MAROFF BIP: A Novel Integrated Anti-sway System for Rolls-Royce Marine Shipboard Cranes (2012-2013)

Project partners

• Rolls-Royce Marine AS
• NTNU in Ålesund
• Offshore Simulation Centre
• Huse Engineering

Introduction

Shipboard cranes are widely used to handle and transfer objects from large container ships to lighters or to the quay, or, for example, to position modules at the seabed in a controlled way. Crane control is a challenging task in which many different aspects play a role such as load sway, positioning accuracy and collision avoidance. Imagine the challenge of installing a 200 ton subsea module at 2000 meters sea depth with an accuracy of centimetres. In general, shipboard cranes are big, heavy and stiff. Typical examples of shipboard crane operations are shown in Figure 1.

Figure 1. Typical shipboard crane operations.

The pendulation caused by the payload and the sway caused by the waves not only limits the functionality of marine facilities in adverse weather conditions, but also poses a threat to the safety of personnel and equipment during off-shore operations. The pendulation is often induced by a combination of the vessel’s motions and the crane operator’s normal actions. In general, the payload acts as a spherical pendulum whose attachment point is manoeuvred using the crane’s degrees of freedom. As the operator commands the various axis of the crane to affect rigid body payload translation and rotation, the payload’s swing degrees of freedom can be excited. This payload pendulation problem becomes much more complicated if the crane is mounted to a moving vessel. An experienced operator can often generate crane inputs correctly, in such a way that the payload is swing-free at the end of the manoeuvre. However, training an operator to use a crane requires significant resources and poses potential hazards. Imagine the challenge of installing a 200 ton sub-sea module at 2000 meters sea depth with an accuracy of centimetres! When considering both working efficiency and safety, quality control is impossible to achieve.

The underlying idea consists of developing an integrated system with control strategies that reduce the effects of payload pendulations and minimize wave impact on shipboard crane manipulation. A novel variable controller will be proposed to control the non-linear pendulation. The project will improve the safety of demanding marine operations. The work will be integrated with the current “crane/winch simulator” developed by the Offshore Simulator Centre. Finally, a real prototype will be built and tested at the Rolls-Royce marine AS.

Main research and development activities

To date, cargo loading operations at sea are often paused in case of unfavourable weather conditions. Without an efficient control mechanism, a modest movement of the ship can result in a large sway motion of the cargo. This can lead to dangerous situations. As a consequence, time and money are often wasted on waiting for better weather conditions, or worse, the risk may be taken to load the cargo in dangerous conditions. The other problem during the lifting and transportation of shipboard cranes with long hoist cables is wave impact. When the payload is hit by the waves on the surface of the sea, it is subject to an impulsive hydrodynamic slamming force which, in harsh sea conditions, can damage the payload. Also in this case, if the sea conditions become prohibitive, the operations have to be suspended.

Regarding the load pendulation, many researchers investigated the problem for fixed-base cranes. As the rolling motion of a ship is dominating, and the cranes usually work from the sides of the ship, the swaying of the payload is mainly confined to two dimensions. Some controllers were originally designed for boom cranes, while others were modifications of earlier work on gantry cranes. Two main approaches can be identified among this research: one targets pendulation suppression throughout the whole transport manoeuvre, while the other is more concerned with end-of-manoeuvre pendulation suppression, the so-called “elimination of residual pendulation”. In both approaches, limited research included the operator as a part of the model plan. Considering the specialties of offshore crane operations, an anti-sway control algorithm was proposed based on energy dissipating principle. The concept consist two parts which is simple but effective: first, the crane end tip always moves following the movements of the load; second, the hoist cable extends when the load sway away from the crane and retracts when the load sway towards the crane end tip. According to tests in the simulated model, the effect of the cable movements accounts for 10% of the total reduced sway time.

Regarding the wave impact, some research is found for heave compensation using a compensated winch system to reduce the forces acting on the load during the water-entry phase. The main problem of this lies in two aspects: first, the fuel consumption of the heave compensation winch introduces a great deal of cost; second, the repetitiveness of extending and retracting the cable deteriorate the cable weariness significantly. Benefited from the flexible control architecture of crane project, a heave compensation control algorithm through manoeuvring the crane itself was investigated and integrated with the anti-sway control algorithm. The crane end tip moves according to the heave motion and thus to maintain a steady position of the load in the vertical direction. The effect of this control for heave compensation is constrained by the dimensions of the crane. In extreme weather condition, to include the winch system for heave compensation will result in better effects.

In the project, Aalesund University College is the main contributor. This project relies on the close collaboration of the project partners. Each member should have enough authority over local resources to resolve all potential intra or inter site-related project problems.

Objectives

After two years cooperated work together with all related partners, we have achieved the followings:

• A control strategy is designed to deal with the load pendulation and sway.
• The control architecture is integrated in a simulation model and will be integrated with the “Crane/winch simulator” developed by the Offshore Simulator Centre (OSC).
• Investigated the possibilities for communication to a real crane system. A set up architecture is designed and tested on a simplified hydraulic system.

In detail, the sub goals have been fulfilled:

• Investigated the problem of the crane payload swing
• Investigated the problem of minimizing wave impact on the payload
• A control strategy based on energy dissipation principle was proposed and simulated
• Integrated control system to reduce payload pendulations and minimize wave impact
• Investigated the architecture system of the OSC
• Integrated the control architecture with the OSC environment
• Included the hydraulic system of the crane and integrated in a simulation model (Extra)
• A hardware set up of the control system was developed (Extra)
• Integrated the proposed control system with shipboard cranes on vessels
• Tested the control algorithm on a simplified hydraulic system (Extra)
• Test the effectiveness of the control concept on vessels
• Transfer the project results to a real system for Rolls-Royce Maritime AS (*)
• The hardware set up of the control system provides possibilities to various interfaces for communication (Extra)
• Complete project summary with a series of simulations and experiments

According to the real project research situations, we added several extra sub working tasks in order to accomplish the project as good as possible. The sub task related to transfer to a real crane system and on-board test is not finished due to the crane from Rolls-Royce was not delivered. As an alternative, we changed to test the current results on a simplified hydraulic system in Aalesund University College to confirm the research outcomes.

Project value and influence

The project will address the development of a novel anti-sway control architecture for different Rolls-Royce marine shipboard cranes, offering stability, safety, and efficiency during lifting, handling, transportation, and other manipulation.

From a technical point of view, the project will offer working efficiency and safety in marine operations. It will reduce the crane payload swing in the roll and pitch directions of the ship using the proposed anti-sway algorithm. Meanwhile, the system could minimize wave impact on the payload through the heave compensation control.

From an industrial application perspective, integration of anti-sway and heave compensation for Rolls-Royce marine deck cranes and robots in real applications is a very promising innovation for maritime industry. The system proposed in the project will relieve human operators of their work-related stress and make efficient and automatic crane controlling possible and easy. Additionally, it will improve the technological level and productivity of the maritime industry.

From an educational perspective, we will integrate the crane control architecture with the training simulation system in the OSC so that the students at AAUC will have a good opportunity to get professional training and preparation for work in the future.

Development of high performance cranes for safe deck operations and advanced marine operations is the strategic core at Rolls-Royce Deck Machinery. The turnover for the deck machinery unit is more than 2 billion NOK and the crane segment is expected to grow. Advanced control and usability allowing for efficient and safe operations is the key differentiator. For maritime industry (RRM and Huse Eng.), sales will be increased due to an increased quality of maritime equipment and vessels. Task completion during operation will be safer and faster, thereby saving valuable time for vessels offshore. Aalesund University College and the Offshore Simulation Centre will benefit from a well established research environment that produces publications and generates publicity around the college. This will lead to an increase in students and publications, contributing positively to national/international university rankings.

The proposed project will highlight the need and the value of bringing robotic technology and interaction design into the maritime sector. A flexible and common control architecture with integrated heave compensation and anti-sway control for marine deck cranes will offer working efficiency and manipulation safety in operations. The human operator will feel comfortable and at ease for crane manipulation. Lowering the operator’s stress and use-related difficulties will provide a safer and more efficient operation. This will reduce the human error rate related to incidents, which can reduce the likelihood of the operator making the wrong decision leading to accidents that may cause damage to the crew, the vessel, and offshore installations also increasing the risk of environmental and social damage. The project will add a new dimension to the company’s profile and offer further means to development for the company beyond this initial investment. Technology developed in this project will be integrated into the simulator at OSC. It will then be implemented step-by-step on real cranes. Several types of cranes of a variety of sizes are in production. A novel “parallel bar” crane is in the development stage and it is assumed that it will be an important supplement in the Rolls-Royce crane assortment. The future step is to implement the new technology on the parallel bar crane first and then implement it on the other cranes. Implementation will be done as fast as possible and is expected to be tested on-board at the end of this project. Winch system will be included for both heave compensation and anti-sway control in the current algorithms and implemented in a real crane system.