Coupled Nonlinear Differential Equations Research Articles

Unsteady radiative–convective flow of a compressible fluid: a numerical approach

This article is designed to inspect the thermal effects of an unsteady compressible flow of a viscous fluid through a symmetric channel. Combined effects of convective heat transfer, magnetic field, and radiation are also given special attention in this article. Basic laws of mass, momentum, and energy for compressible flow are employed in the modeling of the current problem. In addition, slip boundary conditions are also implemented in the analysis of the above thermal flow problem. Coupled nonlinear differential equations are solved numerically using explicit finite difference technique. Finally, the influence of different sundry parameters on the axial velocity, flow rate, and heat transfer are visualized through graphs. Time variant behavior of flow rate is calculated. Outcomes of the results reveal that the increment of the flow rate is related to the increase of compressibility parameters. Enhancement in the temperature profiles in the presence of radiation number is also reported. This model is the most general version of peristalsis of compressible flow in view of natural convection and radiation impact with extensive applications in aircraft industry, geophysics, and other industrial situations (cooling of electronic equipment, heat exchangers, and so forth).

Time‐dependent hydromagnetic stagnation point flow of a Maxwell nanofluid with melting heat effect and amended Fourier and Fick's laws

AbstractAn unsteady stagnation point flow of a Maxwell fluid over a unidirectional linearly stretching sheet is studied under the influence of a magnetic field. The parabolic energy equation, which is based on parabolic Fourier law is replaced with a hyperbolic energy equation incorporating the heat flux model of Cattaneo–Christov. The Buongiorno model is used to characterize the properties of nanofluids using thermophoresis and Brownian diffusion coefficients. The phenomenon of melting heat transfer and slip mechanism is also embodied in the present study. Coupled nonlinear differential equations have appeared when the specified similarity transformations are applied. The mathematical problem is tackled via the homotopy analysis method. The impact of important physical parameters on the velocity, concentration, and temperature are highlighted via graphs. To verify our present results, a comparison is given with a limiting case with an already published article. It is witnessed through the graphs that the higher unsteadiness parameter and melting heat coefficient both are responsible for the reduction in the velocity and temperature of the nanofluid. Also, the velocity slip parameter detracts the velocity profile and affiliated boundary layer thickness of the Maxwell nanofluid.

Nonlinear vibro-acoustic behavior of cylindrical shell under primary resonances

Nonlinear vibro-acoustic behavior of cylindrical shell excited by an oblique incident plane sound wave under primary resonances is analytically examined in this paper. Donnell’s nonlinear shallow shell theory is used to model the cylindrical shell. Coupled nonlinear differential equations of the system are analytically derived using Galerkin’s approach. The Multiple Scales Method is hence, employed to solve the corresponding nonlinear equations. Then, the effects of crucial design parameters including incident sound wave amplitude, damping ratio and thickness of the shell on the characteristics of the sound transmission loss are studied for different resonance cases. In addition, the effect of detuning parameter on the bifurcation and behavior of the limit cycle under primary resonance is examined. The results show that the detuning parameter is a bifurcation parameter and Neimark–Sacker, flip, and period-3 bifurcations occur when this parameter is varied. Also, according to the results, by getting away from the resonance frequencies, excitation level incorporates no significant effect on the transmission loss of the shell.

Nonlinear harmonic vibration analysis of a plate-cavity system

Nonlinear harmonic oscillation of a plate-cavity system is analytically studied in this paper. Von-Karman theory is used to model a rectangular plate backed by an air cavity. Coupled nonlinear differential equations of system are analytically derived using Galerkin’s approach. The Multiple Scales Method (MSM) is then employed to solve the corresponding nonlinear equations. Primary, secondary, and combinational resonance conditions are taken into account and the corresponding closed-form frequency-amplitude relationships are derived. A parametric study is carried out and effects of different parameters on the frequency responses are investigated.

Forward multibeam mixing in diffusion-driven photorefractive media

Multibeam mixing in diffusion-driven media is presented as a diagnostic for the study of nonplane wave photorefractive interactions based on the premise that a complex wavefront can be analyzed as the superposition of many plane waves. Coupled-nonlinear differential equations which describe the interactions of the intensities as they couple through the medium are derived. These equations were numerically solved using a Runge-Kutta algorithm to gain insight as to how the beams interact in the medium. Three beam interactions was experimentally studied in BaTiO/sub 3/ at 514.5 nm to verify the analysis. Results indicate that phase aberrations affect intensity distributions in the enhanced beam.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A solution method for solving coupled nonlinear boundary-value problems

A Strum-Liouville integral transform technique is novelly applied to solve system of coupled nonlinear boundary-value problems approximately. The systems of differential equations consist of a linear differential operator and a nonlinear function of the dependent variables. To illustrate the potential of this technique we consider an example which comes from the modeling of diffusion and nonlinear chemical reaction systems in chemical engineering. The approximate solutions obtained by our technique agree surprising well with the numerically exact solutions obtained by the orthogonal collocation technique. To improve the approximation an iteration scheme in transform space is also defined. Scope—Today, mathematical modeling of physical phenomena often produces (single or coupled) nonlinear differential equations. The true physical situation can, in many cases, be more closely described if the differential equations are allowed to be nonlinear. However, nonlinear differential equations are generally too difficult to be solved analytically apart from a few “tricks” or substitutions which apply only to a handful of equations [1]. An alternative approach is to look for a method which will reduce the problem, via analytical techniques, to a point where a “simple” computer program can solve the rest of the problem. The method introduced in this paper belongs to this class of solution techniques. The method, which in this paper is applied to solving coupled nonlinear boundary-value problems, is a generalization of an idea in a paper by Do and Bailey [2] who apply it to a single nonlinear differential equation of boundary-value type. The equations, to which the technique is applied, arise from Fick's law diffusion into a porous solid and nonlinear reaction within the solid. The solution method employs a Strum-Loiuville integral transform and to account for the nonlinear part an approximation is introduced. An iteration scheme is defined to improved the accuracy of the solution. The system of coupled nonlinear differential equations is reduced to a system of coupled nonlinear algebraic equations which is solved using a Newton-Raphson process. Finally, the solution is expressed as an infinite series, which is summed using a computer. In response to papers by Do and Bailey [3] and Do and Weiland [4], Jerri [5] has tried to put this method on a more mathematical footing, and he shows that this method is a special case of a more general technique he has devised. Jerri uses the idea of Fourier transforms and convolution products to justify his method. The results for the example he considered are good, but he did not state how many iterations he required to obtain the solutions reported. Conclusions and Significance—This paper has presented a very powerful method of solving boundary-value problems with linear operators and a nonlinear function of the dependent variable. The method works well for a single equation or coupled equations and can handle any kind of nonlinear function. We have shown through extensive numerical calculation the accuracy of this solution method, where the accuracy is measured in terms of a ratio of norms. In most cases an error of 4% can be achieved with just one iteration (Tables 2 and 3). Even though the present method has been applied to problems which have arisen from the modeling of chemical engineering problems, it would also be applicable to differential equations arising in other areas, provided they are of the same form.

Compressible Oscillating Boundary Layers

The response of the compressible boundary layer to small fluctuations of the outer flow is investigated. The governing equations and the appropriate boundary conditions are formulated for the first time in considerable generality. It appears that the outer flow properties do not oscillate in phase with each other. Such phase differences are augmented as one proceeds across the boundary layer. Solutions are presented for small amplitudes in the form of asymptotic expansions in powers of a frequency parameter. Ordinary but coupled nonlinear differential equations are derived for self-similar flows. Results are presented for a steady part of the solution that corresponds to flat plate and stagnation flows and oscillations of the outer flow in magnitude or direction.

Excitatory and Inhibitory Interactions in Localized Populations of Model Neurons

Coupled nonlinear differential equations are derived for the dynamics of spatially localized populations containing both excitatory and inhibitory model neurons. Phase plane methods and numerical solutions are then used to investigate population responses to various types of stimuli. The results obtained show simple and multiple hysteresis phenomena and limit cycle activity. The latter is particularly interesting since the frequency of the limit cycle oscillation is found to be a monotonic function of stimulus intensity. Finally, it is proved that the existence of limit cycle dynamics in response to one class of stimuli implies the existence of multiple stable states and hysteresis in response to a different class of stimuli. The relation between these findings and a number of experiments is discussed.