• Structural Monitoring and Maintenance
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• 제10권4호
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• pp.361-379
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• 2023

In cable structure maintenance, particularly for cable-stayed bridges, cable safety assessment relies on estimating cable tension. Conventionally, in Japan, cable tension is estimated from the natural frequencies of the cable using the higher-order vibration method. In recent years, dampers have been installed on cables to reduce cable vibrations. Because the higher-order vibration method is a method for damper-free cables, the damper must be removed to measure the natural frequencies of a cable without a damper. However, cables on some cable-stayed bridges have two dampers: one on the girder side and another on the tower side. Notably, removing and reinstalling the damper on the tower side are considerably more time- and labor-intensive. This paper introduces a tension estimation method for cables with two dampers, using natural frequencies. The proposed method was validated through numerical simulation and experiment. In the numerical tests, without measurement error in the natural frequencies, the maximum estimation error among 100 models was 3.3%. With measurement error of 2%, the average estimation error was within 5%, with a maximum error of 9%. The proposed method has high accuracy because the higher-order vibration method for a damper-free cable still has an estimation error of 5%. The experimental verification emphasizes the importance of accurate damper modeling, highlighting potential discrepancies between existing damper design formula and actual damper behavior. By revising the damper formula, the proposed method achieved accurate cable tension estimation, with a maximum estimation error of approximately 10%.

• 풍력에너지저널
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• 제15권2호
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• pp.23-36
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• 2024

In this study, a health monitoring system was developed for the two most vulnerable parts of a wind tower support structure: the connection between steel towers (L-Flange) and the concrete foundation-steel tower connection. To select assessment parameters for health monitoring, detailed FEM analysis was conducted using the ABAQUS program. Additionally, a testbed was established near the Jeju Woljeongri wind turbine farm to evaluate the applicability of measurement data by installing sensors. Through computational analysis and relevant criteria review, we defined limits for measurement parameters by vulnerable section. We categorized the structural safety evaluation into four stages: normal, caution, warning, and danger, and selected management criteria for each stage. From this, an algorithm to evaluate safety was developed, and a visualized monitoring platform based on the established critical parts monitoring system was developed.

• 한국지진공학회논문집
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• 제17권6호
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• pp.257-269
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• 2013

In this study, the capability of an existing analysis method for the fluid-structure-soil interaction of an offshore wind turbine is expanded to account for the geometric nonlinearity and sea water drag force. The geometric stiffness is derived to take care of the large displacement due to the deformation of the tower structure and the rotation of the footing foundation utilizing linearized stability analysis theory. Linearizing the term in Morison's equation concerning the drag force, its effects are considered. The developed analysis method is applied to the earthquake response analysis of a 5 MW offshore wind turbine. Parameters which can influence dynamic behaviors of the system are identified and their significance are examined.

• 국제초고층학회논문집
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• 제3권3호
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• pp.205-214
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• 2014

The super high rise building construction is characterized by a large quantity of engineering works and structural components, high demanding of construction technology and complex cross operations. As the height of super high rise building increases, the construction difficulties increase, it is challenging the steel structural building construction technology. In this paper, the key technologies in the construction of Chinese modern super high rise steel structure building have been studied. The innovative tower crane supporting frame suspension disassembly technology has been developed to allow the crane supporting frame to turnover in the air without occupying materials stockyard. A new self-elevating platform technique which is capable of striding over structural barriers has been developed. This new technology allows the platform to be self-elevated along variable cross section column with a maximum 600 mm size change. A new automatic submerged arc welding technology has also been developed to ensure the process continuity and quality stability of welding job on the construction site.

• 한국소음진동공학회논문집
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• 제23권5호
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• pp.407-413
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• 2013

This paper deals with the analysis of dynamic characteristics of mooring system of floating-type offshore wind turbine. A spar-type floating structure which consists of a nacelle, a tower and the platform excepting blades, is used to model the floating wind turbine and connect three catenary cables to substructure. The motion of floating structure is simulated when the mooring system is attached using irregular wave Pierson-Moskowitz model. The mooring system is analyzed by changing cable position of floating structure. The dynamic behavior characteristics of mooring system are investigated comparing with cable tension and 6-dof motion of floating structure. These characteristics are much useful to initial design of floating-type structure. From the simulation results, the optimized design parameter that is cable position of connect point of mooring cable can be obtained.

• 해양환경안전학회지
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• 제22권2호
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• pp.233-239
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• 2016

본 연구에서는 LNG-FPSO 선박에 탑재되어 있는 장비들의 운영효율을 최대화하기 위한 상태기반유지보수(CBM) 활동을 지원하는 보전시스템을 개발하였다. 개발된 보전시스템에서는 상태기반유지보수를 수행할 주요 장비들을 식별하여 이를 PWBS(Product Work Breakdown Structure)로 정의하였고 식별된 장비들로부터 실시간 수집되는 센서데이터를 이용하여 장비들의 고장분석과 최적 유지 보수 방안을 결정하기 위한 경제성평가 등을 수행하며, 이들을 수행하기 위해 필요한 입출력 데이터를 저장, 관리하는 고장사례 및 유지보수데이터베이스를 구축하였다. 개발시스템의 성능검증을 현재 개발 중인 LNG-FPSO 선박의 Inlet 시스템의 Compressor와 화물창의 Pump Tower 등과 같은 주요 장비들을 대상으로 실시하였고 이를 바탕으로 상태기반유지보수의 가능성을 확인하였다.

• Structural Engineering and Mechanics
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• 제78권1호
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• pp.87-102
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• 2021

Long span cross-rope suspension structure is an innovative structural system evolved from typical Cross-Rope Suspension (CRS) guyed tower, a type of supporting system with short span suspension cable supporting overhead power transmission lines. In mountainous areas, the span length of suspension cable was designed to be extended to hundreds or over one thousand meters, which is applicable for crossing deep valleys. Vortex Induced Vibration (VIV) of overhead power transmission lines was considered to be one of the major factors of its fatigue and service life. In this paper, VIV and its controlling by Stockbridge damper for long span CRS was discussed. Firstly, energy balance method and finite element method for assessing VIV of CRS were presented. An approach of establishing FE model of long span CRS structure with dampers was introduced. The effect of Stockbridge damper for overall vibration of CRS was compared in both theoretical and numerical approaches. Results indicated that vibration characteristics of conductor in long span CRS compared with traditional tower-line system. Secondly, analysis on long span CRS including Stockbridge damper showed additional dampers installed were essential for controlling maximum dynamic bending stresses of conductors at both ends. Moreover, factors, including configuration and mass of Stockbridge damper, span length of suspension cable and conductor and number of spans of conductor, were assessed for further discussion on VIV controlling of long span CRS.

• 대기
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• 제29권1호
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• pp.41-51
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• 2019

The characteristics of the sea breeze were investigated using the wind and temperature data collected from 300-m tower at Boseong from May 2014 to April 2018. Sea breeze day was detected using following criteria: 1) the presence of a clear change in wind direction near sunrise (between 1 hour after sunrise and 5 hours before sunset) and sunset (from 1500 LST to midnight), 2) presence of thermal forcing of sea breeze and 3) no heavy precipitation (rain < $10mm\;d^{-1}$). Sea breeze days occurred on 569 days for 4 years. The monthly distribution of sea breeze day occurrence shows maxima in May and September and minimum in December. The average onset and cessation times of the sea breeze are 0942 LST and 1802 LST, respectively. Although the 10-m wind shows clockwise rotation with time in the afternoon, the observed hodograph does not show an ideal elliptical shape and has different characteristics depending on the upper synoptic wind direction. Vertical structure of sea breeze shows local maximum of wind speed and local minimum of virtual potential temperature at 40 m in the afternoon for most synoptic conditions except for southeasterly synoptic wind ($60^{\circ}{\sim}150^{\circ}$) which is in the same direction as onshore flow. The local minimum of temperature is due to cold advection by sea breeze. During daytime, the intensity of inversion layer above 40 m is strongest in westerly synoptic wind ($240^{\circ}{\sim}330^{\circ}$) which is in the opposite direction to onshore flow.

• Earthquakes and Structures
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• 제23권2호
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• pp.169-181
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• 2022

To research the dynamic response of the high-rise structure under the rocking ground motion, which we believed that the effect cannot be ignored, especially accompanied by vertical ground motion. Theoretical analysis and shaking table seismic simulation tests were used to study the response of a high-rise structure to excitation of a H-V-R ground motion that included horizontal, vertical, and rocking components. The use of a wavelet analysis filtering technique to extract the rocking component from data for the primary horizontal component in the first part, based on the principle of horizontal pendulum seismogram and the use of a wavelet analysis filtering technique. The dynamic equation of motion for a high-rise structure under H-V-R ground motion was developed in the second part, with extra P-△ effect due to ground rocking displacement was included in the external load excitation terms of the equation of motion, and the influence of the vertical component on the high-rise structure P-△ effect was also included. Shaking table tests were performed for H-V-R ground motion using a scale model of a high-rise TV tower structure in the third part, while the results of the shaking table tests and theoretical calculation were compared in the last part, and the following conclusions were made. The results of the shaking table test were consistent with the theoretical calculation results, which verified the accuracy of the theoretical analysis. The rocking component of ground motion significantly increased the displacement of the structure and caused an asymmetric displacement of the structure. Thus, the seismic design of an engineering structure should consider the additional P-△ effect due to the rocking component. Moreover, introducing the vertical component caused the geometric stiffness of the structure to change with time, and the influence of the rocking component on the structure was amplified due to this effect.

• 정보교육학회논문지
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• 제11권3호
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• pp.317-327
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• 2007

본 연구에서는 온톨로지 이론을 고찰하고, 중학교 기술 가정 교과의 영양소와 식품구성탑 내용을 지원하는 온톨로지 기반 검색 시스템을 설계 및 구현하여 학습을 효율적으로 수행할 수 있도록 하는 방안을 제시하였다. Protege-2000 프레임워크를 기반으로 하여 영양소와 식품구성탑 검색 시스템을 구현하였다. 본 시스템은 XML 기반을 두고 있으므로 차세대 인터넷 기술인 시맨틱 웹과의 연동이 가능하며, 영양학 분야에 공유될 수 있는 의미구조를 제공하여 상호운용이 가능한 지식정보 시스템의 기반을 마련하였다. 아울러 학습자는 스스로 정보검색을 통해 지식을 구조화할 수 있으며, 교수자 역시 이를 교수 학습 과정에 직접 투입하여 학습자들의 학습 성취도 및 흥미 등을 파악할 수 있다. 또한 학습자는 본 시스템을 통해 교수학습과정 뿐 아니라 앞으로의 실생활에서도 온톨로지를 통해 지식을 내면화함으로써 균형 잡히고 건강한 생활을 영위할 수 있을 것으로 생각된다.