An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-...An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.展开更多
In order to improve the reliability of the design and calculation of single piles under the combined vertical and lateral loads, the solutions were presented based on the subgrade reaction method, in which the ultimat...In order to improve the reliability of the design and calculation of single piles under the combined vertical and lateral loads, the solutions were presented based on the subgrade reaction method, in which the ultimate soil resistance was considered and the coefficient of subgrade reaction was assumed to be a constant. The corresponding computational program was developed using FORTRAN language. A comparison between the obtained solutions and the model test results was made to show the validity of the obtained solutions. The calculation results indicate that both the maximum lateral displacement and bending moment increase with the increase of the vertical and lateral loads and the pile length above ground, while decrease as the pile stiffness, the coefficient of subgrade reaction and the yielding displacement of soil increase. It is also shown that the pile head condition controls the pile responses and the vertical load may cause the instability problem to the pile. In general, the proposed method can be employed to calculate the pile responses independent of the magnitude of the pile deflection.展开更多
Safe and aesthetic interaction between horizontal and vertical alignment may significantly occur when they are combined or closed to each other resulting in safety problems.Previous researches have been limited to foc...Safe and aesthetic interaction between horizontal and vertical alignment may significantly occur when they are combined or closed to each other resulting in safety problems.Previous researches have been limited to focusing on qualitative analysis,which are difficult to implement in the design.To assess the quantitative impact of the combination equilibrium of horizontal and sag vertical curves on safety,KNN,SVR and KNN-SVR machine learning methods were applied for model training to analyze the influence of alignment combination of the horizontal curve(HC)and the sag vertical curve(SVC)on accidents.The highway alignment(a total of 1208 km),the traffic data and accident data from 2011 to 2018 of six interstate roads in Washington,D.C.have been used to train the models.The combination equilibrium of horizontal and sag vertical curves is expressed by the variables such as the radius of the horizontal and vertical curves,the length of the horizontal and vertical curves and the dislocation of horizontal and sag vertical curves.KNN model,SVR model,and KNN-SVR model were built by training the variables as well as the accident rate per 100,000,000 vehicle kilometers.The results show that for the HC-SVC alignment combination,the KNN-SVR model has higher accuracy in predicting the accident rate.At the same time,this paper also suggests the value range of the variables when the horizontal curve radius is small.The research conclusions can provide a reference for the subsequent quantitative optimization design and safety improvement of horizontal and vertical alignment combination.展开更多
Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated th...Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated the impact of different operating speeds when negotiating combined horizontal and vertical curves under unfavorable environmental conditions on Wyoming’s interstates via vehicle dynamics simulation software.The simulation tools provided the acting forces on each tire of the vehicle and the side friction(skidding)margins.This allowed for examining the interaction between vehicle dynamics and road geometry in such alignments.Also,linear regression analysis was implemented to investigate the skidding margins based on the simulation results to demonstrate when a vehicle is more likely to deviate from its desired trajectory.Specifically,this examines the contributing factors that significantly influence the skidding margins.The results indicated that:1)the skidding margins are dramatically decreased by adverse weather conditions even with lower degree of curvature and gradient values of combined curves and more particularly at higher operating speeds conditions.Increasing the vehicle speed on the curve by 10%,the skidding margin dropped by 15%.2)Compared to heavy trucks and sports utility vehicles(SUVs),passenger cars require the highest side friction demand.3)The effect of applying brakes on vehicle stability depends on the road surface condition;applying the brakes on snowy road surfaces increases the potential of vehicle skidding especially for heavy trucks.This study assessed the curve speed limits and showed how important to assign safe and appropriate limits speed since the skidding likelihood is significantly sensitive to the vehicle speeds.This study is beneficial to Wyoming’s roadway agencies since hazardous sections having combined horizontal and vertical curves are identified.Also,critical situations that require additional attention from law enforcement agencies are pinpointed.Finally,recommendations that are valuable to roadway agencies are made based on this study’s findings.展开更多
The share of freight transportation is increasing on Wyoming’s roads. These roads are characterized by challenging mountainous terrain and severe crosswinds. The stability of freight trucks in such conditions is of g...The share of freight transportation is increasing on Wyoming’s roads. These roads are characterized by challenging mountainous terrain and severe crosswinds. The stability of freight trucks in such conditions is of great concern to transportation agencies. Therefore, high-fidelity vehicle dynamics simulation modeling was implemented to investigate the rollover propensity of trucks navigating curves. Scenarios included various road geometric designs, truck characteristics and wind conditions. A multiple linear regression model was also developed to investigate the impact of key parameters on truck rollover propensity. The modeling results indicated that wind speed and direction were influential factors in terms of truck roll stability. Trucks had a 76% higher chance of rolling over when subjected to 40 mph winds relative to being subjected to 20 mph winds assuming all else was unchanged. This study also demonstrated that the most unfavorable wind direction was not perpendicular (90 degrees) to the truck since the truck would continuously change its orientation when traversing combined horizontal and vertical curves. Its speed would also constantly fluctuate. On the contrary, this study’s results indicated that the 120-degree wind direction was the most critical one. Also, under blowing lateral wind conditions, the gross weight of the truck was found to be a contributing factor to rollover risk. Its impact varied depending on the radius of the horizontal curve the truck was navigating. This critical interaction was ignored in the road safety literature. This study offered new insights about the impacts of truck rollover precursors and, hence, this would lead to the proposition of effective truck safety countermeasures.展开更多
基金the National Natural Science Foundation of China(Grant No.U1760206 and Grant No.51574083)the 111 Project(2.0)of China(No.BP0719037)for the financial support。
文摘An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.
基金Foundation item： Projects（50708093, 50808159） supported by the National Natural Science Foundation of China
文摘In order to improve the reliability of the design and calculation of single piles under the combined vertical and lateral loads, the solutions were presented based on the subgrade reaction method, in which the ultimate soil resistance was considered and the coefficient of subgrade reaction was assumed to be a constant. The corresponding computational program was developed using FORTRAN language. A comparison between the obtained solutions and the model test results was made to show the validity of the obtained solutions. The calculation results indicate that both the maximum lateral displacement and bending moment increase with the increase of the vertical and lateral loads and the pile length above ground, while decrease as the pile stiffness, the coefficient of subgrade reaction and the yielding displacement of soil increase. It is also shown that the pile head condition controls the pile responses and the vertical load may cause the instability problem to the pile. In general, the proposed method can be employed to calculate the pile responses independent of the magnitude of the pile deflection.
基金supported by Washington DOT for traffic crash and road design datasponsored by the Natural Science Foundation of Guangdong,project number 2022A1515011974+1 种基金the Guangdong Provincial Key Laboratory of Modern Civil Engineering Technology Foundation,project number 2021B1212040003the National Natural Science Founda-tion of China,project number 51878297.
文摘Safe and aesthetic interaction between horizontal and vertical alignment may significantly occur when they are combined or closed to each other resulting in safety problems.Previous researches have been limited to focusing on qualitative analysis,which are difficult to implement in the design.To assess the quantitative impact of the combination equilibrium of horizontal and sag vertical curves on safety,KNN,SVR and KNN-SVR machine learning methods were applied for model training to analyze the influence of alignment combination of the horizontal curve(HC)and the sag vertical curve(SVC)on accidents.The highway alignment(a total of 1208 km),the traffic data and accident data from 2011 to 2018 of six interstate roads in Washington,D.C.have been used to train the models.The combination equilibrium of horizontal and sag vertical curves is expressed by the variables such as the radius of the horizontal and vertical curves,the length of the horizontal and vertical curves and the dislocation of horizontal and sag vertical curves.KNN model,SVR model,and KNN-SVR model were built by training the variables as well as the accident rate per 100,000,000 vehicle kilometers.The results show that for the HC-SVC alignment combination,the KNN-SVR model has higher accuracy in predicting the accident rate.At the same time,this paper also suggests the value range of the variables when the horizontal curve radius is small.The research conclusions can provide a reference for the subsequent quantitative optimization design and safety improvement of horizontal and vertical alignment combination.
基金the generous financial support of the Wyoming Department of Transportation (WYDOT)Mountain-Plains Consortium (MPC) (Grant number: 69A3551747108 (FAST Act)) for this study
文摘Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated the impact of different operating speeds when negotiating combined horizontal and vertical curves under unfavorable environmental conditions on Wyoming’s interstates via vehicle dynamics simulation software.The simulation tools provided the acting forces on each tire of the vehicle and the side friction(skidding)margins.This allowed for examining the interaction between vehicle dynamics and road geometry in such alignments.Also,linear regression analysis was implemented to investigate the skidding margins based on the simulation results to demonstrate when a vehicle is more likely to deviate from its desired trajectory.Specifically,this examines the contributing factors that significantly influence the skidding margins.The results indicated that:1)the skidding margins are dramatically decreased by adverse weather conditions even with lower degree of curvature and gradient values of combined curves and more particularly at higher operating speeds conditions.Increasing the vehicle speed on the curve by 10%,the skidding margin dropped by 15%.2)Compared to heavy trucks and sports utility vehicles(SUVs),passenger cars require the highest side friction demand.3)The effect of applying brakes on vehicle stability depends on the road surface condition;applying the brakes on snowy road surfaces increases the potential of vehicle skidding especially for heavy trucks.This study assessed the curve speed limits and showed how important to assign safe and appropriate limits speed since the skidding likelihood is significantly sensitive to the vehicle speeds.This study is beneficial to Wyoming’s roadway agencies since hazardous sections having combined horizontal and vertical curves are identified.Also,critical situations that require additional attention from law enforcement agencies are pinpointed.Finally,recommendations that are valuable to roadway agencies are made based on this study’s findings.
文摘The share of freight transportation is increasing on Wyoming’s roads. These roads are characterized by challenging mountainous terrain and severe crosswinds. The stability of freight trucks in such conditions is of great concern to transportation agencies. Therefore, high-fidelity vehicle dynamics simulation modeling was implemented to investigate the rollover propensity of trucks navigating curves. Scenarios included various road geometric designs, truck characteristics and wind conditions. A multiple linear regression model was also developed to investigate the impact of key parameters on truck rollover propensity. The modeling results indicated that wind speed and direction were influential factors in terms of truck roll stability. Trucks had a 76% higher chance of rolling over when subjected to 40 mph winds relative to being subjected to 20 mph winds assuming all else was unchanged. This study also demonstrated that the most unfavorable wind direction was not perpendicular (90 degrees) to the truck since the truck would continuously change its orientation when traversing combined horizontal and vertical curves. Its speed would also constantly fluctuate. On the contrary, this study’s results indicated that the 120-degree wind direction was the most critical one. Also, under blowing lateral wind conditions, the gross weight of the truck was found to be a contributing factor to rollover risk. Its impact varied depending on the radius of the horizontal curve the truck was navigating. This critical interaction was ignored in the road safety literature. This study offered new insights about the impacts of truck rollover precursors and, hence, this would lead to the proposition of effective truck safety countermeasures.
