To see the other types of publications on this topic, follow the link: Elliptic cylinder.
Dissertations / Theses on the topic 'Elliptic cylinder'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 31 dissertations / theses for your research on the topic 'Elliptic cylinder.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Finlay, Leslie. "Hydrodynamic Stability of Free Convection from an Inclined Elliptic Cylinder." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2929.
Full textAbstract:
The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.
2
Rand, Peter. "Asymptotic analysis of solutions to elliptic and parabolic problems." Doctoral thesis, Linköping : Matematiska institutionen, Linköpings universitet, 2006. http://www.bibl.liu.se/liupubl/disp/disp2006/tek1044s.pdf.
Full text
3
OLIVEIRA, Laercio Gomes de. "Transferência de calor em reator cilíndrico elíptico de leito fixo: aspectos termofluidodinâmicos e geométricos." Universidade Federal de Campina Grande, 2004. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1722.
Full textAbstract:
Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-09-14T12:44:26Z
No. of bitstreams: 1
LAERCIO GOMES DE OLIVEIRA - TESE (PPGEP) 2004.pdf: 4405529 bytes, checksum: 8b65ffb3723d9c3b423cde424d99a1ef (MD5)Made available in DSpace on 2018-09-14T12:44:26Z (GMT). No. of bitstreams: 1 LAERCIO GOMES DE OLIVEIRA - TESE (PPGEP) 2004.pdf: 4405529 bytes, checksum: 8b65ffb3723d9c3b423cde424d99a1ef (MD5) Previous issue date: 2004-10-08
Neste trabalho, foram desenvolvidos e apresentados vários modelos matemáticos tridimensionais analíticos e numéricos para estudar a transferência de calor no interior de um reator de leito fixo, usando condição na fronteira do sistema: de equilíbrio ou convectiva, condutividade térmica do reator constante ou variável e sistema com ou sem reação química. A modelagem matemática apresentada tem a flexibilidade de adaptar-se a leitos com forma geométrica variando desde um canal retangular até o cilindro elíptico, incluindo o cilindro circular. A metodologia numérica utilizada para resolver as equações diferenciais que representam o fenômeno físico baseia-se no método dos volumes finitos. Para discretizar a equação geral da conservação da energia foi utilizado o esquema WUDS (Weigthed Upstream Diference Scheme) como função de interpolação para os termos convectivos e difusivos e uma formulação totalmente implícita. O sistema de equações algébricas lineares resultantes da discretização da equação da energia em todos os pontos do domínio computacional é resolvido iterativamente pelo método Gauss-Seidel. Resultados da distribuição de temperatura no interior do reator em função das posições radial e angular, em várias posições ao longo do equipamento são mostradas e analisadas. Várias condições de processo foram estudadas, variando-se o coeficiente convectivo de transferência de calor, a razão de aspecto geométrica do reator, a concentração do reagente, a temperatura do fluido na entrada do sistema e a velocidade superficial do fluido. Como uma aplicação deste trabalho, os modelos matemáticos desenvolvidos foram utilizados para ajustar os dados experimentais de temperatura coletados numa célula de medidas térmicas (reator de leito fixo) de seção transversal cilíndrica circular, visando obter estimativas da condutividade térmica e coeficiente de transferência de calor do leito de partículas sob várias condições experimentais, usando-se a técnica do erro quadrático mínimo.
In this work, various analytic and numeric three-dimensional mathematical models were developed and presented to study heat transfer inside a fixed bed reactor, using a equilibrium or convective boundary condition, constant or variable thermal conductivity of the reactor and system with or without chemical reaction. The mathematical modeling presented has been the flexibility of adapting to beds with geometric shape varying from a rectangular channel to the elliptic cylinder, including the cylinder circular. The numeric methodology used to solve the differential equations that represent the physical phenomenon is based in the finite volume method. For discretize the general conservation energy equation the WUDS (Weighted Upstream Differentiates Scheme) scheme was used as interpolation function for convective and diffusive terms and a totally implicit formulation. The linear algebraic equations system resultant of the discretization of the energy equation in all points of the computational domain is iteratively solved by Gauss-Seidel method. Results of the temperature distribution inside the reactor in function of the radial and angular positions, in different positions along the equipment are shown and analyzed. Several process conditions were studied, varying the heat transfer convective coefficient, the reactor geometric aspect ration, the reagent concentration, the temperature and superficial velocity of the fluid in entrance of the system. As an application of this work, the mathematical models developed were used to adjust the temperature experimental data collected in a thermal measures cell (fixed bed reactor) of cylindrical traverse section, seeking estimate thermal conductivity and heat transfer coefficient of the particles bed under several experimental conditions, using the minimum quadratic error technique.
4
Wybrow, M. F. "Oscillatory flows about elliptic and circular cylinders." Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389229.
Full text
5
Paschero, Maurizio. "Improvement of the axial buckling capability of elliptical cylindrical shells." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26613.
Full textAbstract:
A rather thorough and novel buckling analysis of an axially-loaded orthotropic circular cylindrical shell is formulated. The analysis assumes prebuckling rotations are negligible and uses a unique re-defining of the orthotropic material properties in terms of a so-called geometric mean isotropic (GMI) material. Closed-form expressions for the buckling stress in terms of cylinder geometry and orthotropic material properties are presented, the particular closed form depending on the specific character of the orthotropic material relative to the GMI material. With the formulation, the specific character of the buckling deformations - e.g., axisymmetric or nonaxisymmetric, the number of axial and circumferential waves - can be established. By using the maximum radius of curvature of an elliptical cross section in this formulation, the analysis is used to demonstrate the detrimental effects of an elliptical cross section on axial buckling capacity when compared to a circular cross section with the same circumference. Using the circumferentially-varying radius of curvature of an elliptical cross section, the analysis is then further used as the basis for developing two methods for improving the axial buckling capacity of elliptical cylinders. The first approach involves varying the wall thickness of an isotropic elliptical cylinder with circumferential position. Uniformly stable elliptical cross sections which preserve the same critical stress, critical load, or volume of an axially loaded circular cylinder of the same circumference are designed with the formulation. The second approach involves maintaining a uniform wall thickness but varying the orthotropic material properties with circumferential position. This approach is applied to a cylindrical lattice structure where it is assumed that the ribs are dense enough to be able to describe the lattice structure by means of an equivalent homogenized material. The orthotropic properties of the homogenized material are varied by varying the lattice rib angle with circumferential position. Considerable recovery of the axial buckling capacity of the variable-rib-angle design elliptical cylinder compared to the same cylinder constructed in isogrid fashion is demonstrated. In fact, recovery relative to an isogrid circular cylinder of the same circumference is demonstrated. For both approaches confirming finite element models are used to verify the findings. The two different approaches are compared, and finally the two approaches are recognized as special cases of a more general design philosophy.Ph. D.
6
Pankratova, Iryna. "Homogenization of elliptic equations in thin cylinders and related qualitative problems." Luleå : Department of Mathematics, Luleå University of Technology, 2009. http://pure.ltu.se/ws/fbspretrieve/3359289.
Full text
7
McMurray, Jennifer Marie. "Response and Failure of Internally Pressurized Elliptical Composite Cylinders." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/79679.
Full textAbstract:
Presented is an overview of a semi-analytical solution which was developed to study the response of internally pressurized elliptical composite cylinders with clamped boundaries. Using a geometrically linear analysis and the solution scheme, the response of a quasi-isotropic elliptical cylinder is compared with the response of a quasi-isotropic circular cylinder in order to study the effects of elliptical geometry. The distinguishing features of the response of an elliptical cylinder are the inward normal displacement of the cross section at the ends of the major diameter that occur despite the outward force of the internal pressure, the presence of circumferential displacements, and the presence of inplane shear strains. These effects lead to spatial variations, including sign reversals, of a number of displacement, strain, and curvature responses. The responses of a quasi-isotropic elliptical cylinder evaluated using a geometrically linear analysis are then compared to the responses evaluated using a geometrically nonlinear analysis. It is shown that geometric nonlinearities tend to flatten certain responses at the ends of the minor diameter, and reduce the magnitude of certain responses in the boundary region. To study the influence of material orthotropy, the responses of axially-stiff and circumferentially-stiff elliptical cylinders evaluated using geometrically nonlinear analyses are examined. It is shown that in some instances material orthotropy can be used to mitigate the influence of the elliptical geometry and make particular responses look like those of a circular cylinder. An evaluation of failure using the maximum stress and Hashin failure criteria and geometrically linear and nonlinear analyses is presented for elliptical cylinders. These failure criteria involve interlaminar shear stresses which are computed by integrating the equilibrium equations of elasticity through the thickness of the cylinder wall. The failure criteria are used to assess the mode of failure (e.g., tensile or compressive fiber or matrix modes), the location of failure, and the pressure at failure. Both criteria predict first failure to occur at the clamped boundaries because of matrix cracking. The predicted failure pressures and circumferential locations are very similar for the two criteria, and the nonlinear analyses predict slightly higher pressures at somewhat different circumferential locations. First fiber failure is also considered. For this failure the two criteria predict similar failure scenarios for the linear analyses, but they differ in their predictions for the nonlinear analyses. Specifically, using the maximum stress criterion, the circumferentially-stiff elliptical cylinder is predicted to fail due to fiber compression, but the Hashin criterion predicts failure to be due to fiber tension, and at a different circumferential location. Also, first fiber failure pressures are at least a factor of two greater than the first matrix failure pressure.Master of Science
8
Haynie, Waddy. "Torsion of Elliptical Composite Cylindrical Shells." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28547.
Full textAbstract:
The response of elliptical composite cylindrical shells under torsion is studied. The torsional condition is developed by rotating one end of the cylinder relative to the other. Prebuckling, buckling, and postbuckling responses are examined, and material failure is considered. Four elliptical cross sections, defined by their aspect ratio, the ratio of minor to major radii, are considered: 1.00 (circular), 0.85, 0.70, and 0.55. Two overall cylinder sizes are studied; a small size with a radius and length for the circular cylinder of 4.28 in. and 12.85 in., respectively, and a large size with radii and lengths five times larger, and thicknesses two times larger than the small cylinders. The radii of the elliptical cylinders are determined so the circumference is the same for all cylinders of a given size. For each elliptical cylinder, two lengths are considered. One length is equal to the length of the circular cylinder, and the other length has a sensitivity of the buckling twist to changes in the length-to-radius ratio the same as the circular cylinder. A quasi-isotropic lamination sequence of a medium-modulus graphite-epoxy composite material is assumed. The STAGS finite element code is used to obtain numerical results. The geometrically-nonlinear static and transient, eigenvalue, and progressive failure analysis options in the code are employed. Generally, the buckling twist and resulting torque decrease with decreasing aspect ratio. Due to material anisotropy, the buckling values are generally smaller for a negative twist than a positive twist. Relative to the buckling torque, cylinders with aspect ratios of 1.00 and 0.85 show little or no increase in capacity in the postbuckling range, while cylinders with aspect ratios of 0.70 and 0.55 show an increase. Postbuckling shapes are characterized by wave-like deformations, with ridges and valleys forming a helical pattern due to the nature of loading. The amplitudes of the deformations are dependent on cross-sectional geometry. Some elliptical cylinders develop wave-like deformations prior to buckling. Instabilities in the postbuckling range result in shape changes and loss of torque capacity. Material failure occurs on ridges and in valleys. Cylinder size and cross-sectional geometry influence the initiation and progression of failure.Ph. D.
9
Meyers, Carol Ann. "An analytical and experimental investigation of the response of elliptical composite cylinders." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10052007-143144/.
Full text
10
Sun, Miao. "Use of Material Tailoring to Improve Axial Load Capacity of Elliptical Composite Cylinders." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29693.
Full textAbstract:
This study focuses on the improvement of the axial buckling capacity of elliptical composite cylinders through the use of a circumferentially-varying lamination sequence. The concept of varying the lamination sequence around the circumference is considered as a viable approach for off-setting the disadvantages of having the cylinder radius of curvature vary with circumferential position, the source of the reduced buckling capacity when compared to a circular cylinder with the same circumference. Post-buckling collapse behavior and material failure characteristics are also of interest. Two approaches to implementing a circumferential variation of lamination are examined. For the first approach the lamination sequence is varied in a stepwise fashion around the circumference. Specifically, each quadrant of the cylinder circumference is divided into three equal-length regions denoted as the crown, middle, and side regions. Eight different cylinders designs, whereby each region is constructed of either a quasi-isotropic or an axially-stiff laminate of equal thickness, are studied. Results are compared to the baseline case of an elliptical cylinder constructed entirely of a quasi-isotropic laminate. Since the thickness of the quasi-isotropic and axially-stiff laminates are the same, all cylinders weight the same and thus comparisons are meaningful. Improvements upwards of 18% in axial buckling capacity can be achieved with one particular stepwise design. The second approach considers laminations that vary circumferentially in a continuous fashion to mitigate the effects of the continuously-varying radius of curvature. The methodology for determining how to tailor the lamination sequence circumferentially is based on the analytical predictions of a simple buckling analysis for simply-supported circular cylinders. With this approach, axial buckling load improvements upwards of 30% are realized. Of all the cylinders considered, very few do not exhibit material failure upon collapse in the post-buckled state. Of those that do not, there is little, if any, improvement in bucking capacity. Results for the pre-buckling, buckling, post-buckling, and material failure are obtained from the finite-element code ABAQUS using both static and dynamic analyses. Studies with the code demonstrate that the results obtained are converged.Ph. D.
11
Wolford, Gabriela Fernanda. "Failure Initiation and Progression in Internally Pressurized Non-Circular Composite Cylinders." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/43299.
Full textAbstract:
In this study, a progressive failure analysis is used to investigate leakage in internally pressurized non-circular composite cylinders. This type of approach accounts for the localized loss of stiffness when material failure occurs at some location in a structure by degrading the local material elastic properties by a certain factor. The manner in which this degradation of material properties takes place depends on the failure modes, which are determined by the application of a failure criterion. The finite-element code STAGS, which has the capability to perform progressive failure analysis using different degradation schemes and failure criteria, is utilized to analyze laboratory scale, graphite-epoxy, elliptical cylinders with quasi-isotropic, circumferentially-stiff, and axially-stiff material orthotropies. The results are divided into two parts. The first part shows that leakage, which is assumed to develop if there is material failure in every layer at some axial and circumferential location within the cylinder, does not occur without failure of fibers. Moreover before fibers begin to fail, only matrix tensile failures, or matrix cracking, takes place, and at least one layer in all three cylinders studied remain uncracked, preventing the formation of a leakage path. That determination is corroborated by the use of different degradation schemes and various failure criteria. Among the degradation schemes investigated are the degradation of different engineering properties, the use of various degradation factors, the recursive or non-recursive degradation of the engineering properties, and the degradation of material properties using different computational approaches. The failure criteria used in the analysis include the noninteractive maximum stress criterion and the interactive Hashin and Tsai-Wu criteria. The second part of the results shows that leakage occurs due to a combination of matrix tensile and compressive, fiber tensile and compressive, and inplane shear failure modes in all three cylinders. Leakage develops after a relatively low amount of fiber damage, at about the same pressure for three material orthotropies, and at approximately the same location.Master of Science
12
Lo, Hung-Chieh. "Vibration Characteristics of Thin-Walled Noncircular Composite Cylinders." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77207.
Full textAbstract:
The lowest natural frequencies of thin-walled noncircular fiber-reinforced composite cylinders, specifically cylinders with elliptical cross sections, are investigated. Of interest is the variation of the lowest natural frequency, the so-called fundamental frequency, as a function of wall laminate properties, cross-sectional eccentricity and other cylinder geometric parameters. Both simple and clamped support boundary conditions are investigated. Laminate properties that are uniform with circumferential location and laminate properties that vary with circumferential location, by way of varying laminate fiber angle with circumferential location, are considered. As the radius of curvature of a noncircular cylinder varies with circumferential location, it is logical to consider the influence of circumferentially varying fiber orientation on the fundamental frequency. The analysis for predicting the fundamental frequency is based on Donnell shell theory, linear elastic properties, and the use of Hamilton's Principle in conjunction with the Rayleigh-Ritz technique. By use of a so-called shape factor, the magnitude of cylinder normal displacements are modulated to be larger in the regions of the cross section with the largest radius of curvatures and smaller in the regions with the smallest radius of curvature. The final equations for predicting the fundamental frequency are quite complex, but a series of approximations results in a hierarchy of simpler equations, the simplest being referred to as Lo's approximation. The prediction of the fundamental frequencies is spot checked by comparing the results as predicted by the various levels of approximation with predictions of a shell-based finite element model. Considering uniform laminate properties, comparisons between the developed analysis and the finite element model are good for all levels of simpler equations, and excellent in some cases. The developed analysis is subsequently used for parameter studies. It is found that compared to a circular cylinder of the same circumference and with uniform laminate properties, the fundamental frequency of an elliptical cylinder is always less. Surprisingly, based on the results obtained, it appears that for a given cylinder geometry the fundamental frequency is not particularly sensitive to wall lamination sequence, though the wave number in the circumferential direction of the mode shape associated with the fundamental frequency is sensitive to lamination sequence. Considering cylinders with circumferentially varying fiber orientation, comparisons between the developed analysis and the finite element model for most of the cases studied are good. However, the developed equations are limited since it is difficult to find a set of known functions to describe the deformation of an arbitrary lamination sequence when applying the Rayleigh-Ritz technique. In general, in can be concluded that the effect of varying fiber orientation on the fundamental frequency is much less than the influence of cylinder aspect ratio. It can also be concluded that the developed analysis would be an excellent tool for design purposes, as the calculation of the fundamental frequency is done quickly, and design trade-offs studies would be easy.Ph. D.
13
Razera, Andre Luis. "Estudo numérico da maximização da densidade de transferência de calor do escoamento laminar sobre cilindros de seção transversal elíptica utilizando o método Design Construtal." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/156470.
Full textAbstract:
Este trabalho tem como propósito investigar através do método Design Construtal a influência do espaçamento (S0) entre cilindros de seção transversal elíptica na maximização da densidade de transferência de calor em um escoamento externo sob efeito de convecção forçada. A razão de aspecto (r) entre os eixos vertical e horizontal dos cilindros elípticos também é um parâmetro avaliado. O estudo proposto é assumido bidimensional, incompressível, laminar e permanente. O regime de escoamento é dirigido por uma diferença de pressão ΔP, que se mantém através do domínio e é governada pelo número de Bejan (Be). Foram avaliados escoamentos com quatro diferentes números de Bejan, Be = 102, 103, 5.103, 104. O fluido que escoa através do domínio possui as propriedades termofisicas definidas pelo número de Prandtl, Pr = 0,72. O método Design Construtal, associado à busca exaustiva, foi empregado para determinar as restrições, graus de liberdade e o objetivo na avaliação geométrica do sistema A solução numérica das equações de conservação de massa, quantidade de movimento e energia foram resolvidas baseadas no método de volumes finitos, através do código comercial de dinâmica dos fluidos computacional FLUENT®. As geometrias e malha do domínio computacional foram desenvolvidas no pacote GAMBIT®. Como resultados, obteve-se que os casos ótimos apresentaram resultados consideravelmente melhores do que as demais configurações, onde se obteve ganhos de desempenho na densidade de transferência de calor de 50% a 97% em relação às configurações de menor desempenho estudadas. Além disso, foi possível verificar que o sistema adapta sua geometria ótima para cada condição de escoamento, a fim de proporcionar a melhor arquitetura de fluxo para atender ao objetivo térmico de maximizar a transferência de calor em um menor espaço físico, atendendo os princípios da Teoria Construtal.This work investigates, through the Construtal Design method, the influence of the spacing (S0) between cylinders with elliptic cross in the maximization of the heat transfer density in an external flow with forced convection. The aspect ratio (r) between the vertical and horizontal axes of the elliptical cylinders is also evaluated. The proposed study is assumed twodimensional, incompressible, laminar and permanent. The flow regime is directed by a pressure difference ΔP, which is governed by the Bejan number (Be). The flows were evaluated for different values of the Bejan number, Be = 102, 103, 5.103, 104. The fluid flowing through the domain has its thermophysical properties defined by Prandtl number, Pr = 0.72. The Construtal Design method, associated with the exhaustive search, was used to determine the restrictions, degrees of freedom and objective in the geometric evaluation of the system. The numerical solution of the mass conservation, momentum and energy equations is solved based on the finite volume method, using the commercial fluid dynamics software FLUENT ®. The geometries and mesh of the computational domain were developed in the GAMBIT® package. The results show that the optimal cases performs considerably better than the other configurations, with an increase in the heat transfer density of 50% to 97% in comparison to the performance of lower level cases studied. In addition, it was possible to verify that the system adapts its optimal geometry to every flow condition in order to provide a better flow architecture that meets the thermal objective of maximizing a heat transfer in a smaller physical space in agreement with the principles of the Constructal Theory.
14
Najjar-Khatirkolaei, Biglar. "Transverse magnetic wave scattering by elliptic chiral cylinder." Thesis, 2005. http://spectrum.library.concordia.ca/8546/1/MR10245.pdf.
Full textAbstract:
The electromagnetic scattering problem of normal incident waves on an elliptic chiral cylinder is considered. The cylinder is assumed to be homogeneous and isotropic and extends infinitely long in the z direction. An exact boundary value solution for the scattering problem of the TM wave by the elliptic chiral cylinder is analyzed and presented. The solution is based on the separation of variable technique in the elliptic cylinder coordinates system, and expressed in terms of Mathieu and modified Mathieu functions. The incident, transmitted and scattered electromagnetic waves are expressed in terms of an infinite series of wave functions. The matrix forms of the expansion coefficients are found by applying the boundary conditions and orthogonality of the Mathieu functions. The expression of the radar cross section (RCS) per unit length or echo width of electromagnetic wave scattering by elliptic chiral cylinder for co- and cross-polarized waves are derived by using the asymptotic expansions for modified Mathieu functions. Validation of the developed formulation and computer program are investigated by considering many limiting cases such as circular dielectric, circular perfect conducting, and circular chiral cylinders, as well as elliptic dielectric and elliptic perfect conducting cylinders. Numerical results of the forward and back scattered echo widths for both co- and cross-polarized waves for various cases are presented and discussed. The numerical results show the co- and cross-polarized bistatic and monostatic echo widths depend on the frequency and incidence angle of the incident wave, constitutive parameters and geometry of the elliptic chiral cylinder. In general, the echo widths decrease by increasing the chirality admittance, and increase by increasing the axes of the elliptic chiral cylinder.
15
Yang, Sz-Rung, and 楊斯容. "Onset of Vortex Shedding in Flows Past an Elliptic Cylinder." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/78705814374575346391.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
99
In this paper, the local grid refinement is focused by using a nested grid technique. The nested Cartesian grid method is developed for simulating unsteady, viscous, incompressible flows with complex immersed boundaries. The key aspects that need to be considered in developing such a nested grid solver are imposition of interface conditions on the nested-block boundaries and accurate discretization of the governing equation in cells that are with block-interface as a control surface. A new interpolation procedure is presented which allows systematic development of a spatial discretization scheme that preserves the spatial accuracy of the underlying solver. As a result, high efficiency and accuracy nested grid method is developed. This paper describes the development of high efficiency and high precision of the nested grid. By nested grid method to test flowchannels symmetrically placed in the inside,a different length than the oval-shaped cylinder axis obstacles logistics field, arrive at the average lift drag coefficient, vortex escape change, and thus to predict occurrence of vortex vortex escape the criticalReynolds number, find the critical Reynolds number simulation indeed showed increasing state, local refinement grid confirmedthe correctness of some overlap, and arrive at the test method applies to the length axis of the elliptical cylinder than.And from theabove numerical experiments confirm the nested grid method can be efficient to obtain numerical results.
16
Chen, Yi Xu, and 陳奕旭. "Study on stability of couette flow between concentric outer cylinder with elliptic or wavy inner rotating cylinder." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/28527034220442344261.
Full text
17
Khayyatzadeh, Pouya. "Geometry and Anchoring Effects on Elliptic Cylinder Domains of Nematic Phases." Thesis, 2014. http://hdl.handle.net/10012/8146.
Full textAbstract:
Compounds which exhibit liquid crystal phases have been widely used in display technology. The majority of display applications utilize the nematic liquid crystal phase, which is a liquid-like phase which has partial orientational order at the molecular level. The nematic phase exhibits birifringence which can be manipulated through the application of an external field. Subsequently, all liquid crystal-based display technology utilizes the application of an external field to ???switch??? or tune the optical properties of a nematic domain into a desired optical state. In addition to an external field, the geometry and surface interactions of the liquid crystal domain must be precisely controlled in order for the display to operate properly. Liquid crystal displays (LCDs) utilize a rectangular domain, or pixel, within which the nematic domain is exposed to surface anchoring conditions that result in a twist of the nematic alignment through the thickness of the domain.
In this work, a different type of liquid crystal domain that is elliptic is studied which is formed through ???bottom-up??? techniques, such as phase separation of a liquid crystal/polymer mixture to form a polymer-dispersed liquid crystal (PDLC) composite. Nematic domains within PDLCs are spheroidal, as opposed to rectangular for a pixel, and thus exhibit substantially different behaviour in the presence of an external field. The fundamental difference between spheroidal and rectangular nematic domains is that the former requires the presence of defects in nematic order while the latter does not.
The overall objective of this work is to study, for a simplified elliptic cylinder domain, the formation of the nematic domain, the resulting domain texture in the presence of an external field, and the domain texture following release of the external field. These three states are directly related to applications of PDLC films as optical functional materials, where an external (electric) field is used to manipulate the optical properties of the film. The effects of geometry (aspect ratio), surface anchoring, and external field strength are studied through a simulation-based approach using the Landau-de Gennes theory of the nematic phase.
18
Chun, Chien Li, and 簡立君. "Boundary Layer separation of an elliptic cylinder in a uniform shear flow." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/82164064226682650523.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
87
The present research studies the separation of steady boundary-layer over an elliptic cylinder placed in a uniform shear flow. The boundary-layer equations are solved numerically via the conventional space-marching technique. Calculated result shows that in the condition of positive shear rate, with increasing the shear rate, there is not notable variation of the location of separation at the upper half of the elliptic cylinder. But the variation of the location of separation at the lower half of the elliptic cylinder is significant. When the shear rate increases beyond a critical value, separation point will jump from the rear part of the cylinder to the windward side of the cylinder and continue to move in the upstream direction. In the condition of negative shear rate, the jump phenomenon occurs at the upper half of the cylinder, and the variation of the location of separation at the lower half of the elliptic cylinder is not significant.
19
Najjar-Khatirkolaei, Biglar. "Radiation properties of a slotted elliptic cylinder coated by noconfocal chiral and other materials." Thesis, 2009. http://spectrum.library.concordia.ca/976540/1/NR63378.pdf.
Full textAbstract:
Wireless communications technology is one of the most rapidly growing fields. An antenna is a key element that makes wireless communications possible. One of the most popular antennas is the slot antenna which is widely used in many wireless systems. The characteristics of a slot antenna on a perfectly conducting elliptic cylinder coated by nonconfocal materials are investigated theoretically and experimentally. Fields interior and exterior to the slot antenna are found rigorously using the separation of variable technique. The analysis is carried out by expressing the fields in and around the cylinder in terms of Mathieu and modified Mathieu functions. The structure is fed with a line source or a plane wave. The unknown aperture fields on the slot are expressed in terms of Fourier series with unknown expansion coefficients. The expansion coefficients of the interior, aperture and exterior fields are found by enforcing the boundary conditions and employing the addition theorem and orthogonality properties of the Mathieu functions. The general formulations are expressed for the TM case. However, expressions of the eigenfunction expansions for the TE case are given, as well. Furthermore, efficient algorithms for calculating the Mathieu functions are developed using the software package MATLAB. The algorithm developed here for calculating the Mathieu function is compact, fast, and efficient, and compared well with other results in the literature. The exact analytical formulation is used to generate accurate numerical results and studying the effects of different geometrical and materials parameters. Numerical results of the antenna gain, aperture conductance, and aperture voltage (in a receiving mode) are presented and discussed for different design parameters and for both the TM and TE cases. For verification of accuracy and validation of formulations and software program, numerical results for special cases are generated and very good agreement between theory and available data is obtained. The antenna radiation patterns and directivities are computed for different design parameters. The accuracy of the solution is also attested by comparing with HFSS, a commercial CAD package, simulation results. Prototypes of non-coated and dielectric-coated elliptic slot antennas are designed, fabricated, and tested.
20
鄭程鴻. "The bipolar behavior of an elliptic cylinder in an electrolytic cell and metal recovery by fluidized bed electrodes." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/91806523780513265345.
Full text
21
Chen-WeiHsu and 許晨薇. "Implementation of Particle Swarm Optimization Algorithm for Optimizing Elliptic Cylinders in Formation." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/85230903681406019954.
Full textAbstract:
碩士國立成功大學
系統及船舶機電工程學系碩博士班
101
This research uses the single objective particle swarm optimization (PSO) and multiobjective PSO (MOPSO) to implement the optimization for elliptic cylinders in formation in the two-dimesional laminar flow. We start from introducing PSO and MOPSO, and combine MOPSO with ANSYS FLUENT to calculate different formations. Finally we obtain an optimizing formation and also discuss the difference of results between the PSO and MOPSO. In the future, we will take this program to research the V-formation of birds. The framewok of program is written in Microsoft Visual Studio 2008 C#, including PSO algorithm, changing the positons of elliptic cylinders, importing the files to ANSYS FLUENT and returning the data of forces back to PSO in order to correct the next calculation. The main pupose to the research is to automate the optimizing framework of PSO, Rino and ANSYS FLUENT. To study different kinds of bodies, we only have to build an initial model in this program. If we obtain the formation of birds or ships, our research can use the optimizing formation to reduce drag force. We believe it can achieve decreasing fuel consumption in application of military or long-distance navigation.
22
Chang, Ling-Yun, and 張齡勻. "Numerical Study on the Flow Past Two Elliptic Cylinders With Different Attack Angles." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/60874137165907866861.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
98
Article, Cartesian Grid Method is adopted to investigate Flow Past Two Elliptic Cylinders With Different Attack Angles. In solving the Navier-Stokes and continuity equations, a finite volume method is used in conjunction with a two-step fractional-step procedure. The key aspect in developing a Cartesian grid method for flow with complex geometries is imposition of bluff bodies. In this study, a simple concept of Immersed Boundary method is adopted by using distributed body forces in the Navier-Stokes equations instead of the existence of bluff solid bodies. Similar procession has been applied by Ravoux et al. [1] and they referred it as Embedding method. The local grid refinement is also used in this study by applying the nested grid technique. Article, flows past two elliptic cylinders with different attack angles are studied systematically. Flows at different Reynolds numbers with Re=200 and Re=300, different ellipse aspect ratio with aspect ratio=2 and aspect ratio=3, various gape ratio of G=1.6~6.0, and various attack angles of =40 ~ -40 are computed and observed. Article, 29 flows past two elliptic cylinders are studied and 3 different kind of flow patterns are founded. They are In-phase flow, Out of phase flow, and Asymmetry flows, respectively.
23
Liao, Meichuan, and 廖梅娟. "Numerical study on vortex shedding flows past a pair of two elliptic cylinders." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/91928934587223048854.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
100
In this paper, low Reynolds number (Re) flows past a pair of elliptic cylinders in a side-by-side arrangement are solved by numerical simulations and transitions of the flows are investigated. Numerical methods in solving the 2-D Navier-Stokes and continuity equations is a two-step fractional step method, for the numerical simulations of flows past bluff bodies an Immersed Boundary (IB) method has been implemented where local grid refinement procedure is adopted by using a nested grid formulation. Flows with Re ranges between 40~100 and Gap ratio (G) ranges between 0.2~3.0 are solved. From a global point of view, there are a variety of flow patterns. Including steady and vortex shedding flows, semi-single and twin vortex streets, symmetry and deflected flows, biased flip-flopping and stationary flip-flopping vortex shedding flows, in-phase and in anti-phase vortex shedding flows are founded. We numerically solve the variety of flows by tuning Re quasi-stationary and investigate the transition of various flow patterns by nonlinear analysis. Transition diagram of flows past a pair of elliptic cylinders at various Gs are proposed to be presented.
24
Chiu, I.-Cheng, and 邱益成. "The problems of the torsion and the conductivity for composite elliptical cylinder." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/33886551507075441808.
Full textAbstract:
碩士國立成功大學
土木工程學系碩博士班
91
This paper discused that after the composite confocal elliptical cylinder bearing torsion, the cross-section''s actions ,meat warping function of composite confocal elliptical cylinder. And, the two dimensions metrix which have the compsite confical elliptical inclusions with heat potential to find their potential and courrent''s actions. We can use continuity of boundary condition for two continuos confocial ellipical to construct the relation of the stuck of matrix to supply the methold to solve this kind of problems. Because of the conveninet. We ask the composit confocal elliptical with strong layers or weak layers for their warping functions. Except, we ask the confocal elliptiacl relations between inermost layer''s courrrent and the boundary of the potental''s order.
25
Chao, Chih-Chung, and 趙志鍾. "Buoyancy-Driven Flow in the Annulus Between Horizontal Eccentric Elliptical Cylinders." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/74199184712525753850.
Full text
26
Jing-ChingJang and 張景晴. "The Research on Optimizing Formation of Elliptic Cylinders by Combining Particle Swarm Method and Large Eddy Simulation." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/49292321029276296978.
Full text
27
Chen, Po-Jen, and 陳柏任. "Numerical Study On Vortex Shedding Flows Past a Pair of Side-By-Side Elliptic Cylinders With Angle of Attack." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/45821956034949524981.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
101
In this paper, low Reynolds number (Re) flows past a pair of elliptic cylinders in a side-by-side arrangement are solved by numerical simulations and transitions of the flows are investigated. Numerical methods in solving the 2-D Navier-Stokes and continuity equations is a two-step fractional step method, for the numerical simulations of flows past bluff bodies an Immersed Boundary (IB) method has been implemented where local grid refinement procedure is adopted by using a nested grid formulation. Flows with Re ranges between 65~100 and Gap ratio (G) ranges between 0.6 and 1.6 and angle of attack (θ) between -20O<0o<20o are solved. From a global point of view, there are a variety of flow patterns. According to the elliptic cylinders which the comparison with different conditions, different phenomena generated. The change from scratch of elliptic cylinders with angel of attack, the difference of Gap ratio and Reynolds number created the diffenent flows in linein this paper. Including steady and vortex shedding flows, semi-single and twin vortex streets, symmetry and deflected flows, biased flip-flopping and stationary flip-flopping vortex shedding flows, in-phase and in anti-phase vortex shedding flows are founded. We numerically solve the variety of flows by tuning Re quasi-stationary and investigate the transition of various flow patterns by nonlinear analysis. Transition diagram of flows past a pair of elliptic cylinders at various Gs are proposed to be presented.
28
Yang, Hong-An, and 楊宏恩. "Numerical simulation for flow passing around elliptical, circular or square cylinders in a uniform flow." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/15030724739481303787.
Full textAbstract:
碩士國立高雄應用科技大學
模具工程系
99
Abstract This thesis aims to study the wake characteristics by numerical analysis of the wake formed by uniform flow field flow past different objects with the flow dynamics module of COMOSOL Multiphysics simulating package. With this simulation, the relationship between the wakes formed realistically and the objects flowed past could be understood. The basic assumption in this thesis is a two dimensional incompressible flow past 90 DEG rotated elliptical/45 DEG rotated elliptical/0 DEG rotated elliptical/circular/ square cross section objects (5 kinds of cross section object). The scope of this thesis is studying the status of the wake formed for low Reynolds number (Re30~Re100) flow past different kind of objects. Analyzing the start time/the steady time of the flow fluctuation and the wake vibration frequency, then the average velocity/the average pressure and the pressure drop could be taken, and Strounhal number could be calculated finally. From the result of study, following conclusion has been got. There is no wake under low Reynold flow past object, when Reynolds number increase the flow dynamic energy increase too, then the wake began to appear. The average velocity increase with Reynolds number increase after wake appearance. The average velocity will increase when the resistance of object decrease and Reynolds number increase. It is relatively unstable for flow field under low Reynolds number. Strounhal number will decrease when Reynolds number increase that means flow field will relatively stable under high Reynolds number. It was found that Strounhal number is the most small for 0 DEG rotated elliptical cross section object and is the most big for 90 DEG rotated elliptical cross section object, so there are steady wake for 0 DEG rotated elliptical cross section object and the 90 DEG rotated elliptical cross section object will create wake easily and cause unstable flow field. The result of this study may be applied to suppression for the flow fluctuation and vibration frequency of wake created by flow field of architecture. We can use numerical simulation to understand the fluctuation effect caused by physical flow field distribution.
29
hsien, Ho chun, and 何俊賢. "The collocation multipole method for the solution of the acoustic scattering by multiple elliptical cylinders." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/22093187808952121016.
Full textAbstract:
碩士中華科技大學
機電光工程研究所碩士班
99
Abstract In this thesis, the collocation multipole method is presented to solve the problem of the acoustic scattering of a plane sound wave by multiple elliptical cylinders. To satisfy the Helmholtz equation in the elliptical coordinate system, the scattered acoustic field is formulated in terms of angular and radial Mathieu functions. The boundary conditions are satisfied by uniformly collocating points on the boundaries. The acoustic pressure at each boundary point is directly calculated in each elliptical coordinate system through the coordinate transformation. In different coordinate systems, the normal derivative of the acoustic pressure is calculated by using the appropriate directional derivative, an alternative to the addition theorem. By truncating the multipole expansion, a finite linear algebraic system is derived and then the scattered field can be determined according to the given incident acoustic wave. Once the total field is calculated as the sum of the incident field and the scattered field, the near field acoustic pressure along scatterers and the far field scattering pattern can be determined. For the acoustic scattering of one elliptical cylinder, the proposed results match well with those of analytical solution. The scattered fields by two and three elliptical-cylindrical scatterers are critically compared with those provided by the BEM to verify the validity of the present method. Finally, the effects of the convexity of an elliptical scatter, the space among scatterers and the incident wave number and angle on the scattered fields are investigated.
30
Cheng, Feng-Sheng, and 鄭豐笙. "Hysteresis in Anti-phase/In-phase Synchronized Vortex Shedding Forms of Flows Past a Pair of Side-by-Side Elliptic Cylinders." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/21270703035991018320.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
101
Transition of flow past a pair of side-by-side elliptic cylinders with aspect ratio A=2 is investigated by numerical simulations and the bifurcation analysis of the numerical results. It is already known that flows past a pair of elliptical cylinders are influenced by the gap ratio G and Reynolds number Re. Various flow patterns behind the ellipses have been found and the transition diagram from steady to semi-single/twin symmetric/deflected vortex shedding flows have been reported in our previous study (Peng et. al.1). This study focus on transition of in-phase/anti-phase vortex shedding synchronized forms. It is found that the in-phase and anti-phase vortex shedding flows can co-exist at . Hysteresis loops with increasing/decreasing G at constant Reynolds number Re=100 and with increasing/decreasing Re at constant gap ratio G=2.4 are reported, respectively. The hysteresis phenomenon of in-phase/anti-phase vortex shedding synchronized forms is also investigated in flows past a pair of circular cylinders. Keywords:anti-phas;in-phase
31
Ji-Gang, She, and 佘霽剛. "Hysteresis process study of anti-phase/in-phase synchronized vortex shedding forms of flows past a pair of side-by-side elliptic cylinders." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/91027576998258873196.
Full textAbstract:
碩士國立暨南國際大學
土木工程學系
102
In this paper is numerical analysis method to study flow through the transformation process of flows past a pair of side-by-side elliptical cylinders .from the related papers we can see that flows past a pair of elliptical cylinders are influenced by the gap ratio G and Reynolds number Re. Therefore this paper analyzes flows past a pair of elliptical cylinder flow field. The flow field Reynolds number Re to between 10 and 100 the gap ratio G between all types of flow fields between 0.2 to 3.0. the flow field including a semi-single street、twin street steady flows、periodic vortex shedding flows、quasi-periodic vortex shedding flows、chaotic vortex shedding flows、deflected vortex shedding flows、flip-flopped vortex shedding flows、in-phase、anti-phase and other diversified escape the vortex flow field structure. This study is focus on transition of in-phase and anti-phase vortex shedding synchronized forms. We found axial ratio at A= 0.5 Re =100 1.40≤ G ≤1.82 is a bi-stable type and axial ratio A = 1.5 Re =100 2.20 ≤ G ≤ 2.58 there is also bi-stable type after the formation of the image of the analyzed data hysteresis loops graphic paper in the related papers A= 1.0 and A= 2.0 was added to make a more complete comparison of the hysteresis loop phenomenon the average lift coefficient and gap ratio G relationship.