primary magnetic field ('ocean dynamo effect'), and hence it has long been speculated that tsunami flows should produce measurable magnetic field perturbations, although the signal-to-noise ratio would be small because of the influence of the solar magnetic fields. Here, we report on the detection of deep-seafloor electromagnetic perturbations of 10-micron-order induced by a tsunami, which propagated through a seafloor electromagnetometer array network. The observed data extracted tsunami characteristics, including the direction and velocity of propagation as well as sea-level change, first to verify the induction theory. Presently, offshore observation systems for the early forecasting of tsunami are based on the sea-level measurement by seafloor pressure gauges. In terms of tsunami forecasting accuracy, the integration of vectored electromagnetic measurements into existing scalar observation systems would represent a substantial improvement in the performance of tsunami early-warning systems. PMID:24399356
Ayres, Thomas R.
2016-04-01
The Dynamo Clinical Trial evaluates long-term stellar magnetic health through periodic X-ray examinations (by the Chandra Observatory). So far, there are only three subjects enrolled in the DTC: Alpha Centauri A (a solar-like G dwarf), Alpha Cen B (an early K dwarf, more active than the Sun), and Alpha Canis Majoris A (Procyon, a mid-F subgiant similar in activity to the Sun). Of these, Procyon is a new candidate, so it is too early to judge how it will fare. Of the other two, Alpha Cen B has responded well, with a steady magnetic heartbeat of about 8 years duration. The sickest of the bunch, Alpha Cen A, was in magnetic cardiac arrest during 2005-2010, but has begun responding to treatment in recent years, and seems to be successfully cycling again, perhaps achieving a new peak of magnetic health in the 2016 time frame. If this is the case, it has been 20 years since A's last healthful peak, significantly longer than the middle-aged Sun's 11-year magnetic heartbeat, but perhaps in line with Alpha Cen A's more senescent state (in terms of "relative evolutionary age," apparently an important driver of activity). (By the way, don't miss the exciting movie of the Alpha Cen stars' 20-year X-ray dance.)
王建; 张志雁; 万连宾; 牧振伟
2011-01-01
Both the 3-D flow fields of the discharge chute section on steep slope before and after the arrangement of the aerator are numerically simulated through simulating the turbulence based on RNG k ～ ε model and tracing the free water surface with VOF Method. The simulation result shows that VOF model is a better method for simulating the hydraulic issues with free water surface; with which the free water surface of the aerating cavity can be better traced. Furthermore, the result from the numerical simulation coincides perfectly with the measured value of the model, and then, indicates that this method can applied to calculation of the length of the aerating cavity of the aerator.%通过采用RNGk～ε模型模拟湍流,利用VOF法追踪自由水面,对设置掺气槽前后两种方案的陡坡泄槽段三维流场进行数值模拟.模拟结果表明,VOF模型是模拟带自由表面水力学问题的较好方法,能够较好地对掺气空腔的自由面进行追踪.数值模拟结果与模型实测值二者吻合良好,表明该种方法可用于计算掺气槽内掺气空腔的长度.
The treatment of magnetic buoyancy in flux transport dynamo models
Choudhuri, Arnab Rai
2015-01-01
One important ingredient of flux transport dynamo models is the rise of the toroidal magnetic field through the convection zone due to magnetic buoyancy to produce bipolar sunspots and then the generation of the poloidal magnetic field from these bipolar sunspots due to the Babcock-Leighton mechanism. Over the years, two methods of treating magnetic buoyancy, a local method and a non-local method have been used widely by different groups in constructing 2D kinematic models of the flux transport dynamo. We review both these methods and conclude that neither of them is fully satisfactory, presumably because magnetic buoyancy is an inherently 3D process. We also point out so far we do not have proper understanding of why sunspot emergence is restricted to rather low latitudes.
Boundary effects on the MHD dynamo in laboratory plasmas
In recent laboratory experiments, a dynamo-like mechanism has been demonstrated in which a portion of the axisymmetric component of the magnetic field is believed to be sustained by 3D spatial fluctuations in the field and flow. With a conducting shell at the plasma surface, past MHD computation shows that sustainment arises from fluctuations which cause magnetic reconnection. If the conducting wall is retracted from the plasma surface, the fluctuations are amplified and the dynamo sustainment is still active for the times studied, but an increased energy input to the plasma is required through the applied electric field. The retraction of the conducting wall enhances the helicity dissipation rate by the intersection of the fields with the resistive surface which bounds the plasma. This enhanced helicity dissipation is balanced by the helicity injection that accompanies the increased applied electric field. 17 refs., 7 figs., 1 tab
Buoyant Magnetic Loops Generated by Global Convective Dynamo Action
Nelson, Nicholas J; Brun, A Sacha; Miesch, Mark S; Toomre, Juri
2012-01-01
Our global 3D simulations of convection and dynamo action in a Sun-like star reveal that persistent wreaths of strong magnetism can be built within the bulk of the convention zone. Here we examine the characteristics of buoyant magnetic structures that are self-consistently created by dynamo action and turbulent convective motions in a simulation with solar stratification but rotating at three times the current solar rate. These buoyant loops originate within sections of the magnetic wreaths in which turbulent flows amplify the fields to much larger values than is possible through laminar processes. These amplified portions can rise through the convective layer by a combination of magnetic buoyancy and advection by convective giant cells, forming buoyant loops. We measure statistical trends in the polarity, twist, and tilt of these loops. Loops are shown to preferentially arise in longitudinal patches somewhat reminiscent of active longitudes in the Sun, although broader in extent. We show that the strength o...
Inverse dynamo problem in a cylinder
Šimkanin, Ján; Tilgner, A.
2008-01-01
Roč. 102, č. 2 (2008), s. 205-215. ISSN 0309-1929 R&D Projects: GA AV ČR IAA300120704; GA ČR GP205/04/P182 Grant ostatní: INTAS Foundation(CH) 03-51-5807 Institutional research plan: CEZ:AV0Z30120515 Keywords : inverse dynamo problem * invisible dynamo * kinematic dynamo * helical flows * Ponomarenko dynamo Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 1.560, year: 2008
Faraday's first dynamo: A retrospective
Smith, Glenn S.
2013-12-01
In the early 1830s, Michael Faraday performed his seminal experimental research on electromagnetic induction, in which he created the first electric dynamo—a machine for continuously converting rotational mechanical energy into electrical energy. His machine was a conducting disc, rotating between the poles of a permanent magnet, with the voltage/current obtained from brushes contacting the disc. In his first dynamo, the magnetic field was asymmetric with respect to the axis of the disc. This is to be contrasted with some of his later symmetric designs, which are the ones almost invariably discussed in textbooks on electromagnetism. In this paper, a theoretical analysis is developed for Faraday's first dynamo. From this analysis, the eddy currents in the disc and the open-circuit voltage for arbitrary positioning of the brushes are determined. The approximate analysis is verified by comparing theoretical results with measurements made on an experimental recreation of the dynamo. Quantitative results from the analysis are used to elucidate Faraday's qualitative observations, from which he learned so much about electromagnetic induction. For the asymmetric design, the eddy currents in the disc dissipate energy that makes the dynamo inefficient, prohibiting its use as a practical generator of electric power. Faraday's experiments with his first dynamo provided valuable insight into electromagnetic induction, and this insight was quickly used by others to design practical generators.
Andringa, Roel; de Roo, Mees; Hohm, Olaf; Sezgin, Ergin; Townsend, Paul K
2009-01-01
We construct the N=1 three-dimensional supergravity theory with cosmological, Einstein-Hilbert, Lorentz Chern-Simons, and general curvature squared terms. We determine the general supersymmetric configuration, and find a family of supersymmetric adS vacua with the supersymmetric Minkowski vacuum as a limiting case. Linearizing about the Minkowski vacuum, we find three classes of unitary theories; one is the supersymmetric extension of the recently discovered `massive 3D gravity'. Another is a `new topologically massive supergravity' (with no Einstein-Hilbert term) that propagates a single (2,3/2) helicity supermultiplet.
Andringa, Roel; Bergshoeff, Eric A; De Roo, Mees; Hohm, Olaf [Centre for Theoretical Physics, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Sezgin, Ergin [George and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Townsend, Paul K, E-mail: E.A.Bergshoeff@rug.n, E-mail: O.Hohm@rug.n, E-mail: sezgin@tamu.ed, E-mail: P.K.Townsend@damtp.cam.ac.u [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA (United Kingdom)
2010-01-21
We construct the N=1 three-dimensional supergravity theory with cosmological, Einstein-Hilbert, Lorentz Chern-Simons, and general curvature squared terms. We determine the general supersymmetric configuration, and find a family of supersymmetric adS vacua with the supersymmetric Minkowski vacuum as a limiting case. Linearizing about the Minkowski vacuum, we find three classes of unitary theories; one is the supersymmetric extension of the recently discovered 'massive 3D gravity'. Another is a 'new topologically massive supergravity' (with no Einstein-Hilbert term) that propagates a single (2,3/2) helicity supermultiplet.
Evaluation of Model Operational Analyses during DYNAMO
Ciesielski, Paul; Johnson, Richard
2013-04-01
A primary component of the observing system in the DYNAMO-CINDY2011-AMIE field campaign was an atmospheric sounding network comprised of two sounding quadrilaterals, one north and one south of the equator over the central Indian Ocean. During the experiment a major effort was undertaken to ensure the real-time transmission of these data onto the GTS (Global Telecommunication System) for dissemination to the operational centers (ECMWF, NCEP, JMA, etc.). Preliminary estimates indicate that ~95% of the soundings from the enhanced sounding network were successfully transmitted and potentially used in their data assimilation systems. Because of the wide use of operational and reanalysis products (e.g., in process studies, initializing numerical simulations, construction of large-scale forcing datasets for CRMs, etc.), their validity will be examined by comparing a variety of basic and diagnosed fields from two operational analyses (ECMWF and NCEP) to similar analyses based solely on sounding observations. Particular attention will be given to the vertical structures of apparent heating (Q1) and drying (Q2) from the operational analyses (OA), which are strongly influenced by cumulus parameterizations, a source of model infidelity. Preliminary results indicate that the OA products did a reasonable job at capturing the mean and temporal characteristics of convection during the DYNAMO enhanced observing period, which included the passage of two significant MJO events during the October-November 2011 period. For example, temporal correlations between Q2-budget derived rainfall from the OA products and that estimated from the TRMM satellite (i.e., the 3B42V7 product) were greater than 0.9 over the Northern Sounding Array of DYNAMO. However closer inspection of the budget profiles show notable differences between the OA products and the sounding-derived results in low-level (surface to 700 hPa) heating and drying structures. This presentation will examine these differences and
On the saturation of astrophysical dynamos
Dorch, Bertil; Archontis, Vasilis
2004-01-01
In the context of astrophysical dynamos we illustrate that the no-cosines flow, with zero mean helicity, can drive fast dynamo action and we study the dynamo's mode of operation during both the linear and non-linear saturation regimes. It turns out that in addition to a high growth rate in the...
Ms. Swapnali R. Ghadge
2013-08-01
Full Text Available In today’s ever-shifting media landscape, it can be a complex task to find effective ways to reach your desired audience. As traditional media such as television continue to lose audience share, one venue in particular stands out for its ability to attract highly motivated audiences and for its tremendous growth potential the 3D Internet. The concept of '3D Internet' has recently come into the spotlight in the R&D arena, catching the attention of many people, and leading to a lot of discussions. Basically, one can look into this matter from a few different perspectives: visualization and representation of information, and creation and transportation of information, among others. All of them still constitute research challenges, as no products or services are yet available or foreseen for the near future. Nevertheless, one can try to envisage the directions that can be taken towards achieving this goal. People who take part in virtual worlds stay online longer with a heightened level of interest. To take advantage of that interest, diverse businesses and organizations have claimed an early stake in this fast-growing market. They include technology leaders such as IBM, Microsoft, and Cisco, companies such as BMW, Toyota, Circuit City, Coca Cola, and Calvin Klein, and scores of universities, including Harvard, Stanford and Penn State.
Fluctuation dynamo and turbulent induction at low magnetic Prandtl numbers
Schekochihin, A A [Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom); Iskakov, A B [Department of Physics and Astronomy, UCLA, Los Angeles CA 90095-1547 (United States); Cowley, S C [Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom); McWilliams, J C [Department of Atmospheric Sciences, UCLA, Los Angeles CA 90095-1565 (United States); Proctor, M R E [DAMTP, University of Cambridge, Cambridge CB3 0WA (United Kingdom); Yousef, T A [DAMTP, University of Cambridge, Cambridge CB3 0WA (United Kingdom)
2007-08-15
This paper is a detailed report on a programme of direct numerical simulations of incompressible nonhelical randomly forced magnetohydrodynamic (MHD) turbulence that are used to settle a long-standing issue in the turbulent dynamo theory and demonstrate that the fluctuation dynamo exists in the limit of large magnetic Reynolds number Rm >> 1 and small magnetic Prandtl number Pm << 1. The dependence of the critical Rm{sub c} for dynamo versus the hydrodynamic Reynolds number Re is obtained for 1 {approx}< Re {approx}< 6700. In the limit Pm >> 1, Rm{sub c} is at most three times larger than for the previously well established dynamo at large and moderate Prandtl numbers: Rm{sub c} {approx}< 200 for Re {approx}> 6000 compared to Rm{sub c} {approx} 60 for Pm{>=}1. The stability curve Rm{sub c}(Re) (and, it is argued, the nature of the dynamo) is substantially different from the case of the simulations and liquid-metal experiments with a mean flow. It is not as yet possible to determine numerically whether the growth rate of the magnetic energy is {proportional_to}Rm{sup 1/2} in the limit Re >> Rm >> 1, as should be the case if the dynamo is driven by the inertial-range motions at the resistive scale, or tends to an Rm-independent value comparable to the turnover rate of the outer-scale motions. The magnetic-energy spectrum in the low-Pm regime is qualitatively different from the Pm {>=} 1 case and appears to develop a negative spectral slope, although current resolutions are insufficient to determine its asymptotic form. At Rm element of (1,Rm{sub c}), the magnetic fluctuations induced via the tangling by turbulence of a weak mean field are investigated and the possibility of a k{sup -1} spectrum above the resistive scale is examined. At low Rm < 1, the induced fluctuations are well described by the quasistatic approximation; the k{sup -11/3} spectrum is confirmed for the first time in direct numerical simulations. Applications of the results on turbulent induction to
Two spinning ways for precession dynamo
Cappanera, L.; Guermond, J.-L.; Léorat, J.; Nore, C.
2016-04-01
It is numerically demonstrated by means of a magnetohydrodynamic code that precession can trigger dynamo action in a cylindrical container. Fixing the angle between the spin and the precession axis to be 1/2 π , two limit configurations of the spinning axis are explored: either the symmetry axis of the cylinder is parallel to the spin axis (this configuration is henceforth referred to as the axial spin case), or it is perpendicular to the spin axis (this configuration is referred to as the equatorial spin case). In both cases, the centro-symmetry of the flow breaks when the kinetic Reynolds number increases. Equatorial spinning is found to be more efficient in breaking the centro-symmetry of the flow. In both cases, the average flow in the reference frame of the mantle converges to a counter-rotation with respect to the spin axis as the Reynolds number grows. We find a scaling law for the average kinetic energy in term of the Reynolds number in the axial spin case. In the equatorial spin case, the unsteady asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field is mainly dipolar in the equatorial spin case, while it is is mainly quadrupolar in the axial spin case.
The shear-induced alpha-effect and long-term variations in solar dynamo
Pipin, V. V.
2007-01-01
The consequences of the shear-induced alpha effect to the long-term modulation of magnetic activity are examined with the help of the axisymmetric numerical dynamo model that includes the self-consistent description of the angular momentum balance, heat transport and magnetic field generation in the spherical shell. We find that the shear contributions to alpha effect can complicate the long-term behaviour of the large-scale magnetic activity and differential rotation in nonlinear dynamo. Add...
余育苗; 王肖均; 李永池; 王志海
2009-01-01
We present numerical simulation of Kevlar/Vinyl 3D orthogonal woven composite impacted by a spherical bullet with LS-Dyna software. Orthogonal constitutive equation with damage tensor and Hashin failure criteria are adopted for the Kevlar/Vinyl target. Time history of penetration velocity and loading of bullet show that steady penetration process and residual velocity agree well with experimental date. The damage modes basically reflect experimental results. Penetration process and damage modes are studied in details by analyzing damage evolution along the x fiber and interface matrix. It shows that the simulations are in good agreement with experiments.%利用LS-Dyna有限元软件开展球形弹弹道侵彻Kevlar/乙烯基树脂三维正交机织复合材料的模拟研究,靶板采用含损伤的正交各向异性本构模型和Hashin失效准则,子弹剩余速度的计算值和实验值符合较好,破坏形貌和实验基本一致,并给出侵彻速度时程曲线;结合x方向纤维和面内基体的损伤演化图,分析弹道侵彻过程和材料的破坏模式.
Hausman, Kalani Kirk
2014-01-01
Get started printing out 3D objects quickly and inexpensively! 3D printing is no longer just a figment of your imagination. This remarkable technology is coming to the masses with the growing availability of 3D printers. 3D printers create 3-dimensional layered models and they allow users to create prototypes that use multiple materials and colors. This friendly-but-straightforward guide examines each type of 3D printing technology available today and gives artists, entrepreneurs, engineers, and hobbyists insight into the amazing things 3D printing has to offer. You'll discover methods for
Handbook of 3D machine vision optical metrology and imaging
Zhang, Song
2013-01-01
With the ongoing release of 3D movies and the emergence of 3D TVs, 3D imaging technologies have penetrated our daily lives. Yet choosing from the numerous 3D vision methods available can be frustrating for scientists and engineers, especially without a comprehensive resource to consult. Filling this gap, Handbook of 3D Machine Vision: Optical Metrology and Imaging gives an extensive, in-depth look at the most popular 3D imaging techniques. It focuses on noninvasive, noncontact optical methods (optical metrology and imaging). The handbook begins with the well-studied method of stereo vision and
Optimized boundary driven flows for dynamos in a sphere
Khalzov, I V; Cooper, C M; Weisberg, D B; Forest, C B; 10.1063/1.4764048
2012-01-01
We perform numerical optimization of the axisymmetric flows in a sphere to minimize the critical magnetic Reynolds number Rm_cr required for dynamo onset. The optimization is done for the class of laminar incompressible flows of von Karman type satisfying the steady-state Navier-Stokes equation. Such flows are determined by equatorially antisymmetric profiles of driving azimuthal (toroidal) velocity specified at the spherical boundary. The model is relevant to the Madison plasma dynamo experiment (MPDX), whose spherical boundary is capable of differential driving of plasma in the azimuthal direction. We show that the dynamo onset in this system depends strongly on details of the driving velocity profile and the fluid Reynolds number Re. It is found that the overall lowest Rm_cr~200 is achieved at Re~240 for the flow, which is hydrodynamically marginally stable. We also show that the optimized flows can sustain dynamos only in the range Rm_cr
Fluctuation dynamo and turbulent induction at low magnetic Prandtl numbers
Schekochihin, A A; Cowley, S C; McWilliams, J C; Proctor, M R E; Yousef, T A
2007-01-01
This paper is a detailed report on a programme of simulations used to settle a long-standing issue in the dynamo theory and demonstrate that the fluctuation dynamo exists in the limit of large magnetic Reynolds number Rm>>1 and small magnetic Prandtl number Pm1. The dependence of the critical Rm_c vs. the hydrodynamic Reynolds number Re is obtained for 11. The stability curve Rm_c(Re) (and, it is argued, the nature of the dynamo) is substantially different from the case of the simulations and liquid-metal experiments with a mean flow. It is not as yet possible to determine numerically whether the growth rate is ~Rm^{1/2} in the limit ReRm>>1, as should be the case if the dynamo is driven by the inertial-range motions. The magnetic-energy spectrum in the low-Pm regime is qualitatively different from the Pm>1 case and appears to develop a negative spectral slope, although current resolutions are insufficient to determine its asymptotic form. At 1
Gravitational dynamos and the low-frequency geomagnetic secular variation.
Olson, P
2007-12-18
Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions. PMID:18048345
Erlström, M.; Niemi, A.; Lindström, S.; Gunnarsson, N.; Daher, S. Bou
2012-04-01
llviken Halfgraben. Relatively less sand in wells away from the main faults imply a distal position and/or a lack of accumulation space. In this study special emphasis is in building a 3D site model by using the simulation software Petrel, evaluating geostatistical data as well as stochastic simulations by using different geostatistical algorithms and evaluating the benefits in this. The primary aim has been to produce a 3D model of the distribution patterns of the different facies and the porosity. The results will be used for CO2 injection simulation purposes in the continuing work of CO2 Mustang (EU Fp 7 project).
Szkandera, Jan
2009-01-01
Tato bakalářská práce se zabývá návrhem a realizací systému, který umožní obraz scény zobrazovaný na ploše vnímat prostorově. Prostorové vnímání 2D obrazové informace je umožněno jednak stereopromítáním a jednak tím, že se obraz mění v závislosti na poloze pozorovatele. Tato práce se zabývá hlavně druhým z těchto problémů. This Bachelor's thesis goal is to design and realize system, which allows user to perceive 2D visual information as three-dimensional. 3D visual preception of 2D image i...
Mobile tomographs often have the problem that high spatial resolution is impossible owing to the position or setup of the tomograph. While the tree tomograph developed by Messrs. Isotopenforschung Dr. Sauerwein GmbH worked well in practice, it is no longer used as the spatial resolution and measuring time are insufficient for many modern applications. The paper shows that the mechanical base of the method is sufficient for 3D CT measurements with modern detectors and X-ray tubes. CT measurements with very good statistics take less than 10 min. This means that mobile systems can be used, e.g. in examinations of non-transportable cultural objects or monuments. Enhancement of the spatial resolution of mobile tomographs capable of measuring in any position is made difficult by the fact that the tomograph has moving parts and will therefore have weight shifts. With the aid of tomographies whose spatial resolution is far higher than the mechanical accuracy, a correction method is presented for direct integration of the Feldkamp algorithm
X3D: Extensible 3D Graphics Standard
Daly, Leonard; Brutzman, Don
2007-01-01
The article of record as published may be located at http://dx.doi.org/10.1109/MSP.2007.905889 Extensible 3D (X3D) is the open standard for Web-delivered three-dimensional (3D) graphics. It specifies a declarative geometry definition language, a run-time engine, and an application program interface (API) that provide an interactive, animated, real-time environment for 3D graphics. The X3D specification documents are freely available, the standard can be used without paying any royalties,...
3D game environments create professional 3D game worlds
Ahearn, Luke
2008-01-01
The ultimate resource to help you create triple-A quality art for a variety of game worlds; 3D Game Environments offers detailed tutorials on creating 3D models, applying 2D art to 3D models, and clear concise advice on issues of efficiency and optimization for a 3D game engine. Using Photoshop and 3ds Max as his primary tools, Luke Ahearn explains how to create realistic textures from photo source and uses a variety of techniques to portray dynamic and believable game worlds.From a modern city to a steamy jungle, learn about the planning and technological considerations for 3D modelin
Aboufadel, Edward F.
2014-01-01
The purpose of this short paper is to describe a project to manufacture a regular octohedron on a 3D printer. We assume that the reader is familiar with the basics of 3D printing. In the project, we use fundamental ideas to calculate the vertices and faces of an octohedron. Then, we utilize the OPENSCAD program to create a virtual 3D model and an STereoLithography (.stl) file that can be used by a 3D printer.
Rodrigues, Marcos; Robinson, Alan; Alboul, Lyuba; Brink, Willie
2006-01-01
3D face recognition is an open field. In this paper we present a method for 3D facial recognition based on Principal Components Analysis. The method uses a relatively large number of facial measurements and ratios and yields reliable recognition. We also highlight our approach to sensor development for fast 3D model acquisition and automatic facial feature extraction.
Ancient dynamos of terrestrial planets more sensitive to core-mantle boundary heat flows
Hori, K.; Wicht, J.; Dietrich, W.
2014-08-01
The early dynamos of Earth and Mars probably operated without an inner core being present. They were thus exclusively driven by secular cooling and radiogenic heating, whereas the present geodynamo is thought to be predominantly driven by buoyancy fluxes which arise from the release of latent heat and the compositional enrichment associated with inner core solidification. The impact of the inner core growth on the ancient geodynamo has been discussed extensively but is still controversial. The Martian dynamo stopped operating more than 4 Gyr ago but left its signature in the form of a strong crustal magnetization that is much stronger in the southern than in the northern hemisphere. This dichotomy can, for example, be explained by a dynamo predominantly operating in the southern hemisphere due to a heterogeneous heat flux through the core-mantle boundary (CMB). The early Martian dynamo may also have operated without an inner core being present. Here we explore the impact of lateral CMB heat flux variations on dynamos with and without an inner core by comparing numerical dynamos driven by homogeneous internal sources or by bottom buoyancy sources, arising from the inner core boundary (ICB). Three different CMB heat-flux patterns are tested that either break the northern/southern or the azimuthal symmetry. In the dynamos driven by internal heating a rather small CMB heat-flux heterogeneity suffices to break internal symmetries and leads to boundary-induced structures and different field strengths. The effect is much smaller for dynamos driven by ICB buoyancy sources. Our results indicate that the field intensity and morphology of the ancient dynamos of Earth or Mars were more variable and more sensitive to the thermal CMB structure than the geodynamo after onset of inner core growth.
3D MHD Flux emergence experiments
Hood, A.W.; Archontis, V.; Mactaggart, David
2012-01-01
This paper reviews some of the many 3D numerical experiments of the emergence of magnetic fields from the solar interior and the subsequent interaction with the pre-existing coronal magnetic field. The models described here are idealised, in the sense that the internal energy equation only involv...
Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models
Jouve, L.; Proctor, M. R. E.; Lesur, G.
2010-09-01
Context. The Sun is a magnetic star whose cyclic activity is thought to be linked to internal dynamo mechanisms. A combination of numerical modelling with various levels of complexity is an efficient and accurate tool to investigate such intricate dynamical processes. Aims: We investigate the role of the magnetic buoyancy process in 2D Babcock-Leighton dynamo models, by modelling more accurately the surface source term for poloidal field. Methods: To do so, we reintroduce in mean-field models the results of full 3D MHD calculations of the non-linear evolution of a rising flux tube in a convective shell. More specifically, the Babcock-Leighton source term is modified to take into account the delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. Results: We find that the time delays introduced in the equations produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. Aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. The strong effects introduced even by small delays is found to be due to the dependence of the delays on the magnetic field strength at the base of the convection zone, the modulation being much less when time delays remain constant. We do not find any significant influence on the cycle period except when the delays are made artificially strong. Conclusions: A possible new origin of the solar cycle variability is here revealed. This modulated activity and the resulting butterfly diagram are then more compatible with observations than what the standard Babcock-Leighton model produces.
曹洪建; 万德成; 杨驰
2013-01-01
Numerical simulation of 3D dam-breaking wave flows around a square cylinder by our in-house solver naoe-FOAM-SJTU is presented in this paper.The solver naoe-FOAM-SJTU is an unsteady viscous flow code for dealing with hydrodynamic problems in ship and ocean engineering,and developed based on the open source toolbox OpenFOAM.It can be applied to simulate the complex wave-structures interaction and the complex free surface evolution including the wave breaking and turning over phenomena.This paper presents the 3D complex free surface evolution of dam-breaking wave and the phenomena of wave run-up,wave breaking and turning over during the dam-breaking wave interaction with the square cylinder.The vortices field near the cylinder is presented,and the influence of viscous effect is analyzed.The calculated wave impact force on square cylinder shows good agreement with the data from experiment.The numerical results indicate that the naoe-FOAM-SJTU solver can efficiently simulate the complex free-surface evolution,and accurately predict the wave run-up height and impact force on structures.%该文采用自主开发的非定常黏性流动问题求解器naoe-FOAM-SJTU,对三维溃坝波和直立方柱相互作用问题进行数值模拟.求解器naoe-FOAM-SJTU是基于开源代码OpenFOAM的数据结构、工具箱和基本流场求解器,专门面向研究船舶与海洋工程水动力学问题而开发的数值计算程序,它可以模拟三维波与物体相互作用等复杂问题,能够较精确的模拟波浪破碎、翻卷等复杂自由面演化过程.计算结果给出了三维溃坝波的演化过程,包括溃坝波和直立方柱相互作用过程中的波面爬高、破碎及翻卷现象,给出了方柱附近的涡流场；并分析了流体黏性效应的影响,得到了直立方柱受溃坝波拍击作用的水动力时间演化过程图,计算结果与实验数据吻合较好.计算结果表明,采用naoe-FOAM-SJTU求解器可以有效地模拟有复杂波面
周胡; 赵文超; 万德成
2015-01-01
A numerical simulation of 3D viscous flow field around NREL Phase VI wind turbine was carried out with open source software OpenFOAM under nonuniform wind conditions, about which little research has been done. Exponential wind profile which is close to real situations is chosen. Based on this hypothesis, the following aerodynamic results were analyzed, such as the pressure coefficient distribution at different sections, and rotor thrust and wake structures at mean wind speeds of 5 m/ s, 10 m/ s, 15 m/ s and 25 m/ s respectively. At the same time, the results under nonuniform wind conditions were compared with those under uniform conditions to deepen the understanding of the shear wind effects on the flow structure and flow characteristic around the wind turbine.%基于面向对象的开源软件 OpenFOAM，选择美国国家新能源实验室(NREL)Phase VI 风力机为对象，对以往研究较少的非均匀来流风速作用下风力机三维气动粘性流场进行数值模拟。采用较为接近于真实情况的指数型风剖面，计算了轮毂处风速分别为5、10、15和25 m/ s 四种工况下的叶片表面压力分布、叶片的推力、尾涡等气动力数据，并与均匀来流风速下的风力机气动力学性能进行详细的对比，探讨非均匀风剖面对风力机流场结构和流动特性影响的物理现象和规律。
3-D contextual Bayesian classifiers
Larsen, Rasmus
distribution for the pixel values as well as a prior distribution for the configuration of class variables within the cross that is made of a pixel and its four nearest neighbours. We will extend these algorithms to 3-D, i.e. we will specify a simultaneous Gaussian distribution for a pixel and its 6 nearest 3......-D neighbours, and generalise the class variable configuration distributions within the 3-D cross given in 2-D algorithms. The new 3-D algorithms are tested on a synthetic 3-D multivariate dataset....
Taming Supersymmetric Defects in 3d-3d Correspondence
Gang, Dongmin; Romo, Mauricio; Yamazaki, Masahito
2015-01-01
We study knots in 3d Chern-Simons theory with complex gauge group $SL(N,\\mathbb{C})$, in the context of its relation with 3d $\\mathcal{N}=2$ theory (the so-called 3d-3d correspondence). The defect has either co-dimension 2 or co-dimension 4 inside the 6d $(2,0)$ theory, which is compactified on a 3-manifold $\\hat{M}$. We identify such defects in various corners of the 3d-3d correspondence, namely in 3d $SL(N,\\mathbb{C})$ Chern-Simons theory, in 3d $\\mathcal{N}=2$ theory, in 5d $\\mathcal{N}=2$ super Yang-Mills theory, and in the M-theory holographic dual. We can make quantitative checks of the 3d-3d correspondence by computing partition functions at each of these theories. This Letter is a companion to a longer paper, which contains more details and more results.
The combined effect of precession and convection on the dynamo action
Wei, Xing
2016-01-01
To understand the generation of the Earth's and planetary magnetic fields, we investigate numerically the combined effect of precession and convection on the dynamo action in a spherical shell. The convection alone, the precession alone and the combined effect of convection and precession are studied at the low Ekman number at which the precessing flow is already unstable. The key result is that although the precession or convection alone is not strong to support the dynamo action the combined effect of precession and convection can support the dynamo action because of the resonance of precessional and convective instabilities. This result may interpret why the geodynamo maintains for such a long history compared to the Martian dynamo.
Dynamo saturation in direct simulations of the multi-phase turbulent interstellar medium
Bendre, A; Elstner, D
2015-01-01
The ordered magnetic field observed via polarized synchrotron emission in nearby disc galaxies can be explained by a mean-field dynamo operating in the diffuse interstellar medium (ISM). Additionally, vertical-flux initial conditions are potentially able to influence this dynamo via the occurrence of the magneto-rotational instability (MRI). We aim to study the influence of various initial field configurations on the saturated state of the mean-field dynamo. This is motivated by the observation that different saturation behavior was previously obtained for different supernova rates. We perform direct numerical simulations (DNS) of three-dimensional local boxes of the vertically stratified, turbulent interstellar medium, employing shearing-periodic boundary conditions horizontally. Unlike in our previous work, we also impose a vertical seed magnetic field. We run the simulations until the growth of the magnetic energy becomes negligible. We furthermore perform simulations of equivalent 1D dynamo models, with a...
Moss, David; Suleimanov, Valery
2016-01-01
Magnetic fields are important for accretion disc structure. Magnetic fields in a disc system may be transported with the accreted matter. They can be associated with either the central body and/or jet, and be fossil or dynamo excited in situ. We consider dynamo excitation of magnetic fields in accretion discs of accreting binary systems in an attempt to clarify possible configurations of dynamo generated magnetic fields. We first model the entire disc with realistic radial extent and thickness using an alpha-quenching non-linearity. We then study the simultaneous effect of feedback from the Lorentz force from the dynamo-generated field. We perform numerical simulations in the framework of a relatively simple mean-field model which allows the generation of global magnetic configurations. We explore a range of possibilities for the dynamo number, and find quadrupolar-type solutions with irregular temporal oscillations that might be compared to observed rapid luminosity fluctuations. The dipolar symmetry models ...
Statistical Mechanics of Turbulent Dynamos
Shebalin, John V.
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much
3-D Whole-Core Transport Calculation with 3D/2D Rotational Plane Slicing Method
Use of the method of characteristics (MOC) is very popular due to its capability of heterogeneous geometry treatment and widely used for 2-D core calculation, but direct extension of MOC to 3-D core is not so attractive due to huge calculational cost. 2-D/1-D fusion method was very successful for 3-D calculation of current generation reactor types (highly heterogeneous in radial direction but piece-wise homogeneous in axial direction). In this paper, 2-D MOC concept is extended to 3-D core calculation with little modification of an existing 2-D MOC code. The key idea is to suppose 3-D geometry as a set of many 2-D planes like a phone-directory book. Dividing 3-D structure into a large number of 2-D planes and solving each plane with a simple 2-D SN transport method would give the solution of a 3-D structure. This method was developed independently at KAIST but it is found that this concept is similar with that of 'plane tracing' in the MCCG-3D code. The method developed was tested on the 3-D C5G7 OECD/NEA benchmark problem and compared with the 2-D/1-D fusion method. Results show that the proposed method is worth investigating further. A new approach to 3-D whole-core transport calculation is described and tested. By slicing 3-D structure along characteristic planes and solving each 2-D plane problem, we can get 3-D solution. The numerical test results indicate that the new method is comparable with the 2D/1D fusion method and outperforms other existing methods. But more fair comparison should be done in similar discretization level
Rubber Impact on 3D Textile Composites
Heimbs, Sebastian; Van Den Broucke, Björn; Duplessis Kergomard, Yann; Dau, Frederic; Malherbe, Benoit
2012-06-01
A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools.
Formisano, M.; Federico, C.; De Angelis, S.; De Sanctis, M. C.; Magni, G.
2016-05-01
A recent study of Fu et al. analysed the remaining magnetization in the eucrite meteorite Allan Hills A81001, which mostly likely has been produced during the cooling phase of the life of the asteroid Vesta, arguing that an ancient dynamo in the advective liquid metallic core could be set in. Using petrographic and paleomagnetic arguments, Fu et al. estimated a surface magnetic field of at least 2 μT. In this work, we verify the possibility that an early core dynamo took place in Vesta by analysing four different possible fully differentiated configurations of Vesta, characterized by different chondritic compositions, with the constraints on core size and density provided by Ermakov et al. We only incorporate the thermal convection, by neglecting the effects of the compositional convection, so our results in terms of magnetic Reynolds number and duration of the dynamo can be interpreted as a lower bound. The presence of a magnetic field would make Vesta a peculiar object of the Solar system, a `small-Earth', since it has also a differentiated structure like Earth and the magnetic field has preserved Vesta from the space weathering.
Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo
Augustson, Kyle C.; Brun, Allan Sacha; Miesch, Mark; Toomre, Juri
2015-08-01
The 3-D magnetohydrodynamic (MHD) Anelastic Spherical Harmonic (ASH) code, using slope-limited diffusion, is employed to capture convective and dynamo processes achieved in a global-scale stellar convection simulation for a model solar-mass star rotating at three times the solar rate. The dynamo generated magnetic fields possesses many time scales, with a prominent polarity cycle occurring roughly every 6.2 years. The magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation. The polarity reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. An equatorial migration of the magnetic field is seen, which is due to the strong modulation of the differential rotation rather than a dynamo wave. A poleward migration of magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families. This intermittent dynamo state potentially results from the simulations relatively low magnetic Prandtl number. A mean-field-based analysis of this dynamo simulation demonstrates that it is of the α-Ω type. The time scales that appear to be relevant to the magnetic polarity reversal are also identified.
Statistical Model of the 3-D Braided Composites Strength
XIAO Laiyuan; ZUO Weiwei; CAI Ganwei; LIAO Daoxun
2007-01-01
Based on the statistical model for the tensile statistical strength of unidirectional composite materials and the stress analysis of 3-D braided composites, a new method is proposed to calculate the tensile statistical strength of the 3-D braided composites. With this method, the strength of 3-D braided composites can be calculated with very large accuracy, and the statistical parameters of 3-D braided composites can be determined. The numerical result shows that the tensile statistical strength of 3-D braided composites can be predicted using this method.
3D Printing Functional Nanocomposites
Leong, Yew Juan
2016-01-01
3D printing presents the ability of rapid prototyping and rapid manufacturing. Techniques such as stereolithography (SLA) and fused deposition molding (FDM) have been developed and utilized since the inception of 3D printing. In such techniques, polymers represent the most commonly used material for 3D printing due to material properties such as thermo plasticity as well as its ability to be polymerized from monomers. Polymer nanocomposites are polymers with nanomaterials composited into the ...
3D Elevation Program—Virtual USA in 3D
Lukas, Vicki; Stoker, J.M.
2016-01-01
The U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) uses a laser system called ‘lidar’ (light detection and ranging) to create a virtual reality map of the Nation that is very accurate. 3D maps have many uses with new uses being discovered all the time.
3D IBFV : Hardware-Accelerated 3D Flow Visualization
Telea, Alexandru; Wijk, Jarke J. van
2003-01-01
We present a hardware-accelerated method for visualizing 3D flow fields. The method is based on insertion, advection, and decay of dye. To this aim, we extend the texture-based IBFV technique for 2D flow visualization in two main directions. First, we decompose the 3D flow visualization problem in a
Further improvements on TRACE 3-D
TRACE 3-D, an interactive beam-dynamics program that calculates the envelopes of a bunched beam (including linear space-charge forces) through a user-defined transport system, has undergone several upgrades in physics, coding, and capabilities. Recent modifications include centroid tracking (and misalignment capabilities) and an improved beam description that allows study of some nonlinear effects such as wakefields. The Fortran code has been made portable and runs on numerous platforms. It can be used with a variety of graphics packages. The additional beamline elements, new commands, expanded fitting capabilities, improved beam description, and coding modifications have extended TRACE 3-D's usefulness and applicability to the accelerator community. These changes are documented in the third edition of TRACE 3-D Documentation