Doctoral Dissertation Research Improvement: Kinetics of Wind-Blown Sand: An Investigation of Unsteadiness in Saltation Systems

无论是在空气中还是在水中，湍流对泥沙的输送都很重要。然而，很难确定风沙输运中的湍流事件和脉冲之间的联系，特别是在非实验室环境中。实地研究的一个不足之处是，没有人测量风速和跃变(泥沙“跳跃”，这是风输送沙子的主要方式)，并精确而严格地控制时间和空间同步。湍流具有很大的时间和空间梯度，因此期望风速和传输速率与仪器在米级尺度上的分离之间存在强烈的相关性似乎是不合逻辑的。这项博士论文研究项目的目标是建立和量化风和跃变场中不稳定的空间和时间尺度；识别引起输送脉冲的湍流的性质；表征风和输送不稳定的时空维度；以及设计、制造和部署用于探测跳跃沙粒的新传感器。将部署一系列仪器，以同时测量泥沙运移和风速的水平和垂直维度。跳跃传感器和风速计将被放置在相距2厘米的位置，以确保严格控制空间同步。将使用可变间隔时间平均(VITA)、增强VITA和自相关方法来建立湍流风事件与泥沙输送中的脉冲之间的联系。将部署捕集器以获取运输沙子的样本，以确定其粒度特征和水分含量。这项研究将在澳大利亚沿海沙丘系统中进行，但结果将适用于在广泛的环境下在风和水中发生的泥沙输送过程。该项目将提供对沙子对波动(湍流)风条件的响应的基本理解。这一理解是理解风沙输移率模型缺陷的必要先导。这项研究可能会对海岸管理者产生影响，因为他们对泥沙输移率感兴趣。通过吹沙建造的沿海沙丘也提供了抵御洪水的能力；在全球平均海平面正在上升的时候，这一特征尤为重要。增加对风沙过程和由此产生的地貌的了解将提高管理或保护沿海环境的能力。了解风和沙之间的基本关系对于提高预测泥沙输移率的能力至关重要。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Turbulence is important to sediment transport, whether in air or water. Linkages between turbulent events and pulses in aeolian sediment transport have been difficult to establish, however, especially in non-laboratory environments. One deficiency with field-based studies is that none measured wind velocity and saltation (sediment "jumping," the primary mode of sand transport by wind) with precisely and tightly controlled time and space synchronization. Turbulence has large temporal and spatial gradients, so it seems illogical to expect strong correlations between wind speed and transport rates with instrument separations at meter scale. The goal of this doctoral dissertation research project is to establish and quantify the spatial and temporal scales of unsteadiness in wind and saltation fields; to identify the nature of turbulence causing transport pulsing; to characterize the spatial and temporal dimensions of wind and transport unsteadiness; and to design, build, and deploy a new sensor for the detection of saltating sand grains. Arrays of instruments will be deployed to simultaneously measure the horizontal and vertical dimensions of sediment transport and wind speed. Saltation sensors and anemometers will be placed 2 cm apart to ensure tightly controlled space synchronization. Linkages between turbulent wind events and pulses in sediment transport will be established using variable interval time averaging (VITA), enhanced VITA, and autocorrelation methods. Traps will be deployed to obtain samples of transporting sand to determine their grain size characteristics and moisture content. The research will be conducted in an Australian coastal dune system, but the results will be applicable to sediment transport processes occurring in wind and water at a broad range of settings.This project will provide a fundamental understanding of the response of sand to fluctuating (turbulent) wind conditions. This understanding is a necessary precursor to understanding the deficiencies of wind-blown sediment transport rate models. This research may have implications to coastal managers because they are interested in sediment transport rates. Coastal dunes built by blowing sand also provide a defense against flooding; a characteristic that is especially important in a time where the average global sea level is rising. An increased understanding of aeolian processes and the resultant landforms will improve capabilities to manage or preserve coastal environments. It is essential that fundamental relationships between wind and sand are understood to improve the ability to predict sediment transport rates. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.