MRI: Development of Pneumatic Water Wave Genesis, a versatile wavemaker for the UNC Joint Fluids Lab

该项目的目标是开发一种潜在的变革性的新型表面和内部波浪制造方法，基于一种新颖的气动概念，没有机械执行器，并使用它来极大地扩展在UNC联合流体实验室模块化波浪箱中进行的科学研究活动的范围。研究人员打算证明一种在非均匀不可压缩流体中激发一般重力波的方法的可行性。该方法使用一组独立控制的单极子磁通源来提供任意二维流形上的磁通边界条件。开发的实际结果将是一个波浪产生装置，用于现有的0.75[m]宽，36[m]长的波浪槽，其中含有规定的盐分层密度剖面的水。发生器将激发一个1[m] × 0.75[m]的矩形边界，该边界由N个独立的矩形磁通源组成，每个磁通源宽0.75[m]，高1/N[m]，垂直堆叠。这个边界被插入一个波浪槽，形成一个活动水槽的一端。每个源将驱动其孔径上接近空间均匀的体积速度。从而可以激发水平阶为零阶和垂直阶为（N-1）阶的波形。提出的设计灵感来自法国国家科学院-里昂研究所（Gostiaux et al. 2007）最近开发的一种产生单色平面波的机械致动器系统。然而，拟议的设备将远远超出这种设计，通过取消机械运动部件，并取代由能够跟随任意带限控制信号的反馈控制气动激励器产生的空气压力驱动的位移室。这允许产生任意垂直激励剖面，包括但不限于不同周期和方向的单色平面波的叠加。这种设计将进一步实现其他有趣的激励，包括非周期性甚至非重复的脉冲剖面。在未来，这种一般的激励方法原则上可以通过镶嵌任意形状的边界表面，将这些能力扩展到完全二维的边界通量条件。表面波和它们不太为人所知的内部对应波，例如可能发生在淡水和咸水之间的层中，都具有比通常认识到的更重要的后果的特性。举几个例子，一个流氓浪的自发发展可以击沉一艘船；海啸的形成和发展，因为它在开阔水域和登陆时（如在港口）传播，可以在一些地方造成严重破坏，而使其他地方相对毫发无损；内波对咸水层和淡水层混合的影响有助于河口的生态健康和栖息在河口的物种的福祉。通过将猜测转化为坚实的物理和工程数学模型，在造船、灾害预测、环境影响以及许多其他应用领域中有用，不断发展出大量的理论来理解这些所谓的重力波行为，并使其可预测。但这些理论到底有多好呢？科学方法的基础是实验验证，重力波力学也不例外。该项目解决的问题是找到一种在实验室环境中重复产生和可控地改变条件的方法，相当于自然现象，如异常波。通常，与这种现象有关的理论只经过有限的测试，使基于此的海军、环境和生态工程决策容易出错。制造波澜很容易：往波澜罐里扔块石头。创造精确的条件来激发水箱中的异常波，并探索不同的参数如何影响这种行为，甚至是这种波的存在，都需要在控制这些条件方面有相当高的技巧。该项目的目的是开发一种波发生器，用于激发非均匀不可压缩流体中的一般重力波，从而使在受控的实验室环境中对具有社会和工程相关性的现实世界现象进行实验探索。

The goal of this project is to develop a potentially transformative new surface and internal wave-making method, based on a novel pneumatic concept with no mechanical actuators, and use it to dramatically extend the range of scientific research activities taking place in the UNC Joint Fluids Lab modular wavetank. The investigators intend to demonstrate feasibility of a method for excitation of a general family of gravity waves in non-uniform incompressible fluids. The method uses an array of independently controlled monopole flux sources arranged to provide a flux boundary condition over an arbitrary 2D manifold. The tangible results of the development will be a wave generating apparatus for use in an existing 0.75[m] wide by 36[m] long wave tank containing water with prescribed salt-stratified density profiles. The generator will excite a 1[m] by 0.75[m] rectangular boundary comprising N independent rectangular flux sources, each being 0.75[m] wide by 1/N[m] high, stacked up vertically. This boundary is inserted into a wave tank to form one end of an active flume. Each source will drive a near-spatially-uniform volume velocity over its aperture. Wave modes of zeroth horizontal order and up to (N-1)th vertical order can thereby be excited. The proposed design was inspired by a recently developed mechanical actuator system designed at ENS-Lyon (Gostiaux et al. 2007) to produce monochromatic plane waves. However, the proposed apparatus will go well beyond this design, by doing away with the mechanical moving parts, and substituting displacement chambers driven with air pressures generated by feedback-controlled pneumatic exciters capable of following arbitrary band-limited control signals. This allows generation of arbitrary vertical excitation profiles, including but not limited to superpositions of monochromatic plane waves of differing periods and directions. This design will further enable other interesting excitations, including non-periodic or even non repetitive impulse profiles. In the future, this general excitation method can in principle extend these capabilities to fully 2D boundary flux conditions, by tessellating an arbitrarily shaped boundary surface.Both surface waves and their less widely known internal counterparts, which can occur for example in layers between fresh and salt water, have properties of more significant consequences than are generally appreciated. To name a few, the spontaneous development of a rogue wave can sink a ship; the formation and development of a Tsunami as it propagates in open water and upon landfall such as in a harbor can wreak havoc in some places while leaving others relatively unscathed; and the effects of internal waves on mixing stratified salt and fresh water layers contributes to the ecological health of an estuary and the well being of the species inhabiting it. A substantial body of theory continues to be developed to understand these so-called gravity wave behaviors and to render them predictable, by turning guesswork into solid physical and engineering mathematical models useful in naval architecture, disaster prediction, environmental impact, among many other areas of application. But precisely how good are these theories? Fundamental to the Scientific Method is experimental verification, and gravity wave mechanics is no exception. The problem addressed by this project is that of finding a method to repeatably generate and controllably vary the conditions in a laboratory environment equivalent to natural phenomena such as rogue waves. Often, theories pertaining to such phenomena undergo only limited testing, leaving the naval, environmental and ecological engineering decisions based thereon vulnerable to error. Making waves is easy: drop a stone in a wavetank. Creating the exact conditions to excite a rogue wave in a tank, and exploring how varying parameters affects the behavior or even the existence of such a wave requires an exquisite degree of finesse in controlling these conditions. The aim of this project is to develop a wavemaker for excitation of a general family of gravity waves in non-uniform incompressible fluids, thereby enabling experimental exploration in a controlled laboratory environment of real world phenomena having social and engineering relevance.