Elastic Behavior of a Huge Pontoon-Typed Floating Structure among Waves

Research Project

Project/Area Number	07651142
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	海洋工学
Research Institution	Kanazawa Institute of Technology
Principal Investigator	HATTORI Yoichi Kanazawa Institute of Technology, Department of Technology, Professor, 工学部, 教授 (40198768)
Co-Investigator(Kenkyū-buntansha)	FUKASAWA Toichi Kanazawa Institute of Technology, Department of Technology, Professor, 工学部, 教授 (80143171)
Project Period (FY)	1995 – 1996
Project Status	Completed (Fiscal Year 1996)
Budget Amount *help	¥2,100,000 (Direct Cost: ¥2,100,000) Fiscal Year 1996: ¥1,000,000 (Direct Cost: ¥1,000,000) Fiscal Year 1995: ¥1,100,000 (Direct Cost: ¥1,100,000)
Keywords	huge floating strucuture / wave exciting force / characteristics of dynamic response / amplitude of forced vibration / characteristic mode / characteristic value
Research Abstract	The purpose of this research is to clarify the dynamic characteristics of huge pontoon-typed floating structures which encounter waves with various wave lengths, wave heights and wave directions. First a huge floating structure was replaced with a beam on an elastic foundation and the structural response under wave exciting forces was introduced, using mode method, i.e. the amplitude of the displacement of the structure was non-dimensioned and parameters which affect the non-dimensional amplitude were defined. The natural circular frequency omega of the waves were changed from 0 to 2.8 rad/s with the interval of 0.2 rad/s and the corresponding non-dimensional amplitudes were obtained. The amplitude increases with w until about 0.4 rad / s where the amplitude becomes maximum and then next peak comes at about 2.23 rad/s. Later on many peaks are seen with small intervals which correspond to natural circular frequencies of the structure. The mode method needs many terms to be superposed, because the length of the structure is so long and its natural circular frequencies of the structure are arranged with small intervals. Comparing with the results of direct method which were introduced by Suzuki et al, about 100 terms are needed within the range below natural circular frequency of heaving but much more terms become necessary at the range of higher natural circular frequencies. On the other hand the huge floating structure was replaced with a rectangular plate and natural modes were obtained by finite element method. There are two kinds of natural modes ; one is the mode with no change toward breadth direction which corresponds to the mode of a beam and the other is the twisting mode. The natural circular frequencies of the former mode obtained by finite element method show good agreement with those obtained by replacing the structure with a beam on an elastic foundation.