• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.61-73
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• 2009

In this paper, hybrid health monitoring techniques using acceleration-impedance features are newly proposed to detect two damage-type in steel plate-girder bridges, which are girder's stiffness-loss and support perturbation. The hybrid techniques mainly consists of three sequential phases: 1) to alarm the occurrence of damage in global manner, 2) to classify the alarmed damage into subsystems of the structure, and 3) to estimate the classified damage in detail using methods suitable for the subsystems. In the first phase, the global occurrence of damage is alarmed by monitoring changes in acceleration features. In the second phase, the alarmed damage is classified into subsystems by recognizing patterns of impedance features. In the final phase, the location and the extent of damage are estimated by using modal strain energy-based damage index method and root mean square deviation (RMSD) method. The feasibility of the proposed hybrid technique is evaluated on a laboratory-scaled steel plate-girder bridge model for which hybrid acceleration-impedance signatures were measured for several damage scenarios. Also, the effect of temperature on the accuracy of the impedance-based damage monitoring results are experimentally examined from combined scenarios of support damage cases and temperature changes.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.277-277
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• 2022

급경사 산지하천은 호우 시 퇴적 하상이 붕괴하여 하천 유사량을 급격히 증가시키는 계곡형 토석류가 발생하고 도로와 교량에 피해를 일으키기도 한다. 이러한 하천재해를 저감하기 위하여 돌망태 낙차공을 설치하여 하상 안정을 강화하고 급경사에 따른 유수에너지를 줄일 수 있다. 급경사 하상에 설치한 돌망태 낙차공은 하류부 하상의 국부세굴에 따른 파괴위험이 완경사 하상의 경우에 비하여 높으므로 이를 줄이기 위한 연구가 필요하다. 이 연구에서는 광폭경사조절 개수로에 돌망태 낙차공을 설치하고 낙차공의 채움재가 복류의 특성에 미치는 영향을 파악하기 위하여 수리실험을 하였다. 수리실험에서는 최대 20º까지 경사를 조절할 수 있는 길이 1.44m, 폭 0.14m인 직사각형 단면 개수로에 SUS304 구슬을 사용하여 하상과 돌망태 낙차공을 설치하고 실험하였다. 구슬은 크기에 따라 작은구슬(10.31mm), 중간구슬(15.08mm), 큰구슬(20.63mm)을 사용하고, 하상에는 작은구슬을 깔았다. 낙차공의 크기는 길이 16cm이고 폭과 높이는 12cm이며, 돌망태는 작은구슬을 사용한 단일돌망태와 구슬 크기를 달리한 계층돌망태로 구분하였다. 계층돌망태의 상층은 작은구슬, 중층은 중간구슬, 하층은 큰구슬이 채움재로 사용되었다. 단일돌망태의 공극율은 0.399이고 계층돌망태의 공극률은 상층 0.393, 중층 0.517, 하층 0.54이다. 실험유량의 변화는 낙차공 하단부에서 표면류가 발생하지 않는 범위로 한정하였다. 낙차공 하단에서 상류 68cm 지점의 소류력과 낙차공 내부 복류의 수면경사를 측정하였다. 그 결과 단일돌망태보다 계층돌망태가 소류력과 수면경사가 더 작은 것으로 나타났으며 돌망태의 공극을 통한 통수능 차이 때문인 것으로 판단된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.12
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• pp.1150-1158
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• 2013

Artificial cochlear implant system is known as the most efficient and widespread device to patients who have cochlear disorder. However, current commercialized artificial cochleas have inconveniences because of large volume size and high power consumption, requiring further research on improvements in terms of the size, power, and performance. In this paper, we will introduce our fully implantable artificial cochlear implant system, where small-size sensors and actuators are wirelessly connected, focusing on communication system design and its performance simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.713-720
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• 2015

The sizes of the final blades of a low-pressure (LP) steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than the other blades in the same system. As a result, fatigue damage is caused by a large centrifugal force and a low natural frequency of the blade. Recently, many failure cases have been reported due to repeated turbine startups and their prolonged use. In this study, the causes and mechanism of failure of a LP turbine blade were analyzed by using a finite element method to calculate the centrifugal force, the natural frequency of a stress-stiffening effect, and the harmonic response. It was observed that the expected fatigue damage position matched the real crack position at the airfoil's leading edge, and an equivalence fatigue limit approached a notch fatigue limit.

• Clinical and Experimental Pediatrics
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• v.51 no.11
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• pp.1205-1210
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• 2008

Purpose : The development of the corpus callosum occupies the entire period of cerebral formation. The myelination pattern on magnetic resonance imaging (MRI) is very useful to evaluate neurologic development and to predict neurologic outcome in high risk infants. The thickness of the corpus callosum is believed to depend on the myelination process. It is possible to calculate the length and thickness of the corpus callosum on MRI. Thus, we can quantitatively evaluate the development of the corpus callosum. We investigated the clinical significance of measuring various portions of the corpus callosum in neonate with neurologic disorders such as hypoxic brain damage and seizure disorder. Methods : Forty-two neonates were evaluated by brain MRI. We measured the size of the genu, body, transitional zone, splenium, and length of the corpus callosum. Each measurement was divided by the total length of the corpus callosum to obtain its corrected size. The ratio of corpus callosal length and the anteroposterior diameter of the brain was also measured. Results : There was no statistical significance in the sample size of each part of the corpus callosum. However, the corrected size or the ratio of body of the corpus callosum correlated with periventricular leukomalacia and hypoxic ischemic encephalopathy. Conclusion : The abnormal size of the corpus callosum showed a good correlation with periventricular leukomalacia and hypoxic ischemic encephalopathy in neonates. We can predict clinical neurological problems by estimation of the corpus callosum in the neonatal period.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.39 no.4
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• pp.331-338
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• 1994

The experiment was conducted to determine if seed size and seed coat color of soybean might be effective in water uptake and cotyledon damage after imbibition, and hypocotyl elongation. Eight soybean cultivars were separated into two classes of large and small seed based on seed weight, and each class included two cultivars with yellow and black seed color, respectively. Small seed size group was superior in water uptake by seed for 24 hour in imbibition at $25^{\circ}C$ , but its differences decreased as soaking time increased. Small seed cultivars germinated faster and had better germination rate than large ones. However, cultivars with black seed coat showed more slow water uptake at initial time and faster germination than yellow seed, but in 24 hour after imbibition, cultivars with black seed coat had higher water uptake rate than yellow seeds. Small seed cultivar group showed no cotyledon damage in imbibition for 24 hour while large seed cultivars were damaged 78% of cotyledon, and black seed showed low cotyledon damage compared to yellow seed. Hypocotyl length was shorter in large seed rather than in small seed, but hypocotyl thickness in large seed was more thick than in small seed. In correlation coefficients, seed coat rate, embryo rate exhibited significantly negative association with seed weight, and the correlation of seed weight with water uptake in 3 hour after soaking was significantly negative, but in 24 hour showed positive correlation.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.163-174
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• 2004

A number of experiments were performed to investigate the punching shear strength of flat plate-column connections. According to the experiments, the punching shear strength varies significantly with design parameters such as the column size of the connection, reinforcement ratio, and boundary condition. However, current design methods do not properly address the effects of such design parameters. In the present study, a theoratical approach using Rankine's failure cirterion was attempted to define the failure mechanism of the punching shear According to the study, the failure mechanism can be classified into the compression-controlled and the tension-controlled, depending on the amount of bottom re-bars placed at the connection, and the punching shear strength is also significantly affected by the flexural damage of slab. Based on the finding, a new strength model of punching shear was developed, and verified by the comparisons with existing experiments and nonlinear finite element analyses. The comparisons show that the proposed strength model addressing the effects of various design parameters can predict accurately the punching shear strength, compared to the existing strength models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.114-120
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• 2017

In this paper, the effect of the masonry infill walls on the seismic performance of the reinforced concrete(RC) frames with non-seismic details was evaluated through the static test of an masonry infilled RC frame sub-assemblage with non-seismic details of real size, and comparison with the test results of the RC frame sub-assemblage with non-seismic details. As the test results, lots of cracks occurred on the surface of the entire frame due to the compression of the masonry infilled wall, and the beam-column joint finally collapsed with the expansion of the shear crack and buckling(exposure) of the reinforcement. On the other hand, the stiffness of the shear force-story drift relationship decreased due to the wall sliding crack and column flexural cracks, and the strength finally decreased by around 60% of the maximum strength. The damage that concentrated on the upper and lower parts of columns was dispersed in the entire frame such as columns, a beam, and beam-column joints due to the wall, and the specimen was finally collapsed by expansion of the shear crack of the joint, not the shear crack of the column. Also, the stiffness of RC frame increased by 12.42 times and the yield strength by 3.63 times, while the story drift at maximum strength decreased by 0.18 times.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.121-129
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• 2017

In this paper, the shake table test for the masonry infilled reinforced concrete frame with non-seismic details was carried out in order to evaluate its dynamic behaviour and damage under seismic condition. The tested specimens were the RC frame and the masonry infilled RC frame and the dynamic characteristics, such as a resonant period, acceleration response, displacement response and base shear force response, were compared between them. As a result of the shake table test, RC frame specimen had flexural cracks at the top and bottom of the column and shear cracks at the joints. In the case of masonry infilled RC frame, the damage of the frame was relatively minor but the sliding cracks and diagonal shear cracks on the masonry wall were severe at the final excitation. The resonant period of infilled RC frame specimen was shorter than that of the RC frame specimen because the masonry infill contributed to increase the stiffness. The maximum displacement response of the infilled RC frame specimen was decreased by about 20% than the RC frame specimen. It was analyzed that the masonry infill wall applied in this study contributed to increase the lateral strength of the RC frame with non - seismic detail by about 2.2 times and the stiffness by about 1.6 times.