In Depth: The Beast Is Testing Material Fatigue to Improve Future Vessels
10 July, 2018
Photo: The Beast Is Testing Material Fatigue to Improve Future Vessels
Mirek Kaminski wants to improve the design method used for ships. “We want to make vessels more sustainable, more effective and more affordable.”
Kaminski is professor of ship and offshore structures in the Department of Maritime and Transport Technology at Delft University of Technology and he wants to do this by studying material fatigue. The professor created ‘the beast’, a hexapod weighing about 60 tonnes. This machine will test pieces of vessels. “We don’t know what the outcome is going to be, because nothing like this has ever been tested in the world before.”
Until now it’s not been necessary to take material fatigue explicitly into account while designing. If people do take this into account they always use the results of tests that have been done since the twentieth century to discover 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.
Does that mean that all ships navigating our seas right now are actually unsafe? The professor won’t go quite that far. “If a ship doesn’t break down, that usually means it was built too strong. It’s common for too much unnecessary material to be used, which makes ships needlessly expensive.”
But that’s not the main point. “It’s not only a question of using fewer materials, but also adding materials in places where the ship is most likely to suffer damage as a result of fatigue. Essentially you want to only use materials where they’re needed in the future. We can do that by designing more efficiently.” So the level of safety remains the same. “It’s generally said that ships are becoming safer, but actually that’s not true. We want to make them more sustainable, more effective and more affordable.”
The test facility at TU Delft (Delft University of Technology) is where it’s all going to happen. It is the home of the hexapod. Weighing about 60 tonnes, it’s also referred to as ‘the beast’.
Kaminski is planning to put pieces of ships between it, or to be more precise, structural details no larger than 1 cubic metres with welded parts. “Fatigue in ships always concerns welded materials, because welding causes micro-cracks, which weakens the joints between two welded structural elements,” he says. He subsequently exerts the actual forces that a ship will be subject to onto one of these test specimens, as he calls them.
Ultimately Kaminski wants to test all characteristic welded structural joints of a ship for a month, during which he can simulate a lifespan of twenty years. The latter is feasible because he can exert the forces with a higher frequency than in reality, 30 Hz to be precise.
But how exactly will the orange beast do its thing? “The hexapod can generate forces of 100 tonnes in all directions. That’s important because a ship in the waves at sea 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. 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 and high speed on a structure accurately and simultaneously.
Four years ago, he 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. “At a certain point I knew what we had to do. I said: “Bingo!”’ says Kaminski, snapping his fingers. During that Eureka moment, 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. The only company that wanted to build my idea right away was the German company FGB.”
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.
He remembers well the first time he touched his new, six by five by three metres pet. “It felt warm, like a dog. That’s because of the oil that was already in it. That was really amazing. My heart started racing immediately,” the professor says, putting his hand on the machine. “Standing next to it now makes me feel emotional again. My voice starts to tremble and I get tears in my eyes, because for four years it took an enormous effort to design, specify, build and install the hexapod.”
Yet the real work is only just starting for the ship expert, because thanks to the hexapod all kinds of structures can be tested so that new models, formulas and designs can be made that describe reality better than the present one.
Desiree Hoving , TU Delft