Analysis of the turbulent flow and tilt in the codend of a bottom trawl during fishing operations

作者：Kim Yong Hae^*

来源：Ocean Engineering, 2013, 64: 100-108.

DOI：10.1016/j.oceaneng.2013.02.019

• Codend 3-D flow
• Field measurement
• Pitch and roll
• Turbulence rate and period

The water flow inside the codend may affect selectivity via the fish response, such as the herding response or escape behaviour. Turbulent flow was measured at a point in the posterior upper part of the codend of a bottom trawl during six fishing operations using a Nortek Vector as a three-dimensional (3-D) velocimeter, and the relationship between the turbulence rate and codend tilt was analysed at different towing speeds. Turbulent kinetic energy increased to 0.03-0.24 kg m(2) s(-2), but decreased to 12-37% of the turbulence rate with a mean flow velocity of 1.0-1.9 m s(-1). The dominant shortest periods of the 3-D flow using a fast Fourier transform method ranged from 2 to4 s, and the shortest period band using the Morlet continuous wavelet method ranged from 2 to 6 s. The variation in tilt, as represented by the pitch and roll of the codend, decreased significantly with towing speed, whereas the turbulence rate increased with the rate of variation in tilt. These basic results from field measurements could help with understanding the flow inside the codend and could be useful for codend design and further selectivity control.

• 出版日期2013-5-15