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 n...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.展开更多
Currently joysticks are used for ROVs’interface,though they prove to be tedious and there have been cases of severe damage to the vehicle and subsea architecture due to operator fatigue and attention loss.There is an...Currently joysticks are used for ROVs’interface,though they prove to be tedious and there have been cases of severe damage to the vehicle and subsea architecture due to operator fatigue and attention loss.There is anecdotal evidence to suggest that the ease of manoeuvring with a more intuitive interface design would minimise these damage risks and psychological pressures related to operation.In this study we explored options for a more intuitive physical modality of ROV’s interface.Specifically,we modelled alternative controllers and their operating functions in a 3D environment to provide insight on how they could be used.Three possible conceptual ideas were then proposed,which include the joystick with gesture controllers,the steering wheel with the trackball and the steering wheel with gesture controllers.To further strengthen the ideas presented within this paper and reduce the likelihood of authors’bias,industry experts were consulted,and a formal survey targeting ROV pilots was conducted.To establish the most superior design,a trade-off analysis was conducted by developing a weighted ranking system based on the supporting and opposing arguments and the design’s intuitiveness,with human psychology being used as another means of justification.展开更多
文摘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.
文摘Currently joysticks are used for ROVs’interface,though they prove to be tedious and there have been cases of severe damage to the vehicle and subsea architecture due to operator fatigue and attention loss.There is anecdotal evidence to suggest that the ease of manoeuvring with a more intuitive interface design would minimise these damage risks and psychological pressures related to operation.In this study we explored options for a more intuitive physical modality of ROV’s interface.Specifically,we modelled alternative controllers and their operating functions in a 3D environment to provide insight on how they could be used.Three possible conceptual ideas were then proposed,which include the joystick with gesture controllers,the steering wheel with the trackball and the steering wheel with gesture controllers.To further strengthen the ideas presented within this paper and reduce the likelihood of authors’bias,industry experts were consulted,and a formal survey targeting ROV pilots was conducted.To establish the most superior design,a trade-off analysis was conducted by developing a weighted ranking system based on the supporting and opposing arguments and the design’s intuitiveness,with human psychology being used as another means of justification.
