To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employe...To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employed to handle the interactions between the box and the fluids. In this study, both air and water were treated as compressible fluids and their properties were modeled through the equation of states. Calculated results show that the air cushion plays a very important role buffering the impinging. Under the deformed concave bottom an air cushion layer will be easier to form up. For high impact speed, the pressure for the elastic box is much lower than that for the rigid box. Excited by the impact, the impinging box oscillates with about its natural frequency.展开更多
A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into accoun...A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into account. A coordinate transformation technique is employed to generate adaptive moving meshes for the multiphase flow system as images of the time-independent computational meshes in auxiliary domains. The method of characteristics is used to reduce the coupled nonlinear hyperbolic partial differential equations governing the motion of the filling fluid, entrapped air, and blocking fluid to ordinary differential equations. Numerical solution of resulting equations shows that the transient shear stresses have only a small damping effect on the pressure fluctuations. The peak pressure in the entrapped air pocket decreases significantly with increasing initial entrapped air volume, but decreases slightly with increasing initial entrapped air pressure.展开更多
A mathematical model is presented for the charging-up process in an air-entrapped pipeline with moving boundary conditions. A coordinate transformation technique is employed to reduce fluid motion in time-dependent do...A mathematical model is presented for the charging-up process in an air-entrapped pipeline with moving boundary conditions. A coordinate transformation technique is employed to reduce fluid motion in time-dependent domains to ones in time-independent domains. The nonlinear hyperbolic partial differential equations governing the unsteady motion of fluid combined with an equation for transient shear stress between the pipe wall and the flowing fluid are solved by the method of lines. Results show that ignoring elastic effects overestimates the maximum pressure and underestimates the maximum front velocity of filling fluid. The peak pressure of the entrapped air is sensitive to the length of the initial entrapped air pocket.展开更多
The turbulent large eddy simulation (LES) technique and the finite element method (FEM) of computational fluid dynamics (CFD) are used to predict the three-dimensional flow field in a vector flow clean-room under em...The turbulent large eddy simulation (LES) technique and the finite element method (FEM) of computational fluid dynamics (CFD) are used to predict the three-dimensional flow field in a vector flow clean-room under empty state and static state conditions. The partly expanded Taylor-Galerkin (TG) discretization scheme is combined with implicit stream-upwind diffusion in the finite element formulation of the basic equations with Gauss filtering. The vortex viscosity subgrid model is used in the numerical simulation. The numerical results agree well with the available experimental data, showing that the LES method can more accurately predict the size and location of large eddies in clean-rooms than the standard k-ε two equation model.展开更多
A better understanding of airflow characteristics in the upper airway(UA) is crucial in investigating obstructive sleep apnea(OSA), particle sedimentation, drug delivery, and many biomedical problems. Direct visualiza...A better understanding of airflow characteristics in the upper airway(UA) is crucial in investigating obstructive sleep apnea(OSA), particle sedimentation, drug delivery, and many biomedical problems. Direct visualization of air flow patterns in in-vitro models with realistic anatomical structures is a big challenge. In this study, we constructed unique half-side transparent physical models of normal UA based on realistic anatomical structures. A smoke-wire method was developed to visualize the air flow in UA models directly. The results revealed that the airflow through the pharynx was laminar but not turbulent under normal inspiration, which suggested that compared with turbulent models, a laminar model should be more suitable in numerical simulations. The flow predicted numerically using the laminar model was consistent with the observations in the physical models. The comparison of the velocity fields predicted numerically using the half-side and complete models confirmed that it was reasonable to investigate the flow behaviors in UA using the half-side model. Using the laminar model, we simulated the flow and evaluated the effects of UA narrowing caused by rostral fluid shift on pharyngeal resistance. The results suggested that fluid shift could play an important role in the formation of hypopnea or OSA during sleep.展开更多
By using PIC method ,the vertical impact on the water surface for a 2-D su- personic flat-head body with a detached shock wave is studied in this paper.Numerical results show that various complicated flow phenomena su...By using PIC method ,the vertical impact on the water surface for a 2-D su- personic flat-head body with a detached shock wave is studied in this paper.Numerical results show that various complicated flow phenomena such as the supersonic flow around the body,the air cushion effect,the propagation of the shock wave in water,the initial formation of the wa- ter-entry cavity and the pile-up of the water surface are simulated successfully.展开更多
Flood discharge over top outlet of dam is simulated by 2 dimension water air two phase mathematical model. Distribution of dynamic pressure, turbulent kinetic energy (k), turbulent dissipation rate (ε), free wat...Flood discharge over top outlet of dam is simulated by 2 dimension water air two phase mathematical model. Distribution of dynamic pressure, turbulent kinetic energy (k), turbulent dissipation rate (ε), free water surface and velocity field have been obtained. The simulated results were tested by physical model, which shows that the computed results are identical with that of the physical model.展开更多
文摘To elucidate the effects of elasticity the hydrodynamic impact of a 2-D flat-bottom shell box onto a water surface was investigated in detail using the finite element code Dytran. An ALE coupling algorithm was employed to handle the interactions between the box and the fluids. In this study, both air and water were treated as compressible fluids and their properties were modeled through the equation of states. Calculated results show that the air cushion plays a very important role buffering the impinging. Under the deformed concave bottom an air cushion layer will be easier to form up. For high impact speed, the pressure for the elastic box is much lower than that for the rigid box. Excited by the impact, the impinging box oscillates with about its natural frequency.
文摘A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into account. A coordinate transformation technique is employed to generate adaptive moving meshes for the multiphase flow system as images of the time-independent computational meshes in auxiliary domains. The method of characteristics is used to reduce the coupled nonlinear hyperbolic partial differential equations governing the motion of the filling fluid, entrapped air, and blocking fluid to ordinary differential equations. Numerical solution of resulting equations shows that the transient shear stresses have only a small damping effect on the pressure fluctuations. The peak pressure in the entrapped air pocket decreases significantly with increasing initial entrapped air volume, but decreases slightly with increasing initial entrapped air pressure.
文摘A mathematical model is presented for the charging-up process in an air-entrapped pipeline with moving boundary conditions. A coordinate transformation technique is employed to reduce fluid motion in time-dependent domains to ones in time-independent domains. The nonlinear hyperbolic partial differential equations governing the unsteady motion of fluid combined with an equation for transient shear stress between the pipe wall and the flowing fluid are solved by the method of lines. Results show that ignoring elastic effects overestimates the maximum pressure and underestimates the maximum front velocity of filling fluid. The peak pressure of the entrapped air is sensitive to the length of the initial entrapped air pocket.
文摘The turbulent large eddy simulation (LES) technique and the finite element method (FEM) of computational fluid dynamics (CFD) are used to predict the three-dimensional flow field in a vector flow clean-room under empty state and static state conditions. The partly expanded Taylor-Galerkin (TG) discretization scheme is combined with implicit stream-upwind diffusion in the finite element formulation of the basic equations with Gauss filtering. The vortex viscosity subgrid model is used in the numerical simulation. The numerical results agree well with the available experimental data, showing that the LES method can more accurately predict the size and location of large eddies in clean-rooms than the standard k-ε two equation model.
基金supported by the National Nature Science Foundation of China (31670959, 81171422)the National Science and Technology Pillar Program of China (2012BAI05B03)+2 种基金the Key Projects in Science and Technology Program of Beijing Municipal Education Commission, China (KZ201210025022)Beijing Postdoctoral Research Foundation (2016ZZ-45)Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application
文摘A better understanding of airflow characteristics in the upper airway(UA) is crucial in investigating obstructive sleep apnea(OSA), particle sedimentation, drug delivery, and many biomedical problems. Direct visualization of air flow patterns in in-vitro models with realistic anatomical structures is a big challenge. In this study, we constructed unique half-side transparent physical models of normal UA based on realistic anatomical structures. A smoke-wire method was developed to visualize the air flow in UA models directly. The results revealed that the airflow through the pharynx was laminar but not turbulent under normal inspiration, which suggested that compared with turbulent models, a laminar model should be more suitable in numerical simulations. The flow predicted numerically using the laminar model was consistent with the observations in the physical models. The comparison of the velocity fields predicted numerically using the half-side and complete models confirmed that it was reasonable to investigate the flow behaviors in UA using the half-side model. Using the laminar model, we simulated the flow and evaluated the effects of UA narrowing caused by rostral fluid shift on pharyngeal resistance. The results suggested that fluid shift could play an important role in the formation of hypopnea or OSA during sleep.
文摘By using PIC method ,the vertical impact on the water surface for a 2-D su- personic flat-head body with a detached shock wave is studied in this paper.Numerical results show that various complicated flow phenomena such as the supersonic flow around the body,the air cushion effect,the propagation of the shock wave in water,the initial formation of the wa- ter-entry cavity and the pile-up of the water surface are simulated successfully.
文摘Flood discharge over top outlet of dam is simulated by 2 dimension water air two phase mathematical model. Distribution of dynamic pressure, turbulent kinetic energy (k), turbulent dissipation rate (ε), free water surface and velocity field have been obtained. The simulated results were tested by physical model, which shows that the computed results are identical with that of the physical model.
