Researchers have developed a novel model to accurately and efficiently predict the impact of ‘green water’ – water washing on to the deck of an offshore facility during extreme wave conditions.
Transforming energy Infrastructure through Digital Engineering (TIDE) researchers at The University of Western Australia developed the models for Floating Production, Storage and Offloading (FPSO) facilities, which house essential components for hydrocarbon processing.
They include separation systems, water treatment, gas compression equipment, power generation, heating, ventilation and air conditioning systems, control rooms and living spaces.
As part of a plan to optimise hull size and deck layout, industry partners collaborated with TIDE to better understand wave overtopping and resultant green water loading on topside modules and equipment located on the deck to ensure safer and more efficient design.
TIDE researchers conducted tests in UWA’s wave flume, using scale models of a FPSO and its topside modules to recreate extreme wave events and measure how water overtops the vessel and impacts the structures, allowing them to identify the largest green water forces that occur.
TIDE PhD graduate, Dr Min Gao used these experiments and advanced computational fluid dynamics to investigate green water loading on different shaped structures.
Following advice from his supervisor, Emeritus Professor Paul H. Taylor, Dr Gao found a simpler method based on Newton’s conservation of momentum principles that can accurately predict forces that result from shallow, high-speed flows such as green water overtopping.
Written more than 300 years ago, Newtonian momentum theory has previously been shown to be useful for fluid flows in hypersonic aerodynamics but had not been successfully applied to hydrodynamics.
“This finding enabled me to develop an analytical model whereby the impact of the load on topside structures can be accurately estimated using only information on the undisturbed on-deck flow, no matter where components are placed,” Dr Gao said.
Dr Gao’s findings have the potential to make faster and easier estimates of green water loads for offshore design and allow TIDE industry partners to iterate and optimise hull size and layouts.
Professor Scott Draper, co-Deputy Director of the TIDE hub, said previous analytical methods for modelling have been approximate but Dr Gao’s method was more precise.
“This accuracy supports the design of safer, more cost-effective offshore facilities,” Professor Draper said.
Adjunct Associate Professor James Whelan, from UWA’s School of Engineering, said Dr Gao had identified a simpler model that enhanced our understanding and ability to predict load.
“We wanted to ensure that reducing our FPSO hull size didn’t equate to the reduced safety of people and environment by compromising structural reliability,” Associate Professor Whelan said.
“The research undertaken by TIDE, through Dr Gao’s PhD, has materially improved our understanding of green water loading on topside modules, which can now be explored for inclusion in industry standards.”
Applications of the research extend beyond offshore structures with further benefits to be realised, such as understanding potential damage to coastal structures in the event of tropical storms.
“The industry-research relationship we’ve built has forged a trust that enables both parties to have transparency and leads to better outcomes and greater impact – we know what the design challenges are and can use this knowledge to deliver relevant research programs and outputs,” Professor Draper said.