Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this ...Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.展开更多
A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture ...A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture trans-fer characteristics in a representative hill cave have been simulated via a method relying on the Darcy’s law.The simulations have been conducted for both steady and unsteady conditions to discern the influence of permeability and geometric parameters on the thermal and moisture transfer processes.The reliability of the simulation has been verified through comparison of the numerical results with the annual observation data.As revealed by the numericalfindings,the internal temperature of the hill accumulator is proportional to the permeability,outside surface temperature,overground height,underground constant temperature layer depth,and underground tem-perature of the hill,and it is inversely proportional to the horizontal size of the hill.Moreover,in the considered case,the order of magnitude of the permeability of the hill is contained in the range 10-15–10-13,and displays a certain sensitivity to the rainwater seepage.展开更多
The hydroelastic responses of a submerged horizontal solid/porous plate attached at the front of a very large rectangular floating structure(VLFS)under wave action has been investigated in the context of linear water ...The hydroelastic responses of a submerged horizontal solid/porous plate attached at the front of a very large rectangular floating structure(VLFS)under wave action has been investigated in the context of linear water wave theory.Darcy’s law is adopted to represent energy dissipation in pores.It is assumed that the porous plates are made of material with very fine pores so that the normal velocity across the perforated porous is linearly associated with the pressure drop.In the analytic method,the eigenfunction expansion-matching method(EEMM)for multiple domains is applied to solve the hydrodynamic problem and the elastic equation of motion is solved by the modal expansion method.The performance of the proposed submerged horizontal solid/porous plate can be significantly enhanced by selecting optimal design parameters,such as plate length,horizontal position,submerged depth and porosity.It is concluded that good damping effect can be achieved through installation of solid and porous plate.Porous plate has better damping effect at low frequencies,while solid plate has better damping effect at high frequencies.The optimal ratio of plate length to water depth is 0.25-0.375,and the optimal ratio of submerged depth to water depth is 0.09-0.181.展开更多
In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity...In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).展开更多
The numerical determination of static characteristics of bearings allows a cost-efficient and fast pre-design.In this study,two flow models for aerostatic thrust bearings with pressurized porous material are presented...The numerical determination of static characteristics of bearings allows a cost-efficient and fast pre-design.In this study,two flow models for aerostatic thrust bearings with pressurized porous material are presented and analyzed.The models are based on the coupling of the Reynolds equation for lubricants(REL)and the determination of pressure drop through porous material by Darcy’s law.The simplified model is based on the assumption of a one-dimensional axial flow through porous media.The extended model considers the three-dimensional flow in the porous body.The analysis includes pressurized air from 4 to 9 bar(a)with nominal clearance of 5 to 60μm,Commercial CFD(computational fluid dynamics)software was used to verify the results.The extended model allows a more accurate prediction about the performance in the critical gap range.In total,the results show good agreement with CFD within a short computation time.展开更多
A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was dev...A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity.Two experiments with alloy Pb-Sn infiltrating into Al2O3 preform were conducted independently under two different pressures so as to get two different infiltration curves.Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method.By solving the two-variable equation set,two unknown variables were determined.It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment.The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.展开更多
The problem of the creeping flow through a spherical droplet with a non-homogenous porous layer in a spherical container has been studied analytically.Darcy’s model for the flow inside the porous annular region and t...The problem of the creeping flow through a spherical droplet with a non-homogenous porous layer in a spherical container has been studied analytically.Darcy’s model for the flow inside the porous annular region and the Stokes equation for the flow inside the spherical cavity and container are used to analyze the flow.The drag force is exerted on the porous spherical particles enclosing a cavity,and the hydrodynamic permeability of the spherical droplet with a non-homogeneous porous layer is calculated.Emphasis is placed on the spatially varying permeability of a porous medium,which is not covered in all the previous works related to spherical containers.The variation of hydrodynamic permeability and the wall effect with respect to various flow parameters are presented and discussed graphically.The streamlines are presented to discuss the kinematics of the flow.Some previous results for hydrodynamic permeability and drag forces have been verified as special limiting cases.展开更多
The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize...The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize the seepage capacity of porous media.Therefore,based on the statistically fractal scaling law of porous media,fractal geometry is applied to model the multiscale pore structures.And a two-dimensional fractal orifice-throat model with multiscale and tortuous characteristics is proposed for the seepage flow through porous media.The analytical expression for Darcy permeability of porous media is derived,which is validated by comparing with available experimental data.The results show that the Darcy permeability is significantly influenced by porosity,orifice-throat fractal dimension,minimum to maximum diameter ratio,orifice-throat ratio and tortuosity fractal dimension.The present results are helpful for understanding the seepage mechanism of multiscale porous media,and may provide theoretical basis for unconventional oil and gas exploration and development,porous phase transition energy storage composites,CO2 geological sequestration,environmental protection and nuclear waste treatment,etc.展开更多
Polymer-bonded sugars(PBSs)can be used as a substitute material for polymerbonded explosives(PBXs)due to their ability to simulate the mechanical properties of PBXs.In the process of pressing a PBS,the length of the d...Polymer-bonded sugars(PBSs)can be used as a substitute material for polymerbonded explosives(PBXs)due to their ability to simulate the mechanical properties of PBXs.In the process of pressing a PBS,the length of the dwell time has a significant impact on the mechanical properties of the PBS.This reinforcing effect is based on the residual pressure causing the binder to flow and gradually fill each defect.Through the use of Darcy5s principle of binder infiltration and viscoelastic theory,an exponential relationship between the compressive strength of PBS and the dwell time has been derived.From the experiments,it was found that the extreme forces that correspond to the compaction stage of the PBS samples with different dwell times were almost the same;this indicates that there is tolerance to damage during the compaction stage.The existence of the compaction stage is related to the brittleness of the PBS.The experimental results showed that as the dwell time increased,the rate of damage evolution of the specimen decreased.展开更多
In this article,the variation of temperature distribution and fin efficiency in a porous moving fin of rectangular profile is studied.This study is performed using Darcy's model to formulate the governing heat tra...In this article,the variation of temperature distribution and fin efficiency in a porous moving fin of rectangular profile is studied.This study is performed using Darcy's model to formulate the governing heat transfer differential equation.The approximate analytical solution is generated using the variational iteration method(VIM).The power series solution is validated by benchmarking it against the numerical solution obtained by applying the Runge-Kutta fourth order method.A good agreement between the analytical and numerical results is observed.The effects of porosity parameter,Peclet number and other thermo-physical parameters,such as the power index of heat transfer coefficient,convective-conductive parameter,radiative-conductive parameter,thermal conductivity gradient and non-dimensional ambient temperature on non-dimensional temperature are also studied and explained.The results indicate that the fin rapidly dissipates heat to the ambient temperature with an increase in the Peclet number,convection-radiation parameters and the porosity parameter.展开更多
文摘Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.
文摘A hill can be regarded as an environmental carrier of heat.Water,rocks and the internal moisture naturally pre-sent in such environment constitute a natural heat accumulator.In the present study,the heat and moisture trans-fer characteristics in a representative hill cave have been simulated via a method relying on the Darcy’s law.The simulations have been conducted for both steady and unsteady conditions to discern the influence of permeability and geometric parameters on the thermal and moisture transfer processes.The reliability of the simulation has been verified through comparison of the numerical results with the annual observation data.As revealed by the numericalfindings,the internal temperature of the hill accumulator is proportional to the permeability,outside surface temperature,overground height,underground constant temperature layer depth,and underground tem-perature of the hill,and it is inversely proportional to the horizontal size of the hill.Moreover,in the considered case,the order of magnitude of the permeability of the hill is contained in the range 10-15–10-13,and displays a certain sensitivity to the rainwater seepage.
基金financially supported by the National Key R&D Program of China(Grant No.2019YFC1407700)the National Natural Science Foundation of China(Grant No.51779038)。
文摘The hydroelastic responses of a submerged horizontal solid/porous plate attached at the front of a very large rectangular floating structure(VLFS)under wave action has been investigated in the context of linear water wave theory.Darcy’s law is adopted to represent energy dissipation in pores.It is assumed that the porous plates are made of material with very fine pores so that the normal velocity across the perforated porous is linearly associated with the pressure drop.In the analytic method,the eigenfunction expansion-matching method(EEMM)for multiple domains is applied to solve the hydrodynamic problem and the elastic equation of motion is solved by the modal expansion method.The performance of the proposed submerged horizontal solid/porous plate can be significantly enhanced by selecting optimal design parameters,such as plate length,horizontal position,submerged depth and porosity.It is concluded that good damping effect can be achieved through installation of solid and porous plate.Porous plate has better damping effect at low frequencies,while solid plate has better damping effect at high frequencies.The optimal ratio of plate length to water depth is 0.25-0.375,and the optimal ratio of submerged depth to water depth is 0.09-0.181.
文摘In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).
文摘The numerical determination of static characteristics of bearings allows a cost-efficient and fast pre-design.In this study,two flow models for aerostatic thrust bearings with pressurized porous material are presented and analyzed.The models are based on the coupling of the Reynolds equation for lubricants(REL)and the determination of pressure drop through porous material by Darcy’s law.The simplified model is based on the assumption of a one-dimensional axial flow through porous media.The extended model considers the three-dimensional flow in the porous body.The analysis includes pressurized air from 4 to 9 bar(a)with nominal clearance of 5 to 60μm,Commercial CFD(computational fluid dynamics)software was used to verify the results.The extended model allows a more accurate prediction about the performance in the critical gap range.In total,the results show good agreement with CFD within a short computation time.
基金Project(51575447) supported by the National Natural Science Foundation of ChinaProject supported by Top University around World Visiting Plan for Young Teacher’s Cultivating in NWPU,China
文摘A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity.Two experiments with alloy Pb-Sn infiltrating into Al2O3 preform were conducted independently under two different pressures so as to get two different infiltration curves.Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method.By solving the two-variable equation set,two unknown variables were determined.It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment.The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.
基金Project supported by the Science and Engineering Research Board,New Delhi(No.SR/FTP/MS-47/2012)。
文摘The problem of the creeping flow through a spherical droplet with a non-homogenous porous layer in a spherical container has been studied analytically.Darcy’s model for the flow inside the porous annular region and the Stokes equation for the flow inside the spherical cavity and container are used to analyze the flow.The drag force is exerted on the porous spherical particles enclosing a cavity,and the hydrodynamic permeability of the spherical droplet with a non-homogeneous porous layer is calculated.Emphasis is placed on the spatially varying permeability of a porous medium,which is not covered in all the previous works related to spherical containers.The variation of hydrodynamic permeability and the wall effect with respect to various flow parameters are presented and discussed graphically.The streamlines are presented to discuss the kinematics of the flow.Some previous results for hydrodynamic permeability and drag forces have been verified as special limiting cases.
文摘The seepage characteristics of multiscale porous media is of considerable significance in many scientific and engineering fields.The Darcy permeability is one of the key macroscopic physical properties to characterize the seepage capacity of porous media.Therefore,based on the statistically fractal scaling law of porous media,fractal geometry is applied to model the multiscale pore structures.And a two-dimensional fractal orifice-throat model with multiscale and tortuous characteristics is proposed for the seepage flow through porous media.The analytical expression for Darcy permeability of porous media is derived,which is validated by comparing with available experimental data.The results show that the Darcy permeability is significantly influenced by porosity,orifice-throat fractal dimension,minimum to maximum diameter ratio,orifice-throat ratio and tortuosity fractal dimension.The present results are helpful for understanding the seepage mechanism of multiscale porous media,and may provide theoretical basis for unconventional oil and gas exploration and development,porous phase transition energy storage composites,CO2 geological sequestration,environmental protection and nuclear waste treatment,etc.
基金the financial support by NSAF(U133010)NSFC(11472141)K.C.Wong Magna Fund in Ningbo University.
文摘Polymer-bonded sugars(PBSs)can be used as a substitute material for polymerbonded explosives(PBXs)due to their ability to simulate the mechanical properties of PBXs.In the process of pressing a PBS,the length of the dwell time has a significant impact on the mechanical properties of the PBS.This reinforcing effect is based on the residual pressure causing the binder to flow and gradually fill each defect.Through the use of Darcy5s principle of binder infiltration and viscoelastic theory,an exponential relationship between the compressive strength of PBS and the dwell time has been derived.From the experiments,it was found that the extreme forces that correspond to the compaction stage of the PBS samples with different dwell times were almost the same;this indicates that there is tolerance to damage during the compaction stage.The existence of the compaction stage is related to the brittleness of the PBS.The experimental results showed that as the dwell time increased,the rate of damage evolution of the specimen decreased.
文摘In this article,the variation of temperature distribution and fin efficiency in a porous moving fin of rectangular profile is studied.This study is performed using Darcy's model to formulate the governing heat transfer differential equation.The approximate analytical solution is generated using the variational iteration method(VIM).The power series solution is validated by benchmarking it against the numerical solution obtained by applying the Runge-Kutta fourth order method.A good agreement between the analytical and numerical results is observed.The effects of porosity parameter,Peclet number and other thermo-physical parameters,such as the power index of heat transfer coefficient,convective-conductive parameter,radiative-conductive parameter,thermal conductivity gradient and non-dimensional ambient temperature on non-dimensional temperature are also studied and explained.The results indicate that the fin rapidly dissipates heat to the ambient temperature with an increase in the Peclet number,convection-radiation parameters and the porosity parameter.
