Finite Cylinder Research Articles

Corrective and new research frontier of dual-phase -lag non-fourier heat conduction in functionally graded cylindrical materials with bi-directional property variations

This study presents a novel and corrective analysis of Dual-Phase-Lag (DPL) non-fourier heat conduction in functionally graded cylindrical materials with bi-directional property variations. For general purposes, the 2-D DPL model was employed and solved in a polar coordinate system for an FGM cylinder whose material properties vary exponentially in the axial and radial directions. The proposed model's analytical and numerical solutions were obtained through the SOV method and implicit FDM with a non-uniform grid. Moreover, the effect of the inhomogeneity parameter in the Fourier, Cattaneo–Vernotte (C–V), and DPL models has been analyzed. The results indicate that the DPL model achieves temperature stability in less time when contrasted with the C–V model. In addition, the reduced inhomogeneity parameters result in quicker attainment of a steady temperature and the induction of higher temperatures. The thermal wave propagation in the DPL model is consistently greater than that in the C–V model. In addition, an increase in time lag for heat flux enhances thermal wave properties (amplitude, wavelength, propagation speed etc.); conversely, an increase in time lag for temperature gradient counteracts wave properties and augments heat release. Nevertheless, the present outcomes offer a straightforward multivariate analytical and numerical solution for a finite cylinder's non-Fourier heat conduction equation under diverse boundary conditions.

Design and characterisation of an open-jet pressure gradient test rig for an aeroacoustic wind tunnel

This paper summarises an approach to generating controllable pressure gradients within an open-jet configuration for aeroacoustics research. A novel open-jet pressure gradient test rig has been designed for the UNSW Anechoic Wind Tunnel with the help of RANS simulations. A range of pressure gradients is created by adjusting the inclination angle of the top plate to change the cross-sectional area along the streamwise direction gradually. The test model mounting point is located on the bottom plate adjacent to partially opened side walls to allow far-field noise measurements. A comprehensive characterisation of flow quality, pressure gradient parameters and acoustic data quality has been carried out using Particle Imaging Velocimetry (PIV), surface pressure taps, and a microphone array. The test rig produces near-uniform pressure gradient flows at the model mounting point, with momentum Reynolds numbers (Reθ) ranging from 3014 to 11853 and Clauser's pressure gradient parameters (β) from -0.24 to 1.66. The pressure gradients generated by this facility are approximately linear, approaching the model mounting point, and the boundary layer profiles compare favourably with those from conventional hard-walled enclosed pressure gradient wind tunnel facilities. Measurements of airfoil trailing-edge noise from this test rig compare well with classical semi-empirical model predictions. Simultaneous acoustic and flow measurements on a square finite wall-mounted cylinder showcase the capability of this facility for coupled acoustic-flow diagnosis.

Controlled flow around a finite square cylinder through suction at the side and free-end leading edge

Controlled flow around a finite square cylinder through suction at the side and free-end leading edge

Modeling the unsteady wake of an impulsively started circular cylinder using refined potential flow theory

Cylindrical structures find usage in many engineering applications including tethered oil drums and engine canisters slung beneath helicopters in flight. The motion of air around such circular cylindrical structures and the helicopter presents interesting phenomena including flow separation, wakes and turbulence. The physics of these are enshrined in the continuity equation and the Navier–Stokes equations. Therefore, their studies are not only important in mathematics and physics, but they are also required for efficient helicopter operations. In practice, reduced-order models of these operations that take in aerodynamics models of the tethered loads are utilized for stability analysis, flight certification and pilot training because of the prohibitive cost of experimentation and computational analyses of these configurations. However, there is a dearth of realistic analytical models of finite cylinder flows because of the Navier–Stokes problem. Classical potential flow theory provides an avenue to develop such models, but the extant gaps in its predictions significantly preclude its usage for engineering applications. Attempting to bridge these gaps, this article introduces refined potential flow theory in which the governing equations and boundary conditions are satisfied. Viscous effects, fluctuations of the mean flow and three-dimensional effects are also incorporated. For characterization, refined potential flow theory is employed on an incompressible flow over an impulsively started circular cylinder for Reynolds numbers and non-dimensional times in the range 30<Re<104 and 0.2 ≤ T ≤ 77, 047 respectively. There is an excellent prediction of 0.209 for the Strouhal number at Re=3,900 . At this transitional Reynolds number, the harmonics of the Strouhal frequency are also captured, and the characteristic irregular fluctuations at sub-Strouhal frequencies are discernible in the velocity spectra. As the flow becomes more turbulent, these become more pronounced at Re=9,500 when the predicted Strouhal number is within 10% of experimental result. In the fully developed stage, spectra analyses of the wake velocity components at some downstream locations also display Kolmogorov's Five-Thirds law of homogeneous isotropic turbulence. The present model can thus aid the development of reduced-order models of helicopter operations that feature tethered cylindrical loads.

Vortex dynamics induced by a finite wall-mounted cylinder with various corner shapes

Vortex dynamics induced by a finite wall-mounted cylinder with various corner shapes

Multidimensional freezing time using a pseudo-one-dimensional method

This study presents a method to calculate the freezing time of multidimensional objects using a pseudo-one-dimensional method. For example, the temperature of a rectangle in (x,y,t) can be simulated from the two-dimensional heat conduction equation to obtain a pseudo-one-dimensional temperature T(x,t), using the space grid Δx=Lx/(n−1) (where n=m) and Δy=ΔxLy/Lx as references. This procedure can be used to calculate the freezing time (tcalc) at a selected point, such as the center of an object. A computer program with a runtime similar to that of a one-dimensional problem has been developed for the proposed model. The freezing times (tcalc) of 212 multidimensional objects (parallelepipeds, rectangles, and finite cylinders) were then compared with the experimental freezing times (texper). The calculations yielded the following parameters for all 212 objects: minimum error Emin=−3.9%, mean error Emean=0.2%, maximum error Emax=5.0%, standard deviation σn−1=1.4%, and mean absolute error Eabs=1.1%. The freezing times (tcalc) of 100 multidimensional objects (parallelepipeds and rectangles) were then compared with the freezing times of computational experiments (computational simulation) obtained from the literature using the finite element method (tcomput). The calculations yielded the following parameters for all 100 objects: Emin=−2.8%, Emean=0.1%, Emax=3.7%, σn−1=1.4%, and Eabs=1.1%.

Characteristics of the flow around finite wall-mounted square cylinders and the mechanism of tonal noise

Motivated by the need to reduce the noise from train pantographs, numerical simulations are carried out for the flow over finite wall-mounted square cylinders with different aspect ratios at a Reynolds number of 1.5×104. Five aspect ratios (height-to-width ratios) are taken into account, namely, 1.4, 4.3, 7.1, 10, and 12.9. The effect of the aspect ratio on the aerodynamic coefficients, the near-wall flow topologies, and the pressure distributions are studied in detail to give insight into the noise generation mechanisms. The pressure rate of change dp/dt on the cylinder surfaces is adopted to evaluate the dipole noise source. It turns out that distributions of dp/dt are closely related to flow evolutions near the free ends and the wall-mounting junctions of cylinders with different aspect ratios. High levels of dp/dt are found close to lateral trailing edges of the cylinder, while the strength grows quickly as the aspect ratio is increased. The far-field noise emitted from these cylinders is predicted using the Ffowcs Williams–Hawkings acoustic analogy and validated with wind tunnel measurements available in the literature. For receivers located in the cross-flow direction, a single acoustic tone near a Strouhal number of 0.1 is observed for cylinders with aspect ratios not greater than seven, while an additional tone at a higher Strouhal number occurs as the aspect ratio is further increased. The underlying mechanism of the tonal noise emitted to the far field is also investigated by combining the noise source localization and dynamic mode decompositions.

Quantum states and static field ionization of a cylindrical confined hydrogen atom: A diffusion Monte Carlo study

AbstractIn this article, the diffusion Monte Carlo (DMC) method is applied to the study of the quantum states of a hydrogen atom confined into a cylindrical potential well. We present an independent reproduction of previous studies based on different methods, in particular the energy eigenvalues for ground and selected excited states and the polarizability of the ground state, both for finite and infinite cylinders. The static field ionization of ground and excited states of the confined atom is discussed, including the determination of the potential energy surface and equilibrium position of the proton. This study provides a further demonstration of the versatility of the DMC method for this and analogous problems.

Gravity profiles interpretation applying a metaheuristic particle optimization algorithm of mineralized bodies resembled by finite elements

The interpretation of gravity anomalies is crucial for identifying subsurface mineralized targets and understanding the density variations between the targets and the surrounding structures. To confirm the presence of ore and mineral targets, simple geometric bodies are often used. One of the commonly used global metaheuristic algorithms for gravity data analysis is the particle optimization algorithm. In this study, we employed this method to determine the parameters of buried bodies that resemble finite vertical cylinders by inferring gravity anomalies profiles (amplitude coefficient, depth to top, depth to bottom, origin, and length of the target representing the difference between two depths). The algorithm utilizes particle movement to identify the best way to reach the global or optimum solution. The algorithm's performance was evaluated on synthetic-examples with and without noise (5 % and 10 % levels) and also verified on a real dataset for mineral exploration from Canada. The results showed that the algorithm's stability and accuracy were not affected by the presence of noise and multi-models. Moreover, the field case results were consistent with the existing geological information, borehole data, and previously published outcomes.

Mathematical modeling of velocity field induced by the vortex

In new technological applications, it is important to use vortex distributions in the area for obtaining large velocity fields. This paper, it was calculated the distribution of the velocity field and distribution of stream function for ideal incompressible fluid, induced by a different system of the finite number of vortex threads: 1) circular vortex lines in a finite cylinder, positioned on its inner, 2) spiral vortex threads, positioned on the inner surface of the finite cylinder or cone, and 3) linear vortex lines in the plane channel, positioned on its boundary. An original method was used to calculate the components of the velocity vectors. Such kind of procedure allows calculating the velocity fields inside the domain depending on the arrangement, the intensity, and the radii of vortex lines. In this paper, we have developed a mathematical model for the process in the element of Hurricane Energy Transformer. This element is a central figure in the so-called RKA (ReaktionsKraftAnlage) used on the cars’ roofs.

Analytical approach for the design of composite linings in deep tunnels considering the blasting damaged zone

Tunneling using the drilling and blasting method induces a blasting damaged zone around the tunnel, which affects the tunnel stability as well as the resulting support design. In this article, an analytical model that represents the whole-process interaction between the sequentially installed composite linings and the surrounding rock in the presence of the blasting damaged zone is proposed. First, assuming the blasting damaged zone to be a finite cylinder with decreased mechanical parameters, four ground forms according to the distribution of plastic zone are categorized and solved. Furthermore, the fictitious pressure concept is adopted to represent the three-dimensional effect of tunnel advancement, and thus, the construction process of the tunnel can be simulated. After that, the evolution patterns of the whole-process interaction between the composite linings and ground are distinguished. The critical distances and tunnel displacements between different forms in various interaction stages are identified and solved. Finally, the analytical solutions for tunnel displacement and structural responses can be obtained, based on the displacement compatibility conditions between composite linings and the ground. The analytical model is validated by numerical simulations through several typical examples, and the applicability in actual tunnel support design is verified by field monitoring results. Comparisons with an existing model and the conventional convergence-confinement method illustrate the inherent nature and advantages of the proposed model in the support system design. It is found that the blasting damage effect is significant on the tunnel responses, which should be considered in the support design. The proposed model provides a convenient feasible approach in determining the stiffness and support time of the composite linings for tunnels using the drilling and blasting method.

Heat transfer and spreading in a finite-thickness cylinder with spatially varying convective cooling along the side wall

Thermal spreading and constriction resistance play an important role in thermal management of a variety of engineering systems, including semiconductor devices. Moreover, thermal contact resistance at interfaces between materials is also governed by spreading and constriction processes. Most of the past literature on theoretical modeling of thermal spreading from a source into a larger body assumes an adiabatic side wall, whereas several recent thermal management problems involve active cooling at the side wall. This work addresses such scenarios by solving the thermal spreading problem in a finite thickness cylinder with spatially varying convective heat transfer on the side wall. An eigenfunction-based series solution for the temperature field is written, the coefficients of which are shown to be governed by a set of coupled algebraic equations. Results are shown to agree well with past work for special cases of the general analysis presented here. Thermal spreading resistance is computed for a number of practical scenarios, including step function, periodic and sinusoidal convective cooling on the side wall. In each case, it is shown that the temperature distribution is consistent with the nature of the spatially varying boundary condition. A key theoretical insight from this work is that under certain conditions, the classical definition of thermal spreading resistance may become negative due to the presence of two heat sinks in the problem. Therefore, analysis based on total resistance may be more appropriate. This work offers a significant generalization of past papers, making it possible to analyze realistic thermal management problems, in which, side wall cooling plays an important role.

Radiative Transfer in Finite Concentric Cylinders by the Zonal Monte Carlo Method

Solutions to two-dimensional radiative heat transfer in a finite concentric cylinder system with a gray absorbing/emitting medium are generated using the zonal Monte Carlo method. The concept of generic exchange factors is introduced. Based on these factors, solutions for finite concentric cylinders with different geometric configurations and optical thicknesses can be generated accurately and efficiently. Numerical data are presented to demonstrate the two-dimensional effects of radiative heat transfer in finite concentric cylinder systems.

Experiments on Cavitation Control around a Cylinder Using Biomimetic Riblets

Experimental investigations were conducted to uncover the impact of cavitation control—through the use of biomimetic riblets on cavitating flows around a circular cylinder. First, the dynamics of cavitation in the flow behind a finite cylinder (without riblets) was unveiled by visualizing the cavitation clouds and measuring the lift force fluctuations acting on the cylinder. Second, in a significant step forward, a comprehensive explanation was provided for the cavitation control methods using two bio-inspired riblet morphologies positioned in different orientations and locations on the cylinder. For the first time, the impacts of these tiny formations on the flow dynamics and the associated cavitation process were scrutinized. This showed that scalloped riblets, with their curved design, induced secondary vortices near their tips and distorted primary streamwise vortices, and that high velocity gradients near the jagged pattern peaks of sawtooth riblets delayed flow separation, which affected cavitation.

Flow Control Over a Finite Wall-Mounted Square Cylinder by Using Multiple Plasma Actuators

Abstract The present study aims to investigate the effectiveness of plasma actuators in controlling the flow around a finite wall-mounted square cylinder (FWMSC) with a longitudinal aspect ratio of 4. The test is conducted in a small-scale closed return-type wind tunnel. The Reynolds number of the experiments, Red, is 500 based on the width of the bluff body and the freestream velocity. The plasma actuators are installed on the top surface and the rear surface of the square cylinder. The induced flow velocities of the plasma actuators are modulated by adjusting the operating voltage and frequency of the high-voltage generator. In this work, particle image velocimetry (PIV) is used to obtain the velocity fields. Furthermore, force calculations are conducted to investigate the effect of using plasma actuators with different driving voltages on the drag force. Our results show that the plasma actuators can successfully suppress flow separation and reduce the turbulent kinetic energy (TKE) in the wake. A correlation between the drag coefficient and the operating voltage of the power generator is also revealed, and the mean drag coefficient is found to decrease with increasing imposing voltage. The plasma actuators can enhance the momentum exchange and the interactive behavior between the shear layer and the flow separation region, resulting in flow reattachment at the free end and shrinkage of the recirculation zone in the near-wake region of the bluff body. Overall, the present study demonstrates the practical effectiveness of using plasma actuators for flow control around FWMSC.

Gauge theories and quantum gravity in a finite interval of time on a compact space manifold

We study gauge theories and quantum gravity diagrammatically in a finite interval of time τ, on a compact space manifold Ω. The initial, final, and boundary conditions are formulated in gauge invariant and general covariant ways by means of purely virtual extensions of the theories, which allow us to “trivialize” the local symmetries and switch to invariant fields (the invariant metric tensor, invariant quark, and gluon fields, etc.). The evolution operator U(tf,ti) is worked out for arbitrary initial and final states, as well as general boundary conditions on ∂Ω. We show that U(tf,ti) is well defined and diagrammatically unitary for every τ=tf−ti&lt;∞. The formulation is extended to include purely virtual particles. In quantum gravity, where the cosmological constant ΛC challenges the definition of an S matrix, the results allow us to prove unitarity at τ&lt;∞. We work out the frequencies and eigenfunctions in some explicit examples, including Yang-Mills theory on the finite cylinder. Published by the American Physical Society 2024

Suppression of flow separation around a finite wall-mounted square cylinder by suction at the side leading edge

We investigate the control of three-dimensional flow separation around a finite wall-mounted square cylinder by applying suction at the side leading edge. Direct numerical simulations are conducted at a Reynolds number of 250, with suction ratios Γ of 0–2 (where Γ is the absolute value of the suction velocity divided by the free stream velocity). The effect of Γ on the aerodynamic forces acting on the cylinder is studied. The results show that suction reduces the aerodynamic forces, with the best control effect for the fluctuating lift coefficient (corresponding to a reduction of over 70%) achieved at Γ = 0.375. As the suction ratio increases, the pressure drag experienced by the square cylinder decreases. Simultaneously, the mean frictional drag force exerted on the square cylinder increases. The optimal mean drag coefficient (corresponding to a reduction of nearly 20%) is achieved at Γ = 1. The effect of the suction ratio on the flow topology in the wake is also investigated. Suction significantly suppresses the flow separation. As the suction ratio increases, the spanwise counter-rotating vortices in the streamwise and transverse directions decreases in size, and the downwash vortex shrinks, and shifts toward the free end of the square cylinder. The far-wake streamwise base vortex disappears when active suction is applied to the side leading edge. However, a new pair of base vortices splits from the original base vortex and persists into the far wake flow field, forming a quadrupole vortex structure with the tip vortex.

Определение направления оси конечного цилиндра со сферическими заглушками по рассеянию звуковой волны

Рассматривается задача идентификации направления оси конечного упругого цилиндра по рассеянному акустическому полю. Предполагается, что цилиндр имеет сферические заглушки, а его материал является однородной упругой средой. Цилиндр погружен в идеальную жидкость. При фиксированном положении центра цилиндра, ориентация его оси определяется по измерениям акустического давления при рассеянии цилиндром плоской гармонической звуковой волны. Идентификация угловых параметров направления оси выполняется на основе минимизации отклонения наблюдаемого давления от расчетного. The problem of identification the direction of the axis of a finite elastic cylinder by scattered acoustic field is considered. The cylinder is assumed to have spherical plugs. Cylinder material is a homogeneous elastic medium. Body is immersed in an ideal liquid. Location of the cylinders center is assumed to be known. The orientation of the cylinder axis is determined by measuring the acoustic pressure when a plane harmonic sound wave is scattered by the cylinder. Identification of the angular parameters of the axis direction is performed based on minimizing the deviation of the observed pressure from the calculated pressure. sound diffraction, finite elastic cylinder, near acoustic field, boundary element method, number theoretic grids, inverse scattering problem.

Unsteady wake interference of unequal-height tandem cylinders mounted in a turbulent boundary layer

The unsteady wake interference of unequal-height tandem finite wall-mounted cylinders (FWMCs) fully submerged in a turbulent boundary layer (TBL) was investigated using time-resolved particle image velocimetry. The aspect ratios of the cylinders were fixed at $h/d = 5.3$ for the upstream cylinder (UC) and $H/d = 7.0$ for the downstream cylinder (DC) to achieve a height ratio of $h/H = 0.75$ , where d is the diameter of the cylinders. The Reynolds number based on the cylinder diameter was $Re = 5540$ and the submergence ratio was $\delta /H = 1.2$ , where $\delta $ is the TBL thickness. Three main flow regimes of tandem FWMCs were examined by varying the centre-to-centre spacing ( $s$ ) between the cylinders: extended-body ( $s/d = 2$ ), reattachment ( $s/d = 4$ ) and co-shedding ( $s/d = 6$ ) regimes. These test cases denoted as SR2, SR4 and SR6, respectively, were compared with a reference isolated cylinder (SC) with an aspect ratio similar to that of the DC. Spatio-temporal analysis of the flow field showed that the gap region of SR2 is characterized by a strong downwash of alternating low- and high-momentum fluid induced by the approach flow that is deflected from the unsheltered portion of the DC. In contrast, the gap region of SR4 and SR6 exhibited both downwash and upwash flow with a saddle point that moves closer to the mid-height of the UC as the spacing ratio increases. The upwash and downwash shear layers were associated with small-scale vortices with Strouhal numbers larger than that of the Kármán vortex shedding in the spanwise shear layers. The wake structure behind the DC was significantly altered compared with the SC due to sheltering effects, and the spacing ratio had a significant impact on the spatio-temporal evolution of the vortices.

ON THE RECONSTRUCTION OF PRESTRESS FIELDS IN A HOLLOW CYLINDER

The present research is devoted to the development of the theoretical foundations of nondestructive acoustic method for identifying inhomogeneous prestress fields in a hollow cylinder, depending on the probing loading type. A linearized model of steady oscillations of an elastic body in the presence of an inhomogeneous prestress field of arbitrary nature is considered in the standard and weak formulations. On the basis of this model, we formulate a problem for a cantilever-clamped prestressed hollow cylinder that performs steady axisymmetric vibrations under three types of probing loading. A corresponding weak formulation of the problem in the cylindrical coordinate system is presented, in which six independent components of the prestress tensor are taken into account. At that, a case of prestress fields obtained by applying some initial mechanical external static load is considered. In the presence and absence of prestresses of various types, amplitude-frequency dependences are analyzed, and resonant and natural frequencies are found in a wide frequency range. Numerical calculations were carried out using the FEM on a non-uniform grid; mesh refinement is carried out in the vicinity of the boundary points, where the type of boundary conditions changes. Based on the numerical solution of an auxiliary set of direct problems, seven types of prestress fields are constructed, differing in the types of initial loading, most often encountered in practice. To assess the possibility of implementing the procedure for reconstructing prestresses of each of the considered types, a sensitivity analysis was additionally performed, which showed that for some prestress types there are frequencies and types of probing loading for which the presence of prestress is practically not manifested. The sensitivity analysis performed made it possible to implement the optimal method of probing loading when solving the inverse coefficient problem. The statement of the new inverse problem on the restoration of arbitrary inhomogeneous prestress fields in the considered finite hollow cylinder is formulated. When restoring the prestress of a given structure, the inverse problem is reduced to finding a set of parameters from an ill-conditioned algebraic system, which was studied with the help of the A.N. Tikhonov regularization method. Additional data for solving the inverse problem was obtained on the basis of probing both via a single load and via combined probing modes. It has been found that it is most effective to use a combined loading mode and use a sufficiently wide frequency range when selecting sounding frequencies. The results of computational experiments on the reconstruction of six components of the prestress tensor are presented and analyzed, and recommendations are proposed for choosing the optimal modes of acoustic sounding.