Cylinder Arrangement Research Articles

A micromechanical and numerical model for effective thermal conductivity of areca fiber and coconut shell particulate-reinforced hybrid composites

The present investigation reports on the thermal conductivity of areca fiber and coconut shell particulate (CSP)-reinforced polymer composites. The fiber and particulate reinforcement percentages were 10–40wt.% with various weight ratios as 1:1, 1:3, and 3:1. The main focus has been given to the development of a micromechanical model to calculate the effective thermal conductivity of areca fiber and CSP-reinforced hybrid composites. In the numerical study, steady-state one-dimensional heat conduction analysis is performed with a periodic arrangement of cylinders and spherical reinforcement using ANSYS software. Unitherm [Formula: see text]Model 2022 equipment was used to measure the experimental thermal conductivity values of the hybrid composite materials and validated with the micromechanical and numerical values. The experimental results attained for thermal conductivity are supported by the proposed micromechanical model. The measured values of the composites were found to be in very close agreement with the micromechanical model and the numerical analysis. It is concluded from this study that the addition of areca fiber and CSP improves the thermal insulation capability of neat epoxy.

Computation of the Permeability Tensor of Non-Periodic Anisotropic Porous Media from 3D Images

The direct proportionality between the flow rate and the pressure gradient of creeping flows was experimentally discovered by H. Darcy in the 19th century and theoretically justified a couple of decades ago using upscaling methods such as volume averaging or homogenization. X-ray computed micro-tomography (CMT) and pore-scale numerical simulations are increasingly used to estimate the permeability of porous media. However, the most general case of non-periodic anisotropic porous media still needs to be completely numerically defined. Pore-scale numerical methods can be split into two families. The first family is based on a direct resolution of the flow solving the Navier–Stokes equations under the assumption of creeping flow. The second one relies on the resolution of an indirect problem—such as the closure problem derived from the volume averaging theory. They are known to provide the same results in the case of periodic isotropic media or when dealing with representative element volumes. To address the most general case of non-periodic anisotropic porous media, we have identified four possible numerical approaches for the first family and two for the second. We have compared and analyzed them on three-dimensional generated geometries of increasing complexity, based on sphere and cylinder arrangements. Only one, belonging to the first family, has been proved to remain rigorously correct in the most general case. This has been successfully applied to a high-resolution 3D CMT of Carcarb, a carbon fiber preform used in the thermal protection systems of space vehicles. The study concludes with a detailed analysis of the flow behavior (streamlines and vorticity). A quantitative technique based on a vorticity criterion to determine the characteristic length of the material is proposed. Once the characterized length is known, the critical Reynolds number can be estimated and the physical limit of the creeping regime identified.

Prediction of steady flows passing fixed cylinders using deep learning

Considerable attention has been given to deep-learning and machine-learning techniques in an effort to reduce the computational cost of computational fluid dynamics simulation. The present paper addresses the prediction of steady flows passing many fixed cylinders using a deep-learning model and investigates the accuracy of the predicted velocity field. The deep-learning model outputs the x- and y-components of the flow velocity field when the cylinder arrangement is input. The accuracy of the predicted velocity field is investigated, focusing on the velocity profile of the fluid flow and the fluid force acting on the cylinders. The present model accurately predicts the flow when the number of cylinders is equal to or close to that set in the training dataset. The extrapolation of the prediction to a smaller number of cylinders results in error, which can be interpreted as internal friction of the fluid. The results of the fluid force acting on the cylinders suggest that the present deep-learning model has good generalization performance for systems with a larger number of cylinders.

Investigation of Film Boiling Over Tandem Arrangement of Elliptical Cylinders in Vertical Crossflow of Saturated Liquid

Investigation of Film Boiling Over Tandem Arrangement of Elliptical Cylinders in Vertical Crossflow of Saturated Liquid

Flow resistance in channels with large emergent roughness elements

Reducing uncertainty in flow resistance estimation in natural channels requires elucidation of contributing influences. Surface shear and form drag are the major contributors in channels containing large roughness elements under emergent flow conditions. The two effects can be accounted for in the Darcy-Weisbach and Manning equations by adding their associated, separate friction factors or taking the square root of the sum of the squares of the corresponding Manning coefficients. The friction factor for form drag can be estimated from the drag coefficient and areal density of the roughness elements and the flow depth. Predictions of the combined effect are tested against results of laboratory experiments with different arrangements of emergent cylinders on smooth and rough beds, using experimentally determined drag coefficients for the cylinders. The variation of the overall resistance coefficient with flow condition depends on the dominant influence, decreasing with flow depth when surface shear dominates, and increasing with depth when form drag dominates.

A Defective Nanotube Molecule of C552 H496 N24 with Pyridinic and Pyrrolic Nitrogen Atoms.

A 3-nm molecule comprising a cylindrical core and cross-shaped rims was designed and synthesized by developing a modular synthetic route. By using a cyclic precursor from previous studies as a starting material, multiple carbazole units were installed at the rims of the defective cylinder. The defective cylinder was synthetically doped with two types of nitrogen atoms, that is, pyridinic and pyrrolic nitrogen atoms, which resulted in solvatochromic shifts in fluorescence by charge-transfer interactions. The structure of the large, C552 H496 N24 molecule was fully disclosed by crystallographic analyses, and the unique helical arrangement of nitrogen-doped cylinders in the crystal was revealed.

Förster resonance energy transfer in finite length systems and porous media

Förster Resonance Energy Transfer (FRET) is a mechanism widely used to describe the luminescent behavior of a great variety of systems. However, there is a strong need for a complete model of Förster theory to understand donor-acceptor interactions in different confinement geometries and their effects on the luminescent dynamics. Here, a methodology based on Förster theory that allows finding the probability distribution of donors and acceptors in systems of any geometry is presented. We have considered the particular cases of lines with finite length, finite cylinders, and bi-dimensional arrangements of lines and cylinders. Furthermore, using our results, we calculate the quantum yield as a function of the geometric parameters of the structures. Our numerical results show that this methodology is useful to calculate and predict the donor luminescent dynamics in structures of finite length. We find that our model explains the decrease of the transferred energy from donors to acceptors with the separation between lines or cylinders, this behavior is physically consistent. The model presented here extends the use of FRET to the study of structures with bi-dimensional arrays of lines or cylinders (as could be the case of porous media), and finite cylinder structures (as could be the case of nanotubes). In our knowledge, this work is the first theoretical approach to describe the donor-acceptor luminescent dynamics in this kind of systems.

On the acoustical performance of plenum window installed with rigid circular cylinders at low frequency

The low-frequency acoustical performance of plenum window with an array of rigid circular cylinders installed is analysed with the Finite Element Method (FEM) in the current study. This study includes the effect of vibrational glass boundaries, cavity resonance, the opening width of the window, and the arrangement of cylinders, on the sound transmission loss (TL) of the plenum window. The relationship between the above factors with TL is also investigated statistically and simple optimization of the geometry has been done based on the results. Results have shown that including the mechanical vibration of glass does not result in a significant difference with previous results, but an average decrease of 1 dB in TL is observed near the eigenfrequencies of the glass boundary. The effect of opening width on TL is not trivial but frequency-dependent due to the cavity resonance formed between the overlapping regions. Lastly, the introduction of rigid cylinders causes a shift of significant TL to lower frequency regardless of the opening width. The installation of them also seems to have destroyed the formation of cavity resonance, which results in much smaller TL.

DC Arc Resistance Rise by PMMA Cylinder Ablation with Arc Shrinking in Silica Sand Filling Space

Concerning DC arc quenching phenomenon in silica sand filling space, we have proposed a new method for raising an arc column resistance (rcol) by use of polymer‐material arrangement. This paper reveals physical factors for rcol rise on the bases of experimental results using the following cylinders made of: (i) Quartz (SiO2) and (ii) PMMA ((C5H8O2)n) with various inner diameters ϕ. For ϕ = 2 mm case, rcol measured for a PMMA cylinder arrangement indicated higher rcol at low current region, while almost same rcol around current peak. For ϕ = 3 mm case, rcol for the PMMA cylinder was lower than rcol for the quartz case at high current region, while almost comparable between these conditions at low current region. For ϕ = 5 mm case, rcol were almost same during the arc quenching process. To discuss the effect of the rcol rise, the followings were also performed: (i) observation of cylinders after arc quenching and (ii) calculation of the electron density of SiO2/Cu or PMMA/SiO2 mixture vapors. It is concluded that, at high current region, rcol can increase due to the shrinking of the arc conductive diameter caused by the cylinder hole and the silica sand filled inside the cylinder hole. On the other hand, the admixing of the PMMA ablation vapor increases rcol at low current region in the present experiment. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Innovations in Different Abrasive Flow Machining Processes: A Review

With advent of need for fast productivity in terms of material removal and surface roughness of the workpiece, abrasive flow machining (AFM) process is gaining rapid importance in the industries. In this process, the fine finishing of the internal surfaces is done that are difficult to reach spaces using abrasive laden polymer media. The media is extruded past the surface under high pressure with the help of two sets of extrusion piston cylinder arrangements. In this paper, various innovations done in the field of abrasive flow machining have been studied in detail in a tabulated form. It included the applications of the process and the different variant forms of AFM process. Due to addition of external forces in variant of AFM process, high speed machining is obtained with smoother surface integrity. Hence it can be concluded that this form of non-conventional machining process is efficient both in terms of surface roughness and material removal.

Liquid fuel distribution in the combustion chamber by jet impingement on small cylindrical obstacles

Homogenization of lean air-fuel mixture decreases the flame-front temperature and reduces NOx and particulate matter. Impingement of diesel jet onto an arrangement of cylindrical obstacles as a structure close to Porous media, causes high fuel dispersion in the combustion chamber. The injected fuel impinges on the first cylindrical obstacle and splits into two smaller jets and with impingement on other obstacles causes multi-jets splitting in the combustion chamber and fast mixture formation. In this paper, the injection of diesel fuel into a constant pressure chamber is simulated using CFD software. First numerical results of jet length, jet width, jet distribution angle, and spray cone angle shape, were validated with experimental data. Then, effects of obstacles diameter (1, 2 mm), injection pressure (400, 800, 1200 bar), the distance between the nozzle and first obstacle (4–12 mm) for two arrangements of obstacles (one and three cylindrical) on jet length, jet width, jet distribution angle, spray cone angle shape, and jet fuel impingement with hot obstacles impingement, have been investigated. Two new arrangements of cylinders were suggested. First, was an arrangement of three and eight cylinders for the most fuel dispersion for homogeneous mixture formation and second was an arrangement for jet leaving shape similar to liquid leaving the shape of high porosity porous medium (PM). Finally, jet impingement of alumina nano-particles and diesel fuel blend on jet length, jet width, jet distribution angle have been studied. Results show that with increasing the distance between the cylindrical obstacles, the jet length for all geometrical structures increased by about 1 mm, and the largest change for the fuel distribution angle was related to the 8d1 structure with a 19 deg increase. Fuel spray considerably does not change obstacles’ temperature during the injection and the maximum wall film mass is related to an obstacle with a diameter of 1 mm. On the other hand, the addition of alumina nano-particles to diesel fuel decreases the jet length but increases the jet width.

Wake-induced instabilities of parallel circular cylinders with tandem and staggered arrangements

When two circular cylinders are closely arranged in parallel, the downstream cylinder frequently exhibits wake-induced vibrations (WIVs). This study investigates the classifications of WIVs in various arrangements of cylinders by considering the generation mechanisms of WIVs through a series of wind tunnel tests. The generation mechanisms are defined through flutter and time-history analyses using the quasi-steady theory. Finally, this study suggests a classification map of the arrangements with four types of generation mechanisms: vertical flutter, anti-phase coupled flutter, in-phase coupled flutter (quasi-steady applicable), and in-phase coupled flutter (quasi-steady inapplicable). Vertical flutter occurs in closely staggered cylinders and tandem cylinders with a horizontal center distance measuring 2.5–9.5 times the cylinder diameter. A key parameter for distinguishing coupled flutter is the contribution of the aerodynamic coupling terms. Furthermore, for closely staggered cylinders, two types of vibrations occur, depending on the reduced wind velocity. The arrangement of the two cylinders is slightly changed because of the static displacement of the downstream cylinder depending on the wind velocity, resulting in a change in the generation mechanism. The results pertaining to the generation mechanisms effectively explain the WIV responses of the two cylinders in various arrangements.

Performance Of some Corrosion Inhibitors For Carbon Steel In Hydrochloric Acid

Corrosion tests on commercial carbon steel pipe in aerated 0.1N HCl solution under static and flow conditions with ranges of rotation velocity of 400–1400 rpm and temperature of 35 – 60ºC, were carried out by weight loss method, in absence and presence of several inhibitors which were thiourea, ethylenediamine, diethano-lamine and formaldehyde as an adsorption type inhibitors in concentration range 400 – 2000 ppm using rotating cylinder arrangement. The experimental results showed that the corrosion rate in absence and presence of inhibitors is increased with the increasing temperature of the corrosive solution and the rotational velocity and is decreased with increasing the inhibitors concentration for the whole range of
 
 
 
 temperatures and rotational velocities. Highest inhibition efficiency was attained by thiourea with considerable efficiencies for other inhibitors. The order of corrosion inhibitors efficiencies was as follows: thiourea > ethylenediamine > diethanolamine > formaldehyde. Under static conditions maximum inhibition efficiency obtained was 77.59% for thiourea and the minimum inhibition efficiency was 37.12% for formaldehyde depending on inhibitor concentration and temperature. Also the results revealed that the inhibitors efficiency increases with increasing its concentration and decreases with increasing agitation speed and temperature. The thiouurea was found to be good inhibitor even at high agitation velocity while the formaldehyde failed to inhibit corrosion at high velocity.

Increasing Arc Column Resistance During DC Arc‐Quenching Through Arrangement of Polymer Cylinder in Silica Sand

In this study, experiments pertaining to direct current (DC) interruptions are performed in an arc‐quenching chamber filled with silica sand. First, the arc column resistance is measured during DC arc‐quenching to demonstrate the elementary aspects of the arc in the silica‐sand‐filled space. Subsequently, an arrangement comprising a polymer cylinder between electrodes in the silica‐sand‐filled space is proposed to increase the arc column resistance during DC arc‐quenching. A polymethyl methacrylate (PMMA) cylinder is used in the experiments. Measurement results indicate that the arrangement of the PMMA cylinder causes the arc column resistance to increase approximately twofold in comparison with the no‐PMMA cylinder arrangement. Finally, the effect of increasing the arc column resistance is discussed in terms of PMMA and silica vapor. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Investigation of Post-Darcy Flow in Thin Porous Media

We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of cylinders bounded between walls. The simulations span a range of Reynolds numbers, 40 to 4000, where the pressure drop varies nonlinearly with the average velocity, covering nonlinear laminar flow to the fully turbulent regime. The results are compared to those obtained by replacing the bounding walls with symmetric boundaries with the aim to reveal the effect of bounding walls on microscopic characteristics and macroscopic measures, i.e., pressure drop, hydrodynamic dispersion and Reynolds stresses. We use large eddy simulation to directly calculate the Reynolds stresses and turbulent intensity. The simulations show that vortical structures emerge at the boundary between the cylinders and the bounding walls causing a difference between the microscopic flow in the confined and non-confined porous media. This affects the averaged values of pressure drop, the hydrodynamic dispersion and the Reynolds stresses. Finally, the distance between the bounding walls is altered with the particle Reynolds number kept constant. It is observed that the difference between results calculated in confined and non-confined cases increases when the bounding walls are narrower.

Wave transmission and drag coefficients through dense cylinder arrays: Implications for designing structures for mangrove restoration

Mangrove vegetation constitutes a natural coastal defence against waves and erosion. Despite their protective role, mangrove ecosystems have experienced continuous degradation over the last decades due to human causes. At retreating mangrove coastlines, bamboo structures are built to create new habitat for mangrove colonization. Existing structures have experienced mixed rates of success due to the lack of a scientific basis in their design. Optimizing future structure designs requires investigating the effect of the bamboo poles on waves. We consequently conducted laboratory experiments to measure wave transformation, hydrodynamic forces, and flow velocities inside cylinder arrays, mimicking bamboo poles, with varying cylinder configurations and orientations. The experiments provided relationships for wave transmission, wave reflection, and the drag coefficients for configurations with volumetric porosities between n = 0.64 − 0.9. Configurations with a small lateral spacing (causing higher blockage) and a relatively longer streamwise spacing (causing less sheltering) exhibit larger forces and dissipation per element. Such arrangements enable optimizing wave dissipation at locations where the wave direction has low variability over the year. Placing the poles horizontally instead of vertically increases the forces and wave dissipation per element in relatively deeper water. Based on the experiments, we developed a conceptual analytical model that predicts wave reflection and dissipation through cylinder arrays, including blockage and sheltering. The model can reproduce the influence of cylinder arrangement on wave transformation, and it suggests that accurate predictions of sheltering and wave reflection are important to find optimal designs. Overall, these results provide useful insights on how to model and optimize the design of structures for mangrove restoration.

Analysis of the turbulent flow patterns generated in isotropic porous media composed of aligned or centered cylinders

The analysis of the turbulent flow inside porous media composed of infinite arrangements of cylinders with square and circular cross sections disposed in aligned or centered configuration is presented. The porosity (ϕ) was varied from 0.3 to 0.8, at a pore Reynolds number Rep=105, representing fully turbulent flow conditions. The flow cases were solved numerically by using the low-Reynolds Abe-Kondoh-Nagano version of the k-ε model. New correlations are provided for the domains composed of aligned particles in terms of ϕ for the volume averaged turbulence kinetic energy (k), its dissipation rate (ε), and macroscopic pressure gradient (MPG). These correlations are especially useful when it is not possible to model the local details of the porous media in macroscopic turbulence modeling. The highest energetic losses in terms of volume averaged k, ε, and MPG was found for the centered square arrangement. In all cases, these parameters increased abruptly as ϕ decreased, as the pore-scale local pressure gradients and turbulent kinetic energy dissipation rate levels increased. Depending on the case, they were triggered by a combination of sudden expansion-contraction of the flow channels, flow impingement, and the decrease of the effective flow area by flow recirculation. In all cases, the pore-scale local pressure gradients and turbulent kinetic energy dissipation rate levels increased abruptly as ϕ decreased, and consequently the energy losses increased. The tracer dispersion presented similar low homogeneity times for the centered cylinder arrangements. At each porous media, the variations of turbulence intensity, effective flow area, and tortuosity levels in terms of ϕ were not as significant as those observed for the local pressure gradient and dissipation rate. This effect may be considered to improve mixing and reduce pressure drops in devices such as static mixers, heat exchangers, cooling fins arrays, and other devices composed of slender tubes.

Chiral Dielectric Metasurfaces for Highly Integrated, Broadband Circularly Polarized Antenna.

We report on the design of a low-profile integrated millimeter-wave antenna for efficient and broadband circularly polarized electromagnetic radiation. The designed antenna comprises a chiral dielectric metasurface built with a arrangement of dielectric cylinders with slanted-slots at the center. A broadbeam high-gain with wide axial ratio ( dB bandwidth was reached by pairing the electric and magnetic resonances of the dielectric cylinders and the slanted slots when excited by an elliptically polarized driven-patch antenna. This electric-magnetic pairing can be tuned by varying the cylinders diameter and the tilting and rotation angles of the slanted slots. The simulation results indicate impedance-matching bandwidths up to 22.6% (25.3–31.6 GHz) with 3-dB AR bandwidths of 11.6% (26.9–30.2 GHz), which in terms of compactness () and performance are superior to previous antenna designs. Since the simulations were performed by assuming materials and geometries easily implementable experimentally, it is hoped that circularly polarized antennas based on chiral metasurfaces can be integrated into 5G and satellite communications.

Non-Stokesian flow through ordered thin porous media imaged by tomographic-PIV

The 3D flow-fields in a staggered and cubic arrangement of mono-radii cylinders are investigated using tomographic-PIV. The cylinder Reynolds-number is in the range of approx 10 to approx 800 giving an almost complete overview of the transition region. Two pore-scale effects are discovered. The first, visible in the cubic packing, is a spatially alternating lateral velocity field, which has a significant impact on the pressure drop and transversal dispersion. The second effect, present in the staggered array, is an example of a disturbance propagation effect that takes place in the laminar steady region; this manifests as a peculiar and complex flow-pattern. In accordance with other studies, it is shown that Darcy’s law can, from an engineering point of view be valid far beyond the limit for Stokesian flow.Graphic abstract

Mathematical modeling of the dragline travel mechanism with sliding supports

The results of an analytical study of the walking mechanisms of dragline excavators are presented. The advantages and disadvantages of the hydraulically driven walking mechanism are considered. Constructive changes are proposed in the form of installation of sliding supports and horizontal arrangement of traction hydraulic cylinders on support shoes. A method for calculating the forces acting on sliding bearings is presented, which makes it possible to determine the requirements for the physical and mechanical properties of the sliding bearings material, including the hardness and wear resistance of their working surfaces. Examples of using the mathematical model of a three-bearing walking mechanism with sliding supports, created in the MATLAB Simulink software environment, are shown.