An Experimental Study on the Hydrodynamic Drag of Flexible Seaweed Mimics in a Uniform Current

Zhilong Wei, Trygve Kristiansen, David Kristiansen, Yanlin Shao

Research output: Contribution to conferenceConference abstract for conferenceResearchpeer-review

Abstract

An extensive series of model tests was conducted to investigate the hydrodynamic drag of flexible seaweed mimics in a uniform current. The material selected for modelling kelp blades was silicone rubber (E=5.36±0.4MPa, ρ=1264.5±66.0kg/m^3). The primary non-dimensional parameter examined is the Cauchy number (Ca), which represents the ratio of external drag to the internal stiffness of the blade. The experiments spanned a wide range of Ca values, from 102 to 106, revealing two distinct motion regimes: the static regime and the fluttering regime.

In the static regime, a balance between drag force and bending stiffness (buoyancy as well for non-neutrally buoyant structures) leads to a static blade position and a reduction in drag. Upon reaching a critical Ca value, fluttering occurs, and the blade motion becomes dynamic. At this point, a noticeable change in drag reduction is observed, shifting from a monotonically decreasing trend to an almost constant value.

The study found that drag reduction and critical Ca depend little on the blade's aspect ratio. However, the buoyancy parameter (the ratio of buoyancy to bending stiffness) plays a significant role in both regimes. A smaller buoyancy parameter results in a lower critical Ca and greater drag reduction in the static regime, but less drag reduction in the post-critical regime. Additionally, the line density of the blades (number of blades per unit length) significantly affects both the critical Ca and the drag reduction after the critical point. Based on the experimental results, a rough estimate of the drag coefficient CD is also provided.
Original languageEnglish
Publication date2025
Number of pages1
Publication statusPublished - 2025
EventThe 25th DNV Nordic Maritime Universities Workshop - Technical University of Denmark, Kgs. Lyngby, Denmark
Duration: 30 Jan 202531 Jan 2025

Workshop

WorkshopThe 25th DNV Nordic Maritime Universities Workshop
LocationTechnical University of Denmark
Country/TerritoryDenmark
CityKgs. Lyngby
Period30/01/202531/01/2025

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