The way to characterize the behaviour of a naval steel grade E36 subjected to the corrosive fatigue process is investigated. The tests were carried out by bending fatigue of plate specimens with thickness of 10 mm in ...The way to characterize the behaviour of a naval steel grade E36 subjected to the corrosive fatigue process is investigated. The tests were carried out by bending fatigue of plate specimens with thickness of 10 mm in the corrosive environment consisting of an aqueous solution of 3.5% of NaCl which is similar to seawater. Experimental results show that the principal mechanism of degradation of the superficial layer is based on the pit evolution,evidenced by electrochemical,micro and macro structural timely changes such as evolution of electrode potential,evolution of current density,polarization resistance,anodic and cathodic parameters,and dislocation density evolution.展开更多
5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<su...5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<sub>IC</sub>Were studied. It was shown that as the sulfur content increases the sulfur content dissolved in the steelsubstrate remains unchanged. The best contact fatigue property appears at the sulfur content of0.045% （wt.）, and the influence of sulfur content on the fracture toughness of bearing steel is notobvious. Finally, the mechanism of the role of sulfur was investigated.展开更多
Abstract.In this paper,a novel implementation of immersed interface method combined with Stokes solver on a MAC staggered grid for solving the steady two-fluid Stokes equations with interfaces.The velocity components ...Abstract.In this paper,a novel implementation of immersed interface method combined with Stokes solver on a MAC staggered grid for solving the steady two-fluid Stokes equations with interfaces.The velocity components along the interface are introduced as two augmented variables and the resulting augmented equation is then solved by the GMRES method.The augmented variables and/or the forces are related to the jumps in pressure and the jumps in the derivatives of both pressure and velocity,and are interpolated using cubic splines and are then applied to the fluid through the jump conditions.The Stokes equations are discretized on a staggered Cartesian grid via a second order finite difference method and solved by the conjugate gradient Uzawa-typemethod.The numerical results show that the overall scheme is second order accurate.The major advantages of the present IIM-Stokes solver are the efficiency and flexibility in terms of types of fluid flow and different boundary conditions.The proposed method avoids solution of the pressure Poisson equation,and comparisons are made to show the advantages of time savings by the present method.The generalized two-phase Stokes solver with correction terms has also been applied to incompressible two-phase Navier-Stokes flow.展开更多
Amulti-timescale algorithmis proposed for simulating time-dependent problems in micro-and nano-fluidics.The total simulation domain is spatially decomposed into two regions.Molecular dynamics is employed in the crucia...Amulti-timescale algorithmis proposed for simulating time-dependent problems in micro-and nano-fluidics.The total simulation domain is spatially decomposed into two regions.Molecular dynamics is employed in the crucial interfacial regions and continuum hydrodynamics is adopted in the remaining bulk regions.The coupling is through“constrained dynamics”in an overlap region.Our time scheme is based on the time scale separation between the continuum macro time step and molecular micro time step.This allows the molecular dynamics during one macro time step to be treated as in quasi-steady state.Therefore,molecular simulation is only performed in two shorter time intervals.Through linear extrapolation of macroscopic velocities and re-initialization of particle configurations,we can significantly reduce the total computational cost.We demonstrate and discuss our time algorithm through hybrid simulation of channel flow driven by a sinusoidally moving top wall.Converging results are achieved for cases of large separation of time scale with much less computational cost than with the original hybrid simulation without time extrapolation.展开更多
The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokine...The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokinetic(EK)turbulence,and expressed as∇^(n)A,with A being a control scalar.This paper presents a unified theoretical framework for the transport of the energy and other scalar quantities in the turbulence driven by scalar-based volume forces.Several isolated results that have previously been reported in relation to the turbulent thermal convection(related to n=0)and the EK turbulence(related to n=1)are unified in this theoretical framework.With the theory,the following interesting results are predicted:(1)When n<2/3,the transport of the kinetic energy is dominated by the Kolmogorov scaleηand another small scale l_(A).When n>2/3,the transport of the kinetic energy is controlled by three characteristic small scales:l_(K),l_(ηK) and l_(A).(2)The scaling law range can be divided into an inertial subrange and a volume-force-dominated subrange.(3)In the latter case,the exponents of the power spectra of the velocity and the relevant scalar quantity areη_(u)=(4n-11)/5,η_(A)=-(2n+7)/5,respectively.(4)In the equilibrium state,n cannot exceed 4.(5)The positive exponent of l_(A)∼0.024Ra^(0.107±0.016)_(A.l_(0)) is confirmed in the turbulent thermal convection.展开更多
文摘The way to characterize the behaviour of a naval steel grade E36 subjected to the corrosive fatigue process is investigated. The tests were carried out by bending fatigue of plate specimens with thickness of 10 mm in the corrosive environment consisting of an aqueous solution of 3.5% of NaCl which is similar to seawater. Experimental results show that the principal mechanism of degradation of the superficial layer is based on the pit evolution,evidenced by electrochemical,micro and macro structural timely changes such as evolution of electrode potential,evolution of current density,polarization resistance,anodic and cathodic parameters,and dislocation density evolution.
文摘5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<sub>IC</sub>Were studied. It was shown that as the sulfur content increases the sulfur content dissolved in the steelsubstrate remains unchanged. The best contact fatigue property appears at the sulfur content of0.045% （wt.）, and the influence of sulfur content on the fracture toughness of bearing steel is notobvious. Finally, the mechanism of the role of sulfur was investigated.
基金supported by Guangdong Provincial Government of China through the“Computational Science Innovative Research Team”program and the Sun Yat-sen University“Hundred Talents Program”(34000-3181201)and the National Natural Science Foundation of China(No.11101446).
文摘Abstract.In this paper,a novel implementation of immersed interface method combined with Stokes solver on a MAC staggered grid for solving the steady two-fluid Stokes equations with interfaces.The velocity components along the interface are introduced as two augmented variables and the resulting augmented equation is then solved by the GMRES method.The augmented variables and/or the forces are related to the jumps in pressure and the jumps in the derivatives of both pressure and velocity,and are interpolated using cubic splines and are then applied to the fluid through the jump conditions.The Stokes equations are discretized on a staggered Cartesian grid via a second order finite difference method and solved by the conjugate gradient Uzawa-typemethod.The numerical results show that the overall scheme is second order accurate.The major advantages of the present IIM-Stokes solver are the efficiency and flexibility in terms of types of fluid flow and different boundary conditions.The proposed method avoids solution of the pressure Poisson equation,and comparisons are made to show the advantages of time savings by the present method.The generalized two-phase Stokes solver with correction terms has also been applied to incompressible two-phase Navier-Stokes flow.
基金This material is based upon work supported by the National Science Foundation under Grant No.CMMI-0709187.
文摘Amulti-timescale algorithmis proposed for simulating time-dependent problems in micro-and nano-fluidics.The total simulation domain is spatially decomposed into two regions.Molecular dynamics is employed in the crucial interfacial regions and continuum hydrodynamics is adopted in the remaining bulk regions.The coupling is through“constrained dynamics”in an overlap region.Our time scheme is based on the time scale separation between the continuum macro time step and molecular micro time step.This allows the molecular dynamics during one macro time step to be treated as in quasi-steady state.Therefore,molecular simulation is only performed in two shorter time intervals.Through linear extrapolation of macroscopic velocities and re-initialization of particle configurations,we can significantly reduce the total computational cost.We demonstrate and discuss our time algorithm through hybrid simulation of channel flow driven by a sinusoidally moving top wall.Converging results are achieved for cases of large separation of time scale with much less computational cost than with the original hybrid simulation without time extrapolation.
基金Projects supported by the National Natural Science Foundation of China(Grant No.11672229).
文摘The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokinetic(EK)turbulence,and expressed as∇^(n)A,with A being a control scalar.This paper presents a unified theoretical framework for the transport of the energy and other scalar quantities in the turbulence driven by scalar-based volume forces.Several isolated results that have previously been reported in relation to the turbulent thermal convection(related to n=0)and the EK turbulence(related to n=1)are unified in this theoretical framework.With the theory,the following interesting results are predicted:(1)When n<2/3,the transport of the kinetic energy is dominated by the Kolmogorov scaleηand another small scale l_(A).When n>2/3,the transport of the kinetic energy is controlled by three characteristic small scales:l_(K),l_(ηK) and l_(A).(2)The scaling law range can be divided into an inertial subrange and a volume-force-dominated subrange.(3)In the latter case,the exponents of the power spectra of the velocity and the relevant scalar quantity areη_(u)=(4n-11)/5,η_(A)=-(2n+7)/5,respectively.(4)In the equilibrium state,n cannot exceed 4.(5)The positive exponent of l_(A)∼0.024Ra^(0.107±0.016)_(A.l_(0)) is confirmed in the turbulent thermal convection.
