A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structu...A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structures, two self-contained flame sensors are used to track the diffusion and reaction processes with different spatial scales in the flame front, respectively. The dynamic formulation for the proposed SGS combustion model is also performed. Large eddy simulations(LESs) of Bunsen flame F3 are used to evaluate the different SGS combustion models. The results show that the proposed SGS model has the ability in predicting the distributions of temperature and velocity reasonably, while the predictions for the distributions of some species need further improvement. The snapshots of instantaneous normalized progress variables reveal that the flame is more remarkably and severely wrinkled at the flame tip for flame F3.More satisfactory results obtained by the dynamic model indicate that it can preserve the premixed flame propagation characteristics better.展开更多
Large eddy simulations (LES) have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center (DLR). Turbulent combustion is mod- eled by the tabulated thermo-chemis...Large eddy simulations (LES) have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center (DLR). Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function (PDF). A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function (Model I) and //-function (Model II), are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement (AMR) technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.展开更多
The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin,North China.The rich and well-preserved specimens of Halysis in this area fa...The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin,North China.The rich and well-preserved specimens of Halysis in this area facilitate detailed studies for its skeletal construction and tube microstructure.Halysis differs from calcified cyanobacteria and calcareous red and green algae in morphology,skeletal construction and microstructure,as well as reproduction mode.Halysis typically consists of multiple juxtaposed parallel tubes arranged in sheets(‘multiple-tube'type)or is just composed of one tube(‘single-tube'type).In‘multiple-tube'Halysis,tube fission by bifurcation results from the insertion of a microcrystalline wall at the center of a mother tube.This study demonstrates for the first time that the tube walls of Halysis have a laminofibrous(fibronormal)microstructure,composed of fibrous calcite perpendicular to wall surface,and recognizes the‘single-tube'type Halysis composed of one tube;in addition,for the first time,this study finds out that‘multiple-tube'Halysis develops buddings from the conjunction of two tubes and‘single-tube'Halysis shows wide-angle Y-shaped branchings.Based on these findings,this study further compares Halysis with tabulate corals.Halysis appears stratigraphically earlier than Catenipora and Aulopora,and has a smaller tube size.‘Multiple-tube'Halysis resembles Catenipora and‘single-tube'Halysis resembles Aulopora in skeletal construction and microstructure,and in their tube walls of laminofibrous microstructure composed of fibrous calcite perpendicular to the tube wall surface.Catenipora and Halysis are both characterized by the absence of septal spines.The similarities suggest that Halysis may be the ancestor of Catenipora-like and Aulopora-like tabulate corals.展开更多
The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan (JCY) triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representi...The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan (JCY) triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representing various shallow-water platform environments. Highly diversified and abundant heliolitid coral faunas are recognized in the formation and occur over time and space in certain stratigraphic horizons and various lithofacies. Heliolites has been studied using multivariate morphometric analysis applied to differentiate species and evaluate intraspecific and interspecific variations. Ten morphological characters quantified by examination and measurement from transverse and longitudinal thin sections and statistically tested allowed selection of effective characters to discriminate species. Results of frequency histograms, correlation analysis and principle component analysis indicated that certain characters would be suitable for cluster analysis, which were performed on principle component score matrices obtained from the raw data set coordinated with coralla by all those characters. Five major clusters at a relative distance of five on the resulting dendrogram of Heliolites are regarded as morphospecies thus making valid taxa: Heliolites tashanensis Lin and Chow, 1977; Heliolites caracolica (Lin and Chow, 1977); Heliolites columella (Lin and Chow, 1977); Heliolites waicunensis Lin and Chow, 1977; and H. sinensis irregularis Lin and Chow, 1977. The discrimination of these morphospecies by the cluster analysis is verified by discriminant analyses and descriptive statistics.展开更多
Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based o...Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green's functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green's function can be divided into two parts: primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.展开更多
AIM: To investigate the incidence and subsequent changes of outer retinal tubulations(ORTs) in diabetic macular edema(DME) underwent anti-vascular endothelial growth factor(VEGF) therapy, and to assess the possibility...AIM: To investigate the incidence and subsequent changes of outer retinal tubulations(ORTs) in diabetic macular edema(DME) underwent anti-vascular endothelial growth factor(VEGF) therapy, and to assess the possibility of ORT as a biomarker of DME severity or response to anti-VEGF therapy.METHODS: This retrospective and descriptive study included a total of 228 patients(435 eyes) with DME and treated with intravitreal anti-VEGF agents between March 2016 and January 2018. Patients were divided into 2 groups according to the presence of ORTs. High-resolution spectral-domain optical coherence tomography(SD-OCT) images acquired by vertical and horizontal scans and over consecutive visits were analyzed. The evolution of ORT over time, type of fluid and subfoveal photoreceptor integrity on OCT imaging was also assessed. RESULTS: ORTs were identified in 108 eyes of 435 eyes with an overall incidence rate of 24.83% at baseline. ORTs were prone to locate adjacent to the lesions of exudation and/or cystoid edema and possibly situated in outer nuclear layer(ONL), outer plexiform layer(OPL) and/or inner nuclear layer(INL) in eyes with DME. The formation process of ORT led to focal downward displacement of OPL and INL toward RPE near the lesion. During the follow up, 45 eyes had steady ORTs and 63 eyes had dynamic variants in ORTs, including disappearance, reappearance, collapse, diminution, and enlargement. There were higher proportion of closed ORTs and fewer proportion of forming ORTs in eyes with steady ORTs, which showed a statistically significance when compared with eyeswith variant ORTs(P=0.006, P=0.017, respectively). The eyes without ORTs had significantly better final best corrected visual acuity(BCVA) and more BCVA change than those eyes with ORTs in DME patients after antiVEGF therapy(P=0.023, P=0.009, respectively). The disruption of subfoveal photoreceptor integrity in eyes with ORTs was more serious than that in eyes without ORTs(P=0.013). The proportion of stable vision in eyes with ORTs was significantly higher than that in eyes without ORTs, showing statistical significance(P=0.016). ORTs were associated with worse visual prognosis due to damage of the subfoveal photoreceptor integrity. CONCLUSION: ORTs have a high incidence and changes over time in DME with anti-VEGF treatment and may be located at various retinal layers. Persistent ORT can be as a negative biomarker of outcome of DME.展开更多
Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling facto...Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence.The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.展开更多
Flamelet Generated Manifold(FGM)is an example of a chemistry tabulation or a flamelet method that is under attention because of its accuracy and speed in predicting combustion characteristics.However,the main problem ...Flamelet Generated Manifold(FGM)is an example of a chemistry tabulation or a flamelet method that is under attention because of its accuracy and speed in predicting combustion characteristics.However,the main problem in applying the model is a large amount of memory required.One way to solve this problem is to apply machine learning(ML)to replace the stored tabulated data.Four different machine learning methods,including two Artificial Neural Networks(ANNs),a Random Forest(RF),and a Gradient Boosted Trees(GBT),are trained,validated,and compared in terms of various performance measures.The progress variable source term and transport properties are replaced with the ML models.Particular attention was paid to the progress variable source term due to its high gradient and wide range of its value in the control variables space.Data preprocessing is shown to play an essential role in improving the performance of the models.Two ensemble models,namely RF and GBT,exhibit high training efficiency and acceptable accuracy.On the other hand,the ANN models have lower training errors and take longer to train.The four models are then combined with a one-dimensional combustion code to simulate a counterflow non-premixed diffusion flame in engine-relevant conditions.The predictions of the ML-FGM models are compared with detailed chemical simulations and the original FGM model for key combustion properties and representative species profiles.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.91441117 and 51576182)
文摘A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structures, two self-contained flame sensors are used to track the diffusion and reaction processes with different spatial scales in the flame front, respectively. The dynamic formulation for the proposed SGS combustion model is also performed. Large eddy simulations(LESs) of Bunsen flame F3 are used to evaluate the different SGS combustion models. The results show that the proposed SGS model has the ability in predicting the distributions of temperature and velocity reasonably, while the predictions for the distributions of some species need further improvement. The snapshots of instantaneous normalized progress variables reveal that the flame is more remarkably and severely wrinkled at the flame tip for flame F3.More satisfactory results obtained by the dynamic model indicate that it can preserve the premixed flame propagation characteristics better.
基金financial support by the National Natural Science Foundation of China (Nos. 51176178, 50936005)
文摘Large eddy simulations (LES) have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center (DLR). Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function (PDF). A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function (Model I) and //-function (Model II), are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement (AMR) technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.
基金This work was financially supported by the National Science and Technology Major Projea(Grant Nos.2016ZX05004-006 and 2016ZX05004-004)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB26000000)and the National Natural Science Foundation of China(Grant Nos.41502004 and 41902110).
文摘The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin,North China.The rich and well-preserved specimens of Halysis in this area facilitate detailed studies for its skeletal construction and tube microstructure.Halysis differs from calcified cyanobacteria and calcareous red and green algae in morphology,skeletal construction and microstructure,as well as reproduction mode.Halysis typically consists of multiple juxtaposed parallel tubes arranged in sheets(‘multiple-tube'type)or is just composed of one tube(‘single-tube'type).In‘multiple-tube'Halysis,tube fission by bifurcation results from the insertion of a microcrystalline wall at the center of a mother tube.This study demonstrates for the first time that the tube walls of Halysis have a laminofibrous(fibronormal)microstructure,composed of fibrous calcite perpendicular to wall surface,and recognizes the‘single-tube'type Halysis composed of one tube;in addition,for the first time,this study finds out that‘multiple-tube'Halysis develops buddings from the conjunction of two tubes and‘single-tube'Halysis shows wide-angle Y-shaped branchings.Based on these findings,this study further compares Halysis with tabulate corals.Halysis appears stratigraphically earlier than Catenipora and Aulopora,and has a smaller tube size.‘Multiple-tube'Halysis resembles Catenipora and‘single-tube'Halysis resembles Aulopora in skeletal construction and microstructure,and in their tube walls of laminofibrous microstructure composed of fibrous calcite perpendicular to the tube wall surface.Catenipora and Halysis are both characterized by the absence of septal spines.The similarities suggest that Halysis may be the ancestor of Catenipora-like and Aulopora-like tabulate corals.
基金supported by grants to Prof.Dong-Jin Lee from the Korean Research Foundation
文摘The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan (JCY) triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representing various shallow-water platform environments. Highly diversified and abundant heliolitid coral faunas are recognized in the formation and occur over time and space in certain stratigraphic horizons and various lithofacies. Heliolites has been studied using multivariate morphometric analysis applied to differentiate species and evaluate intraspecific and interspecific variations. Ten morphological characters quantified by examination and measurement from transverse and longitudinal thin sections and statistically tested allowed selection of effective characters to discriminate species. Results of frequency histograms, correlation analysis and principle component analysis indicated that certain characters would be suitable for cluster analysis, which were performed on principle component score matrices obtained from the raw data set coordinated with coralla by all those characters. Five major clusters at a relative distance of five on the resulting dendrogram of Heliolites are regarded as morphospecies thus making valid taxa: Heliolites tashanensis Lin and Chow, 1977; Heliolites caracolica (Lin and Chow, 1977); Heliolites columella (Lin and Chow, 1977); Heliolites waicunensis Lin and Chow, 1977; and H. sinensis irregularis Lin and Chow, 1977. The discrimination of these morphospecies by the cluster analysis is verified by discriminant analyses and descriptive statistics.
文摘Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green's functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green's function can be divided into two parts: primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.
基金Supported by the Hubei Provincial Health and Family Planning Commission Joint Fund Project(No.WJ2018H0071)
文摘AIM: To investigate the incidence and subsequent changes of outer retinal tubulations(ORTs) in diabetic macular edema(DME) underwent anti-vascular endothelial growth factor(VEGF) therapy, and to assess the possibility of ORT as a biomarker of DME severity or response to anti-VEGF therapy.METHODS: This retrospective and descriptive study included a total of 228 patients(435 eyes) with DME and treated with intravitreal anti-VEGF agents between March 2016 and January 2018. Patients were divided into 2 groups according to the presence of ORTs. High-resolution spectral-domain optical coherence tomography(SD-OCT) images acquired by vertical and horizontal scans and over consecutive visits were analyzed. The evolution of ORT over time, type of fluid and subfoveal photoreceptor integrity on OCT imaging was also assessed. RESULTS: ORTs were identified in 108 eyes of 435 eyes with an overall incidence rate of 24.83% at baseline. ORTs were prone to locate adjacent to the lesions of exudation and/or cystoid edema and possibly situated in outer nuclear layer(ONL), outer plexiform layer(OPL) and/or inner nuclear layer(INL) in eyes with DME. The formation process of ORT led to focal downward displacement of OPL and INL toward RPE near the lesion. During the follow up, 45 eyes had steady ORTs and 63 eyes had dynamic variants in ORTs, including disappearance, reappearance, collapse, diminution, and enlargement. There were higher proportion of closed ORTs and fewer proportion of forming ORTs in eyes with steady ORTs, which showed a statistically significance when compared with eyeswith variant ORTs(P=0.006, P=0.017, respectively). The eyes without ORTs had significantly better final best corrected visual acuity(BCVA) and more BCVA change than those eyes with ORTs in DME patients after antiVEGF therapy(P=0.023, P=0.009, respectively). The disruption of subfoveal photoreceptor integrity in eyes with ORTs was more serious than that in eyes without ORTs(P=0.013). The proportion of stable vision in eyes with ORTs was significantly higher than that in eyes without ORTs, showing statistical significance(P=0.016). ORTs were associated with worse visual prognosis due to damage of the subfoveal photoreceptor integrity. CONCLUSION: ORTs have a high incidence and changes over time in DME with anti-VEGF treatment and may be located at various retinal layers. Persistent ORT can be as a negative biomarker of outcome of DME.
基金Project supported by the National Natural Science Foundation of China(Nos.91441117 and51576182)
文摘Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence.The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.
基金This work was funded by the Netherlands Organisation for Scientific Research(NWO,project number 14927).
文摘Flamelet Generated Manifold(FGM)is an example of a chemistry tabulation or a flamelet method that is under attention because of its accuracy and speed in predicting combustion characteristics.However,the main problem in applying the model is a large amount of memory required.One way to solve this problem is to apply machine learning(ML)to replace the stored tabulated data.Four different machine learning methods,including two Artificial Neural Networks(ANNs),a Random Forest(RF),and a Gradient Boosted Trees(GBT),are trained,validated,and compared in terms of various performance measures.The progress variable source term and transport properties are replaced with the ML models.Particular attention was paid to the progress variable source term due to its high gradient and wide range of its value in the control variables space.Data preprocessing is shown to play an essential role in improving the performance of the models.Two ensemble models,namely RF and GBT,exhibit high training efficiency and acceptable accuracy.On the other hand,the ANN models have lower training errors and take longer to train.The four models are then combined with a one-dimensional combustion code to simulate a counterflow non-premixed diffusion flame in engine-relevant conditions.The predictions of the ML-FGM models are compared with detailed chemical simulations and the original FGM model for key combustion properties and representative species profiles.