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The modal analysis of a pipe elbow with realistic boundary conditions

Carneiro, J.O.; Melo, F.J.M.Q. de; Rodrigues, J.F.D.; Lopes, H.; Teixeira, Viriato
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.69%
A vibration analysis for the determination of the natural frequencies and the associated eigenmodes of a pipe elbow with end-flanges or tangent terminations was performed. A numerical investigation of this problem was achieved with a semi-analytic definition finite ring element and a commercial finite element code. To assess the accuracy of the numerical solution for the elbow vibration, an experimental modal analysis was performed on a curved and on a straight pipe. The responses were processed by a data acquisition system which performs a fast Fourier transform on the time histories to convert them from a time to frequency domain, these leading to the extraction of natural frequencies and mode shapes associated with the test-specimen. The results were compared with the corresponding ones from the numerical approach and discussion about the results completes the paper.

A new finite element pipe for generalized in-plane pipe loading. Experimental and numerical comparison

Fonseca, E.M.M.; Oliveira, C.A.M de; Melo, F.J.M.Q. de; Piloto, P.A.G.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
26.53%
In structural engineering, the geometry of a large number of structural details may involve the combination of straight and curved parts in order to meet requirements of functionality and/or attractive design. Piping systems are structural elements used in the chemical industry, aeronautical and aerospace engineering, conventional and nuclear power plants and fluid transport in general-purpose process equipment. This paper presents a new finite element pipe with 19 degrees of freedom, where shape functions are set-up from the displacement field parallel to a local reference system. A displacement-based formulation was developed with Fourier series for increasing the structural element distortion capabilities. A finite element pipe may be considered as a part of a toroidal shell. The stress field distribution may be calculated for any cylindrical section pipe. Experimental set-up will be presented for in-plane piping system loading case and experimental stress measurement will be compared with the numerical stresses results obtained with this formulation and with other different commercial codes. The main advantage of this formulation is associated with timeless mesh generation with low number of elements and nodes. Considerable computational effort may be reduce with the use of this finite element pipe.

Perda localizada de carga em gotejadores integrados em tubos de polietileno; Local head losses for integrated drippers in polyethylene pipes

Gomes, Anthony Wellington Almeida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/03/2009 PT
Relevância na Pesquisa
36.6%
A inserção de gotejadores em uma tubulação modifica as linhas de fluxo, provocando turbulência local, que resulta em perdas de carga adicionais maiores que as perdas contínuas na tubulação. Para avaliar a perda total de carga, ao longo da linha lateral de gotejadores, as perdas contínuas e as localizadas, devidas à presença dos emissores no tubo, devem ser consideradas. Este trabalho apresenta os resultados de um experimento conduzido para avaliar as perdas localizadas de carga em gotejadores coaxiais integrados em tubos de polietileno. A perda de carga para diferentes vazões foi determinada em quatro modelos de tubos gotejadores, com sete repetições. Cada segmento de tubo utilizado continha 11 gotejadores. Para cada vazão, a perda localizada de carga foi calculada pela diferença entre a perda de carga no tubo com emissor e a perda de carga continua no tubo uniforme, estimada pela equação de Darcy-Weisbach. Aproximações matemáticas foram sugeridas para calcular a perda de carga com base no coeficiente de carga cinética (K) e em um valor constante de comprimento equivalente (Le). Para cada modelo de tubo gotejador, o coeficiente K foi praticamente independente do número de Reynolds, para R > 10 000, sugerindo que cada gotejador pode ser caracterizado por um valor médio de K...

The modal analysis of a pipe elbow with realistic boundary conditions

Carneiro, J.O.; Melo, F.J.Q. de; Rodrigues, J.F.D.; Lopes, H.; Teixeira, V.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.5%
A vibration analysis for the determination of the natural frequencies and the associated eigenmodes of a pipe elbow with end-flanges or tangent terminations was performed. A numerical investigation of this problem was achieved with a semi-analytic definition finite ring element and a commercial finite element code. To assess the accuracy of the numerical solution for the elbow vibration, an experimental modal analysis was performed on a curved and on a straight pipe. The responses were processed by a data acquisition system which performs a fast Fourier transform on the time histories to convert them from a time to frequency domain, these leading to the extraction of natural frequencies and mode shapes associated with the test-specimen. The results were compared with the corresponding ones from the numerical approach and discussion about the results completes the paper.; (Not applicable)

A finite element formulation for piping structures based on thin shell displacements theory

Fonseca, E.M.M.; Melo, F.J.M.Q.; Madureira, L.R.
Fonte: Nova Science Publicador: Nova Science
Tipo: Parte de Livro
ENG
Relevância na Pesquisa
36.45%
This chapter deals with the more usual formulations in the numerical approaches to the problem of stress analysis of curved pipes under generalized bending loads. The application of curved pipe elements is critically necessary in any piping structure, no matter which the project applications are. Depending on the safety standards ruling the project, it is known that curved pipe elements are much more vulnerable to excessive stressing than straight pipe elements. A larger risk of accessory breakdown during continuous operation after a situation where limiting forces are exceeded is likely to occur. The study of the flexibility and stress state of curved pipes subjected to generalized forces has been an area of interest of many engineers and physicists, given the high interest of the theme in many structural applications.

Estudo da flexibilidade de tubos sob esforços generalizados

Airosa, Marlene Liliana da Silva
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
26.74%
A análise estrutural de tubos é uma ferramenta sempre útil para diversas aplicações. O facto de existir um conjunto de equações que preveja o comportamento destes no momento em que são solicitados, tornaria mais fácil o processo de dimensionamento bem como da escolha da geometria dos tubos. Esta dissertação tem como principal objetivo obter o comportamento de tubos retos e curvos quando lhes é aplicada uma força concentrada ou uma carga distribuída. Numa fase inicial foram usados tubos retos como objeto de estudo, pelo facto de se tratar de uma geometria menos complexa. Numa fase seguinte foram então analisados os de geometria curva. De modo a estabelecer um termo de comparação, foram realizados também ensaios experimentais com o objetivo de analisar o erro da formulação proposta, tendo para o efeito utilizado a geometria menos complexa. Os resultados experimentais obtidos permitiram concluir acerca da assertividade dos modelos propostos, uma vez que a comparação é bastante satisfatória.; Structural analysis of pipes is an invaluable tool for all sorts of applications. Were there to be a set of equations that would describe their behavior under a duty service, it would enable a more documental choice in what concerns both pipe geometry and dimensions. The main objective of this thesis is to obtain a mathematical formulation for the behavior of both straight and curved pipes while prompted by a localized or uniformly distributed load. Firstly...

Study of high Reynolds number pipe flows with porous inserts

Pereira, José C. F.; Malico, Isabel; Hayashi, Thamy C.; Raposo, Jorge M. F.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula Formato: 54240 bytes; application/pdf
ENG
Relevância na Pesquisa
36.5%
This paper reports experiments for the flow at the inlet and outlet of a ceramic foam located in a straight pipe and in a pipe with a 1:4 sudden expansion. For the last latter, the foam, with thickness to diameter ratio between 0.15 and 0.60, was located at different distances from the sudden expansion wall. The LDA velocity measurements obtained allowed investigating the influence of the ceramic foam insert on the flow upstream from the porous medium inlet or downstream from its outlet. Three different pore sizes (10, 20 and 60 pores per inch) were investigated for pore Reynolds numbers in the range 20≤Rep≤400, corresponding to pipe Reynolds numbers of 600≤ReD≤5500 (2400≤ReD≤22000 in the pipe section upstream of the sudden expansion). Experimental results include velocity profiles at the foam exit as function of the Reynolds number and foam thickness, and confirm the outlet multi-jet flow structure and the decay of the strongly fluctuating velocity field induced at the foam exit in the flow downstream from the porous medium.

Axisymmetric Flow of a Generalized Newtonian Fluid in a Straight Pipe Using a Director Theory Approach

Carapau, Fernando; Sequeira, Adélia
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
36.46%
The aim of this paper is to analyze the axisymmetric unsteady flow of an incompressible gen- eralized Newtonian °uid in a straight rigid and impermeable tube with circular cross-section of constant radius. To study this problem, we use an approach based on the Cosserat theory (also called director the- ory) related to °uid dynamics which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. From this system we obtain for a °ow without swirling motion the relationship between mean pressure gradient and volume °ow rate over a ¯nite section of the pipe for the speci¯c case of the power law viscosity function. Moreover, we compare the 3D exact solution for steady volume °ow rate with the corresponding solution obtained by the Cosserat theory using nine directors.

Study of high Reynolds number pipe flows with porous inserts

Pereira, José Carlos F.; Malico, Isabel; Hayashi, Thamy C.; Raposo, Jorge M. F.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.45%
This paper reports experiments and calculations for the flow at the inlet and exit of a ceramic foam located in a straight pipe and in a pipe with a 1:4 sudden expansion. For the latter, the foam, with thickness to diameter ratio between 0.15 and 0.60, was located at different distances from the sudden expansion wall. Three different pore sizes (10, 20 and 60 ppi) were investigated for pore Reynolds numbers in the range 20

Numerical simulation of secondary flow in pneumatic conveying of solid particles in a horizontal circular pipe

Laín,S.; Sommerfeld,M.; Quintero,B.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2009 EN
Relevância na Pesquisa
46.5%
Under certain conditions, a fully developed turbulent flow in a straight pipe may show a secondary flow; for instance, when non-circular cross-section or non-uniform wall roughness around the perimeter of the duct are considered. In horizontal pipe particle-laden gas flow, the non-uniform forcing of the flow by the solids entrained in the gas core may also drive a secondary flow, even with uniform wall roughness along the circumferential direction. In this paper, the effects of wall roughness, particle size and particle mass loading ratio on the secondary flow developing in a horizontal pipe of circular cross-section under turbulent conditions are analysed. The computations are based on the Euler-Lagrange approach accounting for wall roughness and inter-particle collisions (i.e., four-way coupling). In the case of inertial particles, if inter-particle collisions are disregarded, the secondary flow consists of two recirculation cells with an upward flow near the vertical (symmetry) axis and a downward flow close to the walls. On the other hand, when inter-particle collisions are accounted for, the pattern depends on the particle concentration profile: with relatively smooth walls (low roughness), two recirculation cells are found, but with rough walls four recirculation cells are generated. For smaller particles...

Simulação numérica de nanofluidos escoando no interior de dutos retos; Numerical simulation of nanofluids flowing through a straight pipe

Chaupis, Joseph Edher Ramirez
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
46.46%
Esta dissertação teve como objetivo evidenciar a intensificação do coeficiente de transferência de calor por convecção de um escoamento utilizando nanofluidos. Para isto, o nanofluido foi simulado numericamente escoando dentro de uma tubulação horizontal reta, tanto em regime laminar como em regime turbulento, e submetida a uma condição de contorno de fluxo de calor constante através da parede, sob a hipótese que o nanofluido possui características de fluido monofásico com propriedades modificadas. Sabendo-se que as propriedades dos nanofluidos são função das propriedades das nanopartículas e do fluido base, foi utilizada uma variedade de combinações desses componentes a fim de mostrar uma tendência sobre o uso de nanopartículas e fluidos base de diferentes naturezas. Desse modo, foram utilizadas nanopartículas metálicas (prata, cobre e ferro) e de óxidos metálicos (alumina e óxido de cobre) dispersas em água deionizada, etileno glicol e poli-alfa-oleofin. As propriedades dos nanofluidos foram calculadas mediante modelos teóricos conservadores para a condutividade térmica e viscosidade, e aplicando a regra das misturas para a massa específica e o calor específico, com base nas propriedades dos componentes encontradas na literatura. Com as propriedades calculadas...

Strain gage data processing for estimating stress distributions around pipe cross sections.

Taborda Romero, Jesus A.
Fonte: Monterey, California. U.S. Naval Postgraduate School Publicador: Monterey, California. U.S. Naval Postgraduate School
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.39%
This thesis presents a method for estimating the distribution of stress components around the outer circumference of a cross section of a pipe, from the readings of strain gage elements arbitrarily positioned and oriented around this circumference. A least-squares procedure is used to obtain best estimates of the coefficients of Fourier expansions describing such distributions. A digital computer program was developed for applying the method. Data for testing the method and program were generated by a computer program using the best available theory of stress analysis in pipes. Methods for adding random errors to the data were adapted and used for closer simulation of actual situations. A second problem treated in this thesis is that of inferring the loading acting through the cross section of a straight pipe of concentric bore from known stresses at points on the external surface of the cross section which is presumed to be distant from stress concentrations. It is shown that this inference can be made from stresses at only three points of the cross section. A digital computer program was developed to do this.

Centrifugal force reversal from the perspective of rigidly rotating observer

Dalakishvili, Giorgi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.46%
In previous studies the dynamics of the relativistic particle moving along the rotating pipe was investigated. The simple gedanken experiment was considered. It was shown that at large enough velocities a centrifugal force acting on the bead changes its usual sign and attracts towards the rotation axis. The authors studied motion of the particle along the rotating straight pipe in the frame of the observer located in the center of rotation, also dynamics of centrifugally accelerated relativistic particle was studied in the laboratory frame. In the both cases it was shown that centrifugal force changes sign. Recently the problem was studied in the frame of stationary observers. It was argued that centrifugal acceleration reversal is not frame invariant effect. In the present paper we consider motion of particle along the rotating straight line in the frame of an arbitrary stationary observer located at certain distance form the center of rotation and rigidly rotating with constant angular velocity. It is shown that any stationary observer could detect reversal of centrifugal acceleration.; Comment: The goal of this paper is to respond calculations and claims given by Lyutikov, Maxim in his paper : On reversal of centrifugal acceleration in special relativity (arXiv:0903.1113)

Shear dispersion along circular pipes is affected by bends, but the torsion of the pipe is negligible

Roberts, A. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/09/2003
Relevância na Pesquisa
26.58%
The flow of a viscous fluid along a curving pipe of fixed radius is driven by a pressure gradient. For a generally curving pipe it is the fluid flux which is constant along the pipe and so I correct fluid flow solutions of Dean (1928) and Topakoglu (1967) which assume constant pressure gradient. When the pipe is straight, the fluid adopts the parabolic velocity profile of Poiseuille flow; the spread of any contaminant along the pipe is then described by the shear dispersion model of Taylor (1954) and its refinements by Mercer, Watt et al (1994,1996). However, two conflicting effects occur in a generally curving pipe: viscosity skews the velocity profile which enhances the shear dispersion; whereas in faster flow centrifugal effects establish secondary flows that reduce the shear dispersion. The two opposing effects cancel at a Reynolds number of about 15. Interestingly, the torsion of the pipe seems to have very little effect upon the flow or the dispersion, the curvature is by far the dominant influence. Lastly, curvature and torsion in the fluid flow significantly enhance the upstream tails of concentration profiles in qualitative agreement with observations of dispersion in river flow.

Electromagnetic Fields Produced by Moving Sources in a Curved Beam Pipe

Goto, Shin-itiro; Tucker, Robin W
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/08/2008
Relevância na Pesquisa
26.64%
A new geometrical perturbation scheme is developed in order to calculate the electromagnetic fields produced by charged sources in prescribed motion moving in a non-straight perfectly conducting beam pipe. The pipe is regarded as a perturbed infinitely long hollow right-circular cylinder. The perturbation maintains the pipe's circular cross-section while deforming its axis into a planar space-curve with, in general, non-constant curvature. Various charged source models are considered including a charged bunch and an off-axis point particle. In the ultra-relativistic limit this permits a calculation of the longitudinal wake potential in terms of powers of the product of the pipe radius and the arbitrarily varying curvature of the axial space-curve. Analytic expressions to leading order are presented for beam pipes with piecewise defined constant curvature modelling pipes with straight segments linked by circular arcs of finite length. The language of differential forms is used throughout and to illustrate the power of this formalism a pedagogical introduction is developed by deriving the theory ab-initio from Maxwell's equations expressed intrinsically as a differential system on (Minkowski) spacetime.; Comment: 43pages, 7figures

Stability of flow through a slowly diverging pipe

Sahu, Kirti Chandra; Govindarajan, Rama
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.39%
Although the critical Reynolds number for linear instability of the laminar flow in a straight pipe is infinite, we show that it is finite for a divergent pipe, and approaches infinity as the inverse of the divergence angle. The velocity profile at the threshold of inviscid stability is obtained. A non-parallel analysis yields linear instability at surprisingly low Reynolds numbers, of about 150 for a divergence of 3 degrees, which would suggest a role for such instabilities in the transition to turbulence. A multigrid Poisson equation solver is employed for the basic flow, and an extended eigenvalue method for the partial differential equations describing the stability.; Comment: 9 pages, 15 figures, accepted to J. Fluid Mech

Amplitude equations for a linear wave equation in a weakly curved pipe

Goto, Shin-itiro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/10/2009
Relevância na Pesquisa
36.45%
We study boundary effects in a linear wave equation with Dirichlet type conditions in a weakly curved pipe. The coordinates in our pipe are prescribed by a given small curvature with finite range, while the pipe's cross section being circular. Based on the straight pipe case a perturbative analysis by which the boundary value conditions are exactly satisfied is employed. As such an analysis we decompose the wave equation into a set of ordinary differential equations perturbatively. We show the conditions when secular terms due to the curbed boundary appear in the naive peturbative analysis. In eliminating such a secularity with a singular perturbation method, we derive amplitude equations and show that the eigenfrequencies in time are shifted due to the curved boundary.; Comment: To appear in J Phys A: Math. Theor

The laminar flow instability criterion and turbulence in pipe

Arsenjev, S. L.; Lozovitski, I. B.; Sirik, Y. P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/03/2003
Relevância na Pesquisa
36.45%
The identification of stream in the straight pipe as a flexible rod has allowed to present the criterion expression for determination of transition of the laminar flow regime to the turbulent as a loss of stability of the rectilinear static structure of translational motion of stream in pipe and its transition to the flexural-vortical dynamic structure of translational motion, just as a flexible rod buckling. The introduced criterion allows to take into account an influencing of the inlet geometry, the pipe length, the flow velocity, and also of any physical factors on stability of the rectilinear flow structure. It is ascertained, that Reynolds number is the number of local hydrodynamic similarity and it is displayed that one is constituent part of the introduced stability criterion. The developed approach to a problem of stability is applicable for a problem solving on internal flow and external streamline.; Comment: 9 pages

Energy Spectra from Electromagnetic Fields Generated by Ultra-relativistic Charged Bunches in a Perfectly Conducting Cylindrical Beam Pipe

Hale, Alison C; Tucker, Robin W
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/08/2009
Relevância na Pesquisa
26.72%
The spectrum of electromagnetic fields satisfying perfectly conducting boundary conditions in a segment of a straight beam pipe with a circular cross-section is discussed as a function of various source models. These include charged bunches that move along the axis of the pipe with constant speed for which an exact solution to the initial-boundary value problem for Maxwell's equations in the beam pipe is derived. In the ultra-relativistic limit all longitudinal components of the fields tend to zero and the spectral content of the transverse fields and average total electromagnetic energy crossing any section of the beam pipe are directly related to the properties of the ultra-relativistic source. It is shown that for axially symmetric ultra-relativistic bunches interference effects occur that show a striking resemblance to those that occur due to CSR in cyclic machines despite the fact that in this limit the source is no longer accelerating. The results offer an analytic description showing how such enhanced spectral behaviour depends on the geometry of the source and the details of the stochastic distribution of structure within the source. They offer a viable experimental means for inferring properties of the longitudinal charge distribution of bunches with micro-structure in ultra-relativistic motion in straight segments of a beam pipe from observation of the associated electromagnetic energy spectra. They are also of relevance to design criteria where the coherence effects of such fields play a significant role.; Comment: 10 pages...

Start-up flow of a viscoelastic fluid in a pipe with fractional Maxwell's model

Yang, Di; Zhu, Ke-Qin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/06/2010
Relevância na Pesquisa
36.39%
Unidirectional start-up flow of a viscoelastic fluid in a pipe with fractional Maxwell's model is studied. The flow starting from rest is driven by a constant pressure gradient in an infinite long straight pipe. By employing the method of variable separations and Heaviside operational calculus, we obtain the exact solution, from which the flow characteristics are investigated. It is found that the start-up motion of fractional Maxwell's fluid with parameters $\alpha$ and $\beta$, tends to be at rest as time goes to infinity, except the case of $\beta=1$. This observation, which also can be predicted from the mechanics analogue of fractional Maxwell's model, agrees with the classical work of Friedrich and it indicates fractional Maxwell's fluid presents solid-like behavior if $\be\neq 1$ and fluid-like behavior if $\be=1$. For an arbitrary viscoelastic model, a conjecture is proposed to give an intuitive way judging whether it presents fluid-like or solid-like behavior. Also oscillations may occur before the fluid tends to the asymptotic behavior stated above, which is a common phenomenon for viscoelastic fluids.; Comment: 14pages, 7 figures. A revised edition