• 대한토목학회논문집
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• 제7권4호
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• pp.73-81
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• 1987

본 논문에서는 파랑하중에 대한 Tension Leg Platform(TLP)의 tether와 platform의 동적거동해석에 대해서 연구하였다. tether의 동특성 효과를 적절하고도 간단히 고려할 수 있는 platform 해석모델을 제안하여 platform 운동해석을 수행하였으며, tether에 작용하여 인장력에 기인된 기하학적 강성을 고려한 유한요소법을 사용하여 tether의 거동을 해석하였다. 해석 예제용구조물로는 설치수심이 1000ft 및 3000ft인 두 가상적인 TLP를 선택하였으며, 비교를 목적으로 tether의 동특성 효과를 고려하지 않은 기존모델 및 platform과 tether를 조합한 모델 등에 의한 해석도 수행하여, 그 결과를 본 연구에서 제안한 모델에 의한 platform 운동과 tether의 거동 해석결과와 비교분석하였다. 아울러, tether의 통상적인 휨강성 및 tether에 작용하는 파랑하중이 tether의 거동에 미치는 영향정도도 고찰하였다.

• International Journal of Aeronautical and Space Sciences
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• 제8권2호
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• pp.67-75
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• 2007

An attitude control problem for a tethered spacecraft is studied. The tethered spacecraft is viewed as a multi-body spacecraft consisting of a base body, a massless tether that connects the base body and an end mass, and tether actuator dynamics. Moments about the pitch and roll axes of the base spacecraft arise by control of the point of attachment of the tether to the base spacecraft. The control objective is to stabilize the attitude of the base spacecraft while keeping the perturbations of the tether small. Analysis shows that linear equations of motion for the tethered spacecraft are not completely controllable. We study two different control design approaches: (1) we decouple the attitude dynamics from the tether dynamics and we design a linear feedback to achieve stabilization of the attitude dynamics, and (2) we decouple the controllable modes from the uncontrollable mode using Kalman decomposition and we design a linear feedback to achieve stabilization of the controllable modes. Simulation results show that, although it is difficult to control the tether, the tether motion can be maintained within an acceptable range while stabilizing the attitude dynamics of the base spacecraft.

• 한국해양공학회지
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• 제24권1호
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• pp.10-19
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• 2010

ANSYS multi-physics software was applied to solve the coupled dynamic problem related to a full-scale TLP foundation for floating wind turbines. In this coupled dynamics simulation, the forced oscillation imposed on the tethers' top resulting from the sway of the wind turbine platform and the self-excited vortex-induced vibration (VIV) along the tether span have been taken into account. The stability of this tensioned tether system has been validated in the form of separate static and dynamic analyses. The dynamic characteristics of the tensioned tether linked to the floating wind turbine were analyzed by the resultant modal form and its corresponding vortex shedding pattern. The calculated result shows that even a slight forced oscillation imposed on the tethers' top leads to the VIV amplification and enhances the risk of instability in the case of low pretension. It is also found that the "synchronization" would be aggravated when the top tension decreases and the "2P" vortex shedding mode takes place. The increased top tension imposed on the tethers contributes to the stability of the tensioned legs by diminishing the oscillation amplitude markedly.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.710-711
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• 2010

• Ocean Systems Engineering
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• 제1권1호
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• pp.95-111
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• 2011

Increasing numbers of floating offshore wind turbines are planned and designed these days due to their high potential in massive generation of clean energy from water depth deeper than 50 m. In the present study, a numerical prediction tool has been developed for the fully-coupled dynamic analysis of FOWTs in time domain including aero-blade-tower dynamics and control, mooring dynamics, and platform motions. In particular, the focus of the present study is paid to the dynamic coupling between the rotor and floater and the coupled case is compared against the uncoupled case so that their dynamic coupling effects can be identified. For this purpose, a mono-column mini TLP with 1.5MW turbine for 80m water depth is selected as an example. The time histories and spectra of the FOWT motions and accelerations as well as tether top-tensions are presented for the given collinear wind-wave condition. When compared with the uncoupled analysis, both standard deviations and maximum values of the floater-responses/tower-accelerations and tether tensions are appreciably increased as a result of the rotor-floater dynamic coupling, which may influence the overall design including fatigue-life estimation especially when larger blades are to be used.

• Journal of Astronomy and Space Sciences
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• 제20권4호
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• pp.319-326
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• 2003

The motion of each satellite in a tethered satellite system is non-Keplerian in the Earth's gravitational field. In this paper, the tether perturbation force is formulated and compared with the perturbation force due to the Earth's oblateness. Also, the center of mass motion of the tethered satellite system is analyzed. The tether perturbing force on the one of satellites in a tethered satellite system is much bigger than the Earth's oblateness perturbation. The two-body motion approximation of the center of mass is acceptable to describe the motion of the system, when the libration is small.

• Steel and Composite Structures
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• 제2권5호
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• pp.331-354
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• 2002

Tethers of Tension Leg Platform (TLP) are a series structural system where fatigue is the principal mode of failure. The present study is devoted to the fatigue and fatigue fracture reliability study of these tethers. For this purpose, two limit state functions have been derived. These limit state functions are based on S-N curve and fracture mechanics approaches. A detailed methodology for the reliability analysis has then been presented. A sensitivity analysis has been carried out to study the influence of various random variables on tether reliability. The design point, important for probabilistic design, is located on the failure surface. Effect of wind, water depth, service life and number of welded joints are investigated. The effect of uncertainties in various random variables on tether fatigue reliability is highlighted.

• 한국소음진동공학회논문집
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• 제21권8호
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• pp.691-697
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• 2011

The purpose of this study is to analyze nonlinear dynamics of a tethered satellite. The coupled non-linear equations of motion are derived by using the extended Hamilton's principle with the polar coordinate system. In order to analyze the response of tethered satellite, time responses are computed by the Newmark's time integration method. We also investigate the dynamic behavior of the system and the effects of length of tether, tip mass and conveyed fluid through the tether with time variation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.757-761
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• 2008

The aerostat dynamic equation of motion has been built including the tether cable dynamic effects. A numerical program to solve the derived equation of motion has been developed. The dynamic motion of the 32m aerostat has been analyzed under discrete gust and continuous turbulence. The aerostat behaviors under discrete gust which represents a deterministic approach for determining design loads for manned aircraft are solved to verify the effect of aerostat mechanical properties on the aerostat dynamic behavior. Continuous turbulences are simulated for each given altitude, translational mean wind velocity and gust intensity. Dynamic behaviors of the 32m aerostat are simulated for each continuous turbulence conditions. Translational and vertical velocity and pitching behavior and tether reaction force are monitored for each simulation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.300-305
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• 2004

A preliminary study on. field emitter array cathodes was conducted aiming at applying for electrodymanic tether (EDT) propulsion systems. The EDT propulsion systems are assumed to use for active removal systems of post-mission spacecraft, which would otherwise become space debris. A survey on field emit-ter array cathode technology was conducted, and it showed that carbon nanotube (CNT) emitters are suit-able to EDT application. Trial fabrications and evaluation tests of CNT emitters were conducted, which demonstrated a target emission current density of 10 ㎃/$\textrm{cm}^2$. It was found out that the most important technical issue for developing CNT emitters is to improve the performance against voltage breakdown between the emitter and the opposite electrode.