• 대한기계학회논문집A
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• 제36권2호
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• pp.223-230
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• 2012

취성이 큰 재료의 강도는 일반적으로 정규분포 또는 와이블분포로 설명되어 왔으나 감마분포도적합할 수 있다. 재료의 파손이 가해진 응력의 연속된 값 중 가장 큰 값에 좌우된다면 극치분포를 적용하는 것이 합당하다. 본 논문에서는 재료강도가 감마분포를 따르며 극치분포하는 응력이 작용할 경우 응력-강도 간섭이론에 기반하여 신뢰도 계산식을 제시하였으며, 확률분포 파라미터별 신뢰도와 안전율 및 변동계수와의 관계를 통하여 신뢰도 계산식의 유효성을 입증하였다. 안전율과 변동계수에 기반한 신뢰도 예측방법으로 목표 신뢰도가 설정되었을 때 최소한 요구되는 안전율과 최대로 허용되는 응력의 변동계수를 예측할 수 있다.

• 한국산업융합학회 논문집
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• 제23권4_2호
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• pp.653-659
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• 2020

In this study, seismic verification of the bellows used in the plant field was conducted. The pressure used in the analysis was analyzed by applying the design pressure of 15.7bar. For the seismic analysis, the natural frequency of the bellows system was obtained and the stability of the system was evaluated by static seismic analysis comparing the lowest order natural frequency with the dominant frequency of 33 Hz. The material of the bellows system is STS304, and the safety factor is obtained in comparison with the allowable stress. For the seismic analysis, the design response spectrum was prepared and the maximum acceleration was applied to the static seismic analysis and the stability of the entire system was confirmed. Compared to the structural analysis results, the maximum stress of the bellows system increased by about 16.4% and the maximum strain increased by about 3 times when seismic analysis was performed.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1382-1399
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• 2023

Pressure relief valve (PRV) is one of the important control valves used in nuclear power plants, and its sealing performance is crucial to ensure the safety and function of the entire pressure system. For the sealing performance improving purpose, an explicit function that accounts for all design parameters and can accurately describe the relationship between the multi-design parameters and the seal performance is essential, which is also the challenge of the valve seal design and/or optimization work. On this basis, a surrogate model-based design optimization is carried out in this paper. To obtain the basic data required by the surrogate model, both the Finite Element Model (FEM) and the Computational Fluid Dynamics (CFD) based numerical models were successively established, and thereby both the contact stresses of valve static sealing and dynamic impact (between valve disk and nozzle) could be predicted. With these basic data, the polynomial chaos expansion (PCE) surrogate model which can not only be used for inputs-outputs relationship construction, but also produce the sensitivity of different design parameters were developed. Based on the PCE surrogate model, a new design scheme was obtained after optimization, in which the valve sealing stress is increased by 24.42% while keeping the maximum impact stress lower than 90% of the material allowable stress. The result confirms the ability and feasibility of the method proposed in this paper, and should also be suitable for performance design optimizations of control valves with similar structures.

• 플랜트 저널
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• 제14권2호
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• pp.33-38
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• 2018

본 연구에서는 순환유동층보일러의 베드가 과열되어 층 물질의 소결이 발생하고 노 내 유동물질에 의해 보일러튜브가 마모 되는 것을 최소화하기 위하여, 노 하부 베드의 층 물질량 조정을 통한 베드 온도 변화를 실험적으로 연구하였다. 실험은 300MW급 순환유동층보일러인 여수화력 2호기를 대상으로 하였으며 터빈출력, 석탄소비량, 공기량 등을 고정한 상태에서 층 물질 양을 감소시켜 베드 압력을 설계값 4.5KPa에서 2.5KPa까지 감소시켰다. 결론적으로 층 물질 양을 적정하게 줄이면 베드 온도가 저하 되나, 지속적으로 저하되지 않는 것을 확인 하였으며, 베드 압력 3.0KPa, 즉 베드 물질량 110 톤을 변곡점으로 하여 베드 온도는 상승하기 시작하였다. 층 물질량이 충분히 많은 상태에서, 층 물질량이 감소되면 베드 온도는 저하되며, 층 물질량이 적정량 보다 적으면 노 내 유동물질의 순환량 감소로 베드 온도는 상승함을 알 수 있었다. 또한 유동층보일러에서 베드 온도 변화는 단순히 층 물질의 양 뿐만 아니라, 보일러 용량 및 연료의 성상 등에 따라 변화 추이가 매우 다양하게 나타난다는 것을 알 수 있었다.

• 한국강구조학회 논문집
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• 제10권1호통권34호
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• pp.125-135
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• 1998

본 연구에서는 내측지점의 상승 하강을 이용하여 부모멘트구간에 프리스트레스를 도입하는 3경간 연속 프리플렉스 합성형교의 설계방법을 제시하고 이를 전산 프로그램화하여 최적설계를 수행하였다. 최적설계를 위한 목적함수로는 3경간 연속 프리플렉스 합성형교의 재료비용으로 결정하고, 제약방정식은 설계과정 및 시방서에 명시된 최소 설계단면제원과 부재별 허용응력에 근거하여 구성하였다. 최적설계기법으로는 기존의 2경간 최적화 연구에서 제시된 수치적 최적화기법의 하나인 순차 비제약 최소화기법을 재검토 및 수정하여 설계를 수행하였다. 민감도분석 결과에 근거하여 지간길이에 따른 최적설계단면을 결정하고, 여기서 정해진 최종 설계단면을 단순보형 프리플렉스 합성형교의 설계단면과 비교하였다. 그리고 각 지간별 합성보의 형고를 변화시키면서 최적화를 수행하여 형고와 재료비용과의 관계도를 제시하고 최적형고를 결정하였다.

• Earthquakes and Structures
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• 제24권5호
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• pp.317-331
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• 2023

The buckling-restrained braced frames with eccentric configurations (BRBFECs) are stable cyclic behavior and high energy absorption capacity. Furthermore, they have an architectural advantage for creating openings like eccentrically braced frames (EBFs). In the present study, it has been suggested to use the performance-based plastic design (PBPD) method to calculate the design base shear of the BRBFEC systems. Moreover, in this study, to reduce the required steel material, it has been suggested to use the performance-based practical design (PBPD) method instead of the force-based design (FBD) method for the design of this system. The 3-, 6-, and 9-story buildings with the BRBFEC system were designed, and the finite element models were modeled. The seismic performance of the models was investigated using two suits of ground motions representing the maximum considered earthquake (MCE) and design basis earthquake (DBE) seismic hazard levels. The results showed that the models designed with the suggested method, which had lower weights compared to those designed with the FBD method, had a desirable seismic performance in terms of maximum story drift and ductility demand under earthquakes at both MCE and DBE seismic hazard levels. This suggests that the steel weights of the structures designed with the PBPD method are about 13% to 18% lesser than the FBD method. However, the residual drifts in these models were higher than those in the models designed with the FBD method. Also, in earthquakes at the DBE hazard level, the residual drifts in all models except the PBPD-6s and PBPD-9s models were less than the allowable reparability limit.

• 대한조선학회 특별논문집
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• 대한조선학회 2011년도 특별논문집
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• pp.117-126
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• 2011

The buckling assessment of plate panels described in common structural rules (CSR) is to be determined according to the buckling utilization factor with hull girder stresses calculated on net hull girder sectional properties. As the thickness requirement for the buckling assessment of plate panels is not explicitly given in CSR, a lot of time is spent to find the proper thickness of plate panels until reaching to an allowable buckling utilization factor. In this study, in order to reduce time and cost, the thickness requirement of plate panels satisfying buckling assessment was derived. The structural design system included with the thickness requirement for buckling assessment was developed. The system is called as Oil-tanker Automated Structural Investigation System (OASIS). The design result of longitudinal strength members using OASIS was verified by Nauticus Hull which is the rule scantling software of DNV. Finally, optimum design of a double hull tanker for the minimum weight using OASIS was presented.

• 한국해양공학회지
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• 제35권2호
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• pp.141-149
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• 2021

The A60 class deck penetration piece is a fire-resistance apparatus installed on the deck compartment to protect lives and to prevent flame diffusion in the case of a fire accident in a ship or offshore plant. In this study, the sensitivity of the fire-resistance performance and approximation characteristics for the A60 class penetration piece was evaluated by conducting a transient heat-transfer analysis and fire test. The transient heat-transfer analysis was conducted to evaluate the fire-resistance design of the A60 class deck penetration piece, and the analysis results were verified via the fire test. The penetration-piece length, diameter, material type, and insulation density were used as the design factors (DFs), and the output responses were the weight, temperature, cost, and productivity. The quantitative effects of each DF on the output responses were evaluated using the design-of-experiments method. Additionally, an optimum design case was identified to minimize the weight of the A60 class deck penetration piece while satisfying the allowable limits of the output responses. According to the design-of-experiments results, various approximate models, e.g., a Kriging model, the response surface method, and a radial basis function-based neural network (RBFN), were generated. The design-of-experiments results were verified by the approximation results. It was concluded that among the approximate models, the RBFN was able to explore the design space of the A60 class deck penetration piece with the highest accuracy.

• 한국기계가공학회지
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• 제12권6호
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• pp.142-151
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• 2013

This study develops an automation system for metallic mold design that is applicable in forging non-axial symmetric parts. The metallic mold design program is used to design the metallic mold using two-dimensional axial symmetric metallic molds and to predict the stress concentration using finite element analyses. Then, the program redesigns the metallic mold using variables such as the optimal split diameter, maximum allowable inner pressure, fit tolerance, and stress distribution, which are calculated using the metallic mold design program. When the involute spur gear is forged, stress concentration occurs on the tooth root bounded at the symmetric surface. The SCM4 material is suitable for metallic molds because the stress is less than the yield strength of the insert and it acts on the tooth root regardless of the inner pressure. The metallic mold for forging non-axial symmetric parts can be designed through adjusting the magnitude of the contact pressure. The program developed in this study can be applied to metallic mold designs in involute spur gears of forging, which is an ordinary non-axial symmetric part.

• 한국항공우주학회지
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• 제38권4호
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• pp.382-388
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• 2010

본 논문에서는 마그네슘합금 재료로 제작된 F-5E/F의 외부 연료탱크 수평 핀의 균열 발생 원인을 분석하고 적절한 대체 재질을 검토하여 탱크의 투하 안전성을 보장하도록 핀의 형상을 재설계하였다. 재료는 재료의 성질과 조달 용이성을 고려하여 강도 및 파괴 인성이 기존재료보다 강하지만 핀 1개당 65%의 무게증가가 예상되는 알루미늄 합금 2024-T351을 선택하였다. 핀의 무게 증가로 인한 연료탱크 무게 중심의 후방 이동을 허용한계 이내로 유지하기 위하여 크기를 20% 축소하고, 두께 7 mm, 곡률 반경 8.5 mm로 설계된 핀에 대하여 정적 및 동적 응력을 해석한 결과 후방 체결부 및 체결 홀의 안전계수가 증가되었음이 확인되었다.