There is a huge energy potential in ocean waves, but to date little has been done to utilize the wave energy to reduce energy consumption of ships. When a ship travel in following waves, the resistance and energy requirement might be reduced or increased depending on the ship speed and wavelength. Also, it is known that there might be difficulties steering a ship in heavy following seas. Autopilot control might not work properly, and manual steering by experienced helmsmen is often required.
This project aims at developing better understanding of the performance of ships in following seas, with emphasis on the interplay between hull-propeller and rudder. Through this improved understanding, the project will develop methods and guidelines for how and when the energy in the waves can be utilized to reduce fuel consumption. Improved control methods allowing better automatic steering of ships in heavy following waves will be developed, something that is of particular importance for autonomous and automatically controlled ships. For autonomous ships, it is essential to obtain knowledge of the operational conditions ("situational awareness") purely based on measurements, so this aspect is included in the project.
The project includes use of model experiments, advanced numerical simulations and full-scale measurements on two case ships. One case ship is the freight vessel Eidsvaag Pioner with overall length around 75 m, trafficking the Norwegian coast to distribute fish-feed supplies to fish farms. The other case ship to be studied is the new-built Norwegian coastguard vessel KV Jan Mayen with overall length about 136 m.
What are the hydrodynamic operational conditions for the rudder and for the propulsors in following seas and how are the waves influencing the performance of these units and thus the maneuvering performance of the ship? These questions are sought answered by utilization of computational fluid dynamics (CFD-) simulations to study the complex flow at the aft ship. A numerical representation of the case ship Eidsvaag Pioner has been developed for advanced numerical simulations with CFD software. Having control of the physical parameters in the simulation, parameter variations can give valuable insight into the flow characteristics and its dependence on various physical effects.
A scaled physical model of the case ship Eidsvaag Pioner in scale 1/15 has been constructed and tested in the large towing tank at SINTEF Ocean. The tests were so-called planar motion mechanism (PMM-) tests where the model was forced to perform oscillatory motions overlayered towing at constant speed. The purpose of these tests was to document hydrodynamic coefficients of the ship that will be used in the planned development of a numerical ship maneuvering model. These are conventional type of tests. In addition, a series of novel PMM tests in following waves were performed. Further tests with free-running model ship are planned. A special sensor to measure propeller transverse forces is being developed to be used in tests with the free-running model.
The case vessel Eidsvaag Pioner has been instrumented with an extensive sensor package from Kongsberg Maritime for monitoring of engine power, propulsors, rudder, ships course, speed and motions. Wave radar from MIROS has also been installed to monitor wave exposure. This makes possible collection of field data mapping the ship?s operational conditions and performance on her route along the Norwegian coast. Measured time-series data are collected, transferred to shore and processed to identify possible sequences of interest where the ship is exposed to waves undertaking the vessel on its course. How are the automatic steering control system and engine power affected by the wave parameters in such conditions? The instrumented case vessel yields a great opportunity to address this question with possible gain of new knowledge on ship?s operational performance.
The project aims to develop methods to reduce the energy-consumption of ships travelling in following seas, and to develop methods to automatically control the ships in a safe and efficient way during operation in heavy following seas, something which is particularly important for safe operation of autonomous and automatically controlled ships in open ocean conditions. To achieve these objectives, the project will use a combination of numerical and experimental methods, where the experimental methods comprise both model and full scale measurements. A novel feature of the model experiments is measurement of the lateral forces on the propeller during operation in waves.
Based on the increased physical insight gained from experiments and detailed numerical simulations, an improved time-domain simulation tool will be developed, applying weakly non-linear hydrodynamic theory, where the sea-keeping and maneuvering problem is solved simultaneously (contrary to the typical two-timescale solution in use for analyzing maneuvering in waves).
Two ships with extensive instrumentation for monitoring of motions, propulsion parameters and waves will be utilized for collection of full scale data. Based on the results from experiments and simulations, strategies for optimizing the operation in following waves will be made.
The development of control methods will concentrate on developing improved operational awareness, focusing on the sea condition, and on that basis develop control methods for the steering and propulsion to improve efficiency in astern waves, at the same time as operational safety is taken care of. A method to control the ship during rapidly changing conditions will also be developed. This method is expected to be important to increase safety of operation, particularly for autonomous and automatically controlled ships.