• Journal of the Korean Geotechnical Society
• /
• v.16 no.5
• /
• pp.63-74
• /
• 2000

지하구조물 걸설시 발파에 의한 암반의 굴착공법이 일반적으로 사용된다. 그러나 발파에 의한 암반의 굴착은 잔존암반의 손상과 진동을 유발하는 문제점을 가지고 있다. 현재까지는 이러한 암반의 손상과 진동문제를 해결하기 위해 현장계측을 기초로한 경험적인 방법이 이용되어 왔으나 여러 가지 한계점을 지니고 있는 것이 현실이다. 따라서 수치해석에 의한 터널 발파의 모델링을 이용하면 이러한 한계점을 보완할수 있을 것이다. 본 논문에서는 발파에 의한 발파공 주위 암반의 거동을 유한요소해석을 이용하여 규명하고, 토로터널의 표준발파패턴을 기초로 하여 외과공 발파와 외곽공에 인접한 주변공 발파에 의한 암방의 손상의 손상을 비교하여 발파패턴의 적절성을 평가하고자 하였으며, 이를 근거응 발파에 의한 암반의 손상을 최소하기 위한 발파패턴의 최적화를 도모하였다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.11
• /
• pp.810-816
• /
• 2017

This study investigates the relationship between the damage patterns and structural performance levels of a multi-strand 7-wire strand that is used as an important member of stay cables. Stay cables are continuously damaged after completion, and corrosion is the main cause. However, it is difficult to check the damage pattern inside the cable due to its structural characteristics, and it is difficult to evaluate the degradation level of the damage quantitatively. This study derives the relationship between the damage pattern and the performance level of the stranded wire by comparing results and analyzing them through an indoor experiment and finite element analysis. In order to simulate the damage of a 7-wire strand, artificial damage was applied by mechanical precision machining to perform a performance evaluation. The results of the analysis show that regardless of the damage size of the strand, the structural performance deteriorated immediately after the damage. It was experimentally and analytically deduced that the type and amount of damage should be considered as a parameter for evaluating the performance level of the strand. This information can be used for the safety management of a cable stayed bridge by constructing a database according to the pattern and amount of damage.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.390-390
• /
• 2014

Soft-lithography 기술 중의 하나인 Micro-Contact Printing (${\mu}$-CP) 기술은 패턴이 형성된 mold 위에 고분자 물질을 코팅하고 기판과 접촉시켜, 패턴 된 부분만 기판으로 전사시켜 패턴을 형성하는 방법이다. ${\mu}$-CP 기술은 Imprint 방식과 비교하여 잔여물을 제거하기 위한 ashing 공정이 필요 없으며, 상대적으로 패턴이 전사되기 위한 공정 온도와 압력이 낮은 장점이 있다. 한편, 기존의 Photolithography 기술로 유기기판에 패턴을 형성하는 것은 제한이 있으며, 자외선에 의해 유기기판의 특성이 변화될 수 있다. 또한 패턴 형성 후 고분자 패턴을 제거하는 용매가 기판이 손상 받게 된다. 본 실험에서는 poly (1H,1H,2H,2H-perfluorodecyl methacrylate) polymer (PFDMA) films을 패턴 된 poly (dimethylsiloxane) (PDMS) mold 위에 코팅하고 ${\mu}$-CP 기술을 통해 poly (methylmethacrylate) (PMMA), poly (vinyl pyrrolidone) (PVP)등과 같은 유기기판 위에 고분자 패턴 형성을 하였다. 이때 전사 가능한 온도는 상온이며, 압력은 코팅된 PFDMA films이 기판과 접촉될 수 있는 정도만 필요하다. PFDMA가 상온에서 전사 가능한 이유는 유리전이온도가 상온보다 낮기 때문이다. 또한 접촉각을 측정하여 접착력을 계산하면 PFDMA와 기판과의 접착력이 상대적으로 높기 때문이다. PFDMA는 플루오르계 용매에 제거되기 때문에 유기기판의 손상을 최소화 할 수 있다. ${\mu}$-CP 기술을 이용한 PFDMA의 패턴 형성 방법은 물질의 특성으로 flexible 및 organic device 제작에 응용 될 수 있다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.16 no.3
• /
• pp.229-236
• /
• 2003

Artificial neural network has been used for damage assessment by many researchers, but there are still some barriers that must be overcome to improve its accuracy and efficiency. The major problems associated with the conventional artificial neural network, especially the Back Propagation Neural Network(BPNN), are on the need of many training patterns and on the ambiguous relationship between neural network architecture and the convergence of solution. Therefore, the number of hidden layers and nodes in one hidden layer would be determined by trial and error. Also, it takes a lot of time to prepare many training patterns and to determine the optimum architecture of neural network. To overcome these drawbacks, the PNN can be used as a pattern classifier. In this paper, the PNN is used numerically to detect damage in a plate girder railway bridge. Also, the comparison between mode shapes and natural frequencies of the structure is investigated to select the appropriate training pattern for the damage detection in the railway bridge.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.482-482
• /
• 2013

반도체 소자의 미세화와 더불어 세정공정의 중요성이 차지하는 비중이 점점 커지고, 이에 따라 세정 기술 개발에 대한 요구가 증대되고 있다. 기존 세정 기술은 화학약품 위주의 습식 세정 방식으로 표면 손상, 화학 반응, 부산물, 세정 효율 등 여러 가지 어려움이 있다. 따라서 건식세정 방식이 활발하게 도입되고 있으며 대표적인 것이 에어로졸 세정이다. 에어로졸 세정은 기체상의 작동기체를 이용하여 에어로졸을 형성하고 표면 오염물질과 직접 물리적 충돌을 함으로써 세정한다. 하지만 이 또한 생성되는 에어로졸 내 발생 입자로 인해 패턴 손상이 발생하며 이러한 문제점을 극복하기 위하여 본 연구에서는 가스클러스터 장치를 이용한 세정 특성 평가에 관한 연구를 수행하였다. 가스 클러스터란 작동기체의 분자가 수십에서 수백 개 뭉쳐 있는 형태를 뜻하며 이렇게 형성된 클러스터는 수 nm 크기를 형성하게 된다. 그리고 짧은 시간의 응축에 의해 수십 nm 크기까지 성장하게 된다. 에어로졸 세정과 다르게 클러스터가 성장할 환경과 시간을 형성하지 않음으로써 작은 클러스터를 형성하게 되며 이로 인해 패턴 손상을 최소화 하고 상대적으로 높은 효율로 오염입자를 제거하게 된다. 클러스터 세정 장비를 이용한 표면 처리는 충돌에 의한 제거에 기반한다. 따라서 생성 및 가속되는 클러스터로부터 대상으로 전달되는 운동량의 정도가 세정 특성에 영향을 미치며 이는 생성되는 클러스터의 크기에 종속적이다. 생성 클러스터의 크기 분포는 분사 거리, 유량, 분사 각도, 노즐 냉각 온도 등의 변수에 관한 함수이다. 따라서 본 연구에서는 $CO_2$ 클러스터를 이용한 세정 특성을 평가하기 위하여 이러한 변수에 따라서 오염 입자의 종류, 크기에 따른 PRE (particle removal efficiency)를 평가하고 다양한 선폭의 패턴을 이용하여 손상 실험을 수행하였다. 제거 효율에 사용된 입자는 $CeO_2$와 $SiO_2$이며, 각각 30, 50, 100, 300 nm 크기를 정량적으로 오염시킨 쿠폰 웨이퍼를 제조하여 세정 효율을 평가하였다. 정량적 오염에는 SMPS (scanning mobility particle sizer)를 이용한 크기 분류와 정전기적 입자 부착 시스템이 사용되었다. 또한 패턴 붕괴 평가에는 35~180 nm 선폭을 가지는 Poly-Si 패턴을 이용하였다. 실험 결과 클러스터 형성 조건에 따라 상대적으로 낮은 패턴 붕괴에서 95% 이상의 높은 오염입자 제거효율을 전반적으로 보이는 것을 확인할 수 있었다. 따라서 이론적 계산에 기반하여 세정에 요구되는 클러스터 크기를 가정하고, 이를 통하여 세정에 적용할 경우 높은 기존 세정 방법의 단점을 보완하면서 높은 세정 효율을 가지는 대체 세정 방안으로 이용할 수 있음을 확인하였다.

• Journal of Korean Society of Steel Construction
• /
• v.10 no.2 s.35
• /
• pp.279-290
• /
• 1998

An existing Damage Index Method is verified to demonstrate its feasibility for detecting structural damage in truss bridges (1) for which modal parameters are available for a few modes of vibration and (2) for which baseline modal information is not available from its as-built state. The theory of approach to detect locations of damage and to identify baseline modal model is summarized on the basis of system identification theory and modal sensitivity theory. The feasibility of the Damage Index Method is demonstrated using a numerical example of a truss bridge with 11 subsystems of 211 members and for which only two modes of vibration were recorded for post-damaged state.

• Composites Research
• /
• v.35 no.6
• /
• pp.469-476
• /
• 2022

In this paper, the microwave absorbing characteristics after the impact of the radar-absorbing structure (RAS) consisting of periodic pattern sheet (PPS) and glass fiber-reinforced plastic (GFRP) were experimentally investigated. The fabricated RAS effectively absorbed the microwave in the X-band (8.2-12.4 GHz). In order to induce the damage to the RAS, a low-velocity impact test with various impact energy of 15, 40, and 60 J was conducted. Afterward, the impact damage was observed by using visual inspection, non-destructive test, and image processing method. Moreover, the absorbing performance of intact and damaged RAS was measured by the free-space measurement system. The experiment results revealed that the delamination damage from the impact energy of 15 J did not considerably affect the microwave absorbing performance of the RAS. However, fiber breakage and penetration damage with a relatively large damaged area were occuured when the impact energy was increased up to 40 J and 60 J, and these failures significantly degraded the microwave absorbing characteristics of the RAS.

• Investigative Magnetic Resonance Imaging
• /
• v.18 no.3
• /
• pp.232-243
• /
• 2014

Purpose : To evaluate the incidence of secondary contiguous or non-contiguous subchondral bone impactions (SBI) in subaxial cervical spinal injury and associated primary injury patterns. Materials and Methods: A retrospective review of computed tomography, magnetic resonance imaging, and medical records was carried out for 47 patients who had sustained a subaxial cervical spinal injury. Presence, number, level, and sites of secondary contiguous or non-contiguous SBI were recorded. To evaluate primary injury patterns, the level and number of primary injury sites of subaxial cervical spine injury, injury morphology, anterior/posterior discoligamentous complex (ADC/PDC) injury, posterior ligamentous complex (PLC) injury, spinal cord injury, and mechanism of injury (MOI) were analyzed. Differences in primary injury pattern of subaxial cervical spine injury and MOI between patients with and without SBI, and between contiguous or non-contiguous SBI were analyzed using the Mann-Whitney U test, Pearson's chi square test and Fisher's exact test. Results: Eighteen patients (18/47, 38.29%) had developed contiguous (n=9) or non-contiguous (n=9) SBI, most commonly involving T3 (15/47, 31.91%) and 3 levels (6/18, 33.33%). All SBIs had developed near the anterosuperior region of the body and the superior endplate and were the result of a high-impact MOI. SBIs were statistically significant in association with injury morphology and PLC injury (P=0.001, P=0.009, respectively) at the primary injury site. Non-contiguous SBI was more frequently accompanied by upper cervical spinal injuries in association with PDC injuries, as opposed to contiguous SBI, with statistical significance (P=0.009), while no other statistically significant differences were found. Conclusion: Secondary SBIs are common and probably associated with subaxial cervical spinal injuries with high energy compressive flexion forces.

• Journal of the Microelectronics and Packaging Society
• /
• v.16 no.3
• /
• pp.45-51
• /
• 2009

Vertical wet equipment was newly developed in stead of horizontal wet equipment which has been widely used for BGA develop process. We intended to eliminate the collision problem between equipment's transferring rollers and fine circuit patterns, which could be achieved by fixing the BGA panel vertically using jig unit. The process characteristics of vertical wet equipment were evaluated by conducting uniformity evaluation, pattern damage evaluation and defect analysis. The process uniformity of the vertical equipment was measured to be the same level as the uniformity of horizontal equipment. And it was measured that $3{\sim}4{\mu}m$ finer circuit pattern could be processed adopting vertical equipment rather than horizontal equipment.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.6
• /
• pp.359-366
• /
• 2020

In this study, a simulation-based damage estimation method for helidecks is proposed using an artificial neural network. The structural members that share a connecting node in the helideck are regarded as a damage group, and a total of 37,400 damage scenarios are numerically generated by applying randomly assigned damage to up to three damage groups. Modal analysis is then performed for all the damage scenarios, which are selectively used as either training or validation or verification sets based on the purpose of use. An artificial neural network with three hidden layers is constructed using a PyTorch program to recognize the patterns of the modal responses of the helideck model under both damaged and undamaged states, and the network is successively trained to minimize the loss function. Finally, the estimated damage rate from the proposed artificial neural network is compared to the actual assigned damage rate using 400 verification scenarios to show that the neural network is able to estimate the location and amount of structural damage precisely.