Pulse Propagation in Inhomogeneous Media

1974 ◽  
Vol 41 (4) ◽  
pp. 1057-1062 ◽  
Author(s):  
D. B. Longcope ◽  
C. R. Steele
Keyword(s):  
Exact Solution ◽  
Opposite Direction ◽  
Wave Speed ◽  
Pulse Propagation ◽  
Characteristic Length ◽  
Pulse Length ◽  
Approximate Solutions ◽  
The Other ◽  
One Dimensional ◽  
Analytic Wave

Approximate solutions are developed for one-dimensional pulse propagation in a medium with an analytic wave speed when the ratio ε of the pulse length to a characteristic length of the wave speed variation is small. The solutions describe an 0(1) transmitted pulse, given by the WKB solution, and an 0(ε) reflection which may progress in the opposite direction. Two approximations for the reflection are given, one in terms of explicit integrals and the other, which may be uniformly valid, by a combination of explicit integrals and a slowly varying numerical term. Comparisons with the exact solution in several examples show the usefulness of the approximate solutions.

Transient Heat Transfer Analysis of Alloy Solidification

1973 ◽  
Vol 95 (3) ◽  
pp. 324-331 ◽  
Author(s):  
J. C. Muehlbauer ◽  
J. D. Hatcher ◽  
D. W. Lyons ◽  
J. E. Sunderland
Keyword(s):  
Temperature Distribution ◽  
Eutectic Composition ◽  
Approximate Solutions ◽  
The Other ◽  
Heat Transfer Analysis ◽  
Uniform Temperature ◽  
One Dimensional ◽  
Temperature Distributions ◽  
Finite Slab ◽  
Good Agreement

Approximate solutions are obtained for the temperature distribution and rate of phase change for the transient one-dimensional solidification of a finite slab of a binary alloy. The alloy is selected to avoid the eutectic composition so that solidification takes place over a range of temperatures. The slab is initially superheated and has a uniform temperature distribution. Solidification occurs after one surface is cooled by convection while the other surface is insulated. Temperature distributions are determined analytically and experimentally and are in reasonably good agreement.

scholarly journals Construction of a global solution for the one dimensional singularly-perturbed boundary value problem

2017 ◽  
Vol 8 (1-2) ◽  
pp. 52
Author(s):  
Samir Karasuljic ◽  
Enes Duvnjakovic ◽  
Vedad Pasic ◽  
Elvis Barakovic
Keyword(s):  
Exact Solution ◽  
Approximate Solution ◽  
Boundary Value Problem ◽  
Uniform Convergence ◽  
Boundary Value ◽  
Approximate Solutions ◽  
Singularly Perturbed ◽  
One Dimensional ◽  
The One ◽  
Theoretical Results

We consider an approximate solution for the one--dimensional semilinear singularly--perturbed boundary value problem, using the previously obtained numerical values of the boundary value problem in the mesh points and the representation of the exact solution using Green's function. We present an \(\varepsilon\)--uniform convergence of such gained the approximate solutions, in the maximum norm of the order \(\mathcal{O}\left(N^{-1}\right)\) on the observed domain. After that, the constructed approximate solution is repaired and we obtain a solution, which also has \(\varepsilon\)--uniform convergence, but now of order \(\mathcal{O}\left(\ln^2N/N^2\right)\) on \([0,1]\). In the end a numerical experiment is presented to confirm previously shown theoretical results.

scholarly journals Использование усреднения по полям взаимодействия для построения приближенных методов в модели Изинга разбавленного магнетика

2020 ◽  
Vol 62 (8) ◽  
pp. 1209
Author(s):  
С.В. Сёмкин ◽  
В.П. Смагин ◽  
В.И. Люлько
Keyword(s):  
Exact Solution ◽  
Ising Model ◽  
Statistical Physics ◽  
Approximate Solutions ◽  
Dimensional Chain ◽  
Method Of Averaging ◽  
One Dimensional ◽  
Spin Cluster ◽  
General Relations ◽  
Ising Spins

Abstract The method of averaging over interaction fields has been analyzed as applied to the problems of statistical physics. This method has been theoretically justified as applied to a spin cluster. Based on the general relations obtained, approximate solutions for the bond-diluted Ising model are found. These approximate solutions are compared with the exact solution for a one-dimensional chain of bond-diluted Ising spins.

An Exact Periodic Solution of a Hydromagnetic Flow in a Horizontal Channel

1988 ◽  
Vol 55 (4) ◽  
pp. 981-983 ◽  
Author(s):  
K. Vajravelu
Keyword(s):  
Exact Solution ◽  
Periodic Solution ◽  
Flow Field ◽  
Unsteady Flow ◽  
Incompressible Fluid ◽  
Approximate Solutions ◽  
The Other ◽  
Hydromagnetic Flow ◽  
Mean Velocity ◽  
Approximate Form

An exact periodic solution for the hydromagnetic unsteady flow of an incompressible fluid with constant properties is obtained. The hydrodynamic (HD) and the hydromagnetic (HM) cases are studied. The flow field here is a generalization of the well-known Couette flow, in which one wall is at rest and the other wall oscillates in its own plane about a constant mean velocity. In order to have some suggestions about the approximate solutions, the exact solution is compared with its own approximate form.

Approximate analytical solution for the one-dimensional nonlinear Boussinesq equation

2015 ◽  
Vol 25 (4) ◽  
pp. 831-840 ◽  
Author(s):  
Hossein Aminikhah
Keyword(s):  
Exact Solution ◽  
Laplace Transform ◽  
Arbitrary Function ◽  
Perturbation Methods ◽  
Boussinesq Equation ◽  
Approximate Solutions ◽  
Content Type ◽  
One Dimensional ◽  
Homotopy Perturbation ◽  
The One

Purpose – The purpose of this paper is to provide closed-form approximate solutions to the one-dimensional Boussinesq equation for a semi-infinite aquifer when the hydraulic head at the source is an arbitrary function of time. Combination of the Laplace transform and homotopy perturbation methods (LTHPM) are considered as an algorithm which converges rapidly to the exact solution of the nonlinear Boussinesq equation. Design/methodology/approach – The authors present the solution of nonlinear Boussinesq equation by combination of Laplace transform and new homotopy perturbation methods. An important property of the proposed method, which is clearly demonstrated in example, is that spectral accuracy is accessible in solving specific nonlinear nonlinear Boussinesq equation which has analytic solution functions. Findings – The authors proposed a combination of Laplace transform method and homotopy perturbation method to solve the one-dimensional Boussinesq equation. The results are found to be in excellent agreement. The results show that the LTNHPM is an effective mathematical tool which can play a very important role in nonlinear sciences. Originality/value – The authors provide closed-form approximate solutions to the one-dimensional Boussinesq equation for a semi-infinite aquifer when the hydraulic head at the source is an arbitrary function of time. In this work combination of Laplace transform and new homotopy perturbation methods (LTNHPM) are considered as an algorithm which converges rapidly to the exact solution of the nonlinear Boussinesq equation.

A new algorithm for finding CRM-model coefficients

2019 ◽  
Vol 5 (3) ◽  
pp. 164-185 ◽  
Author(s):  
Alexander D. Bekman ◽  
Sergey V. Stepanov ◽  
Alexander A. Ruchkin ◽  
Dmitry V. Zelenin
Keyword(s):  
Approximate Solution ◽  
Optimization Problem ◽  
Optimal Solution ◽  
Complex Form ◽  
Approximate Solutions ◽  
The Other ◽  
Programming Algorithm ◽  
Stochastic Algorithms ◽  
Large Set ◽  
Flow Rates

The quantitative evaluation of producer and injector well interference based on well operation data (profiles of flow rates/injectivities and bottomhole/reservoir pressures) with the help of CRM (Capacitance-Resistive Models) is an optimization problem with large set of variables and constraints. The analytical solution cannot be found because of the complex form of the objective function for this problem. Attempts to find the solution with stochastic algorithms take unacceptable time and the result may be far from the optimal solution. Besides, the use of universal (commercial) optimizers hides the details of step by step solution from the user, for example&nbsp;— the ambiguity of the solution as the result of data inaccuracy.<br> The present article concerns two variants of CRM problem. The authors present a new algorithm of solving the problems with the help of “General Quadratic Programming Algorithm”. The main advantage of the new algorithm is the greater performance in comparison with the other known algorithms. Its other advantage is the possibility of an ambiguity analysis. This article studies the conditions which guarantee that the first variant of problem has a unique solution, which can be found with the presented algorithm. Another algorithm for finding the approximate solution for the second variant of the problem is also considered. The method of visualization of approximate solutions set is presented. The results of experiments comparing the new algorithm with some previously known are given.

scholarly journals On a Generalization of One-Dimensional Kinetics

Mathematics ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1264
Author(s):  
Vladimir V. Uchaikin ◽  
Renat T. Sibatov ◽  
Dmitry N. Bezbatko
Keyword(s):  
Exact Solution ◽  
Asymptotic Behavior ◽  
Constant Velocity ◽  
Telegraph Equation ◽  
Material Derivative ◽  
Symmetric Random Walk ◽  
One Dimensional ◽  
Special Cases ◽  
Fractional Telegraph Equation ◽  
Asymmetric Case

One-dimensional random walks with a constant velocity between scattering are considered. The exact solution is expressed in terms of multiple convolutions of path-distributions assumed to be different for positive and negative directions of the walk axis. Several special cases are considered when the convolutions are expressed in explicit form. As a particular case, the solution of A. S. Monin for a symmetric random walk with exponential path distribution and its generalization to the asymmetric case are obtained. Solution of fractional telegraph equation with the fractional material derivative is presented. Asymptotic behavior of its solution for an asymmetric case is provided.

scholarly journals Markov chain approximation of one-dimensional sticky diffusions

2021 ◽  
Vol 53 (2) ◽  
pp. 335-369
Author(s):  
Christian Meier ◽  
Lingfei Li ◽  
Gongqiu Zhang
Keyword(s):  
Markov Chain ◽  
Approximate Solutions ◽  
Price Model ◽  
One Dimensional ◽  
Markov Chain Approximation ◽  
Alternative Approaches ◽  
Second Order Convergence ◽  
Chain Approximation ◽  
Matrix Exponentials ◽  
Interior Points

AbstractWe develop a continuous-time Markov chain (CTMC) approximation of one-dimensional diffusions with sticky boundary or interior points. Approximate solutions to the action of the Feynman–Kac operator associated with a sticky diffusion and first passage probabilities are obtained using matrix exponentials. We show how to compute matrix exponentials efficiently and prove that a carefully designed scheme achieves second-order convergence. We also propose a scheme based on CTMC approximation for the simulation of sticky diffusions, for which the Euler scheme may completely fail. The efficiency of our method and its advantages over alternative approaches are illustrated in the context of bond pricing in a sticky short-rate model for a low-interest environment and option pricing under a geometric Brownian motion price model with a sticky interior point.

On Approximate Large Deviations for 1D Diffusion

2003 ◽  
Vol 10 (2) ◽  
pp. 381-399
Author(s):  
A. Yu. Veretennikov
Keyword(s):  
Differential Equation ◽  
Exact Solution ◽  
Large Deviations ◽  
Stochastic Differential Equation ◽  
Approximation Scheme ◽  
Sufficient Conditions ◽  
Rate Function ◽  
Euler Approximation ◽  
One Dimensional

Abstract We establish sufficient conditions under which the rate function for the Euler approximation scheme for a solution of a one-dimensional stochastic differential equation on the torus is close to that for an exact solution of this equation.

scholarly journals Effect of Thrust on the Structural Vibrations of a Nonuniform Slender Rocket

2020 ◽  
Vol 25 (2) ◽  
pp. 29
Author(s):  
Desmond Adair ◽  
Aigul Nagimova ◽  
Martin Jaeger
Keyword(s):  
Natural Frequencies ◽  
Equations Of Motion ◽  
Approximate Solutions ◽  
Mode Shapes ◽  
Algebraic Equations ◽  
Structural Vibrations ◽  
Unknown Parameters ◽  
One Dimensional ◽  
Vibration Problems ◽  
Nonuniform Beam

The vibration characteristics of a nonuniform, flexible and free-flying slender rocket experiencing constant thrust is investigated. The rocket is idealized as a classic nonuniform beam with a constant one-dimensional follower force and with free-free boundary conditions. The equations of motion are derived by applying the extended Hamilton’s principle for non-conservative systems. Natural frequencies and associated mode shapes of the rocket are determined using the relatively efficient and accurate Adomian modified decomposition method (AMDM) with the solutions obtained by solving a set of algebraic equations with only three unknown parameters. The method can easily be extended to obtain approximate solutions to vibration problems for any type of nonuniform beam.

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