bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary element estimation of current density distribution and eddy current loss in bundled multi‐wire cables
Authors: Sakurai A. , Tsuchiya T. , Kagawa Y.
Published: August 2005

A numerical approach to the estimation of the current density distribution and the eddy current loss in bundled multi‐wire cables using the boundary element method is proposed. Under the assumption of the gradual twist of the bundled wires, the cables are modelled to be two‐dimensional with respect to their cross‐sections. Three‐phase transmission lines of cyclic symmetrical configuration are considered for which a reduction method is utilized to provide efficient computation. Some numerical demonstrations are made for three types of three‐phase transmission‐line models, consisting of a single wire and three and seven bundled wires. Two cases are considered: one in which the bundled wires are electrically contacted one to another on their surfaces and one in which they are independently insulated. The equivalent resistance is also calculated to examine the skin effect. The skin effect and the effectiveness of the multi‐wire configuration to reduce the skin effect are well demonstrated.
Numerical simulation of current–voltage characteristics of silicon photoconductive circuit elements
Authors: Shakouri H. , Liou J. J.
Published: August 2005

Photoconductive circuit elements (PCEs) are suitable for switching applications: they can be turned on and off rapidly, they can conduct a large current in the ‘on’ state when applying a laser or other optical excitation containing high energy photons exceeding the silicon band gap energy, they have a large resistance in the ‘off’ state when the light is off, and they can be fabricated using a simple process. We report the steady‐ state characteristics of PCEs simulated from a two‐dimensional simulator called PISCES‐2B. The effects of the conducting channel length, the resistivity of the intrinsic silicon, and the type of contact region on the performance of the PCE will be investigated and discussed. Based on the simulation results, optimal PCE device make‐ups will also be suggested.
A variational approach to boundary elements—two‐dimensional Laplace problem
Authors: Sun Y. , Kagawa Y. , Murai T.
Published: August 2005

Variational boundary element formulations are developed. Two functionals based on the dual and complementary energy approach are considered, which provide the upper and lower bound of the solution. Calculated examples of electrostatic fields are demonstrated for their field distributions and capacitances. Validity and the solution accuracy are discussed in comparison with the conventional boundary element solution.
Numerical modelling of viscous flow in silicon thermal oxidation with the boundary element method
Authors: Panjukhin A. V. , Kolobov N. A. , Leontjeva N. A.
Published: August 2005

This paper describes the application of the boundary element method to solving two‐dimensional steady slow viscous flow problems (creeping flow) in thermal silicon oxidation. The proposed method used the velocity–pressure formulation. The use of the incompressibility condition as a boundary condition and the application of the second Green's identity to transform the domain integral into a boundary integral result in a system of three boundary integral equations for velocity components and pressure. Solution of this system to be an ill‐posed problem because of the presence of boundary conditions of the first kind. Two methods of regularization are employed. The numerical results for trench oxidation process are presented.
Numerical modelling of the stationary Maxwell–Lorentz system in technical devices
Authors: Westermann Thomas
Published: August 2005

The particle‐in‐cell method is coupled with boundary‐fitted co‐ordinates in order to model the stationary Maxwell–Lorentz problem in technical devices. New numerical algorithms describing the transition between the grid model and the mesh‐free model are developed and the existing techniques of finite difference schemes for equidistant grids are extended to non‐equidistant, arbitrarily shaped, convex four‐point meshes. The modelling process is described, and both the numerical approximation and the algorithms are discussed. Applications in different technical devices show the flexibility of the method.
The parallel computation of solutions to electrostatic problems using multigrid techniques
Authors: Waring L. C. , Rooney N. , Stewart A. , Fusco V. F.
Published: August 2005

The application of multigrid techniques to the computation of the static solutions of electromagnetic field problems governed by Laplace's equation is described. This technique is compared with the conventional successive over‐relaxation (SOR) method for solving finite difference problems. In contrast to SOR, the number of iterations of multigrid needed to achieve convergence is largely independent of the grid size. It is shown that the relative performance of multigrid is excellent on large grids where the number of iterations of SOR needed to achieve convergence becomes prohibitively large. The technique is illustrated by applying a parallel implementation of multigrid to find a quasistatic solution of a boxed microstrip problem.
Solving eigenvalue and steady‐state problems using time‐domain models
Authors: Nitsche Gunnar
Published: August 2005

A new approach to efficiently compute the low‐frequency eigenmodes of a time‐domain model approximating a linear physical system is proposed. The method is based on principles known from digital signal processing, in particular from parametic spectrum estimation, so it is not surprising that the achievable accuracy is much higher than the accuracy of the usual non‐parametric discrete Fourier transform approach. The algorithm works in the general lossy case even for a very large number of unknowns and can easily be extended to calculate steady‐state solutions under sinusoidal excitations for several different frequencies simultaneously.
Recent developments in numerical integration of differential equations
Authors: Mathis Wolfgang
Published: August 2005

In this paper we demonstrate the use of differential equations by means of an example from network analysis and show that differential/algebraic equations (DAE), rather than explicit ordinary differential equations (ODE), are more suitable for the description of electrical systems and networks. The main ideas of numerical integration of ODEs are presented. We consider this material from the point of view of replacing the ODE by a difference equation (DE). In particular, the relationship between the ODE and the associated DE is discussed. In the last Section the application of integration methods for OEDs upon DAEs and its difficulties are discussed. The paper is intended as a review; but a few new results are also included.
Transmission‐line equivalent curcuit model of minority carrier transient current in quasi‐neutral silicon layers including effects
Authors: Karamakković J. P. , Janković N. D. , Glozić D. B.
Published: August 2005

A novel transmission‐line model for the minority carrier transport through quasi‐neutral arbitrarily doped layers is proposed. Based on detailed drift‐diffusion equations, the novel TLEC includes the inductance that represents the influence of the relaxation‐time term. Coupled with a object‐orientated hybrid circuit simulator, the novel transmission‐line model is implemented for the transient analysis of minority carrier transport. A substantial longer storage time of the minority carrier transient current at the collector end of ultra‐narrow base is predicted owing to inclusion of the relaxation‐time term.
Transmission‐line modelling of the class E amplifier with an analytical method
Authors: Yam Yu‐on , Cheung Chi‐wai , Li Chi‐hung
Published: August 2005

The Transmission line modelling (TLM) technique was used to simulate the class E power amplifier. An analytical method is also used to fix the required component values to ensure the desired output performance of the amplifier. An experiment was carried out to verify the simulation result of the combined method.
Three‐dimensional simulation for negative resistance characteristics of parasitic bipolar transistor in a small‐sized mosfet structure
Authors: Ju Chiping , Zemanian Armen H.
Published: August 2005

The behaviours of parasitic bipolar transistors are investigated by exploring the physical mechanisms of negative resistance characteristics generated in a small‐sized MOSFET structure. Physical experiments and three‐dimensional simulations verify the expected negative resistance characteristics. The effects of variations of device parameters such as injected substrate current levels, doping concentrations, channel widths, and physical device sizes are investigated by simulation. According to simulation results, the operation of a parasitic bipolar transistor is initiated by the injected substrate current; this explains the negative resistance characteristics occurring at low operating voltages.
Maslovian Lagrangian surfaces of constant curvature in complex projective or complex hyperbolic planes
Authors: Chen Bang‐Yen
Published: August 2005

A Lagrangian submanifold is called Maslovian if its mean curvature vector H is nowhere zero and its Maslov vector field JH is a principal direction of AH . In this article we classify Maslovian Lagrangian surfaces of constant curvature in complex projective plane CP 2 as well as in complex hyperbolic plane CH 2. We prove that there exist 14 families of Maslovian Lagrangian surfaces of constant curvature in CP 2 and 41 families in CH 2. All of the Lagrangian surfaces of constant curvature obtained from these families admit a unit length Killing vector field whose integral curves are geodesics of the Lagrangian surfaces. Conversely, locally (in a neighborhood of each point belonging to an open dense subset) every Maslovian Lagrangian surface of constant curvature in CP 2 or in CH 2 is a surface obtained from these 55 families. As an immediate by‐product, we provide new methods to construct explicitly many new examples of Lagrangian surfaces of constant curvature in complex projective and complex hyperbolic planes which admit a unit length Killing vector field. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution operators generated by non‐densely defined operators
Authors: Oka Hirokazu , Tanaka Naoki
Published: August 2005

In this paper it is shown that an evolution operator is generated by a family of closed linear operators whose common domain is not necessarily dense in the underlying Banach space, under the stability condition proposed by the second author from the viewpoint of finite difference approximations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the geometric form of Bernoulli configurations
Authors: Acker Andrew
Published: August 2005

In References 4 and 5, the author studied the geometric form of the free boundary Γ of an annular domain Ω, characterized by the Bernoulli condition that |∇U|=1 on Γ, where U is the capacity potential in Ω. It was shown, for example, that Γ has at most as many ν‐extrema (for a given direction ν) or inflection points as the other boundary component Γ* of Ω, which is assumed given. Our purpose here is to extend the results in References 4 and 5 (wherever possible) to multiply connected regions for which some boundary components are given and others are free boundaries characterized by the Bernoulli condition. We present both positive results and counterexamples.
Non‐linear boundary value problems for the annular membrane: New results on existence of positive solutions
Authors: Grabmüller Hans , Novak Erich
Published: August 2005

The Föppl‐Hencky theory of small finite deflections has been applied to the study of axisymmetric deformations of annular membranes by various authors. The mathematical problem of uniqueness of tensile solutions for the corresponding non‐linear boundary value problems in the full range of physically meaningful boundary data was solved only recently.3, 4 In this paper, a new integral equation technique of solution is developed which yields the existence of tensile solutions for a parameter range of the boundary data where previous investigations on this matter had not been successful. It is shown that tensile solutions no longer exist, when sufficiently large positive radial displacements are prescribed at the inner edge of the annulus.
Radially symmetric solutions of the Poisson–Boltzmann equation
Authors: Krzywicki A. , Nadzieja T. , Meister E.
Published: August 2005

The electrostatic potential u outside of a charged cylinder contained in an infinitely large container of electrolyte satisfies the Poisson–Boltzmann equation Δu = shu and boundary condition ∂u/∂n = − σ on the cylinder and u(∞) = 0. We show that there exists a unique radially symmetric solution of the problem and consider its properties.
On subsolutions of a non‐linear diffusion problem
Authors: Okrasiński W. , Meister E.
Published: August 2005

In the paper a subsolution of a non‐linear diffusion problem in the radial case is constructed. Some integral equation methods are used.
Anisotropic Hele–Shaw flows
Authors: Gilbert Robert P. , Shi Peter
Published: August 2005

The procedure of Elliott and Janovsky is abstracted to a fairly general variational problem. As an application of the methodology a non‐isotropic Hele‐Shaw flow is treated.
On the equivalence of the Schrödinger and the quantum Liouville equations
Authors: Markowich Peter A. , Neunzert H.
Published: August 2005

We present a semigroup analysis of the quantum Liouville equation, which models the temporal evolution of the (quasi) distribution of an electron ensemble under the action of a scalar potential. By employing the density matrix formulation of quantum physics we prove that the quantum Liouville operator generates a unitary group on L2 if the corresponding Hamiltonian is essentially self‐adjoint.

Also, we analyse the existence and non‐negativity of the particale density and prove that the solutions of the quantum Liouville equation converge to weak solutions of the classical Liouville equation as the Planck constant tends to zero (assuming that the potential is sufficiently smooth).
Stationary solutions of the linearized Boltzmann equation in a half‐space
Authors: Golse F. , Poupaud F. , Neunzert H.
Published: August 2005

Stationary half‐space solutions of the linearized Boltzmann equation are studied by energy estimates methods. We extend the results of Bardos, Caflisch and Nicolaenko for a gas of hard spheres to a general potential. Asymptotic behaviour is obtained for hard as well as soft potentials and compared to the case of hard spheres.
Canonical difference scheme for the Hamiltonian equation
Authors: Mengzhao Qin , Törnig W.
Published: August 2005

In this paper we construct canonical difference schemes of any order accuracy based on Padé approximation for Linear canonical systems with constant coefficients. For non‐linear Hamiltonian equations we will use an infinitesimally canonical transformation to construct canonical schemes of any order accuracy.
On the instability of resonances in parallel‐plane waveguides under local perturbations of the boundary
Authors: Morgenröther K. , Werner P.
Published: August 2005

We study the large‐time asymptotics for solutions u(x, t) of the wave equation with Dirichlet boundary data, generated by a time‐harmonic force distribution of frequency ω, in a class of domains with non‐compact boundaries and show that the results obtained in [11] for a special class of local perturbations of Ω0 ≔ ℝ2 × (0,1) can be extended to arbitrary smooth local perturbations Ω of Ω0. In particular, we prove that u is bounded as t → ∞ if Ω does not allow admissible standing waves of frequency ω in the sense of [8]. This implies in connection with [8]. Theorem 3.1 that the logarithmic resonances of the unperturbed domain Ω0 at the frequencies ω = πk (k = 1, 2,…) observed in [14] can be simultaneously removed by small perturbations of the boundary. As a main step of our analysis, the determination of admissible solutions of the boundary value problem ΔU + κ2U = − f in Ω, U = 0 on ∂Ω is reduced to a compact operator equation.
Dense sets and the projection theorem for acoustic harmonic waves in a homogeneous finite depth ocean
Authors: Gilbert R. P. , Xu Yongzhi
Published: August 2005

The scattering of a ‘plane wave’ off a submerged body situated in an ocean of finite depth is investigated. The index of refraction is considered to be depth‐independent. It is shown that the far field is not unique; hence, the problem of determining the shape of an object from its far field is not well‐posed. If solutions are sought among a restricted class of problems the ‘dense set’ property implies that the problem can be made well‐posed.
On a free boundary problem in electrostatics
Authors: Philippin G. A.
Published: August 2005

Let Ωi ⊂ ℝN, i = 0, 1, be two bounded separately star‐shaped domains such that \documentclass{article}\pagestyle{empty}\begin{document}$ \Omega _0 \supset \bar \Omega _1 $\end{document}. We consider the electrostatic potential u defined in \documentclass{article}\pagestyle{empty}\begin{document}$ \Omega : = \Omega _0 \backslash \bar \Omega _1 $\end{document}:

The geometry of the two boundary components Γ0 and Γ1 is not given, but instead the electrostatic potential u is supposed to satisfy the further boundary conditions
magnified image
Using a best possible maximum principle, we show that this free boundary problem has a unique solution which is radially symmetric.
On the numerical treatment of an integral equation arising from a cruciform crack problem
Authors: Monegato G. , Prössdorf S.
Published: August 2005

We consider the following two integral equations
magnified image
the latter subject to the condition ∫v(y)dy = 0, arising from the same problem of determining the distribution of stress in a thin elastic plate in the vicinity of a cruciform crack. In particular, we prove existence and uniqueness of the solutions of the two equations above in C[0, 1]. We also analyse the behaviour of ϕ(x) near the end‐point x = 0.

The therotical result obtained in the first part are then used in the last section to derive optimal rates of convergence for numerical methods, such as Galerkin, collocation and Nyström, applied to equation (1).
On a problem in condensed two‐phase combustion
Authors: Primicerio Mario , Xie Weiqing , Shu Muzeng
Published: August 2005

An exothermic binary chemical reaction of first order is studied, assuming that one of the reactants can undergo a change of phase. In the limit of low activation energy, a one‐dimensional problem is considered and the well‐posedness of the corresponding system of two parabolic equations with a free boundary is proved in a classical sense.
Time stepping procedures for the non‐stationary Stokes equations
Authors: Varnhorn Werner
Published: August 2005

We consider first and second‐order implicit time stepping procedures for the non‐stationary Stokes equations in bounded domains of ℝ3. Using energy estimates we prove the optimal convergence properties in the Sobolev spaces Hm(G)(m = 0, 1, 2) uniformly in time, provided that the Stokes solution has a certain degree of regularity. Here in the case of the second‐order scheme (method of Crank–Nicholson) the Stokes solution has to satisfy a non‐local compatibility condition at the initial time t = O, which can be satisfied by a special initial construction.
Properties of solutions to the initial‐boundary value problem for a porous media‐type equation
Authors: Goncerzewicz Jan
Published: August 2005

The initial‐boundary value problem in a semi‐infinite strip (0, ∞)×(0, T) for a degenerate parabolic equation of the form u, t= φ(u)xx + b(x)φ(u)x is considered. The properties of solutions in the case where the initial function is compactly supported and for constant initial and boundary data are investigated.
One gauge‐invariant system for two‐dimensional relativistic fields: Global solutions, integrability
Authors: Łada Andrzej
Published: August 2005

The system originating from the theory of two‐dimensional hyperbolic chiral fields and the theory of self‐dual Yang‐Mills fields over ℝ2 + 2 is studied. The existence of global solutions for the Cauchy problem is established. It is observed that the system is completely integrable and one method of construction of a new solution is presented.
A remark on a compactness result in electromagnetic theory
Authors: Witsch Karl J.
Published: August 2005

Calderon's extension theorem is a crucial tool in the proof of the compactneσs of the resolvent for the Maxwell operator, and whence this result is proved for domains with the strict cone property. However, the proof only requires an extension operator that extends W2,2‐functions compactly as W1,2‐functions. It is shown that this can be achieved under weaker regularity conditions on the domain: the cone may be replaced by some cusp of an appropriate order.
127I NQR in some iodic acid compunds
Authors: Balicheva T. G. , Grechishkin V. S. , Petrova G. A. , Shishkin V. A.
Published: August 2005

127I NQR frequencies have been measured in 20 compounds including iodates, chromate‐iodates and tri‐iodates. Quadrupole coupling constants and asymmetry parameters have been calculated at 77°K. Lines have been assigned by the two‐frequency method. NQR data show the presence of covalent bonds in iodates and tri‐iodates. In chromate‐iodates the large value of the asymmetry parameter is due to the non‐equivalence of an oxygen atom in the IO3− ion.
Heterocycles contenant du phosphore‐XXI. Etude par RMP de déeriveés de l'oxazaphospholane‐l,3,2: I‐Analyse des spectres des composksés non substitués en 4 et 5.
Authors: Devillers Jean , Roussel Jean , Navech Jacques , Burgada Ramon
Published: August 2005

Les dérivés de l'oxazaphospholane‐1,3,3 du titre donnent des spectres de RMP du type ABKLX. L'analyse sous‐spectrale d'un tel système montre qu'on a le choix entre huit solutions. Des expériences d'INDOR permettent d'établir le diagramme d'énergie et de choisir la bonne soultion.
The effects of chemically induced polarisation in the cage recombination products of the methyl radical
Authors: Kessenikh A. V. , Ignatenko A. V. , Rykov S. V. , Shteinshneider A. Ya.
Published: August 2005

A study of the CIDNP effects on methyl protons was carried out for the cage recombination products formed during the thermal decomposition reactions of peracetyls and peracetylcarbonates. The increase of both the cage recombination product yield and the enhancement of CIDNP on the CH3 protons is shown to be connected with the RCO2 radical lifetime, where R is an alkyl or alkoxy radical. A general theory of CIDNP is presented and the calculated data prove to be in satisfactory agreement with the experimental results.
The influence of N‐protected amino acid residues on the cis/trans isomerism of proline moieties in peptides
Authors: Voelter Wolfgang , Oster Oskar
Published: August 2005

13C NMR spectroscopy is an excellent tool for studying the influence of N‐protecting groups on the cis/trans isomerism of proline residues in proline peptides. This communication demonstrates the usefulness of 13C NMR spectroscopy in investigating conformational problems in protein and peptide chemistry.
Association of increased type I collagen expression and relative stromal overgrowth in mouse epididymis neonatally exposed to diethylstilbestrol
Authors: Yamazaki Koji , Fukata Hideki , Adachi Tetsuya , Tainaka Hitoshi , Kohda Masao , Yamazaki Masashi , Kojima Kensuke , Chiba Kan , Mori Chisato , Komiyama Masatoshi
Published: August 2005

The aim of this study was to investigate the molecular changes that underlie morphological changes in the epididymis following neonatal exposure to potent synthetic estrogen, namely diethylstilbestrol (DES). Newborn male mice were subcutaneously injected with DES or endogenous estrogen, namely 17 β‐estradiol (E2) (5 µg/mouse/day), for the first 5 days. At the age of 2, 4, and 8 weeks, epididymides of the mice were dissected. Characteristic morphological abnormality, such as relative stromal overgrowth, was observed at the age of 2 weeks in the epididymis of DES‐treated mice, but not in E2‐treated mice. Microarray and real‐time RT‐PCR analyses revealed that the expression levels of procollagen type I alpha 1 (col1a1) and col1a2 genes were markedly upregulated at the age of 2 weeks in the epididymis of DES‐treated mice in comparison with the control. Western blot analysis revealed that type I collagen protein expression level in epididymis of DES‐treated mice was elevated at the age of 2 weeks. In situ hybridization analysis revealed that the signals of col1a1 mRNA were detected similarly throughout the stromal tissue of epididymis at the age of 2 weeks in control and DES‐ and E2‐treated mice. The gene expression level of epididymal type III collagen (col3a1), which is found in many stromal connective tissues as well as type I collagen, did not change at the age of 2 weeks in all groups. These results suggest that the increased type I collagen expression is associated with the relative stromal overgrowth in the epididymis of DES‐treated mice. Mol. Reprod. Dev. © 2005 Wiley‐Liss, Inc.
Electromagnetic perspective on the operation of RF coils at 1.5–11.7 Tesla
Authors: Ibrahim Tamer S. , Mitchell Chad , Schmalbrock Petra , Lee Robert , Chakeres Donald W.
Published: August 2005

In this work experimental and numerical studies of the MR signal were performed at frequencies ranging from 64 MHz to 485 MHz, utilizing three different MRI coils: a single‐strut transverse electromagnetic (TEM)‐based coil, a TEM resonator, and a high‐pass birdcage coil. The experimental analyses were conducted using 1.5 and 8 Tesla whole‐body systems and volume RF head coils. The simulation data were obtained utilizing an in‐house‐developed finite difference time domain (FDTD) model. Pertinent data from the numerical and experimental setups were compared, and a remarkable agreement between the two methods was found that clearly demonstrates the effectiveness of the FDTD method when it is applied rigorously. The numerical and experimental studies demonstrate the complexity of the electromagnetic (EM) fields and their role in the MR signal. These studies also reveal unique similarities and differences between the transmit and receive field distributions at various field strengths. Finally, for ultra high‐field operations, it was demonstrated mathematically, numerically, and experimentally that highly asymmetric inhomogeneous images can be acquired even for linear excitation, symmetrical load geometries, and symmetrical load positioning within the coil. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.
Simulation of anisotropic growth of low‐grade gliomas using diffusion tensor imaging
Authors: Jbabdi Saâd , Mandonnet Emmanuel , Duffau Hugues , Capelle Laurent , Swanson Kristin Rae , Pélégrini‐Issac Mélanie , Guillevin Rémy , Benali Habib
Published: August 2005

A recent computational model of brain tumor growth, developed to better describe how gliomas invade through the adjacent brain parenchyma, is based on two major elements: cell proliferation and isotropic cell diffusion. On the basis of this model, glioma growth has been simulated in a virtual brain, provided by a 3D segmented MRI atlas. However, it is commonly accepted that glial cells preferentially migrate along the direction of fiber tracts. Therefore, in this paper, the model has been improved by including anisotropic extension of gliomas. The method is based on a cell diffusion tensor derived from water diffusion tensor (as given by MRI diffusion tensor imaging). Results of simulations have been compared with two clinical examples demonstrating typical growth patterns of low‐grade gliomas centered around the insula. The shape and the kinetic evolution are better simulated with anisotropic rather than isotropic diffusion. The best fit is obtained when the anisotropy of the cell diffusion tensor is increased to greater anisotropy than the observed water diffusion tensor. The shape of the tumor is also influenced by the initial location of the tumor. Anisotropic brain tumor growth simulations provide a means to determine the initial location of a low‐grade glioma as well as its cell diffusion tensor, both of which might reflect the biological characteristics of invasion. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.
Penetration calculations and measurements for a layered soil target
Authors: Byers Rupert K. , Chabai Albert J.
Published: August 2005

A tow‐dimensional finite difference wave propagation code was used to analyse the impact of a rigid, ogival‐nosed penetrator with a target consisting of thin alternating layers of silt, sand, and clay. The response of the idealized target was described with an elastic‐plastic constitutive model depending upon two stress invariants and the history of plastic deformation. Interfacial friction between the penetrator and target was assumed to be negligible.

Comparisons are made of calculated results and those of nominally similar experiments conducted at the Watching Hill test site in Alberta, Canada. Analysis of these comparisons reveals that numerical methods like the one employed in this study can yield insight into penomena, as well as suggesting possible improvements in the calculation technique.
Methods for the numerical solution of the equations of viscoelasticity
Authors: Booker J. R. , Small J. C.
Published: August 2005

In this paper a finite element formulation for a linear viscoelastic ageing material is developed. It is shown that these equations can be solved in the from of an eigenvalue expansion thus reducing the problem to the solution of a set of Volterra Integral equations. An alternative method of solution based on expansion in terms of an operator related to Poisson's ratio is also developed and this solution method is found to significantly reduce the computational effort necessary in the solution of aproblem.
Mathematical modelling of monotonic and cyclic undrained clay behaviour
Authors: Prévost Jean‐Hervé
Published: August 2005

The proposed general analytical model describes the anisotropic, elasto‐plastic, path‐dependent, stress‐strain‐strength properties of inviscid saturated clays under undrained loading conditions. The model combines properties of isotropic and kinematic plasticity by introducing the concept of a field of plastic moduli which is defined in stress space by the relative configuration of yield surfaces. For any loading (or unloading) history, the instantaneous configuration is determined by calculating the translation and contraction (or expansion) of each yield surface. The stress‐strain behaviour of clays can thus be determined for complex loading paths and in particular for cyclic loadings. The stress‐strain relationships are provided for use in finite element analyses. The model parameters required to characterize the behaviour of any given clay can be derived entirely from conventional triaxial or simple shear soil test results. The model's extreme versatility is demonstrated by using it to formulate the behaviour of the Drammen clay under both monotonic and cyclic loading conditions. The parameters are determined by using solely the results from monotonic and cyclic strain‐controlled simple shear experimental tests, and the model's accuracy is evaluated by applying it to predict the results of other tests such as (1) cyclic stress‐controlled simple shear tests, (2) monotonic triaxial loading compression and unloading extension tests, and (3) cyclic stress‐ and strain‐controlled triaxial tests on, this same clay. The theoretical predictions are found to agree extremely well with the experimental test results.
On the time‐dependent effects in advancing tunnels
Authors: Ghaboussi Jamshid , Gioda Giancarlo
Published: August 2005

A finite element study is presented of the short‐term effects that develop when a tunnel is driven in a ground showing viscous behaviour associated with the deviatoric deformations. Axisymmetric conditions around the tunnel centreline are assumed and the process of excavation is simulated by means of a step‐by‐step time incremental technique. The Kelvin's model is used to approximate the medium creep behaviour and a simple procedure is presented that allows the determination of the creep model constants from the laboratory test data. Various rates of advancing, the presence of an unsupported zone close to the tunnel face and the temporary interruption of the excavation process are considered. For the viscous model and the analytical technique used, simple, approximate relationships are presented for the displacements around the tunnel and the overexcavation volume as functions of the rate of excavation advancing.
Numerical approximations in pile‐driving analysis
Authors: Davis R. O. , Phelan P. J.
Published: August 2005

A finite‐difference scheme widely used in analysis of pile driving is examined, the scheme is shown to yield peculiar results in simple symmetric impact problems and to inherently posses an imprecise definition of energy balance. A modified difference scheme is suggested and comparisons of the two methods are shown.
An analytical solution for the consolidation around a driven pile
Authors: Randolph M. F. , Wroth C. P.
Published: August 2005

Field studies have shown that the driving of a displacement pile into cohesive soil generates large excess pore pressures in the vicinity of the pile. These pore pressures are often larger than the effective overburden pressure and facilitate the installation of the pile. The subsequent increase in bearing capacity of the pile is largely controlled by the dissipation of the excess pore pressures and a consequent increase in the effective stresses acting on the pile. The paper presents a closed formanalytical solution for the radial consolidation of the soil around a driven pile, assuming that the soil skeleton deforms elastically. This assumption is examined in the light of the predicted effective stress changes in the soil and is shown to lead to, a realistic model for the decay of pore pressure near the pile with time after driving. Although the solution may be applied to any initial distribution of excess pore pressure, attention is focussed on that due to the expansion of a cylindrical cavity in an ideal elastic, perfectly plastic soil. The resulting logarithmic variation of excess pore pressure with radius is considered to be close to that generated around a pile as a result of driving. In addition to giving estimates of the time needed for a driven pile to achieve its maximum strength, the solution may also be used in the analysis of pressuremeter tests to provide in‐situ measurements of the coefficient of consolidation of the soil.
A constitutive model for sand in triaxial compression
Authors: Nova R. , Wood D. M.
Published: August 2005

Although there is a large number of constitutive models for sand available in the literature it is believed that a fresh approach, striking a balance between complexity and theoretical rigour, is desirable.

The approach here has certain conceptual links with the Cam Clay series of elastic–plastic models, but includes the more general starting assumption that the yield function, plastic potential and failure locus should be given quite distinct mathematical expressions. Possible physical bases for the proposed forms are discussed.

Ways in which the parameters required to define the model may be determined are suggested and the use of the model is then demonstrated. Firstly, it is shown that, where a limited set of experimental data is available, the model is flexible enough to be able to match the test results. Secondly, it is shown that, where a wide range of test results has been produced, it is possible to determine the model constitutive parameters from a small number of tests and proceed to make satisfactory predictionsfor other, quite different, types of test.

The model is developed for sand at a single initial density, but the way in which the constitutive parameters might be expected to vary with density is discussed. The model is described for conditions of triaxial compression, and extension to more general stress states will be needed before it can be put to the test of incorporation in, for example, a finite element program.
Derived failure criteria for granular media
Authors: Davis R. O. , Mullenger G.
Published: August 2005

The failure criterion for a special rate‐type material is derived using a method similar to that of Tokuoka.7 For particular choices of constitutive parameters it is shown that this failure criterion contains, as special cases, failure criteria suggested in four recent works dealing with elastic‐plastic response of granular media.
Finite difference techniques for modelling geothermal reservoirs
Authors: Zyvoloski G. A. , O'Sullivan M. J. , Krol D. E.
Published: August 2005

Two finite difference algorithms suitable for long‐time simulation of the exploitation of a two‐phase geothermal reservoir are presented. One is based on the hopscotch method proposed by Saul'yev1 and analysed further by Gordon2 and Gourlay.3 The other is based on the well‐known ADI method. Both methods use a Newton–Raphson iterative technique in order to obtain accurate solutions of the non‐linear difference equations involved. Rapid convergence of the iterative schemes occurs both for single‐phase and two‐phase reservoir problems. One‐ and two‐dimensional model problems are presented.
Elastic–plastic analysis of geotechnical problems by mathematical programming
Authors: Gioda Giancarlo , de Donato Osvaldo
Published: August 2005

A numerical technique, based on a mathematical programming algorithm, is presented for the solution of geotechnical problems where elastic‐plastic material behaviour is considered. The proposed approach can be adopted for geotechnical media characterized by any suitable yield condition, accounting, if necessary, for workhardening behaviour. The loading process is subdivided into a series of steps applied to a finite element mesh with geometry and material properties constant along each step, but with possible changes between subsequent steps. As an application some typical geotechnical problems are analysed by means of the proposed algorithm and a comparison is made between the available in situ measurements and the numerical results.
Load transfer from an elastic pile to a saturated porous elastic soil
Authors: Niumpradit Boonsrang , Karasudhi Pisidhi
Published: August 2005

The quasi‐static development of the force, pore pressure and displacement is obtained in the system of a circular elastic pile partially embedded in a saturated porous elastic soil, and loaded axially on the top. The porous elastic soil is governed by Biot's theory. The problem is decomposed into two systems, namely, an extended porous elastic half‐space in the absence of the pile characterized by the material constants of the medium, and a fictitious pile represented by a Young's modulus equal to the difference between the Young's moduli of the real pile and the medium. The problem is found to be governed by a Fredholm integral equation of the second kind. Laplace transforms are applied to time functions involved, and Hankel transforms to the radial coordinate of which the origin is at the centre of the pile. Numerical solutions are obtained for final and initial solutions for various practical values of the parameters involved.
Rock stresses due to local buckling of a surface layer (theory and applications)
Authors: Golecki J. J.
Published: August 2005

The theoretical aspects of mining in rock subject to tectonic stressing are still insufficiently clear. While rock mechanics uses Heim's rule and assumes the virgin stress to be generally lithostatic, earth science resorts to the folding theory and to different approaches in explaining geological phenomena.

In this paper, a procedure is proposed for determining tectonic stresses in mining ground below a surface fold, the latter being assumed to originate through local buckling of the surface layer under tectonic action. For the purpose of this hypothesis, the concept of displacement along the interface of the layer and the surrounding incompetent rock is defined. In the case of elastic or viscous incompetent rock, the induced stress is obtainable by an integral equation approach.

A numerical technique was developed accordingly for the zone of contact strain, and special attention is paid to interpretation of the singular integrals representing the boundary stress. Numerical results are presented as an illustration.
Heated mine room and pillar‐secondary creep response
Authors: Tillerson J. R. , Dawson P. R.
Published: August 2005

Heated salt mine room and pillar simulations have been performed to provide information regarding parameters affecting room closure rates to designers of radioactive waste isolation facilities. A coupled secondary creep and heat transfer formulation with large strain capabilities was used to assess the effects of variations in creep law parameters, thermal properties, imposed boundary conditions, temporal integration and meshing resolution on room closure rates. Results indicate that the greatest effect results from variations in parameters appearing in the creep constitutive equation.
A comparison between finite element and finite difference explicit formulations for triangular and quadrilateral plane‐strain elements
Authors: Kunar R. R. , Minowa N.
Published: August 2005

For non‐linear dynamic problems, it has been recognized that an explicit time‐integration method of approach is a very efficient way of solving the dynamic equations of motion. The numerical formulation and computation for such problems fall into the two general categories of finite elements and finite differences. Over the years, there have been many arguments between schools which adopt the finite element approach and those which adopt the finite difference approach. At one extreme, arguments areconcerned with the superiority of each approach and at the other end of the spectrum the arguments are about which approach is a subset of the other. The most common of these arguments are concerned with efficiency and accuracy. This publication addresses the accuracy issue with specific reference to explicit calculations in which the analysis domain is discretized into triangular or quadrilateral plane‐strain elements. It concludes that if the same basic assumptions are made in the two approaches, they, will give identical answers for problems in this category.
A unified yield criterion for cohesionless granular materials
Authors: Mullenger G. , Davis R. O.
Published: August 2005

A general form of the yield criterion derived from a special rate‐type constitutive equation for a granular material provides an appropriate yield surface over a narrow range of material parameters. The complete yield surface is described using a single equation.
Procedure, selection and application of plasticity models for a soil
Authors: Desai C. S. , Phan H. V. , Sture S.
Published: August 2005

A five‐step procedure involving mathematical formulation, identification and determination of parameters and verification is presented for development and selection of appropriate and reliable constitutive law(s) for geologic media. Comprehensive analyses are performed toward determination of an appropriate law for a (artificial) soil. The most suitable model is obtained by critical evaluation of four different plasticity models; here verification and comparisons of predictions with observations from laboratory tests, and with those from two boundary value problems are used as the basis of the selection. The model thus selected is found to be appropriate for applications to relevant practical problems.
‘Infinite domain’ elements in finite element analysis of underground excavations
Authors: Beer G.
Published: August 2005

The Finite Element Method is frequently used to analyse problems involving an ‘infinite domain’. A typical problem is an underground excavation in prestressed infinite medium in either tunnelling or mining operations or a foundation in an infinite half space.

This paper examines the implications of mesh truncation on the accuracy of the accuracy of the solution.

At the same time, a more economical and accurate method of analysing these problems using special ‘infinite domain’ Finite Elements is presented.
On hardening anisotropy of K0‐consolidated clays
Authors: Pietruszczak St. , Mróz Z.
Published: August 2005

The combined isotropic‐kinematic hardening rule for clays is presented using the concept of a multisurface model discussed previously in Reference 1. The mechanical behaviour of clays after one‐dimensional consolidation is next simulated for the axisymmetric stress stress state. A general three‐dimensional formulation of constitutive relations is also presented.
A coupled finite element–rigid block method for transient analysis of rock caverns
Authors: Dowding C. H. , Belytschko T. B. , Yen H. J.
Published: August 2005

A coupled finite element–rigid block model for the transient analysis of caverns in jointed media is presented. This coupling permits the modelling of lined openings in a jointed rock mass as well as the propagation of stress waves to the cavern. Both the finite element and the rigid block algorithms employ explicit time integration; an efficient, stable scheme is developed for coupling the two algorithms. Two numerical examples are given: one is a simple validation, the second is a representation of a lined cavern in a sparsely jointed medium.
The analysis of liquid storage tanks on deep elastic foundations
Authors: Booker J. R. , Small J. C.
Published: August 2005

The behaviour of a cylindrical liquid storage tank resting on a deep homogeneous elastic layer is examined. The analysis employs a substructure approach and proceeds by examining the behaviour of the tank base, the tank walls and the soil separately and developing flexibility matrices for each of these components. These flexibility matrices are then assembled and the complete soil structure system analysed.
Consolidation of axi‐symmetric bodies subjected to non axi‐symmetric loading
Authors: Carter J. P. , Booker J. R.
Published: August 2005

In many cases the analysis of the consolidation of axi‐symmetric bodies subjected to non axi‐symmetric loading may be carried out without recourse to a full three‐dimensional treatment. Advantage may be taken of the axi‐symmetric nature of the body and field quantities such as displacement and pore pressure can be given a Fourier representation. The problem is then reduced from one in three spatial dimensions (r, θ,z) and the time domain to one in two spatial dimensions (r,z) and the time domain.
Rheological behaviour effect of non‐newtonian fluids on steady and unsteady flow through a porous medium
Authors: Pascal H.
Published: August 2005

This paper describes the flow behaviour of certain non‐Newtonian fluids through a porous medium. A generalized Bingham rheological model of power‐law in the presence of a yield stress has been considered. Several problems of fluid mechanics, which appear currently in oil reservoir engineering, have been investigated and the rheological behaviour effect has been emphasized. The short time solutions have been formulated in terms of a moving boundary problem. The approximate solutions in a closed formwere obtained by means of the integral method. Several dimensionless groups have been found to be relevant in evaluating the rheological effect on the steady and unsteady and unsteady flow behaviour. The deviation from Newtonian flow behaviour has been illustrated using several numerical examples.