Conflicting Objectives in Ship Design: Environmental & Safety Regulations Conspire to Complicate Optimization

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The International Maritime Organization (IMO) places restrictions on greenhouse gas emissions from ships and offshore structures. This motivates owners to look for new ways to reduce fuel consumption, and one option is to reduce main engine power. But less power means less "sea margin" for when weather conditions get rough, and owners need to know whether their vessels are still safe. For example, can a given design safely maneuver off a lee shore during storm conditions? Satisfying the new regulations therefore requires more than just down-sizing. Overall propulsive power has to be reduced, but through some combination of engine size and efficiency improvement. CFD provides first-principals solutions to both problems. It can be coupled with optimization codes to search for the combination of design parameters that minimizes required power for a given design. It can also predict maneuvering performance in extreme weather. 

This presentation provides examples for both types of design studies. First, CFD is used to build a “black box” for feeding objective functions to Red Cedar’s HEEDS optimizer. The propellers behind a twin-screw LNG carrier are parameterized, and HEEDS is used to search for the most energy efficiency combination of parameters. Second, simulations are performed for a tanker maneuvering under extreme weather conditions (high wind and large waves) to check that the vessel can turn into the wind and then maintain an acceptable forward speed. Simulations are conducted over a range of power, and the results used to specify minimum acceptable design margins. Validation comparisons are provided by comparing to propeller model test results and the well-documented KVLCC2 tanker seakeeping experiments.

Author Company: 
American Bureau of Shipping
Author Name: 
Richard Korpus