Uniform Circular Cross-section Research Articles

Keratin protein nanofibers from merino wool yarn: a top-down approach for the disintegration of hierarchical wool architecture to extract α-keratin protein nanofibers.

We report the extraction of keratin nanofibers from the medulla of a parent yarn after denaturing the cuticle and cortex microstructures of a merino wool yarn. Controlled alkaline hydrolysis, followed by high-speed blending in acetic acid, allowed for the extraction of keratin protein nanofibers with an average diameter of 25 nm and a length of less than 3 μm. SEM and AFM analyses showed the removal of cuticle cells from the yarn. FT-IR and DSC analyses confirmed the hydrolysis and denaturation of the sheet protein matrix of cuticle cells. XPS analysis provided strong evidence for the gradual removal of the epicuticle, cuticle cells, and cortex of the hierarchical wool structure with an increase in alkaline hydrolysis conditions. It was confirmed that the merino wool yarn subjected to hydrolysis under alkaline conditions exposed its internal fibrillar surface. In an acetic acid medium, these fibrillar surfaces obtained a surface charge, which further supported the defibrillation of the structure into its individual nanofibrils during high-speed blending. The extracted nanostructures constitute mainly α-helical proteins. The morphology of the nanofibers is composed of a uniform circular cross-section based on the images obtained using AFM, TEM, and SEM. The extracted nanofibers were successfully fabricated into transparent sheets that can be used in several applications.

나선형 파동유도관 결합을 통한 초음파센서의 탐지범위 개선

This paper presents a method to improve the detectable range of an ultrasonic sensor for distance measurements by coupling the sensor with a helical waveguide. In particular, this study aimed to decrease the effective length of circularly curved waveguides, in addition to reducing the minimum and maintaining the maximum detectable distances. To this end, finite element analyses were used to predict the ultrasound propagation in a waveguide with a uniform circular cross-section along the spiral path. Two types of cross-sectional sizes were compared: one with a diameter identical to that of the sensor face and another with a diameter twice this value. Furthermore, experiments were performed with fabricated prototypes to evaluate the detectable range by measuring the minimum and maximum detectable distances. Notably, by coupling the helical waveguide with the ultrasonic sensor, the minimum detectable distance was reduced to 1/3 times that for a sensor without the waveguide, while the maximum detectable distance was maintained. Moreover, the effective length of the helical waveguide was decreased, as compared with that of linear or circularly curved waveguides.

Viscous heating effects on heat transfer characteristics of laminar compressible channel flow

The present paper investigates viscous heating effects on heat transfer characteristics of laminar Newtonian compressible channel flow. At first, incompressible Poiseuille flow case is addressed analytically by including viscous dissipation term in energy conservation equation. Temperature distributions in the channel cross-section and local Nusselt numbers are derived as functions of the Brinkman number, highlighting the role of the viscous term. The analysis is numerically supported by a set of CFD simulations. Additional CFD results are employed to extend the analysis to compressible flow case resulting in dedicated local Nusselt number correlations, function of Brinkman and Mach numbers, and expansion-altered temperature profiles. The study assumes no-slip flow and no temperature-jump boundary conditions at the channel wall (Knudsen number Kn<10−3), and addresses both fluid heating and cooling, both uniform heat flux (UHF) and uniform wall temperature (UWT) boundary condition (BC), and both circular (CR) and parallel-plate (PP) channel cross-section.

Numerical Investigation of Thermo-Hydraulic Characteristics of Non-Uniform Transverse Rib Roughened Solar Heater

A 3-D computational fluid dynamics (CFD) investigation on heat transfer and fluid flow of solar air heater duct roughened with transverse rib of non-uniform cross-section of square wave profile has been carried out using ANSYS Academic Research CFD 15.0. For comparison, transverse rib of uniform square and circular cross-section has also been investigated. Relative roughness pitch and relative roughness width of rib roughness have been taken as 10 and 85 respectively. Relative roughness height and Reynolds number were varied from 0.015–0.043 and 3000–15 000, respectively. The present CFD methodology has been validated with the experimental results. The maximum augmentation in Nusselt number over that of smooth duct was 2.2 and the corresponding enhancement of friction factor was 3.4 times.

Unsteady Incompressible Stokes Flow through Porous Pipe of Uniform Circular Cross Section with Periodic Suction and Injection

This work is concerned with the flow of a Newtonian fluid through a pipe of constant circular cross section which is uniformly porous. The governing unsteady equations are solved analytically after converting them to a third order ordinary differential equation using similarity transformation method. Expressions for axial and radial velocity components and pressure distribution are obtained. The characteristics of complex axial velocity and complex radial velocity for different values of parameters are analysed. The effects of small suction and small injection are delineated through graphs. Results reveal that suction or injection has significant influence on the flow.

Super-stretchable graphene oxide macroscopic fibers with outstanding knotability fabricated by dry film scrolling.

Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young's moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large-area GO thin films (e.g., 800-1200 cm(2) or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76%), high toughness (up to 17 J/m(3)), and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple, and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of ca. 0.48 V/μm and high current densities (5.3 A/cm(2)). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared with bar coating followed by dry film scrolling.

Soil‐pile interaction in the pile vertical vibration considering true three‐dimensional wave effect of soil

SUMMARYThe dynamic response of an end bearing pile embedded in a linear visco‐elastic soil layer with hysteretic type damping is theoretically investigated when the pile is subjected to a time‐harmonic vertical loading at the pile top. The soil is modeled as a three‐dimensional axisymmetric continuum in which both its radial and vertical displacements are taken into account. The pile is assumed to be vertical, elastic and of uniform circular cross section. By using two potential functions to decompose the displacements of the soil layer and utilizing the separation of variables technique, the dynamic equilibrium equation is uncoupled and solved. At the interface of soil‐pile system, the boundary conditions of displacement continuity and force equilibrium are invoked to derive a closed‐form solution of the vertical dynamic response of the pile in frequency domain. The corresponding inverted solutions in time domain for the velocity response of a pile subjected to a semi‐sine excitation force applied at the pile top are obtained by means of inverse Fourier transform and the convolution theorem. A comparison with two other simplified solutions has been performed to verify the more rigorous solutions presented in this paper. Using the developed solutions, a parametric study has also been conducted to investigate the influence of the major parameters of the soil‐pile system on the vertical vibration characteristics of the pile. Copyright © 2013 John Wiley &amp; Sons, Ltd.

EFFECTS OF GEOMETRY OF THE INTRAMEDULLARY STEM OF THE ULNA COMPONENT OF HINGED ELBOW JOINT PROSTHESES ON THE BONE AND IMPLANT BENDING STRESSES

Cemented intramedullary stems are commonly used in total elbow arthroplasty and a considerable amount of time and money are spent for the design of such devices. In the endeavor of reducing production cost of implants, it is of particular interest as to how the geometry of the intramedullary stem can be altered in order to reduce the amount of raw material used in the manufacture of these components. The main aim of this study was to establish a simple mechanics model in preliminary designing of an elbow joint, so that the effects of the geometry of the intramedullary stem of the ulna component of hinged elbow joint prostheses on the bending stress distribution in the ulna bone and the prosthesis stem during static loading after cemented fixation of the implant can be readily estimated. Two mathematical models, namely (i) linear load transfer model and (ii) beams on elastic foundation model were used. The material considered is biocompatible stainless steel (316L). The locations of maximum bending stress occurrence were identified. Special attention was given toward identifying the locations of stress concentrations as well as the degree of stress shielding expected with various stem geometries. The results were compared to that obtained using well-established finite element analysis techniques and the beams on elastic foundation model were chosen to interpret the stresses. It was found that reducing the length of the intramedullary stem or alternatively tapering the distal end of the stem results in a considerable reduction of stress shielding and renders the bending stress distribution in the bone to be more natural. The use of a tapered stem of rectangular cross section showed a 50% reduction in material usage and a reduction of stress shielding compared to that for a stem of uniform circular cross section. Tapered rectangular sections gave the best results in terms of functionality and cost effectiveness. This observation agrees very well with the rationale of implant design that is practiced over the years. The stresses found using this study can be used for preliminary checks against yield and fracture of the stem material and bone material.

Water-wave trapping by floating circular cylinders

Under the assumptions of the linearized theory of small-amplitude water waves, it is proved that plane waves, normally incident upon a semi-immersed cylinder of uniform circular cross-section floating freely on the surface of a fluid of infinite depth, are capable of being totally reflected. Numerically, this is shown to occur at a single non-dimensional frequency. This remarkable result is used to construct examples of motion-trapped modes, involving pairs of freely floating cylinders moving either in phase or out of phase. The former case is equivalent to having a motion-trapped mode for a single such cylinder next to a rigid vertical wall. In the latter out-of-phase case, the pair of cylinders move as if they form the wetted sections of a single rigidly connected catamaran structure.

Mechanical model and superelastic properties of carbon microcoils with circular cross-section

Here we report on an unconventional Ni–P alloy-catalyzed, high-throughput, highly reproducible chemical vapor deposition of ultralong carbon microcoils using acetylene precursor in the temperature range 700–750 °C. Scanning electron microscopy analysis reveals that the carbon microcoils have a unique double-helix structure and a uniform circular cross-section. It is shown that double-helix carbon microcoils have outstanding superelastic properties. The microcoils can be extended up to 10–20 times of their original coil length, and quickly recover the original state after releasing the force. A mechanical model of the carbon coils with a large spring index is developed to describe their extension and contraction. Given the initial coil parameters, this mechanical model can successfully account for the geometric nonlinearity of the spring constants for carbon micro- and nanocoils, and is found in a good agreement with the experimental data in the whole stretching process.

Mechanical Properties of Single-Walled Carbon Nanotubes - A Finite Element Approach

In this paper, the mechanical properties, such as the axial and radial Young’s moduli, shear moduli, buckling loads and natural frequencies, of single-walled carbon nanotubes, are estimated by a finite element approach. Each carbon nanotube is simulated as a frame-like structure and the primary bonds between two nearest-neighboring atoms are treated as isotropic beam members with a uniform circular cross-section. In the modeling work, the BEAM4 element in commercial code ANSYS is selected to simulate the carbon bonds and the atoms are nodes. As to the input parameters of the BEAM4 element, they are determined via the concept of energy equivalence between molecular dynamics and structural mechanics, and represented in terms of the force constants of the carbon bonds found in molecular mechanics. Based on this modeling concept, finite element models of both armchair and zigzag types of carbon nanotubes with different sizes are established and the mechanical properties of these tubes are then effectively predicted. Most of the computed results which can be compared with existing results show good agreement. Moreover, the effects of tube diameter, length etc., on the mechanical properties are also investigated.

The decay of suddenly blocked flow in a curved pipe

Pressure-driven viscous flow through a rigid curved pipe of uniform circular cross-section which is suddenly stopped, for example through the instantaneous closure of a valve, is considered here. The profile of the flow at early times after the stoppage is analysed asymptotically, by matching diffusive boundary layers to a core flow that is driven by an axial pressure gradient. This pressure gradient is unknown a priori and, furthermore, exhibits singular behaviour immediately after the stoppage. This analysis therefore provides the flow information at small but finite times that is required for numerical determination of the flow at later times. The limiting case of weak curvature is also considered, where linearization of the governing flow equations is possible. The results illustrate some novel features of the flow which result solely from the pipe’s curvature and the consequences for the flow’s rate of decay are discussed.

Vibration and stability of an axially moving beam immersed in fluid

Vibration and stability are investigated for an axially moving beam in fluid and constrained by simple supports with torsion springs. The equations of motion of the beam with uniform circular cross-section, moving axially in a horizontal plane at a known rate while immersed in an incompressible fluid are derived first. An “axial added mass coefficient” and an initial tension are implemented in these equations. Based on the Differential Quadrature Method (DQM), a solution for natural frequency is obtained and numerical results are presented. The effects of axially moving speed, axial added mass coefficient, and several other system parameters on the dynamics and instability of the beam are discussed. Particularly, natural frequency in terms of the moving speed is presented for fixed–fixed, hinged–hinged and hybrid supports with torsion spring. It is shown that when the moving speed exceeds a certain value, the beam becomes subject to buckling-type instability. The variations of the lowest critical moving speed with several key parameters are also investigated.

Stability of a deploying/extruding beam in dense fluid

The equations of motion of a flexible slender cantilevered beam with uniform circular cross-section, extending axially in a horizontal plane at a known rate while immersed in an incompressible fluid are derived. An “axial added mass coefficient” is implemented in these equations in order to better approximate the mass of fluid which stays attached to the oscillating beam while moving in the axial direction. Realistic initial conditions are given to the system and numerical solutions are obtained. The dynamical behaviour of the system is observed for cases of constant extension rate and for a trapezoidal deployment rate profile. In the case of low constant extension rates, the system displays a phase of oscillation with increasing amplitude and decreasing frequency until the motion is strongly damped and later becomes statically unstable. For faster deployment rates, the beam has a short flutter phase at the beginning of the deployment, followed by a brief phase of damped oscillation until it exhibits static divergence. For fast enough deployment rates, the system is unstable from the beginning and never stabilizes. The effect the axial added mass coefficient has on the system is studied and it is found that it plays two roles in the stability of the system. The trapezoidal deployment rate profile is studied because it is deemed more representative of real-life applications. For long deployment times, the system behaves in a very similar manner to one with low constant extension rate, except that it does not become statically unstable. For shorter deployment times, the maximum amplitude of the tip displacement is usually attained after the beam has stopped extruding.

Three-dimensional flow due to a microcantilever oscillating near a wall: an unsteady slender-body analysis

We compute the drag on a slender rigid cylinder, of uniform circular cross-section, oscillating in a viscous fluid at small amplitude near a horizontal wall. The cylinder's axis lies at an angleαto the horizontal and the cylinder oscillates in a vertical plane normal to either the wall or its own axis. The flow is described using an unsteady slender-body approximation, which we treat both numerically and using an iterative scheme that extends resistive-force theory to account for the leading-order effects of unsteady inertia and the wall. Whenαis small, two independent screening mechanisms are identified which suppress end-effects and produce approximately two-dimensional flow along the majority of the cylinder; however, three-dimensional effects influence the drag at larger tilt angles.

Acoustic measurements and computational results on material specimens with harmonic variation of the cross section

The present work represents both an experimental and theoretical investigation of the behavior of finite cylindrical rods with harmonic variation of the cross section. The matrix method was used to compute the transfer power spectra of elastic rods with uniform circular cross section and of rods with harmonic variation of the cross section with distance. Theoretical and experimental results show that for a rod with periodical variation of the cross section, a new set of supplementary frequencies appear for which the transfer power coefficient has significant values, which are in relation with the space period of the inhomogeneity. Also, due to the radial component of the displacement certain modes are enhanced which satisfy boundary conditions on the surface and are obtained from the zeroes of Bessel functions.

FREE BENDING VIBRATION OF A MULTI-STEP ROTOR

The free bending vibration of a rotating shaft composed of multi-step segments with each segment having a uniform circular cross-section has been analyzed using the Timoshenko beam model. Torque has been applied at each end as in a power-transmission shaft and the gyroscopic effect due to the shaft rotation has also been considered. The separation of time and spatial variables has been performed for the differential equation of motion, and then the spatial solution in a segment of uniform cross-section has been expressed in a closed form. Application of boundary conditions has induced global equations of a rotor system, from which the natural frequencies and corresponding mode shapes have been obtained. The entire procedure is straightforward, and thus the resultant mode shapes are continuous unlike the result of existing methods such as the finite element method and transfer matrix method. Effects of the rotating speed and the applied torque at both ends on the free vibration of the rotating shaft have been discussed. The natural frequencies of the forward and backward modes have been compared with the results using the finite element method. The shear force and bending moment distributions along the shaft at each mode have been derived by differentiating the mode curves.

Computational analysis of flow in a curved tube model of the coronary arteries: effects of time-varying curvature.

The flow through a curved tube whose radius of curvature varies with time was studied in order to better understand flow patterns in coronary arteries. A computational flow model was constructed using commercially available software. The artery model featured a uniform circular cross section, and the curvature was assumed to be constant along the tube, and in one plane. The computational model was verified with the use of a dynamically similar in vitro apparatus. A steady uniform velocity was prescribed at the entrance at a Reynolds number of 300. Two sets of results were obtained: one in which the curvature was held constant at the mean, maximum and minimum radii of curvature (quasistatic), and another in which the curvature was varied sinusoidally in time at a frequency of I Hz (dynamic). The results of the dynamic analysis showed that the wall shear rates varied as much as 52% of the static mean wall shear rate within a region of 10 tube diameters from the inlet. The results of the dynamic analysis were within 6% of the quasistatic predictions. Realistic modeling of the deforming geometry is important in determining which locations in the coronary arteries are subjected to low and oscillating wall shear stresses, flow patterns that have been associated with atherogenesis.

Twist in Balanced-ply Structures

The theory of the bending and twisting of thin rods of uniform circular cross-section, and inextensible centre-line, is used to find an equation for the pretwist that must be inserted into the singles strands to create a balanced two-ply yarn of specified ply twist. In the final section, this result is extended to an N-ply structure.

The equilibrium of the convergence point in two-strand yarn plying

In this paper the theory of the bending and twisting of thin rods of uniform circular cross-section is used to find the relationships between the ply-helix angle, the strand convergence angle, and the applied tensions and torques required to hold the plied strands illustrated in Fig. 1 in equilibrium.The solution of this problem is of importance to the textile yarn manufacturing industry where singles yarns, made from long staple fibres, such as wool, are plied together in order to bind the surface fibres more effectively into the plied yarn structure. This produces warp yarns that are more abrasive resistant.A formula for the relationship between the pre-twist in two initially straight strands, and the helix angle of the plied structure obtained when they are allowed to twist together into a balanced ply structure is also derived in Section 4. A balanced two-ply structure is one that will maintain its configuration without the application of external tension or torque. Balanced ply structures are also important in textile manufacturing processes.