Offshore Boom Research Articles

Constrained model predictive control for 3-D offshore boom cranes

Offshore boom cranes are complex nonlinear underactuated systems, whose control problems, when considering the 3-dimensional (3-D) model affected by ship-induced disturbances, are full of various challenges. In fact, it still remains an open problem to efficiently control the 3-D offshore boom cranes. Moreover, most existing works on offshore cranes concentrate upon designing the force/torque controller, whose performance degrades badly in the presence of friction. In this paper, considering the above issues, a novel model predictive control (MPC) method, which successfully considers the constraints of both input and output of the system, is proposed to achieve satisfactory control performance even under the effect of persistent ship roll and heave perturbations. Specifically, a discrete model is first obtained by some careful transformation and discretization on the unactuated dynamics equations, based on which a novel model predictive controller is constructed. To reduce the complexity of the system, the unactuated states and the accelerations of actuated states are considered as system states and control inputs respectively. After that, the requirements for the payload position accuracy and swing suppression as well as other system constraints, are taken into full account by converting them into input constraints to facilitate subsequent handling. At last, hardware experiments are implemented on a self-built testbed, with the obtained results clearly illustrating the effectiveness and robustness of the proposed method.

Dynamic characteristics of series-parallel hybrid rigid-flexible coupling double-mass underactuated system on floating platform

For heavy cargo swing suppression on offshore boom cranes, a cable-driven series-parallel hybrid double-mass active anti-swing mechanism is proposed, which is a typical non-smooth coupled oscillator. To facilitate the study of dynamic characteristics of the system, the cargo swings were decomposed into two decoupled swings. Then, the kinematics is built using the influence coefficient principle. Considering the longitudinal vibration, cables were regarded as piecewise spring-damping systems. Subsequently, an 18-DOF non-smooth dynamic model with actuators was obtained. Additionally, the influence of the floating platform's excitations and the system's initial state on responses was investigated by numerical solution. Analysis tools such as the phase trajectory and Poincaré map were used to explore the dynamic characteristics, and the results exhibit the existence of out-of-plane behavior, secondary resonance, asymmetric oscillation, and chaos. Finally, experiments were performed to validate the dynamics and performance of an open-loop anti-swing method. This study will be significant for further research on anti-swing controllers.

Online trajectory planning for three-dimensional offshore boom cranes

Efficient control of offshore cranes has attracted world-wide attention in recent years. However, due to the persistent ship roll/heave motion disturbances, it is very challenging to guarantee the transient performance for offshore cranes. To solve this problem, this paper proposes an online trajectory planning method for three-dimensional offshore cranes. Specifically, preliminary trajectories are first designed for different crane motions (e.g., boom luffing rotating, rope hoisting motions), following which the cargoes can be delivered to designated sites. After that, some online adjustment terms are integrated with the pre-defined trajectories, which serve to attenuate or eliminate the undesired cargo swing introduced by both the improper crane operations and the ship motion disturbances. Different from traditional off-line planning methods, the proposed method retains satisfactory robustness (in the sense of swing elimination) due to the extra incorporated terms. The proposed control concept can be extended to trajectory planning of similar underactuated systems.

Nonlinear antiswing control for offshore boom cranes subject to ship roll and heave disturbances

This paper studies the automatic control problem of offshore boom cranes, which often work in harsh sea conditions. First, some novel composite signals are elaborately designed, which consist of both payload swing information and boom/rope positioning error. By utilizing the composite signals as feedback, the constructed nonlinear controller manages to react more efficiently to the uncertainties/disturbances, and hence achieves better overall control performance and stronger robustness. Particularly, the control gains are updated in real time according to the system dynamic response, so as to further improve the efficiency of the designed controller. Through rigorous mathematical deductions, it is proved that the system state variables converge to the desired values asymptotically. The conducted experiments show that the proposed method can accurately position the payload, while simultaneously suppressing its swing motion.

An assessment of the feasibility of using skirt containment boom together with paravanes for offshore response

Abstract The use of conventional offshore containment boom is a recognised way of containing and recovering oil spilt at sea. However, there are various operational and logistical challenges with their use. One of the largest being that their containment becomes ineffective when towed through the water at speeds of greater than 0.75 knots. Containment and collection of oil using high speed systems allows for greater tow speeds (2–3 knots) without failure and can be operated with a paravane as a single ship system. Oil Spill Response Limited (OSRL) have had numerous requests from its members to supply offshore containment and recovery systems suitable for a single vessel deployment. The reason for this was to help with the challenges of low availability of vessels suitable for offshore operations and to reduce high costs. OSRL have used manufacturers guidance to advise its members on the best options however wished to have its own data to further support this guidance and provide user-validated recommendations to its members. OSRL have investigated the viability of using a paravane with a conventional offshore boom using field tests. These tests focused on vessel tow speed, current speed, boom containment effectiveness and encounter area. A number of deployments were carried out using conventional inflation boom and a medium sized paravane in Southampton Water, UK in 2018 (Figure 1). Observations were gathered to identify the point of boom failure when towed at different speeds and whether a suitable encounter area could be achieved. This poster will provide the detail on the feasibility of towing a conventional offshore boom with a single vessel and paravane, see boom configuration in Figure 2. It will outline specifications and parameters which make for a successful / unsuccessful deployment of conventional boom with paravane and provide recommendations for Tier 1 single vessel deployment equipment.

Backstepping Control of Heavy Lift Operations with Crane Vessels

Offshore structures with large mass are installed and removed by heavy lift vessels. During offshore constructions, two safety-critical interconnected operations take place, the dynamic positioning of the vessel and the lifting of the heavy structure by an immovable boom crane on the vessel. Existing studies on offshore boom crane control either neglect the structure (load) dynamics in sway and the vessel movement, or consider the boom angle of the crane controllable. In this paper, we present a control scheme for underactuated offshore structure, taking into consideration the impact of the dynamic positioning of the vessel on the physical load model. The proposed control scheme is designed following a backstepping control approach using command filtering to generate virtual control signals and their derivatives avoiding the analytic differentiation. Simulation results are obtained by applying the control scheme in a dynamic positioned vessel-load model showing that the controller is able to stablize the load position during the vessel dynamic positioning.

Towards structure-independent stabilization for uncertain underactuated Euler–Lagrange systems

Available control methods for underactuated Euler–Lagrange (EL) systems rely on structure-specific constraints that may be appropriate for some systems, but restrictive for others. A generalized (structure-independent) control framework is to a large extent missing, especially in the presence of uncertainty. This paper introduces an adaptive-robust control framework for a quite general class of uncertain underactuated EL systems. Compared to existing literature, the important attributes of the proposed solution are: (i) avoiding structure-specific restrictions, namely, symmetry condition property of the mass matrix, and a priori bounds on non-actuated states or state derivatives; (ii) considering Coriolis, centripetal, friction and gravity terms to be unknown, while only requiring the knowledge of maximum perturbation around a nominal value of the mass matrix; (iii) handling state-dependent uncertainties irrespective of their linear or nonlinear in parameters structure. These features significantly widen the range of underactuated EL systems the proposed solution can handle in comparison to the available methods. Stability is studied analytically and the performance is verified in simulation using offshore boom crane dynamics.

Nonlinear coordination control of offshore boom cranes with bounded control inputs

SummaryOffshore cranes are complicated underactuated systems, which work in harsh sea conditions. Due to the various severe disturbances, the control of offshore cranes has always been a great challenge, which is made even more complicated when considering some practical issues such as actuator saturation and coordination. Until now, few results have been published in the literature on this topic. To address this problem, an efficient nonlinear control method is proposed for offshore boom cranes suffering from both ship roll and heave motion in this paper, which takes full consideration of actuator saturation, as well as the coordination problem between actuators. Furthermore, regarding the various extra nonvanishing disturbances, such as winds, frictions, and unmodeled dynamics, a disturbance observer is designed to estimate and eliminate these uncertainties. The asymptotic stability of the desired equilibrium point is rigorously guaranteed by Lyapunov techniques and LaSalle's invariance theorem. Finally, extensive hardware experimental tests are carried out to demonstrate the feasibility and efficiency of the proposed method. To the best of our knowledge, this paper proposes the first method that considers the saturation and coordination problem for offshore cranes while guaranteeing the asymptotic stability of the desired equilibrium point.

Antiswing Control of Offshore Boom Cranes With Ship Roll Disturbances

Offshore cranes often work in harsh sea conditions. As a result, they may suffer from various external disturbances, especially the persistent and unpredictable ship motion caused by sea waves, which will introduce severe disturbances to the crane dynamics, including the unactuated part. Due to this reason, the control problem for offshore boom cranes presents great challenges, for which only boundedness or stability, instead of the generally desired asymptotic stability, of the closed-loop system can be usually guaranteed by currently available methods. For this problem, a novel nonlinear control strategy for an offshore crane is proposed in this brief, which ensures that the closed-loop system’s equilibrium point is asymptotically stable even in the presence of the persistent ship roll disturbances. The proposed control law is further extended to be an output feedback controller to deal with the situations when the velocities are unavailable, still guaranteeing asymptotic stability. Finally, some experimental results are provided to validate the efficiency of the proposed controllers.

Adaptive repetitive learning control for an offshore boom crane

This paper proposes an efficient nonlinear controller for an offshore boom crane, which is a combination of a learning strategy and an adaptive robust control method. An offshore boom crane is a kind of typical underactuated system which has less number of actuators than its degrees of freedom (DOFs), and it is also a sophisticated nonlinear system with strong-coupling characteristics, therefore, controller design for this kind of system becomes an extremely challenging task. Moreover, different from an overhead crane fixed on land, an offshore boom crane fixed on a vessel suffers from some peculiar disturbances of the attached ship’s multi-dimensional movement induced by waves and ocean currents, which implies that the motion of the ship can cause a tremendous effect on this system. Considering the periodic property of sea waves, this paper proposes an adaptive repetitive learning control strategy containing a learning law to deal with the aforementioned practical problems, as well as an adaptive law to handle the unknown system parameters. Specifically, different from traditional learning control strategy, the proposed control algorithm successfully addresses unknown periods of the periodic disturbances by introducing a period identifier into the control scheme. Meanwhile, the developed control strategy presents good robustness against ever-lasting disturbances and unknown parameters. The stability of the designed closed-loop system is guaranteed in the Lyapunov sense. Furthermore, some comparative experimental results are presented to demonstrate the efficiency of the proposed control method.

Dynamics Analysis and Nonlinear Control of an Offshore Boom Crane

This paper analyzes the dynamics of an offshore boom crane and proposes a high-performance nonlinear controller to drive the system states to track some constructed trajectories. Specifically, by employing Lagrange's method in an attached frame, a dynamic model is obtained for the offshore crane system consisting of the boom and a payload, with specific emphasis on the effect of the vessel's motion on the payload swing. Based on the model, a novel nonlinear control law is designed for the underactuated boom crane, which makes the system states track some planned trajectories successfully, even in the presence of persistent disturbance in harsh sea conditions. The stability of the designed closed-loop system is proven by Lyapunov techniques. Simulation and experimental results are included to demonstrate that the proposed control method significantly reduces the impact of the disturbance in harsh sea conditions.

Model Based Design Optimization of Operational Reliability in Offshore Boom Cranes

AbstractThis paper presents a model based approach for design of reliable electro-hydraulic motion control systems for offshore material handling cranes. The approach targets the system engineer and is based on steady-state computations, dynamic time domain simulation and numerical optimization.In general, the modelling takes into account the limited access to component data normally encountered by engineers working with system design. A system model is presented which includes the most important characteristics of both mechanical system and hydraulic components such as the directional control valve and the counterbalance valve.The model is used to optimize the performance of an initial design by minimizing oscillations, maximizing the load range and maintaining operational reliability.

THE NAPOLI INCIDENT

ABSTRACT MSC Napoli, a United Kingdom-flagged container ship got in trouble during storms in the English Channel on January 18th 2007, whilst en route from Belgium to Portugal carrying approximately 2300 containers, some of which contained dangerous goods. Severe gale force winds caused serious damage to her hull and flooded the engine room. The 26 Man crew was evacuated and the vessel taken under tow, the vessel'S destination was Portland port near Weymouth. En route to Portland, the vessel condition worsened and a decision was made by the SOSREP (Secretary of State'S representative) to deliberately beach the vessel in Lyme bay to prevent the vessel sinking and becoming a major navigational hazard and pollution catastrophe. To counter any oil release, under direction of the environment group, preventative booming was carried out at the river Axe and the river Brit; four other sites were inspected to check the feasibility of booming. These were the estuaries of the Exe, Otter, Teign, and Sid. Removal of the oil from the ships tanks commenced on January 23rd, this operation was able to take place due to favorable winds from the North and North West. Containment and recovery vessels, as well as a vessel fitted with a dispersant spray system, were on location. This system was used on January 24th, following a release of HFO during the lightering operation. A dispersant protocol had previously been produced which gave set of guidelines and persons to contact prior to any operation. Once given permission, a test spray was carried out and the results observed and reported back. Due to the observed results observed, permission was given to spray the slick. With the risk of containers entering the water, oil containment operations with offshore boom was not possible, but container collection plan was put forward using available vessels and anchoring points, a very different type of recovery operation. The author will recount his onsite experiences gained during his leadership of the operation. The accounts of this incident are the views of the author and OSRL EARL.

THE PERFORMANCE OF BOOMS IN AN OFFSHORE ENVIRONMENT

ABSTRACT The Marine Spill Response Corporation, Southwest Region, conducted offshore oil spill training exercises and boom tests between May 22, 1991, and August 2, 1991. Test documents and still and video pictures document the operations and evaluation of each of the nine booms used. The tests determined operational performance in the following areas: boom handling, loading, securing, deploying, retrieving, seagoing performance, response to waves, and tow force.

Guernsey - The Off-Shore Boom

Guernsey - The Off-Shore Boom