Arc Radius Research Articles

Numerical Analysis of Single-Particle Motion Using CFD-DEM in Varying-Curvature Elbows

Centrifugal pumps are the critical components in deep-sea mining. In order to investigate the particle motion in the curved channel of the impeller, three different types of curvature conform to blade profile to simplify the impeller design of pumps. A numerical study is conducted to investigate the flow field in a varying-curvature channel for solid-liquid two-phase flow. The flow of particles within the varying curvature channel is studied by combining the discrete element method (DEM) with computational fluid dynamics (CFD) and a comparison with Particle Image Velocimetry (PIV) test results. The results show that a polyhedral mesh with a small mesh number yields very accurate results, which makes it very suitable for CFD-DEM. Based on this method, the movement of a single particle is compared and analyzed, and the particle-motion law is obtained. The effects of the curvature ratio Cr and area ratio Ar on the motion law for a single particle are studied, and the simulation results are analyzed statistically. The results show that the effect of Cr on both the particle slip velocity and the turbulent kinetic energy only changes its strength, while the distribution law does not change significantly. Compared with the curvature ratio Cr, the area ratio Ar has a greater impact on the particles, and its distribution law becomes clearly different. As the area ratio Ar increases, the arc radius and length of the corresponding particle trajectory decrease.

Overmodulation Strategy for Voltage Source Inverter With a Single DC-Link Current Sensor

With a single shunt resistor, it is possible to sense the phase currents, although some dead regions exist around vertices of the voltage hexagon. In this article, an overmodulation method is presented for such single current shunt inverters. Regions near vertices of voltage hexagon are defined as holding regions, and the rest are defined as linear regions. The overmodulation strategy is developed based on the Fourier analysis: The magnitude of reference voltage determines the arc radius in the linear region and the holding angle of the holding region. By adjusting either the arc radius or the holding angle, the desired modulation index (MI) can be output. It is particularly useful for low-cost inverters, since it is implemented with an additional look-up table for induction motor or permanent magnet synchronous motor control. The linearity is maintained between the reference MI and its output MI until it reaches to the maximum, 12-step operation. In addition, the technique provides the seamless transition from space vector modulation to 12-step operation. The effectiveness is evidenced by the experimental results.

A novel design on smooth rotor profile with meshing clearance for screw vacuum pump

Cross-section profile of rotor takes a great effect on the performance of dry-screw vacuum pump. A novel smooth rotor profile consisting of eight segments of curves, including arcs and conjugate correction curves is proposed. Advantages are that it can be used to solve the unsmooth connection and no meshing clearance in traditional profile. The meshing model for new profile can directly generate stable addendum clearance, tooth clearance, tooth side clearance, and radial clearance. The influences of the epicycloid rotation angle, arc radius and involute offset distance of the conjugate correction curve on the clearances are studied according to established theoretical model. And transient flow field of vacuum pump is analyzed by using the commercial software Ansys-Fluent®. Compared to traditional screw vacuum pump, the results shows that pressure in inlet and pump cavity is lower, and maximum pumping speed is higher, indicating that the proposed design is superior.

Effect of Rare Earth on the Corrosion Resistance of Electroless Ni-Mo-P Composite Coatings

A kind of corrosion-resistant Ni-Mo-P composite coating was deposited on the surface of AZ91D magnesium alloy substrate by electroless plating method with different concentration of Ce(NO3)3 and Nd(NO3)3. The deposition mechanism of Ni-Mo-P composite coating was explored. Furthermore, the effects of Ce(NO3)3 and Nd(NO3)3 concentration on the microstructure and properties of Ni-Mo-P composite coatings were studied. Results indicated that the Ni-Mo-P composite coatings prepared by adding the optimal concentration of Ce(NO3)3 and Nd(NO3)3 had few defects. Meanwhile, the deposition rate of the composite coatings and the adhesion between the coating and the magnesium alloy substrate were improved. When the concentration of Ce(NO3)3 and Nd(NO3)3 were 0.10 and 1.00 g/L, the Ni-Mo-P composite coatings had the minimum corrosion rate of 0.826 and 0.681 g/m2·h, respectively. Herein, compared with the addition of Ce(NO3)3, the Nd(NO3)3 added Ni-Mo-P composite coating has the maximum arc radius of capacitive resistance and significant improvement corrosion resistance.

Structured light-based dynamic 3D measurement system for cold-formed steel hollow sections

In the cold-formed steel hollow section manufacturing process, one of the key stages is forming an inspection to check whether it meets the requirement. In this paper, a dynamic 3D measurement system based on low-cost structured light was presented, which can be used to measure the dimensions of a cold-formed steel hollow section in real-time. The system is mainly composed of four sets line-structured light inspection device. A temporary coordinate is proposed to assist in solving multi the calibration of structured light plane. An optimisation method of L-M algorithm is proposed to solve the problem of stitching accuracy of point cloud contour. A point cloud simplification processing method is proposed for solving main parameters. The side length measurement error of the system is within ±0.05 mm, and the outer arc radius measurement error is within ±0.45 mm. All parallelisable tasks can achieve an acquisition rate of up to 25 fps.

Heat transfer and fluid flow analysis of artificially roughened solar air heater

This study aims for computational investigation of roughened solar air heater (SAH) using artificial roughness in the form of double concave ribs. Solar air heater is a type of heat exchanger that utilises the solar radiation to generate heat energy. Smooth solar air heaters are found inefficient due to low convective heat transfer coefficient from absorber plate to air, thus to enhance the heat transfer rate artificial roughness in the form of double concave ribs is employed. Relative roughness height (e/D), relative roughness pitch (P/e) and relative arc radius (r/e) are chosen as geometric variables and analysed at five different values of Reynold’s number (Re) and their effect on heat transfer, friction factor and thermohydraulic performance parameter (THPP) is studied using commercial CFD software Ansys fluent v.15.0. It has been found that the maximum value of THPP is 1.725 for studied range of parameters. Nusselt number increases with increase in Reynold’s number and vice a versa happens for friction factor but in case of relative arc radius (r/e) both Nusselt number and friction factor decreases with increase in r/e.

Electrochemical Turning of (TiB + TiC)/TC4 Composites Using a Rectangular Cathode

The application of titanium metal matrix composites (Ti-MMCs) in the aerospace industry has increased significantly owing to their excellent mechanical properties. However, these properties also make Ti-MMCs difficult to machine. Many problems can occur with traditional turning, such as tool damage and low efficiency remain. Electrochemical machining is not limited by the physical properties of metal materials, making it an ideal machining method for Ti-MMCs, but there have been few articles evaluating electrochemical turning (ECT) in this application. Therefore, the purpose of this study was to use a cathode tool with a rectangular end face to realize the ECT of particle reinforced Ti-MMCs. Parametric experiments were conducted by varying the machining voltage, workpiece rotation speed, electrolyte pressure, and axial offset to determine their effects on the intermittent feed ECT of a cylindrical workpiece. Finally, intermittent feed ECT was performed on the cylindrical surface with the preferred machining parameters, and a machining area with a circular arc area of 4124 mm2, an average radial removal depth of 1.19 mm, and an average circular arc radius of 42.44 mm was obtained on the cylindrical workpiece, which verified the practical performance of the intermittent feed ECT method for machining titanium matrix composites.

Is the cubic parabola really the best railway transition curve?

Abstract In the current study, the authors tested two railway transition curves in terms of their usefulness for railway practice. The first curve was a cubic parabola – the curve most popular in railway engineering. The second curve was a polynomial of ninth degree, and this curve was chosen due to the fact that this curve satisfies advanced geometrical demands. In this study, the model of a two-axle vehicle was applied. The study relied on the passage of the vehicle model through the route consisted of straight track, railway transition, and circular arc. Three different circular arc radii were used. The value – 0.6 m/s2 – of maximum lateral acceleration in the circular arc was applied. Three different vehicle velocities were also used. In this study, the authors simulated vehicle dynamics for different curves and ten lengths of the curves. As the main criterion, lateral acceleration of the vehicle body was applied. The results for these two mentioned curves were compared.

Correlation of radius of cathode spot of vacuum arc of metals on the size of generated droplets

The simple relation to estimate the cathode spot radius of a vacuum arc of pure metals is obtained. On its basis, is established between the cathode spot radius and the size of droplets generated by the cathode spot a correlation. This enables to find ways to reduce droplets in the plasma flow, which forms coatings by the vacuum electric arc method. The paper presents the results of experimental study of the droplet sizes depending on the vacuum arc current iд. The size and amount of the droplets on an area of 1 mm2 of the coating surface are determined using the ImageSP program. As the initial data, the microstructures of the coatings are used with an increase of: ç100, ç200, ç500, ç1000, ç1500. The droplets have been generated by a cathode spot of a vacuum arc for the alloy of the composition, at.%: 68Al–8Cr–4Nb–20Si. It is established that the number of droplets with a diameter of < 2 μm is generated most of all, and the number of droplets with a diameter > 10 μm is generated least of all. The number of generated droplets with a diameter from 2 to 10 μm slightly depends on the arc current iд. It is noted that the diameter of the alloy droplet is smaller than the diameter of the droplets generated by the cathode spot on its components due to the fact that the radius of the cathode spot on the alloy is smaller than the radius of the cathode spot on its pure components.

Numerical assessment of thermal performance of heated air duct with novel arc profile ribs in non-interrupted arrangement

The use of roughness elements in the form of recurring ribs have been established to be a proficient technique of improving the thermal performance of the heated air ducts. In the present research work, the numerical assessment of the thermal performance of arc profile ribs arranged in a non-interrupted arrangement under forced convection has been presented. The ribs are attached to the bottom side of the heated air duct. The key geometrical parameters examined are a ratio of pitch of the rib to the height (p/y = 4–9), a ratio of the height of the rib to arc radius of the rib (y/r = 0.75–1), a ratio of the height of rib to the height of the duct (y/Y = 0.06–0.1) and Reynold’s numbers (Re) in between 12,270 and 36,810. It is revealed from the numerical evaluation that the novel arc profile ribs placed on the plate aids to encourage the level of turbulence which consequences in the improvement of the heat transfer. The thermal performance indicative parameters such as heat transfer improvement factor (HTIF), friction factor ratio (FFR), and overall thermal performance (OTP) are studied against variation of Reynold number and key geometrical parameters. The Nusselt number, friction factor for the ribbed plate represent an improvement of about 45%, 41% respectively as compared to the plain plate. The findings from the present work are compared with earlier published work for the same range of Re. The magnitude of OTP reported in the present work is higher than unity. Therefore this can be considered as one of the effective techniques for improvement of thermal performance of heated duct under forced convection.

Characterization of Mo-6Ta alloy targets and its magnetron sputtering deposited thin film

In this study, pure Mo and Mo-6Ta alloy targets were produced by a manufacturing method, which is called die pressing with a combination of cold isostatic pressing and hot-pressing sintering technology, and molybdenum thin films were deposited on corning glass substrates using a DC magnetron sputtering system. The effect of alloying with tantalum on the phase structure, grain size, orientation, thin film surface morphologies and electrochemical properties has been investigated by a variety of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) with electron back-scattered diffraction (EBSD), atomic force microscopy (AFM), four-probe resistivity tester, and electrochemical analyzer. The observation of the Mo targets reveals that this manufacturing technology with alloying of tantalum can reduce the target's grain size to lower than 50 μm with random grain orientation. The microstructure of the deposited Mo thin films indicates that the alloyed films have the higher deposition velocity with a dense fine grain structure and smoother surface. The sheet resistivity of the alloyed Mo film increases continuously with the increasing of the sputtering time, and eventually becomes higher than that of the pure Mo film. In electrochemical tests, both of the Mo films show capacitive reactance, and the capacitive arc radius of the alloyed Mo films are obviously larger than that of pure Mo films. The result of alloying with tantalum shows an increase in the corrosion potential of the Mo film from −0.5 V to −0.2 V, indicating improvement of the corrosion resistance of Mo films.

A EFFECT OF CeO2 DOPING ON THE MICROSTRUCTURE AND CORROSION BEHAVIOR OF CoCuNiTi HIGH-ENTROPY ALLOY COATINGS

CoCuNiTi high-entropy alloy coatings with an equal molar ratio were prepared on 45 steel substrates using the laser-cladding method. The effect of CeO2 doping on phase structure, microstructure and corrosion behavior of CoCuNiTi coatings were investigated by X-ray diffraction, optical microscope, scanning electron microscope, and electrochemical workstation. The results show that the phase structure of CoCuNiTi coating doped with 1 w/% CeO2 is transformed from the original dual-phase structure of FCC main phase and BCC phase to the dual-phase structure of BCC main phase and FCC phase, mainly because CeO2 addition helps to improve the temperature gradient and solidification rate during solidification, reduce the nucleation resistance and the diffusion distance of the alloying elements, and provide a liquid environment with longer time, lower viscosity and higher diffusion rate. The microstructure of the two coatings is composed of BCC-phase dendrite and FCC-phase interdendrite. The widths of the primary dendrites of the columnar dendrites in CoCuNiTi cladding layer before and after CeO2 doping are about 8.10 µm and 6.51 µm, respectively. The CoCuNiTi coating doped with 1 w/% CeO2 has the smallest corrosion current density, the largest capacitive reactance arc radius and polarization resistance, and the best corrosion resistance in 3.5 w/% NaCl solution, which is mainly due to making the alloy structure refined and the element distribution uniform after the CeO2 addition.

Corrosion evolution of 15CrMn steel in sulfur-containing sodium aluminate solution

The corrosion behavior of 15CrMn steel in S2−-containing sodium aluminate (SCSA) solution was studied by immersion test and electrochemical methods. The phase analysis and cross-section corrosion products were performed using scanning electron microscope (SEM) and X-ray diffraction (XRD). Results showed a layer of Fe2O3, Fe3O4, and FeNaS2 corrosion product film on the surface of 15CrMn steel after corrosion. The film improved the protective effect on the sample, which led to the decrease of polarization current and the increase of Nyquist’s arc radius at 4 days. As the corrosion time extends to 5 days, the corrosion product layer loosened and partly fell off due to the formation of unstable sulfide on the substrate surface, promoting a new corrosion process.

Numerical investigation on thrust efficiency dropping phenomenon of annular expansion–deflection nozzles

The flow patterns in a large-expansion-ratio annular expansion–deflection (ED) nozzle are numerically investigated, focusing on the flow mechanisms underlying the sudden thrust efficiency (η) dropping phenomenon. The objective of the present work is to provide a physical understanding of the ED nozzle flow physics responsible for the nozzle performance variation. The simulations are performed by solving the Reynolds averaged Navier–Stokes equations in combination with the one-equation Spalart–Allmaras turbulence model. The Advection Upstream Splitting Method is used to discretize the convective fluxes, and the second-order central scheme is used to discretize the viscous fluxes. The present investigation demonstrates that two flow mechanisms exist, which can cause the sudden η dropping: one is supersonic flow impingement at the nozzle exit, and the other is the formation of the internal normal shock. The pintle arc radius downstream of the throat plays an important role in determining the size and redirection of the supersonic core flow region, thus influencing the overall nozzle performance. A large radius dimension gives a higher η value at the first rising stage, a large dropping nozzle pressure ratio (NPR), and a large mode transition NPR. Interestingly, a cap shock is proved possible in the current large-expansion-ratio ED nozzle, in which the near-shroud shock acts as the internal shock in the traditional thrust-optimized or parabolic nozzles.

Geometric analysis of the urethral-vaginal interface curvature in women with and without stress urinary incontinence: A pilot magnetic resonance imaging study.

To evaluate differences in the curvature of the urethral-vaginal interface in women with and without stress urinary incontinence (SUI) using geometric morphometric analysis techniques. We conducted a pilot case-control study using magnetic resonance imaging (MRI) scans of 18 women with and without SUI. The urethral-vaginal interface at the level of the mid-urethra was fitted with a second-order polynomial regression. The chord length and chord-to-vertex length of the resulting parabolic curve were used to calculate the arc length and radius of a circular arc fitted to the interface curvature. Demographic characteristics and Pelvic Organ Prolapse Quantification (POP-Q) parameters were collected. Subjects were stratified by those with and without SUI, as well as by those with and without anterior wall prolapse beyond 2 cm proximal to the hymen (Aa > -2 cm). The radius of the urethral-vaginal interface curvature was not found to be different between subjects with and without SUI (8.8 vs. 9.2 mm, p = 0.53); however, this value was smaller in subjects with Aa > -2 (8.4 vs. 11.9 mm, p = 0.03). The chord length, chord-to-vertex length, and arc length comprising the urethral-vaginal interface curvature were similar between subjects with and without SUI, and between subjects with and without Aa > -2 cm (p > 0.05 for all). In this pilot study population, the radius of the urethral-vaginal interface curvature at the mid-urethra was smaller among women with anterior vaginal wall prolapse beyond 2 cm proximal to the hymen. A difference in the urethral-vaginal interface curvature among women with and without SUI was not found.

Investigation of effects of tire contour on aerodynamic characteristics and its optimization

Reducing the aerodynamic drag is one of the most important approaches for the development of energy-saving and environment-friendly automobiles. The tire contour has a great influence on the aerodynamic characteristics of automobiles. The aim of this study is to investigate the influence of the tire contour design parameters on the aerodynamic characteristics around a closed wheel, and obtain the optimized tire contour to reduce the automobile aerodynamic drag. A passenger car tire 185/65R14 was selected to conduct the wind tunnel test, and the surface pressure coefficients were used to validate the simulation model established using the detached eddy simulation (DES) model. To decrease tire drag, and taking the upper sidewall height, the tread radii, the tread width, and the transition arc radius of the shoulder as four design variables of contour, a combination of the Latin hypercube experimental design, the Kriging surrogate model, and the adaptive simulated annealing (ASA) algorithm were used to optimize the tire contour design parameters. The changes of flow field around the tire, including the velocity, turbulent kinetic energy, and pressure field were compared and analyzed for further understanding of the drag reduction mechanism. It is found that the aerodynamic drag coefficient of the optimized tire is reduced by 14.5%, and the aerodynamic coefficient drag of the car using the optimized tire is reduced by 7%. The present results are expected to provide useful information for designing new tire structures and improving the aerodynamic performance of the automobile.

Experimental study of fretting fatigue in dovetail assembly considering temperature effect based on damage mechanics method

Fretting fatigue of dovetail structure of aero-engine compressor is a very complex phenomenon, which is affected by different factors such as temperature, load, friction coefficient, and arc radius, etc. Aiming at the problem of the high-temperature fretting fatigue life prediction of dovetail structure, the high-temperature effect on fretting fatigue life is analyzed, and then the fretting fatigue life prediction model is established considering the temperature effect by introducing temperature equivalent factor based on the circular flat contact theory and continuous damage mechanics theory. Besides, the criterion of fretting fatigue cracks initiation failure is proposed based on the displacement–strain joint monitoring method in the fretting fatigue tests. The experiment results show that the proposed fretting fatigue life prediction model has a high life prediction ability within ± 2.0 times error band. It is found that the traditional damage mechanics accumulation model cannot reflect the change of fretting fatigue damage only by changing the material performance parameters in a high-temperature environment, needing temperature correction and the proposed fretting fatigue life prediction model considering temperature effect in the exponential form of temperature ratio is feasible.

Influence of Particle Concentration on the Elemental Penetration Region and Properties of Ni-P-SiC Composite Coatings Prepared through Sandblasting and Scanning Electrodeposition on 45 Steel Surfaces

Ni-P-SiC composite coating was prepared on 45 steel surfaces through sandblasting and scanning electrodeposition to explore the relationship between element penetration region and composite coating properties. The single-factor control variable method with particle concentration as the research variable was used. Results showed that with the gradually increasing concentration of SiC nanoparticles, a trend of first increasing and then gradually decreasing was observed for the surface and cross-sectional microstructure of the coating, interpenetration ability of the elements, adhesion performance, and corrosion resistance. The best deposition quality of the coating was obtained when the concentration of SiC nanoparticles was 3 g·L−1. For cross-sectional microstructure, the scratch test revealed that the maximum coating thickness was 17.3 μm, the maximum range of elemental penetration region was 28.39 μm, and the maximum adhesion of the composite coating was 36.5 N. The electrochemical test showed that the composite coating had a −0.30 V self-corrosion potential and 8.45 × 10−7 A·cm−2 self-corrosion current density, the slowest corrosion rate. In addition, the composite coating had the best corrosion resistance and the largest impedance arc radius corresponding to an equivalent impedance value R2 of 3108 Ω.

Porous perovskite-lanthanum cobaltite as an efficient cocatalyst in photoelectrocatalytic water oxidation by bismuth doped g-C3N4

The electrophoretic loading of porous perovskite-lanthanum cobaltite (LaCoO3) on bismuth doped g-C3N4 (Bi@g-C3N4) as a novel photoanode was designed for the efficient photoelectrocatalytic water splitting. Before loading cocatalyst, the photoelectrocatalytic oxygen evolution of g-C3N4 was investigated with various amounts of Bi. The photoconversion efficiency enhanced more than 3.7 times for 3.6% Bi doped compared with that of the pristine g-C3N4. The Mott-Schottky plots showed the amount of band bending for Bi@g-C3N4 is more than that of g-C3N4 resulting in better electron transfer at the photoelectrode/electrolyte interface. By loading LaCoO3 on Bi@g-C3N4 photoanode, the photoconversion efficiency of 2.3% at 0.28 V (vs. RHE) was obtained under visible light which is more than that of Bi@g-C3N4 (0.92% at 0.48 V vs. RHE) alone. The high photocurrent density of 0.40 mA cm−2 was observed for Bi@g-C3N4/LaCoO3 photoanode as compared with Bi@g-C3N4 (0.17 mA cm−2) at the redox potential of O2/H2O. Also, Bi@g-C3N4/LaCoO3 photoanode represents a smaller arc radius in electrochemical impedance spectroscopy Nyquist plot compared with those of g-C3N4 and Bi@g-C3N4.

Modelling of a heavy-current intensively blasted electric arc at atmospheric pressure

The paper deals with intensively blasted electric arc burning in argon in a cylindrical channel of a designed experimental arc heater. The measured values of the arc current, the total voltage between a tungsten cathode and a grounded copper anode, the argon flow rate, and the water flow rates and temperature increments in individual parts of the arc heater characterize the operational conditions, but the parameters of the arc inside remain hidden. The simplified mathematical model has been designed to reveal the arc behavior in the arc heater channel, namely the arc radius and arc temperature development. The model is based on the energy and mass conservation laws and Ohm’s law and utilizes theoretically calculated transport and thermodynamic properties of argon altogether with the measured results as input data. Some simplifying assumptions are applied. A two-zone arrangement with a hot arc zone in the middle and a cold zone near the channel wall is supposed. The arc radius development along the arc heater’s channel is described by Schlichting’s formula for a free beam. Such combinations of three characteristic values of exponent n r, current density j 0 at the cathode tip, and arc temperature T A(s) at the end of the near-cathode layer are sought to enable as close as possible accordance between the computed and experimental data. Thereafter, a slight tuning of these parameters is needed to avoid extreme values of electric field intensity and temperature oscillations near the cathode while not to substantially worsen the reached agreement of measured and computed values. The functionality of the model is demonstrated using four typical sets of experimental data.