• Wind and Structures
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• 제21권6호
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• pp.693-707
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• 2015

The efficiency of wind turbines (WT) is primarily reflected in their ability to generate electricity at any time. Downtimes of WTs due to "conventional" inspections are cost-intensive and undesirable for investors. For this reason, there is a need for structural health monitoring (SHM) systems, to enable service and maintenance on demand and to increase the inspection intervals. In general, monitoring increases the cost effectiveness of WTs. This publication concentrates on the application of two vibration-based SHM algorithms for stability and structural change monitoring of offshore WTs. Only data driven, output-only algorithms based on stochastic subspace identification (SSI) in time domain are considered. The centerpiece of this paper deals with the rough mathematical description of the dynamic behavior of offshore WTs and with the basic presentation of stochastic subspace-based algorithms and their application to these structures. Due to the early stage of the industrial application of SHM on offshore WT on the one side and the required confidentiality to the plant manufacturer and operator on the other side, up to now it is not possible to analyze different isolated structural damages resp. changes in a systematic manner, directly by means of in-situ measurement and to make these "acknowledgements" publicly available. For this reason, the sensitivity of the methods for monitoring purposes are demonstrated through their application on long time measurements from a 1:10 large scale test rig of an offshore WT under different conditions: undamaged, different levels of loosened bolt connections between tower parts, different levels of fouling, scouring and structure inclination. The limitation and further requirements for the approaches and their applicability on real foundations are discussed along the paper.

• Steel and Composite Structures
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• 제24권5호
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• pp.549-559
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• 2017

As few multi-tower single-box multi-cell cable-stayed bridges with corrugated steel webs have been built, analysis is mostly achieved by combining single-girder model, beam grillage model and solid model in support of the design. However, such analysis methods usually suffer from major limitations in terms of the engineering applications: single-girder model fails to account for spatial effect such as shear lag effect of the box girder and the relevant effective girder width and eccentric load coefficient; owing to the approximation in the principle equivalence, the plane grillage model cannot accurately capture shear stress distribution and local stress state in both top and bottom flange of composite box girder; and solid model is difficult to be practically combined with the overall calculation. The usual effective width method fails to provide a uniform and accurate "effective length" (and the codes fail to provide a unified design approach at those circumstance) considering different shear lag effects resulting from dead load, prestress and cable tension in the construction. Therefore, a novel spatial grid model has been developed to account for shear lag effect. The theoretical principle of the proposed spatial grid model has been elaborated along with the relevant illustrations of modeling parameters of composite box girder with corrugated steel webs. Then typical transverse and longitudinal shear lag coefficient distribution pattern at the side-span and mid-span key cross sections have been analyzed and summarized to provide reference for similar bridges. The effectiveness and accuracy of spatial grid analysis methods has been finally validated through a practical cable-stayed bridge.

• 한국항공우주학회지
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• 제38권12호
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• pp.1162-1169
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• 2010

블레이드 제작 공정 및 환경적인 요인에 의해 로터 시스템에는 다양한 불균형 특성이 존재하며 이를 해소하기 위해서는 동적 밸런싱 과정이 요구된다. 본 연구에서는 훨타워 시험으로부터 얻은 블레이드 트랙 결과를 토대로 헬리콥터 로터 시스템 동적 밸런싱의 지표가 되는 시험 D/B의 누적 모듈과 이를 바탕으로 최적의 조절 파라미터 이동량을 산출 할 수 있는 통합 해석 시스템 구축에 대해 고찰하였다. 해석의 간단을 기하기 위해 밸런싱 입력변수의 조절에 대한 블레이드의 응답 특성을 선형으로 가정하고 블레이드 간의 상호 영향성 계수를 도출하였으며, 이로부터 로터 시스템의 특성을 식별하였다. 아울러 유전자 알고리즘을 도입하여 동적 밸런싱을 위한 최적의 블레이드 개별 조절 값을 구하고 이를 시험결과와 비교하였으며, 제시한 방법이 매우 효율적임을 보였다.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.559-577
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• 2016

There are many theoretical analyses and experimental studies of the hydrodynamics for the tension leg platform (TLP) of a floating wind turbine. However, there has been little research on the arrangement of the TLP's internal structure. In this study, a TLP model and a 5-MW wind turbine model as proposed by the Minstitute of Technology and the National Renewable Energy Laboratory have been adopted, respectively, to comprehensively analyze wind effects and wave and current combinations. The external additional coupling loads on the TLP and the effects of the loads on variables of the internal structure have been calculated. The study investigates preliminary layout parameters-namely, the thickness of the tension leg body, the contact mode of the top tower on the tension leg, the internal stiffening arrangement, and the formation of the spoke structure-and conducts sensitivity analyses of the TLP internal structure. Stress is found to be at a maximum at the top of the tension leg structure and the maximum stress has low sensitivity to the load application point. Different methods of reducing maximum stress have been researched and analyzed, and the effectiveness of these methods is analyzed. Filling of the spoke structure with concrete is discussed. Since the TLP structure for offshore wind power is still under early exploration, arrangements and the configuration of the internal structure, exploration and improvements are ongoing. With regard to its research and analysis process, this paper aims to guide future applications of tension leg structures for floating wind turbine.

• 한국CDE학회논문집
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• 제20권1호
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• pp.84-92
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• 2015

In this study, we describe a method to analysis dynamic behavior of an offshore wind turbine in the frequency domain and expected effects of the method. An offshore wind turbine, which is composed of platform, tower, nacelle, hubs, and blades, can be considered as multibody systems. In general, the dynamic analysis of multibody systems are carried out in the time domain, because the equations of motion derived based on the multibody dynamics are generally nonlinear differential equations. However, analyzing the dynamic behavior in time domain takes longer than in frequency domain. In this study, therefore, we describe how to analysis the system multibody systems in the frequency domain. For the frequency domain analysis, the non-linear differential equations are linearized using total derivative and Taylor series expansions, and then the linearized equations are solved in time domain. This method was applied to analysis of double pendulum system for the verification of its effectiveness, and the equations of motion for the offshore wind turbine was derived with assuming that the wind turbine is rigid multibody systems. Using this method, the dynamic behavior analysis of the offshore wind turbine can be expected to take less time.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.27-40
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• 2024

The prediction of VIV amplitude is essential for the design and fatigue life estimation of steel tubes in tubular transmission towers. Limited to costly and time-consuming traditional experimental and computational fluid dynamics (CFD) methods, a machine learning (ML)-based method is proposed to efficiently predict the VIV amplitude of steel tubes in transmission towers. Firstly, by introducing the first-order mode shape to the two-dimensional CFD method, a simplified response analysis method (SRAM) is presented to calculate the VIV amplitude of steel tubes in transmission towers, which enables to build a dataset for training ML models. Then, by taking mass ratio M^*, damping ratio ξ, and reduced velocity U^* as the input variables, a Kriging-based prediction method (KPM) is further proposed to estimate the VIV amplitude of steel tubes in transmission towers by combining the SRAM with the Kriging-based ML model. Finally, the feasibility and effectiveness of the proposed methods are demonstrated by using three full-scale steel tubes with C-shaped, Cross-shaped, and Flange-plate joints, respectively. The results show that the SRAM can reasonably calculate the VIV amplitude, in which the relative errors of VIV maximum amplitude in three examples are less than 6%. Meanwhile, the KPM can well predict the VIV amplitude of steel tubes in transmission towers within the studied range of M^*, ξ and U^*. Particularly, the KPM presents an excellent capability in estimating the VIV maximum amplitude by using the reduced damping parameter S_G.

• 청정기술
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• 제12권1호
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• pp.37-44
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• 2006

산화 무기화합물 및 탄소흡착제와 음이온교환수지를 이용하여 폐수 중의 중금속이온을 분리, 제거하는 특성에 대해 연구하였다. 이를 위하여 DT사에서 제조된 산화 무기화합물인 DT-30, 음이온 교환수지인 DT-60, 탄소화합물로써 DT-80, DT-90을 이용하여 코발트(Cobalt)이온, 세슘(Cesium)이온 및 요오드(Iodide)이온의 평형 분리특성 및 이온교환 탑에서 연속 실험 시 분리특성에 대하여 연구하였다. 그 결과 DT-30은 세슘, DT-80, DT-90은 코발트, DT-60은 요오드에 대해서 우수한 분리특성을 나타내었다. 평형 실험에서 DT-30은 세슘에 대해 온도 증가에 따라 흡착량의 미세한 증가를 보였고, pH변화에 따라 흡착량이 크게 변화되었다. DT-80도 코발트에 대해 pH에 따라 평형 흡착량이 변화하였으나 온도의 변화에는 거의 영향을 받지 않았다. DT-60의 요오드 이온에 대한 평형 흡착량은 pH 또는 온도 변화에 영향을 거의 받지 않았다. 이온교환 탑을 이용하여 연속적으로 중금속 함유 용액을 통과시키면서 실험한 결과에서도 DT-30의 세슘, DT-90의 코발트, DT-60의 요오드에 대한 분리 특성이 좋은 것이 관찰되었다. 이 경우 DT-30의 세슘에 대한 분리특성 및 DT-60의 요오드에 대한 분리특성이 DT-90의 코발트에 대한 분리특성보다 우수한 것으로 나타났다. 이온분리특성에 미치는 불순물의 영향에 대한 조사에서 DT-90은 계면활성제나 오일 등의 불순물에 의해 큰 영향을 받지 않았으나 DT-30은 계면활성제, 오일 등의 존재에 의해 이온분리성능이 크게 저하되었고 DT-60도 계면활성제의 영향을 크게 받는 것으로 관찰되어서 불순물을 전처리 공정에서 제거하는 것이 매우 중요한 것으로 나타났다.

• 한국지진공학회논문집
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• 제8권4호
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• pp.51-62
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• 2004

사장교의 지진응답 제어를 위한 퍼지관리제어기법에 대하여 연구하였다. 제시하는 방법은 복합제어방법의 하나로서, 여러 개의 최적제어기로 이루어진 하부제어기와 퍼지관리자로 구성되는 계층적인 구조를 가진다. 하위제어기들은 사장교의 주요 지진응답들을 저감시키도록 각각 독립적으로 설계되며, 퍼지관리자는 설계된 하위제어기들의 참여율을 조절함으로써 향상된 제진성능을 확보한다. 이는 하위제어기의 정적 제어이득을 퍼지추론과정에 기반하여 실시간으로 변화하는 동적 제어이득으로 변화함으로써 이루어진다. 제안하는 방법으리 적용성을 평가하기 위하여 Dyke 등이 제안한 사장교의 벤치마크 제어문제를 설계 예로 고려하였으며, 사장교 지진응답제어를 위한 제어변수로는 주탑하부의 전단력과 휨모멘트, 주탑상부의 수평변위 및 테크 주탑간 상대변위, 그리고 케이블의 장력을 선정하였다. 벤치마크 사장교에 대하여 제안한 퍼지관리제어기 및 최적제어이론에 기반한 LQG 제어기의 제어성능 비교로부터 제시하는 기법의 효율성을 검증하였다.

• 대한한의학회지
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• 제34권2호
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• pp.41-50
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• 2013

Objectives: As a newcomer to the medical tourism industry, Korea needs to differentiate itself from the leading competing countries to vitalize its early-stage medical tourism industry. This study aims to introduce a strategic plan to vitalize the Korean integrated medical tourism so that Korea can differentiate itself from competing countries and create high added value. Methods: The concept and actual conditions of medical tourism and Oriental medical tourism were examined. A plan to differentiate Korea from the competing countries in the medical tourism industry was studied to create high added-value through strategic vitalization of its medical tourism industry. Results: Korean integrated medical tourism must be developed differently from those of other South-East Asian countries in order to strategically promote the cash-cow medical tourism industry. In order to develop such medical tourism, Korean medical practice, which integrates Western and Oriental medicine, is to be developed through mutual understanding and fusion of other disciplines among medical doctors and Oriental medical doctors who are working in local healthcare for health promotion of local residents and disease prevention and control. This will play a key role in developing a unique medical tourism product of Korea by means of strategic alliances as an integrated medicine. Manpower specialized for integrated medicine is to be specially supplied for Oriental medicine-related business lines at city, county and borough levels, among local governments, that are enthusiastically carrying forward Oriental medical tourism with an interest to promoting more active and strategic business development and raise the effectiveness and efficiency of public health centers handling related medical tourism. Manpower specialized for Korean integrated medical tourism is to be specially supplied for the Ministry of Culture, Health and Tourism, a policy control tower to develop and vitalize high value-added fusion (theme) tourism products such as the Korean integrated medical tourism, in order to discover, promote and support Korean integrated medical tourism's differences from existing medical tourism. Conclusions: The differentiated integrated medical tourism that only Korea can offer in a variety of forms, in order to create a key area of high value-added medical tourism, should be strategically vitalized through a liaison between integrated medicine and tourism and the realization of patient-centered health care services with medical technology developed based on mutual understanding of Western and Oriental medicine.

• 대한토목학회논문집
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• 제32권2B호
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• pp.113-121
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• 2012

유역에서 집중호우가 발생하였을 경우 저수지 내로 고탁수층이 유입된다. 본 연구에서는 성층저수지로 유입된 고탁수층에 대한 선택취수 탁수배제 능력을 검토하기 위하여 3차원적인 접근흐름에 대한 현장실험 및 수치해석 연구를 수행하였다. 다항목수질모니터링시스템(YSI6600EDS)과 초음파유속계(YSI6600ADV)을 이용하여 선택취수시의 온도, 탁도 및 유속분포를 측정하였다. 3차원 모형인 FLOW-3D를 이용하여 저수지 내 취수탑 주변에서 유동형태를 예측하였으며, 현장실험에서의 유속 측정값과 비교분석한 결과 연직유속분포를 잘 모의함을 확인할 수 있었다. 또한 관측 자료들을 분석한 결과에 의하면 표면 취수에 비해 저층 선택취수를 수행하는 것이 고탁수층에 대한 저수지내 탁도 배제능력이 46% 증가하는 것으로 나타났다. 3차원 수치모의 해석결과, 표면취수에 비하여 중층취수를 하는 경우에는 저수지내 탁도 배제능력이 10% 증가하였고, 저층취수를 하는 경우에는 30% 증가하였다. 따라서 저수지 내 고탁수를 배제하기 위해서는 중층 또는 저층의 선택취수를 수행하는 것이 탁수배제 능력 면에서 우수한 것으로 분석되었다. 또한 수치효율이 매우 높은 1차원 SELECT 모형에서도 유사한 결과를 보여 주었다.