• 대한조선학회논문집
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• 제52권3호
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• pp.255-264
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• 2015

Wind load and flow field of a drillship with respect to various super structures were experimentally investigated in KARI 1m-wide wind tunnel with an atmospheric boundary layer simulation. Six-component external balance and Particle image velocimetry technique were used to measure wind load and velocity vectors in the flow-field around the model respectively. The experimental model was an imaginary shaped drillship with an approximated model which has 1/640 scale compared with recent typical drillships. The test Reynolds number based on the overall length was about 1.5×10⁶. It was found that dominant factors influencing on ship wind load are cabin shape and cabin height. Round cabin has smaller axial wind load and narrow boundary layer around the ship than rectangular one, but its yawing moment at certain angles becomes higher. Low cabin height also show positive effects on axial wind load too. Hull shape and forecastle shape show relatively small influences on wind loads except for slight changes around ±45° wind directions.

• Wind and Structures
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• 제13권5호
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• pp.451-469
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• 2010

The majority of weather-related failures of transmission line structures that have occurred in the past have been attributed to high intensity localized wind events, in the form of tornadoes and downbursts. A numerical scheme is developed in the current study to assess the performance of transmission lines under tornado wind load events. The tornado wind field is based on a model scale Computational Fluid Dynamic (CFD) analysis that was conducted and validated in a previous study. Using field measurements and code specifications, the CFD model data is used to estimate the wind fields for F4 and F2 full scale tornadoes. The wind forces associated with these tornado fields are evaluated and later incorporated into a nonlinear finite element three-dimensional model for the transmission line system, which includes a simulation for the towers and the conductors. A comparison is carried between the forces in the members resulting from the tornadoes, and those obtained using the conventional design wind loads. The study reveals the importance of considering tornadoes when designing transmission line structures.

• 전산구조공학
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• 제10권2호
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• pp.203-211
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• 1997

고층건물의 설계에 있어서 지진보다 바람에 의한 영향이 더욱 크므로 바람에 의한 건물의 안전성과 거주성등을 검토하는 것이 중요하다. 이러한 내풍해석은 모형 실험을 통하여 그 결과를 예측할 수 있으나 본 연구에서는 수치해석의 모형 개발에 중점을 두어 변동 풍하중의 3차원 모델과 건물 평면의 비대칭성을 고려하여 동조질량감쇠기를 설치하였을 때의 건물의 진동 성능을 분석하고 있다. 건물의 질량과 강성중심이 일치하지 않아 횡변위와 비틀림이 연계되는 102층의 건물을 예로 들어 내풍해석 및 동조질량감쇠기를 설치하였을 때 진동제어 해석을 수행하여 건물의 변위와 가속도의 평균응답을 구하여 결과를 비교하였다.

• KIEE International Transactions on Power Engineering
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• 제3A권2호
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• pp.63-69
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• 2003

The necessity of compact high temperature superconducting cables is more keenly felt in densely populated metropolitan areas. Because the compact high-temperature superconducting cables can be installed in ducts and tunnels, thereby reducing construction costs and making the use of underground space more effective, the effect of introducing it to the power system will be huge. Seoul, Korea, is selected as a review model for this paper. The loads are estimated by scenario based on a survey and analysis of 345kV and 154kV power supply networks in this area. Based on this, the following elements for an urban transmission system are examined. (1) A method of constructing a model system to introduce high-temperature superconducting cables to metropolitan areas is presented. (2) A case study is conducted through the analysis of power demand scenarios, and the amount of high-temperature superconducting cable to be introduced by scenario is examined. (3) The economy involved in expanding existing cables and introducing high-temperature superconducting cables(ducts or tunnels) following load increase in urban areas is examined and compared., and standards for current cable ducts are calculated. (4) The voltage level that can be accommodated by existing ducts is examined.

• 지질공학
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• 제24권1호
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• pp.81-89
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• 2014

국내 터널현장에서는 일차 지보재의 안정성 및 이차라이닝의 두께와 시공 시기 등을 결정하기 위하여 숏크리트에서 응력 측정을 수행하고 있다. 본 연구에서는 국내 여러 지역의 터널 현장에서 수행된 숏크리트 응력 측정 사례의 분석을 통하여 숏크리트 계측 현황 및 숏크리트 안정성 평가 기준의 문제점을 제시하였다. 또한 개선된 숏크리트 응력 계측 방법을 시공 중인 터널현장에 적용한 사례를 제시하였다. 현재와 같이 숏크리트의 안정성 평가를 측정응력의 절대적 크기를 통하여 수행하기 위해서는 숏크리트 응력 측정의 신뢰성 향상이 필요하다.

• 터널과지하공간
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• 제20권5호
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• pp.318-324
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• 2010

발파나 지진과 같은 충격하중에 의한 재료의 동적특성이 최근 들어 지상 및 지하구조물의 설계에 주목받고 있다. 측정장비의 발달에 힘입어 수백 ${\mu}$-sec에서 파괴가 진행되는 동안에 발생하는 응력과 변형률의 완전한 이력곡선을 얻을 수 있다. SHPB는 암석의 동적거동을 연구하는데 보편적이며 믿을만한 실험장치로 인식되고 있으며, 이 장치에 의한 동적 압축이나 인장강도시험은 조만간 표준시험법으로 제정될 예정이다. 본 보고서는 종래의 사각형 입사파의 단점을 없애기 위하여 사인형태의 응력파를 생성할 수 있는 특별한 모양의 충격자를 고안한 논문을 소개한 것이다. 이 논문은 사인형태의 입사파에 대한 장점을 설명하고 또한 동하중에 대한 암석의 크기효과를 설명하고 있다.

• Smart Structures and Systems
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• 제7권5호
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• pp.365-378
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• 2011

Piezo-based active structural health monitoring (SHM) requires amplifiers specifically designed for capacitive loads. Moreover, with the increase in number of applications of wireless SHM systems, energy efficiency and cost reduction for this type of amplifiers is becoming a requirement. General lab grade amplifiers are big and costly, and not built for outdoor environments. Although some piezoceramic power amplifiers are available in the market, none of them are specifically targeting the wireless constraints and low power requirements. In this paper, a piezoceramic transducer amplifier for wireless active SHM systems has been designed. Power requirements are met by two digital On/Off switches that set the amplifier in a standby state when not in use. It provides a stable ${\pm}180$ Volts output with a bandwidth of 7k Hz using a single 12 V battery. Additionally, both voltage and current outputs are provided for feedback control, impedance check, or actuator damage verification. Vibration control tests of an aluminum beam were conducted in the University of Houston lab, while wireless active SHM tests of a wind turbine blade were performed in the Harbin Institute of Technology wind tunnel. The results showed that the developed amplifier provided equivalent results to commercial solutions in suppressing structural vibrations, and that it allows researchers to perform active wireless SHM on moving objects with no power wires from the grid.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권4호
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• pp.147-155
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• 2007

Mobile air conditioning systems work under widely changing operating conditions. To understand the system behavior under such dynamic conditions, a test facility that can impose transient loads as well as conducting dynamic measurements is needed. To test mobile air conditioning systems including their dynamic performance under various drive cycle patterns without using full scale vehicles in a wind tunnel, a new test facility, called "dynamic simulator," is described. It can replicate real vehicle operating conditions by interacting with the system being tested based on the measured system performance and subsequently adjusting the air properties returning to the test system based on the results of a numerical cabin model. A new dynamic simulator has been designed, constructed, and verified for performing dynamic tests. It was successful in controlling the temperature and relative humidity of the air returning to the test unit within ${\pm}0.7^{\circ}C$ and ${\pm}4%$ of their respective intended values. The verification test under the New European Driving Cycle demonstrated that detailed transient behavior of the mobile air conditioning system could be measured by using this dynamic simulator.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.819-831
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• 2020

Wind load is one of the major design loads for the hull and mooring of offshore floating structures, especially due to much larger windage area above water than under water. By virtue of extreme design philosophy, fully turbulent flow assumption can be justified and the hydrodynamic characteristics of the flow remain almost constant which implies the wind load is less sensitive to the Reynolds number around the design wind speed than wind profile. In the perspective of meteorology, wind profile used for wind load estimation is a part of Atmospheric Boundary Layer (ABL), especially maritime ABL (MBL) and have been studied how to implement the profile without losing turbulence properties numerically by several researchers. In this study, the MBL is implemented using an open source CFD toolkit, OpenFOAM and extended to unstable ABL as well as neutral ABL referred to as NPD profile. The homogeneity of the wind profile along wind direction is examined, especially with NPD profile. The NPD profile was applied to a semi-submersible rig and estimated wind load was compared with the results from wind tunnel test.

• Wind and Structures
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• 제31권6호
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• pp.561-573
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• 2020

Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.