41 
An experimental investigation of the bifurcation in twisted square platesHowell, Robert A. January 1991 (has links)
The bifurcation phenomenon occurring in twisted square plates with free edges subject to contrary selfequilibrating corner loading was examined. In order to eliminate lateral deflection of the test plates due to their own weight, a special loading apparatus was constructed which held the plates in a vertical plane. The complete strain field occurring at the plate centre was measured using two strain gauge rosettes mounted on opposing sides of the plate at the centre. Principal curvatures were calculated and related to corner load for several plates with differing edge length/thickness ratios. A Southwell plot was used relating mean curvature to the ratio mean curvature/Gaussian curvature, from which the Gaussian curvature occurring at bifurcation was determined. The critical dimensionless twist ka was then calculated for each plate size. It was found that there is a linear relation between the critical dimensionless twist ka occurring at bifurcation, and the thickness to edge length ratio h/a ratio, specifically: ka = 10.8h/a. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

42 
Double Hopf bifurcations in two geophysical fluid dynamics modelsLewis, Gregory M. 05 1900 (has links)
We analyze the double Hopf bifurcations which occur in two geophysical fluid dynamics
models: (1) a twolayer quasigeostrophic potential vorticity model with forcing and (2) a
mathematical model of the differentially heated rotating annulus experiment. The bifurcations
occur at the transition between axisymmetric steady solutions and nonaxisymmetric
travelling waves. For both models, the results indicate that, close to the transition, there
are regions in parameter space where there are multiple stable waves. Hysteresis of these
waves is predicted. For each model, center manifold reduction and normal form theory are
used to deduce the local behaviour of the full system of partial differential equations from
a lowdimensional system of ordinary differential equations.
In each case, it is not possible to compute the relevant eigenvalues and eigenfunctions
analytically. Therefore, the linear part of the equations is discretized and the eigenvalues
and eigenfunctions are approximated from the resulting matrix eigenvalue problem. However,
the projection onto the center manifold and reduction to normal form can be done
analytically. Thus, a combination of analytical and numerical methods are used to obtain
numerical approximations of the normal form coefficients, from which the dynamics are
deduced.
The first model differs from those previously studied with bifurcation analysis since
it supports a steady solution which varies nonlinearly with latitude. The results indicate
that the forcing does not qualitatively change the behaviour. However, the form of the
bifurcating solution is affected.
The second model uses the NavierStokes equations in the Boussinesq approximation, in
cylindrical geometry. In addition to the double Hopf bifurcation analysis, a detailed axisymmetric
to nonaxisymmetric transition curve is produced from the computed eigenvalues. A
quantitative comparison with experimental data finds that the computed transition curve,
critical wave numbers and drift rates of the bifurcating waves are reasonably accurate. This
indicates that the analysis, as well as the approximations which are made, are valid. / Science, Faculty of / Mathematics, Department of / Graduate

43 
Hopf Bifurcation Analysis for a Variant of the Logistic Equation with DelaysChifan, Iustina 14 May 2020 (has links)
This thesis contains some results on the behavior of a delay differential equation (DDE) with two delays, at a Hopf bifurcation, for the nonzero equilibrium, using the growth rate, r, as bifurcation parameter. This DDE is a model for population growth, incorporating a maturation delay, and a second delay in the harvesting term. Considering a Taylor expansion of the nondimensionalized model, we find a region of stability for the nonzero equilibrium, after which we find a pair of ODEs which help define the flow on the center manifold. We then find an expression for the first Lypapunov coefficient, which changes sign, so we also find the second Lyapunov coefficient, allowing us to predict multistability in the model. Numerical simulations provide examples of the behavior expected. For a similar model with one delay (PMC model), we prove the Hopf bifurcation at the nonzero equilibrium is always supercritical.

44 
Mathematical Models of the AlphaBeta Phase Transition of QuartzMoss, George W. 25 August 1999 (has links)
We examine discrete models with hexagonal symmetry to compare the sequence of transitions with the alphaincbeta phase transition of quartz. We examine a model by Parlinski which employs interactions of nearest and nextnearest neighbor atoms. We numerically determine the configurations which lead to minimum energy for a range of parameters. We then use Golubitsky's results on systems with hexagonal symmetry to derive the bifurcation diagram for Parlinski's model. Finally, we study a large class of modifications to Parlinski's model and show that all such modifications have the same bifurcation picture as the original model. / Ph. D.

45 
Supercritical and Subcritical Pitchfork Bifurcations in a Buckling Problem for a Graphene Sheet between 2 Rigid SubstratesGrdadolnik, Jake Matthew 28 April 2021 (has links)
No description available.

46 
Results and Examples Regarding Bifurcation with a TwoDimensional KernelKaschner, Scott R. 15 May 2008 (has links)
No description available.

47 
Hopf bifurcation and centre bifurcation in three dimensional LotkaVolterra systemsSalih, Rizgar Haji January 2015 (has links)
This thesis presents a study of the centre bifurcation and chaotic behaviour of three dimensional LotkaVolterra systems. In two dimensional systems, Christopher (2005) considered a simple computational approach to estimate the cyclicity bifurcating from the centre. We generalized the technique to estimate the cyclicity of the centre in three dimensional systems. A lower bounds is given for the cyclicity of a hopf point in the three dimensional LotkaVolterra systems via centre bifurcations. Sufficient conditions for the existence of a centre are obtained via the Darboux method using inverse Jacobi multiplier functions. For a given centre, the cyclicity is bounded from below by considering the linear parts of the corresponding Liapunov quantities of the perturbed system. Although the number obtained is not new, the technique is fast and can easily be adapted to other systems. The same technique is applied to estimate the cyclicity of a three dimensional system with a plane of singularities. As a result, eight limit cycles are shown to bifurcate from the centre by considering the quadratic parts of the corresponding Liapunov quantities of the perturbed system. This thesis also examines the chaotic behaviour of three dimensional LotkaVolterra systems. For studying the chaotic behaviour, a geometric method is used. We construct an example of a three dimensional LotkaVolterra system with a saddlefocus critical point of Shilnikov type as well as a loop. A construction of the heteroclinic cycle that joins the critical point with two other critical points of type planar saddle and axial saddle is undertaken. Furthermore, the local behaviour of trajectories in a small neighbourhood of the critical points is investigated. The dynamics of the Poincare map around the heteroclinic cycle can exhibit chaos by demonstrating the existence of a horseshoe map. The proof uses a Shilnikovtype structure adapted to the geometry of these systems. For a good understanding of the global dynamics of the system, the behaviour at infinity is also examined. This helps us to draw the global phase portrait of the system. The last part of this thesis is devoted to a study of the zeroHopf bifurcation of the three dimensional LotkaVolterra systems. Explicit conditions for the existence of two first integrals for the system and a line of singularity with zero eigenvalue are given. We characteristic the parameters for which a zeroHopf equilibrium point takes place at any points on the line. We prove that there are three 3parameter families exhibiting such equilibria. First order of averaging theory is also applied but we show that it gives no information about the possible periodic orbits bifurcating from the zeroHopf equilibria.

48 
Étude d'un système prédateurproie avec fonction de réponse Holling de type III généraliséeLamontagne, Yann January 2006 (has links)
Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

49 
Teoria de bifurcação e aplicações / Bifurcation theory and applicationsRodriguez Villena, Diana Yovani [UNESP] 08 August 2017 (has links)
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Previous issue date: 20170808 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho, estudamos a teoria de bifurcação e algumas das suas aplicações. Apresentamos alguns resultados básicos e definimos o conceito de ponto de bifurcação. Logo, estudamos a teoria do grau topológico. Em seguida, enunciamos dois teoremas importantes que são os teoremas de Krasnoselski e de Rabinowitz. Finalmente apresentamos um exemplo e duas aplicações do teorema de Rabinowitz nas quais os valores característicos com que lidamos são simples, no exemplo se consegue provar que a segunda alternativa do teorema ocorre, a primeira aplicação é um problema de autovalores não lineares de SturmLiouville para uma E.D.O de segunda ordem na qual se prova que a primeira alternativa do teorema de Rabinowitz é válida e a segunda aplicação é um problema de autovalores para uma equação diferencial parcial quaselinear a qual se prova que também ocorre a primeira alternativa do teorema. / In this work, we study bifurcation theory and its applications. We present some basic results and define the concept of bifurcation point. Then we study the theory of topological degree. Next we state two important theorems that are Krasnoselski's theorem and Rabinowitz's theorem. Finally we present an example and two applications of Rabinowitz theorem in which the characteristic values we deal with are simple, in an example we can prove that the second item of theorem occurs and the first application is a nonlinear SturmLiouville eigenvalue problem for a second order ordinary differential equation were we prove that the first alternative of Rabinowitz's theorem holds and the second application is an eigenvalue problem for a quasilinear elliptic partial differential equation where we prove that the first alternative of the theorem also holds.

50 
Um estudo de bifurcações de codimensão dois de campos de vetores /Arakawa, Vinicius Augusto Takahashi. January 2008 (has links)
Orientador: Claudio Aguinaldo Buzzi / Banca: João Carlos da Rocha Medrado / Banca: Luciana de Fátima Martins / Resumo: Nesse trabalho são apresentados alguns resultados importantes sobre bifurcações de codimensão dois de campos de vetores. O resultado principal dessa dissertação e o teorema que d a o diagrama de bifurcação e os retratos de fase da Bifurcação de BogdanovTakens. Para a demonstracão são usadas algumas técnicas basicas de Sistemas Dinâmicos e Teoria das Singularidades, tais como Integrais Abelianas, desdobramentos de Sistemas Hamiltonianos, desdobramentos versais, Teorema de Preparação de Malgrange, entre outros. Outra importante bifurcação clássica apresentada e a Bifurca cão do tipo HopfZero, quando a matriz Jacobiana possui um autovalor simples nulo e um par de autovalores imagin arios puros. Foram usadas algumas hipóteses que garantem propriedades de simetria do sistema, dentre elas, assumiuse que o sistema era revers vel. Assim como na Bifurcação de BogdanovTakens, foram apresentados o diagrama de bifurcao e os retratos de fase da Bifurcação Hopfzero bifurcação reversível. As técnicas usadas para esse estudo foram a forma normal de Belitskii e o método do Blowup polar. / Abstract: In this work is presented some important results about codimension two bifurcations of vector elds. The main result of this work is the theorem that gives the local bifurcation diagram and the phase portraits of the BogdanovTakens bifurcation. In order to give the proof, some classic tools in Dynamical System and Singularities Theory are used, such as Abelian Integral, versal deformation, Hamiltonian Systems, Malgrange Preparation Theorem, etc. Another classic bifurcation phenomena, known as the HopfZero bifurcation, when the Jacobian matrix has a simple zero and a pair of purely imaginary eigenvalues, is presented. In here, is added the hypothesis that the system is reversible, which gives some symmetry in the problem. Like in BogdanovTakens bifurcation, the bifurcation diagram and the local phase portraits of the reversible Hopfzero bifurcation were presented. The main techniques used are the Belitskii theory to nd a normal forms and the polar Blowup method. / Mestre

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