Journal of the Society of Naval Architects of Korea (대한조선학회논문집)

The Society of Naval Architects of Korea (대한조선학회)
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Wet Damping Estimation of the Segmented Hull Model using the Random Decrement Technique

랜덤 감쇠기법을 이용한 분할모형의 접수 감쇠계수 추정

  • Kim, Yooil (Department of Naval Architecture and Ocean Engineering, College of Engineering, INHA University) ;
  • Park, Sung-Gun (Structure R&D Group, DSME R&D Institute, Daewoo Shipbuilding and Marine Engineering)
  • 김유일 (인하대학교 공과대학 조선해양공학과) ;
  • 박성건 (대우조선해양 중앙연구소 구조R&D그룹)
  • Received : 2013.01.14
  • Accepted : 2013.06.26
  • Published : 2013.08.20
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Abstract

This paper presents the wet damping estimation of the segmented hull model using the random decrement technique together with the continuous wavelet transform. The tested 16 sea states are grouped together based on the speed of the ship in order to figure out the possible influence of the ship speed on the damping ratio. The measured time histories of vertical bending moment for each tested sea state were processed with random decrement technique to derive the free decay signal, from which the damping ratios are estimated. Also, the autocorrelation functions of the filtered signal were calculated and comparison was made with the free decay signal obtained from the random decrement technique. Then the wet damping ratios for each sea state group, as well as precise wet natural frequencies, are estimated by using continuous wavelet transform. It turned out that the wet natural frequencies derived from the measured signal did not show any significant discrepancy compared with those obtained by wet hammering test, whereas the damping ratio did. It was considered that the discrepancy of the damping ratio between in calm and moving water may be attributed to the viscous effects caused by dramatically different flow pattern and relative velocity between the vibrating structure and surrounding fluid particles.

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References

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