A remarkable test facility at TU Delft is where it is all going to happen: the hexapod. Weighing about 60 tonnes (60,000 kilos), it is also referred to as the beast.
Mirek Kaminski, professor of ship and offshore structures in the Department of Maritime and Transport Technology at TU Delft (3mE) wants to improve the design method used for ships by taking fatigue into account.
Until now, material fatigue has not been taken into account explicitly while designing. When it is considered, tests are used that determine when a structure fails based on forces that act in one direction. This uniaxial force is insufficient to describe all of the forces that ships are subject to. After all, waves come from all directions. ‘As soon as we have a more realistic model of how things really are, which takes all forces into account, then we can improve our designs,’ the professor says.
Adding and Cutting in the Right Places
Kaminski will not go so far as to say ships are now actually unsafe. Although material fatigue is an important reason why we lose ships – and we do lose a few a day – Kaminski says that generally ships meet all of the safety requirements. ‘If a ship does not break down, that usually means it was built too strong. It is common for too much unnecessary material to be used, which makes ships needlessly expensive. Still, it is not only a question of using fewer materials, but also of adding materials in places where the ship is most likely to suffer damage as a result of fatigue.'
Hexapod
Kaminski is planning to put pieces of ships, or to be more precise, structural details no larger than 1 m3 with welded parts, between the 6 x 5 x 3 m Hexapod. ‘Fatigue in ships always concerns welded materials, because welding causes micro-cracks that weaken the joints between two welded structural elements.’
He subsequently exerts the actual forces that a ship will be subject to onto one of these test specimens. Ultimately, Kaminski wants to test all characteristic welded structural joints of a ship for a month, during which he can simulate a 20-year-lifespan. The latter is feasible because he can exert the forces with a higher frequency than in reality, 30 Hz to be precise.
‘We do not know what the outcome is going to be, because nothing like this has ever been tested in the world before. But if I were to make an estimate, I would expect the lifespan of multi-axially loaded ship structural elements to shorten by at least a factor of ten relative to those loaded uniaxially. Instead of twenty years, they will last two.’
Six Directions
‘The Hexapod can generate forces of 100 tonnes in all directions. That is important because a ship in waves also has to deal with loads from all directions,’ Kaminski says. He often uses the word multi-axial, which means that the machine can move in six directions in space: surge, sway, heave, roll, pitch and yaw. A mechanical bull and a flight simulator can move like this as well, but the Hexapod is the first machine that can exert six forces on a structure simultaneously. The combination of great power, high speed and accuracy makes the Hexapod unique.
Other Uses for the Hexapod
The use of the Hexapod is not limited to ships. In the future, it can also be put to other use, says Kaminski: 'Cars, for example, aeroplanes that experience turbulence, bridges that trucks drive on, buildings that have to endure earthquakes, windmills that have to deal with wind and so on and so on.’
From Brainstorm to Machine with Six Hydraulic Arms
Four years ago, Kaminski organised a brainstorm session with people from industry and science to come up with a method that will take into account all of the different forces in order to determine the lifespan of a structure. He envisioned a machine with six hydraulic arms, which would enable it to subject material to tremendous forces from six different directions.
'With my sketch of this machine, I then wrote to eleven companies and asked them if they could make something like that. Ten companies immediately threw in the towel. They said: Dream on, Mirek. The only company that wanted to build my idea right away was the German company FGB.’
Dutch Orange
In the meantime, four years have passed and the first and only hexapod in the world is housed at TU Delft. The university invested half of the money itself in the innovative machine, a quarter came from the government and another quarter came from 23 companies – essentially the entire offshore industry participated. Kaminski calls the hexapod his orange beast. ‘It is exactly like the Dutch version of orange. I looked up the colour code myself and passed it on to the manufacturer,’ says the professor.
Watch a video of the Hexapod below.
