The thesis report 'Modelling of the exhaust plume of a submerged exhaust system: A numerical analysis of a submarine exhaust' proved to be the best of eight entries.

During the Kooy Symposium on 11 April, the Kooy Prize was awarded to Maarten Klapwijk (23). While graduating from TU Delft (Master Marine Technology), he researched the accuracy of predicting water surface disturbance due to rising exhaust gases emitted by diesel-electric submarines. The end result of his research is a report with which he graduated cum laude, indicating, among other things, how to use existing CFD (Computational Fluid Dynamics) software to do the most reliable simulation possible.

The Royal Navy is currently operating four diesel-electric Walrus class submarines whose electric motors are used when submerged. The diesel engines are used to charge the batteries required for electric propulsion. This is done while the vessels sail at periscope depth. During recharging, air is taken in through a snorkel pipe while exhaust gases are emitted at the back of the tower, underwater, disturbing the surface there. These exhaust gases and associated disturbances have defence attention for two reasons. Firstly, they restrict visibility through the periscope which compromises operational safety. In addition, these large disturbances could potentially be visible on radar with which a security risk also arises.

As part of the development of new submarines, defence is therefore interested in a numerical model that can simulate the disturbances while also knowing how reliable the results are.

Research
Maarten Klapwijk eagerly took up the issue. "I already knew earlier that I wanted to do something with computer simulations for fluid dynamics, so I wrote to various companies and organisations well before I graduated; including the Ministry of Defence. Coincidentally, at this time, the Defence Materiel Organisation (DMO) had approached my professor with 'an interesting assignment for a graduate student'. The contact was then quickly made and I was able to get started."

He conducted his research in collaboration with DMO at the Laboratory of Aero- and Hydrodynamics at TU Delft where he was supervised by Prof.dr.ir. T. van Terwisga, Ir. G.M. Rotte, Dr. M.J.B.M. Pourquie, Ir. B. Nienhuis, Ir. M.S. Kerkvliet and Dr.ir. M.I. Gerritsma. For his research, Maarten used MARIN's CFD code ReFRESCO to make numerical predictions of the aforementioned surface disturbances.

The project was divided into two parts. In the first part, Maarten studied a simplified problem with which he mapped and modelled the physical properties of the problem. In this way, he figured out which factors were important in simulating the perturbations. He then had to validate them. "At the time, there was little useful data that we could use to test the software. The submarines in use today - the Walrus class - are almost 30 years old, so the most recent unclassified images and experiments were from that time. Nevertheless, they proved valuable because they ultimately allow you to validate whether the results from the simulations with the chosen settings match reality."

Final result
One of the final conclusions was that the estimated uncertainty in the calculated surface elevation is 15%. Furthermore, in both the experiments and simulations, a pulsating behaviour was observed in the rising air that causes additional surface disturbance. The simulations have been validated with experimental data from MARIN.

Broadly applicable
Although Maarten conducted his research on behalf of the DMO, the results are more broadly applicable. "That is certainly a nice bonus of this project. We deliberately paid attention to ensuring that it wouldn't become a secret report, because of this it can also be used by other companies and I can go public with it as a scientist. For instance, I have now also presented the work at a scientific symposium. The fact that the Ministry of Defence has also stated that new submarines will be built only makes it better.

Winning the Kooy Prize came as a complete but very positive surprise. Of course I knew the work was not bad; I graduated with a 9, but I can imagine there are more good entries."

Judgement of the jury
De Kooy Prize jury this year consisted of Dr L. Koene (Board KIVI-DV and jury chairman, NLDA), Ing. L.F. Galle (Ministry of Defence, Materiel Directorate), Prof.dr.ir. PHAJM van Gelder (TU Delft), Prof. dr. ir. F.E. van Vliet (TNO, University of Twente) and Prof. dr. ir. P.J. Oonincx (NLDA). They judged about eight submissions at the end of 2017.

Chairman Bart Koene comments: The eight submissions were without exception of high quality but Maarten's contribution - Modelling of the exhaust plume of a submerged exhaust system: A numerical analysis of a submarine exhaust - was chosen almost unanimously. Discussion was subsequently unnecessary."

Photo vlnr: Jan Wind (chairman KIVI DV), Dr Bart Koene (chairman of the jury), Maarten Klapwijk (winner) Prof.dr.ir. Pieter van Gelder (TU Delft, jury member), Prof.dr.ir. Frank van Vliet (TNO, UTwente, jury member), Prof.dr.ir. Patrick Oonincx (NLDA, jury member).