Antennas on circular cylinders
DEFF Research Database (Denmark)
Knudsen, H. L.
1959-01-01
antenna in a circular cylinder. By a procedure similar to the one used by Silver and Saunders, expressions have been derived for the field radiated from an arbitrary surface current distribution on a cylinder surface coaxial with a perfectly conducting cylinder. The cases where the space between the two...... cylindrical surfaces have the sane characteristic constants and different constants are treated separately. Extensive numerical computations of the field radiated from the slot antennas described here are being carried out, but no numerical results are yet available...
Progress on LES of Flow Past a Circular Cylinder
Mittal, R.
1996-01-01
The objective of the present research is to assess the usefulness of large-eddy simulation (LES) methodology for flows in complex geometries. Flow past a circular cylinder has been calculated using a central-difference based solver, and the results have been compared to those obtained by a solver that employs higher-order upwind biased schemes (Beaudan & Moin, 1994). This comparison allows us to assess the suitability of these schemes for LES in complex geometry flows.
Electromagnetic Casimir Forces in Elliptic Cylinder Geometries
Graham, Noah
2013-01-01
The scattering theory approach makes it possible to carry out exact calculations of Casimir energies in any geometry for which the scattering T-matrix and a partial wave expansion of the free Green's function are available. We implement this program for the case of a perfectly conducting elliptic cylinder, thereby completing the set of geometries where electromagnetic scattering is separable. Particular emphasis is placed on the case of zero radius, where the elliptic cylinder reduces to a st...
Failure of Non-Circular Composite Cylinders
Hyer, M. W.
2004-01-01
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
Numerical simulation for flow around two circular cylinders in tandem
Kondo, Norio; Matsukuma, Daisuke
2005-05-01
We use a third-order upwind finite element scheme in order to perform numerical stabilization of solutions of the Navier Stokes equations and present numerical results of flow around two circular cylinders in tandem arrangement by two- and three-dimensional computations. The two circular cylinders are arranged with some spacings between the cylinders. It is well known from experimental data that the flow around two circular cylinders denotes very complicated phenomena with the variation of spacing between two cylinders. In addition, the time-averaged drag coefficients of two circular cylinders suddenly change at a certain spacing between the cylinders. We, therefore, make an investigation of such phenomena at the Reynolds number of 1000 by the use of a numerical approach, and the obtained numerical results are also qualitatively compared with experimental data.
Identification of Plasmonic Modes in Parabolic Cylinder Geometry by Quasi-Separation of Variables
KURIHARA, Kazuyoshi; Otomo, Akira; Yamamoto, Kazuhiro; TAKAHARA, Junichi; Tani, Masahiko; Kuwashima, Fumiyoshi
2014-01-01
This paper describes the plasmonic modes in the parabolic cylinder geometry as a theoretical complement to the previous paper (J Phys A 42:185401) that considered the modes in the circular paraboloidal geometry. In order to identify the plasmonic modes in the parabolic cylinder geometry, analytic solutions for surface plasmon polaritons are examined by solving the wave equation for the magnetic field in parabolic cylindrical coordinates using quasi-separation of variables in combination with ...
INTERACTION OF A FLOATING ELLIPTIC CYLINDER WITH A VIBRATING CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
SUN Ren; CHWANG Allen T.
2006-01-01
The nonlinear hydrodynamic interaction between a floating elliptic cylinder and a vibrating circular cylinder immersed in an infinite fluid was investigated. By taking the added masses of the two-cylinder system into account, the dynamical equations of motion were formulated from the Lagrange equations of motion. The dynamical behaviors of these two cylinders were analyzed numerically for some typical situations, and the results show that the presence of a vibrating circular cylinder has a significant influence on the planar motion of a floating elliptic cylinder. The hydrodynamic interaction between them results in complicated nonlinear behaviors of the floating cylinder. It is found that oscillatory motion of the elliptic cylinder takes place in response to the vibrating mode of the circular one.
PLANAR MOTION OF A SLIGHTLY DISTORTED CIRCULAR CYLINDER AROUND ANOTHER CIRCULAR ONE
Institute of Scientific and Technical Information of China (English)
SUN Ren; CHWANG Allen T.
2004-01-01
Accurate prediction of the motion of a body moving around another one in an unbounded fluid and determi-nation of the hydrodynamic interaction between them are im-portant in the coastal and offshore engineering. For two-dimensional cases, most of the previous studies were focused on the interaction between circular cylinders without considering the non-circular situation. To break through the limitation of"circular" bodies, in the present paper the boundary perturbation method was employed to investigate the motion of a slightly distorted circular cylinder around a circular one. An approximate complex velocity potential in terms of double infinite series expanded at two singular points was derived using the method of continued fractions. The hydrodynamic interaction between two cylinders was computed by solving the dynamical equations of motion. In a relative coordinate system moving with the uniform stream, the kinetic energy of the fluid was expressed as a function of fifteen added masses. Approximate analytical solutions of added masses in the series form were obtained and applied to determine the trajectories of the slightly distorted circular cylinder around a fixed circular one. Numerical results show that the presence of the circular cylinder affects the planar motion of the slightly distorted cirular cylinder and the initial configuration of the slightly distorted circular cylinder has a decisive influence on the development of its rotational motion.
FORCES ON A NEAR-WALL CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
ZHAN Jing-xia; WANG Jin-jun; ZHANG Pang-feng
2004-01-01
The pressure distribution around a near-wall smooth circular cylinder in cross-flow was mainly investigated. The experiment was conducted at the sub-critical Reynolds number ranging from 2.24·104 to 8.94·104,at which the regular vortex separation exists on an isolated circular cylinder. The experimental results indicate that the forces on a circular cylinder near a plane wall are different from those on an isolated circular cylinder. Drag and lift coefficients of a near-wall circular cylinder strongly depend on gap ratio. The increase of gap ratio results in the increase of drag coefficient and the declination of lift coefficient, drag coefficient ranges from 0.5 to 1.0, and lift coefficient from 0.25 to 0 when gap ratio gradually increases from 0 to 1.0, and then the forces tend to be nearly constant with the increase of gap ratio. The attraction between a cylinder and a plane wall, i.e., downward force, occurs when gap ratio lies in certain range. The existence of cylinder changes the pressure gradient on the plane wall, and the influence extends to the location where x/D＜-3.0 and x/D＞5.0.
Vibrations of Circular Cylinders of a Perfectly Conducting Elastic Material
Directory of Open Access Journals (Sweden)
K. S. Sarma
1972-07-01
Full Text Available The problems of radial vibrations of a long circular solid cylinder with a transverse magnetic field and rotary vibrations of a hollow cylinder with radial magnetic field are solved. The results of the case of an infinite medium with a cylinderical cavity are given. The frequency equation in each case, is solved in particular cases approximately.
Inflation of polymer melts into elliptic and circular cylinders
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Christensen, Jens Horslund; Gøttsche, Søren
2000-01-01
A thin sheet (membrane) of the polymeric material is clamped between a Teflon-coated thermostated plate and a thermostated aluminium cylinder. By applying thermostated air through the plate, the polymer membrane deforms into an elliptic or a circular cylinder. The position of the top of the...
Wake instability issues: From circular cylinders to stalled airfoils
Meneghini, J. R.; Carmo, B. S.; Tsiloufas, S. P.; Gioria, R. S.; Aranha, J. A. P.
2011-07-01
Some recent results regarding the global dynamical behaviour of the wake of circular cylinders and airfoils with massive separation are reviewed in this paper. In order to investigate the effect of interference, the three-dimensional instability modes are analysed for the flow around two circular cylinders in tandem. In the same way, the flow around a stalled airfoil is investigated in order to provide a better understanding of the three-dimensional characteristics of wakes forming downstream of a lifting body with massive separation. These results are compared with those found for an isolated cylinder. Some fundamental differences among these flows are discussed.
Numerical Simulations of Viscous Flow Around Stepped Circular Cylinder
Bjørkli, Rune
2012-01-01
A stepped cylinder could be a desired design for an offshore buoy or SPAR platform. The geometry of a stepped cylinder consists of a small diameter cylinder (d) placed on top of a large diameter cylinder (D). This master thesis has investigated numerically the flow around a stepped cylinder with different diameter ratios (d/D) for a Reynolds number, ReD = 150. The commercial software Fluent v13.0 by Ansys was used for the numerical investigation.The aim of the study has been exploring the nea...
Flow control behind a circular cylinder via a porous cylinder in deep water
Directory of Open Access Journals (Sweden)
Akilli H.
2013-04-01
Full Text Available In this present work, the effects of surrounding outer porous cylinder on vortex structure downstream of a circular inner cylinder are investigated experimentally in deep water flow. The porosity of outer cylinder were selected as β = 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85. Porosity is defined as the ratio of the gap area on the body to the whole body surface area. The ratio of outer cylinder diameter to inner cylinder diameter, Do/Di was selected as 2.0, i.e. the inner cylinder diameter is Di = 30 mm where the outer cylinder diameter is Do = 60 mm. All experiments were carried out above a platform. The water height between the base of the platform and the free surface was adjusted as 340 mm. Free stream velocity is U = 156 mm/s, which corresponds to the Reynolds number of Rei = 5,000 based on the inner cylinder diameter. It has been observed that the outer porous cylinders have influence on the attenuation of vortex shedding in the wake region for all porosities. The turbulent intensity of the flow is reduced at least 45% by the presence of outer porous cylinder compared to the bare cylinder case. The porosities β = 0.4 and 0.5 are most suitable cases to control the flow downstream of the circular cylinder.
Two circular cylinders in cross-flow: A review
Sumner, D.
2010-08-01
Pairs of circular cylinders immersed in a steady cross-flow are encountered in many engineering applications. The cylinders may be arranged in tandem, side-by-side, or staggered configurations. Wake and proximity interference effects, which are determined primarily by the longitudinal and transverse spacing between the cylinders, and also by the Reynolds number, have a strong influence on the flow patterns, aerodynamic forces, vortex shedding, and other parameters. This paper reviews the current understanding of the flow around two “infinite” circular cylinders of equal diameter immersed in a steady cross-flow, with a focus on the near-wake flow patterns, Reynolds number effects, intermediate wake structure and behaviour, and the general trends in the measurements of the aerodynamic force coefficients and Strouhal numbers. A primary focus is on the key experimental and numerical studies that have appeared since the last major review of this subject more than 20 years ago.
Analysis of Aerodynamic Noise Generated from Inclined Circular Cylinder
Institute of Scientific and Technical Information of China (English)
YasutakeHaramoto; ShoujiYasuda; 等
2000-01-01
Making clear the generation mechanism of fluid dynamic noise is essential to reduce noise deriving from turbomachinery.The analysis of the aerodynamic noise generated from circular cylinder is carried out numerically and experimentally in a low noise wind tunnel.in this study,aerodynamic sound radiated from a circular cylinder in uniform flow is predicted numericaslly by the following two step method,First,the three-dimensional unsteady incompressible Navier-Stokes equation is solved using the high order accurate upwind scheme.Next.the sound pressure level at the observed point is calculated from the fluctuating surface pressure on the cylinder.based on modified Lighthill-Curl's equation.It is worth to note that the noise generated from the model is reduced rapidly when it is inclined against the mean flow.In other works,the Peak level of the radiated noise decreases apidly with inclination of the circular cylinder.The simulated SPL for the inclined circular cylinder is compared with the measured value .and good agreement is obtained for the peak spectrum fequency of the sound pressue level and tendency of noise reduction,So we expect that the change of flow structures makes reduction of the aerodynamic noise from the inclined models.
International Nuclear Information System (INIS)
This paper describes an effect of spacing between two adjoining circular cylinders on flow around two-dimensional circular cylinder bundles. The experiment was carried out in an N.P.L blow-down type wind-tunnel with a working section of 500 mm x 500 mm x 2000 mm, and under the Reynolds number 1.3 x 104. The surface-pressure distributions on the circular cylinder were measured and the drag coefficient was determined from these measurements. The flow-pattern around circular cylinders was observed. The power spectrum in the turbulent wake behind circular cylinders was also measured. It was found that the pressure on the rear surface of circular cylinders becomes lower and the drag coefficient increases as the spacing ratio decreases, while the step-change in the drag coefficient occurs at the spacing ratio where the flow pattern around the downstream circular cylinder changes. (author)
Flow instability in flow past O-grooved circular cylinder
International Nuclear Information System (INIS)
This study was devoted to elucidating the change in the flow characteristics of a laminar flow past a circular cylinder by modifying the cylinder shape with O-grooves. A numerical analysis was performed in a two-dimensional framework. The cylinder was represented using an immersed boundary method and marker particles on a Cartesian grid system. The number and locations of the O-grooves were the key parameters. An analysis of the flow pattern and flow induced forces was performed at Re = 40 and 50. In addition, we calculated the critical Reynolds number depending on the number of O-grooves and their locations
Inflation of polymer melts into elliptic and circular cylinders
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Christensen, Jens Horslund; Gøttsche, Søren
2000-01-01
A thin sheet (membrane) of the polymeric material is clamped between a Teflon-coated thermostated plate and a thermostated aluminium cylinder. By applying thermostated air through the plate, the polymer membrane deforms into an elliptic or a circular cylinder. The position of the top of the...... inflating membrane is detected by fibreoptic sensors positioned in the cylinder. The pressure difference across the inflating membrane is measured as well. Measurements were performed on a polyisobutylene melt. As the deformation in this device is highly non-uniform, the response of the material is modelled...
Elliptic cylinder geometry for distinguishability analysis in impedance tomography.
Saka, Birsen; Yilmaz, Atila
2004-01-01
Electrical impedance tomography (EIT) is a technique that computes the cross-sectional impedance distribution within the body by using current and voltage measurements made on the body surface. It has been reported that the image reconstruction is distorted considerably when the boundary shape is considered to be more elliptical than circular as a more realistic shape for the measurement boundary. This paper describes an alternative framework for determining the distinguishability region with a finite measurement precision for different conductivity distributions in a body modeled by elliptic cylinder geometry. The distinguishable regions are compared in terms of modeling error for predefined inhomogeneities with elliptical and circular approaches for a noncircular measurement boundary at the body surface. Since most objects investigated by EIT are noncircular in shape, the analytical solution for the forward problem for the elliptical cross section approach is shown to be useful in order to reach a better assessment of the distinguishability region defined in a noncircular boundary. This paper is concentrated on centered elliptic inhomogeneity in the elliptical boundary and an analytic solution for this type of forward problem. The distinguishability performance of elliptical cross section with cosine injected current patterns is examined for different parameters of elliptical geometry. PMID:14723501
Scattering of SH Waves by Fixed-Rigid Nearly Circular Cylinder
Abdul; Ibrahim BAKIRTAS
2001-01-01
A solution for the two-dimensional scattering and diffraction of plane SH waves by fixed-rigid cylinder of arbitrary shape in an elastic infinite medium is presented. The wave field for arbitary geometry in this paper is computed numericaly by the method weighted residues (moment method). Dynamic stress concentration factors around the arbitrary obstacles are obtained with respect to various dimensionless wave numbers. When the cavity is circular, results obtained from the analytical solution...
Fluid dynamic effects of grooves on circular cylinder surface
Kimura, Takeyoshi; Tsutahara, Michihisa
1991-12-01
It is shown that a groove on the surface of a circular cylinder affects movement of the separation point backward and reduces drag even at Reynolds numbers of about a few thousand. Several types of circular-arc cross-section grooves are studied using flow visualizations and numerical simulations. Whether these grooves are effective depends strongly on their positions, and the most effective positions are about 80 deg, measured from the foremost point. When they are effective, cavity flows are developed inside the grooves. This effect corresponds to that of dimples on golf balls and will explain unique characteristics of the drag curve.
Circular cylinders and pressure vessels stress analysis and design
Vullo, Vincenzo
2014-01-01
This book provides comprehensive coverage of stress and strain analysis of circular cylinders and pressure vessels, one of the classic topics of machine design theory and methodology. Whereas other books offer only a partial treatment of the subject and frequently consider stress analysis solely in the elastic field, Circular Cylinders and Pressure Vessels broadens the design horizons, analyzing theoretically what happens at pressures that stress the material beyond its yield point and at thermal loads that give rise to creep. The consideration of both traditional and advanced topics ensures that the book will be of value for a broad spectrum of readers, including students in postgraduate, and doctoral programs and established researchers and design engineers. The relations provided will serve as a sound basis for the design of products that are safe, technologically sophisticated, and compliant with standards and codes and for the development of innovative applications.
Laminar vortex shedding behind a cooled circular cylinder
Czech Academy of Sciences Publication Activity Database
Trávníček, Zdeněk; Wang, A. B.; Tu, W.Y.
2014-01-01
Roč. 55, č. 2 (2014), s. 1-12. ISSN 0723-4864 R&D Projects: GA ČR GA14-08888S Institutional support: RVO:61388998 Keywords : vortex shedding * cooled circular cylinder * thermal effect Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts Impact factor: 1.670, year: 2014 http://link.springer.com/journal/348/55/2/page/1
Numerical simulation of laminar flow past an oscillating circular cylinder
International Nuclear Information System (INIS)
The problem of unsteady, two dimensional laminar flow past a circular cylinder which performs recti-linear oscillations at an arbitrary angle η with respect to the oncoming uniform flow is considered. The governing Navier-Stokes equations are expressed in terms of a stream-function/vorticity formulation are solved numerically for a fixed Reynolds number R=855. The calculations are performed when the maximum displacement amplitude-to-cylinder radius ratio is 0.26. The recti-linear oscillations are only allowed when η=45o. A boundary-layer type transformation is adopted to scale out the singular nature in the vorticity at the start of the motion. The object of this study is to examine the effect of increase of frequency of the recti-linear oscillations on the near wake structure as well as the hydrodynamic forces acting on the cylinder. The results of this study are in good agreement with previous experimental predictions. (author)
Numerical Simulation of Flow Interference Between Two Circular Cylinders
Gao, F.; Mingham, C. G.; Causon, D. M.
2011-09-01
Viscous flow past two circular cylinders in tandem and side-by-side arrangements is investigated numerically. The solution to the Navier-Stokes equations is obtained by means of a cell-centred finite volume method (FVM) based on a structured Cartesian grid with collocated variable arrangement. The pressure-velocity coupling is evaluated by using the SIMPLE algorithm. The 2D Cartesian cut cell mesh is generated on the horizontal plane, which is extended vertically to form the 3D grid. The simulations are based on the Reynolds number of 200, and the gap between the two cylinders are 1.5-3D for side-by-side arrangement and 3-4D for tandem. Instantaneous velocity contours of the flow around the cylinders and time histories of force coefficients are presented.
Synthesis of antenna arrays radiation patterns on random geometry cylinders
Gabriel'yan, D. D.; Kalchenko, O. V.
2007-01-01
Synthesis algorithm for gain-phase radiation patterns formed by linear electrical vibrators antenna arrays located on random geometry cylinders is discussed. The results of numerical calculations are presented.
Passive jet control of flow around a circular cylinder
Chen, Wen-Li; Gao, Dong-Lai; Yuan, Wen-Yong; Li, Hui; Hu, Hui
2015-11-01
In the present study, a passive flow control method, which is featured by passive windward suction combined with leeward jet over a circular cylinder for drag reduction and dynamic wind loading suppression, was experimentally investigated to manipulate unsteady wake vortex shedding from a circular cylinder. Four perforated pipe designs with different numbers of suction/jet holes (i.e., from 2 to 24 suction/jet holes) were used to create flow communicating channels between the windward and leeward stagnation points of a cylindrical test model. The experimental study was performed in a wind tunnel at a Reynolds number of Re = 4.16 × 104 based on the cylinder diameter and oncoming airflow speed. In addition to measuring surface pressure distributions to determine the dynamic wind loads acting on the test model, a digital particle image velocimetry (PIV) system was also used to quantify the wake flow characteristics in order to assess the effectiveness of the passive jet control method with different perforated pipe designs, in comparison with a baseline case without passive jet control. It was found that the passive jet control method is very effective in manipulating the wake vortex shedding process from the circular cylinder. The perforated pipe designs with more suction/jet holes were found to be more effective in reducing drag and suppressing fluctuating amplitude of the dynamic wind loads acting on the test model. With 24 suction/jet holes evenly distributed over the cylindrical test model (i.e., the N13 design of the present study), the passive jet control method was found to be able to achieve up to 33.7 % in drag reduction and 90.6 % in fluctuating wind loading suppression, in comparison with the baseline case. The PIV measurement results revealed clearly that the passive jet control method would cause airflow jets into the cylinder wake and change the shedding modes of the wake vortex structures from the cylindrical test model. Because of the dynamic
Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder
Akbıyık, Hürrem; Erkan Akansu, Yahya; Yavuz, Hakan; Ertuğrul Bay, Ahmet
2016-03-01
In this paper, an experimental study on flow control around a circular cylinder with splitter plate and plasma actuator is investigated. The study is performed in wind tunnel for Reynolds numbers at 4000 and 8000. The wake region of circular cylinder with a splitter plate is analyzed at different angles between 0 and 180 degrees. In this the study, not only plasma actuators are activated but also splitter plate is placed behind the cylinder. A couple electrodes are mounted on circular cylinder at ±90 degrees. Also, flow visualization is achieved by using smoke wire method. Drag coefficient of the circular cylinder with splitter plate and the plasma actuator are obtained for different angles and compared with the plain circular cylinder. While attack angle is 0 degree, drag coefficient is decreased about 20% by using the splitter plate behind the circular cylinder. However, when the plasma actuators are activated, the improvement of the drag reduction is measured to be 50%.
Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder
Directory of Open Access Journals (Sweden)
Akbıyık Hürrem
2016-01-01
Full Text Available In this paper, an experimental study on flow control around a circular cylinder with splitter plate and plasma actuator is investigated. The study is performed in wind tunnel for Reynolds numbers at 4000 and 8000. The wake region of circular cylinder with a splitter plate is analyzed at different angles between 0 and 180 degrees. In this the study, not only plasma actuators are activated but also splitter plate is placed behind the cylinder. A couple electrodes are mounted on circular cylinder at ±90 degrees. Also, flow visualization is achieved by using smoke wire method. Drag coefficient of the circular cylinder with splitter plate and the plasma actuator are obtained for different angles and compared with the plain circular cylinder. While attack angle is 0 degree, drag coefficient is decreased about 20% by using the splitter plate behind the circular cylinder. However, when the plasma actuators are activated, the improvement of the drag reduction is measured to be 50%.
Acoustic band gaps in two-dimensional square arrays of semi-hollow circular cylinders
Institute of Scientific and Technical Information of China (English)
T.; Kim
2009-01-01
Concave surfaces focus sound while convex surfaces disperse sound. It is therefore interesting to know if it is possible to make use of these two opposite characteristics to enhance the band gap performance of periodic arrays of solid cylinders in air. In this paper, the band gap characteristics of a 2-D square array of semi-hollow circular cylinders embedded in air are investigated, both experimentally and theoretically. In comparison with the types of inclusion studied by previous researchers, a semi-hollow circular cylinder is unique in the sense that it has concave inner surfaces and convex outer surfaces. The finite difference time domain (FDTD) method is employed to study the propagation behavior of sound across the new phononic crystal of finite extent, and the influences of sample size and inclusion orientation on band gap characteristics are quantified in order to obtain the maximum band gap. For reference, the band gap behaviors of solid circular cylinder/air and hollow circular cylinder/air systems are considered and compared with those of semi-hollow circular cylinder/air systems. In addition to semi-hollow circular cylinders, other inclusion topologies such as semi-hollow triangular and square cylinders are also investigated. To validate the theoretical predictions, experimental measurements on square arrays of hollow Al cylinders in air and semi-hollow Al cylinders in air are carried out. The results demonstrate that the semi-hollow circular cylinder/air system has the best overall band gap performance.
Standing torsional waves in a fully saturated, porous, circular cylinder
Solorza, S; 10.1111/j.1365-246X.2004.02198.x
2004-01-01
For dynamic measurement of the elastic moduli of a porous material saturated with viscous fluid using the resonance-bar technique, one also observes attenuation. In this article we have carried out the solution of the boundary-value problem associated with standing torsional oscillations of a finite, poroelastic, circular cylinder cast in the framework of volume-averaged theory of poroelasticity. Analysing this solution by eigenvalue perturbation approach we are able to develop expressions for torsional resonance and temporal attenuation frequencies in which the dependence upon the material properties are transparent. It shows how the attenuation is controlled by the permeability and the fluid properties, and how the resonance frequency drops over its value for the dry solid-frame due to the drag effect of fluid mass. Based upon this work we have a firm basis to determine solid-frame shear modulus, permeability, and tortuosity factor from torsional oscillation experiments.
Movement of a horizontal vortex ring in a circular cylinder
International Nuclear Information System (INIS)
In this paper, we report the numerical and experimental solutions of the vortical flows driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a large background rotation
Fermionic Casimir interaction in cylinder-plate and cylinder-cylinder geometries
Teo, L P
2015-01-01
In this work, we consider the Casimir effect due to massless fermionic fields in the presence of long cylinders. More precisely, we consider the interaction between a cylinder parallel to a plate, between two parallel cylinders outside each other, and between a cylinder lying parallelly inside another cylinder. We derive the explicit formulas for the Casimir interaction energies and compute the leading and the next-to-leading order terms of the small separation asymptotic expansions. As expected, the leading order terms coincide with the proximity force approximations. We compare the results of the next-to-leading order terms of different quantum fields, and show that our results support the ansatz of derivative expansions.
Energy Technology Data Exchange (ETDEWEB)
Oki, M. [Tokai University, Tokyo (Japan); Aoki, K. [Tokai University, Tokyo (Japan). Faculty of Engineering; Nakayama, Y.
1998-09-25
In the flow around a circular cylinder, the sudden decrease in the drag force occurs at around Reynolds number Re = 3 times 10{sup 5}, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In this paper, in order to make clear the flow characteristics around a circular cylinder with grooves, the unsteady flow was analyzed by applying the RNG (Renormalization Group) {kappa}-{epsilon} turbulent model to a flow around a circular cylinder with grooves each of whose section shapes being as same as that of a dimple an a golf ball, with changing Reynolds number. This result made clear the characteristics of lift and drag, Strouhal number, flow pattern behind the circular cylinder, pressure distribution and separation points. Moreover, the time averages of these values almost agreed with the experimental values. 20 refs., 10 figs.
Dual Circularly Polarized Omnidirectional Antenna with Slot Array on Coaxial Cylinder
Bin Zhou; Junping Geng; Zhe Li; Wenzhi Wang; Xianling Liang; Ronghong Jin
2015-01-01
A dual circularly polarized (CP) omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP) port and right hand circularly polarized (RHCP) port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 ...
International Nuclear Information System (INIS)
An experimental investigation was performed in a low-speed wind tunnel in which an elastically mounted circular cylinder was fitted with two accelerometers and surrounded by from one to six identical cylinders in order to study the fluid flow characteristics and predict the possibility of suppressing flow-induced vibration excitation in the test cylinder. The spectral diagram, amplitude and orbital motion of the test cylinder were used to analyze the vibration excitation under differing free stream velocities, natural frequencies of the test cylinder, and number of surrounding cylinders. In this study, for the test cylinder with the same natural frequency as the adjacent cylinders (24 Hz) the amplitude response showed that when the fluid flow velocity exceeded a critical value, which depends on the arrangement of the cylinders, fluid elastic instability occurred. Beyond the critical velocity the cylinder became excited and vibrated in a figure-of-eight pattern along with the line-dominated spectrum, which implies that by having the same frequency along with a phase shift, the characteristic behavior of the cylinder is observed to be like an oscillator with the cross-wise and stream-wise response. From the assessment of the amplitude response of the test cylinder it was observed that the upstream cylinders had a greater influence on the amplitude response than the downstream cylinders. On the other hand, when the test cylinder had a natural frequency different to the adjacent cylinders it was observed that the frequency had a minimal effect on the critical velocity, and yet beyond the critical velocity it had a significant influence on the vibration amplitude response. (paper)
Wang, X. H.; Zhu, W. F.; He, Z. Y.
It is well known that the steady flow past a circular cylinder loses stability at Re takes the value about 50 (Y. Ding et al, 1999). Most papers about the characterization and understanding of the stability for the flow past blunt bodies are mainly carried out for such flow past one circular cylinder. And there is a large variation in the values of Re cr and correspondingly the values of St cr reported by different reseachers. Bhascar and Sunjay (2006) have attributed it to the effect of blockage (here, it means the ratio of the diameter of cylinder to the lateral width of domain). And for high Re cr first decreases and then increases with the increase of the blockage. And the correspondingly values of St cr are quite sensitive to the blockage. In this paper, we attampt to estimate the critical Re for the flow past one square cylinder. It is obviously that geometry symmetry or attack degree will not change just with rotation of the circular cylinder, but for the square cylinder, the symmetry or the degree will not keep for the rotation. So the numerical estimation of the critical Re for the flow past square cylinders should be carried out for the symmetric or unsymmetric geometry boundary conditions separately. Based on the calculation of the lid driven cavity flow at Re=100 and 1000, a second order Euler-Taylor-Galerkin finite element method was used to estimate the critical Reynolds number for flow past one square cylinder with zero attact degree through direct time integration of the NS equationes. The role of blockage on such flow was analysed at Re=100. It was found that the averged St tend to be constant as blockage took the value larger than 50. The critical Reynolds number is then computed. As the result shown, it was estimated that Re Cr =40.11. And the computation for unsymmetric geometry condition will discussed laterly.
Streamwise forced oscillations of circular and square cylinders
Tudball-Smith, Daniel; Leontini, Justin S.; Sheridan, John; Lo Jacono, David
2012-01-01
International audience The modification of a cylinder wake by streamwise oscillation of the cylinder at the vortex shedding frequency of the unperturbed cylinder is reported. Recent numerical simulations [J. S. Leontini, D. Lo Jacono, and M. C. Thompson, "A numerical study of an inline oscillating cylinder in a free stream," J. Fluid Mech. 688, 551-568 (2011)] showed that this forcing results in the primary frequency decreasing proportionally to the square of the forcing amplitude, before ...
Plane Wall Effect of Flow around Two Circular Cylinders in Tandem Arrangement
Triyogi Yuwono,; Wawan Aries Widodo; Heru Mirmanto; Fahmi Fahreza
2011-01-01
The flow characteristic around two circular cylinders in tandem arrangement located near a plane wall were investigated experimentally in a uniform flow at a Reynolds Number of 5.3 x 104. The center to center spacing between the two cylinders relative to the cylinder diameter was constantly maintained at P/D = 1.5. The pressure distributions along the surface of the cylinder and the plane wall were measured by varying the gap-to-diameter of cylinder ratio (G/D) in the range of 0 < G/D < 0.467...
Directory of Open Access Journals (Sweden)
Ahmed W. Mustava
2013-04-01
Full Text Available The effect of a semi-circular cylinders in a two dimensional channel on heat transfer by forced convection from two heat sources with a constant temperature has been studied numerically. Each channel contains two heat sources; one on the upper surface of the channel and the other on the lower surface of the channel. There is semi-circular cylinder under the source in upper surface and there is semi-circular cylinder above the source in lower surface. The location of the second heat source with its semi-cylinder has been changed and keeps the first source with its semi- cylinder at the same location. The flow and temperature field are studied numerically with different values of Reynolds numbers and for different spacing between the centers of the semi-cylinders. The laminar flow field is analyzed numerically by solving the steady forms of the two-dimensional incompressible Navier- Stokes and energy equations. The Cartesian velocity components and pressure on a collocated (non-staggered grid are used as dependent variables in the momentum equations, which discretized by finite volume method, body fitted coordinates are used to represent the complex channel geometry accurately, and grid generation technique based on elliptic partial differential equations is employed. SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The range of Reynolds number is (Re= 100 – 800 and the range of the spacing between the semi-cylinders is(1-4 and the Prandtl number is 0.7.The results showed that increasing the spacing between the semi-cylinders increases the average of Nusselt number of the first heat source for all Reynolds numbers. As well as the results show that the best case among the cases studied to enhance the heat transfer is when the second heat source and its semi-cylinder located on at the distance (S=1.5 from the first half of the cylinder and the Reynolds number is greater than (Re ≥ 400 because of the
Kitagawa, T.; Ohta, H.
2008-07-01
Three-dimensional fluid computations have been performed to investigate the flows around two circular cylinders in tandem arrangements at a subcritical Reynolds number, Re=2.2×104. The center-to-center space between the cylinders was varied from twice the cylinder diameter to five times that, and the flows and fluid-dynamic forces obtained from the simulations are compared with the experimental results reported in the literature. Special attention is paid to the characteristics of the vortices shed from the upstream cylinder such as the convection, the impingement onto the downstream cylinder and the interaction with the vortices from the downstream cylinder. The effects of the vortices from the upstream cylinder on the fluid-dynamic forces acting on the downstream cylinder are discussed.
A cell boundary element method applied to laminar vortex shedding from circular cylinders
Farrant, T; Tan, M; Price, W.G.
2001-01-01
The two-dimensional unsteady incompressible Navier–Stokes equations are solved for flows around arrangements of circular cylinders at Reynolds number 100 and 200. A hybrid boundary element/finite element method is used to discretise the spatial domain together with a second order implicit finite difference approximation in time. The numerical scheme of study is validated for a uniform stream past an isolated circular cylinder by comparing findings with experimental and numerical studies. Both...
Water Wave Scattering by a Nearly Circular Cylinder Submerged Beneath an Ice-cover
Institute of Scientific and Technical Information of China (English)
Rumpa Chakraborty; Birendra Nath Mandal
2015-01-01
Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on water, is investigated here. The cross-section of the nearly circular cylinder is taken as r=a(1+δC(θ)), wherea is the radius of the corresponding circular cross-section of the cylinder,δ is a measure of small departure of the cross-section of the cylinder from its circularity andC(θ) is the shape function. Using a simplified perturbation technique the problem is reduced to two independent boundary value problems up to first order inδ. The first one corresponds to water wave scattering by a circular cylinder submerged in water with an ice-cover, while the second problem describes wave radiation by a submerged circular cylinder and involves first order correction to the reflection and transmission coefficients. The corrections are obtained in terms of integrals involving the shape function. Assuming a general Fourier expansion of the shape function, these corrections are evaluated approximately. It is well known that normally incident wave trains experience no reflection by a circular cylinder submerged in infinitely deep water with an ice cover. It is shown here that the reflection coefficient also vanishes up to first order for some particular choice of the shape function representing a nearly circular cylinder. For these cases, full transmission occurs, only change is in its phase which is depicted graphically against the wave number in a number of figures and appropriate conclusions are drawn.
Kang, XiuYing; Su, YanPing
2012-10-01
Cross-flows around two, three and four circular cylinders in tandem, side-by-side, isosceles triangle and square arrangements are simulated using the incompressible lattice Boltzmann method with a second-order accurate curved boundary condition at Reynolds number 200 and the cylinder center-to-center transverse or/and longitudinal spacing 1.5 D, where D is the identical circular cylinder diameter. The wake patterns, pressure and force distributions on the cylinders and mechanism of flow dynamics are investigated and compared among the four cases. The results also show that flows around the three or four cylinders significantly differ from those of the two cylinders in the tandem and side-by-side arrangements although there are some common features among the four cases due to their similarity of structures, which are interesting, complex and useful for practical applications. This study provides a useful database to validate the simplicity, accuracy and robustness of the Lattice Boltzmann method.
Effect of Inner Circular Cylinder Size on Three-Dimensional Natural Convection in Cubical Enclosure
International Nuclear Information System (INIS)
This study evaluates the effect of a heated circular cylinder's size on three-dimensional natural convection in a cubical enclosure. The Rayleigh number was varied between 103 and 105, and the Prandtl number was maintained at 0.7. In this study, the radius of the circular cylinder was changed by 0.1 L within a range of 0.1.0.4 L. The thermal and fluid flow characteristics were regarded to be independent of time in the range of the Rayleigh number and cylinder radius considered in this study. The surface-averaged Nusselt numbers of the cylinder and the enclosure were found to increase with the increase in the radius of the cylinder. The effect of the cylinder's size on natural convection in the enclosure was analyzed across the thermal and flow fields, and the distributions of the Nusselt numbers
Forcing of a bottom-mounted circular cylinder by steep regular water waves at finite depth
DEFF Research Database (Denmark)
Paulsen, Bo Terp; Bredmose, Henrik; Bingham, Harry B.;
2014-01-01
Forcing by steep regular water waves on a vertical circular cylinder at finite depth was investigated numerically by solving the two-phase incompressible Navier–Stokes equations. Consistently with potential flow theory, boundary layer effects were neglected at the sea bed and at the cylinder...
Poiseuille flow-induced vibrations of two tandem circular cylinders with different mass ratios
Jiang, Ren-Jie; Lin, Jian-Zhong
2016-06-01
Flow-induced vibrations of two tandem circular cylinders with different mass ratios confined between two parallel walls are numerically studied via a lattice Boltzmann method. With fixed Reynolds number Re = 100 and blockage ratio β = 1/4, the effects of mass ratio m* = [0.0625, 16] and streamwise separation between two cylinders S/D = [1.125, 10] on the cylinder motions and vortex wake modes are investigated. A variety of distinct cylinder motion regimes involving the symmetric periodic vibration, biased quasi-periodic vibration, beating vibration, and steady regimes, with the corresponding wake structures, e.g., two rows of alternately rotating vortices, a single row of same-sign vortices, and steady wake, are observed. For each current case, the cylinder motion type is exclusive and in the binary oscillation regime, both cylinders always vibrate at a common primary frequency. The lighter cylinder usually oscillates at a larger amplitude than the heavier one, while the heavier cylinder undergoes larger lift force than the lighter one. The lift force and cylinder displacement always behave as an out-of-phase state. In the gap-interference region, large-amplitude oscillations could be produced extensively and in the wake-interference region, the cylinder motions and fluid flows are mainly dependent on the upstream cylinder. When the separation is large enough, both cylinders behave as two isolated ones. The mechanisms for the excitations of cylinder vibrations have also been analysed.
Institute of Scientific and Technical Information of China (English)
WANG; JinJun; FENG; LiHao; XU; ChaoJun
2007-01-01
Circular cylinder separation control and flow structure influenced by the synthetic jet have been experimentally investigated in a water channel. The synthetic jet issues from a slot and ejects toward upstream from the front stagnation point of the cylinder. It has been found that, similar to the traditional synthetic jet which is positioned near the separation point or inside the separation region, the present synthetic jet arrangement constitutes an efficient way to control flow separation of the circular cylinder, but with a different control mechanism. The present synthetic jet leads to an upstream displacement of the front stagnation point and the formation of a vortex pair near both sides of the exit orifice. When ReU based on the synthetic jet average exit orifice velocity is about lower than 43, a closed envelope forms in front of the windward side of the cylinder during the blowing cycle of synthetic jet, which acts as an apparent modification for the cylinder configuration. When ReU is high enough, an open envelope forms upstream of the cylinder, and the flow around the cylinder becomes much energetic. Thus, regardless of ReU, the present synthetic jet can improve separation for flow around a circular cylinder. With regard to the leeward side, as ReU increases, the flow separation region behind the cylinder gradually disappears. The flow over cylinder may be fully attached when the open envelope forms upstream of the cylinder and ReU is greater than 344. Then, the flow past the cylinder will converge near the back stagnation point of the cylinder, where a new vortex pair shedding periodically is generated due to the high shear layer.
Directory of Open Access Journals (Sweden)
Eskandari Jam Jafar
2014-12-01
Full Text Available In this paper, by using a semi-analytical solution based on multi-layered approach, the authors present the solutions of temperature, displacements, and transient thermal stresses in functionally graded circular hollow cylinders subjected to transient thermal boundary conditions. The cylinder has finite length and is subjected to axisymmetric thermal loads. It is assumed that the functionally graded circular hollow cylinder is composed of N fictitious layers and the properties of each layer are assumed to be homogeneous and isotropic. Time variations of the temperature, displacements, and stresses are obtained by employing series solving method for ordinary differential equation, Laplace transform techniques and a numerical Laplace inversion.
Upper bounds on packing density for circular cylinders with high aspect ratio
Kusner, Wöden
2013-01-01
In the early 1990s, A. Bezdek and W. Kuperberg used a relatively simple argument to show a surprising result: The maximum packing density of circular cylinders of infinite length in $\\mathbb{R}^3$ is exactly $\\pi/\\sqrt{12}$, the planar packing density of the circle. This paper modifies their method to prove a bound on the packing density of finite length circular cylinders. In fact, the maximum packing density for unit radius cylinders of length $t$ in $\\mathbb{R}^3$ is bounded above by $\\pi/...
Seal whisker-inspired circular cylinders reduce vortex-induced vibrations
Beem, Heather; Triantafyllou, Michael
2012-11-01
Recent work shows that the undulatory, asymmetric geometry of harbor seal whiskers passively reduces vortex-induced vibration (VIV) amplitudes to less than 0.1 times the whisker diameter. This reduction holds in frontal flows, but due to the elliptical cross-section of the whisker, flows that approach from large angles of attack generate significant vibrational response. The present study investigates the possibility of extending the vibration reduction to unidirectional bodies, such that flows from all angles cause reduced VIV. A method for developing a new geometry that incorporates the ``whisker'' features into bodies with uniform, circular cross-section is presented. This geometry and multiple variations on it are fabricated into rigid models. Forces are measured on the models while they undergo imposed oscillations and are towed down a water tank. Contour plots of CL , v show peak VIV amplitudes to decrease as much as 28% from that of a standard cylinder. This result holds promise for applications where vibration reduction is desired, regardless of the angle of oncoming flow.
Interaction of oblique waves with an array of long horizontal circular cylinders
Institute of Scientific and Technical Information of China (English)
NG; Chiu-On
2007-01-01
The scattering and radiations of linear oblique waves by multiple long horizontal circular cylinders submerged in water of finite depth are investigated using the multipole expansion method. Analytical expressions for the diffracted and radiated potentials are given as a linear combination of infinite multipoles. The unknown coefficients in the expressions are determined by using the addition theorem of the Bessel function and the cylinder boundary conditions. Also analytical expressions for wave forces, hydrodynamic coefficients and reflection and transmission coeffi-cients are derived. The present analytical solution is verified through the boundary element method and applied to investigate three different cases of the interaction of oblique waves with multiple submerged horizontal circular cylinders. The results show that the number of cylinders, the arrangement and spacing between cylinders play an important role in wave forces, hydrodynamic coefficients and reflection and transmission coefficients. Some interesting and important phenomena are ob-served in numerical experiments.
Interaction of oblique waves with an array of long horizontal circular cylinders
Institute of Scientific and Technical Information of China (English)
SHEN YongMing; ZHENG YongHong; NG Chiu-On
2007-01-01
The scattering and radiations of linear oblique waves by multiple long horizontal circular cylinders submerged in water of finite depth are investigated using the multipole expansion method. Analytical expressions for the diffracted and radiated potentials are given as a linear combination of infinite multipoles. The unknown coefficients in the expressions are determined by using the addition theorem of the Bessel function and the cylinder boundary conditions. Also analytical expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are derived. The present analytical solution is verified through the boundary element method and applied to investigate three different cases of the interaction of oblique waves with multiple submerged horizontal circular cylinders. The results show that the number of cylinders, the arrangement and spacing between cylinders play an important role in wave forces, hydrodynamic coefficients and reflection and transmission coefficients. Some interesting and important phenomena are observed in numerical experiments.
Numerical Simulation of Flow Around a Row of Circular Cylinders Using the Lattice Boltzmann Method
S. Ul Islam; C.Y. Zhou
2009-01-01
This study describes a numerical study of flow past a row of circular cylinders at different Reynolds numbers with different distances between the cylinders using the Lattice Boltzmann Method (LBM). Numerical simulations are performed to investigate the blockage effect for the ranges of Re≤200 and B = W[R]≤25R , where, Re, R and W are the Reynolds numbers, the radius of the cylinders and the distance between the center of the cylinders, respectively. The Strouhal number and drag forces exerte...
Numerical analysis of two and three dimensional buoyancy driven water-exit of a circular cylinder
Directory of Open Access Journals (Sweden)
Moshari Shahab
2014-06-01
Full Text Available With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.
Mathematic modelling of circular cylinder deformation under inner grouwth
Directory of Open Access Journals (Sweden)
A. V. Siasiev
2009-09-01
Full Text Available A task on the intensive deformed state (IDS of a viscoelastic declivous cylinder, which is grown under the action of inner pressure, is considered. The process of continuous increase takes a place on an internal radius so, that a radius and pressure change on set to the given law. The special case of linear law of creeping is considered, and also numeral results are presented as the graphs of temporal dependence of tensions and moving for different points of cylinder.
Prebuckling, Buckling, and Postbuckling Response of Segmented Circular Composite Cylinders
Riddick, Jaret Cleveland
2001-01-01
Discussed is a numerical and experimental characterization of the response of small-scale fiber-reinforced composite cylinders constructed to represent a fuselage design whereby the crown and keel consist of one laminate stacking sequence and the two sides consist of another laminate stacking sequence. This construction is referred to as a segmented cylinder. The response to uniform axial endshortening is discussed. Numerical solutions for the nonlinear prebuckling, buckling, and postbuckling...
Circular Cylinders by Four or Five Points in Space
Devillers, Olivier; Mourrain, Bernard; Preparata, Franco ,; Preparata, Franco P.; Trebuchet, Philippe
2002-01-01
We are interested in computing effectively cylinders through 5 points, and in other problems involved in metrology. In particular, we consider the cylinders through 4 points with a fix radius and with extremal radius. For these different problems, we give bounds on the number of solutions and exemples show that these bounds are optimal. Finally, we describe two algebraic methods which can be used here to solve efficiently these problems and some experimentation results.
On circular Cylinders by Four or Five Points in Space
Devillers, Olivier; Mourrain, Bernard; Preparata, Franco ,; Trebuchet, Philippe
2001-01-01
We are interested in computing effectively cylinders through 5 points, and in other problems involved in metrology. In particular, we consider the cylinders through 4 points with a fix radius and with extremal radius. For these different problems, we give bounds on the number of solutions and exemples show that these bounds are optimal. Finally, we describe two algebraic methods which can be used here to solve efficiently these problems and some experimentation results.
Flow-induced vibrations of two tandem circular cylinders in a parallel-wall channel
Jiang, Ren-Jie; Lin, Jian-Zhong; Ku, Xiao-Ke
2014-10-01
Flow-induced vibrations of one and two tandem circular cylinders in the flow around cylinders in a parallel-wall channel are numerically studied by the lattice Boltzmann method. Within a range of Reynolds number Re = [1, 160], the effects of streamwise separation between two cylinders S/D = [1.25, 3], mass ratio M = [0.05, 5], and blockage ratio β = [1/2, 1/8] on the motions of cylinders and fluids are investigated, respectively. For the case of an isolated cylinder, as the mass ratio is 1, no large-amplitude oscillation is observed, and as the mass ratio is 0.1, the cylinder motion translates from the steady regime to the biased periodic vibration with a large oscillation amplitude gradually as Reynolds number is increased from 1 to 160. For the case of two cylinders in tandem, two steady regimes and a variety of distinct oscillation regimes with the corresponding flow structures are observed. The critical mass ratio of the two tandem cylinders in the strong coupling regime is about an order of magnitude larger than that of an isolated cylinder. For blockage ratio is more than 1/5, the vibration type of the cylinders is exclusive, while for blockage ratio is less than 1/6, the cylinder oscillation state is bistable. The mechanisms of the observed phenomena are also discussed.
Plane Wall Effect of Flow around Two Circular Cylinders in Tandem Arrangement
Directory of Open Access Journals (Sweden)
Triyogi Yuwono,
2011-02-01
Full Text Available The flow characteristic around two circular cylinders in tandem arrangement located near a plane wall were investigated experimentally in a uniform flow at a Reynolds Number of 5.3 x 104. The center to center spacing between the two cylinders relative to the cylinder diameter was constantly maintained at P/D = 1.5. The pressure distributions along the surface of the cylinder and the plane wall were measured by varying the gap-to-diameter of cylinder ratio (G/D in the range of 0 < G/D < 0.467. Surface oil-film techniques were used to investigate the flow patterns on the cylinder. The result showed that for upstream cylinder, in the gap-to-diameter ratio G/D < /D, there is no stagnation point at front side of the upstream cylinder; it is gradually raised as the gap increase. For the downstream cylinder, a peak on the lower side of the front side of the cylinder is apparent in each of the pressure distributions. This peak represents the reattachment of shear layer that separates from lower side of the upstream cylinder. The reattachment point tends to move forward close to the angular position of = 0o as the gap ratio increase. The shear layer bifurcates into two shear layers. One shear layer continues in the downstream direction, and the other shear layer flows in the upstream direction.
Experimental Study on Local Scour Around A Large Circular Cylinder Under Irregular Waves
Institute of Scientific and Technical Information of China (English)
周益人; 陈国平
2004-01-01
A series of physical model tests are conducted for local scour around a circular cylinder of a relatively large diameter (0.15 ＜ D/L ＜ 0.5) under the action of irregular waves. The laws of change of the topography around the cylinder are systematically studied. The effects of wave height, wave period, water depth, sediment grain size and cylinder diameter are taken into account. The mechanism of formation of the topography around the cylinder is analyzed. A detailed analysis is given to bed sediment grain size, and it is considered that the depth of scour around the cylinder under wave action is not inversely proportional to the sediment grain diameter. On such a basis, an equation is proposed for calculation of the maximum depth of scour around a cylinder as well as its position under the action of irregular waves.
International Nuclear Information System (INIS)
A numerical analysis of the effect of the position of a circular cylinder in a 45 .deg. tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between 103 and 105. The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure
International Nuclear Information System (INIS)
In this study, we experimentally examined the vibration response characteristics of two tandem circular cylinders of uniform diameter (d) and relatively low structural damping. Experiments were carried out with inline tandem cylinders in a water channel with two degrees-of-freedom, varying the natural frequency ratio of upstream cylinder to downstream cylinder. The cylinders were cantilever mounted with a low natural frequency in the inline and cross-flow directions (around 50Hz). The spacing between the cylinders was 4.0d. The Reynolds number of the experiments was from 3000 to 22000, varying the reduced velocities from around 1.0 to about 4.5. The oscillating frequencies of the cylinders and the surrounding flow were measured simultaneously using high temporal resolution particle image velocimetry (PIV), which is non-intrusive with respect to the flow, and has high spatial and temporal resolutions. As a result, the closer the value of natural frequencies, the stronger the influence from the upstream cylinder to downstream cylinder was. Also, it was changed by the difference of structural damping between two cylinders. (author)
International Nuclear Information System (INIS)
In this study, we consider the heat transfer characteristics of channel flow in the presence of an infinite streamwise array of equispaced identical rotating circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall for some selected angular speeds. The presence of the rotating circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to heat transfer enhancement on the channel walls. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of varying the gap to enhance heat transfer from the channel walls
Simulation of Viscous Flow Around a Circular Cylinder with OpenFOAM
Finserås, Live Reiten
2013-01-01
Flow around a circular cylinder has been extensively studied, both numerically and experimentally, for a number of years. With the increase in flow-structure interactions around marine structures such as platform legs/columns, pipelines and risers, the study of the complex flow mechanisms that is caused around cylinders at high Reynolds numbers has become increasingly important. The use of computational fluid dynamics (CFD) have proved to be an important tool in order to understand these mech...
Lift of a rotating circular cylinder in unsteady flows
DEFF Research Database (Denmark)
Carstensen, Stefan; Mandviwalla, Xerxes; Vita, Luca;
2012-01-01
A cylinder rotating in steady current experiences a lift known as the Magnus effect. In the present study the effect of waves on the Magnus effect has been investigated. This situation is experienced with the novel floating offshore vertical axis wind turbine (VAWT) concept called the DEEPWIND co...
Investigation of drag reduction through a flapping mechanism on circular cylinder
Asif, Md. Asafuddoula; Gupta, Avijit Das; Rana, M. D. Juwel; Ahmed, Dewan Hasan
2016-07-01
During flapping wing, a bird develops sufficient lift force as well as counteracts drag and increases its speed through different orientations of feathers on the flapping wings. Differently oriented feathers play a significant role in drag reduction during flying of a bird. With an objective to investigate the effect of installation of such flapping mechanism as a mean of drag reduction in case of flow over circular cylinder, this concept has been implemented through installation of continuous and mini flaps, made of MS sheet metal, where flaps are oriented at different angles as like feathers of flapping wings. The experiments are carried out in a subsonic wind tunnel. After validation and comparison with conventional result of drag analysis of a single cylinder, effects of flapping with Reynolds number variation, implementation of different orientations of mini flaps and variation of different interspacing distance between mini flaps are studied to find the most effective angle of attack of drag reduction on the body of circular cylinder. This research show that, installation of continuous flap reduces value of drag co-efficient, CD up to 66%, where as mini flaps are found more effective by reducing it up to 73%. Mini flaps of L/s=6.25, all angled at 30O, at the 30O angular position on the body of circular cylinder has been found the most effective angle of attack for drag reduction in case of flow over circular cylinder.
Unsteady flow around two-dimensional circular cylinder bundles in fluid elastic vibration
International Nuclear Information System (INIS)
We describe the unsteady flow around two-dimensional circular cylinder bundles supported by the leaf spring in the fluid-elastic vibration. The experiment was carried out in a circuit-type wind tunnel having a 200 mm x 200 mm working section of 2,000 mm length at the Reynolds number Re of 6,300. Two-dimensional circular cylinders with diameter D = 20 mm were aligned at regular spaces S in the square array of three rows. The spacing ratio between two adjoining circular cylinders was constant as S/D = 1.5. The time-mean velocity, turbulent intensities and Reynolds stress were measured by use of a laser Doppler velocimeter. The unsteady flow pattern around an oscillating cylinder was observed by the flow visualization in a water channel. Consequently, it was found that the occurrence of the fluid-elastic vibration is caused by the phenomenon of wake-switch for the circular cylinder bundles of three rows. (author)
Das, Pramode K.; Mathew, Sam; Shaiju, A. J.; Patnaik, B. S. V.
2016-02-01
The control of vortex shedding behind a circular cylinder is a precursor to a wide range of external shear flow problems in engineering, in particular the flow-induced vibrations. In the present study, numerical simulation of an energetically efficient active flow control strategy is proposed, for the control of wake vortices behind a circular cylinder at a low Reynolds number of 100. The fluid is assumed to be incompressible and Newtonian with negligible variation in properties. Reflectionally symmetric controllers are designed such that, they are located on a small sector of the cylinder over which, tangential sliding mode control is imparted. In the field of modern controls, proportional (P), integral (I) and differential (D) control strategies and their numerous combinations are extremely popular in industrial practice. To impart suitable control actuation, the vertically varying lift force on the circular cylinder, is synthesised for the construction of an error term. Four different types of controllers considered in the present study are, P, I, PI and PID. These controllers are evaluated for their energetic efficiency and performance. A linear quadratic optimal control problem is formulated, to minimise the cost functional. By performing detailed simulations, it was observed that, the system is energetically efficient, even when the twin eddies are still persisting behind the circular cylinder. To assess the adaptability of the controllers, the actuators were switched on and off to study their dynamic response.
EXPERIMENTAL STUDY OF FLOW STRUCTURE BEHIND A CIRCULAR CYLINDER WITH WAVY SURFACE BY PIV
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The wake behind a circular cylinder with wavy surface was investigated using single-frame PIV technique at Re=5200. The mean flow field and spatial distribution of turbulence statistics in the nodal, saddle and middle planes were presented and compared with those of a smooth cylinder. The near wake behind the wavy cylinder shows pronounced spanwise periodicity of flow structures. Compared with a smooth cylinder, the vortex formation region considerably expands in the streamwise direction, particularly reaching maximum in the saddle plane of the wavy cylinder. However, the longitudinal vortices in the nodal plane were noticeably suppressed in the transverse direction. In addition, the wake in the nodal plane contains the peak value of turbulent kinetic energy and the Reynolds shearing stress due to the intensive entrainment of free flow and the momentum exchange in the spanwise direction.
Carmo, Bruno S.; Assi, Gustavo R. S.; Meneghini, Julio R.
2013-08-01
In this work, we considered the flow around two circular cylinders of equal diameter placed in tandem with respect to the incident uniform flow. The upstream cylinder was fixed and the downstream cylinder was completely free to move in the cross-stream direction, with no spring or damper attached to it. The centre-to-centre distance between the cylinders was four diameters, and the Reynolds number was varied from 100 to 645. We performed two- and three-dimensional simulations of this flow using a Spectral/hp element method to discretise the flow equations, coupled to a simple Newmark integration routine that solves the equation of the dynamics of the cylinder. The differences of the behaviours observed in the two- and three-dimensional simulations are highlighted and the data is analysed under the light of previously published experimental results obtained for higher Reynolds numbers.
Re-examination of laminar flow over twin circular cylinders in tandem arrangement
International Nuclear Information System (INIS)
Viscous fluid flow past two identical circular cylinders in a tandem arrangement is numerically investigated at a typical Reynolds number of 200. By considering a large span of spacing ratio (0.1 ⩽ G/D ⩽ 6.0) with a fine interval of 0.1 or less, the dependences on the spacing ratio of the drag force, lift force, lift fluctuation frequency, torque on the cylinder pair and phase difference between the lift fluctuations of the two cylinders are investigated in detail, where D is the diameter of the cylinder and G the surface-to-surface distance between the cylinders. The phase difference between the lift fluctuations of the two cylinders is addressed based on correlation analysis together with the phase diagram, which has received scarce attention before. The phase difference provides further understanding to the dependence of the wake evolutions behind the twin circular cylinders. The numerical investigations show that diverse regimes can be identified according to the dependence of the hydrodynamics on the spacing ratio. The hydrodynamic discontinuities at G/D = 0.9, which have previously been ignored, are reported in this work. The physical correlations between the hydrodynamic discontinuities and the wake patterns are presented. (paper)
Numerical Simulation of Circular Cylinders in Free-Fall
Energy Technology Data Exchange (ETDEWEB)
Romero Gomez, Pedro DJ; Richmond, Marshall C.
2016-02-05
In this work, we combined the use of (i) overset meshes, (ii) a 6 degree-of-freedom (6- DOF) motion solver, and (iii) an eddy-resolving flow simulation approach to resolve the drag and secondary movement of large-sized cylinders settling in a quiescent fluid at moderate terminal Reynolds numbers (1,500 < Re < 28,000). These three strategies were implemented in a series of computational fluid dynamics (CFD) solutions to describe the fluid-structure interactions and the resulting effects on the cylinder motion. Using the drag coefficient, oscillation period, and maximum angular displacement as baselines, the findings show good agreement between the present CFD results and corresponding data of published laboratory experiments. We discussed the computational expense incurred in using the present modeling approach. We also conducted a preceding simulation of flow past a fixed cylinder at Re = 3,900, which tested the influence of the turbulence approach (time-averaging vs eddy-resolving) and the meshing strategy (continuous vs. overset) on the numerical results. The outputs indicated a strong effect of the former and an insignificant influence of the latter. The long-term motivation for the present study is the need to understand the motion of an autonomous sensor of cylindrical shape used to measure the hydraulic conditions occurring in operating hydropower turbines.
THE INTERACTION OF A COLD ATOMISED SPRAY WITH A CIRCULAR CYLINDER
Directory of Open Access Journals (Sweden)
A. AROUSSI
2010-09-01
Full Text Available The development of non-intrusive diagnostic techniques has significantly increased with the introduction of lasers. Laser based anemometry, such as Laser Doppler (LDA, Phase Doppler (PDA, and Particle Image Velocimetery (PIV can provide an accurate description of flows without interference. This study determines experimentally the fluid motion resulting from the interaction of a liquid spray with a circular cylinder. Two experimental settings were examined: the first is a discharging spray into free air and the second is a spray impinging on a circular cylinder placed 25 cylinder diameters downstream of the nozzle. These sprays were quantified using PIV. A non-intrusive droplet sizing technique was used to characterise the spray. This has shown that, within the spray, the average droplet diameter increases when the circular cylinder is introduced and so does the frequency of occurrence of these large droplets. In the wake behind the cylinder, the smaller droplets were quickly entrained and recirculated, while the larger droplets continued in the general direction of the spray cone.
Vortex shedding of a heated circular cylinder at low Reynolds number
Czech Academy of Sciences Publication Activity Database
Wang, A. B.; Trávníček, Zdeněk; Wu, M. H.
Taiwan: National Cheng Kung University, 2001 - (Hsiao, F.), s. 49-54 [The 4th Pacific International Conference on Aerospace Science and Technology (PICAST 4). Kaohsiung (TR), 22.05.2001] R&D Projects: GA ČR GA101/99/0059 Keywords : heated circular cylinder * laminar flow * vortex shedding Subject RIV: BK - Fluid Dynamics
Modelling the Inflation of Polyisobutylene Into an Elliptic and a Circular Cylinder
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Gøttsche, Søren; Kjær, Erik Michael
2000-01-01
The isothermal inflation of a sheet of a Polyisobutylene melt into a circular and an elliptic cylinder is modelled using the 3D Lagrangian Integral Method. The non-linear properties of the Polyisobutylene are modelled with the Factorized K-BKZ constitutive equation, using a potential function bas...... on the potential function from the Doi-Edwards reptation theory....
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In the present study, analyzed are the variation of added mass for a circular cylinder in the lock-in (synchronization) range of vortex-induced vibration (VIV) and the relationship between added mass and natural frequency. A theoretical minimum value of the added mass coefficient for a circular cylinder at lock-in is given. Developed are semi-empirical formulas for the added mass of a circular cylinder at lock-in as a function of flow speed and mass ratio. A comparison between experiments and numerical simulations shows that the semi-empirical formulas describing the variation of the added mass for a circular cylinder at lock-in are better than the ideal added mass. In addition, computation models such as the wake oscillator model using the present formulas can predict the amplitude response of a circular cylinder at lock-in more accurately than those using the ideal added mass.
Accelerated micropolar fluid--flow past an uniformly rotating circular cylinder
Siddiqui, Abuzar Abid
2016-01-01
In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation for micropolar fluids for this problem into system of finite-difference equations. This system was further solved numerically by point SOR-method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids). The comparison is good. The ...
Vortex-Induced Vibration Suppression of a Circular Cylinder with Vortex Generators
Directory of Open Access Journals (Sweden)
Shi-bo Tao
2016-01-01
Full Text Available The vortex-induced vibration is one of the most important factors to make the engineering failure in wind engineering. This paper focuses on the suppression method of vortex-induced vibration that occurs on a circular cylinder fitted with vortex generators, based on the wind tunnel experiment. The effect of the vortex generators is presented with comparisons including the bare cylinder. The experimental results reveal that the vortex generators can efficiently suppress vortex-induced vibration of the circular cylinder. Vortex generator control can make the boundary layer profile fuller and hence more resistant to separation. The selections of skew angles and the angular position have a significant influence on the vortex generator control effect. By correlation analysis, it can be concluded that the vortex generators can inhibit the communication between the two shear layers and produce streamwise vortices to generate a disturbance in the spanwise direction.
VANISHING OF THREE-DIMENSIONALITY IN THE WAKE BEHIND A ROTATIONALLY OSCILLATING CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The flow behind a three-dimensional rotationally oscillating circular cylinder was studied by a numerical method. The computations were performed at a Reynolds number of 260, which is at a level that the flow wake has developed into a three-dimensional state called Mode-B. The purpose of this paper is to examine the influence of various rotational amplitudes (0.1-0.7) on the wake instability of the flow, while the oscillation frequency is fixed to the value of that measured in the wake of a stationary cylinder. The results show that the rotation with sufficiently high amplitude brings the flow back to its nominal two-dimensional state. Moreover, it is found that the value of the time-averaged drag and the RMS value of the lift are larger than those of a stationary circular cylinder.
RANS-VOF solver for solitary wave run-up on a circular cylinder
Cao, Hong-jian; Wan, De-cheng
2015-04-01
Simulation of solitary wave run-up on a vertical circular cylinder is carried out in a viscous numerical wave tank developed based on the open source codes OpenFOAM. An incompressible two-phase flow solver naoe-FOAM-SJTU is used to solve the Reynolds-Averaged Navier-Stokes (RANS) equations with the SST k- ω turbulence model. The PISO algorithm is utilized for the pressure-velocity coupling. The air-water interface is captured via Volume of Fluid (VOF) technique. The present numerical model is validated by simulating the solitary wave run-up and reflected against a vertical wall, and solitary wave run-up on a vertical circular cylinder. Comparisons between numerical results and available experimental data show satisfactory agreement. Furthermore, simulations are carried out to study the solitary wave run-up on the cylinder with different incident wave height H and different cylinder radius a. The relationships of the wave run-up height with the incident wave height H, cylinder radius a are analyzed. The evolutions of the scattering free surface and vortex shedding are also presented to give a better understanding of the process of nonlinear wave-cylinder interaction.
RANS-VOF Solver for Solitary Wave Run-up on A Circular Cylinder
Institute of Scientific and Technical Information of China (English)
曹洪建; 万德成
2015-01-01
Simulation of solitary wave run-up on a vertical circular cylinder is carried out in a viscous numerical wave tank developed based on the open source codes OpenFOAM. An incompressible two-phase flow solver naoe-FOAM-SJTU is used to solve the Reynolds-Averaged Navier–Stokes (RANS) equations with the SST k-wturbulence model. The PISO algorithm is utilized for the pressure-velocity coupling. The air-water interface is captured via Volume of Fluid (VOF) technique. The present numerical model is validated by simulating the solitary wave run-up and reflected against a vertical wall, and solitary wave run-up on a vertical circular cylinder. Comparisons between numerical results and available experimental data show satisfactory agreement. Furthermore, simulations are carried out to study the solitary wave run-up on the cylinder with different incident wave height H and different cylinder radius a. The relationships of the wave run-up height with the incident wave height H, cylinder radius a are analyzed. The evolutions of the scattering free surface and vortex shedding are also presented to give a better understanding of the process of nonlinear wave-cylinder interaction.
Oscillation-induced sand ripples in a circular geometry.
Rousseaux, Germain; Kruithof, Joachim; Jenffer, Patrice; Wesfreid, José Eduardo
2008-07-01
This study deals with the observation of sand ripples in a circular geometry under oscillatory flow. We characterize the observed patterns as a function of the excitation parameters. We report the time evolution of the corrugated front invading the flat bed. These experiments reveal unambiguously, because of the gradient of shear stress, the existence of two separated thresholds: one for grain motion and the other for the appearance of ripples. In addition, we display the phase diagram of this instability as a function of the Froude number and a Reynolds number. PMID:18764045
Dual Circularly Polarized Omnidirectional Antenna with Slot Array on Coaxial Cylinder
Directory of Open Access Journals (Sweden)
Bin Zhou
2015-01-01
Full Text Available A dual circularly polarized (CP omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP port and right hand circularly polarized (RHCP port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 to 5.95 GHz with an isolation higher than 15 dB between the two CP ports, and the return loss (RL is higher than 10 dB within the bandwidth in both of the two ports. From the measured results, the average axial ratio (AR of the proposed antenna in omnidirectional plane is lower than 1.5 dB.
Experiments on Sphere Cylinder Geometry Dependence in the Electromagnetic Casimir Effect
Mukhopadhyay, Shomeek; Noruzifar, Ehsan; Wagner, Jeffrey; Zandi, Roya; Mohideen, Umar
2013-03-01
We report on ongoing experimental investigations on the geometry dependence of the electromagnetic Casimir force in the sphere-cylinder configuration. A gold coated hollow glass sphere which forms one surface is attached to a Silicon AFM cantilever. The cylinder, which is constructed from tapered optical fiber is also gold coated. The resonance frequency shift of the cantilever is measured as a function of the sphere-cylinder surface separation. The sphere-cylinder electrostatic force is used for alignment of the sphere and the cylinder and also for calibrating the system. The results are compared to numerical simulations in the framework of the Proximity Force Approximation (PFA).
Ishimatsu, Takuto; Morishita, Etsuo; Okunuki, Takeo; Koyama, Hisao
Flows over two circular cylinders in tandem, side-by-side, and staggered arrangements were analyzed using the overset grid method, which is capable of handling a variety of sizes and arrangements. The Reynolds number was 100 based on the cylinder diameter. The present computation code was validated by comparison with benchmark solutions for flow around a single cylinder. Wind-tunnel experiments were conducted for the side-by-side cylinder flow for comparison with numerical simulations. Calculation showed two critical spacings in the tandem arrangement where the aerodynamic forces and Strouhal number change discontinuously. Three critical spacings and four distinct flow patterns were found numerically in the side-by-side arrangement. Similar critical spacings were found in the staggered arrangement calculation and formed critical lines. Furthermore, a pocket region was found for a staggered arrangement surrounded by the critical line.
Experimental Study of the Flow Field around a Circular Cylinder Using Plasma Actuators
Directory of Open Access Journals (Sweden)
Siavash Tabatabaeian
2015-01-01
Full Text Available In this paper different configurations of plasma actuator for controlling the flow around a circular cylinder made of Quartz were experimentally investigated. Three thin plasma actuator electrodes were flush-mounted on the surface of the cylinder and were connected to a DC high voltage power supply for generation of electrical discharge. Different configurations of plasma actuator were used for this study and pressure distribution experiments showed that the existence of the plasma decreases the pressure coefficient of the cylinder and the variation of the pressure coefficient can change the behavior of the lift and drag coefficient of the cylinder for all configurations. According to the pressure distribution data, two configurations of the plasma actuators made the best influence on the aerodynamic performance and also on the drag reduction.
Scattering from a Buried Circular Cylinder Illuminated by a Three-Dimensional Source
DEFF Research Database (Denmark)
Hansen, T.B.; Meincke, Peter
2002-01-01
We employ plane and cylindrical wave expansions with the fast Fourier transform to solve scattering problems involving a circular cylinder buried in soil. The illumination is provided by a three-dimensional source located in air above ground. Plane wave expansions describe transmitted and reflected...... fields at the air-soil interface, and cylindrical wave expansions describe the fields scattered by the cylinder. The two types of expansions are joined by employing explicit expressions that relate cylindrical and plane waves. We neglect multiple interactions between the cylinder and the interface. The...... cylinder and soil can have frequency-dependent permittivities and conductivities. With the formulas cast in a special form the scattered fields can be computed rapidly for fixed-offset configurations in which the location of the source is different for each observation point. Fixed offset is the most...
Directory of Open Access Journals (Sweden)
Yingnan Fu
2015-01-01
Full Text Available Viscous flow past an upstream in-line forced oscillating circular cylinder with a stationary cylinder downstream at Reynolds number of 100 is investigated using a CIP model. The model is established in a Cartesian coordinate system using a high-order difference method to discretise the Navier-Stokes equations. The fluid-structure interaction is treated as a multiphase flow with fluid and solid phases solved simultaneously. An immersed boundary method is used to deal with the fluid-body coupling. The CFD model is firstly applied to the computation of flow past a fixed circular cylinder for its validation; then flow over two stationary tandem cylinders is investigated and good agreements are obtained comparing with existing ones. Computations are then performed with flow past two tandem cylinders with an upstream in-line oscillating cylinder with a small spacing L=2D. Considerable attention is paid to the spectrum characteristics and vortex modes.
Flow-induced vibration of a circular cylinder subjected to wake interference at low Reynolds number
Carmo, B. S.; Sherwin, S. J.; Bearman, P. W.; Willden, R. H. J.
2011-05-01
Two- and three-dimensional numerical simulations of the flow around two circular cylinders in tandem arrangements are performed. The upstream cylinder is fixed and the downstream cylinder is free to oscillate in the transverse direction, in response to the fluid loads. The Reynolds number is kept constant at 150 for the two-dimensional simulations and at 300 for the three-dimensional simulations, and the reduced velocity is varied by changing the structural stiffness. The in-line centre-to-centre distance is varied from 1.5 to 8.0 diameters, and the results are compared to that of a single isolated flexible cylinder with the same structural characteristics, m*=2.0 and ζ=0.007. The calculations show that significant changes occur in the dynamic behaviour of the cylinders, when comparing the flow around the tandem arrangements to that around an isolated cylinder: for the tandem arrangements, the lock-in boundaries are wider, the maximum displacement amplitudes are greater and the amplitudes of vibration for high reduced velocities, outside the lock-in, are very significant. The main responsible for these changes appears to be the oscillatory flow in the gap between the cylinders.
FLOW PAST TWO ROTATING CIRCULAR CYLINDERS IN A SIDE-BY-SIDE ARRANGEMENT
Institute of Scientific and Technical Information of China (English)
GUO Xiao-hui; LIN Jian-zhong; TU Cheng-xu; WANG Hao-li
2009-01-01
Measurements were performed using Particle Image Velocimetry (PIV) to analyze the modification of flow by the combined effects of the rotation and the Reynolds number on the flow past two rotating circular cylinders in a side-by-side-arrangement at a range of , (α is the rotational speed) at one gap spacing of (T and d are the distance between the centers of two cylinders and the cylinder diameter, respectively). A new Immersed-Lattice Boltzmann Method (ILBM) scheme was used to study the effect of the gap spacing on the flow. The results show that the vortex shedding is suppressed as rotational speed increases. The flow reaches a steady state when the vortex shedding for both cylinders is completely suppressed at critical rotational speed. As the rotational speed further increases, the separation phenomenon in the boundary layers disappears at the attachment rotational speed. The critical rotational speed and attachment rotational speed become small as Reynolds number increases. The absolute rotational speed of cylinders should be large at same critical rotational speed and attachment rotational speed in the case of large Reynolds number. The gap spacing has an important role in changing the pattern of vortex shedding. It is very different in the mechanism of vortex shedding suppression for the flows around two rotating cylinders and single rotating cylinder.
Hu, J. C.; Zhou, Y.
Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re=7000 using hot-wire, flow-visualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P, ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle ( ~ 90 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. S-Ia and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P/d and P/d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P/d=1.2~2.5 and or 1.54.0 and 10, where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P/d=20; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d=10. At P/d, the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St≈0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed.
Directory of Open Access Journals (Sweden)
M. Nicolet
2011-11-01
Full Text Available Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ_{±C} is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ_{+C}, respectively δ_{−C} and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ < 0.05 was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performing at backscattering angles which deviate from 180° unlike lidar applications. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation.
Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime
Energy Technology Data Exchange (ETDEWEB)
Miau, J.J.; Tsai, H.W.; Lin, Y.J.; Tu, J.K.; Fang, C.H.; Chen, M.C. [National Cheng Kung University, Department of Aeronautics and Astronautics, Tainan (China)
2011-10-15
Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 x 10{sup 5}-5.86 x 10{sup 5}. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured simultaneously at {theta} = {+-}90 further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident. (orig.)
Şibliyev, Orxan
2012-01-01
ABSTRACT: In this work, a computer program is written for solving the turbulent flow equations on unstructured grids using a Large Eddy Simulation (LES) model in C++ language. To test the code, two cases are considered: laminar, periodic flow past a circular cylinder at Reynolds number, ReD = 100 which is based on the diameter of the cylinder and turbulent flow at ReD = 3900. The turbulence or sub-grid scale (SGS) model is chosen as Smagorinsky model due to its simplicity compared with dy...
Directory of Open Access Journals (Sweden)
M. Nicolet
2012-05-01
Full Text Available Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ_{C} is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ_{+C}, respectively δ_{−C} and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ<0.05 was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performed at backscattering angles which deviate from 180° unlike LIDAR applications. Instruments exploiting the difference in the P_{44}/P_{11} ratio at a scattering angle around 115° are significantly constrained in distinguishing between water and ice because small droplets with size parameters between 5 and 10 do cause very high circular depolarizations at this angle. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation.
Wave Forces on Linear Arrays of Rigid Vertical Circular Cylinders in Regular Wave
Directory of Open Access Journals (Sweden)
V.J. Kurian
2014-06-01
Full Text Available The present investigation aims to experimentally determine the variation of forces and force coefficients acting on circular cylinders, which are arranged in a linear array along the direction of the waves. Most commonly used structural and non-structural elements in the construction of offshore platforms are circular cylindrical members. In many cases, these members are found in very close neighbourhood of each other, thus modifying the surrounding flow and wave forces acting on them. Model tests were conducted in the wave tank on a maximum of four cylinders of the same diameter. A reasonable scale factor was chosen considering the pertinent factors such as water depth, wave generating capability and accuracy of measurements. The cylinders were installed inside the wave tank as vertical cantilevers fixed at the top. Wave forces acting on the cylinders were measured using special wave force sensors exclusively designed and fabricated for the present project, while the wave profiles were recorded using wave probes installed in the wave basin. The results confirmed the presence of a force shielding effect on the trailing cylinders by the leading cylinders with few exceptions. The findings also substantiated the significant modification of the forces on cylinders when they are present in a linear array. A common practice adopted for the design of offshore platforms was identified with a possibility of underestimating the wave forces acting on the cylindrical elements. In many cases, the experimentally computed hydrodynamic force coefficients were found to be lower than the standard values adopted by various design codes. These findings portray the significance of the present work in achieving economy in the design of jacket platforms and risers.
Large eddy simulation of the subcritical flow over a V grooved circular cylinder
Energy Technology Data Exchange (ETDEWEB)
Alonzo-García, A. [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); Gutiérrez-Torres, C. del C., E-mail: cgutierrezt@ipn.mx [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); Jiménez-Bernal, J.A. [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); and others
2015-09-15
Highlights: • We compared numerically the turbulent flow over a smooth circular cylinder and a V grooved cylinder in the subcritical regime. • Turbulence intensities in both streamwise and normal direction suffered attenuations. • The swirls structures on grooves peaks seemed to have a cyclic behavior. • The evolution of the flow inside grooves showed that swirls structures located in peaks suffered elongations in the normal direction. • The secondary vortex structures formed in the grooved cylinder near wake were smaller in comparison of the smooth cylinder flow. - Abstract: In this paper, a comparative numerical study of the subcritical flow over a smooth cylinder and a cylinder with V grooves (Re = 140,000) is presented. The implemented technique was the Large Eddy Simulation (LES), which according to Kolmogorov's theory, resolves directly the most energetic largest eddies and models the smallest and considered universal high frequency ones. The Navier-Stokes (N-S) equations were solved using the commercial software ANSYS FLUENT V.12.1, which applied the finite volume method (FVM) to discretize these equations in their unsteady and incompressible forms. The grid densities were 2.6 million cells and 13.5 million cells for the smooth and V grooved cylinder, respectively. Both meshes were composed of structured hexahedral cells and close to the wall of the cylinders, additional refinements were employed in order to obtain y{sup +<5} values. All cases were simulated during at least 15 vortex shedding cycles with the aim of obtaining significant statistical data. Results: showed that for both cases (smooth and V grooved cylinder flow), the numerical code was capable of reproducing the most important physical quantities of the subcritical regime. Velocity distribution and turbulence intensity in the flow direction suffered a slight attenuation along the wake, as a consequence of grooves perturbation, which also caused an increase in the pressure
Large eddy simulation of the subcritical flow over a V grooved circular cylinder
International Nuclear Information System (INIS)
Highlights: • We compared numerically the turbulent flow over a smooth circular cylinder and a V grooved cylinder in the subcritical regime. • Turbulence intensities in both streamwise and normal direction suffered attenuations. • The swirls structures on grooves peaks seemed to have a cyclic behavior. • The evolution of the flow inside grooves showed that swirls structures located in peaks suffered elongations in the normal direction. • The secondary vortex structures formed in the grooved cylinder near wake were smaller in comparison of the smooth cylinder flow. - Abstract: In this paper, a comparative numerical study of the subcritical flow over a smooth cylinder and a cylinder with V grooves (Re = 140,000) is presented. The implemented technique was the Large Eddy Simulation (LES), which according to Kolmogorov's theory, resolves directly the most energetic largest eddies and models the smallest and considered universal high frequency ones. The Navier-Stokes (N-S) equations were solved using the commercial software ANSYS FLUENT V.12.1, which applied the finite volume method (FVM) to discretize these equations in their unsteady and incompressible forms. The grid densities were 2.6 million cells and 13.5 million cells for the smooth and V grooved cylinder, respectively. Both meshes were composed of structured hexahedral cells and close to the wall of the cylinders, additional refinements were employed in order to obtain y+<5 values. All cases were simulated during at least 15 vortex shedding cycles with the aim of obtaining significant statistical data. Results: showed that for both cases (smooth and V grooved cylinder flow), the numerical code was capable of reproducing the most important physical quantities of the subcritical regime. Velocity distribution and turbulence intensity in the flow direction suffered a slight attenuation along the wake, as a consequence of grooves perturbation, which also caused an increase in the pressure coefficient
Ahmed W. Mustava
2013-01-01
The effect of a semi-circular cylinders in a two dimensional channel on heat transfer by forced convection from two heat sources with a constant temperature has been studied numerically. Each channel contains two heat sources; one on the upper surface of the channel and the other on the lower surface of the channel. There is semi-circular cylinder under the source in upper surface and there is semi-circular cylinder above the source in lower surface. The location of the second heat source wit...
Numerical study of turbulent flow separation over a wall mounted circular cylinder
Yu, Taejong; You, Donghyun
2015-11-01
Flow over a wall-mounted circular cylinder with a finite span and a free end is numerically studied at a range of Reynolds numbers. Separated flow behind a wall-mounted cylinder is characterized by dominant vortical structures developed around and behind the cylinder: i.e., Karman vortices and tip-shedding vortices. The formation and interaction among the vortices are found to be distinct depending on the aspect ratio of the span length to the diameter of the cylinder as well as the Reynolds number. It is also found that drag and lift forces on the cylinder show different dominance of Karman vortices and tip vortices for different span-to-diameter ratios. A detailed analysis of the mean and fluctuating velocity, pressure fields, and spectral characteristics of separated flow is presented for laminar-to-transitional flows over cylinders with different aspect ratios. Supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning Grant NRF-2014R1A2A1A11049599.
Effect of Mach number on transonic flow past a circular cylinder
Institute of Scientific and Technical Information of China (English)
XU ChangYue; CHEN LiWei; LU XiYun
2009-01-01
The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞from 0.85 to 0.98 and the Reynolds number 2×105 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞Mcr, and the other is a quasi-steady flow state with nearly sta-tionary shock waves formed in the near wake for M∞>Mcr, suppressing vortex shedding from the cylin-der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu-tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc 1 in the quasi-steady flow regime, resulting in different evolutions of the shear layers.
Self-excited oscillations of a closely spaced row of circular cylinders in cross-flow
International Nuclear Information System (INIS)
Experiments were carried out to examine the vibratory motion of a single, closely spaced row of circular cylinders or tube arrays, in which flexible cylinders, free to respond in the streamwise direction, are placed alternatively between fixed cylinders. For a transverse cylinder spacing T less than about 2--2.2D, the fluid jets formed in the wake pair up and switch when the flexible cylinders are displaced far enough upstream or downstream. The bistable situation of the jet switching introduces a hysteretic effect which extracts energy from the flow and can excite and maintain large amplitude oscillations. Therefore, self-excited in-line oscillations occur about a mean position upstream of the initial row position. Amplitude and frequency measurements for an oscillating row of T/D = 1.5 were conducted for various free stream velocities yielding Reynolds numbers from 700 to 1,200. Large cylinder response was recorded for reduced velocities based on oscillation frequency ranging between 50 and 61
Computation of Viscous Uniform and Shear Flow over A Circular Cylinder by A Finite Element Method
Institute of Scientific and Technical Information of China (English)
赵明; 滕斌
2004-01-01
The incompressible viscous uniform and shear flow past a circular cylinder is studied. The two-dimensional NavierStokes equations are solved by a finite element method. The governing equations are discretized by a weighted residual method in space. The stable three-step scheme is applied to the momentum equations in the time integration. The numerical model is firstly applied to the computation of the lid-driven cavity flow for its validation. The computed results agree well with the measured data and other numerical results. Then, it is used to simulate the viscous uniform and shear flow over a circular cylinder for Reynolds numbers from 100 to 1000. The transient time interval before the vortex shedding occurs is shortened considerably by introduction of artificial perturbation. The computed Strouhal number, drag and lift coefficients agree well with the experimental data. The computation shows that the finite element model can be successfully applied to the viscous flow problem.
Computational study of subcritical response in flow past a circular cylinder
Cantwell, Christopher D.; Barkley, Dwight
2013-01-01
Flow past a circular cylinder is investigated in the subcritical regime, below the onset of Benard-von Karman vortex shedding at Re_c ~ 47. The transient response of infinitesimal perturbations is computed. The domain requirements for obtaining converged results is discussed at length. It is shown that energy amplification occurs as low as Re=2.2. Throughout much of the subcritical regime the maximum energy amplification increases approximately exponentially in the square of Re reaching 6800 ...
THREE-DIMENSIONAL FLOW AROUND TWO TANDEM CIRCULAR CYLINDERS WITH VARIOUS SPACING AT Re=220
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The flow around two tandem circular cylinders was studied by a three-dimensional numerical simulation of the Navier-Stokes equations at Re=220. The improved virtual boundary method was applied to model the no-slip boundary condition of the cylinders. The results show that as the spacing ratio L/D ≥4, the three dimensionality occurs in the wake. When L/D≤3.5 the wake keeps a two-dimensional state at the Reynolds number Re=220. The critical spacing for the appearance of three-dimensional instability obtained is at the range 3.5＜L/D＜4, similar to the critical spacing found in two-dimensional case. Two sources of instability from upstream and downstream cylinder generate a complicated vortex structures in the wake, investigated by streamlines topology analysis in the streamwise plane. Many other interesting problems were also addressed in this paper.
Unsteady Numerical Simulation of Flow around 2-D Circular Cylinder for High Reynolds Numbers
Institute of Scientific and Technical Information of China (English)
Yanhui Ai; Dakui Feng; Hengkui Ye; Lin Li
2013-01-01
In this paper,2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes,i.e.8.21×104＜Re＜l.54×106.The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a k-ε turbulence model.The calculated results,produced flow structure drag and lift coefficients,as well as Strouhal numbers.The findings were in good agreement with previous published data,which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers.Meanwhile,an effective measure was presented to control the lift force on a cylinder,which points the way to decrease the vortex induced vibration of marine structure in future.
Soret and Dufour effects in steady flow of a viscous conducting fluid through a circular cylinder
International Nuclear Information System (INIS)
This paper presents an exact solution to the problem of the steady laminar fully developed free convective mass transfer flow of a viscous incompressible electrically conducting fluid through a circular cylinder under constant pressure gradient influenced by a magnetic field in the azimuthal direction in presence of constant heat source and chemical reaction. The Soret and Dufour effects are considered but the electrical and the induced magnetic fields are neglected. The effects of different physical parameters entering into the problem on the velocity, temperature and concentration fields and on the coefficient of the skin friction, the rates of heat and mass transfer at surface of the cylinder and mass flux across a normal section of the cylinder are discussed through graphs. (author)
Nemeth, Michael P.
2014-01-01
Nonlinear and bifurcation buckling equations for elastic, stiffened, geometrically perfect, right-circular cylindrical, anisotropic shells subjected to combined loads are presented that are based on Sanders' shell theory. Based on these equations, a three-parameter approximate Rayleigh-Ritz solution and a classical solution to the buckling problem are presented for cylinders with simply supported edges. Extensive comparisons of results obtained from these solutions with published results are also presented for a wide range of cylinder constructions. These comparisons include laminated-composite cylinders with a wide variety of shell-wall orthotropies and anisotropies. Numerous results are also given that show the discrepancies between the results obtained by using Donnell's equations and variants of Sanders' equations. For some cases, nondimensional parameters are identified and "master" curves are presented that facilitate the concise representation of results.
CALCULATION OF VISCOUS FLOW AROUND CIRCULAR CYLINDER WITH THREE-DIMENSIONAL NUMERICAL SIMULATION
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Three-dimensional numerical simulation of a uniform incompressible viscous flow around a stationary circular cylinder was conducted. The CFX-4 software was used to calculate the hydrodynamic characteristics of the flow and the finite volume method for incompressible Navier-Stokes equations was employed in the program. The simulation of the flow was performed for Re=103 and Re=104 respectively within the sub-critical region. In order to overcome numerical instability for the high Reynolds number flows, a quadratic upwind scheme was incorporated for the Navier-Stokes equations. The periodicity boundary condition was used at the ends of the cylinder. It was found that the evolution of the lift and drag coefficients in each plane along the cylinder span is different. Comparison between the predicted results based on the three-dimensional and the two-dimensional analysis was also given. It is concluded that at the high Reynolds number the effect of three-dimensionality of the flow around the circular cylinder is remarkable, and in addition hydrodynamic coefficients with of 3-D simulation are less than those given by 2-D simulation.
Mathematical Modeling of Partial-Porous Circular Cylinders with Water Waves
Directory of Open Access Journals (Sweden)
Min-Su Park
2015-01-01
Full Text Available The interaction of water waves with partially porous-surfaced circular cylinders was investigated. A three-dimensional numerical modeling was developed based on the complete mathematical formulation of the eigenfunction expansion method in the potential flow. Darcy’s law was applied to describe the porous boundary. The partial-porous cylinder is composed of a porous-surfaced body near the free surface, and an impermeable-surfaced body with an end-capped rigid bottom below the porous region. The optimal ratio of the porous portion to the impermeable portion can be adopted to design an effective ocean structure with minimal hydrodynamic impact. To scrutinize the hydrodynamic interactions in N partial-porous circular cylinders, the computational fluid domain is divided into three regions: an exterior region, N inner porous body regions, and N regions beneath the body. Wave excitation forces and wave run-up on multibodied partial-porous cylinders are calculated and compared for various porous-portion ratios and wave conditions, all of which significantly influence the hydrodynamic property.
An Approximate Method for Calculation of Fluid Force and Response of A Circular Cylinder at Lock-in
Institute of Scientific and Technical Information of China (English)
WANG Yi
2008-01-01
In this paper, equations calculating lift force of a rigid circular cylinder at lock-in in uniform flow are deduced in detail. Besides, equations calculating the lift force on a long flexible circular cylinder at lock-in are deduced based on mode analysis of a multi-degree freedom system. The simplified forms of these equations are also given. Furthermore, an approximate method to predict the forces and response of rigid circular cylinders and long flexible circular cylinders at lock-in is introduced in the case of low mass-damping ratio. A method to eliminate one deficiency of these equations is introduced. Comparison with experimental results shows the effectiveness of this approximate method.
Flow patterns and heat transfer around six in-line circular cylinders at low Reynolds number
Fornarelli, Francesco; Lippolis, Antonio
2014-01-01
The flow field and the heat transfer around six in-line iso-thermal circular cylinders has been studied by mean of numerical simulations. Two values of the center to center spacing ($s=3.6d$ and $4d$, where $d$ is the cylinder diameter) at Reynolds number of $100$ and Prandtl number of $0.7$ has been investigated. Similarly to the in-line two cylinder configuration, in this range a transition in the flow and in the heat transfer occurs. Two different flow patterns have been identified: the stable shear layer (SSL) mode and the shear layer secondary vortices (SLSV) mode, at $3.6$ and $4$ spacing ratio ($s/d$), respectively. At $s/d=3.6$ the flow pattern causes the entrainment of cold fluid on the downstream cylinders enhancing the heat transfer. On the other hand at $s/d=4$ two stable opposite shear layer prevent the cold fluid entrainment over the downstream cylinders reducing their heat exchange. The overall time average heat transfer of the array is enhanced up to 25% decreasing the spacing ratio from $4$ t...
Secondary instability in the wake of the flow around two circular cylinders in tandem arrangements
Carmo, Bruno; Meneghini, Julio; Sherwin, Spencer
2008-11-01
The stability of three-dimensional perturbations about two-dimensional time-periodic vortex wakes of the flow around two identical circular cylinders in tandem arrangements is investigated. The centre-to-centre separation is varied from 1.5 to 5 cylinder diameters. Direct linear stability analysis is employed to determine the shape, wavelength and onset of unstable three-dimensional perturbations. In addition the non-linear character of the bifurcations is identified through three-dimensional direct numerical simulations performed in the vicinity of the critical points. It is found that, for configurations with large cylinder separations, the first stages of the wake transition are similar to those observed in the flow around an isolated cylinder, although the onset of the secondary instability occurs at a lower Reynolds number. In contrast, for small separations the transition route is significantly different, resembling that of the flow in a periodically driven cavity. For these configurations the onset of the first instability arises at a higher Reynolds number than in the case of an isolated cylinder.
Czech Academy of Sciences Publication Activity Database
Kharlamov, Alexander A.; Filip, Petr
2012-01-01
Roč. 77, č. 1 (2012), s. 77-85. ISSN 0022-0833 Institutional research plan: CEZ:AV0Z20600510 Keywords : circular cylinders * cylinder between two walls * generalised method of images * ideal fluid * potential flow Subject RIV: BK - Fluid Dynamics Impact factor: 1.075, year: 2012
Transition to turbulence in the separated shear layers of yawed circular cylinders
International Nuclear Information System (INIS)
Spatial and temporal resolution of transition to turbulence inside the free-shear layers of two yawed circular cylinders is the subject of the present investigation. These physics were resolved using the large-eddy simulation (LES) methodology. An O-type grid was implemented such that the spatial scales of the LES computation fully resolved the energy range physics of the shear layers at Reynolds number ReD = 8000 based on the cylinder diameter. The two test cases modeled the cylinder span skewed at angles 45o and 60o from the horizontal axis. Observations revealed the same transition process as the normal cross-flow state. Soon after separation, Tollmien-Schlichting disturbances were predicted that evolved into Kelvin-Helmholtz (K-H) eddies before absorption by the large-scale Karman-type vortices. These eddies defaulted to a spanwise wavy pattern similar to a normal cross-flow due to their three-dimensional instability. No mixed modes were found between the K-H (Bloor) and Strouhal frequencies. The effect of yaw angle shortened the transition process. As a result, peak turbulence levels inside the wake formation zone approach the downstream cylinder periphery. In addition, the dimensionless frequencies of the K-H eddies lie above the normal cross-flow relationship as formulated by . Disparity between the yawed and normal cross-flow states was further emphasized by the shear-layer transition characteristics. Although each property displayed the expected exponential growth during transition to turbulence, their dimensionless form was miss-aligned with those of the normal cross-flow case. Based on the present evidence, additional simulations (and/or experimental measurements) are necessary to form conclusive arguments regarding the expected behavior of the transition characteristics within the free-shear layers of yawed circular cylinders.
Plane section of cone and cylinder in computer geometry
Obradović Ratko M.; Milojević Zoran
2005-01-01
In this paper a mathematical apparatus for determination of plane section of cone and cylinder was formed. By using the descriptive geometric approach the contour lines of these quadrics were determined. The fact that the tangent lines of a circle could be transformed to the tangent lines of an ellipse using affinity was employed. In that way surfaces are represented by contour lines (tangent lines of basic ellipse in oblique projection) and thus they have a realistic view. Intersecting plane...
Energetically efficient Proportional-Integral control of flow past a circular cylinder
Kesavadas, Pramode; Anand, Vijay; Patnaik, B. S. V.; Shaiju, A. J.
2015-11-01
In this numerical study, we present an energetically efficient Proportional (P) and Integral (I) control strategy for the cessation of vortex shedding behind a circular cylinder. Reflectionally symmetric controllers are designed such that, they are located on a small sector of the cylinder over which, tangential sliding mode control is imparted. Energetically efficient optimal parameters for the P, I and PI controls have been numerically assessed. An estimation of the time-averaged kinetic energy of different flow regimes using Proper Orthogonal Decomposition (POD) is also carried out. These values are obtained with and without the optimal controllers. The Navier-Stokes equations along with an evolution equation for the PI controller, is numerically solved using finite volume method. The optimization procedure is formulated as a standard Linear Quadratic (LQ) problem and the time-averaged kinetic energy is obtained by summation of POD eigenvalues. The energetic efficiency for the, I controller was observed to be superior compared to the other two classes of controllers. By performing detailed fluid flow simulations, it was observed that, the system is energetically efficient, even when the twin eddies are still persisting behind the circular cylinder. The first author wishes to acknowledge the Ministry of Human Resource Development, Govt. of India.
Huang, Zhu
2015-03-01
The periodic unsteady natural convection flow and heat transfer in a square enclosure containing a concentric circular cylinder is numerically studied. The temperature of the inner circular cylinder fluctuates periodically with time at higher averaged value while the temperature of the enclosure keeps lower constant, and the natural convection is driven by the temperature difference. The two-dimensional natural convection is simulated with high accuracy temporal spectral method and local radial basis functions method. The Rayleigh number is studied in the range 103 ≤ Ra ≤ 106, the temperature pulsating period ranges from 0.01 to 100 and the temperature pulsating amplitudes are a = 0.5, 1.0 and 1.5. Numerical results reveal that the fluid flow and heat transfer is strongly dependent on the pulsating temperature of inner cylinder. Comparing with the steady state natural convection, the heat transfer is enhanced generally for the time-periodic unsteady natural convection, and the local maximum heat transfer rate is observed for Ra = 105 and 106. Moreover, the phenomenon of backward heat transfer is discussed quantitatively. Also, the influence of pulsating temperature on the unsteady fluid flow and heat transfer are discussed and analyzed.
Bifurcation of cylinders for wetting and dewetting models with striped geometry
López, Rafael
2011-01-01
We show that some pieces of cylinders bounded by two parallel straight-lines bifurcate in a family of periodic non-rotational surfaces with constant mean curvature and with the same boundary conditions. These cylinders are initial interfaces in a problem of microscale range modeling the morphologies that adopt a liquid deposited in a chemically structured substrate with striped geometry or a liquid contained in a right wedge with Dirichlet and capillary boundary condition on the edges of the ...
Study of Flowrate Measurement Characteristics of a Circular Cylinder with a Slit%带狭缝圆柱钝体流量测量特性研究
Institute of Scientific and Technical Information of China (English)
王慧; 黄咏梅
2013-01-01
The flowrate characteristics of vortex flowmeter is closely related to the size and geometry shape of vortex bluff body. A new kind of circular cylinder with a slit structure is proposed and applied to vortex flowmeter. Theoretical analysis shows that the slit can be regarded as a feedback channel, which can effectively accelerate vortex shedding and increase vortex intensity. Experiments were carried out in a water pipe with a diameter of 50 mm. Vortex signals produced by circular cylinder with a slit and trapezoidal cylinder respectively at different flowrate were collected. This paper mainly focuses on analyzing the low flowrate measurement performance of circular cylinder with a slit. Experimental results show that compared with trapezoidal cylinder circular cylinder with a slit possesses following characteristics:vortex signal intensity is stronger, signal-to-noise ratio is higher, the Reynolds number of measurement range can be as low as 9. 5í103 and linearity of Strouhal number is better as well. Theoretical analysis and experimental results manifest that circular cylinder with a slit possesses good flowrate meas-urement features and can be applied to vortex flowmeter successfully.%涡街流量计的流量特性与旋涡发生体的形状和几何尺寸密切相关,提出了一种新型的带狭缝圆柱发生体结构并应用于涡街流量计。理论分析表明狭缝可以看作是一个反馈通道,可有效加快旋涡脱落并增强旋涡强度。在内径为50 mm的管道中进行实验,采集不同流量下带狭缝圆柱与梯形柱绕流产生的涡街信号,重点讨论带狭缝圆柱的小流量测量性能。实验表明,与梯形柱相比,带狭缝圆柱涡街信号更强,信噪比高,雷诺数测量范围可低至9.5×103,斯特劳哈尔数线性度更好。理论分析与实验结果表明,带狭缝圆柱具有较好的流量测量特性,可应用于涡街流量计。
MULTI-MODE OF VORTEX-INDUCED VIBRATION OF A FLEXIBLE CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
XIE Fang-fang; DENG Jian; ZHENG Yao
2011-01-01
The vortex-induced vibration of a flexible circular cylinder is investigated at a constant Reynolds number of 1 000.The finite-volume method on moving meshes is applied for the fluid flow,and the Euler-Bemoulli beam theory is used to model the dynamic response of a flexible cylinder.The relationship between the reduced velocity and the amplitude response agrees well with the experimental results.Moreover,five different vibrating modes appear in the simulation.From the comparisons of their vortex structures,the strength of the wake flow is related to the exciting vibrating mode and different vortex patterns arise for different vibrating modes.Only 2P pattern appears in the first vibrating mode while 2S-2P patterns occur in the other vibrating modes if monitoring at different sections along the length of the cylinder.The vibration of the flexible cylinder can also greatly alter the three-dimensionality in the wake,which needs further studies in our future work,especially in the transition region for the Reynolds number from 170 to 300.
Numerical Simulation of Wave Scour Around A Large-Scale Circular Cylinder
Institute of Scientific and Technical Information of China (English)
赵明; 滕斌; 柳淑学
2002-01-01
A numerical model is developed for estimation of local scour around a large circular cylinder under wave action. The model includes wave diffraction around structures, bed shear stress calculation inside the wave boundary layer and topographical change model. The wave model is based on the improved Boussinesq equations for varying depth. The wave boundary layer is calculated by solving the integrated momentum equation over the boundary layer. The bed shear stress due to streaming, an important factor affecting the sediment transport around a large-scale cylinder, is calculated. The Lagrangian drift velocity is included in calculation of the suspended sediment transport rates. The model is implemented by a finite element method and the results from the present model, which agree well with experimental data, are compared with those from other methods.
Stokes ﬂow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions
Indian Academy of Sciences (India)
Satya Deo
2004-08-01
The problem of creeping ﬂow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions is investigated. The Brinkman equation for the ﬂow inside the porous cylinder and the Stokes equation outside the porous cylinder in their stream function formulations are used. The force experienced by each porous circular cylinder in a cell is evaluated. Explicit expressions of stream functions are obtained for both the inside and outside ﬂow ﬁelds. The earlier results reported by Happel and Kuwabara for ﬂow past a solid cylinder in Happel’s and Kuwabara’s cell model, have been deduced. Analytical expressions for the velocity components, pressure, vorticity and stress- tensor are also obtained.
A numerical study of flow about fixed and flexibly mounted circular cylinders
Energy Technology Data Exchange (ETDEWEB)
Meling, Trond Stokka
1998-12-31
Motivated by the needs of the offshore oil industry, this thesis studies flow around a circular cylinder that is either fixed or flexibly mounted. The latter configuration is susceptible to vortex-induced vibrations. To predict the results numerically, a two-dimensional procedure was developed to handle the fluid domain, the structural problem and the non-linear interaction between the two media. The arbitrary Lagrangian-Eulerian approach was employed in order to handle moving boundaries. The fluid forces and the cylinder kinematics are solved in a staggered fashion. A velocity-correction method is employed to solve the incompressible Navier-Stokes equations where the Galerkin finite element method is used for the spatial discretization of the fluid domain. The second-order equation of motion of the cylinder is solved by a 4th order Rung-Kutta scheme. Various numerical schemes for solving the convection-diffusion equation involved are tested. All the schemes, except the rational Runge-Kutta, were found to smear the vortex street. To predict the flow field at high Reynolds number several turbulence models were tested. The modified 2-layer K-epsilon model with all elements in the boundary layer was found to predict results in remarkably good agreement with experimental results. Self-excited vibration tests of circular cylinders are also performed showing that the presented model is able to capture the lock-in phenomenon with reasonable accuracy, both in the laminar- and in the subcritical Reynolds number regime. 136 refs., 67 figs., 13 tabs.
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Directory of Open Access Journals (Sweden)
Koo Bonguk
2014-09-01
Full Text Available The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Koo, Bonguk; Yang, Jianming; Yeon, Seong Mo; Stern, Frederick
2014-09-01
The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Koo Bonguk; Yang Jianming; Yeon Seong Mo; Stern Frederick
2014-01-01
The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless param...
DEFF Research Database (Denmark)
Acampora, Antonio; Georgakis, Christos T.
2013-01-01
vary from those estimated through use of aerodynamic coefficients of single circular cylinders, as reported in literature. To address this issue, wind tunnel tests were performed on a 1:2.3 scale section model of the Øresund Bridge cables, with and without the presence of helical fillets. In this paper......Moderate vibrations continue to be recorded on the Øresund Bridge twin-stay cables. System identification techniques have been applied to investigate the aerodynamic characteristics of the cables based on ambient vibration measurements. As might be expected, the measured aerodynamic damping ratios...
Numerical Simulation of Polymer Injection in Turbulent Flow Past a Circular Cylinder
Richter, David
2011-01-01
Using a code developed to compute high Reynolds number viscoelastic flows, polymer injection from the upstream stagnation point of a circular cylinder is modeled at Re = 3900. Polymer stresses are represented using the FENE-P constitutive equations. By increasing polymer injection rates within realistic ranges, significant near wake stabilization is observed. Rather than a turbulent detached shear layer giving way to a chaotic primary vortex (as seen in Newtonian flows at high Re), a much more coherent primary vortex is shed, which possesses an increased core pressure as well as a reduced level of turbulent energy. © 2011 American Society of Mechanical Engineers.
Stabilization of vortices in the wake of a circular cylinder using harmonic forcing
DEFF Research Database (Denmark)
Chamoun, George Chaouki; Schilder, Frank; Brøns, Morten
2011-01-01
We explore whether vortex flows in the wake of a fixed circular cylinder can be stabilized using harmonic forcing. We use Fo¨ppl's point vortex model augmented with a harmonic point source-sink mechanism which preserves conservation of mass and leaves the system Hamiltonian. We discover a region of...... Lyapunov-stable vortex motion for an appropriate selection of parameters. We identify four unique parameters that affect the stability of the vortices: the uniform flow velocity, vortex equilibrium positions, forcing amplitude, and forcing frequency. We assess the robustness of the controller using a...
Cohen, Raymond; Iaccarino, Gianluca
2005-11-01
Previously published exprimental data of the flow around two circular cylinders arranged in tandem have shown that for small spacings between the cylinders, the shear layer from the upstream cylinder reattaches to the downstream cylinder, hence creating a recirculation region in between the two cylinders. The experimental data was obtained at Re=65,000 and it was found that beyond a critical spacing (L/D ˜ 4.0), the upstream shear layer ceases to attach to the downstream cylinder, resulting in a dramatic change in the flow mechanisms. Previous numerical studies using two-dimensional RANS and URANS were unsatisfactory at predicting the length of the recirculation region of the upstream cylinder and consequently badly predicted the hydrodynamic forces between the two cylinders. In this study, Large Eddy Simulation with a dynamic Smagorinsky subgrid-scale model was used to investigate the flow around two circular cylinders arranged in tandem. Results from high Reynolds numbers simulations will be presented and practical considerations in using LES in such a flow configuration will be discussed.
LARGE-EDDY AND DETACHED-EDDY SIMULATIONS OF THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The separated turbulent flow around a circular cylinder is investigated using Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES, or hybrid RANS/LES methods), and Unsteady Reynolds-Averaged Navier-Stokes (URANS). The purpose of this study is to examine some typical simulation approaches for the prediction of complex separated turbulent flow and to clarify the capability of applying these approaches to a typical case of the separated turbulent flow around a circular cylinder. Several turbulence models, I.e. Dynamic Sub-grid Scale (SGS) model in LES, the DES-based Spalart-Allmaras (S-A) and Shear-Stress- Transport (SST) models in DES, and the S-A and SST models in URANS, are used in the calculations. Some typical results, e.g., the mean pressure and drag coefficients, velocity profiles, Strouhal number, and Reynolds stresses, are obtained and compared with previous computational and experimental data. Based on our extensive calculations, we assess the capability and performance of these simulation approaches coupled with the relevant turbulence models to predict the separated turbulent flow.
Second-order wave diffraction by a circular cylinder using scaled boundary finite element method
International Nuclear Information System (INIS)
The scaled boundary finite element method (SBFEM) has achieved remarkable success in structural mechanics and fluid mechanics, combing the advantage of both FEM and BEM. Most of the previous works focus on linear problems, in which superposition principle is applicable. However, many physical problems in the real world are nonlinear and are described by nonlinear equations, challenging the application of the existing SBFEM model. A popular idea to solve a nonlinear problem is decomposing the nonlinear equation to a number of linear equations, and then solves them individually. In this paper, second-order wave diffraction by a circular cylinder is solved by SBFEM. By splitting the forcing term into two parts, the physical problem is described as two second-order boundary-value problems with different asymptotic behaviour at infinity. Expressing the velocity potentials as a series of depth-eigenfunctions, both of the 3D boundary-value problems are decomposed to a number of 2D boundary-value sub-problems, which are solved semi-analytically by SBFEM. Only the cylinder boundary is discretised with 1D curved finite-elements on the circumference of the cylinder, while the radial differential equation is solved completely analytically. The method can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.
RICHTER, DAVID
2010-03-29
The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cylinder wake transition. Simulations at two distinct Reynolds numbers (Re = 100 and Re = 300) revealed dramatic differences based on the choice of the polymer extensibility (L2 in the FENE-P model), as well as a stabilizing tendency of viscoelasticity. For the Re = 100 case, attention was focused on the effects of increasing polymer extensibility, which included a lengthening of the recirculation region immediately behind the cylinder and a sharp increase in average drag when compared to both the low extensibility and Newtonian cases. For Re = 300, a suppression of the three-dimensional Newtonian mode B instability was observed. This effect is more pronounced for higher polymer extensibilities where all three-dimensional structure is eliminated, and mechanisms for this stabilization are described in the context of roll-up instability inhibition in a viscoelastic shear layer. © 2010 Cambridge University Press.
Dynamic response of a clamped/free hollow circular cylinder under travelling torsional impact loads
International Nuclear Information System (INIS)
Impact-induced vibrations in the casing of a gas centriguge due to a sudden failure of the spinning rotor (crash) can cause structural disintegrity of the casing. In order to study the influence of the rotor failure bahaviour and the impact load histories on the dynamic response of the casing, a simple crash model is proposed in this paper to analyse the transient torsional response due to tangential components of the impact loads. The casing is modeled as a linear-elastic hollow circular cylinder, clamped at the lower end and free at the upper end. The rotor is thought to breakup in identical sections in a sequence determined by its fracture behaviour. Each section is assumed to cause an axi-symmetric load distribution at the inner surface of the casing. Therefore the problem is essentially reduced to the analysis of a clamped/free cylinder under travelling torsional impact loads. The problem is solved by representing the impact loads as local pulses acting over the length of the sections. A perturbation method is used to show that the general two-dimensional theory of axi-symmetric torsional wave propagation in circular cylinders, for the problem under consideration, may be approximated by the elementary one-dimensional theory. Solutions are obtained according to the usual modal expansion approach. Measurements of transient torsional responses are shown to be in good agreement with the calculated responses by choosing a suitable shape of the pulses. The effects of travelling velocity and pulse shape are investigated. Finally the transfer of kinetic energy in the rotor to vibrational energy of torsion in the casing is studied. (orig.)
Plane section of cone and cylinder in computer geometry
Directory of Open Access Journals (Sweden)
Obradović Ratko M.
2005-01-01
Full Text Available In this paper a mathematical apparatus for determination of plane section of cone and cylinder was formed. By using the descriptive geometric approach the contour lines of these quadrics were determined. The fact that the tangent lines of a circle could be transformed to the tangent lines of an ellipse using affinity was employed. In that way surfaces are represented by contour lines (tangent lines of basic ellipse in oblique projection and thus they have a realistic view. Intersecting plane α is a plane normal to a frontal plane. For determination of intersecting points of intersecting curve between the plane α and the quadrics, the lock of auxiliary planes, which contain the vertex of quadrics, was used. Each auxiliary plane from the observed lock intersect the surface in two lines which intersect the given plane α in two points. By using a sufficient number of auxiliary planes the intersecting curve as a set of pairs of points for all auxiliary planes is determined and the intersecting curve was drawn by lightening of these pairs of points on the graphical screen.
International Nuclear Information System (INIS)
This experimental study investigated the characteristics of flow induced vibration of two elastically supported circular cylinders in a side by side arrangement. In particular, the characteristics of the flow induced vibration of the two cylinders are investigated by changing the flow speed at each spacing ratio L/D (L is the space between two cylinders and D is the diameter of the cylinder). To clarify the mechanism generating the flow induced vibration of the cylinders, the flow patterns around the two vibrating cylinders are also investigated using a flow visualization test that reproduces the flow induced vibration of the cylinders with a forced vibration apparatus. As a result, it is clarified that the flow induced vibration characteristics of the two cylinders arranged side by side switch among four patterns as the flow between the two cylinders is switched. Among the three arrangements considered (tandem, staggered, and side by side), the arrangement that generates flow induced vibration of the two cylinders most easily is the side by side arrangement
On vortex shedding and prediction of vortex-induced vibrations of circular cylinders
Energy Technology Data Exchange (ETDEWEB)
Halse, Karl Henning
1997-12-31
In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.
3D UTD Modeling of a Measured Antenna Disturbed by a Dielectric Circular Cylinder in WBAN Context
Plouhinec, Eric; Uguen, Bernard; Mhedhbi, Meriem; Avrillon, Stéphane
2014-01-01
This paper describes a work realized for On-Body antennas characterization: the 3D deterministic modeling of a measured antenna disturbed by a dielectric circular cylinder of finite length. This prediction model is based on the ray-tracing technique for the electromagnetic wave paths search and the Uniform Theory of Diffraction (UTD) for the modeling of the electromagnetic waves interactions with the cylinder. After a detailed description, the model is validated in 3D with measurements made f...
Limiting Geometries of Two Circular Maldacena-Wilson Loop Operators
Arutyunov, G.; Plefka, J.; Staudacher, M.
2001-01-01
We further analyze a recent perturbative two-loop calculation of the expectation value of two axi-symmetric circular Maldacena-Wilson loops in [Script N] = 4 gauge theory. Firstly, it is demonstrated how to adapt the previous calculation of anti-symmetrically oriented circles to the symmetric case. By shrinking one of the circles to zero size we then explicitly work out the first few terms of the local operator expansion of the loop. Our calculations explicitly demonstrate that circular Mald...
Energy Technology Data Exchange (ETDEWEB)
Maeda, G. (University of the Ryukyus, Okinawa (Japan))
1992-09-01
Concerning the pressure distribution around a circular cylinder placed in uniform flow, there is a big difference between theoretical analysis and test results of potential flow. This is because vortex street is formed due to boundary layer separation in real viscous flow. In this study, placing a circular cylinder in the middle of uniform flow between two parallel walls, the potential flow around the cylinder was analyzed in the case where Karman vortex street is formed behind the cyinder. Static pressure on the surface of the cylinder near the positions where vortex is formed is supposed to decrease because of energy transfer to the vortex. Magnitude of the pressure drop is then calculated from the strength of the vortex obtained in the test. The pressure distribution around the circular cylinder without vortex has minimum pressure coefficient of about [minus]3 and occurs at 90[degree]. When Karman vortex street is placed downstream, minimum pressure coefficient is about [minus]2 and its position is around 80[degree]. It is also clarified that the profile of the pressure distribution around the cylinder almost agrees with the test result. 4 refs., 10 figs.
Sobera, M.P.; Kleijn, C.R.
2008-01-01
We study flow and heat transfer to a cylinder in cross flow at Re = 3,900–80,000 by means of three-dimensional transient RANS (T-RANS) simulations, employing an RNG k − ε turbulence model. Both the case of a bare solid cylinder and that of a solid cylinder surrounded at some fixed distance by a thin porous layer have been studied. The latter configuration is a standard test geometry for measuring the insulating and protective performance of garments. In this geometry, the flow in the space be...
Numerical investigation of flow and scour around a vertical circular cylinder
DEFF Research Database (Denmark)
Baykal, Cüneyt; Sumer, B. Mutlu; Fuhrman, David R.;
2015-01-01
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynoldsaveraged Navier–Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortexshedding processes, (iii) sediment transport...... (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment...
International Nuclear Information System (INIS)
An unsteady thermoelastic study, taking consideration of the length effects, was made of a finite short circular cylinder under an arbitrary heat supply along its cylindrical surface in the longitudinal direction. The analysis was treated by the thermoelastic potential method using a general form of the Love's displacement function which has not so far been used. The results obtained were compared with those of an approximate solution for the finite cylinder using Saint-Venant's principle. From the results the effects of the length-to-diameter ratio evidently appear in the transient thermal stress distributions for the finite short cylinder. (Auth.)
Institute of Scientific and Technical Information of China (English)
Lei Shi; Chengchun Zhang; Jing Wang; Luquan Ren
2012-01-01
Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder.As one of the flow control methods,a bionic method,inspired by the serrations at the leading edge of owls' wing,was proposed in this paper.The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated.At a free stream speed of 24.5 m·s-1,corresponding to Reynolds number of 1.58 × 104,the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder,thus reduce the aerodynamic noise.A qualitative-view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.
Limiting geometries of two circular Maldacena-Wilson loop operators
International Nuclear Information System (INIS)
We further analyze a recent perturbative two-loop calculation of the expectation value of two axi-symmetric circular Maldacena-Wilson loops in N=4 gauge theory. Firstly, it is demonstrated how to adapt the previous calculation of anti-symmetrically oriented circles to the symmetric case. By shrinking one of the circles to zero size we then explicitly work out the first few terms of the local operator expansion of the loop. Our calculations explicitly demonstrate that circular Maldacena-Wilson loops are non-BPS observables precisely due to the appearance of unprotected local operators. The latter receive anomalous scaling dimensions from non-ladder diagrams. Finally, we present new insights into a recent conjecture claiming that coincident circular Maldacena-Wilson loops are described by a Gaussian matrix model. We report on a novel, supporting two-loop test, but also explain and illustrate why the existing arguments in favor of the conjecture are flawed. (author)
Edge properties of principal fractional quantum Hall states in the cylinder geometry
Soulé, Paul; Jolicoeur, Thierry
2012-01-01
We study fractional quantum Hall states in the cylinder geometry with open boundaries. We focus on principal fermionic 1/3 and bosonic 1/2 fractions in the case of hard-core interactions. The gap behavior as a function of the cylinder radius is analyzed. By adding enough orbitals to allow for edge modes we show that it is possible to measure the Luttinger parameter of the non-chiral liquid formed by the combination of the two counterpropagating edges when we add a small confining potential. W...
Piezoelectric energy harvesting from vortex-induced vibrations of circular cylinder
Mehmood, A.; Abdelkefi, A.; Hajj, M. R.; Nayfeh, A. H.; Akhtar, I.; Nuhait, A. O.
2013-09-01
The concept of harvesting energy from a circular cylinder undergoing vortex-induced vibrations is investigated. The energy is harvested by attaching a piezoelectric transducer to the transverse degree of freedom. Numerical simulations are performed for Reynolds numbers (Re) in the range 96≤Re≤118, which covers the pre-synchronization, synchronization, and post-synchronization regimes. Load resistances (R) in the range 500 Ω≤R≤5 MΩ are considered. The results show that the load resistance has a significant effect on the oscillation amplitude, lift coefficient, voltage output, and harvested power. The results also show that the synchronization region widens when the load resistance increases. It is also found that there is an optimum value of the load resistance for which the harvested power is maximum. This optimum value does not correspond to the case of largest oscillations, which points to the need for a coupled analysis as performed here.
Bouakkaz, R.; Talbi, K.; Khelil, Y.; Salhi, F.; Belghar, N.; Ouazizi, M.
2014-01-01
The heat transfer and air flow around an unconfined heated rotating circular cylinder is investigated numerically for varying rotation rates ( α = 0-6) in the Reynolds number range of 20-200. The numerical calculations are carried out by using a finite volume method based commercial computational fluid dynamics solver FLUENT. The successive changes in the flow pattern are studied as a function of the rotation rate. Suppression of vortex shedding occurs as the rotation rate increases ( α > 2). A second kind of instability appears for higher rotation speed where a series of counter-clockwise vortices is shed in the upper shear layer. The rotation attenuates the secondary instability and increases the critical Reynolds number for the appearance of this instability. Besides, time-averaged (lift and drag coefficients and Nusselt number) results are obtained and compared with the literature data. A good agreement has been obtained for both the local and averaged values.
Experimental study of ice accretion on circular cylinders at moderate low temperatures
DEFF Research Database (Denmark)
Koss, Holger H.; Gjelstrup, Henrik; Georgakis, Christos T.
For the assessment of aerodynamic instability of iced bridge cables various calculation models are available. Input for these models are amongst others aerodynamic load coefficients usually determined in wind tunnel tests on generic or simplified models of iced cable sections. Even though icing of...... structures is widely studied, the particular climatic boundary conditions regarding bridge cable vibrations have so far been omitted. The presented study was performed in March 2009 in the Altitude Icing Wind Tunnel at the National Research Council of Canada (NRC) in Ottawa with the purpose of establishing...... detailed knowledge on the shape characteristics of ice accretion on circular cylinders under the specific conditions where large amplitude vibration of iced bridge have been observed in nature. Hence, the study shall serve as a reference and the results will be used for validation of numerical and...
A PIV study of the wake of a circular cylinder subjected to low amplitude flow perturbations
International Nuclear Information System (INIS)
The 'locked-on' vortex shedding patterns resulting from the interaction of a fixed circular cylinder and an approaching flow with low-amplitude perturbations superimposed on it was studied by means of PIV measurements. The forced wake exhibits two different wake modes or states for a perturbation frequency below twice that of the natural vortex shedding frequency; the first one is a Karman-like vortex street formed by shedding of two single vortices per cycle (2S mode), whereas the other is most appropriately characterised by the splitting of the shed vortices into pairs (2P mode). For a perturbation frequency above twice that of the natural shedding frequency only the 2S mode is observed. Proper orthogonal decomposition is employed to further elucidate the existence of the two wake modes. (authors)
Torsion of Noncircular Composite Cylinders
Rouse, Marshall; Hyer, Michael W.; Haynie, Waddy T.
2005-01-01
The paper presents a brief overview of the predicted deformation and failure characteristics of noncircular composite cylinders subjected to torsion. Using a numerical analysis, elliptical cylinders with a minor-to-major diameter ratio of 0.7 are considered. Counterpart circular cylinders with the same circumference as the elliptical cylinders are included for comparison. The cylinders are constructed of a medium-modulus graphite-epoxy material in a quasi-isotropic lay-up. Imperfections generated from the buckling mode shapes are included in the initial cross-sectional geometry of the cylinders. Deformations until first fiber failure, as predicted using the maximum stress failure criterion and a material degradation scheme, are presented. For increasing levels of torsion, the deformations of the elliptical cylinders, in the form of wrinkling of the cylinder wall, occur primarily in the flatter regions of the cross section. By comparison the wrinkling deformations of the circular cylinders are more uniformly distributed around the circumference. Differences in the initial failure and damage progression and the overall torque vs. twist relationship between the elliptical and circular cylinders are presented. Despite differences in the response as the cylinders are being loaded, at first fiber failure the torque and twist for the elliptical and circular cylinders nearly coincide.
Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow
International Nuclear Information System (INIS)
Synchronized vibrations were measured for a circular cylinder subjected to a water cross flow in the subcritical Reynolds numbers in order to compare the synchronized vibration range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on it. A small peak vibration in the lift direction was found when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency in only the subcritical region. The ratio of the Karman vortex frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortices began was about 1/4 in the subcritical region, and increased to 0,32 at the Strouhal number of 0,29 in the supercritical region. The frequency ratio at the beginning of the lock-in vibration in the drag direction by the Karman vortex was about 1/2, and that in the lift direction decreased from 1 to about 0,8 with decreasing Strouhal number. (author)
Three-dimensional flow around two circular cylinders in tandem arrangement
Deng, Jian; Ren, An-Lu; Zou, Jian-Feng; Shao, Xue-Ming
2006-06-01
The spatial evolutions of vortices and transition to three dimensionality in the wake of two tandem circular cylinders are numerically studied. The virtual body method developed from virtual boundary method is applied to model the no-slip boundary condition of the cylinders. Two different aspects of this problem are considered. Firstly, the spacing ratio L/D is varied from 1.5 to 8 and the Reynolds number is set unchanged at Re=220. It is shown that three dimensionality appears in the wake for L/D⩾4, whereas the flow wake keeps a two-dimensional state for L/D⩽3.5. The critical spacing for the appearance of three-dimensional instability is deduced at the range of 3.5two-dimensional case. For L/D=3.5, a mode of small-scale three-dimensional instability, named mode A, is observed to appear at Re=250 and persists over the Reynolds number range of 250-270. The three-dimensional results are compared with the two-dimensional flow with the same configuration.
Numerical investigation of the flow around two circular cylinders in tandem
Carmo, B. S.; Meneghini, J. R.
2006-08-01
The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two- and three-dimensional simulations of the flow. The centre-to-centre distance (l) of the investigated configurations varies from 1.5 to 8 diameters (D), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re>190, when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the (Re,l) pair of drag inversion.
Energy Harvester Based on the Synchronization Phenomenon of a Circular Cylinder
Directory of Open Access Journals (Sweden)
Junlei Wang
2014-01-01
Full Text Available A concept of generating power from a circular cylinder undergoing vortex-induced vibration (VIV was investigated. Two lead zirconate titanate (PZT beams which had high power density were installed on the cylinder. A theoretical model has been presented to describe the electromechanical coupling of the open-circuit voltage output and the vibration amplitudes based on a second-order nonlinear Van der pol equation and Gauss law. A numerical computation was applied to measure the capacity of the power generating system. The lift and drag coefficient and the vortex shedding frequency were obtained to verify how the nondimensional parameter reduced velocity Ur affects the fluid field. Meanwhile, a single-degree of freedom system has been added to describe the VIV, presynchronization, and synchronization together with postsynchronization regimes of oscillating frequencies. And the amplitudes of the vibration have been obtained. Finally, the vibrational amplitudes and the voltage output could go up to a high level in the synchronization region. The maximum value of the voltage output and the corresponding reduced velocity Ur were 8.42 V and 5.6, respectively.
Directory of Open Access Journals (Sweden)
Guo-qiang Tang
2015-10-01
Full Text Available Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of and , where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of and on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of and . For very small values of , the vortex shedding is completely suppressed, resulting in the root mean square (RMS values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of and . It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.
Wei, Q; Mazzitelli, F C Lombardo F D; Onofrio, R
2011-01-01
We report on measurements performed on an apparatus aimed to study the Casimir force in the cylinder-plane configuration. The electrostatic calibrations evidence anomalous behaviors in the dependence of the electrostatic force and the minimizing potential upon distance. We discuss analogies and differences of these anomalies with respect to those already observed in the sphere-plane configuration. At the smallest explored distances we observe frequency shifts of non-Coulombian nature preventing the measurement of the Casimir force in the same range. We also report on measurement performed in the parallel plane configuration, showing that the dependence on distance of the minimizing potential, if present at all, is milder than in the sphere-plane or cylinder-plane geometries. General considerations on the interplay between the distance-dependent minimizing potential and the precision of Casimir force measurements in the range relevant to detect the thermal corrections for all geometries are finally reported.
Continuous dependence on initial geometry in linear elastodynamics on a half cylinder
Knops, R.J.; Quintanilla de Latorre, Ramón
2009-01-01
Continuous dependence on the initial time geometry is established for the mean-square integral of the displacement in a linear inhomogeneous anisotropic elastic semi-infinite cylinder in motion subject to a prescribed time-dependent base displacement and initial data. A bound, newly derived for the total energy, in conjunction with backward continuation in time of the unperturbed and perturbed displacements, is employed to obtain the result. Peer Reviewed
Ghazanfarian, Jafar; Saghatchi, Roozbeh; Gorji-Bandpy, Mofid
2015-12-01
This paper studies the two-dimensional (2D) water-entry and exit of a rotating circular cylinder using the Sub-Particle Scale (SPS) turbulence model of a Lagrangian particle-based Smoothed-Particle Hydrodynamics (SPH) method. The full Navier-Stokes (NS) equations along with the continuity have been solved as the governing equations of the problem. The accuracy of the numerical code is verified using the case of water-entry and exit of a nonrotating circular cylinder. The numerical simulations of water-entry and exit of the rotating circular cylinder are performed at Froude numbers of 2, 5, 8, and specific gravities of 0.25, 0.5, 0.75, 1, 1.75, rotating at the dimensionless rates of 0, 0.25, 0.5, 0.75. The effect of governing parameters and vortex shedding behind the cylinder on the trajectory curves, velocity components in the flow field, and the deformation of free surface for both cases have been investigated in detail. It is seen that the rotation has a great effect on the curvature of the trajectory path and velocity components in water-entry and exit cases due to the interaction of imposed lift and drag forces with the inertia force.
Institute of Scientific and Technical Information of China (English)
2008-01-01
In our previous study, the effects of the interval between the cylinder and the airfoil on the aerodynamic sound were investigated and compared with the cases of single circular and single airfoil. In this study, the effects of the attack angle of the airfoil located downstream on the characteristics of aerodynamic sound and the wake structure are investigated at a given interval between the cylinder and the airfoil. It is found that the sound pressure level of DFN and the peak frequency decrease with increasing attack angle of airfoil because of the diffusive wake structure due to the increased back pressure of circular cylinder, which is caused by the blocking effect of airfoil. It is shown that the sound sources are corresponded to the attack points of shedding vortex form the upstream circular cylinder to the downstream airfoil. We conclude that the pressure fluctuation at the airfoil surface effects on the sound pressure level, from the flow visualizations and the exploration test of sound source.
Todorov, M D
1998-01-01
The classical Helmholtz problem is applied for modelling and numerical investigation of inviscid cusp-ended separated flow around circular cylinder. Two coordinate systems are used: polar for initial calculations and parabolic as topologically most suited for infinite stagnation zone. Scaling by the shape of the unknown free line renders the problem to computational domain with fixed boundaries. Difference schemes and algorithm for Laplace equation and for Bernoulli integral are devised. A separated flow with drag coefficient $C_x=0$ like the so called ``critical'' flow is obtained. The pressure distribution on the surface of cylinder and the detachment point compares quantitatively very well with the predictions of the hodograph method.
A Comparison of Ultrasound Tomography Methods in Circular Geometry
Energy Technology Data Exchange (ETDEWEB)
Leach, R R; Azevedo, S G; Berryman, J G; Bertete-Aquirre, H R; Chambers, D H; Mast, J E; Littrup, P; Duric, N; Johnson, S A; Wuebbeling, F
2002-01-24
Extremely high quality data was acquired using an experimental ultrasound scanner developed at Lawrence Livermore National Laboratory using a 2D ring geometry with up to 720 transmitter/receiver transducer positions. This unique geometry allows reflection and transmission modes and transmission imaging and quantification of a 3D volume using 2D slice data. Standard image reconstruction methods were applied to the data including straight-ray filtered back projection, reflection tomography, and diffraction tomography. Newer approaches were also tested such as full wave, full wave adjoint method, bent-ray filtered back projection, and full-aperture tomography. A variety of data sets were collected including a formalin-fixed human breast tissue sample, a commercial ultrasound complex breast phantom, and cylindrical objects with and without inclusions. The resulting reconstruction quality of the images ranges from poor to excellent. The method and results of this study are described including like-data reconstructions produced by different algorithms with side-by-side image comparisons. Comparisons to medical B-scan and x-ray CT scan images are also shown. Reconstruction methods with respect to image quality using resolution, noise, and quantitative accuracy, and computational efficiency metrics will also be discussed.
Critical heat flux in circular tube geometries using Freon-12
International Nuclear Information System (INIS)
Experimental and analytical investigations on critical heat flux have been performed in circular tubes of different diameters ranging from 2 mm to 16 mm. More than 1500 data points have been obtained in a large range of parameters: pressure 1.0 MPa to 3.0 MPa, mass flux 1.0 Mg/m2s to 6.0 Mg/m2s and exit steam quality -0.75 to +0.60. The effect of different parameters on CHF have been discussed. The test data have been compared with different CHF prediction methods. A very good agreement between the test data in the 8 mm diameter tube and the CHF look-up table shows that the test results in Freon-12 can be well transferred to water conditions by using fluid-to-fluid scaling laws available. The experimental data reveal that the effect of the tube diameter on CHF is governed mainly by exit steam quality and tube diameter itself. None of the equations or models available in the literature can reproduce the measured diameter effect with sufficient accuracy. (author)
Kirkil, Gokhan; Constantinescu, George
2015-07-01
The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on the results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake, in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely long circular cylinders, the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. This is because even at very high cylinder Reynolds numbers, ReD, the flow regime remains subcritical in the vicinity of the bed surface due to the reduction of the incoming flow velocity within the bottom boundary layer. The paper provides a detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (ReD = 16 000, subcritical flow regime) and Reynolds numbers at which the transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (ReD = 5 ∗ 105, supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices, vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed. Being able to quantitatively and qualitatively describe these changes is critical to understand Reynolds-number-induced scale effects on sediment erosion mechanisms around cylinders mounted on a loose bed, which is a problem of
Dynamic viscoelastic effects on sound wave scattering by an eccentric compound circular cylinder
Hasheminejad, Seyyed M.; Kazemirad, Siavash
2008-12-01
The classical method of separation of variables in conjunction with the translational addition theorem for cylindrical wave functions are employed to obtain an exact solution for two-dimensional interaction of a harmonic plane acoustic wave with an infinitely long (visco)elastic circular cylinder which is eccentrically coated by another (visco)elastic material and is submerged in an ideal unbounded acoustic medium. The novel features of Havriliak-Negami model for dynamic viscoelastic material behaviour are used to take the rheological properties of the coating (and/or core) material into consideration. The analytical results are illustrated with numerical examples in which a steel rod eccentrically coated with (an eccentric steel shell filled with) dissipative materials of distinct viscoelastic properties is insonified by plane sound waves at selected angles of incidence. The effects of incident wave frequency, angle of incidence, core eccentricity and dynamic viscoelastic material properties on the backscattered form function spectra are examined. Limiting cases are considered and fair agreements with available solutions are obtained.
Turbulence statistics of flow over scoured cohesive sediment bed around circular cylinder
Debnath, K.; Manik, M. K.; Mazumder, B. S.
2012-06-01
The effect of clay content on the mean flow, turbulence intensities, Reynolds shear stress and conditional statistics of the Reynolds shear stress was investigated within and above the equilibrium scour hole around circular cylinder embedded in cohesive sediment bed having clay fractions 0.1 and 0.2. Detailed three dimensional velocity components were measured at three different cross-sections: upstream, sideward and downstream of the pier covering flow regions within and above the scour hole using 3D Micro acoustic Doppler velocimeter (ADV). It is observed that within the scour hole region the sweeping events play a dominant role at both the side and the front of the pier while the ejection events play a dominant role in the outer flow region. At the scour hole surface a thin layer of ejection dominant pocket is seen both at the pier front and the side. This resulted in kolk-boils phenomenon at the interface layer of sweep and ejection dominance which probably instigated the scouring process. In addition, the mean time interval of the turbulent bursting events within and above the scour hole is presented.
Analytical study of heat transfer from circular cylinder in liquid metals
Khan, W. A.; Culham, J. R.; Yovanovich, M. M.
2006-09-01
In this study the influence of a thin hydrodynamic boundary layer on the heat transfer from a single circular cylinder in liquid metals having low Prandtl number (0.004 0.03) is investigated under isothermal and isoflux boundary conditions. Two separate analytical heat transfer models, viscous and inviscid, are developed to clarify the discrepancy between previous results. For both models, integral approach of the boundary layer analysis is employed to derive closed form expressions for the calculation of the average heat transfer coefficients. For an inviscid model, the energy equation is solved using potential flow velocity only whereas for a viscous model, a fourth-order velocity profile is used in the hydrodynamic boundary layer and potential flow velocity is used outside the boundary layer. The third-order temperature profile is used inside the thermal boundary layer for both models. It is shown that the inviscid model gives higher heat transfer coefficients whereas viscous flow model gives heat transfer results in a fairly good agreement with the previous experimental/numerical results.
Analytical study of heat transfer from circular cylinder in liquid metals
Energy Technology Data Exchange (ETDEWEB)
Khan, W.A.; Culham, J.R.; Yovanovich, M.M. [University of Waterloo, Microelectronics Heat Transfer Laboratory, Department of Mechanical Engineering, Waterloo, ON (Canada)
2006-09-15
In this study the influence of a thin hydrodynamic boundary layer on the heat transfer from a single circular cylinder in liquid metals having low Prandtl number (0.004-0.03) is investigated under isothermal and isoflux boundary conditions. Two separate analytical heat transfer models, viscous and inviscid, are developed to clarify the discrepancy between previous results. For both models, integral approach of the boundary layer analysis is employed to derive closed form expressions for the calculation of the average heat transfer coefficients. For an inviscid model, the energy equation is solved using potential flow velocity only whereas for a viscous model, a fourth-order velocity profile is used in the hydrodynamic boundary layer and potential flow velocity is used outside the boundary layer. The third-order temperature profile is used inside the thermal boundary layer for both models. It is shown that the inviscid model gives higher heat transfer coefficients whereas viscous flow model gives heat transfer results in a fairly good agreement with the previous experimental/numerical results. (orig.)
Dinarvand Saeed; Abbassi Abbas; Hosseini Reza; Pop Ioan
2015-01-01
This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy a...
Czech Academy of Sciences Publication Activity Database
Král, Radomil
2014-01-01
Roč. 77, October (2014), s. 906-914. ISSN 0017-9310 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0060; GA ČR(CZ) GBP105/12/G059 Institutional support: RVO:68378297 Keywords : circular cylinder * unsteady heat transfer * temperature distribution * wind tunnel experiment * porous material Subject RIV: JN - Civil Engineering Impact factor: 2.383, year: 2014 http://www. science direct.com/ science /article/pii/S0017931014005171
García Aguilar, Andrés; Sipus, Zvonimir; Sierra Pérez, Manuel
2012-01-01
A novel formulation for the surface impedance characterization is introduced for the canonical problem of surface fields on a perfect electric conductor (PEC) circular cylinder with a dielectric coating due to a electric current source using the Uniform Theory of Diffraction (UTD) with an Impedance Boundary Condition (IBC). The approach is based on a TE/TM assumption of the surface fields from the original problem. Where this surface impedance fails, an optimization is performed to minimize t...
Czech Academy of Sciences Publication Activity Database
Král, Radomil
2014-01-01
Roč. 77, October (2014), s. 906-914. ISSN 0017-9310 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0060; GA ČR(CZ) GBP105/12/G059 Institutional support: RVO:68378297 Keywords : circular cylinder * unsteady heat transfer * temperature distribution * wind tunnel experiment * porous material Subject RIV: JN - Civil Engineering Impact factor: 2.383, year: 2014 http://www.sciencedirect.com/science/article/pii/S0017931014005171
NUMERICAL SIMULATION OF AN OSCILLATING FLOW PAST A CIRCULAR CYLINDER IN THE VICINITY OF A PLANE WALL
Institute of Scientific and Technical Information of China (English)
SHAH Syed Bilai Hussain; LU Xi-yun
2008-01-01
Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D ≤ 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D > 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frequency and the vortex shedding frequency from an isolated stationary cylinder.
Ding, H.; Shu, C.; Yeo, K. S.; Xu, D.
2007-01-01
In this paper, the mesh-free least square-based finite difference (MLSFD) method is applied to numerically study the flow field around two circular cylinders arranged in side-by-side and tandem configurations. For each configuration, various geometrical arrangements are considered, in order to reveal the different flow regimes characterized by the gap between the two cylinders. In this work, the flow simulations are carried out in the low Reynolds number range, that is, Re=100 and 200. Instantaneous vorticity contours and streamlines around the two cylinders are used as the visualization aids. Some flow parameters such as Strouhal number, drag and lift coefficients calculated from the solution are provided and quantitatively compared with those provided by other researchers.
3-D CFD simulation of natural convection of air over a circular cylinder in a cuboidal box
International Nuclear Information System (INIS)
The objective of this study is to investigate the transient 3-D numerical simulations of natural convection of air around a circular cylinder (76.2 mm OD and 560 mm length) enclosed in a cuboidal box of 1000 mm X 600 mm X 1200 mm. The value of Ra number is 1.3 X 106. The 2-D numerical simulations are also performed and the comparison between the 2-D and 3-D numerical simulations has been presented in terms of Nusselt number. The effect of top wall to cylinder distance on the flow pattern has also been investigated for the case of conducting ceiling. The flow becomes unstable and oscillating depending on the distance between cylinder and ceiling. The time varying behavior of the Nu number has also shown. (author)
SOME OBSERVATIONS OF TWO INTERFERING VIV CIRCULAR CYLINDERS OF UNEQUAL DIAMETERS IN TANDEM
Institute of Scientific and Technical Information of China (English)
HUANG Shan; SWORN Andy
2011-01-01
Analysis of model test results was carried out to investigate the hydrodynamic interaction between a pair of elastically-supported rigid cylinders of dissimilar diameters in a water flume.The two cylinders are placed in tandem with one situated in the wake of the other.The diameter of the upstream cylinder is twice as large as that of the downstream cylinder.The spacing between the two cylinders ranges from 1 to 10 times the larger cylinder diameter.The Reynolds numbers are within the sub-critical range.The cylinders are free to oscillate in both the in-line and the cross-flow directions.The reduced velocity ranges from 1 to 10 and the low damping ratio of the model test set-up at 0.006 gives a combined m.ass-damping parameter of 0.02.It is found that the lift on and the cross-flow motion of the downstream cylinder have the frequency components derived from the upstream cylinder's vortex shedding as well as from its own vortex shedding,and the relative importance of the two sources of excitation is influenced by the spacing between the two cylinders.The downstream cylinder's VIV response appears to be largely dependent upon the actual reduced velocity of the cylinder.
Numerical investigation of flow and scour around a vertical circular cylinder.
Baykal, C; Sumer, B M; Fuhrman, D R; Jacobsen, N G; Fredsøe, J
2015-01-28
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynolds-averaged Navier-Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortex-shedding processes, (iii) sediment transport (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment transport is not accounted for. Alternatively, the effects of vortex shedding are found to be limited to the very early stage of the scour process. Flow features such as the horseshoe vortex, as well as lee-wake vortices, including their vertical frequency variation, are discussed. Large-scale counter-rotating streamwise phase-averaged vortices in the lee wake are likewise demonstrated via numerical flow visualization. These features are linked to scour around a vertical pile in a steady current. PMID:25512595
Interaction theory of hypersonic laminar near-wake flow behind an adiabatic circular cylinder
Hinman, W. Schuyler; Johansen, C. T.
2015-12-01
The separation and shock wave formation on the aft-body of a hypersonic adiabatic circular cylinder were studied numerically using the open source software OpenFOAM. The simulations of laminar flow were performed over a range of Reynolds numbers (8× 10^3 < Re < 8× 10^4 ) at a free-stream Mach number of 5.9. Off-body viscous forces were isolated by controlling the wall boundary condition. It was observed that the off-body viscous forces play a dominant role compared to the boundary layer in displacement of the interaction onset in response to a change in Reynolds number. A modified free-interaction equation and correlation parameter has been presented which accounts for wall curvature effects on the interaction. The free-interaction equation was manipulated to isolate the contribution of the viscous-inviscid interaction to the overall pressure rise and shock formation. Using these equations coupled with high-quality simulation data, the underlying mechanisms resulting in Reynolds number dependence of the lip-shock formation were investigated. A constant value for the interaction parameter representing the part of the pressure rise due to viscous-inviscid interaction has been observed at separation over a wide range of Reynolds numbers. The effect of curvature has been shown to be the primary contributor to the Reynolds number dependence of the free-interaction mechanism at separation. The observations in this work have been discussed here to create a thorough analysis of the Reynolds number-dependent nature of the lip-shock.
Jordan, Stephen A.
2016-05-01
Long thin circular cylinders commonly serve as towed sonar tracking devices, where the radius-of-curvature along the longitudinal axis is quite low [ρr = O(10-4)]. Because no understanding presently exists about the direct impact of longitudinal curvature on the turbulent statistics, the long cylinder is simply viewed as a chain of straight segments at various (increasing then decreasing) small inclinations to the freestream direction. Realistically, even our statistical evidence along straight thin cylinders at low incidence angles is inadequate to build solid evidence towards forming reliable empirical models. In the present study, we address these shortcomings by executing Large-Eddy Simulations (LESs) of straight and longitudinally curved thin cylinders at low to moderate turbulent radius-based Reynolds numbers (500 ≤ Rea ≤ 3500) and small angles-of-incidence (α = 0° → 9°). Coupled with the previous experimental measurements and numerical results, the new expanded database (311 ≤ Rea ≤ 56 500) delivered sufficient means to propose power-law expressions for the longitudinal evolution of the skin friction, normal drag, and turbulent boundary layer (TBL) length scales. Surprisingly, the LES computations of the curved cylinders at analogous geometric and kinematic conditions as the straight cylinder showed similar character in terms of the longitudinal skin friction. Beyond incidence 1°-3° (upper end corresponds to the highest simulated Rea), the skin friction was directly proportional to the yaw angle and monotonically shifted downward with higher Rea. Conversely, the flow structure, normal drag, TBL length scales, Reynolds stresses, and the separation state of the transverse shear layers towards regular vortex shedding for the curved cylinder were highly dissimilar than the straight one at equivalent incidence angles.
Machynia, Adam
Analytic solutions to the static and stationary boundary value field problems relative to an arbitrary configuration of parallel cylinders are obtained by using translational addition theorems for scalar Laplacian polar functions, to express the field due to one cylinder in terms of the polar coordinates of the other cylinders such that the boundary conditions can be imposed at all the cylinder surfaces. The constants of integration in the field expressions of all the cylinders are obtained from a truncated infinite matrix equation. Translational addition theorems are available for scalar cylindrical and spherical wave functions but such theorems are not directly available for the general solution of the Laplace equation in polar coordinates. The purpose of deriving these addition theorems and applying them to field problems involving systems of cylinders is to obtain exact analytic solutions with controllable accuracies, thereby, yielding benchmark solutions to validate other approximate numerical methods.
Suppression of Flow Separation Around A Circular Cylinder by Utilizing Lorentz Force
Institute of Scientific and Technical Information of China (English)
ZHANG Hui; FAN Bao-chun; CHEN Zhi-hua; ZHOU Ben-mou
2008-01-01
Both experimental and numerical investigations on the flow past a cylinder under the influence of Lorentz force (electromagnetic force) were conducted in an electrically low-conducting fluid. The Lorentz force is applied both locally, wholly and periodically on the surface of the cylinder, and their control effects for flow separation were investigated Both experimental and numerical results show that Lorentz force can suppress the flow separation with Lorentz force applied on both local and whole surface of the cylinder. However, when the periodic and opposite Lorentz force adopted, the cylinder wake cannot be stabilized.
Institute of Scientific and Technical Information of China (English)
LUO Lin-cong; ZHANG Guan-min; PAN Ji-hong; TIAN Mao-cheng
2013-01-01
This paper presents a two-dimensional CFD study of the falling film evaporation of horizontal tubes with different shapes applied in the seawater desalination.The flow and heat transfer characteristics of the falling water film on one circular tube and two non-circular shaped tubes,a drop-shaped tube and an oval-shaped tube,are analyzed,respectively.The Volume Of Fluid (VOF)method is employed to investigate the influence of the mass flow rate and the feeder height on the distribution of the film thickness and the heat transfer performance.The numerical results show that the minimum value of the film thickness appears approximately at the angular positions of 125°,160° and 170° for the smooth circular,oval-and drop-shaped tubes,respectively.The film thickness grows with the increase of the mass flow rate and the decrease of the feeder height,while the variation pattern varies for different tubes.Moreover,compared with the circular tube,the drop-and oval-shaped tubes have a lower dimensionless temperature and a thinner thermal boundary layer,which means a better heat transfer performance.Finally,the numerical results correlate well with the experimental and predicted data in literature.
Singha, Sintu; Nagarajan, Kaushik Kumar; Sinhamahapatra, K. P.
2016-05-01
Incompressible flows at low Reynolds numbers over two identical side-by-side circular cylinders have been investigated numerically using unstructured finite volume method. The gap between the cylinders (g) and Reynolds number (Re) considered in the study lies respectively in the range of 0.2 ≤ g/D ≤ 4.0 (D being the diameter of the cylinder) and 20 ≤ Re ≤ 160. Low Reynolds number steady flows are given considerable importance. Two types of wakes are observed in the steady flow regime; the first type is characterized by attached vortices as in the case of an isolated cylinder and the other type is identified by detached standing vortices in the downstream. Reynolds number at which flow turns unsteady is quantified for each gap width. Five different types of wake patterns are observed in the unsteady flow regime: single bluff body wake, deflected wake, flip-flopping wake, in-phase synchronized, and anti-phase synchronized wakes. Present simulations of the evolution of single bluff-body wake demonstrate presence of vortices in the gap side too. The very long time simulations show that below a limiting Re depending on the gap, there is a transition of fully developed initial anti-phase flow to the in-phase flow at a later time. The limiting Reynolds number for this phase bifurcation phenomenon is evaluated in the (Re, g/D) space. A properly calibrated reduced order model based stability analysis is carried out to investigate the phase transition.
Gunnoo, Hans; Abcha, Nizar; Ezersky, Alexander
2016-02-01
The influence of harmonic surface wave on non-regular Karman Vortex Street is investigated. In our experiments, Karman Street arises behind a vertical circular cylinder in a water flow and harmonic surface waves propagating upstream. It is found that surface waves can modify regimes of shedding in Karman Street: frequency lock-in and synchronization of vortex shedding can arise. Intensive surface waves can excite symmetric vortex street instead of chess-like street, and completely suppress shedding behind the cylinder. It is shown experimentally that such effects occur if frequency of harmonic surface wave is approximately twice higher than the frequency of vortex shedding. Region of frequency lock-in is found on the plane amplitude-frequency of surface wave.
Mansour, M A; El-Kabeir, S M
2000-01-01
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids.
Mansour, M. A.; El-Hakiem, M. A.; El Kabeir, S. M.
2000-10-01
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids.
International Nuclear Information System (INIS)
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids
Directory of Open Access Journals (Sweden)
Nemati Hasan
2011-01-01
Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.
Guo, Li; Zhang, Xing; He, Guowei
2016-02-01
The flows past a circular cylinder at Reynolds number 3900 are simulated using large-eddy simulation (LES) and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier-Stokes equations. The dynamic global coefficient version of the Vreman's subgrid scale (SGS) model is used to compute the sub-grid stresses. Curle's integral of Lighthill's acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctuations obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman's SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.
Directory of Open Access Journals (Sweden)
Wang Ye-Long
2012-01-01
Full Text Available A direct forcing method for the simulation of particulate flows based on immersed boundary-lattice Boltzmann method is used to study the flow of power-law fluid through an infinite array of circular cylinders with cylinder separations of 20a (a is the cylinder radius with laminar shedding behind cylinders. Time averaged drag coefficient, maximum of lift coefficient and Strouhal number are given out with the power-law index in the range of 0.4 ≤ n ≤ 1.8 and Re in the range of 50 ≤ Re ≤ 140.
International Nuclear Information System (INIS)
This paper presents a study of the bistable phenomenon which occurs in the turbulent flow impinging on circular cylinders placed side-by-side. Time series of axial and transversal velocity obtained with the constant temperature hot wire anemometry technique in an aerodynamic channel are used as input data in a finite mixture model, to classify the observed data according to a family of probability density functions. Wavelet transforms are applied to analyze the unsteady turbulent signals. Results of flow visualization show a predominantly two-dimensional behavior. A double-well energy model is suggested to describe the behavior of the bistable phenomenon in this case. (author)
DEFF Research Database (Denmark)
Johansson, Jens; Nielsen, Mogens Peter
The uniform flow around a circular cylinder at Reynolds number 1e5 is simulated in a three dimensional domain by means of the newly developed Self-induced angular Moment Method, SMoM, turbulence model. The global force coefficients, Strouhal number, pressure distributions and wall shear stress...... distributions are compared to experimental findings reported in literature. The SMoM turbulence model is found to provide maximum, minimum and time-mean pressure coefficient distributions in very good agreement with experimental findings....
B. Harshavardhan; Mallikarjuna, J. M.
2013-01-01
In this investigation, a CFD analysis has been carried out on in-cylinder fluid flows and air-fuel interaction in Direct Injection Spark Ignition (DISI) engine by changing combustion chamber geometry during intake and compression stroke at an engine speed of 1500 rpm for four different types of piston profiles viz., flat piston, flat piston with centre bowl, dome piston with centre bowl and pentroof offset bowl piston. A polyhedral trimmed cell has been taken for meshing of the geometries usi...
Electromagnetic Casimir Forces of Parabolic Cylinder and Knife-Edge Geometries
Graham, Noah; Emig, Thorsten; Rahi, Sahand Jamal; Jaffe, Robert L; Kardar, Mehran
2011-01-01
An exact calculation of electromagnetic scattering from a perfectly conducting parabolic cylinder is employed to compute Casimir forces in several configurations. These include interactions between a parabolic cylinder and a plane, two parabolic cylinders, and a parabolic cylinder and an ordinary cylinder. To elucidate the effect of boundaries, special attention is focused on the "knife-edge" limit in which the parabolic cylinder becomes a half-plane. Geometrical effects are illustrated by considering arbitrary rotations of a parabolic cylinder around its focal axis, and arbitrary translations perpendicular to this axis. A quite different geometrical arrangement is explored for the case of an ordinary cylinder placed in the interior of a parabolic cylinder. All of these results extend simply to nonzero temperatures.
Directory of Open Access Journals (Sweden)
Pankaj Thakur
2014-01-01
Full Text Available Thermal stress and strain rates in a thick walled rotating cylinder under steady state temperature has been derived by using Seth’s transition theory. For elastic-plastic stage, it is seen that with the increase of temperature, the cylinder having smaller radii ratios requires lesser angular velocity to become fully plastic as compared to cylinder having higher radii ratios The circumferential stress becomes larger and larger with the increase in temperature. With increase in thickness ratio stresses must be decrease. For the creep stage, it is seen that circumferential stresses for incompressible materials maximum at the internal surface as compared to compressible material, which increase with the increase in temperature and measure n.
Bifurcation of Vortex Breakdown Patterns in a Circular Cylinder with two Rotating Covers
DEFF Research Database (Denmark)
Brøns, Morten; Bisgaard, Anders
2006-01-01
We analyse the topology of vortex breakdown in a closed cylindrical container in the steady domain under variation of three parameters, the aspect ratio of the cylinder, the Reynolds number, and the ratio of the angular velocities of the covers. We develop a general post-processing method to obtain...
Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs
Stürmer, Julian; Grimm, Stephan; Kalide, Andre; Sutherland, Adam P; Seifahrt, Andreas; Schuster, Kay; Bean, Jacob L; Quirrenbach, Andreas
2016-01-01
Optical fibers are a key component for high-resolution spectrographs to attain high precision in radial velocity measurements. We present a custom fiber with a novel core geometry - a 'D'-shape. From a theoretical standpoint, such a fiber should provide superior scrambling and modal noise mitigation, since unlike the commonly used circular and polygonal fiber cross sections, it shows chaotic scrambling. We report on the fabrication process of a test fiber and compare the optical properties, scrambling performance, and modal noise behavior of the D-fiber with those of common polygonal fibers.
Geometry effects on magnetization dynamics in circular cross-section wires
International Nuclear Information System (INIS)
Three-dimensional magnetic memory design based on circular-cross section nanowires with modulated diameter is the emerging field of spintronics. The consequences of the mutual interaction between electron spins and local magnetic moments in such non-trivial geometries are still open to debate. This paper describes the theoretical study of domain wall dynamics within such wires subjected to spin polarized current. We used our home-made finite element software to characterize the variety of domain wall dynamical regimes observed for different constriction to wire diameter ratios d/D. Also, we studied how sizeable geometry irregularities modify the internal micromagnetic configuration and the electron spin spatial distribution in the system, the geometrical reasons underlying the additional contribution to the system's nonadiabaticity, and the specific domain wall width oscillations inherent to fully three-dimensional systems
Numerical Study on the Charge Transport in a Space between Concentric Circular Cylinders
Suh, Y. K.; Baek, K H
2014-01-01
Electrification is one of the key factors to be considered in the design of power transformers utilizing dielectric liquid as a coolant. Compared with enormous quantity of experimental and analytical studies on electrification, numerical simulations are very few. This paper describes essential elements of numerical solution methods for the charge transport equations in a space between concentric cylinders. It is found that maintaining the conservation property of the convective terms in the g...
Mechanism of Tonal Noise Generation from Circular Cylinder with Spiral Fin
Institute of Scientific and Technical Information of China (English)
Ryo Yamashita; Hidechito Hayashi; Tetsuya Okumura; Hiromitsu Hamakawa
2014-01-01
The pitch of the spiral finned tube influences seriously to the acoustic resonance in the heat exchanger.In this research,the flow characteristics in relating to the aeolian tone from the finned cylinder are studied by the numerical simulation.It is observed that the tonal noise generated from the finned tube at two pitch spaces.The ratio of the fin pitch to the cylinder diameter is changed at 0.11 and 0.27.The tone level increases and the frequency decreases with the pitch shorter.The separation flow from the cylinder generates the span-wise vortices,Karman vortices,and the separation flow from the fin generates the stream-wise vortices.When the fin pitch ratio is small,the stream-wise vortices line up to span-wise and become weak rapidly.Only the Karman vortices are remained and integrate in span.So the Karman vortex became large.This causes the low frequency and the large aeolian tone.
The Flow Field Downstream of a Dynamic Low Aspect Ratio Circular Cylinder: A Parametric Study
Gildersleeve, Samantha; Dan, Clingman; Amitay, Michael
2015-11-01
Flow past a static, low aspect ratio cylinder (pin) has shown the formation of vortical structures, namely the horseshoe and arch-type vortex. These vortical structures may have substantial effects in controlling flow separation over airfoils. In the present experiments, the flow field associated with a low aspect ratio cylinder as it interacts with a laminar boundary layer under static and dynamic conditions was investigated through a parametric study over a flat plate. As a result of the pin being actuated in the wall-normal direction, the structures formed in the wake of the pin were seen to be a strong function of actuation amplitude, driving frequency, and aspect ratio of the cylinder. The study was conducted at a Reynolds number of 1875, based on the local boundary layer thickness, with a free stream velocity of 10 m/s. SPIV data were collected for two aspect ratios of 0.75 and 1.125, actuation amplitudes of 6.7% and 16.7%, and driving frequencies of 175 Hz and 350 Hz. Results indicate that the presence and interactions between vortical structures are altered in comparison to the static case and suggest increased large-scale mixing when the pin is driven at the shedding frequency (350 Hz). Supported by the Boeing Company.
Mandal, A. C.; Waechter, R. T.
1994-01-01
Waechter and Philip (1985) obtained the asymptotic expansion of the mean infiltration rate for large s from a buried circular cylinder using a scattering analog. Here s(= αl/2) is defined as the ratio of the characteristic length l of the water supply surface (in fact, its radius) to the sorptive length 2α-1 of the soil and a satisfies the relationship K(ψ) = K(0) eαψ, where K is the hydraulic conductivity, and ψ is the moisture potential. This exact solution cannot be used directly to obtain the separate contributions to the mean infiltration rate from the top and the bottom halves of the cylinder; our analysis is based on a new class of special functions derived from the modified Bessel equation with a forcing term. In this paper, we obtain the separate asymptotics for the two halves for large s to make a comparison with the results of the trench problem (Waechter and Mandal, 1993). The asymptotic expansions for top and bottom halves are (2/π)(0.69553s-2/3) and (2/π)(1+0.30066s-2/3), respectively, whereas for a semicircular trench, the mean infiltration rate is given by (2/π)(1+0.30066s-2/3).
International Nuclear Information System (INIS)
This paper presents a study of the bistable phenomenon which occurs in the turbulent flow impinging on circular cylinders placed side-by-side. Time series of axial and transversal velocity obtained with the constant temperature hot wire anemometry technique in an aerodynamic channel are used as input data in a finite mixture model, to classify the observed data according to a family of probability density functions. Wavelet transforms are applied to analyze the unsteady turbulent signals. Results of flow visualization show that the flow is predominantly two-dimensional. A double-well energy model is suggested to describe the behavior of the bistable phenomenon in this case. -- Highlights: ► Bistable flow on two parallel cylinders is studied with hot wire anemometry as a first step for the application on the analysis to tube bank flow. ► The method of maximum likelihood estimation is applied to hot wire experimental series to classify the data according to PDF functions in a mixture model approach. ► Results show no evident correlation between the changes of flow modes with time. ► An energy model suggests the presence of more than two flow modes
Lift forces on a circular cylinder in cross flow resulting from heat/mass transfer
Czech Academy of Sciences Publication Activity Database
Trávníček, Zdeněk; Maršík, F.; Vít, Tomáš; Broučková, Zuzana; Pavelka, Miroslav
Southampton: WIT Press, 2013 - (Carlomagno, G.; Brebbia, C.; Hernández, S.), s. 149-159 ISBN 978-1-84564-732-2. ISSN 1746-4064. [Computational Methods and Experimental Measurements (CMEM) 2013. Coruna (ES), 02.07.2013-04.07.2013] R&D Projects: GA ČR(CZ) GCP101/11/J019; GA AV ČR(CZ) IAA200760801 Institutional support: RVO:61388998 Keywords : cylinder in cross flow * magnus effect * active flow control Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts http://library.witpress.com/pages/paperinfo.asp?PaperID=24858
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
We analyze thickness-shear vibration of an axially poled circular cylindrical tube with unattached electrodes and air gaps. Both free and electrically forced vibrations are studied. Exact solutions are obtained from the equations of linear piezoelectricity. Resonant frequencies and the impedance of the transducer are calculated from the solution. Results show that the resonant frequencies are sensitive to the dimensions of the air gaps when the gaps are thin. The impedance depends strongly on the air gaps.
Lockwood, Vernard E.; McKinney, Linwood W.
1960-01-01
A two-dimensional lifting circular cylinder has been tested over a Mach number range from 0.011 to 0.32 and a Reynolds number range from 135,000 to 1,580,000 to determine the force and pressure distribution characteristics. Two flaps having chords of 0.37 and 6 percent of the cylinder diameter, respectively, and attached normal to the surface were used to generate lift. A third configuration which had 6-percent flaps 1800 apart was also investigated. All flaps were tested through a range of angular positions. The investigation also included tests of a plain cylinder without flaps. The lift coefficient showed a wide variation with Reynolds number for the 6-percent flap mounted on the bottom surface at the 50-percent-diameter station, varying from a low of about 0.2 at a Reynolds number of 165,000 to a high of 1.54 at a Reynolds number of 350,000 and then decreasing almost linearly to a value of 1.0 at a Reynolds number of 1,580,000. The pressure distribution showed that the loss of lift with Reynolds number above the critical was the result of the separation point moving forward on the upper surface. Pressure distributions on a plain cylinder also showed similar trends with respect to the separation point. The variation of drag coefficient with Reynolds number was in direct contrast to the lift coefficient with the minimum drag coefficient of 0.6 occurring at a Reynolds number of 360,000. At this point the lift-drag ratios were a maximum at a value of 2.54. Tests of a flap with a chord of 0.0037 diameter gave a lift coefficient of 0.85 at a Reynolds number of 520,000 with the same lift-drag ratio as the larger flap but the position of the flap for maximum lift was considerably farther forward than on the larger flap. Tests of two 6-percent flaps spaced 180 deg apart showed a change in the sign of the lift developed for angular positions of the flap greater than 132 deg at subcriti- cal Reynolds numbers. These results may find use in application to air- craft using
Experimental Study of Wave Forces on Vertical Circular Cylinders in Long and Short Crested Sea
DEFF Research Database (Denmark)
Høgedal, Michael
in the transverse wave forces on the structure, whereas the vertical forces generally are unaffected. In this study the effect from wave directionality on the horizontal wave forces on a slender vertical cylinder in a laboratory environment is investigated. In addition wave forces from regular waves......The three-dimensional structure of ocean waves is generally ignored in favour of two-dimensional waves, which are easier to handle from a theoretical and computational point of view. For design fixed structures where horizontal in-line and resultant wave forces are important, this is normally on...... the safe side, as the directional spreading of the wave field Ieads to reduced horizontal velocities and acceleration; in the fluid and hence a reduction of the resultant and in-line wave forces on the structure. The directional spreading of the horizontal velocity field generally causes an increase...
Gao, Shaoyan; Li, Pengbo; Li, Fuli
2013-03-01
The plasmon resonance-induced near electric field focusing and enhancement of three-layered silver nano-cylinder has been studied by quasi-static electricity. A field enhancement factor of more than 102 times can be obtained in the middle dielectric wall between the inner silver wire and outer tube around the resonance wavelengths of 400-500 nm. Because of the anti-symmetric coupling between the bonding tube plasmon and the wire plasmon, the incident electric field could be fine focused between the two metallic surfaces by decreasing the middle wall thickness. As a result of the curvature-dependent surface charge concentration, thinner dielectric wall with small diameter provides stronger local field enhancement. It provides the potential applications of plamonic nano-structures for high-density and high-contrast optical data storage under the diffraction limit.
Waka, R.; Yoshino, F.; Hayashi, T.
1985-06-01
An experiment was carried out to understand effects of the slot shape at the cylinder-side-wall juncture and the angular location of a blowing slot on the spanwise distributions of various characteristic values near the side-wall of a circular cylinder with tangential blowing. The range of the side-wall effects and the characteristic values near the side-wall are much influenced by the slot shape and the location of the slot. When the slot shaped like a knife edge, termed 'Edge', is used, the range of the side-wall effects becomes narrower as the angular location of the blowing slot is farther downstream.
International Nuclear Information System (INIS)
Steady mixed convection boundary layer flow from an isothermal horizontal circular cylinder embedded in a porous medium filled with a nano-fluid has been studied for both cases of a heated and cooled cylinder using the Buongiorno-Darcy mathematical nano-fluid model. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme. The solutions for the flow and heat transfer characteristics are evaluated numerically for various values of the governing parameters, namely the constant mixed convection parameter λ, the traditional Lewis number Le, the buoyancy ratio parameter Nr, the Brownian motion parameter Nb and the thermophoresis parameter Nt. It is found that in the present case of the porous medium flow, the separation is always suppressed at negative values of λ. When λ changes from -2.1 to 0, one has a 'heating' of the cylinder, but a heating in the negative range of λ (λ 0) delays the separation of the boundary layer and if the cylinder is hot enough (large values of λ > 0), then it is suppressed completely at a positive value of λ, somewhere between 0.88 and 0.89. On the other hand, cooling the cylinder (λ < 0) brings the boundary layer separation point nearer to the lower stagnation point and for a sufficiently cold cylinder (large values of λ < 0) there will not be a boundary layer on the cylinder. (authors)
Wang, Chenglei; Tang, Hui; Yu, Simon C. M.; Duan, Fei
2016-05-01
This paper studies the control of two-dimensional vortex-induced vibrations (VIVs) of a single circular cylinder at a Reynolds number of 100 using a novel windward-suction-leeward-blowing (WSLB) concept. A lattice Boltzmann method based numerical framework is adopted for this study. Both open-loop and closed-loop controls are implemented. In the open-loop control, three types of actuation arrangements, including the pure suction on the windward side of the cylinder, the pure blowing on the leeward side, and the general WSLB on both sides, are implemented and compared. It is found that the general WSLB is the most effective, whereas the pure suction is the least effective. In the closed-loop control, the proportional (P), integral (I), and proportional-integral (PI) control schemes are applied to adjust the WSLB velocities according to the flow information obtained from a sensor. The effects of four key control parameters including the proportional gain constant, the integral gain constant, the length of data history used for the feedback, and the location of the sensor are investigated. It is found that the use of only P control fails to completely suppress the VIV, the use of only I control can achieve the complete suppression, and the PI control performs the best in terms of both the control effectiveness and efficiency. In the PI control, there exists an optimal length of data history for the feedback, at which the VIV control is the most efficient. There also exist the minimum required WSLB velocities for the VIV suppression, independent of the control schemes. Moreover, it is found that the VIV control is independent of the sensor location.
Energy Technology Data Exchange (ETDEWEB)
Premnath, Kannan N [Department of Mechanical Engineering, University of Colorado Denver, 1200 Larimer Street, Denver, CO 80217 (United States); Pattison, Martin J [HyPerComp Inc., 2629 Townsgate Road, Suite 105, Westlake Village, CA 91361 (United States); Banerjee, Sanjoy, E-mail: kannan.premnath@ucdenver.edu, E-mail: kannan.np@gmail.com [Department of Chemical Engineering, City College of New York, City University of New York, New York, NY 10031 (United States)
2013-10-15
Lattice Boltzmann method (LBM) is a kinetic based numerical scheme for the simulation of fluid flow. While the approach has attracted considerable attention during the last two decades, there is a need for systematic investigation of its applicability for complex canonical turbulent flow problems of engineering interest, where the nature of the numerical properties of the underlying scheme plays an important role for their accurate solution. In this paper, we discuss and evaluate a LBM based on a multiblock approach for efficient large eddy simulation of three-dimensional external flow past a circular cylinder in the transitional regime characterized by the presence of multiple scales. For enhanced numerical stability at higher Reynolds numbers, a multiple relaxation time formulation is considered. The effect of subgrid scales is represented by means of a Smagorinsky eddy-viscosity model, where the model coefficient is computed locally by means of a dynamic procedure, providing better representation of flow physics with reduced empiricism. Simulations are performed for a Reynolds number of 3900 based on the free stream velocity and cylinder diameter for which prior data is available for comparison. The presence of laminar boundary layer which separates into a pair of shear layers that evolve into turbulent wakes impose particular challenge for numerical methods for this condition. The relatively low numerical dissipation introduced by the inherently parallel and second-order accurate LBM is an important computational asset in this regard. Computations using five different grid levels, where the various blocks are suitably aligned to resolve multiscale flow features show that the structure of the recirculation region is well reproduced and the statistics of the mean flow and turbulent fluctuations are in satisfactory agreement with prior data. (paper)
Premnath, Kannan N.; Pattison, Martin J.; Banerjee, Sanjoy
2013-10-01
Lattice Boltzmann method (LBM) is a kinetic based numerical scheme for the simulation of fluid flow. While the approach has attracted considerable attention during the last two decades, there is a need for systematic investigation of its applicability for complex canonical turbulent flow problems of engineering interest, where the nature of the numerical properties of the underlying scheme plays an important role for their accurate solution. In this paper, we discuss and evaluate a LBM based on a multiblock approach for efficient large eddy simulation of three-dimensional external flow past a circular cylinder in the transitional regime characterized by the presence of multiple scales. For enhanced numerical stability at higher Reynolds numbers, a multiple relaxation time formulation is considered. The effect of subgrid scales is represented by means of a Smagorinsky eddy-viscosity model, where the model coefficient is computed locally by means of a dynamic procedure, providing better representation of flow physics with reduced empiricism. Simulations are performed for a Reynolds number of 3900 based on the free stream velocity and cylinder diameter for which prior data is available for comparison. The presence of laminar boundary layer which separates into a pair of shear layers that evolve into turbulent wakes impose particular challenge for numerical methods for this condition. The relatively low numerical dissipation introduced by the inherently parallel and second-order accurate LBM is an important computational asset in this regard. Computations using five different grid levels, where the various blocks are suitably aligned to resolve multiscale flow features show that the structure of the recirculation region is well reproduced and the statistics of the mean flow and turbulent fluctuations are in satisfactory agreement with prior data.
Seismic response of liquid sloshing in the annular region formed by coaxial circular cylinders
International Nuclear Information System (INIS)
As to the sloshing of liquid in the storage tanks having free surface in earthquakes, there have been many reports, but these are limited to those of relatively simple structures and forms. As the cxamples of complex structures, there are chemical reaction towers, stress removal tanks for BWRs, reactor vessels for FBRs and so on. In these structures, annular parts are formed inside, and as to the sloshing in such annular parts, there is only the report of Aslam et al. In this study, examination was carried out on the earthquake response of the liquid sloshing in the annular part of a double walled cylinder which appears relatively frequently among complex structures. In the analysis, attenuation was taken into account in addition to the method of Aslam et al., the walls of an axisymmetric vessel were regarded as rigid, and infinitesinal displacement and incompressible invicid fluid were assumed. The velocity potential satisfying boundary conditions was determined assuming irrotational flow, and the solution of transient response when n sine waves resonating with the sloshing of first order mode were inputted was derived. Two kinds of double walled vessels were vibrated with a large vibrating table, and the response was measured. (Kako, I.)
2-D Urans Simulations of Vortex Induced Vibrations of Circular Cylinder at Trsl3 Flow Regime
Directory of Open Access Journals (Sweden)
Omer Kemal Kinaci
2016-01-01
Full Text Available Research on vortex-induced vibrations (VIV mainly involves experimental science but building laboratory setups to investigate the flow are expensive and time consuming. Computational fluid dynamics (CFD methods may offer a faster and a cheaper way to understand this phenomenon depending on the solution approach to the problem. The context of this paper is to present the author’s computational approach to solve for vortex-induced vibrations which cover extensive explanations on the mathematical background, the grid structure and the turbulence models implemented. Current computational research on VIV for smooth cylinders is currently restricted to flows that have Reynolds numbers below 10,000. This paper describes the method to approach the problem with URANS and achieves to return satisfactory results for higher Reynolds numbers.The computational approach is first validated with a benchmark experimental study for rather low Reynolds number which falls into TrSL2 flow regime. Then, some numerical results up to Re=130,000, which falls into TrSL3 flow regime,are given at the end of the paper to reveal the validity of the approach for even higher Reynolds numbers.
Direct Numerical Simulation of Flow around a Circular Cylinder Controlled Using Plasma Actuators
Directory of Open Access Journals (Sweden)
Taichi Igarashi
2014-01-01
by means of direct numerical simulation (DNS. The Reynolds number based on the freestream velocity and the cylinder diameter is set at ReD=1000. The plasma actuators are placed at ±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.
Asymmetrical boundary layer separation at the base of a two cylinder geometry
Boyle, M. T.; Langston, L. S.
1989-01-01
This paper reports on the experimental description of the three-dimensional horseshoe vortex system occurring at the base of two cylinder mounted side by side on an endwall. The spacing between the two cylinders is adjusted to generate a family of viscous flows. Flow visualization performed in a water tunnel provides a qualitative understanding of the flow over a range of flow variables. A detailed wind tunnel experiment provides a quantitative description of the flow at a single test condition. At Re(D) = 2.5 x 10 to the 5th the measurements show an asymmetrical primary vortex with a wide flat cross section. A small counterrotating vortex is found between the primary vortex and the cylinder leading edge.
Directory of Open Access Journals (Sweden)
Dinarvand Saeed
2015-01-01
Full Text Available This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy analysis method (HAM. Expressions for velocity and temperature fields are developed in series form. In this study, three different types of nanoparticles are considered, namely alumina (, titania (, and copper ( with water as the base fluid. For copper-water nanofluid, graphical results are presented to describe the influence of the nanoparticle volume fraction on the velocity and temperature fields for the forced and mixed convection flows. Moreover, the features of the flow and heat transfer characteristics are analyzed and discussed for foregoing nanofluids. It is found that the skin friction coefficient and the heat transfer rate at the surface are highest for copper-water nanofluid compared to the alumina-water and titania-water nanofluids.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The structure of double diffusive convection in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fields: in the stratification state, the isothermal lines near the sidewall are higher than that near the symmetry axis, while the isoconcentration lines near the symmetry axis are relatively high. The mechanism of these non-horizontal stratifications is illustrated by comparing double-diffusive convection with natural convection driven by thermal buoyancy or solutal buoyancy alone. The effects of Lewis number Le and buoyancy ratio N on the non-hor- izontal stratifications of thermal and solutal fields are also investigated. The results show that: at a given time (t = 0.2), with an increase in Le (Le = 0-15), the area influenced by solute diffusion decreases; for isothermal line, the gradients of it initially increase, but it tends to be horizontal at the top of the cavity when the Lewis number is higher than 10. When N varies from 0 to 2, the isoconcentration lines tend to be horizontal while the gradients of isothermal line increase.
Czech Academy of Sciences Publication Activity Database
Peer, Petra; Filip, Petr; Stěnička, M.; Pavlínek, V.
2014-01-01
Roč. 59, č. 3 (2014), s. 221-235. ISSN 0001-7043 R&D Projects: GA ČR(CZ) GAP105/11/2342 Institutional support: RVO:67985874 Keywords : electrorheology * parallel plates * concentric cylinders * silicone oil * PANI powders Subject RIV: BK - Fluid Dynamics
Czech Academy of Sciences Publication Activity Database
Trávníček, Zdeněk; Wang, A.B.
2011-01-01
Roč. 25, č. 8 (2011), s. 1881-1884. ISSN 1738-494X R&D Projects: GA ČR(CZ) GCP101/11/J019 Institutional research plan: CEZ:AV0Z20760514 Keywords : heated circular cylinder * effective temperature * vortex shedding Subject RIV: BK - Fluid Dynamics Impact factor: 0.448, year: 2011 http://www.springerlink.com/content/2131l38t2u0504u6/
Hussain Ahmad; Tariq Javed; Abuzar Ghaffari
2016-01-01
In the present article, radiation effect on mixed convection boundary layer flow of a viscoelastic fluid over a horizontal circular cylinder with constant heat flux has been numerically analyzed. The governing boundary layer equations are transformed to dimensionless nonlinear partial differential equations. The equations are solved numerically by using Keller-box method. The computed results are in excellent agreement with the previous studies. Skin friction coefficient and Nusselt number ar...
Numerical Analysis and Optimization of Engine Cylinder Fins of Varying
Saravanan
2014-01-01
The main aim of the project is to analyze the thermal properties by varying geometry, material and thickness of cylinder fins. Parametric models of cylinder with fins have been developed to predict the transient thermal behavior. The models are created by varying the geometry, rectangular, circular and curved shaped fins and also by varying thickness of the fins. The 3D modeling software used is Pro/Engineer.The analysis is done using ANSYS. Presently Material used for manufac...
Directory of Open Access Journals (Sweden)
Yokoi Y.
2014-03-01
Full Text Available In this study, the flow features of vortex shedding from a circular cylinder forced-oscillating in the in-line direction were investigated by use of flow visualization experiment and numerical simulation at the Reynolds number Re=620, with varied amplitude ratio and varied frequency ratio. As a result of the experiments, it was found that although the flow structure around the circular cylinder is two-dimensional in the lock-in state of simultaneous vortex shedding, the large scale three-dimensional instability is observed in the lock-in state of alternate vortex shedding through a time lag in the boundary layer separation along the cylinder span. As a result of calculations, two typical flow patterns of the lock-in were shown, and it was confirmed that the calculated flow patterns were in reasonable agreement with previous experimental results. The fluid force act on the oscillating cylinder was investigated. It was clarified that the amplitude of the lift coefficient was larger than the amplitude of the drag coefficient in the lock-in of alternate vortex shedding, and the amplitude of the drag coefficient was larger than the amplitude of the lift coefficient in the lock-in of simultaneous vortex shedding. When the amplitude ratio 2a/d grows, this tendency becomes remarkable.
Towards a precision measurement of the Casimir force in a cylinder-plane geometry
Brown-Hayes, Michael; Dalvit, Diego A. R.; Mazzitelli, Francisco D.; Kim, Woo-Joong; Onofrio, Roberto
2005-01-01
We report on a proposal aimed at measuring the Casimir force in a cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibrati...
Lockwood, Vernard E.
1961-01-01
A wind-tunnel investigation has been made to determine the ground effect on the aerodynamic characteristics of a lifting circular cylinder using tangential blowing from surface slots to generate high lift coefficients. The tests were made on a semispan model having a length 4 times the cylinder diameter and an end plate of 2.5 diameters. The tests were made at low speeds at a Reynolds number of approximately 290,000, over a range of momentum coefficients from 0.14 to 4.60, and over a range of groundboard heights from 1.5 to 10 cylinder diameters. The investigation showed an earlier stall angle and a large loss of lift coefficient as the groundboard was brought close to the cylinder when large lift coefficients were being generated. For example, at a momentum coefficient of 4.60 the maximum lift coefficient was reduced from a value of 20.3 at a groundboard height of 10 cylinder diameters to a value of 8.7 at a groundboard height of 1.5 cylinder diameters. In contrast to this there was little effect on the lift characteristics of changes in groundboard height when lift coefficients of about 4.5 were being generated. At a height of 1.5 cylinder diameters the drag coefficients generally increased rapidly when the slot position angle for maximum lift was exceeded. Slightly below the slot position angle for maximum lift, the groundboard had a beneficial effect, that is, the drag for a given lift was less near the groundboard than away from the groundboard. The variation of maximum circulation lift coefficient (maximum lift coefficient minus momentum coefficient) obtained in this investigation is in general agreement with a theory developed for a jet-flap wing which assumes that the loss in circulation is the result of blockage of the main stream beneath the wing.
Sobera, M.P.; Kleijn, C.R.
2008-01-01
We study flow and heat transfer to a cylinder in cross flow at Re = 3,900–80,000 by means of three-dimensional transient RANS (T-RANS) simulations, employing an RNG k − ε turbulence model. Both the case of a bare solid cylinder and that of a solid cylinder surrounded at some fixed distance by a thin
Energy Technology Data Exchange (ETDEWEB)
Sharma, B.R. [Dibrugarh University, Department of Mathematics, Dibrugarh, Assam (India); Singh, R.N. [Marwari Hindi High School, Dibrugarh (India)
2010-08-15
The effect of a radial magnetic field on separation of a binary mixture of incompressible viscous thermally and electrically conducting fluids confined between two concentric rotating circular cylinders with different angular velocity is examined. The equations governing the motion, temperature and concentration in cylindrical polar coordinate are solved analytically. The solution obtained in closed form for concentration distribution is plotted against the radial distances from the surface of the inner circular cylinder for various values of non-dimensional parameters. It is found that the non-dimensional parameters viz. the Hartmann number, thermal diffusion number, baro diffusion number, rotational Reynolds number, the product of Prandtl number and Eckert number, magnetic Prandtl number and the ratio of the angular velocities of inner and outer cylinders affects the species separation of rarer and lighter component significantly. The problem discussed here derives its application in the basic fluid dynamics separation processes to separate the rarer component of the different isotopes of heavier molecules where electromagnetic method of separation does not work. (orig.)
Supramolecular Chemistry: Induced Circular Dichroism to Study Host-Guest Geometry
Mendicuti, Francisco; Gonzalez-Alvarez, Maria Jose
2010-01-01
In this laboratory experiment, students obtain information about the structure of a host-guest complex from the interpretation of circular dichroism measurements. The value and sign of the induced circular dichroism (ICD) on an achiral chromophore guest when it complexes with a cyclodextrin can be related to the guest penetration and its…
Energy Technology Data Exchange (ETDEWEB)
Kawamura, T.; Nakao, T.; Takahashi, M.; Hayashi, M.; Goto, N. [Hitachi, Ltd., Tokyo (Japan)
1999-07-25
Vortex-induced vibrations were measured for a circular cylinder subjected to a water cross flow at supercritical Reynolds numbers for a wide range of reduced velocities. Turbulence intensities were changed from 1% to 13% in order to investigate the effect of the Strouhal number on the region of synchronization by symmetrical and Karman vortex shedding. The reduced damping of the test cylinder was about 0.1 in water. The surface roughness of the cylinder was a mirror-polished surface. Strouhal number decreased from about 0.48 to 0.29 with increasing turbulence intensity. Synchronized vibrations were observed even at supercritical Reynolds numbers where fluctuating fluid force was small. Reduced velocities at which drag and lift direction lock-in by Karman vortex shedding were initiated decreased with increasing Strouhal number. When Strouhal number was about 0.29, the self-excited vibration in drag direction by symmetrical vortex shedding began at which the frequency ratio of Karman vortex shedding frequency to the natural frequency of cylinder was 0.32. (author)
Park, Han G.
An experimental investigation is carried out on the processes of heat transfer associated with a heated circular cylinder in crossflow. Two studies are made. First, a study of the transport of heat in the near wake (x/Dthermochromic liquid crystal (TLC) particles which change their reflected wavelength as function of temperature. By calibrating reflected wavelength versus temperature using a color multi-CCD camera, the local temperature of the flow may be deduced. The velocity is measured by using the same particles as Lagrangian flow tracers, and local velocity or displacement of the flow may be measured by cross-correlating two sequential images. A limitation of DPIV/T, which is the low level of precision (5% - 20% of the temperature span of TLC particles), may be overcome by a process in which the temperature at a given location is computed by averaging the temperatures of the particles within a specified sampling window. This process increases the precision to 2% - 10%.In the study of the heat transport in the near wake, the velocity and temperature measurements obtained from DPIV/T are decomposed into their mean, coherent, and incoherent components using the triple decomposition. It is found that the heat from the cylinder is transported down the wake mostly by the mean heat flux and is laterally transported out of the wake by the coherent and the incoherent heat fluxes. In examining the direction of the turbulent heat flux vectors, the vectors are found not to be co-linear with the gradient of mean temperature. This misalignment implies that the gradient transport models are inappropriate for modeling the turbulent heat transport in the near wake of a circular cylinder. In examining the production of turbulence, it is found that that kinetic energy fluctuations are produced in the saddle regions (regions where the fluid is being stretched in one direction and compressed in another) while the temperature fluctuations are produced at the edges of center regions
Institute of Scientific and Technical Information of China (English)
陈瑞志; 黄华; 詹杰民; 朱梦华; 郭宗晓
2015-01-01
基于 Biot 渗流固结理论和水波绕射理论，应用特征函数展开法，推导了对应透空复合圆柱的绕射波势和波浪引起的海床内渗流压力分布的解析解式，由此计算了作用于固立透空复合圆柱底部上由波浪渗流压力所导致的浮托力和倾覆力矩，并与水平和垂直绕射波浪力和力矩进行了相应比较。计算结果表明，复合柱上部圆柱侧表面的透空性对水平方向的波浪直接作用有明显的减弱效应，对波浪渗流倾覆力矩也有一定的减弱效应，而对垂直方向的波浪直接作用及波浪渗流浮托力影响较小。海况条件和复合圆柱几何条件等因素的相对变化对波浪渗流作用均存在一定的影响，其中对渗流倾覆力矩的影响更为明显。在一定条件下，波浪渗流作用与绕射波浪作用可以具有相同的量级。%Based on Biot seepage consolidation theory and wave diffraction theory,the analytical solu-tions to the diffracted water wave potentials and the wave-induced seepage pressures referring to porous compound vertical circular cylinder resting on permeable elastic seabed are derived by applying the eigen-function expansion approach,and then the wave-induced lift force and overturn moment caused by the seepage pressure on the bottom of compound vertical circular cylinder are accordingly evaluated and are compared with direct diffracted wave force and moment.The results demonstrate that the porosity of the lateral surface of the circular column resting on a circular base will lead an obvious reduction in direct horizontal wave loads on compound cylinder and certain reduction in seepage overturn moment on the bot-tom of compound cylinder,and having slight influence on direct vertical wave loads and wave-induced seepage uplift force on compound cylinder .The variation of ocean condition and structure geometry con-dition may have some influence on wave-induced seepage loads,especially on seepage
Carmo, B. S.; Meneghini, J. R.; Sherwin, S. J.
2010-05-01
The possible states in the flow around two identical circular cylinders in tandem arrangements are investigated for configurations in the vicinity of the drag inversion separation. By means of numerical simulations, the hysteresis in the transition between the shedding regimes is studied and the relationship between (three-dimensional) secondary instabilities and shedding regime determination is addressed. The differences observed in the behavior of two- and three-dimensional flows are analyzed, and the regions of bistable flow are delimited. Very good agreement is found between the proposed scenario and results available in the literature.
Directory of Open Access Journals (Sweden)
Pankaj Thakur
2014-01-01
Full Text Available The non-homogeneity is assumed due to variation of modulus of compression. It has seen that in the presence of temperature, a cylinder made of non-homogeneous material k<0 (Non-homogeneity is less at internal surface than at outer surface require high pressure to become fully plastic as is required for initial yielding and this pressure goes on increasing with the increases in temperature, showing that a cylinder made of non-homogeneous material k<0 is on the safer side of design. For homogeneous case, it has been observed that the circumferential stress has maximum value at the external surface of the cylinder made of incompressible material as compared to compressible material. For Homogeneous case, with effects of temperature reduces the stresses at the external surface of the cylinder in comparison to pressure effects only. Strain rates are found to be maximum at the internal surface of the cylinder made of compressible material and they decrease with the radius. With the introduction of temperature effect, the creep rates have higher values at the internal surface but lesser values at the external surface as compare to a cylinder subjected to pressure only.
International Nuclear Information System (INIS)
An incompressible unsteady viscous two-dimensional finite volume Navier-Stokes solver is developed using 'consistent flux reconstruction' technique on a collocated unstructured mesh comprising of triangular cells. In this solver, the full Navier-Stokes equations have been solved numerically in the physical plane itself without using any transformation to the computational plane. The cell face centre velocities are reconstructed explicitly by solving the momentum equations on flux reconstruction control volumes defined judiciously around the respective cell face centres. This is followed by solution of the cell centre pressure field using a discrete Poisson equation developed from the reconstructed velocities and updating the cell centre velocities by using an explicit scheme. In the present investigation, the solver has been applied to unconfined flow past a single cylinder, two cylinders and three cylinders for Reynolds number (Re) = 100 and 200. To validate the numerical code the present results for single and two cylinder arrangements were compared with results available from literature and found to be agreeing well. For the two and three cylinder configurations flow has been computed for various gaps between cylinders and for both side-by-side and tandem arrangements. Different wake patterns like in-phase and anti-phase synchronized wake patterns, flip-flopping, deflected wake patterns and steady wake patterns are observed depending on the Reynolds number and the gap spacing.
Numerical Simulation of Flow-induced Vibration of Tandem Circular Cylinders%串列双圆柱流致振动数值模拟
Institute of Scientific and Technical Information of China (English)
及春宁; 杨立红; 黄继露; 刘爽
2014-01-01
基于开源程序OpenFOAM和动网格技术，利用切应力平衡法建立水流作用下的海上风电基础局部冲刷数学模型。通过模拟结果与实验数据的对比发现，所建立的冲刷数学模型能够合理反映圆柱型单桩基础周围的水流结构，冲刷深度与实验结果吻合较好。%Numerical simulation is carried out for the flow-induced vibrations(FIV)of the elastically-mounted tandem cylinders in laminar flow by using immersed boundary method in the process of harvesting VIVACE ocean current energy (Vortex Induced Vibration Aquatic Clean Energy). The research results show the crosscurrent displacement of the upstream and downstream cylinders,vortex shedding frequency,lift-drag coefficient and the curve of the phase difference between lift force and displacement being affected by reduced flow velocity. In addition,analysis is made for the influence of cylinder’s spacing ratio on the hydrodynamic and FIV response characteristics of the tandem circular cylinders.
About the basic laws of non-isothermal cross-flow past of a circular cylinder with beads mix
International Nuclear Information System (INIS)
The influence of mechanical impurities in the fluid on the structure of the flow near a stationary, rotating cylinder, on its hydrodynamic characteristics and the heat exchange with the stream was investigated numerically. It was shown that the presence of impurities in the liquid leads to a significant change in the pattern of the flow, to increase in the resistance and heat transfer of a stationary cylinder, reducing the lifting force. The emissivity of the rotating cylinder in a fluid flow with an admixture of substantially depends on the dimensionless velocity of the surface. If the speed is less critical, equal to 3.0, the heat is intensified. At higher values, on the contrary, the heat transfer deteriorates. The necessity of considering these circumstances when developing technologies for deposition of functional coatings is evidential
DEFF Research Database (Denmark)
Demartino, Cristoforo; Koss, Holger; Ricciardelli, Francesco
2013-01-01
temperatures are considered. The tested cylinder is a specimen of a HDPE tube used for bridge hanger protection. The wind tunnel tests shall serve as a reference, and the results can be used for the evaluation of possible aerodynamic instability phenomena. A preliminary evaluation of possible galloping...
International Nuclear Information System (INIS)
This note describes the development of a short program for a personal computer to calculate the solid angle subtended by a right cylinder detector to a circular or rectangular, plane or thick source at any position and orientation to the cylinder. The program also calculates the number of hits on the cylinder side and on each end, and the average path-length through the detector volume (assuming no scattering or absorption). The current performance of personal computers makes it realistic to model the order of 109 simulations of radiation emission and achieve accuracies of solid angle estimates typically better than 0.03%. (authors)
Rayleigh-Bénard convection at high Prandtl numbers in circular and square geometry
Johnston, Stephen R.; Fonda, Enrico; Sreenivasan, Katepalli R.; Ranjan, Devesh
2015-11-01
Experiments using water and simulations have shown that flow structures and turbulent fluctuations in Rayleigh-Bénard convection are affected by the shape of the container. We study the effect of the geometry in both square and cylindrical test cells of aspect ratio of order unity in high Prandtl fluids (up to 104). Flow visualization using a photochromic dye seeded throughout the fluid allows us to uninvasively study the evolution of the large scale structures. We discuss the observations in the two geometries and compare them with previous observations at low Prandtl numbers.
Institute of Scientific and Technical Information of China (English)
杨锦文; 何意; 鲍锋
2014-01-01
The flow around cylinder is one of the classic research issues of fluid mechanics.The modifica-tion of the cylindrical geometry will affect the cylinder’s pressure distribution and near wake flow structures. The present study on slotted cylinder has some certain values in engineering applications such as vortex gen-erator in flow meters and heat convection.Large eddy stimulation based on 3-D Fluent code was carried out for cylinders with slit,with respect to test model of ratio of slit width to diameter s/d =0.15 on five different Reynolds numbers (Re =1500、3000、4400、5837、7200).By the means of qualitative flow visualization and quantitative PIV experiments,the flow patterns between the slit and the shedding vortex of the baseline and slotted cylinder were carefully investigated,measuring and predicting of the shedding vortex frequency were included.The results of numerical simulation agreed well with the experimental measurement.The experi-mental and computational results show that the flow in the slit demonstrated periodic motion,this oscillating vent-flow has greatly altered the near wake flow features.The periodic oscillation in the slit has enhanced the periodicity of the flow around circular cylinder;consequently,the slotted cylinder exhibited an increase in shedding vortex frequency and Strouhal number compared with their baseline case at the same Reynolds numbers.Meanwhile,The wake of the slotted cylinder presented obvious three dimensional features.%基于 Fluent 软件平台采用大涡模拟（LES）的方法对开缝圆柱绕流进行了三维数值仿真，计算了五组不同雷诺数（Re ＝1500、3000、4400、5837、7200）情况下缝宽比 s/d ＝0．15的开缝圆柱绕流流场。通过定性的流动显示和定量的 PIV 实验，对 s/d ＝0．15情况下开缝圆柱内部缝隙流动以及旋涡脱落情况进行了细致研究，并测量了基准圆柱与开缝圆柱的脱落涡频率。数值模拟与实验测量结果符合
Bai, Xiao-Dong; Zhang, Wei; Guo, An-Xin; Wang, Yong
2016-04-01
A global stability analysis is performed for the flip-flopping wake pattern behind two side-by-side cylinders with emphasis on the unstable vorticity field. The combination of direct numerical simulation with the state-of-art lattice Boltzmann method and dynamic mode decomposition is used to analyse such wake pattern for the first time. The vorticity mode of the secondary instability is extracted from the flow. Such mode is found to be symmetrical with respect to the geometric axis of symmetry. Furthermore, a new scenario is found for the high order harmonics that there is a pair of two tertiary modes as a result of nonlinear interaction between the mode related to the secondary instability and the global mode of the in-phase synchronized vortex shedding base flow. Besides, the reason for the Fourier spectra of the lift on the two cylinders being the same is also illustrated for this case.
International Nuclear Information System (INIS)
A proper orthogonal decomposition (POD) method is applied to the problem of a two-dimensional flow past two side-by-side circular cylinders. Based on the POD bases, which are constructed by a snapshot method, a low-dimensional model is established for representing two-dimensional incompressible Navier-Stokes equations. Coupled with the low-dimensional model, the Chiba method is used to analyze the global stability of the basic flow. Different bifurcation paths at three major regions are revealed, in good agreement with the available results by other methods. However, the computation amount in the POD method is low, which shows the availability and advantage of the POD method. (fundamental areas of phenomenology(including applications))
Institute of Scientific and Technical Information of China (English)
AHMED N A
2006-01-01
A comprehensive hot wire investigation of the flow around a circular cylinder is carried out in an 18" × 18" wind tunnel to look into the dominant frequencies at the stagnation, separation and separated shear layers in the transition Reynolds number range. The majority of the experiments are carried out at Reynolds number of 4.5 × 104, with additional transition frequency tests at Reynolds numbers of 2.9 × 104, 3.3 × 104 and 9.7 × 104 respectively. The results are analysed in terms of power spectral density. While the frequency associated with stagnation is found to be essentially due to vortex shedding, frequency doubling of vortex shedding is also evident in the separated shear layers.Two peaks associated with transition frequencies are detected and their possible implications are presented.
Penland, Jim A
1954-01-01
Pressure-distribution and force tests of a circular cylinder have been made in the Langley 11-inch hypersonic tunnel at a Mach number of 6.86, a Reynolds number of 129,000 based on diameter, and angles of attack up to 90 degrees. The results are compared with the hypersonic approximation of Grimminger, Williams, and Young and with a simple modification of the Newtonian flow theory. The comparison of experimental results shows that either theory gives adequate general aerodynamic characteristics but that the modified Newtonian theory gives a more accurate prediction of the pressure distribution. The calculated crossflow drag coefficients plotted as a function of crossflow Mach number were found to be in reasonable agreement with similar results obtained from other investigations at lower supersonic Mach numbers. Comparison of the results of this investigation with data obtained at a lower Mach number indicates that the drag coefficient of a cylinder normal to the flow is relatively constant for Mach numbers above about 4.
Wang, Kun
2012-01-01
Photoacoustic computed tomography (PACT), also known as optoacoustic tomography, is an emerging imaging modality that has great potential for a wide range of biomedical imaging applications. In this Note, we derive a hybrid reconstruction formula that is mathematically exact and operates on a data function that is expressed in the temporal frequency and spatial domains. This formula explicitly reveals new insights into how the spatial frequency components of the sought-after object function are determined by the temporal frequency components of the data function measured with a circular or spherical measurement geometry in two- and three-dimensional implementations of PACT, respectively. The structure of the reconstruction formula is surprisingly simple compared with existing Fourier-domain reconstruction formulae. It also yields a straightforward numerical implementation that is robust and two orders of magnitude more computationally efficient than filtered backprojection algorithms.
Wang, Zhi-Yong; Qiu, Qi; Wang, Yun-Xiang; Shi, Shuang-Jin
2016-01-01
The (1, 0)+(0, 1) representation of the group SL(2, C) provides a six-component spinor equivalent to the electromagnetic field tensor. By means of the (1, 0)+(0, 1) description, one can treat the photon field in curved spacetime via spin connection and the tetrad formalism, which is of great advantage to study the gravitational spin-orbit coupling of photons. Once the gravitational spin-orbit coupling is taken into account, the traditional radius of the circular photon orbit in the Schwarzschild geometry should be replaced with two different radiuses corresponding to the photons with the helicities of +1 and -1, respectively. Owing to the splitting of energy levels induced by the spin-orbit coupling, photons (from Hawking radiations, say) escaping from a Schwarzschild black hole are partially polarized, provided that their initial velocities possess nonzero tangential components.
Acoustic excitation of the circular Bragg endash Fresnel lens in backscattering geometry
International Nuclear Information System (INIS)
An increment of the x-ray flux in crystal Bragg endash Fresnel lens (BFL) focus in backscattering geometry obtained by means of acoustic excitation of the BFL crystal substrate has been investigated. The dependence of the x ray close-quote s total reflected power versus ultrasound parameters has been studied in a low frequency range (10 endash 50 MHz). The proposed technique allows an increase in the flux in a BFL focus by a factor of 2 which almost achieves the kinematic limit. copyright 1997 American Institute of Physics
CFD Simulation of In-Cylinder Flow on Different Piston Bowl Geometries in a DI Diesel Engine
Directory of Open Access Journals (Sweden)
S. K. Gugulothu
2016-01-01
Full Text Available The combustion process in the diesel engine should be controlled to avoid both excessive maximum cylinder pressure and an excessive rate of pressure rise, in terms of crank angle. At the same time, the process should be so rapid that substantially all the fuel is burned early in the expansion stroke. In this direction, piston configuration plays a crucial role. Four configurations i.e., flat, inclined, central bowl, and inclined offset bowl piston have been studied. This study is concerned with the CFD analysis has been carried out on two valve four stroke diesel engine to analyze the in-cylinder air motion during suction stroke, pressure and temperature variation inside the cylinder during the compression stroke for various configurations. The engine specifications are considered from the literature. For numerical analysis, Ansys15 CFD software has been used, for meshing polyhedral trimmed cells were adopted. In-cylinder flows were analyzed by solving mass, momentum and energy equation. From this study, it is concluded that analysis has been carried out for each crank angle degree during suction and compression stroke for all the piston configurations, tumble ratio varies mainly with crank angle position. At the end of the compression stroke fuel is injected and the performance of different piston bowls are analyzed.
Directory of Open Access Journals (Sweden)
Nepal C. Roy
2016-06-01
Full Text Available Unsteady mixed convection boundary-layer flow of an electrically conducting micropolar fluid past a circular cylinder is investigated taking into account the effect of thermal radiation and heat generation or absorption. The reduced non-similar boundary-layer equations are solved using the finite difference method. It is found that the magnitude of the friction factor and the couple stress significantly increases due to the increase of the mixed convection parameter, the conduction-radiation parameter, the surface temperature parameter, the heat absorption parameter and the frequency parameter. However the magnitude of the heat transfer rate decreases with these parameters. The converse characteristics are observed for the Prandtl number. The magnitude of the couple stress and the heat transfer rate is seen to decrease whereas the magnitude of the skin factor increases with increasing the vortex viscosity parameter. The magnetic field parameter reduces the skin factor, couple stress and heat transfer rate. The amplitude of oscillation of the transient skin factor and couple stress gradually increases owing to an increase of $\\xi$. But the transient heat transfer rate is found to be oscillating with almost the same amplitude for any value of $\\xi$. The amplitude of oscillation of the transient skin factor and couple stress increases with an increase of $S$ and $\\xi$ while the amplitude of the transient heat transfer rate increases with increasing Pr and $S$.
Directory of Open Access Journals (Sweden)
Hussain Ahmad
2016-01-01
Full Text Available In the present article, radiation effect on mixed convection boundary layer flow of a viscoelastic fluid over a horizontal circular cylinder with constant heat flux has been numerically analyzed. The governing boundary layer equations are transformed to dimensionless nonlinear partial differential equations. The equations are solved numerically by using Keller-box method. The computed results are in excellent agreement with the previous studies. Skin friction coefficient and Nusselt number are emphasized specifically. These quantities are displayed against the curvature parameter. The effects of pertinent parameters involved in the problem namely effective Prandtl number and mixed convection parameter on skin friction coefficient and Nusselt number are shown through graphs and table. Boundary layer separation points are also calculated with and without radiation and a comparison is shown. The presence of radiation helps to decrease or increase the skin friction coefficient for the negative or positive values of the mixed convection parameter accordingly. The decrease in value of effective Prandtl number helps to increase the value of skin friction coefficient and Nusselt number for viscoelastic fluids.
Energy Technology Data Exchange (ETDEWEB)
Tsutsui, T.; Igarashi, T. [National Defense Academy, Kanagawa (Japan); Kamemoto, K. [Yokohama National University, Yokohama (Japan). Faculty of Engineering
1996-02-25
Experimental investigations and numerical analysis were carried out to clarify the behavior of an interactive flow around two circular cylinders with different diameters, in particular, the phenomenon that the shear layer separated from the main cylinder reattaches to the rear surface due to the Coanda effect. Numerical analysis was simplified by applying a vortex method and a boundary element method. The results obtained were as follows. The reattachment due to the Coanda effect appeared intermittently and could simulated. Negative lift acted on the main cylinder, and the calculated lift and drag coefficient showed good agreement with those of experiments. The calculated Strouhal numbers were 20-30% higher than the experimental ones. 17 refs., 17 figs.
Introduction to combinatorial geometry
International Nuclear Information System (INIS)
The combinatorial geometry package as used in many three-dimensional multimedia Monte Carlo radiation transport codes, such as HETC, MORSE, and EGS, is becoming the preferred way to describe simple and complicated systems. Just about any system can be modeled using the package with relatively few input statements. This can be contrasted against the older style geometry packages in which the required input statements could be large even for relatively simple systems. However, with advancements come some difficulties. The users of combinatorial geometry must be able to visualize more, and, in some instances, all of the system at a time. Errors can be introduced into the modeling which, though slight, and at times hard to detect, can have devastating effects on the calculated results. As with all modeling packages, the best way to learn the combinatorial geometry is to use it, first on a simple system then on more complicated systems. The basic technique for the description of the geometry consists of defining the location and shape of the various zones in terms of the intersections and unions of geometric bodies. The geometric bodies which are generally included in most combinatorial geometry packages are: (1) box, (2) right parallelepiped, (3) sphere, (4) right circular cylinder, (5) right elliptic cylinder, (6) ellipsoid, (7) truncated right cone, (8) right angle wedge, and (9) arbitrary polyhedron. The data necessary to describe each of these bodies are given. As can be easily noted, there are some subsets included for simplicity
Chen, Wen-Li; Li, Hui; Hu, Hui
2014-04-01
An experimental investigation was conducted to assess the effectiveness of a suction flow control method for vortex-induced vibration (VIV) suppression. The flow control method uses a limited number of isolated suction holes to manipulate the vortex shedding in the wake behind a circular cylinder in order to reduce the unsteadiness of the dynamic wind loads acting on the cylinder. The experimental study was performed at Re ≈ 3.0 × 104, i.e., in the typical Reynolds number range of VIV for the cables of cable-stayed bridges. In addition to measuring the surface pressure distributions to determine the resultant dynamic wind loads acting on the test model, a digital particle image velocimetry system was used to conduct detailed flow field measurements to reveal the changes in the shedding process of the unsteady wake vortex structures from the test model with and without the suction flow control. The effects of important controlling parameters (i.e., the azimuthal locations of the suction holes in respect to the oncoming airflow, the spanwise spacing between the suction holes, and the suction flow rate through the suction holes) on the wake flow characteristics, the surface pressure distributions, and the resultant dynamic wind loads were assessed quantitatively. While a higher suction flow rate and smaller spanwise spacing between the suction holes were beneficial to the effectiveness of the suction flow control, the azimuthal locations of the suction holes were found to be very critical for reducing the fluctuating amplitudes of the dynamic wind loads acting on the test model using the suction flow control method. With the suction holes located at the proper azimuthal locations on the test model (i.e., at the azimuthal angle of θ = 90° and 270° for the present study), the characteristics of the wake flow behind the test model were found to change significantly along the entire span of the test model, even though only a limited number of the isolated suction
Pedoe, Dan
1988-01-01
""A lucid and masterly survey."" - Mathematics Gazette Professor Pedoe is widely known as a fine teacher and a fine geometer. His abilities in both areas are clearly evident in this self-contained, well-written, and lucid introduction to the scope and methods of elementary geometry. It covers the geometry usually included in undergraduate courses in mathematics, except for the theory of convex sets. Based on a course given by the author for several years at the University of Minnesota, the main purpose of the book is to increase geometrical, and therefore mathematical, understanding and to he
Dooner, David B
2012-01-01
Building on the first edition published in 1995 this new edition of Kinematic Geometry of Gearing has been extensively revised and updated with new and original material. This includes the methodology for general tooth forms, radius of torsure', cylinder of osculation, and cylindroid of torsure; the author has also completely reworked the '3 laws of gearing', the first law re-written to better parallel the existing 'Law of Gearing" as pioneered by Leonard Euler, expanded from Euler's original law to encompass non-circular gears and hypoid gears, the 2nd law of gearing describing a unique relat
DEFF Research Database (Denmark)
Byg din egen boomerang, kast den, se den flyve, forstå hvorfor og hvordan den vender tilbage, og grib den. Det handler om opdriften på vingerne når du flyver, men det handler også og allermest om den mærkværdige gyroskop-effekt, du bruger til at holde balancen, når du kører på cykel. Vi vil bruge...... matematik, geometri, og fysik til at forstå, hvad det er, der foregår....
Almendros, J.; University of Granada, Spain; Ibanez, J.; University of Granada, Spain; Alguacil, G.; University of Granada, Spain; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia
1999-01-01
The zero-lag cross-correlation technique, used for array analysis in the hypothesis of plane waves, has been modified to allow the wave front to be circular. Synthetic tests have been performed to check the capability of the method
Dropwise Condensation on Hydrophobic Cylinders
Park, Kyoo-Chul; Hoang, Michelle; McManus, Brendan; Aizenberg, Joanna
2016-01-01
In this work, we studied the effect of the diameter of horizontal hydrophobic cylinders on droplet growth. We postulate that the concentration gradient created by natural convection around a horizontal circular cylinder is related to the droplet growth on the cylinder by condensation. We derive a simple scaling law of droplet growth and compare it with experimental results. The predicted negative exponent of drop diameter (d) as a function of cylinder diameter (D) at different time points is similar to the general trend of experimental data. Further, this effect of cylinder diameter on droplet growth is observed to be stronger than the supersaturation conditions created by different surface temperatures.
Scattering by a nihility cylinder
Lakhtakia, A
2006-01-01
The total scattering and the extinction efficiencies of a nihility cylinder of infinite length and circular cross--section are identical and independent of the polarization state of a normally incident plane wave.
Energy Technology Data Exchange (ETDEWEB)
Kano, I. [Yamagata University, Yamagata (Japan). Faculty of Engineering
2000-01-25
The flow around a rotating circular cylinder that is close to a moving plate has been investigated numerically and experimentally for the high Reynolds number (Re=3.3 x 10{sup 4}-5 x 10{sup 4}). Two different flow patterns were observed under the same conditions by changing peripheral velocity of the circular cylinder. The transition of the flow pattern occurs when the jet through a small gap (H/D =0.1) switches from the moving plate to the cylinder wall. This phenomenon is known as some kind of the Coanda effect. Furthermore the Coanda effect was accompanied by hysteretic effect. Computation of the two-dimensional unsteady Navier-Stokes equations was also conducted. The numerical results qualitatively agreed with the experimental ones. It was found that the Coanda effect and the hysteretic phenomenon were greatly related to the standing vortex that exists behind the cylinder. (author)
Sub-wavelength resonances in polygonal metamaterial cylinders
DEFF Research Database (Denmark)
Arslanagic, Samel; Breinbjerg, Olav
It has been shown that the sub-wavelength resonances of circular MTM cylinders also occur for polygonal MTM cylinders. This is the case for lossless and non-dispersive cylinders as well as lossy and dispersive cylinders. The sub-wavelength resonances are thus not limited to structures of canonical...
Vortex-Induced Vibration (VIV) Reduction Properties of Seal Whisker-Like Geometries
Hans, Hendrik; Miao, Jianmin; Triantafyllou, Michael
2013-11-01
Biological studies have shown that harbor seal whiskers are capable of reducing Vortex-Induced Vibrations (VIV). As the whiskers have convoluted geometry, it is necessary to evaluate the parameters that define their VIV reduction properties. Whisker-Like Geometries (WLGs) consisting of all but one feature on the true whisker geometry are designed. Comparison of VIV on these WLGs with VIV on circular and elliptical cylinders at Re = 500 is performed. Three-dimensional simulations of flow past these geometries, which are allowed to freely vibrate in crossflow, are performed with the Implicit Large Eddy Simulation as the turbulence model. The results indicate that the existence of axial undulations is the most dominant feature that affects the VIV reduction. The smallest VIV is observed on WLGs with dual-axial undulations and the largest VIV is observed on the circular cylinder. Variations in the features of the WLGs result in noticeable changes in their VIV. The circular cylinder is observed to response as a steady system while the WLGs with dual-axial undulations are observed to respond as a chaotic system. The response of WLGs with single-axial undulations is found to depend on their detailed features. I would like to acknowledge the support and funding from National Research Foundation (NRF) through CENSAM of Singapore-MIT Alliance for Research and Technology and Nanyang Technological University.
Stress analysis of cylinder to cylinder intersections
International Nuclear Information System (INIS)
Cylinder to cylinder intersections have numerous applications in the power industry from different piping junctions to pressure vessel nozzles. A specific purpose computer program has been installed at the author's establishment for finite element analysis of such geometries. Some of the experiences are presented giving a short overview of the analysis of unreinforced man-holes, demonstrating how a more economical design has been verified by analysis. The program installed has linear-elastic and elasto-plastic capabilities. Further, it is prepared for heat transfer analysis with subsequent thermal stress computation. An efficient pre- and post-processor has also been installed and enhanced by the author. The software used is at its present stage capable for problem definition with input data such as outside/ inside diameters, length and number of subdivisions. Similarly simple is the load definition and the graphic representation of the full output. (author)
Electromagnetic Wave Scattering By the Coated Impedance Cylinder
Directory of Open Access Journals (Sweden)
V.I. Vyunnik
2010-01-01
Full Text Available In this work the boundary conditions for the impedance circular cylinder coated by a low contrast dielectric thin layer are derived. Expression for the reduced impedance of the cylinder is obtained. Conditions and applicability limits of the proposed approach are defined. Influence of the coating impedance on the reduced impedance of the cylinder is investigated.
International Nuclear Information System (INIS)
We investigate the electromagnetic fields and the radiation intensity for a charged particle moving along an arbitrary closed orbit around a dielectric cylinder immersed into a homogeneous medium. These results generalize our previous research in the special case of a circular orbit. For the latter geometry it has been shown that under certain conditions strong narrow peaks appear in the angular distribution of the radiation intensity in the exterior medium. We discuss the influence of the trajectory shift from the circular one on the characteristics of the peaks.
Département des Ressources humaines
2004-01-01
Administrative Circular N° 2 (Rev. 2) - May 2004 Guidelines and procedures concerning recruitment and probation period of staff members This circular has been revised. It cancels and replaces Administrative Circular N° 2 (Rev. 1) - March 2000. Administrative Circular N° 9 (Rev. 3) - May 2004 Staff members contracts This circular has been revised. It cancels and replaces Administrative Circular N° 9 (Rev. 2) - March 2000. Administrative Circular N° 26 (Rev. 4) - May 2004 Procedure governing the career evolution of staff members This circular has also been revised. It Administrative Circulars Administrative Circular N° 26 (Rev. 3) - December 2001 and brings up to date the French version (Rev. 4) published on the HR Department Web site in January 2004. Operational Circular N° 7 - May 2004 Work from home This circular has been drawn up. Operational Circular N° 8 - May 2004 Dealing with alcohol-related problems...
Casimir force between eccentric cylinders
Dalvit, Diego A. R.; Lombardo, Fernando C.; Mazzitelli, Francisco D.; Onofrio, Roberto
2004-01-01
We consider the Casimir interaction between a cylinder and a hollow cylinder, both conducting, with parallel axis and slightly different radii. The Casimir force, which vanishes in the coaxial situation, is evaluated for both small and large eccentricities using the proximity approximation. The cylindrical configuration offers various experimental advantages with respect to the parallel planes or the plane-sphere geometries, leading to favourable conditions for the search of extra-gravitation...
Optimization of compound pressure cylinders
G.H. Majzoobi; A. Ghomi
2006-01-01
Purpose: The purpose of this paper is optimization of the weight of compound cylinder for a specific pressure. The variables are shrinkage radius and shrinkage tolerance.Design/methodology/approach: SEQ technique for optimization, the finite element code, ANSYS for numerical simulation are employed to predict the optimized conditions. The results are verified by testing a number of closed end cylinders with various geometries, materials and internal pressures.Findings: The weight of a compoun...
WHIPPO. WALTER B.; Rohrkaste, G. R.; Miller, John E.
1989-01-01
Shape gauge and associated computer constitute system measuring deviations of large cylinders from roundness. Shaped and held somewhat like crossbow, measures relative locations of three points on surface of large, round object. By making connected series of measurements around periphery technician using gauge determines deviation of object from perfect circularity. Used to measure straightness, roundness, or complicated shapes of such large geometrical objects as surfaces of aircraft and hulls of ships.
Sub-wavelength resonances in polygonal metamaterial cylinders
Arslanagic, Samel; Breinbjerg, Olav
2008-01-01
It has been shown that the sub-wavelength resonances of circular MTM cylinders also occur for polygonal MTM cylinders. This is the case for lossless and non-dispersive cylinders as well as lossy and dispersive cylinders. The sub-wavelength resonances are thus not limited to structures of canonical shapes but occurs also for other shapes and they are determined more by the material parameters than the geometrical parameters.
Flow-induced vibration of circular cylindrical structures
Energy Technology Data Exchange (ETDEWEB)
Chen, S.S.
1985-06-01
This report summarizes the flow-induced vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders. 219 figs., 30 tabs. (JDB)
Flow-induced vibration of circular cylindrical structures
International Nuclear Information System (INIS)
This report summarizes the flow-induced vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders. 219 figs., 30 tabs
Oscillatory motion of a viscous fluid in a gap between vibrating cylinders
Energy Technology Data Exchange (ETDEWEB)
Chechko, G.A.; Khodakovskii, N.I.; Sklepovoi, V.N. [Cybernetics Institute, Kiev (Ukraine)
1994-06-05
We investigate the achievement of intensive periodic vortical motion between two quasiconcentric cylinders of circular cross section, undergoing periodic oscillations with integral frequencies about a motionless axis parallel to the axes of the cylinders. 3 refs., 2 figs.
Local buckling in cylinders with stringer stiffened
International Nuclear Information System (INIS)
Some results of a nonlinear analysis of the local elastic stability in uniform axially compressed stringer - stiffened circular cylinders are presented. The possibility to occur bifurcation loads due to anti-symetrical secundary mode are analyzed. The utilization of stringer stiffened as suggested by the ortotropic theory, can lead to the interaction between local and global deformation mode, resulting in primary bifurcation loads lower than the classical critical load of the isotropic cylinder. (E.G.)
Suppression of Brazier Effect in Multilayered Cylinders
Hiroyuki Shima; Motohiro Sato; Sung-Jin Park
2014-01-01
When a straight hollow tube having circular cross-section is bent uniformly into an arc, the cross-section tends to ovalize or flatten due to the in-plane stresses induced by bending; this ovalization phenomenon is called the Brazier effect. The present paper is aimed at theoretical formulation of the Brazier effect observed in multilayered cylinders, in which a set of thin hollow cylinders are stacked concentrically about the common axis. The results indicate that mechanical couplings betwee...
Institute of Scientific and Technical Information of China (English)
张月婷; 陈红珍; 丁赤飚; 王宏琦
2012-01-01
结合多径散射理论和雷达成像原理,针对圆柱型固定顶油罐和浮动顶油罐的SAR图像的多径散射提出了一种预测模型,该预测模型建立了多径散射机制引起的图像上的近似聚焦位置、强度与油罐、雷达相关参数的关系.同时,结合仿真实验和Terra-SAR图像验证了该模型的有效性,分析了油罐目标的多径特征,并针对Terra-SAR图像利用基于模型的方法有效提取了油罐目标的几何参数.结果和分析表明,该方法比传统的方法在精度、稳定性上均有所提高.%Combining scattering theory and principle of SAR, a novel prediction model is proposed based on the multi-path scattering characteristics in the SAR image of cylinder tanks, for both the fixed and the floating top styles. The model can provide the relationship between the geometry parameters of the tank, the SAR parameters, the approximated position, and the scatting strength of the bright region in the SAR image. The validity of this model is proved by analyzing the Terra-SAR data and simulation experiments. Furthermore, geometry extraction is successfully implemented on the Terra-SAR data. The results show that the model is better than traditional methods in precision and stability.
Geometry essentials for dummies
Ryan, Mark
2011-01-01
Just the critical concepts you need to score high in geometry This practical, friendly guide focuses on critical concepts taught in a typical geometry course, from the properties of triangles, parallelograms, circles, and cylinders, to the skills and strategies you need to write geometry proofs. Geometry Essentials For Dummies is perfect for cramming or doing homework, or as a reference for parents helping kids study for exams. Get down to the basics - get a handle on the basics of geometry, from lines, segments, and angles, to vertices, altitudes, and diagonals Conque
Energy Technology Data Exchange (ETDEWEB)
Kano, I.; Yagita, M.; Jia, W. [Yamagata University, Yamagata (Japan). Faculty of Engineering; Iwata, M. [Kawasaki Heavy Industries, Ltd., Kobe (Japan)
2000-01-25
The flow around a rotating circular cylinder placed at various heights above a moving plate has been investigated numerically and experimentally for the high Reynolds number (Re=3.3 x 10{sup 4}-6.6 x 10{sup 4}). The flow was affected considerably by the boundary layer on the moving plate and the initial conditions of the experiment. Starting from different initial conditions, two different flow patterns were observed for small gaps (0.03{<=}H/D{<=}0.12) under the same experimental conditions. The transition of the flow pattern occurs when the jet through the gap switches from the moving plate to the cylinder wall. This phenomenon is known as some kind of the Coanda effect. Computation of the two-dimensional unsteady Navier-Stokes equations was also conducted. The numerical results qualitatively agreed with the experimental ones. The standing vortex was found at 2.5 diameters behind the cylinder in the case of Coanda effect. (author)
International Nuclear Information System (INIS)
We measured circular dichroism in resonant x-ray scattering 3dn→2p53dn+1→3s13dn+1 with incidence perpendicular to the magnetization where the absorption dichroism vanishes. The advantages of photon scattering over other techniques make it possible to study a wide range of materials. The Ni L3 dichroism in NiFe2O 4 is (28±5)% in agreement with a localized model. In the metal Co the dichroism is reduced to (10.4±1)% (L3) and (6.8±1.5)% (7.5 eV above L3 ), indicating a large sensitivity to the nature of the valence states despite the fact that this spectroscopy is based on inner shell transitions. copyright 1999 The American Physical Society
Effect of Surface Coatings on Cylinders Exposed to Underwater Shock
Kwon, Y.W.; J.K. Bergersen; Shin, Y.S.
1994-01-01
The response of a coated cylinder (metallic cylinder coated with a rubber material) subjected to an underwater explosion is analyzed numerically. The dynamic response of the coated cylinder appears to be adversely affected when impacted by an underwater shock wave under certain conditions of geometry and material properties of the coating. When adversely affected, significant deviations in values of axial stress, hoop stress, and strain are observed. The coated cylinder exhibits a larger defo...
Effect of surface coating on cylinders subjected to underwater shock
Bergersen, John K.
1992-01-01
Approved for public release, distribution unlimited The response of a composite cylinder (metallic cylinder coated with a rubber material) subjected to an underwater explosion was analyzed numerically. Qualitative differences between coated and uncoated cylinders were investigated. The dynamic response of the coated cylinder was found to be adversely affected when impacted by an underwater shock wave under certain conditions of geometry and material properties of the coating. When adversel...
Analysis of fatigue life for tube trailer cylinders
Xinqi YU; Bolong SONG; Zhang, Zhao; Qinggang LIU
2015-01-01
Risk of fatigue failure exists in the tube trailer cylinders under the condition of internal pressure variation and inertial load caused through road transport. In order to estimate the safety state of the cylinders under the action of alternating load, the model of certain geometry sizes is built based on the widely used tube trailer cylinders. The fatigue analysis of tube trailer gas cylinders is made aiming at the action of the internal pressure and the inertial load. The fatigue life dist...
Davies, J. A.; Perry, C. H.; Trines, R. M. G. M.; Harrison, R. A.; Lugaz, N.; Möstl, C.; Liu, Y. D.; Steed, K.
2013-11-01
The twin-spacecraft STEREO mission has enabled simultaneous white-light imaging of the solar corona and inner heliosphere from multiple vantage points. This has led to the development of numerous stereoscopic techniques to investigate the three-dimensional structure and kinematics of solar wind transients such as coronal mass ejections (CMEs). Two such methods—triangulation and the tangent to a sphere—can be used to determine time profiles of the propagation direction and radial distance (and thereby radial speed) of a solar wind transient as it travels through the inner heliosphere, based on its time-elongation profile viewed by two observers. These techniques are founded on the assumption that the transient can be characterized as a point source (fixed phi, FP, approximation) or a circle attached to Sun-center (harmonic mean, HM, approximation), respectively. These geometries constitute extreme descriptions of solar wind transients, in terms of their cross-sectional extent. Here, we present the stereoscopic expressions necessary to derive propagation direction and radial distance/speed profiles of such transients based on the more generalized self-similar expansion (SSE) geometry, for which the FP and HM geometries form the limiting cases; our implementation of these equations is termed the stereoscopic SSE method. We apply the technique to two Earth-directed CMEs from different phases of the STEREO mission, the well-studied event of 2008 December and a more recent event from 2012 March. The latter CME was fast, with an initial speed exceeding 2000 km s-1, and highly geoeffective, in stark contrast to the slow and ineffectual 2008 December CME.
Circular chemiresistors for microchemical sensors
Ho, Clifford K.
2007-03-13
A circular chemiresistor for use in microchemical sensors. A pair of electrodes is fabricated on an electrically insulating substrate. The pattern of electrodes is arranged in a circle-filling geometry, such as a concentric, dual-track spiral design, or a circular interdigitated design. A drop of a chemically sensitive polymer (i.e., chemiresistive ink) is deposited on the insulating substrate on the electrodes, which spreads out into a thin, circular disk contacting the pair of electrodes. This circularly-shaped electrode geometry maximizes the contact area between the pair of electrodes and the polymer deposit, which provides a lower and more stable baseline resistance than with linear-trace designs. The circularly-shaped electrode pattern also serves to minimize batch-to-batch variations in the baseline resistance due to non-uniform distributions of conductive particles in the chemiresistive polymer film.
Topology of vortex creation in the cylinder wake
DEFF Research Database (Denmark)
Brøns, Morten; Bisgaard, Anders Villefrance
We analyze the topology of the two-dimensional flow around a circular cylinder at moderate Reynolds numbers in the regime where the vortex wake is created. A normal form for the stream function close to the cylinder is presented and used to predict the streamline pattern both in the steady and the...
Flow-induced vibrations of a rotating cylinder
Bourguet, Rémi; Lo Jacono, David
2014-01-01
International audience The flow-induced vibrations of a circular cylinder, free to oscillate in the cross-flow direction and subjected to a forced rotation about its axis, are analysed by means of two- and three-dimensional numerical simulations. The impact of the symmetry breaking caused by the forced rotation on the vortex-induced vibration (VIV) mechanisms is investigated for a Reynolds number equal to 100, based on the cylinder diameter and inflow velocity. The cylinder is found to osc...
International Nuclear Information System (INIS)
Information circulars are published from time to time under the symbol INFCIRC/. . . . for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A list of the circulars which were of current interest on 15 January 1969 is given below, followed by an index to their subject matter. Other circulars can be traced by reference to earlier issues of the present document.
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Eggen, Svein; Kjær, Erik Michael
2001-01-01
The bubble inflation technique has been used for some time as a rheological characterization method for polymeric materials. Recently, this technique has been modified to the inflation of a polymeric sheet into a circular cylinder. In this work, the experimental inflation of sheets (or membranes......) of polymeric melts into a circular cylinder is modelled numerically to obtain the general extensional properties of the material....
International Nuclear Information System (INIS)
Information circulars are published from time to time under the symbol INFCIRC/... for the purpose of bringing matters of general interest to the attention of all Members of the Agency. The present revision contains INFCIRCs published up to mid-August 1994. A complete numerical list of information circulars is reproduced with their titles in the Annex
International Nuclear Information System (INIS)
The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Members of the Agency. This revision contains INFCIRCs published up to mid-August 1992. A complete numerical lift of Information Circulars with their titles is reproduced in an Annex
International Nuclear Information System (INIS)
The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Member States. This revision contains INFCIRCs published up to the end of May 1999, grouped by field of activity. A complete list of information circulars in numerical order is given in an annex
International Nuclear Information System (INIS)
Information circulars are published from time to time under the symbol INFCIRC/. for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A list of the circulars that were current on 31 December 1964 is given, followed by an index to their subject matter.
International Nuclear Information System (INIS)
The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Member States. This revision contains INFCIRCs published up to February 1997, grouped by field of activity. A complete list of information circulars in numerical order is given in an annex
International Nuclear Information System (INIS)
Information circulars are published from time to time under the symbol INFCIRC/... for the purpose of bringing matters of general interest to the attention of all Members of the Agency. The present revision contains INFCIRCs published up to the end of April 2002. A complete numerical list of information circulars is reproduced with their titles in the Annex
Optical absorption for parallel cylinder arrays
Robles, P; Rojas, R.; Claro, F.
2001-01-01
We study the long wavelength electromagnetic resonances of interacting cylinder arrays. By using a normal modes expansion where the effects of geometry and material are separated, it is shown that two parallel cylinders with different radii have electromagnetic modes distributed symmetrically about depolarization factor 1/2. Both sets couple to longitudinal and transverse components of the external field, but amplitudes of symmetric depolarization factors become exchanged when considering lon...
Mitri, F. G.
2016-07-01
This paper presents two key contributions; the first concerns the development of analytical expressions for the axial and transverse acoustic radiation forces exerted on a 2D rigid elliptical cylinder placed in the field of plane progressive, quasi-standing, or standing waves with arbitrary incidence. The second emphasis is on the acoustic radiation torque per length. The rigid elliptical cylinder case is important to be considered as a first-order approximation of the behavior of a cylindrical fluid column trapped in air because of the significant acoustic impedance mismatch at the particle boundary. Based on the rigorous partial-wave series expansion method in cylindrical coordinates, non-dimensional acoustic radiation force and torque functions are derived and defined in terms of the scattering coefficients of the elliptic cylinder. A coupled system of linear equations is obtained after applying the Neumann boundary condition for an immovable surface in a non-viscous fluid and solved numerically by matrix inversion after performing a single numerical integration procedure. Computational results for the non-dimensional force components and torque, showing the transition from the progressive to the (equi-amplitude) standing wave behavior, are performed with particular emphasis on the aspect ratio a/b, where a and b are the semi-axes of the ellipse, the dimensionless size parameter, as well as the angle of incidence ranging from end-on to broadside incidence. The results show that the elliptical geometry has a direct influence on the radiation force and torque, so that the standard theory for circular cylinders (at normal incidence) leads to significant miscalculations when the cylinder cross section becomes non-circular. Moreover, the elliptical cylinder experiences, in addition to the acoustic radiation force, a radiation torque that vanishes for the circular cylinder case. The application of the formalism presented here may be extended to other 2D surfaces of
Free vibrations of circular cylindrical shells
Armenàkas, Anthony E; Herrmann, George
2013-01-01
Free Vibrations of Circular Cylindrical Shells deals with thin-walled structures that undergo dynamic loads application, thereby resulting in some vibrations. Part I discusses the treatment of problems associated with the propagation of plane harmonic waves in a hollow circular cylinder. In such search for solutions, the text employs the framework of the three-dimensional theory of elasticity. The text explains the use of tables of natural frequencies and graphs of representative mode shapes of harmonic elastic waves bounding in an infinitely long isotropic hollow cylinder. The tables are
The flow past a cactus-inspired grooved cylinder
El-Makdah, Adnan M.; Oweis, Ghanem F.
2013-02-01
The star-shaped cross section of giant cylindrical cactus plants is thought to be aerodynamically favorable for protection against toppling by strong winds. Particle image velocimetry is used to investigate the flow details within the surface grooves and in the immediate wake of a cactus-inspired model cylinder with eight longitudinal grooves, at biologically relevant Reynolds numbers between 50 × 103 and 170 × 103. The wake flow is analyzed and compared to a similarly sized circular cylinder. At the lowest Re tested, the wakes from the two geometries are similar. At higher Re, the cactus wake exhibits superior behavior as seen from the mean and turbulent velocities, suggesting that the flow mechanisms are Re dependent. The flow within the surface grooves reveals counter rotating rollers, while the geometrical ridges act as vortex generators known to help with the surface flow attachment. Lastly, a simplistic analysis is described to recover, qualitatively, certain time-dependent flow features from the randomly acquired PIV realizations.
Numerical Investigation of 3D Flow Around Two Tandem Cylinders
Kalvig, Ragnhild Birgitte Hidle
2015-01-01
Circular cylinders in tandem arrangement are used in many marine applications like dual pipelines and dual risers. Turbulent flow in 3D around two tandem cylinders is simulated numerically using Large Eddy Simulation (LES) with a Smagorinsky subgrid scale model. The Reynolds number based on the cylinder diameter of 1 meter and free stream velocity of $U=1.31$ m/s is 13100, which is in the subcritical flow regime. The center-to-center spacing between the cylinders is $S/D=5$. The software used...
National Oceanic and Atmospheric Administration, Department of Commerce — Circular Updates are periodic sequentially numbered instructions to debriefing staff and observers informing them of changes or additions to scientific and specimen...
International Nuclear Information System (INIS)
The document summarizes the information circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Members of the Agency. In the main body of the document only those documents which are regarded as likely to be of current interest are listed. A complete numerical list of information circulars with their titles is reproduced in the Annex
Flow characteristics of the two tandem wavy cylinders and drag reduction phe-nomenon
Institute of Scientific and Technical Information of China (English)
邹琳; 郭丛波; 熊灿
2013-01-01
This paper presents an extensive numerical study of 3-D laminar flow around two wavy cylinders in the tandem arrangement for spacing ratios (L/Dm ) ranging from 1.5 to 5.5 at a low Reynolds number of 100. The investigation focuses on the effects of spacing ratio (L/Dm ) and wavy surface on the 3-D near wake flow patterns, the force and pressure coefficients and the vortex shedding frequency for the two tandem wavy cylinders. Flows around the two tandem circular cylinders are also obtained for comparison. With the spacing ratio in the range of L/Dm=1.5-5.5 , unlike two tandem circular cylinders, the wavy cylinders in the tandem arrangement do not have the wake interference behaviour of three basic types. The vortex shedding behind the upstream wavy cylinder occurs at a further downstream position as compared with that of the upstream circular cylinder. This leads to the weakening of the effect of the vibration of the cylinders as well as a distinct drag reduction. The effects of the drag reduction and the control of the vibration of the two wavy cylinders in tandem become more and more evident when L/Dm³4.0, with a distinct vortex shedding in the upstream cylinder regime for the two circular cylinders in tandem.
Modelling functional effects of muscle geometry.
van der Linden, B J; Koopman, H F; Grootenboer, H J; Huijing, P A
1998-04-01
Muscle architecture is an important aspect of muscle functioning. Hence, geometry and material properties of muscle have great influence on the force-length characteristics of muscle. We compared experimental results for the gastrocnemius medialis muscle (GM) of the rat to model results of simple geometric models such as a planimetric model and three-dimensional versions of this model. The capabilities of such models to adequately calculate muscle geometry and force-length characteristics were investigated. The planimetric model with elastic aponeurosis predicted GM muscle geometry well: maximal differences are 6, 1, 4 and 6% for fiber length, aponeurosis length, fiber angle and aponeurosis angle respectively. A slanted cylinder model with circular fiber cross-section did not predict muscle geometry as well as the planimetric model, whereas the geometry results of a second slanted cylinder model were identical to the planimetric model. It is concluded that the planimetric model is capable of adequately calculating the muscle geometry over the muscle length range studied. However, for modelling of force-length characteristics more complex models are needed, as none of the models yielded results sufficiently close to experimental data. Modelled force-length characteristics showed an overestimation of muscle optimum length by 2 mm with respect to experimental data, and the force at the ascending limb of the length force curve was underestimated. The models presented neglect important aspects such as non-linear geometry of muscle, certain passive material properties and mechanical interactions of fibers. These aspects may be responsible for short-comings in the modelling. It is argued that, considering the inability to adequately model muscle length-force characteristics for an isolated maximally activated (in situ) muscle, it is to be expected that prediction will fail for muscle properties in conditions of complex movement with many interacting factors. Therefore
Tailoring Effective Media by Mie Resonances of Radially-Anisotropic Cylinders
Henrik Kettunen; Henrik Wallén; Ari Sihvola
2015-01-01
This paper studies constructing advanced effective materials using arrays of circular radially-anisotropic (RA) cylinders. Homogenization of such cylinders is considered in an electrodynamic case based on Mie scattering theory. The homogenization procedure consists of two steps. First, we present an effectively isotropic model for individual cylinders, and second, we discuss the modeling of a lattice of RA cylinders. Radial anisotropy brings us extra parameters, which makes it possible to adj...
Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters
WANG, YONG-TAO; Zhong-min YAN; Wang, Hui-Min
2013-01-01
The flow past two tandem circular cylinders of different diameters was simulated using the ?nite volume method. The diameter of the downstream main cylinder (D) was kept constant, and the diameter of the upstream control cylinder (d) varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder (G) ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio (G/D)...
International Nuclear Information System (INIS)
Theoretical description of the wave propagation in an elliptical cylinder multilayer structure under the conditions of H polarization and E polarization is presented. A transfer matrix method has been developed for elliptical cylinder waves. The formulas of reflection and transmission coefficients for an elliptical cylinder multilayer structure are driven. Reflection and transmission coefficients of elliptical cylinder waves by a single elliptical cylinder interface is presented. The obtained formulas can be generalized to the cold plasma filled structures and thus the obtained results in the limit of circular cylinder structures are investigated
Spinning geometry = Twisted geometry
International Nuclear Information System (INIS)
It is well known that the SU(2)-gauge invariant phase space of loop gravity can be represented in terms of twisted geometries. These are piecewise-linear-flat geometries obtained by gluing together polyhedra, but the resulting geometries are not continuous across the faces. Here we show that this phase space can also be represented by continuous, piecewise-flat three-geometries called spinning geometries. These are composed of metric-flat three-cells glued together consistently. The geometry of each cell and the manner in which they are glued is compatible with the choice of fluxes and holonomies. We first remark that the fluxes provide each edge with an angular momentum. By studying the piecewise-flat geometries which minimize edge lengths, we show that these angular momenta can be literally interpreted as the spin of the edges: the geometries of all edges are necessarily helices. We also show that the compatibility of the gluing maps with the holonomy data results in the same conclusion. This shows that a spinning geometry represents a way to glue together the three-cells of a twisted geometry to form a continuous geometry which represents a point in the loop gravity phase space. (paper)
2003-01-01
Operational Circular N° 4 - April 2003 Conditions for use by members of the CERN personnel of vehicles belonging to or rented by CERN - This circular has been drawn up. Operational Circular N° 5 - October 2000 Use of CERN computing facilities - Further details on the personal use of CERN computing facilities Operational Circular N° 5 and its Subsidiary Rules http://cern.ch/ComputingRules defines the rules for the use of CERN computing facilities. One of the basic principles governing such use is that it must come within the professional duties of the user concerned, as defined by the user's divisional hierarchy. However, personal use of the computing facilities is tolerated or allowed provided : a) It is in compliance with Operational Circular N° 5 and not detrimental to official duties, including those of other users; b) the frequency and duration is limited and there is a negligible use of CERN resources; c) it does not constitute a political, commercial and/or profit-making activity; d) it is not...
Application of circular filter inserts
International Nuclear Information System (INIS)
High efficiency particulate air (HEPA) filters are used in the ventilation of nuclear plant as passive clean-up devices. Traditionally, the work-horse of the industry has been the rectangular HEPA filter. An assessment of the problems associated with remote handling, changing, and disposal of these rectangular filters suggested that significant advantages to filtration systems could be obtained by the adoption of HEPA filters with circular geometry for both new and existing ventilation plants. This paper covers the development of circular geometry filters and highlights the advantages of this design over their rectangular counterparts. The work has resulted in a range of commercially available filters for flows from 45 m3/h up to 3400 m3/h. This paper also covers the development of a range of sizes and types of housings that employ simple change techniques which take advantage of the circular geometry. The systems considered here have been designed in response to the requirements for shielded (remote filter change) and for unshielded facilities (potentially for bag changing of filters). Additionally the designs have allowed for the possibility of retrofitting circular geometry HEPA filters in place of the rectangular geometry filter
A Forced System of Two Cylinders with Various Spacings
Institute of Scientific and Technical Information of China (English)
邹建锋; 任安禄; 邓见
2004-01-01
The spectrum characteristics and wake structures for a circular cylinder oscillating in a wake are investigated by use of the currently modified virtual boundary method. A forced system of two cylinders with a small spacing (the downstream one is made to oscillate in the transverse direction) is studied and interesting flow characteristics are observed. A vortex switch and the change of vortex modes (between 2S mode and 2P mode) are observed in the "lock-in" region. Vortex bands are formed and lost with the increasing excitation frequency. Information concerning saddle points in the flow field is obtained for different excitation frequencies. For a forced system of two cylinders with a large spacing, the upstream cylinder sheds vortexes because there is no downstream cylinder oscillating in the wake. No distinct "lock-in" response is found for the downstream cylinder.
Age-related changes in chest geometry during cardiopulmonary resuscitation.
Dean, J M; Koehler, R C; Schleien, C L; Michael, J R; Chantarojanasiri, T; Rogers, M C; Traystman, R J
1987-06-01
We studied alterations of chest geometry during conventional cardiopulmonary resuscitation in anesthetized immature swine. Pulsatile force was applied to the sternum in increments to determine the effects of increasing compression on chest geometry and intrathoracic vascular pressures. In 2-wk- and 1-mo-old piglets, permanent changes in chest shape developed due to incomplete recoil of the chest along the anteroposterior axis, and large intrathoracic vascular pressures were generated. In 3-mo-old animals, permanent chest deformity did not develop, and large intrathoracic vascular pressures were not produced. We propose a theoretical model of the chest as an elliptic cylinder. Pulsatile displacement along the minor axis of an ellipse produces a greater decrease in cross-sectional area than displacement of a circular cross section. As thoracic cross section became less circular due to deformity, greater changes in thoracic volume, and hence pressure, were produced. With extreme deformity at high force, pulsatile displacement became limited, diminishing pressure generation. We conclude that changes in chest geometry are important in producing intrathoracic intravascular pressure during conventional cardiopulmonary resuscitation in piglets. PMID:3610916
Analysis of fatigue life for tube trailer cylinders
Directory of Open Access Journals (Sweden)
Xinqi YU
2015-08-01
Full Text Available Risk of fatigue failure exists in the tube trailer cylinders under the condition of internal pressure variation and inertial load caused through road transport. In order to estimate the safety state of the cylinders under the action of alternating load, the model of certain geometry sizes is built based on the widely used tube trailer cylinders. The fatigue analysis of tube trailer gas cylinders is made aiming at the action of the internal pressure and the inertial load. The fatigue life distribution of cylinders is obtained under the condition of different loads through the numerical simulation by ANSYS Workbench. The analysis results show that under internal pressure, gas cylinders have limited fatigue life, but can satisfy the requirements; when the inertial load exceeds a certain value, natural gas cylinders of tube trailer is under finite life state, which does not meet the requirements of strength, therefore the inertial load should be controlled.
Directory of Open Access Journals (Sweden)
Prasenjit Dey
2016-01-01
Full Text Available An unsteady two-dimensional forced convection over a square cylinder with sharp and rounded corner edge is numerically analyzed for the low Reynolds number laminar flow regime. In this study, the analysis is carried out for Reynolds number (Re in the range of 80 to 180 with Prandtl number (Pr variation from 0.01 to 1000 for various corner radius (r=0.50, 0.51, 0.54, 0.59, 0.64 and 0.71. The lateral sides of the computational domain are kept constant to maintain the blockage as 5%. Heat transfer due to unsteady forced convection has been predicted by Artificial Neural network (ANN. The present ANN is trained by the input and output data which has been acquired from the numerical simulation, performed in finite volume based Computational Fluid Dynamics (CFD commercial software FLUENT. The heat transfer characteristics over the sharp and rounded corner square cylinder are evaluated by analyzing the local Nusselt number (Nulocal, average Nusselt number (Nuavg at various Reynolds number, Prandtl numbers and for various corner radii. It is found that the heat transfer rate of a circular cylinder can be enhanced by 12% when Re is varying and 14% when Prandtl number is varying by introducing a new cylinder geometry of corner radius r=0.51. It is found that the unsteady forced convection heat transfer over a cylinder can be predicted appropriately by ANN. It is also observed that the back propagation ANN can predict the heat transfer characteristics of forced convection very quickly compared to a standard CFD method.
Modeling Heat and Mass Transfer from Fabric-Covered Cylinders
Phillip Gibson
2009-01-01
Fabric-covered cylinders are convenient analogs forclothing systems. The geometry is well defined andincludes many of the effects that are important ingarments. Fabric-covered cylinder models are usedin conjunction with laboratory measurements ofmaterial properties to calculate heat and mass transferproperties of clothing under specific conditions ofenvironmental wind speed, temperature, and relativehumidity.
Modeling Heat and Mass Transfer from Fabric-Covered Cylinders
Directory of Open Access Journals (Sweden)
Phillip Gibson
2009-03-01
Full Text Available Fabric-covered cylinders are convenient analogs forclothing systems. The geometry is well defined andincludes many of the effects that are important ingarments. Fabric-covered cylinder models are usedin conjunction with laboratory measurements ofmaterial properties to calculate heat and mass transferproperties of clothing under specific conditions ofenvironmental wind speed, temperature, and relativehumidity.
Evaluation of Cylinder Volume Estimation Methods for In–Cylinder Pressure Trace Analysis
Adrian Irimescu
2012-01-01
In–cylinder pressure trace analysis is an important investigation tool frequently employed in the study of internal combustion engines. While technical data is usually available for experimental engines, in some cases measurements are performed on automotive engines for which only the most basic geometry features are available. Therefore, several authors aimed to determine the cylinder volume and length of the connecting rod by other methods than direct measurement. This stu...
Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters
Directory of Open Access Journals (Sweden)
Yong-tao WANG
2013-10-01
Full Text Available The flow past two tandem circular cylinders of different diameters was simulated using the ?nite volume method. The diameter of the downstream main cylinder (D was kept constant, and the diameter of the upstream control cylinder (d varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder (G ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio (G/D and the diameter ratio between the two cylinders (d/D have important effects on the drag and lift coef?cients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and ?ow characteristics.
International Nuclear Information System (INIS)
The document summarizes the Information Circulars published by the IAEA under the symbol INFCIRC/ for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A complete list of INFCIRCs in numerical order with their titles is given in the Annex
Energy Technology Data Exchange (ETDEWEB)
Daichin, Sang Joon Lee [Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, 790-784, Nam-gu, Pohang (Korea)
2004-05-01
The flow fields behind elliptic cylinders adjacent to a free surface were investigated experimentally in a circulating water channel. A range of cylinder aspect ratios (AR=2, 3, 4) were considered, while the cross-sectional area of the elliptical cylinder was kept constant. The main objective of this study was to investigate the effect of cylinder aspect ratio and a free surface on the flow structure in the near-wake behind elliptic cylinders. For each elliptic cylinder, the flow structure was analyzed for various values of the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV (Particle Image Velocimetry) system. For each experimental condition, 350 instantaneous velocity fields were obtained and ensemble-averaged to obtain the mean velocity field and spatial distribution of the mean vorticity statistics. The results show that near-wake can be classified into three typical flow patterns: formation of a Coanda flow, generation of substantial jet-like flow, and attachment of this jet flow to the free surface. The general flow structure observed behind the elliptic cylinders resembles the structure previously reported for a circular cylinder submerged near a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder differ from those observed for a circular cylinder. These trends are enhanced as cylinder aspect ratio is increased. In addition, the free surface distortion is also discussed in the paper. (orig.)
Daichin, K. V.; Lee, Sang Joon
The flow fields behind elliptic cylinders adjacent to a free surface were investigated experimentally in a circulating water channel. A range of cylinder aspect ratios (AR=2, 3, 4) were considered, while the cross-sectional area of the elliptical cylinder was kept constant. The main objective of this study was to investigate the effect of cylinder aspect ratio and a free surface on the flow structure in the near-wake behind elliptic cylinders. For each elliptic cylinder, the flow structure was analyzed for various values of the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV (Particle Image Velocimetry) system. For each experimental condition, 350 instantaneous velocity fields were obtained and ensemble-averaged to obtain the mean velocity field and spatial distribution of the mean vorticity statistics. The results show that near-wake can be classified into three typical flow patterns: formation of a Coanda flow, generation of substantial jet-like flow, and attachment of this jet flow to the free surface. The general flow structure observed behind the elliptic cylinders resembles the structure previously reported for a circular cylinder submerged near a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder differ from those observed for a circular cylinder. These trends are enhanced as cylinder aspect ratio is increased. In addition, the free surface distortion is also discussed in the paper.
Numerical simulation of flows around two unyawed and yawed wavy cylinders in tandem arrangement
Lam, K.; Lin, Y. F.; Zou, L.; Liu, Y.
2012-01-01
The turbulent flows around two fixed unyawed and yawed wavy cylinders in tandem arrangement at a subcritical Reynolds number of 3900 were studied using three-dimensional large eddy simulation. A range of spacing (L) between the cylinders from 1.5Dm to 5.5Dm with yaw angles of α=0°, 30° were investigated so as to identify the effects of cylinder spacing ratio and yaw angle as well as the coupling effects of the two wavy cylinders in tandem. The instantaneous near wake flow patterns around the cylinders were captured. Flows around circular cylinders with the same configurations were also obtained for comparison. The effects of the vortex shedding from the upstream cylinder on the fluid-dynamic forces acting on the downstream one were examined. Results show that vortex shedding behind the upstream wavy cylinder occurs at a further downstream position compared with that of the circular upstream cylinder. This leads to the weakening of the effect of bodies' vibration of the cylinders as well as an evident reduction of drag. With a yaw angle of 30°, the vortex formation lengths behind both the upstream and downstream cylinders decrease, typically for the wavy cylinders configuration. However, the effects of drag reduction and the control of bodies' vibration still exist except for the spacing ratio of L/Dm=3.5, which is in the critical spacing ratio regime for two wavy cylinders in tandem.
Poon, Eric; Ooi, Andrew; Pan, Wei; Liu, Yun; Ye, Yufei; Xue, Yuan; Barlis, Peter; Moore, Stephen
2013-11-01
Pulsatile flow past two circular cylinder rings in tandem inside a circular pipe is carried out numerically at resting blood flow rate (around 200mL/min) to study the effect of stent-malapposition (distance between cylinders surface and the circular pipe wall) on the hemodynamics impact inside a coronary artery. The corresponding Reynolds number based on pipe diameter for this blood flow rate is Re = 600. Stent-malappostion is chosen to be 0.25-1 diameter from the circular pipe wall and the two circular cylinders are 36 diameters apart. At 0.25 diameter stent-malapposition, the flow between the cylinders and the wall slows down significantly as the boundary layers from the cylinder and the wall meet. At 0.5 diameter stent-malapposition, the flow between the leading cylinder and the wall increases substantially, leading to unsteady vortices rolling away from the wall and a dramatic increase in wall shear stress. However, the vortices behind the trailing cylinder are stable even though the two cylinders in tandem are 36 diameters apart as flow pusatility affects the velocity recovery behind the leading cylinder. At 1 diameter stent-malapposition, the vortices behind the leading cylinder become stable again.
Lattice Boltzmann simulation of flow around a confined circular cyclinder
International Nuclear Information System (INIS)
A two dimensional lattice Boltzmann model (LBM) based on a single time relaxation BGK model has been developed. Several benchmark problems including the Poiseuille flow, the lid driven cavity flow and the flow around a circular cylinder have been performed employing a d2q9 lattice. The laminar flow around a circular cylinder within a channel has been extensively investigated using the present lattice Boltzmann model. Both symmetric and asymmetric placement configurations of the circular cylinder within the channel have been considered. A new treatment for the outlet velocity and pressure (density) boundary conditions has been proposed and validated. The present LBM results are in excellent agreement with those of the other existing CFD results. Careful examination of the LBM results and an appropriate calculation of the lift coefficient based on the rectangular lattice representation of the circular cylinder reveals that the periodic oscillation of the lift coefficient has a second harmonic when the cylinder is placed asymmetrically within the channel. The second harmonic could be associated with an asymmetrical shedding pattern of the vortices behind the cylinder from the upper and lower sides of the cylinder. (author)
Measurements of the Flowfield Interaction Between Tandem Cylinders
Neuhart, Dan H.; Jenkins, Luther N.; Choudhari, Meelan M.; Khorrami, Mehdi R.
2009-01-01
This paper presents the most recent measurements from an ongoing investigation of the unsteady wake interference between a pair of circular cylinders in tandem. The purpose of this investigation is to help build an in-depth experimental database for this canonical flow configuration that embodies the effects of component interaction in landing gear noise. This new set of measurements augments the previous database at the primary Reynolds number (based on tunnel speed and cylinder diameter) of 1.66 105 in four important respects. First, better circumferential resolution of surface pressure fluctuations is obtained via cylinder "clocking". Second, higher resolution particle image velocimetry measurements of the shear layer separating from the cylinders are achieved. Third, the effects of simultaneous boundary layer trips along both the front and rear cylinders, versus front cylinder alone in the previous measurements, are studied. Lastly, on-surface and off-surface characteristics of unsteady flow near the "critical" cylinder spacing, wherein the flow switches intermittently between two states that are characteristic of lower and higher spacings, are examined. This critical spacing occurs in the middle of a relatively sudden change in the drag of either cylinder and is characterized by a loud intermittent noise and a flow behavior that randomly transitions between shear layer attachment to the rear cylinder and constant shedding and rollup in front of it. Analysis of this bistable flow state reveals much larger spanwise correlation lengths of surface pressure fluctuations than those at larger and smaller values of the cylinder spacing.
Measurement of the flow past a cactus-inspired cylinder
Oweis, Ghanem F.; El-Makdah, Adnan M.
2012-11-01
Desert cacti are tall cylindrical plants characterized by longitudinal u- or v-shaped grooves that run parallel to the plant axis, covering its surface area. We study the wake flow modifications resulting from the introduction of cactus-inspired surface grooves to a circular cylinder. Particle image velocimetry PIV is implemented in a wind tunnel to visualize and quantify the wake flow from a cactus cylinder in cross wind and an equivalent circular cylinder at Re O(1E5). The cactus wake exhibits superior behavior over its circular counterpart as seen from the mean and turbulent velocity profiles. The surface flow within the grooves is also probed to elucidate the origins of the wake alterations. Lastly, we use simple statistical analysis based only on the wake velocity fields, under the assumption of periodicity of the shedding, to recover the time varying flow from the randomly acquired PIV snapshots.
Convective heat transfer from a heated elliptic cylinder at uniform wall temperature
Energy Technology Data Exchange (ETDEWEB)
Kaprawi, S.; Santoso, Dyos [Mechanical Department of Sriwijaya University, Jl. Raya Palembang-Prabumulih Km. 32 Inderalaya 50062 Ogan Ilir (Indonesia)
2013-07-01
This study is carried out to analyse the convective heat transfer from a circular and an elliptic cylinders to air. Both circular and elliptic cylinders have the same cross section. The aspect ratio of cylinders range 0-1 are studied. The implicit scheme of the finite difference is applied to obtain the discretized equations of hydrodynamic and thermal problem. The Choleski method is used to solve the discretized hydrodynamic equation and the iteration method is applied to solve the discretized thermal equation. The circular cylinder has the aspect ratio equal to unity while the elliptical cylinder has the aspect ratio less than unity by reducing the minor axis and increasing the major axis to obtain the same cross section as circular cylinder. The results of the calculations show that the skin friction change significantly, but in contrast with the elliptical cylinders have greater convection heat transfer than that of circular cylinder. Some results of calculations are compared to the analytical solutions given by the previous authors.
Division des ressources humaines
2000-01-01
N° 2 (Rev. 1) - March 2000Guidelines and procedures concerning recruitment and probation period of staff membersN° 9 (Rev. 2) - March 2000Staff members contractsN° 16 (Rev. 2) - January 2000TrainingN° 30 (Rev. 1) - January 2000Indemnities and reimbursements upon taking up appointment and termination of contractN° 32 - February 2000Principles and procedures governing complaints of harassmentThese circular have been amended (No 2, N° 9, N° 16 and N° 30) or drawn up (N° 32).Copies are available in the Divisional Secretariats.Note:\tAdministrative and operational circulars, as well as the lists of those in force, are available for consultation in the server SRV4_Home in the Appletalk zone NOVELL (as GUEST or using your Novell username and password), volume PE Division Data Disk.The Word files are available in the folder COM, folder Public, folder ADM.CIRC.docHuman Resources DivisionTel. 74128
Oscillations of elastically mounted cylinders in regular waves
Institute of Scientific and Technical Information of China (English)
苏炜; 詹杰民; 李毓湘
2014-01-01
Under the assumption of potential flow and linear wave theory, a semi-analytic method based on eigenfunciton expansion is proposed to predict the hydrody-namic forces on an array of three bottom-mounted, surface-piercing circular cylinders. The responses of the cylinders induced by wave excitation are determined by the equa-tions of motion coupled with the solutions of the wave radiation and diffraction problems. Experiments for three-cylinder cases are then designed and performed in a wave flume to determine the accuracy of this method for regular waves.
Oscillatory flow about a cylinder pair with unequal radii
Energy Technology Data Exchange (ETDEWEB)
Coenen, W, E-mail: wcoenen@ing.uc3m.es [Área de Mecánica de Fluidos, Universidad Carlos III de Madrid, Avenida Universidad 30, E-28911 Leganés, Madrid (Spain)
2013-10-15
We consider the oscillating flow about a pair of circular cylinders of unequal diameter. In addition to the relative size of the cylinders, the distance between them can be varied, as can the angle that the undisturbed oscillatory flow makes with the line joining the cylinder centres. For small-amplitude vibrations a time-independent, or steady streaming, motion develops that persists beyond the Stokes layer that forms at the solid boundary. This persistent streaming is considered for large values of a suitably defined streaming Reynolds number. (paper)
Oscillatory flow about a cylinder pair with unequal radii
International Nuclear Information System (INIS)
We consider the oscillating flow about a pair of circular cylinders of unequal diameter. In addition to the relative size of the cylinders, the distance between them can be varied, as can the angle that the undisturbed oscillatory flow makes with the line joining the cylinder centres. For small-amplitude vibrations a time-independent, or steady streaming, motion develops that persists beyond the Stokes layer that forms at the solid boundary. This persistent streaming is considered for large values of a suitably defined streaming Reynolds number. (paper)
Stability of the charged radiating cylinder
Energy Technology Data Exchange (ETDEWEB)
Sharif, M., E-mail: msharif.math@pu.edu.pk; Zaeem Ul Haq Bhatti, M., E-mail: mzaeem.math@gmail.com
2014-01-24
We discuss the dynamical instability of cylindrically symmetric isotropic geometry under the effect of electromagnetic field. The interior geometry of the dynamical collapse is matched with an exterior geometry through Darmois junction conditions. The perturbation scheme is used to describe the collapse equation and categorize the Newtonian and post-Newtonian regions in radiating as well as non-radiating eras. It is concluded that energy density, pressure, radiation density and electromagnetic field control the stability of the cylinder leading to more unstable configuration.
FORCE REDUCTION OF FLOW AROUND A SINUSOIDAL WAVY CYLINDER
Institute of Scientific and Technical Information of China (English)
ZOU Lin; LIN Yu-feng
2009-01-01
A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re=3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.
Stabilization of flow past a cylinder with rounded corners
Zhang, Wei; Samtaney, Ravi
2015-11-01
We present results of global linear stability analysis for flow past a cylinder in the low Reynolds number regime Re = 50 - 110 . The four corners of the square cylinder are rounded with a radius of curvature R+ = R / D in which R is the rounding radius and D is the cylinder diameter. Analysis is carried out for R+ = 0 . 00 (square cylinder with sharp corners) to R+ = 0 . 50 (circular cylinder) to investigate its effect on the stability characteristics of the flow. The results reveal that the flow may be stabilized by the rounding of the corners for Re beyond which further rounding has a destabilizing effect on the flow. The stabilization is less effective as the Reynolds number increases and for Re = 110 the square (resp. circular) cylinder has the least (resp. most) unstable growth rate. As R+ increases, the peak of the perturbation kinetic energy growth shifts closer to the cylinder and rapidly damps in the downstream region. The perturbation kinetic energy budget is examined and with the largest contribution due to the transfer of energy from the shear of the base flow. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/1394-01.The IBM Blue Gene/P Shaheen at KAUST was utilized for the simulations.
An Analytical Method of Auxiliary Sources Solution for Plane Wave Scattering by Impedance Cylinders
DEFF Research Database (Denmark)
Larsen, Niels Vesterdal; Breinbjerg, Olav
Analytical Method of Auxiliary Sources solutions for plane wave scattering by circular impedance cylinders are derived by transformation of the exact eigenfunction series solutions employing the Hankel function wave transformation. The analytical Method of Auxiliary Sources solution thus obtained...
Imperfection effects on the buckling of hydrostatically loaded cylinders
DEFF Research Database (Denmark)
Pinna, Rodney; Madsen, Søren
2015-01-01
in design has also increased. Practical guidance on how to do this is fairly limited, in particular for geometries or load conditions other than the standard cases. The effect of imperfections on the collapse load of cylinders under axial load has been studied extensively, as such cylinders show the......The presence of geometric and other imperfections in cylinders has been known to result in collapse loads well below those predicted from eigenvalue analysis for a long time. As the designer's ability to routinely employ non-linear FEA has increased, the importance of modelling such imperfections...... largest imperfection sensitivity. Work on cylinders with other loading conditions, such as hydrostatic loading, is more limited. Similarly, there is limited work on cylinders with boundary conditions other than simply-supported ends. This paper looks at the case of cylinders under hydrostatic load, which...
Effect of Surface Coatings on Cylinders Exposed to Underwater Shock
Directory of Open Access Journals (Sweden)
Y.W. Kwon
1994-01-01
Full Text Available The response of a coated cylinder (metallic cylinder coated with a rubber material subjected to an underwater explosion is analyzed numerically. The dynamic response of the coated cylinder appears to be adversely affected when impacted by an underwater shock wave under certain conditions of geometry and material properties of the coating. When adversely affected, significant deviations in values of axial stress, hoop stress, and strain are observed. The coated cylinder exhibits a larger deformation and higher internal energy in the metallic material. Rubber coatings appeared to inhibit energy dissipation from the metallic material to the surrounding water medium. A parametric study of various coatings was performed on both aluminum and steel cylinders. The adverse effect of the coating decreased when the stiffness of the rubber layer increased, indicating the existence of a threshold value. The results of this study indicate that the stiffness of the coating is a critical factor to the shock hardening of the coated cylinder.
Energy Technology Data Exchange (ETDEWEB)
Alderson, J.H. [Martin Marietta Energy Systems, Inc., Paducah, KY (United States)
1991-12-31
Cylinders containing depleted uranium hexafluoride (UF{sub 6}) in storage at the Department of Energy (DOE) gaseous diffusion plants, managed by Martin Marietta Energy Systems, Inc., are being evaluated to determine their expected storage life. Cylinders evaluated recently have been in storage service for 30 to 40 years. In the present environment, the remaining life for these storage cylinders is estimated to be 30 years or greater. The group of cylinders involved in recent tests will continue to be monitored on a periodic basis, and other storage cylinders will be observed as on a statistical sample population. The program has been extended to all types of large capacity UF{sub 6} cylinders.
Fagnard, Jean-François; Elschner, S.; Hobl, A.; Bock, J.; Vanderheyden, Benoît; Vanderbemden, Philippe
2012-01-01
This paper deals with the magnetic properties of bulk high temperature superconducting cylinders used as magnetic shields. We investigate, both numerically and experimentally, the magnetic properties of a hollow cylinder with two axial slits which cut the cylinder in equal halves. Finite element method modelling has been used with a three-dimensional geometry to help us in understanding how the superconducting currents flow in such a cut cylinder and therefore how the magnetic shielding prope...
Delamination of Composite Cylinders
Davies, Peter; Carlsson, Leif A.
The delamination resistance of filament wound glass/epoxy cylinders has been characterized for a range of winding angles and fracture mode ratios using beam fracture specimens. The results reveal that the delamination fracture resistance increases with increasing winding angle and mode II (shear) fraction (GΠ/G). It was also found that interlaced fiber bundles in the filament wound cylinder wall acted as effective crack arresters in mode I loading. To examine the sensitivity of delamina-tion damage on the strength of the cylinders, external pressure tests were performed on filament-wound glass/epoxy composite cylinders with artificial defects and impact damage. The results revealed that the cylinder strength was insensitive to the presence of single delaminations but impact damage caused reductions in failure pressure. The insensitivity of the failure pressure to a single delamination is attributed to the absence of buckling of the delaminated sublaminates before the cylinder wall collapsed. The impacted cylinders contained multiple delaminations, which caused local reduction in the compressive load capability and reduction in failure pressure. The response of glass/epoxy cylinders was compared to impacted carbon reinforced cylinders. Carbon/epoxy is more sensitive to damage but retains higher implosion resistance while carbon/PEEK shows the opposite trend.
Approximation by Cylinder Surfaces
DEFF Research Database (Denmark)
Randrup, Thomas
1997-01-01
We present a new method for approximation of a given surface by a cylinder surface. It is a constructive geometric method, leading to a monorail representation of the cylinder surface. By use of a weighted Gaussian image of the given surface, we determine a projection plane. In the orthogonal...... projection of the surface onto this plane, a reference curve is determined by use of methods for thinning of binary images. Finally, the cylinder surface is constructed as follows: the directrix of the cylinder surface is determined by a least squares method minimizing the distance to the points in the...
Optimization of autofrettage in thick-walled cylinders
Directory of Open Access Journals (Sweden)
A. Ghomi
2006-04-01
Full Text Available Purpose: The purpose of this paper is optimization of the weight of compound cylinder for a specific pressure. The variables are shrinkage radius and shrinkage tolerance.Design/methodology/approach: SEQ technique for optimization, the finite element code, ANSYS for numerical simulation are employed to predict the optimized conditions. The results are verified by testing a number of closed end cylinders with various geometries, materials and internal pressures.Findings: The weight of a compound cylinder could reduce by 60% with respect to a single steel cylinder. The reduction is more significant at higher working pressures. While the reduction of weight is negligible for k<2.5, it increases markedly for 2.5
Evaluation of Cylinder Volume Estimation Methods for In–Cylinder Pressure Trace Analysis
Directory of Open Access Journals (Sweden)
Adrian Irimescu
2012-09-01
Full Text Available In–cylinder pressure trace analysis is an important investigation tool frequently employed in the study of internal combustion engines. While technical data is usually available for experimental engines, in some cases measurements are performed on automotive engines for which only the most basic geometry features are available. Therefore, several authors aimed to determine the cylinder volume and length of the connecting rod by other methods than direct measurement. This study performs an evaluation of two such methods. The most appropriate way was found to be the estimation of connecting rod length based on general engine category as opposed to the use of an equation that predicts cylinder volume with good accuracy around top dead centre for most geometries.
Johnson, Erica
2006-01-01
Hoping to develop in her students an understanding of mathematics as a way of thinking more than a way of doing, the author of this article describes how her students worked on a spatial reasoning problem stemming from an iteratively constructed sequence of cylinders. She presents an activity of making cylinders out of paper models, and for every…
Corrosion of breached UF6 storage cylinders
International Nuclear Information System (INIS)
This paper describes the corrosion processes that occurred following the mechanical failure of two steel 14-ton storage cylinders containing depleted UF6. The failures both were traced to small mechanical tears that occurred during stacking of the cylinders. Although subsequent corrosion processes greatly extended the openings in the wall. the reaction products formed were quite protective and prevented any significant environmental insult or loss of uranium. The relative sizes of the two holes correlated with the relative exposure times that had elapsed from the time of stacking. From the sizes and geometries of the two holes, together with analyses of the reaction products, it was possible to determine the chemical reactions that controlled the corrosion process and to develop a scenario for predicting the rate of hydrolysis of UF6, the loss rate of HF, and chemical attack of a breached UF6 storage cylinder
Omnidirectional, circularly polarized, cylindrical microstrip antenna
Stanton, Philip H. (Inventor)
1985-01-01
A microstrip cylindrical antenna comprised of two concentric subelements on a ground cylinder, a vertically polarized (E-field parallel to the axis of the antenna cylinder) subelement on the inside and a horizontally polarized (E-field perpendicular to the axis) subelement on the outside. The vertical subelement is a wraparound microstrip radiator. A Y-shaped microstrip patch configuration is used for the horizontally polarized radiator that is wrapped 1.5 times to provide radiating edges on opposite sides of the cylindrical antenna for improved azimuthal pattern uniformity. When these subelements are so fed that their far fields are equal in amplitude and phased 90.degree. from each other, a circularly polarized EM wave results. By stacking a plurality of like antenna elements on the ground cylinder, a linear phased array antenna is provided that can be beam steered to the desired elevation angle.
Tandem Cylinder Noise Predictions
Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.
2007-01-01
In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to
Nonlinear Fracture Mechanics and Plasticity of the Split Cylinder Test
DEFF Research Database (Denmark)
Olesen, John Forbes; Østergaard, Lennart; Stang, Henrik
2006-01-01
properties. This implies that the linear elastic interpretation of the ultimate splitting force in term of the uniaxial tensile strength of the material is only valid for special situations, e.g. for very large cylinders. Furthermore, the numerical analysis suggests that the split cylinder test is not well......The split cylinder testis subjected to an analysis combining nonlinear fracture mechanics and plasticity. The fictitious crack model is applied for the analysis of splitting tensile fracture, and the Mohr-Coulomb yield criterion is adopted for modelling the compressive crushing/sliding failure. Two...... demonstrates the influence of varying geometry or constitutive properties. For a split cylinder test in load control it is shown how the ultimate load is either plasticity dominated or fracture mechanics dominated. The transition between the two modes is related to changes in geometry or constitutive...
Miniaturised cylinder head production by rapid prototyping
Melo, Rodrigo; Monteiro, A. Caetano; Martins, Jorge; Coene, Stijn; Puga, Hélder; Barbosa, J
2009-01-01
This work shows the development of the design and manufacturing of a very small engine, namely its head. The engine works under the 4-stroke cycle, therefore having a very complex cylinder head, housing the camshaft, valves and its auxiliaries (seats, guides, springs), spark plug, inlet and exhaust passages and a coolant chamber. The geometries, both inner and outer are highly intricate which makes the production of such a part a very difficult job. In addition, when the engine is...
Cylinder light concentrator and absorber: theoretical description
Kildishev, Alexander V.; Prokopeva, Ludmila J.; Narimanov, Evgenii
2010-01-01
We present a detailed theoretical description of a broadband omnidirectional light concentrator and absorber with cylinder geometry. The proposed optical "trap" captures nearly all the incident light within its geometric cross-section, leading to a broad range of possible applications from solar energy harvesting to thermal light emitters and optoelectronic components. We have demonstrated that an approximate lamellar black-hole with a moderate number of homogeneous layers, while giving the d...
Cylinder Flow Control Using Plasma Actuators
Kozlov, Alexey; Thomas, Flint
2007-11-01
In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. Two optimized quartz dielectric plasma actuators mounted on the cylinder surface utilizing an improved saw-tooth waveform high-voltage generator allowed flow control at Reynolds number approaching supercritical. Using either steady or unsteady actuation, it is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. PIV based flow fields and wake velocity profiles obtained with hot-wire anemometry show large reductions in vortex shedding, wake width and turbulence intensity.
Transient thermal stress problem for a circumferentially cracked hollow cylinder
Nied, H. F.; Erdogan, F.
1982-01-01
The transient thermal stress problem for a hollow elasticity cylinder containing an internal circumferential edge crack is considered. It is assumed that the problem is axisymmetric with regard to the crack geometry and the loading, and that the inertia effects are negligible. The problem is solved for a cylinder which is suddenly cooled from inside. First the transient temperature and stress distributions in an uncracked cylinder are calculated. By using the equal and opposite of this thermal stress as the crack surface traction in the isothermal cylinder the crack problem is then solved and the stress intensity factor is calculated. The numerical results are obtained as a function of the Fourier number tD/b(2) representing the time for various inner-to-outer radius ratios and relative crack depths, where D and b are respectively the coefficient of diffusivity and the outer radius of the cylinder.
Hard sphere packings within cylinders.
Fu, Lin; Steinhardt, William; Zhao, Hao; Socolar, Joshua E S; Charbonneau, Patrick
2016-02-23
Arrangements of identical hard spheres confined to a cylinder with hard walls have been used to model experimental systems, such as fullerenes in nanotubes and colloidal wire assembly. Finding the densest configurations, called close packings, of hard spheres of diameter σ in a cylinder of diameter D is a purely geometric problem that grows increasingly complex as D/σ increases, and little is thus known about the regime for D > 2.873σ. In this work, we extend the identification of close packings up to D = 4.00σ by adapting Torquato-Jiao's adaptive-shrinking-cell formulation and sequential-linear-programming (SLP) technique. We identify 17 new structures, almost all of them chiral. Beyond D ≈ 2.85σ, most of the structures consist of an outer shell and an inner core that compete for being close packed. In some cases, the shell adopts its own maximum density configuration, and the stacking of core spheres within it is quasiperiodic. In other cases, an interplay between the two components is observed, which may result in simple periodic structures. In yet other cases, the very distinction between the core and shell vanishes, resulting in more exotic packing geometries, including some that are three-dimensional extensions of structures obtained from packing hard disks in a circle. PMID:26843132
NONLINEAR FREE SURFACE ACTION WITH AN ARRAY OF VERTICAL CYLINDERS
Institute of Scientific and Technical Information of China (English)
HUANG J. B.
2004-01-01
Nonlinear diffraction of regular waves by an array of bottom-seated circular cylinders is investigated in frequency domain, based on a Stokes expansion approach. A complete semi-analytical solution is developed which allows an efficient evaluation of the second-order potentials in the entire fluid domain, and the wave forces on the structure. Expressions are derived for the second-order potential in the vicinity of individual cylinders. These expressions have a simple form, thus providing an effective means for investigating the wave enhancement due to nonlinear interactions with multiple cylinders. Based on the present method, the wave run-up and free-surface elevations around an array of two, three and four cylinders are investigated numerically.
Radiation dose rates from UF{sub 6} cylinders
Energy Technology Data Exchange (ETDEWEB)
Friend, P.J. [Urenco, Capenhurst (United Kingdom)
1991-12-31
This paper describes the results of many studies, both theoretical and experimental, which have been carried out by Urenco over the last 15 years into radiation dose rates from uranium hexafluoride (UF{sub 6}) cylinders. The contents of the cylinder, its history, and the geometry all affect the radiation dose rate. These factors are all examined in detail. Actual and predicted dose rates are compared with levels permitted by IAEA transport regulations.
Longitudinal Weld Land Buckling in Compression-Loaded Orthogrid Cylinders
Thornburgh, Robert P.; Hilburger, Mark W.
2010-01-01
Large stiffened cylinders used in launch vehicles (LV), such as the Space Shuttle External Tank, are manufactured by welding multiple curved panel sections into complete cylinders. The effects of the axial weld lands between the panel sections on the buckling load were studied, along with the interaction between the acreage stiffener arrangement and the weld land geometry. This document contains the results of the studies.
Elastic and viscoelastic solutions to rotating functionally graded hollow and solid cylinders
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Analytical solutions to rotating functionally graded hollow and solid long cylinders are developed. Young's modulus and material density of the cylinder are as* sumed to vary exponentially in the radial direction, and Poisson's ratio is assumed to be constant. A unified governing equation is derived from the equilibrium equations, compat-ibility equation, deformation theory of elasticity and the stress-strain relationship. The governing second-order differential equation is solved in terms of a hypergeometric func-tion for the elastic deformation of rotating functionally graded cylinders. Dependence of stresses in the cylinder on the inhomogeneous parameters, geometry and boundary conditions is examined and discussed. The proposed solution is validated by comparing the results for rotating functionally graded hollow and solid cylinders with the results for rotating homogeneous isotropic cylinders. In addition, a viscoelastic solution to the rotating viscoelastic cylinder is presented, and dependence of stresses in hollow and solid cylinders on the time parameter is examined.
Self-sustained oscillations between two tandem cylinders at Reynolds number 1,000
Kuo, C. H.; Chein, S. M.; Hsieh, H. J.
2008-04-01
This study focuses on the self-sustained oscillatory flow characteristics between two tandem circular cylinders of equal diameter placed in a uniform inflow. The Reynolds number ( Re D ), based on the cylinder diameter, was around 1,000 and all experiments were performed in a recirculating water channel. The streamwise distance between two tandem cylinders ranged within 1.5 ≤ X c/ D ≤ 7.0. Here X c denotes the center-to-center distance between two tandem cylinders. For all experiments studied herein, quantitative velocity measurements were performed using hot-film anemometer and the LDV system. The laser sheet technique was employed for qualitative flow visualization. The wavelet transform was applied to elucidate the temporal variation and phase difference between two spectral components of the velocity signals detected in the flow field. The remarkable finding was that when two tandem circular cylinders were spaced at a distance within 4.5 ≤ X c/ D ≤ 5.5, two symmetrical unstable shear layers with a certain wavelength were observed to impinge onto the downstream cylinder. The responding frequency ( f u ), measured between these two cylinders, was much higher than the natural shedding frequency behind a single isolated cylinder at the same Re D . This responding frequency decreased as the distance X c/ D increased. Not until X c/ D ≥ 6.0, did it recover to the natural shedding frequency behind a single isolated cylinder. Between two tandem cylinders, the Strouhal numbers ( St c = f u X c/Uc) maintained a nearly constant value of 3, indicating the self-sustained oscillating flow characteristics with a wavelength X c/3. Here U c is the convection speed of the unstable shear layers between two tandem cylinders. At Re D = 1,000, the self-sustained oscillating characteristics between two tandem circular cylinders were proven to exhibit a sustained flow pattern, not just a sporadic phenomenon.
Casimir interaction between a plate and a cylinder
Emig, T.; Jaffe, R. L.; Kardar, M.; Scardicchio, A.
2006-01-01
We find the exact Casimir force between a plate and a cylinder, a geometry intermediate between parallel plates, where the force is known exactly, and the plate--sphere, where it is known at large separations. The force has an unexpectedly weak decay \\sim L/(H^3 \\ln(H/R)) at large plate--cylinder separations H (L and R are the cylinder length and radius), due to transverse magnetic modes. Path integral quantization with a partial wave expansion additionally gives a qualitative difference for ...
Vortex-induced vibration of a harbor-vibrissa-shaped cylinder: Experimental measurements.
Liu, Yingzheng; Wang, Shaofei
2015-11-01
Influence of the unique surface variation of the harbor seal vibrissa on its vortex-induced vibration was extensively investigated in a low-speed wind tunnel. Toward this end, a scaled-up model of the harbor-vibrissa-shaped cylinder was employed for measurement, while a circular cylinder sharing the same hydraulic diameter, mass ratio and nature frequency was used as baseline case. Two configurations with and without the approaching Karman-vortex street were respectively tested for both cylinders at various free stream flow speeds. Here, the Karman-vortex street was generated by placing a circular cylinder far up stream. A laser displacement sensor having a high time-spatial resolution was used to capture the cross-stream displacement of the cylinders. The fluctuating pressure distribution on the surface and the wake flow pattern were captured by microphone array and the planar Particle Image Velocimetry, respectively. National Natural Science Foundation of China (grant nos. 51176108, and 11372189).
The Casimir force between a microfabricated elliptic cylinder and a plate
Decca, R S; Klimchitskaya, G L; Krause, D E; Lopez, D; Mostepanenko, V M
2011-01-01
We investigate the Casimir force between a microfabricated elliptic cylinder (cylindrical lens) and a plate made of real materials. After a brief discussion of the fabrication procedure, which typically results in elliptic rather than circular cylinders, the Lifshitz-type formulas for the Casimir force and for its gradient are derived. In the specific case of equal semiaxes, the resulting formulas coincide with those derived previously for circular cylinders. The nanofabrication procedure may also result in asymmetric cylindrical lenses obtained from parts of two different cylinders, or rotated through some angle about the axis of the cylinder. In these cases the Lifshitz-type formulas for the Casimir force between a lens and a plate and for its gradient are also derived, and the influence of lens asymmetry is determined. Additionally, we obtain an expression for the shift of the natural frequency of a micromachined oscillator with an attached elliptic cylindrical lens interacting with a plate via the Casimir...
Dynamics of Controlled Boundary Layer Separation on a Circular Cylinder
Czech Academy of Sciences Publication Activity Database
Uruba, Václav; Matějka, Milan; Procházka, Pavel
Praha : Ústav termomechaniky AV ČR, v. v. i., 2008 - (Jonáš, P.; Uruba, V.), s. 61-62 ISBN 978-80-87012-14-7. [Colloquium FLUID DYNAMICS 2008. Praha (CZ), 22.10.2008-24.10.2008] R&D Projects: GA AV ČR IAA2076403; GA ČR GA101/08/1112 Institutional research plan: CEZ:AV0Z20760514 Keywords : boundary layer * separation * control * synthetic jet Subject RIV: BK - Fluid Dynamics www.it.cas.cz/dt
Dynamics of controlled boundary layer separation on a circular cylinder
Czech Academy of Sciences Publication Activity Database
Uruba, Václav; Matějka, Milan
Ostritz - St.Marienthal : DLR Berlin, 2008 - (Hage, W.; Wassen, E.; Choi, K.), s. 1-2 [European Drag Reduction and Flow Control Meeting 2008. Ostritz - St.Marienthal (DE), 08.09.2008-11.09.2008] R&D Projects: GA AV ČR IAA2076403; GA ČR GA101/08/1112 Institutional research plan: CEZ:AV0Z20760514 Keywords : boundary layer * separation * dynamics Subject RIV: BK - Fluid Dynamics http://edrfcm2008.cfd.tu-berlin.de/
On the Wake of an Inclined Circular Cylinder
Taubert, Lutz
2010-01-01
Diese Arbeit begann mit einer Machbarkeitsstudie über die potentielle Nutzung aktiver Strömungskontrolle für die Lagekontrolle eines Tankrüssels für die Luftbetankung, der vereinfachend als angestellter Kreiszylinder betrachtet werden kann. Die Vorversuche an einem einfachen Modell wurden sehr erfolgreich abgeschlossen. Daran anschließend wurde eine grundlegende Untersuchung der Umströmung eines unendlichen angestellten Kreiszylinders mit aktiver Strömungskontrolle durchgeführt. Druckverteilu...
Energy Technology Data Exchange (ETDEWEB)
Dalvit, Diego A1 [Los Alamos National Laboratory; Rodriguez, Alejandro W [MASS INST OF TECH; Munday, J N [HARVARD UNIV; Joannopoulos, J D [MASS INST OF TECH
2008-01-01
Using accurate numerical methods for finite-size nonplanar objects, we demonstrate a stable mechanical suspension of a silica cylinder within a metallic cylinder separated by ethanol, via a repulsive Casimir force between the silica and the metal. We investigate cylinders with both circular and square cross sections, and show that the latter exhibit a stable orientation as well as a stable position, employing a new method to accurately compute Casimir torques for finite objects. Furthermore, the stable orientation of the square cylinder is shown to undergo an unusual 45 transition as a function of the separation lengthscale, and this transition is explained as a consequence of material dispersion.
Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves
Mitri, F. G.
2015-12-01
The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.
Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves
Energy Technology Data Exchange (ETDEWEB)
Mitri, F. G., E-mail: F.G.Mitri@ieee.org [Chevron, Area 52 Technology–ETC, Santa Fe, New Mexico 87508 (United States)
2015-12-07
The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.
Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves
International Nuclear Information System (INIS)
The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries
Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves
Mitri, F. G.
2015-12-01
The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.
Comparing standard Bonner spheres and high-sensitivity Bonner cylinders
International Nuclear Information System (INIS)
Standard Bonner spheres and proposed high-sensitivity Bonner cylinders were calibrated in a neutron calibration room, using a 252Cf source. The Bonner sphere system consists of 11 polyethylene (PE) spheres of various diameters and 4 extended spheres that comprise embedded metal shells. Similar to the design of Bonner spheres, a set of Bonner cylinders was assembled using a large cylindrical 3He tube as the central probe, which was wrapped using various thicknesses of PE. A layer of lead was employed inside one of the PE cylinders to increase the detection efficiency of high-energy neutrons. The central neutron probe used in the Bonner cylinders exhibited an efficiency of ∼17.9 times higher than that of the Bonner spheres. However, compared with the Bonner spheres, the Bonner cylinders are not fully symmetric in their geometry, exhibiting angular dependence in their responses to incoming neutrons. Using a series of calculations and measurements, this study presents a systematic comparison between Bonner spheres and cylinders in terms of their response functions, detection efficiencies, angular dependences and spectrum unfolding. A high-sensitivity Bonner cylinder spectrometer was developed to facilitate neutron spectrum measurement in low-intensity environments such as the site boundaries of nuclear facilities or accelerators. The proposed spectrometer system comprises 11 cylinders of various PE thicknesses and an extended cylinder with an embedded lead shell. Compared with the standard Bonner spheres, the detection efficiency of the device increased by a factor of >10 because a large 3He tube was employed. However, the Bonner cylinders are not symmetric in their polar angle, and this causes the advantage of isotropic response to be lost. A systematic comparison was conducted between the standard Bonner spheres and the proposed Bonner cylinders, examining their response functions, calibration measurements, angular dependences and spectrum unfolding. (authors)
Casimir force between a microfabricated elliptic cylinder and a plate
Energy Technology Data Exchange (ETDEWEB)
Decca, R. S. [Department of Physics, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202 (United States); Fischbach, E. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Klimchitskaya, G. L. [North-West Technical University, Millionnaya Street 5, St.Petersburg, 191065 (Russian Federation); Krause, D. E. [Physics Department, Wabash College, Crawfordsville, Indiana 47933 (United States); Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Lopez, D. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Mostepanenko, V. M. [Noncommercial Partnership ' ' Scientific Instruments' ' , Tverskaya Street 11, Moscow, 103905 (Russian Federation)
2011-10-15
We investigate the Casimir force between a microfabricated elliptic cylinder (cylindrical lens) and a plate made of real materials. After a brief discussion of the fabrication procedure, which typically results in elliptic rather than circular cylinders, the Lifshitz-type formulas for the Casimir force and for its gradient are derived. In the specific case of equal semiaxes, the resulting formulas coincide with those derived previously for circular cylinders. The nanofabrication procedure may also result in asymmetric cylindrical lenses obtained from parts of two different cylinders, or rotated through some angle about the axis of the cylinder. In these cases, the Lifshitz-type formulas for the Casimir force between a lens and a plate and for its gradient are also derived, and the influence of lens asymmetry is determined. Additionally, we obtain an expression for the shift of the natural frequency of a micromachined oscillator with an attached elliptic cylindrical lens interacting with a plate via the Casimir force in a nonlinear regime.
Farrokhabadi, Amin; Abadian, Naeime; Rach, Randolph; Abadyan, Mohamadreza
2014-09-01
The Casimir force can induce instability and adhesion in freestanding nanostructures. Previous research efforts in this area have exclusively focused on modeling the instability in structures with planar or rectangular cross-section, while, to the best knowledge of the authors, no attention has been paid to investigate this phenomenon for nanowires with circular cross-section. In this study, effects of the Casimir force on the instability and adhesion of freestanding Cylinder-Plate and Cylinder-Cylinder geometries are investigated, which are commonly encountered in real nanodevices. To compute the Casimir force, two approaches, i.e. the proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation (scattering theory) for large separations, are considered. A continuum mechanics theory is employed, in conjunction with the Euler-beam model, to obtain constitutive equations of the systems. The governing nonlinear constitutive equations of the nanostructures are solved using two different approaches, i.e. the analytical modified Adomian decomposition (MAD) and the numerical finite difference method (FDM). The detachment length and minimum gap, both of which prevent the Casimir force-induced adhesion, are computed for both configurations.
Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 4
International Nuclear Information System (INIS)
The last in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models in the series are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: (1) the experimental data provide design information directly applicable to nozzles in cylindrical vessels, and (2) the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 4 had an outside diameter of 10 in., and the nozzle had an outside diameter of 1.29 in., giving a d0/D0 ratio of 0.129. The OD/thickness ratios were 50 and 20.2 for the cylinder and nozzle respectively. Thirteen separate loading cases were analyzed. For each loading condition one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for each of the 13 loadings were obtained using 157 three-gage strain rosettes located on the inner and outer surfaces. Each of the 13 loading cases was also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)
Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 3
International Nuclear Information System (INIS)
The third in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: the experimental data provide design information directly applicable to nozzles in cylindrical vessels; and the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 3 had a 10 in. OD and the nozzle had a 1.29 in. OD, giving a d0/D0 ratio of 0.129. The OD/thickness ratios for the cylinder and the nozzle were 50 and 7.68 respectively. Thirteen separate loading cases were analyzed. In each, one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for all the loadings were obtained using 158 three-gage strain rosettes located on the inner and outer surfaces. The loading cases were also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)
Oscillations and translation of a free cylinder in a confined flow
D'Angelo, Maria Veronica; Hulin, Jean-Pierre; Auradou, Harold
2013-01-01
An oscillatory instability has been observed experimentally on an horizontal cylinder free to move and rotate between two parallel vertical walls of distance H; its characteristics differ both from vortex shedding driven oscillations and from those of tethered cylinders in the same geometry. The vertical motion of the cylinder, its rotation about its axis and its transverse motion across the gap have been investigated as a function of its diameter D, its density s, of the mean vertical veloci...
Circularity and Lambda Abstraction
DEFF Research Database (Denmark)
Danvy, Olivier; Thiemann, Peter; Zerny, Ian
2013-01-01
In this tribute to Doaitse Swierstra, we present the rst transformation between lazy circular programs a la Bird and strict cir- cular programs a la Pettorossi. Circular programs a la Bird rely on lazy recursive binding: they involve circular unknowns and make sense equa- tionally. Circular...... unknowns from what is done to them, which we lambda-abstract with functions. The circular unknowns then become dead variables, which we eliminate. The result is a strict circu- lar program a la Pettorossi. This transformation is reversible: given a strict circular program a la Pettorossi, we introduce...
Three-dimensional clustering of Janus cylinders by convex curvature and hydrophobic interactions.
Kim, Jongmin; Oh, Myung Seok; Choi, Chang-Hyung; Kang, Sung-Min; Kwak, Moo Jin; You, Jae Bem; Im, Sung Gap; Lee, Chang-Soo
2015-06-28
The three-dimensional (3D) clustering of Janus cylinders is controlled by simply tuning the cylinder geometry and hydrophobic interactions. Janus cylinders were prepared by combining two approaches: micromolding and initiated chemical vapor deposition (iCVD). Hydrophilic cylinders with a flat- or convex-top curvature were prepared by micromolding based on surface tension-induced flow. The iCVD process then provides a hydrophobic domain through the simple and precise deposition of a polymer film on the top surface, forming monodisperse Janus microcylinders. We use these Janus cylinders as building blocks to form 2D or 3D clusters via hydrophobic interactions in methanol. We investigate how cylinder geometry or degree of hydrophobic interaction affects the resulting cluster geometries. The convex-top Janus cylinders lead to 3D clustering through tip-to-tip interactions, and the flat-top Janus cylinders lead to 2D clustering through face-to-face attraction. The number of Janus cylinders in 3D clusters is tuned by controlling the degree of hydrophobic (or hydrophilic) interaction. PMID:26008176
Microstrip-fed Wideband Circularly Polarized Printed Antenna
Bao, Xiulong; Ammann, Max; McEvoy, Patrick
2010-01-01
A wideband circularly-polarized printed antenna is proposed, which employs an asymmetrical dipole and a slit in the ground plane which are fed by an L-shaped microstrip feedline using a via. The proposed antenna geometry is arranged so that the orthogonal surface currents, which are generated in the dipole, feedline and ground plane, have the appropriate phase to provide circular polarization. A parametric study of the key parameters is made and the mechanism for circular polarization is desc...
Regimes of flow induced vibration for tandem, tethered cylinders
Nave, Gary; Stremler, Mark
2015-11-01
In the wake of a bluff body, there are a number of dynamic response regimes that exist for a trailing bluff body depending on spacing, structural restoring forces, and the mass-damping parameter m* ζ . For tandem cylinders with low values of m* ζ , two such regimes of motion are Gap Flow Switching and Wake Induced Vibration. In this study, we consider the dynamics of a single degree-of-freedom rigid cylinder in the wake of another in these regimes for a variety of center-to-center cylinder spacings (3-5 diameters) and Reynolds numbers (4,000-11,000). The system consists of a trailing cylinder constrained to a circular arc around a fixed leading cylinder, which, for small angle displacements, bears a close resemblance to the transversely oscillating cylinders found more commonly in existing literature. From experiments on this system, we compare and contrast the dynamic response within these two regimes. Our results show sustained oscillations in the absence of a structural restoring force in all cases, providing experimental support for the wake stiffness assumption, which is based on the mean lift toward the center line of flow.
The Interaction Vortex Flow Around Two Bluff Cylinders
Directory of Open Access Journals (Sweden)
Hirao K.
2013-04-01
Full Text Available In this study, the interaction vortex flow features around a pair of parallel arranged bluff cylinders were observed by visualizing water flow experiment at the range of the gap ratio G/d=0~3. It was obtained that the result of established wind tunnel test and the result of this water tank test agreed about the characteristics of vortex shedding when varying the distance of circular cylinder gap. The flow pattern and vortex shedding frequency of another type bluff cylinder (triangular and square cylinder were also investigated. As a result of the experiment, it was shown that the flow pattern of wake flow was divided into three kinds (coupled vortex streets, biased gap flow and single vortex street regardless of the cylinder section shape and cylinder size. Then, the region of the appearance of flow pattern was shown about each case. In the case where two each other independent vortex streets were formed, three typical flow patterns of vortex formation (in-phase coupled vortex streets, out-of-phase coupled vortex streets and complication coupled vortex streets were observed. It was known that three configuration of vortex formation appear intermittently and alternatively.
The amplitude of fluid-induced vibration of cylinders in axial flow
International Nuclear Information System (INIS)
This report describes a new empirical expression of the amplitude of transverse vibration of cylindrical beams and clusters of cylinders in axial flow, for application to reactor fuel. The expression is based on reported experimental observations covering a variety of geometries, cylinder materials and types of support in water, superheated steam and two-phase mixture flows. (author)
DEFF Research Database (Denmark)
Margheritini, Lucia; Taraborrelli, Valeria Taraborrelli
Margheritini and Valeria Taraborrelli(valeria.taraborrelli@hotmail.it) with a total of 3 day visit from the developers. Laboratory tests in irregular waves will be performed by Lucia Margheritini. The report is aimed at the first stage testing of the Rolling Cylinder wave energy device. This phase includes...
Equivariant harmonic cylinders
Burstall, F. E.; Kilian, M.
2005-01-01
We prove that a primitive harmonic map is equivariant if and only if it admits a holomorphic potential of degree one. We investigate when the equivariant harmonic map is periodic, and as an application discuss constant mean curvature cylinders with screw motion symmetries.
'Buffeting of single cylinders'
International Nuclear Information System (INIS)
The fluctuating lift and drag induced on a rigid cylinder immersed in a turbulent flow in the range of Reynolds numbers straddling the transition from subcritical to supercritical regime is examined. The buffeting forces are induced in response to turbulence generated by grids. In the present experiments, the integral scales of turbulence, l, for the grids used are less than the cylinder diameter (l/d < 1). Interpretation of these and other published data strongly suggest that the free stream disturbances (turbulence) affect the force response in two ways. In the absence of grid turbulence below a certain threshold level, it appears to simply modulate the spanwise spatial coherence of vortex shedding. In this situation, the spectral character retains the discrete or monochromatic Strouhal nature, while the RMS force levels decrease with increase in the measured free stream disturbance. On the other hand, the cylinder response to broad band excitation by the high intensity grid generated turbulence is no longer discrete although the spectral character still retains a 'humped' shape of a band pass filter. Centre band frequency of this band pass is very nearly, although not quite, the Strouhal frequency in the 'clean' flow. In any event, the RMS amplitudes continue to decline as the turbulent intensity is increased. While the evidence is suggestive, it is not as yet complete. The data on hand strongly suggest the domination of the cylinder buffeting phenomenon by the shed wake, at the lease for l/d < 1. A principle can also be extracted from the data. The persistence of the Strouhal frequency into the buffeting response spectrum suggests that the time scale so represented is inherent to flow/cylinder interactions even when the upstream flow is highly turbulent (and l/d < 1). (author)
2015-01-01
This stimulating volume offers a broad collection of the principles of geometry and trigonometry and contains colorful diagrams to bring mathematical principles to life. Subjects are enriched by references to famous mathematicians and their ideas, and the stories are presented in a very comprehensible way. Readers investigate the relationships of points, lines, surfaces, and solids. They study construction methods for drawing figures, a wealth of facts about these figures, and above all, methods to prove the facts. They learn about triangle measure for circular motion, sine and cosine, tangent
Institute of Scientific and Technical Information of China (English)
SHEN Guo-quan; XIAO Yuan-chun
2003-01-01
@@ "Mo" literally means "rubbing between two things"and "eliminating". Circular-rubbing is one of the earliest manipulations used in clinical practice. Circular-rubbing differs from pressing actually. Pressing is a static manipulation and acts to inhibit motion; circular-rubbing is a movable manipulation and serves to eliminate stationary. Circular-rubbing can be performed by either the palm or the finger.
Poisson cylinders in hyperbolic space
Broman, Erik; Tykesson, Johan
2015-01-01
We consider the Poisson cylinder model in d-dimensional hyperbolic space. We show that in contrast to the Euclidean case, there is a phase transition in the connectivity of the collection of cylinders as the intensity parameter varies. We also show that for any non-trivial intensity, the diameter of the collection of cylinders is infinite.
International Nuclear Information System (INIS)
Highlights: → The work explores a new electrochemical reactor by using square rotating cylinders. → The results show that it is superior to the traditional circular rotating cylinder. → A dimensionless design equation for the new reactor was correlated. → The oxalic acid removal by the new reactor was succeeded and found promising. → The energy consumption per kg oxalic acid removed by the unit was calculated. - Abstract: Rates of mass transfer at a rotating square cylinder were measured by an electrochemical technique which involved measuring the limiting current of the cathodic reduction of K3Fe(CN)6 in a large excess of NaOH solution. Variables studied were: cylinder rotation speed, physical properties of the solution and cylinder equivalent diameter. The data for the condition 1577 0.33Re0.45 For a given set of conditions the rate of mass transfer at the square rotating cylinder was found to be higher than that at the traditional circular rotating cylinder by an amount ranging from 47% to 200% depending on Re. The use of the square rotating cylinder electrode in removing oxalic acid from wastewater by anodic oxidation on Pb/PbO anode was examined and found to be promising.
Effect of free surface on near-wake flow of elliptic cylinders with different aspect ratios
Lee, Sang Joon; Daichin, -
2003-04-01
The flow fields behind elliptic cylinders with different aspect ratios adjacent to a free surface were investigated experimentally in a circulating water channel. The elliptic cylinders tested in this study have same cross section area. For each elliptic cylinder, the experiments were carried out under different conditions by varying the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV system. For each experimental condition, 350 instantaneous velocity fields were captured and ensemble-averaged to obtain the mean flow field information and spatial distribution of turbulent statistics. The near-wakes can be basically classified into three typical patterns, which are formation of Coanda effect, generation of substantial jet-like flow, and attachment of jet flow to the free surface. The general flow structures behind the elliptic cylinder are similar to previous results for a circular submerged near to a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller than those for the circular cylinder. These trends are enhance with increasing of the cylinder aspect ratios.
Guggenheimer, Heinrich W
1977-01-01
This is a text of local differential geometry considered as an application of advanced calculus and linear algebra. The discussion is designed for advanced undergraduate or beginning graduate study, and presumes of readers only a fair knowledge of matrix algebra and of advanced calculus of functions of several real variables. The author, who is a Professor of Mathematics at the Polytechnic Institute of New York, begins with a discussion of plane geometry and then treats the local theory of Lie groups and transformation groups, solid differential geometry, and Riemannian geometry, leading to a
Rodger, Alison
1995-01-01
Molecular Geometry discusses topics relevant to the arrangement of atoms. The book is comprised of seven chapters that tackle several areas of molecular geometry. Chapter 1 reviews the definition and determination of molecular geometry, while Chapter 2 discusses the unified view of stereochemistry and stereochemical changes. Chapter 3 covers the geometry of molecules of second row atoms, and Chapter 4 deals with the main group elements beyond the second row. The book also talks about the complexes of transition metals and f-block elements, and then covers the organometallic compounds and trans
Properties of Sub-wavelength Resonances in Metamaterial Cylinders
DEFF Research Database (Denmark)
Arslanagic, Samel; Clausen, N.C.J.; Pedersen, R.R.;
2008-01-01
The analytical solution for the canonical configuration with electric line source illumination of concentric metamaterial cylinders is employed to study the properties of the observed sub-wavelength resonances. The near- and far-field distributions, the frequency and geometry bandwidths, and the...
Calculating of mutual coupling coefficients in presence cylinder
Zvezdina, Marina Yu.
2003-01-01
The problem of the selection of the singularity of the Green's function spectral representation when calculating the mutual coupling coefficients of longitudinal electrical dipoles located near the impedance circular cylinder is solved. The current distribution in the dipoles is approximated by the generalized modes. The calculation results of both addition values caused by the singularity and the mutual coupling coefficients for the case when two longitudinal dipoles are located near the imp...
Motion of multiple cylinders in potential flow of ideal fluid
Czech Academy of Sciences Publication Activity Database
Kharlamov, Alexander A.; Filip, Petr
Praha : Ústav termomechaniky AV ČR v. v. i., 2011 - (Jonáš, P.; Uruba, V.), s. 21 ISBN 978-80-87012-36-9. [Colloquium FLUID DYNAMICS 2011. Praha (CZ), 19.10.2011-21.10.2011] Institutional research plan: CEZ:AV0Z20600510 Keywords : generalised images method * potential flow * ideal fluid * circular cylinders Subject RIV: BK - Fluid Dynamics
Rotating fermions inside a cylinder
Ambrus, Victor E
2015-01-01
We study rotating thermal states of a quantum fermion field inside a cylinder in Minkowski space-time. Two possible boundary conditions for the fermion field on the cylinder are considered: the spectral and MIT bag boundary conditions. If the radius of the cylinder is sufficiently small, rotating thermal expectation values are finite everywhere inside the cylinder. We also study the Casimir divergences on the boundary. The rotating thermal expectation values and the Casimir divergences have different properties depending on the boundary conditions applied at the cylinder. This is due to the local nature of the MIT bag boundary condition, while the spectral boundary condition is nonlocal.
Numerical Study of Flow Over a Cylinder Using an Immersed Boundary Finite Volume Method
Ranjith Maniyeri
2014-01-01
Immersed boundary (IB) method has proved its efficacy in handling complex fluid-structure interaction problems in the field of Computational Fluid Dynamics (CFD). We present a two–dimensional computational model based on an immersed boundary finite volume method to study flow over a stationary circular cylinder. Lagrangian coordinates are used to describe the cylinder and Eulerian coordinates are employed to describe the fluid flow. The Navier-Stokes equations ...
Cylinder light concentrator and absorber: theoretical description.
Kildishev, Alexander V; Prokopeva, Ludmila J; Narimanov, Evgenii E
2010-08-01
We present a detailed theoretical description of a broadband omnidirectional light concentrator and absorber with cylinder geometry. The proposed optical "trap" captures nearly all the incident light within its geometric cross-section, leading to a broad range of possible applications--from solar energy harvesting to thermal light emitters and optoelectronic components. We have demonstrated that an approximate lamellar black-hole with a moderate number of homogeneous layers, while giving the desired ray-optical performance, can provide absorption efficiencies comparable to those of ideal devices with a smooth gradient in index. PMID:20721056
Fertelli, Ahmet; Günhan, Gökhan; Buyruk, Ertan
2016-06-01
In the present study, it is aimed to calculate the effect of ice formation on different cylinder geometries placed in a rectangular cavity filled with water. For this aim Fluent package program was used to solve the flow domain numerically and temperature distribution and ice formation depending on time were illustrated. Water temperature in the cavity and cylinder surface temperature were assumed as 4, 8 and -10 °C respectively and firstly temperature distribution, velocity vector, liquid fraction and ratio of Ai/Ac (formed ice area/cross sectional area of cylinder) were determined for cylinders with different placement in fixed volume.
Low-Re flow past an isolated cylinder with rounded corners
Zhang, Wei
2016-06-29
Direct numerical simulation is performed for flow past an isolated cylinder at Re=1,000. The corners of the cylinder are rounded at different radii, with the non-dimensional radius of curvature varying from R+=R/D=0.000 (square cylinder with sharp corners) to 0.500 (circular cylinder), in which R is the corner radius and D is the cylinder diameter. Our objective is to investigate the effect of the rounded corners on the development of the separated and transitional flow past the cylinder in terms of time-averaged statistics, time-dependent behavior, turbulent statistics and three-dimensional flow patterns. Numerical results reveal that the rounding of the corners significantly reduces the time-averaged drag and the force fluctuations. The wake flow downstream of the square cylinder recovers the slowest and has the largest wake width. However, the statistical quantities do not monotonically vary with the corner radius, but exhibit drastic variations between the cases of square cylinder and partially rounded cylinders, and between the latter and the circular cylinder. The free shear layer separated from the R+=0.125 cylinder is the most stable in which the first roll up of the wake vortex occurs furthest from the cylinder and results in the largest recirculation bubble, whose size reduces as R+ further increases. The coherent and incoherent Reynolds stresses are most pronounced in the near-wake close to the reattachment point, while also being noticeable in the shear layer for the square and R+=0.125 cylinders. The wake vortices translate in the streamwise direction with a convection velocity that is almost constant at approximately 80% of the incoming flow velocity. These vortices exhibit nearly the same trajectory for the rounded cylinders and are furthest away from the wake centerline for the square one. The flow past the square cylinder is strongly three-dimensional as indicated by the significant primary and secondary enstrophy, while it is dominated by the
Detecting a subsurface cylinder by a Time Reversal MUSIC like method
Solimene, Raffaele; Dell'Aversano, Angela; Leone, Giovanni
2014-05-01
In this contribution the problem of imaging a buried homogeneous circular cylinder is dealt with for a two-dimensional scalar geometry. Though the addressed geometry is extremely simple as compared to real world scenarios, it can be considered of interest for a classical GPR civil engineering applicative context: that is the subsurface prospecting of urban area in order to detect and locate buried utilities. A large body of methods for subsurface imaging have been presented in literature [1], ranging from migration algorithms to non-linear inverse scattering approaches. More recently, also spectral estimation methods, which benefit from sub-array data arrangement, have been proposed and compared in [2].Here a Time Reversal MUSIC (TRM) like method is employed. TRM has been initially conceived to detect point-like scatterers and then generalized to the case of extended scatterers [3]. In the latter case, no a priori information about the scatterers is exploited. However, utilities often can be schematized as circular cylinders. Here, we develop a TRM variant which use this information to properly tailor the steering vector while implementing TRM. Accordingly, instead of a spatial map [3], the imaging procedure returns the scatterer's parameters such as its center position, radius and dielectric permittivity. The study is developed by numerical simulations. First the free-space case is considered in order to more easily introduce the idea and the problem mathematical structure. Then the analysis is extended to the half-space case. In both situations a FDTD forward solver is used to generate the synthetic data. As usual in TRM, a multi-view/multi-static single-frequency configuration is considered and emphasis is put on the role played by the number of available sensors. Acknowledgement This work benefited from networking activities carried out within the EU funded COST Action TU1208 "Civil Engineering Applications of Ground Penetrating Radar." [1] A. Randazzo and R
Pottmann, Helmut
2014-11-26
Around 2005 it became apparent in the geometry processing community that freeform architecture contains many problems of a geometric nature to be solved, and many opportunities for optimization which however require geometric understanding. This area of research, which has been called architectural geometry, meanwhile contains a great wealth of individual contributions which are relevant in various fields. For mathematicians, the relation to discrete differential geometry is significant, in particular the integrable system viewpoint. Besides, new application contexts have become available for quite some old-established concepts. Regarding graphics and geometry processing, architectural geometry yields interesting new questions but also new objects, e.g. replacing meshes by other combinatorial arrangements. Numerical optimization plays a major role but in itself would be powerless without geometric understanding. Summing up, architectural geometry has become a rewarding field of study. We here survey the main directions which have been pursued, we show real projects where geometric considerations have played a role, and we outline open problems which we think are significant for the future development of both theory and practice of architectural geometry.
Maor, Eli
2014-01-01
If you've ever thought that mathematics and art don't mix, this stunning visual history of geometry will change your mind. As much a work of art as a book about mathematics, Beautiful Geometry presents more than sixty exquisite color plates illustrating a wide range of geometric patterns and theorems, accompanied by brief accounts of the fascinating history and people behind each. With artwork by Swiss artist Eugen Jost and text by acclaimed math historian Eli Maor, this unique celebration of geometry covers numerous subjects, from straightedge-and-compass constructions to intriguing configur
Geometry of Periodic Monopoles
Maldonado, Rafael
2013-01-01
BPS monopoles on $\\mathbb{R}^2\\timesS^1$ correspond, via the generalized Nahm transform, to certain solutions of the Hitchin equations on the cylinder $\\mathbb{R}\\times S^1$. The moduli space M of two monopoles with their centre-of-mass fixed is a 4-dimensional manifold with a natural hyperk\\"ahler metric, and its geodesics correspond to slow-motion monopole scattering. The purpose of this paper is to study the geometry of M in terms of the Nahm/Hitchin data, i.e. in terms of structures on $\\mathbb{R}\\times S^1$. In particular, we identify the moduli, derive the asymptotic metric on M, and discuss several geodesic surfaces and geodesics on M. The latter include novel examples of monopole dynamics.
Anaesthesia gas supply: Gas cylinders
Directory of Open Access Journals (Sweden)
Uma Srivastava
2013-01-01
Full Text Available Invention of oxygen cylinder was one of the most important developments in the field of medical practice. Oxygen and other gases were compressed and stored at high pressure in seamless containers constructed from hand-forged steel in1880. Materials technology has continued to evolve and now medical gas cylinders are generally made of steel alloys or aluminum. The filling pressure as well as capacity has increased considerably while at the same time the weight of cylinders has reduced. Today oxygen cylinder of equivalent size holds a third more oxygen but weighs about 20 kg less. The cylinders are of varying sizes and are color coded. They are tested at regular intervals by the manufacturer using hydraulic, impact, and tensile tests. The top end of the cylinder is fitted with a valve with a variety of number and markings stamped on it. Common valve types include: Pin index valve, bull nose, hand wheel and integral valve. The type of valve varies with cylinder size. Small cylinders have a pin index valve while large have a bull nose type. Safety features in the cylinder are: Color coding, pin index, pressure relief device, Bodok seal, and label attached etc., Safety rules and guidelines must be followed during storage, installation and use of cylinders to ensure safety of patients, hospital personnel and the environment.
Anaesthesia gas supply: gas cylinders.
Srivastava, Uma
2013-09-01
Invention of oxygen cylinder was one of the most important developments in the field of medical practice. Oxygen and other gases were compressed and stored at high pressure in seamless containers constructed from hand-forged steel in1880. Materials technology has continued to evolve and now medical gas cylinders are generally made of steel alloys or aluminum. The filling pressure as well as capacity has increased considerably while at the same time the weight of cylinders has reduced. Today oxygen cylinder of equivalent size holds a third more oxygen but weighs about 20 kg less. The cylinders are of varying sizes and are color coded. They are tested at regular intervals by the manufacturer using hydraulic, impact, and tensile tests. The top end of the cylinder is fitted with a valve with a variety of number and markings stamped on it. Common valve types include: Pin index valve, bull nose, hand wheel and integral valve. The type of valve varies with cylinder size. Small cylinders have a pin index valve while large have a bull nose type. Safety features in the cylinder are: Color coding, pin index, pressure relief device, Bodok seal, and label attached etc., Safety rules and guidelines must be followed during storage, installation and use of cylinders to ensure safety of patients, hospital personnel and the environment. PMID:24249883
Anaesthesia Gas Supply: Gas Cylinders
Srivastava, Uma
2013-01-01
Invention of oxygen cylinder was one of the most important developments in the field of medical practice. Oxygen and other gases were compressed and stored at high pressure in seamless containers constructed from hand-forged steel in1880. Materials technology has continued to evolve and now medical gas cylinders are generally made of steel alloys or aluminum. The filling pressure as well as capacity has increased considerably while at the same time the weight of cylinders has reduced. Today oxygen cylinder of equivalent size holds a third more oxygen but weighs about 20 kg less. The cylinders are of varying sizes and are color coded. They are tested at regular intervals by the manufacturer using hydraulic, impact, and tensile tests. The top end of the cylinder is fitted with a valve with a variety of number and markings stamped on it. Common valve types include: Pin index valve, bull nose, hand wheel and integral valve. The type of valve varies with cylinder size. Small cylinders have a pin index valve while large have a bull nose type. Safety features in the cylinder are: Color coding, pin index, pressure relief device, Bodok seal, and label attached etc., Safety rules and guidelines must be followed during storage, installation and use of cylinders to ensure safety of patients, hospital personnel and the environment. PMID:24249883
DEFF Research Database (Denmark)
Rusch, W.; Appel-Hansen, Jørgen; Klein, C; Mittra, R
1976-01-01
The relationship between the induced field ratio (IFR) of a cylinder and aperture blocking of a constant-phase aperture by cylindrical struts is discussed. An analytical technique is presented whereby the IFR of rectangular cylinders can be calculated using the method-of-moments with internal...... constraint points. An experimental technique using a forward-scattering range is used to measure the IFR's of square and circular cylinders in an anechoic chamber. These experimental results are compared with the theory, and their implications on aperture blocking losses and boresight cross polarization are...
Vortex-induced vibration of a square-section cylinder with incidence angle variation
Zhao, Jisheng; Nemes, Andras; Lo Jacono, David; Sheridan, John
2010-01-01
Vortex-induced vibration (VIV) occurs when vortex shedding from a body results in fluctuating forces that, in turn, cause the body to vibrate. This can result in undesired large-amplitude vibrations leading to structural damage or catastrophic failure. While much has been done on the VIV of a circular cylinder less has been done on other canonical bluff bodies, such as rectangular cylinders. The present experimental work studied the VIV of a square cross-section cylinder in a water channel, w...
International Nuclear Information System (INIS)
This article has dealt with the development and modeling of various contact theories for biological nanoparticles shaped as cylinders and circular crowned rollers for application in the manipulation of different biological micro/nanoparticles based on Atomic Force Microscope. First, the effective contact forces were simulated, and their impact on contact mechanics simulation was investigated. In the next step, the Hertz contact model was simulated and compared for gold and DNA nanoparticles with the three types of spherical, cylindrical, and circular crowned roller type contact geometries. Then by reducing the length of the cylindrical section in the circular crowned roller geometry, the geometry of the body was made to approach that of a sphere, and the results were compared for DNA nanoparticles. To anticipatory validate the developed theories, the results of the cylindrical and the circular crowned roller contacts were compared with the results of the existing spherical contact simulations. Following the development of these contact models for the manipulation of various biological micro/nanoparticles, the cylindrical and the circular crowned roller type contact theories were modeled based on the theories of Lundberg, Dowson, Nikpur, Heoprich, and Hertz for the manipulation of biological micro/nanoparticles. Then, for a more accurate validation, the results obtained from the simulations were compared with those obtained by the finite element method and with the experimental results available in previous articles. The previous research works on the simulation of nanomanipulation have mainly investigated the contact theories used in the manipulation of spherical micro/nanoparticles. However since in real biomanipulation situations, biological micro/nanoparticles of more complex shapes need to be displaced in biological environments, this article therefore has modeled and compared, for the first time, different contact theories for use in the biomanipulation of
Korayem, M. H.; Khaksar, H.; Taheri, M.
2013-11-01
This article has dealt with the development and modeling of various contact theories for biological nanoparticles shaped as cylinders and circular crowned rollers for application in the manipulation of different biological micro/nanoparticles based on Atomic Force Microscope. First, the effective contact forces were simulated, and their impact on contact mechanics simulation was investigated. In the next step, the Hertz contact model was simulated and compared for gold and DNA nanoparticles with the three types of spherical, cylindrical, and circular crowned roller type contact geometries. Then by reducing the length of the cylindrical section in the circular crowned roller geometry, the geometry of the body was made to approach that of a sphere, and the results were compared for DNA nanoparticles. To anticipatory validate the developed theories, the results of the cylindrical and the circular crowned roller contacts were compared with the results of the existing spherical contact simulations. Following the development of these contact models for the manipulation of various biological micro/nanoparticles, the cylindrical and the circular crowned roller type contact theories were modeled based on the theories of Lundberg, Dowson, Nikpur, Heoprich, and Hertz for the manipulation of biological micro/nanoparticles. Then, for a more accurate validation, the results obtained from the simulations were compared with those obtained by the finite element method and with the experimental results available in previous articles. The previous research works on the simulation of nanomanipulation have mainly investigated the contact theories used in the manipulation of spherical micro/nanoparticles. However since in real biomanipulation situations, biological micro/nanoparticles of more complex shapes need to be displaced in biological environments, this article therefore has modeled and compared, for the first time, different contact theories for use in the biomanipulation of
Lefschetz, Solomon
2012-01-01
An introduction to algebraic geometry and a bridge between its analytical-topological and algebraical aspects, this text for advanced undergraduate students is particularly relevant to those more familiar with analysis than algebra. 1953 edition.
Current collection by a long conducting cylinder in a flowing magnetized plasma
Singh, Nagendra; Vashi, Bharat I.
1990-01-01
The numerical techniques, the definitions, and the normalizations used in the simulations of plasma flow past a long conducting cylinder with a magnetic field along the cylinder axis are described. The effect of cross-field plasma transport on the current collection without any contribution to the current from the field-aligned motion of the plasma particles is highlighted. The electric fields in the structure create a two-cell circulation of the electrons near the cylinder. The cell in the wake region has negative potentials. A fan-shaped circulation cell forms around the cylinder and in this cell the potential is generally positive. The geometry and the size of this positive cell affect the current collection. The potential structure around the cylinder is examined, along with its effect on the current collection and its oscillatory behavior. The variation of the time-average current as a function of the relative motion between the plasma and the cylinder is also investigated.
Embedding problems in symplectic geometry
Schlenk, Felix
2005-01-01
Symplectic geometry is the geometry underlying Hamiltonian dynamics, and symplectic mappings arise as time-1-maps of Hamiltonian flows. The spectacular rigidity phenomena for symplectic mappings discovered in the last two decades show that certain things cannot be done by a symplectic mapping. For instance, Gromov''s famous "non-squeezing'''' theorem states that one cannot map a ball into a thinner cylinder by a symplectic embedding. The aim of this book is to show that certain other things can be done by symplectic mappings. This is achieved by various elementary and explicit symplectic embedding constructions, such as "folding", "wrapping'''', and "lifting''''. These constructions are carried out in detail and are used to solve some specific symplectic embedding problems. The exposition is self-contained and addressed to students and researchers interested in geometry or dynamics.
PUBLICATION OF ADMINISTRATIVE CIRCULAR
HR Department
2008-01-01
ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee meeting of 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in departmental secretariats. Human Resources Department Tel. 78003
Publication of administrative circular
HR Department
2009-01-01
ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee on 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in Departmental Secretariats. Human Resources Department Tel. 78003
Raybould, T. A.; Fedotov, V. A.; Papasimakis, N.; Kuprov, I.; Youngs, I. J.; Chen, W. T.; Tsai, D. P.; Zheludev, N. I.
2016-07-01
We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism will be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics.
Black holes on cylinders are not algebraically special
International Nuclear Information System (INIS)
We give a Petrov classification for five-dimensional metrics. We give an almost complete classification of Ricci-flat metrics that are static, have an SO(3) isometry group and have Petrov type 22. We use this classification to look for the metric of a black hole on a cylinder, i.e., a black hole with asymptotic geometry four-dimensional Minkowski space times a circle. Although a black string wrapped around the S1 and the five-dimensional black hole are both algebraically special, it turns out that the black hole on a cylinder is not
Non-invasive determination of external forces in vortex-pair-cylinder interactions
Hartmann, D.; Schröder, W.; Shashikanth, B. N.
2012-06-01
Expressions for the conserved linear and angular momenta of a dynamically coupled fluid + solid system are derived. Based on the knowledge of the flow velocity field, these expressions allow the determination of the external forces exerted on a body moving in the fluid such as, e.g., swimming fish. The verification of the derived conserved quantities is done numerically. The interaction of a vortex pair with a circular cylinder in various configurations of motions representing a generic test case for a dynamically coupled fluid + solid system is investigated in a weakly compressible Navier-Stokes setting using a Cartesian cut-cell method, i.e., the moving circular cylinder is represented by cut cells on a moving mesh. The objectives of this study are twofold. The first objective is to show the robustness of the derived expressions for the conserved linear and angular momenta with respect to bounded and discrete data sets. The second objective is to study the coupled dynamics of the vortex pair and a neutrally buoyant cylinder free to move in response to the fluid stresses exerted on its surface. A comparison of the vortex-body interaction with the case of a fixed circular cylinder evidences significant differences in the vortex dynamics. When the cylinder is fixed strong secondary vorticity is generated resulting in a repeating process between the primary vortex pair and the cylinder. In the neutrally buoyant cylinder case, a stable structure consisting of the primary vortex pair and secondary vorticity shear layers stays attached to the moving cylinder. In addition to these fundamental cases, the vortex-pair-cylinder interaction is studied for locomotion at constant speed and locomotion at constant thrust. It is shown that a similar vortex structure like in the neutrally buoyant cylinder case is obtained when the cylinder moves away from the approaching vortex pair at a constant speed smaller than the vortex pair translational velocity. Finally, the idealized
Approximation of Surfaces by Cylinders
DEFF Research Database (Denmark)
Randrup, Thomas
1998-01-01
We present a new method for approximation of a given surface by a cylinder surface. It is a constructive geometric method, leading to a monorail representation of the cylinder surface. By use of a weighted Gaussian image of the given surface, we determine a projection plane. In the orthogonal...... projection of the surface onto this plane, a reference curve is determined by use of methods for thinning of binary images. Finally, the cylinder surface is constructed as follows: the directrix of the cylinder surface is determined by a least squares method minimizing the distance to the points in the...
'PRIZE': A program for calculating collision probabilities in R-Z geometry
International Nuclear Information System (INIS)
PRIZE is an IBM7090 program which computes collision probabilities for systems with axial symmetry and outputs them on cards in suitable format for the PIP1 program. Its method of working, data requirements, output, running time and accuracy are described. The program has been used to compute non-escape (self-collision) probabilities of finite circular cylinders, and a table is given by which non-escape probabilities of slabs, finite and infinite circular cylinders, infinite square cylinders, cubes, spheres and hemispheres may quickly be calculated to 1/2% or better. (author)
The capillary interaction between two vertical cylinders
Cooray, Himantha
2012-06-27
Particles floating at the surface of a liquid generally deform the liquid surface. Minimizing the energetic cost of these deformations results in an inter-particle force which is usually attractive and causes floating particles to aggregate and form surface clusters. Here we present a numerical method for determining the three-dimensional meniscus around a pair of vertical circular cylinders. This involves the numerical solution of the fully nonlinear Laplace-Young equation using a mesh-free finite difference method. Inter-particle force-separation curves for pairs of vertical cylinders are then calculated for different radii and contact angles. These results are compared with previously published asymptotic and experimental results. For large inter-particle separations and conditions such that the meniscus slope remains small everywhere, good agreement is found between all three approaches (numerical, asymptotic and experimental). This is as expected since the asymptotic results were derived using the linearized Laplace-Young equation. For steeper menisci and smaller inter-particle separations, however, the numerical simulation resolves discrepancies between existing asymptotic and experimental results, demonstrating that this discrepancy was due to the nonlinearity of the Laplace-Young equation. © 2012 IOP Publishing Ltd.
DEFF Research Database (Denmark)
Hansen, Lennard Højbjerg
2014-01-01
It has been an accepted precept in film theory that specific stylistic features do not express specific content. Nevertheless, it is possible to find many examples in the history of film in which stylistic features do express specific content: for instance, the circular camera movement is used...... circular camera movement. Keywords: embodied perception, embodied style, explicit narration, interpretation, style pattern, television style...
Keskinen, Jukka-Pekka; Vuorinen, Ville; Kaario, Ossi; Larmi, Martti
2015-01-01
Julkaisun kokoteksti on luettavissa vain Aalto-tunnuksilla. Please note that access to the fulltext is limited to Aalto staff and students. Large eddy simulation (LES) in an axisymmetric piston-cylinder geometry was carried out using three LES approaches: 1) Smagorinsky subgrid scale model, 2) implicit LES, and 3) scale selective discretisation (SSD). In addition to the LES subgrid scale model sensitivity study, two additional simulations were carried out in order to understand the role...
Connes, Alain
1994-01-01
This English version of the path-breaking French book on this subject gives the definitive treatment of the revolutionary approach to measure theory, geometry, and mathematical physics developed by Alain Connes. Profusely illustrated and invitingly written, this book is ideal for anyone who wants to know what noncommutative geometry is, what it can do, or how it can be used in various areas of mathematics, quantization, and elementary particles and fields.Key Features* First full treatment of the subject and its applications* Written by the pioneer of this field* Broad applications in mathemat
Robinson, Gilbert de B
2011-01-01
This brief undergraduate-level text by a prominent Cambridge-educated mathematician explores the relationship between algebra and geometry. An elementary course in plane geometry is the sole requirement for Gilbert de B. Robinson's text, which is the result of several years of teaching and learning the most effective methods from discussions with students. Topics include lines and planes, determinants and linear equations, matrices, groups and linear transformations, and vectors and vector spaces. Additional subjects range from conics and quadrics to homogeneous coordinates and projective geom
Levenson, Esther; Tsamir, Pessia
2011-01-01
Recently the issue of early childhood mathematics has come to the fore and with it the importance of teaching geometrical concepts and reasoning from a young age. Geometry is a key domain mentioned in many national curricula and may also support the learning of other mathematical topics, such as number and patterns. This book is based on the rich experience (research and practice) of the authors and is devoted entirely to the learning and teaching of geometry in preschool. The first part of the book is dedicated to children's geometrical thinking, building concept images in line with concept d
Berger, Marcel
2010-01-01
Both classical geometry and modern differential geometry have been active subjects of research throughout the 20th century and lie at the heart of many recent advances in mathematics and physics. The underlying motivating concept for the present book is that it offers readers the elements of a modern geometric culture by means of a whole series of visually appealing unsolved (or recently solved) problems that require the creation of concepts and tools of varying abstraction. Starting with such natural, classical objects as lines, planes, circles, spheres, polygons, polyhedra, curves, surfaces,
Perfect Circular Dichroic Metamirrors
Wang, Zuojia; Liu, Yongmin
2015-01-01
In nature, the beetle Chrysina gloriosa derives its iridescence by selectively reflecting left-handed circularly polarized light only. Here, for the first time, we introduce and demonstrate the optical analogue based on an ultrathin metamaterial, which we term circular dichroic metamirror. A general method to design the circular dichroic metasmirror is presented under the framework of Jones calculus. It is analytically shown that the metamirror can be realized by two layers of anisotropic metamaterial structures, in order to satisfy the required simultaneous breakings of n-fold rotational (n>2) and mirror symmetries. We design an infrared metamirror, which shows perfect reflectance for left-handed circularly polarized light without reversing its handedness, while almost completely absorbs right-handed circularly polarized light. These findings offer new methodology to realize novel chiral optical devices for a variety of applications, including polarimetric imaging, molecular spectroscopy, as well as quantum ...
Circular object recognition based on shape parameters
Institute of Scientific and Technical Information of China (English)
Chen Aijun; Li Jinzong; Zhu Bing
2007-01-01
To recognize circular objects rapidly in satellite remote sensing imagery, an approach using their geometry properties is presented.The original image is segmented to be a binary one by one dimension maximum entropy threshold algorithm and the binary image is labeled with an algorithm based on recursion technique.Then, shape parameters of all labeled regions are calculated and those regions with shape parameters satisfying certain conditions are recognized as circular objects.The algorithm is described in detail, and comparison experiments with the randomized Hough transformation (RHT) are also provided.The experimental results on synthetic images and real images show that the proposed method has the merits of fast recognition rate, high recognition efficiency and the ability of anti-noise and anti-jamming.In addition, the method performs well when some circular objects are little deformed and partly misshapen.
ŢĂLU D.L.MIHAI; ŢĂLU D.L. ŞTEFAN
2010-01-01
This paper analyse through the finite element method (FEM) the hydraulic cylinder of linear hydraulic motor from horizontal Hydraulic Press – 2 MN. The analysis of the hydraulic cylinder of linear hydraulic motor from horizontal Hydraulic Press – 2 MN was made for determination of displacements and deformations. A three-dimensional model of the hydraulic cylinder with a complex geometry was generated based on the designed data. Finite element analysis was performed using COSMOSWorks software....
Kirillova O.I.
2012-01-01
The problem of determining the stress state near the thin rigid inclusions in an infinite cylinder of arbitrary cross-section under oscillations of longitudinal shear. We propose an approach to satisfy the conditions separately on the surface of inclusions and on the boundary of the cylinder. The approximate formulas for calculating stress intensity factors are obtained to investigate the influence of frequency oscillations, geometry of the cylinder and location of the inclusions on their val...
Gordienko, S.; Baeva, T.; Pukhov, A.
2005-01-01
It is shown that plasma-based optics can be used to guide and focus highly divergent laser-generated ion beams. A hollow cylinder is considered, which initially contains a hot electron population. Plasma streaming toward the cylinder axis maintains a focusing electrostatic field due to the positive radial pressure gradient. The cylinder works as thick lens, whose parameters are obtained from similarity theory for freely expanding plasma in cylindrical geometry. Because the lens parameters are...
Directory of Open Access Journals (Sweden)
Kirillova O.I.
2012-12-01
Full Text Available The problem of determining the stress state near the thin rigid inclusions in an infinite cylinder of arbitrary cross-section under oscillations of longitudinal shear. We propose an approach to satisfy the conditions separately on the surface of inclusions and on the boundary of the cylinder. The approximate formulas for calculating stress intensity factors are obtained to investigate the influence of frequency oscillations, geometry of the cylinder and location of the inclusions on their values.
Bounds on Two-Phase Frictional Pressure Gradient and Void Fraction in Circular Pipes
Awad, M M; Muzychka, Y. S.
2014-01-01
Simple rules are developed for obtaining rational bounds for two-phase frictional pressure gradient and void fraction in circular pipes. The bounds are based on turbulent-turbulent flow assumption. Both the lower and upper bounds for frictional pressure gradient are based on the separate cylinders formulation. For frictional pressure gradient, the lower bound is based on the separate cylinders formulation that uses the Blasius equation to represent the Fanning friction factor while the upper ...
Desseyn, H. O.; And Others
1985-01-01
Compares linear-nonlinear and planar-nonplanar geometry through the valence-shell electron pairs repulsion (V.S.E.P.R.), Mulliken-Walsh, and electrostatic force theories. Indicates that although the V.S.E.P.R. theory has more advantages for elementary courses, an explanation of the best features of the different theories offers students a better…
A whisker sensor: role of geometry and boundary conditions
Hans, Hendrik; Valdivia Y Alvarado, Pablo; Thekoodan, Dilip; Jianmin, Miao; Triantafyllou, Michael
2011-11-01
Harbor seal whiskers are currently being studied for their role in sensing and tracking of the fluid structures left in wakes. Seal whiskers are exposed to incoming flows and are subject to self-induced vibrations. The whisker's unusual geometry is thought to reduce these self-induced disturbances and facilitate a stable reference for wake sensing. An experimental platform was designed to measure flow-induced displacements and vibrations at the base of whisker-like models. Four different whisker-like models (scale: 3x) were towed at different speeds down a towing tank and base displacements in the direction of motion and in the perpendicular axis were measured. Each model incorporated a particular geometrical feature found in harbor seal whiskers. Three different visco-elastic supports were used to mimic various boundary conditions at the base of the whisker models. The effects of geometrical features and boundary conditions on measured base vibrations at three relevant Reynolds numbers are discussed. The material properties of a model's base influence its sensitivity. When compared to a circular cylinder model, whisker models show almost no sign of VIV.
A numerical investigation of sub-wavelength resonances in polygonal metamaterial cylinders
DEFF Research Database (Denmark)
Arslanagic, Samel; Breinbjerg, Olav
2009-01-01
The sub-wavelength resonances, known to exist in metamaterial radiators and scatterers of circular cylindrical shape, are investigated with the aim of determining if these resonances also exist for polygonal cylinders and, if so, how they are affected by the shape of the polygon. To this end, a set...
Solvable critical dense polymers on the cylinder
International Nuclear Information System (INIS)
A lattice model of critical dense polymers is solved exactly on a cylinder with finite circumference. The model is the first member LM(1,2) of the Yang–Baxter integrable series of logarithmic minimal models. The cylinder topology allows for non-contractible loops with fugacity α that wind around the cylinder or for an arbitrary number l of defects that propagate along the full length of the cylinder. Using an enlarged periodic Temperley–Lieb algebra, we set up commuting transfer matrices acting on states whose links are considered distinct with respect to connectivity around the front or back of the cylinder. These transfer matrices satisfy a functional equation in the form of an inversion identity. For even N, this involves a non-diagonalizable braid operator J and an involution R = − (J3 − 12J)/16 = (−1)F with eigenvalues R=(-1)l/2. This is reminiscent of supersymmetry with a pair of defects interpreted as a fermion. The number of defects l thus separates the theory into Ramond (l/2 even), Neveu–Schwarz (l/2 odd) and Z4 (l odd) sectors. For the case of loop fugacity α = 2, the inversion identity is solved exactly sector by sector for the eigenvalues in finite geometry. The eigenvalues are classified according to the physical combinatorics of the patterns of zeros in the complex spectral-parameter plane. This yields selection rules for the physically relevant solutions to the inversion identity. The finite-size corrections are obtained from Euler–Maclaurin formula. In the scaling limit, we obtain the conformal partition functions as sesquilinear forms and confirm the central charge c = − 2 and conformal weights Δ, Δ-bar =Δt=(t2-1)/8. Here t=l/2 and t=2r-s element of N in the l even sectors with Kac labels r = 1, 2, 3,...;s = 1, 2 while t ∈ Z - ½ in the l odd sectors. Strikingly, the l/2 odd sectors exhibit a W-extended symmetry but the l/2 even sectors do not. Moreover, the naive trace summing over all l even sectors does not yield a
Pewsey, Arthur; Ruxton, Graeme D
2013-01-01
Circular Statistics in R provides the most comprehensive guide to the analysis of circular data in over a decade. Circular data arise in many scientific contexts whether it be angular directions such as: observed compass directions of departure of radio-collared migratory birds from a release point; bond angles measured in different molecules; wind directions at different times of year at a wind farm; direction of stress-fractures in concretebridge supports; longitudes of earthquake epicentres or seasonal and daily activity patterns, for example: data on the times of day at which animals are c
The effects of axis ratio on laminar fluid flow around an elliptical cylinder
International Nuclear Information System (INIS)
An elliptical cylinder is a generic shape which represents a flat plate at its minor to major axis ratio (AR) limits of zero and infinity, and a circular cylinder at AR of unity. While incompressible flows over a streamwise flat plate (AR = 0), a cross-stream flat plate (AR = ∞), and a circular cylinder have been studied extensively, the role of AR on the detailed flow structure is still not well understood. Therefore, a numerical study was conducted to examine the flow field around an elliptical cylinder over a range of ARs from 0.3 to 1, with the major axis parallel to the free-stream, at a Reynolds number of 40 based on the hydraulic diameter. The control volume approach of FLUENT was used to solve the fluid flow equations, assuming the flow over the cylinder is unbounded, steady, incompressible and two-dimensional. It has been found that a pair of steady vortices forms when AR reaches a critical value of 0.34; below this value no vortices are formed behind the elliptical cylinder. Various wake parameters, drag coefficient, pressure and velocity distributions, have been characterized as functions of AR. The wake size and the drag coefficient are found to increase with the increase of AR. Quadratic correlations have been obtained to describe the relations of wake length and drag coefficient with axis ratio
Petersen, Peter
2016-01-01
Intended for a one year course, this text serves as a single source, introducing readers to the important techniques and theorems, while also containing enough background on advanced topics to appeal to those students wishing to specialize in Riemannian geometry. This is one of the few Works to combine both the geometric parts of Riemannian geometry and the analytic aspects of the theory. The book will appeal to a readership that have a basic knowledge of standard manifold theory, including tensors, forms, and Lie groups. Important revisions to the third edition include: a substantial addition of unique and enriching exercises scattered throughout the text; inclusion of an increased number of coordinate calculations of connection and curvature; addition of general formulas for curvature on Lie Groups and submersions; integration of variational calculus into the text allowing for an early treatment of the Sphere theorem using a proof by Berger; incorporation of several recent results about manifolds with posit...
Directory of Open Access Journals (Sweden)
Leonardo Paris
2012-06-01
Full Text Available Lo studio degli ingranaggi si basa sulle geometrie coniugate in cui due curve o due superfici si mantengono costantemente in contatto pur se in movimento reciproco. La teoria geometrica degli ingranaggi fino alla fine del XIX secolo era uno dei molteplici rami nelle applicazioni della Geometria Descrittiva. Lo studio si basa sulla conoscenza delle principali proprietà delle curve piane e gobbe e delle loro derivate. La specificità del tema è che queste geometrie nel momento in cui si devono relazionare con le loro coniugate, devono rispettare dei vincoli che altrimenti non avrebbero. Si vuole evidenziare attraverso casi concreti il ruolo della geometria descrittiva nel passaggio dal teorico al pratico riproponendo in chiave informatica, temi e procedure di indagine spesso passati in secondo piano se non addirittura dimenticati.
Rallian "equivalent" cylinders reconsidered: comparisons with literal compartments.
Goldfinger, M D
2005-06-01
In Rall's "equivalent" cylinder morphological-to-electrical transformation, neuronal arborizations are reduced to single unbranched core-conductors. The conventional assumption that such an "equivalent" reconstructs the electrical properties of the fibers it represents was tested directly; electrical properties and responses of "equivalent" cylinders were compared with those of their literal branch constituents for fibers with a single symmetrical bifurcation. The numerical solution methods were validated independently by their accurate reconstruction of the responses of an analog circuit configured with compartmental architecture to solve the cable equation for passive fibers with a symmetrical bifurcation. In passive fibers, "equivalent" cylinders misestimated the spatial distribution of voltage amplitudes and steady-state input resistance, partly due to the lack of axial current bifurcation. In active fibers with a single propagating action potential, the spatial distributions of point-to-point conduction velocity values (measured in meters/second) for a literal branch point differed significantly from those of their "equivalent" cylinders. "Equivalent" cylinders also underestimated the diameter-dependent delay in propagation through the branch point and branches, due to the larger "equivalent" diameter. Corrections to the "equivalent" cylinder did not reconcile differences between "equivalent" and literal models. However, "equivalent" and literal branch fibers had the same (a) steady-state resistance "looking into" an isolated symmetrical branch point and (b) geometry-independent point-to-point propagation velocity when measured in space constants per millisecond except within +/-1 space constant from the geometrical inhomogeneity. In summary, Rall's "equivalent" cylinders did not accurately reconstruct all passive or active electrophysiological properties and responses of their literal compartments. For the modeling of individual neurons, the requirement of
General Geometry and Geometry of Electromagnetism
Shahverdiyev, Shervgi S.
2002-01-01
It is shown that Electromagnetism creates geometry different from Riemannian geometry. General geometry including Riemannian geometry as a special case is constructed. It is proven that the most simplest special case of General Geometry is geometry underlying Electromagnetism. Action for electromagnetic field and Maxwell equations are derived from curvature function of geometry underlying Electromagnetism. And it is shown that equation of motion for a particle interacting with electromagnetic...
J-holomorphic curves with boundary in bounded geometry
Groman, Yoel; Solomon, Jake P.
2013-01-01
The fundamental properties of $J$-holomorphic maps depend on two inequalities: The gradient inequality gives a pointwise bound on the differential of a $J$-holomorphic map in terms of its energy. The cylinder inequality stipulates and quantifies the exponential decay of energy along cylinders of small total energy. We show these inequalities hold uniformly if the geometry of the target symplectic manifold and Lagrangian boundary condition is appropriately bounded.
Scalar cylinder-plate and cylinder-cylinder Casimir interaction in higher dimensional spacetime
Teo, L P
2015-01-01
We study the cylinder-plate and the cylinder-cylinder Casimir interaction in the $(D+1)$-dimensional Minkowski spacetime due to the vacuum fluctuations of massless scalar fields. Different combinations of Dirichlet (D) and Neumann (N) boundary conditions are imposed on the two interacting objects. For the cylinder-cylinder interaction, we consider the case where one cylinder is inside the other, and the case where the two cylinders are outside each other. By computing the transition matrices of the objects and the translation matrices that relate different coordinate systems, the explicit formulas for the Casimir interaction energies are derived. Using perturbation technique, we compute the small separation asymptotic expansions of the Casimir interaction energies up to the next-to-leading order terms. The leading terms coincide with the respective results obtained using proximity force approximation, which is of order $d^{-D+1/2}$, where $d$ is the distance between the two objects. The results on the next-to...
Stability of the expansion-free charged cylinder
International Nuclear Information System (INIS)
We study the instability of cylindrically symmetric expansion-free anisotropic geometry in the presence of electromagnetic field. For smooth matching of the interior geometry with the exterior, junction conditions are formulated. The perturbation scheme is taken into account to describe the dynamical equation and categorize the Newtonian, post-Newtonian as well as post-post Newtonian regime. It is concluded that physical parameters, i.e., energy density, principal stresses of the fluid and electric charge control the stability of the cylinder
Steady flow through a constricted cylinder by multiparticle collision dynamics.
Bedkihal, Salil; Kumaradas, J Carl; Rohlf, Katrin
2013-10-01
The flow characterization of blood through healthy and diseased flow geometries is of interest to researchers and clinicians alike, as it may allow for early detection, and monitoring, of cardiovascular disease. In this paper, we use a numerically efficient particle-based flow model called multiparticle collision dynamics (MPC for short) to study the effect of compressibility and slip of flow of a Newtonian fluid through a cylinder with a local constriction. We use a cumulative averaging method to compare our MPC results to the finite-element solution of the incompressible no-slip Navier-Stokes equations in the same geometry. We concentrate on low Reynolds number flows [[Formula: see text
Stability of the expansion-free charged cylinder
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Bhatti, M. Zaeem Ul Haq, E-mail: msharif.math@pu.edu.pk, E-mail: mzaeem.math@gmail.com [Department of Mathematics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590 (Pakistan)
2013-10-01
We study the instability of cylindrically symmetric expansion-free anisotropic geometry in the presence of electromagnetic field. For smooth matching of the interior geometry with the exterior, junction conditions are formulated. The perturbation scheme is taken into account to describe the dynamical equation and categorize the Newtonian, post-Newtonian as well as post-post Newtonian regime. It is concluded that physical parameters, i.e., energy density, principal stresses of the fluid and electric charge control the stability of the cylinder.
Process designing for laser forming of circular sheet metal
Institute of Scientific and Technical Information of China (English)
Q. Nadeem; W. J. Seong; S. J. Na
2012-01-01
Laser forming is a new type of flexible manufacturing process that has become viable for the shaping of metallic components.Process designing of laser forming involves finding a set of process parameters,including laser power,laser scanning paths,and scanning speed,given a prescribed shape.To date,research has focused on process designing for rectangular plates,and only a few studies are presented for axis-symmetric geometries like circular plates.In the present study,process designing for axis-symmetric geometries-with focus on class of shapes--is handled using a formerly proposed distance-based approach.A prescribed shape is achieved for geometries such as quarter-circular and half-circular ring plates.Experimental results verify the applicability of the proposed method for a class of shapes.%Laser forming is a new type of flexible manufacturing process that has become viable for the shaping of metallic components. Process designing of laser forming involves finding a set of process parameters, including laser power, laser scanning paths, and scanning speed, given a prescribed shape. To date, research has focused on process designing for rectangular plates, and only a few studies are presented for axis-symmetric geometries like circular plates. In the present study, process designing for axis-symmetric geometries-with focus on class of shapes-is handled using a formerly proposed distance-based approach. A prescribed shape is achieved for geometries such as quarter-circular and half-circular ring plates. Experimental results verify the applicability of the proposed method for a class of shapes.
Water Entry and Exit of Horizontal Cylinder in Free Surface Flow
International Nuclear Information System (INIS)
This paper describes two-dimensional numerical simulations of the water entry and exit of horizontal circular cylinder at constant velocity. The deformation of free surface is described by Navier-Stokes (N S) equations of incompressible and viscous fluid with additional transport equation of the volume-of-fluid (VOF). The motion of the cylinder is modeled by the associated momentum source term implemented in the Phoenicis (Parabolic Hyperbolic Or Elliptic Numerical Integration Code Series) code. The domain is discretized by a fixed Cartesian grid using a finite volume method and the cylinder is represented and cut cell method. The simulated results are compared with the numerical results of Lin (2007). This comparison shows good agreement in terms of free surface evolution for water exit and sinking. However, for water entry, the jet flow simulated by Lin is not reproduced. The free surface deformation around the cylinder in downward direction is accurately predicted
Modeling of Piezoelectric Energy Harvesting from Freely Oscillating Cylinders in Water Flow
Directory of Open Access Journals (Sweden)
Min Zhang
2014-01-01
Full Text Available A concept of energy harvesting from vortex-induced vibrations of a rigid circular cylinder with two piezoelectric beams attached is investigated. The variations of the power levels with the free stream velocity are determined. A mathematical approach including the coupled cylinder motion and harvested voltage is presented. The effects of the load resistance, piezoelectric materials, and circuit combined on the natural frequency and damping of the vibratory system are determined by performing a linear analysis. The dynamic response of the cylinder and harvested energy are investigated. The results show that the harvested level in SS and SP&PS modes is the same with different values of load resistance. For four different system parameters, the results show that the bigger size of cylinder with PZT beams can obtain the higher harvested power.
Institute of Scientific and Technical Information of China (English)
Amir Mahmood; Saima Parveen; Najeeb Alam Khan
2011-01-01
The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a second grade fluid, between two infinite coaxial circular cylinders,are determined by means of the Laplace and Hankel transforms. At time t = 0, the fluid and both the cylinders are at rest and at t = 0+, cylinders suddenly begin to oscillate around their common axis in a simple harmonic way having angular frequencies ωl and ω2. The obtained solutions satisfy the governing differential equation and all imposed initial and boundary conditions. The solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for Newtonian fluid are also obtained as limiting cases of our general solutions.
Enumeration of holomorphic cylinders in log Calabi-Yau surfaces. I
Yu, Tony Yue
2015-01-01
We define the counting of holomorphic cylinders in log Calabi-Yau surfaces. Although we start with a complex log Calabi-Yau surface, the counting is achieved by applying methods from non-archimedean geometry. This gives rise to new geometric invariants. We prove that the counting satisfies a property of symmetry. Explicit calculations are given for a del Pezzo surface in detail, which verify the conjectured wall-crossing formula for the focus-focus singularity. Our holomorphic cylinders are e...
CONTACT STRESSES IN A TRANSVERSELY ISOTROPIC SOLID CYLINDER LATERALLY COMPRESSED BY AN INDENTER
YAPICI, Ahmet; Avci, Ahmet; Uyaner, Mesut
2004-01-01
In this study, an elastostatic contact problem for a laterally compressed transversely isotropic cylinder subjected to radial compression through a circumferential rigid indenter is considered. The extent of the contact region and the stress distribution are sought. It is assumed that the contact between the cylinder and the rigid indenter is frictionless and only compressive normal tractions can be transmitted through the interface. Due to the geometry of the configuration, Fourier transform...
Heat transfer to a horizontal cylinder in a shallow bubble column
Tow, Emily W.; Lienhard, John H.
2014-01-01
Heat transfer coefficient correlations for tall bubble columns are unable to predict heat transfer in shallow bubble columns, which have unique geometry and fluid dynamics. In this work, the heat transfer coefficient is measured on the surface of a horizontal cylinder immersed in a shallow air–water bubble column. Superficial velocity, liquid depth, and cylinder height and horizontal position with respect to the sparger orifices are varied. The heat transfer coefficient is found to increase w...
Rotating Cylinder Treatment System Demonstration
In August 2008, a rotating cylinder treatment system (RCTSTM) demonstration was conducted near Gladstone, CO. The RCTSTM is a novel technology developed to replace the aeration/oxidation and mixing components of a conventional lime precipitation treatment s...
Plasmonic corrugated cylinder-cone terahertz probe.
Yao, Haizi; Zhong, Shuncong
2014-08-01
The spoof surface plasmon polariton (SPP) effect on the electromagnetic field distribution near the tip of a periodically corrugated metal cylinder-cone probe working at the terahertz regime was studied. We found that radially polarized terahertz radiation could be coupled effectively through a spoof SPP into a surface wave and propagated along the corrugated surface, resulting in more than 20× electric field enhancement near the tip of probe. Multiple resonances caused by the antenna effect were discussed in detail by finite element computation and theoretical analysis of dispersion relation for spoof SPP modes. Moreover, the key figures of merit such as the resonance frequency of the SPP can be flexibly tuned by modifying the geometry of the probe structure, making it attractive for application in an apertureless background-free terahertz near-field microscope. PMID:25121543
Scalar cylinder-plate and cylinder-cylinder Casimir interaction in higher dimensional spacetime
Teo, Lee-Peng
2015-07-01
We study the cylinder-plate and the cylinder-cylinder Casimir interaction in the (D +1 )-dimensional Minkowski spacetime due to the vacuum fluctuations of massless scalar fields. Different combinations of Dirichlet (D) and Neumann (N) boundary conditions are imposed on the two interacting objects. For the cylinder-cylinder interaction, we consider the case where one cylinder is inside the other and the case where the two cylinders are outside each other. By computing the transition matrices of the objects and the translation matrices that relate different coordinate systems, the explicit formulas for the Casimir interaction energies are derived. From these formulas, we compute the large separation and small separation asymptotic behaviors of the Casimir interaction. For the cylinder-plate interaction with R ≪L , where R is the radius of the cylinder and L is the distance from the center of the cylinder to the plate, the order of decay of the Casimir interaction only depends on the boundary conditions imposed on the cylinder. The orders are L-D +1/ln (L ) and L-D -1/ln L , respectively, for the Dirichlet and Neumann boundary conditions on the cylinder. For two cylinders with radii R1 and R2 lying parallelly outside each other, the orders of decay of the Casimir interaction energies when R1+R2≪L are L-D +1/(ln L )2, L-D -1/ln L , and L-D -3, respectively, for DD, DN/ND, and NN boundary conditions, where L is the distance between the centers of the cylinders. The more interesting and important characteristic of Casimir interaction appears at small separation. Using the perturbation technique, we compute the small separation asymptotic expansions of the Casimir interaction energies up to the next-to-leading-order terms. The leading terms coincide with the respective results obtained using the proximity force approximation, which is of order d-D +1 /2 , where d is the distance between the two objects. The results on the next-to-leading-order terms are more
Finite Element Models and Properties of a Stiffened Floor-Equipped Composite Cylinder
Grosveld, Ferdinand W.; Schiller, Noah H.; Cabell, Randolph H.
2010-01-01
Finite element models were developed of a floor-equipped, frame and stringer stiffened composite cylinder including a coarse finite element model of the structural components, a coarse finite element model of the acoustic cavities above and below the beam-supported plywood floor, and two dense models consisting of only the structural components. The report summarizes the geometry, the element properties, the material and mechanical properties, the beam cross-section characteristics, the beam element representations and the boundary conditions of the composite cylinder models. The expressions used to calculate the group speeds for the cylinder components are presented.
Compact waveguide circular polarizer
Energy Technology Data Exchange (ETDEWEB)
Tantawi, Sami G.
2016-08-16
A multi-port waveguide is provided having a rectangular waveguide that includes a Y-shape structure with first top arm having a first rectangular waveguide port, a second top arm with second rectangular waveguide port, and a base arm with a third rectangular waveguide port for supporting a TE.sub.10 mode and a TE.sub.20 mode, where the end of the third rectangular waveguide port includes rounded edges that are parallel to a z-axis of the waveguide, a circular waveguide having a circular waveguide port for supporting a left hand and a right hand circular polarization TE.sub.11 mode and is coupled to a base arm broad wall, and a matching feature disposed on the base arm broad wall opposite of the circular waveguide for terminating the third rectangular waveguide port, where the first rectangular waveguide port, the second rectangular waveguide port and the circular waveguide port are capable of supporting 4-modes of operation.
Wetting on Lines and Lattices of Cylinders
Osborn, W. R.; Yeomans, J. M.
1994-01-01
This paper discusses wetting and capillary condensation transitions on a line and a rectangular array of cylinders using an interface potential formalism. For a line of cylinders, there is a capillary condensation transition followed by complete wetting if the cylinders are sufficiently close together. Both transitions disappear as the cylinder separation is increased. The dependence of the wetting phase diagram of a rectangular array of cylinders is discussed as a function of the chemical po...
Optimum Stirling engine geometry
Energy Technology Data Exchange (ETDEWEB)
Senft, J.R. [University of Wisconsin, River Walls, WI (United States). Mathematics Dept.
2002-07-01
This paper combines the author's work on mechanical efficiency of reciprocating engines with the classic Schmidt thermodynamic model for Stirling engines and revisits the problem of identifying optimal engine geometry. All previous optimizations using the Schmidt theory focused on obtaining a maximal specific indicated cyclic work. This does not necessarily produce the highest shaft output. Indeed, some optima based upon indicated work would yield engines that cannot run at all due to excessive intrinsic mechanical losses. The analysis presented in this paper shows how to optimize for shaft or brake work output. Specifically, it presents solutions to the problem of finding the piston-to-displacer swept volume ratio and phase angle which will give the maximum brake output for a given total swept volume, given temperature extremes, a given mean operating pressure, and a given engine mechanism effectiveness. The paper covers the split-cylinder or gamma-type Stirling in detail, serving as a model for similar analysis of the other Stirling engine configurations. (author)
Effect of particle geometry and micro-structure on fast pyrolysis of beech wood
Westerhof, R.J.M.; Nygard, H.; Swaaij, van W.P.M.; Kersten, S.R.A.; Brilman, D.W.F.
2012-01-01
The influence of particle geometry and microstructure in fast pyrolysis of beech wood has been investigated. Milled wood particles (<0.08–2.4 mm) and natural wood cylinders (2–14 mm) with different lengths (10–50 mm) and artificial wood cylinders (Dp = 0.5–14 mm) made of steel walls, filled with sma
Khirevich, Siarhei; Höltzel, Alexandra; Tallarek, Ulrich
2011-06-28
We study the time and length scales of hydrodynamic dispersion in confined monodisperse sphere packings as a function of the conduit geometry. By a modified Jodrey-Tory algorithm, we generated packings at a bed porosity (interstitial void fraction) of ε=0.40 in conduits with circular, rectangular, or semicircular cross section of area 100πd(p)(2) (where d(p) is the sphere diameter) and dimensions of about 20d(p) (cylinder diameter) by 6553.6d(p) (length), 25d(p) by 12.5d(p) (rectangle sides) by 8192d(p) or 14.1d(p) (radius of semicircle) by 8192d(p), respectively. The fluid-flow velocity field in the generated packings was calculated by the lattice Boltzmann method for Péclet numbers of up to 500, and convective-diffusive mass transport of 4×10(6) inert tracers was modelled with a random-walk particle-tracking technique. We present lateral porosity and velocity distributions for all packings and monitor the time evolution of longitudinal dispersion up to the asymptotic (long-time) limit. The characteristic length scales for asymptotic behaviour are explained from the symmetry of each conduit's velocity field. Finally, we quantify the influence of the confinement and of a specific conduit geometry on the velocity dependence of the asymptotic dispersion coefficients. PMID:21576163
Experimental investigation of a flow-induced oscillating cylinder with two-degree-of-freedom
International Nuclear Information System (INIS)
The vibration induced by flow, called flow-induced vibration, causes abnormal driving and machinery-related noise. Although the phenomenon of flow-induced vibration of bluff bodies has been studied extensively, the vast majority of these studies have concentrated solely on one-degree-of-freedom oscillation as in-line or cross-flow. Moreover, there are only three studies have carried out for two-degree-of-freedom oscillation tests, especially, these three studies have done with elastically mounted cylinder. In the present study, the experiment focuses on two-degree-of-freedom free-oscillation tests in a water channel. The circular cylinder is cantilever in shape with same mass ratio and small natural frequency (typically 65Hz) between in-line and cross-flow direction. Raynolds number is range from 1.17x103 to 2.6x104. The frequency of circular cylinder vibration and the flow vibration around the circular cylinder were measured simultaneously using DynamicPIV measurement techniques, which are non-intrusive with respect to the flow and have high spatial and time resolutions. In the results, the vibration phenomenon was found to have anisotropy. There was a discrepancy between the vibration frequency in the flow direction and the vibration frequency perpendicular thereto, and it was found that the difference was function of the reduced velocity. In order to observe the mechanism of the vibration anisotropy, modeling was carried out. (author)
Orientifolds of Matrix theory and Noncommutative Geometry
Kim, Nakwoo(Department of Physics and Research Institute of Basic Science, Kyung Hee University, 26 Kyungheedaero, Dongdaemun-gu, Seoul, 130-701, Korea)
1999-01-01
We study explicit solutions for orientifolds of Matrix theory compactified on noncommutative torus. As quotients of torus, cylinder, Klein bottle and M\\"obius strip are applicable as orientifolds. We calculate the solutions using Connes, Douglas and Schwarz's projective module solution, and investigate twisted gauge bundle on quotient spaces as well. They are Yang-Mills theory on noncommutative torus with proper boundary conditions which define the geometry of the dual space.
Zhou, Tianci; Faulkner, Thomas; Fradkin, Eduardo
2016-01-01
We investigate the entanglement entropy (EE) of circular entangling cuts in the 2+1-dimensional quantum Lifshitz model, whose ground state wave function is a spatially conformal invariant state of the Rokhsar-Kivelson type, whose weight is the Gibbs weight of 2D Euclidean free boson. We show that the finite subleading corrections of EE to the area-law term as well as the mutual information are conformal invariants and calculate them for cylinder, disk-like and spherical manifolds with various spatial cuts. The subtlety due to the boson compactification in the replica trick is carefully addressed. We find that in the geometry of a punctured plane with many small holes, the constant piece of EE is proportional to the number of holes, indicating the ability of entanglement to detect topological information of the configuration. Finally, we compare the mutual information of two small distant disks with Cardy's relativistic CFT scaling proposal. We find that in the quantum Lifshitz model, the mutual information al...
Rocking by rolling: super-fast near-collisional dynamics of perturbed vertical cylinders
Srinivasan, M
2007-01-01
A slightly tilted vertical cylinder on a table-top rights itself, coming to a halt after "rocking" for a while. These rocking motions may involve collisions of the cylinder's circular bottom surface with the table-top. Here we study the more likely motions that almost but do not quite involve a face-down collision of the cylinder's bottom with the table-top. For ideal cylinders that can roll without slip or slide without friction on their circular bottoms, the typical rocking motions do not involve collisions. Instead, they involve slow inverted pendulum-like motions interrupted by infinitely fast rolling or sliding motions during which the contact point with the table shifts by a finite angle in infinitesimal time. We derive simple asymptotic formulas for this "angle of turn" of the contact point for two simple cases: sliding without friction and rolling without slip. These formulas for the angle of turn depend only on the properties of the cylinder and the assumed friction law. These results explain why not...
Wiimote Experiments: Circular Motion
Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary
2013-01-01
The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a…
Shock structure in non-circular jets
Morris, Philip J.; Bhat, Thonse R. S.
1989-01-01
The shock-cell structure of supersonic jets with non-circular exit geometry is modeled using a linearized analysis. The model takes into account the finite thickness of the jet shear layer using realistic velocity and density profiles. The effects of the shear layer turbulence are included by incorporating eddy-viscosity terms. A finite-difference numerical method is used to solve the steady linearized equations of motion. A body-fitted coordinate system is used to describe the shear layer. The variation of the pressure fluctuation with downstream distance is given for circular jets and for an elliptic jet of aspect ratio 2.0. Comparisons with experimental data are made. Difficulties with the numerical technique are also discussed.
Interacting delayed critical 38.1-cm-diam uranium (93.2) metal cylinders at large distance
International Nuclear Information System (INIS)
A delayed critical experiment was performed with two 38.10-cm-diam, ∼7.62-cm-thick unmoderated and unreflected uranium metal cylinders to study the interaction of two loosely coupled large flat cylinders. Previously tightly coupled, two component uranium metal assemblies of 27.93-cm-diam cylinders had been assembled to delayed criticality and the results reported. For this experiment, the uranium metal density was 18.75 g U/cm3, and the enrichment was 93.15 wt% 235U. The two right circular cylinders were coaxial and separated 1.3 m; thus the fractional solid angle subtended by one cylinder as seen from the other is ∼5 X 10-3. This delayed critical configuration is a useful experiment for assessing the convergence of Monte Carlo calculations of the neutron multiplication factor because it is a very loosely coupled system, a problem that has been designated as open-quotes keff of the worldclose quotes. The neutron multiplication factor of one of the interacting cylinders is 0.994, and the solid angle seen by the other cylinder is such that very few neutrons starting in one cylinder reach the other cylinder. This assembly was configured on a vertical assembly machine in the east cell of the Oak Ridge Critical Experiments Facility in 1965 and was unreported until this paper. The east cell of this facility is a 10.6- x 10.6- x 9.1-m room with thick concrete walls. The lower cylinder of this assembly was located 3.5 m from the 1.5-m-thick west wall, 3.9 m from the 0.61-m-thick north wall, and 2.8 m above the concrete floor. The calculation of two such loosely coupled cylinders by Monte Carlo methods can be a problem because the interaction between cylinders is so small
A numerical study of the motion of a neutrally buoyant cylinder in two dimensional shear flow
Pan, Tsorng-Whay; Chen, Shih-Di; Chu, Chin-Chou; Chang, Chien-Cheng
2012-01-01
In this paper, we investigate the motion of a neutrally buoyant cylinder of circular or elliptic shape in two dimensional shear flow of a Newtonian fluid by direct numerical simulation. The numerical results are validated by comparisons with existing theoretical, experimental and numerical results, including a power law of the normalized angular speed versus the particle Reynolds number. The centerline between two walls is an expected equilibrium position of the cylinder mass center in shear flow. When placing the particle away from the centerline initially, it migrates toward another equilibrium position for higher Reynolds numbers due to the interplay between the slip velocity, the Magnus force, and the wall repulsion force.
Small black holes on cylinders
International Nuclear Information System (INIS)
We find the metric of small black holes on cylinders, i.e. neutral and static black holes with a small mass in d-dimensional Minkowski space times a circle. The metric is found using an ansatz for black holes on cylinders proposed in J. High Energy Phys. 05, 032 (2002). We use the new metric to compute corrections to the thermodynamics which is seen to deviate from that of the (d+1)-dimensional Schwarzschild black hole. Moreover, we compute the leading correction to the relative binding energy which is found to be non-zero. We discuss the consequences of these results for the general understanding of black holes and we connect the results to the phase structure of black holes and strings on cylinders
Investigating the transitional state between circular plates and shallow spherical shells
Moayyad Al-Nasra; Mohamad Daoud
2015-01-01
The stiffness of circular plates can be increased by inducing a rise at the center of these plates; this rise converts the circular plates from two-dimensional stiffness elements into three-dimensional stiffness elements. This slight change in the geometry shifts the state of stresses from mainly bending stresses to tensilecompressive stresses. The rise at the center of a circular plate is increased gradually to the point where a shell element is formed. This paper focuses on this particul...
PERCOLATION OF RANDOM CYLINDER AGGREGATES
Directory of Open Access Journals (Sweden)
Dominique Jeulin
2011-05-01
Full Text Available The percolation threshold ρc of Boolean models of cylinders with their axis parallel to a given direction is studied by means of simulations. An efficient method of construction of percolating connected components was developed, and is applied to one or two scales Boolean model, in order to simulate the presence of aggregates. The invariance of the percolation threshold with respect to affine transformations in the common direction of the axis of cylinders is approximately satisfied on simulations. The prediction of the model (ρc close to 0.16 is consistent with experimental measurements on plasma spray coatings, which motivated this study.
Affine varieties with equivalent cylinders
Yu, JT; Shpilrain, V
2001-01-01
A well-known cancellation problem asks when, for two algebraic varieties $V_1, V_2 \\subseteq {\\bf C}^n$, the isomorphism of the cylinders $V_1 \\times {\\bf C}$ and $V_2 \\times {\\bf C}$ implies the isomorphism of $V_1$ and $V_2$. In this paper, we address a related problem: when the equivalence (under an automorphism of ${\\bf C}^{n+1}$) of two cylinders $V_1 \\times {\\bf C}$ and $V_2 \\times {\\bf C}$ implies the equivalence of their bases $V_1$ and $V_2$ under an automorphism of ${\\bf C}^n$? We c...
Enhancement of polarizabilities of cylinders with cylinder-slab resonances
Xiao, Meng; Huang, Xueqin; Liu, H.; Chan, C. T.
2015-02-01
If an object is very small in size compared with the wavelength of light, it does not scatter light efficiently. It is hence difficult to detect a very small object with light. We show using analytic theory as well as full wave numerical calculation that the effective polarizability of a small cylinder can be greatly enhanced by coupling it with a superlens type metamaterial slab. This kind of enhancement is not due to the individual resonance effect of the metamaterial slab, nor due to that of the object, but is caused by a collective resonant mode between the cylinder and the slab. We show that this type of particle-slab resonance which makes a small two-dimensional object much ``brighter'' is actually closely related to the reverse effect known in the literature as ``cloaking by anomalous resonance'' which can make a small cylinder undetectable. We also show that the enhancement of polarizability can lead to strongly enhanced electromagnetic forces that can be attractive or repulsive, depending on the material properties of the cylinder.
Dynamic modeling and response of rigid embedded cylinders
International Nuclear Information System (INIS)
Following a brief review of the limitations of a popular technique for modeling the soil action in analyses of the dynamic response of deeply embedded cylindrical foundations and structures, the sources of the limitations are identified and a modification is proposed which, while retaining the attractiveness of the original model, defines correctly the action of the system. In the proposed approach, the soil medium is modeled by a series of elastically constrained, rather than unconstrained, thin horizontal layers with a circular hole at the center. The impedances of the constrained layers are established and are then used to evaluate the dynamic response of a rigid vertical cylinder embedded in a uniform viscoelastic stratum of constant thickness and infinite extent in the horizontal direction. The cylinder and the stratum are presumed to be supported on a non-deformable base undergoing a uniform horizontal motion. The effects of both harmonic and earthquake induced ground motions are considered. The response quantities examined include the dynamic force per unit of cylinder height and the corresponding base shear and base moment. The system investigated simulates the design of underground storage tanks at Hanford for the storage of radioactive wastes
Inertial rise of a meniscus on a vertical cylinder
O’Kiely, Doireann
2015-03-03
© © 2015 Cambridge University PressA. We consider the inertia-dominated rise of a meniscus around a vertical circular cylinder. Previous experiments and scaling analysis suggest that the height of the meniscus, h-{m}, grows with the time following the initiation of rise, t, like h-{m}\\\\propto t^{1/2}. This is in contrast to the rise on a vertical plate, which obeys the classic capillary-inertia scaling h-{m}\\\\propto t^{2/3}. We highlight a subtlety in the scaling analysis that yielded h-{m}\\\\propto t^{1/2} and investigate the consequences of this subtlety. We develop a potential flow model of the dynamic problem, which we solve using the finite element method. Our numerical results agree well with previous experiments but suggest that the correct early time behaviour is, in fact, h-{m}\\\\propto t^{2/3}. Furthermore, we show that at intermediate times the dynamic rise of the meniscus is governed by two parameters: the contact angle and the cylinder radius measured relative to the capillary length scale, t^{2/3}. This result allows us to collapse previous experimental results with different cylinder radii (but similar static contact angles) onto a single master curve.
A circular aperture array for ultrasonic tomography and quantitative NDE
Energy Technology Data Exchange (ETDEWEB)
Nielsen, S.A.
1998-08-01
The main topics of this thesis are ultrasonic tomography and ultrasonic determination of elastic stiffness constants. Both issues are based on a synthetic array with transducer elements distributed uniformly along a circular aperture, i.e., a circular aperture array. The issues are treated both theoretically and experimentally by broadband pulse techniques. Ultrasonic tomography, UCT, from a circular aperture is a relatively new imaging technique in Non-destructive Evaluation (NDE) to acquire cross sectional images in bulk materials. A filtered back-projection algorithm is used to reconstruct images in four different experiments and results of attenuation, velocity and reflection tomograms in Plexiglas of AlSi-alloy cylinders are presented. Two kinds of ultrasonic tomography are introduced: bistatic and monostatic imaging. Both techniques are verified experimentally by Plexiglas cylinders. Different reconstruction artifacts are discussed and theoretical resolution constraints are discussed for various configurations of the circular aperture array. The monostatic technique is used in volumetric imaging. In the experimental verification artificial and real discontinuities in a cylindrical AlSi-alloy are compared with similar discontinuities in a Plexiglas specimen. Finally, some limitations to UCT are discussed. The circular aperture array is used to determine five independent elastic stiffness constants of a unidirectional glass/PET (Poly Ethylene Teraphtalate) laminate. Energy flux propagation and attenuation of ultrasonic waves are considered and velocity surfaces are calculated for different planes of interest. Relations between elastic stiffness constants and engineering constants (i.e., Young`s moduli, shear moduli and Poisson`s ratios) are discussed for an orthotropic composite. Six micromechanical theories are reviewed, and expressions predicting the elastic engineering constants are evaluated. The micromechanical predicted elastic stiffness constants for the
Directory of Open Access Journals (Sweden)
Jae Won Kim
1999-01-01
Full Text Available A study is made of steady state flow of a viscous fluid, driven by a rotating endwall disk having radial blades in a finite geometry. Numerical solutions to the Navier-Stokes equations are obtained for the flows in the cylindrical cavity. The bottom endwall disk of the vessel is impulsively rotating at a constant rotating speed ft with respect to the longitudinal axis of it. Details of the three components velocity field are examined at high Reynolds number for its engineering application. The main parameter for this study is the number of the radial blades of a rotating pulsator. The numerical results for the fluid flows and pressure distribution, for both an odd and an even number of the blades are procured. The present output offers an optimal number of the blades for rotating machinery such as agitator. The grid-net for the numerical computation is constructed on a body-fitted coordinate system transformed from physical coordinates. It is also flexible to suit any number of blades attached on the rotating bottom disk. The algorithm for the numerical computation is based on the SIMPLE release by Patankar, and the results are validated with prior published data. In addition, a characteristic model is prepared for the pressure measurement. The pressure measurements performed for the present model are consistent with this computational work. The explicit effect of the blade on the overall flow character is scrutinized. The numerical data are processed to describe the behavior of the meridional velocities under different blade conditions. Also, the traces of particles are plotted to assess the effects. Pronounced differences are noted and these results supply comprehensive data for practical application.
Circular orbits in extremal Reissner-Nordstrom spacetime
Energy Technology Data Exchange (ETDEWEB)
Pradhan, Parthapratim, E-mail: pppradhan77@gmail.co [Department of Physics, Vivekananda Satabarshiki Mahavidyalaya, Manikpara, Paschim Medinipur, WestBengal 721513 (India); Majumdar, Parthasarathi, E-mail: parthasarathi.majumdar@saha.ac.i [Saha Institute of Nuclear Physics, Kolkata 700 064 (India)
2011-01-17
Circular null geodesic orbits, in extremal Reissner-Nordstrom spacetime, are examined with regard to their stability, and compared with similar orbits in the near-extremal situation. Extremization of the effective potential for null circular orbits shows the existence of a stable circular geodesic in the extremal spacetime, precisely on the event horizon which coincides with the null geodesic generator. Such a null orbit on the horizon is also indicated by the global minimum of the effective potential for circular timelike orbits. This type of geodesic is of course absent in the corresponding near-extremal spacetime, as we show here, testifying to differences between the extremal limit of a generic RN spacetime and the exactly extremal geometry.
Optimization and improvement of Halbach cylinder design
DEFF Research Database (Denmark)
Bjørk, Rasmus; Bahl, Christian Robert Haffenden; Smith, Anders; Pryds, Nini
2008-01-01
In this paper we describe the results of a parameter survey of a 16 segmented Halbach cylinder in three dimensions in which the parameters internal radius, rin, external radius, rex, and length, L, have been varied. Optimal values of rex and L were found for a Halbach cylinder with the least...... possible volume of magnets with a given mean flux density in the cylinder bore. The volume of the cylinder bore could also be significantly increased by only slightly increasing the volume of the magnets, for a fixed mean flux density. Placing additional blocks of magnets on the end faces of the Halbach...... cylinder also improved the mean flux density in the cylinder bore, especially so for short Halbach cylinders with large rex. Moreover, magnetic cooling as an application for Halbach cylinders was considered. A magnetic cooling quality parameter, Lambdacool, was introduced and results showed that this...
Nonideal ultrathin mantle cloak for electrically large conducting cylinders.
Liu, Shuo; Zhang, Hao Chi; Xu, He-Xiu; Cui, Tie Jun
2014-09-01
Based on the concept of the scattering cancellation technique, we propose a nonideal ultrathin mantle cloak that can efficiently suppress the total scattering cross sections of an electrically large conducting cylinder (over one free-space wavelength). The cloaking mechanism is investigated in depth based on the Mie scattering theory and is simultaneously interpreted from the perspective of far-field bistatic scattering and near-field distributions. We remark that, unlike the perfect transformation-optics-based cloak, this nonideal cloaking technique is mainly designed to minimize simultaneously several scattering multipoles of a relatively large geometry around considerably broad bandwidth. Numerical simulations and experimental results show that the antiscattering ability of the metasurface gives rise to excellent total scattering reduction of the electrically large cylinder and remarkable electric-field restoration around the cloak. The outstanding cloaking performance together with the good features of and ultralow profile, flexibility, and easy fabrication predict promising applications in the microwave frequencies. PMID:25401449
Video Analysis of Rolling Cylinders
Phommarach, S.; Wattanakasiwich, P.; Johnston, I.
2012-01-01
In this work, we studied the rolling motion of solid and hollow cylinders down an inclined plane at different angles. The motions were captured on video at 300 frames s[superscript -1], and the videos were analyzed frame by frame using video analysis software. Data from the real motion were compared with the theory of rolling down an inclined…
Bo, Pengbo
2011-07-01
The most important guiding principle in computational methods for freeform architecture is the balance between cost efficiency on the one hand, and adherence to the design intent on the other. Key issues are the simplicity of supporting and connecting elements as well as repetition of costly parts. This paper proposes so-called circular arc structures as a means to faithfully realize freeform designs without giving up smooth appearance. In contrast to non-smooth meshes with straight edges where geometric complexity is concentrated in the nodes, we stay with smooth surfaces and rather distribute complexity in a uniform way by allowing edges in the shape of circular arcs. We are able to achieve the simplest possible shape of nodes without interfering with known panel optimization algorithms. We study remarkable special cases of circular arc structures which possess simple supporting elements or repetitive edges, we present the first global approximation method for principal patches, and we show an extension to volumetric structures for truly threedimensional designs. © 2011 ACM.
Switchable circular beam deflectors
Shang, Xiaobing; Joshi, Pankaj; Tan, Jin-Yi; De Smet, Jelle; Cuypers, Dieter; Baghdasaryan, Tigran; Vervaeke, Michael; Thienpont, Hugo; De Smet, Herbert
2016-04-01
In this work, we report two types of electrically tunable photonic devices with circularly symmetric polarization independent beam steering performance (beam condensing resp. beam broadening). The devices consist of circular micro grating structures combined with nematic liquid crystal (LC) layers with anti-parallel alignment. A single beam deflector converts a polarized and monochromatic green laser beam (λ =543.5 nm) into a diffraction pattern, with the peak intensity appearing at the third order when 0~{{V}\\text{pp}} is applied and at the zeroth order (no deflection) for voltages above 30~{{V}\\text{pp}} . Depending on the shape of the grating structure (non-inverted or inverted), the deflection is inwards or outwards. Both grating types can be made starting from the same diamond-tooled master mold. A polarized white light beam is symmetrically condensed resp. broadened over 2° in the off state and is passed through unchanged in the on state. By stacking two such devices with mutually orthogonal LC alignment layers, polarization independent switchable circular beam deflectors are realized with a high transmittance (>80%), and with the same beam steering performance as the polarization dependent single devices.
Recollision with circular polarization
Mauger, Francois; Kamor, Adam; Bandrauk, Andre; Chandre, Cristel; Uzer, Turgay
2013-05-01
Since its identification in the 90s, the recollision scenario has revealed to be very helpful in explaining many phenomena in atomic and molecular systems subjected to strong and short laser pulses, and it is now at the core of the strong field physics and attosecond science. For linearly polarized laser fields, the recollision scenario has been able to explain nonsequential double ionization (NSDI), high harmonic generation (HHG) and laser induced diffraction (LIED), just to cite them. The same scenario also predicts the absence of recollision when the field is circularly polarized, therefore leading to the absence of NSDI, HHG or LIED. Recently, the influence of the ellipticity of the laser has drawn an increasing level of interest in the strong field community as it is seen as a way to control the electronic dynamics and, for instance, HHG. Using classical models, the common belief of the absence of recollision with circularly polarized laser fields has been proven wrong. In my talk I will present classical and quantum evidence of the presence of recollision with circular polarization. I will discuss the conditions under which such recollisions happen and what they imply.
Modelling of Flow around Two Aligned Cylinders
DEFF Research Database (Denmark)
Pedersen, Ronnie; Leth, Søren
2009-01-01
Flow around two cylinders is considered, where closed form solutions are compared to numerical results in order to justify the practical use of the theoretical solutions when the flow in front of the cylinders is analysed. For a relatively highly mutual distance between the cylinders the numerica...... and analytical results are comparable. Opposite, when the cylinders are closely placed the potential flow solutions become inadequate compared to the numerical findings....
Modelling of Flow around Two Aligned Cylinders
Pedersen, Ronnie; Leth, Søren
2009-01-01
Flow around two cylinders is considered, where closed form solutions are compared to numerical results in order to justify the practical use of the theoretical solutions when the flow in front of the cylinders is analysed. For a relatively highly mutual distance between the cylinders the numerical and analytical results are comparable. Opposite, when the cylinders are closely placed the potential flow solutions become inadequate compared to the numerical findings.
Polarizability of nanowires at surfaces: Exact solution for general geometry
Jung, Jesper; Pedersen, Thomas G.
2012-01-01
The polarizability of a nanostructure is an important parameter that determines the optical properties. An exact semi-analytical solution of the electrostatic polarizability of a general geometry consisting of two segments forming a cylinder that can be arbitrarily buried in a substrate is derived using bipolar coordinates, cosine-, and sine-transformations. Based on the presented expressions, we analyze the polarizability of several metal nanowire geometries that are important within plasmon...
Inversion of the circular averages transform using the Funk transform
International Nuclear Information System (INIS)
The integral of a function defined on the half-plane along the semi-circles centered on the boundary of the half-plane is known as the circular averages transform. Circular averages transform arises in many tomographic image reconstruction problems. In particular, in synthetic aperture radar (SAR) when the transmitting and receiving antennas are colocated, the received signal is modeled as the integral of the ground reflectivity function of the illuminated scene over the intersection of spheres centered at the antenna location and the surface topography. When the surface topography is flat the received signal becomes the circular averages transform of the ground reflectivity function. Thus, SAR image formation requires inversion of the circular averages transform. Apart from SAR, circular averages transform also arises in thermo-acoustic tomography and sonar inverse problems. In this paper, we present a new inversion method for the circular averages transform using the Funk transform. For a function defined on the unit sphere, its Funk transform is given by the integrals of the function along the great circles. We used hyperbolic geometry to establish a diffeomorphism between the circular averages transform, hyperbolic x-ray and Funk transforms. The method is exact and numerically efficient when fast Fourier transforms over the sphere are used. We present numerical simulations to demonstrate the performance of the inversion method. Dedicated to Dennis Healy, a friend of Applied Mathematics and Engineering
Yonushonis, T. M.; Wiczynski, P. D.; Myers, M. R.; Anderson, D. D.; McDonald, A. C.; Weber, H. G.; Richardson, D. E.; Stafford, R. J.; Naylor, M. G.
1999-01-01
In-cylinder components and tribological system concepts were designed, fabricated and tested at conditions anticipated for a 55% thermal efficiency heavy duty diesel engine for the year 2000 and beyond. A Cummins L10 single cylinder research engine was used to evaluate a spherical joint piston and connecting rod with 19.3 MPa (2800 psi) peak cylinder pressure capability, a thermal fatigue resistant insulated cylinder head, radial combustion seal cylinder liners, a highly compliant steel top compression ring, a variable geometry turbocharger, and a microwave heated particulate trap. Components successfully demonstrated in the final test included spherical joint connecting rod with a fiber reinforced piston, high conformability steel top rings with wear resistant coatings, ceramic exhaust ports with strategic oil cooling and radial combustion seal cylinder liner with cooling jacket transfer fins. A Cummins 6B diesel was used to develop the analytical methods, materials, manufacturing technology and engine components for lighter weight diesel engines without sacrificing performance or durability. A 6B diesel engine was built and tested to calibrate analytical models for the aluminum cylinder head and aluminum block.
Instantaneous flow field above the free end of finite-height cylinders and prisms
International Nuclear Information System (INIS)
Highlights: • PIV measurements of the flow above the free end of finite-height bodies. • Effect of cross-sectional shape of the models on the instantaneous flow. • Small-scale structures generated by the separated shear layer were revealed. • Effect of aspect ratio on the reattachment of the separated flow on the free end. -- Abstract: The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied experimentally using particle image velocimetry (PIV). Cylinders and prisms with aspect ratios of AR = 9, 7, 5, and 3 were tested at a Reynolds number of Re = 4.2 × 104. The bodies were mounted normal to a ground plane and were partially immersed in a turbulent zero-pressure-gradient boundary layer, where the boundary layer thickness relative to the body width was δ/D = 1.6. PIV measurements were made above the free ends of the bodies in a vertical plane aligned with the flow centreline. The present PIV results provide insight into the effects of aspect ratio and body shape on the instantaneous flow field. The recirculation zone under the separated shear layer is larger for the square prism of AR = 3 compared to the more slender prism of AR = 9. Also, for a square prism with low aspect ratio (AR = 3), the influence of the reverse flow over the free end surface becomes more significant compared to that for a higher aspect ratio (AR = 9). For the circular cylinder, a cross-stream vortex forms within the recirculation zone. As the aspect ratio of the cylinder decreases, the reattachment point of the separated flow on the free end surface moves closer to the trailing edge. For both the square prism and circular cylinder cases, the instantaneous velocity vector field and associated in-plane vorticity field revealed small-scale structures mostly generated by the separated shear layer
Transitions to three-dimensional flows in a cylinder driven by oscillations of the sidewall
Panadès Guinart, Carles; Marqués Truyol, Francisco; Lopez, Juan M.
2010-01-01
The transition from two-dimensional to three-dimensional flows in a finite circular cylinder driven by an axially oscillating sidewall is explored in detail. The complete symmetry group of this flow, including a spatio-temporal symmetry related to the oscillating sidewall, is Z2xO(2). Previous studies in flows with the same symmetries, such as symmetric bluff-body wakes and periodically forced rectangular cavities, were unable to obtain the theoretically predicted bifurcation t...