In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gra...In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gradient.Typically,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)states.The boundary conditions considered in the present work allow a conductive state and are representative of typical geological applications.In an earlier work,we carried out a linear stability analysis of the conductive state.It was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal rolls.Moreover,a non-zero velocity component exists in z-direction.In the present work,threedimensional non-linear convection regimes are studied.The original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear theory.The number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity geometry.Calculations carried out at low supercriticalities show that a direct bifurcation takes place.With increasing supercriticality,no transitions to other convective regimes are detected.The situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.展开更多
A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief lit...A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.展开更多
The thermal environmental characteristics are experim-entally studied in terms of different air supply volumes and outdoor meteorological parameters in a large-space building which is air conditioned with a low sidewa...The thermal environmental characteristics are experim-entally studied in terms of different air supply volumes and outdoor meteorological parameters in a large-space building which is air conditioned with a low sidewall air supply.The experimental results show that the indoor vertical temperature distributions under different condition are similar.The maximum vertical temperature difference(MVTD)is up to about 20 ℃,and it linearly changes with the sol-air temperature.The indoor vertical temperature gradients(VTGs)in the upper,central and lower zones are different.The influence of the sol-air temperature on the VTGs in the upper and the lower zones is greater than that in the central zone.The characteristics of the VTGs in the three zones affected by the air supply volume are the same as those affected by the sol-air temperature.Besides,because of the small air velocity,the predicted mean vote(PMV)on comfort in the occupied zone is slightly high and the air temperature difference between the head and the ankle is usually more than 3 ℃.展开更多
Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries....Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries.Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered.The prediction capabilities of these analytical models were evaluated by using large eddy simulation(LES) for a hypothetical shaft.The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate,vertical temperatures profile and pressure difference as well.Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area.Further,it is also shown that the analytical models perform better than KLOTE's model does in the mass flow rate prediction.展开更多
Spatio-temporal distribution of chub mackerel Scomber japonicus is strongly susceptible to climate variability.In this study,a weighting-based habitat suitability index(HSI)model was established to assess the impacts ...Spatio-temporal distribution of chub mackerel Scomber japonicus is strongly susceptible to climate variability.In this study,a weighting-based habitat suitability index(HSI)model was established to assess the impacts of Pacific Decadal Oscillation(PDO)on habitat range and distribution of S.japonicus in the East China Sea(ECS)using vertical water temperature at depths of 2.5 m,25 m and 50 m.Results showed that the optimal HSI model selected from ten weighting scenarios can yield reliable predictions.Correlation analysis revealed a significant negative relationship between the PDO index and water temperature anomaly at different depths.The water temperatures at three different layers on the fishing ground of S.japonicus tended to be low in the warm PDO phase and high in the cold PDO phase,respectively.The range of suitable habitats and its spatial distribution exhibited large differences between the warm and cold PDO regimes.During a warm PDO phase,vertical water temperature became cool,and the monthly preferred water temperature at each depth for S.japonicus shifted southeastward.Consequently,habitat quality dramatically decreased,and suitable habitat ranges also reduced and moved southeastward.Conversely,in a cool PDO phase,with the warmer vertical water temperature and northwestward shift of the preferred water temperature,the suitable habitats enlarged and migrated in the same direction.Our findings indicate that the PDO produced significant impacts on habitat range and distribution of S.japonicus in the East China Sea.展开更多
The Japanese common squid Todarodes pacificus is widely distributed in the Sea of Japan,the East China Sea and the Northwest Pacific Ocean,and is largely exploited by the Asia-Pacific countries.In this study,the impac...The Japanese common squid Todarodes pacificus is widely distributed in the Sea of Japan,the East China Sea and the Northwest Pacific Ocean,and is largely exploited by the Asia-Pacific countries.In this study,the impacts of regime shift of the Pacific Decadal Oscillation(PDO)during 1977-2015 on the autumn cohort of T.pacificus were assessed by examining the variations in vertical water temperatures at depths of 0 m(Temp_0 m),50 m(Temp_50 m)and 100 m(Temp_100 m)and the distribution pattern of preferred spawning ground(SSG).Spatial and temporal correlation analysis revealed that the PDO index exhibited a significantly negative relationship with vertical water temperatures at different depths and was negatively related to catch-per-unit-effort(CPUE)and stock biomass of T.pacificus.In addition,water temperatures in the specific three water layers were positively associated with CPUE.The PDO regime shift strongly affected the thermal condition and spawning ground of T.pacificus.Comparing to the negative PDO,the waters from the surface to the deep became cool in the positive PDO phase;correspondingly,the area of SSG largely contracted at different depths.Consequently,the CPUE and stock biomass of T.pacificus profoundly decreased.From the results it can be concluded that the PDO regime shift-driven changes in vertical thermal condition and SSG ranges can yield substantial impacts on T.pacificus abundance.展开更多
Considering the percentage of dissatisfied due to local thermal sensation(PD LTSV),a vertical air temperature difference(ΔT_(d))threshold of about 3°C was recommended in standards.However,some novel air distribu...Considering the percentage of dissatisfied due to local thermal sensation(PD LTSV),a vertical air temperature difference(ΔT_(d))threshold of about 3°C was recommended in standards.However,some novel air distribution methods might create large positive(which means the head warmer than the feet,vice versa)or negativeΔT_(d),with no suitable proved criteria to be used.In this study,sixteen subjects were seated in a climatic box placed in a climate chamber to evaluate thermal sensation and percentage of dissatisfied with negative and positiveΔT_(d) in different whole-body thermal conditions.Air temperatures were controlled independently at the upper and lower body parts,with 13 different air temperature sets combined with 22°C,25°C,28°C,and 31°C(i.e.-9°C≤ΔT_(d)≤9°C).Results showed that subjects were more thermally sensitive at the upper body and with positiveΔT_(d) than at the lower body or with negativeΔT_(d).The 80%acceptableΔT_(d) range is about-8 to 7°C in overall neutral(TSV=0),-7°C to 6°C in slightly cool(TSV=-0.5)conditions,which is wider than-3 to 3°C in slightly warm conditions(TSV=+0.5).By considering the factors of both TSV andΔT_(d),a new overall percentage of dissatisfied index(OPD P)was proposed.Case studies show that the new OPD P index is more precise and suitable for the evaluations of different air distributions to predict overall percentage of dissatisfied in thermal environments with vertical air temperature difference.展开更多
In order to obtain a better understanding of flow characteristics of displacement ventilation, the three-dimensional numerical models are developed using the CFD technology. The numerical simulation results are verifi...In order to obtain a better understanding of flow characteristics of displacement ventilation, the three-dimensional numerical models are developed using the CFD technology. The numerical simulation results are verified by experiments, based on this, the velocity and temperature distribution of three-dimensional displacement ventilation system with single and double heat sources are studied. Velocity and temperature fields under two different cases of heat source are analyzed and compared. The numerical results show that there are three layers in vertical temperature fields of displacement ventilation system with single or double heat sources, and the vertical temperature distribution of single heat source is different from that of double heat sources. When indoor load is large, the comfort requirement of people indoor can't be satisfied with displacement ventilation system only, thus an additional refrigeration system is necessary. Furthermore, under the condition of two heat sources, the displacement ventilation parameters can't be computed simply according to single heat source inlet parameters, therefore the interaction between heat sources should be considered.展开更多
基金financial support from the Ministry of Science and Higher Education of the Russian Federation(Topic No.121031700169-1).
文摘In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gradient.Typically,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)states.The boundary conditions considered in the present work allow a conductive state and are representative of typical geological applications.In an earlier work,we carried out a linear stability analysis of the conductive state.It was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal rolls.Moreover,a non-zero velocity component exists in z-direction.In the present work,threedimensional non-linear convection regimes are studied.The original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear theory.The number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity geometry.Calculations carried out at low supercriticalities show that a direct bifurcation takes place.With increasing supercriticality,no transitions to other convective regimes are detected.The situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.
基金Project(2015CB057701)supported by the National Basic Research Program of ChinaProject(51308071)supported by the National Natural Science Foundation of China+3 种基金Project(13JJ4057)supported by Natural Science Foundation of Hunan Province,ChinaProject(201408430155)supported by the Foundation of China Scholarship CouncilProject(2015319825120)supported by the Traffic Department of Applied Basic Research,ChinaProject(12K076)supported by the Open Foundation of Innovation Platform in Hunan Provincial Universities,China
文摘A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.
基金The National Natural Science Foundation of China(No.50478113)the Leading Academic Discipline Project of Shanghai Municipal Education Commission(No.J50502)
文摘The thermal environmental characteristics are experim-entally studied in terms of different air supply volumes and outdoor meteorological parameters in a large-space building which is air conditioned with a low sidewall air supply.The experimental results show that the indoor vertical temperature distributions under different condition are similar.The maximum vertical temperature difference(MVTD)is up to about 20 ℃,and it linearly changes with the sol-air temperature.The indoor vertical temperature gradients(VTGs)in the upper,central and lower zones are different.The influence of the sol-air temperature on the VTGs in the upper and the lower zones is greater than that in the central zone.The characteristics of the VTGs in the three zones affected by the air supply volume are the same as those affected by the sol-air temperature.Besides,because of the small air velocity,the predicted mean vote(PMV)on comfort in the occupied zone is slightly high and the air temperature difference between the head and the ankle is usually more than 3 ℃.
基金Project(50838009) supported by the National Natural Science Foundation of ChinaProject(2010DFA72740-03) supported by the National Key Technology Research and Development Program of China
文摘Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries.Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered.The prediction capabilities of these analytical models were evaluated by using large eddy simulation(LES) for a hypothetical shaft.The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate,vertical temperatures profile and pressure difference as well.Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area.Further,it is also shown that the analytical models perform better than KLOTE's model does in the mass flow rate prediction.
基金the National Key R&D Program of China(No.2018YFD0900906)the National Natural Science Foundation of China(No.41906073)+1 种基金the Natural Science Foundation of Shanghai(No.19ZR1423000)the Shanghai Universities First-Class Disciplines Project(Fisheries A).
文摘Spatio-temporal distribution of chub mackerel Scomber japonicus is strongly susceptible to climate variability.In this study,a weighting-based habitat suitability index(HSI)model was established to assess the impacts of Pacific Decadal Oscillation(PDO)on habitat range and distribution of S.japonicus in the East China Sea(ECS)using vertical water temperature at depths of 2.5 m,25 m and 50 m.Results showed that the optimal HSI model selected from ten weighting scenarios can yield reliable predictions.Correlation analysis revealed a significant negative relationship between the PDO index and water temperature anomaly at different depths.The water temperatures at three different layers on the fishing ground of S.japonicus tended to be low in the warm PDO phase and high in the cold PDO phase,respectively.The range of suitable habitats and its spatial distribution exhibited large differences between the warm and cold PDO regimes.During a warm PDO phase,vertical water temperature became cool,and the monthly preferred water temperature at each depth for S.japonicus shifted southeastward.Consequently,habitat quality dramatically decreased,and suitable habitat ranges also reduced and moved southeastward.Conversely,in a cool PDO phase,with the warmer vertical water temperature and northwestward shift of the preferred water temperature,the suitable habitats enlarged and migrated in the same direction.Our findings indicate that the PDO produced significant impacts on habitat range and distribution of S.japonicus in the East China Sea.
基金This study was financially supported by the Shanghai Talent Development Funding for the Project(No.2021078)the National Natural Science Foundation of China(No.41906073)the Construction and Application Demonstration of Natural Resources Satellite Remote Sensing Technology System(No.202101003).
文摘The Japanese common squid Todarodes pacificus is widely distributed in the Sea of Japan,the East China Sea and the Northwest Pacific Ocean,and is largely exploited by the Asia-Pacific countries.In this study,the impacts of regime shift of the Pacific Decadal Oscillation(PDO)during 1977-2015 on the autumn cohort of T.pacificus were assessed by examining the variations in vertical water temperatures at depths of 0 m(Temp_0 m),50 m(Temp_50 m)and 100 m(Temp_100 m)and the distribution pattern of preferred spawning ground(SSG).Spatial and temporal correlation analysis revealed that the PDO index exhibited a significantly negative relationship with vertical water temperatures at different depths and was negatively related to catch-per-unit-effort(CPUE)and stock biomass of T.pacificus.In addition,water temperatures in the specific three water layers were positively associated with CPUE.The PDO regime shift strongly affected the thermal condition and spawning ground of T.pacificus.Comparing to the negative PDO,the waters from the surface to the deep became cool in the positive PDO phase;correspondingly,the area of SSG largely contracted at different depths.Consequently,the CPUE and stock biomass of T.pacificus profoundly decreased.From the results it can be concluded that the PDO regime shift-driven changes in vertical thermal condition and SSG ranges can yield substantial impacts on T.pacificus abundance.
基金The work presented in this paper is financially supported by the Fundamental Research Funds for the Central Universities(Grant No.2019CDYGYB026)。
文摘Considering the percentage of dissatisfied due to local thermal sensation(PD LTSV),a vertical air temperature difference(ΔT_(d))threshold of about 3°C was recommended in standards.However,some novel air distribution methods might create large positive(which means the head warmer than the feet,vice versa)or negativeΔT_(d),with no suitable proved criteria to be used.In this study,sixteen subjects were seated in a climatic box placed in a climate chamber to evaluate thermal sensation and percentage of dissatisfied with negative and positiveΔT_(d) in different whole-body thermal conditions.Air temperatures were controlled independently at the upper and lower body parts,with 13 different air temperature sets combined with 22°C,25°C,28°C,and 31°C(i.e.-9°C≤ΔT_(d)≤9°C).Results showed that subjects were more thermally sensitive at the upper body and with positiveΔT_(d) than at the lower body or with negativeΔT_(d).The 80%acceptableΔT_(d) range is about-8 to 7°C in overall neutral(TSV=0),-7°C to 6°C in slightly cool(TSV=-0.5)conditions,which is wider than-3 to 3°C in slightly warm conditions(TSV=+0.5).By considering the factors of both TSV andΔT_(d),a new overall percentage of dissatisfied index(OPD P)was proposed.Case studies show that the new OPD P index is more precise and suitable for the evaluations of different air distributions to predict overall percentage of dissatisfied in thermal environments with vertical air temperature difference.
文摘In order to obtain a better understanding of flow characteristics of displacement ventilation, the three-dimensional numerical models are developed using the CFD technology. The numerical simulation results are verified by experiments, based on this, the velocity and temperature distribution of three-dimensional displacement ventilation system with single and double heat sources are studied. Velocity and temperature fields under two different cases of heat source are analyzed and compared. The numerical results show that there are three layers in vertical temperature fields of displacement ventilation system with single or double heat sources, and the vertical temperature distribution of single heat source is different from that of double heat sources. When indoor load is large, the comfort requirement of people indoor can't be satisfied with displacement ventilation system only, thus an additional refrigeration system is necessary. Furthermore, under the condition of two heat sources, the displacement ventilation parameters can't be computed simply according to single heat source inlet parameters, therefore the interaction between heat sources should be considered.