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Practical Ship Hydrodynamics Episode 8

Tham khảo tài liệu 'practical ship hydrodynamics episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Ship seakeeping 131 for commercial passenger transport. For fast cargo ships the reduced speed in seaways can considerably influence transport efficiency. A hull form which is superior in calm water may well become inferior in moderate seaways. Warships also often require good seakeeping to supply stable platforms for weapon systems helicopters or planes. Unfortunately computational methods for conventional ships are usually not at all or only with special modifications suitable for fast and unconventional ships. The special High-speed strip theory see section 4.4.1 has been successfully applied in various forms to both fast monohulls and multihulls. Japanese validation studies showed that for a fast monohull with transom stern the HSST fared much better than both conventional strip methods and threedimensional GFM and RSM. However the conventional strip methods and the three-dimensional methods did not use any special treatment of the large transom stern of the test case. This impairs the validity of the conclusions. Researchers at the MIT have shown that at least for time-domain RSM the treatment of transom sterns is possible and yields good results also for fast ships albeit at a much higher computational effort than the HSST. In most cases HSST should yield the best cost-benefit ratio for fast ships. It is claimed often in the literature that conventional strip methods are only suitable for low ship speeds. However benchmark tests show that strip methods can yield good predictions of motion RAOs up to Froude numbers Fn 0.6 provided that proper care is taken and the dynamic trim and sinkage and the steady wave profile at the hull is included to define the average submergence of the strips. The prediction of dynamic trim and sinkage is relatively easy for fast displacement ships but difficult for planing boats. Neglecting these effects i.e. computing for the calm-water wetted surface may be a significant reason why often in the literature a lower Froude number .