We propose a new flame index for the transported probability density function(PDF) method. The flame index uses mixing flux projections of Lagrangian particles on mixture fraction and progress variable directions as t...We propose a new flame index for the transported probability density function(PDF) method. The flame index uses mixing flux projections of Lagrangian particles on mixture fraction and progress variable directions as the metrics to identify the combustion mode, with the Burke-Schumann solution as a reference. A priori validation of the flame index is conducted with a series of constructed turbulent partially premixed reactors. It indicates that the proposed flame index is able to identify the combustion mode based on the subgrid mixing information. The flame index is then applied the large eddy simulation/PDF datasets of turbulent partially premixed jet flames. Results show that the flame index separate different combustion modes and extinction correctly. The proposed flame index provides a promising tool to analyze and model the partially premixed flames adaptively.展开更多
We propose a hybrid scheme combing the diffuse interface method and the material point method to simulate the complex interactions between the multiphase compressible flow and elastoplastic solid.The multiphase flow i...We propose a hybrid scheme combing the diffuse interface method and the material point method to simulate the complex interactions between the multiphase compressible flow and elastoplastic solid.The multiphase flow is modelled by the multi-component model and solved using a generalized Godunov method in the Eulerian grids,while the elastoplastic solid is solved by the classical material point method in a combination of Lagrangian particles and Eulerian background grids.In order to facilitate the simulation of fluid-solid interactions,the solid variables are further interpolated to the cell center and coexist with the fluid in the same cell.An instantaneous relaxation procedure of velocity and pressure is adopted to simulate the momentum and energy transfers between various materials,and to keep the system within a tightly coupled interaction.Several numerical examples,including shock tube problem,gasbubble problem,air blast,underwater explosion and high speed impact applications are presented to validate the numerical scheme.展开更多
We develop and assess a model of the turbulent burning velocity ST over a wide range of conditions.The aim is to obtain an explicit ST model for turbulent combustion modeling and flame analysis.The model consists of s...We develop and assess a model of the turbulent burning velocity ST over a wide range of conditions.The aim is to obtain an explicit ST model for turbulent combustion modeling and flame analysis.The model consists of sub models of the stretch factor and the turbulent flame area.The stretch factor characterizes the flame response of turbulence stretch and incorporates detailed chemistry and transport effects with a lookup table of laminar counterflow flames.The flame area model captures the area growth based on Lagrangian statistics of propagating surfaces and considers the effects of turbulence length scales and fuel characteristics.The present model predicts sT via an algebraic expression without free parameters.We assess the model using 490 cases of the direct numerical simulation or experiment reported from various research groups on planar and Bunsen flames over a wide range of conditions,covering fuels from hydrogen to n-dodecane,pressures from 1 to 30 atm,lean and rich mixtures,turbulence intensity ratios from 0.1 to 177.6,and turbulence length ratios from 0.5 to 66.7.Despite the scattering sT data in the literature,the comprehensive comparison shows that the proposed ST model has an overall good agreement over the wide range of conditions,with the averaged modeling error of 28.1%.展开更多
We propose a hybrid scheme combing the level set method and the multicomponent diffuse interface method to simulate complex multi-phase flows.The overall numerical scheme is based on a sharp interface framework where ...We propose a hybrid scheme combing the level set method and the multicomponent diffuse interface method to simulate complex multi-phase flows.The overall numerical scheme is based on a sharp interface framework where the level set method is adopted to capture the material interface,the Euler equation is used to describe a single-phase flow on one side of the interface and the six-equation diffuse interface model is applied to model the multi-phase mixture or gas-liquid cavitation on the other side.An exact Riemann solver,between the Euler equation and the six-equation model with highly nonlinear Mie-Gr¨uneisen equations of state,is developed to predict the interfacial states and compute the phase interface flux.Several numerical examples,including shock tube problems,cavitation problems,air blast and underwater explosion applications are presented to validate the numerical scheme and the Riemann solver.展开更多
In the first of a series of papers,wewill study a discontinuous Galerkin(DG)framework for many electron quantum systems.The salient feature of this framework is the flexibility of using hybrid physics-based local orbi...In the first of a series of papers,wewill study a discontinuous Galerkin(DG)framework for many electron quantum systems.The salient feature of this framework is the flexibility of using hybrid physics-based local orbitals and accuracy-guaranteed piecewise polynomial basis in representing the Hamiltonian of the many body system.Such a flexibility is made possible by using the discontinuous Galerkin method to approximate the Hamiltonian matrix elements with proper constructions of numerical DG fluxes at the finite element interfaces.In this paper,we will apply the DG method to the density matrix minimization formulation,a popular approach in the density functional theory of many body Schrodinger equations.The density matrix minimization is to find the minima of the total energy,expressed as a functional of the density matrixρ(r,r′),approximated by the proposed enriched basis,together with two constraints of idempotency and electric neutrality.The idempotency will be handled with theMcWeeny’s purification while the neutrality is enforced by imposing the number of electrons with a penalty method.A conjugate gradient method(a Polak-Ribiere variant)is used to solve the minimization problem.Finally,the linear-scaling algorithm and the advantage of using the local orbital enriched finite element basis in the DG approximations are verified by studying examples of one dimensional lattice model systems.展开更多
In this paper,we propose a robust finite volume scheme to numerically solve the shallow water equations on complex rough topography.The major difficulty of this problem is introduced by the stiff friction force term a...In this paper,we propose a robust finite volume scheme to numerically solve the shallow water equations on complex rough topography.The major difficulty of this problem is introduced by the stiff friction force term and the wet/dry interface tracking.An analytical integration method is presented for the friction force term to remove the stiffness.In the vicinity of wet/dry interface,the numerical stability can be attained by introducing an empirical parameter,the water depth tolerance,as extensively adopted in literatures.We propose a problem independent formulation for this parameter,which provides a stable scheme and preserves the overall truncation error of δ(Δx^(3)).The method is applied to solve problems with complex rough topography,coupled with h-adaptive mesh techniques to demonstrate its robustness and efficiency.展开更多
We propose a robust approximate solver for the hydro-elastoplastic solid material,a general constitutive law extensively applied in explosion and high speed impact dynamics,and provide a natural transformation between...We propose a robust approximate solver for the hydro-elastoplastic solid material,a general constitutive law extensively applied in explosion and high speed impact dynamics,and provide a natural transformation between the fluid and solid in the case of phase transitions.The hydrostatic components of the solid is described by a family of general Mie-Gruneisen equation of state(EOS),while the deviatoric component includes the elastic phase,linearly hardened plastic phase and fluid phase.The approximate solver provides the interface stress and normal velocity by an iterative method.The well-posedness and convergence of our solver are proved with mild assumptions on the equations of state.The proposed solver is applied in computing the numerical flux at the phase interface for our compressible multi-medium flow simulation on Eulerian girds.Several numerical examples,including Riemann problems,shock-bubble interactions,implosions and high speed impact applications,are presented to validate the approximate solver.展开更多
基金sponsored by King Abdullah University of Science and Technology(KAUST)the National Natural Science Foundation of China(Grant No.91841302)。
文摘We propose a new flame index for the transported probability density function(PDF) method. The flame index uses mixing flux projections of Lagrangian particles on mixture fraction and progress variable directions as the metrics to identify the combustion mode, with the Burke-Schumann solution as a reference. A priori validation of the flame index is conducted with a series of constructed turbulent partially premixed reactors. It indicates that the proposed flame index is able to identify the combustion mode based on the subgrid mixing information. The flame index is then applied the large eddy simulation/PDF datasets of turbulent partially premixed jet flames. Results show that the flame index separate different combustion modes and extinction correctly. The proposed flame index provides a promising tool to analyze and model the partially premixed flames adaptively.
文摘We propose a hybrid scheme combing the diffuse interface method and the material point method to simulate the complex interactions between the multiphase compressible flow and elastoplastic solid.The multiphase flow is modelled by the multi-component model and solved using a generalized Godunov method in the Eulerian grids,while the elastoplastic solid is solved by the classical material point method in a combination of Lagrangian particles and Eulerian background grids.In order to facilitate the simulation of fluid-solid interactions,the solid variables are further interpolated to the cell center and coexist with the fluid in the same cell.An instantaneous relaxation procedure of velocity and pressure is adopted to simulate the momentum and energy transfers between various materials,and to keep the system within a tightly coupled interaction.Several numerical examples,including shock tube problem,gasbubble problem,air blast,underwater explosion and high speed impact applications are presented to validate the numerical scheme.
基金supported by the National Natural Science Foundation of China(Grant Nos.91841302,11925201,and 11988102)the National Key Research and Development.Program of China(Grant No.2020YFE0204200)。
文摘We develop and assess a model of the turbulent burning velocity ST over a wide range of conditions.The aim is to obtain an explicit ST model for turbulent combustion modeling and flame analysis.The model consists of sub models of the stretch factor and the turbulent flame area.The stretch factor characterizes the flame response of turbulence stretch and incorporates detailed chemistry and transport effects with a lookup table of laminar counterflow flames.The flame area model captures the area growth based on Lagrangian statistics of propagating surfaces and considers the effects of turbulence length scales and fuel characteristics.The present model predicts sT via an algebraic expression without free parameters.We assess the model using 490 cases of the direct numerical simulation or experiment reported from various research groups on planar and Bunsen flames over a wide range of conditions,covering fuels from hydrogen to n-dodecane,pressures from 1 to 30 atm,lean and rich mixtures,turbulence intensity ratios from 0.1 to 177.6,and turbulence length ratios from 0.5 to 66.7.Despite the scattering sT data in the literature,the comprehensive comparison shows that the proposed ST model has an overall good agreement over the wide range of conditions,with the averaged modeling error of 28.1%.
文摘We propose a hybrid scheme combing the level set method and the multicomponent diffuse interface method to simulate complex multi-phase flows.The overall numerical scheme is based on a sharp interface framework where the level set method is adopted to capture the material interface,the Euler equation is used to describe a single-phase flow on one side of the interface and the six-equation diffuse interface model is applied to model the multi-phase mixture or gas-liquid cavitation on the other side.An exact Riemann solver,between the Euler equation and the six-equation model with highly nonlinear Mie-Gr¨uneisen equations of state,is developed to predict the interfacial states and compute the phase interface flux.Several numerical examples,including shock tube problems,cavitation problems,air blast and underwater explosion applications are presented to validate the numerical scheme and the Riemann solver.
基金support of U.S.Army Research Office(grant number W911NF-11-1-0364)support of NSFC(grant number 11011130029)and of SRF for ROCS,SEM.
文摘In the first of a series of papers,wewill study a discontinuous Galerkin(DG)framework for many electron quantum systems.The salient feature of this framework is the flexibility of using hybrid physics-based local orbitals and accuracy-guaranteed piecewise polynomial basis in representing the Hamiltonian of the many body system.Such a flexibility is made possible by using the discontinuous Galerkin method to approximate the Hamiltonian matrix elements with proper constructions of numerical DG fluxes at the finite element interfaces.In this paper,we will apply the DG method to the density matrix minimization formulation,a popular approach in the density functional theory of many body Schrodinger equations.The density matrix minimization is to find the minima of the total energy,expressed as a functional of the density matrixρ(r,r′),approximated by the proposed enriched basis,together with two constraints of idempotency and electric neutrality.The idempotency will be handled with theMcWeeny’s purification while the neutrality is enforced by imposing the number of electrons with a penalty method.A conjugate gradient method(a Polak-Ribiere variant)is used to solve the minimization problem.Finally,the linear-scaling algorithm and the advantage of using the local orbital enriched finite element basis in the DG approximations are verified by studying examples of one dimensional lattice model systems.
文摘In this paper,we propose a robust finite volume scheme to numerically solve the shallow water equations on complex rough topography.The major difficulty of this problem is introduced by the stiff friction force term and the wet/dry interface tracking.An analytical integration method is presented for the friction force term to remove the stiffness.In the vicinity of wet/dry interface,the numerical stability can be attained by introducing an empirical parameter,the water depth tolerance,as extensively adopted in literatures.We propose a problem independent formulation for this parameter,which provides a stable scheme and preserves the overall truncation error of δ(Δx^(3)).The method is applied to solve problems with complex rough topography,coupled with h-adaptive mesh techniques to demonstrate its robustness and efficiency.
基金supports provided by the National Natural Science Foundation of China(Grant Nos.91630310,11421110001,and 11421101)and Science Challenge Project(No.TZ 2016002).
文摘We propose a robust approximate solver for the hydro-elastoplastic solid material,a general constitutive law extensively applied in explosion and high speed impact dynamics,and provide a natural transformation between the fluid and solid in the case of phase transitions.The hydrostatic components of the solid is described by a family of general Mie-Gruneisen equation of state(EOS),while the deviatoric component includes the elastic phase,linearly hardened plastic phase and fluid phase.The approximate solver provides the interface stress and normal velocity by an iterative method.The well-posedness and convergence of our solver are proved with mild assumptions on the equations of state.The proposed solver is applied in computing the numerical flux at the phase interface for our compressible multi-medium flow simulation on Eulerian girds.Several numerical examples,including Riemann problems,shock-bubble interactions,implosions and high speed impact applications,are presented to validate the approximate solver.
