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Literatura académica sobre el tema "Non-Cylindrical domains"

Autor: Grafiati

Publicado: 25 de mayo de 2024

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Artículos de revistas sobre el tema "Non-Cylindrical domains"

Schindlmayr, G. "Capillary Surfaces in Non-Cylindrical Domains". Zeitschrift für Analysis und ihre Anwendungen 19, n.º 3 (2000): 747–62. http://dx.doi.org/10.4171/zaa/978.

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Jenaliyev, M. T., A. M. Serik y M. G. Yergaliyev. "On the solvability of a boundary value problem for a two-dimensional system of Navier-Stokes equations in a cone". BULLETIN OF THE KARAGANDA UNIVERSITY-MATHEMATICS 113, n.º 1 (29 de marzo de 2024): 84–100. http://dx.doi.org/10.31489/2024m1/84-100.

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Due to the fact that the Navier-Stokes equations are involved in the formulation of a large number of interesting problems that are important from an applied point of view, these equations have been the object of attention of mechanics, mathematicians and other scientists for several decades in a row. But despite this, many problems for the Navier-Stokes equation remain unexplored to this day. In this work, we are exploring the solvability of a boundary value problem for a two-dimensional Navier-Stokes system in a non-cylindrical degenerating domain, namely, in a cone with its vertex at the origin. Previously, we studied cases of the linearized Navier-Stokes system or non-degenerating cylindrical domains, so this work is a logical continuation of our previous research in this direction. To the above-mentioned degenerate domain we associate a family of non-degenerate truncated cones, which, in turn, are formed by a oneto-one transformation into cylindrical domains, where for the problem under consideration we established uniform a priori estimates with respect to changes in the index of the domains. Further, using a priori estimates and the Faedo-Galerkin method, we established the existence, uniqueness of solution in Sobolev classes, and its regularity as the smoothness of the given functions increases.

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Brown, Russell M., Wei Hu y Gary M. Lieberman. "Weak solutions of parabolic equations in non-cylindrical domains". Proceedings of the American Mathematical Society 125, n.º 6 (1997): 1785–92. http://dx.doi.org/10.1090/s0002-9939-97-03759-3.

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Kuliev, Komil y Lars-Erik Persson. "An extension of Rothe’s method to non-cylindrical domains". Applications of Mathematics 52, n.º 5 (octubre de 2007): 365–89. http://dx.doi.org/10.1007/s10492-007-0021-6.

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Bernardi, Marco Luigi, Gianni Arrigo Pozzi y Giuseppe Savaré. "Variational Equations of Schroedinger-Type in Non-cylindrical Domains". Journal of Differential Equations 171, n.º 1 (marzo de 2001): 63–87. http://dx.doi.org/10.1006/jdeq.2000.3834.

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Bran, Cristina, Jose Angel Fernandez-Roldan, Rafael P. del Real, Agustina Asenjo, Oksana Chubykalo-Fesenko y Manuel Vazquez. "Magnetic Configurations in Modulated Cylindrical Nanowires". Nanomaterials 11, n.º 3 (28 de febrero de 2021): 600. http://dx.doi.org/10.3390/nano11030600.

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Cylindrical magnetic nanowires show great potential for 3D applications such as magnetic recording, shift registers, and logic gates, as well as in sensing architectures or biomedicine. Their cylindrical geometry leads to interesting properties of the local domain structure, leading to multifunctional responses to magnetic fields and electric currents, mechanical stresses, or thermal gradients. This review article is summarizing the work carried out in our group on the fabrication and magnetic characterization of cylindrical magnetic nanowires with modulated geometry and anisotropy. The nanowires are prepared by electrochemical methods allowing the fabrication of magnetic nanowires with precise control over geometry, morphology, and composition. Different routes to control the magnetization configuration and its dynamics through the geometry and magnetocrystalline anisotropy are presented. The diameter modulations change the typical single domain state present in cubic nanowires, providing the possibility to confine or pin circular domains or domain walls in each segment. The control and stabilization of domains and domain walls in cylindrical wires have been achieved in multisegmented structures by alternating magnetic segments of different magnetic properties (producing alternative anisotropy) or with non-magnetic layers. The results point out the relevance of the geometry and magnetocrystalline anisotropy to promote the occurrence of stable magnetochiral structures and provide further information for the design of cylindrical nanowires for multiple applications.

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Kubica, A., P. Rybka y K. Ryszewska. "Weak solutions of fractional differential equations in non cylindrical domains". Nonlinear Analysis: Real World Applications 36 (agosto de 2017): 154–82. http://dx.doi.org/10.1016/j.nonrwa.2017.01.005.

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Paronetto, Fabio. "An existence result for evolution equations in non-cylindrical domains". Nonlinear Differential Equations and Applications NoDEA 20, n.º 6 (14 de marzo de 2013): 1723–40. http://dx.doi.org/10.1007/s00030-013-0227-0.

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De Caldas, C. S. Q., J. Límaco y R. K. Barreto. "Beam evolution equation with variable coefficients in non-cylindrical domains". Mathematical Methods in the Applied Sciences 31, n.º 3 (2007): 339–61. http://dx.doi.org/10.1002/mma.912.

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Bottois, Arthur, Nicolae Cîndea y Arnaud Münch. "Optimization of non-cylindrical domains for the exact null controllability of the 1D wave equation". ESAIM: Control, Optimisation and Calculus of Variations 27 (2021): 13. http://dx.doi.org/10.1051/cocv/2021010.

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This work is concerned with the null controllability of the one-dimensional wave equation over non-cylindrical distributed domains. The controllability in that case has been obtained by Castro et al. [SIAM J. Control Optim. 52 (2014)] for domains satisfying the usual geometric optic condition. We analyze the problem of optimizing the non-cylindrical support q of the control of minimal L2(q)-norm. In this respect, we prove a uniform observability inequality for a class of domains q satisfying the geometric optic condition. The proof based on the d’Alembert formula relies on arguments from graph theory. Numerical experiments are discussed and highlight the influence of the initial condition on the optimal domains.

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Tesis sobre el tema "Non-Cylindrical domains"

Rivera, Noriega Jorge. "Some remarks on certain parabolic differential operators over non-cylindrical domains /". free to MU campus, to others for purchase, 2001. http://wwwlib.umi.com/cr/mo/fullcit?p3025649.

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Klovienė, Neringa. "Non-stationary Poiseuille type solutions for the second grade fluid flow problem in cylindrical domains". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130124_081843-47698.

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In the dissertation one of the Rivlin-Erikson differential type fluids model – the second grade fluids flow problem is considered. The problem is studied in three different unbounded domains: • the two-dimensional channel, • the three-dimensional axially symmetric pipe, • the three-dimensional pipe with an arbitrary cross section. For the two-dimensional channel and the three-dimensional axially symmetric pipe we assume that the initial data and the external force have only the last component and are independent of the coordinate x_n: u_0(x,t)=(0, …, u_{n0}(x’,t)), f(x,t)=(0, …, f_n(x’,t)). We look for an unidirectional (having just the last component) solution u(x,t) =(0, …, u_n(x’,t)), which satisfies the flux condition. Such solution we call Poiseuille type solution. In the first two cases the existence of a unique unidirectional Poiseuille type solution is proved and the relation between the flux of the velocity field and the pressure drop (the gradient of the pressure) is found. The analogous results were obtained for the time periodic problem in the two-dimensional channel. It is shown that in the three-dimensional pipe with an arbitrary cross section the unidirectional solution does not exists even if data are unidirectional. However, for sufficiently small data in this case exists a unique solution having all three components u(x’,t)=( u_1, u_2, u_3). To analyze the problem we use Galerkin method with the special bases.
Disertacijoje nagrinėjamas vienas iš Rivlin-Eriksono diferencialinio tipo skysčių matematinių modelių – antrojo laipsnio skysčių tekėjimo uždavinys. Problema analizuojama su papildomai užduota srauto sąlyga trijose skirtingose srityse: • begalinėje juostoje, • begaliniame sukimosi cilindre, • begaliniame vamzdyje su bet kokiu skerspjūviu. Tariama, kad pradinio greičio ir išorės jėgų vektoriai nepriklauso nuo paskutinės koordinatės ir yra išreikšti pavidalu u_0(x,t)=(0, …, u_{n0}(x’,t)), f(x,t)=(0, …, f_n(x’,t)). Ieškoma antrojo laipsnio skysčių tekėjimo uždavinio Puazeilio tipo u(x,t) =(0, …, u_n(x’,t)) sprendinio. Begalinėje dvimatėje juostoje ir begaliniame trimačiame sukimosi cilindre įrodytas kryptinio Puazeilio tipo sprendinio egzistavimas ir rastas sąryšis tarp srauto ir slėgio gradiento. Analogiški rezultatai gauti pradiniam ir kraštiniam antrojo laipsnio skysčių tekėjimo uždaviniui periodinėje pagal laiką begalinėje dvimatėje juostoje. Darbe parodyta, kad begaliniame trimačiame vamzdyje, su bet kokiu skerspjūviu, kryptinis (priklausantis tik nuo paskutinės komponentės) Puazeilio tipo sprendinys neegzistuoja net jei pradiniai duomenys yra kryptiniai. Nagrinėjamas bendresnis atvejis, kai Puazeilio tipo sprendinys priklauso nuo visų trijų komponenčių u(x’,t)=( u_1, u_2, u_3). Disertacijoje įrodyta, kad esant mažiems pradiniams duomenims egzistuoja vienintelis uždavinio sprendinys. Sprendžiant buvo naudojamas Galiorkino aproksimacijų metodas ir specialios bazės.

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Nägele, Philipp [Verfasser] y Michael [Akademischer Betreuer] Růžička. "Monotone operator theory for unsteady problems on non-cylindrical domains = Monotone Operatoren-Theorie für instationäre Probleme auf nicht-zylindrischen Gebieten". Freiburg : Universität, 2015. http://d-nb.info/111932758X/34.

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Mokhtari, Yacine. "Stabilisation et contrôle de quelques systèmes hyperboliques". Electronic Thesis or Diss., Bourgogne Franche-Comté, 2021. http://www.theses.fr/2021UBFCD024.

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Cette thèse est consacrée à l’étude de deux problèmes issus de la théorie du contrôle des EDP. Dans un premier temps, on étudie le comportement asymptotique de la solution du système de von Kàrmàn viscoélastique unidimensionnel avec retard. On montre que ce dernier est bien posé dans un espace fonctionnel convenable en utilisant la méthode de Faedo-Galerkin. Pour établir notre résultat de stabilité, on utilise la méthode de Lyapunov en construisant une fonctionnelle adéquate. Dans un deuxième temps, on étudie le problème de la contrôlabilité et de la stabilisation par le bord pour l’équation des ondes unidimensionnelle dans un domaine non cylindrique. Pour la contrôlabilité, on utilise la méthode des caractéristiques pour construire l’unique solution du problème. Nous sommes alors capables de donner l’expression explicite du contrôle pour lequel le système atteint le point d’équilibre après un certain temps. De plus, on montre que ce temps est optimal. Pour la stabilisation, nous fournissons une condition nécessaire et suffisante pour que l’énergie du système décroisse à un taux prédéterminé. De plus, l’influence de la géométrie du domaine et l’influence d’un amortisseur dépendant du temps sont clarifiées. Dans un troisième temps, on étudie la contrôlabilité par le bord de deux ´équations d’ondes couplées par un couplage d’ordre un avec coefficients qui dépendent de l’espace et du temps. On fournit une condition nécessaire et suffisante pour la contrôlabilité exacte en haute fréquences dansle cas général et pour la continuation unique dans le cas cascade
This thesis is devoted to the study of two problems related to the theory of control of PDE.In a first time, we study the asymptotic behavior of the solution to the one-dimensional viscoelastic von Kàrmàn system with delay. We prove that the latter system is well-posed in a suitable functional space using the Faedo-Galerkin method. To establish our stability result, we employ the Lyapunov method by using a suitable candidate functional.In a second time, we study the problem of boundary controllability and stabilization for the one-dimensional wave equation in non-cylindrical domains. For the controllability, one uses the characteristics method to build the unique solution. We will then be able to give the explicit expression of the controls for which the system reaches the equilibrium point after a certain time. Moreover, we show that this time is optimal.For the stabilization, we provide a necessary and sufficient condition that guarantees the energy decay at any desired rate. In addition, the influences of the domain geometry and time-dependent feedback are clarified. In a third time, we study the boundary controllability of two coupled one-dimensional wave equations with first-order coupling terms with coefficients depending on space and time. We give a necessary and sufficient conditions for both exact controllability in high frequency in the general case and for the unique continuation in the cascade case

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Bavelis, Konstantinos. "Finite-element time-domain modelling of cylindrical structures with a modal non-reflecting boundary condition". Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/36763/.

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This dissertation presents Galerkin weighted residual Finite-Element Time-Domain (FETD) formulations using a 2D cylindrical modal non-reflecting boundary condition (MNRBC) for the modelling of plane wave scattering from cylindrical structures of arbitrary cross-section surrounded by free space. Chapter 1 begins by presenting the motivation for this work. Key concepts regarding cylindrical geometries are introduced at this stage. The Galerkin weighted residual Finite-Element method is briefly outlined. Chapter 2 presents a novel scattered field FETD-MNRBC formulation for the transverse electric polarisation of a modal non-reflecting boundary condition for plane wave scattering from perfectly electrically conductive (PEC) cylindrical structures of arbitrary cross-section. The boundary condition is based on a Vector-Fitting (VF) approximation of the boundary kernel appearing in the time-domain formulation. The convolution integral appearing in the time-domain formulation of the boundary condition is calculated recursively using the Vector-Fitting coefficients. Accurate numerical results are shown for the bistatic scattering width (BSW) that validate the approach. Chapter 3 focuses on the VF approximation of the cylindrical boundary kernel. Two approaches are investigated; the so called Vector-Fitting G function approximation (VFG) and the Vector-Fitting U function approximation (VFU). Both approaches produce satisfactory finite-element results with the VFU being more versatile. Chapter 4 presents, for the first time, the total field FETD-MNRBC formulation for both transverse electric and transverse magnetic polarisations. The VFU approach is employed. The structures considered in this chapter are not only PEC cylinders but also dielectric ones of various cross-sections and various values of relative permittivity and permeability. The numerical results demonstrate the good accuracy of this formulation. Chapter 5 combines the cylindrical modal non-reflecting boundary condition with the Floquet theorem and extends this formulation, for the first time, to azimuthally periodic cylinders using scattered and total field time-domain formulations. The advantages and disadvantages of the periodic modal non-reflecting boundary condition approach are discussed and numerical results for the BSW are shown. Chapter 6 presents a novel sparse-matrix scattered field FETD-MNRBC formulation in which the fully dense submatrices associated with the boundary integral are avoided. Through numerical results the accuracy of the proposed formulation is investigated. Chapter 7 concludes the work by summarizing the main achievements and discussing its impact in electromagnetics.

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Mejri, Youssef. "Problèmes inverses pour l’équation de Schrödinger". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0506/document.

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Les travaux de recherche présentés dans cette thèse sont consacrés à l’étude de la stabilité dans divers problèmes inverses associés à l’équation de Schrödinger magnétique. Dans la première partie, on s’intéresse à un problème inverse concernant l’équation de Schrödinger autonome posée dans un domaine cylindrique non borné, avec potentiel magnétique périodique. On démontre à l’aide d’une construction de solutions particulières, dites solutions de type "optique géométrique", que le champ magnétique induit par le potentiel périodique est déterminé de façon stable à partir une infinité d’observations latérales de la solution, contenues dans l’opérateur de Dirichlet-Neumann. La deuxième partie de la thèse porte sur le même type de problèmes inverses mais associés à l’équation de Schrödinger magnétique non autonome. Dans un premier temps, on montre l’existence d’une unique solution régulière de cette équation dans un domaine borné ou non. Ensuite, on s’intéresse au problème inverse de la détermination simultanée des potentiels magnétique et électrique dans un domaine borné, à partir d’un nombre fini d’observations latérales de la solution. Enfin, on prouve que dans un domaine cylindrique infini, le potentiel magnétique peut être reconstruit de façon Lipschitz stable à partir d’un nombre fini d’observations de type Neumann
This thesis, is devoted to the study of inverse problems related to the Schrödinger equation. The first partof the thesis is devoted to study the boundary inverse problem of determining the alignedmagnetic field appearing in the magnetic Schrödinger equation in a periodic quantum cylindricalwaveguide. From the Dirichlet-to-Neumann map of the magnetic Schrödinger equation,we prove a Hölder stability estimate with respect to the Dirichlet-to-Neumann map, by meansof the geometrical optics solutions of the magnetic Schrödinger equation.The second part of this thesis deals with the inverse problem of determining the magnetic field and the electricpotential appearing in the magnetic Schrödinger equation, from the knowledge of a finitenumber of lateral observations of the solution

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Lázaro, Heraclio Ledgar López [UNESP]. "Atratores pullback para equações parabólicas semilineares em domínios não cilíndricos". Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/136350.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
The problem that we are going to study in this work, is motivated by the dynamics of differential equations nonautonomous. We will establish the existence and uniqueness of solution for a class of parabolic semilineares equations with Dirichlet boundary condition, in a family of domains that varies with time. In addition, certain hypotheses about the non-linearity, we will show the existence of a family of attractors pullback.
O problema que vamos estudar neste trabalho é motivado pela dinâmica de equações diferenciais não autônomas. Vamos estabelecer a existência e unicidade de solução para uma classe de equaçõoes parabólicas semilineares com condição de fronteira de Dirichlet, em uma família de domínios que varia com o tempo. Além disso, sob certas hipóteses sobre a não linearidade, mostraremos a existência de uma família de atratores pullback.

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SILVA, Luciano Cipriano da. "Observações sobre controle hierárquico em domínio não cilíndrico". Universidade Federal de Campina Grande, 2013. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1363.

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Capes
Neste trabalho estudamos o controle hierárquico, para um sistema parabólico, em um domínio não cilíndrico. O controle hierárquico é um problema que consiste em aproximar, em um tempo fixado, as soluções das equações de estado que temos, (essas soluções dependem de funções chamadas controles), de um estado considerado ideal, através de um sistema de líder, que é o controle independente, e seguidores, que são os controles que dependem da ação do líder. Começamos fazendo uma transformação do problema original para um equivalente em domínio cilíndrico, então estudamos o controle hierárquico deste sistema. Usaremos a estratégia de Stackelberg-Nash, processo no qual, para cada escolha do líder, procuramos por seguidores que satisfaçam um certo problema de minimização, as soluções deste problema formam o que chamamos de Equilíbrio de Nash, resolvido esse problema, trabalhamos para provar que o sistema é aproximadamente controlável usando o líder. Resolvemos ainda um sistema sistema de otimalidade para os seguidores.
We present hierarchic control to a parabolic system in a noncylindrical domain. The hierarchic control is a problem that is how to bring in a fixed time, the solutions of the equations of state we have, (these solutions depend on a functions called controls), a state considered ideal, througha system of leading, independent control, and followers, the leader controls dependents. We start by making a transformation of the original problem to an equivalent cylindrical domain, then do the hierarchic control of this problem. We use the strategy Stackelberg-Nash, a process in which each leader’s choice, look for followers to satisfy a minimization problem, the solution of this problem form what we call the Nash equilibrium, solved this problem, work to prove that the approximately system is controllable using the leader. We further resolve to a of optimality for followers.

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Capítulos de libros sobre el tema "Non-Cylindrical domains"

Bögelein, Verena, Frank Duzaar y Christoph Scheven. "Evolutionary Problems in Non-Cylindrical Domains". En Harnack Inequalities and Nonlinear Operators, 43–60. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-73778-8_3.

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"Boundary Control for Non-Autonomous Parabolic Equations in Non-Cylindrical Domains". En Boundary Control and Variation, 17–28. CRC Press, 1994. http://dx.doi.org/10.1201/9781482277685-7.

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Actas de conferencias sobre el tema "Non-Cylindrical domains"

Nakatsuka, Yuki, Reima Iwatsu, Jae Min Hyun y Hide S. Koyama. "Unsteady Vortex Breakdown Phenomena in an Enclosed Cylindrical Container With a Rotating Endwall Disk". En ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4751.

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Abstract A high-quality precision-controlled turntable apparatus was fabricated to probe the dynamic behavior of a viscous fluid contained in a cylindrical container. Vortex breakdown(s) produced by a rotating endwall disk was visualized by using a fluorescent dye injection technique, and its flow field was measured by using a particle image velocimetry. This flow is characterized by two non-dimensional parameters, i.e., the height-to-radius ratio H/R and the rotating Reynolds number Re = Ω2/v. Limiting boundaries for single, double and triple vortex breakdowns in steady flow were re-plotted to compare with the previous visualization studies of Escudier. The locations of stagnation points of the vortex breakdown bubble(s) in steady flow were measured quantitatively. The overall experimental results in the steady flow were in excellent agreement with Escudier’s data. In unsteady flow, the amplitude and time period of periodic axial oscillation, and the polar angle and time period of precession, were measured. The domains for periodic axial oscillation and for precession in unsteady flow were delineated.

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Rosetti, Guilherme F., Kazuo Nishimoto y Jaap de Wilde. "Vortex-Induced Vibrations on Flexible Cylindrical Structures Coupled With Non-Linear Oscillators". En ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79022.

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The recent escalade of the oil prices encourages the search and exploration of new oil fields. This represents a challenge to engineers, due to more difficult conditions of operation in harsh environments and deeper reservoirs. The offshore industry faces, in the edge of technology with new necessities and limiting conditions imposed by the environment, an increase in the cost of production. It is, therefore, of vital importance to have the equipments operating at the most optimized conditions in order to reduce these costs. VIV software developed in the frequency domain was successful in designing risers and pipelines using large safety factors and making conservative assumptions. These tools only predict single-mode vibrations. In this perspective, the present paper describes the results obtained from a new time-domain code developed to assess the vortex-induced vibrations of a long flexible cylinder. A time-domain analysis was chosen because this suits the problem well, since it is able to predict and calculate different modes of vibrations. In the model, a cylinder is divided into elements that can be exposed to an arbitrary current profile. Each of these elements is free to oscillate parallel and transversely to the flow, and is coupled to a pair of van der Pol’s wake oscillators. This simulates the vortex shedding and, therefore, the fluctuating nature of drag and lift coefficient during the occurrence of VIV. The governing equations are solved by 4th-Order Runge-Kutta schemes in time domain. The new time-domain model is compared with small scale model test data from benchmarking.

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Lizhi Cui. "Existence and controllability for a one-dimensional wave equation in a non-cylindrical domain". En 2014 11th World Congress on Intelligent Control and Automation (WCICA). IEEE, 2014. http://dx.doi.org/10.1109/wcica.2014.7052830.

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Hubbard, Carol y Yong Se Kim. "Geometric Assistance for the Construction of Non-Polyhedral Solids From Orthographic Views". En ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/cie-4288.

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Abstract As the extensive use of solid models becomes widespread, it is important to have a mechanism by which existing engineering drawings can be converted into solid models. Therefore, a geometric assistant which can aid in the construction of solid models is beneficial. In this paper, we present key operations for a system called the Assistant for the Rapid Construction of Solids (ARCS), that provides this assistance given a set of two orthographic views. ARCS is based on the Visual Reasoning Tutor (VRT), a system we developed that provides users with the geometric framework to build polyhedral solids from their orthographic views. However, the geometric domain of ARCS encompasses non-polyhedral solids with cylindrical and spherical surfaces, such as those found in typical mechanical parts. We have devised the Cylindrical and Spherical Warping operations to create cylindrical and spherical surfaces, which use interactive computer graphics that guide a human user to build non-polyhedral faces of a solid. These operations are then illustrated with an example using ARCS to create the solid model of a typical mechanical part from its orthographic projections.

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Korde, Umesh A. y R. Cengiz Ertekin. "Near-Optimal Time-Domain Control of Small Buoys in Irregular Waves". En ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24570.

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Within the linear theory framework, smooth optimal control for maximum energy conversion in irregular waves requires independent synthesis of two non-causal impulse response functions operating on the body oscillations near the free surface, and one non-causal impulse response function relating the exciting force to the incident wave profile at the body. Full cancellation of reactive forces and matching of radiation damping thus requires knowledge or estimation of device velocity into the future. As suggested in the literature, the control force can be synthesized in long-crested waves by suitably combining the ‘full’ impulse response functions with wave surface elevation information at an appropriately determined distance up-wave of the device. This paper applies the near-optimal control approach investigated earlier by one of the authors (Korde, UA, Applied Ocean Research, to appear) to small floating cylindrical buoys. Absorbed power performance is compared with two other cases, (i) when single-frequency tuning is used based on non-real time adjustment of the reactive and resistive loads to maximize conversion at the spectral peak frequency, and (ii) when no control is applied with damping set to a constant value. Time domain absorbed power results are discussed.

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Kim, Daejong, An Sung Lee y Bum Seog Choi. "Evaluation of Foil Bearing Performance and Nonlinear Rotordynamics of 120kW Oil-Free Gas Turbine Generator". En ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95800.

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This paper presents design approach of air foil bearings (AFBs) for 120kWe gas turbine generator, which is a single spool configuration with gas generator turbine and alternator rotor connected by a diaphragm coupling. Total four radial AFBs support the two rotors, and one set of double acting thrust foil bearing is located inside the gas generator turbine. The rotor configuration results in eight degree of freedom (DOF) rotordynamic motions, which are two cylindrical modes and two conical modes from the two rotors. Stiffness of bump foils of candidate AFB was estimated from measured structural stiffness of the bearing, and implemented to computational model for linear stiffness and damping coefficients of the bearing and frequency-domain modal impedances for cylindrical and conical modes. Stiffness of the diaphragm coupling was evaluated using finite element analysis and implemented to non-linear rotordynamic analyses of entire engine. Analyses show conical mode of turbine rotor is the main source of instability of entire engine when AFB clearance is not selected properly. Optimum AFB clearance is suggested from frequency domain modal analyses and nonlinear transient analyses.

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Liu, Wanhui, Daejong Kim y Kai Feng. "Effect of Axial Force on Rotordynamics of a Rigid Rotor Supported by Foil Bearings". En ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76261.

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This paper investigates the effect of gas foil thrust bearing (GFTB) on the rotordynamic performance of the rotor-gas foil bearing (GFB) system. A rigid rotor supported on two gas foil journal bearings (GFJB) and a pair of GFTBs is studied using a five degree of freedom (5-DOF) model. The studies were performed in both frequency domain using excitation frequency-dependent bearing coefficients (modal analyses) and non-linear analyses (time domain orbit simulations). Modal analyses were performed for both symmetrically and asymmetrically supported rotor systems. For the symmetric rotor, the modal stiffness for the conical mode increases with the axial force, while cylindrical mode is not affected. The axial force has little effects on the modal damping for both the cylindrical mode and conical mode. Thus, the natural frequency and threshold speed (stability limit) for the conical mode increases as the axial force increases, while these values for the cylindrical mode remain almost constant. For the asymmetric rotor, the modal stiffness for both the cylindrical mode and conical mode increases with the axial force, and thus both natural frequency and threshold speed increase with the axial force. Rotor lateral vibrations were also predicted using synchronous bearing coefficients (of both GFJB and GFTB) for both conical and cylindrical modes. The predicted rotor lateral responses show the critical speed increases with axial force for both cylindrical mode and conical mode. The nonlinear analysis using time-domain orbit simulation was also performed including the effect of axial force on the GFTB. The effect of axial force on the stability of the rotor system were discussed. The predicted results showed that the stability of rotor system improved as the axial force increases for Case 1 when the out of phase imbalances were added on the rotor. However, the stability of the rotor system for Case 2 not only influenced by the axial force but also influenced by how asymmetry the rotor is. For the in phase imbalances, the onset speed of subsynchronous motion decreases as axial force increases for the large asymmetric rotor bearing system and the decrement of the onset speed of subsynchronous decreases as the asymmetry of the rotor bearing system decreases. For the out of phase imbalances, the onset speed of subsynchronous motion also decreases as axial force increases for the large asymmetric rotor, but an opposite trend was shown as the asymmetry of the rotor decreases.

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Archambault, J. L., S. Lacroix y A. W. Snyder. "HE1m self-guided modes : vector solutions and stability". En Nonlinear Guided-Wave Phenomena. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/nlgwp.1991.tud4.

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Self-focusing in a medium of intensity-dependent refractive index has been extensively studied since the 60's. A particular case of self-focusing is the self-guided mode for which the natural tendency of a light beam to diffract is exactly compensated by the presence of a positive Kerr-law nonlinearity. A self-guided mode can also be seen as a mode of the waveguide it induces[1]. In this paper, we present a study of the HE1 m self-guided modes of circular cross-section in an ideal (homogeneous, non-saturable and without absorption) Kerr-law nonlinear medium. Although scalar theory predicts, within its domain of validity, that these modes are unstable, our exact vectorial analysis shows that they are stable to cylindrical perturbations. This result. is in accordance with the recent work of Chen and Snyder who established the need of taking into account the polarization of self-guided cylindrical TE and TM modes[2].

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Gonc¸alves de Lacerda, Thiago Aˆngelo, Gilberto Bruno Ellwanger, Marcos Queija de Siqueira y Elizabeth Frauches Netto Siqueira. "Time Domain Methodology for Vortex-Induced Motion Analysis in Monocolumn Platform". En ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79806.

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The offshore oil exploration in Brazil has been, traditionally, made by semi-submersible and moored ship-based units. The need for more restricted wave-induced motions has demanded new conceptions of floating structures, in which the mono-column concept distinguishes itself. Due to its cylindrical shape hull, this floating unit could present a significant low frequency vibratory movement caused by the vortex shedding phenomenon. This kind of phenomenon on huge structures like platforms is usually known as VIM (Vortex Induced Motions). The main objective of this work is to evaluate a time domain methodology applied in VIM problems. This methodology uses a Van der Pol equation to represent the vortex shedding phenomenon. The force calculation schemes presented in this work are applied in physical examples and its results will be compared to model test data. The analyses were performed in a non linear dynamic analysis program, using a six degree of freedom model, developed for this study.

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Chalasani, N. R. y Miles Greiner. "Natural Convection/Radiation Heat Transfer Simulations of an Enclosed Array of Vertical Rods". En ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93734.

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Experiments performed by others measured the temperature of twelve heated vertical rods within a constant temperature, internally finned cylindrical enclosure. Measurements were performed for a range of air and helium pressures and a range of rod heat generation rates. In the current work, three-dimensional computational fluid dynamics simulations of natural convection and radiation heat transfer within this domain were conducted to benchmark the simulation techniques. These calculations accurately reproduced the local and average temperatures when the heat generation rate was sufficiently low that the velocity field is steady. Future simulations will be used to design experiments that model spent nuclear fuel within non-isothermal cells of storage packages.

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