Wind-sand flow simulation and radius optimization of highway embankment under different vertical curve radius

It is of great practical value to explore the correlation between the vertical curve radius of desert highway and the increase of sand accumulation in local lines,and to select the appropriate vertical curve radius for reducing the risk of sand accumulation.In this study,three-dimensional models of desert highway embankments with different vertical curve radii were constructed,and Fluent software was used to simulate the wind-sand flow field and sand accumulation distribution of vertical curve embankments.The results show that:(1)Along the direction of the road,the concave and the convex vertical curve embankments have the effect of collecting and diverging the wind-sand flow,respectively.When the radius of the concave vertical curve is 3000 m,5000 m,8000 m,10000 m and 20000 m,the wind velocity in the middle of the vertical curve is 31.76%,22.58%,10.78%,10.53%and 10.44%,higher than that at both ends.When the radius of the convex vertical curve is 6500 m,8000 m,10000 m,20000 m and 30000 m,the wind velocity at both ends of the vertical curve is 14.06%,9.99%,6.14%,3.22%and 2.41%,higher than that in the middle.The diversion effect also decreases with the increase of the radius.(2)The conductivity of the concave and convex vertical curve embankments with different radii is greater than 1,which is the sediment transport roadbed.The conductivity increases with the increase of radius and gradually tends to be stable.When the radius of the concave and convex vertical curves reaches 8000 m and 20000 m respectively,the phenomenon of sand accumulation is no longer serious.Under the same radius condition,the concave vertical curve embankment is more prone to sand accumulation than the convex one.(3)Considering the strength of the collection and diversion of the vertical curve embankment with different radii,and the sand accumulation of the vertical curve embankment in the desert section of Wuma Expressway,the radius of the concave vertical curve is not less than 8000 m,and the radius of the convex vertical curve is not less than 20000 m,which can effectively reduce the sand accumulation of the vertical curve embankment.In the desert highway area,the research results of this paper can provide reference for the design of vertical curve to ensure the safe operation of desert highway.

Characteristics of wheel-rail vibration of the vertical section in high-speed railways

In order to analyze the characteristics of wheel-rail vibration of the vertical section in a high-speed railway, a vehicle-line dynamics model is established using the dynamics software SIMPACK. Through this model, the paper analyzes the influence of vertical section parameters, including vertical section slope and vertical curve radius, on wheel-rail dynamics interaction and the acting region of wheel-rail vibration. In addition, the characteristics of wheel- rail vibration of the vertical section under different velocities are investigated. The results show that the variation of wheel load is not sensitive to the vertical section slope but is greatly affected by the vertical curve radius. It was also observed that the smaller the vertical curve radius is, the more severe the interaction between the wheel and rail be- comes. Furthermore, the acting region of wheel-rail vibration expands with the vertical curve radius increasing. On another note, it is necessary to match the slope and vertical curve radius reasonably, on account of the influence of operation speed on the characteristics of wheel-rail vibration. This is especially important at the design stage of vertical sec- tions for lines of different grades.

Radius model of convex vertical curve of freeway based on attachment coefficient

A longitudinal slope brake model was established for the radius calculation of vertical curve of freeway through analyzing the dynamics of brake-running of vehicles running on the longitudinal slope road section. To satisfy the requirement of sight distance, a relation model was established for the attachment coefficient and the convex vertical curve radius. Using MATLAB simulation technique, the convex vertical curve radius at different attachment conditions was calculated accurately and a three-dimensional figure was drawn to describe the relation between the adhesive coefficient, the driving velocity and the radius of vertical curve. The correlation between the convex vertical curve radius and the adhesive coefficient was further analyzed and compared with National Technical Standards. The suggested radius of vertical curve was then put forward to provide a theoretical platform for the security design of the convex vertical curve.

Effect of structural parameters on the hydrodynamic performance of vertical curved V-Type otter board

In order to study the influence mechanism of structural type and size on the hydrodynamic performance of vertical curved V-type otter board,this paper based on the computational fluid dynamics method,a three-dimensional numerical model of vertical curved V-type otter board is established to calculate and analyze its hydrodynamic performance,and the validity of the numerical simulation results is verified by designing and constructing a scaled model for dynamic flume experiments.On this basis,the effects of different structural parameters,such as the deflector angle,camber,and spacing,on the hydrodynamic performance of the vertical curved V-Type otter board are investigated and the optimal structural design scheme is determined.The results demonstrate that single or synchronous changes of the angle,camber,and spacing of the two deflectors have varying degrees of impact on the hydrodynamic performance of the vertical curved V-Type otter board.To improve the expansion effect of the otter board,setting the angle of the deflector A to 40◦and that of the deflector B to 30◦,or setting the camber of deflectors A and B to 18%,or setting the spacing between deflectors A and B to 380 mm and that between the deflector and the main panel to 670 mm can increase the lift coefficient of the vertical curved V-Type otter board to its maximum value.Considering the overall performance of the otter board,when the angle of the deflector A is set to 25◦and that of the deflector B is set to 30◦,or the camber of the deflector A is set to 6% and that of the deflector B is set to 9%,or the spacing between deflectors A and B is set to 340 mm and that between the deflector and the main panel is set to 610 mm,the lift-to-drag ratio of the otter board can be increased to its maximum value.

Impact of combined alignments and adverse weather conditions on vehicle skidding

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.

Causes and Remedies of the Japan＇s Long-lasting Recession： Lessons for China

Japan has suffered from sluggish economic growth and recession since the early 1990s. In this paper, we analyze the causes of the prolonged slowdown of the Japanese economy （the lost decade）. Economies Nobel laureate Paul Krugman has argued that Japan＇s lost decade is an example of a liquidity trap. However, our empirical analysis shows that stagnation of the Japanese economy comes from its vertical IS curve rather than a horizontal LM curve, so the Japanese economy has been facing structural problems rather than a temporary downturn. The vertical IS curve is caused by an insensitivity of investrnent to a lower interest rate partly because of the decline of sales due to the aging population and firms not wanting to invest. The structural problems come from the aging demographic, which is often neglected by scholars and policy-makers, and also from the allocation of transfers from the central government to local governments, and the unwillingness of Japanese banks to lend money to startup businesses and small and medium enterprises （SMEs）, mainly because of Basel capital requirements. Many countries, like China, are expected to face similar issues, particularly given the aging population. The present paper will address why the Japanese economy has been trapped in a prolonged slowdown and provide some remedies for revitalizing the economy.