Large container ships up to 400 metres in length will in future be designed with greater safety in mind. This will be done by updating a model developed at DTU.
Because ships are now being built longer and longer, the problem of whipping is also growing. Whipping occurs when a ship is subjected to sudden stress, for example in high waves when its bow or stern is lifted up above the waves and then slams back into the water. This severely strains the ship’s steel hull and can damage and weaken the entire structure.
The problem is well known and has caused major damage to ships in the past. The worst cases occurred in 2007 and 2013, when two 300-metre container ships broke in half in stormy seas. In both cases, it was subsequently established that whipping had been a contributing factor. The trend towards building longer ships - up to 400 metres - makes it even more important to take whipping into account when designing the ships. Currently, ships use data from sensors to determine, for example, when it is necessary to slow down or change direction in relation to the waves to reduce the effects of whipping.
A faster and simpler model
Over the last 10 years, DTU has developed a unique analytical framework that can simulate the vibration the ship is exposed to through the impact of the waves. To simulate these complicated physical conditions, a Computational Fluid Dynamics model is used that includes very extensive computer calculations that take a long time to complete. This is partly because the calculations in a design process have to take into account both the effects of a three-hour storm with high waves and the impact of vibrations throughout the ship’s 30-year life.
An important prerequisite for DTU’s analytical framework is the development of a faster model for predicting situations in which the waves can cause whipping and which subsequently need to be further investigated. However, to date this ‘predictor’ has not been accurate enough to be used in ship design. Therefore, the new DTU project aims to develop a new, simpler, and more precise predictor.
“We want to develop a new predictor that can be used to narrow down the critical points of ship design when it comes to whipping. Using the large analytical framework, we should then be able to calculate these scenarios in a few minutes instead of hours,” says Yanlin Shao of DTU Mechanical Engineering, who is in charge of the new project.
The aim is that the new predictor together with the analysis framework will provide a whipping analysis that can be used in the construction of ships, both in Denmark and the rest of the world.
“To achieve this, we’re also working with DNV GL, who prepare and regularly update design guidelines that must be followed worldwide when building new ships. DNV GL is interested in using our new predictor in a pilot project to address the problems of whipping,” says Yanlin Shao.
The project has just started and Yanlin Shao hopes to have a model ready for testing within two years.