LNG ship for tomorrow could be ordered today

LNG carrier machinery systems are highly complex

JULY 20, 2015 — DNV GL reports that the LNGreen joint industry project has been completed. The partners — DNV GL and industry specialists from GTT, shipbuilder Hyundai Heavy Industries (HHI) and shipowner GasLog— contributed their know-how and experience to develop tomorrow’s LNG carrier using the latest technology, within the bounds of existing shipbuilding methods.

The resulting concept vessel is said to have a significantly improved environmental footprint, a higher level of energy efficiency, as well as an improved boil-off rate and cargo capacity, making it better suited to future trading patterns than existing vessels.

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.

Martin Davies, the Project Manager at DNV GL, says that “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.”

The total efficiency was assessed using an integrated systems approach. LNG carrier machinery systems are highly complex featuring tightly integrated sub-systems and components, like the BOG 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.

A rigorous model-based approach, using DNV GL COSSMOS, was used 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 was sufficient for operation in the targeted environmental conditions.

Cargo containment optimization was investigated by GTT and HHI. 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 cu.m cargo capacity, cargo tank optimization by GTT and HHI allowed for a cargo capacity increase to 182,800 cu m, while maintaining the same main dimensions (length overall, breadth, draft) and taking into consideration newly introduced regulations and compatibility restrictions.

Nikolaos Kakalis, Manager of DNV GL Research & Development in Greece and responsible for COSSMOS development commented that “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 optimization computer platform as well as state-of-the-art hull optimization 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.”