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Dynamic positioning operability assessment by using thrust allocation optimization
Published in Selma Ergin, C. Guedes Soares, Sustainable Development and Innovations in Marine Technologies, 2022
C. Fruzzetti, S. Donnarumma, M. Martelli, F. Maggiani
A dynamic positioning system aims to maintain a given position or to follow a given track at low speed controlling simultaneously the surge, sway, and yaw motions. As briefly introduced, the system requires the development of control and allocation logics able to compute the right set-points to send to the actuators starting from the error with respect to the desired position. During the design stages and hence in this analysis, only the force allocation subsystem is taken into account to statically verify that the external forces are sustainable by the propulsion configuration (i.e. the equilibrium between the delivered and the external forces need to be verified). Defining the thrust requirement for each actuator, starting from the vector of required forces and moments, it is necessary to carry out this verification. In this case, the equilibrium is evaluated in the horizontal plane and the two configurations lead to having at least six unknowns. This means that the system is over-actuated and it is not possible to have an analytical solution to the problem. Therefore, to solve the dynamic positioning problem through a static approach it becomes necessary initially to define the external forces involved and then to solve the allocation problem.
Offshore Seamanship
Published in D. J. House, The Command Companion of Seamanship Techniques, 2007
Dynamic positioning is the term used to describe a vessel’s ability to hold station by means of position referencing. It is a concept which is extensively employed on specialized vessels within the offshore industry aboard offshore supply vessels (OSVs), diving support vessels (DSVs), cable laying or other similar survey vessels.
Survey on reliability analysis of dynamic positioning systems
Published in Ships and Offshore Structures, 2023
Fang Wang, Liang Zhao, Yong Bai
The field of offshore dynamic positioning (DP) faces new challenges in safety and risk control due to technological innovations and expanding areas of application. In recent decades, the utilisation of DP systems has significantly increased, resulting in heightened levels of autonomy and complexity on maritime vessels. The International Maritime Organisation (IMO) defines a DP vessel as one that exclusively maintains its position and heading through active thrusters (IMO 1994). Since its inception in the 1960s, DP technology has become indispensable in various maritime and offshore industries. Presently, DP applications encompass a range of critical operations, such as station-keeping for mobile offshore drilling units (MODUs), platform-support vessels during loading/offloading to platforms, diving vessels, loading operations of shuttle tankers from a floating production, storage, and offloading units (FPSOs), and manoeuvring of pipe-layer vessels (Sanchez-Varela et al. 2021; Wang et al. 2022; Gao et al. 2022; Zinchenko et al. 2020). The consequences of a loss of position during these operations can be severe, with the potential for catastrophic outcomes. For instance, the sudden loss of position for a MODU can escalate into a blow-out in the worst-case scenario.
Deep reinforcement learning in dynamic positioning control: by rewarding small response of riser angles
Published in Ships and Offshore Structures, 2022
Fang Wang, Yong Bai, Jie Bai, Liang Zhao
Dynamic Positioning (DP) involves maintaining a vessel’s position and heading while using a computer programme to control the vessel’s actuators. Early work included the use of notch and low-pass filtering, while today’s methods tend to linearise the dynamics and use linear quadratic estimation based on the work carried out by Kalman in the 1960s. Applications include a solution proposed by Balchen et al. (1980) who combined the Kalman Filter (KF) with optimal control. However, as the vessel dynamics are highly nonlinear, inaccuracies arise due to modelling errors as well as time varying environmental or operating conditions. More advanced control methods aiming to combat these issues include the use of gain scheduling, exemplified by Tannuri et al. (2006), who used model-reference adaptive control.
Control of underactuated marine crafts with matched disturbances
Published in International Journal of Control, 2022
Justin M. Kennedy, Alejandro Donaire, Jason J. Ford
Dynamic positioning is the task of stabilising a marine craft to a set position in the presence of environmental disturbances using the vessel's actuators (Sørensen, 2011). This stable positioning is important for certain offshore applications such as cable-laying, diving, and inter-ship transfers (Fossen & Perez, 2009). In general, crafts performing dynamic positioning tasks are fully actuated, however, there has been interest in control designs for underactuated crafts, see for example Aguiar and Pascoal (2007); Do et al. (2002a); Panagou and Kyriakopoulos (2014); Pettersen et al. (2004); Xie et al. (2017). These operations can be dramatically affected by the presence of environmental disturbances acting on the marine craft. The disturbances can be separated into two main forces (Fossen, 2011). The quickly-varying wave forces that act on the vessel at the frequency of the waves, and the slowly-varying or wave-drift forces that arise from long-term ocean currents and wind. These environmental disturbances can be characterised by their frequency spectrum as either a stochastic process (St. Denis & Pierson, 1953) or, as used in offshore engineering applications, as a discrete-frequency representation (Faltinsen, 1990).