应土木工程与力学学院、西部灾害与环境力学教育部重点实验室邀请，美国阿拉巴马大学地理系Douglas J. Sherman教授将于2024年8月20日做学术报告，欢迎广大师生参加。
- 报告题目：Wind-Blown Sand: Flux Profiles, Saltation, Reptation, and Creep
- 报 告 人：Douglas J. Sherman教授
- 报告时间：2024年8月20日10:30
- 报告地点：祁连堂322
- 主 持 人：黄宁 教授
报告人简介
Douglas J. Sherman，阿拉巴马大学地理系教授，在多伦多大学获得博士学位。Sherman教授的主要致力于海岸和风沙地貌和沉积过程的研究。根据Google Scholar（2024年8月）的数据显示，他发表了200多篇文章，有6350多次被引用，i100索引为20。他最近的主要研究包括人类对海岸沉积的影响、海岸沉积动力学以及风沙物理学。现为美国科学促进会的会士，并于2023年获得国际风沙研究学会颁发的杰出职业奖(Distinguished Career Award)。
报告摘要
Most wind-blown sand moves as saltation, in concentrations that decrease at exponential rates away from the surface. The trajectories of saltating grains increase in height and length as their coefficient of restitution increases, as is the case for the smaller particles in a grain population. Conversely, it has been indicated that mean saltation trajectory heights, hs50, increase with mean grain size, d50. Similarly, reptation trajectories increase in height with mean grain size. This relationship has important implications for creep transport, all of which moves as reptation. The relationship between hs50 and shear velocity, u*, has also been controversial, with some research indicating a positive relationship while more recent work suggests that there is no relationship. This study presents field data from a series of experiments measuring flux profiles to investigate the sets of relationships associated with the development of aeolian mass flux profiles.
Measurements were made at three sites in the Mojave/Sonoran Deserts of Southern California (CA sites) and three sites in the Jericoacoara National Park in Ceará, Brazil (BR sites). Sites were chosen to represent a range of grain sizes. At each site the data gathering protocols were similar. Flux profile data were obtained using vertical stacks of mesh-traps, grain size statistics were obtained from the trapped sand, and shear velocities were estimated using 3-D ultrasonic anemometer measurements. A total of 63 flux profiles and related data were evaluated.
We evaluated changes in hs50 and dimensionless grain size, hs50 / d50, with changes in u*, dimensionless shear velocity (u* /u*t, where the latter is the threshold shear velocity, estimated with d50), and d50. Regression analysis of these sets of variables found statistically-significant relationships only between hs50 and u* /u*t (inverse: R2 = 62%, P < 0.0001) and hs50 with d50 (positive: R2 = 53%, P < 0.0001). In summary, according to these data, median saltation height depends only on mean grain size.
Reptation load includes or is the same as creep load. The median reptation trajectory height is of the order of 10 d50. Using mean grain sizes to apportion flux loads, the data indicate that creep comprises 4.2% of total load. Further analysis found no significant relationship between creep proportions and u* or u* /u*t. The findings from the analyses summarized above point to further empiricism to improve our understanding of fundamental aeolian processes.