• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.107-113
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• 2009

In this study, the importance of failure analysis on large ring forged products was assessed and the process and methodology were introduced. Failure analysis case study of the large ring forged steel product with approximately 10 mm long internal crack found by non-destructive test (NDT) was presented. The micrographic and fractographic observations and the verifying tests were conducted on the cracked specimen to identify the possible metallurgical reason for the defects, and the metallurgical aspects of internal crack formation were discussed.

• Structural Engineering and Mechanics
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• 제70권4호
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• pp.431-443
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• 2019

The present paper illustrates a numerical investigation on the failure behaviour of ring-stiffened cylinder subjected to external hydrostatic pressure. The published test data of steel welded ring-stiffened cylinder are surveyed and collected. Eight test models are chosen for the verification of the modelling and FE analyses procedures. The imperfection as the consequences of the fabrication processes, such as initial geometric deformation and residual stresses due to welding and cold forming, which reduced the ultimate strength, are simulated. The results show that the collapse pressure and failure mode predicted by the nonlinear FE analyses agree acceptably with the experimental results. In addition, the failure mode parameter obtained from the characteristic pressure such as interframe buckling pressure known as local buckling pressure, overall buckling pressure, and yield pressure are also examined through the collected data and shows a good correlation. A parametric study is then conducted to confirm the failure progression as the basic parameters such as the shell radius, thickness, overall length of the compartment, and stiffener spacing are varied.

• 항공우주시스템공학회지
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• 제10권3호
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• pp.52-58
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• 2016

The elastomeric O-ring is the most-commonly-used seal due to its excellent sealing capacity, and its availability in various costs and sizes; furthermore, its importance has lasted over a long duration. However, a dearth of research exists in Korea regarding the elastomeric O-ring and the corresponding techniques. The constituent parts of elastomeric rubber are important; to determine their properties, the uni-axial tension and equi-biaxial tension need to be tested. Also, the non-linear analysis method reduces the design cost. An O-ring failure causes leaks and vibration. In this paper, foreign objects are used to affect an O-ring and its performance so that all angles of the O-ring design can be considered. This paper presents a solution for the O-ring-failure problem using a finite-element analysis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권6호
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• pp.711-729
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• 2018

This paper reports on the experimental investigations on the failure modes of ring-stiffened cylinder models subjected to external hydrostatic pressure. Nine models were welded from general structural steel. The shells were initially formed by cold-rolling, and flat-bar ring frames were welded to the shell. The hydrostatic pressure tests were conducted by using water as the medium in pressure chambers. The details of the preparation and main test were briefly explained. The investigation identified the consequence of the structural failure modes, including: shell yielding, local shell buckling between ring stiffeners, overall buckling of the shell together with the stiffeners, and interactive buckling mode combining local and overall buckling. In addition, the ultimate strengths were predicted by using existing design codes. Non-linear numerical computations were also conducted by employing the actual imperfection coordinates. Finally, accuracy and reliability of the predictions of design formulae and numerical were substantiated with the test results.

• ETRI Journal
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• 제34권2호
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• pp.199-209
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• 2012

In transport networks, a multi-ring architecture is very useful to facilitate network planning and to design and provide more resilient services for customers. Unlike traditional synchronous optical network multi-rings, the service resiliency of Ethernet-based multi-rings is significantly impacted by the ring hierarchy because a link or node failure in a certain level ring triggers filtering database flush actions in all higher level rings as well as in the ring with the failure, and consequently a large amount of duplicated data frames may be flooded. In this paper, we investigate how the ring hierarchy impacts the service resiliency of multi-ring networks. Based on extensive experiments on various single- and multiple-link failures, we suggest two effective inter-ring connection rules to minimize the transient traffic and to ensure more resilient multi-ring networks. In addition, we consider a flush optimization technique called e-ADV, and show that the combination of e-ADV and multi-ring structures satisfying our inter-ring connection rules results in a more attractive survivability performance.

• 한국강구조학회 논문집
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• 제26권3호
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• pp.219-229
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• 2014

원형 강관으로 보강된 GFRP 재질의 원통형 쉘구조에 대한 극한 휨 실험 및 범용 유한요소해석 프로그램인 ABAQUS를 사용한 전산해석을 수행하였다. 개인하수처리 시설의 설계 기준에서 제시된 직사각형 단면형상의 GFRP 재질의 보강링이 적용된 설계기준을 바탕으로 원형 강관 보강링에 대한 단면 재료 특성이 반영된 식을 검토하여 설계하였다. 보강링의 단면, GFRP 본체의 직경과 두께에 의한 극한 거동 특성을 분석하기 위하여 총 4개의 시험체를 설계 제작하여 집중하중 정적재하 시험을 수행하였다. 실험결과 강관 보강링이 사용된 GFRP 쉘구조는 휨파괴가 발생할 때까지 충분한 연성도를 가지고 있으며, 강관 보강링의 휨강성 증가에 따른 전체 구조물의 강도증진이 효과적임을 확인하였다.

• KEPCO Journal on Electric Power and Energy
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• 제8권1호
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• pp.5-7
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• 2022

KEPCO's plan is undergoing a trial operation to replace the open-loop section with ring main units configuration where underground distribution lines are installed, by linking the multi-way circuit breakers auto (MCA) on the power side of each pad-mounted transformer. However, ring main units application mentioned above may cause the ripple effects, when implementing the configuration without a study of protection coordination. Because ring main units with classical pre-set protection devices contribution in fault condition didn't consider yet. For the reliable ring main units operation, it is necessary to resolve several protection issues such as the protection coordination with substation side, prevention of the transformer inrush current. These issues can radically deteriorate the distribution system reliability Hence, it is essential to design proper protection coordination to reduce these types of problems. This paper presents a scheme of ring main units' configuration and MCA's settings of time-current curves to preserve the performance of protection coordination among the switchgears considering constraints, e.g. prevention of the ripple effects (on the branch section when a transformer failure occurs and the mainline when a branch line failure occurs). It was confirmed that the propagation of the failure for each interrupter segment could be minimized by applying the proposed TCC and the interrupter settings for the MCAs (branch, transformer). Further, it was verified that the undetected area of the distribution automation system (DAS) could be supplemented by having the MCA configurated ring main units operate first, instead of the internal protection equipment in the transformer such as the fuse, STP when a transformer failure occurs.

• Structural Monitoring and Maintenance
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• 제8권4호
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• 정보보호학회논문지
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• 제34권2호
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• pp.157-166
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• 2024

LWE(learning with errors) 문제 기반의 공개키 암호는 기법 설계 및 파라미터 설정에 따라 복호화 실패율이 주어지는데, 높은 복호화 실패율은 실용성의 저하를 불러올뿐만 아니라 기법에 대한 공격으로 이어질 수 있음이 밝혀진 바 있다[1]. 따라서, KpqC 1차 라운드에 제안된 Ring-LWE 기반 KEM 기법인 TiGER[2]는 오류 보정 코드 (error correction code) Xef와 D2 인코딩 방법을 사용함으로써 복호화 실패율을 낮추고자 하였다. 그런데, Ring-LWE 문제에 기반한 암호화 기법 중 오류 보정 코드를 사용하는 기법의 경우 흔히 가정하는 각 비트 오류의 독립성이 성립하지 않음이 알려진 바 있다[3]. TiGER의 복호화 실패율 계산은 이를 고려하지 않은바, 본 논문에서는 오류 의존성을 고려하여 복호화 실패율을 다시 계산한다. 또한, TiGER(v2.0)의 비트 오류가 잘못 계산되었음을 발견하여 올바른 비트 오류 계산 식과 그에 따라 새로 계산한 복호화 실패율을 제시한다.

• 한국공간구조학회논문집
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• 제18권4호
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• pp.61-68
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• 2018

Tensile load tests were conducted on High-Shear Ring Anchors (HRAs) after shear load had been applied to the HRAs, which had been developed to reduce the number of the anchors. Test variables include the embedment length of the rod and the width of the specimens and a total of 12 specimens were tested. Test results show that the HRAs pulled out due to bond failure or steel failure occurred in case that the HRAs were installed to the members with 300mm or greater width and the embedment length of 160mm (the actual embedment of rod is 140mm) or deeper. Except 4 HRAs showing steel failure of rod, the minimum and average of test-to-prediction by ACI 318-14 ratios are 1.18 and 1.79, respectively. The tensile strength of HRAs, after shear load was applied to the HRAs, can be safely evaluated by the minimum among the concrete breakout strength and bond strength with the actual embedment length of the rod.