Final Report Summary - HANDLING WAVES (Decision support system for ship operation in rough weather)
The objective of the HANDLING WAVES project was to develop an on-board decision support system for tactical decisions of ship handling in waves, considering in particular rough sea conditions. Besides monitoring in real time the accelerations on the ship, the system incorporated numerical models to:
- estimate actual relative motions at the bow and wave induced structural loads;
- estimate probabilities of occurrence of rogue waves and their effects on the ship motions and structural loads;
- estimate probabilities of occurrence of large amplitude roll motions and capsizing;
- predict the near term changes in motions and loads that would arise from any change in course and speed by the shipmaster.
The project also carried out in service pilot applications in three ships.
The activity of the project has been organised into six technical work packages which objectives are described in the following:
Work package 1:
The objectives of this task included:
- improve the understanding of the mechanisms of generation of the rogue waves, of their geometries and of the probability of occurrence in wave records;
- improve the methodology to generate experimentally in a seakeeping tank deterministic rogue waves and extreme wave groups;
- generate in a seakeeping tank a set of tailor-made wave groups that include rogue waves for posterior experimental analysis of rogue wave kinematics and the effects of rogue waves on ship structures;
- improve the existing probabilistic models to account for the probability occurrence of rogue waves in a synoptic scale.
Work package 2:
The objective of this task was to investigate experimentally conditions that lead to the loss of ship stability and capsizing of ships and also to unexpected large roll motions. Although the subject of large amplitude motions and in particular the intact and dynamic stability at large angles has been much studied in the past, there are still several aspects that remain unclear and in fact represent a threat to the ship safety and operability. These aspects, which were investigated in this task, included: the motions induced by rogue waves, the loss of stability at large wave crests, parametric rolling and broaching due to loss of directional stability.
To accomplish these objectives an experimental program was carried out with models of three different ships in deterministic wave sequences that include rogue waves, extreme wave groups and other adverse wave conditions. Besides improving the understanding of these complex phenomena that compromise the ship safety and operability, the new experimental data supported the calibration and validation of numerical models that estimate these ship responses.
This work package dealt with experimental tests with self propelled models for measurements of motions and capsizing conditions, while work package 3 dealt with experiments with captive segmented models for measurement of structural loads.
Work package 3:
The behaviour of ships when they encounter rogue waves and the related effects on the ship structures are still basically unknown, although it is generally accepted that the consequences may be dramatic. The objective of this task was to carry out a program of experimental tests with three models of ships in deterministic wave sequences that include rogue waves and extreme wave groups. The effects to be analysed included local (slamming and green water on deck) and global structural wave induced loads. The results from these tests firstly enhanced the understanding of the behaviour of the ship when subjected to extreme waves. Secondly, the results permitted the calibration and validation of existing numerical methods to predict the structural loads induced by rogue waves.
Work package 4:
This task dealt with the development and application of methods for numerical calculation of ship responses. The decision support system to be installed onboard of ships was based on various numerical procedures and results regarding the ship behaviour in waves. This way the objective here was to validate and generalise the existing methods, and develop the new needed ones. More specifically:
- The existing nonlinear time domain seakeeping code was generalised to include the effects of slamming and green water on deck induced by rogue waves.
- A data base with the motions and structural loads induced by all possible wave conditions was produced for one ship, which was then used to develop a neural network model that relates the ship accelerations with the structural loads. This way the wave induced structural loads were assessed via the measured accelerations instead of using less reliable and more complex strain gauges.
- Finally, a method was developed which allows the estimation of the sea spectra from the measured motion records. This way one avoids the use of much more expensive and complex systems based on X band radars.
Work package 5:
The onboard decision support system was developed in this task. The objective of the system was to improve the ship performance at sea by informing the shipmaster on the level of various ship responses to the waves, comparing the actual ship responses with safety and comfort criteria, and advising on the best route.
Work package 6:
Demonstrate the applicability of the system through pilot applications on different ship types, namely a bulk carrier, a ferry and a container ship. After the development of the onboard decision support system, in this WP the system was installed on three ships for testing under operational conditions during a period of approximately three months.
- estimate actual relative motions at the bow and wave induced structural loads;
- estimate probabilities of occurrence of rogue waves and their effects on the ship motions and structural loads;
- estimate probabilities of occurrence of large amplitude roll motions and capsizing;
- predict the near term changes in motions and loads that would arise from any change in course and speed by the shipmaster.
The project also carried out in service pilot applications in three ships.
The activity of the project has been organised into six technical work packages which objectives are described in the following:
Work package 1:
The objectives of this task included:
- improve the understanding of the mechanisms of generation of the rogue waves, of their geometries and of the probability of occurrence in wave records;
- improve the methodology to generate experimentally in a seakeeping tank deterministic rogue waves and extreme wave groups;
- generate in a seakeeping tank a set of tailor-made wave groups that include rogue waves for posterior experimental analysis of rogue wave kinematics and the effects of rogue waves on ship structures;
- improve the existing probabilistic models to account for the probability occurrence of rogue waves in a synoptic scale.
Work package 2:
The objective of this task was to investigate experimentally conditions that lead to the loss of ship stability and capsizing of ships and also to unexpected large roll motions. Although the subject of large amplitude motions and in particular the intact and dynamic stability at large angles has been much studied in the past, there are still several aspects that remain unclear and in fact represent a threat to the ship safety and operability. These aspects, which were investigated in this task, included: the motions induced by rogue waves, the loss of stability at large wave crests, parametric rolling and broaching due to loss of directional stability.
To accomplish these objectives an experimental program was carried out with models of three different ships in deterministic wave sequences that include rogue waves, extreme wave groups and other adverse wave conditions. Besides improving the understanding of these complex phenomena that compromise the ship safety and operability, the new experimental data supported the calibration and validation of numerical models that estimate these ship responses.
This work package dealt with experimental tests with self propelled models for measurements of motions and capsizing conditions, while work package 3 dealt with experiments with captive segmented models for measurement of structural loads.
Work package 3:
The behaviour of ships when they encounter rogue waves and the related effects on the ship structures are still basically unknown, although it is generally accepted that the consequences may be dramatic. The objective of this task was to carry out a program of experimental tests with three models of ships in deterministic wave sequences that include rogue waves and extreme wave groups. The effects to be analysed included local (slamming and green water on deck) and global structural wave induced loads. The results from these tests firstly enhanced the understanding of the behaviour of the ship when subjected to extreme waves. Secondly, the results permitted the calibration and validation of existing numerical methods to predict the structural loads induced by rogue waves.
Work package 4:
This task dealt with the development and application of methods for numerical calculation of ship responses. The decision support system to be installed onboard of ships was based on various numerical procedures and results regarding the ship behaviour in waves. This way the objective here was to validate and generalise the existing methods, and develop the new needed ones. More specifically:
- The existing nonlinear time domain seakeeping code was generalised to include the effects of slamming and green water on deck induced by rogue waves.
- A data base with the motions and structural loads induced by all possible wave conditions was produced for one ship, which was then used to develop a neural network model that relates the ship accelerations with the structural loads. This way the wave induced structural loads were assessed via the measured accelerations instead of using less reliable and more complex strain gauges.
- Finally, a method was developed which allows the estimation of the sea spectra from the measured motion records. This way one avoids the use of much more expensive and complex systems based on X band radars.
Work package 5:
The onboard decision support system was developed in this task. The objective of the system was to improve the ship performance at sea by informing the shipmaster on the level of various ship responses to the waves, comparing the actual ship responses with safety and comfort criteria, and advising on the best route.
Work package 6:
Demonstrate the applicability of the system through pilot applications on different ship types, namely a bulk carrier, a ferry and a container ship. After the development of the onboard decision support system, in this WP the system was installed on three ships for testing under operational conditions during a period of approximately three months.
