Passivity-based Trajectory-tracking for Marine Craft with Disturbance Rejection

This paper presents a Hamiltonian model of marine vehicle dynamics in six degrees of freedom in both body-fixed and inertial momentum coordinates. The model in body-fixed coordinates presents a particular structure of the mass matrix that allows the adaptation and application of passivity-based control interconnection and damping assignment design methodologies developed for robust stabilisation of mechanical systems in terms of generalised coordinates. As an example of application, we follow this methodology to design a passivity-based tracking controller with integral action for fully actuated vehicles in six degrees of freedom. We also describe a momentum transformation that allows an alternative model representation that resembles general port-Hamiltonian mechanical systems with a coordinate dependent mass matrix. This can be seen as an enabling step towards the adaptation of the theory of control of port-Hamiltonian systems developed in robotic manipulators and multi-body mechanical systems to the case of marine craft dynamics.

Deriving optimal fishing effort for managing Australia's Moreton Bay multispecies trawl fishery with aggregated effort data

Deriving an estimate of optimal fishing effort or even an approximate estimate is very valuable for managing fisheries with multiple target species. The most challenging task associated with this is allocating effort to individual species when only the total effort is recorded. Spatial information on the distribution of each species within a fishery can be used to justify the allocations, but often such information is not available. To determine the long-term overall effort required to achieve maximum sustainable yield (MSY) and maximum economic yield (MEY), we consider three methods for allocating effort: (i) optimal allocation, which optimally allocates effort among target species; (ii) fixed proportions, which chooses proportions based on past catch data; and (iii) economic allocation, which splits effort based on the expected catch value of each species. Determining the overall fishing effort required to achieve these management objectives is a maximizing problem subject to constraints due to economic and social considerations. We illustrated the approaches using a case study of the Moreton Bay Prawn Trawl Fishery in Queensland (Australia). The results were consistent across the three methods. Importantly, our analysis demonstrated the optimal total effort was very sensitive to daily fishing costs-the effort ranged from 9500-11 500 to 6000-7000, 4000 and 2500 boat-days, using daily cost estimates of $0, $500, $750, and $950, respectively. The zero daily cost corresponds to the MSY, while a daily cost of $750 most closely represents the actual present fishing cost. Given the recent debate on which costs should be factored into the analyses for deriving MEY, our findings highlight the importance of including an appropriate cost function for practical management advice. The approaches developed here could be applied to other multispecies fisheries where only aggregated fishing effort data are recorded, as the literature on this type of modelling is sparse.

The impact of global positioning systems and plotters on fishing power in the northern prawn fishery, Australia

The impact of global positioning systems (GPS) and plotter systems on the relative fishing power of the northern prawn fishery fleet on tiger prawns (Penaeus esculentus Haswell, 1879, and P. semisulcatus de Haan, 1850) was investigated from commercial catch data. A generalized linear model was used to account for differences in fishing power between boats and changes in prawn abundance. It was found that boats that used a GPS alone had 4% greater fishing power than boats without a CPS. The addition of a plotter raised the power by 7% over boats without the equipment. For each year between the first to third that a fisher has been working with plotters, there is an additional 2 or 3% increase. It appears that when all boats have a GPS and plotter for at least 3 years, the fishing power of the fleet will increase by 12%. Management controls have reduced the efficiency of each boat and lowered the number of days available to fish, but this may not have been sufficient to counteract the increases. Further limits will be needed to maintain the desired levels of mortality.

Clarification of the low-frequency modelling concept for marine craft

This article presents some remarks on models currently used in low speed manoeuvring and dynamic positioning problems. It discusses the relationship between the classical hydrodynamic equations for manoeuvring and seakeeping, and offers insight into the models used for simulation and control system design.

Analysis and prevention of extreme vibration in high speed craft - A research framework

Extreme vibration has been reported for small, high speed craft in the maritime sector, with performance and health threatening effects on boat operators and crew. Musculoskeletal injuries are an enduring problem for high speed craft passengers. Spinal or joint injuries and neurological disorders may occur from repetitive pounding over rough water, continued vibration and single impact events. The risk from whole body vibration (WBV) induced through the small vessels mainly depends on time spent on the craft, which can’t be changed in a military scenario; as well as the number of shocks and jolts, and their magnitude and frequency. In the European Union for example, physical agents directives require all employers to control exposure to a number of physical agents including noise and vibration. The EC Vibration Directive 2002/44/EC then sets out regulations for the control of health and safety risks from the exposure of workers to hand arm vibration (HAV) and WBV in the workplace. Australia has exposure standards relating to WBV, AS 2670.1-2001 – Evaluation of human exposure to whole body vibration. This standard is identical to the ISO 2631-1:1997, Mechanical vibration and shock – Evaluation of human exposure to whole-body vibration. Currently, none of the jurisdictions in Australia have specific regulations for vibration exposures in workplaces. However vibration is mentioned to varying degrees in their general regulations, codes of practice and guidance material. WBV on high speed craft is normally caused by “continuous 'hammering' from short steep seas or wind against tide conditions. Shock on High Speed Craft is usually caused by random impacts. Military organisations need the knowledge to make informed decisions regarding their marine operations, compliance with legislation and potentially harmful health effects, and develop and implement appropriate counter-measures. Marine case studies in the UK such as published MAIB (Marine Accident Investigation Branch) reports show injuries that have occurred in operation, and subsequent MCA (Maritime Coastguard Agency) guidance is provided (MGN 436 (M+F), WHOLE-BODY VIBRATION: Guidance on Mitigating Against the Effects of Shocks and Impacts on Small Vessels. MCA, 2011). This paper proposes a research framework to study the origin, impact and pathways for prevention of WBV in small, high speed craft in a maritime environment.