• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2014년도 춘계학술대회
• /
• pp.253-254
• /
• 2014

In offshore, various external forces such as wind force, wave force and impulsive breaking wave force act on offshore structures. Many researches about this forces are published. Kim and Cao(2008) published researche on wave force of vertical cylinder. Kim and Go(2013) performed research on the subgrade reaction by external forces. Among this forces, impulsive breaking force is more massive than other forces, especially. Therefore, the studies about impulsive breaking wave forces have been carried out. Chun and Shim(1999) analyzed dynamic behavior of cylindrical pile subjected to impulsive breaking wave force. In this study, when the impulsive breaking wave force acts on the offshore wind turbine, the subgrade reaction acting on the mono-pile of the offshore wind turbine is calculated by p-y curve. The calculation is carried out to the multi-layered.

• 한국해양공학회지
• /
• 제21권1호
• /
• pp.1-6
• /
• 2007

While a typhoon is traveling, characteristics of its wind fields are continuously changing, producing severe changes in local water level and wave conditions, especially, when a typhoon comes into shallow water. However, there have not been many studies related to local typhoon effects, especially, considering real time changes of wind direction related to the coastal topography. In the study, the characteristics of the wind field by typhoon and topographical characteristics in shallow water are considered, as well as conditions of wave climate estimation. These are performed by the SWAN (Simulating waves nearshore) model, in order to estimate the growth of wave energy due to the wind field. It can be strongly suggested that the wave energy of theof an inner bay should be estimated when the direction of the bay entrance and the wind direction of the typhoon are identical. The result of the numerical calculations is in better agreement with the observed data than the result of the conventional estimation techniques.

• 국제강구조저널
• /
• 제18권4호
• /
• pp.1431-1439
• /
• 2018

For floating buildings may fl oat on the water for a long time, they are constantly affected by various environmental loads such as wind and wave loads. In this study to find the wave effect on the floating building, five models are designed using steel moment resisting frame. It is assumed that the lower part of the floating building is a reinforced concrete pontoon, while the upper part is a three-story steel frame. To analyze floating buildings affected by wind and wave loads, hydro-dynamic and substructure analysis are performed. As input loads, this study set limits that the mean wind velocity is 35 m/s and the significant wave height is 0.5 m for the residential building. From the hydrodynamic analysis, the time-history acceleration of building is obtained and transformed into a base ground input for a substructure analysis of the superstructure of the building. Finally the mean of the maximum from 30 dynamic analysis of the floating buildings are used to be compared with the results of the same model on the ground. It was shown that the dynamic results with wind and wave loads are not always lesser than the static results which are calculated with static equivalent wind load for a building that is located on the ground.

• Smart Structures and Systems
• /
• 제24권1호
• /
• pp.53-65
• /
• 2019

Misaligned wind-wave and seismic loading render offshore wind turbines suffering from excessive bi-directional vibration. However, most of existing research in this field focused on unidirectional vibration mitigation, which is insufficient for research and real application. Based on the authors' previous work (Sun and Jahangiri 2018), the present study uses a three dimensional pendulum tuned mass damper (3d-PTMD) to mitigate the nacelle structural response in the fore-aft and side-side directions under wind, wave and near-fault ground motions. An analytical model of the offshore wind turbine coupled with the 3d-PTMD is established wherein the interaction between the blades and the tower is modelled. Aerodynamic loading is computed using the Blade Element Momentum (BEM) method where the Prandtl's tip loss factor and the Glauert correction are considered. Wave loading is computed using Morison equation in collaboration with the strip theory. Performance of the 3d-PTMD is examined on a National Renewable Energy Lab (NREL) monopile 5 MW baseline wind turbine under misaligned wind-wave and near-fault ground motions. The robustness of the mitigation performance of the 3d-PTMD under system variations is studied. Dual linear TMDs are used for comparison. Research results show that the 3d-PTMD responds more rapidly and provides better mitigation of the bi-directional response caused by misaligned wind, wave and near-fault ground motions. Under system variations, the 3d-PTMD is found to be more robust than the dual linear TMDs to overcome the detuning effect. Moreover, the 3d-PTMD with a mass ratio of 2% can mitigate the short-term fatigue damage of the offshore wind turbine tower by up to 90%.

• 한국항해항만학회지
• /
• 제46권1호
• /
• pp.11-17
• /
• 2022

풍랑특보는 우리나라 부근을 항행하는 선박 및 해상 업무 종사자에게 큰 영향을 미친다. 이 연구에서는 최근 11년(2010-2020년) 동안 기상청에서 발표한 서해·남해·동해의 앞바다 및 먼바다의 풍랑특보와 주요 해양기상부이의 관측자료를 비교·분석하여 풍랑특보의 적절성을 평가하였다. 각 해역에 대한 풍랑특보와 해양기상부이 관측자료를 일별, 월별, 연별로 통계를 내어 연평균, 월평균, 계절별로 비교한 결과, 풍랑특보의 적중률이 전 해역에 걸쳐 매우 낮았으며, 특히 남해 앞바다와 제주도 앞바다의 적중률은 겨울에 가장 낮은 것으로 분석되었다. 해상에서의 풍랑특보가 어선의 어업활동, 여객선 운항 및 관광, 해상 레저활동 등에 미치는 영향을 고려할 때 해양기상 예·특보의 정확성을 개선할 필요가 있음을 확인하였다.

• 한국태양에너지학회 논문집
• /
• 제30권5호
• /
• pp.44-55
• /
• 2010

The proposed offshore wind farm projects, i.e., Mooudo offshore, Yeonggwang-Gochang offshore, Saemangeum offshore, Imjado offshore and Gadeokdo-Dadeapo offshore, were compared and analyzed using the Korea National Wind Mapand Wind Farm Suitability Assessment System developed by the Korea Institute of Energy Research. The suitability of the proposed areas was comprehensively assessed using geographic, economic constraints, wave condition and wind resource factors, but the focus of this paper was on the geographic constraints and wave conditions. Imjado had several geographical constraints, despite having a good wind power density, while Saemangeum had a relatively low wave height, shallow water depth, close substation and slow tidal current. It is anticipating that the present comparison and analysis could be used as reference guidelines when selecting and preparing the design of large-scale offshore wind farm in the near future.

• Ocean Systems Engineering
• /
• 제5권3호
• /
• pp.139-160
• /
• 2015

The global performance of the 5MW OC4 semisubmersible floating wind turbine in random waves was numerically simulated by using the turbine-floater-mooring fully coupled and time-domain dynamic analysis program FAST-CHARM3D. There have been many papers regarding floating offshore wind turbines but the effects of second-order wave-body interactions on their global performance have rarely been studied. The second-order wave forces are actually small compared to the first-order wave forces, but its effect cannot be ignored when the natural frequencies of a floating system are outside the wave-frequency range. In the case of semi-submersible platform, second-order difference-frequency wave-diffraction forces and moments become important since surge/sway and pitch/roll natural frequencies are lower than those of typical incident waves. The computational effort related to the full second-order diffraction calculation is typically very heavy, so in many cases, the simplified approach called Newman's approximation or first-order-wave-force-only are used. However, it needs to be justified against more complete solutions with full QTF (quadratic transfer function), which is a main subject of the present study. The numerically simulated results for the 5MW OC4 semisubmersible floating wind turbine by FAST-CHARM3D are also extensively compared with the DeepCWind model test results by Technip/NREL/UMaine. The predicted motions and mooring tensions for two white-noise input-wave spectra agree well against the measure values. In this paper, the numerical static-offset and free-decay tests are also conducted to verify the system stiffness, damping, and natural frequencies against the experimental results. They also agree well to verify that the dynamic system modeling is correct to the details. The performance of the simplified approaches instead of using the full QTF are also tested.

• 해양환경안전학회지
• /
• 제21권5호
• /
• pp.599-607
• /
• 2015

본 연구에서는 파랑수치모형(SWAN)을 사용하여 우리나라 연안역에서의 장기 파랑을 후측모델링하고, 그 활용성에 대하여 논하였다. 파랑후측모델링을 위한 입력 바람자료(NCEP, ECMWF, JMA-MSM)를 검토한 결과, JMA-MSM의 예측정확도가 높게 나타났지만 상대적으로 자료제공기간이 짧아 자료제공기간이 긴 ECMWF 바람자료를 채택하였다. 파랑후측모델링은 파랑관측부이가 설치되어 검증이 가능한 2001년부터 2014년까지의 ECMWF 바람자료를 이용하여 수행하였으며, 생성된 모델 결과는 기상청, 국립해양조사원의 파랑관측 부이자료를 이용하여 검증하였다. 파랑후측모델링 검증결과 파랑관측 부이자료와 잘 일치하였으며, 특히 태풍과 같은 이벤트 기간의 해역 상황을 전반적으로 잘 재현하였다. 이를 통하여 현재 파랑관측부이 자료의 한계인 결측기간 동안의 파랑자료를 대체할 수 있음을 확인하였다. 하지만 일부 정점에서는 이벤트 기간 동안의 최대파고를 과소평가하는 것으로 나타났으며, 이러한 이유는 바람입력자료의 시간간격 및 해상도, 수심자료, 격자크기 등의 한계로 파악된다. 본 파랑후측모델링 결과는 연안역에서의 침식원인규명 특히, 이벤트 시기의 파랑특성과 연계한 분석이 가능하며, 원하는 연안지점에서의 파랑후측정보를 생산할 수 있어 연안재해취약성평가 등에 활용이 가능하다.

• 대기
• /
• 제19권1호
• /
• pp.93-106
• /
• 2009

Analysis has been made on the wind wave characteristics in terms of significant wave height ($H_s$) near the Korean marginal seas in the 2006 - 2007 year using the third generation wave model, WAVEWATCH - III model. In order to evaluate its performance, its results were compared with the observed data using KMA ocean buoy. The two year average RMSE between modeled and observed Hs shows reasonably small value of about 0.37 m. The accuracy of predicted values in the year 2007 is increased mainly due to finer model grid size and better accurate wind field. The model used in this study predicts very well the characteristics ($H_s$) of wind waves near the Korean Peninsular. Simulated monthly wind waves show the evident seasonal variations due to Typhoons in summer season. When Typhoons approach to Korean Peninsular, the accuracy of wind waves predictions is lower than that of annual mean value.

• 신재생에너지
• /
• 제6권3호
• /
• pp.39-46
• /
• 2010

With growing of wind turbine industry, offshore wind energy is getting more attention in recent years. Among all the components of offshore wind turbines, the foundation of the offshore wind turbine plays a key role in stability of whole system. In this work, the 5 MW NREL reference wind turbine with rated speed of 11.4 m/s is used for load calculation. Wind and wave loads are calculated using GH-Bladed (Garard Hassan) and FAST (NREL). Additionally, FE simulation is carried out to investigate the wave effect on the support structure. Meanwhile, this work is to simulate systemic and optimized load cases for the foundation analysis of wind turbine system.