Decreasing Radius Of Curvature Research Articles

Kinetics and mechanical work done to move the body centre of mass along a curve.

When running on a curve, the lower limbs interact with the ground to redirect the trajectory of the centre of mass of the body (CoM). The goal of this paper is to understand how the trajectory of the CoM and the work done to maintain its movements relative to the surroundings (Wcom) are modified as a function of running speed and radius of curvature. Eleven participants ran at different speeds on a straight line and on circular curves with a 6 m and 18 m curvature. The trajectory of the CoM and Wcom were calculated using force-platforms measuring the ground reaction forces and infrared cameras recording the movements of the pelvis. To follow a circular path, runners overcompensate the rotation of their trajectory during contact phases. The deviation from the circular path increases when the radius of curvature decreases and speed increases. Interestingly, an asymmetry between the inner and outer lower limbs emerges as speed increases. The method to evaluate Wcom on a straight-line was adapted using a referential that rotates at heel strike and remains fixed during the whole step cycle. In an 18 m radius curve and at low speeds on a 6 m radius, Wcom changes little compared to a straight-line run. Whereas at 6 m s-1 on a 6 m radius, Wcom increases by ~25%, due to an augmentation in the work to move the CoM laterally. Understanding these adaptations provides valuable insight for sports sciences, aiding in optimizing training and performance in sports with multidirectional movements.

Influence of Anatomical Root Factors on Cyclic Fatigue Resistance of Heat Treated NiTi Instrument: A Review

Endodontic treatments have been improved over the last decade by the use of nickel titanium (NiTi) alloys. NiTi instrument had shape memory and superelastic properties which made the instrument more flexible, so the treatment quality was enhanced by eliminating the procedural errors. Although the numerous benefits of the NiTi instruments, the fracture was the most frequent failure that may be happened during its use due to flexural (cyclic) or torsional fatigue. Various thermo-mechanical heat treatments have been applied to NiTi instruments to improve fracture resistance and clinical performance. Several parameters influenced the fatigue resistance of NiTi files, and the most important factor that affected the likelihood of NiTi instrument fatigue was the root canal shape. Data collected of 100 papers from the Goggle scholar and Scien ceDirect database. After excluding 60 unrelated papers, thi s review of 40 included related studies aims to evaluate an overview of the anatomical root-related factors affecting t he cyclic fatigue of heat-treated NiTi instruments. Concl uded that the separation rates of file increased when the radius of curvature decreases and when the angle of curvature increased. Canals with the double curvatures increase the risk of cyclic fatigue. Also, the resistance to cyclic fatigue of NiTi files was affected by the canal curvature posit ion, with a short failure life coronally. So even in the improve ment of wire metallurgy and designs of instrument, the anatomy of canal still impact on the cyclic fatigue and should be considered during preparation especially with th e new concept of minimally invasive endodontic treatmen t.

Improvement of the bubble separation through eccentric planar cyclones: Experiments and CFD simulations

Planar cyclones have great advantages as electrolyzers, photocatalytic reactors, and gas–liquid separators. For planar cyclones, the separation efficiency of bubbles is a key parameter. The effect of eccentricity on bubble separation efficiency in planar cyclones was studied through a combination of experiments and simulations. When eccentricity dc = 0 mm, the separation efficiency of the bubbles decreased with an increase in the liquid injection velocity. This indicates that a greater centrifugal acceleration in planar cyclones does not contribute to bubble separation. Eccentricity dc = −5 mm resulted in a higher bubble separation efficiency. Each planar cyclone was divided into 12 sub-regions with equal areas. When eccentricity dc = −5 mm, subregions 11 and 12 exhibited larger bubble sizes, and a higher bubble separation efficiency was achieved. The area weighted average sauter mean diameter ds reached 0.47 mm and 0.475 mm and area weighted average gas volume fraction εs reached 2.75 % in subregion 11 when liquid Reynolds numberRel = 20075.4 and gas Reynolds number Reg = 23.8. The maximum separation efficiency can be increased from 43 % to 60 % when Rel = 20075.4 and Reg = 6.8 when the eccentricity varies from 0 to − 5 mm. Bubble size changes due to coalescence and breakup have an important influence on bubble separation. The trajectory of bubbles exhibits helix. The gradually decreasing curvature radius of the bubble trajectory dominates the bubble separation. Eccentric swirling field provides a sudden decrease in the swirl radius which promotes the reduction of the curvature radius of the bubble trajectory. This study provides an optimization method for the structural design of cyclones.

Effect of a Circular Cylinder on Hydrodynamic Characteristics over a Strongly Curved Channel

Curved channels are one of the most fundamental units of natural or artificial channels, in which there are different kinds of obstacles; these include vegetation patches, bridge piles, electrical tower foundations, etc., which are all present over a channel bend, and can significantly alter the hydrodynamic characteristics of a channel when compared to a bare bed. In this study, laboratory experiments and numerical simulations were combined to investigate the effect of a circular cylinder on the flow characteristics of a 180-degree U-shaped curved channel. Experimental data, including on water depth and three-dimensional velocity, which was obtained by utilizing acoustic Doppler velocimetry (ADV), were used to calibrate and verify the simulation results of the Reynolds-Averaged Navier–Stokes (RANS) model in the FLOW-3D software. Numerical results show that a larger cylinder diameter leads to an overall greater depth-averaged velocity at the section, a greater shear stress acting on the banks on which the cylinder is placed, and a greater increase in the depth-averaged velocity along the concave bank compared to that along the convex bank. When the diameter of the cylinder placed at the 90° section increases, two weaker circulations with the same direction are found near the water surface; for the submerged one, the two weaker circulations appear at the further downstream section, unlike the emergent one. The degree of variation degree in the shear stress acting on the banks is larger than that of the flowrate. As the flowrate increases or the radius of curvature decreases, the secondary flow intensity correspondingly elevates. However, the curvature radius of the curved channel plays a more important role in the secondary flow intensity than the flowrate does. For both the emergent and submergent cylinders, the large cylinder produces a greater secondary flow strength, but the emergent one has a greater secondary flow strength than the submergent one. In summary, the present study provides valuable knowledge on the hydrodynamics of flow around emergent and submergent structures over a curved channel, which could improve the future design of these structures.

Energy barrier for ion field emission from a dielectric liquid sphere.

Ion field emission from the surface of a dielectric liquid is commonly modeled as a kinetic process with an energy barrier lowered by the strength of the electric field. Expressions for the energy barrier exist for simplified cases such as a planar surface and a conducting sphere. This article derives an analytical expression for the more general case of a dielectric sphere, which is the continuum model and geometry for most cases of interest. The energy barrier is computed using the method of image charges, and compared to existing expressions for simpler models. The energy barrier increases at decreasing dielectric constant and decreasing radius of curvature. Ion emission from typical systems (the ideal Taylor cone and charged nanodroplets) differs substantially when calculated with either our model or with existing simpler models.

Combining Pancharatnam–Berry Phase and Conformal Coding Metasurface for Dual-Band RCS Reduction

A flexible, dual-broadband, and polarization-insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1 bit coding units “0” and “1” are formed by the Pancharatnam–Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this communication can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26–12.87 and 14.84–19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained, while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

Dynamic response of single curved fiber-metal hybrid lamina composites subject to low-velocity impact

Fiber-metal hybrid lamina composites (FM-HLCs) are a new kind of fiber-metal composites, which aims at addressing the metal-composite interface failure in conventional fiber-metal laminates. In the current study, the low-velocity impact tests were conducted to examine the dynamic response of single curved FM-HLCs. The influence of weave pattern of fiber-metal hybrid lamina, impact velocity and radius of curvature on the dynamic response is considered in the experiment. The deformation/failure modes, force-time histories and energy absorption were obtained. The high-speed cameras were used to capture the deformation/failure processes of FM-HLCs and the instantaneous images for digital image correlation analysis. The results indicate that the “fiber-metal hybrid lamina” strategy can efficiently help maintain the integrity of FM-HLCs outside the impact region. The increase of fiber content can efficiently decrease the deformation/failure region and permanent deflection of FM-HLCs, thus, enhancing its impact resistance. When the fiber content along circumferential and longitudinal directions is not consistent or the radius of curvature decreases, there forms an elliptical deformation region of FM-HLCs. The current work is expected to be of significance for the follow-up research and the potential applications of FM-HLCs. In addition, it is also a good reference for investigating the dynamic response of orthotropic panels/shells under low-velocity impact.

Dynamic response of horizontally curved composite steel I-girder bridges

The dynamics behavior of horizontally curved composite steel I-girder bridges is investigated by using three-dimensional finite element models. The analyzed bridge is modeled by using ANSYS 15.0 program with SOILD185 and SHELL181 elements to represent concrete and steel members, respectively. AASHTO HL-93 truck is simulated as 3D mass-spring-damper model consisting of five lumped-masses which connected by rigid beams and supported by spring-damper elements which are used to represent the suspension of vehicle body and tires. Gap and actuator elements are used to represent the separation between the tires and road surface and surface roughness condition, respectively. Four different roughness profiles are generated based on power spectral density (PSD) for very good, good, average, and poor roads. The dynamic analysis is carried out under different cases of vehicular loading positions for bridges with radius of curvature ranged from (35 to 200 m). Seven vehicle speeds are chosen to investigate the effect of this factor on the bridge dynamic response, also the effect of bump height at approach span is studied. The results are presented in terms of Impact Factors (IM). The results show that the IM-radius of curvature relationship is significantly influenced by the position of vehicle on transverse sections of the bridge. For the out-lane loading, the IM values for all girders tend to increase as the radius of curvature decreases. A 45 km/hr vehicle speed provides higher IM value for the good roughness bridge to be at 120 km/hr under poor road surface. The bump heights has a significant effect on IMs at lower speed limit, where the IM value increases with the increasing of bump height.

2D Propagation Simulation of Variation Parameters of U-shape Fiber Optic

Fiber optic has extraordinary properties and is suitable in sensor applications due to its special potential. Currently, macro bending characteristics of newly developed hetero core fiber optic element are designed and evaluated. This paper presents the preliminary results obtained from the numerical simulation analysis of the bending sensitivity of U-shape fiber optics toward the 2D electromagnetic wave in terms of mesh, curvature radius, core fiber size, and turn number. Fiber optics with core sizes of 4, 9, 50, and 62.5 μm were designed. In addition, the combination of core diameters 50-4-50, 50-9-50, 62.5-4-62.5, and 62.5-9-62.5 μm is evaluated to compare the outcome of transmission power in terms of hetero core structure of fiber optic. Simulation is performed using COMSOL Multiphysics simulation tool. The developed U-shape fiber optic is designed to sense the distortion of reducing power transmission by comparing input and output power. Results show that the selected mesh depends on the size of geometry bending fiber optics, and fine and finer mesh is the best for U-shape fiber optic. Furthermore, the power flow on the fiber decreases with the decreasing curvature radius and increasing turn number. The fiber with a core size combination of 62.5–4–62.5 um has high sensitivity in terms of loss. The attained results possess higher potential in the field of sensor applications, such as displacement, strain, pressure, and monitoring respiration, on human body. This study serves as a basis for further investigation of nanomaterial coating on fiber optics, thereby enhancing its credibility for sensing.

Fibre misalignment and breakage in 3D printing of continuous carbon fibre reinforced thermoplastic composites

This paper investigates the formation of manufacturing induced fibre misalignment and breakage during fused filament fabrication (FFF) 3D printing of 1 K continuous carbon fibre filament. Single stripes at various turning angles and curvatures are printed by a desktop printer Prusa i3 using a specific brass nozzle and characterised using X-ray computed micro-tomography (µCT) and optical microscopy. A finite element (FE) model of the printing process is also established to support the experimental measurement. It has been found that high porosity and fibre misalignment in the printed straight stripe result from the weak fibre/matrix interface and the uneven pressure executed by the nozzle. Increase of turning angle and/or reducing of curvature radius leads to more aggravated printing defects, including shape inaccuracy, fibre twisting, folding and misalignment, due to the excessive force from the nozzle, debonding with the print bed and the unmatched geometry of nozzle outlet and fibre filament. Severe fibre breakage and significant change of thickness can be seen in the samples with turning angles larger than 120° or curvature radius smaller than 5 mm, while the wrinkles of the stripe in the inner periphery appear more frequently as the curvature radius decreases.

Analysis of additional stress for a curved shield tunnel

This paper focuses on analytical solutions of additional stresses for a curved shield tunnel. General equations of additional stress caused by construction loadings were deduced by rewritten Mindlin solutions, and additional thrust and friction force were considered. In addition, theoretical formulae of additional stress caused by soil loss were deduced based on the three-dimensional image theory, and the actual processes of synchronous grouting and over-excavation were considered. Then, by using a curved tunnel in Zhuhai City, China as a case study, the distribution laws of additional stress along the directions of advancement and circumference were investigated. Under the coaction of construction loadings and soil loss, it was found that the distributions of σx and σy along the advancement direction for curved tunnels are similar to those for straight-line tunnels. However, the soil around a curved tunnel is more likely to yield because the difference between the normal stresses in two directions is greater than that for soil around a straight-line tunnel. Additional stresses caused by soil loss along the circumferential direction for a curved tunnel were found to no longer have the characteristics of strictly axial symmetry. The values of compressive stress σx and σy at the outer side of the curved tunnel were found to be greater and smaller than those at the inner side, respectively. As the curvature radius decreases, the maximum tensile stresses σx and σy for curved tunnels were found to decrease and increase, respectively. Furthermore, an insufficient quantity of injection grouting will trigger detrimental effects to nearby structures during the approaching excavation.

Enhancing out-of-plane compressive performance of carbon fiber composite honeycombs

This paper focuses on strengthening carbon fiber composite honeycombs which provide the higher strength than other competitive lightweight materials by the design of curved wall topology. And the carbon fiber composite curved honeycombs (CCCHs) are manufactured via a molding and bonding process. The out-of-plane compressive properties of the woven and unidirectional laminated CCCHs are measured and analyzed. In addition, the effects of curvature radius and wall thickness on the compressive strength of the laminated CCCHs are investigated. The experimental results show that the out-of-plane compressive strengths increase when only the curvature radius decreases or the wall thickness increases. By comparison, the out-of-plane compressive strengths of the laminated CCCHs show superior to those of almost existing competitive lightweight honeycombs, and it can be considered as a selective lightweight sandwich structure. It provides a possibility for the honeycomb structure to be used as load-bearing components.

Analog Models of Fold-and-Thrust Wedges in Progressive Arcs: A Comparison With the Gibraltar Arc External Wedge

The timing and kinematics of the different type of structures and the associated vertical axis-rotations that permit an arcuate external wedge to acquire progressively its curved shape throughout its deformation history --known as progressive arcs-- are key questions in natural cases of arcuate fold-and-thrust belts, that we want to address through analogue modelling. We present laboratory models of fold-and-thrust belts formed with a backstop that deforms in map view to simulate progressive arcs in a thin-skinned tectonic regime. Our set-up makes use of a deformable backstop rigid enough to push-from-behind the initial parallelepiped but deformable in map view. This innovative design permits us to increase the amplitude of the arc indenting in the model as its radius of curvature decreases, that is, it simulates a progressive arc. Taking the Gibraltar arc external wedge situated in the western Mediterranean to scale our models in terms of rheology, velocities and sizes, four types of experiments were made. We varied the type of substratum (sand or silicone), the silicone thickness and the width and length of the initial analogue pack in order to test the influence of each of these parameters on the resulting fold-and-thrust belts. All experiments led to the formation of arcuate wedges where strain was partitioned into: a) arc-perpendicular shortening, accommodated by thrusts which main structural trend is broadly subparallel to the indenter shape and with divergent transport directions, and b) arc-parallel stretching, accommodated by normal and conjugate strike-slip faults. The normal and strike-slip faults contributed to the fold-and-thrust belt segmentation and the formation of independent blocks that rotated clockwise and counterclockwise depending on their position within the progressive arc. Our experiments allow simulating and understanding the finite deformation mode of the external wedge of the Gibraltar arc. Accordingly, they shed light on how an arcuate fold-and-thrust belt can develop progressively in terms of structural trend and transport directions, types and distribution of the structures accommodating strain partition and timing of vertical-axis rotations.

Process Intensification by Using a Helical Capillary Microreactor for a Continuous Flow Synthesis of Peroxypropionic Acid and Its Kinetic Study

Peroxypropionic acid (PPA) is an important organic chemical compound. Due to its versatile oxidizing properties, it is used in the oil, chemical and other industries. In this article, an attempt was made for the production of PPA in a Teflon helical capillary microreactor without and with homogeneous catalyst. The article reports the perhydrolysis of PPA with the effect of various parameters such as concentration of hydrogen peroxide, molar ratio of reactants, radius of curvature of the microreactor, concentration of catalyst and temperature. The reaction is slow, as the PPA equilibrium was found to be reached within 10 min at a temperature of 50 °C and at 10 mol % catalyst loading based on propionic acid. The reaction was carried out in 13.25 and 23.25 mm radius of curvature of the microreactor in which 4.0375 and 3.488 mol/L concentrations of PPA respectively were obtained at 50 ºC and 10 mol % catalyst. It indicates that as radius of curvature decreases, better mixing was provided among the reactants for the reaction to give enhanced yield and selectivity. From the experimental data and the kinetic expressions, the expressions of activation energies and reaction rate constants were determined. For PPA synthesis and hydrolysis, the activation energies were 43.897 and 20.658 kJ/mol respectively without catalyst, while the activation energies for both the cases were 42.314 and 17.514 kJ/mol respectively with catalyst of 10 mol% based on propionic acid. The dean number, curve tube friction factor and pressure drop also determined for the helical capillary microreactor.

Hydrodynamics maneuver of a single helical flagellum swimming robot at low-Reynolds condition

Helical swimming robots with a capable propulsion system at low-Reynolds numbers have been proposed for many applications. Although linear propulsion characteristics of swimming robots with a single helical flagellum have been extensively studied, the characteristics of maneuverability have not been completely investigated yet. This study presents a new method for the maneuverability of the helical swimming robot with a single helical flagellum. This mechanism is based on the change in the angle between the helical and body axes. This study shows that a change in the aforementioned angle can enable the swimming robot to have turning maneuvers in clockwise or counterclockwise directions. Moreover, the swimming robot will move in a straight line if the helical and body axes are parallel. To investigate this new method and predict the robot’s behavior at various inclination angles, a hydrodynamics model is used. To validate the hydrodynamics model, an experimental prototype of a macro-size swimming robot with specific inclination angles is fabricated. The results indicate that the helical swimming robot swims on circular trajectories through specific inclination angles between the helical flagellum and the body axis. Moreover, the radius of curvature decreases by increasing the inclination angle. Results of the validated hydrodynamics model indicate that the turning velocity has approximately a constant value at different inclination angles depending on the rotational frequency and geometrical parameters of the swimming robot. Finally, the effects of geometrical parameters of the body and the helical flagellum on the radius of curvature and turning velocity are investigated through the proposed hydrodynamics model. The verified results indicate that the hydrodynamics model provides a viable alternative model to predict the behavior of a helical swimming robot at various inclination angles within a range of design variables. This new method can be introduced as a mechanism for maneuverability of the helical swimming robots with a single helical flagellum and will be able to control the parameters in this type of swimmers for the implementation of predefined missions.

Transparent conductive CuS film prepared on A4 sized PET substrate by chemical bath deposition method

Transparent conductive CuS film was prepared on A4 sized polyethylene terephthalate (PET) substrate through chemical bath deposition method reacting at a mild temperature of 35 °C by using copper nitrate and thiourea as precursors and triethanolamine as complexing agent. Characterization studies showed that the as prepared nanoparticles were closely packed and tightly adhered onto the surface of the PET substrate with the highest ASTM 5B level, and formed a homogeneous nanosized CuS film with satisfied conductivity and transmittance. It was found that the light transmittance with the film was negatively correlated with its conductivity. When the light transmittance for the film prepared under optimized conditions was enhanced from 55.0 to 71.7%, the conductivity underwent a consistent deterioration, and the corresponding sheet resistance value was increased from 74.12 to 196.20 Ω/□. Although bending operation was testified to be an important influencing factor on the properties of the film and could let its resistance vary along with the decrease of curvature radius, the amplitude of variation was limited. Both of conductivity and transmittance remained almost unchanged for the film to which hundreds of severe bending operations were subjected.

Heat transfer performance and entropy generation of helical square tubes with various curvature radiuses

Having key advantages of higher heat transfer and compact size, helical tubes have been commonly adopted in major industry applications especially heat exchangers and chemical reactors. On top of their encouraging industrial adoption, helical tubes have attracted significant attention from researchers worldwide due to its complex flow behavior. This study addresses the flow characteristic and heat transfer performance of a laminar flow inside helical tubes with various curvature diameters. The laminar flow of a Newtonian fluid inside helical tubes is investigated by utilizing a computational fluid dynamics approach. Both constant wall temperature and constant wall heat flux conditions are examined. Their heat transfer performance is numerically evaluated and compared by utilizing the concept of Figure of Merit (FoM). In addition, the inefficiency of the helical tube is analyzed by utilizing entropy generation analysis. The results indicate that heat transfer performance increases as the curvature radius decreases. Albeit higher pressure drop, helical coil generate lower entropy than straight tube.

Directionally induced quasi-phase matching in homogeneous AlGaAs waveguides.

We report on the experimental observation of quasi-phase matching in a homogeneous waveguide. By fabricating a monolithic snake-shaped suspended AlGaAs nanowire on a (001) GaAs wafer, we demonstrate the unraveled version of a χ(2) whispering-gallery-mode microdisk, obtaining second-harmonic generation in the optical telecom wavelength range. With a radius of curvature of 50μm and four spatial oscillations along the (110) average direction, a splitting of the second-harmonic spectrum occurs around the phase-matching wavelength of the corresponding straight waveguide. This splitting, which increases as the radius of curvature decreases, provides a useful degree of freedom for the design of small-footprint nonlinear photonic devices on-chip.

Modeling of multiple shots for analyzing shot peening controlled parameters on formed curvature radius

The desired peening outcome of the peening process like curvature is based on the reasonable determination of shot peening (SP) parameters. In this work, an assessment about accuracy of randomly distributed shots model was performed by comparing the experimental test. And, the comprehensive nonlinear dynamic elastic-plastic finite element analysis was conducted to reveal the difference between the regularly ordered shots model and the randomly distributed shots model in terms of induced stress and residual stress. The comparison indicated a difference between those two kinds of models under high coverage. Based on the randomly distributed shots model, we also found curvature radius increased with increasing thickness but decreased with shot velocity and increasing coverage. At last, we analyzed the reason by associating the residual distributions. Contrary to the shot peening parameters, shot velocity and coverage, the thickness of the strip is the most influential factor which inhibits the decrease of curvature radius. It should be noted that the over-high impact velocity will lead to a buckling distortion on the strip. Furthermore, the relation between the impact velocity and coverage was developed.

Flow separation effects on shoreline sediment transport

Field-tested numerical model simulations are used to estimate the effects of an inlet, ebb shoal, wave height, wave direction, and shoreline geometry on the variability of bathymetric change on a curved coast with a migrating inlet and strong nearshore currents. The model uses bathymetry measured along the southern shoreline of Martha's Vineyard, MA, and was validated with waves and currents observed from the shoreline to ~10-m water depth. Between 2007 and 2014, the inlet was open and the shoreline along the southeast corner of the island eroded ~200m and became sharper. Between 2014 and 2015, the corner accreted and became smoother as the inlet closed. Numerical simulations indicate that variability of sediment transport near the corner shoreline depends more strongly on its radius of curvature (a proxy for the separation of tidal flows from the coast) than on the presence of the inlet, the ebb shoal, or wave height and direction. As the radius of curvature decreases (as the corner sharpens), tidal asymmetry of nearshore currents is enhanced, leading to more sediment transport near the shoreline over several tidal cycles. The results suggest that feedbacks between shoreline geometry and inner-shelf flows can be important to coastal erosion and accretion in the vicinity of an inlet.