# Person: ERBAY, Saadet

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ArticlePublication Metadata only Derivation of generalized Camassa-Holm equations from Boussinesq-type equations(Informa Group, 2016) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In this paper we derive generalized forms of the Camassa-Holm (CH) equation from a Boussinesq-type equation using a two-parameter asymptotic expansion based on two small parameters characterizing nonlinear and dispersive effects and strictly following the arguments in the asymptotic derivation of the classical CH equation. The resulting equations generalize the CH equation in two different ways. The first generalization replaces the quadratic nonlinearity of the CH equation with a general power-type nonlinearity while the second one replaces the dispersive terms of the CH equation with fractional-type dispersive terms. In the absence of both higher-order nonlinearities and fractional-type dispersive effects, the generalized equations derived reduce to the classical CH equation that describes unidirectional propagation of shallow water waves. The generalized equations obtained are compared to similar equations available in the literature, and this leads to the observation that the present equations have not appeared in the literature.Show more ArticlePublication Open Access Thresholds for global existence and blow-up in a general class of doubly dispersive nonlocal wave equations(Elsevier, 2014-01) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In this paper we study the global existence and blow-up of solutions for a general class of nonlocal nonlinear wave equations with power-type nonlinearities, View the MathML source, where the nonlocality enters through two pseudo-differential operators L and B. We establish thresholds for global existence versus blow-up using the potential well method which relies essentially on the ideas suggested by Payne and Sattinger. Our results improve the global existence and blow-up results given in the literature for the present class of nonlocal nonlinear wave equations and cover those given for many well-known nonlinear dispersive wave equations such as the so-called double-dispersion equation and the traditional Boussinesq-type equations, as special cases.Show more ArticlePublication Metadata only A comparison of solutions of two convolution-type unidirectional wave equations(Taylor and Francis, 2023) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In this work, we prove a comparison result for a general class of nonlinear dispersive unidirectional wave equations. The dispersive nature of one-dimensional waves occurs because of a convolution integral in space. For two specific choices of the kernel function, the Benjamin–Bona–Mahony equation and the Rosenau equation that are particularly suitable to model water waves and elastic waves, respectively, are two members of the class. We first prove an energy estimate for the Cauchy problem of the non-local unidirectional wave equation. Then, for the same initial data, we consider two distinct solutions corresponding to two different kernel functions. Our main result is that the difference between the solutions remains small in a suitable Sobolev norm if the two kernel functions have similar dispersive characteristics in the long-wave limit. As a sample case of this comparison result, we provide the approximations of the hyperbolic conservation law.Show more Conference paperPublication Open Access Unidirectional wave motion in a nonlocally and nonlinearly elastic medium: The KdV, BBM and CH equations(Estonian Academy of Sciences, 2015) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more We consider unidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral with a suitable kernel function. We first give a brief review of asymptotic wave models describing the unidirectional propagation of small-but-finite amplitude long waves. When the kernel function is the well-known exponential kernel, the asymptotic description is provided by the Korteweg–de Vries (KdV) equation, the Benjamin–Bona–Mahony (BBM) equation, or the Camassa–Holm (CH) equation. When the Fourier transform of the kernel function has fractional powers, it turns out that fractional forms of these equations describe unidirectional propagation of the waves. We then compare the exact solutions of the KdV equation and the BBM equation with the numerical solutions of the nonlocal model. We observe that the solution of the nonlocal model is well approximated by associated solutions of the KdV equation and the BBM equation over the time interval considered.Show more ArticlePublication Metadata only The Camassa-Holm approximation to the double dispersion equation for arbitrarily long times(Springer, 2022-09) Erbay, Saadet; Erkip, A.; Kuruk, G.; Natural and Mathematical Sciences; ERBAY, SaadetShow more In the present paper we prove the validity of the Camassa-Holm equation as a long wave limit to the double dispersion equation which describes the propagation of bidirectional weakly nonlinear and dispersive waves in an infinite elastic medium. First we show formally that the right-going wave solutions of the double dispersion equation can be approximated by the solutions of the Camassa-Holm equation in the long wave limit. Then we rigorously prove that the solutions of the double dispersion and the Camassa-Holm equations remain close over a long time interval, determined by two small parameters measuring the effects of nonlinearity and dispersion.Show more ArticlePublication Metadata only Convergence of a semi-discrete numerical method for a class of nonlocal nonlinear wave equations(EDP Sciences, 2018-09-13) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In this article, we prove the convergence of a semi-discrete numerical method applied to a general class of nonlocal nonlinear wave equations where the nonlocality is introduced through the convolution operator in space. The most important characteristic of the numerical method is that it is directly applied to the nonlocal equation by introducing the discrete convolution operator. Starting from the continuous Cauchy problem defined on the real line, we first construct the discrete Cauchy problem on a uniform grid of the real line. Thus the semi-discretization in space of the continuous problem gives rise to an infinite system of ordinary differential equations in time. We show that the initial-value problem for this system is well-posed. We prove that solutions of the discrete problem converge uniformly to those of the continuous one as the mesh size goes to zero and that they are second-order convergent in space. We then consider a truncation of the infinite domain to a finite one. We prove that the solution of the truncated problem approximates the solution of the continuous problem when the truncated domain is sufficiently large. Finally, we present some numerical experiments that confirm numerically both the expected convergence rate of the semi-discrete scheme and the ability of the method to capture finite-time blow-up of solutions for various convolution kernels.Show more ArticlePublication Metadata only Long-time existence of solutions to nonlocal nonlinear bidirectional wave equations(American Institute of Mathematical Sciences, 2019-05) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more We consider the Cauchy problem defined for a general class of nonlocal wave equations modeling bidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral. We prove a long-time existence result for the nonlocal wave equations with a power-type nonlinearity and a small parameter. As the energy estimates involve a loss of derivatives, we follow the Nash-Moser approach proposed by Alvarez-Samaniego and Lannes. As an application to the long-time existence theorem, we consider the limiting case in which the kernel function is the Dirac measure and the nonlocal equation reduces to the governing equation of one-dimensional classical elasticity theory. The present study also extends our earlier result concerning local well-posedness for smooth kernels to nonsmooth kernels.Show more ArticlePublication Metadata only The Camassa-Holm equation as the long-wave limit of the improved Boussinesq equation and of a class of nonlocal wave equations(AIMS, 2016-11) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In the present study we prove rigorously that in the long-wave limit, the unidirectional solutions of a class of nonlocal wave equations to which the improved Boussinesq equation belongs are well approximated by the solutions of the Camassa-Holm equation over a long time scale. This general class of nonlocal wave equations model bidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral. To justify the Camassa-Holm approximation we show that approximation errors remain small over a long time interval. To be more precise, we obtain error estimates in terms of two independent, small, positive parameters \epsilon and \delta measuring the effect of nonlinearity and dispersion, respectively. We further show that similar conclusions are also valid for the lower order approximations: the Benjamin-Bona-Mahony approximation and the Korteweg-de Vries approximation.Show more Conference paperPublication Open Access Some remarks on the stability and instability properties of solitary waves for the double dispersion equation(Estonian Academy of Sciences, 2015) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more In this article we give a review of our recent results on the instability and stability properties of travelling wave solutions of the double dispersion equation utt − uxx + auxxxx − buxxtt = −(|u|p−1u)xx for p > 1, a ≥ b > 0. After a brief reminder of the general class of nonlocal wave equations to which the double dispersion equation belongs, we summarize our findings for both the existence and orbital stability/instability of travelling wave solutions to the general class of nonlocal wave equations. We then state (i) the conditions under which travelling wave solutions of the double dispersion equation are unstable by blow-up and (ii) the conditions under which the travelling waves are orbitally stable. We plot the instability/stability regions in the plane defined by wave velocity and the quotient b/a for various values of p.Show more ArticlePublication Open Access Convergence of a linearly regularized nonlinear wave equation to the p-system(TÜBİTAK, 2023) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A. K.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, SaadetShow more We consider a second-order nonlinear wave equation with a linear convolution term. When the convolution operator is taken as the identity operator, our equation reduces to the classical elasticity equation which can be written as a p-system of first-order differential equations. We first establish the local well-posedness of the Cauchy problem. We then investigate the behavior of solutions to the Cauchy problem in the limit as the kernel function of the convolution integral approaches to the Dirac delta function, that is, in the vanishing dispersion limit. We consider two different types of the vanishing dispersion limit behaviors for the convolution operator depending on the form of the kernel function. In both cases, we show that the solutions converge strongly to the corresponding solutions of the classical elasticity equation.Show more

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