Pulse-jet propulsion for commercial ships

A new propulsion system inspired by the swimming technique used by squids and jellyfish may lead to substantially reduced fuel consumption and CO2 emissions for modern ships. These animals generate motion by periodically sucking water into a hollow cavity in their body and then squeezing it out at a higher velocity. The result is periodic pulses of high-speed water that push the animals forward with an oscillating thrust force, often called “pulse jets” for short. The energy consumption is drastically reduced compared to creating the same force with a steady jet stream due to special flow structures created by the pulses. This research project will investigate a new method to create similar pulse jets using a conventional propeller. An oscillating thrust force may be challenging for a standard propulsion system but is made possible by utilising recent innovations in thruster technology from Kongsberg Maritime. Rapid and precise dynamic operation of the rotational speed of the propeller can be achieved using a modern electric motor placed on the outside of the propeller, known as rim-drives in the industry. Kongsberg is the leading supplier of such drives. Some of the research questions in this project are as follows: Will this new pulse jet technique achieve the same performance gains observed for squids and jellyfish? Can the system be used even in challenging conditions, such as in bad weather and during complex ship operations? The questions will be explored by using a combination of experiments and simulations. Experiments will be performed in state-of-the-art hydrodynamic laboratories using scaled-down versions of the propulsion system, including the special motor arrangement and the control systems needed to achieve pulse jets. Simulations will be performed using established maritime industry tools and custom models explicitly developed for this project.

Squids and jellyfish achieve remarkable performance by utilising a special swimming technique. They generate thrust by periodically sucking water into a hollow cavity in their body and then squeezing it out at a higher velocity. The result is periodic pulses of high-speed water that push the animals forward with an oscillating thrust force, often called pulse jets for short. Due to special flow structures in the wake, this technique results in impressive energy savings, when compared to generating the same amount of thrust with a steady jet stream. This research project will investigate a new method to create pulse jets that, unlike previous attempts, do not need complex mechanical solutions. It is therefore both suitable and realistic to apply for commercial ships. The idea is to use existing thruster hardware but controlled in a new way. This is made possible due to recent innovations from Kongsberg Maritime in both thruster configurations and electrical drives. The goal is to explore whether the new method can achieve similar, or better, energy savings as reported for other pulse jet mechanisms. The method will be evaluated in both ideal conditions and when utilised during challenging ship operations such as station keeping and low-speed manoeuvrability. This will be done through extensive use of CFD simulations and physical experiments to do design explorations and performance evaluations. In addition, simplified modelling will be developed to allow for further optimisation of the system as well as co-simulation of many ship systems together in complex operations. Special focus will be on developing a simplified hydrodynamic model that is suitable for capturing the time-dependent dynamic nature of the pulse jet. The expected outcome of this project is a new technology for thrusters that can lead to a substantial reduction in fuel consumption for ships.