Semi-circular Cylinder Research Articles

Effect of a splitter plate on flow over a semi-circular cylinder

In this study, two-dimensional unsteady laminar flow over a semi-circular cylinder (SCC) near a splitter plate was investigated numerically. Adding a splitter plate along the wake centreline downstream of the bluff bodies is an efficient passive means of controlling fully developed vortex shedding. Numerical simulations were done for different Reynolds numbers ranging from 100 to 500 in three different gaps ( g: g = 0.0 D to 4.5 D) and two different splitter lengths ( LSP = 1 and 2 D). Results indicate that by increasing the gap ratio, vortex shedding formed in the wake is suppressed and the oscillating amplitude of the lift coefficient decreases. On the other hand, drag, lift, and pressure coefficients representing the flow characteristics also vary as a function of the gap ratio at different Reynolds numbers. Extensive results on streamline patterns, wake characteristics (recirculation length), drag, lift, and pressure coefficients are presented to elucidate the interplay between the gap ratio and the Reynolds number and their influence on drag. Using the splitter plate at the downstream of the SCC causes the stretching of the vortex core and moves the centre of the vortex cores towards the leading edge of the plate. This phenomenon is caused by the reduction of the lift and drag coefficients.

Acoustic radiation torque on an irregularly shaped scatterer in an arbitrary sound field

To eliminate the limitation of the conventional acoustic radiation torque theory, which is only applicable to a disklike scatterer in a plane sound field, a new theory is established to calculate the radiation torque on any irregularly shaped scatterer in any arbitrary sound field. First, with the aid of the conservation law of angular momentum, the acoustic radiation torque is expressed as the angular momentum flux through a spherical surface with the center at the scatterer's centroid. Second, the velocity potential of the scattered field is derived, taking into account the influences of the translational and rotational movements of the scatterer induced by the first order stress of the incident sound field. Finally, a general calculating formula of the acoustic radiation torque is achieved. For a disklike scatterer in a plane sound filed, results from the above formula are well identical with those conventional formulas. By studying the case of a semicircular cylinder scatterer in a standing-wave sound field, it is found that for an irregularly shaped scatterer its rotation velocity is normally nonzero and the radiation torque changes with the spatial attitude.

The effect of gravity on flow past a semi-circular cylinder with a constant pressure wake

The flow past a semi-cylinder with a trailing wake region is considered. In the absence of gravity the only known high Reynolds number solutions have tangential separation from the body and a cusped shape at the back of the wake. This flow can be a simple model for several situations, including the classical approximation of a constant pressure wake and the flow past an object with a region of trapped fluid of different density (or an air cavity) attached on the downstream side. Here we relax the assumption of high flow speeds to examine the effects of gravity. It is shown that there are situations in which a stagnation point can form either on the body or at the tail of the wake and that there is a minimum velocity beneath which a cavity will not form. Non-uniqueness in the parameter space is found in certain cases.

Collision Probabilities in r-θ-z Geometry

An improved version of a numerical method for computing collision probabilities is developed for r-θ-z geometry. It is concluded from the results of numerous test cases that the method can be used to compute collision probabilities in this geometry with an accuracy better than 0.1% in typically <1 s (occasionally, in a few seconds when dealing with difficult cases) on the Athlon 64 3200+ processor. The developed algorithm is implemented into the framework of the collision probability method and tested for one-group criticality problems for finite circular and semicircular cylinders.

Vortex shedding and galloping of open semi-circular and parabolic cylinders in cross-flow

An experimental wind-tunnel study was undertaken to investigate the flow-induced vibration behaviour of open semi-circular and parabolic cylinders in cross-flow. The motivation for the research was to investigate the cause of the fatigue failures of a number of parabolic section rotary mixing blades in a large mixing vessel. Results are presented for force coefficients as a function of angle of incidence of the flow, Strouhal number and amplitude response. It is shown that the parabolic cylinder is subject to large amplitude vortex shedding resonance and, when the elastic axis is sufficiently downstream of the section's centre of gravity, galloping instability.

Prediction of hydrodynamic loading on a mini TLP with free surface effects

This paper describes the extension of a fluid-flow simulations method to capture the free surface evolution around a full-scale Tension Leg Platform (TLP). The focus is on the prediction of the resulting hydrodynamic loading on the various elements of the TLP in turbulent flow conditions and, in particular, on quantifying the effects of the free surface distortion on this loading. The basic method uses finite-volume techniques to discretize the differential equations governing conservation of mass and momentum in three dimensions. The time-averaged forms of the equations are used, and the effects of turbulence are accounted for by using a two-equation, eddy-viscosity closure. The method is extended here via the incorporation of surface-tracking algorithm on a moving grid to predict the free-surface shape. The algorithm was checked against experimental measurements from two benchmark flows: the flow over a submerged semi-circular cylinder and the flow around a floating parabolic hull. Predictions of forces on a model TLP were then obtained both with and without allowing for the deformation of the free surface. The results suggest that the free surface effects on the hydrodynamic loads are small for the values of Froude number typically encountered in offshore engineering practice.

Interferometric measurement of density in nonstationary shock wave reflection flow and comparison with CFD

We present density measurements from the application of interferometry and Fourier transform fringe analysis to the problem of nonstationary shock wave reflection over a semicircular cylinder and compare our experimental measurements to theoretical results from a CFD simulation of the same problem. The experimental results demonstrate our ability to resolve detailed structure in this complex shock wave reflection problem, allowing visualization of multiple shocks in the vicinity of the triple point, plus visualization of the shear layer and an associated vortical structure. Comparison between CFD and experiment show significant discrepancies with experiment producing a double Mach Reflection when CFD predicts a transitional Mach reflection.

반원형실린더 초기후류를 위한 입자와법의 하이브리드 확산기법

Unsteady behavior of the early wake in the viscous flow field past an Impulsively started semicircular cylinder is studied numerically In this paper, we propose the hybrid diffusion scheme to simulate dynamic characteristics of wake such as a fishtail-like flapping and an alternate vortex-shedding more accurately. This diffusion scheme based on particle strength exchange is mixed With the stochastic nature of random walk method Also, the viscous splitting algorithm which calculates convective and diffusion terms successively is applied In order to handle random walk method effectively Consequently, the early behavior of wake due to the breakdown of symmetrical vorticity balance is more practically simulated With the vortex particle methodbr/

Measurement of turbulent flow field at a vertical semicircular cylinder attached to the sidewall of a rectangular channel

Measurement of three-dimensional turbulent flow field at a vertical semicircular cylinder, attached to the sidewall of a rectangular channel, was taken in the laboratory using an Acoustic Doppler Velocimeter (ADV). The distributions of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. The vector plots of flow field at azimuthal and horizontal planes show the presence of a primary vortex upstream of the cylinder. The bed shear stresses in the vicinity of the cylinder are determined from the Reynolds stresses and velocity gradients.

Excitation of trapped water waves by the forced motion of structures

A numerical and analytical investigation is made into the response of a fluid when a two-dimensional structure is forced to move in a prescribed fashion. The structure is constructed in such a way that it supports a trapped mode at one particular frequency. The fluid motion is assumed to be small and the time-domain equations for linear water-wave theory are solved numerically. In addition, the asymptotic behaviour of the resulting velocity potential is determined analytically from the relationship between the time- and frequency-domain solutions. The trapping structure has two distinct surface-piercing elements and the trapped mode exhibits a vertical ‘pumping’ motion of the fluid between the elements. When the structure is forced to oscillate at the trapped-mode frequency an oscillation which grows in time but decays in space is observed. An oscillatory forcing at a frequency different from that of the trapped mode produces bounded oscillations at both the forcing and the trapped-mode frequency. A transient forcing also gives rise to a localized oscillation at the trapped-mode frequency which does not decay with time. Where possible, comparisons are made between the numerical and asymptotic solutions and good agreement is observed. The calculations described above are contrasted with the results from a similar forcing of a pair of semicircular cylinders which intersect the free surface at the same points as the trapping structure. For this second geometry no localized or unbounded oscillations are observed. The trapping structure is then given a sequence of perturbations which transform it into the two semicircular cylinders and the time-domain equations solved for a transient forcing of each structural geometry in the sequence. For small perturbations of the trapping structure, localized oscillations are produced which have a frequency close to that of the trapped mode but with amplitude that decays slowly with time. Estimates of the frequency and the rate of decay of the oscillation are made from the time-domain calculations. These values correspond to the real and imaginary parts of a pole in the complex force coefficient associated with a frequency-domain potential. An estimate of the position of this pole is obtained from calculations of the added mass and damping for the structure and shows good agreement with the time-domain results. Further time-domain calculations for a different trapping structure with more widely spaced elements show a number of interesting features. In particular, a transient forcing leads to persistent oscillations at two distinct frequencies, suggesting that there is either a second trapped mode, or a very lightly damped near-trapped mode. In addition a highly damped pumping mode is identified.

3차원 거동이 고려된 형상기억합금 작동기 부착 복합재 쉘의 변형해석

형상기억합금은 스마트 구조물에서 작동기로 널리 쓰인다. 형상기억합금은 초기변위를 부고 열을 가하게 되면 단위 부피당 큰 회복력과 변위를 발생한다. 형상기억합금의 이론 특성은 인공근육, 작동기, 소음 및 진동감쇠, 형상의 변형 제어 등에 응용될 수 있다. 본 논문에서는 형상기억합금의 3차원 비선형 구성방정식을 이용하여 재료의 거동특성을 해석하고, 형상기억합금이 부착된 스마트구조로 응용될 수 있는 공기 흡입 덕트, 항공기 및 잠수함 동체 등의 구조를 압력이 존재하는 원형 및 복원을 해석하였다. 수치해석결과, 형상기억합금 엑츄에이터가 내압 하에서 작동하자 단면은 변형전의 모습(낮은 응력상태)으로 회복되었다. Shape memory alloys (SMA) are often used in smart structures as active components. Their ability to provide large recovery forces and displacements has been useful in many applications, including devices for artificial muscles, active structural acoustic control, and shape control. Based on the 3-dimensional SMA constitutive equation in this paper, the radial displacement control of externally pressurized circular and semicircular composite cylinders under external pressure with a thin SMA layer bonded on its inner surface or inserted between composite layers in investigated using 3-dimensional finite element analysis. Upon actuation through resistive heating, SMAs start to transform from martensitic into austenitic state, simultaneously recover the prestrain, and thus cause the composite cylinders to go back to their original shapes of the cylinder cross-sections.

559 半円柱の揚抗力特性

559 半円柱の揚抗力特性

Influence of Cross-Sectional Configuration on Karman Vortex Excitation

The influence of cross-sectional configuration on Karman vortex excitation was investigated experimentally using a circular, a semi-circular and a triangular cylinder with an equal height. The cylinders were supported elastically in a wind tunnel for a cross-flow oscillation test, with virtually equal effective mass, spring constant and damping factor. Although the "lock-in" of Karman vortex shedding has been confirmed to occur on all three cylinders when a certain oscillation amplitude and frequency are given, the Karman vortex excitation behavior of the elastically supported systems differs drastically among the three cylinders. The mechanism for the effect of the cross-sectional configuration on the Karman vortex excitation is attributed to the movement of the separation point. In the case of the circular cylinder, the separation point moves forward and backward around the maximum height position synchronizing with the cylinder oscillation, thus the alternating lift force becomes higher. On the other hand, movement of the separation point is limited to the upstream arc for the semicircular cylinder and fixed at the downstream edge for the triangular cylinder.

레벨셋법을 이용한 이동 집중격자 생성법에 대한 연구

Eulerian개념을 사용한 격자계 내 임의의 경계면 주위 점성유동 해석에서, 운동하며 변형하는 경계면 근방 해의 정도를 향상시키기 위해서 격자생성시 경계면으로 격자점들을 집중시켜주는 레벨셋법에 바탕을 둔 격자변형법을 도입하였다. 본 연구에서는 격자점들을 경계면 근방으로 집중되는 정도를 용이하게 조절할 수 있도록 새로운 형태의 모니터함수를 제시하였다. 집중격자계를 사용함으로 얻어지는 향상된 해의 정도의 검증을 위하여 바닥에 고정된 반원 실린더 주위 정상유동에 대하여 가상경계법을 함께 사용하여 해석하였다. 수치계산결과는 물체적합 격자계를 사용해서 얻은 결과와 매우 잘 일치하였으며, 집중격자법을 사용하지 않은 해석결과보다 향상된 결과를 보여주었다. 수치계산의 또 다른 예제로서 다수의 고정된 물체주위 유동해석으로 확장 적용하여 공학적 유용성을 검증하였다. 마지막으로 이동 집중격자계의 생성법의 적용을 위해서 움직이면서 변형을 일으키는 2차원 기포상승문제를 해석하였다. 수치해석결과에서 격자점들은 매시간 기포의 변형에 맞추어 적합하게 집중된 형태를 잘 보여주었으며, 고정된 격자계를 사용한 결과와 잘 일치하였다. In order to improve the accuracy of the solution near the boundary in an analysis of viscous flow around an arbitrary boundary which move and be deformed using an Eulerian concept, a level-set based grid deformation method is introduced to concentrate grid points near the boundary. This paper presents a new monitor function which can easily control the level of the concentration of grid points along the boundary. Computations for steady flow around a semi-circular cylinder mounted on the bottom of the flow domain were carried out to check the improvement of the solution using the adaptive grid system with an immersed boundary method. The present numerical results show a good agreement with the solutions obtained by a body fitted grid system and more accurate solutions than those computed with non-adaptive grid system. For the validation of mechanical usefulness of the present method, an expanded analysis of flow around multi-body fixed in the flow domain was carried out. Finally, the present moving adaptive grid method was applied to a two-dimensional bubble rise problem. The computed results show well adapted grid points around the boundary of the bubble at every time and a good agreement with the result calculated by fixed grid system.

The olfactory tubing maze: a new apparatus for studying learning and memory processes in mice

In order to have an ethologically relevant behavioral task, we developed the olfactory tubing maze to study learning and memory processes in mice. Mice have to make two olfactory-reward associations across three training sessions. The maze is made up of four identical testing chambers connected to each other by semicircular cylinders. After having chosen one of two odors presented on each side of a testing chamber, the mice have to run to the next testing chamber. From one testing chamber to the next, the side for presentating each odor is randomly assigned. The mouse must run through the entire circular maze to make a response at the four testing chambers. A complete session consists of 20 trials made by running five times clockwise through the maze with 4 trials per run. The training and data recording are fully automated by a custom-made software program. Three different experiments were performed. The results indicated that mice can easily make the olfactory discriminative associations in this new apparatus. Analysis of the data suggests that it would be possible using this olfactory tubing maze to study sub-categories of memory similar in some respects to those observed in humans. Consequently, possible effects on learning and memory of classical treatments (i.e. pharmacological or lesions) or genetic modifications in transgenic or gene-targeting mice could be tested.

Application of local grid refinement to vortex motion due to a solitary wave passing over a submerged body

AbstractA numerical method based on the streamfunction–vorticity formulation is applied to simulate the two‐dimensional, transient, viscous flow with a free surface. This method successfully uses the locally refined grid in an inviscid–viscous model to explore the processes of vortex formation due to a solitary wave passing over a submerged bluff body. The two particular bodies considered here are a blunt rectangular block and a semicircular cylinder. Flow visualization to track dyelines is carried out in the laboratory in order to confirm the validity of the numerical results. Numerical results examined by different grid configurations ensure the locally refined grid to be useful in practical application. Flow phenomena, including the vortex motion and wave patterns during non‐linear wave–structure interaction, are also discussed. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Casimir energy of a semi-circular infinite cylinder

The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for the electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions which are the consequence of the edges or corners in the boundaries. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.

一様剪断流中に置かれた半円柱まわりの流れの可視化

The variation of stagnation points and the behavior of vortices in the rear of semicircular cylinder in the uniform shear flow are studied by the visualization technique of the hydrogen bubble method. Especially, in the case of the shear flow, there was not a vortex on the side with the faster speed of the mainstream and it found that the vortex was generating only on the slower speed side.

Particulars of the cross- and spanwise near-wake development of a short Semicircular-section Shell, through the TransitionRe-range (60 ≤Re ≤ 600)

Within the fundamental context of quasi-2D bluff-body near-wake investigation, we analyse the way the initial wake vortices (primary and secondary vortices) form and develop with time behind a short (5.2:1) cylindrical semicircular shell (hollow at the back), after an impulsive start in translation. The study includes the transition regime and non-usual cross-sectional shapes. The structure of the vortices is examined by means of precise visualizations both in the mid-cross and mid-span planes. The particulars induced by the hollow face are deduced from a comparison with the cases of analogous solid cylinders and more particularly with the full semicircular cylinder (Boisaubert et al., 1996; Coutanceau et al., 1998). The crosswise analysis shows that, except some fundamental difference at the separation initiation and some differences in details, a similar development of the Benard-Karman-vortices is observed, thus : - the regime of the occurring structures changes beyond the first phase of development (i.e. t* ≥ 6) when Reynolds number is passing through a critical value Re_c (here 120 ≤ Re_c ≤ 140) - Kelvin-Helmholtz instabilities are detected for Re = 600 in the rolled-up separated shear layers originating from the sharp body-edges. On the contrary, the spanwise analysis reveals that the hollow face plays an important role in the time-development of the induced body-end three-dimensionalities (end-vortices and opposite spanwise currents) and intrinsic three-dimensionalities respectively. Thus, as opposed to solid bodies similarly limited in span, the emergence of clear patterns of secondary Taylor-Gortler-like vortices in the near wake have been experimentally proved for the first time when Re passes beyond the transition value of Re_t a 200. The consequence on the global structure of the flow is deduced.

On the existence of three solutions for a supercritical steady flow of a heavy fluid over obstructions

The paper is devoted to the solution of the steady problem of ideal incompressible fluid flow over a semi-circular cylinder located at the bottom. Calculations showed that the problem has at least three solutions for the Froude number. In the absence of an obstruction at the bottom, the proposed algorithm allows one to construct solitary waves up to limiting waves. The paper reports the most important wave characteristics: circulation, mass, and potential and kinetic energy. Analysis of the calculation results leads to the conclusion that all maximum values of the solitary-wave characteristics are attained before the maximum amplitude and the maximum of the mass does not coincide with the maxima of the total energy and the Froude number.