• Composites Research
• /
• v.15 no.2
• /
• pp.11-17
• /
• 2002

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF (polyvinylidene fluoride) film sensors are used for monitoring impact damage in Gr/Ep composite panels. Both PVDF film sensors and strain gages are attached to the surface of Gr/Ep specimens. A series of impact tests at various impact energy by changing impact mass the height are performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as indentation, matrix cracking, and delamination, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.

• Korean Journal of Applied Biomechanics
• /
• v.15 no.3
• /
• pp.117-132
• /
• 2005

It was to study a following research of "A Kinematic Analysis of Air-rolling-breakfall in Judo". The purpose of this study was to analyze the Center of Gravity(COG) variables when performing Air-rolling-breakfall motion, while passing forward over(PFO) to the vertical-hurdles(2m height, take off board 1m height) in judo. Subjects were four males of Y. University squad, who were trainees of the demonstration exhibition team, representatives of national level judoists and were filmed by four 5-VHS 16mm video cameras(60field/sec.) through the three dimensional film analysis methods.COG variable were anterior-posterior directional COG and linear velocity of COG, vertical directional COG and linear velocity of COG. The data collections of this study were digitized by KWON3D program computed The data were standardized using cubic spline interpolation based by calculating the mean values and the standard deviation calculated for each variables. When performing the Air-rolling-breakfall, from the data analysis and discussions, the conclusions were as follows : 1. Anterior-posterior directional COG(APD-COG) when performing Air-rolling-breakfall motion, while PFO over to the vertical-hurdles(2m height) in judo. The range of APD-COG by forward was $0.31{\sim}0.41m$ in take-off position(event 1), $1.20{\sim}1.33m$ in the air-top position(event 2), $2.12{\sim}2.30m$ in the touch-down position(event 3), gradually and $2.14{\sim}2.32m$ in safety breakfall position(event 4), respectively. 2 The linear velocity of APD-COG was $1.03{\sim}2.14m/sec$. in take-off position(event 1), $1.97{\sim}2.22m/sec$. gradually in the air-top position(event 2), $1.05{\sim}1.32m/sec$. in the touch-down position (event 3), gradual decrease and $0.91{\sim}1.23m/sec$. in the safety breakfall position(event 4), respectively. 3. The vertical directional COG(VD-COG) when performing Air-rolling-breakfall motion, while PFO to the vertical-hurdles(2m height) in judo. The range of VD-COG toward upward from mat was $1.35{\sim}1.46m$ in take-off position(event 1), the highest $2.07{\sim}2.23m$ in the air-top position(event 2), and after rapid decrease $0.3{\sim}0.58m$ in the touch-down position(event 3), gradual decrease $0.22{\sim}0.50m$ in safety breakfall position(event 4), respectively. 4. The linear velocity of VlJ.COG was $1.60{\sim}1.87m/sec$. in take-off position(event 1), $0.03{\sim}0.08m/sec$. gradually in the air-top position(event 2), $-4.37{\sim}\;-4.76m/sec$. gradual decrease in the touch-down position(event 3), gradual decrease and -4.40${\sim}\;-4.77m/sec$. in safety breakfall position(event 4), respectively. When performing Air-rolling-breakfall showed parabolic movement from take-off position to air-top position, and after showed vertical fall movement from air-top position to safety breakfall. In conclusion, Ukemi(breakfall) is safety fall method Therefore, actions need for performing safety fall movement, that decrease and minimize shock and impact during Air-rolling-breakfall from take-off board action to air-top position must be maximize of angular momentum, and after must be minimize in touch-down position and safety breakfall position.

• Nuclear Engineering and Technology
• /
• v.50 no.8
• /
• pp.1387-1401
• /
• 2018

An aircraft impact (AI) on a nuclear power plant (NPP) is considered to be a beyond-design-basis event that draws considerable attention in the nuclear field. As some NPPs have already adopted the seismic isolation technology, and there are relevant standards to guide the application of this technology in future NPPs, a new challenge is that nuclear power engineers have to determine a reasonable method for performing AI analysis of base-isolated NPPs. Hence, dynamic influences of the seismic isolation on the vibration and structural damage characteristics of the base-isolated CPR1000 containment are studied under various aircraft loads. Unlike the seismic case, the impact energy of AI is directly impacting on the superstructure. Under the coupled influence of the seismic isolation and the various AI load, the flexible isolation layer weakens the constraint function of the foundation on the superstructure, the results show that the seismic isolation bearings will produce a large horizontal deformation if the AI load is large enough, the acceleration response at the base-mat will also be significantly affected by the different horizontal stiffness of the isolation bearing. These concerns require consideration during the design of the seismic isolation system.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.35 no.2
• /
• pp.13-20
• /
• 2019

This study was conducted in order to validate the nose shape factors of projectile in existing impact formulas for high-strength concrete in the event of collision with high-speed projectiles. In order to conduct the high-speed impact experiment, specified concrete strengths of 35, 100, and 120 MPa were prepared and tested in collision with both conical and hemispherical projectiles. The results showed that the measured penetration depth did not decrease linearly as concrete strength increased. Comparing the ratio penetration depth to the kinetic energy of the conical and hemispherical projectiles, the difference in the ratios for high strength concrete was observed to decline as concrete strength increased. However, in the modified NDRC and the Hughes formulas, the difference in the predicted penetration depth of the conical and hemispherical projectiles was constant despite increasing concrete strength. The modified NDRC and Hughes formulas should be improved upon so as to be applied to high strength concrete.

• International Journal of Advanced Culture Technology
• /
• v.12 no.2
• /
• pp.334-344
• /
• 2024

In Dangjin, Chungcheongnam-do, there are not only power plants and large steel complexes, but also small and medium-sized air pollutant emission facilities. The dust generated by these facilities has a very small particle size and a large surface area due to condensation and physical and chemical reactions, and is discharged containing various harmful substances. Therefore, this study analyzed the distribution of particulate matter and heavy metal concentrations by particle size in the vicinity of the steel complex, residential area, and reference point using an eight-stage Cascade Impactor. Overall, the direct impact sites with a short distance from the steel complex had the highest concentration, followed by the indirect impact sites, and the non-impact sites had the lowest concentration, indicating that they are directly affected by the steel complex. The atmospheric dust concentration distribution showed a bimodal distribution with a minimum value around the 1.1 to 2.1 ㎛ particle diameter. However, during the yellow dust event, the maximum concentration was biased toward coarse particles. The proportion of PM2.5 in the dust tended to be higher in winter, while the ratio between PM2.5 and PM10 was relatively higher in spring. Regardless of the location of the impact point, heavy metals in the dust were dominated by iron and aluminum, followed by zinc, lead, and manganese.

• Atmosphere
• /
• v.31 no.4
• /
• pp.377-394
• /
• 2021

The recent largest forest fire in the Yeongdong region, Goseung/Okgae fires of 2019 occurred during YangGang wind event. The wind can be locally gusty and extremely dry, particularly in the complex terrain of Yeongdong. These winds can cause and/or rapidly spread wildfires, the threat of which is serious during the dry spring season. This study examines the spatial variability of the surface wind and its coupling with the upper atmospheric wind using the data during the IOP of the Gangwon Yeongdong Wind Experiments (G-WEX) conducted in 2020 and the data during YangGang wind event on 4~5 April 2019. In the case of IOPs, strong wind at the surface with a constant wind direction appears in the mountain area, and weak wind with large variability in wind direction appears from foothill to the coast in the vicinity of Gangneung region. However, in the 2019 event, strong wind at the surface with a constant wind direction appears in the entire region from the mountain to the coast, even with the stronger wind in the coast than in some part of the mountain area. The characteristics of the upper atmospheric wind related with the spatial distribution of surface wind show that during IOPs of G-WEX, a strong downdraft exists near the mountaintop in the level of about 1 to 4 km. However, in the 2019 event a strong downdraft is reinforced, when its location moves toward the coast and descends close to the ground. These downdrafts are generated by the breaking of mountain waves.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.62 no.4
• /
• pp.13-22
• /
• 2020

The Doam Lake watershed has a significant impact on the downstream water system due to nutrients and sediment outflow during rainfall caused by steep slopes, soil losses, and fertilization. These non-point sources are unclear in the discharge area and are affected by land use patterns, soil characteristics, and topographical features of the watershed. Therefore, this study conducted rainfall monitoring from July to October 2019 in Songcheon upstream of the Doam Lake watershed, one of the non-point pollution source management areas. Then, after analyzing rainfall runoff, Event Mean Concentration (EMC) and Mass First Flush ratio (MFFn) were calculated to compare and analyze the characteristics of rainfall and the non-point pollutant discharge. As a result of the analysis, it showed various non-point pollutant emission characteristics for each rainfall event. In addition, the concentration of EMC and the MFFn were affected by the average rainfall intensity and the maximum rainfall intensity, and were not significantly affected by the number of antecedent drying days. In the future, it is expected that effective non-point source reduction measures and management measures according to rainfall intensity through continuous monitoring and analysis will be needed.

• Journal of the Korean Institute of Gas
• /
• v.27 no.4
• /
• pp.19-26
• /
• 2023

Earthquakes are one of the most important disasters affecting underground structures. Urban gas underground pipes may cause safety problems of structures in the event of an earthquake. Since Korea began digital observation, the number of earthquakes has been steadily increasing. The seismic design standard for urban gas pipes was established in 2008, but it is difficult to estimate the impact of pipes in the event of an earthquake based on the installation of pipes. In this study, structural analysis was performed on PE (polyethylene pipe) pipes and PLP (polyethylene coated steel pipe) pipes, which are mainly used as buried pipes in Korea, according to environmental and pipe variables in the event of an earthquake. This study sought to find the variables of the most vulnerable buried pipe by modeling pipes through Computer Aided Engineering (CAE) and generating displacement on the ground. Through this study, it was confirmed that the larger the elastic modulus of the soil, the deeper the buried depth, the smaller the tube diameter, and the higher the pressure, the more PLP pipes are affected by earthquakes than PE. Based on these results, the vulnerable points of buried urban gas pipes are inferred and used for special inspections of buried pipes in the event of an earthquake.

• Korean Management Science Review
• /
• v.27 no.3
• /
• pp.161-196
• /
• 2010

This paper empirically investigates the impact of winning a service quality award on the market value in Korea. We estimates the mean "abnormal" change in the stock prices of sample firms when information of winning a service quality award was publicly announced. To access the validity of the research question, this paper employed collected 47 firms data that received the Korean Service Quality Awards so far. Event study methodology was used to analyze the effect of Korean service quality awards. The findings are as follows; The average abnormal returns on the event date are not significant at the 0.05 level which means that the receiving Korean Service Quality Awards has no influence on the firms' market value. On the other hand successive awarded firms have an increasing effect on the market value and it is significant at the 0.05 level. Furthermore, the results show that the factors of firm size such as firm's total assets are critical to vary the firms' abnormal returns. There might be some limitations in this study. The most obvious problem is the limitation of sample size. Although 518 sample cases were found during the period from 2000 to 2008, most of the cases were deleted according to the sample criteria. We are expecting the future research with more data and more precise results. Furthermore, our research consider the only two service award institutions even though there are several different service award authorities in Korea. It is needed to expand the research scope and range to adopt the various service award institutions for the future work.

• The Korean Journal of Financial Management
• /
• v.26 no.1
• /
• pp.65-94
• /
• 2009

The event of change in KOSPI 200 Index composition is one of the main subjects for the test of EMH. According to EMH, when a certain event is not related with firm's fundamental value, stock price should not change after the announcement of news. This hypothesis leads us to the conclusion of horizontal demand curve of stock. This logic was questioned by Shleifer(1986) and argued that downward sloping demand curve hypothesis was supported. But Harris and Gruel(1986) found a different empirical evidence that price reversal occurs in the long run, which is called price pressure hypothesis. They argued that short term price effect by large block trading (price pressure) is offset in the long run because these event is unrelated to fundamental value. Therefor, they argued that EMH can not be rejected in the long run. Until now, there are two empirical studies with Korean market data in this area. Using a data with same time period of $1996{\sim}1999$, Kweon and Park(2000) and Ahn and Park(2005) showed that stock price or beta is not significantly affected by change in index composition. This study retested this event expanding sample period from 1996 to 2006, and analyzed why this event was considered an uninformative events in the preceding studies. We analyzed a market impact by separating samples according to firm size and market condition. In case of newly enlisted firm, we found the evidence supporting price pressure hypothesis on average. However, we found the long run price effect in the sample of large firms under bearish markets. At the same time, we know that the number of samples under the category of large firms under bearish markets is relatively small, which drives the same result of supporting the hypothesis that change in index composition is a non-informative event on average. Also, the long run price effect of large size firms under bearish markets was supported by the analyses using trading volumes. On the other hand, in case of delisting from the index, we found the long run price effect but that was not supported by trading volume analyses.