Cylinder Of Finite Height Research Articles

Radiation from an annular slot antenna symmetrically covered by a dielectric cylinder of finite height

In this paper, the radiation properties of an annular slot antenna of infinitesimal aperture and radius a, cut in an infinite ground plane and covered by a dielectric cylinder of finite height, are investigated analytically. The excitation is assumed to be a circumferentially constant voltage at the slot opposite edges. The unknown electromagnetic field is expressed using the mixed mode spectrum of a radial dielectric waveguide. Then, by enforcing the satisfaction of the appropriate boundary conditions, an integral equation is derived in terms of the unknown electric field distribution Ez. This equation is solved by employing Galerkin's technique and the electromagnetic field distributions are computed in all the regions of the 3-D space. Finally, based on these results, the input impedance and the far field pattern of the antenna are obtained. Numerical results are presented for several cases.

Barotropic flow over finite isolated topography: steady solutions on the beta-plane and the initial value problem

Solutions for inviscid rotating flow over a right circular cylinder of finite height are studied, and comparisons are made to quasi-geostrophic solutions. To study the combined effects of finite topography and the variation of the Coriolis parameter with latitude a steady inviscid model is used. The analytical solution consists of one part which is similar to the quasi-geostrophic solution that is driven by the potential vorticity anomaly over the topography, and another, similar to the solution of potential flow around a cylinder, that is driven by the matching conditions on the edge of the topography. When the characteristic Rossby wave speed is much larger than the background flow velocity, the transport over the topography is enhanced as the streamlines follow lines of constant background potential vorticity. For eastward flow, the Rossby wave drag can be very much larger than that predicted by quasi-geostrophic theory. The combined effects of finite height topography and time-dependence are studied in the inviscid initial value problem on the f-plane using the method of contour dynamics. The method is modified to handle finite topography. When the topography takes up most of the layer depth, a stable oscillation exists with all of the fluid which originates over the topography rotating around the topography. When the Rossby number is order one, a steady trapped vortex solution similar to the one described by Johnson (1978) may be reached.

Vibrations of a pair of elastically supported tall building models in a uniform stream

Experimental investigations were carried out to examine the flow features around a pair of elastically supported square cylinders and the associated flow-excited vibrations. Square cylinders of finite height were placed side by side in parallel to model adjacent tall buildings. The undisturbed uniform cross stream is along the side of the buildings. The experiment was carried vit in a recirculating water channel. The flow field was visualized using hydrogen bubble technique. Time sequential photography was used to quantify the development of the vortex pattern and the vibrational characteristics of the building models.

Vibrations of a pair of elastically supported tall building models in a uniform stream

Experimental investigations were carried out to examine the flow features around a pair of elastically supported square cylinders and the associated flow-excited vibrations. Square cylinders of finite height were placed side by side in parallel to model adjacent tall buildings. The undisturbed uniform cross stream is along the side of the buildings. The experiment was carried vit in a recirculating water channel. The flow field was visualized using hydrogen bubble technique. Time sequential photography was used to quantify the development of the vortex pattern and the vibrational characteristics of the building models.

Pressure and force fluctuations on isolated circular cylinders of finite height in boundary layer flows

Abstract This paper presents spatio-temporal measurements of a fluctuating pressure field acting on isolated roughened cylinders of finite height in simulated turbulent boundary layer flows at subcritical Reynolds numbers. The cylinder surface is roughened by placing discrete roughness elements along the height at four circumferential locations. The resulting surface roughness configuration helps to modify the flow over the cylinder, which leads to the pressure field that exhibits characteristics similar to the transcritical Reynolds numbers. The space-time measurements of the random pressure field allowed computations of the mean and r.m.s. pressure coefficients, power spectral density, spanwise and circumferential correlations, and their eigenfunction expansions. A manifold-pneumatic averaging technique was utilized to evaluate time varying area-averaged loads at various levels along the model height. The spatially averaged measurements of the pressure field over the roughened cylinder facilitated the estimation of local and mode-generalized alongwind and acrosswind aerodynamic force coefficients, their spectral descriptions and multi-level force correlations. An increase in the turbulence level influences the fluctuating pressure field through modifications which take place in the structure of the boundary layer over the cylinder and the structure of the separated shear layers.

Time-domain farfield scattering of plane acoustic waves by a penetrable object in the Born approximation

The low-contrast or (first-order) Born approximation is applied to the time-domain scattering of a plane acoustic wave by a penetrable object of bounded extent embedded in a homogeneous fluid. Closed-form analytic expressions are obtained for the spherical-wave farfield scattering amplitude related to homogeneous objects of the following shapes: an ellipsoid, an elliptic cone of finite height, an elliptic cylinder of finite height, and a tetrahedron. Relaxation effects are included. The results are, amongst others, useful as test cases for time-domain inverse-scattering algorithms.

Time domain Born approximation to the far‐field scattering of plane electromagnetic waves by a penetrable object

The low‐contrast or (first‐order) Born approximation is applied to the time domain scattering of a plane electromagnetic wave by a penetrable object of bounded extent, embedded in an isotropic and homogeneous medium. Closed‐form analytic expressions are obtained for the spherical wave far‐field scattering amplitude related to homogeneous objects of the following shapes: an ellipsoid, an elliptic cone of finite height, an elliptic cylinder of finite height, and a tetrahedron. Relaxation effects and anisotropy of the scattering object are included. The results are, among others, useful as test cases for time domain inverse scattering algorithms.

Time-domain far-field scattering of plane scalar waves in the Born approximation

The low-contrast or (first-order) Born approximation is applied to the time-domain scattering of a plane scalar wave by an object of bounded extent present in a homogeneous embedding. Closed-form analytic expressions are obtained for the spherical-wave far-field scattering amplitude related to homogeneous objects of the following shapes: an ellipsoid, an elliptic cylinder of finite height, and a tetrahedron. Dispersion is included. Apart from their intrinsic interest, the results may be useful as test cases for time-domain inverse-scattering algorithms.

Interior and exterior solutions for boundary value problems in composite elastic and viscous media

We present the solutions for the boundary value problems of elasticity when a homogeneous and isotropic solid of an arbitrary shape is embedded in an infinite homogeneous isotropic medium of different properties. The solutions are obtained inside both the guest and host media by an integral equation technique. The boundaries considered are an oblong, a triaxial ellipsoid and an elliptic cyclinder of a finite height and their limiting configurations in two and three dimensions. The exact interior and exterior solutions for an ellipsoidal inclusion and its limiting configurations are presented when the infinite host medium is subjected to a uniform strain. In the case of an oblong or an elliptic cylinder of finite height the solutions are approximate. Next, we present the formula for the energy stored in the infinite host medium due to the presence of an arbitrary symmetrical void in it. This formula is evaluated for the special case of a spherical void. Finally, we analyse the change of shape of a viscous incompressible ellipsoidal region embedded in a slowly deforming fluid of a different viscosity. Two interesting limiting cases are discussed in detail.

Flow around a Finite Circular Cylinder on a Flat Plate : Cylinder height greater than turbulent boundary layer thickness

Some flow visualization experiments and measurements of surface pressure, Strouhal number, etc. around a finite circular cylinder on a flat plate have been performed in order to study the effect of a three-dimensional flow. The slenderness parameter of the cylinder is in a range of l/d=1∼8, where the slenderness parameter influences remarkably the flow behavior. From an analysis of mean and periodical motion in the near-wake flow, the following results are obtained. (1) The separation velocity at the side wall is lower than that of a two-dimensional cylinder, and this decreases the drag coefficients. (2) A pair of trailing vortices exist right below the free-end. (3) Down-wash flow and the trailing vortex near the free-end dominate the behavior of Karman vortex shedding. Finally, based on these results, the flow models around the finite height cylinder are presented.

The integral-transform method for solving neutron transport problems with general anisotropic scattering in a cylinder of finite height

In this paper, we present a mathematical technique for solving the integral transport equation for the criticality of a homogeneous cylinder of finite height. The purpose of the present paper is two-fold : firstly, to show that our earlier formalism can be generalized to any order of anisotropy, and secondly to generate the numerical results, which could serve as benchmarks when scattering is linearly anisotropic. We expand the scattering function in spherical harmonics to retain the Lth order of anisotropy. Thereafter, we write the integral transport equations for the Fourier-transformed spherical harmonic moments of the angular flux. In conformity with the integral-transform method for multidimensional geometry, the kernels of these integral equations are represented in their respective factorized form, which consists of a series of products of suitable spherical Bessel functions. The Fourier-transformed spherical harmonic moments are also represented in their separable form by expanding them in a series of products of spherical Bessel functions, commensurate with the symmetry of finite cylindrical geometry. The criticality problem for the cylinder of finite height is then posed as a matrix eigen value problem whose eigen vector is composed of the expansion coefficients mentioned above. The general matrix element is expressed as a product of certain integrals of Bessel functions, which can be evaluated by recursion relations derived in this paper. Finally, a comparison between the present benchmark results and S N results ( twotran) in ( r–z) goemetry is presented when scattering is linearly anisotropic.

Interference Between Two Circular Cylinders of Finite Height Vertically Immersed in a Turbulent Boundary Layer

Measurements were made of the circumferential pressure distributions around two cylinders of finite height h and diameter d, spaced a distance s apart and vertically immersed in a turbulent boundary layer. The angle of attack φ and the dimensionless spacing s/d were varied. Drag and lift characteristics of both cylinders were classified into three regions divided by two zero-lift lines, namely 0 ≲ φ ≲ 30 deg, 30 ≲ φ ≲ 120 deg, and 120 ≲ φ ≲ 180 deg, in which interference between the two cylinders was found to be almost negligible for s/d ≳ 4.0, except for an influence in the wake region of the upstream cylinder.

Flow around Circular Cylinders of Finite Height Placed Vertically in Turbulent Boundary Layers

An experimental investigation is carried out on a flow around a circular cylinder vertically mounted on a smooth plane wall along which a turbulent boundary layer is fully developed. Pressure drag of the cylinder is correlated with the height h, the diameter d of the cylinder and the characteristics of the boundary layer. The pressure drag coefficient CD is found to be expressed in the form CD=a(h/δ)b, where δ is the thickness of the boundary layer and the values of a and b are dependent on h/δ. when h/δ&lsin; 1. 1, a and b are linear functions of d/δ, while they are constant in the range h/δ> 1. 1.

Aerodynamics of two parallel circular cylinders of finite height at simulated high Reynolds numbers

The interference of flow between two circular cylinders in some critical arrangement may lead to two different flow patterns which intermittently change over producing different aerodynamic forces. Three such critical arrangements have been found for two cylinders of infinite aspect ratio. The free-end of cylindrical structures of finite height inevitably introduces a strong three-dimensional flow which may or may not suppress the bistable nature of the interference at critical spacings. The simultaneous pressure distribution measurements made on both cylinders at various levels from the ground revealed that the bistable biased flow in the side-by-side arrangement is still a prominent feature for the cylinders of finite height. The intermittent blocking of the intense gap flow for some staggered arrangements was observed to continue unabated for the finite cylinders.

Flow Around a Circular Cylinder of Finite Height Placed Vertically in Turbulent Boundary Layer

Flow Around a Circular Cylinder of Finite Height Placed Vertically in Turbulent Boundary Layer

Natural Convection of a Heat-Generating Fluid Within Closed Vertical Cylinders and Spheres

Steady natural convective flow fields were numerically and experimentally characterized for 0.7 Prandtl number fluids having constant, uniformly distributed, internal heat sources. The bounding isothermal walls containing the fluid were considered to be either a sphere or a cylinder of finite height. An instrumented cylinder containing radioactive tritium gas was used to demonstrate experimental and analytical agreement for local temperatures over a range of Grashof numbers. For the spherical geometry, a generalized correlation was obtained for the surface-averaged Nusselt number as a function of a modified Grashof number.