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Designing a Hydro-Structural Ship Model to Experimentally Measure its Vertical Bending and Torsional Vibrations

  • Houtani, Hidetaka (Fluids Engineering & Ship Performance Evaluation Department, National Maritime Research Institute) ;
  • Komoriyama, Yusuke (Structural Strength Evaluation Department, National Maritime Research Institute) ;
  • Matsui, Sadaoki (Structural Strength Evaluation Department, National Maritime Research Institute) ;
  • Oka, Masayoshi (Structural Strength Evaluation Department, National Maritime Research Institute) ;
  • Sawada, Hiroshi (Fluids Engineering & Ship Performance Evaluation Department, National Maritime Research Institute) ;
  • Tanaka, Yoshiteru (Structural Strength Evaluation Department, National Maritime Research Institute) ;
  • Tanizawa, Katsuji (Fluids Engineering & Ship Performance Evaluation Department, National Maritime Research Institute)
  • Received : 2018.10.02
  • Accepted : 2018.11.30
  • Published : 2018.12.31

Abstract

We herein propose a new design procedure of a flexible container ship model where the vertical bending and torsional vibration modes are similar to its prototype. To achieve similarity in torsional vibration mode shapes, the height of the shear center of the model must be located below the bottom hull, similar to an actual container ship with large opening decks. Therefore, we designed a ship model by imparting appropriate stiffness to the hull, using urethane foam without a backbone. We built a container ship model according to this design strategy and validated its dynamic elastic properties using a decay test. We measured wave-induced structural vibrations and present the results of tank experiments in regular and freak waves.

Keywords

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Fig. 1 Cross-sectional view of the left half of a box-shaped model.

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Fig. 2 (a) Deck widths of the model and (b) vertical bending stiffness EI at each square station.

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Fig. 4 Pictures (a, b) and schematic cross-sectional view (c) of the hydro-structural container ship model. (a) side view, (b) inside the hull. The location of the attached strain gauges are indicated in (c).

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Fig. 5 Results of the three-point bending test and torsion test. (a) Correlation between vertical bending strains ∊v and vertical bending moments, (b) correlation between deflection δz and vertical bending moment, and (c) correlation between torsional strain ∊T and torsional moment. BT: beam theory, FE: FE analysis.

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Fig. 6 FE analysis for a vertical bending test of a urethane plate with an FBG strain gauge. (a) Schematics of the cantilevered plate, and (b) FE analysis. Location of the FBG gauge is indicated by a red ellipse. The colors indicate the magnitude of normal stress; red: large, blue: small.

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Fig. 7 Time series obtained from the decay tests. (a) Vertical bending moment and (b) torsional moment.

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Fig. 8 Vertical bending and torsional moments measured in the towing experiment in the regular wave. (a) Time series of the vertical bending moment, (b) frequency spectrum of the vertical bending moment, (c) time series of the torsional moment, and (d) frequency spectrum of the torsional moment.

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Fig. 9 Wave elevation, ship motions, and vertical acceleration at FP measured in the towing experiment in the freak wave.

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Fig. 10 Vertical bending and torsional moments measured in the towing experiment in the freak wave. (a) Time series of the vertical bending moment, (b) frequency spectrum of the vertical bending moment, (c) time series of the torsional moment, and (d) frequency spectrum of the torsional moment. The lowest natural frequencies are indicated by arrows.

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Fig. 3 Vibration-mode analysis with FE models. (a) 1st torsional mode, (b) 1st vertical bending mode.

Table 1 Principal dimensions and quantities related to the midship section. α is the model scale.

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Table 2 Designed values related to stiffness at the midship section.

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Table 3 Comparison of the wet natural frequencies. Unit: Hz

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Acknowledgement

Supported by : KAKENHI

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