Rapid monitoring of river hydrodynamics and morphology using acoustic holography

准确的河流流量测量对于建立校准良好、可靠的模拟模型至关重要，这些模型能够准确地预测洪水发生的时间和程度，并为有效管理河流流域的水资源提供所需的数据。本项目将开发一种新的声波全息测量方法，用于遥测河道内的流速、水深和河床特性。所提出的全息方法记录了动态流面上的反射声波的图案(全息图)，并使用该图案来重建整个三维空间区域的水面波场。该项目将使用计算流体力学和湍流理论的最新进展。其基本概念是，湍动河流的自由面从来不是平坦的，而且总是动态粗糙的。有确凿的证据表明，河流自由面的三维形态是由水流内部的湍流结构引起的。这些结构在河床上产生并上升到自由面，并以面波模式的形式表现出来，面波以特定的速度传播，而不一定与平均地表水速度一致。因此，自由面波纹图携带了关于水流中基本水动力过程的全面信息，包括水流速度、深度、湍流尺度和强度以及床面粗糙度特性。这一过程是非常复杂的，过去由于缺乏准确和可靠的仪器和准确的流体动力学模型来将自由表面波型与下面的流动结构联系起来，所以对它的研究还不够充分。因此，现在有机会清楚地了解在河流自由表面上观察到的模式与河流环境中的基本湍流结构和河床表面粗糙度如何相互作用。这种湍流河流流体动力学的新知识与新的声学全息测量能力相结合，将在河流流量监测的准确性、空间分辨率和部署速度方面提供范例转变。在这方面，与国际上这一领域更广泛的研究背景相比，拟议的工作具有非常高的新颖性。这项提议是及时的，因为它将大大有助于我们需要更好地了解我们的自然环境，特别是在极端条件下，以及在机器人和自主传感器技术的发展方面。这些技术在David Willetts的一份报告中被概述为英国应该推广和开发的“八大技术”之一。威利茨夫妇的报告还指出，对河流的实时预报、更好的水资源管理和自主监控工具的需求非常明显，这些都需要准确的车载传感。我们的项目朝着提供技术来满足这些需求迈出了重要的一步。新的传感器技术还将在波传播、反问题、全息术、信号处理和计算流体力学领域发展新的理论基础。

Accurate flow measurement in rivers is vital to build well calibrated, reliable simulation models able to predict accurately the timing and extent of floods, and also to provide the data needed for effective management of water resources in a river catchment. This project will develop a new method of acoustic wave holography to measure remotely the velocity, flow depth and bed characteristics within river channels. The proposed holography method records the pattern of reflected acoustic waves (the hologram) above a dynamic flow surface and uses this pattern to reconstruct the water surface wave field throughout a three-dimensional region of space. The project will use recent advances in computational fluid mechanics and turbulence theory. The underpinning concept is that the free surface of turbulent river flows is never flat and is always dynamically rough. There is overwhelming evidence that the 3-dimensional pattern of the free surface of a river flow is caused by the turbulence structures within the flow. These structures are generated at the river bed and rise to the free surface and express themselves in the form of a pattern of surface waves which propagate at a particular velocity which does not necessarily coincide with the mean surface water velocity. Therefore, the free surface wave pattern carries comprehensive information about the underlying hydrodynamic processes in the flow, including the flow velocity, depth, turbulence scale and intensity and bed roughness characteristics. This process is very complex and it has not been sufficiently studied in the past because of a lack of accurate and robust instruments and accurate fluid dynamics models to relate the free surface wave pattern to the flow structure beneath. Thus, there is now an opportunity to develop a clear understanding how the pattern observed on the free surface of a river flow and the underlying turbulence structures and bed surface roughness in fluvial environments interact. This new knowledge in the hydrodynamics of turbulent river flows combined with new acoustic holographic measurement capabilities will provide a paradigm shift in the accuracy, spatial resolution and speed of deployment of flow monitoring in rivers. In this respect, the proposed work has a very high degree of novelty in comparison to the broader research context of this area internationally. The proposal is timely because it will contribute significantly to the need for us to better understand our natural environment especially under extreme conditions and in the development of Robotics and Autonomous Sensor technologies. These technologies were outlined in a report by David Willetts as one of the "Eight Great Technologies" that should be promoted and developed by the UK. The Willetts' report also states a clear need for real time forecasting of rivers, better water resource management and autonomous surveillance vehicles which require accurate on-board sensing. Our project takes an important step towards providing technology to address these requirements. The new sensor technology will also enable new theoretical foundations to be developed in the areas of wave propagation, inverse problems, holography, signal processing and computational fluid dynamics.