• Earthquakes and Structures
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• 제25권6호
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• pp.455-467
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• 2023

This study focuses on demonstrating the effectiveness of vibration control of tuned rotary mass damper (TRMD) for reducing the bidirectional and torsional response of the irregular asymmetric structure with voided slabs under earthquake excitations. The TRMD arranged in plane of one-story eccentric structure is proposed as a distributed tuned rotary mass damper (DTRMD) system. Lagrange's equation is used to derive the equations of motion of the controlled system. The optimum position and number of TRMD are numerically investigated under harmonic excitation and the control effects of different distributions are discussed. Furthermore, a shaking table test is conducted under different excitation cases, including free vibration, forced vibration and seismic wave to investigate the absorption performance of the device. The numerical simulations of different distributions of the TRMDs show that the DTRMDs are more effective in reduction of the displacement response of the asymmetric structure under the same mass ratio, even when the degree of eccentricity becomes large. However, with small degree of eccentricity, the unreasonable asymmetrical arrangement may cause the increase of the peak value of the rotational angular displacement. Finally, the experimental investigations exhibit similar results of translational displacement of the structure. It is concluded that the vibration of the irregular asymmetric structure can be controlled more economically and effectively by reducing the mass ratio through reducing the quantity of TRMDs at the high stiffness end.

• 한국기계연구소 소보
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• 통권17호
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• pp.157-165
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• 1987

The SWATH concept hull form which is capable of high speed navigation with small oscillatory motions in waves, was developed from the catamaran type hull forms. This paper describes how the motion of a SWATH ship in irregular waves can be reduced by regulating the stabilizing fins. The optimal regulator and LQG (Linear Quadratic Gaussian) controller for vertical plane motion have been applied for both platforming mode and contouring mode controls. The calculations of hydrodynamic coefficients and external forces are possible for defining the system equation for the design purpose of motion control. Performances of the controlled system are compared with those of original system.

• 한국해양공학회지
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• 제25권5호
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• pp.64-68
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• 2011

The motion responses of a 5-MW floating offshore wind turbine were simulated in regular and irregular waves and its RAOs and significant motion responses were calculated, respectively. The floating offshore wind turbine employed in this simulation was the OC3-Hywind designed by the National Renewable Research Laboratory, USA. The numerical simulation was carried out using MOSES (Multi-Operational Structural Engineering Simulator), which is widely used to analyze and design floating offshore structures in the gas and oil industry.

• 한국해양공학회지
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• 제31권3호
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• pp.202-207
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• 2017

This paper presents the results of an experimental study on the motions and mooring characteristics of a floating vertical axis wind turbine system. Based on a comparison of regular wave experiment results, the motions of structures with different types of mooring are almost the same. Based on the tension response results of a regular wave experiment with a catenary mooring system, the mooring lines in front of the structure have a larger tension effect than the back of the structure by the drifted offset of the structure. The dynamic response spectrum of the structure in the irregular wave experiments showed no significant differences in response to differences in the mooring system. As a result of the comparison of the tension response spectra, the mooring lines have a larger value with a drifted offset for the structure, as shown in the previous regular wave experiment. The results of the dynamic response of the structure under irregular wave and wind conditions showed that the heave motion response is influenced by the coupled effect with the mooring lines of the surge and pitch motion due to the drifted offset and steady heeling. In addition, the mooring lines in front of the structure have a very large tension force compared to the mooring lines in back of the structure as a result of the drifted offset of the structure.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2023년도 추계학술대회
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• pp.242-243
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• 2023

소형선박 운항은 해양 환경 및 기상조건에 따라 선박이 파도에 대해 다양한 방향으로 입사각을 가지게 된다. 특히 소형선박의 경우 입사각에 따라 운동의 특성이 크게 달라지며 이는 안정성과 밀접한 관계가 있다. 본 연구는 불규칙파에서 소형선박이 운항 중일 때 입사각에 따른 운동특성을 시뮬레이션과 실험을 통하여 비교분석 하였다. 불규칙파는 실제 소형선박이 운항하는 연안의 파랑 데이터를 바탕으로 만들었다. 선속에 따라 선박의 횡요동요를 분석하였으며 선속이 느릴 때에는 선수사파에서 가장 큰 횡요동요가 발생하였으며 선속이 빨라짐에 따라 선수사파의 횡요동요는 감소하나 선미사파의 횡요동요가 커지는 것을 알 수 있다. 따라서 선속에 따른 입사파 각도를 변경하여 선박의 운항할 경우 선박의 안정성과 운항 효율성을 개선할 수 있을 것이다.

• Ocean Systems Engineering
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• 제13권4호
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• pp.349-365
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• 2023

Targeting a floating wave and offshore wind hybrid power generation system (FWWHybrid) designed in the Republic of Korea, this study examines the impact of the interaction, with multiple wave energy converters (WECs) placed on the platform, on platform motion. To investigate how the motion of WECs affects the behavior of the FWWHybrid platform, it was numerically compared with a scenario involving a 'single-body' system, where multiple WECs are constrained to the platform. In the case of FWWHybrid, because the platform and multiple WECs move in response to waves simultaneously as a 'multi-body' system, hydrodynamic interactions between these entities come into play. Additionally, the power take-off (PTO) mechanism between the platform and individual WECs is introduced for power production. First, the hydrostatic/dynamic coefficients required for numerical analysis were calculated in the frequency domain and then used in the time domain analysis. These simulations are performed using the extended HARP/CHARM3D code developed from previous studies. By conducting regular wave simulations, the response amplitude operator (RAO) for the platform of both single-body and multi-body scenarios was derived and subsequently compared. Next, to ascertain the difference in response in the real sea environment, this study also includes an analysis of irregular waves. As the floating body maintains its position through connection to a catenary mooring line, the impact of the slowly varying wave drift load cannot be disregarded. To assess the influence of the 2^nd-order wave exciting load, irregular wave simulations were conducted, dividing them into cases where it was not considered and cases where it was included. The analysis of multi-degree-of-freedom behavior confirmed that the action of multiple WECs had a substantial impact on the platform's response.

• 한국해양공학회지
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• 제37권1호
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• pp.8-19
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• 2023

In recent years, modular-type floating islands have been considered as a promising option for future ocean space utilization. A modular floating island consists of a number of standardized pontoon-type modules and connectors between them. In this study, the motion responses of a modular floating island in waves was investigated based on frequency-domain numerical analysis. The numerical method is based on the potential flow theory and adopts a higher-order boundary element method with Green's function. First, motion RAOs were directly compared with the model test data by reference to validate the present numerical method. Then, numerical investigations were conducted to analyze the motion characteristics of the floating island by considering various modules shapes and arrangements. It was found that motion responses were reduced in a single central module compared to when divided central modules were used. Finally, the effect of modular arrangement on the motion responses in irregular waves was discussed. It was confirmed that multiple-layer outer modules are more effective in calming the central module than using single-layer outer modules, except under very long period conditions.

• 대한조선학회논문집
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• 제38권2호
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• pp.10-18
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• 2001

초대형 해상 공항은 길이나 폭이 수 킬로미터인 거대 구조물이며, 해상에 계류된 해상공항의 설계에 있어 파도에 의한 1차항 파강제력과 2차항 파강제력은 반드시 고려하여야 한다. 본 논문에서 파중에서 돌핀계류된 해상공항에 대한 운동응답의 시간영역해석이 제시된다. 운동방정식에서 동유체력 계수와 파도에 의한 힘은 주파수 영역의 3차원 패널 방법으로부터 계산되며, 동시에 돌핀계류계에 대한 계류력과 수평방향의 표류력이 본 계산에서 얻어진다. 본 논문의 계산 예로 일본에서 실증실험을 수행한 phase I 해상공항에 대해 불규칙파 중에서 시간영역 해석이 제시된다.

• Journal of Advanced Marine Engineering and Technology
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• 제40권8호
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• pp.704-709
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• 2016

Wave energy generation systems can be divided into oscillating water chamber type, over topping device type and wave activating body type. The wave activating body type converts wave energy to kinetic energy, and the power generation amount increases as the motion of an activating body increases. In this paper, the wave energy convertor consists of a main body, which has an H-shape, and the activating body. These are connected by a bar-type bridge. By the incident wave, when the activating body moves with vertical motion this motion is consequently converted into rotational motion. The twisting moment and angular velocity at a shaft of convertor are calculated according to various conditions of the incident wave and the shape of the activating body. This can be used as a basic idea for determining the design of wave activating body type convertor.

• Journal of Multimedia Information System
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• 제7권4호
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• pp.269-276
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• 2020

The small craft including jet-board for leisure are commonly smaller than the general commercial vessels. For the floating vessel, the motion analysis is significantly important component to design the shape. It is, however, hardly predicting its behavior by using conventional boundary element method due to violating small amplitude assumption for potential theory. The computational fluid dynamics method can afford to simulate such small craft, but its grid system was not able to calculate motion, because movable body disturbs the grid system by confliction. The dynamics fluid body interaction model with over-set mesh system can be dealt with movable floating body under irregular ocean wave. In this study, several cases were considered to reveal that DFBI is essential method to predict floating body motion. The single phase simulate was conducted to establish the shape perfection, and then the validated vessel was simulated with ocean waves weather DFBI option on or off. Through the comparison, the results between the cases of DFBI on and off shows significantly difference. It was claimed that the DFBI was necessary not only to calculation body motion, but also to predict accurate drag and lift force on the floating body for small size craft.