World Aquaculture - December 2014

44 / 76

42 DECEMBER 2014 • WORLD AQUACULTURE •
help optimize aquaculture netting used in future applications.
Extrapolating our small-scale results to a 20-m diameter net pen in
open-ocean conditions, a 10-mm increase of the mesh void can lead
to a 0.4 GN reduction in the drag force.
Conclusions
With net-pen farms increasingly situated farther offshore, it has
become even more important to understand flow dynamics around
aquaculture pens to predict the load forces applied to the net and to
optimise the farm environment. We have observed that a change in
surface porosity can result in drastically different flow dynamics and
changed dispersion rates of particulate matter through nets.1
A change in surface porosity has an impact on the drag force,
as expected. However, porosity alone is not the main factor in
determining the level of drag, but that it is primarily imposed by the
mesh void size and to some lesser extent by twine thickness.
These results provide a better understanding of the fluid-
structure interaction on a porous structure similar to those used in
commercial net-pen aquaculture and provide a starting point for net-
pen design optimization.
Acknowledgments
The experiments spanned a one-year period and are part
of an ongoing research project on nets of aquaculture pens. This
work is supported by a Faculty of Engineering Faculty Research
Development Fund at the University of Auckland, New Zealand.
Notes
B. Levy, J.E. Cater, R.J. Clarke and J.P. Denier, Department of
Engineering Science, University of Auckland, New Zealand
H. Friedrich, Department of Civil and Environmental Engineering,
University of Auckland, New Zealand
Corresponding author e-mail:
1 Levy, B., H. Friedrich, J.E. Cater, R.J. Clarke and J.P. Denier.
2014. Impact of twine/mesh ratio on the flow dynamics through a
porous cylinder. Experiments in Fluids (submitted).
References
Klebert, P., P. Lader, L.C. Gansel and F. Oppedal. 2013.
Hydrodynamic interactions on net panel and aquaculture fish
cages: A review. Ocean Engineering 58:260-274.
Meggitt, D. and T. Gulli. 2014. An autonomous wave-powered energy
system for net-pen aquaculture. World Aquaculture 45:39-41.
Williamson, C.H.K. 1996. Vortex dynamics in the cylinder wake.
Annual Review of Fluid Mechanics 28:477-539.
Wood, C.J. 1967. Visualization of an incompressible wake with base
bleed. Journal of Fluid Mechanics 29:259-272.
30 YEARS
Aquaculture CanadaOM 2014
June 1-4, 2014
St. Andrews, New Brunswick
“AAC 30th Anniversary – Excellence in Research & Innovation”
This is an exciting year for the Aquaculture Association of Canada as it marks our 30th Anniversary!
There have been numerous innovations in the aquaculture industry over the past 30 years and we
want to celebrate the contributions that the Association and its members have had on the successful
development of the industry in Canada.
The annual conference serves as the main event for the Association and is Canada’s national forum
to bring together the business, science and technology of aquaculture.
Conference coordinator:
Joanne Burry
Tel : 709-437-7203
Email :
Of Excellence
in Research
& Innovation