Circular Cross-sectional Geometry Research Articles

A Numerical Comparison of 2D and 3D CFD Modelling for Contraction and Expansion Geometries with an Emphasis on Solid Particles Erosion

In this study, erosion patterns and magnitude are compared between the outputs of 2D and 3D CFD models in contraction and expansion geometries. ANSYS Fluent software was used to model a circular cross-section geometry with a contraction and the results were compared to published experimental data. The simulation findings showed that there is good agreement between the 2D and 3D CFD models and the experimental data in terms of fluid flow properties such as velocity profiles and magnitude. It also demonstrated that the 2D and 3D CFD models' representations of erosion patterns and magnitudes are equivalent. The 3D CFD simulations were able to provide more information than the 2D CFD simulations, particularly in terms of erosion distribution over the entire geometry.

Wind-induced vibration of structural cables

The wind-induced vibration of cables has been widely studied over the past decades because of cables’ many applications in cable-stayed, suspension, and tied-arched bridges, and power transmission lines. They have been mostly investigated through research conducted on rigid model cables with a finite length and circular cross-sectional geometry that represents a section model of a long cable. These models have been considered accurate because the behavior of flow over a cable and circular cylinder is similar, although there are structural differences between them. Cables usually experience small- to large-amplitude vibration due to wind loads that causes fatigue failure and poses a significant threat to the safety and serviceability of these structures. Although this paper mainly focuses on reviewing the past studies about different types of wind-induced cable vibration, some general information related to circular cylinders has been briefly reported for better understanding of the flow over cables. This paper incorporates an extensive review based on the existing papers about different sources of wind-induced cable vibration consisting of vortex-induced vibration, rain-wind-induced vibration, dry galloping, ice galloping, and wake galloping. Furthermore, this paper explains the mechanism, vibration source, and a mitigation solution for each type based on the past studies using wind tunnel experiments, computational fluid dynamics, field measurements, or analytical approaches. This review helps to better understand the aerodynamics and fluid–structure interactions of cables with or without ice/rain on the surface, while static and dynamic wind loads act on the structure.

A Theoretical Study on Circular Wire and Flat Strip Conductor Inductance for Magnetic Resonance-Shielded Phased-Array Circular Coils

Phased-array radiofrequency (RF) coils are commonly used for signal reception in magnetic resonance for their large spatial coverage, typical of volume coils, and for their high signal-to-noise ratio, usually associated with surface coils. The simplest design of phased-array coils is an array of circular loops whose conductor can be constituted by flat strip or circular wire cross-sectional geometry, often partially enclosed in an RF shield for minimizing electromagnetic interference. This paper proposes a method for the analytical calculation of the mutual inductance between two circular loops constituting a dual-element phased-array coil by taking into account the conductor’s geometry and the effect of an eventual RF shield.

Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: development and evaluation of a test method for curved structures in a high-alkaline environment

Innovative circular, hollow, laminated veneer lumber (LVL) beech sections for use as temporary geotechnical soil reinforcement members are currently being developed. Appropriate surface gluing quality between the veneers is fundamental to this subsoil application of the permanently cement-embedded, engineered timber product. The circular cross-section geometry and the permanently high-alkaline environment of the structural member is not covered by presently standardized testing and conditioning methods for examining LVL surface bond line quality. The sample conditioning and tensile shear test method compliant with EN 302-1 (Adhesives for load-bearing timber structures—test methods—part 1: determination of longitudinal tensile shear strength, European Committee for Standardization, Brussels, 2013) was modified to determine bonding parameters for circular, hollow LVL sections. Bond line curvature, groove cutting depth and sample geometry were found to greatly influence stress distribution, percentage of wood failure and tensile shear strength. Short-term alkaline treatment of test samples did not significantly influence the bonding performance, wood failure percentage, tensile shear strength and fracture patterns. To improve tensile shear strength, adhesives with different material rigidities were used and compared. An orthotropic, elastic numerical analysis revealed a greater influence of adherent elasticity than adhesive elasticity on the stress distribution within the bond line. With regard to determining the bond line integrity of curved veneer poles, a sample geometry compliant with EN 302-1 (2013) was developed and numerically evaluated.

Nonlinear vibration and adhesion instability of Casimir-induced nonlocal nanowires with the consideration of surface energy

The following research work deals with the size-dependent dynamic instability of suspended nanowires in the presence of Casimir force and surface effects. Specifically, the Casimir-induced instability of nanostructures with circular cross-section and cylinder-plate geometry is studied. Following the Gurtin–Murdoch model and nonlocal elasticity, the governing equation of motion for nanowires is derived. To express the Casimir attraction of cylinder-plate geometry, two approaches, e.g. proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation for large separations are studied. To overcome the difficulties for solving a nonlinear problem, a step-by-step numerical method is utilized. The effects of nonlocal parameter, surface energy and vacuum fluctuations on the dynamic instability characteristic and adhesion time of nanowires are studied. It is observed that the phase portrait of Casimir-induced nanowires exhibit periodic and homoclinic orbits.

Femtosecond laser written waveguides with MoS_2 as satuable absorber for passively Q-switched lasing

This work reports on the passively Q-switched waveguide laser system based on Nd:YAG crystal and MoS2 satuable absorber. A depressed cladding waveguide with circular cross-sectional geometry has been produced in Nd:YAG crystal by direct femtosecond laser writing at low-repetition rate. The confocal microscopic investigation of the structure reveals the well-preserved microphotoluminescence features in the waveguide core. With chemical-vapor-deposition (CVD) MoS2 membrane as satuable absorber, the passive Q-switching of the Nd:YAG waveguide system has been achieved under optical pump, reaching maximum average output power of 85.2 mW, corresponding to single-pulse energy of 112 nJ, at wavelength of 1064 nm. The repetition rate of the pulsed waveguide laser system is tunable from 0.51 to 1.10 MHz, and the obtained minimum pulse duration is 203 ns.

Fluid flow and mass transfer characteristics of enhanced CO2 capture in a minichannel reactor

CO2 absorption using amine solvents can be significantly enhanced by the use of microscale reactors having high surface area to volume ratio. The present paper reports an experimental investigation of the fluid flow and mass transfer characteristics during reactive gas–liquid absorption in a minichannel reactor. Absorption of CO2 mixed with N2 into aqueous diethanolamine was studied in a channel having hydraulic diameter of 762μm and a circular cross-sectional geometry. High-speed imaging of the two-phase flow was conducted to visualize the flow regimes. Image-processing analysis of the acquired flow patterns was performed to determine the interfacial area. The performance of the reactor was studied with respect to the absorption efficiency, pressure drop, mass transfer coefficient, interfacial area, enhancement factor, and Sherwood number. Parametric studies investigating the effects of phase superficial velocity, liquid reactant concentration, and CO2 concentration in the gas phase were performed and are discussed. High levels of absorption efficiency, close to 100%, were observed under certain operating conditions. An empirical model for the Sherwood number was developed and compared against experimental data. The mass transfer coefficient was found to be higher at reduced channel lengths, which was attributed to improved utilization of the absorption capacity of the amine solution for a given reactor volume. The presently achieved values of mass transfer coefficient and specific interfacial area are between 1 and 4 orders of magnitude higher than those reported for most conventional absorption systems.

Power Losses in a Three-Phase Single-Pole Gas-Insulated Transmission Line (GIL)

This paper presents an analytical method for determining the power losses in the three-phase gas-insulated transmission line (i.e., high-current busduct) of circular cross-section geometry. The mathematical model takes into account the skin effect and the proximity effects, as well as the complete electromagnetic coupling between phase conductors and enclosures (i.e., screens). The power losses produced by high-current busducts are usually calculated numerically with the use of a computer. However, the analytical calculation of the power losses is preferable, because it results in a mathematical expression for showing its dependences on various parameters of the line arrangement. Moreover, knowledge of the relations between electrodynamics and constructional parameters is necessary in the optimization construction process of the high-current busducts.

Fabrication of a circular PDMS microchannel for constructing a three-dimensional endothelial cell layer

We describe a simple and efficient fabrication method for generating microfluidic channels with a circular cross-sectional geometry by exploiting the reflow phenomenon of a thick positive photoresist. Initial rectangular shaped positive photoresist micropatterns on a silicon wafer, which were fabricated by a conventional photolithography process, were converted into a half-circular shape by tuning the temperature to around 105 °C. Through optimization of the reflow conditions, we could obtain a perfect circular micropattern of the positive photoresist, and control the diameter in a range from 100 to 400 μm. The resultant convex half-circular photoresist was used as a template for fabricating a concave polydimethylsiloxane (PDMS) through a replica molding process, and a circular PDMS microchannel was produced by bonding two half-circular PDMS layers. A variety of channel dimensions and patterns can be easily prepared, including straight, S-curve, X-, Y-, and T-shapes to mimic an in vivo vascular network. To form an endothelial cell layer, we cultured primary human umbilical vein endothelial cells inside circular PDMS microchannels, and demonstrated successful cell adhesion, proliferation, and alignment along the channel.

Coupled Electromagnetic and Thermal Analysis of Single-Phase Insulated High-Current Busducts and GIL Systems

This paper presents a mathematical model for the coupled electromagnetic and thermal analysis of the single-phase insulated high-current busducts of circular cross-section geometry and of gas-insulated transmission lines (GIL). The mathematical model, accompanied by a numerical solution procedure, features an exact current distribution in phase conductors and shields of the busduct or GIL system, accounting for the skin and proximity effects, and including the complete electromagnetic coupling between phase conductors and shields. The current distribution is based on the conductor filament method in combination with the mesh-current method. The mathematical model further couples the analysis of current distribution with the computation of (Joule) power losses and subsequent temperature increase in the high-current busducts or GIL systems, accounting for the material properties (electrical conductivity, thermal emission and convection coefficients) as well as for the surrounding ambient properties (ambient temperature, wind and solar radiation influences).

Numerical Analysis of the Magnetic Field of High-Current Busducts and GIL Systems

This paper presents a numerical computation method for determining the magnetic field of high-current busducts of circular cross-section geometry, based on the subdivision of the busduct phase conductors and screens into the conductor filaments and the subsequent application of the mesh-current method, with the aid of the geometric mean distance method. The mathematical model takes into account the skin effect and the proximity effects, as well as the complete electromagnetic coupling between phase conductors and metal enclosures (i.e., screens) of the single-phase isolated busduct system (of circular cross-section geometry). This model could be readily applied to the computation of the magnetic field of the Gas Insulated Transmission Lines (GIL) as well.

Wrinkle-crease interaction behavior simulation of a rectangular membrane under shearing

Wrinkling analysis of a rectangular membrane with a single crease under shearing is performed to understand the wrinkle-crease interaction behaviors. The crease is considered by introducing the residual stresses from creasing and the effective modulus into the baseline configuration with assumed circular cross-sectional crease geometry. The wrinkling analysis of the creased membrane is then performed by using the direct perturb-force (DP) simulation technique which is based on our modified displacement components (MDC) method. Results reveal that the crease may influence the stress transfer path in the membrane and further change the wrinkling direction. The crease appears to improve the bending stiffness of the membrane which has an effective resistance on the wrinkling evolution. The effects of the crease orientation on wrinkle-crease interaction are studied toward the end of this paper. The results show that the wrinkling amplitude, wavelength, and direction increase as the crease orientation increases, and the wrinkling number decreases with the increasing crease orientation. These results will be of great benefit to the analysis and the control of the wrinkles in the membrane structures.

Skeletal strain patterns and growth in the emu hindlimb during ontogeny

Most studies examining changes in mechanical performance in animals across size have typically focused on inter-specific comparisons across large size ranges. Scale effects, however, can also have important consequences in vertebrates as they increase in size and mass during ontogeny. The goal of this study was to examine how growth and development in the emu (Dromaius novaehollandiae) hindlimb skeleton reflects the demands placed upon it by ontogenetic changes in locomotor mechanics and body mass. Bone strain patterns in the femur and tibiotarsus (TBT) were related to ontogenetic changes in limb kinematics, ground reaction forces, and ontogenetic scaling patterns of the cross-sectional bone geometry, curvature and mineral ash content over a 4.4-fold increase in leg length and 65-fold increase in mass. Although the distribution of principal and axial strains remained similar in both bones over the ontogenetic size range examined, principal strains on the cranial femur and caudal femur and TBT increased significantly during growth. The ontogenetic increase in principal strains in these bones was likely caused by isometry or only slight positive allometry in bone cross-sectional geometry during growth, while relative limb loading remained similar. The growth-related increase in bone strain magnitude was likely mitigated by increased bone mineralization and decreased curvature. Throughout most of ontogeny, shear strains dominated loading in both bones. This was reflected in the nearly circular cross-sectional geometry of the femur and TBT, suggesting selection for resistance to high torsional loads, as opposed to the more eccentric cross-sectional geometries often associated with the bending common to tetrapods with parasagittal limb orientations, for which in vivo bone strains have typically been measured to date.

Strain energy minimum and vibrational properties of single-walled aluminosilicate nanotubes

We study the origin of the strain energy minimum in a single-walled aluminosilicate nanotube via a harmonic force-constant model and molecular dynamics simulations. The model is based on a circular crosssection geometry of the nanotube composed of semirigid AlO6 octahedra and SiO4 tetrahedra. The monodispersity in the nanotube diameter is explained in terms of a minimum in the strain energy due to differences in bond energies on the inner and outer surfaces. The model also reproduces the diameter dependence of the radial breathing mode RBM frequency and is in accord with midinfrared spectroscopic characterization.

Evidence for anisotropic vibration of diatomic adsorbates—NO and CO chemisorbed on stepped Pt(112)

Both NO and CO preferentially chemisorb on step sites of the Pt(112) crystal orienting the intermolecular bond in the downstairs direction. Using the digital electron stimulated desorption-ion angular distribution method (ESDIAD), an elliptical angular distribution of the desorbing O+ ions was detected from the NO/Pt(112) system, with the longer axis of the ellipse normal to the step-edge direction. On the other hand, the O+ ESDIAD pattern from the CO/Pt(112) system shows an approximately cylindrical symmetric shape. Heating of the crystal leads to broadening of the ion desorption patterns in both cases without change in the patterns’ elliptical or circular cross-sectional geometry. These results are interpreted as being due to ion desorption from NO molecules bonded to two Pt atoms on the step edge and vibrating with a longer amplitude in the direction perpendicular to the step. In the case of CO, bonded to a single Pt atom, the amplitude of vibration is approximately the same in directions parallel and perpendicular to the step edge. Thus, in certain cases ESDIAD patterns may be used to determine the hybridization state of adsorbates.

Unusual identities for special functions from waveguide propagation analyses

The analysis of electromagnetic wave propagation in cylindrical waveguides with step discontinuities leads naturally to sets of unusual identities for various special functions. Emphasis is placed on those expressions associated with classical rectangular and circular cross-sectional geometry. From a mathematical point of view it turns out, as expected, that the identities are related to bilinear expansions for Green's functions affiliated with Sturm-Liouville boundary-value problems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>