This paper describes the application of a three-dimensional lattice Boltzmann method(LBM)to Newtonian and non-Newtonian(Bingham fluid in this work)flows with free surfaces.A mass tracking algorithm was incorporated to...This paper describes the application of a three-dimensional lattice Boltzmann method(LBM)to Newtonian and non-Newtonian(Bingham fluid in this work)flows with free surfaces.A mass tracking algorithm was incorporated to capture the free surface,whereas Papanastasiou's modified model was used for Bingham fluids.The lattice Boltzmann method was first validated using two benchmarks:Newtonian flow through a square cross-section tube and Bingham flow through a circular cross-section tube.Afterward,the dam-break problem for the Newtonian fluid and the slump test for Bingham fluid were simulated to validate the free-surface-capturing algorithm.The numerical results were in good agreement with analytical results,as well as other simulations,thereby proving the validity and correctness of the current method.The proposed method is a promising substitute for time-consuming and costly physical experiments to solve problems encountered in geotechnical and geological engineering,such as the surge and debris flow induced by a landslide or earthquake.展开更多
Granular mass flows （e.g., debris flows/avalanches） in landslide-prone areas are of great concern because they often cause catastrophic disasters as a result of their long run-out distances and large impact forces. ...Granular mass flows （e.g., debris flows/avalanches） in landslide-prone areas are of great concern because they often cause catastrophic disasters as a result of their long run-out distances and large impact forces. To investigate the factors influencing granular mass flow mobility, experimental tests were conducted in a flume model. Granular materials consisting of homogeneous sand and non- homogeneous sandy soil were used for studying particle size effects. Run-out tests with variable flow masses, water contents, and sloping channel confinement parameters were conducted as well. The results indicated that granular mass flow mobility was significantly influenced by the initial water content; a critical water content corresponding to the smallest flow mobility exists for different granular materials. An increase in the total flow mass generally induced a reduction in the travel angle （an increase in flow mobility）. Consistent with field observations, the travel angles for different granular materials decreased roughly in proportion to the logarithm of mass. The flume model tests illustrate that the measured travel angles increase as the proportion of fine particles increases. Interestingly, natural terrain possesses critical confinement characteristics for different granular mass flows.展开更多
Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids...Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.展开更多
Liquid foam is a dense packing of gas bubbles in a small amount of surfactant solution. Liquid drains out of foams until equilibrium is reached due to the compromise between gravity and capillarity, which greatly affe...Liquid foam is a dense packing of gas bubbles in a small amount of surfactant solution. Liquid drains out of foams until equilibrium is reached due to the compromise between gravity and capillarity, which greatly affects the stability of foam. Based on a series of work on foam structure and drainage we conducted previously, this paper reports the results on coalescence of an original forced drainage wave at a low flow rate with subsequent drainage waves with higher flow rates. The evolutions of viscous energy and surface energy during the process of coalescence are theoretically analyzed.展开更多
A biaxial shearing test on granular materials is numerically simulated by distinct element method (DEM). The evolution of the microstructures of granular materials during isotropic compression and shearing is investig...A biaxial shearing test on granular materials is numerically simulated by distinct element method (DEM). The evolution of the microstructures of granular materials during isotropic compression and shearing is investigated, on which a yield function is derived. The new yield function has a similar form as the one used in the modified Cam-clay model and explains the yield characteristics of granular materials under the isotropic compression and shear process through the change of the contact distribution N(θ) defining the contacts at particle contact angle θ.展开更多
The homotopy analysis method (HAM), as a new mathematical tool, has been employed to solve many nonlinear problems. As a fundamental equation in non-equilibrium statistical mechanics, the Boltzmann integro-differentia...The homotopy analysis method (HAM), as a new mathematical tool, has been employed to solve many nonlinear problems. As a fundamental equation in non-equilibrium statistical mechanics, the Boltzmann integro-differential equation (BE) describing the movement of particles is of strong nonlinearity. In this work, HAM is preliminarily applied to dilute granular flow which is relatively simple. By choosing the Maxwell velocity distribution function as the initial solution, the concrete expression of the first-order approximate solution to BE with collision term being the BGK model is given. Furthermore it is consistent with the solution using Chapman-Enskog method but does not rely on little parameters.展开更多
The biological patterning of the drosophila retina in vivo has striking resemblance to liquid bubbles,in which the surface mechanics due to N-cadherin within a sub-group of retina cells can be mimicked by surface tens...The biological patterning of the drosophila retina in vivo has striking resemblance to liquid bubbles,in which the surface mechanics due to N-cadherin within a sub-group of retina cells can be mimicked by surface tension.In this work,the aggregating patterns were reasonably simplified into 2D clusters consisting of 2—6 identical bubbles confined within a shrinking boundary.By using a hybrid fluid dy-namics model proposed for liquid foams,the aggregating process of 2―6 retina cells was studied.Assuming the minimal perimeter for patterning cells to be the condition of stability patterns,the stable converged patterns we simulated in this work are the same as the experimental observations.More importantly,a new pattern of 6 cells was obtained which was found physically more stable than the other two reported by Hayashi and Carthew[1].Aggregating perimeters of cells,i.e.the surface energy,showed a good linear fit with the cell numbers.展开更多
基金support from the Natural Science Foundation of China(Grant Nos.11272048,51239006 and 11572178)the Tsinghua University Initiative Scientific Research Program
文摘This paper describes the application of a three-dimensional lattice Boltzmann method(LBM)to Newtonian and non-Newtonian(Bingham fluid in this work)flows with free surfaces.A mass tracking algorithm was incorporated to capture the free surface,whereas Papanastasiou's modified model was used for Bingham fluids.The lattice Boltzmann method was first validated using two benchmarks:Newtonian flow through a square cross-section tube and Bingham flow through a circular cross-section tube.Afterward,the dam-break problem for the Newtonian fluid and the slump test for Bingham fluid were simulated to validate the free-surface-capturing algorithm.The numerical results were in good agreement with analytical results,as well as other simulations,thereby proving the validity and correctness of the current method.The proposed method is a promising substitute for time-consuming and costly physical experiments to solve problems encountered in geotechnical and geological engineering,such as the surge and debris flow induced by a landslide or earthquake.
基金financial support from the Science and Technology Service Network Initiative Program of the Chinese Academy of Sciences (grant no.KFJ-EW-STS-094-2)"Hundred Talents" Program of the Chinese Academy of Sciences (Sulijun)+2 种基金the National Natural Science Foundation of China (grant no.41201012, 51208218)the Hundred Young Talents Program of the Institute of Mountain Hazards and Environment (grant no.SDSQB-2013-01)the Chinese Academy of Sciences Visiting Professorship for Senior International Scientists (grant no.2012T1Z0042)
文摘Granular mass flows （e.g., debris flows/avalanches） in landslide-prone areas are of great concern because they often cause catastrophic disasters as a result of their long run-out distances and large impact forces. To investigate the factors influencing granular mass flow mobility, experimental tests were conducted in a flume model. Granular materials consisting of homogeneous sand and non- homogeneous sandy soil were used for studying particle size effects. Run-out tests with variable flow masses, water contents, and sloping channel confinement parameters were conducted as well. The results indicated that granular mass flow mobility was significantly influenced by the initial water content; a critical water content corresponding to the smallest flow mobility exists for different granular materials. An increase in the total flow mass generally induced a reduction in the travel angle （an increase in flow mobility）. Consistent with field observations, the travel angles for different granular materials decreased roughly in proportion to the logarithm of mass. The flume model tests illustrate that the measured travel angles increase as the proportion of fine particles increases. Interestingly, natural terrain possesses critical confinement characteristics for different granular mass flows.
基金supported by the National Key Basic Research Program of China(Grant No.2010CB731504)the Natural Science Foundation of China(Grant Nos.11034010,11272048 and 51239006)+1 种基金European Commission Marie Curie Actions(Grant No.IRSES-294976)the State Key Laboratory of Hydroscience and Engineering(Grant No.2013-KY-2)
文摘Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
基金the National Natural Science Foundation of China (Grant No.20776142)
文摘Liquid foam is a dense packing of gas bubbles in a small amount of surfactant solution. Liquid drains out of foams until equilibrium is reached due to the compromise between gravity and capillarity, which greatly affects the stability of foam. Based on a series of work on foam structure and drainage we conducted previously, this paper reports the results on coalescence of an original forced drainage wave at a low flow rate with subsequent drainage waves with higher flow rates. The evolutions of viscous energy and surface energy during the process of coalescence are theoretically analyzed.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 10672050, 10872016)
文摘A biaxial shearing test on granular materials is numerically simulated by distinct element method (DEM). The evolution of the microstructures of granular materials during isotropic compression and shearing is investigated, on which a yield function is derived. The new yield function has a similar form as the one used in the modified Cam-clay model and explains the yield characteristics of granular materials under the isotropic compression and shear process through the change of the contact distribution N(θ) defining the contacts at particle contact angle θ.
基金Supported by the National Basic Research Program of China (Grant No. 2007CB714101)Research Fund of the State Key Laboratory for Hydroscience and Engineering in Tsinghua University (Grant No. 2008-ZY-6)
文摘The homotopy analysis method (HAM), as a new mathematical tool, has been employed to solve many nonlinear problems. As a fundamental equation in non-equilibrium statistical mechanics, the Boltzmann integro-differential equation (BE) describing the movement of particles is of strong nonlinearity. In this work, HAM is preliminarily applied to dilute granular flow which is relatively simple. By choosing the Maxwell velocity distribution function as the initial solution, the concrete expression of the first-order approximate solution to BE with collision term being the BGK model is given. Furthermore it is consistent with the solution using Chapman-Enskog method but does not rely on little parameters.
基金the National Natural Science Foundation of China(Grant Nos.20336040 and 20490201)
文摘The biological patterning of the drosophila retina in vivo has striking resemblance to liquid bubbles,in which the surface mechanics due to N-cadherin within a sub-group of retina cells can be mimicked by surface tension.In this work,the aggregating patterns were reasonably simplified into 2D clusters consisting of 2—6 identical bubbles confined within a shrinking boundary.By using a hybrid fluid dy-namics model proposed for liquid foams,the aggregating process of 2―6 retina cells was studied.Assuming the minimal perimeter for patterning cells to be the condition of stability patterns,the stable converged patterns we simulated in this work are the same as the experimental observations.More importantly,a new pattern of 6 cells was obtained which was found physically more stable than the other two reported by Hayashi and Carthew[1].Aggregating perimeters of cells,i.e.the surface energy,showed a good linear fit with the cell numbers.
