Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensi...Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.展开更多
Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are...Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.展开更多
With the worldwide development of nuclear power plant and requirement of saving energy and resource, high thermal efficiency and economical competitiveness are achieved by using supercritical COR2R with spe-cial therm...With the worldwide development of nuclear power plant and requirement of saving energy and resource, high thermal efficiency and economical competitiveness are achieved by using supercritical COR2R with spe-cial thermal properties and better flow and heat transfer characters. In this paper, heat transfer of supercritical COR2R has been investigated in square and triangle array tube-bundle of cooled system in reactor using com-putational fluid dynamics (CFD) code FLUENT, and the basic knowledge of heat transfer of supercritical COR2R and first experience of CFD simulation are obtained. The effect of mesh structures, turbulence models, as well as flow channel size is analyzed. The choice of turbulence model adopted in simulating supercritical COR2R is recommended. Comparing the effect of heat transfer with supercritical COR2R and supercritical water as cooled medium, the results show that the former was higher. The new idea is provided for choice of cooled medium and improving thermal efficiency this paper.展开更多
In order to study the safety factor and instability process of cohesive soil slope, the discrete element method(DEM) was applied. DEM software PFC2 D was used to simulate the triaxial test to study the influence of th...In order to study the safety factor and instability process of cohesive soil slope, the discrete element method(DEM) was applied. DEM software PFC2 D was used to simulate the triaxial test to study the influence of the particle micro parameters on the macroscopic characteristics of cohesive soil and calibrate the micro parameters of DEM model on this basis. Embankment slope stability analysis was carried out by strength reduction and gravity increase method, it is shown that the safety factor obtained by strength reduction method is more conservative, and the arc-shaped feature of the sliding surface under the gravity increase method is more obvious. Throughout the progressive failure process, the failure trends, maximum displacements, and velocity changes obtained by the two methods were consistent. When slope was destroyed, the upper part was cracked, the middle part was sheared, and the lower part was destroyed by extrusion. The conclusions of this paper can be applied to the safety factor calculation of cohesive soil slopes and the analysis of the instability process.展开更多
Regard for the fuzziness and the randomness in some acoustic fields,a method for the numerical analysis of the 2D acoustic field with Fuzzy-Random parameters was proposed based on the equivalent conversion of informat...Regard for the fuzziness and the randomness in some acoustic fields,a method for the numerical analysis of the 2D acoustic field with Fuzzy-Random parameters was proposed based on the equivalent conversion of information entropy.In the proposed method,a fuzzyrandom acoustic field was treated as a pure fuzzy acoustic field or a pure random acoustic field by transforming all the variables into fuzzy variables or random variables.Perturbation finite element methods for analyzing the two-dimensional acoustic fuzzy and random field are deduced.The sound pressure response of a 2D acoustic tube and the 2D acoustic cavity of a car with fuzzy-random parameters were analyzed by the proposed method and the Monte Carlo method,the results show that the proposed method can be well applied to the numerical analysis of the 2D acoustic field with fuzzy-random parameters,and has good prospect of engineering application.展开更多
Aiming at the problem that the epistemic uncertain parameters exist in an acoustic field, an evidence theory-based finite element method （ETFEM） is proposed by introducing the evidence theory, in which the focal ele...Aiming at the problem that the epistemic uncertain parameters exist in an acoustic field, an evidence theory-based finite element method （ETFEM） is proposed by introducing the evidence theory, in which the focal element and basic probability assignment （BPA） are used to describe the epistemic uncertainty. In order to reduce the computational cost, the interval analysis technique based on perturbation method is adopted to acquire the approximate sound pressure response bounds for each focal element. The corresponding formulations of intervals of expectation and standard deviation of the sound pressure response with epistemic uncertainty are deduced. The sound pressure response of a 2D acoustic tube and a 2D car acoustic cavity with epistemic uncertain parameters are analyzed by the proposed method. The proposed method is verified through the comparison of the analysis results of random acoustic field with that of epistemic uncertain acoustic field. Numerical analysis results show that the proposed method can analyze the 2D acoustic field with epistemic uncertainty effectively, and has good prospect of engineering application.展开更多
In the context of SARS-CoV-2 pandemic,mathematical modelling has played a funda-mental role for making forecasts,simulating scenarios and evaluating the impact of pre-ventive political,social and pharmaceutical measur...In the context of SARS-CoV-2 pandemic,mathematical modelling has played a funda-mental role for making forecasts,simulating scenarios and evaluating the impact of pre-ventive political,social and pharmaceutical measures.Optimal control theory represents a useful mathematical tool to plan the vaccination campaign aimed at eradicating the pandemic as fast as possible.The aim of this work is to explore the optimal prioritisation order for planning vaccination campaigns able to achieve specific goals,as the reduction of the amount of infected,deceased and hospitalized in a given time frame,among age classes.For this purpose,we introduce an age stratified SIR-like epidemic compartmental model settled in an abstract framework for modelling two-doses vaccination campaigns and conceived with the description of COVID19 disease.Compared to other recent works,our model incorporates all stages of the COVID-19 disease,including death or recovery,without accounting for additional specific compartments that would increase computa-tional complexity and that are not relevant for our purposes.Moreover,we introduce an optimal control framework where the model is the state problem while the vaccine doses administered are the control variables.An extensive campaign of numerical tests,featured in the Italian scenario and calibrated on available data from Dipartimento di Protezione Civile Italiana,proves that the presented framework can be a valuable tool to support the planning of vaccination campaigns.Indeed,in each considered scenario,our optimization framework guarantees noticeable improvements in terms of reducing deceased,infected or hospitalized individuals with respect to the baseline vaccination policy.展开更多
文摘Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.
基金This work was financially supported by the National Natural Science Foundation of China(No.42102217)the University Synergy Innovation Program of Anhui Province(No.GXXT-2021-018)+3 种基金the Natural Science Research Project of Anhui University(No.KJ2020A0315No.KJ2020A0317)the Natural Science Foundation of Anhui Province(No.2108085MD134)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-2005).
文摘Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.
文摘With the worldwide development of nuclear power plant and requirement of saving energy and resource, high thermal efficiency and economical competitiveness are achieved by using supercritical COR2R with spe-cial thermal properties and better flow and heat transfer characters. In this paper, heat transfer of supercritical COR2R has been investigated in square and triangle array tube-bundle of cooled system in reactor using com-putational fluid dynamics (CFD) code FLUENT, and the basic knowledge of heat transfer of supercritical COR2R and first experience of CFD simulation are obtained. The effect of mesh structures, turbulence models, as well as flow channel size is analyzed. The choice of turbulence model adopted in simulating supercritical COR2R is recommended. Comparing the effect of heat transfer with supercritical COR2R and supercritical water as cooled medium, the results show that the former was higher. The new idea is provided for choice of cooled medium and improving thermal efficiency this paper.
基金Project(51808116) supported by the National Natural Science Foundation of ChinaProject(BK20180404) supported by the Natural Science Foundation of Jiangsu Province, China+1 种基金Project(KFJ170106) supported by the Changsha University of Science & Technology via Open Fund of National Engineering Laboratory of Highway Maintenance Technology,ChinaProject(242020R40133) supported by Fundamental Research Funds for the Central Universities, China。
文摘In order to study the safety factor and instability process of cohesive soil slope, the discrete element method(DEM) was applied. DEM software PFC2 D was used to simulate the triaxial test to study the influence of the particle micro parameters on the macroscopic characteristics of cohesive soil and calibrate the micro parameters of DEM model on this basis. Embankment slope stability analysis was carried out by strength reduction and gravity increase method, it is shown that the safety factor obtained by strength reduction method is more conservative, and the arc-shaped feature of the sliding surface under the gravity increase method is more obvious. Throughout the progressive failure process, the failure trends, maximum displacements, and velocity changes obtained by the two methods were consistent. When slope was destroyed, the upper part was cracked, the middle part was sheared, and the lower part was destroyed by extrusion. The conclusions of this paper can be applied to the safety factor calculation of cohesive soil slopes and the analysis of the instability process.
基金supported by the Independent Subject of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body in Hunan University(60870002)
文摘Regard for the fuzziness and the randomness in some acoustic fields,a method for the numerical analysis of the 2D acoustic field with Fuzzy-Random parameters was proposed based on the equivalent conversion of information entropy.In the proposed method,a fuzzyrandom acoustic field was treated as a pure fuzzy acoustic field or a pure random acoustic field by transforming all the variables into fuzzy variables or random variables.Perturbation finite element methods for analyzing the two-dimensional acoustic fuzzy and random field are deduced.The sound pressure response of a 2D acoustic tube and the 2D acoustic cavity of a car with fuzzy-random parameters were analyzed by the proposed method and the Monte Carlo method,the results show that the proposed method can be well applied to the numerical analysis of the 2D acoustic field with fuzzy-random parameters,and has good prospect of engineering application.
基金supported by the National Natural Science Foundation of China(11572121)Independent Research Project of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body(71375004)
文摘Aiming at the problem that the epistemic uncertain parameters exist in an acoustic field, an evidence theory-based finite element method （ETFEM） is proposed by introducing the evidence theory, in which the focal element and basic probability assignment （BPA） are used to describe the epistemic uncertainty. In order to reduce the computational cost, the interval analysis technique based on perturbation method is adopted to acquire the approximate sound pressure response bounds for each focal element. The corresponding formulations of intervals of expectation and standard deviation of the sound pressure response with epistemic uncertainty are deduced. The sound pressure response of a 2D acoustic tube and a 2D car acoustic cavity with epistemic uncertain parameters are analyzed by the proposed method. The proposed method is verified through the comparison of the analysis results of random acoustic field with that of epistemic uncertain acoustic field. Numerical analysis results show that the proposed method can analyze the 2D acoustic field with epistemic uncertainty effectively, and has good prospect of engineering application.
文摘In the context of SARS-CoV-2 pandemic,mathematical modelling has played a funda-mental role for making forecasts,simulating scenarios and evaluating the impact of pre-ventive political,social and pharmaceutical measures.Optimal control theory represents a useful mathematical tool to plan the vaccination campaign aimed at eradicating the pandemic as fast as possible.The aim of this work is to explore the optimal prioritisation order for planning vaccination campaigns able to achieve specific goals,as the reduction of the amount of infected,deceased and hospitalized in a given time frame,among age classes.For this purpose,we introduce an age stratified SIR-like epidemic compartmental model settled in an abstract framework for modelling two-doses vaccination campaigns and conceived with the description of COVID19 disease.Compared to other recent works,our model incorporates all stages of the COVID-19 disease,including death or recovery,without accounting for additional specific compartments that would increase computa-tional complexity and that are not relevant for our purposes.Moreover,we introduce an optimal control framework where the model is the state problem while the vaccine doses administered are the control variables.An extensive campaign of numerical tests,featured in the Italian scenario and calibrated on available data from Dipartimento di Protezione Civile Italiana,proves that the presented framework can be a valuable tool to support the planning of vaccination campaigns.Indeed,in each considered scenario,our optimization framework guarantees noticeable improvements in terms of reducing deceased,infected or hospitalized individuals with respect to the baseline vaccination policy.
