2003 Fiscal Year Final Research Report Summary
A study on non-linear viscous farces acting on a ship with large amplitude of motions
| Project/Area Number |
12305065
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
船舶工学
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| Research Institution | OSAKA PREFECTURE UNIERSITY |
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Principal Investigator |
IKEDA Yoshiho Osaka Prefecture University, Marine System Engineering, Professor, 大学院・工学研究科, 教授 (10117989)
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| Co-Investigator(Kenkyū-buntansha) |
KURODA Takako Hokkaido University, Graduate School of Fisheries Sciences, JSPS Research Fellow, 大学院・水産科学研究科, 日本学術振興会特別研究員
KATAYAMA Toru Osaka Prefecture University, Marine system Engineering, Research Associate, 大学院・工学研究科, 助手 (20305650)
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| Project Period (FY) |
2000 – 2003
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| Keywords | ship motion / ship / large motion / non-linear / rolling / drift motion / viscous forces / bilgekeels |
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| Research Abstract |
In heavy waves, ship motions are strongly non-linear and unstable. In the present study, the characteristics of the non-linear ship motions are investigated and the roles of non-linear viscous forces on them are revealed.
It is experimentally found that in heavy beam seas a ship is experienced large amplitude roll motion in wide range of wave frequencies and a jump phenomena appears at a certain wave frequency. The large and unstable roll motions appear for a ship with similar roll and heave natural frequencies and in high wave with high frequency. it is revealed that fast drift motion of the ship cause the large and unstable roll motion by changing encounter frequency, wave-induced drift force, viscous drift resistance, roll damping and wave-induced roll exciting moment. This fact suggests that roll motion of a ship in heavy beam seas should be treated as an coupled motion of wave-frequency ship motions and steady drift motion.
A prediction method of roll damping of a ship with steady drift motion is deduced on the basis of a roll prediction method by the head investigator of the present research project. It is confirmed that the predicted results by the method are in fairly good agreement with experimental results.
The drift resistance acting on a ship with large roll motion is experimentally investigated to find the characteristics. The experiments revealed that the drift resistance coefficient due to viscosity is not constant but depends on Kc number which is defined by taking the effect of drift motion into account. A prediction method of the coefficient is deduced.
The characteristics of viscous damping forces acting a heaving body with bilge keels are experimentally investigated. It is found that strong non-linearity appears in the hydrodynamic forces because of unsymmetrical strong vortex shedding in large amplitude
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