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  • Articles  (137)
  • optimal control  (70)
  • numerical simulation  (67)
  • Springer  (137)
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  • Articles  (137)
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  • Springer  (137)
  • American Geophysical Union
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  • 1
    ISSN: 1572-8757
    Keywords: methane adsorption ; on-board storage ; mathematical modeling ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The charge of natural gas adsorption storage systems is studied numerically, With emphasis given to the impact on its dynamics of intraparticle diffusional resistances to mass transport. Besides adsorption kinetics and thermal effects, the simulation model takes into account both mass transport inside the adsorbent and hydrodynamics of flow through the packed bed. Numerical results are presented for change with methane of a 50 liter cylindrical reservoir, filled with hypothetical adsorbents with diffusional time constants in the range 10−3 s1 D/R p 2 ≤ ∞. and with the adsorption equilibrium curve of a commercially available activated carbon with a good adsorptive storage capacity. An attempt is made to assemble the charge histories for different values ofD/R p 2 , in a single cure by using a modilied time scale.
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  • 2
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    Adsorption 4 (1998), S. 337-344 
    ISSN: 1572-8757
    Keywords: pressure swing adsorption ; mathematical models ; numerical simulation ; finite difference ; adaptive time stepping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Three different finite-difference routines were compared for solving the nonlinear, coupled, partial differential and algebraic equations that describe pressure swing adsorption processes. A successive substitution method (SS), a block LU decomposition procedure (BLUD), and the method of lines approach with adaptive time stepping (DASSL) were used to simulate and compare the computation times required to reach the periodic state for two different PSA systems: PSA-air drying and PSA-solvent vapor recovery. For both systems, the results showed that DASSL was nearly twice as fast as BLUD, whereas SS was nearly an order of magnitude slower than BLUD. DASSL and BLUD were also very robust and accurate, as nearly identical bed profiles were obtained from both methods under both transient and periodic state conditions.
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  • 3
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    Annals of operations research 98 (2000), S. 45-64 
    ISSN: 1572-9338
    Keywords: optimal control ; partial differential equations ; numerical methods ; transdermal systems ; acetylene reactors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We present an approach to compute optimal control functions in dynamic models based on one-dimensional partial differential algebraic equations (PDAE). By using the method of lines, the PDAE is transformed into a large system of usually stiff ordinary differential algebraic equations and integrated by standard methods. The resulting nonlinear programming problem is solved by the sequential quadratic programming code NLPQL. Optimal control functions are approximated by piecewise constant, piecewise linear or bang-bang functions. Three different types of cost functions can be formulated. The underlying model structure is quite flexible. We allow break points for model changes, disjoint integration areas with respect to spatial variable, arbitrary boundary and transition conditions, coupled ordinary and algebraic differential equations, algebraic equations in time and space variables, and dynamic constraints for control and state variables. The PDAE is discretized by difference formulae, polynomial approximations with arbitrary degrees, and by special update formulae in case of hyperbolic equations. Two application problems are outlined in detail. We present a model for optimal control of transdermal diffusion of drugs, where the diffusion speed is controlled by an electric field, and a model for the optimal control of the input feed of an acetylene reactor given in form of a distributed parameter system.
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  • 4
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    Annals of operations research 98 (2000), S. 65-87 
    ISSN: 1572-9338
    Keywords: train control ; optimal control ; discrete control ; optimal switching times
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We consider the problem of determining an optimal driving strategy in a train control problem with a generalised equation of motion. We assume that the journey must be completed within a given time and seek a strategy that minimises fuel consumption. On the one hand we consider the case where continuous control can be used and on the other hand we consider the case where only discrete control is available. We pay particular attention to a unified development of the two cases. For the continuous control problem we use the Pontryagin principle to find necessary conditions on an optimal strategy and show that these conditions yield key equations that determine the optimal switching points. In the discrete control problem, which is the typical situation with diesel-electric locomotives, we show that for each fixed control sequence the cost of fuel can be minimised by finding the optimal switching times. The corresponding strategies are called strategies of optimal type and in this case we use the Kuhn–Tucker equations to find key equations that determine the optimal switching times. We note that the strategies of optimal type can be used to approximate as closely as we please the optimal strategy obtained using continuous control and we present two new derivations of the key equations. We illustrate our general remarks by reference to a typical train control problem.
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  • 5
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    Annals of operations research 98 (2000), S. 333-351 
    ISSN: 1572-9338
    Keywords: production planning ; stochastic dynamic programming ; optimal control ; long-run average cost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We consider a production planning problem in a two-machine flowshop subject to breakdown and repair of machines and subject to nonnegativity and upper bound constraints on work-in-process. The objective is to choose machine production rates over time to minimize the long-run average inventory/backlog and production costs. For sufficiently large upper bound on the work-in-process, the problem is formulated as a stochastic dynamic program. We then establish a verification theorem and a partial characterization of the optimal control policy if it exists.
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  • 6
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    Statistical inference for stochastic processes 2 (1999), S. 135-150 
    ISSN: 1572-9311
    Keywords: polymer crystallization ; counting process ; Central Limit Theorem ; martingale ; maximum likelihood estimator ; confidence interval ; Kolmogorov-Smirnov type test ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The nucleation phase of the crystallization of polymers is described in terms of a stochastic spatial counting process, whose intensity depends upon the available volume. Estimation of the relevant parameters of the process are obtained via the maximum likelihood method [6]. The asymptotic properties of the estimators (proved in [6]) are applied to study their qualitative behaviour, as a function of the available volume and time. In this paper, a goodness of fit of the stochastic model proposed has been carried out via a Kolmogorov-Smirnov approach.
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  • 7
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    Set-valued analysis 8 (2000), S. 31-50 
    ISSN: 1572-932X
    Keywords: stability in optimization ; generalized equations ; Lipschitz continuity ; mathematical programming ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study two continuity concepts for set-valued maps that play central roles in quantitative stability analysis of optimization problems: Aubin continuity and Lipschitzian localization. We show that various inverse function theorems involving these concepts can be deduced from a single general result on existence of solutions to an inclusion in metric spaces. As applications, we analyze the stability with respect to canonical perturbations of a mathematical program in a Hilbert space and an optimal control problem with inequality control constraints. For stationary points of these problems, Aubin continuity and Lipschitzian localization coincide; moreover, both properties are equivalent to surjectivity of the map of the gradients of the active constraints combined with a strong second-order sufficient optimality condition.
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  • 8
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    Set-valued analysis 8 (2000), S. 111-126 
    ISSN: 1572-932X
    Keywords: viability ; optimal control ; value function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we explain that various (possibly discontinuous) value functions for optimal control problem under state-constraints can be approached by a sequence of value functions for suitable discretized systems. The key-point of this approach is the characterization of epigraphs of the value functions as suitable viability kernels. We provide new results for estimation of the convergence rate of numerical schemes and discuss conditions for the convergence of discrete optimal controls to the optimal control for the initial problem.
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  • 9
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    Annals of operations research 98 (2000), S. 19-44 
    ISSN: 1572-9338
    Keywords: optimal control ; nonlinear systems ; parabolic systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We consider first nonlinear systems of the form x=A(x)x+B(x)u together with a standard quadratic cost functional and replace the system by a sequence of time-varying approximations for which the optimal control problem can be solved explicitly. We then show that the sequence converges. Although it may not converge to a global optimal control of the nonlinear system, we also consider a similar approximation sequence for the equation given by the necessary conditions of the maximum principle and we shall see that the first method gives solutions very close to the optimal solution in many cases. We shall also extend the results to parabolic PDEs which can be written in the above form on some Hilbert space.
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  • 10
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    Acta applicandae mathematicae 57 (1999), S. 287-338 
    ISSN: 1572-9036
    Keywords: sub-Riemannian geometry ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper is a continuation of a series of papers, dealing with contact sub-Riemannian metrics on R3. We study the special case of contact metrics that correspond to isoperimetric problems on the plane. The purpose is to understand the nature of the corresponding optimal synthesis, at least locally. It is equivalent to studying the associated sub-Riemannian spheres of small radius. It appears that the case of generic isoperimetric problems falls down in the category of generic sub-Riemannian metrics that we studied in our previous papers (although, there is a certain symmetry). Thanks to the classification of spheres, conjugate-loci and cut-loci, done in those papers, we conclude immediately. On the contrary, for the Dido problem on a 2-d Riemannian manifold (i.e. the problem of minimizing length, for a prescribed area), these results do not apply. Therefore, we study in details this special case, for which we solve the problem generically (again, for generic cases, we compute the conjugate loci, cut loci, and the shape of small sub-Riemannian spheres, with their singularities). In an addendum, we say a few words about: (1) the singularities that can appear in general for the Dido problem, and (2) the motion of particles in a nonvanishing constant magnetic field.
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  • 11
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    Acta applicandae mathematicae 46 (1997), S. 29-48 
    ISSN: 1572-9036
    Keywords: Hamilton–Jacobi–Bellman equations ; nonlinear potentials ; nonlinear PDE ; viscosity solutions ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A formal method of constructing the viscosity solutions for abstract nonlinear equations of Hamilton–Jacobi–Bellman (HJB) type was developed in the previous work of the author. A new advantage of this method (which was called an ‘nonlinear potentials’ method) is that it gives a possibility to choose at the first step an expected regularity of the solution and then – to construct this solution. This makes the whole procedure more simple because an analysis of regularity of viscosity solutions is usually the most complicated step. Nonlinear potentials method is a generalization of Krylov's approach to study HJB equations. In this article nonlinear potentials method is applied to elliptic degenerate HJB equations in Rd with variable coefficients.
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  • 12
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    Czechoslovak mathematical journal 47 (1997), S. 409-424 
    ISSN: 1572-9141
    Keywords: R δ-set ; homotopic ; contractible ; evolution triple ; evolution inclusion ; compact embedding ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In the paper we study the topological structure of the solution set of a class of nonlinear evolution inclusions. First we show that it is nonempty and compact in certain function spaces and that it depends in an upper semicontinuous way on the initial condition. Then by strengthening the hypothesis on the orientor field F(t, x), we are able to show that the solution set is in fact an R δ-set. Finally some applications to infinite dimensional control systems are also presented.
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  • 13
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    Czechoslovak mathematical journal 48 (1998), S. 291-312 
    ISSN: 1572-9141
    Keywords: evolution triple ; optimal control ; monotone operator ; hemicontinuous operator ; parabolic system ; property (Q)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider nonlinear systems with a priori feedback. We establish the existence of admissible pairs and then we show that the Lagrange optimal control problem admits an optimal pair. As application we work out in detail two examples of optimal control problems for nonlinear parabolic partial differential equations.
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  • 14
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    Astrophysics and space science 256 (1997), S. 51-75 
    ISSN: 1572-946X
    Keywords: Numerical modeling ; numerical simulation ; electric space ; plasma universe ; cosmology ; galaxies ; filamentation ; electrical currents ; quasars ; double radio galaxies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Advances in the simulation of astrophysical and cosmic plasmas are the direct result of advances in computational capabilities, today consisting of new techniques such as multilevel concurrent simulation, multi-teraflop computational platforms and experimental facilities for producing and diagnosing plasmas under extreme conditions for the benchmarking of simulations. Examples of these are the treatment of mesoscalic plasma and the scaling to astrophysical and cosmic dimensions and the Accelerated Strategic Computing Initiative whose goal is to construct petaflop (1015 floating operations per second) computers, and pulsed power and laser inertial confinement plasmas where megajoules of energy are delivered to highly-diagnosed plasmas. This paper concentrates on the achievements to date in simulating and experimentally producing plasmas scaled to both astrophysical and cosmic plasma dimensions. A previous paper (Part I, Peratt, 1997) outlines the algorithms and computational growth.
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  • 15
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    Journal of marine science and technology 1 (1996), S. 94-104 
    ISSN: 1437-8213
    Keywords: numerical simulation ; field data ; multilevel model ; Tokyo Bay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A multilevel model was applied to the calculation of permanent current and density variation in Tokyo Bay, and the change of the state of stratification and the accompanying current field was simulated. In the numerical simulation, the observed field data such as wind conditions and atmospheric temperature were used as input to the calculation, and the results were compared with the observed values of currents, salinity, and sea temperature. Comparison of simulation results and observed data revealed that the numerical simulation could describe well the current and density field governed by wind under stratified conditions. In particular, the long-term variations of the vertical structure of salinity and temperature from summer to autumn could be predicted qualitatively, as could the long-term variations of the vertical structure of salinity and temperature from summer to autumn. Additionally, the effects of boundary conditions on the results of numerical simulations were examined. As a result, it was clarified that the simulation results of salinity stratification were strongly affected by the boundary conditions such as river discharge and the vertical structure of salinity at the open boundary adjacent to the outer ocean.
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  • 16
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    Journal of marine science and technology 1 (1996), S. 105-113 
    ISSN: 1437-8213
    Keywords: slow drift viscous damping ; wave effect ; horizontal cylinder ; model experiment ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The hydrodynamic forces acting on a circular cylinder and a rectangular cylinder undergoing slow drift oscillation in regular waves were investigated experimentally and numerically. Forced oscillation tests with low frequency and large amplitude in regular waves and forced two-harmonic oscillation with combined low and high frequencies were carried out in the experimental study. In the numerical study a finite-difference method was used to simulate viscous flow around a two-dimensional oscillating cylinder. The results of experiments showed that a horizontal rectangular cylinder oscillating slowly in waves has much higher damping coefficients than one oscillating in two-harmonic mode, while the numerical study indicated that such differences in the damping coefficient arise partly from the different effects of one-direction harmonic flow and rotating flow on the vortex shedding caused by the slow drift oscillation.
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  • 17
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    Journal of statistical physics 81 (1995), S. 237-253 
    ISSN: 1572-9613
    Keywords: Reaction-diffusion ; BGK model ; kinetic theory ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We are interested in applying lattice BGK models to the diffusion-driven reactive systemA+B→C, which was investigated by Gálfi and Rácz with an asymptotic analysis and by Chopard and Droz with a cellular automaton model. The lattice BGK model is free from noise and flexible for various applications. We derive the general reaction-diffusion equations for the lattice BGK models under the assumption of local diffusive equilibrium. Two fourth-order terms are derived and verified by numerical simulations. The motivation of this study is to compare the lattice BGK results with existing results before we apply the models to more complicated systems. The scalings concern two exponents α and β appearing in the production rate ofC componentR(x, t)∼t −β G(xt −α ). We find the same values for α=1/6 and β=2/3 as Gálfi and Rácz found at the long time limit. AGaussian-like function forG is numerically obtained, which confirms a similar result of Gálfi and Rácz. On the one hand, when compared with the asymptotic analysis, lattice BGK models are easy to apply to cases where no analytic or asymptotic results exist; on the other hand, when compared with cellular automaton models, lattice BGK models are faster, simpler, and more accurate. The discrepancy of the results between the cellular automaton model and the lattice BGK models for the exponents comes from the role of the intrinsic fluctuation. Once the time and space correlation of stochastic stirring is given, we can incorporate a random fluctuating term in lattice BGK models. The Schlögl model is also tested, showing the ability of lattice BGK models for generating Turing patterns, which may stimulate further interesting investigations.
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  • 18
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    Journal of statistical physics 85 (1996), S. 427-454 
    ISSN: 1572-9613
    Keywords: Steady Boltzmann equation ; boundary value problem ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss steady boundary value problems for the Boltzmann equation with inflow and diffusive boundary conditions in one, two, and three dimensions, with suitable truncations of the collision kernel. General existence and uniqueness results are obtained if the domain is sufficiently small. In one dimension, the existence of solutions on general intervals is obtained by abstract fixed-point theory.
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  • 19
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    Journal of statistical physics 86 (1997), S. 1067-1087 
    ISSN: 1572-9613
    Keywords: Brownian motion ; friction coefficients ; fluctuation-induced transport ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The behavior of a test particle in a rarefied gas of classical particles is investigated. considering different interaction mechanisms (specular and diffuse reflection, respectively). For large mass ratio between test and gas particles, analytical expressions for the linear friction coefficient are derived. Moreover, the existence of directed motion of asymmetric test particles with distinct initial conditions (but in the absence of any gradients) is shown. The analytical results are supported by a numerical simulation technique applicable to systems with any mass ratio, which is described here in detail.
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  • 20
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    Journal of statistical physics 93 (1998), S. 449-465 
    ISSN: 1572-9613
    Keywords: Granular media ; pattern ; convection ; enhanced diffusion ; granular temperature ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Motions of individual particles within the stripe and square patterns formed in oscillated granular media are studied using numerical simulations. Our event-driven molecular dynamics simulations yield standing wave patterns in good accord with those observed in experiments at the same frequency and acceleration amplitude. The patterns are subharmonic and so return to their initial macroscopic state after two external cycles. However, simulations reveal that individual particles do not return to their initial position. In addition to diffusive motion, an organized flow of particles within the patterns is found; associated with each peak and each valley of the pattern is a pair of counterrotating convection rolls. The diffusion is anisotropic: transport perpendicular to stripes is enhanced over that parallel to stripes. This enhancement is computed as a function of the layer depth, acceleration amplitude, frequency, and coefficient of restitution of the particles, and is attributed to the effect of the advective motion. Velocity distributions, granular temperature, and the dependence of the diffusion coefficient parallel to the stripes on the average granular temperature are studied.
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  • 21
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    Journal of statistical physics 95 (1999), S. 903-923 
    ISSN: 1572-9613
    Keywords: homogeneous nucleation ; density functional theory ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Significant progress has been made in recent years in measuring homogeneous nucleation rates in a variety of liquid–vapor and liquid–solid transitions. These studies have revealed serious shortcomings of classical nucleation theory. New theoretical work and simulation studies of simplified model systems have provided a better understanding of homogeneous nucleation, but many challenges remain. This article summarizes some recent developments, with an emphasis on the field-theoretic approach pioneered by Cahn and Hilliard in their study of nucleation in a two-component incompressible fluid in 1959.
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  • 22
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    Journal of statistical physics 81 (1995), S. 5-16 
    ISSN: 1572-9613
    Keywords: Fluid dynamics ; turbulence ; channel flow ; lattice Boltzmann equation ; numerical simulation ; finite volume ; k-ɛ turbulence model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Some of the most urgent challenges facing the lattice Boltzmann equation (LBE) to rival state-of-the-art computer fluid dynamics (CFD) techniques are discussed. A novel LBE scheme fork-ɛ turbulence modeling is proposed.
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  • 23
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    Acta mechanica solida Sinica 8 (1995), S. 45-50 
    ISSN: 0894-9166
    Keywords: spallation ; microscopic observation ; micro- damage mechanism ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Spall tests in pure copper and LY12 aluminum alloy are performed. The mechanism of the nucleation, growth and coalescence of micro-voids is observed by means of microscopic observation of the recovered specimens. The model presented in Ref. [4] is incorporated in a hydrodynamic one-dimensional finite-difference computer code to simulate the processes of spallation in pure copper and LY12 aluminum alloy specimens. This model can satisfactorily describe the processes of spallation.
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  • 24
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    Pure and applied geophysics 144 (1995), S. 621-631 
    ISSN: 1420-9136
    Keywords: Noto-Hanto-Oki earthquake tsunami ; source model ; spectral synthesis ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A source model was discussed for a small tsunami accompanied by the Noto-Hanto-Oki earthquake (M s 6.6), striking Japan on 7 February, 1994. Assuming a fault model under the sea bottom, we estimated the focal parameters jointly, using synthesized tsunami source spectra as well as the tsunami numerical simulation. The fault proposed by this study consists of a plane sized 15×15 km, dipping N47°W with the dip angle of 42°, which is almost pure reverse fault (slip angle 87°) with a dislocation of 1 meter. The numerical simulation shows that the shallow sea in the source region caused a comparatively long recurring tsunami (the periods are 12–18 minutes) in spite of its small size. The model fault is corresponding to an aftershock area of this earthquake.
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  • 25
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    Pure and applied geophysics 144 (1995), S. 855-874 
    ISSN: 1420-9136
    Keywords: Earthquake ; tsunamis ; runup ; South Kuril Islands ; numerical simulation ; tide gage ; subsidence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 1994 Shikotan earthquake was one of the greatest earthquakes in recent years with a magnitude ofM s 8.0. A tsunami survey was conducted by Russian and U.S. geophysicists from October 16–30, 1994, less than two weeks after the earthquake. The survey results and a numerical hindcast simulation are reported. Tsunami focusing effect at locations supposedly sheltered by the island chain is discussed. Based on the obtained data, tsunamis which attacked Shikotan Island are characterized as long waves (the order of 10–20 min wave period) with a positive leading wave. Possible consequences of the positive leading wave form are discussed in relation to the observed minimal destruction of beach vegetation and relatively small transport of marine sediment onto the shore. The high-quality tide-gage record in Malokurilskaya Bay indicates the occurrence of a 53 cm subsidence at the site.
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  • 26
    ISSN: 1420-9136
    Keywords: The 1992 Flores earthquake tsunami ; numerical simulation ; landslide ; hydraulic pressure ; tsunami damage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Numerical analysis of the 1992 Flores Island, Indonesia earthquake tsunami is carried out with the composite fault model consisting of two different slip values. Computed results show good agreement with the measured runup heights in the northeastern part of Flores Island, except for those in the southern shore of Hading Bay and at Riangkroko. The landslides in the southern part of Hading Bay could generate local tsunamis of more than 10 m. The circular-arc slip model proposed in this study for wave generation due to landslides shows better results than the subsidence model, It is, however, difficult to reproduce the tsunami runup height of 26.2 m at Riangkroko, which was extraordinarily high compared to other places. The wave propagation process on a sea bottom with a steep slope, as well as landslides, may be the cause of the amplification of tsunami at Riangkroko. The simulation model demonstrates that the reflected wave along the northeastern shore of Flores Island, accompanying a high hydraulic pressure, could be the main cause of severe damage in the southern coast of Babi Island.
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  • 27
    ISSN: 0894-9166
    Keywords: stochastic damage ; micro-mechanics model ; low cycle fatigue ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A numerical simulation of stochastic damage evolution process in the condition of low cycle fatigue loading is discussed. The relations between damage variables and micro-cracks are obtained by means of the micro-mechanics model of the representative volume element proposed by Lemaitre and Dufailly[10]. The stochastic initial damage values are introduced in consideration of the inherent micro-defects in materials. The model combined with a finite element method is applied to simulate the damage evolution process under low cycle fatigue loading. The micro-cracks on the sur face of a specimen of 19Mn6 alloy steel are measured with a replica technique. The numerical results show that the nonhomogeneity of damage and the localization of the fatigue failure are well shown by the proposed simulations, and the fatigue lives are reasonably predicted.
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  • 28
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    Journal of nondestructive evaluation 18 (1999), S. 39-57 
    ISSN: 1573-4862
    Keywords: phased array transducers ; dynamic beam steering ; acoustic pressure field ; optimum array transducer design ; numerical simulation ; visualization and imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Ultrasonic beam steering characteristics for linear phased array transducers are simulated numerically by visualizing the full-field acoustic pressure field of the waves radiated from a linear phased array transducer. The influences of various transducer parameters on the beam steering properties are studied, including number of elements, inter-element spacing, element size, frequency of the transducer and the steering angle. In addition, the effects of these parameters on the near field characteristics are investigated by analyzing the acoustic pressure profile in the steering direction. The simulation results agree well with the analytical solutions which are valid only in the far field. A suggested scheme for optimal transducer design is presented.
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  • 29
    ISSN: 1573-1499
    Keywords: bioremediation ; numerical simulation ; carbon tetrachloride ; denitrification
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    Topics: Geosciences , Computer Science
    Notes: Abstract When injecting nutrients during active bioremediation, various nutrient addition strategies can be employed in order to remediate the site at minimal expense. In particular, if more than one nutrient is required, a pulse addition strategy can be devised in which these nutrients are added as temporally separated pulses such that the biostimulated portion of the flow field can be maximized. In this manuscript, results of numerical simulations are reported which demonstrate this effect. Previously published kinetic expressions describing microbial growth and carbon tetrachloride degradation under denitrifying conditions are used in these simulations. The simulations indicate that volumetric treatment can be accomplished by injecting long duration nutrient pulses of different nutrients that are separated by a long period where only unamended water is injected. This strategy will cause the nutrient pulses to overlap at a considerable distance from the injection point, while maintaining concentrations that are high enough to ensure significantbiomass growth and contaminant destruction.
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    Transport in porous media 28 (1997), S. 335-372 
    ISSN: 1573-1634
    Keywords: heterogeneous fractures ; preferential flow paths ; two-phase flow ; boiling and condensation ; vapor-dominated geothermal reservoirs ; nuclear waste disposal ; numerical simulation
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    Topics: Geosciences , Technology
    Notes: Abstract Water injection into unsaturated fractured rock at above-boiling temperatures gives rise to complex fluid flow and heat transfer processes. Examples include water injection into depleted vapor-dominated geothermal reservoirs, and emplacement of heat-generating nuclear wastes in unsaturated fractured rock. We conceptualize fractures as two-dimensional heterogeneous porous media, and use geostatistical techniques to generate synthetic permeability distributions in the fracture plane. Water flow in hot high-angle fractures is simulated numerically, taking into account the combined action of gravity, capillary, and pressure forces, and conductive heat transfer from the wall rocks which gives rise to strong vaporization. In heterogeneous fractures boiling plumes are found to have dendritic shapes, and to be subject to strong lateral flow effects. Fractures with spatially-averaged homogeneous permeabilities tend to give poor approximations for vaporization behavior and liquid migration patterns. Depending on water flow rates, rock temperature, and fracture permeability, liquid water can migrate considerable distances through fractured rock that is at above-boiling temperatures and be only partially vaporized.
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    Journal of fluorescence 8 (1998), S. 273-280 
    ISSN: 1573-4994
    Keywords: Fluorescence quenching ; transient effect ; Smoluchowski–Collins–Kimball model ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Numerical simulations designed to illuminate the opportunities for and limitations on recovering the parameters in the Smoluchowski–Collins–Kimball (SCK) model of time-dependent fluorescence quenching from the data of time-correlated single-photon counting experiments have been carried out. Two “donors” with lifetimes of 880 and 410 ps, corresponding to the unquenched S2 lifetimes of 2,2,3,3-tetramethylindanethione (TMIT) and 9,9-dimethylanthrathione (DMAT) in inert perfluoroalkane solvents at room temperature, were used for purposes of illustration. The failure of the single-exponential decay model due to the transient effect can be detected at lower quencher concentrations for longer-lived fluorophores. While good values of the diffusion coefficient, effective encounter distance, and scaling parameters can be recovered at sufficiently high quencher concentrations, the simulations show that values of the specific rate constant, κ, can be expected to vary by up to two orders of magnitude when it is recovered from typical time-correlated single-photon counting data even if the data can be reliably described by the SCK model. The ability to differentiate between SCK kinetics and single-exponential kinetics by using fluorophores of varying unquenched lifetimes has also been explored.
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    Acta mechanica Sinica 13 (1997), S. 304-312 
    ISSN: 1614-3116
    Keywords: unsteady vortex control ; numerical simulation ; airfoil at high incidence
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The effects of leading-edge blowing-suction on the vortex flow past an airfoil at high incidence are investigated numerically by solving the Navier-Stokes equations. The results indicate that the frequency of the flowfield excited by the periodic blowing-suction locks into the forcing frequency, which is half of the dominant frequency for the flow past a fixed airfoil without injection. In that case, a well-developed primary leading-edge vortex occupies the upper surface of the airfoil and the largest lift augmentation is obtained.
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    Acta mechanica Sinica 13 (1997), S. 193-202 
    ISSN: 1614-3116
    Keywords: numerical simulation ; pulverized-coal combustor ; two-phase flow
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase flows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.
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  • 34
    ISSN: 1614-3116
    Keywords: reservoir ; multiphase flow ; solid deformation ; coupled model ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A mathematical model for coupled multiphase fluid flow and sedimentation deformation is developed based on fluid-solid interaction mechanism. A finite difference-finite element numerical approach is presented. The results of an example show that the fluid-solid coupled effect has great influence on multiphase fluid flow and reservoir recovery performances, and the coupled model has practical significance for oilfield development.
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    Acta mechanica Sinica 13 (1997), S. 210-217 
    ISSN: 1614-3116
    Keywords: numerical simulation ; motion of contact line ; interface tracking
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The paper proposes a physical model for the motion of the contact line and the gas-liquid interface. The local motion of the contact line at the solid wall is assumed and the interface between gas and liquid is traced by a level function. The numerically. The motion of the water column in a vertical pipe is computed and the results are in good agreement with experimental data.
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    Acta mechanica Sinica 15 (1999), S. 116-125 
    ISSN: 1614-3116
    Keywords: vortex control ; separation flow ; delta wing ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The numerical investigation has been performed to explore the feasibility of vortex control by leading edge sucking excitation on a delta wing. The results reveal that the flow on the upper surface of the delta wing changes significantly in a wide range of the angle of attack. For the vortical flow at moderate angle of attack, the secondary and tertiary vortices are weakened or suppressed, and the total lift is almost unchanged. For the stalled flow at high angle of attack, the leading edge concentrated vortex is recovered, and the lift is enhanced with increasing suction rate. For the bluff-body flow at even high angles of attack, the lift can still be improved. The concentrated vortex disappears on the upper surface, and the load increment is nearly unchanged along the chordwise direction.
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    Acta mechanica Sinica 11 (1995), S. 20-33 
    ISSN: 1614-3116
    Keywords: dynamic programming ; robot manipulators ; optimal control ; dynamic modelling method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A certain number of considerations should be taken into account in the dynamic control of robot manipulators as highly complex non-linear systems. In this article, we provide a detailed presentation of the mechanical and electrical implications of robots equipped with DC motor actuators. This model takes into account all non-linear aspects of the system. Then, we develop computational algorithms for optimal control based on dynamic programming. The robot's trajectory must be predefined, but performance criteria and constraints applying to the system are not limited and we may adapt them freely to the robot and the task being studied. As an example, a manipulator arm with 3 degress of freedom is analyzed.
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    Acta mechanica Sinica 16 (2000), S. 41-47 
    ISSN: 1614-3116
    Keywords: turbulent combustion ; second-order moment model ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A new second-order moment model for turbulent combustion is applied in the simulation of methane-air turbulent jet flame. The predicted results are compared with the experimental results and with those predicted using the wellknown EBU-Arrhenius model and the original second-order moment model. The comparison shows the advantage of the new model that it requires almost the same computational storage and time as that of the original second-order moment model, but its modeling results are in better agreement with experiments than those using other models. Hence, the new second-order moment model is promising in modeling turbulent combustion with NOx formation with finite reaction rate for engineering application.
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    Acta mechanica Sinica 11 (1995), S. 200-208 
    ISSN: 1614-3116
    Keywords: transonic flow ; high angle of attack ; vortex-breakdown ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The transonic flowfields and vortex-breakdown over a slender wing with the angle of attack from 10° to 28° are studied numerically, and the emphasis is on the secondary separation and the charateristics of vortex-breakdown. The results indicated that: (a) TVD schemes have strong capability for capturing vortices in three-dimensional transonic separated flow at large angle of attack. (b) The development of secondary vortices is more complex than that of leading-edge ones, and is affected by wing's configuration, angle of attack and compressibility simultaneously, and the effect of compressibility is more severe at low angle of attack. (c) The starting angle of attack for vortex-breakdown (when vortex bursting point crosses trailing-edge) is about 18° forM∞=0.85, then the bursting point moves upstream quickly with increasing angle of attack. (d) At α=24°, breakdown occurs over most part of upper side, and the wing begins to stall. Therefore, there is a large lag of angle of attack between the beginning of vortex-breakdown and the stall of the wing. (e) This lag increase with the decreasing of Mach number.
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    Acta mechanica Sinica 13 (1997), S. 97-105 
    ISSN: 1614-3116
    Keywords: reacting mixing layer ; N-S equations ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this paper, the supersonic chemically reacting mixing layer is simulated with the third order ENN scheme, based on the Navier-Stokes equations, containing transport equations of all species. The numerical results show that the thickness of mixing layer increases gradually along the flow direction, and that the Kelvin-Helmholtz instabilities may not exist in mixing layer flows.
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    Acta mechanica Sinica 14 (1998), S. 130-138 
    ISSN: 1614-3116
    Keywords: thermocapillary-driven flow ; buoyancy-driven flow ; crystal growth ; numerical simulation ; flow instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Thermocapillary- and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical solutions of the two-dimensional Navier-Stokes equations coupled with the energy equation. We studied the thermocapillary and buoyancy convection in the cavities, filled with low-Prandtl-number fluids, with two aspect-ratiosA=1 and 4, Grashof number up to 105 and Reynolds number ⋎Re⋎≤104. Our results show that thermocapillary can have a quite significant effect on the stability of a primarily buoyancy-driven flow, as well as on the flow structures and dynamic behavior for both additive effect (i.e., positiveRe) and opposing effect (i.e., negativeRe).
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  • 42
    ISSN: 1614-3116
    Keywords: weak axisymmetric fountain ; numerical simulation ; unsteady evolution ; fountain height ; fountain width
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Weak axisymmetrical fountains resulting from the injection of a dense fluid upwards into a large container of homogeneous fluid of lower density has been studied numerically in this paper using a time-accurate finite volume scheme. The behaviour of fountains for both the uniform and parabolic profiles of the discharge velocity at the fountain source has been investigated. The evolution of transient fountain flow has been analysed and two distinct stages of evolution have been identified. The time trace of the position of the fountain front has been presented and the initial, temporary and final fountain height and fountain width have been determined.
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    Numerical algorithms 19 (1998), S. 235-246 
    ISSN: 1572-9265
    Keywords: DAEs ; elastic multibody systems ; numerical simulation ; slider crank ; 65L05 ; 70-08
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Elastic multibody systems arise in the simulation of vehicles, robots, air- and spacecrafts. They feature a mixed structure with differential-algebraic equations (DAEs) governing the gross motion and partial differential equations (PDEs) describing the elastic deformation of particular bodies. We introduce a general modelling framework for this new application field and discuss numerical simulation techniques from several points of view. Due to different time scales, singular perturbation theory and model reduction play an important role. A slider crank mechanism with a 2D FE grid for the elastic connecting rod illustrates the techniques.
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    Applied mathematics and mechanics 17 (1996), S. 365-372 
    ISSN: 1573-2754
    Keywords: turbulent flow ; three dimensional ; numerical simulation ; suddenly expanded rectangular duct
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, to simulate the three dimensional turbulent flow in suddenly expanded rectangular duct numerically, the SIMPLEC algorithm is employed to solve the incompressible Navier-Stokes equation with k-ɛ turbulence model. The numerical results show well the three dimensional turbulent flow field in the rectangular duct behind the sudden expansion cross-section, and agree fairly well with the experimental result of the length of the main circumfluence. The numerical method of this paper can be applied to numerical analysis of this kind of turbulent flow.
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    Applied mathematics and mechanics 17 (1996), S. 247-255 
    ISSN: 1573-2754
    Keywords: highly viscoelastic flow ; lubricating approximation ; varying thick slit channel ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The distributive law of flow rate is studied for highly viscoelastic flow in three-dimensional slit channel with varying thickness by using Finite Block Element Method (FBM). As an example, the influence of restrictive block on flow rate is obtained in fish channel of the plate extruding die and the results of numerical simulation are in concordance with the approximatical analytical solution. It is proved that FBM can be considered as an important tool for CAD/CAM.
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    Applied mathematics and mechanics 16 (1995), S. 603-606 
    ISSN: 1573-2754
    Keywords: turbulence ; complicated pipe flow ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, turbulence in a complicated pipe is simulated by using the kε model. The ladder-like mesh approximation is used to solve the problem of complicated boundary with the result of numerical simulation favorable. Two computational examples are given to validate the strong adaptability and stability of k-ε model.
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    Applied mathematics and mechanics 18 (1997), S. 61-68 
    ISSN: 1573-2754
    Keywords: viscoplastic dynamics ; optimal control ; variational principle ; finite element method
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper presents the optimal control variational principle for Perzyna model which is one of the main constitutive relation of viscoplasticity in dynamics. And it could also be transformed to solve the parametric quadratic programming problem. The FEM form of this problem and its implementation have also been discussed in the paper.
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    Applied mathematics and mechanics 21 (2000), S. 707-714 
    ISSN: 1573-2754
    Keywords: flexible cable with large sag ; multiple rigid body system dynamics ; numerical simulation ; violation correction ; O313. 3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Discrete model of flexible cable with large sag is established by using multiple rigid body-spherical hinge model, and dynamic equation of that discrete model is derived according to dynamics theory of multiple rigid body system. Displacement and velocity of system are revised to elininate violation phenomenon of the differential-algebra equation in numerical simulation based on the theory of generalized inverse of matrices. Numerical simulation proves the validity of our method.
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    Applied mathematics and mechanics 19 (1998), S. 95-100 
    ISSN: 1573-2754
    Keywords: turbulence model ; Reynolds stress ; wind flow ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract It is assumed in this paper that for a high Reynolds number nearly homogeneous wind flow, the Reynolds stresses are uniquely related to the mean velocity gradients and the two independent turbulent scaling parameters k and ε. By applying dimensional analysis and owing to the Cayley-Hamilton theorem for tensors, a new turbulence enclosure model so-called the extended k-ε model has been developed. The coefficients of the model expression were determined by the wind tunnel experimental data of homogeneous shear turbulent flow. The model was compared with the standard k-ε model in its composition and the prediction of the Reynold's normal stresses. Using the new model the numerical simulation of wind flow around a square cross-section tall building was performed. The results show that the extended k-ε model improves the prediction of wind velocities around the building and wind pressures on the building envelope.
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    Applied mathematics and mechanics 19 (1998), S. 669-676 
    ISSN: 1573-2754
    Keywords: rectangular ferromagnetic plates ; magnetoelasticity ; bending and instability ; nonlinearity ; numerical simulation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, the phenomenon of magnetoelastic bending is theoretically simulated for soft ferromagnetic rectangular thin plates in applied magnetic fields. A numerical program of 3d FEM is established to capture the nonlinear coupling intercation between magnetic fields and bending deflection. After the nonlinear characteristic of the bending deflection and the magnetic (field) force is quantitatively displayed, we discuss the critical magnetic field and the effect of the incident angle of obliquely applied magnetic field on the critical field to the phenomenon of magnetoelastic instability.
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    Applied mathematics and mechanics 19 (1998), S. 717-723 
    ISSN: 1573-2754
    Keywords: mixing layer ; viscoelastic second-order fluids ; numerical simulation ; pseudo-spectral method ; coherent structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Numerical simulations have been performed in time-developing plane mixing layers of the viscoelastic second-order fluids with pseudo-spectral method. Roll-up, pairing and merging of large eldies were examined at high Reynolds numbers and low Deborah numbers. The effect of viscoelastics on the evolution of the large coherent structure was shown by making a comparison between the second-order and Newtonian fluids at the same Reynolds numbers.
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    Applied mathematics and mechanics 16 (1995), S. 515-520 
    ISSN: 1573-2754
    Keywords: singular perturbation ; nonlinear state regulator ; optimal control ; diagonalization technique
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper will seek the optimal control and corresponding trajectories of the singularly perturbed nonlinear state regulator problem. Under appropriate hypotheses, it will be possible to complete an asymptotic solution which is uniformly valid when σ→0.
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    Applied mathematics and mechanics 17 (1996), S. 1021-1029 
    ISSN: 1573-2754
    Keywords: forming process ; numerical simulation ; non-incremental algorithm ; time-space function
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract A non-incremental time-space algorithm is proposed for numerical analysis of forming process with the inclusion of geometrical, matérial, contact-frictional non-linearities. Unlike the widely used Newton-Raphson counterpart, the present scheme features an iterative solution procedure on entire time and space domain. Validity and feasibility of the present scheme are further justified by the numerical investigation herewith presented.
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    Applied mathematics and mechanics 20 (1999), S. 405-412 
    ISSN: 1573-2754
    Keywords: oil and water ; migration-accumulation ; numerical simulation ; alternating-direction ; implicit interactive scheme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Numerical simulation of oil migration and accumulation is to describe the history of oil migration and accumulation in basin evolution. It is of great value in the exploration oil resources and their rational evaluation. This paper, puts forward the mathematical model and the modified method of alternating-direction implicit interactive scheme. For the famous hydraulic experiment of secondary migration-accumulation (cut plane and plane problem), it has been done the numerical simulation test, and both the computational and experimental results are identical.
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    Discrete event dynamic systems 5 (1995), S. 343-355 
    ISSN: 1573-7594
    Keywords: optimal control ; FMS scheduling ; maximum principle ; instant setups
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    Topics: Mathematics
    Notes: Abstract A continuous time dynamic model of discrete scheduling problems for a large class of manufacturing systems is considered in the present paper. The realistic manufacturing based on multi-level bills of materials, flexible machines, controllable buffers and deterministic demand profiles is modeled in the canonical form of optimal control. Carrying buffer costs are minimized by controlling production rates of all machines that can be set up instantly. The maximum principle for the model is studied and properties of the optimal production regimes are revealed. The solution method developed rests on the iterative approach generalizing the method of projected gradient, but takes advantage of the analytical properties of the optimal solution to reduce significantly computational efforts. Computational experiments presented demonstrate effectiveness of the approach in comparison with pure iterative method.
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    Discrete event dynamic systems 8 (1998), S. 353-364 
    ISSN: 1573-7594
    Keywords: scheduling ; optimal control ; time-decomposition methods
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    Topics: Mathematics
    Notes: Abstract This paper discusses dynamic methods for solving a class of multi-project scheduling problems in which rates of job performances are controllable and resources such as money, energy or manpower per time unit, are renewable and continuously divisible. The objective is to complete the projects as close to the common due date as possible. Two different ways of imposing sequential precedence relations between project jobs are explored by formulating two dynamic models and studying their relationships on the optimal solution. Efficient time-decomposition algorithms for finding either globally optimal schedules or lower bound guided near-optimal solutions are suggested and computationally tested.
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    Discrete event dynamic systems 8 (1998), S. 175-201 
    ISSN: 1573-7594
    Keywords: hybrid systems ; optimal control ; calculus of variations ; manufacturing systems ; queueing systems ; nonsmooth optimization ; two point boundary value problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We propose a modeling framework for a class of hybrid systems which arise in many manufacturing environments and study related optimal control problems. In this framework, discrete entities have a state characterized by a temporal component whose evolution is described by event-driven dynamics, and a physical component whose evolution is described by time-driven dynamics. As a first step towards developing an optimal control theory for such hybrid systems, we formulate a problem consisting of a single-stage manufacturing process and use calculus of variations techniques to obtain structural properties and an explicit algorithm for deriving optimal policies.
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    Discrete event dynamic systems 8 (1998), S. 37-54 
    ISSN: 1573-7594
    Keywords: Production planning ; stochastic dynamic programming ; vanishing discount approach ; optimal control ; long-run average cost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper is concerned with the problem of production planning in a flexible manufacturing system consisting of a single or parallel failure-prone machines producing a number of different products. The objective is to choose the rates of production of the various products over time in order to meet their demands at the minimum long-run average cost of production and surplus. The analysis proceeds with a study of the corresponding problem with a discounted cost. It is shown using the vanishing discount approach for the average cost problem that the Hamilton-Jacobi-Bellman equation in terms of directional derivatives has a solution consisting of the minimal average cost and the so-called potential function. The result helps in establishing a verification theorem, and in specifying an optimal control policy in terms of the potential function. The results settle a hitherto open problem as well as generalize known results.
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    Journal of oceanography 56 (2000), S. 409-418 
    ISSN: 1573-868X
    Keywords: Trigger meanders ; Kuroshio ; numerical simulation ; baroclinic instability ; two-layer quasigeostrophic model ; Tokara Strait ; coastal geometry of Kyushu
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract We examine the processes underlying the generation and propagation of the small meander of the Kuroshio south of Japan which occurs prior to the transition from the non-large meander path to the large meander path. The study proceeds numerically by using a two-layer, flat-bottom, quasi-geostrophic inflow-outflow model which takes account of the coastal geometries of Kyushu, Nansei Islands, part of the East China Sea, and the Izu Ridge. The model successfully reproduces the observed generation and propagation features of what is called "trigger meander" until it passes by Cape Shiono-misaki; presumably because of the absence of the bottom topography, the applicability of the present numerical model becomes questionable after the trigger meander passes by Cape Shiono-misaki. The generation of the trigger meander off the south-eastern coast of Kyushu is shown to be associated with the increase in the supply of cyclonic vorticity by the enhanced current velocity in the upper layer along the southern coast of Kyushu where the no-slip boundary condition is employed. Thereafter, the trigger meander propagates eastward while inducing an anticyclone-cyclone-cyclone pair in the lower layer. The lower-layer cyclone induced in this way, in particular, plays a crucial role in intensifying the trigger meander trough via cross-stream advection in the upper layer; the intensified trigger meander trough then further amplifies the lower-layer cyclone. This joint evolution of the upper-layer meander trough and the lower-layer cyclone indicates that baroclinic instability is the dominant mechanism underlying the rapid amplification of the eastward propagating trigger meander.
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    Transport in porous media 35 (1999), S. 37-47 
    ISSN: 1573-1634
    Keywords: automata ; diffusion in porous media ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A thermodynamic automaton model of fluid flow in porous media is presented. The model is a nonrelativistic version of a Lorentz invariant lattice gas model constructed by Udey et al. (1998). In the previous model it was shown that the energy momentum tensor and the relativistic Boltzman equation can be rigorously derived from the collision and propagation rules. In the present paper we demonstrate that this nonrelativistic model can be used to accurately simulate well known results involving single phase flow and diffusion in porous media. The simulation results show that (1) one-phase flow simulations in porous media are consistent with Darcy's law; (2) the apparent diffusion coefficient decreases with a decrease in permeability; (3) small scale heterogeneity does not affect diffusion significantly in the cases considered.
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    Transport in porous media 35 (1999), S. 375-394 
    ISSN: 1573-1634
    Keywords: groundwater ; density driven flow ; numerical simulation ; salt dome.
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    Topics: Geosciences , Technology
    Notes: Abstract Case 5, Level 1 of the international HYDROCOIN groundwater flow modeling project is an example of idealized flow over a salt dome. The groundwater flow is strongly coupled to solute transport since density variations in this example are large (20%). Several independent teams simulated this problem using different models. Results obtained by different codes can be contradictory. We develop a new numerical model based on the mixed hybrid finite elements approximation for flow, which provides a good approximation of the velocity, and the discontinuous finite elements approximation to solve the advection equation, which gives a good approximation of concentration even when the dispersion tensor is very small. We use the new numerical model to simulate the salt dome flow problem. In this paper we study the effect of molecular diffusion and we compare linear and non‐linear dispersion equations. We show the importance of the discretization of the boundary condition on the extent of recirculation and the final salt distribution. We study also the salt dome flow problem with a more realistic dispersion (very small dispersion tensor). Our results are different to prior works with regard to the magnitude of recirculation and the final concentration distribution. In all cases, we obtain recirculation in the lower part of the domain, even for only dispersive fluxes at the boundary. When the dispersion tensor becomes very small, the magnitude of recirculation is small. Swept forward displacement could be reproduced by using finite difference method to compute the dispersive fluxes instead of mixed hybrid finite elements.
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    Transport in porous media 38 (2000), S. 319-344 
    ISSN: 1573-1634
    Keywords: ferrofluids ; magnetic fluids ; subsurface barrier verification ; magneto pressure ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two‐dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field‐scale application of ferrofluids for barrier verification.
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    Transport in porous media 23 (1996), S. 337-354 
    ISSN: 1573-1634
    Keywords: numerical simulation ; upscaling ; renormalisation ; error analysis
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    Topics: Geosciences , Technology
    Notes: Abstract In this paper we briefly discuss the background to the problems of finding effective flow properties when moving from a detailed representation of reservoir geology to a coarse gridded model required for reservoir performance simulation. The basic requirements for the upscaled properties are also discussed. We then consider one technique, renormalization, that in recent years has shown promise as an accurate, yet fast, method. The mathematical background of the renormalization approach is examined. A rigorous formalism is developed that allows an explicit calculation of the error terms to be made. In a very simple case use of the correction terms is shown to produce a dramatic improvement in accuracy of the method.
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    Transport in porous media 24 (1996), S. 275-296 
    ISSN: 1573-1634
    Keywords: chemical flooding ; ternary ; immiscible ; surfactant ; numerical simulation ; interfacial tension ; phase behavior ; miscibility ; capillarity ; numerical grid ; adsorption ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This is the second of two joint papers which study the influence of several physical properties on the transport phenomena in chemical flooding. To that aim, we use a previously reported ternary two-phase model into which representative physical properties have been incorporated as concentration-dependent functions. Physical properties such as phase behavior, interfacial tensions, residual saturations, relative permeabilities, phase viscosities and wettability have been analyzed in the first paper. In this paper, we discuss the influence of capillary pressure, adsorption of the chemical component onto the rock and dispersion. Although arising from different phenomenological sources, these transport mechanisms show some similar effects on concentration profiles and on oil recovery. They are studied for systems with different phase behavior. A numerical analysis is also presented in order to determine the relevance of the number of grid blocks taken in the discretization of the differential equations. This numerical analysis provides useful guidelines for the selection of the appropriate numerical grid in each type of displacement.
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    Transport in porous media 35 (1999), S. 345-373 
    ISSN: 1573-1634
    Keywords: groundwater ; density driven flow ; numerical simulation ; mixed finite elements ; discontinuous finite elements ; Elder problem.
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    Topics: Geosciences , Technology
    Notes: Abstract A new numerical model for the resolution of density coupled flow and transport in porous media is presented. The model is based on the mixed hybrid finite elements (MHFE) and discontinuous finite elements (DFE) methods. MHFE is used to solve the flow equation and the dispersive part of the transport equation. This method is more accurate in the calculation of velocities and ensures continuity of fluxes from one element to the adjacent one. DFE is used to solve the convective part of the transport equation. Combined with a slope limiting procedure, it avoids numerical instabilities and creates a very limited numerical dispersion, even for high grid Peclet number. Flow and transport equations are coupled by a standard iterative scheme. Residual based criterion is used to stop the iterations. Simulations of an unstable equilibrium show the effects of the criteria used to stop the iterations and the stopping criterion in the solver. The effects are more important for finer grids than for coarser grids. The numerical model is verified by the simulation of standard benchmarks: the Henry and the Elder test cases. A good agreement is found between the revised semi‐analytical Henry solution and the numerical solution. The Elder test case was also studied. The simulations were similar to those presented in previous works but with significantly less unknowns (i.e. coarser grids). These results show the efficiency of the used numerical schemes.
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    Transport in porous media 40 (2000), S. 171-200 
    ISSN: 1573-1634
    Keywords: flow and mass transport ; density driven flow ; numerical simulation ; Henry's problem
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    Topics: Geosciences , Technology
    Notes: Abstract The proposed numerical code simulates the displacement of two miscible fluids through a saturated porous medium (2D configuration). Coupling between flow and transport is carried out by an equation of state. In the mixing zone, the density is assumed to vary as a function of concentration. The model uses a combination of the mixed hybrid finite element method and the discontinuous finite element method. Applied in its classical development, the mixed hybrid finite element method leads to a non-conservative formulation of the mass balance equation. However, one of the main reasons for using this technique is the ability to conserve mass cell-by-cell. Consequently, a new formulation that makes it possible to hold the conservative form of the continuity equation and so preserve the mass cell-wise is proposed. Although the pertinence of these approaches could have also been tested on other standard benchmarks, e.g., Elder's problem or salt dome problem, we have voluntarily limited ourselves to Henry's problem (1964). This choice was dictated by the possibility of a comparison with a semi-analytical solution. Contrary to previous numerical results, the comparison is made for the whole mixing zone. The very good agreement between our results and the semi-analytical solution shows the robustness and the efficiency of this approach for the seawater intrusion problems.
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    Transport in porous media 24 (1996), S. 81-106 
    ISSN: 1573-1634
    Keywords: concrete ; drying ; moisture content distribution ; gravimetric method ; numerical simulation ; Darcy flow ; heat and mass transport
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    Topics: Geosciences , Technology
    Notes: Abstract Moisture content changes during drying were investigated in the present work. Particular emphasis was placed on the initial stage of drying of saturated concrete, where moisture contents are high. For this stage of drying, experimental data are lacking, and no comprehensive theory exists to describe it. The present investigation was performed experimentally and numerically for drying of cylinders with one exposed end, made of normal weight and lightweight concrete with varying water to cement ratio (w/c). The gravimetric technique was employed to obtain the spatial distribution of moisture content. The experimental results obtained indicate that drying of concrete becomes diffusion controlled when the average moisture content decreases below 70 to 80% of the initial saturation. Typical drying rates are in the order of magnitude of 0.18 kg/day/m2 and 0.02 kg/day/m2 for the first and the second stage of drying, respectively. The lightweight concrete cylinders as compared to those made of normal weight concrete exhibited higher levels of moisture content throughout the process. At high w/c ratios, the moisture profiles for both types of cylinders, as expected, show steeper changes with time. Large, constant drying rates were observed both experimentally and numerically in the beginning of the drying. The numerical model developed is based on a generalized mathematical formulation for mass and heat transfer in porous media, and its predictions are in agreement with the experimental data within the uncertainty range of the input data.
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    Transport in porous media 24 (1996), S. 247-273 
    ISSN: 1573-1634
    Keywords: chemical flooding ; ternary ; immiscible ; surfactant ; numerical simulation ; wettability ; interfacial tension ; mobility control ; phase behavior ; miscibility
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    Topics: Geosciences , Technology
    Notes: Abstract A one-dimensional ternary two-phase simulator has been extended to include improved physical properties. These physical properties - such as phase behavior, interfacial tension, residual saturations, relative permeabilities, phase viscosities, wettability, capillary pressure, adsorption and dispersion - are modeled as concentration dependent functions. Their functionality completely controls the chemical flood transport phenomena. In this paper, the influence of phase behavior, interfacial tension reduction, mobility control and wettability alteration on chemical flooding are analyzed. In a subsequent paper the influence of capillary pressure, adsorption, and physical and numerical dispersion will be presented. The main application of the simulator here presented is to describe enhanced oil recovery processes. It may also be applied to describe oil spill cleaning and groundwater contamination.
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    Mathematical notes 60 (1996), S. 383-388 
    ISSN: 1573-8876
    Keywords: optimal control ; nonlinear singular system ; state constraints ; penalty method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A control system described by a nonlinear equation of parabolic type is considered in the situation where there may be no global solution. A particular optimal control problem subject to state constraints is studied. A proof of the existence of an optimal control is presented. The penalty method is used to obtain necessary conditions for optimal control. A proof of the convergence of this method is given. The successive approximation method is used to obtain an approximate solution for the conditions derived.
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    Geotechnical and geological engineering 16 (1998), S. 201-213 
    ISSN: 1573-1529
    Keywords: capillary barrier ; surface cover ; unsaturated flow ; numerical simulation ; numerical model
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    Topics: Geosciences
    Notes: Abstract This paper presents a comparison of numerical simulations to the measured response of capillary barrier field tests. The simulations were of pilot-scale tests of four 7 m long, 1.2 m thick capillary barriers, two with 5% slopes and two with 10% slopes, with and without an included unsaturated drainage layers. The unsaturated drainage layer was included to encourage lateral drainage. The 5% sloped barriers were subjected to a period of constant infiltration for a period of 74 days, while the 10% system with the drainage layer had water added for 26 days and the conventional capillary barrier with a 10% slope was subjected to 43 days of infiltration. The numerical modelling was conducted using both drying and wetting soil moisture characteristic curves to determine their influence on the results. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. It was found that the use of wetting curve data provided a better fit to the field data, more accurately predicting the amount and timing of the percolate produced. © Rapid Science Ltd. 1998
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    Natural hazards 13 (1996), S. 39-54 
    ISSN: 1573-0840
    Keywords: debris flow ; Bagnold's dilatant model ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Debris flow is the flow of solid-fluid mixture and was treated as the flow of a continuum in routing in this study. A mathematical model was proposed to describe debris flow including deposition process and then solved numerically with suitable boundary conditions. Laboratory experiments were also conducted for comparison and calibration of the numerical results as well as for investigation of debris flow phenomena. The numerical model was also applied to simulate the debris flow caused by heavy rainfall in Tungman village of Hualien County located in the east of Taiwan on 23 June 1990. The simulated bed topographies in alluvial fan were in good agreement with those obtained from laboratory experiments and field observations.
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    Natural hazards 17 (1998), S. 163-176 
    ISSN: 1573-0840
    Keywords: volcanic risk ; pyroclastic flows ; pyroclastic surges ; human survival ; physical modelling ; numerical simulation ; Vesuvius
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Volcanic eruptions increasingly present catastrophic natural risks with hundreds of millions of people now living in areas of active volcanism and major conurbations around active eruptive centres. Interdisciplinary studies in disaster reduction have an important role in volcanic emergency management through advancing our understanding of the physical impacts of eruptive phenomena and the causes of death and injury in explosive eruptions. Numerical modelling of pyroclastic flows, amongst the most destructive of eruptive phenomena, provides new opportunities to improve the evaluation of the potential destructiveness of volcanic events and their human impacts in densely populated areas. In this work, the results of numerical modelling of pyroclastic flow propagation at Vesuvius have been analysed in terms of the physical parameters (temperature, ash in air concentration, and dynamic pressure) that are most critical for human survival. Our numerical simulations of eruptions of Vesuvius indicate that a large area exists where total destruction may not be inevitable in small to medium scale events, a finding that has prompted us to explore further the implications for human survival as part of an interdisciplinary approach to disaster reduction. The lessons of modelling at Vesuvius should be integrated into civil protection plans for other urban centres threatened by volcanoes.
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    Bulletin of engineering geology and the environment 57 (1999), S. 253-261 
    ISSN: 1435-9537
    Keywords: Key words waste dump ; ground water ; numerical simulation ; Mots clés stockage de déchets ; eaux souterraines ; simulation numérique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé La possibilité d'utiliser une carrière d'argile abandonnée comme terrain de décharge de déchets sidérurgiques a été soigneusement évaluée en vue de sauvegarder les ressources en eaux souterraines du site. L'eau de la nappe phréatique est de qualité médiocre. Son aquifère est constitué par une formation de calcarénite, son mur par des argiles ayant fait l'objet d'exploitations. Au-dessous, une couche de calcarénite repose transgressivement sur la plateforme carbonatée des Pouilles. Les roches carbonatées de cet aquifère profond renferment une nappe qui s'écoule jusqu'à la Mer Ionienne. Un diaphragme plastique, étanche à l'eau et inerte aux produits de percolation a été réalisé pour protéger les eaux souterraines contre les risques de pollution par les déchets industriels de la décharge. Le dispositif a été conçu suite à une évaluation soignée des impacts possibles sur les eaux souterraines. Le terrain de décharge est, de plus, situé près d'établissements industriels dont les fondations sont au niveau de la nappe phréatique. Ces fondations et des tranchées ferroviaires influent grandement sur la circulation de l'eau souterraine. Enfin, des techniques de calcul numérique appliquéà l'hydrogéologie ont permis d'estimer l'impact d'une tranchée de drainage sur la circulation des eaux souterraines ainsi que l'influence de cette tranchée sur les ouvrages et établissements industriels présents sur le site.
    Notes: Abstract  The use of a deserted clay quarry to collect iron manufacturing-derived special wastes has been carefully assessed with a view to protecting ground water resources. The shallower ground water is of low quantity and poor quality. It is encompassed by a calcarenite aquifer, the bottom of which consists of clays. A limited calcarenite layer is found below, transgressively lying over the main Apulian carbonate shelf. The aquifer carbonate rocks enclose large ground water resources which ultimately flows into the Ionian Sea. A plastic waterproof diaphragm inert to percolation products has been installed to protect ground water against pollution hazards resulting from the disposal of industrial wastes. The dump is actually located in the vicinity of major industrial plants, the basements of which corresponds to the shallow aquifer. Both the basements and the railway cuttings greatly affect the ground water flow. Hydrogeological applied numerical calculation techniques have been used to evaluate the impact of a drainage trench on the ground water flow together with any noticeable influence of the latter on construction works and industrial plants in place.
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    Astrophysics and space science 233 (1995), S. 169-173 
    ISSN: 1572-946X
    Keywords: molecular clouds ; shock fronts ; numerical simulation
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    Topics: Physics
    Notes: Abstract Shocks propagating in the interstellar medium (ISM) play an important role in the life of molecular clouds. Through a theoretical study of interaction between clouds and shocks we can understand, for example, the density distribution of observed molecular clouds and the first steps of star formation. The only way to study of interaction in detail is via a numerical hydrodynamical simulation. In this paper we present the first results of a hydrocode which is able to follow the processes after the collision between the cloud and shock front. Our main theoretical result is that the chemical processes (e.g. H2 dissociation) can affect the dynamical processes significantly. Global parameters of the cloud are calculated for the comparision of the simulation and the observations.
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    International journal of thermophysics 17 (1996), S. 329-345 
    ISSN: 1572-9567
    Keywords: diffraction ; forced Rayleigh scattering ; laser-induced thermal grating ; numerical simulation ; thermal diffusivity ; toluene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements.
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    ISSN: 1572-9559
    Keywords: injection seeding ; spectral narrowing ; optically pumped D2O laser ; high power ; numerical simulation ; semiclassical theory
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    Topics: Physics
    Notes: Abstract Spectrally narrow, pulsed outputs consisting of almost a single mode have been obtained from an optically-pumped high-power (200kW) D2O laser by adopting the injection seeding method, where single-mode radiation (seed pulse) from a low-power, compact D2O laser has been injected into the main D2O laser. Spectrally narrow outputs with high power having spectral widths as narrow as 5 MHz have been obtained, when the seed pulses with frequency tuned to one longitudinal mode of the main D2O laser have been injected at a time sufficiently before the lasing of the main laser took place. The experimental results have been compared with those of numerical simulation modified to include the injection field with varying injection times.
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    Journal of optimization theory and applications 105 (2000), S. 263-276 
    ISSN: 1573-2878
    Keywords: optimal control ; distributed-parameter systems ; Pontryagin maximum principle ; Ekeland variational principle ; unbounded controls
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    Topics: Mathematics
    Notes: Abstract We prove the maximum principle for an optimal control problem governed by the system $$y'(t) + A(t)y(t) = f(t,y(t),u(t)),{\text{ }}u(t) \in U(t), $$ with state constraint $$(y(0),y(T)) \in C \subset H \times H $$ , under three different hypotheses: (H1) C is a convex set with nonempty interior; (H2) $$C = \{ y_0 \} \times C_{0,} {\text{ with }}C_0 $$ a convex set with nonempty interior in H and the evolution system satisfying compactness hypotheses; (H3) the periodic case $$y(0) = y(T)$$ , with the evolution system satisfying compactness hypotheses. We do not assume the controls to be bounded. We give some examples for distributed control problems.
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    Journal of optimization theory and applications 106 (2000), S. 231-264 
    ISSN: 1573-2878
    Keywords: hierarchical control ; manufacturing systems ; stochastic dynamic programming ; optimal control ; long-run average cost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider a production planning problem for a dynamic jobshop producing a number of products and subject to breakdown and repair of machines. The machine capacities are assumed to be finite-state Markov chains. As the rates of change of the machine states approach infinity, an asymptotic analysis of this stochastic manufacturing systems is given. The analysis results in a limiting problem in which the stochastic machine availability is replaced by its equilibrium mean availability. The long-run average cost for the original problem is shown to converge to the long-run average cost of the limiting problem. The convergence rate of the long-run average cost for the original problem to that of the limiting problem together with an error estimate for the constructed asymptotic optimal control is established.
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    Journal of optimization theory and applications 106 (2000), S. 627-655 
    ISSN: 1573-2878
    Keywords: variational inequalities ; optimal control ; state constraint ; maximum principle
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    Topics: Mathematics
    Notes: Abstract This work deals with the necessary conditions of optimality for some optimal control problems governed by elliptic variational inequalities. Boundary control and state constrained problems are considered. The techniques used are based on those in Ref. 1 and a new penalty functional is defined in this paper.
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    Journal of optimization theory and applications 107 (2000), S. 275-286 
    ISSN: 1573-2878
    Keywords: optimal control ; thresholds ; multiple equilibria ; instability ; concavity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An important and numerous literature argues that nonconcavity (often convexity with respect to the state) of the Hamiltonian leads to multiple steady states, instability, and a threshold. This threshold property provides a powerful paradigm to explain history dependency and hysteresis. This paper shows that economically relevant properties (in particular, multiple steady states and thresholds) are possible in strict concave models too. Two corresponding necessary conditions with intuitive economic interpretation are derived.
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    Journal of optimization theory and applications 86 (1995), S. 251-261 
    ISSN: 1573-2878
    Keywords: Degenerate diffusions ; ergodic control ; optimal control ; Markov control ; stationary solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract For the ergodic control problem with degenerate diffusions, the existence of an optimal solution is established for various interesting classes of solutions.
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    Journal of optimization theory and applications 87 (1995), S. 33-45 
    ISSN: 1573-2878
    Keywords: Maximum principle ; distributed-parameter systems ; optimal control ; structural control ; hyperbolic partial differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A maximum principle is developed for a class of problems involving the optimal control of a damped-parameter system governed by a linear hyperbolic equation in one space dimension that is not necessarily separable. A convex index of performance is formulated, which consists of functionals of the state variable, its first- and second-order space derivatives, its first-order time derivative, and a penalty functional involving the open-loop control force. The solution of the optimal control problem is shown to be unique. The adjoint operator is determined, and a maximum principle relating the control function to the adjoint variable is stated. The proof of the maximum principle is given with the help of convexity arguments. The maximum principle can be used to compute the optimal control function and is particularly suitable for problems involving the active control of structural elements for vibration suppression.
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    Journal of optimization theory and applications 87 (1995), S. 235-267 
    ISSN: 1573-2878
    Keywords: Sampled-data systems ; multivariable control systems ; robust control ; multirate controllers ; control systems design ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper deals with the problem of designing multirate-output contrlleers for sampled-dataH ∞-optimal control of linear continuous-time systems. Two formulations of the problem are studied. In the first, the intersample behavior of the disturbance and the controlled output signals is not considered, whereas in the second the continuous-time nature of these signals is taken into account. It is shown that, in both cases and unter appropriate conditions, it is plausible to reduce the repective initial problem to an associated discrete-timeH ∞-optimization problem for which a fictitious static state feedback controller is to be designed. This fact has a beneficial influence on the theoretical and numerical complexity of the problem, since only one algebraic Riccati equation is to be solved here, as compared to two algebraic Riccati equations needed in known techniques concerning theH ∞-optimization problem with dynamic measurement feedback.
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  • 84
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    Journal of optimization theory and applications 88 (1996), S. 671-688 
    ISSN: 1573-2878
    Keywords: Infinite-horizon problems ; optimal control ; transversality condition ; stability ; Lyapunov exponents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We present necessary conditions of optimality for an infinitehorizon optimal control problem. The transversality condition is derived with the help of stability theory and is formulated in terms of the Lyapunov exponents of solutions to the adjoint equation. A problem without an exponential factor in the integral functional is considered. Necessary and sufficient conditions of optimality are proved for linear quadratic problems with conelike control constraints.
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  • 85
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    Journal of optimization theory and applications 94 (1997), S. 533-560 
    ISSN: 1573-2878
    Keywords: Polynomial differential equations ; convergence of solutions ; neural network systems ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study polynomial ordinary differential systems $$\dot M(t) = QM - M(M'QM){\text{, }}M(0) = M_0 ,t \geqslant 0,$$ whereQ≥0 is an n×n matrix and M(t) is an n×k matrix. It is proven that, as t grows to infinity, the solution M(t) tends to a limit BU, where U is a k×k orthogonal matrix and B is an n×k matrix whose columns are k pairwise orthogonal, normalized eigenvectors of Q. Moreover, for almost every M 0, these eigenvectors correspond to the k maximal eigenvalues of Q; for an arbitrary Q with independent columns, we provide a procedure of computing B by employing elementary matrix operations on M 0. This result is significant for the study of certain neural network systems, and in this context it shows that M(∞) provides a principal component analyzer.
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  • 86
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    Journal of optimization theory and applications 94 (1997), S. 311-334 
    ISSN: 1573-2878
    Keywords: Mixed penalty method ; Frank–Wolfe method ; optimal control ; relaxed control ; lumped systems ; distributed systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider a general optimization problem which is an abstract formulation of a broad class of state-constrained optimal control problems in relaxed form. We describe a generalized mixed Frank–Wolfe penalty method for solving the problem and prove that, under appropriate assumptions, accumulation points of sequences constructed by this method satisfy the necessary conditions for optimality. The method is then applied to relaxed optimal control problems involving lumped as well as distributed parameter systems. Numerical examples are given.
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  • 87
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    Journal of optimization theory and applications 94 (1997), S. 619-634 
    ISSN: 1573-2878
    Keywords: Microeconomic models ; optimal control ; linear controls ; singular subarcs ; necessary conditions ; minimum principle as LP ; direct collocation method ; indirect multiple shooting method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An optimal control problem with four linear controls describing a sophisticated concern model is investigated. The numerical solution of this problem by combination of a direct collocation and an indirect multiple shooting method is presented and discussed. The approximation provided by the direct method is used to estimate the switching structure caused by the four controls occurring linearly. The optimal controls have bang-bang subarcs as well as constrained and singular subarcs. The derivation of necessary conditions from optimal control theory is aimed at the subsequent application of an indirect multiple shooting method but is also interesting from a mathematical point of view. Due to the linear occurrence of the controls, the minimum principle leads to a linear programming problem. Therefore, the Karush–Kuhn–Tucker conditions can be used for an optimality check of the solution obtained by the indirect method.
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  • 88
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    Journal of optimization theory and applications 96 (1998), S. 589-626 
    ISSN: 1573-2878
    Keywords: Nonlinear control ; optimal control ; Hamilton–Jacobi–Bellman equation ; feedback synthesis ; successive approximation ; Galerkin approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we develop a new method to approximate the solution to the Hamilton–Jacobi–Bellman (HJB) equation which arises in optimal control when the plant is modeled by nonlinear dynamics. The approximation is comprised of two steps. First, successive approximation is used to reduce the HJB equation to a sequence of linear partial differential equations. These equations are then approximated via the Galerkin spectral method. The resulting algorithm has several important advantages over previously reported methods. Namely, the resulting control is in feedback form and its associated region of attraction is well defined. In addition, all computations are performed off-line and the control can be made arbitrarily close to optimal. Accordingly, this paper presents a new tool for designing nonlinear control systems that adhere to a prescribed integral performance criterion.
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  • 89
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    Journal of optimization theory and applications 98 (1998), S. 161-173 
    ISSN: 1573-2878
    Keywords: Robust stabilization ; optimal control ; time-delay systems ; Razumikhin-type approach
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, using a Razumikhin-type approach, the stabilization of a class of uncertain nonlinear systems with time-varying delay is considered. The proposed controller is based on a specific optimal control problem. Global asymptotic stability is guaranteed for the proposed control if some algebraic condition is met. An example illustrates the use of the main result.
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  • 90
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    Journal of global optimization 9 (1996), S. 183-216 
    ISSN: 1573-2916
    Keywords: Dynamic setups ; production and setup control ; optimal control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically.
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  • 91
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    Studia geophysica et geodaetica 42 (1998), S. 41-60 
    ISSN: 1573-1626
    Keywords: atmospheric boundary layer ; numerical simulation ; turbulence parametrization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Influence of the surface roughness, geostrophic wind speed and initial stable stratification on surface layer scales, namely the friction velocity, temperature scale and the Monin-Obukhov length, and on non-dimensional profiles has been studied in quasi-stationary PIAPBLM (Prague Institute of Atmospheric Physics Boundary Layer Model) runs. Modifications of the stability functions, of the non-local mixing length concept, and of surface layer parametrization have improved the model results. With the ground temperature kept constant in time, the boundary layer is subjected to a turbulent cooling induced by surface roughness and to a counteracting turbulent heat transfer directed downwards. If the wind speed is lower, a rather mixed layer develops capped by a more stable layer. The estimated Monin-Obukhov length then slightly increases and the non-dimensional gradients overpredict the empirical values even more.
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  • 92
    ISSN: 1573-1626
    Keywords: geomagnetic pulsations ; ionospheric filtration ; numerical simulation
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Summary This supplement to paper by Prikner and Vagner (1991) describes the optimum algorithm for the automated computer program of numerical simulation of the total wave field anywhere within the ionospheric filter. The matrix method of thin layers in an inhomogeneous, anisotropic and dissipative ionosphere has been applied. The application of this method enables in situ measurements of geomagnetic pulsations in the ionosphere to be compared with the results of the numerical simulation.
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  • 93
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    Applied mathematics and mechanics 21 (2000), S. 725-732 
    ISSN: 1573-2754
    Keywords: two-phase flow ; numerical simulation ; TVD schemes ; detonation wave ; O381 ; O241
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In order to investigate parameters of FAE (fuel air explosive) explosion, the two-phase gas-droplet conservation equations with two-dimensional axial symmetry in the Euler coordinate were used. High-resolution implicit TVD (total variation diminishing) schemes were applied to gas phase equations and MacCormack schemes to liquid equations. The for mation and propagation of gas-droplet detonation wave were simulated numerically. The simulation results and the others are compared with a good agreement.
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  • 94
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    Applied mathematics and mechanics 20 (1999), S. 999-1009 
    ISSN: 1573-2754
    Keywords: mechanics of immiscible flow ; 3-dimensional migration-accumulation of oil resources ; splitting-up ; numerical simulation ; Dongying hollow ; O231.82
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Numerical simulation of oil migration and accumulation is to describe the history of oil migration and accumulation in basin evolution. It is of great value in the exploration of oil resources and their rational evaluation. In this paper, from such actual conditions at the effects of mechanics of fluids in porous media and 3-dimensional geology characteristics, a kind of modified method of second order splitting-up implicit interactive scheme is put forward. For the famous hydraulic experiment of secondary migration-accumulation, the numerical simulation test has been done, and both the computational and experimental results are basically identical. For the actual problem of Dongying hollow of Shengli Petroleum Oil Field, the numerical simulation test and the actual conditions are basically coincident. Thus the well-known problem has been solved.
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  • 95
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    Applied mathematics and mechanics 21 (2000), S. 1161-1168 
    ISSN: 1573-2754
    Keywords: space manipulator ; motion planning ; optimal control ; wavelet analysis ; TP241
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The optimal control problem of nonholonomic motion planning of space manipulator was discussed. Utilizing the method of wavelet analysis, the discrete orthogonal wavelets were introduced to solve the optimal control problem, the classical Fourier basic functions were replaced by the wavelet expansion approximation. A numerical algorithm of optimal control was proposed based on wavelet analysis. The numerical simulation shows, the method is effective for nonholonomic motion planning of space manitulator.
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  • 96
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    Applied mathematics and mechanics 21 (2000), S. 1371-1380 
    ISSN: 1573-2754
    Keywords: soliton ; standing soliton ; cubic Schrödinger equation ; numerical simulation ; O353.1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Standing soliton was studied by numerical simulation of its governing equation, a cubic Schrödiger equation with a complex conjugate term, which was derived by Miles and was accepted. The value of linear damping in Miles equation was studied. Calculations showed that linear damping effects strongly on the formation of a standing soliton and Laedke and Spatschek stable condition is only a necessary condition, but not a sufficient one. The interaction of two standing solitons was simulated. Simulations showed that the interaction pattern depends on system parameters. Calculations for the different initial condition and its development indicated that a stable standing soliton can be formed only for proper initial disturbance, otherwise the disturbance will disappear or develop into several solitons.
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  • 97
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    Applied mathematics and mechanics 16 (1995), S. 229-236 
    ISSN: 1573-2754
    Keywords: method of multiple scales ; principal resonance curve ; numerical simulation ; chaotic motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper based on [1] we go further into the study of chaotic behaviour of the forced oscillator containing a square nonlinear term by the methods of multiple scales and numerical simulation. Relation between the chaotic domain and principal resonance curve is discussed. By analyzing the stability of principal resonance curve we infer that chaotic motion would occur near the frequency at which the principal resonance curve has vertical tangent. Results of numerical simulation confirm this inference. Thus we offer an effective way to seek the chaotic motion of the systems which are hard to be investigated by Melnikov method.
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  • 98
    ISSN: 1573-2754
    Keywords: dynamic system ; parameters identification ; optimal control ; HJB equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Based on the contents of part (I) and stochastic optimal control theory, the concept of optimal control solution to parameters identification of stochastic dynamic system is discussed at first. For the completeness of the theory developed in this paper and part (I), then the procedure of establishing Hamilton-Jacobi-Bellman (HJB) equations of parameters identification problem is presented. And then, parameters identification algorithm of stochastic dynamic system is introduced. At last, an application example-local nonlinear parameters identification of dynamic system is presented.
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  • 99
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    Journal of optimization theory and applications 102 (1999), S. 15-36 
    ISSN: 1573-2878
    Keywords: Domain decomposition ; partial differential equations ; Riccati equation ; optimal control ; feedback law ; synthesis ; wave equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We present an iterative domain decomposition method for the optimal control of systems governed by linear partial differential equations. The equations can be of elliptic, parabolic, or hyperbolic type. The space region supporting the partial differential equations is decomposed and the original global optimal control problem is reduced to a sequence of similar local optimal control problems set on the subdomains. The local problems communicate through transmission conditions, which take the form of carefully chosen boundary conditions on the interfaces between the subdomains. This domain decomposition method can be combined with any suitable numerical procedure to solve the local optimal control problems. We remark that it offers a good potential for using feedback laws (synthesis) in the case of time-dependent partial differential equations. A test problem for the wave equation is solved using this combination of synthesis and domain decomposition methods. Numerical results are presented and discussed. Details on discretization and implementation can be found in Ref. 1.
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  • 100
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    Journal of optimization theory and applications 102 (1999), S. 299-313 
    ISSN: 1573-2878
    Keywords: Comparison of methods ; optimal control ; sensitivity ; shooting methods ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A new method for solving optimal control problems, here called multiple NOC shooting, is presented. It is developed from NOC shooting. It has some advantages over its parent and over multiple shooting, which are both successful, high-accuracy methods for optimal control. A comparison of the three methods is given, incorporating two examples.
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