• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.723-726
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• 2011

전 세계적으로 사회기반시설 및 신재생 에너지 생산을 위한 공간부족 문제를 해결하기 위하여 초대형 부유구조물에 대한 관심이 증가하고 있다. 다양한 사용분야에 대한 안정성 확보를 위해 파랑하중에 의한 동적 응답과 부유체의 강성 대비 길이 효과로 인해 발생할 수 있는 특이 거동에 대한 분석이 필요하다. 초대형 부유구조물의 경우 중앙부에 비해 양끝 단에서 과도한 응답이 발생하며, 이를 해결하기 위해 입사파가 들어오는 초대형 부유구조물의 단부에 부착되는 다양한 감요장치(anti-motion device)가 제안되어지고 있다. 초대형 부유구조물에 감요장치가 적용될 경우 입사파에 의한 동적 파압을 감소시켜 구조물의 전반적인 응답을 줄여줄 수는 있지만 감요장치의 질량이 클 경우 오히려 끝단의 응답을 증폭시킬 수 있다. 본 논문에서는 양단 자유 경계조건의 탄성지지된 보를 이용하여 초대형 부유구조물의 길이와 끝단에 부착된 감요장치의 질량으로 인한 영향을 분석하였다.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.31-37
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• 1994

3-Dimensional panel method is now developed to the level that one can calculate the lift of a three dimensional body with the same accuracy of wind tunnel test and some current codes can consider the boundary layer effects due to the viscosity and unsteady motion in the calculation of lift. This paper is also aimed to develop these kinds of computing programs, and as a beginning, the authors restricted the problems to the steady potential flow cases. The calculation of 3-Dimensional body, wing and tandem wing carried out, using source panel and vortex ring panel. Finally, the interactions between 3-Dimension symmetric body and a wing are also calculated.

• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.393-401
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• 2018

This paper reports a novel mobile-type wave energy harvesting system. The proposed system adopts a wave glider's propulsion mechanism. A wave glider's blades were mounted on a circular layout and generated a rotational motion. Combining the wave converting system with the wave glider, a mobile floating-type robotic buoy system was developed. It enabled the relocation of the buoy position, as well as station-keeping for long term operation. It had a small size and could efficiently harvest wave energy. A feasibility study and modeling were carried out, and a prototype system was constructed. Various tank tests were performed to optimize the proposed wave energy harvesting system.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.170-179
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• 2018

This paper introduces a new method to study the hydroelastic behavior of hinged Very Large Floating Structures (VLFSs). A hinged two-module structure is used to confirm the present approach. For each module, the hydroelasticity theory proposed by Lu et al. (2016) is adopted to consider the coupled effects of wave dynamics and structural deformation. The continuous condition at the connection position between two adjacent modules is also satisfied. Then the hydroelastic motion equation can be established and numerically solved to obtain the vertical displacement, force and bending moment of the hinged structure. The results calculated by the present new method are compared with those obtained using three-dimensional hydroelasticity theory (Fu et al., 2007), which shows rather good agreement.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.4
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• pp.449-456
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• 2015

In this paper, attaching various damping plates to the cylindrical structure and performing numerical simulations try to study heave RAO and natural period for cylinder. Most of all, we identified heave RAO of the cylinder by simulations of the motion and the wave. And then, we performed numerical simulations by changing the size and shape of heave damping plate attached to the cylinder and reviewed the heave RAO and natural period for each case. The conclusions of this research are as follows. Firstly, the natural period of cylindrical structure is increased by attached to the cylinder with heave damping plate and the heave RAO of cylindrical structure is reduced in the peak period for incident wave by attached to the cylinder with from the size of 1.30D for heave damping plate. Secondly, circular plate has long natural period than Y-type plate in all of these sections. Finally, the motion response spectrum considering the marine environment of Piranema field was identified as the heave motion of cylindrical structure is remarkably reduced with both circular plate and Y-type plate in the peak period for incident wave.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1887-1895
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• 2013

In this study, physical experiments were performed in a two-dimensional wave flume to investigate the hydraulic and structural performance of a SFT model. The experiments were made by generating regular waves of different heights and periods under various conditions of buoyancy to weight ratio (BWR) and water depth as well. Through the analysis of the experimental data, it was clarified that the sway and heave motions of the tunnel body linearly increased with wave height and period. In contrast, the roll motion was rather insignificant unless wave height and period were comparatively large as the design wave. Similarly proportional relationship with respect to wave height and period was obtained in case of the maximum tensile force acting on the tension legs and the wave loads on the tunnel body. Regarding the change of water depth or BWR conditions, generally decreasing trend was obtained according to increase of water depth but decrease of BWR for both of the magnitudes of structural behaviors or wave loadings on the SFT structure.

• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.99-110
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• 2017

This paper presents the study of the bending behavior of mooring chain links for keeping the position of the offshore floating structures. In general, chain links have been thought as the axial members due to the fundamental boundary condition. But, the flexural stiffness can be induced to the contact surface between chain links when friction occurs at the surface of the chain links due to high tensile force. Especially, the mooring chains for offshore floating platforms are highly tensioned. If the floater suffers rotational motion and the mooring chain links are highly tensioned, the rotation between contact links, induced by the floater rotation, generates the bending moment and relevant stresses due to the unexpected bending stiffness. In 2005, the mooring chain links for the Girassol Buoy Platform were failed after just 5 months after facility installation, and the accident investigation research concluded the chain failure was mainly caused by the fatigue due to the unexpected bending stress fluctuation. This study investigates the pattern of the induced bending stiffness and stresses of the highly tensioned chain links by nonlinear finite element analysis.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1183-1188
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• 2005

In this paper, we propose a 3D automated measuring system which measures the mandibular movements and the reference plane of the jaw movements. In diagnosis and treatment of the malocclusions, it is necessary to estimate the mandibular movements and the reference plane of the jaw movements. The proposed system is configured with double stereo-cameras, PC, two moving pattern plates(MPPs), two fixed pattern plates(FPPs) and one orbital marker. The virtual pattern plate is applied to calculate the homogeneous transformation matrices which describe the coordinates systems of the FPP and MPP with respect to the world coordinates system. To estimate the parameters of the hinge axis, the Euler's theorem is applied. The hinge axis points are intersections between the FPPs and the hinge axis. The coordinates of a hinge axis point with respect to the MPP coordinates system are set up to fixed value. And then, the paths of the jaw movement can be calculated by applying the homogeneous transformation matrix to fixed hinge axis point. To examine the accuracy of the measurements, experiments of measuring the hinge axis points and floating paths of them are performed using the jaw motion simulator. As results, the measurement errors of the hinge axis points are within reasonable boundary, and the floating paths are very similar to the simulator's moving path.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.611-619
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• 2008

In most shipyards Floating Dock-gate System is adapted for dry docks. For the safe launching of ships in dry docks, smooth operation of dock-gate must be guaranteed. So it is very important to grasp its behavior in waves for securing the high productivity and the safety of workers. Its seakeeping ability was estimated numerically at the floating conditions and the free roll decay and the seakeeping model tests of dock-gate was carried out with bilge-keels of 3 different widths which have a scale of 1 to 20. More than 20% decrease of roll motion was observed in irregular beam seas by applying a bilge-keel system to the dock-gate that is long and narrow.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.9-20
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• 2018

Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.