Error Analysis of the Enthalpy Method for the Stefan Problem

In this paper an error bound is derived for a practical piecewiselinear finite-element approximation of an enthalpy formulationof the multidimensional Stefan problem with an implicit timediscretization. It is shown that if the time step t is O(h),then the error in the temperature measured in the L² norm isO(h).     

An Efficient Method for the Multi-Depot Location—Allocation Problem

This paper describes a procedure based on large-scale nonlinear programming for solving the multidepot location-allocation problem. Both the location of depots and the allocation of customers are allowed to vary simultaneously. Numerical experience on a 5 x 50 and a 10 x 50 example is described, and possible extensions to the basic model are discussed.     

Quasistationary Approximation for the Stefan Problem

To justify the quasistationary approximation for the Stefan problem, the difference between the solution to the Hele-Show problem and the solution to the Stefan problem with small parameter ε at the time-derivative in the equation is considered. Bibliography: 7 titles. __________ Translated from Problemy Matematicheskogo Analiza, No. 31, 2005, pp. 167–178.     

Solution of the Two-Dimensional Stefan Problem by the Singularity-Separating Method

In this paper the idea of "singularity-separating" presented in [10] is used to solve a two-dimensional phase-change problem. A difference scheme with second-order accuracy everywhere, including the region near the boundary between two phases, is constructed for the above problem. Through the computation it is shown that the singularity-separating method, whose accuracy is high, is efficient for two-dimensional phase-change problem.     

Viscosity Solutions for the Two-Phase Stefan Problem

We introduce a notion of viscosity solutions for the two-phase Stefan problem, which incorporates possible existence of a mushy region generated by the initial data. We show that a comparison principle holds between viscosity solutions, and investigate the coincidence of the viscosity solutions and the weak solutions defined via integration by parts. In particular, in the absence of initial mushy region, viscosity solution is the unique weak solution with the same boundary data.     

An Efficient Genetic Algorithm for the p-Median Problem

We propose a new genetic algorithm for a well-known facility location problem. The algorithm is relatively simple and it generates good solutions quickly. Evolution is facilitated by a greedy heuristic. Computational tests with a total of 80 problems from four different sources with 100 to 1,000 nodes indicate that the best solution generated by the algorithm is within 0.1% of the optimum for 85% of the problems. The coding effort and the computational effort required are minimal, making the algorithm a good choice for practical applications requiring quick solutions, or for upper-bound generation to speed up optimal algorithms.     

An Efficient Algorithm for the Complex Roots Problem

Given a univariate polynomialf(z) of degreenwith complex coefficients, whose norms are less than 2^min magnitude, the root problem is to find all the roots off(z) up to specified precision 2^−μ. Assuming the arithmetic model for computation, we provide an algorithm which has complexityO(nlog⁵nlogB), whereb= χ + μ, and χ = max{n,m}. This improves on the previous best known algorithm of Pan for the problem, which has complexityO(n²log²nlog(m+ μ)). A remarkable property of our algorithm is that it does not require any assumptions about the root separation off, which were either explicitly, or implicitly, required by previous algorithms. Moreover it also has a work-efficient parallel implementation. We also show that both the sequential and parallel implementations of the algorithm work without modification in the Boolean model of arithmetic. In this case, it follows from root perturbation estimates that we need only specify θ = ⌈n(B+ logn+ 3)⌉ bits of the binary representations of the real and imaginary parts of each of the coefficients off. We also show that by appropriate rounding of intermediate values, we can bound the number of bits required to represent all complex numbers occurring as intermediate quantities in the computation. The result is that we can restrict the numbers we use in every basic arithmetic operation to those having real and imaginary parts with at most φ bits, where[formula]and[formula]Thus, in the Boolean model, the overall work complexity of the algorithm is only increased by a multiplicative factor ofM(φ) (whereM(ψ) =O(ψ(log ψ) log log ψ) is the bit complexity for multiplication of integers of length ψ). The key result on which the algorithm is based, is a new theorem of Coppersmith and Neff relating the geometric distribution of the zeros of a polynomial to the distribution of the zeros of its high order derivatives. We also introduce several new techniques (splitting sets and “centered” points) which hinge on it. We also observe that our root finding algorithm can be efficiently parallelized to run in parallel timeO(log⁶nlogB) usingnprocessors.     

An Efficient Algorithm for the Knapsack Sharing Problem

The Knapsack Sharing Problem (KSP) is an NP-Hard combinatorial optimization problem, admitted in numerous real world applications. In the KSP, we have a knapsack of capacity c and a set of n objects, namely N, where each object j, j = 1,...,n, is associated with a profit p _j and a weight w _j. The set of objects N is composed of m different classes of objects J _i, i = 1,...,m, and N = ^m _i=1 J _i. The aim is to determine a subset of objects to be included in the knapsack that realizes a max-min value over all classes.In this article, we solve the KSP using an approximate solution method based upon tabu search. First, we describe a simple local search in which a depthparameter and a tabu list are used. Next, we enhance the algorithm by introducing some intensifying and diversifying strategies. The two versions of the algorithm yield satisfactory results within reasonable computational time. Extensive computational testing on problem instances taken from the literature shows the effectiveness of the proposed approach.     

Two-Phase Stefan Problem as the Limit Case of Two-Phase Stefan Problem with Kinetic Condition

Both one-dimensional two-phase Stefan problem with the thermodynamic equilibrium condition u(R(t),t)=0 and with the kinetic rule u_ε(R_ε(t),t)=εR_ε′(t) at the moving boundary are considered. We prove, when ε approaches zero, R_ε(t) converges to R(t) in C^1+δ/2[0,T] for any finite T>0, 0<δ<1.     

一类Stefan问题的适定性

本文讨论在烧蚀缓慢的情况下发汗控制微分方程并证明了其解的适定性。     

On the Numerical Solution of the One-dimensional Stefan Problem by Newton's Method

Recently Baumeister, Hoffmann & Jochum (1980) have treatedthe one-dimensional Stefan Problem numerically by applying Newton'smethod. Here the convergence is proved for a slightly modifiedNewton procedure.     

A Stochastic Stefan Problem

We consider a stochastic perturbation of the Stefan problem. The noise is Brownian in time and smoothly correlated in space. We prove existence and uniqueness and characterize the domain of existence.     

Global Stability and Decay for the Classical Stefan Problem

The classical one‐phase Stefan problem describes the temperature distribution in a homogeneous medium undergoing a phase transition, such as ice melting to water. This is accomplished by solving the heat equation on a time‐dependent domain whose boundary is transported by the normal derivative of the temperature along the evolving and a priori unknown free boundary. We establish a global‐in‐time stability result for nearly spherical geometries and small temperatures, using a novel hybrid methodology, which combines energy estimates, decay estimates, and Hopf‐type inequalities.© 2015 Wiley Periodicals, Inc.     

A Two-Sided Contracting Stefan Problem

Abstract

We study a novel two-sided Stefan problem—motivated by the study of certain 2D interfaces—in which boundaries at both sides of the sample encroach into the bulk with rate equal to the boundary value of the gradient. Here the density is in [0, 1] and takes the two extreme values at the two free boundaries. It is noted that the problem is borderline ill-posed: densities in excess of unity liable to cause catastrophic behavior. We provide a general proof of existence and uniqueness for these systems under the condition that the initial data is in [0, 1] and with some mild conditions near the boundaries. Applications to 2D shapes are provided, in particular motion by weighted mean curvature for the relevant interfaces is established.     

Stefan Problem with Phase Relaxation

Taking account of a microscopical model for dynamical supercoolingand superheating effects, the usual equilibrium condition prescribinga fixed temperature at the interface between two phases is replacedby relaxation dynamics for the phase variable x, representingthe concentration of one of the two phases. At first the approach of "non-equilibrium thermodynamics" isfollowed and a parabolic system is formulated; existence, uniquenessand regularity properties of the L²-solution are obtained bymeans of the theory of non-linear semigroups of contractions.These developments are also generalized to phase transitionsin heterogeneous systems. Then the heat diffusion equation is coupled with the relaxationdynamics for x and the well-posedness of an initial- and boundary-valueproblem is proved. The standard Stefan problem is obtained asa limit case. Also, a model for glass formation by very fastcooling is proposed. Finally, Fourier's conduction law is replaced by relaxationdynamics for the heat flux; this corresponds to assuming wavepropagation for the heat. An existence result is proved forthe corresponding problem and the limit behaviour as the relaxationtime vanishes is studied.     

An Efficient Algorithm for Solving the Rectilinear Multifacility Location Problem

One of the efficient methods for solving large rectilinear multifacilitylocation problems is the Direct Search method. The only drawbackof this method lies in the following difficulty. In some situations,when t new facilities are located together at one point, thenumber of arithmetic operations which are needed to establishoptimality is proportional to t²2^t. Therefore the method needsa prohibitive amount of computation time whenever t exceeds,say, 20. This paper gives a simple remedy for this problem.The paper states and proves a new necessary and sufficient optimalitycondition. This condition transforms the problem of computinga descent direction into a constrained linear least-squaresproblem. The latter problem is solved by a relaxation methodthat takes advantage of its special structure. The new techniqueis incorporated into the Direct Search method. This yields animproved algorithm that handles efficiently very large clusters.Numerical results are included.     

Similarity Solutions to the Stefan Problem and the Binary Alloy Problem

We present a catalogue of explicit similarity solutions to theStefan problem and the binary alloy problem; the most generalcase includes convective heat transfer due to a fluid motiondriven by a density change at the solid-liquid interface. Thefree boundary is either an ellipsoid or a hyperboloid; in thelatter case we note that for certain parameter regimes theremay be two solutions (with different initial data), a situationwhich does not occur in the one-dimensional case.     

Dynamics of Thermally-Insulated Nonequilibrium Stefan Problem

We study a two-phase Stefan problem with kinetics. Here we prove existence of a finite-dimensional attractor for the problem without heat losses. Fot the most part we use a more elegant technique of energetic type estimates in appropriately defined weighted Sobolev spaces as opposite to the parabolic potentials of [9]. We demonstrate existence of compact attractors in the Sobolev spaces and prove that the attractor consists of sufficiently regular functions. This allows us to show that the Hausdorff dimension of the attractor is finite.     

The Stefan Problem with Nonlinear Convection

In this paper, we consider the time dependent Stefan problem with convection in the fluid phase governed by the Navier-Stokes equation and with adherence of the fluid on the lateral boundaries. The existence of a weak solution is obtained via the introduction of a temperature dependent penalty term in the fluid flow equation, together with the application of various compactness arguments.