A modified Galerkin/finite element method for the numerical solution of the Serre-Green-Naghdi system

A new modified Galerkin / Finite Element Method is proposed for the numerical solution of the fully nonlinear shallow water wave equations. The new numerical method allows the use of low-order Lagrange finite element spaces, despite the fact that the system contains third order spatial partial derivatives for the depth averaged velocity of the fluid. After studying the efficacy and the conservation properties of the new numerical method, we proceed with the validation of the new numerical model and boundary conditions by comparing the numerical solutions with laboratory experiments and with available theoretical asymptotic results

Effect of the initial conditions on a one-dimensional model of small-amplitude wave propagation in shallow water: II: Blowup for nonsmooth conditions.

Abstract Purpose – The purpose of this paper is to analyze numerically the blowup in finite time of the solutions to a one-dimensional, bidirectional, nonlinear wave model equation for the propagation of small-amplitude waves in shallow water, as a function of the relaxation time, linear and nonlinear drift, power of the nonlinear advection flux, viscosity coefficient, viscous attenuation, and amplitude, smoothness and width of three types of initial conditions. Design/methodology/approach – An implicit, first-order accurate in time, finite difference method valid for semipositive relaxation times has been used to solve the equation in a truncated domain for three different initial conditions, a first-order time derivative initially equal to zero and several constant wave speeds. Findings – The numerical experiments show a very rapid transient from the initial conditions to the formation of a leading propagating wave, whose duration depends strongly on the shape, amplitude and width of the initial data as well as on the coefficients of the bidirectional equation. The blowup times for the triangular conditions have been found to be larger than those for the Gaussian ones, and the latter are larger than those for rectangular conditions, thus indicating that the blowup time decreases as the smoothness of the initial conditions decreases. The blowup time has also been found to decrease as the relaxation time, degree of nonlinearity, linear drift coefficient and amplitude of the initial conditions are increased, and as the width of the initial condition is decreased, but it increases as the viscosity coefficient is increased. No blowup has been observed for relaxation times smaller than one-hundredth, viscosity coefficients larger than ten-thousandths, quadratic and cubic nonlinearities, and initial Gaussian, triangular and rectangular conditions of unity amplitude.Funding for open access charge: Universidad de Málaga / CBU

Lineer olmayan sobolev türü kısmi türevli diferansiyel denklemlerin tanh-coth yöntemi ile çözümü

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Birçok fiziksel olguyu açıklayan Sobolev türü denklemler, boyuta ve zamana bağlı türevleri, en yüksek mertebeden türevli terimlerinde bulundurmaları ile karakterize edilmektedir. En yüksek mertebeli türevlerinde sadece bir tane zamana bağlı türev bulunduran denklemler ise pseudoparabolik denklem olarak adlandırılır ve bu denklemler Sobolev türü denklemlerin özel bir durumudur. Bu çalıĢmada iyi bilinen Sobolev ve pseudoparabolik denklem türleri ele alınmıĢ ve bu denklemlerin genel özellikleri verilmiĢtir. Tanh-coth yöntemi lineer olmayan kısmi türevli diferansiyel denklemlerin hareketli dalga çözümlerini bulmada etkili ve güvenilir bir yöntemdir. Bugüne kadar bu yöntem yoğun olarak kullanılmıĢ ve yöntemin Riccati denklemi kullanılarak elde edilen modifikasyonları literatürde tartıĢılmıĢtır. Bu tezde, tanh-coth yönteminin temel özellikleri ve bu yöntemin diğer uzantıları ele alınmıĢtır. Buna ek olarak tanhcoth yöntemi, sembolik hesaplama sistemleri yardımıyla Sobolev türü denklemlerin tam çözümlerini araĢtırmada kullanılmıĢ ve bu denklemlerin birçok hareketli dalga çözümü elde edilmiĢtir. Elde edilen bu sonuçlar daha önce elde edilen bilgilerin bir doğrulaması ve geliĢtirilmesi olarak görülebilir. ÇalıĢma boyunca, cebirsel iĢlemler için Maple ve Scientific Work Place programları kullanılmıĢtır.Sobolev type equations have been used to describe many physical phenomena and they are characterized by having mixed time and space derivatives appearing in the highest-order terms of an partial differential equation. Equations with a one time derivative appearing in the highest order term are called pseudoparabolic and they are special case of Sobolev equations. In this work, well-known Sobolev and pseudoparabolic type equations have been considered and general properties of these equations have been given. The tanh-coth is a powerful and reliable technique for finding travelling wave solutions for nonlinear partial differential equations. This method has been used extensively and it was subjected by some modifications using the Riccati equation. The main features of the tanh-coth method and various extension forms of this method have been discussed in this thesis. Furthermore, the tanh-coth method with the aid of symbolic computational systems has been employed to investigate exact solutions of Sobolev type equations and abundant travelling wave solutions have been found. The results obtained can be viewed as a verification and improvement of the previously known data. Throughout the study, Maple and Scientific Work Place was used to deal with the tedious algebraic operations

A FILTER-FORCING TURBULENCE MODEL FOR LARGE EDDY SIMULATION INCORPORATING THE COMPRESSIBLE POOR MAN\u27S NAVIER--STOKES EQUATIONS

A new approach to large-eddy simulation (LES) based on the use of explicit spatial filtering combined with backscatter forcing is presented. The forcing uses a discrete dynamical system (DDS) called the compressible ``poor man\u27s\u27\u27 Navier--Stokes (CPMNS) equations. This DDS is derived from the governing equations and is shown to exhibit good spectral and dynamical properties for use in a turbulence model. An overview and critique of existing turbulence theory and turbulence models is given. A comprehensive theoretical case is presented arguing that traditional LES equations contain unresolved scales in terms generally thought to be resolved, and that this can only be solved with explicit filtering. The CPMNS equations are then incorporated into a simple forcing in the OVERFLOW compressible flow code, and tests are done on homogeneous, isotropic, decaying turbulence, a Mach 3 compression ramp, and a Mach 0.8 open cavity. The numerical results validate the general filter-forcing approach, although they also reveal inadequacies in OVERFLOW and that the current approach is likely too simple to be universally applicable. Two new proposals for constructing better forcing models are presented at the end of the work