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- Elsevier
- Instituto Politécnico de Bragança
- Biblioteca Digitais de Teses e Dissertações da USP
- Nova Science
- Universidade de Aveiro
- Universidade de Évora
- Brazilian Society of Chemical Engineering
- Universidade Federal de Uberlândia
- Monterey, California. U.S. Naval Postgraduate School
- Universidade Cornell
- Mais Publicadores...

## The modal analysis of a pipe elbow with realistic boundary conditions

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.

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

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.

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

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%

#Drip irrigation#Equivalent length of straight pipe.#Irrigação por gotejamento#Kinetic head coefficient#Local head loss#Obstruction index#Perda de carga#Tubos.

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...

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## The modal analysis of a pipe elbow with realistic boundary conditions

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)

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

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.

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## Estudo da flexibilidade de tubos sob esforços generalizados

Fonte: Universidade de Aveiro
Publicador: Universidade de Aveiro

Tipo: Dissertação de Mestrado

POR

Relevância na Pesquisa

26.74%

#Engenharia mecânica - Teses de mestrado#Tubagens - Modelos matemáticos#Encurvadura#Equações de Euler#Equações de Von Kármán

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...

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## Study of high Reynolds number pipe flows with porous inserts

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.

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

Fonte: Universidade de Évora
Publicador: Universidade de Évora

Tipo: Artigo de Revista Científica

POR

Relevância na Pesquisa

36.46%

#Cosserat theory,#nine directors,#steady solution,#axisymmetric motion,#volume fow rate,#power law viscosity function.

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.

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## Study of high Reynolds number pipe flows with porous inserts

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

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

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...

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

Fonte: Universidade Federal de Uberlândia
Publicador: Universidade Federal de Uberlândia

Tipo: Dissertação

POR

Relevância na Pesquisa

46.46%

#Engenharia Mecânica#Calor - Transmissão#Condutividade térmica#Nanofluidos#Simulação numérica#Transferência de calor#Condutividade térmica#Nanofluids#Numerical simulation#Heat transfer#Thermal conductivity

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...

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

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.

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## Centrifugal force reversal from the perspective of rigidly rotating observer

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)

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

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.

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## Electromagnetic Fields Produced by Moving Sources in a Curved Beam Pipe

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

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## Stability of flow through a slowly diverging pipe

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

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

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

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## The laminar flow instability criterion and turbulence in pipe

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

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

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...

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

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

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