Wave damping by flexible vegetation: Connecting individual blade dynamics to the meadow scale
Wave damping by flexible vegetation: Connecting individual blade dynamics to the meadow scale
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DOI：
10.1016/j.coastaleng.2019.01.008
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发表时间：
2019-05-01
影响因子：
4.4
通讯作者：
Nepf, Heidi
中科院分区：
文献类型：
--
作者：
Lei, Jiarui;Nepf, Heidi
水生植被提供了价值很高的生态系统服务，包括减少波浪，保护海岸线和减少再悬浮。本研究提出了一个基于物理的模型来预测与淹没草甸的植物形态，灵活性和拍摄密度的函数波衰减。特别是，该研究考虑了植物的刚性（鞘）和柔性（叶片）部分。灵活的植物重新配置响应波轨道速度，减少波衰减相对于一个刚性的植物相同的形态。重构对波衰减的影响可以使用有效叶片长度l（e）来表征，其表示产生与长度l的柔性叶片相同的阻力的刚性叶片的长度。有效叶片长度取决于柯西数，柯西数定义了水动力阻力与叶片刚度的比值，以及叶片长度与波浪轨道偏移的比值。本实验室研究考虑了如何确定为单个叶片的比例律可以用来预测波衰减的草甸上的多个植物，每个植物由多个叶片连接在一个刚性的茎（鞘）。首先，在一系列波浪条件下研究了单个模型叶片（由低密度聚乙烯制成）上的阻力和运动，以便为理论上确定的有效叶片长度1的比例律提供经验系数。第二，有效的叶片长度预测个别叶片被纳入草地规模的模型来预测波衰减的草地。草地尺度模型考虑了单个植物的刚性和柔性部分。最后，在不同植物密度（每床面积的枝条）的草甸上测量波衰减，并将测量的衰减用于验证波衰减模型。波衰减被证明是相似的草地上定期和随机安排的植物。
Aquatic vegetation provides ecosystem services of great value, including the damping of waves, which protects shorelines and reduces resuspension. This study proposes a physically-based model to predict the wave decay associated with a submerged meadow as a function of plant morphology, flexibility, and shoot density. In particular, the study considers both the rigid (sheath) and flexible (blade) segments of the plant. Flexible plants reconfigure in response to wave orbital velocity, which diminishes wave decay relative to a rigid plant of the same morphology. The impact of reconfiguration on wave decay can be characterized using an effective blade length, l(e), which represents the length of a rigid blade that generates the same drag as the flexible blade of length l. The effective blade length depends on the Cauchy number, which defines the ratio of hydrodynamic drag to blade stiffness, and the ratio of blade length to wave orbital excursion. This laboratory study considered how the scaling laws determined for individual blades can be used to predict the wave decay over a meadow of multiple plants, each consisting of multiple blades attached at a rigid stem (sheath). First, the drag force on and motion of individual model blades (made of low-density polyethylene) was studied for a range of wave conditions to provide empirical coefficients for the theoretically determined scaling laws for effective blade length, 1,. Second, the effective blade length predicted for individual blades was incorporated into a meadow-scale model to predict wave decay over a meadow. The meadow-scale model accounts for both the rigid and flexible parts of individual plants. Finally, wave decay was measured over meadows of different plant density (shoots per bed area), and the measured decay was used to validate the wave-decay model. Wave decay was shown to be similar over meadows with regular and random arrangements of plants.