Search

In present-day land and marine controlled-source electromagnetic (CSEM) surveys, electromagnetic fields are commonly generated using wires that are hundreds of metres long. Nevertheless, simulations of CSEM data often approximate these sources as point dipoles. Although this is justified for sufficiently large source-receiver distances, many real surveys include frequencies and distances at which the dipole approximation is inaccurate. For 1D layered media, electromagnetic (EM) fields for point dipole sources can be computed using well-known quasi-analytical solutions and fields for sources of finite length can be synthesized by superposing point dipole fields. However, the calculation of numerous point dipole fields is computationally expensive, requiring a large number of numerical integral evaluations. We combine a more efficient representation of finite-length sources in terms of components related to the wire and its end points with very general expressions for EM fields in 1D layered media. We thus obtain a formulation that requires fewer numerical integrations than the superposition of dipole fields, permits source and receiver placement at any depth within the layer stack and can also easily be integrated into 3D modelling algorithms. Complex source geometries, such as wires bent due to surface obstructions, can be simulated by segmenting the wire and computing the responses for each segment separately. We first describe our finite-length wire expressions and then present 1D and 3D examples of EM fields due to finite-length sources for typical land and marine survey geometries and discuss differences to point dipole fields. [ABSTRACT FROM AUTHOR]

A linear motor that uses a finite length Halbach array as its magnetic field causes a thrust force ripple owing to end effects. In this paper, the theoretical and numerical analysis methods of the Halbach array are investigated. The results of the electromagnetic field analysis are compared to confirm the validity of the theoretical and numerical solutions. Moreover, we focus on the magnetic pole period and coil arrangement of the finite length Halbach field type linear motor to eliminate the influence of the end effects, and report the relationship with the end effects. [ABSTRACT FROM AUTHOR]

The so-called non-uniform fast Fourier transform (NFFT) is a family of algorithms for efficiently computing the Fourier transform of finite-length signals, whenever the time or frequency grid is non-uniformly spaced. Among the five usual NFFT types, types 4 and 5 involve an inversion problem, and this makes them the most intensive computationally. The usual efficient methods for these last types are either based on a fast multipole (FM) or on an iterative conjugate gradient (CG) method. The purpose of this study is to present efficient methods for these type-4 and type-5 NFFTs in the one-dimensional case that just require three NFFTs of types 1 or 2 plus some additional fast Fourier transforms (FFTs). Fundamentally, they are based on exploiting the Lagrange formula structure. The proposed methods roughly provide a factor-ten improvement on the FM and CG alternatives in computational burden. The study includes several numerical examples in double precision, in which the proposed and the Gaussian elimination, CG and FM methods are compared, both in terms of round-off error and computational burden. [ABSTRACT FROM AUTHOR]

Very‐low‐frequency (VLF) transmitting antennas have a crucial influence on the nearby electromagnetic environment. Commercial software packages, such as CST Studio Suite (CST) or Altair FEKO (FEKO), are always utilised to calculate the electric fields of VLF antennas, which consume considerable computing resources and time. The classical method of electric field calculation, the charge simulation method (CSM), is first applied to the calculation of electric field near the VLF transmitting antenna. The distribution characteristics of three‐dimensional electric fields were analysed. The electric field surrounding the antenna exhibited axial symmetry. The highest electric field strength was at the top of the antenna, and as the distance from the antenna increased, the electric field strength exponentially decreased. The comparisons are performed between the results of the CSM and those of commercial software, the average relative errors of CSM on two observation paths are very small, 2.20% and 2.21%, respectively. Meanwhile, the CSM shows considerable advantages in saving calculation resources and improving efficiency. Additionally, the comparison between CSM calculation and the measured data is carried out. The results show that this method can accurately calculate the electric field near VLF transmitting antenna and offer valuable insights and a new solution. [ABSTRACT FROM AUTHOR]

The analytical solution of a wave equation that describes the propagation of a femtosecond laser pulse in a dispersion-free finite-length spatially chirped medium with 1D periodic inhomogeneity is presented. Such media are important to modern optics and are found in holograms, lasers, Bragg reflectors, compressors, and other applications. FDTD numerical modeling confirms the validity of our analytic results. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 269–273, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10891 [ABSTRACT FROM AUTHOR]

For broadband active noise control applications with a rapidly changing primary path, it is desirable to find algorithms with a rapid convergence, a fast tracking performance, and a low computational cost. Recently, a promising algorithm has been presented, called the fast-array Kalman filter, which uses rotation matrices to calculate the filter parameters. However, when this algorithm is implemented, it can show unstable behavior because of finite precision error propagation. In this paper, a novel algorithm is presented, which exhibits the fast convergence and tracking properties and the linear calculation complexity of the fast-array Kalman filter but does not suffer from the mentioned numerical problems. This is accomplished by running two finite length growing memory recursive least squares filters in parallel and using a convex combination of the two filters when the control signal is calculated. A reset of the filter parameters with proper re-initialization is enforced periodically. The mixing parameters will be chosen in such a way that the total available information used for the calculation of the control signal will be approximately equal at every time instance. The performance of the filter is shown in numerical simulations and real-time lab experiments. The numerical experiments show that the algorithm performs better numerically than the fast-array sliding window recursive least squares filter, while achieving a comparable convergence rate and tracking performance. The real-time lab experiments confirm the behavior shown in the simulations. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Steel well casings in or near a hydrocarbon reservoir can be used as source electrodes in time-lapse monitoring using grounded line electromagnetic methods. A requisite component of carrying out such monitoring is the capability to numerically model the electromagnetic response of a set of source electrodes of finite length. We present a modelling algorithm using the finite-element method for calculating the electromagnetic response of a three-dimensional conductivity model excited using a vertical steel-cased borehole as a source. The method is based on a combination of the method of moments and the Coulomb-gauged primary-secondary potential formulation. Using the method of moments, we obtain the primary field in a half-space due to an energized vertical steel casing by dividing the casing into a set of segments, each assumed to carry a piecewise constant alternating current density. The primary field is then substituted into the primary-secondary potential finite-element formulation of the three-dimensional problem to obtain the secondary field. To validate the algorithm, we compare our numerical results with: (i) the analytical solution for an infinite length casing in a whole space, excited by a line source, and (ii) a three-layered Earth model without a casing. The agreement between the numerical and analytical solutions demonstrates the effectiveness of our algorithm. As an illustration, we also present the time-lapse electromagnetic response of a synthetic model representing a gas reservoir undergoing water flooding. [ABSTRACT FROM AUTHOR]

With a view to accurate and fast time domain analysis of nonuniform transmission lines, a method is presented for applying the FDTD method to a finite length nonuniform transmission line. A step response analysis is carried out for a parabolic line as one of the nonuniform transmission lines. Effectiveness of this approach is confirmed by comparison with analytical solutions and other methods. An equation for the voltage at the initial rising duration of the step response of a nonuniform transmission line is derived. It is shown that if the nonuniform transmission line has the characteristic impedance with a continuous distribution the initial arriving voltage can be determined by the characteristic impedance at both ends of the transmission line. As an application, a method is described for approximating the step response waveform of a parabolic line to a step wave. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 85(2): 22–31, 2002 [ABSTRACT FROM AUTHOR]

The delta gap model and the frill magnetic current model are often used as models for the feed point in numerical calculations for cylindrical antennas. When the delta gap model with finite gap width is used, the electrical field produced by the magnetic current of the feed point may be included in the excitation function of the integral equation so that a solution separated into the external and internal surface currents of a hollow cylindrical antenna can be derived. Such an analytic solution, however, has been obtained only for the case in which the cylindrical antenna has infinite length or is placed between two parallel conductive plates. This paper considers a cylindrical antenna of finite length using the same integral equation. As the first step, a numerical calculation of the excitation function for the feed point is considered. The excitation function is derived numerically by a method based on mode expansion in cylindrical coordinates and by a method based on the electric vector potential of the magnetic current ring. The properties of the excitation function are examined. As the next step, the cylindrical antenna is numerically analyzed by the method of moments. In all of these analytical procedures, the current is represented by piecewise sinusoidal functions on the surface of the cylinder, and the Galerkin method is applied. The convergence of the input admittance thus obtained is compared to the results of various other methods, such as point matching without considering the magnetic current at the gap (approximation by the two-dimensional surface current and the one-dimensional axial current), and approximation of the axial current by the frill magnetic current feed model. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(3): 65–76, 2001 [ABSTRACT FROM AUTHOR]

This paper examines the influence of branches and bends on the propagation of electromagnetic waves inside tunnels excited by the fundamental mode, and considers an approximation of surface impedance for the boundary conditions and wall surfaces of a tunnel (impedance tunnel) in a two-dimensional space. An analysis method was formulated by the boundary element method to analyze the propagation of electromagnetic waves inside the tunnel. To analyze an infinitely long tunnel by the boundary element method, the tunnel is terminated at a finite length and fictitious wall surfaces are installed at the ends. As for a metallic waveguide, it is necessary to provide adjustment conditions analytically for the fictitious surfaces. The tunnel was separated into the excitation side tunnel and the output side tunnel with a fictitious surface in each part. A method which connected the analytical solution of a unit on impedance tunnel and the solution of the boundary element method over the fictitious surfaces was used. Microwave simulation experiments were conducted with bakelite plates for T-type and cross-type branch- es and L-bends. As a result we confirmed good agreement between calculated values and experimental measurements except in the vicinity of the inside walls of the output side tunnel. [ABSTRACT FROM AUTHOR]

Imperfect walls at the device perimeter are allowed. A new dyadic Green's function is found by specification of the source as a finite-length singularity in the z direction on the device boundary contour at location φ′ and the use of mode matching. The new dyadic Green's function allows fields and s parameters to be found, dependent on the external material parameters. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 235–242, 1997 [ABSTRACT FROM AUTHOR]

In this work, a finite‐element formulation for modeling mixed‐mode delamination in layered structures, consisting of two‐node Timoshenko beam finite elements with quadratic linked interpolation and corresponding 4‐node interface elements is presented and compared to a more common approach where linear Lagrange interpolation is used. The principal novelty of the proposed approach is that the vertical displacements of the beam elements, as well as the transversal relative displacements of the interface elements, are interpolated using a quadratic linked interpolation that also takes into account the nodal cross‐sectional rotations of the beam elements. At the same time, the axial displacements and cross‐sectional rotations are interpolated using linear Lagrange polynomials. A bilinear cohesive zone model is embedded in the interface finite elements for delamination modes I and II. Numerical analyses based on the examples from the literature with metal joints show that the formulation with quadratic linked interpolation improves the convergence and robustness of the solution with respect to the approach with linear interpolation. On the other hand, in case of composites with stiff adhesives this formulation exhibits a peculiar behavior with spurious oscillations of the normal interface tractions that leads to a poor performance in mode‐I and mixed‐mode tests. This problem can be easily solved by canceling the quadratic term in the interpolation function and using the standard Lagrange interpolation in such cases. [ABSTRACT FROM AUTHOR]

In the present study, the influence of numerical analysis involves the transfer of heat for moving fin under convection and radiation with fluid properties depending on internal heat generation is considered. The temperature field for the fin is derived based on the defined geometry. This is transformed into a linear model as per the boundary conditions. The dimensionless analysis is performed, and the equations obtained are solved by Runge–Kutta Fehlberg fourth‐order method coupled with the shooting method. The effects of the relative parameters are studied and depicted graphically. Finally, the computational observation indicates that there is an enhancement of temperature variation under the influence of thermal conductivity gradient, heat generation, and opposite behavior results. In understanding the thermal characteristics of various effects, it was seen that thermo geometric film, radiation conduction, and Peclet number were very useful for many industrial applications. To validate the numerical scheme, a comparative study has been done with an earlier result on a few nondimensional parameters and was found in good agreement. [ABSTRACT FROM AUTHOR]

A parallel concatenated coding structure, which can improve the performance of polar codes in finite-length regime, is proposed. In the proposed structure, the encoder is built using two systematic polar codes (SPCs), and the decoder adopts iterative belief propagation decoding algorithm. Numerical results in the binary-input additive white Gaussian noise channel indicate that the proposed coding scheme can improve BER performance of polar codes significantly. Specially, BER of the proposed coding scheme with length 192 is almost equal to that of original SPCs with length 256, when the code rate is 1/3. [ABSTRACT FROM AUTHOR]

Main modelling approaches used for investigating the Photonic bandgap (PBG) devices are reviewed. In particular, the model based on Leaky Mode Propagation (LMP) method is described. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, can be carried out by a computer program based on the LMP approach. The numerical results have been validated by comparisons with those obtained by using other more complex and expensive models. The new model shows some significant advantages in terms of very low computational time, absence of any a priori theoretical assumptions and approximations, capability of simulating the actual physical behaviour of the device and fast determination of the bandgap position.Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The analysis of a charged particle traveling through one, two, or infinite conducting rings is presented. The problem is formulated in the spectral domain as integral equations of Fredholm type, solved by Galerkin's method employing entire domain functions factorising the correct edge behaviour of the unknown induced current. As a result, high accuracy and numerical stability are achieved. Numerical results are presented, proving the effectiveness of the method, and the parameters relevant to accelerator physics are calculated. [ABSTRACT FROM AUTHOR]

We study stochastic clearing systems with a discrete‐time Markovian input process, and an output mechanism that intermittently and instantaneously clears the system partially or completely. The decision to clear the system depends on both quantities and delays of outstanding inputs. Clearing the system incurs a fixed cost, and outstanding inputs are charged a delay penalty, which is a general increasing function of the quantities and delays of individual inputs. By recording the quantities and delays of outstanding inputs in a sequence, we model the clearing system as a tree‐structured Markov decision process over both a finite and infinite horizon. We show that the optimal clearing policies, under realistic conditions, are of the on‐off type or the threshold type. Based on the characterization of the optimal policies, we develop efficient algorithms to compute parameters of the optimal policies for such complex clearing systems for the first time. We conduct a numerical analysis on the impact of the nonlinear delay penalty cost function, the comparison of the optimal policy and the classical hybrid policy (ie, quantity and age thresholds), and the impact of the state of the input process. Our experiments demonstrate that (a) the classical linear approximation of the cost function can lead to significant performance differences; (b) the classical hybrid policy may perform poorly (as compared to the optimal policies); and (c) the consideration of the state of the input process makes significant improvement in system performance. [ABSTRACT FROM AUTHOR]

The proposed 1D elastic metamaterial rod finds application in non-destructive evaluation, as a filter in the transduction side, where only the torsional and flexural modes need to be generated by isolating longitudinal modes. In this Letter, this is achieved by obtaining a wide bandgap in low-frequency ultrasound regime. The novelty of the proposed design arises from the use of a high impedance mismatch between the materials selected for the rod. The proposed concept is demonstrated and verified with numerical simulations. The effectiveness of the proposed technique is confirmed by comparing the results obtained from the rod made of a single material. [ABSTRACT FROM AUTHOR]

Mesoscale eddies stir along the neutral plane, and the resulting neutral diffusion is a fundamental aspect of subgrid‐scale tracer transport in ocean models. Calculating neutral diffusion traditionally involves calculating neutral slopes and three‐dimensional tracer gradients. The calculation of the neutral slope traditionally occurs by computing the ratio of the horizontal to vertical locally referenced potential density derivative. However, this approach is problematic in regions of weak vertical stratification, prompting the use of a variety of ad hoc regularization methods that can lead to rather nonphysical dependencies for the resulting neutral tracer gradients. Here we use a VErtical Non‐local Method "VENM," a search algorithm that requires no ad hoc regularization and significantly improves the numerical accuracy of calculating neutral slopes, neutral tracer gradients, and associated neutral diffusive fluxes. We compare and contrast VENM against a more traditional method, using an independent objective neutrality condition combined with estimates of spurious diffusion, heat transport, and water mass transformation rates. VENM is more accurate, both physically and numerically, and should form the basis for future efforts involving neutral diffusion calculations from observations and possibly numerical model simulations. Key Points: We provide a vertically nonlocal method (VENM) to calculate neutral slopes and gradientsA VENM‐like method is numerically and physically more accurate than most used methodsVENM can fundamentally improve physics for data analyses and numerical modeling [ABSTRACT FROM AUTHOR]

Summary: The finite element simulation of liquid sloshing under microgravity is focused on in this paper. For this class of flows, an important issue is to implement the contact angle boundary condition appropriately. A novel method of adding infinitely small free‐surface mesh just adjacent to the contact line is proposed here, which coincides with the physical definition of the contact angle. This free‐surface mesh has its orientation determined according to the contact angle, and the mean curvature at the contact line can be computed using this orientation. Hence, surface tension force can be computed and incorporated as an essential boundary condition into the pressure solve. This method is convenient to be applied in three‐dimensional simulations, and the use of relatively coarse meshes near the contact line is allowed. In order to validate the proposed method, several numerical simulations of flows in two‐dimensional circular and three‐dimensional cylindrical and spherical containers are presented, including calculation of equilibrium positions of the free surfaces, unsteady flows of liquid reorientation, and large‐amplitude nonlinear liquid sloshing under lateral excitation in microgravity. Parts of the numerical results are compared with the theoretical and published experimental results. A novel method of adding infinitely small free‐surface mesh just adjacent to the contact line is proposed for implementing contact angle condition, which coincides with the physical definition of the contact angle. This method is convenient to be applied in 3D simulations, and the use of relatively coarse meshes near the contact line is allowed. Three‐dimensional sloshing in cylindrical and spherical containers is simulated, and strong nonlinear phenomena of liquid sloshing under microgravity are exhibited. [ABSTRACT FROM AUTHOR]

We describe the shrinking target set for the Bedford–McMullen carpets, with targets being either cylinders or geometric balls. [ABSTRACT FROM AUTHOR]

Depending on its mechanical and thermal advantages, solid rotor induction motors (SRIMs) are widely used in demanding high‐speed applications. Since eddy currents are set free in SRIMs, great part of rotor losses is caused by space harmonics created in the air‐gap. Rotor losses are increased tremendously in high‐speed applications with the remarkable increase in driving frequency. Here, an innovative design representing a novel stator and rotor combination that is not achieved in previous studies is proposed by structural changes to stator to eliminate major effective space harmonics. An unconventional stator slotting pattern and winding distribution is calculated by nature‐inspired numerical optimisation techniques while keeping the fundamental winding factor relatively high. An example design where novel concepts are implemented is presented and a comparison is given in terms of important operational quantities with that of a standard SRIM. [ABSTRACT FROM AUTHOR]

Quantifying reductions in streamflow due to groundwater pumping ("streamflow depletion") is essential for conjunctive management of groundwater and surface water resources. Analytical models are widely used to estimate streamflow depletion but include potentially problematic assumptions such as simplified stream‐aquifer geometry and rely on largely untested depletion apportionment equations to distribute depletion from a well among different stream reaches. Here, we use archetypal numerical models to evaluate the sensitivity of five depletion apportionment equations to stream networks with varying drainage densities, topographic relief, and groundwater recharge rates; and statistically evaluate the sources of error for each equation. We introduce a new depletion apportionment equation called web squared which considers stream network geometry, and find that it performs the best under most conditions tested. For all depletion apportionment equations, performance decreases with increases in drainage density, relief, or recharge rates, and all equations struggle to estimate depletion in short stream reaches. Poorly performing apportionment equations tend to underestimate streamflow depletion relative to numerical model results, leading to a negative bias and underpredicted variability, while error in the best performing apportionment equations tends to be due to imperfect correlation. From a management perspective, apportionment equations with error due to bias and variability are preferable as they correctly identify which reaches will be affected and can be statistically corrected. Overall, these results indicate that the web squared method introduced here, which explicitly considers stream geometry, performs the best over a range of real‐world conditions, and will be most accurate in flatter and drier environments. Plain Language Summary: Pumping groundwater for human uses such as irrigation can reduce flow in streams by intercepting water which otherwise would have eventually flowed into the river channel or causing water to flow out of the stream into the subsurface. This "streamflow depletion" reduces the water available to downstream users and ecosystems. Due to a lack of data and resources, relatively simple ("analytical") groundwater models are often used to estimate pumping impacts, but they are based on unrealistic assumptions, such as straight streams. In this study, we introduce a new "depletion apportionment" equation used to estimate pumping impacts that considers the spatial configuration of real stream networks. By comparing it to more complex ("numerical") groundwater models, we find that our new equation works better than existing equations under a variety of conditions. All of the depletion apportionment equations we test perform best in flatter, drier settings where streams are spaced further apart. Finally, we compare the causes of error among equations, which have different implications for water management decisions. Overall, our results show that stream geometry is an important factor to consider when making groundwater pumping decisions, and the new depletion apportionment equation introduced here is a useful tool for water managers. Key Points: New streamflow depletion apportionment equation with stream geometry performs best across a variety of stream network geometriesPerformance of all depletion apportionment equations decreases with increased drainage density, relief, and groundwater recharge ratesSpatial application of Kling‐Gupta Efficiency is useful for identifying different sources of error and accompanying management implications [ABSTRACT FROM AUTHOR]

In this paper, a novel parameter space approach that uses volume rendering is proposed to visualize controller parameter sets that consist of three controller parameters. An off-line design method for robust control using plant response data is also studied. A solution set with equal l2 gain can be visualized as isosurfaces in three-dimensional space, and the designer can visually select an appropriate parameter. This numerical method is applicable to many practical specifications, in contrast to analytical methods based on solving equations. An estimation method based on the extension theoremand amethod using bandpass filters are both considered as possiblemethods for estimating the l2 gain of the sensitivity functions when using grid points on the order of tens of thousands to create the volume data. The former method is superior to the latter with respect to accuracy but impractical with respect to computational load. The latter method is hence practical, because the computing time is reduced to less than 0.05 s for about 300,000 grid points by parallel computation with a graphical processing unit. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a new two-stage decoding scheme for low-density parity-check codes to lower the error-floor, which consists of the conventional belief propagation (BP) decoding algorithm as the first-stage decoding and the redecodings with manipulated log-likelihood ratios (LLRs) of variable nodes as the second-stage decoding. In the first-stage decoding, an early stopping criterion is proposed for early detection of decoding failure and the candidate set of the variable nodes are determined, which can be partly included in the small trapping sets. In the second-stage decoding, the scores of the variable nodes in the candidate set are computed by the proposed unreliable path search algorithm and the variable nodes are sorted in ascending order by their scores for the re-decoding trials. Each re-decoding trial is performed by BP decoding algorithm with manipulated LLR of a selected variable node in the candidate set one at a time with the second early stopping criterion. The parallel unreliable path search algorithm is also proposed for practical application of the proposed algorithm. Numerical results show that the proposed early stopping criteria and the proposed decoding algorithms for the second-stage decoding can correct most of the unsuccessfully decoded codewords by the first-stage decoding in the error-floor region. [ABSTRACT FROM AUTHOR]

In the practice of geotechnical engineering, the case of a ring footing carrying a set of concentrated point loads is a common problem. At times, the induced vertical and angular displacements for the ring footing need to be evaluated at a relatively precise level. By making use of the governing set of equations derived for the case of a general curved beam, expressions that can be easily implemented in modern computing software are derived for the vertical and angular displacements of a ring footing of rectangular cross section as functions of the radial position. The loading case considered is a vertical point load, and the soil is modelled as elastic. Estimates of the displacements have been shown for a common range of practical applications. The behaviour for a set of concentrated loads may be evaluated using the derived equations through direct superposition. Nonlinear finite element analysis is used to evaluate the vertical deflection and angular twist of the ring foundation. Numerical analysis performed for three ring foundations with different radii and cross sections is reported to validate the accuracy of the derived analytical solution. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present solutions to both trifurcated and pentafurcated spaced waveguides using the mode matching (or eigenfunction expansion) method. While the trifurcated problem with mean fluid flow has been solved previously using the Wiener-Hopf technique, we solve this problem to validate and demonstrate our method. We then show how we can easily generalize the method to the pentafurcated problem that has not been solved previously. We observe that mode matching method is easier to derive and generalize than the Wiener-Hopf technique. We also investigate the numerical solution in detail for various geometries to model practical exhaust systems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We consider numerical instability that can be observed in simulations of solitons of the nonlinear Schrödinger equation (NLS) by a split-step method (SSM) where the linear part of the evolution is solved by a finite-difference discretization. The von Neumann analysis predicts that this method is unconditionally stable on the background of a constant-amplitude plane wave. However, simulations show that the method can become unstable on the background of a soliton. We present an analysis explaining this instability. Both this analysis and the features and threshold of the instability are substantially different from those of the Fourier SSM, which computes the linear part of the NLS by a spectral discretization. For example, the modes responsible for the numerical instability are not similar to plane waves, as for the Fourier SSM or, more generally, in the von Neumann analysis. Instead, they are localized at the sides of the soliton. This also makes them different from 'physical' (as opposed to numerical) unstable modes of nonlinear waves, which (the modes) are localized around the 'core' of a solitary wave. Moreover, the instability threshold for thefinite-difference split-step method is considerably relaxed compared with that for the Fourier split-step. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 1002-1023, 2016 [ABSTRACT FROM AUTHOR]

Discrete derived categories were studied initially by Vossieck ['The algebras with discrete derived category', J. Algebra 243 (2001) 168-176] and later by Bobiński, Geiß and Skowroński ['Classification of discrete derived categories', Cent. Eur. J. Math. 2 (2004) 19-49]. In this article, we define the CW complex of silting pairs for a triangulated category and show that it is contractible in the case of discrete derived categories. We provide an explicit embedding from the silting CW complex into the stability manifold. By work of Qiu and Woolf ['Contractible stability spaces and faithful braid group actions', Preprint, 2014, arXiv:1407.5986], there is a deformation retract of the stability manifold onto the silting pairs CW complex. We obtain that the space of stability conditions of discrete derived categories is contractible. [ABSTRACT FROM AUTHOR]

Given a description of the stacking statistics of layered close-packed structures in the form of a hidden Markov model, analytical expressions are developed for the pairwise correlation functions between the layers. These may be calculated analytically as explicit functions of model parameters or the expressions may be used as a fast, accurate and efficient way to obtain numerical values. Several examples are presented, finding agreement with previous work as well as deriving new relations. [ABSTRACT FROM AUTHOR]

A differential geometric description of crystals with continuous distributions of lattice defects and undergoing potentially large deformations is presented. This description is specialized to describe discrete defects, i.e., singular defect distributions. Three isolated defects are considered in detail: the screw dislocation, the wedge disclination, and the point defect. New analytical solutions are obtained for elastic fields of these defects in isotropic solids of finite extent, whereby terms up to second order in strain, involving elastic constants up to third order, are retained in the stress components. The strain measure used in the nonlinear elastic potential - a symmetric function, expressed in material coordinates, of the inverse deformation gradient - differs from that used in previous solutions for crystal defects, and is thought to provide a more realistic depiction of mechanics of large deformation than previous theory involving third-order Lagrangian elastic constants and the Green strain tensor. For the screw dislocation and wedge disclination, effects of core pressure and/or possible contraction along the defect line are considered, and radial displacement contributions arise that are absent in the linear elastic solution, affecting dilatation. Stress components are shown to differ from those of linear elastic solutions near defect cores. Volume change from point defects is strongly affected by elastic nonlinearity. [ABSTRACT FROM AUTHOR]

A connected, linearly ordered subset [ABSTRACT FROM AUTHOR]

The paper deals with the concept of magnetic current loop as a source model for finite thin-wire antennas. The formulation is based on the Pocklington integro-differential equation with reduced kernel, which is handled by means of various numerical techniques, mostly using the Galerkin-Bubnov variant of Indirect Boundary Element Method. Extensive numerical experiments were carried out on various dipole and monopole antennas using different sources (delta gap, magnetic frill, and magnetic current loop), and results for input admittance are compared with measured data. The magnetic current loop source ensures accurate solution for input admittance. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper aims to provide a guideline for numerical modeling of reinforced concrete (RC) frame elements for the seismic performance assessment of a structure. Several types of numerical models of RC frame elements are available in nonlinear structural analysis packages. Because the numerical models are formulated based on different assumptions and theories, the models' accuracy, computing time, and applicability vary, which poses a great difficulty to practicing engineers and limits their confidence in the analysis results. In this study, the applicability of five representative numerical models of RC frame elements is evaluated through comparison with 320 experimental results available from the Pacific Earthquake Engineering Research column database. The accuracy of a numerical model is evaluated according to its initial stiffness, peak strength, and energy dissipation capacity of the global responses. In addition, a parametric study of a cantilever RC column subjected to earthquake excitation is carried out to systematically evaluate the consequence of the adopted numerical models on the maximum inelastic structural responses. It is found from this study that the accuracy of the numerical models is sensitive to shear force demand-capacity ratio. If a structural period is short and the structure is shear critical, the use of numerical models that can explicitly capture the shear deformation and failure is suggested. If the structural period is long, the selection of a numerical model does not greatly influence the global response of the structure. The paper also presents statistical parameters of each numerical model, which can be used for probabilistic seismic performance assessment. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The goal of this work is to develop an efficient numerical model of foil‐type windings. An equivalent lumped‐parameter circuit model is presented, which is suitable for the computation of the terminal impedance within a broad frequency range and for internal voltage propagation studies. Owing to the special geometrical winding shape, particular attention has been paid to the calculation of the involved lumped parameters where efficient and accurate formulas for parameter determination are presented. The core influence is investigated for the broad frequency range by taking into account the frequency dependency of core material properties. Simulated results compared to measurements show that the proposed equivalent circuit in combination with the applied formulas for parameter determination can be used with full success for the computation of the terminal impedance and internal voltage distribution studies. [ABSTRACT FROM AUTHOR]

SUMMARY We propose a controller tuning method that considers closed-loop stability after controller tuning without a mathematical plant model. We propose fictitious correlation-based tuning that yields reasonable controller parameters using a small amount of input and output data. However, closed-loop stability after controller tuning is not guaranteed in this approach. In this investigation, we impose a stability constraint on the parameter update in order to maintain closed-loop stability at each parameter update. Further, by introducing particle swarm optimization instead of the Gauss-Newton method to solve the constrained nonlinear optimization problem, the initial value dependence is considerably reduced. The effectiveness of the proposed method is confirmed by a numerical example and experimental results. [ABSTRACT FROM AUTHOR]

This study deals with an analytic model for slotted solid‐rotor line‐start permanent‐magnet motors. The impact of non‐linearity of solid‐rotor impedance is taken into account in the proposed dynamic model by applying a numerical method. The rotor parameters are calculated as functions of rotor slip in the starting stage. Compared to the time‐step finite element method, the proposed method is faster because, the rotor parameters can directly be utilised in the circuit model to simulate the transient start‐up process of the line‐start solid‐rotor synchronous motors. Eventually, a four‐pole, 250 V, 1500 rpm, 1050 W, three‐phase synchronous motor with a slotted solid rotor is designed and prototyped to experimentally validate the capabilities of the proposed analytic model. [ABSTRACT FROM AUTHOR]

ABSTRACT The present paper investigates the influence of micropolar lubrication on the stability of a constant flow valve compensated multi-recess conical hybrid journal bearing system. Eringen's micropolar fluid theory has been used to model the micropolar lubrication in a fluid-film bearing system. The modified Reynolds equation of the micropolar lubricated bearing system has been solved using finite element method. Performance characteristics parameters of four pocket hybrid journal bearing system have been computed for the values of semi-cone angle 10°, 20° and for the judiciously selected micropolar parameters. Numerically simulated results indicate that the value of stability threshold speed margin gets increased substantially with the use of micropolar lubricant vis-à-vis Newtonian lubricant. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This article studies a fully adaptive finite difference method for solving quenching-type nonlinear reaction-diffusion equations over circular domains. Although an auxiliary condition at the origin and radial symmetry are imposed, adaptations are accomplished via arc-length-based monitoring functions in space and time, respectively. The monotonicity and positivity of the numerical solution are proved following a suitable grid constraint, and the numerical stability is ensured in the von Neumann sense. Theoretical bounds of the critical quenching radius are obtained and then refined through the computation. Computational examples are provided to illustrate the effectiveness and plausibility of the new adaptive computational procedure developed. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 472-489, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT In recent decades, numerous models for airfoil bearings have been developed. However, these models are not sufficiently accurate for rotor response prediction in the presence of nonlinearities. It is essential to control the instabilities due to the nonlinear behaviour in order to quantify the energy dissipation in the bearings. By means of a variational approach, the flexible structure is modelled as a thin medium subject to a compressible fluid pressure, under isothermal conditions, in the laminar and turbulent regimes. The model is constructed using the finite element method for the structure response. Internal dry friction is taken into account with Coulomb's law and an updated Lagrangian method. The structure model is coupled with Reynolds equation to obtain the rotor displacement, using the equations of motion for the complete mechanical system. This work is performed to show the influence of the thin structure approach on the rotor behaviour and the field pressure. The link between deflection of the bumps and dry friction is established. The structure buckling is increased by both friction between the sheets and energy dissipation. A second objective is to identify the subsynchronous frequencies in order to establish the relevance of the new airfoil model for nonlinear and instability investigations. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A super Camassa-Holm equation with peakon solutions is proposed, which is associated with a 3 × 3 matrix spectral problem with two potentials. With the aid of the zero-curvature equation, we derive a hierarchy of super Harry Dym type equations and establish their Hamiltonian structures. It is shown that the super Camassa-Holm equation is exactly a negative flow in the hierarchy and admits exact solutions with N peakons. As an example, exact 1-peakon solutions of the super Camassa-Holm equation are given. Infinitely many conserved quantities of the super Camassa-Holm equation and the super Harry Dym type equation are, respectively, obtained. [ABSTRACT FROM AUTHOR]

In the production of small batches of customized parts, high flexibility and frequent switching of production from one product variant to another could not allow for the implementation of a control chart to monitor the process. In fact, when a short-run production should be started, the distribution parameters of the quality characteristics to be monitored are frequentlytextitunknown and the production run is too short to get sufficient Phase I samples. To overcome this problem, the statistical properties of Shewhart t charts monitoring a short production run have been recently discussed in literature. In this paper, we investigate their economic performance: the SPC inspection cost optimization is constrained by the manufacturing and the inspection activities configuration. The decision variables of the problem include the chart design parameters and the size of batches of parts to be worked and released to the local inspection area. A numerical analysis aimed at evaluating the economic performance of the Shewhart t chart vs the Shewhart chart with known parameters has been performed. The expected economic loss associated with the implementation of the Shewhart t chart is acceptable with respect to the 'ideal' condition of the control chart with known parameters when the cost optimization is achieved without a statistical constraint limiting the number of expected false alarms. Finally, the effect of an erroneous initial set-up on the correctness of the inspection cost estimation has been investigated. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: Metallic implants may cause serious tissue heating during magnetic resonance (MR) imaging. This heating occurs due to the induced currents caused by the radio-frequency (RF) field. Much work has been done to date to understand the relationship between the RF field and the induced currents. Most of these studies, however, were based purely on experimental or numerical methods. This study has three main purposes: (1) to define the RF heating properties of an implant lead using two parameters; (2) to develop an analytical formulation that directly explains the relationship between RF fields and induced currents; and (3) to form a basis for analysis of complex cases. Methods: In this study, a lumped element model of the transmission line was modified to model leads of implants inside the body. Using this model, leads are defined using two parameters: impedance per unit length, Z, and effective wavenumber along the lead, kt. These two parameters were obtained by using methods that are similar to the transmission line theory. As long as these parameters are known for a lead, currents induced in the lead can be obtained no matter how complex the lead geometry is. The currents induced in bare wire, lossy wire, and insulated wire were calculated using this new method which is called the modified transmission line method or MoTLiM. First, the calculated induced currents under uniform electric field distribution were solved and compared with method-of-moments (MoM) calculations. In addition, MoTLiM results were compared with those of phantom experiments. For experimental verification, the flip angle distortion due to the induced currents was used. The flip angle distribution around a wire was both measured by using flip angle imaging methods and calculated using current distribution obtained from the MoTLiM. Finally, these results were compared and an error analysis was carried out. Results: Bare perfect electric, bare lossy, and insulated perfect electric conductor wires under uniform and linearly varying electric field exposure were solved, both for 1.5 T and 3 T scanners, using both the MoTLiM and MoM. The results are in agreement within 10% mean-square error. The flip angle distribution that was obtained from experiments was compared along the azimuthal paths with different distances from the wire. The highest mean-square error was 20% among compared cases. Conclusions: A novel method was developed to define the RF heating properties of implant leads with two parameters and analyze the induced currents on implant leads that are exposed to electromagnetic fields in a lossy medium during a magnetic resonance imaging (MRI) scan. Some simple cases are examined to explain the MoTLiM and a basis is formed for the analysis of complex cases. The method presented shows the direct relationship between the incident RF field and the induced currents. In addition, the MoTLiM reveals the RF heating properties of the implant leads in terms of the physical features of the lead and electrical properties of the medium. [ABSTRACT FROM AUTHOR]

We show that if the sum of the resistances of an electrical network N is finite, then there is a unique electrical current in N, provided that we do not allow, in a sense made precise in the paper, any flow to escape to infinity. [ABSTRACT FROM PUBLISHER]

In multi-modal interactions including haptics, problems such as input sensor noise, temporal mismatch between graphics and haptics, and non-constant refresh rates may cause non-smooth force/torque display. This paper proposes temporal smoothing technique for haptic interaction using a sensing glove in multi-modal applications. The proposed technique employs two processes: (1) a noise reduction method is applied to reduce jitter noise at the sensors in the sensing glove and (2) an adaptive force extrapolation is applied for time-varying haptic and video frame rates. To demonstrate the performance of the proposed method, we developed a test platform to assess a simple box model and relatively complex models such as gamephone, portable media player (PMP). It was subsequently demonstrated that the proposed method can support smooth haptic interactions in multi-modal applications where a haptic device and a sensing glove are used. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

It is well known that option valuation problems with multiple-state variables are often problematic to solve. When valuing options using lattice-type techniques such as finite-difference methods, the curse of dimensionality ensures that additional-state variables lead to exponential increases in computational effort. Monte Carlo methods are immune from this curse but, despite advances, require a great deal of adaptation to treat early exercise features. Here the multiunderlying asset Black–Scholes problem, including early exercise, is studied using the tools of singular perturbation analysis. This considerably simplifies the pricing problem by decomposing the multi-dimensional problem into a series of lower-dimensional problems that are far simpler and faster to solve than the full, high-dimensional problem. This paper explains how to apply these singular perturbation techniques and explores the significant efficiency improvement from such an approach. [ABSTRACT FROM AUTHOR]

In recent years, wavelet transform which gives expression in the time–frequency domain has been adopted for a nonstationary process. The authors have proposed a new spectral analytical method in the time–frequency domain. In the conventional spectral analytical methods, the decomposition and the reconstruction of signals have been obtained analytically. The proposed method consists of two approaches. We call these approaches Approach 1 and Approach 2. In this paper, we show the decomposition and reconstruction of signals based on Approach 1. First, we show that the signal is decomposed to the signal elements. They are called the decomposition waves, and all of these decomposed waves are added to obtain the reconstructed wave. Next, we show the magnitude characteristic and the phase characteristic between the original signal and the reconstructed wave. Then the conditions between the signal and the reconstructed wave are derived to realize a sufficiently approximated wave. By a numeric calculation example, we show the approximation ability by the proposed method. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(11): 37–45, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10182 [ABSTRACT FROM AUTHOR]

A general numerical solution based on finite-difference time-domain (FDTD) is presented to calculate the radiation characteristics of wire antennas on space probes. The method is versatile and can treat conductor loss, arbitrary-shaped probes, and wires as well as inhomogenities. Numerical results are obtained and compared with those for a few specific cases available in the literature. Additionally, laboratory models of the antennas have been built and their properties have been measured for comparison with computed results. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]