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Changes in Dynamic Characteristics of Monopile-Type Offshore Structures According to Tidal Environments and Boundary Conditions

다양한 조류 환경 및 경계 조건에 따른 모노파일형 해상구조물의 동특성 변화 분석

Jung, Byung-Jin;Park, Jong-Woong;Yi, Jin-Hak;Park, Jin-Soon
정병진;박종웅;이진학;박진순

  • Received : 2014.01.23
  • Accepted : 2014.08.19
  • Published : 2014.08.30

Abstract

Because a change in the natural frequencies of a structure indicates structural health problems, monitoring the natural frequencies crucial. Long-term measurement for the Uldolmok tidal current power plant structure has shown that its natural frequencies fluctuate with a constant cycle twice a day. In this study, lab-scale tests to investigate the causes of these natural frequency fluctuations were carried out in a circulating water channel. Three independent variables in the tests that could affect the fluctuation of the natural frequencies were the water level, current velocity, and boundary condition between the specimen and the bottom of the circulating water channel. The experimental results were verified with numerical ones using ABAQUS. It was found that the fluctuation of the natural frequencies was governed by a decrease in stiffness due to the boundary condition much more than the effect of added mass. In addition, it was found that the natural frequency would decrease with an increase in the tidal current velocity because of its nonlinearity when the boundary condition was severely deteriorated due to damage.

Keywords

Natural frequency;Added mass;Monopile-type offshore structures;Tidal effects;Circulating water channel;Boundary condition

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Acknowledgement

Grant : 조류발전 시스템 성능향상 기술개발

Supported by : 한국해양과학기술원