The current storm wave hazard assessment tends to rely on a statistical method using wave models and fewer historical data which do not consider the effects of tidal and storm surge.In this paper,the wave-current coup...The current storm wave hazard assessment tends to rely on a statistical method using wave models and fewer historical data which do not consider the effects of tidal and storm surge.In this paper,the wave-current coupled model ADCIRC+SWAN was used to hindcast storm events in the last 30 years.We simulated storm wave on the basis of a large set of historical storms in the North-West Pacific Basin between 1985 and 2015 in Houshui Bay using the wave-current coupled model ADCIRC+SWAN to obtain the storm wave level maps.The results were used for the statistical analysis of the maximum significant wave heights in Houshui Bay and the behavior of wave associated with storm track.Comparisons made between observations and simulated results during typhoon Rammasun(2014)indicate agreement.In addition,results demonstrate that significant wave height in Houshui Bay is dominated by the storm wind velocity and the storm track.Two groups of synthetic storm tracks were designed to further investigate the worst case of typhoon scenarios.The storm wave analysis method developed for the Houshui Bay is significant in assisting government's decision-making in rational planning of deep sea net-cage culture.The method can be applied to other bays in the Hainan Island as well.展开更多
In order to study the effects of ventilation modes and outlet height on the airflow field of a nursery piggery,computational fluid dynamics (CFD) technology was used to simulate the wind speed and temperature of an ex...In order to study the effects of ventilation modes and outlet height on the airflow field of a nursery piggery,computational fluid dynamics (CFD) technology was used to simulate the wind speed and temperature of an experimental pig house in the cold northern region.This study was conducted with simulation and a comparative analysis of transverse ventilation,longitudinal ventilation and roof air intake modes.Furthermore,the effects of the air outlet height of 0.7,0.6 and 0.5 m with the roof air inlet mode on the environment in the pig house were studied.Field experiments verified the model of roof air intake model.The results showed inadequate ventilation in both the vertical and horizontal ventilation.However,the airfield gradients were less variable and more balanced when using the rooftop air intake mode.The variation of outlet height significantly affected nursery pig houses’ airflow velocity and temperature.Roof air inlet mode with an outlet height of 0.7 m was better than the other two.The normalized mean square error (NMSE) of air velocity and temperature was less than 0.01,and the simulation analysis could genuinely reflect the distribution of the airflow field in the nursery.展开更多
Rational urban design helps to build sustainable cities with high ventilation capacity and pollutant removal ca-pacity,but the effect of building height on ventilation and pollutant dispersion inside asymmetric canyon...Rational urban design helps to build sustainable cities with high ventilation capacity and pollutant removal ca-pacity,but the effect of building height on ventilation and pollutant dispersion inside asymmetric canyons has not been fully studied.In this paper,we studied the effect of increasing the degree of building height asym-metry(DBHA)on canyon ventilation and pollutant diffusion in shallow and deep asymmetric street canyons by considering six different building height ratios(BHR=3/4,1/2,1/3,4/3,2/1 and 3/1).The results show that increasing the DBHA in asymmetric canyons can improve the ventilation and pollutant removal capacity.For step-up canyons,increasing the downwind building height is very useful to improve ventilation and pollutant re-moval.For shallow/deep step-up canyons with BHR=1/3,the air exchange rate(ACH)increased to 211.2%and 380.1%of the flat canyons,respectively.The spatially-average pollutant concentration in the pedestrian zones(leeward Kavg∗ang windward Kavg∗)decreases significantly with the increase of DBHA,especially for the deep step-up canyon with BHR=1/3,the leeward Kavg∗and windward Kavg∗decrease to 15.3%and 3%,respectively.Also,increasing the upwind building height can also improve the ventilation capacity in the step-down canyons.For the deep step-down canyon with BHR=3/1,the leeward Kavg∗and windward Kavg∗decreased to 40.6%and 24.1%of the deep flat canyon,respectively.Notably,the ventilation capacity is very low for step-down canyons with BHR=4/3,and for step-down canyons with BHR≥2/1,the ventilation capacity and pollutant removal capacity increase significantly with the increase of DBHA.Therefore,in urban planning,step-down canyons with BHR=4/3 should be avoided and designed to satisfy the condition of BHR≥2/1.These findings will be a valuable reference for urban designers to build sustainable cities with high ventilation capacity.展开更多
Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation rati...Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation ratio of wind barriers on the difference of the average pressure coefficient between the train windward and leeward surface(ΔCp)has not been fully investigated.To determine the influence of the interaction among the three factors,namely the wind barrier height(H),ventilation ratio(R),and distance to the train(D),twenty five numerical simulation cases with different structural parameters were considered based on an orthogonal design.The shear stress transfer(SST)k-ωturbulent model was employed to calculate the wind pressure coefficients,and the calculation accuracy was validated by using wind tunnel experiments.The results indicated that with an increase in R,ΔCp first decreased and then increased,andΔCp decreased while D increased.Moreover,with the increase in H,ΔCp first increased and then decreased.Therefore,these three factors must be considered during the installation of wind barriers.Furthermore,according to a range analysis(judging the relative importance of the three factors intuitively),the three factors were ranked in the following order:R>H>D.Based on a variance analysis,R was found to be of high significance toΔCp,followed by H,which was significant,whereas D had relatively insignificant influence.Finally,the optimal values of R and H were determined to be 20%and 110 mm,respectively.And when R=40%,H=85 mm,the train was relatively unsafe under these such conditions.The findings of this study provide significant guidance for the structural design of wind barriers.展开更多
The temporal variation of ventilation coefficient was estimated and a simple model for the prediction of urban ventilation coefficient in Changsha was developed. Firstly, Pearson correlation analysis was used to inves...The temporal variation of ventilation coefficient was estimated and a simple model for the prediction of urban ventilation coefficient in Changsha was developed. Firstly, Pearson correlation analysis was used to investigate the relationship between meteorological parameters and mixing layer height during 2005-2009 in Changsha, China. Secondly, the multi-linear regression model between daytime and nighttime was adopted to predict the temporal ventilation coefficient. Thirdly, the validation of the model between the predicted and observed ventilation coefficient in 2010 was conducted. The results showed that ventilation coefficient significantly varied and remained high during daytime, while it stayed relatively constant and low during nighttime. In addition, the diurnal ventilation coefficient was distinctly negatively correlated with PM10 (particle with the diameter less than 10 μm) concentration in Changsha, China. The predicted ventilation coefficient agreed well with the observed values based on the multi-linear regression models during daytime and nighttime. The urban temporal ventilation coefficient could be accurately predicted by some simple meteorological parameters during daytime and nighttime. The ventilation coefficient played an important role in the PM10 concentration level.展开更多
Stratified air distribution(STRAD)systems have been intensively investigated in recent decades for their energy-saving potential and good indoor air quality performance.However,the evaluation indices used to optimize ...Stratified air distribution(STRAD)systems have been intensively investigated in recent decades for their energy-saving potential and good indoor air quality performance.However,the evaluation indices used to optimize STRAD systems and the normalization methods for weight calculation vary from one research to another.This study aims to investigate the impacts of evaluation indices on the optimal return vent height of a room cooled by an impinging jet ventilation system(one type of STRAD system).The effects of several widely used normalization methods(i.e.,vector normalization,sum normalization,min-max normalization,and no normalization)on indices weights are investigated.The evaluation indices are cooling coil load(Q_(coil)),energy-saving potential(ΔQ_(coil)),mean age of air(MAA),CO_(2) mass fraction,temperature difference between the head and ankles(ΔT_(0.1-1.1)),predicted mean vote(PMV),predicted percentage of dissatisfied(PPD),and draft rate(DR).The multi-criteria optimization method is the entropy-based technique for order preference by similarity to ideal solution(E-TOPSIS).As a result,the min-max normalization method evens the weight of each index and results in unreasonable relative weights.Consequently,the raw matrix(i.e.,the normalization is omitted)is suggested for weight calculation.Among these indices,ΔT_(0.1-1.1) and PPD play critical roles.WithoutΔT_(0.1-1.1),the optimal return vent height changes from mid-level to near-floor,while without PPD,it changes to near-ceiling.Another important result is that the Q_(coil) plays the most trivial role,followed by MAA and DR.Therefore,the optimal return vent height is not determined by energy-saving performance but by performances of thermal comfort.展开更多
目的针对传统颈椎融合器与患者解剖形貌匹配程度较低的临床问题,建立一款具备高度调节功能且外形与椎体相匹配的颈椎融合器,并对其生物力学性能进行评价。方法按照颈椎前路解压术(anterior cervical discectomy and fusion,ACDF)建立颈...目的针对传统颈椎融合器与患者解剖形貌匹配程度较低的临床问题,建立一款具备高度调节功能且外形与椎体相匹配的颈椎融合器,并对其生物力学性能进行评价。方法按照颈椎前路解压术(anterior cervical discectomy and fusion,ACDF)建立颈椎C4~5节段融合模型,模拟前屈、后伸、左右侧弯、左右旋转不同运动工况,计算融合器与椎体终板的应力。3D打印制备融合器后进行体外力学实验,探究融合器的安全性与稳定性。结果该融合器可保持融合C4~5节段颈椎活动度(range of motion,ROM)为1°~2.8°,降低至自然节段ROM的40%~80%。在体外压缩试验中,融合器屈服载荷为(2721.67±209)N,满足服役状态下生理载荷的最大需求。结论所设计的高度可调融合器显示出较优的生物力学性能,且可以减少手术中的选型步骤。展开更多
基金supported by the Technology Development Foundation for Research Institutes of Hainan Province(No.TV45987)
文摘The current storm wave hazard assessment tends to rely on a statistical method using wave models and fewer historical data which do not consider the effects of tidal and storm surge.In this paper,the wave-current coupled model ADCIRC+SWAN was used to hindcast storm events in the last 30 years.We simulated storm wave on the basis of a large set of historical storms in the North-West Pacific Basin between 1985 and 2015 in Houshui Bay using the wave-current coupled model ADCIRC+SWAN to obtain the storm wave level maps.The results were used for the statistical analysis of the maximum significant wave heights in Houshui Bay and the behavior of wave associated with storm track.Comparisons made between observations and simulated results during typhoon Rammasun(2014)indicate agreement.In addition,results demonstrate that significant wave height in Houshui Bay is dominated by the storm wind velocity and the storm track.Two groups of synthetic storm tracks were designed to further investigate the worst case of typhoon scenarios.The storm wave analysis method developed for the Houshui Bay is significant in assisting government's decision-making in rational planning of deep sea net-cage culture.The method can be applied to other bays in the Hainan Island as well.
基金Supported by the National Natural Science Foundation of China(32072787)。
文摘In order to study the effects of ventilation modes and outlet height on the airflow field of a nursery piggery,computational fluid dynamics (CFD) technology was used to simulate the wind speed and temperature of an experimental pig house in the cold northern region.This study was conducted with simulation and a comparative analysis of transverse ventilation,longitudinal ventilation and roof air intake modes.Furthermore,the effects of the air outlet height of 0.7,0.6 and 0.5 m with the roof air inlet mode on the environment in the pig house were studied.Field experiments verified the model of roof air intake model.The results showed inadequate ventilation in both the vertical and horizontal ventilation.However,the airfield gradients were less variable and more balanced when using the rooftop air intake mode.The variation of outlet height significantly affected nursery pig houses’ airflow velocity and temperature.Roof air inlet mode with an outlet height of 0.7 m was better than the other two.The normalized mean square error (NMSE) of air velocity and temperature was less than 0.01,and the simulation analysis could genuinely reflect the distribution of the airflow field in the nursery.
文摘Rational urban design helps to build sustainable cities with high ventilation capacity and pollutant removal ca-pacity,but the effect of building height on ventilation and pollutant dispersion inside asymmetric canyons has not been fully studied.In this paper,we studied the effect of increasing the degree of building height asym-metry(DBHA)on canyon ventilation and pollutant diffusion in shallow and deep asymmetric street canyons by considering six different building height ratios(BHR=3/4,1/2,1/3,4/3,2/1 and 3/1).The results show that increasing the DBHA in asymmetric canyons can improve the ventilation and pollutant removal capacity.For step-up canyons,increasing the downwind building height is very useful to improve ventilation and pollutant re-moval.For shallow/deep step-up canyons with BHR=1/3,the air exchange rate(ACH)increased to 211.2%and 380.1%of the flat canyons,respectively.The spatially-average pollutant concentration in the pedestrian zones(leeward Kavg∗ang windward Kavg∗)decreases significantly with the increase of DBHA,especially for the deep step-up canyon with BHR=1/3,the leeward Kavg∗and windward Kavg∗decrease to 15.3%and 3%,respectively.Also,increasing the upwind building height can also improve the ventilation capacity in the step-down canyons.For the deep step-down canyon with BHR=3/1,the leeward Kavg∗and windward Kavg∗decreased to 40.6%and 24.1%of the deep flat canyon,respectively.Notably,the ventilation capacity is very low for step-down canyons with BHR=4/3,and for step-down canyons with BHR≥2/1,the ventilation capacity and pollutant removal capacity increase significantly with the increase of DBHA.Therefore,in urban planning,step-down canyons with BHR=4/3 should be avoided and designed to satisfy the condition of BHR≥2/1.These findings will be a valuable reference for urban designers to build sustainable cities with high ventilation capacity.
基金Project(51822803)supported by the National Natural Science Foundation of ChinaProject(2019JJ50688)supported by Hunan Provincial Natural Science Foundation,China+1 种基金Project(kq1905005)supported by Training Program for Excellent Young Innovators of Changsha,ChinaProject(CX20210775)supported by Hunan Provincial Innovative Foundation for Postgraduates,China。
文摘Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation ratio of wind barriers on the difference of the average pressure coefficient between the train windward and leeward surface(ΔCp)has not been fully investigated.To determine the influence of the interaction among the three factors,namely the wind barrier height(H),ventilation ratio(R),and distance to the train(D),twenty five numerical simulation cases with different structural parameters were considered based on an orthogonal design.The shear stress transfer(SST)k-ωturbulent model was employed to calculate the wind pressure coefficients,and the calculation accuracy was validated by using wind tunnel experiments.The results indicated that with an increase in R,ΔCp first decreased and then increased,andΔCp decreased while D increased.Moreover,with the increase in H,ΔCp first increased and then decreased.Therefore,these three factors must be considered during the installation of wind barriers.Furthermore,according to a range analysis(judging the relative importance of the three factors intuitively),the three factors were ranked in the following order:R>H>D.Based on a variance analysis,R was found to be of high significance toΔCp,followed by H,which was significant,whereas D had relatively insignificant influence.Finally,the optimal values of R and H were determined to be 20%and 110 mm,respectively.And when R=40%,H=85 mm,the train was relatively unsafe under these such conditions.The findings of this study provide significant guidance for the structural design of wind barriers.
基金Project(51178466) supported by the National Natural Science Foundation of ChinaProject(FANEDD200545) supported by Foundation for the Author of National Excellent Doctoral Dissertation of ChinaProject(2011JQ006) supported by Fundamental Research Funds of the Central Universities of China
文摘The temporal variation of ventilation coefficient was estimated and a simple model for the prediction of urban ventilation coefficient in Changsha was developed. Firstly, Pearson correlation analysis was used to investigate the relationship between meteorological parameters and mixing layer height during 2005-2009 in Changsha, China. Secondly, the multi-linear regression model between daytime and nighttime was adopted to predict the temporal ventilation coefficient. Thirdly, the validation of the model between the predicted and observed ventilation coefficient in 2010 was conducted. The results showed that ventilation coefficient significantly varied and remained high during daytime, while it stayed relatively constant and low during nighttime. In addition, the diurnal ventilation coefficient was distinctly negatively correlated with PM10 (particle with the diameter less than 10 μm) concentration in Changsha, China. The predicted ventilation coefficient agreed well with the observed values based on the multi-linear regression models during daytime and nighttime. The urban temporal ventilation coefficient could be accurately predicted by some simple meteorological parameters during daytime and nighttime. The ventilation coefficient played an important role in the PM10 concentration level.
基金This research is supported by Teaching Development Grant(PJ#6000738)Strategic Research Grant(PJ#7005679),City University of Hong Kong,Hong Kong SAR.The authors thank Dr.Kobayashi from Osaka City University for his kindly sharing of experimental data.
文摘Stratified air distribution(STRAD)systems have been intensively investigated in recent decades for their energy-saving potential and good indoor air quality performance.However,the evaluation indices used to optimize STRAD systems and the normalization methods for weight calculation vary from one research to another.This study aims to investigate the impacts of evaluation indices on the optimal return vent height of a room cooled by an impinging jet ventilation system(one type of STRAD system).The effects of several widely used normalization methods(i.e.,vector normalization,sum normalization,min-max normalization,and no normalization)on indices weights are investigated.The evaluation indices are cooling coil load(Q_(coil)),energy-saving potential(ΔQ_(coil)),mean age of air(MAA),CO_(2) mass fraction,temperature difference between the head and ankles(ΔT_(0.1-1.1)),predicted mean vote(PMV),predicted percentage of dissatisfied(PPD),and draft rate(DR).The multi-criteria optimization method is the entropy-based technique for order preference by similarity to ideal solution(E-TOPSIS).As a result,the min-max normalization method evens the weight of each index and results in unreasonable relative weights.Consequently,the raw matrix(i.e.,the normalization is omitted)is suggested for weight calculation.Among these indices,ΔT_(0.1-1.1) and PPD play critical roles.WithoutΔT_(0.1-1.1),the optimal return vent height changes from mid-level to near-floor,while without PPD,it changes to near-ceiling.Another important result is that the Q_(coil) plays the most trivial role,followed by MAA and DR.Therefore,the optimal return vent height is not determined by energy-saving performance but by performances of thermal comfort.
文摘目的针对传统颈椎融合器与患者解剖形貌匹配程度较低的临床问题,建立一款具备高度调节功能且外形与椎体相匹配的颈椎融合器,并对其生物力学性能进行评价。方法按照颈椎前路解压术(anterior cervical discectomy and fusion,ACDF)建立颈椎C4~5节段融合模型,模拟前屈、后伸、左右侧弯、左右旋转不同运动工况,计算融合器与椎体终板的应力。3D打印制备融合器后进行体外力学实验,探究融合器的安全性与稳定性。结果该融合器可保持融合C4~5节段颈椎活动度(range of motion,ROM)为1°~2.8°,降低至自然节段ROM的40%~80%。在体外压缩试验中,融合器屈服载荷为(2721.67±209)N,满足服役状态下生理载荷的最大需求。结论所设计的高度可调融合器显示出较优的生物力学性能,且可以减少手术中的选型步骤。
