Investigations into the Influence of High Dynamic Loads and Interaction Phenomena on Performance of Marine Propulsors

INTER-THRUST is a research and development project within the frameworks of the MARTEC II programme, which is established by the European Commission ERA-Net scheme under the Seventh Framework Programme. The project is supported by the research funding organizations in Norway and Germany. The INTER-THRUST Consortium joins SINTEF Ocean (formerly, Norwegian Marine Technology Research Institute ? MARINTEK) (Norway), Hamburg University of Technology (TUHH, Germany), Voith Turbo Schneider Propulsion GmbH & Co. KG (Germany), Jastram GmbH und Co. KG (Germany), and Havyard Group AS (Norway). The INTER-THRUST project is focused on systematic investigations into the high dynamic loads acting on the main propulsors and auxiliary thrusters of ships and arising from the influence of various factors such as extreme off-design operation, geometrical complexities and surface irregularities of ship hull and propulsion systems, interaction phenomena and environmental conditions. Addressing vessels equipped with innovative tunnel thrusters and main propulsors, the project aims at simulation of their realistic operation conditions in full scale by means of advanced methods of Computational Fluid Dynamics (CFD). The results of extensive numerical studies form the basis for development of engineering models to estimate the loss of thruster efficiency and assess its impact on vessel operational characteristics. The most important results of the INTER-THRUST project concern the following aspects: Performance characteristics of pushing ducted thrusters in straight and oblique flow conditions (e.g. due to heading angle or sea current), during azimuthing with constant rotational speed, in presence of free surface, including the occurrence of ventilation phenomenon, in regular waves of different height and period, and subject to wave induced planar motions. The operation conditions include bollard, trawling and transit. Performance of bow tunnel thrusters, including the influence of tunnel and propeller design parameters, tunnel integration into ship hull, influence of sea current of different speed and direction angle, thruster-thruster interaction at synchronous and dynamic positioning operation modes. Development of calculation models for the design calculation of tunnel thrusters. Development of next generation CFD-based vessel manoeuvring simulation models.

The project has resulted in the development of new, high-fidelity computational methods for the analysis of main propulsor and tunnel thruster performance under extreme off-design conditions. By using these methods one can obtain a realistic assessment of thrust/efficiency losses, manoeuvring forces, dynamic loads and pressure fluctuations developed on propulsion systems in seaways, which is essential for safety and efficiency of marine operations, including those performed in exposed sea areas and in confined waters. The developed methods are implemented in the industrial companies. The project results are expected to generate added value in the participating companies and give advantage for the Norwegian industry and trade, where shipbuilding plays an important role. Ultimately, it will have positive impact on the economy in the sectors where the vessels are operated, including offshore exploitation and transportation.

During operation marine propulsors may experience considerable deterioration of their performance due to high dynamic loads arising from the influence of various factors. These factors include extreme off-design operation, geometrical complexities of ship hull, integration of auxiliary thrusters into the ship hull, constructive surface irregularities at the location of thrusters and interaction between the auxiliary thrusters and main propulsor, and they can be significantly magnified by the environmental influences such as currents and waves. The implications of high dynamic loads and interaction have to be taken into account already at the design stage, in order to reduce fuel consumption, maintain specified levels of noise and vibration, and avoid undesired consequences such as propulsor damages failure. In the present project, the basis for successful solution of the aforementioned problems is sought in the development based on the methods of Computational Fluid Dynamics (CFD) of reliable numerical models to simulate the underlying flow phenomena such as flow separation, vorticity transport and cavitation in full scale conditions. The detailed numerical models described above have the twofold use. On the one hand, they provide research methods to tackle demanding design criteria. On the other hand, they serve as a basis for the development of engineering tools used in routine design practice, guidelines and recommendation as regards the minimization of negative consequences of dynamic loads acting on the thrusters, undesired interaction phenomena and cavitation. Based on the results of numerical studies, simplified mathematical models will be developed to estimate the loss of thruster efficiency and its impact on vessel maneuvering characteristics. The project will focus on the vessels equipped with tunnel thrusters. The target cases of vessel and propulsion systems for investigation will be suggested by the industrial partners in the project.