ENERGY EXCHANGE BETWEEN FLUID AND FLAPPING/BENDING STRUCTURES

具有长而灵活的叶子或茎的水下植物通常存在于许多水生环境中，包括河流，湖泊和沿海海水。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，包括作为避难所栖息地、食物来源、捕获和储存颗粒、减少河床沉积物侵蚀和浊度。用工程术语来说，水生植物可以定义为复合的、各向异性的、粘弹性的、高度非均质的结构。水生植物生活在流动的水中，它们承受着复杂的载荷，这些载荷通常由张力、压缩、弯曲、扭转和剪切混合而成。复杂的和规模依赖的流体-植物相互作用仍然没有很好地理解。特别是，在当前与拖动产生和拖动控制机制相关的知识中存在许多空白。水生植物通常嵌入在由各种边界（包括植物自身引入的边界）产生的多尺度边界层（BLs）的叠加中。河流和河口的边界层不同于典型边界层。特别是，它们往往是深度有限的，并且具有多尺度结构，涉及床的粗糙度效应和不同尺度（如斑块、茎和叶）植物边界的内部效应。天然流BLs的另一个重要特征是流动深度与粗糙度高度的比例较低，因此，使用对数速度剖面等传统方法来描述BLs时应谨慎。*** *在低淹没边界层中，水生植物受到流水施加的阻力。一个有趣的和尚未开发的流体-结构相互作用是多个柔性体的弯曲，而不是阻碍流动。这种情况是水生植物生命的一部分，它们的形态与它们必须忍受的流体流动密切相关。水生植物利用各种策略来减少阻力。叶片折叠和植物形状流线型是响应速度变化而不涉及波浪或颤振的静态重构的例子。动态重配置是非线性相互作用的结果，导致颤振的出现，即使在固定的流速下也会不断改变植物的形状。虽然最近的实验研究集中在流动水中植物的重新配置，但这一现象的理论和物理解释仍然没有得到很好的理解。本研究旨在推动柔性结构在边界层流动和波动作用下的流体结构相互作用的最新建模。为了研究流体流动与柔性结构之间的能量交换，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.