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，湍流对沉积物的输送都很重要。然而，在风沙输运过程中，湍流事件和脉冲之间的联系很难确定，特别是在非实验室环境中。实地研究的一个不足之处在于，没有测量风速和跃动（沉积物“跳跃”，风搬运沙子的主要方式），精确而严格地控制时间和空间同步。湍流具有很大的时空梯度，因此在米尺度上期望风速和输运率与仪器分离之间有很强的相关性似乎是不合逻辑的。本博士论文研究项目的目标是建立和量化风场和跃场非定常的时空尺度；识别引起输运脉冲的湍流的性质；表征风和输运不稳定性的时空维度；并设计、建造和部署一种新的传感器，用于探测悬浮沙粒。将部署一系列仪器，同时测量泥沙输送和风速的水平和垂直维度。跳跃传感器和风速计将相距2厘米，以确保严格控制空间同步。紊流风事件与沉积物输运脉冲之间的联系将通过变间隔时间平均（VITA）、增强VITA和自相关方法建立。将部署陷阱以获取运输砂的样本，以确定其粒度特征和水分含量。这项研究将在澳大利亚海岸沙丘系统中进行，但其结果将适用于在广泛的环境中发生的风和水的沉积物运输过程。该项目将提供对波动（湍流）风条件下沙的响应的基本理解。这种认识是理解风吹泥沙输运速率模型的不足的必要前提。这项研究可能会对海岸管理者产生影响，因为他们对沉积物运输速率很感兴趣。由吹沙形成的海岸沙丘也可以抵御洪水；这一特征在全球平均海平面上升的时代尤为重要。对风成过程和由此产生的地貌的进一步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运率的能力至关重要。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.