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Experimental modelling of transverse oscillations in aquaculture netting parallel to the flow sounds baffling

Citation

Johnson, A and Balash, C, Experimental modelling of transverse oscillations in aquaculture netting parallel to the flow sounds baffling, China Ocean Engineering, 29, (3) pp. 391-400. ISSN 0890-5487 (2015) [Refereed Article]

Copyright Statement

Copyright 2015 Chinese Ocean Engineering Society and Springer-Verlag Berlin Heidelberg

DOI: doi:10.1007/s13344-015-0027-x

Abstract

Numerous studies have been undertaken to improve the viability, durability and suitability of materials and methods used for aquaculture enclosures. While many of the previous studies considered macro-deformation of nets, there is a paucity of information on netting micro-deformation. When aquaculture pens are towed, industry operators have observed the motion described as "baffling" the transverse oscillation of the net planes parallel and near parallel to the flow. The difficulty to observe and assess baffling motion in a controlled experimental environment is to sufficiently reproduce netting boundary conditions and the flow environment experienced at sea. The focus of the present study was to develop and assess experimental methods for visualisation and quantification of these transverse oscillations. Four netrig configurations with varied boundary conditions and model-netting properties were tested in a flume tank. While the Reynolds number was not equivalent to full-scale, usage of the pliable and fine mesh model netting that enabled baffling to develop at low flow velocities was deemed to be of a larger relevance to this initial study. Baffling was observed in the testing frame that constrained the net sheet on the leading edge, similarly to a flag attachment onto a pole. Baffling motion increased the hydrodynamic drag of the net by 35%58% when compared to the previously developed formula for taut net sheets aligned parallel to the flow. Furthermore, it was found that the drag due to baffling decreased with the increasing velocity over the studied Reynolds numbers (below 200); and the drag coefficient was non-linear for Reynolds numbers below 120. It is hypothesised that baffling motion is initially propagated by vortex shedding of the netting twine which causes the netting to oscillate; there after the restoring force causes unstable pressure differences on each side of the netting which excites the amplitude of the netting oscillations.

Item Details

Item Type:Refereed Article
Keywords:baffling, aquaculture pen, netting micro-deformation, netting drag, model net testing
Research Division:Engineering
Research Group:Maritime Engineering
Research Field:Ocean Engineering
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in Engineering
Author:Johnson, A (Mr Andrew Johnson)
Author:Balash, C (Dr Cheslav Balash)
ID Code:105332
Year Published:2015
Web of Science® Times Cited:3
Deposited By:NC Maritime Engineering and Hydrodynamics
Deposited On:2015-12-18
Last Modified:2017-06-22
Downloads:0

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