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By Shin Hyung Rhee, Fluent Inc.
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Pathlines around a submarine showing the flow generated by the propeller at the rear of the ship
Shipping is one of the most ancient methods of transporting goods. In the twenty-first century, ships are still responsible for over 90% (by volume) of the worldwide transport of goods. Due partly to its long history and partly to its intractability, naval architecture was, at one time, considered more of an art than a science. With recent trends in advanced numerical simulation technologies and high performance computing, however, this view has changed. Nowadays computational simulation tools are as important as physical model testing and attract an increasing number of field engineers and designers.
Free surface, colored by elevation, surrounding the IIHR surface piercing foil
Surface waves, colored by elevation, generated by the passage of a DD5415 destroyer hull
CFD has reached maturity as a powerful marine design tool capable of accurately predicting complex flow phenomena. A key advantage is its ability to model the complicated geometries that are typical of real-world equipment. In recent years, CFD capabilities have been expanded through the development of new physical models. Turbulence models have been developed that are well-suited to the complex flow around ship hulls. Free surface models have been improved to the point where they can simulate breaking ocean waves as well as liquid sloshing in a tank, a phenomenon that is common on liquid natural gas (LNG) carriers. Cavitation models have been developed and employed for various applications, such as cavitating propellers, rudder cavitation, and super-cavitating vehicles. Other multiphase models have been developed to simulate the flow inside ballast tanks as well as oil leaks. The multi-species reacting flow capability is available for analyses ranging from stack gas dispersion and cabin/cargo-hold ventilation to engine design and engine room fires. Recently the implementation of a six-degrees-of-freedom (6DOF) dynamic mesh capability in FLUENT 6.2 has enabled ships and other objects to move as the result of external forces, rather than on a prescribed trajectory. With the 6DOF option, more sophisticated seakeeping and maneuvering simulations have become possible.
The articles in this supplement illustrate many of these features as they have been put to use for marine applications. Ventilation of a refrigeration system on a container ship is examined (article Cooling It on the High Seas), as is a process used for bilge water cleanup (article Clean Bill of Ballast Water Health). Some of the CFD work that is ongoing at a Bulgarian shipyard is reviewed (article A Sea of Marine Research at BSHC), and a method for extracting 3D data sets for marine laboratory tests is described (article A New Dimension in PIV). Propeller modeling is the focus of three articles, starting on (article Propelling the French Navy). Two of these examine cavitation (article Open Water Propeller Cavitation and Cavitation in the Wake of a Ship). Finally, the sailing yacht pictured on the supplement cover is one of several simulations of aero and hydrodynamics (article Reaching for Better Yacht Design).
The future of CFD is brighter than ever with increasing computational power and ongoing development of physical models and numerical simulation technologies. Moreover, the seamless integration with other CAE tools for CAD import, structural analysis, and design will bring forth the age of the virtual shipyard in the very near future.
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