• Journal of electromagnetic engineering and science
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• 제9권2호
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• pp.85-97
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• 2009

As operating frequency is raised and as more integration with active and passive elements is required, it becomes difficult to fabricate more than 120 ${\Omega}$ characteristic impedance of a mierostrip line. To solve this problem, an equivalent high impedance transmission-line section is suggested, which consists mainly of a pair of coupled-line sections with two shorts. However, it becomes a transmission-line section only when its electrical length is fixed and its coupling power is more than half. To have transmission-line characteristics(perfect matching), independently of coupling power and electrical length, two identical open stubs are added and conventional design equations of evenand odd-mode impedances are modified, based on the fact that the modified design equations have the linear combinations of conventional ones. The high impedance transmission-line section is a passive component and therefore should be perfectly matched, at least at a design center frequency. For this, two different solutions are derived for the added open stub and two types of high impedance transmission-line sections with 160 ${\Omega}$ characteristic impedance are simulated as the electrical lengths of the coupled-line sections are varied. The simulation results show that the determination of the available bandwidth location depends on which solution is chosen. As an application, branch-line hybrids with very weak coupling power are investigated, depending on where an isolated port is located, and two types of branch-line hybrids are derived for each case. To verify the derived branch-line hybrids, a microstrip branch-line hybrid with -15 dB coupling power, composed of two 90$^{\circ}$ and two 270$^{\circ}$ transmission-line sections, is fabricated on a substrate of ${\varepsilon}_r$= 3.4 and h=0.76 mm and measured. In this case, 276.7 ${\Omega}$ characteristic impedance is fabricated using the suggested high impedance transmission-line sections. The measured coupling power is -14.5 dB, isolation and matching is almost perfect at a design center frequency of 2 GHz, showing good agreement with the prediction.

• 한국전산구조공학회논문집
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• 제16권2호
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• pp.115-124
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• 2003

이 논문에서는 기존의 보-거더 구조계 주차장 구조물에 대한 차량하중영향 연구를 토대로, 플랫 슬래브 구조계에서 차량하중영향에 대한 연구를 수행하였다. 먼저, 최대부재력을 일으키는 차량하중의 적용을 위해 플랫 슬래브의 주요 설계지점에 대한 영향면을 구성하였으며, 플랫 슬래브의 등가차량하중계수를 인공 신경망기법을 이용하여, 슬래브 두께, 지판 두께, 지판 크기, 슬래브의 단변, 장변 길이 등 주요구조변수로 제시하였다. 사용된 신경망의 훈련은 많은 패턴수를 갖는 비선형 회귀분석에 적합한 Levenberg-Marquardt 알고리즘을 이용하였으며 해석결과와 인공 신경망의 출력의 비교를 통해 알고리즘의 유효성을 검증하였다. 플랫 슬래브 구조계의 등가차량하중계수를 살펴보면, 보-거더 구조계의 경우와 유사하게 주열대와 중간대의 정모멘트 부재력에서 차량하중에 매우 취약함을 알 수 있었다.

• 한국전산구조공학회논문집
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• 제13권3호
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• pp.295-304
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• 2000

본 연구의 목적은 지진하중에 대한 응력 해석을 수행하여 ASME, Class 3 설계요건에 따라 스트레이너의 구조건진성을 평가하는 것이다. 스트레이너에 대한 설계요건이 ASME 코드 내에 명백하게 규정되어 있지 않기 때문에 본체는 밸브 설계요건인 ND-3500을 적용하고, 양쪽 플랜지 연결부는 배관 설계요건 중 ND-3658.3을 적용하였으며, 하단의 덮개 플랜지는 Appendix XI에 따라 설계 및 해석을 수행하였다. 본 연구에서는 T형 스트레이너를 쉘로 모델링하여 유한요소법을 사용하여 지진하중에 의해 스트레이너가 응답하는 모드 형상 및 고유진동수를 계산하여 충분히 강건한 구조물임을 입증한 후 정적 해석을 수행하여 주관과 분기 관이 접합하는 연결부위와 같은 위험단면에서의 막응력과 굽힘 응력을 구하였다. 각 하중조합에 대해 코드에서 규정하고있는 허용 값과 비교한 결과 스트레이너는 지진하중이 작용하는 경우 구조적 건전성을 유지하고 있음을 확인하였다. 아울러 인접 배관을 연결해주는 플랜지 연결부의 응력을 규정에 따라 구한 후 설계요건에 의한 허용 값과 비교하여 건전성을 만족함을 알 수 있었다.

• Journal of Radiation Protection and Research
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• 제22권1호
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• pp.47-58
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• 1997

MCNP4A 코드를 이용하여 MIRD 인형팬텀의 정면과 후방에서 입사하는 넓고 평행한 감마선빔에 대한 단위 공기커마당 유효선량 환산계수와 단위 플르언스당 장기의 등가선량을 계산하였다. 본 연구에서 고려한 감마선은 0.03-10 MeV 에너지 구간에서 20개의 단일에너지에 대해 수행되었다. 환산계수의 계산결과를 ICRP/ICRU의 연구결과 발표예정 출판물에 주어진 해당되는 값과 비교한 결과 편차 10%이내에서 일치하고 있다. 결과의 차이가 발생한 이유는 MIRD 팬텀과 ADAM/EVE 팬텀의 기하학적 차이가 주원인이며 또한 계산에 사용된 전산코드와 단면적 차이 등으로 판단된다. 특정 식도 모델을 사용한 결과로부터 얻어진 유효선량과 흉선과 췌장에 대한 등가선량을 채택함으로써 얻어지는 유효선량은 약간(최고 5%)의 차이를 보인다. 기타장기로부터 상부대장을 제외했을 때 본 연구에서 다루었던 감마선 선량학적 측면의 경우에서는 중요하지 않은 것으로 나타났다.

• 콘크리트학회논문집
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• 제26권4호
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• pp.555-562
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• 2014

성능 기반 내진설계를 위해서는 지진후 건물의 사용성과 복원성에 대한 명확한 목표가 필요하다. 이를 위해서는 건물의 구성 재료의 검토가 필요하고, 특히, 부재에 잔류하는 변형을 지표로 사용하는 것은 유용하다. 프리스트레스트 콘크리트는 PC 강재의 원점지향적 성질 덕분에 많이 이용이 될 것으로 생각된다. 이 연구는 PSC 보부재의 잔류 변형을 연구하고 산정하는 것에 목표를 두고 있다. '등가 소성 힌지 길이법'을 바탕으로 위험단면에서의 곡률과 등가 소성 힌지 길이를 이용하여 부재의 변형각을 구하는 식을 유도한다. '분할 요소 해석법'을 통하여 PC강재와 콘크리트 사이의 부착-미끄러짐을 고려하면서 힘의 균형과 변형을 적합 조건을 만족하는 해석값을 도출했다. 잔류 변형률에 영향을 미치는 각종 요인들을 파라미터 스터디를 통하여 잔류 변형률 산정식에 필요한 각종 수치를 결정했다. 그중에서 잔류변형에 많은 영향을 미치는 피크시 등가 소성 힌지 길이, 잔류 변형시 등가 소성 힌지 길이 및 피크시부터 잔류 변형시에 발생하는 위험 단면 위치에서의 곡률 감소량에 대하여 중점적으로 검토를 실시했다. 이 연구 결과를 바탕으로 앞으로 활발한 연구가 진행되기를 기대한다.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.349-365
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• 2022

Steel fibre-reinforced concrete (SFRC) is an emerging class of composite for construction. However, a reliable method to assess the flexural behaviour of SFRC structural member is in lack. An analytical technique is proposed for determining the moment-curvature response of concrete beams reinforced with steel fibres and longitudinal bars (R/SFRC members). The behaviour of the tensile zone of such members is highly complex due to the interaction between the residual (tension softening) stresses of SFRC and the tension stiffening stresses. The current study suggests a transparent and mechanically sound method to combine these two stress concepts. Tension stiffening is modelled by the reinforcement-related approach assuming that the corresponding stresses act in the area of tensile reinforcement. The effect is quantified based on the analogy between the R/SFRC member and the equivalent RC member having identical geometry and materials except fibres. It is assumed that the resultant tension stiffening force for the R/SFRC member can be calculated as for the equivalent RC member providing that the reinforcement strain in the cracked section of these members is the same. The resultant tension stiffening force can be defined from the moment-curvature relation of the equivalent RC member using an inverse technique. The residual stress is calculated using an existing model that eliminates the need for dedicated mechanical testing. The proposed analytical technique was validated against test data of R/SFRC beams and slabs.

• 한국주조공학회지
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• 제10권1호
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• pp.31-42
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• 1990

The full mould casting process in one of the newly developed techniques which has many advantages. Unbonded sand mould has been prepared for the major mould and $CO^2$ gas mould has been used occasionally for comparison. Patterns were built up with expanded polystyrene and coated with three different materials. Silica, graphite and zircon were used for the coating layer. The effects on fluidity and temperature loss of molten metals were investigated. The molten metals were Al-5% Si alloy, Cu-30% Zn alloy and gray iron of approximately 4.0% of carbon equivalent. Experimental variables were runner section area, superheat, sprue height, coating materials, coating thickness and apparent density of EPS pattern. The effects of coating materials on fluidity and temperature loss of the molten metals during transient pouring are summarized as follows : As runner section area, superheat and sprue height increased, fluidity increased. Temperature loss decreased as runner section area and sprue height increased. However, reversed effects were observed in the case of superheat increment. The coating materials decreased the fluidity of each alloy in the order of silica, graphite and zircon. Zircon brought to the highest temperature loss among the coating materials used. The fluidity increased in the order gray iron, Cu-30% Zn and Al-5% Si alloy while temperature loss in the reverse order. Especially in case of reduced pressure process, the fluidity was increased apparently. Al-5% Si alloy showed the lowest temperature loss among the alloys. The increment of the apparent density of EPS pattern resulted in the fluidity decrease and temperature loss increase. The relation between fluidity and temperature loss of each alloy can be expressed by the following equation within the coating thickness limit of 0.5-1.5㎜. F^*={\frac{a}{T^*-b}}-c$ where, $F^*$ : fluidity in the Full mould, $T^*$ : temperature loss in the mould. a : parameter for full mould. b, c : constants.

• 한국의류산업학회지
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• 제12권6호
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• pp.789-795
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• 2010

The purpose of this study was to examine the appropriate surplus of clothing for a jacket bodice pattern of middle-aged obese men by using the 3D virtual twin and virtual garment simulation system. The results were as follows ; 1. BMI rate of middle-aged males was 28.13 which was equivalent to mild obesity, whereas WHR(W/H ratio from waist to hips) rate was near 1.00 which was highly dangerous against their obesity. In case of middle-aged obese men, the WHR was significantly higher than the entire middle-aged men's average and the section shape in which their thickness was relatively more than width. 2. As a result of appearances evaluation through virtual garment simulation, the cut-off amount of the side seam and the center back was regulated accordingly. Hereby, the final tolerance range was set up at 21.15 cm at the hips, so that the appearances became better and the bilateral distribution of the cross section and space length was formed symmetrically. Especially in case of increasing the cross amount of hems to produce a natural silhouette of the waist-to-hips parts, the ease of buttocks was judged to be moderate, but it turned out that a wavy cross section was made and the silhouette was not good. Thus it was found to be not good that the ease of the hips became excessively increased in proportion as circumference of waist and belly were increased in obesity. The use of the virtual twin made it impossible to comprehend the appearances and ease correspondent to motions. In order to evaluate wearing fitness, therefore, the system should be improved so as to change arm positions and perform various motions.

• 한국도로학회논문집
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• 제20권3호
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• pp.65-73
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• 2018

PURPOSES : In this study, the propriety of expansion joint spacing of airport concrete pavement was examined by using weather and material characteristics. METHODS : A finite element model for simulating airport concrete pavement was developed and blowup occurrence due to temperature increase was analyzed. The critical temperature causing the expansion of concrete slab and blow up at the expansion joint was calculated according to the initial vertical displacement at the joint. The amount of expansion that can occur in the concrete slab for 20 years of design life was calculated by summing the expansion and contraction by temperature, alkali-silica reaction, and drying shrinkage. The effective expansion of pavement section between adjacent expansion joints was calculated by subtracting the effective width of expansion joint from the summation of the expansion of the pavement section. The temperature change causing the effective expansion of pavement section was also calculated. The effective expansion equivalent temperature change was compared to the critical temperature, which causes the blowup, according to expansion joint spacing to verify the propriety of expansion joint applied to the airport concrete pavement. RESULTS : When an initial vertical displacement of the expansion joint was 3mm or less, the blowup never occurred for 300m of joint spacing which is used in Korean airports currently. But, there was a risk of blow-up when an initial vertical displacement of the expansion joint was 5mm or more due to the weather or material characteristics. CONCLUSIONS : It was confirmed that the intial vertical displacement at the expansion joint could be managed below 3mm from the previous research results. Accordingly it was concluded that the 300m of current expansion joint spacing of Korean airports could be used without blowup by controling the alkali-silica reaction below its allowable limit.

• 한국강구조학회 논문집
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• 제14권4호
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• pp.549-556
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• 2002

바닥구조의 진동을 평가하는데 있어 기존의 고유진동수 예측식에 의한 방법이 사용되어지고 있다. 그러나, 이러한 예측식들은 재료에 따른 구분이 없기 때문에 실제와느나 다른 결과를 보이게 된다. 또한, 합성데크 플레이트 슬래브의 경우, 고유진동수를 예측하기 위해 슬래브의 단면을 환산해야 하는데, 각 데크 플레이트의 특성상 그 형태가 상이함으로 인하여 많은 어려움을 느끼게 된다. 따라서, 본 논문에서는 슬래브의 단면을 환산하기 위한 새로운 단순화된 방법을 제시하였다. 그리고, 실제 측정값과 가장 오차율이 적은 "LRFD"에 제안된 고유진동수 산출식을 보정하여 기존 예측시에 비해 약 14.3%의 오차율을 개선하는 새로운 예측보정식을 제안하고, 이에 대한 일반적인 적용가능성을 검증하였다.