The direct field boundary impedance of two-dimensional periodic structures with application to high frequency vibration prediction.

Science.gov (United States)

Langley, Robin S; Cotoni, Vincent

2010-04-01

Large sections of many types of engineering construction can be considered to constitute a two-dimensional periodic structure, with examples ranging from an orthogonally stiffened shell to a honeycomb sandwich panel. In this paper, a method is presented for computing the boundary (or edge) impedance of a semi-infinite two-dimensional periodic structure, a quantity which is referred to as the direct field boundary impedance matrix. This terminology arises from the fact that none of the waves generated at the boundary (the direct field) are reflected back to the boundary in a semi-infinite system. The direct field impedance matrix can be used to calculate elastic wave transmission coefficients, and also to calculate the coupling loss factors (CLFs), which are required by the statistical energy analysis (SEA) approach to predicting high frequency vibration levels in built-up systems. The calculation of the relevant CLFs enables a two-dimensional periodic region of a structure to be modeled very efficiently as a single subsystem within SEA, and also within related methods, such as a recently developed hybrid approach, which couples the finite element method with SEA. The analysis is illustrated by various numerical examples involving stiffened plate structures.

An outgoing energy flux boundary condition for finite difference ICRP antenna models

International Nuclear Information System (INIS)

Batchelor, D.B.; Carter, M.D.

1992-11-01

For antennas at the ion cyclotron range of frequencies (ICRF) modeling in vacuum can now be carried out to a high level of detail such that shaping of the current straps, isolating septa, and discrete Faraday shield structures can be included. An efficient approach would be to solve for the fields in the vacuum region near the antenna in three dimensions by finite methods and to match this solution at the plasma-vacuum interface to a solution obtained in the plasma region in one dimension by Fourier methods. This approach has been difficult to carry out because boundary conditions must be imposed at the edge of the finite difference grid on a point-by-point basis, whereas the condition for outgoing energy flux into the plasma is known only in terms of the Fourier transform of the plasma fields. A technique is presented by which a boundary condition can be imposed on the computational grid of a three-dimensional finite difference, or finite element, code by constraining the discrete Fourier transform of the fields at the boundary points to satisfy an outgoing energy flux condition appropriate for the plasma. The boundary condition at a specific grid point appears as a coupling to other grid points on the boundary, with weighting determined by a kemel calctdated from the plasma surface impedance matrix for the various plasma Fourier modes. This boundary condition has been implemented in a finite difference solution of a simple problem in two dimensions, which can also be solved directly by Fourier transformation. Results are presented, and it is shown that the proposed boundary condition does enforce outgoing energy flux and yields the same solution as is obtained by Fourier methods

Bubble boundary estimation in an annulus two-phase flow using electrical impedance tomography

International Nuclear Information System (INIS)

Lee, Jeong Seong

2008-02-01

For the visualization of the phase boundary in an annulus two-phase flows, the electrical impedance tomography (EIT) technique is introduced. In EIT, a set of predetermined electrical currents is injected trough the electrodes placed on the boundary of the flow passage and the induced electrical potentials are measured on the electrode. With the relationship between the injected currents and the induced voltages, the electrical conductivity distribution across the flow domain is estimated through the image reconstruction algorithm. In this, the conductivity distribution corresponds to the phase distribution. In the application of EIT to two-phase flows where there are only two conductivity values, the conductivity distribution estimation problem can be transformed into the boundary estimation problem. This paper considers a bubble boundary estimation with EIT in an annulus two-phase flows. And in many industrial cases there are a priori known internal structures inside the vessels which could be used as internal electrodes in tomographical imaging. In this paper internal electrodes were considered in electrical impedance tomography. As the image reconstruction algorithm, the unscented Kalman filter (UKF) is adopted since from the control theory it is reported that the UKF shows better performance than the extended Kalman filter (EKF) that has been commonly used. The UKF algorithm was formulated to be incorporate into the image reconstruction algorithm for the present problem. Also, phantom experiments have been conducted to evaluate the improvement by UKF

The acoustic field of a point source in a uniform boundary layer over an impedance plane

Science.gov (United States)

Zorumski, W. E.; Willshire, W. L., Jr.

1986-01-01

The acoustic field of a point source in a boundary layer above an impedance plane is investigated anatytically using Obukhov quasi-potential functions, extending the normal-mode theory of Chunchuzov (1984) to account for the effects of finite ground-plane impedance and source height. The solution is found to be asymptotic to the surface-wave term studies by Wenzel (1974) in the limit of vanishing wind speed, suggesting that normal-mode theory can be used to model the effects of an atmospheric boundary layer on infrasonic sound radiation. Model predictions are derived for noise-generation data obtained by Willshire (1985) at the Medicine Bow wind-turbine facility. Long-range downwind propagation is found to behave as a cylindrical wave, with attention proportional to the wind speed, the boundary-layer displacement thickness, the real part of the ground admittance, and the square of the frequency.

Simultaneous reconstruction of outer boundary shape and conductivity distribution in electrical impedance tomography

KAUST Repository

Hyvönen, Nuutti

2016-01-05

The simultaneous retrieval of the exterior boundary shape and the interior admittivity distribution of an examined body in electrical impedance tomography is considered. The reconstruction method is built for the complete electrode model and it is based on the Frechet derivative of the corresponding current-to-voltage map with respect to the body shape. The reconstruction problem is cast into the Bayesian framework, and maximum a posteriori estimates for the admittivity and the boundary geometry are computed. The feasibility of the approach is evaluated by experimental data from water tank measurements.

Method of interior boundaries in a mixed problem of acoustic scattering

Directory of Open Access Journals (Sweden)

P. A. Krutitskii

1999-01-01

Full Text Available The mixed problem for the Helmholtz equation in the exterior of several bodies (obstacles is studied in 2 and 3 dimensions. The Dirichlet boundary condition is given on some obstacles and the impedance boundary condition is specified on the rest. The problem is investigated by a special modification of the boundary integral equation method. This modification can be called ‘Method of interior boundaries’, because additional boundaries are introduced inside scattering bodies, where impedance boundary condition is given. The solution of the problem is obtained in the form of potentials on the whole boundary. The density in the potentials satisfies the uniquely solvable Fredholm equation of the second kind and can be computed by standard codes. In fact our method holds for any positive wave numbers. The Neumann, Dirichlet, impedance problems and mixed Dirichlet–Neumann problem are particular cases of our problem.

Consistent boundary conditions for open strings

International Nuclear Information System (INIS)

Lindstroem, Ulf; Rocek, Martin; Nieuwenhuizen, Peter van

2003-01-01

We study boundary conditions for the bosonic, spinning (NSR) and Green-Schwarz open string, as well as for (1+1)-dimensional supergravity. We consider boundary conditions that arise from (1) extremizing the action, (2) BRST, rigid or local supersymmetry, or κ(Siegel)-symmetry of the action, (3) closure of the set of boundary conditions under the symmetry transformations, and (4) the boundary limits of bulk Euler-Lagrange equations that are 'conjugate' to other boundary conditions. We find corrections to Neumann boundary conditions in the presence of a bulk tachyon field. We discuss a boundary superspace formalism. We also find that path integral quantization of the open string requires an infinite tower of boundary conditions that can be interpreted as a smoothness condition on the doubled interval; we interpret this to mean that for a path-integral formulation of open strings with only Neuman boundary conditions, the description in terms of orientifolds is not just natural, but is actually fundamental

Estimating surface acoustic impedance with the inverse method.

Science.gov (United States)

Piechowicz, Janusz

2011-01-01

Sound field parameters are predicted with numerical methods in sound control systems, in acoustic designs of building and in sound field simulations. Those methods define the acoustic properties of surfaces, such as sound absorption coefficients or acoustic impedance, to determine boundary conditions. Several in situ measurement techniques were developed; one of them uses 2 microphones to measure direct and reflected sound over a planar test surface. Another approach is used in the inverse boundary elements method, in which estimating acoustic impedance of a surface is expressed as an inverse boundary problem. The boundary values can be found from multipoint sound pressure measurements in the interior of a room. This method can be applied to arbitrarily-shaped surfaces. This investigation is part of a research programme on using inverse methods in industrial room acoustics.

Simultaneous reconstruction of shape and generalized impedance functions in electrostatic imaging

International Nuclear Information System (INIS)

Cakoni, Fioralba; Hu, Yuqing; Kress, Rainer

2014-01-01

Determining the geometry and the physical nature of an inclusion within a conducting medium from voltage and current measurements on the accessible boundary of the medium can be modeled as an inverse boundary value problem for the Laplace equation subject to appropriate boundary conditions on the inclusion. We continue the investigations on the particular inverse problem with a generalized impedance condition started in Cakoni and Kress (2013 Inverse Problems 29 015005) by presenting an inverse algorithm for the simultaneous reconstruction of both the shape of the inclusion and the two impedance functions via a boundary integral equation approach. In addition to describing the reconstruction algorithm and illustrating its feasibility by numerical examples we also provide some extensions to the uniqueness results in Cakoni and Kress (2013 Inverse Problems 29 015005). (paper)

Concentric artificial impedance surface for directional sound beamforming

Directory of Open Access Journals (Sweden)

Kyungjun Song

2017-03-01

Full Text Available Utilizing acoustic metasurfaces consisting of subwavelength resonant textures, we design an artificial impedance surface by creating a new boundary condition. We demonstrate a circular artificial impedance surface with surface impedance modulation for directional sound beamforming in three-dimensional space. This artificial impedance surface is implemented by revolving two-dimensional Helmholtz resonators with varying internal coiled path. Physically, the textured surface has inductive surface impedance on its inner circular patterns and capacitive surface impedance on its outer circular patterns. Directional receive beamforming can be achieved using an omnidirectional microphone located at the focal point formed by the gradient-impeding surface. In addition, the uniaxial surface impedance patterning inside the circular aperture can be used for steering the direction of the main lobe of the radiation pattern.

Circular resistor networks for electrical impedance tomography with partial boundary measurements

International Nuclear Information System (INIS)

Borcea, L; Mamonov, A V; Druskin, V

2010-01-01

We introduce an algorithm for the numerical solution of electrical impedance tomography (EIT) in two dimensions, with partial boundary measurements. The algorithm is an extension of the one in Borcea et al (2008 Inverse Problems 24 035013 (31pp)) and Vasquez (2006 PhD Thesis Rice University, Houston, TX, USA) for EIT with full boundary measurements. It is based on resistor networks that arise in finite volume discretizations of the elliptic partial differential equation for the potential on so-called optimal grids that are computed as part of the problem. The grids are adaptively refined near the boundary, where we measure and expect better resolution of the images. They can be used very efficiently in inversion, by defining a reconstruction mapping that is an approximate inverse of the forward map, and acts therefore as a preconditioner in any iterative scheme that solves the inverse problem via optimization. The main result in this paper is the construction of optimal grids for EIT with partial measurements by extremal quasiconformal (Teichmüller) transformations of the optimal grids for EIT with full boundary measurements. We present the algorithm for computing the reconstruction mapping on such grids, and we illustrate its performance with numerical simulations. The results show an interesting trade-off between the resolution of the reconstruction in the domain of the solution and distortions due to artificial anisotropy induced by the distribution of the measurement points on the accessible boundary

Pyramidal resistor networks for electrical impedance tomography with partial boundary measurements

International Nuclear Information System (INIS)

Borcea, L; Mamonov, A V; Druskin, V; Vasquez, F Guevara

2010-01-01

We introduce an inversion algorithm for electrical impedance tomography (EIT) with partial boundary measurements in two dimensions. It gives stable and fast reconstructions using sparse parameterizations of the unknown conductivity on optimal grids that are computed as part of the inversion. We follow the approach in Borcea et al (2008 Inverse Problems 24 035013) and Vasquez (2006 PhD thesis Rice University, Houston, TX, USA) that connects inverse discrete problems for resistor networks to continuum EIT problems, using optimal grids. The algorithm in Borcea et al (2008 Inverse Problems 24 035013) and Vasquez (2006 PhD Thesis Rice University, Houston, TX, USA) is based on circular resistor networks, and solves the EIT problem with full boundary measurements. It is extended in Borcea et al (2010 Inverse Problems 26 045010) to EIT with partial boundary measurements, using extremal quasi-conformal mappings that transform the problem to one with full boundary measurements. Here we introduce a different class of optimal grids, based on resistor networks with pyramidal topology, that is better suited for the partial measurements setup. We prove the unique solvability of the discrete inverse problem for these networks and develop an algorithm for finding them from the measurements of the Dirichlet to Neumann map. Then, we show how to use the networks to define the optimal grids and to approximate the unknown conductivity. We assess the performance of our approach with numerical simulations and compare the results with those in Borcea et al (2010)

Reconstruction of boundary conditions from internal conditions using viability theory

KAUST Repository

Hofleitner, Aude; Claudel, Christian G.; Bayen, Alexandre M.

2012-01-01

This article presents a method for reconstructing downstream boundary conditions to a HamiltonJacobi partial differential equation for which initial and upstream boundary conditions are prescribed as piecewise affine functions and an internal condition is prescribed as an affine function. Based on viability theory, we reconstruct the downstream boundary condition such that the solution of the Hamilton-Jacobi equation with the prescribed initial and upstream conditions and reconstructed downstream boundary condition satisfies the internal value condition. This work has important applications for estimation in flow networks with unknown capacity reductions. It is applied to urban traffic, to reconstruct signal timings and temporary capacity reductions at intersections, using Lagrangian sensing such as GPS devices onboard vehicles.

Reconstruction of boundary conditions from internal conditions using viability theory

KAUST Repository

Hofleitner, Aude

2012-06-01

This article presents a method for reconstructing downstream boundary conditions to a HamiltonJacobi partial differential equation for which initial and upstream boundary conditions are prescribed as piecewise affine functions and an internal condition is prescribed as an affine function. Based on viability theory, we reconstruct the downstream boundary condition such that the solution of the Hamilton-Jacobi equation with the prescribed initial and upstream conditions and reconstructed downstream boundary condition satisfies the internal value condition. This work has important applications for estimation in flow networks with unknown capacity reductions. It is applied to urban traffic, to reconstruct signal timings and temporary capacity reductions at intersections, using Lagrangian sensing such as GPS devices onboard vehicles.

Dynamic Phase Boundary Estimation in Two-phase Flows Based on Electrical Impedance Tomography

International Nuclear Information System (INIS)

Lee, Jeong Seong; Muhammada, Nauman Malik; Kim, Kyung Youn; Kim, Sin

2008-01-01

For the dynamic visualization of the phase boundary in two-phase flows, the electrical impedance tomography (EIT) technique is introduced. In EIT, a set of predetermined electrical currents is injected through the electrodes placed on the boundary of the flow passage and the induced electrical potentials are measured on the electrodes. With the relationship between the injected currents and the induced voltages, the electrical conductivity distribution across the flow domain is estimated through the image reconstruction algorithm where the conductivity distribution corresponds to the phase distribution. In the application of EIT to two-phase flows where there are only two conductivity values, the conductivity distribution estimation problem can be transformed into the boundary estimation problem. This paper considers phase boundary estimation with EIT in annular two-phase flows. As the image reconstruction algorithm, the unscented Kalman filter (UKF) is adopted since from the control theory it is reported that the UKF shows better performance than the extended Kalman filter (EKF) that has been commonly used. For the present problem, the formulation of UKF algorithm involved its incorporation in the adopted image reconstruction algorithm. Also, phantom experiments have been conducted to evaluate the improvement reported by UKF

Boundary conditions in random sequential adsorption

Science.gov (United States)

Cieśla, Michał; Ziff, Robert M.

2018-04-01

The influence of different boundary conditions on the density of random packings of disks is studied. Packings are generated using the random sequential adsorption algorithm with three different types of boundary conditions: periodic, open, and wall. It is found that the finite size effects are smallest for periodic boundary conditions, as expected. On the other hand, in the case of open and wall boundaries it is possible to introduce an effective packing size and a constant correction term to significantly improve the packing densities.

Quantum “violation” of Dirichlet boundary condition

Directory of Open Access Journals (Sweden)

I.Y. Park

2017-02-01

Full Text Available Dirichlet boundary conditions have been widely used in general relativity. They seem at odds with the holographic property of gravity simply because a boundary configuration can be varying and dynamic instead of dying out as required by the conditions. In this work we report what should be a tension between the Dirichlet boundary conditions and quantum gravitational effects, and show that a quantum-corrected black hole solution of the 1PI action no longer obeys, in the naive manner one may expect, the Dirichlet boundary conditions imposed at the classical level. We attribute the ‘violation’ of the Dirichlet boundary conditions to a certain mechanism of the information storage on the boundary.

Quantum “violation” of Dirichlet boundary condition

Energy Technology Data Exchange (ETDEWEB)

Park, I.Y., E-mail: inyongpark05@gmail.com

2017-02-10

Dirichlet boundary conditions have been widely used in general relativity. They seem at odds with the holographic property of gravity simply because a boundary configuration can be varying and dynamic instead of dying out as required by the conditions. In this work we report what should be a tension between the Dirichlet boundary conditions and quantum gravitational effects, and show that a quantum-corrected black hole solution of the 1PI action no longer obeys, in the naive manner one may expect, the Dirichlet boundary conditions imposed at the classical level. We attribute the ‘violation’ of the Dirichlet boundary conditions to a certain mechanism of the information storage on the boundary.

Application of stochastic Galerkin FEM to the complete electrode model of electrical impedance tomography

International Nuclear Information System (INIS)

Leinonen, Matti; Hakula, Harri; Hyvönen, Nuutti

2014-01-01

The aim of electrical impedance tomography is to determine the internal conductivity distribution of some physical body from boundary measurements of current and voltage. The most accurate forward model for impedance tomography is the complete electrode model, which consists of the conductivity equation coupled with boundary conditions that take into account the electrode shapes and the contact resistances at the corresponding interfaces. If the reconstruction task of impedance tomography is recast as a Bayesian inference problem, it is essential to be able to solve the complete electrode model forward problem with the conductivity and the contact resistances treated as a random field and random variables, respectively. In this work, we apply a stochastic Galerkin finite element method to the ensuing elliptic stochastic boundary value problem and compare the results with Monte Carlo simulations

Impedance characterization of PV modules in outdoor conditions

DEFF Research Database (Denmark)

Oprea, Matei-lon; Thorsteinsson, Sune; Spataru, Sergiu

2016-01-01

Impedance spectroscopy (IS) has been used for laboratory characterizations of photovoltaic (PV) technologies under well controlled conditions. This work applies IS for outdoor characterization of PV panels, in order to observe the effect of irradiance (G) and temperature (T) on the PV module’s...

Experimental impedance investigation of an ultracapacitor at different conditions for electric vehicle applications

Science.gov (United States)

Zhang, Lei; Hu, Xiaosong; Wang, Zhenpo; Sun, Fengchun; Dorrell, David G.

2015-08-01

Ultracapacitors (UCs) are being increasingly deployed as a short-term energy storage device in various energy systems including uninterruptable power supplies, electrified vehicles, renewable energy systems, and wireless communication. They exhibit excellent power density and energy efficiency. The dynamic behavior of a UC, however, strongly depends on its impedance characteristics. In this paper, the impedance characteristics of a commercial UC are experimentally investigated through the well-adopted Electrochemical Impedance Spectroscopy (EIS) technique. The implications of the UC operating conditions (i.e., temperature and state of charge (SOC)) to the impedance are systematically examined. The results show that the impedance is highly sensitive to the temperature and SOC; and the temperature effect is more significant. In particular, the coupling effect between the temperature and SOC is illustrated, as well as the high-efficiency SOC window, which is highlighted. To further verify the reliability of the EIS-based investigation and to probe the sensitivity of UC parameters to the operating conditions, a dynamic model is characterized by fitting the collected impedance data. The interdependence of UC parameters (i.e., capacitance and resistance elements) on the temperature and SOC is quantitatively revealed. The impedance-based model is demonstrated to be accurate in two driving-cycle tests.

On Hydroelastic Body-Boundary Condition of Floating Structures

DEFF Research Database (Denmark)

Xia, Jinzhu

1996-01-01

A general linear body boundary condition of hydroelastic analysis of arbitrary shaped floating structures generalizes the classic kinematic rigid-body (Timman-Newman) boundary condition for seakeeping problems. The new boundary condition is consistent with the existing theories under certain...

Resistive wall impedance of the LHC beam screen without slots calculated by boundary element method

CERN Document Server

Tsutsui, H

2002-01-01

In order to calculate the resistive wall impedance of the LHC beam screen without slots, the Boundary Element Method (BEM) is used. The result at 1 GHz is Re(ZL/L) = 6.689×10−3 Ω/m, Re(Zx/L) = 1.251 Ω/m2, Re(Zy/L) = 1.776 Ω/m2, andRe(2Z0,2 cos/kL) = −0.525 Ω/m2, assuming σ = 5.8 × 109 /Ωm.

Real Objects Can Impede Conditional Reasoning but Augmented Objects Do Not.

Science.gov (United States)

Sato, Yuri; Sugimoto, Yutaro; Ueda, Kazuhiro

2018-03-01

In this study, Knauff and Johnson-Laird's (2002) visual impedance hypothesis (i.e., mental representations with irrelevant visual detail can impede reasoning) is applied to the domain of external representations and diagrammatic reasoning. We show that the use of real objects and augmented real (AR) objects can control human interpretation and reasoning about conditionals. As participants made inferences (e.g., an invalid one from "if P then Q" to "P"), they also moved objects corresponding to premises. Participants who moved real objects made more invalid inferences than those who moved AR objects and those who did not manipulate objects (there was no significant difference between the last two groups). Our results showed that real objects impeded conditional reasoning, but AR objects did not. These findings are explained by the fact that real objects may over-specify a single state that exists, while AR objects suggest multiple possibilities. Copyright © 2017 Cognitive Science Society, Inc.

Perturbation method for calculation of narrow-band impedance and trapped modes

International Nuclear Information System (INIS)

Heifets, S.A.

1987-01-01

An iterative method for calculation of the narrow-band impedance is described for a system with a small variation in boundary conditions, so that the variation can be considered as a perturbation. The results are compared with numeric calculations. The method is used to relate the origin of the trapped modes with the degeneracy of the spectrum of an unperturbed system. The method also can be applied to transverse impedance calculations. 6 refs., 6 figs., 1 tab

Antireflective Boundary Conditions for Deblurring Problems

Directory of Open Access Journals (Sweden)

Marco Donatelli

2010-01-01

Full Text Available This survey paper deals with the use of antireflective boundary conditions for deblurring problems where the issues that we consider are the precision of the reconstruction when the noise is not present, the linear algebra related to these boundary conditions, the iterative and noniterative regularization solvers when the noise is considered, both from the viewpoint of the computational cost and from the viewpoint of the quality of the reconstruction. In the latter case, we consider a reblurring approach that replaces the transposition operation with correlation. For many of the considered items, the anti-reflective algebra coming from the given boundary conditions is the optimal choice. Numerical experiments corroborating the previous statement and a conclusion section end the paper.

Integral Method of Boundary Characteristics: Neumann Condition

Science.gov (United States)

Kot, V. A.

2018-05-01

A new algorithm, based on systems of identical equalities with integral and differential boundary characteristics, is proposed for solving boundary-value problems on the heat conduction in bodies canonical in shape at a Neumann boundary condition. Results of a numerical analysis of the accuracy of solving heat-conduction problems with variable boundary conditions with the use of this algorithm are presented. The solutions obtained with it can be considered as exact because their errors comprise hundredths and ten-thousandths of a persent for a wide range of change in the parameters of a problem.

Solution of moving boundary problems with implicit boundary condition

International Nuclear Information System (INIS)

Moyano, E.A.

1990-01-01

An algorithm that solves numerically a model for studying one dimensional moving boundary problems, with implicit boundary condition, is described. Landau's transformation is used, in order to work with a fixed number of nodes at each instant. Then, it is necessary to deal with a parabolic partial differential equation, whose diffusive and convective terms have variable coefficients. The partial differential equation is implicitly discretized, using Laasonen's scheme, always stable, instead of employing Crank-Nicholson sheme, as it has been done by Ferris and Hill. Fixed time and space steps (Δt, Δξ) are used, and the iteration is made with variable positions of the interface, i.e. varying δs until a boundary condition is satisfied. The model has the same features of the oxygen diffusion in absorbing tissue. It would be capable of estimating time variant radiation treatments of cancerous tumors. (Author) [es

Fluid-solid boundary conditions for multiparticle collision dynamics

International Nuclear Information System (INIS)

Whitmer, Jonathan K; Luijten, Erik

2010-01-01

The simulation of colloidal particles suspended in solvent requires an accurate representation of the interactions between the colloids and the solvent molecules. Using the multiparticle collision dynamics method, we examine several proposals for stick boundary conditions, studying their properties in both plane Poiseuille flow (where fluid interacts with the boundary of a stationary macroscopic solid) and particle-based colloid simulations (where the boundaries are thermally affected and in motion). In addition, our simulations compare various collision rules designed to remove spurious slip near solid surfaces, and the effects of these rules on the thermal motion of colloidal particles. Furthermore, we demonstrate that stochastic reflection of the fluid at solid boundaries fails to faithfully represent stick boundary conditions, and conclude that bounce-back conditions should be applied at both mobile and stationary surfaces. Finally, we generalize these ideas to create partial slip boundary conditions at both stationary and mobile surfaces.

Surface free energy for systems with integrable boundary conditions

International Nuclear Information System (INIS)

Goehmann, Frank; Bortz, Michael; Frahm, Holger

2005-01-01

The surface free energy is the difference between the free energies for a system with open boundary conditions and the same system with periodic boundary conditions. We use the quantum transfer matrix formalism to express the surface free energy in the thermodynamic limit of systems with integrable boundary conditions as a matrix element of certain projection operators. Specializing to the XXZ spin-1/2 chain we introduce a novel 'finite temperature boundary operator' which characterizes the thermodynamical properties of surfaces related to integrable boundary conditions

Nonlinear Elliptic Boundary Value Problems at Resonance with Nonlinear Wentzell Boundary Conditions

Directory of Open Access Journals (Sweden)

Ciprian G. Gal

2017-01-01

Full Text Available Given a bounded domain Ω⊂RN with a Lipschitz boundary ∂Ω and p,q∈(1,+∞, we consider the quasilinear elliptic equation -Δpu+α1u=f in Ω complemented with the generalized Wentzell-Robin type boundary conditions of the form bx∇up-2∂nu-ρbxΔq,Γu+α2u=g on ∂Ω. In the first part of the article, we give necessary and sufficient conditions in terms of the given functions f, g and the nonlinearities α1, α2, for the solvability of the above nonlinear elliptic boundary value problems with the nonlinear boundary conditions. In other words, we establish a sort of “nonlinear Fredholm alternative” for our problem which extends the corresponding Landesman and Lazer result for elliptic problems with linear homogeneous boundary conditions. In the second part, we give some additional results on existence and uniqueness and we study the regularity of the weak solutions for these classes of nonlinear problems. More precisely, we show some global a priori estimates for these weak solutions in an L∞-setting.

Drilling electrode for real-time measurement of electrical impedance in bone tissues.

Science.gov (United States)

Dai, Yu; Xue, Yuan; Zhang, Jianxun

2014-03-01

In order to prevent possible damages to soft tissues, reliable monitoring methods are required to provide valuable information on the condition of the bone being cut. This paper describes the design of an electrical impedance sensing drill developed to estimate the relative position between the drill and the bone being drilled. The two-electrode method is applied to continuously measure the electrical impedance during a drill feeding movement: two copper wire brushes are used to conduct electricity in the rotating drill and then the drill is one electrode; a needle is inserted into the soft tissues adjacent to the bone being drilled and acts as another electrode. Considering that the recorded electrical impedance is correlated with the insertion depth of the drill, we theoretically calculate the electrode-tissue contact impedance and prove that the rate of impedance change varies considerably when the drill bit crosses the boundary between two different bone tissues. Therefore, the rate of impedance change is used to determine whether the tip of the drill is located in one of cortical bone, cancellous bone, and cortical bone near a boundary with soft tissue. In vitro experiments in porcine thoracic spines were performed to demonstrate the feasibility of the impedance sensing drill. The experimental results indicate that the drill, used with the proposed data-processing method, can provide accurate and reliable breakthrough detection in the bone-drilling process.

Discrete transparent boundary conditions for Schroedinger-type equations

International Nuclear Information System (INIS)

Schmidt, F.; Yevick, D.

1997-01-01

We present a general technique for constructing nonlocal transparent boundary conditions for one-dimensional Schroedinger-type equations. Our method supplies boundary conditions for the θ-family of implicit one-step discretizations of Schroedinger's equation in time. The use of Mikusinski's operator approach in time avoids direct and inverse transforms between time and frequency domains and thus implements the boundary conditions in a direct manner. 14 refs., 9 figs

Low profile conformal antenna arrays on high impedance substrate

CERN Document Server

Singh, Hema; Jha, Rakesh Mohan

2016-01-01

This book presents electromagnetic (EM) design and analysis of dipole antenna array over high impedance substrate (HIS). HIS is a preferred substrate for low-profile antenna design, owing to its unique boundary conditions. Such substrates permit radiating elements to be printed on them without any disturbance in the radiation characteristics. Moreover HIS provides improved impedance matching, enhanced bandwidth, and increased broadside directivity owing to total reflection from the reactive surface and high input impedance. This book considers different configurations of HIS for array design on planar and non-planar high-impedance surfaces. Results are presented for cylindrical dipole, printed dipole, and folded dipole over single- and double-layered square-patch-based HIS and dogbone-based HIS. The performance of antenna arrays is analyzed in terms of performance parameters such as return loss and radiation pattern. The design presented shows acceptable return loss and mainlobe gain of radiation pattern. Thi...

Task reports on developing techniques for scattering by 3D composite structures and to generate new solutions in diffraction theory using higher order boundary conditions

Science.gov (United States)

Volakis, John L.

1991-01-01

There are two tasks described in this report. First, an extension of a two dimensional formulation is presented for a three dimensional body of revolution. A Fourier series expansion of the vector electric and magnetic fields is employed to reduce the dimensionality of the system, and an exact boundary condition is employed to terminate the mesh. The mesh termination boundary is chosen such that it leads to convolutional boundary operators for low O(n) memory demand. Second, rigorous uniform geometrical theory of diffraction (UTD) diffraction coefficients are presented for a coated convex cylinder simulated with generalized impedance boundary conditions. Ray solutions are obtained which remain valid in the transition region and reduce uniformly those in the deep lit and shadow regions. A uniform asymptotic solution is also presented for observations in the close vicinity of the cylinder.

Temperature jump boundary conditions in radiation diffusion

International Nuclear Information System (INIS)

Alonso, C.T.

1976-12-01

The radiation diffusion approximation greatly simplifies radiation transport problems. Yet the application of this method has often been unnecessarily restricted to optically thick regions, or has been extended through the use of such ad hoc devices as flux limiters. The purpose of this paper is to review and draw attention to the use of the more physically appropriate temperature jump boundary conditions for extending the range of validity of the diffusion approximation. Pioneering work has shown that temperature jump boundary conditions remove the singularity in flux that occurs in ordinary diffusion at small optical thicknesses. In this review paper Deissler's equations for frequency-dependent jump boundary conditions are presented and specific geometric examples are calculated analytically for steady state radiation transfer. When jump boundary conditions are applied to radiation diffusion, they yield exact solutions which are naturally flux- limited and geometry-corrected. We believe that the presence of temperature jumps on source boundaries is probably responsible in some cases for the past need for imposing ad hoc flux-limiting constraints on pure diffusion solutions. The solution for transfer between plane slabs, which is exact to all orders of optical thickness, also provides a useful tool for studying the accuracy of computer codes

Boundary condition histograms for modulated phases

International Nuclear Information System (INIS)

Benakli, M.; Gabay, M.; Saslow, W.M.

1997-11-01

Boundary conditions strongly affect the results of numerical computations for finite size inhomogeneous or incommensurate structures. We present a method which allows to deal with this problem, both for ground state and for critical properties: it combines fluctuating boundary conditions and specific histogram techniques. Our approach concerns classical as well as quantum systems. In particular, current-current correlation functions, which probe large scale coherence of the states, can be accurately evaluated. We illustrate our method on a frustrated two dimensional XY model. (author)

Casimir pistons with general boundary conditions

Directory of Open Access Journals (Sweden)

Guglielmo Fucci

2015-02-01

Full Text Available In this work we analyze the Casimir energy and force for a scalar field endowed with general self-adjoint boundary conditions propagating in a higher dimensional piston configuration. The piston is constructed as a direct product I×N, with I=[0,L]⊂R and N a smooth, compact Riemannian manifold with or without boundary. The study of the Casimir energy and force for this configuration is performed by employing the spectral zeta function regularization technique. The obtained analytic results depend explicitly on the spectral zeta function associated with the manifold N and the parameters describing the general boundary conditions imposed. These results are then specialized to the case in which the manifold N is a d-dimensional sphere.

Modelling classroom conditions with different boundary conditions

DEFF Research Database (Denmark)

Marbjerg, Gerd Høy; Jeong, Cheol-Ho; Brunskog, Jonas

2014-01-01

A model that combines image source modelling and acoustical radiosity with complex boundary condition, thus including phase shifts on reflection has been developed. The model is called PARISM (Phased Acoustical Radiosity and Image Source Model). It has been developed in order to be able to model...

Absorbing boundary conditions for Einstein's field equations

Energy Technology Data Exchange (ETDEWEB)

Sarbach, Olivier [Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Edificio C-3, Cd. Universitaria. C. P. 58040 Morelia, Michoacan (Mexico)

2007-11-15

A common approach for the numerical simulation of wave propagation on a spatially unbounded domain is to truncate the domain via an artificial boundary, thus forming a finite computational domain with an outer boundary. Absorbing boundary conditions must then be specified at the boundary such that the resulting initial-boundary value problem is well posed and such that the amount of spurious reflection is minimized. In this article, we review recent results on the construction of absorbing boundary conditions in General Relativity and their application to numerical relativity.

Trickle-down boundary conditions in aeolian dune-field pattern formation

Science.gov (United States)

Ewing, R. C.; Kocurek, G.

2015-12-01

One the one hand, wind-blown dune-field patterns emerge within the overarching boundary conditions of climate, tectonics and eustasy implying the presence of these signals in the aeolian geomorphic and stratigraphic record. On the other hand, dune-field patterns are a poster-child of self-organization, in which autogenic processes give rise to patterned landscapes despite remarkable differences in the geologic setting (i.e., Earth, Mars and Titan). How important are climate, tectonics and eustasy in aeolian dune field pattern formation? Here we develop the hypothesis that, in terms of pattern development, dune fields evolve largely independent of the direct influence of 'system-scale' boundary conditions, such as climate, tectonics and eustasy. Rather, these boundary conditions set the stage for smaller-scale, faster-evolving 'event-scale' boundary conditions. This 'trickle-down' effect, in which system-scale boundary conditions indirectly influence the event scale boundary conditions provides the uniqueness and richness of dune-field patterned landscapes. The trickle-down effect means that the architecture of the stratigraphic record of dune-field pattern formation archives boundary conditions, which are spatially and temporally removed from the overarching geologic setting. In contrast, the presence of an aeolian stratigraphic record itself, reflects changes in system-scale boundary conditions that drive accumulation and preservation of aeolian strata.

Integrable boundary conditions and modified Lax equations

International Nuclear Information System (INIS)

Avan, Jean; Doikou, Anastasia

2008-01-01

We consider integrable boundary conditions for both discrete and continuum classical integrable models. Local integrals of motion generated by the corresponding 'transfer' matrices give rise to time evolution equations for the initial Lax operator. We systematically identify the modified Lax pairs for both discrete and continuum boundary integrable models, depending on the classical r-matrix and the boundary matrix

Energy principle with included boundary conditions

International Nuclear Information System (INIS)

Lehnert, B.

1994-01-01

Earlier comments by the author on the limitations of the classical form of the extended energy principle are supported by a complementary analysis on the potential energy change arising from free-boundary displacements of a magnetically confined plasma. In the final formulation of the extended principle, restricted displacements, satisfying pressure continuity by means of plasma volume currents in a thin boundary layer, are replaced by unrestricted (arbitrary) displacements which can give rise to induced surface currents. It is found that these currents contribute to the change in potential energy, and that their contribution is not taken into account by such a formulation. A general expression is further given for surface currents induced by arbitrary displacements. The expression is used to reformulate the energy principle for the class of displacements which satisfy all necessary boundary conditions, including that of the pressure balance. This makes a minimization procedure of the potential energy possible, for the class of all physically relevant test functions which include the constraints imposed by the boundary conditions. Such a procedure is also consistent with a corresponding variational calculus. (Author)

Integrability and boundary conditions of supersymmetric systems

International Nuclear Information System (INIS)

Yue Ruihong; Liang Hong

1996-01-01

By studying the solutions of the reflection equations, we find out a series of integrable supersymmetric systems with different boundary conditions. The Hamiltonian contains four free parameters which describe the contribution of the boundary terms

Wearable sensors for patient-specific boundary shape estimation to improve the forward model for electrical impedance tomography (EIT) of neonatal lung function.

Science.gov (United States)

Khor, Joo Moy; Tizzard, Andrew; Demosthenous, Andreas; Bayford, Richard

2014-06-01

Electrical impedance tomography (EIT) could be significantly advantageous to continuous monitoring of lung development in newborn and, in particular, preterm infants as it is non-invasive and safe to use within the intensive care unit. It has been demonstrated that accurate boundary form of the forward model is important to minimize artefacts in reconstructed electrical impedance images. This paper presents the outcomes of initial investigations for acquiring patient-specific thorax boundary information using a network of flexible sensors that imposes no restrictions on the patient's normal breathing and movements. The investigations include: (1) description of the basis of the reconstruction algorithms, (2) tests to determine a minimum number of bend sensors, (3) validation of two approaches to reconstruction and (4) an example of a commercially available bend sensor and its performance. Simulation results using ideal sensors show that, in the worst case, a total shape error of less than 6% with respect to its total perimeter can be achieved.

Boundary conditions in rational conformal field theories

International Nuclear Information System (INIS)

Behrend, Roger E.; Pearce, Paul A.; Petkova, Valentina B.; Zuber, Jean-Bernard

2000-01-01

We develop further the theory of Rational Conformal Field Theories (RCFTs) on a cylinder with specified boundary conditions emphasizing the role of a triplet of algebras: the Verlinde, graph fusion and Pasquier algebras. We show that solving Cardy's equation, expressing consistency of a RCFT on a cylinder, is equivalent to finding integer valued matrix representations of the Verlinde algebra. These matrices allow us to naturally associate a graph G to each RCFT such that the conformal boundary conditions are labelled by the nodes of G. This approach is carried to completion for sl(2) theories leading to complete sets of conformal boundary conditions, their associated cylinder partition functions and the A-D-E classification. We also review the current status for WZW sl(3) theories. Finally, a systematic generalisation of the formalism of Cardy-Lewellen is developed to allow for multiplicities arising from more general representations of the Verlinde algebra. We obtain information on the bulk-boundary coefficients and reproduce the relevant algebraic structures from the sewing constraints

Einstein boundary conditions for the 3+1 Einstein equations

International Nuclear Information System (INIS)

Frittelli, Simonetta; Gomez, Roberto

2003-01-01

In the 3+1 framework of the Einstein equations for the case of a vanishing shift vector and arbitrary lapse, we calculate explicitly the four boundary equations arising from the vanishing of the projection of the Einstein tensor along the normal to the boundary surface of the initial-boundary value problem. Such conditions take the form of evolution equations along (as opposed to across) the boundary for certain components of the extrinsic curvature and for certain space derivatives of the three-metric. We argue that, in general, such boundary conditions do not follow necessarily from the evolution equations and the initial data, but need to be imposed on the boundary values of the fundamental variables. Using the Einstein-Christoffel formulation, which is strongly hyperbolic, we show how three of the boundary equations up to linear combinations should be used to prescribe the values of some incoming characteristic fields. Additionally, we show that the fourth one imposes conditions on some outgoing fields

On the Boussinesq-Burgers equations driven by dynamic boundary conditions

Science.gov (United States)

Zhu, Neng; Liu, Zhengrong; Zhao, Kun

2018-02-01

We study the qualitative behavior of the Boussinesq-Burgers equations on a finite interval subject to the Dirichlet type dynamic boundary conditions. Assuming H1 ×H2 initial data which are compatible with boundary conditions and utilizing energy methods, we show that under appropriate conditions on the dynamic boundary data, there exist unique global-in-time solutions to the initial-boundary value problem, and the solutions converge to the boundary data as time goes to infinity, regardless of the magnitude of the initial data.

Quadratic Functionals with General Boundary Conditions

International Nuclear Information System (INIS)

Dosla, Z.; Dosly, O.

1997-01-01

The purpose of this paper is to give the Reid 'Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in terms of Riccati equation solutions

On filter boundary conditions in topology optimization

DEFF Research Database (Denmark)

Clausen, Anders; Andreassen, Erik

2017-01-01

Most research papers on topology optimization involve filters for regularization. Typically, boundary effects from the filters are ignored. Despite significant drawbacks the inappropriate homogeneous Neumann boundary conditions are used, probably because they are trivial to implement. In this paper...

Boundary conditions for the gravitational field

International Nuclear Information System (INIS)

Winicour, Jeffrey

2012-01-01

A review of the treatment of boundaries in general relativity is presented with the emphasis on application to the formulations of Einstein's equations used in numerical relativity. At present, it is known how to treat boundaries in the harmonic formulation of Einstein's equations and a tetrad formulation of the Einstein-Bianchi system. However, a universal approach valid for other formulations is not in hand. In particular, there is no satisfactory boundary theory for the 3+1 formulations which have been highly successful in binary black hole simulation. I discuss the underlying problems that make the initial-boundary-value problem much more complicated than the Cauchy problem. I review the progress that has been made and the important open questions that remain. Science is a differential equation. Religion is a boundary condition. (Alan Turing, quoted in J D Barrow, 'Theories of Everything') (topical review)

Asymptotic boundary conditions for dissipative waves: General theory

Science.gov (United States)

Hagstrom, Thomas

1990-01-01

An outstanding issue in the computational analysis of time dependent problems is the imposition of appropriate radiation boundary conditions at artificial boundaries. Accurate conditions are developed which are based on the asymptotic analysis of wave propagation over long ranges. Employing the method of steepest descents, dominant wave groups are identified and simple approximations to the dispersion relation are considered in order to derive local boundary operators. The existence of a small number of dominant wave groups may be expected for systems with dissipation. Estimates of the error as a function of domain size are derived under general hypotheses, leading to convergence results. Some practical aspects of the numerical construction of the asymptotic boundary operators are also discussed.

Asymptotic boundary conditions for dissipative waves - General theory

Science.gov (United States)

Hagstrom, Thomas

1991-01-01

An outstanding issue in computational analysis of time dependent problems is the imposition of appropriate radiation boundary conditions at artificial boundaries. Accurate conditions are developed which are based on the asymptotic analysis of wave propagation over long ranges. Employing the method of steepest descents, dominant wave groups are identified and simple approximations to the dispersion relation are considered in order to derive local boundary operators. The existence of a small number of dominant wave groups may be expected for systems with dissipation. Estimates of the error as a function of domain size are derived under general hypotheses, leading to convergence results. Some practical aspects of the numerical construction of the asymptotic boundary operators are also discussed.

Boundary conditions and subelliptic estimates for geometric Kramers-Fokker-Planck operators on manifolds with boundaries

CERN Document Server

Nier, Francis

2018-01-01

This article is concerned with the maximal accretive realizations of geometric Kramers-Fokker-Planck operators on manifolds with boundaries. A general class of boundary conditions is introduced which ensures the maximal accretivity and some global subelliptic estimates. Those estimates imply nice spectral properties as well as exponential decay properties for the associated semigroup. Admissible boundary conditions cover a wide range of applications for the usual scalar Kramer-Fokker-Planck equation or Bismut's hypoelliptic laplacian.

Experimental test of proximity effect theories by surface impedance measurements on the Pb-Sn system

International Nuclear Information System (INIS)

Hook, J.R.; Battilana, J.A.

1976-01-01

The proximity effect in the Pb-Sn system in zero magnetic field has been studied by measuring the surface impedance at 3 GHz of a thin film of tin evaporated on to a bulk lead substrate. The results are compared with the predictions of theories of the proximity effect. It is found that good agreement can be obtained by using a theory due to Hook and Waldram of the spatial variation of the superconducting order parameter Δ inside each metal together with suitable boundary conditions on Δ at the interface between the metals. The required boundary conditions are a generalization to the case of non-zero electron reflection at the interface of the boundary conditions given by Zaitsev for the Ginsburg-Landau equation. (author)

Adaptive boundary conditions for exterior flow problems

CERN Document Server

Boenisch, V; Wittwer, S

2003-01-01

We consider the problem of solving numerically the stationary incompressible Navier-Stokes equations in an exterior domain in two dimensions. This corresponds to studying the stationary fluid flow past a body. The necessity to truncate for numerical purposes the infinite exterior domain to a finite domain leads to the problem of finding appropriate boundary conditions on the surface of the truncated domain. We solve this problem by providing a vector field describing the leading asymptotic behavior of the solution. This vector field is given in the form of an explicit expression depending on a real parameter. We show that this parameter can be determined from the total drag exerted on the body. Using this fact we set up a self-consistent numerical scheme that determines the parameter, and hence the boundary conditions and the drag, as part of the solution process. We compare the values of the drag obtained with our adaptive scheme with the results from using traditional constant boundary conditions. Computati...

Lyapunov Based Estimation of Flight Stability Boundary under Icing Conditions

Directory of Open Access Journals (Sweden)

Binbin Pei

2017-01-01

Full Text Available Current fight boundary of the envelope protection in icing conditions is usually defined by the critical values of state parameters; however, such method does not take the interrelationship of each parameter and the effect of the external disturbance into consideration. This paper proposes constructing the stability boundary of the aircraft in icing conditions through analyzing the region of attraction (ROA around the equilibrium point. Nonlinear icing effect model is proposed according to existing wind tunnel test results. On this basis, the iced polynomial short period model can be deduced further to obtain the stability boundary under icing conditions using ROA analysis. Simulation results for a series of icing severity demonstrate that, regardless of the icing severity, the boundary of the calculated ROA can be treated as an estimation of the stability boundary around an equilibrium point. The proposed methodology is believed to be a promising way for ROA analysis and stability boundary construction of the aircraft in icing conditions, and it will provide theoretical support for multiple boundary protection of icing tolerant flight.

Minimization of heat slab nodes with higher order boundary conditions

International Nuclear Information System (INIS)

Solbrig, C.W.

1992-01-01

The accuracy of a numerical solution can be limited by the numerical approximation to the boundary conditions rather than the accuracy of the equations which describe the interior. The study presented in this paper compares the results from two different numerical formulations of the convective boundary condition on the face of a heat transfer slab. The standard representation of the boundary condition in a test problem yielded an unacceptable error even when the heat transfer slab was partitioned into over 300 nodes. A higher order boundary condition representation was obtained by using a second order approximation for the first derivative at the boundary and combining it with the general equation used for inner nodes. This latter formulation produced reasonable results when as few as ten nodes were used

Transport synthetic acceleration with opposing reflecting boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Zika, M R; Adams, M L

2000-02-01

The transport synthetic acceleration (TSA) scheme is extended to problems with opposing reflecting boundary conditions. This synthetic method employs a simplified transport operator as its low-order approximation. A procedure is developed that allows the use of the conjugate gradient (CG) method to solve the resulting low-order system of equations. Several well-known transport iteration algorithms are cast in a linear algebraic form to show their equivalence to standard iterative techniques. Source iteration in the presence of opposing reflecting boundary conditions is shown to be equivalent to a (poorly) preconditioned stationary Richardson iteration, with the preconditioner defined by the method of iterating on the incident fluxes on the reflecting boundaries. The TSA method (and any synthetic method) amounts to a further preconditioning of the Richardson iteration. The presence of opposing reflecting boundary conditions requires special consideration when developing a procedure to realize the CG method for the proposed system of equations. The CG iteration may be applied only to symmetric positive definite matrices; this condition requires the algebraic elimination of the boundary angular corrections from the low-order equations. As a consequence of this elimination, evaluating the action of the resulting matrix on an arbitrary vector involves two transport sweeps and a transmission iteration. Results of applying the acceleration scheme to a simple test problem are presented.

Revisit boundary conditions for the self-adjoint angular flux formulation

Energy Technology Data Exchange (ETDEWEB)

Wang, Yaqi [Idaho National Lab. (INL), Idaho Falls, ID (United States); Gleicher, Frederick N. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-03-01

We revisit the boundary conditions for SAAF. We derived the equivalent parity variational form ready for coding up. The more rigorous approach of evaluating odd parity should be solving the odd parity equation coupled with the even parity. We proposed a symmetric reflecting boundary condition although neither positive definiteness nor even-odd decoupling is achieved. A simple numerical test verifies the validity of these boundary conditions.

Evaluation of general non-reflecting boundary conditions for industrial CFD applications

Science.gov (United States)

Basara, Branislav; Frolov, Sergei; Lidskii, Boris; Posvyanskii, Vladimir

2007-11-01

The importance of having proper boundary conditions for the calculation domain is a known issue in Computational Fluid Dynamics (CFD). In many situations, it is very difficult to define a correct boundary condition. The flow may enter and leave the computational domain at the same time and at the same boundary. In such circumstances, it is important that numerical implementation of boundary conditions enforces certain physical constraints leading to correct results which then ensures a better convergence rate. The aim of this paper is to evaluate recently proposed non-reflecting boundary conditions (Frolov et al., 2001, Advances in Chemical Propulsion) on industrial CFD applications. Derivation of the local non-reflecting boundary conditions at the open boundary is based on finding the solution of linearized Euler equations vanishing at infinity for both incompressible and compressible formulations. This is implemented into the in-house CFD package AVL FIRE and some numerical details will be presented as well. The key applications in this paper are from automotive industry, e.g. an external car aerodynamics, an intake port, etc. The results will show benefits of using effective non-reflecting boundary conditions.

Influence of acoustic dominant mode propagation in a trifurcated lined duct with different impedances

International Nuclear Information System (INIS)

Ayub, M; Tiwana, M H; Mann, A B

2010-01-01

In this study, we analyzed the diffraction of the acoustic dominant mode in a parallel-plate trifurcated waveguide with normal impedance boundary conditions in the case where surface impedances of the upper and lower infinite plates are different from each other. The acoustic dominant mode is incident in a soft/hard semi-infinite duct located symmetrically in the infinite lined duct. The solution of the boundary value problem using Fourier transform leads to two simultaneous modified Wiener-Hopf equations that are uncoupled using the pole removal technique. Two infinite sets of unknown coefficients are involved in the solution, which satisfy two infinite systems of linear algebraic equations. These systems are solved numerically. The new kernel functions are factorized. Some graphical results showing the influence of sundry parameters of interest on the reflection coefficient are presented.

Computational method for estimating boundary of abdominal subcutaneous fat for absolute electrical impedance tomography.

Science.gov (United States)

Yamaguchi, Tohru F; Okamoto, Yoshiwo

2018-01-01

Abdominal fat accumulation is considered an essential indicator of human health. Electrical impedance tomography has considerable potential for abdominal fat imaging because of the low specific conductivity of human body fat. In this paper, we propose a robust reconstruction method for high-fidelity conductivity imaging by abstraction of the abdominal cross section using a relatively small number of parameters. Toward this end, we assume homogeneous conductivity in the abdominal subcutaneous fat area and characterize its geometrical shape by parameters defined as the ratio of the distance from the center to boundary of subcutaneous fat to the distance from the center to outer boundary in 64 equiangular directions. To estimate the shape parameters, the sensitivity of the noninvasively measured voltages with respect to the shape parameters is formulated for numerical optimization. Numerical simulations are conducted to demonstrate the validity of the proposed method. A 3-dimensional finite element method is used to construct a computer model of the human abdomen. The inverse problems of shape parameters and conductivities are solved concurrently by iterative forward and inverse calculations. As a result, conductivity images are reconstructed with a small systemic error of less than 1% for the estimation of the subcutaneous fat area. A novel method is devised for estimating the boundary of the abdominal subcutaneous fat. The fidelity of the overall reconstructed image to the reference image is significantly improved. The results demonstrate the possibility of realization of an abdominal fat scanner as a low-cost, radiation-free medical device. Copyright © 2017 John Wiley & Sons, Ltd.

Open boundary condition, Wilson flow and the scalar glueball mass

International Nuclear Information System (INIS)

Chowdhury, Abhishek; Harindranath, A.; Maiti, Jyotirmoy

2014-01-01

A major problem with periodic boundary condition on the gauge fields used in current lattice gauge theory simulations is the trapping of topological charge in a particular sector as the continuum limit is approached. To overcome this problem open boundary condition in the temporal direction has been proposed recently. One may ask whether open boundary condition can reproduce the observables calculated with periodic boundary condition. In this work we find that the extracted lowest glueball mass using open and periodic boundary conditions at the same lattice volume and lattice spacing agree for the range of lattice scales explored in the range 3 GeV≤(1/a)≤5 GeV. The problem of trapping is overcome to a large extent with open boundary and we are able to extract the glueball mass at even larger lattice scale ≈ 5.7 GeV. To smoothen the gauge fields we have used recently proposed Wilson flow which, compared to HYP smearing, exhibits better systematics in the extraction of glueball mass. The extracted glueball mass shows remarkable insensitivity to the lattice spacings in the range explored in this work, 3 GeV≤(1/a)≤5.7 GeV.

Entropy Stability and the No-Slip Wall Boundary Condition

KAUST Repository

Svä rd, Magnus; Carpenter, Mark H.; Parsani, Matteo

2018-01-01

We present an entropy stable numerical scheme subject to no-slip wall boundary conditions. To enforce entropy stability only the no-penetration boundary condition and a temperature condition are needed at a wall, and this leads to an L bound on the conservative variables. In this article, we take the next step and design a finite difference scheme that also bounds the velocity gradients. This necessitates the use of the full no-slip conditions.

Entropy Stability and the No-Slip Wall Boundary Condition

KAUST Repository

Svärd, Magnus

2018-01-18

We present an entropy stable numerical scheme subject to no-slip wall boundary conditions. To enforce entropy stability only the no-penetration boundary condition and a temperature condition are needed at a wall, and this leads to an L bound on the conservative variables. In this article, we take the next step and design a finite difference scheme that also bounds the velocity gradients. This necessitates the use of the full no-slip conditions.

Exploring exotic states with twisted boundary conditions

International Nuclear Information System (INIS)

Agadjanov, Dimitri

2017-01-01

he goal of this thesis is to develop methods to study the nature and properties of exotic hadrons from lattice simulations. The main focus lies in the application of twisted boundary conditions. The thesis consists of a general introduction and the collection of three papers, represented respectively in three chapters. The introduction of the thesis reviews the theoretical background, which is further used in the rest of the thesis. Further implementing partially twisted boundary conditions in the scalar sector of lattice QCD is studied. Then we develop a method to study the content of the exotic hadrons by determining the wave function renormalization constant from lattice simulations, exploiting the dependence of the spectrum on the twisted boundary conditions. The final chapter deals with a novel method to study the multi-channel scattering problem in a finite volume, which is relevant for exotic states. Its key idea is to extract the complex hadron-hadron optical potential, avoiding the difficulties, associated with the solution of the multi-channel Luescher equation.

Exploring exotic states with twisted boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Agadjanov, Dimitri

2017-09-11

he goal of this thesis is to develop methods to study the nature and properties of exotic hadrons from lattice simulations. The main focus lies in the application of twisted boundary conditions. The thesis consists of a general introduction and the collection of three papers, represented respectively in three chapters. The introduction of the thesis reviews the theoretical background, which is further used in the rest of the thesis. Further implementing partially twisted boundary conditions in the scalar sector of lattice QCD is studied. Then we develop a method to study the content of the exotic hadrons by determining the wave function renormalization constant from lattice simulations, exploiting the dependence of the spectrum on the twisted boundary conditions. The final chapter deals with a novel method to study the multi-channel scattering problem in a finite volume, which is relevant for exotic states. Its key idea is to extract the complex hadron-hadron optical potential, avoiding the difficulties, associated with the solution of the multi-channel Luescher equation.

Characteristic impedance of a microchannel with two immiscible microfluids

Science.gov (United States)

Jaramillo Raquejo, Daniela

2014-05-01

Consider the case of a microcapillary of radius R with two microfluidic immiscible. The micro-capillary region 0 expressed in terms of Bessel functions. Similarly, the characteristic impedance of the microcapillary is expressed by a complex formula Bessel functions. Obtain the analytical results are important for designing engineering microdevices with applications in pharmaceutical, food engineering, nanotechnology and biotechnology in general in particular. For future research it is interesting to consider the case of boundary conditions with memory effects.

Divergence-Free Wavelets on the Hypercube : General Boundary Conditions

NARCIS (Netherlands)

Stevenson, R.

2016-01-01

On the n-dimensional hypercube, for given k∈N, wavelet Riesz bases are constructed for the subspace of divergence-free vector fields of the Sobolev space Hk((0,1)n)n with general homogeneous Dirichlet boundary conditions, including slip or no-slip boundary conditions. Both primal and suitable dual

Spectral asymmetry for bag boundary conditions

International Nuclear Information System (INIS)

Beneventano, C G; Santangelo, E M; Wipf, A

2002-01-01

We give an expression, in terms of boundary spectral functions, for the spectral asymmetry of the Euclidean Dirac operator in two dimensions, when its domain is determined by local boundary conditions and the manifold is of product type. As an application, we explicitly evaluate the asymmetry in the case of a finite-length cylinder and check that the outcome is consistent with our general result. Finally, we study the asymmetry in a disc, which is a non-product case, and propose an interpretation

Diffusive growth of a single droplet with three different boundary conditions

Science.gov (United States)

Tavassoli, Z.; Rodgers, G. J.

2000-02-01

We study a single, motionless three-dimensional droplet growing by adsorption of diffusing monomers on a 2D substrate. The diffusing monomers are adsorbed at the aggregate perimeter of the droplet with different boundary conditions. Models with both an adsorption boundary condition and a radiation boundary condition, as well as a phenomenological model, are considered and solved in a quasistatic approximation. The latter two models allow particle detachment. In the short time limit, the droplet radius grows as a power of the time with exponents of 1/4, 1/2 and 3/4 for the models with adsorption, radiation and phenomenological boundary conditions, respectively. In the long time limit a universal growth rate as $[t/\\ln(t)]^{1/3}$ is observed for the radius of the droplet for all models independent of the boundary conditions. This asymptotic behaviour was obtained by Krapivsky \\cite{krapquasi} where a similarity variable approach was used to treat the growth of a droplet with an adsorption boundary condition based on a quasistatic approximation. Another boundary condition with a constant flux of monomers at the aggregate perimeter is also examined. The results exhibit a power law growth rate with an exponent of 1/3 for all times.

Classically integrable boundary conditions for symmetric-space sigma models

International Nuclear Information System (INIS)

MacKay, N.J.; Young, C.A.S.

2004-01-01

We investigate boundary conditions for the non-linear sigma model on the compact symmetric space G/H. The Poisson brackets and the classical local conserved charges necessary for integrability are preserved by boundary conditions which correspond to involutions which commute with the involution defining H. Applied to SO(3)/SO(2), the non-linear sigma model on S 2 , these yield the great circles as boundary submanifolds. Applied to GxG/G, they reproduce known results for the principal chiral model

A suitable boundary condition for bounded plasma simulation without sheath resolution

International Nuclear Information System (INIS)

Parker, S.E.; Procassini, R.J.; Birdsall, C.K.; Cohen, B.I.

1993-01-01

We have developed a technique that allows for a sheath boundary layer without having to resolve the inherently small space and time scales of the sheath region. We refer to this technique as the logical sheath boundary condition. This boundary condition, when incorporated into a direct-implicit particle code, permits large space- and time-scale simulations of bounded systems, which would otherwise be impractical on current supercomputers. The lack of resolution of the collector sheath potential drop obtained from conventional implicit simulations at moderate values of ω pe Δt and Δz/λ De provides the motivation for the development of the logical sheath boundary condition. The algorithm for use of the logical sheath boundary condition in a particle simulation is presented. Results from simulations which use the logical sheath boundary condition are shown to compare reasonably well with those from an analytic theory and simulations in which the sheath is resolved

Nested Bethe Ansatz for Spin Ladder Model with Open Boundary Conditions

International Nuclear Information System (INIS)

Wu Junfang; Zhang Chunmin; Yue Ruihong; Li Runling

2005-01-01

The nested Bethe ansatz (BA) method is applied to find the eigenvalues and the eigenvectors of the transfer matrix for spin-ladder model with open boundary conditions. Based on the reflection equation, we find the general diagonal solution, which determines the general boundary interaction in the Hamiltonian. We introduce the spin-ladder model with open boundary conditions. By finding the solution K ± of the reflection equation which determines the nontrivial boundary terms in the Hamiltonian, we diagonalize the transfer matrix of the spin-ladder model with open boundary conditions in the framework of nested BA.

Effective Stress Law in Unconventional Reservoirs under Different Boundary Conditions

Science.gov (United States)

Saurabh, S.; Harpalani, S.

2017-12-01

Unconventional reservoirs have attracted a great deal of research interest worldwide during the past two decades. Low permeability and specialized techniques required to exploit these resources present opportunities for improvement in both production rates and ultimate recovery. Understanding subsurface stress modifications and permeability evolution are valuable when evaluating the prospects of unconventional reservoirs. These reservoir properties are functions of effective stress. As a part of this study, effective stress law, specifically the variation of anisotropic Biot's coefficient under various boundary conditions believed to exist in gas reservoirs by different researchers, has been established. Pressure-dependent-permeability (PdK) experiments were carried out on San Juan coal under different boundary conditions, that is, uniaxial strain condition and constant volume condition. Stress and strain in the vertical and horizontal directions were monitored throughout the experiment. Data collected during the experiments was used to determine the Biot's coefficient in vertical and horizontal directions under these two boundary conditions, treating coal as transversely isotropic. The variation of Biot's coefficient was found to be well correlated with the variation in coal permeability. Based on the estimated values of Biot's coefficients, a theory of variation in its value is presented for other boundary conditions. The findings of the study shed light on the inherent behavior of Biot's coefficient under different reservoir boundary conditions. This knowledge can improve the modeling work requiring estimation of effective stress in reservoirs, such as, pressure-/stress- dependent permeability. At the same time, if the effective stresses are known with more certainty by other methods, it enables assessment of the unknown reservoir boundary conditions.

An(1) affine Toda field theories with integrable boundary conditions revisited

International Nuclear Information System (INIS)

Doikou, Anastasia

2008-01-01

Generic classically integrable boundary conditions for the A n (1) affine Toda field theories (ATFT) are investigated. The present analysis rests primarily on the underlying algebra, defined by the classical version of the reflection equation. We use as a prototype example the first non-trivial model of the hierarchy i.e. the A 2 (1) ATFT, however our results may be generalized for any A n (1) (n > 1). We assume here two distinct types of boundary conditions called some times soliton preserving (SP), and soliton non-preserving (SNP) associated to two distinct algebras, i.e. the reflection algebra and the (q) twisted Yangian respectively. The boundary local integrals of motion are then systematically extracted from the asymptotic expansion of the associated transfer matrix. In the case of SNP boundary conditions we recover previously known results. The other type of boundary conditions (SP), associated to the reflection algebra, are novel in this context and lead to a different set of conserved quantities that depend on free boundary parameters. It also turns out that the number of local integrals of motion for SP boundary conditions is 'double' compared to those of the SNP case.

Entropy Stable Wall Boundary Conditions for the Compressible Navier-Stokes Equations

Science.gov (United States)

Parsani, Matteo; Carpenter, Mark H.; Nielsen, Eric J.

2014-01-01

Non-linear entropy stability and a summation-by-parts framework are used to derive entropy stable wall boundary conditions for the compressible Navier-Stokes equations. A semi-discrete entropy estimate for the entire domain is achieved when the new boundary conditions are coupled with an entropy stable discrete interior operator. The data at the boundary are weakly imposed using a penalty flux approach and a simultaneous-approximation-term penalty technique. Although discontinuous spectral collocation operators are used herein for the purpose of demonstrating their robustness and efficacy, the new boundary conditions are compatible with any diagonal norm summation-by-parts spatial operator, including finite element, finite volume, finite difference, discontinuous Galerkin, and flux reconstruction schemes. The proposed boundary treatment is tested for three-dimensional subsonic and supersonic flows. The numerical computations corroborate the non-linear stability (entropy stability) and accuracy of the boundary conditions.

On boundary conditions in three-dimensional AdS gravity

Energy Technology Data Exchange (ETDEWEB)

Miskovic, Olivera [Instituto de Fisica, P. Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile) and Departamento de Fisica, P. Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)]. E-mail: olivera.miskovic@ucv.cl; Olea, Rodrigo [Departamento de Fisica, P. Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile) and Centro Multidisciplinar de Astrofisica, CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisbon (Portugal)]. E-mail: rolea@fisica.ist.utl.pt

2006-09-07

A finite action principle for three-dimensional gravity with negative cosmological constant, based on a boundary condition for the asymptotic extrinsic curvature, is considered. The bulk action appears naturally supplemented by a boundary term that is one half the Gibbons-Hawking term, that makes the Euclidean action and the Noether charges finite without additional Dirichlet counterterms. The consistency of this boundary condition with the Dirichlet problem in AdS gravity and the Chern-Simons formulation in three dimensions, and its suitability for the higher odd-dimensional case, are also discussed.

Automated Boundary Conditions for Wind Tunnel Simulations

Science.gov (United States)

Carlson, Jan-Renee

2018-01-01

Computational fluid dynamic (CFD) simulations of models tested in wind tunnels require a high level of fidelity and accuracy particularly for the purposes of CFD validation efforts. Considerable effort is required to ensure the proper characterization of both the physical geometry of the wind tunnel and recreating the correct flow conditions inside the wind tunnel. The typical trial-and-error effort used for determining the boundary condition values for a particular tunnel configuration are time and computer resource intensive. This paper describes a method for calculating and updating the back pressure boundary condition in wind tunnel simulations by using a proportional-integral-derivative controller. The controller methodology and equations are discussed, and simulations using the controller to set a tunnel Mach number in the NASA Langley 14- by 22-Foot Subsonic Tunnel are demonstrated.

Boundary conditions for the numerical solution of elliptic equations in exterior regions

International Nuclear Information System (INIS)

Bayliss, A.; Gunzburger, M.; Turkel, E.

1982-01-01

Elliptic equations in exterior regions frequently require a boundary condition at infinity to ensure the well-posedness of the problem. Examples of practical applications include the Helmholtz equation and Laplace's equation. Computational procedures based on a direct discretization of the elliptic problem require the replacement of the condition at infinity by a boundary condition on a finite artificial surface. Direct imposition of the condition at infinity along the finite boundary results in large errors. A sequence of boundary conditions is developed which provides increasingly accurate approximations to the problem in the infinite domain. Estimates of the error due to the finite boundary are obtained for several cases. Computations are presented which demonstrate the increased accuracy that can be obtained by the use of the higher order boundary conditions. The examples are based on a finite element formulation but finite difference methods can also be used

On domain wall boundary conditions for the XXZ spin Hamiltonian

DEFF Research Database (Denmark)

Orlando, Domenico; Reffert, Susanne; Reshetikhin, Nicolai

In this note, we derive the spectrum of the infinite quantum XXZ spin chain with domain wall boundary conditions. The eigenstates are constructed as limits of Bethe states for the finite XXZ spin chain with quantum sl(2) invariant boundary conditions....

Solution of a Problem Linear Plane Elasticity with Mixed Boundary Conditions by the Method of Boundary Integrals

Directory of Open Access Journals (Sweden)

Nahed S. Hussein

2014-01-01

Full Text Available A numerical boundary integral scheme is proposed for the solution to the system of …eld equations of plane. The stresses are prescribed on one-half of the circle, while the displacements are given. The considered problem with mixed boundary conditions in the circle is replaced by two problems with homogeneous boundary conditions, one of each type, having a common solution. The equations are reduced to a system of boundary integral equations, which is then discretized in the usual way, and the problem at this stage is reduced to the solution to a rectangular linear system of algebraic equations. The unknowns in this system of equations are the boundary values of four harmonic functions which define the full elastic solution and the unknown boundary values of stresses or displacements on proper parts of the boundary. On the basis of the obtained results, it is inferred that a stress component has a singularity at each of the two separation points, thought to be of logarithmic type. The results are discussed and boundary plots are given. We have also calculated the unknown functions in the bulk directly from the given boundary conditions using the boundary collocation method. The obtained results in the bulk are discussed and three-dimensional plots are given. A tentative form for the singular solution is proposed and the corresponding singular stresses and displacements are plotted in the bulk. The form of the singular tangential stress is seen to be compatible with the boundary values obtained earlier. The efficiency of the used numerical schemes is discussed.

Simulations of QCD and QED with C* boundary conditions

Science.gov (United States)

Hansen, Martin; Lucini, Biagio; Patella, Agostino; Tantalo, Nazario

2018-03-01

We present exploratory results from dynamical simulations of QCD in isolation, as well as QCD coupled to QED, with C* boundary conditions. In finite volume, the use of C* boundary conditions allows for a gauge invariant and local formulation of QED without zero modes. In particular we show that the simulations reproduce known results and that masses of charged mesons can be extracted in a completely gauge invariant way. For the simulations we use a modified version of the HiRep code. The primary features of the simulation code are presented and we discuss some details regarding the implementation of C* boundary conditions and the simulated lattice action. Preprint: CP3-Origins-2017-046 DNRF90, CERN-TH-2017-214

Critical effects of downstream boundary conditions on vortex breakdown

Science.gov (United States)

Kandil, Osama; Kandil, Hamdy A.; Liu, C. H.

1992-01-01

The unsteady, compressible, full Navier-Stokes (NS) equations are used to study the critical effects of the downstream boundary conditions on the supersonic vortex breakdown. The present study is applied to two supersonic vortex breakdown cases. In the first case, quasi-axisymmetric supersonic swirling flow is considered in a configured circular duct, and in the second case, quasi-axisymmetric supersonic swirling jet, that is issued from a nozzle into a supersonic jet of lower Mach number, is considered. For the configured duct flow, four different types of downstream boundary conditions are used, and for the swirling jet flow from the nozzle, two types of downstream boundary conditions are used. The solutions are time accurate which are obtained using an implicit, upwind, flux-difference splitting, finite-volume scheme.

Boundary conditions for plasma fluid models at the magnetic presheath entrance

International Nuclear Information System (INIS)

Loizu, J.; Ricci, P.; Halpern, F. D.; Jolliet, S.

2012-01-01

The proper boundary conditions at the magnetic presheath entrance for plasma fluid turbulence models based on the drift approximation are derived, focusing on a weakly collisional plasma sheath with T i ≪T e and a magnetic field oblique to a totally absorbing wall. First, the location of the magnetic presheath entrance is rigorously derived. Then boundary conditions at the magnetic presheath entrance are analytically deduced for v ||i , v ||e , n, φ, T e , and for the vorticity ω=∇ ⊥ 2 φ. The effects of E × B and diamagnetic drifts on the boundary conditions are also investigated. Kinetic simulations are performed that confirm the analytical results. Finally, the new set of boundary conditions is implemented in a three-dimensional global fluid code for the simulation of plasma turbulence and, as an example, the results of a tokamak scrape-off layer simulation are discussed. The framework presented can be generalized to obtain boundary conditions at the magnetic presheath entrance in more complex scenarios.

A device adaptive inflow boundary condition for Wigner equations of quantum transport

International Nuclear Information System (INIS)

Jiang, Haiyan; Lu, Tiao; Cai, Wei

2014-01-01

In this paper, an improved inflow boundary condition is proposed for Wigner equations in simulating a resonant tunneling diode (RTD), which takes into consideration the band structure of the device. The original Frensley inflow boundary condition prescribes the Wigner distribution function at the device boundary to be the semi-classical Fermi–Dirac distribution for free electrons in the device contacts without considering the effect of the quantum interaction inside the quantum device. The proposed device adaptive inflow boundary condition includes this effect by assigning the Wigner distribution to the value obtained from the Wigner transform of wave functions inside the device at zero external bias voltage, thus including the dominant effect on the electron distribution in the contacts due to the device internal band energy profile. Numerical results on computing the electron density inside the RTD under various incident waves and non-zero bias conditions show much improvement by the new boundary condition over the traditional Frensley inflow boundary condition

Local Tensor Radiation Conditions For Elastic Waves

DEFF Research Database (Denmark)

Krenk, S.; Kirkegaard, Poul Henning

2001-01-01

A local boundary condition is formulated, representing radiation of elastic waves from an arbitrary point source. The boundary condition takes the form of a tensor relation between the stress at a point on an arbitrarily oriented section and the velocity and displacement vectors at the point....... The tensor relation generalizes the traditional normal incidence impedance condition by accounting for the angle between wave propagation and the surface normal and by including a generalized stiffness term due to spreading of the waves. The effectiveness of the local tensor radiation condition...

Positive solutions of nonlinear fractional boundary value problems with Dirichlet boundary conditions

Directory of Open Access Journals (Sweden)

Qingkai Kong

2012-02-01

Full Text Available In this paper, we study the existence and multiplicity of positive solutions of a class of nonlinear fractional boundary value problems with  Dirichlet boundary conditions. By applying the fixed point theory on cones we establish a series of criteria for the existence of one, two, any arbitrary finite number, and an infinite number of positive solutions. A criterion for the nonexistence of positive solutions is also derived. Several examples are given for demonstration.

Phase boundary estimation in electrical impedance tomography using the Hooke and Jeeves pattern search method

International Nuclear Information System (INIS)

Khambampati, Anil Kumar; Kim, Kyung Youn; Ijaz, Umer Zeeshan; Lee, Jeong Seong; Kim, Sin

2010-01-01

In industrial processes, monitoring of heterogeneous phases is crucial to the safety and operation of the engineering structures. Particularly, the visualization of voids and air bubbles is advantageous. As a result many studies have appeared in the literature that offer varying degrees of functionality. Electrical impedance tomography (EIT) has already been proved to be a hallmark for process monitoring and offers not only the visualization of the resistivity profile for a given flow mixture but is also used for detection of phase boundaries. Iterative image reconstruction algorithms, such as the modified Newton–Raphson (mNR) method, are commonly used as inverse solvers. However, their utility is problematic in a sense that they require the initial solution in close proximity of the ground truth. Furthermore, they also rely on the gradient information of the objective function to be minimized. Therefore, in this paper, we address all these issues by employing a direct search algorithm, namely the Hooke and Jeeves pattern search method, to estimate the phase boundaries that directly minimizes the cost function and does not require the gradient information. It is assumed that the resistivity profile is known a priori and therefore the unknown information will be the size and location of the object. The boundary coefficients are parameterized using truncated Fourier series and are estimated using the relationship between the measured voltages and injected currents. Through extensive simulation and experimental result and by comparison with mNR, we show that the Hooke and Jeeves pattern search method offers a promising prospect for process monitoring

On the symmetry of the boundary conditions of the volume potential

Science.gov (United States)

Kal'menov, Tynysbek Sh.; Arepova, Gaukhar; Suragan, Durvudkhan

2017-09-01

It is well known that the volume potential determines the mass or the charge distributed over the domain with density f. The volume potential is extensively used in function theory and embedding theorems. It is also well known that the volume potential gives a solution to an inhomogeneous equation. And it generates a linear self-adjoint operator. It is known that self-adjoint differential operators are generated by boundary conditions. In our previous papers for an arbitrary domain a boundary condition on the volume potential is given. In the past, it was not possible to prove the self-adjointness of these obtained boundary conditions. In the present paper, we prove the symmetry of boundary condition for the volume potential.

Neutron transport assembly calculation with non-zero net current boundary condition

International Nuclear Information System (INIS)

Jo, Chang Keun

1993-02-01

Fuel assembly calculation for the homogenized group constants is one of the most important parts in the reactor core analysis. The homogenized group constants of one a quarter assembly are usually generated for the nodal calculation of the reactor core. In the current nodal calculation, one or a quarter of the fuel assembly corresponds to a unit node. The homogenized group constant calculation for a fuel assembly proceeds through cell spectrum calculations, group condensation and cell homogenization calculations, two dimensional fuel assembly calculation, and then depletion calculations of fuel rods. To obtain the assembly wise homogenized group constants, the two dimensional transport calculation is usually performed. Most codes for the assembly wise homogenized group constants employ a zero net current boundary condition. CASMO-3 is such a code that is in wide use. The zero net current boundary condition is plausible and valid in an infinite reactor composed of the same kind of assemblies. However, the reactor is finite and the core is constructed by different kinds of assemblies. Hence, the assumption of the zero net current boundary condition is not valid in the actual reactor. The objective of this study is to develop a homogenization methodology that can treat any actual boundary condition, i.e. non-zero net current boundary condition. In order to treat the non-zero net current boundary condition, we modify CASMO-3. For the two-dimensional treatment in CASMO-3, a multigroup integral transport routine based on the method of transmission probability is used. The code performs assembly calculation with zero net current boundary condition. CASMO-3 is modified to consider the inhomogeneous source at the assembly boundary surface due to the non-zero net current. The modified version of CASMO-3 is called CASMO-3M. CASMO-3M is applied to several benchmark problems. In order to obtain the inhomogeneous source, the global calculation is performed. The local calculation

The analytical solution for drug delivery system with nonhomogeneous moving boundary condition

Science.gov (United States)

Saudi, Muhamad Hakimi; Mahali, Shalela Mohd; Harun, Fatimah Noor

2017-08-01

This paper discusses the development and the analytical solution of a mathematical model based on drug release system from a swelling delivery device. The mathematical model is represented by a one-dimensional advection-diffusion equation with nonhomogeneous moving boundary condition. The solution procedures consist of three major steps. Firstly, the application of steady state solution method, which is used to transform the nonhomogeneous moving boundary condition to homogeneous boundary condition. Secondly, the application of the Landau transformation technique that gives a significant impact in removing the advection term in the system of equation and transforming the moving boundary condition to a fixed boundary condition. Thirdly, the used of separation of variables method to find the analytical solution for the resulted initial boundary value problem. The results show that the swelling rate of delivery device and drug release rate is influenced by value of growth factor r.

Classically integrable boundary conditions for affine Toda field theories

International Nuclear Information System (INIS)

Bowcock, P.; Corrigan, E.; Dorey, P.E.; Rietdijk, R.H.

1995-01-01

Boundary conditions compatible with classical integrability are studied both directly, using an approach based on the explicit construction of conserved quantities, and indirectly by first developing a generalisation of the Lax pair idea. The latter approach is closer to the spirit of earlier work by Sklyanin and yields a complete set of conjectures for permissible boundary conditions for any affine Toda field theory. (orig.)

Facilitating conditions for boundary-spanning behavior in governance networks

OpenAIRE

Meerkerk, Ingmar; Edelenbos, Jurian

2017-01-01

textabstractThis article examines the impact of two facilitating conditions for boundary-spanning behaviour in urban governance networks. While research on boundary spanning is growing, there is little attention for antecedents. Combining governance network literature on project management and organizational literature on facilitative and servant leadership, we examine two potential conditions: a facilitative project management style and executive support. We conducted survey research among p...

A simple and efficient outflow boundary condition for the incompressible Navier–Stokes equations

Directory of Open Access Journals (Sweden)

Yibao Li

2017-01-01

Full Text Available Many researchers have proposed special treatments for outlet boundary conditions owing to lack of information at the outlet. Among them, the simplest method requires a large enough computational domain to prevent or reduce numerical errors at the boundaries. However, an efficient method generally requires special treatment to overcome the problems raised by the outlet boundary condition used. For example, mass flux is not conserved and the fluid field is not divergence-free at the outlet boundary. Overcoming these problems requires additional computational cost. In this paper, we present a simple and efficient outflow boundary condition for the incompressible Navier–Stokes equations, aiming to reduce the computational domain for simulating flow inside a long channel in the streamwise direction. The proposed outflow boundary condition is based on the transparent equation, where a weak formulation is used. The pressure boundary condition is derived by using the Navier–Stokes equations and the outlet flow boundary condition. In the numerical algorithm, a staggered marker-and-cell grid is used and temporal discretization is based on a projection method. The intermediate velocity boundary condition is consistently adopted to handle the velocity–pressure coupling. Characteristic numerical experiments are presented to demonstrate the robustness and accuracy of the proposed numerical scheme. Furthermore, the agreement of computational results from small and large domains suggests that our proposed outflow boundary condition can significantly reduce computational domain sizes.

Oblique radiation lateral open boundary conditions for a regional climate atmospheric model

Science.gov (United States)

Cabos Narvaez, William; De Frutos Redondo, Jose Antonio; Perez Sanz, Juan Ignacio; Sein, Dmitry

2013-04-01

The prescription of lateral boundary conditions in regional atmospheric models represent a very important issue for limited area models. The ill-posed nature of the open boundary conditions makes it necessary to devise schemes in order to filter spurious wave reflections at boundaries, being desirable to have one boundary condition per variable. On the other side, due to the essentially hyperbolic nature of the equations solved in state of the art atmospheric models, external data is required only for inward boundary fluxes. These circumstances make radiation lateral boundary conditions a good choice for the filtering of spurious wave reflections. Here we apply the adaptive oblique radiation modification proposed by Mikoyada and Roseti to each of the prognostic variables of the REMO regional atmospheric model and compare it to the more common normal radiation condition used in REMO. In the proposed scheme, special attention is paid to the estimation of the radiation phase speed, essential to detecting the direction of boundary fluxes. One of the differences with the classical scheme is that in case of outward propagation, the adaptive nudging imposed in the boundaries allows to minimize under and over specifications problems, adequately incorporating the external information.

Spectral distribution of scalar particles created by a moving boundary with Robin boundary condition

International Nuclear Information System (INIS)

Mintz, B.; Farina, C; Maia Neto, P.A.; Rodrigues, R.B.

2006-01-01

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic boundary. By deriving a Bogoliubov transformation between the input and output bosonic field operators, we calculate the spectral distribution of created particles. The particular cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases, yielding equal spectra (this result is valid only in this space-time dimensionality). The creation effect for the field under Dirichlet BC turns out to be an upper bound for the spectra derived for Robin BC. Also, we show that the particle creation phenomenon with Robin conditions can be considerably reduced (with respect to the Dirichlet or Neumann cases) by selecting a particular mechanical oscillation frequency of the moving boundary. (author)

Scattering through a straight quantum waveguide with combined boundary conditions

Czech Academy of Sciences Publication Activity Database

Briet, Ph.; Dittrich, Jaroslav; Soccorsi, E.

2014-01-01

Roč. 55, č. 11 (2014), s. 112104 ISSN 0022-2488 R&D Projects: GA ČR(CZ) GA14-06818S Institutional support: RVO:61389005 Keywords : quantum waveguide * scattering * Dirichlet boundary condition * Neumann boundary condition Subject RIV: BE - Theoretical Physics Impact factor: 1.243, year: 2014

'Duality twisted'boundary conditions in n-state Potts Models

International Nuclear Information System (INIS)

Schuetz, G.

1992-11-01

We discuss a new class of toroidal boundary conditions for one-dimensional quantum Hamiltonian with S n symmetry which are related to two-dimensional n-state Potts models in the extreme anisotropic Hamiltonian limit. At their self-dual point (a point were a second-order phase transition occurs for n=2,3,4) the duality transformation is shown to be an additional symmetry giving rise to a new class of 'duality twisted' toroidal boundary conditions. This corresponding Hamiltonians are given in terms of generators of the periodic Temprely-Lieb algebra with an odd number of generators. We discuss as an example the critical Ising model. Here the complete spectrum for the new boundary conditions can be obtained from a projection mechanism in the spin-1/2 XXZ Heisenberg chain. (author)

Impedance Method for Leak Detection in Zigzag Pipelines

Science.gov (United States)

Lay-Ekuakille, A.; Vergallo, P.; Trotta, A.

2010-01-01

Transportation of liquids is a primary aspect of human life. The most important infrastructure used accordingly is the pipeline. It serves as an asset for transporting different liquids and strategic goods. The latter are for example: chemical substances, oil, gas and water. Thus, it is necessary to monitor such infrastructures by means of specific tools. Leakage detection methods are used to reveal liquid leaks in pipelines for many applications, namely, waterworks, oil pipelines, industry heat exchangers, etc. The configuration of pipelines is a key issue because it impacts on the effectiveness of the method to be used and, consequently, on the results to be counterchecked. This research illustrated an improvement of the impedance method for zigzag pipeline by carrying out an experimental frequency analysis that has been compared with other methods based on frequency response. Hence, the impedance method is generally used for simple (straight) pipeline configurations because complicated pipelines with many curves introduce difficulties and major uncertainties in the calculation of characteristic impedance and in the statement of boundary conditions. The paper illustrates the case of a water pipeline where the leakage is acquired thanks to pressure transducers.

Temperature field conduction solution by incomplete boundary condition

Energy Technology Data Exchange (ETDEWEB)

Novakovic, M; Petrasinovic, Lj; Djuric, M [Tehnoloski fakultet, Novi Sad (Yugoslavia); Perovic, N [Institut za Nuklearne Nauke Boris Kidric, Belgrade (Yugoslavia)

1977-01-01

The problem of determination of one part boundary conditions temperatures for Fourier partial differential equation when the other part of boundary condition and derivates (heat fluxes) are known is a practical interest as it enables one to determine and accessible temperature by measuring temperatures on other side, of the wall. Method developed and applied here consist of transforming the Fourier partial differential equation by time discretisation in sets of pairs of ordinary differential equations for temperature and heat flux. Such pair of differential equations of first order was solved by Runge-Kutta method. The integration proceeds along space interval simultaneosly for all time intervals. It is interesting to note that this procedure does not require the initial condition.

Einstein boundary conditions in relation to constraint propagation for the initial-boundary value problem of the Einstein equations

International Nuclear Information System (INIS)

Frittelli, Simonetta; Gomez, Roberto

2004-01-01

We show how the use of the normal projection of the Einstein tensor as a set of boundary conditions relates to the propagation of the constraints, for two representations of the Einstein equations with vanishing shift vector: the Arnowitt-Deser-Misner formulation, which is ill posed, and the Einstein-Christoffel formulation, which is symmetric hyperbolic. Essentially, the components of the normal projection of the Einstein tensor that act as nontrivial boundary conditions are linear combinations of the evolution equations with the constraints that are not preserved at the boundary, in both cases. In the process, the relationship of the normal projection of the Einstein tensor to the recently introduced 'constraint-preserving' boundary conditions becomes apparent

Downstream-Conditioned Maximum Entropy Method for Exit Boundary Conditions in the Lattice Boltzmann Method

Directory of Open Access Journals (Sweden)

Javier A. Dottori

2015-01-01

Full Text Available A method for modeling outflow boundary conditions in the lattice Boltzmann method (LBM based on the maximization of the local entropy is presented. The maximization procedure is constrained by macroscopic values and downstream components. The method is applied to fully developed boundary conditions of the Navier-Stokes equations in rectangular channels. Comparisons are made with other alternative methods. In addition, the new downstream-conditioned entropy is studied and it was found that there is a correlation with the velocity gradient during the flow development.

Experimental verification of free-space singular boundary conditions in an invisibility cloak

International Nuclear Information System (INIS)

Wu, Qiannan; Gao, Fei; Song, Zhengyong; Lin, Xiao; Zhang, Youming; Zhang, Baile; Chen, Huanyang

2016-01-01

A major issue in invisibility cloaking, which caused intense mathematical discussions in the past few years but still remains physically elusive, is the plausible singular boundary conditions associated with the singular metamaterials at the inner boundary of an invisibility cloak. The perfect cloaking phenomenon, as originally proposed by Pendry et al for electromagnetic waves, cannot be treated as physical before a realistic inner boundary of a cloak is demonstrated. Although a recent demonstration has been done in a waveguide environment, the exotic singular boundary conditions should apply to a general environment as in free space. Here we fabricate a metamaterial surface that exhibits the singular boundary conditions and demonstrate its performance in free space. Particularly, the phase information of waves reflected from this metamaterial surface is explicitly measured, confirming the singular responses of boundary conditions for an invisibility cloak. (paper)

Experimental verification of free-space singular boundary conditions in an invisibility cloak

Science.gov (United States)

Wu, Qiannan; Gao, Fei; Song, Zhengyong; Lin, Xiao; Zhang, Youming; Chen, Huanyang; Zhang, Baile

2016-04-01

A major issue in invisibility cloaking, which caused intense mathematical discussions in the past few years but still remains physically elusive, is the plausible singular boundary conditions associated with the singular metamaterials at the inner boundary of an invisibility cloak. The perfect cloaking phenomenon, as originally proposed by Pendry et al for electromagnetic waves, cannot be treated as physical before a realistic inner boundary of a cloak is demonstrated. Although a recent demonstration has been done in a waveguide environment, the exotic singular boundary conditions should apply to a general environment as in free space. Here we fabricate a metamaterial surface that exhibits the singular boundary conditions and demonstrate its performance in free space. Particularly, the phase information of waves reflected from this metamaterial surface is explicitly measured, confirming the singular responses of boundary conditions for an invisibility cloak.

Single Mode Theory for Impedance Eduction in Large-Scale Ducts with Grazing Flow

Science.gov (United States)

Watson, Willie R.; Gerhold, Carl H.; Jones, Michael G.; June, Jason C.

2014-01-01

An impedance eduction theory for a rigid wall duct containing an acoustic liner with an unknown impedance and uniform grazing flow is presented. The unique features of the theory are: 1) non-planar waves propagate in the hard wall sections of the duct, 2) input data consist solely of complex acoustic pressures acquired on a wall adjacent to the liner, and 3) multiple higher-order modes may exist in the direction perpendicular to the liner and the opposite rigid wall. The approach is to first measure the axial propagation constant of a dominant higher-order mode in the liner sample section. This axial propagation constant is then used in conjunction with a closed-form solution to a reduced form of the convected Helmholtz equation and the wall impedance boundary condition to educe the liner impedance. The theory is validated on a conventional liner whose impedance spectrum is educed in two flow ducts with different cross sections. For the frequencies and Mach numbers of interest, no higher-order modes propagate in the hard wall sections of the smaller duct. A benchmark method is used to educe the impedance spectrum in this duct. A dominant higher-order vertical mode propagates in the larger duct for similar test conditions, and the current theory is applied to educe the impedance spectrum. Results show that when the theory is applied to data acquired in the larger duct with a dominant higher-order vertical mode, the same impedance spectra is educed as that obtained in the small duct where only the plane wave mode is present and the benchmark method is used. This result holds for each higher-order vertical mode that is considered.

A new approach to implement absorbing boundary condition in biomolecular electrostatics.

Science.gov (United States)

Goni, Md Osman

2013-01-01

This paper discusses a novel approach to employ the absorbing boundary condition in conjunction with the finite-element method (FEM) in biomolecular electrostatics. The introduction of Bayliss-Turkel absorbing boundary operators in electromagnetic scattering problem has been incorporated by few researchers. However, in the area of biomolecular electrostatics, this boundary condition has not been investigated yet. The objective of this paper is twofold. First, to solve nonlinear Poisson-Boltzmann equation using Newton's method and second, to find an efficient and acceptable solution with minimum number of unknowns. In this work, a Galerkin finite-element formulation is used along with a Bayliss-Turkel absorbing boundary operator that explicitly accounts for the open field problem by mapping the Sommerfeld radiation condition from the far field to near field. While the Bayliss-Turkel condition works well when the artificial boundary is far from the scatterer, an acceptable tolerance of error can be achieved with the second order operator. Numerical results on test case with simple sphere show that the treatment is able to reach the same level of accuracy achieved by the analytical method while using a lower grid density. Bayliss-Turkel absorbing boundary condition (BTABC) combined with the FEM converges to the exact solution of scattering problems to within discretization error.

Boundary conditions for the diffusion equation in radiative transfer

International Nuclear Information System (INIS)

Haskell, R.C.; Svaasand, L.O.; Tsay, T.; Feng, T.; McAdams, M.S.; Tromberg, B.J.

1994-01-01

Using the method of images, we examine the three boundary conditions commonly applied to the surface of a semi-infinite turbid medium. We find that the image-charge configurations of the partial-current and extrapolated-boundary conditions have the same dipole and quadrupole moments and that the two corresponding solutions to the diffusion equation are approximately equal. In the application of diffusion theory to frequency-domain photon-migration (FDPM) data, these two approaches yield values for the scattering and absorption coefficients that are equal to within 3%. Moreover, the two boundary conditions can be combined to yield a remarkably simple, accurate, and computationally fast method for extracting values for optical parameters from FDPM data. FDPM data were taken both at the surface and deep inside tissue phantoms, and the difference in data between the two geometries is striking. If one analyzes the surface data without accounting for the boundary, values deduced for the optical coefficients are in error by 50% or more. As expected, when aluminum foil was placed on the surface of a tissue phantom, phase and modulation data were closer to the results for an infinite-medium geometry. Raising the reflectivity of a tissue surface can, in principle, eliminate the effect of the boundary. However, we find that phase and modulation data are highly sensitive to the reflectivity in the range of 80--100%, and a minimum value of 98% is needed to mimic an infinite-medium geometry reliably. We conclude that noninvasive measurements of optically thick tissue require a rigorous treatment of the tissue boundary, and we suggest a unified partial-current--extrapolated boundary approach

On Stable Wall Boundary Conditions for the Hermite Discretization of the Linearised Boltzmann Equation

Science.gov (United States)

Sarna, Neeraj; Torrilhon, Manuel

2018-01-01

We define certain criteria, using the characteristic decomposition of the boundary conditions and energy estimates, which a set of stable boundary conditions for a linear initial boundary value problem, involving a symmetric hyperbolic system, must satisfy. We first use these stability criteria to show the instability of the Maxwell boundary conditions proposed by Grad (Commun Pure Appl Math 2(4):331-407, 1949). We then recognise a special block structure of the moment equations which arises due to the recursion relations and the orthogonality of the Hermite polynomials; the block structure will help us in formulating stable boundary conditions for an arbitrary order Hermite discretization of the Boltzmann equation. The formulation of stable boundary conditions relies upon an Onsager matrix which will be constructed such that the newly proposed boundary conditions stay close to the Maxwell boundary conditions at least in the lower order moments.

A Method of Function Space for Vertical Impedance Function of a Circular Rigid Foundation on a Transversely Isotropic Ground

Directory of Open Access Journals (Sweden)

Morteza Eskandari-Ghadi

2014-06-01

Full Text Available This paper is concerned with investigation of vertical impedance function of a surface rigid circular foundation resting on a semi-infinite transversely isotropic alluvium. To this end, the equations of motion in cylindrical coordinate system, which because of axissymmetry are two coupled equations, are converted into one partial differential equation using a method of potential function. The governing partial differential equation for the potential function is solved via implementing Hankel integral transforms in radial direction. The vertical and radial components of displacement vector are determined with the use of transformed displacement-potential function relationships. The mixed boundary conditions at the surface are satisfied by specifying the traction between the rigid foundation and the underneath alluvium in a special function space introduced in this paper, where the vertical displacements are forced to satisfy the rigid boundary condition. Through exercising these restraints, the normal traction and then the vertical impedance function are obtained. The results are then compared with the existing results in the literature for the simpler case of isotropic half-space, which shows an excellent agreement. Eventually, the impedance functions are presented in terms of dimensionless frequency for different materials. The method presented here may be used to obtain the impedance function in any other direction as well as in buried footing in layered media.

Essential Boundary Conditions with Straight C1 Finite Elements in Curved Domains

International Nuclear Information System (INIS)

Ferraro, N.M.; Jardin, S.C.; Luo, X.

2010-01-01

The implementation of essential boundary conditions in C1 finite element analysis requires proper treatment of both the boundary conditions on second-order differentials of the solution and the curvature of the domain boundary. A method for the imposition of essential boundary conditions using straight elements (where the elements are not deformed to approximate a curved domain) is described. It is shown that pre-multiplication of the matrix equation by the local rotation matrix at each boundary node is not the optimal transformation. The uniquely optimal transformation is found, which does not take the form of a similarity transformation due to the non-orthogonality of the transformation to curved coordinates.

The boundary conditions for point transformed electromagnetic invisibility cloaks

International Nuclear Information System (INIS)

Weder, Ricardo

2008-01-01

In this paper we study point transformed electromagnetic invisibility cloaks in transformation media that are obtained by transformation from general anisotropic media. We assume that there are several point transformed electromagnetic cloaks located in different points in space. Our results apply in particular to the first-order invisibility cloaks introduced by Pendry et al and to the high-order invisibility cloaks introduced by Hendi et al and by Cai et al. We identify the appropriate cloaking boundary conditions that the solutions of Maxwell equations have to satisfy at the outside, ∂K + , and at the inside, ∂K - , of the boundary of the cloaked object K in the case where the permittivity and the permeability are bounded below and above in K. Namely, that the tangential components of the electric and the magnetic fields have to vanish at ∂K + -which is always true-and that the normal components of the curl of the electric and the magnetic fields have to vanish at ∂K - . These results are proven requiring that energy be conserved. In the case of one spherical cloak with a spherically stratified K and a radial current at ∂K we verify by an explicit calculation that our cloaking boundary conditions are satisfied and that cloaking of active devices holds, even if the current is at the boundary of the cloaked object. As we prove our results for media that are obtained by transformation from general anisotropic media, our results apply to the cloaking of objects with passive and active devices contained in general anisotropic media, in particular to objects with passive and active devices contained inside general crystals. Our results suggest a method to enhance cloaking in the approximate transformation media that are used in practice. Namely, to coat the boundary of the cloaked object (the inner boundary of the cloak) with a material that imposes the boundary conditions above. As these boundary conditions have to be satisfied for exact transformation

Canonical group quantization and boundary conditions

International Nuclear Information System (INIS)

Jung, Florian

2012-01-01

In the present thesis, we study quantization of classical systems with non-trivial phase spaces using the group-theoretical quantization technique proposed by Isham. Our main goal is a better understanding of global and topological aspects of quantum theory. In practice, the group-theoretical approach enables direct quantization of systems subject to constraints and boundary conditions in a natural and physically transparent manner -- cases for which the canonical quantization method of Dirac fails. First, we provide a clarification of the quantization formalism. In contrast to prior treatments, we introduce a sharp distinction between the two group structures that are involved and explain their physical meaning. The benefit is a consistent and conceptually much clearer construction of the Canonical Group. In particular, we shed light upon the 'pathological' case for which the Canonical Group must be defined via a central Lie algebra extension and emphasise the role of the central extension in general. In addition, we study direct quantization of a particle restricted to a half-line with 'hard wall' boundary condition. Despite the apparent simplicity of this example, we show that a naive quantization attempt based on the cotangent bundle over the half-line as classical phase space leads to an incomplete quantum theory; the reflection which is a characteristic aspect of the 'hard wall' is not reproduced. Instead, we propose a different phase space that realises the necessary boundary condition as a topological feature and demonstrate that quantization yields a suitable quantum theory for the half-line model. The insights gained in the present special case improve our understanding of the relation between classical and quantum theory and illustrate how contact interactions may be incorporated.

Periodic Boundary Conditions in the ALEGRA Finite Element Code

International Nuclear Information System (INIS)

Aidun, John B.; Robinson, Allen C.; Weatherby, Joe R.

1999-01-01

This document describes the implementation of periodic boundary conditions in the ALEGRA finite element code. ALEGRA is an arbitrary Lagrangian-Eulerian multi-physics code with both explicit and implicit numerical algorithms. The periodic boundary implementation requires a consistent set of boundary input sets which are used to describe virtual periodic regions. The implementation is noninvasive to the majority of the ALEGRA coding and is based on the distributed memory parallel framework in ALEGRA. The technique involves extending the ghost element concept for interprocessor boundary communications in ALEGRA to additionally support on- and off-processor periodic boundary communications. The user interface, algorithmic details and sample computations are given

Discrete Green's Theorem, Green's Functions and Stable Radiative FDTD Boundary Conditions

NARCIS (Netherlands)

Arnold, J.M.; Hon, de B.P.

2007-01-01

We propose a radiative boundary condition for the discrete-grid formulation of Helmholtz’ equation, based on rational approximation in the frequency domain of a Green’s function for the discretised system. This boundary condition is free from instabilities.

Repulsive Casimir force from fractional Neumann boundary conditions

International Nuclear Information System (INIS)

Lim, S.C.; Teo, L.P.

2009-01-01

This Letter studies the finite temperature Casimir force acting on a rectangular piston associated with a massless fractional Klein-Gordon field at finite temperature. Dirichlet boundary conditions are imposed on the walls of a d-dimensional rectangular cavity, and a fractional Neumann condition is imposed on the piston that moves freely inside the cavity. The fractional Neumann condition gives an interpolation between the Dirichlet and Neumann conditions, where the Casimir force is known to be always attractive and always repulsive respectively. For the fractional Neumann boundary condition, the attractive or repulsive nature of the Casimir force is governed by the fractional order which takes values from zero (Dirichlet) to one (Neumann). When the fractional order is larger than 1/2, the Casimir force is always repulsive. For some fractional orders that are less than but close to 1/2, it is shown that the Casimir force can be either attractive or repulsive depending on the aspect ratio of the cavity and the temperature.

The influence of the magnetic boundary conditions on the nature of astrophysical convection

International Nuclear Information System (INIS)

Lopez, J.M.; Murphy, J.O.

1983-01-01

The effects of employing two forms of the boundary conditions for the magnetic field disturbance, H, are demonstrated. The appropriate conditions on H for current-free boundaries can be written as DHt-aH=0. The second case uses the conditions DH=0 at the lower and upper boundaries

On the use of Kontorovich-Lebedev transform in electromagnetic diffraction by an impedance cone

KAUST Repository

Salem, Mohamed; Kamel, Aladin Hassan; Bagci, Hakan

2012-01-01

We consider the boundary-value problem for the Helmholtz equation connected with an infinite circular cone with an impedance boundary on its face. The scheme of solution includes applying the Kontorovich-Lebedev (KL) transform to reduce the problem to that of a KL spectral amplitude function satisfying a singular integral equation of the non-convolution type with a variable coefficient. The singularities of the spectral function are deduced and representations for the field at the tip of the cone and in the near and far field regions are given together with the conditions of validity of these representations. © 2012 IEEE.

On the use of Kontorovich-Lebedev transform in electromagnetic diffraction by an impedance cone

KAUST Repository

Salem, Mohamed

2012-08-01

We consider the boundary-value problem for the Helmholtz equation connected with an infinite circular cone with an impedance boundary on its face. The scheme of solution includes applying the Kontorovich-Lebedev (KL) transform to reduce the problem to that of a KL spectral amplitude function satisfying a singular integral equation of the non-convolution type with a variable coefficient. The singularities of the spectral function are deduced and representations for the field at the tip of the cone and in the near and far field regions are given together with the conditions of validity of these representations. © 2012 IEEE.

Canonical group quantization and boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Jung, Florian

2012-07-16

In the present thesis, we study quantization of classical systems with non-trivial phase spaces using the group-theoretical quantization technique proposed by Isham. Our main goal is a better understanding of global and topological aspects of quantum theory. In practice, the group-theoretical approach enables direct quantization of systems subject to constraints and boundary conditions in a natural and physically transparent manner -- cases for which the canonical quantization method of Dirac fails. First, we provide a clarification of the quantization formalism. In contrast to prior treatments, we introduce a sharp distinction between the two group structures that are involved and explain their physical meaning. The benefit is a consistent and conceptually much clearer construction of the Canonical Group. In particular, we shed light upon the 'pathological' case for which the Canonical Group must be defined via a central Lie algebra extension and emphasise the role of the central extension in general. In addition, we study direct quantization of a particle restricted to a half-line with 'hard wall' boundary condition. Despite the apparent simplicity of this example, we show that a naive quantization attempt based on the cotangent bundle over the half-line as classical phase space leads to an incomplete quantum theory; the reflection which is a characteristic aspect of the 'hard wall' is not reproduced. Instead, we propose a different phase space that realises the necessary boundary condition as a topological feature and demonstrate that quantization yields a suitable quantum theory for the half-line model. The insights gained in the present special case improve our understanding of the relation between classical and quantum theory and illustrate how contact interactions may be incorporated.

On two-point boundary correlations in the six-vertex model with domain wall boundary conditions

Science.gov (United States)

Colomo, F.; Pronko, A. G.

2005-05-01

The six-vertex model with domain wall boundary conditions on an N × N square lattice is considered. The two-point correlation function describing the probability of having two vertices in a given state at opposite (top and bottom) boundaries of the lattice is calculated. It is shown that this two-point boundary correlator is expressible in a very simple way in terms of the one-point boundary correlators of the model on N × N and (N - 1) × (N - 1) lattices. In alternating sign matrix (ASM) language this result implies that the doubly refined x-enumerations of ASMs are just appropriate combinations of the singly refined ones.

Sensitivity analysis of an impedance void distribution in annular and bubbly flow: A theoretical study

International Nuclear Information System (INIS)

Lemonnier, H.; Nakach, R.; Favreau, C.; Selmer-Olsen, S.

1989-01-01

Impedance void meters are frequently used to measure area-averaged void fraction in pipes. This is primarily due to two reasons: first, this method is non-intrusive since the measurement can be done from electrodes flush mounted in the walls, and second, the signal processing equipment is simple. Impedance probes may be calibrated by using a pressure drop measurement or quick closing valves system and low attention is generally paid to void distribution effects. It can be proved that in annular flow, the departure from radial symmetry has a strong influence on the measured mean film thickness. This can be easily demonstrated by solving the Laplace equation for the electrical potential by simple analytical methods. When some spatial symmetry conditions are encountered, it is possible to calculate directly the conductance of the two-phase medium without calculating completely the potential. A solution of this problem by using the separation of variable technique is also presented. There, the main difficulty is due to the mixity of the boundary conditions: the boundary condition is both Neumann and Dirichlet type on the same coordinate curve. This formulation leads to a non-separable problem which is solved by truncating an infinite algebraic set of linear equations. (orig.)

An effective absorbing layer for the boundary condition in acoustic seismic wave simulation

Science.gov (United States)

Yao, Gang; da Silva, Nuno V.; Wu, Di

2018-04-01

Efficient numerical simulation of seismic wavefields generally involves truncating the Earth model in order to keep computing time and memory requirements down. Absorbing boundary conditions, therefore, are applied to remove the boundary reflections caused by this truncation, thereby allowing for accurate modeling of wavefields. In this paper, we derive an effective absorbing boundary condition for both acoustic and elastic wave simulation, through the simplification of the damping term of the split perfectly matched layer (SPML) boundary condition. This new boundary condition is accurate, cost-effective, and easily implemented, especially for high-performance computing. Stability analysis shows that this boundary condition is effectively as stable as normal (non-absorbing) wave equations for explicit time-stepping finite differences. We found that for full-waveform inversion (FWI), the strengths of the effective absorbing layer—a reduction of the computational and memory cost coupled with a simplistic implementation—significantly outweighs the limitation of incomplete absorption of outgoing waves relative to the SPML. More importantly, we demonstrate that this limitation can easily be overcome through the use of two strategies in FWI, namely variable cell size and model extension thereby fully compensating for the imperfectness of the proposed absorbing boundary condition.

Single particle nonlocality, geometric phases and time-dependent boundary conditions

Science.gov (United States)

Matzkin, A.

2018-03-01

We investigate the issue of single particle nonlocality in a quantum system subjected to time-dependent boundary conditions. We discuss earlier claims according to which the quantum state of a particle remaining localized at the center of an infinite well with moving walls would be specifically modified by the change in boundary conditions due to the wall’s motion. We first prove that the evolution of an initially localized Gaussian state is not affected nonlocally by a linearly moving wall: as long as the quantum state has negligible amplitude near the wall, the boundary motion has no effect. This result is further extended to related confined time-dependent oscillators in which the boundary’s motion is known to give rise to geometric phases: for a Gaussian state remaining localized far from the boundaries, the effect of the geometric phases is washed out and the particle dynamics shows no traces of a nonlocal influence that would be induced by the moving boundaries.

Preconditioned characteristic boundary conditions based on artificial compressibility method for solution of incompressible flows

Science.gov (United States)

Hejranfar, Kazem; Parseh, Kaveh

2017-09-01

The preconditioned characteristic boundary conditions based on the artificial compressibility (AC) method are implemented at artificial boundaries for the solution of two- and three-dimensional incompressible viscous flows in the generalized curvilinear coordinates. The compatibility equations and the corresponding characteristic variables (or the Riemann invariants) are mathematically derived and then applied as suitable boundary conditions in a high-order accurate incompressible flow solver. The spatial discretization of the resulting system of equations is carried out by the fourth-order compact finite-difference (FD) scheme. In the preconditioning applied here, the value of AC parameter in the flow field and also at the far-field boundary is automatically calculated based on the local flow conditions to enhance the robustness and performance of the solution algorithm. The code is fully parallelized using the Concurrency Runtime standard and Parallel Patterns Library (PPL) and its performance on a multi-core CPU is analyzed. The incompressible viscous flows around a 2-D circular cylinder, a 2-D NACA0012 airfoil and also a 3-D wavy cylinder are simulated and the accuracy and performance of the preconditioned characteristic boundary conditions applied at the far-field boundaries are evaluated in comparison to the simplified boundary conditions and the non-preconditioned characteristic boundary conditions. It is indicated that the preconditioned characteristic boundary conditions considerably improve the convergence rate of the solution of incompressible flows compared to the other boundary conditions and the computational costs are significantly decreased.

Second order bounce back boundary condition for the lattice Boltzmann fluid simulation

International Nuclear Information System (INIS)

Kim, In Chan

2000-01-01

A new bounce back boundary method of the second order in error is proposed for the lattice Boltzmann fluid simulation. This new method can be used for the arbitrarily irregular lattice geometry of a non-slip boundary. The traditional bounce back boundary condition for the lattice Boltzmann simulation is of the first order in error. Since the lattice Boltzmann method is the second order scheme by itself, a boundary technique of the second order has been desired to replace the first order bounce back method. This study shows that, contrary to the common belief that the bounce back boundary condition is unilaterally of the first order, the second order bounce back boundary condition can be realized. This study also shows that there exists a generalized bounce back technique that can be characterized by a single interpolation parameter. The second order bounce back method can be obtained by proper selection of this parameter in accordance with the detailed lattice geometry of the boundary. For an illustrative purpose, the transient Couette and the plane Poiseuille flows are solved by the lattice Boltzmann simulation with various boundary conditions. The results show that the generalized bounce back method yields the second order behavior in the error of the solution, provided that the interpolation parameter is properly selected. Coupled with its intuitive nature and the ease of implementation, the bounce back method can be as good as any second order boundary method

Vibration Analysis of Annular Sector Plates under Different Boundary Conditions

Directory of Open Access Journals (Sweden)

Dongyan Shi

2014-01-01

Full Text Available An analytical framework is developed for the vibration analysis of annular sector plates with general elastic restraints along each edge of plates. Regardless of boundary conditions, the displacement solution is invariably expressed as a new form of trigonometric expansion with accelerated convergence. The expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz technique. This work allows a capability of modeling annular sector plates under a variety of boundary conditions and changing the boundary conditions as easily as modifying the material properties or dimensions of the plates. Of equal importance, the proposed approach is universally applicable to annular sector plates of any inclusion angles up to 2π. The reliability and accuracy of the current method are adequately validated through numerical examples.

Decoupling in an expanding universe boundary RG-flow affects initial conditions for inflation

CERN Document Server

Schalm, K; Van der Schaar, J P; Schalm, Koenraad; Shiu, Gary; Schaar, Jan Pieter van der

2004-01-01

We study decoupling in FRW spacetimes, emphasizing a Lagrangian description throughout. To account for the vacuum choice ambiguity in cosmological settings, we introduce an arbitrary boundary action representing the initial conditions. RG flow in these spacetimes naturally affects the boundary interactions. As a consequence the boundary conditions are sensitive to high-energy physics through irrelevant terms in the boundary action. Using scalar field theory as an example, we derive the leading dimension four irrelevant boundary operators. We discuss how the known vacuum choices, e.g. the Bunch-Davies vacuum, appear in the Lagrangian description and square with decoupling. For all choices of boundary conditions encoded by relevant boundary operators, of which the known ones are a subset, backreaction is under control. All, moreover, will generically feel the influence of high-energy physics through irrelevant (dimension four) boundary corrections. Having established a coherent effective field theory framework ...

Dielectric and impedance spectroscopic studies of neodymium gallate

Energy Technology Data Exchange (ETDEWEB)

Sakhya, Anup Pradhan, E-mail: npshakya31@gmail.com [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Dutta, Alo [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India)

2016-05-01

The AC electrical properties of a polycrystalline neodymium gallate, NdGaO{sub 3} (NGO), synthesized by the sol–gel method have been investigated by employing impedance spectroscopy in the frequency range from 42 Hz to 5 MHz and in the temperature range from 323 K to 593 K. The X-ray diffraction analysis shows that the compound crystallizes in the orthorhombic phase with Pbnm space group at room temperature. Two relaxation processes with different relaxation times are observed from the impedance as well as modulus spectroscopic measurements, which have been attributed to the grain and the grain boundary effects at different temperatures in NGO. The complex impedance data are analyzed by an electrical equivalent circuit consisting of a resistance and a constant phase element in parallel. It has been observed that the value of the capacitance and the resistance associated with the grain boundary is higher than those associated with the grain. The temperature dependent electrical conductivity shows the negative temperature coefficient of resistance. The frequency dependent conductivity spectra are found to follow the power law.

Galerkin methods for Boltzmann-Poisson transport with reflection conditions on rough boundaries

Science.gov (United States)

Morales Escalante, José A.; Gamba, Irene M.

2018-06-01

We consider in this paper the mathematical and numerical modeling of reflective boundary conditions (BC) associated to Boltzmann-Poisson systems, including diffusive reflection in addition to specularity, in the context of electron transport in semiconductor device modeling at nano scales, and their implementation in Discontinuous Galerkin (DG) schemes. We study these BC on the physical boundaries of the device and develop a numerical approximation to model an insulating boundary condition, or equivalently, a pointwise zero flux mathematical condition for the electron transport equation. Such condition balances the incident and reflective momentum flux at the microscopic level, pointwise at the boundary, in the case of a more general mixed reflection with momentum dependant specularity probability p (k →). We compare the computational prediction of physical observables given by the numerical implementation of these different reflection conditions in our DG scheme for BP models, and observe that the diffusive condition influences the kinetic moments over the whole domain in position space.

Impedance models in time domain

NARCIS (Netherlands)

Rienstra, S.W.

2005-01-01

Necessary conditions for an impedance function are derived. Methods available in the literature are discussed. A format with recipe is proposed for an exact impedance condition in time domain on a time grid, based on the Helmholtz resonator model. An explicit solution is given of a pulse reflecting

δ'-function perturbations and Neumann boundary-conditions by path integration

International Nuclear Information System (INIS)

Grosche, C.

1994-02-01

δ'-function perturbations and Neumann boundary conditions are incorporated into the path integral formalism. The starting point is the consideration of the path integral representation for the one dimensional Dirac particle together with a relativistic point interaction. The non-relativistic limit yields either a usual δ-function or a δ'-function perturbation; making their strengths infinitely repulsive one obtains Dirichlet, respectively Neumann boundary conditions in the path integral. (orig.)

Matrix albedo for discrete ordinates infinite-medium boundary condition

International Nuclear Information System (INIS)

Mathews, K.; Dishaw, J.

2007-01-01

Discrete ordinates problems with an infinite exterior medium (reflector) can be more efficiently computed by eliminating grid cells in the exterior medium and applying a matrix albedo boundary condition. The albedo matrix is a discretized bidirectional reflection distribution function (BRDF) that accounts for the angular quadrature set, spatial quadrature method, and spatial grid that would have been used to model a portion of the exterior medium. The method is exact in slab geometry, and could be used as an approximation in multiple dimensions or curvilinear coordinates. We present an adequate method for computing albedo matrices and demonstrate their use in verifying a discrete ordinates code in slab geometry by comparison with Ganapol's infinite medium semi-analytic TIEL benchmark. With sufficient resolution in the spatial and angular grids and iteration tolerance to yield solutions converged to 6 digits, the conventional (scalar) albedo boundary condition yielded 2-digit accuracy at the boundary, but the matrix albedo solution reproduced the benchmark scalar flux at the boundary to all 6 digits. (authors)

The influence of boundary conditions on domain structure stability in spin wave approximation

International Nuclear Information System (INIS)

Wachinewski, A.

1974-01-01

Instead of the usually used Born-Karman cyclic conditions, boundary conditions which take into account the situation of the boundary lattice sites lying on the crystal's surface are assumed. It is shown that the particular choice of the boundary conditions secures the stability of domain structure in ferromagnet (positive spin wave energies), without including the Winter term in Hamiltonian. (author)

Magnetohydrodynamic boundary layer flow past a porous substrate with Beavers-Joseph boundary condition

International Nuclear Information System (INIS)

Jat, R.N.; Chaudhary, Santosh

2009-01-01

The flow of an electrically conducting fluid past a porous substrate attached to the flat plate with Beavers-Joseph boundary condition under the influence of a uniform transverse magnetic field has been studied. Taking suitable similar variables, the momentum equation is transformed to ordinary differential equation and solved by standard techniques. The energy equation is solved by considering two boundary layers, one in the porous substrate and the other above the porous substrate. The velocity and temperature distributions along with Nusselt number are discussed numerically and presented through graphs. (author)

The exact solution to the one-dimensional Poisson–Boltzmann equation with asymmetric boundary conditions

DEFF Research Database (Denmark)

Johannessen, Kim

2014-01-01

The exact solution to the one-dimensional Poisson–Boltzmann equation with asymmetric boundary conditions can be expressed in terms of the Jacobi elliptic functions. The boundary conditions determine the modulus of the Jacobi elliptic functions. The boundary conditions can not be solved analytically...

Moisture distribution computed from electrical impedance tomographic data of a bentonite clay/sand material

International Nuclear Information System (INIS)

Strobel, G.S.

1995-11-01

Moisture contents values were calculated from electrical impedance-computed tomography measurements and compared with thermocouple psychrometer moisture values. The measurements were taken, in situ and under isothermal conditions, in a bentonite clay/sand packed borehole at the Underground Research Laboratory. Two sets of impedances moisture contents were calculated from the impedance valves--independent of each other. For one set, impedance measurements were fitted to the psychrometer moisture values in a least-squares fit to a generalized calibration curve and, for the second set, an impedance-moisture relationship from laboratory calibrations was applied. The impedance-computed moisture content data showed low scatter and the trends were consistent between the three sets of values. However, the moisture content data computed from the calibration curve were more consistent with those expected from physical arguments. The moisture values from the psychrometer readings were offset and, consequently, so were those produced after applying the fitting strategy. Internal redistribution of moisture appears to have had a more significant effect on the system than did inflow at the boundary. Inflow did cause a significant change but this was localized, during this period, to the outer ∼ 0.05 m of the test hole. No comment was made as to what internal processes caused these responses. (author) 9 refs., 2 tabs., 5 figs

Effects of boundary conditions on thermomechanical calculations: Spent fuel test - climax

International Nuclear Information System (INIS)

Butkovich, T.R.

1982-10-01

The effects of varying certain boundary conditions on the results of finite-element calculations were studied in relation to the Spent Fuel Test - Climax. The study employed a thermomechanical model with the ADINA structural analysis. Nodal temperature histories were generated with the compatible ADINAT heat flow codes. The boundary conditions studied included: (1) The effect of boundary loading on three progressively larger meshes. (2) Plane strain vs plane stress conditions. (3) The effect of isothermal boundaries on a small mesh and on a significantly larger mesh. The results showed that different mesh sizes had an insignificant effect on isothermal boundaries up to 5 y, while on the smallest and largest mesh, the maximum temperature difference in the mesh was 0 C. In the corresponding ADINA calculation, these different mesh sizes produce insignificant changes in the stress field and displacements in the region of interest near the heat sources and excavations. On the other hand, plane stress produces horizontal and vertical stress differences approx. 9% higher than does plane strain

Influence of different boundary conditions on analysis of SSI

International Nuclear Information System (INIS)

Wang Jiachun

2005-01-01

In the discussions of structural response to earthquakes, it has been assumed that the foundation medium is very stiff and that the seismic motions applied at the structure support points are the same as the free-field earthquake motions at those locations; in other words, the effects of soil structure interaction (SSI) have been neglected. However, its effects can be significant when the structure supported on a soft soil. Structures on the ground are affected by ground motion when there is seismic loading. The inability of the foundation to resist to deformation of soil would cause huge damages on the structures. The different codes and boundary conditions affect on analysis results of SSI. A comparison of the reactor buildings response as predicted by CLASSI and FLUSH shows substantial differences. To absorb, rather than reflect, the outwardly radiated energy, transmitting boundary conditions and soil structure interface should be taken into consideration in analysis of SSI. The paper discusses influence of several different boundary conditions on analysis of SSI. (author)

On Impulsive Boundary Value Problems of Fractional Differential Equations with Irregular Boundary Conditions

Directory of Open Access Journals (Sweden)

Guotao Wang

2012-01-01

Full Text Available We study nonlinear impulsive differential equations of fractional order with irregular boundary conditions. Some existence and uniqueness results are obtained by applying standard fixed-point theorems. For illustration of the results, some examples are discussed.

Entropy Stable Wall Boundary Conditions for the Three-Dimensional Compressible Navier-Stokes Equations

Science.gov (United States)

Parsani, Matteo; Carpenter, Mark H.; Nielsen, Eric J.

2015-01-01

Non-linear entropy stability and a summation-by-parts framework are used to derive entropy stable wall boundary conditions for the three-dimensional compressible Navier-Stokes equations. A semi-discrete entropy estimate for the entire domain is achieved when the new boundary conditions are coupled with an entropy stable discrete interior operator. The data at the boundary are weakly imposed using a penalty flux approach and a simultaneous-approximation-term penalty technique. Although discontinuous spectral collocation operators on unstructured grids are used herein for the purpose of demonstrating their robustness and efficacy, the new boundary conditions are compatible with any diagonal norm summation-by-parts spatial operator, including finite element, finite difference, finite volume, discontinuous Galerkin, and flux reconstruction/correction procedure via reconstruction schemes. The proposed boundary treatment is tested for three-dimensional subsonic and supersonic flows. The numerical computations corroborate the non-linear stability (entropy stability) and accuracy of the boundary conditions.

Effects of Uncertainties in Electric Field Boundary Conditions for Ring Current Simulations

Science.gov (United States)

Chen, Margaret W.; O'Brien, T. Paul; Lemon, Colby L.; Guild, Timothy B.

2018-01-01

Physics-based simulation results can vary widely depending on the applied boundary conditions. As a first step toward assessing the effect of boundary conditions on ring current simulations, we analyze the uncertainty of cross-polar cap potentials (CPCP) on electric field boundary conditions applied to the Rice Convection Model-Equilibrium (RCM-E). The empirical Weimer model of CPCP is chosen as the reference model and Defense Meteorological Satellite Program CPCP measurements as the reference data. Using temporal correlations from a statistical analysis of the "errors" between the reference model and data, we construct a Monte Carlo CPCP discrete time series model that can be generalized to other model boundary conditions. RCM-E simulations using electric field boundary conditions from the reference model and from 20 randomly generated Monte Carlo discrete time series of CPCP are performed for two large storms. During the 10 August 2000 storm main phase, the proton density at 10 RE at midnight was observed to be low (Dst index is bounded by the simulated Dst values. In contrast, the simulated Dst values during the recovery phases of the 10 August 2000 and 31 August 2005 storms tend to underestimate systematically the observed late Dst recovery. This suggests a need to improve the accuracy of particle loss calculations in the RCM-E model. Application of this technique can aid modelers to make efficient choices on either investing more effort on improving specification of boundary conditions or on improving descriptions of physical processes.

Three-party quantum teleportation using thermal states in Heisenberg XX model with open boundary condition

International Nuclear Information System (INIS)

Bhan, Jaemi; Kwon, Younghun

2007-01-01

Recently Yeo showed that thermal states in Heisenberg XX model with periodic boundary condition could be used for three-party quantum teleportation. However it is hard to implement the periodic boundary condition in spin chain. So instead of imposing the periodic boundary condition, we consider open boundary condition in Heisenberg XX model and investigate the possibility of using thermal states in Heisenberg XX model with open boundary condition. Using this way, we find the best fidelity conditions to three known protocols in three-party quantum teleportation. It turns out that the best fidelity in every protocol would be 23

Antishocks in the ASEP with open boundaries conditioned on low current

International Nuclear Information System (INIS)

Belitsky, V; Schütz, G M

2013-01-01

We study the time evolution of the ASEP on a finite lattice with L sites and open boundaries, conditioned on an atypically low current up to a finite time t. By an exact computation, we show that for a one-parameter family of boundary densities and a special value of the conditioned current, an initial product measure with an antishock at site k evolves into a convex combination of such antishocks at sites k′. The weights p(k′, t|k, 0) are shown to be the transition probabilities of simple biased random walk with reflecting boundaries. We compute explicitly these transition rates. Our result implies that the antishock remains microscopically stable under the locally conditioned dynamics. (paper)

On the wave equation with semilinear porous acoustic boundary conditions

KAUST Repository

Graber, Philip Jameson; Said-Houari, Belkacem

2012-01-01

The goal of this work is to study a model of the wave equation with semilinear porous acoustic boundary conditions with nonlinear boundary/interior sources and a nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. The main difficulty in proving the local existence result is that the Neumann boundary conditions experience loss of regularity due to boundary sources. Using an approximation method involving truncated sources and adapting the ideas in Lasiecka and Tataru (1993) [28], we show that the existence of solutions can still be obtained. Second, we prove that under some restrictions on the source terms, then the local solution can be extended to be global in time. In addition, it has been shown that the decay rates of the solution are given implicitly as solutions to a first order ODE and depends on the behavior of the damping terms. In several situations, the obtained ODE can be easily solved and the decay rates can be given explicitly. Third, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution ceases to exists and blows up in finite time. Moreover, in either the absence of the interior source or the boundary source, then we prove that the solution is unbounded and grows as an exponential function. © 2012 Elsevier Inc.

On the wave equation with semilinear porous acoustic boundary conditions

KAUST Repository

Graber, Philip Jameson

2012-05-01

The goal of this work is to study a model of the wave equation with semilinear porous acoustic boundary conditions with nonlinear boundary/interior sources and a nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. The main difficulty in proving the local existence result is that the Neumann boundary conditions experience loss of regularity due to boundary sources. Using an approximation method involving truncated sources and adapting the ideas in Lasiecka and Tataru (1993) [28], we show that the existence of solutions can still be obtained. Second, we prove that under some restrictions on the source terms, then the local solution can be extended to be global in time. In addition, it has been shown that the decay rates of the solution are given implicitly as solutions to a first order ODE and depends on the behavior of the damping terms. In several situations, the obtained ODE can be easily solved and the decay rates can be given explicitly. Third, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution ceases to exists and blows up in finite time. Moreover, in either the absence of the interior source or the boundary source, then we prove that the solution is unbounded and grows as an exponential function. © 2012 Elsevier Inc.

''Free-space'' boundary conditions for the time-dependent wave equation

International Nuclear Information System (INIS)

Lindman, E.L.

1975-01-01

Boundary conditions for the discrete wave equation which act like an infinite region of free space in contact with the computational region can be constructed using projection operators. Propagating and evanescent waves coming from within the computational region generate no reflected waves as they cross the boundary. At the same time arbitrary waves may be launched into the computational region. Well known projection operators for one-dimensional waves may be used for this purpose in one dimension. Extensions of these operators to higher dimensions along with numerically efficient approximations to them are described for higher-dimensional problems. The separation of waves into ingoing and outgoing waves inherent in these boundary conditions greatly facilitates diagnostics

An Irrotational Flow Field That Approximates Flat Plate Boundary Conditions

OpenAIRE

Ruffa, Anthony A.

2004-01-01

An irrotational solution is derived for the steady-state Navier-Stokes equations that approximately satisfies the boundary conditions for flow over a finite flat plate. The nature of the flow differs substantially from boundary layer flow, with severe numerical difficulties in some regions.

Schrödinger functional boundary conditions and improvement for N > 3

DEFF Research Database (Denmark)

Hietanen, A.; Karavirta, T.; Vilaseca, P.

2014-01-01

The standard method to calculate non-perturbatively the evolution of the running coupling of a SU(N ) gauge theory is based on the Schrodinger functional (SF). In this paper we construct a family of boundary fields for general values of N which enter the standard definition of the SF coupling. We...... provide spatial boundary conditions for fermions in several representations which reduce the condition number of the squared Dirac operator. In addition, we calculate the improvement coefficients for N > 3 needed to remove boundary cutoff effects from the gauge action. After this, residual cutoff effects...

Solution to random differential equations with boundary conditions

Directory of Open Access Journals (Sweden)

Fairouz Tchier

2017-04-01

Full Text Available We study a family of random differential equations with boundary conditions. Using a random fixed point theorem, we prove an existence theorem that yields a unique random solution.

Casimir energy in d-dimensional rectangular geometries, under mixed boundary conditions

International Nuclear Information System (INIS)

Silva, J.C. da; Placido, Hebe Q.; Santana, A.E.; M Neto, Arthur

1997-01-01

The Casimir energy and its temperature corrections are presented for the electromagnetic field confined in a d-dimensional hypercavity. The expressions are derived considering Dirichlet boundary conditions for each pair of hyperplanes defining a confined direction (the homogeneous case); or yet, by choosing different boundary conditions (Dirichlet or Neumann) at each hyperplane of the pair (the mixed case). (author)

Bosonization relations as bag boundary conditions

International Nuclear Information System (INIS)

Nadkarni, S.; Nielsen, H.B.; Zahed, I.

1984-10-01

The more sophisticated bag models of hadrons become, the less precisely they seem to determine the bag radius. Idealizing this situation leads to the concept of exact bag models - ''Cheshire Cat'' models, CCM'S - where the physics is completely insensitive to changes in the bag radius. CCM's are constructed explitly in 1+1-dimensions, where exact bosonization relations are known. In the formalism of bag models, these relations appear as boundary conditions which ensure that the shifting of the bag wall has no physical effect. Other notable features of 1+1-dimensional CCM's are: (i) Fermion number, though classically confined, can escape the bag via a vector current anomaly at the surface. (ii) Essentially the same boundary action works for a variety of models and its symmetries determine those of the external boson fields. Remarkably enough, this 1+1-dimensional boundary action has precisely the same form as the one used in 3+1-dimensional chiral bag models, lending support to the belief that the latter are indeed approximateCCM's. These 1+1-dimensional results are expected to provide useful guidelines in the attempt to, at least approximately, besonize 3+1-dimensional QCD. (orig.)

Bifurcation of positive solutions to scalar reaction-diffusion equations with nonlinear boundary condition

Science.gov (United States)

Liu, Ping; Shi, Junping

2018-01-01

The bifurcation of non-trivial steady state solutions of a scalar reaction-diffusion equation with nonlinear boundary conditions is considered using several new abstract bifurcation theorems. The existence and stability of positive steady state solutions are proved using a unified approach. The general results are applied to a Laplace equation with nonlinear boundary condition and bistable nonlinearity, and an elliptic equation with superlinear nonlinearity and sublinear boundary conditions.

Calculation of effective impedance of polycrystals in weak magnetic fields

International Nuclear Information System (INIS)

Kaganova, I.M.

2006-01-01

We present results for the effective surface impedance tensor (EIT) of polycrystals of metals in a weak uniform magnetic field H. The frequency region corresponds to the region in which the local impedance boundary conditions are applicable. We suppose that the resistivity tensor ρ ik (H) of the single crystal grains out of which the polycrystal is composed, is known up to the terms of O(H 2 ). For polycrystals of metals of arbitrary symmetry, the elements of the EIT can be calculated to the same order in H, even if the tensor ρ ik (H) is strongly anisotropic. As examples, we write down the EIT of polycrystals of (i) cubic metals (ii) metals with ellipsoidal Fermi surfaces, and (iii) metals of tetragonal symmetry whose tensor ρ ik (0) is strongly anisotropic. Although polycrystals are metals that are isotropic on average, in the presence of a uniform magnetic field the structure of the EIT is not the same as the structure of the impedance tensor of an isotropic metal with a spherical Fermi surface. The results cannot be improved either by taking into account higher powers of H, or with respect to the anisotropy of the single crystal grains

Variational constraints for electrical-impedance tomography

International Nuclear Information System (INIS)

Berryman, J.G.; Kohn, R.V.

1990-01-01

The task of electrical-impedance tomography is to invert boundary measurements for the conductivity distribution of a body. This inverse problem can be formulated so the primary data are the measured powers dissipated across injection electrodes. Then, since these powers are minima of the pertinent (dual) variational principles, feasibility constraints can be found for the nonlinear inversion problem. When power may be measured accurately, the existence of these dual variational principles implies that any exact solution must lie at a point of intersection of the two feasibility boundaries

Boundary conditions for open quantum systems driven far from equilibrium

Science.gov (United States)

Frensley, William R.

1990-07-01

This is a study of simple kinetic models of open systems, in the sense of systems that can exchange conserved particles with their environment. The system is assumed to be one dimensional and situated between two particle reservoirs. Such a system is readily driven far from equilibrium if the chemical potentials of the reservoirs differ appreciably. The openness of the system modifies the spatial boundary conditions on the single-particle Liouville-von Neumann equation, leading to a non-Hermitian Liouville operator. If the open-system boundary conditions are time reversible, exponentially growing (unphysical) solutions are introduced into the time dependence of the density matrix. This problem is avoided by applying time-irreversible boundary conditions to the Wigner distribution function. These boundary conditions model the external environment as ideal particle reservoirs with properties analogous to those of a blackbody. This time-irreversible model may be numerically evaluated in a discrete approximation and has been applied to the study of a resonant-tunneling semiconductor diode. The physical and mathematical properties of the irreversible kinetic model, in both its discrete and its continuum formulations, are examined in detail. The model demonstrates the distinction in kinetic theory between commutator superoperators, which may become non-Hermitian to describe irreversible behavior, and anticommutator superoperators, which remain Hermitian and are used to evaluate physical observables.

Determination of beam coupling impedance in the frequency domain

Energy Technology Data Exchange (ETDEWEB)

Niedermayer, Uwe

2016-07-01

The concept of beam coupling impedance describes the electromagnetic interaction of uniformly moving charged particles with their surrounding structures in the Frequency Domain (FD). In synchrotron accelerators, beam coupling impedances can lead to beam induced component heating and coherent beam instabilities. Thus, in order to ensure the stable operation of a synchrotron, its impedances have to be quantified and their effects have to be controlled. Nowadays, beam coupling impedances are mostly obtained by Fourier transform of wake potentials, which are the results of Time Domain (TD) simulations. However, at low frequencies, low beam velocity, or for dispersive materials, TD simulations become unhandy. In this area, analytical calculations of beam coupling impedance in the FD, combined with geometry approximations, are still widely used. This thesis describes the development of two electromagnetic field solvers to obtain the beam coupling impedance directly in the FD, where the beam velocity is only a parameter and dispersive materials can be included easily. One solver is based on the Finite Integration Technique (FIT) on a staircase mesh. It is implemented both in 2D and 3D. However, the staircase mesh is inefficient on curved structures, which is particularly problematic for the modeling of a dipole source, that is required for the computation of the transverse beam coupling impedance. This issue is overcome by the second solver developed in this thesis, which is based on the Finite Element Method (FEM) on an unstructured triangular mesh. It is implemented in 2D and includes an optional Surface Impedance Boundary Condition (SIBC). Thus, it is well suited for the computation of longitudinal and transverse impedances of long beam pipe structures of arbitrary cross-section. Besides arbitrary frequency and beam velocity, also dispersive materials can be chosen, which is crucial for the computation of the impedance of ferrite kicker magnets. Numerical impedance

Boundary condition effect on response modification factor of X-braced steel frames

Directory of Open Access Journals (Sweden)

Walid A. Attia

2018-04-01

Full Text Available Design of the structures to resist seismic force depends on the theory of dissipation in elastic energy that already exists in response modification factor “R-factor”. The main problem in codes gives a constant value for R-factor, since change in boundary conditions of building change in behavior of braced steel frame structures and that effects on R-factor. This study is an attempt to assess overstrength, ductility and response modification factor of X-braced steel frame under change in boundary conditions, as change in the direction of strong axis of column and connection support type of column besides variation in storey and bays numbers to be 21 frames and each frame has 8 different boundary conditions as sum of 168 cases for analysis. These frames were analyzed by using nonlinear static “pushover” analysis. As results of this study change in support type and direction of strong axis of column give large change in value of R-factor; the minimum value was 4.37 and maximum value 10.97. Minimum value is close to code value that’s mean the code is more conservative in suggesting of R-factor and gives a large factor of safety. Change in the location of bracing gives change in value of R-factor for all boundary conditions. Change in direction of strong axis of columns and support type didn’t give change in value of fundamental period, all boundary conditions. Keywords: Response modification factor, Ductility reduction factor, Overstrength factor, Boundary conditions, Brace frame, Nonlinear static analysis “Pushover”

Impedance measurements on YB/sub 2/Cu/sub 3/O/sub 7-delta) interpretation and trapping parameters

International Nuclear Information System (INIS)

Yasmeen, S.; Mohammad, M.; Khan, A.Y.; Subhani, M.S.

1997-01-01

Two probe impedance spectroscopic studies were carried out on YBa/sub 2/Cu/sub 3/ O/sub 7-delta/ two different sintering conditions i.e. at before final sintering and at after final sintering. In both condition ac impedance studies were done in the frequency range of 1Hz to 100kHz and at different temperatures from room temperature down to 78K. Measurements were done with contacts opposite side (i.e., ceramic behaves as a resister) as well as on opposite sides (i.e., ceramic behaves as a capacitor). Results were obtained in the form of Nyquist plot. Log, Yi/omega Vs log f plot and Yr/omega Vs log f plot. These plots were explained through equivalent circuits. The bulk resistance Rb, the grain boundary resistance R/sub b/ and grain boundary capacitance C/sub gb/ were obtained through these plots. The ac conductivities were also obtained at all temperatures. The log sigma g Vs log omega (frequency) plots were interpreted invoking the theory of ac conductivity in polycrystalline solids. The trapping parameters (binding energy, the hopping distance etc.) were calculated and interpreted. (author)

Identification of Critical Transmission Limits in Injection Impedance Plane

DEFF Research Database (Denmark)

Jóhannsson, Hjörtur; Østergaard, Jacob; Nielsen, Arne Hejde

2012-01-01

In this paper, equations are derived that describe the mapping of critical boundaries and characteristic lines from the three dimensionalPQV-surface into the two-dimensional injection impedance plane (load impedance plane for both positive and negativeresistance). The expressions derived....... The situational awareness method will bedescribed in a later paper, where this paper focuses on the derivations of some system characteristics in the injection (or load)impedance plane. The critical lines from the PQV-surface that are mapped into the impedance plane are the ones representing theconditions where...... the partial derivatives of the variables P,Q and V in respect to each other become zero. In addition to the mappingof the critical lines, some characteristic lines are mapped as well. These include the mapping of the lines of constant P,Q,Vand d from the PQV-surface into the impedance plane. All of the mapped...

Uniqueness theorems for differential pencils with eigenparameter boundary conditions and transmission conditions

Science.gov (United States)

Yang, Chuan-Fu

Inverse spectral problems are considered for differential pencils with boundary conditions depending polynomially on the spectral parameter and with a finite number of transmission conditions. We give formulations of the associated inverse problems such as Titchmarsh-Weyl theorem, Hochstadt-Lieberman theorem and Mochizuki-Trooshin theorem, and prove corresponding uniqueness theorems. The obtained results are generalizations of the similar results for the classical Sturm-Liouville operator on a finite interval.

Simple Navier’s slip boundary condition for the non-Newtonian Lattice Boltzmann fluid dynamics solver

DEFF Research Database (Denmark)

Svec, Oldrich; Skoček, Jan

2013-01-01

The ability of the Lattice Boltzmann method, as the fluid dynamics solver, to properly simulate macroscopic Navier’s slip boundary condition is investigated. An approximate equation relating the Lattice Boltzmann variable slip boundary condition with the macroscopic Navier’s slip boundary condition...

BOUNDARY CONDITIONS IN GAP GEOMETRY

Energy Technology Data Exchange (ETDEWEB)

Rothenstein, W.; Helholtz, J.

1963-11-15

The procedure for calculnting the monoenergetic angular flux density in lattice cells including voids between fuel and moderator is discussed. Boundary conditions describThe thermal energy of a nuclear reactor may be conserved by using as the reactor coolant a hydrocarbon fraction boiling within the range 220 to 650 deg C (preferably 340 to 550 deg C) and containing not more than 5% of extraneous materials having neutron cross sections of > 10 barns. The hot coolant may either be cracked outside of the reactor or used to heat another petroleum hydrocarbon which is to be converted. (D.L.C.)

Atmospheric-radiation boundary conditions for high-frequency waves in time-distance helioseismology

Science.gov (United States)

Fournier, D.; Leguèbe, M.; Hanson, C. S.; Gizon, L.; Barucq, H.; Chabassier, J.; Duruflé, M.

2017-12-01

The temporal covariance between seismic waves measured at two locations on the solar surface is the fundamental observable in time-distance helioseismology. Above the acoustic cut-off frequency ( 5.3 mHz), waves are not trapped in the solar interior and the covariance function can be used to probe the upper atmosphere. We wish to implement appropriate radiative boundary conditions for computing the propagation of high-frequency waves in the solar atmosphere. We consider recently developed and published radiative boundary conditions for atmospheres in which sound-speed is constant and density decreases exponentially with radius. We compute the cross-covariance function using a finite element method in spherical geometry and in the frequency domain. The ratio between first- and second-skip amplitudes in the time-distance diagram is used as a diagnostic to compare boundary conditions and to compare with observations. We find that a boundary condition applied 500 km above the photosphere and derived under the approximation of small angles of incidence accurately reproduces the "infinite atmosphere" solution for high-frequency waves. When the radiative boundary condition is applied 2 Mm above the photosphere, we find that the choice of atmospheric model affects the time-distance diagram. In particular, the time-distance diagram exhibits double-ridge structure when using a Vernazza Avrett Loeser atmospheric model.

Mixed problems for linear symmetric hyperbolic systems with characteristic boundary conditions

International Nuclear Information System (INIS)

Secchi, P.

1994-01-01

We consider the initial-boundary value problem for symmetric hyperbolic systems with characteristic boundary of constant multiplicity. In the linear case we give some results about the existence of regular solutions in suitable functions spaces which take in account the loss of regularity in the normal direction to the characteristic boundary. We also consider the equations of ideal magneto-hydrodynamics under perfectly conducting wall boundary conditions and give some results about the solvability of such mixed problem. (author). 16 refs

Impedance Spectroscopy Study of the Effect of Environmental Conditions on the Microstructure Development of Sustainable Fly Ash Cement Mortars.

Science.gov (United States)

Ortega, José Marcos; Sánchez, Isidro; Climent, Miguel Ángel

2017-09-25

Today, the characterisation of the microstructure of cement-based materials using non-destructive techniques has become an important topic of study, and among them, the impedance spectroscopy has recently experienced great progress. In this research, mortars with two different contents of fly ash were exposed to four different constant temperature and relative humidity environments during a 180-day period. The evolution of their microstructure was studied using impedance spectroscopy, whose results were contrasted with mercury intrusion porosimetry. The hardening environment has an influence on the microstructure of fly ash cement mortars. On one hand, the impedance resistances R₁ and R₂ are more influenced by the drying of the materials than by microstructure development, so they are not suitable for following the evolution of the porous network under non-optimum conditions. On the other hand, the impedance spectroscopy capacitances C₁ and C₂ allow studying the microstructure development of fly ash cement mortars exposed to those conditions, and their results are in accordance with mercury intrusion porosimetry ones. Finally, it has been observed that the combined analysis of the abovementioned capacitances could be very useful for studying shrinkage processes in cement-based materials kept in low relative humidity environments.

Flow boundary conditions for chain-end adsorbing polymer blends.

Science.gov (United States)

Zhou, Xin; Andrienko, Denis; Delle Site, Luigi; Kremer, Kurt

2005-09-08

Using the phenol-terminated polycarbonate blend as an example, we demonstrate that the hydrodynamic boundary conditions for a flow of an adsorbing polymer melt are extremely sensitive to the structure of the epitaxial layer. Under shear, the adsorbed parts (chain ends) of the polymer melt move along the equipotential lines of the surface potential whereas the adsorbed additives serve as the surface defects. In response to the increase of the number of the adsorbed additives the surface layer becomes thinner and solidifies. This results in a gradual transition from the slip to the no-slip boundary condition for the melt flow, with a nonmonotonic dependence of the slip length on the surface concentration of the adsorbed ends.

Scalar field dynamics in a BTZ background with generic boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Garbarz, Alan; La Madrid, Joan [UBA y IFIBA, CONICET, Departamento de Fisica, FCEyN, Buenos Aires (Argentina); Leston, Mauricio [Pabellon IAFE-CONICET, Instituto de Astronomia y Fisica del Espacio, Buenos Aires (Argentina)

2017-11-15

We revisit the dynamics of a massive scalar field in a Banados, Teitelboim, and Zanelli background taking into account the lack of global hyperbolicity of the spacetime. We approach this issue using the strategy of Ishibashi and Wald which finds a unique smooth solution as the causal evolution of initial data, each possible evolution corresponding to a positive self-adjoint extension of certain operator in a Hilbert space on the initial surface. Moreover, solutions obtained this way are the most general ones satisfying a few physically sensible requirements. This procedure is intimately related to the choice of boundary conditions and the existence of bound states. We find that the scalar field dynamics in the (effective) mass window -3/4 ≤ m{sub e}{sup 2}l{sup 2} < 0 can be well defined within a one-parametric family of distinct boundary conditions (-3/4 being the conformally coupled case), while for m{sub e}{sup 2}l{sup 2} ≥ 0 the boundary condition is unique (only one self-adjoint extension is possible). It is argued that there is no sensible evolution possible for m{sub e}{sup 2}l{sup 2} < -1, and also it is shown that in the range m{sub e}{sup 2}l{sup 2} element of [-1, -3/4) there is a U(1) family of allowed boundary conditions, however, the positivity of the self-adjoint extensions is only motivated but not proven. We focus mainly on describing the dynamics of such evolutions given the initial data and all possible boundary conditions, and in particular we show the energy is always positive and conserved. (orig.)

Attractor of Beam Equation with Structural Damping under Nonlinear Boundary Conditions

Directory of Open Access Journals (Sweden)

Danxia Wang

2015-01-01

Full Text Available Simultaneously, considering the viscous effect of material, damping of medium, and rotational inertia, we study a kind of more general Kirchhoff-type extensible beam equation utt-uxxtt+uxxxx-σ(∫0l‍(ux2dxuxx-ϕ(∫0l‍(ux2dxuxxt=q(x, in  [0,L]×R+ with the structural damping and the rotational inertia term. Little attention is paid to the longtime behavior of the beam equation under nonlinear boundary conditions. In this paper, under nonlinear boundary conditions, we prove not only the existence and uniqueness of global solutions by prior estimates combined with some inequality skills, but also the existence of a global attractor by the existence of an absorbing set and asymptotic compactness of corresponding solution semigroup. In addition, the same results also can be proved under the other nonlinear boundary conditions.

Stabilizing local boundary conditions for two-dimensional shallow water equations

KAUST Repository

Dia, Ben Mansour

2018-03-27

In this article, we present a sub-critical two-dimensional shallow water flow regulation. From the energy estimate of a set of one-dimensional boundary stabilization problems, we obtain a set of polynomial equations with respect to the boundary values as a requirement for the energy decrease. Using the Riemann invariant analysis, we build stabilizing local boundary conditions that guarantee the stability of the hydrodynamical state around a given steady state. Numerical results for the controller applied to the nonlinear problem demonstrate the performance of the method.

Enhancement of single mode operation in coaxial optical waveguide using DB boundary conditions

Science.gov (United States)

Lohia, Pooja; Prajapati, Y.; Saini, J. P.; Rai, B. S.

2014-11-01

In this study, a competent numerical strategy to compute the dispersion of optical waveguides is presented and propagation of electromagnetic waves in a coaxial optical waveguide with DB boundary conditions is instigated. For this intend, cylindrical coordinates are here being used to derive the DB boundary conditions and to obtain field components for the modes. The propagation constant for the waveguide to be studied is determined by solving the Bessel and the modified Bessel functions. The cutoff frequencies for various lower order modes have been calculated and their dispersion characteristics are plotted correspondingly. The behavior of the coaxial optical waveguide under DB boundary conditions is shown to be significantly different from that of coaxial optical waveguide and conventional optical waveguide under traditional or tangential boundary conditions. Finally, the effect of waveguide dimensions on the mode cutoff frequencies and fabrication issues are also addressed.

Hydrogeological boundary settings in SR 97. Uncertainties in regional boundary settings and transfer of boundary conditions to site-scale models

International Nuclear Information System (INIS)

Follin, S.

1999-06-01

The SR 97 project presents a performance assessment (PA) of the overall safety of a hypothetical deep repository at three sites in Sweden arbitrarily named Aberg, Beberg and Ceberg. One component of this PA assesses the uncertainties in the hydrogeological modelling. This study focuses on uncertainties in boundary settings (size of model domain and boundary conditions) in the regional and site-scale hydrogeological modelling of the three sites used to simulating the possible transport of radionuclides from the emplacement waste packages through the host rock to the accessible environment. Model uncertainties associated with, for instance, parameter heterogeneity and structural interpretations are addressed in other studies. This study concludes that the regional modelling of the SR 97 project addresses uncertainties in the choice of boundary conditions and size of model domain differently at each site, although the overall handling is acceptable and in accordance with common modelling practice. For example, the treatment of uncertainties with regard to the ongoing post-glacial flushing of the Baltic Shield is creditably addressed although not exhaustive from a modelling point of view. A significant contribution of the performed modelling is the study of nested numerical models, i.e., the numerical interplay between regional and site-scale numerical models. In the site-scale modelling great efforts are made to address problems associated with (i) the telescopic mesh refinement (TMR) technique with regard to the stochastic continuum approach, and (ii) the transfer of boundary conditions between variable-density flow systems and flow systems that are constrained to treat uniform density flow. This study concludes that the efforts made to handle these problems are acceptable with regards to the objectives of the SR 97 project

Boundary conditions and dualities: vector fields in AdS/CFT

International Nuclear Information System (INIS)

Marolf, Donald; Ross, Simo F.

2006-01-01

In AdS, scalar fields with masses slightly above the Breitenlohner-Freedman bound admit a variety of possible boundary conditions which are reflected in the Lagrangian of the dual field theory. Generic small changes in the AdS boundary conditions correspond to deformations of the dual field theory by multi-trace operators. Here we extend this discussion to the case of vector gauge fields in the bulk spacetime using the results of Ishibashi and Wald [hep-th/0402184]. As in the context of scalar fields, general boundary conditions for vector fields involve multi-trace deformations which lead to renormalization-group flows. Such flows originate in ultra-violet CFTs which give new gauge/gravity dualities. At least for AdS 4 /CFT 3 , the dual of the bulk photon appears to be a propagating gauge field instead of the usual R-charge current. Applying similar reasoning to tensor fields suggests the existence of a duality between string theory on AdS 4 and a quantum gravity theory in three dimensions

Nonlinear fractional differential equations and inclusions of arbitrary order and multi-strip boundary conditions

Directory of Open Access Journals (Sweden)

Bashir Ahmad

2012-06-01

Full Text Available We study boundary value problems of nonlinear fractional differential equations and inclusions of order $q in (m-1, m]$, $m ge 2$ with multi-strip boundary conditions. Multi-strip boundary conditions may be regarded as the generalization of multi-point boundary conditions. Our problem is new in the sense that we consider a nonlocal strip condition of the form: $$ x(1=sum_{i=1}^{n-2}alpha_i int^{eta_i}_{zeta_i} x(sds, $$ which can be viewed as an extension of a multi-point nonlocal boundary condition: $$ x(1=sum_{i=1}^{n-2}alpha_i x(eta_i. $$ In fact, the strip condition corresponds to a continuous distribution of the values of the unknown function on arbitrary finite segments $(zeta_i,eta_i$ of the interval $[0,1]$ and the effect of these strips is accumulated at $x=1$. Such problems occur in the applied fields such as wave propagation and geophysics. Some new existence and uniqueness results are obtained by using a variety of fixed point theorems. Some illustrative examples are also discussed.

Transducer placement for robustness to variations in boundary conditions for active structural acoustic control

Science.gov (United States)

Sprofera, Joseph D.; Clark, Robert L.; Cabell, Randolph H.; Gibbs, Gary P.

2005-05-01

Turbulent boundary layer (TBL) noise is considered a primary contribution to the interior noise present in commercial airliners. There are numerous investigations of interior noise control devoted to aircraft panels; however, practical realization is a potential challenge since physical boundary conditions are uncertain at best. In most prior studies, pinned or clamped boundary conditions were assumed; however, realistic panels likely display a range of boundary conditions between these two limits. Uncertainty in boundary conditions is a challenge for control system designers, both in terms of the compensator implemented and the location of transducers required to achieve the desired control. The impact of model uncertainties, specifically uncertain boundaries, on the selection of transducer locations for structural acoustic control is considered herein. The final goal of this work is the design of an aircraft panel structure that can reduce TBL noise transmission through the use of a completely adaptive, single-input, single-output control system. The feasibility of this goal is demonstrated through the creation of a detailed analytical solution, followed by the implementation of a test model in a transmission loss apparatus. Successfully realizing a control system robust to variations in boundary conditions can lead to the design and implementation of practical adaptive structures that could be used to control the transmission of sound to the interior of aircraft. Results from this research effort indicate it is possible to optimize the design of actuator and sensor location and aperture, minimizing the impact of boundary conditions on the desired structural acoustic control.

Homogenized boundary conditions and resonance effects in Faraday cages

OpenAIRE

Hewett, DP; Hewitt, IJ

2016-01-01

We present a mathematical study of two-dimensional electrostatic and electromagnetic shielding by a cage of conducting wires (the so-called `Faraday cage e ect'). Taking the limit as the number of wires in the cage tends to in nity we use the asymptotic method of multiple scales to derive continuum models for the shielding, involving homogenized boundary conditions on an e ective cage boundary. We show how the resulting models depend on key cage parameters such as the...

Explicit treatment for Dirichlet, Neumann and Cauchy boundary conditions in POD-based reduction of groundwater models

Science.gov (United States)

Gosses, Moritz; Nowak, Wolfgang; Wöhling, Thomas

2018-05-01

In recent years, proper orthogonal decomposition (POD) has become a popular model reduction method in the field of groundwater modeling. It is used to mitigate the problem of long run times that are often associated with physically-based modeling of natural systems, especially for parameter estimation and uncertainty analysis. POD-based techniques reproduce groundwater head fields sufficiently accurate for a variety of applications. However, no study has investigated how POD techniques affect the accuracy of different boundary conditions found in groundwater models. We show that the current treatment of boundary conditions in POD causes inaccuracies for these boundaries in the reduced models. We provide an improved method that splits the POD projection space into a subspace orthogonal to the boundary conditions and a separate subspace that enforces the boundary conditions. To test the method for Dirichlet, Neumann and Cauchy boundary conditions, four simple transient 1D-groundwater models, as well as a more complex 3D model, are set up and reduced both by standard POD and POD with the new extension. We show that, in contrast to standard POD, the new method satisfies both Dirichlet and Neumann boundary conditions. It can also be applied to Cauchy boundaries, where the flux error of standard POD is reduced by its head-independent contribution. The extension essentially shifts the focus of the projection towards the boundary conditions. Therefore, we see a slight trade-off between errors at model boundaries and overall accuracy of the reduced model. The proposed POD extension is recommended where exact treatment of boundary conditions is required.

Lattice Boltzmann simulations of pressure-driven flows in microchannels using Navier–Maxwell slip boundary conditions

KAUST Repository

Reis, Tim

2012-01-01

We present lattice Boltzmann simulations of rarefied flows driven by pressure drops along two-dimensional microchannels. Rarefied effects lead to non-zero cross-channel velocities, nonlinear variations in the pressure along the channel. Both effects are absent in flows driven by uniform body forces. We obtain second-order accuracy for the two components of velocity the pressure relative to asymptotic solutions of the compressible Navier-Stokes equations with slip boundary conditions. Since the common lattice Boltzmann formulations cannot capture Knudsen boundary layers, we replace the usual discrete analogs of the specular diffuse reflection conditions from continuous kinetic theory with a moment-based implementation of the first-order Navier-Maxwell slip boundary conditions that relate the tangential velocity to the strain rate at the boundary. We use these conditions to solve for the unknown distribution functions that propagate into the domain across the boundary. We achieve second-order accuracy by reformulating these conditions for the second set of distribution functions that arise in the derivation of the lattice Boltzmann method by an integration along characteristics. Our moment formalism is also valuable for analysing the existing boundary conditions. It reveals the origin of numerical slip in the bounce-back other common boundary conditions that impose conditions on the higher moments, not on the local tangential velocity itself. © 2012 American Institute of Physics.

Boundary conditions for quasiclassical Green's function for superfluid Fermi systems

International Nuclear Information System (INIS)

Nagai, K.; Hara, J.

1988-01-01

The authors show that the quasiclassical Green's Function for Fermi liquids can be constructed from the solutions of the Bogoliubov-de Gennes equation within the Andreev approximation and derive self-consistent relations to be satisfied by the quasiclassical Green's function at the surfaces. The so-called normalization condition for the quasiclassical Green's function is obtained from this self-consistent relation. They consider a specularly reflecting wall, a randomly rippled wall, and a proximity boundary as model surfaces. Their boundary condition for the randomly rippled wall is different from that derived by Buchholtz and Rainer and Buchholtz

The neutron transport with general boundary conditions (II)

International Nuclear Information System (INIS)

Boulanouar, Mohamed

2012-01-01

This Note deals with the one-dimensional transport operator, on an unbounded domain, endowed with general boundary conditions. We show the generation of a strongly continuous semigroup and we study its spectral properties. In particular, we prove the existence of a leading eigenvalue. (author)

Revisiting Johnson and Jackson boundary conditions for granular flows

Energy Technology Data Exchange (ETDEWEB)

Li, Tingwen; Benyahia, Sofiane

2012-07-01

In this article, we revisit Johnson and Jackson boundary conditions for granular flows. The oblique collision between a particle and a flat wall is analyzed by adopting the classic rigid-body theory and a more realistic semianalytical model. Based on the kinetic granular theory, the input parameter for the partial-slip boundary conditions, specularity coefficient, which is not measurable in experiments, is then interpreted as a function of the particle-wall restitution coefficient, the frictional coefficient, and the normalized slip velocity at the wall. An analytical expression for the specularity coefficient is suggested for a flat, frictional surface with a low frictional coefficient. The procedure for determining the specularity coefficient for a more general problem is outlined, and a working approximation is provided.

Investigation of body's impedance under different conditions for electro-acupuncture

International Nuclear Information System (INIS)

Ahmed, M.M.; Abrarov, S.; Khan, R.R.; Maqsood, R.S.; Qaiser, M.A.; Karimov, Kh. S.

2001-01-01

A computer controlled automated setup has been designed to investigate the body acupuncture points (bio-active points) by using a probes matrix which exerts a uniform pressure on the body. 16 probes matrix was placed in a 15 : 15 mm/sup 2/ dielectric substrate with 5 mm inter probe distance, compatible with the average diameter of the points. These probes have been designed to facilitate a semiconductor injection laser for probing of the points along with optical and/or electric signal. The bioactive points were identified by evaluating the impedance between each probe and a hand held electrode through a micro-controlled scan. This also allowed the selection of an appropriate signal - DC, AC or tidal waveform, for the electric treatment of bioactive points. It has been found that body impedance decreases with the increase of measuring voltage. Moreover, for current-voltage characteristics a nonlinearity coefficient in the range 2-3 was also observed. The study revealed that at low applied voltages 0.l V, the impedance depends on the polarity of the applied signal. Furthermore, body impedance decreases nonlinearly by increasing the probe's pressure on the skin, which may be attributed to piezo resistive effect. By using the AC and Dc measurements an appropriate body equivalent circuit is proposed in this investigation. (author)

A study on calculation method for mechanical impedance of air spring

International Nuclear Information System (INIS)

Changgeng, Shuai; Penghui, Li; Rustighi, Emiliano

2016-01-01

This paper proposes an approximate analytic method of obtaining the mechanical impedance of air spring. The sound pressure distribution in cylindrical air spring is calculated based on the linear air wave theory. The influences of different boundary conditions on the acoustic pressure field distribution in cylindrical air spring are analysed. A 1-order ordinary differential matrix equation for the state vector of revolutionary shells under internal pressure is derived based on the non-moment theory of elastic thin shell. Referring to the transfer matrix method, a kind of expanded homogeneous capacity high precision integration method is introduced to solve the non-homogeneous matrix differential equation. Combined the solved stress field of shell with the calculated sound pressure field in air spring under the displacement harmonic excitation, the approximate analytical expression of the input and transfer mechanical impedance for the air spring can be achieved. The numerical simulation with the Comsol Multiphysics software verifies the correctness of theoretical analysis result. (paper)

Three Boundary Conditions for Computing the Fixed-Point Property in Binary Mixture Data.

Directory of Open Access Journals (Sweden)

Leendert van Maanen

Full Text Available The notion of "mixtures" has become pervasive in behavioral and cognitive sciences, due to the success of dual-process theories of cognition. However, providing support for such dual-process theories is not trivial, as it crucially requires properties in the data that are specific to mixture of cognitive processes. In theory, one such property could be the fixed-point property of binary mixture data, applied-for instance- to response times. In that case, the fixed-point property entails that response time distributions obtained in an experiment in which the mixture proportion is manipulated would have a common density point. In the current article, we discuss the application of the fixed-point property and identify three boundary conditions under which the fixed-point property will not be interpretable. In Boundary condition 1, a finding in support of the fixed-point will be mute because of a lack of difference between conditions. Boundary condition 2 refers to the case in which the extreme conditions are so different that a mixture may display bimodality. In this case, a mixture hypothesis is clearly supported, yet the fixed-point may not be found. In Boundary condition 3 the fixed-point may also not be present, yet a mixture might still exist but is occluded due to additional changes in behavior. Finding the fixed-property provides strong support for a dual-process account, yet the boundary conditions that we identify should be considered before making inferences about underlying psychological processes.

The Hardy inequality with boundary or intermediate conditions

Czech Academy of Sciences Publication Activity Database

Kufner, Alois

2017-01-01

Roč. 8, č. 2 (2017), s. 105-109 ISSN 2077-9879 Institutional support: RVO:67985840 Keywords : Hardy's inequality * boundary conditions Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics http://www.mathnet.ru/ php /archive.phtml?wshow=paper&jrnid=emj&paperid=259&option_lang=eng

The Hardy inequality with boundary or intermediate conditions

Czech Academy of Sciences Publication Activity Database

Kufner, Alois

2017-01-01

Roč. 8, č. 2 (2017), s. 105-109 ISSN 2077-9879 Institutional support: RVO:67985840 Keywords : Hardy's inequality * boundary conditions Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=emj&paperid=259&option_lang=eng

An iterative kernel based method for fourth order nonlinear equation with nonlinear boundary condition

Science.gov (United States)

Azarnavid, Babak; Parand, Kourosh; Abbasbandy, Saeid

2018-06-01

This article discusses an iterative reproducing kernel method with respect to its effectiveness and capability of solving a fourth-order boundary value problem with nonlinear boundary conditions modeling beams on elastic foundations. Since there is no method of obtaining reproducing kernel which satisfies nonlinear boundary conditions, the standard reproducing kernel methods cannot be used directly to solve boundary value problems with nonlinear boundary conditions as there is no knowledge about the existence and uniqueness of the solution. The aim of this paper is, therefore, to construct an iterative method by the use of a combination of reproducing kernel Hilbert space method and a shooting-like technique to solve the mentioned problems. Error estimation for reproducing kernel Hilbert space methods for nonlinear boundary value problems have yet to be discussed in the literature. In this paper, we present error estimation for the reproducing kernel method to solve nonlinear boundary value problems probably for the first time. Some numerical results are given out to demonstrate the applicability of the method.

A One-Dimensional Wave Equation with White Noise Boundary Condition

International Nuclear Information System (INIS)

Kim, Jong Uhn

2006-01-01

We discuss the Cauchy problem for a one-dimensional wave equation with white noise boundary condition. We also establish the existence of an invariant measure when the noise is additive. Similar problems for parabolic equations were discussed by several authors. To our knowledge, there is only one work which investigated the initial-boundary value problem for a wave equation with random noise at the boundary. We handle a more general case by a different method. Our result on the existence of an invariant measure relies on the author's recent work on a certain class of stochastic evolution equations

Dirac perturbations on Schwarzschild-anti-de Sitter spacetimes: Generic boundary conditions and new quasinormal modes

Science.gov (United States)

Wang, Mengjie; Herdeiro, Carlos; Jing, Jiliang

2017-11-01

We study Dirac quasinormal modes of Schwarzschild-anti-de Sitter (Schwarzschild-AdS) black holes, following the generic principle for allowed boundary conditions proposed in [M. Wang, C. Herdeiro, and M. O. P. Sampaio, Phys. Rev. D 92, 124006 (2015)., 10.1103/PhysRevD.92.124006]. After deriving the equations of motion for Dirac fields on the aforementioned background, we impose vanishing energy flux boundary conditions to solve these equations. We find a set of two Robin boundary conditions are allowed. These two boundary conditions are used to calculate Dirac normal modes on empty AdS and quasinormal modes on Schwarzschild-AdS black holes. In the former case, we recover the known normal modes of empty AdS; in the latter case, the two sets of Robin boundary conditions lead to two different branches of quasinormal modes. The impact on these modes of the black hole size, the angular momentum quantum number and the overtone number are discussed. Our results show that vanishing energy flux boundary conditions are a robust principle, applicable not only to bosonic fields but also to fermionic fields.

Quantum communication through a spin ring with twisted boundary conditions

International Nuclear Information System (INIS)

Bose, S.; Jin, B.-Q.; Korepin, V.E.

2005-01-01

We investigate quantum communication between the sites of a spin ring with twisted boundary conditions. Such boundary conditions can be achieved by a magnetic flux through the ring. We find that a nonzero twist can improve communication through finite odd-numbered rings and enable high-fidelity multiparty quantum communication through spin rings (working near perfectly for rings of five and seven spins). We show that in certain cases, the twist results in the complete blockage of quantum-information flow to a certain site of the ring. This effect can be exploited to interface and entangle a flux qubit and a spin qubit without embedding the latter in a magnetic field

The effects of external conditions in turbulent boundary layers

Science.gov (United States)

Brzek, Brian G.

The effects of multiple external conditions on turbulent boundary layers were studied in detail. These external conditions include: surface roughness, upstream turbulence intensity, and pressure gradient. Furthermore, the combined effects of these conditions show the complicated nature of many realistic flow conditions. It was found that the effects of surface roughness are difficult to generalize, given the importance of so many parameters. These parameters include: roughness geometry, roughness regime, roughness height to boundary layer thickness, (k/delta), roughness parameter, ( k+), Reynolds number, and roughness function (Delta B+). A further complication, is the difficulty in computing the wall shear stress, tauw/rho. For the sand grain type roughness, the mean velocity and Reynolds stresses were studied in inner and outer variables, as well as, boundary layer parameters, anisotropy tensor, production term, and viscous stress and form drag contributions. To explore the effects of roughness and Reynolds number dependence in the boundary layer, a new experiment was carefully designed to properly capture the x-dependence of the single-point statistics. It was found that roughness destroys the viscous layer near the wall, thus, reducing the contribution of the viscous stress in the wall region. As a result, the contribution in the skin friction due to form drag increases, while the viscous stress decreases. This yields Reynolds number invariance in the skin friction, near-wall roughness parameters, and inner velocity profiles as k + increases into the fully rough regime. However, in the transitionally rough regime, (i.e., 5 component shows the largest influence of roughness, where the high peak near the wall was decreased and became nearly flat for the fully rough regime profiles. In addition, the Reynolds stresses in outer variables show self-similarity for fixed experimental conditions. However, as the roughness parameter, k +, increases, all Reynolds stress

Impedance spectroscopy of ceramic solid electrolytes

International Nuclear Information System (INIS)

Muccillo, R.; Cosentino, I.C.; Florio, D.Z. de; Franca, Y.V.

1996-01-01

The Impedance Spectroscopy (IS) technique has been used to the study of Th O 2 :Y 2 O 3 , Zr O 2 :La 2 O 3 and Zr O 2 :Y 2 O 3 solid electrolytes. The results show that solid solution has been attained, grain boundaries act as oxygen-ion blockers, and the importance of the IS technique to study phase transformation in ceramics. (author)

Eigenstates of a particle in an array of hexagons with periodic boundary condition

Directory of Open Access Journals (Sweden)

A Nemati

2013-10-01

Full Text Available In this paper the problem of a particle in an array of hexagons with periodic boundary condition is solved. Using the projection operators, we categorize eigenfunctions corresponding to each of the irreducible representations of the symmetry group . Based on these results, the Dirichlet and Neumann boundary conditions are discussed.

Molecular Dynamics with Helical Periodic Boundary Conditions

Czech Academy of Sciences Publication Activity Database

Kessler, Jiří; Bouř, Petr

2014-01-01

Roč. 35, č. 21 (2014), s. 1552-1559 ISSN 0192-8651 R&D Projects: GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033 Grant - others:GA AV ČR(CZ) M200551205; GA MŠk(CZ) LM2010005 Institutional support: RVO:61388963 Keywords : periodic boundary conditions * helical symmetry * molecular dynamics * protein structure * amyloid fibrils Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.589, year: 2014

Boundary conditions in conformal and integrable theories

CERN Document Server

Petkova, V B

2000-01-01

The study of boundary conditions in rational conformal field theories is not only physically important. It also reveals a lot on the structure of the theory ``in the bulk''. The same graphs classify both the torus and the cylinder partition functions and provide data on their hidden ``quantum symmetry''. The Ocneanu triangular cells -- the 3j-symbols of these symmetries, admit various interpretations and make a link between different problems.

Boundary terms and junction conditions for the DGP π-Lagrangian and galileon

International Nuclear Information System (INIS)

Dyer, Ethan; Hinterbichler, Kurt

2009-01-01

In the decoupling limit of DGP, π describes the brane-bending degree of freedom. It obeys second order equations of motion, yet it is governed by a higher derivative Lagrangian. We show that, analogously to the Einstein-Hilbert action for GR, the π-Lagrangian requires Gibbons-Hawking-York type boundary terms to render the variational principle well-posed. These terms are important if there are other boundaries present besides the DGP brane, such as in higher dimensional cascading DGP models. We derive the necessary boundary terms in two ways. First, we derive them directly from the brane-localized π-Lagrangian by demanding well-posedness of the action. Second, we calculate them directly from the bulk, taking into account the Gibbons-Hawking-York terms in the bulk Einstein-Hilbert action. As an application, we use the new boundary terms to derive Israel junction conditions for π across a sheet-like source. In addition, we calculate boundary terms and junction conditions for the galileons which generalize the DGP π-Lagrangian, showing that the boundary term for the n-th order galileon is the (n-1)-th order galileon.

First-principle proof of the modified collision boundary conditions for the hard-sphere system

International Nuclear Information System (INIS)

Tessarotto, Massimo; Cremaschini, Claudio

2014-01-01

A fundamental issue lying at the foundation of classical statistical mechanics is the determination of the collision boundary conditions that characterize the dynamical evolution of multi-particle probability density functions (PDF) and are applicable to systems of hard-spheres undergoing multiple elastic collisions. In this paper it is proved that, when the deterministic N-body PDF is included in the class of admissible solutions of the Liouville equation, the customary form of collision boundary conditions adopted in previous literature becomes physically inconsistent and must actually be replaced by suitably modified collision boundary conditions.

Slarti: A boundary condition editor for a coupled climate model

Science.gov (United States)

Mickelson, S. A.; Jacob, R. L.; Pierrehumbert, R.

2006-12-01

One of the largest barriers to making climate models more flexible is the difficulty in creating new boundary conditions, especially for "deep time" paleoclimate cases where continents are in different positions. Climate models consist of several mutually-interacting component models and the boundary conditions must be consistent between them. We have developed a program called Slarti which uses a Graphical User Interface and a set of consistency rules to aid researchers in creating new, consistent, boundary condition files for the Fast Ocean Atmosphere Model (FOAM). Users can start from existing mask, topography, or bathymetry data or can build a "world" entirely from scratch (e.g. a single island continent). Once a case has been started, users can modify mask, vegetation, bathymetry, topography, and river flow fields by drawing new data through a "paint" interface. Users activate a synchronization button which goes through the fields to eliminate inconsistencies. When the changes are complete and save is selected, Slarti creates all the necessary files for an initial run of FOAM. The data is edited at the highest resolution (the ocean-land surface in FOAM) and then interpolated to the atmosphere resolution. Slarti was implemented in Java to maintain portability across platforms. We also relied heavily on Java Swing components to create the interface. This allowed us to create an object-oriented interface that could be used on many different systems. Since Slarti allows users to visualize their changes, they are able to see areas that may cause problems when the model is ran. Some examples would be lakes from the river flow field and narrow trenches within the bathymetry. Through different checks and options available through its interface, Slarti makes the process of creating new boundary conditions for FOAM easier and faster while reducing the chance for user errors.

How to approximate the heat equation with Neumann boundary conditions by nonlocal diffusion problems

OpenAIRE

Cortazar, C.; Elgueta, M.; Rossi, J. D.; Wolanski, N.

2006-01-01

We present a model for nonlocal diffusion with Neumann boundary conditions in a bounded smooth domain prescribing the flux through the boundary. We study the limit of this family of nonlocal diffusion operators when a rescaling parameter related to the kernel of the nonlocal operator goes to zero. We prove that the solutions of this family of problems converge to a solution of the heat equation with Neumann boundary conditions.

Reconsidering the boundary conditions for a dynamic, transient mode I crack problem

KAUST Repository

Leise, Tanya

2008-11-01

A careful examination of a dynamic mode I crack problem leads to the conclusion that the commonly used boundary conditions do not always hold in the case of an applied crack face loading, so that a modification is required to satisfy the equations. In particular, a transient compressive stress wave travels along the crack faces, moving outward from the loading region on the crack face. This does not occur in the quasistatic or steady state problems, and is a special feature of the transient dynamic problem that is important during the time interval immediately following the application of crack face loading. We demonstrate why the usual boundary conditions lead to a prediction of crack face interpenetration, and then examine how to modify the boundary condition for a semi-infinite crack with a cohesive zone. Numerical simulations illustrate the resulting approach.

Matrix factorisations for rational boundary conditions by defect fusion

International Nuclear Information System (INIS)

Behr, Nicolas; Fredenhagen, Stefan

2015-01-01

A large class of two-dimensional N=(2,2) superconformal field theories can be understood as IR fixed-points of Landau-Ginzburg models. In particular, there are rational conformal field theories that also have a Landau-Ginzburg description. To understand better the relation between the structures in the rational conformal field theory and in the Landau-Ginzburg theory, we investigate how rational B-type boundary conditions are realised as matrix factorisations in the SU(3)/U(2) Grassmannian Kazama-Suzuki model. As a tool to generate the matrix factorisations we make use of a particular interface between the Kazama-Suzuki model and products of minimal models, whose fusion can be realised as a simple functor on ring modules. This allows us to formulate a proposal for all matrix factorisations corresponding to rational boundary conditions in the SU(3)/U(2) model.

Matrix factorisations for rational boundary conditions by defect fusion

Energy Technology Data Exchange (ETDEWEB)

Behr, Nicolas [Department of Mathematics, Heriot-Watt University,Riccarton, Edinburgh, EH14 4AS (United Kingdom); Maxwell Institute for Mathematical Sciences,Edinburgh (United Kingdom); Fredenhagen, Stefan [Max-Planck-Institut für Gravitationsphysik, Albert-Einstein-Institut,D-14424 Golm (Germany)

2015-05-11

A large class of two-dimensional N=(2,2) superconformal field theories can be understood as IR fixed-points of Landau-Ginzburg models. In particular, there are rational conformal field theories that also have a Landau-Ginzburg description. To understand better the relation between the structures in the rational conformal field theory and in the Landau-Ginzburg theory, we investigate how rational B-type boundary conditions are realised as matrix factorisations in the SU(3)/U(2) Grassmannian Kazama-Suzuki model. As a tool to generate the matrix factorisations we make use of a particular interface between the Kazama-Suzuki model and products of minimal models, whose fusion can be realised as a simple functor on ring modules. This allows us to formulate a proposal for all matrix factorisations corresponding to rational boundary conditions in the SU(3)/U(2) model.

Modified impedance source inverter for power conditioning system

Indian Academy of Sciences (India)

DC link voltage boost, reduced total harmonic distortion of output current and voltage, better voltage gain and wide range of output voltage controlcan be achieved easily with improved power quality. Experimental set-up of the modified impedance source inverter with Field Programmable Gate Array (FPGA) controller has ...

Magnetic resonance electrical impedance tomography (MREIT): conductivity and current density imaging

International Nuclear Information System (INIS)

Seo, Jin Keun; Kwon, Ohin; Woo, Eung Je

2005-01-01

This paper reviews the latest impedance imaging technique called Magnetic Resonance Electrical Impedance Tomography (MREIT) providing information on electrical conductivity and current density distributions inside an electrically conducting domain such as the human body. The motivation for this research is explained by discussing conductivity changes related with physiological and pathological events, electromagnetic source imaging and electromagnetic stimulations. We briefly summarize the related technique of Electrical Impedance Tomography (EIT) that deals with cross-sectional image reconstructions of conductivity distributions from boundary measurements of current-voltage data. Noting that EIT suffers from the ill-posed nature of the corresponding inverse problem, we introduce MREIT as a new conductivity imaging modality providing images with better spatial resolution and accuracy. MREIT utilizes internal information on the induced magnetic field in addition to the boundary current-voltage measurements to produce three-dimensional images of conductivity and current density distributions. Mathematical theory, algorithms, and experimental methods of current MREIT research are described. With numerous potential applications in mind, future research directions in MREIT are proposed

Comparison of mass transport using average and transient rainfall boundary conditions

International Nuclear Information System (INIS)

Duguid, J.O.; Reeves, M.

1976-01-01

A general two-dimensional model for simulation of saturated-unsaturated transport of radionuclides in ground water has been developed and is currently being tested. The model is being applied to study the transport of radionuclides from a waste-disposal site where field investigations are currently under way to obtain the necessary model parameters. A comparison of the amount of tritium transported is made using both average and transient rainfall boundary conditions. The simulations indicate that there is no substantial difference in the transport for the two conditions tested. However, the values of dispersivity used in the unsaturated zone caused more transport above the water table than has been observed under actual conditions. This deficiency should be corrected and further comparisons should be made before average rainfall boundary conditions are used for long-term transport simulations

Natural frequency analysis of fluid conveying pipeline with different boundary conditions

International Nuclear Information System (INIS)

Huang Yimin; Liu Yongshou; Li Baohui; Li Yanjiang; Yue Zhufeng

2010-01-01

In this study, the natural frequency of fluid-structure interaction in pipeline conveying fluid is investigated by eliminated element-Galerkin method, and the natural frequency equations with different boundary conditions are obtained. Furthermore, the expressions of first natural frequency are simplified in the case of different boundary conditions. Taking into account the Coriolis force, as an example, the natural frequency of a straight pipe simply supported at both ends is studied. In a given boundary condition, the four components (mass, stiffness, length and flow velocity) which relate to the natural frequency of pipeline conveying fluid are studied in detail and the results indicate that the effect of Coriolis force on natural frequency is inappreciable. Then the relationship between natural frequency of the pipeline conveying fluid and that of Euler beam is analyzed. Finally, a dimensionless flow velocity and limit values are presented, and they can be used to estimate the effect of the flow velocity on natural frequency. All the conclusions are well suited to nuclear plant and other industry fields.

Boundary conditions for free surface inlet and outlet problems

KAUST Repository

Taroni, M.; Breward, C. J. W.; Howell, P. D.; Oliver, J. M.

2012-01-01

We investigate and compare the boundary conditions that are to be applied to free-surface problems involving inlet and outlets of Newtonian fluid, typically found in coating processes. The flux of fluid is a priori known at an inlet, but unknown

Boundary Conditions, Data Assimilation, and Predictability in Coastal Ocean Models

National Research Council Canada - National Science Library

Samelson, Roger M; Allen, John S; Egbert, Gary D; Kindle, John C; Snyder, Chris

2007-01-01

...: The specific objectives of this research are to determine the impact on coastal ocean circulation models of open ocean boundary conditions from Global Ocean Data Assimilation Experiment (GODAE...

Impedance Analysis of the Conditioning of PBI–Based Electrode Membrane Assemblies for High Temperature PEM Fuel Cells

DEFF Research Database (Denmark)

Araya, Samuel Simon; Vang, Jakob Rabjerg; Andreasen, Søren Juhl

2013-01-01

This work analyses the conditioning of single fuel cell assemblies based on different membrane electrode assembly (MEA) types, produced by different methods. The analysis was done by means of electrochemical impedance spectroscopy, and the changes in the fitted resistances of the all the tested...

Rate-Independent Processes with Linear Growth Energies and Time-Dependent Boundary Conditions

Czech Academy of Sciences Publication Activity Database

Kružík, Martin; Zimmer, J.

2012-01-01

Roč. 5, č. 3 (2012), s. 591-604 ISSN 1937-1632 R&D Projects: GA AV ČR IAA100750802 Grant - others:GA ČR(CZ) GAP201/10/0357 Institutional research plan: CEZ:AV0Z10750506 Keywords : concentrations * oscillations * time - dependent boundary conditions * rate-independent evolution Subject RIV: BA - General Mathematics http://library.utia.cas.cz/separaty/2011/MTR/kruzik-rate-independent processes with linear growth energies and time - dependent boundary conditions.pdf

Impedance Scaling and Impedance Control

International Nuclear Information System (INIS)

Chou, W.; Griffin, J.

1997-06-01

When a machine becomes really large, such as the Very Large Hadron Collider (VLHC), of which the circumference could reach the order of megameters, beam instability could be an essential bottleneck. This paper studies the scaling of the instability threshold vs. machine size when the coupling impedance scales in a ''normal'' way. It is shown that the beam would be intrinsically unstable for the VLHC. As a possible solution to this problem, it is proposed to introduce local impedance inserts for controlling the machine impedance. In the longitudinal plane, this could be done by using a heavily detuned rf cavity (e.g., a biconical structure), which could provide large imaginary impedance with the right sign (i.e., inductive or capacitive) while keeping the real part small. In the transverse direction, a carefully designed variation of the cross section of a beam pipe could generate negative impedance that would partially compensate the transverse impedance in one plane

Off-wall boundary conditions for turbulent flows obtained from buffer-layer minimal flow units

Science.gov (United States)

Garcia-Mayoral, Ricardo; Pierce, Brian; Wallace, James

2012-11-01

There is strong evidence that the transport processes in the buffer region of wall-bounded turbulence are common across various flow configurations, even in the embryonic turbulence in transition (Park et al., Phys. Fl. 24). We use this premise to develop off-wall boundary conditions for turbulent simulations. Boundary conditions are constructed from DNS databases using periodic minimal flow units and reduced order modeling. The DNS data was taken from a channel at Reτ = 400 and a zero-pressure gradient transitional boundary layer (Sayadi et al., submitted to J . FluidMech .) . Both types of boundary conditions were first tested on a DNS of the core of the channel flow with the aim of extending their application to LES and to spatially evolving flows. 2012 CTR Summer Program.

Something different - caching applied to calculation of impedance matrix elements

CSIR Research Space (South Africa)

Lysko, AA

2012-09-01

Full Text Available of the multipliers, the approximating functions are used any required parameters, such as input impedance or gain pattern etc. The method is relatively straightforward but, especially for small to medium matrices, requires spending time on filling... of the computing the impedance matrix for the method of moments, or a similar method, such as boundary element method (BEM) [22], with the help of the flowchart shown in Figure 1. Input Parameters (a) Search the cached data for a match (b) A match found...

Sensitivity analysis of an impedance void meter to the void distribution in annular flow: A theoretical study

Energy Technology Data Exchange (ETDEWEB)

Lemonnier, H.; Nakach, R.; Favreau, C.; Selmer-Olsen, S. (CEA Centre d' Etudes Nucleaires de Grenoble, 38 (France). Service d' Etudes Thermohydrauliques)

1991-04-01

Impedance void meters are frequently used to measure the are-averaged void fraction in pipes. This is primarily for two reasons: firstly, this method is non-instrusive since the measurement can be made by electrodes flush mounted in the walls, and secondly, the signal processing equipment is simple. Impedance probes may be calibrated by using a pressure drop measurement or a quick closing valve system. In general, little attention is paid to void distribution effects. It can be proved that in annular flow, the departure from radial symmetry has a strong influence on the measured mean film thickness. This can be easily demonstrated by solving the Laplace equation for the electrical potential by simple analytical methods. When some spatial symmetry conditions are encountered, it is possible to calculate directly the conductance of the two-phase medium without a complete calculation of the potential. A solution of this problem by using the separation of variables technique is also presented. The main difficulty with this technique is the mixed nature of the boundary conditions: the boundary condition is both of Neumann and of Drichlet type on the same coordinate curve. This formulation leads to a non-separable problem, which is solved by truncating an infinite algebraic set of linear equations. The results, although strictly valid in annular flow, may give the correct trends when applied to bubbly flow. Finally, the theory provides an error estimate and a design criterion to improve the probe reliability. (orig.).

Sensitivity analysis of an impedance void meter to the void distribution in annular flow: A theoretical study

International Nuclear Information System (INIS)

Lemonnier, H.; Nakach, R.; Favreau, C.; Selmer-Olsen, S.

1991-01-01

Impedance void meters are frequently used to measure the are-averaged void fraction in pipes. This is primarily for two reasons: firstly, this method is non-instrusive since the measurement can be made by electrodes flush mounted in the walls, and secondly, the signal processing equipment is simple. Impedance probes may be calibrated by using a pressure drop measurement or a quick closing valve system. In general, little attention is paid to void distribution effects. It can be proved that in annular flow, the departure from radial symmetry has a strong influence on the measured mean film thickness. This can be easily demonstrated by solving the Laplace equation for the electrical potential by simple analytical methods. When some spatial symmetry conditions are encountered, it is possible to calculate directly the conductance of the two-phase medium without a complete calculation of the potential. A solution of this problem by using the separation of variables technique is also presented. The main difficulty with this technique is the mixed nature of the boundary conditions: the boundary condition is both of Neumann and of Drichlet type on the same coordinate curve. This formulation leads to a non-separable problem, which is solved by truncating an infinite algebraic set of linear equations. The results, although strictly valid in annular flow, may give the correct trends when applied to bubbly flow. Finally, the theory provides an error estimate and a design criterion to improve the probe reliability. (orig.)

Construction of the Nuclear Effective Interaction from Energy Eigenstates and Boundary Conditions

Science.gov (United States)

McElvain, Kenneth; Haxton, Wick

2017-01-01

The original Harmonic Oscillator Based Effective Theory (HOBET) work by Haxton and Luu reduced H = T +VNN , with VNN a realistic potential, to Heff in a small basis defined by projection operator P while correctly including all scattering by H through an excluded space Q. Scattering by T is analytically included to all orders, leaving the ET expansion focused on the short range VNN. Results do not depend on the size P as the effect of scattering through Q is fully included, also distinguishing HOBET from other methods. In this talk we abandon VNN and determine the LECs of the ET expansion from energy levels and boundary conditions. In the infinite volume continuum case every energy is an eigenvalue of H with an associated scattering state. In the LQCD context boundary conditions are periodic. In either case the ET LECs can be determined from energy, boundary condition pairs. We show that the Cartesian HO ET LECs can be expressed in terms of the spherical ones, giving a spherical, infinite volume ET, bypassing the use of Luscher's method. The approach cleanly isolates operator mixing induced by the finite box, sequestering effects that vanish in the continuum limit in a Green's function constrained to match the boundary conditions. Supported by the DOE under contracts DE-SC00046548 and DE-AC02-98CH10886.

A fast Cauchy-Riemann solver. [differential equation solution for boundary conditions by finite difference approximation

Science.gov (United States)

Ghil, M.; Balgovind, R.

1979-01-01

The inhomogeneous Cauchy-Riemann equations in a rectangle are discretized by a finite difference approximation. Several different boundary conditions are treated explicitly, leading to algorithms which have overall second-order accuracy. All boundary conditions with either u or v prescribed along a side of the rectangle can be treated by similar methods. The algorithms presented here have nearly minimal time and storage requirements and seem suitable for development into a general-purpose direct Cauchy-Riemann solver for arbitrary boundary conditions.

Boundary conditions estimation of scoop dosimeter for primary sorting during earthworks

International Nuclear Information System (INIS)

Batij, V.G.; Pravdivyj, A.A.; Stoyanov, A.I.

2005-01-01

Simple method of radioactive waste first separation using collimated dosimeter, which is placed on boom of power shovel, is proposed, and separation process mathematic modeling for boundary conditions definition of sorting under 'Ukryttya' object high gamma background condition are carry out

Modeling and Grid impedance Variation Analysis of Parallel Connected Grid Connected Inverter based on Impedance Based Harmonic Analysis

DEFF Research Database (Denmark)

Kwon, JunBum; Wang, Xiongfei; Bak, Claus Leth

2014-01-01

This paper addresses the harmonic compensation error problem existing with parallel connected inverter in the same grid interface conditions by means of impedance-based analysis and modeling. Unlike the single grid connected inverter, it is found that multiple parallel connected inverters and grid...... impedance can make influence to each other if they each have a harmonic compensation function. The analysis method proposed in this paper is based on the relationship between the overall output impedance and input impedance of parallel connected inverter, where controller gain design method, which can...

Variational multiscale enrichment method with mixed boundary conditions for elasto-viscoplastic problems

Science.gov (United States)

Zhang, Shuhai; Oskay, Caglar

2015-04-01

This manuscript presents the formulation and implementation of the variational multiscale enrichment (VME) method for the analysis of elasto-viscoplastic problems. VME is a global-local approach that allows accurate fine scale representation at small subdomains, where important physical phenomena are likely to occur. The response within far-fields is idealized using a coarse scale representation. The fine scale representation not only approximates the coarse grid residual, but also accounts for the material heterogeneity. A one-parameter family of mixed boundary conditions that range from Dirichlet to Neumann is employed to study the effect of the choice of the boundary conditions at the fine scale on accuracy. The inelastic material behavior is modeled using Perzyna type viscoplasticity coupled with flow stress evolution idealized by the Johnson-Cook model. Numerical verifications are performed to assess the performance of the proposed approach against the direct finite element simulations. The results of verification studies demonstrate that VME with proper boundary conditions accurately model the inelastic response accounting for material heterogeneity.

On uniqueness of an inverse problem in electromagnetic obstacle scattering for an impedance cylinder

International Nuclear Information System (INIS)

Nakamura, Gen; Wang, Haibing; Sleeman, Brian D

2012-01-01

We consider an inverse problem for the scattering of an obliquely incident electromagnetic wave by an impedance cylinder. In previous work, we have shown that the direct scattering problem is governed by a pair of Helmholtz equations subject to coupled oblique boundary conditions, where the wave number depends on the frequency and the incident angle with respect to the axis of the cylinder. In this paper, we are concerned with the inverse problem of uniquely identifying the cross-section of an unknown cylinder and the impedance function from the far-field patterns at fixed frequency and a range of incident angles. A uniqueness result for such an inverse scattering problem is established. Our method is based on the analyticity of solution to the direct scattering problem, which is justified by using the Lax–Phillips method together with the perturbation theory of Fredholm operators. (paper)

A new technique for observationally derived boundary conditions for space weather

Science.gov (United States)

Pagano, Paolo; Mackay, Duncan Hendry; Yeates, Anthony Robinson

2018-04-01

Context. In recent years, space weather research has focused on developing modelling techniques to predict the arrival time and properties of coronal mass ejections (CMEs) at the Earth. The aim of this paper is to propose a new modelling technique suitable for the next generation of Space Weather predictive tools that is both efficient and accurate. The aim of the new approach is to provide interplanetary space weather forecasting models with accurate time dependent boundary conditions of erupting magnetic flux ropes in the upper solar corona. Methods: To produce boundary conditions, we couple two different modelling techniques, MHD simulations and a quasi-static non-potential evolution model. Both are applied on a spatial domain that covers the entire solar surface, although they extend over a different radial distance. The non-potential model uses a time series of observed synoptic magnetograms to drive the non-potential quasi-static evolution of the coronal magnetic field. This allows us to follow the formation and loss of equilibrium of magnetic flux ropes. Following this a MHD simulation captures the dynamic evolution of the erupting flux rope, when it is ejected into interplanetary space. Results.The present paper focuses on the MHD simulations that follow the ejection of magnetic flux ropes to 4 R⊙. We first propose a technique for specifying the pre-eruptive plasma properties in the corona. Next, time dependent MHD simulations describe the ejection of two magnetic flux ropes, that produce time dependent boundary conditions for the magnetic field and plasma at 4 R⊙ that in future may be applied to interplanetary space weather prediction models. Conclusions: In the present paper, we show that the dual use of quasi-static non-potential magnetic field simulations and full time dependent MHD simulations can produce realistic inhomogeneous boundary conditions for space weather forecasting tools. Before a fully operational model can be produced there are a

Evolution of passive movement in advective environments: General boundary condition

Science.gov (United States)

Zhou, Peng; Zhao, Xiao-Qiang

2018-03-01

In a previous work [16], Lou et al. studied a Lotka-Volterra competition-diffusion-advection system, where two species are supposed to differ only in their advection rates and the environment is assumed to be spatially homogeneous and closed (no-flux boundary condition), and showed that weaker advective movements are more beneficial for species to win the competition. In this paper, we aim to extend this result to a more general situation, where the environmental heterogeneity is taken into account and the boundary condition at the downstream end becomes very flexible including the standard Dirichlet, Neumann and Robin type conditions as special cases. Our main approaches are to exclude the existence of co-existence (positive) steady state and to provide a clear picture on the stability of semi-trivial steady states, where we introduced new ideas and techniques to overcome the emerging difficulties. Based on these two aspects and the theory of abstract competitive systems, we achieve a complete understanding on the global dynamics.

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Directory of Open Access Journals (Sweden)

Weiye Huo

2015-02-01

Full Text Available Particle image velocimetry (PIV is utilized to measure the non-reacting flow field in a reflow combustor with multiple and single swirlers. The velocity field, vortex structure and total vorticity levels are experimentally obtained using two different boundary conditions, representing a single confined swirler and multiple swirlers in an annular combustor. The influence of the boundary conditions on the flow field at several locations downstream of the swirlers is experimentally investigated, showing that the central vortex in the multi-swirler case is more concentrated than in the single-swirler case. The vorticity of the central vortex and average cross-sectional vorticity are relatively low at the swirler outlet in both cases. Both of these statistics gradually increase to the maximum values near 20 mm downstream of the swirler outlet, and subsequently decrease. It is also found that the central vortex in the multi-swirler case is consistently greater than the single-swirler case. These results demonstrate the critical influence of boundary conditions on flow characteristic of swirling flow, providing insight into the difference of the experiments on test-bed combustor and the full-scale annular combustors.

On solving wave equations on fixed bounded intervals involving Robin boundary conditions with time-dependent coefficients

Science.gov (United States)

van Horssen, Wim T.; Wang, Yandong; Cao, Guohua

2018-06-01

In this paper, it is shown how characteristic coordinates, or equivalently how the well-known formula of d'Alembert, can be used to solve initial-boundary value problems for wave equations on fixed, bounded intervals involving Robin type of boundary conditions with time-dependent coefficients. A Robin boundary condition is a condition that specifies a linear combination of the dependent variable and its first order space-derivative on a boundary of the interval. Analytical methods, such as the method of separation of variables (SOV) or the Laplace transform method, are not applicable to those types of problems. The obtained analytical results by applying the proposed method, are in complete agreement with those obtained by using the numerical, finite difference method. For problems with time-independent coefficients in the Robin boundary condition(s), the results of the proposed method also completely agree with those as for instance obtained by the method of separation of variables, or by the finite difference method.

Role of Boundary Conditions in Monte Carlo Simulation of MEMS Devices

Science.gov (United States)

Nance, Robert P.; Hash, David B.; Hassan, H. A.

1997-01-01

A study is made of the issues surrounding prediction of microchannel flows using the direct simulation Monte Carlo method. This investigation includes the introduction and use of new inflow and outflow boundary conditions suitable for subsonic flows. A series of test simulations for a moderate-size microchannel indicates that a high degree of grid under-resolution in the streamwise direction may be tolerated without loss of accuracy. In addition, the results demonstrate the importance of physically correct boundary conditions, as well as possibilities for reducing the time associated with the transient phase of a simulation. These results imply that simulations of longer ducts may be more feasible than previously envisioned.

The effect of external boundary conditions on condensation heat transfer in rotating heat pipes

Science.gov (United States)

Daniels, T. C.; Williams, R. J.

1979-01-01

Experimental evidence shows the importance of external boundary conditions on the overall performance of a rotating heat pipe condenser. Data are presented for the boundary conditions of constant heat flux and constant wall temperature for rotating heat pipes containing either pure vapor or a mixture of vapor and noncondensable gas as working fluid.

Models for Predicting Boundary Conditions in L-Mode Tokamak Plasma

International Nuclear Information System (INIS)

Siriwitpreecha, A.; Onjun, T.; Suwanna, S.; Poolyarat, N.; Picha, R.

2009-07-01

Full text: The models for predicting temperature and density of ions and electrons at boundary conditions in L-mode tokamak plasma are developed using an empirical approach and optimized against the experimental data obtained from the latest public version of the International Pedestal Database (version 3.2). It is assumed that the temperature and density at boundary of L-mode plasma are functions of engineering parameters such as plasma current, toroidal magnetic field, total heating power, line averaged density, hydrogenic particle mass (A H ), major radius, minor radius, and elongation at the separatrix. Multiple regression analysis is carried out for these parameters with 86 data points in L-mode from Aug (61) and JT60U (25). The RMSE of temperature and density at boundary of L-mode plasma are found to be 24.41% and 18.81%, respectively. These boundary models are implemented in BALDUR code, which will be used to simulate the L-mode plasma in the tokamak

Self-adjoint elliptic operators with boundary conditions on not closed hypersurfaces

Science.gov (United States)

Mantile, Andrea; Posilicano, Andrea; Sini, Mourad

2016-07-01

The theory of self-adjoint extensions of symmetric operators is used to construct self-adjoint realizations of a second-order elliptic differential operator on Rn with linear boundary conditions on (a relatively open part of) a compact hypersurface. Our approach allows to obtain Kreĭn-like resolvent formulae where the reference operator coincides with the ;free; operator with domain H2 (Rn); this provides an useful tool for the scattering problem from a hypersurface. Concrete examples of this construction are developed in connection with the standard boundary conditions, Dirichlet, Neumann, Robin, δ and δ‧-type, assigned either on a (n - 1) dimensional compact boundary Γ = ∂ Ω or on a relatively open part Σ ⊂ Γ. Schatten-von Neumann estimates for the difference of the powers of resolvents of the free and the perturbed operators are also proven; these give existence and completeness of the wave operators of the associated scattering systems.

Coupling the Gaussian Free Fields with Free and with Zero Boundary Conditions via Common Level Lines

Science.gov (United States)

Qian, Wei; Werner, Wendelin

2018-06-01

We point out a new simple way to couple the Gaussian Free Field (GFF) with free boundary conditions in a two-dimensional domain with the GFF with zero boundary conditions in the same domain: Starting from the latter, one just has to sample at random all the signs of the height gaps on its boundary-touching zero-level lines (these signs are alternating for the zero-boundary GFF) in order to obtain a free boundary GFF. Constructions and couplings of the free boundary GFF and its level lines via soups of reflected Brownian loops and their clusters are also discussed. Such considerations show for instance that in a domain with an axis of symmetry, if one looks at the overlay of a single usual Conformal Loop Ensemble CLE3 with its own symmetric image, one obtains the CLE4-type collection of level lines of a GFF with mixed zero/free boundary conditions in the half-domain.

Involving the Navier-Stokes equations in the derivation of boundary conditions for the lattice Boltzmann method.

Science.gov (United States)

Verschaeve, Joris C G

2011-06-13

By means of the continuity equation of the incompressible Navier-Stokes equations, additional physical arguments for the derivation of a formulation of the no-slip boundary condition for the lattice Boltzmann method for straight walls at rest are obtained. This leads to a boundary condition that is second-order accurate with respect to the grid spacing and conserves mass. In addition, the boundary condition is stable for relaxation frequencies close to two.

Probability distribution of magnetization in the one-dimensional Ising model: effects of boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Antal, T [Physics Department, Simon Fraser University, Burnaby, BC V5A 1S6 (Canada); Droz, M [Departement de Physique Theorique, Universite de Geneve, CH 1211 Geneva 4 (Switzerland); Racz, Z [Institute for Theoretical Physics, Eoetvoes University, 1117 Budapest, Pazmany setany 1/a (Hungary)

2004-02-06

Finite-size scaling functions are investigated both for the mean-square magnetization fluctuations and for the probability distribution of the magnetization in the one-dimensional Ising model. The scaling functions are evaluated in the limit of the temperature going to zero (T {yields} 0), the size of the system going to infinity (N {yields} {infinity}) while N[1 - tanh(J/k{sub B}T)] is kept finite (J being the nearest neighbour coupling). Exact calculations using various boundary conditions (periodic, antiperiodic, free, block) demonstrate explicitly how the scaling functions depend on the boundary conditions. We also show that the block (small part of a large system) magnetization distribution results are identical to those obtained for free boundary conditions.

Boundary Layer Ducting of Low-elevation GNSS Ocean Reflected Signals

DEFF Research Database (Denmark)

Høeg, Per; von Benzon, Hans-Henrik; Durgonics, Tibor

for the data retrievals and the precision and the accuracy, are of interest for assessing the observational data content.Simulations of the low-elevation ocean reflected GNSS signal reveal a ducting of the signalwhen applying a model of the boundary layer. This effect is presented during varying conditions...... of the sea surface roughness, ocean wind and temperature, density and gradient of the water vapor profile in the boundary layer.The model for the sea surface roughness impedance, wind speed, and rms ocean wave-heightshow a stronger signal damping for a smoother ocean surfaces (sea state 0) compared...... to a rough sea (sea state 4). While the real part of the signal shows the reverse effect. At the same time the reflection zone enhances for rough sea states. Simulations, including a standard atmosphere and a boundary layer, give a significant ducting of the received signal, leading to a much larger...

Generalized nematohydrodynamic boundary conditions with application to bistable twisted nematic liquid-crystal displays

KAUST Repository

Fang, Angbo

2008-12-08

Parallel to the highly successful Ericksen-Leslie hydrodynamic theory for the bulk behavior of nematic liquid crystals (NLCs), we derive a set of coupled hydrodynamic boundary conditions to describe the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable π -twist NLC cell reveals a complete picture of the dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times. © 2008 The American Physical Society.

A nonlinear free boundary problem with a self-driven Bernoulli condition

OpenAIRE

Dipierro, Serena; Karakhanyan, Aram; Valdinoci, Enrico

2017-01-01

We study a Bernoulli type free boundary problem with two phases J[u]=∫Ω|∇u(x)|2dx+Φ(M−(u),M+(u)),u−u¯∈W1,20(Ω), where u¯∈W1,2(Ω) is a given boundary datum. Here, M1 and M2 are weighted volumes of {u≤0}∩Ω and {u>0}∩Ω, respectively, and Φ is a nonnegative function of two real variables. We show that, for this problem, the Bernoulli constant, which determines the gradient jump condition across the free boundary, is of global type and it is indeed determined by the weighted volumes of the phas...

A quenched study of the Schroedinger functional with chirally rotated boundary conditions. Non-preturbative tuning

Energy Technology Data Exchange (ETDEWEB)

Lopez, J. Gonzalez [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Jansen, K. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Renner, D.B. [Jefferson Lab, Newport News, VA (United States); Shindler, A. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik

2012-08-23

The use of chirally rotated boundary conditions provides a formulation of the Schroedinger functional that is compatible with automatic O(a) improvement of Wilson fermions up to O(a) boundary contributions. The elimination of bulk O(a) effects requires the non-perturbative tuning of the critical mass and one additional boundary counterterm. We present the results of such a tuning in a quenched setup for several values of the renormalized gauge coupling, from perturbative to nonperturbative regimes, and for a range of lattice spacings. We also check that the correct boundary conditions and symmetries are restored in the continuum limit. (orig.)

A quenched study of the Schroedinger functional with chirally rotated boundary conditions. Non-preturbative tuning

International Nuclear Information System (INIS)

Lopez, J. Gonzalez; Jansen, K.; Renner, D.B.; Shindler, A.

2012-01-01

The use of chirally rotated boundary conditions provides a formulation of the Schroedinger functional that is compatible with automatic O(a) improvement of Wilson fermions up to O(a) boundary contributions. The elimination of bulk O(a) effects requires the non-perturbative tuning of the critical mass and one additional boundary counterterm. We present the results of such a tuning in a quenched setup for several values of the renormalized gauge coupling, from perturbative to nonperturbative regimes, and for a range of lattice spacings. We also check that the correct boundary conditions and symmetries are restored in the continuum limit. (orig.)

Existence and asymptotic behavior of the wave equation with dynamic boundary conditions

KAUST Repository

Graber, Philip Jameson; Said-Houari, Belkacem

2012-01-01

The goal of this work is to study a model of the strongly damped wave equation with dynamic boundary conditions and nonlinear boundary/interior sources and nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. In addition, we show that in the strongly damped case solutions gain additional regularity for positive times t>0. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution grows as an exponential function. Moreover, in the absence of the strong damping term, we prove that the solution ceases to exists and blows up in finite time. © 2012 Springer Science+Business Media, LLC.

Existence and asymptotic behavior of the wave equation with dynamic boundary conditions

KAUST Repository

Graber, Philip Jameson

2012-03-07

The goal of this work is to study a model of the strongly damped wave equation with dynamic boundary conditions and nonlinear boundary/interior sources and nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. In addition, we show that in the strongly damped case solutions gain additional regularity for positive times t>0. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution grows as an exponential function. Moreover, in the absence of the strong damping term, we prove that the solution ceases to exists and blows up in finite time. © 2012 Springer Science+Business Media, LLC.

Confinement dynamics and boundary condition studies in the Reversed Field Pinch

International Nuclear Information System (INIS)

Schoenberg, K.F.; Ingraham, J.C.; Moses, R.W. Jr.

1988-01-01

The study of confinement dynamics, including investigation of the boundary conditions required for plasma sustainment, are central to the development of the Reversed Field Pinch (RFP) concept. Recently, several insights into confinement have emerged from a detailed investigation RFP electron and ion dynamics. These insights derive from the recognition that both magnetohydrodynamic (MHD) and electron kinetic effects play an important and coupled role in RFP stability, sustainment, and confinement. In this paper, we summarize the results of confinement studies on the ZT-40M experiment, and boundary condition studies on the Wisconsin non-circular RFP experiment. A brief description of the newly commissioned Madison Symmetric Torus (MST) is also presented. 28 refs., 3 figs

Impedance spectroscopy study of Na{sub 1/2}Sm{sub 1/2}TiO{sub 3} ceramic

Energy Technology Data Exchange (ETDEWEB)

Barik, S K; Choudhary, R N.P. [I.I.T., Department of Physics and Meteorology, Kharagpur (India); Mahapatra, P K [Vidyasagar University, Department of Physics and Technophysics, Midnapur, West Bengal (India)

2007-07-15

Complex impedance analysis of a valence-compensated perovskite ceramic oxide Na{sub 1/2}Sm{sub 1/2}TiO{sub 3}, prepared by a mixed oxide (solid-state reaction) method, has been carried out. The formation of single-phase material was confirmed by X-ray diffraction studies, and it was found to be an orthorhombic phase at room temperature. In a scanning electron microscope, grains separated by well-defined boundaries are visible, which is in good agreement with that of impedance analysis. Alternating current impedance measurements were made over a wide temperature range (31-400 C) in an air atmosphere. Complex impedance and modulus plots helped to separate out the contributions of grain and grain boundaries to the overall polarization or electrical behavior. The physical structure of the samples was visualized most prominently at higher temperatures (275 C) from the Nyquist plots showing inter- and intragranular impedance present in the material. The frequency dependence of electrical data is also analyzed in the framework of the conductivity and modulus formalisms. The bulk resistance, evaluated from the impedance spectrum, was observed to decrease with rise in temperature, showing a typical negative temperature coefficient of resistance-type behavior like that of semiconductors. The modulus mechanism indicates the non-Debye type of conductivity relaxation in the materials, which is supported by the impedance data. (orig.)

On flows of viscoelastic fluids under threshold-slip boundary conditions

Science.gov (United States)

Baranovskii, E. S.

2018-03-01

We investigate a boundary-value problem for the steady isothermal flow of an incompressible viscoelastic fluid of Oldroyd type in a 3D bounded domain with impermeable walls. We use the Fujita threshold-slip boundary condition. This condition states that the fluid can slip along a solid surface when the shear stresses reach a certain critical value; otherwise the slipping velocity is zero. Assuming that the flow domain is not rotationally symmetric, we prove an existence theorem for the corresponding slip problem in the framework of weak solutions. The proof uses methods for solving variational inequalities with pseudo-monotone operators and convex functionals, the method of introduction of auxiliary viscosity, as well as a passage-to-limit procedure based on energy estimates of approximate solutions, Korn’s inequality, and compactness arguments. Also, some properties and estimates of weak solutions are established.

Reflected forward-backward SDEs and obstacle problems with boundary conditions

Directory of Open Access Journals (Sweden)

Jin Ma

2001-01-01

Full Text Available In this paper we study a class of forward-backward stochastic differential equations with reflecting boundary conditions (FBSDER for short. More precisely, we consider the case in which the forward component of the FBSDER is restricted to a fixed, convex region, and the backward component will stay, at each fixed time, in a convex region that may depend on time and is possibly random. The solvability of such FBSDER is studied in a fairly general way. We also prove that if the coefficients are all deterministic and the backward equation is one-dimensional, then the adapted solution of such FBSDER will give the viscosity solution of a quasilinear variational inequality (obstacle problem with a Neumann boundary condition. As an application, we study how the solvability of FBSDERs is related to the solvability of an American game option.

On a stochastic Burgers equation with Dirichlet boundary conditions

Directory of Open Access Journals (Sweden)

Ekaterina T. Kolkovska

2003-01-01

Full Text Available We consider the one-dimensional Burgers equation perturbed by a white noise term with Dirichlet boundary conditions and a non-Lipschitz coefficient. We obtain existence of a weak solution proving tightness for a sequence of polygonal approximations for the equation and solving a martingale problem for the weak limit.

Investigating effects of boundary conditions on the evaluation of R-factor of un-braced steel frames

Directory of Open Access Journals (Sweden)

Masood M.M. Irheem

2017-08-01

Full Text Available Design of Structures to resist seismic load depends on the theory of dissipation in elastic of energy that already exists in response modification factor “R-factor”. The main problem in codes gives a constant value for R-factor, since change in boundary conditions of building change in behavior of steel frame structures and that effect on R-factor. This study is an attempt to assess overstrength, ductility and response modification factor of un-braced steel frames under change in boundary conditions as change in the direction of strong axis of column and support type beside to variation in story and bay number to be 9 frame and each frame has 8 different boundary conditions as sum of 72 case for analysis. These frames were analyzed by using nonlinear static “pushover” analysis using SAP2000 program. As a result of this study R-factor does not has a constant value, when change in boundary conditions R-factor directly changes, minimum value of 8 boundary conditions is close to the code value that is mean the code is more conservative and give a large factor of safety. Ductility reduction factor increases with increasing number of story for all boundary conditions, but overstrength has different rule. Response modification factor, overstrength factor and ductility reduction factor decrease when fundamentals period increasing for the studied frames.

An Evaluation of a Phase-Lag Boundary Condition for Francis Hydroturbine Simulations Using a Pressure-Based Solver

Science.gov (United States)

Wouden, Alex; Cimbala, John; Lewis, Bryan

2014-11-01

While the periodic boundary condition is useful for handling rotational symmetry in many axisymmetric geometries, its application fails for analysis of rotor-stator interaction (RSI) in multi-stage turbomachinery flow. The inadequacy arises from the underlying geometry where the blade counts per row differ, since the blade counts are crafted to deter the destructive harmonic forces of synchronous blade passing. Therefore, to achieve the computational advantage of modeling a single blade passage per row while preserving the integrity of the RSI, a phase-lag boundary condition is adapted to OpenFOAM® software's incompressible pressure-based solver. The phase-lag construct is accomplished through restating the implicit periodic boundary condition as a constant boundary condition that is updated at each time step with phase-shifted data from the coupled cells adjacent to the boundary. Its effectiveness is demonstrated using a typical Francis hydroturbine modeled as single- and double-passages with phase-lag boundary conditions. The evaluation of the phase-lag condition is based on the correspondence of the overall computational performance and the calculated flow parameters of the phase-lag simulations with those of a baseline full-wheel simulation. Funded in part by DOE Award Number: DE-EE0002667.

Influence of Boundary Conditions on the Simulation of a Diamond-Type Lattice Structure: A Preliminary Study

Directory of Open Access Journals (Sweden)

Patrick Terriault

2017-01-01

Full Text Available Emergent additive manufacturing processes allow the use of metallic porous structures in various industrial applications. Because these structures comprise a large number of ordered unit cells, their design using conventional modeling approaches, such as finite elements, becomes a real challenge. A homogenization technique, in which the lattice structure is simulated as a fully dense volume having equivalent material properties, can then be employed. To determine these equivalent material properties, numerical simulations can be performed on a single unit cell of the lattice structure. However, a critical aspect to consider is the boundary conditions applied to the external faces of the unit cell. In the literature, different types of boundary conditions are used, but a comparative study is definitely lacking. In this publication, a diamond-type unit cell is studied in compression by applying different boundary conditions. If the porous structure’s boundaries are free to deform, then the periodic boundary condition is found to be the most representative, but constraint equations must be introduced in the model. If, instead, the porous structure is inserted in a rigid enclosure, it is then better to use frictionless boundary conditions. These preliminary results remain to be validated for other types of unit cells loaded beyond the yield limit of the material.

Automatic generation of boundary conditions using demons nonrigid image registration for use in 3-D modality-independent elastography.

Science.gov (United States)

Pheiffer, Thomas S; Ou, Jao J; Ong, Rowena E; Miga, Michael I

2011-09-01

Modality-independent elastography (MIE) is a method of elastography that reconstructs the elastic properties of tissue using images acquired under different loading conditions and a biomechanical model. Boundary conditions are a critical input to the algorithm and are often determined by time-consuming point correspondence methods requiring manual user input. This study presents a novel method of automatically generating boundary conditions by nonrigidly registering two image sets with a demons diffusion-based registration algorithm. The use of this method was successfully performed in silico using magnetic resonance and X-ray-computed tomography image data with known boundary conditions. These preliminary results produced boundary conditions with an accuracy of up to 80% compared to the known conditions. Demons-based boundary conditions were utilized within a 3-D MIE reconstruction to determine an elasticity contrast ratio between tumor and normal tissue. Two phantom experiments were then conducted to further test the accuracy of the demons boundary conditions and the MIE reconstruction arising from the use of these conditions. Preliminary results show a reasonable characterization of the material properties on this first attempt and a significant improvement in the automation level and viability of the method.

A partially reflecting random walk on spheres algorithm for electrical impedance tomography

Energy Technology Data Exchange (ETDEWEB)

Maire, Sylvain, E-mail: maire@univ-tln.fr [Laboratoire LSIS Equipe Signal et Image, Université du Sud Toulon-Var, Av. Georges Pompidou, BP 56, 83162 La Valette du Var Cedex (France); Simon, Martin, E-mail: simon@math.uni-mainz.de [Institute of Mathematics, Johannes Gutenberg University, 55099 Mainz (Germany)

2015-12-15

In this work, we develop a probabilistic estimator for the voltage-to-current map arising in electrical impedance tomography. This novel so-called partially reflecting random walk on spheres estimator enables Monte Carlo methods to compute the voltage-to-current map in an embarrassingly parallel manner, which is an important issue with regard to the corresponding inverse problem. Our method uses the well-known random walk on spheres algorithm inside subdomains where the diffusion coefficient is constant and employs replacement techniques motivated by finite difference discretization to deal with both mixed boundary conditions and interface transmission conditions. We analyze the global bias and the variance of the new estimator both theoretically and experimentally. Subsequently, the variance of the new estimator is considerably reduced via a novel control variate conditional sampling technique which yields a highly efficient hybrid forward solver coupling probabilistic and deterministic algorithms.

Ferroelectric relaxor behaviour and impedance spectroscopy of Bi2O3-doped barium zirconium titanate ceramics

Science.gov (United States)

Mahajan, Sandeep; Thakur, O P; Bhattacharya, D K; Sreenivas, K

2009-03-01

Bi2O3-doped barium zirconate titanate ceramics, Ba1-xBix(Zr0.05Ti0.95)O3, have been prepared by the conventional solid-state reaction method. The ferroelectric relaxor behaviour and dielectric properties have been investigated in detail. By XRD analysis, it is suggested that up to x = 0.04, Bi3+ substitutes A-site ion, and thereafter with higher Bi3+ content, it enters the B-site sub lattice. Substitution of Bi3+ ions induces ferroelectric relaxor behaviour and the degree of relaxation behaviour increases with bismuth concentration. The remanent polarization and strain behaviour show a slight increase with the substitution level. The degree of hysteresis (strain versus electric field) also reduces from 21.4% to 4.6% with bismuth substitution. Impedance measurements were made on the prepared sample over a wide range of temperatures (300-723 K) and frequencies (40 Hz-1 MHz), which show the presence of both bulk and grain boundary effects in the material. The bulk and grain boundary conductivities determined from impedance study indicate the Arrhenius-type thermally activated process. Impedance spectroscopy is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries to the complex impedance of a ceramic system, accurately estimating its electrical conductivity as well as its corresponding activation energies and drawing conclusions on its structural properties.

Ferroelectric relaxor behaviour and impedance spectroscopy of Bi2O3-doped barium zirconium titanate ceramics

International Nuclear Information System (INIS)

Mahajan, Sandeep; Thakur, O P; Bhattacharya, D K; Sreenivas, K

2009-01-01

Bi 2 O 3 -doped barium zirconate titanate ceramics, Ba 1-x Bi x (Zr 0.05 Ti 0.95 )O 3 , have been prepared by the conventional solid-state reaction method. The ferroelectric relaxor behaviour and dielectric properties have been investigated in detail. By XRD analysis, it is suggested that up to x = 0.04, Bi 3+ substitutes A-site ion, and thereafter with higher Bi 3+ content, it enters the B-site sub lattice. Substitution of Bi 3+ ions induces ferroelectric relaxor behaviour and the degree of relaxation behaviour increases with bismuth concentration. The remanent polarization and strain behaviour show a slight increase with the substitution level. The degree of hysteresis (strain versus electric field) also reduces from 21.4% to 4.6% with bismuth substitution. Impedance measurements were made on the prepared sample over a wide range of temperatures (300-723 K) and frequencies (40 Hz-1 MHz), which show the presence of both bulk and grain boundary effects in the material. The bulk and grain boundary conductivities determined from impedance study indicate the Arrhenius-type thermally activated process. Impedance spectroscopy is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries to the complex impedance of a ceramic system, accurately estimating its electrical conductivity as well as its corresponding activation energies and drawing conclusions on its structural properties.

Influence of model boundary conditions on blood flow patterns in a patient specific stenotic right coronary artery.

Science.gov (United States)

Liu, Biyue; Zheng, Jie; Bach, Richard; Tang, Dalin

2015-01-01

In literature, the effect of the inflow boundary condition was investigated by examining the impact of the waveform and the shape of the spatial profile of the inlet velocity on the cardiac hemodynamics. However, not much work has been reported on comparing the effect of the different combinations of the inlet/outlet boundary conditions on the quantification of the pressure field and flow distribution patterns in stenotic right coronary arteries. Non-Newtonian models were used to simulate blood flow in a patient-specific stenotic right coronary artery and investigate the influence of different boundary conditions on the phasic variation and the spatial distribution patterns of blood flow. The 3D geometry of a diseased artery segment was reconstructed from a series of IVUS slices. Five different combinations of the inlet and the outlet boundary conditions were tested and compared. The temporal distribution patterns and the magnitudes of the velocity, the wall shear stress (WSS), the pressure, the pressure drop (PD), and the spatial gradient of wall pressure (WPG) were different when boundary conditions were imposed using different pressure/velocity combinations at inlet/outlet. The maximum velocity magnitude in a cardiac cycle at the center of the inlet from models with imposed inlet pressure conditions was about 29% lower than that from models using fully developed inlet velocity data. Due to the fact that models with imposed pressure conditions led to blunt velocity profile, the maximum wall shear stress at inlet in a cardiac cycle from models with imposed inlet pressure conditions was about 29% higher than that from models with imposed inlet velocity boundary conditions. When the inlet boundary was imposed by a velocity waveform, the models with different outlet boundary conditions resulted in different temporal distribution patterns and magnitudes of the phasic variation of pressure. On the other hand, the type of different boundary conditions imposed at the

Predictability of Japan/East Sea (JES) System to Uncertain Initial/Lateral Boundary Conditions and Surface Winds

National Research Council Canada - National Science Library

Fang, Chin-Lung

2003-01-01

.... Change in either initial or boundary condition leads to a variety of model solutions. It is necessary to specify realistic initial and boundary conditions to achieve better understanding and prediction of the ocean behavior...

Effects of microscopic boundary conditions on plastic deformations of small-sized single crystals

DEFF Research Database (Denmark)

Kuroda, Mitsutoshi; Tvergaard, Viggo

2009-01-01

The finite deformation version of the higher-order gradient crystal plasticity model proposed by the authors is applied to solve plane strain boundary value problems, in order to obtain an understanding of the effect of the higher-order boundary conditions. Numerical solutions are carried out...

Mode solutions for a Klein-Gordon field in anti-de Sitter spacetime with dynamical boundary conditions of Wentzell type

Science.gov (United States)

Dappiaggi, Claudio; Ferreira, Hugo R. C.; Juárez-Aubry, Benito A.

2018-04-01

We study a real, massive Klein-Gordon field in the Poincaré fundamental domain of the (d +1 )-dimensional anti-de Sitter (AdS) spacetime, subject to a particular choice of dynamical boundary conditions of generalized Wentzell type, whereby the boundary data solves a nonhomogeneous, boundary Klein-Gordon equation, with the source term fixed by the normal derivative of the scalar field at the boundary. This naturally defines a field in the conformal boundary of the Poincaré fundamental domain of AdS. We completely solve the equations for the bulk and boundary fields and investigate the existence of bound state solutions, motivated by the analogous problem with Robin boundary conditions, which are recovered as a limiting case. Finally, we argue that both Robin and generalized Wentzell boundary conditions are distinguished in the sense that they are invariant under the action of the isometry group of the AdS conformal boundary, a condition which ensures in addition that the total flux of energy across the boundary vanishes.

Discontinuous Sturm-Liouville Problems with Eigenvalue Dependent Boundary Condition

Energy Technology Data Exchange (ETDEWEB)

Amirov, R. Kh., E-mail: emirov@cumhuriyet.edu.tr; Ozkan, A. S., E-mail: sozkan@cumhuriyet.edu.tr [Cumhuriyet University, Department of Mathematics Faculty of Art and Science (Turkey)

2014-12-15

In this study, an inverse problem for Sturm-Liouville differential operators with discontinuities is studied when an eigenparameter appears not only in the differential equation but it also appears in the boundary condition. Uniqueness theorems of inverse problems according to the Prüfer angle, the Weyl function and two different eigenvalues sets are proved.

Regularization of moving boundaries in a Laplacian field by a mixed Dirichlet-Neumann boundary condition : exact results

NARCIS (Netherlands)

B.J. Meulenbroek (Bernard); U. M. Ebert (Ute); L. Schäfer

2005-01-01

textabstractThe dynamics of ionization fronts that generate a conducting body, are in simplest approximation equivalent to viscous fingering without regularization. Going beyond this approximation, we suggest that ionization fronts can be modeled by a mixed Dirichlet-Neumann boundary condition. We

Influence of the Outer Boundary Condition on models of AGB stars

Science.gov (United States)

Wagstaff, G.; Weiss, A.

2018-04-01

Current implementations of the stellar atmosphere typically derive boundary conditions for the interior model from either grey plane-parallel atmospheres or scaled solar atmospheres, neither of which can be considered to have appropriate underlying assumptions for the Thermally Pulsing Asymptotic Giant Branch (TP-AGB). This paper discusses the treatment and influence of the outer boundary condition within stellar evolution codes, and the resulting effects on the AGB evolution. The complex interaction of processes, such as the third dredge up and mass loss, governing the TP-AGB can be affected by varying the treatment of this boundary condition. Presented here are the results from altering the geometry, opacities and the implementation of a grid of MARCS/COMARCS model atmospheres in order to improve this treatment. Although there are changes in the TP-AGB evolution, observable quantities, such as the final core mass, are not significantly altered as a result of the change of atmospheric treatment. During the course of the investigation, a previously unseen phenomena in the AGB models was observed and further investigated. This is believed to be physical, although arising from specific conditions which make its presence unlikely. If it were present in stars, this phenomenon would increase the carbon-star lifetime above 10Myr and increase the final core mass by ˜0.1M⊙ in the narrow initial-mass range where it was observed (˜2 - 2.3M⊙).

Experimental verification of electrostatic boundary conditions in gate-patterned quantum devices

Science.gov (United States)

Hou, H.; Chung, Y.; Rughoobur, G.; Hsiao, T. K.; Nasir, A.; Flewitt, A. J.; Griffiths, J. P.; Farrer, I.; Ritchie, D. A.; Ford, C. J. B.

2018-06-01

In a model of a gate-patterned quantum device, it is important to choose the correct electrostatic boundary conditions (BCs) in order to match experiment. In this study, we model gated-patterned devices in doped and undoped GaAs heterostructures for a variety of BCs. The best match is obtained for an unconstrained surface between the gates, with a dielectric region above it and a frozen layer of surface charge, together with a very deep back boundary. Experimentally, we find a  ∼0.2 V offset in pinch-off characteristics of 1D channels in a doped heterostructure before and after etching off a ZnO overlayer, as predicted by the model. Also, we observe a clear quantised current driven by a surface acoustic wave through a lateral induced n-i-n junction in an undoped heterostructure. In the model, the ability to pump electrons in this type of device is highly sensitive to the back BC. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software.

Artificial Boundary Conditions for the Numerical Simulation of Unsteady Acoustic Waves

National Research Council Canada - National Science Library

Tsynkov, S. V

2003-01-01

We construct non-local artificial boundary conditions (ABCs) for the numerical simulation of genuinely time-dependent acoustic waves that propagate from a compact source in an unbounded unobstructed space...

Simulation of microcirculatory hemodynamics: estimation of boundary condition using particle swarm optimization.

Science.gov (United States)

Pan, Qing; Wang, Ruofan; Reglin, Bettina; Fang, Luping; Pries, Axel R; Ning, Gangmin

2014-01-01

Estimation of the boundary condition is a critical problem in simulating hemodynamics in microvascular networks. This paper proposed a boundary estimation strategy based on a particle swarm optimization (PSO) algorithm, which aims to minimize the number of vessels with inverted flow direction in comparison to the experimental observation. The algorithm took boundary values as the particle swarm and updated the position of the particles iteratively to approach the optimization target. The method was tested in a real rat mesenteric network. With random initial boundary values, the method achieved a minimized 9 segments with an inverted flow direction in the network with 546 vessels. Compared with reported literature, the current work has the advantage of a better fit with experimental observations and is more suitable for the boundary estimation problem in pulsatile hemodynamic models due to the experiment-based optimization target selection.

An analytical boundary element integral approach to track the boundary of a moving cavity using electrical impedance tomography

International Nuclear Information System (INIS)

Khambampati, Anil Kumar; Kim, Sin; Lee, Bo An; Kim, Kyung Youn

2012-01-01

This paper is about locating the boundary of a moving cavity within a homogeneous background from the voltage measurements recorded on the outer boundary. An inverse boundary problem of a moving cavity is formulated by considering a two-phase vapor–liquid flow in a pipe. The conductivity of the flow components (vapor and liquid) is assumed to be constant and known a priori while the location and shape of the inclusion (vapor) are the unknowns to be estimated. The forward problem is solved using the boundary element method (BEM) with the integral equations solved analytically. A special situation is considered such that the cavity changes its location and shape during the time taken to acquire a full set of independent measurement data. The boundary of a cavity is assumed to be elliptic and is parameterized with Fourier series. The inverse problem is treated as a state estimation problem with the Fourier coefficients that represent the center and radii of the cavity as the unknowns to be estimated. An extended Kalman filter (EKF) is used as an inverse algorithm to estimate the time varying Fourier coefficients. Numerical experiments are shown to evaluate the performance of the proposed method. Through the results, it can be noticed that the proposed BEM with EKF method is successful in estimating the boundary of a moving cavity. (paper)

Universal parity effects in the entanglement entropy of XX chains with open boundary conditions

International Nuclear Information System (INIS)

Fagotti, Maurizio; Calabrese, Pasquale

2011-01-01

We consider the Rényi entanglement entropies in the one-dimensional XX spin-chains with open boundary conditions in the presence of a magnetic field. In the case of a semi-infinite system and a block starting from the boundary, we derive rigorously the asymptotic behavior for large block sizes on the basis of a recent mathematical theorem for the determinant of Toeplitz plus Hankel matrices. We conjecture a generalized Fisher–Hartwig form for the corrections to the asymptotic behavior of this determinant that allows the exact characterization of the corrections to the scaling at order o(l -1 ) for any n. By combining these results with conformal field theory arguments, we derive exact expressions also in finite chains with open boundary conditions and in the case when the block is detached from the boundary

Validation of Boundary Conditions for CFD Simulations on Ventilated Rooms

DEFF Research Database (Denmark)

Topp, Claus; Jensen, Rasmus Lund; Pedersen, D.N.

2001-01-01

The application of Computational Fluid Dynamics (CFD) for ventilation research and design of ventilation systems has increased during the recent years. This paper provides an investigation of direct description of boundary conditions for a complex inlet diffuser and a heated surface. A series...

Communication: modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions.

Science.gov (United States)

Bardhan, Jaydeep P; Knepley, Matthew G

2014-10-07

We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.

Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

International Nuclear Information System (INIS)

Bardhan, Jaydeep P.; Knepley, Matthew G.

2014-01-01

We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry

Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Bardhan, Jaydeep P. [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115 (United States); Knepley, Matthew G. [Computation Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

2014-10-07

We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.

Bound states in waveguides with complex Robin boundary conditions

Czech Academy of Sciences Publication Activity Database

Novák, Radek

2016-01-01

Roč. 96, 3-4 (2016), s. 251-281 ISSN 0921-7134 R&D Projects: GA ČR(CZ) GA14-06818S Institutional support: RVO:61389005 Keywords : non-self-adjointness * waveguide * Robin boundary conditions * spectral analysis * essential spectrum * weak coupling * Birman-Schwinger principle * reality of the spectrum Subject RIV: BE - Theoretical Physics Impact factor: 0.933, year: 2016

Regularization of moving boundaries in a Laplacian field by a mixed dirichlet-neumann boundary condition: Exact results

NARCIS (Netherlands)

Meulenbroek, B.; Ebert, U.; Schäfer, L.

2005-01-01

The dynamics of ionization fronts that generate a conducting body are in the simplest approximation equivalent to viscous fingering without regularization. Going beyond this approximation, we suggest that ionization fronts can be modeled by a mixed Dirichlet-Neumann boundary condition. We derive

Explicit formulation for natural frequencies of double-beam system with arbitrary boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Mirzabeigy, Alborz; Madoliat, Reza [Iran University of Science and Technology, Narmak, Tehran (Iran, Islamic Republic of); Dabbagh, Vahid [University of Malaya, Kuala Lumpur (Malaysia)

2017-02-15

In this paper, free transverse vibration of two parallel beams connected through Winkler type elastic layer is investigated. Euler- Bernoulli beam hypothesis has been applied and it is assumed that boundary conditions of upper and lower beams are similar while arbitrary without any limitation even for non-ideal boundary conditions. Material properties and cross-section geometry of beams could be different from each other. The motion of the system is described by a homogeneous set of two partial differential equations, which is solved by using the classical Bernoulli-Fourier method. Explicit expressions are derived for the natural frequencies. In order to verify accuracy of results, the problem once again solved using modified Adomian decomposition method. Comparison between results indicates excellent accuracy of proposed formulation for any arbitrary boundary conditions. Derived explicit formulation is simplest method to determine natural frequencies of double-beam systems with high level of accuracy in comparison with other methods in literature.

Adapting a Fourier pseudospectral method to Dirichlet boundary conditions for Rayleigh-Bénard convection

Directory of Open Access Journals (Sweden)

I. C. Ramos

2015-10-01

Full Text Available We present the adaptation to non-free boundary conditions of a pseudospectral method based on the (complex Fourier transform. The method is applied to the numerical integration of the Oberbeck-Boussinesq equations in a Rayleigh-Bénard cell with no-slip boundary conditions for velocity and Dirichlet boundary conditions for temperature. We show the first results of a 2D numerical simulation of dry air convection at high Rayleigh number (. These results are the basis for the later study, by the same method, of wet convection in a solar still. Received: 20 Novembre 2014, Accepted: 15 September 2015; Edited by: C. A. Condat, G. J. Sibona; DOI:http://dx.doi.org/10.4279/PIP.070015 Cite as: I C Ramos, C B Briozzo, Papers in Physics 7, 070015 (2015

RECTC/RECTCF, 2. Order Elliptical Partial Differential Equation, Arbitrary Boundary Conditions

International Nuclear Information System (INIS)

Hackbusch, W.

1983-01-01

1 - Description of problem or function: A general linear elliptical second order partial differential equation on a rectangle with arbitrary boundary conditions is solved. 2 - Method of solution: Multi-grid iteration

Effect of magnetization boundary condition on cavity magnon polariton of YIG thin film

Science.gov (United States)

Jiang, H. H.; Xiao, Y.; Hu, C. M.; Guo, H.; Xia, K.

2018-06-01

Motivated by recent studies of cavity magnon polariton (CMP), we extended a previous theoretical work to generalize microwave transmission calculation with various magnetization boundary condition of YIG thin film embedded in cavity. It is found that numerical implementation given in this paper can be easily applied to other magnetization boundary condition and extended to magnetic multilayers. Numerical results show that ferromagnetic resonance mode of microwave transmission spectrum, which is absent in previous calculation, can be recovered by altering the pinning condition of surface spins. The demonstrated reliability of our theory opens attractive perspectives for studying CMP of thin film with complicated surface magnetization distribution and magnetic multilayers.

Global exponential stability and periodicity of reaction-diffusion delayed recurrent neural networks with Dirichlet boundary conditions

International Nuclear Information System (INIS)

Lu Junguo

2008-01-01

In this paper, the global exponential stability and periodicity for a class of reaction-diffusion delayed recurrent neural networks with Dirichlet boundary conditions are addressed by constructing suitable Lyapunov functionals and utilizing some inequality techniques. We first prove global exponential converge to 0 of the difference between any two solutions of the original reaction-diffusion delayed recurrent neural networks with Dirichlet boundary conditions, the existence and uniqueness of equilibrium is the direct results of this procedure. This approach is different from the usually used one where the existence, uniqueness of equilibrium and stability are proved in two separate steps. Furthermore, we prove periodicity of the reaction-diffusion delayed recurrent neural networks with Dirichlet boundary conditions. Sufficient conditions ensuring the global exponential stability and the existence of periodic oscillatory solutions for the reaction-diffusion delayed recurrent neural networks with Dirichlet boundary conditions are given. These conditions are easy to check and have important leading significance in the design and application of reaction-diffusion recurrent neural networks with delays. Finally, two numerical examples are given to show the effectiveness of the obtained results

On the physical solutions to the heat equation subjected to nonlinear boundary conditions

International Nuclear Information System (INIS)

Gama, R.M.S. da.

1990-01-01

This work consists of a discussion on the physical solutions to the steady-state heat transfer equation, when it is subjected to nonlinear boundary conditions. It will be presented a functional, whose minimum occurs for the (unique) physical solution to the condidered heat transfer problem, suitable for a large class of typical (nonlinear) boundary conditions (representing the radiative/convective loss from the body to the environment). It will be demonstrated that these problems admit-always one, and only one, physical solution (which represents the absolute temperature). (author)

Heat conduction in a plate-type fuel element with time-dependent boundary conditions

International Nuclear Information System (INIS)

Faya, A.J.G.; Maiorino, J.R.

1981-01-01

A method for the solution of boundary-value problems with variable boundary conditions is applied to solve a heat conduction problem in a plate-type fuel element with time dependent film coefficient. The numerical results show the feasibility of the method in the solution of this class of problems. (Author) [pt

Existence of 2m-1 Positive Solutions for Sturm-Liouville Boundary Value Problems with Linear Functional Boundary Conditions on the Half-Line

Directory of Open Access Journals (Sweden)

Yanmei Sun

2012-01-01

Full Text Available By using the Leggett-Williams fixed theorem, we establish the existence of multiple positive solutions for second-order nonhomogeneous Sturm-Liouville boundary value problems with linear functional boundary conditions. One explicit example with singularity is presented to demonstrate the application of our main results.

Impact of SSSC on Measured Impedance in Single Phase to Ground Fault Condition on 220 kV Transmission Line

Directory of Open Access Journals (Sweden)

Mohamed ZELLAGUI

2012-08-01

Full Text Available This paper presents and compares the impact of SSSC on measured impedance for single phase to ground fault condition. The presence of Static Synchronous SSSC on a transmission line has a great influence on the ZRelay in distance protection. The protection of the high voltage 220 kV single circuit transmission line in eastern Algerian electrical transmission networks is affected in the case with resistance fault RF. The paper investigate the effect of Static Synchronous Series Compensator (SSSC on the measured impedance (Relay taking into account the distance fault point (n and fault resistance (RF. The resultants simulation is performed in MATLAB software environment.

Nonsteady heat conduction code with radiation boundary conditions

International Nuclear Information System (INIS)

Fillo, J.A.; Benenati, R.; Powell, J.

1975-01-01

A heat-transfer model for studying the temperature build-up in graphite blankets for fusion reactors is presented. In essence, the computer code developed is for two-dimensional, nonsteady heat conduction in heterogeneous, anisotropic solids with nonuniform internal heating. Thermal radiation as well as bremsstrahlung radiation boundary conditions are included. Numerical calculations are performed for two design options by varying the wall loading, bremsstrahlung, surface layer thickness and thermal conductivity, blanket dimensions, time step and grid size. (auth)

Particles in a magnetic field and plasma analogies: doubly periodic boundary conditions

International Nuclear Information System (INIS)

Forrester, P J

2006-01-01

The N-particle free fermion state for quantum particles in the plane subject to a perpendicular magnetic field, and with doubly periodic boundary conditions, is written in a product form. The absolute value of this is used to formulate an exactly solvable one-component plasma model and further motivates the formulation of an exactly solvable two-species Coulomb gas. The large N expansion of the free energy of both these models exhibits the same O(1) term. On the basis of a relationship to the Gaussian free field, this term is predicted to be universal for conductive Coulomb systems in doubly periodic boundary conditions

Identification of complex model thermal boundary conditions based on exterior temperature measurement

International Nuclear Information System (INIS)

Lu Jianming; Ouyang Guangyao; Zhang Ping; Rong Bojun

2012-01-01

Combining the advantages of the finite element software in temperature field analyzing with the multivariate function optimization arithmetic, a feasibility method based on the exterior temperature was proposed to get the thermal boundary conditions, which was required in temperature field analyzing. The thermal boundary conditions can be obtained only by some temperature measurement values. Taking the identification of the convection heat transfer coefficient of a high power density diesel engine cylinder head as an example, the calculation result shows that when the temperature measurement error was less than 0.5℃, the maximum relative error was less than 2%. It is shown that the new method was feasible (authors)

Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

Science.gov (United States)

Bardhan, Jaydeep P.; Knepley, Matthew G.

2014-01-01

We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry. PMID:25296776

Grain boundary microchemistry and metallurgical characterization of Eurofer'97 after simulated service conditions

International Nuclear Information System (INIS)

Fernandez, P.; Garcia-Mazario, M.; Lancha, A.M.; Lapena, J.

2004-01-01

The aim of this paper is to describe the microstructural investigations, the mechanical properties (hardness, tensile and charpy) and the grain boundary microchemistry studied by Auger electron spectroscopy (AES), of the Eurofer'97 steel aged in the range of temperatures from 400 to 600 deg. C up to 10,000 h. After these thermal aging treatments the steel showed a high microstructural stability, and similar values of hardness, ultimate tensile strength and 0.2% proof stress regardless of the material condition. A slight DBTT increase was observed in the material aged at 600 deg. C for 5000 and 10,000 h. The Auger results showed chromium enrichment at grain boundaries in all material conditions. In addition, phosphorus was detected at the grain boundaries after the aging treatments at 500 deg. C

Critical deflagration waves leading to detonation onset under different boundary conditions

International Nuclear Information System (INIS)

Lin Wei; Zhou Jin; Lin Zhi-Yong; Fan Xiao-Hua

2015-01-01

High-speed turbulent critical deflagration waves before detonation onset in H 2 –air mixture propagated into a square cross section channel, which was assembled of optional rigid rough, rigid smooth, or flexible walls. The corresponding propagation characteristic and the influence of the wall boundaries on the propagation were investigated via high-speed shadowgraph and a high-frequency pressure sampling system. As a comprehensive supplement to the different walls effect investigation, the effect of porous absorbing walls on the detonation propagation was also investigated via smoke foils and the high-frequency pressure sampling system. Results are as follows. In the critical deflagration stage, the leading shock and the closely following turbulent flame front travel at a speed of nearly half the CJ detonation velocity. In the preheated zone, a zonary flame arises from the overlapping part of the boundary layer and the pressure waves, and then merges into the mainstream flame. Among these wall boundary conditions, the rigid rough wall plays a most positive role in the formation of the zonary flame and thus accelerates the transition of the deflagration to detonation (DDT), which is due to the boost of the boundary layer growth and the pressure wave reflection. Even though the flexible wall is not conducive to the pressure wave reflection, it brings out a faster boundary layer growth, which plays a more significant role in the zonary flame formation. Additionally, the porous absorbing wall absorbs the transverse wave and yields detonation decay and velocity deficit. After the absorbing wall, below some low initial pressure conditions, no re-initiation occurs and the deflagration propagates in critical deflagration for a relatively long distance. (paper)

Liouville equation with boundary conditions derived from classical strings

International Nuclear Information System (INIS)

Marnelius, R.

1983-01-01

It is shown in terms of the classical string theory that a breaking of the Weyl invariance necessarily requires the Liouville equation for the variable phi=1n rho, where rho is the variable that appears in the conformal gauge gsub(α#betta#)=rhoetasub(α#betta#). Appropriate boundary conditions on phi for open and closed strings are then derived. (orig.)

DYNAMIC SURFACE BOUNDARY-CONDITIONS - A SIMPLE BOUNDARY MODEL FOR MOLECULAR-DYNAMICS SIMULATIONS

NARCIS (Netherlands)

JUFFER, AH; BERENDSEN, HJC

1993-01-01

A simple model for the treatment of boundaries in molecular dynamics simulations is presented. The method involves the positioning of boundary atoms on a surface that surrounds a system of interest. The boundary atoms interact with the inner region and represent the effect of atoms outside the

Impedance spectroscopy of PZT ceramics--measuring diffusion coefficients, mixed conduction, and Pb loss.

Science.gov (United States)

Donnelly, Niall J; Randall, Clive A

2012-09-01

Sintering of lead zirconate titanate (PZT) at high temperatures results in loss of Pb unless an ambient Pb activity is maintained. The tell-tale sign of Pb loss is an increased conductivity, usually manifested in unacceptably high values of tanδ. The conductivity is caused by oxygen vacancies and/or electron holes which are a byproduct of Pb evaporation. In the first part of this paper, it is shown how impedance spectroscopy can be used to separate ionic and electronic conductivity in a properly designed sample by selection of appropriate boundary conditions. Subsequently, impedance is used to probe defect concentrations in PZT during prolonged annealing at 700°C. It is found that oxygen vacancies are generated during annealing in air but the rate of generation actually decreases upon lowering the ambient pO(2). These results are explained by a model of Pb evaporation which, in this case, leads predominantly to oxygen vacancy generation. In principle, this effect could be used to generate a specific vacancy concentration in similar Pb-based oxides.

Moment-based boundary conditions for lattice Boltzmann simulations of natural convection in cavities

KAUST Repository

Allen, Rebecca

2016-06-29

We study a multiple relaxation time lattice Boltzmann model for natural convection with moment-based boundary conditions. The unknown primary variables of the algorithm at a boundary are found by imposing conditions directly upon hydrodynamic moments, which are then translated into conditions for the discrete velocity distribution functions. The method is formulated so that it is consistent with the second order implementation of the discrete velocity Boltzmann equations for fluid flow and temperature. Natural convection in square cavities is studied for Rayleigh numbers ranging from 103 to 108. An excellent agreement with benchmark data is observed and the flow fields are shown to converge with second order accuracy. Copyright © 2016 Inderscience Enterprises Ltd.

Bayesian Inference for Linear Parabolic PDEs with Noisy Boundary Conditions

KAUST Repository

Ruggeri, Fabrizio; Sawlan, Zaid A; Scavino, Marco; Tempone, Raul

2016-01-01

In this work we develop a hierarchical Bayesian setting to infer unknown parameters in initial-boundary value problems (IBVPs) for one-dimensional linear parabolic partial differential equations. Noisy boundary data and known initial condition are assumed. We derive the likelihood function associated with the forward problem, given some measurements of the solution field subject to Gaussian noise. Such function is then analytically marginalized using the linearity of the equation. Gaussian priors have been assumed for the time-dependent Dirichlet boundary values. Our approach is applied to synthetic data for the one-dimensional heat equation model, where the thermal diffusivity is the unknown parameter. We show how to infer the thermal diffusivity parameter when its prior distribution is lognormal or modeled by means of a space-dependent stationary lognormal random field. We use the Laplace method to provide approximated Gaussian posterior distributions for the thermal diffusivity. Expected information gains and predictive posterior densities for observable quantities are numerically estimated for different experimental setups.

Bayesian Inference for Linear Parabolic PDEs with Noisy Boundary Conditions

KAUST Repository

Ruggeri, Fabrizio

2015-01-07

In this work we develop a hierarchical Bayesian setting to infer unknown parameters in initial-boundary value problems (IBVPs) for one-dimensional linear parabolic partial differential equations. Noisy boundary data and known initial condition are assumed. We derive the likelihood function associated with the forward problem, given some measurements of the solution field subject to Gaussian noise. Such function is then analytically marginalized using the linearity of the equation. Gaussian priors have been assumed for the time-dependent Dirichlet boundary values. Our approach is applied to synthetic data for the one-dimensional heat equation model, where the thermal diffusivity is the unknown parameter. We show how to infer the thermal diffusivity parameter when its prior distribution is lognormal or modeled by means of a space-dependent stationary lognormal random field. We use the Laplace method to provide approximated Gaussian posterior distributions for the thermal diffusivity. Expected information gains and predictive posterior densities for observable quantities are numerically estimated for different experimental setups.

Bayesian Inference for Linear Parabolic PDEs with Noisy Boundary Conditions

KAUST Repository

Ruggeri, Fabrizio

2016-01-06

In this work we develop a hierarchical Bayesian setting to infer unknown parameters in initial-boundary value problems (IBVPs) for one-dimensional linear parabolic partial differential equations. Noisy boundary data and known initial condition are assumed. We derive the likelihood function associated with the forward problem, given some measurements of the solution field subject to Gaussian noise. Such function is then analytically marginalized using the linearity of the equation. Gaussian priors have been assumed for the time-dependent Dirichlet boundary values. Our approach is applied to synthetic data for the one-dimensional heat equation model, where the thermal diffusivity is the unknown parameter. We show how to infer the thermal diffusivity parameter when its prior distribution is lognormal or modeled by means of a space-dependent stationary lognormal random field. We use the Laplace method to provide approximated Gaussian posterior distributions for the thermal diffusivity. Expected information gains and predictive posterior densities for observable quantities are numerically estimated for different experimental setups.

Asymptotic stability and blow up for a semilinear damped wave equation with dynamic boundary conditions

KAUST Repository

Gerbi, Stéphane

2011-12-01

In this paper we consider a multi-dimensional wave equation with dynamic boundary conditions, related to the KelvinVoigt damping. Global existence and asymptotic stability of solutions starting in a stable set are proved. Blow up for solutions of the problem with linear dynamic boundary conditions with initial data in the unstable set is also obtained. © 2011 Elsevier Ltd. All rights reserved.

Asymptotic stability and blow up for a semilinear damped wave equation with dynamic boundary conditions

KAUST Repository

Gerbi, Sté phane; Said-Houari, Belkacem

2011-01-01

In this paper we consider a multi-dimensional wave equation with dynamic boundary conditions, related to the KelvinVoigt damping. Global existence and asymptotic stability of solutions starting in a stable set are proved. Blow up for solutions of the problem with linear dynamic boundary conditions with initial data in the unstable set is also obtained. © 2011 Elsevier Ltd. All rights reserved.

Nonlinear $q$-fractional differential equations with nonlocal and sub-strip type boundary conditions

Directory of Open Access Journals (Sweden)

Bashir Ahmad

2014-06-01

Full Text Available This paper is concerned with new boundary value problems of nonlinear $q$-fractional differential equations with nonlocal and sub-strip type boundary conditions. Our results are new in the present setting and rely on the contraction mapping principle and a fixed point theorem due to O'Regan. Some illustrative examples are also presented.

Assessment of a PML Boundary Condition for Simulating an MRI Radio Frequency Coil

Directory of Open Access Journals (Sweden)

Yunsuo Duan

2008-01-01

Full Text Available Computational methods such as the finite difference time domain (FDTD play an important role in simulating radiofrequency (RF coils used in magnetic resonance imaging (MRI. The choice of absorbing boundary conditions affects the final outcome of such studies. We have used FDTD to assess the Berenger's perfectly matched layer (PML as an absorbing boundary condition for computation of the resonance patterns and electromagnetic fields of RF coils. We first experimentally constructed a high-pass birdcage head coil, measured its resonance pattern, and used it to acquire proton (1H phantom MRI images. We then computed the resonance pattern and B1 field of the coil using FDTD with a PML as an absorbing boundary condition. We assessed the accuracy and efficiency of PML by adjusting the parameters of the PML and comparing the calculated results with measured ones. The optimal PML parameters that produce accurate (comparable to the experimental findings FDTD calculations are then provided for the birdcage head coil operating at 127.72 MHz, the Larmor frequency of 1H at 3 Tesla (T.

Analysis on Forced Vibration of Thin-Wall Cylindrical Shell with Nonlinear Boundary Condition

Directory of Open Access Journals (Sweden)

Qiansheng Tang

2016-01-01

Full Text Available Forced vibration of thin-wall cylindrical shell under nonlinear boundary condition was discussed in this paper. The nonlinear boundary was modeled as supported clearance in one end of shell and the restraint was assumed as linearly elastic in the radial direction. Based on Sanders’ shell theory, Lagrange equation was utilized to derive the nonlinear governing equations of cylindrical shell. The displacements in three directions were represented by beam functions and trigonometric functions. In the study of nonlinear dynamic responses of thin-wall cylindrical shell with supported clearance under external loads, the Newmark method is used to obtain time history, frequency spectrum plot, phase portraits, Poincare section, bifurcation diagrams, and three-dimensional spectrum plot with different parameters. The effects of external loads, supported clearance, and support stiffness on nonlinear dynamics behaviors of cylindrical shell with nonlinear boundary condition were discussed.

Soil-structure interaction - a general method to calculate soil impedance

International Nuclear Information System (INIS)

Farvacque, M.; Gantenbein, F.

1983-01-01

A correct analysis of the seismic response of nuclear power plant buildings needs to take into account the soil structure interaction. The most classical and simple method consists in characterizing the soil by a stiffness and a damping function for each component of the translation and rotation of the foundation. In a more exact way an impedance function of the frequency may be introduced. Literature provides data to estimate these coefficients for simple soil and foundation configurations and using linear hypothesis. This paper presents a general method to calculate soil impedances which is based on the computation of the impulsive response of the soil using an axisymmetric 2D finite element Code (INCA). The Fourier transform of this response is made in the time interval before the return of the reflected waves on the boundaries of the F.E. domain. This procedure which limits the perturbing effects of the reflections is improved by introducing absorbing boundary elements. A parametric study for homogeneous and layered soils has been carried out using this method. (orig.)

Influence of Contact Angle Boundary Condition on CFD Simulation of T-Junction

Science.gov (United States)

Arias, S.; Montlaur, A.

2018-03-01

In this work, we study the influence of the contact angle boundary condition on 3D CFD simulations of the bubble generation process occurring in a capillary T-junction. Numerical simulations have been performed with the commercial Computational Fluid Dynamics solver ANSYS Fluent v15.0.7. Experimental results serve as a reference to validate numerical results for four independent parameters: the bubble generation frequency, volume, velocity and length. CFD simulations accurately reproduce experimental results both from qualitative and quantitative points of view. Numerical results are very sensitive to the gas-liquid-wall contact angle boundary conditions, confirming that this is a fundamental parameter to obtain accurate CFD results for simulations of this kind of problems.

Reconstruction of surface impedance of an object located over a planar PEC surface

International Nuclear Information System (INIS)

Uenal, Guel Seda; Cayoeren, Mehmet; Tetik, Evrim

2008-01-01

A method for the determination of inhomogeneous surface impedance of an arbitrary shaped cylindrical object located over a perfectly conducting (PEC) plane is presented. The problem is reduced to the solution of an ill-posed integral equation by the use of single layer representation which is handled by Truncated Singular Value Decomposition (TSVD). The total field and its normal derivative on the boundary of the object which are required for the evaluation of the surface impedance are obtained through Nystroem method. The method can also be used in shape reconstruction by using the relation between the shape of a PEC object and its equivalent one in terms of the surface impedance. The numerical implementations yield quite satisfactory results.

Physically-consistent wall boundary conditions for the k-ω turbulence model

DEFF Research Database (Denmark)

Fuhrman, David R.; Dixen, Martin; Jacobsen, Niels Gjøl

2010-01-01

A model solving Reynolds-averaged Navier–Stokes equations, coupled with k-v turbulence closure, is used to simulate steady channel flow on both hydraulically smooth and rough beds. Novel experimental data are used as model validation, with k measured directly from all three components of the fluc......A model solving Reynolds-averaged Navier–Stokes equations, coupled with k-v turbulence closure, is used to simulate steady channel flow on both hydraulically smooth and rough beds. Novel experimental data are used as model validation, with k measured directly from all three components...... of the fluctuating velocity signal. Both conventional k = 0 and dk/dy = 0 wall boundary conditions are considered. Results indicate that either condition can provide accurate solutions, for the bulk of the flow, over both smooth and rough beds. It is argued that the zero-gradient condition is more consistent...... with the near wall physics, however, as it allows direct integration through a viscous sublayer near smooth walls, while avoiding a viscous sublayer near rough walls. This is in contrast to the conventional k = 0 wall boundary condition, which forces resolution of a viscous sublayer in all circumstances...

OpenCL-Based FPGA Accelerator for 3D FDTD with Periodic and Absorbing Boundary Conditions

Directory of Open Access Journals (Sweden)

Hasitha Muthumala Waidyasooriya

2017-01-01

Full Text Available Finite difference time domain (FDTD method is a very poplar way of numerically solving partial differential equations. FDTD has a low operational intensity so that the performances in CPUs and GPUs are often restricted by the memory bandwidth. Recently, deeply pipelined FPGA accelerators have shown a lot of success by exploiting streaming data flows in FDTD computation. In spite of this success, many FPGA accelerators are not suitable for real-world applications that contain complex boundary conditions. Boundary conditions break the regularity of the data flow, so that the performances are significantly reduced. This paper proposes an FPGA accelerator that computes commonly used absorbing and periodic boundary conditions in many 3D FDTD applications. Accelerator is designed using a “C-like” programming language called OpenCL (open computing language. As a result, the proposed accelerator can be customized easily by changing the software code. According to the experimental results, we achieved over 3.3 times and 1.5 times higher processing speed compared to the CPUs and GPUs, respectively. Moreover, the proposed accelerator is more than 14 times faster compared to the recently proposed FPGA accelerators that are capable of handling complex boundary conditions.

Electrical transport properties of CoMn0.2−xGaxFe1.8O4 ferrites using complex impedance spectroscopy

Directory of Open Access Journals (Sweden)

Chien-Yie Tsay

2016-05-01

Full Text Available In this study, we report the influence of Ga content on the microstructural, magnetic, and AC impedance properties of Co-based ferrites with compositions of CoMn0.2−xGaxFe1.8O4 (x=0, 0.1, and 0.2 prepared by the solid-state reaction method. Experimental results showed that the as-prepared Co-based ferrites had a single-phase spinel structure; the Curie temperature of Co-based ferrites decreased with increasing Ga content. All ferrite samples exhibited a typical hysteresis behavior with good values of saturation magnetization at room temperature. The electrical properties of Co-based ferrites were investigated using complex impedance spectroscopy analysis in the frequency range of 100 kHz-50 MHz at temperatures of 150 to 250 oC. The impedance analysis revealed that the magnitudes of the real part (Z’ and the imaginary part (Z” of complex impedance decreased with increasing temperature. Only one semicircle was observed in each complex impedance plane plot, which revealed that the contribution to conductivity was from the grain boundaries. It was found that the relaxation time for the grain boundary (τgb also decreased with increasing temperature. The values of resistance for the grain boundary (Rgb significantly increased with increasing Ga content, which indicated that the incorporation of Ga into Co-based ferrites enhanced the electrical resistivity.

An Outflow Boundary Condition Model for Noninvasive Prediction of Fractional Flow Reserve in Diseased Coronary Arteries.

Science.gov (United States)

Fayssal, Iyad A; Moukalled, Fadl; Alam, Samir; Isma'eel, Hussain

2018-04-01

This paper reports on a new boundary condition formulation to model the total coronary myocardial flow and resistance characteristics of the myocardial vascular bed for any specific patient when considered for noninvasive diagnosis of ischemia. The developed boundary condition model gives an implicit representation of the downstream truncated coronary bed. Further, it is based on incorporating patient-specific physiological parameters that can be noninvasively extracted to account for blood flow demand to the myocardium at rest and hyperemic conditions. The model is coupled to a steady three-dimensional (3D) collocated pressure-based finite volume flow solver and used to characterize the "functional significance" of a patient diseased coronary artery segment without the need for predicting the hemodynamics of the entire arterial system. Predictions generated with this boundary condition provide a deep understanding of the inherent challenges behind noninvasive image-based diagnostic techniques when applied to human diseased coronary arteries. The overall numerical method and formulated boundary condition model are validated via two computational-based procedures and benchmarked with available measured data. The newly developed boundary condition is used via a designed computational methodology to (a) confirm the need for incorporating patient-specific physiological parameters when modeling the downstream coronary resistance, (b) explain the discrepancies presented in the literature between measured and computed fractional flow reserve (FFRCT), and (c) discuss the current limitations and future challenges in shifting to noninvasive assessment of ischemia.

A Two-Dimensional Transverse Magnetic Propagation Model of a Sine Wave Using Mur Boundary Conditions

National Research Council Canada - National Science Library

Korjack, T

1997-01-01

.... The nonreflecting boundary conditions due to Mur were used at the boundary surfaces. Electric field intensity distributions resulted over a progressive time expansion to illustrate the propagation effect over the entire 2-D mesh...

Hawking radiation, effective actions and covariant boundary conditions

International Nuclear Information System (INIS)

Banerjee, Rabin; Kulkarni, Shailesh

2008-01-01

From an appropriate expression for the effective action, the Hawking radiation from charged black holes is derived, using only covariant boundary conditions at the event horizon. The connection of our approach with the Unruh vacuum and the recent analysis [S.P. Robinson, F. Wilczek, Phys. Rev. Lett. 95 (2005) 011303, (gr-qc/0502074); S. Iso, H. Umetsu, F. Wilczek, Phys. Rev. Lett. 96 (2006) 151302, (hep-th/0602146); R. Banerjee, S. Kulkarni, (arXiv: 0707.2449 [hep-th])] of Hawking radiation using anomalies is established

The role of lateral boundary conditions in simulations of mineral aerosols by a regional climate model of Southwest Asia

Energy Technology Data Exchange (ETDEWEB)

Marcella, Marc Pace [Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Cambridge, MA (United States); Massachusetts Institute of Technology, Cambridge, Massachusetts (United States); Eltahir, Elfatih A.B. [Massachusetts Institute of Technology, Cambridge, Massachusetts (United States)

2012-01-15

The importance of specifying realistic lateral boundary conditions in the regional modeling of mineral aerosols has not been examined previously. This study examines the impact of assigning values for mineral aerosol (dust) concentrations at the lateral boundaries of Regional Climate Model version 3 (RegCM3) and its aerosol model over Southwest Asia. Currently, the dust emission module of RegCM3 operates over the interior of the domain, allowing dust to be transported to the boundaries, but neglecting any dust emitted at these points or from outside the domain. To account for possible dust occurring at, or entering from the boundaries, mixing ratios of dust concentrations from a larger domain RegCM3 simulation are specified at the boundaries of a smaller domain over Southwest Asia. The lateral boundary conditions are monthly averaged concentration values ({mu}g of dust per kg of dry air) resolved in the vertical for all four dust bin sizes within RegCM3's aerosol model. RegCM3 simulations with the aerosol/dust model including lateral boundary conditions for dust are performed for a five year period and compared to model simulations without prescribed dust concentrations at the boundaries. Results indicate that specifying boundary conditions has a significant impact on dust loading across the entire domain over Southwest Asia. More specifically, a nearly 30% increase in aerosol optical depth occurs during the summer months from specifying realistic dust boundary conditions, bringing model results closer to observations such as MISR. In addition, smaller dust particles at the boundaries have a more important impact than large particles in affecting the dust loading within the interior of this domain. Moreover, increases in aerosol optical depth and dust concentrations within the interior domain are not entirely caused by inflow from the boundaries; results indicate that an increase in the gradient of concentration at the boundaries causes an increase of

Molecular dynamics simulations of a fully hydrated dipalmitoyl phosphatidylcholine bilayer with different macroscopic boundary conditions and parameters

NARCIS (Netherlands)

Tieleman, D.P; Berendsen, H.J.C.

1996-01-01

We compared molecular dynamics simulations of a bilayer of 128 fully hydrated phospholipid (DPPC) molecules, using different parameters and macroscopic boundary conditions. The same system was studied under constant pressure, constant volume, and constant surface tension boundary conditions, with

Thermal boundary conditions for electrons in a weakly ionized gas near a catalytic wall

International Nuclear Information System (INIS)

Chekmarev, I.

1981-01-01

A technique of matched asymptotic expansions is used to examine the derivation of hydrodynamic transport equations for the external region of a weakly ionized multitemperature gas near an absorbing and conducting wall. An approximate moment solution is constructed for the Knudsen boundary layer. The conditions for the matching of the external and internal expansions lead to a new form of the hydrodynamic boundary conditions, from which the singular behavior of the energy equation for electrons near the wall has been eliminated

Recharge and Lateral Groundwater Flow Boundary Conditions for the Saturated Zone Site-Scale Flow and Transport Model

Energy Technology Data Exchange (ETDEWEB)

B. Arnold; T. Corbet

2001-12-18

The purpose of the flow boundary conditions analysis is to provide specified-flux boundary conditions for the saturated zone (SZ) site-scale flow and transport model. This analysis is designed to use existing modeling and analysis results as the basis for estimated groundwater flow rates into the SZ site-scale model domain, both as recharge at the upper (water table) boundary and as underflow at the lateral boundaries. The objective is to provide consistency at the boundaries between the SZ site-scale flow model and other groundwater flow models. The scope of this analysis includes extraction of the volumetric groundwater flow rates simulated by the SZ regional-scale flow model to occur at the lateral boundaries of the SZ site-scale flow model and the internal qualification of the regional-scale model for use in this analysis model report (AMR). In addition, the scope includes compilation of information on the recharge boundary condition taken from three sources: (1) distributed recharge as taken from the SZ regional-scale flow model, (2) recharge below the area of the unsaturated zone (UZ) site-scale flow model, and (3) focused recharge along the Fortymile Wash channel.

Polynomial Collocation for Handling an Inaccurately Known Measurement Configuration in Electrical Impedance Tomography

DEFF Research Database (Denmark)

Hyvönen, Niina; Kaarnioja, V.; Mustonen, L.

2017-01-01

The objective of electrical impedance tomography is to reconstruct the internal conductivity of a physical body based on measurements of current and potential at a finite number of electrodes attached to its boundary. Although the conductivity is the quantity of main interest in impedance...... tomography, a real-world measurement configuration includes other unknown parameters as well: The information on the contact resistances, electrode positions, and body shape is almost always incomplete. In this work, the dependence of the electrode measurements on all aforementioned model properties...

Wideband impedance measurements of DC motors under dynamic load conditions

NARCIS (Netherlands)

Diouf, F.; Buesink, Frederik Johannes Karel; Leferink, Frank Bernardus Johannes; Duval, Fabrice; Bensetti, Mohamed

2013-01-01

One of the principal conducted EMI(electromagnetic interferences) sources of low voltage DC (direct current) motors is the commutation occurring during rotation. In this paper the small-signal impedance of low voltage DC motors under different functioning modes, including the dynamic one is studied

Compensation for geometric modeling errors by positioning of electrodes in electrical impedance tomography

DEFF Research Database (Denmark)

Hyvönen, N.; Majander, H.; Staboulis, Stratos

2017-01-01

Electrical impedance tomography aims at reconstructing the conductivity inside a physical body from boundary measurements of current and voltage at a finite number of contact electrodes. In many practical applications, the shape of the imaged object is subject to considerable uncertainties...

Recursive solution for dynamic response of one-dimensional structures with time-dependent boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Abadi, Mohammad Tahaye [Aerospace Research Institute, Tehran (Iran, Islamic Republic of)

2015-10-15

A recursive solution method is derived for the transient response of one-dimensional structures subjected to the general form of time dependent boundary conditions. Unlike previous solution methods that assumed the separation of variables, the present method involves formulating and solving the dynamic problems using the summation of two single-argument functions satisfying the motion equation. Based on boundary and initial conditions, a recursive procedure is derived to determine the single-argument functions. Such a procedure is applied to the general form of boundary conditions, and an analytical solution is derived by solving the recursive equation. The present solution method is implemented for base excitation problems, and the results are compared with those of the previous analytical solution and the Finite element (FE) analysis. The FE results converge to the present analytical solution, although considerable error is found in predicting a solution method on the basis of the separation of variables. The present analytical solution predicts the transient response for wave propagation problems in broadband excitation frequencies.

Recursive solution for dynamic response of one-dimensional structures with time-dependent boundary conditions

International Nuclear Information System (INIS)

Abadi, Mohammad Tahaye

2015-01-01

A recursive solution method is derived for the transient response of one-dimensional structures subjected to the general form of time dependent boundary conditions. Unlike previous solution methods that assumed the separation of variables, the present method involves formulating and solving the dynamic problems using the summation of two single-argument functions satisfying the motion equation. Based on boundary and initial conditions, a recursive procedure is derived to determine the single-argument functions. Such a procedure is applied to the general form of boundary conditions, and an analytical solution is derived by solving the recursive equation. The present solution method is implemented for base excitation problems, and the results are compared with those of the previous analytical solution and the Finite element (FE) analysis. The FE results converge to the present analytical solution, although considerable error is found in predicting a solution method on the basis of the separation of variables. The present analytical solution predicts the transient response for wave propagation problems in broadband excitation frequencies.

Optimum heat power cycles for specified boundary conditions

International Nuclear Information System (INIS)

Ibrahim, O.M.; Klein, S.A.; Mitchell, J.W.

1991-01-01

In this paper optimization of the power output of Carnot and closed Brayton cycles is considered for both finite and infinite thermal capacitance rates of the external fluid streams. The method of Lagrange multipliers is used to solve for working fluid temperatures that yield maximum power. Analytical expressions for the maximum power and the cycle efficiency at maximum power are obtained. A comparison of the maximum power from the two cycles for the same boundary conditions, i.e., the same heat source/sink inlet temperatures, thermal capacitance rates, and heat exchanger conductances, shows that the Brayton cycle can produce more power than the Carnot cycle. This comparison illustrates that cycles exist that can produce more power than the Carnot cycle. The optimum heat power cycle, which will provide the upper limit of power obtained from any thermodynamic cycle for specified boundary conditions and heat exchanger conductances is considered. The optimum heat power cycle is identified by optimizing the sum of the power output from a sequence of Carnot cycles. The shape of the optimum heat power cycle, the power output, and corresponding efficiency are presented. The efficiency at maximum power of all cycles investigated in this study is found to be equal to (or well approximated by) η = 1 - sq. root T L.in /φT H.in where φ is a factor relating the entropy changes during heat rejection and heat addition

Graph Theory-Based Technique for Isolating Corrupted Boundary Conditions in Continental-Scale River Network Hydrodynamic Simulation

Science.gov (United States)

Yu, C. W.; Hodges, B. R.; Liu, F.

2017-12-01

Development of continental-scale river network models creates challenges where the massive amount of boundary condition data encounters the sensitivity of a dynamic nu- merical model. The topographic data sets used to define the river channel characteristics may include either corrupt data or complex configurations that cause instabilities in a numerical solution of the Saint-Venant equations. For local-scale river models (e.g. HEC- RAS), modelers typically rely on past experience to make ad hoc boundary condition adjustments that ensure a stable solution - the proof of the adjustment is merely the sta- bility of the solution. To date, there do not exist any formal methodologies or automated procedures for a priori detecting/fixing boundary conditions that cause instabilities in a dynamic model. Formal methodologies for data screening and adjustment are a critical need for simulations with a large number of river reaches that draw their boundary con- dition data from a wide variety of sources. At the continental scale, we simply cannot assume that we will have access to river-channel cross-section data that has been ade- quately analyzed and processed. Herein, we argue that problematic boundary condition data for unsteady dynamic modeling can be identified through numerical modeling with the steady-state Saint-Venant equations. The fragility of numerical stability increases with the complexity of branching in river network system and instabilities (even in an unsteady solution) are typically triggered by the nonlinear advection term in Saint-Venant equations. It follows that the behavior of the simpler steady-state equations (which retain the nonlin- ear term) can be used to screen the boundary condition data for problematic regions. In this research, we propose a graph-theory based method to isolate the location of corrupted boundary condition data in a continental-scale river network and demonstrate its utility with a network of O(10^4) elements. Acknowledgement

Toroidal current asymmetry and boundary conditions in disruptions

Science.gov (United States)

Strauss, Henry

2014-10-01

It was discovered on JET that disruptions were accompanied by toroidal asymmetry of the plasma current. The toroidal current asymmetry ΔIϕ is proportional to the vertical current moment ΔMIZ , with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was claimed that this could only be explained by Hiro current. It is shown that instead it is essentially a kinematic effect produced by the VDE displacement of a 3D magnetic perturbation. This is verified by M3D simulations. The simulation results do not require penetration of plasma into the boundary, as in the Hiro current model. It is shown that the normal velocity perpendicular to the magnetic field vanishes at the wall, in the small Larmor radius limit of electromagnetic sheath boundary conditions. Plasma is absorbed into the wall only via the parallel velocity, which is small, penetrates only an infinitesimal distance into the wall, and does not affect forces exerted by the plasma on the wall. Supported by USDOE and ITER.

Acoustic impedances of ear canals measured by impedance tube

DEFF Research Database (Denmark)

Ciric, Dejan; Hammershøi, Dorte

2007-01-01

During hearing sensitivity tests, the sound field is commonly generated by an earphone placed on a subject ear. One of the factors that can affect the sound transmission in the ear is the acoustic impedance of the ear canal. Its importance is related to the contribution of other elements involved...... in the transmission such as the earphone impedance. In order to determine the acoustic impedances of human ear canals, the standardized method for measurement of complex impedances used for the measurement of the audiometric earphone impedances is applied. It is based on the transfer function between two microphone...... locations in an impedance tube. The end of the tube representing the measurement plane is placed at the ear canal entrance. Thus, the impedance seen from the entrance inward is measured on 25 subjects. Most subjects participated in the previous measurement of the ratio between the pressures at the open...

Effects of boundary conditions on temperature and density in an EXTRAP Z-pinch

International Nuclear Information System (INIS)

Drake, J.R.; Karlsson, P.

1985-08-01

Using the fluid equations, we examine transport in an Extrap configuration by carrying out calculations incorporating model profiles for the density and temperature. The goal of this analysis is to examine the scaling of the pinch equilibrium plasma density, temperature and radius with parameters that are characteristic for Extrap Z-pinches. These parameters include the discharge current, the neutral hydrogen filling density, an oxygen impurity fractional concentration and the condition at the pinch boundary. An Extrap Z-pinch is a pinch discharge where the current channel has a characteristic non-circular cross-section achieved by bounding the discharge by a magnetic separatrix produced when a vacuum octupole magnetic field, generated by currents in external conductors, combines with the self-magnetic field produced by the discharge current. The pinch boundary is changed from a plasma-vacuum boundary to an interface between a high-beta pinch plasma and a low-beta plasma contained in the vacuum magnetic field. The energy that is lost from the pinch region sustains this boundary layer. The introduction of a separatrix boundary around the pinch with four X-point nulls deteriorates the containment of the pinch somewhat. However the presence of the warm, low-beta plasma scrape-off layer, which provides a boundary condition on the pinch, tends to counteract the negative effects of the poorer confinement. Thus the equilibrium parameters that characterize the pinch may not be severely deteriorated by the introduction of the separatrix when the entire configuration, including the scrape-off layer, is considered. (author)

Real-Time Thevenin Impedance Computation

DEFF Research Database (Denmark)

Sommer, Stefan Horst; Jóhannsson, Hjörtur

2013-01-01

operating state, and strict time constraints are difficult to adhere to as the complexity of the grid increases. Several suggested approaches for real-time stability assessment require Thevenin impedances to be determined for the observed system conditions. By combining matrix factorization, graph reduction......, and parallelization, we develop an algorithm for computing Thevenin impedances an order of magnitude faster than previous approaches. We test the factor-and-solve algorithm with data from several power grids of varying complexity, and we show how the algorithm allows realtime stability assessment of complex power...

Bayesian-based estimation of acoustic surface impedance: Finite difference frequency domain approach.

Science.gov (United States)

Bockman, Alexander; Fackler, Cameron; Xiang, Ning

2015-04-01

Acoustic performance for an interior requires an accurate description of the boundary materials' surface acoustic impedance. Analytical methods may be applied to a small class of test geometries, but inverse numerical methods provide greater flexibility. The parameter estimation problem requires minimizing prediction vice observed acoustic field pressure. The Bayesian-network sampling approach presented here mitigates other methods' susceptibility to noise inherent to the experiment, model, and numerics. A geometry agnostic method is developed here and its parameter estimation performance is demonstrated for an air-backed micro-perforated panel in an impedance tube. Good agreement is found with predictions from the ISO standard two-microphone, impedance-tube method, and a theoretical model for the material. Data by-products exclusive to a Bayesian approach are analyzed to assess sensitivity of the method to nuisance parameters.

Development of stress boundary conditions in smoothed particle hydrodynamics (SPH) for the modeling of solids deformation

Science.gov (United States)

Douillet-Grellier, Thomas; Pramanik, Ranjan; Pan, Kai; Albaiz, Abdulaziz; Jones, Bruce D.; Williams, John R.

2017-10-01

This paper develops a method for imposing stress boundary conditions in smoothed particle hydrodynamics (SPH) with and without the need for dummy particles. SPH has been used for simulating phenomena in a number of fields, such as astrophysics and fluid mechanics. More recently, the method has gained traction as a technique for simulation of deformation and fracture in solids, where the meshless property of SPH can be leveraged to represent arbitrary crack paths. Despite this interest, application of boundary conditions within the SPH framework is typically limited to imposed velocity or displacement using fictitious dummy particles to compensate for the lack of particles beyond the boundary interface. While this is enough for a large variety of problems, especially in the case of fluid flow, for problems in solid mechanics there is a clear need to impose stresses upon boundaries. In addition to this, the use of dummy particles to impose a boundary condition is not always suitable or even feasibly, especially for those problems which include internal boundaries. In order to overcome these difficulties, this paper first presents an improved method for applying stress boundary conditions in SPH with dummy particles. This is then followed by a proposal of a formulation which does not require dummy particles. These techniques are then validated against analytical solutions to two common problems in rock mechanics, the Brazilian test and the penny-shaped crack problem both in 2D and 3D. This study highlights the fact that SPH offers a good level of accuracy to solve these problems and that results are reliable. This validation work serves as a foundation for addressing more complex problems involving plasticity and fracture propagation.

Edge states and conformal boundary conditions in super spin chains and super sigma models

International Nuclear Information System (INIS)

Bondesan, Roberto; Jacobsen, Jesper L.; Saleur, Hubert

2011-01-01

The sigma models on projective superspaces CP N+M-1|N with topological angle θ=πmod2π flow to non-unitary, logarithmic conformal field theories in the low-energy limit. In this paper, we determine the exact spectrum of these theories for all open boundary conditions preserving the full global symmetry of the model, generalizing recent work on the particular case M=0 [C. Candu et al., JHEP 1002 (2010) 015]. In the sigma model setting, these boundary conditions are associated with complex line bundles, and are labelled by an integer, related with the exact value of θ. Our approach relies on a spin chain regularization, where the boundary conditions now correspond to the introduction of additional edge states. The exact values of the exponents then follow from a lengthy algebraic analysis, a reformulation of the spin chain in terms of crossing and non-crossing loops (represented as a certain subalgebra of the Brauer algebra), and earlier results on the so-called one- and two-boundary Temperley-Lieb algebras (also known as blob algebras). A remarkable result is that the exponents, in general, turn out to be irrational. The case M=1 has direct applications to the spin quantum Hall effect, which will be discussed in a sequel.

Edge states and conformal boundary conditions in super spin chains and super sigma models

Energy Technology Data Exchange (ETDEWEB)

Bondesan, Roberto, E-mail: roberto.bondesan@cea.f [LPTENS, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris (France); Institute de Physique Theorique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Jacobsen, Jesper L. [LPTENS, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris (France); Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris (France); Saleur, Hubert [Institute de Physique Theorique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Physics Department, USC, Los Angeles, CA 90089-0484 (United States)

2011-08-11

The sigma models on projective superspaces CP{sup N+M-1{vert_bar}N} with topological angle {theta}={pi}mod2{pi} flow to non-unitary, logarithmic conformal field theories in the low-energy limit. In this paper, we determine the exact spectrum of these theories for all open boundary conditions preserving the full global symmetry of the model, generalizing recent work on the particular case M=0 [C. Candu et al., JHEP 1002 (2010) 015]. In the sigma model setting, these boundary conditions are associated with complex line bundles, and are labelled by an integer, related with the exact value of {theta}. Our approach relies on a spin chain regularization, where the boundary conditions now correspond to the introduction of additional edge states. The exact values of the exponents then follow from a lengthy algebraic analysis, a reformulation of the spin chain in terms of crossing and non-crossing loops (represented as a certain subalgebra of the Brauer algebra), and earlier results on the so-called one- and two-boundary Temperley-Lieb algebras (also known as blob algebras). A remarkable result is that the exponents, in general, turn out to be irrational. The case M=1 has direct applications to the spin quantum Hall effect, which will be discussed in a sequel.

Does bioelectrical impedance analysis accurately estimate the condition of threatened and endangered desert fish species?

Science.gov (United States)

Dibble, Kimberly L.; Yard, Micheal D.; Ward, David L.; Yackulic, Charles B.

2017-01-01

Bioelectrical impedance analysis (BIA) is a nonlethal tool with which to estimate the physiological condition of animals that has potential value in research on endangered species. However, the effectiveness of BIA varies by species, the methodology continues to be refined, and incidental mortality rates are unknown. Under laboratory conditions we tested the value of using BIA in addition to morphological measurements such as total length and wet mass to estimate proximate composition (lipid, protein, ash, water, dry mass, energy density) in the endangered Humpback Chub Gila cypha and Bonytail G. elegans and the species of concern Roundtail Chub G. robusta and conducted separate trials to estimate the mortality rates of these sensitive species. Although Humpback and Roundtail Chub exhibited no or low mortality in response to taking BIA measurements versus handling for length and wet-mass measurements, Bonytails exhibited 14% and 47% mortality in the BIA and handling experiments, respectively, indicating that survival following stress is species specific. Derived BIA measurements were included in the best models for most proximate components; however, the added value of BIA as a predictor was marginal except in the absence of accurate wet-mass data. Bioelectrical impedance analysis improved the R2 of the best percentage-based models by no more than 4% relative to models based on morphology. Simulated field conditions indicated that BIA models became increasingly better than morphometric models at estimating proximate composition as the observation error around wet-mass measurements increased. However, since the overall proportion of variance explained by percentage-based models was low and BIA was mostly a redundant predictor, we caution against the use of BIA in field applications for these sensitive fish species.

Eigenvalue inequalities for the Laplacian with mixed boundary conditions

Czech Academy of Sciences Publication Activity Database

Lotoreichik, Vladimir; Rohleder, J.

2017-01-01

Roč. 263, č. 1 (2017), s. 491-508 ISSN 0022-0396 R&D Projects: GA ČR(CZ) GA14-06818S Institutional support: RVO:61389005 Keywords : Laplace operator * mixed boundary conditions * eigenvalue inequality * polyhedral domain * Lipschitz domain Subject RIV: BE - Theoretical Physics OBOR OECD: Atomic, molecular and chemical physics (physics of atoms and molecules including collision, interaction with radiation, magnetic resonances, Mössbauer effect) Impact factor: 1.988, year: 2016

Advanced impedance modeling of solid oxide electrochemical cells

DEFF Research Database (Denmark)

Graves, Christopher R.; Hjelm, Johan

2014-01-01

Impedance spectroscopy is a powerful technique for detailed study of the electrochemical and transport processes that take place in fuel cells and electrolysis cells, including solid oxide cells (SOCs). Meaningful analysis of impedance measurements is nontrivial, however, because a large number...... techniques to provide good guesses for the modeling parameters, like transforming the impedance data to the distribution of relaxation times (DRT), together with experimental parameter sensitivity studies, is the state-of-the-art approach to achieve good EC model fits. Here we present new impedance modeling...... electrode and 2-D gas transport models which have fewer unknown parameters for the same number of processes, (ii) use of a new model fitting algorithm, “multi-fitting”, in which multiple impedance spectra are fit simultaneously with parameters linked based on the variation of measurement conditions, (iii...

Hyers-Ulam stability for second-order linear differential equations with boundary conditions

Directory of Open Access Journals (Sweden)

Pasc Gavruta

2011-06-01

Full Text Available We prove the Hyers-Ulam stability of linear differential equations of second-order with boundary conditions or with initial conditions. That is, if y is an approximate solution of the differential equation $y''+ eta (x y = 0$ with $y(a = y(b =0$, then there exists an exact solution of the differential equation, near y.

A domain-decomposition method to implement electrostatic free boundary conditions in the radial direction for electric discharges

Science.gov (United States)

Malagón-Romero, A.; Luque, A.

2018-04-01

At high pressure electric discharges typically grow as thin, elongated filaments. In a numerical simulation this large aspect ratio should ideally translate into a narrow, cylindrical computational domain that envelops the discharge as closely as possible. However, the development of the discharge is driven by electrostatic interactions and, if the computational domain is not wide enough, the boundary conditions imposed to the electrostatic potential on the external boundary have a strong effect on the discharge. Most numerical codes circumvent this problem by either using a wide computational domain or by calculating the boundary conditions by integrating the Green's function of an infinite domain. Here we describe an accurate and efficient method to impose free boundary conditions in the radial direction for an elongated electric discharge. To facilitate the use of our method we provide a sample implementation. Finally, we apply the method to solve Poisson's equation in cylindrical coordinates with free boundary conditions in both radial and longitudinal directions. This case is of particular interest for the initial stages of discharges in long gaps or natural discharges in the atmosphere, where it is not practical to extend the simulation volume to be bounded by two electrodes.

Algorithm for calculating synthetic seismograms in a layered half-space with application of matrix impedance

Science.gov (United States)

Pavlov, V. M.

2013-01-01

A new algorithm is proposed for calculating the complete synthetic seismograms from a point source in the form of the sum of a single force and a dipole with an arbitrary seismic moment tensor in a plane layered medium composed of homogenous elastic isotropic layers. Following the idea of (Alekseev and Mikhailenko, 1978), an artificial cylindrical boundary is introduced, on which the boundary conditions are specified. For this modified problem, the exact solution (in terms of the displacements and stresses on the horizontal plane areal element) in the frequency domain is derived and substantiated. The unknown depth-dependent coefficients form the motion-stress vector, whose components satisfy the known system of ordinary differential equations. This system is solved by the method that involves the matrix impedance and propagator for the vector of motion, as previously suggested by the author in (Pavlov, 2009). In relation to the initial problem, the reflections from the artificial boundary are noise, which, to a certain degree, can be suppressed by selecting a long enough distance to this boundary and owing to the presence of a purely imaginary addition to the frequency. The algorithm is not constrained by the thickness of the layers, is applicable for any frequency range, and is suitable for computing the static offset.

Analysis of smart beams with piezoelectric elements using impedance matrix and inverse Laplace transform

International Nuclear Information System (INIS)

Li, Guo-Qing; Miao, Xing-Yuan; Hu, Yuan-Tai; Wang, Ji

2013-01-01

A comprehensive study on smart beams with piezoelectric elements using an impedance matrix and the inverse Laplace transform is presented. Based on the authors’ previous work, the dynamics of some elements in beam-like smart structures are represented by impedance matrix equations, including a piezoelectric stack, a piezoelectric bimorph, an elastic straight beam or a circular curved beam. A further transform is applied to the impedance matrix to obtain a set of implicit transfer function matrices. Apart from the analytical solutions to the matrices of smart beams, one computation procedure is proposed to obtained the impedance matrices and transfer function matrices using FEA. By these means the dynamic solution of the elements in the frequency domain is transformed to that in Laplacian s-domain and then inversely transformed to time domain. The connections between the elements and boundary conditions of the smart structures are investigated in detail, and one integrated system equation is finally obtained using the symbolic operation of TF matrices. A procedure is proposed for dynamic analysis and control analysis of the smart beam system using mode superposition and a numerical inverse Laplace transform. The first example is given to demonstrate building transfer function associated impedance matrices using both FEA and analytical solutions. The second example is to verify the ability of control analysis using a suspended beam with PZT patches under close-loop control. The third example is designed for dynamic analysis of beams with a piezoelectric stack and a piezoelectric bimorph under various excitations. The last example of one smart beam with a PPF controller shows the applicability to the control analysis of complex systems using the proposed method. All results show good agreement with the other results in the previous literature. The advantages of the proposed methods are also discussed at the end of this paper. (paper)

Influence of Spanwise Boundary Conditions on Slat Noise Simulations

Science.gov (United States)

Lockard, David P.; Choudhari, Meelan M.; Buning, Pieter G.

2015-01-01

The slat noise from the 30P/30N high-lift system is being investigated through computational fluid dynamics simulations with the OVERFLOW code in conjunction with a Ffowcs Williams-Hawkings acoustics solver. In the present study, two different spanwise grids are being used to investigate the effect of the spanwise extent and periodicity on the near-field unsteady structures and radiated noise. The baseline grid with periodic boundary conditions has a short span equal to 1/9th of the stowed chord, whereas the other, longer span grid adds stretched grids on both sides of the core, baseline grid to allow inviscid surface boundary conditions at both ends. The results indicate that the near-field mean statistics obtained using the two grids are similar to each other, as are the directivity and spectral shapes of the radiated noise. However, periodicity forces all acoustic waves with less than one wavelength across the span to be two-dimensional, without any variation in the span. The spanwise coherence of the acoustic waves is what is needed to make estimates of the noise that would be radiated from realistic span lengths. Simulations with periodic conditions need spans of at least six slat chords to allow spanwise variation in the low-frequencies associated with the peak of broadband slat noise. Even then, the full influence of the periodicity is unclear, so employing grids with a fine, central region and highly stretched meshes that go to slip walls may be a more efficient means of capturing the spanwise decorrelation of low-frequency acoustic phenomena.

Modeling Stochastic Boundary Conditions in a Coastal Catchment using a Bayesian Network: An Application to the Houston Ship Channel, Texas

Science.gov (United States)

Couasnon, Anaïs; Sebastian, Antonia; Morales-Nápoles, Oswaldo

2017-04-01

Recent research has highlighted the increased risk of compound flooding in the U.S. In coastal catchments, an elevated downstream water level, resulting from high tide and/or storm surge, impedes drainage creating a backwater effect that may exacerbate flooding in the riverine environment. Catchments exposed to tropical cyclone activity along the Gulf of Mexico and Atlantic coasts are particularly vulnerable. However, conventional flood hazard models focus mainly on precipitation-induced flooding and few studies accurately represent the hazard associated with the interaction between discharge and elevated downstream water levels. This study presents a method to derive stochastic boundary conditions for a coastal watershed. Mean daily discharge and maximum daily residual water levels are used to build a non-parametric Bayesian network (BN) based on copulas. Stochastic boundary conditions for the watershed are extracted from the BN and input into a 1-D process-based hydraulic model to obtain water surface elevations in the main channel of the catchment. The method is applied to a section of the Houston Ship Channel (Buffalo Bayou) in Southeast Texas. Data at six stream gages and two tidal stations are used to build the BN and 100-year joint return period events are modeled. We find that the dependence relationship between the daily residual water level and the mean daily discharge in the catchment can be represented by a Gumbel copula (Spearman's rank correlation coefficient of 0.31) and that they result in higher water levels in the mid- to upstream reaches of the watershed than when modeled independently. This indicates that conventional (deterministic) methods may underestimate the flood hazard associated with compound flooding in the riverine environment and that such interactions should not be neglected in future coastal flood hazard studies.

Validation of a CFD code for Unsteady Flows with cyclic boundary Conditions

International Nuclear Information System (INIS)

Kim, Jong-Tae; Kim, Sang-Baik; Lee, Won-Jae

2006-01-01

Currently Lilac code is under development to analyze thermo-hydraulics of a high-temperature gas-cooled reactor (GCR). Interesting thermo-hydraulic phenomena in a nuclear reactor are usually unsteady and turbulent. The analysis of the unsteady flows by using a three dimension CFD code is time-consuming if the flow domain is very large. Hopefully, flow domains commonly encountered in the nuclear thermo-hydraulics is periodic. So it is better to use the geometrical characteristics in order to reduce the computational resources. To get the benefits from reducing the computation domains especially for the calculations of unsteady flows, the cyclic boundary conditions are implemented in the parallelized CFD code LILAC. In this study, the parallelized cyclic boundary conditions are validated by solving unsteady laminar and turbulent flows past a circular cylinder

Performance advantages of CPML over UPML absorbing boundary conditions in FDTD algorithm

Science.gov (United States)

Gvozdic, Branko D.; Djurdjevic, Dusan Z.

2017-01-01

Implementation of absorbing boundary condition (ABC) has a very important role in simulation performance and accuracy in finite difference time domain (FDTD) method. The perfectly matched layer (PML) is the most efficient type of ABC. The aim of this paper is to give detailed insight in and discussion of boundary conditions and hence to simplify the choice of PML used for termination of computational domain in FDTD method. In particular, we demonstrate that using the convolutional PML (CPML) has significant advantages in terms of implementation in FDTD method and reducing computer resources than using uniaxial PML (UPML). An extensive number of numerical experiments has been performed and results have shown that CPML is more efficient in electromagnetic waves absorption. Numerical code is prepared, several problems are analyzed and relative error is calculated and presented.

AdS boundary conditions and the Topologically Massive Gravity/CFT correspondence

NARCIS (Netherlands)

Skenderis, K.; Taylor, M.; van Rees, B.C.

2009-01-01

The AdS/CFT correspondence provides a new perspective on recurrent questions in General Relativity such as the allowed boundary conditions at infinity and the definition of gravitational conserved charges. Here we review the main insights obtained in this direction over the last decade and apply the

Ferroelectric relaxor behaviour and impedance spectroscopy of Bi{sub 2}O{sub 3}-doped barium zirconium titanate ceramics

Energy Technology Data Exchange (ETDEWEB)

Mahajan, Sandeep; Thakur, O P; Bhattacharya, D K [Electroceramics Group, Solid State Physics Laboratory, Lucknow Road, Delhi-110054 (India); Sreenivas, K, E-mail: omprakasht@hotmail.co [Department of Physics and Astrophysics, University of Delhi- 110007 (India)

2009-03-21

Bi{sub 2}O{sub 3}-doped barium zirconate titanate ceramics, Ba{sub 1-x}Bi{sub x}(Zr{sub 0.05}Ti{sub 0.95})O{sub 3}, have been prepared by the conventional solid-state reaction method. The ferroelectric relaxor behaviour and dielectric properties have been investigated in detail. By XRD analysis, it is suggested that up to x = 0.04, Bi{sup 3+} substitutes A-site ion, and thereafter with higher Bi{sup 3+} content, it enters the B-site sub lattice. Substitution of Bi{sup 3+} ions induces ferroelectric relaxor behaviour and the degree of relaxation behaviour increases with bismuth concentration. The remanent polarization and strain behaviour show a slight increase with the substitution level. The degree of hysteresis (strain versus electric field) also reduces from 21.4% to 4.6% with bismuth substitution. Impedance measurements were made on the prepared sample over a wide range of temperatures (300-723 K) and frequencies (40 Hz-1 MHz), which show the presence of both bulk and grain boundary effects in the material. The bulk and grain boundary conductivities determined from impedance study indicate the Arrhenius-type thermally activated process. Impedance spectroscopy is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries to the complex impedance of a ceramic system, accurately estimating its electrical conductivity as well as its corresponding activation energies and drawing conclusions on its structural properties.

Homogenization of the evolution Stokes equation in a perforated domain with a stochastic Fourier boundary condition

KAUST Repository

Bessaih, Hakima

2015-04-01

The evolution Stokes equation in a domain containing periodically distributed obstacles subject to Fourier boundary condition on the boundaries is considered. We assume that the dynamic is driven by a stochastic perturbation on the interior of the domain and another stochastic perturbation on the boundaries of the obstacles. We represent the solid obstacles by holes in the fluid domain. The macroscopic (homogenized) equation is derived as another stochastic partial differential equation, defined in the whole non perforated domain. Here, the initial stochastic perturbation on the boundary becomes part of the homogenized equation as another stochastic force. We use the twoscale convergence method after extending the solution with 0 in the holes to pass to the limit. By Itô stochastic calculus, we get uniform estimates on the solution in appropriate spaces. In order to pass to the limit on the boundary integrals, we rewrite them in terms of integrals in the whole domain. In particular, for the stochastic integral on the boundary, we combine the previous idea of rewriting it on the whole domain with the assumption that the Brownian motion is of trace class. Due to the particular boundary condition dealt with, we get that the solution of the stochastic homogenized equation is not divergence free. However, it is coupled with the cell problem that has a divergence free solution. This paper represents an extension of the results of Duan and Wang (Comm. Math. Phys. 275:1508-1527, 2007), where a reaction diffusion equation with a dynamical boundary condition with a noise source term on both the interior of the domain and on the boundary was studied, and through a tightness argument and a pointwise two scale convergence method the homogenized equation was derived. © American Institute of Mathematical Sciences.

Cellular Neural Network Method for Critical Slab with Albedo Boundary Condition

International Nuclear Information System (INIS)

Pirouzmanda, A.; Hadada, K.; Suh, K. Y.

2010-01-01

The neutron transport problems have been studied theoretically and numerically for years. A number of researchers have studied the criticality problems of one-speed neutrons in homogeneous slabs and spheres using various methods. The Chebyshev polynomial approximation method (T N method) has lately been developed and improved for the neutron transport equation in slab geometry. The one-speed time-dependent neutron transport equation using the Cellular Neural Network (CNN) for the vacuum boundary condition has previously been solved. In this paper, we demonstrate the capacity of CNN in calculating the critical slab thickness for different boundary conditions and its variation with moments N. The architecture of the CNN has already been dealt with thoroughly. Essentially, the CNN is used to model a first-order system of the partial differential equations (PDEs). The original equations in the T N approximation are also a set of PDEs. The CNN approach lends itself to analog VLSI implementation. In this study, the CNN model is implemented using the HSpice software package

Electromagnetic scattering of a vector Bessel beam in the presence of an impedance cone

KAUST Repository

Salem, Mohamed

2013-07-01

The electromagnetic field scattering of a vector Bessel beam in the presence of an infinite circular cone with an impedance boundary on its surface is considered. The impinging field is normal to the tip of the cone and is expanded in terms of vector spherical wave functions; a Kontorovich-Lebedev (KL) transform is employed to expand the scattered fields. The problem is reduced to a singular integral equation with a variable coefficient of the non-convolution type. The singularities of the spectral function are deduced and representations for the field at the tip of the cone as well as other regions are given together with the conditions of validity of these representations. © 2013 IEEE.

Deficiency indices and singular boundary conditions in quantum mechanics

International Nuclear Information System (INIS)

Bulla, W.

1984-01-01

We consider Schroedinger operators H in L 2 (Rsup(n)), n from IN, with countably infinitely many local singularities of the potential which are separated from each other by a positive distance. It is proved that due to locality each singularity yields a separate contribution to the deficiency index of H. In the special case where the singularities are pointlike and the potential exhibits certain symmetries near these points we give an explicit construction of self-adjoint boundary conditions

Homogenized boundary conditions and resonance effects in Faraday cages

Science.gov (United States)

Hewitt, I. J.

2016-01-01

We present a mathematical study of two-dimensional electrostatic and electromagnetic shielding by a cage of conducting wires (the so-called ‘Faraday cage effect’). Taking the limit as the number of wires in the cage tends to infinity, we use the asymptotic method of multiple scales to derive continuum models for the shielding, involving homogenized boundary conditions on an effective cage boundary. We show how the resulting models depend on key cage parameters such as the size and shape of the wires, and, in the electromagnetic case, on the frequency and polarization of the incident field. In the electromagnetic case, there are resonance effects, whereby at frequencies close to the natural frequencies of the equivalent solid shell, the presence of the cage actually amplifies the incident field, rather than shielding it. By appropriately modifying the continuum model, we calculate the modified resonant frequencies, and their associated peak amplitudes. We discuss applications to radiation containment in microwave ovens and acoustic scattering by perforated shells. PMID:27279775

Homogenized boundary conditions and resonance effects in Faraday cages

Science.gov (United States)

Hewett, D. P.; Hewitt, I. J.

2016-05-01

We present a mathematical study of two-dimensional electrostatic and electromagnetic shielding by a cage of conducting wires (the so-called `Faraday cage effect'). Taking the limit as the number of wires in the cage tends to infinity, we use the asymptotic method of multiple scales to derive continuum models for the shielding, involving homogenized boundary conditions on an effective cage boundary. We show how the resulting models depend on key cage parameters such as the size and shape of the wires, and, in the electromagnetic case, on the frequency and polarization of the incident field. In the electromagnetic case, there are resonance effects, whereby at frequencies close to the natural frequencies of the equivalent solid shell, the presence of the cage actually amplifies the incident field, rather than shielding it. By appropriately modifying the continuum model, we calculate the modified resonant frequencies, and their associated peak amplitudes. We discuss applications to radiation containment in microwave ovens and acoustic scattering by perforated shells.

The fermion boundary condition and the THETA-angle in QED2

International Nuclear Information System (INIS)

Hrasko, P.

1983-09-01

The order parameter of the Schwinger model is calculated in the Euclidean functional integral approach. It is shown that the symmetry breaking angle THETA is intimately connected to the boundary condition imposed on the fermions. The transition to the Euclidean description involves both imaginary time and imaginary THETA. (author)

Implementation and Testing of Advanced Surface Boundary Conditions Over Complex Terrain in A Semi-idealized Model

Science.gov (United States)

Li, Y.; Epifanio, C.

2017-12-01

In numerical prediction models, the interaction between the Earth's surface and the atmosphere is typically accounted for in terms of surface layer parameterizations, whose main job is to specify turbulent fluxes of heat, moisture and momentum across the lower boundary of the model domain. In the case of a domain with complex geometry, implementing the flux conditions (particularly the tensor stress condition) at the boundary can be somewhat subtle, and there has been a notable history of confusion in the CFD community over how to formulate and impose such conditions generally. In the atmospheric case, modelers have largely been able to avoid these complications, at least until recently, by assuming that the terrain resolved at typical model resolutions is fairly gentle, in the sense of having relatively shallow slopes. This in turn allows the flux conditions to be imposed as if the lower boundary were essentially flat. Unfortunately, while this flat-boundary assumption is acceptable for coarse resolutions, as grids become more refined and the geometry of the resolved terrain becomes more complex, the appproach is less justified. With this in mind, the goal of our present study is to explore the implementation and usage of the full, unapproximated version of the turbulent flux/stress conditions in atmospheric models, thus taking full account of the complex geometry of the resolved terrain. We propose to implement the conditions using a semi-idealized model developed by Epifanio (2007), in which the discretized boundary conditions are reduced to a large, sparse-matrix problem. The emphasis will be on fluxes of momentum, as the tensor nature of this flux makes the associated stress condition more difficult to impose, although the flux conditions for heat and moisture will be considered as well. With the resulotion of 90 meters, some of the results show that the typical differences between flat-boundary cases and full/stress cases are on the order of 10%, with extreme

A two-dimensional vibration analysis of piezoelectrically actuated microbeam with nonideal boundary conditions

Science.gov (United States)

Rezaei, M. P.; Zamanian, M.

2017-01-01

In this paper, the influences of nonideal boundary conditions (due to flexibility) on the primary resonant behavior of a piezoelectrically actuated microbeam have been studied, for the first time. The structure has been assumed to treat as an Euler-Bernoulli beam, considering the effects of geometric nonlinearity. In this work, the general nonideal supports have been modeled as a the combination of horizontal, vertical and rotational springs, simultaneously. Allocating particular values to the stiffness of these springs provides the mathematical models for the majority of boundary conditions. This consideration leads to use a two-dimensional analysis of the multiple scales method instead of previous works' method (one-dimensional analysis). If one neglects the nonideal effects, then this paper would be an effort to solve the two-dimensional equations of motion without a need of a combination of these equations using the shortening or stretching effect. Letting the nonideal effects equal to zero and comparing their results with the results of previous approaches have been demonstrated the accuracy of the two-dimensional solutions. The results have been identified the unique effects of constraining and stiffening of boundaries in horizontal, vertical and rotational directions. This means that it is inaccurate to suppose the nonideality of supports only in one or two of these directions like as previous works. The findings are of vital importance as a better prediction of the frequency response for the nonideal supports. Furthermore, the main findings of this effort can help to choose appropriate boundary conditions for desired systems.

On the boundary conditions and validity of the neutral shielding model of a refuelling pellet

International Nuclear Information System (INIS)

Chang, C.T.

1982-02-01

By comparing the ablation time of a hydrogen pellet in a tokamak discharge with the time required for the sublimation process, the vaporization of the pellet is shown to be a dynamic phase transition - i.e. the transport of heat is due to the propagation of an evaporation front. Based on this finding, an alternative boundary condition, consistent with the energy conservation law, is formulated. Computational results utilizing the new boundary condition indicate that the ablatant near the pellet surface is hotter and less dense compared with the results which make use of the previous condition of the vanishing flux. The discrepancy between the two solutions becomes less significant once the ablatant reaches the sonic radius. The scaling law of the pellet ablation rate is unaffected by this change of boundary condition. The present analysis shows that the validity of the neutral shielding model is based mainly on the existence of a thin envelope around the pellet where strong energy absorption occurs and is insensitive to the actual vaporization process occuring at the pellet surface. (Auth.)

A Unified Spectro-Geometric-Ritz Method for Vibration Analysis of Open and Closed Shells with Arbitrary Boundary Conditions

Directory of Open Access Journals (Sweden)

Dongyan Shi

2016-01-01

Full Text Available This paper presents free vibration analysis of open and closed shells with arbitrary boundary conditions using a spectro-geometric-Ritz method. In this method, regardless of the boundary conditions, each of the displacement components of open and closed shells is represented simultaneously as a standard Fourier cosine series and several auxiliary functions. The auxiliary functions are introduced to accelerate the convergence of the series expansion and eliminate all the relevant discontinuities with the displacement and its derivatives at the boundaries. The boundary conditions are modeled using the spring stiffness technique. All the expansion coefficients are treated equally and independently as the generalized coordinates and determined using Rayleigh-Ritz method. By using this method, a unified vibration analysis model for the open and closed shells with arbitrary boundary conditions can be established without the need of changing either the equations of motion or the expression of the displacement components. The reliability and accuracy of the proposed method are validated with the FEM results and those from the literature.

MHD axisymmetric flow of power-law fluid over an unsteady stretching sheet with convective boundary conditions

Directory of Open Access Journals (Sweden)

Jawad Ahmed

Full Text Available This paper examines the boundary layer flow and heat transfer characteristic in power law fluid model over unsteady radially stretching sheet under the influence of convective boundary conditions. A uniform magnetic field is applied transversely to the direction of the flow. The governing time dependent nonlinear boundary layer equations are reduced into nonlinear ordinary differential equations with the help of similarity transformations. The transformed coupled ordinary differential equations are then solved analytically by homotopy analysis method (HAM and numerically by shooting procedure. Effects of various governing parameters like, power law index n, magnetic parameter M, unsteadiness A, suction/injection S, Biot number γ and generalized Prandtl number Pr on velocity, temperature, local skin friction and the local Nusselt number are studied and discussed. It is found from the analysis that the magnetic parameter diminishes the velocity profile and the corresponding thermal boundary layer thickness. Keywords: Axisymmetric flow, Power law fluid, Unsteady stretching, Convective boundary conditions

Electrochemical Characterization of a PEMEC Using Impedance Spectroscopy

DEFF Research Database (Denmark)

Elsøe, Katrine; Grahl-Madsen, L.; Hjelm, Johan

2017-01-01

In this study, electrochemical impedance spectroscopy (EIS) is applied in combination with cyclic voltammetry (CV) and current density – cell voltage curves (iV-curves) to investigate the processes contributing to the total impedance of a polymer electrolyte membrane electrolysis cell (PEMEC). i......V-curves were linear above 0.35 A cm−2 implying ohmic processes to be performance limiting, however the impedance spectra showed three arcs indicating three electrochemical reactions at these conditions not to be purely ohmic, but also to have capacitive properties. A hypothesis that the composite Ir...

Influence of Variable Thermal Conductivity on MHD Boundary Layer Slip Flow of Ethylene-Glycol Based Cu Nanofluids over a Stretching Sheet with Convective Boundary Condition

Directory of Open Access Journals (Sweden)

N. Bhaskar Reddy

2014-01-01

Full Text Available An analysis is carried out to investigate the influence of variable thermal conductivity and partial velocity slip on hydromagnetic two-dimensional boundary layer flow of a nanofluid with Cu nanoparticles over a stretching sheet with convective boundary condition. Using similarity transformation, the governing boundary layer equations along with the appropriate boundary conditions are transformed to a set of ordinary differential equations. Employing Runge-kutta fourth-order method along with shooting technique, the resultant system of equations is solved. The influence of various pertinent parameters such as nanofluid volume fraction parameter, the magnetic parameter, radiation parameter, thermal conductivity parameter, velocity slip parameter, Biot number, and suction or injection parameter on the velocity of the flow field and heat transfer characteristics is computed numerically and illustrated graphically. The present results are compared with the existing results for the case of regular fluid and found an excellent agreement.

Homogenization of the evolution Stokes equation in a perforated domain with a stochastic Fourier boundary condition

KAUST Repository

Bessaih, Hakima; Efendiev, Yalchin; Maris, Florin

2015-01-01

The evolution Stokes equation in a domain containing periodically distributed obstacles subject to Fourier boundary condition on the boundaries is considered. We assume that the dynamic is driven by a stochastic perturbation on the interior

Applying Boundary Conditions Using a Time-Dependent Lagrangian for Modeling Laser-Plasma Interactions

Science.gov (United States)

Reyes, Jonathan; Shadwick, B. A.

2016-10-01

Modeling the evolution of a short, intense laser pulse propagating through an underdense plasma is of particular interest in the physics of laser-plasma interactions. Numerical models are typically created by first discretizing the equations of motion and then imposing boundary conditions. Using the variational principle of Chen and Sudan, we spatially discretize the Lagrangian density to obtain discrete equations of motion and a discrete energy conservation law which is exactly satisfied regardless of the spatial grid resolution. Modifying the derived equations of motion (e.g., enforcing boundary conditions) generally ruins energy conservation. However, time-dependent terms can be added to the Lagrangian which force the equations of motion to have the desired boundary conditions. Although some foresight is needed to choose these time-dependent terms, this approach provides a mechanism for energy to exit the closed system while allowing the conservation law to account for the loss. An appropriate time discretization scheme is selected based on stability analysis and resolution requirements. We present results using this variational approach in a co-moving coordinate system and compare such results to those using traditional second-order methods. This work was supported by the U. S. Department of Energy under Contract No. DE-SC0008382 and by the National Science Foundation under Contract No. PHY- 1104683.

Mechanical impedance of the human body in vertical direction.

Science.gov (United States)

Holmlund, P; Lundström, R; Lindberg, L

2000-08-01

The mechanical impedance of the human body in sitting posture and vertical direction was measured during different experimental conditions, such as vibration level (0.5-1.4 m/s2), frequency (2-100 Hz), body weight (57-92 kg), relaxed and erect upper body posture. The outcome shows that impedance increases with frequency up to a peak at about 5 Hz after which it decreases in a complex manner which includes two additional peaks. The frequency at which the first and second impedance peak occurs decreases with higher vibration level. Erect, compared with relaxed body posture resulted in higher impedance magnitudes and with peaks located at somewhat higher frequencies. Heavy persons show higher impedance magnitudes and peaks at lower frequencies.

Effects of Boundary Conditions on the Parametric Resonance of Cylindrical Shells under Axial Loading

Directory of Open Access Journals (Sweden)

T.Y. Ng

1998-01-01

Full Text Available In this paper, a formulation for the dynamic stability analysis of circular cylindrical shells under axial compression with various boundary conditions is presented. The present study uses Love’s first approximation theory for thin shells and the characteristic beam functions as approximate axial modal functions. Applying the Ritz procedure to the Lagrangian energy expression yields a system of Mathieu–Hill equations the stability of which is analyzed using Bolotin’s method. The present study examines the effects of different boundary conditions on the parametric response of homogeneous isotropic cylindrical shells for various transverse modes and length parameters.

Radiation impedance of condenser microphones and their diffuse-field responses

DEFF Research Database (Denmark)

Barrera Figueroa, Salvador; Rasmussen, Knud; Jacobsen, Finn

2010-01-01

and (b) measuring the pressure on the membrane of the microphone. The first measurement is carried out by means of laser vibrometry. The second measurement cannot be implemented in practice. However, the pressure on the membrane can be calculated numerically by means of the boundary element method......The relation between the diffuse-field response and the radiation impedance of a microphone has been investigated. Such a relation can be derived from classical theory. The practical measurement of the radiation impedance requires (a) measuring the volume velocity of the membrane of the microphone...... at frequencies below the resonance frequency of the microphone. Although the method may not be of great practical utility, it provides a useful validation of the estimates obtained by other means....

Experimental Investigation of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

Science.gov (United States)

Hultgren, Lennart S.; Volino, Ralph J.

2002-01-01

Modern low-pressure turbine airfoils are subject to increasingly stronger pressure gradients as designers impose higher loading in an effort to improve efficiency and to reduce part count. The adverse pressure gradients on the suction side of these airfoils can lead to boundary-layer separation, particularly under cruise conditions. Separation bubbles, notably those which fail to reattach, can result in a significant degradation of engine efficiency. Accurate prediction of separation and reattachment is hence crucial to improved turbine design. This requires an improved understanding of the transition flow physics. Transition may begin before or after separation, depending on the Reynolds number and other flow conditions, has a strong influence on subsequent reattachment, and may even eliminate separation. Further complicating the problem are the high free-stream turbulence levels in a real engine environment, the strong pressure gradients along the airfoils, the curvature of the airfoils, and the unsteadiness associated with wake passing from upstream stages. Because of the complicated flow situation, transition in these devices can take many paths that can coexist, vary in importance, and possibly also interact, at different locations and instances in time. The present work was carried out in an attempt to systematically sort out some of these issues. Detailed velocity measurements were made along a flat plate subject to the same nominal dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil ('Pak-B'). The Reynolds number based on wetted plate length and nominal exit velocity, Re, was varied from 50;000 to 300; 000, covering cruise to takeoff conditions. Low, 0.2%, and high, 7%, inlet free-stream turbulence intensities were set using passive grids. These turbulence levels correspond to about 0.2% and 2.5% turbulence intensity in the test section when normalized with the exit velocity. The Reynolds number and free

On the extraction of spectral quantities with open boundary conditions

International Nuclear Information System (INIS)

Bruno, Mattia; Korcyl, Piotr; Lottini, Stefano; Schaefer, Stefan; Korzec, Tomasz

2014-11-01

We discuss methods to extract decay constants, meson masses and gluonic observables in the presence of open boundary conditions. The ensembles have been generated by the CLS effort and have 2+1 flavors of O(a)-improved Wilson fermions with a small twisted-mass term as proposed by Luescher and Palombi. We analyse the effect of the associated reweighting factors on the computation of different observables.

Electromagnetic scattering of a vector Bessel beam in the presence of an impedance cone

KAUST Repository

Salem, Mohamed; Bagci, Hakan

2013-01-01

The electromagnetic field scattering of a vector Bessel beam in the presence of an infinite circular cone with an impedance boundary on its surface is considered. The impinging field is normal to the tip of the cone and is expanded in terms

Direct numerical simulation of turbulent flows over superhydrophobic surfaces with gas pockets using linearized boundary conditions

Science.gov (United States)

Seo, Jongmin; Bose, Sanjeeb; Garcia-Mayoral, Ricardo; Mani, Ali

2012-11-01

Superhydrophobic surfaces are shown to be effective for surface drag reduction under laminar regime by both experiments and simulations (see for example, Ou and Rothstein, Phys. Fluids 17:103606, 2005). However, such drag reduction for fully developed turbulent flow maintaining the Cassie-Baxter state remains an open problem due to high shear rates and flow unsteadiness of turbulent boundary layer. Our work aims to develop an understanding of mechanisms leading to interface breaking and loss of gas pockets due to interactions with turbulent boundary layers. We take advantage of direct numerical simulation of turbulence with slip and no-slip patterned boundary conditions mimicking the superhydrophobic surface. In addition, we capture the dynamics of gas-water interface, by deriving a proper linearized boundary condition taking into account the surface tension of the interface and kinematic matching of interface deformation and normal velocity conditions on the wall. We will show results from our simulations predicting the dynamical behavior of gas pocket interfaces over a wide range of dimensionless surface tensions. Supported by the Office of Naval Research and the Kwanjeong Educational Scholarship Foundation.

Implementation and verification of a coupled fire model as a thermal boundary condition within P3/THERMAL

International Nuclear Information System (INIS)

Hensinger, D.M.; Gritzo, L.A.; Koski, J.A.

1996-01-01

A user-defined boundary condition subroutine has been implemented within P3/THERMAL to represent the heat flux between a noncombusting object and an engulfing fire. The heat flux calculations includes a simple 2D fire model in which energy and radiative heat transport equations are solved to produce estimates of the heat fluxes at the fire-object interface. These estimates reflect radiative coupling between a cold object and the flow of hot combustion gases which has been observed in fire experiments. The model uses a database of experimental pool fire measurements for far field boundary conditions and volumetric heat release rates. Taking into account the coupling between a structure and the fire is an improvement over the σT 4 approximation frequently used as a boundary condition for engineered system response and is the preliminary step in the development of a fire model with a predictive capability. This paper describes the implementation of the fire model as a P3/THERMAL boundary condition and presents the results of a verification calculation carried out using the model

AC impedance behavior of a practical-size single-cell SOFC under DC current

Energy Technology Data Exchange (ETDEWEB)

Momma, Akihiko; Kaga, Yasuo; Takano, Kiyonami; Nozaki, Ken; Negishi, Akira; Kato, Ken; Kato, Tohru [Fuel Cell Group, Energy Electronics Institute, National Institute of Advanced Industrial Science and Technology, Umezono Tsukuba-shi, Ibaraki 305-8568 (Japan); Inagaki, Toru; Yoshida, Hiroyuki [Energy Use R and D Center, The Kansai Electric Power Company, Inc., 11-20 Nakoji, 3-Chome, Amagasaki, Hyogo 661-0974 (Japan); Hosoi, Kei; Hoshino, Koji; Akbay, Taner; Akikusa, Jun; Yamada, Masaharu; Chitose, Norihisa [Central Research Institute, Naka Research Center, Mitsubishi Materials Corp. 1002-14 Mukohyama, Naka-machi, Naka-gun, Ibaraki 311-0102 (Japan)

2004-10-29

AC impedance measurements were carried out using practical-size planar disc-type SOFC which employs lanthanum gallate as a solid electrolyte. The data were obtained under practical conditions of gas flow rate and DC current. Under these conditions, the gas conversion impedance (GCI), which originates from the change of the electromotive force (EMF) caused by the change in anodic gaseous concentrations along the flow direction, was observed in the low-frequency range of the data obtained. The overlapping impedance together with GCI on the low-frequency arc was also estimated. Experimentally obtained GCI was in good agreement with that calculated. It was concluded that GCI was predominant in the impedance data obtained under practical conditions. The shift of the high-frequency intercept in the complex impedance diagrams was shown to appear as a result of the change in the distribution of gaseous composition in the anode. The dependency of the low-frequency arc on temperature was also shown, and it was assumed that the overlapped impedance varies as the temperature changes. The validity of the impedance measurement, as a diagnostic means to evaluate the gas flow in SOFC stack, was suggested.

Effect of velocity boundary conditions on the heat transfer and flow topology in two-dimensional Rayleigh-Bénard convection.

Science.gov (United States)

van der Poel, Erwin P; Ostilla-Mónico, Rodolfo; Verzicco, Roberto; Lohse, Detlef

2014-07-01

The effect of various velocity boundary condition is studied in two-dimensional Rayleigh-Bénard convection. Combinations of no-slip, stress-free, and periodic boundary conditions are used on both the sidewalls and the horizontal plates. For the studied Rayleigh numbers Ra between 10(8) and 10(11) the heat transport is lower for Γ=0.33 than for Γ=1 in case of no-slip sidewalls. This is, surprisingly, the opposite for stress-free sidewalls, where the heat transport increases for a lower aspect ratio. In wider cells the aspect-ratio dependence is observed to disappear for Ra ≥ 10(10). Two distinct flow types with very different dynamics can be seen, mostly dependent on the plate velocity boundary condition, namely roll-like flow and zonal flow, which have a substantial effect on the dynamics and heat transport in the system. The predominantly horizontal zonal flow suppresses heat flux and is observed for stress-free and asymmetric plates. Low aspect-ratio periodic sidewall simulations with a no-slip boundary condition on the plates also exhibit zonal flow. In all the other cases, the flow is roll like. In two-dimensional Rayleigh-Bénard convection, the velocity boundary conditions thus have large implications on both roll-like and zonal flow that have to be taken into consideration before the boundary conditions are imposed.

Implementation of Unsplit Perfectly Matched Layer Absorbing Boundary Condition in 3 Dimensional Finite Difference Time Domain Method

Directory of Open Access Journals (Sweden)

B. U. Musa

2017-04-01

Full Text Available The C++ programming language was used to implement three-dimensional (3-D finite-difference time-domain (FDTD technique to simulate radiation of high frequency electromagnetic waves in free space. To achieve any meaningful results the computational domain of interest should have to be truncated in some way and this is achieved by applying absorbing boundary conditions. A uniaxial perfectly matched layer (UPML absorbing boundary condition is used in this work. The discretised equations of the UPML in FDTD time stepping scheme were derived and has been successfully implemented using the computer program. Simulation results showed that the UPML behaves as an absorber. This was confirmed by comparing the results with another boundary condition, the Mur ABC.

Renormalization of boundary conditions for distribution functions of quasiparticles obeying quantum statistics at interfaces between crystalline grains

International Nuclear Information System (INIS)

Grendel, M.

1981-01-01

Boundary conditions for distribution functions of quasiparticles scattered by an interface between two crystalline grains are presented. Contrary to former formulations where Maxwell-Boltzmann statistics was considered, the present boundary conditions take into account the quantum statistics (Fermi-Dirac or Bose-Einstein) of quasiparticles. Provided that small deviations only from thermodynamic equilibrium are present, the boundary conditions are linearized, and then their ''renormalization'' is investigated in case of elastic scattering. The final results of the renormalization, which are obtained for a simplified model of an interface, sugo.est that the portion of the Fermi (Bose)-quasiparticles reflected or transmitted specularly is decreased (increased) in comparison with the case of quasiparticles obeying Maxwell-Boltzmann statistics. (author)

Accurate characterization of 3D diffraction gratings using time domain discontinuous Galerkin method with exact absorbing boundary conditions

KAUST Repository

Sirenko, Kostyantyn

2013-07-01

Exact absorbing and periodic boundary conditions allow to truncate grating problems\\' infinite physical domains without introducing any errors. This work presents exact absorbing boundary conditions for 3D diffraction gratings and describes their discretization within a high-order time-domain discontinuous Galerkin finite element method (TD-DG-FEM). The error introduced by the boundary condition discretization matches that of the TD-DG-FEM; this results in an optimal solver in terms of accuracy and computation time. Numerical results demonstrate the superiority of this solver over TD-DG-FEM with perfectly matched layers (PML)-based domain truncation. © 2013 IEEE.

IMPROVEMENT OF ACCURACY OF RADIATIVE HEAT TRANSFER DIFFERENTIAL APPROXIMATION METHOD FOR MULTI DIMENSIONAL SYSTEMS BY MEANS OF AUTO-ADAPTABLE BOUNDARY CONDITIONS

Directory of Open Access Journals (Sweden)

K. V. Dobrego

2015-01-01

Full Text Available Differential approximation is derived from radiation transfer equation by averaging over the solid angle. It is one of the more effective methods for engineering calculations of radia- tive heat transfer in complex three-dimensional thermal power systems with selective and scattering media. The new method for improvement of accuracy of the differential approximation based on using of auto-adaptable boundary conditions is introduced in the paper. The  efficiency  of  the  named  method  is  proved  for  the  test  2D-systems.  Self-consistent auto-adaptable boundary conditions taking into consideration the nonorthogonal component of the incident to the boundary radiation flux are formulated. It is demonstrated that taking in- to consideration of the non- orthogonal incident flux in multi-dimensional systems, such as furnaces, boilers, combustion chambers improves the accuracy of the radiant flux simulations and to more extend in the zones adjacent to the edges of the chamber.Test simulations utilizing the differential approximation method with traditional boundary conditions, new self-consistent boundary conditions and “precise” discrete ordinates method were performed. The mean square errors of the resulting radiative fluxes calculated along the boundary of rectangular and triangular test areas were decreased 1.5–2 times by using auto- adaptable boundary conditions. Radiation flux gaps in the corner points of non-symmetric sys- tems are revealed by using auto-adaptable boundary conditions which can not be obtained by using the conventional boundary conditions.

Air Quality and Meteorological Boundary Conditions during the MCMA-2003 Field Campaign

Science.gov (United States)

Sosa, G.; Arriaga, J.; Vega, E.; Magaña, V.; Caetano, E.; de Foy, B.; Molina, L. T.; Molina, M. J.; Ramos, R.; Retama, A.; Zaragoza, J.; Martínez, A. P.; Márquez, C.; Cárdenas, B.; Lamb, B.; Velasco, E.; Allwine, E.; Pressley, S.; Westberg, H.; Reyes, R.

2004-12-01

A comprehensive field campaign to characterize photochemical smog in the Mexico City Metropolitan Area (MCMA) was conducted during April 2003. An important number of equipment was deployed all around the urban core and its surroundings to measure gas and particles composition from the various sources and receptor sites. In addition to air quality measurements, meteorology variables were also taken by regular weather meteorological stations, tethered balloons, radiosondes, sodars and lidars. One important issue with regard to the field campaign was the characterization of the boundary conditions in order to feed meteorological and air quality models. Four boundary sites were selected to measure continuously criteria pollutants, VOC and meteorological variables at surface level. Vertical meteorological profiles were measured at three other sites : radiosondes in Tacubaya site were launched every six hours daily; tethered balloons were launched at CENICA and FES-Cuautitlan sites according to the weather conditions, and one sodar was deployed at UNAM site in the south of the city. Additionally to these measurements, two fixed meteorological monitoring networks deployed along the city were available to complement these measurements. In general, we observed that transport of pollutants from the city to the boundary sites changes every day, according to the coupling between synoptic and local winds. This effect were less important at elevated sites such as Cerro de la Catedral and ININ, where synoptic wind were more dominant during the field campaign. Also, local sources nearby boundary sites hide the influence of pollution coming from the city some days, particularly at the La Reforma site.

Two transparent boundary conditions for the electromagnetic scattering from two-dimensional overfilled cavities

Science.gov (United States)

Du, Kui

2011-07-01

We consider electromagnetic scattering from two-dimensional (2D) overfilled cavities embedded in an infinite ground plane. The unbounded computational domain is truncated to a bounded one by using a transparent boundary condition (TBC) proposed on a semi-ellipse. For overfilled rectangular cavities with homogeneous media, another TBC is introduced on the cavity apertures, which produces a smaller computational domain. The existence and uniqueness of the solutions of the variational formulations for the transverse magnetic and transverse electric polarizations are established. In the exterior domain, the 2D scattering problem is solved in the elliptic coordinate system using the Mathieu functions. In the interior domain, the problem is solved by a finite element method. Numerical experiments show the efficiency and accuracy of the new boundary conditions.

Effect of boundary conditions on measured water retention behavior within soils

Science.gov (United States)

Galindo-torres, S.; Scheuermann, A.; Pedroso, D.; Li, L.

2013-12-01

The Soil Water Characteristic Curve (SWCC) is a practical representation of the behavior of soil water by relating the suction (difference between the air and water pressures to the moisture content (water saturation). The SWCC is characterized by a hysteresis loop, which is thought to be unique in that any drainage-imbibition cycle lies within a main hysteresis loop limited by two different curves for drainage and imbibition. This 'uniqueness' is the main argument for considering the SWCC as a material-intrinsic feature that characterizes the pore structure and its interaction with fluids. Models have been developed with the SWCC as input data to describe the evolution of the water saturation and the suction within soils. One example of these models is the widely used Richard's equation [1]. In this work we present a series of numerical simulations to evaluate the 'unique' nature of the SWCC. The simulations involves the use of the Lattice Boltzmann Method (LBM) [2] within a regular soil, modelling the flow behavior of two immiscible fluids: wetting and non-wetting. The soil is packed within a cubic domain to resemble the experimental setups that are commonly used for measuring the SWCC[3]. The boundary conditions ensure that the non-wetting phase enters through one cubic face and the wetting phase enters trough the opposite phase, with no flow boundary conditions in the remaining 4 cubic faces. The SWCC known features are inspected including the presence of the common limit curves for different cycles involving varying limits for the suction. For this stage of simulations, the SWCC is indeed unique. Later, different boundary conditions are applied with the two fluids each injected from 3 opposing faces into the porous medium. The effect of this boundary condition change is a net flow direction, which is different from that in the previous case. A striking result is observed when both SWCC are compared and found to be noticeable different. Further analysis is

Nonlinear parabolic problems with Neumann-type boundary conditions and L^1-data

Directory of Open Access Journals (Sweden)

Abderrahmane El Hachimi

2007-11-01

$$ \\frac{\\partial u}{\\partial t}-\\triangle_{p}u+\\alpha(u=f \\quad \\text{in } ]0,\\ T[\\times\\Omega, $$ with Neumann-type boundary conditions and initial data in $L^1$. Our approach is based essentially on the time discretization technique by Euler forward scheme.

Formulation and numerical implementation of micro-scale boundary conditions for particle aggregates

NARCIS (Netherlands)

Liu, J.; Bosco, E.; Suiker, A.S.J.

2017-01-01

Novel numerical algorithms are presented for the implementation of micro-scale boundary conditions of particle aggregates modelled with the discrete element method. The algorithms are based on a servo-control methodology, using a feedback principle comparable to that of algorithms commonly applied

Hybrid Fourier pseudospectral/discontinuous Galerkin time-domain method for arbitrary boundary conditions

NARCIS (Netherlands)

Pagan Munoz, R.; Hornikx, M.C.J.

The wave-based Fourier Pseudospectral time-domain (Fourier-PSTD) method was shown to be an effective way of modeling outdoor acoustic propagation problems as described by the linearized Euler equations (LEE), but is limited to real-valued frequency independent boundary conditions and predominantly

Characterization and evaluation of EB-PVD thermal barrier coatings by impedance spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Zhang Chunxia; Liu Fushun; Gong Shengkai; Xu Huibin [School of Materials Science and Engineering, Beihang Univ., Beijing, BJ (China)

2005-07-01

Two layer thermal barrier coatings (TBCs) were prepared by EB-PVD (electron beam-physical vapor deposition) at different substrate temperatures in the range of 823 to 1123 K, and their microstructure was investigated with SEM and AC impedance as a function of substrate temperature and thermal cycling time. YSZ layer of all TBCs samples is in column structure, but the grain size and growth orientation are different with substrate. In this research, impedance spectra (IS) was measured as a function of thermal cycling between 1323 K and 298 K for these thermal barrier coatings. Grain boundary and bulk can be distinguished from analysis of AC impedance spectroa to provide information about the relation between microstructure and electric properties. The change in IS until failure was found to be related with the thickness, microcracks and macrocracks of TGO and the change in the interfacial of TGO/YSZ. (orig.)

Hermitian boundary conditions at a Dirichlet singularity: the Marletta--Rozenblum model

International Nuclear Information System (INIS)

Berry, M V

2009-01-01

In domains B with smoothly-varying boundary conditions, points where wavefunctions are required to vanish were recently identified as 'Dirichlet singularities' (D points) where the Hamiltonian H does not define discrete eigenvalues and a scattering phase is undetermined (Berry and Dennis 2008 J. Phys. A: Math. Theor. 41 135203). This is explained (Marletta and Rozenblum 2009 J. Phys. A: Math. Theor. 42 125204) by the observation, illustrated with an exactly-solvable separable model, that a D point requires the specification of an additional parameter defining a family of self-adjoint extensions of H. Here the underlying theory is presented in an elementary way, and a D point is identified as a leak, through which current can flow into or out of B. Hermiticity seals the leak, ensuring that no current flows though the D point (as well as across the boundary of B). The solvable model is examined in detail for bound states, where B is a semidisk, and for wave reflections, where B is a half-plane. The quantization condition for a nonseparable billiard is obtained explicitly

A Comparative Experimental Study of Fixed Temperature and Fixed Heat Flux Boundary Conditions in Turbulent Thermal Convection

Science.gov (United States)

Huang, Shi-Di; Wang, Fei; Xi, Heng-Dong; Xia, Ke-Qing

2014-11-01

We report an experimental study of the influences of thermal boundary condition in turbulent thermal convection. Two configurations were examined: one was fixed heat flux at the bottom boundary and fixed temperature at the top (HC cells); the other was fixed temperature at both boundaries (CC cells). It is found that the flow strength in the CC cells is on average 9% larger than that in the HC ones, which could be understood as change in plume emission ability under different boundary conditions. It is further found, rather surprisingly, that flow reversals of the large-scale circulation occur more frequently in the CC cell, despite a stronger large-scale flow and more uniform temperature distribution over the boundaries. These findings provide new insights into turbulent thermal convection and should stimulate further studies, especially experimental ones. This work is supported by the Hong Kong Research Grants Council under Grant No. CUHK 403712.

Multiregion, multigroup collision probability method with white boundary condition for light water reactor thermalization calculations

International Nuclear Information System (INIS)

Ozgener, B.; Ozgener, H.A.

2005-01-01

A multiregion, multigroup collision probability method with white boundary condition is developed for thermalization calculations of light water moderated reactors. Hydrogen scatterings are treated by Nelkin's kernel while scatterings from other nuclei are assumed to obey the free-gas scattering kernel. The isotropic return (white) boundary condition is applied directly by using the appropriate collision probabilities. Comparisons with alternate numerical methods show the validity of the present formulation. Comparisons with some experimental results indicate that the present formulation is capable of calculating disadvantage factors which are closer to the experimental results than alternative methods

Inverse Relation between Condition of Heart Failure and Intrathoracic Impedance Measured by Implantable Cardioverter Defibrillator—A case report—

Directory of Open Access Journals (Sweden)

Kohei Matsushita, MD

2005-01-01

Full Text Available The patient was a 78-year-old man with dilated cardiomyopathy. His cardio-thoracic ratio was 60.4% and left ventricular ejection fraction (LVEF was 33%. He had been repeatedly admitted for congestive heart failure. He underwent implantation of an implantable cardioverter-defibrillator (ICD for ventricular fibrillation. We compared the values of BNP and shock impedance stored by the ICD. The correlation coefficient (p-value between BNP and shock impedance was −0.700 (p < 0.0005, increase of BNP and shock impedance was −0.778 (p < 0.0001, percent increase of BNP and shock impedance was −0.767 (p < 0.0005. In conclusion, there is an inverse relation between BNP and shock impedance, and measurements of shock impedance may be useful in the management of congestive heart failure.

Modeling long period swell in Southern California: Practical boundary conditions from buoy observations and global wave model predictions

Science.gov (United States)

Crosby, S. C.; O'Reilly, W. C.; Guza, R. T.

2016-02-01

Accurate, unbiased, high-resolution (in space and time) nearshore wave predictions are needed to drive models of beach erosion, coastal flooding, and alongshore transport of sediment, biota and pollutants. On highly sheltered shorelines, wave predictions are sensitive to the directions of onshore propagating waves, and nearshore model prediction error is often dominated by uncertainty in offshore boundary conditions. Offshore islands and shoals, and coastline curvature, create complex sheltering patterns over the 250km span of southern California (SC) shoreline. Here, regional wave model skill in SC was compared for different offshore boundary conditions created using offshore buoy observations and global wave model hindcasts (National Oceanographic and Atmospheric Administration Wave Watch 3, WW3). Spectral ray-tracing methods were used to transform incident offshore swell (0.04-0.09Hz) energy at high directional resolution (1-deg). Model skill is assessed for predictions (wave height, direction, and alongshore radiation stress) at 16 nearshore buoy sites between 2000 and 2009. Model skill using buoy-derived boundary conditions is higher than with WW3-derived boundary conditions. Buoy-driven nearshore model results are similar with various assumptions about the true offshore directional distribution (maximum entropy, Bayesian direct, and 2nd derivative smoothness). Two methods combining offshore buoy observations with WW3 predictions in the offshore boundary condition did not improve nearshore skill above buoy-only methods. A case example at Oceanside harbor shows strong sensitivity of alongshore sediment transport predictions to different offshore boundary conditions. Despite this uncertainty in alongshore transport magnitude, alongshore gradients in transport (e.g. the location of model accretion and erosion zones) are determined by the local bathymetry, and are similar for all predictions.

Current Percolation in Medium with Boundaries under Quantum Hall Effect Conditions

Directory of Open Access Journals (Sweden)

M. U. Malakeeva

2012-01-01

Full Text Available The current percolation has been considered in the medium with boundaries under quantum Hall effect conditions. It has been shown that in that case the effective Hall conductivity has a nonzero value due to percolation of the Hall current through the finite number of singular points (in our model these are corners at the phase joints.

Convergence and periodic solutions for the input impedance of a standard ladder network

International Nuclear Information System (INIS)

Ucak, C; Acar, C

2007-01-01

The input impedance of an infinite ladder network is computed by using the recursive relation and by assuming that the input impedance does not change when a new block is added to the network. However, this assumption is not true in general and standard textbooks do not always treat these networks correctly. This paper develops a general solution to obtain the input impedance of a standard ladder network of impedances and admittances for any number of blocks. Then, this result is used to provide the convergence condition for the infinite ladder network. The conditions which lead to periodic input impedance are exploited. It is shown that there are infinite numbers of periodic points and no paradoxical behaviour exists in the standard ladder network

Development of a Discrete Mass Inflow Boundary Condition for MFIX

Directory of Open Access Journals (Sweden)

Jordan Musser

2011-02-01

Full Text Available MFIX (Multiphase Flow with Interphase eXchanges is an open source software package developed by the National Energy Technology Laboratory (NETL used for modeling the chemical reactions, heat transfer, and hydrodynamics of fluid-solid systems. Currently, the stable publically available release of MFIX does not include a discrete mass inflow boundary condition (DMIBC for its discrete element method (DEM package. Inflow boundary conditions are useful for simulating systems where particles are consumed through chemical reactions and an incoming feed is necessary to sustain the reaction. To implement the DMIBC an inlet staging area is designated outside the computational domain and particles are passed through the wall region associated with the inlet. Forces incurred on entering particles, generated from collisions with particles already in the system, are ignored whereas, particles already in the system respond to contact forces and react accordingly, moving away from the inlet. This approach prevents any unphysical overlap between new and existing particles. It also ensures that particles entering the system will enter the computational domain regardless of opposing forces. Once an incoming particle is fully within the domain, it reacts appropriately to any and all contact force. This approach for a DMIBC has been implemented and is available within the current development version of MFIX.

The Casimir effect for pistons with transmittal boundary conditions

Science.gov (United States)

Fucci, Guglielmo

2017-11-01

This work focuses on the analysis of the Casimir effect for pistons subject to transmittal boundary conditions. In particular we consider, as piston configuration, a direct product manifold of the type I × N where I is a closed interval of the real line and N is a smooth compact Riemannian manifold. By utilizing the spectral zeta function regularization technique, we compute the Casimir energy of the system and the Casimir force acting on the piston. Explicit results for the force are provided when the manifold N is a d-dimensional sphere.

Superradiant instabilities in the Kerr-mirror and Kerr-AdS black holes with Robin boundary conditions

Science.gov (United States)

Ferreira, Hugo R. C.; Herdeiro, Carlos A. R.

2018-04-01

It has been recently observed that a scalar field with Robin boundary conditions (RBCs) can trigger both a superradiant and a bulk instability for a Bañados-Teitelboim-Zanelli (BTZ) black hole (BH) [1]. To understand the generality and scrutinize the origin of this behavior, we consider here the superradiant instability of a Kerr BH confined either in a mirrorlike cavity or in anti-de Sitter (AdS) space, triggered also by a scalar field with RBCs. These boundary conditions are the most general ones that ensure the cavity/AdS space is an isolated system and include, as a particular case, the commonly considered Dirichlet boundary conditions (DBCs). Whereas the superradiant modes for some RBCs differ only mildly from the ones with DBCs, in both cases, we find that as we vary the RBCs the imaginary part of the frequency may attain arbitrarily large positive values. We interpret this growth as being sourced by a bulk instability of both confined geometries when certain RBCs are imposed to either the mirrorlike cavity or the AdS boundary, rather than by energy extraction from the BH, in analogy with the BTZ behavior.

6d Dirac fermion on a rectangle; scrutinizing boundary conditions, mode functions and spectrum

Directory of Open Access Journals (Sweden)

Yukihiro Fujimoto

2017-09-01

Full Text Available We classify possible boundary conditions of a 6d Dirac fermion Ψ on a rectangle under the requirement that the 4d Lorentz structure is maintained, and derive the profiles and spectrum of the zero modes and nonzero KK modes under the two specific boundary conditions, (i 4d-chirality positive components being zero at the boundaries and (ii internal chirality positive components being zero at the boundaries. In the case of (i, twofold degenerated chiral zero modes appear which are localized towards specific directions of the rectangle pointed by an angle parameter θ. This leads to an implication for a new direction of pursuing the origin of three generations in the matter fields of the standard model, even though triple-degenerated zero modes are not realized in the six dimensions. When such 6d fermions couple with a 6d scalar with a vacuum expectation value, θ contributes to a mass matrix of zero-mode fermions consisting of Yukawa interactions. The emergence of the angle parameter θ originates from a rotational symmetry in the degenerated chiral zero modes on the rectangle extra dimensions since they do not feel the boundaries. In the case of (ii, this rotational symmetry is promoted to the two-dimensional conformal symmetry though no chiral massless zero mode appears. We also discuss the correspondence between our model on a rectangle and orbifold models in some details.

Global Discrete Artificial Boundary Conditions for Time-Dependent Wave Propagation

Science.gov (United States)

Ryaben'kii, V. S.; Tsynkov, S. V.; Turchaninov, V. I.

2001-12-01

We construct global artificial boundary conditions (ABCs) for the numerical simulation of wave processes on unbounded domains using a special nondeteriorating algorithm that has been developed previously for the long-term computation of wave-radiation solutions. The ABCs are obtained directly for the discrete formulation of the problem; in so doing, neither a rational approximation of “nonreflecting kernels” nor discretization of the continuous boundary conditions is required. The extent of temporal nonlocality of the new ABCs appears fixed and limited; in addition, the ABCs can handle artificial boundaries of irregular shape on regular grids with no fitting/adaptation needed and no accuracy loss induced. The nondeteriorating algorithm, which is the core of the new ABCs, is inherently three-dimensional, it guarantees temporally uniform grid convergence of the solution driven by a continuously operating source on arbitrarily long time intervals and provides unimprovable linear computational complexity with respect to the grid dimension. The algorithm is based on the presence of lacunae, i.e., aft fronts of the waves, in wave-type solutions in odd-dimensional spaces. It can, in fact, be built as a modification on top of any consistent and stable finite-difference scheme, making its grid convergence uniform in time and at the same time keeping the rate of convergence the same as that of the unmodified scheme. In this paper, we delineate the construction of the global lacunae-based ABCs in the framework of a discretized wave equation. The ABCs are obtained for the most general formulation of the problem that involves radiation of waves by moving sources (e.g., radiation of acoustic waves by a maneuvering aircraft). We also present systematic numerical results that corroborate the theoretical design properties of the ABC algorithm.

Nonlocal beam models for buckling of nanobeams using state-space method regarding different boundary conditions

International Nuclear Information System (INIS)

Sahmani, S.; Ansari, R.

2011-01-01

Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions analysis

Nonlocal beam models for buckling of nanobeams using state-space method regarding different boundary conditions

Energy Technology Data Exchange (ETDEWEB)

Sahmani, S.; Ansari, R. [University of Guilan, Rasht (Iran, Islamic Republic of)

2011-09-15

Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions analysis.

Effect of lanthanum substitution on dielectric relaxation, impedance response, conducting and magnetic properties of strontium hexaferrite

Energy Technology Data Exchange (ETDEWEB)

Want, Basharat, E-mail: bawant@kashmiruniversity.ac.in; Bhat, Bilal Hamid; Ahmad, Bhat Zahoor

2015-04-05

Highlights: • The substitution of La affects the dielectric and magnetic properties of strontium hexaferrite. • The electric behaviour of the compound follows the Koop’s phenomenological theory. • The impedance study shows the role of grain boundaries to the electric properties of the compound. • The substitution of La to strontium hexaferrite reduces the resistive nature of grain boundaries. - Abstract: Lanthanum strontium hexaferrite Sr{sub 1−x}La{sub x}Fe{sub 12}O{sub 19} (x = 0, 0.08, 0.13 , 0.18) has been successfully synthesized by using citrate-precursor method and characterized by different techniques. The X-ray diffraction results revealed that the sample is crystalline in nature and is of single phase with the space group P63/mmc. The dielectric, conducting and impedance related studies have been carried out as a function of frequency and concentration of lanthanum in the frequency ranges of 20 Hz–3 MHz. Impedance studies were performed in the frequency domain to distinguish between bulk and grain boundary contributions of the material to the overall dielectric response. The electric response of the material was also modeled by an equivalent circuit and different circuit parameters were calculated. Magnetic characterization of the material was also performed and the effect of lanthanum concentration was studied. The hysteresis loop obtained from the magnetometer showed that with the increase of lanthanum concentration, the saturation magnetisation decreases while as coercivity increases.

Large Scale Skill in Regional Climate Modeling and the Lateral Boundary Condition Scheme

Science.gov (United States)

Veljović, K.; Rajković, B.; Mesinger, F.

2009-04-01

Several points are made concerning the somewhat controversial issue of regional climate modeling: should a regional climate model (RCM) be expected to maintain the large scale skill of the driver global model that is supplying its lateral boundary condition (LBC)? Given that this is normally desired, is it able to do so without help via the fairly popular large scale nudging? Specifically, without such nudging, will the RCM kinetic energy necessarily decrease with time compared to that of the driver model or analysis data as suggested by a study using the Regional Atmospheric Modeling System (RAMS)? Finally, can the lateral boundary condition scheme make a difference: is the almost universally used but somewhat costly relaxation scheme necessary for a desirable RCM performance? Experiments are made to explore these questions running the Eta model in two versions differing in the lateral boundary scheme used. One of these schemes is the traditional relaxation scheme, and the other the Eta model scheme in which information is used at the outermost boundary only, and not all variables are prescribed at the outflow boundary. Forecast lateral boundary conditions are used, and results are verified against the analyses. Thus, skill of the two RCM forecasts can be and is compared not only against each other but also against that of the driver global forecast. A novel verification method is used in the manner of customary precipitation verification in that forecast spatial wind speed distribution is verified against analyses by calculating bias adjusted equitable threat scores and bias scores for wind speeds greater than chosen wind speed thresholds. In this way, focusing on a high wind speed value in the upper troposphere, verification of large scale features we suggest can be done in a manner that may be more physically meaningful than verifications via spectral decomposition that are a standard RCM verification method. The results we have at this point are somewhat

Detection of irradiated potatoes by impedance measurement

International Nuclear Information System (INIS)

Hayashi, T.; Todoriki, S.; Otobe, K.; Sugiyama, J.

1996-01-01

Potato is one of the major food items to be treated with ionising radiation and potatoes are irradiated on a large scale in several countries. Every year around 15,000 t of potatoes are irradiated at doses of 60 to 150 Gy (average dose is about 100 Gy) in Japan. Although various methods to detect irradiated potatoes have been investigated, no established method has been reported. Measuring electrical conductivity or impedance of potatoes has been reported as a promising method for the detection of irradiated potatoes. In previous studies it has been found that the ratio of impedance magnitude at 50 kHz to that at 5 kHz, measured immediately after puncturing a potato tuber, is dependent upon the dose applied to the tuber, independent of storage temperature and stable during storage after irradiation. The aim of this study was to establish the optimum conditions for impedance measurement and to examine the applicability of the impedance measuring method to various cultivars (cv.) of potatoes. (author)

On the boundary conditions and optimization methods in integrated digital image correlation

NARCIS (Netherlands)

Kleinendorst, S.M.; Verhaegh, B.J.; Hoefnagels, J.P.M.; Ruybalid, A.; van der Sluis, O.; Geers, M.G.D.; Lamberti, L.; Lin, M.-T.; Furlong, C.; Sciammarella, C.

2018-01-01

In integrated digital image correlation (IDIC) methods attention must be paid to the influence of using a correct geometric and material model, but also to make the boundary conditions in the FE simulation match the real experiment. Another issue is the robustness and convergence of the IDIC

Combined conduction and radiation in a two-layer planar medium with flux boundary condition

International Nuclear Information System (INIS)

Ho, C.H.; Ozisik, M.N.

1987-01-01

The interaction of conduction and radiation is investigated under both transient and steady-state conditions for an absorbing, emitting, and isotropically scattering two-layer slab having opaque coverings at both boundaries. The slab is subjected to an externally applied constant heat flux at one boundary surface and dissipates heat by radiation into external ambients from both boundary surfaces. An analytic approach is applied to solve the radiation part of the problem, and a finite-difference scheme is used to solve the conduction part. The effects of the conduction-to-radiation parameter, the single scattering albedo, the optical thickness, and the surface emissivity on the temperature distribution are examined

Charged hadrons in local finite-volume QED+QCD with C* boundary conditions

CERN Document Server

Lucini, Biagio; Ramos, Alberto; Tantalo, Nazario

2016-01-01

In order to calculate QED corrections to hadronic physical quantities by means of lattice simulations, a coherent description of electrically-charged states in finite volume is needed. In the usual periodic setup, Gauss's law and large gauge transformations forbid the propagation of electrically-charged states. A possible solution to this problem, which does not violate the axioms of local quantum field theory, has been proposed by Wiese and Polley, and is based on the use of C* boundary conditions. We present a thorough analysis of the properties and symmetries of QED in isolation and QED coupled to QCD, with C* boundary conditions. In particular we learn that a certain class of electrically-charged states can be constructed in this setup in a fully consistent fashion, without relying on gauge fixing. We argue that this class of states covers most of the interesting phenomenological applications in the framework of numerical simulations. We also calculate finite-volume corrections to the mass of stable charg...

POSITIVE SOLUTIONS OF A NONLINEAR THREE-POINT EIGENVALUE PROBLEM WITH INTEGRAL BOUNDARY CONDITIONS

Directory of Open Access Journals (Sweden)

FAOUZI HADDOUCHI

2015-11-01

Full Text Available In this paper, we study the existence of positive solutions of a three-point integral boundary value problem (BVP for the following second-order differential equation u''(t + \\lambda a(tf(u(t = 0; 0 0 is a parameter, 0 <\\eta < 1, 0 <\\alpha < 1/{\\eta}. . By using the properties of the Green's function and Krasnoselskii's fixed point theorem on cones, the eigenvalue intervals of the nonlinear boundary value problem are considered, some sufficient conditions for the existence of at least one positive solutions are established.

Time reversal method with stabilizing boundary conditions for Photoacoustic tomography

International Nuclear Information System (INIS)

Chervova, Olga; Oksanen, Lauri

2016-01-01

We study an inverse initial source problem that models photoacoustic tomography measurements with array detectors, and introduce a method that can be viewed as a modification of the so called back and forth nudging method. We show that the method converges at an exponential rate under a natural visibility condition, with data given only on a part of the boundary of the domain of wave propagation. In this paper we consider the case of noiseless measurements. (paper)

Effect of real-time boundary wind conditions on the air flow and pollutant dispersion in an urban street canyon—Large eddy simulations