Effects of gravel mulch on aeolian transport:a field wind tunnel simulation

The shape,size and coverage of gravels have significant impacts on aeolian sand transport.This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation.The tested gravel coverage increased from 5% to 80%,with a progressive increment of 5%.The gravels used in the experiments have three sizes in diameter.Wind velocities were measured using 10 sand-proof pitot-static probes,and mean velocity fields were obtained and discussed.The results showed that mean velocity fields obtained over different gravel mulches were similar.The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces.The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly.According to the present study,the optimal gravel coverage was found to be around 30% or 40%.Threshold velocity linearly increased with gravel coverage.Sand transport rate first increased with height above the wind tunnel floor（Hf）,reaching a peak at some midpoint,and then decreased.

A Model of the Sea-Land Transition of the Mean Wind Profile in the Tropical Cyclone Boundary Layer Considering Climate Changes

The tropical cyclone boundary layer(TCBL)connecting the underlying terrain and the upper atmosphere plays a crucial role in the overall dynamics of a tropical cyclone system.When tropical cyclones approach the coastline,the wind field inside the TCBL makes a sea-land transition to impact both onshore and offshore structures.So better understanding of the wind field inside the TCBL in the sea-land transition zone is of great importance.To this end,a semiempirical model that integrates the sea-land transition model from the Engineering Sciences Data Unit(ESDU),Huang's refined TCBL wind field model,and the climate change scenarios from the Coupled Model Intercomparison Project Phase 6(CMIP6)is used to investigate the influence of climate changes on the sea-land transition of the TCBL wind flow in Hong Kong.More specifically,such a semiempirical method is employed in a series of Monte-Carlo simulations to predict the wind profiles inside the TCBL across the coastline of Hong Kong under the impact of future climate changes.The wind profiles calculated based on the Monte-Carlo simulation results reveal that,under the influences of the most severe climate change scenario,slightly higher and significantly lower wind speeds are found at altitudes above and below 400 m,respectively,compared to the wind speeds recommended in the Hong Kong Wind Code of Practice.Such findings imply that the wind profile model currently adopted by the Hong Kong authorities in assessing the safety of low-to high-rise buildings may be unnecessarily over-conservative under the influence of climate change.On the other hand,the coded wind loads on super-tall buildings slightly underestimate the typhoon impacts under the severe climate change conditions anticipated for coastal southern China.

内蒙古典型沙尘天气过程中风速廓线及PM_(10)的变化特征(英文)

Based on the data of the wind speed from 20 m meteorological tower and PM10 mass concentration in Zhurihe region from January of 2005 to April of 2006,the evolution characteristics of wind speed profile in near surface layer and PM10 in three representative dust weather processes (dust storm,blowing sand and floating dust) were analyzed.The results showed that wind speed was higher during dust storm and blowing sand with remarkable vertical gradient.The speed in floating dust was relatively lower and increased during the whole process.In general,wind speed after dust weather was smaller with respect to that before the event.The average mass concentrations of PM10 in the processes of dust storm,blowing sand and floating dust were in the ranges of 5 436.38-10 000,1 799.49-4 006.06 and 1 765.53 μg/m3,respectively.

Wind-tunnel experimental studies of the spatial snow distribution over grass and bush surfaces

The snow is one of the most important water resources in grassland in northern and western China, while the wind blowing snow due to the strong wind there is a common phenomenon, which can lead to heavy disasters to harm the local animal husbandry and transportation. A reasonable arrangement of the snow protection forests is one of the most economical and effective methods to prevent the wind blowing snow, and a great number of investigations were carried out for its wind block effects. However, the deposition patterns of the snowfall and the blowing snow in the forests are still largely unknown. In this study, the wind tunnel experiments are performed to investigate the influences of the vegetation (grass and bush) on the wind speed profiles and the spatial distribution of the accumulated snow, by using the bran as the snow substitute. The snow blocking abilities of two bush models are analyzed to show the effects of different coverages. The results show that the grass and the bush have different effects on the wind speed profiles, and the snow-blocking abilities of the vegetation and the resulting spatial distribution are determined by the amount of the snowfall, the wind speed, and the height and the coverage of the vegetation. For the engineering design, if the snow is required on the windward side of the vegetation or in the vegetation, the densely arranged forest belts are needed, if the snow is required to accumulate on the leeward side of the vegetation, the sparse forest belts can be used. This work would be helpful as a reference to the reasonable arrangement of the snow-protection forests in pastoral areas.