Convex Cylinder Research Articles

Parametric analysis on throttling elements of conical throttling valve for hydrogen decompression in hydrogen fuel cell vehicles

As the most common component of the pressure management system in hydrogen fuel cell vehicle (HFCV), the structure of conical throttling valve affects the hydrogen decompression performance significantly, which plays an important role in the safe and stable application of hydrogen. In this paper, parametric analysis on throttling elements of conical throttling valve for hydrogen decompression is presented. The hydrogen decompression and flow model is built based on the real gas model. The velocity, pressure, temperature and turbulent kinetic energy are monitored for reflecting the hydrogen flow characteristics. The influence of the cone angle and the pressure difference between inlet and outlet on the hydrogen decompression performance is studied. The results are shown that cone angle and pressure difference significantly affect flow patterns and flow characteristics in the flow region near the cone surface of valve core. There is stronger turbulent flow along the cone surface under the smaller cone angle and higher pressure difference. When the cone angle is below 45°, the flow pattern flowing out along the cone surface transforms from free jet to parallel flow along the cylindrical surface. The multiple high-velocity regions are generated behind the narrow throttling gap under large pressure difference. With the decrease of pressure difference, the position of maximum velocity gradually moves closer to the flow region of narrow throttling gap. The optimizing structure with a convex cylinder has a positive effect on improving the flow patterns and hydrogen decompression performance. The stability of decompression can be achieved within a short distance by the optimization structure of the convex cylinder. This study can provide a reference for the design of conical throttling valves for hydrogen decompression in hydrogen fuel cell vehicles.

Surface tension force on a partially submerged horizontal concave cylinder

A horizontal cylinder with a concave cross-section partially submerged in a liquid at a given position may permit multiple menisci around itself. The number and stabilities of the menisci are analysed, and how the menisci change during the processes of gradually hoisting and lowering the cylinder is explained by bifurcation theory. The restoring force on the concave cylinder and the rebounding potential energy (defined as the work done by the restoring force during the whole hoisting process to represent the potential rebounding capacity of a cylinder on water) are also investigated. The results show that, when the radius of the concave arc is smaller than the critical value, the concave cylinder at a given position permits multiple possible menisci. The equilibria form fold bifurcations with the position of the cylinder as the bifurcation parameter, and two successive fold bifurcations can form a one-fold hysteresis loop. The force–distance curve representing the relation between the restoring force and the position of the cylinder also has corresponding hysteresis loops, where the restoring force will jump (i.e. change discontinuously) at the bifurcation points. In contrast to a convex cylinder, a concave cylinder can have different values of the restoring force at the same height because of multiple menisci, and the values depend on whether it is hoisted or lowered. Under the condition of a fixed cross-sectional area, the optimal cross-sectional shape is determined when the maximum rebounding potential energy is reached, and it is close to the shape with the critical concave arc angle for the existence of multiple possible menisci. The cross-sections with concave parts are preferable to circular, laterally planed and corner-concave cross-sections. This paper provides an effective method of enhancing the restoring force and potential rebounding height of a robotic water strider insect or particles on the surface of water.

Experimental study on the performance of pyramid solar still with novel convex and dish absorbers and wick materials

Solar still is a famous technique of the desalination methods, but it suffers from the low productivity. In this paper, novel structured convex absorbers were proposed in a pyramid solar still. The performance of the pyramid solar still (PSS) was experimentally investigated when using a convex cylinder absorber shape (CCPSS) and dish shape of absorber (CDPSS) instead of the flat absorber. The proposed absorber shapes increased the surface areas of exposure and evaporation and reduced the water depth to minimum inside the distiller. Also, the experimentations were conducted when using different heights of convex dish shape (5, 10, 15, and 20 cm) to obtain the optimum convex height of the dish absorber. Besides, the system was experimentally investigated when using two different wick materials of cotton cloth and jute wicks that were put over the convex surface. Furthermore, the performance of CDPSS was tested when painting the absorber by black paint mixed with different nanocomposites of titanium oxide (TiO2) copper oxide (CuO) and silver (Ag). Systems performance based on economic, enviroeconomic, CO2 reduction, and energy point of view was studied. Experimental results revealed that the CDPSS provided better performance than either CCPSS or PSS. Also, the optimum height of dish absorber that obtained the best performance of CDPSS was 15 cm, where at this height (15 cm), the increase in productivity of CDPSS was 54% with jute cloth over that of the PSS. The highest productivity of CDPSS was obtained when using Ag followed by CuO and then TiO2, where the average daily productivity of CDPSS with jute and Ag was 6750 mL/m2.day compared to 3800 mL/m2.day for that of PSS (improvement = 78% and efficiency = 45.7%). Besides, the rate of CO2 mitigation for the CDPSS with Ag, CuO, TiO2 and without nanoparticles was about 13.5, 12.7, 12.5, 10.17 tons/y respectively. Also, the enviroeconomic parameter (Z^') was 147.6, 181.2, 184.1, and 195.1 per year for the (CDPSS), (CDPSS + TiO2), (CDPSS + CuO), and (CDPSS + Ag), respectively for 365 operating days and lifetime 20 years. Finally, the costs of the distilled water of PSS and CDPSS with jute cloth and silver nanoparticles were 0.018 and 0.015 $/L, respectively.

Quasi-absolute interferometric testing of cylinders.

A three-step quasi-absolute testing method for optical cylinders is proposed in this Letter. Three measurements are taken at the so-called cat's eye position and confocal null testing positions with a computer-generated hologram (CGH) rotated around the axis parallel to that of the cylinder. The quasi-absolute surface error of the cylinder is obtained by simple operations including addition/subtraction and flip of the datasets. The uncertainty is traceable to an optical flat. Two different CGHs are used for a convex cylinder and give consistent quasi-absolute testing results of the surface error, which experimentally validates the method.

Numerical Investigation of Unsteady Flow Dynamics in a Packed Bed

Numerical simulation of unsteady flow of a compressible fluid in a fixed bed filled with porous elements has been performed. The research was carried out via ANSYS Fluent software. The scientific substantiation and verification of the physical and mathematical approaches incorporated in ANSYS Fluent for the problem of unsteady flow in a fixed bed has been carried out. For the computational domain, the interfaces of the flow area and the surface of porous particles are coupled by combining the contacts into a component part. The numerical results were verified using experimental data. The study was carried out in the range of velocity from 0.25 to 3.25 m/s. An expression is proposed for determining the pressure drop in a fixed bed, in which the pressure drop depends on the velocity, flow properties and the linear coefficient of local resistance. The values of the linear coefficient of local resistance are determined for the most common nozzle shapes in the industry: cylinder, Raschig ring, convex cylinder with 7 holes, sphere with 7 holes. It was found that with an increase in velocity, the value of the linear coefficient of local resistance decreases.

Mirror Kirchhoff Approximation for Predicting Shadowing Effect by a PEC Convex Cylinder

This paper extends the two-dimensional Mirror Kirchhoff Approximation (MKA) to predict the shadowing gain by a conductor convex cylinder accurately and efficiently. The conventional MKA is applied only to the rectangular cylinder. This paper proposes the extension of MKA to more general convex shapes such as an elliptical cylinder. The proposal models the convex scatterer as the combination of several rectangular cylinders and applying MKA repeatedly. The proposed method is validated for an elliptical cylinder by comparing the Method of Moment (MoM) in terms of complexity and accuracy. The results imply that the proposed method presents good accuracy. Calculating time is improved by 40 times compared with MoM for the case of $100\lambda\times 40\lambda$ ellipse.

Volumetric Lagrangian particle tracking measurements of jet impingement on convex cylinder

Impinging jets are widely used for heat and mass transfer because they are applicable to any type of body and can be easily implemented. They are also used in various industrial fields and design techniques. Previous research investigated e.g. a jet impinging onto a flat surface. However, since most of the mechanical parts have curvature on their surface, it is necessary to study more detailed properties of the jet impinging on a curved surface using advanced measurements. Therefore, in this study, three-dimensional flow structures of a round jet impinging on a convex cylinder surface were measured using volumetric Lagrangian particle tracking (LPT).

Exploring the potential benefits of using metasurface for galloping energy harvesting

Inspired by the successful applications of metasurfaces in many other fields, this paper aims to explore the potential application of metasurfaces in designing aerodynamic systems. Bluff bodies are proposed to be wrapped in metasurfaces for improving galloping energy harvesting. Three different metasurfaces with convex cylinder, tri-prim, and wedge ornaments are designed. A general aeroelastic model for a galloping energy harvester is developed. The aerodynamic force is represented by a polynomial function with its coefficients being determined from three-dimensional CFD simulations. Subsequently, physical prototypes of the proposed galloping piezoelectric energy harvesters are fabricated, and experimental tests are conducted. The theoretical model is validated by the experimental results. The analytical method and three-dimensional CFD simulation are combined to predict the dynamic responses of the metasurface-wrapped GPEHs. Besides, the results show that the metasurface can significantly change the aerodynamic characteristics of the bluff body, and it is learned that a bluff body wrapped in convex cylinder metasurface could bring benefits for promoting galloping energy harvesting performance. Further experimental studies are conducted to reveal the effects of convex ornament parameters on the galloping energy harvesting performance. It is found that using the metasurface distributed with convex cylinder ornaments of diameter 6 mm and height 9 mm leads to the largest vibration displacement and largest voltage output. Compared to the typical GPEH, the maximum vibration displacement and maximum output voltage of the proposed galloping piezoelectric energy harvester can be increased by 26.81% and 26.14%, respectively. The vortex shedding processes around the wind flow fields near the bluff bodies wrapped in metasurfaces are simulated. The underlying aerodynamic mechanism of the influence of the metasurfaces is unveiled. Finally, based on the validated theoretical model, a parametric study is carried out to investigate the effects of the load resistance and electromechanical coupling strength on the galloping energy harvesting performance. It is concluded that increasing the coupling strength to a certain level and tuning the load resistance to the optimal value could further improve the power output. However, when the electromechanical coupling strength increases to a certain extent, the power output will reach the saturation state, and the coupling strength is extremely large. Therefore, a piezoelectric element with a moderate coupling coefficient is recommended for practical applications from the perspective of economic benefit.

Discrimination of Object Curvature Based on a Sparse Tactile Sensor Array.

Object curvature plays an important role in grasping and manipulation. To be more exact, local curvature is a more useful information for grasping practically. Vision and touch are the two main methods to extract surface curvature of an object, but vision is often limited since the complete contact area is invisible during manipulation. In this paper, the authors propose an object curvature estimation method based on an artificial neural network algorithm through a lab-developed sparse tactile sensor array. The compliant layer covering on the sensor is indispensable for fitting the curved surface. Three types (plane, convex sphere, and convex cylinder) of sample and each type of sample including 30 different radiuses (1 mm to 30 mm) were used in the experiment. The overall classification accuracy was 93.1%. The average curvature radius estimating error based on an artificial neural network (ANN) algorithm was 1.87 mm. When the radius of curvature was bigger than 5 mm, the average relative error was smaller than 20%. As a comparison, the sensor array density we used in this paper was less than 9/cm2, which was smaller than the density of human SAII receptors, but the discrimination result was close to the SAII receptors. Comparison with the curvature discrimination ability of the human body showed that this method has a promising application prospect.

Two-Parameter Power Formalism for Structural Screening of Ion Mobility Trends: Applied Study on Artificial Molecular Switches.

Recent literature provides increasing samples of structural studies relying on ion mobility coupled to mass spectrometry in view of characterizing gas-phase conformation and energetics properties of biomolecular ions. A typical framework consists in experimentally monitoring the collisional cross sections for various experimental conditions and using them as references to select appropriate candidate structures issued from theoretical modeling. Although it has proved successful for structural assignment, this process is resource costly and lengthy, namely due to intricacies in the selection of appropriate input geometries. In the present work, we propose simplified methodologies dedicated to the systematic screening of ion mobility data acquired on systems built from repetitive subunits and detail their application to challenging artificial molecular switch systems. Capitalizing on coarse-grained design, we first demonstrate how the assimilation of subunits into adequately assembled building-blocks can be used for fast assignments of a system topology. Further focusing on topology-specific differential ion mobility trends, we show that the building-block assemblies can be fused into single fully convex solid figure models, i.e., sphere and cylinder, whose projected areas follow a two-parameter power formalism A × nB. We show that the fitting parameters A and B were assigned as structural descriptors respectively associated with the dimensions of each constitutive subunit, i.e., size parameter, and with their assembled tridimensional arrangement, i.e., shape parameter. The present work provides a ready-to-use method for the screening of IM-MS data sets that is expected to facilitate the eventual design of input structures whenever advanced modeling calculations are required.

Flow dynamics of sweeping jet impingement upon a large convex cylinder

Flow dynamics associated with sweeping jets impinging upon a convex cylinder are experimentally examined in a water tank using time-resolved particle image velocimetry (TR-PIV). The cylinder has a large cylinder-jet diameter ratio (D/Dh = 15) and is placed 4 Dh from the jet exit, where Dh is the hydrodynamic diameter of the jet exit. The sweeping jets with two spreading angles as a result of different Reynolds numbers are considered, and a steady impinging jet is examined for comparison. As the baseline case, the steady impinging jet can only cover a small area along the convex surface. At both Reynolds numbers, Re = 3.3 × 103 and Re = 10 × 103, the jet has a strong impact on the convex surface by direct impingement only within a small region between angular angles of θ ≈ ±8° away from the centerline. However, the sweeping jet has a spreading angle of about 30° at the lower Re = 3.3 × 103. As a result, the jet exerts a more even distribution of the impingement in a larger region along the convex surface. Near-wall vortices induced by the impingement are identified to cause early separation of the wall jet flow from the convex surface. The sweeping jet has a much larger spreading angle of about 80° at the higher Re = 10 × 103. As such, the sweeping jet impinges upon the lateral sides of the cylinder at about θ ≈ ±45°, resulting in a weak impingement around the centerline. In addition, the jet column breaks during the sweeping motion: the jet close to the exit switches to one side of the cylinder, while the remaining jet develops on the other side. Proper orthogonal decomposition (POD) analysis reveals that the remaining jet mainly contributes to the impingement at the higher Reynolds number. In general, compared with a steady jet, a sweeping jet can cover a much larger area, even half of a big convex cylinder, with strong impingement.

Vortical structures and behaviour of an elliptic jet impinging upon a convex cylinder

A study on a Reh = 2100, AR = 3 elliptic jet impinging upon different convex cylinders at a jet-to-cylinder separation distance of H/dh = 4 has been conducted. Laser induced fluorescence (LIF) and digital particle image velocimetry (DPIV) techniques were utilized to investigate the effects of cylinder-to-jet diameter-ratio (i.e. D/dh = 1.15, 2.3 and 4.6) and jet orientation upon the vortical structures and their behaviour. Results show that comparable flow developments occur along both convex surfaces and straight-edges when the elliptic jet minor-plane is aligned with the cylindrical axis (i.e. EJ1 configuration), while more non-uniform flow behaviour occurs when the elliptic jet major-plane is aligned with cylindrical axis (i.e. EJ2 configuration). Additionally, significant vortex engulfment behaviour between adjacent ring-vortices upon impingement is observed along the elliptic jet minor-plane regardless of exact impingement configuration, which subsequently leads to different flow modes. Braid vortices play a surprisingly interesting role, where they lead to cross-stream and upstream vortical motions for D/dh = 1.15 and 2.3 cylinders under EJ1 configuration. In contrast, they interact with adjacent jet ring-vortices and rib structures for D/dh = 4.6 cylinder. Proper orthogonal decomposition (POD) analyses provided additional information on the unique vortical behaviour identified in the flow fields, while momentum thickness profiles characterize the mixing layers in relation to the different configurations. Lastly, wall shear stress distributions under the above-mentioned flow conditions have also been determined and related to the vortical structures and behaviour.

On the interaction of a planar shock with a three-dimensional light gas cylinder

Experimental and numerical investigations on the interaction of a planar shock wave with two-dimensional (2-D) and three-dimensional (3-D) light gas cylinders are performed. The effects of initial interface curvature on flow morphology, wave pattern, vorticity distribution and interface movement are emphasized. In experiments, a wire-restriction method based on the soap film technique is employed to generate N$_{2}$ cylinders surrounded by SF$_{6}$ with well-characterized shapes, including a convex cylinder, a concave cylinder with a minimum-surface feature and a 2-D cylinder. The high-speed schlieren pictures demonstrate that fewer disturbance waves exist in the flow field and the evolving interfaces develop in a more symmetrical way relative to previous studies. By combining the high-order weighted essentially non-oscillatory construction with the double-flux scheme, numerical simulation is conducted to explore the detailed 3-D flow structures. It is indicated that the shape and the size of 3-D gas cylinders in different planes along the vertical direction change gradually due to the existence of both horizontal and vertical velocities of the flow. At very early stages, pressure oscillations in the vicinity of evolving interfaces induced by complex waves contribute much to the deformation of the 3-D gas cylinders. As time proceeds, the development of the shocked volume would be dominated by the baroclinic vorticity deposited on the interface. In comparison with the 2-D case, the oppositely (or identically) signed principal curvatures of the concave (or convex) SF$_{6}$/N$_{2}$ boundary cause complex high pressure zones and additional vorticity deposition, and the upstream interface from the symmetric slice of the concave (or convex) N$_{2}$ cylinder moves with an inhibition (or a promotion). Finally, a generalized 3-D theoretical model is proposed for predicting the upstream interface movements of different gas cylinders and the present experimental and numerical findings are well predicted.

Investigating the ocular temperature rise during femtosecond laser lens fragmentation: an in vitro study.

To investigate the trend of temperature variation during lens fragmentation simulated by a femtosecond laser on an in vitro eye model. In our experimental study, a convex cylinder of gelatinous material, usually employed in femtosecond laser calibration, was used to simulate both an anterior segment and a crystalline lens during fragmentation performed with the Victus femtosecond laser (Technolas Perfect Vision GmbH, Germany; Bausch + Lomb Incorporated, USA). Two radiated energies (7000 nJ and 9000 nJ) and three cutting patterns (crosses, circles and cross + circle) were applied. Trends of temperature variation as a function of time were obtained using a T-type thermocouple. The maximum value of temperature rise during lens fragmentation ranged from 3.53 to 5.13°C; the rise was directly proportional to the intensity of the radiated energy (7000 nJ or 9000 nJ) and the cutting pattern performed. This behavior was experimentally represented by an asymmetric function with a characteristic bell curve shape, whereas it was mathematically described by a transport diffusive model. Since the temperature rise at the fragmentation volume base resulted to be around 5°C in our in vitro study, lens fragmentation performed using the Victus femtosecond laser might be considered safe form a thermal point of view.

A simple optical system delivering a tunable micrometer pink beam that can compensate for heat-induced deformations.

The radiation from an undulator reflected from one or more optical elements (usually termed `pink-beam') is used in photon-hungry experiments. The optical elements serve as a high-energy cutoff and for focusing purposes. One of the issues with this configuration is maintaining the focal spot dimension as the energy of the undulator is varied, since this changes the heat load absorbed by the first optical element. Finite-element analyses of the power absorbed by a side water-cooled mirror exposed to the radiation emitted by an undulator at the Advanced Photon Source (APS) and at the APS after the proposed upgrade (APSU) reveals that the mirror deformation is very close to a convex cylinder creating a virtual source closer to the mirror than the undulator source. Here a simple optical system is described based on a Kirkpatrick-Baez pair which keeps the focus size to less than 2 µm (in the APSU case) with a working distance of 350 mm despite the heat-load-induced change in source distance. Detailed ray tracings at several photon energies for both the APS and APSU show that slightly decreasing the angle of incidence on the mirrors corrects the change in the `virtual' position of the source. The system delivers more than 70% of the first undulator harmonic with very low higher-orders contamination for energies between 5 and 10 keV.

The Contour Deformation Method for Calculating the High-Frequency Scattered Field by the Fock Current on the Surface of the 3-D Convex Cylinder

In this paper, the high-frequency diffracted waves like the creeping waves are comprehensively analyzed by the Fock currents. On invoking the contour deformation method, the highly oscillatory Fock currents are efficiently calculated. Furthermore, the workload for the calculation of Fock currents is frequency-independent. To capture the high-frequency wave physics phenomenon, the Fock current is separated into the classical physical optics (PO) current and the nonuniform (NU)-Fock current along the shadow boundary and in the deep shadow region. To calculate the highly oscillatory scattered wave fields from the Fock current, quadratic approximations of the phase functions in the integrand are adopted. On invoking the numerical steepest descent path (NSDP) method, the scattered wave fields are efficiently calculated with frequency-independent computational effort and error controllable accuracy in each frequency-independent segment. Meanwhile, the high-frequency creeping wave coming from the NU-Fock current is efficiently captured by the NSDP method. Numerical results for the Fock currents, the high-frequency NU-diffracted and scattered far fields on the convex cylinders are given to validate the efficiency of the proposed method. Furthermore, the contour deformation method for computing the Fock currents offers a clear physical picture for the high-frequency wave fields on the convex scatterer.

Dynamics of laminar circular jet impingement upon convex cylinders

Flow dynamics associated with a laminar circular jet impinging upon a convex cylinder has been investigated by laser-induced fluorescence and digital particle-image velocimetry techniques. Cylinder-to-jet diameter ratios of 1, 2, and 4 were investigated, while the jet-to-cylinder separation distance was kept at four jet diameters throughout. Flow visualization and λ2 criterion results show that once the jet ring-vortices impinge upon the cylindrical surface, they move away from the impingement point by wrapping themselves partially around the surface. As the cylinder diameter increases, wall boundary layer separation, vortex dipole formation, and separation locations are initiated earlier along the cylindrical surface, producing significantly larger wakes. Along the cylinder straight-edges, ring-vortex cores are significantly smaller after impingement. This is due to accentuated vortex-stretching caused by partial wrapping around the cylindrical surface by the ring-vortices, on top of their movement away from the impingement point. Interestingly, vortex dipoles demonstrate a strong tendency to travel upstream and interact with other upstream vortex dipoles, instead of moving downstream gradually seen for flat-surface jet-impingements. Wall shear stress results are also presented to quantify the effects of cylinder diameter-ratio on surface skin friction distribution. Finally, these preceding observations are corroborated and explained in a three-dimensional flow dynamics model presented here.

Isoperimetric inequalities in convex cylinders and cylindrically bounded convex bodies

In this paper we consider the isoperimetric profile of convex cylinders \(K\times {\mathbb {R}}^q\), where \(K\) is an \(m\)-dimensional convex body, and of cylindrically bounded convex sets, i.e, those with a relatively compact orthogonal projection over some hyperplane of \({\mathbb {R}}^{n+1}\), asymptotic to a right convex cylinder of the form \(K\times {\mathbb {R}}\), with \(K\subset {\mathbb {R}}^n\). Results concerning the concavity of the isoperimetric profile, existence of isoperimetric regions, and geometric descriptions of isoperimetric regions for small and large volumes are obtained.

Translating spacelike graphs by mean curvature flow with prescribed contact angle

This article demonstrates the existence for all time of the nonparametric spacelike mean curvature flow with contact angle boundary condition, where the boundary manifold is a convex cylinder. We also consider the asymptotic behavior of the flow and prove that the flow converges to a spacelike hypersurface (unique up to translation) moving at a constant speed if solutions to an elliptic system exist.

Using simple shape three-dimensional rigid inclusions to enhance porous layer absorption.

The absorption properties of a metaporous material made of non-resonant simple shape three-dimensional rigid inclusions (cube, cylinder, sphere, cone, and ring torus) embedded in a rigidly backed rigid-frame porous material are studied. A nearly total absorption can be obtained for a frequency lower than the quarter-wavelength resonance frequency due to the excitation of a trapped mode. To be correctly excited, this mode requires a filling fraction larger in three-dimensions than in two-dimensions for purely convex (cube, cylinder, sphere, and cone) shapes. At long wavelengths compared to the spatial period, a cube is found to be the best purely convex inclusion shape to embed in a cubic unit cell, while the embedment of a sphere or a cone cannot lead to an optimal absorption for some porous material properties and dimensions of the unit cell. At a fixed position of purely convex shape inclusion barycenter, the absorption coefficient only depends on the filling fraction and does not depend on the shape below the Bragg frequency arising from the interaction between the inclusion and its image with respect to the rigid backing. The influence of the incidence angle and of the material properties, namely, the flow resistivity is also shown. The results of the modeling are validated experimentally in the case of cubic and cylindrical inclusions.