• Wind and Structures
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• 제37권6호
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• pp.461-471
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• 2023

The main objective of this study was to establish design guidelines for three key design variables (spar thickness, spar diameter, and total draft) by examining their impact on the stress distribution and resonant frequency of a 2.5-MW spar-type floating offshore wind turbine substructure under extreme marine conditions, such as during Typhoon Bolaven. The current findings revealed that the substructure experienced maximum stress at wave frequencies of either 0.199 Hz or 0.294 Hz, consistent with previously reported experimental findings. These results indicated that the novel simulation method proposed in this study, which simultaneously combines hydrodynamic diffraction analysis, computational dynamics analysis, and structural analysis, was successfully validated. It also demonstrated that our proposed simulation method precisely quantified the stress distribution of the substructure. The novel findings, which reveal that the maximum stress of the substructure increases with an increase in total draft and a decrease in spar thickness and spar diameter, offer valuable insights for optimizing the design of spar-type floating offshore wind turbine substructures operating in various harsh marine environments.

• 해양환경안전학회지
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• 제23권5호
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• pp.558-565
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• 2017

해양환경의 극한 환경조건에 노출 된 고정식 및 부유식 해양구조물의 안전성과 설계비용 효율성에 있어서 파랑-구조물 상호작용의 정확한 예측은 중요하다. 본 연구에서는 규칙파 중 원형 기둥에 대한 파랑-구조물 상호작용을 해석하였다. 3차원 이상유동(two-phase flow)을 해석하기 위해 오픈소스 전산유체역학 라이브러리인 오픈폼을 사용하였다. 4개의 원형기둥이 정사각형 배열을 이루고 있을 때 규칙파의 입사각도에 따른 상호작용을 해석하였다. 원형 기둥 구조물에서의 wave run-up을 입사파의 기울기에 따라 비교하였다. 원형 기둥과 입사파의 상호작용으로 인해 원형 기둥 사이에 높은 파가 생성되는 것을 확인하였다. 본 해석 결과는 구조물과 입사파의 상호작용에 의한 air gap에 대한 연구의 기초자료로 활용될 것으로 기대된다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.343-347
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• 2008

In Korea it continues to grow elderly population, especially the elderly who lived alone and above-average temperatures is increased by global worming lately. So that, to take immediate action and to solve social isolation for elderly people living alone, we prospect it plays an important role ubiquitous information technology(IT) such as Geosensor based on GIS, RFID and wireless sensor networks, etc. In this paper, we searched domestic and foreign response status of heat wave for the elderly and proposed u-Care service for the elderly to stay indoors during heatwave warning. In future, we will design u-Care system and carry out various researches on accuracy, revitalization, the law, etc.

• 한국수자원학회논문집
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• 제46권11호
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• pp.1089-1101
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• 2013

본 논문에서는 미래 극한기후의 변화를 확인하고자 지역기후모형을 이용하여, STARDEX에서 제시한 극한지수를 계산하고 경향성 분석을 통해 미래 극한기후의 지속성과 공간적 분포의 변화양상을 파악하였다. 강수관련 극한지수를 분석한 결과, 수도권과 경기도, 강원도 영동지역, 남해안 지역에서 증가경향성이 확인되었고, 중부 내륙지역에서는 감소경향성이 전망되었다. 기온관련 극한지수를 분석한 결과 기후변화로 인해 미래 우리나라의 평균 기온이 현재보다 증가하는 것을 알 수 있었다. 강수관련 극한지수 중 집중호우 한계점은 경향성에 대한 기울기 값이 서귀포에서 0.229, 지속기간 5일 최대 강수량은 서귀포에서 5.692, 최대 건조지속기간은 속초에서 0.099로 확인되었다. 기온관련 극한지수 중 Hotdays 한계점의 경향성에 대한 기울기 값은 인천에서 0.077, 최대혹서기기간은 울진에서 0.162, Coldnight 한계점은 인제에서 0.075, 동결일수는 통영에서 -0.193으로 확인되었다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.214-214
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• 2003

During a model test of Hutton TLP, a "ringing" response was first observed about 20 years ago. This phenomenon is a resonant build up over the time of wave period and this burst-like motion can cause the extreme load on the TLP tether. It is often detected in the large and steep irregular waves but the generation mechanism leading to the "ringing" is not yet well understood. According to the research since then, the higher order harmonic components may account for the "ringing" on the floating offshore structures. The main purpose of the present research is, thus, to measure the higher harmonic forces exerted on a vertical truncated circular column and to compare them with available data. A vertical truncated cylinder with a diameter of 3.5inch and a draft of 10.5inch is used as a test structure, which is a scaled model of ISSC TLP column. The cylinder is installed at a distance of 45ft from the wave maker in order to avoid parasitic waves created in the wave flap. Attached to the upper part of the cylinder are two force gages to measure the horizontal (surge) and vertical (heave) forces on the cylinder. The incoming waves are Stokes waves with a slope ranging from 0.06 to 0.24. The forces and waves are measured for 60 seconds with a sampling rate of 50 Hz. Among the recorded data, the first 10 waves are excluded because of transient behavior of the waves and the next The horizontal and vertical forces are analyzed up to 5th order harmonics. The horizontal forces are then compared to the values from the theoretical model called "FNV model". In addition, force transfer functions are also investigated. Major findings in this research are below. 1) The first order forces measured are slightly larger than the theoretical values of "FNV model" 2) The "FNV model" considerably overpredicts the second order forces. 3) The larger the amplitude and more extreme the wave slope, the smaller the predictions are compared to the experimental. 4) The higher harmonic forces are significantly smaller than the first harmonic force for all wave parameters. 5) The normalized forces vs. waves slopes are almost constant in the lower harmonics but vary a lot in the higher harmonics. 6) The trend of forces is more nonlinear in the horizontal forces than in the vertical forces as the wave slope increases. 7) The part of the results above is also observed by other researchers and confirmed again through the present work.

• 대한기계학회논문집A
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• 제37권2호
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• pp.257-263
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• 2013

본 논문에서는 파력에너지를 전기에너지로 변환시키는 파력발전기를 다물체 동역학을 이용하여 모델링 하였으며, 계류시스템이 부유식 파력발전기에 미치는 영향에 대해서 분석하였다. 계류시스템이 파력발전기에 미치는 영향을 줄이기 위한 연구가 많이 이루어지고 있다. 구속방정식과 힘 요소를 이용하여 다물체 시스템을 모델링 하였으며, 3 차원 파랑하중을 적용하여 부유체에 작용하는 파력을 모델링 하였다. 파력발전기의 거동과 발전량을 분석하기 의해 상용 다물체 동역학 해석프로그램인 MSC/ADAMS 를 이용하였다. 계류시스템이 있을 때와 없을 때의 결과를 비교하였고, 특히 극한 파랑하중이 작용했을 때의 시뮬레이션을 통해 파력발전기의 안정성을 평가하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.655-662
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• 2003

Slope stability is an important issue ill civil engineering works or in open pit mines where both economy and efficiency is required. These are the long-term stability problems which depend on the change of physical properties under a certain weather condition. These can also result in progress of weathering which can change mechanical or hydro-geological properties of rock mass considerably. In this study, weathering in nature was simulated by freeze-thaw test and Soxhlet test which represent mechanical and chemical weathering respectively. Measured were elastic wave velocities, absorption rate, volume change. Uniaxial compression strengths before and after the weathering tests were also measured. The change in weight and volume of the specimens were not clearly related to the weathering process, but P, S wave velocities were clearly decreased as weathering progresses. For some class of rocks, P-wave velocity was increased probably because of the saturation due to improved connectivity of the pre-existing pores. Based on the test results, stability of the slopes were analyzed using FLAC$\^$2D/. Due to the reduced strength parameters, the factors of safety were decreased for the selected sites.

• 비파괴검사학회지
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• 제35권6호
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• pp.389-397
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• 2015

Recently, wave propagation imaging based on laser scanning-generated elastic waves has been intensively used for nondestructive inspection. However, the proficiency of the conventional software based system reduces when the scan area is large since the processing time increases significantly due to unavoidable processor multitasking, where computing resources are shared with multiple processes. Hence, the field programmable gate array (FPGA) was introduced for a wave propagation imaging method in order to obtain extreme processing time reduction. An FPGA board was used for the design, implementing post-processing ultrasonic wave propagation imaging (UWPI). The results were compared with the conventional system and considerable improvement was observed, with at least 78% (scanning of $100{\times}100mm^2$ with 0.5 mm interval) to 87.5% (scanning of $200{\times}200mm^2$ with 0.5 mm interval) less processing time, strengthening the claim for the research. This new concept to implement FPGA technology into the UPI system will act as a break-through technology for full-scale automatic inspection.

• Journal of Ship and Ocean Technology
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• 제3권3호
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• pp.1-12
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• 1999

Spectral fatigue damage calculations has been performed on four ships in order to assess the effect that the probabilistic modeling of sea states has on the estimated fatigue life. The damage estimation method is based on the Miner- Palmgren fatigue damage formulation and a spectral approach is used to determine the necessary variances of the stress processes. Both the horizontal and vertical hull girder bending induced stress process together with the local water pressure induced stress process is taken into account. The wave scatter diagrams are applied in the calculations and their fatigue severity is assessed by analyzing the results obtained with the ten scatter diagrams and the four ships. All four ships are analyzed both in full load and ballast conditions and while traveling at both full and reduced speed. It is found that the fatigue severity of a wave scatter diagram is dependent on several parameters, some of these being the extreme wave hight extrapolated from the scatter diagram and the mean zero up-crossing period in conjunction with the ship length . Based on these three parameters and expression is derived in order to calculate one single number describing the fatigue severity of a scatter diagram with respect to a certain ship.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.11-24
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• 2017

The present work focuses multi-objective optimization of blade sweep for a Wells turbine. The blade-sweep parameters at the mid and the tip sections are selected as design variables. The peak-torque coefficient and the corresponding efficiency are the objective functions, which are maximized. The numerical analysis has been carried out by solving 3D RANS equations based on k-w SST turbulence model. Nine design points are selected within a design space and the simulations are run. Based on the computational results, surrogate-based weighted average models are constructed and the population based multi-objective evolutionary algorithm gave Pareto optimal solutions. The peak-torque coefficient and the corresponding efficiency are enhanced, and the results are analysed using CFD simulations. Two extreme designs in the Pareto solutions show that the peak-torque-coefficient is increased by 28.28% and the corresponding efficiency is decreased by 13.5%. A detailed flow analysis shows the separation phenomena change the turbine performance.