Wide Range Of Curvatures Research Articles

A Mach-Zehnder-based optical fiber sensor enables multi-directional and wide-range curvature sensing with the assistance of CNN

In this work, wide-range curvature sensing in multiple directions was achieved by combining a Mach-Zehnder-based optical fiber sensor (OFS) with convolutional neural networks (CNNs). The experimental results show that the curvature sensitivity of the proposed sensor is − 8.8320 nm/m−1 in the range of 0–3.1171 m−1. The application of CNNs significantly improves the measurement range to 0–10.4167 m−1, and the sensor can realize measurements over a wide curvature range in four directions. The accuracy of the measurements can still be guaranteed despite a sudden decrease in the number of wavelength sampling points, and curvature direction recognition was realized. Further, OFSs can achieve a wide range of curvature sensing in 12 directions by taking full advantage of the information contained in the transmission spectrum. The proposed technique is highly versatile and conducive to the popularization of OFSs in the field of curvature measurement.

Method for reconstruction of axisymmetric capillary wave surface topography using inverse ray-tracing of refracted laser sheet

Capillary waves can be used to measure the fundamental fluid properties such as surface tension as well as, potentially, the viscosity of Newtonian fluids. This requires the measurement of various wave parameters, mainly wavelength, amplitude, and decay coefficient. However, the different scales of magnitudes make it a challenging task. Optical methods are well suited to analyze such problems due to their non-intrusive nature and high dynamic measurement resolution in both space and time. These methods are further categorized as point methods for a single probe measurement and space–time methods for transient measurement of the complete surface. Dynamic space–time methods are preferred despite the associated complex post-processing since they enable reconstruction of the wave surface. Some existing methods are discussed, and an improved method is then proposed to actually solve the associated inverse optics problem. In the method, an axisymmetric wave surface is re-constructed by analyzing the refracted laser sheet. The assumptions, simplifications, and constraints are taken to be compatible with experimental aspects for future validation. It is derived using the fundamental concepts in physics and the only major assumption of the axisymmetric nature of wave surface. The method exploits the underlying symmetry in the topography, making it more versatile, and suited for linear and non-linear capillary waves and waves with planar wavefront. The impact of parameters on the final result is determined through numerical simulations. Very low error (average and maximum) values are observed between reference and reconstructed topography for damped and undamped wave surfaces with a wide range of curvatures. Optimum values of critical parameters and associated reasoning are presented.

Novel Bending Sensor Based on a Solution-Processed Cu2O Film with High Resolution Covering a Wide Curvature Range.

A Cu2O film is prepared on a flexible polyethylene terephthalate substrate for a bending sensor using the spin–spray method, a facile and low-environmental-load solution process. The Cu2O bending sensor shows high sensitivity and high resolution not only over a wide range of curvatures (0 < κ < 0.21 mm–1) but also for very small curvature changes (Δκ = ∼ 0.03 mm–1). The bending response of the sensor exhibited a curvature change of high linearity with a good gauge factor (18.2) owing to the grain-boundary resistance and piezoresistive effects of the fabricated Cu2O film. In addition, the sensor possesses good repeatability, stability, and long-term (>30 days) and mechanical fatigue durability (1000 bending–release cycles). The sensor is capable of detailed monitoring of large- and small-scale human motions, such as finger bending, wrist bending, nodding, mouth opening/closing, and swallowing. In addition, excellent stability and repeatability of the monitoring performance is observed over a wide range of motion angles and speeds. All of these results demonstrate the potential of the flexible bending sensor based on the Cu2O film as a candidate for healthcare monitoring and wearable electronics.

Numerical investigation of flow characteristics and heat transfer performance in curve channel with periodical wave structure

Flow and heat transfer in curve channel have been studied extensively due to the presence of the secondary flow induced by the centrifugal force. However, for the curved channel with small curvature, weakened centrifugal force reduces the intensity of secondary flow and heat transfer enhancement is attenuated accordingly. For sake of maintaining high heat transfer efficiency in curve channel with a wide range of curvature, periodical wave structure was introduced into the smooth-curve channel by this study. A three-dimensional model of the curve-wave structure was established and numerical simulation was carried out to explore the flow characteristics and heat transfer performance in the proposed channel. In addition, the effects of the wave amplitude on the channel performance were analyzed. The results showed that the heat transfer of smooth-curve channel can be enhanced remarkably by applying wave structure on the channel wall, and the overall performance factor indicates that the heat transfer argumentation outweighs the pressure loss penalty. It was also found that the heat transfer in the curve-wave channel can be further enhanced by increasing wave amplitude. The most effective heat transfer enhancement can be achieved based on the evaluation of the overall performance factor.

Stress intensity factor for clamped SENT specimen containing non-straight crack front and side grooves

Three-dimensional (3D) finite element analyses (FEA) of clamped single-edge notched tension (SENT) specimens are performed to evaluate the stress intensity factor (SIF). Both the average and local SIF values over the crack front are evaluated. Plane-sided (PS) specimens containing both straight and curved crack fronts and side-grooved (SG) specimens containing straight crack fronts are considered including six average crack lengths (i.e. aave/W=0.2–0.7). PS specimens with three thickness-to-width ratios (i.e. B/W=0.5, 1 and 2) are analyzed. The curved crack front is assumed to be bowed symmetrically and characterized by a power-law expression with a wide range of curvatures. For SG specimens, one relative thickness (B/W=1) and ten depths of side groove are considered. The 3D SIF are compared with the present two-dimensional (2D) SIF. It is observed that the 2D SIF are sufficient as the difference between the 2D and 3D SIFs is in general within 10% if the crack front straightness requirements reported in the literature is satisfied. An empirical 3D SIF solution is developed that can potentially serve as a driving force for an assessment in actual structures that has similar crack geometries and loading configurations.

Effects of crack front curvature on J–R curve testing using clamped SE(T) specimens of homogeneous materials

Three-dimensional (3D) finite element analyses (FEA) of clamped single-edge tension (SE(T)) specimens are performed to investigate the impact of the crack front curvature on the elastic compliance, compliance rotation correction factor and average J-integral evaluated over the crack front. Specimens with six average crack lengths (i.e. aave/W = 0.2–0.7) and three thickness-to-width ratios (i.e. B/W = 0.5, 1 and 2) are analyzed. The curved crack front is assumed to be bowed symmetrically and characterized by a power-law expression with a wide range of curvatures. Several crack front straightness requirements for SE(B) and C(T) specimens specified in BS7448, ISO and ASTM E1820 standards are reviewed. Based on results of the numerical investigation, new crack front straightness criteria for the SE(T) specimen are proposed in the context of the nine-point measurement by using as a criterion that the errors in the estimated compliance and average J values should be no more than five percent. The proposed criteria depend on both aave/W and B/W, and are more advantageous than those specified in the BS, ISO and ASTM standards in terms of controlling the differences in J and compliance between the specimens with curved and straight crack fronts.

The importance of experimental design on measurement of dynamic interfacial tension and interfacial rheology in diffusion-limited surfactant systems

Abstract Pendant bubble and drop devices are invaluable tools in understanding surfactant behavior at fluid–fluid interfaces. The simple instrumentation and analysis are used widely to determine adsorption isotherms, transport parameters, and interfacial rheology. However, much of the analysis performed is developed for planar interfaces. The application of a planar analysis to drops and bubbles (curved interfaces) can lead to erroneous and unphysical results. We revisit this analysis for a well-studied surfactant system at air–water interfaces over a wide range of curvatures as applied to both expansion/contraction experiments and interfacial elasticity measurements. The impact of curvature and transport on measured properties is quantified and compared to other scaling relationships in the literature. The results provide tools to design interfacial experiments for accurate determination of isotherm, transport and elastic properties.

Evaluation of the Shape Symmetry of Bilateral Normal Corneas in a Chinese Population

PurposeTo investigate the bilateral symmetry of the global corneal topography in normal corneas with a wide range of curvature, astigmatism and thickness valuesDesignCross-Sectional StudyMethodsTopography images were recorded for the anterior and posterior surfaces of 342 participants using a Pentacam. Elevation data were fitted to a general quadratic model that considered both translational and rotational displacements. Comparisons between fellow corneas of estimates of corneal shape parameters (elevation, radius in two main directions, Rx and Ry, and corresponding shape factors, Qx and Qy) and corneal position parameters (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) were statistically analyzed.ResultsThe general quadratic model provided average RMS of fit errors with the topography data of 1.7±0.6 µm and 5.7±1.3 µm in anterior and posterior corneal surfaces. The comparisons showed highly significant bilateral correlations with the differences between fellow corneas in Rx, Ry, Qx and Qy of anterior and posterior surfaces remaining insignificantly different from zero. Bilateral differences in elevation measurements at randomly-selected points in both corneal central and peripheral areas indicated strong mirror symmetry between fellow corneas. The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively. Rotational displacement angle α along X axis had similar distributions in bilateral corneas, while rotation angle β along Y axis showed both eyes tilting towards the nasal side. Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.ConclusionsAnalysis of corneal topography demonstrated strong and statistically-significant mirror symmetry between bilateral corneas. This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.

Numerical simulation of Dean number and curvature effects on magneto-biofluid flow through a curved conduit

A numerical study is performed to investigate the magnetohydrodynamic viscous steady biofluid flow through a curved pipe with circular cross section under various conditions. A spectral method is applied as the principal tool for the numerical simulation with Fourier series, Chebyshev polynomials, collocation methods and an iteration method as secondary tools. The combined effects of Dean number, Dn , magnetic parameter, Mg , and tube curvature, δ, are studied. The flow patterns have been shown graphically for large Dean numbers as well as magnetic parameter and a wide range of curvatures, 0.01 ≤δ≤ 0.2. Two-vortex solutions have been found. Axial velocity has been found to increase with an increase of Dean number, whereas it is suppressed with greater curvature and magnetic parameters. For high magnetic parameter and Dean number and low curvature, almost all the fluid vortex strengths are weak. The study is relevant to magnetohydrodynamic blood flow in the cardiovascular system.

Effects of Dean Number and Curvature on Fluid Flow through a Curved Pipe with Magnetic Field

Abstract Numerical study is performed to investigate the Magnetohydrodynamics fluid flow through a curved pipe with circular cross-section under various conditions. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The Magnetohydrodynamics incompressible viscous steady flow through a curved pipe with circular cross-section is investigated numerically to examine the combined effects of high Dean Number D n , magnetic parameter M g and non- dimensional curvature δ . The flow patterns have been shown graphically for large Dean Numbers as well as magnetic parameter and a wide range of curvatures 0.01 ≤ δ ≤ 0.4 .Two vortex solutions have been found. Axial velocity has been found to increase with the increase of Dean Number and decrease with the increase of curvature and magnetic parameter. For high magnetic parameter, Dean Number and low curvature almost all the fluid particles strength are weak.

Bending sensor based on intermodal interference properties of two-dimensional waveguide array fiber

We propose a highly sensitive bending sensor based on the intermodal interference properties of a strongly coupled two-dimentional waveguide array fiber (WAF). The interference resonance peaks formed by the SMF-WAF-SMF Mach-Zehnder interferometer are intrinsically the result of interference between the LP(01)-like supermode and other higher order supermodes, displaying supernormal sensitivity to bending in a wide curvature range. The bending sensitivity of the intermodal MZI is a quadratic function of curvature, and the resonance wavelength shift is up to 100 nm within a curvature range 0-10 m(-1). The fabrication reveals briefness, and temperature response shows little impact on the bend sensing precision. The high bending sensitivity and wide sensing range can make this device a candidate for bending discrimination and measurement in widespread areas.

NMR-NOE and MD Simulation Study on Phospholipid Membranes: Dependence on Membrane Diameter and Multiple Time Scale Dynamics

Motional correlation times between the hydrophilic and hydrophobic terminal groups in lipid membranes are studied over a wide range of curvatures using the solution-state (1)H NMR-nuclear Overhauser effect (NOE) and molecular dynamics (MD) simulation. To enable (1)H NMR-NOE measurements for large vesicles, the transient NOE method is combined with the spin-echo method, and is successfully applied to a micelle of 1-palmitoyl-lysophosphatidylcholine (PaLPC) with diameter of 5 nm and to vesicles of dipalmitoylphosphatidylcholine (DPPC) with diameters ranging from 30 to 800 nm. It is found that the NOE intensity increases with the diameter up to ∼100 nm, and the model membrane is considered planar on the molecular level beyond ∼100 nm. While the NOE between the hydrophilic terminal and hydrophobic terminal methyl groups is absent for the micelle, its intensity is comparable to that for the neighboring group for vesicles with larger diameters. The origin of NOE signals between distant sites is analyzed by MD simulations of PaLPC micelles and DPPC planar bilayers. The slow relaxation is shown to yield an observable NOE signal even for the hydrophilic and hydrophobic terminal sites. Since the information on distance and dynamics cannot be separated in the experimental NOE alone, the correlation time in large vesicles is determined by combining the experimental NOE intensity and MD-based distance distribution. For large vesicles, the correlation time is found to vary by 2 orders of magnitude over the proton sites. This study shows that NOE provides dynamic information on large vesicles when combined with MD, which provides structural information.

Stable solution zone for fluid flow through curved pipe with circular cross-section

Numerical study is performed to examine numerically the stable solution for the incompressible viscous steady flow through a curved pipe with circular cross-section. Also the combined effects of high Dean Number Dn and curvature δ on the flow are investigated. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The flow patterns have been shown graphically for large Dean Numbers and a wide range of curvature, 0.01≤δ≤0.9.Two vortex solutions have been found for secondary flow. Axial velocity has been found to increase with the increase of Dean number and decrease with the increase of curvature. For high Dean number and low curvature almost all the fluid particles leave the inner half of the cross-section. The stable solution zone increases with the increase of curvature up to a certain limit, then decrease.DOI: 10.3329/jname.v7i1.3630

A piezolaminated composite degenerated shell finite element for active control of structureswith distributed piezosensors and actuators

This paper deals with the formulation of a nine-noded piezolaminated degenerated shellfinite element for modeling and analysis of multilayer composite general shell structureswith bonded/embedded distributed piezoelectric sensors and actuators. The distributedPZT sensors and actuators used in the composite smart structures are relatively thin andcould have arbitrary variation of curvatures and thicknesses. They cannot be modeled withshell elements based on curvilinear shell theories which would need the specification ofconstant shell curvatures and thicknesses. Modeling them with piezo finite elementsavailable in popular commercial codes like ABAQUS, ANSYS, MARC, etc, would needrelatively greater computational effort as they are based on solid element formulation. Inview of these, the present proposed degenerated piezoelectric shell element would be abetter choice giving good computational accuracy and efficiency. The main advantageof a degenerate shell element is that it is not based on any shell theories andis applicable over a wide range of curvatures and thicknesses. This element isdeveloped by using the degenerate solid approach based on Reissner–Mindlinassumptions which allow the shear deformation and rotary inertia effect to be consideredand the 3D field is reduced to a 2D field in terms of mid-surface nodal variables.Uniformly reduced integration is carried out to overcome membrane locking and shearlocking and the numerical integration is carried out in all three directions toobtain accurate results. The present element has 45 elastic degrees of freedomand 10 electric degrees of freedom per piezoelectric layer in the element. Thepotential induced due to bending deformation is more accurately represented byassuming quadratic variation of the electric potential through the thickness of eachpiezoelectric layer. This is achieved by interpolating using nodal mid-plane electricpotentials and one electric degree of freedom representing the potential differencebetween the top and bottom surfaces of the piezoelectric layer. Few case studiesof composite general shells with piezoelectric sensors and actuators have beenconsidered by modeling them with the above elements and the active vibration controlperformance has been studied using linear quadratic Gaussian (LQG) control.

A parameter study for static and dynamic denting

A parametric study of the factors controlling static and dynamic denting, as well as local stiffness, has been made on simplified panels of different sizes, curvatures, thicknesses and strengths. Analyses have been performed using the finite element method to predict dent resistance and panel stiffness. A parametric approach is used with finite element models of simplified panels. Two sizes of panels with square plan dimensions and a wide range of curvatures are analysed for several combinations of material thickness and strength, all representative of automotive closure panels. Analysis was performed using the implicit finite element code, LS-NIKE, and the explicit dynamic code, LS-DYNA for the static and dynamic cases, respectively. Panel dent resistance and stiffness behaviour are shown to be complex phenomena and strongly interrelated. Factors favouring improved dent resistance include increased yield strength and panel thickness. Panel stiffness also increases with thickness and with higher curvatures but decreases with size and very low curvatures. Conditions for best dynamic and static dent performance are shown to be inherently in conflict ; that is, panels with low stiffness tend to perform well under impact loading but demonstrate inferior static dent performance. Stiffer panels are prone to larger dynamic dents due to higher contact forces but exhibit good static performance through increased resistance to oil canning.

Contour integration in color vision: a common process for the blue–yellow, red–green and luminance mechanisms?

We compare the performance of the red–green, blue–yellow and luminance postreceptoral mechanisms on a contour integration task requiring the linking of oriented Gabor elements across space to extract a winding ‘path’ or contour. We first establish that for all three mechanisms curvature and contrast are independent; losses in performance due to one cannot be compensated by changes in the other. We then compare contour integration by the three mechanisms using a method that controls for their differences in cone contrast thresholds. Our results show that despite the poor orientation discrimination thresholds and poor spatial sampling found for the blue–yellow mechanism, all three mechanisms perform similarly on contour integration over a wide range of curvatures. Furthermore, all three mechanisms have the same dependence on path curvature. We also investigate the effects of adding external orientation noise. Our results imply that the internal orientation noise for extracting ‘aligned’ path elements is similar in the three mechanisms and for all path curvatures, and the relative efficiencies are also similar for the three mechanisms. To account for our results, we propose that the three postreceptoral mechanisms use a common contour integration process. This linking process, however, cannot be color-blind; our last experiment shows that linking between different chromatic mechanisms or between opposite spatial phases disrupts contour integration. We thus propose that the common integration process remains sensitive to the color contrast and phase of its inputs.

Correlation of flame speed with stretch in turbulent premixed methane/air flames

Direct numerical simulations of two-dimensional unsteady premixed methane/air flames are performed to determine the correlation of flame-speed with stretch over a wide range of curvatures, and strain rates generated by intense two-dimensional turbulence. Lean and stoichiometric premixtures are considered with a detailed C1-mechanism for methane oxidation. The computed correlation shows the existence of two distinct stable branches. It further shows that exceedingly large negative values of stretch can be obtained solely through curvature effects, which give rise to an overall nonlinear correlation of the flame speed with stretch. Over a narrower stretch range, −1≤Ka≤1, which includes 90% of the sample, the correlation is approximately linear, and, hence, the asymptotic theory for stretch is practically applicable. Overall, one-third of the sample has negative stretch. In this linear range, the Markstein number associated with the positive branch is determined for different initial turbulence intensities. For high turbulence intensity, the large eddy turnover time becomes shorter than a flame time, and the flame propagation becomes less responsive to unsteady straining. Reductions in strain Markstein numbers by as much as 37% from comparable steady counterflow computations are reported. In addition to the conventional positive branch, a negative-branch is identified. This negative branch occurs when a flame cusp, with a center of curvature in the burnt gases is subjected to intense compressive strain, resulting in a negative displacement speed. Negative flame speeds are also encountered for extensive tangential strain rates exceeding a Karlovitz number of unity, a value consistent with steady counterflow computations. In both situations, consistent with earlier findings, the source of the reduction in flame speed is attributed to an imbalance between diffusion and reaction.

Anomalous height increases upon bending for an Alexander–de Gennes polymer brush

We examine the bending of an Alexander–de Gennes polymer brush over a wide range of curvature from weak to strong. Two different models are used, a blob model and a simpler Flory mean field model. In both cases the height change upon bending is anomalous. In the case of a blob model the height increases for weak bending. In the Flory model there is no height change to first order in the curvature. This is in sharp contrast to more sophisticated theories for brushes with free ends, and may have applications to real-life Alexander–de Gennes brushes which have been synthesized recently.

Bending Performance of Fiber-Optic Cable Sheaths: Application of New Apparatus and Techniques

Apparatus and techniques were developed by which moment-curvature curves can be generated over a wide range of curvatures, cable diameters, and environmental conditions. The resulting curves can be used to analyze bending performance in the same way as stress-strain curves are used to analyze tensile performance. In the first series of tests using this apparatus, five wire-reinforced fiber-optic cable sheaths were tested at room temperature. The wire reinforcement had a dominant, theoretically predictable effect on the bending stiffness of certain designs, while it was relatively unimportant in others. The key difference is the degree of encapsulation of the reinforcement, which can be controlled by simple changes in design. In addition, buckling performance can be improved by increasing the cross-sectional rigidity. In both cases, tensile performance is relatively unaffected. These findings are exemplified by the performances of a single-ply and a crossply design. Compared to the single ply, the crossply has the more rigid cross section and the lower degree of encapsulation. Both sheaths have nearly equal bending stiffness throughout the entire range of curvature, and the buckling radius of the crossply design (7.4 cm) is better than that of the single-ply design (8.4 cm) despite a 2 to 1 advantage in tensile stiffness. An effective design sequence has evolved from the results of this study: (a) select reinforcement for tensile performance, (b) adjust cross-sectional rigidity for buckling performance, and (c) adjust reinforcement encapsulation for bending stiffness performance. In this sequence, each step is nearly independent of the others.

Excitation of a Curved Slab Waveguide

The problem of exciting a surface wave on a hollow dielectric cylinder by an electric current line source is solved. Using the method of Watson, fields are expressed in terms of the residue series and the integral, which correspond to discrete and continuous modes of the curved slab waveguide. Strictly, all the discrete modes of the curved slab guide have radiation loss, and these modes are divided into three groups; those with practically negligible loss (<10-10 nepers/radian) (trapped modes), those with considerable loss (>several nepers/radian) (leaky modes), and the transition modes. The results clarify the behavior of bent slab guides over a wide range of curvature.