In the practice of pipeline transport of oil,oil products and gas to perform turns of trunk and field pipelines in vertical and horizontal planes are used bends of various designs such as:elbows with bending radius of...In the practice of pipeline transport of oil,oil products and gas to perform turns of trunk and field pipelines in vertical and horizontal planes are used bends of various designs such as:elbows with bending radius of 1.0DN or 1.5DN and standardized angles of 30°,45°,60°,90°;induction bends with bending angles from 1°to 90°;cold bends with bending angles depending on the nominal diameter DN.展开更多
Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that...Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that the particle transport patterns are similar and independent of the particle size and other parameters when suspended nanoparticles flow in a straight tube. At the outside edge, particle deposition is the most intensive, while deposition at the inside edge is the weakest. In the upper and lower parts of the tube, depositions are approximately the same for different Schmidt numbers. Curvatures of tube, Reynolds number, and Schmidt number have second-order, forth-order, and first-order effects on the relative deposition efficiency, respectively.展开更多
Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method(TEMOM)is employed to study dynamics of nanoparticles with Brownian motion,base...Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method(TEMOM)is employed to study dynamics of nanoparticles with Brownian motion,based on the flow field from numerical simulation.A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code.It is found that for the simulated particulate flow system,the particle mass concentration,number concentration,particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time.The distribution of particle mass concentration at different time is independent of the initial particle size.More particles are concen-trated at outer edge of the bend.Coagulation plays more important role at initial stage than that in the subsequent period.The increase of Reynolds number and initial particle size leads to the increase of particle number concentration.The particle polydispersity,mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.展开更多
The present paper intends to introduce a new method for reducingbends erosion from particles impacts: the ribbed bend erosionprotection method. Ribs are evenly fixed in the range of 20 deg-80deg on the inner-wall of i...The present paper intends to introduce a new method for reducingbends erosion from particles impacts: the ribbed bend erosionprotection method. Ribs are evenly fixed in the range of 20 deg-80deg on the inner-wall of inside 90 deg bend and the bend (includingribs) is made of medium carbon steel. Three-dimensional numericalworks is performed and the result shows satisfactory agreement withthe experimental measurement. Numerical simulation studies thecharacteristics of axial gas flow along the bend and secondary flowat cross section.展开更多
The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the re...The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.展开更多
Mechanical properties of weld metal are the key factors affecting the quality of heavy-wall X80 hot induction bends. The effects of bending parameters on the mechanical properties of weld metal for hot bends were inve...Mechanical properties of weld metal are the key factors affecting the quality of heavy-wall X80 hot induction bends. The effects of bending parameters on the mechanical properties of weld metal for hot bends were investigated by simulation conducted on a Gleeble 3500 thermal simulator. Continuous cooling transformation （CCT） dia- grams of the weld metal were also constructed. The influences of hot bending parameters （such as reheating temperature, cooling rate, and tempering temperature） on the microstructure and mechanical properties of weld metal were also analyzed. Results show that the strength of all weld metal specimens is higher than the value indicated in the technical specification and increases with the increase of reheating temperature, cooling rate, and tempering tempera ture. The impact toughness is apparently related to the variation of reheating temperature, cooling rate, and tempering temperature.展开更多
A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water su...A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water surface and the effect of transverse circulating current induced by the hydraulic structure of bend flow were fully considered. A theoretical formula for the incipient velocity of non-cohesive and non-uniform sediment in sloping river bends was developed. The results from the theoretical formula compared well with the experimental data.展开更多
In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since...In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since river bends are not uniform-some are divergent and others convergent-in this study, after the SSIIM 3-D model was calibrated using the result of measurements along a uniform 180° bend with a width of 0.6 m, a similar but convergent 180v bend, 0.6 m to 0.45 m wide, was simulated using the SSI1M 3-D numerical model. Flow characteristics of the convergent 180° bend, including lengthwise and vertical velocity profiles, primary and secondary flows, lengthwise and widtbwise slopes of the water surface, and the helical flow strength, were compared with those of the uniform 180° bend. The verification results of the model show that the numerical model can effectively simulate the flow field in the uniform bend. In addition, this research indicates that, in a convergent channel, the maximum velocity path at a plane near the water surface crosses the channel＇s centerline at about a 30° to 40° cross-section, while in the uniform bend, this occurs at about the 50° cross-section. The varying range of the water surface elevation is wider in the convergent channel than in the uniform one, and the strength of the helical flow is generally greater in the uniform channel than in the convergent one. Also, unlike the uniform bend, the convergent bend exhibits no rotational cell against the main direction of secondary flow rotation at the 135° cross-section.展开更多
While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate t...While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate the bearing capacity of pipelines.In order to study the effect of cross-section distortion on the performance of small-radius induction bends,3D(D refers to pipe diameter)induction bends were manufactured based on different combinations of process parameters.Then,the cross-section distortion,structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis,distortion analysis,physical and chemical property test,micro-structural analysis and so on.The following results were obtained.First,the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends,and the roundness of 3D bends is about 2e4 times that of 5D bends.Second,the cross-section distortion of 3D bends is obvious,so its heating temperature varies greatly in different parts,leading to different structure morphologies and contents.As a result,the numerical distribution of mechanical properties of each part of 3D bends(e.g.intrados,extrados and neutral zone)is discrete.Third,the strength at the intrados of most bends doesn't meet the standard,and it is sorted form the higher to the lower as extrados,neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength.Fourth,the strength at intrados and extrados decreases with the increase of roundness.The strength at intrados decreases with the increase of thickening rates.And the strength at extrados increases with the increase of thinning rates.展开更多
An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distribution...An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.展开更多
A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution pr...A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution process in large radius bend that brings about an overall heat transfer augmentation, especially at the outer side of the bend, and the significant deterioration at the inner side. The influence of two major parameters, namely, the bend-to-tube radius ratio and the bulk Reynolds number on the flow structure as well as on the local heat transfer is investigated.展开更多
We numerically investigate the effect of in-plane bending strain on valley-resolved conductance and valley polarization in a graphene nanoribbon with zigzag edges.The central region of the nanoribbon is bent into an a...We numerically investigate the effect of in-plane bending strain on valley-resolved conductance and valley polarization in a graphene nanoribbon with zigzag edges.The central region of the nanoribbon is bent into an arc with central angleφ.We find that the bending strain reduces the conductance but enhances the valley polarization.In the valley-resolved conductance spectra,there exist single-valley plateaus near the Dirac points and distinct Fano-type dips.Accordingly,a plateau of full valley polarization appears,which expands significantly at largeφ.At valleyresolved conductance dips,the valley polarization can be much larger than that in the unstrained case.The bending-induced enhancement of valley polarization can be explained by the features of pseudo-Landau levels in the bent region.Strain-induced valley polarization depends nonmonotonously on the nanoribbon width.These findings could be helpful in designing valleytronic devices with flexibility.展开更多
This study explores a novel method for processing cotton stalks—an abundant agricultural byproduct—into long strips that serve as sustainable raw material for engineered bio-based panels.To evaluate the effect of ra...This study explores a novel method for processing cotton stalks—an abundant agricultural byproduct—into long strips that serve as sustainable raw material for engineered bio-based panels.To evaluate the effect of raw material morphology on panel’s performance,two types of cotton stalk-based panels were developed:one using long strips,maintaining fiber continuity,and the other using ground particles,representing conventional processing.A wood strand-based panel made from commercial southern yellow pine strands served as the control.All panels were bonded using phenol-formaldehyde resin and hot-pressed to a target thickness of 12.7 mm and density of 640 kg/m^(3).Their mechanical and physical properties were evaluated through internal bond,bending,thickness swelling,and water absorption tests.Both cotton stalk-based panels showed improved bonding performance compared to the control.The internal bond of the strip-based panel was nearly four times higher than that of the control,while the particlebased panel exceeded it by a factor of two.The strip-based panel showed approximately 15% lower bending stiffness than the wood strand-based panel,yet it surpassed it in load-carrying capacity by 5%.In contrast,the particleboard showed significantly lower bending performance than the strip-based and control panels,despite particle processing being a more conventional method.Both cotton stalk-based panels exhibited higher water absorption and thickness swelling than the wood strand panel.Overall,cotton stalk-based panels—particularly those using strip processing—show promisingmechanical properties,suggesting potential applications in sheathing,furniture,and interior paneling.However,improvements in dimensional stability are needed for broader use.展开更多
In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random...In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random statistical method. The zones and rate of erosion on the wall in a bend are determined. The results are in accordance with the experiment, which indicate that the erosion is influenced by gas velocity, particle size and bend curvature.展开更多
Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules d...Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules derived from planar coronene and kekulene molecules(graphene helicoids and spiral nanoribbons)are analyzed using molecular dynamics simulations.The interatomic interactions are described by a force field including valence bonds,bond angles,torsional and dihedral angles,as well as van derWaals interactions.While the tension/compression of such nanosprings has been analyzed in the literature,this study investigates other modes of deformation,including bending and twisting.Depending on the geometric characteristics of the carbon nanosprings,the formation of structural and helix reversal topological defects is described.During these structural transformations of the nanosprings,only van der Waals bonds break and recover,but breaking or recovery of covalent bonds does not take place.It is found that nanosprings demonstrate a significantly higher coefficient of axial thermal expansion than many metals and alloys.Under axial compression,Euler instability leads to lateral bending with continuous deformation of the nanospring axis at relatively low compression,while at high compression,bending kinks form.Various types of topological defects form on the instantly released nanospring during its relaxation from a highly stretched configuration.These results are useful for the development of nanosensors operating over a wide temperature range.展开更多
Since the view that the localized rail third-order bending mode can cause high-order polygonization(mainly 18-23)of high-speed train wheels was put forward in 2017,many scholars have attempted to link a connection bet...Since the view that the localized rail third-order bending mode can cause high-order polygonization(mainly 18-23)of high-speed train wheels was put forward in 2017,many scholars have attempted to link a connection between the localized rail bending modes and wheel polygonization phenomenon and polygonal wheel passing frequency.This paper first establishes a flexible track model considering the structural and parametric characteristics of fasteners,verifies the model by using vehicle tracking test data,then investigates the influence of fastener parameter matching on the localized rail bending modes,and obtains the following conclusions:(1)There is nearly a 1:1 mapping relationship between the localized rail bending modal frequency and polygonal wheel passing(PWP)frequency,which supports that the localized rail bending mode is one of the causes of wheel polygonization.(2)The iron plate of the fastener system plays a role of dynamic vibration absorber in the vehicle-rail coupled system,and the fastener parameters significantly influence the localized rail bending modal vibration.Finally,this paper proposes a design principle of a high-frequency vibration-absorbing fastener,which provides a feasible solution to mitigate the localized rail bending modal vibration and high-order wheel polygonization.Meanwhile,it points out that this measure may induce other high-frequency vibration problems,e.g.,aggravating modal vibration above 800 Hz.Further,this paper proposes a concept of differentiated arrangement of fasteners,suggesting that different high-frequency vibration-absorbing fasteners be installed in different sections of the whole line to make the localized rail bending modal frequency of the whole line disordered,thus disrupting and further mitigating the development of the wheel polygonization.展开更多
We demonstrate a high-speed rotating slit beam shaping method for femtosecond(fs)laser three-dimensional(3D)isotropic inscription in glass materials.By integrating fs laser direct writing with a real-time rotating sli...We demonstrate a high-speed rotating slit beam shaping method for femtosecond(fs)laser three-dimensional(3D)isotropic inscription in glass materials.By integrating fs laser direct writing with a real-time rotating slit mechanism,a 3D symmetric spherical focal field distribution is created in the laser-irradiated regions of transparent substrates.The corresponding focal field distribution is theoretically calculated and validated by examining the features of laser-inscribed lines in glass samples.Moreover,we investigate the influences of laser writing speed and slit rotational speed on the fabrication resolution in glass,and discuss the formation mechanism of the generated periodic microstructures.To showcase its powerful capability for3D isotropic fabrication,the high-speed rotating slit beam shaping method is applied to create straight optical waveguides,bending optical waveguides,and hollow microchannels in the glass.The proposed method holds great potential for the facile manufacture of diverse 3D isotropic microstructures and devices within transparent materials across various applications,including advanced photonics,microoptics,micro-electromechanical systems,and microfluidics.展开更多
Functionally graded material(FGM)plates are widely used in various engineering structures owing to their tailor-made mechanical properties,whereas cracked homogeneous plates constitute a canonical setting in fracture ...Functionally graded material(FGM)plates are widely used in various engineering structures owing to their tailor-made mechanical properties,whereas cracked homogeneous plates constitute a canonical setting in fracture mechanics analysis.These two classes of problems respectively embody material non-uniformity and geometric discontinuity,thereby imposing more stringent requirements on numerical methods in terms of high-order field continuity and accurate defect representation.Based on the classical Kirchhoff-Love plate theory,a numerical manifold method(MLS-NMM)incorporating moving least squares(MLS)interpolation is developed for bending analysis of FGM plates and fracture simulation of homogeneous plates with defects.The method constructs an H^(2)-regular approximation with high-order continuous weighting functions and,combined with the separation of mathematical and physical covers,establishes a unified framework that accurately handles material gradients and cracks without mesh reconstruction.For the crack tip,a singular physical cover incorporating the Williams asymptotic field is introduced to achieve local enrichment,enabling the natural capture of displacement discontinuity and stress singularity.Stress intensity factors are extracted using the interaction integral method,and the dimensionless J-integral shows a maximum relative error below 1.2%compared with the reference solution.Numerical results indicate that MLS-NMM exhibits excellent convergence performance:using 676 mathematical nodes,the nondimensional central deflection of both FGM and homogeneous plates agrees with reference solutions with a maximum relative error below 0.81%,and no shear locking occurs.A systematic analysis reveals that for a simply supported on all four edges(SSSS)FGM square plate with a/h=10,the nondimensional central deflection increases by 212%as the gradient index nrises from 0 to 5.For a homogeneous plate containing a central crack with c/a=0.6,the nondimensional central deflection increases by approximately 46%compared with the intact plate.Under weak boundary constraints(e.g.,SFSF),the deformation is markedly amplified,with the deflection reaching more than three times that under strong constraints(SCSC).The proposed method provides an efficient,reconstruction-free numerical tool for high-accuracy bending and fracture analyses of FGM and cracked thin-plate structures.展开更多
文摘In the practice of pipeline transport of oil,oil products and gas to perform turns of trunk and field pipelines in vertical and horizontal planes are used bends of various designs such as:elbows with bending radius of 1.0DN or 1.5DN and standardized angles of 30°,45°,60°,90°;induction bends with bending angles from 1°to 90°;cold bends with bending angles depending on the nominal diameter DN.
基金supported by the National Natural Science Foundation of China (No. 10632070)
文摘Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that the particle transport patterns are similar and independent of the particle size and other parameters when suspended nanoparticles flow in a straight tube. At the outside edge, particle deposition is the most intensive, while deposition at the inside edge is the weakest. In the upper and lower parts of the tube, depositions are approximately the same for different Schmidt numbers. Curvatures of tube, Reynolds number, and Schmidt number have second-order, forth-order, and first-order effects on the relative deposition efficiency, respectively.
基金Supported by the Major Program of the National Natural Science Foundation of China（10632070）
文摘Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method(TEMOM)is employed to study dynamics of nanoparticles with Brownian motion,based on the flow field from numerical simulation.A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code.It is found that for the simulated particulate flow system,the particle mass concentration,number concentration,particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time.The distribution of particle mass concentration at different time is independent of the initial particle size.More particles are concen-trated at outer edge of the bend.Coagulation plays more important role at initial stage than that in the subsequent period.The increase of Reynolds number and initial particle size leads to the increase of particle number concentration.The particle polydispersity,mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.
基金Supported by the National Natural Science Foundation of China (No. 29876034).
文摘The present paper intends to introduce a new method for reducingbends erosion from particles impacts: the ribbed bend erosionprotection method. Ribs are evenly fixed in the range of 20 deg-80deg on the inner-wall of inside 90 deg bend and the bend (includingribs) is made of medium carbon steel. Three-dimensional numericalworks is performed and the result shows satisfactory agreement withthe experimental measurement. Numerical simulation studies thecharacteristics of axial gas flow along the bend and secondary flowat cross section.
基金supported by the National Natural Science Foundation of China(Grants No.11361002 and 91230111)the Natural Science Foundation of Ningxia,China(Grant No.NZ13086)+1 种基金the Project of Beifang University of Nationalities,China(Grant No.2012XZK05)the Foreign Expert Project of Beifang University of Nationalities,China,and the Visiting Scholar Foundation of State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,China(Grant No.2013A011)
文摘The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.
基金Sponsored by National Natural Science Foundation of China(51171162)R & D Project of CITIC-CBMM(2011-D056-3)
文摘Mechanical properties of weld metal are the key factors affecting the quality of heavy-wall X80 hot induction bends. The effects of bending parameters on the mechanical properties of weld metal for hot bends were investigated by simulation conducted on a Gleeble 3500 thermal simulator. Continuous cooling transformation （CCT） dia- grams of the weld metal were also constructed. The influences of hot bending parameters （such as reheating temperature, cooling rate, and tempering temperature） on the microstructure and mechanical properties of weld metal were also analyzed. Results show that the strength of all weld metal specimens is higher than the value indicated in the technical specification and increases with the increase of reheating temperature, cooling rate, and tempering tempera ture. The impact toughness is apparently related to the variation of reheating temperature, cooling rate, and tempering temperature.
基金Supported by the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(No.51021004)the National Natural Science Foundation of China(No.50979066 and No.51009105)the Natural Science Foundation of Tianjin(No.12JCQNJC05600)
文摘A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water surface and the effect of transverse circulating current induced by the hydraulic structure of bend flow were fully considered. A theoretical formula for the incipient velocity of non-cohesive and non-uniform sediment in sloping river bends was developed. The results from the theoretical formula compared well with the experimental data.
文摘In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since river bends are not uniform-some are divergent and others convergent-in this study, after the SSIIM 3-D model was calibrated using the result of measurements along a uniform 180° bend with a width of 0.6 m, a similar but convergent 180v bend, 0.6 m to 0.45 m wide, was simulated using the SSI1M 3-D numerical model. Flow characteristics of the convergent 180° bend, including lengthwise and vertical velocity profiles, primary and secondary flows, lengthwise and widtbwise slopes of the water surface, and the helical flow strength, were compared with those of the uniform 180° bend. The verification results of the model show that the numerical model can effectively simulate the flow field in the uniform bend. In addition, this research indicates that, in a convergent channel, the maximum velocity path at a plane near the water surface crosses the channel＇s centerline at about a 30° to 40° cross-section, while in the uniform bend, this occurs at about the 50° cross-section. The varying range of the water surface elevation is wider in the convergent channel than in the uniform one, and the strength of the helical flow is generally greater in the uniform channel than in the convergent one. Also, unlike the uniform bend, the convergent bend exhibits no rotational cell against the main direction of secondary flow rotation at the 135° cross-section.
基金supported by the National Major Research and Development Project“Research on Disaster-caused Mechanism and Evolution Rules of Damages of Oil&Gas Pipelines and Storage&Transportation Facilities”(No.:2016YFC0802101)Scientific New Star Project of Shaanxi Province“Quality Forecast and Defect Control of Mold-free Hot-bending Cross Section with Small Radius of Pipe Material with Large Caliber”(No.:2015KJXX-73).
文摘While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate the bearing capacity of pipelines.In order to study the effect of cross-section distortion on the performance of small-radius induction bends,3D(D refers to pipe diameter)induction bends were manufactured based on different combinations of process parameters.Then,the cross-section distortion,structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis,distortion analysis,physical and chemical property test,micro-structural analysis and so on.The following results were obtained.First,the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends,and the roundness of 3D bends is about 2e4 times that of 5D bends.Second,the cross-section distortion of 3D bends is obvious,so its heating temperature varies greatly in different parts,leading to different structure morphologies and contents.As a result,the numerical distribution of mechanical properties of each part of 3D bends(e.g.intrados,extrados and neutral zone)is discrete.Third,the strength at the intrados of most bends doesn't meet the standard,and it is sorted form the higher to the lower as extrados,neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength.Fourth,the strength at intrados and extrados decreases with the increase of roundness.The strength at intrados decreases with the increase of thickening rates.And the strength at extrados increases with the increase of thinning rates.
基金Project support by the National Natural Science Foundation of China (Grant No: 50479034), the Natural Science Foundation of Tianjin (Grant No: 05YFSZSF02100).
文摘An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.
文摘A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution process in large radius bend that brings about an overall heat transfer augmentation, especially at the outer side of the bend, and the significant deterioration at the inner side. The influence of two major parameters, namely, the bend-to-tube radius ratio and the bulk Reynolds number on the flow structure as well as on the local heat transfer is investigated.
基金supported by the public welfare project(Normal Education Quality Improvement Plan)by the China Education Development Foundation(Grant No.TZJH202202)the National Natural Science Foundation of China(Grant No.12274370)。
文摘We numerically investigate the effect of in-plane bending strain on valley-resolved conductance and valley polarization in a graphene nanoribbon with zigzag edges.The central region of the nanoribbon is bent into an arc with central angleφ.We find that the bending strain reduces the conductance but enhances the valley polarization.In the valley-resolved conductance spectra,there exist single-valley plateaus near the Dirac points and distinct Fano-type dips.Accordingly,a plateau of full valley polarization appears,which expands significantly at largeφ.At valleyresolved conductance dips,the valley polarization can be much larger than that in the unstrained case.The bending-induced enhancement of valley polarization can be explained by the features of pseudo-Landau levels in the bent region.Strain-induced valley polarization depends nonmonotonously on the nanoribbon width.These findings could be helpful in designing valleytronic devices with flexibility.
基金supported by the intramural research program of the U.S.Department of Agriculture,National Institute of Food and Agriculture,Biobased Economy Through Biobased Products,under Award#2023-68016-40132.
文摘This study explores a novel method for processing cotton stalks—an abundant agricultural byproduct—into long strips that serve as sustainable raw material for engineered bio-based panels.To evaluate the effect of raw material morphology on panel’s performance,two types of cotton stalk-based panels were developed:one using long strips,maintaining fiber continuity,and the other using ground particles,representing conventional processing.A wood strand-based panel made from commercial southern yellow pine strands served as the control.All panels were bonded using phenol-formaldehyde resin and hot-pressed to a target thickness of 12.7 mm and density of 640 kg/m^(3).Their mechanical and physical properties were evaluated through internal bond,bending,thickness swelling,and water absorption tests.Both cotton stalk-based panels showed improved bonding performance compared to the control.The internal bond of the strip-based panel was nearly four times higher than that of the control,while the particlebased panel exceeded it by a factor of two.The strip-based panel showed approximately 15% lower bending stiffness than the wood strand-based panel,yet it surpassed it in load-carrying capacity by 5%.In contrast,the particleboard showed significantly lower bending performance than the strip-based and control panels,despite particle processing being a more conventional method.Both cotton stalk-based panels exhibited higher water absorption and thickness swelling than the wood strand panel.Overall,cotton stalk-based panels—particularly those using strip processing—show promisingmechanical properties,suggesting potential applications in sheathing,furniture,and interior paneling.However,improvements in dimensional stability are needed for broader use.
文摘In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random statistical method. The zones and rate of erosion on the wall in a bend are determined. The results are in accordance with the experiment, which indicate that the erosion is influenced by gas velocity, particle size and bend curvature.
基金funded by the Russian Science Foundation(RSF),grant No.25-73-20038(conceptualization,methodology,manuscript writing).
文摘Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules derived from planar coronene and kekulene molecules(graphene helicoids and spiral nanoribbons)are analyzed using molecular dynamics simulations.The interatomic interactions are described by a force field including valence bonds,bond angles,torsional and dihedral angles,as well as van derWaals interactions.While the tension/compression of such nanosprings has been analyzed in the literature,this study investigates other modes of deformation,including bending and twisting.Depending on the geometric characteristics of the carbon nanosprings,the formation of structural and helix reversal topological defects is described.During these structural transformations of the nanosprings,only van der Waals bonds break and recover,but breaking or recovery of covalent bonds does not take place.It is found that nanosprings demonstrate a significantly higher coefficient of axial thermal expansion than many metals and alloys.Under axial compression,Euler instability leads to lateral bending with continuous deformation of the nanospring axis at relatively low compression,while at high compression,bending kinks form.Various types of topological defects form on the instantly released nanospring during its relaxation from a highly stretched configuration.These results are useful for the development of nanosensors operating over a wide temperature range.
基金supported by the National Natural Science Foundation of China(Grant Nos.:52202423,U2268211,and 52475136)the China Postdoctoral Science Foundation(Grant Nos.:2022M712636 and 2023T160546)+1 种基金the Natural Science Foundation of Sichuan Province(Grant No.:2025ZNSFSC0398)the Independent R&D Project of the State Key Laboratory of Traction Power(Grant No.:2023TPL-T14).
文摘Since the view that the localized rail third-order bending mode can cause high-order polygonization(mainly 18-23)of high-speed train wheels was put forward in 2017,many scholars have attempted to link a connection between the localized rail bending modes and wheel polygonization phenomenon and polygonal wheel passing frequency.This paper first establishes a flexible track model considering the structural and parametric characteristics of fasteners,verifies the model by using vehicle tracking test data,then investigates the influence of fastener parameter matching on the localized rail bending modes,and obtains the following conclusions:(1)There is nearly a 1:1 mapping relationship between the localized rail bending modal frequency and polygonal wheel passing(PWP)frequency,which supports that the localized rail bending mode is one of the causes of wheel polygonization.(2)The iron plate of the fastener system plays a role of dynamic vibration absorber in the vehicle-rail coupled system,and the fastener parameters significantly influence the localized rail bending modal vibration.Finally,this paper proposes a design principle of a high-frequency vibration-absorbing fastener,which provides a feasible solution to mitigate the localized rail bending modal vibration and high-order wheel polygonization.Meanwhile,it points out that this measure may induce other high-frequency vibration problems,e.g.,aggravating modal vibration above 800 Hz.Further,this paper proposes a concept of differentiated arrangement of fasteners,suggesting that different high-frequency vibration-absorbing fasteners be installed in different sections of the whole line to make the localized rail bending modal frequency of the whole line disordered,thus disrupting and further mitigating the development of the wheel polygonization.
基金supported by the National Key Research and Development Program of China(2022YFA1404800)National Natural Science Foundation of China(12174107,12004221,12192254,92250304,W2441005,12334014,12192251)+4 种基金Natural Science Foundation of Shandong Province(ZR2024QA024,ZR2021ZD02)Postdoctoral Innovation Talents Support Program of Shandong Province(No.SDBX2019005)Shanghai Municipal Science and Technology Major ProjectFundamental Research Funds for the Central UniversitiesEngineering Research Center for Nanophotonics&Advanced Instrument,Ministry of Education,East China Normal University(No.2023nmc005)。
文摘We demonstrate a high-speed rotating slit beam shaping method for femtosecond(fs)laser three-dimensional(3D)isotropic inscription in glass materials.By integrating fs laser direct writing with a real-time rotating slit mechanism,a 3D symmetric spherical focal field distribution is created in the laser-irradiated regions of transparent substrates.The corresponding focal field distribution is theoretically calculated and validated by examining the features of laser-inscribed lines in glass samples.Moreover,we investigate the influences of laser writing speed and slit rotational speed on the fabrication resolution in glass,and discuss the formation mechanism of the generated periodic microstructures.To showcase its powerful capability for3D isotropic fabrication,the high-speed rotating slit beam shaping method is applied to create straight optical waveguides,bending optical waveguides,and hollow microchannels in the glass.The proposed method holds great potential for the facile manufacture of diverse 3D isotropic microstructures and devices within transparent materials across various applications,including advanced photonics,microoptics,micro-electromechanical systems,and microfluidics.
基金supported by Beijing Natural Science Foundation(L233025)。
文摘Functionally graded material(FGM)plates are widely used in various engineering structures owing to their tailor-made mechanical properties,whereas cracked homogeneous plates constitute a canonical setting in fracture mechanics analysis.These two classes of problems respectively embody material non-uniformity and geometric discontinuity,thereby imposing more stringent requirements on numerical methods in terms of high-order field continuity and accurate defect representation.Based on the classical Kirchhoff-Love plate theory,a numerical manifold method(MLS-NMM)incorporating moving least squares(MLS)interpolation is developed for bending analysis of FGM plates and fracture simulation of homogeneous plates with defects.The method constructs an H^(2)-regular approximation with high-order continuous weighting functions and,combined with the separation of mathematical and physical covers,establishes a unified framework that accurately handles material gradients and cracks without mesh reconstruction.For the crack tip,a singular physical cover incorporating the Williams asymptotic field is introduced to achieve local enrichment,enabling the natural capture of displacement discontinuity and stress singularity.Stress intensity factors are extracted using the interaction integral method,and the dimensionless J-integral shows a maximum relative error below 1.2%compared with the reference solution.Numerical results indicate that MLS-NMM exhibits excellent convergence performance:using 676 mathematical nodes,the nondimensional central deflection of both FGM and homogeneous plates agrees with reference solutions with a maximum relative error below 0.81%,and no shear locking occurs.A systematic analysis reveals that for a simply supported on all four edges(SSSS)FGM square plate with a/h=10,the nondimensional central deflection increases by 212%as the gradient index nrises from 0 to 5.For a homogeneous plate containing a central crack with c/a=0.6,the nondimensional central deflection increases by approximately 46%compared with the intact plate.Under weak boundary constraints(e.g.,SFSF),the deformation is markedly amplified,with the deflection reaching more than three times that under strong constraints(SCSC).The proposed method provides an efficient,reconstruction-free numerical tool for high-accuracy bending and fracture analyses of FGM and cracked thin-plate structures.
