Finite Element Numerical Simulation Method Research Articles

Analytic expression of the temperature increment in a spin transfer torque nanopillar structure

The temperature increment due to the Joule heating in a nanopillar spin transfer torque system is investigated. We obtain a time-dependent analytic solution of the heat conduction equation in nanopillar geometry by using the Green's function method after some simplifications of the problem. While Holm's equation is applicable only to steady states in metallic systems, our solution describes the time dependence and is also applicable to a nanopillar-shaped magnetic tunneling junction with an insulator barrier layer. The validity of the analytic solution is confirmed by numerical finite element method simulations and by the comparison with Holm's equation.

Volcano‐Tectonic Interaction and Its Relation with the State of Volcanic Activity

AbstractWe develop a three‐dimensional viscoelastic model including a magma chamber and an extrusive volcano to show that there is a volcano‐tectonic interaction by the finite element numerical simulation method. First, we describe the characters of surface deformation, stress distribution and super pressure in the magma chamber with the magma supplying in different states. Then, we analyse the effect of tectonic stress field change on the magma chamber. The results show that a change of 10 MPa in stress boundary condition can bring ±1.2~1.6 MPa change of super pressure in the magma chamber. Such an order of magnitude of stress can trigger the unrest in volcanic systems, and then cause volcanic activities.

The ALE Method for Oil/Water Two-Phase Flow in Deforming Porous Media

Abstract The main objective of this paper is to establish a consistent geometrical frame focusing on the coupling between hydro-mechanical aspects. An arbitrary Lagrangian and Eulerian method (ALE) has been used to deal with the numerical simulation for oil/water flow in deforming porous media. When the mesh motion is equal to the velocity of the deformed porous media, the convection term referred to as the relative velocity between fluid flow and the skeleton deformation is removed from the Finite Element Method (FEM) formula. Therefore, some difficulty in FEM numerical simulation has been solved. A classical oil/water flow coupled with solid deformation is simulated by ALE code with an iterative scheme. An ALE with a fully implicit and sequential iterative algorithm [Implicit Pressure Explicit Saturation (IMPES) method], which calculates the oil phase pressure and water phase saturation with least squares FEM, is used to simulate the oil/water two-phase fluid flow. Compared with general reservoir simulation, the ALE method could reach a consistent frame description or a more rigorous definition of the parameters for the solid phase and the flow phase. This may be very important for larger deformations in stratum induced by petroleum production and tracking the moving interface in multi-phase fluid flow. Introduction Such independent variables such as stress, strain and deformation in a continuum are described by Lagrangian or Eulerian coordinates. The Lagrangian description, generally, is employed extensively for solid mechanics, and the Eulerian description is preferred for situations which involve large flows and large distortions such as fluid mechanics. The coupling models or mathematical equations for two-phase flow in deforming porous media belong to the inner coupling. It is recognized that the independent variables for a solid phase and a fluid phase are difficult to distinguish and they should be regarded as overlapping contiuums. So a consistent coordinate frame description for this kind of coupled model is necessary, and many results have been presented. The mass equation, introduced by Bear(1), employed an Eulerian description through continuum theory for multi-phase flow. Cooper(2) derived the one-dimensional governing equations of groundwater flow in Eulerian and deforming coordinates. In the deforming coordinates, the form of governing equations does not involve the convective term which is introduced by the motion of porous media. The two-phase flow in deformed porous media was simulated under deforming coordinates by Xue(3). When the assumption with a steady and a small displacement is given, some results have been obtained with Eulerian mesh. The governing equations for oil/water flow in deformed porous media are derived using the assumption that presented by a number of authors (4–9). Although the deforming ordinates concept is proposed, a consistent coordinate frame description for three-dimensional flow in deformed porous and finite deformations has not been satisfactorily resolved. The main object of this paper is to build a consistent coordinate frame description through the ALE theory for the coupling of two-phase flow and deforming porous media. Furthermore, an injection water example is given with the finite element method.

Finite Element Numerical Simulation and PIV Measurement of Flow Field inside Metering-in Spool Valve

The finite element method (FEM) and particle image velocimetry (PIV) technique are utilized to get the flow field along the inlet passage, the chamber, the metering port and the Outlet passage of spool valve at three different valve openings. For FEM numerical simulation, the stream function psi -vorticity omega forms of continuity and Navier-Stokes equations are employed and FEM is applied to discrete the equations. Homemade simulation codes are executed to compute the values of stream function and vorticity at each node in the flow domain, then according to the correlation between stream function and velocity components, the velocity vectors of the whole field are calculated. For PIV experiment, pulse Nd: YAG laser is exploited to generate laser beam, cylindrical and spherical lenses are combined each other to produce 1.0 mm thickness laser sheet to illuminate the object plane, Polystyrene spherical particle with diameter of 30-50 mu m is seeded in the fluid as a tracing particles, Kodak ES1.0 CCD camera is employed to capture the images of interested, the images are processed with fast Fourier transform (FFT) cross-correlation algorithm and the processing results is displayed. Both results of numerical simulation and PIV experimental show that there are three main areas in the spool valve where vortex is formed. Numerical results also indicate that the valve opening have some effects on the flow structure of the valve. The investigation is helpful for qualitatively analyzing the energy loss, noise generating, steady state flow forces and even designing the geometry structure and flow passage.

Proof-of-principle of surface detection with air-guided quantum cascade lasers

We report a proof-of-principle of surface detection with air-guided quantum cascade lasers. Laser ridges were designed to exhibit an evanescent electromagnetic field on their top surface that can interact with material or liquids deposited on the device. We employ photoresist and common solvents to provide a demonstration of the sensor setup. We observed spectral as well as threshold currents changes as a function of the deposited material absorption curve. A simple model, supplemented by 2D numerical finite element method simulations, allows one to explain and correctly predict the experimental results.

A New Optimization Method of Constitutive Equation for Hot Working Based on Physical Simulation and Numerical Simulation

This paper advances a new optimization method about material constitutive equation on the basis of physical simulation and numerical simulation results which basic thinking can be described as the following: through comparing the results of the material deformation process under actual experimental conditions and virtually simulated by the finite element numerical simulation method with the constitutive equation established on the basis of the physical simulation, the constitutive equation established by the experimental data is optimized in turn. Based on it, this paper advances a visco/plastic constitutive equation to depict the semi-solid thixo-forming and the constitutive equation is analyzed and optimized through coupling of the physical simulation and numerical simulation. It is observed that this method can effectively eliminate the influence of the factor outside material itself on the constitutive equation. So, it can exactly depict the deformation behavior of the materials and improve the accuracy and reliability of the numerical simulation.

A magnetic heat pump with porous magneto caloric material

AbstractAt present magnetic refrigeration shows a realistic potential to penetrate into some niche markets in the field of cold and hot “production”. It is well known that a refrigerator for cooling and a heat pump for heating are machines based on the same principle. A small review on magnetic heat pump studies is outlined and a simple engineering calculation scheme to determine the coefficient of performance for a magnetic heat pump with a rotary porous structure heat exchanger is presented. Magnetic heat flux line distributions are calculated by a 2‐d finite element method numerical simulation program with the objective to obtain high field's μ0H with not too heavy permanent magnets assemblies. The porous structures are geometrically optimised to obtain maximal magnetic field inductions. It is shown that for a water/ethylene‐glycol magnetic heat pump the coefficient of performance is higher than that of a conventional heat pump. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

204 層間を部分的に非接着にした積層材のFEM自由振動解析

In this study, several different types of delamination (partial debonding in the adhesive layers) were introduced in carbon fiber reinforced plastic (CFRP) laminated cantilever beams and then experimental measurements and finite element method (FEM) numerical analysis and simulation were applied to free vibration of those specimens made in this study. The experimental measurement showed that first bending mode frequencies and their modal loss factors varied when delaminations were introduced in the specimens. Distributions in each laminate with delamination of transverse shear strain energy and contact pressure were also obtained by FEM and then quantitatively examined.

Production of hyperpolarized xenon in a static pump cell: Numerical simulations and experiments

Hyperpolarized $^{129}\mathrm{Xe}$ finds numerous applications in NMR spectroscopy and magnetic resonance imaging. The production of hyperpolarized $^{129}\mathrm{Xe}$ by spin-exchange optical pumping is therefore an important experimental issue. We model the three-dimensional transport processes within a so-called batch mode pump cell via numerical finite element method simulations and compare the results with experimental data. In particular, the influence of different experimental parameters, such as temperature, xenon and nitrogen partial pressure, laser power, and radius-to-length ratio of a cylindrical pump cell, is evaluated. The developed numerical method is capable of describing the spin-exchange optical pumping process in a realistic manner.

FEM time domain analysis for the detection of depth and thickness of cylindrical defects in metallic plates

In this work, we will present a strategy for the evaluation of depth and thickness of defects like holes and cracks in metallic plates via the analysis of the response in frequency of a suitable eddy-current detection system. In order to obtain the data for the inversion in real time, the analysis in frequency domain is deduced by the analysis of the response of the system to an exciting rectangular voltage pulse of suitable length, according to the size of defect to detect. By finite element method numerical simulations in time domain of the detection system applied to known defect configurations, we have found some interesting information for the inverse problem solution. In this paper, we present the theory of the detection technique above mentioned and results about numerical and experimental analysis.

Efficient modeling of a biaxial micromirror with decoupled mechanism

This paper presents the design methodology of the biaxial micromirror. Firstly, the robotic theory is utilized to derive the general decoupling structural dynamics, which further lead to the formation of the mirror components in the example structure. Then, in regard to the chosen square shape mirror plate, the quartet triangles are selected as the four electrodes with a unique distribution, which extends the decoupled mechanism into the electromechanical domain so that the entire system can be analyzed by using the design theory of single axis mirrors. The pull-in characteristics are further derived and the design performance indices explicitly link with the critical geometrical parameters. For the first time insights are provided for the design synthesis of biaxial micromirror. In addition, the simple analytical approach developed for this case is found to be effective and the results match well with those from the finite element method (FEM) simulation. Using this analytical approach to obtain the initial geometrical parameters can significantly reduce the design efforts, since the numerical FEM simulation only serves for verification and fine-tuning.

Tectonic stress field and its effect on hydrocarbon migration and accumulation in Mesozoic and Cenozoic in Kuqa depression, Tarim basin

Through rock acoustic emission experiments and structural deformation analysis, the tectonic stages in Meso-Cenozoic in the Kuqa depression of the Tarim basin are firstly divided. Then, combining with rock magnetic fabric analysis and memory information, the distribution characteristics of tectonic stress field of every tectonic stage are quantificationally resumed. At the same time, according to the distribution relation of tectonic stress field of hydrocarbon formation stage by the finite element numerical simulation method and the known hydrocarbon reservoirs, the effects of tectonic stress field on hydrocarbon migration and accumulation are further analyzed. The Kuqa depression has mainly experienced six tectonic movements since Mesozoic. Except that the tectonic stress field of the Early Yanshan stage (208—135 Ma) showed northeast-southwest extensional stress field where the orientation of the maximum principal compressive stress (σ 1 ) was northwest-southeast, the others were compressive stress field where the orientations of the maximum principal compressive stress (σ 1 ) were near north-south. Along with the closure of the paleo-Tethys ocean, the Kuqa depression in the Indosinian stage (250—208 Ma) was in strong compressive circumstance with apparently big maximum principal stress (σ 1 ) magnitude. Due to the equilibrium adjustment of interior Eurasia, the Kuqa depression in the Early Yanshan stage (208—135 Ma) was in weak extensional circumstance with apparently small maximum principal stress (σ 1 ) magnitude. From the Late Yanshan stage (135—65 Ma) on, with a series of collision events occurring at the south edge of Eurasia, the Kuqa depression was in compressive circumstance again in which the maximum principal stress (σ 1 ) magnitude was from small to big in turn. The Late Himalayan stage (2.6—0.7 Ma) was the main tectonic deformation stage with the biggest principal compressive stress (σ 1 ) magnitude. Tectonic stress field plays a dominant role in hydrocarbon formation, it not only forms migration channels and trap structures for hydrocarbon accumulation, but also is the main drive power for hydrocarbon migration vertically along faults.

Systematic numerical simulation of rock tunnel stability considering different rock conditions and construction effects

This paper outlines the construction process mechanics (CPM) principle for analysing the stability of rock tunnels and presents finite element method (FEM) numerical simulation and prediction on the deformation and failure of the rock masses surrounding tunnels under various rock mass properties and excavating and support conditions. Based on numerical modelling, a series of predicting curves for rock mass response and deformation are obtained, which provides the basis of guiding the design and construction of rock tunnels in Taiwan.

2‐D numerical simulation of differential viscoelastic fluids in a single‐screw continuous mixer: Application of viscoelastic finite element methods

AbstractViscoelastic effects on mixing flows obtained with kneading paddles in a single‐screw, continuous mixer were explored using 2‐D finite element method numerical simulations. The single‐mode Phan–Thien Tanner nonlinear, viscoelastic fluid model was used with parameters for a dough‐like material. The viscoelastic limits of the simulations were found using elastic viscous stress splitting, 4 × 4 sub‐elements for stress, streamline upwind, and streamline upwind Petrov–Galerkin (SUPG). Mesh refinement and comparison between methods was also done. The single‐screw mixer was modeled by taking the kneading paddle as the point of reference, fixing the mesh in time. Rigid rotation and no slip boundary conditions at the walls were used with inertia taken into account. Results include velocity, pressure, and stress profiles. The addition of viscoelasticity caused the shear and normal stresses to vary greatly from the viscous results, with a resulting loss of symmetry in the velocity and pressure profiles in the flow region. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 22–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10038

An experimental and numerical study of particle size distribution effects on the sintering of porous ceramics

A single-step processing method has been established to prepare asymmetric porous alumina microstructures by a controlled sedimentation technique. Fine powder from an aqueous suspension is consolidated over a casting slab. Metastable surface chemical control of the suspension properties was able to induce a highly porous flat disc structure with a continuously increasing mean pore size from top to bottom. Formation of this gradient structure was facilitated by using a powder with a very broad particle size distribution. These structures can be used as either ultrafiltration media or as substrates for inorganic membrane making. Sintering can readily introduce defects into functionally gradient ceramics. Despite these problems, the asymmetric structures considered in this paper can be readily sintered without warpage or cracking. In this regard, a finite element method numerical simulation had been developed to model the sintering characteristics of functionally gradient ceramic structures. The key for being able to predict a non-warped structure was the incorporation into the model of the powder particle size distribution as a field variable. Across the vertical section of the structure, the distributions were broad and overlapping, all with a significant fines tail. These characteristics accelerate and homogenize local sintering rates, such that the net result is a non-warped fused structure. This paper presents recent advances with the simulation, where sample geometry, porosity and particle size distribution evolutions were traced alongside measurements made on physical specimens. In general the model corresponded well with the experimental observations. The correct accounting of observed trends lends confidence to the underlying sintering mechanisms incorporated into the model.

Particle size distribution effects in an FEM model of sintering porous ceramics

A numerical simulation is presented on the sintering of porous alumina structures prepared by a controlled sedimentation technique. By forming this functionally gradient material with a very broad powder size distribution, the samples were able to remain flat through sintering. This experimental result is reflected in the present simulation results, which incorporated particle size distribution effects. In general, sintering functionally gradient ceramics can often introduce defects. Despite these common problems, the asymmetric structures considered in this paper featured a vertical functionality of continuously overlapping broad powder size distributions in the structure. This arrangement served to homogenize sintering rates. Modelling presented in connection with this shows that such structures can be readily sintered without warpage or cracking. To demonstrate these effects, a finite element method numerical simulation was developed to model the sintering characteristics of porous asymmetric ceramic structures by incorporating the powder particle size distribution into the model as a field variable. This work presents novel advances in the sintering model such that the contributions to the desired product properties attributable to particle size distribution effects can be demonstrated. These additions to the model produce numerical results which properly match observed structural profiles of physical samples.

A Numerical Simulation of 2‐D Geoelectric Section with Biquadratic Change of Potential for Resistivity Sounding by the Finite Element Method

AbstractNow on performance of using finite element method in the numerical calculation of resistivity surveying, people always become accustomed to take discussions as view from the total potential. The electrical properties, such as conductivity and potential, are generally assumed to be the mean value or the linear variation. With respect to the problem, a new finite element numerical simulation method for resistivity sounding of 2‐D geoelectric section is presented in the paper, whose research object is anomalous potential. The major difference between this method and the traditional methods in the same category lies in interpolating conductivity with a bilinear function, and interpolating potential with a biquadratic function within each grid cell. In this sense, this method can make the forward of potential and the apparent resistivity derived from the potential more agree with the variation rule of actual geoelectric field than ever. Additionally, the number of mesh cell is also cut down by a long way. The following examples illustrate the accuracy and effectiveness of the method.