Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species ric...Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.展开更多
In this paper,the quantitative approach is applied on the study of coniferous forestbased on the data which were collected by the field investigation in Daxinganling region.The mainpurpose is objectively to show the p...In this paper,the quantitative approach is applied on the study of coniferous forestbased on the data which were collected by the field investigation in Daxinganling region.The mainpurpose is objectively to show the position of communities in the space and the relationship be-tween the community and environment.By means of ordination,it is found that dahurian larch for-est,mongolian scots pine forest and korean fir forest lie in different positions. Gradient analysis ofthree dominant types of conigerous forest has revealed the difference of ecological amplitude,thedifference is one of the important reasons that determine the different communities in the differentenvironment.展开更多
We investigated the composition of plant communities to quantify their relationships with environmental parameters in the Chitral Hindukush range of Pakistan. We sampled tree vegetation using the Point Centered Quart...We investigated the composition of plant communities to quantify their relationships with environmental parameters in the Chitral Hindukush range of Pakistan. We sampled tree vegetation using the Point Centered Quarter （PCQ） method while understory vegetation was sampled in 1.5-m circular quadrats. Cedrus deodara is the national symbol of Pakistan and was dominant in the sampled communities. Because environmental variables determine vegetation types, we analyzed and evaluated edaphic and topographic factors. DCA-Ordination showed the major gradient as an amalgam of elevation （p〈0.05） and slope （p〈0.01） as the topographic factors correlated with species distribution. Soil variables were the factors of environmental significance along DCA axes. However, among these factors, Mg2＋ , K ＋ and N2＋ contributed not more than 0.054% 0.20% and 0.073%, respectively, to variation along the first ordination axis. We conclude that the principal reason for weak or no correlation with many edaphic variables was the anthropogenic disturbance of vegetation. The understory vegetation was composed of perennial herbs in most communities and was most dense under the tree canopy. The understory vegetation strongly regulates tree seedling growth and regeneration patterns. We recommend further study of the understory vegetation using permanent plots to aid development of forest regeneration strategies.展开更多
We studied woodland vegetation in broad-leaved deciduous woodlands of Metema in northwestern Amhara regional state, Ethiopia to determine plant community types and species distribution patterns and their relationships...We studied woodland vegetation in broad-leaved deciduous woodlands of Metema in northwestern Amhara regional state, Ethiopia to determine plant community types and species distribution patterns and their relationships with environmental variables, including altitude, pH, cation exchange capacity, electrical conductivity （EC）, and moisture. We used a selective approach with a systematic sampling design. A total of 74 quadrats, each 25m × 25m at intervals of 150-200 m were sampled along the established transect lines. For herbaceous vegetation and soil data collection, five subquadrats each lm x lm were established at the four corners and the center of each quadrat. Three community types were identified using TWINSPAN analysis. All three community types showed high diversity （Shannon-Weiner index）, the highest in community type II at 3.55. The highest similarity coefficient was 0.49 （49%） between community types II and III, reflecting 0.51 （51%） dissimilarity in their species richness. The canonical correspondence ordination diagram revealed that the distribution pattern of community type I was explained by moisture while that of community types III and II was explained by EC and altitude and moisture, respectively. Altitude was the most statistically significant environmental variable, followed by moisture and EC in determining the total variation in species composition and distribution patterns while pH and cation exchange capacity were non significant. In conclusion, we recommend that any intervention should take into account these three discrete community types and their environmental settings to make the intervention more successful.展开更多
Forests in Northeast China in the Greater and Lesser Khingan Mountains(GKM and LKM)account for nearly 1/3 of the total state-owned forests in the country.Regional and historical comparisons of forest plants and macrof...Forests in Northeast China in the Greater and Lesser Khingan Mountains(GKM and LKM)account for nearly 1/3 of the total state-owned forests in the country.Regional and historical comparisons of forest plants and macrofungi will favor biological conservation,forest management and economic development.A total of 1067 sampling plots were surveyed on forest composition and structure,with a macrofungi survey at Liangshui and Huzhong Nature Reserves in the center of two regions.Regional and historical differences of these parameters were analyzed with a redundancy ordination of their complex associations.There were 61-76 families,189-196 genera,and 369-384 species,which was only 1/3 of the historical records.The same dominant species were larch and birch with Korean pine(a climax species)less as expected from past surveys in the LKM.Shrub and herb species were different in the two regions,as expected from historical records.There was 10-50%lower species diversity(except for herb evenness),but 1.8-to 4-time higher macrofungi diversity in the GKM.Compared with the LKM,both tree heights and macrofungi density were higher.Nevertheless,current heights averaging 10 m are half of historical records(>20 m in the 1960s).Edible macrofungi were the highest proportion in both regions,about twice that of other fungal groups,hav-ing important roles in the local economy.A major factor explaining plant diversity variations in both regions was herb cover,followed by shrubs in the GKM and herb-dominant species in the LKM.Factors responsible for macrofungi variations were tree density and shrub height.Vaccinium vitis-idaea and Larix gmelinii in the GKM but tree size and diversity were important factors in the LKM.Our findings highlighted large spatial and historical differences between the GKM and LKM in plant-macrofungal composition,forest structure,and their complex associations,which will favor precise conservation and management of forest resources in two region in the future.展开更多
Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend ...Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend on climate, edaphic and biotic factors which are not well correlated with plant community structures. This study aimed to explore the relationships between understory vegetation and abiotic factors in natural and planted forest ecosystems. A non-metric multidimensional scaling(NMS) ordination technique was applied to represent forest understory vegetation among five forest communities, i.e., a dry miscellaneous forest(DMF), a sal mixed forest(SMF), a teak plantation(TP), a low-land miscellaneous forest(LMF) and a savanna area(SAV) of the Katerniaghat Wildlife Sanctuary, located in northern India. Microclimatic variables, such as photosynthetically active radiation(PAR), air temperature(AT), soil temperature(ST), ambient atmospheric CO 2 concentration, absolute air humidity(AH), physical and chemical soil properties as well as biological properties were measured. Understory species were assessed via 100 random quadrats(5 m × 5 m) in each of the five forests in which a total of 75 species were recorded encompassing 67 genera from 37 families, consisting of 32 shrubs and 43 plant saplings. DMF was the most dense forest with 34,068 understory individuals per ha of different species, whereas the lowest understory population(13,900 per ha) was observed in the savanna. Ordination and correlation revealed that microclimate factors are most important in their effect compared to edaphic factors, on the development of understory vegetation in the various forest communities in the north of India.展开更多
The key issue in accelerating method of characteristics(MOC)transport calculations is in obtaining a completely equivalent low-order neutron transport or diffusion equation.Herein,an equivalent low-order angular flux ...The key issue in accelerating method of characteristics(MOC)transport calculations is in obtaining a completely equivalent low-order neutron transport or diffusion equation.Herein,an equivalent low-order angular flux nonlinear finite difference equation is proposed for MOC transport calculations.This method comprises three essential features:(1)the even parity discrete ordinates method is used to build a low-order angular flux nonlinear finite difference equation,and different boundary condition treatments are proposed;(2)two new defined factors,i.e.,the even parity discontinuity factor and odd parity discontinuity factor,are strictly defined to achieve equivalence between the low-order angular flux nonlinear finite difference method and MOC transport calculation;(3)the energy group and angle are decoupled to construct a symmetric linear system that is much easier to solve.The equivalence of this low-order angular flux nonlinear finite difference equation is analyzed for two-dimensional(2D)pin,2D assembly,and 2D C5G7 benchmark problems.Numerical results demonstrate that a low-order angular flux nonlinear finite difference equation that is completely equivalent to the pin-resolved transport equation is established.展开更多
The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in...The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in the S N method to automatically optimize the angular distribution and minimize angular discretization errors with lower expenses.The proposed method enables linear dis-continuous finite element quadrature sets over an icosahe-dron to vary their quadrature orders in a one-twentieth sphere so that fine resolutions can be applied to the angular domains that are important.An error estimation that operates in conjunction with the spherical harmonics method is developed to determine the locations where more refinement is required.The adaptive quadrature sets are applied to three duct problems,including the Kobayashi benchmarks and the IRI-TUB research reactor,which emphasize the ability of this method to resolve neutron streaming through ducts with voids.The results indicate that the performance of the adaptive method is more effi-cient than that of uniform quadrature sets for duct transport problems.Our adaptive method offers an appropriate placement of angular unknowns to accurately integrate angular fluxes while reducing the computational costs in terms of unknowns and run times.展开更多
The China dual-functional lithium–lead test blanket module(DFLL-TBM) is a liquid Li Pb blanket concept developed by the Institute of Nuclear Energy Safety Technology of the Chinese Academy of Sciences for testing in ...The China dual-functional lithium–lead test blanket module(DFLL-TBM) is a liquid Li Pb blanket concept developed by the Institute of Nuclear Energy Safety Technology of the Chinese Academy of Sciences for testing in ITER to validate relevant tritium breeding and shielding technologies. In this study, neutronic calculations of DFLL-TBM were carried out using a massively parallel three-dimensional transport code, Hydra, with the Fusion Evaluated Nuclear Data Library/MG. Hydra was developed by the Nuclear Engineering Computational Physics Lab based on the discrete ordinates method and has been devoted to neutronic analysis and shielding evaluation for nuclear facilities. An in-house Monte Carlo code(MCX) was employed to verify the discretized calculation model used by Hydra for the DFLL-TBM calculations. The results showed two key aspects:(1) In most material zones,Hydra solutions are in good agreement with the reference MCX results within 1%, and the maximal relative difference of the neutron flux is merely 3%, demonstrating the correctness of the calculation model;(2) while the current DFLL-TBM design meets the operation shielding requirement of ITER for 4 years, it does not satisfy the tritium self-sufficiency requirement. Compared to the two-step approach, Hydra produces higher accuracies as it does not rely on the homogenization technique during the calculation process. The parallel efficiency tests of Hydra using the DFLL-TBM model also showed that this code maintains a high parallel efficiency on O(100) processors and, as a result, is able to significantly improve computing performance through parallelization. Parameter studies have been carried out by varying the thickness of the beryllium armor layer and the tritium breeding zone to understand the influence of the beryllium layer and breeding zone thickness on tritium breeding performance. This establishes a foundation for further improvement in the tritium production performance of DFLL-TBM.展开更多
In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre e...In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre expansion is widely used in discrete ordinates transport codes because of algebraic simplifications with spherical harmonics for the scattering source.However,negative cross sections caused by the finitely truncated expansion may give rise to a negative source and flux.A simple method is adopted,based on integrating functions of scattering moments,to evaluate anisotropy and convergence of expanded functions.A series of problems were designed with angular fluxes of different anisotropy,and numerical simulations were performed using the ARES transport code to study different treatments and algorithms for scattering.Results show that the diagonal transport approximation is more stable and obtains a similar accuracy with the extended approximation.A conservative fixup for the negative source could ensure particle balance and improve computational accuracy significantly for photon transport.The effect of anisotropic scattering is problem-dependent,and no distinct differences among various methods are observed for volume source problems with a continuous energy source.For beam source problems,flux results are sensitive to negative scattering functions,and strictly nonnegative cross sections need to be implemented.展开更多
A finite-rate method is used to simulate the three-dimensional combustion process in a plasma generator with CH4 as the fuel. The simulation was run with RNG k-ε model to simulate turbulence, with eddy-dissipation-co...A finite-rate method is used to simulate the three-dimensional combustion process in a plasma generator with CH4 as the fuel. The simulation was run with RNG k-ε model to simulate turbulence, with eddy-dissipation-concept (EDC) model to simulate the combustion and with discrete ordinates model to simulate radiation. The numerical results show that the flow field characteristics and the parameter distributions are under the condition of rich fuels, and these results provide valuable information when optimizing the plasma generator design and organizing its flow fields.展开更多
Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis fo...Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis for evaluating the importance of a forest in the protection of carabid beetle diversity.Carabids were captured by pitfall traps during their seasonal activity from 2012 to 2013 in a poplar-birch forest,ash-walnut forest and broad-leaved Korean pine forest.A total of 5252 individuals,representing 21 species,were collected.Carabid abundance was highest in the broad-leaved Korean pine forest and lowest in the ash-walnut forest.Carabus billbergi Mannerheim and Pterostichus pertinax(Tschitscherine)were the dominant beetle species in each stand.Carabus canaliculatus Adams was dominant in the poplar-birch and ash-walnut forests,and Leistus niger Gebler was dominant in the ash-walnut forest.The carabids were affected differently by stand factors.C.billbergi and P.pertinax was positively correlated with mean DBH.C.canaliculatus and L.niger were not positively correlated with any stand factors.The broad-leaved Korean pine forest with greater age,large DBH and thick leaf litter fostered a high diversity of carabid species.The main yearly activity period for most carabids was during July.Different carabid species responded differently to seasonality,and the activity period of several species was relatively late(August)in the year.展开更多
The complex structure and strong heterogeneity of advanced nuclear reactor systems pose challenges for high-fidelity neutron-shielding calculations. Unstructured meshes exhibit strong geometric adaptability and can ov...The complex structure and strong heterogeneity of advanced nuclear reactor systems pose challenges for high-fidelity neutron-shielding calculations. Unstructured meshes exhibit strong geometric adaptability and can overcome the deficiencies of conventionally structured meshes in complex geometry modeling. A multithreaded parallel upwind sweep algorithm for S_(N) transport was proposed to achieve a more accurate geometric description and improve the computational efficiency. The spatial variables were discretized using the standard discontinuous Galerkin finite-element method. The angular flux transmission between neighboring meshes was handled using an upwind scheme. In addition, a combination of a mesh transport sweep and angular iterations was realized using a multithreaded parallel technique. The algorithm was implemented in the 2D/3D S_(N) transport code ThorSNIPE, and numerical evaluations were conducted using three typical benchmark problems:IAEA, Kobayashi-3i, and VENUS-3. These numerical results indicate that the multithreaded parallel upwind sweep algorithm can achieve high computational efficiency. ThorSNIPE, with a multithreaded parallel upwind sweep algorithm, has good reliability, stability, and high efficiency, making it suitable for complex shielding calculations.展开更多
基金This study was supported by the Chinese Academy of Sciences (A grant KZCX2-406) the National Natural Science Foundation of China (NSFC39970123) and Changbai Mountain Open Research Station.
文摘Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.
文摘In this paper,the quantitative approach is applied on the study of coniferous forestbased on the data which were collected by the field investigation in Daxinganling region.The mainpurpose is objectively to show the position of communities in the space and the relationship be-tween the community and environment.By means of ordination,it is found that dahurian larch for-est,mongolian scots pine forest and korean fir forest lie in different positions. Gradient analysis ofthree dominant types of conigerous forest has revealed the difference of ecological amplitude,thedifference is one of the important reasons that determine the different communities in the differentenvironment.
基金supported by the Higher Education Commission of Pakistan
文摘We investigated the composition of plant communities to quantify their relationships with environmental parameters in the Chitral Hindukush range of Pakistan. We sampled tree vegetation using the Point Centered Quarter （PCQ） method while understory vegetation was sampled in 1.5-m circular quadrats. Cedrus deodara is the national symbol of Pakistan and was dominant in the sampled communities. Because environmental variables determine vegetation types, we analyzed and evaluated edaphic and topographic factors. DCA-Ordination showed the major gradient as an amalgam of elevation （p〈0.05） and slope （p〈0.01） as the topographic factors correlated with species distribution. Soil variables were the factors of environmental significance along DCA axes. However, among these factors, Mg2＋ , K ＋ and N2＋ contributed not more than 0.054% 0.20% and 0.073%, respectively, to variation along the first ordination axis. We conclude that the principal reason for weak or no correlation with many edaphic variables was the anthropogenic disturbance of vegetation. The understory vegetation was composed of perennial herbs in most communities and was most dense under the tree canopy. The understory vegetation strongly regulates tree seedling growth and regeneration patterns. We recommend further study of the understory vegetation using permanent plots to aid development of forest regeneration strategies.
基金supported by Special Fund for Public Welfare Technology Research of Agricultural Industry (200903014)
文摘We studied woodland vegetation in broad-leaved deciduous woodlands of Metema in northwestern Amhara regional state, Ethiopia to determine plant community types and species distribution patterns and their relationships with environmental variables, including altitude, pH, cation exchange capacity, electrical conductivity （EC）, and moisture. We used a selective approach with a systematic sampling design. A total of 74 quadrats, each 25m × 25m at intervals of 150-200 m were sampled along the established transect lines. For herbaceous vegetation and soil data collection, five subquadrats each lm x lm were established at the four corners and the center of each quadrat. Three community types were identified using TWINSPAN analysis. All three community types showed high diversity （Shannon-Weiner index）, the highest in community type II at 3.55. The highest similarity coefficient was 0.49 （49%） between community types II and III, reflecting 0.51 （51%） dissimilarity in their species richness. The canonical correspondence ordination diagram revealed that the distribution pattern of community type I was explained by moisture while that of community types III and II was explained by EC and altitude and moisture, respectively. Altitude was the most statistically significant environmental variable, followed by moisture and EC in determining the total variation in species composition and distribution patterns while pH and cation exchange capacity were non significant. In conclusion, we recommend that any intervention should take into account these three discrete community types and their environmental settings to make the intervention more successful.
基金This work was supported by the National Natural Science Foundation of China(Grant No.41730641)Project from Ministry of Science and Technology of China(Basic Research project:2014FY110600 and 13-5 Project:2016YFA0600802).
文摘Forests in Northeast China in the Greater and Lesser Khingan Mountains(GKM and LKM)account for nearly 1/3 of the total state-owned forests in the country.Regional and historical comparisons of forest plants and macrofungi will favor biological conservation,forest management and economic development.A total of 1067 sampling plots were surveyed on forest composition and structure,with a macrofungi survey at Liangshui and Huzhong Nature Reserves in the center of two regions.Regional and historical differences of these parameters were analyzed with a redundancy ordination of their complex associations.There were 61-76 families,189-196 genera,and 369-384 species,which was only 1/3 of the historical records.The same dominant species were larch and birch with Korean pine(a climax species)less as expected from past surveys in the LKM.Shrub and herb species were different in the two regions,as expected from historical records.There was 10-50%lower species diversity(except for herb evenness),but 1.8-to 4-time higher macrofungi diversity in the GKM.Compared with the LKM,both tree heights and macrofungi density were higher.Nevertheless,current heights averaging 10 m are half of historical records(>20 m in the 1960s).Edible macrofungi were the highest proportion in both regions,about twice that of other fungal groups,hav-ing important roles in the local economy.A major factor explaining plant diversity variations in both regions was herb cover,followed by shrubs in the GKM and herb-dominant species in the LKM.Factors responsible for macrofungi variations were tree density and shrub height.Vaccinium vitis-idaea and Larix gmelinii in the GKM but tree size and diversity were important factors in the LKM.Our findings highlighted large spatial and historical differences between the GKM and LKM in plant-macrofungal composition,forest structure,and their complex associations,which will favor precise conservation and management of forest resources in two region in the future.
基金the support of CSIR funding under budget head NWP-020
文摘Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend on climate, edaphic and biotic factors which are not well correlated with plant community structures. This study aimed to explore the relationships between understory vegetation and abiotic factors in natural and planted forest ecosystems. A non-metric multidimensional scaling(NMS) ordination technique was applied to represent forest understory vegetation among five forest communities, i.e., a dry miscellaneous forest(DMF), a sal mixed forest(SMF), a teak plantation(TP), a low-land miscellaneous forest(LMF) and a savanna area(SAV) of the Katerniaghat Wildlife Sanctuary, located in northern India. Microclimatic variables, such as photosynthetically active radiation(PAR), air temperature(AT), soil temperature(ST), ambient atmospheric CO 2 concentration, absolute air humidity(AH), physical and chemical soil properties as well as biological properties were measured. Understory species were assessed via 100 random quadrats(5 m × 5 m) in each of the five forests in which a total of 75 species were recorded encompassing 67 genera from 37 families, consisting of 32 shrubs and 43 plant saplings. DMF was the most dense forest with 34,068 understory individuals per ha of different species, whereas the lowest understory population(13,900 per ha) was observed in the savanna. Ordination and correlation revealed that microclimate factors are most important in their effect compared to edaphic factors, on the development of understory vegetation in the various forest communities in the north of India.
基金the National Key R&D Program of China(No.2018YFE0180900).
文摘The key issue in accelerating method of characteristics(MOC)transport calculations is in obtaining a completely equivalent low-order neutron transport or diffusion equation.Herein,an equivalent low-order angular flux nonlinear finite difference equation is proposed for MOC transport calculations.This method comprises three essential features:(1)the even parity discrete ordinates method is used to build a low-order angular flux nonlinear finite difference equation,and different boundary condition treatments are proposed;(2)two new defined factors,i.e.,the even parity discontinuity factor and odd parity discontinuity factor,are strictly defined to achieve equivalence between the low-order angular flux nonlinear finite difference method and MOC transport calculation;(3)the energy group and angle are decoupled to construct a symmetric linear system that is much easier to solve.The equivalence of this low-order angular flux nonlinear finite difference equation is analyzed for two-dimensional(2D)pin,2D assembly,and 2D C5G7 benchmark problems.Numerical results demonstrate that a low-order angular flux nonlinear finite difference equation that is completely equivalent to the pin-resolved transport equation is established.
基金supported by the National Natural Science Foundation of China(No.11975097)the Fundamental Research Funds for the Central Universities(No.2019MS038).
文摘The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in the S N method to automatically optimize the angular distribution and minimize angular discretization errors with lower expenses.The proposed method enables linear dis-continuous finite element quadrature sets over an icosahe-dron to vary their quadrature orders in a one-twentieth sphere so that fine resolutions can be applied to the angular domains that are important.An error estimation that operates in conjunction with the spherical harmonics method is developed to determine the locations where more refinement is required.The adaptive quadrature sets are applied to three duct problems,including the Kobayashi benchmarks and the IRI-TUB research reactor,which emphasize the ability of this method to resolve neutron streaming through ducts with voids.The results indicate that the performance of the adaptive method is more effi-cient than that of uniform quadrature sets for duct transport problems.Our adaptive method offers an appropriate placement of angular unknowns to accurately integrate angular fluxes while reducing the computational costs in terms of unknowns and run times.
基金the National Key Research and Development Program of China(Nos.2018YFB0204301,2017YFB0202104,and 2017YFE0302200)。
文摘The China dual-functional lithium–lead test blanket module(DFLL-TBM) is a liquid Li Pb blanket concept developed by the Institute of Nuclear Energy Safety Technology of the Chinese Academy of Sciences for testing in ITER to validate relevant tritium breeding and shielding technologies. In this study, neutronic calculations of DFLL-TBM were carried out using a massively parallel three-dimensional transport code, Hydra, with the Fusion Evaluated Nuclear Data Library/MG. Hydra was developed by the Nuclear Engineering Computational Physics Lab based on the discrete ordinates method and has been devoted to neutronic analysis and shielding evaluation for nuclear facilities. An in-house Monte Carlo code(MCX) was employed to verify the discretized calculation model used by Hydra for the DFLL-TBM calculations. The results showed two key aspects:(1) In most material zones,Hydra solutions are in good agreement with the reference MCX results within 1%, and the maximal relative difference of the neutron flux is merely 3%, demonstrating the correctness of the calculation model;(2) while the current DFLL-TBM design meets the operation shielding requirement of ITER for 4 years, it does not satisfy the tritium self-sufficiency requirement. Compared to the two-step approach, Hydra produces higher accuracies as it does not rely on the homogenization technique during the calculation process. The parallel efficiency tests of Hydra using the DFLL-TBM model also showed that this code maintains a high parallel efficiency on O(100) processors and, as a result, is able to significantly improve computing performance through parallelization. Parameter studies have been carried out by varying the thickness of the beryllium armor layer and the tritium breeding zone to understand the influence of the beryllium layer and breeding zone thickness on tritium breeding performance. This establishes a foundation for further improvement in the tritium production performance of DFLL-TBM.
基金supported by the National Natural Science Foundation of China(Nos.11505059,11575061)the Fundamental Research Funds for Central Universities(No.2017XS087)
文摘In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre expansion is widely used in discrete ordinates transport codes because of algebraic simplifications with spherical harmonics for the scattering source.However,negative cross sections caused by the finitely truncated expansion may give rise to a negative source and flux.A simple method is adopted,based on integrating functions of scattering moments,to evaluate anisotropy and convergence of expanded functions.A series of problems were designed with angular fluxes of different anisotropy,and numerical simulations were performed using the ARES transport code to study different treatments and algorithms for scattering.Results show that the diagonal transport approximation is more stable and obtains a similar accuracy with the extended approximation.A conservative fixup for the negative source could ensure particle balance and improve computational accuracy significantly for photon transport.The effect of anisotropic scattering is problem-dependent,and no distinct differences among various methods are observed for volume source problems with a continuous energy source.For beam source problems,flux results are sensitive to negative scattering functions,and strictly nonnegative cross sections need to be implemented.
文摘A finite-rate method is used to simulate the three-dimensional combustion process in a plasma generator with CH4 as the fuel. The simulation was run with RNG k-ε model to simulate turbulence, with eddy-dissipation-concept (EDC) model to simulate the combustion and with discrete ordinates model to simulate radiation. The numerical results show that the flow field characteristics and the parameter distributions are under the condition of rich fuels, and these results provide valuable information when optimizing the plasma generator design and organizing its flow fields.
基金supported by grants from the National Natural Science Foundation of China(31600517)the Science and Technology Development Project of Jilin Province(20180201059NY)+2 种基金Science and Technology Research Project of Jilin Provincial Education Department(JJKH20190651KJ)Open Project of Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains,Ministry of Education(GPES202003)National College Students’Innovation and Entrepreneurship Training Program(202110201030)。
文摘Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis for evaluating the importance of a forest in the protection of carabid beetle diversity.Carabids were captured by pitfall traps during their seasonal activity from 2012 to 2013 in a poplar-birch forest,ash-walnut forest and broad-leaved Korean pine forest.A total of 5252 individuals,representing 21 species,were collected.Carabid abundance was highest in the broad-leaved Korean pine forest and lowest in the ash-walnut forest.Carabus billbergi Mannerheim and Pterostichus pertinax(Tschitscherine)were the dominant beetle species in each stand.Carabus canaliculatus Adams was dominant in the poplar-birch and ash-walnut forests,and Leistus niger Gebler was dominant in the ash-walnut forest.The carabids were affected differently by stand factors.C.billbergi and P.pertinax was positively correlated with mean DBH.C.canaliculatus and L.niger were not positively correlated with any stand factors.The broad-leaved Korean pine forest with greater age,large DBH and thick leaf litter fostered a high diversity of carabid species.The main yearly activity period for most carabids was during July.Different carabid species responded differently to seasonality,and the activity period of several species was relatively late(August)in the year.
文摘The complex structure and strong heterogeneity of advanced nuclear reactor systems pose challenges for high-fidelity neutron-shielding calculations. Unstructured meshes exhibit strong geometric adaptability and can overcome the deficiencies of conventionally structured meshes in complex geometry modeling. A multithreaded parallel upwind sweep algorithm for S_(N) transport was proposed to achieve a more accurate geometric description and improve the computational efficiency. The spatial variables were discretized using the standard discontinuous Galerkin finite-element method. The angular flux transmission between neighboring meshes was handled using an upwind scheme. In addition, a combination of a mesh transport sweep and angular iterations was realized using a multithreaded parallel technique. The algorithm was implemented in the 2D/3D S_(N) transport code ThorSNIPE, and numerical evaluations were conducted using three typical benchmark problems:IAEA, Kobayashi-3i, and VENUS-3. These numerical results indicate that the multithreaded parallel upwind sweep algorithm can achieve high computational efficiency. ThorSNIPE, with a multithreaded parallel upwind sweep algorithm, has good reliability, stability, and high efficiency, making it suitable for complex shielding calculations.
