• 대한기계학회논문집B
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• 제35권9호
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• pp.923-932
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• 2011

본 연구에서는 복합화력발전소 가스터빈 출구가스 안내덕트 내부의 가스유동장이 배열회수보일러 전열기구에 미치는 영향을 CFD기법을 이용하여 분석하였다. 안내덕트 내부 난류흐름의 경우, 유속의 편차가 크고 선회 효과 및 상승류 현상이 심한 특징을 가지고 있음으로 이와 같은 유동의 수치해석을 위해 2개 방정식 난류점성 모델 중 RNG k-${\epsilon}$ 모델을 사용하였으며 유동장의 영향을 가장 많이 받는 배열 회수보일러 최종과열기관의 열전달특성변화를 파악하기 위하여 NTU 방식을 이용한 수치해석결과와, 산업계에서 적용하는 설계기법에 의한 결과를 비교하였다.

• 한국콘텐츠학회논문지
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• 제10권5호
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• pp.241-251
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• 2010

본 연구는 의료기관 종사자들의 특성에 따른 스트레스 정도와 직무스트레스에 스트레스 측정영역들의 영향력을 확인하기 위하여 부산지역 9개 의료기관(종합병원 2개, 병원 7개) 종사자 475명을 대상으로 실증분석을 하였다. 연구결과는 다음과 같은 이론적, 실무적 시사점을 제공하고 있다. 첫째, 종사자특성에 따라 직무스트레스는 유의한 차이가 있었다. 둘째, 직무스트레스에 가장 큰 영향을 주는 스트레스 측정영역은 직무요구이었으며, 가장 낮은 영향영역은 직장문화이었다. 셋째, 직무스트레스 한국인 참고치와 비교시 남성은 직무요구 영역, 여성은 직무불안정 영역이 상위 50% 범주에 해당되었다. 본 연구결과 의료기관 의 조직관리는 종사자특성에 따라 스트레스 요소를 고려하여야 함을 인식하게 되었다.

• 대한기계학회논문집A
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• 제20권9호
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• pp.2894-2900
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• 1996

The stream generator tubes represent an integral part of a major barrier against the fission product release to the environment. So, the rupture of these tubes could permit flow of reactor coolant into the secondary system and injure the safety of reactor coolant system. Therefore, if the crack was detected during In-Service Inspection of tubes the cracked tube should be evaluated by the pulgging criteria and plugged or not. In this study, the fracture mechanics evaluation is carried out on the thru-wall axial crack due to Primary Water Stress Corrosion Cracking in the roll transition aone of steam generator tube to help the assurence the integrity of tubes and estabilish the plugging criteria. Due to the Inconel which is used as tube material is more ductile than others, the plastic instability repture theory was used to calculate the critical and allowable crack length. Based on Leak Before Break concept the leak rate for the critical crack length and the allowable leak rate are compared and the safety of tubes was given.

• 정보화정책
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• 제23권3호
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• pp.43-63
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• 2016

본 연구는 인터넷 다국어도메인의 국제표준화에 대한 국제커뮤니케이션을 분석하여 그 대중화 실패 요인을 이해하고자 한다. 조직화 이론을 활용하여 ICANN에서 다국어도메인에 대한 필요성이 제기되는 초기 담론을 관찰하고, 기술적으로 계층적 방식이 선택되는 과정에서 어떤 갈등이 있었는지 살펴보며, 선택된 결정이 주요 이해당사자들에게 어떻게 받아들여졌는지 살펴본다. 분석 결과, 대중화 실패 요인은 미국을 중심으로 하는 ICANN과 그 필요성을 제기하였던 비영어권 국가 간의 인식론적 차이에서 찾을 수 있다. '정보격차 해소'와 '문화적 가치 추구'라는 담론은 '인터넷 인프라의 안정성'이라는 ICANN의 기술적 담론과 충돌한다. 이로써 국제표준화는 10년이라는 오랜 시간이 걸렸고 시장에서는 다양한 서비스들이 난립하는 결과를 초래하였다. 한국의 적용 사례를 보면, 도메인 무단 점유, 홍보 비용, 기술적 불안정성 및 이용자의 혼란 등 사회적 역효과가 대중들에게 외면받게 되는 요인으로 작용하였고 정부는 일관성 있는 정책을 제시하는데 실패했다.

• 응용통계연구
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• 제29권5호
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• pp.807-822
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• 2016

LN-GPD 합성 분포는 몸통부분은 로그-정규분포를 두터운 꼬리에 대해서는 GPD분포를 따르도록 합성한 분포로 두터운 몸통과 꼬리를 동시에 가지는 자료를 절삭없이 효율적으로 다룰 수 있는 분포이다. 하지만 임계점을 포함하고 있기에 최대우도추정량은 매우 불안정함이 잘 알려져 있어 본 논문이서는 이를 극복하기 위해서 임계점을 먼저 추정하고 나머지 모수들에 대해서 따로 추정하는 2단계 추정 방법들에 대해서 살펴보고 그 성능을 비교해 보았다. 그 결과 동시 추정하는 최대우도추정량의 경우 불안정한 추정이 GPD 분포의 꼬리 지수에서 두드러 졌으며 임계점에 대해서는 비교적 잘 추정함을 알 수 있었다. 이와 반대로 여러 비모수적인 방법들은 꼬리 지수는 만족스럽게 잘 추정하였으나 임계점의 경우 편의가 있음을 관찰할 수 있었다. 실증자료 분석을 위해 2단계 추정법을 이스라엘 은행의 콜센터에서 수집한 서비스 시간에 대한 자료에 적합해 보았으며 그 결과 LN-GPD 합성 분포를 사용하는 것이 로그-정규분포 혹은 GPD 분포 단독으로 사용하는 것보다 자료의 손실도 없이 더 좋은 적합도를 보임을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.712-718
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• 2015

Cast duplex stainless steels are susceptible to thermal aging during long-term service at temperatures ranging from $280^{\circ}C$ to $450^{\circ}C$. To analyze the effect of thermal aging on leak-before-break (LBB) behavior, three-dimensional finite element analysis models were built for circumferentially cracked pipes. Based on the elasticeplastic fracture mechanics theory, the detectable leakage crack length calculation and J-integral stability assessment diagram approach were carried out under different bending moments. The LBB curves and LBB assessment diagrams for unaged and thermally aged pipes were constructed. The results show that the detectable leakage crack length for thermally aged pipes increases with increasing bending moments, whereas the critical crack length decreases. The ligament instability line and critical crack length line for thermally aged pipes move downward and to the left, respectively, and unsafe LBB assessment results will be produced if thermal aging is not considered. If the applied bending moment is increased, the degree of safety decreases in the LBB assessment.

• Steel and Composite Structures
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• 제25권1호
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• pp.105-116
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• 2017

This paper presents the dynamic stability study of laminated composite plates with different force combinations and aspect ratios. Optimum non-diverging stacking is obtained for certain loading combination and aspect ratio. In addition, the stability force is maximized for a definite operating frequency. A dynamic version of the principle of virtual work for laminated composites is used to obtain force-frequency relation. Since dynamic stiffness governs the divergence or flutter, an efficient optimization method is necessary for the response functional and the relevant constraints. In this way, a model based on the ant colony optimization (ACO) algorithm is proposed to search for the proper stacking. The ACO algorithm is used since it treats with large number of dynamic stability parameters. Governing equations are formulated using classic laminate theory (CLT) and von-Karman plate technique. Load-frequency relations are explicitly obtained for fundamental and secondary flutter modes of simply supported composite plate with arbitrary aspect ratio, stacking and boundary load, which are used in optimization process. Obtained results are compared with the finite element method results for validity and accuracy convince. Results revealed that the optimum stacking with stable dynamic response and maximum critical load is in angle-ply mode with almost near-unidirectional fiber orientations for fundamental flutter mode. In addition, short plates behave better than long plates in combined axial-shear load case regarding stable oscillation. The interaction of uniaxial and shear forces intensifies the instability in long plates than short ones which needs low-angle layup orientations to provide required dynamic stiffness. However, a combination of angle-ply and cross-ply stacking with a near-square aspect ratio is appropriate for the composite plate regarding secondary flutter mode.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Tribology and Lubricants
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• 제40권2호
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• pp.39-46
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• 2024

The Morton effect (ME) is an instability phenomenon occurring in rotating machineries supported by fluid film bearings and is induced by the thermal deformation of the overhung mass, which is a part of the rotating shaft. Herein, we describe the ME during the high-speed balancing test of a 20 MW class steam turbine. Additionally, to predict the rotating speed at which the ME occurs, we apply the sensitivity vector theory for the steam turbine. During the operation of the steam turbine, we observe a continuous increase in vibration and hysteresis near the rated speed, which is typical of the ME. Increasing the temperature of the lubricating oil supplied to the bearings from 40 to 60℃ suppresses the occurrence of the ME. The rotordynamic analysis for the steam turbine suggests the existence of a mode in which the overhung mass undergoes significant deformation near the rated speed, and we presume that such a mode will increase the occurrence of the ME. The predicted rotating speed of ME occurrence, obtained through the sensitivity vector method, correlates with the test results. Moreover, increasing the temperature of the supplied lubricating oil mitigates the occurrence of ME by reducing the sensitivity between the temperature deviation vector and unbalance mass vector.

• 한국운동역학회지
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• 제16권2호
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• pp.1-8
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• 2006

The purpose of this study was to evaluate normalized jerk according to shoes, slope, and velocity during walking. Eleven different test subjects used three different types of shoes (running shoes, mountain climbing boots, and elevated forefoot walking shoes) at various walking speeds(1.19, 1.25, 1.33, 1.56, 1.78, 1.9, 2, 2.11, 2.33m/sec) and gradients(0, 3, 6, 10 degrees) on a treadmill. Since there were concerns about using the elevated forefoot shoes on an incline, these shoes were not used on a gradient. Motion Analysis (Motion Analysis Corp. Santa Rosa, CA USA) was conducted with four Falcon high speed digital motion capture cameras. Utilizing the maximum smoothness theory, it was hypothesized that there would be differences in jerk according to shoe type, velocity, and slope. Furthermore, it was assumed that running shoes would have the lowest values for normalized jerk because subjects were most accustomed to wearing these shoes. The results demonstrated that elevated forefoot walking shoes had lowest value for normalized jerk at heel. In contrast, elevated forefoot walking shoes had greater normalized jerk at the center of mass at most walking speeds. For most gradients and walking speeds, hiking boots had smaller medio-lateral directional normalized jerk at ankle than running shoes. These results alluded to an inverse ratio for jerk at the heel and at the COM for all types of shoes. Furthermore, as velocity increased, medio-lateral jerk was reduced for all gradients in both hiking boots and running shoes. Due to the fragility of the ankle joint, elevated forefoot walking shoes could be recommended for walking on flat surfaces because they minimize instability at the heel. Although the elevated forefoot walking shoes have the highest levels of jerk at the COM, the structure of the pelvis and spine allows for greater compensatory movement than the ankle. This movement at the COM might even have a beneficial effect of activating the muscles in the back and abdomen more than other shoes. On inclines hiking boots would be recommended over running shoes because hiking boots demonstrated more medio-lateral stability on a gradient than running shoes. These results also demonstrate the usefulness of normalized jerk theory in analyzing the relationship between the body and shoes, walking velocity, and movement up a slope.