Three-dimensional vortex flow near the endwall of a short cylinder in crossflow: Uniform-diameter circular cylinder

International Nuclear Information System (INIS)

Chen, S.B.; Sanitjai, S.; Ghosh, K.; Goldstein, R.J.

2012-01-01

Flow characteristics, around a short uniform-diameter circular cylinder in crossflow, are investigated experimentally. Extensive flow visualization using oil-lampblack and smoke-wire methods have been performed. Near-wake velocity measurements have been performed using a hotwire anemometer. Complex secondary flows are observed on and around the cylinder in crossflow. Multiple vortices are observed in the horseshoe vortex system near the cylinder–endwall junction. Based on this flow visualization and local mass transfer measurement results, a six-vortex secondary flow model has been proposed. - Highlights: ► Flow visualizations and velocity measurements for a short circular cylinder. ► Six vortices in the horseshoe vortex system upstream of the base of the cylinder. ► Cross-stream turbulence intensity profiles show a similarity in their shape.

Bubbly flows around a two-dimensional circular cylinder

Science.gov (United States)

Lee, Jubeom; Park, Hyungmin

2016-11-01

Two-phase cross flows around a bluff body occur in many thermal-fluid systems like steam generators, heat exchangers and nuclear reactors. However, our current knowledge on the interactions among bubbles, bubble-induced flows and the bluff body are limited. In the present study, the gas-liquid bubbly flows around a solid circular cylinder are experimentally investigated while varying the mean void fraction from 5 to 27%. The surrounding liquid (water) is initially static and the liquid flow is only induced by the air bubbles. For the measurements, we use the high-speed two-phase particle image velocimetry techniques. First, depending on the mean void fraction, two regimes are classified with different preferential concentration of bubbles in the cylinder wake, which are explained in terms of hydrodynamic force balances acting on rising bubbles. Second, the differences between the two-phase and single-phase flows (while matching their Reynolds numbers) around a circular cylinder will be discussed in relation to effects of bubble dynamics and the bubble-induced turbulence on the cylinder wake. Supported by a Grant (MPSS-CG-2016-02) through the Disaster and Safety Management Institute funded by Ministry of Public Safety and Security of Korean government.

Magnetohydrodynamic flow past a circular cylinder

International Nuclear Information System (INIS)

Swarup, S.; Sinha, P.C.

1977-01-01

This paper deals with the slow-flow problem of an incompressible, viscous, electrically conducting fluid past a circular cylinder in an alignment magnetic field. The solutions for the velocity and magnetic fields as sought by the method of matched asymptotic expansions under the assumptions R,Rsub(m) 2 ) and O(R/log M), respectively. (Auth.)

Influence of rotation on the near-wake development behind an impulsively started circular cylinder

Science.gov (United States)

Coutanceau, M.; Menard, C.

1985-09-01

A rotating body, travelling through a fluid in such a way that the rotation axis is at right angles to the translational path, experiences a transverse force, called the Magnus force. The present study is concerned with a rotating cylinder which is in a state of translational motion. In the considered case, the existence of a lift force may be explained easily on the basis of the theory of inviscid fluids. An experimental investigation provides new information regarding the mechanism of the near-wake development of the classical unsteady flow and the influence of the rotational effects. Attention is given to the experimental technique, aspects of flow topology and notation, the time development of the wake flow pattern, the time evolution of certain flow properties, the flow structure in the neighborhood of the front stagnation point, and the influence of the Reynolds number on flow establishment.

Boundary value problems of the circular cylinders in the strain-gradient theory of linear elasticity

International Nuclear Information System (INIS)

Kao, B.G.

1979-11-01

Three boundary value problems in the strain-gradient theory of linear elasticity are solved for circular cylinders. They are the twisting of circular cylinder, uniformly pressuring of concentric circular cylinder, and pure-bending of simply connected cylinder. The comparisons of these solutions with the solutions in classical elasticity and in couple-stress theory reveal the differences in the stress fields as well as the apparent stress fields due to the influences of the strain-gradient. These aspects of the strain-gradient theory could be important in modeling the failure behavior of structural materials

Stokes flow past a swarm of porous circular cylinders with Happel ...

Indian Academy of Sciences (India)

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 ...

Experimental study on flow past a rotationally oscillating cylinder

Science.gov (United States)

Gao, Yang-yang; Yin, Chang-shan; Yang, Kang; Zhao, Xi-zeng; Tan, Soon Keat

2017-08-01

A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number (Re=300) placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise- and- counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry (PIV) technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and timeaveraged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed. The effects of four rotation angle and frequency ratios F r ( F r= f n/ f v, the ratio of the forcing frequency f n to the natural vortex shedding frequency f v) on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤ F r≤1.0.

Experiments of flow-induced in-line oscillation of a circular cylinder in a water tunnel. 2. Influence of the aspect ratio of a cantilevered circular cylinder

International Nuclear Information System (INIS)

Nakamura, Akira; Okajima, Atsushi; Kosugi, Takashi

2001-01-01

The flow-induced in-line oscillation of a cantilevered circular cylinder was experimentally studied through free-oscillation tests in a water tunnel. The response displacement amplitude at a circular cylinder tip was measured at reduced velocity from 1.0 to 4.0. A cantilevered cylinder was supported by a plate spring mounted on the water tunnel wall. The cylinder aspect ratio was varied from 5 to 21 to investigate the effect of aspect ratio on the response displacement. It is found that cylinders with aspect ratios of 5 and 10 have one excitation region, while cylinders with aspect ratios of 14 and 21 have two excitation regions. The aspect ratio, therefore, affects the amplitude of the excitation regions. The influence of end-effect was also investigated using cylinders with an end plate attached to the free end. Since the cylinders with an end plate show two excitation regions, even at an aspect ratio of 5, the flow around the free end of a cantilevered cylinder causes the end-effect. The mechanism of vibration was investigated using a cylinder with a splitter plate in wake to prevent alternate vortices. The amplitude is greater than those of a normal cylinder without a splitter plate, especially at V r =2.3 to 3.0, where a cylinder with an end plate shows the second excitation region. In order words, the alternate vortices suppress the amplitude in this range. The maximum amplitude of each excitation region decreases in proportion to C n and the amplitude of the first excitation is more sensitive to C n . (author)

High Reynolds number oscillations of a circular cylinder

OpenAIRE

Hirata, Miguel H.; Pereira, Luiz Antonio A.; Recicar, Jan N.; Moura, Washington H. de

2008-01-01

This paper concerns the numerical simulation of the flow around an oscillating circular cylinder, which moves with constant velocity in a quiescent Newtonian fluid with constant properties. For each time step of the simulation a number of discrete Lamb vortices is placed close to the body surface; the intensity of each of these is determined such as to satisfy the no-slip boundary condition. The aerodynamic loads acting on the surface of cylinder are computed using the integral formulation de...

Natural convection in square enclosure induced by inner circular cylinder with time-periodic pulsating temperature

KAUST Repository

Huang, Zhu; Zhang, Wei; Xi, Guang

2015-01-01

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

Electromagnetic forces on type-II superconducting rotating cylinders

International Nuclear Information System (INIS)

Saif, A.G.; Refai, T.F.; El-Sabagh, M.A.

1995-01-01

Analytical solutions of the electromagnetic fields are presented for a system composed of an infinitely long superconducting cylinder rotating about its axis and placed parallel to two infinitely long normal conducting wires. Both wires carry the same alternating current. From the obtained electromagnetic fields the electromagnetic power loss on the cylinder surface, electromagnetic forces due to induced currents, electromagnetic torque, and the work opposing the rotation of the cylinder are calculated. (orig.)

Stability analysis of cylinders with circular cutouts

Science.gov (United States)

Almroth, B. O.; Brogan, F. A.; Marlowe, M. B.

1973-01-01

The stability of axially compressed cylinders with circular cutouts is analyzed numerically. An extension of the finite-difference method is used which removes the requirement that displacement components be defined in the directions of the grid lines. The results of this nonlinear analysis are found to be in good agreement with earlier experimental results.

Mathematical Modeling of Partial-Porous Circular Cylinders with Water Waves

Directory of Open Access Journals (Sweden)

Min-Su Park

2015-01-01

Full Text Available The interaction of water waves with partially porous-surfaced circular cylinders was investigated. A three-dimensional numerical modeling was developed based on the complete mathematical formulation of the eigenfunction expansion method in the potential flow. Darcy’s law was applied to describe the porous boundary. The partial-porous cylinder is composed of a porous-surfaced body near the free surface, and an impermeable-surfaced body with an end-capped rigid bottom below the porous region. The optimal ratio of the porous portion to the impermeable portion can be adopted to design an effective ocean structure with minimal hydrodynamic impact. To scrutinize the hydrodynamic interactions in N partial-porous circular cylinders, the computational fluid domain is divided into three regions: an exterior region, N inner porous body regions, and N regions beneath the body. Wave excitation forces and wave run-up on multibodied partial-porous cylinders are calculated and compared for various porous-portion ratios and wave conditions, all of which significantly influence the hydrodynamic property.

Vibration of a group of circular cylinders subjected to fluid flow

International Nuclear Information System (INIS)

Chen, S.

1981-01-01

Many structural and mechanical components consist of multiple circular cylinders, such as heat exchanger tubes and nuclear fuel bundles. These components are subjected to fluid flow. The fluid flow represents a source of energy that can induce and sustain vibration. The fluid moving with vibrating structures has an important effect on the dynamic characteristics of the structure. The objective of this paper is to review the dynamics of multiple circular cylinders in stationary fluid, parallel flow and cross flow, and to present general design guides to avoid detrimental vibration and instability. 77 refs

Experimental investigation of the mutual interference flow of two circular cylinders by flow visualization

Science.gov (United States)

Yokoi, Yoshifumi; Vitkovičová, Rut

In order to understand the aspect of the mutual interference flow from two circular cylinders, the visual observation experiment was performed by use a water flow apparatus. The purpose of this study is accumulation of the basic image data for comparing with numerical computation or previous experimental results. In this report, the intervals of two circular cylinders were varied, the visualization experiment was performed, and the vortex shedding characteristics and the flow pattern in each case were investigated. The cylinder setting conditions were seven kinds (the position of the rear-side circular cylinder is changed). The cylinder diameter ratios were four kinds (D/d=1.0, 1.67, 2.5 and 5.0). The variation of Reynolds number was three kinds (Re=548.7, 1200 and 2500). The dye oozing streak method was used in this visualization experiment. Although the previous PIV experimental result and present result obtained the same flow feature, the aspect of an interference flow became clear by changing the color of tracer ink.

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.

Experimental investigation of the mutual interference flow of two circular cylinders by flow visualization

Directory of Open Access Journals (Sweden)

Yokoi Yoshifumi

2017-01-01

Full Text Available In order to understand the aspect of the mutual interference flow from two circular cylinders, the visual observation experiment was performed by use a water flow apparatus. The purpose of this study is accumulation of the basic image data for comparing with numerical computation or previous experimental results. In this report, the intervals of two circular cylinders were varied, the visualization experiment was performed, and the vortex shedding characteristics and the flow pattern in each case were investigated. The cylinder setting conditions were seven kinds (the position of the rear-side circular cylinder is changed. The cylinder diameter ratios were four kinds (D/d=1.0, 1.67, 2.5 and 5.0. The variation of Reynolds number was three kinds (Re=548.7, 1200 and 2500. The dye oozing streak method was used in this visualization experiment. Although the previous PIV experimental result and present result obtained the same flow feature, the aspect of an interference flow became clear by changing the color of tracer ink.

Flow and coherent structures around circular cylinders in shallow water

Science.gov (United States)

Zeng, Jie; Constantinescu, George

2017-06-01

Eddy-resolving numerical simulations are conducted to investigate the dynamics of the large-scale coherent structures around a circular cylinder in an open channel under very shallow flow conditions where the bed friction significantly affects the wake structure. Results are reported for three test cases, for which the ratio between the cylinder diameter, D, and the channel depth, H, is D/H = 10, 25, and 50, respectively. Simulation results show that a horseshoe vortex system forms in all test cases and the dynamics of the necklace vortices is similar to that during the breakaway sub-regime observed for cases when a laminar horseshoe vortex forms around the base of the cylinder. Given the shallow conditions and turbulence in the incoming channel flow, the necklace vortices occupy a large fraction of the flow depth (they penetrate until the free surface in the shallower cases with D/H = 25 and 50). The oscillations of the necklace vortices become less regular with increasing polar angle magnitude and can induce strong amplification of the bed shear stress beneath their cores. Strong interactions are observed between the legs of the necklace vortices and the eddies shed in the separated shear layers in the cases with D/H = 25 and 50. In these two cases, a vortex-street type wake is formed and strong three-dimensional effects are observed in the near-wake flow. A secondary instability in the form of arrays of co-rotating parallel horizontal vortices develops. Once the roller vortices get away from the cylinder, the horizontal vortices in the array orient themselves along the streamwise direction. This instability is not present for moderately shallow conditions (e.g., D/H ≈ 1) nor for very shallow cases when the wake changes to an unsteady bubble type (e.g., D/H = 50). For cases when this secondary instability is present, the horizontal vortices extend vertically over a large fraction of the flow depth and play an important role in the vertical mixing of fluid

Re-examination of laminar flow over twin circular cylinders in tandem arrangement

Energy Technology Data Exchange (ETDEWEB)

Liu, Ming-Ming; Lu, Lin; Teng, Bin; Tang, Guo-Qiang [State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024 (China); Zhao, Ming [School of Computing, Engineering and Mathematics, University of Western Sydney, Penrith 2751 (Australia)

2014-04-01

Viscous fluid flow past two identical circular cylinders in a tandem arrangement is numerically investigated at a typical Reynolds number of 200. By considering a large span of spacing ratio (0.1 ⩽ G/D ⩽ 6.0) with a fine interval of 0.1 or less, the dependences on the spacing ratio of the drag force, lift force, lift fluctuation frequency, torque on the cylinder pair and phase difference between the lift fluctuations of the two cylinders are investigated in detail, where D is the diameter of the cylinder and G the surface-to-surface distance between the cylinders. The phase difference between the lift fluctuations of the two cylinders is addressed based on correlation analysis together with the phase diagram, which has received scarce attention before. The phase difference provides further understanding to the dependence of the wake evolutions behind the twin circular cylinders. The numerical investigations show that diverse regimes can be identified according to the dependence of the hydrodynamics on the spacing ratio. The hydrodynamic discontinuities at G/D = 0.9, which have previously been ignored, are reported in this work. The physical correlations between the hydrodynamic discontinuities and the wake patterns are presented. (paper)

Re-examination of laminar flow over twin circular cylinders in tandem arrangement

International Nuclear Information System (INIS)

Liu, Ming-Ming; Lu, Lin; Teng, Bin; Tang, Guo-Qiang; Zhao, Ming

2014-01-01

Viscous fluid flow past two identical circular cylinders in a tandem arrangement is numerically investigated at a typical Reynolds number of 200. By considering a large span of spacing ratio (0.1 ⩽ G/D ⩽ 6.0) with a fine interval of 0.1 or less, the dependences on the spacing ratio of the drag force, lift force, lift fluctuation frequency, torque on the cylinder pair and phase difference between the lift fluctuations of the two cylinders are investigated in detail, where D is the diameter of the cylinder and G the surface-to-surface distance between the cylinders. The phase difference between the lift fluctuations of the two cylinders is addressed based on correlation analysis together with the phase diagram, which has received scarce attention before. The phase difference provides further understanding to the dependence of the wake evolutions behind the twin circular cylinders. The numerical investigations show that diverse regimes can be identified according to the dependence of the hydrodynamics on the spacing ratio. The hydrodynamic discontinuities at G/D = 0.9, which have previously been ignored, are reported in this work. The physical correlations between the hydrodynamic discontinuities and the wake patterns are presented. (paper)

Classification of gap flow regimes in two side-by-side circular cylinders

CSIR Research Space (South Africa)

Atkins, M

2014-02-01

Full Text Available The behavior of the flow around two circular cylinders arranged in a side-by-side configuration strongly depends on the transverse center-to-center gap spacing ratio (T/D) where D is the cylinder diameter. Based on the observed wake structure [13...

Steady particulate flows in a horizontal rotating cylinder

Science.gov (United States)

Yamane, K.; Nakagawa, M.; Altobelli, S. A.; Tanaka, T.; Tsuji, Y.

1998-06-01

Results of discrete element method (DEM) simulation and magnetic resonance imaging (MRI) experiments are compared for monodisperse granular materials flowing in a half-filled horizontal rotating cylinder. Because opacity is not a problem for MRI, a long cylinder with an aspect ratio ˜7 was used and the flow in a thin transverse slice near the center was studied. The particles were mustard seeds and the ratio of cylinder diameter to particle diameter was approximately 50. The parameters compared were dynamic angle of repose, velocity field in a plane perpendicular to the cylinder axis, and velocity fluctuations at rotation rates up to 30 rpm. The agreement between DEM and MRI was good when the friction coefficient and nonsphericity were adjusted in the simulation for the best fit.

Lattice Boltzmann simulation of viscoelastic flow past a confined free rotating cylinder

Science.gov (United States)

Xia, Yi; Zhang, Peijie; Lin, Jianzhong; Ku, Xiaoke; Nie, Deming

2018-05-01

To study the dynamics of rigid body immersed in viscoelastic fluid, an Oldroyd-B fluid flow past an eccentrically situated, free rotating cylinder in a two-dimensional (2D) channel is simulated by a novel lattice Boltzmann method. Two distribution functions are employed, one of which is aimed to solve Navier-Stokes equation and the other to the constitutive equation, respectively. The unified interpolation bounce-back scheme is adopted to treat the moving curved boundary of cylinder, and the novel Galilean invariant momentum exchange method is utilized to obtain the hydrodynamic force and torque exerted on the cylinder. Results show that the center-fixed cylinder rotates inversely in the direction where a cylinder immersed in Newtonian fluid do, which generates a centerline-oriented lift force according to Magnus effect. The cylinder’s eccentricity, flow inertia, fluid elasticity and viscosity would affect the rotation of cylinder in different ways. The cylinder rotates more rapidly when located farther away from the centerline, and slows down when it is too close to the wall. The rotation frequency decreases with increasing Reynolds number, and larger rotation frequency responds to larger Weissenberg number and smaller viscosity ratio, indicating that the fluid elasticity and low solvent viscosity accelerates the flow-induced rotation of cylinder.

Laminar vortex shedding behind a cooled circular cylinder

Czech Academy of Sciences Publication Activity Database

Trávníček, Zdeněk; Wang, A. B.; Tu, W.Y.

2014-01-01

Roč. 55, č. 2 (2014), s. 1-12 ISSN 0723-4864 R&D Projects: GA ČR GA14-08888S Institutional support: RVO:61388998 Keywords : vortex shedding * cooled circular cylinder * thermal effect Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts Impact factor: 1.670, year: 2014 http://link.springer.com/journal/348/55/2/page/1

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.

Energetically efficient proportional-integral-differential (PID) control of wake vortices behind a circular cylinder

International Nuclear Information System (INIS)

Das, Pramode K; Mathew, Sam; Shaiju, A J; Patnaik, B S V

2016-01-01

The control of vortex shedding behind a circular cylinder is a precursor to a wide range of external shear flow problems in engineering, in particular the flow-induced vibrations. In the present study, numerical simulation of an energetically efficient active flow control strategy is proposed, for the control of wake vortices behind a circular cylinder at a low Reynolds number of 100. The fluid is assumed to be incompressible and Newtonian with negligible variation in properties. Reflectionally symmetric controllers are designed such that, they are located on a small sector of the cylinder over which, tangential sliding mode control is imparted. In the field of modern controls, proportional (P), integral (I) and differential (D) control strategies and their numerous combinations are extremely popular in industrial practice. To impart suitable control actuation, the vertically varying lift force on the circular cylinder, is synthesised for the construction of an error term. Four different types of controllers considered in the present study are, P, I, PI and PID. These controllers are evaluated for their energetic efficiency and performance. A linear quadratic optimal control problem is formulated, to minimise the cost functional. By performing detailed simulations, it was observed that, the system is energetically efficient, even when the twin eddies are still persisting behind the circular cylinder. To assess the adaptability of the controllers, the actuators were switched on and off to study their dynamic response. (paper)

Beating motion of a circular cylinder in vortex-induced vibrations

Science.gov (United States)

Shen, Linwei; Chan, Eng-Soon; Wei, Yan

2018-04-01

In this paper, beating phenomenon of a circular cylinder in vortex-induced vibration is studied by numerical simulations in a systematic manner. The cylinder mass coefficients of 2 and 10 are considered, and the Reynolds number is 150. Two distinctive frequencies, namely cylinder oscillation and vortex shedding frequencies, are obtained from the harmonic analysis of the cylinder displacement. The result is consistent with that observed in laboratory experiments. It is found that the cylinder oscillation frequency changes with the natural frequency of the cylinder while the reduced velocity is varied. The added-mass coefficient of the cylinder in beating motion is therefore estimated. Meanwhile, the vortex shedding frequency does not change dramatically in the beating situations. In fact, it is very close to 0.2. Accordingly, the lift force coefficient has two main components associated with these two frequencies. Besides, higher harmonics of the cylinder oscillation frequency appear in the spectrum of the lift coefficient. Moreover, the vortex shedding timing is studied in the beating motion by examining the instantaneous flow fields in the wake, and two scenarios of the vortex formation are observed.

Targeted energy transfer in laminar vortex-induced vibration of a sprung cylinder with a nonlinear dissipative rotator

Science.gov (United States)

Blanchard, Antoine; Bergman, Lawrence A.; Vakakis, Alexander F.

2017-07-01

We computationally investigate the dynamics of a linearly-sprung circular cylinder immersed in an incompressible flow and undergoing transverse vortex-induced vibration (VIV), to which is attached a rotational nonlinear energy sink (NES) consisting of a mass that freely rotates at constant radius about the cylinder axis, and whose motion is restrained by a rotational linear viscous damper. The inertial coupling between the rotational motion of the attached mass and the rectilinear motion of the cylinder is ;essentially nonlinear;, which, in conjunction with dissipation, allows for one-way, nearly irreversible targeted energy transfer (TET) from the oscillating cylinder to the nonlinear dissipative attachment. At the intermediate Reynolds number Re = 100, the NES-equipped sprung cylinder undergoes repetitive cycles of slowly decaying oscillations punctuated by intervals of chaotic instabilities. During the slowly decaying portion of each cycle, the dynamics of the cylinder is regular and, for large enough values of the ratio ε of the NES mass to the total mass (i.e., NES mass plus cylinder mass), can lead to significant vortex street elongation with partial stabilization of the wake. As ε approaches zero, no such vortex elongation is observed and the wake patterns appear similar to that for a sprung cylinder with no NES. We apply proper orthogonal decomposition (POD) to the velocity flow field during a slowly decaying portion of the solution and show that, in situations where vortex elongation occurs, the NES, though not in direct contact with the surrounding fluid, has a drastic effect on the underlying flow structures, imparting significant and continuous passive redistribution of energy among POD modes. We construct a POD-based reduced-order model for the lift coefficient to characterize energy transactions between the fluid and the cylinder throughout the slowly decaying cycle. We introduce a quantitative signed measure of the work done by the fluid on the

PIV measurement of the complex and transient cross-flow over a circular cylinder

International Nuclear Information System (INIS)

Kuwabara, Joji; Someya, Satoshi; Okamoto, Koji

2007-01-01

This paper describe about measurement for the complex and transient cross-flow over a circular cylinder with the dynamic (time resolved) PIV (particle image velocimetry) techniques. The experiment was carried out water flow tunnel with a working section of 50x50 mm, at the Reynolds number 6.7 x 10 3 to 2.7 x 10 4 . This circular cylinder constructed with MEXFLON resin, the end of circular cylinder is rigidly supported and the other is free. The MEXFLON is fluorine resin; its refractive index is almost same as the water with high transparency. Very high speed water flow among the test section had been clearly visualized and captured by high speed camera. The fluctuations of the flow structure also are clearly obtained with high spatial and high temporal resolution, 512x512pixel with 10,000fps. It corresponds to set up number of thousands LDV array at the test section. Consequently, we found there are asynchronous vibration between parallel-ward and perpendicular-ward to main flow. (author)

Shear-induced autorotation of freely rotatable cylinder in a channel flow at moderate Reynolds number

Science.gov (United States)

Xia, Yi; Lin, Jianzhong; Ku, Xiaoke; Chan, Tatleung

2018-04-01

Flow past a center-pinned freely rotatable cylinder asymmetrically confined in a two-dimensional channel is simulated with the lattice Boltzmann method for a range of Reynolds number 0.1 ≤ Re ≤ 200, eccentricity ratio 0/8 ≤ ɛ ≤ 7/8, and blockage ratio 0.1 ≤ β ≤ 0.5. It is found that the inertia tends to facilitate the anomalous clockwise rotation of the cylinder. As the eccentricity ratio increases, the cylinder rotates faster in the counterclockwise direction and then slows down at a range of Re 40, there exists an anomalous clockwise rotation for the cylinder at a low eccentricity ratio and the domain where the cylinder rotates anomalously becomes larger with the increase in the Reynolds number. In a channel with a higher blockage ratio, the rotation of the cylinder is more sensitive to the change of cylinder lateral position, and the separatrix at which the cylinder remains a state of rest moves upward generally. The cylinder is more likely to rotate counterclockwise and the rotating velocity is larger. At a lower blockage ratio, the anomalous clockwise rotation is more likely to occur, and the largest rotating velocity occurs when the blockage ratio is equal to 0.3. The mechanism of distinct rotational behavior of the cylinder is attributed to the transformation of distribution of shear stress which is resulted from the variation of pressure drop, the shift of maximum or minimum pressure zones along the upper and lower semi-cylinder surface, and the movement of stagnant point and separate point. Finally, the effects of the cylinder rotation on the flow structure and hydrodynamic force exerted on the cylinder surface are analyzed as well.

Enstrophy-based proper orthogonal decomposition of flow past rotating cylinder at super-critical rotating rate

Science.gov (United States)

Sengupta, Tapan K.; Gullapalli, Atchyut

2016-11-01

Spinning cylinder rotating about its axis experiences a transverse force/lift, an account of this basic aerodynamic phenomenon is known as the Robins-Magnus effect in text books. Prandtl studied this flow by an inviscid irrotational model and postulated an upper limit of the lift experienced by the cylinder for a critical rotation rate. This non-dimensional rate is the ratio of oncoming free stream speed and the surface speed due to rotation. Prandtl predicted a maximum lift coefficient as CLmax = 4π for the critical rotation rate of two. In recent times, evidences show the violation of this upper limit, as in the experiments of Tokumaru and Dimotakis ["The lift of a cylinder executing rotary motions in a uniform flow," J. Fluid Mech. 255, 1-10 (1993)] and in the computed solution in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)]. In the latter reference, this was explained as the temporal instability affecting the flow at higher Reynolds number and rotation rates (>2). Here, we analyze the flow past a rotating cylinder at a super-critical rotation rate (=2.5) by the enstrophy-based proper orthogonal decomposition (POD) of direct simulation results. POD identifies the most energetic modes and helps flow field reconstruction by reduced number of modes. One of the motivations for the present study is to explain the shedding of puffs of vortices at low Reynolds number (Re = 60), for the high rotation rate, due to an instability originating in the vicinity of the cylinder, using the computed Navier-Stokes equation (NSE) from t = 0 to t = 300 following an impulsive start. This instability is also explained through the disturbance mechanical energy equation, which has been established earlier in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)].

Forced vibrations of rotating circular cylindrical shells

International Nuclear Information System (INIS)

Igawa, Hirotaka; Maruyama, Yoshiyuki; Endo, Mitsuru

1995-01-01

Forced vibrations of rotating circular cylindrical shells are investigated. Basic equations, including the effect of initial stress due to rotation, are formulated by the finite-element method. The characteristic relations for finite elements are derived from the energy principle by considering the finite strain. The equations of motion can be separated into quasi-static and dynamic ones, i.e., the equations in the steady rotating state and those in the vibration state. Radial concentrated impulses are considered as the external dynamic force. The transient responses of circular cylindrical shells are numerically calculated under various boundary conditions and rotating speeds. (author)

Evaluation of Flow Accelerated Corrosion of Carbon Steel with Rotating Cylinder

International Nuclear Information System (INIS)

Park, Tae Jun; Lee, Eun Hee; Kim, Kyung Mo; Kim, Hong Pyo

2012-01-01

Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major issue in nuclear industry. Rotating cylinder FAC test facility was designed and fabricated and then performance of the facility was evaluated. The facility is very simple in design and economic in fabrication and can be used in material and chemistry screening test. The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO), and temperature. Fluid velocity is controlled with rotating speed of the cylinder with a test specimen. FAC test of SA106 Gr. B carbon steel under 4 m/s flow velocity was performed with the rotating cylinder at DO concentration of less than 1 ppb and of 1.3 ppm. Also a corrosion test of the carbon steel at static condition, that is at zero fluid velocity, of test specimen and solution was performed at pH from 8 to 10 for comparison with the FAC data. For corrosion test in static condition, the amount of non adherent corrosion product was almost constant at pH ranging from 8 to 10. But adherent corrosion product decreased with increasing pH. This trend is consistent with decrease of Fe solubility with an increase in pH. For FAC test with rotating cylinder FAC test facility, the amount of non adherent corrosion product was also almost same for both DO concentrations. The rotating cylinder FAC test facility will be further improved by redesigning rotating cylinder and FAC specimen geometry for future work

Flow control by combining radial pulsation and rotation of a cylinder in uniform flow

Science.gov (United States)

Oualli, H.; Hanchi, S.; Bouabdallah, A.; Gad-El-Hak, M.

2008-11-01

Flow visualizations and hot-wire measurements are carried out to study a circular cylinder undergoing simultaneous radial pulsation and rotation and placed in a uniform flow. The Reynolds number is in the range of 1,000--22,000, for which transition in the shear layers and near wake is expected. Our previous experimental and numerical investigations in this subcritical flow regime have established the existence of an important energy transfer mechanism from the mean flow to the fluctuations. Radial pulsations cause and enhance that energy transfer. Certain values of the amplitude and frequency of the pulsations lead to negative drag (i.e. thrust). The nonlinear interaction between the Magnus effect induced by the steady rotation of the cylinder and the near-wake modulated by the bluff body's pulsation leads to alteration of the omnipresent Kármán vortices and the possibility of optimizing the lift-to-drag ratio as well as the rates of heat and mass transfer. Other useful applications include the ability to enhance or suppress the turbulence intensity, and to avoid the potentially destructive lock-in phenomenon in the wake of bridges, electric cables and other structures.

Boundary layer flow past a circular cylinder in axial flow

International Nuclear Information System (INIS)

Sawchuk, S.P.; Zamir, M.; Camiletti, S.E.

1985-01-01

This paper discusses a study of the laminar boundary layer on a semi-infinite circular cylinder in axial incompressible flow. Unlike previous studies, the present study investigates a full range of this boundary layer problem to determine skin friction, heat transfer and other integral properties of the boundary layer

Three-dimensional vortex flow near the endwall of a short cylinder in crossflow: Stepped-diameter circular cylinder

International Nuclear Information System (INIS)

Chen, S.B.; Sanitjai, S.; Ghosh, K.; Goldstein, R.J.

2012-01-01

The effect of geometry on the flow around a cylinder in crossflow is investigated in this study. Three different stepped-diameter circular cylinders (SDCC s) with varying step heights are used. Extensive flow visualization using the oil-lampblack and smoke-wire techniques and near wake velocity measurements using a hotwire anemometer reveal complex secondary flows on and around the SDCC. Six vortices are observed in the horseshoe vortex system near the cylinder–endwall junction and six additional vortices are found in the step-induced vortex system on the step surface. Based on these experimental results, new secondary flow models are proposed. The step-induced vortices separate from the step surface at both sides and move toward the endwall, washing down the sides of the top/bottom larger diameter cylinders and interact with the separated shear layer and horseshoe vortices. In this process, they modify the near wake flow significantly: they produce an increase in velocity near the endwall region (below the step) and a decrease in velocity near the mid-span region, even altering the oscillatory behavior of the wake. - Highlights: ► Extensive flow visualization for stepped-diameter circular cylinders in crossflow. ► Six vortices in the horseshoe vortex system near the base. ► Six additional step-induced vortices on the upstream symmetry plane of step surface. ► Power spectral analysis for u′ shows oscillatory nature of the wake.

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 reflect...... commonly used transmitter-receiver configuration for ground-penetrating radar (GPR). Numerical simulations involving time domain fields and fixed-offset configurations determine the radar responses of various types of pipes and conductive soils encountered in GPR.......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...

Numerical simulation of VAWT on the effects of rotation cylinder

Science.gov (United States)

Xing, Shuda; Cao, Yang; Ren, Fuji

2017-06-01

Based on Finite Element Analysis Method, studying on Vertical Axis Wind Turbine (VAWT) which is added rotating cylinder in front of its air foils, especially focusing on the analysis of NACA6 series air foils about variation of lift to drag ratio. Choosing the most suitable blades with rotary cylinder added on leading edge. Analysis indicates that the front rotating cylinders on the VAWT is benefit to lift rise and drag fall. The most suitable air foil whose design lift coefficient is 0.8, the blades relative thickness is 20%, and the optimistic tip speed ratio is about 7.

Vortex shedding control of circular cylinder by perforated shroud in deep water

Directory of Open Access Journals (Sweden)

Ozkan Gokturk M.

2017-01-01

Full Text Available The aim of the present study is to control the vortex shedding downstream of a circular cylinder (inner cylinder by the existence of outer perforated cylinder concentrically located around the inner cylinder in deep water. The flow characteristics downstream of concentrically placed coupled cylinders were investigated quantitatively by the Particle Image Velocimetry (PIV technique. Diameter of the outer perforated cylinder and inner cylinder were kept constant as Do=100 mm and Di=50 mm. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to the Reynolds number of ReDo=10,000 based on the outer cylinder diameter. Experiments were conducted for six porosities (β = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 in order to show the effect of these parameters on the flow control. Maximum values of both Reynolds shear stress, and turbulence kinetic energy, significantly decreased with the existence of outer perforated cylinder and also, the location of peak magnitudes of turbulence statistics occurred at locations further downstream compared to the bare cylinder case. The most effective control was revealed for the porosity of β=0.7.

Vortex shedding control of circular cylinder by perforated shroud in deep water

Science.gov (United States)

Ozkan, Gokturk M.; Durhasan, Tahir; Pinar, Engin; Aksoy, Muhammed M.; Akilli, Huseyin; Sahin, Beşir

The aim of the present study is to control the vortex shedding downstream of a circular cylinder (inner cylinder) by the existence of outer perforated cylinder concentrically located around the inner cylinder in deep water. The flow characteristics downstream of concentrically placed coupled cylinders were investigated quantitatively by the Particle Image Velocimetry (PIV) technique. Diameter of the outer perforated cylinder and inner cylinder were kept constant as Do=100 mm and Di=50 mm. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to the Reynolds number of ReDo=10,000 based on the outer cylinder diameter. Experiments were conducted for six porosities (β = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) in order to show the effect of these parameters on the flow control. Maximum values of both Reynolds shear stress, and turbulence kinetic energy, significantly decreased with the existence of outer perforated cylinder and also, the location of peak magnitudes of turbulence statistics occurred at locations further downstream compared to the bare cylinder case. The most effective control was revealed for the porosity of β=0.7.

In-cylinder tumble flows and performance of a motorcycle engine with circular and elliptic intake ports

Science.gov (United States)

Huang, R. F.; Lin, K. H.; Yeh, C.-N.; Lan, J.

2009-01-01

The temporal and spatial evolution processes of the flows in the cylinder of a four-valve, four-stroke, single cylinder, reciprocating motorcycle engine installed with the elliptic and circular intake ports were experimentally studied by using the particle image velocimetry (PIV). The engine was modified to fit the requirements of PIV measurement. The velocity fields measured by the PIV were analyzed and quantitatively presented as the tumble ratio and turbulence intensity. In the symmetry plane, both the circular and elliptic intake ports could initiate a vortex around the central region during the intake stroke. During the compression stroke, the central vortex created in the cylinder of the engine with the circular intake port disappeared, while that in the engine cylinder with the elliptic intake port further developed into the tumble motion. In the offset plane, weak vortical structures were initiated by the bluff-body effect of the intake valves during the intake stroke. The vortical structures induced by the elliptic intake port were more coherent than those generated by the circular intake port; besides, this feature extends to the compression stroke. The cycle-averaged tumble ratio and the turbulence intensity of the engine with the elliptic intake port were dramatically larger than those of the engine with the circular intake port. The measured engine performance was improved a lot by installing the elliptic intake port. The correlation between the flow features and the enhancement of the engine performance were argued and discussed.

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.

A numerical simulation of VIV on a flexible circular cylinder

International Nuclear Information System (INIS)

Xie Fangfang; Deng Jian; Zheng Yao; Xiao Qing

2012-01-01

In this paper, numerical simulations of a flexible circular cylinder subjected to a vortex-induced vibration (VIV) are conducted. The Reynolds number for simulations is fixed at 1000. The finite volume method is applied for modeling fluid flow with the moving meshes feature. The dynamic response of a flexible cylinder fixed at both ends is modeled by the Euler–Bernoulli beam theory. The comparison between two-dimensional (2D) simulations and 3D simulations for the flexible cylinder shows that the maximum response amplitude of the cross-flow oscillation is about 0.57D for 2D rigid cylinders (modeled by a spring–damper–mass model) and 1.03D for flexible cylinders, respectively. The results from 3D simulations are closer to previous experimental results. Furthermore, the results obtained with various frequency ratios show that different wake patterns exist according to the frequency ratio, such as 2S mode, 2P mode and some more complicated modes. The wake pattern is different at various sections along the cylinder length, due to the fact that the two ends of the beam are fixed. The vibration of the flexible cylinder can also greatly alter the three dimensionality in the wake, which is our research in future work, especially in the transition region for Reynolds number ranging from 170 to 300. (paper)

Non-intrusive investigation of flow and heat transfer characteristics of a channel with a built-in circular cylinder

Science.gov (United States)

Vyas, Apoorv; Mishra, Biswajit; Agrawal, Atul; Srivastava, Atul

2018-03-01

Interferometry-based experimental investigation of heat transfer phenomena associated with a channel fitted with a circular cylinder has been reported. Experiments have been performed with water as the working fluid, and the range of Reynolds number considered is 75 ≤ Re ≤ 165. The circular cylinder, placed at the inlet section of the channel, provides a blockage ratio of 0.5. The experimental methodology has been benchmarked against the results of transient numerical simulations. In order to assess the performance of the channel fitted with a circular cylinder for possible heat transfer enhancement from the channel wall(s), experiments have also been performed on a plane channel (without a cylinder). The interferometry-based experiments clearly highlighted the influence of the built-in cylinder in generating the flow instabilities and alterations in the thermal boundary layer profile along the heated wall of the channel. The phenomenon of vortex shedding behind the cylinder was successfully captured. A gradual increase in the vortex shedding frequency was observed with increasing Reynolds number. Quantitative data in the form of two-dimensional temperature distributions revealed an increase in the strength of wall thermal gradients in the wake region of the cylinder due to the periodic shedding of the vortices. In turn, a clear enhancement in the wall heat transfer rates was observed for the case of the channel fitted with a cylinder vis-à-vis the plane channel. To the best of the knowledge of the authors, the work reported is one of the first attempts to provide the planar field experimental data for a channel configuration with a built-in circular cylinder using non-intrusive imaging techniques and has the potential to serve as one of the benchmark studies for validating the existing as well as future numerical studies in the related area.

Background-oriented schlieren imaging of flow around a circular cylinder at low Mach numbers

Science.gov (United States)

Stadler, Hannes; Bauknecht, André; Siegrist, Silvan; Flesch, Robert; Wolf, C. Christian; van Hinsberg, Nils; Jacobs, Markus

2017-09-01

The background-oriented schlieren (BOS) imaging method has, for the first time, been applied in the investigation of the flow around a circular cylinder at low Mach numbers (Msuccessive imaging at incremental angular positions around the cylinder. This density distribution has been found to agree well with the pressure measurements and with potential theory where appropriate.

Mechanism of transition to turbulence in a circular cylinder wake in a channel

Directory of Open Access Journals (Sweden)

Molochnikov Valery

2017-01-01

Full Text Available Transition to turbulence in the circular cylinder wake has been studied experimentally and numerically at growing Reynolds number. Good agreement of calculation results with the flow visualization and measurements of instantaneous vector fields of velocity and vorticity has been demonstrated. The growing Reynolds number is shown to make large-scale vortex generation onset move upstream. It also triggers the transition to 3D flow pattern in the cylinder wake. This process is accompanied by non-monotonous behavior of the profiles of velocity and its turbulent fluctuations at equal distances from the cylinder. Non-monotonous behavior of the cylinder drag has been revealed for the Reynolds numbers ranging from 120 to 300.

Spatial atomic layer deposition on flexible substrates using a modular rotating cylinder reactor

International Nuclear Information System (INIS)

Sharma, Kashish; Hall, Robert A.; George, Steven M.

2015-01-01

Spatial atomic layer deposition (ALD) is a new version of ALD based on the separation of reactant gases in space instead of time. In this paper, the authors present results for spatial ALD on flexible substrates using a modular rotating cylinder reactor. The design for this reactor is based on two concentric cylinders. The outer cylinder remains fixed and contains a series of slits. These slits can accept a wide range of modules that attach from the outside. The modules can easily move between the various slit positions and perform precursor dosing, purging, or pumping. The inner cylinder rotates with the flexible substrate and passes underneath the various spatially separated slits in the outer cylinder. Trimethyl aluminum and ozone were used to grow Al 2 O 3 ALD films at 40 °C on metallized polyethylene terephthalate (PET) substrates to characterize this spatial ALD reactor. Spectroscopic ellipsometry measurements revealed a constant Al 2 O 3 ALD growth rate of 1.03 Å/cycle with rotation speeds from 40 to 100 RPM with the outer cylinder configured for one Al 2 O 3 ALD cycle per rotation. The Al 2 O 3 ALD growth rate then decreased at higher rotation rates for reactant residence times < 5 ms. The Al 2 O 3 ALD films were also uniform to within <1% across the central portion of metallized PET substrate. Fixed deposition time experiments revealed that Al 2 O 3 ALD films could be deposited at 2.08 Å/s at higher rotation speeds of 175 RPM. Even faster deposition rates are possible by adding more modules for additional Al 2 O 3 ALD cycles for every one rotation of the inner cylinder

Plane Wall Effect of Flow around Two Circular Cylinders in Tandem Arrangement

Directory of Open Access Journals (Sweden)

Triyogi Yuwono,

2011-02-01

Full Text Available The flow characteristic around two circular cylinders in tandem arrangement located near a plane wall were investigated experimentally in a uniform flow at a Reynolds Number of 5.3 x 104. The center to center spacing between the two cylinders relative to the cylinder diameter was constantly maintained at P/D = 1.5. The pressure distributions along the surface of the cylinder and the plane wall were measured by varying the gap-to-diameter of cylinder ratio (G/D in the range of 0 < G/D < 0.467. Surface oil-film techniques were used to investigate the flow patterns on the cylinder. The result showed that for upstream cylinder, in the gap-to-diameter ratio G/D < /D, there is no stagnation point at front side of the upstream cylinder; it is gradually raised as the gap increase. For the downstream cylinder, a peak on the lower side of the front side of the cylinder is apparent in each of the pressure distributions. This peak represents the reattachment of shear layer that separates from lower side of the upstream cylinder. The reattachment point tends to move forward close to the angular position of  = 0o as the gap ratio increase. The shear layer bifurcates into two shear layers. One shear layer continues in the downstream direction, and the other shear layer flows in the upstream direction.

Mixed convection of ferrofluids in a lid driven cavity with two rotating cylinders

Directory of Open Access Journals (Sweden)

Fatih Selimefendigil

2015-09-01

Full Text Available Mixed convection of ferrofluid filled lid driven cavity in the presence of two rotating cylinders were numerically investigated by using the finite element method. The cavity is heated from below, cooled from driven wall and rotating cylinder surfaces and side vertical walls of the cavity are assumed to be adiabatic. A magnetic dipole source is placed below the bottom wall of the cavity. The study is performed for various values of Reynolds numbers (100 ≤ Re ≤ 1000, angular rotational speed of the cylinders (−400 ≤ Ω ≤ 400, magnetic dipole strengths (0 ≤ γ ≤ 500, angular velocity ratios of the cylinders (0.25≤Ωi/Ωj≤4 and diameter ratios of the cylinders (0.5≤Di/Dj≤2. It is observed that flow patterns and thermal transport within the cavity are affected by variation in Reynolds number and magnetic dipole strength. The results of this investigation revealed that cylinder angular velocities, ratio of the angular velocities and diameter ratios have profound effect on heat transfer enhancement within the cavity. Averaged heat transfer enhancements of 181.5 % is achieved for clockwise rotation of the cylinder at Ω = −400 compared to motionless cylinder case. Increasing the angular velocity ratio from Ω2/Ω1=0.25 to Ω2/Ω1=4 brings about 91.7 % of heat transfer enhancement.

Rotational superradiance in fluid laboratories

CERN Document Server

Cardoso, Vitor; Richartz, Mauricio; Weinfurtner, Silke

2016-01-01

Rotational superradiance has been predicted theoretically decades ago, and is the chief responsible for a number of important effects and phenomenology in black hole physics. However, rotational superradiance has never been observed experimentally. Here, with the aim of probing superradiance in the lab, we investigate the behaviour of sound and surface waves in fluids resting in a circular basin at the center of which a rotating cylinder is placed. We show that with a suitable choice for the material of the cylinder, surface and sound waves are amplified. By confining the superradiant modes near the rotating cylinder, an instability sets in. Our findings are experimentally testable in existing fluid laboratories and hence offer experimental exploration and comparison of dynamical instabilities arising from rapidly rotating boundary layers in astrophysical as well as in fluid dynamical systems.

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.

On the development of lift and drag in a rotating and translating cylinder

Science.gov (United States)

Martin-Alcantara, Antonio; Sanmiguel-Rojas, Enrique; Fernandez-Feria, Ramon

2014-11-01

The two-dimensional flow around a rotating cylinder is investigated numerically using a vorticity forces formulation with the aim of analyzing the flow structures, and their evolutions, that contribute to the lift and drag forces on the cylinder. The Reynolds number, based on the cylinder diameter and steady free-stream speed, considered is Re = 200 , while the non-dimensional rotation rate (ratio of the surface speed and free-stream speed) selected were α = 1 and 3. For α = 1 the wake behind the cylinder for the fully developed flow is oscillatory due to vortex shedding, and so are the lift and drag forces. For α = 3 the fully developed flow is steady with constant (high) lift and (low) drag. Each of these cases is considered in two different transient problems, one with angular acceleration of the cylinder and constant speed, and the other one with translating acceleration of the cylinder and constant rotation. Special attention is paid to explaining the mechanisms of vortex shedding suppression for high rotation (when α = 3) and its relation to the mechanisms by which the lift is enhanced and the drag is almost suppressed when the fully developed flow is reached. Supported by the Ministerio de Economia y Competitividad of Spain Grant No. DPI2013-40479-P.

Absolute measurement of the viscosity of classical and quantum fluids by rotating-cylinder viscometers

International Nuclear Information System (INIS)

Donnelly, R.J.; LaMar, M.M.

1987-01-01

We discuss the use of rotating-cylinder viscometers to determine absolute shear viscosities of classical fluids and of helium II in the context of past and current knowledge of the stability and flow of these fluids between concentric cylinders. We identify a problem in measuring the absolute viscosity when the inner cylinder is rotating and the outer cylinder is at rest. We conclude by discussing the design of viscometers for absolute viscosity measurements in helium I and helium II

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...

Vibrational Suspension of Light Sphere in a Tilted Rotating Cylinder with Liquid

Directory of Open Access Journals (Sweden)

Victor G. Kozlov

2014-01-01

Full Text Available The dynamics of a light sphere in a quickly rotating inclined cylinder filled with liquid under transversal vibrations is experimentally investigated. Due to inertial oscillations of the sphere relative to the cavity, its rotation velocity differs from the cavity one. The intensification of the lagging motion of a sphere and the excitation of the outstripping differential rotation are possible under vibrations. It occurs in the resonant areas where the frequency of vibrations coincides with the fundamental frequency of the system. The position of the sphere in the center of the cylinder could be unstable. Different velocities of the sphere are matched with its various quasistationary positions on the axis of rotating cavity. In tilted rotating cylinder, the axial component of the gravity force appears; however, the light sphere does not float to the upper end wall but gets the stable position at a definite distance from it. It makes possible to provide a vibrational suspension of the light sphere in filled with liquid cavity rotating around the vertical axis. It is found that in the wide range of the cavity inclination angles the sphere position is determined by the dimensionless velocity of body differential rotation.

Bingham liquid flow between two cylinders induced by inner ring rotation

Science.gov (United States)

Jaroslav, Štigler; Simona, Fialová

2017-09-01

This paper deals with the fluid flow between two cylinders induced by inner ring rotation. The gap width between the cylinders, in case that they are both concentric, is 1mm, the gap and inner ring radius ratio 0.013 and the radius ratio 0.987. Attention is focused on rotation speed and eccentricity influence on the flow. Calculations were done for both Newtonian liquid and Bingham plastic liquid with the yield stress threshold 50 Pa.

Performance Evaluation of Rotating Cylinder Type Coffee Bean Roaster

Directory of Open Access Journals (Sweden)

Sutarsi

2010-04-01

Full Text Available One strategy attempts to reduce dependence on primary commodity markets are overseas market expansion and development of secondary products. In the secondary product processing coffee beans is required of supporting equipment to facilitate these efforts. Research Center for Indonesian Coffee and Cocoa has developed coffee bean roaster. However, there are still many people who do not know about the technical aspects of roaster machine type of rotating cylinder so that more people use traditional ways to roast coffee beans. In order for the benefits of this machine is better known society it is necessary to study on the technical aspects. The purpose of this research is to evaluate the technical performance of the coffee beans roaster machine type of rotating cylinder. These include the technical aspects of work capacity of the machine, roasting technical efficiency, fuel requirements, and power requirements of using roaster machine. Research methods are including data collection, calculation and analysis. The results showed that the roaster machine type of a rotating cylinder has capacity of 12.3 kg/hour. Roasting efficiency is 80%. Fuel consumption is 0.6 kg. The calculated amount of the used power of current measurement is the average of 0.616 kW.

Rotation of an immersed cylinder sliding near a thin elastic coating

Science.gov (United States)

Rallabandi, Bhargav; Saintyves, Baudouin; Jules, Theo; Salez, Thomas; Schönecker, Clarissa; Mahadevan, L.; Stone, Howard A.

2017-07-01

It is known that an object translating parallel to a soft wall in a viscous fluid produces hydrodynamic stresses that deform the wall, which in turn results in a lift force on the object. Recent experiments with cylinders sliding under gravity near a soft incline, which confirmed theoretical arguments for the lift force, also reported an unexplained steady-state rotation of the cylinders [B. Saintyves et al., Proc. Natl. Acad. Sci. USA 113, 5847 (2016), 10.1073/pnas.1525462113]. Motivated by these observations, we show, in the lubrication limit, that an infinite cylinder that translates in a viscous fluid parallel to a soft wall at constant speed and separation distance must also rotate in order to remain free of torque. Using the Lorentz reciprocal theorem, we show analytically that for small deformations of the elastic layer, the angular velocity of the cylinder scales with the cube of the sliding speed. These predictions are confirmed numerically. We then apply the theory to the gravity-driven motion of a cylinder near a soft incline and find qualitative agreement with the experimental observations, namely, that a softer elastic layer results in a greater angular speed of the cylinder.

Rotational friction coefficient of a permeable cylinder in a viscous fluid

NARCIS (Netherlands)

Wiegel, F.W.

1979-01-01

An exact expression is derived for the rotational friction coefficient of a cylinder of infinite length and constant permeability immersed in an incompressible viscous fluid. An asymptotic expression for the translational friction coefficient of a permeable cylinder moving in a sheet of viscous

Simulations of three-dimensional viscoelastic flows past a circular cylinder at moderate Reynolds numbers

KAUST Repository

RICHTER, DAVID; IACCARINO, GIANLUCA; SHAQFEH, ERIC S. G.

2010-01-01

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

Transient thermal stresses in a circular cylinder with constrained ends

International Nuclear Information System (INIS)

Goshima, Takahito; Miyao, Kaju

1986-01-01

This paker deals with the transient thermal stresses in a finite circular cylinder constrained at both end surfaces and subjected to axisymmetric temperature distribution on the lateral surface. The thermoelastic problem is formulated in terms of a thermoelastic displacement potential and three harmonic stress functions. Numerical calculations are carried out for the case of the uniform temperature distribution on the lateral surface. The stress distributions on the constrained end and the free suface are shown graphically, and the singularity in stresses appearing at the circumferencial edge is considered. Moreover, the approximate solution based upon the plane strain theory is introduced in order to compare the rigorous one, and it is considered how the length of the cylinder and the time proceeds affect on the accuracy of the approximation. (author)

Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

Science.gov (United States)

Miau, J. J.; Tsai, H. W.; Lin, Y. J.; Tu, J. K.; Fang, C. H.; Chen, M. C.

2011-10-01

Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 × 105-5.86 × 105. 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 θ = ±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.

Computer modeling of the stalled flow of a rotating cylinder and the reverse magnus effect

Science.gov (United States)

Belotserkovskii, S. M.; Kotovskii, V. N.; Nisht, M. I.; Fedorov, R. M.

1985-02-01

Unsteady stalled flow around a rotating cylinder is investigated in a numerical experiment. Attention is mostly given to the reverse Magnus effect which was discovered in tube experiments at some critical rotational speed of the cylinder.

Magnus effect on laminar flow around a rotating cylinder

International Nuclear Information System (INIS)

Amarante, J.C.A.

1989-01-01

The laminar flow around a rotating cylinder is studied, through the numerical solution of the full Navier-Stokes equations, for Reynolds number, based on cylinder radius, varying between 0.5 and 25 and for non-dimensional tangential velocities of the body surface between zero and 8. The Taylor and Hughes method is employed in the theoretical investigation. The Magnus lift coefficient and the drag coefficient are obtained and the presure and vorticity distribution are calculated. (author)

Three-dimensional transition in the wake of a circular cylinder by direct numerical simulation

International Nuclear Information System (INIS)

Kang, S. J.; Mo, J. O.; Lee, Y. H.; Tanahashi, M.; Miyauchi, T.

2001-01-01

Three-dimensional time-dependent flow past a circular cylinder is numerically investigated using direct numerical simulation for Reynolds number 280 and 300. The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward-Euler time integration. In x-y plane, the convection term is applied by the 5th order upwind scheme and the pressure and viscosity terms are applied by the 4th order central difference. And in spanwise, Navier-Stokes equation is distributed using of spectral method. At Reynolds number 259 the two-dimensional wake becomes linearly unstable to a second branch of modes with wavelength about 1.0 diameters at onset (B-mode). Present results of three-dimensional effects of in wake of a circular cylinder is represented with spanwise and streamwise vorticity contours as Reynolds numbers

Large Eddy simulation of turbulent flow past a circular cylinder in the subcritical and critical regimes

Energy Technology Data Exchange (ETDEWEB)

Lee, Kyongjun; Yang, Kyung-Soo [Inha University, Incheon (Korea, Republic of)

2017-04-15

Large Eddy simulation (LES) results of turbulent flow past a circular cylinder for the specified Reynolds numbers (Re = 63100, 126000, 252000) are presented. An immersed boundary method was employed to facilitate implementation of a circular cylinder in a Cartesian grid system. A dynamic subgrid-scale model, in which the model coefficient is dynamically determined by the current resolved flow field rather than assigned a prefixed constant, was implemented for accurate turbulence modeling. For better resolution near the cylinder surface and in the separated free-shear layers, a composite grid was used. Flow statistics including mean and rms values of force coefficients and Strouhal number of vortex shedding, are presented. Flow visualization using vorticity or Q contours are also shown. Our results are in better agreement with the MARIN measurements compared with RANS calculations reported in the previous ITTC workshop, confirming that LES is a more appropriate simulation methodology than a RANS approach to predict VIV for marine structures.

Buckling Analysis for Stiffened Anisotropic Circular Cylinders Based on Sanders Nonlinear Shell Theory

Science.gov (United States)

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.

Three-dimensional coating and rimming flow: a ring of fluid on a rotating horizontal cylinder

KAUST Repository

Leslie, G. A.

2013-01-29

The steady three-dimensional flow of a thin, slowly varying ring of Newtonian fluid on either the outside or the inside of a uniformly rotating large horizontal cylinder is investigated. Specifically, we study \\'full-ring\\' solutions, corresponding to a ring of continuous, finite and non-zero thickness that extends all of the way around the cylinder. In particular, it is found that there is a critical solution corresponding to either a critical load above which no full-ring solution exists (if the rotation speed is prescribed) or a critical rotation speed below which no full-ring solution exists (if the load is prescribed). We describe the behaviour of the critical solution and, in particular, show that the critical flux, the critical load, the critical semi-width and the critical ring profile are all increasing functions of the rotation speed. In the limit of small rotation speed, the critical flux is small and the critical ring is narrow and thin, leading to a small critical load. In the limit of large rotation speed, the critical flux is large and the critical ring is wide on the upper half of the cylinder and thick on the lower half of the cylinder, leading to a large critical load. We also describe the behaviour of the non-critical full-ring solution and, in particular, show that the semi-width and the ring profile are increasing functions of the load but, in general, non-monotonic functions of the rotation speed. In the limit of large rotation speed, the ring approaches a limiting non-uniform shape, whereas in the limit of small load, the ring is narrow and thin with a uniform parabolic profile. Finally, we show that, while for most values of the rotation speed and the load the azimuthal velocity is in the same direction as the rotation of the cylinder, there is a region of parameter space close to the critical solution for sufficiently small rotation speed in which backflow occurs in a small region on the upward-moving side of the cylinder. © 2013

Three-dimensional coating and rimming flow: a ring of fluid on a rotating horizontal cylinder

KAUST Repository

Leslie, G. A.; Wilson, S. K.; Duffy, B. R.

2013-01-01

The steady three-dimensional flow of a thin, slowly varying ring of Newtonian fluid on either the outside or the inside of a uniformly rotating large horizontal cylinder is investigated. Specifically, we study 'full-ring' solutions, corresponding to a ring of continuous, finite and non-zero thickness that extends all of the way around the cylinder. In particular, it is found that there is a critical solution corresponding to either a critical load above which no full-ring solution exists (if the rotation speed is prescribed) or a critical rotation speed below which no full-ring solution exists (if the load is prescribed). We describe the behaviour of the critical solution and, in particular, show that the critical flux, the critical load, the critical semi-width and the critical ring profile are all increasing functions of the rotation speed. In the limit of small rotation speed, the critical flux is small and the critical ring is narrow and thin, leading to a small critical load. In the limit of large rotation speed, the critical flux is large and the critical ring is wide on the upper half of the cylinder and thick on the lower half of the cylinder, leading to a large critical load. We also describe the behaviour of the non-critical full-ring solution and, in particular, show that the semi-width and the ring profile are increasing functions of the load but, in general, non-monotonic functions of the rotation speed. In the limit of large rotation speed, the ring approaches a limiting non-uniform shape, whereas in the limit of small load, the ring is narrow and thin with a uniform parabolic profile. Finally, we show that, while for most values of the rotation speed and the load the azimuthal velocity is in the same direction as the rotation of the cylinder, there is a region of parameter space close to the critical solution for sufficiently small rotation speed in which backflow occurs in a small region on the upward-moving side of the cylinder. © 2013 Cambridge

Experimental investigation of thermal processes in the multi-ring Couette system with counter rotation of cylinders

Science.gov (United States)

Mamonov, V. N.; Nazarov, A. D.; Serov, A. F.; Terekhov, V. I.

2016-01-01

The effect of parameters of the multi-ring Couette system with counter rotating coaxial cylinders on the process of thermal energy release in a viscous liquid filling this system is considered with regard to the problem of determining the possibility of creating the high-performance wind heat generator. The multi-cylinder rotor design allows directly conversion of the mechanical power of a device consisting of two "rotor" wind turbines with a common axis normal to the air flow into the thermal energy in a wide range of rotational speed of the cylinders. Experimental results on the measurement of thermal power released in the pilot heat generator at different relative angular speeds of cylinder rotation are presented.

Lagrangian Visualization and Real-Time Identification of the Vortex Shedding Time in the Wake of a Circular Cylinder

Science.gov (United States)

Rockwood, Matthew P.

The flow around a circular cylinder, a canonical bluff body, has been extensively studied in the literature to determine the mechanisms that cause the formation of vortices in the cylinder wake. Understanding of these mechanisms has led to myriad attempts to control the vortices either to mitigate the oscillating forces they cause, or to augment them in order to enhance mixing in the near-wake. While these flow control techniques have been effective at low Reynolds numbers, they generally lose effectiveness or require excessive power at Reynolds numbers commonly experienced in practical applications. For this reason, new methods for identifying the locations of vortices and their shedding time could increase the effectiveness of the control techniques. In the current work, two-dimensional, two-component velocity data was collected in the wake of a circular cylinder using a planar digital particle image velocimetry (DPIV) measurement system at Reynolds numbers of 9,000 and 19,000. This experimental data, as well as two-dimensional simulation data at a Reynolds number of 150, and three-dimensional simulation data at a Reynolds number of 400, is used to calculate the finite-time Lyapunov exponent (FTLE) field. The locations of Lagrangian saddles, identified as non-parallel intersections of positive and negative time FTLE ridges, are shown to indicate the timing of von Karman vortex shedding in the wake of a circular cylinder. The Lagrangian saddle found upstream of a forming and subsequently shedding vortex is shown to clearly accelerate away from the cylinder surface as the vortex begins to shed. This provides a novel, objective method to determine the timing of vortex shedding. The saddles are impossible 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 Lagrangian saddle acceleration without direct access to the FTLE, the saddle dynamics are connected to measurable surface quantities

Thin circular cylinder under axisymmetrical thermal and mechanical loading

International Nuclear Information System (INIS)

Arnaudeau, F.; Zarka, J.; Gerij, J.

1977-01-01

To assess structural integrity of components subjected to cyclic thermal loadings one must look at thermal ratchetting as a possible failure mode. Considering a thin circular cylinder subjected to constant internal pressure and cyclically varying thermal gradient through the thickness Bree, J. Strain Analysis 2 (1967) No.3, obtained a diagram that serves as a foundation for many design rules (e.g.: ASME code). The upper part of the french LMFBR main vessel is subjected to an axisymmetrical axial thermal loading and an axial load (own weight). Operation of the reactor leads to cyclic variations of the axial thermal loading. The question that arises is whether or not the Bree diagram is realistic for such loading conditions. A special purpose computer code (Ratch) was developed to analyse a thin circular cylinder subjected to axisymmetrical mechanical and thermal loadings. The Mendelson's approach of this problem is followed. Classical Kirchoff-Love hypothesis of thin shells is used and a state of plane stress is assumed. Space integrations are performed by Gaussian quadrature in the axial direction and by Simpson's one third rule throughout the thickness. Thermoelastic-plastic constitutive equations are solved with an implicit scheme (Nguyen). Thermovisco-plastic constitutive equations are solved with an explicit time integration scheme (Treanor's algorithm especially fitted). A Bree type diagram is obtained for an axial step of temperature which varies cyclically and a sustained constant axial load. The material behavior is assumed perfectly plastic and creep effect is not considered. Results show that the domain where no ratchetting occurs is reduced when compared with the domain predicted by the Bree diagram

Flow over an inline oscillating circular cylinder in the wake of a stationary circular cylinder

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yang; Zhu, Keqiang, E-mail: zhukeqiang@nbu.edu.cn [Faculty of Maritime and Transportation, Ningbo University, Ningbo 315211 (China)

2017-02-15

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 {sub e}/ f {sub 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. (paper)

Wake behind circular cylinder excited by spanwise periodic disturbances

Science.gov (United States)

Sasaki, Yudai; Uchida, Iwami; Sakakibara, Jun

2017-11-01

We experimentally investigated the influence of flow control of the wake behind a circular cylinder excited by temporal periodic disturbances with spanwise phase variations using plasma actuators, motivated by reducing drag forces by suppressing development of large scale vortices. Plasma actuators were segmented in the spanwise direction, phase differences were given to adjacent electrodes. This experiment was conducted at Re =8000 and the wake was visualized by PIV. Compared to without forcing, when the phase difference is 180° and non-dimensional forcing frequency is higher than approximately 1.0, small vortices induced by periodic disturbance emerged in the free shear layer and the drag forces decreased.

Natural convection in square enclosure induced by inner circular cylinder with time-periodic pulsating temperature

KAUST Repository

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.

Effect of instability of vortex streets behind circular cylinder on lock-in oscillation

International Nuclear Information System (INIS)

Masaya Kondo

2005-01-01

Full text of publication follows: The effects of the instability of vortex streets formed in the wakes of a circular cylinder on lock-in oscillation was investigated using a splitter plate and a phase-estimation methodology. The lock-in oscillation at the reduced velocity of 2.5 ≤ Vr < ∼ 3.5 is a self excited oscillation with alternate vortices. The amplitude of the lock-in oscillation is changed with the reduced velocity, although the oscillation frequency and the external force frequency caused by vortices is insensitive to the reduced velocity. Author reported that the amplitude changed with the energy input, which changed with the relationship between the phase of the external force and the phase of the cylinder displacement. The report suggested that the timing of the vortices shedding would change with the reduced velocity. The reason of the timing change, however, has not been clarified yet. This paper presents an explanation of the timing change using the instability of the vortex streets formed in the wake. The distance with a next vortex in a vortex street behind a cylinder at the lock-in condition changes with reduced velocity. On the assumption that the distance between two vortex streets formed in a wake of the cylinder is a constant, only one reduced velocity satisfied the stable condition called 'Karman Vortex Street'. It means that two vortex streets formed at the lock-in condition would be instable essentially, and the vortices would interact each other to form the stable condition. The interaction among the vortices would affect not only for the shed vortices in the wake but also for the growing-up vortex on the cylinder surface. Therefore, the instability of the vortex streets would affect the timing of the vortices shedding. A flow-induced oscillation test using a circular cylinder with a splitter plate was performed to confirm such an instability. The splitter plate was installed in the far wake of the cylinder to terminate the interaction

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.

Unsteady heat transfer from a circular cylinder for Reynolds numbers from 3000 to 15,000

International Nuclear Information System (INIS)

Nakamura, Hajime; Igarashi, Tamotsu

2004-01-01

Unsteady heat transfer from a circular cylinder to the cross-flow of air was investigated experimentally for Reynolds numbers from 3000 to 15,000. Fluctuating heat transfer on the cylinder surface was measured using a heat flux sensor, and time-spatial characteristics of the heat transfer were measured using an infrared thermograph. The present measurements showed that the alternating rolling-up of the shear layers that separated from the cylinder forms an alternating reattached flow at the rear of the cylinder in the range of Re>5000-8000, due to the forward movement of the vortex formation region with increasing Reynolds number. This leads to a sharp increase in the time-averaged Nusselt number around the rear stagnation point of the cylinder. The heat transfer in the separated flow region has spanwise nonuniformity throughout the examined Reynolds number range. The wavelength of this nonuniformity corresponds to that of the streamwise vortices formed in the near-wake

Examination of hydrodynamic force acting on a circular cylinder in vortex-induced vibrations in synchronization

Energy Technology Data Exchange (ETDEWEB)

Shen, Linwei; Sun, Zhilin [Ocean College, Zhejiang University, Zhoushan, 316021 (China); Chan, Eng-Soon, E-mail: shenlinwei@zju.edu.cn [Department of Civil and Environmental Engineering, National University of Singapore, No. 1 Engineering Drive 2, Singapore 117576 (Singapore)

2017-04-15

An immersed boundary method is employed to simulate vortex-induced vibrations (VIV) of a circular cylinder in two dimensions. The Reynolds number is 150, and the cylinder mass ratios of 2 and 10 are considered. The synchronization regions for these two mass ratios are determined by the simulations. It is found that the cycle-averaged added mass is about zero at the reduced velocity of 6.1. The instantaneous frequency, which is obtained by Hilbert transformation of the cylinder oscillating displacement, exhibits an important feature whereby the cylinder oscillation in the VIV synchronization region is modulated with a frequency twice the displacement prevailing frequency. The cylinder displacement could still be well approximated by a sine function with a constant frequency and amplitude. However, the lift force acting on the cylinder cannot be estimated in the same manner. In fact, both the lift force amplitude and frequency are modulated. The suggested expression provides a better approximation of the lift force. Moreover, it reveals that the presence of the higher harmonics in the lift force is the result of the amplitude and frequency modulation. (paper)

The effect of heat generation on mixed convection flow in nano fluids over a horizontal circular cylinder

Science.gov (United States)

Juliyanto, Bagus; Widodo, Basuki; Imron, Chairul

2018-04-01

The purpose of this research is to study the effect of heat generation on mixed convection flow on Nano fluids over a horizontal circular cylinder of a heated in two dimension form. A stream of fluids are steady and incompressible, a stream flowing vertically upwards for circular cylinder and the boundary layer at the stagnation point. Three different types of nanoparticles considered are Cu, Al2O3, and TiO2. Mixed convection flow in Nano fluids on the surface of a circular cylinder will cause the boundary layer. The governing boundary layer equations are transformed into a non-dimensional form, and then the non-dimensional forms are transformed into a similar boundary equations by using stream function. Furthermore, an implicit finite-difference scheme known as the Keller-box method is applied to solve numerically the resulting similar boundary layer equations. The result of the research by varying the non-dimensional parameters are mixed convection, Prandtl number, nanoparticle volume fraction, heat generation, and radius of a cylinder are as follows. First, the velocity profile increase and temperature profile decrease when mixed convection parameter increase. Second, the velocity and temperature profiles decrease when Prandtl number parameter increase. Third, the velocity profile with the variation of nanoparticle volume fraction (χ) is increased when the value of χ is 0,1 ≤ χ ≤ 0,15 and the velocity profile decreases when the value of χ is 0,19 ≤ χ ≤ 0,5 while the temperature profile is increasing when the value of χ is 0,1 ≤ χ ≤ 0,5. Fourth, the velocity and temperature profiles increase when heat generation and the radius of the cylinder increase. The last, Cu, Al 2 O 3, and TiO 2 nanoparticles produce the same velocity and temperature profiles, but the three types of nanoparticles are different at the velocity and temperature values.

Direct numerical simulations of flow and heat transfer over a circular cylinder at Re = 2000

NARCIS (Netherlands)

Vidya, Mahening Citra; Beishuizen, N.A.; van der Meer, Theodorus H.

2016-01-01

Unsteady direct numerical simulations of the flow around a circular cylinder have been performed at Re = 2000. Both two-dimensional and three-dimensional simulations were validated with laminar cold flow simulations and experiments. Heat transfer simulations were carried out and the time-averaged

On the motion of a compressible fluid in a rotating cylinder

International Nuclear Information System (INIS)

Brouwers, J.J.H.

1976-06-01

The secondary flow of an incompressible fluid or a perfect gas in a rotating cylinder is taken as a small perturbation on the isothermal state of rigid body rotation. Three types of flow are identified by increasing length-to-radius ratio L. These correspond to Esup(1/2) -1 and E -1 approximately L, where E is the Ekman number based on the radius and taken to be small. In the first range a geostrophic flow in the interior extended by Ekman layers near the end caps and Stewartson layers near the cylinder wall is found. For L approximately Esup(-1/2) and L approximately E -1 both Stewartson layers successively expand to the interior. For L approximately> E -1 radial diffusion of momentum is an important parameter describing the flow in the main section of the cylinder. For the perfect gas, special attention is focussed on strong radial density gradients. The modified Ekman number Esub(m) based on the density at the cylinder wall and on the density scale height is taken to be small. Increasing the ratio of the length to the radial density scale height Lsub(m) again three types of flow are distinguished. These correspond to Esub(m)sup(1/2) -1 and Esub(m)sup(-1) approximately Lsub(m). Compared to the incompressible fluid, two essential differences are found. (i) An inviscid flow characteristic for the first range is only observed in a limited region near the cylinder wall. Diffusive processes are important in the core of the cylinder. (ii) A change of the flow type appears when both Stewartson layers successively expand over the small radial density scale height. Diffusive regions come up from the centre of the cylinder and join. A change of the flow type appears at relatively small values of L. The theory discusses the efficiency of gas ultracentrifuges for isotope separation

Two-phase cross-flow-induced forces acting on a circular cylinder

International Nuclear Information System (INIS)

Hara, F.

1982-01-01

This paper clarifies the characteristics of unsteady flow-induced lift and drag forces acting on a circular cylinder immersed perpendicular to a two-phase bubbly air-water flow, in conjunction with Karman vortex shedding and pressure fluctuations. Experimental results presented show that Karman vortex shedding disappears over a certain value of air concentration in the two-phase flow. Related to this disappearance, flow-induced forces are rather small and periodical in low air concentration but become very large and random in higher air concentration. 7 refs

Generalisation of the method of images for the calculation of inviscid potential flow past several arbitrarily moving parallel circular cylinders

Czech Academy of Sciences Publication Activity Database

Kharlamov, Alexander A.; Filip, Petr

2012-01-01

Roč. 77, č. 1 (2012), s. 77-85 ISSN 0022-0833 Institutional research plan: CEZ:AV0Z20600510 Keywords : circular cylinders * cylinder between two walls * generalised method of images * ideal fluid * potential flow Subject RIV: BK - Fluid Dynamics Impact factor: 1.075, year: 2012

Effect of the Presence of Semi-circular Cylinders on Heat Transfer From Heat Sources Placed in Two Dimensional Channel

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

Multiple Long-Time Solutions for Intermediate Reynolds Number Flow past a Circular Cylinder with a Nonlinear Inertial and Dissipative Attachment

Science.gov (United States)

Blanchard, Antoine B. E.; Bergman, Lawrence A.; Vakakis, Alexander F.; Pearlstein, Arne J.

2016-11-01

We consider two-dimensional flow past a linearly-sprung cylinder allowed to undergo rectilinear motion normal to the mean flow, with an attached "nonlinear energy sink" consisting of a mass allowed to rotate about the cylinder axis, and whose rotational motion is linearly damped by a viscous damper. For Re fluid density, dimensionless damping coefficient, and ratio of the rotating mass to the total mass, we find that different inlet transients lead to different long-time solutions, including solutions that are steady and symmetric (with a motionless cylinder), time-periodic, quasi-periodic, and chaotic. The results show that over a wide range of the parameters, the steady symmetric motionless-cylinder solution is locally, but not globally, stable. Supported by NSF Grant CMMI-1363231.

Two dimensional numerical analysis of aerodynamic characteristics for rotating cylinder on concentrated air flow

Science.gov (United States)

Alias, M. S.; Rafie, A. S. Mohd; Marzuki, O. F.; Hamid, M. F. Abdul; Chia, C. C.

2017-12-01

Over the years, many studies have demonstrated the feasibility of the Magnus effect on spinning cylinder to improve lift production, which can be much higher than the traditional airfoil shape. With this characteristic, spinning cylinder might be used as a lifting device for short take-off distance aircraft or unmanned aerial vehicle (UAV). Nonetheless, there is still a gap in research to explain the use of spinning cylinder as a good lifting device. Computational method is used for this study to analyse the Magnus effect, in which two-dimensional finite element numerical analysis method is applied using ANSYS FLUENT software to examine the coefficients of lift and drag, and to investigate the flow field around the rotating cylinder surface body. Cylinder size of 30mm is chosen and several configurations in steady and concentrated air flows have been evaluated. All in all, it can be concluded that, with the right configuration of the concentrated air flow setup, the rotating cylinder can be used as a lifting device for very short take-off since it can produce very high coefficient of lift (2.5 times higher) compared with steady air flow configuration.

Laminar natural convection heat transfer from a horizontal circular cylinder to liquid metals

International Nuclear Information System (INIS)

Sugiyama, K.; Ma, Y.; Ishiguro, R.

1991-01-01

The objective of the present study is to clarify the heat transfer characteristic of natural convection around a horizontal circular cylinder immersed in liquid metals. Experimental work concerning liquid metals sometimes involves such a degree of error that is impossible to understand the observed characteristics in measurement. Numerical analysis is a powerful means to overcome this experimental disadvantage. In the present paper the authors first show that the Boussinesq approximation is more applicable heat transfer rates, even for a cylinder with a relatively large temperature difference (>100K) between the heat transfer surface and fluid. It is found from a comparison of the present results with previous work that the correlation equations that have already been proposed predict values lower than the present ones

Vortex breakdown in a cylinder with a rotating bottom and a flat stress-free surface

International Nuclear Information System (INIS)

Serre, E.; Bontoux, P.

2007-01-01

Vortex breakdown and transition to time-dependent regimes are investigated in a cylinder (H/R = 4) with a rotating disk and a free-surface. The aim of this study is to show how, by changing upstream conditions it is possible to alter on the flow, particularly the vortex breakdown process. The understanding of such effects on vortex breakdown is very useful in the development of a control strategy in order to intensify or remove the phenomenon. The flow dynamics are explored through numerical solution of the three-dimensional Navier-Stokes equations based on high-order spectral approximations. The use of a flat, stress-free model for the air/water interface is shown to be entirely satisfactory at least for moderate Reynolds numbers. A particular interest of these results is to show how the bubble related to the vortex breakdown becomes attached to the free-surface and grows in diameter as the Reynolds number is increased, Re ≥ 2900. Such a phenomenon removes the cylindrical vortex core upstream of the breakdown which is usually included in classical theories based on idealized models of vortex flows. The flow is shown to be unstable to three-dimensional perturbations for sufficiently large rotation rates. The bifurcated state takes the form of a k = 3 rotating wave at Re = 3000. The existence of the free-surface promotes the onset of periodicity, with a critical Reynolds number about 15% lower than in the case with a rigid cover. Moreover, the successive bifurcations occur over a much shorter range of Reynolds numbers and lead rapidly to a multi-frequency regime with more than five different frequencies. In the unsteady regime, the vortex breakdown is characterized by an elongated, asymmetric recirculation zone, attached to the free-surface and precessing around the axis of the container. By increasing the rotation, the circular stagnation line on the free-surface takes a more irregular form and starts to move around the axis of the cylinder in the same sense as

MHD natural convection in open inclined square cavity with a heated circular cylinder

Science.gov (United States)

Hosain, Sheikh Anwar; Alim, M. A.; Saha, Satrajit Kumar

2017-06-01

MHD natural convection in open cavity becomes very important in many scientific and engineering problems, because of it's application in the design of electronic devices, solar thermal receivers, uncovered flat plate solar collectors having rows of vertical strips, geothermal reservoirs, etc. Several experiments and numerical investigations have been presented for describing the phenomenon of natural convection in open cavity for two decades. MHD natural convection and fluid flow in a two-dimensional open inclined square cavity with a heated circular cylinder was considered. The opposite wall to the opening side of the cavity was first kept to constant heat flux q, at the same time the surrounding fluid interacting with the aperture was maintained to an ambient temperature T∞. The top and bottom wall was kept to low and high temperature respectively. The fluid with different Prandtl numbers. The properties of the fluid are assumed to be constant. As a result a buoyancy force is created inside the cavity due to temperature difference and natural convection is formed inside the cavity. The Computational Fluid Dynamics (CFD) code are used to discretize the solution domain and represent the numerical result to graphical form.. Triangular meshes are used to obtain the solution of the problem. The streamlines and isotherms are produced, heat transfer parameter Nu are obtained. The results are presented in graphical as well as tabular form. The results show that heat flux decreases for increasing inclination of the cavity and the heat flux is a increasing function of Prandtl number Pr and decreasing function of Hartmann number Ha. It is observed that fluid moves counterclockwise around the cylinder in the cavity. Various recirculations are formed around the cylinder. The almost all isotherm lines are concentrated at the right lower corner of the cavity. The object of this work is to develop a Mathematical model regarding the effect of MHD natural convection flow around

Mixed convection heat transfer simulation in a rectangular channel with a variable speed rotational cylinder

Science.gov (United States)

Khan, Md Imran; Billah, Md. Mamun; Rahman, Mohammed Mizanur; Hasan, Mohammad Nasim

2017-12-01

Numerical simulation of steady two-dimensional heat transfer in a rectangular channel with a centered variable speed cylinder has been performed in this paper. In this setup, an isoflux heater is placed at the bottom wall of the channel while the upper wall is kept isothermal with a low temperature. The cylinder's peripheral speed to maximum inlet fluid velocity ratio (ξ) is varied from 0.5 to 1.5 for both clockwise and anticlockwise rotational cases. Air has been considered as working fluid while other system parameters such as Grashof and Reynolds numbers are varied. The effects of rotational speed, Grashof and Reynolds numbers on the streamline pattern, isothermal lines, local and average Nusselt number are analyzed and presented. It is observed the cylinder's rotational direction and speed has a significant effect on the flow pattern, temperature distribution as well as heat transfer characteristics.

Control of flow around a circular cylinder wrapped with a porous layer by magnetohydrodynamic

Energy Technology Data Exchange (ETDEWEB)

Bovand, M. [Department of Mechanical Engineering, Semnan Branch, Islamic Azad University, Semnan (Iran, Islamic Republic of); Rashidi, S. [Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775-1111 (Iran, Islamic Republic of); Esfahani, J.A., E-mail: abolfazl@um.ac.ir [Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775-1111 (Iran, Islamic Republic of); Saha, S.C.; Gu, Y.T. [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001 (Australia); Dehesht, M. [School of Mechanical Engineering, Semnan University, P.O. Box 35196-45399, Semnan (Iran, Islamic Republic of)

2016-03-01

The present study focuses on the analysis of two-dimensional Magnetohydrodynamic (MHD) flow past a circular cylinder wrapped with a porous layer in different laminar flow regimes. The Darcy-Brinkman-Forchheimer model has been used for simulating flow in porous medium using finite volume based software, Fluent 6.3. In order to analyze the MHD flow, the mean and instantaneous drag and lift coefficients and stream patterns are computed to elucidate the role of Stuart number, N and Darcy number, Da. It is revealed that the magnetic fields are capable to stabilize flow and suppress the vortex shedding of vortices. The N-Re plane shows the curves for separating steady and periodic flow regimes, N{sub cr} and disappearing of vortex, N{sub diss}. For validate the solution, the obtained C{sub D} and St are compared with available results of literature. - Highlights: • The value of interaction parameter, N{sub cr}, depends on the Reynolds number. • N{sub cr} for porous-wrapped solid cylinder is less than the value of solid cylinder. • The St number of porous-wrapped cylinder is less than that of the rigid one. • When Da is decreased, St also decreases.

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...

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.

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

of secondary load cycles. Special attention was paid to this secondary load cycle and the flow features that cause it. By visual observation and a simplified analytical model it was shown that the secondary load cycle was caused by the strong nonlinear motion of the free surface which drives a return flow......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...... at the back of the cylinder following the passage of the wave crest. The numerical computations were further analysed in the frequency domain. For a representative example, the secondary load cycle was found to be associated with frequencies above the fifth- and sixth-harmonic force component. For the third...

Experimental vortex breakdown topology in a cylinder with a free surface

DEFF Research Database (Denmark)

Lo Jacono, D.; Nazarinia, M.; Brøns, Morten

2009-01-01

The free SLII-face, flow in it circular cylinder driven by a rotating bottom disk IS Studied experimentally using particle image velocimetry. Results are compared With computational,11 results assuming I stress-free surface A dye visualization Study by Spohn et al ["Observations of vortex breakdown...... in in open cylindrical container with I rotating bottom," Exp. Fluids 14. 70 (1993)]v as well as several numerical computations. has found a range of different vortex breakdown Structures in this flow. We confirm the existence of a transition where the top of the breakdown bubble crosses from the axis...... to the surface, which has previously only been found numerically. We employ a technique by Brons et al ["Topology of vortex breakdown bubbles in I cylinder with rotating bottom and free surface J. Fluid Mech 428. 133 (2001)] to find the corresponding bifurcation curve in the parameter plane, which has hitherto...

Experimental study of the effect of icing on the aerodynamics of circular cylinders - Part II: Inclined flow

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....

Large eddy simulation of the subcritical flow over a V grooved circular cylinder

International Nuclear Information System (INIS)

Alonzo-García, A.; Gutiérrez-Torres, C. del C.; Jiménez-Bernal, J.A.

2015-01-01

Highlights: • We compared numerically the turbulent flow over a smooth circular cylinder and a V grooved cylinder in the subcritical regime. • Turbulence intensities in both streamwise and normal direction suffered attenuations. • The swirls structures on grooves peaks seemed to have a cyclic behavior. • The evolution of the flow inside grooves showed that swirls structures located in peaks suffered elongations in the normal direction. • The secondary vortex structures formed in the grooved cylinder near wake were smaller in comparison of the smooth cylinder flow. - Abstract: In this paper, a comparative numerical study of the subcritical flow over a smooth cylinder and a cylinder with V grooves (Re = 140,000) is presented. The implemented technique was the Large Eddy Simulation (LES), which according to Kolmogorov's theory, resolves directly the most energetic largest eddies and models the smallest and considered universal high frequency ones. The Navier-Stokes (N-S) equations were solved using the commercial software ANSYS FLUENT V.12.1, which applied the finite volume method (FVM) to discretize these equations in their unsteady and incompressible forms. The grid densities were 2.6 million cells and 13.5 million cells for the smooth and V grooved cylinder, respectively. Both meshes were composed of structured hexahedral cells and close to the wall of the cylinders, additional refinements were employed in order to obtain y +<5 values. All cases were simulated during at least 15 vortex shedding cycles with the aim of obtaining significant statistical data. Results: showed that for both cases (smooth and V grooved cylinder flow), the numerical code was capable of reproducing the most important physical quantities of the subcritical regime. Velocity distribution and turbulence intensity in the flow direction suffered a slight attenuation along the wake, as a consequence of grooves perturbation, which also caused an increase in the pressure coefficient

Niobium carbide synthesis by solid-gas reaction using a rotating cylinder reactor

International Nuclear Information System (INIS)

Fontes, F.A.O.; Gomes, K.K.P.; Oliveira, S.A.; Souza, C.P.; Sousa, J.F.; Rio Grande do Norte Univ., Natal, RN

2004-01-01

A rotating cylinder reactor was designed for the synthesis of niobium carbide powders at 1173 K. Niobium carbide, NbC, was prepared by carbothermal reduction starting from commercial niobium pentoxide powders. The reactor was heated using a custom-made, two-part, hinged, electric furnace with programmable temperature control. The design and operational details of the reactor are presented. The longitudinal temperature gradient inside the reactor was determined. Total reaction time was monitored by a gas chromatograph equipped with an FID detector for determination of methane concentrations. The results show that time of reaction depended on rotation speed. NbC was also prepared in a static-bed alumina reactor using the same conditions as in the previous case. The niobium carbide powders were characterized by X-ray diffraction and compared with commercially available products. Morphological, particle size distribution and surface area analyses were obtained using SEM, LDPS and BET, respectively. Therefore, the present study offers a significant technological contribution to the synthesis of NbC powders in a rotating cylinder reactor. (author)

Dynamic response of a clamped/free hollow circular cylinder under travelling torsional impact loads

International Nuclear Information System (INIS)

Jonker, J.B.

1982-01-01

Impact-induced vibrations in the casing of a gas centriguge due to a sudden failure of the spinning rotor (crash) can cause structural disintegrity of the casing. In order to study the influence of the rotor failure bahaviour and the impact load histories on the dynamic response of the casing, a simple crash model is proposed in this paper to analyse the transient torsional response due to tangential components of the impact loads. The casing is modeled as a linear-elastic hollow circular cylinder, clamped at the lower end and free at the upper end. The rotor is thought to breakup in identical sections in a sequence determined by its fracture behaviour. Each section is assumed to cause an axi-symmetric load distribution at the inner surface of the casing. Therefore the problem is essentially reduced to the analysis of a clamped/free cylinder under travelling torsional impact loads. The problem is solved by representing the impact loads as local pulses acting over the length of the sections. A perturbation method is used to show that the general two-dimensional theory of axi-symmetric torsional wave propagation in circular cylinders, for the problem under consideration, may be approximated by the elementary one-dimensional theory. Solutions are obtained according to the usual modal expansion approach. Measurements of transient torsional responses are shown to be in good agreement with the calculated responses by choosing a suitable shape of the pulses. The effects of travelling velocity and pulse shape are investigated. Finally the transfer of kinetic energy in the rotor to vibrational energy of torsion in the casing is studied. (orig.)

Numerical simulation of flow past twin near-wall circular cylinders in tandem arrangement at low Reynolds number

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.

Combined Effect of Surface Roughness and Wake Splitter Plate on the Aerodynamic Characteristics of a Circular Cylinder

Science.gov (United States)

Saisanthosh, Iyer; Arunkumar, K.; Ajithkumar, R.; Srikrishnan, A. R.

2017-09-01

This paper is focussed on numerical investigation of flow around a stationary circular cylinder (diameter, D) with selectively applied surface roughness (roughness strips with thickness ‘k’) in the presence of a wake splitter plate (length, L). The plate leading edge is at a distance of ‘G’ from the cylinder base. For this study, the commercial software ANSYS Fluent is used. Fluid considered is water. Study was conducted the following cases (a) plain cylinder (b) cylinder with surface roughness (without splitter plate) (c) Cylinder with splitter plate (without surface roughness) and (d) cylinder with both roughness and splitter plate employed. The study Reynolds number (based on D) is 17,000 and k/δ = 1.25 (in all cases). Results indicate that, for cylinder with splitter plate (no roughness), lift coefficient gradually drops till G/D=1.5 further to which it sharply increases. Whereas, drag coefficient and Strouhal number undergoes slight reduction till G/D=1.0 and thereafter, gradually increase. Circumferential location of strip (α) does not influence the aerodynamic parameters significantly. With roughness alone, drag is magnified by about 1.5 times and lift, by about 2.7 times that of the respective values of the smooth cylinder. With splitter plate, for roughness applied at all ‘α’ values, drag and lift undergoes substantial reduction with the lowest value attained at G/D=1.0.

Numerical Simulation of Polymer Injection in Turbulent Flow Past a Circular Cylinder

KAUST Repository

Richter, David; Shaqfeh, Eric S. G.; Iaccarino, Gianluca

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.

A New Dual Circularly Polarized Feed Employing a Dielectric Cylinder-Loaded Circular Waveguide Open End Fed by Crossed Dipoles

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.

Harmonic oscillations of a circular cylinder moving with constant velocity in a quiescent fluid

OpenAIRE

Jan Novaes Recica; Luiz Antonio Alcântara Pereira; Miguel Hiroo Hirata

2008-01-01

The flow around an oscillating circular cylinder which moves with constant velocity in a quiescent Newtonian fluid with constant properties is analyzed. The influences of the frequency and amplitude oscillation on the aerodynamic loads and on the Strouhal number are presented. For the numerical simulation, a cloud of discrete Lamb vortices are utilized. For each time step of the simulation, a number of discrete vortices are placed close to the body surface; the intensity of theirs is determin...

Experimental study and CFD simulation of rotational eccentric cylinder in a magnetorheological fluid

International Nuclear Information System (INIS)

Omidbeygi, F.; Hashemabadi, S.H.

2012-01-01

In this study, a magnetorheological (MR) fluid is prepared using carbonyl iron filings and low viscosity lubricating oil. The effects of magnetic field and weight percentage of particles on the viscosity of the MR fluid have been measured using a rotational viscometer. The yield stress under an applied magnetic field was also obtained experimentally. In the absence of an applied magnetic field, the MR fluid behaves as a Newtonian fluid. When the magnetic field is applied, the MR fluid behaves like Bingham plastics with a magnetic field dependent yield stress. Afterward, the results compared with those of CFD simulation of two eccentric cylinders in the MR fluid. Results show that the influences of MR effects, caused by the applied magnetic field, on the model characteristics are significant and not negligible. The viscosity is enhanced by increasing of the magnetic field, eccentricity ratio and weight percentage of suspensions. The MR effects and increasing of weight percentage and eccentricity ratio also provide an enhancement in the yield stresses and required total torque for rotation of inner cylinder. Also the simulation results indicate a good representation of the experiment by the model. - Highlights: ► Preparation of a magnetorheological fluid with carbonyl iron particles in lubricating oil. ► Rheological measurement for influence of solid content and magnetic field intensity. ► Simulation of eccentric rotating cylinder in prepared MR fluid with CFD techniques.

Wall shear stress from a rotating cylinder in cross flow using the electrochemical technique

International Nuclear Information System (INIS)

Labraga, L.; Bourabaa, N.; Berkah, T.

2002-01-01

The wall shear rate from a rotating cylinder in a uniform flow was measured with flush-mounted electrochemical mass transfer probes. The experiments were performed using two rectangular electrodes in a sandwich arrangement. Initially, the frequency response of that probe was numerically studied using an inverse mass transfer method in order to restore the whole wall shear stress in the time domain starting from the measured transfer coefficients given by the split probe. The experiments were performed in the range of velocity ratios 0 4, points of zero shear stress on the rotating cylinder vanish, which is in fact consistent with the previous arguments that the cylinder is surrounded by a set of closed streamlines. This experimental study shows that, when their dynamic behaviour is known, the electrochemical probes are able to sense complex fine structures not observed up to now by previous analytical, numerical or experimental methods, even when non-linear effects are not negligible. (orig.)

Mixed convection boundary-layer flow from a horizontal circular cylinder with a constant surface heat flux

Energy Technology Data Exchange (ETDEWEB)

Nazar, R.; Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)

2004-02-01

The laminar mixed convection boundary-layer flow of a viscous and incompressible fluid past a horizontal circular cylinder, which is maintained at a constant heat flux and is placed in a stream flowing vertically upward has been theoretically studied in this paper. The solutions for the flow and heat transfer characteristics are evaluated numerically for different values of the mixed convection parameter {lambda} with the Prandtl number Pr = 1 and 7, respectively. It is found, as for the case of a heated or cooled cylinder, considered by Merkin [5], that assisting flow delays separation of the boundary-layer and can, if the assisting flow is strong enough, suppress it completely. The opposing flow, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently strong opposing flows there will not be a boundary-layer on the cylinder. (orig.)

Control of vortex breakdown in a closed cylinder with a small rotating rod

DEFF Research Database (Denmark)

Lo Jacono, D.; Sørensen, Jens Nørkær; Thompson, M.C.

2008-01-01

Effective control of vortex breakdown in a cylinder with a rotating lid was achieved with small rotating rods positioned on the stationary lid. After validation with accurate measurements using a novel stereoscopic particle image velocimetry (SPIV) technique, analysis of numerical simulations using...... a high-order spectral element method has been undertaken. The effect of a finite length rod creates additional source terms of vorticity as the rod rotates. These additional source terms and their spatial locations influence the occurrence of the vortex breakdown....

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....... Sensitivity tests of the extent of the inner Navier–Stokes/VOF domain were carried out. Numerical computations of wave loads on surface piercing circular cylinders at intermediate water depths are presented. Four different test cases of increasing complexity were considered; 1) weakly nonlinear regular waves...

On the inverse Magnus effect for flow past a rotating cylinder

Science.gov (United States)

John, Benzi; Gu, Xiao-Jun; Barber, Robert W.; Emerson, David R.

2016-11-01

Flow past a rotating cylinder has been investigated using the direct simulation Monte Carlo method. The study focuses on the occurrence of the inverse Magnus effect under subsonic flow conditions. In particular, the variations in the coefficients of lift and drag have been investigated as a function of the Knudsen and Reynolds numbers. Additionally, a temperature sensitivity study has been carried out to assess the influence of the wall temperature on the computed aerodynamic coefficients. It has been found that both the Reynolds number and the cylinder wall temperature significantly affect the drag as well as the onset of lift inversion in the transition flow regime.

Simulations of three-dimensional viscoelastic flows past a circular cylinder at moderate Reynolds numbers

KAUST Repository

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.

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.

Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders

International Nuclear Information System (INIS)

Paoletti, M. S.; Lathrop, D. P.

2011-01-01

We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω 1 , Ω 2 ) parameter space at high Reynolds numbers, where Ω 1 (Ω 2 ) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=(Ω 1 -Ω 2 )/Ω 2 fully determines the state and torque G as compared to G(Ro=∞)≡G ∞ . The ratio G/G ∞ is a linear function of Ro -1 in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].

Turbulent heat transfer studies in annulus with inner cylinder rotation

International Nuclear Information System (INIS)

Kuzay, T.M.; Scott, C.J.

1977-01-01

Experimental investigations of turbulent heat transfer are made in a large-gap annulus with both rotating and nonrotating inner cylinder. The vertical annular channel has an electrically heated outer wall; the inner wall i thermally and electrically insulated. The axial air flow is allowed to develop before rotation and heating are imparted. The resulting temperature fields are investigated using thermocouple probes located near the channel exit. The wall heat flux, wall axial temperature development, and radial temperature profiles are measured. For each axial Reynolds number, three heat flux rates are used. Excellent correlation is established between rotational and nonrotational Nusselt number. The proper correlation parameter is a physical quantity characterizing the flow helix. This parameter is the inverse of the ratio of axial travel of the flow helix in terms of hydraulic diameter, per half revolution of the spinning wall

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1998-12-31

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.

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.

Flow around a cylinder surrounded by a permeable cylinder in shallow water

Energy Technology Data Exchange (ETDEWEB)

Ozkan, Gokturk M.; Akilli, Huseyin; Sahin, Besir [Cukurova University, Department of Mechanical Engineering, Faculty of Engineering and Architecture, Adana (Turkey); Oruc, Vedat [Dicle University, Department of Mechanical Engineering, Diyarbakir (Turkey)

2012-12-15

The change in flow characteristics downstream of a circular cylinder (inner cylinder) surrounded by an outer permeable cylinder was investigated in shallow water using particle image velocimetry technique. The diameter of the inner cylinder and the water height were kept constant during the experiments as d=50 mm and h{sub w}=25 mm, respectively. The depth-averaged free-stream velocity was also kept constant as U=170 mm/s which corresponded to a Reynolds number of Re{sub d}=8,500 based on the inner cylinder diameter. In order to examine the effect of diameter and porosity of the outer cylinder on flow characteristics of the inner cylinder, five different outer cylinder diameters (D=60, 70, 80, 90 and 100 mm) and four different porosities ({beta}=0.4, 0.5, 0.6 and 0.7) were used. It was shown that both porosity and outer cylinder diameter had a substantial effect on the flow characteristics downstream of the circular cylinder. Turbulent statistics clearly demonstrated that in comparison with the bare cylinder (natural case), turbulent kinetic energy and Reynolds stresses decreased remarkably when an outer cylinder was placed around the inner cylinder. Thereby, the interaction of shear layers of the inner cylinder has been successfully prevented by the presence of outer cylinder. It was suggested by referring to the results that the outer cylinder having 1.6{<=}D/d{<=}2.0 and 0.4{<=}D/d{<=}0.6 should be preferred to have a better flow control in the near wake since the peak magnitude of turbulent kinetic energy was considerably low in comparison with the natural case and it was nearly constant for these mentioned porosities {beta}, and outer cylinder to inner cylinder diameter ratios D/d. (orig.)

Flow of Giesekus viscoelastic fluid in a concentric annulus with inner cylinder rotation

International Nuclear Information System (INIS)

Ravanchi, Maryam Takht; Mirzazadeh, Mahmoud; Rashidi, Fariborz

2007-01-01

An approximate analytical solution is derived for the steady state, purely tangential flow of a viscoelastic fluid obeying the Giesekus constitutive equation in a concentric annulus with inner cylinder rotation. An approximation is used for the estimation of radial normal stress. The effect of Weissenberg number (We), radius ratio (κ) and mobility factor (α) on velocity distribution and fRe are investigated. The results show that the velocity gradient near the inner cylinder increases as the fluid elasticity increases. The results also show that fRe decreases with increasing fluid elasticity

Harmonic oscillations of a circular cylinder moving with constant velocity in a quiescent fluid

Directory of Open Access Journals (Sweden)

Jan Novaes Recica

2008-01-01

Full Text Available The flow around an oscillating circular cylinder which moves with constant velocity in a quiescent Newtonian fluid with constant properties is analyzed. The influences of the frequency and amplitude oscillation on the aerodynamic loads and on the Strouhal number are presented. For the numerical simulation, a cloud of discrete Lamb vortices are utilized. For each time step of the simulation, a number of discrete vortices are placed close to the body surface; the intensity of theirs is determined such as to satisfy the no-slip boundary condition.

Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow

International Nuclear Information System (INIS)

Kawamura, T.; Nakao, T.; Hayashi, M.; Murayama, K.

2001-01-01

Synchronized vibrations were measured for a circular cylinder subjected to a water cross flow in the subcritical Reynolds numbers in order to compare the synchronized vibration range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on it. A small peak vibration in the lift direction was found when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency in only the subcritical region. The ratio of the Karman vortex frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortices began was about 1/4 in the subcritical region, and increased to 0,32 at the Strouhal number of 0,29 in the supercritical region. The frequency ratio at the beginning of the lock-in vibration in the drag direction by the Karman vortex was about 1/2, and that in the lift direction decreased from 1 to about 0,8 with decreasing Strouhal number. (author)

Standing torsional waves in a fully saturated, porous, circular cylinder

CERN Document Server

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.

Second-order wave diffraction by a circular cylinder using scaled boundary finite element method

International Nuclear Information System (INIS)

Song, H; Tao, L

2010-01-01

The scaled boundary finite element method (SBFEM) has achieved remarkable success in structural mechanics and fluid mechanics, combing the advantage of both FEM and BEM. Most of the previous works focus on linear problems, in which superposition principle is applicable. However, many physical problems in the real world are nonlinear and are described by nonlinear equations, challenging the application of the existing SBFEM model. A popular idea to solve a nonlinear problem is decomposing the nonlinear equation to a number of linear equations, and then solves them individually. In this paper, second-order wave diffraction by a circular cylinder is solved by SBFEM. By splitting the forcing term into two parts, the physical problem is described as two second-order boundary-value problems with different asymptotic behaviour at infinity. Expressing the velocity potentials as a series of depth-eigenfunctions, both of the 3D boundary-value problems are decomposed to a number of 2D boundary-value sub-problems, which are solved semi-analytically by SBFEM. Only the cylinder boundary is discretised with 1D curved finite-elements on the circumference of the cylinder, while the radial differential equation is solved completely analytically. The method can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.

Precession of a rapidly rotating cylinder flow: traverse through resonance

Science.gov (United States)

Lopez, Juan; Marques, Francisco

2014-11-01

The flow in a rapidly rotating cylinder that is titled and also rotating around another axis can undergo sudden transitions to turbulence. Experimental observations of this have been associated with triadic resonances. The experimental and theoretical results are well-established in the literature, but there remains a lack of understanding of the physical mechanisms at play in the sudden transition from laminar to turbulent flow with very small variations in the governing parameters. Here, we present direct numerical simulations of a traverse in parameter space through an isolated resonance, and describe in detail the bifurcations involved in the sudden transition. U.S. National Science Foundation Grant CBET-1336410 and Spanish Ministry of Education and Science Grant (with FEDER funds) FIS2013-40880.

Dynamics of a flexible splitter plate in the wake of a circular cylinder

Science.gov (United States)

Shukla, S.; Govardhan, R. N.; Arakeri, J. H.

2013-08-01

Rigid splitter plates in the wake of bluff bodies are known to suppress the primary vortex shedding. In the present work, we experimentally study the problem of a flexible splitter plate in the wake of a circular cylinder. In this case, the splitter plate is free to continuously deform along its length due to the fluid forces acting on it; the flexural rigidity (EI) of the plate being an important parameter. Direct visualizations of the splitter plate motions, for very low values of flexural rigidity (EI), indicate periodic traveling wave type deformations of the splitter plate with maximum tip amplitudes of the order of 1 cylinder diameter. As the Reynolds number based on cylinder diameter is varied, two regimes of periodic splitter plate motions are found that are referred to as mode I and mode II, with a regime of aperiodic motions between them. The frequency of plate motions in both periodic modes is found to be close to the plane cylinder Strouhal number of about 0.2, while the average frequencies in the non-periodic regime are substantially lower. The measured normalized phase speed of the traveling wave for both periodic modes is also close to the convection speed of vortices in the plane cylinder wake. As the flexural rigidity of the plate (EI) is increased, the response of the plate was found to shift to the right when plotted with flow speed or Re. To better capture the effect of varying EI, we define and use a non-dimensional bending stiffness, K*, similar to the ones used in the flag flutter problem, K=EI/(0.5ρUL), where U is the free-stream velocity and L is the splitter plate length. Amplitude data for different EI cases when plotted against this parameter appear to collapse on to a single curve for a given splitter plate length. Measurements of the splitter plate motions for varying splitter plate lengths indicate that plates that are substantially larger than the formation length of the plane cylinder wake have similar responses, while shorter

Experimental study of a particle velocity immersed in a fluid in rotation

International Nuclear Information System (INIS)

Cesar, S.B.G.

1981-12-01

An incompressible viscous fluid is confined within a circular cylinder whose wall and top are fixed while the botton rotates with constant angular speed. The velocity components of a particule immersed in the fluid above, was determined. The method utilized employs filming the particle during its motion. Experimental measurements were made at rotational speeds between 50 and 190 rps, at inter-disc spacing between 10 and 40 cm, and the particle is let loose at distances between static disc and 5 cm above the inferior disc. The results show that the method utilized is valid in a radial region within the cylinder between 1.0 [pt

Flow-induced vibration of circular cylindrical structures

International Nuclear Information System (INIS)

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

Inertial wave beams and inertial wave modes in a rotating cylinder with time-modulated rotation rate

Science.gov (United States)

Borcia, Ion D.; Ghasemi V., Abouzar; Harlander, Uwe

2014-05-01

Inertial gravity waves play an crucial role in atmospheres, oceans, and the fluid inside of planets and moons. In the atmosphere, the effect of rotation is neglected for small wavelength and the waves bear the character of internal gravity waves. For long waves, the hydrostatic assumption is made which in turn makes the atmosphere inelastic with respect to inertial motion. In contrast, in the Earth's interior, pure inertial waves are considered as an important fundamental part of the motion. Moreover, as the deep ocean is nearly homogeneous, there the inertial gravity waves bear the character of inertial waves. Excited at the oceans surface mainly due to weather systems the waves can propagate downward and influence the deep oceans motion. In the light of the aforesaid it is important to understand better fundamental inertial wave dynamics. We investigate inertial wave modes by experimental and numerical methods. Inertial modes are excited in a fluid filled rotating annulus by modulating the rotation rate of the outer cylinder and the upper and lower lids. This forcing leads to inertial wave beams emitted from the corner regions of the annulus due to periodic motions in the boundary layers (Klein et al., 2013). When the forcing frequency matches with the eigenfrequency of the rotating annulus the beam pattern amplitude is increasing, the beams broaden and mode structures can be observed (Borcia et al., 2013a). The eigenmodes are compared with analytical solutions of the corresponding inviscid problem (Borcia et al, 2013b). In particular for the pressure field a good agreement can be found. However, shear layers related to the excited wave beams are present for all frequencies. This becomes obvious in particular in the experimental visualizations that are done by using Kalliroscope particles, highlighting relative motion in the fluid. Comparing the eigenfrequencies we find that relative to the analytical frequencies, the experimental and numerical ones show a small

Sub-wavelength resonances in polygonal metamaterial cylinders

DEFF Research Database (Denmark)

Arslanagic, Samel; Breinbjerg, Olav

2008-01-01

It has been shown that the sub-wavelength resonances of circular MTM cylinders also occur for polygonal MTM cylinders. This is the case for lossless and non-dispersive cylinders as well as lossy and dispersive cylinders. The sub-wavelength resonances are thus not limited to structures of canonical...

DETERMINATION OF CRITICAL ROTATIONAL SPEED OF CIRCULAR SAWS FROM NATURAL FREQUENCIES OF ANNULAR PLATE WITH ANALOGOUS DIMENSIONS

Directory of Open Access Journals (Sweden)

Ante Skoblar

2016-03-01

Full Text Available It is suitable to reduce thickness of circular saw when trying to enhance usability of wood raw material, but reducing thickness also causes reduction of permissible rotational speed which reduces sawing speed. If one increase circular saw rotational speed over permissible one the quality of machined surfaces will reduce because of enhanced vibrations. Permissible rotational speed can be calculated from critical rotational speed which can be defined from natural frequencies of the saw. In this article critical rotational speeds of standard clamped saws (with flat disk surface and without slots are calculated by using finite element method and classical theory of thin plates on annular plates. Mode shapes and natural frequencies of annular plates are determined by using Bessel functions and by using polynomial functions. Obtained results suggest that standard clamped circular saws without slots and with relatively small teeth can be determined from classical theory of thin plates for annular plates with accuracy depending on clamping ratio.

Transient thermal stresses in a transversely isotropic finite hollow circular cylinder due to arbitrary surface heat generations

International Nuclear Information System (INIS)

Sugano, Yoshihiro; Nakanishi, Takanori.

1980-01-01

The materials macroscopically regarded as anisotropic materials such as fiber-reinforced composite materials have become to be used for the structural elements at elevated temperature, and the studies on the problem of thermal stress in anisotropic bodies are carried out actively. The unsteady thermal stress in anisotropic finite circular cylinders has not been analyzed so far. In this study, the problem of unsteady thermal stress in an anisotropic finite circular cylinder having arbitrary surface heat generation in axial direction on the internal and external surfaces, and emitting heat from both ends and the internal and external surfaces, was analyzed. For the analysis of temperature distribution, generalized finite Fourier transformation and finite Hankel transformation were used, and thermal stress and thermal displacement were analyzed by the use of the stress function of Singh. By adopting the function used for the transformation nucleus in generalized finite Fourier transformation as the stress function, the analysis was made without separating symmetric and opposite symmetric problems. Numerical calculation was carried out on the basis of the analytical results, and the effects of the anisotropy in thermal conductivity, Young's modulus and linear expansion on unsteady temperature distribution, thermal stress and thermal displacement were quantitatively examined. (Kako, I.)

Control of vortex breakdown in a closed cylinder with a rotating lid

DEFF Research Database (Denmark)

Jørgensen, Bo Hoffmann; Sørensen, Jens Nørkær; Aubry, Nadine

2010-01-01

The flow within a closed cylinder with a rotating lid is considered as a prototype for fundamental studies of vortex breakdown. Numerical simulations for various parameter values have been carried out to reproduce the known effect of a thin rotating rod positioned along the center axis as well...... as analyze the influence of local vorticity sources. As expected, the results show that the breakdown bubbles in the steady axisymmetric flow can be affected dramatically, i.e., fully suppressed or significantly enhanced, by rotating the rod. The main contribution of this article is to show that the observed...... behavior can be explained by the vorticity generated by the rod locally near the rotating lid and near the fixed lid, as analogous behavior is caused by the introduction of local vorticity sources in the flow without a rod. Moreover, we describe the influence on the breakdown bubbles of the vorticity...

Thin circular cylinder under axisymmetrical thermal and mechanical loading

International Nuclear Information System (INIS)

Arnaudeau, F.; Zarka, J.; Gerij, J.

1977-01-01

A special purpose computer code (Ratch) was developed to analyse a thin circular cylinder subjected to axisymmetrical mechanical and thermal loadings. The Mendelson's approach of this problem is followed. Classical Kirchoff-Love hypothesis of thin shells is used and a state of plane stress is assumed. Space integrations are performed by Gaussian quadrature in the axial direction and by Simpson's one third rule throughout the thickness. Thermoelastic-plastic constitutive equations are solved with an implicit scheme (Nguyen). Thermovisco-plastic constitutive equations are solved with an explicit time integration scheme (Treanor's algorithm especially fitted). A Bree type diagram is obtained for an axial step of temperature which varies cyclically and a sustained constant axial load. The material behavior is assumed perfectly plastic and creep effect is not considered. Results show that the domain where ratchetting occurs is reduced when compared with the domain predicted by the Bree diagram. To investigate the effect of material hardening the authors verify Halphen's Theorem which states that a structure made of material with kinematic hardening behavior and constant properties with temperature will always shake down to a periodic behavior. (Auth.)

Large circular dichroism and optical rotation in titanium doped chiral silver nanorods

Energy Technology Data Exchange (ETDEWEB)

Titus, Jitto; Perera, A.G. Unil [Department of Physics and Astronomy, Optoelectronics Laboratory, GSU, Atlanta, GA (United States); Larsen, George; Zhao, Yiping [Department of Physics and Astronomy, Nanolab, UGA, Athens, GA (United States)

2016-10-15

The circular dichroism of titanium-doped silver chiral nanorod arrays grown using the glancing angle deposition (GLAD) method is investigated in the visible and near infrared ranges using transmission ellipsometry and spectroscopy. These films are found to have significant circular polarization effects across broad ranges of the visible to NIR spectrum, including large values for optical rotation. The characteristics of these circular polarization effects are strongly influenced by the morphology of the deposited arrays. Thus, the morphological control of the optical activity in these nanostructures demonstrates significant optimization capability of the GLAD technique for fabricating chiral plasmonic materials. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Analysis of blood flow with nanoparticles induced by uniform magnetic field through a circular cylinder with fractional Caputo derivatives

Science.gov (United States)

Abdullah, M.; Butt, Asma Rashid; Raza, Nauman; Alshomrani, Ali Saleh; Alzahrani, A. K.

2018-01-01

The magneto hydrodynamic blood flow in the presence of magnetic particles through a circular cylinder is investigated. To calculate the impact of externally applied uniform magnetic field, the blood is electrically charged. Initially the fluid and circular cylinder is at rest but at time t =0+ , the cylinder starts to oscillate along its axis with velocity fsin (Ωt) . To obtain the mathematical model of blood flow with fractional derivatives Caputo fractional operator is employed. The solutions for the velocities of blood and magnetic particles are procured semi analytically by using Laplace transformation method. The inverse Laplace transform has been calculated numerically by using MATHCAD computer software. The obtained results of velocities are presented in Laplace domain in terms of modified Bessel function I0 (·) . The obtained results satisfied all imposed initial and boundary conditions. The hybrid technique that is employed here less computational effort and time cost as compared to other techniques used in literature. As the limiting cases of our results the solutions of the flow model with ordinary derivatives has been procured. Finally, the impact of Reynolds number Re, fractional parameter α and Hartmann number Ha is analyzed and portrayed through graphs. It is worthy to pointing out that fractional derivatives brings remarkable differences as compared to ordinary derivatives. It also has been observed that velocity of blood and magnetic particles is weaker under the effect of transverse magnetic field.

Topology of vortex Breakdown bubbles in a cylinder with rotating bottom and Free surface

DEFF Research Database (Denmark)

Brøns, Morten; Voigt, Lars Peter Kølgaard; Sørensen, Jens Nørkær

2001-01-01

The flow patterns in the steady, viscous flow in a cylinder with a rotating bottom and a free surface are investigated by a combination of topological and numerical methods. Assuming the flow is axisymmetric, we derive a list of possible bifurcations of streamline structures on varying two...

A study of the vortex structures around circular cylinder mounted on vertical heated plate

Science.gov (United States)

Malah, Hamid; Chumakov, Yurii S.; Levchenya, Alexander M.

2018-05-01

In recent years, studies of natural convection boundary layer interacting with obstacles draw much of attention, because of its practical applications. Pressure gradient resulting from this interaction leads to separation of the boundary layer. The formation of vortex structure around obstacle is characteristic to any kind of convection flow. In this paper, we describe the formation of three-dimensional vortex structure for the case of natural convection flow around the circular cylinder mounted on vertical heated plate. Navier-Stokes equations were used for numerical computations. The results proved the presence of a horseshoe vortex system in the case of natural convection flow as in the forced convection flow.

Electric-line-source illumination of a circular cylinder of lossless double-negative material: an investigation of near field, directivity, and radiation resistance

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...

Stabilization of flow past a rounded cylinder

Science.gov (United States)

Samtaney, Ravi; Zhang, Wei

2016-11-01

We perform global linear stability analysis on low-Re flow past a rounded cylinder. The cylinder corners are rounded with a radius R, normalized as R+ = R / D where D is the cylinder diameter, and its effect on the flow stability characteristics is investigated. We compute the critical Reynolds number (Recr) for the onset of first instability, and quantify the perturbation growth rate for the super-critical flows. It is found that the flow can be stabilized by partially rounding the cylinder. Compared with the square and circular cylinders, the partially rounded cylinder has a higher Recr , attaining a maximum at around R+ = 0 . 30 , and the perturbation growth rate of the super-critical flows is reduced for Re R+ -> 0 . 00), while only the near-wake backflow is crucial for circular-like cylinders (R+ -> 0 . 50). The stability analysis results are also verified with those of the direct simulations and very good agreement is achieved. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/1394-01. The supercomputer Shaheen at KAUST was utilized for the simulations.

Global stability analysis of axisymmetric boundary layer over a circular cylinder

Science.gov (United States)

Bhoraniya, Ramesh; Vinod, Narayanan

2018-05-01

This paper presents a linear global stability analysis of the incompressible axisymmetric boundary layer on a circular cylinder. The base flow is parallel to the axis of the cylinder at inflow boundary. The pressure gradient is zero in the streamwise direction. The base flow velocity profile is fully non-parallel and non-similar in nature. The boundary layer grows continuously in the spatial directions. Linearized Navier-Stokes (LNS) equations are derived for the disturbance flow quantities in the cylindrical polar coordinates. The LNS equations along with homogeneous boundary conditions forms a generalized eigenvalues problem. Since the base flow is axisymmetric, the disturbances are periodic in azimuthal direction. Chebyshev spectral collocation method and Arnoldi's iterative algorithm is used for the solution of the general eigenvalues problem. The global temporal modes are computed for the range of Reynolds numbers and different azimuthal wave numbers. The largest imaginary part of the computed eigenmodes is negative, and hence, the flow is temporally stable. The spatial structure of the eigenmodes shows that the disturbance amplitudes grow in size and magnitude while they are moving towards downstream. The global modes of axisymmetric boundary layer are more stable than that of 2D flat-plate boundary layer at low Reynolds number. However, at higher Reynolds number they approach 2D flat-plate boundary layer. Thus, the damping effect of transverse curvature is significant at low Reynolds number. The wave-like nature of the disturbance amplitudes is found in the streamwise direction for the least stable eigenmodes.

Numerical Characterisation of Active Drag and Lift Control for a Circular Cylinder in Cross-Flow

Directory of Open Access Journals (Sweden)

Philip McDonald

2017-11-01

Full Text Available Synthetic jet actuators have shown promise to control drag and lift for a bluff body in cross-flow. Using unsteady RANS CFD modelling, a significant modification of the drag coefficient for a circular cylinder in cross-flow at R e = 3900 is achieved by varying the actuation frequency. The variation in actuation frequency corresponds to a range in Stokes number of 2.4 < S t o < 6.4. The trends in drag coefficient modification largely agree with the findings of past publications, achieving a maximum drag reduction at S t o = 4.9 for a fixed jet Reynolds number of the synthetic jet of R e U ¯ o = 12. A decrease in the adverse pressure gradient near the jet orifice correlated with a momentum increase in the viscous sublayer and stronger vortical structures at the rear of the cylinder. In these same conditions, a decrease in turbulence intensity was observed in the far field wake, which is a relevant finding in the context of wind and tidal turbine arrays.

Lattice Boltzmann simulation of flow around a confined circular cyclinder

International Nuclear Information System (INIS)

Ashrafizaadeh, M.; Zadehgol, A.

2002-01-01

A two dimensional lattice Boltzmann model (LBM) based on a single time relaxation BGK model has been developed. Several benchmark problems including the Poiseuille flow, the lid driven cavity flow and the flow around a circular cylinder have been performed employing a d2q9 lattice. The laminar flow around a circular cylinder within a channel has been extensively investigated using the present lattice Boltzmann model. Both symmetric and asymmetric placement configurations of the circular cylinder within the channel have been considered. A new treatment for the outlet velocity and pressure (density) boundary conditions has been proposed and validated. The present LBM results are in excellent agreement with those of the other existing CFD results. Careful examination of the LBM results and an appropriate calculation of the lift coefficient based on the rectangular lattice representation of the circular cylinder reveals that the periodic oscillation of the lift coefficient has a second harmonic when the cylinder is placed asymmetrically within the channel. The second harmonic could be associated with an asymmetrical shedding pattern of the vortices behind the cylinder from the upper and lower sides of the cylinder. (author)

Derivative Geometric Modeling of Basic Rotational Solids on CATIA

Institute of Scientific and Technical Information of China (English)

MENG Xiang-bao; PAN Zi-jian; ZHU Yu-xiang; LI Jun

2011-01-01

Hybrid models derived from rotational solids like cylinders, cones and spheres were implemented on CATIA software. Firstly, make the isosceles triangular prism, cuboid, cylinder, cone, sphere, and the prism with tangent conic and curved triangle ends, the cuboid with tangent cylindrical and curved rectangle ends, the cylinder with tangent spherical and curved circular ends as the basic Boolean deference units to the primary cylinders, cones and spheres on symmetrical and some critical geometric conditions, forming a series of variant solid models. Secondly, make the deference units above as the basic union units to the main cylinders, cones, and spheres accordingly, forming another set of solid models. Thirdly, make the tangent ends of union units into oblique conic, cylindrical, or with revolved triangular pyramid, quarterly cylinder and annulus ends on sketch based features to the main cylinders, cones, and spheres repeatedly, thus forming still another set of solid models. It is expected that these derivative models be beneficial both in the structure design, hybrid modeling, and finite element analysis of engineering components and in comprehensive training of spatial configuration of engineering graphics.

Experimental study and CFD simulation of rotational eccentric cylinder in a magnetorheological fluid

Science.gov (United States)

Omidbeygi, F.; Hashemabadi, S. H.

2012-07-01

In this study, a magnetorheological (MR) fluid is prepared using carbonyl iron filings and low viscosity lubricating oil. The effects of magnetic field and weight percentage of particles on the viscosity of the MR fluid have been measured using a rotational viscometer. The yield stress under an applied magnetic field was also obtained experimentally. In the absence of an applied magnetic field, the MR fluid behaves as a Newtonian fluid. When the magnetic field is applied, the MR fluid behaves like Bingham plastics with a magnetic field dependent yield stress. Afterward, the results compared with those of CFD simulation of two eccentric cylinders in the MR fluid. Results show that the influences of MR effects, caused by the applied magnetic field, on the model characteristics are significant and not negligible. The viscosity is enhanced by increasing of the magnetic field, eccentricity ratio and weight percentage of suspensions. The MR effects and increasing of weight percentage and eccentricity ratio also provide an enhancement in the yield stresses and required total torque for rotation of inner cylinder. Also the simulation results indicate a good representation of the experiment by the model.

An experimental investigation of unsteady thermal processes on a pre-cooled circular cylinder of porous material in the wind

Czech Academy of Sciences Publication Activity Database

Král, Radomil

2014-01-01

Roč. 77, October (2014), s. 906-914 ISSN 0017-9310 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0060; GA ČR(CZ) GBP105/12/G059 Institutional support: RVO:68378297 Keywords : circular cylinder * unsteady heat transfer * temperature distribution * wind tunnel experiment * porous material Subject RIV: JN - Civil Engineering Impact factor: 2.383, year: 2014 http://www.sciencedirect.com/science/article/pii/S0017931014005171

Coupled thermal stress analysis of a hollow circular cylinder with transversely isotropic properties

International Nuclear Information System (INIS)

Tanigawa, Y.; Ootao, Y.

1987-01-01

If we shall analyze the thermal stress problems exactly in a transient state in continuum media, discussed with both the coupling and inertia effect, it has be shown that the thermomechanical coupling term shows a significant role than the inertia term for the common commercial alloys. In the present paper, we have considered the continuum medium with transversely isotropic material property, which has an isotropic property in r-θ plane, and analyzed the transient thermal stress problem of an infinitely long hollow circular cylinder due to an axisymmetrical partial heating. In order to get the thermal and thermoelastic fundamental differential equations separated in each field, we have introduced a perturbation technique. And then, we have carried out numerical calculations for several values of thermal and thermoelastic orthotropical parameters. (orig./GL)

Plasma rotation by electric and magnetic fields in a discharge cylinder

Science.gov (United States)

Wilhelm, H. E.; Hong, S. H.

1977-01-01

A theoretical model for an electric discharge consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field is developed to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential equations which describe the electric potential and the plasma velocity fields is solved in closed form. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number and the Hall coefficient. As a result of Lorentz forces, the plasma rotates with speeds as high as 1 million cm/sec around its axis of symmetry at typical conditions. As an application, it is noted that rotating discharges of this type could be used to develop a high-density plasma-ultracentrifuge driven by j x B forces, in which the lighter (heavier) ion and atom components would be enriched in (off) the center of the discharge cylinder.

Effect of instantaneous rotational speed on the analysis of measured diesel engine cylinder pressure data

International Nuclear Information System (INIS)

Antonopoulos, Antonis K.; Hountalas, Dimitrios T.

2012-01-01

Highlights: ► The effect of in-cycle speed fluctuation on cylinder pressure measurement is investigated. ► A phasing error is introduced when sampling cylinder pressure at constant time intervals. ► The phasing error increases with the increase of engine load and decrease of engine speed. ► Measurement using constant sampling rate affects estimation of HRR, ignition angle etc. - Abstract: Diesel engine cylinder pressure measurements are widely used in field and lab applications to support among other control, monitoring and diagnostic applications. There are two methods to measure cylinder pressure, the use of a crank angle encoder, which guarantees pressure samples at fixed crank angles, and the use of constant time sampling rate. The last is frequently used due to its simplicity or because of practical restrictions. However, in order to perform thermodynamic calculations it is necessary to attribute a crank angle value to each measured pressure value. But if the in-cycle rotational speed fluctuates and this is neglected, an error will result in the values derived from the processing of the measured cylinder pressure. For this reason in the present work an experimental investigation is conducted on a single cylinder diesel test engine to identify the aforementioned problem. During the tests cylinder pressure and instantaneous speed were recorded using an accurate crank angle reference. These where then used to simulate the measurement of cylinder pressure digitized using a fixed time step. The comparison of the two cylinder pressure traces and the thermodynamic parameters derived from them, reveals the introduction of an error which depends on engine load and speed.

Scattering of obliquely incident standing wave by a rotating transversely isotropic cylinder

CSIR Research Space (South Africa)

Shatalov, MY

2006-05-01

Full Text Available stream_source_info Shatalov2_2006.pdf.txt stream_content_type text/plain stream_size 15905 Content-Encoding UTF-8 stream_name Shatalov2_2006.pdf.txt Content-Type text/plain; charset=UTF-8 1 CSIR Material Science..., Tshwane University of Technology, South Africa. 2 CSIR Material Science and Manufacturing Abstract It is known that vibrating patterns of an isotropic cylinder, subjected to inertial rotation over the symmetry axis, precess in the direction...

A numerical investigation of sub-wavelength resonances in polygonal metamaterial cylinders

DEFF Research Database (Denmark)

Arslanagic, Samel; Breinbjerg, Olav

2009-01-01

The sub-wavelength resonances, known to exist in metamaterial radiators and scatterers of circular cylindrical shape, are investigated with the aim of determining if these resonances also exist for polygonal cylinders and, if so, how they are affected by the shape of the polygon. To this end, a set...... 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...

A dynamical systems analysis of the kinematics of time-periodic vortex shedding past a circular cylinder

Science.gov (United States)

Ottino, Julio M.

1991-01-01

Computer flow simulation aided by dynamical systems analysis is used to investigate the kinematics of time-periodic vortex shedding past a two-dimensional circular cylinder in the context of the following general questions: (1) Is a dynamical systems viewpoint useful in the understanding of this and similar problems involving time-periodic shedding behind bluff bodies; and (2) Is it indeed possible, by adopting such a point of view, to complement previous analyses or to understand kinematical aspects of the vortex shedding process that somehow remained hidden in previous approaches. We argue that the answers to these questions are positive. Results are described.

Low-Re flow past an isolated cylinder with rounded corners

KAUST Repository

Zhang, Wei; Samtaney, Ravi

2016-01-01

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

Hydraulic jumps in a partially filled rotating cylinder

International Nuclear Information System (INIS)

Lundgren, T.S.; Berman, A.S.

1979-06-01

A nonlinear analysis is made of the fluid dynamics of a thin film of liquid completely spun up along the cylindrical wall of a rotating cylinder. The analysis allows for the possibility of hydraulic jumps in the liquid film. Conditions are simulated under which jumps can occur. Under the assumption that synchronous runouts are small relative to the film thickness, a sample calculation of jump position and extent for various operating frequencies is presented. Comparison with experimental observations indicate good qualitative agreement between the analysis and the experiment. Under the additional restriction of constant film thickness and a simple lumped-parameter dynamic model for the rotor and its supports, an analysis is also provided which predicts the amplitude and frequency of the asynchronous runout as a function of operating frequency. A numerical example of the results of such a calculation is provided. 6 figures

Circular Polarizations of Gravitational Waves from Core-Collapse Supernovae: A Clear Indication of Rapid Rotation.

Science.gov (United States)

Hayama, Kazuhiro; Kuroda, Takami; Nakamura, Ko; Yamada, Shoichi

2016-04-15

We propose to employ the circular polarization of gravitational waves emitted by core-collapse supernovae as an unequivocal indication of rapid rotation deep in their cores just prior to collapse. It has been demonstrated by three dimensional simulations that nonaxisymmetric accretion flows may develop spontaneously via hydrodynamical instabilities in the postbounce cores. It is not surprising, then, that the gravitational waves emitted by such fluid motions are circularly polarized. We show, in this Letter, that a network of the second generation detectors of gravitational waves worldwide may be able to detect such polarizations up to the opposite side of the Galaxy as long as the rotation period of the core is shorter than a few seconds prior to collapse.

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.)

Determination of Pole and Rotation Period of not Stabilized Artificial Satellite by Use of Model "diffuse Cylinder"

Science.gov (United States)

Kolesnik, S. Ya.; Dobrovolsky, A. V.; Paltsev, N. G.

The algorithm of determination of orientation of rotation axis (pole) and rotation period of satellite, simulated by a cylinder, which is precessing around of vector of angular moment of pulse with constant nutation angle is offered. The Lambert's law of light reflection is accepted. Simultaneously, dependence of light reflection coefficient versus phase angle is determined. The model's simulation confirm applicability of this method. Results of the calculations for artificial satellite No 28506 are carried out.

On the effective temperature and Reynolds number concept for a heated circular cylinder: commentary of the article by Baranyi et al

Czech Academy of Sciences Publication Activity Database

Trávníček, Zdeněk; Wang, A.B.

2011-01-01

Roč. 25, č. 8 (2011), s. 1881-1884 ISSN 1738-494X R&D Projects: GA ČR(CZ) GCP101/11/J019 Institutional research plan: CEZ:AV0Z20760514 Keywords : heated circular cylinder * effective temperature * vortex shedding Subject RIV: BK - Fluid Dynamics Impact factor: 0.448, year: 2011 http://www.springerlink.com/content/2131l38t2u0504u6/

Numerical Simulation and Experiment of a Lifting Body with Leading-Edge Rotating Cylinder

OpenAIRE

A. Badarudin; C. S. Oon; S. N. Kazi; N. Nik-Ghazali; Y. J. Lee; W. T. Chong

2013-01-01

An experimental and simulation flight test has been carried out to evaluate the longitudinal gliding characteristics of a lifting body with blunted half-cone geometry. The novelty here is the lifting body's pitch control mechanism, which consists of a pair of leading-edge rotating cylinders. Flight simulation uses aerodynamic data from computational fluid dynamics supported by wind-tunnel test. Flight test consists of releasing an aluminum lifting body model from a moving vehicle at the appro...

Nonlinear state-space modelling of the kinematics of an oscillating circular cylinder in a fluid flow

Science.gov (United States)

Decuyper, J.; De Troyer, T.; Runacres, M. C.; Tiels, K.; Schoukens, J.

2018-01-01

The flow-induced vibration of bluff bodies is an important problem of many marine, civil, or mechanical engineers. In the design phase of such structures, it is vital to obtain good predictions of the fluid forces acting on the structure. Current methods rely on computational fluid dynamic simulations (CFD), with a too high computational cost to be effectively used in the design phase or for control applications. Alternative methods use heuristic mathematical models of the fluid forces, but these lack the accuracy (they often assume the system to be linear) or flexibility to be useful over a wide operating range. In this work we show that it is possible to build an accurate, flexible and low-computational-cost mathematical model using nonlinear system identification techniques. This model is data driven: it is trained over a user-defined region of interest using data obtained from experiments or simulations, or both. Here we use a Van der Pol oscillator as well as CFD simulations of an oscillating circular cylinder to generate the training data. Then a discrete-time polynomial nonlinear state-space model is fit to the data. This model relates the oscillation of the cylinder to the force that the fluid exerts on the cylinder. The model is finally validated over a wide range of oscillation frequencies and amplitudes, both inside and outside the so-called lock-in region. We show that forces simulated by the model are in good agreement with the data obtained from CFD.

Uniform flow around a circular cylinder in the subcritical range - using the Self-induced angular Moment Method turbulence model

DEFF Research Database (Denmark)

Johansson, Jens; Nielsen, Mogens Peter

The uniform flow around a circular cylinder at Reynolds number 1e5 is simulated in a three dimensional domain by means of the newly developed Self-induced angular Moment Method, SMoM, turbulence model. The global force coefficients, Strouhal number, pressure distributions and wall shear stress...... distributions are compared to experimental findings reported in literature. The SMoM turbulence model is found to provide maximum, minimum and time-mean pressure coefficient distributions in very good agreement with experimental findings....

Computational efficiency improvement with Wigner rotation technique in studying atoms in intense few-cycle circularly polarized pulses

International Nuclear Information System (INIS)

Yuan, Minghu; Feng, Liqiang; Lü, Rui; Chu, Tianshu

2014-01-01

We show that by introducing Wigner rotation technique into the solution of time-dependent Schrödinger equation in length gauge, computational efficiency can be greatly improved in describing atoms in intense few-cycle circularly polarized laser pulses. The methodology with Wigner rotation technique underlying our openMP parallel computational code for circularly polarized laser pulses is described. Results of test calculations to investigate the scaling property of the computational code with the number of the electronic angular basis function l as well as the strong field phenomena are presented and discussed for the hydrogen atom

THE FORMATION AND ERUPTION OF A SMALL CIRCULAR FILAMENT DRIVEN BY ROTATING MAGNETIC STRUCTURES IN THE QUIET SUN

Energy Technology Data Exchange (ETDEWEB)

Yang, Bo; Jiang, Yunchun; Yang, Jiayan; Hong, Junchao; Xu, Zhe, E-mail: boyang@ynao.ac.cn, E-mail: yjy@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences, P.O. Box 110, Kunming 650011 (China)

2015-04-20

We present the first observation of the formation and eruption of a small circular filament driven by a rotating network magnetic field (RNF) in the quiet Sun. In the negative footpoint region of an inverse J-shaped dextral filament, the RNF was formed by the convergence to supergranular junctions of several magnetic flux patches of the same polarity, and it then rotated counterclockwise (CCW) for approximately 11 hr and showed up as a CCW rotating EUV cyclone, during which time the filament gradually evolved into a circular filament that surrounded the cyclone. When the calculated convergence and vortex flows appeared around the RNF during its formation and rotation phases, the injected magnetic helicity calculation also showed negative helicity accumulation during the RNF rotation that was consistent with the dextral chirality of the filament. Finally, the RNF rotation stopped and the cyclone disappeared, and, probably due to an emerging bipole and its forced cancellation with the RNF, the closure filament underwent an eruption along its axis in the (clockwise) direction opposite to the rotation directions of the RNF and cyclone. These observations suggest that the RNFs might play an important role in the formation of nearby small-scale circular filaments as they transport and inject magnetic energy and helicity, and the formation of the EUV cyclones may be a further manifestation of the helicity injected into the corona by the rotation of the RNFs in the photosphere. In addition, the new emerging bipole observed before the filament eruption might be responsible for destabilizing the system and triggering the magnetic reconnection which proves useful for the filament eruption.

Faraday effect in hollow quantum cylinder of finite thickness

International Nuclear Information System (INIS)

Ismailov, T.G.; Jabrailova, G.G.

2009-01-01

The interband Faraday rotation in hollow quantum cylinder of finite thickness is theoretically investigated. Faraday rotation in the dependence on incident light energy for different values of cylinder thickness. It is seen that the resonance peaks appear on Faraday rotation curve. The roles of selection are obtained

A low-background piston-cylinder-type hybrid high pressure cell for muon-spin rotation/relaxation experiments

Science.gov (United States)

Shermadini, Z.; Khasanov, R.; Elender, M.; Simutis, G.; Guguchia, Z.; Kamenev, K. V.; Amato, A.

2017-10-01

A low background double-wall piston-cylinder-type pressure cell is developed at the Paul Scherrer Institute. The cell is made from BERYLCO-25 (beryllium copper) and MP35N nonmagnetic alloys with the design and dimensions which are specifically adapted to muon-spin rotation/relaxation (μSR) measurements. The mechanical design and performance of the pressure cell are evaluated using finite-element analysis (FEA). By including the measured stress-strain characteristics of the materials into the finite-element model, the cell dimensions are optimized with the aim to reach the highest possible pressure while maintaining the sample space large (6 mm in diameter and 12 mm high). The presented unconventional design of the double-wall piston-cylinder pressure cell with a harder outer MP35N sleeve and a softer inner CuBe cylinder enables pressures of up to 2.6 GPa to be reached at ambient temperature, corresponding to 2.2 GPa at low temperatures without any irreversible damage to the pressure cell. The nature of the muon stopping distribution, mainly in the sample and in the CuBe cylinder, results in a low-background μSR signal.

A study of direct- and pulse-current chromium electroplating on rotating cylinder electrode (RCE)

International Nuclear Information System (INIS)

Chang, J.H.; Hsu, F.Y.; Liao, M.J.; Huang, C.A.

2007-01-01

Direct- and pulse-current (DC and PC) chromium electroplating on Cr-Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50 deg. C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60 A dm -2 , respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit

Mechanism of drag reduction for circular cylinders with patterned surface

International Nuclear Information System (INIS)

Butt, U.; Jehring, L.; Egbers, C.

2014-01-01

Highlights: • Reduced drag of patterned cylinders over a wide range of Re numbers. • Hexagonal patterns cannot be characterized as roughness structures. • Hexagonal bumps affect the flow like spherical dimples of smaller k/d ratio do. • Main separation is delayed caused by a partial separation. • Angle of a separation line is not constant over the length of cylinder. -- Abstract: In this paper, the flow over cylinders with a patterned surface (k/d = 1.98 × 10 −2 ) is investigated in a subsonic wind tunnel over Reynolds numbers ranging from 3.14 × 10 4 to 2.77 × 10 5 by measuring drag, flow visualization and measuring velocity profiles above the surface of the cylinders, to observe the effect of hexagonal patterns on the flow of air. These patterns can also be referred as hexagonal dimples or bumps depending on their configuration. The investigations revealed that a patterned cylinder with patterns pressed outwards has a drag coefficient of about 0.65 times of a smooth one. Flow visualization techniques including surface oil-film technique and velocity profile measurement were employed to elucidate this effect, and hence present the mechanism of drag reduction. The measurement of velocity profiles using hot-wire anemometry above the surface reveal that a hexagonal bump cause local separation generating large turbulence intensity along the separating shear layer. Due to this increased turbulence, the flow reattaches to the surface with higher momentum and become able to withstand the pressure gradient delaying the main separation significantly. Besides that, the separation does not appear to occur in a straight line along the length of the cylinder as in case of most passive drag control methods, but follow exactly the hexagonal patterns forming a wave with its crest at 115° and trough at 110°, in contrast to the laminar separation line at 85° for a smooth cylinder

Vortex-induced vibrations of circular cylinder in cross flow at supercritical Reynolds numbers; Chorinkai Reynolds su ryoiki ni okeru enchu no uzu reiki shindo

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)

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.

Finite mixture model applied in the analysis of a turbulent bistable flow on two parallel circular cylinders

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.

Measurements of Convective Heat Transfer from a Horizontal Cylinder Rotating in a Pool of Water

International Nuclear Information System (INIS)

Becker, Kurt M.

1963-05-01

The present paper deals with measurements of heat transfer from a horizontal cylinder rotating in water. The experimental results have been correlated by the equation Nu = 0.11.Re 0.68 .Pr 0.4 for a range of rotating Reynolds numbers from 1000 to 46000, and Prandtl numbers from 2.2 to 6.4, This equation compares very well with the experimental and theoretical information available for air in published works. The analogy suggested by Anderson and Saunders between natural convection from a horizontal plate and the present type of flow has been used to predict the Nusselt numbers. Analytical and experimental results have been found to compare very well with each other

Measurements of Convective Heat Transfer from a Horizontal Cylinder Rotating in a Pool of Water

Energy Technology Data Exchange (ETDEWEB)

Becker, Kurt M

1963-05-15

The present paper deals with measurements of heat transfer from a horizontal cylinder rotating in water. The experimental results have been correlated by the equation Nu = 0.11.Re{sup 0.68}.Pr{sup 0.4} for a range of rotating Reynolds numbers from 1000 to 46000, and Prandtl numbers from 2.2 to 6.4, This equation compares very well with the experimental and theoretical information available for air in published works. The analogy suggested by Anderson and Saunders between natural convection from a horizontal plate and the present type of flow has been used to predict the Nusselt numbers. Analytical and experimental results have been found to compare very well with each other.

Polygon formation and surface flow on a rotating fluid surface

DEFF Research Database (Denmark)

Bergmann, Raymond; Tophøj, Laust Emil Hjerrild; Homan, T. A. M.

2011-01-01

We present a study of polygons forming on the free surface of a water flow confined to a stationary cylinder and driven by a rotating bottom plate as described by Jansson et al. (Phys. Rev. Lett., vol. 96, 2006, 174502). In particular, we study the case of a triangular structure, either completely...... there the symmetry breaking proceeds like a low-dimensional linear instability. We show that the circular state and the unstable manifold connecting it with the polygon solution are universal in the sense that very different initial conditions lead to the same circular state and unstable manifold. For a wet triangle......, we measure the surface flows by particle image velocimetry (PIV) and show that there are three vortices present, but that the strength of these vortices is far too weak to account for the rotation velocity of the polygon. We show that partial blocking of the surface flow destroys the polygons and re...

Dynamic Interaction of Interfacial Point Source Loading and Cylinder in an Elastic Quarter with Anti-plane Shear

Science.gov (United States)

Chun, Gao; Hui, Qi; Nan, Pan Xiang; Bo, Zhao Yuan

2017-07-01

Theoretical steady state solution of a semi-circular cylinder impacted by an anti-plane point loading in a vertical bound of an elastic quarter is formulated in this paper through using image method and wave function expansion series. The elastic quarter is extended as a half space, and the semi-circular interfacial cylinder is extended as a circular cylinder. Displacement field is constructed as series of Fourier-Hankel and Fourier-Bessel wave functions. At last, circular boundary is expanded as Fourier series to determine coefficients of wave function. Numerical results show that material parameters have two widely divergent effects on the radial and circumferential dynamic stress distribution.

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...

Vortex Breakdown Generated by off-axis Bifurcation in a cylinder with rotating covers

DEFF Research Database (Denmark)

Bisgaard, Anders; Brøns, Morten; Sørensen, Jens Nørkær

2006-01-01

Vortex breakdown of bubble type is studied for the flow in a cylinder with rotating top and bottom covers. For large ratios of the angular velocities of the covers, we observe numerically that the vortex breakdown bubble in the steady regime may occur through the creation of an off-axis vortex ring....... This scenario does not occur in existing bifurcation theory based on a simple degeneracy in the flow field. We extend the theory to cover a non-simple degeneracy, and derive the associated bifurcation diagrams. We show that the vortex breakdown scenario involving a vortex ring can be explained from this theory...

Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H2+ subject to tailored (ω , 2 ω ) counter-rotating laser fields

Science.gov (United States)

Heslar, John; Telnov, Dmitry A.; Chu, Shih-I.

2018-04-01

Recently, studies of high-order harmonics (HHG) from atoms driven by bichromatic counter-rotating circularly polarized laser fields as a source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup have received considerable attention. Here, we demonstrate the ability to control the electron recollisions giving three returns per one cycle of the fundamental frequency ω by using tailored bichromatic (ω , 2 ω ) counter-rotating circularly polarized laser fields with a molecular target. The full control of the electronic pathway is first analyzed by a classical trajectory analysis and then extended to a detailed quantum study of H2+ molecules in bichromatic (ω , 2 ω ) counter-rotating circularly polarized laser fields. The radiation spectrum contains doublets of left- and right-circularly polarized harmonics in the XUV ranges. We study in detail the below-, near-, and above-threshold harmonic regions and describe how excited-state resonances alter the ellipticity and phase of the generated harmonic peaks.

Hydrodynamic stability of thermoviscous liquid film inside a rotating horizontal cylinder: Heating and cooling effects

Science.gov (United States)

Kumawat, Tara Chand; Tiwari, Naveen

2018-03-01

Steady two-dimensional solutions and their stability analysis are presented for thin film of a thermoviscous liquid flowing inside a cylinder rotating about its horizontal axis. The inner surface of the cylinder is either uniformly hotter or colder than the enveloping air. The mass, momentum, and energy equations are simplified using thin-film approximation. The analytically obtained film thickness evolution equation consists of various dimensionless parameters such as gravitational number, Bond number, Biot number, thermoviscosity number, and Marangoni number. The viscosity of the liquid is considered as an exponential function of temperature. The viscosity increases (decreases) within the film thickness away from the inner surface of the cylinder when the surface is uniformly hotter (colder) than the atmosphere. For hotter (colder) surface, the film thickness on the rising side decreases (increases) when convective heat transfer at the free surface is increased. The surface tension gradient at the free surface generates Marangoni stress that has a destabilizing (stabilizing) effect on the thin film flow in the case of a hotter (colder) cylinder. The thermoviscosity number stabilizes (destabilizes) the flow on a heating (cooling) surface and this effect increases with an increase in the heat transfer at the free surface. For a hotter surface and in the presence of Marangoni stress, the convective heat transfer at the interface has the destabilizing effect for small values of the Biot number and assumes a stabilizing role for larger values. Non-linear simulations show consistency with the linear stability analysis.

Bifurcation and stability analysis of rotating chemical spirals in circular domains: Boundary-induced meandering and stabilization

Science.gov (United States)

Bär, Markus; Bangia, Anil K.; Kevrekidis, Ioannis G.

2003-05-01

Recent experimental and model studies have revealed that the domain size may strongly influence the dynamics of rotating spirals in two-dimensional pattern forming chemical reactions. Hartmann et al. [Phys. Rev. Lett. 76, 1384 (1996)], report a frequency increase of spirals in circular domains with diameters substantially smaller than the spiral wavelength in a large domain for the catalytic NO+CO reaction on a microstructured platinum surface. Accompanying simulations with a simple reaction-diffusion system reproduced the behavior. Here, we supplement these studies by a numerical bifurcation and stability analysis of rotating spirals in a simple activator-inhibitor model. The problem is solved in a corotating frame of reference. No-flux conditions are imposed at the boundary of the circular domain. At large domain sizes, eigenvalues and eigenvectors very close to those corresponding to infinite medium translational invariance are observed. Upon decrease of domain size, we observe a simultaneous change in the rotation frequency and a deviation of these eigenvalues from being neutrally stable (zero real part). The latter phenomenon indicates that the translation symmetry of the spiral solution is appreciably broken due to the interaction with the (now nearby) wall. Various dynamical regimes are found: first, the spiral simply tries to avoid the boundary and its tip moves towards the center of the circular domain corresponding to a negative real part of the “translational” eigenvalues. This effect is noticeable at a domain radius of Rrotation as a function of a control parameter and the domain size reveals that the meandering instability in large domains becomes suppressed, and the spiral rotation becomes rigid, at a critical radius Rcr,0. Boundary

Numerical simulation and global linear stability analysis of low-Re flow past a heated circular cylinder

KAUST Repository

Zhang, Wei; Samtaney, Ravi

2016-01-01

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.

Numerical simulation and global linear stability analysis of low-Re flow past a heated circular cylinder

KAUST Repository

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.

Application of turbulence modeling to predict surface heat transfer in stagnation flow region of circular cylinder

Science.gov (United States)

Wang, Chi R.; Yeh, Frederick C.

1987-01-01

A theoretical analysis and numerical calculations for the turbulent flow field and for the effect of free-stream turbulence on the surface heat transfer rate of a stagnation flow are presented. The emphasis is on the modeling of turbulence and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow. The free stream is steady and incompressible with a Reynolds number of the order of 10 to the 5th power and turbulence intensity of less than 5 percent. For this analysis, the flow field is divided into three regions: (1) a uniform free-stream region where the turbulence is homogeneous and isotropic; (2) an external viscid flow region where the turbulence is distorted by the variation of the mean flow velocity; and, (3) an anisotropic turbulent boundary layer region over the cylinder surface. The turbulence modeling techniques used are the kappa-epsilon two-equation model in the external flow region and the time-averaged turbulence transport equation in the boundary layer region. The turbulence double correlations, the mean velocity, and the mean temperature within the boundary layer are solved numerically from the transport equations. The surface heat transfer rate is calculated as functions of the free-stream turbulence longitudinal microlength scale, the turbulence intensity, and the Reynolds number.

Transient thermal stresses in a transversely isotropic finite composite hollow circular cylinder due to arbitrary surface heat-generations and surrounding temperatures

International Nuclear Information System (INIS)

Sugano, Y.

1981-01-01

An exact solution is given for the temperature distribution, the thermal stresses and displacements in a transversely isotropic finite composite hollow circular cylinder composed of two distinct cylindrical laminae. The temperature field is determined by using of the Laplace transform and the finite Fourier-cosine transform, respectively, with respect to time and axial coordinate included in the governing equation and the associated thermal stresses and displacements are analvsed by the use of a set of stress functions closely related to the Love's function valid for the axisymmetric isothermal problem of isotropic bodies. (orig.)

PIV Measurements of He II Counterflow Around a Cylinder

International Nuclear Information System (INIS)

Fuzier, S.; Van Stiver, S. W.; Zhang, T.

2006-01-01

The induced flow field of counterflow He II across a circular cylinder has been quantitatively studied using the particle image velocimetry (PIV) technique. Two different size cylinders (6.35 mm and 2 mm in diameter) were used and placed in a 20 mm wide rectangular channel. In these experiments, large-scale eddy motion generated by the He II counterflow was observed both in front of and behind the cylinder, an effect which has no analogue in classical fluids

Rotating circular strings, and infinite non-uniqueness of black rings

International Nuclear Information System (INIS)

Emparan, Roberto

2004-01-01

We present new self-gravitating solutions in five dimensions that describe circular strings, i.e., rings, electrically coupled to a two-form potential (as e.g., fundamental strings do), or to a dual magnetic one-form. The rings are prevented from collapsing by rotation, and they create a field analogous to a dipole, with no net charge measured at infinity. They can have a regular horizon, and we show that this implies the existence of an infinite number of black rings, labeled by a continuous parameter, with the same mass and angular momentum as neutral black rings and black holes. We also discuss the solution for a rotating loop of fundamental string. We show how more general rings arise from intersections of branes with a regular horizon (even at extremality), closely related to the configurations that yield the four-dimensional black hole with four charges. We reproduce the Bekenstein-Hawking entropy of a large extremal ring through a microscopic calculation. Finally, we discuss some qualitative ideas for a microscopic understanding of neutral and dipole black rings. (author)

Rotated infrared antenna transmitarray for the manipulation of circularly polarized wavefronts

Directory of Open Access Journals (Sweden)

He Yuchu

2014-01-01

Full Text Available An IR optical transmitarray is presented based on Antenna Array Sheet (AAS for the manipulation of circularly polarized light. The unit cell of the transmitarray comprises three layers of metallic elliptical patches. Complete phase control is achieved through the local rotation of each unit cell. Thin refraction and focusing transmitarrays of this sort are demonstrated at infrared frequencies. Moreover, a new concept for realizing a polarization-discriminating device is introduced based on a flat refracting lens. These devices are compatible with current fabrication technology and can become crucial for the integration with other IR and nano-photonic devices.

Nonlinear spin-up in a circular cylinder

NARCIS (Netherlands)

van de Konijnenberg, J.A.; Heijst, van G.J.F.

1995-01-01

Nonlinear spin-up in a circular cylindrical tank is investigated experimentally and compared with the Wedemeyer model. The experiments were performed with water, using tracer particles floating at the free surface in order to visualize the flow field. The experimentally determined vorticity profiles

Effect of longitudinal and transverse vibrations of an upstream square cylinder on vortex shedding behind two inline square cylinders

International Nuclear Information System (INIS)

Patil, Pratish P; Tiwari, Shaligram

2009-01-01

The characteristics of unsteady wakes behind a stationary square cylinder and another upstream vibrating square cylinder have been investigated numerically with the help of a developed computational code. The effect of longitudinal as well as transverse vibrations of the upstream cylinder is studied on the coupled wake between the two cylinders, which is found to control the vortex shedding behavior behind the downstream stationary cylinder. Computations are carried out for a fixed value of Reynolds number (Re = 200) and three different values of excitation frequencies of the upstream cylinder, namely less than, equal to and greater than the natural frequency of vortex shedding corresponding to flow past a stationary square cylinder. The vortex shedding characteristics of the unsteady wakes behind the vibrating and stationary cylinders are found to differ significantly for longitudinal and transverse modes of vibration of the upstream cylinder. The wake of the downstream stationary cylinder is found to depict a synchronization behavior with the upstream cylinder vibration. The spacing between the two cylinders has been identified to be the key parameter influencing the synchronization phenomenon. The effect of cylinder spacing on the wake synchronization and the hydrodynamic forces has been examined. In addition, a comparison of the drag forces for flow past transversely vibrating square and circular cylinders for similar amplitudes and frequencies of cylinder vibration has been presented while employing the tested computational code.

A low-background piston-cylinder type hybrid high pressure cell for muon-spin rotation/relaxation experiments

OpenAIRE

Shermadini, Z.; Khasanov, R.; Elender, M.; Simutis, G.; Guguchia, Z.; Kamenev, K. V.; Amato, A.

2017-01-01

A low background double-wall piston-cylinder-type pressure cell is developed at the Paul Scherrer Institute. The cell is made from BERLYCO-25 (beryllium copper) and MP35N nonmagnetic alloys with the design and dimensions which are specifically adapted to muon-spin rotation/relaxation (muSR) measurements. The mechanical design and performance of the pressure cell are evaluated using finite-element analysis (FEA). By including the measured stress-strain characteristics of the material into the ...

Low-Re flow past an isolated cylinder with rounded corners

KAUST Repository

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

A numerical experiment that provides new results regarding the inception of separation in the flow around a circular cylinder

Science.gov (United States)

Malamataris, Nikolaos; Liakos, Anastasios

2015-11-01

The exact value of the Reynolds number regarding the inception of separation in the flow around a circular cylinder is still a matter of research. This work connects the inception of separation with the calculation of a positive pressure gradient around the circumference of the cylinder. The hypothesis is that inception of separation occurs when the pressure gradient becomes positive around the circumference. From the most cited laboratory experiments that have dealt with that subject of inception of separation only Thom has measured the pressure gradient there at very low Reynolds numbers (up to Re=3.5). For this reason, the experimental conditions of his tunnel are simulated in a new numerical experiment. The full Navier Stokes equations in both two and three dimensions are solved with a home made code that utilizes Galerkin finite elements. In the two dimensional numerical experiment, inception of separation is observed at Re=4.3, which is the lowest Reynolds number where inception has been reported computationally. Currently, the three dimensional experiment is under way, in order to compare if there are effects of three dimensional theory of separation in the conditions of Thom's experiments.

Axial slit wall effect on the flow instability and heat transfer in rotating concentric cylinders

Energy Technology Data Exchange (ETDEWEB)

Liu, Dong; Chao, Chang Qing; Wang, Ying Ze; Zhu, Fang Neng [School of Energy and Power Engineering, Jiangsu University, Zhenjiang (China); Kim, Hyoung Bum [School of Mechanical and Aerospace Engineering, Gyeongsang National University, Jinju (Korea, Republic of)

2016-12-15

The slit wall effect on the flow instability and heat transfer characteristics in Taylor-Couette flow was numerically studied by changing the rotating Reynolds number and applying the negative temperature gradient. The concentric cylinders with slit wall are seen in many rotating machineries. Six different models with the slit number 0, 6, 9, 12, 15 and 18 were investigated in this study. The results show the axial slit wall enhances the Taylor vortex flow and suppresses the azimuthal variation of wavy Taylor vortex flow. When negative temperature gradient exists, the results show that the heat transfer augmentation appears from laminar Taylor vortex to turbulent Taylor flow regime. The heat transfer enhancement become stronger as increasing the Reynolds number and slit number. The larger slit number model also accelerates the flow transition regardless of the negative temperature gradient or isothermal condition.

Axial slit wall effect on the flow instability and heat transfer in rotating concentric cylinders

International Nuclear Information System (INIS)

Liu, Dong; Chao, Chang Qing; Wang, Ying Ze; Zhu, Fang Neng; Kim, Hyoung Bum

2016-01-01

The slit wall effect on the flow instability and heat transfer characteristics in Taylor-Couette flow was numerically studied by changing the rotating Reynolds number and applying the negative temperature gradient. The concentric cylinders with slit wall are seen in many rotating machineries. Six different models with the slit number 0, 6, 9, 12, 15 and 18 were investigated in this study. The results show the axial slit wall enhances the Taylor vortex flow and suppresses the azimuthal variation of wavy Taylor vortex flow. When negative temperature gradient exists, the results show that the heat transfer augmentation appears from laminar Taylor vortex to turbulent Taylor flow regime. The heat transfer enhancement become stronger as increasing the Reynolds number and slit number. The larger slit number model also accelerates the flow transition regardless of the negative temperature gradient or isothermal condition

Jeans Instability of the Self-Gravitating Viscoelastic Ferromagnetic Cylinder with Axial Nonuniform Rotation and Magnetic Field

Science.gov (United States)

Dhiman, Joginder Singh; Sharma, Rajni

2017-12-01

The effects of nonuniform rotation and magnetic field on the instability of a self gravitating infinitely extending axisymmetric cylinder of viscoelastic ferromagnetic medium have been studied using the Generalised Hydrodynamic (GH) model. The non-uniform magnetic field and rotation are acting along the axial direction of the cylinder and the propagation of the wave is considered along the radial direction, while the ferrofluid magnetization is taken collinear with the magnetic field. A general dispersion relation representing magnetization, magnetic permeability and viscoelastic relaxation time parameters is obtained using the normal mode analysis method in the linearized perturbation equation system. Jeans criteria which represent the onset of instability of self gravitating medium are obtained under the limits; when the medium behaves like a viscous liquid (strongly coupled limit) and a Newtonian liquid (weakly coupled limit). The effects of various parameters on the Jeans instability criteria and on the growth rate of self gravitating viscoelastic ferromagnetic medium have been discussed. It is found that the magnetic polarizability due to ferromagnetization of medium marginalizes the effect of non-uniform magnetic field on the Jeans instability, whereas the viscoelasticity of the medium has the usual stabilizing effect on the instability of the system. Further, it is found that the cylindrical geometry is more stable than the Cartesian one. The variation of growth rate against the wave number and radial distance has been depicted graphically.

Vortex Shedding from Finned Circular Cylinders

Science.gov (United States)

1980-11-01

FINNED CIRCULAR CYLINDERSo ,rm"" 1..UTNOI .)R*., r. *.040, 111SPOR- / T NuMBII f.John G. elute asOHans J.’/, ugt -. . . , ,<-. -. ,:. =., .. Siil P3RPIO...fins and other sharp protuberances. These purely two-dimensional flows then may be used in a strip theory to include at least some aspects of three...boundary- layer theory . Such a prediction method, together with a technique to provide for a vortex sheet at the separation point, will be included in

Modeling flow for modified concentric cylinder rheometer geometry

Science.gov (United States)

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.

The capillary interaction between two vertical cylinders

KAUST Repository

Cooray, Himantha; Cicuta, Pietro; Vella, Dominic

2012-01-01

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

Development of free surface flow between concentric cylinders with vertical axes

International Nuclear Information System (INIS)

Watanabe, T; Toya, Y; Nakamura, I

2005-01-01

Numerical and experimental studies are conducted on flows developing between two concentric cylinders with vertical axes. The inner cylinder rotates and the outer and the lower end wall are fixed. The upper boundary is a free surface. The flow is at rest in an initial state, and the inner cylinder impulsively begins to rotate or its rotation speed linearly increases to a prescribed value. The acceleration rate of the inner cylinder changes the formation processes of flows and/or the final flow modes. Time-dependent flows appear at higher Reynolds numbers, and the numerical and experimental results of the power spectra show some agreements. It is suggested that critical Reynolds numbers appear, at which the fluctuations in the displacement of the free surface and the kinetic energy of a velocity component steeply increase

Effects of curvature on rarefied gas flows between rotating concentric cylinders

Science.gov (United States)

Dongari, Nishanth; White, Craig; Scanlon, Thomas J.; Zhang, Yonghao; Reese, Jason M.

2013-05-01

The gas flow between two concentric rotating cylinders is considered in order to investigate non-equilibrium effects associated with the Knudsen layers over curved surfaces. We investigate the nonlinear flow physics in the near-wall regions using a new power-law (PL) wall-scaling approach. This PL model incorporates Knudsen layer effects in near-wall regions by taking into account the boundary limiting effects on the molecular free paths. We also report new direct simulation Monte Carlo results covering a wide range of Knudsen numbers and accommodation coefficients, and for various outer-to-inner cylinder radius ratios. Our simulation data are compared with both the classical slip flow theory and the PL model, and we find that non-equilibrium effects are not only dependent on Knudsen number and accommodation coefficient but are also significantly affected by the surface curvature. The relative merits and limitations of both theoretical models are explored with respect to rarefaction and curvature effects. The PL model is able to capture some of the nonlinear trends associated with Knudsen layers up to the early transition flow regime. The present study also illuminates the limitations of classical slip flow theory even in the early slip flow regime for higher curvature test cases, although the model does exhibit good agreement throughout the slip flow regime for lower curvature cases. Torque and velocity profile comparisons also convey that a good prediction of integral flow properties does not necessarily guarantee the accuracy of the theoretical model used, and it is important to demonstrate that field variables are also predicted satisfactorily.

Measuring the Extensional Properties of linear and branched Polymer Melts using Membrane Inflation into a Cylinder

DEFF Research Database (Denmark)

Rasmussen, Henrik Koblitz; Eggen, Svein; Kjær, Erik Michael

2001-01-01

The bubble inflation technique has been used for some time as a rheological characterization method for polymeric materials. Recently, this technique has been modified to the inflation of a polymeric sheet into a circular cylinder. In this work, the experimental inflation of sheets (or membranes......) of polymeric melts into a circular cylinder is modelled numerically to obtain the general extensional properties of the material....

Lattice Boltzmann simulation of the convective heat transfer from a stream-wise oscillating circular cylinder

International Nuclear Information System (INIS)

Bao Sheng; Chen Sheng; Liu Zhaohui; Zheng Chuguang

2012-01-01

Highlights: ► Heat transfer is enhanced by small and slow stream-wise oscillation. ► The average Nu decreases with increasing oscillation frequency. ► The RMS Nu increases with increasing frequency. ► The mean and RMS Nu reach a local maximum value in locked regime. ► Similar frequency effect is found for different Reynolds numbers. - Abstract: In this paper, we studied the convective heat transfer from a stream-wise oscillating circular cylinder. Two dimensional numerical simulations are conducted at Re = 100–200, A = 0.1–0.4 and F = f o /f s = 0.2–3.0 with the aid of the lattice Boltzmann method. In particular, detailed attentions are paid on the extensive numerical results elucidating the influence of oscillation frequency, oscillation amplitude and Reynolds number on the time-average and RMS value of the Nusselt number. Over the ranges of conditions considered herein, the heat transfer characteristics are observed to be influenced in an intricate manner by the value of the oscillation frequency (F), oscillation amplitude (A) and Reynolds number (Re). Firstly, the heat transfer is enhanced when the cylinder oscillates stream-wise with small amplitude and low frequency, while it will be reduced by large amplitude and high frequency. Secondly, the average Nusselt number (Nu (ave)) decreases against the increasing value of oscillation frequency, while the RMS value of the Nusselt number, Nu (RMS), displays an opposite trend. Third, we obtained a similar frequency effect on the heat transfer over the range of Reynolds numbers investigated in this paper. In addition, detailed analyses on phase portraits, energy spectrum are also made.

Experimental Study on Natural Convection Heat Transfer From two Parallel Horizontal Cylinders in Horizontal Cylindrical Enclosure

Directory of Open Access Journals (Sweden)

Ahmed T. Ahmed

2013-05-01

Full Text Available  An experimental study on natural convection heat transfer from two parallel horizontal cylinders in horizontal cylindrical enclosure was carried out under condition of constant surfaces temperature for two cylinders and cylindrical enclosure. The study included the effect of Rayleigh number, rotation angle that represent the confined angle between the passing horizontal plane in cylindrical enclosure center and passing line in two cylinders centers, and the spaces between two cylinders on their heat loss ability.39An experimental set-up was used for this purpose which consist watercontainer, test section which is formed of plastic cylinder that represent the cylindrical enclosure, and two heating elements which are formed of two copper cylinders with (19 mm in diameters heated internally by electrical sources that represents transfer and heat loss elements through this set-up.      The experiments were done at the range of Rayleigh number between ( , cylinders rotation angle at ( , and spacing ratio at ( .     The study showed that the ability of heat loss from two cylinders is a function of Rayleigh number, cylinders rotation angle, and the spaces between them. This ability is increased by increasing of Rayleigh number and it was showed that this ability reaches maximum value at the first cylinder ( and minimum value at the second cylinder ( at spacing ratio (S/D=3 and rotation angle ( for the first and ( for the second cylinder respectively.      The effective variables on natural convection heat transfer from the above two cylinders are related by two correlating equations, each one explains dimensionless relation of heat transfer from each cylinder that represented by Nusselt number against Rayleigh number, rotation angle, and the spacing ratio between two cylinders. 

Induced charge electrophoresis of a conducting cylinder in a nonconducting cylindrical pore and its micromotoring application

Science.gov (United States)

Feng, Huicheng; Wong, Teck Neng; Che, Zhizhao

2016-08-01

Induced charge electrophoresis of a conducting cylinder suspended in a nonconducting cylindrical pore is theoretically analyzed and a micromotor is proposed that utilizes the cylinder rotation. The cylinder velocities are analytically obtained in the Dirichlet and the Neumann boundary conditions of the electric field on the cylindrical pore. The results show that the cylinder not only translates but also rotates when it is eccentric with respect to the cylindrical pore. The influences of a number of parameters on the cylinder velocities are characterized in detail. The cylinder trajectories show that the cylinder approaches and becomes stationary at certain positions within the cylindrical pore. The proposed micromotor is capable of working under a heavy load with a high rotational velocity when the eccentricity is large and the applied electric field is strong.

Mechanism of tonal noise generation from circular cylinder with spiral fin

Science.gov (United States)

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.

Absolute Configuration of 3-METHYLCYCLOHEXANONE by Chiral Tag Rotational Spectroscopy and Vibrational Circular Dichroism

Science.gov (United States)

Evangelisti, Luca; Holdren, Martin S.; Mayer, Kevin J.; Smart, Taylor; West, Channing; Pate, Brooks

2017-06-01

The absolute configuration of 3-methylcyclohexanone was established by chiral tag rotational spectroscopy measurements using 3-butyn-2-ol as the tag partner. This molecule was chosen because it is a benchmark measurement for vibrational circular dichroism (VCD). A comparison of the analysis approaches of chiral tag rotational spectroscopy and VCD will be presented. One important issue in chiral analysis by both methods is the conformational flexibility of the molecule being analyzed. The analysis of conformational composition of samples will be illustrated. In this case, the high spectral resolution of molecular rotational spectroscopy and potential for spectral simplification by conformational cooling in the pulsed jet expansion are advantages for chiral tag spectroscopy. The computational chemistry requirements for the two methods will also be discussed. In this case, the need to perform conformer searches for weakly bound complexes and to perform reasonably high level quantum chemistry geometry optimizations on these complexes makes the computational time requirements less favorable for chiral tag rotational spectroscopy. Finally, the issue of reliability of the determination of the absolute configuration will be considered. In this case, rotational spectroscopy offers a "gold standard" analysis method through the determination of the ^{13}C-subsitution structure of the complex between 3-methylcyclohexanone and an enantiopure sample of the 3-butyn-2-ol tag.

Generation and evolution of turbulence in an annulus between two concentric rotating cylinders

International Nuclear Information System (INIS)

Kataoka, K.; Deguchi, T.

1987-01-01

The objective of the present work is to observe the generation and spectral evolution of time-dependent wavy disturbances in the Taylor-Couette flow. It is well known that as the Reynolds number Re = R/sub i/Ω d/ν, based on the rotation speed (Ω: angular velocity) of the inner cylinder, is gradually increased, the following five dynamical transitions occur stepwise in sequence: laminar Couette flow → laminar Taylor vortex flow → wavy vortex flow → quasi-periodic wavy vortex flow → weakly turbulent wavy vortex flow → turbulent vortex flow. Time-dependent wavy disturbances appear when the transition to wavy vortex flow occurs as a result of instability of the laminar Taylor vortex flow. The disturbances are regularly periodic because it results from the azimuthally traveling waves. The next transition to the quasi-periodic wavy vortex flow is accompanied by the amplitude modulation of the wave motion. The first fundamental frequency f/sub 1/ comes from the passing frequency of the azimuthally traveling waves and the second fundamental frequency f/sub 2/ from the modulation frequency. When the transition to the weakly turbulent wavy vortex flow occurs, chaotic turbulence first appears, A spectral analysis is made to analyze the temporal variation in the local velocity gradient measured on both the inner and outer cylinder walls by using an electrochemical technique

Flow past an axially aligned spinning cylinder: Experimental Study

Science.gov (United States)

Carlucci, Pasquale; Buckley, Liam; Mehmedagic, Igbal; Carlucci, Donald; Thangam, Siva

2017-11-01

Experimental investigation of flow past a spinning cylinder is presented in the context of its application and relevance to flow past projectiles. A subsonic wind tunnel is used to perform experiments on the flow past a spinning cylinder that is mounted on a forward sting and oriented such that its axis of rotation is aligned with the mean flow. The experiments cover a Reynolds number of range of up to 45000 and rotation numbers of up to 2 (based on cylinder diameter). Time-averaged mean flow and turbulence profiles in the wake flow are presented with and without spin along with comparison to published experimental data. Funded in part by the U. S. Army ARDEC, Picatinny Arsenal, NJ.

Electrochemical reactor with rotating cylinder electrode for optimum electrochemical recovery of nickel from plating rinsing effluents

Energy Technology Data Exchange (ETDEWEB)

Hernández-Tapia, J.R.; Vazquez-Arenas, J., E-mail: jgva@xanum.uam.mx; González, I.

2013-11-15

Highlights: • Rotating cylinder cathode enhanced mass transport rates of Ni(II) species. • pH control around 4 is crucial to recover high purity nickel. • Increasing cathodic currents increased energy consumptions for nickel recovery. • Specific energy consumptions increase drastically at the end of electrolysis. -- Abstract: This study is devoted to analyze the metallic electrochemical recovery of nickel from synthetic solutions simulating plating rinsing discharges, in order to meet the water recycling policies implemented in these industries. These effluents present dilute Ni(II) concentrations (100 and 200 ppm) in chloride and sulfate media without supporting electrolyte (397–4202 μS cm{sup −1}), which stems poor current distribution, limited mass transfer, ohmic drops and enhancement of parasitic reactions. An electrochemical reactor with rotating cylinder electrode (RCE) and a pH controller were utilized to overcome these problems. The pH control around 4 was crucial to yield high purity nickel, and thus prevent the precipitation of hydroxides and oxides. Macroelectrolysis experiments were systematically conducted to analyze the impacts of the applied current density in the recovery efficiency and energy consumption, particularly for very diluted effluents (100 and 200 ppm Ni(II)), which present major recovery problems. Promising nickel recoveries in the order of 90% were found in the former baths using a current density of −3.08 mA cm{sup −2}, and with overall profits of 9.64 and 14.69 USD kg{sup −1}, respectively. These estimations were based on the international market price for nickel ($18 USD kg{sup −1})

Aerodynamic loading on a cylinder behind an airfoil

Energy Technology Data Exchange (ETDEWEB)

Zhang, H.J.; Huang, L.; Zhou, Y. [Hong Kong Polytechnic University, Department of Mechanical Engineering, Kowloon (Hong Kong)

2005-05-01

The interaction between the wake of a rotor blade and a downstream cylinder holds the key to the understanding and control of electronic cooling fan noise. In this paper, the aerodynamic characteristics of a circular cylinder are experimentally studied in the presence of an upstream NACA 4412 airfoil for the cylinder-diameter-based Reynolds numbers of Re{sub d}=2,100-20,000, and the airfoil chord-length-based Reynolds numbers of Re{sub c}=14,700-140,000. Lift and drag fluctuations on the cylinder, and the longitudinal velocity fluctuations of the flow behind the cylinder were measured simultaneously using a load cell and two hot wires, respectively. Data analysis shows that unsteady forces on the cylinder increase significantly in the presence of the airfoil wake. The dependence of the forces on two parameters is investigated, that is, the lateral distance (T) between the airfoil and the cylinder, and the Reynolds number. The forces decline quickly as Tincreases. For Re{sub c}<60,000, the vortices shed from the upstream airfoil make a major contribution to the unsteady forces on the cylinder compared to the vortex shedding from the cylinder itself. For Re{sub c}>60,000, no vortices are generated from the airfoil, and the fluctuating forces on the cylinder are caused by its own vortex shedding. (orig.)

Finite-size resonance dielectric cylinder in a rectangular waveguide

International Nuclear Information System (INIS)

Chuprina, V.N.; Khizhnyak, N.A.

1988-01-01

The problem on resonance spread of an electromagnetic wave by a dielectric circular cylinder of finite size in a rectangular waveguide is solved by a numerical-analytical method. The cylinder axes are parallel. The cylinder can be used as a resonance tuning element in accelerating SHF-sections. Problems on cutting off linear algebraic equation systems, to which relations of macroscopic electrodynamics in the integral differential form written for the concrete problem considered here are reduced by analytical transformations, are investigated in the stage of numerical analysis. Theoretical dependences of the insertion of the voltage standing wave coefficient on the generator wave length calculated for different values of problem parameters are constracted

Prediction model of velocity field around circular cylinder over various Reynolds numbers by fusion convolutional neural networks based on pressure on the cylinder

Science.gov (United States)

Jin, Xiaowei; Cheng, Peng; Chen, Wen-Li; Li, Hui

2018-04-01

A data-driven model is proposed for the prediction of the velocity field around a cylinder by fusion convolutional neural networks (CNNs) using measurements of the pressure field on the cylinder. The model is based on the close relationship between the Reynolds stresses in the wake, the wake formation length, and the base pressure. Numerical simulations of flow around a cylinder at various Reynolds numbers are carried out to establish a dataset capturing the effect of the Reynolds number on various flow properties. The time series of pressure fluctuations on the cylinder is converted into a grid-like spatial-temporal topology to be handled as the input of a CNN. A CNN architecture composed of a fusion of paths with and without a pooling layer is designed. This architecture can capture both accurate spatial-temporal information and the features that are invariant of small translations in the temporal dimension of pressure fluctuations on the cylinder. The CNN is trained using the computational fluid dynamics (CFD) dataset to establish the mapping relationship between the pressure fluctuations on the cylinder and the velocity field around the cylinder. Adam (adaptive moment estimation), an efficient method for processing large-scale and high-dimensional machine learning problems, is employed to implement the optimization algorithm. The trained model is then tested over various Reynolds numbers. The predictions of this model are found to agree well with the CFD results, and the data-driven model successfully learns the underlying flow regimes, i.e., the relationship between wake structure and pressure experienced on the surface of a cylinder is well established.

Vortex interactions in a two side-by-side cylinder near-wake

International Nuclear Information System (INIS)

Wang, Z.J.; Zhou, Y.

2005-01-01

The flow behind two side-by-side circular cylinders is experimentally investigated based on laser-illuminated flow-visualization, particle image velocimetry and hot-wire measurements. The flow is classified as three regimes: single street (the cylinder center-to-center spacing T/d 2.0). Special attention is given to the regime of 1.2 2.0, the flow structure change from the anti-phase to in-phase mode starts with a phase shift between gap vortices. The dynamical role of gap bleeding between cylinders for L/d < 1.2 is also examined

Analysis on Flow Induced Motion of Cylinders with Different Cross Sections and the Potential Capacity of Energy Transference from the Flow

Directory of Open Access Journals (Sweden)

Jijian Lian

2017-01-01

Full Text Available The energy in flow induced motion (FIM was harnessed in recent years. In this study, the energy transfer ratio was derived to estimate the energy transference from the flow to the FIM. Then the FIM characteristics and energy transference of cylinders with different cross sections were experimentally investigated. The main findings are listed as follows. (a Circular cylinders and diamond prisms both present a self-limited motion. The maximum amplitude ratio of circular cylinder is around 1~1.2 which is higher than that of diamond prism (0.4~0.5. (b Triangle prisms and right square prisms present a self-unlimited motion. For triangle prism, amplitude ratio increases over 1.8; for right square prisms, amplitude ratio reaches 1.2. (c The maximum transfer ratios of circular cylinder and triangle prism are 80% and 57%, respectively, which are much higher than those of other prisms, indicating that circular cylinder and triangle prism have better performances in energy transference. (d The transfer ratio is strongly dependent on the damping and mass; higher damping or mass will promote a higher transfer ratio. (e Beyond the critical transfer ratios, amplitude variation coefficients are around 10%~30% resulting in a better performance in stationarity.

Hydrodynamic study of the rotating cylinder mixer of a laboratory centrifugal extractor

International Nuclear Information System (INIS)

Philipponeau, Yannick.

1979-08-01

As part of a research programme on solvent extraction kinetics the Fontenay-aux-Roses Nuclear Research Centre has undertaken to build a new centrifugal extractor prototype. The work was centred on a hydrodynamic study of the rotating cylinder mixer of the extractor, using a test apparatus specially designed for this purpose. This apparatus was used to determine the flow conditions of a liquid alone in the annular space of the mixer as a function of the working specifications. The existence of several types of flow was established. The stability region of which was determined as a function of different parameters for a number of liquid-liquid systems. The experiments showed in addition that two kinds of dispersion can be obtained, differing by the nature of the continuous phase. This was determined for various parameters of certain liquid-liquid systems. From this research the hydrodynamic behavior of the CEA centrifugal extractor prototype mixer is thus known [fr

Phenomenological modeling of the thermal dynamics of a rotating cylinder heated by electromagnetic induction; Modelisation phenomenologique de la dynamique thermique d'un cylindre rotatoire chauffe par induction electromagnetique

Energy Technology Data Exchange (ETDEWEB)

Perez, S. [Universidad de Carabobo, Facultad de Ingenieria, Valencia (Venezuela); Therien, N.; Broadbent, A.D. [Sherbrooke Univ., Faculte de Genie, Quebec (Canada)

2001-07-01

This work concerns the development of a phenomenological model describing the temperature dynamics of a metal cylinder heated by electric induction. The model used takes into consideration in an explicit way the different mechanisms of energy transfer from the cylinder towards the environment, in particular the convection and radiant heat transfers. The conduction process, which takes place inside the cylinder as a response to the temperature gradient at the periphery of the cylinder, has been characterized too. The process of energy induction inside the cylinder has been characterized in a precise way. The experiments show that the induction is localized in the part of the cylinder facing the inductors and that the induction presents a distributed feature in the induction section. The model proposed is based on the concept of substantial derivative. It calculates the response of the process with respect to these disturbances and with respect to the rotation speed of the cylinder and to the electric power supplied to the system. (J.S.)

Generation of a rotating liquid liner by tangential injection

International Nuclear Information System (INIS)

Burton, R.L.; Turchi, P.J.; Jenkins, D.J.; Lanham, R.E.; Cameron, J.; Cooper, A.L.

1979-01-01

Efficient compression of low mass-density payloads by the implosion of higher mass-density liquid cylinders or liners, as in the NRL LINUS concept for controlled thermonuclear fusion, requires rotation of the liner material to avoid Rayleigh--Taylor instabilities at the liner-payload interface. Experimentally, such implosions have been demonstrated with liners formed within rotating implosion chambers. The present work uses a scale-model experimental apparatus to investigate the possibility of creating liner rotation by tangential injection of the liquid liner material. Different modes of behavior are obtained depending on the fluid exhaust procedures. Right-circular, cylindrical free surfaces are achieved with axial exhaust of fluid at radii interior to the injection nozzles, for which the liner exhibits a combination of solid-body and free vortex flows in different regions. Measurements allow estimates of power losses to viscous shear, turbulence, etc. A simple model based on open-channel flow is then derived, which is in good agreement with experiment, and is used to extrapolate results to the scale of a possible LINUS fusion reactor

Techniques for the construction of an elliptical-cylindrical model using circular rotating tools in non CNC machines

International Nuclear Information System (INIS)

Villalobos Mendoza, Brenda; Cordero Davila, Alberto; Gonzalez Garcia, Jorge

2011-01-01

This paper describes the construction of an elliptical-cylindrical model without spherical aberration using vertical rotating tools. The engine of the circular tool is placed on one arm so that the tool fits on the surface and this in turn is moved by an X-Y table. The test method and computer algorithms that predict the desired wear are described.

Inertial rise of a meniscus on a vertical cylinder

KAUST Repository

O’ Kiely, Doireann; Whiteley, Jonathan P.; Oliver, James M.; Vella, Dominic

2015-01-01

© © 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

Temporal flow instability for Magnus-Robins effect at high rotation rates

Science.gov (United States)

Sengupta, T. K.; Kasliwal, A.; de, S.; Nair, M.

2003-06-01

The lift and drag coefficients of a circular cylinder, translating and spinning at a supercritical rate is studied theoretically to explain the experimentally observed violation of maximum mean lift coefficient principle, that was proposed heuristically by Prandtl on the basis of inviscid flow model. It is also noted experimentally that flow past a rotating and translating cylinder experiences temporal instability-a fact not corroborated by any theoretical studies so far. In the present paper we report very accurate solution of Navier-Stokes equation that displays the above-mentioned instability and the violation of the maximum limit. The calculated lift coefficient exceeds the limit of /4π, instantaneously as well as in time-averaged sense. The main purpose of the present paper is to explain the observed temporal instability sequence in terms of a new theory of instability based on full Navier-Stokes equation that does not require making any assumption about the flow field, unlike other stability theories.

The effects of axis ratio on laminar fluid flow around an elliptical cylinder

International Nuclear Information System (INIS)

Faruquee, Zakir; Ting, David S-K.; Fartaj, Amir; Barron, Ronald M.; Carriveau, Rupp

2007-01-01

An elliptical cylinder is a generic shape which represents a flat plate at its minor to major axis ratio (AR) limits of zero and infinity, and a circular cylinder at AR of unity. While incompressible flows over a streamwise flat plate (AR = 0), a cross-stream flat plate (AR = ∞), and a circular cylinder have been studied extensively, the role of AR on the detailed flow structure is still not well understood. Therefore, a numerical study was conducted to examine the flow field around an elliptical cylinder over a range of ARs from 0.3 to 1, with the major axis parallel to the free-stream, at a Reynolds number of 40 based on the hydraulic diameter. The control volume approach of FLUENT was used to solve the fluid flow equations, assuming the flow over the cylinder is unbounded, steady, incompressible and two-dimensional. It has been found that a pair of steady vortices forms when AR reaches a critical value of 0.34; below this value no vortices are formed behind the elliptical cylinder. Various wake parameters, drag coefficient, pressure and velocity distributions, have been characterized as functions of AR. The wake size and the drag coefficient are found to increase with the increase of AR. Quadratic correlations have been obtained to describe the relations of wake length and drag coefficient with axis ratio

Transient Simulation of a Rotating Conducting Cylinder in a Transverse Magnetic Field

Science.gov (United States)

2016-09-01

the boundary conditions and magnetic field excitation. The balloon (no fringing at infinity ) boundary condition is used for the model. Two magnetic...cylinder to study the effects of the magnetic responses of the cylinder in the time history . Table 1 summarizes the electromagnetic properties of the...and phase shift angles of the magnetic flux density in the time history , at the center of the structural steel, aluminum, and copper cylinder

Numerical Simulation of Flows about a Stationary and a Free-Falling Cylinder Using Immersed Boundary-Finite Difference Lattice Boltzmann Method

Directory of Open Access Journals (Sweden)

Roberto Rojas

2013-03-01

Full Text Available The applicability of the immersed boundary-finite difference lattice Boltzmann method (IB-FDLBM to high Reynolds number flows about a circular cylinder is examined. Two-dimensional simulations of flows past a stationary circular cylinder are carried out for a wide range of the Reynolds number, Re, i.e., 1 ≤ Re ≤ 1×105. An immersed boundary-lattice Boltzmann method (IB-LBM is also used for comparison. Then free-falling circular cylinders are simulated to demonstrate the feasibility of predicting moving particles at high Reynolds numbers. The main conclusions obtained are as follows: (1 steady and unsteady flows about a stationary cylinder are well predicted with IB-LBM and IB-FDLBM, provided that the spatial resolution is high enough to satisfy the conditions of numerical stability, (2 high spatial resolution is required for stable IB-LBM simulation of high Reynolds number flows, (3 IB-FDLBM can stably simulate flows at very high Reynolds numbers without increasing the spatial resolution, (4 IB-FDLBM gives reasonable predictions of the drag coefficient for 1 ≤ Re ≤ 1×105, and (5 IB-FDLBM gives accurate predictions for the motion of free-falling cylinders at intermediate Reynolds numbers.

Circular polarization of gravitational waves from non-rotating supernova cores: a new probe into the pre-explosion hydrodynamics

Science.gov (United States)

Hayama, Kazuhiro; Kuroda, Takami; Kotake, Kei; Takiwaki, Tomoya

2018-06-01

We present an analysis of the circular polarization of gravitational waves (GWs) using results from three-dimensional (3D), general relativistic (GR) core-collapse simulations of a non-rotating 15 M⊙ star. For the signal detection, we perform a coherent network analysis taking into account the four interferometers of LIGO Hanford, LIGO Livingston, VIRGO, and KAGRA. We focus on the Stokes V parameter, which directly characterizes the asymmetry of the GW circular polarization. We find that the amplitude of the GW polarization becomes bigger for our 3D-GR model that exhibits strong activity of the standing accretion shock instability (SASI). Our results suggest that the SASI-induced accretion flows to the proto-neutron star (PNS) lead to a characteristic, low-frequency modulation (100-200 Hz) in both the waveform and the GW circular polarization. By estimating the signal-to-noise ratio of the GW polarization, we demonstrate that the detection horizon of the circular polarization extends by more than a factor of several times farther comparing to that of the GW amplitude. Our results suggest that the GW circular polarization, if detected, could provide a new probe into the pre-explosion hydrodynamics such as the SASI activity and the g-mode oscillation of the PNS.

Circular polarization of gravitational waves from non-rotating supernova cores: a new probe into the pre-explosion hydrodynamics

Science.gov (United States)

Hayama, Kazuhiro; Kuroda, Takami; Kotake, Kei; Takiwaki, Tomoya

2018-04-01

We present an analysis of the circular polarization of gravitational-waves (GWs) using results from three-dimensional (3D), general relativistic (GR) core-collapse simulations of a non-rotating 15M⊙ star. For the signal detection, we perform a coherent network analysis taking into account the four interferometers of LIGO Hanford, LIGO Livingston, VIRGO, and KAGRA. We focus on the Stokes V parameter, which directly characterizes the asymmetry of the GW circular polarization. We find that the amplitude of the GW polarization becomes bigger for our 3D-GR model that exhibits strong activity of the standing accretion shock instability (SASI). Our results suggest that the SASI-induced accretion flows to the proto-neutron star (PNS) lead to a characteristic, low-frequency modulation (100 ˜ 200 Hz) in both the waveform and the GW circular polarization. By estimating the signal-to-noise ratio of the GW polarization, we demonstrate that the detection horizon of the circular polarization extends by more than a factor of several times farther comparing to that of the GW amplitude. Our results suggest that the GW circular polarization, if detected, could provide a new probe into the pre-explosion hydrodynamics such as the SASI activity and the g-mode oscillation of the PNS.

General circular velocity relation of a test particle in a 3D gravitational potential: application to the rotation curves analysis and total mass determination of UGC 8490 and UGC 9753

Science.gov (United States)

Repetto, P.; Martínez-García, E. E.; Rosado, M.; Gabbasov, R.

2018-06-01

In this paper, we derive a novel circular velocity relation for a test particle in a 3D gravitational potential applicable to every system of curvilinear coordinates, suitable to be reduced to orthogonal form. As an illustration of the potentiality of the determined circular velocity expression, we perform the rotation curves analysis of UGC 8490 and UGC 9753 and we estimate the total and dark matter mass of these two galaxies under the assumption that their respective dark matter haloes have spherical, prolate, and oblate spheroidal mass distributions. We employ stellar population synthesis models and the total H I density map to obtain the stellar and H I+He+metals rotation curves of both galaxies. The subtraction of the stellar plus gas rotation curves from the observed rotation curves of UGC 8490 and UGC 9753 generates the dark matter circular velocity curves of both galaxies. We fit the dark matter rotation curves of UGC 8490 and UGC 9753 through the newly established circular velocity formula specialized to the spherical, prolate, and oblate spheroidal mass distributions, considering the Navarro, Frenk, and White, Burkert, Di Cintio, Einasto, and Stadel dark matter haloes. Our principal findings are the following: globally, cored dark matter profiles Burkert and Einasto prevail over cuspy Navarro, Frenk, and White, and Di Cintio. Also, spherical/oblate dark matter models fit better the dark matter rotation curves of both galaxies than prolate dark matter haloes.

Experimental study on the influence of the rotating cylinder and circling pistons on churning losses in axial piston pumps

OpenAIRE

Zhang, Junhui; Li, Ying; Xu, Bing; Pan, Min; Lv, Fei

2017-01-01

Pressure and performance requirements of axial piston pumps and the proportion of churning losses in axial piston pumps increase significantly with increasing speed. To investigate the primary distribution of churning losses in axial piston pumps at various ranges of speed, a test rig was set up in which other friction losses can be eliminated, thus making it possible to investigate the net churning losses in an axial piston pump. The influence of the rotating cylinder block and pistons on ch...

Transient thermal stresses in composite hollow circular cylinder due to partial heat generation

International Nuclear Information System (INIS)

Goshima, Takahito; Miyao, Kaju

1979-01-01

Clad materials are adopted for the machines and structures used in contact with high temperature, corrosive atmosphere in view of their strength and economy. Large thermal stress sometimes arises in clad cylinders due to uneaven temperature field and the difference in linear thermal expansion. Vessels are often heated uneavenly, and shearing stress occurs, which is not observed in uniform heating. In this study, infinitely long, concentric cylinders of two layers were analyzed, when the internal heat changing in stepped state is generated in cylindrical form. The unsteady thermal stress occurred was determined, using thermo-elastic potential and stress functions, and assuming the thermal properties and elastic modulus of materials as constant regardless of the temperature. Laplace transformation was used, and the basic equations for thermo-elastic displacement were employed as the basis of calculation. The analysis of the temperature distribution and stress is explained. Numerical calculation was carried out on the example of an internal cylinder of SUS 304 stainless steel and an external cylinder of mild steel. The maximum shearing stress occurred in the direction of 40 deg from the heat source, and was affected largely by the position of heat generation. The effect became remarkable as time elapsed. (Kako, I.)

Effect of Rayleigh accelerations applied to an initially moving fluid. [in circular cylinders under low gravity associated with space flight

Science.gov (United States)

Dressler, R. F.; Robertson, S. J.; Spradley, L. W.

1982-01-01

The General Interpolant Method computer code was used to analyze two-dimensional unsteady thermal convection in circular cylinders under variable low-g conditions associated with space flight. When an acceleration vector was applied parallel to the thermal gradient, in the case of a fluid at rest, no convection resulted for the stable direction, and an instability led to Rayleigh convection for the opposite direction. However, when the acceleration had a component orthogonal to the gradient, convection resulted at any Rayleigh number. The effect on convection of both types of acceleration, applied concurrently or sequentially, was investigated, including the case when the resultant vector varied in direction with time. An analysis of experimental results shows that for space flight conditions, the Rayleigh accelerations induce significant, but not dominating, changes in the established convection even when the Rayleigh number is less than critical.

Influence of obstacle aspect ratio on tripped cylinder wakes

International Nuclear Information System (INIS)

Araújo, Tiago B.; Sicot, Christophe; Borée, Jacques; Martinuzzi, Robert J.

2012-01-01

Highlights: ► Influence of a tripwire on wake properties of a surface-mounted circular cylinder. ► Height-to-diameter aspect ratios of 3 and 6 are considered. ► Critical positions for the tripwire lead to an abrupt change in the wake structure. ► Results further suggest that the tripwire can strengthen 2D wake properties. - Abstract: The influence of an asymmetrically mounted, single tripwire on the shedding and wake characteristics of a vertical, surface-mounted finite circular cylinder is investigated experimentally. Height-to-diameter aspect ratios of 3 and 6 are considered. It is shown that a critical position for the tripwire exists, which is characterised in an abrupt change in the shedding frequency and wake structure. Results further suggest that the tripwire can strengthen 2D wake properties. The influence of the aspect ratio is due to tip-wake flow interactions and thus differs fundamentally from two-dimensional geometries.

Linear and nonlinear stability of a thermally stratified magnetically driven rotating flow in a cylinder.

Science.gov (United States)

Grants, Ilmars; Gerbeth, Gunter

2010-07-01

The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by a rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilize the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. These rolls can only be excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this nonlinear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and nonlinear components of this transition by direct numerical simulation of the flow response to noise. It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.

A study of energy dissipation and critical speed of granular flow in a rotating cylinder

Science.gov (United States)

Dragomir, Sergiu C.; Sinnott, Mathew D.; Semercigil, S. Eren; Turan, Özden F.

2014-12-01

Tuned vibration absorbers may improve the safety of flexible structures which are prone to excessive oscillation magnitudes under dynamic loads. A novel absorber design proposes sloshing of granular material in a rotating cylinder where the granular material is the energy dissipating agent. As the conventional dissipative elements require maintenance due to the nature of their function, the new design may represent a virtually maintenance free alternative. The angular speed of the cylinder containing particles has a critical centrifuging speed, after which particles remain permanently in contact with the walls and there can be no further dissipation. Until the critical speed, however, dissipation increases proportionally with the angular speed. It is then vital to know the value of the critical speed as the limit of dissipation. The focus of the present study is on determination of the critical centrifuge speed. This critical speed is also of practical importance in bulk-material handling rotary mills, such as dryers and crushers. Experiments and numerical simulations, using Discrete Element Method, are used to determine the critical centrifuging speed. In addition, predictions are given and guidelines are offered for the choice of material properties to maximize the energy dissipation. As a result of a parametric study, the coefficient of friction is found to have the greatest significance on the centrifuging speed.

Oscillatory Stokes Flow Past a Slip Cylinder

Science.gov (United States)

Palaniappan, D.

2013-11-01

Two-dimensional transient slow viscous flow past a circular cylinder with Navier slip boundary conditions is considered in the limit of low-Reynolds number. The oscillatory Stokes flow problem around a cylinder is solved using the stream function method leading to an analytic solution in terms of modified Bessel functions of the second kind. The corresponding steady-state behavior yields the familiar paradoxical result first detected by Stokes. It is noted that the two key parameters, viz., the frequency λ, and the slip coefficient ξ have a significant impact on the flow field in the vicinity of the cylinder contour. In the limit of very low frequency, the flow is dominated by a term containing a well-known biharmonic function found by Stokes that has a singular behavior at infinity. Local streamlines for small times show interesting flow patterns. Attached eddies due to flow separation - observed in the no-slip case - either get detached or pushed away from the cylinder surface as ξ is varied. Computed asymptotic results predict that the flow exhibits inviscid behavior far away from the cylinder in the frequency range 0 < λ << 1 . Although the frequency of oscillations is finite, our exact solutions reveal fairly rapid transitions in the flow domain. Research Enhancement grant, TAMUCC.

Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 3

International Nuclear Information System (INIS)

Gwaltney, R.C.; Bolt, S.E.; Corum, J.M.; Bryson, J.W.

1975-06-01

The third in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: the experimental data provide design information directly applicable to nozzles in cylindrical vessels; and the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 3 had a 10 in. OD and the nozzle had a 1.29 in. OD, giving a d 0 /D 0 ratio of 0.129. The OD/thickness ratios for the cylinder and the nozzle were 50 and 7.68 respectively. Thirteen separate loading cases were analyzed. In each, one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for all the loadings were obtained using 158 three-gage strain rosettes located on the inner and outer surfaces. The loading cases were also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)

Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 4

International Nuclear Information System (INIS)

Gwaltney, R.C.; Bolt, S.E.; Bryson, J.W.

1975-06-01

The last in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models in the series are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: (1) the experimental data provide design information directly applicable to nozzles in cylindrical vessels, and (2) the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 4 had an outside diameter of 10 in., and the nozzle had an outside diameter of 1.29 in., giving a d 0 /D 0 ratio of 0.129. The OD/thickness ratios were 50 and 20.2 for the cylinder and nozzle respectively. Thirteen separate loading cases were analyzed. For each loading condition one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for each of the 13 loadings were obtained using 157 three-gage strain rosettes located on the inner and outer surfaces. Each of the 13 loading cases was also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)

Aerodynamics and Hovering Control of LTA Vehicles

Science.gov (United States)

1977-05-01

not at all the usual terminology for Magnus Force which is usually thought of as arising from viscous effects when cylinder or sphere is rotating and...Number for Circular Cylinders 9 Ratio of the Drag Coefficient of a Circular Cylinder 29 of Finite Length to That of a Cylincer of Infinite Length as...Application of Non-Linear Drag 82 30 Directional Stability Derivative 83 31 Center of Lateral Pressure Location 84 32 Dihedral Effect Derivative 85 v Figures

Introducing an experimental split-cylinder to study flows with geophysical interest: First steps and first results

Science.gov (United States)

Rodriguez-Garcia, Jesus O.; Burguete, Javier

2017-11-01

A new experimental setup has been developed in order to study rotating flows. Our research is derived from the experiments carried out in our group relating to this kind of flows, and the setup is inspired by the simulations performed by Lopez & Gutierrez-Castillo using a split-cylinder flow. In their work they study the different bifurcations taking place into the flow, among others, finding inertial waves in different configurations of the movement of the split-cylinder. Our setup consists in a split-cylinder in which each half can move in co-rotation or in counter-rotation. Moreover, we can set the rotation velocity of each half independently in order to study these different configurations of the flow. The aspect ratio defined as Γ = H / R can be modified, where H is the internal length of the cylinder and R is its radius. With this setup, we study the flow developed inside the split-cylinder depending on the Reynolds number like the different symmetry-breaking that should appear according to Lopez & Gutierrez-Castillo. To obtain the experimental data we use both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) techniques. The firsts results got are in the co-rotation case rotating one half faster than the other. We acknowledge support from Spanish Government Grant FIS 2014-54101-P. Jesús O. Rodríguez-García acknowledge research Grant from Asociación de Amigos de la Universidad de Navarra.

Equatorial circular motion in Kerr spacetime

International Nuclear Information System (INIS)

Pugliese, Daniela; Quevedo, Hernando; Ruffini, Remo

2011-01-01

We analyze the properties of circular orbits of test particles on the equatorial plane of a rotating central mass whose gravitational field is described by the Kerr spacetime. For rotating black holes and naked singularities we explore all the spatial regions where circular orbits can exist and analyze the behavior of the energy and the angular momentum of the corresponding test particles. In particular, we find all the radii at which a test particle can have zero angular momentum due to the repulsive gravity effects generated by naked singularities. We classify all the stability zones of circular orbits. It is shown that the geometric structure of the stability zones of black holes is completely different from that of naked singularities.

Taylor vortices in the flow between two coaxial cylinders one of which has a step change in radius

International Nuclear Information System (INIS)

Raju, V R K

2014-01-01

A numerical study of the flow between two coaxial cylinders, where one of the cylinders has a step change in radius, is carried out. The inner cylinder rotates and the outer cylinder is stationary. Computation is restricted to axisymmetric motion since instability in flow between coaxial cylinders is found to first occur in the form of axisymmetric Taylor vortices. In the presence of a step, Taylor vortices are found to appear first in the region where the gap between the cylinders is larger and approximately when the local Taylor number in this region reaches the critical Taylor number for onset of instability. Subsequently, Taylor vortices appear in the region where the gap is narrower, and when the local Taylor number in that region exceeds the critical Taylor number. The Taylor vortices have inward flow at a stationary end plate, and outward flow at an end plate which rotates with the same angular velocity as the inner cylinder. Similar results were obtained by Sprague et al (2008 Phys. Fluids 20 014102) for a step on inner cylinder configuration. The step functions as another end plate, if the step size is large. Whereas, it has no effect, if the step size is small. In most situations, these determine whether the number of Taylor vortices in the wide and narrow gap regions is even or odd. When the end plates rotate synchronously, but at a different speed from the inner cylinder, a change from even to odd or odd to even number of vortices in each region occurs at certain rotation rates of the end plates by sudden appearance or disappearance of a vortex at the end of the column. For a certain range of rotation rates of the end plates, the total number of vortices in the entire fluid column is odd, although the end conditions are symmetrical. (paper)

User manual for EXCALIBUR: A FE-BI numerical laboratory for cavity-backed antennas in a circular cylinder, version 1.2

Science.gov (United States)

Kempel, Leo C.

1994-01-01

The Finite Element-Boundary Integral (FE-BI) technique was used to analyze the scattering and radiation properties of cavity-backed patch antennas recessed in a metallic groundplane. A program, CAVITY3D, was written and found to yield accurate results for large arrays without the usual high memory and computational demand associated with competing formulations. Recently, the FE-BI approach was extended to cavity-backed antennas recessed in an infinite, metallic circular cylinder. EXCALIBUR is a computer program written in the Radiation Laboratory of the University of Michigan which implements this formulation. This user manual gives a brief introduction to EXCALIBUR and some hints as to its proper use. As with all computational electromagnetics programs (especially finite element programs), skilled use and best performance are only obtained through experience. However, several important aspects of the program such as portability, geometry generation, interpretation of results, and custom modification are addressed.

Circular states of atomic hydrogen

International Nuclear Information System (INIS)

Lutwak, R.; Holley, J.; Chang, P.P.; Paine, S.; Kleppner, D.; Ducas, T.

1997-01-01

We describe the creation of circular states of hydrogen by adiabatic transfer of a Rydberg state in crossed electric and magnetic fields, and also by adiabatic passage in a rotating microwave field. The latter method permits rapid switching between the two circular states of a given n manifold. The two methods are demonstrated experimentally, and results are presented of an analysis of the field ionization properties of the circular states. An application for the circular states is illustrated by millimeter-wave resonance in hydrogen of the n=29→n=30 transition. copyright 1997 The American Physical Society

Forward scattering from square cylinders in the resonance region with application to aperture blockage

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...

Controlling chaos in a fluid flow past a movable cylinder

International Nuclear Information System (INIS)

Vallejo, Juan C.; Marino, Ines P.; Sanjuan, Miguel A.F.; Kurths, Juergen

2003-01-01

The model of a two-dimensional fluid flow past a cylinder is a relatively simple problem with a strong impact in many applied fields, such as aerodynamics or chemical sciences, although most of the involved physical mechanisms are not yet well known. This paper analyzes the fluid flow past a cylinder in a laminar regime with Reynolds number, Re, around 200, where two vortices appear behind the cylinder, by using an appropriate time-dependent stream function and applying non-linear dynamics techniques. The goal of the paper is to analyze under which circumstances the chaoticity in the wake of the cylinder might be modified, or even suppressed. And this has been achieved with the help of some indicators of the complexity of the trajectories for the cases of a rotating cylinder and an oscillating cylinder

The effect of the rotational orientation of circular photomultipliers in a PET camera block detector design

International Nuclear Information System (INIS)

Uribe, J.; Wong, Wai-Hoi; Hu, Guoju

1996-01-01

This is a study of the effects of geometric asymmetries in circular photomultipliers (PMT) on the design of PET position-sensitive block detectors. The dynodes of linear-focus circular PMT's are asymmetric relative to the axis of the photocathode, despite the rotational symmetry of the photocathode. Hence, there are regional photocathode differences in the anode signal, which affect the decoding characteristics of position sensitive block detectors. This orientation effect, as well as the effect of introducing light diffusers, are studied in a block detector design (BGO) using the PMT-quadrant-sharing configuration. The PMT studied is the Philips XP-1911 (19mm diameter). Seven symmetrical and representative orientations of the four decoding PMT were investigated, as well as one asymmetric orientation. The measurements performed include block-composite pulse-height spectra and crystal decoding maps. Two orientation effects were observed: (A) distortion variation in decoding maps, and (B) decoding resolution variation. The introduction of circular plastic pieces, used as light diffusers, prove to be useful by improving the decoding of crystals on the periphery of the detector block and minimizing distortion in the decoding map. These measurements have shown optimal PMT orientations for the PMT-quadrant-sharing design, as well as for conventional block designs

SCRLH-TL Based Sequential Rotation Feed Network for Broadband Circularly Polarized Antenna Array

Directory of Open Access Journals (Sweden)

B. F. Zong

2016-04-01

Full Text Available In this paper, a broadband circularly polarized (CP microstrip antenna array using composite right/left-handed transmission line (SCRLH-TL based sequential rotation (SR feed network is presented. The characteristics of a SCRLH-TL are initially investigated. Then, a broadband and low insertion loss 45º phase shifter is designed using the SCRLH-TL and the phase shifter is employed in constructing a SR feed network for CP antenna array. To validate the design method of the SR feed network, a 2×2 antenna array comprising sequentially rotated coupled stacked CP antenna elements is designed, fabricated and measured. Both the simulated and measured results indicate that the performances of the antenna element are further enhanced when the SR network is used. The antenna array exhibits the VSWR less than 1.8 dB from 4 GHz to 7 GHz and the 3 dB axial ratio (AR from 4.4 GHz to 6.8 GHz. Also, high peak gain of 13.7 dBic is obtained. Besides, the normalized radiation patterns at the operating frequencies are symmetrical and the side lobe levels are low at φ=0º and φ=90º.

State preparation and detector effects in quantum measurements of rotation with circular polarization-entangled photons and photon counting

Science.gov (United States)

Cen, Longzhu; Zhang, Zijing; Zhang, Jiandong; Li, Shuo; Sun, Yifei; Yan, Linyu; Zhao, Yuan; Wang, Feng

2017-11-01

Circular polarization-entangled photons can be used to obtain an enhancement of the precision in a rotation measurement. In this paper, the method of entanglement transformation is used to produce NOON states in circular polarization from a readily generated linear polarization-entangled photon source. Detection of N -fold coincidences serves as the postselection and N -fold superoscillating fringes are obtained simultaneously. A parity strategy and conditional probabilistic statistics contribute to a better fringe, saturating the angle sensitivity to the Heisenberg limit. The impact of imperfect state preparation and detection is discussed both separately and jointly. For the separated case, the influence of each system imperfection is pronounced. For the joint case, the feasibility region for surpassing the standard quantum limit is given. Our work pushes the state preparation of circular polarization-entangled photons to the same level as that in the case of linear polarization. It is also confirmed that entanglement can be transformed into different frames for specific applications, serving as a useful scheme for using entangled sources.

Vacuum in the presence of electromagnetic fields and rotating boundaries

International Nuclear Information System (INIS)

Manogue, C.A.

1984-01-01

Two investigations of the properties of the vacuum are made. The first is a reconsideration of the classic Klein paradox, particle creation due to the presence of very strong external electromagnetic potentials. Expectation values of the current, momentum, and number operators, each of which is a measure of particle creation, are calculated for both massive spin zero and massive spin one half fields. The relationship between super-radiance and pair creation is explained. A review of past work by other authors is included and common conceptual errors are pointed out. The second investigation concerns the rotation of the vacuum caused by the rotation of boundaries. Just as the presence of boundaries can create a change in the vacuum expectation value of the energy density (the Casimir effect), the rotation of such boundaries can create changes in the vacuum expectation value of the momentum density. Calculations of the Casimir effect are made for a massless scalar field confined to an infinitely long square box. The change in the vacuum expectation value of the momentum density is calculated if this same box is rotating around its long central axis. In contrast, it is shown that for an infinitely long circular cylinder there is no change in the momentum density

Effect of corner radius in stabilizing the low-Re flow past a cylinder

KAUST Repository

Zhang, Wei

2017-08-03

We perform global linear stability analysis on low-Re flow past an isolated cylinder with rounded corners. The objective of the present work is to investigate the effect of the cylinder geometry (corner radius) on the stability characteristics of the flow. Our investigation sheds light on new physics that the flow can be stabilized by partially rounding the cylinder in the critical and weakly super-critical flow regimes. The flow is first stabilized and then gradually destabilized as the cylinder varies from square to circular geometry. The sensitivity analysis reveals that the variation of stability is attributed to the different spatial variation trends of the backflow velocity in the near- and far-wake regions for various cylinder geometries. The results from the stability analysis are also verified with those of the direct simulations and very good agreement is achieved.

Effect of corner radius in stabilizing the low-Re flow past a cylinder

KAUST Repository

Zhang, Wei; Samtaney, Ravindra

2017-01-01

We perform global linear stability analysis on low-Re flow past an isolated cylinder with rounded corners. The objective of the present work is to investigate the effect of the cylinder geometry (corner radius) on the stability characteristics of the flow. Our investigation sheds light on new physics that the flow can be stabilized by partially rounding the cylinder in the critical and weakly super-critical flow regimes. The flow is first stabilized and then gradually destabilized as the cylinder varies from square to circular geometry. The sensitivity analysis reveals that the variation of stability is attributed to the different spatial variation trends of the backflow velocity in the near- and far-wake regions for various cylinder geometries. The results from the stability analysis are also verified with those of the direct simulations and very good agreement is achieved.

Three-dimensional study of flow past a square cylinder at low Reynolds numbers

International Nuclear Information System (INIS)

Saha, A.K.; Biswas, G.; Muralidhar, K.

2003-01-01

The spatial evolution of vortices and transition to three-dimensionality in the wake of a square cylinder have been numerically studied. A Reynolds number range between 150 and 500 has been considered. Starting from the two-dimensional Karman vortex street, the transition to three-dimensionality is found to take place at a Reynolds number between 150 and 175. The three-dimensional wake of the square cylinder has been characterized using indicators appropriate for the wake of a bluff body as described by the earlier workers. In these terms, the secondary vortices of Mode-A are seen to persist over the Reynolds number range of 175-240. At about a Reynolds number of 250, Mode-B secondary vortices are present, these having predominantly small-scale structures. The transitional flow around a square cylinder exhibits an intermittent low frequency modulation due to the formation of a large-scale irregularity in the near-wake, called vortex dislocation. The superposition of vortex dislocation and the Mode-A vortices leads to a new pattern, labelled as Mode-A with dislocations. The results for the square cylinder are in good accordance with the three-dimensional modes of transition that are well-known in the circular cylinder wake. In the case of a circular cylinder, the transition from periodic vortex shedding to Mode-A is characterized by a discontinuity in the Strouhal number-Reynolds number relationship at about a Reynolds of 190. The transition from Mode-A to Mode-B is characterized by a second discontinuity in the frequency law at a Reynolds number of ∼250. The numerical computations of the present study with a square cylinder show that the values of the Strouhal number and the time-averaged drag-coefficient are closely associated with each other over the range of Reynolds numbers of interest and reflect the spatial structure of the wake

A Numerical Approach to the Dynamic Response of the Deployment System during a Circular Cylinder Crossing through the Wave Zone

Directory of Open Access Journals (Sweden)

Xiaozhou Hu

2017-01-01

Full Text Available The dynamic response of the deployment system while deploying a circular cylinder crossing wave surface and the following submerging process are investigated numerically. The present numerical approach is based on the combination of solution methods of cable dynamics and computational fluid dynamics (CFD. For the implementation of the numerical approach, a cosimulation platform based on a CFD code and MATLAB is developed to study the fluid-solid interaction problem in the process. To generate regular waves, a numerical wave tank is built based on a piston-type wave generation method and a wave damping method applying porous media. Numerical simulations are performed based on the cosimulation platform. The sensitivities of cable tension, velocity, and acceleration of deployed body to different input parameters are investigated, including phase angles, wave heights, and periods of regular waves and deploying velocities, and the effects of those input parameters on dynamic responses of the deployment system are also discussed.

From Newton's bucket to rotating polygons

DEFF Research Database (Denmark)

Bach, B.; Linnartz, E. C.; Vested, Malene Louise Hovgaard

2014-01-01

We present an experimental study of 'polygons' forming on the free surface of a swirling water flow in a partially filled cylindrical container. In our set-up, we rotate the bottom plate and the cylinder wall with separate motors. We thereby vary rotation rate and shear strength independently...... and move from a rigidly rotating 'Newton's bucket' flow to one where bottom and cylinder wall are rotating oppositely and the surface is strongly turbulent but flat on average. Between those two extremes, we find polygonal states for which the rotational symmetry is spontaneously broken. We investigate...... the phase diagram spanned by the two rotational frequencies at a given water filling height and find polygons in a regime, where the two frequencies are sufficiently different and, predominantly, when they have opposite signs. In addition to the extension of the family of polygons found with the stationary...

Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis

Science.gov (United States)

Meliga, Philippe

2017-07-01

We provide in-depth scrutiny of two methods making use of adjoint-based gradients to compute the sensitivity of drag in the two-dimensional, periodic flow past a circular cylinder (Re≲189 ): first, the time-stepping analysis used in Meliga et al. [Phys. Fluids 26, 104101 (2014), 10.1063/1.4896941] that relies on classical Navier-Stokes modeling and determines the sensitivity to any generic control force from time-dependent adjoint equations marched backwards in time; and, second, a self-consistent approach building on the model of Mantič-Lugo et al. [Phys. Rev. Lett. 113, 084501 (2014), 10.1103/PhysRevLett.113.084501] to compute semilinear approximations of the sensitivity to the mean and fluctuating components of the force. Both approaches are applied to open-loop control by a small secondary cylinder and allow identifying the sensitive regions without knowledge of the controlled states. The theoretical predictions obtained by time-stepping analysis reproduce well the results obtained by direct numerical simulation of the two-cylinder system. So do the predictions obtained by self-consistent analysis, which corroborates the relevance of the approach as a guideline for efficient and systematic control design in the attempt to reduce drag, even though the Reynolds number is not close to the instability threshold and the oscillation amplitude is not small. This is because, unlike simpler approaches relying on linear stability analysis to predict the main features of the flow unsteadiness, the semilinear framework encompasses rigorously the effect of the control on the mean flow, as well as on the finite-amplitude fluctuation that feeds back nonlinearly onto the mean flow via the formation of Reynolds stresses. Such results are especially promising as the self-consistent approach determines the sensitivity from time-independent equations that can be solved iteratively, which makes it generally less computationally demanding. We ultimately discuss the extent to

Multi-directional random wave interaction with an array of cylinders

DEFF Research Database (Denmark)

Ji, Xinran; Liu, Shuxue; Bingham, Harry B.

2015-01-01

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...

Sunspots and the physics of magnetic flux tubes. IV - Aerodynamic lift on a thin cylinder in convective flows

Science.gov (United States)

Tsinganos, K. C.

1979-01-01

The aerodynamic lift exerted on a long circular cylinder immersed in a convective flow pattern in an ideal fluid is calculated to establish the equilibrium position of the cylinder. The calculations establish the surprising result that the cylinder is pushed out the upwellings and the downdrafts of the convective cell, into a location midway between them. The implications for the intense magnetic flux tubes in the convection beneath the surface of the sun are considered.

Strain-based finite elements for the analysis of cylinders with holes and normally intersecting cylinders

International Nuclear Information System (INIS)

Sabir, A.B.

1983-01-01

A finite element solution to the problems of stress distribution for cylindrical shells with circular and elliptical holes and also for normally intersecting thin elastic cylindrical shells is given. Quadrilateral and triangular curved finite elements are used in the analysis. The elements are of a new class, based on simple independent generalised strain functions insofar as this is allowed by the compatibility equations. The elements also satisfy exactly the requirements of strain-free-rigid body displacements and uses only the external 'geometrical' nodal degrees of freedom to avoid the difficulties associated with unnecessary internal degrees of freedom. We first develop strain based quadrilateral and triangular elements and apply them to the solution of the problem of stress concentrations in the neighbourhood of small and large circular and elliptical holes when the cylinders are subjected to a uniform axial tension. These results are compared with analytical solutions based on shallow shell approximations and show that the use of these strain based elements obviates the need for using an inordinately large number of elements. Normally intersecting cylinders are common configurations in structural components for nuclear reactor systems and design information for such configurations are generally lacking. The opportunity is taken in the present paper to provide a finite element solution to this problem. A method of substructing will be introduced to enable a solution to the large number of non banded set of simultaneous equations encountered. (orig./HP)

Instantaneous flow field above the free end of finite-height cylinders and prisms

International Nuclear Information System (INIS)

Rostamy, N.; Sumner, D.; Bergstrom, D.J.; Bugg, J.D.

2013-01-01

Highlights: • PIV measurements of the flow above the free end of finite-height bodies. • Effect of cross-sectional shape of the models on the instantaneous flow. • Small-scale structures generated by the separated shear layer were revealed. • Effect of aspect ratio on the reattachment of the separated flow on the free end. -- Abstract: The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied experimentally using particle image velocimetry (PIV). Cylinders and prisms with aspect ratios of AR = 9, 7, 5, and 3 were tested at a Reynolds number of Re = 4.2 × 10 4 . The bodies were mounted normal to a ground plane and were partially immersed in a turbulent zero-pressure-gradient boundary layer, where the boundary layer thickness relative to the body width was δ/D = 1.6. PIV measurements were made above the free ends of the bodies in a vertical plane aligned with the flow centreline. The present PIV results provide insight into the effects of aspect ratio and body shape on the instantaneous flow field. The recirculation zone under the separated shear layer is larger for the square prism of AR = 3 compared to the more slender prism of AR = 9. Also, for a square prism with low aspect ratio (AR = 3), the influence of the reverse flow over the free end surface becomes more significant compared to that for a higher aspect ratio (AR = 9). For the circular cylinder, a cross-stream vortex forms within the recirculation zone. As the aspect ratio of the cylinder decreases, the reattachment point of the separated flow on the free end surface moves closer to the trailing edge. For both the square prism and circular cylinder cases, the instantaneous velocity vector field and associated in-plane vorticity field revealed small-scale structures mostly generated by the separated shear layer

Water Entry and Exit of Horizontal Cylinder in Free Surface Flow

International Nuclear Information System (INIS)

Hafsia, Zouhaier; Maalel, Khlifa; Mnasri, Chokri; Mohamed, Omri

2009-01-01

This paper describes two-dimensional numerical simulations of the water entry and exit of horizontal circular cylinder at constant velocity. The deformation of free surface is described by Navier-Stokes (N S) equations of incompressible and viscous fluid with additional transport equation of the volume-of-fluid (VOF). The motion of the cylinder is modeled by the associated momentum source term implemented in the Phoenicis (Parabolic Hyperbolic Or Elliptic Numerical Integration Code Series) code. The domain is discretized by a fixed Cartesian grid using a finite volume method and the cylinder is represented and cut cell method. The simulated results are compared with the numerical results of Lin (2007). This comparison shows good agreement in terms of free surface evolution for water exit and sinking. However, for water entry, the jet flow simulated by Lin is not reproduced. The free surface deformation around the cylinder in downward direction is accurately predicted

Effect of slip on vortex dynamics and forcing of a superhydrophobic cylinder

Science.gov (United States)

Muralidhar, Pranesh; Daniello, Robert; Ferrer, Nangelie; Rothstein, Jonathan

2011-11-01

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. In this presentation, a series of experiments will be presented which investigate the effect of superhydrophobic-induced slip on the vortex dynamics in the wake of a cylinder and the change in the drag and lift forces thereof. In these experiments, circular cylinders are coated with a series of superhydrophobic surfaces fabricated from PDMS with well-defined micron-sized patterns of surface roughness. Using force measurements and PIV (Particle Image Velocimetry), we will show that these surfaces have a noticeable effect on the drag/lift and vortex dynamics of cylinders. When compared to a smooth, no-slip cylinder, we will show that the lift/drag and the amount of raw vorticity that is shed in the wake of the superhydrophobic cylinder decreases. In addition, we will show that the forcing is sensitive to changes of feature spacing, size and orientation.

Literature review and experimental results for a cylinder with perforations and protrusions at high Reynolds numbers

Science.gov (United States)

Jones, G. S.; Horvath, T. J.; Stainback, P. C.; Beasley, W. D.; Mcghee, R. J.

1987-01-01

The NASA Langley Low Turbulence Pressure Tunnel has been used to conduct an experimental study of the flow around a series of circular cylinders; the models used consisted of a baseline, smooth cylinder together with a cylinder that could be reconfigured with six different arrangements of two types of surface irregularity. Mean lift and drag forces were measured on all seven model configurations, and correlations were made between unsteady pressure in the wake region and fluctuating lift forces, in order to identify coherent structures.

Design guide for calculating fluid damping for circular cylindrical structures

International Nuclear Information System (INIS)

Chen, S.S.

1983-06-01

Fluid damping plays an important role for structures submerged in fluid, subjected to flow, or conveying fluid. This design guide presents a summary of calculational procedures and design data for fluid damping for circular cylinders vibrating in quiescent fluid, crossflow, and parallel flow

Sunspots and the physics of magnetic flux tubes. IV. Aerodynamic lift on a thin cylinder in convective flows

International Nuclear Information System (INIS)

Tsinganos, K.C.

1979-01-01

The aerodynamic lift exerted on a long circular cylinder immersed in a convective flow pattern in an ideal fluid is calculated to establish the equilibrium position of the cylinder. The calculations establish the surprising result that the cylinder is pushed out of the upwellings and the downdrafts of the convective cell, into a location midway between them.The implications for the intense magnetic flux tubes in the convection beneath the surface of the Sun are considered

Assessing of the effect of hydrodynamics in the growth of scale (CaCO3) in rotating cylinder electrode

Science.gov (United States)

García, M.; Espinosa Cardenal, E. J.; Vera, E.

2017-12-01

Fouling is a common problem related to different industries in which the solubility of dissolved minerals in water changes leading to the formation of deposits on the surface of the equipment, for instance, in oil production the scale can be formed on the wellbore, on the well tubing or superficial facilities. Over the last years, several studies have been carried out in order to determine the effect of operational conditions in the scale growth but there are no conclusive results. This paper presents the results of calcium carbonate deposition on the surface of stainless steel AISI 316 at 71°C, and the influence of rotating velocity on the quantity and morphology of the generated scale. The tests were carried out by using a rotating cylinder electrode and X-Ray Diffraction (DRX), and Scanning Electron Microscopy (SEM) of the scale obtained was analysed. The results show that the amount of scale formed changes regarding the velocity of the fluid, as well as the morphology of the deposited crystals.

Circular orbits and acceleration of particles by near-extremal dirty rotating black holes: general approach

International Nuclear Information System (INIS)

Zaslavskii, Oleg B

2012-01-01

We study the effect of collisions of ultrahigh energy particles near the black hole horizon (BSW effect) for two scenarios: when one of the particles either (i) moves on a circular orbit or (ii) plunges from it toward the horizon. It is shown that such circular near-horizon orbits can exist for near-extremal black holes only. This includes the innermost stable orbit (ISCO), marginally bound orbit (MBO) and photon one (PhO). We consider generic ‘dirty’ rotating black holes not specifying the metric and show that the energy in the center-of-mass frame has the universal scaling dependence on the surface gravity κ. Namely, E c.m. ∼ κ −n where for the ISCO, n= 1/3 in case (i) or n= 1/2 in case (ii). For the MBO and PhCO, n= 1/2 in both scenarios that agrees with recent calculations of Harada and Kimura for the Kerr metric. We also generalize the Grib and Pavlov observations made for the Kerr metric. The magnitude of the BSW effect on the location of collision has a somewhat paradoxical character: it decreases when approaching the horizon. (paper)

Circular orbits and acceleration of particles by near-extremal dirty rotating black holes: general approach

Science.gov (United States)

Zaslavskii, Oleg B.

2012-10-01

We study the effect of collisions of ultrahigh energy particles near the black hole horizon (BSW effect) for two scenarios: when one of the particles either (i) moves on a circular orbit or (ii) plunges from it toward the horizon. It is shown that such circular near-horizon orbits can exist for near-extremal black holes only. This includes the innermost stable orbit (ISCO), marginally bound orbit (MBO) and photon one (PhO). We consider generic ‘dirty’ rotating black holes not specifying the metric and show that the energy in the center-of-mass frame has the universal scaling dependence on the surface gravity κ. Namely, Ec.m. ˜ κ-n where for the ISCO, n=\\frac{1}{3} in case (i) or n=\\frac{1}{2} in case (ii). For the MBO and PhCO, n=\\frac{1}{2} in both scenarios that agrees with recent calculations of Harada and Kimura for the Kerr metric. We also generalize the Grib and Pavlov observations made for the Kerr metric. The magnitude of the BSW effect on the location of collision has a somewhat paradoxical character: it decreases when approaching the horizon.

Finite elements model of a rotating half-bridge belonging to a circular settling tank

Science.gov (United States)

Dascalescu, A. E.; Lazaroiu, G.; Scupi, A. A.; Oanta, E.

2016-08-01

A circular settling tank is an open reservoir used for the gravitational separation of the sludge and of the clarified water which is discharged in the launder which is mounted at the periphery of the basin. The extraction of the sludge is done by the use of a rotating half-bridge which sweeps the sludge, vacuums it using a system of scrapping blades and suction pipes, collects it in some local sludge chambers and pour it in a central collecting tank. The rotating half-bridge is a complex structure under a complex system of loads, therefore advanced instruments of investigation are required to assess the state of strains and stresses in this structure. Until now an analytical model was developed based on the hypotheses specific to the strength of materials academic discipline. The numerical models presented in the paper use the finite element method to determine the displacements of the main beam loaded by the weight of the structure and by the Archimedes’ forces. The results of the models developed so far are conclusive for the future directions of research which aims a higher degree of accuracy of the models and of the according research methodology.

Stress intensity factors of corner cracks in two nozzle-cylinder intersections

International Nuclear Information System (INIS)

Kobayashi, A.S.; Polvanich, N.; Emery, A.F.; Love, W.J.

1977-01-01

In a recent paper, the authors presented the stress-intensity-magnification factors of a quarter-elliptical surface crack in a quarter-infinite solid and a circular crack approaching a reentry corner in a three-quarter infinite solid. These stress-intensity-magnification factors were used together with a curvature-correction factor to estimate the stress-intensity factor of a corner crack at a nozzle-cylinder intersection. Through appropriate superposition of the above stress-intensity-magnification factors, stress-intensity factors for hypothetical corner cracks at a nozzle-cylinder intersection subjected to internal pressure and transient thermal-stress loadings can be obtained. A description of a computer code based on this procedure as well as its applications in analyzing two corner-crack problems at a nozzle-cylinder intersection are discussed in this paper

Stress intensity factors of corner cracks in two nozzle-cylinder interactions

International Nuclear Information System (INIS)

Kobayashi, A.S.; Polvanich, N.; Emery, A.F.; Love, W.J.

1977-01-01

In a recent paper, the authors presented the stress-intensity-magnification factors of a quarter-elliptical surface crack in a quarter-infinite solid and a circular crack approaching a reentry corner in a three-quarter infinite solid. These stress-intensity-magnification factors were used together with a curvature-correction factor to estimate the stress-intensity factor of a corner crack at a nozzle-cylinder interaction. Through appropriate superposition of the above stress-intensity-magnification factors, stress-intensity factors for hypothetical corner cracks at a nozzle-cylinder intersection subjected to internal pressure and transient thermal-stress loadings can be obtained. A description of a computer code based on this procedure as well as its applications in analyzing two corner-crack probems at a nozzle-cylinder intersection are discussed in this paper. (Auth.)

Effect of constant heat flux at outer cylinder on stability of viscous ...

African Journals Online (AJOL)

In this paper, the stability of the Couette flow of a viscous incompressible fluid between two concentric rotating cylinders is studied in the presence of a radial temperature gradient, when the outer cylinder is maintained at a constant heat flux. The analytical solution of the eigen-value problem is obtained by using the ...

Computation of transitional flow past a circular cylinder using multiblock lattice Boltzmann method with a dynamic subgrid scale model

International Nuclear Information System (INIS)

Premnath, Kannan N; Pattison, Martin J; Banerjee, Sanjoy

2013-01-01

Lattice Boltzmann method (LBM) is a kinetic based numerical scheme for the simulation of fluid flow. While the approach has attracted considerable attention during the last two decades, there is a need for systematic investigation of its applicability for complex canonical turbulent flow problems of engineering interest, where the nature of the numerical properties of the underlying scheme plays an important role for their accurate solution. In this paper, we discuss and evaluate a LBM based on a multiblock approach for efficient large eddy simulation of three-dimensional external flow past a circular cylinder in the transitional regime characterized by the presence of multiple scales. For enhanced numerical stability at higher Reynolds numbers, a multiple relaxation time formulation is considered. The effect of subgrid scales is represented by means of a Smagorinsky eddy-viscosity model, where the model coefficient is computed locally by means of a dynamic procedure, providing better representation of flow physics with reduced empiricism. Simulations are performed for a Reynolds number of 3900 based on the free stream velocity and cylinder diameter for which prior data is available for comparison. The presence of laminar boundary layer which separates into a pair of shear layers that evolve into turbulent wakes impose particular challenge for numerical methods for this condition. The relatively low numerical dissipation introduced by the inherently parallel and second-order accurate LBM is an important computational asset in this regard. Computations using five different grid levels, where the various blocks are suitably aligned to resolve multiscale flow features show that the structure of the recirculation region is well reproduced and the statistics of the mean flow and turbulent fluctuations are in satisfactory agreement with prior data. (paper)

Computation of transitional flow past a circular cylinder using multiblock lattice Boltzmann method with a dynamic subgrid scale model

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)

Mixed convection heat transfer enhancement in a cubic lid-driven cavity containing a rotating cylinder through the introduction of artificial roughness on the heated wall

Science.gov (United States)

Kareem, Ali Khaleel; Gao, Shian

2018-02-01

The aim of the present numerical investigation is to comprehensively analyse and understand the heat transfer enhancement process using a roughened, heated bottom wall with two artificial rib types (R-s and R-c) due to unsteady mixed convection heat transfer in a 3D moving top wall enclosure that has a central rotating cylinder, and to compare these cases with the smooth bottom wall case. These different cases (roughened and smooth bottom walls) are considered at various clockwise and anticlockwise rotational speeds, -5 ≤ Ω ≤ 5, and Reynolds numbers of 5000 and 10 000. The top and bottom walls of the lid-driven cavity are differentially heated, whilst the remaining cavity walls are assumed to be stationary and adiabatic. A standard k-ɛ model for the Unsteady Reynolds-Averaged Navier-Stokes equations is used to deal with the turbulent flow. The heat transfer improvement is carefully considered and analysed through the detailed examinations of the flow and thermal fields, the turbulent kinetic energy, the mean velocity profiles, the wall shear stresses, and the local and average Nusselt numbers. It has been concluded that artificial roughness can strongly affect the thermal fields and fluid flow patterns. Ultimately, the heat transfer rate has been dramatically increased by involving the introduced artificial rips. Increasing the cylinder rotational speed or Reynolds number can enhance the heat transfer process, especially when the wall roughness exists.

Rotating flow

CERN Document Server

Childs, Peter R N

2010-01-01

Rotating flow is critically important across a wide range of scientific, engineering and product applications, providing design and modeling capability for diverse products such as jet engines, pumps and vacuum cleaners, as well as geophysical flows. Developed over the course of 20 years' research into rotating fluids and associated heat transfer at the University of Sussex Thermo-Fluid Mechanics Research Centre (TFMRC), Rotating Flow is an indispensable reference and resource for all those working within the gas turbine and rotating machinery industries. Traditional fluid and flow dynamics titles offer the essential background but generally include very sparse coverage of rotating flows-which is where this book comes in. Beginning with an accessible introduction to rotating flow, recognized expert Peter Childs takes you through fundamental equations, vorticity and vortices, rotating disc flow, flow around rotating cylinders and flow in rotating cavities, with an introduction to atmospheric and oceanic circul...

An Analytical Method of Auxiliary Sources Solution for Plane Wave Scattering by Impedance Cylinders

DEFF Research Database (Denmark)

Larsen, Niels Vesterdal; Breinbjerg, Olav

2004-01-01

Analytical Method of Auxiliary Sources solutions for plane wave scattering by circular impedance cylinders are derived by transformation of the exact eigenfunction series solutions employing the Hankel function wave transformation. The analytical Method of Auxiliary Sources solution thus obtained...

Dynamics of Plug Formation in a Circular Cylinder Under Low Bond Number Conditions: Experiment and Simulation

Science.gov (United States)

Hallaby, Ghazi; Kizito, John P.

2016-08-01

The goal of the current study is to investigate the dynamics of two phase interface under a low Bond number condition. Silicone oil is injected into a cylinder under a Bond number of about 0.47 via a side tube forming a T-junction with the former. The time evolution of the interface of silicon oil in a cylinder is captured using a high speed camera. The volume at which the plug is formed is then determined using an image processing tool to analyze the captured images. A numerical simulation is carried out where fluid is injected into a cylinder, under a less than unity Bond number condition, via a side tube. Numerical and experimental results are then compared.

Experimental data and numerical predictions of a single-phase flow in a batch square stirred tank reactor with a rotating cylinder agitator

Science.gov (United States)

Escamilla-Ruíz, I. A.; Sierra-Espinosa, F. Z.; García, J. C.; Valera-Medina, A.; Carrillo, F.

2017-09-01

Single-phase flows in stirred tank reactors have useful characteristics for a wide number of industrial applications. Usually, reactors are cylindrical vessels and complex impeller designs, which are often highly energy consuming and produce complicated flow patterns. Therefore, a novel configuration consisting of a square stirred tank reactor is proposed in this study with potential advantages over conventional reactors. In the present work hydrodynamics and turbulence have been studied for a single-phase flow in steady state operating in batch condition. The flow was induced by drag from a rotating cylinder with two diameters. The effects of drag from the stirrer as well as geometrical parameters of the system on the hydrodynamic behavior were investigated using Computational Fluids Dynamics (CFD) and non-intrusive Laser Doppler Anemometry, (LDA). Data obtained from LDA measurements were used for the validation of the CFD simulations, and to detecting the macro-instabilities inside the tank, based on the time series analysis for three rotational speeds N = 180, 1000 and 2000 rpm. The numerical results revealed the formation of flow patterns and macro-vortex structures in the upper part of the tank as consequence of the Reynolds number and the stream discharge emanated from the cylindrical stirrer. Moreover, increasing the cylinder diameter has an impact on the number of recirculation loops as well as the energy consumption of the entire system showing better performance in the presence of turbulent flows.

Collective circular motion in synchronized and balanced formations with second-order rotational dynamics

Science.gov (United States)

Jain, Anoop; Ghose, Debasish

2018-01-01

This paper considers collective circular motion of multi-agent systems in which all the agents are required to traverse different circles or a common circle at a prescribed angular velocity. It is required to achieve these collective motions with the heading angles of the agents synchronized or balanced. In synchronization, the agents and their centroid have a common velocity direction, while in balancing, the movement of agents causes the location of the centroid to become stationary. The agents are initially considered to move at unit speed around individual circles at different angular velocities. It is assumed that the agents are subjected to limited communication constraints, and exchange relative information according to a time-invariant undirected graph. We present suitable feedback control laws for each of these motion coordination tasks by considering a second-order rotational dynamics of the agent. Simulations are given to illustrate the theoretical findings.

Scattering by cavity-backed antennas on a circular cylinder

Science.gov (United States)

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.

Analysis of VAWT aerodynamics and design using the Actuator Cylinder flow model

DEFF Research Database (Denmark)

Aagaard Madsen, Helge; Schmidt Paulsen, Uwe; Vita, Luca

2012-01-01

The actuator cylinder flow model is defined as the ideal VAWT rotor. Radial directed volume forces are applied on the circular path of the VAWT rotor airfoil and constitute an energy conversion in the flow. The power coefficient for the ideal as well as the real energy conversion is defined...

Experimental investigation of flow characteristics around four square-cylinder arrays at subcritical Reynolds numbers

Directory of Open Access Journals (Sweden)

Mingyue Liu

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.

Photoelastic investigation of the stresses in a stepped cylinder under internal pressure

International Nuclear Information System (INIS)

Sawa, Yoshiaki; Nishida, Masataka

1985-01-01

The states of stress distribution of the stepped cylinder under inner-pressure are studied by means of stress freezing photoelastic method. The experimental results reveal that fiber stress concentration occurs on the circular arc and hoop stress concentration occurs at the jointing point of the straight line and the arc and that each maximum value of fiver stress and hoop stress depends very greatly on the diameter of a small cylinder and the radius of curvature. And the relationship between the stress concentration factors and these shape factors are given. Effects of wall thickness on the stress concentration factors are also determined. (author)

Numerical investigations of passive scalar transport in Taylor-Couette flows: Counter-rotation effect

Science.gov (United States)

Ouazib, Nabila; Salhi, Yacine; Si-Ahmed, El-Khider; Legrand, Jack; Degrez, G.

2017-07-01

Numerical methods for solving convection-diffusion-reaction (CDR) scalar transport equation in three-dimensional flow are used in the present investigation. The flow is confined between two concentric cylinders both the inner cylinder and the outer one are allowed to rotate. Direct numerical simulations (DNS) have been achieved to study the effects of the gravitational and the centrifugal potentials on the stability of incompressible Taylor-Couette flow. The Navier-Stokes equations and the uncoupled convection-diffusion-reaction equation are solved using a spectral development in one direction combined together with a finite element discretization in the two remaining directions. The complexity of the patterns is highlighted. Since, it increases as the rotation rates of the cylinders increase. In addition, the effect of the counter-rotation of the cylinders on the mass transfer is pointed out.

Structural Design of Two-Cylinder Single Overhead Camshaft

Science.gov (United States)

Zhao, Yuxia; Zhang, Kangsheng; Di, Jiejian

2018-01-01

Due to the higher performance demand, the camshaft is the key driving part in the engine. Because it is eccentric circular section part, it is very difficult to design and manufacture this kind of axial parts. Take two-cylinder single overhead camshaft for an example, the entire process of camshaft design is analyzed. The practice has proved that the method has simple, flexible and efficient advantages, and it can greatly shorten the design of artificial computing time.

Flow around an oscillating cylinder: computational issues

Energy Technology Data Exchange (ETDEWEB)

Jiang, Fengjian; Gallardo, José P; Pettersen, Bjørnar [Department of Marine Technology, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Andersson, Helge I, E-mail: fengjian.jiang@ntnu.no [Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)

2017-10-15

We consider different computational issues related to the three-dimensionalities of the flow around an oscillating circular cylinder. The full time-dependent Navier–Stokes equations are directly solved in a moving reference frame by introducing a forcing term. The choice of quantitative validation criteria is discussed and discrepancies of previously published results are addressed. The development of Honji vortices shows that short simulation times may lead to incorrect quasi-stable vortex patterns. The viscous decay of already established Honji vortices is also examined. (paper)

Cylinder head fastening structure for internal combustion engines

Energy Technology Data Exchange (ETDEWEB)

Futakuchi, Y.; Oshiro, N.

1988-01-26

In a construction for an overhead cam internal combustion engine comprising a cylinder head adapted to be affixed to another component of the engine by at least one fastener having a tool receiving portion for tightening thereof and having a bearing cap affixed to the cylinder head and rotatably journaling the overhead camshaft, the improvement is described comprising the bearing cap having a portion overlying the fastener tool receiving portion, and means defining an access opening passing through the bearing cap and adapted to pass a tool for tightening of the fastener without removal of the bearing cap.

Equilibrium of current driven rotating liquid metal

International Nuclear Information System (INIS)

Velikhov, E.P.; Ivanov, A.A.; Zakharov, S.V.; Zakharov, V.S.; Livadny, A.O.; Serebrennikov, K.S.

2006-01-01

In view of great importance of magneto-rotational instability (MRI) as a fundamental mechanism for angular momentum transfer in magnetized stellar accretion disks, several research centers are involved in experimental study of MRI under laboratory conditions. The idea of the experiment is to investigate the rotation dynamics of well conducting liquid (liquid metal) between two cylinders in axial magnetic field. In this Letter, an experimental scheme with immovable cylinders and fluid rotation driven by radial current is considered. The analytical solution of a stationary flow was found taking into account the external current. Results of axially symmetric numerical simulations of current driven fluid dynamics in experimental setup geometry are presented. The analytical solution and numerical simulations show that the current driven fluid rotation in axial magnetic field provides the axially homogeneous velocity profile suitable for MRI study in classical statement

Reduction of sound transmission across plenum windows by incorporating an array of rigid cylinders

Science.gov (United States)

Tang, S. K.

2018-02-01

The potential improvement of plenum window noise reduction by installing rigid circular cylinder arrays into the window cavity is investigated numerically using the finite-element method in this study. A two-dimensional approach is adopted. The sound transmission characteristics and propagation within the plenum window are also examined in detail. Results show that the installation of the cylinders in general gives rise to broadband improvement of noise reduction across a plenum window regardless of the direction of sound incidence. Such acoustical performance becomes better when more cylinder columns are installed, but it is suggested that the number of cylinder rows should not exceed two. Results also show that the cylinder positions relative to the nodal/anti-nodal planes of the acoustic modes are crucial in the noise reduction enhancement mechanisms. Noise reduction can further be enhanced by staggering the cylinder rows, such that each cylinder row supports the development of a different acoustic mode. For the simple cylinder arrangements considered in this study, the traffic noise reduction enhancement observed in this study can be as high as 4-5 dB, which is already comparable to or higher than the maximum achieved by installing sound absorption into a plenum window.

Velocity distribution of liquid in rotary cylinder when a rotary disc is disposed in contact with a liquid surface; Ekimen ni kaitenenban no arubaai no kaiten entonai ekitai no sokudo bunpu

Energy Technology Data Exchange (ETDEWEB)

Karino, Fumimaru; Kawai, Kazuho; Domoto, Takuya; Takahashi, Toru [Kyoto University, Tokyoto (Japan)

1999-02-05

As a model of a flow in a crucible of Cz method, which is a crystal growth method, a system was formed by flowing water into a rotary cylindrical container and disposing a rotary disc in contact with a free surface of the liquid, and this system was used to determine the velocity distribution in the cylindrical container by a laser Doppler hydrometer. The effects of cylinder rotation Reynolds number, disc rotation Reynolds number, the distance between the disc and the cylinder bottom, and the radius ratio of the disc to the cylinder on the determined radial distribution of tangential time average velocity were examined. As a result, it was found that, in the cases where only the cylinder is rotated, where only the disc is rotated, and where an absolute value of the rotation angular velocity ratio of the disc to the cylinder is small when the cylinder and the disc are rotated in directions inverse to each other, the radial distribution of the time average tangential velocity shows a distribution substantially the same independent on vertical positions, thus Taylor-Proudman theorem is valid. It was further known that, when the disc and the cylinder are rotated in inverse directions and the absolute value of the angular velocity ratio is great, the effect of the disc rotation is remarkable, and particularly, this effect becomes greater in the lower flow than near the disc. (translated by NEDO)

CSA: An efficient algorithm to improve circular DNA multiple alignment

Directory of Open Access Journals (Sweden)

Pereira Luísa

2009-07-01

Full Text Available Abstract Background The comparison of homologous sequences from different species is an essential approach to reconstruct the evolutionary history of species and of the genes they harbour in their genomes. Several complete mitochondrial and nuclear genomes are now available, increasing the importance of using multiple sequence alignment algorithms in comparative genomics. MtDNA has long been used in phylogenetic analysis and errors in the alignments can lead to errors in the interpretation of evolutionary information. Although a large number of multiple sequence alignment algorithms have been proposed to date, they all deal with linear DNA and cannot handle directly circular DNA. Researchers interested in aligning circular DNA sequences must first rotate them to the "right" place using an essentially manual process, before they can use multiple sequence alignment tools. Results In this paper we propose an efficient algorithm that identifies the most interesting region to cut circular genomes in order to improve phylogenetic analysis when using standard multiple sequence alignment algorithms. This algorithm identifies the largest chain of non-repeated longest subsequences common to a set of circular mitochondrial DNA sequences. All the sequences are then rotated and made linear for multiple alignment purposes. To evaluate the effectiveness of this new tool, three different sets of mitochondrial DNA sequences were considered. Other tests considering randomly rotated sequences were also performed. The software package Arlequin was used to evaluate the standard genetic measures of the alignments obtained with and without the use of the CSA algorithm with two well known multiple alignment algorithms, the CLUSTALW and the MAVID tools, and also the visualization tool SinicView. Conclusion The results show that a circularization and rotation pre-processing step significantly improves the efficiency of public available multiple sequence alignment

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

Broadband computation of the scattering coefficients of infinite arbitrary cylinders.

Science.gov (United States)

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.

Comparison of Flow Structures in the Downstream Region of a Cylinder with Flexible Strip

Directory of Open Access Journals (Sweden)

Tekşin Süleyman

2015-01-01

Full Text Available The present study investigates the details of flow structure to downstream of a circular cylinder mounted on a flat surface, in successive plan-view plane both in the boundary layer and up level region. The behavior of the flow in the wake of the bare cylinder and attached a flexible strip which has a 1400 N/mm2 modulus of elasticity vinyl PVC transperent film. The length of strip 240 mm (L/D=4 is investigated using Particle Image Velocimetry (PIV technique for Reynolds numbers based on the cylinder diameter of 2500. The flow data downstream of the cylinder are presented using time-averaged velocity vector map, Vavg, streamline patterns, ψavg, vorticity contours, ωavg, and Reynolds stress correlations, u’u’ avg, v’v’ avg, u’v’ avg and rms velocity values. The locations of the peak values of Reynolds stress correlations and other data are also presented in both bare cylinder and attached body in order to determine the regions under high fluctuations. Another L/D ratios will be investigated in other experiments.

A different approach on the onset of separation in the flow around a circular cylinder

Science.gov (United States)

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 separation is computed in all of his six cases for Re = 6 . 14 . Images of this smallest eddy are shown for the first time where all characteristics of eddies are recognisable (vortex centre, separation length etc). The vorticity of the flow is computed along the cylinder surface and it is shown that, at separation, vorticity changes sign. Byproducts of this 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 work done on that subject so far.

Large eddy simulation of turbulent flow for wall mounted cantilever cylinders of aspect ratio 6 and 10

International Nuclear Information System (INIS)

Afgan, Imran; Moulinec, Charles; Prosser, Robert; Laurence, Dominique

2007-01-01

The flow structure around wall mounted circular cylinders of finite heights is numerically investigated via large eddy simulation (LES). The cylinder aspect ratios (AR) are 6 and 10 and the Reynolds number (Re) based on cylinder diameter and free stream velocity is 20,000 for both cases. The cantilever cylinder mounted on a flat plate is chosen since it gives insight into two entirely different flow phenomena; the tip effects of the free end (which show strong three-dimensional wake structures) and the base or junction effects (due to interaction of flow between the cylinder and the flat plate). Regular vortex shedding is found in the wake of the higher aspect ratio case as was anticipated, along with a strong downwash originating from the flow over the free end of the cylinder, whereas irregular and intermittent vortex shedding occurs in the lower aspect ratio case. Pressure distributions are computed along the length of the cylinder and compared to experimental results. Lift and drag values are also computed, along with Strouhal numbers

Circular dichroism in a three-dimensional semiconductor chiral photonic crystal

Energy Technology Data Exchange (ETDEWEB)

Takahashi, S.; Ota, Y.; Tatebayashi, J. [Institute of Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Tajiri, T. [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Iwamoto, S.; Arakawa, Y. [Institute of Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

2014-08-04

Circular dichroism covering the telecommunication band is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC). We design a rotationally stacked woodpile PhC structure where neighboring layers are rotated by 60° and three layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. Due to the large contrast of refractive indices between GaAs and air, the experimentally obtained circular dichroism extends over a wide wavelength range, with the transmittance of right-handed circularly polarized incident light being 85% and that of left-handed light being 15% at a wavelength of 1.3 μm. The obtained results show good agreement with numerical simulations.

HF DBD plasma actuators for reduction of cylinder noise in flow

Science.gov (United States)

Kopiev, V. F.; Kazansky, P. N.; Kopiev, V. A.; Moralev, I. A.; Zaytsev, M. Yu

2017-11-01

Surface high frequency dielectric barrier discharge (HF DBD) was used to reduce flow-induced noise, radiated by circular cylinder in cross flow. Effect of HF DBD actuators is studied for flow velocity up to 80 m s-1 (Reynolds numbers up to 2.18 · 105), corresponding to the typical aircraft landing approach speed. Noise measurements were performed by microphone array in anechoic chamber; averaged flow parameters were studied by particle image velocimetry (PIV). Actuator was powered by high-frequency voltage in hundreds kHz range in steady or modulated mode with the modulation frequency of 0.3-20 kHz (Strouhal number St of 0.4 to 20). It is demonstrated that upstream directed plasma actuators are able to reduce the vortex noise of a cylinder by 10 dB. Noise reduction is accompanied by significant reorganization of the wake behind a cylinder, decreasing both wake width and turbulence level. The physical mechanism related to broadband noise control by HF DBD actuator is also discussed.

Vortex-induced vibrations of a square cylinder under linear shear flow

Energy Technology Data Exchange (ETDEWEB)

Sun, Wenjuan; Zhou, Dai; Han, Zhaolong [School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Tu, Jiahuang, E-mail: tujiahuang1982@163.com, E-mail: han.arkey@gmail.com [College of Civil Engineering and Mechanics, Xiangtan University, Xiangtan, Hunan 411105 (China)

2017-04-15

This paper investigates the numerical vortex-induced vibration (VIV) of a square cylinder which is connected to a 2-DOF mass-spring system and is immersed in the planar shear flow by employing a characteristic-based split (CBS) finite element method (FEM). The reduced mass of the square cylinder is M {sub r} = 2, while the reduced velocity, U {sub r}, is changed from 3 to 12 with an increment of Δ U {sub r} = 1. The effects of some key parameters on the cylinder dynamic responses, vibrating frequencies, the flow patterns as well as the energy transferred between the fluid and cylinder are revealed. In this study, the key parameters are selected as follows: shear ratio ( k  = 0, 0.05 and 0.1) and Reynolds numbers ( Re  = 80 and 160). Numerical results demonstrate that the X – Y trajectories of the cylinder mainly appear as a symmetrical figure ‘8’ in uniform flow ( k  = 0) and an unsymmetrical figure ‘8’ and ‘O’ in shear flows ( k  = 0.05 and 0.1). The maximum oscillation amplitudes of the square cylinder in both the inline and transverse directions have distinct characteristics compared to that of a circular cylinder. Two kinds of flow patterns, ‘2S’ and ‘P + S’, are mainly observed under the shear flow. Also, the mean values of the energy of the cylinder system increase with the reduced velocity, while the root mean square (rms) of the energy reaches its peak value at reduced velocity U {sub r} = 5. (paper)

Flow over a cylinder with a hinged-splitter plate

Science.gov (United States)

Shukla, S.; Govardhan, R. N.; Arakeri, J. H.

2009-05-01

Previous work on rigid splitter plates in the wake of a bluff body has shown that the primary vortex shedding can be suppressed for sufficiently long splitter plates. In the present work, we study the problem of a hinged-splitter plate in the wake of a circular cylinder. The splitter plate can rotate about the hinge at the base of the cylinder due to the unsteady fluid forces acting on it, and hence the communication between the two sides of the wake is not totally disrupted as in the rigid splitter plate case. In our study, we investigate this problem in the limit where the stiffness and internal damping associated with the hinge are negligible, and the mass ratio of the splitter plate is small. The experiments show that the splitter plate oscillations increase with Reynolds numbers at low values of Re, and are found to reach a saturation amplitude level at higher Re, Re>4000. This type of saturation amplitude level that appears to continue indefinitely with Re, appears to be related to the fact that there is no structural restoring force, and has been observed previously for transversely oscillating cylinders with no restoring force. In the present case, the saturation tip amplitude level can be up to 0.45D, where D is the cylinder diameter. For this hinged-rigid splitter plate case, it is found that the splitter plate length to cylinder diameter ratio (L/D) is crucial in determining the character and magnitude of the oscillations. For small splitter plate lengths (L/D⩽3.0), the oscillations appear to be nearly periodic with tip amplitudes of about 0.45D nearly independent of L/D. The nondimensional oscillation frequencies (fD/U) on the other hand are found to continuously vary with L/D from fD/U≈0.2 at L/D=1 to fD/U≈0.1 at L/D=3. As the splitter plate length is further increased beyond L/D⩾4.0, the character of the splitter plate oscillations suddenly changes. The oscillations become aperiodic with much smaller amplitudes. In this long splitter plate

Scattering by an infinite homogenous anisotropic elliptic cylinder in terms of Mathieu functions and Fourier series.

Science.gov (United States)

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.

View factor for radiation heat exchange between the wall and end of a cylinder

International Nuclear Information System (INIS)

Al-Bahadili, H.; Wood, J.

1991-01-01

In a paper by previous authors (Carlson and Garcia (1984) Ann. Nucl. Energy Vol 11, No 4), a numerical integration technique (trapezoidal rule) is developed for the approximate calculation of view factors for radiant heat transfer, for both internal and external radiation, from the curved surface of a right circular cylinder. In that paper the variation of view factor for internal radiation (wall to bottom of cylinder) with height, H, of the cylinder, is shown to reach a maximum value of about 0.36 when H is about 0.3. This behaviour is remarked upon in the text. We wish to make two points: (i) the internal view factors for the cylinder can be determined analytically (ii) the view factor behavior shown is erroneous. In fact, the view factor decreases monatonically as H increases, achieving its greatest value (0.5) as H tends to zero. H is normalised to a radius of unity. (author)

Adaptive panoramic tomography with a circular rotational movement for the formation of multifocal image layers

Energy Technology Data Exchange (ETDEWEB)

Kim, D. S.; Cho, H. S.; Park, Y. O.; Je, U. K.; Hong, D. K.; Choi, S. I.; Koo, Y. S. [Yonsei University, Wonju (Korea, Republic of)

2012-02-15

Panoramic radiography with which only structures within a certain image layer are in focus and others out of focus on the panoramic image has become a popular imaging technique especially in dentistry. However, the major drawback to the technique is a mismatch between the structures to be focused and the predefined image layer mainly due to the various shapes and sizes of dental arches and/or to malpositioning of the patient. These result in image quality typically inferior to that obtained using intraoral radiographic techniques. In this paper, to overcome these difficulties, we suggest a new panoramic reconstruction algorithm, the so-called adaptive panoramic tomography (APT), capable of reconstructing multifocal image layers with no additional exposure. In order to verify the effectiveness of the proposed algorithm, we performed systematic simulation studies with a circular rotational movement and investigated the image performance.

Adaptation of a zero-dimensional cylinder pressure model for diesel engines using the crankshaft rotational speed

Science.gov (United States)

Weißenborn, E.; Bossmeyer, T.; Bertram, T.

2011-08-01

Tighter emission regulations are driving the development of advanced engine control strategies relying on feedback information from the combustion chamber. In this context, it is especially seeked for alternatives to expensive in-cylinder pressure sensors. The present study addresses these issues by pursuing a simulation-based approach. It focuses on the extension of an empirical, zero-dimensional cylinder pressure model using the engine speed signal in order to detect cylinder-wise variations in combustion. As a special feature, only information available from the standard sensor configuration are utilized. Within the study, different methods for the model-based reconstruction of the combustion pressure including nonlinear Kalman filtering are compared. As a result, the accuracy of the cylinder pressure model can be enhanced. At the same time, the inevitable limitations of the proposed methods are outlined.

A comparative analysis on the shed vortices from the wake of finned, foam-wrapped cylinders

Energy Technology Data Exchange (ETDEWEB)

Khashehchi, Morteza [Department of Agro-Technology, College of Aburaihan, University of Tehran, Tehran (Iran, Islamic Republic of); Ashtiani Abdi, Iman; Hooman, Kamel, E-mail: m.khashehchi@ut.ac.ir [School of Mechanical and mining Engineering, University of Queensland, Brisbane (Australia)

2017-08-15

The wake characteristics behind a finned and a foam-wrapped circular cylinder has been compared in a study (Khashehchi et al 2014 Exp. Therm. Fluid Sci. 52 328–38) done by the Authors. In this paper, the shed vortices from the wake of the same cylinders have been studied. Shedding in a bluff body has an important effect on increasing the pressure drop downstream of the object. Here, we have used particle image velocimetry to investigate the detached vortices from the wake behind a foam-wrapped and a finned cylinder. The standard case of cross-flow over a bare cylinder, i.e. no surface extension, has also been tested as a benchmark. The experiments have been performed for Reynolds numbers 2000 based on the mean air velocity and the cylinder’s outer diameter. To identify the features of each aforementioned case, linear stochastic estimation has been applied to the velocity fields. Results show that unlike the fin, adding foam to the cylinder surface increases the size of detached vortices and amplifies the core strength. Moreover, foam-wrapped cylinder in contrast to the finned one produces strong three-dimensionality. Interestingly, finned cylinder’s results show less three-dimensionality compared to the bare cylinder. (paper)

Two cylinder permanent magnet stirrer for liquid metals

Science.gov (United States)

Bojarevičs, A.; Baranovskis, R.; Kaldre, I.; Milgrāvis, M.; Beinerts, T.

2017-07-01

To achieve a uniform liquid metal composition and temperature distribution, stirring is often necessary for industrial processes. Here, a novel permanent magnet system for liquid melt stirring is proposed. It promises very low energy consumption and options for multiple different flow types compared to traditional travelling magnetic field inductors or mechanical stirrers. The proposed system has a simple design: it consists of two rotating permanent magnet cylinders, which are magnetized transversely to the axis of the cylinders. The experimental device was developed and tested under various regimes using GaInSn alloy in a cylindrical crucible. Aluminum stirring by permanent magnets in laboratory scale is tested, and stirring impact on directional solidification of metallic alloys is experimentally investigated.

Analysis of VAWT aerodynamics and design using the Actuator Cylinder flow model

DEFF Research Database (Denmark)

Aagaard Madsen, Helge; Schmidt Paulsen, Uwe; Vita, Luca

2014-01-01

The actuator cylinder (AC) flow model is defined as the ideal VAWT rotor. Radial directed volume forces are applied on the circular path of the VAWT rotor airfoil and constitute an energy conversion in the flow. The power coefficient for the ideal as well as the real energy conversion is defined....... obtainable power coefficient for a fixed pitch VAWT is constrained by the fundamental cyclic variation of inflow angle and relative velocity leading to a loading that deviates considerably from the uniform loading.......The actuator cylinder (AC) flow model is defined as the ideal VAWT rotor. Radial directed volume forces are applied on the circular path of the VAWT rotor airfoil and constitute an energy conversion in the flow. The power coefficient for the ideal as well as the real energy conversion is defined....... The describing equations for the two-dimensional AC model are presented and a solution method splitting the final solution in a linear and non-linear part is briefly described. A family of loadforms approaching the uniform loading is used to study the ideal energy conversion indicating that the maximum power...

Application of the rotating cylinder electrode in molten LiCl-KCl eutectic containing uranium(III)- and magnesium(II)-chloride

Energy Technology Data Exchange (ETDEWEB)

Rappleye, Devin, E-mail: rappleye1@llnl.gov; Simpson, Michael F.

2017-04-15

The application of the rotating cylinder electrode (RCE) to molten LiCl-KCl eutectic mixtures for electroanalytical measurements is presented. This enabled the measurement of the limiting current which was observed to follow a linear trend with the rotational rate raised to 0.64–0.65 power on average, which closely agrees with existing RCE mass-transfer correlations. This is the first publication of electroanalytical RCE measurements in LiCl-KCl eutectic based molten salt mixtures, to our knowledge. These measurements were made in mixtures of molten LiCl-KCl eutectic containing UCl{sub 3} and MgCl{sub 2}. Kinetic parameters were calculated for Mg{sup 2+} in LiCl-KCl eutectic. The exchange current density (i{sub o}) of Mg{sup 2+} deposition varied with mole fraction (x) according to i{sub o}(A cm{sup −2}) = 1.64x{sup 0.689}. The parameters from RCE measurements were also applied in an electrochemical co-deposition model entitled DREP to detect and predict the deposition rate of U and Mg. DREP succeeded in detecting the co-deposition of U and Mg, even when Mg constituted less than 0.5 wt% of the deposit.

New type of centrifugal extractor

International Nuclear Information System (INIS)

Miyauchi, T.; Tolich, A.

1975-01-01

The main principles of a centrifugal extractor design which can be used in the reprocessing of spent fuel with high degree of burning out are given. The extractor consists of two rotating coaxial cylinders. The contact of liquid phases is done in the circular space between the cylinders. By the cylinder rotating the phases are dispersed and the interface, as well as the extraction rate is increased. The given principles of the extractor design are realized in two simplified laboratory installations. The preliminary data obtained point out that much greater rates of the phases contact are achieved in centrifugal extractors than in extraction columns

Rotationally invariant correlation filtering

International Nuclear Information System (INIS)

Schils, G.F.; Sweeney, D.W.

1985-01-01

A method is presented for analyzing and designing optical correlation filters that have tailored rotational invariance properties. The concept of a correlation of an image with a rotation of itself is introduced. A unified theory of rotation-invariant filtering is then formulated. The unified approach describes matched filters (with no rotation invariance) and circular-harmonic filters (with full rotation invariance) as special cases. The continuum of intermediate cases is described in terms of a cyclic convolution operation over angle. The angular filtering approach allows an exact choice for the continuous trade-off between loss of the correlation energy (or specificity regarding the image) and the amount of rotational invariance desired

Analytic solutions of Oldroyd-B fluid with fractional derivatives in a circular duct that applies a constant couple

Directory of Open Access Journals (Sweden)

M.B. Riaz

2016-12-01

Full Text Available The aim of this article was to analyze the rotational flow of an Oldroyd-B fluid with fractional derivatives, induced by an infinite circular cylinder that applies a constant couple to the fluid. Such kind of problem in the settings of fractional derivatives has not been found in the literature. The solutions are based on an important remark regarding the governing equation for the non-trivial shear stress. The solutions that have been obtained satisfy all imposed initial and boundary conditions and can easily be reduced to the similar solutions corresponding to ordinary Oldroyd-B, fractional/ordinary Maxwell, fractional/ordinary second-grade, and Newtonian fluids performing the same motion. The obtained results are expressed in terms of Newtonian and non-Newtonian contributions. Finally, the influence of fractional parameters on the velocity, shear stress and a comparison between generalized and ordinary fluids is graphically underlined.

Performance of a Horizontal Double Cylinder Type of Fresh Coffee Cherries Pulping Machine

Directory of Open Access Journals (Sweden)

Sukrisno Widyotomo

2009-05-01

Full Text Available Pulping is one important step in wet coffee processing method. Usually, pulping process uses a machine which constructed using wood or metal materials. A horizontal single cylinder type coffee pulping machine is the most popular machine in coffee processor and market. One of the weakness of a horizontal single cylinder type coffee pulping machine is high of broken beans. Broken beans is one of major aspect in defect system that result in low quality. Indonesian Coffee and Cocoa Research Institute has designed and tested a horizontal double cylinder type coffee pulping machine. Material tested is Robusta cherry, mature, 60—65% (wet basis moisture content, which size compostition of coffee cherries was 50.8% more than 15 mm diameter, 32% more than 10 mm diameter, and 16.6% to get through 10 mm hole diameter; 690—695 kg/m3 bulk density, and clean from methal and foreign materials. The result showed that this machine has 420 kg/h optimal capacity in operational conditions, 1400 rpm rotor rotation speed for unsorted coffee cherries with composition 53.08% whole parchment coffee, 16.92% broken beans, and 30% beans in the wet skin. For small size coffee cherries, 603 kg/h optimal capacity in operational conditions, 1600 rpm rotor rotation speed with composition 51.30% whole parchment coffee, 12.59% broken beans, and 36.1% beans in the wet skin. Finally, for medium size coffee cherries, 564 kg/h optimal capacity in operational conditions, 1800 rpm rotor rotation speed with composition 48.64% whole parchment coffee, 18.5% broken beans, and 32.86% beans in the wet skin.Key words : coffee, pulp, pulper, cylinder, quality.

Refueling system with small diameter rotatable plugs

International Nuclear Information System (INIS)

Ritz, W.C.

1987-01-01

This patent describes a liquid-metal fastbreeder nuclear reactor comprising a reactor pressure vessel and closure head therefor, a reactor core barrel disposed within the reactor vessel and enclosing a reactor core having therein a large number of closely spaced fuel assemblies, and the reactor core barrel and the reactor core having an approximately concentric circular cross-sectional configuration with a geometric center in predetermined location within the reactor vessel. The improved refueling system described here comprises: a large controllably rotatable plug means comprising the substantial portion of the closure head, a reactor upper internals structure mounted from the large rotatable plug means. The large rotatable plug means has an approximately circular configuration which approximates the cross-sectional configuration of the reactor core barrel with a center of rotation positioned a first predetermined distance from the geometric center of the reactor core barrel so that the large rotatable plug means rotates eccentrically with respect to the reactor core barrel; a small controllably rotatable plug means affixed to the large rotatable plug means and rotatable with respect thereto. The small rotatable plug means has a center of rotation which is offset a second predetermined distance from the rotational center of the large rotatable plug means so that the small rotatable plug means rotates eccentrically with respect to the large rotatable plug means

HF DBD plasma actuators for reduction of cylinder noise in flow

International Nuclear Information System (INIS)

Kopiev, V F; Kopiev, V A; Zaytsev, M Yu; Kazansky, P N; Moralev, I A

2017-01-01

Surface high frequency dielectric barrier discharge (HF DBD) was used to reduce flow-induced noise, radiated by circular cylinder in cross flow. Effect of HF DBD actuators is studied for flow velocity up to 80 m s −1 (Reynolds numbers up to 2.18 · 10 5 ), corresponding to the typical aircraft landing approach speed. Noise measurements were performed by microphone array in anechoic chamber; averaged flow parameters were studied by particle image velocimetry (PIV). Actuator was powered by high-frequency voltage in hundreds kHz range in steady or modulated mode with the modulation frequency of 0.3–20 kHz (Strouhal number St of 0.4 to 20). It is demonstrated that upstream directed plasma actuators are able to reduce the vortex noise of a cylinder by 10 dB. Noise reduction is accompanied by significant reorganization of the wake behind a cylinder, decreasing both wake width and turbulence level. The physical mechanism related to broadband noise control by HF DBD actuator is also discussed. (paper)

Determination of the absolute configurations of natural products via density functional theory calculations of optical rotation, electronic circular dichroism, and vibrational circular dichroism: the cytotoxic sesquiterpene natural products quadrone, suberosenone, suberosanone, and suberosenol A acetate.

Science.gov (United States)

Stephens, P J; McCann, D M; Devlin, F J; Smith, A B

2006-07-01

The determination of the absolute configurations (ACs) of chiral molecules using the chiroptical techniques of optical rotation (OR), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) has been revolutionized by the development of density functional theory (DFT) methods for the prediction of these properties. Here, we demonstrate the significance of these advances for the stereochemical characterization of natural products. Time-dependent DFT (TDDFT) calculations of the specific rotations, [alpha](D), of four cytotoxic natural products, quadrone (1), suberosenone (2), suberosanone (3), and suberosenol A acetate (4), are used to assign their ACs. TDDFT calculations of the ECD of 1 are used to assign its AC. The VCD spectrum of 1 is reported and also used, together with DFT calculations, to assign its AC. The ACs of 1 derived from its [alpha](D), ECD, and VCD are identical and in agreement with the AC previously determined via total synthesis. The previously undetermined ACs of 2-4, derived from their [alpha](D) values, have absolute configurations of their tricyclic cores identical to that of 1. Further studies of the ACs of these molecules using ECD and, especially, VCD are recommended to establish more definitively this finding. Our studies of the OR, ECD, and VCD of quadrone are the first to utilize DFT calculations of all three properties for the determination of the AC of a chiral natural product molecule.

Dissipative particle dynamics simulation of flow generated by two rotating concentric cylinders: II. Lateral dissipative and random forces

International Nuclear Information System (INIS)

Filipovic, N; Haber, S; Kojic, M; Tsuda, A

2008-01-01

Traditional DPD methods address dissipative and random forces exerted along the line connecting neighbouring particles. Espanol (1998 Phys. Rev. E 57 2930-48) suggested adding dissipative and random force components in a direction perpendicular to this line. This paper focuses on the advantages and disadvantages of such an addition as compared with the traditional DPD method. Our benchmark system comprises fluid initially at rest occupying the space between two concentric cylinders rotating with various angular velocities. The effect of the lateral force components on the time evolution of the simulated velocity profile was also compared with that of the known analytical solution. The results show that (i) the solution accuracy at steady state has improved and the error has been reduced by at least 30% (in one case by 75%), (ii) the DPD time to reach steady state has been halved, (iii) the CPU time has increased by only 30%, and (iv) no significant differences exist in density and temperature distributions

Breakdown of large-scale circulation in turbulent rotating convection

NARCIS (Netherlands)

Kunnen, R.P.J.; Clercx, H.J.H.; Geurts, Bernardus J.

2008-01-01

Turbulent rotating convection in a cylinder is investigated both numerically and experimentally at Rayleigh number Ra = $10^9$ and Prandtl number $\\sigma$ = 6.4. In this Letter we discuss two topics: the breakdown under rotation of the domain-filling large-scale circulation (LSC) typical for

Light-induced circular birefringence in cyanoazobenzene side-chain liquid-crystalline polyester films

DEFF Research Database (Denmark)

Naydenova, I; Nikolova, L; Ramanujam, P.S.

1999-01-01

We report the inducement of large circular birefringence (optical activity) in films of a cyanoazobenzene side-chain liquid-crystalline polyester on illumination with circularly polarized light. The polyester has no chiral groups and is initially isotropic. The induced optical rotation is up to 5...

Performance of a Horizontal Triple Cylinder Type Pulping Machine

Directory of Open Access Journals (Sweden)

Sukrisno Widyotomo

2011-05-01

Full Text Available Pulping is one important step in wet coffee processing method. Pulping process usually uses a machine which constructed by wood or metal materials. A horizontal single cylinder type of fresh coffee cherries pulping machine is the most popular machine in coffee processing. One of the weaknesses of a horizontal single cylinder type of fresh coffee cherries pulping machine is higher in broken beans. Broken bean is one of mayor aspects in defect system that contribute to low quality. Indonesian Coffee and Cocoa Research Institute has designed and tested a horizontal double cylinder type of fresh coffee cherries pulping machine which resulted in 12.6—21.4% of broken beans. To reduce percentage of broken beans, Indonesian Coffee and Cocoa Research Institute has developed and tested a horizontal triple cylinder type of fresh coffee cherries pulping machine. Material tested was fresh mature Robusta coffee cherries, 60—65% (wet basis moisture content; has classified on 3 levels i.e. unsorted, small and medium, and clean from metal and foreign materials. The result showed that the machine produced 6,340 kg/h in optimal capacity for operational conditions, 1400 rpm rotor rotation speed for unsorted coffee cherries with composition 55.5% whole parchment coffee, 3.66% broken beans, and 1% beans in wet skin.Key words : coffee, pulp, pulper, cylinder, quality.

Inertial rise of a meniscus on a vertical cylinder

KAUST Repository

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.

Computational analysis of water entry of a circular section at constant velocity based on Reynold's averaged Navier-Stokes method

Science.gov (United States)

Uddin, M. Maruf; Fuad, Muzaddid-E.-Zaman; Rahaman, Md. Mashiur; Islam, M. Rabiul

2017-12-01

With the rapid decrease in the cost of computational infrastructure with more efficient algorithm for solving non-linear problems, Reynold's averaged Navier-Stokes (RaNS) based Computational Fluid Dynamics (CFD) has been used widely now-a-days. As a preliminary evaluation tool, CFD is used to calculate the hydrodynamic loads on offshore installations, ships, and other structures in the ocean at initial design stages. Traditionally, wedges have been studied more than circular cylinders because cylinder section has zero deadrise angle at the instant of water impact, which increases with increase of submergence. In Present study, RaNS based commercial code ANSYS Fluent is used to simulate the water entry of a circular section at constant velocity. It is seen that present computational results were compared with experiment and other numerical method.

Rotational Diffusion of Macromolecules and Nanoparticles Modeled as Non-Overlapping Bead Arrays in an Effective Medium

Directory of Open Access Journals (Sweden)

Umar Twahir

2011-05-01

Full Text Available In this work, the retarding influence of a gel on the rotational motion of a macromolecule is investigated within the framework of the Effective Medium (EM model. This is an extension of an earlier study that considered the effect of a gel on the translational motion of a macromolecule [Allison, S. et al. J. Phys. Chem. B 2008, 112, 5858-5866]. The macromolecule is modeled as an array of non-overlapping spherical beads with no restriction placed on their size or configuration. Specific applications include the rotational motion of right circular cylinders and wormlike chains modeled as strings of identical touching beads. The procedure is then used to examine the electric birefringence decay of a 622 base pair DNA fragment in an agarose gel. At low gel concentration (M £ 0.010 gm/mL, good agreement between theory and experiment is achieved if the persistence length of DNA is taken to be 65 nm and the gel fiber radius of agarose is taken to be 2.5 nm. At higher gel concentrations, the EM model substantially underestimates the rotational relaxation time of DNA and this can be attributed to the onset of direct interactions that become significant when the effective particle size becomes comparable to the mean gel fiber spacing.

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...

Unsteady mixed convection of a micropolar fluid past a circular cylinder due to time-dependent free stream velocity and temperature

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 $S$.

Radiation and scattering by cavity-backed antennas on a circular cylinder

Science.gov (United States)

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.

Rotating Polygons on a Fluid Surface

DEFF Research Database (Denmark)

Bohr, Tomas; Jansson, Thomas; Haspang, Martin

spontaneously and the surface can take the shape of a rigidly rotating polygon. With water we have observed polygons with up to 6 corners. The rotation speed of the polygons does not coincide with that of the plate, but it is often mode-locked, such that the polygon rotates by one corner for each complete...... and R. Miraghaie, ”Symmetry breaking in free-surface cylinder flows”, J. Fluid Mech., 502, 99 (2004)). The polygons occur at much larger Reynolds numbers, for water around 500.000. Correspondingly, the dependence on viscosity is rather small....

Piezoelectric shunt damping of a circular saw blade with autonomous power supply for noise and vibration reduction

Science.gov (United States)

Pohl, Martin; Rose, Michael

2016-01-01

Circular saws are widespread tools for machining metal, wood or even ceramics. Due to the thin blade and excitation by the workpiece contact of the cutting edges, circular saws are prone to vibration and intense noise emission. Damping the blade will lower the hearing protection requirements of the users and possibly increase precision. Therefore a new damping concept for circular saw blades is presented in this paper. It is based on negative capacitance shunted piezoelectric transducers which are applied to the saw blade core. The required energy for the electronics is harvested from the rotation by a generator, so that no change of the machine tool is required. All components are integrated into an autonomous saw tool. Finally, the system is experimentally investigated without rotation, in idling and in cutting condition in a circular saw test stand in the Institute for Machine Tools and Production Engineering (IWF) at TU Braunschweig. The experimental investigation shows a good reduction of the vibration amplitude over a wide frequency range in the non-rotating condition. When rotating, the damping effect is lower and limited to some narrow frequency bands. The proposed reason for the reduced damping effect in rotating condition consists in the saturation of the electronic circuits due to the limited supply voltage capabilities.

Influence of non-integer-order derivatives on unsteady unidirectional motions of an Oldroyd-B fluid with generalized boundary conditions

Science.gov (United States)

Zafar, A. A.; Riaz, M. B.; Shah, N. A.; Imran, M. A.

2018-03-01

The objective of this article is to study some unsteady Couette flows of an Oldroyd-B fluid with non-integer derivatives. The fluid fills an annular region of two infinite co-axial circular cylinders. Flows are due to the motion of the outer cylinder, that rotates about its axis with an arbitrary time-dependent velocity while the inner cylinder is held fixed. Closed form solutions of dimensionless velocity field and tangential tension are obtained by means of the finite Hankel transform and the theory of Laplace transform for fractional calculus. Several results in the literature including the rotational flows through an infinite cylinder can be obtained as limiting cases of our general solutions. Finally, the control of the fractional framework on the dynamics of fluid is analyzed by numerical simulations and graphical illustrations.

Particle transport across a circular shear layer with coherent structures

International Nuclear Information System (INIS)

Nielsen, A.H.; Lynov, J.P.; Juul Rasmussen, J.

1998-01-01

In the study of the dynamics of coherent structures, forced circular shear flows offer many desirable features. The inherent quantisation of circular geometries due to the periodic boundary conditions makes it possible to design experiments in which the spatial and temporal complexity of the coherent structures can be accurately controlled. Experiments on circular shear flows demonstrating the formation of coherent structures have been performed in different physical systems, including quasi-neutral plasmas, non-neutral plasmas and rotating fluids. In this paper we investigate the evolution of such coherent structures by solving the forced incompressible Navier-Stokes equations numerically using a spectral code. The model is formulated in the context of a rotating fluid but apply equally well to low frequency electrostatic oscillations in a homogeneous magnetized plasma. In order to reveal the Lagrangian properties of the flow and in particular to investigate the transport capacity in the shear layer, passive particles are traced by the velocity field. (orig.)

The capillary interaction between two vertical cylinders

KAUST Repository

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.

Vibration due to non-circularity of a rotating ring having discrete radial supports - With application to thin-walled rotor/magnetic bearing systems

Science.gov (United States)

Fakkaew, Wichaphon; Cole, Matthew O. T.

2018-06-01

This paper investigates the vibration arising in a thin-walled cylindrical rotor subject to small non-circularity and coupled to discrete space-fixed radial bearing supports. A Fourier series description of rotor non-circularity is incorporated within a mathematical model for vibration of a rotating annulus. This model predicts the multi-harmonic excitation of the rotor wall due to bearing interactions. For each non-circularity harmonic there is a set of distinct critical speeds at which resonance can potentially arise due to flexural mode excitation within the rotor wall. It is shown that whether each potential resonance occurs depends on the multiplicity and symmetry of the bearing supports. Also, a sufficient number of evenly spaced identical supports will eliminate low order resonances. The considered problem is pertinent to the design and operation of thin-walled rotors with active magnetic bearing (AMB) supports, for which small clearances exist between the rotor and bearing and so vibration excitation must be limited to avoid contacts. With this motivation, the mathematical model is further developed for the case of a distributed array of electromagnetic actuators controlled by feedback of measured rotor wall displacements. A case study involving an experimental system with short cylindrical rotor and a single radial AMB support is presented. The results show that flexural mode resonance is largely avoided for the considered design topology. Moreover, numerical predictions based on measured non-circularity show good agreement with measurements of rotor wall vibration, thereby confirming the validity and utility of the theoretical model.

Comparison of two superconducting elliptical undulators for generating circularly polarized light

Directory of Open Access Journals (Sweden)

C. S. Hwang

2004-09-01

Full Text Available The potential use of two planar superconducting elliptical undulators—a vertically wound racetrack coil structure and a staggered array structure—to generate a circularly polarized hard x-ray source was investigated. The magnetic poles and wires of the up and down magnet arrays were rotated in alternating directions on the horizontal plane, an elliptical field is generated to provide circularly polarized light in the electron-storage ring and the energy-recovery linac accelerator. Rapid switching between right- and left-circularly polarized radiations is performed using two undulators with oppositely rotated wires and poles. Given a periodic length of 15 mm and a gap of 5 mm, the magnetic-flux densities in the elliptical undulator are B_{z}=1.2   T (B_{x}=0.6   T and B_{z}=0.35   T (B_{x}=0.15   T in the planar vertically wound racetrack coil and the staggered structure with poles rotated by 35° and 25°, respectively. In maximizing the merit of the flux and the width of the effective field region in the two superconducting elliptical undulators, the trade-off rotation angles of the coils and poles are 20° and 5°, for vertically wound racetrack coil and staggered undulators, respectively.

Buoyancy-driven instability in a vertical cylinder: Binary fluids with Soret effect. I - General theory and stationary stability results

Science.gov (United States)

Hardin, G. R.; Sani, R. L.; Henry, D.; Roux, B.

1990-01-01

The buoyancy-driven instability of a monocomponent or binary fluid completely contained in a vertical circular cylinder is investigated, including the influence of the Soret effect for the binary mixture. The Boussinesq approximation is used, and the resulting linear stability problem is solved using a Galerkin technique. The analysis considers fluid mixtures ranging from gases to liquid metals. The flow structure is found to depend strongly on both the cylinder aspect ratio and the magnitude of the Soret effect. The predicted stability limits are shown to agree closely with experimental observations.

Spinning cylinder experiments SC-I and SC-II: A review of results and analyses provided to the FALSIRE project

International Nuclear Information System (INIS)

Morland, E.; Sherry, A.H.

1993-01-01

A series of six large-scale experiments have been carried out at AEA Technology using the Spinning Cylinder test facility. Results from two of those experiments (SC-I and SC-II) have been provided to Project FALSIRE and are reviewed in this paper. The Spinning Cylinder tests were carried out using hollow cylinders of 1.4m outer diameter, 0.2m wall thickness and 1.3m length, containing full-length axial defects and fabricated from a modified A508 Class 3 steel. The first Spinning Cylinder test (SC-I) was an investigation of stable ductile growth induced via mechanical (primary) loading and under conditions of contained yielding. Mechanical loading was provided in the hoop direction by rotating the cylinder about its major axis within an enclosed oven. The second test (SC-II) investigated stable ductile growth under severe thermal shock (secondary) loading again under conditions of contained yielding. In this case thermal shock was produced by spraying cold water on the inside surface of the heated cylinder whilst it was rotating. For each experiment, results are presented in terms of a number of variables, eg. crack growth, temperature, stress, strain and applied K and J. In addition, an overview of the analyses of the FALSIRE Phase-1 report is also presented with respect to test SC-I and SC-II. 4 refs., 14 figs., 13 tabs

Rotation influence on the plasma helical instability

International Nuclear Information System (INIS)

Gutkin, T.I.; Tsypin, V.S.; Boleslavskaya, G.I.

1980-01-01

The influence of the rotation on helical instability of a plasma with the fixed boundaries (HIFB) is investigated taking into account the compressibility. A case of infinitely long cylinder with distributed current is considered. Cases when a rotating plasma is confined by current magnetic field are analytically considered. It is shown that in the case of the fixed boundary taking into account the compressibility in the HIFB increment increases and the picture of the rotation influence on HIFB considerably changes. Besides, it is shown that in the case of high plasma pressures HIFB can stabilize as a result of the rotation

Experimental determination of probe-length requirements for studies of the turbulent wake behind a cylinder

International Nuclear Information System (INIS)

Sheih, C.M.; Finnigan, J.J.; Bradley, E.F.; Mulhearn, P.J.

1979-01-01

The attenuation of turbulence and mean velocity signals due to the line averaging imposed by hot wires when used in the wake of an isolated circular cylinder has been investigated in a wind tunnel by measurements using several choices of hot-wire length, cylinder diameter, and freestream mean velocity. The results are presented graphically in order to provide a practical method for determining attenuation of the turbulence and mean velocity signals obtained in a wake. The length scale of the wake can be defined as L=0.6[(x-x/sub o/) d]/sup 1/2/, where x is the downstream distance from the cylinder, d is the cylinder diameter, and x/sub o/=25d. For all the wires tested, the attenuation of the measured turbulence signal is limited to within 5% only if the wire length is smaller than 0.1 L. For a wire normal to the cylinder and cross wind, the attenuation of the signal of the mean velocity-defect factor, expressed as (1-u/u/sub infinity/), where u and u/sub infinity/ are local and free-stream velocities, respectively, is less than 5% only if the wire is less than 0.5 L in length

Reynolds-Stress and Triple-Product Models Applied to Flows with Rotation and Curvature

Science.gov (United States)

Olsen, Michael E.

2016-01-01

Predictions for Reynolds-stress and triple product turbulence models are compared for flows with significant rotational effects. Driver spinning cylinder flowfield and Zaets rotating pipe case are to be investigated at a minimum.

The use of a rotating cylinder electrode to recover zinc from rinse water generated by the electroplating industry.

Science.gov (United States)

Matlalcuatzi, Sairi; Nava, José L

2012-01-01

This work concerns the application of a laboratory scale rotating cylinder electrode (RCE) to recover zinc from rinse water generated by the electrolytic zinc process (initially 1,300, 4,400, 50, 20 mg L(-1) of Zn(II), Fe(III), Ag(I) and Cr(VI), respectively, at pH 2), although it is also applicable to other electroplating industries. Experimental results demonstrated the convenience of the removal of ferric ions, as (Fe(OH)(3(s))) by a pH adjustment to 4, before zinc electro recovery on the RCE. The generation of smooth zinc deposits on the RCE was obtained at Reynolds numbers within the range of 15,000 ≤ Re ≤ 124,000 and limiting current densities (J(L)) in the interval of -4.8 to -13 mA cm(-2). The zinc recovery reached a conversion of 67% in 90 min of electrolysis for Re = 124,000 and J = -13 mA cm(-2), 21% current efficiency, and energy consumption of 9.5 kWh m(-3). The treated solution can be recycled back through the same rinsing process.

An analytical study of the effects of transverse shear deformation and anisotropy on natural vibration frequencies of laminated cylinders

Science.gov (United States)

Jegley, Dawn C.

1988-01-01

Natural vibration frequencies of orthotropic and anisotropic simply supported right circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of natural vibration frequencies predicted by first-order transverse-shear deformation theory and the higher-order theory shows that an additional allowance for transverse shear deformation has a negligible effect on the lowest predicted natural vibration frequencies of laminated cylinders but significantly reduces the higher natural vibration frequencies. A parametric study of the effects of ply orientation on the natural vibration frequencies of laminated cylinders indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry is more important in predicting transverse-shear deformation effects. Interaction curves for cylinders subjected to axial compressive loadings and low natural vibration frequencies indicate that transverse shearing effects are less important in predicting low natural vibration frequencies than in predicting axial compressive buckling loads. The effects of anisotropy are more important than the effects of transverse shear deformation for most strongly anisotropic laminated cylinders in predicting natural vibration frequencies. However, transverse-shear deformation effects are important in predicting high natural vibration frequencies of thick-walled laminated cylinders. Neglecting either anisotropic effects or transverse-shear deformation effects leads to non-conservative errors in predicted natural vibration frequencies.

An analytical study of the effects of transverse shear deformation and anisotropy on natural vibation frequencies of laminated cylinders

Science.gov (United States)

Jegley, Dawn C.

1989-01-01

Natural vibration frequencies of orthotropic and anisotropic simply supported right circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of natural vibration frequencies predicted by first-order transverse-shear deformation theory and the higher-order theory shows that an additional allowance for transverse shear deformation has a negligible effect on the lowest predicted natural vibration frequencies of laminated cylinders but significantly reduces the higher natural vibration frequencies. A parametric study of the effects of ply orientation on the natural vibration frequencies of laminated cylinders indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry is more important in predicting transverse-shear deformation effects. Interaction curves for cylinders subjected to axial compressive loadings and low natural vibration frequencies indicate that transverse shearing effects are less important in predicting low natural vibration frequencies than in predicting axial compressive buckling loads. The effects of anisotropy are more important than the effects of transverse shear deformation for most strongly anisotropic laminated cylinders in predicting natural vibration frequencies. However, transverse-shear deformation effects are important in predicting high natural vibration frequencies of thick-walled laminated cylinders. Neglecting either anisotropic effects or transverse-shear deformation effects leads to non-conservative errors in predicted natural vibration frequencies.

Faraday rotation measurement method and apparatus

Science.gov (United States)

Brockman, M. H. (Inventor)

1981-01-01

A method and device for measuring Faraday rotation of a received RF signal is described. A simultaneous orthogonal polarization receiver compensates for a 3 db loss due to splitting of a received signal into left circular and right circular polarization channels. The compensation is achieved by RF and modulation arraying utilizing a specific receiver array which also detects and measures Faraday rotation in the presence or absence of spin stabilization effects on a linear polarization vector. Either up-link or down-link measurement of Faraday rotation is possible. Specifically, the Faraday measurement apparatus utilized in conjunction with the specific receiver array provides a means for comparing the phase of a reference signal in the receiver array to the phase of a tracking loop signal related to the incoming signal, and comparing the phase of the reference signal to the phase of the tracking signal shifted in phase by 90 degrees. The averaged and unaveraged signals, are compared, the phase changes between the two signals being related to Faraday rotation.

Numerical investigation on flow-induced vibration of a triangular cylinder at a low Reynolds number

Energy Technology Data Exchange (ETDEWEB)

Wang, Huakun; Zhao, Dongliang; Yang, Wenyu; Yu, Guoliang, E-mail: yugl@sjtu.edu.cn [State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, People’s Republic of China (China)

2015-02-01

Flow-induced vibration (FIV) of a triangular cylinder is numerically investigated at a Reynolds number of Re = 100. The four-step fractional finite element method is employed to solve the two-dimensional (2D) incompressible Navier–Stokes equations. The cylinder is endowed with a two-degree-of-freedom motion with the reduced mass ratio of M{sub r} = 2. Three typical flow incidence angles, α = 0°, 30° and 60°, are examined to identify the effect of incidence angle on the vibration characteristics of the cylinder. For each α, computations are conducted in a wide range of reduced velocities 2 U{sub r} ≤ 18. The numerical results show that at α = 0° and 30°, the responses of the cylinder are dominated by vortex-induced vibration which resembles that of a circular cylinder. At α = 0°, the peak amplitude of transverse vibration is the smallest among the three investigated α, and most of the cylinder motions exhibit a regular figure-eight trajectory. Some single-loop trajectories are observed at α = 30°, where the vibration frequency in the in-line direction is always identical to that in the transverse direction. At α = 60°, the triangular cylinder undergoes a typical transverse galloping with large amplitude and low frequency, and the vibration trajectories appear to be regular or irregular figure-eight patterns, which are strongly affected by the reduced velocity. (paper)

Computational simulations of hydrogen circular migration in protonated acetylene induced by circularly polarized light

Energy Technology Data Exchange (ETDEWEB)

Shi, Xuetao; Li, Wen; Schlegel, H. Bernhard, E-mail: hbs@chem.wayne.edu [Department of Chemistry, Wayne State University, Detroit, Michigan 48202 (United States)

2016-08-28

The hydrogens in protonated acetylene are very mobile and can easily migrate around the C{sub 2} core by moving between classical and non-classical structures of the cation. The lowest energy structure is the T-shaped, non-classical cation with a hydrogen bridging the two carbons. Conversion to the classical H{sub 2}CCH{sup +} ion requires only 4 kcal/mol. The effect of circularly polarized light on the migration of hydrogens in oriented C{sub 2}H{sub 3}{sup +} has been simulated by Born-Oppenheimer molecular dynamics. Classical trajectory calculations were carried out with the M062X/6-311+G(3df,2pd) level of theory using linearly and circularly polarized 32 cycle 7 μm cosine squared pulses with peak intensity of 5.6 × 10{sup 13} W/cm{sup 2} and 3.15 × 10{sup 13} W/cm{sup 2}, respectively. These linearly and circularly polarized pulses transfer similar amounts of energy and total angular momentum to C{sub 2}H{sub 3}{sup +}. The average angular momentum vectors of the three hydrogens show opposite directions of rotation for right and left circularly polarized light, but no directional preference for linearly polarized light. This difference results in an appreciable amount of angular displacement of the three hydrogens relative to the C{sub 2} core for circularly polarized light, but only an insignificant amount for linearly polarized light. Over the course of the simulation with circularly polarized light, this corresponds to a propeller-like motion of the three hydrogens around the C{sub 2} core of protonated acetylene.

Nearest Neighbor Estimates of Entropy for Multivariate Circular Distributions

Directory of Open Access Journals (Sweden)

Neeraj Misra

2010-05-01

Full Text Available In molecular sciences, the estimation of entropies of molecules is important for the understanding of many chemical and biological processes. Motivated by these applications, we consider the problem of estimating the entropies of circular random vectors and introduce non-parametric estimators based on circular distances between n sample points and their k th nearest neighbors (NN, where k (≤ n – 1 is a fixed positive integer. The proposed NN estimators are based on two different circular distances, and are proven to be asymptotically unbiased and consistent. The performance of one of the circular-distance estimators is investigated and compared with that of the already established Euclidean-distance NN estimator using Monte Carlo samples from an analytic distribution of six circular variables of an exactly known entropy and a large sample of seven internal-rotation angles in the molecule of tartaric acid, obtained by a realistic molecular-dynamics simulation.

Cylinder monitoring program

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.

EFFECT OF VARIOUS POROUS STRUCTURES ON THE SHLIOMIS MODEL BASED FERROFLUID LUBRICATION OF THE FILM SQUEEZED BETWEEN ROTATING ROUGH CURVED CIRCULAR PLATES

Directory of Open Access Journals (Sweden)

Jimit R Patel

2014-12-01

Full Text Available Efforts have been made to analyze the Shliomis model based ferrofluid lubrication of a squeeze film between rotating rough curved circular plates where the upper plate has a porous facing. Different models of porosity are treated. The stochastic modeling of Christensen and Tonder has been employed to evaluate the effect of surface roughness. The related stochastically averaged Reynolds type equation is numerically solved to obtain the pressure distribution, leading to the calculation of load carrying capacity. The results presented in graphical form establish that the Kozeny-Carman model is more favorable as compared to the Irmay one from the design point of view. It is observed that the Shliomis model based ferrofluid lubrication performs relatively better than the Neuringer-Rosensweig one. Although the bearing suffers due to transverse surface roughness, with a suitable choice of curvature parameters and rotational ratio, the negative effect of porosity and standard deviation can be minimized by the ferrofluid lubrication at least in the case of negatively skewed roughness.

System for circular and complex tomography

International Nuclear Information System (INIS)

Hellstrom, M.J.

1979-01-01

This invention discloses a system for conducting circular as well as complex tomographic procedures utilizing apparatus which has no mechanical linkage between the X-ray source and the X-ray receptor. The path of travel of the X-ray source both circularly and linearly is sensed by electromagnetic radiation and more particularly by light radiation which is generated by a laser. The linear travel is sensed by means of reflected laser radiation directed to the X-ray source and fed to an interferometer. The circular travel, on the other hand, is sensed by means of a laser gyroscope also receiving light radiation from a laser. Optical energy sensing means is thus used to generate command signals which are coupled to respective drive motors which act to rotate and when desirable, translate the X-ray receptor so that its motion follows the motion, both orbital and linear, of the X-ray source for performing any desired type of tomographic procedure

Dynamic modelling of the expansion cylinder of an open Joule cycle Ericsson engine: A bond graph approach

International Nuclear Information System (INIS)

Creyx, M.; Delacourt, E.; Morin, C.; Desmet, B.

2016-01-01

A dynamic model using the bond graph formalism of the expansion cylinder of an open Joule cycle Ericsson engine intended for a biomass-fuelled micro-CHP system is presented. Dynamic phenomena, such as the thermodynamic evolution of air, the instantaneous air mass flow rates linked to pressure drops crossing the valves, the heat transferred through the expansion cylinder wall and the mechanical friction losses, are included in the model. The influence on the Ericsson engine performances of the main operating conditions (intake air pressure and temperature, timing of intake and exhaust valve closing, rotational speed, mechanical friction losses and heat transfer at expansion cylinder wall) is studied. The operating conditions maximizing the performances of the Ericsson engine used in the a biomass-fuelled micro-CHP unit are an intake air pressure between 6 and 8 bar, a maximized intake air temperature, an adjustment of the intake and exhaust valve closing corresponding to an expansion cycle close to the theoretical Joule cycle, a rotational speed close to 800 rpm. The heat transfer at the expansion cylinder wall reduces the engine performances. - Highlights: • A bond graph dynamic model of the Ericsson engine expansion cylinder is presented. • Dynamic aspects are modelled: pressure drops, friction losses, wall heat transfer. • Influent factors and phenomena on the engine performances are investigated. • Expansion cycles close to the theoretical Joule cycle maximize the performances. • The heat transfer at the expansion chamber wall reduces the performances.

Circular polarimetry of the magnetic compact binary AM Herculis

Energy Technology Data Exchange (ETDEWEB)

Piirola, V; Vilhu, O; Tuominen, I

1982-01-01

Circular polarimetry in the red and simultaneous photometric observations in the UBVRI bands during the period June 1 to 3, 1981, of AM Herculis are discussed. Peak value of negative circular polarization (- 15 %) is stronger than observed in 1976 to 1979. Variations in the shape of the polarization and light curves occur from night to night. Positive crossover and reversal of the sign of the circular polarization are only marginal. Long term changes in polarization may be partly due to precession of the axis of rotation of the white dwarf about the binary axis. However, the duration of the phase interval where circular polarization remains close to zero changes on a time scale of days, casting doubt on precession models. The changing shape and position of the accretion columns with respect to the magnetic axis could explain short term variations. (ESA)

Inertial Waves and Steady Flows in a Liquid Filled Librating Cylinder

Science.gov (United States)

Subbotin, Stanislav; Dyakova, Veronika

2018-05-01

The fluid flow in a non-uniformly rotating (librating) cylinder about a horizontal axis is experimentally studied. In the absence of librations the fluid performs a solid-body rotation together with the cavity. Librations lead to the appearance of steady zonal flow in the whole cylinder and the intensive steady toroidal flows near the cavity corners. If the frequency of librations is twice lower than the mean rotation rate the inertial waves are excited. The oscillating motion associated with the propagation of inertial wave in the fluid bulk leads to the appearance of an additional steady flow in the Stokes boundary layers on the cavity side wall. In this case the heavy particles of the visualizer are assembled on the side wall into ring structures. The patterns are determined by the structure of steady flow, which in turn depends on the number of reflections of inertial wave beams from the cavity side wall. For some frequencies, inertial waves experience spatial resonance, resulting in inertial modes, which are eigenmodes of the cavity geometry. The resonance of the inertial modes modifies the steady flow structure close to the boundary layer that is manifested in the direct rebuilding of patterns. It is shown that the intensity of zonal flow, as well as the intensity of steady flows excited by inertial waves, is proportional to the square of the amplitude of librations.

Phenomenological modeling of the drying of a thin cloth with a rotating cylinder heated by electromagnetic induction; Modelisation phenomenologique du sechage d'une nappe mince avec un cylindre rotatoire chauffe par induction electromagnetique

Energy Technology Data Exchange (ETDEWEB)

Perez, S. [Universidad de Carabobo, Facultad de Ingenieria, Valencia (Venezuela); Therien, N.; Broadbent, A.D. [Sherbrooke Univ., Faculte de Genie, Quebec (Canada)

2001-07-01

A phenomenological model of the evolution of the humidity and temperature during the drying of a thin fiber cloth in contact with a metal surface heated by electric induction is presented. The model calculates also the temperature inside the cylinder with respect to its position. Differential mass and energy statuses are established and the concept of substantial derivative is used to bind the state variables with respect to the time and position. The conduction, convection, radiant heat transfer, thermal induction, and energy transfer due to water vaporization are explicitly considered. The model takes into consideration the disturbances due to the variations of the humidity of the cloth at the input of the process. It calculates the response of the process in front of these disturbances and in front of the rotation speed of the cylinder and the electric power supplied to the system. Multiple experiments performed on a bench test have permitted to characterize the response of the drying process (temperature of the cylinder, humidity and temperature of the cloth) under different combinations of conditions. (J.S.)

The Eckert number phenomenon - experimental investigations of heat transfer on moving walls, e.g. rotating cylinders; Das Eckert-Zahl-Phaenomen - Experimentelle Untersuchungen zum Waermeuebergang an einer bewegten Wand am Modellfall eines rotierenden Zylinders

Energy Technology Data Exchange (ETDEWEB)

Gschwendtner, M.

2000-07-01

The Eckert number phenomenon - theoretically investigated by Geropp in 1969 - describes a turnover in heat transfer at a moving wall at an Eckert number EC=1. This report is the first to confirm the Eckert number phenomenon experimentally. Heat transfer on a heated, vertically rotating cylinder in a crossflow was investigated at extreme rotational speeds, i.e. in the range where the predicted phenomenon will occur. A heating concept had to be developed which allowed an input of heating power independent of rotational speed and which therefore had to be contact-free. The complex thermofluiddynamic processes in the boundary layer around the rotating cylinder were investigated and measured using predominantly optical measuring techniques. The results show that the temperature difference between the wall and the surrounding fluid had a significant effect on the predicted turnover of heat transfer at the wall. Moreover, maximum heat transfer occurs at an Eckert number Ec=0.3, which is of great importance for the cooling of hot surfaces in an airstream. [German] Das Eckert-Zahl-Phaenomen - von Geropp 1969 theoretisch untersucht - beschreibt den Umschlag des Waermeueberganges an einer bewegten Wand bei einer Eckert-ZahlEc{approx}1. In der vorliegenden Arbeit wird das Eckert-Zahl-Phaenomen zum ersten Mal experimentell bestaetigt. Dazu wurde der Waermeuebergang am Modellfall eines queransgestroemten, beheizten, vertikalrotierenden Zylinders untersucht. Aufgrund der fuer die Experimente notwendigen extremen Drehzahlen musste fuer die Zylinderheizung ein Konzept entwickelt werden, das eine beruehrungsfreie und damit drehzahlunabhaengige Leistungseinspeisung erlaubte. Mit vorwiegend optischen Messmethoden wurden die komplexen thermofluiddynamischen Vorgaenge in der Grenzschicht um den rotierenden Zylinder untersucht und vermessen. Die Ergebnisse zeigen u.a., dass die Temperaturdifferenz zwischen Wand und Umgebung von entscheidender Bedeutung fuer die Richtungsumkehr des

Turbulent natural convection in an enclosure formed by an array of vertical cylinders

International Nuclear Information System (INIS)

McEligot, D.M.; Stoots, C.M.; Christenson, W.A.; O'Brien, J.E.; Larson, T.K.; Mecham, D.C.; Lussie, W.G.

1992-04-01

A number of situations can be hypothesized to occur in an advanced or special purpose nuclear reactor such that the core is filled with a gas but there is no forced flow to remove the thermal energy evolved. Typically, the dimensions are so large that the magnitudes of the governing parameters indicate that the flow regime is probably turbulent. The generic situation considered in the present work is natural convection between heated, slender, vertical, circular cylinders and a surrounding array of cooler vertical cylinders in a triangular pattern. Experiments were conducted by resistively heating a vertical circular cylinder of length-to-diameter ratio of about 160 centered inside a concentric perforated tube which was, in turn, surrounded by three larger diameter tubes cooled internally with water flow. The medium was air. In order to deduce the contribution due to thermal radiation, thermal emissivities of the tubes were determined in-situ during the experiment and the emissivities of samples of the surfaces involved were measured separately. The ratio of the test section temperature to the cooling tube temperature was varied up to 2.6 by adjusting the electrical power. The Rayleigh number, based on tube diameter and properties evaluated at the cooling tube temperature, ranged from 2.9 x 10 4 to 9.2 x 10 5 . Results indicate that the convective heat transfer parameters for the perforated tube are about fifteen per cent higher than for the smooth bare tube centered in the same position relative to the array. The Nusselt number for convective heat transfer across the annulus-between the heated test section and the perforated tube corresponded to parallel laminar flow. Data with water films flowing down the outside surfaces of the cooling tubes demonstrated no significant change in the convective heat transfer parameters deduced

Experimental apparatus and its operational characteristics for MHD rotating machine with superconducting rotor

International Nuclear Information System (INIS)

Katsurai, Makoto; Karasaki, Takashi; Sekiguchi, Tadashi; Matsuda, Shoji; Ichikawa, Hayao.

1976-01-01

This paper presents the construction and operational characteristics of the experimental apparatus of MHD rotating machine with superconducting rotor, which has the electromechanical energy conversion function based on the inductive interactions between travelling magnetic field produced by the rotor and MHD working fluid. The machine consists of a rotating-dewar type superconducting rotor and a coaxially rotating metal cylinder which simulates the liquid metal MHD working fluid, and the both of them are driven separately by speed-controlled driving motors. The superconducting magnets installed in the rotor has the 8 shaped winding whose outer diameter is 11 cm and hight is 11 cm, and with the excitation current of 200 A (rating), it produces screw type magnetic field in the inductive interaction region of the cylinder with the peak value of 0.2 Wb/m 2 , whereas the average field strength reaches almost 4 Wb/m 2 inside the winding. In this condition, mutual interaction force is 30 N in the peripheral direction and 8 N in the axial direction and the total driving power of motors is 1,300 W when the relative rotation speed of the rotor and the cylinder is 800 rpm. Observed characteristics of this machine are for the most part in agreement with those estimated by the theoretical analysis. (auth.)

Sourcewise represented green's function of the circular waveguide

International Nuclear Information System (INIS)

Prijmenko, S.D.; Bondarenko, L.A.

2007-01-01

Singular part of the Green's function of unbounded space is singled out in explicit form and contains all singularities, including a delta-shaped singularity. The problem of construction of Green's function for a field is solved, as a problem for diffraction of potential and rotational components electric field intensity of a point current source on the circular waveguide walls. The singling out of the electric field intensity singularity in an explicit form about a source enables to develop an effective algorithm of Green's function calculation at any distance between the source point and observation point in a circular waveguide

On rotational solutions for elliptically excited pendulum

International Nuclear Information System (INIS)

Belyakov, Anton O.

2011-01-01

The author considers the planar rotational motion of the mathematical pendulum with its pivot oscillating both vertically and horizontally, so the trajectory of the pivot is an ellipse close to a circle. The analysis is based on the exact rotational solutions in the case of circular pivot trajectory and zero gravity. The conditions for existence and stability of such solutions are derived. Assuming that the amplitudes of excitations are not small while the pivot trajectory has small ellipticity the approximate solutions are found both for high and small linear dampings. Comparison between approximate and numerical solutions is made for different values of the damping parameter. -- Highlights: → We study rotations of the mathematical pendulum when its pivot moves along an ellipse. → There are stable exact solutions for a circular pivot trajectory and zero gravity. → Asymptotic solutions are found for an elliptical pivot trajectory

3D shape extraction segmentation and representation of soil microstructures using generalized cylinders

Science.gov (United States)

Ngom, Ndèye Fatou; Monga, Olivier; Ould Mohamed, Mohamed Mahmoud; Garnier, Patricia

2012-02-01

This paper focuses on the modeling of soil microstructures using generalized cylinders, with a specific application to pore space. The geometric modeling of these microstructures is a recent area of study, made possible by the improved performance of computed tomography techniques. X-scanners provide very-high-resolution 3D volume images ( 3-5μm) of soil samples in which pore spaces can be extracted by thresholding. However, in most cases, the pore space defines a complex volume shape that cannot be approximated using simple analytical functions. We propose representing this shape using a compact, stable, and robust piecewise approximation by means of generalized cylinders. This intrinsic shape representation conserves its topological and geometric properties. Our algorithm includes three main processing stages. The first stage consists in describing the volume shape using a minimum number of balls included within the shape, such that their union recovers the shape skeleton. The second stage involves the optimum extraction of simply connected chains of balls. The final stage copes with the approximation of each simply optimal chain using generalized cylinders: circular generalized cylinders, tori, cylinders, and truncated cones. This technique was applied to several data sets formed by real volume computed tomography soil samples. It was possible to demonstrate that our geometric representation supplied a good approximation of the pore space. We also stress the compactness and robustness of this method with respect to any changes affecting the initial data, as well as its coherence with the intuitive notion of pores. During future studies, this geometric pore space representation will be used to simulate biological dynamics.

Generation of circular polarization of the cosmic microwave background

International Nuclear Information System (INIS)

Alexander, Stephon; Ochoa, Joseph; Kosowsky, Arthur

2009-01-01

The standard cosmological model, which includes only Compton scattering photon interactions at energy scales near recombination, results in zero primordial circular polarization of the cosmic microwave background. In this paper we consider a particular renormalizable and gauge-invariant standard model extension coupling photons to an external vector field via a Chern-Simons term, which arises as a radiative correction if gravitational torsion couples to fermions. We compute the transport equations for polarized photons from a Boltzmann-like equation, showing that such a coupling will source circular polarization of the microwave background. For the particular coupling considered here, the circular polarization effect is always negligible compared to the rotation of the linear polarization orientation, also derived using the same formalism. We note the possibility that limits on microwave background circular polarization may probe other photon interactions and related fundamental effects such as violations of Lorentz invariance.

Cylindrical magnetization model for glass-coated microwires with circular anisotropy: Statics

International Nuclear Information System (INIS)

Torrejon, J.; Thiaville, A.; Adenot-Engelvin, A.L.; Vazquez, M.; Acher, O.

2011-01-01

The static magnetization profile of glass-coated microwires with effective circular anisotropy is investigated using micromagnetics. In this family of microwires, the ferromagnetic nucleus with an amorphous character presents a magnetic structure composed of an inner region with axial domains and an outer region with circular domains, due to magnetoelastic anisotropy. A one-dimensional micromagnetic model is developed, taking into account both the exchange and magnetoelastic anisotropy energies, and solved quasi analytically. The total energy, magnetization profiles and magnetization curves are investigated as a function of radius and anisotropy constant of the nucleus. This work represents a fundamental study of the magnetization process in these amorphous microwires and provides guidelines for the production of microwires with tailored magnetic properties. En passant, the nucleation problem in an infinite cylinder, introduced by W.F. Brown, is revisited. - Research highlights: → Magnetic microwires with circular anisotropy are studied by micromagnetic model. → The ratio R/Δ is a fundamental quantity to determine the magnetic structure. → Reduction of diameter and anisotropy favours the growth of axial core.

Cylinder renormalization for Siegel disks and a constructive Measurable Riemann Mapping Theorem

CERN Document Server

Gaydashev, D G

2006-01-01

The boundary of the Siegel disk of a quadratic polynomial with an irrationally indifferent fixed point with the golden mean rotation number has been observed to be self-similar. The geometry of this self-similarity is universal for a large class of holomorphic maps. A renormalization explanation of this universality has been proposed in the literature. However, one of the ingredients of this explanation, the hyperbolicity of renormalization, has not been proved yet. The present work considers a cylinder renormalization - a novel type of renormalization for holomorphic maps with a Siegel disk which is better suited for a hyperbolicity proof. A key element of a cylinder renormalization of a holomorphic map is a conformal isomorphism of a dynamical quotient of a subset of $\\field{C}$ to a bi-infinite cylinder $\\field{C} / \\field{Z}$. A construction of this conformal isomorphism is an implicit procedure which can be performed using the Measurable Riemann Mapping Theorem. We present a constructive proof of the Mea...

A method of self-pursued boundary value on a body and the Magnus effect calculated with this method

Science.gov (United States)

Yoshino, Fumio; Hayashi, Tatsuo; Waka, Ryoji

1991-03-01

A computational method, designated 'SPB', is proposed for the automatic determination of the stream function Phi on an arbitrarily profiled body without recourse to empirical factors. The method is applied to the case of a rotating, circular cross-section cylinder in a uniform shear flow, and the results obtained are compared with those of both the method in which the value of Phi is fixed on a body and the conventional empirical method; it is in view of this established that the SPB method is very efficient and applicable to both steady and unsteady flows. The SPB method, in addition to yielding the aerodynamic forces acting on a cylinder, shows that the Magnus effect lift force decreases as the velocity gradient of the shear flow increases while the cylinder's rotational speed is kept constant.

Experimental study of natural convection heat transfer from an isothermal combined geometry (downward cone- cylinder)

Energy Technology Data Exchange (ETDEWEB)

Mokhtari, A. [Yazd Univ., Yazd (Iran, Islamic Republic of). Dept. of Mechanical Engineering; Goharkhah, M.; Ashjaee, M. [Tehran Univ., Tehran (Iran, Islamic Republic of). Dept. of Mechanical Engineering

2009-07-01

Laminar free convection heat transfer from an isothermal combined geometry which consists of a downward cone attached to a vertical cylinder was studied. In particular, a Mach-Zehnder interferometer was used to determine the change in local and average heat transfer coefficients on the surface of an isothermal combined geometry for different vertex angles. The effect of the vertex angle on heat transfer was also investigated by keeping the height of the cylinder and slant length of the cone constant for all objects. The experimental data showed that the local heat transfer coefficient on the conical part increased in the vicinity of the cylinder and cone intersection. The distance between the point of minimum heat transfer coefficient on the cone and vertex of the cone decreased as the vertex angle increased. The maximum average Nusselt number for a constant Rayleigh number was obtained for the geometry with the smallest vertex angle. For all objects, the average Nusselt number increased with an increase in the Rayleigh number. An experiment was carried out on a vertical isothermal cylinder of circular cross section in order to validate the experimental approach. An analytical solution was found to be in good agreement with experimental results. 31 refs., 9 figs.

Numerical simulation of two-dimensional flows over a circular cylinder using the immersed boundary method

International Nuclear Information System (INIS)

Lima E Silva, A.L.F.; Silveira-Neto, A.; Damasceno, J.J.R.

2003-01-01

In this work, a virtual boundary method is applied to the numerical simulation of a uniform flow over a cylinder. The force source term, added to the two-dimensional Navier-Stokes equations, guarantees the imposition of the no-slip boundary condition over the body-fluid interface. These equations are discretized, using the finite differences method. The immersed boundary is represented with a finite number of Lagrangian points, distributed over the solid-fluid interface. A Cartesian grid is used to solve the fluid flow equations. The key idea is to propose a method to calculate the interfacial force without ad hoc constants that should usually be adjusted for the type of flow and the type of the numerical method, when this kind of model is used. In the present work, this force is calculated using the Navier-Stokes equations applied to the Lagrangian points and then distributed over the Eulerian grid. The main advantage of this approach is that it enables calculation of this force field, even if the interface is moving or deforming. It is unnecessary to locate the Eulerian grid points near this immersed boundary. The lift and drag coefficients and the Strouhal number, calculated for an immersed cylinder, are compared with previous experimental and numerical results, for different Reynolds numbers

DOA and Polarization Estimation Using an Electromagnetic Vector Sensor Uniform Circular Array Based on the ESPRIT Algorithm.

Science.gov (United States)

Wu, Na; Qu, Zhiyu; Si, Weijian; Jiao, Shuhong

2016-12-13

In array signal processing systems, the direction of arrival (DOA) and polarization of signals based on uniform linear or rectangular sensor arrays are generally obtained by rotational invariance techniques (ESPRIT). However, since the ESPRIT algorithm relies on the rotational invariant structure of the received data, it cannot be applied to electromagnetic vector sensor arrays (EVSAs) featuring uniform circular patterns. To overcome this limitation, a fourth-order cumulant-based ESPRIT algorithm is proposed in this paper, for joint estimation of DOA and polarization based on a uniform circular EVSA. The proposed algorithm utilizes the fourth-order cumulant to obtain a virtual extended array of a uniform circular EVSA, from which the pairs of rotation invariant sub-arrays are obtained. The ESPRIT algorithm and parameter pair matching are then utilized to estimate the DOA and polarization of the incident signals. The closed-form parameter estimation algorithm can effectively reduce the computational complexity of the joint estimation, which has been demonstrated by numerical simulations.

A fluid Foucault pendulum: the impossibility of achieving solid-body rotation on Earth

Science.gov (United States)

Blum, Robert; Zimmerman, Daniel; Triana, Santiago; Lathrop, Daniel

2012-11-01

Rotating fluid dynamics is key to our understanding of the Earth's atmosphere, oceans, and core, along with a plethora of astrophysical objects. Laboratory study of these natural systems often involves spinning experimental devices, which are assumed to tend to rigid rotation when unstirred. We present results showing that even at the tabletop scale, there is a measurable oscillatory flow driven by the precession of the experiment's axis as the earth rotates. We measure this flow in a rotating cylinder with an adjustable aspect ratio. The horizontal flow in the rotating frame is measured using particle tracking. The steady state is well-described by an inertial mode whose amplitude is maximum when the height to diameter ratio is 0.995, which matches theoretical predictions. We also quantify the resonant amplitude of the inertial mode in the cylinder and estimate the amplitude in other devices. We compare our results to similar studies done in spherical devices. [Triana et al., JGR, 117 (2012), B04103][Boisson et al., EPL, 98 (2012), 59002].

Design & fabrication of two seated aircraft with an advanced rotating leading edge wing

Science.gov (United States)

Al Ahmari, Saeed Abdullah Saeed

The title of this thesis is "Design & Fabrication of two Seated Aircraft with an Advanced Rotating Leading Edge Wing", this gives almost a good description of the work has been done. In this research, the moving surface boundary-layer control (MSBC) concept was investigated and implemented. An experimental model was constructed and tested in wind tunnel to determine the aerodynamic characteristics using the leading edge moving surface of modified semi-symmetric airfoil NACA1214. The moving surface is provided by a high speed rotating cylinder, which replaces the leading edge of the airfoil. The angle of attack, the cylinder surfaces velocity ratio Uc/U, and the flap deflection angle effects on the lift and drag coefficients and the stall angle of attack were investigated. This new technology was applied to a 2-seat light-sport aircraft that is designed and built in the Aerospace Engineering Department at KFUPM. The project team is led by the aerospace department chairman Dr. Ahmed Z. AL-Garni and Dr. Wael G. Abdelrahman and includes graduate and under graduate student. The wing was modified to include a rotating cylinder along the leading edge of the flap portion. This produced very promising results such as the increase of the maximum lift coefficient at Uc/U=3 by 82% when flaps up and 111% when flaps down at 40° and stall was delayed by 8degrees in both cases. The laboratory results also showed that the effective range of the leading-edge rotating cylinder is at low angles of attack which reduce the need for higher angles of attack for STOL aircraft.

Rotating Liner Engine: Improving Efficiency of Heavy Duty Diesels by Significant Friction Reduction, and Extending the Life of Heavy Duty Engines.

Energy Technology Data Exchange (ETDEWEB)

Dardalis, Dimitrios

2013-12-31

This report describes the work on converting a 4 cylinder Cummins ISB engine into a single cylinder Rotating Liner Engine functioning prototype that can be used to measure the friction benefits of rotating the cylinder liner in a high pressure compression ignition engine. A similar baseline engine was also prepared, and preliminary testing was done. Even though the fabrication of the single cylinder prototype was behind schedule due to machine shop delays, the fundamental soundness of the design elements are proven, and the engine has successfully functioned. However, the testing approach of the two engines, as envisioned by the original proposal, proved impossible due to torsional vibration resonance caused by the single active piston. A new approach for proper testing has been proposed,

Dynamics of a discrete geotropic sensor subject to rotation-induced gravity compensation

Energy Technology Data Exchange (ETDEWEB)

Silver, I.L.

1976-01-01

A clinostat achieves gravity compensation by providing circular rotation with uniform speed, about a horizontal axis. The dynamics of an assumed, discrete and free-moving subcellular gravity receptor, subject to clinostat rotation, is analyzed. The results imply that there is an optimum rotation rate; higher speeds result in circular motions with diameters more comparable to thermal noise fluctuations, but with greater linear velocities due to increasing centrifugal forces. An optimizing function is proposed. The nucleolus and mitochondrion is chosen as a gravity receptor for illustrating the use of this theory. The characteristics of their clinostat-induced motions are incorporated with experimental results on Avena plant shoots in an illustrative example.

Engine Cylinder Temperature Control

Science.gov (United States)

Kilkenny, Jonathan Patrick; Duffy, Kevin Patrick

2005-09-27

A method and apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine. The cylinder is fluidly connected to an intake manifold and an exhaust manifold. The method and apparatus includes increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and varying operation of an intake valve located between the intake manifold and the cylinder to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.

Delamination of Composite Cylinders

Science.gov (United States)

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.

Broadband, Low Sidelobe, Zero Height, Slotted Circular Disk Antenna

African Journals Online (AJOL)

A rigorous mathematical theory for a rotationally symmetrical slotted circular disk antenna was developed. The theory applies the principle of "Gradient Invariance" of electromagnetic fields to determine the field components that are unique and single valued at any point in space. To detemine the radiation characteristics of ...

The structure of sidewall boundary layers in conned rotating Rayleigh-Bénard convection

NARCIS (Netherlands)

Kunnen, R.P.J.; Clercx, H.J.H.; van Heijst, G.J.F.

2013-01-01

Turbulent rotating convection is usually studied in a cylindrical geometry, as this is its most convenient experimental realization. In our previous work (Kunnen et al., J. Fluid Mech., vol. 688, 2011, pp. 422–442) we studied turbulent rotating convection in a cylinder with the emphasis on the

Comparison of Methods to Predict Lower Bound Buckling Loads of Cylinders Under Axial Compression

Science.gov (United States)

Haynie, Waddy T.; Hilburger, Mark W.

2010-01-01

Results from a numerical study of the buckling response of two different orthogrid stiffened circular cylindrical shells with initial imperfections and subjected to axial compression are used to compare three different lower bound buckling load prediction techniques. These lower bound prediction techniques assume different imperfection types and include an imperfection based on a mode shape from an eigenvalue analysis, an imperfection caused by a lateral perturbation load, and an imperfection in the shape of a single stress-free dimple. The STAGS finite element code is used for the analyses. Responses of the cylinders for ranges of imperfection amplitudes are considered, and the effect of each imperfection is compared to the response of a geometrically perfect cylinder. Similar behavior was observed for shells that include a lateral perturbation load and a single dimple imperfection, and the results indicate that the predicted lower bounds are much less conservative than the corresponding results for the cylinders with the mode shape imperfection considered herein. In addition, the lateral perturbation technique and the single dimple imperfection produce response characteristics that are physically meaningful and can be validated via testing.

SHIELDING OF A UNIFORM ALTERNATING MAGNETIC FIELD USING A CIRCULAR PASSIVE LOOP

Directory of Open Access Journals (Sweden)

V. S. Grinchenko

2015-04-01

Full Text Available The magnetic and electromagnetic shields are used to reduce the magnetic field in local spaces. Usually these shields are implemented in the form of a box or a cylinder. At the same time the magnetic field reduction in local spaces by means of passive loops is not considered in detail yet. So, the present study considers shielding capabilities of a circular passive loop. The authors have performed an analytical and numerical modeling of a process of a uniform harmonic magnetic field shielding. The simulated results permit to find out the spatial distribution of the shielded magnetic field. Dependencies of shielding effectiveness on the passive loop radius and cross-section are determined. Moreover, the non-monotonic behavior of the loop radius dependence is shown. We have substantiated that the shielded volume of a circular passive loop is advisable to limit by the sphere with a half loop radius. Presented results give parameters of the circular passive loop that reduces the rms value of the magnetic flux density by 30 %.

Internal combustion engine cylinder-to-cylinder balancing with balanced air-fuel ratios

Science.gov (United States)

Harris, Ralph E.; Bourn, Gary D.; Smalley, Anthony J.

2006-01-03

A method of balancing combustion among cylinders of an internal combustion engine. For each cylinder, a normalized peak firing pressure is calculated as the ratio of its peak firing pressure to its combustion pressure. Each cylinder's normalized peak firing pressure is compared to a target value for normalized peak firing pressure. The fuel flow is adjusted to any cylinder whose normalized peak firing pressure is not substantially equal to the target value.

Inertial migration of particles in Taylor-Couette flows

Science.gov (United States)

Majji, Madhu V.; Morris, Jeffrey F.

2018-03-01

An experimental study of inertial migration of neutrally buoyant particles in the circular Couette flow (CCF), Taylor vortex flow (TVF) and wavy vortex flow (WVF) is reported. This work considers a concentric cylinder Taylor-Couette device with a stationary outer cylinder and rotating inner cylinder. The device has a radius ratio of η = ri/ro = 0.877, where ri and ro are the inner and outer radii of the flow annulus. The ratio of the annular width between the cylinders (δ = ro - ri) and the particle diameter (dp) is α = δ/dp = 20. For η = 0.877, the flow of a Newtonian fluid undergoes transitions from CCF to TVF and TVF to WVF at Reynolds numbers Re = 120 and 151, respectively, and for the dilute suspensions studied here, these critical Reynolds numbers are almost unchanged. In CCF, particles were observed to migrate, due to the competition between the shear gradient of the flow and the wall interactions, to an equilibrium location near the middle of the annulus with an offset toward the inner cylinder. In TVF, the vortex motion causes the particles to be exposed to the shear gradient and wall interactions in a different manner, resulting in a circular equilibrium region in each vortex. The radius of this circular region grows with increase in Re. In WVF, the azimuthal waviness results in fairly well-distributed particles across the annulus.

Experimental study of the effect of icing on the aerodynamics of circular cylinders - Part I: Cross flow

DEFF Research Database (Denmark)

Demartino, Cristoforo; Koss, Holger; Ricciardelli, Francesco

2013-01-01

and temperatures are considered. The tested cylinder is a specimen of a HDPE tube used for bridge hanger protection. The wind tunnel tests shall serve as a reference, and the results can be used for the evaluation of possible aerodynamic instability phenomena. A preliminary evaluation of possible galloping...

FARADAY ROTATION: EFFECT OF MAGNETIC FIELD REVERSALS

International Nuclear Information System (INIS)

Melrose, D. B.

2010-01-01

The standard formula for the rotation measure (RM), which determines the position angle, ψ = RMλ 2 , due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution Δψ needed to correct this omission. In contrast with a result proposed by Broderick and Blandford, Δψ is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correction to the dispersion measure at low frequencies.

FARADAY ROTATION: EFFECT OF MAGNETIC FIELD REVERSALS

Energy Technology Data Exchange (ETDEWEB)

Melrose, D B [SIfA, School of Physics, University of Sydney, NSW 2006 (Australia)

2010-12-20

The standard formula for the rotation measure (RM), which determines the position angle, {psi} = RM{lambda}{sup 2}, due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution {Delta}{psi} needed to correct this omission. In contrast with a result proposed by Broderick and Blandford, {Delta}{psi} is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correction to the dispersion measure at low frequencies.

Liquid metal flow in a finite-length cylinder with a rotating magnetic field

International Nuclear Information System (INIS)

Gelfgat, Yu.M.; Gorbunov, L.A.; Kolevzon, V.

1993-01-01

A liquid metal flow induced by a rotating magnetic field in a cylindrical container of finite height was investigated experimentally. It was demonstrated that the flow in a rotating magnetic field is similar to geophysical flows: the fluid rotates uniformly with depth and the Ekman layer exists at the container bottom. Near the vertical wall the flow is depicted in the form of a confined jet whose thickness determines the instability onset in a rotating magnetic field. It was shown that the critical Reynolds number can be found by using the jet velocity u 0 for Re cr =u 2 0 /ν∂u/∂r. The effect of frequency of a magnetic field on the fluid flow was also studied. An approximate theoretical model is presented for describing the fluid flow in a uniform rotating magnetic field. (orig.)

Cylindrical acoustic levitator/concentrator having non-circular cross-section

Science.gov (United States)

Kaduchak, Gregory; Sinha, Dipen N.

2003-11-11

A low-power, inexpensive acoustic apparatus for levitation and/or concentration of aerosols and small liquid/solid samples having particulates up to several millimeters in diameter in air or other fluids is described. It is constructed from a commercially available, hollow piezoelectric crystal which has been formed with a cylindrical cross-section to tune the resonance frequency of the breathing mode resonance of the crystal to that of the interior cavity of the cylinder. When the resonance frequency of the interior cylindrical cavity is matched to the breathing mode resonance of the cylindrical piezoelectric transducer, the acoustic efficiency for establishing a standing wave pattern in the cavity is high. By deforming the circular cross-section of the transducer, the acoustic force is concentrated along axial regions parallel to the axis of the transducer. The cylinder does not require accurate alignment of a resonant cavity. The concentrated regions of acoustic force cause particles in the fluid to concentrate within the regions of acoustic force for separation from the fluid.

Azimuthal magnetorotational instability with super-rotation

Science.gov (United States)

Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.

2018-02-01

It is demonstrated that the azimuthal magnetorotational instability (AMRI) also works with radially increasing rotation rates contrary to the standard magnetorotational instability for axial fields which requires negative shear. The stability against non-axisymmetric perturbations of a conducting Taylor-Couette flow with positive shear under the influence of a toroidal magnetic field is considered if the background field between the cylinders is current free. For small magnetic Prandtl number the curves of neutral stability converge in the (Hartmann number,Reynolds number) plane approximating the stability curve obtained in the inductionless limit . The numerical solutions for indicate the existence of a lower limit of the shear rate. For large the curves scale with the magnetic Reynolds number of the outer cylinder but the flow is always stable for magnetic Prandtl number unity as is typical for double-diffusive instabilities. We are particularly interested to know the minimum Hartmann number for neutral stability. For models with resting or almost resting inner cylinder and with perfectly conducting cylinder material the minimum Hartmann number occurs for a radius ratio of \\text{in}=0.9$ . The corresponding critical Reynolds numbers are smaller than 4$ .

Dynamical behavior of surface tension on rotating fluids in low and microgravity environments

Science.gov (United States)

Hung, R. J.; Tsao, Y. D.; Hong, B. B.; Leslie, F. W.

1989-01-01

Consideration is given to the time-dependent evolutions of the free surface profile (bubble shapes) of a cylindrical container, partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry in low and microgravity environments. The dynamics of the bubble shapes are calculated for four cases: linear time-dependent functions of spin-up and spin-down in low and microgravity, linear time-dependent functions of increasing and decreasing gravity at high and low rotating cylinder speeds, time-dependent step functions of spin-up and spin-down in low gravity, and sinusoidal function oscillation of the gravity environment in high and low rotating cylinder speeds. It is shown that the computer algorithms developed by Hung et al. (1988) may be used to simulate the profile of time-dependent bubble shapes under variations of centrifugal, capillary, and gravity forces.

Strength tests of thin-walled elliptic duralumin cylinders in pure bending and in combined pure bending and torsion

Science.gov (United States)

Lundquist, Eugene E; Stowell, Elbridge Z

1942-01-01

An analysis is presented of the results of tests made by the Massachusetts Institute of Technology and by the National Advisory Committee for Aeronautics on an investigation of the strength of thin-walled circular and elliptic cylinders in pure bending and in combined torsion and bending. In each of the loading conditions, the bending moments were applied in the plane of the major axis of the ellipse.

Entropy generation due to external fluid flow and heat transfer from a cylinder between parallel planes

Directory of Open Access Journals (Sweden)

Melhem Omar A.

2017-01-01

Full Text Available In the present study, second law analysis is introduced for circular cylinder confined between parallel planes. An analytical approach is adopted to study the effects of block age, Reynolds and Prandtl numbers on the entropy generation due to the laminar flow and heat transfer. Four different fluids are considered in the present analysis for comparison purposes. Heat transfer for the cylinder at an isothermal boundary condition is incorporated. In general, the entropy generation rate decreases as the blockage ratio decreases. In addition, the entropy generation rate increases with increasing Reynolds and Prandtl numbers. At a fixed Reynolds number, the effect of block age becomes more notice able for higher Prandtl number fluid. Similarly, for the same fluid, the effect of block age becomes more no tice able as the Reynolds number increases.

A new method for fabrication of thin plates and thin-walled cylinder made of fiber reinforced metal (FRM) and its application for the rotating drum of the nuclear fuel centrifugal separator

International Nuclear Information System (INIS)

Okamura, Tatsuya

1978-01-01

The composite materials using resins as the base materials show the defect that the characteristics deteriorate rapidly at elevated temperature. Therefore the FRMs using relatively ductile metals as the base materials combined with reinforcing fibers have been considered. The result of study on the combination of base materials and fibers and the manufacturing method is rarely reported in Japan. In FRMs, direct contact of fibers mutually must be avoided, especially making nodes lowers the strength extremely. The fibers must be long monofilaments of 0.1 to 0.2 mm diameter. High precision wire winding machines are required for making uniform FRMs. For the diffusion joining of preformed materials, in which fibers are put in order on metallic foils, pressure and heat are applied. The author succeeded to develop the technique for making thin-walled cylinders of FRMs, including the method of winding brittle filaments and the method of pressurizing and heating based on the difference of thermal expansion of dies. The mechanical properties of thin plates and thin-walled cylinders made of monofilaments of B, SiC and SUS and aluminum alloy foils were obtained, and rotation test of the cylinders was carried out. It was clarified that the FRMs of B-Al and SiC-Al groups are very excellent materials, and most suitable for the rotary drums of super-high speed centrifuges. (Kako, I.)

The Exact Solution for Linear Thermoelastic Axisymmetric Deformations of Generally Laminated Circular Cylindrical Shells

Science.gov (United States)

Nemeth, Michael P.; Schultz, Marc R.

2012-01-01

A detailed exact solution is presented for laminated-composite circular cylinders with general wall construction and that undergo axisymmetric deformations. The overall solution is formulated in a general, systematic way and is based on the solution of a single fourth-order, nonhomogeneous ordinary differential equation with constant coefficients in which the radial displacement is the dependent variable. Moreover, the effects of general anisotropy are included and positive-definiteness of the strain energy is used to define uniquely the form of the basis functions spanning the solution space of the ordinary differential equation. Loading conditions are considered that include axisymmetric edge loads, surface tractions, and temperature fields. Likewise, all possible axisymmetric boundary conditions are considered. Results are presented for five examples that demonstrate a wide range of behavior for specially orthotropic and fully anisotropic cylinders.

An analytical study of the effects of transverse shear deformation and anisotropy on buckling loads of laminated cylinders. M.S. Thesis - George Washington Univ.

Science.gov (United States)

Jegley, Dawn C.

1987-01-01

Buckling loads of thick-walled orthotropic and anisotropic simply supported circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of buckling loads predicted by the conventional first-order transverse-shear deformation theory and the higher-order theory show that the additional allowance for transverse shear deformation has a negligible effect on the predicted buckling loads of medium-thick metallic isotropic cylinders. However, the higher-order theory predicts buckling loads which are significantly lower than those predicted by the first-order transverse-shear deformation theory for certain short, thick-walled cylinders which have low through-the-thickness shear moduli. A parametric study of the effects of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 45 degree plies are most sensitive to transverse-shear deformation effects. Interaction curves for buckling loads of cylinders subjected to axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are as sensitive to transverse-shear deformation effects as buckling loads due to axial compressive loadings. The effects of anisotropy are important over a much wider range of cylinder geometries than the effects of transverse shear deformation.

Magneto-rotational instability in differentially rotating liquid metals

International Nuclear Information System (INIS)

Velikhov, E.P.; Ivanov, A.A.; Lakhin, V.P.; Serebrennikov, K.S.

2006-01-01

We study the stability of Couette flow between two cylinders in the presence of axial magnetic field in local WKB approximation. We find the analytical expression of the critical angular velocity minimized over the wave number and the imposed magnetic field as a function of the measure of deviation of the rotation law from the Rayleigh line. The result found is in a good agreement with the previously known numerical results based on the global analysis. We perform a minimization of the critical Reynolds number over the wave number at fixed magnetic field both analytically and numerically. We show that a compromise between resistive suppression of magneto-rotational instability at weak magnetic field and the increase of the critical Reynolds number with the increase of magnetic field is possible. It takes place at moderate values of magnetic field of order 3x10 2 gauss giving the critical Reynolds number of order 4x10 4

Normalized lift: an energy interpretation of the lift coefficient simplifies comparisons of the lifting ability of rotating and flapping surfaces.

Science.gov (United States)

Burgers, Phillip; Alexander, David E

2012-01-01

For a century, researchers have used the standard lift coefficient C(L) to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½ρv(2), where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders.This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/ρ·S), compared against the total kinetic energy required for generating said lift, ½v(2). This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and forward flight, and a hovering dipteran.The maximum standard lift coefficient for a fixed wing without flaps in steady flow is around 1.5, yet for a rotating cylinder it may exceed 9.0, a value that implies that a rotating cylinder generates nearly 6 times the maximum lift of a wing. The maximum normalized lift for a rotating cylinder is 1.5. We suggest that the normalized lift can be used to evaluate propellers, rotors, flapping wings of animals and micro air vehicles, and underwater thrust-generating fins in the same way the lift coefficient is currently used to evaluate fixed wings.

Chiral retrieval method based on right circularly polarized and left circularly polarized waves

International Nuclear Information System (INIS)

Martín, Ernesto; Muñoz, Juan; Margineda, José; Molina-Cuberos, Gregorio J; García-Collado, Ángel J

2014-01-01

The free-wave characterization of metamaterials is usually carried out by illuminating a sample with a linearly polarized plane electromagnetic wave. At points before and after the sample, sensors are introduced to measure the transverse components of the field, in order to compute the reflection and transmission coefficients related with the co- and cross-polar field components. Based on this information, retrieval algorithms allow parameters like rotation angle, effective chirality and refraction index to be calculated. Here we propose to use the transmission signals under illumination with plane circularly polarized waves, without sensing the reflection signal, to calculate the chirality parameter and the rotation angle due to the electromagnetic activity of the material. This new method, which allows a simpler characterization of a chiral slab, is applied to the study of metamaterials composed of both periodic and random distributions of metallic structures with chiral symmetry. The experimental results are contrasted with simulations and alternative measurements obtained using linearly polarized waves. (paper)

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.

Magnetic fields produced by rotating symmetrical bodies with homogeneous surface charge density

International Nuclear Information System (INIS)

Espejel-Morales, R; Murguía-Romero, G; Calles, A; Cabrera-Bravo, E; Morán-López, J L

2016-01-01

We present a numerical calculation for the stationary magnetic field produced by different rotating bodies with homogeneous and constant surface charge density. The calculation is done by superposing the magnetic field produced by a set of loops of current which mimic the magnetic field produced by belts of current defined by slices of fixed width. We consider the cases of a sphere, ellipsoids, open and closed cylinders and a combination of these in a dumbbell -like shell. We also plot their magnetic field lines using a technique that make use of the Runge–Kutta fourth-order method. Up to our knowledge, the case of closed cylinders was not calculated before. In contrast to previous results, we find that the magnetic field inside finite hollow bodies is homogeneous only in the case of a sphere. This is consequence of the fact that, for the sphere, the surface of any slice taken perpendicularly to the rotation axis, depends only on its thickness, like in the case of an infinite cylinder. (paper)

Behavior of a heavy cylinder in a horizontal cylindrical liquid-filled cavity at modulated rotation

International Nuclear Information System (INIS)

Kozlov, Nikolai V; Vlasova, Olga A

2016-01-01

The behavior of a heavy cylindrical solid in a horizontal cylindrical cavity is experimentally investigated. The cavity is filled with a viscous liquid and rotates. Two rotation regimes are considered. The first one is steady rotation. A number of body motion regimes are found depending on the cavity rotation speed. The second regime is a modulated rotation, in which the rotation speed is varying periodically. It can be presented as a sum of steady rotation and librations. On the whole, three different cases of the body repulsion from the cavity wall are observed. In the first case, the repulsion occurs when the body slides over a rotating cavity wall. In the second case, the body being in the centrifuged state—when it rotates with the fluid—detaches from the cavity wall under the action of gravity. In the third case, at librations, the wall performs oscillations and the body is repulsed from the wall due to the nonlinear viscous interaction with the fluid. (paper)

Administrative Circulars

CERN Document Server

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...

Precise Measurement of Velocity Dependent Friction in Rotational Motion

Science.gov (United States)

Alam, Junaid; Hassan, Hafsa; Shamim, Sohaib; Mahmood, Waqas; Anwar, Muhammad Sabieh

2011-01-01

Frictional losses are experimentally determined for a uniform circular disc exhibiting rotational motion. The clockwise and anticlockwise rotations of the disc, that result when a hanger tied to a thread is released from a certain height, give rise to vertical oscillations of the hanger as the thread winds and unwinds over a pulley attached to the…

Molecular electron recollision dynamics in intense circularly polarized laser pulses

Science.gov (United States)

Bandrauk, André D.; Yuan, Kai-Jun

2018-04-01

Extreme UV and x-ray table top light sources based on high-order harmonic generation (HHG) are focused now on circular polarization for the generation of circularly polarized attosecond pulses as new tools for controlling electron dynamics, such as charge transfer and migration and the generation of attosecond quantum electron currents for ultrafast magneto-optics. A fundamental electron dynamical process in HHG is laser induced electron recollision with the parent ion, well established theoretically and experimentally for linear polarization. We discuss molecular electron recollision dynamics in circular polarization by theoretical analysis and numerical simulation. The control of the polarization of HHG with circularly polarized ionizing pulses is examined and it is shown that bichromatic circularly polarized pulses enhance recollision dynamics, rendering HHG more efficient, especially in molecules because of their nonspherical symmetry. The polarization of the harmonics is found to be dependent on the compatibility of the rotational symmetry of the net electric field created by combinations of bichromatic circularly polarized pulses with the dynamical symmetry of molecules. We show how the field and molecule symmetry influences the electron recollision trajectories by a time-frequency analysis of harmonics. The results, in principle, offer new unique controllable tools in the study of attosecond molecular electron dynamics.

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

-linear springs. The initial packing of the particles is generated by the ballistic deposition method. Salient micromechanical features of closed die and isostatic powder compaction are elucidated for both frictionless and sticking contacts. It is found that substantial rearrangement of frictionless particles......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...

Steady state quantum discord for circularly accelerated atoms

Energy Technology Data Exchange (ETDEWEB)

Hu, Jiawei, E-mail: hujiawei@nbu.edu.cn [Center for Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China); Yu, Hongwei, E-mail: hwyu@hunnu.edu.cn [Center for Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China); Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha, Hunan 410081 (China)

2015-12-15

We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptotic value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.

Measurement of small light absorption in microparticles by means of optically induced rotation

DEFF Research Database (Denmark)

Angelsky, O. V.; Bekshaev, A. Ya; Maksimyak, P. P.

2015-01-01

The absorption parameters of micro-particles have been associated with the induced spin exerted upon the particle, when embedded in a circularly polarized coherent field. The induced rotational speed is theoretically analyzed, showing the influence of the beam parameters, the parameters of the pa......The absorption parameters of micro-particles have been associated with the induced spin exerted upon the particle, when embedded in a circularly polarized coherent field. The induced rotational speed is theoretically analyzed, showing the influence of the beam parameters, the parameters...

Can walking motions improve visually induced rotational self-motion illusions in virtual reality?

Science.gov (United States)

Riecke, Bernhard E; Freiberg, Jacob B; Grechkin, Timofey Y

2015-02-04

Illusions of self-motion (vection) can provide compelling sensations of moving through virtual environments without the need for complex motion simulators or large tracked physical walking spaces. Here we explore the interaction between biomechanical cues (stepping along a rotating circular treadmill) and visual cues (viewing simulated self-rotation) for providing stationary users a compelling sensation of rotational self-motion (circular vection). When tested individually, biomechanical and visual cues were similarly effective in eliciting self-motion illusions. However, in combination they yielded significantly more intense self-motion illusions. These findings provide the first compelling evidence that walking motions can be used to significantly enhance visually induced rotational self-motion perception in virtual environments (and vice versa) without having to provide for physical self-motion or motion platforms. This is noteworthy, as linear treadmills have been found to actually impair visually induced translational self-motion perception (Ash, Palmisano, Apthorp, & Allison, 2013). Given the predominant focus on linear walking interfaces for virtual-reality locomotion, our findings suggest that investigating circular and curvilinear walking interfaces offers a promising direction for future research and development and can help to enhance self-motion illusions, presence and immersion in virtual-reality systems. © 2015 ARVO.

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

Science.gov (United States)

Mitri, F. G.

2015-12-01

The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.

Determination of the Static Friction Coefficient from Circular Motion

Science.gov (United States)

Molina-Bolívar, J. A.; Cabrerizo-Vílchez, M. A.

2014-01-01

This paper describes a physics laboratory exercise for determining the coefficient of static friction between two surfaces. The circular motion of a coin placed on the surface of a rotating turntable has been studied. For this purpose, the motion is recorded with a high-speed digital video camera recording at 240 frames s[superscript-1], and the…

Self-organization in circular shear layers

DEFF Research Database (Denmark)

Bergeron, K.; Coutsias, E.A.; Lynov, Jens-Peter

1996-01-01

Experiments on forced circular shear layers performed in both magnetized plasmas and in rotating fluids reveal qualitatively similar self-organization processes leading to the formation of patterns of coherent vortical structures with varying complexity. In this paper results are presented from...... both weakly nonlinear analysis and full numerical simulations that closely reproduce the experimental observations. Varying the Reynolds number leads to bifurcation sequences accompanied by topological changes in the distribution of the coherent structures as well as clear transitions in the total...

Gas Cylinder Safety, Course 9518

Energy Technology Data Exchange (ETDEWEB)

Glass, George [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-10-27

This course, Gas Cylinder Safety (#9518), presents an overview of the hazards and controls associated with handling, storing, using, and transporting gas cylinders. Standard components and markings of gas cylinders are also presented, as well as the process for the procurement, delivery, and return of gas cylinders at Los Alamos National Laboratory (LANL).

Ranking of Cylinder Liner Materials in Two Stroke Marine Diesel Engines

DEFF Research Database (Denmark)

Pedersen, Michael Torben; Imran, Tajammal; Klit, Peder

2009-01-01

is made into a ring and the piston ring into a block. A short introduction of the test apparatus and its abilities is presented and discussed. Results from comparison and characterisation of five different cylinder liner materials run with a fixed piston ring material are presented. A preliminary ranking...... of the materials is given based on the materials tribological performance. The materials are evaluated on basis of friction force, oil film thickness variation, temperature variation and rotational speed....

Wave propagation in a piezoelectric solid bar of circular cross-section immersed in fluid

International Nuclear Information System (INIS)

Ponnusamy, P.

2013-01-01

Wave propagation in a piezoelectric solid bar of circular cross-section immersed in fluid is discussed using three-dimensional theory of piezoelectricity. The equations of motion of the cylinder are formulated using the constitutive equations of a piezoelectric material. The equations of motion of the fluid are formulated using the constitutive equations of an inviscid fluid. Three displacement potential functions are introduced to uncouple the equations of motion, electric conduction. The frequency equation of the coupled system consisting of cylinder and fluid is developed under the assumption of perfect-slip boundary conditions at the fluid–solid interfaces. The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 material bar immersed in fluid. The computed non-dimensional wave numbers are presented in the form of dispersion curves. The secant method is used to obtain the roots of the frequency equation. -- Highlights: ► Wave propagation in a piezoelectric solid bar of circular cross-section immersed in fluid is analyzed using secant method. ► Solid–fluid interaction for piezoelectric material of PZT-4 is analyzed using the boundary conditions. ► The computed non-dimensional wave numbers are plotted in the form of dispersion curves and studied its characters. ► A comparison is made between the non-dimensional wave numbers obtained by the author with the literature results

Fiber Tracking Cylinder Nesting

International Nuclear Information System (INIS)

Stredde, H.

1999-01-01

The fiber tracker consists of 8 concentric carbon fiber cylinders of varying diameters, from 399mm to 1032.2mm and two different lengths. 1.66 and 2.52 meters. Each completed cylinder is covered over the entire o.d. with scintillating fiber ribbons with a connector on each ribbon. These ribbons are axial (parallel to the beam line) at one end and stereo (at 3 deg. to the beam line) at the other. The ribbon connectors have dowel pins which are used to match with the connectors on the wave guide ribbons. These dowel pins are also used during the nesting operation, locating and positioning measurements. The nesting operation is the insertion of one cylinder into another, aligning them with one another and fastening them together into a homogeneous assembly. For ease of assembly. the nesting operation is accomplished working from largest diameter to smallest. Although the completed assembly of all 8 cylinders glued and bolted together is very stiff. individual cylinders are relatively flexible. Therefore. during this operation, No.8 must be supported in a manner which maintains its integrity and yet allows the insertion of No.7. This is accomplished by essentially building a set of dummy end plates which replicate a No.9 cylinder. These end plates are mounted on a wheeled cart that becomes the nesting cart. Provisions for a protective cover fastened to these rings has been made and will be incorporated in finished product. These covers can be easily removed for access to No.8 and/or the connection of No.8 to No.9. Another wheeled cart, transfer cart, is used to push a completed cylinder into the cylinder(s) already mounted in the nesting cart.

An Approximate Solution to the Plastic Indentation of Circular Sandwich Panels

Science.gov (United States)

Xie, Z.

2018-05-01

The plastic indentation response of circular sandwich panels loaded by the flat end of a cylinder is investigated employing a velocity field model. Using the principles of virtual velocities and minimum work, an expression for the indenter load in relation to the indenter displacement and displacement field of the deformed face sheet is derived. The analytical solutions obtained are in good agreement with those found by simulations using the ABAQUS code. The radial tensile strain of the deformed face sheet and the ratio of energy absorption rate of the core to that of the face sheet are discussed.

Hydromagnetic stability of rotating stratified compressible fluid flows

Energy Technology Data Exchange (ETDEWEB)

Srinivasan, V; Kandaswamy, P [Dept. of Mathematics, Bharathiar University, Coimbatore, Tamil Nadu, India; Debnath, L [Dept. of Mathematics, University of Central Florida, Orlando, USA

1984-09-01

The hydromagnetic stability of a radially stratified compressible fluid rotating between two coaxial cylinders is investigated. The stability with respect to axisymmetric disturbances is examined. The fluid system is found to be thoroughly stable to axisymmetric disturbances provided the fluid rotates very rapidly. The system is shown to be unstable to non-axisymmetric disturbances, and the slow amplifying hydromagnetic wave modes propagate against the basic rotation. The lower and upper bounds of the azimuthal phase speeds of the amplifying waves are determined. A quadrant theorem on the slow waves characteristic of a rapidly rotating fluid is derived. Special attention is given to the effects of compressibility of the fluid. Some results concerning the stability of an incompressible fluid system are obtained as special cases of the present analysis.

Advection within side-by-side liquid micro-cylinders in a cross-flow

Science.gov (United States)

Dong, Qingming; Sau, Amalendu

2017-11-01

The gaseous SO2 entrainment from outer air stream and dispersion in binary and ternary liquid micro-cylinders appearing side-by-side are examined hereby. The separation/attachment regulated non-uniform interfacial momentum exchange creates main stream driven "primary" and shear reversed "secondary" vortices in the liquid cylinders. At separation points, the sense of rotation of the generated "primary-secondary" vortex pair remains inward directed. We define such a vortex pair as the "inflow" type. However, at stagnation or attachment points, the sense of rotation of a "primary-primary" or "secondary-secondary" vortex pair remains outward directed, and such a vortex pair is defined as the "outflow" type. For the coupled water cylinders facing an oncoming stream contaminated by gaseous SO2, its absorption and internal transport are effectively controlled by dominant "inflow" and "outflow" natured dynamics of the said vortex pairs, besides by diffusion. The evolving "inflow" natured "primary-secondary" vortex pairs at separation points actively entrain the outer SO2, whereas the "outflow" natured vortex-pairs oppose SO2 entry through the stagnation regions. Moreover, the blockage induced steady-symmetric, steady-deflected, and flip-flopping air-jets through gaps, for varied gap-ratio (1 ≤ G/R ≤ 4) and Reynolds number (30 ≤ Re ≤ 160), create distinctive impact both on quantitative SO2 absorption (mso2 ') and convective nature of the SO2 transport in upper, lower, and middle cylinders, by virtue of modified strength and size of the inflow and outflow paired vortices. The present study shows that the tiny "secondary vortices" play important roles in SO2 entrainment and in effectively controlling the local absorption rate Rs o2. The sudden acceleration and upward/downward deflection of gap-flows enhanced near-neck advective SO2 entrainment by suitably strengthening the "inflow" natured local vortex dynamics. Conversely, for the reduced size of secondary vortices

Wake flow behaviour behind a smaller cylinder oscillating in the wake of an upstream stationary cylinder

Energy Technology Data Exchange (ETDEWEB)

Gao, Yangyang; Sun, Zhilin [Ocean College, Zhejiang University, Hangzhou 310058 (China); Tan, Danielle S [Maritime Research Centre, Nanyang Technological University, Singapore 639798 (Singapore); Yu, Dingyong [College of Engineering, Ocean University of China, 266100 (China); Tan, Soon Keat, E-mail: yygao@zju.edu.cn [Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 639798 (Singapore)

2014-04-01

The flow patterns around a cylinder oscillating freely in the wake of a larger cylinder upstream were investigated using the particle image velocimetry technique. The upstream cylinder was fixed at both ends while the downstream smaller cylinder was held by springs such that it was free to oscillate in the transverse direction. The flow patterns, amplitudes of oscillation and vortex shedding frequencies were compared with those of a single cylinder. In the presence of the upstream cylinder, the three parameters characterizing the oscillation response of the smaller cylinder—amplitude of oscillation, vortex shedding frequency and Reynolds stresses—were greatly reduced. While their magnitude increased with gap ratio, these three parameters were still smaller than the corresponding magnitudes for a single oscillating cylinder. The peak values of turbulence statistics such as Reynolds shear stress and normal stress behind the oscillating downstream cylinder were similarly reduced, and increased with gap ratios. (paper)

SPACETRAN, Radiation Leakage from Cylinder with ANISN Flux Calculation

International Nuclear Information System (INIS)

Cramer, S.N.; Solomito, M.

1974-01-01

1 - Nature of physical problem solved: SPACETRAN is designed to calculate the energy-dependent total flux or some proportional quantity such as kerma, due to the radiation leakage from the surface of a right-circular cylinder at detector positions located at arbitrary distances from the surface. The assumptions are made that the radiation emerging from the finite cylinder has no spatial dependence and that a vacuum surrounds the cylinder. 2 - Method of solution: There are three versions of the program in the code package. SPACETRAN-I uses the surface angular fluxes calculated by the discrete ordinates SN code ANISN, as input. SPACETRAN-II assumes that the surface angular flux for all energies can be represented as a function (Cos(PHI))**N, where PHI is the angle between surface outward normal and radiation direction, and N is an integer specified by the user. For both versions the energy group structure and the number and location of detectors is arbitrary. The flux (or response function) for a given energy group at some detection point is computed by summing the contributions from each surface area element over the entire surface. The surface area elements are defined by input data. SPACETRAN-III uses surface angular fluxes from DOT-3. SPACETRAN-I handles contributions either from a cylinder 'end' or 'side', so the total contributions must be obtained by adding the results of separate end and side runs. ANISN angular fluxes are specified for discrete directions. In general, the direction between the detector and contributing area will not exactly coincide with one of these discrete directions. In this case, the ANISN angular flux for the 'closest' discrete direction is used to approximate the contribution to the detector. SPACETRAN-II handles contributions from both the side and end of a cylinder in a single run. Since the assumed angular distribution is specified by a continuous function, it is not necessary to perform the angle selection described above. For

Low-frequency variations in the wake of a circular cylinder at Re = 3900

International Nuclear Information System (INIS)

Lehmkuhl, Oriol; Rodríguez, Ivette; Pérez-Segarra, Carlos D; Oliva, Assensi; Borrell, Ricard

2011-01-01

Flow around cylindrical structures is of relevance for many practical applications. Knowledge of flow-related unsteady loading of such structures is crucial for hydro - and aerodynamic control and design. In order to obtain a deeper knowledge of this kind of flow, a DNS have been performed at Re D = 3900 (Re D = U ref D/ν). The instantaneous velocity signals of probes located in the separated shear-layer and in the vortex formation region exhibit the presence of low-frequency variations. The statistical analysis of these signals suggest that low-frequency variations in the vortex formation length, suction base pressure and intermittencies in the shear layer are closely related. It is shown that these variations are the responsible of the large scattering of data obtained in different experimental and numerical results, as well as the U-shape and V-shape stream-wise velocity profiles observed in the very near wake of the cylinder.

Low-frequency variations in the wake of a circular cylinder at Re = 3900

Energy Technology Data Exchange (ETDEWEB)

Lehmkuhl, Oriol; Rodriguez, Ivette; Perez-Segarra, Carlos D; Oliva, Assensi [Heat and Mass Transfer Technological Center, Politechnical University of Catalonia (Spain); Borrell, Ricard, E-mail: cttc@cttc.upc.edu [TermoFluids S.L. (Spain)

2011-12-22

Flow around cylindrical structures is of relevance for many practical applications. Knowledge of flow-related unsteady loading of such structures is crucial for hydro - and aerodynamic control and design. In order to obtain a deeper knowledge of this kind of flow, a DNS have been performed at Re{sub D} = 3900 (Re{sub D} = U{sub ref}D/{nu}). The instantaneous velocity signals of probes located in the separated shear-layer and in the vortex formation region exhibit the presence of low-frequency variations. The statistical analysis of these signals suggest that low-frequency variations in the vortex formation length, suction base pressure and intermittencies in the shear layer are closely related. It is shown that these variations are the responsible of the large scattering of data obtained in different experimental and numerical results, as well as the U-shape and V-shape stream-wise velocity profiles observed in the very near wake of the cylinder.

Nuclear spin circular dichroism

International Nuclear Information System (INIS)

Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia

2014-01-01

Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra

Wiggler as spin rotators for RHIC

International Nuclear Information System (INIS)

Luccio, A.; Conte, M.

1993-01-01

The spin of a polarized particle in a circular accelerator can be rotated with an arrangement of dipoles with field mutually perpendicular and perpendicular to the orbit. To achieve spin rotation, a given field integral value is required. The device must be designed in a way that the particle orbit is distorted as little as possible. It is shown that wigglers with many periods are suitable to achieve spin rotation with minimum orbit distortions. Wigglers are also more compact than more established structures and will use less electric power. Additional advantages include their use for non distructive beam diagnostics. Results are given for the Relativistic Heavy Ion Collider (RHIC) in the polarized proton mode

A study on the annular leakage-flow-induced vibrations. 1st report. Stability for translational and rotational single-degree-of-freedom systems

International Nuclear Information System (INIS)

Li, Dong-Wei; Kaneko, Shigehiko; Hayama, Shinji

1999-01-01

This study reports the stability of annular leakage-flow-induced vibrations. The pressure distribution of fluid between a fixed outer cylinder and a vibrating inner cylinder was obtained in the case of a translationally and rotationally coupled motion of the inner cylinder. The unsteady fluid force acting on the inner cylinder in the case of translational and rotational single-degree-of-freedom vibrations was then expressed in terms proportional to the acceleration, velocity, and displacement. Then the critical flow rate (at which stability was lost) was determined for an annular leakage-flow-induced vibration. Finally, the stability was investigated theoretically. It is known that instability will occur in the case of a divergent passage, but the critical flow rate depends on the passage increment in a limited range: the eccentricity of the passage and the pressure loss factor at the inlet of the passage lower the stability. (author)

Normalized Lift: An Energy Interpretation of the Lift Coefficient Simplifies Comparisons of the Lifting Ability of Rotating and Flapping Surfaces

Science.gov (United States)

Burgers, Phillip; Alexander, David E.

2012-01-01

For a century, researchers have used the standard lift coefficient CL to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½ρv 2, where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders. This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/ρ·S), compared against the total kinetic energy required for generating said lift, ½v2. This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and forward flight, and a hovering dipteran. The maximum standard lift coefficient for a fixed wing without flaps in steady flow is around 1.5, yet for a rotating cylinder it may exceed 9.0, a value that implies that a rotating cylinder generates nearly 6 times the maximum lift of a wing. The maximum normalized lift for a rotating cylinder is 1.5. We suggest that the normalized lift can be used to evaluate propellers, rotors, flapping wings of animals and micro air vehicles, and underwater thrust-generating fins in the same way the lift coefficient is currently used to evaluate fixed wings. PMID:22629326

Normalized lift: an energy interpretation of the lift coefficient simplifies comparisons of the lifting ability of rotating and flapping surfaces.

Directory of Open Access Journals (Sweden)

Phillip Burgers

Full Text Available For a century, researchers have used the standard lift coefficient C(L to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½ρv(2, where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders.This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/ρ·S, compared against the total kinetic energy required for generating said lift, ½v(2. This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and forward flight, and a hovering dipteran.The maximum standard lift coefficient for a fixed wing without flaps in steady flow is around 1.5, yet for a rotating cylinder it may exceed 9.0, a value that implies that a rotating cylinder generates nearly 6 times the maximum lift of a wing. The maximum normalized lift for a rotating cylinder is 1.5. We suggest that the normalized lift can be used to evaluate propellers, rotors, flapping wings of animals and micro air vehicles, and underwater thrust-generating fins in the same way the lift coefficient is currently used to evaluate fixed wings.

Stationary Magnetohydrodynamic Models of Three-Dimensional Rigidly Rotating Magnetized Coronae

International Nuclear Information System (INIS)

Al-Salti, Nasser; Neukirch, Thomas

2009-01-01

Example solutions of a theory for stationary 3D non-potential solutions of the MHD equations (in the co-rotating frame of reference) are presented. As a first step we present solutions for the mathematically simpler case of a massive central cylinder, but the theory can also be applied to spherical bodies. The fundamental equation of the theory is linear and in the cylindrical case it can be solved using standard methods. Possible application is the structure of coronae of (fast) rotating stars.

X-ray tube incorporating a rotating anode with magnetic bearings

International Nuclear Information System (INIS)

1979-01-01

This patent describes an X-ray tube incorporating a rotating anode. The rotor consists of a single, soft-magnetic dish which is fixed on the axis and which seals the magnetic yoke of the stator. Looking in the direction of the axis, one side is equipped with two circular pole surfaces, one at least of which is provided with circular pole-shoes, separated from one another by concentric grooves. (T.P.)

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

International Nuclear Information System (INIS)

Mitri, F. G.

2015-01-01

The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

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.

Magnetic circular Dichroism and Faraday rotation of cesium-argon excimers and cesium dimers

International Nuclear Information System (INIS)

Islam, M.A.

1981-01-01

Magnetic Circular Dichroism (MCD) and Faraday Rotation (FR) of excimer absorption bands in gases are measured to obtain the first direct information about the angular momentum quantum numbers and the angular momentum coupling schemes of excimer molecules. So far, there has been no experimental method to obtain information about the axial angular momentum and the angular momentum coupling schemes of excimer molecules. In this experiment, the MCD and the FR of cesium-argon excimer and cesium dimer absorption bands between 5000 A and 10,000 A are measured for the range of temperature from 116 0 to 355 0 C. Of particular interest is the blue wing of D 2 line in cesium which has been the subject of vigorous investigation. The measured MCD data at the blue wing of D 2 line clearly shows that the assignment of 2 μ/sub 1/2/ to this excited state assuming Hund's case (b) is a poor approximation. By a simple inspection of the MCD data, it is found that the coupling scheme is more nearly Hund's case (c) than Hynd's case (b). Several other new and interesting results are obtained. The blue wing associated with 5D transition in atomic cesium is devoid of MCD and exhibits strong MCD in the red wings. Thus, the assignment of 2 μ/sub 1/2/ and 2 π to the blue and red wings, respectively, assuming Hund's case (a) and (b), is a very good approximation. Again the yellow-green band associated with 7s-6s transition in atomic cesium shows no MCD. It is therefore also a good approximation to assign 2 μ/sub 1/2/ to the upper state assuming Hund's case (b). Much more information can be obtained by a detailed analysis of the MCD data

Spherical null geodesics of rotating Kerr black holes

International Nuclear Information System (INIS)