Search

In recent years, the finite-difference time-domain (FDTD) method has been used to simulate a wide range of frequency dependent media. The accuracy of these simulations often depends on how accurately the complex dielectric constant is simulated in the sampled time domain used by FDTD. This paper describes the process of modelling the complex dielectric constant as a digital filtering problem and uses Z transforms to convert the frequency domain expression to a sampled time domain expression. Copyright © 1999 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A new approach using FIT-formulation (Finite Integration Technique) (T. Weiland, Electron. Commun., 31, 116–120 (1977); Int. J. Numer. Model., 9, 295–319 (1996)) for simulating waveguide propagation of optical pulses is presented. FIT-methods are widespread in use for broadband linear simulations. In recent years, several attempts have been made to describe different dispersive material-characteristics such as Drude, Debye or Lorentz dispersion. Today advanced FDTD-formulations (Finite Difference Time Domain) also consider non-linear effects (P. M. Goorjian and A. Taflove, IEEE Opt. Lett., 17(3), 180–182 (1992); D. M. Sullivan, IEEE Trans. Microwave Theory Techniques, 43(3), 676–682 (1995)). In the following presented method third-order non-linear effects were described, which can be observed in isotropic media in frequency ranges of optical pulses, by updating material polarization terms using classical descriptions of Lorentz dispersion, Raman scattering and the Kerr effect. The basic idea is transforming these description formulas into sets of linear differential equations and solving them with the help of the general exponential solution. Copyright © 1999 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work we base our analysis on a seminal paper by Paul Germain (1973) in which the principle of virtual work is used to found microstructured continuum mechanics. Recently, it was shown that a particular considered microstructured continuum can be regarded as a second gradient continuum of the kind studied by Germain. To prove how these theoretical ideas can be useful in applications, we present the paradigmatic case of pantographic metamaterials, in which the deformation energy may depend only on placement second gradient being independent on placement first gradient. In this case, the numerical simulations become more efficient by introducing the Lagrange multipliers which are dual in work of the introduced kinematical constraint, so proving that the viewpoint about stress presented originally by Lagrange is the most fruitful one. [ABSTRACT FROM AUTHOR]

Rarefaction wave gun can significantly reduce the recoil and the barrel heat without affecting projectile velocity during the launching process. This paper aims to improve the understanding of the muzzle flow characteristics during a rarefaction wave gun firing and clarify the different ballistic behaviors between the rarefaction wave gun and the traditional gun. First, the mathematical models and the numerical methods of the muzzle flow with the interior ballistic process were established. Then, the numerical simulation results were compared with the experimental data to validate the reliability and accuracy. Next, the rarefaction wave propagation behavior was described, and the interior ballistic process of the rarefaction wave gun was compared with that of the traditional gun. Then the development law of the muzzle flow field for the rarefaction wave gun coupled with the interior ballistics process was studied. Finally, the different detailed results of the muzzle flow between the traditional gun and the rarefaction wave gun were investigated. The development processes of the muzzle flow in both guns are generally similar, but the strength of the main flow parameters and the ballistic performances for the rarefaction wave gun are smaller than that for the traditional gun due to the rarefaction wave influence. This paper could provide a valuable reference for the research and design on the rarefaction wave gun. [ABSTRACT FROM AUTHOR]

In this paper, a delayed mosquito population suppression model with stage and sex structure is constructed incorporating periodic releases of the sterile mosquito and its sexual lifespan. Sterile mosquitoes are released periodically into the field to suppress the wild mosquito population, and only sexually active sterile mosquitoes are included in the interaction system of these two populations. According to the relationship between the release period T$$ T $$ and the sexual lifespan T1$$ {T}_1 $$, we study the dynamic behaviors of the system, such as the existence of positive periodic solutions and the stability of extinction equilibrium in three cases. A series of numerical simulations are performed, which not only verify the reliability of the theoretical results but also make a numerical analysis of the open problems raised in the theoretical research. [ABSTRACT FROM AUTHOR]

For all humanity, the sudden outbreak of Corona Virus Disease 2019 has been an important problem. Timely and effective media coverage is considered to be one of the effective approaches to control the spread of epidemic in early stage. In this paper, a Sentiment‐enabled Susceptible‐Exposed‐Infected‐Recovered (SEIR) model is established to reveal the relationship between the propagation of the epidemic and media coverage. The authors take the positive and negative media coverage into consideration when implementing the Sentiment‐enabled SEIR model. This model is constructed by parameterizing the number of current confirmed cases, cumulative cured cases, cumulative deaths, and media coverage. The numerical simulation and sensitivity analysis are conducted based on the Sentiment‐enabled SEIR model. The numerical analysis confirms the rationality of the Sentiment‐enabled SEIR model. The sensitivity analysis shows that positive media coverage acts a pivotal part in reducing the figure for confirmed cases. Negative media coverage has an effect on the figure for confirmed cases is not as significant as that of positive media coverage, but it is not negligible. [ABSTRACT FROM AUTHOR]

The aim of this paper is to establish a precise illustration for the structure of the nonconstant steady states for a Beddington–DeAngelis and Tanner predator–prey reaction–diffusion system with prey‐taxis. We treat the nonlinear prey‐taxis as a bifurcation parameter to analyze the bifurcation structure of the system. Furthermore, the exported global bifurcation theorem, under a rather natural condition, offers the existence of nonconstant steady states. In the proof, a priori estimates of steady states will play an important role. The local stability analysis with a numerical simulation and bifurcation analysis are given. Finally, some conclusions including biological meanings are performed to summarize our main analytic results and future investigations. [ABSTRACT FROM AUTHOR]

This paper presents a novel perspective on fully distributed adaptive protocol design for bipartite consensus under directed communication graphs. It is revealed that the fully distributed protocol is indeed a PI‐gain design approach. Based on such PI‐gain method, fully distributed observer‐based protocols are proposed to solve the consensus problem of nonlinear multi‐agent systems over directed cooperative‐antagonistic networks, where the neural network approximation is introduced to tackle the unknown nonlinearity. Fully distributed continuous protocols are further presented by modifying the sign function with a decaying variable, which takes the advantage of avoiding chattering problem. Theoretical analysis and numerical simulations are given to support our main results. [ABSTRACT FROM AUTHOR]

Since the pioneering work of Turing, it has been known that diffusion can destablise a homogeneous solution that is stable in the underlying model in the absence of diffusion. The destabilisation of the homogeneous solutions leads to the generation of patterns. In recent years, techniques have been developed to analyse so‐called localised spatial structures. These are solutions in which the spatial structure occurs in a localised region. Unlike Turing patterns, they do not spread out across the whole domain. We investigate the existence of localised structures that occur in two predator‐prey models. The functionalities chosen have been widely used in the literature. The existence of localised spatial structures has not investigated previously. Indeed, it is easy to show that these models cannot exhibit the Turing instability. This has perhaps led earlier researchers to conclude that interesting spatial solutions can therefore not occur for these models. The novelty of our paper is that we show the existence of stationary localised patterns in systems which do not undergo the Turing instability. The mathematical tools used are a combination of Linear and weakly nonlinear analysis with supporting numerical methods. By combining these methods, we are able to identify conditions for a wide range of increasing exotic behaviour. This includes the Belyckov‐Devaney transition, a codimension two spatial instability point and the formation of localised patterns. The combination of spectral computations and numerical simulations reveals the crucial role played by the Hopf bifurcation in mediating the stability of localised spatial solutions. Finally, numerical solutions in two spatial dimensions confirms the onset of intricate spatio‐temporal patterns within the parameter regions identified within one spatial dimension. [ABSTRACT FROM AUTHOR]

The purpose of this article is to report on improvements on the interpretation and insights emerging from dynamic decomposition weight analysis (DDWA). These improvements emerged from efforts to further automate and expand the eigenvalue elasticity analysis methods and resolve inconsistencies in assumptions made in published reports of DDWA usage. In addition to making available to the broad system dynamics community an improved toolset to perform eigenvalue elasticity analysis, in this paper we clarify the set of assumptions needed to obtain reliable results and develop a new framework to assess the impact of model parameters on the projections of behavior modes on stock behavior. We illustrate the use of these developments by updating a previously published model analysis. The paper concludes by summarizing our findings and their implications for the further development of structural dominance analysis. © 2018 System Dynamics Society [ABSTRACT FROM AUTHOR]

Parylene C flyer coated with copper film was often used to shock and initiate insensitive explosives in exploding foil initiator (EFI). However, there were few studies on the acceleration process of parylene C−Cu flyer and the shock initiation induced by parylene C−Cu flyer. In this paper, exploding bridge foil was treated as a kind of special explosive to launch parylene C−Cu flyer, and an instantaneous explosion model was established to describe the acceleration process mathematically. Then, two‐dimensional numerical simulations were carried out using ANSYS/AUTODYN software to analyse the flight history and morphology of parylene C−Cu flyer, as well as the effect of copper film on flyer velocity. Finally, shock initiation of parylene C−Cu flyer impacting ultrafine hexanitrostilbene (HNS‐IV) was also simulated, and the initiation threshold was determined by adjusting the flyer velocity at the collision moment. Compared with previous work, calculated results exhibit good agreement with the experimental data, that is addition of Cu film can indeed improve the shock pressure but leads to lower flyer velocity. For parylene C−Cu flyer with the thickness of 25 μm–3.6 μm, its flyer velocity drops to half of parylene C flyer under same operation conditions, and the initiation threshold that can initiate the HNS‐IV pellet is 2300 m/s. All the results demonstrate that the numerical approach will be useful for the optimization of parylene C−Cu flyer, even any kind of multi‐layer flyer. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we develop new governing equations for thermo‐gradient‐dependent theory of plasticity. They include the coupled effects of thermal elastic‐plastic theory, including balance and constitutive equations. To demonstrate the salient feature of the gradient‐dependent model of plasticity, particular attention is addressed to isotropic hardening with second sound effects to eliminate the paradox of infinite speed of thermal signals. The resulting system of partial differential equations formally describes the coupled thermomechanical behavior of the gradient‐dependent elasto‐plastic system. Then, we develop an appropriate state‐space form and, by using the semigroup theory, we prove the well‐posedness and the exponential stability of the thermo‐gradient‐dependent elasto‐plastic one‐dimensional problem. Finally, we perform numerical simulations to validate the proposed model and to show its capability. [ABSTRACT FROM AUTHOR]

gggggAssume that an n × n dot matrix is stored in consecutive n words of a computer with one word being n bit. This paper discusses eight operations to rotate or transpose the dot matrix in horizontal/vertical! slant direction. As is well known, such operations form a group. This paper presents a unified description of the algorithms, and it is shown that all eight algorithms can be derived by suit- ably setting the constants in the unified algorithm. Then it is shown that the algorithms can be transformed to each other by simple transformation rules for the constants, and those transformation rules are shown to form a group. The foregoing algorithms for the dot matrix are not unique, and there can be different descriptions for the algorithm producing the same result. Consequently, there can be various versions of the eight algorithms as well as versions of transformation rules. This paper shows that one of the two groups formed by the transformation rules is isomorphic to the group of algorithms, but the other is not isomorphic. [ABSTRACT FROM AUTHOR]

Anomalous diffusion problems are used to describe the evolution of particle's motion in crowded environments with many applications, such as modeling the intracellular transport and disordered media. In the present paper, we develop a Petrov–Galerkin spectral method for the fourth‐order anomalous fractional diffusion equations. For the dimension reduction, we use a discretization in time by the convolution quadrature. We then introduce the basis sets for the trial‐and‐test spaces using modal Bernstein basis functions with a presentation of the method in a weak spectral formulation along with a discussion of the structure of the resulting systems, the convergence, and stability of the proposed method. The theoretical results are supported by illustrating some numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, an efficient numerical procedure for the generalized nonlinear time‐fractional Klein–Gordon equation is presented. We make use of the typical finite difference schemes to approximate the Caputo time‐fractional derivative, while the spatial derivatives are discretized by means of the cubic trigonometric B‐splines. Stability and convergence analysis for the numerical scheme are discussed. We apply our scheme to some typical examples and compare the obtained results with the ones found by other numerical methods. The comparison shows that our scheme is quite accurate and can be applied successfully to a variety of problems of applied nature. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, a propagator matrix method applied to logging-while-drilling tools is introduced and extended to deal with the anisotropic and radially inhomogeneous earth formations. This method expands the Maxwell's equations in the transverse direction, constructs the relationship between propagator matrix and reflection matrix, and obtains the solution by using the reflection matrix. We systematically derived the formulas of propagator matrix method in isotropic media, uniaxially anisotropic media, fully anisotropic media, and radially inhomogeneous media respectively. In order to obtain the propagator matrix in complex media, we used the fourth-order Runge-Kutta scheme. Numerical experiments show that, compared with traditional methods, the propagator matrix method has wide range of applications while maintaining low computational costs and high accuracy. All algorithms presented in the paper have been parallelized and implemented on a high-performance computing platform. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we study a one-dimensional morphogenesis model considered by C. Stinner et al. (Math. Meth. Appl. Sci. 2012; 35: 445-465). Under homogeneous boundary conditions, we prove the existence of nonconstant positive steady states through local bifurcation theories. Then we rigorously study the stability of these nonconstant solutions when the sensitivity functions are chosen to be linear and logarithmic, respectively. Finally, we present numerical solutions to illustrate the formation of stable inhomogeneous spatial patterns. Our numerical simulations show that this model can develop very complicated and interesting structures even over one-dimensional finite domains. [ABSTRACT FROM AUTHOR]

The three‐dimensional displacement of two‐phase flow in porous media is a preliminary problem of numerical simulation of energy science and mathematics. The mathematical model is formulated by a nonlinear system of partial differential equations to describe incompressible miscible case. The pressure is defined by an elliptic equation, and the concentration is defined by a convection‐dominated diffusion equation. The pressure generates Darcy velocity and controls the dynamic change of concentration. We adopt a conservative block‐centered scheme to approximate the pressure and Darcy velocity, and the accuracy of Darcy velocity is improved one order. We use a block‐centered upwind multistep method to solve the concentration, where the time derivative is approximated by multistep method, and the diffusion term and convection term are treated by a block‐centered scheme and an upwind scheme, respectively. The composite algorithm is effective to solve such a convection‐dominated problem, since numerical oscillation and dispersion are avoided and computational accuracy is improved. Block‐centered method is conservative, and the concentration and the adjoint function are computed simultaneously. This physical nature is important in numerical simulation of seepage fluid. Using the convergence theory and techniques of priori estimates, we derive optimal estimate error. Numerical experiments and data show the support and consistency of theoretical result. The argument in the present paper shows a powerful tool to solve the well‐known model problem. [ABSTRACT FROM AUTHOR]

Precast concrete elements are commonly employed in the construction industry, however failing to comply with manufacturers' guidelines and poor construction practice can lead to loss of efficiency compromising the usability of the building. This paper presents two case studies where ground penetrating radar surveys, performed to investigate the cause of failure of precast concrete elements, were supported by the finite difference time domain numerical approach. In the first case, the model was built after the survey for a better understanding of the complex reflection patterns unexpectedly experienced and to provide a clear interpretation; in the second case, the numerical simulation was performed prior to the survey, according to the information already available on the precast unit. The synthetic radargrams were then used as a valuable reference to assess the precast element internal conditions: on site, the comparison of the real radargrams with the synthetic ones allowed to address safely the intrusive works necessary to determine the concrete quality and during the processing step, any deviation from the ideal ground penetrating radar response gave potentially an indication of anomalies in the assembly operations that could be identified. The finite difference time domain method should then be considered as complementary to ground penetrating radar surveys aimed to investigate precast elements. [ABSTRACT FROM AUTHOR]

The increase in extraction height will increase the mining‐induced overlying strata failure height. In this scenario, the strata pressure behavior is strong in a fully mechanized face with large mining height (FMFLMH), which frequently causes coal wall falls, roof falls, and hydraulic support failure accidents (e.g., support closure and hydraulic column damage). The key to solving these issues is to determine support's working resistance of the FMFLMH. In this paper, comprehensive theoretical analysis, numerical simulation, and field observation were applied to determine the support's working resistance in the FMFLMH based on movement type of the first subordinate key stratum (SKS 1). First, six kinds of movement types of SKS 1 in the FMFLMH are found and defined by theoretical analysis and numerical simulation, which are the direct caving movement type of cantilever structure (direct caving), the double‐sided rotation movement type of cantilever structure (double‐side rotation), the quadratic rotation movement type of cantilever structure (quadratic rotation), the alternative movement type of cantilever structure hinged structure (alternate hinged), the voussoir beam structure movement type (voussoir), and the short voussoir beam structure movement type (short voussoir), respectively. Besides, based on this, the support load calculation model of each movement type was established, and a formula for the support working resistance of each movement type was obtained. Finally, the correctness of the formulae for the support working resistance under six types of movement of SKS 1 were verified using measurement data from four FMFLMHs in China. These research results have important guiding significance for reasonable selection of support and ensuring safe mining of the FMFLMH. [ABSTRACT FROM AUTHOR]

Eulerian‐based smoke simulations are sensitive to the initial parameters and grid resolutions. Due to the numerical dissipation on different levels of the grid and the nonlinearity of the governing equations, the differences in simulation resolutions will result in different results. This makes it challenging for artists to preview the animation results based on low‐resolution simulations. In this paper, we propose a learning‐based flow correction method for fast previewing based on low‐resolution smoke simulations. The main components of our approach lie in a deep convolutional neural network, a grid‐layer feature vector and a special loss function. We provide a novel matching model to represent the relationship between low‐resolution and high‐resolution smoke simulations and correct the overall shape of a low‐resolution simulation to closely follow the shape of a high‐resolution down‐sampled version. We introduce the grid‐layer concept to effectively represent the 3D fluid shape, which can also reduce the input and output dimensions. We design a special loss function for the fluid divergence‐free constraint in the neural network training process. We have demonstrated the efficacy and the generality of our approach by simulating a diversity of animations deviating from the original training set. In addition, we have integrated our approach into an existing fluid simulation framework to showcase its wide applications. [ABSTRACT FROM AUTHOR]

Fused deposition modeling based 3D‐printing is becoming increasingly popular due to it's low‐cost and simple operation and maintenance. While it produces rugged prints made from a wide range of materials, it suffers from an inherent printing limitation where it cannot produce overhanging surfaces of non‐trivial size. This limitation can be handled by constructing temporary support‐structures, however this solution involves additional material costs, longer print time, and often a fair amount of labor in removing it. In this paper we present a new method for partitioning general solid objects into a small number of parts that can be printed with no support. The partitioning is computed by applying a sequence of cutting‐planes that split the object recursively. Unlike existing algorithms, the planes are not chosen at random, rather they are derived from shape analysis routines that identify and resolve various commonly‐found geometric configurations. In addition, we guide this search by a revised set of conditions that both ensure the objects' printability as well as realistically model the printing capabilities of the printer at hand. Evaluation of the new method demonstrates its ability to efficiently obtain support‐free partitionings typically containing fewer parts compared to existing methods that rely on support‐structures. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a novel operator splitting approach for corotated FEM simulations. The deformation energy of the corotated linear material model consists of two additive terms. The first term models stretching in the individual spatial directions and the second term describes resistance to volume changes. By formulating the backward Euler time integration scheme as an optimization problem, we show that the first term is invariant to rotations. This allows us to use an operator splitting approach and to solve both terms individually with different numerical methods. The stretching part is solved accurately with an optimization integrator, which can be done very efficiently because the system matrix is constant over time such that its Cholesky factorization can be precomputed. The volume term is solved approximately by using the compliant constraints method and Gauss‐Seidel iterations. Further, we introduce the analytic polar decomposition which allows us to speed up the extraction of the rotational part of the deformation gradient and to recover inverted elements. Finally, this results in an extremely fast and robust simulation method with high visual quality that outperforms standard corotated FEMs by more than two orders of magnitude and even the fast but inaccurate PBD and shape matching methods by more than one order of magnitude without having their typical drawbacks. This enables a very efficient simulation of complex scenes containing more than a million elements. [ABSTRACT FROM AUTHOR]

Summary: This paper investigates the distributed tracking control of a group of underactuated quadrotors in the presence of actuator faults in three‐dimensional space. Using consensus protocol and sliding mode algorithm, a distributed finite‐time fault‐tolerant formation control scheme is developed. The whole closed‐loop system is composed by position loop, attitude loop, and propeller speed loop. A propeller speed fault‐tolerant controller is developed to deal with the unexpected faults of quadrotors. The finite‐time stability of the closed‐loop system is guaranteed through Lyapunov analysis. Finally, the efficiency of the proposed algorithm is illustrated by some numerical simulations. [ABSTRACT FROM AUTHOR]

SUMMARY This paper focuses on the assessment of a discontinuous Galerkin method for the simulation of vortical flows at high Reynolds number. The Taylor-Green vortex at Re = 1600 is considered. The results are compared with those obtained using a pseudo-spectral solver, converged on a 5123 grid and taken as the reference. The temporal evolution of the dissipation rate, visualisations of the vortical structures and the kinetic energy spectrum at the instant of maximal dissipation are compared to assess the results. At an effective resolution of 2883, the fourth-order accurate discontinuous Galerkin method (DGM) solution ( p = 3) is already very close to the pseudo-spectral reference; the error on the dissipation rate is then essentially less than a percent, and the vorticity contours at times around the dissipation peak overlap everywhere. At a resolution of 3843, the solutions are indistinguishable. Then, an order convergence study is performed on the slightly under-resolved grid (resolution of 1923). From the fourth order, the decrease of the error is no longer significant when going to a higher order. The fourth-order DGM is also compared with an energy conserving fourth-order finite difference method (FD4). The results show that, for the same number of DOF and the same order of accuracy, the errors of the DGM computation are significantly smaller. In particular, it takes 7683 DOF to converge the FD4 solution. Finally, the method is also successfully applied on unstructured high quality meshes. It is found that the dissipation rate captured is not significantly impacted by the element type. However, the element type impacts the energy spectrum in the large wavenumber range and thus the small vortical structures. In particular, at the same resolution, the results obtained using a tetrahedral mesh are much noisier than those obtained using a hexahedral mesh. Those obtained using a prismatic mesh are already much better, yet still slightly noisier. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY The multiport scattering (S-) parameter matrix is increasingly utilized to compose models of large bit-width interconnect systems with broadband characteristics (frequency range of zero to tens of gigahertz) to perform increasingly accurate signal-integrity and power-integrity simulations. The search for an optimal solution space often requires generation of S-parameter models of interconnect systems for various signal/ground pin mappings, a process that can be computationally costly if the structure is electromagnetically solved for each distinct pin mapping. To expedite this model-generation process, we propose a method in which an N-port structure is electromagnetically solved only once to yield an N × N S-matrix; then, a linear system is formulated and solved to yield an ( N − M) × ( N − M) post-suppressed S-matrix (where M is the number of suppressed ports). This approach results in significant computational savings through elimination of electromagnetic field-solver runs for each distinct pin mapping. Included in this paper is a discussion about the limitations of this technique and several numerical examples. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: Aiming to accurately simulate seismic dynamic response of rock masses using the numerical manifold method (NMM), boundary settings must be treated carefully. In this paper, 4 issues in boundary settings are investigated to improve the performance of NMM: (1) Nonreflecting boundaries including the viscous boundary and viscoelastic boundary are considered; (2) A free‐field boundary is incorporated into NMM to accurately simulate external source wave motion; (3) A seismic input boundary is considered, and the force input method is introduced; and (4) A static‐dynamic unified boundary is incorporated for the convenience of transforming displacement boundary into other types of boundaries, such as nonreflecting boundaries and seismic input boundary. Several benchmark problems are solved to validate the improved NMM. Simulation results agree well with analytical ones, indicating that the improved NMM is able to simulate seismic dynamic response of rock masses reliably and correctly. [ABSTRACT FROM AUTHOR]

Abstract: This paper summarizes a numerical and experimental investigation of free convective heat transfer in an open‐ended cavity between two horizontal parallel circular plates. The upper plate is maintained at an ambient temperature and the lower one is heated. Air is used as the heat transfer medium. The numerical model equations are solved using a control volume‐based finite differences method, and the experimental study was performed using holographic interferometry. Streamlines and isotherm patterns are presented and discussed for different aspect ratios (A) and Rayleigh numbers (Ra). Heat transfer at the surface of the lower plate is thoroughly inspected in the ranges 0.1 ≤ A ≤ 1 and 10 2 ≤ R a ≤ 5 × 10 6. Useful correlations of Nusselt numbers in terms of R a and A are given with their validity ranges. Also, an investigation of both numerical and experimental results is performed. It shows similar temperature field aspect with some differences in the radial boundary layer thickness and a small deviation in the heat transfer. [ABSTRACT FROM AUTHOR]

When experimental resources are significantly constrained, resolution V fractional factorial designs are often prohibitively large for experiments with 6 or more factors. Resolution IV designs may also be cost prohibitive, as additional experimentation may be required to de-alias active 2-factor interactions (2FI). This paper introduces 20-run no-confounding screening designs for 6 to 12 factors as alternatives to resolution IV designs. No-confounding designs have orthogonal main effects, and since no 2FI is completely confounded with another main effects or 2FI, the experimental results can be analyzed without follow-on experimentation. The paper concludes with the results of a Monte Carlo simulation used to assess the model-fitting accuracy of the recommended designs. [ABSTRACT FROM AUTHOR]

Reliability demonstration test (RDT) is a critical and necessary step before the acceptance of an industrial system. Generally, a RDT focuses on designing a test plan through which one can judge whether the system reliability indices meet specific requirements. There are many established RDT plans, but few have incorporated the reliability growth aspects of the corresponding products. In this paper, we examine a comprehensive test plan that involves information concerning the reliability growth stage. An approach for RDT under the assumption of the power-law model is proposed. It combines data related to the growth stage with those pertaining to the test stage of the product to reduce the cost of the test. Through simulation studies and numerical examples, we illustrate the characteristics of the test plan and significant reduction in test costs through our approach. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we consider a three-dimensional viral model with delay. We first investigate the linear stability and the existence of a Hopf bifurcation. It is shown that Hopf bifurcations occur as the delay τ passes through a sequence of critical values. Then, using the normal form theory and center manifold reduction, we derive the explicit formulaes that determine the stability, the direction, and the period of bifurcating periodic solutions. Numerical simulations are carried out to illustrate the validity of the main results. Finally, some brief conclusions are given. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Numerical modelling plays an important role in helping us understand the characteristics of seismic wave propagation. The presence of spurious reflections from the boundaries of the truncated computational domain is a prominent problem in finite difference computations. The nearly perfectly matched layer has been proven to be a very effective boundary condition to absorb outgoing waves in both electromagnetic and acoustic media. In this paper, the nearly perfectly matched layer technique is applied to elastic isotropic media to further test the method's absorbing ability. The staggered-grid finite-difference method (fourth-order accuracy in space and second-order accuracy in time) is used in the numerical simulation of seismic wave propagation in 2D Cartesian coordinates. In the numerical tests, numerical comparisons between the nearly perfectly matched layer and the convolutional perfectly matched layer, which is considered the best absorbing layer boundary condition, is also provided. Three numerical experiments demonstrate that the nearly perfectly matched layer has a similar performance to the convolutional perfectly matched layer and can be a valuable alternative to other absorbing layer boundary conditions. [ABSTRACT FROM AUTHOR]

In this paper, the second in a series, the accuracy and performance of the high-order spectral volume (SV) method for moment models in device simulations is enhanced by employing the penalty and BR2 formulations for discretizing the second derivative diffusive fluxes. The potential equation is also discretized using the above formulations. The actual accuracy and the numerical orders are obtained by performing accuracy studies. An n -n-n diode was assumed for simulation purposes. The results obtained by solving steady-state hydrodynamic (HD) and energy transport (ET) models are compared with the existing local discontinuous Galerkin formulation (LDG) results. The newer formulations yield more accurate solutions than the ones which used the LDG formulation. In addition, the newer formulations converge to steady state much faster than the LDG formulation. The BR2 formulation is compact and hence can be easily parallelized. The penalty formulation is however not compact. In general, the numerical results are very promising and indicate that the newer diffusive flux formulations are more accurate, converge faster, have greater potential and hence are suited better than the LDG for higher dimensional device problems. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper demonstrates the capability of our previously published undoped Double-Gate (DG) MOSFET explicit and analytical compact model to also forecast the effect of the volume inversion (VI) on the intrinsic capacitances. For that purpose, we present simulation results for these capacitances. We show now that the model presents an accurate dependence on the silicon layer thickness, consistent with two-dimensional numerical simulations, for both thin and thick silicon films. As opposed to our previous work, here we test the capacitance model for three different film thicknesses and also show that the transition from VI regime to dual gate behaviour is well simulated. We demonstrate in this paper that even if the current drive and transconductance are enhanced in VI regime, our results show that intrinsic capacitances are higher as well, which may limit the high-speed (delay time) behaviour of DG MOSFETs under VI regime. The good agreement between the numerical simulations and our model shows the high potential of our complete DG MOSFET model. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this article is to propose an exact SPECT region of interest (ROI) reconstruction method using truncated transmission and truncated emission data. Methods: Recently, the authors published two articles in Physics in Medicine and Biology with two results in SPECT ROI emission image reconstruction. The first result states that if the transmission data are truncated but the emission data are not truncated, the emission image can be exactly reconstructed, provided the entire emission image is inside the region where the transmission data are not truncated. The second result states that if the transmission data are not truncated, the emission ROI can be exactly reconstructed with truncated emission data. This article combines these two results and obtains a new result that the emission ROI can be exactly reconstructed if both transmission and emission data are truncated. Results: Computer simulations are performed to verify the proposed ROI image reconstruction algorithm. Conclusions: Exact SPECT ROI image reconstruction is possible using truncated transmission and emission projections with some prior information about the attenuator and the emission distribution. [ABSTRACT FROM AUTHOR]

This paper presents an innovative method for naturally and smoothly morphing point-sampled surfaces via dynamic meshless simulation on point-sampled surfaces. While most existing literature on shape morphing emphasizes the issue of finding a good correspondence map between two object representations, this research primarily investigates the challenging problem of how to find a smooth, physically-meaningful transition path between two homeomorphic point-set surfaces. We analyze the deformation of surface involved in the morphing process using concepts in differential geometry and continuum mechanics. The morphing paths can be determined by optimizing an energy functional, which characterizes the intrinsic deformation of the surface away from its rest shape. As demonstrated in the examples, our method automatically produces a series of natural and physically-plausible in-between shapes, which greatly alleviates the shrinking, stretching, and self-intersection problems that often occur when linear interpolation is employed for the morphing of two objects. We envision that our new technique will continue to broaden the application scope of point-set surfaces and their dynamic animation. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We describe a representation for tree leaves and an interactive modeling system for creating realistic close-up images of leaf clusters. The planar outline of the leaf and the larger members of its venation system are strong factors in the recognition of plant species and as such are essential to realistic imaging. The larger veins also play a major biological role in determining the leaf surface shape and it is this role that we mimic in the shape modeling discussed in this paper. The proposed representation uses a model of a leaf consisting of a three-dimensional skeleton formed by its larger veins and a surface membrane representing the leaf lamina that spans the void between the veins. The veins play two roles. They can be interactively modified to create the 3-D shape of the leaf model. They also provide for realistic light and shadow effects when rendered as generalized cylinders using measured width parameters. The representation consists of two coupled data structures, a tree data structure of veins for the leaf skeleton and an unstructured triangular mesh for the leaf membrane. The skeleton is modified by the user of the modeling system, and the membrane mesh is a surface mesh that follows the skeleton shape computed using harmonic interpolation. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Structure-soil-structure interaction (SSSI) phenomena under earthquake excitations are investigated in this paper. Based on the results of the shaking table test, this work presents a 3-dimensional finite element numerical simulation method using ANSYS software. In the simulation, an equivalent linear model is assumed for soil behavior, and contact elements are adopted to consider the nonlinearity state of the interface between foundation and surrounding soil. In addition, constrained equations are added to manage the uncoordinated degrees of freedom. By comparing the results of the finite element analysis with data obtained from the shaking table test, the dynamic response of the shaking table test can be simulated properly. Finally, the dynamic response of adjacent structures considering the SSSI effect is analyzed. The results show that with increased excitation, contact pressure, strain amplitude, and pile slip increase, whereas the peak acceleration magnification coefficient decreases. These results are significant for studying the effect of SSSI on seismic responses of structures. [ABSTRACT FROM AUTHOR]

In this paper, a protocol and a control law are designed for a single robot so that a team of such robots can interact and cooperate to reach the displacements from an eligible reference formation. Each robot is equipped with displacement sensors of limited sensing ranges. Communication channels are assumed to be unavailable to the team, and each robot works in stealth mode. The team is scalable such that new robots can be recruited, and existing robots can be dismissed. In order for the team size to be scalable, the extended formation based on relative displacement is established as the reference formation. Thus, using the extended formation as a reference, the control law and the protocol could be flexible. As potential conflicts deflect the robot team from the desired formation, the control law is designed to expose the conflicts to the involved neighboring robots such that the protocol can resolve them. A numerical example is given to illustrate how an extended formation is designed, and a simulation example is conducted to demonstrate the performance and merits of the proposed techniques. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The human shoulder is a complicated musculoskeletal structure and is a perfect compromise between mobility and stability. The objective of this paper is to provide a thorough review of previous finite element (FE) studies in biomechanics of the human shoulder complex. Those FE studies to investigate shoulder biomechanics have been reviewed according to the physiological and clinical problems addressed: glenohumeral joint stability, rotator cuff tears, joint capsular and labral defects and shoulder arthroplasty. The major findings, limitations, potential clinical applications and modelling techniques of those FE studies are critically discussed. The main challenges faced in order to accurately represent the realistic physiological functions of the shoulder mechanism in FE simulations involve (1) subject-specific representation of the anisotropic nonhomogeneous material properties of the shoulder tissues in both healthy and pathological conditions; (2) definition of boundary and loading conditions based on individualised physiological data; (3) more comprehensive modelling describing the whole shoulder complex including appropriate three-dimensional (3D) representation of all major shoulder hard tissues and soft tissues and their delicate interactions; (4) rigorous in vivo experimental validation of FE simulation results. Fully validated shoulder FE models would greatly enhance our understanding of the aetiology of shoulder disorders, and hence facilitate the development of more efficient clinical diagnoses, non-surgical and surgical treatments, as well as shoulder orthotics and prosthetics. © 2016 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Identifying vortices is the key to understanding the turbulence in plasma shear layers. This paper aims to provide general guidelines for identifying 3‐D vortex structures. Currently, no single precise definition of a vortex is universally accepted, despite the significance of vortices in fluid and plasma dynamics. Recently, various vortex identification methods using Galilean invariance have been proposed by numerous researchers. These methods are general for different fluid and plasma visualization applications. In the present paper, we describe how we have identified 105 vortex structures by applying these methods to Cluster data near the duskside of the magnetopause. Four sets of Cluster satellite magnetic field data are used to linearly approximate the magnetic field. We identify the 3‐D magnetic vortex structures by using various vortex identification criteria as follows: (i) the first criterion is Q‐criterion that defines vortices as regions in which the vorticity energy prevails over other energies; (ii) the second criterion is the λ2‐criterion that is related to the minus eigenvalue of the Hessian matrix of the pressure terms; and (iii) the third criterion called the geometrical line‐type method requires the existence of Galilean‐invariant vortex core inside the four Cluster tetrahedral regions. In reality, both Q‐ and λ2‐criteria are also related to Galilean invariance. The present analysis evidences that the geometrical line‐type method is more precise than the other two using Cluster satellite magnetic field data. Key Points: 3‐D vortex detection technique is developed and applied to tetrahedral satellite configurationFirst time in the world, 3‐D vortex structures are detected using Cluster satellite in space at/around magnetopauseWe found almost the same number of clockwise and counterclockwise rotation vortices that suggests possible existence of double vortex rows [ABSTRACT FROM AUTHOR]

The digital sinusoidal oscillator considered in this paper is one of the signal sources employed in the digital signal processing system. A construction of the oscillator is discussed where the memory capacity is reduced and the increasing rate of the noise is suppressed by interpolating the output of the oscillator of table look-up type or feedback type. A design method for the interpolation filter is presented first where no interpolation error is produced if the coefficient wordlength of the interpolation filter is infinite. Then, considering the case where the wordlength is kept finite, the hold-type sampling expander is proposed where the waveform distortion is kept low compared with the traditional zero-interpolation-type sampling rate expander. The distortion in the proposed method is analyzed where the wordlength of the interpolation filter coefficient is kept finite, and the waveform distortion is shown to be low. The increasing rate of the round-off error is examined by a computer simulation for the oscillator, which is obtained by applying the interpolation to the feedback-type oscillator. The effectiveness of the interpolation is demonstrated. Finally, a construction of the block-digital sinusoidal oscillator is shown with a smaller hardware complexity than in the traditional method, by constructing the block-structured oscillator by realizing the proposed interpolation filter as a polyphase filter. [ABSTRACT FROM AUTHOR]

An adaptive digital. filter (orthogonal function-type ADF) composed of an orthogonal function system which can locate poles of a transfer function in arbitrary positions in the unit circle in the z plane is known as a way to improve convergence speed in the case in which input is a colored signal (such as voice). However, no sufficient theoretical investigation has been done on the reason why this ADF rapidly converges to the colored signal input. This paper derives an equivalent circuit of an orthogonal function-type ADF in the case in which poles of a transfer function are located in equal space on the unit circle in the z plane. Then the convergence speed using this equivalent circuit is considered. It is shown that the orthogonal function-type ADF is equivalent to a construction due to a periodic process of an input of the known ADF using the frequency sampling filter (frequency sampling-type ADF). In other words, even if Input is colored like voice and aperiodic process, in the orthogonal function type it is shown that orthogonality between tap coefficient inputs is preserved. Furthermore, these studied results are verified by computer simulations. [ABSTRACT FROM AUTHOR]

One of the most important measures for the construction of the active RC filter is the element sensitivity. One of the effective means to reduce the element sensitivity is the method to simulate the conventional LC filter with both ends terminated by resistors, This paper considers the realization of the low-pass filter by I,C simulation using GIC or by the node-voltage simulation. The prototype LC filter is discussed to solve the bias instability problem, which is a problem in the realization. First, an LC filter is proposed which is obtained by adding an inductor in parallel with the input resistor of the conventional doubly terminated LC filter. The method of constructing the filter is discussed. Then a method is presented to simulate the filter using GIC. Finally, the 5th-order Chebyshev low-pass filter is constructed and its characteristics are measured. The element sensitivity is analyzed using a computer, and it is verified that the proposed circuit has a low element sensitivity. [ABSTRACT FROM AUTHOR]

This paper describes the basic items needed for design and simulation of optical integrated circuits and analysis tools for optical waveguides. Because the finite element method and beam propagation method are emphasized, the scalar wave approximation (which has been extensively used) is used in the discussion. In addition, using examples of analyses on various optical integrated circuits, the design and simulation technologies for optical integrated circuits will be introduced. [ABSTRACT FROM AUTHOR]

Differential PCM (DPCM) has often been used for encoding of images, but its efficiency is very poor at low transmission rates. Discussion of DPCM is based on an autoregressive (AR) model which is causal In the case of raster scan sampling. However, originally, images do not satisfy causality in this sense, and a better description of the two-dimensional image Information can be obtained by an interpolative model representing the relations between neighboring pixels. This paper proposes a two-dimensional interpolative DPCM which is based on such a model. This method has the following special feature: if the output samples of a DPCM process based on a causal AR model are regarded as intermediate decoded values, then the final decoded values are yielded by a filtering process based on an Interpolative model. The results of simulation using actual images demonstrate SN ratio improvement at a low bit rate (1 bit/pel) and also the stability of encoding characteristics in the case of quantitative step-size variations. It is shown that fixing of the prediction and interpolation coefficients results only in slight deterioration. [ABSTRACT FROM AUTHOR]

This paper presents an adapted Gummel method (AGM) used in the two-dimensional device simulation of an amorphous-silicon (a-Si) thin-film transistor (TFT). Firstly, the AGM for amorphous silicon is developed by modifying the Gummel method (GM) for crystalline silicon. Secondly, the AGM is implemented into a two-dimensional device simulator for the simulation of a-Si TFTs. The simulation results show that the AGM converges well while the GM fails to converge for the simulation of a-Si TFTs. Hence, the AGM is a useful technique for the simulation and analysis of a-Si TFTs. © 1997 by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Coupling multiphysical systems by means of a co-simulation, the data between the subsystems are interchanged at a discrete macro time grid, also denoted as communication time grid. Between the communication points the coupling variables are approximated so that the numerical solvers in the subsystems can calculate the differential equations. Classical approximation techniques based on extrapolation entail a discontinuity in the equations in each macro time step which can slow down the numerical time integration. In the paper at hand a C0-continuous technique for approximating the coupling variables is reconsidered and the numerical stability and the local error of the method are compared to the classical Lagrange approximation approach. Further, the method is enhanced to a C1-continuous (continuous and differentiable) approximation technique. Both methods are investigated in combination with different numerical coupling approaches (sequential Gauss-Seidel scheme, parallel Jacobi scheme, force/displacement coupling, displacement/displacement coupling) which are commonly applied for co-simulation in technical applications. It is shown that the C1-continuous approximation technique yields a similar numerical stability and a similar local error as the Lagrange approach which results in a comparable or even better overall performance (taking into account the advantage of continuity at the numerical calculation of the subsystem differential equations). Applying the C0-continuous approach, a similar numerical stability is obtained. However, the order of the local error is significantly lower than for the C1-continuous method and the Lagrange approach. [ABSTRACT FROM AUTHOR]

The transport mechanism of chloride ions in concrete during wetting and drying cycles of varying duration is evaluated in this paper. The experimental test results were used to validate a numerical simulation model in order to assess the influence of diffusion coefficient, surface chloride ion concentration and ratio of dry-wet cycle durations on the transport mechanism of chloride ions in concrete. Experimental and numerical analysis results indicate that the maximum transmission depth of chloride ions in concrete depends on the diffusion coefficient and the dry-wet cycle regime but has little relationship with the surface concentration of chloride. The chloride ion transmission in the surface zone accelerates only if the dry-wet ratio is > 1. As the dry-wet ratio increases, so the chloride ion transmission accelerates. It tends to become stable when the dry-wet ratio reaches 5:1. The dry-wet cycles accelerate the transport process of chloride ions within a certain distance from the surface; beyond this distance, chloride ions in the complete immersion specimen migrate more rapidly than those under dry-wet cycles. The peak concentration of chloride ions within the convection zone has a relationship with the diffusion coefficient, the surface chloride ion concentration and the dry-wet regime. The smaller the diffusion coefficient, the higher the surface chloride concentration; the greater the dry-wet ratio, the higher the peak of convection can be. [ABSTRACT FROM AUTHOR]

In this paper, a unified cubic flux-controlled memristor is proposed, and how to choose its parameters to obtain an appropriate memristor is investigated. The relevant frequency band of the exciting source that enables the memristor to keep its characteristics (call it mem-frequency band) is analyzed, and the matter of high mem-frequency is also clinched. Based on the trend of their i-v curves versus time, the memristors are divided into two types: P and N. The design, simulations and experiments of the circuits for the presented memristor model are given to describe its dynamical behaviors. The results from simulations and experiments are in good agreement with the theoretical analysis, which are of special guidance for designing such device to satisfy the requirements in practical engineering. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]