Study on Eigenvalue Analysis for a Towed Cable - Free Boundary at the Bottom End

J. Ocean Eng. Technol. 2009;23(1):74-80.

Jung Dong-Ho,Kim Hyeon-Ju,Moon Deok-Soo,Lee Seung-Won

Ocean System Research Laboratory KORDI,Ocean System Research Laboratory KORDI,Ocean System Research Laboratory KORDI,Ocean System Research Laboratory KORDI

예인되는 케이블의 고유치 해석에 관한 연구 - 하부 끝단 자유 경계조건

정동호,김현주,문덕수,이승원

한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부

Keywords: Towed cable, Vortex-induced vibration, Natural frequency, Lock-in, Numerical study

핵심용어: 예인케이블, 와류유기진동, 고유진동수, 록-인, 수치해석

Abstract

In this study, the static and modal analyses to find the characteristic of eigenvalues for a towed cable were with a free boundary condition at the bottom end carried out with numerical study. The resulting numerical code with finite element method was used to study sample problems for a cable with towing speeds. After tracing the equilibrium state with a towing speed through the static analysis, modal analysis on the basis of static results was performed. The static top tension for a critical towing speed is nearly 50 percent of what it was for a free hanging pipe. From static analyses, it is found that towing speed has a noticeable effect on top tension of a towed pipe. At a high towing speed, differences between the first and second periods become larger. Compared to the fundamental period for a free hanging pipe, that for a towed pipe with a critical towing speed is approximately 1.4 times larger. This result is very important point in that the lock in condition and tension of the towed cable system with top excitation can be predicted. The corrected close form solution to solve natural periods for a towed cable was presented in this study. The code is validated by comparison of the results of theoretical and numerical studies. Two results were in very good agreement. This study can contribute to predicting the lock-in condition and tension for a towed cable or pipe with top excitation.