Mechanisms of the formation of wind-blown sand hazards and the sand control measures in Gobi areas under extremely strong winds along the Lanzhou-Xinjiang high-speed railway

The Lanzhou-Xinjiang high-speed railway(HSR)traverses areas of the Gobi Desert where extremely strong winds are frequent.These strong winds cause sand/gravel hazards,an unaddressed issue that often seriously compromises the safe operation of the HSR.This paper studies the mechanisms leading to wind-blown sand hazards and the outcomes of sand control projects in these areas.The main findings are as follows:(1)Cold northern airflows over the Tian Shan mountain range are accelerated by the wind tunnels and downslope effect as they pass over complex terrain comprising passes,gullies,and proluvial fans.Consequently,the wind intensity often increases two-to threefold,creating frequent high-speed winds that lead to severe sand damage along the HSR.(2)In the Gobi areas with extremely strong winds,sand grains can be lifted as high as 9 m from the ground into the air,far higher than in other areas of the desert.The sand transport rate decreases exponentially with increasing height.Both wind speed and particle size determine saltation height.Coarser particles and stronger winds provide the particles with a higher kinetic energy as they collide with the ground.In the wind zones of Baili and Yandun,the analysed study areas,the saltation layer height of wind-blown sand/gravel exceeds 3 and 2 m,respectively.(3)Based on the above findings,recently emerging sand control materials,suitable for the areas of interest,were screened and developed.Furthermore,under the proposed principle of‘supplementing blocking with trapping’,a comprehensive sand control measure was established,featuring sandblocking belts comprised of multiple rows,and high,vertical sand-trapping installations with a large grids size.The installed system showed a high efficacy,reducing sand transport rate by 87.87%and significantly decreasing the deposition of sand along a trial section of the HSR.

Characteristics of strong winds at the Runyang Suspension Bridge based on field tests from 2005 to 2008

Field measurement of strong wind characteristics is of great significance for the development of bridge wind engineering. Located in east China, the Runyang Suspension Bridge (RSB) with a main span of 1490 m is the longest bridge in China and the third longest in the world. During the last four years, the RSB has suffered from typhoons and strong northern winds on more than ten occasions. To determine the strong wind characteristics of the RSB, wind measurement data obtained from field tests during strong winds and data from the wind environment monitoring subsystem of the structural health monitoring system (SHMS) of the RSB were combined to analyze the wind speed and direction, variation in wind speed with height, turbulence intensity, turbulence integral length, wind friction speed and the power spectrum. Comparative studies on the characteristics of these different strong winds were carried out based on the current wind-resistant design specification for highway bridges. Results showed that some regularity in wind characteristics can be found in these different typhoons passing through the RSB. The difference between a strong northern wind and a typhoon is relatively clear, and in summer the typhoon is the dominant wind load acting on the RSB. In addition, there were some differences between the measured strong wind characteristics and the values suggested by the specification, especially in respect to turbulence intensity and turbulence integral length. Results provide measurement data for establishing a strong wind characteristic database for the RSB and for determining the strong wind characteristic parameter values of this coastal area in east China.

THE ANALYSIS ON THE STATISTICAL CHARACTER OF QUIKSCAT SCATTEROMETER WINDS AND STRONG WIND FREQUENCY USING REMOTE SENSOR DATA FROM QUIKSCAT

The statistical character of QuikSCAT scatterometer winds is showed. And Monthly change and special distribution character of strong wind frequency and monthly wind fields in South China Sea is analyzed. It is shown in the result that the QuikSCAT scatterometer winds can be relied upon for the South China Sea; two winds, one the wintertime northeasterly and the other summertime southwesterly. The northeasterly centers at the Bashi Strait and Taiwam Strait and its secondary center and the maximum center of the southwesterly are in the central and southern South China Sea.

Evaluation of survival stow position and stability analysis for heliostat under strong wind

Heliostats are sensitive to the wind load, thus as a key indicator, the study on the static and dynamic stability bearing capacity for heliostats is very important. In this work, a numerical wind tunnel was established to calculate the wind load coefficients in various survival stow positions. In order to explore the best survival stow position for the heliostat under the strong wind, eigenvalue buckling analysis method was introduced to predict the critical wind load theoretically. Considering the impact of the nonlinearity and initial geometrical imperfection, the nonlinear post-buckling behaviors of the heliostat were investigated by load-displacement curves in the full equilibrium process. Eventually, combining B-R criterion with equivalent displacement principle the dynamic critical wind speed and load amplitude coefficient were evaluated. The results show that the determination for the best survival stow position is too hasty just by the wind load coefficients. The geometric nonlinearity has a great effect on the stability bearing capacity of the heliostat, while the effects of the material nonlinearity and initial geometrical imperfection are relatively small. And the heliostat is insensitive to the initial geometrical imperfection. In addition, the heliostat has the highest safety factor for wind-resistant performance in the stow position of 90-90 which can be taken as the best survival stow position. In this case, the extreme survival wind speeds for the static and dynamic stability are 150 m/s and 36 m/s, respectively.

Determination method of load balance ranges for train operation safety under strong wind

The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).

Non-stationary Buffeting Response Analysis of Long Span Suspension Bridge Under Strong Wind Loading

The non-stationary buffeting response of long span suspension bridge in time domain under strong wind loading is computed. Modeling method for generating non-stationary fluctuating winds with probabilistic model for non-stationary strong wind fields is first presented. Non-stationary wind forces induced by strong winds on bridge deck and tower are then given a brief introduction. Finally,Non-stationary buffeting response of Pulite Bridge in China,a long span suspension bridge,is computed by using ANSYS software under four working conditions with different combination of time-varying mean wind and time-varying variance. The case study further confirms that it is necessity of considering non-stationary buffeting response for long span suspension bridge under strong wind loading,rather than only stationary buffeting response.

Numerical modelling of the sea level under the actions of the tide and strong wind in the Bohai Sea

In this paper, the numerical modelling of the tidal level and current in the Bohai Sea was carried out with ADI method, by taking the sum of four main tidal components M2,S2K2,O1 as the open boundary condition. The calculated values were consistent with the predicted ones (the observed values in the case of calm) in the Tidal Table. On the basis of the modelling of the tide, the sea level and current fields under the effects of strong wind were simulated. The calculated results were also quite satisfactory.

The influence of different underlying surface on sand-duststorm in northern China

In this paper, a quantitative research on the relationship between different underlying surface and sand-dust storm has been made by using 40 years meteorological data of five different types of underlying surface in northern China, which include farmland, grassland, sandland, gobi and salt crust. These metrological data comprise sand-dust storm days and strong wind days. By analyzing, we can find that there are certain correlations between the days of sand-dust storm and strong wind for different underlying surface, which has great influence on sand-dust storm. But there are pronounced differences in different types of underlying surface. The sand-dust storm days of grassland, gobi and salt crust, with smaller interannual variation are obviously less than strong wind days. On the other hand, the sand-dust storm days of farmland and sandland increase evidently, even in many years, are much more than strong wind days. The differences are mainly induced by the influencing mechanism of different underlying surface on sand-dust storm. Grassland, gobi and salt crust with stable underlying surface are not prone to sand-dust storm under strong wind condition. Whereas, the underlying surface of farmland and sandland is unstable, that is easy to induce sand-dust storm under strong wind condition.

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES WITH THE CONSIDERATION OF OROGRAPHIC FACTORS

Based on the barotropic primitive equation in the polar coordinate system and the appropriate assumption, we obtained the mathematical equation of orographic forcing on unit mass air parcel. With the consideration of the frictional stress of the sea and land, supposing that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure is circular, a set of equations are derived, which describe the impact of orographic slope error, the central pressure error and position error of tropical cyclones on the wind field in the tropical cyclone. Typhoon Wipha (2007) is selected to verify the above interpretation method. The results show that the orographic slope, the frictional coefficient, the intensity and position of the cyclone are the important factors which have great influence on the interpretation of wind information about tropical cyclones. The dynamic interpretation method gives very good results, especially for the coastal area. It is applicable to improving the forecasts of the wind field in tropical cyclones.

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES

Based on the primitive equations in polar coordinates and with the supposition that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure agrees with the Fujita formula, a set of equations are derived, which describe the impact of perturbations of central pressure, position of tropical cyclones, direction and velocity of movement of tropical cyclones on the wind field. It is proved that the second order approximation of the kinetic energy of tropical cyclones can be described by the equations under linear approximation. Typhoon Wipha (2007) is selected to verify the above interpretation method, and the results show that the interpretation method of the wind field could give very good results before the landfall of tropical cyclones, while making no apparent improvement after the landfall. The dynamical interpretation method in this paper is applicable to improving the forecasts of the wind field of tropical cyclones close to the coast.

Analysis of the extremely cold and heavy snowfall in North America in January 2015

With global warming and declining Arctic sea ice area in autumn observed by satellites since 1979, anomalous cold snaps in recent winters have affected large parts of North America, Europe, and East Asia. In January 2015, North America suffered extremely cold and heavy snowfall events. As revealed in this paper, the NCEP reanalysis data show that the temperature decreased significantly in January 2015 in North America, including the air temperature in the troposphere and the surface air temperature. Moreover, snow cover increased obviously in January 2015 in North America, while there was a significant negative anomaly of geopotential height. The wind formed the anomalous pattern, which favored cold currents blowing to the North American continent from the polar region, and bringing plenty of water vapor. Our results suggest that the anomalous north wind and decreasing westerly jet stream, which allowed cold and moist air to easily penetrate the North American continent from the Arctic, was one of the main reasons for the extremely cold and heavysnow winter of 2015 in North America.

The Interannual and Interdecadal Variations of Tropical Cyclone Affecting Shandong Province

Based on tropical cyclone yearbook data from 1949 to 2006, climate characteristics, such as interdecadal variation, period of tropical cyclone frequency, rainstorm and strong wind, intensity characteristics, were analyzed. Main results were as follows： tropical cyclone affecting Shanalong Province was mainly from the last ten-day of July to the last ten-day of August, and its interdecadal variation was obvious. The marked periodic variation of every 2.4 and 5 years was found according to power spectrum analysis. It showed obvious weakening tendency about tropical cyclone＇s intensity by using Kendall test. It also showed that August was the strongest month among a year for rainstorm frequency and intensity, and flood disaster was more easily to occur during this month. It was distinct for frequency＇s interdecadal variation of tropical cyclone causing rainstorm and strong wind. Marked period was existed about annual average precipitation and strong wind. At the same time, the cause of the variation was discussed.

Damage index estimation by analysis of meteorological disasters on film plastic greenhouses

This study focuses on the analysis of the effect of meteorological disasters on film plastic greenhouses by typhoons,heavy snow,strong wind,and heavy rain.The data of meteorological disasters from 1998 to 2015 were analyzed on provincial basis to calculate the damage rate depending on the weather cause.The cumulative damage area is 20279 hm2.The damage rates of typhoons,heavy snow,strong wind,and heavy rain are 46.4%,47.4%,2.5%,and 3.8%,respectively.The damage index of the greenhouse,which is the ratio of the greenhouse area to the cumulative damage area,was proposed to estimate the disaster risk for 17 administrative districts.The damage index data and the cumulative damage areas were divided using the Jenks’Natural Breaks method.The average damage index is 0.66,and the damage indices are high in the metropolitan cities.