Section Of Cylinder Research Articles

The interaction between flow-induced vibration mechanisms of a square cylinder with varying angles of attack

AbstractThis study examines the influence of angle of attack of a square section cylinder on the cylinder’s flow-induced vibration, where the direction of the vibration is transverse to the oncoming flow. Our experiments, which traversed the velocity–angle of attack parameter space in considerable breadth and depth, show that a low-mass ratio body can undergo combinations of both vortex-induced vibration and galloping. When the body has an angle of attack that makes it symmetric to the flow, such as when it assumes the square or diamond orientation, the two mechanisms remain independent. However, when symmetry is lost we find a mixed mode response with a new branch of vortex-induced oscillations that exceeds the amplitudes resulting from the two phenomena independently. The oscillations of this higher branch have amplitudes larger than the ‘upper branch’ of vortex-induced vibrations and at half the frequency. For velocities above this resonant region, the frequency splits into two diverging branches. Analysis of the amplitude response reveals that the transition between galloping and vortex-induced vibrations occurs over a narrow range of angle of incidence. Despite the rich set of states found in the parameter space the vortex shedding modes remain very similar to those found previously in vortex-induced vibration.

Evaluating Wind Loads on Bridge Decks Using Velocity Fields

The wind loads including forces and moments on bridge decks are evaluated in the current study using the velocity fields and their derivatives. Based on the conservation of momentum and momentum moment, the integral over the control volume is converted to the surface integral over the boundary of the control volume using the divergence theorem. The wind forces and moments can be calculated based on the obtained velocity fields and their derivatives around bridge decks, and the pressure terms in the equations are canceled out. Velocity fields are obtained from computational fluid dynamics (CFD) simulations and particle image velocimetry (PIV) wind tunnel experiments. Results from different turbulence models are compared with each other and wind tunnel experimental results in the literature. The calculated wind loads from numerical integrations of velocity fields from PIV experiments or CFD numerical simulations are compared with the results from a direct integration of the CFD-simulated surface pressure and the results from force-balance measurements in the wind tunnel. The results from several cases with different sizes of control volumes and space resolutions for both the square cylinder section and the twin-box girder section are discussed.

Circumferential stiffness tailoring of general cross section cylinders for maximum buckling load with strength constraints

Stiffness tailoring of laminated composite structures using steered fibre tows is a design method that maximally uses the directional properties of composite materials. Cylindrical structures usually have circular cross sections while some application, geometric or aerodynamic requirements can necessitate other cross sections, e.g. elliptical. Circumferential tailoring can increase the buckling load of thin cylinders by compensating for non-uniform sectional loading such as bending and/or varying radius of curvature in general cylinders. Here, strength constraints are considered in maximum buckling load design, to ensure that the failure load is greater than the buckling load. A two-step optimisation framework is used to separate the theoretical and manufacturing issues in design. A computationally cheap semi-analytical finite difference method is used to solve the linear static and buckling problems. Conservative failure envelopes based on Tsai-Wu failure criterion are used for strength evaluation. To avoid repetitive analyses, successive convex approximation method is used. For demonstration, circumferential tailoring framework is applied to a circular cylinder under bending and an elliptical cylinder under axial compression. The improvements in buckling capacity of variable over constant stiffness designs are shown and verified using nonlinear buckling analysis in the commercial FEM software AbaqusTM, and the mechanisms of improvements are investigated.

Failure Analysis of High Density Polyethylene Butt Weld Joint

This article discusses a detailed failure analysis conducted on high density polyethylene which acts as the liner of composite compresses natural gas cylinder. Leakage from the cylinder was observed after about 2000 cycles of hydrostatic pressure testing at 250 bars. Visual inspection revealed that the leakage occurred from the circumferential fusion joint between the cylinder and dome section. The cylinder and dome sections were produced from different techniques and joined together by using a heated tool butt welding process conducted by a local manufacturer. The joined components work as an integral part. The investigation was carried out using various techniques including mechanical, thermal and metallurgical examination. Fractography of the failed joint surface showed stepwise marks typical of a fatigue failure. Mechanical testing results showed that the strength of dome section was significantly lower than that of the cylinder section. Moreover, both the tensile and fatigue strength of joint was also almost half that of the cylinder. The fracture surface of the broken welded joint showed brittle failure. The melting points of both the cylinder and the dome sections were found almost same by differential scanning calorimeter but large difference was found between the melt point indexes of both sections. The results suggested that the failure was actually a stress cracking via a process of slow crack growth, which occurred due to use of a dome material having inferior properties and very high melt flow index. These properties inhibited proper fusion and resulted in a poor weld joint. Consequently, the weld joint of lower strength eventually failed in macroscopically brittle manner upon cyclic loading.

Optical cloaking of cylindrical objects by using covers made of core–shell nanoparticles

In this Letter, we propose an engineered design of optical cloaks based on the scattering cancellation technique and intended to reduce the observability of cylindrical objects. The cover, consisting of a periodic arrangement of core-shell nanospheres, is designed in such a way to exhibit near-zero values of the real part of the homogenized effective permittivity at optical frequencies. Full-wave numerical simulations, considering the measured data of the dielectric function of the plasmonic material composing the shell, show that the cloak is able to reduce by about 6 dB the scattering cross section of a finite-length cylinder at around 740 THz with a -3 dB fractional bandwidth of about 7%. We show also that this result is not significantly affected by the perturbation of the periodic alignment of the core-shell nanospheres, due to possible fabrication issues or to an amorphous arrangement.

Application of a new cylindrical element formulation in finite element structural analysis of FGM hollow cylinders

A finite element formulation is derived for the structural analysis of functionally graded hollow cylinders. The power-law distribution model is used for the composition of the constituent material in the thickness direction. According to property variation in FG cylinders, it is difficult to analyze them using the conventional element formulation. In order to facilitate the process of modeling and analyzing the FG cylinders, the finite element formulation is based on a newly designed cylindrical element. The new cylindrical element allows for property variations along the thickness, which results in considerable reduction of the required elements and eliminates the need to mesh the cross section of the FG cylinder. In this study static as well as modal analysis of FG cylinders are performed and the deformations and natural frequencies are compared with those obtained from conventional elements and previous studies. The results indicate high accuracy and good agreement with previous studies and conventional FEM.

Experiments on Preparation of Cutting Tool Edge Using Abrasive Water Jet

Preparation of cutting tool edge using micro abrasive water jet is proposed in this paper. A specific designed water jet machine tool with four axes was developed. Also a specially designed abrasive nozzle assembly for preparation of cutting tool edge has designed. The inside diameter of orifice is Ø125μm. The abrasive nozzle has three sections, i.e. the contraction section, the cylinder section and the diffusion section. The diffusion section has a quasi rectangular profile. Experiments on preparation of coated inserts of cutting tool using micro abrasive water jet have been carried out. The silicon carbide solid abrasive with 400 meshes was used during the experiment.The results show that the sharp edge was rounded by micro abrasive water jet. A honed edge with very small radius exists and irregular zigzag edge was disappeared after preparation. Experiments also show that the linear waviness on the surface was eliminated completely by preparation process. The surface roughness of the coated inserts increased to Ra 0.526μm from Ra 0.025μm after preparation. It demonstrates that the tool edge strength could be enhanced and the micro defects could be eliminated during this course. It proved that preparation of cutting tool edge by micro abrasive water jet is feasible and practical. Because of effective, efficient, environmental friendly and higher quality compared with other preparation method, it has promising application in the field of cutting tool manufacturing.

Flow patterns and vortex shedding behavior behind a square cylinder

The flow structures, wake-flow characteristics and drag coefficients of a square cylinder at various Reynolds numbers ( Re) and incidence angles ( θ) were experimentally studied in an open-loop wind tunnel. The cross section of square cylinder is characterized by the aspect ratio ( AR) and blockage ratio ( BR) of 25% and 4%, respectively. The Reynolds number is changed from 4000 to 36,000 and the incidence angle is adjusted from 0° to 45°. The flow patterns near/behind the square cylinder were determined using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow-topology method was applied to analyze the flow patterns by calculating the separatrices, alleyways and critical points. Experimental results showed that the flow structures around the square cylinder exhibit three modes—leading-edge separation, separation bubble and attached flow. The surface-pressure profile, drag coefficient ( C D ), lift coefficient ( C L ) and vortex shedding frequency were detected/calculated using a pressure transducer and hot-wire anemometer. The lift coefficient did not significantly vary with Re. The minimum C D occurs at θ=12°, whereas the minimum C L occurs at θ=13°. The minimum projected-Strouhal-number ( St d ) occurs at θ=0° while the maximum St d occurs at θ=15°.

Finite Element Simulation and Experimental Study of the Effect of Cone Parameter on Thickness Distribution in Hydroforming of Conical-Cylindrical Cups

Forming conical parts is one of the complex and difficult fields in sheet metal forming processes; because of the low contact area of the sheet with the punch in the initial stages of forming, too much tension is applied to the sheet causing burst occurrence. Furthermore, since the major part of the sheet surface between the blank holder and punch tip is free, wrinkles appear on the wall of the drawn parts. Therefore, these parts are normally formed in the industry by spinning, explosive forming or multi-stage deep drawing processes. In this paper, the parameters in the process of hydroforming conical parts along with using finite element simulation and experimental procedures have been studied. The punch radiuses parameters (the punch tip radius and the radius between the conical and cylinder section and their effects on the bursting and thickness distribution were investigated.

On nonlinear stability of linear pinch

Nonlinear stability of cylindrical configurations with free boundaries is studied for electro-conducting fluids. First, the initial boundary value problem is correctly set for the full system governing flows of incompressible, electrically conducting fluids in Ω t with unknown free surface. Notice that when the domain exterior to the fluid is a dielectric or the vacuum, also the electromagnetic field in becomes an unknown parameter of the problem. Second a nonlinear stability criterion for the rest state of an electro-conducting, incompressible fluid confined in a section of a right cylinder with lateral free boundary in the vacuum is proposed. This criterion proposes an alternative definition of perturbation, and is deeply relied to the unknown motion of the boundary. Third, if the fluid has non-significant magnetic susceptibility, in the presence of not too large surface currents, for large initial data, nonlinear stability is proved in a suitable class of global regular solutions. Kinematic viscosity, magnetic diffusivity, surface tension may be only non-negative in the absence of surface currents.

Nanowire charging in collisionless plasma

We calculate the collision cross section of a charged finite cylinder (nanowire) with a beam of ions and electrons in collisionless plasma. We find that, while the shape and area of the cross section has complex dependence on the charge and orientation of the nanowire relative to the charged beam, its orientational average has a remarkably simple form: for attractive interactions, it is a linear function of the electrostatic ratio qjqpe2/4πϵ0L0kT, where qje is the charge of the ions/electrons, qpe is the charge on the cylinder, L0 is the half-length of the nanowire, T is the temperature of the charged species, and ϵ0 is the permittivity of free space. This linearity persists into the repulsive regime up until the cross sectional area is reduced to about 5% of its value for neutral collisions. We calculate the corresponding charging currents and show that the charging behavior of the nanowire in Maxwellian plasma is described by an equivalent sphere whose radius depends only on the aspect ratio of the nanowire. For small aspect ratios, the equivalent sphere has the same surface area as the nanowire.

Adaptive sparse grid method for RCS estimation of object with uncertain shape

Presented is an adaptive sparse grid method to efficiently estimate the radar cross section (RCS) of a 2D cylinder with uncertain holes, as well as uncertain locations, sizes and number of the holes. This model has been applied extensively in microwave engineering, e.g. frequency selective surface (FSS). Stochastic collocation method is employed to solve the resulting stochastic differential equation. The Gauss-Patterson formula is used in the sparse grid method. The adaptive sparse grid method is based on Richardson extrapolation. Numerical results show the proposed method works very well.

Influence of corner radius on the near wake structure of a transversely oscillating square cylinder

The near wake flow field features of transversely oscillating square section cylinders with different corner radii were studied in an attempt to assess the influence of corner radius. The investigation was performed by using particle image velocimetry (PIV) technique in a water channel with a turbulence intensity of 6.5%. Five models were studied with r/B=0, 0.1, 0.2, 0.3 and 0.5 (r is the corner radius and B is the characteristic dimension of the body), and the body oscillation was limited to lock-in condition (at fe/fo=1.0; fe is the excitation frequency and fo is the vortex shedding frequency from a stationary cylinder at the same Re). The corner radius was found to significantly influence the flow features around the bodies. Except for r/B=0.5, for all the other cases of r/B ratios, cycle-to cycle variation in the mode of vortex shedding was observed in the case of oscillating cylinders inducing highly non-linear wake characteristics. Apart from variation in the shedding mode, changes in shedding cycle timing were also observed for sharp and rounded square cylinders. The hgher the r/B ratio, shedding in the near wake was found to be more uniform (lesser variation in shedding cycle timings). Another admissible shedding mechanism is newly identified to operate in the near wake of oscillating cylinders now being called as the ‘passive shedding’ mechanism. Results indicate that increasing the corner radius suppresses the possible instabilities of the cylinder.

Modeling of an Elastomeric Friction Damper

Abstract Frictional resistance of a hollow rubber cylinder steadily sliding inside a rigid sleeve has been studied theoretically and reported here. This is inspired by a new class of elastomeric friction damper consisting of an unbonded rubber cylinder, axially compressed and radially expanding to contact an outer rigid sleeve and generate friction. By considering the force equilibrium of each thin section of the rubber cylinder and adapting the principle of superposition, the tri-bological problem was decomposed into three fundamental sub-problems, which were solved consecutively. The results shed lights on the functional effects of various design parameters such as part dimensions, friction coefficient, and Young's modulus on the total friction force. Finite element analyses were also performed, and the results were compared with the closed-form solutions.

A Model To Predict the Concentration of Dispersed Solid Particles in an Aqueous Medium Confined inside Horizontal Cylindrical Channels

The deposition of solid particles in cylindrical channels has received considerable attention, because of its direct application in industry. However, an adequate mathematical expression that studies the separation and suspension of dispersed particles present in horizontal cylindrical channels is still missing. In this paper, we developed and solved a time-dependent, two-dimensional convective-dispersive model that simulates the deposition and suspension of dispersed particles immersed in a fluid medium inside the cross section of a horizontal cylindrical channel in a stagnant situation. The results of the modeling are compared with a series of experiments that permit one to know the concentration of the particles in different points in the cross section of a horizontal cylinder. These experiments were performed using particles in the micrometer range dispersed in an aqueous medium. The conditions that permit to control the suspension and deposition of the particles inside a liquid medium with cylindrical geometry are unveiled by the presented model.

Fundamentals of rotating detonations

A rotating detonation propagating at nearly Chapman–Jouguet velocity is numerically stabilized on a two-dimensional simple chemistry flow model. Under purely axial injection of a combustible mixture from the head end of a toroidal section of coaxial cylinders, the rotating detonation is proven to give no average angular momentum at any cross section, giving an axial flow. The detonation wavelet connected with an oblique shock wave ensuing to the downstream has a feature of unconfined detonation, causing a deficit in its propagation velocity. Due to Kelvin–Helmholtz instability existing on the interface of an injected combustible, unburnt gas pockets are formed to enter the junction between the detonation and oblique shock waves, generating strong explosions propagating to both directions. Calculated specific impulse is as high as 4,700 s.

Evaluation of the streaming potential effect of piping phenomena using a finite cylinder model

Piping phenomena into the upstream face of an earth dam can be approximated by a finite cylinder model. A formula of the streaming potential (SP) effect of such a model was developed by integrating an equation of an infinite cylinder section. Numerical modelling allows the conclusion that the oblong SP field shape of a model is only for relatively long and shallow piping models. The SP field shape of a model can actually be circular below a certain ratio value between the depth and length of the model. The resulting SP field of a finite cylinder is symmetrical with respect to its middle point, which allows, in some cases, reaching conclusions about piping phenomena outside the measured area. This finite cylinder formula needs smaller values of moments of polarisation to generate SP data almost identical to the SP magnitudes obtained from the expression of an infinite cylinder section. A random component was added to the SP effect of several computed models. Relatively short and deep piping phenomena can pass unnoticed, especially for a low signal-to-noise ratio. However, detection of anomalous patterns can be improved if the measured data are pre-processed according to a “studentized” deviate concept, which is then subjected to a statistical test based on the Chebyshev inequality. A field example of an SP piping process was detected at the upstream face of an earth dam. Its existence was also confirmed by a geoelectrical survey.

Safety analysis on a vibrating prismatic body: A data-mining approach

In this paper, the flow-induced oscillation of a prismatic body, viz., a square section cylinder (test cylinder) under interference conditions is analysed considering it as representing a typical building structure. The analysis is carried out using a data-mining tool called ‘Decision Tree’ mainly in view of assessing the safety of the structure (test cylinder) with respect to the vibratory amplitude. To achieve this aim, wind tunnel studies have been conducted on the vibratory response of the test cylinder when it is vibrating in the vicinity of another square cylinder (interfering cylinder) which is placed at various locations relative to the test cylinder. The amplitude data thus obtained is suitably classified to carry out the safety analysis. All the data gathered pertains to at a single value of reduced velocity (10.0). Experiments have been carried out for various size ratios ( b/ B) of the test cylinder (upstream structure) and the interfering cylinder with values of 0.5, 1.0, 1.5 and 2.0. The results indicate that, for certain combinations of the parameters – relative position ( L/ B, T/ B) and size ratio ( b/ B), the upstream structure could vibrate with high amplitudes making the structural environment ‘critical’ (unsafe). In practical situations (such as in the case of tall buildings), the critical combinations of these parameters could be identified and eliminated for ensuring structural safety. Parametric combinations ensuring safe structural condition are also identified. Decision Tree also brings out the order of importance of various parameters influencing the interference excitation of the structure (test cylinder); L/ B is shown to be the most influencing parameter. The results also show that, for L/ B > 3.0, there is a higher possibility for the structure to become unsafe when compared to the conditions at L/ B ⩽ 3.0.

Two-dimensional scattering of a plane wave from a periodic array of dielectric cylinders with arbitrary shape

A two-dimensional scattering of a plane wave from a periodic array of dielectric cylinders with arbitrary shape using the multigrid-moment method is examined. The scattered field is expressed in terms of the integral form by an infinite summation of the surface integral over the cross section of the reference cylinder. The integral form is converted into the matrix equation by using the moment method. The integration in the elements of the matrix equation is evaluated by the lattice-sums technique to obtain a precise solution. The multigrid method is applied to the matrix equation to improve the CPU time. The CPU time and the residual norm are examined numerically for a given number of iterations and cycle indices. Then the effects of shape and material of the periodic structure on the power reflection coefficient of the fundamental Floquet mode are shown. In addition, the results indicate the effect of changing the relative permittivity of the dielectric coated body and the reflection coefficient.

Solutions to electromagnetic compatibility problems using artificial neural networks representation of vector finite element method

The solutions to electromagnetic compatibility problems are given by combining vector finite element method (VFEM) with neural network (NN). Two methods for this combination are presented. Solution results compare well with VFEM and analytical solutions. The first method (Method 1) eliminates the need to store the memory exhaustive global matrix of VFEM. This is possible with NN since back propagation needs the estimated vector in order to compare with the right side vector. The second method (Method 2) stores the VFEM global matrix in a compact form using the sparsity and symmetry of the global matrix and then uses the stored matrix elements as the neuron's weights for the NN architecture. Further, preconditioning techniques are used to accelerate the convergence of the training algorithm. To demonstrate the applicability and usefulness of the methods, various structures are solved including crosstalk on printed circuit board, radar cross section of lossy and lossless cylinders with apertures and penetrated fields inside these cylinders.