The LNGreen concept uses existing technology to improve energy efficiency and performance. Click to enlarge.

LNGreen investigated the improvement of efficiency and performance of LNG carriers by considering actual operational conditions and optimization in terms of hydrodynamics, machinery and system configuration. These developments were based on DNV GL’s integrated systems engineering approach COSSMOS; state-of-the-art computational fluid dynamics calculations (CFD); and a containment system design tailored to a specific operational profile and anticipated trades.

(Developed by DNV GL Strategic Research & Innovation, DNV COSSMOS is a computer platform that models, simulates and optimizes complex and integrated ship machinery systems with respect to energy efficiency, emissions, costs and safety. With COSSMOS, DNV GL is able to analyze alternative configurations in new vessels, perform assessment and optimization in ships in operation systems, and evaluate the potential of new technologies.)

Using enabling computer tools we managed to develop a vessel which is approximately 8% more energy efficient and has increased its cargo volume capacity by 5%. The design is future compliant with new IGC code, Panama requirements as well as significant advances in a range of features, including the speed-range flexibility, hull form and boil-off rate.

—Martin Davies, the Project Manager at DNV GL

The total efficiency was assessed using an integrated systems approach. LNG carrier machinery systems are highly complex featuring tightly integrated sub-systems and components, such as BOG (boil-off gas) compression trains; gas management system; reliquefaction (if any); propulsion and/or generating engines; exhaust gas economizers; and boilers.

The primary fuel—i.e. boil-off gas—has variable properties depending on LNG cargo type and in-voyage boil-off rate conditions. In addition, the ships usually operate on a number of trading routes. Their operating profiles vary in terms of speed, propulsion, electrical and heat demand. The above features require a rigorous model-based approach, using DNV GL COSSMOS, to assess the integrated machinery system under realistic operating conditions as experienced by GasLog.

HHI and DNV GL carried out the hydrodynamic performance evaluation by comparing CFD simulations. Different CFD codes were applied for the comparison of resistance and self-propulsion performance but different scale effects were also considered. In addition, added resistance caused by wind and waves was investigated in order to ensure that the required power is sufficient for operation in the targeted environmental conditions.

GTT and HHI investigated cargo containment optimization. The tank shape, necessary reinforcements and boil-off rate calculations were examined to develop alternative cargo tank designs that could yield additional cargo capacity. With a starting design point of 174,000 m³ cargo capacity, cargo tank optimization by GTT and HHI allowed for a cargo capacity increase to 182,800 m³, while maintaining the same main dimensions (length overall, breadth, draft) and taking into consideration newly introduced regulations and compatibility restrictions.

Fusing unique competencies of key experts from across the industry, like HHI, GTT, and GasLog, with advanced tools like the COSSMOS machinery systems simulation and optimisation computer platform as well as state-of-the-art hull optimisation software, we bring innovation in practice that can generate tangible added value. As LNGreen utilizes existing technology it is important to stress that this concept design could be ordered today.

—Nikolaos Kakalis, Manager of DNV GL Research & Development in Greece and responsible for COSSMOS development