Based on the fluid motion equations, the physical meaning of eddy viscosity coefficient and the rationality of the Boussinesq hypothesis are discussed in this paper. The effect of the coefficient on numerical stabilit...Based on the fluid motion equations, the physical meaning of eddy viscosity coefficient and the rationality of the Boussinesq hypothesis are discussed in this paper. The effect of the coefficient on numerical stability is analyzed briefly. A semi-enclosed rectangular sea area, with an orthogonal spur dike, is applied in a 2-D numerical model to study the effect of horizontal eddy viscosity coefficient (A(H)), The computed result shows that A(H) has little influence on the tidal level and averaged flow velocity, but has obvious influence on the intensity and the range of return flow around near the spur dike. Correspondingly, a wind-driven current pool and an annular current are applied in a 3-D numerical model respectively to study the effect of vertical eddy viscosity coefficient (A(V)). The computed result shows that the absolute value of A(V) is inversely proportional to that of horizontal velocity, and the vertical gradient value of A(V) determines the vertical distribution of horizontal velocity, The distribution form of A(V) is theoretically recommended as a parabolic type, of which the maximum value appears at 0.5 H.展开更多
This paper considers the stationary flow of incompressible micropolar fluid through a thin cylindrical pipe governed by the pressure drop between pipe’s ends. Its goal is to investigate the influence of the viscosity...This paper considers the stationary flow of incompressible micropolar fluid through a thin cylindrical pipe governed by the pressure drop between pipe’s ends. Its goal is to investigate the influence of the viscosity coefficients on the effective flow. Depending on the magnitude of viscosity coefficients with respect to the pipe’s thickness, it derives different asymptotic models and discusses their properties.展开更多
Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of...Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of the sediments adjacent to the foundation and the stability of the structures.This is especially true when the structures are founded on cohesive sedimentary bed.In this study,the viscosity of soft cohesive sediments adjacent to a vibrating pillar was considered,and as a primary index of the rheological characteristics of the sediments.The investigation was performed using the sinking ball method.The experimental findings indicated that the viscosity of cohesive sediments decrease with increase of the liquidity index and vibration intensity.A simple semi-empirical formula was proposed.The structures of the cohesive sediments were destroyed due to the mechanical vibration,and the sediments were fluidized during vibration loads.The shear strength of the cohesive sediments decreased with increased vibration intensity,not only because of the increased pore water pressure but also the decreased viscosity of cohesive sediments following sediment fluidization.展开更多
In this paper, we investigate the free boundary value problem (FBVP) for the cylindrically symmetric isentropic compressible Navier-Stokes equations (CNS) with density- dependent viscosity coefficients in the case...In this paper, we investigate the free boundary value problem (FBVP) for the cylindrically symmetric isentropic compressible Navier-Stokes equations (CNS) with density- dependent viscosity coefficients in the case that across the free surface stress tensor is balanced by a constant exterior pressure. Under certain assumptions imposed on the initial data, we prove that there exists a unique global strong solution which tends pointwise to a non-vacuum equilibrium state at an exponential time-rate as the time tends to infinity.展开更多
A fiber-array probe is designed to measure the damping behavior of a small perturbed shock wave in an opaque substance, by which the effective viscosity of substance under the condition of high temperature and high pr...A fiber-array probe is designed to measure the damping behavior of a small perturbed shock wave in an opaque substance, by which the effective viscosity of substance under the condition of high temperature and high pressure can be constrained according to the flyer-impact technique. It shows that the measurement precision of the shock arrival time by using this technique is within 2 ns. To easily compare with the results given by electrical pin technique, the newly developed method is used to investigate the effective viscosity of aluminum (Al). The shear viscosity coefficient of A1 is determined to be 1700 Pa.s at 71 GPa with a strain rate of 3.6× 10^6 s-1, which is in good agreement with the results of other methods. The advantage of the new technique over the electrical pin one is that it is applicable for studying the non-conductive substances.展开更多
A new approach to model viscosity in the conservation of momentum equations is presented and discussed. Coefficient of viscosity is modeled in such a way that it reaches asymptotically to infinity at the solid boundar...A new approach to model viscosity in the conservation of momentum equations is presented and discussed. Coefficient of viscosity is modeled in such a way that it reaches asymptotically to infinity at the solid boundary but still yields a finite value for the shear stress at the solid wall. Basic objective of this research is to show that certain combinations of higher order normal velocity gradients become zero at the solid boundary. Malled solutions for the Couette flow and Poiseuille flow between two parallel plates are obtained by modeling the coefficient of viscosity in a novel way. Also, viscous drag computed by our model is expected to yield higher values than the values predicted by the existing models, which matches closely to the experimental data.展开更多
A complex interface exists between waterflow and solid particles during hydraulic soil erosion.In this study,the particle discrete element method(DEM)has been used to simulate the hydraulic erosion of a granular soil ...A complex interface exists between waterflow and solid particles during hydraulic soil erosion.In this study,the particle discrete element method(DEM)has been used to simulate the hydraulic erosion of a granular soil under moving bed conditions and surrounding terrain changes.Moreover,the weakly compressible smoothed particle hydrodynamics(WCSPH)approach has been exploited to simulate the instability process of the free surfacefluid and its propagation characteristics at the solid–liquid interface.The influence of a suspended medium on the waterflow dynamics has been characterized using the mixed viscosity concept accounting for the solid–liquid mixed particle volume ratio.Numerical simulations of wall-jet scouring and reservoir sedimentflushing on a mobile bed were performed and validated with experiments.The results show that the proposed WCSPH–DEM coupling model is highly suitable for determining parameters,such as the local maximum scour depth,the scour pit width,and the sand bed profile.The effects on the hydraulic erosion process of two important para-meters of the mixed viscosity coefficient(initial solid volume concentration and initial viscosity coefficient)are also discussed to a certain extent in this study.展开更多
The loss tangent and storage modulus of cement mortar containing treated silica fume and styrene-acrylic are measured. Shaking table tests on three groups of 1/4 models of high damping concrete frames are conducted to...The loss tangent and storage modulus of cement mortar containing treated silica fume and styrene-acrylic are measured. Shaking table tests on three groups of 1/4 models of high damping concrete frames are conducted to compare the effects of reducing vibration. A relationship between the viscosity coefficient of high damping concrete and the damping coefficient of structure is established by analyzing dynamic parameters like damping ratio and frequency, and comparing responses of relative displacement and absolute acceleration. Surface treatment of silica fume and styrene-acrylic emulsion prior to incorporation in a cement mortar increases the loss tangent of the resulting composite by 40-400% as compared to the cement mortar without any admixtures, and the damping ratio of the reinforced concrete is raised by 7%-9%. In addition, a theoretical method of determining the viscosity coefficient of the material on the basis of shaking table test results is put forward.展开更多
This paper uses the Taylor expansion to seek an approximate Korteweg- de Vries equation (KdV) solution to a higher-order traffic flow model with sufficiently large diffusion. It demonstrates the validity of the appr...This paper uses the Taylor expansion to seek an approximate Korteweg- de Vries equation (KdV) solution to a higher-order traffic flow model with sufficiently large diffusion. It demonstrates the validity of the approximate KdV solution considering all the related parameters to ensure the physical boundedness and the stability of the solution. Moreover, when the viscosity coefficient depends on the density and velocity of the flow, the wave speed of the KdV solution is naturally related to either the first or the second characteristic field. The finite element method is extended to solve the model and examine the stability and accuracy of the approximate KdV solution.展开更多
This paper is concerned with the Cauchy problems of one-dimensional compressible Navier-Stokes equations with density-dependent viscosity coefcients.By assumingρ0∈L1(R),we will prove the existence of weak solution...This paper is concerned with the Cauchy problems of one-dimensional compressible Navier-Stokes equations with density-dependent viscosity coefcients.By assumingρ0∈L1(R),we will prove the existence of weak solutions to the Cauchy problems forθ〉0.This will improve results in Jiu and Xin’s paper(Kinet.Relat.Models,1(2):313–330(2008))in whichθ〉12is required.In addition,We will study the large time asymptotic behavior of such weak solutions.展开更多
This paper is concerned with the free boundary value problem(FBVP) for the cylindrically symmetric barotropic compressible Navier-Stokes equations(CNS) with density-dependent viscosity coefficients in the case tha...This paper is concerned with the free boundary value problem(FBVP) for the cylindrically symmetric barotropic compressible Navier-Stokes equations(CNS) with density-dependent viscosity coefficients in the case that across the free surface stress tensor is balanced by a constant exterior pressure. Under certain assumptions imposed on the initial data, the unique cylindrically symmetric strong solution is shown to exist globally in time and tend to a non-vacuum equilibrium state exponentially as time tends to infinity.展开更多
The bubble packing method can generate high-quality node sets in simple and complex domains.However,its efficiency remains to be improved.This study is a part of an ongoing effort to introduce several acceleration sch...The bubble packing method can generate high-quality node sets in simple and complex domains.However,its efficiency remains to be improved.This study is a part of an ongoing effort to introduce several acceleration schemes to reduce the cost of simulation.Firstly,allow the viscosity coefficient c in the bubble governing equations to change according the coordinate of the bubble which are defined separately as odd and normal bubbles,and meanwhile with the saw-shape relationship with time or iterations.Then,in order to relieve the over crowded initial bubble placement,two coefficients w1 and w2 are introduced to modify the insertion criterion.The range of those two coefficients are discussed to be w1=1,w2∈[0.5,0.8].Finally,a self-adaptive termination condition is logically set when the stable system equilibrium is achieved.Numerical examples illustrate that the computing cost can significantly decrease by roughly 80%via adopting various combination of proper schemes(except the uniform placement example),and the average qualities of corresponding Delaunay triangulation substantially exceed 0.9.It shows that those strategies are efficient and can generate a node set with high quality.展开更多
The Langevin equation including particle emission was used to reproduce the recently measured spin distribution of evaporation residue cross sections in the reaction ^16O+^184W at beam energies of 84, 92, 100, 108, 1...The Langevin equation including particle emission was used to reproduce the recently measured spin distribution of evaporation residue cross sections in the reaction ^16O+^184W at beam energies of 84, 92, 100, 108, 116 and 120 MeV. By comparing the theoretical calculations with the experimental data, the validity of the stochastic approach to dissipative fission is verified. Moreover, a pre-saddle nuclear viscosity coefficient of 5×10^21 s^-1 is extracted.展开更多
The FePC-based bulk metallic glasses(BMGs)have been demonstrated to possess high plasticity and good soft magnetic properties.However,the relatively poor glass forming ability(GFA)and thermal stabilities limited t...The FePC-based bulk metallic glasses(BMGs)have been demonstrated to possess high plasticity and good soft magnetic properties.However,the relatively poor glass forming ability(GFA)and thermal stabilities limited their application in industries.The effects of microalloying with B in FePC-based BMGs on the GFA and thermal behaviors were systematically investigated.It was found that a small amount of B addition can dramatically enhance the GFA of FePC-based BMGs,which in turn leads to the critical maximum diameter up to 2 mm for full glass formation even using low cost raw materials.The underlying mechanism of the enhancement of GFA from the competing crystalline phase with amorphous phase,the average thermal expansion coefficient and dynamic viscosity were discussed in detail.展开更多
文摘Based on the fluid motion equations, the physical meaning of eddy viscosity coefficient and the rationality of the Boussinesq hypothesis are discussed in this paper. The effect of the coefficient on numerical stability is analyzed briefly. A semi-enclosed rectangular sea area, with an orthogonal spur dike, is applied in a 2-D numerical model to study the effect of horizontal eddy viscosity coefficient (A(H)), The computed result shows that A(H) has little influence on the tidal level and averaged flow velocity, but has obvious influence on the intensity and the range of return flow around near the spur dike. Correspondingly, a wind-driven current pool and an annular current are applied in a 3-D numerical model respectively to study the effect of vertical eddy viscosity coefficient (A(V)). The computed result shows that the absolute value of A(V) is inversely proportional to that of horizontal velocity, and the vertical gradient value of A(V) determines the vertical distribution of horizontal velocity, The distribution form of A(V) is theoretically recommended as a parabolic type, of which the maximum value appears at 0.5 H.
基金supported by the Ministry of Science, Education and Sports, Republic of Croatia (03703727872797)
文摘This paper considers the stationary flow of incompressible micropolar fluid through a thin cylindrical pipe governed by the pressure drop between pipe’s ends. Its goal is to investigate the influence of the viscosity coefficients on the effective flow. Depending on the magnitude of viscosity coefficients with respect to the pipe’s thickness, it derives different asymptotic models and discusses their properties.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.52001206).
文摘Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of the sediments adjacent to the foundation and the stability of the structures.This is especially true when the structures are founded on cohesive sedimentary bed.In this study,the viscosity of soft cohesive sediments adjacent to a vibrating pillar was considered,and as a primary index of the rheological characteristics of the sediments.The investigation was performed using the sinking ball method.The experimental findings indicated that the viscosity of cohesive sediments decrease with increase of the liquidity index and vibration intensity.A simple semi-empirical formula was proposed.The structures of the cohesive sediments were destroyed due to the mechanical vibration,and the sediments were fluidized during vibration loads.The shear strength of the cohesive sediments decreased with increased vibration intensity,not only because of the increased pore water pressure but also the decreased viscosity of cohesive sediments following sediment fluidization.
基金supported by NNSFC(11101145),supported by NNSFC(11326140 and11501323)China Postdoctoral Science Foundation(2012M520360)+1 种基金Doctoral Foundation of North China University of Water Sources and Electric Power(201032),Innovation Scientists and Technicians Troop Construction Projects of Henan Provincethe Doctoral Starting up Foundation of Quzhou University(BSYJ201314 and XNZQN201313)
文摘In this paper, we investigate the free boundary value problem (FBVP) for the cylindrically symmetric isentropic compressible Navier-Stokes equations (CNS) with density- dependent viscosity coefficients in the case that across the free surface stress tensor is balanced by a constant exterior pressure. Under certain assumptions imposed on the initial data, we prove that there exists a unique global strong solution which tends pointwise to a non-vacuum equilibrium state at an exponential time-rate as the time tends to infinity.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10974160 and 11002120)the Fundamental Research Funds for the Central Universities (Grant No.SWJTU12CX085)
文摘A fiber-array probe is designed to measure the damping behavior of a small perturbed shock wave in an opaque substance, by which the effective viscosity of substance under the condition of high temperature and high pressure can be constrained according to the flyer-impact technique. It shows that the measurement precision of the shock arrival time by using this technique is within 2 ns. To easily compare with the results given by electrical pin technique, the newly developed method is used to investigate the effective viscosity of aluminum (Al). The shear viscosity coefficient of A1 is determined to be 1700 Pa.s at 71 GPa with a strain rate of 3.6× 10^6 s-1, which is in good agreement with the results of other methods. The advantage of the new technique over the electrical pin one is that it is applicable for studying the non-conductive substances.
文摘A new approach to model viscosity in the conservation of momentum equations is presented and discussed. Coefficient of viscosity is modeled in such a way that it reaches asymptotically to infinity at the solid boundary but still yields a finite value for the shear stress at the solid wall. Basic objective of this research is to show that certain combinations of higher order normal velocity gradients become zero at the solid boundary. Malled solutions for the Couette flow and Poiseuille flow between two parallel plates are obtained by modeling the coefficient of viscosity in a novel way. Also, viscous drag computed by our model is expected to yield higher values than the values predicted by the existing models, which matches closely to the experimental data.
基金funded by the National Natural Science Foundation of China(No.51568022)the Science and Technology Project of Education Department,Jiangxi Province,China(No.GJJ217404).
文摘A complex interface exists between waterflow and solid particles during hydraulic soil erosion.In this study,the particle discrete element method(DEM)has been used to simulate the hydraulic erosion of a granular soil under moving bed conditions and surrounding terrain changes.Moreover,the weakly compressible smoothed particle hydrodynamics(WCSPH)approach has been exploited to simulate the instability process of the free surfacefluid and its propagation characteristics at the solid–liquid interface.The influence of a suspended medium on the waterflow dynamics has been characterized using the mixed viscosity concept accounting for the solid–liquid mixed particle volume ratio.Numerical simulations of wall-jet scouring and reservoir sedimentflushing on a mobile bed were performed and validated with experiments.The results show that the proposed WCSPH–DEM coupling model is highly suitable for determining parameters,such as the local maximum scour depth,the scour pit width,and the sand bed profile.The effects on the hydraulic erosion process of two important para-meters of the mixed viscosity coefficient(initial solid volume concentration and initial viscosity coefficient)are also discussed to a certain extent in this study.
基金the National Natumal Science Foundation of China(No.50608025)Guangdong Provincial Natural Science Foundation of(No.05300894)China Postdoctoral Science Foundation(No.20060390804)
文摘The loss tangent and storage modulus of cement mortar containing treated silica fume and styrene-acrylic are measured. Shaking table tests on three groups of 1/4 models of high damping concrete frames are conducted to compare the effects of reducing vibration. A relationship between the viscosity coefficient of high damping concrete and the damping coefficient of structure is established by analyzing dynamic parameters like damping ratio and frequency, and comparing responses of relative displacement and absolute acceleration. Surface treatment of silica fume and styrene-acrylic emulsion prior to incorporation in a cement mortar increases the loss tangent of the resulting composite by 40-400% as compared to the cement mortar without any admixtures, and the damping ratio of the reinforced concrete is raised by 7%-9%. In addition, a theoretical method of determining the viscosity coefficient of the material on the basis of shaking table test results is put forward.
基金supported by the National Natural Science Foundation of China(Nos.11072141 and11272199)the National Basic Research Program of China(No.2012CB725404)+2 种基金the Shanghai Program for Innovative Research Team in Universitiesthe Research Grants Council of the Hong KongSpecial Administrative Region,China(No.HKU7184/10E)the National Research Foundationof Korea(MEST)(No.NRF-2010-0029446)
文摘This paper uses the Taylor expansion to seek an approximate Korteweg- de Vries equation (KdV) solution to a higher-order traffic flow model with sufficiently large diffusion. It demonstrates the validity of the approximate KdV solution considering all the related parameters to ensure the physical boundedness and the stability of the solution. Moreover, when the viscosity coefficient depends on the density and velocity of the flow, the wave speed of the KdV solution is naturally related to either the first or the second characteristic field. The finite element method is extended to solve the model and examine the stability and accuracy of the approximate KdV solution.
基金Supported by the National Natural Science Foundation of China(No.10771170)
文摘This paper is concerned with the Cauchy problems of one-dimensional compressible Navier-Stokes equations with density-dependent viscosity coefcients.By assumingρ0∈L1(R),we will prove the existence of weak solutions to the Cauchy problems forθ〉0.This will improve results in Jiu and Xin’s paper(Kinet.Relat.Models,1(2):313–330(2008))in whichθ〉12is required.In addition,We will study the large time asymptotic behavior of such weak solutions.
基金supported by National Natural Science Foundation of China(No.41630530),National Natural Science Foundation of China(No.41575109)Key Research Program of Frontier Sciences,CAS(Grant No.QYZDY-SSW-DQC002)
文摘This paper is concerned with the free boundary value problem(FBVP) for the cylindrically symmetric barotropic compressible Navier-Stokes equations(CNS) with density-dependent viscosity coefficients in the case that across the free surface stress tensor is balanced by a constant exterior pressure. Under certain assumptions imposed on the initial data, the unique cylindrically symmetric strong solution is shown to exist globally in time and tend to a non-vacuum equilibrium state exponentially as time tends to infinity.
基金National Natural Science Foundation of China(No.11071196,90916027).
文摘The bubble packing method can generate high-quality node sets in simple and complex domains.However,its efficiency remains to be improved.This study is a part of an ongoing effort to introduce several acceleration schemes to reduce the cost of simulation.Firstly,allow the viscosity coefficient c in the bubble governing equations to change according the coordinate of the bubble which are defined separately as odd and normal bubbles,and meanwhile with the saw-shape relationship with time or iterations.Then,in order to relieve the over crowded initial bubble placement,two coefficients w1 and w2 are introduced to modify the insertion criterion.The range of those two coefficients are discussed to be w1=1,w2∈[0.5,0.8].Finally,a self-adaptive termination condition is logically set when the stable system equilibrium is achieved.Numerical examples illustrate that the computing cost can significantly decrease by roughly 80%via adopting various combination of proper schemes(except the uniform placement example),and the average qualities of corresponding Delaunay triangulation substantially exceed 0.9.It shows that those strategies are efficient and can generate a node set with high quality.
基金Supported by National Natural Science Foundation of China(10405007)
文摘The Langevin equation including particle emission was used to reproduce the recently measured spin distribution of evaporation residue cross sections in the reaction ^16O+^184W at beam energies of 84, 92, 100, 108, 116 and 120 MeV. By comparing the theoretical calculations with the experimental data, the validity of the stochastic approach to dissipative fission is verified. Moreover, a pre-saddle nuclear viscosity coefficient of 5×10^21 s^-1 is extracted.
基金financially supported by the National Natural Science Foundation of China(Nos.51301142and 51671162)China Postdoctoral Science Foundation(Nos.2015T80957and 2014M562279)+1 种基金Chongqing Research Program of Basic Research and Frontier Technology(No.cstc2015jcyjBX0107)the Fundamental Research Funds for the Central Universities(Nos.XDJK2015C064and XDJK2015C003)
文摘The FePC-based bulk metallic glasses(BMGs)have been demonstrated to possess high plasticity and good soft magnetic properties.However,the relatively poor glass forming ability(GFA)and thermal stabilities limited their application in industries.The effects of microalloying with B in FePC-based BMGs on the GFA and thermal behaviors were systematically investigated.It was found that a small amount of B addition can dramatically enhance the GFA of FePC-based BMGs,which in turn leads to the critical maximum diameter up to 2 mm for full glass formation even using low cost raw materials.The underlying mechanism of the enhancement of GFA from the competing crystalline phase with amorphous phase,the average thermal expansion coefficient and dynamic viscosity were discussed in detail.