NEXT MINUTES OCEAN WAVE AND VESSEL MOTION PREDICTIONS FOR MORE EFFICIENT OFFSHORE LIFTING OPERATIONS

This next minutes Wave Prediction Software using standard onboard navigation radars is being developed. Algorithms able to obtain next minutes wave patterns is developed, based on the physical behavior of waves. Ocean wave dynamics is the main challenge for all ocean operations. Any information of useful accuracy about instantaneous wave heights and periods of acceptable accuracy is not available today. Execution of subsea lifting operations is based on experience and subjective assessments due to lack of information about wave conditions. Especially for subsea lifting operations, ocean waves and vessel motions are the biggest challenge. For all offshore and ocean operations, there is great potential in reducing both waiting time and completion time by predicting accurate waves and vessel motions for the next minutes. The onboard operators want prediction of optimal vessel heading for minimum vessel movements before starting a lifting operation. Then they wish to predict large incoming waves for the next minutes, to be able to decide whether to start a critical lifting operation before or wait after a big wave. Then the operation can be started much earlier, although subjective evaluations and conservative guidelines will give waiting time of several days or even weeks. Wave propagation model tests have been carried out to check the accuracy of the wave prediction method and to evaluate the most important non-linear wave effects to be included for the onboard next minutes wave prediction software. An operating vessel is used to test the prototypes in cooperation between the partners in the project. The project has used radar and wave prediction specialists in addition to meteorologists to check wave prediction methods against advanced wave buoys, with good correlation. Systems and software are installed on board an operating vessel and comprehensive full-scale testing is carried out. A real-time connection to onshore has been established so that both analysis of measurements and software updates are done from onshore. Information from both the prediction and logging of wave and vessel motions and simulator (digital twin of the vessel and subsea lift system) is displayed on the bridge. Comparisons have been made between simulated results of the complete subsea lifting operation against full scale measurements, based on the measured motions, and there is good correlation. It is carried out three independent full-scale measurements, where predicted waves a few minutes ahead were compared with measured waves in front of the test vessel. Both tests showed that wave predictions based on standard navigation radar were significantly more accurate than expected. This is mainly due to major improvements in the method of reconstructing immediate wave pattern, while also the methods for calculating the wave pattern ahead in time are continuously improved. The algorithms have to be continuously tested, improved and quality assured by continuous full-scale measurements over a long period of time. We use our synthetic Wavesim software that simulate random sea states and a synthetic radar for further testing and improvement of accuracy, based on full-scale measurements. It is also crucial to further develop accurate calculations of vessel motions for the actual loading conditions of the vessel.

Ocean wave dynamics is the main challenge for all ocean operations. The main objective was to develop next minutes waves and vessel motions predictions. Extensive field tests on an offshore vessel showed that the wave spectrum that reached the vessel was well predicted for minimum the next 4 to 5 minutes based on standard X-band navigation radars. The accuracy and robustness to be improved by further development and full-scale testing. Key focus is to predict large incoming waves for the next minutes, to be able to decide whether to start a critical operation before or to wait after a big wave. A fully operating onboard prototype version of real-time visualization and user interface was also installed on the test vessel. Several new continuation projects, based on cooperation with MIT Ocean Research and their competence on next minutes wave predictions, and panel codes for all kinds of hydrodynamic calculations, are proposed.

Background and objectives: Thousands of vessels are challenged with complicated offshore crane and lifting operations in ocean waves on a daily basis. The most important need for captains and offshore managers is to get accurate information about actual wave situation and to predict waves and vessel motions ahead in time, in particular to reduce waiting time. Crane and lifting operations will be much more efficient and safe by developing new onboard active real-time decision support tools based on accurate information about real-time wave patterns and next minutes wave and vessel motion predictions Critical R&D challenges: Decision support for crane operations is today based on historic data or oceanographic data several hour or days ahead in time. Today there is not available real-time oceanographic wave data of useful accuracy for reliable predictions minutes ahead in time. The main need will be to conduct fully nonlinear wave simulations to predict accurate wave data for the next minutes from wave radar or Lidar to be installed onboard vessels. The major source that affects the accuracy of wave prediction is the accuracy of recovering a snapshot of the wave patterns. Further it is crucial to establish the zone within which sea-surface elevation may be predicted to within the required accuracy on linear wave theory,which is much simpler and faster to implement computationally. Anticipated potential: By using real-time measurements and next minutes predictions it will be possible to operate in higher sea states than according to the existing DNV-OS-H101 B500 weather restricted operations criteria.Today offshore lifting operations are often limited to significant wave heights of 1.5 - 2 meters. Typically, only by increasing the limitation on maximum wave heights by 0.5 meters the waiting time might be reduced from one week to one day. For all partners it is expected to be significant increase of competitiveness by documenting reduced costs of subsea operations.