• 대한기계학회논문집A
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• 제37권4호
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• pp.475-481
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• 2013

직접구동형 서보밸브의 제어시스템은 비선형적이며 밸브스풀에 미치는 유체력의 영향은 매우 크고 부하압력의 크기에 좌우된다. 제어시스템의 설계요구조건을 만족시키기 위해, 제약직접탐색방법인 유전자 알고리즘과 콤플렉스법을 적절히 활용하여 진상-지상제어기 및 미분피드백제어기의 최적 상수값을 탐색하였다. 최적 제어기 상수값을 대입하여 제어시스템을 시뮬레이션한 결과 설계요구조건을 만족하였다.

• Wind and Structures
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• 제30권3호
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• pp.219-229
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• 2020

Net pressures on roofs and walls of buildings are dependent on the internal and external pressure fluctuations. The variation of internal and external pressures are influenced by the size and location of the openings. The correlation of external and internal pressure influences the net pressures acting on cladding on different parts of the roof and walls. The peak internal and peak external pressures do not occur simultaneously, therefore, a reduction can be applied to the peak internal and external pressures to obtain a peak net pressure for cladding design. A 1:200 scale wind tunnel model study was conducted to determine the correlations of external and internal pressures and effective reduction to net pressures (i.e., net pressure factors, F_C) for roof and wall cladding. The results show that external and internal pressures on the windward roof and wall edges are well correlated. The largest ${\mathcal{C}}_{{\check{p},net}$, highest correlation coefficient and the highest F_C are obtained for different wind directions within 90° ≤ θ ≤ 135°, where the large openings are on the windward wall. The study also gives net pressure factors F_C for areas on the roof and wall cladding for nominally sealed buildings and the buildings with a large windward wall opening. These factors indicate that a 5% to 10% reduction to the action combination factor, K_C specified in AS/NZS 1170.2(2011) is possible for some critical design scenarios.

• 한국항해항만학회지
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• 제30권2호
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• pp.137-143
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• 2006

The optimum grillage design belongs to nonlinear constrained optimization problem. The determination of beam scantlings for the grillage structure is a very crucial matter out of whole structural design process. The performance of optimization methods, based on penalty functions, is highly problem-dependent and many methods require additional tuning of some variables. This additional tuning is the influences of penalty coefficient, which depend strongly on the degree of constraint violation. Moreover, Binary-coded Genetic Algorithm (BGA) meets certain difficulties when dealing with continuous and/or discrete search spaces with large dimensions. With the above reasons, Real-coded Micro-Genetic Algorithm ($R{\mu}GA$) is proposed to find the optimum beam scantlings of the grillage structure without handling any of penalty functions. $R{\mu}GA$ can help in avoiding the premature convergence and search for global solution-spaces, because of its wide spread applicability, global perspective and inherent parallelism. Direct stiffness method is used as a numerical tool for the grillage analysis. In optimization study to find minimum weight, sensitivity study is carried out with varying beam configurations. From the simulation results, it has been concluded that the proposed $R{\mu}GA$ is an effective optimization tool for solving continuous and/or discrete nonlinear real-world optimization problems.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.776-781
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• 2008

A ground heat exchanger in a GSHP system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on the thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This paper is part of a research project aiming at constructing a database of these site-specific properties, especially ground effective thermal conductivity. The objective was to develop and evaluation method, and to provide this knowledge to design engineers. To achieve these goals, thermal response tests were conducted using a testing device at nearly 150 locations in Korea. The in-situ thermal response is the temperature development over time when a known heating load imposed, e.g. by circulating a heat carrier fluid through the test exchangers. The line-source model was then applied to the response test data because of its simplicity. From the data analysis, the range of ground effective thermal conductivity at various sites is $1.5{\sim}4.0\;W$/mK. The results also show that the ground effective thermal conductivity varies with grouting materials as well as regional geological conditions and groundwater flow.

• 한국산학기술학회논문지
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• 제13권9호
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• pp.4277-4283
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• 2012

고장력볼트 마찰이음에서 접촉면의 표면상태에 따라 다양한 값을 갖는 미끄러짐계수는 볼트의 축력과 미끄러짐하중에 의해 결정되어진다. 또한 접촉면적은 미끄러짐하중에 영향을 미치게 되므로 볼트구멍에 따라 변하는 접촉면적은 미끄러짐계수와 상관관계를 갖게 된다. 본 연구에서는 부재의 종류, 볼트의 직경 및 볼트구멍의 크기에 따른 미끄러짐계수와 미끄러짐하중의 변화를 파악하기 위하여 32개의 시험편을 제작하여 휨시험 및 인장시험을 실시하였다. 과대볼트구멍으로 제작된 시험편의 미끄러짐하중은 표준볼트구멍으로 제작된 미끄러짐하중의 80%이상의 강도를 발휘하였으며 설계 미끄러짐강도를 상회하였다. 또한 과대볼트구멍으로 제작된 시험편과 표준볼트구멍으로 제작된 시험편의 순단면적비와 미끄러짐비간에는 상당한 상관성을 가지는 것으로 나타났다. 그러나 시험결과가 각 시험체에 따라 다소의 차이를 보이는 것은 미끄러짐계수의 중요한 파라메타인 고장력볼트의 도입축력이 감소하기 때문인 것으로 판단된다. 볼트구멍 크기의 증가는 미끄러짐 계수 뿐 아니라 볼트 축력의 감소를 야기시키므로 설계강도의 감소를 초래하는 것은 자명한 사실이지만 외국의 경우와 같이 구조적 안정을 위협하지 않는 범위 내에서 볼트구멍에 대한 규정에 유연성을 갖는 것도 시공성과 효율성에 긍정적인 요소가 될 것으로 기대된다.

• 한국지진공학회논문집
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• 제10권1호
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• pp.9-16
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• 2006

횡저항 시스템의 설계는 구조 엔지니어의 경험과 노하우에 의존하는 경향이 크다. 또한 건물의 보유성능을 평가하여 설계과정에 적절히 반영할 수 있는 방법이 제시되어있지 않다. 따라서 본 연구에서는 구조물이 실제 보유하고 있는 유효보유성능(available full capacity, $R_{ac}$)과 설계기준에서 제시하고 있는 요구보유성능(minimum required capacity, $R_{code}$)에 의해 건물의 횡저항 시스템을 합리적으로 설계하는 방안을 제시하고자 한다. 제안 방법은 기존 구조 설계과정에 비선형 해석에 의한 횡저항 성능 평가가 추가된 것으로, 우선 기본 설계를 마친 후, 푸쉬오버(pushover)해석을 통해 구조물의 실제 횡저항 성능을 평가한다. 비선형 평가단계에서는 푸쉬오버(pushover) 해석을 수행하고 이선형화를 통해 항복밑면전단력$(V_Y)$을 결정한다. 그리고 설계풍밑면전단력$(V_{wind})$이 설계지진밑면전단력$(V_D)$보다 큰 경우 항복밑면전단력보다 설계풍밑면전단력이 작은 값임을 확인한 후에, 구조물이 보유한 $R_{ac}$를 산정한다. 설계지진밑면전단력이 큰 경우에는 바로 유효보유성능을 산정하고 이 유효 보유성능$(R_{ac})$이 요구보유성능$(R_{code})$에 근접하도록 피드백 과정을 통하여 부재를 재설계한다. 본 논문에서는 간단한 2차원 철골 가새가 설치된 철근콘크리트 구조를 이용하여 두 가지 경우에 대하여 제안한 합리적인 횡저항 시스템의 설계를 적용하였다. 그 결과 기본설계와 비선형 정적해석의 피드백 과정의 반복을 통하여 요구보유 성능에 근접한 유효보유성능을 갖는 횡저항 시스템을 설계하는 것이 가능하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.593-598
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• 2002

Routinely, strength method for the determination of the nominal moment of reinforced concrete beam is assumed to also be suitable for strengthening beams with carbon fiber sheets since typically strengthening beams compromise 98% by volume of reinforced concrete. Flexural capacity of strengthening beam is absolutely dependent upon the type of reinforcement materials, amount of reinforcement, anchoring system, adhesion capacity between reinforcement material and concrete. Therefore, it might be incorrect to use strength method for analysis and design of strengthening beam without considering the differences in the load-deflection curves, mechanism of failure, state of stress distribution, failure strain of the reinforcement. An flexural analysis based on force equilibrium and strain comparability has been developed for strengthening beam. Systematic experimental investigations are compared with analytical results. Then, the adaptation of strength method for strengthening beam have also been discussed.

• Journal of Power Electronics
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• 제14권2호
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• pp.237-248
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• 2014

Pulse-width modulated (PWM) full-bridge boost converters are used in applications where the output voltage is considerably higher than the input voltage. Zero-voltage-switching (ZVS) is typically implemented in these converters. A new ZVS-PWM full-bridge converter is proposed in this paper. The proposed converter does not have any of the disadvantages associated with other converters of this type, including a complicated auxiliary circuit, increased current stresses in the main power switches, and load-dependent ZVS operation. The operation of the proposed converter, its steady-state characteristics, and its design are explained and examined. The feasibility of the converter is confirmed with results obtained from an experimental prototype.

• Computers and Concrete
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• 제17권2호
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• pp.215-225
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• 2016

High performance materials such as Fiber Reinforced Plastic (FRP) are often used for retrofitting structures against blast loads due to its ductility and strength. The effectiveness of retrofit materials needs to be precisely evaluated for the retrofitting design based on the dynamic material responses under blast loads. In this study, the blast resistance of Carbon Fiber Reinforced Plastic (CFRP) and Kevlar/Glass hybrid fabric (K/G) retrofitted reinforced concrete (RC) wall is analyzed by using the explicit analysis code LS-DYNA, which accommodates the high-strain rate dependent material models. Also, the retrofit effectiveness of FRP fabrics is evaluated by comparing the analysis results for non-retrofitted and retrofitted walls. The verification of the analysis is performed through comparisons with the previous experimental results.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권12호
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• pp.616-623
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• 2003

Conventional P/PI speed controller of today's servo drives should be manually tuned the controller switching set-point by trial-and-errors, which may translate the drive system down-time and loss of productivity. The adjustable drive performance is heavily dependent on the quality of the expert knowledge and becomes inadequate in applications where the operating conditions change in a wide range, i.e., tracking command, acceleration/deceleration time, and load disturbances. In this paper, the demands on simple controls/setup are discussed for industry servo drives. Analyzing the frequency content of motor torque command, P/PI control mode switching is automatically performed with some prior knowledge of the mechanical dynamics. The dynamic performance of the proposed scheme assures a desired tracking response curve with minimal oscillation and settling time over the whole operating conditions. For comprehensive comparison of traditional P/PI control scheme, extensive test is carried out on actual servo system.