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...
Natural convection from circular cylinders
Boetcher, Sandra K S
2014-01-01
This book presents a concise, yet thorough, reference for all heat transfer coefficient correlations and data for all types of cylinders: vertical, horizontal, and inclined. This book covers all natural convection heat transfer laws for vertical and inclined cylinders and is an excellent resource for engineers working in the area of heat transfer engineering.
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.
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.
Analysis of aerodynamic noise generated from inclined circular cylinder
Haramoto, Yasutake; Yasuda, Shouji; Matsuzaki, Kazuyoshi; Munekata, Mizue; Ohba, Hideki
2000-06-01
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 numerically 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 words, the peak level of the radiated noise decreases rapidly 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 frequency of the sound pressure 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.
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.
Casimir Energy of a Semi-Circular Infinite Cylinder
Nesterenko, V V; Scarpetta, G
2001-01-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only a half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
Casimir energy of a semi-circular infinite cylinder
Nesterenko, V. V.; Lambiase, G.; Scarpetta, G.
2001-05-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for the electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions which are the consequence of the edges or corners in the boundaries. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
Design guide for single circular cylinder in turbulent crossflow. [LMFBR
Energy Technology Data Exchange (ETDEWEB)
Mulcahy, T.M.
1982-03-01
A design procedure is proposed for predicting the dynamic structural response of a circular cylinder in turbulent crossflow. The procedure is based on recently obtained data for a stationary, rigid cylinder and on existing information. The procedure is not applicable to conditions where the wake vortex shedding frequency locks into a structural natural frequency. This report is self-contained in that all the information and structural analysis methods employed in the procedure are reviewed and developed. Also, an example is given to illustrate the use of the method for a typical reactor component. The calculated responses are found to be very small.
Laminar vortex shedding behind a cooled circular cylinder
Trávníček, Zdeněk; Wang, An-Bang; Tu, Wen-Yun
2014-02-01
This paper addresses the functional demonstration of a hot air flow generator driven by convective heat transfer and the airflow behind a cooled circular cylinder in cross flow in the low velocity range. The wake flow was investigated experimentally using flow visualization, hot-wire anemometry, and laser Doppler anemometry. An evaluation of the free-stream velocity from the vortex shedding frequency was derived for the isothermal and non-isothermal cases and demonstrated using simple stroboscope measurements. The results confirm that cylinder cooling destabilizes the wake flow in air, i.e., the laminar steady regime can be changed into the vortex shedding regime, and the vortex shedding frequency increases as the cylinder temperature decreases. This thermal effect of cylinder cooling is consistent with its counterpart, the known effect of flow stabilization by cylinder heating. The effective temperature and effective Reynolds number concept have been further quantitatively evaluated, and the extension of their validity to the case of cooled cylinders has been confirmed.
Flow over an inline oscillating circular cylinder in the wake of a stationary circular cylinder
Zhang, Yang; Zhu, Keqiang
2017-02-01
Flow interference between an upstream stationary cylinder and an inline oscillating cylinder is studied with the lattice Boltzmann method. With a fixed Reynolds number Re = 100 and pitch ratio L/D = 4, the effects of oscillation amplitude A/D = [0.25, 1] and frequency f e/f s = [0.5, 2] are investigated. The wake response state is categorized into lock-in and non-lock-in. The lock-in zone in the bifurcation diagram of amplitude versus frequency is discontinuous. Response states of upstream and downstream wakes are similar under the conditions of small amplitude or low frequency. However, with large oscillating parameters, the two wakes are prone to be in different states as the flow field becomes irregular. Two distinct flow regimes have been identified, i.e., single-cylinder and two-cylinder shedding regimes. The presence of single-cylinder shedding regime is attributed to the low shedding frequency of the downstream cylinder at large amplitude. Hydrodynamic forces of the oscillating tandem system are discussed. The results reveal that forces on the two cylinders behave differently and that the absence of vortices in the gap flow significantly reduces the forces exerting on the tandem system.
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.
Sensitivity analysis of small circular cylinders as wake control
Meneghini, Julio; Patino, Gustavo; Gioria, Rafael
2016-11-01
We apply a sensitivity analysis to a steady external force regarding control vortex shedding from a circular cylinder using active and passive small control cylinders. We evaluate the changes on the flow produced by the device on the flow near the primary instability, transition to wake. We numerically predict by means of sensitivity analysis the effective regions to place the control devices. The quantitative effect of the hydrodynamic forces produced by the control devices is also obtained by a sensitivity analysis supporting the prediction of minimum rotation rate. These results are extrapolated for higher Reynolds. Also, the analysis provided the positions of combined passive control cylinders that suppress the wake. The latter shows that these particular positions for the devices are adequate to suppress the wake unsteadiness. In both cases the results agree very well with experimental cases of control devices previously published.
Optimal control of circular cylinder wakes using long control horizons
Flinois, Thibault L B
2015-01-01
The classical problem of minimizing the drag of a circular cylinder by using body rotation is revisited in an adjoint-based optimal control framework. The cylinder's unsteady and fully unconstrained rotation rate is optimized at Reynolds numbers of 100 and 200 and over horizons that are longer than in previous studies, where they are typically of the order of a vortex shedding period or shorter. In the best configuration, the drag is reduced by $19\\%$, the vortex shedding is effectively suppressed, and this low drag state is maintained with minimal cylinder rotation after transients. Without closed-loop control, which maintains a specific phase relationship between the actuation and the shedding, the wake is not stabilized. A comparison is also given between the performance of optimizations for different horizon lengths and cost functions. It is shown that the long horizons used are necessary in order to stabilize the vortex shedding efficiently.
Mechanism of Secondary Instability of Flow around a Circular Cylinder
Dou, Hua-Shu; Ben, An-Qing; Fluid Mechanics Research Team Team
2016-11-01
Flow around a circular cylinder in infinite domain is simulated with large eddy simulation at Re =200, and the mechanism of the origin of secondary vortex street is analyzed. The simulation results show that the vortex street generated in the cylinder near wake disappears as the flow moving downstream. Secondary instability occurs in far wake of the cylinder after the primary vortex street dying away. The processes of first instability and secondary instability in the cylinder wake are recorded in the simulation. The instability of the entire flow field is studied with the energy gradient theory. It is found that it is the high value of the energy gradient function generated by the zero velocity gradients that leads to the instability. As the vortex developing at rear of the cylinder, the value of the energy gradient function becomes low downstream, which leads to the vortex dying away. At further downstream, the value of the energy gradient function is enlarged again because of the role of perturbation, which leads to the secondary instability. It can be concluded that the interaction of the variation of the value of the energy gradient function and the perturbation leads to the occurrence of secondary instability.
Study of the wake flow around a circular cylinder
Energy Technology Data Exchange (ETDEWEB)
Lee, Jae Sung; Kim, Sang Il; Seung, Sam Sun [Kangwon National University, Chuncheon (Korea, Republic of)
2015-11-15
This experimental study investigated the wake flow around an elastically supported circular cylinder. In this study, the Reynolds numbers are varied in the region of 1.4x10{sup 4}≤Re≤3.2x10{sup 4}. Under these conditions, we have captured the process of the wake mechanism and the moving path of the vortex by measuring the velocity at each position in the wake around the cylinder. Further, these facts from the wind tunnel test are proved by a flow visualization test through a water channel. From the result, we have arrived at the following conclusions : i) The process (formationgrowthcollapse) of vortex is observed in the wake around the cylinder, ii) The vortex efflux angle is approximately 16 degrees⁓17 degrees under the experimental conditions. These angles have no relationship with the velocity change and the existence of flow-induced vibrations of the cylinder, and iii) The moving path of the vortex center is obtained by spectrum analysis of the fluctuating velocity behind the cylinder. These are confirmed by conducting visualization tests.
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%.
Optimization of Feedback Control of Flow over a Circular Cylinder
Son, Donggun; Kim, Euiyoung; Choi, Haecheon
2012-11-01
We perform a feedback gain optimization of the proportional-integral-differential (PID) control for flow over a circular cylinder at Re = 60 and 100. We measure the transverse velocity at a centerline location in the wake as a sensing variable and provide blowing and suction at the upper and lower slots on the cylinder surface as an actuation. The cost function to minimize is defined as the mean square of the sensing variable, and the PID control gains are optimized by iterative feedback tuning method which is a typical model free gain optimization method. In this method, the control gains are iteratively updated by the gradient of cost function until the control system satisfies a certain stopping criteria. The PID control with optimal control gains successfully reduces the velocity fluctuations at the sensing location and attenuates (or annihilates) vortex shedding in the wake, resulting in the reduction in the mean drag and lift fluctuations. Supported by the NRF Program (2011-0028032).
Visualization and modal decomposition of vortex street behind circular cylinder
Directory of Open Access Journals (Sweden)
Čížek J.
2013-04-01
Full Text Available Time resolved particle image velocimetry measurement of vortex street behind circular cylinder was carried out. Vorex street was measured for Reynolds numbers up to few thousands. Obtained results were processed by visualizations of moving particles and by standard evaluation of vector fields from the set of images. Modal decomposition of measured flow field was done using propper orthogonal decomposition where the structure of energetically most important modes was identified for several Reynolds numbers. The values of Strouhal number was analyzed from temporal evolution of dominant modes obtained using proper orthogonal decomposition.
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.
Modeling flow for modified concentric cylinder rheometer geometry
Ekeruche, Karen; Connelly, Kelly; Kavehpour, H. Pirouz
2016-11-01
Rheology experiments on biological fluids can be difficult when samples are limited in volume, sensitive to degradation, and delicate to extract from tissues. A probe-like geometry has been developed to perform shear creep experiments on biological fluids and to use the creep response to characterize fluid material properties. This probe geometry is a modified concentric cylinder setup, where the gap is large and we assume the inner cylinder rotates in an infinite fluid. To validate this assumption we perform shear creep tests with the designed probe on Newtonian and non-Newtonian fluids and vary the outer cylinder container diameter. We have also created a numerical model based on the probe geometry setup to compare with experimental results at different outer cylinder diameters. A creep test is modeled by applying rotation to the inner cylinder and solving for the deformation of the fluid throughout the gap. Steady state viscosity values are calculated from creep compliance curves and compared between experimental and numerical results.
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.
Lattice Boltzmann Numerical Simulation of a Circular Cylinder
Institute of Scientific and Technical Information of China (English)
冯士德; 赵颖; 郜宪林; 季仲贞
2002-01-01
The lattice Boltzmann equation (LBE) model based on the Boltzmann equation is suitable for the numerical simulation of various flow fields. The fluid dynamics equation can be recovered from the LBE model. However,compared to the Navier-Stokes transport equation, the fluid dynamics equation derived from the LBE model is somewhat different in the viscosity transport term, which contains not only the Navier-Stokes transport equation but also nonsteady pressure and momentum flux terms. The two nonsteady terms can produce the same function as the random stirring force term introduced in the direct numerical or large-eddy vortex simulation of turbulence.Through computation of a circular cylinder, it is verified that the influence of the two nonsteady terms on flow field stability cannot be ignored, which is helpful for the study of turbulence.
Circular cylinders with soft porous cover for flow noise reduction
Geyer, Thomas F.; Sarradj, Ennes
2016-03-01
The use of porous materials is one of several approaches to passively control or minimize the generation of flow noise. In order to investigate the possible reduction of noise from struts and other protruding parts (for example components of the landing gear or pantographs), acoustic measurements were taken in a small aeroacoustic wind tunnel on a set of circular cylinders with a soft porous cover. The aim of this study was to identify those materials that result in the best noise reduction, which refers to both tonal noise and broadband noise. The porous covers were characterized by their air flow resistivity, a parameter describing the permeability of an open-porous material. The results show that materials with low air flow resistivities lead to a noticeable flow noise reduction. Thereby, the main effect of the porous cylinder covers is that the spectral peak of the aeolian tone due to vortex shedding appears much narrower, but is not suppressed completely. Based on the measurement results, a basic model for the estimation of the total peak level of the aeolian tone was derived. In addition to the minimization of the vortex shedding noise, a reduction of broadband noise can be observed, especially at higher Reynolds numbers. The noise reduction increases with decreasing air flow resistivity of the porous covers, which means that materials that are highly permeable to air result in the best noise reduction.
Effect of High Porosity Screen on the Near Wake of a Circular Cylinder
Directory of Open Access Journals (Sweden)
Sahin B.
2013-04-01
Full Text Available The change in flow characteristics downstream of a circular cylinder (inner cylinder surrounded by a permeable cylinder (outer cylinder made of a high porosity screen was investigated in shallow water using Particle Image Velocimetry (PIV technique. The diameter of the inner cylinder, outer cylinder and the water height were kept constant during the experiments as d = 50 mm, D = 100 mm and hw = 50 mm, respectively. The depth-averaged free stream velocity was also kept constant as U = 180 mm/s which corresponded to a Reynolds number of Red = 9000 based on the inner cylinder diameter. It was shown that the outer permeable cylinder had a substantialeffect on the vortex formation and consequent vortex shedding downstream of the circular cylinder, especially in the near wake. The time averaged vorticity layers, streamlines and velocity vector field depict that the location of the interaction of vortices considerably changed by the presence of the outer cylinder. Turbulent statistics clearly demonstrated that in comparison to the natural cylinder, turbulent kinetic energy and Reynolds stresses decreased remarkably downstream of the inner cylinder. Moreover, spectra of streamwise velocity fluctuations showed that the vortex shedding frequency significantly reduced compared to the natural cylinder case.
Convective heat transfer from circular cylinders located within perforated cylindrical shrouds
Daryabeigi, K.; Ash, R. L.
1986-01-01
The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied. The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective heat transfer to bare cylinders up to 50%. The maximum enhancement occurred for a radius ratio of 1.4 and ventilation factors between 0.2 and 0.3. It was found that shroud orientation influenced the heat transfer, with maximum heat transfer generally occurring when the shroud's holes were centered on either side of the stagnation line. However, the hole orientation effect is of second order compared to the influence of ventilation factor and radius ratio.
Experiments on the flow past long circular cylinders in a shear flow
Energy Technology Data Exchange (ETDEWEB)
Kappler, M. [Universitaet Karlsruhe, Institut fuer Hydromechanik, Karlsruhe (Germany); Helmut-Schmidt-Universitaet, Universitaet der Bundeswehr Hamburg (Germany); Rodi, W. [Universitaet Karlsruhe, Institut fuer Hydromechanik, Karlsruhe (Germany); Szepessy, S. [Alfa Laval, Tumba (Sweden); Badran, O. [Al-Balqa' Applied University, FET, Amman (Jordan)
2005-03-01
This paper describes an experimental investigation of the flow past circular cylinders, with the mean flow perpendicular to the cylinder axis, at conditions that yield a strong three-dimensional behaviour. The experiments were carried out in the subcritical regime. Long cylinders with end plates were subjected to shear flow with a linear velocity profile in the spanwise direction generated by means of a curved gauze. It was concluded that spanwise cellular structures of vortex shedding emerged in the wake, more clearly for some boundary conditions than others. These structures are characterised by a portion of spanwise length, a cell, having constant shedding frequency over a time average, which implies that there were no vortex dislocations inside that cell during that time. These features were studied using flow visualisation and hot-film anemometry. Spectra of the local shedding frequency are shown, revealing the effect of the shear parameter {beta}(=0.02 and 0.04) and aspect ratio L/D(=20.6 and 8) on the stability and geometry of the cells at several Reynolds numbers in the range of 3.13 x 10{sup 3}{<=}Re{sub m}{<=}1.25 x 10{sup 4}. (orig.)
Institute of Scientific and Technical Information of China (English)
NING Dezhi; TENG Bin; SONG Xiangqun
2005-01-01
In this paper, the principle of mirror image is used to transform the problem of wave diffraction from a circular cylinder in front of orthogonal vertical walls into the problem of diffraction of four symmetric incident waves from four symmetrically arranged circular cylinders, and then the eigenfunction expansion of velocity potential and Grafs addition theorem are used to give the analytical solution to the wave diffraction problem. The relation of the total wave force on cylinder to the distance between the cylinder and orthogonal vertical walls and the incidence angle of wave is also studied by numerical computation.
Acoustic band gaps in two-dimensional square arrays of semi-hollow circular cylinders
Institute of Scientific and Technical Information of China (English)
LU TianJian; GAO GuoQin; MA ShouLin; JIN Feng; 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 per-formance 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 cyl-inder/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 meas-urements on square arrays of hollow AI cylinders in air and semi-hollow AI cylinders in air are carried out. The results demonstrate that the semi-hollow circular cylinder/air system has the best overall band gap performance.
Kovalenko, V. M.; Byehkov, N. M.; Kisel, G. A.; Dikovskaia, N. D.
1984-03-01
Measurements have been made of pressure distributions and pulsations in a cross flow past a circular cylinder placed near a plane screen of finite length. The experiments reported here have been carried out under low turbulence conditions over a range of Reynolds numbers that includes the critical values. The boundary layer separation points and the evolution of the front critical point and other characteristic zones with the distance to the screen are determined. The components of the aerodynamic force acting on the cylinder and the Strouhal number are calculated on the basis of the predominant pulsation frequencies on the cylinder.
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
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.
Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder
Shih, Chang-Lung; Chen, Wei-Cheng; Chang, Keh-Chin; Wang, Muh-Rong
2016-06-01
There are two general concerns in the velocity measurements of turbulence. One is the temporal characteristics which governs the turbulent mixing process. Turbulence is rotational and is characterized by high levels of fluctuating vorticity. In order to obtain the information of vorticity dynamics, the spatial characteristics is the other concern. These varying needs can be satisfied by using a variety of diagnostic techniques such as invasive physical probes and non-invasive optical instruments. Probe techniques for the turbulent measurements are inherently simple and less expensive than optical methods. However, the presence of a physical probe may alter the flow field, and velocity measurements usually become questionable when probing recirculation zones. The non-invasive optical methods are mostly made of the foreign particles (or seeding) instead of the fluid flow and are, thus, of indirect method. The difference between the velocities of fluid and foreign particles is always an issue to be discussed particularly in the measurements of complicated turbulent flows. Velocity measurements of the turbulent wake flow over a circular cylinder will be made by using two invasive instruments, namely, a cross-type hot-wire anemometry (HWA) and a split-fiber hot-film anemometry (HFA), and a non-invasive optical instrument, namely, particle image velocimetry (PIV) in this study. Comparison results show that all three employed diagnostic techniques yield similar measurements in the mean velocity while somewhat deviated results in the root-mean-squared velocity, particularly for the PIV measurements. It is demonstrated that HFA possesses more capability than HWA in the flow measurements of wake flow. Wake width is determined in terms of either the flatness factor or shear-induced vorticity. It is demonstrated that flow data obtained with the three employed diagnostic techniques are capable of yielding accurate determination of wake width.
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 surf...
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.
Flow Features of Three Side-by-side Circular Cylinders at Low Reynolds Number
Directory of Open Access Journals (Sweden)
Liu Junkao
2016-01-01
Full Text Available In order to study the fluctuation of kinetic parameter of cylinder matrix in incompressible stationary flow, the flow fluid around three side-by-side circular cylinders are simulated using Immersed Boundary–Lattice Boltzmann method (IB-LBM. Drag and lift force of the three cylinders are investigated as the interval between each cylinder varied from zero to five times of the cylinder diameter. Five flow patterns are defined according to the vortices structure in the downstream of the cylinders. Power spectrum analysis of lift force is developed to explain the vortex patterns. Through the research, we find the strength and phase of the gap flow play an important role in the vortex formatting process. The vortices shedding from different cylinders neutralize and combine in the near wake, contributing a lot to the variation of forces.
Control of mean and fluctuating forces on a circular cylinder at high Reynolds numbers
Institute of Scientific and Technical Information of China (English)
Chuanping Shao; Jianming Wang
2007-01-01
A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 x 104 to 1.0 x 105. The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.
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.
Aerodynamic modification to a circular cylinder to enhance the piezoelectric wind energy harvesting
Hu, Gang; Tse, K. T.; Kwok, K. C. S.; Song, Jie; Lyu, Yuan
2016-11-01
This study aims to expand the aeroelastic unstable range of a circular cylinder for improving the efficiency of a vortex-induced vibration (VIV)-based wind energy harvester. The kinetic energy of the harvester is provided by flow-induced vibration of a circular cylinder. Two small-diameter cylindrical rods were attached on two sides of the circular cylinder parallel to the cylinder axis and symmetrical to the stagnation line at a series of circumferential locations. This was inspired by rain-wind-induced vibrations of stay-cables of cable-stayed bridges. It was found that attaching two small-diameter cylindrical rods at the circumferential location θ = 60° significantly expands the aeroelastic unstable range for the circular cylinder. The wind energy harvester with this configuration harnesses the wind energy beyond the VIV onset wind speed and is sustained over the range of wind speed. Therefore, this configuration possesses a dramatic superiority over a plain circular cylinder as the kinetic source of a wind energy harvester.
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.
Wave Run-up on A Coaxial Perforated Circular Cylinder
Institute of Scientific and Technical Information of China (English)
ZHU Da-tong
2011-01-01
This paper describes a plane regular wave interaction with a combined cylinder which consists of a solid inner column and a coaxial perforated outer cylinder. The outer perforated surface is a thin porous cylinder with an annular gap between it and the inner cylinder. The non-linear boundary condition at the perforated wall is a prime focus in the study;energy dissipation at the perforated wall occurs through the resistance to the fluid across the perforated wall. Explicit analytical formulae are presented to calculate the wave run-up on the outer and inner surfaces of the perforated cylinderand the surface of the inner column. The theoretical results of the wave run-up are compared with previous experimental data. Numerical results have also been obtained: when the ratio of the annular gap between the two cylinders to incidentwavelength (b-a)/L≤0.1, the wave run-up on the inner surface of the perforated cylinder and the surface of inner column can partially or completely exceed the incident wave height.
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.
Interaction of circular cylinder wake with a short asymmetrically located downstream plate
Yucel, S. B.; Cetiner, O.; Unal, M. F.
2010-07-01
This study reveals the interaction patterns of separated shear layers from a circular cylinder with a short downstream plate and their reflection on the frequency and the formation length of the vortices from the cylinder as a function of plate location relative to the cylinder. The effect of horizontal ( G/D) and vertical ( Z/D) distances between the cylinder and the plate on the near wake is studied via Digital Particle Image Velocimetry (DPIV) in a water channel for Reynolds numbers of 200, 400 and 750, based on the cylinder diameter D. It is shown that the interaction of wake with the plate of length D can be categorized depending on the horizontal and the vertical distances between the cylinder and the plate. For the vertical distance range of Z/D ≤ 0.7, there is a critical horizontal spacing before which the shear layers from the cylinder are inhibited to form vortices in front of the plate. Resulting elongated recirculation region between the plate and the cylinder suggests modification of the absolutely unstable near wake of free circular cylinder in favor of convective instability. Z/D = 0.9 provides a passage from Z/D ≤ 0.7 to ≥1.1 and is associated with a dominant effect on the near-wake characteristics of interaction of shear layers from the cylinder with those from the downstream plate. For Z/D ≥ 1.1, there is again, yet a smaller critical horizontal spacing after which vortices interact with decreased downstream plate interference. In this vertical separation distance range, a gap flow between the plate and the cylinder plays a determining role on the formation length and St number of vortices for small horizontal spacing values.
Flow and Heat Transfer Characteristics behind Circular Cylinders with Different Size
布施, 肇; 鳥居, 修一; 有薗, 美和; フセ, ハジメ; トリイ, シュウイチ; アリゾノ, ミワ; FUSE, Hajime; Torii, Shuichi; ARIZONO, Miwa
1992-01-01
An experimental study is conducted on heat transfer from slightly heated circular cylinders with various diameters in cross flow under the same condition of the free-stream turbulence. Emphasis is placed on the influence of the diameter of the cylinder, D, on the heat transfer coefficient at the rear stagnation point. By using a hot-wire anemometer, spectrum analysis of the anemometer signal with a Fourier analyzer is eｔmployed to investigate the separated shear layer formed behind the circul...
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...
Energy Technology Data Exchange (ETDEWEB)
Das, Pramode K; Mathew, Sam; Shaiju, A J; Patnaik, B S V, E-mail: bsvp@iitm.ac.in [Fluid Mechanics Laboratory, Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai 600 036 (India)
2016-02-15
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. (paper)
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.
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).
Experimental study of noise emitted by circular cylinders with large roughness
Alomar, Antoni; Angland, David; Zhang, Xin; Molin, Nicolas
2014-12-01
The aerodynamic noise generated by high Reynolds number flow around a bluff body with large surface roughness was investigated. This is a relevant problem in many applications, in particular aircraft landing gear noise. A circular cylinder in cross-flow and a zero-pressure-gradient turbulent boundary layer with various types of roughness was tested in a series of wind tunnel experiments. It has been shown that distributed roughness covering a circular cylinder affects the spectra over the entire frequency range. Roughness noise is dominant at high frequencies, and the peak frequency is well described by Howe's roughness noise model when scaled with the maximum outer velocity. There are differences between hemispherical and cylindrical roughness elements for both the circular cylinder and the zero-pressure-gradient turbulent boundary layer cases, indicating a dependence on roughness shape, not described by the considered roughness noise models. Cylindrical roughness generates higher noise levels at the highest frequencies, especially for the zero-pressure-gradient turbulent boundary layer case. Cable-type roughness aligned with the mean flow does not generate roughness noise, and its spectrum has been found to collapse with the smooth cylinder at medium and high frequencies. At low and medium frequencies the noise spectra have the same features as the smooth cylinder, but with higher shedding peak levels and fall-off levels, despite the decrease in spanwise correlation length. Roughness induces early separation, and thus a shift of the spectra to lower frequencies.
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.
Inflation of polymer melts into elliptic and circular cylinders
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Christensen, Jens Horslund; Gøttsche, Søren
2000-01-01
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...... by a finite element method (the 3D Lagrangian integral method). Here, the non-linear properties are modelled with a constitutive equation of the Factorised K-BKZ type, using a potential function F(u')), where u') represents the potential function from the Doi-Edwards reptation theory. The linear viscoelastic...
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.
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...
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...
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.
Proper orthogonal decomposition analysis of vortex shedding behind a rotating circular cylinder
Directory of Open Access Journals (Sweden)
Dol Sharul Sham
2016-01-01
Full Text Available Turbulence studies were made in the wake of a rotating circular cylinder in a uniform free stream with the objective of describing the patterns of the vortex shedding up to suppression of the periodic vortex street at high velocity ratios, λ. The results obtained in the present study establish that shedding of Kármán vortices in a rotating circular cylinder-generated wake is modified by rotation of the cylinder. Alternate vortex shedding is highly visible when λ < 2.0 although the strength of the separated shear layers differ due to the rotation of the cylinder. The spectral density in the wakes indicate significant changes at λ = 2.0. The results indicate that the rotation of the cylinder causes significant disruption in the structure of the flow. Alternate vortex shedding is weak, distorted and close to being suppressed at λ = 2.0. It is clear that flow asymmetries will weaken vortex shedding, and when the asymmetries are significant enough, total suppression of a periodic street occurs. Particular attention was paid to the decomposition of the flow using Proper Orthogonal Decomposition (POD. By analyzing this decomposition with the help of Particle Image Velocimetry (PIV data, it was found that large scales contribute to the coherent motion. Vorticity structures in the modes become increasingly irregular with downstream distance, suggesting turbulent interactions are occurring at the more downstream locations, especially when the cylinder rotates.
Effect of steady rotation on low Reynolds number vortex shedding behind a circular cylinder
Satish, Paluri; Patwardhan, Saurabh S.; Ramesh, O. N.
2013-08-01
In this paper control of oblique vortex shedding in the wake behind a straight circular cylinder is explored experimentally and computationally. Towards this, steady rotation of the cylinder about its axis is used as a control device. Some limited studies are also performed with a stepped circular cylinder, where at the step the flow is inevitably three-dimensional irrespective of the rotation rate. When there is no rotation, the vortex shedding pattern is three dimensional as described in many previous studies. With a non-zero rotation rate, it is demonstrated experimentally as well as numerically that the shedding pattern becomes more and more two-dimensional. At sufficiently high rotation rates, the vortex shedding is completely suppressed.
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.
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 ...
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.
Institute of Scientific and Technical Information of China (English)
XIA Yong; LU De-Tang; LIU Yang; XU You-Sheng
2009-01-01
The multiple-relaxation-time lattice Boltzmann method (MRT-LBM) is implemented to numerically simulate the cross flow over a longitudinal vibrating circular cylinder.This research is carried out on a three-dimensional (3D) finite cantilevered cylinder to investigate the effect of forced vibration on the wake characteristics and the 319 effect of a cantilevered cylinder.To meet the accuracy of this method,the present calculation is carried out at a low Reynolds number Re = 100,as well as to make the vibration obvious,we make the vibration strong enough.The calculation results indicate that the vibration has significant influence on the wake characteristics. When the vibrating is big enough,our early works show that the 2D vortex shedding would be locked up by vibration.Contrarily,this phenomenon would not appear in the present 313 case because of the end effect of the cantilevered cylinder.
Directory of Open Access Journals (Sweden)
F. Rehimi
2011-01-01
Full Text Available Experiments were performed at low Reynolds numbers in the range 75 Re 275 in the wake of a circular cylinder of dc diameter placed symmetrically between two parallel walls of H height. 2D2C particle image velocimetry (PIV was used to investigate the flow downstream the cylinder. In the unsteady flow regime downstream the cylinder, the detached primary vortices (Pi interact with walls generating secondary ones (Pi’ and modify the cylinder wake dynamic. The kinematical properties (advection velocity, circulation, rotation kinetic energy, etc. of the generated secondary vortices are studied and compared with the primary ones in order to show how the walls influence the von Kármán vortex street. The authors propose here a relation between the circulations and kinetic energies of primary and secondary vortices.
Scattering by cavity-backed antennas on a circular cylinder
Kempel, Leo C.; Volakis, John L.
1994-01-01
Conformal arrays are popular antennas for aircraft, spacecraft, and land vehicle platforms due to their inherent low weight and drag properties. However, to date there has been a dearth of rigorous analytical or numerical solutions to aid the designer. In fact, it has been common practice to use limited measurements and planar approximations in designing such non-planar antennas. The finite element-boundary integral method is extended to scattering by cavity-backed structures in an infinite, metallic cylinder. In particular, the formulation specifics such as weight functions, dyadic Green's function, implementation details and particular difficulties inherent to cylindrical structures are discussed. Special care is taken to ensure that the resulting computer program has low memory demand and minimal computational requirements. Scattering results are presented and validated as much as possible.
Radiation by cavity-backed antennas on a circular cylinder
Kempel, Leo C.; Volakis, John L.; Sliva, Randy
1994-01-01
Conformal antenna arrays are popular antennas for aircraft, spacecraft and land vehicle platforms due to their inherent low weight, cost and drag properties. However, to date there has been a dearth of rigorous analytical or numerical solutions to aid the designer. In fact, it has been common practice to use limited measurements and planar approximations in designing such non-planar antennas. The finite element-boundary integral method is extended to radiation by cavity-backed structures in an infinite, metallic cylinder. The formulation is used to investigate the effect of cavity size on the radiation pattern for typical circumferentially and axially polarized patch antennas. Curvature effect on the gain, pattern shape, and input impedance is also studied. Finally, the accuracy of the FE-BI approach for a microstrip patch array is demonstrated.
Directory of Open Access Journals (Sweden)
Arash Azimi
2015-04-01
Full Text Available Numerical study has been carried out for slot air jet impingement cooling of horizontal concentric circular cylinders. The slot air jet is situated at the symmetry line of a horizontal cylinder along the gravity vector and impinges to the bottom of the outer cylinder which is designated as θ=0°. The outer cylinder is partially opened at the top with width of W=30mm and is kept at constant temperature T= 62°C. Inner cylinder which is a part of the slot jet structure is chosen to be insulated. The effects of jet Reynolds number in the range of 100≤ Rej ≤1000 and the ratio of spacing between nozzle and outer cylinder surface to the jet width for H=4.2 and H=12.5 on the local and average Nusselt numbers are examined. In the numerical study, FLUENT CFD package is used and validated by comparing the results with the experimental data at the same Reynolds number. It is observed that the maximum Nusselt number occurs at the stagnation point at (θ=0° and the local heat transfer coefficient decrease on the circumference of the cylinder with increase of θ as a result of thermal boundary layer thickness growth. Also results show that the local and average heat transfer coefficients are raised by increasing the jet Reynolds number and by decreasing the nozzle-to-surface spacing.
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.
NUMERICAL SIMULATION OF FLOW OVER TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT*
Institute of Scientific and Technical Information of China (English)
DEHKORDI Behzad Ghadiri; MOGHADDAM Hesam Sarvghad; JAFARI Hamed Houri
2011-01-01
In this article, the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes. The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid. The great source term technique is employed to identify the cylinders placed in the flow field. To apply the boundary conditions, the ghost-cell technique is used. The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder. Finally,the flow around two circular cylinders in a tandem arrangement is simulated and analyzed. The flow visualization parameters, the Strouhal numbers, and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow. The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.
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.)
Self-propelled flexible fin in the wake of a circular cylinder
Park, Sung Goon; Kim, Boyoung; Sung, Hyung Jin
2016-11-01
The behavior of a self-propelled flexible fin behind a circular cylinder in a uniform flow was explored using the immersed boundary method. The transverse heaving motion of the leading edge of the fin was prescribed, whereas the lateral behavior was spontaneously determined by the hydrodynamic interactions between the fin and the fluid environment. Three different behaviors were observed: propulsion upstream, drift downstream, and holding stationary at an equilibrium position. In a uniform flow, the fin could not overcome the positive net drag, and it drifted downstream. By contrast, a fin in the wake of a cylinder was propelled toward the circular cylinder during the heaving motion. The trailing edge of the fin passively fluttered along the oncoming vortices, thereby propelling the fin upstream. During the upstream propulsion behavior, the fin was propelled through the vortex cores. The fin was observed to remain stationary at a heaving frequency equal to the vortex shedding frequency, and a slaloming behavior was observed between the oncoming vortical structures. The fin was not propelled toward the cylinder during the slaloming behavior; rather, it lingered at a certain streamwise distance from the cylinder. Several equilibrium positions were dynamically determined from the interaction between the fin and the vortical fluid environment. The equilibrium position depended on the initial longitudinal position and the phase of the fin heaving motion with respect to the phase of the vortex shedding. The power input required to drive the heaving motion was reduced during the slaloming behavior.
Accelerated micropolar fluid-flow past an uniformly rotating circular cylinder
Siddiqui, Abuzar Abid
2016-10-01
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 into a system of finite-difference equations. This system was further solved numerically by point successive-over-relaxation 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 enhancement of lift and reduction in drag is observed if the micropolarity effects are intensified. Same is happened if the rotation of a cylinder increases. Furthermore, the vortex-pair in the wake is delayed to successively higher times as rotation parameter increases. In addition, the rotation helps not only in dissolving vortices adjacent to the cylinder and adverse pressure region but also in dissolving the boundary layer separation. Furthermore, the rotation reduces the micropolar spin boundary layer.
Accelerated micropolar fluid–flow past an uniformly rotating circular cylinder
Directory of Open Access Journals (Sweden)
Abuzar Abid Siddiqui
2016-10-01
Full Text Available 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 into a system of finite-difference equations. This system was further solved numerically by point successive-over-relaxation 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 enhancement of lift and reduction in drag is observed if the micropolarity effects are intensified. Same is happened if the rotation of a cylinder increases. Furthermore, the vortex-pair in the wake is delayed to successively higher times as rotation parameter increases. In addition, the rotation helps not only in dissolving vortices adjacent to the cylinder and adverse pressure region but also in dissolving the boundary layer separation. Furthermore, the rotation reduces the micropolar spin boundary layer.
THREE-DIMENSIONAL INSTABILITY OF AN OSCILLATING VISCOUS FLOW PAST A CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
陆夕云; 凌国灿
2003-01-01
A systematically numerical study of the sinusoidally oscillating viscous flowaround a circular cylinder was performed to investigate vortical instability by solving thethree-dimensional incompressible Navier-Stokes equations. The transition from two- to three-dimensional flow structures along the axial direction due to the vortical instability appears,and the three-dimensional structures lie alternatively on the two sides of the cylinder.Numerical study has been taken for the Keulegan-Carpenter(KC) numbers from 1 to 3.2and frequency parameters from 1O0 to 600. The force behaviors are also studied by solvingthe Morison equation. Calculated results agree well with experimental data and theoreticalprediction.
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
Directory of Open Access Journals (Sweden)
T. Poornima
2016-01-01
Full Text Available A mathematical model is presented for an optically dense fluid past an isothermal circular cylinder with chemical reaction taking place in it. A constant, static, magnetic field is applied transverse to the cylinder surface. The cylinder surface is maintained at a constant temperature. New variables are introduced to transform the complex geometry into a simple shape and the boundary layer conservation equations, which are parabolic in nature, are normalized into non-similar form and then solved numerically with the well-tested, efficient, implicit, Crank-Nicolson finite difference scheme. Numerical computations are made and the effects of the various material parameters on the velocity, temperature and concentration as well as the surface skin friction and surface heat and mass transfer rates are illustrated graphs and tables. Increasing magnetohydrodynamic body force parameter (M is found to decelerate the flow but enhance temperatures. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. Local Nusselt number is also found to be enhanced with increasing radiation parameter.
NUMERICAL SIMULATION OF FLOW OVER TWO SIDE-BY-SIDE CIRCULAR CYLINDERS
Institute of Scientific and Technical Information of China (English)
SARVGHAD-MOGHADDAM Hesam; NOOREDIN Navid; GHADIRI-DEHKORDI Behzad
2011-01-01
In the present paper,the unsteady,viscous,incompressible and 2-D flow around two side-by-side circular cylinders was simulated using a Cartesian-staggered grid finite volume based method.A great-source term technique was employed to identify the solid bodies (cylinders) located in the flow field and boundary conditions were enforced by applying the ghost-cell technique.Finally,the characteristics of the flow around two side-by-side cylinders were comprehensively obtained through several computational simulations.The computational simulations were performed for different transverse gap ratios (1.5≤T/D≤4) in laminar (Re =100,200 ) and turbulent (Re =104) regimes,where T and D are the distance between the centers of cylinders and the diameter of cylinders,respectively.The Reynolds number is based on the diameter of cylinders,D.The pressure field and vorticity distributions along with the associated streamlines and the time histories of hydrodynamic forces were also calculated and analyzed for different gap ratios.Generally,different flow patterns were observed as the gap ratio and Reynolds number varied.Accordingly,the hydrodynamic forces showed irregular variations for small gaps while they took a regular pattern at higher spacing ratios.
Interaction Between Waves and An Array of Floating Porous Circular Cylinders
Institute of Scientific and Technical Information of China (English)
ZHAO Fen-fang; KINOSHITA Takeshi; BAO Wei-guang; HUANG Liu-yi; LIANG Zhen-lin; WAN Rong
2012-01-01
The present study theoretically as well as experimentally investigates the interaction between waves and an array of porous circular cylinders with or without an inner porous plate based on the linear wave theory.To design more effective floating breakwaters,the transmission rate of waves propagating through the array is evaluated.Each cylinder in the array is partly made of porous materials.Specifically,it possesses a porous sidewall and an impermeable bottom.In addition,an inner porous plate is horizontally fixed inside the cylinders.It dissipates the wave more effectively and eliminates the sloshing phenomenon.The approach suggested by Kagemoto and Yue (1986) is adopted to solve the multiple-scatter problem,while a hierarchical interaction theory is adopted to deal with hydrodynamic interactions among a great number of bodies,which efficiently saves computation time.Meanwhile,a series of model tests with an array of porous cylinders is performed in a wave basin to validate the theoretical work and the calculated results.The draft of the cylinders,the location of the inner porous plate,and the spacing between adjacent cylinders are also adjusted to investigate their effects on wave dissipation.
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.
Spatially distributed control for optimal drag reduction of the flow past a circular cylinder
Poncet, Philippe; Hildebrand, Roland; Cottet, Georges-Henri; Koumoutsakos, Petros
We report high drag reduction in direct numerical simulations of controlled flows past circular cylinders at Reynolds numbers of 300 and 1000. The flow is controlled by the azimuthal component of the tangential velocity of the cylinder surface. Starting from a spanwise-uniform velocity profile that leads to high drag reduction, the optimization procedure identifies, for the same energy input, spanwise-varying velocity profiles that lead to higher drag reduction. The three-dimensional variations of the velocity field, corresponding to modes A and B of three-dimensional wake instabilities, are largely responsible for this drag reduction. The spanwise wall velocity variations introduce streamwise vortex braids in the wake that are responsible for reducing the drag induced by the primary spanwise vortices shed by the cylinder. The results demonstrate that extending two-dimensional controllers to three-dimensional flows is not optimal as three-dimensional control strategies can lead efficiently to higher drag reduction.
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.
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.
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.
Study Of Three Dimensional Propagation Of Waves In Hollow Poroelastic Circular Cylinders
Shah S. A.
2015-01-01
Employing Biot’s theory of wave propagation in liquid saturated porous media, waves propagating in a hollow poroelastic circular cylinder of infinite extent are investigated. General frequency equations for propagation of waves are obtained each for a pervious and an impervious surface. Degenerate cases of the general frequency equations of pervious and impervious surfaces, when the longitudinal wavenumber k and angular wavenumber n are zero, are considered. When k=0, the plane-strain vibrati...
Institute of Scientific and Technical Information of China (English)
Xu Wan-hai; Yu Jian-xing; Du Jie; CHENG An-kang; KANG Hao
2012-01-01
The streamwise flow-induced vibration of a circular cylinder with symmetric vortex shedding in the first instability range is investigated,and a wake oscillator model for the dynamic response prediction is proposed.An approach is applied to calibrate the empirical parameters in the present model; the numerical and experimental results are compared to validate the proposed model.It can be found that the present prediction model is accurate and sufficiently simple to be easily applied in practice.
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.
Numerical simulation of turbulent flow around a forced moving circular cylinder on cut cells
Institute of Scientific and Technical Information of China (English)
BAI Wei
2013-01-01
Fixed and forced moving circular cylinders in turbulent flows are studied by using the Large Eddy Simulation (LES) and two-equation based Detached Eddy Simulation (DES) turbulence models. The Cartesian cut cell approach is adopted to track the body surface across a stationary background grid covering the whole computational domain. A cell-centered finite volume method of second-order accuracy in both time and space is developed to solve the flow field in fluid cells, which is also modified accordingly in cut cells and merged cells. In order to compare different turbulence models, the current flow past a fixed circular cylinder at a mode- rate Reynolds number,Re=3 900, is tested first. The model is also applied to the simulation of a forced oscillating circular cylinder in the turbulent flow, and the influences of different oscillation amplitudes, frequencies and free stream velocities are discussed. The numerical results indicate that the present numerical model based on the Cartesian cut cell approach is capable of solving the turbu- lent flow around a body undergoing motions, which is a foundation for the possible future study on wake induced oscillation and vor- tex induced vibration.
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.
DEFF Research Database (Denmark)
Demartino, Cristoforo; Koss, Holger; Ricciardelli, Francesco
2013-01-01
In this paper, the effects of ice accretion due to in-cloud icing on the aerodynamics of vertical circular cylinders is examined. Aerodynamic force coefficients with varying angle of attack were found, as a function of the wind speed; ice accretions deriving from different flow velocities and tem...... instability regions is made using the Den Hartog criterion. A short description of the accretion is given as well. A parallel paper deals with the case of circular cylinders in inclined flow....
Ekmekci, A.; Rockwell, D.
2010-01-01
Flow control induced by a single wire that is attached on the outer surface and parallel to the span of a stationary circular cylinder is investigated experimentally. The Reynolds number has a value of 10 000 and the wire diameter is nearly two orders of magnitude smaller than the cylinder diameter,
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.
Simulation of the Flow past a Circular Cylinder Using an Unsteady Panel Method
DEFF Research Database (Denmark)
Ramos García, Néstor; Sarlak, H.; Andersen, Søren Juhl;
2016-01-01
In the present work, an in-house UnSteady Double Wake Model (USDWM) is developed for simulating general flow problems behind bodies. The model is presented and used to simulate flows past a circular cylinder at subcritical, supercritical, and transcritical flows. The flow model is a two-dimension......In the present work, an in-house UnSteady Double Wake Model (USDWM) is developed for simulating general flow problems behind bodies. The model is presented and used to simulate flows past a circular cylinder at subcritical, supercritical, and transcritical flows. The flow model is a two......-dimensional panel method which uses the unsteady double wake technique to model flow separation and its dynamics. In the present work the separation location is obtained from experimental data and fixed in time. The highly unsteady flow field behind the cylinder is analyzed in detail. The results are compared...... with experiments and Unsteady Reynolds-Averaged Navier Stokes (URANS) simulations and show good agreement in terms of the vortex shedding characteristics, drag, and pressure coefficients for the different flow regimes....
Relating surface pressure to Lagrangian wake topology around a circular cylinder in cross flow
Rockwood, Matthew; Green, Melissa
2016-11-01
The tracks of Lagrangian saddles, identified as non-parallel intersections of positive and negative-time finite-time Lyapunov exponent (FTLE) ridges, have been shown to indicate the timing of von Karman vortex shedding in the wake of bluff bodies. The saddles are difficult to track in real-time, however, since future flow field data is needed for the computation of the FTLE fields. In order to detect the topological changes without direct access to the FTLE, the saddle dynamics are correlated to measurable surface quantities on a circular cylinder in cross flow. The Lagrangian saddle found upstream of a forming and subsequently shedding vortex has been shown to accelerate away from the cylinder surface as the vortex sheds. In previous numerical results at Re = 150 , this acceleration coincides with the peak in lift force over the cylinder, and also with a minimum in the static pressure at a location slightly upstream of the mean separation location. In the current work, this result is compared with experimental data at Re = O (10 , 000) . Successful validation would provide a strategy for locating sensitive regions on the cylinder surface where vortex shedding could be detected using simple pressure transducers. This work was supported by the Air Force Office of Scientific Research under AFOSR Award No. FA9550-14-1-0210.
Large Eddy Simulation of the Subcritical Flow over a U-Grooved Circular Cylinder
Directory of Open Access Journals (Sweden)
A. Alonzo-García
2014-07-01
Full Text Available With the aim of numerically replicating a drag reduction phenomenon induced by grooves presence, this paper presents a comparative large eddy simulation study of the flow over a smooth circular cylinder, and the flow over a U-grooved cylinder, at Re = 140,000, which is near transition between the subcritical and critical flow regimes. The grid densities were 2.6 million cells and 20.7 million cells for the smooth and the U-grooved cylinder, respectively. Both meshes were composed of hexahedral cells disposed in a structured form with additional refinements in near-wall regions, in order to obtain y+< 5 values. The cases were simulated during 25 vortex shedding cycles with the purpose of obtaining significant statistic data through the commercial software FLUENT V.12.1, which solved the Navier-Stokes equations in their unsteady and incompressible forms. Regarding the U-grooved cylinder flow, parameters such as the drag coefficient, lengths of recirculation, the transition from subcritical to critical flow, and the formation of a wake formed by secondary vortices of smaller sizes were predicted satisfactorily by the LES technique. From the manner in which the flow separates at different angles for both valleys and peaks of the U-grooves, a distinctive transitional mechanism induced by grooves presence is conjectured.
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.
Three-Dimensional Instability of Flow Around Two Circular Cylinders in Tandem Arrangement
Institute of Scientific and Technical Information of China (English)
DENG Jian; REN An-lu; ZOU Jian-feng
2005-01-01
The spatial evolution of vortices and transition to three-dimensionality in the wake of two circular cylinders in tandem arrangement have been numerically studied. An improved virtual body method developed from the virtual boundary method is used here. A Reynolds number range between 220 and 270 has been considered, and the spacing between two cylinders is selected as L/D=3 and L/D=3.5. When L/D=3, the secondary vortices of Mode-A are seen to appear at Re=240 and persist over the range of the Reynolds number of 240～270. When L/D=3.5, the similar critical Reynolds number has been found at Re=250. No obvious discontinuity has been found in the Strouhal-Reynolds number relationship, and this is different from three-dimensional flow around a single cylinder at the critical Reynolds number. The spanwise wavelength is about four times the diameter of the cylinder, and it is the characteristic wavelength for Mode-A instability. This paper can give some foremost insight into the three-dimensional instability of flow by complicated geometrical configuration.
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 LARGE EDDY SIMULATION OF THE NEAR WAKE OF A CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
陆夕云; 凌国灿
2002-01-01
Viscous flow around a circular cylinder at a subcritical Reynoldsnumber is investigated using a large eddy simulation (LES) coupled with theSmagorinsky subgrid-scale (SGS) model. A fractional-step method with a second-order in time and a combined finite-difference/spectral approximations are used tosolve the filtered three-dimensional incompressible Navier-Stokes equations. Calcula-tions have been performed with and without the SGS model. Turbulence statisticalbehaviors and flow structures in the near wake of the cylinder are studied. Somecalculated results, including the lift and drag coefficients, shedding frequency, peakReynolds stresses, and time-average velocity profile, are in good agreement with theexperimental and computational data, which shows that the Smagorinsky model canreasonably predict the global features of the flow and some turbulent statistical be-haviors.
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.
DEFF Research Database (Denmark)
Hourigan, K.; Rao, A.; Brøns, Morten
2013-01-01
The wake transitions of generic bluff bodies, such as a circular cylinder, near a wall are important because they provide understanding of different transition paths towards turbulence, and give some insight into the effect of surface modifications on the flow past larger downstream structures....... In this article, the fundamentals of vorticity generation and transport for the two-dimensional flow of incompressible Newtonian fluids are initially reviewed. Vorticity is generated only at boundaries by tangential pressure gradients or relative acceleration. After generation, it can cross......-annihilate with opposite-signed vorticity, and can be stored at a free surface, thus conserving the total vorticity, or circulation. Vorticity generation, diffusion and storage are demonstrated for a cylinder translating and rotating near a wall. The wake characteristics and the wake transitions are shown to change...
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
DEFF Research Database (Denmark)
Acampora, Antonio; Georgakis, Christos T.
2013-01-01
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...... 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...
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...
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.
Scattering of a partially-coherent wave from a material circular cylinder.
Hyde, Milo W; Bogle, Andrew E; Havrilla, Michael J
2013-12-30
The case of a partially-coherent wave scattered from a material circular cylinder is investigated. Expressions for the TMz and TEz scattered-field cross-spectral density functions are derived by utilizing the plane-wave spectrum representation of electromagnetic fields and cylindrical wave transformations. From the analytical scattered-field cross-spectral density functions, the mean scattering widths are derived and subsequently validated via comparison with those computed from Method of Moments Monte Carlo simulations. The analytical relations as well as the simulation results are discussed and physically interpreted. Key insights are noted and subsequently analyzed.
Directory of Open Access Journals (Sweden)
Jae-Hoon Bang
2016-01-01
Full Text Available This paper presents a new dual circularly polarized feed that provides good axial ratio over wide angles and low cross-polarized radiation in backward direction. A circular waveguide open end is fed with two orthogonally polarized waves in phase quadrature by a pair of printed crossed dipoles and a compact connectorized quadrature hybrid coupler. The waveguide aperture is loaded with a dielectric cylinder to reduce the cross-polarization beyond 90 degrees off the boresight. The fabricated feed has, at 5.5 GHz, 6.33-dBic copolarized gain, 3-dB beamwidth of 106°, 10-dB beamwidth of 195°, 3-dB axial ratio beamwidth of 215°, maximum cross-polarized gain of −21.4 dBic, and 27-dB port isolation. The reflection coefficient of the feed is less than −10 dB at 4.99–6.09 GHz.
Prediction Model for Vortex-Induced Vibration of Circular Cylinder with Data of Forced Vibration
Institute of Scientific and Technical Information of China (English)
PAN Zhi-yuan; CUI Wei-cheng; LIU Ying-zhong
2007-01-01
A model based on the data from forced vibration experiments is developed for predicting the vortex-induced vibrations (VIV) of elastically mounted circular cylinders in flow. The assumptions for free and forced vibration tests are explored briefly. Energy equilibrium is taken into account to set up the relationship between the dynamic response of self-excited oscillations and the force coefficients from forced vibration experiments. The gap between these two cases is bridged straightforwardly with careful treatment of key parameters. Given reduced mass m* and material damping ratio ζ of an elastically mounted circular cylinder in flow, the response characteristics such as amplitude, frequency, lock-in range, added mass coefficient, cross-flow fluid force and the corresponding phase angle can be predicted all at once. Instances with different combination of reduced mass and material damping ratio are compared to investigate their effects on VIV. The hysteresis phenomenon can be interpreted reasonably. The predictions and the results from recent experiments carried out by Williamson's group are in rather good agreement.
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.
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.
An Experimental Investigation of Some Three-Dimensional Effects of Stationary Circular Cylinders
Weiss, Lesley G.; Szewczyk, Albin A.
1999-11-01
Some effects of three-dimensionality on the near wake of a circular cylinder were investigated in the subcritical Reynolds number range. The three-dimensional effects were imposed by a linear shear approach flow and taper in the cylinder. A rake of 16 hot-wires was placed in the near wake in order to investigate the effects of three-dimensionality on the vortex shedding along the span. Results of the present investigation indicate that the three-dimensionality triggers the formation of constant frequency cells. The number and size of the cells are dependent on the combination of nonuniformity in the flow and cylinder. When based on midspan values of diameter and velocity the Strouhal number remains constant within each cell and is centered around the two-dimensional Strouhal number. If the Strouhal number is based on local values it tends to vary linearly within each cell and jump between cell boundaries. A pseudo-visualization technique using time series data is used to show the splitting of vortex cells of different frequency.
Mass transfer from a circular cylinder: Effects of flow unsteadiness and slight nonuniformities
Marziale, M. L.; Mayle, R. E.
1984-01-01
Experiments were performed to determine the effect of periodic variations in the angle of the flow incident to a turbine blade on its leading edge heat load. To model this situation, measurements were made on a circular cylinder oscillating rotationally in a uniform steady flow. A naphthalene mass transfer technique was developed and used in the experiments and heat transfer rates are inferred from the results. The investigation consisted of two parts. In the first, a stationary cylinder was used and the transfer rate was measured for Re = 75,000 to 110,000 and turbulence levels from .34 percent to 4.9 percent. Comparisons with both theory and the results of others demonstrate that the accuracy and repeatability of the developed mass transfer technique is about + or - 2 percent, a large improvement over similar methods. In the second part identical flow conditions were used but the cylinder was oscillated. A Strouhal number range from .0071 to .1406 was covered. Comparisons of the unsteady and steady results indicate that the magnitude of the effect of oscillation is small and dependent on the incident turbulence conditions.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method (DVM) was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for tracking individual solid particles. A dispersion function was defined to represent the dispersion scale of the particle.The wake vortex patterns, the distributions and the time series of dispersion functions of particles with different Stokes numbers were obtained. Numerical results show that the particle distribution in the wake of the circular cylinder is closely related to the particle's Stokes number and the structure of wake vortices: (1) the intermediate sized particles with Stokes numbers, St, of 0.25, 1.0 and 4.0 can not enter the vortex cores and concentrate near the peripheries of the vortex structures, (2) in the circular cylinder wake, the dispersion intensity of particles decreases as St is increased from 0.25 to 4.0.
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.
Institute of Scientific and Technical Information of China (English)
魏中磊; 张子强; H.E.Fiedler
1995-01-01
The behavior of synchronization in an open flow dynamical system, especially in an excited wake flow behind a 2-D oscillating circular cylinder with Reynolds number Re ranging from 45 to 200 is presented. The experiment reveals that only under certain conditions can the competition between frequencies of oscillating cylinder and the vortex shedding in the wake flow result in "window of chaos" with the mixed RTN and Feigenbaum scenario in the range of Re<185.
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
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...
Flow Around a Slender Circular Cylinder: A Case Study on Distributed Hopf Bifurcation
Directory of Open Access Journals (Sweden)
J. A. P. Aranha
2009-01-01
Full Text Available This paper presents a short overview of the flow around a slender circular cylinder, the purpose being to place it within the frame of the distributed Hopf bifurcation problems described by the Ginzburg-Landau equation (GLE. In particular, the chaotic behavior superposed to a well tuned harmonic oscillation observed in the range Re > 270, with Re being the Reynolds number, is related to the defect-chaos regime of the GLE. Apparently new results, related to a Kolmogorov like length scale and the rms of the response amplitude, are derived in this defect-chaos regime and further related to the experimental rms of the lift coefficient measured in the range Re > 270.
Drag Prediction in the Near Wake of a Circular Cylinder based on DPIV Data
Directory of Open Access Journals (Sweden)
Onur Son
2016-01-01
Full Text Available This study focuses on drag prediction in the near-wake of a circular cylinder by use of mean velocity profiles and discusses the closest location where a wake survey would yield an accurate result. Although the investigation considers both the mean and fluctuating velocities, the main focus is on the mean momentum deficit which should be handled properly beyond a critical distance. Digital Particle Image Velocimetry (DPIV experiments are performed in a Reynolds number range of 100 to 1250. Wake characteristics such as vortex formation length (L and wake width (t are determined and their relations to drag prediction are presented. Drag coefficients determined by momentum deficit formula are found to be in good agreement with experimental and numerical literature data in present Reynolds number regime.
Numerical Simulation of Local Scour Around A Large Circular Cylinder Under Wave Action
Institute of Scientific and Technical Information of China (English)
赵明; 滕斌
2001-01-01
A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around a large circular cylinder under wave action. The wave model is based on an elliptic mild slope equation.The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by a finite element method. The results of this model are compared with those from other methods and agree well with experimental data.
Experimental study of ice accretion on circular cylinders at moderate low temperatures
DEFF Research Database (Denmark)
Koss, Holger H.; Gjelstrup, Henrik; Georgakis, Christos T.
2012-01-01
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 o...... and experimental simulations and for future work in a recently developed climatic wind tunnel facility specifically built to investigate cable vibration....... 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...
Static fluid interfaces external to a right circular cylinder--experiment and theory
Energy Technology Data Exchange (ETDEWEB)
Kovitz, A.A.
1975-01-01
Studies of interfacial static shapes, based upon the existence of a surface (or interfacial) tension, have a long history. This work restricts itself to axisymmetric rod menisci. Experimental and numerical results are given for static axisymmetric interfacial surfaces of unbounded extent external to circular cylinders. The new results are (1) experiments with water and mercury menisci in air, noting the interfacial shape, and in particular, the height of the contact circle above the free surface at which breakoff occurs; (2) numerical computations in the manner of Huh and Scriven, in the case extended to reveal the existence of an envelope of solutions; (3) analytical results for very large and very small contact circle radii which agree with the numerical results in the appropriate regions; and (4) analytical representations of the envelope for the asymptotic solutions noted above, and by a curve- fitting technique for the intermediate range of contact circle radii. (17 refs.)
Flow past a circular cylinder with a permeable wake splitter plate
Cardell, Gregory S.
1993-08-01
Measurements in the near wake region of a circular cylinder in a uniform flow in the Reynolds number range 2.5 x 10(exp 3) is approximately less than Re is approximately less than 1.8 x 10(exp 4) with permeable splitter plates spanning the wake center plane are presented. Permeability is defined by the pressure drop across the plates, and the relationship between permeability and plate solidity is determined for a set of plates constructed from woven wire mesh permitting unambiguous characterization of the splitter plates by the solidity. The effects of different solidities on the flow in the near wake are investigated using smoke wire flow visualization, hot-wire anemometry, and measurements of the mean pressure at the cylinder surface, and the results are related to cylinder flow without a splitter plate. Flow visualization results demonstrate that the introduction of low solidity splitter plates does not change the basic near wake structure, and that sufficiently high solidity uncouples the large-scale wake instability from the body, with the primary vortex formation occurring downstream of the separation bubble due to instability of the wake profile. Hot-wire and surface pressure measurements confirm and quantify the flow visualization results, showing that the permeable splitter plates reduce the drag and modify the primary wake frequency. When the solidity is high enough that the wake is convectively unstable, the base pressure is independent of the Reynolds number and solidity. For a wide range of solidities, the same asymptotic value of the Strouhal number is reached at high Reynolds numbers. The relationship between the Strouhal number and the base pressure is discussed.
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.
Secondary vortex street in the wake of two tandem circular cylinders at low Reynolds number.
Wang, Si-ying; Tian, Fang-bao; Jia, Lai-bing; Lu, Xi-yun; Yin, Xie-zhen
2010-03-01
The experiments on two tandem circular cylinders were conducted in a horizontal soap film tunnel for the Reynolds number Re=60 , 80, and 100 and the nondimensional center-to-center spacing Gamma ranging in 1 approximately 12. The flow patterns were recorded by a high-speed camera and the vortex shedding frequency was obtained by a spatiotemporal evolution method. The secondary vortex formation (SVF) mode characterized by the formation of a secondary vortex street in the wake of the downstream cylinder was found at large gamma. Moreover, some typical modes predicted by previous investigations, including the single bluff-body, shear layer reattachment, and synchronization of vortex shedding modes, were also revisited in our experiments. Further, numerical simulations were carried out using a space-time finite-element method and the results confirmed the existence of the SVF mode. The mechanism of SVF mode was analyzed in terms of the numerical results. The dependence of the Strouhal number Sr on Gamma was given and the flow characteristics relevant to the critical spacing values and the hysteretic mode transitions were investigated.
Buoyancy effect on the flow pattern and the thermal performance of an array of circular cylinders
Fornarelli, Francesco; Oresta, Paolo
2016-01-01
In this paper we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are iso-thermal and they are aligned with the Earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between -1 and 1. Two values of center to center spacing (s=3.6d - 4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=-1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard d...
Instability of the shear layer in the near wake of a circular cylinder
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The instability of the shear layer separated from a circular cylinder is studied with the Reynolds number (Re) of 3000～104 by numerically solving the two-dimensional Navier-Stokes equations. In the wake of the cylinder, primary vortex shedding with natural frequency fs occurs, and the instability of the shear layer with frequency ft develops, which leads to mixing layer eddies and interacts with the primary shedding vortices. However, there remains some uncertainties regarding to the variation of the shear layer characteristic frequency with the Reynolds number. Based on the previous experimental work, several relationships of ft/fs with Re has been proposed including ft/fs～Re0.5 by Bloor, ft/fs～Re0.87 by Wei and Smith and ft/fs～Re0.67 by Prasad and Williamson. The objective of this study is to predict reasonably the relation of the shear layer instability frequency with the Reynolds number based on the present accurate calculation with the high-order schemes and high-resolution spectrum analysis. According to our calculated results, a variation for the normalized shear-layer frequency of the form ft/fs～Re0.69 is predicted numerically, which is in good agreement with a recent experimental measurement of Re0.67 and physical prediction of Re0.7.
Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow
Energy Technology Data Exchange (ETDEWEB)
Kawamura, Tsutomu; Nakao, Toshitsugu; Hayashi, Masaaki; Murayama, Kouichi [Hitachi Ltd., Tokyo (Japan)
2001-11-01
Synchronized vibrations were measured for a circular cylinder in a water cross flow at subcritical Reynolds numbers to compare the synchronization range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on the range. A small vibration in the lift direction was found in only the subcritical region when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency. The ratio of the Karman vortex shedding frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortex shedding 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 shedding was about 1/2, and that in the lift direction decreased from 1 to 0.8 with decreasing Strouhal number. (author)
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.
DEFF Research Database (Denmark)
Demartino, C.; Georgakis, Christos T.; Ricciardelli, F.
are produced from HDPE, as used for bridge stays. Variations in the accretion parameters were chosen to generate the most common natural ice formations, which might also be expected to produce bridge cable vibrations. A parallel paper deals with the case of circular cylinders in cross flow....
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...
Control of flow structure in the wake region of circular cylinder with meshy wire in deep water
Directory of Open Access Journals (Sweden)
Burcu Oğuz
2016-08-01
Full Text Available In this study the aim is decreasing the effect and the intensity of the temporary loads resulted from vortex shedding that have an impact on the cylinder (chimneys, high buildings etc. located in deep water and the object or objects in the wake region and definition of the optimum values (wire thickness and porosity β With different thickness and different porosity ratios the effect of meshy wire that surrounded a circular cylinder of D=50 mm diameter was observed at Re_D=5000. The porosity ratios were four different values between a range of β=0.5-0.8 with an interval of 0.1. The thicknesses of wire were 1 mm, 2 mm, 3 mm and 4 mm. The flow structure in the wake region of circular cylinder was tried to be controlled by meshy wire that surrounded the cylinder. Experiments were carried out by using particle image velocimetry (PIV technique. Comparing with bare cylinder results, turbulence kinetic energy (TKE and Reynolds shear stress values increase with wire thicknesses of b=1 mm, 2 mm for all porosity ratios and decrease with b=3 mm, 4 mm. With porosity ratio of β=0.6 and wire thickness of b=4 mm TKE and Reynolds shear stress results show that meshy wire controls the flow in the wake region of the cylinder. Frequency value results also define that best flow control is obtained with β=0.6 and b=4 mm.
Lu, Lin; Guo, Xiao-ling; Tang, Guo-qiang; Liu, Ming-ming; Chen, Chuan-qi; Xie, Zhi-hua
2016-09-01
Numerical results of fluid flow over a rotationally oscillating circular cylinder with splitter plate are presented here. Different from the previous examinations with freely rotatable assembly, the fluid and structure interactions are treated as a coupled dynamic system by fully considering the structural inertia, stiffness, and damping. The hydrodynamic characteristics are examined in terms of reduced velocity Ur at a relatively low Reynolds number Re = 100 for different plate lengths of L/D = 0.5, 1.0, and 1.5, where Ur = U/(Dfn), Re = UD/υ and fn = (κ/J)0.5/2π with U the free stream velocity, D the diameter of the circular cylinder, υ the fluid kinematic viscosity, fn the natural frequency, J the inertial moment, κ the torsional stiffness, and L the plate length. Contrast to the freely rotating cylinder/plate body, that is, in the limit of κ → 0 or Ur →∞, remarkable rotary oscillation is observed at relatively low reduced velocities. For the typical case with L/D = 1.0, the maximum amplitude may reach five times that at the highest reduced velocity of Ur = 15.0 considered in this work. At the critical reduced velocity Ur = 4.2, notable hydrodynamic jumps are identified for the rotation amplitude, response frequency, mean drag coefficient, lift amplitude, and vortex shedding frequency. Moreover, the phase angle between the fluid moment and rotary oscillation abruptly changes from 0 to π at Ur = 6.5. Due to the combined effect of fluid moment, rotation response, and phase difference, the natural frequency of the rotating body varies in flow, leading to a wide regime of lock-in/synchronization (Ur ≥4.2, for L/D = 1.0). The phenomenon of rotation bifurcation, i.e., the equilibrium position of the rotary oscillation deflects to a position which is not parallel to the free stream, is found to only occur at higher reduced velocities. The longer splitter plate has the lower critical reduced velocity. The occurrence of bifurcation is attributed to the
Choi, H.; You, D.; Choi, M.-R.; Kang, S.-H.
1996-11-01
Laminar vortex sheddings behind a circular cylinder with and without splitter plates attached to the cylinder at low Reynolds numbers are simulated by solving the unsteady incompressible Navier-Stokes equations. The Strouhal number, lift and drag rapidly change with the length of the splitter plate. Far-field noise from the vortex shedding behind the cylinder is computed using the Curle's formulation of the Lighthill acoustic analogy. The acoustic source functions are obtained from the computed near-field velocity and pressure. Numerical results show that the volume quadrupole noise is small at a low Mach number, compared to the surface dipole noise from the cylinder. Variations of the far-field noise characteristics with respect to the splitter plate are being investigated and will be shown in the final presentation. ^* Supported by KOSEF under Contract No. 961-1009-075-2
Directory of Open Access Journals (Sweden)
Mutlu Mustafa
2016-01-01
Full Text Available Energy storage systems are being more important to compensate irregularities of renewable energy sources and yields more profitable to invest. Compressed air energy storage (CAES systems provide sufficient of system usability, then large scale plants are found around the world. The compression process is the most critical part of these systems and different designs must be developed to improve efficiency such as liquid piston. In this study, a liquid piston is analyzed with CFD tools to look into the effect of piston speed, compression ratio and cylinder geometry on compression efficiency and required work. It is found that, increasing piston speeds do not affect the piston work but efficiency decreases. Piston work remains constant at higher than 0.05 m/s piston speeds but the efficiency decreases from 90.9 % to 74.6 %. Using variable piston speeds has not a significant improvement on the system performance. It is seen that, the effect of compression ratio is increasing with high piston speeds. The required power, when the compression ratio is 80, is 2.39 times greater than the power when the compression ratio is 5 at 0.01 m/s piston speed and 2.87 times greater at 0.15 m/s. Cylinder geometry is also very important because, efficiency, power and work alter by L/D, D and cylinder volume respectively.
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.
Phenomenology of a flow around a circular cylinder at sub-critical and critical Reynolds numbers
Capone, Alessandro; Klein, Christian; Di Felice, Fabio; Miozzi, Massimo
2016-07-01
In this work, the flow around a circular cylinder is investigated at Reynolds numbers ranging from 79 000 up to 238 000 by means of a combined acquisition system based on Temperature Sensitive Paint (TSP) and particle velocimetry. The proposed setup allows simultaneous and time-resolved measurement of absolute temperature and relative skin friction fields onto the cylinder surface and near-wake velocity field. Combination of time-resolved surface measurements and planar near-field velocity data allows the investigation of the profound modifications undergone by the wall shear stress topology and its connections to the near-field structure as the flow regime travels from the sub-critical to the critical regime. Laminar boundary-layer separation, transition, and re-attachment are analyzed in the light of temperature, relative skin friction maps, and Reynolds stress fields bringing about a new perspective on the relationship between boundary layer development and shear layer evolution. The fast-responding TSP employed allows high acquisition frequency and calculation of power spectral density from surface data. Correlation maps of surface and near-wake data provide insight into the relationship between boundary-layer evolution and vortex shedding. We find that as the Reynolds number approaches the critical state, the separation line oscillations feature an increasingly weaker spectrum peak compared to the near-wake velocity spectrum. In the critical regime, separation line oscillations are strongly reduced and the correlation to the local vorticity undergoes an overall decrease giving evidence of modifications in the vortex shedding mechanism.
Flow above the free end of a surface-mounted finite-height circular cylinder: A review
Sumner, D.
2013-11-01
The wake of a surface-mounted finite-height circular cylinder and the associated vortex patterns are strongly dependent on the cylinder aspect ratio and the thickness of the boundary layer on the ground plane relative to the dimensions of the cylinder. Above a critical aspect ratio, the mean wake is characterized by streamwise tip vortex structures and Kármán vortex shedding from the sides of the cylinder. Below a critical aspect ratio, a unique mean wake structure is observed. Recent experimental studies in the literature that used phase-averaged techniques, as well as recent numerical simulations, have led to an improved physical understanding of the near-wake vortex flow patterns. However, the flow above the free end of the finite circular cylinder, and its relationship to the near wake, has not been systematically studied. The effects of aspect ratio and boundary layer thickness on the free-end flow field are also not completely understood, nor has the influence of Reynolds number on the free-end flow field been fully explored. Common features associated with the free end include separation from the leading edge, a mean recirculation zone containing a prominent cross-stream arch (or mushroom) vortex, and reattachment onto the free-surface. Other flow features that remain to be clarified include a separation bubble near the leading edge, one or two cross-stream vortices within this separation bubble, the origins of the streamwise tip or trailing vortices, and various critical points in the near-surface flow topology. This paper reviews the current understanding of the flow above the free end of a surface-mounted finite-height circular cylinder, with a focus on models of the flow field, surface oil flow visualization studies, pressure and heat flux distributions on the free-end surface, measurements of the local velocity field, and numerical simulations, found in the literature.
Influence of hydrodynamic slip on convective transport in flow past a circular cylinder
Rehman, Nidhil M. A.; Kumar, Anuj; Shukla, Ratnesh K.
2017-02-01
The presence of a finite tangential velocity on a hydrodynamically slipping surface is known to reduce vorticity production in bluff body flows substantially while at the same time enhancing its convection downstream and into the wake. Here, we investigate the effect of hydrodynamic slippage on the convective heat transfer (scalar transport) from a heated isothermal circular cylinder placed in a uniform cross-flow of an incompressible fluid through analytical and simulation techniques. At low Reynolds (Re≪ 1 ) and high Péclet (Pe≫ 1 ) numbers, our theoretical analysis based on Oseen and thermal boundary layer equations allows for an explicit determination of the dependence of the thermal transport on the non-dimensional slip length l_s . In this case, the surface-averaged Nusselt number, Nu transitions gradually between the asymptotic limits of Nu ˜ Pe^{1/3} and Nu ˜ Pe^{1/2} for no-slip (l_s → 0 ) and shear-free (l_s → ∞) boundaries, respectively. Boundary layer analysis also shows that the scaling Nu ˜ Pe^{1/2} holds for a shear-free cylinder surface in the asymptotic limit of Re≫ 1 so that the corresponding heat transfer rate becomes independent of the fluid viscosity. At finite Re, results from our two-dimensional simulations confirm the scaling Nu ˜ Pe^{1/2} for a shear-free boundary over the range 0.1 ≤ Re≤ 10^3 and 0.1≤ Pr≤ 10 . A gradual transition from the lower asymptotic limit corresponding to a no-slip surface, to the upper limit for a shear-free boundary, with l_s , is observed in both the maximum slip velocity and the Nu. The local time-averaged Nusselt number Nu_{θ } for a shear-free surface exceeds the one for a no-slip surface all along the cylinder boundary except over the downstream portion where unsteady separation and flow reversal lead to an appreciable rise in the local heat transfer rates, especially at high Re and Pr. At a Reynolds number of 10^3 , the formation of secondary recirculating eddy pairs results in
Interaction theory of hypersonic laminar near-wake flow behind an adiabatic circular cylinder
Hinman, W. Schuyler; Johansen, C. T.
2016-11-01
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 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.
Transition waves and nonlinear interactions in the near wake of a circular cylinder
Institute of Scientific and Technical Information of China (English)
凌国灿; Allen T.Chwang; 牛家玉; 王冬(女菱)
1997-01-01
Transition waves and interactions between two kinds of instability-vortex shedding and transition wave in the near wake of a circular cylinder in the Reynolds number range 3 000-10 000 are studied by a domain decomposition hybrid numerical method.Based on high resolution power spectral analyses for velocity new results on the Reynolds-number dependence of the transition wave frequency,i.e.ft/fa~Re0.87 are obtained.The new predictions are in good agreement with the experimental results of Wei and Smith but different from Braza’s prediction and some early experimental results ft/fa-Re0.5 given by Bloor et al.The multi-interactions between two kinds of vortex are clearly visualized numerically.The strong nonlinear interactions between the two independent frequencies (ft,fa) leading to spectra broadening to form the coupling mfs±nft are predicted and analyzed numerically,and the characteristics of the transition are described.Longitudinal variations of the transition wave and its coupling are reported.Deta
FEATURES OF THE SUPERCRITICAL TRANSITION IN THE WAKE OF A CIRCULAR CYLINDER
Institute of Scientific and Technical Information of China (English)
熊俊; 凌国灿; 朱克勤
2002-01-01
The features of the wake behind a uniform circular cylinder at Re=200, which is just beyond the critical Reynolds number of 3-D transition, areinvestigated in detail by direct numerical simulations by solving 3-D incompressible Navier-Stokes equations using mixed spectral-spectral-element method. The high-order splitting algorithm based on the mixed stiffly stable scheme is employed inthe time discretization. Due to the nonlinear evolution of the secondary instabilityof the wake, the spanwise modes with different wavelengths emerge. The spanwisecharacteristic length determines the transition features and global properties of thewake. The existence of the spanwise phase difference of the primary vortices sheddingis confirmed by Fourier analysis of the time series of the spanwise vorticity and at-tributed to the dominant spanwise mode. The spatial energy distributions of variousmodes and the velocity profiles in the near wake are obtained. The numerical resultsindicate that the near wake is in 3-D quasi-periodic laminar state with transitionalbehaviors at this supercritical Reynolds number.
Study Of Three Dimensional Propagation Of Waves In Hollow Poroelastic Circular Cylinders
Directory of Open Access Journals (Sweden)
Shah S.A.
2015-08-01
Full Text Available Employing Biot’s theory of wave propagation in liquid saturated porous media, waves propagating in a hollow poroelastic circular cylinder of infinite extent are investigated. General frequency equations for propagation of waves are obtained each for a pervious and an impervious surface. Degenerate cases of the general frequency equations of pervious and impervious surfaces, when the longitudinal wavenumber k and angular wavenumber n are zero, are considered. When k=0, the plane-strain vibrations and longitudinal shear vibrations are uncoupled and when k≠0 these are coupled. It is seen that the frequency equation of longitudinal shear vibrations is independent of the nature of the surface. When the angular (or circumferential wavenumber is zero, i.e., n=0, axially symmetric vibrations and torsional vibrations are uncoupled. For n≠0 these vibrations are coupled. The frequency equation of torsional vibrations is independent of the nature of the surface. By ignoring liquid effects, the results of a purely elastic solid are obtained as a special case.
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.
Zhou Yun Song; Wang Fu He
2003-01-01
We investigate the properties of guide modes localized at the interfaces of photonic crystal (PC) heterostructures which are composed of two semi-infinite two-dimensional PCs consisting of non-circular air cylinders with different rotating angles embedded in a homogeneous host dielectric. Photonic band gap structures are calculated with the use of the plane-wave expansion method in combination with a supercell technique. We consider various configurations, for instance, rectangular (square) lattice-rectangular (square) air cylinders, and different rotating angles of the cylinders in the lattices on either side of the interface of a heterostructure. We find that the absolute gap width and the number of guide modes strongly depend on geometric and physical parameters of the heterostructures. It is anticipated that the guide modes in such heterostructures can be engineered by adjusting parameters.
Institute of Scientific and Technical Information of China (English)
A.Avci; A.Bulu; A.Yapici
2006-01-01
A contact problem for an infinitely long hollow cylinder is considered.The cylinder is compressed by an outer rigid ring with a circular profile.The material of the cylinder is linearly elastic and isotropic.The extent of the contact region and the pressure distribution are sought.Governing equations of the elasticity theory for the axisymmetric problem in cylindrical coordinates are solved by Fourier transfoms and general expressions for the displacements are obtained.Using the boundary conditions,the formulation is reduced to a singular integral equation.This equation is solved by using the Gaussian quadrature.Then the pressure distribution on the contact region is determined.Numerical results for the contact pressure and the distance characterizing the contact area are given in graphical form.
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.
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.
Institute of Scientific and Technical Information of China (English)
GHOZLANI Belgacem; HAFSIA Zouhaier; MAALEL Khlifa
2012-01-01
In order to identify the influence of shape comers on the instantaneous forces in the case of oscillating bodies,the simulated flow field is compared for two kinds of cross sections:diamond prism and circular cylinder.For these two flow configurations,the same Reynolds number and a Keulegan-Carpenter are considered.To compute the dynamic flow field surrounding the body,the Navier-Stokes transport equationsin a non-inertial reference frame attached to the body are considered.Hence,a source term is added locally to the momentum equation to take into account the body acceleration.The proposed model is solved using the PHOENICS code.For the oscillating circular cylinder,the simulated results are in good agreement with the experimental data available in the litterature.After validation of this proposed model,flow field for diamond prism is determined.For both bodies,the process of the vortex formation is similar,with the formation of a recirculation zone in the near-wake containing a symmetric pair of vortices of equal strength and opposite rotation.The length of recirculation zone varies approximately linearly with time.However,the in-line force coefficient of the oscillating diamond prism is found to be greatest,since the recirculation zone is longer compared with that of the oscillating circular cylinder.
Influence of ventilated shrouds on the convective heat transfer to a circular cylinder
Daryabeigi, Kamran; Ash, Robert L.; Dillon-Townes, Lawrence A.
1987-01-01
Convective heat transfer to shrouded cylinders in transverse flow has been studied over the Reynolds number range 2000-20,000. The influence of shroud ventilation, relative shroud diameters, and orientation of the ventilation holes was studied. In some cases, average inner-cylinder Nusselt numbers were found to exceed the comparable bare-cylinder values by as much as 50 percent. Cylinder heat convection was influenced more by the degree of ventilation and shroud diameter than by hole orientation. An equivalent inner bare cylinder diameter, based on degree of shroud ventilation and shroud diameter, was developed which can be useful in shroud design studies.
Evaluation of InGaN/GaN light-emitting diodes of circular geometry.
Wang, X H; Fu, W Y; Lai, P T; Choi, H W
2009-12-07
Blue GaN light emitting diodes (LEDs) in the shape of cuboids and circular disks have been fabricated by laser micromachining. The proposed circular geometry serves to enhance overall light extraction on a macro-scale and to improve uniformity of the emission pattern due to the rotational symmetry of the chip. Analysis of the chip shaping effect is carried out by ray-tracing simulations and further supported with mathematical modeling using ideal LED models, and subsequently verified with fabricated devices. In comparison, a 10% improvement in overall emission was observed for circular LEDs over the regular cuboids, consistent with simulations and calculations. The measured emission pattern from the circular LED confirms the axial symmetry of the emission beam.
Energy Technology Data Exchange (ETDEWEB)
Hong, S.H.; Welty, J.R.
1999-09-01
In any process involving high temperatures such as heat treatment, power generation, and other engineering applications, radiation heat transfer is an important mechanism. This paper presents the distribution of radiation heat flux within an enclosure containing a horizontal circular cylinder. Cases were examined both with and without an absorbing, emitting, and scattering medium present. The bottom surface of the square enclosure was considered a uniform heat flux surface, and the other surfaces were considered perfectly absorbing. A circular cylinder was located at various positions along the vertical centerline of the enclosure; its length was that of the enclosure depth. In the first part of this study (cases 1 and 2), different configurations were used with an optically thin ({tau} {much{underscore}lt} 1) medium in the enclosure, and in the second, different optical thicknesses were used with a fixed enclosure size. The amount of radiant energy transferred to the cylinder depends on its location, the optical thickness of the participating medium, and the enclosure depth. For the optically thin cases ({tau} {much{underscore}lt} 1) the Monte Carlo solution calculates geometric view factors.
Three-dimensional flow around two circular cylinders of different diameters in a close proximity
Thapa, Jitendra; Zhao, Ming; Cheng, Liang; Zhou, Tongming
2015-08-01
Flow past two cylinders of different diameters in close proximity is simulated numerically for a constant diameter ratio of 0.45, a gap ratio of 0.0625, and a Reynolds number of 1000 (defined using the diameter of the main cylinder). The effect of the position angle α of the small cylinder relative to the large one on force coefficients and wake flow patterns are studied. Depending on the position angle α of the small cylinder, four wake flow modes are identified: the upstream interference mode for α = 0°, 22.5°, and 45°, the intermittent attached gap flow mode for α = 67.5° and 90°, the attached gap flow mode for α = 112.5° and 135°, and the wake interference mode for α = 157.5° and 180°. The RMS lift coefficients of both cylinders are reduced significantly compared with that of a single cylinder, regardless of the position angle of the small cylinder. Although the variation trends of the mean drag and lift coefficients with the position angle of the small cylinder obtained from the two-dimensional (2D) and three-dimensional (3D) simulations are similar, the 2D simulations overestimate the mean drag coefficient, the RMS drag and lift coefficients compared with those obtained from the 3D simulations.
Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage.
Directory of Open Access Journals (Sweden)
Tu Cheng-Xu
2014-01-01
Full Text Available The field characteristics of two side-by-side rotating circular cylinders in a cross-flow is investigated under different rotation types, at T/D = 1.11,1.6, and 3, respectively (T is the center spacing between the cylinders, and D is the cylinder diameter. A similar flow pattern which is the most efficient to narrow the lowpressure area is identified for rotation type A, independent of T/D ratio, and two typical flow patterns are found under different spacings for rotation type B and type C, respectively. It is confirmed that there is an optimal rotational speed of 1.7-2, under rotation type A to attenuate the vortices, velocity drop, and turbulence intensity tremendously. As rotational speed increases to the optimal value, both the velocity drop and turbulence intensity decrease and their distributions are smooth. The results indicate that the shear layers which are accelerated following the free-stream direction would have significant influence on the flow modification, and different rotation types actually arrange these shear layers in diverse ways to change the flow pattern. Pitch ratio is capable to transform the gap flow, which is usually including the shear layers referred, thus this parameter can modify the wake of the two cylinders at different rotation types.
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.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A flow past two side-by-side identical circular cylinders was numerically investigated with the unstructured spectral element method. From the computational results at various non-dimensional distances between cylinder centers T/D and the Reynolds number Re, a total of nine kinds of wake patterns were observed: four steady wake patterns, including single bluff-body steady pattern, separated double-body steady pattern and transition steady pattern for sub-critical Reynolds numbers and biased steady pattern for super-critical Reynolds numbers, and five unsteady wake patterns, including single bluff-body periodic pattern, biased quasi-steady pattern, quasi-periodic (flip-flopping) pattern, in-phase-synchronized pattern and anti-phase-synchronized pattern. Time evolution of lift and drag coefficients corresponding to each unsteady wake pattern was given.
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.
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.
Vortex-Induced Vibration of a Circular Cylinder Fitted with a Single Spanwise Tripwire
Vaziri, Ehsan; Ekmekci, Alis
2016-11-01
A spanwise tripwire can be used to alter the coherence and strength of the vortex shedding from cylindrical structures. While this has been well-documented for cylinders in stationary state, there exists a lack of understanding regarding the control induced by spanwise tripwires for cylinders undergoing vortex-induced vibration (VIV). The current experimental research investigates the consequences of spanwise tripping on VIV of a cylinder. Experiments are conducted in a recirculating water tunnel at a Reynolds number of 10,000. The test setup allows the rigid test cylinder to have one-degree-of-freedom vibration in the cross-flow direction as a result of fluid forcing. To measure the cylinder motion, a high-resolution laser displacement sensor is used. The tripwire diameter to cylinder diameter ratio is fixed at 6.1%. Various angular positions of tripwire are studied ranging from 40 to 90 degrees. It is shown that the tripwire location controls the pattern, amplitude, frequency, and mid-position of oscillations significantly. Different oscillation modes are classified based on the observed oscillation pattern, amplitude and frequency. Oscillation amplitude can be reduced by 61% with respect to the amplitude of a clean cylinder undergoing VIV under the same flow condition.
Energy Technology Data Exchange (ETDEWEB)
De Paula, A.V.; Moeller, S.V., E-mail: vagtinski@mecanica.ufrgs.br, E-mail: svmoller@ufrgs.br [UFRGS - Univ. Federal do Rio Grande do Sul, PROMEC - Programa de Pos Graduacao em Engenharia Mecanica, Porto Alegre, RS (Brazil)
2011-07-01
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)
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.
Study Report of Design Guide for Single Circular Cylinder in Axial Flow
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The vibration of a flexible cylinder in axial flow is random, so the quantities of interests are the root-mean-square value of the response and the amplitude distribution. This design guideline presents a relationship for calculating the
2015-07-01
the direct response and the single and double ground bounce contributions. An arbitrarily oriented cylinder is treated by augmenting the solution with...response and the single and double ground bounce contributions. An arbitrarily oriented cylinder is treated by augmenting the solution with...angle in azimuth (measured from + x̂ ). Without the loss of generality, a vertically polarized (TMz) plane wave is taken as the source of excitation
Control of flow past a circular cylinder via a spanwise surface wire: effect of the wire scale
Energy Technology Data Exchange (ETDEWEB)
Ekmekci, Alis [University of Toronto Institute for Aerospace Studies, Toronto, ON (Canada); Rockwell, Donald [Lehigh University, Department of Mechanical Engineering, Bethlehem, PA (United States)
2011-09-15
Flow phenomena induced by a single spanwise wire on the surface of a circular cylinder are investigated via a cinema technique of particle image velocimetry (PIV). The primary aim of this investigation is to assess the effect of the wire scale. To this end, consideration is given to wires with different diameters that are 0.5, 1.2, and 2.9% of the cylinder diameter. The Reynolds number has a subcritical value of 10,000. Compared to the thickness of the unperturbed boundary layer developing around the cylinder between 5 and 75 from the forward stagnation point, the former two wires have smaller scales and the latter has a larger scale. Two angular locations of the wire, defined with respect to the forward stagnation point of the cylinder, are found to be critical. When the wire is located at these critical angles, either the most significant extension or the contraction of the time-mean separation bubble occurs in the near wake. These critical angles depend on the wire scale: the smaller the wire, the larger the critical angle. The small-scale and large-scale wires that have diameters of 1.2 and 2.9% of the cylinder diameter induce bistable shear-layer oscillations between different separation modes when placed at their respective critical angles corresponding to maximum extension of the near-wake bubble. These oscillations have irregular time intervals that are much longer than the time scale associated with the classical Karman instability. Moreover, the large-scale wire can either significantly attenuate or intensify the Karman mode of vortex shedding at the critical states; in contrast, the small-scale wires do not notably alter the strength of the Karman instability. (orig.)
Mechanism of tonal noise generation from circular cylinder with spiral fin
Yamashita, Ryo; Hayashi, Hidechito; Okumura, Tetsuya; Hamakawa, Hiromitsu
2014-12-01
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.
Numerical Investigation of Heat Transfer on the Surface of a Circular Cylinder in Cross-Flow
Directory of Open Access Journals (Sweden)
Gizem ŞENCAN
2015-03-01
Full Text Available In the present study, numerical analysis of heat transfer from heated cylinder, located inrectangular channel normal to the flow direction is studied. Finite volume based ANSYS-FLUENT 14 codeis used in the solution of governing equations. Three different turbulence models as Std. k-ε, RNG k-ε andRealizable k-ε are used in computations for four different Reynolds numbers, Re= 4000, 8000, 16000, and32000. It is found that numerical results obtained with Std. and RNG k-ε turbulence models are in goodagreement with experimental data for maximum value of local Nusselt number on the cylinder. As expectedthat local Nusselt numbers increase with increasing Reynolds number for almost all points on cylinder.
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.
Heat Transfer and Pressure Drop Data for Circular Cylinders in Ducts and Various Arrangements
1951-09-01
cities - and Constant Spacing iii Scinch, Duct - ~-^ - - -r =• -~ - -- - - - - 37;, Single, Cylinder’ and Three- Cylinders in line" with Yard...heating coils surrounded by .a 3/Scinch thicis shell of ^anslte, .an asbest -cs-cemens material; oo’CiSlstljig of 35 per cent Portland cement .and lä per...gradients did, not permit very accurate de-* teraiinationä--&t low flois veio- cities because of ihseösitivity af She fee generalization of the, pressure
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...
A different approach on the onset of separation in the flow around a circular cylinder
Malamataris, Nikolaos; Sarris, I.; Pazis, D.; Liakos, A.
2016-11-01
The onset of separation in the flow around a cylinder is revisited with new insight. The goal of the research is to compute the smallest Reynolds number where the separation actual occurs rather than computing small eddies and extrapolating to the value of the Reynolds number where separation may occur. To this purpose, an accurate home made code is designed with Galerkin finite elements. The computational domain is chosen as the laboratory experiments by Taneda. It is found that in all six different choices of Taneda's diameters of the cylinders he used, separation is not observed for Re research is the computation of the drag coefficient for Reynolds numbers starting from 1 .10-5 up to 40. In addition, the separation angle (point where vorticity changes sign) is computed for 6 . 14 research aims to be the most thorough work done on that subject so far.
Computation of Added Mass and Damping Coefficients of a Horizontal Circular Cylinder in Open Foam
DEFF Research Database (Denmark)
Chen, Hao; Christensen, Erik Damgaard
2016-01-01
This paper presents numerical computation of added massand damping coefficients of a slender horizontal cylinder in thefree surface zone, which typically serves as a fish cage floater. A fully viscous two phase flow solver in OpenFOAM was employed in the numerical computation. The purpose...... was to validate the capability of this solver and dynamic mesh functionality. A two dimensional numerical wave tank was set up, and two wave relaxation zones were used to reduce the size of the computational domain. Harmonic forced oscillations of the cylinder were performed at different frequencies...... and amplitudes. The mesh at free surface zone was refined based on the radiated wave heights at different oscillation frequencies in order to properly resolve the radiated waves. The result shows that in most frequency ranges, the numerical computation agreed well with the experimental data and analytical...
Transition to Turbulence in the Separated Shear Layers of Yawed Circular Cylinders
2010-04-15
where her hot - wire anemometer measurements found their streamwise appearance (after separation) to be inversely proportional to the cylinder Reynolds...Smith (1986) conducted hot - wire anemometer measurements where they reported expo- nents b = 0.87 and b = 0.773, respectively, for the Bloor power- law...measured when using anemometry . Prasad and Wil- liamson (1996) compiled their anemometer measurements along with those of Bloor as well as Wei and
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.
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.
Cotrell, David L.; Pearlstein, Arne J.
2000-11-01
We report computations of the velocity field for flows driven by rotation of a screw in a circular cylinder with an applied opposing pressure gradient. Use of a helical coordinate system in a frame rotating with the screw reduces the flow calculation to a steady one, which is taken to be fully-developed in the helical direction. The full incompressible Navier-Stokes equations in primitive-variables form are solved numerically using a finite-element method employing quadrilateral elements with quadratic velocity and linear pressure interpolation. A consistent penalty method is used to satisfy incompressibility. The screw cross-section is rectangular. The effect of screw clearance and other geometric parameters on the velocity field will be discussed for low and intermediate Reynolds numbers and compared to the Stokes flow case.
Nemati, Hasan; Sedighi, Kurosh; Farhadi, Mousa; Pirouz, Mohammad Mohammadi; Fattahi, Ehsan
2010-03-01
A numerical investigation of the two-dimensional laminar flow around side-by-side rotating circular cylinders using Lattice Boltzmann method is conducted. The effects of variation of rotational speed ratio β and different gap spacings g* at Reynolds number of 100 are studied. A various range of rotational speed ratio 0 ≤ β ≤ 2 for four different gap spacings of 3, 1.5, 0.7 and 0.2 are investigated. Flow conditions and its characteristics, such as lift and drag coefficients and Strouhal number, is studied. The results indicated that as β increases, the flow changes its condition from periodic to steady after a critical rotational speed. Results also indicated that variation of the gap spacing and rotational speed has significant effect on wake pattern. Wake pattern in turn has significant effect on the Strouhal number. Finally, the result is compared with experimental and other numerical data.
Directory of Open Access Journals (Sweden)
NHM. A. Azim
2013-01-01
Full Text Available The present work is devoted to the numerical study of laminar magnetohydrodynamic (MHD conjugate natural convection flow from a horizontal circular cylinder taking into account Joule heating and internal heat generation. The governing equations and the associated boundary conditions for this analysis are made nondimensional forms using a set of dimensionless variables. Thus, the nondimensional governing equations are solved numerically using finite difference method with Keller box scheme. Numerical outcomes are found for different values of the magnetic parameter, conjugate conduction parameter, Prandtl number, Joule heating parameter, and heat generation parameter for the velocity and the temperature within the boundary layer as well as the skin friction coefficients and the rate of heat transfer along the surface. It is found that the skin friction increases, and heat transfer rate decreases for escalating value of Joule heating parameter and heat generation parameter. Results are presented graphically with detailed discussion.
Zhang, Wei
2016-03-31
We perform two-dimensional unsteady Navier-Stokes simulation and global linear stability analysis of flow past a heated circular cylinder to investigate the effect of aided buoyancy on the stabilization of the flow. The Reynolds number of the incoming flow is fixed at 100, and the Richardson number characterizing the buoyancy is varied from 0.00 (buoyancy-free case) to 0.10 at which the flow is still unsteady. We investigate the effect of aided buoyancy in stabilizing the wake flow, identify the temporal and spatial characteristics of the growth of the perturbation, and quantify the contributions from various terms comprising the perturbed kinetic energy budget. Numerical results reveal that the increasing Ri decreases the fluctuation magnitude of the characteristic quantities monotonically, and the momentum deficit in the wake flow decays rapidly so that the flow velocity recovers to that of the free-stream; the strain on the wake flow is reduced in the region where the perturbation is the most greatly amplified. Global stability analysis shows that the temporal growth rate of the perturbation decreases monotonically with Ri, reflecting the stabilization of the flow due to aided buoyancy. The perturbation grows most significantly in the free shear layer separated from the cylinder. As Ri increases, the location of maximum perturbation growth moves closer to the cylinder and the perturbation decays more rapidly in the far wake. The introduction of the aided buoyancy alters the base flow, and destabilizes the near wake shear layer mainly through the strain-induced transfer term and the pressure term of the perturbed kinetic energy, whereas the flow is stabilized in the far wake as the strain is alleviated. © 2016 Elsevier Ltd. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Paula, A.V. de, E-mail: vagtinski@mecanica.ufrgs.br [PROMEC – Programa de Pós Graduação em Engenharia Mecânica, UFRGS – Universidade Federal do Rio Grande do Sul, Porto Alegre, RS (Brazil); Möller, S.V., E-mail: svmoller@ufrgs.br [PROMEC – Programa de Pós Graduação em Engenharia Mecânica, UFRGS – Universidade Federal do Rio Grande do Sul, Porto Alegre, RS (Brazil)
2013-11-15
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.
Vortex Structures and Behavior of a Flow Past Two Rotating Circular Cylinders Arranged Side-by-Side
Institute of Scientific and Technical Information of China (English)
GUO Xiao-Hui; LIN Jian-Zhong; NIE De-Ming
2009-01-01
We present a study on the vortex structures and behavior of a Sow past two rotating circular cylinders arranged side-by-side at a range of absolute rotational speeds (|a| ≤ 2) for two different gap spacings g* = 1.5 and 0.7 at Reynolds numbers Re = 160 and 200. The results show that the flow becomes stabilized and finally steady beyond the critical rotational speed as|a| increases, regardless of the variation in Re and g". The value of critical rotational speed increases with increasing Re. The wake patterns change in the unsteady regimes for g* = 1.5 and 0.7. With increasing|a|, the time-averaged drag coefficient Cd decreases and the lift coefficient Cl increases, respectively. Cp at Re = 160 and g* = 0.7 decreases rapidly, resulting in the smallest value at the same |a| for 1 ≤ |a|≤ 2. Cd augments with increasing g* at the same|a|. For g* = 1.5, Cd has a little disparity between the cases of Re = 160 and 200. For the How past two still cyhnders, (C)L is inversely proportional to g* of two cylinders for a fixed |a|, and is not dependent on Re.
The drag-adjoint field of a circular cylinder wake at Reynolds numbers 20, 100 and 500
Wang, Qiqi
2012-01-01
This paper analyzes the adjoint solution of the Navier-Stokes equation. We focus on flow across a circular cylinder at three Reynolds numbers, ReD = 20, 100 and 500. The objective function in the adjoint formulation is the drag on the cylinder. We use classical fluid mechanics approaches to analyze the adjoint solution, which is a vector field similar to a flow field. Production and dissipation of kinetic energy of the adjoint field is discussed. We also derive the evolution of circulation of the adjoint field along a closed material contour. These analytical results are used to explain three numerical solutions of the adjoint equations presented in this paper: The adjoint solution at ReD = 20, a viscous steady state flow, exhibits a downstream suction and an upstream jet, opposite of expected behavior of a flow field. The adjoint solution at ReD = 100, a periodic 2D unsteady flow, exhibits periodic, bean shaped circulation the near wake region. The adjoint solution at ReD = 500, a turbulent 3D unsteady flow,...
Energy Technology Data Exchange (ETDEWEB)
Haneda, Y.; Kurasawa, H. (Nagano National College of Technology, Nagano (Japan)); Tsuchiya, Y. (Shinshu Univ., Nagano (Japan). Faculty of Engineering); Suzuki, K. (Kyoto Univ., Kyoto (Japan). Faculty of Engineering)
1994-04-25
The flow field and heat transfer around a circular cylinder is investigated experimentally when two dimensional jet is impinged on a circular cylinder mounted near two flat plates which are set at a fixed inclination against the axis of jet. Flow field varies markedly depending on whether the minimum channel width is the minimum space B between the flat plates or the space C between the cylinder and the plates. The local Nusselt number of the cylinder strongly depends on the value of space C between the cylinder and the plates. The minimum and maximum locations correspond to the locations of separation and reattachment, respectively, of the flow around the cylinder. When the ratio between the nozzle-to-cylinder distance L and the short side h of the nozzle is 3 (L/h=3), the mean Nusselt number around the cylinder becomes the maximum when C/D is 0.1 where D is the diameter of the cylinder, and increases by about 9 to 12% as compared with the case where no plate is provided. For L/h=7 and L/h=10, the mean Nusselt number does not increase distinctly as compared with the case where no flat plate is provided. 16 refs., 15 figs.
Institute of Scientific and Technical Information of China (English)
Siavash TABATABAEIAN; Masoud MIRZAEI; Asghar SADIGHZADEH; Vahid DAMIDEH; Abdollah SHADARAM
2012-01-01
In this paper,the effects of the existence of plasma actuator electrodes and also various configurations of the actuator for controlling the flow field around a circular cylinder are experimentally investigated.The cylinder is made of PVC (Polyvinyl Chloride) and considered as a dielectric barrier.Two electrodes are flush-mounted on the surface of the cylinder and are connected to a DC high voltage power supply for generation of electrical discharge.Pressure distribution results show that the existence of the electrodes and also the plasma are able to change the pressure distribution around the cylinder and consequently the lift and drag coefficients.It is found that the effect of the existence of the electrodes is comparable with the effect of plasma actuator in controlling the flow field around the cylinder and this effect is not reported by other researchers.Eventually it is concluded that the existence of the electrodes or any extra objects on the cylinder and also the existence of the plasma are capable of changing the flow field structure around the cylinder so that the behavior of the lift and drag coefficients of the cylinder will be changed significantly.
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.
A finite element-boundary integral method for cavities in a circular cylinder
Kempel, Leo C.; Volakis, John L.
1992-01-01
Conformal antenna arrays offer many cost and weight advantages over conventional antenna systems. However, due to a lack of rigorous mathematical models for conformal antenna arrays, antenna designers resort to measurement and planar antenna concepts for designing non-planar conformal antennas. Recently, we have found the finite element-boundary integral method to be very successful in modeling large planar arrays of arbitrary composition in a metallic plane. We extend this formulation to conformal arrays on large metallic cylinders. In this report, we develop the mathematical formulation. In particular, we discuss the shape functions, the resulting finite elements and the boundary integral equations, and the solution of the conformal finite element-boundary integral system. Some validation results are presented and we further show how this formulation can be applied with minimal computational and memory resources.
Radiation and scattering by cavity-backed antennas on a circular cylinder
Kempel, Leo C.; Volakis, John L.
1993-01-01
Conformal arrays are popular antennas for aircraft and missile platforms due to their inherent low weight and drag properties. However, to date there has been a dearth of rigorous analytical or numerical solutions to aid the designer. In fact, it has been common practice to use limited measurements and planar approximations in designing such non-planar antennas. The finite element-boundary integral method is extended to scattering and radiation by cavity-backed structures in an infinite, metallic cylinder. In particular, the formulation specifics such as weight functions, dyadic Green's function, implementation details, and particular difficulties inherent to cylindrical structures are discussed. Special care is taken to ensure that the resulting computer program has low memory demand and minimal computational requirements. Both scattering and radiation parameters are computed and validated as much as possible.
A finite element-boundary integral method for conformal antenna arrays on a circular cylinder
Kempel, Leo C.; Volakis, John L.
1992-01-01
Conformal antenna arrays offer many cost and weight advantages over conventional antenna systems. In the past, antenna designers have had to resort to expensive measurements in order to develop a conformal array design. This was due to the lack of rigorous mathematical models for conformal antenna arrays. As a result, the design of conformal arrays was primarily based on planar antenna design concepts. Recently, we have found the finite element-boundary integral method to be very successful in modeling large planar arrays of arbitrary composition in a metallic plane. We are extending this formulation to conformal arrays on large metallic cylinders. In doing so, we will develop a mathematical formulation. In particular, we discuss the finite element equations, the shape elements, and the boundary integral evaluation. It is shown how this formulation can be applied with minimal computation and memory requirements.
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)
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.
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.
DEFF Research Database (Denmark)
Arslanagic, Samel; Breinbjerg, Olav
2006-01-01
the properties of the near field, inside as well as outside the cylinder, and the far-field. Third, the variations of these fields are examined, as well as the radiation resistance and radiation pattern, as functions of the geometrical and electromagnetic parameters of the configuration. It is demonstrated......This work investigates the properties of an antenna-like configuration with an electric line source radiating in the presence of a double-negative circular cylinder. First, the analytical eigenfunction-series solution is derived. Second, this solution is employed in numerical calculations to study...
Influence of the Geometry of Beveled Edges on the Stress-Strain State of Hydraulic Cylinders
Buyalich, G. B.; Anuchin, A. V.; Serikov, K. P.
2016-04-01
The studies were carried out to determine the influence of forms obtained when preparing edges for welding a cylinder for hydraulic legs; the maximum stresses were defined at the location of weld roots, depending on variable parameters. The stress-strain states were calculated using finite element method.
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
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...... (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......-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....
Munhoz, D. S.; Bityurin, V. A.; Klimov, A. I.; Moralev, I. A.
2016-11-01
An experimental study of the flow around a circular cylinder model with magnetohydrodynamic (MHD) actuator was carried out in subsonic wind tunnels (M electrical discharge was used in this MHD actuator. This intense pulsed-periodic discharge had the following characteristics: voltage amplitude up to 15 kV, current amplitude up to 16 A and frequency up to 1 kHz. Permanent magnets with an induction of B = 0.1 T on the model surface were placed inside the cylindrical model. Annular electrodes were situated on the surface of the cylindrical model. The Lorentz force causes the rotation of the electric arc on the model surface. In turn, the movement of the arc discharge induces the rotation of the gas near the surface of the model. In this experiment were carried out the measurement of the flow velocity profile near the surface of the model on the following operational modes: with plasma and without plasma. A parametric study of the aerodynamic performance of the model was fulfilled with respect to the discharge parameters and the flow velocity. To measure the velocity profile was used particle image velocimetry method.
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.
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.
Salcedo, Erick; Cajas, Juan C.; Treviño, César; Martínez-Suástegui, Lorenzo
2016-11-01
This paper presents a two-dimensional numerical study for mixed convection in a laminar cross-flow with a pair of stationary equal-sized isothermal cylinders in tandem arrangement confined in a channel. The governing equations are solved using the control volume method on a nonuniform orthogonal Cartesian grid, and the immersed boundary method is employed to identify the cylinders placed in the flow field. The numerical scheme is first validated against standard cases of symmetrically confined isothermal circular cylinders in plane channels, and grid convergence tests were also examined. The objective of the present study was to investigate the influence of buoyancy and the blockage ratio constraint on the flow and heat transfer characteristics of the immersed cylinder array. Using a fixed Reynolds number based on cylinder diameter of ReD = 200 , a fixed value of the Prandtl number of Pr = 7 , and a blockage ratio of D/H = 0.2 , all possible flow regimes are considered by setting the longitudinal spacing ratio (σ = L/D ) between the cylinder axes to 2, 3, and 5 for values of the buoyancy parameter (Richardson number) in the range -1≤ Ri≤ 4 . The interference effects and complex flow features are presented in the form of mean and instantaneous velocity, vorticity, and temperature distributions. The results demonstrate how the buoyancy, spacing ratio, and wall confinement affect the wake structure and vortex dynamics. In addition, local and average heat transfer characteristics of both cylinders are comprehensively presented for a wide range in the parametric space.
Salcedo, Erick; Cajas, Juan C.; Treviño, César; Martínez-Suástegui, Lorenzo
2017-04-01
This paper presents a two-dimensional numerical study for mixed convection in a laminar cross-flow with a pair of stationary equal-sized isothermal cylinders in tandem arrangement confined in a channel. The governing equations are solved using the control volume method on a nonuniform orthogonal Cartesian grid, and the immersed boundary method is employed to identify the cylinders placed in the flow field. The numerical scheme is first validated against standard cases of symmetrically confined isothermal circular cylinders in plane channels, and grid convergence tests were also examined. The objective of the present study was to investigate the influence of buoyancy and the blockage ratio constraint on the flow and heat transfer characteristics of the immersed cylinder array. Using a fixed Reynolds number based on cylinder diameter of ReD = 200, a fixed value of the Prandtl number of Pr = 7, and a blockage ratio of D/H = 0.2, all possible flow regimes are considered by setting the longitudinal spacing ratio (σ = L/D) between the cylinder axes to 2, 3, and 5 for values of the buoyancy parameter (Richardson number) in the range -1≤ Ri≤ 4. The interference effects and complex flow features are presented in the form of mean and instantaneous velocity, vorticity, and temperature distributions. The results demonstrate how the buoyancy, spacing ratio, and wall confinement affect the wake structure and vortex dynamics. In addition, local and average heat transfer characteristics of both cylinders are comprehensively presented for a wide range in the parametric space.
Scattering of guided SH_wave by a partly debonded circular cylinder in a traction free plate
Institute of Scientific and Technical Information of China (English)
WANG; Xiaomin
2001-01-01
Techniques, 1969, MTT_17(3): 148.［14］Wang, X.M.C., Ying, F., Li, M.X., Scattering of antiplane shear wave by a circular cylinder in a traction free plate, submitted to J.Acoust.Soc.Am.［15］Auld, B.A., Acoustic Fields and Waves in Solids, Vol Ⅱ, New York: John Wiley & Sons, 1973, 73-160.［16］Bostrom, A., Elastic wave scattering from an interface crack: antiplane strain, J.Appl.Mech., 1987, 54(2): 503.
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.)
Influence of flexible fins on vortex-induced load over a circular cylinder at low Reynolds number
Jaiman, Rajeev K.; Gurugubelli, Pardha S.
2016-11-01
Rigid fins/fairings are known to reduce the vortex induced periodic forces exerting on a cylinder by extending the shear layers interaction further downstream to avoid alternate oppositely-signed shed vortices in the afterbody region. In this work, we present a numerical analysis on the effect of flexible fins with their leading edges fixed tangentially to the cylinder and the trailing edges are free to flap in the wake of two-dimensional (2D) cylinder. Two-dimensional simulations are carried out with varying non-dimensional flexural rigidity, KB ∈ [0.01, 1] at a fixed a non-dimensional mass ratio, m* = 0 . 1 and Reynolds number, Re = 100, defined based on the cylinder diameter. We investigate the role of flexibility in altering the wake flow and load generation over the cylinder body. As the KB is reduced, there exists a critical KB below which the flexible fins lose their stability to perform flapping and the drag acting on combined cylinder flexible fins begins to increase. However surprisingly, we observe that due to the flexible fin flapping the periodic lift forces acting on the cylinder drops significantly. We show that we can achieve an approx. 62.5% decrease in the nett periodic lift forces when compared to the bare cylinder.
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)
Uzol, Oguz
Short cylindrical pin fins with circular cross-sections are one of the most common types of cooling devices used in turbine blades. However it is by no means clear that the circular shape is the most efficient geometry in terms of heat transfer enhancement and pressure loss minimization. Therefore, novel pin fin concepts and geometries are developed and introduced as alternatives to conventional circular pin fins. The idea of using fluidic oscillators as turbulent heat transfer enhancement devices led to the novel concept of "oscillator fin". Also the idea of using more elliptical fin shapes resulted in the development of the SEF (Standard Elliptical Fin), the N fin (Derived from NACA four-digit series of airfoils) and the Egg fin (A hybrid circular-elliptical fin). Detailed experimental and computational investigations are performed in order to determine the heat transfer and pressure loss characteristics of these new concepts and the results are compared to the characteristics of conventional circular pin fins. The experimental analysis included endwall convective heat transfer coefficient measurements, wake total pressure surveys and wake flow field measurements and visualizations using particle image velocimetry (PIV). The isolated single fin measurements revealed that the oscillator fin concept is not working as expected and does not provide any advantage over circular fins. The SEFs and the N fins were found to be the most effective cooling devices in terms of both heat transfer enhancement and pressure loss minimization. The characteristics of the SEF and N fins are also determined for a 2 row staggered array configuration. It is observed that the endwall heat transfer enhancement capability of the SEFs and the N fins is about 25% less than the circular fins. However these elliptical fins caused tremendous reduction in loss levels from 100% to 200%. The main reason of this high levels of pressure loss in circular fin arrays is determined to be the huge low
Institute of Scientific and Technical Information of China (English)
ALONZO-GARCA A; GUTIRREZ-TORRES C del C; JIMNEZ BERNAL J A; MOLLINEDO-PONCE de LEN H R; MARTINEZ-DELGADILLO S A; BARBOSA-SALDAA J G
2015-01-01
This paper presents a CFD study about the effect of the V and U grooves in the flow over four cylinders in diamond shape configuration at subcritical flow conditions(Re=41000). Thek-ε Realizable turbulence model was implemented to fully structured hexahedral grids with near-wall refinements. Results showed that the numerical model was able to reproduce the impinging flow pattern and the repulsive forces present in the lateral cylinders of the smooth cylinder array. As a consequence of the flow alignment induced by the grooves, a jet-flow is formed between the lateral cylinders, which could cause an important vortex induced vibration effect especially in the rear cylinder. The magnitudes of the shear stresses at the valleys and peaks for the V grooved cylinders were lower than those of the U grooved cylinders, but the separation points were delayed due the U grooves presence. It is discussed the presence of a blowing effect caused by counter-rotating eddies located near the grooves peaks that cause a decrease of the shear stresses in the valleys, and promote them at the peaks.
Energy Technology Data Exchange (ETDEWEB)
J. B. Briggs (INEEL POC); R. E. Rothe
1999-06-14
About three dozen previously unreported critical configurations are presented for very complex geometries filled with high concentration enriched uranyl nitrate solution. These geometries resemble a tall, thin Central Column (or trunk of a ''tree'') having long, thin arms (or ''branches'') extending up to four directions off the column. Arms are equally spaced from one another in vertical planes, and that spacing ranges from arms in contact to quite wide spacings. Both the Central Column and the many different arms are critically safe by themselves with each, alone, is filled with fissile solution; but, in combination, criticality occurs due to the interactions between arms and the column. Such neutronic interactions formed the principal focus of this study. While these results are fresh to the nuclear criticality safety industry and to those seeking novel experiments against which to validate computer codes, the experiments, themselves, are not recent. Over 100 experiments were performed at the Rocky Flats Critical Mass Laboratory between September, 1967, and February of the following year.
Critical Parameters of Complex Geometry Intersecting Cylinders Containing Uranyl Nitrate Solution
Energy Technology Data Exchange (ETDEWEB)
Rothe, Robert Emil; Briggs, Joseph Blair
1999-06-01
About three dozen previously unreported critical configurations are presented for very complex geometries filled with high concentration enriched uranyl nitrate solution. These geometries resemble a tall, thin Central Column (or trunk of a "tree") having long, thin arms (or "branches") extending up to four directions off the column. Arms are equally spaced from one another in vertical planes; and that spacing ranges from arms in contact to quite wide spacings. Both the Central Column and the many different arms are critically safe by themselves when each, alone, is filled with fissile solution; but, in combination, criticality occurs due to the interactions between arms and the column. Such neutronic interactions formed the principal focus of this study. While these results are fresh to the nuclear criticality safety industry and to those seeking novel experiments against which to validate computer codes, the experiments, themselves, are not recent. Over 100 experiments were performed at the Rocky Flats Critical Mass Laboratory between September, 1967, and February of the following year.
Ellison, Peter
2012-10-01
Component design and position are major factors in achieving adequate range of motion post hip replacement. It is therefore important to understand how implant design and positioning impact the motion available before impingement. The Yoshimine-Ginbayashi equations allow the theoretical range of motion of total hip replacements to be calculated accurately and quickly. However, a significant limitation of these equations is that they can only be applied to femoral neck geometry with a circular cross section. The objective of the present study was to reformulate the equations to allow fast and accurate calculation of the range of motion for prostheses with any femoral neck geometry. Using vector analysis, formulae were derived such that the range of motion could be calculated from the cross section of the neck at the point of impingement, cup radius at the point of impingement, cup inclination angle, cup anteversion angle, neck angle of the femoral component from the transverse plane and neck anteversion. The range of motion was calculated for circular, truncated circle and free-form femoral neck geometry under a range of component positions. These values were successfully compared with those measured from analysis of solid models in three-dimensional computer-aided design software. The method of analysis presented offers a powerful new technique enabling hip prostheses to be analysed in an accurate and efficient manner, therefore facilitating optimisation of the design geometry, assessment of existing pre-clinical designs and clinical pre- or postoperative evaluation.
A simple strategy to establish preliminary engine cylinder geometry for optimum combustion
Energy Technology Data Exchange (ETDEWEB)
Harish Kumar, R. [Sri Siddhartha Inst. of Technology, Karnataka (India); Antony, A.J. [Sahyadri Inst. of Technology, Mangalore, Karnataka (India)
2009-07-01
The design of modern spark ignition engines presents a challenge for automotive engineers in terms of striking the right combination of engine operating parameters and geometry. Most modern spark ignition engines have a compression ratio in the range 8 to 11 and the engine geometry is dictated by the choice of the bore/stroke (B/Ls) ratio in addition to various other design considerations such as the location and size of valves and location of spark plugs. Small engines generally have a B/Ls ratio ranging from 0.7 to 1.3 while large stationary engines have a ratio of less than 0.7. For a given displacement volume, a longer stroke allows for smaller bore which results in less surface area in the combustion chamber with a correspondingly smaller heat loss, which increases thermal efficiency within the combustion chamber. However the longer stroke results in higher piston speed and higher friction losses which reduces the brake power output of the engine. If the stroke is shortened, the bore must be increased which reduces the friction losses but increases the heat transfer losses. This paper presented a simple thermodynamics approach based on one dimensional thermodynamic model of the combustion chamber to establish the appropriate B/Ls ratio depending on the operating conditions of the engine such as its compression ratio, speed, and fuel equivalence ratios, in conjunction with a nearly full fledged simulation program for optimum combustion in spark ignition engines. The paper described the engine test rig as well as the experimental procedure. The development of the mathematical model was also explained. It was concluded that there is a significant relationship between the compression ratio of the engine and the B/Ls ratio. These valves must match for optimum combustion and optimum specific power output. 10 refs., 1 tab., 5 figs.
Directory of Open Access Journals (Sweden)
Ramin Kamali-Moghadam
2016-01-01
Full Text Available Three-dimensional unsteady flow field around a finite circular cylinder standing in a flat-plate boundary layer is studied. For this purpose, two different numerical turbulence approaches as wall adapted local eddyviscosity LES (LES-WALE and the zonal hybrid RANS-LES approach of Detached-Eddy Simulation (Zonal-DES are used. Analysis is carried out for a finite circular cylinder with diameter of D = 3 mm and length-to-diameter ratio of L/D=6 which leads to the Reynolds number 2×104. Numerical simulation has been performed based on the LES-WALE and Zonal-DES turbulence models using coarse and fine grids. Ability and accuracy of two models in capturing the complex physics of present phenomenon are investigated by comparing their results with each other and validated experimental results. Also, effect of several important parameters such as time-averaged pressure coefficient, velocity, vortex shedding frequency and performance of the LES-WALE and Zonal-DES turbulence models are studied.
Institute of Scientific and Technical Information of China (English)
LIN Zhenhua; ZHAO Dongliang; SONG Jinbao
2011-01-01
Different advection schemes and two-equation turbulence closure models based on eddy viscosity concept are used to compute the drag coefficient around a circular cylinder at high Reynolds number (106).The numerical results from these simulations are compared with each other and with experimental data in order to evaluate the performance of different combinations of advection scheme and two-equation turbulence model.The separate contributions from form drag and friction drag are also analyzed.The computational results show that the widely used standard k-ε turbulence closure is not suitable for such kind of study,while the other two-equation turbulence closure models produce acceptable results.The influence of the different advection schemes on the final results are small compared to that produced by the choice of turbulence closure method.The present study serves as a reference for the choice of advection schemes and turbulence closure models for more complex numerical simulation of the flow around a circular cylinder at high Reynolds number.
Institute of Scientific and Technical Information of China (English)
徐万海; 杜杰; 余建星; 李敬成
2011-01-01
A wake oscillator model is presented for the stream-wise vortex-induced vibration of a circular cylinder in the second excitation region. The near wake dynamics related to the fluctuating nature of alternate vortex shedding is modeled based on the classical van der Pol equation. An appropriate approach used in cross-Sow VIV is developed to estimate the model empirical parameters. The comparison between our calculations and experiments is carried out to validate the proposed model. It is found that the present model results agree fairly well with the experimental data.%A wake oscillator model is presented for the stream-wise vortex-induced vibration of a circular cylinder in the second excitation region.The near wake dynamics related to the fluctuating nature of alternate vortex shedding is modeled based on the classical van der Pol equation.An appropriate approach used in cross-flow VIV is developed to estimate the nodel empirical parameters.The comparison between our calculations and experiments is carried out to validate the proposed model.It is found that the present model results agree fairly well with the experimental data.
Directory of Open Access Journals (Sweden)
Hongsheng Chen
2015-12-01
Full Text Available Coupled heat transfer and chemical reaction of fluid flow in complex boundaries are explored by introducing two additional properties, i.e. particle type and energy state into the Lattice gas automata (LGA Frisch–Hasslacher–Pomeau (FHP-II model. A mix-redistribute of energy and type of particles is also applied on top of collision rules to ensure randomness while maintaining the conservation of mass, momentum and energy. Simulations of heat transfer and heterogeneous reaction of gas flow passing a circular porous cylinder in a channel are presented. The effects of porosity of cylinder, gas inlet velocity, and reaction probability on the reaction process are further analyzed with respect to the characteristics of solid morphology, product concentration, and temperature profile. Numerical results indicate that the reaction rate increases with increasing reaction probability as well as gas inlet velocity. Cylinders with a higher value of porosity and more homogeneous structure also react with gas particles faster. These results agree well with the basic theories of gas–solid reactions, indicating the present model provides a method for describing gas–solid reactions in complex boundaries at mesoscopic level.
无限圆柱体旋转运动时的热应力%Thermal Stresses in an Infinite Circular Cylinder Subjected to Rotation
Institute of Scientific and Technical Information of China (English)
A·M·阿伯德-艾拉; G·A·叶海亚; 黄雅意
2012-01-01
The present investigation was concerned with a study effect of rotation on an infinite circular cylinder subjected to certain boundary conditions. An analytical procedure for evaluation of thermal stresses, displacements and temperature in rotating cylinder subjected to thermal load along the radius was presented. The dynamic thermal stresses in an infinite elastic cylinder of radius a due to a constant temperature applied to a variable portion of the curved surface while the rest of surface was maintained at zero temperature was discussed. Such situation could arise due to melting of insulating material deposited on the surface cylinder. A solution and numerical results were obtained for the stress components, displacement components, and temperature. It was shown that the results obtained from the present semi-analytical method were in a good agreement with those obtained using the previously developed methods.%研究旋转对确定边界条件下无限圆柱体的影响.当热荷载沿径向作用时,给出了旋转圆柱体中热应力、位移和温度的分析过程.当无限弹性圆柱体部分弯曲界面有常温作用,而其余界面维持零温度时,讨论其热动应力的分布.圆柱体表面绝缘材料熔化时出现这种情况.得到了应力分量、位移分量和温度的解和数值结果.提出的半解析法所得到的结果,与早期采用方法所得到的结果比较,发现两者显示出很好的一致性.
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
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.
Institute of Scientific and Technical Information of China (English)
HUANG Yuan-dong; ZHANG Hong-wu; WU Wen-quan
2005-01-01
Particle-laden gas flows past a circular cylinder at the Reynolds number of 2×105 were numerically investigated. The Discrete Vortex Method (DVM) was employed to evaluate the unsteady gas flow fields and a Lagrangian approach was applied for tracking individual solid particles. The vortex patterns and the distributions of particles with different Stokes numbers were obtained. Numerical results show that: (1) at small Stokes number (St=0.01) the particles move with the fluid and could be found evenly throughout the flow, (2) the regions around the vortex cores, where few particles exist, become wider as the stokes number of particles increases from 0.01 to 1.0, (3) at middle Stokes number (St=1.0, 10) centrifugal forces throw the particles out of the wake vortices, (4) at high Stokes number (St=100, 1000) the particles are not affected by the vortices,and their motion is determined by their inertia effects.
Tham, Leony; Nazar, Roslinda; Pop, Ioan
2016-09-01
The steady laminar mixed convection boundary layer flow from a horizontal circular cylinder in a nanofluid embedded in a porous medium, which is maintained at a constant surface heat flux, has been studied by using the Buongiorno-Darcy nanofluid model for both cases of a heated and cooled cylinder. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller box method. The solutions for the flow and heat transfer characteristics are evaluated numerically and studied for various values of the governing parameters, namely the Lewis number, Brownian number, mixed convection parameter, buoyancy ratio parameter and thermophoresis parameter. It is also found that the boundary layer separation occurs at the opposing fluid flow, that is when the mixed convection parameter is negative. It is also observed that increasing the mixed convection parameter delays the boundary layer separation and the separation can be completely suppressed for sufficiently large values of the mixed convection parameter. The Brownian and buoyancy ratio parameters appear to affect the fluid flow and heat transfer profiles.
Response of a circular steel plate with different weld geometries subject to impact loading
Directory of Open Access Journals (Sweden)
Meyer L.W.
2012-08-01
Full Text Available The dynamic response of clamped circular steel plates was experimentally investigated under impact loading. The experiments were performed using a high energy drop weight machine with a 5 ton drop weight, which falls from a height of 0.8 m and results in a total impact energy of 40 kJ. Target plates of 10 mm thickness and 580 mm diameter were welded in three different geometrical configurations of weld elements on the lower side. The impact process was carried out using a hemispherical punch. The force was registered by strain gages on the punch. A full dynamic strain field measurement was applied on the tension side using two high speed cameras. The evaluation of the strain field was carried out with the speckle photography technique. The effect of cracks and welding on the deformation and failure behavior was studied using pre-cracked disks and plates with welded webs, welded circular discs and also with a weld seam only. The failure of the plates was registered using the high speed cameras and from the force signal. The results are analyzed and discussed regarding the behavior of the material and component under high rate loading.
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.
Acoustic resonances in cylinder bundles oscillating in a compressibile fluid
Energy Technology Data Exchange (ETDEWEB)
Lin, W.H.; Raptis, A.C.
1984-12-01
This paper deals with an analytical study on acoustic resonances of elastic oscillations of a group of parallel, circular, thin cylinders in an unbounded volume of barotropic, compressible, inviscid fluid. The perturbed motion of the fluid is assumed due entirely to the flexural oscillations of the cylinders. The motion of the fluid disturbances is first formulated in a three-dimensional wave form and then casted into a two-dimensional Helmholtz equation for the harmonic motion in time and in axial space. The acoustic motion in the fluid and the elastic motion in the cylinders are solved simultaneously. Acoustic resonances were approximately determined from the secular (eigenvalue) equation by the method of successive iteration with the use of digital computers for a given set of the fluid properties and the cylinders' geometry and properties. Effects of the flexural wavenumber and the configuration of and the spacing between the cylinders on the acoustic resonances were thoroughly investigated.
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.
Institute of Scientific and Technical Information of China (English)
陈宇翔; 郜冶; 刘乾坤
2011-01-01
In order to study the slamming problem of a horizontal circular cylinder, a numerical water tank was set up. While water was entering a neutrally buoyant circular cylinder, the volume of fluid ( VOF) method coupled with the dynamic mesh method was used to simulate the liquid-gas multiphase flow and the cylinder motion. Free surface deformation such as jet formation, movement, and the air cushion effect was captured; vertical motion of the cylinder was predicted and the turbulent effect of the water-entry into the cylinder was discussed. Favorable agreement was obtained between computational results and the datas of the experiments. The cylinder motion was also predicted accurately by the computation and the turbulent effect was not significant during the water-entry into the cylinder.%为了研究水平圆柱砰击入水问题,建立了数值水池,应用VOF结合动网格技术的方法对零浮力水平圆柱入水过程的气液两相流动和刚体运动耦合的问题进行了数值模拟.捕捉了圆柱入水过程中射流的形成、运动和空气垫效应等自由表面的变化现象,模拟了圆柱竖直运动过程；讨论了湍流粘性对圆柱入水的影响.结果表明:圆柱入水的数值模拟结果和实验数据符合很好；圆柱运动轨迹同样和实验吻合；湍流粘性对圆柱入水过程影响很小.
Nagamatsu, H. T.; Duffy, R. E.
1984-01-01
Low and high pressure shock tubes were designed and constructed for the purpose of obtaining heat transfer data over a temperature range of 390 to 2500 K, pressures of 0.3 to 42 atm, and Mach numbers of 0.15 to 1.5 with and without pressure gradient. A square test section with adjustable top and bottom walls was constructed to produce the favorable and adverse pressure gradient over the flat plate with heat gages. A water cooled gas turbine nozzle cascade which is attached to the high pressure shock tube was obtained to measuse the heat flux over pressure and suction surfaces. Thin-film platinum heat gages with a response time of a few microseconds were developed and used to measure the heat flux for laminar, transition, and turbulent boundary layers. The laminar boundary heat flux on the shock tube wall agreed with Mirel's flat plate theory. Stagnation point heat transfer for circular cylinders at low temperature compared with the theoretical prediction, but for a gas temperature of 922 K the heat fluxes were higher than the predicted values. Preliminary flat plate heat transfer data were measured for laminar, transition, and turbulent boundary layers with and without pressure gradients for free-stream temperatures of 350 to 2575 K and flow Mach numbers of 0.11 to 1.9. The experimental heat flux data were correlated with the laminar and turbulent theories and the agreement was good at low temperatures which was not the case for higher temperatures.
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.
Institute of Scientific and Technical Information of China (English)
QI E-rong; LI Guo-ya; LI Wei; WU Jian; ZHANG Xin
2006-01-01
In the gap-ratio range of 0.0≤G≤7.0, a particle image velocimetry PIV is applied to conduct a systematic experimental research of the flow around a horizontal circular cylinder in the cross-flow of shallow water. The velocity distribution of transient flow field at various gap-ratios is obtained. Based on these data, the phenomena and rules of the vortex and its course of generation, development and evolvement at various gap-ratios are analyzed, and it is found that there are similar unshedding vortex structures at G = 0.0 and G = 7.0, and others are structures of shedding vortex. The figures of typical vortex movements are given. Based on this, the differences between the transient flow field and the time-averaged flow field and the characteristics of the vortex structures are analyzed. In addition when the Strouhal number keeps constant (about 0.2) concerning vortex shedding have been discussed. The findings of this paper are of guiding significance for engineering issues with similar flowing features.
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 $S$.
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
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.
The boundary element method applied to viscous and vortex shedding flows around cylinders
Farrant, Tim
Studies are presented to further extend the use of the boundary element method (BEM) for the solution of viscous flows around bluff bodies, governed by the incompressible Navier-Stokes equations. Two distinct formulations are applied to various flows around cylindrical geometries for Reynolds numbers Tan (1994) and known herein as the global BEM, was coded to execute in parallel on multi-processor computers. Reductions in execution time were achieved and the method was employed to solve an oscillating cylinder problem. In this study, the displacement undergone by the body was very large but the Reynolds number was always Tan et al (1998). A validation for isolated and double circular cylinders in a uniform stream was performed against experimental evidence to demonstrate the method's stability and accuracy for laminar vortex shedding with geometries involving multiply connected domains. Finally, computational results for flows around four equispaced circular cylinders of equal diameter and two cylinders, one circular the other elliptical, are reported. Many of the concepts established for the flow around two cylinders of equal diameter were found to be useful in interpretation of these more complicated arrangements.
Institute of Scientific and Technical Information of China (English)
ZHANG Yu; YAN Hong-zhi; ZENG Tao; ZENG Yi-yu
2016-01-01
In order to effectively improve meshing performance of spiral bevel and hypoid gears generated by the duplex helical method, the effects of straight lined and circular cutting edges profile on meshing and contact of spiral bevel and hypoid gears were investigated analytically. Firstly, a mathematical model of spiral bevel and hypoid gears with circular blade profile was established according to the cutting characteristics of the duplex helical method. Based on a hypoid gear drive, the tooth bearings and the functions of transmission errors of four design cases were analyzed respectively by the use of the tooth contact analysis (TCA), and the contact stresses of the four design cases were analyzed and compared using simulation software. Finally, the curvature radius of the circular profile blade was optimized. The results show that the contact stresses are availably reduced, and the areas of edge contact and severe contact stresses can be avoided by selecting appropriate circular blade profile. In addition, the convex and concave sides are separately modified by the use of different curvature radii of inside and outside blades, which can increase the flexibility of the duplex helical method.
Institute of Scientific and Technical Information of China (English)
周云龙; 刁成东; 曹茹
2009-01-01
When a gas-liquid two-phase fluid in a vertically ascending tube with a rectangular section transversely scours a horizontally arranged cylinder,under certain conditions,an alternating vortex shedding phenomenon will occur at the back of the cylinder.By adopting a tube-wall pressure-difference method to study the vortex shedding characteristics of the above flow transversely sweeping across a circular cylinder and a square one,the authors have identified the vortex street shedding frequency and the variation of Strouhal number.During the test,the Reynolds number ranges from 0.9×10~4 to 2.3×10~4 and the sectional gas content has a variation range of 0 to 0.2.The test results indicate that in a certain range of gas content,the vortex-street shedding frequency and Strouhal numbers of the two types of cylinders will increase with an increase of the sectional gas content.The increment gradient of the square cylinder Strouhal number is independent of the Reynolds number while that of the circular one is susceptible to the influence of the Reynolds number.%气液两相流体在垂直上升矩形截面管道内横向冲刷水平布置的柱体时,一定条件下会在柱体后面产生旋涡交替脱落现象.利用管壁压差法来研究气液两相流横掠圆柱体和方柱体时的旋涡脱落特性,得到了涡街的脱落频率和斯特罗哈数的变化情况.实验中雷诺数的范围为0.9×10~4～2.3×10~4,截面含气率的范围为0～0.2.实验结果表明:在一定的含气率范围内,两种柱体涡街的脱落频率与斯特罗哈数都随着截面含气率的增大而增大;方柱体斯特罗哈数增大的梯度与雷诺数无关,圆柱体斯特罗哈数增大的梯度受雷诺数的影响.
Park, Yun Soo; Lee, Hwan Gi; Yang, Chung-Mo; Kim, Dong-Seok; Bae, Jin-Hyuk; Cho, Seongjae; Lee, Jung-Hee; Kang, In Man
2013-01-01
GaN light-emitting diodes (LEDs) based on circular mesa structure are fabricated and their electrical and optical characterizations are performed. The uniform current flow in the circular LED (C-LED) was conducted in the radial direction, from the n-type GaN island electrode at the center to the p-type GaN ring electrode around the perimeter. The symmetric electrode structuring substantially improved the electrical and optical performances. The operating voltage for C-LED at a reference current (100 mA) was 20.9% lower than that of a conventionally structured LED (CV-LED). Also, C-LED showed 19.4% higher optical output power than CV-LED.
Institute of Scientific and Technical Information of China (English)
周强; 曹曙阳; 王通; 周志勇
2012-01-01
Three-dimensional direct numerical simulation (DNS) and large eddy simulation (LES) were performed to investigate aerodynamic forces on a circular cylinder in linear shear flow at Reynolds number of Re =60 ~1 000. The shear parameter β, which is based on the velocity gradient, cylinder diameter and upstream mean velocity at the center plane of the cylinder, varies from 0 to 0. 30. The changes of the stagnation point, separation points, and lift coefficients with the variation of shear parameter were studied. The results show that the stagnation point moves to the high-velocity side almost linearly with shear parameter, which mainly influences the aerodynamic forces acting on a circular cylinder in shear flow. Both the Reynolds number and shear parameter influence the movement of the stagnation point and separation point. The lift force increases with the increase of shear parameter and at the same time from the high-velocity side to the low-velocity side.%采用由速度梯度、圆柱半径以及圆柱中心平面上的来流平均速度定义的无量纲剪切参数β来描述速度剪切的强度.在雷诺数Re =60～1000范围内,运用三维直接数值模拟(DNS)和大涡模拟(LES)两种方法对速度剪切流中的圆柱体的绕流特性进行了数值模拟.研究了驻点、高速和低速两侧分离点、圆柱表面压力分布以及不稳定尾流结构随剪切参数的变化及其对雷诺数的依赖性,从而得到了剪切流中圆柱体的气动力以及脱落特性,并对其机理进行了详细探讨.
Institute of Scientific and Technical Information of China (English)
庞建华; 宗智; 周力; 邹丽
2016-01-01
采用基于边界瞬时涡量守恒（IVCBC）的纯拉格朗日涡方法，结合并列双圆柱的结构特点，建立双圆柱绕流数值计算模型。在间隙率T/D=1.1~2.6时，并列双圆柱绕流会出现宽尾流（WW）和窄尾流（NW）现象。利用两圆柱间隙中心点的诱导速度方向与间隙流的偏转方向同步的特性，提出一种区别宽、窄尾流的数值计算方法；比较间隙流的偏转方向与该间隙中点的速度偏转方向，并进行典型的算例分析。结果表明：该方法能准确区别宽尾流和窄尾流，可为数值研究这一特殊区域的流体特征提供重要的数值计算方法。%A pure-Lagrangian vortex method, based on Instantaneous Vorticity Conserved Boundary Condi⁃tions (IVCBC), is adopted to build the numerical calculation model of flow around double circular cylinders that have the same structure characteristics of two side by side circular cylinders. The Wide Wake(WW) and Narrow Wake(NW)appear in the range of pitch ratio T/D=1.1~2.6. A scheme is proposed to distin⁃guish the NW and WW through the direction synchronism between induced velocity at the middle of double circular cylinders and deflection of gap flow. By comparing the directions of the above two flowing condi⁃tions and analyzing the classic case, it is concluded that the proposed method could distinguish WW and NW accurately, which offers an important numerical calculation method for investigating the flow character⁃istics in this range.
Flow-induced vibrations of four square-arranged circular cylinders%正方形顺排排列四圆柱流致振动响应研究
Institute of Scientific and Technical Information of China (English)
及春宁; 陈威霖; 徐万海
2016-01-01
Flow-induced vibrations of four square-arranged circular cylinders with a center-to-center spacing ratio of s /D =5.0 and zero attack angle were numerically investigated.The vibrations were constrained in cross-flow direction,the reduced flow-velocity was in the range of Ur =2.0 ~50.0 and Reynolds number was Re =100.Results showed that the responses of two upstream cylinders are similar to those of VIV of an isolated cylinder,the initial and lower branches are clearly observed;the upstream two cylinders reach their maximum vibration amplitude of Ymax /D =0.56 at the reduced flow-velocity Ur =4.4,it is close to that of an isolated cylinder Ymax /D =0.57;the two downstream cylinders reach their maximum amplitude Ymax /D =0.997 at the reduced flow-velocity Ur =7.9,it is 74.8% larger than that of an isolated cylinder;three asymmetric vibration regions are observed,i.e.,the first asymmetric vibration region is 4.5 10.5;the asymmetric vibration features of the cylinders are closely related to asymmetric wake patterns and stably biased gap flows.%对间距比 s／D ＝5．0正方形顺排排列四圆柱流致振动进行了数值模拟研究，圆柱仅横流向振动，雷诺数为Re ＝100，折合流速为 Ur ＝2．0～50．0。研究发现，上游两圆柱的响应与单圆柱涡激振动相似，呈现出明显的初始分支和下端分支。上游两圆柱的振幅均在折合流速 Ur ＝4．4时达到最大值 Ymax ／D ＝0．56，与单圆柱涡激振动最大振幅 Ymax ／D ＝0．57相近。下游两圆柱的振幅在折合流速 Ur ＝7．9时达到最大值 Ymax ／D ＝0．997，比单圆柱涡激振动最大振幅增大了74．8％。正方形顺排排列四圆柱流致振动响应中出现了三个不对称区间，分别为第一不对称区间4．5＜Ur ＜5．9、第二不对称区间6．9＜Ur ＜7．2和第三不对称区间 Ur ＞10．5。圆柱不对称的振动响应特性和圆柱间隙流稳定偏斜有关。
Institute of Scientific and Technical Information of China (English)
王莉萍
2001-01-01
In this paper,we discuss the general case of the Riemann- Hilbertboundary value problem for analytic functions of several complex variabl es in several circular ring cylinder domain.Through the transformation of analyt ic functions, we have derived the solvability for the ordinary Riemann-Hilbert boundary value problems for an analytic function of several complex variables. A nd we present the integral expressions of the solution.%讨论多圆环柱域上多个复变量的解析函数的一般形式的Riemann-Hilbert边值问题。通过函数的解析变换，导出了解析函数一般形式的Riemann-Hilbert边值问题的可解性，并给出了解的积分表达式。
Nabanja, Sheila P.; Kolodziejski, Leslie A.; Petrich, Gale S.; Sander, Michelle Y.; Morse, Jonathan L.; Shtyrkova, Katia; Ippen, Erich P.; Kärtner, Franz X.
2013-04-01
A semiconductor Saturable Bragg Reflector (SBR) is a mirror structure comprising alternating layers of high and low refractive index materials with an incorporated saturable absorber. SBRs can be used to initiate and sustain ultra-short pulses in various laser systems. In order to form ultra-short pulses, SBRs with high reflectivity over a broad wavelength range are required. Furthermore, large-area SBRs facilitate easy integration in a laser cavity. One of the key elements for the realization of broad band SBRs is the development of the thermal oxidation process that creates buried low-index AlxOy layers over large areas. The design, fabrication, characterization, and implementation of broad band, high index contrast III-V/AlxOy SBRs in the form of circular mesas, as well as inverted mesa structures, is presented.
DEFF Research Database (Denmark)
Johansson, Jens; Christensen, Silas Sverre
2017-01-01
Helical strakes are known to reduce or suppress vortex-induced vibrations, VIV, of circular structures. The design of the strakes is generally recommended to be a triple-start helical strake system, with a strake height corresponding to approximately 10% of the diameter of the structure and 15% f...
Measurement of convective heat transfer to solid cylinders inside ventilated shrouds
Daryabeigi, K.; Germain, E. F.; Ash, R. L.
1984-01-01
The influence of ventilated cylindrical shrouds on the convective heat transfer to circular cylinders has been studied experimentally. Geometries studied were similar to those used in commercially available platinum resistance thermometers. Experiments showed that thermal response (convection) was enhanced when the shroud ventilation factor was approximately 20 percent (80 percent solid), and that maximum enhancement occurred when the ventilation holes were located symmetrically on either side of the stagnation lines.
Institute of Scientific and Technical Information of China (English)
姜旭; 张量
2016-01-01
本文用微分几何的方法求解出椭球面上圆截线所在平面的一般方程。%This paper uses differential geometry method to obtain the general equations of the planes which contain the circular cross sections on an ellipsoid.
2015-09-01
flared base is expected to provide a closer emulation of trunk geometries encountered in nature. Only the 3-dB error lines for the analytical solution...On the Validity of an Analytical Solution for Characterizing Backscattering from Tree Trunks at P-Band by DaHan Liao...Validity of an Analytical Solution for Characterizing Backscattering from Tree Trunks at P-Band by DaHan Liao Sensors and Electron Devices
Institute of Scientific and Technical Information of China (English)
陈启刚; 齐梅兰; 李金钊
2016-01-01
To investigate the kinematic characteristics of horseshoe vortex upstream of cylinders, the swirl⁃ing strength method is introduced to identify horseshoe vortices, and a method of fitting the local velocity field with an elliptic vortex are proposed to characterize these vortices. The elliptic vortex is constructed by overlapping the Oseen vortex with an inclined unidirectional shear flow. The proposed methods were used to investigate the time-averaged horseshoe vortex upstream of a circular cylinder in open channel flow. The time averaged horseshoe vortex is captured by averaging instantaneous velocity fields measured with PIV. The results show that, in flows with cylinder Reynolds number larger than 104, the position of horseshoe vortex is unchanged while the upstream separation point moves downstream slowly. The distances from the vortex center to the cylinder axis and the bed are 0.67D and 0.06D, respectively, with D being the cylin⁃der diameter. Comparing with those in open channel flows,the horseshoe vortex and separation point in tur⁃bulent boundary layers are further upstream. With the increasing of cylinder Reynolds number, the horse⁃shoe vortex strengthens itself but keeps the size unchanged, results in increasing shear stress on the bed. The dependence of vortex-induced shear stress with the flow strength indicates that it is physically reason⁃able to formulate equations for local scour based on the kinematic characteristics of horseshoe vortex.%马蹄涡是水下柱体结构周围床面冲刷的主要动力。为掌握马蹄涡的运动学特征，引入了基于旋转强度的马蹄涡识别方法，提出了基于椭圆涡拟合的马蹄涡特征提取方法，其中，椭圆涡由Oseen涡和倾斜单向剪切流叠加而成。基于上述方法，通过开展明渠圆柱绕流PIV实验，对柱体上游对称面时均流场中马蹄涡的运动学特征进行了研究。结果表明，在柱体雷诺数大于104的紊流柱体绕流中，
Energy Technology Data Exchange (ETDEWEB)
Iida, A.; Kato, C.; Otaguro, T. [Hitachi, Ltd., Tokyo (Japan); Fujita, H. [Nihon University, Tokyo (Japan). College of Science and Technology
1996-12-25
The mechanism of aerodynamic sound generation from a circular cylinder is investigated experimentally using coherence functions between surface pressure fluctuation and radiated sound at Reynolds numbers from 10{sup 4} to 1.4 {times} 10{sup 5}. The correlation between the surface pressure fluctuation and the radiated sound at the fundamental frequency is good, indicating the strong contribution of ordered structures to aerodynamic sound generation. The characteristic length of ordered structure Lc is estimated using the integral scale of the spanwise coherence function of surface pressure fluctuations. The sound pressure is calculated using a modified Curle`s equation, with the characteristic length and measured surface pressure fluctuations. The predicted spectra of radiated sound are in good agreement with those actually measured up to five times the fundamental frequency. This result shows that Lc, is useful for estimating the character of radiated sound from a circular cylinder. 16 refs., 13 figs., 2 tabs.
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.
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...
Energy Technology Data Exchange (ETDEWEB)
Iida, A.; Kato, C.; Takano, Y. [Hitachi, Ltd., Tokyo (Japan); Fujita, H. [Tokyo Institute of Technology, Tokyo (Japan)
1995-12-25
Spanwise coherent structure of surface pressure fluctuation on a circular cylinder is studied experimentally in order to obtain quantitative information for understanding the generation mechanism of aerodynamic sound from the cylinder at Reynolds numbers between 5{times}10{sup 3} and 1.4{times}10{sup 5}. Span wise distribution of the coherence function between surface pressures is kept as high as up to several diameters for the frequency components of the so-called orderly structure, or the Karman vortex shedding frequency and its harmonics, while the coherence function for the turbulent frequency component decays rapidly span wise to half-diameter. Span wise coherence function of the surface pressure is calculated as an exponential function of span wise spacing and Reynolds number. The correlation length of the flow structure is found to be inversely proportional to Re{sup 1/2}. 18 refs., 13 figs., 1 tab.
Comparison of calculated and experimental results of fragmenting cylinder experiments
Energy Technology Data Exchange (ETDEWEB)
WILSON,L.T.; REEDAL,D.R.; KIPP,MARLIN E.; MARTINEZ,REINA R.; GRADY,D.E.
2000-06-02
The Grady-Kipp fragmentation model provides a physically based method for determining the fracture and breakup of materials under high loading rates. Recently, this model has been implemented into the CTH Shock Physics Code and has been used to simulate several published experiments. Materials studied in this paper are AerMet 100 steel and a 90% tungsten alloy. The experimental geometry consists of a right circular cylinder filled with an explosive main charge that is initiated at its center. The sudden expansion of the resulting detonation products causes fracture of the cylinder. Strain rates seen in the cylinder are on the order of 10{sup 4} s{sup {minus}1}. The average fragment sizes calculated with the Grady-Kipp fragmentation model successfully replicate the mean fragment size obtained from the experimental fragment distribution. When Poisson statistics are applied to the calculated local average fragment sizes, good correlation is also observed with the shape of the experimental cumulative fragment distribution. The experimental fragmentation results, CTH numerical simulations, and correlation of these numerical results with the experimental data are described.
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)
Rosu, Grigore; Goguen, Joseph; Norvig, Peter (Technical Monitor)
2001-01-01
Circular coinduction is a technique for behavioral reasoning that extends cobasis coinduction to specifications with circularities. Because behavioral satisfaction is not recursively enumerable, no algorithm can work for every behavioral statement. However. algorithms using circular coinduction can prove every practical behavioral result that we know. This paper proves the correctness of circular coinduction and some consequences.
Experimental investigation of the interaction of two cylinders in the flow pattern
Directory of Open Access Journals (Sweden)
Vitkovičová Rut
2015-01-01
Full Text Available This article discusses the behaviour and interaction of two circular cylinders in the flow pattern when one of the cylinders affects wake of the second cylinder. The wake behind the cylinder was investigated experimentally by using a time resolved PIV and CTA method. Velocity fields were obtained for several regimes of Reynolds numbers and several positions of the second cylinder. A frequency of vortex shedding was gained from the acquired images.
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
Two interacting cylinders in cross flow
Alam, Md. Mahbub; Meyer, J. P.
2011-11-01
Cylindrical structures in a group are frequently seen on land and in the ocean. Mutual flow interaction between the structures makes the wake very excited or tranquil depending on the spacing between the structures. The excited wake-enhancing forces in some cases cause a catastrophic failure of the structures. This paper presents results of an experimental investigation of Strouhal number (St), time-mean, and fluctuating forces on, and flow structures around, two identical circular cylinders at stagger angle α = 0 °-180 ° and gap-spacing ratio T/D=0.1-5, where T is the gap width between the cylinders, and D is the diameter of a cylinder. While forces were measured using a load cell, St was from spectral analysis of fluctuating pressures measured on the side surfaces of the cylinders. A flow visualization test was conducted to observe flow structures around the cylinders. Based on forces, St, and flow structures, 19 distinct flow categories in the ranges of α and T/D investigated are observed, including one quadristable flow, three kinds of tristable flows, and four kinds of bistable flows. The quadristable, tristable, and bistable flows ensue from instabilities of the gap flow, shear layers, vortices, separation bubbles, and wakes, engendering a strong jump or drop in forces and St of the cylinders. The two cylinders interact with each other in six different mechanisms, namely interaction between boundary layer and cylinder, shear layer or wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex. While the interaction between vortex and cylinder results in a very high fluctuating drag, that between vortex and shear layer results in a high fluctuating lift. On the other hand, the interaction between shear layer or wake and cylinder weakens mean and fluctuating forces and flow unsteadiness. A mutual discussion of forces, St, and flow structures is presented in this paper.
Institute of Scientific and Technical Information of China (English)
向星居; 熊红亮; 袁明磊; 于靖波; 陈柳生; 王智栋
2015-01-01
surfaces.It is durable enough to withstand the aerodynamic forces.With the development of porous PSP,there has been a need for accurate characterization of the response time of PSP.Dynamic calibration methods have been developed to meet this need.Response time of PSP was measured from a step change of pressure created by solenoid valve and pulsating jet. Two dynamic calibration devices were developed to test the response time of PSP.For unsteady calibration the paint was sprayed onto 20 mm × 20 mm aluminum plates.Photo multiplier tube (PMT)was used as the light detector,which is the most critical component in the dynamic cali-bration device.Several fast response PSP was developed and tested.The typical response time of PSP is 0.2ms.The static calibration system was used to get the relation between the pressure and luminescence intensity.PSP samples were installed in a pressure chamber in which both the pres-sure and temperature can be set.The sample was excited by UV light and its photoluminescence was detected by a CCD digital camera.The experiment was conducted at different pressures and temperatures.After data processing,the relationship between the luminescence intensity and pressure can be obtained.To demonstrate the capability of PSP for pressure measurements in hy-personic wind tunnel,a cylinder mounted on a flat plate was tested in a Mach 5 hypersonic wind tunnel.The experiment was conducted in the blow down hypersonic wind tunnel FD-03 of China Academy of Aerospace Aerodynamics (CAAA).The diameter of circular cylinder is 25mm.The pressure on the plate surface was measured by several pressure taps simultaneously.The temper-ature of the model was detected by a Pt100 temperature sensor in real time.A 200-mm-diameter observation window on the ceiling was used as the optical access.Two 450W xenon lamps with bandpass filter (365±10 nm)were used for excitation light.The emission from the PSP was de-tected by photron high-speed camera SA5 with 12-bit intensity
Institute of Scientific and Technical Information of China (English)
王通; 曹曙阳; 周强
2011-01-01
Aerodynamic lift of a circular cylinder in linear shear flows with its axis normal to the plane of the velocity shear profile is investigated at subcritical Reynolds number numerically and experimentally. The shear parameter β, which is based on the velocity gradient, cylinder diameter and upstream mean ve-locity at the center plane of the cylinder, is defined to represent intensity of shear flow. Linear shear flows are easily generated in actively controlled wind tunnels for model experiments. Large eddy simula-tion with dynamic Smagorinsky subgrid model is performed to supply physical explanations of the flow phenomenon. It is found that the stagnation point shifts to the high velocity side in linear shear flows at subcritical Reynolds number and it influences the aerodynamic force acting on a circular cylinder greatly. A mean lift occurs due to the asymmetrical distribution of pressure around the cylinder, and it acts from the high velocity side to low velocity side at subcritical Reynolds number.%通过风洞模型试验和数值模拟研究亚临界雷诺数范围内线性剪切流场中圆柱的气动升力特性.剪切流强度采用由速度梯度、圆柱半径及圆柱中心前方来流的平均速度所定义的无量纲剪切参数β来表示.在风洞模型试验中使用主动控制风洞来方便地生成线性剪切流.在数值模拟中采用基于动态Smagorinsky亚格子模型的大涡模拟方法.研究发现,在亚临界雷诺数线性剪切流中,驻点向高速侧漂移,驻点移动对圆柱气动力有明显的影响；圆柱周围的压力分布不对称,产生一个由高速侧向低速侧作用的升力.
On Uniform Motion of a Periodic System of Absolutely Rigid Stamps, in the Hollow Cylinder
Directory of Open Access Journals (Sweden)
Amirjanyan H. A.
2011-03-01
Full Text Available Axissymetric stress state of the infinite hollow cylinder when on the inner surface of the cylinder acts a periodic system of uniformly moving circular stamps and the outer surface is free of loads or rigidly clamped is considered The behavior of the contact stresses, acting under the stamp, in dependence on the physical and geometrical parameters of the cylinder is studied.
A numerical investigation of sub-wavelength resonances in polygonal metamaterial cylinders
DEFF Research Database (Denmark)
Arslanagic, Samel; Breinbjerg, Olav
2009-01-01
of polygonal cylinders excited by a nearby electric line current is analyzed numerically and it is shown, through detailed analysis of the near-field distribution and radiation resistance, that these polygonal cylinders do indeed support sub-wavelength resonances similar to those of the circular cylinders...
Energy Technology Data Exchange (ETDEWEB)
Davies, J. A.; Perry, C. H.; Harrison, R. A. [RAL Space, Rutherford Appleton Laboratory, Harwell Oxford, OX11 0QX (United Kingdom); Trines, R. M. G. M. [Central Laser Facility, Rutherford Appleton Laboratory, Harwell Oxford, OX11 0QX (United Kingdom); Lugaz, N. [Space Science Centre, University of New Hampshire, Durham, NH 03824 (United States); Möstl, C. [Space Science Laboratory, University of California, Berkeley, CA 94720 (United States); Liu, Y. D. [State Key Laboratory of Space Weather, National Space Science Centre, Chinese Academy of Sciences, Beijing 100190 (China); Steed, K., E-mail: jackie.davies@stfc.ac.uk [Centre for mathematical Plasma Astrophysics, KU Leuven, B-3001 Leuven (Belgium)
2013-11-10
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 φ, 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{sup –1}, and highly geoeffective, in stark contrast to the slow and ineffectual 2008 December CME.
Ilin, K
2010-01-01
We study the steady streaming between two infinitely long circular cylinders produced by small amplitude transverse vibrations of the inner cylinder about the axis of the outer cylinder. The Vishik-Lyusternik method is employed to construct an asymptotic expansion of the solution of the Navier-Stokes equations in the limit of high-frequency vibrations for Reynolds numbers of order of unity. The effect of the Stokes drift of fluid particles is also studied. It is shown that it is nonzero not only within the boundary layers but also in higher order terms of the expansion of the averaged outer flow.
Circular motion in NUT space-time
Jefremov, Paul
2016-01-01
We consider circular motion in the NUT (Newman-Unti-Tamburino) space-time. Among other things, we determine the location of circular time-like geodesic orbits, in particular of the innermost stable circular orbit (ISCO) and of the marginally bound circular orbit. Moreover, we discuss the von Zeipel cylinders with respect to the stationary observers and with respect to the Zero Angular Momentum Observers (ZAMOs). We also investigate the relation of von Zeipel cylinders to inertial forces, in particular in the ultra-relativistic limit. Finally, we generalise the construction of thick accretion tori ("Polish doughnuts") which are well known on the Schwarzschild or Kerr background to the case of the NUT metric. We argue that, in principle, a NUT source could be distinguished from a Schwarzschild or Kerr source by observing the features of circular matter flows in its neighbourhood.
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.
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.
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
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.
Geometry from Information Geometry
Caticha, Ariel
2015-01-01
We use the method of maximum entropy to model physical space as a curved statistical manifold. It is then natural to use information geometry to explain the geometry of space. We find that the resultant information metric does not describe the full geometry of space but only its conformal geometry -- the geometry up to local changes of scale. Remarkably, this is precisely what is needed to model "physical" space in general relativity.
Free vibrations of circular cylindrical shells
Armenàkas, Anthony E; Herrmann, George
1969-01-01
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
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.
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.
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.
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.
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...
Vortex noise from nonrotating cylinders and airfoils
Schlinker, R. H.; Amiet, R. K.; Fink, M. R.
1976-01-01
An experimental study of vortex-shedding noise was conducted in an acoustic research tunnel over a Reynolds-number range applicable to full-scale helicopter tail-rotor blades. Two-dimensional tapered-chord nonrotating models were tested to simulate the effect of spanwise frequency variation on the vortex-shedding mechanism. Both a tapered circular cylinder and tapered airfoils were investigated. The results were compared with data for constant-diameter cylinder and constant-chord airfoil models also tested during this study. Far-field noise, surface pressure fluctuations, and spanwise correlation lengths were measured for each configuration. Vortex-shedding noise for tapered cylinders and airfoils was found to contain many narrowband-random peaks which occurred within a range of frequencies corresponding to a predictable Strouhal number referenced to the maximum and minimum chord. The noise was observed to depend on surface roughness and Reynolds number.
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.
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...
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.
The Interaction Vortex Flow Around Two Bluff Cylinders
Hirao K.; Yokoi Y.
2013-01-01
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 squ...
Experimental free convection heat transfer from inclined square cylinders
Ali, Mohamed
2016-10-01
Natural convection from axisymmetric objects such as vertical or horizontal cylinders and spheres are two dimensional. However, for inclined circular or noncircular cylinders the flow and heat transfer is three dimensional and hence more complex and needs more attention. This study investigates the steady state mechanism of natural convection from inclined square cylinders in air. Five different cylinders of 1 m length, 8 × 8, 7 × 7, 6 × 6, 4 × 4 and 2.5 × 2.5 cm2 cross sections are used. The cylinders are heated using inserted heating element of 6 mm in diameter. Self-adhesive thermocouples are used at the upper, bottom and at one side of the cylinders for temperature measurement. Three inclination angles to the horizontal 30, 45 and 60o are used for each cylinder with uniform heat flux boundary conditions. For each cylinder, about ten heat fluxes are used to generate the heat transfer data. Local and average heat transfer coefficient is determined for each cylinder at each inclination angle for each uniform heat flux. Laminar and transition to turbulent regimes are obtained and characterized. Local critical axial distance where heat transfer coefficient changes the mode is obtained for each heat flux. Local and averaged Nusselt numbers are correlated with the modified Rayleigh numbers for all angles.
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.
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.
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
Beamforming with a circular array of microphones mounted on a rigid sphere (L)
DEFF Research Database (Denmark)
Tiana Roig, Elisabet; Jacobsen, Finn; Fernandez Grande, Efren
2011-01-01
Beamforming with uniform circular microphone arrays can be used for localizing sound sources over 360. Typically, the array microphones are suspended in free space or they are mounted on a solid cylinder. However, the cylinder is often considered to be infinitely long because the scattering problem...... has no exact solution for a finite cylinder. Alternatively one can use a solid sphere. This investigation compares the performance of a circular array mounded on a rigid sphere with that of such an array in free space and mounted on an infinite cylinder, using computer simulations. The examined...
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
Frequency spectra of laminated piezoelectric cylinders
Siao, J. C.-T.; Dong, S. B.; Song, J.
1994-07-01
A finite-element method is presented for determining the vibrational characteristics of a circular cylinder composed of bonded piezoelectric layers. Finite-element modeling occurs in the radial direction only using quadratic polynomials and the variationally derived partial differential equations are functions of the hoop and axial coordinates (theta, z) and time t. Using solution form Q exp (i(xi(z) + n(theta) + (omega)t)), with Q as the nodal amplitudes, leads to an algebraic eigensystem where any one of the three parameters (n, xi, omega), the circumferential or axial wave number or natural frequency, can act as the eigenvalue. Integer values always are assigned to n, leaving two possible eigenvalue problems. With omega as the eigenvalue and real values assigned to xi, the solutions represent propagating waves or harmonic standing vibrations in an infinite cylinder. When xi is the eigenvalue and real values assigned to omega, this eigensystem admits both real and complex eigendata. Real xi's represent propagating waves or harmonic standing vibrations as noted before. Complex conjugate pairs of xi 's describe end vibrations, which arise when an incident wave impinges upon a free end of a cylindrical bar. They are standing waves whose amplitudes decay sinusoidally or exponentially from the free end into the interior. Two examples are given to illustrate the method of analysis, viz., a solid piezoelectric cylinder of PZT-4 ceramic material and a two-layer cylinder of PZT-4 covering an isotropic material.
Hard sphere packings within cylinders.
Fu, Lin; Steinhardt, William; Zhao, Hao; Socolar, Joshua E S; Charbonneau, Patrick
2016-03-07
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.
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.
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.
Approximation by Cylinder Surfaces
DEFF Research Database (Denmark)
Randrup, Thomas
1997-01-01
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 projection within a tolerance given by the reference curve, and the rulings are lines perpendicular to the projection plane. Application of the method in ship design is given....
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.
Total positive curvature of circular DNA
DEFF Research Database (Denmark)
Bohr, Jakob; Olsen, Kasper Wibeck
2013-01-01
molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular...... micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature......The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain...
Heat transfer in a conical porous cylinder with partial heating
Yunus Khan, T. M.; Anjum Badruddin, Irfan; Quadir, G. A.
2016-09-01
The current work simulates the heat transfer across a porous medium fixed in an annular conical cylinder. The geometry is such that the lower part is conical annulus supporting a regular annular cylinder. The porous medium is fixed between inner and outer radius of conical annular cylinder. The inner radius until conical section is heated with constant temperature Th whereas the outer radius is cooled to isothermal temperature Tc such that Th>Tc . The heat transfer phenomenon in this case can be described by two coupled partial differential equations which are solved using finite element method by using 3-node triangular elements. The heat transfer characteristics in this case are quite different from other geometries being discussed in the literature. It is observed that the fluid flow is stronger in the conical section as compared to the cylindrical part of porous geometry. A very few isothermal lines penetrate into the cylindrical porous region as compared to that of conical section.
Thomas, R
2006-07-01
The problem of disentangling complex dynamic systems is addressed, especially with a view to identifying those variables that take part in the essential qualitative behaviour of systems. The author presents a series of reflections about the methods of formalisation together with the principles that govern the global operation of systems. In particular, a section on circuits, nuclei, and circular causality and a rather detailed description of the analytic use of the generalised asynchronous logical description, together with a brief description of its synthetic use (OreverseO logic). Some basic rules are recalled, such as the fact that a positive circuit is a necessary condition of multistationarity. Also, the interest of considering as a model, rather than a well-defined set of differential equations, a variety of systems that differ from each other only by the values of constant terms is emphasised. All these systems have a common Jacobian matrix and for all of them phase space has exactly the same structure. It means that all can be partitioned in the same way as regards the signs of the eigenvalues and thus as regards the precise nature of any steady states that might be present. Which steady states are actually present, depends on the values of terms of order zero in the ordinary differential equations (ODEs), and it is easy to find for which values of these terms a given point in phase space is steady. Models can be synthesised first at the level of the circuits involved in the Jacobian matrix (that determines which types and numbers of steady states are consistent with the model), then only at the level of terms of order zero in the ODE's (that determines which of the steady states actually exist), hence the title 'Circular casuality'.
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.
Topology of vortex creation in the cylinder wake
DEFF Research Database (Denmark)
Brøns, Morten; Bisgaard, Anders Villefrance
2010-01-01
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 periodic regime, where two different vortex shedding scenarios are identified. The theoretical predictions are verified numerically. For the vorticity, a very different topology occurs with infinite nested sequences of iso-curves moving downstream. General equations of motion for critical points...
Experimental study on the near wake behind two side-by-side cylinders of unequal diameters
Gao, Yangyang; Yu, Dingyong; Tan, Soonkeat; Wang, Xikun; Hao, Zhiyong
2010-10-01
The wake structure behind two side-by-side circular cylinders with unequal diameter was investigated using the particle image velocimetry (PIV) technique. This investigation focused on the asymmetrical flow within the subcritical Reynolds number regime. A comparison between the time-averaged mean flow field of one cylinder and that of two side-by-side cylinders of unequal diameter was made for elucidating the mean flow characteristics attributable to the latter. The distribution of mean velocity behind two side-by-side unequal cylinders was distinctly different from that behind one cylinder, and an asymmetric combination was observed behind the two cylinders. The present paper also presents the authors' interpretation of the generation mechanism of gap flow deflection based on the instantaneous vorticity contours and velocity distribution. The effect of Reynolds number on flow structure was studied by analyzing the mean velocity distribution and time-averaged wake structures. The results showed that vortex formation length decreases with Reynolds number.
Tailoring Effective Media by Mie Resonances of Radially-Anisotropic Cylinders
Directory of Open Access Journals (Sweden)
Henrik Kettunen
2015-05-01
Full Text Available 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 adjust the desired effective response for a fixed frequency. The analysis still remains simple enough, enabling a derivation of analytical design equations. The considered applications include generating artificial magnetism using all-dielectric cylinders, which is currently a very sought-after phenomenon in optical frequencies. We also study how negative refraction is achieved using magnetodielectric RA cylinders.
Kopiev, V. F.; Belyaev, I. V.; Zaytsev, M. Yu.; Kazansky, P. N.; Kopiev, V. A.; Moralev, I. A.
2015-03-01
The effect of high-frequency dielectric barrier discharge plasma actuators on the noise of a flow around a circular cylinder is experimentally studied. It is shown that the plasma actuators are able to reduce the vortex noise of a cylinder within the range of velocities typical for aeroacoustic applications.
Directory of Open Access Journals (Sweden)
Sanjeev Sharma
2009-05-01
Full Text Available Elastic-plastic stresses for a transversely isotropic thick-walled rotating cylinder under internal pressure have been obtained by using Seth’s transition theory. It has been observed that a thick-walled circular cylinder made of isotropic material yields at the internal surface at a high pressure as compared to cylinder made of transversely isotropic material. With the increase in angular speed, much less pressure is required for initial yielding at the internal surface for transversely isotropic material as compared to isotropic material. For fullyplastic state, circumferential stress is maximum at the external surface. Thick-walled circular cylinder made of transversely isotropic material requires high percentage increase in pressure to become fully plastic as compared to isotropic cylinder. Therefore, circular cylinder made of transversely isotropic material is on the safer side of the design as compared to cylinder made of isotropic material.Defence Science Journal, 2009, 59(3, pp.260-264, DOI:http://dx.doi.org/10.14429/dsj.59.1519
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.
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
Yokoi, Y.; Hirao, K.
2013-04-01
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 EXPERIMENT WITH FARADAY CYLINDER
Institute of Scientific and Technical Information of China (English)
薛英
2004-01-01
Suppose there are two electricity testers, A and B(Figure A) . And a metal cylinder C which is almost closed (called Faraday Cylinder)is fixed to tester B, making both tester B and cylinder C charged. As a result, the aluminium foil on tester B opens.
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...
Spurious internal fields in scattering by a cylinder
Nye, J F
2003-01-01
Numerical computations of scattering of electromagnetic waves by hollow conductors can produce spurious internal fields. This well-known effect is examined in detail, at an elementary level, for two-dimensional scattering by a circular cylinder. A plane electromagnetic wave of fixed frequency is scattered from a perfectly conducting hollow circular cylinder. The scattered wave may be regarded as produced by a current density in the cylindrical boundary, which can be readily computed from standard theory. Alternatively, the boundary may be divided into N discrete intervals and the current density may be computed by expressing an appropriate integral equation in discretized form. There is then a difference between the computed and exact current densities that is purely an artefact of the discretization. Provided the radius is not chosen to correspond to an internal resonance, the error in the current density does approach zero as N increases, but in an unusual way: if the radius is just below a resonance value,...
An experimental study of sound generated by flows around cylinders of different cross-section
King, W. F.; Pfizenmaier, E.
2009-12-01
The sound radiated by rigid cylinders placed transversely in a uniform stream has been measured in an anechoic wind tunnel over a range of Mach numbers ( M=0.09-0.2). The cylinders have different cross-sections, e.g., circular, square, rectangular, elliptic, and circular with lateral ribs or knurled surfaces. Different length to diameter ratios of the cylinders are also investigated. Results are presented as narrow band spectra, measured in the far field (acoustic as well as geometric). All spectra are presented with dimensionless (scaled) axes, as well as the original dimensional scales. It is shown that elliptic cross-sections are less noisy, compared to all other cylinders, but noise abatement techniques such as lateral ribs and knurled surfaces can also reduce tonal radiated noise. Two practical applications of these experiments are the reduction of radiated noise from pantographs of high-speed railway trains, and from the landing gear of modern passenger aircraft.
Experimental Investigation of Scattering from Randomly Rough Plastic Cylinders
1992-09-01
fluid, here following the form from Morse and Ingard [20] and Skudrzyk [21]. First, the adiabatic equation of state relating the pressure, p, and...wavelength, we get the standard relation between the particle velocity and the pressure u = -VP. (2.6) Rayleigh [19] and Morse and Ingard [20] derive the...the internal and scattered fields, Rayleigh [191 and Morse and Ingard [20] solve for the scattered field from an infinitely long circular cylinder by
Fertelli, Ahmet; Günhan, Gökhan; Buyruk, Ertan
2017-02-01
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.
A novel porous Ffowcs-Williams and Hawkings acoustic methodology for complex geometries
Nitzkorski, Zane Lloyd
Predictive noise calculations from high Reynolds number flows in complex engineering geometry are becoming a possibility with the high performance computing resources that have become available in recent years. Increasing the applicability and reliability of solution methodologies have been two key challenges toward this goal. This dissertation develops a porous Ffowcs-Williams and Hawkings methodology that uses a novel endcap methodology, and can be applied to unstructured grids. The use of unstructured grids allows complex geometry to be represented while porous formulation eliminates difficulties with the choice of acoustic Green's function. Specifically, this dissertation (1) proposes and examines a novel endcap procedure to account for spurious noise, (2) uses the proposed methodology to investigate noise production from a range of subcritical Reynolds number circular cylinders, and (3) investigates a trailing edge geometry for noise production and to illustrate the generality of the Green's function. Porous acoustic analogies need an endcap scheme in order to prevent spurious noise due to truncation errors. A dynamic end cap methodology is proposed to account for spurious contributions to the far--field sound within the context of the Ffowcs--Williams and Hawkings (FW--H) acoustic analogy. The quadrupole source terms are correlated over multiple planes to obtain a convection velocity which is then used to determine a corrective convective flux at the FW--H porous surface. The proposed approach is first demonstrated for a convecting potential vortex. The correlation is investigated by examining it pass through multiple exit planes. It is then evaluated by computing the sound emitted by flow over a circular cylinder at Reynolds number of 150 and compared to other endcap methods, such as Shur et al. [1]. Insensitivity to end plane location and spacing and the effect of the dynamic convection velocity are computed. Subcritical Reynolds number circular cylinder
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The velocity field and the adequate shear stress corresponding to the longitudinal flow of a fractional second grade fluid,between two infinite coaxial circular cylinders,are determined by applying the Laplace and finite Hankel transforms.Initially the fluid is at rest,and at time t=0~+, the inner cylinder suddenly begins to translate along the common axis with constant acceleration. The solutions that have been obtained are presented in terms of generalized G functions.Moreover, these solutions satisfy ...
An Embedded Boundary Algorithm for Large Eddy Simulations in Complex Geometries
Directory of Open Access Journals (Sweden)
Cristian CARLANESCU
2012-06-01
Full Text Available The paper presents a novel implementation of the embedded boundary algorithm in a Large Eddy Simulation CFD algorithm. The embedded boundary method aims at allowing the simulation of complex geometry flows on Cartesian computational grids, increasing the numerical accuracy of the method, while maintaining acceptable computational requirements and ease of implementation. The novelty of the present implementation consists in a new method for determining the interpolation points required for computing the state vector at the location required for a correct embedded boundary condition application. The paper also includes method validation results for two flow cases: a laminar Poiseuille flow and laminar and turbulent flows past circular cylinders. The simulation results are in good agreement with the analytical solution (where available and with experimental measurements in the literature.
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
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
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
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
Lee, Jeongseog; Safdi, Benjamin R
2014-01-01
Entanglement entropy in even dimensional conformal field theories (CFTs) contains well-known universal terms arising from the conformal anomaly. Renyi entropies are natural generalizations of the entanglement entropy that are much less understood. Above two spacetime dimensions, the universal terms in the Renyi entropies are unknown for general entangling geometries. We conjecture a new structure in the dependence of the four-dimensional Renyi entropies on the intrinsic and extrinsic geometry of the entangling surface. We provide evidence for this conjecture by direct numerical computations in the free scalar and fermion field theories. The computation involves relating the four-dimensional free massless Renyi entropies across cylindrical entangling surfaces to corresponding three-dimensional massive Renyi entropies across circular entangling surfaces. Our numerical technique also allows us to directly probe other interesting aspects of three-dimensional Renyi entropy, including the massless renormalized Reny...
DEFF Research Database (Denmark)
Rusch, W.; Appel-Hansen, Jørgen; Klein, C
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...
Scattering by an elliptic cylinder with a strongly elongated cross section
Andronov, I. V.; Lavrov, Yu. A.
2015-07-01
The paper continues an earlier study devoted to the asymptotic behavior of the field in the boundary layer near the surface of an elliptic cylinder. Using the Kirchhoff formula, the previously derived asymptotics are recalculated to the far field asymptotics, which are considered within a narrow sector near the major axis of the cylinder's cross section. The resulting asymptotic expressions are uniform with respect to the parameter characterizing the elongation of the ellipse and make it possible to trace the variation of the far field pattern from the limiting case of a strip to the case of a circular cylinder.
Adaptronic tools for superfinishing of cylinder bores
Roscher, Hans-Jürgen; Hochmuth, Carsten; Hoffmann, Michael; Praedicow, Michael
2012-04-01
Today in the production of internal combustion engines it is possible to make pistons as well as cylinders, for all practical purposes, perfectly round. The negative consequences of the subsequent assembly processes and operation of the engine is that the cylinders and pistons are deformed, resulting in a loss of power and an increase in fuel consumption. This problem can be solved by using an adaptronic tool, which can machine the cylinder to a predetermined nonround geometry, which will deform to the required geometry during assembly and operation of the engine. The article describes the actuatory effect of the tool in conjunction with its measuring and controlling algorithms. The adaptronic tool consists out the basic tool body and three axially-staggered floating cutter groups, these cutter groups consist out of guides, actuators and honing stones. The selective expansion of the tool is realised by 3 piezoelectric multilayer-actuators deployed in a series - parallel arrangement. It is also possible to superimpose actuator expansion on the conventional expansion. A process matrix is created during the processing of the required and actual contour data in a technology module. This is then transferred over an interface to the machine controller where it is finally processed and the setting values for the piezoelectric actuators are derived, after which an amplifier generates the appropriate actuator voltages. A slip ring system on the driveshaft is used to transfer the electricity to the actuators in the machining head. The functioning of the adaptronic form-honing tool and process were demonstrated with numerous experiments. The tool provides the required degrees of freedom to generate a contour that correspond to the inverse compound contour of assembled and operational engines.
Macquart, JP
2002-01-01
We discuss the constraints that recent observations place on circular polarisation in AGN. In many sources the circular polarisation is variable on short timescales, indicating that it originates in compact regions of the sources. The best prospects for gleaning further information about circular po
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.
Graustein, William C
2006-01-01
This first course in differential geometry presents the fundamentals of the metric differential geometry of curves and surfaces in a Euclidean space of three dimensions. Written by an outstanding teacher and mathematician, it explains the material in the most effective way, using vector notation and technique. It also provides an introduction to the study of Riemannian geometry.Suitable for advanced undergraduates and graduate students, the text presupposes a knowledge of calculus. The first nine chapters focus on the theory, treating the basic properties of curves and surfaces, the mapping of
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
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.
Lefschetz, Solomon
2005-01-01
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.
Circular and Elliptic Submerged Impinging Water Jets
Claudey, Eric; Benedicto, Olivier; Ravier, Emmanuel; Gutmark, Ephraim
1999-11-01
Experiments and CFD have been performed to study circular and elliptic jets in a submerged water jet facility. The tests included discharge coefficient measurement to evaluate pressure losses encountered in noncircular nozzles compared to circular ones. Three-dimensional pressure mappings on the impingement surface and PIV measurement of the jet mean and turbulent velocity have been performed at different compound impingement angles relative to the impingement surface and at different stand-off distances. The objective was to investigate the effect of the non-circular geometry on the flow field and on the impact region. The tests were performed in a close loop system in which the water was pumped through the nozzles into a clear Plexiglas tank. The Reynolds numbers were typically in the range of 250000. Discharge coefficients of the elliptic nozzle was somewhat lower than that of the circular jet but spreading rate and turbulence level were higher. Pressure mapping showed that the nozzle exit geometry had an effect on the pressure distribution in the impact region and that high-pressure zones were generated at specific impact points. PIV measurements showed that for a same total exit area, the elliptic jets affected a surface area that is 8the equivalent circular. The turbulence level in the elliptic jet tripled due to the nozzle design. Results of the CFD model were in good agreement with the experimental data.
Self-sustained oscillations between two tandem cylinders at Reynolds number 1,000
Energy Technology Data Exchange (ETDEWEB)
Kuo, C.H.; Chein, S.M.; Hsieh, H.J. [National Chung Hsing University, Department of Mechanical Engineering, Taichung (China)
2008-04-15
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{sub 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{sub c}/D {<=} 7.0. Here X{sub 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{sub 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{sub u}), measured between these two cylinders, was much higher than the natural shedding frequency behind a single isolated cylinder at the same Re{sub D}. This responding frequency decreased as the distance X{sub c}/D increased. Not until X{sub 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{sub c} = f{sub u} X{sub c}/U{sub c}) maintained a nearly constant value of 3, indicating the self-sustained oscillating flow characteristics with a wavelength X{sub c}/3. Here U{sub c} is the convection speed of the unstable shear layers between two tandem cylinders. At Re{sub 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
Low-frequency oscillations of a cylinder in a viscous fluid
Amin, Norsarahaida
1988-05-01
The flow induced by a circular cylinder oscillating in a viscous fluid when the amplitude of the oscillation is small and the frequecy is low is considered. This solution, obtained by the method of matched asymptotic expansions, is compared with the solution obtained from an Oseen approximation to the governing equations by Andres and Ingard (1953).
2000-09-29
electromagnetic waves by a Narrow anisotropically conductive strip," Radiotekh. Elektron ., vol. 44, no. 7, pp. 800-805, 1999. [3] A. N. Sivov, A. D...Chuprin, and A. D. Shatrov, "Low-frequency resonance in a hollow circular cylinder with perfect conductivity along helical lines," Radiotekh. Elektron
Burdette, A C
1971-01-01
Analytic Geometry covers several fundamental aspects of analytic geometry needed for advanced subjects, including calculus.This book is composed of 12 chapters that review the principles, concepts, and analytic proofs of geometric theorems, families of lines, the normal equation of the line, and related matters. Other chapters highlight the application of graphing, foci, directrices, eccentricity, and conic-related topics. The remaining chapters deal with the concept polar and rectangular coordinates, surfaces and curves, and planes.This book will prove useful to undergraduate trigonometric st
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
Strong Trinucleotide Circular Codes
Directory of Open Access Journals (Sweden)
Christian J. Michel
2011-01-01
Full Text Available Recently, we identified a hierarchy relation between trinucleotide comma-free codes and trinucleotide circular codes (see our previous works. Here, we extend our hierarchy with two new classes of codes, called DLD and LDL codes, which are stronger than the comma-free codes. We also prove that no circular code with 20 trinucleotides is a DLD code and that a circular code with 20 trinucleotides is comma-free if and only if it is a LDL code. Finally, we point out the possible role of the symmetric group ∑4 in the mathematical study of trinucleotide circular codes.
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
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
Towards DNS/LES of cavitating flows in complex geometries
Gnanaskandan, Aswin; Mahesh, Krishnan
2012-11-01
We are developing a numerical method for DNS/LES of turbulent cavitating flows in complex geometries. The multiphase medium is represented using a homogeneous equilibrium model that assumes thermal equilibrium between the liquid and the vapor phase. The governing equations are the compressible Navier Stokes equations for the liquid/vapor mixture along with a transport equation for the vapor mass fraction. A separate total energy equation is solved, as opposed to assuming isothermal flow. The unstructured compressible algorithm in (Park & Mahesh, AIAA Paper 2007-0722) has been extended to solve for multiphase flows. A characteristic filter based shock capturing scheme, extended to handle non-ideal gases and mixtures, is applied in a predictor-corrector approach, ensuring that the shock-capturing is active only in the regions of discontinuity. A segregated implicit method is used to address the stiffness of the system. We discuss our numerical method, validation using benchmark problems and its application to study cavitation behind a circular cylinder for three different cavitation numbers σ = 2.0, 1.0 and 0.7. This work is supported by the Office of Naval Research.
Pottmann, Helmut; Eigensatz, Michael; Vaxman, A.; Wallner, Johannes
2015-01-01
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
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...
Nonlinear Fracture Mechanics and Plasticity of the Split Cylinder Test
DEFF Research Database (Denmark)
Olesen, John Forbes; Østergaard, Lennart; Stang, Henrik
2006-01-01
models are presented, a simple semi-analytical model based on analytical solutions for the crack propagation in a rectangular prismatic body, and a finite element model including plasticity in bulk material as well as crack propagation in interface elements. A numerical study applying these models...... 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...
Spatio-temporal spectral analysis of a forced cylinder wake
D'Adamo, Juan; Wesfreid, José Eduardo
2011-01-01
The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at $Re=100$. Two-dimensional particle image velocimetry on the mid-plane perpendicular to the axis of cylinder is used to characterize the spatial development of the flow and its stability properties. The lock-in phenomenon that determines the boundaries between regions of the forcing parameter space were the wake is globally unstable or convectively unstable is scrutinized using the experimental data. A novel method based on the analysis of power density spectra of the flow allows us to give a detailed description of the forced wake, shedding light on the energy distribution in the different frequency components and in particular on a cascade-like mechanism evidenced for a high amplitude of the forcing oscillation. In addition, a calculation of the drag from the velocity field is performed, allowing us to relate the resulting force on the body to the wake properties.
Broadband computation of the scattering coefficients of infinite arbitrary cylinders.
Blanchard, Cédric; Guizal, Brahim; Felbacq, Didier
2012-07-01
We employ a time-domain method to compute the near field on a contour enclosing infinitely long cylinders of arbitrary cross section and constitution. We therefore recover the cylindrical Hankel coefficients of the expansion of the field outside the circumscribed circle of the structure. The recovered coefficients enable the wideband analysis of complex systems, e.g., the determination of the radar cross section becomes straightforward. The prescription for constructing such a numerical tool is provided in great detail. The method is validated by computing the scattering coefficients for a homogeneous circular cylinder illuminated by a plane wave, a problem for which an analytical solution exists. Finally, some radiation properties of an optical antenna are examined by employing the proposed technique.
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.
Wood Crosscutting Process Analysis for Circular Saws
Directory of Open Access Journals (Sweden)
Jozef Krilek
2016-11-01
Full Text Available This article deals with the influence of some cutting parameters (geometry of cutting edge, wood species, and circular saw type and cutting conditions on the wood crosscutting process carried out with circular saws. The establishment of torque values and feeding power for the crosswise wood cutting process has significant implications for designers of crosscutting lines. The conditions of the experiments are similar to the working conditions of real machines, and the results of individual experiments can be compared with the results obtained via similar experimental workstations. Knowledge of the wood crosscutting process, as well as the choice of suitable cutting conditions and tools could decrease wood production costs and save energy. Changing circular saw type was found to have the biggest influence on cutting power of all factors tested.
Approximation of Surfaces by Cylinders
DEFF Research Database (Denmark)
Randrup, Thomas
1998-01-01
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 projection within a tolerance given by the reference curve, and the rulings are lines perpendicular to the projection plane. Application of the method in ship design is given....
Circularity and Lambda Abstraction
DEFF Research Database (Denmark)
Danvy, Olivier; Thiemann, Peter; Zerny, Ian
2013-01-01
circular unknowns as dead variables, and we apply the functions to them. The result is a lazy circular program a la Bird. We illustrate the two transformations by mapping an algebraic construct to an isomorphic one with new leaves, reading a binary number as sug- gested by Knuth, and backpatching...
Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4 : 1 in Crossflow
Institute of Scientific and Technical Information of China (English)
QI Shou-liang; LI Qing-ling; WANG Ru-zhu
2005-01-01
The heat transfer features around the elliptic cylinder of axis ratio 4: 1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified.The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.
A low-order model for flow control studies in cylinder wakes
Balasubramanian, Ganapathi; Olinger, David J.; Demetriou, Michael
1998-11-01
Control of three-dimensional wake structures behind circular cylinders is investigated using a previously developed coupled map lattice. The map consists of circle map oscillators along the cylinder span coupled by a diffusion model. Our goal is to develop an efficient model for flow control studies in cylinder wakes. Complex vortex shedding patterns, such as vortex dislocations and frequency cells, are observed behind vibrating cables in uniform freestream flows and stationary cylinders in sheared flows. These structures are controlled by the addition of periodic control signals to the forcing term in the map. Discontinuous nonlinear control theory is used to derive the control laws. Parallel shedding is realized for the case of uniform flow and oblique shedding is achieved for sheared inflows. The effectiveness of the discontinuous nonlinear control theory is compared with the previous application of chaos control theory to the coupled map lattice.
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 ...
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...
Kreyszig, Erwin
1991-01-01
An introductory textbook on the differential geometry of curves and surfaces in three-dimensional Euclidean space, presented in its simplest, most essential form, but with many explanatory details, figures and examples, and in a manner that conveys the theoretical and practical importance of the different concepts, methods and results involved. With problems at the end of each section, and solutions listed at the end of the book. Includes 99 illustrations.
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...
Kämper, Jan-Hinrich; Nöllenburg, Martin
2011-01-01
We present a new circular-arc cartogram model in which countries are drawn with circular arcs instead of straight-line segments. Given a geographic map and values associated with each country in the map, the cartogram is a new map in which the areas of the countries represent the corresponding values. In the circular-arc cartogram model straight-line segments can be replaced with circular arcs in order to achieve the desired areas, while the corners of the polygons defining each country remain fixed. The countries in circular-arc cartograms have the aesthetically pleasing appearance of clouds or snowflakes, depending on whether their edges are bent outwards or inwards. This makes is easy to determine whether a country has grown or shrunk, just by its overall shape. We show that determining whether a given map and area-values can be realized with a circular-arc cartogram is an NP-hard problem. Next we describe a heuristic method for constructing circular-arc cartograms, which uses a max-flow computation on the...
DEFF Research Database (Denmark)
Merrild, Heidi; Guldager Jensen, Kasper; Sommer, John
2016-01-01
of the circular strategies is not only in the future. Increased flexibility, optimized operation and maintenance, as well as a healthier building, is low-hanging fruit that can be harvested today. The project’s principles can be implemented in industrialized construction in a large scale today. That is proven......Natural resources are scarce and construction accounts for 40 percent of the material and energy consumption in Europe. This means that a switch to a circular future is necessary. ’Building a Circular Future’ maps out where we are, where we are going, and what is needed for this conversion to take...
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
Ciarlet, Philippe G
2007-01-01
This book gives the basic notions of differential geometry, such as the metric tensor, the Riemann curvature tensor, the fundamental forms of a surface, covariant derivatives, and the fundamental theorem of surface theory in a selfcontained and accessible manner. Although the field is often considered a classical one, it has recently been rejuvenated, thanks to the manifold applications where it plays an essential role. The book presents some important applications to shells, such as the theory of linearly and nonlinearly elastic shells, the implementation of numerical methods for shells, and
Pressure cylinders under fire condition
Directory of Open Access Journals (Sweden)
Jan Hora
2016-03-01
Full Text Available The presence of pressure cylinders under fire conditions significantly increases the risk rate for the intervening persons. It is considerably problematic to predict the pressure cylinders behaviour during heat exposition, its destruction progress and possible following explosion of the produced air–gas mixture because pressure cylinders and its environment generate a highly complicated dynamic system during an uncontrolled destruction. The large scale tests carried out by the Pilsen Fire and Rescue Department and the Rapid Response Unit of the Czech Republic Police in October 2012 and in May 2014 in the Military area Brdy and in the area of the former Lachema factory in Kaznějov had several objectives, namely, to record, qualify and quantify some of the aspects of an uncontrolled heat destruction procedure of an exposed pressure cylinder in an enclosed space and to qualify and describe the process of a controlled destruction of a pressure cylinder by shooting through it including basic tactical concepts. The article describes the experiments that were carried out.
Magnetism in curved geometries
Streubel, Robert; Fischer, Peter; Kronast, Florian; Kravchuk, Volodymyr P.; Sheka, Denis D.; Gaididei, Yuri; Schmidt, Oliver G.; Makarov, Denys
2016-09-01
Extending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system, curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, the curvilinear geometry manifests two exchange-driven interactions, namely effective anisotropy and antisymmetric exchange, i.e. Dzyaloshinskii-Moriya-like interaction. As a consequence, a family of novel curvature-driven effects emerges, which includes magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. The broad range of altered physical properties makes these curved architectures appealing in view of fundamental research on e.g. skyrmionic systems, magnonic crystals or exotic spin configurations. In addition to these rich physics, the application potential of three-dimensionally shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications, spin-wave filters, advanced magneto-encephalography devices for diagnosis of epilepsy or for energy-efficient racetrack memory devices. These recent developments ranging from theoretical predictions over fabrication of three-dimensionally curved magnetic thin films, hollow cylinders or wires, to their characterization using integral means as well as the development of advanced tomography approaches are in the focus of this review.
Administrative & Operational Circulars - Reminder
HR Department
2011-01-01
All Administrative and Operational Circulars are available on the intranet site of the Human Resources Department at the following address: http://cern.ch/hr-docs/admincirc/admincirc.asp Department Head Office
Circular words and applications
Directory of Open Access Journals (Sweden)
Benoît Rittaud
2011-08-01
Full Text Available We define the notion of circular words, then consider on such words a constraint derived from the Fibonacci condition. We give several results on the structure of these circular words, then mention possible applications to various situations: periodic expansion of numbers in numeration systems, "gcd-property" of integer sequences, partition of the prefix of the fixed point of the Fibonacci substitution, spanning trees of a wheel. Eventually, we mention some open questions.
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...... such as the circular camera movement. Keywords: embodied perception, embodied style, explicit narration, interpretation, style pattern, television style...
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.
Blower Cooling of Finned Cylinders
Schey, Oscar W; Ellerbrock, Herman H , Jr
1937-01-01
Several electrically heated finned steel cylinders enclosed in jackets were cooled by air from a blower. The effect of the air conditions and fin dimensions on the average surface heat-transfer coefficient q and the power required to force the air around the cylinders were determined. Tests were conducted at air velocities between the fins from 10 to 130 miles per hour and at specific weights of the air varying from 0.046 to 0.074 pound per cubic foot. The fin dimensions of the cylinders covered a range in pitches from 0.057 to 0.25 inch average fin thicknesses from 0.035 to 0.04 inch, and fin widths from 0.67 to 1.22 inches.
Filament winding cylinders. I - Process model
Lee, Soo-Yong; Springer, George S.
1990-01-01
A model was developed which describes the filament winding process of composite cylinders. The model relates the significant process variables such as winding speed, fiber tension, and applied temperature to the thermal, chemical and mechanical behavior of the composite cylinder and the mandrel. Based on the model, a user friendly code was written which can be used to calculate (1) the temperature in the cylinder and the mandrel, (2) the degree of cure and viscosity in the cylinder, (3) the fiber tensions and fiber positions, (4) the stresses and strains in the cylinder and in the mandrel, and (5) the void diameters in the cylinder.
Interaction between leading and trailing edge vortex shedding: effects of bluff body geometry
Taylor, Zachary; Kopp, Gregory; Gurka, Roi
2011-11-01
Elongated bluff bodies are distinguished from shorter bluff bodies (e.g., circular cylinders) by the fact that they have separating-reattaching flow at the leading edge as well as having vortex shedding at the trailing edge. Engineering examples of these bodies include heat exchanger fins and long-span suspension bridges. We have performed experiments on elongated bluff bodies of varying geometry. These experiments have been performed at Reynolds numbers O(104) based on the thickness of the model. Both surface pressure measurements (using 512 simultaneously sampled pressure taps) and PIV are used to quantify the flow fields of these bodies. The leading edge separation angle is controlled by changing the leading edge geometry. It is observed that the size of the leading edge separation bubble increases with increasing leading edge separation angle. As the size of the leading edge separation bubble increases, it is shown to continually decrease the shedding frequency for a given elongation ratio. It is suggested that the shedding frequency is diminished because the trailing edge vortex shedding is affected by the structures being shed from the leading edge separation bubble. The implications of this competition between leading and trailing edge flows will be explored.
Interaction dynamics of gap flow with vortex-induced vibration in side-by-side cylinder arrangement
Liu, Bin; Jaiman, Rajeev K.
2016-12-01
A numerical investigation of the vortex-induced vibration (VIV) in a side-by-side circular cylinder arrangement has been performed in a two-dimensional laminar flow environment. One of the cylinders is elastically mounted and only vibrates in the transverse direction, while its counterpart remains stationary in a uniform flow stream. When the gap ratio is sufficiently small, the flip-flopping phenomenon of the gap flow can be an additional time-dependent interference to the flow field. This phenomenon was reported in the experimental work of Bearman and Wadcock ["The interaction between a pair of circular cylinders normal to a stream," J. Fluid Mech. 61(3), 499-511 (1973)] in a side-by-side circular cylinder arrangement, in which the gap flow deflects toward one of the cylinders and switched its sides intermittently. Albeit one of the two cylinders is free to vibrate, the flip-flop of a gap flow during VIV dynamics can still be observed outside the lock-in region. The exact moments of the flip-flop phenomenon due to spontaneous symmetry breaking are observed in this numerical study. The significant characteristic vortex modes in the near-wake region are extracted via dynamic modal analysis and the interference between the gap flow and VIV is found to be mutual. In a vibrating side-by-side arrangement, the lock-in region with respect to reduced velocity becomes narrower due to the interference from its stationary counterpart. The frequency lock-in occurs and ends earlier than that of an isolated vibrating circular cylinder subjected to an identical flow environment. Similar to a tandem cylinder arrangement, in the post-lock-in region, the maximum vibration amplitudes are escalated compared with those of an isolated circular cylinder configuration. On the other hand, subjected to the influence from VIV, the biased gap flow deflects toward the vibrating cylinder quasi-stably during the frequency lock-in process. This behavior is different from the reported bi
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.
Numerical Investigation of the Effect of Corner Radius on Forced Oscillating Square Cylinder
Directory of Open Access Journals (Sweden)
Sajjad Miran
2016-01-01
Full Text Available The purpose of this work is to numerically visualize the flow past forced oscillating square cylinder and investigate the effect of corner radius on flow induced forces. The finite volume code was applied to simulate the two dimensional flow past forced oscillating square cylinder with different radius to diameter ratios, (R/D = 0 referring to a square cylinder with sharp edges and R/D = 0.5 as a circular cylinder. The near wake of a square section cylinder with an increment of R/D = 0.1 was studied as the body undergoes a complete oscillatory cycle at lock-in condition, F = fe / fs = 1 (where fe is the excitation frequency and fs is the vortex shedding frequency for the stationary cylinder. The computational model was validated for flow past oscillating cylinder with R/D = 0.5 at frequency ratios F = 0.5, 1.0 and 1.50, using as the lock-in and lock-out limits and the results shown good agreement. It was observed that computed value of Strouhal Number is nearly same for both stationary and oscillation case and a similar trend was observed, as R/D ratio increases. However, the results obtained from oscillation cylinder cases show the significant increase in root mean square value of lift coefficient (CL,RMS and mean drag coefficient (CD as compared to the stationary cylinder. Finally, It was found that the percentage increase of CL,RMS is higher than CD in force oscillating condition for R/D = 0, whereas both values decreases with the increase of R/D.
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.
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...
Anisotropic Poisson Processes of Cylinders
Spiess, Malte
2010-01-01
Main characteristics of stationary anisotropic Poisson processes of cylinders (dilated k-dimensional flats) in d-dimensional Euclidean space are studied. Explicit formulae for the capacity functional, the covariance function, the contact distribution function, the volume fraction, and the intensity of the surface area measure are given which can be used directly in applications.
Compact waveguide circular polarizer
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.
Natural convective heat transfer from square cylinder
Novomestský, Marcel; Smatanová, Helena; Kapjor, Andrej
2016-06-01
This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable
Beamforming with a circular microphone array for localization of environmental sources of noise
DEFF Research Database (Denmark)
Tiana Roig, Elisabet; Jacobsen, Finn; Fernandez Grande, Efren
2010-01-01
It is often enough to localize environmental sources of noise from different directions in a plane. This can be accomplished with a circular microphone array, which can be designed to have practically the same resolution over 360. The microphones can be suspended in free space or they can...... be mounted on a solid cylinder. This investigation examines and compares two techniques based on such arrays, the classical delay-and-sum beamforming and an alternative method called circular harmonics beamforming. The latter is based on decomposing the sound field into a series of circular harmonics...
Beamforming with a circular microphone array for localization of environmental noise sources
DEFF Research Database (Denmark)
Tiana Roig, Elisabet; Jacobsen, Finn; Fernandez Grande, Efren
2010-01-01
It is often enough to localize environmental sources of noise from different directions in a plane. This can be accomplished with a circular microphone array, which can be designed to have practically the same resolution over 360. The microphones can be suspended in free space or they can...... be mounted on a solid cylinder. This investigation examines and compares two techniques based on such arrays, the classical delay-and-sum beamforming and an alternative method called circular harmonics beamforming. The latter is based on decomposing the sound field into a series of circular harmonics...
Comparison of aerodynamic noise from three nose-cylinder combinations
Guenther, R. A.; Reding, M. P.
1970-01-01
Results of experiments with three different cylinder and blunted nose combinations are discussed. Combinations include smooth cylinder with single 15 deg cone, smooth cylinder with double cone of 25 and 10 deg, and longitudinally corrugated cylinder with similar double cone.
Flow-induced cylinder noise formulated as a diffraction problem for low Mach numbers
Gloerfelt, X.; Pérot, F.; Bailly, C.; Juvé, D.
2005-10-01
The role of surfaces in the mechanism of sound generation by low Mach number flows interacting with solid nonvibrating surfaces is well established by the classical aeroacoustic papers by Powell, Doak, Ffowcs Williams, Crighton, or Howe. It can be formulated as a problem of diffraction of the flow sources by the rigid body. The present study illustrates this statement in the case of flow-induced cylinder noise. Curle's formulation is analytically and numerically compared to a formulation based on an exact Green's function tailored to a cylindrical geometry. The surface integral of Curle's formulation represents exactly the diffraction effects by the rigid body. The direct and scattered parts of the sound field are studied. In this low Mach number configuration, the cylinder is compact, and the scattered (dipole) field dominates the direct (quadrupole) field. The classical properties of the scattering by a cylinder are retrieved by considering a point quadripole source near the cylinder surface.
Directory of Open Access Journals (Sweden)
Mahmoud Shariati
2017-01-01
Full Text Available his paper investigates the variations of mode I stress intensity factor (KI for inner penny-shaped and circumferential cracks in functionally graded solid and hollow thick walled cylinders, respectively with the changes of crack geometry, material gradation and loading conditions. The functionally graded material of cylinders consists of epoxy and glass. It is assumed that the mechanical properties vary with a power law in the radial direction of cylinders. Micromechanical models for conventional composites are used to estimate the material properties of functionally graded cylinders. The equations of motion obtained from the extended finite element discretization are solved by the Newmark method in the time domain. The interaction integral method is employed to calculate the mode I stress intensity factor (KI. The MATLAB programming environment was implemented to solve the problem.
Experimental study on the near wake behind two side-by-side cylinders of unequal diameters
Energy Technology Data Exchange (ETDEWEB)
Gao Yangyang; Yu Dingyong [College of Engineering, Ocean University of China, Qingdao 266100 (China); Tan, Soonkeat [School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Wang Xikun [Maritime Research Center, Nanyang Technological University, Singapore 639798 (Singapore); Hao Zhiyong, E-mail: gaoyangyangouc@163.co [Shanghai Maritime University, Shanghai 200135 (China)
2010-10-15
The wake structure behind two side-by-side circular cylinders with unequal diameter was investigated using the particle image velocimetry (PIV) technique. This investigation focused on the asymmetrical flow within the subcritical Reynolds number regime. A comparison between the time-averaged mean flow field of one cylinder and that of two side-by-side cylinders of unequal diameter was made for elucidating the mean flow characteristics attributable to the latter. The distribution of mean velocity behind two side-by-side unequal cylinders was distinctly different from that behind one cylinder, and an asymmetric combination was observed behind the two cylinders. The present paper also presents the authors' interpretation of the generation mechanism of gap flow deflection based on the instantaneous vorticity contours and velocity distribution. The effect of Reynolds number on flow structure was studied by analyzing the mean velocity distribution and time-averaged wake structures. The results showed that vortex formation length decreases with Reynolds number.
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.
Wake-induced vibrations in Tandem Cylinders
Mysa, Ravi Chaithanya; Jaiman, Rajeev Kumar
2015-11-01
The upstream cylinder is fixed in the tandem cylinders arrangement. The downstream cylinder is placed at a distance of four diameters from the upstream cylinder in the free stream direction and is mounted on a spring. The dynamic response of the downstream cylinder is studied at Reynolds number of 10,000. The transverse displacement amplitude of the downstream cylinder is larger compared to that of single cylinder in the post-lock-in region. The transverse dynamic response of the downstream cylinder in the post-lock-in region is characterized by a dominant low frequency component compared to shed frequency, which is nearer to the structural natural frequency. The interaction of upstream wake with the downstream cylinder is carefully analyzed to understand the introduction of low frequency component in the transverse load along with the shed frequency. We found that the stagnation point moves in proportional to the velocity of the cylinder and is in-phase with the velocity. The low frequency component in the stagnation point movement on the downstream cylinder is sustained by the interaction of upstream wake. The frequencies in the movement of the stagnation point is reflected in the transverse load resulting in large deformation of the cylinder. The authors wish to acknowledge support from A*STAR- SERC and Singapore Maritime Institute.
Gao, Nan; Zhang, Yuchao; Xie, Changqing
2011-11-01
We introduce circular Fibonacci gratings (CFGs) that combine the concept of circular gratings and Fibonacci structures. Theoretical analysis shows that the diffraction pattern of CFGs is composed of fractal distributions of impulse rings. Numerical simulations are performed with two-dimensional fast Fourier transform to reveal the fractal behavior of the diffraction rings. Experimental results are also presented and agree well with the numerical results. The fractal nature of the diffraction field should be of great theoretical interest, and shows potential to be further developed into practical applications, such as in laser measurement with wideband illumination.
Compressibility effects on the flow past a rotating cylinder
Teymourtash, A. R.; Salimipour, S. E.
2017-01-01
In this paper, laminar flow past a rotating circular cylinder placed in a compressible uniform stream is investigated via a two-dimensional numerical simulation and the compressibility effects due to the combination of the free-stream and cylinder rotation on the flow pattern such as forming, shedding, and removing of vortices and also the lift and drag coefficients are studied. The numerical simulation of the flow is based on the discretization of convective fluxes of the unsteady Navier-Stokes equations by second-order Roe's scheme and an explicit finite volume method. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by a dual time stepping approach. In order to validate the operation of a computer program, some results are compared with previous experimental and numerical data. The results of this study show that the effects due to flow compressibility such as normal shock wave caused the interesting variations on the flow around the cylinder even at a free-stream with a low Mach number. At incompressible flow around the rotating cylinder, increasing the speed ratio, α (ratio of the surface speed to free-stream velocity), causes the ongoing increase in the lift coefficient, but in compressible flow for each free-stream Mach number, increasing the speed ratio results in obtaining a limited lift coefficient (a maximum mean lift coefficient). In addition, results from the compressible flow indicate that by increasing the free-stream Mach number, the maximum mean lift coefficient is decreased, while the mean drag coefficient is increased. It is also found that by increasing the Reynolds number at low Mach numbers, the maximum mean lift coefficient and critical speed ratio are decreased and the mean drag coefficient and Strouhal number are increased. However at the higher Mach numbers, these parameters become independent of the Reynolds number.
Bordenave, Charles
2011-01-01
These expository notes are centered around the circular law theorem, which states that the empirical spectral distribution of a n \\times n random matrix with i.i.d. entries of variance 1/n tends to the uniform law on the unit disc of the complex plane as the dimension n tends to infinity. This phenomenon is the non-Hermitian counterpart of the semi circular limit for Wigner random Hermitian matrices, and the quarter circular limit for Marchenko-Pastur random covariance matrices. We present a proof in a Gaussian case, due to Silverstein, based on a formula by Ginibre, and a proof of the universal case by revisiting the approach of Tao and Vu, based on the Hermitization of Girko, the logarithmic potential, and the control of the small singular values. Beyond the finite variance model, we also consider the case where the entries have heavy tails, by using the objective method of Aldous and Steele borrowed from randomized combinatorial optimization. The limiting law is then no longer the circular law and is relat...
Prins, M.; Mohammadi, S.; Slob, N.
2015-01-01
Recently the Circular Economy (CE) concept has gained momentum in the Netherlands, propounding that environmental impact reduction can provide a significant positive economical impulse. The government, larger parts of the industry as a whole, as well as the construction industry, has warmly received
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…
Transposable elements and circular DNAs
Mourier, Tobias
2016-09-26
Circular DNAs are extra-chromosomal fragments that become circularized by genomic recombination events. We have recently shown that yeast LTR elements generate circular DNAs through recombination events between their flanking long terminal repeats (LTRs). Similarly, circular DNAs can be generated by recombination between LTRs residing at different genomic loci, in which case the circular DNA will contain the intervening sequence. In yeast, this can result in gene copy number variations when circles contain genes and origins of replication. Here, I speculate on the potential and implications of circular DNAs generated through recombination between human transposable elements.
Multi-directional random wave interaction with an array of cylinders
DEFF Research Database (Denmark)
Ji, Xinran; Liu, Shuxue; Bingham, Harry B.;
2015-01-01
. The biggest transverse force is found to occur on the rear cylinder rather than the front one. This is quite different from the results in unidirectional waves and should be paid much more attention in the design of offshore structures. At last, the possibility of the near-trapping under the multi......Based on the linear theory of wave interaction with an array of circular bottom-mounted vertical cylinders, systematic calculations are made to investigate the effects of the wave directionality on wave loads in short-crested seas. The multi-directional waves are specified using a discrete form...... of the Mitsuyasu-type spreading function. The time series of multi-directional wave loads, including both the wave run-up and wave force, can be simulated. The effect of wave directionality on the wave run-up and wave loading on the cylinders is investigated. For multi-directional waves, as the distribution...
Velocity field in a vicinity of cylinder bouncing off horizontal wall
Chara, Z.; Kysela, B.; Dolansky, J.
2016-06-01
The paper describes experimental and numerical investigations of velocity fields around a circular cylinder colliding perpendicularly with a plane wall. The cylinder of the diameter D = 20 mm was moving vertically in a water tank and the motion was recorded by a fast digital camera. Reynolds numbers ranged from 3000 to 8100 and the initial positions L of the cylinder above the wall were L/D = 2.5; 3.5; 4.5 and 5.5. An evolution of fluid agitation in an area close to the impact point was based on the results of the velocity field measurements. The numerical simulations were performed using a 2D-LES model.
Centrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake
D'Adamo, Juan; Wesfreid, José Eduardo
2015-01-01
The wake flow around a circular cylinder at $Re\\approx100$ performing rotatory oscillations has been thoroughly discussed in the literature, mostly focusing on the modifications to the natural B\\'enard-von K\\'arm\\'an vortex street that result from the forced shedding modes locked to the rotatory oscillation frequency. The usual experimental and theoretical frameworks at these Reynolds numbers are quasi-two-dimensional, since the secondary instabilities bringing a three-dimensional structure to the cylinder wake flow occur only at higher Reynolds numbers. In the present paper we show that a three-dimensional structure can appear below the usual three-dimensionalization threshold, when forcing with frequencies lower than the natural vortex shedding frequency, at high amplitudes, as a result of a previously unreported mechanism: a pulsed centrifugal instability of the oscillating Stokes layer at the wall of the cylinder. The present numerical investigation lets us in this way propose a physical explanation for t...
Mao, Shi-Chun; Wu, Zhen-Sen
2008-12-01
An exact solution to the two-dimensional scattering properties of an anisotropic elliptic cylinder for transverse electric polarization is presented. The internal field in an anisotropic elliptic cylinder is expressed as integral representations of Mathieu functions and Fourier series. The coefficients of the series expansion are obtained by imposing boundary conditions on the anisotropic-free-space interface. A matrix is developed to solve the nonorthogonality properties of Mathieu functions at the interface between two different media. Numerical results are given for the bistatic radar cross section and the amplitude of the total magnetic field along the x and y axes. The result is in agreement with that available as expected when an elliptic cylinder degenerates to a circular one.
Convective heat transfer measurement involving flow past stationary circular disks
Energy Technology Data Exchange (ETDEWEB)
Wedekind, G.L. (Oakland Univ., Rochester, MI (United States))
1989-11-01
Considerable empirical data exist in the literature for forced convection heat transfer involving external flow over a variety of geometries, and for various ranges of Reynolds number. This author is not aware of any published empirical data for forced convection heat transfer involving flow past a simple stationary circular disk, whose axis is perpendicular to the flow. Such is the purpose of this paper.
High-resolution simulations of the flow around an impulsively started cylinder using vortex methods
Koumoutsakos, Petros; Leonard, A.
1995-01-01
The development of a two-dimensional viscous incompressible flow generated from a circular cylinder impulsively started into rectilinear motion is studied computationally. An adaptative numerical scheme, based on vortex methods, is used to integrate the vorticity/velocity formulation of the Navier–Stokes equations for a wide range of Reynolds numbers (Re = 40 to 9500). A novel technique is implemented to resolve diffusion effects and enforce the no-slip boundary condition. The Biot–Savart law...
Generalized Bistability in Origami Cylinders
Reid, Austin; Adda-Bedia, Mokhtar; Lechenault, Frederic
Origami folded cylinders (origami bellows) have found increasingly sophisticated applications in space flight, medicine, and even experimental nuclear physics. In spite of this interest, a general understanding of the dynamics of an origami folded cylinder has been elusive. By solving the fully constrained behavior of a periodic fundamental origami cell defined by unit vectors, we have found an analytic solution for all possible rigid-face states accessible from a cylindrical Miura-ori pattern. Although an idealized bellows has two rigid-face configurations over a well-defined region, a physical device, limited by nonzero material thickness and forced to balance hinge with plate-bending energy, often cannot stably maintain a stowed configuration. We have identified and measured the parameters which control this emergent bistability, and have demonstrated the ability to fabricate bellows with tunable deployability.
Cylinder components properties, applications, materials
2016-01-01
Owing to the ever-increasing requirements to be met by gasoline and diesel engines in terms of CO2 reduction, emission behavior, weight, and service life, a comprehensive understanding of combustion engine components is essential today. It is no longer possible for professionals in automotive engineering to manage without the corresponding expertise, whether they work in the field of design, development, testing, or maintenance. This technical book provides in-depth answers to questions about design, production, and machining of cylinder components. In this second edition, every section has been revised and expanded to include the latest developments in the combustion engine. Content Piston rings Piston pins and piston pin circlips Bearings Connecting rods Crankcase and cylinder liners Target audience Engineers in the field of engine development and maintenanceLecturers and students in the areas of mechanical engineering, engine technology, and vehicle constructionAnyone interested in technology Publisher MAH...
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
Counting Polyominoes on Twisted Cylinders
Barequet, Gill; Moffie, Micha; Ribó, Ares; Rote, Günter
2005-01-01
International audience; We improve the lower bounds on Klarner's constant, which describes the exponential growth rate of the number of polyominoes (connected subsets of grid squares) with a given number of squares. We achieve this by analyzing polyominoes on a different surface, a so-called $\\textit{twisted cylinder}$ by the transfer matrix method. A bijective representation of the "states'' of partial solutions is crucial for allowing a compact representation of the successive iteration vec...
Design and Analysis of Cylinder and Cylinder head of 4-stroke SI Engine for weight reduction
Directory of Open Access Journals (Sweden)
Ravindra R. Navthar
2012-03-01
Full Text Available The present paper deals with design of cylinder & cylinder head with air cooling system for 4 strokes 4 cylinder SI engine. The main objective of design is to reduce weight to power ratio & will result in producing high specific power. The authors have proposed preliminary design cylinder & cylinder head of a horizontallyopposed SI engine, which develops 120 BHP and posses the maximum rotational speed of 6000rpm. Four stroke opposed engine is inherently well balanced due to opposite location of moving masses and also it provides efficient air cooling. For the requirement of weight reduction the material selected for design of cylinder and cylinder head is Aluminum alloy that is LM-13. The cylinder bore coating using NIKASIL coating was done to improve strength of cylinder with minimum weight..
Miles, P. C.; Green, R. M.; Witze, P. O.
1994-01-01
The in-cylinder flow field of a Schnuerle (loop) scavenged two-stroke engine has been examined under conditions simulating both blower and crankcase driven scavenging. Measurements of the radial component of velocity were obtained along the cylinder centerline during fired operation at delivery ratios of 0.4, 0.6, and 0.8. Both mean velocity profiles and root mean square velocity fluctuations near top center show a strong dependence on the scavenging method. Complementary in-cylinder pressure measurements indicate that combustion performance is better under blower driven scavenging for the engine geometry studied.
Kappa Coefficients for Circular Classifications
Warrens, Matthijs J.; Pratiwi, Bunga C.
2016-01-01
Circular classifications are classification scales with categories that exhibit a certain periodicity. Since linear scales have endpoints, the standard weighted kappas used for linear scales are not appropriate for analyzing agreement between two circular classifications. A family of kappa coefficie
Fire testing of bare uranium hexafluoride cylinders
Energy Technology Data Exchange (ETDEWEB)
Pryor, W.A. [PAI Corp., Oak Ridge, TN (United States)
1991-12-31
In 1965, the Oak Ridge Gaseous Diffusion Plant (ORGDP), now the K-25 Site, conducted a series of tests in which bare cylinders of uranium hexafluoride (UF{sub 6}) were exposed to engulfing oil fires for the US Atomic Energy Commission (AEC), now the US Department of Energy (DOE). The tests are described and the results, conclusions, and observations are presented. Two each of the following types of cylinders were tested: 3.5-in.-diam {times} 7.5-in.-long cylinders of Monel (Harshaw), 5.0-in.-diam {times} x 30-in.-long cylinders of Monel, and 8-in.-diam {times} 48-in.-long cylinders of nickel. The cylinders were filled approximately to the standard UF{sub 6} fill limits of 5, 55, and 250 lb, respectively, with a U-235 content of 0.22%. The 5-in.- and 8-in.-diam cylinders were tested individually with and without their metal valve covers. For the 3.5-in.-diam Harshaw cylinders and the 5.0-in.-diam cylinder without a valve cover, the valves failed and UF{sub 6} was released. The remaining 6 cylinders ruptured explosively in time intervals ranging from about 8.5 to 11 min.
Fire testing of bare uranium hexafluoride cylinders
Energy Technology Data Exchange (ETDEWEB)
Pryor, W.A. [PAI Corp., Oak Rige, TN (United States)
1991-12-31
In 1965, the Oak Ridge Gaseous Diffusion Plant (ORGDP), now the K-25 Site, conducted a series of tests in which bare cylinders of uranium hexafluoride (UF{sub 6}) were exposed to engulfing oil fires for the US Atomic Energy Commission (AEC), now the US Department of Energy (DOE). The tests are described and the results, conclusions, and observations are presented. Two each of the following types of cylinders were tested: 3.5-in.-diam {times} 7.5-in.-long cylinders of Monel (Harshaw), 5.0-in.-diam {times} 30-in.-long cylinders of Monel, and 8-in.-diam {times} 48-in.-long cylinders of nickel. The cylinders were filled approximately to the standard UF{sub 6} fill limits of 5, 55, and 250 lb, respectively, with a U-235 content of 0.22%. The 5-in.- and 8-in.-diam cylinders were tested individually with and without their metal valve covers. For the 3.5-in.-diam Harshaw cylinders and the 5.0-in.-diam cylinder without a valve cover the valves failed and UF{sub 6} was released. The remaining cylinders ruptured explosively in time intervals ranging from about 8.5 to 11 min.
Slow light and band gaps in metallodielectric cylinder arrays.
Shainline, Jeffrey M; Xu, Jimmy
2009-05-25
We consider two-dimensional three-component photonic crystals wherein one component is modeled as a drude-dispersive metal. It is found that the dispersion relation of light in this environment depends critically on the configuration of the metallic and dielectric components. In particular, for the case of an incident electromagnetic wave with electric field vector parallel to the axis of the cylinders it is shown that the presence of dielectric shells covering the metallic cylinders leads to a closing of the structural band gap with increased filling factor, as would be expected for a purely dielectric photonic crystal. For the same polarization, the photonic band structure of an array of metallic shell cylinders with dielectric cores do not show the closing of the structural band gap with increased filling factor of the metallic component. In this geometry, the photonic band structure contains bands with very small values of group velocity with some bands having a maximum of group velocity as small as .05c.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
This paper investigates the vibration characteristics of diesel engine cylinder heads by means of the time series method.With the concept of "Assumed System", the vibration transfer function of real cylinder head structures is established using the autoregressive-moving average models (ARMA models) of cylinder head surface vibration signals.Then this transfer function is successfully used to reconstruct the gas pressure trace inside the cylinder from measured cylinder head vibration signals.This offers an effective means for diesel engine cylinder pressure detection and condition monitoring.
Thermal conductivity modeling of circular-wire nanocomposites
Hsieh, Tse-Yang; Yang, Jaw-Yen
2010-08-01
A phonon Boltzmann equation solver using multiblock-structured grid system is developed and applied to study transverse thermal transport in silicon-germanium circular-wire nanocomposite (silicon nanowires embedded in germanium host matrix). Past studies usually assume geometric simplification for the circular-wire nanocomposite, so the heat transfer is actually modeled in a square-wire nanocomposite. To demonstrate geometry effect, phonon transport in both the circular-wire and square-wire nanocomposites are investigated with various wire spacings, volume fractions, and dimensions. In ballistic phonon transport, due to the smoothness of circular shape, the circular wire imposes less thermal resistance than the square wire. Nevertheless, in the geometric simplification, the wire spacing of the square-wire nanocomposite is larger than that of the circular-wire nanocomposite. The usual geometric simplification can overestimate the thermal conductivity of the circular-wire nanocomposite. The obtained results can provide essential information for the development of bulk-nanostructured thermoelectric devices.
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.
Analysis of an indirect neutron signature for enhanced UF6 cylinder verification
Kulisek, J. A.; McDonald, B. S.; Smith, L. E.; Zalavadia, M. A.; Webster, J. B.
2017-02-01
The International Atomic Energy Agency (IAEA) currently uses handheld gamma-ray spectrometers combined with ultrasonic wall-thickness gauges to verify the declared enrichment of uranium hexafluoride (UF6) cylinders. The current method provides relatively low accuracy for the assay of 235U enrichment, especially for natural and depleted UF6. Furthermore, the current method provides no capability to assay the absolute mass of 235U in the cylinder due to the localized instrument geometry and limited penetration of the 186-keV gamma-ray signature from 235U. Also, the current verification process is a time-consuming component of on-site inspections at uranium enrichment plants. Toward the goal of a more-capable cylinder assay method, the Pacific Northwest National Laboratory has developed the hybrid enrichment verification array (HEVA). HEVA measures both the traditional 186-keV direct signature and a non-traditional, high-energy neutron-induced signature (HEVANT). HEVANT enables full-volume assay of UF6 cylinders by exploiting the relatively larger mean free paths of the neutrons emitted from the UF6. In this work, Monte Carlo modeling is used as the basis for characterizing HEVANT in terms of the individual contributions to HEVANT from nuclides and hardware components. Monte Carlo modeling is also used to quantify the intrinsic efficiency of HEVA for neutron detection in a cylinder-assay geometry. Modeling predictions are validated against neutron-induced gamma-ray spectra from laboratory measurements and a relatively large population of Type 30B cylinders spanning a range of enrichments. Implications of the analysis and findings on the viability of HEVA for cylinder verification are discussed, such as the resistance of the HEVANT signature to manipulation by the nearby placement of neutron-conversion materials.
Analysis of an Indirect Neutron Signature for Enhanced UF6 Cylinder Verification
Energy Technology Data Exchange (ETDEWEB)
Kulisek, Jonathan A.; McDonald, Benjamin S.; Smith, Leon E.; Zalavadia, Mital A.; Webster, Jennifer B.
2017-02-21
The International Atomic Energy Agency (IAEA) currently uses handheld gamma-ray spectrometers combined with ultrasonic wall-thickness gauges to verify the declared enrichment of uranium hexafluoride (UF6) cylinders. The current method provides relatively low accuracy for the assay of 235U enrichment, especially for natural and depleted UF6. Furthermore, the current method provides no capability to assay the absolute mass of 235U in the cylinder due to the localized instrument geometry and limited penetration of the 186-keV gamma-ray signature from 235U. Also, the current verification process is a time-consuming component of on-site inspections at uranium enrichment plants. Toward the goal of a more-capable cylinder assay method, the Pacific Northwest National Laboratory has developed the hybrid enrichment verification array (HEVA). HEVA measures both the traditional 186-keV direct signature and a non-traditional, high-energy neutron-induced signature (HEVANT). HEVANT enables full-volume assay of UF6 cylinders by exploiting the relatively larger mean free paths of the neutrons emitted from the UF6. In this work, Monte Carlo modeling is used as the basis for characterizing HEVANT in terms of the individual contributions to HEVANT from nuclides and hardware components. Monte Carlo modeling is also used to quantify the intrinsic efficiency of HEVA for neutron detection in a cylinder-assay geometry. Modeling predictions are validated against neutron-induced gamma-ray spectra from laboratory measurements and a relatively large population of Type 30B cylinders spanning a range of enrichments. Implications of the analysis and findings on the viability of HEVA for cylinder verification are discussed, such as the resistance of the HEVANT signature to manipulation by the nearby placement of neutron-conversion materials.
FLOW PATTERNS AND FORCE CHARACTERISTICS OF LAMINAR FLOW PAST FOUR CYLINDERS IN DIAMOND ARRANGEMENT
Institute of Scientific and Technical Information of China (English)
ZOU Lin; LIN Yu-feng; LU Hong
2011-01-01
A three-dimensional numerical investigation of cross-flow past four circular cylinders in a diamond arrangement at Reynolds number of 200 is carried out. With the spacing ratios ( L/D ) ranging from 1.2 to 5.0, the flow patterns can be classified into three basic regimes. The critical spacing ratio for the transition from narrow gap flow pattern to vortex impingement flow pattern around the cylinders is found to be L/D = 3.0, while a single bluff-body flow pattern is observed at L/D = 1.2. The relationship between the three-dimensional flow patterns and force characteristics around the four cylinders shows that the variation of forces and Strouhal numbers against L/D are generally governed by these three kinds of flow patterns. It is concluded that the spacing ratio has important effects on the development of the free shear layers about the cylinders and hence has significant effects on the force and pressure characteristics of the four cylinders with different spacing ratios.
Directory of Open Access Journals (Sweden)
Liu Mingyue
2015-09-01
Full Text Available The Deep Draft Semi-Submersible (DDS concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around α = 15°. Furthermore, the flow around circular-section-cylinder arrays is also discussed in comparison with that of square cylinders.
Fatigue Tests with Densit Cylinders - D4
DEFF Research Database (Denmark)
Ellegaard, Peter
This report contains descriptions and results of a series of fatigue tests performed during the autumn of 2005 at the Stuctural Research Laboratory, Aalborg University. Cylinders with a diameter of 45 mm and a height of 90 mm were used as test specimens; the material was Densit Ducorit D4. Four...... cylinders were tested statically under compression and the rest of the cylinders (30) were tested under fatigue conditions with a load varying sinusoidally....
Rarita-Schwinger Type operators on Cylinders
2011-01-01
Here we define Rarita-Schwinger operators on cylinders and construct their fundamental solutions. Further the fundamental solutions to the cylindrical Rarita-Schwinger type operators are achieved by applying translation groups. In turn, a Borel-Pompeiu Formula, Cauchy Integral Formula and a Cauchy Transform are presented for the cylinders. Moreover we show a construction of a number of conformally inequivalent spinor bundles on these cylinders. Again we construct Rarita-Schwinger operators an...
Cylinder valve packing nut studies
Energy Technology Data Exchange (ETDEWEB)
Blue, S.C. [Martin Marietta Energy Systems, Inc., Paducah, KY (United States)
1991-12-31
The design, manufacture, and use of cylinder valve packing nuts have been studied to improve their resistance to failure from stress corrosion cracking. Stress frozen photoelastic models have been analyzed to measure the stress concentrations at observed points of failure. The load effects induced by assembly torque and thermal expansion of stem packing were observed by strain gaging nuts. The effects of finishing operations and heat treatment were studied by the strain gage hole boring and X-ray methods. Modifications of manufacturing and operation practices are reducing the frequency of stress corrosion failures.
Quantum Mechanics on the cylinder
González, J A; Tosiek, J
2003-01-01
A new approach to deformation quantization on the cylinder considered as phase space is presented. The method is based on the standard Moyal formalism for R^2 adapted to (S^1 x R) by the Weil--Brezin--Zak transformation. The results are compared with other solutions of this problem presented by Kasperkovitz and Peev (Ann. Phys. vol. 230, 21 (1994)0 and by Plebanski and collaborators (Acta Phys. Pol. vol. B 31}, 561 (2000)). The equivalence of these three methods is proved.
NONLINEAR FARADAY WAVES IN A PARAMETRICALLY EXCITED CIRCULAR CYLINDRICAL CONTAINER
Institute of Scientific and Technical Information of China (English)
菅永军; 鄂学全; 柏威
2003-01-01
In the cylindrical coordinate system, a singular perturbation theory of multiple-scale asymptotic expansions was developed to study single standing water wave mode bysolving potential equations of water waves in a rigid circular cylinder, which is subject to avertical oscillation. It is assumed that the fluid in the circular cylindrical vessel is inviscid ,incompressible and the motion is irrotational, a nonlinear amplitude equation with cubicand vertically excited terms of the vessel was derived by expansion of two-time scales withoutconsidering the effect of surface tension. It is shown by numerical computation that differentfree surface standing wave patterns will be formed in different excited frequencies andamplitudes. The contours of free surface waves are agreed well with the experimental resultswhich were carried out several years ago.
Inner cylinder of the CMS vacuum tank.
Patrice Loïez
2002-01-01
The vacuum tank of the CMS magnet system consists of inner and outer stainless-steel cylinders and houses the superconducting coil. The inner cylinder contains all the barrel sub-detectors, which it supports via a system of horizontal rails. The cylinder is pictured here in the vertical position on a yellow platform mounted on the ferris-wheel support structure. This will allow it to be pivoted and inserted into the outer cylinder already attached to the innermost ring of the barrel yoke.
Fire exposure of empty 30B cylinders
Energy Technology Data Exchange (ETDEWEB)
Ziehlke, K.T. [MJB Technical Associates, Inc., Knoxville, TN (United States)
1991-12-31
Cylinders for UF{sub 6} handling, transport, and storage are designed and built as unfired pressure vessels under ASME Boiler and Pressure Vessel Code criteria and standards. They are normally filled and emptied while UF{sub 6} is in its liquid phase. Transport cylinders such as the Model 30B are designed for service at 200 psi and 250{degrees}F, to sustain the process conditions which prevail during filling or emptying operations. While in transport, however, at ambient temperature the UF{sub 6} is solid, and the cylinder interior is well below atmospheric pressure. When the cylinders contain isotopically enriched product (above 1.0 percent U-235), they are transported in protective overpacks which function to guard the cylinders and their contents against thermal or mechanical damage in the event of possible transport accidents. Two bare Model 30B cylinders were accidentally exposed to a storage warehouse fire in which a considerable amount of damage was sustained by stored materials and the building structure, as well as by the cylinder valves and valve protectors. The cylinders were about six years old, and had been cleaned, inspected, hydrotested, and re-certified for service, but were still empty at the time of the fire. The privately-owned cylinders were transferred to DOE for testing and evaluation of the fire damage.
Overseas shipments of 48Y cylinders
Energy Technology Data Exchange (ETDEWEB)
Tanaka, R.T.; Furlan, A.S. [Cameco Corp., Port Hope, Ontario (Canada)
1991-12-31
This paper describes experiences with two incidents of overseas shipments of uranium hexafluoride (UF{sub 6}) cylinders. The first incident involved nine empty UF{sub 6} cylinders in enclosed sea containers. Three UF{sub 6} cylinders broke free from their tie-downs and damaged and contaminated several sea containers. This paper describes briefly how decontamination was carried out. The second incident involved a shipment of 14 full UF{sub 6} cylinders. Although the incident did not cause an accident, the potential hazard was significant. The investigation of the cause of the near accident is recounted. Recommendations to alleviate future similar incidents for both cases are presented.
Optimization and improvement of Halbach cylinder design
DEFF Research Database (Denmark)
Bjørk, Rasmus; Bahl, Christian Robert Haffenden; Smith, Anders;
2008-01-01
that this parameter was optimal for long Halbach cylinders with small rex. Using the previously mentioned additional blocks of magnets can improve the parameter by as much as 15% as well as improve the homogeneity of the field in the cylinder bore. ©2008 American Institute of Physics......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...
Oxygen transfer in circular surface aeration tanks.
Rao, Achanta Ramakrishna; Patel, Ajey Kumar; Kumar, Bimlesh
2009-06-01
Surface aeration systems employed in activated sludge plants are the most energy-intensive units of the plants and typically account for a higher percentage of the treatment facility's total energy use. The geometry of the aeration tank imparts a major effect on the system efficiency. It is said that at optimal geometric conditions, systems exhibits the maximum efficiency. Thus the quantification of the optimal geometric conditions in surface aeration tanks is needed. Optimal geometric conditions are also needed to scale up the laboratory result to the field installation. In the present work, experimental studies have been carried out on baffled and unbaffled circular surface aeration tanks to ascertain the optimal geometric conditions. It is found that no optimal geometric conditions exist for the liquid/water depth in circular surface aeration tanks; however, for design purposes, a standard value has been assumed. Based on the optimal geometric conditions, a scale-up equation has been developed for the baffled circular surface aeration tanks.
Effects of viscoelasticity in the high Reynolds number cylinder wake
Richter, David
2012-01-16
At Re = 3900, Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing the FENE-P rheological model) that viscoelasticity greatly reduces the amount of turbulence in the wake, reverting it back to a state which qualitatively appears similar to the Newtonian mode B instability which occurs at lower Re. By focusing on the separated shear layers, it is found that viscoelasticity suppresses the formation of the Kelvin-Helmholtz instability which dominates for Newtonian flows, consistent with previous studies of viscoelastic free shear layers. Through this shear layer stabilization, the viscoelastic far wake is then subject to the same instability mechanisms which dominate for Newtonian flows, but at far lower Reynolds numbers. © Copyright Cambridge University Press 2012.
Architectural Surfaces and Structures from Circular Arcs
Shi, Ling
2013-12-01
In recent decades, the popularity of freeform shapes in contemporary architecture poses new challenges to digital design. One of them is the process of rationalization, i.e. to make freeform skins or structures affordable to manufacture, which draws the most attention from geometry researchers. In this thesis, we aim to realize this process with simple geometric primitives, circular arcs. We investigate architectural surfaces and structures consisting of circular arcs. Our focus is lying on how to employ them nicely and repetitively in architectural design, in order to decrease the cost in manufacturing. Firstly, we study Darboux cyclides, which are algebraic surfaces of order ≤ 4. We provide a computational tool to identify all families of circles on a given cyclide based on the spherical model of M ̈obius geometry. Practical ways to design cyclide patches that pass through certain inputs are presented. In particular, certain triples of circle families on Darboux cyclides may be suitably arranged as 3-webs. We provide a complete classification of all possible 3-webs of circles on Darboux cyclides. We then investigate the circular arc snakes, which are smooth sequences of circu- lar arcs. We evolve the snakes such that their curvature, as a function of arc length, remains unchanged. The evolution of snakes is utilized to approximate given surfaces by circular arcs or to generated freeform shapes, and it is realized by a 2-step pro- cess. More interestingly, certain 6-arc snake with boundary constraints can produce a smooth self motion, which can be employed to build flexible structures. Another challenging topic is approximating smooth freeform skins with simple panels. We contribute to this problem area by approximating a negatively-curved 5 surface with a smooth union of rational bilinear patches. We provide a proof for vertex consistency of hyperbolic nets using the CAGD approach of the rational B ́ezier form. Moreover, we use Darboux transformations for the
Dynamics of immiscible liquids in a rotating horizontal cylinder
Kozlov, N. V.; Kozlova, A. N.; Shuvalova, D. A.
2016-11-01
The dynamics of an interface between two immiscible liquids of different density is studied experimentally in a horizontal cylinder at rotation in the gravity field. Two liquids entirely fill the cavity volume, and the container is rotated sufficiently fast so that the liquids are centrifuged. The light liquid forms a column extended along the rotation axis, and the heavy liquid forms an annular layer. Under the action of gravity, the light liquid column displaces steadily along the radius, downwards in the laboratory frame. As a result, fluid oscillations in the cavity frame are excited at the interface, which lead to the generation of a steady streaming, and the fluid comes into a slow lagging rotation with respect to the cylinder walls. The dynamics of the studied system is determined by the ratio of the gravity acceleration to the centrifugal one—the dimensionless acceleration. In experiments, the system is controlled by the means of variation of the rotation rate, i.e., of the centrifugal force. At a critical value of the dimensionless acceleration the circular interface looses stability, and an azimuthal wave is excited. This leads to a strong increase in the interface differential velocity. A theoretical analysis is done based on the theory of centrifugal waves and a frequency equation is obtained. Experimental results are in good agreement with the theory at the condition of small wave amplitudes. Mechanism of steady streaming generation is analyzed based on previously published theoretical results obtained for the limiting case when the light phase is a solid cylinder. A qualitative agreement is found.
Controlled oscillations of a cylinder: forces and wake modes
Carberry, J.; Sheridan, J.; Rockwell, D.
2005-08-01
The wake states from a circular cylinder undergoing controlled sinusoidal oscillation transverse to the free stream are examined. As the frequency of oscillation passes through the natural Kármán frequency there is a transition between two distinctly different wake states: the low- and high-frequency states. The transition corresponds to a change in the structure of the near wake and is also characterized by a jump in the phase and amplitude of both the total and vortex lift. Over the range of flow and oscillation parameters studied the wake states exhibit a number of universal features. The phases of the vortex lift and drag forces have characteristic values for the low- and high-frequency states, which appear to be directly related to the phase of vortex shedding. A split force concept is employed, whereby instantaneous force traces and images allow discrimination between the actual loading and the physics, and their conventional time-averaged representations. The wake states for the forced oscillations show some remarkable similarities to the response branches of elastically mounted cylinders. The equivalence between forced and self-excited oscillations is addressed in detail using concepts of energy transfer.
Gao, Steven; Zhu, Fuguo
2013-01-01
This book presents a comprehensive insight into the design techniques for different types of CP antenna elements and arrays In this book, the authors address a broad range of topics on circularly polarized (CP) antennas. Firstly, it introduces to the reader basic principles, design techniques and characteristics of various types of CP antennas, such as CP patch antennas, CP helix antennas, quadrifilar helix antennas (QHA), printed quadrifilar helix antennas (PQHA), spiral antenna, CP slot antennas, CP dielectric resonator antennas, loop antennas, crossed dipoles, monopoles and CP horns. Adva
A Convenient Storage Rack for Graduated Cylinders
Love, Brian
2004-01-01
An attempt is made to find a solution to the occasional problem of a need for storing large numbers of graduated cylinders in many teaching and research laboratories. A design, which involves the creation of a series of parallel channels that are used to suspend inverted graduated cylinders by their bases, is proposed.
Optimization and improvement of Halbach cylinder design
Bjørk, R; Smith, A; Pryds, N
2014-01-01
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, $r_{\\mathrm{\\scriptsize{in}}}$, external radius, $r_{\\mathrm{\\scriptsize{ex}}}$, and length, $L$, have been varied. Optimal values of $r_{\\mathrm{\\scriptsize{ex}}}$ 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 increase 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 $r_{\\mathrm{\\scriptsize{ex}}}$. Moreover magnetic cooling as an application for Halbach cylinders was considered. A magnetic cooling quality parameter, $\\Lambda_{\\mathrm{cool}}$, was introduced and results showed that this...
Walking droplets in confined geometries
Filoux, Boris; Mathieu, Olivier; Vandewalle, Nicolas
2014-11-01
When gently placing a droplet onto a vertically vibrated bath, coalescence may be avoided: the drop bounces permanently. Upon increasing forcing acceleration, a drop interacts with the wave it generates, and becomes a ``walker'' with a well defined velocity. In this work, we investigate the confinement of a walker in a mono-dimensional geometry. The system consists of linear submarine channels used as waveguides for a walker. By studying the dynamics of walkers in those channels, we discover some 1D-2D transition. We also propose a model based on an analogy with ``Quantum Wires.'' Finally, we consider the situation of a walker in a circular submarine channel, and examine the behavior of several walking droplets in this system. We show the quantization of the drop distances, and correlate it to their bouncing modes.
Bru, Luis A; Di Molfetta, Giuseppe; Pérez, Armando; Roldán, Eugenio; Silva, Fernando
2016-01-01
We consider the 2D alternate quantum walk on a cylinder. We concentrate on the study of the motion along the open dimension, in the spirit of looking at the closed coordinate as a small or "hidden" extra dimension. If one starts from localized initial conditions on the lattice, the dynamics of the quantum walk that is obtained after tracing out the small dimension shows the contribution of several components, which can be understood from the study of the dispersion relations for this problem. In fact, these components originate from the contribution of the possible values of the quasi-momentum in the closed dimension. In the continuous space-time limit, the different components manifest as a set of Dirac equations, with each quasi-momentum providing the value of the corresponding mass. We briefly discuss the possible link of these ideas to the simulation of high energy physical theories that include extra dimensions.
Mahé, Louis; Roy, Marie-Françoise
1992-01-01
Ten years after the first Rennes international meeting on real algebraic geometry, the second one looked at the developments in the subject during the intervening decade - see the 6 survey papers listed below. Further contributions from the participants on recent research covered real algebra and geometry, topology of real algebraic varieties and 16thHilbert problem, classical algebraic geometry, techniques in real algebraic geometry, algorithms in real algebraic geometry, semialgebraic geometry, real analytic geometry. CONTENTS: Survey papers: M. Knebusch: Semialgebraic topology in the last ten years.- R. Parimala: Algebraic and topological invariants of real algebraic varieties.- Polotovskii, G.M.: On the classification of decomposing plane algebraic curves.- Scheiderer, C.: Real algebra and its applications to geometry in the last ten years: some major developments and results.- Shustin, E.L.: Topology of real plane algebraic curves.- Silhol, R.: Moduli problems in real algebraic geometry. Further contribu...
Cylinder packing by simulated annealing
Directory of Open Access Journals (Sweden)
M. Helena Correia
2000-12-01
Full Text Available This paper is motivated by the problem of loading identical items of circular base (tubes, rolls, ... into a rectangular base (the pallet. For practical reasons, all the loaded items are considered to have the same height. The resolution of this problem consists in determining the positioning pattern of the circular bases of the items on the rectangular pallet, while maximizing the number of items. This pattern will be repeated for each layer stacked on the pallet. Two algorithms based on the meta-heuristic Simulated Annealing have been developed and implemented. The tuning of these algorithms parameters implied running intensive tests in order to improve its efficiency. The algorithms developed were easily extended to the case of non-identical circles.Este artigo aborda o problema de posicionamento de objetos de base circular (tubos, rolos, ... sobre uma base retangular de maiores dimensões. Por razões práticas, considera-se que todos os objetos a carregar apresentam a mesma altura. A resolução do problema consiste na determinação do padrão de posicionamento das bases circulares dos referidos objetos sobre a base de forma retangular, tendo como objetivo a maximização do número de objetos estritamente posicionados no interior dessa base. Este padrão de posicionamento será repetido em cada uma das camadas a carregar sobre a base retangular. Apresentam-se dois algoritmos para a resolução do problema. Estes algoritmos baseiam-se numa meta-heurística, Simulated Annealling, cuja afinação de parâmetros requereu a execução de testes intensivos com o objetivo de atingir um elevado grau de eficiência no seu desempenho. As características dos algoritmos implementados permitiram que a sua extensão à consideração de círculos com raios diferentes fosse facilmente conseguida.
Operational circular No. 1 (Rev. 1) – Operational circulars
HR Department
2011-01-01
Operational Circular No. 1 (Rev. 1) is applicable to members of the personnel and other persons concerned. Operational Circular No. 1 (Rev. 1) entitled "Operational circulars", approved following discussion at the Standing Concertation Committee meeting on 4 May 2011, is available on the intranet site of the Human Resources Department: https://hr-docs.web.cern.ch/hr-docs/opcirc/opcirc.asp It cancels and replaces Operational Circular No. 1 entitled "Operational Circulars” of December 1996. This new version clarifies, in particular, that operational circulars do not necessarily arise from the Staff Rules and Regulations, and the functional titles have been updated to bring them into line with the current CERN organigram. Department Head Office
Circularly Polarized MHOHG with Bichromatic Circularly Polarized Laser Pulses
Bandrauk, Andre D.; Mauger, Francois; Uzer, Turgay
2016-05-01
Circularly polarized MHOHG-Molecular High Order Harmonic Generation is shown to occur efficiently with intense ultrashort bichromatic circularly polarized pulses due to frequent electron-parent -ion recollision with co-or counter-rotating incident circular pulses as predicted in 1995. We show in this context that molecules offer a very robust and efficient frameworkfor the production of circularly polarized harmonics for the generation of single circularly polarized ``attosecond'' pulses. The efficiency of such new MHOHG is shown to depend on the compatibility of the symmetry of the molecular medium with the net electric field generated by the combination of the laser pulses.Using a time-dependent symmetry analysis with concrete examples such as H 2 + vs H 3 + we show how all the features(harmonic order and ∧ polarization) of MHOHG can be explained and predicted.
Digital Differential Geometry Processing
Institute of Scientific and Technical Information of China (English)
Xin-Guo Liu; Hu-Jun Bao; Qun-Sheng Peng
2006-01-01
The theory and methods of digital geometry processing has been a hot research area in computer graphics, as geometric models serves as the core data for 3D graphics applications. The purpose of this paper is to introduce some recent advances in digital geometry processing, particularly mesh fairing, surface parameterization and mesh editing, that heavily use differential geometry quantities. Some related concepts from differential geometry, such as normal, curvature, gradient,Laplacian and their counterparts on digital geometry are also reviewed for understanding the strength and weakness of various digital geometry processing methods.
Energy Technology Data Exchange (ETDEWEB)
Morton, C., E-mail: chris.morton@ucalgary.ca [Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Dr NW, Calgary, Alberta T2N 1N4 (Canada); Yarusevych, S. [Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Ave W, Waterloo, Ontario N2L 3G1 (Canada); Scarano, F. [Department of Aerospace Engineering, Delft University of Technology, 2628 Delft (Netherlands)
2016-02-15
This experimental study focuses on the near wake development of a dual step cylinder geometry consisting of a long base cylinder of diameter d to which a larger diameter (D) cylinder of length L is attached coaxially at mid-span. The experiments cover a range of Reynolds numbers, 2000 ≤ Re{sub D} ≤ 5000, diameter ratios, 1.33 ≤ D/d ≤ 2.0 and large cylinder aspect ratios, 0.5 ≤ L/D ≤ 5 using Tomographic particle image velocimetry. Distinct changes in wake topology are observed varying the above parameters. Supporting previous experimental studies on the same geometry involving flow visualization and planar measurements, four distinct flow regimes are identified to which a distinct three-dimensional wake topology can be associated. The vortex-dominated wake dynamical behaviour is investigated with Proper Orthogonal Decomposition (POD) and conditional averaging of three-dimensional velocity fields is used to exemplify the different shedding regimes. The conditionally averaged flow fields are shown to quantitatively resolve flow features equivalent to those obtained from a reduced order model consisting of the first ten to twenty POD modes, identifying the dominant vortex shedding cells and their interactions.
Nondestructive relative permittivity and loss tangent measurements using a split-cylinder resonator
Janezic, Michael Daniel
To keep pace with the expanding wireless and electronics industries, manufacturers are developing innovative materials for improving system performance, and there is a critical need to accurately characterize the electrical properties of these new materials at microwave frequencies. To address this need, this thesis develops a nondestructive method for measuring the relative permittivity and loss tangent of dielectric substrates using a split-cylinder resonator. Three theoretical models for the split-cylinder resonator are derived using mode-matching, least-squares boundary residual, and Hankel-transform methods, from which one can calculate the relative permittivity and loss tangent of a dielectric substrate from measurements of the split-cylinder resonator's TE0np resonant frequency and quality factor. Each of these models has several advantages over previously published models. First, the accuracy of the relative permittivity measurement is increased because each model accurately models the fringing fields that extend beyond the cylindrical-cavity sections. Second, to increase the accuracy of the loss tangent measurement, each model accurately separates the conductive metal losses of the split-cylinder resonator from the dielectric losses of the substrate. Finally, in contrast to previous models for the split-cylinder resonator that use only the TE011 resonant mode, each of the new models include the higher-order TE0np resonant modes, thereby broadening the frequency range over which one can make relative permittivity and loss tangent measurements. In a comparison of the three models, the mode-matching method was found to be superior on the basis of measurement accuracy and computational speed. Relative permittivity and loss tangent measurements for several dielectric materials are performed using a split-cylinder resonator and are in good agreement with measurements made using a circular-cylindrical cavity, split-post resonator, and dielectric post resonator
Jenkins, Luther N.; Khorrami, Mehdi R.; Choudhari, Meelan M.; McGinley, Catherine B.
2005-01-01
A joint computational and experimental study has been performed at NASA Langley Research Center to investigate the unsteady flow generated by the components of an aircraft landing gear system. Because the flow field surrounding a full landing gear is so complex, the study was conducted on a simplified geometry consisting of two cylinders in tandem arrangement to isolate and characterize the pertinent flow phenomena. This paper focuses on the experimental effort where surface pressures, 2-D Particle Image Velocimetry, and hot-wire anemometry were used to document the flow interaction around the two cylinders at a Reynolds Number of 1.66 x 10(exp 5), based on cylinder diameter, and cylinder spacing-todiameter ratios, L/D, of 1.435 and 3.70. Transition strips were applied to the forward cylinder to produce a turbulent boundary layer upstream of the flow separation. For these flow conditions and L/D ratios, surface pressures on both the forward and rear cylinders show the effects of L/D on flow symmetry, base pressure, and the location of flow separation and attachment. Mean velocities and instantaneous vorticity obtained from the PIV data are used to examine the flow structure between and aft of the cylinders. Shedding frequencies and spectra obtained using hot-wire anemometry are presented. These results are compared with unsteady, Reynolds-Averaged Navier-Stokes (URANS) computations for the same configuration in a companion paper by Khorrami, Choudhari, Jenkins, and McGinley (2005). The experimental dataset produced in this study provides information to better understand the mechanisms associated with component interaction noise, develop and validate time-accurate computer methods used to calculate the unsteady flow field, and assist in modeling of the radiated noise from landing gears.
Conceptual Ideas for New Nondestructive UF6 Cylinder Assay Techniques
Energy Technology Data Exchange (ETDEWEB)
Miller, Karen A. [Los Alamos National Laboratory
2012-05-02
Nondestructive assay (NDA) measurements of uranium cylinders play an important role in helping the International Atomic Energy Agency (IAEA) safeguard uranium enrichment plants. Traditionally, these measurements have consisted of a scale or load cell to determine the mass of UF{sub 6} in the cylinder combined with a gamma-ray measurement of the 186 keV peak from {sup 235}U to determine enrichment. More recently, Los Alamos National Laboratory (LANL) and Pacific Northwest National Laboratory (PNNL) have developed systems that exploit the passive neutron signal from UF{sub 6} to determine uranium mass and/or enrichment. These include the Uranium Cylinder Assay System (UCAS), the Passive Neutron Enrichment Meter (PNEM), and the Hybrid Enrichment Verification Array (HEVA). The purpose of this report is to provide the IAEA with new ideas on technologies that may or may not be under active development but could be useful for UF{sub 6} cylinder assay. To begin, we have included two feasibility studies of active interrogation techniques. There is a long history of active interrogation in the field of nuclear safeguards, especially for uranium assay. Both of the active techniques provide a direct measure of {sup 235}U content. The first is an active neutron method based on the existing PNEM design that uses a correlated {sup 252}Cf interrogation source. This technique shows great promise for UF{sub 6} cylinder assay and is based on advanced technology that could be implemented in the field in the near term. The second active technique is nuclear resonance fluorescence (NRF). In the NRF technique, a bremsstrahlung photon beam could be used to illuminate the cylinder, and high-resolution gamma-ray detectors would detect the characteristic de-excitation photons. The results of the feasibility study show that under certain measurement geometries, NRF is impractical for UF6 cylinder assay, but the 'grazing transmission' and 'secant transmission' geometries
Oscillations and translation of a free cylinder in a confined flow
D'Angelo, Maria Veronica; 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 velocity U of the fluid and of its viscosity. For a blockage ratio D/H above 0.5 and a Reynolds number Re larger then 14, oscillations of the rolling angle of the cylinder about its axis and of its transverse coordinate in the gap are observed together with periodic variations of the vertical velocity. Their frequency f is the same for the sedimentation of the cylinder in a static fluid (U = 0) and for a non-zero mean flow (U 6= 0). The Strouhal number St associated to the oscillation varies as 1/Re with : St.Re = 3 $\\pm$ 0.15....
VORTEX INDUCED VIBRATIONS OF FINNED CYLINDERS
Institute of Scientific and Technical Information of China (English)
SHA Yong; WANG Yong-xue
2008-01-01
This article presents the results of a numerical simulation on the vortex induced vibration of various finned cylinders at low Reynolds number. The non-dimensional, incompressible Navier-Stokes equations and continuity equation were adopted to simulate the fluid around the cylinder. The cylinder (with or without fins) in fluid flow was approximated as a mass-spring system. The fluid-body interaction of the cylinder with fins and uniform flow was numerically simulated by applying the displacement and stress iterative computation on the fluid-body interfaces. Both vortex structures and response amplitudes of cylinders with various arrangements of fins were analyzed and discussed. The remarkable decrease of response amplitude for the additions of Triangle60 fins and Quadrangle45 fins was found to be comparable with that of bare cylinder. However, the additions of Triangle00 fins and Quadrangle00 fins enhance the response amplitude greatly. Despite the assumption of two-dimensional laminar flow, the present study can give a good insight into the phenomena of cylinders with various arrangements of fins.
Institute of Scientific and Technical Information of China (English)
GUO Enli; MO Xiaohuan
2006-01-01
In this paper,a survey on Riemann-Finsler geometry is given.Non-trivial examples of Finsler metrics satisfying different curvature conditions are presented.Local and global results in Finsler geometry are analyzed.
Meyer, Walter J
2006-01-01
Meyer''s Geometry and Its Applications, Second Edition, combines traditional geometry with current ideas to present a modern approach that is grounded in real-world applications. It balances the deductive approach with discovery learning, and introduces axiomatic, Euclidean geometry, non-Euclidean geometry, and transformational geometry. The text integrates applications and examples throughout and includes historical notes in many chapters. The Second Edition of Geometry and Its Applications is a significant text for any college or university that focuses on geometry''s usefulness in other disciplines. It is especially appropriate for engineering and science majors, as well as future mathematics teachers.* Realistic applications integrated throughout the text, including (but not limited to): - Symmetries of artistic patterns- Physics- Robotics- Computer vision- Computer graphics- Stability of architectural structures- Molecular biology- Medicine- Pattern recognition* Historical notes included in many chapters...
Expansion of Metallic Cylinders under Explosive Loading
Directory of Open Access Journals (Sweden)
M.S. Bola
1992-07-01
Full Text Available The behaviour of expanding metallic cylinders under explosive loading was studied. Using ultra high speed photography, the expansion characteristics of aluminium and copper metallic cylinders have been evaluated with different c/m ratio, and by changing the nature of high explosive. The results obtained are comparable to those predicted by the Gurney's energy and momentum balance equations. A cylinder test has been established for comparative to the metal by octol, TNT, PEK-1, baratol and composition B are calculated. The results are in close agreement with those calculated by Kury et al.
Mofakhami, M.R.; H. Hosseini Toudeshky; Sh. Hosseini Hashemi
2008-01-01
In this paper sound transmission through the multilayered viscoelastic air filled cylinders subjected to the incident acoustic wave is studied using the technique of separation of variables on the basis of linear three dimensional theory of elasticity. The effect of interior acoustic medium on the mode maps (frequency vs geometry) and noise reduction is investigated. The effects of internal absorption and external moving medium on noise reduction are also evaluated. The dynamic viscoelastic p...
Reduction in NO{sub x} emission of diesel engines by in-cylinder catalysis
Energy Technology Data Exchange (ETDEWEB)
Bannikov, M.G.; Draper, P.H.; Chattha, J.A. [Ghulam Ishaq Khan Institute of Engineering Sciences and Technology (Pakistan); Vasilev, I.P.; Gavrilenko, P.N. [East Ukrainian National University (Ukraine)
2003-07-01
In-cylinder catalysis as a method for reducing the nitrogen oxides emission of diesel engines has been investigated experimentally. Desirable effects could be achieved only when intensive interaction of combustion products with the catalyst-coated surface was provided. It was found that a design based on a combustion chamber of variable geometry could give useful results, particularly for non-turbocharged engines. (author)
Ratchetting and creep-fatigue evaluation for nozzle-to-cylinder intersection. [LMFBR
Energy Technology Data Exchange (ETDEWEB)
Barsoum, R.S.; Loomis, R.W.; Stewart, B.D.
1976-01-01
The study is part of an analytical investigation on the applicability of the simplified ratchetting and creep-fatigue rules to LMFBR component geometry. Both the detailed inelastic rules and the simplified elastic rules are applied to the results obtained from a three-dimensional finite element analysis of the nozzle-to-cylinder intersection. The results of both evaluations are compared at several locations on the surface, and an assessment of the degree of conservatism of the simplified methods is discussed.
ESTIMATION OF 2-D DOA USING NON-CIRCULAR MUSIC METHOD FOR UNIFORM CIRCULAR AND RECTANGULAR ARRAYS
Institute of Scientific and Technical Information of China (English)
Li Rui; Shi Xiaowei; Xu Le; Bi Xiaojun; Li Ping
2011-01-01
This paper extends the Non-Circular MUltiple SIgnal Classification (MUSIC) (NC-MUSIC)method for the common array geometries including Uniform Circular Arrays (UCAs) and Uniform Rectangular Arrays (URAs),which enables the algorithm to estimate 2-D Direction Of Arrival (DOA).A comparison between UCAs and URAs of NC-MUSIC is made in this paper.The simulations show that the NC-MUSIC method doubles the maximum estimation number of standard MUSIC.Using non-circular signals,the performance of URAs is improved remarkably while the improvement of UCAs is not so significantly.Moreover,the influence of arrays structures on the NC-MUSIC method is dis-cussed.
Investigation of Effect of Boundary Layer on Flow Structure Around a Cylinder with a Strip
Directory of Open Access Journals (Sweden)
Yayla Sedat
2015-01-01
Full Text Available In this study, the flow characteristic of the circular cylinder was placed vertically in channel which has dimensions as 8000 mm, 1000 mm, 750 mm, lenght, width and height repectively, was investigated. The cylinder was located in boundary layer with a diameter of 60 mm (D and a elastic stripwhich has a 1400 N/mm2 modulus of elasticity vinyl PVC transperent film was attached behind the cylinder. Lenght of the strip (L was 240 mm L/D=4. The Reynolds number was fixed at Re=7500. The time-averaged and instantaneous velocity vector maps, vorticity contours, Reynold shear and normal stresses, turbulent kinetic energy and frequency of shedding were obtained using the particle image velocimetry (PIV technique. It was found that the elastic plate which exists behind the cylinder has a slight influence on the flow structure of the wake-boundary layer interaction. Values of turbulent kinetic energy, streamwise Reynold stress, transverse Reynold stresses were decreased by attaching strip.
3D measurement using circular gratings
Harding, Kevin
2013-09-01
3D measurement using methods of structured light are well known in the industry. Most such systems use some variation of straight lines, either as simple lines or with some form of encoding. This geometry assumes the lines will be projected from one side and viewed from another to generate the profile information. But what about applications where a wide triangulation angle may not be practical, particularly at longer standoff distances. This paper explores the use of circular grating patterns projected from a center point to achieve 3D information. Originally suggested by John Caulfield around 1990, the method had some interesting potential, particularly if combined with alternate means of measurement from traditional triangulation including depth from focus methods. The possible advantages of a central reference point in the projected pattern may offer some different capabilities not as easily attained with a linear grating pattern. This paper will explore the pros and cons of the method and present some examples of possible applications.
Spontaneous helicity of a polymer with side-loops confined to a cylinder
Chaudhuri, Debasish
2011-01-01
Inspired by recent experiments on the spatial organization of bacterial chromosomes, we consider a type of "bottle brush" polymer consisting of a flexible backbone chain, to which flexible side loops are connected. We show that such a model with an open linear backbone spontaneously adopts a helical structure with a well-defined pitch when confined to small cylindrical volume. This helicity persists over a range of sizes and aspect-ratios of the cylinder, provided the packing fraction of the chain is suitably large. We analyze this results in terms of the interplay between the effective stiffness and actual intra-chain packing effects caused by the side-loops in response to the confinement. For the case of a circular backbone, mimicking e.g. the E. coli chromosome, the polymer adopts a linearized configuration of two parallel helices connected at the cylinder poles.
Effects of wind-tunnel noise on swept-cylinder transition at Mach 3.5
Creel, T. R., Jr.; Beckwith, I. E.; Chen, F.-J.
1986-01-01
Transition data are reported for circular cylinders at swept angles of 45 and 60 degrees in the Mach 3.5 pilot-low-disturbance tunnel where free-stream noise levels are varied from approximately .05-0.5 percent in terms of the rms fluctuating pressure normalized by the mean static pressure. Results indicate that end plate or boundary layer trip disturbances at the upstream end of the cylinders cause turbulent flow along the entire test Reynolds number range of 10-170 thousand per inch. With all end plate and trip disturbances removed, transition at the attachment lines occurred at free-stream Reynolds numbers based on diameters of about 70-80 thousand, independent of stream noise levels. The installation of small trips on the attachement lines caused transition at lower Reynolds numbers, depending on both the roughness height and the wind tunnel noise level.
Towards Future Circular Colliders
AUTHOR|(CDS)2108454; Zimmermann, Frank
2016-01-01
The Large Hadron Collider (LHC) at CERN presently provides proton-proton collisions at a centre-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics programme will extend through the second half of the 2030’s. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ∼100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCC-ee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on $Nb_3Sn$ superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton c...
AUTHOR|(CDS)2108454; Zimmermann, Frank
2015-01-01
In response to a request from the 2013 Update of the European Strategy for Particle Physics, the global Future Circular Collider (FCC) study is preparing the foundation for a next-generation large-scale accelerator infrastructure in the heart of Europe. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh), to be accommodated in a new ∼100 km tunnel near Geneva. It also includes the design of a high-luminosity electron-positron collider (FCC-ee), which could be installed in the same tunnel as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3Sn superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton collider. The interna...
AUTHOR|(CDS)2108454; Zimmermann, Frank
2015-01-01
In response to a request from the 2013 Update of the European Strategy for Particle Physics, the global Future Circular Collider (FCC) study is preparing the foundation for a next-generation large-scale accelerator infrastructure in the heart of Europe. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh), to be accommodated in a new ∼100 km tunnel near Geneva. It also includes the design of a high-luminosity electron-positron collider (FCC-ee), which could be installed in the same tunnel as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detector, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3Sn superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton collider. The internat...
Introduction to projective geometry
Wylie, C R
2008-01-01
This lucid introductory text offers both an analytic and an axiomatic approach to plane projective geometry. The analytic treatment builds and expands upon students' familiarity with elementary plane analytic geometry and provides a well-motivated approach to projective geometry. Subsequent chapters explore Euclidean and non-Euclidean geometry as specializations of the projective plane, revealing the existence of an infinite number of geometries, each Euclidean in nature but characterized by a different set of distance- and angle-measurement formulas. Outstanding pedagogical features include w
Symplectic geometries on supermanifolds
Lavrov, P M
2007-01-01
Extension of symplectic geometry on manifolds to the supersymmetric case is considered. In the even case it leads to the even symplectic geometry (or, equivalently, to the geometry on supermanifolds endowed with an non-degenerate Poisson bracket) or to the geometry on an even Fedosov supermanifolds. It is proven that in the odd case there are two different scalar symplectic structures (namely, an odd closed differential 2-form and the antibracket) which can be used for construction of different symplectic geometries on supermanifolds.
Multipole Analysis of Circular Cylindircal Magnetic Systems
Energy Technology Data Exchange (ETDEWEB)
Selvaggi, Jerry P. [Rensselaer Polytechnic Inst., Troy, NY (United States)
2005-12-01
This thesis deals with an alternate method for computing the external magnetic field from a circular cylindrical magnetic source. The primary objective is to characterize the magnetic source in terms of its equivalent multipole distribution. This multipole distribution must be valid at points close to the cylindrical source and a spherical multipole expansion is ill-equipped to handle this problem; therefore a new method must be introduced. This method, based upon the free-space Green's function in cylindrical coordinates, is developed as an alternative to the more familiar spherical harmonic expansion. A family of special functions, called the toroidal functions or Q-functions, are found to exhibit the necessary properties for analyzing circular cylindrical geometries. In particular, the toroidal function of zeroth order, which comes from the integral formulation of the free-space Green's function in cylindrical coordinates, is employed to handle magnetic sources which exhibit circular cylindrical symmetry. The toroidal functions, also called Q-functions, are the weighting coefficients in a ''Fourier series-like'' expansion which represents the free-space Green's function. It is also called a toroidal expansion. This expansion can be directly employed in electrostatic, magnetostatic, and electrodynamic problems which exhibit cylindrical symmetry. Also, it is shown that they can be used as an alternative to the Elliptic integral formulation. In fact, anywhere that an Elliptic integral appears, one can replace it with its corresponding Q-function representation. A number of problems, using the toroidal expansion formulation, are analyzed and compared to existing known methods in order to validate the results. Also, the equivalent multipole distribution is found for most of the solved problems along with its corresponding physical interpretation. The main application is to characterize the external magnetic field due to a six
Magnetohydrodynamic Flow Between Concentric Rotating Porous Cylinders
Directory of Open Access Journals (Sweden)
S. N. Dube
1971-10-01
Full Text Available An attempt has been made to study the steady laminar flow of a incompressible electrically conducting fluid between infinitely long concentric rotating porous cylinders under the influence of radial magnetic field. A solution has been obtained under the assumption of uniform conditions along the axis of the cylinders. The cylinders being porous, a hyperbolic radial velocity distribution has been superimposed over the circumferential velocity produced due to rotation. There is a Bernoulli type pressure variation in the radial in the direction. When the inner cylinder is at rest the shearing stress at it and the torque transmitted to it decrease as R (=v/Sub/1y/Sub1/v= v/Sub2y/Sub2/v increases and the magnetic parameter lambda (=4sigma mue/sube/sup2A/Sup2/Mue will further decrease them.
Stepanishen, P. R.; Ramakrishna, S.
1994-09-01
A new internal source distribution method is combined with the singular value decomposition method to determine the acoustic impedance and associated impulse response for an infinite cylinder with a plane of symmetry and a normal velocity with a specified circumferential variation. An internal linear distribution of unknown monopole and/or dipole line sources along the plane of symmetry is determined to match the specified harmonic normal velocity on the surface in a least mean square error sense. After the discretization of the source distributions, the subsequent solution of a set or sets of linear algebraic equations for the internal source distributions is obtained using the singular value decomposition method. Line integrals for the associated surface pressure, the acoustic impedance and the corresponding impulse response are then simply evaluated by quadrature methods. Numerical results for the acoustic impedances and associated impulse responses are presented for circular cylinders vibrating with various natural in vacuo modal shapes. Numerical results for acoustic impedances and associated impulse responses for elliptical cylinders vibrating with various natural in vacuo modal shapes are then presented, and their characteristics are discussed and compared to the corresponding results for circular cylinders.
Methods for euclidean geometry
Byer, Owen; Smeltzer, Deirdre L
2010-01-01
Euclidean plane geometry is one of the oldest and most beautiful topics in mathematics. Instead of carefully building geometries from axiom sets, this book uses a wealth of methods to solve problems in Euclidean geometry. Many of these methods arose where existing techniques proved inadequate. In several cases, the new ideas used in solving specific problems later developed into independent areas of mathematics. This book is primarily a geometry textbook, but studying geometry in this way will also develop students' appreciation of the subject and of mathematics as a whole. For instance, despite the fact that the analytic method has been part of mathematics for four centuries, it is rarely a tool a student considers using when faced with a geometry problem. Methods for Euclidean Geometry explores the application of a broad range of mathematical topics to the solution of Euclidean problems.
Gualtieri, Marco
2010-01-01
Generalized Kahler geometry is the natural analogue of Kahler geometry, in the context of generalized complex geometry. Just as we may require a complex structure to be compatible with a Riemannian metric in a way which gives rise to a symplectic form, we may require a generalized complex structure to be compatible with a metric so that it defines a second generalized complex structure. We explore the fundamental aspects of this geometry, including its equivalence with the bi-Hermitian geometry on the target of a 2-dimensional sigma model with (2,2) supersymmetry, as well as the relation to holomorphic Dirac geometry and the resulting derived deformation theory. We also explore the analogy between pre-quantum line bundles and gerbes in the context of generalized Kahler geometry.
Dynamic Fracture Simulations of Explosively Loaded Cylinders
Energy Technology Data Exchange (ETDEWEB)
Arthur, Carly W. [Univ. of California, Davis, CA (United States). Dept. of Civil and Environmental Engineering; Goto, D. M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2015-11-30
This report documents the modeling results of high explosive experiments investigating dynamic fracture of steel (AerMet® 100 alloy) cylinders. The experiments were conducted at Lawrence Livermore National Laboratory (LLNL) during 2007 to 2008 [10]. A principal objective of this study was to gain an understanding of dynamic material failure through the analysis of hydrodynamic computer code simulations. Two-dimensional and three-dimensional computational cylinder models were analyzed using the ALE3D multi-physics computer code.
Energy Technology Data Exchange (ETDEWEB)
Hill, L.G.; Catanach, R.A.
1998-07-01
Five 1-inch diameter cylinder tests were fired in support of the W-76 high explosive surveillance program. Three of the tests used baseline material, and two used stockpile return material. The diagnostics were electrical pins to measure detonation velocity and a streak camera to measure wall motion. The data was analyzed for cylinder energy, Gurney energy, and detonation velocity. The results of all three measures were consistent for all five tests, to within the experimental accuracy.
Study of Multi-Cylinder Engine Manifolds
1944-10-31
were developed so that mnifolds for any number of cylinders could be analyzed for max- I= zm volumetrie efficiency. Eletricaleebanioal analoCies can be...deceleration of the air& The vibrations are almot Identical to thse In single cylinder intake pipes. The mmi- a= volumetrie efficiency bould be...pipe 14 in. total volume 7- In- 3 area of pipew 0.86 in 2 Table I gives the actual and calculated speeds for peak volumetri efficiencies for a sIngle
Statistical analyses of a screen cylinder wake
Mohd Azmi, Azlin; Zhou, Tongming; Zhou, Yu; Cheng, Liang
2017-02-01
The evolution of a screen cylinder wake was studied by analysing its statistical properties over a streamwise range of x/d={10-60}. The screen cylinder was made of a stainless steel screen mesh of 67% porosity. The experiments were conducted in a wind tunnel at a Reynolds number of 7000 using an X-probe. The results were compared with those obtained in the wake generated by a solid cylinder. It was observed that the evolution of the statistics in the wake of the screen cylinder was different from that of a solid cylinder, reflecting the differences in the formation of the organized large-scale vortices in both wakes. The streamwise evolution of the Reynolds stresses, energy spectra and cross-correlation coefficients indicated that there exists a critical location that differentiates the screen cylinder wake into two regions over the measured streamwise range. The formation of the fully formed large-scale vortices was delayed until this critical location. Comparison with existing results for screen strips showed that although the near-wake characteristics and the vortex formation mechanism were similar between the two wake generators, variation in the Strouhal frequencies was observed and the self-preservation states were non-universal, reconfirming the dependence of a wake on its initial condition.
Extension to nonlinear stability theory of the circular Couette flow
Yau, Pun Wong; Wang, Shixiao; Rusak, Zvi
2016-11-01
A nonlinear stability analysis of the viscous circular Couette flow to axisymmetric perturbations under axial periodic boundary conditions is developed. The analysis is based on investigating the properties of a reduced Arnol'd energy-Casimir function Ard of Wang (2009). We show that all the inviscid flow effects as well as all the viscous-dependent terms related to the flow boundaries vanish. The evolution of ΔArd depends solely on the viscous effects of the perturbation's dynamics inside the flow domain. The requirement for the temporal decay of ΔArd leads to novel sufficient conditions for the nonlinear stability of the circular Couette flow in response to axisymmetric perturbations. Comparisons with historical studies show that our results shed light on the experimental measurements of Wendt (1933) and significantly extend the classical nonlinear stability results of Serrin (1959) and Joseph & Hung (1971). When the flow is nonlinearly stable and evolves axisymmetrically for all time, then it always decays asymptotically in time to the circular Couette flow determined uniquely by the setup of the rotating cylinders. This study provides new physical insights into a classical flow problem that was studied for decades.
Digitalizing the Circular Economy
Reuter, Markus A.
2016-12-01
Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of metallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT. It is the linkage of the global carrier metallurgical processing system infrastructure that maximizes the recovery of all minor and technology elements in its associated refining metallurgical infrastructure. This will be illustrated through the following: (1) System optimization models for multimetal metallurgical processing. These map large-scale m-IoT systems linked to computer-aided design tools of the original equipment manufacturers and then establish a recycling index through the quantification of RE. (2) Reactor optimization and industrial system solutions to realize the "CE (within a) Corporation—CEC," realizing the CE of society. (3) Real-time measurement of ore and scrap properties in intelligent plant structures, linked to the modeling, simulation, and optimization of industrial extractive process
Towards future circular colliders
Benedikt, Michael; Zimmermann, Frank
2016-09-01
The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030's. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ˜100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e - Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.
Wang, Shaofei; Liu, Yingzheng
2016-03-01
The wake dynamics behind a seal-vibrissa-shaped cylinder, which are closely related to the seal's extraordinary ability to faithfully track the hydrodynamic trails of its upstream prey, were extensively studied by using time-resolved particle image velocity. Four cylindrical configurations that shared the same hydrodynamic diameter (i.e., a circular cylinder, an elliptical cylinder, a wavy cylinder, and a vibrissa-shaped cylinder) were chosen for the comparative study at the Reynolds number 1.8 × 103. The instantaneous flow fields behind the cylinders were measured along their vertical and horizontal planes. The distinct global differences between the wakes were determined from the streamline patterns, the reverse-flow intermittences, and both the streamwise and longitudinal velocity fluctuation intensities. Compared to the other three systems tested, the vibrissa-shaped cylinder system was characterized by a considerably reduced recirculation zone in the nodal plane, the existence of a very stably reversed flow, and substantial reductions in the streamwise and longitudinal velocity fluctuation intensities. Further cross-correlation of the fluctuating longitudinal velocities showed that the unsteady events behind the vibrissa-shaped cylinder were poorly organized by sequence and considerably constrained in their spatial extent. Finally, a dynamic mode decomposition (DMD) was performed on the instantaneously varying wake flows. In the wavy cylinder system, a single dominant DMD mode at St = 0.2 (corresponding to Karman vortex street) was detected in both the saddle and nodal planes. Although the dominant DMD modes at St = 0.23 and 0.3 were determined in the saddle and nodal planes of the vibrissa-shaped cylinder system, respectively, the spatial pattern of these two DMD modes showed resolved vortical structures that were highly distorted and constrained to an extremely limited space. These DMD modes had much less energy than those in the other three systems. The
Vortex-induced Vibration of a Flexible Free-hanging Circular Cantilever
Directory of Open Access Journals (Sweden)
R. W. Prastianto
2009-11-01
Full Text Available An experimental investigation on time-dependent motion of a flexible free-hanging circular cantilever subjected to uniform cross-flows has been carried out. The free-end condition cantilever has a 34.4 aspect ratio and a low mass ratio of about 1.24. The cylinder freely oscillates in both inline and transverse to the flow. Reynolds number varied from 10,800 to 37,800. The “jump phenomenon” was also found in the inline motion of the cylinder that agrees well with an existing comparable work, even occurred at lower flow velocity, Ur, due to distinct conditions of the test. At high flow velocities, the 3rd higher harmonic frequencies of the cylinder transverse response became predominant that produce quite different motion characteristics compared to the other existing comparable works with 2-dimensional bottom-end condition, even same in bidirectional motion aspect. Generally, the results suggested that the flexible free-hanging cantilever generate different vortex wake mode than either, a uniform (a short-rigid flexibly-mounted cylinder or a linear amplitude variation along the span case (a pivoted cylinder.
The compaction of a random distribution of metal cylinders by the discrete element method
DEFF Research Database (Denmark)
Redanz, Pia; Fleck, N. A.
2001-01-01
The cold compaction of a 2D random distribution of metal circular cylinders has been investigated numerically by the discrete element method. Each cylindrical particle is located by a node at its centre and the plastic indentation of the contacts between neighbouring particles is represented by non...... takes place. leading to yield surfaces of similar shape but about half the size of that found for affine motion, as reported in [J. Mech. Phys. Solids 40 (1992) 1139 43 (1995) 1409; 47 (1999) 785]. An increase in the level of inter-particle friction leads to a reduction in the degree of local particle...
RESULTS RESULTING FROM AUTOFRETTAGE OF CYLINDER
Institute of Scientific and Technical Information of China (English)
ZHU Ruilin
2008-01-01
Autofrettage is used to introduce advantageous residual stresses into wall of a cylinder and to even distributions of total stresses. Basic theory on autofrettage has been functioning for several decades. It is necessary to reveal profound relations between parameters in the theory. Therefore, based on the 3rd strength theory, δei/δy, δei/δy, δei′/δy, δei′/δy and their relations, as well as p/δy, are studied under ideal conditions, where δei/δy is equivalent stress of total stresses at elastoplastic juncture/yield strength, δei/δy is equivalent stress of total stresses at inside surface/yield strength, δei′/δy is equivalent stress of residual stresses at elastoplastic juncture/yield strength, δei′/δy is equivalent stress of residual stresses at inside surface/yield strength, p/δy is load-bearing capacity of an autofrettaged cylinder/yield strength. Theoretical study on the parameters results in noticeable results and laws. The main idea is: to satisfy |δei′|=δy, the relation between kj and k is , where k is outside/inside radius ratio of a cylinder, kj is ratio of elastoplastic juncture radius to inside radius of a cylinder; when the plastic region covers the whole wall of a cylinder, for compressive yield not to occur after removing autofrettage pressure, the ultimate k is k=2.218 46, with k=2.218 46, a cylinder's ultimate load-bearing capacity equals its entire yield pressure, or =lnk; when kj≤=1.648 72, no matter how great k is, compressive yield never occurs after removing pa; the maximum and optimum load-bearing capacity of an autofrettaged cylinder is just two times the loading which an unautofrettaged cylinder can bear elastically, or , thus the limit of the load-bearing capacity of an autofrettaged cylinder is also just 2 times that of an unautofrettaged cylinder.
An efficient domain decomposition strategy for wave loads on surface piercing circular cylinders
DEFF Research Database (Denmark)
Paulsen, Bo Terp; Bredmose, Henrik; Bingham, Harry B.
2014-01-01
A fully nonlinear domain decomposed solver is proposed for efficient computations of wave loads on surface piercing structures in the time domain. A fully nonlinear potential flow solver was combined with a fully nonlinear Navier–Stokes/VOF solver via generalized coupling zones of arbitrary shape...
Experimental Study of Wave Forces on Vertical Circular Cylinders in Long and Short Crested Sea
DEFF Research Database (Denmark)
Høgedal, Michael
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 ...... with miniature pressure transducers. The experiments were carried out in the 3-D wave tank in the Hydraulics & Coastal Engineering Laboratory at Aalborg University and in the off-shore basin at the Danish Hydraulic Institute....
Accurate computation of wave loads on a bottom fixed circular cylinder
DEFF Research Database (Denmark)
Paulsen, Bo Terp; Bredmose, Henrik; Bingham, Harry B.
2012-01-01
to a range of other problems. The central idea is to drive an inner CFD model that resolves the flow around the structure with an outer wave model that is based on potential flow theory. By letting the potential flow solver describe the waves in the outer flow domain and the Navier-Stokes solver describe......-dimensional water waves up to the point of breaking. The CFD solver is the open source CFD toolbox OpenFOAMR in combination with the newly developed waves2Foam utility, which in [5] has been successfully applied to calculations of free surface flows. The numerical solution is obtained by solving the incompressible...
Bárány, Imre; Vilcu, Costin
2016-01-01
This volume presents easy-to-understand yet surprising properties obtained using topological, geometric and graph theoretic tools in the areas covered by the Geometry Conference that took place in Mulhouse, France from September 7–11, 2014 in honour of Tudor Zamfirescu on the occasion of his 70th anniversary. The contributions address subjects in convexity and discrete geometry, in distance geometry or with geometrical flavor in combinatorics, graph theory or non-linear analysis. Written by top experts, these papers highlight the close connections between these fields, as well as ties to other domains of geometry and their reciprocal influence. They offer an overview on recent developments in geometry and its border with discrete mathematics, and provide answers to several open questions. The volume addresses a large audience in mathematics, including researchers and graduate students interested in geometry and geometrical problems.
Explorations of Dusty Debris Disk Geometry
Dennihy, E; Clemens, J C
2016-01-01
As the sample of white dwarfs with signatures of planetary systems has grown, statistical studies have begun to suggest our picture of compact debris disk formation from disrupted planetary bodies is incomplete. Here we present the results of an effort to extend the preferred dust disk model introduced by \\citet{jur03} to include elliptical geometries. We apply this model the observed distribution of fractional infrared luminosities, and explore the difference in preferred parameter spaces for a circular and highly elliptical model on a well-studied dusty white dwarf.
Holonomy in the Schwarzschild-Droste Geometry
Rothman, T; Murugan, J; Rothman, Tony; Ellis, George F. R.; Murugan, Jeff
2001-01-01
Parallel transport of vectors in curved spacetimes generally results in a deficit angle between the directions of the initial and final vectors. We examine such holonomy in the Schwarzschild-Droste geometry and find a number of interesting features that are not widely known. For example, parallel transport around circular orbits results in a quantized band structure of holonomy invariance. We also examine radial holonomy and extend the analysis to spinors and to the Reissner-Nordstr\\"om metric, where we find qualitatively different behavior for the extremal ($Q = M$) case. Our calculations provide a toolbox that will hopefully be useful in the investigation of quantum mechanical problems involving parallel transport.
Euclidean geometry and transformations
Dodge, Clayton W
1972-01-01
This introduction to Euclidean geometry emphasizes transformations, particularly isometries and similarities. Suitable for undergraduate courses, it includes numerous examples, many with detailed answers. 1972 edition.
O'Leary, Michael
2010-01-01
Guides readers through the development of geometry and basic proof writing using a historical approach to the topic. In an effort to fully appreciate the logic and structure of geometric proofs, Revolutions of Geometry places proofs into the context of geometry's history, helping readers to understand that proof writing is crucial to the job of a mathematician. Written for students and educators of mathematics alike, the book guides readers through the rich history and influential works, from ancient times to the present, behind the development of geometry. As a result, readers are successfull
Fundamental concepts of geometry
Meserve, Bruce E
1983-01-01
Demonstrates relationships between different types of geometry. Provides excellent overview of the foundations and historical evolution of geometrical concepts. Exercises (no solutions). Includes 98 illustrations.
Algorithms in Algebraic Geometry
Dickenstein, Alicia; Sommese, Andrew J
2008-01-01
In the last decade, there has been a burgeoning of activity in the design and implementation of algorithms for algebraic geometric computation. Some of these algorithms were originally designed for abstract algebraic geometry, but now are of interest for use in applications and some of these algorithms were originally designed for applications, but now are of interest for use in abstract algebraic geometry. The workshop on Algorithms in Algebraic Geometry that was held in the framework of the IMA Annual Program Year in Applications of Algebraic Geometry by the Institute for Mathematics and Its
Directory of Open Access Journals (Sweden)
A. K. Aggarwal
2014-01-01
Full Text Available The objective of this paper is to provide guidance for the design of the thick-walled cylinder made up of transversely isotropic material so that collapse of cylinder due to influence of internal and external pressure can be avoided. The concept of transition theory based on Lebesgue strain measure has been used to simplify the constitutive equations. Results have been analyzed theoretically and discussed numerically. From this analysis, it has been concluded that, under the influence of internal and external pressure, circular cylinder made up of transversely isotropic material (beryl is on the safer side of the design as compared to the cylinders made up of isotropic material (steel. This is because of the reason that percentage increase in effective pressure required for initial yielding to become fully plastic is high for beryl as compared to steel which leads to the idea of “stress saving” that reduces the possibility of collapse of thick-walled cylinder due to internal and external pressure.
Drexel, Rober E; Mcadams, William H
1945-01-01
Report reviews published data and presents some new data on heat transfer to air flowing in round tubes, in rectangular ducts, and around finned cylinders. The available data for heat transfer to air in straight ducts of rectangular and circular cross section have been correlated in plots of Stanton number versus Reynolds number to provide a background for the study of the data for finned cylinders. Equations are recommended for both the streamlined and turbulent regions, and data are presented for the transition region between turbulent and laminar flow. Use of hexagonal ends on round tubes causes the characteristics of laminar flow to extend to high Reynolds numbers. Average coefficients for the entire finned cylinder have been calculated from the average temperature at the base of the fins and an equation which was derived to allow for the effectiveness of the fins. The available results for each finned cylinder are correlated herein in terms of graphs of Stanton number versus Reynolds number. In general, for a given Reynolds number, the Stanton number increases with increases in both spacing and width of the fins, and is apparently independent of cylinder diameter and temperature difference. For a given coefficient of heat transfer improved baffles and rough or wavy surfaces give a substantial reduction in pumping power per unit of heat transfer surface and a somewhat smaller decrease in pressure drop. (author)
Multi-frequency response of a cylinder subjected to vortex shedding and support motions
Energy Technology Data Exchange (ETDEWEB)
Vikestad, Kyrre
1998-12-31
This thesis deals with an experimental investigation of vortex induced vibrations of a circular cylinder. The purpose of the experiment was to identify the influence from a controlled disturbance of the cylinder motions on the response caused by vortex shedding. The cylinder investigated is 2 m long and the diameter is 10 cm. The cylinder is elastically mounted in an apparatus using springs, where the foundation of one of the springs can have a harmonic motion. The apparatus is placed on a carriage in a 25 m long towing tank. Towing velocities are varied between 0.140 m/s and 0.655 m/s corresponding to reduced velocity range from 2.8 to 13.2. The still water natural frequency is 0.497 Hz, and the natural frequency in air is 0.634 Hz. The cylinder is only able to oscillate in the cross-flow direction. The support motion frequency was varied between 0.26 Hz and 1.01 Hz, and the force motion amplitude was varied using 2, 4 and 6 cm support amplitudes. Three sets of experiments were carried out: (1) Still water oscillations due to harmonic support motion excitation, support amplitude and frequencies varied, (2) Towing tests with no support motion, the velocity is varied, (3) Combined excitation: Towing tests with support motion. All possible combinations of experiments (1) and (2) are carried out. The two first experiments provide reference values for the combined excitation experiments and for verification purposes. The results reveal the ability of the external disturbance to influence the vortex shedding process both regarding frequency and the resulting response amplitudes. Results for added mass, in-line drag and damping are also obtained. The work may be of use in deep water floating petroleum production. 81 refs., 73 figs., 6 tabs.
Performance limits of ion extraction systems with non-circular apertures
Shagayda, A.; Madeev, S.
2016-04-01
A three-dimensional computer simulation is used to determine the perveance limitations of ion extraction systems with non-circular apertures. The objective of the study is to analyze the possibilities to improve mechanical strength of the ion optics made of carbon-carbon composite materials. Non-circular grid apertures are better suited to the physical structure of carbon-carbon composite materials, than conventionally used circular holes in a hexagonal pattern, because they allow a fewer number of cut fibers. However, the slit-type accelerating systems, usually regarded as the main alternative to the conventional ion optics, have an intolerably narrow range of operating perveance values at which there is no direct ion impingement on the acceleration grid. This paper presents results of comparative analysis of a number of different ion optical systems with non-circular apertures and conventional ion optical systems with circular apertures. It has been revealed that a relatively wide perveance range without direct ion impingement may be obtained with apertures shaped as a square with rounded corners. Numerical simulations show that this geometry may have equivalent perveance range as the traditional geometry with circular apertures while being more mechanically robust. In addition, such important characteristics, as the effective transparency for both the ions and the neutral atoms, the height of the potential barrier reflecting the downstream plasma electrons and the angular divergence of the beamlet also can be very close to these parameters for the optics with circular apertures.
Flexural vibrations of finite composite poroelastic cylinders
Indian Academy of Sciences (India)
Sandhya Rani Bandari; Srisailam Aleti; Malla Reddy Perati
2015-04-01
This paper deals with the flexural vibrations of composite poroelastic solid cylinder consisting of two cylinders that are bonded end to end. Poroelastic materials of the two cylinders are different. The frequency equations for pervious and impervious surfaces are obtained in the framework of Biot’s theory of wave propagation in poroelastic solids. The gauge invariance property is used to eliminate one arbitrary constant in the solution of the problem. This would lower the number of boundary conditions actually required. If the wavelength is infinite, frequency equations are degenerated as product of two determinants pertaining to extensional vibrations and shear vibrations. In this case, it is seen that the nature of the surface does not have any influence over shear vibrations unlike in the case of extensional vibrations. For illustration purpose, three composite cylinders are considered and then discussed. Of the three, two are sandstone cylinders and the third one is resulted when a cylindrical bone is implanted with Titanium. In either case, phase velocity is computed against aspect ratios.
Energy Technology Data Exchange (ETDEWEB)
Park, S.H. [Oak Ridge K-25 Site, Oak Ridge, TN (United States)
1991-12-31
With the increasing number of nuclear reactors for power generation, there is a comparable increase in the amount of UF{sub 6} being transported. Likewise, the probability of having an accident involving UF{sub 6}-filled cylinders also increases. Accident scenarios which have been difficult to assess are those involving a filled UF{sub 6} cylinder subjected to fire. A study is underway at the Oak Ridge K-25 Site, as part of the US DOE Enrichment Program, to provide empirical data and a computer model that can be used to evaluate various cylinder-in-fire scenarios. It is expected that the results will provide information leading to better handling of possible fire accidents as well as show whether changes should be made to provide different physical protection during shipment. The computer model being developed will be capable of predicting the rupture of various cylinder sizes and designs as well as the amount of UF{sub 6}, its distribution in the cylinder, and the conditions of the fire.
Guided Circumferential Waves in Layered Poroelastic Cylinders
Directory of Open Access Journals (Sweden)
Shah S.A.
2016-12-01
Full Text Available The present paper investigates the propagation of time harmonic circumferential waves in a two-dimensional hollow poroelastic cylinder with an inner shaft (shaft-bearing assembly. The hollow poroelastic cylinder and inner shaft are assumed to be infinite in axial direction. The outer surface of the cylinder is stress free and at the interface, between the inner shaft and the outer cylinder, it is assumed to be free sliding and the interfacial shear stresses are zero, also the normal stress and radial displacements are continuous. The frequency equation of guided circumferential waves for a permeable and an impermeable surface is obtained. When the angular wave number vanish the frequency equation of guided circumferential waves for a permeable and an impermeable surface degenerates and the dilatational and shear waves are uncoupled. Shear waves are independent of the nature of surface. The frequency equation of a permeable and an impermeable surface for bore-piston assembly is obtained as a particular case of the model under consideration when the outer radius of the hollow poroelastic cylinder tends to infinity. Results of previous studies are obtained as a particular case of the present study. Nondimensional frequency as a function of wave number is presented graphically for two types of models and discussed. Numerical results show that, in general, the first modes are linear for permeable and impermeable surfaces and the frequency of a permeable surface is more than that of an impermeable surface.
Base Stress of the Opened Bottom Cylinder Structures
Institute of Scientific and Technical Information of China (English)
刘建起; 孟晓娟
2004-01-01
The base stress of the opened bottom cylinder structure differs greatly from that of the structure with a closed bottom. By investigating the inner soil pressure on the cylinder wall and the base stress of the cylinder base, which were obtained from the model experiments, the interactions among the filler inside the cylinder,subsoil and cylinder are analyzed. The adjusting mechanism of frictional resistance between the inner filler and the wall of the cylinder during the overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the base stress of the opened bottom cylinder structure is proposed. Meanwhile, the formulas for calculating the effective anti-overturning ratio of the opened bottom cylinder are derived.
Euclidean Geometry via Programming.
Filimonov, Rossen; Kreith, Kurt
1992-01-01
Describes the Plane Geometry System computer software developed at the Educational Computer Systems laboratory in Sofia, Bulgaria. The system enables students to use the concept of "algorithm" to correspond to the process of "deductive proof" in the development of plane geometry. Provides an example of the software's capability and compares it to…
Supersymmetric Sigma Model geometry
Lindström, Ulf
2012-01-01
This is a review of how sigma models formulated in Superspace have become important tools for understanding geometry. Topics included are: The (hyper)k\\"ahler reduction; projective superspace; the generalized Legendre construction; generalized K\\"ahler geometry and constructions of hyperk\\"ahler metrics on Hermitean symmetric spaces.
1996-01-01
Designs and Finite Geometries brings together in one place important contributions and up-to-date research results in this important area of mathematics. Designs and Finite Geometries serves as an excellent reference, providing insight into some of the most important research issues in the field.
Supersymmetric Sigma Model Geometry
Ulf Lindström
2012-01-01
This is a review of how sigma models formulated in Superspace have become important tools for understanding geometry. Topics included are: The (hyper)k\\"ahler reduction; projective superspace; the generalized Legendre construction; generalized K\\"ahler geometry and constructions of hyperk\\"ahler metrics on Hermitean symmetric spaces.
Geometry of multihadron production
Energy Technology Data Exchange (ETDEWEB)
Bjorken, J.D.
1994-10-01
This summary talk only reviews a small sample of topics featured at this symposium: Introduction; The Geometry and Geography of Phase space; Space-Time Geometry and HBT; Multiplicities, Intermittency, Correlations; Disoriented Chiral Condensate; Deep Inelastic Scattering at HERA; and Other Contributions.
Bergshoeff, Eric A.; Riccioni, Fabio; Alvarez-Gaumé, L.
2011-01-01
We probe doubled geometry with dual fundamental branes. i.e. solitons. Restricting ourselves first to solitonic branes with more than two transverse directions we find that the doubled geometry requires an effective wrapping rule for the solitonic branes which is dual to the wrapping rule for fundam
Flow interaction between a streamwise oscillating cylinder and a downstream stationary cylinder
Xu, S. J.; Gan, L.; Zhou, Y.
2016-11-01
In this paper, we present some experimental results about the physical effects of a cylinder's streamwise oscillation motion on a downstream one in a tandem arrangement. The upstream cylinder undergoes a controlled simple harmonic oscillation at amplitudes A/ d = 0.2-0.8, where d is the cylinder diameter, and the frequency ratio of f_e/f_s = 0-3.0, where f_e is the cylinder oscillation frequency and f_s is the natural frequency of vortex shedding from a single stationary cylinder. Under these conditions, the vortex shedding is locked to the controlled oscillation motion. Flow visualisation using the planar laser-induced fluorescence and qualitative measurements using hot-wire anemometry reveal three distinct flow regimes behind the downstream cylinder. For f_e/f_s > (f_e/f_s)_c, where (f_e/f_s)_c is a critical frequency ratio which depends on A/ d and Reynolds number Re, a so-called SA-mode occurs. The upstream oscillating cylinder generates binary vortices symmetrically arranged about the centreline, each containing a pair of counter-rotating vortices, and the downstream cylinder sheds vortices alternately at 0.5f_e. For 0.7-1.0 < f_e/f_s < (f_e/f_s)_c a complex vortex street that consists of two outer rows of vortices generated by the oscillating cylinder and two inner rows of vortices shed from the downstream stationary cylinder, which is referred to as AA-mode. For 0.3-0.6 < f_e/f_s< 0.8-1.0, one single staggered vortex street (A-mode) is observed. It is also found that, when f_e/f_s is near unity, the streamwise interaction of the two cylinders gives rise to the most energetic wake in the cross-stream direction, in terms of its maximum width, and the wake is AA-mode-like. The effects of other parameters such as the spacing between the two cylinders, Re and A/ d on the flow pattern are also discussed in details. The observations are further compared to the stationary tandem cylinder cases.
Sugawara, Akira; Ueda, Kazuhiro; Nakayama, T.; Lee, N.; Yamamoto, H.
2016-10-01
Magnetisation reversal of micron-sized Nd2Fe14B single crystals with magnetisation as weak as 10-9 emu (1 µm size) was studied. Single-crystal specimens (cylinders with diameter and height of 1 to 6 µm) were prepared by focused-ion beam so that both the magnetic easy and hard axes were included in the basal plane. Their magnetic hysteresis loops were measured when they were rotated with respect to the cylindrical axis by using microbeam hard-x-ray magnetic circular dichroism (XMCD) under transmission geometry. It was found that coercivity is inversely proportional to the cosine of the angle between the magnetocrystalline easy axis and magnetic-field direction and that the magnetisation reversal is dominated by domain-wall pinning in two different modes. One is related to penetration of the reversed domain nucleated in a subsurface soft layer into the bulk hard phase, of which the hysteresis loops exhibit a single-stage abrupt jump in magnetization. The other mode is pinning of the walls within the bulk grain, of which the hysteresis loops exhibit a plateau. The multi-domain structure associated with the pinning was confirmed by XMCD mapping. The proposed method fills the gap between conventional bulk magnetic measurement and submicron-scale electrical-transport measurement for nanofabricated thin films and/or fine particles. It is expected to provide new insights into elemental magnetisation processes in micron-scale regions.
Zhou, Tianci; Chen, Xiao; Faulkner, Thomas; Fradkin, Eduardo
2016-09-01
We investigate the entanglement entropy (EE) of circular entangling cuts in the 2 + 1-dimensional quantum Lifshitz model. The ground state in this model is a spatially conformal invariant state of the Rokhsar-Kivelson type, whose amplitude 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 also scales at long distance with a power determined by the lowest scaling dimension local operator in the theory.