ENERGY EXCHANGE BETWEEN FLUID AND FLAPPING/BENDING STRUCTURES

具有长而灵活的叶或茎的沉水植物通常在许多水生环境中发现，包括河流、湖泊和沿海海域。这些植物对其环境的生态健康和水质做出了许多重大贡献，包括充当避难所、食物来源、捕获和储存颗粒、减少床沙侵蚀和浑浊。用工程术语将水生植物定义为复合材料、各向异性、粘弹性、高度非均质结构。水生植物生活在流动的水域中，承受着复杂的载荷，通常表现为拉伸、压缩、弯曲、扭转和剪切的混合。复杂的、依赖于尺度的流体-植物相互作用仍然没有被很好地理解。特别是，在与阻力产生和阻力控制机制相关的现有知识中存在许多空白。 下半身 水生植物通常埋藏在由各种边界产生的多尺度边界层(BLS)的叠加中，包括植物本身引入的边界。河流和河口的边界层不同于典型的边界层。特别是，它们往往是深度受限的，它们具有多尺度结构，包括河床粗糙度的影响和不同尺度上的植物边界的内部效应，如斑块、茎和叶。天然水流边界层的另一个重要特征是水流深度与粗糙度高度之比很小，因此传统的描述它们的方法，如应用对数流速剖面，应谨慎使用。 下半身 在低淹没边界层中，水生植物受到水流的拖曳。一种有趣且未被探索的流体-结构相互作用是多个柔性体的弯曲，这些柔性体阻碍了流动。这种情况是水生植物生命的一部分，水生植物的形态与它们生存所必须承受的液体流动密切相关。水生植物利用各种策略将阻力降至最低。树叶折叠和植物形状流线化代表了静态重构的例子，以响应变化的速度，而不涉及波浪性或颤动。动态重构是非线性相互作用的结果，即使在固定的流速下，颤振的出现也会不断地改变植物的形状。虽然最近的实验研究主要集中在植物在流水中的重构，但对这一现象的理论和物理解释仍然不是很清楚。本建议旨在推进柔性结构在边界层流动和波浪作用下的流体结构相互作用的最新模拟。为了研究流体流动与柔性结构之间的能量交换，我们计划进行实验和数值模拟。

Submerged plants with long, flexible leaves or stems are commonly found in many aquatic environments, including rivers, lakes and coastal marine waters. These plants make many significant contributions to the ecological health and water quality of their environments, including acting as sanctuary habitats, sources of food, capturing and storing particulates, reducing bed sediment erosion and turbidity. Using the engineering terminology, the aquatic plants can be defined as composite, anisotropic, viscoelastic, highly heterogeneous structures. Living in flowing waters, aquatic plants experience complex loads which are often presented by a mixture of tension, compression, bending, torsion and shear. The complex and scale dependent fluid-plant interactions are still not well understood. In particular, there are many gaps in the current knowledge related to drag-generating and drag control mechanisms.     Aquatic plants are typically embedded in a superposition of multi-scale boundary layers (BLs) generated by a variety of boundaries including those introduced by the plants themselves. BLs in streams and estuaries differ from the canonical boundary layers. In particular, they are often depth-limited, and they have a multi-scale structure involving effect of the bed roughness and internal effects of the plant boundaries at different scales such as patch, stem and leaf. Another important feature of natural stream BLs is a low ratio of flow depth to roughness height and therefore conventional approaches for their description, such as application of the logarithmic velocity profile, should be done with caution.     In low-submergence boundary layers, aquatic plants experience drag forces imposed by the flowing water. An interesting and unexplored fluid-structure interaction is bending of multiple flexible bodies that are instead obstructing a flow. Such a situation is part of the life of aquatic plants whose morphologies are intimately related to the fluid flows they must endure to survive. Aquatic plants utilize various strategies to minimize the drag. Leaves folding and plant shape streamlining represent examples of the static reconfiguration in response to the changing velocity without involvement of waviness or flutter. Dynamic reconfiguration is a result of non-linear interactions leading to the appearance of flutter constantly changing the plant shape even at a fixed flow velocity. Although recent experimental studies have focused on the plant reconfiguration in flowing water,the theoretical and physical interpretations of this phenomenon are still not well understood. The present proposal is intended to advance the state-of-the-art modeling of the fluid structure interactions of flexible structures subjected to boundary layer flow and wave action. Experiments and numerical simulations are planned to study energy exchange between the fluid flow and flexible structures.