Experiments in the open sea create new knowledge about how waves originate, develop and affect the surroundings with their strength. This will make it possible to maintain facilities such as oil platforms in the North Sea for a longer period of time.

Using mathematical and physical theory and advanced computer simulation, researchers all over the world have been working for decades on describing waves and wave loading. They have become adept at analysing how the sea absorbs energy from the wind and converts it to waves that break and interact with each other, ocean currents and the format of the sea bed.

However, there is a certain amount of uncertainty associated with the existing theoretical, numerical and analytical descriptions of wave loading. Reality is often far more stochastic than can be accounted for, even using advanced simulations. Danish wave researchers will therefore now start using full-scale measurements.

“We’ll create new knowledge about wave loading with a focus on how it affects offshore structures. It’s very difficult to upscale experimental results of the way fluids flow around an object, and we therefore need studies at sea. With new full-scale tests, we can gain more reliable and accurate insight into how waves interact and fatigue our oil platforms in the North Sea,” says Professor Christos Thomas Georgakis.

Until recently, he was responsible for the scientific activities regarding wave loading at the Danish Hydrocarbon Research and Technology Centre, the overall aim of which is to identify new technological solutions that boost oil and gas extraction in the Danish sector of the North Sea.

Improved safety on large platforms

One of the main objectives of the wave research at Aarhus University is to reduce the expenses that are currently associated with repair, retrofit and maintenance of the existing oil platforms. It actually requires detailed familiarity with the way ocean movements continuously wear down the constructions through corrosion and fatigue.

“North Sea oil is a valuable energy resource for Denmark, and it will unfortunately not last forever. It’s therefore crucial that we get as much as possible out of it – with the least possible resource consumption. The sea causes enormous wear on offshore constructions, and the engineering challenge is to more accurately identify how much they can withstand. Today we have to shut down the oil platforms in some cases because we don’t know whether they can withstand the wave loading,” says Professor Georgakis.

He expects that more accurate knowledge about the interaction between loading and wave structure will make it possible to take decisions on an informed basis and extend the service life of the platforms in the North Sea until such time as Denmark is ready for a complete green transition.

“We’ll develop a reliable method to characterise waves and predict the consequences of their loading. The oil and gas industry needs new knowledge for making decisions about which platforms they should shut down or keep running, and what maintenance and retrofit measures they should invest in,” he continues.

Studies in the laboratory and at sea

In order to understand the mechanisms underlying the wear and tear of the waves, the researchers will also start using large areas of the North Sea for near full-scale experiments. Using laser technology, they are studying conditions such as the form and distribution of the waves as well as the undercurrent conditions in natural surroundings.

They are also planning to equip an unmanned oil platform with different sensors and scanners that measure the direct response of the construction to the waves in the form of vibrations.

The researchers are comparing all of this with the results of extensive experiments in one of the world’s most advanced wave tanks at Newcastle University which can combine waves, wind and current. In this way, they can systematically identify the computational uncertainties connected with simulating real sea conditions.

“By comparing tests at sea with tank experiments, we hope to create a better load model and thereby more accurate assessments of the impact of wave loading on offshore constructions,” says Professor Georgakis. The researchers will eventually use the test results to develop offshore constructions that are capable of reducing the wear and tear of the sea based on the design alone.