A high convergent precision exact analytic method for differential equation with variable coefficients

1993 ◽  
Vol 14 (3) ◽  
pp. 201-207 ◽  
Author(s):  
Ji Zhen-yi ◽  
Yeh Kai-yuan
Keyword(s):  
Differential Equation ◽  
Variable Coefficients ◽  
Analytic Method ◽  
Exact Analytic Method

Integration of Partial Differential Equation for Transient Linear Flow of Gas-Condensate Fluids in Porous Structures

1964 ◽  
Vol 4 (04) ◽  
pp. 291-306 ◽  
Author(s):  
C. Kenneth Eilerts
Keyword(s):  
Differential Equation ◽  
Partial Differential Equation ◽  
Effective Permeability ◽  
Flow Characteristics ◽  
Compressibility Factor ◽  
Variable Coefficients ◽  
Back Pressure ◽  
Absolute Permeability ◽  
Partial Differential ◽  
Linear Flow

Abstract Finite difference equations were programmed and used to integrate the second-order, second-degree, partial differential equation with variable coefficients that represents the transient linear flow of gas-condensate fluids. Effect was given to the change with pressure of the compressibility factor, the viscosity, and the effective permeability and to change of the absolute permeability with distance. Integrations used as illustrations include recovery of fluid from a reservoir at a constant production rate followed by recovery at a declining rate calculated to maintain a constant pressure at the producing boundary. The time required to attain such a limiting pressure and the fraction of the reserve recovered in that time vary markedly with properties of the fluid represented by the coefficients. Fluid also is returned to the reservoir at a constant rate, until initial formation pressure is attained at the input boundary, and then at a calculated rate that will maintain but not exceed the limiting pressure. The computing programs were used to calculate the results that would be obtained in a series of back-pressure tests made at selected intervals of reservoir depletion. If effect is given to the variations in properties of the fluid that actually occur, then a series of back-pressure curves one for each stage of reserve depletion -- is required to indicate open-flow capacity and related flow characteristics dependably. The isochronal performance method for determining flow characteristics of a well was simulated by computation. Introduction The back-pressure test procedure is based on a derivation of the equation for steady-state radial flow of a gas, the properties of which are of necessity assumed to remain unchanged in applying the test results. The properties of most natural gases being recovered from reservoirs change as the reserve is depleted and pressures decline, and the results of an early back-pressure test may not be dependable for estimating the future delivery capacity of a well. The compressibility factor of a fluid under an initial pressure of 10,000 psia can change 45 per cent and the viscosity can change 70 per cent during the productive life of the reservoir. There are indications that the effective permeability to the flowing fluid can become 50 per cent of the original absolute permeability before enough liquid collects in the structure about a well as pressure declines to permit flow of liquid into the well. The advent of programmed electronic computing made practicable the integration of nonlinear, second-order, partial differential equations pertaining to flow in reservoirs. Aronofsky and Porter represented the compressibility factor and the viscosity by a linear relationship, and integrated the equation for radial flow of gas for pressures up to 1,200 psi. Bruce, Peaceman, Rachford and Rice integrated the partial differential equations for both linear and radial unsteady-state flow of ideal gas in porous media. Their published results were a substantial guide in this study of integration of the partial differential equation of linear flow with coefficients of the equation variable. The computing program was developed to treat effective permeability as being both distance-dependent and pressure-dependent. In this study all examples of effective permeability are assumptions designed primarily to aid in developing programs for giving effect to this and other variable coefficients. The accumulation of data for expressing the pressure dependency of the effective permeability is the objective of a concurrent investigation. SPEJ P. 291^

IMPLEMENTATIONS OF BOUNDARY–DOMAIN INTEGRO-DIFFERENTIAL EQUATION FOR DIRICHLET BVP WITH VARIABLE COEFFICIENT

2016 ◽  
Vol 78 (6-5) ◽  
Author(s):  
Nurul Akmal Mohamed ◽  
Nur Fadhilah Ibrahim ◽  
Mohd Rozni Md Yusof ◽  
Nurul Farihan Mohamed ◽  
Nurul Huda Mohamed
Keyword(s):  
Differential Equation ◽  
Quadrature Formula ◽  
Spectral Properties ◽  
Variable Coefficient ◽  
Logarithmic Singularity ◽  
Neumann Series ◽  
Numerical Results ◽  
Analytic Method ◽  
Elliptic Type ◽  
Integro Differential Equation

In this paper, we present the numerical results of the Boundary-Domain Integro-Differential Equation (BDIDE) associated to Dirichlet problem for an elliptic type Partial Differential Equation (PDE) with a variable coefficient. The numerical constructions are based on discretizing the boundary of the problem region by utilizing continuous linear iso-parametric elements while the domain of the problem region is meshed by using iso-parametric quadrilateral bilinear domain elements. We also use a semi-analytic method to handle the integration that exhibits logarithmic singularity instead of using Gauss-Laguare quadrature formula. The numerical results that employed the semi-analytic method give better accuracy as compared to those when we use Gauss-Laguerre quadrature formula. The system of equations that obtained by the discretized BDIDE is solved by an iterative method (Neumann series expansion) as well as a direct method (LU decomposition method). From our numerical experiments on all test domains, the relative errors of the solutions when applying semi-analytic method are smaller than when we use Gauss-Laguerre quadrature formula for the integration with logarithmic singularity. Unlike Dirichlet Boundary Integral Equation (BIE), the spectral properties of the Dirichlet BDIDE is not known. The Neumann iterations will converge to the solution if and only if the spectral radius of matrix operator is less than 1. In our numerical experiment on all the test domains, the Neumann series does converge. It gives some conclusions for the spectral properties of the Dirichlet BDIDE even though more experiments on the general Dirichlet problems need to be carried out.

Stationary Problems of Moisture-Elasticity for Inhomogeneous Thick-Walled Shells

2013 ◽  
Vol 671-674 ◽  
pp. 571-575 ◽  
Author(s):  
Vladimir I. Andreev ◽  
Anatoliy S. Avershyev
Keyword(s):  
Differential Equation ◽  
Modulus Of Elasticity ◽  
Clay Soil ◽  
Variable Coefficients ◽  
Accurate Solution ◽  
Constant Modulus ◽  
Solid Mass ◽  
Spherical Cavities ◽  
Symmetric Formulation ◽  
Stationary Problems

This paper contains a solution of the problem of determining stress state in clay soil near a cylindrical and spherical cavities for the propagation of the moisture out of the cavity into the solid mass. The problem is solved in a stationary symmetric formulation taking into account changes the modulus of elasticity of soil moisture. The problem is reduced to a differential equation with variable coefficients. This complicates the solution of the problem compared with the solutions for constant modulus of elasticity, but it provides a more accurate solution.

Rotating Disk Shape: Is the Equation Nonlinear?

1989 ◽  
Vol 111 (4) ◽  
pp. 456-458
Author(s):  
R. R. Jettappa
Keyword(s):  
Differential Equation ◽  
Linear Equation ◽  
Rotating Disk ◽  
Variable Coefficients ◽  
Thin Disk ◽  
Second Order ◽  
First Order ◽  
Governing Differential Equation ◽  
Centrifugal Loading

The determination of the shape of a rotating disk under centrifugal loading is considered. It is shown that the governing differential equation for the shape of a rotating thin disk is reducible to a linear equation of second order with variable coefficients. However, the form of this equation is such that it can be treated as an equation of first order thereby facilitating the integration by quadratures. All this is possible without any additional mathematical assumptions so that the results are exact within the limitations of the thin disk theory.

Direct Similarity Reduction and New Exact Solutions for the Variable-Coefficient Kadomtsev–Petviashvili Equation

2015 ◽  
Vol 70 (6) ◽  
pp. 445-450 ◽  
Author(s):  
Rehab M. El-Shiekh
Keyword(s):  
Differential Equation ◽  
Ordinary Differential Equation ◽  
Variable Coefficient ◽  
Nonlinear Partial Differential Equation ◽  
Direct Methods ◽  
Periodic Wave ◽  
Variable Coefficients ◽  
Nonlinear Phenomena ◽  
Similarity Reduction ◽  
Petviashvili Equation

AbstractIn this paper, the generalized (3+1)-dimensional variable-coefficient Kadomtsev–Petviashvili equation (VCKPE), which can describe nonlinear phenomena in fluids or plasmas, is studied by using two different Clarkson and Kruskal (CK) direct methods, namely, the classical CK and the modified enlarged CK method. A similarity reduction to a (2+1)-dimensional nonlinear partial differential equation and a direct similarity reduction to a nonlinear ordinary differential equation are obtained, respectively. By solving the reduced ordinary differential equation, new solitary, periodic, and singular solutions for the VCKPE are obtained. Some figures for the soliton and periodic wave solutions are given to reflect the effect of the variable coefficients on the solution propagation. Finally, the comparison between the two different CK techniques indicates that the modified enlarged CK technique is clearly more powerful and simple than the classical CK technique.

Inclusion of a Support Friction Into a Computerized Solution of a Self-Compensating Pipeline

1972 ◽  
Vol 94 (3) ◽  
pp. 797-802 ◽  
Author(s):  
J. Sobieszczanski
Keyword(s):  
Differential Equation ◽  
Computer Program ◽  
Fourth Order ◽  
Order Differential Equation ◽  
Bending Moment ◽  
Variable Coefficients ◽  
Point Boundary ◽  
Friction Forces ◽  
The One ◽  
Fourth Order Differential Equation

Thermal elongations of a pipeline are compensated in many cases by bending of pipeline branches. If the pipeline lies on a horizontal rough and flat foundation that bending is influenced by friction forces. Analysis of that influence is given in the paper. A nonlinear, fourth order differential equation with variable coefficients governing the phenomenon is derived and solved numerically as a two-point boundary problem. A version of the solution suitable for a pipeline on discrete supports has been developed. It may be used in conjunction with any existing computer program for pipeline stress analysis. The results demonstrate existence of a very significant additional bending moment due to friction. It may exceed several times the one computed for a pipeline on frictionless foundation.

scholarly journals Oscillation criteria for differential equations with piecewise constant argument

2001 ◽  
Vol 32 (4) ◽  
pp. 293-304
Author(s):  
Zhiguo Luo ◽  
Jianhua Shen
Keyword(s):  
Differential Equation ◽  
Continuous Functions ◽  
Variable Coefficients ◽  
Piecewise Constant ◽  
Piecewise Constant Argument ◽  
Greatest Integer Function ◽  
Special Case ◽  
Oscillation And Nonoscillation Criteria ◽  
Oscillation And Nonoscillation ◽  
Constant Argument

We obtain some new oscillation and nonoscillation criteria for the differential equation with piecewise constant argument $$ x'(t) + a(t)x(t) + b(x) x([t-k]) = 0, $$ where $ a(t) $ and $ b(t) $ are continuous functions on $ [-k, \infty) $, $ b(t) \ge 0 $, $ k $ is a positive integer and $ [ \cdot ] $ denotes the greatest integer function. The method used is based on the treatment of certain difference equation with variable coefficients. Our results extend theorems in [15]. As a special case, our results also improve the conclusions obtained by Aftabizadeh, Wiener and Xu [3].

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