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7 March 2019

Bulk Carrier Design at DNV GL

Bulk carriers in dirty ore and coal sectors are required to meet an increasing range of efficiency, safety and ecological standards.

DNV GL recently assisted with bulk carrier optimisation services for hull and machinery for a new type design Ultramax-size vessel called Diamond 2.

Type designs bear high-level engineering efforts

Ships with the fullness of a bulk carrier are difficult to analyse with computational fluid dynamics (CFD) due to a high share of viscous effects in resistance and propulsion. This makes hydrodynamic optimisation of bulk carriers expensive, although the outcome is considered marginal compared with a faster container vessel with even more installed power.

Building costs of a bulker often hardly exceed the steel price. Properties could immediately cancel high-level engineering such as optimisation if there was not such a large fleet of bulkers sailing the oceans. This is a good reason for Graig Shipping Group and Econovo to get into the market with a state-of-the-art Ultramax-type design from which presumably around 100 units will be delivered.

World-leading technology for hydrodynamics

For the hydrodynamic hull design, the well-known ECO-Lines services of DNV GL were used. The Diamond 2 received the complete package of treatments from wave reduction and aft-body propulsion optimisation on to an optimised twisted aft ship and a highly efficient design propeller.

CAESES is linked in the process chain for automatically generating the hull geometry. From there, all necessary data is taken into account, including constraint values and numerous outputs for robust analysis such as reparametrised surfaces for grid generation in FS-Flow and STL meshes for the OpenFOAM-based RANS solver. This setup is a very powerful and efficient design process to quickly find the optimal design candidate.

Promising performance prediction

For this bulk carrier optimisation, the objective is the power consumption on five draft / speed combinations with typical time-at-sea weightings (operational profile). Whereas ships with high wave resistance ratio often see double digit optimisation results, it is a huge success for a bulker to be improved by 5% in the operation range. The ship was tested in SVA Potsdam (before the application of an asymmetric stern) and was compared to an anonymous fleet of four similar vessels.

Final results

The final hull features an optimised asymmetric stern instead of appendages. Simulations show another 2.6% power reduction due to the twisted inflow. A high-efficiency propeller and a rudder with a vortex-reducing bulb complete the propulsion system. Graig expects the efficiency enhancements to result in a fuel consumption of 14.6t per day at an optimised speed of 12k.

This paper aims to provide an overview of practical vessel shape optimisation using computational fluid dynamics (CFD) to inform the reader of the common techniques...
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