Numerical Modelling (numerical + modelling)

Distribution by Scientific Domains


Selected Abstracts


Numerical Modelling of Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes,

ADVANCED ENGINEERING MATERIALS, Issue 10 2009
Wei Lu
Abstract The flow boiling heat transfer performance in horizontal metal-foam tubes is numerically investigated based on the flow pattern map retrieved from experimental investigations. The flow pattern and velocity profile are generally governed by vapour quality and mass flow rate of the fluid. The porous media non-equilibrium heat transfer model is employed for modelling both vapour and liquid phase zones. The modelling predictions have been compared with experimental results. The effects of metal-foam morphological parameters, heat flux and mass flux on heat transfer have been examined. The numerical predictions show that the overall heat transfer coefficient of the metal-foam filled tube increases with the relative density (1-porosity), pore density (ppi), mass and heat flux. [source]


Introduction to the special issue ,Numerical Modelling of Metamaterial Properties, Structures and Devices'

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 2 2006
Christophe Caloz Guest Editor
No abstract is available for this article. [source]


TLM for diffusion: consistent first time step.

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2002
Two-dimensional case
Abstract In initializing a transmission line matrix (TLM) diffusion model it is necessary to consider both initial concentration (temperature) and initial flow. As usual, only one of them is given; an auxiliary formula is necessary to calculate the distribution for the first time step. It has been shown that the standard formula may introduce additional numerical errors (International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6:135; International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6:161) and that these errors can persist over many time steps. In this paper, we show how an initial modification to the normal TLM algorithm can remove such errors, and we demonstrate the method by applying it to a two-dimensional TLM heat diffusion model for a copper plate. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Dynamics of multiple intertidal bars over semi-diurnal and lunar tidal cycles, North Lincolnshire, England

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2008
Selma van Houwelingen
Abstract Multiple intertidal bars are common features of wave-dominated sandy beaches, yet their short-term (<1 month) and small-scale (<1 km) morphology and dynamics remain poorly understood. This study describes the morphodynamics of multiple intertidal bars in North Lincolnshire, England, during single and lunar tidal cycles under two contrasting conditions , first when significant wave height was <0·5 m and second when significant wave height frequently exceeded 1 m. The relative importance of swash, surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model. The beach featured four intertidal bars and both cross-shore and longshore bar morphology evolved during the field investigation, particularly under medium to high wave-energy conditions. Numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions (Hs < 0·5 m) and that surf zone processes become more common during neap tides and under more energetic (Hs < 0·5 m) conditions. Surf processes dominate the inner two bars, though swash influence increases in a landward direction. The numerical modelling results combined with low tide survey data and high-resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes. This is because shoaling waves do not induce significant sediment transport to have any morphological effect, whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone. It was found, however, that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar, making this process important for bar morphodynamics. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Structure, reactivity and spectroscopic properties of minerals from lateritic soils: insights from ab initio calculations

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2007
E. Balan
Summary We review here some recent applications of ab initio calculations to the modelling of spectroscopic and energetic properties of minerals, which are key components of lateritic soils or govern their geochemical properties. Quantum mechanical ab initio calculations are based on density functional theory and density functional perturbation theory. Among the minerals investigated, zircon is a typical resistant primary mineral. Its resistance to weathering is at the origin of the peculiar geochemical behaviour of Zr, an element often used in mass balance calculations of continental weathering. Numerical modelling gives a unique picture of the origin of the chemical durability and radiation-induced amorphization of zircon. We also present several applications of ab initio calculations to the description of properties of secondary minerals, such as kaolinite-group minerals and gibbsite. Special attention is given to the calculation of infrared and Raman spectra. Surface properties and particle shape are major properties of finely-divided materials such as clay minerals. We show how theoretical modelling of infrared spectroscopic data provides information on natural samples at both the microscopic (atomic structure) and macroscopic (particle shape) length-scale. The systematic comparison of experimental and theoretical data significantly improves our understanding of mineral transformations during soil formation and evolution in lateritic environments. [source]


Numerical modelling of fatigue crack initiation and growth of martensitic steels

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2010
N. JEZERNIK
ABSTRACT This paper presents a numerical simulation of micro-crack initiation that is based on Tanaka-Mura micro-crack nucleation model. Three improvements were added to this model. First, multiple slip bands where micro-cracks may occur are used in each grain. Second improvement deals with micro-crack coalescence by extending existing micro-cracks along grain boundaries and connecting them into a macro-crack. The third improvement handles segmented micro-crack generation, where a micro-crack is not nucleated in one step like in Tanaka-Mura model, but is instead generated in multiple steps. High cycle fatigue testing was also performed and showed reasonably good correlation of proposed model to experimental results. Because numerical model was directed at simulating fatigue properties of thermally cut steel, edge properties of test specimens were additionally inspected in terms of surface roughness and micro-structural properties. [source]


Cleavage fracture of RPV steel following warm pre-stressing: micromechanical analysis and interpretation through a new model

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9-10 2006
S. R. BORDET
ABSTRACT In this paper, the warm pre-stress (WPS) effect on the cleavage fracture of an 18MND5 (A533B) RPV steel is investigated. This effect, which describes the effective enhancement of the cleavage fracture toughness at low temperature following a prior loading at high temperature, has received great interest in light of its significance in the integrity assessment of structures, such as nuclear pressure vessels, subjected to thermal transients. Several loading cycles between room temperature (RT) and ,150 °C are considered: Load-Unload-Cool-Fracture (LUCF), Load-Cool-Fracture (LCF) and Load-Cool with Increasing K-Fracture (LCIKF). All experiments complied with the conservative principle, which states that no fracture will occur if the applied stress intensity factor (SIF) decreases (or is held constant) while the temperature at the crack-tip decreases, even if the fracture toughness of the virgin material is exceeded. The experimental results indicate that an effective WPS effect is present even at small pre-load (Kwps= 40 MPa,m), and that a minimum critical slope (,,K/,T) in the LCIKF cycle has to be exceeded to induce cleavage fracture between RT and ,150 °C. Numerical modelling was performed using mixed isotropic and kinematic hardening laws identified on notched tensile (NT) specimens, tested in tension to large strains (up to 40%), followed by large compressive strains. Detailed microstructural investigations on compact tensile (CT) and NT fracture test specimens were performed so as to determine the nature of the cleavage initiation sites, as well as the local mechanical conditions at fracture. Based on this local information, a new cleavage model was calibrated and applied to predict the probability of cleavage fracture after WPS: it is shown that the predictions are in good agreement with the experimental results. [source]


Numerical modelling of 3D fluid flow and oxygen isotope exchange in fractured media: spatial distribution of isotope patterns

GEOFLUIDS (ELECTRONIC), Issue 4 2007
C. SAVARD
Abstract An understanding of fluid flow, mass transport and isotopic exchange in fractured rock is required to understand the origin of several geological processes including hydrothermal mineral deposits. The numerical model HydroGeoSphere simulates 3D advection, molecular diffusion, mechanical dispersion and isotopic exchange in a discretely fractured porous media, and can be used to better understand the processes of mass transport and isotopic exchange in fractured rocks. Study of 18O isopleth patterns for different types of fractures and fracture networks with a range of structural complexity and hydraulic properties shows that fracture properties and geometry control mass transport and isotopic exchange. The hydraulic properties, as well as the density, spacing, and connectivity of fractures determine the isotopic patterns. Asymmetries in the geometry of oxygen isotope patterns could be used to determine the direction of hydrothermal fluid flow. [source]


Overpressure and petroleum generation and accumulation in the Dongying Depression of the Bohaiwan Basin, China

GEOFLUIDS (ELECTRONIC), Issue 4 2001
X. Xie
Abstract The occurrence of abnormally high formation pressures in the Dongying Depression of the Bohaiwan Basin, a prolific oil-producing province in China, is controlled by rapid sedimentation and the distribution of centres of active petroleum generation. Abnormally high pressures, demonstrated by drill stem test (DST) and well log data, occur in the third and fourth members (Es3 and Es4) of the Eocene Shahejie Formation. Pressure gradients in these members commonly fall in the range 0.012,0.016 MPa m,1, although gradients as high as 0.018 MPa m,1 have been encountered. The zone of strongest overpressuring coincides with the areas in the central basin where the principal lacustrine source rocks, which comprise types I and II kerogen and have a high organic carbon content (>2%, ranging to 7.3%), are actively generating petroleum at the present day. The magnitude of overpressuring is related not only to the burial depth of the source rocks, but to the types of kerogen they contain. In the central basin, the pressure gradient within submember Es32, which contains predominantly type II kerogen, falls in the range 0.013,0.014 MPa m,1. Larger gradients of 0.014,0.016 MPa m,1 occur in submember Es33 and member Es4, which contain mixed type I and II kerogen. Numerical modelling indicates that, although overpressures are influenced by hydrocarbon generation, the primary control on overpressure in the basin comes from the effects of sediment compaction disequilibrium. A large number of oil pools have been discovered in the domes and faulted anticlines of the normally pressured strata overlying the overpressured sediments; the results of this study suggest that isolated sandstone reservoirs within the overpressured zone itself offer significant hydrocarbon potential. [source]


On accuracy of the finite-difference and finite-element schemes with respect to P -wave to S -wave speed ratio

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010
Peter Moczo
SUMMARY Numerical modelling of seismic motion in sedimentary basins often has to account for P -wave to S -wave speed ratios as large as five and even larger, mainly in sediments below groundwater level. Therefore, we analyse seven schemes for their behaviour with a varying P -wave to S -wave speed ratio. Four finite-difference (FD) schemes include (1) displacement conventional-grid, (2) displacement-stress partly-staggered-grid, (3) displacement-stress staggered-grid and (4) velocity,stress staggered-grid schemes. Three displacement finite-element schemes differ in integration: (1) Lobatto four-point, (2) Gauss four-point and (3) Gauss one-point. To compare schemes at the most fundamental level, and identify basic aspects responsible for their behaviours with the varying speed ratio, we analyse 2-D second-order schemes assuming an elastic homogeneous isotropic medium and a uniform grid. We compare structures of the schemes and applied FD approximations. We define (full) local errors in amplitude and polarization in one time step, and normalize them for a unit time. We present results of extensive numerical calculations for wide ranges of values of the speed ratio and a spatial sampling ratio, and the entire range of directions of propagation with respect to the spatial grid. The application of some schemes to real sedimentary basins in general requires considerably finer spatial sampling than usually applied. Consistency in approximating first spatial derivatives appears to be the key factor for the behaviour of a scheme with respect to the P -wave to S -wave speed ratio. [source]


Numerical modelling of complex resistivity effects on a homogenous half-space at low frequencies

GEOPHYSICAL PROSPECTING, Issue 3 2006
T. Ingeman-Nielsen
ABSTRACT The many different existing models describing the spectral behaviour of the resistivity of geological materials at low frequency, combined with the lack of available field data, render the interpretation of complex resistivity (CR) data very difficult. With a recent interest in CR-measurements for environmental applications and thanks to technological progress, the use of wide-band frequency equipment seems promising, and it is expected to shed light on the different results among the published solutions to the electromagnetic (EM) coupling problem. We review the theory of EM-coupling over a homogeneous half-space with CR-effects and study some aspects of the complex coupling function. We advocate the use of the CR-based coupling function in the interpretation process, in order to obtain a better understanding of the physical processes involved in CR-effects. Application of the model to real field data shows systematic good agreement in two simple cases, even over wide ranges of frequencies. Interpretation with a double Cole,Cole model is applied for comparison, and in spite of good fits to the data, large differences are observed in the interpreted low-frequency dispersion. We conclude that the use of a second Cole,Cole model to describe EM-coupling may corrupt the interpretation of the low-frequency dispersion, even when only the normal range of frequencies (<100 Hz) is considered, and that the use of the actual EM-coupling expression is essential when the goal is a better understanding of interaction between CR-effects and EM-coupling. [source]


Numerical modelling of the potential effects of a dam on a coastal aquifer in S. Spain

HYDROLOGICAL PROCESSES, Issue 9 2009
M. L. Calvache
Abstract This study presents the results of a three-dimensional variable-density numerical modelling of the Motril-Salobreña coastal aquifer and the possible effects of the entry into service in May 2005 of the Rules Dam, located just 17 km from the coast. Present parameters of the Motril-Salobreña aquifer show that the system's conditions are very similar to a natural regime. The dam will substantially alter aquifer recharge, as the entry flow through the alluvial sediments of the Guadalfeo River will be entirely cut off or drastically reduced. Different scenarios reproducing the possible evolution of the aquifer under operation of the Rules Dam have been modelled. In most cases, results indicate that the conditions of the aquifer would worsen, with a general advance of the freshwater,saltwater interface. The area with most risk of saltwater intrusion is the old mouth of the Guadalfeo River, where the mixing zone could advance 1200 m inland. It is proposed that maintaining a 5,6 Mm3 year,1 ,ecological flow' in the Guadalfeo River could prevent this saline advance. This application demonstrates that variable-density models are potentially useful tools for estimating the effects of dams on the hydrodynamic and hydrochemical conditions of a coastal aquifer. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Numerical modelling of dynamic consolidation on granular soils

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2008
S. López-Querol
Abstract The application of Pastor,Zienkiewicz constitutive model for sands to dynamic consolidation problems is presented in this paper. This model is implemented in a coupled code formulated in terms of displacements for both solid and fluid phases (u,w formulation), which is firstly compared with u,pw formulation for some simple examples. Its range of validity, previously established for elastic problems and harmonic loading, is explored. Once the suitability of the u,w formulation has been ascertained for this kind of dynamic problems in soils, one- and two-dimensional (plane strain) dynamic consolidation numerical examples are provided, aiming to give some light into the physics of this ground improvement technique. A ,wave of dryness', observed at the soil surface during the impact in field cases, is numerically reproduced and justified. Some hints on the influence of the loading zone size are also given. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Numerical modelling of regional faults in land subsidence prediction above gas/oil reservoirs

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2008
Massimiliano Ferronato
Abstract The stress variation induced by gas/oil production may activate pre-existing regional faults. This may enhance the expected land subsidence due to the generation of mechanically weak points close to the producing field. A class of elasto-plastic interface elements (IE), specifically designed to address the mechanical behaviour of faults over a regional scale, is integrated into a finite element (FE) geomechanical model and used to investigate the role exerted by active faults in anthropogenic land subsidence. The importance of regional faults depends on a variety of factors including depth of the depleted reservoir, fault number, orientation and size, geomechanical properties of porous medium, pore pressure drawdown induced by fluid production, etc. With the aid of some representative examples, a useful indication is provided as to where and how fault activation may influence both magnitude and extent of the land subsidence bowl above producing gas/oil reservoirs, pointing to a generally limited impact on the ground surface. The simulation of a real faulted gas reservoir in a complex 3-D setting shows that the proposed IE can be simply and efficiently incorporated into a FE geomechanical model, thus improving the quality of the stress and displacement prediction. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Numerical modelling of compensation grouting above shallow tunnels

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2005
C. Wisser
Abstract This paper describes the development of a numerical model for compensation grouting which is a useful technique for the protection of surface structures from the potentially damaging movements arising from tunnel construction. Pipes are inserted into the ground between the tunnel and the overlaying structure from an access shaft. Buildings on the surface are instrumented and movements are carefully monitored. Once the deformations exceed a certain Trigger Level, grout is injected into the ground to prevent damage. In the finite element model described here, compensation grouting is modelled by applying an internal pressure to zero-thickness interface elements embedded in the mesh. An ,observational algorithm' is used, where the deformations of the surface are monitored and used to control the injection process. Example analyses of compensation grouting are given for three-dimensional tunnel construction underneath a greenfield site. Different strategies are used to control the injection process and their effectiveness in preventing surface movement is assessed. The numerical model is shown to replicate general behaviour expected in the field and is capable of modelling the control of ground surface movements at a greenfield site. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Numerical modelling for earthquake engineering: the case of lightly RC structural walls

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7-8 2004
J. Mazars
Abstract Different types of numerical models exist to describe the non-linear behaviour of reinforced concrete structures. Based on the level of discretization they are often classified as refined or simplified ones. The efficiency of two simplified models using beam elements and damage mechanics in describing the global and local behaviour of lightly reinforced concrete structural walls subjected to seismic loadings is investigated in this paper. The first model uses an implicit and the second an explicit numerical scheme. For each case, the results of the CAMUS 2000 experimental programme are used to validate the approaches. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Numerical modelling of fluid flow in microscopic images of granular materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2002
E. Masad
Abstract A program for the simulation of two-dimensional (2-D) fluid flow at the microstructural level of a saturated anisotropic granular medium is presented. The program provides a numerical solution to the complete set of Navier,Stokes equations without a priori assumptions on the viscous or convection components. This is especially suited for the simulation of the flow of fluids with different density and viscosity values and for a wide range of granular material porosity. The analytical solution for fluid flow in a simple microstructure of porous medium is used to verify the computer program. Subsequently, the flow field is computed within microscopic images of granular material that differ in porosity, particle size and particle shape. The computed flow fields are shown to follow certain paths depending on air void size and connectivity. The permeability tensor coefficients are derived from the flow fields, and their values are shown to compare well with laboratory experimental data on glass beads, Ottawa sand and silica sands. The directional distribution of permeability is expressed in a functional form and its anisotropy is quantified. Permeability anisotropy is found to be more pronounced in the silica sand medium that consists of elongated particles. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Numerical modelling of hydro-mechanical behaviour of collapsible soils

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008
L. M. Costa
Abstract This paper presents a numerical simulation of the response of unsaturated soil under different loads, with special attention devoted to the phenomenon of pore collapse during wetting. A coupled hydro-mechanical formulation, implemented in the computational code CODE_BRIGHT, is first presented. Then the model is applied to assess material parameter from laboratory tests and to simulate, as boundary value problems, new and appealing in situ tests designed in the Federal University of Pernambuco. The soil considered is a collapsible soil located in the semi-arid region of the northeast of Brazil. Two situations are analysed: (i) the soil is initially at its natural water content and then flooded at some determined stress level, (ii) the soil is previously flooded and then loaded. Comparison between output results of numerical simulations and experimental data shows a very good agreement, which validate to some extent the proposed experimental procedure and the model formulation. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Numerical modelling of elastic wave scattering in frequency domain by the partition of unity finite element method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2009
A. El Kacimi
Abstract In this paper, we investigate a numerical approach based on the partition of unity finite element method, for the time-harmonic elastic wave equations. The aim of the proposed work is to accurately model two-dimensional elastic wave problems with fewer elements, capable of containing many wavelengths per nodal spacing, and without refining the mesh at each frequency. The approximation of the displacement field is performed via the standard finite element shape functions, enriched by superimposing pressure and shear plane wave basis, which incorporate knowledge of the wave propagation. A variational framework able to handle mixed boundary conditions is described. Numerical examples dealing with the radiation and the scattering of elastic waves by a circular body are presented. The results show the performance of the proposed method in both accuracy and efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Numerical modelling of chemical effects of magma solidification problems in porous rocks

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2005
Chongbin Zhao
Abstract The solidification of intruded magma in porous rocks can result in the following two consequences: (1) the heat release due to the solidification of the interface between the rock and intruded magma and (2) the mass release of the volatile fluids in the region where the intruded magma is solidified into the rock. Traditionally, the intruded magma solidification problem is treated as a moving interface (i.e. the solidification interface between the rock and intruded magma) problem to consider these consequences in conventional numerical methods. This paper presents an alternative new approach to simulate thermal and chemical consequences/effects of magma intrusion in geological systems, which are composed of porous rocks. In the proposed new approach and algorithm, the original magma solidification problem with a moving boundary between the rock and intruded magma is transformed into a new problem without the moving boundary but with the proposed mass source and physically equivalent heat source. The major advantage in using the proposed equivalent algorithm is that a fixed mesh of finite elements with a variable integration time-step can be employed to simulate the consequences and effects of the intruded magma solidification using the conventional finite element method. The correctness and usefulness of the proposed equivalent algorithm have been demonstrated by a benchmark magma solidification problem. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Numerical modelling of the pressure wave propagation in the arterial flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6-7 2003
Giuseppe Pontrelli
Abstract A differential model of blood flow through an arterial vessel is presented. It consists of a one-dimensional model describing the non-linear fluid,wall interaction coupled with a simple lumped parameter model which accounts for outlet boundary conditions. The model includes a local stiffening of the vessel and the wave propagation of disturbances due to prosthetic implantations is also studied. The non-linear problem is solved by a finite-difference method on a staggered grid and some numerical simulations are analysed and discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Numerical modelling of free-surface flows in ship hydrodynamics

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2003
U. P. Bulgarelli
Abstract Current trends in the investigation of ship hydrodynamics are reviewed with emphasis on the problem of wave-body interaction. This includes the classical seakeeping problem and as a special case, the problem of prediction for the drag encountered by a ship advancing in calm water. Specific issues related to the numerical treatment of the air,water interface are examined, with emphasis on the modelling of wave breaking. The discussion on the large-scale modelling of the flow around ships is focused on the prediction of wave loads, ship motions and resistance in calm water. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Numerical modelling of equilibrium charge separation in poled devices

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2001
A. De Francesco
Abstract We describe an efficient numerical procedure for the equilibrium solution of the internal electric field distribution resulting from poling of photo-refractive materials. This technique has been developed to model the equilibrium state in poled bulk devices requiring bulk charge neutrality to facilitate the modelling of blocking boundaries for a high externally applied voltage (bias) in the kV range for a small number of points. This technique is an improvement on existing conventional numerical techniques employed for modelling semiconductor devices that are intended for low bias. This method can also accommodate the modelling of planar insulators and organic optical materials. We develop an algorithm incorporating the existing Newton,Raphson method for solving Kukhtarev's equations that enforces conservation of charge within the modelled system. We apply this technique to model one-dimensional charge separation in ultraviolet (UV) excited poling of glass and, report numerical equilibrium electric field distribution for a 2 kV bias. The convergence behaviour of the algorithm is investigated and compared against the Newton,Raphson method. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Numerical modelling of anisotropy and eddy current effects in ferromagnetic laminations using a co-energy formulation

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5 2001
L. R. Dupré
Abstract The paper deals with a numerical model for the evaluation of electromagnetic fields in one steel lamination under the influence of a rotating magnetic flux, taking into account anisotropy effects. For this purpose a detailed material model, described by a differential permeability tensor, is included in the macroscopic electromagnetic field calculations in one lamination. Here, by geometrical and physical considerations, the governing Maxwell equations are reduced to a system of parabolic PDEs for the components of the magnetic field vector, under appropriate boundary and initial conditions. We present a suitable numerical approximation based upon a finite element,finite difference method, which properly takes into account the material characteristics. The study leads to a more realistic numerical modelling of the electromagnetic phenomena inside electric and magnetic conducting laminations due to anisotropy effects. Numerical results are compared with those from simplified analytical formulae. Copyright © 2001 John Wiley & Sons, Ltd. [source]


IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY

JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2007
S.F. Jones
Numerical modelling is used to investigate for the first time the interactions between a petroleum system and sill intrusion in the NE Sverdrup Basin, Canadian Arctic Archipelago. Although hydrocarbonexploration has been successful in the western Sverdrup Basin, the results in the NE part of thebasin have been disappointing, despite the presence of suitable Mesozoic source rocks, migrationpaths and structural/stratigraphic traps, many involving evaporites. This was explained by (i) theformation of structural traps during basin inversion in the Eocene, after the main phase ofhydrocarbon generation, and/or (ii) the presence of evaporite diapirs locally modifying the geothermalgradient, leading to thermal overmaturity of hydrocarbons. This study is the first attempt at modellingthe intrusion of Cretaceous sills in the east-central Sverdrup Basin, and to investigate how theymay have affected the petroleum system. A one-dimensional numerical model, constructed using PetroMod9.0®, investigates the effectsof rifting and magmatic events on the thermal history and on petroleum generation at the DepotPoint L-24 well, eastern Axel Heiberg Island (79°23,40,N, 85°44,22,W). The thermal history isconstrained by vitrinite reflectance and fission-track data, and by the tectonic history. The simulationidentifies the time intervals during which hydrocarbons were generated, and illustrates the interplaybetween hydrocarbon production and igneous activity at the time of sill intrusion during the EarlyCretaceous. The comparison of the petroleum and magmatic systems in the context of previouslyproposed models of basin evolution and renewed tectonism was an essential step in the interpretationof the results from the Depot Point L-24 well. The model results show that an episode of minor renewed rifting and widespread sill intrusionin the Early Cretaceous occurred after hydrocarbon generation ceased at about 220 Ma in theHare Fiord and Van Hauen Formations. We conclude that the generation potential of these deeperformations in the eastern Sverdrup Basin was not likely to have been affected by the intrusion ofmafic sills during the Early Cretaceous. However, the model suggests that in shallower sourcerocks such as the Blaa Mountain Formation, rapid generation of natural gas occurred at 125 Ma, contemporaneous with tectonic rejuvenation and sill intrusion in the east-central Sverdrup Basin. A sensitivity study shows that the emplacement of sills increased the hydrocarbon generation ratesin the Blaa Mountain Formation, and facilitated the production of gas rather than oil. [source]


Numerical modelling of transient photoconductivity for density-of-states determination in microcrystalline silicon

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2004
R. Brüggemann
Abstract Numerical modelling of transient photoconductivity in microcrystalline silicon allows to identify characteristic features for different models for the density-of-states in microcrystalline silicon. Construction of the density-of-states by Fourier-transform analysis of simulated transient photocurrents identifies discrepancies with the input density-of-states which may be helpful for refining the density-of-states from experimental data. Two scenarios are presented for the effect that the shift of the Fermi level or of n-type doping imposes on the transient photocurrent decay. States, masked and not directly accessible to electrons, may still be identified by the decay analysis. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Numerical modelling and simulation of pulverized solid-fuel combustion in swirl burners

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009
H. Ettouati
Abstract A finite-volume numerical model for computer simulation of pulverized solid-fuel combustion in furnaces with axisymmetric-geometry swirl burner is presented. The simulation model is based on the k,,,, single phase turbulence model, considering the presence of the dispersed solid phase via additional source terms in the gas phase equations. The dispersed phase is treated by the particle source in cell (PSIC) method. Solid fuel particle devolatilization, homogenous and heterogeneous chemical reaction processes are modelled via a global combustion model. The radiative heat transfer equation is also resolved using the finite volume method. The numerical simulation code is validated by comparing computational and experimental results of pulverized coal in an experimental furnace equipped with a swirl burner. It is shown that the developed numerical code can successfully predict the flow field and flame structure including swirl effects and can therefore be used for the design and optimization of pulverized solid-fuel swirl burners. On présente un modèle numérique de volumes finis pour la simulation par ordinateur de la combustion de combustibles solides pulvérisés dans des fours munis de brûleur à tourbillon axisymétrique. Le modèle de simulation repose sur le modèle de turbulence monophasique k,,,,, et décrit la présence de la phase solide dispersée par le biais de termes-sources additionnels dans les équations de la phase gazeuse. La phase dispersée est traitée par la méthode PSIC. La dévolatilisation des particules combustibles solides et les procédés de réaction chimique homogène et hétérogène sont modélisés à l'aide d'un modèle de combustion global. L'équation de transfert de chaleur radiatif est également résolue par la méthode des volumes finis. Le code de simulation numérique a été validé en comparant les résultats des calculs par ordinateur avec des expériences pour du charbon pulvérisé dans un four expérimental équipé d'un brûleur à tourbillon. On montre que le code numérique peut prédire avec succès le champ d'écoulement et la structure de flamme y compris les effets tourbillonnaires et qu'il peut donc servir à la conception et à l'optimisation des brûleurs à tourbillons pour les combustibles solides pulvérisés. [source]


Numerical modelling of the vertical structure and dark halo parameters in disc galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 7 2010
A. Khoperskov
Abstract The non-linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N-body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo-to-disc mass ratio is predicted from the simulations. The method of assessment of the spherical-to-disc mass ratio for edge-on spiral galaxies with a small bulge is considered. Modelling of eight edge-on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark-to-luminous mass ratio in our galaxies is of the order of one within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Numerische Modellierung von Holz und Verbindungselementen in Holz-Beton-Verbundkonstruktionen

BAUTECHNIK, Issue 6 2005
Marco Grosse Dipl.-Ing.
Durch die Anwendung der FEM können auch komplexe Strukturen berechnet werden, die sich nicht mehr als Stab- oder Flächentragwerke abbilden lassen. Es ist daher naheliegend, auch das Tragverhalten von Bauteilen oder Bauteilkomponenten in Abhängigkeit von verschiedenen Einflußparametern mit Hilfe von FE-Modellen zu simulieren. Um dabei aber Versagensmechanismen abbilden zu können, ist es notwendig, das Materialverhalten der Baustoffe im Nachbruchbereich zu berücksichtigen. Es wird ein konstitutives Materialmodell für den Werkstoff Holz vorgestellt, welches das räumlich anisotrope und vom Beanspruchungsmodus abhängige, nichtlineare Tragverhalten einbezieht. Durch die Kombination mit einem leistungsfähigen Betonmodell ist es möglich, Holz-Beton-Verbundkonstruktionen zu untersuchen. Anhand der Simulationen von Scherversuchen mit verschiedenen Schubverbindungselementen soll die Leistungsfähigkeit solcher numerischer Modelle verdeutlicht werden. Numerical modelling of timber and connection elements used in timber-concrete composite structures. Complex load carrying structures that can not be reproduced as framework ore simple surface models can be calculated using the Finite Element Method. Therefore it seems desirable to simulate the structural behaviour of members or components considering several influence parameters with the help of FE-models too. However, to model the failure mechanism it is necessary to take into account the material behaviour in the critical and post critical range. An adequate numerical model for timber that considers the specific anisotropic and load dependent strength and degradation behaviour is introduced. In combination with an capable model for concrete it is possible to examine timber concrete composite structures. The effectiveness of such models is verified by simulations of shear tests with several fastener elements. [source]


Numerische Modellierungen mit einem zyklisch-viskoplastischen Stoffansatz für granulare Böden

BAUTECHNIK, Issue 1 2005
vormals Universität Kassel Tim Stöcker Dr.-Ing.
In der Geotechnik, insbesondere aber im Verkehrswegebau, gewinnt die Frage der Boden-Bauwerk-Interaktion bei nichtruhenden Lasteinwirkungen zunehmend an Bedeutung. Dabei stehen neben sicherheitsrelevanten Aspekten besonders Fragen zur Gebrauchstauglichkeit sowie wirtschaftliche Aspekte im Vordergrund. Ziel einer anwendungsorientierten Forschung muß daher die Entwicklung eines praxisorientierten Verfahrens zur ingenieurmäßigen Modellierung der Langzeitverformungen bzw. des Langzeitverhaltens des Baugrundes unter nichtruhender Belastung sein. Die dargestellten Arbeiten beschäftigen sich daher mit der Implementierung, Validierung und Anwendung eines neuen, im folgenden als "zyklisch-viskoplastisch" bezeichneten Stoffansatzes für granulare Böden unter nichtruhender Lasteinwirkung. Die wesentlichen Grundlagen dieses Ansatzes sind dabei im Heft 4, 2004, dieser Zeitschrift beschrieben, [1]. Das erreichte Ziel war, den Stoffansatz für numerische Berechnungsmodelle ingenieurmäßig aufzubereiten, zu implementieren, sowie das Berechnungsmodell zu verifizieren und auf reale Problemstellungen anzuwenden. Numerical modelling with a cyclic viscoplastic constitutive approach for granular soils. In modern Geotechnics, especially in track engineering, research for soil-structure interaction under cyclic loading has been gaining importance over the past decades. Next to states of system/structure failure, the long-term (deformation) behaviour is of major interest, as it has a major impact on e.g. maintenance costs in track engineering. Hence, the objective of this work is to be seen in the necessity of investigations on the long-term deformation behaviour of granular soils and ballast under cyclic loading. In the present paper the validation and implementation of a cyclic viscoplastic constitutive approach for granular under cyclic dynamic loading, [1], into a numerical model is carried out. The investigation and set up of a theoretical and physical complete model has not been intended. The objective rather is the development of an engineering type model, appropriate for practical tasks. Some modelling examples are given to illustrate modelling capacities. [source]