Rapid monitoring of river hydrodynamics and morphology using acoustic holography

精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，这些模型能够准确预测洪水的时间和范围，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技术，用于远程测量河道内的流速、流深和河床特征。所提出的全息方法记录了动态流表面上反射声波的模式（全息图），并利用该模式重建了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。基本的概念是，湍急的河流的自由表面从来不是平坦的，总是动态粗糙的。有压倒性的证据表明，河流流动的自由表面的三维模式是由流动中的湍流结构引起的。这些结构在河床上产生，上升到自由水面，并以表面波的形式表现出来，这些表面波以特定的速度传播，不一定与平均地表水速度一致。因此，自由表面波型包含了流动中底层水动力过程的全面信息，包括流速、深度、湍流尺度和强度以及床层粗糙度特征。这一过程非常复杂，由于缺乏准确可靠的仪器和精确的流体动力学模型来将自由表面波模式与下面的流动结构联系起来，过去对它的研究还不够充分。因此，现在有机会对在河流自由表面上观察到的模式和河流环境中潜在的湍流结构和河床表面粗糙度如何相互作用有一个清晰的认识。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，将为河流流量监测的准确性、空间分辨率和部署速度提供范式转变。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。这个建议是及时的，因为它将大大有助于我们更好地了解我们的自然环境，特别是在极端条件下，以及机器人和自主传感器技术的发展。这些技术在David Willetts的一份报告中被概述为英国应该推广和发展的“八大技术”之一。Willetts的报告还明确指出了对河流实时预报、更好的水资源管理和需要精确车载传感的自动监控车辆的需求。我们的项目朝着提供满足这些需求的技术迈出了重要的一步。新的传感器技术还将为波传播、逆问题、全息、信号处理和计算流体动力学等领域提供新的理论基础。

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.