Regular Cylinder Research Articles

Flow control over tandem cylinders using plasma actuators

The flow over two circular cylinders, arranged in a tandem setup, is controlled with the help of dielectric-barrier-discharge (DBD) plasma actuators mounted on the upstream cylinder at a Reynolds number (Re) of 4700. The plasma actuators are mounted at ±80∘ from the forward stagnation point of the upstream cylinder. Three tandem configurations are tested, where the distance, L, by which the cylinder centers are separated are fixed at 3, 4, and 5 cylinder diameters (D). For each configuration, the plasma actuators are operated at two distinct blowing ratios (BR) of 0.8 and 1.4, which are named as the low-power and high-power forcing cases, respectively. Results include static-pressure measurements on the downstream cylinder and wake surveys using Particle Image Velocimetry (PIV). High-power forcing changes the flow pattern in the L=3D upstream wake from reattached to co-shedding flow, enabling alternating vortex shedding to occur between the tandem cylinders. High-power forcing also significantly weakens vortex shedding from the upstream cylinder for L=4D and L=5D. This weakening is manifested through 39.27% and 35.32% reductions in the total area of vorticity contours for L=4D and L=5D, respectively. However, the effect of this cancellation is most prominent on the downstream cylinder when the separation distance is L/D=3. During forcing with BR = 1.4, the static pressure on the downstream cylinder resembles that of a flow over a regular cylinder for all the cases tested. Hence, at this blowing ratio, the wake signature of the upstream cylinder is severely diminished, by delaying the shear-layer separation point. During forcing with BR = 0.8, no significant effect on the downstream cylinder is observed.

Excitation Equations for Longitudinally-Azimutally Irregular Waveguides Taking into Account the Finite of the Walls Conductivity

Excitation equations for longitudinal-azimuthally irregular waveguides are formulated taking into account losses in the walls. The inner surface of the waveguide walls is given by an arbitrary smooth function b(ϕ, z). The coordinate transformation method replaces the original cylindrical coordinate system r, ϕ, z with a new one ρ, ϕ, z, where ρ = r/(b(ϕ, z)). The new system defines the waveguide boundary as ρ = 1 = const, i. e. the waveguide geometry transforms as a regular cylinder. Taking these functions into account, the standard procedure of the incomplete Galerkin method is used to determine the amplitudes of partial waves. The resulting general equations can be used in the calculation and optimization of both microwave and EHF electronic devices of various types, as well as passive microwave devices of various applications.

The Significance of Cross-Sectional Shape Accuracy and Non-Linear Elasticity on the Numerical Modelling of Cerebral Veins under Tensile Loading.

Traumatic brain injury (TBI) is a serious global health issue, leading to serious disabilities. One type of TBI is acute subdural haematoma (ASDH), which occurs when a bridging vein ruptures. Many numerical models of these structures, mainly based on the finite element method, have been developed. However, most rely on linear elasticity (without validation) and others on simplifications at the geometrical level. An example of the latter is the assumption of a regular cylinder with a constant radius, or the geometry of the vein acquired from medical images. Unfortunately, these do not replicate the real conditions of a mechanical tensile test. In this work, the main goal is to evaluate the influence of the vein's geometry in its mechanical behaviour under tensile loading, simulating the real conditions of experimental tests. The second goal is to implement a hyperelastic model of the bridging veins where it would be possible to observe its non-linear elastic behaviour. The results of the developed finite element models were compared to experimental data available in the literature and other models. It was possible to conclude that the geometry of the vein structure influences the tensile stress-strain curve, which means that flattened specimens should be modelled when validating constitutive models for bridging veins. Additionally, the implementation of hyperelastic material models has been verified, highlighting the potential application of the Marlow and reduced polynomial (of fourth and sixth orders) constitutive models.

Diffusion Resistance of Segmented Channels.

The geometry of ion and metabolite channels in membranes of biological cells and organelles is usually far from that of a regular right cylinder. Rather, the channels have complex shapes that are characterized by the so-called vestibules and constriction zones which play roles of molecular filters determining the channel selectivity. In the present paper we discuss several channel structures with varying radius that approximate most of the cases found in nature, specifically, channels of smoothly varying radius and channels composed of multiple cylindrical sections of different lengths and radii including channels containing very thin circular constrictions. We consider diffusive transport of electrically neutral molecules driven by the concentration gradient and derive analytical expressions for the diffusion resistance - the integral parameter that describes steady-state transport properties of membrane channels.

Spin-dependent transport through a magnetic Möbius strip: comparison with a regular magnetic cylinder

Spin-dependent transport through a magnetic Möbius strip: comparison with a regular magnetic cylinder

Nanoscale Saturn Systems Based on C60/70 Bucky Ball and a Newly Designed [4]Cyclopara-1,2-diphenylethylene Hoop: A Strategy for Fullerene Encapsulation Release and Selective Recognition for C70.

A new carbonaceous nanohoop, [4]cyclopara-1,2-diphenylethylene ([4]CPDPE, composed by four 1,2-diphenylethylene units linked via the para of the phenyls), is designed together with two rational synthesis paths being proposed. The Saturn-like host-guest systems formed with the [4]CPDPE nanoring and fullerene C60/70 are explored using density functional theory calculations. The results evidence that the geometry mutual matching between [4]CPDPE and C60/70 is perfect, and the [4]CPDPE⊃C60/70 complexes could be formed spontaneously with high binding energies. Thermodynamic calculation results show that it essentially prefers to selectively recognize C70 over its smaller cousin C60. More interestingly, the [4]CPDPE nanoring could present the regular ring cylinder and the saddle shapes via configuration transformation between its all-trans form and all-cis form, so as to theoretically realize the fullerene encapsulation and release under photoirradiation. Furthermore, the 2:1 interaction structure ([4]CPDPE2⊃Dimer-C60) and properties are investigated. Additionally, the ultraviolet-visible (UV-vis) spectra are simulated, and host-guest noncovalent interaction (NCI) regions are investigated based on the electron density and reduced density gradient (RDG), which may be helpful for a deep understanding of the present designed systems in future.

Mechanistic Insights into Molecular Crystalline Organometallic Heterogeneous Catalysis through Parahydrogen-Based Nuclear Magnetic Resonance Studies.

The heterogeneous solid-gas reactions of crystals of [Rh(L2)(propene)][BArF4] (1, L2 = tBu2PCH2CH2PtBu2) with H2 and propene, 1-butene, propyne, or 1-butyne are explored by gas-phase nuclear magnetic resonance (NMR) spectroscopy under batch conditions at 25 °C. The temporal evolution of the resulting parahydrogen-induced polarization (PHIP) effects measures catalytic flux and thus interrogates the efficiency of catalytic pairwise para-H2 transfer, speciation changes in the crystalline catalyst at the molecular level, and allows for high-quality single-scan 1H, 13C NMR gas-phase spectra for the products to be obtained, as well as 2D-measurements. Complex 1 reacts with H2 to form dimeric [Rh(L2)(H)(μ-H)]2[BArF4]2 (4), as probed using EXAFS; meanwhile, a single-crystal of 1 equilibrates NMR silent para-H2 with its NMR active ortho isomer, contemporaneously converting into 4, and 1 and 4 each convert para-H2 into ortho-H2 at different rates. Hydrogenation of propene using 1 and para-H2 results in very high initial polarization levels in propane (>85%). Strong PHIP was also detected in the hydrogenation products of 1-butene, propyne, and 1-butyne. With propyne, a competing cyclotrimerization deactivation process occurs to afford [Rh(tBu2PCH2CH2PtBu2)(1,3,4-Me3C6H3)][BArF4], while with 1-butyne, rapid isomerization of 1-butyne occurs to give a butadiene complex, which then reacts with H2 more slowly to form catalytically active 4. Surprisingly, the high PHIP hydrogenation efficiencies allow hyperpolarization effects to be seen when H2 is taken directly from a regular cylinder at 25 °C. Finally, changing the chelating phosphine to Cy2PCH2CH2PCy2 results in initial high polarization efficiencies for propene hydrogenation, but rapid quenching of the catalyst competes to form the zwitterion [Rh(Cy2PCH2CH2PCy2){η6-(CF3)2(C6H3)}BArF3].

Numerical investigation of cooling ability in heat-generating porous debris bed after severe accident in PWR

A porous debris bed formed after a severe accident is a structure composed of different sized particles. Due to the fission reaction in the debris bed, decay heat is continuously released. Therefore, the cooling ability should be investigated to determine the safety of the debris bed. In this paper, two-phase conservation equations with closure correlations are proposed for the boiling phenomenon inside the pool. For the flow resistance, the drag force between the gas and liquid in the continuous fluid is considered as well as the flow resistance of the solid to fluid in the porous medium area. The heat transfer model takes into account the heat transfer between solid phase and fluid phases as well as the heat and mass transfer between gas and liquid. All calculations are conducted based on the CFD method, and the related models are written into the CFD calculation program in the form of a User Defined Function (UDF). After the necessary validation of the proposed correlations, the analysis and discussion are based on the effect of the heating type, the non-uniform distribution of structural parameters, and the shape of the geometry. The results show the key effect of natural convection between the different boundary settings of the heating type. The time series of strong natural convection formation and the decay power of heat are the factors that are determined for the position of the boiling crisis. In addition, the limited power density is determined by the top half of the debris bed. The increase in structural parameters and operating pressure leads to a better cooling ability. For the shape of the debris bed, a regular cylinder is a better structure for heat removal, while the conical shape significantly reduces the limited power density, which is dangerous for the long-term cooling of the debris bed. The cooling ability would be improved if a downcomer existed in the porous debris bed. These three research parts are conducive to deepening the understanding of the process of a serious accident.

Low gas consumption in tracking detectors for outdoor applications

Gaseous detectors are one of the popular particle tracking technologies in high energy physics, and there are multiple applications where the detectors must tolerate outdoor conditions, e.g. in the emerging field of muography. Gaseous tracking detectors are attractive choices due to their high efficiency, good resolution and large sensitive area at a reasonable cost and low weight, but to achieve these, the gas system is usually not sealed. Continuous gas flow results gas consumption and thus regular gas cylinder replacement which limits applicability. In this paper we present a practical solution to reduce gas flow to a negligible level, keeping the construction cost-efficient and low weight, by a properly chosen buffer tube at the end of the gas line, which makes the system able to withstand large temperature and pressure fluctuations.

Fluid flow and heat transfer around square cylinder with dual splitter plates arranged at novel positions

In this paper, the effect of the dual splitter plates on the fluid flow and heat transfer characteristics around a regular square cylinder for a low Reynolds number flow ( Re = 100) is presented. The placement of the dual splitter plates is novel of its kind as these plates are located at the top and bottom surfaces of the cylinder rather than the conventional locations, that is, at the upstream and downstream of the cylinder. Here, two splitter plates of the same width ( w) with varying lengths and location are considered. A numerical investigation is performed using the open-source code, OpenFOAM. A base solver, icoFOAM is used after modifying the code by incorporating the energy equation in it. The primary wake bubble is found closer to the cylinder rear surface when the dual plates are introduced. It is also noticed that the separation angle and the recirculation length are smaller in the dual plates cases than that are in the cases without the dual plates. A mixed effect of the dual plates on the fluid forces is observed in the present study. A maximum reduction on the mean drag coefficient and root mean square of the lift coefficient is found as 3% and 24%, and maximum increment as 75% and 87%, respectively. However, a substantial enhancement on the overall heat transfer is noticed with the dual plates compared to that of the bare cylinder. A maximum enhancement of 40% is observed in the heat transfer around the square cylinder. In addition, thermal-hydraulic performance is calculated for finding the trade-off between the fluid forces and the heat transfer. The maximum value of thermal-hydraulic performance is found as 1.35 in the present study depending on the mean drag coefficient and 3.65 depending on the root mean square of the lift coefficient. Further, a novel combined thermo-fluid regime is defined for the square cylinder with dual splitter plates from which the location of the plates can be determined according to the demand on the heat transfer and fluid forces.

An assessment of turbulence transportation near regular and random permeable interfaces

Turbulent channel flow with a porous wall is investigated using direct numerical simulation, where the porous media domain consists of regular or random circular cylinder arrays. We compare the statistics and structure of the mean flow and turbulence in the channel flow with a bulk Reynolds number of 2500 and two porosities (φ=0.6 and 0.8) for the porous media. It is shown that the random interface significantly affects the dynamics of turbulence and the time-averaged flow. More intense mixing is observed near the random interface due to augmented form-induced shear stresses. Due to the strong dependence of induced flow direction on the interface geometry, we segmented the flow field into two types of areas based on the slope angle formed by the top-layer cylinders: the windward area and leeward area. The conditional average of turbulence kinematic energy budget over each type of area reveals their respective role in turbulence transportation more explicitly. In addition, we use finite-time Lyapunov exponents to inspect the Lagrangian coherent structures in the flow fields, which reveal the preferential fluid trajectories in the random porous medium geometry.

Insertion loss of regular finite cylinder arrays with porous layers between the rows.

It has been demonstrated recently via simulations in a duct that the sound transmission loss of porous materials can be increased with embedded periodic scatterers [Jena and Qiu, J. Acoust. Soc. Am. 147, 978-983 (2020)]. In this paper, the insertion loss (IL) of two types of finite size structures constructed by installing two parallel porous sheets within rows of periodic scatterers is investigated in free field. One structure uses rigid cylindrical shells, while the other uses split ring shells, which are obtained by making uniform vertical slits in cylindrical shells. The simulation results show that the mixed structure has larger IL than the summation of the ILs of the individual periodic scatterers and two parallel porous sheets in the frequency range after the first bandgap due to Bragg diffraction, and an additional peak in IL is introduced for the split ring scatterers due to their local resonance. The amplitude, frequency, and bandwidth of the resonance peak can be tuned by changing the geometry of the slit for some specific broadband sound absorption. Finally, the experiment results obtained in an anechoic chamber are presented to support the simulation results and analyses.

Gas sensor based on rGO/ZnO aerogel for efficient detection of NO2 at room temperature

In this paper, a simple, low cost and easy to operate hydrothermal method was successfully used to synthesize rGO/ZnO aerogel in one step. Then the obtained sample is prepared into a sensor to test its sensing performance against NO2. The prepared material is characterized in a series of ways. The SEM and TEM results also show that the rGO/ZnO aerogel after freeze-drying is a regular cylinder with a large pore network structure with cross-linking inside, and ZnO is uniformly distributed on the surface of the rGO sheet layer. To further confirm that the pore structure inside the aerogel increased the specific surface area, the samples were characterized by BET, and the specific surface area of aerogel was 108.79 m2/g. These results indicate that rGO/ZnO aerogel has a large surface area, which enhances the active sites at the surface/interface and makes it a promising gas sensing material. The results showed that the rGO/ZnO aerogel had a NO2 response of 13% to 20 ppm at room temperature. And has a good response recovery, reproducibility is good. This is mainly due to the rapid charge transfer rate of the heterogeneous interface of the composite. rGO/ZnO aerogel has a potential application prospect in gas sensor field due to its simple and easy preparation method and excellent performance at room temperature.

Analysis of tensile response of flexible pipe with ovalization under hydrostatic pressure

Flexible pipes play an important role in the transportation of oil and gas from the seabed to floating production units. They are also employed to inject water or gas into offshore wells. In deep-sea oil and gas extraction, flexible pipes must be able to withstand very high tensile and hydrostatic pressures. In this paper, an equivalent method is used to represent the complex carcass layer and the pressure armor layer as a regular cylinder, and then a numerical model of a 2.5" flexible pipe was developed and verified by experiment. A tensile analysis of flexible pipes with different degrees of initial ovalization indicated that ovalization of 0–1% does not affect the tensile rigidity, but increasing the ovalization creates an uneven load and stress concentration on the tensile armor layer. When a flexible pipe is subjected to hydrostatic pressure, the outer pressure increases the tensile rigidity of the flexible pipe more than the annular pressure, but the reduction of the ultimate tensile load is clear. A high annular pressure can cause the collapse of the carcass layer.

Micrometer-level 3D measurement techniques in complex scenes based on stripe-structured light and photometric stereo.

Compared with existing depth cameras, such as RGB-D, RealSense and Kinect, stripe-based structured light (SL) has the potential for micrometer-level 3D measurement; this can be attributed to its higher coding capacity. While surface texture, high-reflective region, and occlusion remain some of the main sources leading to degraded reconstruction quality in complex objects, methods that are only based on SL cannot completely solve such problems in complex object reconstruction. In this paper, we developed an advanced fusion strategy for the reconstruction of complex objects in micrometer-level 3D measurement. This includes solving the above-mentioned inherent problems of a stripe-based SL system with the aid of photometric stereo (PS). Firstly, to improve the robustness of decoding and eliminate the effects of noise and occlusion on stripe detection, a novel scene-adaptive decoding algorithm based on a binary tree was proposed. Further, a robust and practical calibration method for area light sources in the PS system, which utilizes the absolute depth information from SL system, was introduced. A piecewise integration algorithm, which is based on a subregion divided by Gray code, was proposed by combining the depth values from SL with the normal information from PS. Remarkably, this method eliminates the effects of surface texture and high-reflective region on the reconstruction quality and improves the resolution to camera-level resolution. In experimental parts, a regular cylinder was reconstructed to demonstrate micrometer-level measurement accuracy and resolution enhancement by the proposed method. Then, improvement of the reconstruction accuracy for objects with surface texture was validated with a regular pyramid that had textures on it and a white paper with characters printed on it. Lastly, a complex object containing multiple phenomena was reconstructed with the newly proposed method to show its effectiveness for micrometer-level 3D measurement in complex objects. Evaluation of our proposed method shows the improvement of the proposed method on the existing methods being used for micrometer-level 3D measurement in complex objects.

Ends and middle: Global force balance and septum location in fission yeast.

The fission yeast cell is shaped as a very regular cylinder ending by hemi-spheres at both cell ends. Its conserved phenotypes are often used as read-outs for classifying interacting genes and protein networks. Using Pascal and Young-Laplace laws, we proposed a framework where scaling arguments predicted shapes. Here we probed quantitatively one of these relations which predicts that the division site would be located closer to the cell end with the larger radius of curvature. By combining genetics and quantitative imaging, we tested experimentally whether altered shapes of cell end correlate with a displaced division site, leading to asymmetric cell division. Our results show that the division site position depends on the radii of curvatures of both ends. This new geometrical mechanism for the proper division plane positioning could be essential to achieve even partitioning of cellular material at each cell division.

A decade of CH<sub>4</sub>, CO and N<sub>2</sub>O in situ measurements at Lauder, New Zealand: assessing the long-term performance of a Fourier transform infrared trace gas and isotope analyser

Abstract. We present a 10-year (January 2007–December 2016) time series of continuous in situ measurements of methane (CH4), carbon monoxide (CO) and nitrous oxide (N2O) made by an in situ Fourier transform infrared trace gas and isotope analyser (FTIR) operated at Lauder, New Zealand (45.04 S, 169.68 E, 370 m a. m. s. l.). Being the longest continuous deployed operational FTIR system of this type, we are in an ideal position to perform a practical evaluation of the multi-year performance of the analyser. The operational methodology, measurement precision, reproducibility, accuracy and instrument reliability are reported. We find the FTIR has a measurement repeatability of the order of 0.37 ppb (1σ standard deviation) for CH4, 0.31 ppb for CO and 0.12 ppb for N2O. Regular target cylinder measurements provide a reproducibility estimate of 1.19 ppb for CH4, 0.74 ppb for CO and 0.27 ppb for N2O. FTIR measurements are compared to co-located ambient air flask samples acquired at Lauder since May 2009, which allows a long-term assessment of the FTIR data set across annual and seasonal composition changes. Comparing FTIR and co-located flask measurements show that the bias (FTIR minus flask) for CH4 of −1.02 ± 2.61 ppb and CO of −0.43 ± 1.60 ppb are within the Global Atmospheric Watch (GAW)-recommended compatibility goals of 2 ppb. The N2O FTIR flask bias of −0.01 ± 0.77 ppb is within the GAW-recommended compatibility goals of 0.1 ppb and should be viewed as a serendipitous result due to the large standard deviation along with known systematic differences in the measurement sets. Uncertainty budgets for each gas are also constructed based on instrument precision, reproducibility and accuracy. In the case of CH4, systematic uncertainty dominates, whilst for CO and N2O it is comparable to the random uncertainty component. The long-term instrument stability, precision estimates and flask comparison results indicate the FTIR CH4 and CO time series meet the GAW compatibility recommendations across multiple years of operation (and instrument changes) and are sufficient to capture annual trends and seasonal cycles observed at Lauder. The differences between FTIR and flask N2O measurements need to be reconciled. Trend analysis of the 10-year time series captures seasonal cycles and the secular upward trend of CH4 and N2O. The CH4 and CO time series have the required precision and accuracy at a high enough temporal resolution to be used in inversion models in a data-sparse region of the world.

Three-dimensional numerical simulation of air flow and fiber dynamic in carding region in carding machine

Regular cylinder metallic card clothing has a limited carding efficiency. As a result of the limited dimensions, any measurement between the cylinder and flat area is difficult to make. In this study, an approach is first proposed to simulate the flow field and a fiber finite-element model on the moving surface of the teeth and produce a new design of misaligned-teeth card clothing, with the aim of improving the carding efficiency. A comparison is made between regular and misaligned-teeth card clothing types with respect to flow field simulation and fiber mechanical properties. The results show that the force resulting from the tangential velocity between the cylinder and flat is as great as 1.86 × 10−3 N, sufficient to pull fiber out of tufts, and that the tangential velocity (from 3880 to 2500 mm/s) plays a major role in this area, as opposed to the axial velocity (from 0 to 190 mm/s). Through this comparison, the misalignment design can result in a different tangential velocity distribution from that of traditional card clothing, which helps fibers between two lines of teeth move into neighboring lines of teeth, thereby increasing the likelihood that fibers will be carded. For fiber mechanical analysis, different air forces are loaded on fibers. This comparison shows that for fibers in the channel, the misalignment can help fibers move toward the teeth. Therefore, this misaligned-teeth card clothing is thought to prove more effective in practice.

Heat transfer in a conical porous cylinder with partial heating

The current work simulates the heat transfer across a porous medium fixed in an annular conical cylinder. The geometry is such that the lower part is conical annulus supporting a regular annular cylinder. The porous medium is fixed between inner and outer radius of conical annular cylinder. The inner radius until conical section is heated with constant temperature Th whereas the outer radius is cooled to isothermal temperature Tc such that Th>Tc. The heat transfer phenomenon in this case can be described by two coupled partial differential equations which are solved using finite element method by using 3-node triangular elements. The heat transfer characteristics in this case are quite different from other geometries being discussed in the literature. It is observed that the fluid flow is stronger in the conical section as compared to the cylindrical part of porous geometry. A very few isothermal lines penetrate into the cylindrical porous region as compared to that of conical section.

Step-Scan T-Cell Fourier Transform Infrared Photoacoustic Spectroscopy (FTIR-PAS) for Monitoring Environmental Air Pollutants

Air pollutants have adverse effects on the Earth’s climate system. There is an urgent need for cost-effective devices capable of recognizing and detecting various ambient pollutants. An FTIR photoacoustic spectroscopy (FTIR-PAS) method based on a commercial FTIR spectrometer developed for air contamination monitoring will be presented. A resonant T-cell was determined to be the most appropriate resonator in view of the low-frequency requirement and space limitations in the sample compartment. Step-scan FTIR-PAS theory for regular cylinder resonator has been described as a reference for prediction of T-cell vibration principles. Both simulated amplitude and phase responses of the T-cell show good agreement with measurement data Carbon dioxide IR absorption spectra were used to demonstrate the capacity of the FTIR-PAS method to detect ambient pollutants. The theoretical detection limit for carbon dioxide was found to be 4 ppmv. A linear response to carbon dioxide concentration was found in the range from 2500 ppmv to 5000 ppmv. The results indicate that it is possible to use step-scan FTIR-PAS with a T-cell as a quantitative method for analysis of ambient contaminants.