OPERATIONS

Ground-breaking wave research

THE Australian Maritime Collage has concluded work on improving the lack of understanding of the loads and motions on floating offshore structures in huge wave states that contributed to load issues and deaths during hurricanes in key oil producing regions in recent years.

Ground-breaking wave research

 One worker tragically died and two more were seriously injured when a large wave hit a platform in the North Sea in 2015, while more than 300 installations were damaged, or in some cases lost, in a series of hurricanes including Katrina, Ivan and Rita.
 
The AMC says a lack of understanding of the behaviour of offshore platforms in large swells, and how they interact with waves, contributed to the devastation. 
 
"Armed with an understanding of exactly how and where offshore platforms are impacted when extreme weather hits, maritime engineers would be able to design structures accordingly," the AMC said in a report issued this morning.
 
"While an undersized structure may collapse, an oversized one may become too heavy to operate — or too costly. 
 
"Key to the safe and efficient design of offshore structures, therefore, is being able to predict accurately how a wave's forces will impact a structure during severe weather conditions at sea."
 
Dr Nagi Abdussamie conducted his postgraduate research using numerical and experimental techniques to investigate the phenomena, using computational fluid dynamics to simulate the interaction of a tension leg platform — a type of offshore platform — in cyclonic wave conditions.
 
His findings were validated with a scale model of the offshore platform, which was tested in wave conditions in a 10m-long towing tank at the AMC.
 
Dr Abdussamie, who was awarded a PhD for his research, said that prior to his work being done there was "very little known" about the interaction of the wave and the structure, and the resulting loads when a large wave hits the platform.
 
"We found that there is a strongly non-linear wave diffraction under the platform, which can lead to increasing wave heights and significant impact loads on the platform. 
 
"This is despite the fact that, theoretically, the wave should have passed the platform with no impact."
 
The modelling showed waves that were higher than theory predicted, and hit the platform, including the deck, which is normally designed to sit above the ‘splash zone' and is not expected to be reached by a wave.
 
Based on this finding, Dr Abdussamie concluded that offshore oil and gas structure designs must consider the deck — the topside of the structure, which sits above the sea level and has equipment installed upon it. Most platforms today are not designed for the possibility that the deck could be hit by a wave.
 
The damage caused by a wave hitting the deck could be avoided by increasing the air gap — the space between the sea level and the topside deck — although this could raise the platform's centre of gravity, which could in turn affect its stability.
 
An alternative solution would be to reinforce areas of the topside structure to ensure they can withstand such rare waves; which would require a precise understanding of the load magnitudes that the structure would be subjected to.
 
The research was advised by Dr Yuriy Drobyshevski from Intecsea, which designs large offshore platforms. 
 
"Although events where waves hit offshore platform decks can have disastrous consequences, the causes and physics of such events remain poorly understood and not well predictable," Dr Drobyshevski said.
 
AMC senior lecturer Dr Roberto Ojeda, who supervised the research, said it broke new ground as cutting-edge simulation techniques of wave-in-deck events were validated against high-fidelity towing tank model-scale experiments.  
 
"The experimental validation of the numerical techniques gives us enough confidence to apply them to various scenarios covering a wide range of environmental conditions," Dr Ojeda said.
 
 

A growing series of reports, each focused on a key discussion point for the energy sector, brought to you by the Energy News Bulletin Intelligence team.

A growing series of reports, each focused on a key discussion point for the energy sector, brought to you by the Energy News Bulletin Intelligence team.

editions

ENB Cost Report 2023

ENB’s latest Cost Report findings provide optimism as investments in oil and gas, as well as new energy rise.

editions

ENB Future of Energy Report 2023

ENB’s inaugural Future of Energy Report details the industry outlook on the medium-to-long-term future for the sector in the Asia Pacific region.

editions

ENB Cost Report 2021

This industry-wide report aims to understand current cost levels across the energy industry

editions

ENB Social Licence Report 2021

In its second year, this research now includes trends and new findings surrounding impacts and responses as the energy industry seeks to secure and maintain a social licence to operate.